Biology subjects

Jensen, T. E.

Publications and source records attributed to Jensen, T. E..

16 recordsLinked to original sources

bioRxiv2026

A quantitative redox proteome of the human muscle response to exercise

Reactive oxygen species (ROS) regulate protein function through reversible cysteine oxidation. In human skeletal muscle, exercise-induced ROS initiates adaptations such as mitochondrial biogenesis, increased insulin sensitivity, and hypertrophy. However, specific protein targets of ROS regulation during exercise remain unclear owing to longstanding challenges in analyzing redox proteomes in vivo. We applied cysteine derivatization and multiplexed proteomics to map muscle protein cysteine oxidation in humans during exercise. The OxiMuscle dataset quantifies reversible modifications across 9,177 unique cysteine sites on 2,782 proteins, comprising 17,492 individual cysteine site measurements in young men undergoing three types of exercise, providing the first comprehensive, site-resolved and quantitative analysis of the exercise-regulated redox cysteine proteome in humans. We systematically define cysteine oxidation targets regulated by at least one form of exercise, many of which reside in proteins with established roles in muscle physiology. Among these sites is a redox-regulated cysteine on the autophagy receptor protein p62. We demonstrate that reversible oxidation of this cysteine regulates p62-mediated autophagy upon myotube contraction and mouse muscle adaptation to exercise in vivo. Together, these results define a redox-driven mechanism linking exercise-induced autophagy to muscle adaptation. More broadly, our findings offer a comprehensive resource on redox-signaling networks in human muscle, accessible at http://oximuscle-alb-1899330623.us-east-1.elb.amazonaws.com/.

cell biology↗

bioRxiv2026

Functionally Mature Bioengineered Human Skeletal Muscle Tissues Capture Essential Aspects of Glucose Metabolism

Human skeletal muscle is a major regulator of whole-body metabolic homeostasis, yet mechanistic insight into human muscle plasticity is limited by the lack of in vitro models with adult-like metabolic and functional maturity. Here, we develop a workflow for generating bioengineered human skeletal muscle tissues that undergo coordinated structural, molecular, and functional maturation and stabilize in an adult-like state by day 21. Time-resolved RNA-seq and protein profiling reveal consolidation of contractile programs alongside progressive metabolic maturation, including increased mitochondrial electron transport chain content, mature mitochondrial network organization, and upregulation of glucose- and glycogen-handling proteins as well as muscle-enriched AMPK isoforms. Functionally, the tissues develop physiological force-frequency behavior, post-tetanic potentiation, and reproducible fatigue responses that are exacerbated by hypoxia and glucose withdrawal. Exercise-like chronic stimulation increases force and endurance with hypertrophy-like remodeling, and these adaptations reverse with detraining. The model also captures pharmacological responsiveness. {beta}2-adrenergic stimulation activates canonical signaling, increases force, limits disuse-related decline, and improves endurance in a glucose-dependent manner. Under physiological insulin and IGF-1 conditions, tissues show robust insulin-stimulated glucose uptake and glycogen synthesis, with punctate glucose transporter 4 (GLUT4) localization. Finally, knockdown of muscle glycogen synthase (GYS1) preserves peak tetanic force but impairs endurance and force recovery under fuel stress, indicating that glycogen metabolism is a key determinant of human muscle resilience.

cell biology↗

bioRxiv2025

Chemogenetic Mitochondrial H2O2 Generation Triggers Dose-Dependent Skeletal Muscle Wasting Signatures

Mitochondrial hydrogen peroxide (mtH2O2) has long been implicated in skeletal muscle atrophy, yet its direct role in vivo has remained unresolved due to methodological constraints. Here, we aimed to establish a chemogenetic platform for precise, compartment-specific induction of mtH2O2 in adult skeletal muscle and to investigate how graded redox stress impacts on muscle proteostasis in vivo. Using mitochondria-targeted D-amino acid oxidase (mtDAAO), we show that prolonged and/or high mtH2O2 exposure progressively activates proteolytic and denervation-associated pathways, culminating in myofiber damage and regeneration. Remarkably, even low exposure to mtH2O2 is sufficient to acutely suppress protein synthesis and induce disuse-like atrophy, without structural damage or overt oxidative stress. This approach provides a powerful in vivo framework to dissect subcellular redox-controlled signaling in muscle and identifies mtH2O2 as a modulator of muscle proteostasis, with therapeutic relevance for muscle-wasting conditions.

molecular biology↗

bioRxiv2025

The metabolic and molecular mechanisms underlying running-induced energy compensation

Exercise not only regulates energy expenditure but also appetite, yet the underpinnings remain unclear. We describe that increased energy intake is a defense against energy loss that depends on initial running distance and operates independently of diet and age. Running caused a rapid circadian-dependent fat remodeling leading to a decline in circulating leptin accompanied by the activation of hypothalamic neurons. We discovered that the activation of the {beta}3-adrenergic receptor drives running-induced fat loss and the lower leptin triggers energy compensation by upregulating Neuropeptide Y. Once energy compensation is achieved, running is associated with molecular changes in hypothalamic signaling related to appetite and functional adaptations, such as enhanced sensitivity to hunger and satiety signals and increased responsiveness to appetite suppression induced by -Melanocyte-Stimulating Hormone. The increased food intake persisted without fat rebound beyond running in both lean and obese young mice, uncovering a new homeostatic balance in young mice.

physiology↗

bioRxiv2024

Housing temperature dictates the systemic and tissue specific molecular responses to cancer in mice

Cancer cachexia is a metabolic condition affecting up to 80% of patients with cancer. Cachexia is mediated by reduced muscle and fat mass and impaired function, and it lowers survival for patients. With no approved drugs to treat cachexia, preclinical efforts focus on understanding the molecular mechanisms underlying this condition to reveal treatment targets. Housing laboratory mice at ambient temperature imposes cold stress, leading to induced thermogenic activity and consequent whole-body metabolic adaptations. Yet, the impact of housing temperature in in vivo preclinical cachexia remains unknown. We found that thermoneutral (TN) housing in C26 carcinoma-bearing (C26) mice affected lean and fat mass, but not muscle weight or force. TN housing improved glucose tolerance in C26 mice, while enhancing circulating abundance of FGF21 and IL-6. Thermogenic tissues, especially brown adipose tissue, exhibited housing temperature-dependent molecular responses to cancer in oxygen consumption, ATP levels and SERCA ATPase activity, which are all crucial for cancer-induced whole-body metabolic adaptations. We conclude that molecular and systemic adaptations to cancer in mice critically depend on housing temperature, which should be considered in the design and interpretation of preclinical cancer studies.

physiology↗

bioRxiv2023

The mitochondrial mRNA stabilizing protein, SLIRP, regulates skeletal muscle mitochondrial structure and respiration by exercise-recoverable mechanisms

Summary and graphical abstractDecline in mitochondrial function associates with decreased muscle mass and strength in multiple conditions, including sarcopenia and type 2 diabetes. Optimal treatment could include improving mitochondrial function, however, there are limited and equivocal data regarding the molecular cues controlling muscle mitochondrial plasticity. Here we uncover the mitochondrial-mRNA-stabilizing protein SLIRP, in complex with LRPPRC, as a PGC-1 target that regulates mitochondrial structure, respiration, and mitochondrially-encoded-mRNA pools in skeletal muscle. Exercise training effectively counteracted mitochondrial defects induced by loss of LRPPRC/SLIRP, despite sustained low mitochondrially-encoded-mRNA pools, via increased mitoribosome translation capacity. In humans, exercise training robustly increased muscle SLIRP and LRPPRC protein content across exercise modalities and sexes, yet this increase was less prominent in subjects with type 2 diabetes. Our work identifies a mechanism of post-transcriptional mitochondrial regulation in skeletal muscle through mitochondrial mRNA stabilization. It emphasizes exercise as an effective approach to alleviate mitochondrial defects by possibly increasing mitoribosome capacity. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=142 SRC="FIGDIR/small/564600v2_ufig1.gif" ALT="Figure 1"> View larger version (61K): org.highwire.dtl.DTLVardef@1cdc6c5org.highwire.dtl.DTLVardef@b4cb1borg.highwire.dtl.DTLVardef@182871corg.highwire.dtl.DTLVardef@7462ea_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2023

The Rho GTPase Rac1 mediates exercise training adaptations

Exercise training elicits tremendous health benefits; however, the molecular underpinnings are poorly understood. As one of the most regulated groups of proteins following acute exercise in human muscle, Rho GTPases are unexplored candidates for mediating the beneficial effects of exercise. The Rho GTPase Rac1 was activated during multiple exercise modalities and remained elevated hours after resistance exercise in human muscle. Inducible muscle-specific Rac1 knockout (Rac1 imKO) mice, displayed attenuated muscle protein synthesis, glycogen resynthesis and p38 MAPK signaling in recovery from contractions. Exercise training upregulated Rac1 protein content in human and mouse muscle. Overexpression of hyperactive Rac1 elevated reactive oxidant species production during exercise yet did not induce a trained muscle phenotype. In Rac1 imKO mice, the improvements in running capacity and muscle mass after exercise training were diminished. Using gain- and loss-of-function mouse models and human muscle biopsies, we identify Rac1 as a regulator of exercise training adaptions. HighlightsO_LIVarious exercise modalities activate Rac1 signaling in human skeletal muscle. C_LIO_LIHSP27, MNK1, and CREB are Rac1-dependent contraction-responsive targets in muscle. C_LIO_LIPost-contraction protein synthesis requires Rac1 but not NOX2. C_LIO_LIRac1-NOX2 signaling is necessary for post-contraction glycogen resynthesis. C_LIO_LIExercise training increases Rac1 protein content in human and mouse muscles. C_LIO_LIRac1 mediates critical adaptations to exercise training. C_LI

molecular biology↗

bioRxiv2023

Reducing the mitochondrial oxidative burden alleviates lipid-induced insulin resistance in human skeletal muscle

Pre-clinical models suggest a causative nexus between mitochondrial oxidative stress and insulin resistance. However, the translational and pathophysiological significance of this mechanism in humans remains unclear. Herein, we employed an invasive in vivo mechanistic approach in humans to manipulate mitochondrial redox state while assessing insulin action. To this end, we combined intravenous infusion of a lipid overload with intake of a mitochondria-targeted antioxidant (mtAO) in conjunction with insulin clamp studies. During lipid overload, insulin-stimulated muscle glucose uptake, as determined by the femoral arteriovenous balance technique, was increased by mtAO. At the muscle molecular level, mtAO did not affect canonical insulin signaling but augmented insulin-stimulated GLUT4 translocation while decreasing the mitochondrial oxidative burden under lipid oversupply. Ex vivo studies revealed that mtAO ameliorated features of mitochondrial bioenergetics, including diminished mitochondrial H2O2 emission, in muscle fibers exposed to high intracellular lipid levels. These findings provide translational and mechanistic evidence implicating mitochondrial oxidants in the development of lipid-induced muscle insulin resistance in humans. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/535538v2_ufig1.gif" ALT="Figure 1"> View larger version (86K): org.highwire.dtl.DTLVardef@157d44eorg.highwire.dtl.DTLVardef@13358dborg.highwire.dtl.DTLVardef@e958eorg.highwire.dtl.DTLVardef@17cbc6f_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2022

AMPK is elevated in human cachectic muscle and prevents cancer-induced metabolic dysfunction in mice

BackgroundMetabolic dysfunction and cancer cachexia are associated with poor cancer prognosis, yet the molecular mechanisms causing cancer-induced metabolic dysfunction and cachexia remain to be defined. A key link between metabolic- and muscle mass-regulation is adenosine monophosphate-activated protein kinase (AMPK). As AMPK could be a potential treatment, it is important to determine the function for AMPK in cancer-associated metabolic dysfunction and cachexia. Here we determined the function of AMPK in cancer-associated metabolic dysfunction, insulin resistance, and cachexia. MethodsIn vastus lateralis muscle biopsies from pre-cachectic and cachectic patients with Non-Small-Cell Lung Carcinoma (NSCLC), AMPK signaling and expression were examined by immunoblotting. To investigate the role of muscle AMPK, male mice overexpressing a dominant-negative AMPK2 (kinase-dead) specifically in striated muscle (mAMPK-KD) were inoculated with Lewis Lung Carcinoma (LLC) cells. In a subsequent cohort, male LLC-tumor-bearing mice were treated with/without 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) to activate AMPK for 13 days. Littermate mice were used as control. Metabolic phenotyping of mice was performed via indirect calorimetry, body composition analyses, glucose- and insulin tolerance tests, tissue-specific 2-deoxy- glucose (2-DG) uptake, and immunoblotting. ResultsIn muscle from patients with NSCLC, we found increased expression of AMPK subunits 1, 2, {beta}2, {gamma}1, and {gamma}3; ranging from +27% to +79% compared to healthy control subjects. AMPK subunit expression correlated with indices of cachexia, including cross sectional area and weight loss. Tumor-bearing mAMPK-KD mice presented increased fat loss as well as glucose and insulin intolerance. LLC in mAMPK-KD mice displayed lower insulin-stimulated 2-DG uptake in skeletal muscle (quadriceps; -35%, soleus; -49%, EDL; -48%) and the heart (-29%) compared to non-tumor-bearing mice. In skeletal muscle, mAMPK-KD abrogated the tumor-induced increase in phosphorylation of TBC1D4thr642. Additionally, protein expression of TBC1D4 (+26%), pyruvate dehydrogenase (PDH, +94%), and PDH-kinases (PDKs, +45% to +100%), and glycogen synthase (+48%) were increased in skeletal muscle of tumor-bearing mice in an AMPK-dependent manner. Lastly, chronic AICAR treatment elevated hexokinase-II protein expression and normalized phosphorylation of p70S6Kthr389 (mTORC1 substrate) and ACCser212 (AMPK substrate) and rescued the cancer-induced insulin intolerance. ConclusionsUpregulated protein expression of AMPK subunits observed in skeletal muscle of (pre)cachectic patients with non-small-cell lung carcinoma. This seemed protective inferred by AMPK-deficient tumor-bearing mice being highly prone to developing metabolic dysfunction, which included the AMPK-dependent regulation of several proteins involved in glucose metabolism. These observations highlight the potential for targeting AMPK to counter cancer-associated metabolic dysfunction and cachexia. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=141 SRC="FIGDIR/small/495096v1_ufig1.gif" ALT="Figure 1"> View larger version (49K): org.highwire.dtl.DTLVardef@7ff169org.highwire.dtl.DTLVardef@1c249aeorg.highwire.dtl.DTLVardef@736350org.highwire.dtl.DTLVardef@17d2be2_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2021

Cancer causes dysfunctional insulin signaling and glucose transport in a muscle-type specific manner

Metabolic dysfunction and insulin resistance are emerging as hallmarks of cancer and cachexia, and impair cancer prognosis. Yet, the molecular mechanisms underlying impaired metabolic regulation is not fully understood. To elucidate the mechanisms behind cancer-induced insulin resistance in muscle, we isolated extensor digitorum longus (EDL) and soleus muscles from Lewis Lung Carcinoma tumor-bearing mice. Three weeks after tumor inoculation, muscles were isolated and stimulated with or without a submaximal dose of insulin (1.5 nM). Glucose transport was measured using 2-[3H]Deoxy-Glucose and intramyocellular signaling was investigated using immunoblotting. In soleus muscles from tumor-bearing mice, insulin-stimulated glucose transport was abrogated concomitantly with abolished insulin-induced TBC1D4 and GSK3 phosphorylation. In EDL, glucose transport and TBC1D4 phosphorylation were not impaired in muscles from tumor-bearing mice, while AMPK signaling was elevated. Anabolic insulin signaling via phosphorylation of the mTORC1 targets, p70S6K thr389 and ribosomal-S6 ser235, were decreased by cancer in soleus muscle while increased or unaffected in EDL. In contrast, the mTOR substrate, pULK1 ser757, was reduced in both soleus and EDL by cancer. Hence, cancer causes considerable changes in skeletal muscle insulin signaling that is dependent of muscle-type, which could contribute to metabolic dysregulation in cancer. Thus, skeletal muscle could be a target for managing metabolism in cancer. HighlightsO_LICancer abrogates insulin-stimulated glucose transport selectively in oxidative soleus muscle C_LIO_LIMultiple TBC1D4 phosphorylation sites are reduced in cancer-associated muscle insulin resistance C_LIO_LICancer leads to increased AMPK signaling in the glycolytic EDL muscle C_LIO_LICancer alters anabolic insulin signaling in soleus and EDL muscle C_LI

physiology↗

bioRxiv2020

The role of group I p21-activated kinases in contraction-stimulated skeletal muscle glucose transport

AimMuscle contraction stimulates skeletal muscle glucose transport. Since it occurs independently of insulin, it is an important alternative pathway to increase glucose uptake in insulin-resistant states, but the intracellular signalling mechanisms are not fully understood. Muscle contraction activates group I p21-activated kinases (PAKs) in mouse and human skeletal muscle. PAK1 and PAK2 are downstream targets of Rac1, which is a key regulator of contraction-stimulated glucose transport. Thus, PAK1 and PAK2 could be downstream effectors of Rac1 in contraction-stimulated glucose transport. The current study aimed to test the hypothesis that PAK1 and/or PAK2 regulate contraction-induced glucose transport. MethodsGlucose transport was measured in isolated soleus and extensor digitorum longus (EDL) mouse skeletal muscle incubated either in the presence or absence of a pharmacological inhibitor (IPA-3) of group I PAKs or originating from whole-body PAK1 knockout (KO), muscle-specific PAK2 (m)KO or double whole-body PAK1 and muscle-specific PAK2 knockout mice. ResultsIPA-3 attenuated (-22%) the increase in muscle glucose transport in response to electrically-stimulated contraction. PAK1 was dispensable for contraction-stimulated glucose uptake in both soleus and EDL muscle. Lack of PAK2, either alone (-13%) or in combination with PAK1 (-14%), reduced contraction-stimulated glucose transport compared to control littermates in EDL, but not soleus muscle. ConclusionContraction-stimulated glucose transport in isolated glycolytic mouse EDL muscle is partly dependent on PAK2, but not PAK1.

cell biology↗

bioRxiv2019

Tumor-bearing mice display reduced insulin-stimulated glucose uptake and microvascular perfusion and exhibit increased hepatic glucose production

BackgroundRedirecting glucose from skeletal muscle and adipose tissue, likely benefits the tumors energy demand to support tumor growth, as cancer patients with type 2 diabetes have 30% increased mortality rates. The aim of this study was to elucidate tissue-specific contributions and molecular mechanisms underlying cancer-induced metabolic perturbations. MethodsGlucose uptake in skeletal muscle and white adipose tissue (WAT), as well as hepatic glucose production, were determined in control and Lewis lung carcinoma (LLC) tumor-bearing C57BL/6 mice using isotopic tracers. Skeletal muscle microvascular perfusion was analyzed via a real-time contrast-enhanced ultrasound technique. Finally, the role of fatty acid turnover on glycemic control was determined by treating tumor-bearing insulin-resistant mice with nicotinic acid or etomoxir. ResultsLLC tumor-bearing mice displayed reduced insulin-induced blood-glucose-lowering and glucose intolerance, which was restored by etomoxir or nicotinic acid. Insulin-stimulated glucose uptake was 30-40% reduced in skeletal muscle and WAT of mice carrying large tumors. Despite compromised glucose uptake, tumor-bearing mice displayed upregulated insulin-stimulated phosphorylation of TBC1D4Thr642 (+18%), AKTSer474 (+65%), and AKTThr309 (+86%) in muscle. Insulin caused a 70% increase in muscle microvascular perfusion in control mice, which was abolished in tumor-bearing mice. Additionally, tumor-bearing mice displayed increased (+45%) basal (not insulin-stimulated) hepatic glucose production. ConclusionsCancer can result in marked perturbations on at least six metabolically essential functions; i) insulins blood-glucose-lowering effect, ii) glucose tolerance, iii) skeletal muscle and WAT insulin-stimulated glucose uptake, iv) intramyocellular insulin signaling, v) muscle microvascular perfusion, and vi) basal hepatic glucose production in mice. The mechanism causing cancer-induced insulin resistance may relate to fatty acid metabolism.

cancer biology↗

bioRxiv2019

Phosphoproteomic identification of Xin as a novel requirement for skeletal muscle disuse atrophy

BackgroundImmobilization of skeletal muscle in a stretched position is associated with marked protection against disuse atrophy. Some intramyocellular changes in known proteins and post-translational modifications were previously linked to this phenomenon but there are likely many presently unknown proteins and post-translational modifications that contribute to this beneficial effect.\n\nMethodsTo identify novel proteins and phosphorylation events involved in stretch-induced reduction of disuse atrophy, we conducted a global unbiased screen of the changes occurring in skeletal muscle in control vs. 1 day and 1 week stretched cast-immobilized mouse tibialis anterior muscle, using quantitative tandem mass spectrometry on HILIC-fractionated muscle peptides with follow-up studies in transgenic mice and humans.\n\nResultsOur mass spectrometry analyses detected 11714 phosphopeptides and 2081 proteins, of which 53 phosphopeptides and 5 proteins, 125 phosphopeptides and 43 proteins were deregulated after 1D and 7D of stretched immobilization, respectively. The sarcomere and muscle tendinous junction-associated putative multi-adaptor protein Xin was among the most highly upregulated proteins both in terms of phosphorylation and protein expression and was confirmed to increase with stretch but not disuse atrophy in mice and to increase and decrease with exercise and cast immobilization, respectively, in humans. Xin-/- mice were partially protected against disuse but not denervation atrophy in both stretched and flexed immobilized muscles compared to WT.\n\nConclusionThis study identified Xin as a novel protein involved in disuse atrophy and also provides a resource to guide future hypothesis-driven investigations into uncovering critical factors in the protection against disuse atrophy.

physiology↗

bioRxiv2019

Mechanisms involved in follistatin-induced increased insulin action in skeletal muscle

BackgroundSkeletal muscle wasting is often associated with insulin resistance. A major regulator of muscle mass is the transforming growth factor {beta} (TGF-{beta}) superfamily, including activin A, which causes atrophy. TGF-{beta} superfamily ligands also negatively regulate insulin-sensitive proteins, but whether this pathway contributes to insulin action remains to be determined.\n\nMethodsTo elucidate if TGF-{beta} superfamily ligands regulate insulin action we used an adeno-associated virus gene editing approach to overexpress the activin A inhibitor, follistatin (Fst288) in mouse muscle of lean and diet-induced obese mice. We determined basal and insulin-stimulated 2 deoxy-glucose uptake using isotopic tracers in vivo. Furthermore, to evaluate whether circulating Fst and activin A concentrations are associated with obesity, insulin resistance, and weight loss in humans we analysed serum from morbidly obese subjects before, 1 week, and 1 year after Roux-en-Y gastric bypass (RYGB).\n\nResultsFst288 muscle overexpression markedly increased in vivo insulin-stimulated (but not basal) glucose uptake (+75%, p<0.05) and increased protein expression and intracellular insulin signalling of AKT, TBC1D4, PAK1, PDH-E1, and p70S6K (p<0.05). No correlation was observed between the Fst288-driven hypertrophy and the increase in insulin-stimulated glucose uptake but Fst288 increased basal and insulin-stimulated protein synthesis. Importantly, Fst288 completely normalized muscle glucose uptake in insulin-resistant diet-induced obese mice. RYGB surgery doubled circulating Fst and reduced Activin A (-24%, p<0.05) concentration 1 week after surgery before any significant weight loss in morbidly obese normoglycemic patients, while major weight loss after 1 year did not further change the concentrations.\n\nConclusionsWe here present evidence that Fst is a potent regulator of insulin action in muscle and in addition to AKT and p70S6K, we identify TBC1D1, TBC1D4 and PAK1 as Fst targets. A possible role for Fst in regulating glycemic control is suggested because circulating Fst more than doubled post RYGB surgery, a treatment that markedly improved insulin sensitivity. These findings demonstrate the therapeutic potential of inhibiting TGF-{beta} superfamily ligands to improve insulin action and Fsts relevance to muscle wasting associated insulin resistant conditions in mice and humans.

physiology↗

bioRxiv2019

The role of p-21 activated kinases (PAKs) in glucose homeostasis and skeletal muscle glucose uptake

ObjectiveSkeletal muscle glucose uptake is essential for maintaining whole-body glucose homeostasis and accounts for the majority of glucose disposal in response to insulin. The group I p21-activated kinase (PAK) isoforms PAK1 and PAK2 are activated in response to insulin in skeletal muscle. Interestingly, PAK1/2 signalling is impaired in insulin-resistant mouse and human skeletal muscle and PAK1 has been suggested to be required for insulin-stimulated GLUT4 translocation. However, the relative contribution of PAK1 and PAK2 to insulin-stimulated glucose uptake in mature skeletal muscle is unresolved. The aim of the present investigation was to determine the requirement for PAK1 and PAK2 in whole-body glucose homeostasis and insulin-stimulated glucose uptake in skeletal muscle. MethodsGlucose uptake was measured in isolated skeletal muscle incubated with a pharmacological inhibitor (IPA-3) of group I PAKs and in muscle from whole-body PAK1 knockout (KO), muscle-specific PAK2 (m)KO and double whole-body PAK1 and muscle-specific PAK2 knockout mice. ResultsThe whole-body respiratory exchange ratio was largely unaffected by lack of PAK1 and/or PAK2. Whole-body glucose tolerance was mildly impaired in PAK2 mKO, but not PAK1 KO mice. IPA-3 partially reduced (-20%) insulin-stimulated glucose uptake in mouse soleus muscle. In contrast to a previous study of GLUT4 translocation in PAK1 KO mice, PAK1 KO muscles displayed normal insulin-stimulated glucose uptake in vivo and in isolated muscle. On the contrary, glucose uptake was slightly reduced in response to insulin in glycolytic extensor digitorum longus muscle lacking PAK2, alone (-18%) or in combination with PAK1 KO (-12%). ConclusionsInsulin-stimulated glucose uptake partly relies on PAK2, but not PAK1, in mouse skeletal muscle. Thus, the present study challenges that group I PAKs, and especially PAK1, are major regulators of whole-body glucose homeostasis and insulin-stimulated glucose uptake in skeletal muscle.

cell biology↗

bioRxiv2019

Exercise-stimulated muscle ROS production and glucose uptake requires NADPH oxidase 2

Reactive oxygen species (ROS) act as intracellular compartmentalized second messengers mediating metabolic stress-adaptation. In skeletal muscle fibers, ROS have been suggested to stimulate glucose transporter 4 (GLUT4)-dependent glucose transport during artificially evoked contraction ex vivo but whether myocellular ROS production is stimulated by in vivo exercise to control metabolism is unclear. Here, we combined exercise in humans and mice with fluorescent dyes, genetically-encoded biosensors, and NADPH oxidase 2 (NOX2) loss-of-function models to demonstrate that NOX2 is the main source of cytosolic ROS during moderate-intensity exercise in skeletal muscle. Furthermore, two NOX2 loss-of-function mouse models lacking either p47phox or Rac1 presented striking phenotypic similarities, including greatly reduced exercise-stimulated glucose uptake and GLUT4 translocation. These findings indicate that NOX2 is a major myocellular ROS source regulating glucose transport capacity during moderate-intensity exercise.

physiology↗