OBJECTIVES:Skeletal muscle is a central regulator of metabolic health, serving as the primary site of postprandial glucose uptake and playing a critical role in whole-body insulin sensitivity. Despite its importance, the molecular mechanisms governing muscle differentiation (myogenesis) and their modulation by metabolic interventions remain poorly defined. This study identifies the clathrin adaptor protein Picalm (phosphatidylinositol-binding clathrin assembly protein) as a novel regulator of myogenesis and investigates its regulation in response to exercise training and intermittent fasting. METHODS:Functional characterization of Picalm was conducted in C2C12 myoblasts and primary myocytes using siRNA-mediated knockdown. Clathrin-mediated endocytosis was performed using dynamin inhibition (Dyngo-4a) and via an EGF internalization assay. Surface proteome alterations were analyzed by plasma membrane proteomics, and autophagy dynamics were assessed via immunoblotting and fluorescence imaging. Jasplakinolide was used to rescue differentiation defects by enhancing actin polymerization. RESULTS:Picalm-depleted C2C12 myoblasts exhibited impaired differentiation, presumably due to diminished intracellular trafficking dynamics of cell surface proteins. Inhibition of dynamin-dependent endocytosis phenocopied the differentiation defect and further aggravated myogenesis in Picalm-depleted cells, indicating that Picalm-dependent endocytic function is required for efficient differentiation. Consistent with this, Picalm knockdown significantly decreased clathrin-dependent uptake of EGF. Proteome analysis of a plasma membrane-enriched fraction revealed increased abundance of over 100 proteins after Picalm knockdown, particularly candidates involved in vesicular trafficking (Vamp3, Vamp5), actin remodeling (Actn1, Actn4, Rhog, Rock1, Rock2) and cell adhesion (integrin receptors). In line with this, Picalm knockdown resulted in impaired maturation and lysosomal degradation of autophagic vesicles. Remarkably, pharmacological stabilization of actin filaments with Jasplakinolide restored myogenic differentiation in Picalm-deficient cells, highlighting a functional link between actin remodeling and myogenesis. CONCLUSIONS:Picalm regulates skeletal muscle differentiation by supporting clathrin-mediated endocytosis and plasma membrane remodeling, thereby maintaining trafficking-dependent control of actin organization. Its expression is responsive to metabolic cues such as exercise and intermittent fasting. These findings reveal a novel molecular link between nutrient signaling and myogenesis, with implications for metabolic disease and muscle regeneration.

Human skeletal muscle is the principal site of insulin-stimulated glucose disposal and a major mediator of exercise-induced metabolic benefits, yet human models that preserve metabolic and exercise responsiveness remain limited. We generated primary human skeletal muscle organoids from donor-derived CD56+ myoblasts using a collagen-based extracellular matrix and serum-free IGF1-guided differentiation. The organoids formed aligned contractile tissues containing oxidative and glycolytic fiber type-like myotubes, displayed enhanced mitochondrial respiration, insulin-stimulated glucose uptake, and reproducible force generation. Electrical pulse stimulation induced AMPK activation, increased glucose utilization and lactate production, and upregulated canonical exercise-responsive genes including NR4A3 and PPARGC1A. Notably, transcriptional responses to in vitro exercise overlapped with acute exercise responses observed in skeletal muscle biopsies from the same donors. The organoids further detected functional impairments of skeletal muscle performance induced by TGF-β1 and metformin and increased speed generation by testosterone treatment. These findings establish a donor-specific human skeletal muscle platform that recapitulates key features of insulin action and exercise adaptation and may enable mechanistic studies of skeletal muscle metabolism, exercise responsiveness, and therapeutic interventions relevant to diabetes.

Intermuscular adipose tissue (IMAT) is increasingly recognized as a contributor to insulin resistance and metabolic dysfunction in type 2 diabetes (T2D). Accumulation of IMAT was found to correlate with impaired skeletal muscle insulin sensitivity, as well as a generally reduced muscle strength and physical performance in humans. Beyond serving as an energy depot at physiological levels, increased IMAT is thought to actively impair muscle metabolism through secretion of adipokines, cytokines and lipid intermediates that create an inflammatory environment and modulate insulin signaling pathways. This review discusses current evidence on the pathophysiological role of IMAT based on clinical studies, including interventions, and current mechanistic insight from biopsied human IMAT. We further explore traditional and emerging methods to investigate IMAT that could expand mechanistic understanding of IMAT-muscle-crosstalk, highlighting their strengths and limitations. Human in vitro co-culture-models are valuable future tools for dissecting cellular and molecular responses. Despite growing interest in IMAT as a potential key player in metabolic disease, uncertainty remains about its origin, regulation and functionality. We suggest further research to integrate and intertwine traditional imaging techniques, multi-omics characterization of IMAT biopsies and advanced, physiologically relevant human in vitro systems to close these knowledge gaps to develop therapeutic strategies targeting metabolic disease.

Stehen wir am Anfang vom Ende der Adipositas- und der Typ-2-Diabetes-Epidemie, da die Wirksamkeit und Sicherheit der Inkretin-Rezeptoragonisten alle bisherigen therapeutischen Ansätze bei weitem übertreffen, noch effektivere Substanzen in der pipeline sind und auch die Versorgungsprobleme gelöst werden können? Eine spannende Frage, die Patienten, Ärzte und Diabetesforschende gleichermaßen betrifft. In einigen Jahren wird man feststellen können, ob wirklich ein neues Zeitalter in der Adipositas- und Diabetestherapie mit der Zulassung dieser Substanzen begonnen hat.

A bidirectional relationship exists between metabolic dysfunction-associated steatotic liver disease (MASLD) and its progressive inflammatory form, metabolic dysfunction-associated steatohepatitis (MASH), and sarcopenia, with each worsening the prevalence and prognosis of the other. Hepatokines have recently been shown to affect skeletal muscle metabolism and function, both in the context of MASLD and wasting diseases. We here explored the possibility of targeting hepatokines to counteract MASLD-induced sarcopenia. Integrating mouse and human liver transcriptomics with muscle proteomics from MCD- and GAN-diet induced murine MASH models with sarcopenia, we identified three MASH-induced hepatokines, namely LCN2, LGALS3 and OPN. These hepatokines were elevated in the circulation of mouse MASH models with sarcopenia and in sarcopenic patients with advanced chronic liver disease. C2C12 myotubes treated with liver-secreted proteins as well as recombinant LCN2 and LGALS3 exhibited atrophy. Stable isotope tracing and mitochondrial respiration showed that liver-secreted proteins altered mitochondrial metabolism in C2C12 myotubes, which was recapitulated in primary human myotubes. Human 3D skeletal muscle organoids treated with recombinant proteins exhibited functional impairment. Virus-mediated knockdown of LCN2 in liver of mice with MASH improved muscle function and myotube size, whereas virus-mediated overexpression of LCN2 in the liver aggravated MASH-induced myotube atrophy. Targeting hepatokines may therefore be a feasible future therapeutic strategy against sarcopenia.

Clinical practice guidelines recommend defined weight loss goals for the prevention of type 2 diabetes (T2D) in those individuals with increased risk, such as prediabetes. However, achieving prediabetes remission, that is, reaching normal glucose regulation according to American Diabetes Association criteria, is more efficient in preventing T2D than solely reaching weight loss goals. Here we present a post hoc analysis of the large, multicenter, randomized, controlled Prediabetes Lifestyle Intervention Study (PLIS), demonstrating that prediabetes remission is achievable without weight loss or even weight gain, and that it also protects against incident T2D. The underlying mechanisms include improved insulin sensitivity, β-cell function and increments in β-cell-GLP-1 sensitivity. Weight gain was similar in those achieving prediabetes remission (responders) compared with nonresponders; however, adipose tissue was differentially redistributed in responders and nonresponders when compared against each other-while nonresponders increased visceral adipose tissue mass, responders increased adipose tissue in subcutaneous depots. The findings were reproduced in the US Diabetes Prevention Program. These data uncover essential pathways for prediabetes remission without weight loss and emphasize the need to include glycemic targets in current clinical practice guidelines to improve T2D prevention.

OBJECTIVES:Endurance exercise reduces the risk of metabolic diseases by improving skeletal muscle metabolism, particularly in individuals with overweight and obesity. As biological sex impacts glucose and fatty acid handling in skeletal muscle, we hypothesized sex differences at the transcriptomic and proteomic level in the acute response to exercise and after an 8-week exercise intervention. METHODS:We analyzed skeletal muscle biopsies from 25 sedentary subjects (16f/9 m) with overweight and obesity using transcriptomics and proteomics at baseline, after acute exercise, and following an 8-week endurance training program. Regulation of sex-specific differences was studied in primary myotubes from the donors. RESULTS:At baseline, differentially methylated CpG-sites potentially explain up to 59% of transcriptomic and 67% of proteomic sex differences. Differences were dominated by higher abundance of fast-twitch fiber type proteins, and transcripts and proteins regulating glycogen degradation and glycolysis in males. Females showed higher abundance of proteins regulating fatty acid uptake and storage. Acute exercise induced stress-responsive transcripts and serum myoglobin predominantly in males. Both sexes adapted to 8-week endurance training by upregulating mitochondrial proteins involved in TCA cycle, oxidative phosphorylation, and β-oxidation. Training equalized fast-twitch fiber type protein levels, mainly by reducing them in males. In vivo sex differences in autosomal genes were poorly retained in myotubes but partially restored by sex hormone treatment. CONCLUSIONS:Our findings highlight sex-specific molecular signatures that reflect known differences in glucose and lipid metabolism between female and male skeletal muscle. After just 8 weeks of endurance training, these sex differences were attenuated, suggesting a convergence towards a shared beneficial adaptation at the molecular level.

Exercise is a potent skeletal muscle stimulus and one of the most effective strategies to prevent muscle loss and type 2 diabetes. Biological sex-based differences are reported for aerobic capacity, muscle mass, and exercise performance. We aimed to provide a yet missing comprehensive picture of molecular differences between female and male skeletal muscle at baseline, after acute exercise and training. Further we investigated which differences were conserved in vitro. We characterized muscle biopsies from 25 (16f/9m) subjects in a multi-omics approach employing epigenomics, transcriptomics and proteomics at baseline, after acute exercise and 8 weeks of supervised endurance training. Donor matched myoblasts and myotubes were analyzed in vitro. We found differential CpG-site methylation in 16.012 genes, 1.366 differentially expressed genes and 120 proteins at baseline. Differential transcripts were associated with translational regulation, histone methylation, glucose homeostasis and insulin signaling. Type-2 fast-twitch fiber-type proteins were elevated in males, along with proteins regulating glycolysis. Y-linked transcript expression was conserved in vitro, but only a few differences in expression of autosomal genes, e.g. elevated LDHB in females. Acute exercise upregulated oxidative stress-responsive transcripts predominantly in males. After 8-week-training, both sexes had upregulated mitochondrial proteins involved in substrate oxidation and ATP production, while glycolytic fiber marker MYH1 and MYH3 were only reduced in males. Thus, sex specific differences exist in resting skeletal muscle and in exercise adaptation on epigenomic, transcriptomic and proteomic level. The few conserved differences in vitro hint towards hormonal or yet undefined mechanisms. Training might mitigate initially differential responses to exercise. The question remains whether there are sex specific differences within individual fiber-types or whether it is just a matter of composition. Disclosure S.I. Dreher: None. T. Goj: None. C. von Toerne: None. M. Hoene: None. M. Irmler: None. M. Ouni: None. M. Jähnert: None. J. Beckers: None. A. Peter: None. A.L. Birkenfeld: None. A. Schürmann: None. S.M. Hauck: None. C. Weigert: None.

Biological sex has a strong impact on skeletal muscle metabolism and performance. By a comprehensive investigation of epigenetic, transcriptomic and proteomic differences between female and male skeletal muscle of untrained subjects we provide a molecular basis for the sexual dimorphism of glucose and lipid metabolism. The sex-specific multi-OMICs profiles indicate higher degree of glucose turnover and higher abundance of fast-twitch fibers in males and high degree of lipid handling in females. Eight-week endurance training equalized initial differences toward an endurance-trained proteomic profile in both sexes. The untrained muscle of females was more resistant to an acute exercise challenge since stress-responsive transcripts were predominantly upregulated in males. In myotubes from the same donors, transcriptomic differences were hardly conserved, but could be partially restored by treatment with sex hormones. In conclusion, after only 8 weeks training mitigates deeply rooted sex-specific molecular profiles in skeletal muscle toward a common metabolically beneficial response. ### Competing Interest Statement The authors have declared no competing interest.

Introduction: Omentin (intelectin-1) is an adipokine produced by the stromal vascular fraction of visceral adipose tissue and has been positively associated with insulin sensitivity. The underlying mechanism of action, however, is largely unknown. It has been described that omentin may increase insulin sensitivity and glucose uptake of adipocytes, but effects on other insulin-sensitive tissues such as skeletal muscle are unexplored. We therefore investigated effects of omentin on insulin sensitivity and metabolism of primary human myotubes. Methods: Primary human myotubes were treated with 0.5 or 2 µg/mL omentin and subsequently protein detection, glucose uptake assay, lactate assay, and lipidomics analysis were performed. Results: Omentin did not affect skeletal muscle insulin signaling, as assessed by basal and insulin-stimulated phosphorylation of IRS1 and AKT. Omentin increased basal, but not insulin-stimulated glucose uptake. While increased glycolytic activity was confirmed by elevated lactate release after omentin treatment, effects on cellular lipid composition were limited to an increase in total triacylglycerol concentration. Increased glucose uptake by omentin was counteracted by addition of extracellular lactotransferrin, which can bind to omentin. Conclusions: Overall, increased basal glucose uptake in skeletal muscle cells suggests differential effects of omentin on insulin-sensitive tissues. Moreover, an involvement of lactotransferrin in omentin’s mechanism of action may partially explain contradictory results of epidemiological studies on the role of omentin in different diseases.

Context Exercise training is known to improve glucose tolerance and reverse insulin resistance in people with obesity. However, some individuals fail to improve or even decline in their clinical traits following exercise intervention.Objective This study focused on gene expression and DNA methylation signatures in skeletal muscle of low (LRE) and high responders (RES) to 8 weeks of supervised endurance training.Methods We performed skeletal muscle gene expression and DNA methylation analyses in LRE and RES before and after exercise intervention. Additionally, we applied the least absolute shrinkage and selection operator (LASSO) approach to identify predictive marker genes of exercise outcome.Results We show that the two groups differ markedly already before the intervention. RES were characterized by lower expression of genes involved in DNA replication and repair, and higher expression of extracellular matrix (ECM) components. The LASSO approach identified several novel candidates (eg, ZCWPW2, FOXRED1, STK40) that have not been previously described in the context of obesity and exercise response. Following the intervention, LRE reacted with expression changes of genes related to inflammation and apoptosis, RES with genes related to mitochondrial function. LRE exhibited significantly higher expression of ECM components compared to RES, suggesting improper remodeling and potential negative effects on insulin sensitivity. Between 45% and 70% of differences in gene expression could be linked to differences in DNA methylation.Conclusion Together, our data offer an insight into molecular mechanisms underlying differences in response to exercise and provide potential novel markers for the success of intervention.

fast die Hälfte der Teilnehmer einer aktuellen Statista-Umfrage gaben jeweils "Mehr Sport treiben" und "Gesünder ernähren" als ihre guten Vorsätze für das Jahr 2024 an.

Human skeletal muscle models are highly valuable to study how exercise prevents type 2 diabetes without invasive biopsies. Current models did not fully recapitulate the function of skeletal muscle especially during exercise. By supplementing insulin-like growth factor 1 (IGF1), the authors developed a functional human skeletal muscle model characterized by inducible contractility and increased oxidative and insulin-sensitive metabolism. The novel protocol overcomes the limitations of previous standards and enables investigation of exercise on a molecular level.

This Special Issue was initiated to celebrate and congratulate Prof [...]

Aims/hypothesis While physical activity is clearly beneficial in combating type 2 diabetes, the underlying molecular mechanisms are incompletely understood. Moreover, there is a considerable degree of variability in the individual response to exercise-based lifestyle interventions that remains to be explained. We aimed to identify novel exercise-induced metabolites that could mediate the improvement in glycemic control and reduction of obesity and contribute to individual differences in the response to exercise interventions. Methods We studied acute exercise- and training-induced changes in plasma metabolites in sedentary subjects with overweight (8 male, 14 female) participating in an eight-week supervised training program flanked by two acute endurance exercise sessions. Plasma metabolites were quantified using LC- and CE-MS. In a separate study (n=9 lean males), we assessed metabolite fluxes over the leg using arterial and venous catheters. Functional analyses were performed in primary blood mononuclear cells (PBMCs) stimulated with lipopolysaccharide (LPS) or the saturated fatty acid palmitate. Results The amino acid breakdown products 3-phenyllactic acid (PLA), 4-hydroxyphenyllactic acid and indolelactic acid were increased after both acute exercise and training. All three aromatic lactic acids, which so far mainly received attention as bacterial metabolites, exhibited an efflux from the leg. PLA showed the largest increase after both acute exercise and training, of 57% and 20% respectively. The magnitude of the acute exercise-induced increase in PLA correlated with a decrease in subcutaneous adipose tissue volume and an improvement in insulin sensitivity over the course of the intervention. Furthermore, both isomers, D- and L-PLA, counteracted inflammatory cytokine production in PBMCs. Conclusions/interpretation Our findings indicate that PLA is physiologically released from skeletal muscle and can contribute to the anti-inflammatory effects of exercise as well as to individual difference in the response to lifestyle interventions in humans. PLA and potentially, aromatic lactic acids in general may be particularly relevant metabolic regulators because they can be produced both endogenously and by the microbiome. Trial registration ClinicalTrials.gov NCT03151590 ### Competing Interest Statement The authors have declared no competing interest. ### Clinical Trial NCT03151590 ### Funding Statement This study was supported in part by grants from the Mobility Programme of the Sino-German Center for Research Promotion (M-0257), the Strategic Leading Science and Technology Project B of the Chinese Academy of Sciences (XDB38020200), the German Federal Ministry of Education and Research (BMBF) to the German Centre for Diabetes Research (DZD e.V., 01GI0925) and by grants from the German Diabetes Association (DDG) to MH and AM. AM is currently funded by a clinician scientist program from the medical faculty of the University of Tuebingen. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Written consent was obtained from all participants and the study was approved by the ethics committee of the University of Tuebingen and registered at Clinicaltrials.gov. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes

das Jahr 2023 neigt sich dem Ende zu und Sie erhalten die letzte Ausgabe dieses Jahres von Diabetologie und Stoffwechsel, die noch einmal wichtige Neuigkeiten, Beiträge, Nachrichten und Diskussionsbeiträge für Sie bietet.

BACKGROUND:Remission of type 2 diabetes can occur as a result of weight loss and is characterised by liver fat and pancreas fat reduction and recovered insulin secretion. In this analysis, we aimed to investigate the mechanisms of weight loss- induced remission in people with prediabetes. METHODS:In this prespecified post-hoc analysis, weight loss-induced resolution of prediabetes in the randomised, controlled, multicentre Prediabetes Lifestyle Intervention Study (PLIS) was assessed, and the results were validated against participants from the Diabetes Prevention Program (DPP) study. For PLIS, between March 1, 2012, and Aug 31, 2016, participants were recruited from eight clinical study centres (including seven university hospitals) in Germany and randomly assigned to receive either a control intervention, a standard lifestyle intervention (ie, DPP-based intervention), or an intensified lifestyle intervention for 12 months. For DPP, participants were recruited from 23 clinical study centres in the USA between July 31, 1996, and May 18, 1999, and randomly assigned to receive either a standard lifestyle intervention, metformin, or placebo. In both PLIS and DPP, only participants who were randomly assigned to receive lifestyle intervention or placebo and who lost at least 5% of their bodyweight were included in this analysis. Responders were defined as people who returned to normal fasting plasma glucose (FPG; <5·6 mmol/L), normal glucose tolerance (<7·8 mmol/L), and HbA1c less than 39 mmol/mol after 12 months of lifestyle intervention or placebo or control intervention. Non-responders were defined as people who had FPG, 2 h glucose, or HbA1c more than these thresholds. The main outcomes for this analysis were insulin sensitivity, insulin secretion, visceral adipose tissue (VAT), and intrahepatic lipid content (IHL) and were evaluated via linear mixed models. FINDINGS:Of 1160 participants recruited to PLIS, 298 (25·7%) had weight loss of 5% or more of their bodyweight at baseline. 128 (43%) of 298 participants were responders and 170 (57%) were non-responders. Responders were younger than non-responders (mean age 55·6 years [SD 9·9] vs 60·4 years [8·6]; p<0·0001). The DPP validation cohort included 683 participants who lost at least 5% of their bodyweight at baseline. Of these, 132 (19%) were responders and 551 (81%) were non-responders. In PLIS, BMI reduction was similar between responders and non-responders (responders mean at baseline 32·4 kg/m2 [SD 5·6] to mean at 12 months 29·0 kg/m2 [4·9] vs non-responders 32·1 kg/m2 [5·9] to 29·2 kg/m2 [5·4]; p=0·86). However, whole-body insulin sensitivity increased more in responders than in non-responders (mean at baseline 291 mL/[min × m2], SD 60 to mean at 12 months 378 mL/[min × m2], 56 vs 278 mL/[min × m2], 62, to 323 mL/[min × m2], 66; p<0·0001), whereas insulin secretion did not differ within groups over time or between groups (responders mean at baseline 175 pmol/mmol [SD 64] to mean at 12 months 163·7 pmol/mmol [60·6] vs non-responders 158·0 pmol/mmol [55·6] to 154·1 pmol/mmol [56·2]; p=0·46). IHL decreased in both groups, without a difference between groups (responders mean at baseline 10·1% [SD 8·7] to mean at 12 months 3·5% [3·9] vs non-responders 10·3% [8·1] to 4·2% [4·2]; p=0·34); however, VAT decreased more in responders than in non-responders (mean at baseline 6·2 L [SD 2·9] to mean at 12 months 4·1 L [2·3] vs 5·7 L [2·3] to 4·5 L [2·2]; p=0·0003). Responders had a 73% lower risk of developing type 2 diabetes than non-responders in the 2 years after the intervention ended. INTERPRETATION:By contrast to remission of type 2 diabetes, resolution of prediabetes was characterised by an improvement in insulin sensitivity and reduced VAT. Because return to normal glucose regulation (NGR) prevents development of type 2 diabetes, we propose the concept of remission of prediabetes in analogy to type 2 diabetes. We suggest that remission of prediabetes should be the primary therapeutic aim in individuals with prediabetes. FUNDING:German Federal Ministry for Education and Research via the German Center for Diabetes Research; the Ministry of Science, Research and the Arts Baden-Württemberg; the Helmholtz Association and Helmholtz Munich; the Cluster of Excellence Controlling Microbes to Fight Infections; and the German Research Foundation.

CONTEXT:One acute bout of exercise leads to a rapid increase in the systemic cytokine concentration. Regular exercise might alter the cytokine response, in particular in beforehand untrained and obese individuals.OBJECTIVE:Using a proximity extension assay, we studied the effects of acute exercise as well as endurance training on a panel of 92 cytokines related to inflammation.METHODS:A total of 22 individuals (30 ± 9 years; peak oxygen uptake [VO2peak] 25.2 ± 4.2 mL/[kg × min]; body mass index [BMI] 31.7 ± 4.4) participated in an 8-week endurance exercise intervention. Blood samples were collected before and immediately after 30 minutes' ergometer exercise at 80% VO2peak.RESULTS:Before and after the training intervention, 40 and 37 cytokines, respectively, were acutely increased more than 1.2-fold (Benjamini-Hochberg [BH]-adjusted P < .05). The exercise intervention did not change the acute increase in cytokines nor the resting cytokine levels, whereas fitness was improved and adiposity reduced. The increase in fitness led to a slight increase in power output when exercising at the same heart rate, which might explain the comparable increase in cytokines before and after the intervention. The largest acute increase was found for OSM, TGFA, CXCL1 and 5, and TNFSF14 (≥ 1.9-fold, BH-adjusted P < .001). The transcript levels of these proteins in whole blood were also elevated, particularly in the trained state. Only the acute increase in IL6 (1.3-fold) was related to the increase in lactate, confirming the lactate-driven secretion of IL6.CONCLUSION:Our comprehensive proteomics approach detected several underexplored serum exerkines with up to now less understood function in the adaptation to exercise.

Metformin-induced glycolysis and lactate production can lead to acidosis as a life-threatening side effect, but slight increases in blood lactate levels in a physiological range were also reported in metformin-treated patients. However, how metformin increases systemic lactate concentrations is only partly understood. Because human skeletal muscle has a high capacity to produce lactate, the aim was to elucidate the dose-dependent regulation of metformin-induced lactate production and the potential contribution of skeletal muscle to blood lactate levels under metformin treatment. This was examined by using metformin treatment (16-776 μM) of primary human myotubes and by 17 days of metformin treatment in humans. As from 78 µM, metformin induced lactate production and secretion and glucose consumption. Investigating the cellular redox state by mitochondrial respirometry, we found metformin to inhibit the respiratory chain complex I (776 µM, P < 0.01) along with decreasing the [NAD+]:[NADH] ratio (776 µM, P < 0.001). RNA sequencing and phospho-immunoblot data indicate inhibition of pyruvate oxidation mediated through phosphorylation of the pyruvate dehydrogenase (PDH) complex (39 µM, P < 0.01). On the other hand, in human skeletal muscle, phosphorylation of PDH was not altered by metformin. Nonetheless, blood lactate levels were increased under metformin treatment (P < 0.05). In conclusion, the findings suggest that metformin-induced inhibition of pyruvate oxidation combined with altered cellular redox state shifts the equilibrium of the lactate dehydrogenase (LDH) reaction leading to a dose-dependent lactate production in primary human myotubes.NEW & NOTEWORTHY Metformin shifts the equilibrium of lactate dehydrogenase (LDH) reaction by low dose-induced phosphorylation of pyruvate dehydrogenase (PDH) resulting in inhibition of pyruvate oxidation and high dose-induced increase in NADH, which explains the dose-dependent lactate production of differentiated human skeletal muscle cells.

Background Exercise exerts many health benefits by directly inducing molecular alterations in physically utilized skeletal muscle. Molecular adaptations of subcutaneous adipose tissue (SCAT) might also contribute to the prevention of metabolic diseases. Aim To characterize the response of human SCAT based on changes in transcripts and mitochondrial respiration to acute and repeated bouts of exercise in comparison to skeletal muscle. Methods Sedentary participants (27 ± 4 yrs) with overweight or obesity underwent 8-week supervised endurance exercise 3×1h/week at 80% VO2peak. Before, 60 min after the first and last exercise bout and 5 days post intervention, biopsies were taken for transcriptomic analyses and high-resolution respirometry ( n = 14, 8 female/6 male). Results In SCAT, we found 37 acutely regulated transcripts (FC > 1.2, FDR < 10%) after the first exercise bout compared to 394, respectively, in skeletal muscle. Regulation of only 5 transcripts overlapped between tissues highlighting their differential response. Upstream and enrichment analyses revealed reduced transcripts of lipid uptake, storage and lipogenesis directly after exercise in SCAT and point to β-adrenergic regulation as potential major driver. The data also suggest an exercise-induced modulation of the circadian clock in SCAT. Neither term was associated with transcriptomic changes in skeletal muscle. No evidence for beigeing/browning was found in SCAT along with unchanged respiration. Conclusions Adipose tissue responds completely distinct from adaptations of skeletal muscle to exercise. The acute and repeated reduction in transcripts of lipid storage and lipogenesis, interconnected with a modulated circadian rhythm, can counteract metabolic syndrome progression toward diabetes.