bluuebunny/crossref_metadata_2025_split huggingface dataset:
Highland Andean Populations Show Reduced Variation in the Hypoxic Ventilatory Response
Authors: Heinrich Erica C. , Gaio Eduardo , Powell Frank L. , Macarlupú José Luis , Anza‐Ramirez Cecilia , Corante Noemi , Vizcardo‐Galindo Gustavo , Villafuerte Francisco C. , Simonson Tatum S. 
Published: November 2023

Multiple adaptive phenotypes for high‐altitude and hypoxic stress have developed by distinct evolutionary trajectories in highland populations. For example, considerable variation is observed in the hypoxic ventilatory response (HVR) of Tibetans, while high altitude Andean populations show blunted responses and low variation in this trait. Evidence suggests that genetic background plays a major role in these adaptations as native highlanders exhibit adaptive signals in genomic regions containing genes related to the hypoxic response. In some cases these signals are associated with physiological differences, such as hemoglobin concentration in Tibetans, which is relatively lower than levels observed in Andeans. Few adaptive signals have been reported in more than one highland population. This suggests distinct genetic contributions to different adaptive processes in these groups. We aim to link additional hypoxia‐related phenotypes to their underlying genetic basis in order to understand how different populations have adapted to life at high altitude. The present studies examine how ventilatory control and oxygen delivery differ in high altitude Andean populations compared to lowlanders. We measured the HVR in 50 lifelong male residents of Cerro de Pasco (CDP) (4,330 m) and compared to 15 sea‐level residents tested at UC San Diego (SL) and after acclimatization at 3,800 m (HA). Andean hemoglobin values ranged from 15.2 to 27.5 g/dL (20.1 ± 2.9 g/dL, M ± SD). Consistent with previous reports, CDP residents have similar ventilation in normoxia compared to HA (CDP: 0.21 ± 0.06, HA: 0.19 ± 0.08 L·min−1·kg−1, t(62)=1.54, p=0.22) CDP residents also demonstrate a blunted HVR with less variability than observed in SL or HA (CDP: 0.002 ± 0.005, SL: 0.008 ± 0.009, HA: 0.020 ±0.013 L·min−1·kg−1·%−1, F(2, 77)=33.256, p<<0.001). Although CDP showed essentially no increase in ventilation in acute hypoxia, it is possible that oxygen delivery may increase with cardiac output, as evidenced by the expected increase in heart rate in isocapnic hypoxia (F(5,290) = 12.54, p << 0.001). CDP also consistently maintain lower end‐tidal CO2 values (26.93 ± 4.13 torr) compared to SL (34.99 ± 2.25 torr), as expected for acclimatization to high altitude, and also lower than HA (30.07 ± 2.58 torr) (F(2, 77)=29.68, p<<0.001), as expected for acclimatization to a lower altitude. Using DNA samples collected from CDP, we will test if allelic variation in candidate genes previously identified to be involved in the hypoxic response (and under selection in high‐altitude populations) explains any of the variation in these physiological variables.Support or Funding InformationThis work was supported by NIH grant T32HL098062 to FLP.
Novel Insight Regarding the Trajectory and Time‐course of Immobilisation Induced Impairment of Limb Glucose Uptake in Healthy Volunteers
Authors: Burns Aisling , Nixon Aline , Stephens Francis , Francis Susan , Gowland Penny , Greenhaff Paul 
Published: November 2023

Immobilisation impairs muscle glucose uptake, which is local to the affected limb. The trajectory and time‐course of this effect in man is unknown, but is central to understanding the mechanistic basis of immobilisation induced insulin resistance and therefore was the focus of this study.Ten healthy, young men (age 24.8±1.9 yr, body mass 72.0±8.2kg, body mass index 23.6±2.6kg/m2) completed an oral glucose tolerance test (OGTT, 75g dextrose) before (0) and at 24, 48 and 72 hr after immobilisation of the non‐dominant arm (IMM) in a cast and having subjects wear an arm support sling. On each visit, brachial artery blood flow (BAF) was measured throughout the OGTT using Doppler ultrasound and forearm glucose uptake (FGU), calculated as a function of BAF and the difference in forearm arterialised venous to venous blood glucose concentration (AV‐V), was determined at baseline and at 10 min intervals for the initial 120 min following glucose ingestion and every 15 min for 60 min thereafter. Arterialised‐venous serum insulin concentration was determined at baseline and at 20 min intervals after glucose ingestion for 120 min and every 30 min thereafter. The same measurements were also made in the non‐immobilised arm (NIMM) at 0 and 72 hr thereby establishing a control intervention. Area under the curve (AUC) for the total 180 min was calculated for FGU, BAF and serum insulin, and time (immobilised limb) and treatment (0 and 72 hr both limbs) effects were determined using repeated measures one‐way ANOVA with Tukey post‐hoc and two‐way ANOVA with Sidak post hoc analysis, respectively. Values represent mean ± SEM and statistical significance was set at p<0.05. The University of Nottingham Medical School Ethics Committee approved the study.Forearm glucose uptake was not different between limbs at baseline (9.5±2.2 and 8.7±1.8 mmol.180min−1 in NIM and IMM, respectively), and was not reduced from baseline at 72 hr in the NIM limb (12.7±3.0 mmol.180min−1). However, FGU was less than at baseline in the IMM limb at 24 hr (38%; 5.4±1.1 mmol.180min−1, p<0.05), 48 hr (67%; 3.8±0.5 mmol.180min−1, p=0.01) and 72 hr (46%; 4.7±0.7 mmol.180min−1, p=0.06), and was also less than in NIM at 72 hr (p<0.01).Brachial artery blood flow and arterialised‐venous serum insulin responses during the OGTT were generally unaffected by immobilisation and no different between limbs (data not shown). This study confirms the inhibitory effect of immobilisation on glucose uptake is local to the affected limb. The novel insight generated is that this effect is marked, rapid (38% within 24 hr) and sustained, and appears to be overtly muscle centric. The mechanistic basis of this precipitous induction of insulin resistance and its significance to inactivity induced impairment of metabolic health warrant further investigation.Support or Funding InformationArthritis Research United Kingdom
Beta‐aminoisobutyrate, a circulating metabolite which regulates beta‐cell insulin secretory function
Authors: Solomon Thomas P , Gillum Matthew 
Published: November 2023

Glucose‐stimulated insulin secretion and insulin‐stimulated glucose disposal (insulin sensitivity) are related by an inverse function. A reduction in insulin sensitivity promotes increased insulin secretion in order to compensate. The mechanism for this is unknown. The objective of this work was to identify a circulating metabolite that may explain this regulation between the insulin sensitive tissue and the endocrine pancreas.By elevating plasma glucose to ~11 mM for 24 hours we experimentally‐induced a diabetic‐like state of hyperglycemia in healthy human subjects. This caused insulin resistance and compensatory hyperinsulinemia. Using metabolomics (LC and GC‐MS) we measured 358 metabolites in plasma samples collected at baseline and after 24 hours of hyperglycemia. We then identified a short‐list of circulating metabolites which were associated with hyperglycemia‐induced changes in insulin secretory compensation.We then measured the same 358 metabolites in the plasma of patients with type 2 diabetes. Some of these compounds were also differentially‐regulated in plasma between healthy subjects and patients with type 2 diabetes, a disease where insulin secretory function is impaired. The shortlist of compounds which correlated with group differences (i.e. healthy vs. diabetic) and hyperglycemic‐induced changes in insulin secretion were then used to incubate rat islets in culture experiments.We identified beta‐aminoisobutyrate as a metabolite that suppressed glucose‐stimulated insulin secretion from rat islets in a dose‐response fashion. Interestingly, beta‐aminoisobutyrate is a metabolite that has been demonstrated in mice to be secreted from skeletal muscle, thus identifying it as a potential muscle‐derived regulator of beta‐cell insulin secretion. Ongoing work is determining the in vivo effect of beta‐aminoisobutyrate on insulin secretory function and determining whether it is secreted from skeletal muscle in humans.Support or Funding InformationThis work was primarily funded by the Novo Nordisk Foundation (TS).
The Sirtuin SIRT6 Represses Expression of Cachexia‐Associated Cytokine Myostatin by Blocking its NF‐kB‐Dependent Gene Transcription
Authors: Gupta Mahesh , Samant Sadhana , Bao Riyue , Pillai Vinodkumar 
Published: November 2023

IntroductionLoss of body weight and involuntary muscle wasting (cachexia) is associated with many terminal diseases, including heart failure, cancer, COPD and liver cirrhosis. One of the most critical mediators of cachexia‐associated muscle wasting is myostatin (Mstn), a member of the TGFβ superfamily, which is secreted from muscle cells. Mstn binds to activin receptor‐IIB and suppresses both muscle cell growth and differentiation. SIRT6 is a chromatin associated NAD‐dependent deacetylase, which has been shown to regulate wide range of cellular processes, and considered to be an anti‐aging molecule. While SIRT6KO mice display muscle atrophy, retarded body size, metabolic defects and development of heart failure, over expression of SIRT6 has been shown to extend lifespan of mice. This study was undertaken to study the role of SIRT6 in growth and wasting of skeletal muscle.Methods and ResultsWe prepared RNA from SIRT6 knocked down neonatal rat cardiac myocytes and subjected it to deep RNA sequencing. The results showed that SIRT6 deficiency led to increased expression of Mstn (22 fold) and activin receptor‐IIB (3 fold), together with decreased expression of myosin heavy chain proteins (18 fold). These results were confirmed by western blotting. We also detected significantly increased levels of Mstn in the condition media of SIRT6 knocked‐down cardiomyocytes, compared to media prepared from control cells. To test the functional significance of Mstn secreted from cardiomyocytes, we exposed C2C12 cells to media prepared from SIRT6 deficient and control cells. The condition media of SIRT6 deficient cells, but not of control cells, blocked the C2C12 cells differentiation, as measured by expression levels of myosin heavy chain protein, thus confirming that the Mstn secreted from cardiomyocytes was functionally active. To underpin the mechanism through which SIRT6 controls the expression of Mstn gene we performed the ChIP assay. We found that SIRT6 was bound to the Mstn promoter at the NF‐kB binding sites. The treatment of cells with a NF‐kB inhibitor, Bay‐11‐7082, significantly reduced the occupancy of SIRT6 to the Mstn promoter, thus suggesting that SIRT6 suppresses Mstn expression by negatively regulating NF‐kB‐dependent transcription of Mstn gene promoter.ConclusionLoss of SIRT6 has been linked with development of many chronic diseases. Our data suggest that induction of cachexia with these diseases may be resulting from increased expression of Mstn due to SIRT6 deficiency. Therefore, SIRT6 activation may be considered a therapeutic intervention for the management of cachexia.Support or Funding InformationNIH RO1‐HL117041NIH RO1‐HL111455
Identification and Characterization of Allograft Inflammatory Factor 1‐Like (Aif1L) in Skeletal Muscle
Authors: Tran Kien , Waddell David 
Published: November 2023

Skeletal muscle wasting, or atrophy, frequently results from decreased protein synthesis and an associated increase in protein degradation. This shift towards a reduction in protein content of the cell can result from various physiological conditions, including immobilization, denervation, and aging. Muscle RING Finger 1 (MuRF1), an E3 ubiquitin ligase, has been found to be upregulated during almost all conditions of muscle wasting and is believed to play an important role in targeting proteins for degradation. However, preliminary data described in this study provides new evidence that MuRF1 may also act as a transcriptional modulator of atrophy‐induced gene activity, including the regulation of allograft inflammatory factor 1‐like (Aif1L). Aif1L has been identified as a novel skeletal muscle gene that is upregulated in wild‐type mice, while MuRF1‐null mice show blunted upregulation in response to denervation. Aif1L is predicated to contain an EF‐hand domain, which can act as a calcium ion binding domain, and since calcium ions are crucial for proper muscle contraction this gene was investigated further. In order to confirm that Aif1L in expressed in muscle cells, the cDNA of Aif1L was cloned from the C2C12 mouse myoblast cell line and fused with a green fluorescence protein (GFP) tag. C2C12 cells were then transfected with the Aif1L‐GFP expression plasmid in order to localize the Aif1L protein in proliferating myoblast cells. C2C12 cells transiently overexpression Aif1L‐GFP showed punctate fluorescence localized to the perinuclear region of the cytoplasm. The results presented here in combination with additional research into the transcriptional regulation and function of Aif1L will help contribute new insight into the molecular genetic mechanisms of skeletal muscle atrophy and may provide a more complete understanding of how MuRF1 may transcriptionally regulate neurogenic atrophy‐induced gene expression during muscle wasting.Support or Funding InformationUniversity of North Florida Transformational Learning Opportunity Grant
Basal and Stretch‐induced Myotube Protein Synthesis Regulation by gp130 Signaling
Authors: GAO SONG , Carson James A. 
Published: November 2023

Mechanical stimulation from muscle contractions or stretch can induce mTOR signaling and protein synthesis in cultured myotubes. Mechanical stimulation also induces muscle expression of IL‐6 family of cytokines, which can activate intracellular signaling pathways through glycoprotein 130 (gp130). Although several gp130 downstream targets, such as Akt and ERK1/2, can regulate mTOR activity, the role for gp130 initiated signaling in the stretch activation of mTOR signaling and protein synthesis has not been established. The purpose of this study was to investigate gp130 signaling on mTORC1 activation, and whether gp130 signaling is necessary for stretch‐induced protein synthesis in cultured myotubes. C2C12 myotubes were static stretched (5%) for 24h. Signaling was manipulated by gp130 siRNA transfection into cells or administration of neutralizing antibody in culture media. Phosphorylation of signaling molecules and puromycin incorporation (indicator of protein synthesis) were measured by western blot. We report that gp130 siRNA knock‐down decreased myotube basal p70S6K phosphorylation (T389) and protein synthesis. Activation of gp130 signaling by IL‐6 administration increased myotube Akt phosphorylation (T308) and protein synthesis, but not p70S6K phosphorylation. Static stretch for 24h increased myotube p70S6K phosphorylation, protein synthesis, and IL‐6 mRNA expression. Stretch in the presence of gp130 antibody attenuated the stretch‐induction of myotube p70S6K phosphorylation, and blocked the stretch‐induction of protein synthesis. These results demonstrate that gp130 dependent signaling has a role in the regulation of basal and stretch‐induced myotube protein synthesis, however, the cellular mechanism regulating protein synthesis differs between the 2 conditions.Support or Funding InformationR01 CA121249 to JAC from the National Cancer Institute
Human Proteomes – From Basic Science To Understanding Drug Action
Authors: Kuster Bernhard 
Published: November 2023

Proteomes are characterized by large protein‐abundance differences, cell‐type‐ and time‐dependent expression patterns and post‐translational modifications, all of which carry biological information that is not accessible by genomics or transcriptomics. Here we present a mass‐spectrometry‐ based draft of the human proteome and a public, high‐performance, in‐memory database for real‐time analysis of terabytes of big data, called ProteomicsDB. The information assembled from human tissues, cell lines and body fluids enabled estimation of the size of the protein‐coding genome, the analysis of messenger RNA and protein‐expression profiles of human tissues revealed conserved control of protein abundance and integration of drug‐sensitivity data enabled the identification of proteins predicting resistance or sensitivity. The same overall technology also allows tracking drug actions in cells and lysates on a target‐class or proteome‐wide scale with many implications for drug discovery. We present examples for the use of chemical probes and chemical proteomics to find new uses of existing drugs, to identify toxicity targets, to elucidate the mechanism of action of drugs in cancer cells, the identification of resistance mechanisms and how the activity status of cancer cells as assessed by post‐translational modification of proteomes influences the efficacy of drugs.Support or Funding InformationCenter for Integrated Protein Science MunichGerman Consortium for Translational Cancer ResearchSAP SE
Expression of the Dystrophin‐Associated Protein Complex in the Absence of Skeletal Muscle AMPK
Authors: Dial Athan G , Lally James S , Bujak Adam L , Steinberg Gregory R , Ljubicic Vladimir 
Published: November 2023

The dystrophin‐associated protein complex (DAPC) is composed of proteins that are highly expressed along the sarcolemma. The DAPC provides a mechanical link between the intracellular cytoskeleton and extracellular matrix, as well as a signal transduction apparatus from the periphery to the interior of muscle fibers. The signalling molecule AMP‐activated protein kinase (AMPK) is a powerful regulator of phenotypic plasticity. Recent evidence has shown that chronic AMPK activation alters the expression of DAPC components. However, a more comprehensive understanding of the influence of AMPK on the DAPC is lacking. Therefore, the purpose of this study was to investigate the role of AMPK in the expression of the DAPC. Extensor digitorum longus (EDL) and soleus (SOL) muscles representing fast glycolytic and slow oxidative tissues, respectively, were obtained from wild‐type (WT) mice, as well as from mice deficient in both isoforms of the AMPK‐β subunit in skeletal muscle (AMPK‐MKO). RT‐PCR and Western blotting measured mRNA and protein content of DAPC components, respectively. In WT animals, utrophin and laminin mRNA expression, as well as laminin and β‐dystroglycan protein content were ~25–60% higher (p < 0.05) in the SOL versus EDL muscle. In contrast, neuronal nitric oxide synthase (nNOS) mRNA was 60% lower in SOL. The AMPK‐MKO animals displayed a different pattern of fiber‐type specific expression of DAPC components. In these mice, laminin, γ‐sarcoglycan (SG), dystrophin, and utrophin transcripts, as well as dystrophin and utrophin protein expression were 40–55% greater (p < 0.05) in the SOL versus the EDL. β‐SG and nNOS mRNA content were lower in the EDL muscle of AMPK‐MKO mice, as compared to their WT counterparts. We also assessed the expression of peroxisome proliferator activated receptor coactivator‐1α (PGC‐1α) and Ca2+/calmodulin dependent protein kinase II (CAMKII), factors that contribute to the upstream regulation of the DAPC. PGC‐1α mRNA content was higher in SOL relative to EDL muscles of both genotypes. CAMKIIα protein expression was significantly lower in SOL muscles versus EDL muscles of WT and AMPK‐MKO, while CAMKIIβ exhibited the opposite pattern. PGC‐1α mRNA tended to be higher in the muscles from AMPK‐MKO mice compared to WT animals. Conversely, CAMKII mRNA content tended to be reduced in the AMPK‐MKO muscles, as compared to WT. These data indicate a fiber‐type specificity to DAPC expression in skeletal muscle. Furthermore, AMPK deficiency results in a differential profile of DAPC components, as well as in alternations in the expression of alternative upstream DAPC regulators. Our results suggest that AMPK contributes to the expression profile of the DAPC.Support or Funding InformationNatural Sciences and Engineering Research Council of Canada, Canada Research Chairs
Regional Gradients in Tissue Anisotropy During Pressure Overload Hypertrophy in the Rat Left Ventricle
Authors: Carruth Eric D. , McCulloch Andrew D. , Omens Jeffrey H. 
Published: November 2023

Many studies have shown that the structural composition of the normal heart is spatially non‐uniform. We hypothesized that due to spatial differences in tissue structure and function, hypertrophic growth occurs non‐uniformly, especially in moderate hypertrophy. Using high resolution, high fidelity diffusion tensor magnetic resonance imaging (DT‐MRI), we calculated and compared fractional anisotropy (FA) in several regions of aortic banded and sham hearts.Preliminary results indicate that the FA is decreased uniformly in severe hypertrophy (mean 0.16) compared to sham controls (mean 0.22). A decrease in FA is consistent with known changes in myocyte shape during concentric hypertrophy, wherein cell width increases more than cell length. In mild‐moderate hypertrophy, the mean FA across the entire LV (0.21) was comprised of two subpopulations with mean FA 0.11 and 0.23. The subpopulation with lower FA was isolated to the subendocardium, whereas the higher FA values were localized in the mid‐and subepicardium. We conclude that hypertrophic growth occurs either earlier, with higher sensitivity, or both in the subendocardium, and we propose that endogenous spatial differences in cell and tissue structure (and therefore function) lead to this variation in hypertrophic growth.Support or Funding InformationNIH/NHLBI Training Grant #2015‐0453NIH/NIGMS #P50 GM094503‐04