Disrupted circadian oscillations in type 2 diabetes are linked to altered rhythmic mitochondrial metabolism in skeletal muscle

Funding: The authors are supported by grants from the AstraZeneca SciLifeLab Research Programme, Novo Nordisk Foundation (NNF14OC0011493, and NNF17OC0030088), Swedish Diabetes Foundation (DIA2018-357), Swedish Research Council (2015-00165 and 2018-02389), the Knut and Alice Wallenberg Foundation (2018-0094), the Strategic Research Programme in Diabetes at Karolinska Institutet (2009-1068), the Stockholm County Council (SLL20170159), and the Swedish Research Council for Sport Science (P2019-0140). B.M.G. was supported by fellowships from the Novo Nordisk Foundation (NNF19OC0055072), the Wenner-Gren Foundation, an Albert Renold Travel Fellowship from the European Foundation for the Study of Diabetes, and an Eric Reid Fund for Methodology from the Biochemical Society. N.J.P. and L.S.-P. were supported by an Individual Fellowship from the Marie Skłodowska-Curie Actions (European Commission: 704978 and 675610). X.Z. and K.A.E. were supported by NIH R01AR066082. N.J.P. was supported by grants from the Sigurd och Elsa Goljes Minne and Lars Hierta Memorial Foundations (Sweden). We acknowledge the Beta Cell in-vivo Imaging/Extracellular Flux Analysis core facility supported by the Strategic Research Program in Diabetes for the usage of the Seahorse flux analyzer. Additional support was received from the Novo Nordisk Foundation Center for Basic Metabolic Research at the University of Copenhagen (NNF18CC0034900). The Novo Nordisk Foundation Center for Basic Metabolic Research is an independent research center at the University of Copenhagen, partially funded by an unrestricted donation from the Novo Nordisk Foundation. We acknowledge the Single-Cell Omics platform at the Novo Nordisk Foundation Center for Basic Metabolic Research for technical and computational expertise and support. Schematics are created with BioRender.com.Peer reviewedPublisher PD

Mitochondria-localized AMPK responds to local energetics and contributes to exercise and energetic stress-induced mitophagy

Mitochondria form a complex, interconnected reticulum that is maintained through coordination among biogenesis, dynamic fission, and fusion and mitophagy, which are initiated in response to various cues to maintain energetic homeostasis. These cellular events, which make up mitochondrial quality control, act with remarkable spatial precision, but what governs such spatial specificity is poorly understood. Herein, we demonstrate that specific isoforms of the cellular bioenergetic sensor, 5′ AMP-activated protein kinase (AMPKα1/α2/β2/γ1), are localized on the outer mitochondrial membrane, referred to as mitoAMPK, in various tissues in mice and humans. Activation of mitoAMPK varies across the reticulum in response to energetic stress, and inhibition of mitoAMPK activity attenuates exercise-induced mitophagy in skeletal muscle in vivo. Discovery of a mitochondrial pool of AMPK and its local importance for mitochondrial quality control underscores the complexity of sensing cellular energetics in vivo that has implications for targeting mitochondrial energetics for disease treatment

Central infusion of leptin does not increase AMPK signaling in skeletal muscle of sheep

In sheep, central leptin infusion reduces food intake and increases energy expenditure in adipose tissue and skeletal muscle. The mechanisms for these peripheral effects of central leptin in sheep are not known but, on the basis of rodent studies, may involve AMPK. In mice, central leptin acutely increases both skeletal muscle AMPK activation and glucose uptake. Thus, to investigate whether these effects exist in higher-order mammals, ovariectomized Corriedale ewes (n = 4 per group) received a continuous lateral ventricular infusion (60 μl/h) of either leptin (50 μg/h) or artificial cerebrospinal fluid (aCSF; CON) for 8 days. Tritiated glucose (3-3H-glucose) was infused intravenously for calculation of whole body glucose turnover during both acute (6 h) and chronic (7–8 days) leptin/aCSF infusion. Muscle biopsies were also obtained. Leptin infusion reduced (P < 0.05) food intake and body weight, and it also increased plasma epinephrine concentration at 6 h and 7 days, suggesting increased sympathetic nerve activity. Despite this, and in contrast to rodent studies, central leptin infusion did not increase skeletal muscle AMPKα Thr172 phosphorylation or ACCβ Ser221 phosphorylation. Surprisingly, the glucose rate of appearance (glucose Ra) and rate of disappearance (glucose Rd) were reduced by both acute and chronic leptin infusion. Direct infusion of the AMPK activator 5-aminoimidazole-4-carboxyamide-ribonucleoside (AICAR) into the femoral artery increased skeletal muscle AMPK phosphorylation. In conclusion, although central leptin infusion in sheep caused the predicted reduction in food intake and increases plasma epinephrine concentration, it had no effect on AMPK activation in skeletal muscle and actually reduced glucose disposal. This suggests that there are species differences in the peripheral responses to central leptin infusion

Short-term exercise training early in life restores deficits in pancreatic β-cell mass associated with growth restriction in adult male rats

Fetal growth restriction is associated with reduced pancreatic β-cell mass, contributing to impaired glucose tolerance and diabetes. Exercise training increases β-cell mass in animals with diabetes and has long-lasting metabolic benefits in rodents and humans. We studied the effect of exercise training on islet and β-cell morphology and plasma insulin and glucose, following an intraperitoneal glucose tolerance test (IPGTT) in juvenile and adult male Wistar-Kyoto rats born small. Bilateral uterine vessel ligation performed on day 18 of pregnancy resulted in Restricted offspring born small compared with sham-operated Controls and also sham-operated Reduced litter offspring that had their litter size reduced to five pups at birth. Restricted, Control, and Reduced litter offspring remained sedentary or underwent treadmill running from 5 to 9 or 20 to 24 wk of age. Early life exercise increased relative islet surface area and β-cell mass across all groups at 9 wk, partially restoring the 60–68% deficit (P < 0.05) in Restricted offspring. Remarkably, despite no further exercise training after 9 wk, β-cell mass was restored in Restricted at 24 wk, while sedentary littermates retained a 45% deficit (P = 0.05) in relative β-cell mass. Later exercise training also restored Restricted β-cell mass to Control levels. In conclusion, early life exercise training in rats born small restored β-cell mass in adulthood and may have beneficial consequences for later metabolic health and disease

Exercise early in life in rats born small does not normalize reductions in skeletal muscle PGC-1α in adulthood

We have previously shown that 4 wk of exercise training early in life normalizes the otherwise greatly reduced pancreatic &beta;-cell mass in adult male rats born small. The aim of the current study was to determine whether a similar normalization in adulthood of reduced skeletal muscle mitochondrial biogenesis markers and alterations in skeletal muscle lipids of growth-restricted male rats occurs following early exercise training. Bilateral uterine vessel ligation performed on day 18 of gestation resulted in Restricted offspring born small (P &lt; 0.05) compared with both sham-operated Controls and a sham-operated Reduced litter group. Offspring remained sedentary or underwent treadmill running from 5&ndash;9 (early exercise) or 20&ndash;24 (later exercise) wk of age. At 24 wk of age, Restricted and Reduced litter offspring had lower (P &lt; 0.05) skeletal muscle peroxisome proliferator-activated receptor &gamma; coactivator-1&alpha; (PGC-1&alpha;) protein expression compared with Control offspring. Early exercise training had the expected effect of increasing skeletal muscle markers of mitochondrial biogenesis, but, at this early age (9 wk), there was no deficit in Restricted and Reduced litter skeletal muscle mitochondrial biogenesis. Unlike our previous observations in pancreatic &beta;-cell mass, there was no &ldquo;reprogramming&rdquo; effect of early exercise on adult skeletal muscle such that PGC-1&alpha; was lower in adult Restricted and Reduced litter offspring irrespective of exercise training. Later exercise training increased mitochondrial biogenesis in all groups. In conclusion, although the response to exercise training remains intact, early exercise training in rats born small does not have a reprogramming effect to prevent deficits in skeletal muscle markers of mitochondrial biogenesis in adulthood. <br /