Afternoon exercise is more efficacious than morning exercise at improving blood glucose levels in individuals with type 2 diabetes : a randomised crossover trial

Data availability The data analysed during the current study are available from the corresponding author on reasonable request. Funding The authors are supported by grants from Novo Nordisk Foundation (NNF14OC0011493 and NNF14OC0009941), Swedish Diabetes Foundation (DIA2015-052), Wenner-Gren Foundation, Swedish Research Council (2015-00165), Strategic Research Program in Diabetes at Karolinska Institutet (2009-1068), Stockholm County Council (SLL20150517 and SLL20170159) and Swedish Heart Lung Foundation (20150423).Peer reviewedPublisher PD

Three weeks of interrupting sitting lowers fasting glucose and glycemic variability, but not glucose tolerance, in free-living women and men with obesity

Funding This work was supported by grants from the Novo Nordisk Foundation (NNF14OC0011493, NNF14OC0009941, NNF18CC0034900), Swedish Diabetes Foundation (DIA2018-357), Diabetes Wellness Sverige (1849-PG), Swedish Research Council (2015-00165, 2018-02389), the Strategic Research Programme in Diabetes at Karolinska Institutet (2009-1068), the Knut and Alice Wallenberg Foundation (2018-0094), and the Stockholm County Council (SLL20170159). D.D. is supported by the National Health and Medical Research Council and the Victorian Government’s OIS scheme. Acknowledgements We thank the Swedish Metabolomics Centre (Umeå University) for assisting with the lipidomic analysis and Mariam Nordstrand for efforts in the recruitment and screening of participants, and in muscle biopsy procedure. The current addresses for S.P. and B.M.G. are the School of Life Sciences, University of Nottingham, Nottingham, UK, and The Rowett Institute, University of Aberdeen, Aberdeen, UK, respectively.Peer reviewedPostprin

Cell selectivity in succinate receptor SUCNR1/GPR91 signaling in skeletal muscle

Succinate is released by skeletal muscle during exercise and activates SUCNR1/GPR91. Signaling of SUCNR1 is involved in metabolite-sensing paracrine communication in skeletal muscle during exercise. However, the specific cell types responding to succinate and the directionality of communication are unclear. We aim to characterize the expression of SUCNR1 in human skeletal muscle. De novo analysis of transcriptomic datasets demonstrated that SUCNR1 mRNA is expressed in immune, adipose, and liver tissues, but scarce in skeletal muscle. In human tissues, SUCNR1 mRNA was associated with macrophage markers. Single-cell RNA sequencing and fluorescent RNAscope demonstrated that in human skeletal muscle, SUCNR1 mRNA is not expressed in muscle fibers but coincided with macrophage populations. Human M2-polarized macrophages exhibit high levels of SUCNR1 mRNA and stimulation with selective agonists of SUCNR1 triggered Gq- and Gi-coupled signaling. Primary human skeletal muscle cells were unresponsive to SUCNR1 agonists. In conclusion, SUCNR1 is not expressed in muscle cells and its role in the adaptive response of skeletal muscle to exercise is most likely mediated via paracrine mechanisms involving M2-like macrophages within the muscle. NEW & NOTEWORTHY Macrophages but not skeletal muscle cells respond to extracellular succinate via SUCNR1/GPR91

Comparative profiling of skeletal muscle models reveals heterogeneity of transcriptome and metabolism

We acknowledge the Beta Cell in-vivo Imaging/Extracellular Flux Analysis core facility, supported by the Strategic Research Program (SRP) in Diabetes, for the use of the Seahorse flux analyzer. AUTHOR CONTRIBUTIONS A.M.A. and N.J.P. conceived and designed research; A.M.A., L.S.P., J.A.B.S., B.M.G., M.S., L.D., A.V.C., and N.J.P. performed experiments; A.M.A., L.S.P., J.A.B.S., B.M.G., M.S., L.D., A.V.C., and N.J.P. analyzed data; A.M.A., L.S.P., J.A.B.S., B.M.G., M.S., L.D., A.V.C., A.K., J.R.Z., and N.J.P. interpreted results of experiments; A.M.A. and N.J.P. prepared figures; A.M.A. and N.J.P. drafted manuscript; A.M.A., L.S.P., J.A.B.S., B.M.G., M.S., L.D., A.V.C., A.K., J.R.Z., and N.J.P. edited and revised manuscript; A.M.A., L.S.P., J.A.B.S., B.M.G., M.S., L.D., A.V.C., A.K., J.R.Z., and N.J.P. approved final version of manuscript.Peer reviewedPublisher PD

Cellular and molecular mechanisms of skeletal muscle atrophy after spinal cord injury

Spinal cord injury leads to a rapid and profound loss of skeletal muscle mass. Muscle atrophy consequently promotes metabolic disturbances and leads to increased risk of type 2 diabetes and cardiovascular disease. Prevention of such consequences requires a deeper understanding of underlying molecular and cellular changes, which promote muscle atrophy. This thesis attempts to elucidate some of the mechanisms responsible for muscle atrophy induced by spinal cord injury; specifically, changes in the abundance of regulators of protein metabolism and enzymes responsible for oxidative stress homeostasis in skeletal muscle. Additionally, we examined the impact of spinal cord injury on the differentiation capacity of satellite cells, measured in vitro. Our results suggest most profound changes in skeletal muscle within the first three months post-injury, including higher reactive oxygen species production, apoptosis, and protein turnover. Conversely, we show retained intrinsic satellite cell differentiation capacity, despite substantial changes within skeletal muscle. Collectively, the studies in this thesis encourage efforts to maintain protein metabolism balance and oxidative stress homeostasis during the early post-spinal cord injury phases, as well as rehabilitative interventions targeting satellite cell activation

Altered oxidative stress and antioxidant defence in skeletal muscle during the first year following spinal cord injury

Oxidative stress promotes protein degradation and apoptosis in skeletal muscle undergoing atrophy. We aimed to determine whether spinal cord injury leads to changes in oxidative stress, antioxidant capacity, and apoptotic signaling in human skeletal muscle during the first year after spinal cord injury. Vastus lateralis biopsies were obtained from seven individuals 1, 3, and 12 months after spinal cord injury and from seven able‐bodied controls. Protein content of enzymes involved in reactive oxygen species production and detoxification, and apoptotic signaling were analyzed by western blot. Protein carbonylation and 4‐hydroxynonenal protein adducts were measured as markers of oxidative damage. Glutathione content was determined fluorometrically. Protein content of NADPH oxidase 2, xanthine oxidase, and pro‐caspase‐3 was increased at 1 and 3 months after spinal cord injury compared to able‐bodied controls. Furthermore, total and reduced glutathione content was increased at 1 and 3 months after spinal cord injury. Conversely, mitochondrial complexes and superoxide dismutase 2 protein content were decreased 12 months after spinal cord injury compared to able‐bodied controls. In conclusion, we provide indirect evidence of increased reactive oxygen species production and increased apoptotic signaling at 1 and 3 months after spinal cord injury. Concomitant increases in glutathione antioxidant defences may reflect adaptations poised to maintain redox homeostasis in skeletal muscle following spinal cord injury

Normalization of disrupted clock gene expression in males with tetraplegia: a crossover randomized placebo-controlled trial of melatonin supplementation

Study design: Crossover double blind, randomized placebo-controlled trial. Objectives: Circadian oscillators are located both in the brain and in peripheral organs. Melatonin, the main brain-derived hormone governing circadian variations, is highly associated with daylight patterns. However, in subjects with tetraplegia the melatonin levels are blunted. Here we studied peripheral oscillators in peripheral blood mononuclear cells (PBMCs) in males with tetraplegia by examining how exogenous melatonin may influence the expression of clock gene mRNAs. Setting: Sunnaas Rehabilitation Hospital, Nesoddtangen, Norway. Methods: Six males with tetraplegia received 2 mg of melatonin or placebo 4 days before the study period. We also included six able-bodied men sleeping or kept awake during the night. Plasma samples were collected four times during a 24-h period. The mRNA expression levels of the clock genes PER1, PER2, BMAL1, and REV-ERBα were quantified in PBMCs using quantitative RT-PCR. Results: The mRNA expression levels of PER-1 and –2 and REV-ERBα were increased at 04:00 h compared with the able-bodied controls (p < 0.05). Melatonin supplementation changed mRNA peak-time toward the time of supplementation. Conclusions: Several peripheral clock genes displayed distorted expression levels in tetraplegia. Supplementation with melatonin changed the mRNA expression levels of these genes toward those observed among able-bodied

Dataset for: Retained differentiation capacity of human skeletal muscle satellite cells from spinal cord-injured individuals

Despite the well-known role of satellite cells in skeletal muscle plasticity, the effect of spinal cord injury on their function in humans remains unknown. We determined whether spinal cord injury affects the intrinsic ability of satellite cells to differentiate and produce metabolically healthy myotubes. We obtained <i>vastus lateralis</i> biopsies from eight spinal cord-injured and six able-bodied individuals. Satellite cells were isolated, grown and differentiated <i>in vitro</i>. Gene expression was measured by quantitative PCR. Abundance of differentiation markers and regulatory proteins was determined by Western blotting. Protein synthesis and fatty acid oxidation were measured by radioactive tracer-based assays. Activated satellite cells (myoblasts) and differentiated myotubes derived from skeletal muscle of able-bodied and spinal cord-injured individuals expressed similar (p>0.05) mRNA levels of myogenic regulatory factors. Myod1 expression was higher in myoblasts from spinal cord-injured individuals. Desmin and myogenin protein content was increased upon differentiation in both groups, while myotubes from spinal cord-injured individuals contained more type I and II myosin heavy chain. Phosphorylated and total protein levels of Akt-mTOR and FoxO signalling axes and protein synthesis rate in myotubes were similar (p>0.05) between groups. Additionally, fatty acid oxidation of myotubes from spinal cord-injured individuals was unchanged (p>0.05) compared to able-bodied controls. Our results indicate that the intrinsic differentiation capacity of satellite cells and metabolic characteristics of myotubes are preserved following spinal cord injury. This may inform potential interventions targeting satellite cell activation to alleviate skeletal muscle atrophy