Endurance exercise stimulates peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha) expression in skeletal muscle, and forced expression of PGC-1alpha changes muscle metabolism and exercise capacity in mice. However, it is unclear if PGC-1alpha is indispensible for endurance exercise-induced metabolic and contractile adaptations in skeletal muscle. In this study, we showed that endurance exercise-induced expression of mitochondrial enzymes (cytochrome oxidase IV and cytochrome c) and increases of platelet endothelial cell adhesion molecule-1 (PECAM-1, CD31)-positive endothelial cells in skeletal muscle, but not IIb-to-IIa fiber-type transformation, were significantly attenuated in muscle-specific Pgc-1alpha knockout mice. Interestingly, voluntary running effectively restored the compromised mitochondrial integrity and superoxide dismutase 2 (SOD2) protein expression in skeletal muscle in Pgc-1alpha knockout mice. Thus, PGC-1alpha plays a functional role in endurance exercise-induced mitochondrial biogenesis and angiogenesis, but not IIb-to-IIa fiber-type transformation in mouse skeletal muscle, and the improvement of mitochondrial morphology and antioxidant defense in response to endurance exercise may occur independently of PGC-1alpha function. We conclude that PGC-1alpha is required for complete skeletal muscle adaptations induced by endurance exercise in mice.
Diabetic cardiomyopathy (DbCM), which consists of cardiac hypertrophy and failure in the absence of traditional risk factors, is a major contributor to increased heart failure risk in type 2 diabetes patients. In rodent models of DbCM, cardiac hypertrophy and dysfunction have been shown to depend upon saturated fatty acid (SFA) oversupply and de novo sphingolipid synthesis. However, it is not known whether these effects are mediated by bulk SFAs and sphingolipids or by individual lipid species. In this report, we demonstrate that a diet high in SFA induced cardiac hypertrophy, left ventricular systolic and diastolic dysfunction, and autophagy in mice. Furthermore, treatment with the SFA myristate, but not palmitate, induced hypertrophy and autophagy in adult primary cardiomyocytes. De novo sphingolipid synthesis was required for induction of all pathological features observed both in vitro and in vivo, and autophagy was required for induction of hypertrophy in vitro. Finally, we implicated a specific ceramide N-acyl chain length in this process and demonstrated a requirement for (dihydro)ceramide synthase 5 in cardiomyocyte autophagy and myristate-mediated hypertrophy. Thus, this report reveals a requirement for a specific sphingolipid metabolic route and dietary SFAs in the molecular pathogenesis of lipotoxic cardiomyopathy and hypertrophy. IntroductionObesity and diabetes present two of the most important health challenges facing the Western world at this time. Patients suffering from type 2 diabetes (T2D) are subject to a number of major health risks, including a greatly increased risk of heart failure (1). This is due in part to the development of diabetic cardiomyopathy (DbCM), which occurs independently of other traditional risk factors (2). DbCM promotes cardiac remodeling and impairs cardiac function (1). Importantly, individuals with T2D and the metabolic syndrome present with dyslipidemia, and recent studies have suggested that DbCM may occur as a result of lipid overload and subsequent lipotoxic events (ref. 2, reviewed in ref. 3). In particular, oversupply of saturated fatty acids (SFAs) has been implicated in this process.Previous studies of lipotoxic DbCM in rodents have relied on several important transgenic models. The B6.Cg-Lep ob /J (ob/ob) and B6.BKS(D)-Lepr db /J (db/db) mouse models, which lack the genes encoding leptin and the leptin receptor, respectively, are both very popular models that develop obesity and a DbCM-like cardiac phenotype (reviewed in ref. 4). Other less common models, including the Atgl-knockout mouse and the LpL GPI transgenic mouse, also induce lipotoxic cardiomyopathy by perturbing cardiac lipid uptake, handling, or metabolism (reviewed in ref. 4). While these transgenic models robustly induce lipid overload in cardiomyocytes, the very disruptions that produce lipotoxic DbCM also drastically alter patterns of lipid uptake and handling in a nonphysiologic way. In contrast, wild-type mice fed standard lard-based high-fat diets (LBD) failed to develop a DbCM-like phenotyp...
SUMMARY Evidence is emerging that the PGC-1 coactivators serve a critical role in skeletal muscle metabolism, function, and disease. Mice with total PGC-1 deficiency in skeletal muscle (PGC-1α−/−βf/f/MLC-Cre mice) were generated and characterized. PGC-1α−/−βf/f/MLC-Cre mice exhibit a dramatic reduction in exercise performance compared to single PGC-1α- or PGC-1β-deficient mice and wild-type controls. The exercise phenotype of the PGC-1α−/−βf/f/MLC-Cre mice was associated with a marked diminution in muscle respiratory capacity and mitochondrial structural derangements consistent with fusion/fission and biogenic defects together with rapid depletion of muscle glycogen stores during exercise. Surprisingly, the skeletal muscle fiber type profile of the PGC-1α−/−βf/f/MLC-Cre mice was not significantly different than the wild-type mice. Moreover, insulin sensitivity and glucose tolerance were not altered in the PGC-1α−/−βf/f/MLC-Cre mice. Taken together, we conclude that PGC-1 coactivators are necessary for the oxidative and mitochondrial programs of skeletal muscle but are dispensable for fundamental fiber type determination and insulin sensitivity.
Regular endurance exercise induces skeletal muscle contractile and metabolic adaptations, conferring salutary health benefits, such as protection against the metabolic syndrome. The plasticity of skeletal muscle has been extensively investigated, but how the adaptive processes are precisely controlled is largely unknown. Using muscle-specific gene deletion in mice, we now show that p38γ mitogen-activated protein kinase (MAPK), but not p38α and p38β, is required for endurance exercise-induced mitochondrial biogenesis and angiogenesis, whereas none of the p38 isoforms are required for IIb-to-IIa fiber-type transformation. These phenotypic findings were further supported by microarray and real-time PCR analyses revealing contractile activity-dependent p38γ target genes, including peroxisome proliferator-activated receptor γ co-activator-1α (Pgc-1α) and vascular endothelial growth factor (Vegf), in skeletal muscle following motor nerve stimulation. Gene transfer-mediated overexpression of a dominant negative form of p38γ, but not that of p38α or p38β, blocked motor nerve stimulation-induced Pgc-1α transcription. These findings provide direct evidence for an obligated role of p38γ MAPK-PGC-1α regulatory axis in endurance exercise-induced metabolic adaptation, but not contractile adaptation, in skeletal muscle.
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