Biology subjects

Sylow, L.

Publications and source records attributed to Sylow, L..

At least 19 recordsLinked to original sources

bioRxiv2026

Rac1 deficiency reduces mitochondrial respiratory capacity, impairs fatty acid metabolism and causes muscle wasting

BackgroundThe age-related progressive decline in skeletal muscle function is characterised by declining mitochondrial quality control and perturbed fatty acid metabolism, contributing to frailty and increased mortality. The actin cytoskeleton, a key structural component of skeletal muscle, has recently been implicated in mitochondrial anchoring and dynamics. However, the role of actin-regulating proteins, including the Rho GTPase Rac1, in mitochondrial function and age-associated metabolic and functional muscle deterioration remains undefined. MethodsSkeletal muscle from mice with inducible muscle-specific deletion of Rac1 (Rac1 imKO) underwent unbiased mass spectrometry-based proteomic profiling. Mitochondrial morphology was assessed by transmission electron microscopy, and physiological parameters, including muscle mass and contraction-stimulated palmitate oxidation in isolated soleus muscle, were evaluated. Mitochondrial respiratory function was determined by high-resolution respirometry in permeabilised gastrocnemius skeletal muscle fibre bundles. Biochemically, muscular triacylglycerol (TG) content, mRNA (qPCR) and protein (immunoblotting) content were determined. In vastus lateralis muscle biopsies from healthy, untrained young (20-30 years) and old, sarcopenic (83-94 years) men, Rac1 and mitochondrial respiratory protein abundances were measured. A complementary human genetic association analysis was performed using the FinnGen dataset. ResultsRac1 deficiency triggered muscle wasting in middle-aged mice (Gastrocnemius: -10%; Quadriceps: -7%). Preceding muscle wasting, gene set enrichment analysis identified enrichment in fatty acid metabolism and oxidative phosphorylation pathways, consistent with increased mitochondrial volume density in Rac1 imKO muscle (subsarcolemmal: +467%; intermyofibrillar: +166%). Despite mitochondrial expansion at this stage, Rac1 deficiency attenuated the increase in palmitate oxidation in response to muscle contraction (-62%). At the muscle-wasting stage, Rac1 imKO muscle exhibited reduced mitochondrial respiratory capacity (-25-32%). Additionally, the mitochondrial dysfunction was associated with an accumulation of muscle TG (+78%, p = 0.096) and upregulation of fatty acid transporter, CD36 protein content (+25%), indicative of altered fatty acid handling. In humans, Rac1 muscle protein content was increased in old, sarcopenic subjects compared to young (+41%), and negatively correlated with quadriceps cross-sectional area (CSA) (r = -0.475) and type II fibre CSA (r = -0.466). In old, sarcopenic muscle, Rac1 protein content correlated negatively with protein content of multiple mitochondrial respiratory complexes (CI: r = -0.690, CIV: r = -0.938, CV: r = -0.704). GWAS further identified associations between Rac1 SNP variants and lipid metabolic and muscle-wasting diseases. ConclusionsMuscle Rac1 deficiency reduces mitochondrial respiratory capacity and metabolic flexibility through impaired fatty acid metabolism, leading to muscle wasting and highlighting a potential therapeutic target in age-related functional decline.

Molecular Biology↗

bioRxiv2026

Plasma proteomics identifies an IL-6–associated SAA axis linked to muscle wasting in patients with cancer cachexia

Nearly half of patients with advanced lung cancer develop cachexia, a debilitating syndrome that worsens prognosis. We conducted longitudinal clinical and plasma proteomic profiling of 67 patients with non-small cell lung cancer, with and without cachexia, during first-line treatment. Patients with cachexia at diagnosis exhibited elevated risk of hospitalization and treatment-delaying toxicity. At diagnosis, 128 plasma proteins were upregulated and 67 downregulated in cachectic relative to non-cachectic patients. Longitudinal assessments of body composition, physical performance, metabolism, clinical outcomes, and nutritional risk revealed distinct fat and muscle wasting phenotype trajectories. 71 proteins were associated with fat loss, 92 with muscle loss, and 177 with concurrent muscle and weight loss. We identified and functionally validated 8 plasma proteins linked to muscle loss and adverse clinical outcomes. In a separate cohort of 147 patients with advanced pancreatic cancer receiving the interleukin-6 (IL-6) inhibitor tocilizumab, pharmacological suppression of serum amyloid A (SAA) levels following IL-6 inhibition suggests a systemic IL-6-SAA axis. These results collectively highlight SAA1 and SAA2 as IL-6-driven, cachexia-associated factors that reduce human myotube width. These findings uncover new potential therapeutic targets for cachexia.

Systems Biology↗

bioRxiv2026

Decreased food intake contributes to elevated insulin-responsiveness in pre-clinical cancer cachexia

PurposeCancer cachexia is a life-threatening complication of advanced malignancies, driven by anorexia and profound systemic metabolic reprogramming. Insulin action in skeletal muscle is markedly impaired in patients with cancer and may contribute directly to cachexia pathogenesis. However, the interplay between reduced nutrient intake and cancer-associated metabolic rewiring in cachexia remains poorly defined. Clarifying this relationship is essential for identifying the fundamental drivers of cachexia and for developing effective therapeutic strategies. MethodsWe assessed metabolic rewiring by glucose tolerance test and isotopic tracers to determine muscle insulin-stimulated glucose uptake in male cachectic and non-cachectic C26- and KPC-tumor-bearing, as well as mice towards C26 cachectic mice. ResultsCachectic C26-tumor-bearing mice displayed reduced body weight, lean, and fat mass, and food intake (-20%, -15%, -75%, -40%, respectively). Cachectic C26- and KPC-tumor mice showed improved glucose tolerance compared to non-cachectic mice, correlating inversely with tumor size. Ex vivo insulin-stimulated glucose uptake was elevated in soleus (+78%) and extensor digitorum longus (+35%) muscle from cachectic C26-cancer mice compared to non-cachectic and control mice. This increase was associated with enhanced AKT signaling. This was phenocopied in pair-fed non-tumor-bearing mice to match the food intake of cachectic mice, where glucose tolerance, insulin-stimulated glucose uptake ex vivo, and AKT signaling were all enhanced by food restriction. ConclusionsOur findings suggest that enhanced skeletal muscle insulin responsiveness in cachectic tumor-bearing mice is due to anorexia-induced adaptations, highlighting AKT signaling as a key node connecting nutrient status to muscle glucose metabolism in cancer cachexia. HighlightsO_LIC26 and KPC cancer-induced weight loss (cachexia) increases glucose tolerance in mice C_LIO_LIInsulin responsiveness is increased in cachectic, but not in non-cachectic, tumor-bearing mice. C_LIO_LILowered food intake drives elevated muscle insulin responsiveness in cachectic mice C_LI

molecular biology↗

bioRxiv2025

Proteomic and phospho-proteomic longitudinal signatures of human skeletal muscle in lung cancer cachexia

Weight loss is a potentially deadly hallmark of many cancers, including lung cancer. In particular, the loss of skeletal muscle mass and function impairs survival and lowers quality of life. Despite being a major determinant of prognosis, the molecular drivers of muscle wasting remain ill-defined. Therefore, there is a critical need for human molecular data to support the development of effective therapies for this currently untreatable condition. Here, we utilize cutting-edge proteomics technology to longitudinally map the proteome and phosphoproteome of skeletal muscle from patients with newly diagnosed, advanced-stage non-small cell lung cancer during their treatment. Leveraging deep in vivo clinical phenotyping of activity, body composition, muscle quality, and nutritional risk, we identified 118/174 muscle proteins/phospho-sites associated with cachexia at diagnosis with indications of sexual dimorphism. Treatment altered 278 proteins and 1,155 phospho-sites, of which 137/91 proteins/phospho-sites were associated with muscle wasting. Our findings highlight disrupted calcium, anabolic, and stress signalling, alongside extracellular matrix and mitochondrial alterations, as key molecular features of cachexia in non-small cell lung cancer. These clinically anchored proteomic and phosphoproteomic signatures provide potential targets for future research.

molecular biology↗

bioRxiv2025

Pathophysiological remodeling of the skeletal muscle microenvironment in patients with lung cancer

Background Muscle wasting, systemic inflammation, and functional decline are highly prevalent and detrimental in patients with advanced-stage non small cell lung cancer (NSCLC). Methods: In this cross sectional study, we investigated NSCLC associated muscle remodeling by analyzing skeletal muscle biopsies from patients with NSCLC (n = 18) and matched controls (n = 18) using quantitative proteomics, histology, fluorescence-activated cell sorting, gene expression profiling, and high resolution respirometry. Findings: NSCLC muscle was characterized by type II muscle fiber atrophy, greater collagen deposition, and redistribution of lipids to the extracellular matrix (ECM), together with remodeling of the inflammatory, immune, ECM and mitochondrial proteome. Additionally, mitochondrial respiratory capacity and morphology were altered in patients with NSCLC, which was associated with increased oxidative stress and dysregulated calcium handling. Concomitantly, we detected STAT3 activation and immune cell alterations, which may negatively impact skeletal muscle health in patients with NSCLC. Finally, we identified a shift in fibro-adipogenic progenitors (FAPs), favoring the CD90 subtype. Mechanistically, conditioned media from patient-derived FAPs reduced myotube width in vitro, uncovering a novel mechanism by which altered paracrine signaling from the muscle resident stromal compartment drives atrophy in cancer cachexia. Interpretation: These findings provide human evidence that altered FAP composition, mitochondrial homeostasis, calcium handling, and immune cell landscape accompany muscle wasting in NSCLC, which may inform therapeutic strategies to preserve skeletal muscle health in patients with cancer.

molecular biology↗

bioRxiv2025

Activin receptor type IIA/B blockade increases muscle mass and strength, but compromises glycemic control in mice

Short abstractO_ST_ABSPurposeC_ST_ABSBlocking the Activin receptor type IIA and B (ActRIIA/IIB) has clinical potential to increase muscle mass and improve glycemic control in obesity, cancer, and aging. However, the impact of blocking ActRIIA/IIB on strength, metabolic regulation and insulin action remains unclear. MethodsHere, we investigated the effect of short- (10 mg/kg once, 40h) or long-term (10 mg/kg twice weekly, 21 days) antibody targeting ActRIIA/IIB (ActRIIA/IIBab) in lean and diet-induced obese mice and engineered human muscle tissue. ResultsShort-term ActRIIA/IIB administration in lean mice increased insulin-stimulated glucose uptake in skeletal muscle by 76-105%. Despite this, ActRIIA/IIB-treated mice exhibited 33% elevated fasting blood glucose and glucose intolerance. Moreover, long-term ActRIIA/IIB treatment increased average muscle mass (20%) and reduced fat mass (-8%) in obese mice but did not change insulin-stimulated glucose uptake in skeletal muscle or adipose tissue, yet induced marked glucose intolerance, and increased hepatic glucose output in response to pyruvate. Concomitantly, long-term ActRIIA/IIBab treatment increased strength (30%) in mouse soleus muscle and prevented activin A-induced loss of tissue strength in engineered human muscle tissue. Surprisingly, long-term ActRIIA/IIBab treatment lowered volitional running (-250%). ConclusionOur findings demonstrate that, in accordance with human studies, ActRIIA/IIB blockade holds promise for increasing muscle mass, strength, and insulin sensitivity. However, contrary to the improved glycemic control in humans, ActRIIA/IIB blockade in mice causes severe glucose intolerance and lowers voluntary physical activity. Our study underscores the complex metabolic and functional consequences of ActRIIA/IIB blockade, and highlight species differences on glycemic control, which warrant further investigation.

molecular biology↗

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

Pantothenate Kinase 4 controls efficient skeletal muscle energy substrate metabolism via acetyl-CoA

Metabolic inflexibility in skeletal muscle (SkM) is closely linked to metabolic diseases. Exercise improves metabolic flexibility, rendering it a valuable discovery tool of mechanisms promoting efficient metabolism of glucose and lipids. We herein discover pantothenate kinase 4 (PanK4) as a conserved exercise target with high abundance in SkM. We go on to show that murine muscle Pank4 is dysregulated with high-fat diet feeding, and identify human PANK4 variants that associate with glycemic control and body mass index traits, indicating important roles of PanK4 in glucose metabolism and growth. Consistent with the latter, germline deletion of PanK4 reduces circulating IGF-1 and stunts growth in mice. Deletion specifically in mouse SkM reveals that PanK4 facilitates fatty acid oxidation by acting as a regulator of SkM acetyl-CoA, a key node in metabolism of both glucose and lipids. Consequently, without PanK4, elevated SkM acetyl-CoA levels allosterically gridlock key enzymes required for efficient lipid and glucose utilization, and these SkM metabolic perturbations manifest in whole-body insulin resistance. As proof of principle, we show that an increase in muscle PanK4 lowers SkM acetyl-CoA and increases SkM glucose utilization. Our findings identify PanK4 as a novel regulator of SkM energy substrate metabolism, warranting inclusion in comprehensive strategies against metabolic disease.

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↗

bioRxiv2020

Conditioned media from MCF7 and BT474 breast cancer cells induce insulin resistance in skeletal muscle myotubes

BackgroundMetabolic disorders are prevalent in women with breast cancer, increasing mortality and cancer recurrence rates. Despite clinical implications, the cause of breast cancer-associated metabolic dysfunction remains poorly understood. Skeletal muscle is crucial for insulin-stimulated glucose uptake, thus key to whole-body glucose homeostasis. In this study, we determined the effect of breast cancer cell-conditioned media on skeletal muscle glucose uptake in response to insulin. MethodL6 myotubes overexpressing myc-tagged GLUT4 (GLUT4myc-L6) were incubated with 40% conditioned media from tumorigenic MCF7 or BT474, or non-tumorigenic control MCF10A breast cells. Mass-spectrometry-based proteomics was applied to detect molecular rewiring in response to breast cancer in the muscle. Expression of myogenesis and inflammation markers, GLUT4 translocation, [3H]-2-deoxyglucose (2DG) uptake, and intramyocellular insulin signalling were determined. ResultsBreast cancer cell-conditioned media induced proteomic changes in pathways related to sarcomere organisation, actin filament binding, and vesicle trafficking, disrupted myogenic differentiation, activated an inflammatory response via NF-{kappa}B, and induced muscle atrophy. Basal and insulin-stimulated GLUT4 translocation and 2DG uptake were reduced in myotubes treated with breast cancer cell-conditioned media compared to the control. Insulin signalling via the Rho GTPase Rac1 was blocked in breast cancer-treated myotubes, while Akt-TBC1D4 signalling was unaffected. ConclusionConditioned media from MCF7 and BT474 breast cancer cells reduced skeletal muscle glucose uptake via inhibition of GLUT4 translocation and intramyocellular insulin signalling by selectively blocking Rac1 activation and inducing inflammation. These findings indicate that the rewiring of skeletal muscle proteome, inflammation, and insulin signalling could play a role in metabolic dysfunction in patients with breast cancer.

cancer 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

Housing temperature influences exercise training adaptations in mice

Exercise training is a powerful means to combat metabolic pathologies. Mice are extensively used to describe the benefits of exercise, but mild cold stress induced by housing temperatures may confound translation to humans. Thermoneutral housing is a strategy to make mice more metabolically similar to humans but its effects on exercise adaptations are unknown. Using voluntary wheel running, we show that thermoneutral housing blunted exercise-induced improvements in insulin action in muscle and adipose tissue. Moreover, thermoneutrality reduced the effects of training on energy expenditure, body composition, muscle and adipose tissue protein expressions, and the gut microbiome. The majority of these thermoneutral-dependent training adaptations could not be ascribed to a lower voluntary running volume. Thus, we conclude that organismal adaptations to exercise training in mice critically depend upon housing temperature. Our findings underscore the importance of housing temperature as an important parameter in the design and interpretation of murine exercise studies.\n\nHighlightsO_LIHousing at 30{degrees}C blunts several adaptations to exercise training in mice\nC_LIO_LIExercise-sensitive protein induction is dampened at 30{degrees}C in skeletal muscle\nC_LIO_LI30{degrees}C-housing blunts training-induced increase in insulin-stimulated glucose uptake\nC_LIO_LIGlucose tolerance is not improved by voluntary exercise training at 30{degrees}C housing\nC_LIO_LIDecreased running in 30{degrees}C housing is not due to overheating\nC_LI\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC=\"FIGDIR/small/651588v1_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (68K):\norg.highwire.dtl.DTLVardef@1e5b6acorg.highwire.dtl.DTLVardef@3be37corg.highwire.dtl.DTLVardef@1d3febborg.highwire.dtl.DTLVardef@f8da30_HPS_FORMAT_FIGEXP M_FIG Graphical abstract\n\nC_FIG

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↗