bluuebunny/crossref_metadata_2025 huggingface dataset:
Contribution of Prostaglandins to the Inspiratory Muscle Metaboreflex‐Induced Cardiovascular Consequences
Authors: Smith Joshua R , Didier Kaylin D , Hammer Shane M , Alexander Andrew M , Kurti Stephanie P , Barstow Thomas J , Harms Craig A
Published: November 2023

Activation of the inspiratory muscle metaboreflex leads to increases in mean arterial pressure (MAP) and limb vascular resistance (LVR) as well as decreases in limb blood flow (Q̇L). Inhibition of prostaglandin synthesis has previously been shown to attenuate skeletal muscle metaboreflex‐induced increases in muscle sympathetic nerve activity. However, it is not known if inhibition of prostaglandins will also attenuate the cardiovascular consequences of the inspiratory muscle metaboreflex.

Purpose

The purpose of this study was to determine the contribution of prostaglandins to the inspiratory muscle metaboreflex. We hypothesized that compared to placebo, inhibition of prostaglandin synthesis would attenuate inspiratory muscle metaboreflex‐induced1) increases in MAP and LVR and 2) decreases in Q̇L.

Methods

Seven college‐aged men were recruited and visited the laboratory on three different occasions. Subjects orally consumed ibuprofen (IB, 10mg/kg) or placebo (PLA) 90min prior to a cold pressor test (CPT) and inspiratory resistive breathing task (IRBT) at 65% of their maximal inspiratory mouth pressure. During the IRBTs, the breathing frequency was 20 breaths per min with a 50% duty cycle. At rest and during the IRBTs, MAP was measured via automated oscillometry, Q̇L was measured via Doppler ultrasound, and LVR was calculated. End tidal CO2 remained at baseline levels during the IRBTs. EMG was recorded on the leg to ensure no muscle contraction occurred.

Results

During the 65% IRBT, compared to PLA, IB led to greater (p<0.01) increases in MAP (IB: 16.8±6.7 mmHg; PLA: 8.4±4.7 mmHg) and LVR (IB: 68.6±27.7 %; PLA: 51.7±22.2 %). The decrease in Q̇L was not different (p=0.72) between IB (−27.7±11.0 %) and PLA (−26.7±9.3 %). The increase in MAP during the CPT was not different (p=0.87) between IB (IB: 24.7±10.9 mmHg) and PLA (PLA: 24.1±5.9 mmHg).

Conclusion

Contrary to our hypotheses, inhibition of prostaglandin synthesis, via ibuprofen, led to greater inspiratory muscle metaboreflex‐induced increases in MAP and LVR.

Support or Funding Information

Supported by ACSM Foundation Doctoral Grant
The role played by oxidative stress in evoking the exercise pressor reflex in health and simulated peripheral artery disease
Authors: Harms Jonathan E , Kim Joyce S , Kuczmarski J Matthew , Thomas Gail D , Kaufman Marc P
Published: November 2023

Contraction of skeletal muscle evokes the exercise pressor reflex (EPR), which is expressed in part by increases in heart rate and arterial pressure. Patients with peripheral artery disease (PAD) show an exaggerated EPR, sometimes report pain when walking and have an increased risk for cardiac arrthymias. Previous research has suggested that reactive oxygen species (ROS) mediate the exaggerated EPR associated with PAD. To examine the effects of ROS on the exercise pressor reflex, we infused a superoxide scavenger, Tiron, into the superficial epigastric artery of decerebrated rats. In some of these rats, we simulated PAD by ligating a femoral artery for 72 hours before the experiment. The peak EPR in ligated rats during saline infusion into the superficial epigastric artery averaged 31 ± 4 mmHg; n=12), whereas the peak EPR in these rats during Tiron infusion (1g/kg/hour) averaged (13 ± 2; p<0.001); the attenuating effect of Tiron on the EPR was partly reversed when saline was reinfused into the superficial epigastric artery (21 ± 2; p<0.01 vs tiron). Tiron infusion had no effect on the EPR in rats with patent femoral arteries (n=9). Western blots showed that the triceps surae muscles taken from rats whose femoral arteries were ligated expressed more Nox2 and p67phox, which are components of NADPH oxidase, than did triceps surae muscles taken from rats whose femoral arteries were freely perfused. Tiron added to muscle homogenates reduced ROS production in vitro. Our results provide further evidence that ROS mediates the exaggeration of EPR in rats with simulated PAD.

Support or Funding Information

Funded by NIH R01 AR059397, NIH R01 HL130987, and NIH P01 HL096570
Sestrin 2 and 3 Gene Expressions Correlate with Homeostasis Model Assessment of Insulin Resistance and Beta Cell Secretory Status in Older Men
Authors: Zeng Nina , Sharma Pankaja , Ramzan Farha , Mitchell Sarah M. , D'Souza Randall F. , Prodhan Utpal , Milan Amber M. , Mitchell Cameron J. , Cameron‐Smith David
Published: November 2023

Sestrins are a family of stress‐inducible proteins composed of three members (Sesn 1/2/3). They are involved in many physiological processes such as protecting organisms against oxidative stress by acting as antioxidants and playing a critical role in metabolic and glucose homeostasis by activating AMP‐activated Protein Kinase (AMPK), Mammalian Target of Rapamycin Complex 2 (mTORC2) and inhibiting mTORC1. Sesn3 has been observed to be upregulated in muscle biopsies obtained from patients with type 2 diabetes. Recent identification of the 3D structure of the human Sestrin 2 revealed a leucine‐binding pocket in its C‐terminal domain, suggesting a role as an intracellular leucine sensor.

The objective of the study was to further characterise the gene expression of each individual Sestrin members in the skeletal muscle of a non‐diabetic population.

Fasted plasma and muscle biopsies from vastus lateralis were collected from twenty‐eight men (74.1 ± 3.6 years). Plasma levels of fasting amino acid, glucose, insulin and lipid profiles were characterised. The Homeostasis Model Assessment (HOMA) software was used to estimate insulin sensitivity (HOMA %S) and beta cell secretory status (HOMA %B), as percentages of a normal reference population. The gene expressions of Sesn 1/2/3 were determined and correlated with the baseline blood chemistry and HOMA‐index.

The average HOMA%S of the subjects was 94.0 ± 44.0 % and HOMA%B was 86.2 ± 20.2%, while insulin resistance (HOMA‐IR) was 1.3 ± 0.6. HOMA‐IR and HOMA%B were positively correlated with body mass index, waist circumference, body fat mass, percent body fat and triglyceride (all p values <0.05 and r >0.45).

The gene expressions of Sesn2/3 correlated positively with insulin (p=0.03, 0.04; r=0.42, 0.39); HOMA‐IR (p= 0.04, 0.05; r=0.40, 0.38) and HOMA%B (p=0.002, 0.03; r=0.57, 0.41) respectively. Circulating baseline leucine concentration correlated positively with only Sesn 2 (p=0.01, r=0.45). Furthermore, the gene expressions of Sesn1 did not correlate with Sesn2/3.

Although Sesn 1/2/3 share strong sequence homology, their expressed genes are differentially regulated, with Sesn2 correlating to plasma leucine, whilst Sens2 and 3 correlate to insulin sensitivity. Each Sestrin paralog appears to play a unique physiological role.
Muscle‐Specific Calpastatin Overexpression Prevents Sarcopenia of Aging
Authors: Schroder Elizabeth A , Song Xiao‐Hong , Wang Lin , Supinski Gerald S , Callahan Leigh Ann
Published: November 2023

Sarcopenia is a major cause of disability. The precise mechanisms responsible for aging‐related muscle weakness and atrophy are not known. However, recent studies suggest that pathologic activation of calpain modulates skeletal muscle dysfunction in aging. We tested the hypothesis that skeletal muscle‐specific overexpression of calpastatin, the endogenous inhibitor of calpain, would ameliorate aging‐associated decrements in muscle function. Five month old and 25 month old wild type (WT) and muscle‐specific calpastatin overexpressing (CalpOX) male mice (n=23) were studied. Grip strength was used as an index of total forelimb strength. To assess hindlimb strength, we measured extensor digitorum longus (EDL) mass and muscle specific force generation. Aging significantly reduced fore‐limb grip strength (0.94 ± 0.06 vs 1.47 ± 0.06N for old WT vs young WT, respectively, p<0.001). Importantly, calpastatin overexpression mitigated the aging‐induced reductions in fore‐limb grip strength (0.94 ± 0.06 vs 1.22 ± 0.05 for old WT vs old CalpOX, respectively, p=0.007). Aging also induced loss of EDL mass; calpastatin overexpression significantly ameliorated these reductions (7.63 ± 0.33 vs. 9.17 ± 0.45 mg for old WT vs old CalpOX, respectively, p=0.02). While calpastatin overexpression increased EDL muscle mass, EDL force per unit mass was similar between old WT and old CalpOX animals. To our knowledge, this is the first report of the effects of muscle‐specific calpastatin overexpression on skeletal muscle function in aging rodents. These findings support the concept that calpain activation plays a role in aging‐induced sarcopenia. We speculate that therapeutic agents which attenuate calpain activation may preserve muscle function in the elderly.

Support or Funding Information

R01HL112085, 5I01BX002132, R01HL113494
Hypothalamic Pathways Involved in Adenosine A1 Receptor Agonist‐Induced Hibernation in the Arctic Ground Squirrel (Urocitellus paryii)
Authors: Frare Carla , Drew Kelly L.
Published: November 2023

Hibernation is an adaptive strategy characterized by metabolic suppression and regulation of thermogenesis to maintain energy balance in adverse environmental conditions. Previous study shows the role of adenosine A1 receptor agonist in promoting hibernation in the arctic ground squirrels. N6‐cyclohexyladenosine (CHA), an adenosine A1 receptor agonist, suppresses thermogenesis in a seasonally dependent manner. CHA induces hibernation in winter, while the effect is transient in summer: arctic ground squirrels counteract an initial decrease in metabolism restoring their euthermic values. These observations suggest that a higher order process regulates the seasonal CHA‐response, but if this phenomenon is driven by a seasonal modulation of thermogenesis is not known. The hypothalamus controls energy homeostasis regulating thermogenesis, in part, via the hypothalamic‐pituitary‐thyroid (HPT) axis. The intent of this research is to identify the hypothalamic nuclei activated in a seasonally dependent manner in response to CHA. Arctic ground squirrels were treated with CHA or vehicle at different seasonal points (summer and winter) and brains were collected 3h after treatment. Immunohistochemistry was used to localize active nuclei as indicated by cFos‐immunoreactivity (mouse anti‐cFos 1:20,000, Santa Cruz) focusing on the nuclei involved in thermoregulation and energy homeostasis. Specific markers (e.g. rabbit anti pro‐TRH 1:10,000 gift from Eva Redei) were used to define the phenotype of cFos‐ir neurons. Data show similar cFos‐ir in the paraventricular nucleus. These results suggest that mechanisms downstream to hypothalamic modulation of thermogenesis contribute to the higher order process regulating the seasonal CHA‐response.

Support or Funding Information

NIH R15NS070779 and Alaska INBRE P20GM103395
AICAR Attenuates Olanzapine‐Induced Hyperglycaemia and Insulin Resistance in C57BL6 Mice
Authors: Bush Natasha , Castellani Laura , Wright David C
Published: November 2023

Olanzapine (OLZ), an antipsychotic drug used in the treatment of schizophrenia, induces undesirable side effects including hyperglycaemia, glucose intolerance, dyslipidaemia, weight gain and insulin resistance, often resulting in the development of Type 2 Diabetes (T2D). The acute effects of OLZ on blood glucose are likely caused by a reduction in insulin secretion, the development of insulin resistance and increases in liver glucose production. 5′AMP‐activated protein kinase (AMPK) is a cellular energy sensor activated during exercise that has been shown to increase insulin sensitivity and increase insulin‐independent glucose uptake. Though having some off‐target effects, 5‐aminoimidazole‐4‐carboxamide riboside (AICAR) is a pharmacological agent that can activate AMPK in vivo. The purpose of this investigation was to determine if co‐treatment with AICAR would prevent acute OLZ‐induced increases in blood glucose in C57BL6 mice. AMPK and ACC phosphorylation was increased in liver, epididymal adipose tissue and triceps muscles 30 minutes following an injection of (AICAR) (250 mg/kg, IP injection) compared to vehicle treated mice. OLZ (5 mg/kg) caused rapid (15 minutes) and sustained increases in blood glucose that was prevented with AICAR co‐treatment. Treatment with OLZ attenuated the ability of insulin (0.75 U/kg, IP) to reduce blood glucose levels and this was partially prevented by AICAR. OLZ led to an exaggerated increase in blood glucose during a pyruvate tolerance test (2 g/kg, IP) and this was mitigated by AICAR. The results of the current study provide evidence that AICAR prevents OLZ‐induced hyperglycemia by preventing the development of peripheral insulin resistance and blunting increases in liver glucose output.

Support or Funding Information

D.C.W. is a Tier II Canada Research Chair. This research was funded by a NSERC Discovery Grant to D.C.W. N.B. was funded by CGS‐M (CIHR).
The Cellular Response to C‐peptide is Dependent on the Concentration of Glucose and Insulin
Authors: Rossiter Jackie Lee , Kolar Grant R , Yosten Gina LC
Published: November 2023

The role of insulin in the regulation of blood glucose has been the subject of extensive research. Insulin and C‐peptide, a 31 amino acid peptide, are co‐produced and co‐secreted by pancreatic beta islet cells. In 2013, a candidate receptor for C‐peptide was identified by our group to be the G‐protein coupled receptor, GPR 146. On release the relative concentrations of insulin to C‐peptide are 1:1, however due to differences in sites and rates of catabolism, in plasma the relative ratios of insulin to C‐peptide are 1:5. There is a growing body of evidence to support a physiologic role for C‐peptide in the prevention of co‐morbidities associated with microvascular damage in individuals with diabetes. These co‐morbidities include increased incidence of cardiovascular disease, retinopathies, renal failure and poor wound healing. We hypothesized that the cellular response to C‐peptide is dependent on the relative concentrations of C‐peptide, glucose, and insulin. In this study, HEK293 cells were incubated with varying levels of glucose (40 mg/dl, 115mg/dl, or 450 mg/dl), C‐peptide (0, 0.1nM, 1.0nM, or 10nM), or insulin (0, 100pM, 1000pM, or 2000pM). HEK293 cell responses were evaluated by comparing relative levels of cFOS, GPR146, and insulin receptor (IR) mRNA expression. Incubation of HEK293 in high glucose with basal levels (0.1nM) of C‐peptide resulted in HEK293 activation as measured by cFOS mRNA. Basal (0.1nM) C‐peptide induces production of GPR146 mRNA in conditions of low and high glucose but had no significant effect in normal glucose conditions. However, for HEK293 cells incubated with basal C‐peptide and high glucose, the addition of insulin ameliorated cellular activation induced by C‐peptide. Thus, the cellular responses to C‐peptide were dependent on ambient levels of glucose and insulin. These findings have important implications for the development of C‐peptide based therapies. C‐peptide therapeutics may be of benefit in high glucose conditions, however those benefits may be confounded the presence of exogenous insulin that exceeds physiologic parameters of insulin to C‐peptide (1:5).

Support or Funding Information

HL121456
Low Phosphorus Diet Enhances Insulin Sensitivity
Authors: Lin Yi , Berger Lindsey , Sun Zhongjie
Published: November 2023

Dietary phosphorus excess as a result of the ever growing consumption of highly processed foods, particularly fast food, restaurant meals, and convenience foods has been associated with developments of ageing related diseases such as cardiovascular diseases, kidney dysfunction, and bone loss in general human population. Insulin resistance is the main feature of aged human population especially in pandemic patients with type 2 diabetes. It is of great interest to know the impact of low phosphorus diet on glucose homeostasis such as insulin resistance and glucose tolerance. Here we study glucose homeostasis in male and female 129Sv mice fed with low phosphorus diet (0.2% of Pi) vs normal diet (0.3% of Pi). Interestingly, the fasting basal glucose level dropped significantly in male mice after being fed with low Pi diet for 4 weeks, compared to male mice fed with normal diet. In addition, low Pi diet significantly enhanced insulin sensitivity in both male and female mice in week 4 and week 9, compared to male and female mice fed on normal diet. No consist change in glucose tolerance was observed in mice of either genders. Furthermore, low Pi diet did significantly lower serum Pi levels in mice of both genders without interrupting their growing pattern of body weights during the 9‐week feeding period. Together, these data indicated that low Pi diet regulates glucose homeostasis likely via enhancing insulin sensitivity in mice. Therefore, low Pi diet might be one of strategies in the treatment of pandemic type 2 diabetes.
Effect of resistance exercise training in mitophagy of diabetic rats
Authors: Jorge luciana , Silva Kleiton Augusto , Luiz Rafael S , Rampaso Rodolfo R , Schor Nestor
Published: November 2023

Diabetic nephropathy (DN) is a progressive complication arising from diabetes. The repertoire of kidney cell response to injury includes cell division, cell hypertrophy, apoptosis and mitochondrial dysfunction. Increasing evidence indicates that the disruption of mitochondrial may be important in the development and progression of DN. On the other hand, the resistance exercise training is fundamental as non‐pharmacological intervention to prevent those complications. In this study, we investigated the effect of resistance exercise training (RET) on the DN pathogenesis. Male Wistar rats were divided into 4 groups: control (C=8), control trained (CT=8), diabetic (D=8) and diabetic trained (DT=8). Diabetes Mellitus (DM) (glycemia>250mg/dL) was induced by streptozootocina (STZ) (50mg/kg, i.v.). Trained groups were submitted to resistance exercise training protocol on ladder climb for 8 weeks. DN were accompanied by urinary volume and microalbuminuria and the expression of DRP‐1 and LC3 protein was evaluated by western blotting. The results indicate RET improved renal parameters in the DT group showing a decreased urinary volume (DS:160; DT:120; CS:13 and CT:14ml), microalbuminuria (DS:8.7; DT:4.7; CS:1.5; CT:2.3mg/24h). The renal expression of DRP‐1 and LC3 were enhanced in DS group and RET normalized this expression. Our findings demonstrated that RET increases in physical capacity and mitochondrial and renal benefits following training protocol, regardless of any improvement in glycemic control

Support or Funding Information

CNPQ, CAPES, Fapesp, FOC
Metformin Normalises Medullary Hypoxia in The Diabetic Rat Kidney
Authors: Christensen Michael , Schiffer Tomas , Nørregaard Rikke , Palm Fredrik
Published: November 2023

Background

Metformin is the first choice treatment of type‐2 diabetes where it can lower the level of blood glucose by inhibiting hepatic gluconeogenesis and increase cellular glucose uptake. Besides the effect on blood glucose metformin has also shown protective effects in several renal diseases including diabetic nephropathy. The development of hypoxia in the kidney is suggested to be an important driving force for the development of diabetic nephropathy and we therefore wanted to investigate how metformin affects the oxygenation levels and mitochondrial function in the diabetic kidney.

Methods

Sprague Dawley rats were injected with streptozotocin (STZ) (50 mg/kg) and when rats were diabetic, metformin (250 mg/kg) was administrated in the drinking water. Rats were prepared for In Vivo measurements 25–30 days after STZ injection. Rats were anesthetized, placed on a heating pad, tracheotomized and a catheter was placed in the left femoral vein for infusion of Ringer solution containing H‐inulin and Para‐aminohippurate. The left femoral artery was catheterized for blood pressure measurements and blood sampling. The left kidney was exposed by a subcostal flank incision, immobilized in a plastic cup and catheters were placed in the left ureter as well as bladder for collection of urine. Intrarenal pO2 was measured in kidney cortex and medulla by oxygen microsensors. To assess mitochondrial function, mitochondria were isolated from kidney cortex and medulla and analyzed by high‐resolution respirometry (Oroboros, O2‐K)

Important findings

Diabetic rats showed increased glomerular filtration rate (GFR), which was not affected by metformin treatment. PO2 was lower both in the outer medulla as well as cortex in the diabetic animals. Metformin treatment elevated PO2 in the outer medulla both in the control animals as well as in the diabetic animals. Isolated mitochondria from the outer medulla of diabetic rats showed a significantly higher GDP dependent respiration which was normalized by metformin treatment indicating inhibition of uncoupling protein 2 (UCP2) activity.

Conclusion

Metformin increases PO2 in the outer medulla both in control and diabetic animals, this could in part be mediated by inhibition of UCP2.
In Vivo Knockdown of I‐mfa Using The Targeted Nanoparticle Delivery System Ameliorated Renal Injury in Diabetic Mice
Authors: Ma Yuhong , Li Weizu , Jiang Hui , Wang Yanxia , Zuckerman Jonathan , Davis Mark , Ma Rong
Published: November 2023

Accumulation of extracellular matrix (ECM) proteins in glomerulus is one of early features of diabetic nephropathy. Glomerular mesangial cell (MC) is the major source of ECM. Inhibitor of Myogenic Family isoform a (I‐mfa) is a cytosolic protein interacting with components of Wnt/β‐catenin pathway and of store‐operated Ca2+ signaling pathway, both of which are involved in the development of diabetic nephropathy. The present study was carried out to determine if I‐mfa in MCs contributed to renal injury in diabetic mice. Twelve male mice were randomly divided into 4 groups (3 mice each group): non‐diabetes, diabetes, diabetes treated with scramble siRNA, and diabetes treated with siRNA against I‐mfa. Diabetes was generated by multiple low‐dose streptozotocin (STZ, 50 mg/kg) injections (intraperitoneal, once one day for 5 days) at an age of 6 weeks. Mice in group of non diabetes were injected with 10 mM citrate buffer (vehicle). Diabetes was indicated by a fasting blood glucose level of > 300 mg/dl. Scramble or I‐mfa siRNA treatment started 24 weeks after STZ injection and the treatment lasted 2 weeks. All siRNAs (10 mg/kg body weight) were delivered by our recently established‐targeted nanoparticle/siRNA delivery system which is glomerular mesangial cell specific. We found that STZ treatment significantly increased blood glucose level after 4 weeks of injection and reduced body weight 26 weeks after treatment. I‐mfa siRNA treatment did not improve hyperglycemia, but lessened renal hypertrophy in STZ mice. Furthermore, diabetic mice showed significantly greater 24 hour urine output and this diabetic uresis was compromised by I‐mfa siRNA treatment. Although knocking down I‐mfa did not mitigate albuminuria, it lowered the level of blood urea nitrogen in diabetic mice. Consistent with the functional data, histological examination showed improved mesangial expansion and glomerular fibrosis in I‐mfa siRNA‐treated STZ mice. Immunohistochemical examination showed a significant reduction of protein abundance of glomerular fibronectin and collagen IV in the siRNA‐treated diabetic mice. Taken together, our data indicate that I‐mfa in MCs is involved in the development of diabetic kidney disease and thus, could be a potential therapeutic target for diabetic nephropathy.

Support or Funding Information

AHA Southwestern Affiliate; Harry S. Moss Heart Trust; University Outstanding Talent Cultivated Projects of Anhui Province, China (gxfxZD2016118 and gxfxZD2016162)
GYY4137 modulates plasminogen activator inhibitor‐1‐dependent extracelluar matrix turnover in diabetic kidney via RAR/RXR signaling
Authors: John AM Sashi Papu , Pushpakumar Sathnur , Sen Utpal
Published: November 2023

Introduction

Diabetic kidney is associated with dysregulation of retinoic acid metabolism. Retinoic acid receptor (RARs) and Retinoid X receptor (RXRs) are nuclear receptors that function as transcriptional regulators of several genes involved in renal pathology; however, their role in the development of renal fibrosis in diabetes remains unknown. Further, peroxisome proliferator‐activated receptors (PPARs) and RAR is known to control RXR signaling leading to differential gene expression. A recent study has also linked RAR and RXR to increased expression of Plasminogen activator inhibitor‐1 (PAI‐1), a serine protease implicated in extracellular matrix (ECM) accumulation in diabetic nephropathy (DN). Hydrogen sulfide (H2S), a gasotransmitter with potent antioxidant and anti‐inflammatory property has been shown to mitigate adverse effects in DN; however, its role in targeting other molecular events in ECM turnover remains unexplored. The purpose of this study was to determine the role of RAR and RXR in the progression of DN and whether GYY4137, a H2S donor can mitigate ECM accumulation by modulation of PPAR/RAR controlled RXR signaling.

Methods

C57BL6/‐Ins2Akita/J, (Akita) mice representing type‐I diabetes and C57BL6/J (WT) mice were treated without or with GYY4137 (0.5 mg/Kg/d, IP, × 8 weeks). In vitro studies were done in mouse glomerular endothelial cells (MGECs) and treated with GYY4137 (250uM) for 24 h.

Results

In diabetic kidneys, the mRNA and protein expression of PPARγ was decreased and the expressions of RARs, RXRs and PAI‐1 were upregulated. Diabetic kidneys demonstrated increased matrix metalloproteinase‐9 expression and activity. Further, MMP‐13 was upregulated in diabetic mice. Immunohistochemistry showed increased collagen IV, laminin and fibronectin in the glomerular and interstitial areas. GYY4137 treatment reversed the changes above. In vitro studies demonstrated that PPARγ antagonism and RAR agonism in MGECs resulted in increased RXR signaling and PAI‐1 expression and was reversed following GYY4137 treatment. In addition, GYY4137 reduced the mRNA levels of Collagen IV, laminin and fibronectin and normalized the levels of elastin.

In conclusion, our data suggests that RXR signaling plays a significant role in excessive ECM turnover and GYY4137 modulates RXR signaling to reduce PAI‐1 mediated renal fibrosis in type‐I diabetes.

Support or Funding Information

DK104653, HL104103 and 15SDG25840013
Up‐regulatory of Transforming Growth Factor‐beta via Advanced Glycation End Products‐induced Oxidative Stress on NRK‐52E cells
Authors: Jeong So‐Ra , Yang Sung‐Yong , Lee Kwang‐Won
Published: November 2023

Advanced glycation end products (AGEs) play a critical role to diabetic nephropathy by stimulating fibrosis. Through binding to their cell surface receptor, receptor for AGEs (RAGE), they induce oxidative stress and AGE‐RAGE axis has been main cause intracellular signaling pathway. The AGE‐RAGE‐mediated generation of reactive oxygen species (ROS) stimulates transforming growth factor (TGF)‐β. NRK‐52E cells, the kidney proximal epithelial cell line, is commonly used representative kidney cell in the study of diabetic nephropathy. In this previous study, glycolaldehyde‐bovine serum albumin (BSA), glyceraldehyde‐BSA, and methylglyoxal‐BSA are the good generation of ROS on the cells. We were prepared BSA with respectively 20 mmol/L of glyceraldehyde, glycolaldehyde, methylglyoxal under aerobic conditions for 7days at 37°C in the incubator. These AGEs treatments are significantly increased ROS and TGF‐β expression of mRNA and protein level in NRK‐52E cells. These results may contribute to fibrosis in proximal epithelial cells and a renal dysfunction. AGEs may play a critical role in renal fibrosis leading to diabetic nephropathy. We will suggest that AGE‐induced predominantly through a TGF‐β1‐independent pathway, renal fibrosis leading to diabetic nephropathy
A ventral medial prefrontal cortex–dorsomedial hypothalamus monosynaptic pathway that drives sympathetic stress responses
Authors: Kataoka Naoya , Nakamura Kazuhiro
Published: November 2023

Psychological stress causes a variety of sympathetic responses in mammals, which help the body react quickly and effectively to the stressor. We have reported that stress induces thermogenesis in brown adipose tissue (BAT), hyperthermia and tachycardia by activating a direct neural pathway from the dorsomedial hypothalamus (DMH) to the rostral medullary raphe (rMR). However, the mechanism by which stress signals activate the DMH neurons driving the sympathetic stress responses remains unknown. Here we demonstrate that the ventral medial prefrontal cortex (vmPFC) is a major source of the stress signals to the DMH by performing in vivo physiological, optogenetic and neuroanatomical experiments in rats. Indicating the importance of glutamatergic inputs to the DMH in sympathetic stress responses, blockade of glutamate receptors in the DMH with bilateral nanoinjections of AP5/CNQX diminished BAT thermogenesis and hyperthermia evoked by social defeat stress, a sociopsychological stress model. Retrograde neural tracing from the DMH revealed numerous projections from the mPFC to the DMH, and anterograde tracing visualized putative synaptic connections of vmPFC‐derived glutamatergic axons to DMH neurons projecting to the rMR. Rats exposed to social defeat stress exhibited increased expression of Fos, a marker for neuronal activation, in DMH‐projecting neurons in the vmPFC, and inactivation of vmPFC neurons with bilateral muscimol nanoinjections diminished BAT thermogenic, hyperthermic, tachycardic and pressor responses evoked by social defeat stress. In contrast, inhibition of neurons in the dorsal part of the mPFC (dmPFC) exhibited a weaker inhibitory effect on these stress responses. Selective stimulation of vmPFC–DMH monosynaptic transmission using an in vivo optogenetic technique elicited BAT thermogenesis and tachycardia, which were both blocked by bilateral AP5/CNQX injections into the DMH. However, selective stimulation of dmPFC–DMH transmission did not increase BAT thermogenesis or tachycardia. These results indicate that the vmPFC–DMH glutamatergic monosynaptic pathway provides the DMH with excitatory stress signals to activate the DMH– rMR sympathoexcitatory pathway driving sympathetic stress responses.

Support or Funding Information

Funding: Grants‐in‐Aids for Scientific Research from MEXT, Japan (16K19006 to NK, 16H05128 & 15H05932 to KN); Takeda Science Foundation (KN); Uehara Memorial Foundation (KN); Brain Science Foundation (KN).
Four weeks of exposure to environmentally relevant levels of second hand smoke decreases heart rate variability—but not baroreflex sensitivity—in mice
Authors: Karey Emma , Pan Shiyue , Chen Yi‐Je , Pinkerton Kent E , Chen Chao
Published: November 2023

BACKGROUND

Second hand smoke (SHS), a source of environmental air pollution exposure, is a significant risk factor for cardiovascular morbidity and mortality. Impaired autonomic function, as indexed by decreased heart rate variability (HRV), has been implicated as one of the underlying mechanisms of increased arrhythmia susceptibility that often precedes sudden cardiac death. We previously showed, in mice, that short term (3 days) exposure to a high level of SHS (30 mg/m3, 6 hr/d) reduced HRV that persisted after this acute window of SHS exposure. However, we have limited information on the time course of SHS‐induced cardiovascular dysfunction at more environmentally relevant concentrations. Here, we sought to test the hypothesis that an environmentally relevant level of SHS decreases HRV and baroreflex sensitivity (BRS), while increasing blood pressure (BP) and BP variability (BPV).

METHODS

Adult male C57BL/6J mice were implanted with BP/ECG telemetry devices. Two weeks after recovering from surgery, mice were randomly assigned to either filtered air (FA, n=10 for HRV, n=5 for BPV and BRS) or SHS (n=6) groups. SHS exposure level was similar to that of a “smoky bar” (3 mg/m3) for 6hr/d, 5d/wk for 4wk. Weekly, 36 hours of continuous BP and ECG recordings were performed after five days of exposure. Data were divided into three 12‐hour periods: the dark cycle immediate after the 5th day of exposure and the following light and dark cycles. Standard time domain HRV parameters were determined from normal‐to‐normal R wave intervals (SDNN, CV% and rMSSD). BRS was determined with the sequence method using systolic BP.

RESULTS

SHS exposure for four weeks did not change BP and HR in either dark or light cycle. SHS significantly decreased short term HRV (rMSSD) during the light cycle in as few as two weeks of exposure (28% lower than FA group, p<0.05). However, there was no significant change in overall HRV (SDNN and CV%) after four weeks of SHS exposure. These data suggest that the initial change in cardiac autonomic regulation is likely mediated by reduced vagal regulation. There was a trend, but not statistically significant effect, for an increase in BPV (12% higher than FA group) after four weeks of SHS exposure; however, no change in BRS was observed after four weeks of SHS exposure. These data suggest that changes in cardiac regulation precede changes in BP regulation, and that the cardiac vagal limb of the autonomic nervous system is particularly sensitive to SHS exposure.

CONCLUSIONS

We conclude that this environmentally relevant dose of SHS can impair cardiovascular regulation in a time‐dependent manner, further emphasizing the importance of regulating and limiting exposure to SHS.

Support or Funding Information

R01 ES025229; T32 HL086350
Pressor Hyperreactivity to Stress Corresponds to Greater Vasoconstriction and Sympathetic Responsiveness and is Prevented by Renal Denervation
Authors: Knuepfer Mark M , Burris Sarah K , Perry Jeffrey L
Published: November 2023

Renal denervation is effective in reducing arterial pressure in some patients with resistant hypertension. The cardiovascular reactivity hypothesis proposes that enhanced pressor responsiveness to stressful stimuli in humans predicts predisposition to develop hypertension and cardiovascular disease. Clinical studies have suggested, but not always verified, that pressor hyperreactivity correlates with greater muscle sympathetic nerve activity (SNA) responses. Our laboratory has shown that outbred Sprague‐Dawley male rats have variable pressor responsiveness to acute stress (air jet or cold water exposure). We reported that rats with larger acute pressor responses to stress lose this greater sensitivity after renal denervation or selective deafferentation using intrarenal capsaicin administration. We hypothesized that greater pressor sensitivity in the rat model reflects greater sympathetic responsiveness and dependence on renal sensory input to promote sympathetic tone. Rats were instrumented for recording arterial pressure (AP), heart rate, ascending aortic blood flow as a measure of cardiac output and both renal and adrenal SNA. After recovery, rats were tested with a brief air jet (1 sec, 30 psi) to the face, and with cold water exposure (1 cm deep for 1 min) while recording hemodynamic and sympathetic variables. As expected, both renal and adrenal SNA were significantly increased, particularly during the initial few seconds after onset of the stressor exposure. Rats were separated into those with larger and those with smaller pressor responses (32.5 ±1.5 vs 23.6±0.9 mmHg) to cold stress. The differences correlated with greater increases in calculated systemic vascular resistance (44.1±3.3 vs 33.4±2.4%). They also correlated with greater increases in renal SNA (660±54 vs 488±32%, p<0.013) and greater increases in adrenal SNA (713±99 vs 450±48%, p<0.034). As noted, the differences in hemodynamic responses were prevented by renal denervation in a separate group of rats. After renal denervation, all rats had similar pressor and vasoconstrictor responses to cold water stress. We conclude that rats have variable pressor responsiveness that is correlated with greater renal and adrenal SNA. We predict that this model may reveal a means to study sympathetic hyperreactivity and how this is related to predisposition to develop cardiovascular disease. In the future, we will verify that SNA responses are also normalized by renal denervation.

Support or Funding Information

Supported by USPHS DA13256 and St. Louis University.
Small‐conductance Ca2+‐activated K+ (SK) channels regulate pre‐sympathetic neurons in the hypothalamic paraventricular nucleus (PVN) and parasympathetic cardiomotor neurons (CMN) in the nucleus ambiguus (NA): Pathological changes
Authors: Cheng Zixi , Lin Ming , Toney Glenn M. , Chen Qinghui
Published: November 2023

SK channels regulate action potential (AP) firing patterns and neuronal excitability in a Ca2+ dependent manner. Here, we report on (1) the functional role of SK channels in pre‐sympathetic neurons of the PVN and parasympathetic CMN of the NA and (2) the pathological contributions of SK channels in salt‐sensitive hypertension (SSH), maternal diabetes (MD) and chronic intermittent hypoxia (CIH). For PVN: Whole cell patch‐clamp recordings were made in brain slices from PVN neurons retrogradely labelled from the rostral ventrolateral medulla (RVLM). In current‐clamp recordings, we found that depolarizing current injections evoked action potentials that underwent spike‐frequency adaptation (SFA). Bath application of apamin increased PVN‐RVLM neuronal excitability, while attenuating current evoked SFA and the amplitude of the ensuing after hyperpolarization potential (AHP). In voltage‐clamp recordings, step depolarization elicited a Ca2+‐dependent delayed outward current (IAHP) that temporally corresponded to the AHP. IAHP was nearly abolished by the SK channel blocker apamin. Neurons from rats with SSH had diminished SK currents and enhanced excitability, which reflected reduced SFA and diminished AHP amplitude. Collectively, these data indicate that SK channels in PVN‐RVLM neurons play an important role in regulating excitability and suggest that diminished SK channel current in SSH could lead to increased neuronal discharge and thereby contribute to sympathoexcitation in this model of neurogenic hypertension. For CMN: The tracer XRITC was injected into the pericardial space to label parasympathetic CMN in mice. Two days later, whole cell recordings were made from labeled CMN in brainstem slices. In current‐clamp recordings, depolarizing current injections evoked spike trains that underwent SFA. Bath application of apamin increased neuronal excitability, abolished SFA and suppressed the amplitude of the AHP. In voltage clamp recordings, a Ca2+‐dependent, apamin‐sensitive IAHP was identified. In mice with MD and mice exposed to CIH, the apamin sensitive IAHP was enhanced and excitability was reduced, suggesting that SK channels negatively regulate AP discharge of CMN and could contribute to impaired vagal baroreflex control of the heart in these disease models. Ongoing studies in disease models seek to determine mechanisms to explain why SK channel function is diminished in PVN pre‐sympathetic neurons but enhanced in NA parasympathetic neurons.

Support or Funding Information

Support: HL‐79636 (ZC), HL‐088052 (GMT) and HL‐122952 (QHC).
Physiological Plasticity and Tolerance of Fundulid Killifish Species to Aquatic Hypoxia
Authors: Hoffman Ryan , Borowiec Brittney , Scott Graham , Adams Chelsea , Galvez Fernando
Published: November 2023

Aquatic hypoxia is a naturally occurring phenomenon in waters subject to high primary production, eutrophication, and salinity‐derived stratification. Fish utilize a suite of physiological responses in order to cope with aquatic hypoxia. Species that regularly experience repeated bouts of hypoxia may rely more heavily on compensatory responses in order to survive. We hypothesized that species from hypoxia‐prone environments such as estuaries are more tolerant to hypoxia than species living in stable environments. We also hypothesized that species from variable environments would show a greater scope for phenotypic plasticity in their physiological acclimation responses to hypoxia. Fundulid killifish species from different ecological niches (marine‐tolerant Lucania parva and Fundulus confluentus and freshwater‐tolerant L. goodei and F. rathbuni) were acclimated for 21–28 d to either constant hypoxia or diurnal cycles of intermittent hypoxia (12 h normoxia: 12 h hypoxia). We then assessed the resting O2 consumption rates and hypoxia tolerance (critical O2 tension, O2 tension at loss of equilibrium, and time to loss of equilibrium at 0.6 kPa O2). Our results show that F. confluentus, an estuarine killifish, demonstrated much greater hypoxia tolerance than F. rathbuni, which inhabits freshwater rivers and creeks. Also, the sister taxa, Lucania parva and L. goodei demonstrated very similar baseline hypoxia tolerance. Acclimation to intermittent or constant hypoxia often (but not always) significantly improved hypoxia tolerance, but there were no clear patterns of variation in this plasticity between species from different environments. Our data suggest that plasticity can vary between even closely related species. Future work will compare the unique physiological strategies of each species for coping with hypoxia.

Support or Funding Information

We would like to thank the American Physiological Society's Undergraduate Summer Research Fellowship program, Louisiana Sea Grant, Louisiana State University, McMaster University, the Society of Experimental Biology, the National Science Foundation, and the Natural Sciences and Engineering Research Council of Canada for funding and support.
Diving Mice vs. Torpid Mice: A Comparison of Cardiovascular Regulation
Authors: Hult Elissa M , Bingaman Mark Jake , Swoap Steven John
Published: November 2023

The diving response is a coordinated physiological response to submersion into water, and is used widely amongst mammals. The physiological response is composed of three primary effects: an immediate drop in heart rate, a reduced drive to breathe, and constriction of peripheral blood vessels. The diving response is important, not only because of its dramatic influence of the autonomic nervous system, but also because it inhibits or alters normal homeostatic reflexes such as the drive to breathe. We hypothesized that the cardiovascular effects and neural circuitry involved in the murine dive response are similar to those used in daily torpor. In this study, telemeters that measure arterial pressure and body temperature were implanted into female C57Bl/6J mice. These mice were trained to swim then voluntarily dive underwater for a distance of 60 cm over a 5 second period. After a recovery period, the same mice were calorically restricted to induce a bout of torpor. Just before the dive, the interbeat interval (IBI) was 87±3 msec and diastolic pressure was 100±8 mmHg. Diving caused a dramatic bradycardia immediately at the onset of each dive (IBI increased to 464±60 msec) and diastolic pressure dropped to 56±9 mmHg, that coincided with elevated peripheral resistance. Mice experienced a short bout (~5 sec) hypertension (diastolic pressure rose to 133±9 mmHg) upon emergence. The bradycardia and hypotension were dependent on vagal influence, as pre‐treatment with atropine blocked these responses. The same absolute changes to heart rate, blood pressure, and total peripheral resistance were observed in the torpid mouse, albeit at a different time scale. These data suggest that the drivers of the cardiovascular changes during a bout of torpor and during the diving response are likely shared.

Support or Funding Information

Supported by 1R15HL120072‐01A1 to SJS
Autonomic Control of Thermogenic Capacity is Optimized in Deer Mice Native to High or Low Altitudes
Authors: Wearing Oliver H , Tate Kevin B , Scott Graham R
Published: November 2023

The North American deer mouse (Peromyscus maniculatus) ranges from below sea level to above 4,300 m elevation. To survive the cold hypoxic conditions at altitude, highland populations must sustain high rates of aerobic thermogenesis in an oxygen scarce environment. Here, we investigated whether differences in autonomic control of the cardiovascular system contributes to the increased thermogenic capacity (V̇O2max) of deer mice native to high altitudes. We compared captive breeding colonies derived from wild populations at high and low altitudes, and measured V̇O2max in cold hypoxia following intraperitoneal (i.p.) injection of adrenergic agonists/antagonists. Following control saline injection, highland mice had higher mass‐specific V̇O2max than lowland mice. Both α‐adrenergic agonist and antagonist reduced V̇O2max by a similar magnitude in both populations, indicating that α‐adrenergic vascular tone is naturally optimized to enhance blood flow to tissues responsible for thermogenic V̇O2max, and that functional sympatholysis does not contribute to population differences in V̇O2max. β2‐adrenergic tone had no effects on V̇O2max, suggesting that these receptors are not required to achieve thermogenic V̇O2max. β1‐adrenergic tone appears to be maximized to achieve V̇O2max in both populations, because β1‐agonist (dobutamine) had no effect on V̇O2max whereas β1‐antagonist (metoprolol) reduced V̇O2max. Preliminary experiments in anaesthetized mice confirmed that pharmacological agents entered the circulation after i.p. injection and had predictable effects on heart rate and blood pressure. Our results therefore suggest that autonomic control of the cardiovascular system is optimized during thermogenesis in hypoxia, such that population differences in V̇O2max do not arise from evolved changes in autonomic control.

Support or Funding Information

Supported by NSERC of Canada