bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three Hours of Intermittent Hypoxia in Young Healthy Humans Induces Electrocardiographic Changes
Authors: Baker Sarah E. , Newhouse Lauren P. , Joyner Michael J. , Curry Timothy B. , Limberg Jacqueline K. 
Published: November 2023

BackgroundIndividuals with sleep apnea experience repeated intermittent hypoxic exposures during sleep. Previous work in sleep apnea showed patients have an increased heart rate (HR), corrected QT interval (QTc), QTc dispersion and P‐wave maximum duration and dispersion (max‐min P‐wave duration). Such changes have been linked to increased risk of cardiovascular disease and sudden cardiac death. Unfortunately, the mechanisms contributing to these changes are not completely understood. Given that individuals with sleep apnea experience repeated intermittent hypoxic exposures during sleep, we tested the hypothesis that exposure to intermittent hypoxia (IH) in young healthy adults would result in similar ECG changes to those seen in patients with sleep apnea.MethodsTo test this hypothesis, we completed ECG analysis of 7 healthy humans (6M/1F, Age=29±5 years, BMI=24±4kg/m2) without sleep apnea before and after 3‐hours of exposure to IH. Subjects were exposed to hypoxic gas (0.05 FiO2) for 25‐seconds separated by 2‐minutes of room air breathing. This resulted in 25 hypoxic events per hour in which oxygen saturation was significantly reduced (Normoxia: 97%, Hypoxia: 89%, p<0.01). ECG analysis was completed in Lab Chart 7 software and consisted of measurement of intervals (RR, PR, QT), durations (P, QRS), and amplitudes (P, Q, R, S, T) during 10 minutes of normoxic quiet rest before and after IH exposure. QTc was calculated using Bazett's formula (QT duration/√HR). Dispersion of QTc and P waves were calculated as max duration ‐min duration.ResultsHR was significantly increased following IH (60±8 vs. 66±8 beats/min, baseline vs. post‐IH, respectively, p<0.05). There was no significant change in P‐wave maximum duration or dispersion following IH. QT interval was significantly decreased and QTc was significantly increased following IH (QT interval: 377±13 vs. 368±8ms, QTc: 377±22 vs 384±22ms, baseline vs. post‐IH, p<0.05 for both). QTc dispersion was not significantly different from baseline following IH.ConclusionsWe found that 3 hours of experimentally‐induced IH in young healthy individuals resulted in increased HR, decreased QT interval, and increased QTc. These data suggest that IH exposure experienced by patients with sleep apnea may contribute to ECG changes commonly observed in this population and subsequent increases in cardiovascular morbidity and mortality.Support or Funding InformationFunding: DK90541 (MJJ), HL120570 (JKL)
REDD1 Alters the Rate of Muscle Hypertrophy following Functional Overload
Authors: Gordon Bradley Scott , Nader Gustavo , Steiner Jennifer L , Jefferson Leonard S , Kimball Scot R 
Published: November 2023

Overload‐induced skeletal muscle hypertrophy is due to an accretion of muscle protein, however the events that initiate the response are poorly understood. We recently showed that expression of Regulated in Development and DNA Damage 1 (REDD1), a repressor of signaling through the mechanistic target of rapamycin in complex 1 (mTORC1), significantly reduces the rate of protein synthesis following an acute bout of high frequency muscle contractions. However, it is unknown whether REDD1 expression alters the rate of overload‐induced muscle hypertrophy. To address this question, REDD1+/+ and REDD1−/− mice were subjected to unilateral functional overload (OV) of the plantaris by removal of the synergists while the contralateral sham leg served as an internal control. Mice were allowed to recover for 3 or 5 days. After 3 days of OV, mice were fasted for 16 hr, and puromycin was injected 30 min prior to sacrifice for measurement of the rate of protein synthesis. The percent increase in plantaris wet weight relative to sham was significantly greater in REDD1−/− mice at both time points which was due to increased protein content. Further examination of the early events after 3 days of OV revealed a similar rate of protein synthesis between genotypes despite increased mTORC1 activation in the REDD1−/− mice compared to controls (phosphorylation of p70S6K1 (Thr389) and 4E‐BP1 (Ser65)). Additionally, the increase in RNA content as well as the content of the 45S pre‐rRNA was not different between genotypes after 3 days OV. There was also no difference in the content of ubiquinated proteins between genotypes. These data suggest REDD1 expression regulates muscle mass following OV due to initiating events that occur prior to 3 day of OV.Support or Funding InformationSupported by NIH grant DK15658 (LSJ)
The role of denervation in cytokine‐mediated muscle dysfunction in muscles of old mice
Authors: Staunton Caroline Amy , Pollock Natalie , Lightfoot Adam , Vasilaki Aphrodite , Barrett‐Jolley Richard , McArdle Anne , Jackson Malcolm 
Published: November 2023

Age‐related loss of muscle mass and function occurs over a substantial portion of later life and greatly influences the quality of life of older people. The causes of this dysfunction are unknown, but substantial remodelling and loss of motor units and denervation are evident in muscles of old mice. Full denervation of muscle caused elevations in the rate of mitochondrial H202 production. Data from our laboratory have demonstrated that H202 was elevated in muscle at 3 days post‐denervation and remained significantly elevated for 10 days, compared with sham controls. Further work from our laboratory has shown that this increase in H2O2 is also evident in the innervated portion of partially denervated muscle. The aim of this study was (1) to use intra‐vital imaging in Thy1‐CFP mice to determine the structure of peripheral axons and neuromuscular junctions in single muscle fibers in vivo and to simultaneously monitor H202 in the muscle fibers using AAV6‐Hyper2‐Cyto mice; (2) to examine the downstream effects of increased H2O2, including NF‐kB activation and production of pro‐inflammatory cytokines in whole muscles and in individual fibers and (3) whether these processes contribute to age‐related muscle dysfunction. Data demonstrate that the increased H2O2 in fully denervated muscle of adult mice was associated with activation of NF‐kB and increased production of pro‐inflammatory cytokines; IL‐6 (302% increase), MCP1 (324% increase) and CXCL1 (261% increase), all as early as 1 day post‐denervation (p<0.05, Students T‐Test), in a similar manner to quiescent muscles of old mice. These data suggest that denervation of individual muscle fibers in old mice results in significant elevations in H2O2 production in both denervated and innervated fibers and that this may play a role in the increased activation of NF‐kB and local production of pro‐inflammatory cytokines seen in muscles of old mice. Additional studies will explore neuromuscular transmission using electrophysiology in single fibers to determine the effects of different degrees of loss of neuromuscular junction integrity on neuromuscular transmission and the relationship of this to H202 production.Support or Funding InformationSupported by the UK Medical Research Council.
Repeated bouts of resistance training with short interval activate Akt‐mTOR signaling, but not protein synthesis in mouse skeletal muscle
Authors: Takegaki Junya , Arihara Yuki , Ogasawara Riki , Tsutaki Arata , Nakazato Koichi , Ishii Naokata 
Published: November 2023

Resistance training activates Akt‐mTOR signaling pathway, thereby stimulates the protein synthesis within skeletal muscle. However, insufficient recovery period between training bouts may lead to the accumulation of fatigue, known as “overtraining”.PurposeTo obtain an insight into the mechanism of overtraining, changes in muscle protein synthesis and Akt‐mTOR signaling activity were investigated with changing the interval between training bouts.MethodsMale C57BL/6J mice were randomly assigned into four groups: Control (Cont), resistance‐trained with 3 bouts at interval of 72h (72H), 24h (24H) and 8h (8H). The resistance exercise consisted of 50 repetitions of maximal isometric contraction of the tibialis anterior muscle. The muscle contraction was induced by transcutaneous electrical stimulation of deep fibular nerve under anesthesia. Muscle samples were collected 6h after the final exercise session, and kept frozen until analysis. Fifteen minutes prior to the muscle sampling, mice were injected with 0.04 μmol/g puromycin.ResultsPhosphorylation of Akt and p70S6K was observed in 24H and 8H, and that in 8H was significantly higher than in 24H. The phosphorylation of rpS6 was observed in all exercised groups, and was higher in 24H and 8H than in other groups. Puromycin‐incorporated proteins, i.e., newly synthesized proteins in ribosomes, increased in 72H, but not in 24H and 8H.ConclusionThe present results suggest that bouts of resistance training with interval shorter than 24h do not cause an increase in protein synthesis, even though activate Akt‐mTOR signaling pathway.
The Use of an Adenine Diet to Induce Uremic Cardiac Hypertrophy in Mice
Authors: Adamic Emily M , Von Schulze Alex , Amat‐Fernandez Clara , Lee Harold , Daniel Dorothy , Wacker Michael J , Touchberry Chad D 
Published: November 2023

Over 90% of patients with chronic kidney disease (CKD) will develop cardiac hypertrophy and approximately half of them will die from cardiovascular disease. Recently, our lab and others have shown that uremic toxins like fibroblast growth factor 23 can directly induce pathological cardiac hypertrophy. While the understanding of the mechanisms responsible for cardiac hypertrophy in uremia is improving, there is a strong need to establish a simple, non‐surgical, and reproducible mouse model of uremic cardiac hypertrophy. An adenine diet has been shown to cause nephropathy and uremia; however, the link between ingestion of adenine and uremic cardiac hypertrophy has not been established. The objective of the present study was to develop a mouse model of dietary adenine‐induced uremia that results in cardiac hypertrophy. Thirty CD1 mice were randomly divided into two groups and fed for 12 weeks: 1) a control group (CON, n=15) fed standard feed, and 2) an adenine (0.2–0.15%) diet intervention group (AD, n=15). The percentage of adenine was adjusted weekly based on temporal assessments of blood urea nitrogen (BUN) to ensure initiation and maintenance of renal injury. Throughout the protocol, the BUN in AD mice was significantly elevated (~80 mg/dl) compared to that of the controls (~30 mg/dl). Post‐intervention, serum levels of BUN (+118%), creatinine (+72%), and phosphate (+107%) were significantly higher in the AD mice. Kidney mass/body mass ratio was significantly lower (−38%) in AD mice, suggesting renal atrophy. The AD mice also had increased heart mass/body mass ratio (+25%) and increased ventricular wall thickness, consistent with hypertrophy. Our data suggests that over 12 weeks, the induction of uremia in the AD group resulted in cardiac hypertrophy. Adenine diet fed mice may be a suitable model to study novel therapeutic treatments to prevent or treat the development of cardiac hypertrophy during uremia.Support or Funding InformationUniversity of Memphis Faculty Research Grant to CDT; Honors Summer Research Fellowship, University of Memphis Helen Hardin Honors Program to EMA
Striatin expression is altered during cardiac remodeling and it regulates cardiomyocyte response to adrenergic stimuli
Authors: Alotaibi Shahd , Alsolme Ebtehal , Alsomali Rahmah , Kvietys Peter , Dzimiri Nduna , Nader Moni 
Published: November 2023

Mounting evidence implicates striatin in regulating cardiac function by virtue of its interaction with regulators of the L‐type calcium channel (LCC), i.e. caveolin‐3, protein phosphatase 2A, and calmodulin. We have previously shown that knockdown (KD) of striatin using shRNA (shRNA‐STRN) in neonatal rat cardiomyocytes reduced the rate of their spontaneous contraction and desensitized them to isoproterenol. We aimed to explore if the expression of STRN is altered during cardiac remodeling using Spontaneously Hypertensive Rats (SHR) and if STRN modulates the adrenergic response in cardiomyocytes. Herein, we show that STRN expression is higher in the left ventricle (LV) of SHR when compared to Wistar Kyoto (WKY) rats at the age of 4 weeks. Surprisingly, at the age of 18 weeks, the expression of STRN in LV was less in SHR when compared to WKY rats. KD of STRN in cultured cardiomyocytes did not affect the expression of the LCC. However, confocal microscopy revealed that an isoproterenol challenge resulted in less intracellular calcium [Ca2+]i in cardiomyocytes with lower amounts of STRN (KD) when compared to control cells (benign shRNA). Moreover, the rise in [Ca2+]i with respect to the baseline levels, was lower in shRNA‐STRN cardiomyocytes. Collectively, our data show that STRN levels are altered during the development of cardiac pathology. In addition, STRN plays a fundamental role in regulating cardiac [Ca2+]i responses to adrenergic stimuli and emerges as a novel therapeutic target for cardiac diseases.Support or Funding InformationThis work is supported by a KACST operating grant (#13‐BIO1452‐20) to MN and PK, and by Alfaisal University.
High‐Throughput Contractile Force Screening for Discovery of Novel Bronchodilators
Authors: Park Chan , Burger Stephanie , Watts Eleanor , Frykenberg Matthew , Tambe Dhananjay , Zhou Enhua , Krishinan Ramaswamy , Marinkovic Aleksander , Tschumperlin Daniel , Butler James , Solway Julian , Fredberg Jeffrey 
Published: November 2023

In pathologies of the heart, blood vessels, and airways, and in cancer as well, the ultimate therapeutic target is often modulation of cellular contractile force. For discovering new therapies, drug screening technologies typically use biochemical or structural surrogates for contractile force rather than contractile force itself. Because such approaches are indirect, some hits are false while other potential hits could be missed. To fill this gap, we developed a new high‐throughput method that utilizes cellular contractile force directly as the reporter ‐‐called contractile force screening (CFS)‐‐ and established feasibility of CFS in the context of drug discovery in asthma. During an acute asthma attack, contractile forces generated by airway smooth muscle cells act to constrict the airway and thus obstruct airflow. To dilate constricted airways, asthma patients use bronchodilators to reduce these contractile forces and thus allow the airway to open more fully, but currently available bronchodilator medications often fail to relax that muscle sufficiently, especially in severe asthma. To address this unmet need for more effective bronchodilator medications, we implemented CFS to evaluate 10,000 small molecule compounds selected randomly from the Chembridge DIVERset® library.Acrylamide gels were made in 96‐well plates and fluorescent markers and collagen were coated onto gel surfaces. Upon each gel we cultured primary human airway smooth muscle (HASM) cells to near confluence. Drug effects were quantified as the ‘force response ratio’, namely, the ratio of the contractile forces before and after drug addition. By screening mixtures of 8 compounds simultaneously, we were able to evaluate 2000 compounds per week in quadruplicate. After retesting individual compounds from initially positives, we identified 2 individual compounds that relaxed HASM cells in a dose‐dependent and a non‐toxic manner. The mechanism of action is still under investigation but we found that these compounds work independent of cAMP. CFS provides a convenient, rapid, and inexpensive platform for drug discovery based upon a physiological endpoint, namely, cell contractile force. Furthermore, CFS technology has the potential to become a new high‐content assay for drug discovery in any disease process in which cellular contractile force plays a central role.Support or Funding InformationNIH P50HL107171 (CADET phase I), R01EY019696 (Eye BRP), NRF GRN (NRF‐2013S1A2A2035518)
Ablation of the Semaphorin 3F‐Neuropilin 2 Axis Increases Contractility in Bladder Smooth Muscle
Authors: Bielenberg Diane R , Vasquez Evalynn , Doyle Claire , Lukianov Stefan , Cristofaro Vivian , Sullivan Maryrose P , Adam Rosalyn M 
Published: November 2023

IntroductionImpairment of the strength or duration of bladder smooth muscle (SM) contraction characterizes a prevalent but poorly understood clinical condition termed detrusor underactivity (DU). DU is a complex disorder that arises from diverse neuromuscular insults. DU reduces voiding efficiency and can lead to significant urologic complications. Despite significant morbidity, no effective treatment exists for this condition. Neuropilins (Nrp) are transmembrane receptors that bind class 3 semaphorin (Sema3) proteins. We identified bladder SM as a major site of expression of Nrp2 in vivo, and showed that bladder SM strips from mice with genetic deletion of Nrp2 displayed increased contractility compared to those from wild‐type littermates, identifying Nrp2 as a negative regulator of SM contractility. In this study we expanded our analysis of this signaling axis by examining the localization of the Nrp2 ligand, Sema3F, in bladder tissue and compared the contractility of bladder SM in Sema3F knockout mice compared to wild‐type mice. We tested the hypothesis that Nrp2 deletion in vivo improves bladder SM function under conditions of DU.MethodsNrp2 and Sema3F protein expression was localized by immunohistochemistry. Partial bladder outlet obstruction (pBOO) was created surgically in male mice at 3 mos of age by urethral occlusion. We used SM22a‐CreERT2:Nrp2fl/fl mice to achieve tamoxifen‐inducible SM‐specific Nrp2 knockout either before creation of pBOO or during the decompensation phase following pBOO. Nrp2‐expressing mice (Nrp2fl/fl mice) were used as controls and sham surgery was performed to control for pBOO. Bladder SM contractility was assessed by isometric tension testing.ResultsSema3F expression was found in the urothelium and Nrp2 expression was highest in the bladder SM, suggesting a paracrine signaling axis. Sema3F deletion resulted in increased contractility of bladder SM similar to that seen in Nrp2 KO mice. After pBOO, bladder weight increased in both Nrp2‐intact and Nrp2‐deleted mice. Bladder SM from mice in which Nrp2 was deleted prior to pBOO displayed increased contractility at all time points after pBOO compared to tissues from Nrp2‐intact mice. Bladder SM from mice in which Nrp2 was deleted during decompensation showed increased force of contraction compared to obstructed mice in which Nrp2 was not deleted (p<0.05).ConclusionsThese observations demonstrate that downregulation of Nrp2 by genetic deletion promotes increased bladder SM contractility under conditions of chronic bladder outlet obstruction. Importantly, they show that deletion of Nrp2 in mice that have already undergone bladder decompensation can restore SM contractile function, suggesting that Nrp2 may be a therapeutic target in conditions characterized by detrusor underactivity.Support or Funding InformationVascular Biology Program, Boston Children's Hospital; NIDDK DK65298
Integrin‐Linked Kinase Enhances Skeletal Muscle Fatty Acid Metabolism In Vivo
Authors: Lark Daniel S , Trefts Elijah , James Merrygay , Zent Roy , Pozzi Ambra , Wasserman David H 
Published: November 2023

Accumulation of extracellular matrix (ECM) components and activation of specific integrin receptors contribute to skeletal muscle (SkM) insulin resistance in the high fat (HF)‐fed mouse. Integrin‐linked kinase (ILK) is an adaptor protein that serves as a hub for the integrin signaling but its role in metabolism is poorly defined. A shift from glucose to fatty acid (FA) oxidation is a hallmark of insulin resistance and diabetes, but the mechanisms responsible for this shift in nutrient utilization are unclear. Integrins have been implicated in the transcriptional regulation of mitochondrial biogenesis and are known to interact with FA transporters at the plasma membrane. The objective of this study was to test the novel hypothesis that integrins, through ILK signaling, enhance SkM FA metabolism under insulin resistant conditions.SkM‐specific ILK knockout mice (mILK‐KO) were generated using mice expressing Cre recombinase on the human SkM actin (HSA) promoter. Body weight was measured weekly and body composition was measured immediately prior to and following energy balance studies. mILK‐KO and their wild type (WT) littermates were fed a chow or HF diet (60% calories from fat) for 27 weeks then placed in metabolic cages for five days (n=6–9/group). Tissues were collected after a 5‐h fast. Pyruvate and FA‐supported mitochondrial respiratory capacity was measured in permeabilized SkM myofibers (PmFBs) from the soleus and EDL. Muscle free fatty acids (FFAs) and triglycerides (TGs) were measured in gastrocnemius with gas chromatography. Comparisons were made using Student's t‐test or 2‐way ANOVA as appropriate.HF‐fed mILK‐KO mice had a decreased reliance on FA oxidation compared to their WT littermates, as suggested by the increase in RQ. This RQ difference was independent of changes in whole body energy expenditure, body composition, food consumption or spontaneous activity. RQ was unchanged in mILK‐KO mice fed a chow diet. FA‐supported PmFB respiration was decreased in EDL, but not soleus, of HF‐fed mILK‐KO mice. Respiration in chow‐fed mice was not affected by muscle ILK deletion. Total muscle FFAs and TGs were increased by HF feeding but lower in mILK‐KO mice fed a HF diet. Muscle lipids were unaffected by ILK deletion in mice on a chow diet.These data are the first to demonstrate a mechanistic role for integrin signaling in the regulation of SkM FA metabolism in vivo and suggest that integrin signaling, through ILK, responds to nutrient overload by enhancing the uptake, storage and oxidation of FAs in SkM. These findings provide strong support for a model where extracellular cues (e.g. ECM expansion) cause a coordinated shift in cellular energetics, a paradigm that may permit for therapeutic targeting of oxidative metabolism through integrin receptors.Support or Funding InformationFunding for this project was provided by the following NIH grants: R01 DK054902, U24 DK059637, P30 DK020593, and T32 DK007061.