The atypical antipsychotic quetiapine induces hyperlipidemia by activating intestinal PXR signaling.

Quetiapine, one of the most prescribed atypical antipsychotics, has been associated with hyperlipidemia and an increased risk for cardiovascular disease in patients, but the underlying mechanisms remain unknown. Here, we identified quetiapine as a potent and selective agonist for pregnane X receptor (PXR), a key nuclear receptor that regulates xenobiotic metabolism in the liver and intestine. Recent studies have indicated that PXR also plays an important role in lipid homeostasis. We generated potentially novel tissue-specific PXR-KO mice and demonstrated that quetiapine induced hyperlipidemia by activating intestinal PXR signaling. Quetiapine-mediated PXR activation stimulated the intestinal expression of cholesterol transporter Niemann-Pick C1-Like 1 (NPC1L1) and microsomal triglyceride transfer protein (MTP), leading to increased intestinal lipid absorption. While NPC1L1 is a known PXR target gene, we identified a DR-1-type PXR-response element in the MTP promoter and established MTP as a potentially novel transcriptional target of PXR. Quetiapine's effects on PXR-mediated gene expression and cholesterol uptake were also confirmed in cultured murine enteroids and human intestinal cells. Our findings suggest a potential role of PXR in mediating adverse effects of quetiapine in humans and provide mechanistic insights for certain atypical antipsychotic-associated dyslipidemia.

Related papers:

title: Quetiapine: a review of its use in the treatment of bipolar depression.
abstract: Quetiapine (Seroquel) is the only atypical antipsychotic approved in the US for use as monotherapy in both bipolar mania and depression, offering potential compliance advantages. Monotherapy with oral quetiapine 300 mg/day is effective in the treatment of patients with bipolar I or II depression. Rapid and sustained improvements in depressive and anxiety symptoms are seen with quetiapine, as well as improvements in health-related quality of life (HR-QOL). Quetiapine is generally well tolerated in bipolar depression and is not associated with an increased risk of treatment-emergent mania. Thus, despite the current lack of data from active comparator trials, quetiapine monotherapy should be considered a first-line option for the acute treatment of bipolar depression.

title: Role of quetiapine beyond its clinical efficacy in bipolar disorder: From neuroprotection to the treatment of psychiatric disorders (Review)
abstract: The aim of the present review was to discuss the following aspects of treatment with quetiapine in psychiatric disorders: i) Neurocognition and functional recovery in bipolar disorder (BD); ii) neuroprotective profile in different models; and iii) potential off-label indications. A PubMed search was conducted of articles published in English between 2000 and 2012 on quetiapine, cross-referenced with the terms ‘anxiety’, ‘attention deficit disorder’, ‘borderline personality disorder’, ‘dementia’, ‘insomnia’, ‘major depressive disorder’ (MDD), ‘obsessive-compulsive disorder’, ‘post-traumatic stress disorder’, ‘remission’, ‘cognition’, ‘neurobiology’, ‘neuroprotection’, ‘efficacy’ and ‘effectiveness’. Articles were selected from meta-analyses, randomized clinical trials and open trials, and the results were summarized. Quetiapine, when studied in off-label conditions, has shown efficacy as a monotherapy in MDD and general anxiety disorder. Quetiapine also appears to exhibit a small beneficial effect in dementia. The review of other conditions was affected by methodological limitations that precluded any definitive conclusions on the efficacy or safety of quetiapine. Overall, the present review shows evidence supporting a potential role for quetiapine in improving cognition, functional recovery and negative symptoms in a cost-effective manner in BD. These benefits of quetiapine are potentially associated with its well-described neuroprotective effects; however, further studies are clearly warranted.

title: Efficacy of Quetiapine Monotherapy in Bipolar I and II Depression: A Double-blind, Placebo-controlled Study (The BOLDER II Study)
abstract: This study evaluated the efficacy and tolerability of quetiapine monotherapy for depressive episodes in patients with bipolar I or II disorder (Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition) who were randomized to 8 weeks of double-blind treatment with quetiapine (300 or 600 mg/d; once daily, evening dosing) or placebo. Patients were assessed weekly using the Montgomery-Åsberg Depression Rating Scale (MADRS) and Hamilton Depression Rating Scale (HAM-D). The primary end point was change in MADRS total score from baseline to Week 8 (analysis of covariance/last-observation-carried-forward analysis). Of 509 patients randomized, 59% completed the study. Improvements from baseline in mean MADRS total scores were significantly greater with quetiapine 300 and 600 mg/d than with placebo from first evaluation (Week 1) through Week 8 (both P ≤ 0.001 vs. placebo). Therapeutic effect sizes at Week 8 were 0.61 and 0.54 for quetiapine 300 and 600 mg/d, respectively. Improvements in mean HAM-D scores were also significantly greater with both quetiapine doses than with placebo (P < 0.001) as early as Week 1 and throughout the study. The MADRS response and remission rates were also significantly greater in both quetiapine dose groups compared with placebo. Improvements in primary and secondary outcomes were observed with both 300 and 600 mg/d quetiapine without major differences between the doses. Common adverse events included dry mouth, sedation, somnolence, dizziness, and constipation. The incidence of treatment-emergent mania or hypomania was lower with quetiapine treatment than placebo. This study demonstrates that quetiapine monotherapy is an effective and well-tolerated treatment for depressive episodes in bipolar disorder, confirming the results observed from a previous study (BipOLar DEpRession [BOLDER] I).

title: Quetiapine versus other atypical antipsychotics for schizophrenia.
abstract: In many countries, second-generation ('atypical') antipsychotic drugs have become the first-line drug treatment for people with schizophrenia. It is not clear how the effects of the various second-generation antipsychotic drugs differ.



To evaluate the effects of quetiapine compared with other second-generation (atypical) antipsychotic drugs in the treatment of people with schizophrenia and schizophrenia-like psychoses.



We searched the Cochrane Schizophrenia Group Trials Register (May 2010), inspected references of all identified studies, and contacted relevant pharmaceutical companies, drug approval agencies and authors of trials for additional information.



We included all randomised controlled trials (RCTs) comparing oral quetiapine with other oral forms of atypical antipsychotic medication in people with schizophrenia or schizophrenia-like psychoses.



We extracted data independently. For dichotomous data, we calculated risk ratios (RRs) and their 95% confidence intervals (CIs) on an intention-to-treat basis based on a random-effects model. We calculated number needed to treat for an additional beneficial outcome (NNTB) where appropriate. For continuous data, we calculated mean differences (MDs), again based on a random-effects model.



Efficacy data tended to favour the control drugs over quetiapine (Positive and Negative Syndrome Scale (PANSS) total score vs olanzapine: 11 RCTs, n = 1486, mean quetiapine endpoint score 3.67 higher, CI 1.95 to 5.39, low quality; vs risperidone: 13 RCTs, n = 2155, mean quetiapine endpoint score 1.74 higher, CI 0.19 to 3.29, moderate quality; vs paliperidone: 1 RCT, n = 319, mean quetiapine endpoint score 6.30 higher, CI 2.77 to 9.83, moderate quality), but the clinical meaning of these data is unclear. No clear mental state differences were noted when quetiapine was compared with clozapine, aripiprazole or ziprasidone. Compared with olanzapine, quetiapine produced slightly fewer movement disorders (7 RCTs, n = 1127, RR use of antiparkinson medication 0.51, CI 0.32 to 0.81, moderate quality) and less weight gain (8 RCTs, n = 1667, RR 0.68, CI 0.51 to 0.92, moderate quality) and glucose elevation, but increased QTc prolongation (3 RCTs, n = 643, MD 4.81, CI 0.34 to 9.28). Compared with risperidone, quetiapine induced slightly fewer movement disorders (8 RCTs, n = 2163, RR use of antiparkinson medication 0.5, CI 0.36 to 0.69, moderate quality), less prolactin increase (7 RCTs, n = 1733, MD -35.25, CI -43.59 to -26.91) and some related adverse effects but greater cholesterol increase (6 RCTs, n = 1473, MD 8.57, CI 4.85 to 12.29). On the basis of limited data, compared with paliperidone, quetiapine induced fewer parkinsonian side effects (1 RCT, n = 319, RR use of antiparkinson medication 0.64, CI 0.45 to 0.91, moderate quality) and less prolactin increase (1 RCT, n = 319, MD -49.30, CI -57.80 to -40.80) and weight gain (1 RCT, n = 319, RR weight gain of 7% or more of total body weight 2.52, CI 0.5 to 12.78, moderate quality). Compared with ziprasidone, quetiapine induced slightly fewer extrapyramidal adverse effects (1 RCT, n = 522, RR use of antiparkinson medication 0.43, CI 0.2 to 0.93, moderate quality) and less prolactin increase. On the other hand, quetiapine was more sedating and led to greater weight gain (2 RCTs, n = 754, RR 2.22, CI 1.35 to 3.63, moderate quality) and cholesterol increase when compared with ziprasidone.



Available evidence from trials suggests that most people who start quetiapine stop taking it within a few weeks (around 60%). Comparisons with amisulpride, sertindole and zotepine do not exist. Although efficacy data favour olanzapine and risperidone compared with quetiapine, the clinical meaning of these data remains unclear. Quetiapine may produce fewer parkinsonian effects than paliperidone, aripiprazole, ziprasidone, risperidone and olanzapine. Quetiapine appears to have a similar weight gain profile to risperidone, as well as clozapine and aripiprazole (although data are very limited for the latter two comparators). Quetiapine may produce greater weight gain than ziprasidone and less weight gain than olanzapine and paliperidone. Most data that have been reported within existing comparisons are of very limited value because of assumptions and biases within them. Much scope is available for further research into the effects of this widely used drug.

title: Bodyweight Gain with Atypical Antipsychotic
abstract: The atypical antipsychotics have been shown to have superior efficacy compared with typical antipsychotics such as haloperidol, particularly in the treatment of negative symptoms of schizophrenia. Furthermore, they induce less extrapyramidal effects. However, following clinical use, marked bodyweight gain has been frequently observed with some of the atypical antipsychotic drugs.In order to examine and compare the frequency, amount and conditions of bodyweight gain during treatment with atypical antipsychotics, studies concerning bodyweight gain with these agents were identified through a MEDLINE search from 1966 to March 2000.Although comparison is limited by the different designs and recruitment procedures of the reviewed studies, the available data support the notion that the frequency as well as the amount of bodyweight gain is high in patients treated with olanzapine (average bodyweight gain 2.3 kg/month), clozapine (1.7 kg/month), quetiapine (1.8 kg/month), and possibly also zotepine (2.3 kg/month). Moderate changes in bodyweight have been observed in the treatment with risperidone (average bodyweight gain 1.0 kg/month). Ziprasidone seems to induce only slight bodyweight changes (0.8 kg/month). Bodyweight gain most frequently occurs in the first 12 weeks of treatment. Patients who were underweight at the beginning of treatment are at highest risk of gaining bodyweight.The underlying pathomechanism still remains largely unclear. The relative receptor affinities of the atypical antipsychotics for histamine H1 receptors as well as the ratio of their affinity for serotonin 5-HT2 and dopamine D2 receptors appear to be the most robust correlate of bodyweight gain. Furthermore, the induction of leptin secretion may have an important impact on bodyweight gain in patients treated with atypical antipsychotics.Although many questions concerning the pathogenesis of bodyweight gain remain unresolved, this adverse effect has to be taken into consideration when prescribing the atypical antipsychotics, particularly in view its affect on compliance during long term treatment and the long term effects of obesity on mortality and morbidity.

title: The effects of antipsychotic therapy on serum lipids: a comprehensive review
abstract: The purpose of this paper is to review the literature since 1970 documenting the effects of antipsychotic agents on serum lipids, including a discussion of possible mechanisms for the observed phenomena, the clinical significance and recommendations for monitoring hyperlipidemia during antipsychotic therapy.



High-potency conventional antipsychotics (e.g., haloperidol) and the atypical antipsychotics, ziprasidone, risperidone and aripiprazole, appear to be associated with lower risk of hyperlipidemia. Low-potency conventional antipsychotics (e.g., chlorpormazine, thioridazine) and the atypical antipsychotics, quetiapine, olanzapine and clozapine, are associated with higher risk of hyperlipidemia. Possible hypotheses for lipid dysregulation include weight gain, dietary changes and the development of glucose intolerance.



Given the multiple cardiovascular risk factors seen in patients with schizophrenia, great care must be exercised in the choice of antipsychotic therapy to minimize the medical burden of additional risk imposed by hyperlipidemia. It is recommended that a lipid panel be obtained at baseline in all patients with schizophrenia, annually thereafter for patients on agents associated with lower risk of hyperlipidemia and quarterly in patients on agents associated with higher risk for hyperlipidemia. All patients with persistent dyslipidemia should be referred for lipid-lowering therapy or switched to a less lipid-offending antipsychotic agent.

title: Antipsychotic effects on estimated 10-year coronary heart disease risk in the CATIE schizophrenia study
abstract: Persons with schizophrenia die earlier than the general population, in large part due to cardiovascular disease. The study objective was to examine effects of different antipsychotic treatments on estimates of 10-year coronary heart disease (CHD) risk calculated by the Framingham Heart Study formula.



Change in 10-year risk for CHD was compared between treatment groups in 1125 patients followed for 18 months or until treatment discontinuation in the Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) Schizophrenia Trial.



The covariate-adjusted mean change in 10-year CHD risk differed significantly between treatments. Olanzapine was associated with a 0.5% (SE 0.3) increase and quetiapine, a 0.3% (SE 0.3) increase; whereas risk decreased in patients treated with perphenazine, -0.5% (SE 0.3), risperidone, -0.6% (SE 0.3), and ziprasidone -0.6% (SE 0.4). The difference in 10-year CHD risk between olanzapine and risperidone was statistically significant (p=0.004). Differences in estimated 10-year CHD risk between drugs were most marked in the tertile of subjects with a baseline CHD risk of at least 10%. Among individual CHD risk factors used in the Framingham formula, only total and HDL cholesterol levels differed between treatments.



These results indicate that the impact on 10-year CHD risk differs significantly between antipsychotic agents, with olanzapine producing the largest elevation in CHD risk of the agents studied in CATIE.

title: Effects of switching from olanzapine, quetiapine, and risperidone to aripiprazole on 10-year coronary heart disease risk and metabolic syndrome status: Results from a randomized controlled trial
abstract: This study examined the clinical significance of switching from olanzapine, quetiapine, or risperidone to aripiprazole by examining changes in predicted risk of cardiovascular disease (CVD) according to the Framingham Risk Score (FRS) and metabolic syndrome status. FRS estimates 10-year risk of "hard" coronary heart disease (CHD) outcomes (myocardial infarction and coronary death) while metabolic syndrome is associated with increased risk of CVD, stroke, and diabetes mellitus.



Changes in FRS and metabolic syndrome status were compared between patients with BMI ≥ 27 and non-HDL-C ≥ 130 mg/dL randomly assigned to stay on stable current treatment (olanzapine, quetiapine, or risperidone) or switch to treatment with aripiprazole with 24 weeks of follow-up. All study participants were enrolled in a behavioral program that promoted healthy diet and exercise.



The pre-specified analyses included 89 switchers and 98 stayers who had post-baseline measurements needed to assess changes. Least squares mean estimates of 10-year CHD risk decreased more for the switch (from 7.0% to 5.2%) than the stay group (from 7.4% to 6.4%) (p = 0.0429). The odds ratio for having metabolic syndrome (stay vs. switch) at the last observation was 1.748 (95% CI 0.919, 3.324, p = 0.0885).



Switching from olanzapine, quetiapine, or risperidone to aripiprazole was associated with larger reductions in predicted 10-year risk of CHD than the behavioral program alone. The advantage of switching on metabolic syndrome was not statistically significant. The benefits of switching must be balanced against its risks, which in this study included more discontinuations of the study treatment but no significant increase in symptoms or hospitalizations.

title: Hyperlipidemia following treatment with antipsychotic medications.
abstract: This study attempted to estimate the relative risk of developing hyperlipidemia after treatment with antipsychotics in relation to no antipsychotic treatment.



A matched case-control analysis was performed with pharmacy and claims data from California Medicaid (Medi-Cal). Patients were excluded if they were treated for medical disorders or prescribed medications known to increase their risk of hyperlipidemia. Cases were ages 18 to 64 years with schizophrenia, major depression, bipolar disorder, or other affective psychoses and incident hyperlipidemia. Cases were matched to up to six control subjects by age, sex, race, and psychiatric diagnosis. Both groups were prescribed either no antipsychotic medication or had two or more prescriptions for one and only one antipsychotic medication during the 60 days prior to the first indication of hyperlipidemia (cases) or matched index date (controls) in the billing record. Conditional logistic regressions were used to derive odds ratios and 95% confidence intervals (95% CIs) of each antipsychotic medication in relation to no antipsychotic medication.



A total of 13,133 incident cases of hyperlipidemia were matched to 72,140 control subjects. As compared with no antipsychotic medication, treatment with clozapine (odds ratio: 1.82, 95% CI: 1.61-2.05), risperidone (odds ratio: 1.53, 95% CI: 1.43-1.64), quetiapine (odds ratio: 1.52, 95% CI: 1.40-1.65), olanzapine (odds ratio: 1.56, 95% CI: 1.47-1.67), ziprasidone (odds ratio: 1.40, 95% CI: 1.19-1.65), and first-generation antipsychotics (odds ratio: 1.26, 95% CI: 1.14-1.39), but not aripiprazole (odds ratio: 1.19, 95% CI: 0.94-1.52) was associated with a significant increase in risk of incident hyperlipidemia.



These findings suggest that most commonly prescribed antipsychotic medications increase the risk of developing hyperlipidemia in patients with schizophrenia or mood disorders.

title: Long-term metabolic effects of aripiprazole, ziprasidone and quetiapine: a pragmatic clinical trial in drug-naïve patients with a first-episode of non-affective psychosis
abstract: IntroductionThe use of second-generation antipsychotics (SGA) has been associated with metabolic changes. However, there are differences in the metabolic profile between SGAs. We have previously observed that ziprasidone had a more benign early metabolic profile compared to aripiprazole and quetiapine. However, a long-term follow-up is preferred to detect clinically relevant impairment in metabolic parameters. We aimed to compare the effect of aripiprazole, ziprasidone, and quetiapine on metabolic measures in first-episode non-affective psychosis patients after 1 year of treatment.Material and methodsOne hundred and sixty-five drug-naïve patients, suffering from a first episode of non-affective psychosis, were randomly assigned to receive quetiapine, ziprasidone, or aripiprazole. Weight and glycemic/lipid parameters were recorded at baseline and after 1 year of treatment.ResultsAfter 1 year of antipsychotic treatment, we found significant increments in weight, BMI, total cholesterol, LDL-cholesterol, triglycerides, and the triglyceride/HDL index in the sample as a whole. These changes produced a significant rise in the percentage of patients with obesity, hypercholesterolemia, and hypertriglyceridemia. However, when comparing the differential effect of each antipsychotic medication, we found no significant differences in any of the metabolic parameters between antipsychotics groups after 1 year of treatment.ConclusionWe concluded that the antipsychotics studied present similar metabolic profiles. However, the primary exposure to SGAs during the first year of psychosis was associated with significant increases in weight and metabolic parameters, leading to increments in obesity, hypertriglyceridemia, and hypercholesterolemia.

title: SXR, a novel steroid and xenobiotic-sensing nuclear receptor.
abstract: An important requirement for physiologic homeostasis is the detoxification and removal of endogenous hormones and xenobiotic compounds with biological activity. Much of the detoxification is performed by cytochrome P-450 enzymes, many of which have broad substrate specificity and are inducible by hundreds of different compounds, including steroids. The ingestion of dietary steroids and lipids induces the same enzymes; therefore, they would appear to be integrated into a coordinated metabolic pathway. Instead of possessing hundreds of receptors, one for each inducing compound, we propose the existence of a few broad specificity, low-affinity sensing receptors that would monitor aggregate levels of inducers to trigger production of metabolizing enzymes. In support of this model, we have isolated a novel nuclear receptor, termed the steroid and xenobiotic receptor (SXR), which activates transcription in response to a diversity of natural and synthetic compounds. SXR forms a heterodimer with RXR that can bind to and induce transcription from response elements present in steroid-inducible cytochrome P-450 genes and is expressed in tissues in which these catabolic enzymes are expressed. These results strongly support the steroid sensor hypothesis and suggest that broad specificity sensing receptors may represent a novel branch of the nuclear receptor superfamily.

title: Peptide Mimetic HIV Protease Inhibitors Are Ligands for the Orphan Receptor SXR*
abstract: The orphan nuclear receptor SXR coordinately regulates drug clearance in response to a wide variety of xenobiotic compounds. This signaling system protects the body from exposure to toxic compounds; however, it can also pose a severe barrier to drug therapy. We now demonstrate that the human immunodeficiency virus (HIV) protease inhibitor ritonavir binds SXR and activates its target genes. This represents an example of a commonly used therapeutic agent that effectively activates SXR. We also show that other protease inhibitors are weaker (saquinavir) or unable to activate SXR (nelfinavir, indinavir) thus defining analogs that fail to induce SXR-regulated clearance pathways. Interestingly, HIV protease inhibitors are distinct from previously known SXR ligands in that they are peptide mimetic compounds. This expands the ligand specificity of SXR to include this unique chemical class whose pharmaceutical significance is expanding. Finally, we show that SXR ligands activate expression of multiple resistance protein 2, a critical regulator of bile flow and biliary drug excretion. These findings have important implications for the role of SXR in regulating drug clearance and hepatic disorders associated with impaired bile flow.

title: Pregnane X Receptor Mediates Dyslipidemia Induced by the HIV Protease Inhibitor Amprenavir in Mice
abstract: Human immunodeficiency virus (HIV) protease inhibitors (PIs) have been used successfully in extending the life span of people infected with HIV. The use of PIs has also been associated with dyslipidemia and an increased risk of cardiovascular disease, but the underlying mechanisms remain elusive. Several PIs have been implicated in activating the nuclear receptor pregnane X receptor (PXR), which acts as a xenobiotic sensor to regulate xenobiotic metabolism in the liver and intestine. Recent studies indicate that PXR may also play an important role in the regulation of lipid homeostasis. In the present study, we identified amprenavir, a widely used HIV PI, as a potent PXR-selective agonist. Computational docking studies combined with site-direct mutagenesis identified several key residues within the ligand-binding pocket of PXR that constitute points of interaction with amprenavir. Amprenavir efficiently activated PXR and induced PXR target gene expression in vitro and in vivo. Short-term exposure to amprenavir significantly increased plasma total cholesterol and atherogenic low-density lipoprotein cholesterol levels in wild-type mice, but not in PXR-deficient mice. Amprenavir-mediated PXR activation stimulated the expression of several key intestinal genes involved in lipid homeostasis. These findings provide critical mechanistic insight for understanding the impact of PIs on cardiovascular disease and demonstrate a potential role of PXR in mediating the adverse effects of HIV PIs in humans.

title: The nuclear pregnane X receptor: a key regulator of xenobiotic metabolism.
abstract: The nuclear pregnane X receptor (PXR; NR1I2) is an important component of the body's adaptive defense mechanism against toxic substances including foreign chemicals (xenobiotics). PXR is activated by a large number of endogenous and exogenous chemicals including steroids, antibiotics, antimycotics, bile acids, and the herbal antidepressant St. John's wort. Elucidation of the three-dimensional structure of the PXR ligand binding domain revealed that it has a large, spherical ligand binding cavity that allows it to interact with a wide range of hydrophobic chemicals. Thus, unlike other nuclear receptors that interact selectively with their physiological ligands, PXR serves as a generalized sensor of hydrophobic toxins. PXR binds as a heterodimer with the 9-cis retinoic acid receptor (NR2B) to DNA response elements in the regulatory regions of cytochrome P450 3A monooxygenase genes and a number of other genes involved in the metabolism and elimination of xenobiotics from the body. Although PXR evolved to protect the body, its activation by a variety of prescription drugs represents the molecular basis for an important class of harmful drug-drug interactions. Thus, assays that detect PXR activity will be useful in developing safer prescription drugs.

title: Novel functions of PXR in cardiometabolic disease.
abstract: Cardiometabolic disease emerges as a worldwide epidemic and there is urgent need to understand the molecular mechanisms underlying this chronic disease. The chemical environment to which we are exposed has significantly changed in the past few decades and recent research has implicated its contribution to the development of many chronic human diseases. However, the mechanisms of how exposure to chemicals contributes to the development of cardiometabolic disease are poorly understood. Numerous chemicals have been identified as ligands for the pregnane X receptor (PXR), a nuclear receptor functioning as a xenobiotic sensor to coordinately regulate xenobiotic metabolism via transcriptional regulation of xenobiotic-detoxifying enzymes and transporters. In the past decade, the function of PXR in the regulation of xenobiotic metabolism has been extensively studied by many laboratories and the role of PXR as a xenobiotic sensor has been well-established. The identification of PXR as a xenobiotic sensor has provided an important tool for the study of new mechanisms through which xenobiotic exposure impacts human chronic diseases. Recent studies have revealed novel and unexpected roles of PXR in modulating obesity, insulin sensitivity, lipid homeostasis, atherogenesis, and vascular functions. These studies suggest that PXR signaling may contribute significantly to the pathophysiological effects of many known xenobiotics on cardiometabolic disease in humans. The discovery of novel functions of PXR in cardiometabolic disease not only contributes to our understanding of "gene-environment interactions" in predisposing individuals to chronic diseases but also provides strong evidence to inform future risk assessment for relevant chemicals. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

title: The steroid and xenobiotic receptor (SXR), beyond xenobiotic metabolism
abstract: The steroid and xenobiotic receptor (SXR) (also known as pregnane X receptor or PXR) is a nuclear hormone receptor activated by a diverse array of endogenous hormones, dietary steroids, pharmaceutical agents, and xenobiotic compounds. SXR has an enlarged, flexible, hydrophobic ligand binding domain (LBD) which is remarkably divergent across mammalian species and SXR exhibits considerable differences in its pharmacology among mammals. The broad response profile of SXR has led to the development of “the steroid and xenobiotic sensor hypothesis”. SXR has been established as a xenobiotic sensor that coordinately regulates xenobiotic clearance in the liver and intestine via induction of genes involved in drug and xenobiotic metabolism. In the past few years, research has revealed new and mostly unsuspected roles for SXR in modulating inflammation, bone homeostasis, vitamin D metabolism, lipid homeostasis, energy homeostasis and cancer. The identification of SXR as a xenobiotic sensor has provided an important tool for studying new mechanisms through which diet, chemical exposure, and environment ultimately impact health and disease. The discovery and pharmacological development of new PXR modulators might represent an interesting and innovative therapeutic approach to combat various diseases.

title: Nuclear receptor PXR: discovery of a pharmaceutical anti-target.
abstract: Transcriptional induction of the gene encoding cytochrome P450 3A oxygenase (CYP3A) causes a prominent class of dangerous drug-drug interactions wherein one drug accelerates the metabolism of another. In our 1998 JCI paper, we reported the cloning of the human nuclear receptor PXR and demonstrated that it mediates CYP3A induction. We determined that PXR is expressed in liver, acts through a DNA response element located in the CYP3A promoter, and is activated by a structurally diverse collection of drugs that induce CYP3A. Our findings revealed the molecular basis for the CYP3A induction class of drug-drug interactions and provided a high-throughput means for screening out drug candidates with this activity.

title: Activation of PXR induces hypercholesterolemia in wild-type and accelerates atherosclerosis in apoE deficient mice[S]
abstract: The nuclear hormone receptor pregnane X receptor (PXR; also called SXR) functions as a xenobiotic sensor to coordinately regulate xenobiotic metabolism via transcriptional regulation of xenobiotic-detoxifying enzymes and transporters. Although many clinically relevant PXR ligands have been shown to affect cholesterol levels, the role of PXR in cholesterol homeostasis and atherosclerosis has not been thoroughly investigated. Here, we report that activation of PXR by feeding the PXR agonist pregnenolone 16&agr;-carbonitrile (0.02%) for 2 weeks to wild-type (WT) mice significantly increased total cholesterol levels and atherogenic lipoproteins VLDL and LDL levels, but had no effect in PXR knockout (PXR−/−) mice. Chronic PXR activation in atherosclerosis prone apolipoprotein E deficient (ApoE−/−) mice was found to decrease HDL levels and increase atherosclerotic cross-sectional lesion area at both the aortic root and in the brachiocephalic artery by 54% (P < 0.001) and 116% (P < 0.01), respectively. PXR activation significantly regulated genes in the liver involved in lipoprotein transportation and cholesterol metabolism, including CD36, ApoA-IV, and CYP39A1, in both WT and ApoE−/− mice. Furthermore, PXR activation can increase CD36 expression and lipid accumulation in peritoneal macrophages of ApoE−/− mice. In summary, PXR activation in WT mice increases levels of the atherogenic lipoproteins VLDL and LDL, whereas in ApoE−/− mice, PXR increases atherosclerosis, perhaps by diminishing levels of the antiatherogenic ApoA-IV and increasing lipid accumulation in macrophages.—Zhou, C., N. King, K. Y. Chen, and J. L. Breslow. Activation of PXR induces hypercholesterolemia in wild-type and accelerates atherosclerosis in apoE deficient mice.

title: A Novel Pregnane X Receptor-mediated and Sterol Regulatory Element-binding Protein-independent Lipogenic Pathway*
abstract: The pregnane X receptor (PXR) was isolated as a xenosensor regulating xenobiotic responses. In this study, we show that PXR plays an endobiotic role by impacting lipid homeostasis. Expression of an activated PXR in the livers of transgenic mice resulted in an increased hepatic deposit of triglycerides. This PXR-mediated lipid accumulation was independent of the activation of the lipogenic transcriptional factor SREBP-1c (sterol regulatory element-binding protein 1c) and its primary lipogenic target enzymes, including fatty-acid synthase (FAS) and acetyl-CoA carboxylase 1 (ACC-1). Instead, the lipid accumulation in transgenic mice was associated with an increased expression of the free fatty acid transporter CD36 and several accessory lipogenic enzymes, such as stearoyl-CoA desaturase-1 (SCD-1) and long chain free fatty acid elongase. Studies using transgenic and knock-out mice showed that PXR is both necessary and sufficient for Cd36 activation. Promoter analyses revealed a DR-3-type of PXR-response element in the mouse Cd36 promoter, establishing Cd36 as a direct transcriptional target of PXR. The hepatic lipid accumulation and Cd36 induction were also seen in the hPXR “humanized” mice treated with the hPXR agonist rifampicin. The activation of PXR was also associated with an inhibition of pro-β-oxidative genes, such as peroxisome proliferator-activated receptor α (PPARα) and thiolase, and an up-regulation of PPARγ, a positive regulator of CD36. The cross-regulation of CD36 by PXR and PPARγ suggests that this fatty acid transporter may function as a common target of orphan nuclear receptors in their regulation of lipid homeostasis.

title: Chronic exposure to rifaximin causes hepatic steatosis in pregnane X receptor-humanized mice.
abstract: Rifaximin, a nonsystemic antibiotic that exhibits low gastrointestinal absorption, is a potent agonist of human pregnane X receptor (PXR), which contributes to its therapeutic efficacy in inflammatory bowel disease. To investigate the effects of long-term administration of rifaximin on the liver, PXR-humanized mice were administered rifaximin for 6 months; wild-type and Pxr-null mice were treated in parallel as controls. Histological analysis revealed time-dependent intense hepatocellular fatty degeneration and increased hepatic triglycerides in PXR-humanized mice and not in wild-type and Pxr-null mice. After long-term treatment, PXR target genes were induced in small intestine and liver, with significant up-regulation in the expression of hepatic genes related to triglyceride synthesis and lipid accumulation. However, no significant hepatic accumulation of rifaximin was found, even after 6 months of treatment, in PXR-humanized mice. Genes in the small intestine that are involved in the uptake of fatty acids and triglycerides were induced along with increased triglyceride accumulation in intestinal epithelial cells of PXR-humanized mice; this was not observed in wild-type and Pxr-null mice. These findings suggest that long-term administration of rifaximin could lead to PXR-dependent hepatocellular fatty degeneration as a result of activation of genes involved in lipid uptake, thus indicating a potential adverse effect of rifaximin on liver function after long-term exposure.

title: Intestinal pregnane X receptor links xenobiotic exposure and hypercholesterolemia.
abstract: Recent studies have associated endocrine-disrupting chemical (EDC) exposure with the increased risk of cardiovascular disease in humans, but the underlying mechanisms responsible for these associations remain elusive. Many EDCs have been implicated in activation of the nuclear receptor pregnane X receptor (PXR), which acts as a xenobiotic sensor to regulate xenobiotic metabolism in the liver and intestine. Here we report an important role of intestinal PXR in linking xenobiotic exposure and hyperlipidemia. We identified tributyl citrate (TBC), one of a large group of Food and Drug Administration-approved plasticizers for pharmaceutical or food applications, as a potent and selective PXR agonist. TBC efficiently activated PXR and induced PXR target gene expression in vitro and in vivo. Interestingly, TBC activated intestinal PXR but did not affect hepatic PXR activity. Exposure to TBC increased plasma total cholesterol and atherogenic low-density lipoprotein cholesterol levels in wild-type mice, but not in PXR-deficient mice. TBC-mediated PXR activation stimulated the expression of an essential cholesterol transporter, Niemann-Pick C1-like 1 (NPC1L1), in the intestine. Promoter analysis revealed a DR-4 type of PXR response element in the human NPC1L1 promoter, and TBC promoted PXR recruitment onto the NPC1L1 promoter. Consistently, TBC treatment significantly increased lipid uptake by human and murine intestinal cells and deficiency of PXR inhibited TBC-elicited lipid uptake. These findings provide critical mechanistic insight for understanding the impact of EDC-mediated PXR activation on lipid homeostasis and demonstrate a potential role of PXR in mediating the adverse effects of EDCs on cardiovascular disease risk in humans.

title: Bisphenol A and Its Analogues Activate Human Pregnane X Receptor
abstract: Bisphenol A (BPA) is a base chemical used extensively in many consumer products. BPA and its analogues are present in environmental and human samples. Many endocrine-disrupting chemicals, including BPA, have been shown to activate the pregnane X receptor (PXR), a nuclear receptor that functions as a master regulator of xenobiotic metabolism. However, the detailed mechanism by which these chemicals activate PXR remains unknown.  We investigated the mechanism by which BPA interacts with and activates PXR and examined selected BPA analogues to determine whether they bind to and activate PXR.  Cell-based reporter assays, in silico ligand–PXR docking studies, and site-directed mutagenesis were combined to study the interaction between BPA and PXR. We also investigated the influence of BPA and its analogues on the regulation of PXR target genes in human LS180 cells.  We found that BPA and several of its analogues are potent agonists for human PXR (hPXR) but do not affect mouse PXR activity. We identified key residues within hPXR’s ligand-binding pocket that constitute points of interaction with BPA. We also deduced the structural requirements of BPA analogues that activate hPXR. BPA and its analogues can also induce PXR target gene expression in human LS180 cells.  The present study advances our understanding of the mechanism by which BPA interacts with and activates human PXR. Activation of PXR by BPA may explain some of the adverse effects of BPA in humans.

title: The coregulator exchange in transcriptional functions of nuclear receptors.
abstract: Nuclear receptors (NR) comprise a family of transcription factors that regulate gene expression in a liganddependent manner. Members of the NR superfamily include receptors for steroid hormones, such as estrogens (ER) and glucocorticoids (GR), receptors for nonsteroidal ligands, such as thyroid hormones (TR) and retinoic acid (RAR), as well as receptors that bind diverse products of lipid metabolism, such as fatty acids and prostaglandins (for review, see Beato et al. 1995; Chambon 1995; Mangelsdorf and Evans 1995). The NR superfamily also includes a large number of so-called orphan receptors for which regulatory ligands have not been identified (Mangelsdorf and Evans 1995). Although many orphan receptors are likely to be regulated by small-molecular-weight ligands, other mechanisms of regulation, such as phosphorylation (Hammer et al. 1999; Tremblay et al. 1999) have also proven to be of importance. Remarkably, the sequence of the Caenorhabditis elegans genome has revealed the presence of >200 members of the NR family, suggesting a critical role of these proteins in environmental adaptation (Sluder et al. 1999). Although mammalian genomes are unlikely to contain such a large complement of these factors, >24 distinct classes of NR have been identified in humans, and these factors exert diverse roles in the regulation of growth, development, and homeostasis. Based on their importance in biology and medicine, as well as the relatively simple mechanism of regulation, NR represent one of the most intensively studied and best-understood classes of transcription factors at the molecular level. Members of the NR family regulate transcription by several mechanisms . Nuclear receptors can activate or repress target genes by binding directly to DNA response elements as homoor heterodimers or by binding to other classes of DNA-bound transcription factors. A subset of NRs, including TR and RAR, can actively repress target genes in the presence or absence of ligand binding, and many NR have been demonstrated to inhibit transcription in a ligand-dependent manner by antagonizing the transcriptional activities of other classes of transcription factors. These activities have been linked to interactions with general classes of molecules that appear to serve coactivator or corepressor function. In this review, we will discuss recent progress concerning the molecular mechanisms by which NR cofactor interactions serve to activate or repress transcription.

title: Non-nucleoside reverse transcriptase inhibitor efavirenz activates PXR to induce hypercholesterolemia and hepatic steatosis.
abstract: The most prescribed non-nucleoside reverse transcriptase inhibitor, efavirenz, has been associated with elevated risk of dyslipidemia and hepatic steatosis in HIV-infected patients but the underlying mechanisms remain elusive. Herein, we investigated the role of pregnane X receptor (PXR) in mediating the adverse effects of efavirenz on lipid homeostasis.



Cell-based reporter assays, primary cell culture, and multiple mouse models including conditional knockout and humanized mice were combined to study the impact of efavirenz on PXR activities and lipid homeostasis in vitro and in vivo. A novel liver-specific Pxr knockout mouse model was also generated to determine the contribution of hepatic PXR signaling to efavirenz-elicited dyslipidemia and hepatic steatosis.



We found that efavirenz is a potent PXR-selective agonist that can efficiently activate PXR and induce its target gene expression in vitro and in vivo. Treatment with efavirenz-induced hypercholesterolemia and hepatic steatosis in mice but deficiency of hepatic PXR abolished these adverse effects. Interestingly, efavirenz-mediated PXR activation regulated the expression of several key hepatic lipogenic genes including fatty acid transporter CD36 and cholesterol biosynthesis enzyme squalene epoxidase (SQLE), leading to increased lipid uptake and cholesterol biosynthesis in hepatic cells. While CD36 is a known PXR target gene, we identified a DR-2-type of PXR-response element in the SQLE promoter and established SQLE as a direct transcriptional target of PXR. Since PXR exhibits considerable differences in its pharmacology across species, we also confirmed these findings in PXR-humanized mice and human primary hepatocytes.



The widely prescribed antiretroviral drug efavirenz induces hypercholesterolemia and hepatic steatosis by activating PXR signaling. Activation of PXR should be taken into consideration for patients undergoing long-term treatment with PXR agonistic antiretroviral drugs.



Efavirenz is widely prescribed for HIV-infected patients but has some side effects. It can increase lipid levels in patients' blood and liver. Here we show that efavirenz can activate a unique liver protein called PXR which mediates the adverse effects of efavirenz on lipid levels in mouse models.

title: Quetiapine Attenuates Glial Activation and Proinflammatory Cytokines in APP/PS1 Transgenic Mice via Inhibition of Nuclear Factor-κB Pathway
abstract: In Alzheimer’s disease, growing evidence has shown that uncontrolled glial activation and neuroinflammation may contribute independently to neurodegeneration. Antiinflammatory strategies might provide benefits for this devastating disease. The aims of the present study are to address the issue of whether glial activation and proinflammatory cytokine increases could be modulated by quetiapine in vivo and in vitro and to explore the underlying mechanism.  Four-month–old amyloid precursor protein (APP) and presenilin 1 (PS1) transgenic and nontransgenic mice were treated with quetiapine (5mg/kg/d) in drinking water for 8 months. Animal behaviors, total Aβ levels, and glial activation were evaluated by behavioral tests, enzyme-linked immunosorbent assay, immunohistochemistry, and Western blot accordingly. Inflammatory cytokines and the nuclear factor kappa B pathway were analyzed in vivo and in vitro.  Quetiapine improves behavioral performance, marginally affects total Aβ40 and Aβ42 levels, attenuates glial activation, and reduces proinflammatory cytokines in APP/PS1 mice. Quetiapine suppresses Aβ1-42-induced activation of primary microglia by decresing proinflammatory cytokines. Quetiapine inhibits the activation of nuclear factor kappa B p65 pathway in both transgenic mice and primary microglia stimulated by Aβ1–42.  The antiinflammatory effects of quetiapine in Alzheimer’s disease may be involved in the nuclear factor kappa B pathway. Quetiapine may be an efficacious and promising treatment for Alzheimer’s disease targeting on neuroinflammation.

title: A simple practice guide for dose conversion between animals and human
abstract: Understanding the concept of extrapolation of dose between species is important for pharmaceutical researchers when initiating new animal or human experiments. Interspecies allometric scaling for dose conversion from animal to human studies is one of the most controversial areas in clinical pharmacology. Allometric approach considers the differences in body surface area, which is associated with animal weight while extrapolating the doses of therapeutic agents among the species. This review provides basic information about translation of doses between species and estimation of starting dose for clinical trials using allometric scaling. The method of calculation of injection volume for parenteral formulation based on human equivalent dose is also briefed.

title: To scale or not to scale: the principles of dose extrapolation
abstract: The principles of inter‐species dose extrapolation are poorly understood and applied. We provide an overview of the principles underlying dose scaling for size and dose adjustment for size‐independent differences. Scaling of a dose is required in three main situations: the anticipation of first‐in‐human doses for clinical trials, dose extrapolation in veterinary practice and dose extrapolation for experimental purposes. Each of these situations is discussed. Allometric scaling of drug doses is commonly used for practical reasons, but can be more accurate when one takes into account species differences in pharmacokinetic parameters (clearance, volume of distribution). Simple scaling of drug doses can be misleading for some drugs; correction for protein binding, physicochemical properties of the drug or species differences in physiological time can improve scaling. However, differences in drug transport and metabolism, and in the dose–response relationship, can override the effect of size alone. For this reason, a range of modelling approaches have been developed, which combine in silico simulations with data obtained in vitro and/or in vivo. Drugs that are unlikely to be amenable to simple allometric scaling of their clearance or dose include drugs that are highly protein‐bound, drugs that undergo extensive metabolism and active transport, drugs that undergo significant biliary excretion (MW > 500, ampiphilic, conjugated), drugs whose targets are subject to inter‐species differences in expression, affinity and distribution and drugs that undergo extensive renal secretion. In addition to inter‐species dose extrapolation, we provide an overview of dose extrapolation within species, discussing drug dosing in paediatrics and in the elderly.

title: Role of the gut in lipid homeostasis.
abstract: Intestinal lipid transport plays a central role in fat homeostasis. Here we review the pathways regulating intestinal absorption and delivery of dietary and biliary lipid substrates, principally long-chain fatty acid, cholesterol, and other sterols. We discuss the regulation and functions of CD36 in fatty acid absorption, NPC1L1 in cholesterol absorption, as well as other lipid transporters including FATP4 and SRB1. We discuss the pathways of intestinal sterol efflux via ABCG5/G8 and ABCA1 as well as the role of the small intestine in high-density lipoprotein (HDL) biogenesis and reverse cholesterol transport. We review the pathways and genetic regulation of chylomicron assembly, the role of dominant restriction points such as microsomal triglyceride transfer protein and apolipoprotein B, and the role of CD36, l-FABP, and other proteins in formation of the prechylomicron complex. We will summarize current concepts of regulated lipoprotein secretion (including HDL and chylomicron pathways) and include lessons learned from families with genetic mutations in dominant pathways (i.e., abetalipoproteinemia, chylomicron retention disease, and familial hypobetalipoproteinemia). Finally, we will provide an integrative view of intestinal lipid homeostasis through recent findings on the role of lipid flux and fatty acid signaling via diverse receptor pathways in regulating absorption and production of satiety factors.

title: Multiple functions of microsomal triglyceride transfer protein
abstract: Microsomal triglyceride transfer protein (MTP) was first identified as a major cellular protein capable of transferring neutral lipids between membrane vesicles. Its role as an essential chaperone for the biosynthesis of apolipoprotein B (apoB)-containing triglyceride-rich lipoproteins was established after the realization that abetalipoproteinemia patients carry mutations in the MTTP gene resulting in the loss of its lipid transfer activity. Now it is known that it also plays a role in the biosynthesis of CD1, glycolipid presenting molecules, as well as in the regulation of cholesterol ester biosynthesis. In this review, we will provide a historical perspective about the identification, purification and characterization of MTP, describe methods used to measure its lipid transfer activity, and discuss tissue expression and function. Finally, we will review the role MTP plays in the assembly of apoB-lipoprotein, the regulation of cholesterol ester synthesis, biosynthesis of CD1 proteins and propagation of hepatitis C virus. We will also provide a brief overview about the clinical potentials of MTP inhibition.

title: Niemann-Pick C1 Like 1 Protein Is Critical for Intestinal Cholesterol Absorption
abstract: Dietary cholesterol consumption and intestinal cholesterol absorption contribute to plasma cholesterol levels, a risk factor for coronary heart disease. The molecular mechanism of sterol uptake from the lumen of the small intestine is poorly defined. We show that Niemann-Pick C1Like 1(NPC1L1) protein plays a critical role in the absorption of intestinal cholesterol. NPC1L1 expression is enriched in the small intestine and is in the brush border membrane of enterocytes. Although otherwise phenotypically normal, NPC1L1-deficient mice exhibit a substantial reduction in absorbed cholesterol, which is unaffected by dietary supplementation of bile acids. Ezetimibe, a drug that inhibits cholesterol absorption, had no effect in NPC1L1 knockout mice, suggesting that NPC1L1 resides in an ezetimibe-sensitive pathway responsible for intestinal cholesterol absorption.

title: Differing rates of cholesterol absorption among inbred mouse strains yield differing levels of HDL-cholesterol[S]
abstract: Inbred strains of mice with differing susceptibilities to atherosclerosis possess widely varying plasma HDL levels. Cholesterol absorption and lipoprotein formation were compared between atherosclerosis-susceptible, low-HDL C57BL6/J mice and atherosclerosis-resistant, high-HDL FVBN/J mice. [3H]cholesterol and triglyceride appeared in the plasma of FVB mice gavaged with cholesterol in olive oil at a much higher rate than in C57 mice. The plasma cholesterol was found almost entirely as HDL-cholesterol in both strains. Inhibition of lipoprotein catabolism with Tyloxapol revealed that the difference in the rate of [3H]cholesterol appearance in the plasma was due entirely to a greater rate of chylomicron secretion from the intestine of the FVB mice. Lipid absorption into the 2nd quarter of the small intestine is greater in the FVB mice and indicates that this region may contain the factors that give rise to the differences in absorption observed between the two mouse strains. Additionally, ad libitum feeding prior to cholesterol gavage accentuates the absorption rate differences compared with fasting. The resultant remodeling of the increased levels of chylomicron in the plasma may contribute to increased plasma HDL. Intestinal gene expression analysis reveals several genes that may play a role in these differences, including microsomal triglyceride transfer protein and ABCG8.

title: Lipid Absorption Defects in Intestine-specific Microsomal Triglyceride Transfer Protein and ATP-binding Cassette Transporter A1-deficient Mice*
abstract: The combined roles of intestinal MTP and ABCA1 in tissue and plasma lipid homeostasis are unknown.  Intestine-specific ablation of MTP and ABCA1 severely impairs acute fat and cholesterol absorption.  MTP and ABCA1 are critical for lipid absorption.  Reducing both intestinal MTP and ABCA1 might reduce plasma lipid concentrations. We have previously described apolipoprotein B (apoB)-dependent and -independent cholesterol absorption pathways and the role of microsomal triglyceride transfer protein (MTP) and ATP-binding cassette transporter A1 (ABCA1) in these pathways. To assess the contribution of these pathways to cholesterol absorption and to determine whether there are other pathways, we generated mice that lack MTP and ABCA1, individually and in combination, in the intestine. Intestinal deletions of Mttp and Abca1 decreased plasma cholesterol concentrations by 45 and 24%, respectively, whereas their combined deletion reduced it by 59%. Acute cholesterol absorption was reduced by 28% in the absence of ABCA1, and it was reduced by 92–95% when MTP was deleted in the intestine alone or together with ABCA1. MTP deficiency significantly reduced triglyceride absorption, although ABCA1 deficiency had no effect. ABCA1 deficiency did not affect cellular lipids, but Mttp deficiency significantly increased intestinal levels of triglycerides and free fatty acids. Accumulation of intestinal free fatty acids, but not triglycerides, in Mttp-deficient intestines was prevented when mice were also deficient in intestinal ABCA1. Combined deficiency of these genes increased intestinal fatty acid oxidation as a consequence of increased expression of peroxisome proliferator-activated receptor-γ (PPARγ) and carnitine palmitoyltransferase 1α (CPT1α). These studies show that intestinal MTP and ABCA1 are critical for lipid absorption and are the main determinants of plasma and intestinal lipid levels. Reducing their activities might lower plasma lipid concentrations.

title: Mice lacking ANGPTL8 (Betatrophin) manifest disrupted triglyceride metabolism without impaired glucose homeostasis
abstract: Here we show that ANGPTL8 plays a major role in the trafficking of triglycerides to peripheral tissues in response to food intake in mice. Circulating triglycerides are predominantly delivered to skeletal muscle and heart during fasting and are partitioned to adipose tissue upon refeeding. The postprandial increase in triglyceride delivery to adipose tissue is abolished in mice lacking ANGPTL8; consequently, the mice fail to replenish triglyceride stores in adipose tissue. Despite major alterations in triglyceride metabolism, no defects in glucose metabolism were detected in Angptl8−/− mice. The finding that plasma triglyceride levels are lower in Angptl8+/− mice suggests that even partial inhibition of ANGPTL8 may provide therapeutic benefit for treatment of dyslipidemia. Angiopoietin-like protein (ANGPTL)8 (alternatively called TD26, RIFL, Lipasin, and Betatrophin) is a newly recognized ANGPTL family member that has been implicated in both triglyceride (TG) and glucose metabolism. Hepatic overexpression of ANGPTL8 causes hypertriglyceridemia and increased insulin secretion. Here we examined the effects of inactivating Angptl8 on TG and glucose metabolism in mice. Angptl8 knockout (Angptl8−/−) mice gained weight more slowly than wild-type littermates due to a selective reduction in adipose tissue accretion. Plasma levels of TGs of the Angptl8−/− mice were similar to wild-type animals in the fasted state but paradoxically decreased after refeeding. The lower TG levels were associated with both a reduction in very low density lipoprotein secretion and an increase in lipoprotein lipase (LPL) activity. Despite the increase in LPL activity, the uptake of very low density lipoprotein-TG is markedly reduced in adipose tissue but preserved in hearts of fed Angptl8−/− mice. Taken together, these data indicate that ANGPTL8 plays a key role in the metabolic transition between fasting and refeeding; it is required to direct fatty acids to adipose tissue for storage in the fed state. Finally, glucose and insulin tolerance testing revealed no alterations in glucose homeostasis in mice fed either a chow or high fat diet. Thus, although absence of ANGPTL8 profoundly disrupts TG metabolism, we found no evidence that it is required for maintenance of glucose homeostasis.

title: Carboxylesterase1/Esterase-x Regulates Chylomicron Production in Mice
abstract: Elevated postprandial plasma triacylglycerol (TG) concentrations are commonly associated with obesity and the risk of cardiovascular disease. Dietary fat contributes to this condition through the production of chylomicrons. Carboxylesterases have been mainly studied for their role in drug metabolism, but recently they have been shown to participate in lipid metabolism; however, their role in intestinal lipid metabolism is unknown. Carboxylesterase1/esterase-x (Ces1/Es-x) deficient mice become obese, hyperlipidemic and develop hepatic steatosis even on standard chow diet. Here, we aimed to explore the role of Ces1/Es-x in intestinal lipid metabolism. Six-month old wild-type and Ces1/Es-x deficient mice were maintained on chow diet and intestinal lipid metabolism and plasma chylomicron clearance were analyzed. Along the intestine Ces1/Es-x protein is expressed only in proximal jejunum. Ablation of Ces1/Es-x expression results in postprandial hyperlipidemia due to increased secretion of chylomicrons. The secreted chylomicrons have aberrant protein composition, which results in their reduced clearance. In conclusion, Ces1/Es-x participates in the regulation of chylomicron assembly and secretion. Ces1/Es-x might act as a lipid sensor in enterocytes regulating chylomicron secretion rate. Ces1/Es-x might represent an attractive pharmacological target for the treatment of lipid abnormalities associated with obesity, insulin resistance and fatty liver disease.

title: Reduced Triglyceride Secretion in Response to an Acute Dietary Fat Challenge in Obese Compared to Lean Mice
abstract: Obesity results in abnormally high levels of triglyceride (TG) storage in tissues such as liver, heart, and muscle, which disrupts their normal functions. Recently, we found that lean mice challenged with high levels of dietary fat store TGs in cytoplasmic lipid droplets in the absorptive cells of the intestine, enterocytes, and that this storage increases and then decreases over time after an acute dietary fat challenge. The goal of this study was to investigate the effects of obesity on intestinal TG metabolism. More specifically we asked whether TG storage in and secretion from the intestine are altered in obesity. We investigated these questions in diet-induced obese (DIO) and leptin-deficient (ob/ob) mice. We found greater levels of TG storage in the intestine of DIO mice compared to lean mice in the fed state, but similar levels of TG storage after a 6-h fast. In addition, we found similar TG storage in the intestine of lean and DIO mice at multiple time points after an acute dietary fat challenge. Surprisingly, we found remarkably lower TG secretion from both DIO and ob/ob mice compared to lean controls in response to an acute dietary fat challenge. Furthermore, we found altered mRNA levels for genes involved in regulation of intestinal TG metabolism in lean and DIO mice at 6 h fasting and in response to an acute dietary fat challenge. More specifically, we found that many of the genes related to TG synthesis, chylomicron synthesis, TG storage, and lipolysis were induced in response to an acute dietary fat challenge in lean mice, but this induction was not observed in DIO mice. In fact, we found a significant decrease in intestinal mRNA levels of genes related to lipolysis and fatty acid oxidation in DIO mice in response to an acute dietary fat challenge. Our findings demonstrate altered TG handling by the small intestine of obese compared to lean mice.

title: Intestinal Phospholipid Remodeling Is Required for Dietary-Lipid Uptake and Survival on a High-Fat Diet.
abstract: Phospholipids are important determinants of membrane biophysical properties, but the impact of membrane acyl chain composition on dietary-lipid absorption is unknown. Here we demonstrate that the LXR-responsive phospholipid-remodeling enzyme Lpcat3 modulates intestinal fatty acid and cholesterol absorption and is required for survival on a high-fat diet. Mice lacking Lpcat3 in the intestine thrive on carbohydrate-based chow but lose body weight rapidly and become moribund on a triglyceride-rich diet. Lpcat3-dependent incorporation of polyunsaturated fatty acids into phospholipids is required for the efficient transport of dietary lipids into enterocytes. Furthermore, loss of Lpcat3 amplifies the production of gut hormones, including GLP-1 and oleoylethanolamide, in response to high-fat feeding, contributing to the paradoxical cessation of food intake in the setting of starvation. These results reveal that membrane phospholipid composition is a gating factor in passive lipid absorption and implicate LXR-Lpcat3 signaling in a gut-brain feedback loop that couples absorption to food intake.

title: Postprandial chylomicron formation and fat absorption in multidrug resistance gene 2 P-glycoprotein-deficient mice.
abstract: It has been proposed that biliary phospholipids fulfill specific functions in the absorption of dietary fat from the intestine, but the physiological significance has not been established. The aim of this study was to evaluate the role of biliary phospholipids in dietary fat absorption in vivo by using mice homozygous or heterozygous for disruption of the Mdr2 gene (Mdr2((-/-)), )) and control (Mdr2((+/+))) mice. Mdr2((-/-)) mice do not secrete phospholipids and cholesterol into bile, and bile salt secretion is not impaired. ) mice show only impaired (-40%) phospholipid secretion.



Methods included an analysis of time dependency of intestinal uptake and plasma appearance of intragastrically administered (radiolabeled) triglycerides and measurement of 3-day fecal fat balance with low- and high-fat diets.



Intragastric administration of olive oil resulted in a rapid increase in plasma triglycerides in Mdr2((+/+)) and Mdr2((+/-)) but not in Mdr2((-/-)) mice. The "postprandial response" of plasma triglycerides could be partially restored in Mdr2((-/-)) mice by intraduodenal infusion of whole rat bile. After intragastric [(3)H]triolein administration in Triton WR1339-pretreated animals, the appearance of (3)H-triglycerides in plasma was reduced by 70% in Mdr2((-/-)) compared with Mdr2((+/+)) mice, excluding accelerated lipolysis as the cause of defective triglyceride response in Mdr2((-/-)) mice. (3)H-triglycerides accumulated in enterocytes in Mdr2((-/-)) mice. Surprisingly, the efficacy of fat absorption as derived from balance studies was not affected and was only minimally affected in Mdr2((-/-)) mice fed low (14 energy percent)- and high (35 energy percent)-fat diets, respectively (all >95%).



The results show that biliary lipid secretion is necessary for postprandial appearance in plasma of chylomicrons in vivo but not for quantitative absorption of dietary lipids.

title: Human Enteroids/Colonoids and Intestinal Organoids Functionally Recapitulate Normal Intestinal Physiology and Pathophysiology*
abstract: Identification of Lgr5 as the intestinal stem cell marker as well as the growth factors necessary to replicate adult intestinal stem cell division has led to the establishment of the methods to generate “indefinite” ex vivo primary intestinal epithelial cultures, termed “mini-intestines.” Primary cultures developed from isolated intestinal crypts or stem cells (termed enteroids/colonoids) and from inducible pluripotent stem cells (termed intestinal organoids) are being applied to study human intestinal physiology and pathophysiology with great expectations for translational applications, including regenerative medicine. Here we discuss the physiologic properties of these cultures, their current use in understanding diarrhea-causing host-pathogen interactions, and potential future applications.

title: Intestinal Subepithelial Myofibroblasts Support the Growth of Intestinal Epithelial Stem Cells
abstract: Intestinal epithelial stem cells (ISCs) are the focus of recent intense study. Current in vitro models rely on supplementation with the Wnt agonist R-spondin1 to support robust growth, ISC self-renewal, and differentiation. Intestinal subepithelial myofibroblasts (ISEMFs) are important supportive cells within the ISC niche. We hypothesized that co-culture with ISEMF enhances the growth of ISCs in vitro and allows for their successful in vivo implantation and engraftment. ISC-containing small intestinal crypts, FACS-sorted single ISCs, and ISEMFs were procured from C57BL/6 mice. Crypts and single ISCs were grown in vitro into enteroids, in the presence or absence of ISEMFs. ISEMFs enhanced the growth of intestinal epithelium in vitro in a proximity-dependent fashion, with co-cultures giving rise to larger enteroids than monocultures. Co-culture of ISCs with supportive ISEMFs relinquished the requirement of exogenous R-spondin1 to sustain long-term growth and differentiation of ISCs. Mono- and co-cultures were implanted subcutaneously in syngeneic mice. Co-culture with ISEMFs proved necessary for successful in vivo engraftment and proliferation of enteroids; implants without ISEMFs did not survive. ISEMF whole transcriptome sequencing and qPCR demonstrated high expression of specific R-spondins, well-described Wnt agonists that supports ISC growth. Specific non-supportive ISEMF populations had reduced expression of R-spondins. The addition of ISEMFs in intestinal epithelial culture therefore recapitulates a critical element of the intestinal stem cell niche and allows for its experimental interrogation and biodesign-driven manipulation.

title: Niemann-Pick C1 Like 1 (NPC1L1) Is the Intestinal Phytosterol and Cholesterol Transporter and a Key Modulator of Whole-body Cholesterol Homeostasis*
abstract: Niemann-Pick C1 Like 1 (NPC1L1) is a protein localized in jejunal enterocytes that is critical for intestinal cholesterol absorption. The uptake of intestinal phytosterols and cholesterol into absorptive enterocytes in the intestine is not fully defined on a molecular level, and the role of NPC1L1 in maintaining whole body cholesterol homeostasis is not known. NPC1L1 null mice had substantially reduced intestinal uptake of cholesterol and sitosterol, with dramatically reduced plasma phytosterol levels. The NPC1L1 null mice were completely resistant to diet-induced hypercholesterolemia, with plasma lipoprotein and hepatic cholesterol profiles similar to those of wild type mice treated with the cholesterol absorption inhibitor ezetimibe. Cholesterol/cholate feeding resulted in down-regulation of intestinal NPC1L1 mRNA expression in wild type mice. NPC1L1 deficiency resulted in up-regulation of intestinal hydroxymethylglutaryl-CoA synthase mRNA and an increase in intestinal cholesterol synthesis, down-regulation of ABCA1 mRNA, and no change in ABCG5 and ABCG8 mRNA expression. NPC1L1 is required for intestinal uptake of both cholesterol and phytosterols and plays a major role in cholesterol homeostasis. Thus, NPC1L1 may be a useful drug target for the treatment of hypercholesterolemia and sitosterolemia.

title: Inactivating Mutations in NPC1L1 and Protection from Coronary Heart Disease
abstract: Ezetimibe lowers plasma levels of low-density lipoprotein (LDL) cholesterol by inhibiting the activity of the Niemann–Pick C1-like 1 (NPC1L1) protein. However, whether such inhibition reduces the risk of coronary heart disease is not known. Human mutations that inactivate a gene encoding a drug target can mimic the action of an inhibitory drug and thus can be used to infer potential effects of that drug.  We sequenced the exons of NPC1L1 in 7364 patients with coronary heart disease and in 14,728 controls without such disease who were of European, African, or South Asian ancestry. We identified carriers of inactivating mutations (nonsense, splice-site, or frameshift mutations). In addition, we genotyped a specific inactivating mutation (p.Arg406X) in 22,590 patients with coronary heart disease and in 68,412 controls. We tested the association between the presence of an inactivating mutation and both plasma lipid levels and the risk of coronary heart disease.  With sequencing, we identified 15 distinct NPC1L1 inactivating mutations; approximately 1 in every 650 persons was a heterozygous carrier for 1 of these mutations. Heterozygous carriers of NPC1L1 inactivating mutations had a mean LDL cholesterol level that was 12 mg per deciliter (0.31 mmol per liter) lower than that in noncarriers (P = 0.04). Carrier status was associated with a relative reduction of 53% in the risk of coronary heart disease (odds ratio for carriers, 0.47; 95% confidence interval, 0.25 to 0.87; P = 0.008). In total, only 11 of 29,954 patients with coronary heart disease had an inactivating mutation (carrier frequency, 0.04%) in contrast to 71 of 83,140 controls (carrier frequency, 0.09%).  Naturally occurring mutations that disrupt NPC1L1 function were found to be associated with reduced plasma LDL cholesterol levels and a reduced risk of coronary heart disease. (Funded by the National Institutes of Health and others.

title: MicroRNA-30c reduces hyperlipidemia and atherosclerosis by decreasing lipid synthesis and lipoprotein secretion
abstract: Hyperlipidemia is a risk factor for various cardiovascular and metabolic disorders. Overproduction of lipoproteins, a process that is dependent on microsomal triglyceride transfer protein (MTP), can contribute to hyperlipidemia. We show that microRNA-30c (miR-30c) interacts with the 3′ untranslated region of MTP mRNA and induces its degradation, leading to reductions in MTP activity and in apolipoprotein B (APOB) secretion. miR-30c also reduces lipid synthesis independently of MTP. Hepatic overexpression of miR-30c reduced hyperlipidemia in Western diet–fed mice by decreasing lipid synthesis and the secretion of triglyceride-rich ApoB-containing lipoproteins and decreased atherosclerosis in Apoe−/− mice. Furthermore, inhibition of hepatic miR-30c by anti–miR-30c increased hyperlipidemia and atherosclerosis. Therefore, miR-30c coordinately reduces lipid biosynthesis and lipoprotein secretion, thereby regulating hepatic and plasma lipid concentrations. Raising miR-30c levels might be useful in treating hyperlipidemias and associated disorders.

title: Increased Intestinal Lipid Absorption Caused by Ire1β Deficiency Contributes to Hyperlipidemia and Atherosclerosis in Apolipoprotein E–Deficient Mice
abstract: High fasting serum lipid levels are significant risk factors for atherosclerosis. However, the contributions of postprandial excursions in serum lipoproteins to atherogenesis are less well-characterized. This study aims to delineate whether changes in intestinal lipid absorption associated with loss of inositol-requiring enzyme 1β (Ire1β) would affect the development of hyperlipidemia and atherosclerosis in Apoe−/− mice. We used Ire1β-deficient mice to assess the contribution of intestinal lipid absorption to atherosclerosis. Here, we show that Ire1b−/−/Apoe−/− mice contain higher levels of intestinal microsomal triglyceride transfer protein, absorb more lipids, exhibit hyperlipidemia, and have higher levels of atherosclerotic plaques compared with Apoe−/− mice when fed chow and western diets. These studies indicate that Ire1β regulates intestinal lipid absorption and that increased intestinal lipoprotein production contributes to atherosclerosis.

title: Mutual repression between steroid and xenobiotic receptor and NF-kappaB signaling pathways links xenobiotic metabolism and inflammation.
abstract: While it has long been known that inflammation and infection reduce expression of hepatic cytochrome P450 (CYP) genes involved in xenobiotic metabolism and that exposure to xenobiotic chemicals can impair immune function, the molecular mechanisms underlying both of these phenomena have remained largely unknown. Here we show that activation of the nuclear steroid and xenobiotic receptor (SXR) by commonly used drugs in humans inhibits the activity of NF-kappaB, a key regulator of inflammation and the immune response. NF-kappaB target genes are upregulated and small bowel inflammation is significantly increased in mice lacking the SXR ortholog pregnane X receptor (PXR), thereby demonstrating a direct link between SXR and drug-mediated antagonism of NF-kappaB. Interestingly, NF-kappaB activation reciprocally inhibits SXR and its target genes whereas inhibition of NF-kappaB enhances SXR activity. This SXR/PXR-NF-kappaB axis provides a molecular explanation for the suppression of hepatic CYP mRNAs by inflammatory stimuli as well as the immunosuppressant effects of xenobiotics and SXR-responsive drugs. This mechanistic relationship has clinical consequences for individuals undergoing therapeutic exposure to the wide variety of drugs that are also SXR agonists.

title: Evidence for multiple complementary pathways for efficient cholesterol absorption in mice Published, JLR Papers in Press, April 16, 2005. DOI 10.1194/jlr.M500023-JLR200
abstract: Apolipoprotein B (apoB)-dependent and apoB-independent pathways for cholesterol transport have been described in cultured cells. Here, we show that the apoB-independent pathway involves apoA-I-containing high density lipoproteins (HDLs). Cholesterol secretion by the HDLs, but not by the apoB pathway, was significantly reduced in primary enterocytes isolated from chow- and cholesterol-fed apoA-I−/− mice. These enterocytes were capable of cholesterol efflux when apoA-I was provided extracellularly. In apoA-I−/− mice, the absorption of a bolus of cholesterol was similar in control and apoA-I−/− mice fed chow or high-cholesterol diet. However, short-term studies revealed that cholesterol absorption was occurring over longer lengths of the intestine, and cholesterol but not triglyceride transport to the plasma and liver in chow- and cholesterol-fed apoA-I−/− mice was significantly reduced. These studies indicate that in apoA-I deficiency, there is a delay in cholesterol absorption, but cholesterol is eventually absorbed because of the compensatory apoB pathway. Nonetheless, long-term studies involving multiple feedings showed significant reduction in cholesterol absorption after 4 days. We propose that multiple compensatory mechanisms ensure efficient cholesterol absorption in mice.

title: Intestinal Phospholipid Remodeling Is Required for Dietary-Lipid Uptake and Survival on a High-Fat Diet.
abstract: Phospholipids are important determinants of membrane biophysical properties, but the impact of membrane acyl chain composition on dietary-lipid absorption is unknown. Here we demonstrate that the LXR-responsive phospholipid-remodeling enzyme Lpcat3 modulates intestinal fatty acid and cholesterol absorption and is required for survival on a high-fat diet. Mice lacking Lpcat3 in the intestine thrive on carbohydrate-based chow but lose body weight rapidly and become moribund on a triglyceride-rich diet. Lpcat3-dependent incorporation of polyunsaturated fatty acids into phospholipids is required for the efficient transport of dietary lipids into enterocytes. Furthermore, loss of Lpcat3 amplifies the production of gut hormones, including GLP-1 and oleoylethanolamide, in response to high-fat feeding, contributing to the paradoxical cessation of food intake in the setting of starvation. These results reveal that membrane phospholipid composition is a gating factor in passive lipid absorption and implicate LXR-Lpcat3 signaling in a gut-brain feedback loop that couples absorption to food intake.

title: Using primary murine intestinal enteroids to study dietary TAG absorption, lipoprotein synthesis, and the role of apoC-III in the intestine[S]
abstract: Since its initial report in 2009, the intestinal enteroid culture system has been a powerful tool used to study stem cell biology and development in the gastrointestinal tract. However, a major question is whether enteroids retain intestinal function and physiology. There have been significant contributions describing ion transport physiology of human intestinal organoid cultures, as well as physiology of gastric organoids, but critical studies on dietary fat absorption and chylomicron synthesis in primary intestinal enteroids have not been undertaken. Here we report that primary murine enteroid cultures recapitulate in vivo intestinal lipoprotein synthesis and secretion, and reflect key aspects of the physiology of intact intestine in regard to dietary fat absorption. We also show that enteroids can be used to elucidate intestinal mechanisms behind CVD risk factors, including tissue-specific apolipoprotein functions. Using enteroids, we show that intestinal apoC-III overexpression results in the secretion of smaller, less dense chylomicron particles along with reduced triacylglycerol secretion from the intestine. This model significantly expands our ability to test how specific genes or genetic polymorphisms function in dietary fat absorption and the precise intestinal mechanisms that are critical in the etiology of metabolic disease.

title: Targeting IκB kinase β in Adipocyte Lineage Cells for Treatment of Obesity and Metabolic Dysfunctions
abstract: IκB kinase β (IKKβ), a central coordinator of inflammation through activation of nuclear factor‐κB, has been identified as a potential therapeutic target for the treatment of obesity‐associated metabolic dysfunctions. In this study, we evaluated an antisense oligonucleotide (ASO) inhibitor of IKKβ and found that IKKβ ASO ameliorated diet‐induced metabolic dysfunctions in mice. Interestingly, IKKβ ASO also inhibited adipocyte differentiation and reduced adiposity in  (HF)‐fed mice, indicating an important role of IKKβ signaling in the regulation of adipocyte differentiation. Indeed, CRISPR/Cas9‐mediated genomic deletion of IKKβ in 3T3‐L1 preadipocytes blocked these cells differentiating into adipocytes. To further elucidate the role of adipose progenitor IKKβ signaling in diet‐induced obesity, we generated mice that selectively lack IKKβ in the white adipose lineage and confirmed the essential role of IKKβ in mediating adipocyte differentiation in vivo. Deficiency of IKKβ decreased HF‐elicited adipogenesis in addition to reducing inflammation and protected mice from diet‐induced obesity and insulin resistance. Further, pharmacological inhibition of IKKβ also blocked human adipose stem cell differentiation. Our findings establish IKKβ as a pivotal regulator of adipogenesis and suggest that overnutrition‐mediated IKKβ activation serves as an initial signal that triggers adipose progenitor cell differentiation in response to HF feeding. Inhibition of IKKβ with antisense therapy may represent as a novel therapeutic approach to combat obesity and metabolic dysfunctions. Stem Cells 2016;34:1883–1895

title: Perinatal Bisphenol A Exposure Increases Atherosclerosis in Adult Male PXR-Humanized Mice
abstract: Bisphenol A (BPA) is a base chemical used extensively in numerous consumer products, and human exposure to BPA is ubiquitous. Higher BPA exposure has been associated with an increased risk of atherosclerosis and cardiovascular disease (CVD) in multiple human population-based studies. However, the underlying mechanisms responsible for the associations remain elusive. We previously reported that BPA activates the xenobiotic receptor pregnane X receptor (PXR), which has proatherogenic effects in animal models. Because BPA is a potent agonist for human PXR but does not affect rodent PXR activity, a suitable PXR-humanized apolipoprotein E-deficient (huPXR•ApoE-/-) mouse model was developed to study BPA's atherogenic effects. Chronic BPA exposure increased atherosclerosis in the huPXR•ApoE-/- mice. We report that BPA exposure can also activate human PXR signaling in the heart tubes of huPXR•ApoE-/- embryos, and perinatal BPA exposure exacerbated atherosclerosis in adult male huPXR•ApoE-/- offspring. However, atherosclerosis development in female offspring was not affected by perinatal BPA exposure. Perinatal BPA exposure did not affect plasma lipid levels but increased aortic and atherosclerotic lesional fatty acid transporter CD36 expression in male huPXR•ApoE-/- offspring. Mechanistically, PXR epigenetically regulated CD36 expression by increasing H3K4me3 levels and decreasing H3K27me3 levels in the CD36 promoter in response to perinatal BPA exposure. The findings from the present study contribute to our understanding of the association between BPA exposure and increased atherosclerosis or CVD risk in humans, and activation of human PXR should be considered for future BPA risk assessment.

title: Myeloid β-Catenin Deficiency Exacerbates Atherosclerosis in Low-Density Lipoprotein Receptor-Deficient Mice
abstract: The Wnt/β-catenin signaling is an ancient and evolutionarily conserved pathway that regulates essential aspects of cell differentiation, proliferation, migration and polarity. Canonical Wnt/β-catenin signaling has also been implicated in the pathogenesis of atherosclerosis. Macrophage is one of the major cell types involved in the initiation and progression of atherosclerosis, but the role of macrophage β-catenin in atherosclerosis remains elusive. This study aims to investigate the impact of β-catenin expression on macrophage functions and atherosclerosis development.  To investigate the role of macrophage canonical Wnt/β-catenin signaling in atherogenesis, we generated β-cateninΔmyeLDLR−/− mice (low-density lipoprotein receptor–deficient mice with myeloid-specific β-catenin deficiency). As expected, deletion of β-catenin decreased macrophage adhesion and migration properties in vitro. However, deficiency of β-catenin significantly increased atherosclerotic lesion areas in...

title: IKKβ is a β-catenin kinase that regulates mesenchymal stem cell differentiation.
abstract: Mesenchymal stem cells (MSCs) can give rise to both adipocytes and osteoblasts, but the molecular mechanisms underlying MSC fate determination remain poorly understood. IκB kinase β (IKKβ), a central coordinator of inflammation and immune responses through activation of NF-κB, has been implicated as a critical molecular link between obesity and metabolic disorders. Here, we show that IKKβ can reciprocally regulate adipocyte and osteoblast differentiation of murine and human MSCs through an NF-κB-independent mechanism. IKKβ is a β-catenin kinase that phosphorylates the conserved degron motif of β-catenin to prime it for β-TrCP-mediated ubiquitination and degradation, thereby increasing adipogenesis and inhibiting osteogenesis in MSCs. Animal studies demonstrated that deficiency of IKKβ in BM mesenchymal stromal cells increased bone mass and decreased BM adipocyte formation in adult mice. In humans, IKKβ expression in adipose tissue was also positively associated with increased adiposity and elevated β-catenin phosphorylation. These findings suggest IKKβ as a key molecular switch that regulates MSC fate, and they provide potentially novel mechanistic insights into the understanding of the cross-regulation between the evolutionarily conserved IKKβ and Wnt/β-catenin signaling pathways. The IKKβ-Wnt axis we uncovered may also have important implications for development, homeostasis, and disease pathogenesis.