Exercise and PGC-1?-independent synchronization of type I muscle metabolism and vasculature by ERR?.
ABSTRACT: How type I skeletal muscle inherently maintains high oxidative and vascular capacity in the absence of exercise is unclear. We show that nuclear receptor ERR? is highly expressed in type I muscle and, when transgenically expressed in anaerobic type II muscles (ERRGO mice), dually induces metabolic and vascular transformation in the absence of exercise. ERRGO mice show increased expression of genes promoting fat metabolism, mitochondrial respiration, and type I fiber specification. Muscles in ERRGO mice also display an activated angiogenic program marked by myofibrillar induction and secretion of proangiogenic factors, neovascularization, and a 100% increase in running endurance. Surprisingly, the induction of type I muscle properties by ERR? does not involve PGC-1?. Instead, ERR? genetically activates the energy sensor AMPK in mediating the metabovascular changes in ERRGO mice. Therefore, ERR? represents a previously unrecognized determinant that specifies intrinsic vascular and oxidative metabolic features that distinguish type I from type II muscle.
Project description:PGC1? is a pleiotropic co-factor that affects angiogenesis, mitochondrial biogenesis, and oxidative muscle remodeling via its association with multiple transcription factors, including the master oxidative nuclear receptor ERR?. To decipher their epistatic relationship, we explored ERR? gain of function in muscle-specific PGC1?/? double-knockout (PKO) mice. ERR?-driven transcriptional reprogramming largely rescues muscle damage and improves muscle function in PKO mice, inducing mitochondrial biogenesis, antioxidant defense, angiogenesis, and a glycolytic-to-oxidative fiber-type transformation independent of PGC1?/?. Furthermore, in combination with voluntary exercise, ERR? gain of function largely restores mitochondrial energetic deficits in PKO muscle, resulting in a 5-fold increase in running performance. Thus, while PGC1s can interact with multiple transcription factors, these findings implicate ERRs as the major molecular target through which PGC1?/? regulates both innate and adaptive energy metabolism.
Project description:Oxidative myofibers in the skeletal muscles express high levels of angiogenic factors, have dense vasculature, and promptly revascularize during ischemia. Estrogen-related receptor-gamma (ERR?) activates genes that govern metabolic and vascular features typical to oxidative myofibers. Therefore, ERR?-dependent remodeling of the myofibers may promote neoangiogenesis and restoration of blood perfusion in skeletal muscle ischemia.To investigate the muscle fiber type remodeling by ERR? and its role in the vascular recovery of ischemic muscle.Using immunohistology, we show that skeletal muscle-specific transgenic overexpression of ERR? increases the proportions of oxidative and densely vascularized type IIA and IIX myofibers and decreases glycolytic and less vascularized type IIB myofibers. This myofiber remodeling results in a higher basal blood flow in the transgenic skeletal muscle. By applying unilateral hind limb ischemia to transgenic and wild-type mice, we found accelerated revascularization (fluorescent microangiography), restoration of blood perfusion (laser Doppler flowmetry), and muscle repair (Evans blue dye exclusion) in transgenic compared to wild-type ischemic muscles. This ameliorative effect is linked to enhanced neoangiogenesis (CD31 staining and microfil perfusion) by ERR?. Using cultured muscle cells in which ERR? is inactivated, we show that the receptor is dispensable for the classical hypoxic response of transcriptional upregulation and secretion of vascular endothelial growth factor A. Rather, the ameliorative effect of ERR? is linked to the receptor-mediated increase in oxidative myofibers that inherently express and secrete high levels of angiogenic factors.The ERR? is a hypoxia-independent inducer of neoangiogenesis that can promote reparative revascularization.
Project description:Dissecting exercise-mimicking pathways that can replicate the benefits of exercise in obesity and diabetes may lead to promising treatments for metabolic disorders. Muscle estrogen-related receptor gamma (ERR?) is induced by exercise, and when over-expressed in the skeletal muscle mimics exercise by stimulating glycolytic-to-oxidative myofiber switch, mitochondrial biogenesis and angiogenesis in lean mice. The objective of this study was to test whether muscle ERR? in obese mice mitigates weight gain and insulin resistance. To do so, ERR? was selectively over-expressed in the skeletal muscle of obese and diabetic db/db mice. Muscle ERR? over-expression successfully triggered glycolytic-to-oxidative myofiber switch, increased functional mitochondrial content and boosted vascular supply in the db/db mice. Despite aerobic remodeling, ERR? surprisingly failed to improve whole-body energy expenditure, block muscle accumulation of triglycerides, toxic diacylglycerols (DAG) and ceramides or suppress muscle PKC? sarcolemmal translocation in db/db mice. Consequently, muscle ERR? did not mitigate impaired muscle insulin signaling or insulin resistance in these mice. In conclusion, obesity and diabetes in db/db mice are not amenable to selective ERR?-directed programming of classic exercise-like effects in the skeletal muscle. Other biochemical pathways or integrated whole-body effects of exercise may be critical for resisting diabetes and obesity.
Project description:The estrogen-related receptor-? (ERR?) regulates mitochondrial biogenesis and glucose and fatty acid oxidation during differentiation in skeletal myocytes. However, whether ERR? controls metabolic remodeling during skeletal muscle regeneration in vivo is unknown. We characterized the time course of skeletal muscle regeneration in wild-type (M-ERR?WT) and muscle-specific ERR?(-/-) (M-ERR?(-/-)) mice after injury by intramuscular cardiotoxin injection. M-ERR?(-/-) mice exhibited impaired regeneration characterized by smaller myofibers with increased centrally localized nuclei and reduced mitochondrial density and cytochrome oxidase and citrate synthase activities relative to M-ERR?WT. Transcript levels of mitochondrial transcription factor A, nuclear respiratory factor-2a, and peroxisome proliferator-activated receptor (PPAR)-? coactivator (PGC)-1?, were downregulated in the M-ERR?(-/-) muscles at the onset of myogenesis. Furthermore, coincident with delayed myofiber recovery, we observed reduced muscle ATP content (-45% vs. M-ERR?WT) and enhanced AMP-activated protein kinase (AMPK) activation in M-ERR?(-/-) muscle. We subsequently demonstrated that pharmacologic postinjury AMPK activation was sufficient to delay muscle regeneration in WT mice. AMPK activation induced ERR? transcript expression in M-ERR?WT muscle and in C2C12 myotubes through induction of the Esrra promoter, indicating that ERR? may control gene regulation downstream of the AMPK pathway. Collectively, these results suggest that ERR? deficiency during muscle regeneration impairs recovery of mitochondrial energetic capacity and perturbs AMPK activity, resulting in delayed myofiber repair.
Project description:We show that the orphan nuclear receptor ERRg is expressed at high levels in type I muscle and when transgenically expressed in anaerobic type II muscles (ERRGO mice) or cultured cells, powerfully regulates VEGF expression, angiogenesis and vascular supply in absence of exercise. ERRGO mice show increased expression of genes promoting fat metabolism, mitochondrial respiration and type I fiber specification. In parallel, the type II muscle in ERRGO mice display an activated angiogenic program marked by myofibrillar induction and secretion of pro-angiogenic factors, frank neo-vascularization and a 100% increase in running endurance. Surprisingly, the induction of VEGF and type I muscle properties by ERRg does not involve the transcriptional co-activator PGC1a. Instead, ERRg genetically activates the energy sensor AMPK which is typically inactive in absence of exercise. Therefore, ERRg and AMPK, known regulators of mitochondrial function and metabolism, together control a novel angiogenic pathway that anatomically synchronizes vascular arborization to oxidative metabolism revealing an exercise-independent mechanism for matching supply and demand. Keywords: ERRgamma overexpression compared to wild-type Overall design: Comparison of gene expression from quadriceps muscles isolated from wild type and alpha-skeletal actin-ERRgamma-transgenic mice.
Project description:We show that the orphan nuclear receptor ERRg is expressed at high levels in type I muscle and when transgenically expressed in anaerobic type II muscles (ERRGO mice) or cultured cells, powerfully regulates VEGF expression, angiogenesis and vascular supply in absence of exercise. ERRGO mice show increased expression of genes promoting fat metabolism, mitochondrial respiration and type I fiber specification. In parallel, the type II muscle in ERRGO mice display an activated angiogenic program marked by myofibrillar induction and secretion of pro-angiogenic factors, frank neo-vascularization and a 100% increase in running endurance. Surprisingly, the induction of VEGF and type I muscle properties by ERRg does not involve the transcriptional co-activator PGC1a. Instead, ERRg genetically activates the energy sensor AMPK which is typically inactive in absence of exercise. Therefore, ERRg and AMPK, known regulators of mitochondrial function and metabolism, together control a novel angiogenic pathway that anatomically synchronizes vascular arborization to oxidative metabolism revealing an exercise-independent mechanism for matching supply and demand. Keywords: ERRgamma overexpression compared to wild-type Comparison of gene expression from quadriceps muscles isolated from wild type and alpha-skeletal actin-ERRgamma-transgenic mice.
Project description:Specialized contractile function and increased mitochondrial number and oxidative capacity are hallmark features of myocyte differentiation. The estrogen-related receptors (ERRs) can regulate mitochondrial biogenesis or mitochondrial enzyme expression in skeletal muscle, suggesting that ERRs may have a role in promoting myogenesis. Therefore, we characterized myogenic programs in primary myocytes isolated from wild-type (M-ERR?WT) and muscle-specific ERR?(-/-) (M-ERR?(-/-)) mice. Myotube maturation and number were decreased throughout differentiation in M-ERR?(-/-) primary myocytes, resulting in myotubes with reduced mitochondrial content and sarcomere assembly. Compared with M-ERR?WT myocytes at the same differentiation stage, the glucose oxidation rate was reduced by 30% in M-ERR?(-/-) myotubes, while medium-chain fatty acid oxidation was increased by 34% in M-ERR?(-/-) myoblasts and 36% in M-ERR?(-/-) myotubes. Concomitant with increased reliance on mitochondrial ?-oxidation, H(2)O(2) production was significantly increased by 40% in M-ERR?(-/-) myoblasts and 70% in M-ERR?(-/-) myotubes compared to M-ERR?WT myocytes. ROS activation of FoxO and NF-?B and their downstream targets, atrogin-1 and MuRF1, was observed in M-ERR?(-/-) myocytes. The antioxidant N-acetyl cysteine rescued myotube formation and atrophy gene induction in M-ERR?(-/-) myocytes. These results suggest that loss of ERR? causes metabolic defects and oxidative stress that impair myotube formation through activation of skeletal muscle atrophy pathways.
Project description:Muscle fitness is an important determinant of health and disease. However, the molecular mechanisms involved in the coordinate regulation of the metabolic and structural determinants of muscle endurance are still poorly characterized. Herein, we demonstrate that estrogen-related receptor ? (ERR?, NR3B1) is essential for skeletal muscle fitness. Notably, we show that ERR?-null animals are hypoactive and that genetic or therapeutic disruption of ERR? in mice results in reduced exercise tolerance. Mice lacking ERR? also exhibited lactatemia at exhaustion. Gene expression profiling demonstrates that ERR? plays a key role in various metabolic processes important for muscle function including energy substrate transport and use (Ldhd, Slc16a1, Hk2, and Glul), the tricarboxylic acid cycle (Cycs, and Idh3g), and oxidative metabolism (Pdha1, and Uqcrq). Metabolomics studies revealed impairment in replenishment of several amino acids (eg, glutamine) during recovery to exercise. Moreover, loss of ERR? was found to alter the expression of genes involved in oxidative stress response (Hmox1), maintenance of muscle fiber integrity (Trim63, and Hspa1b), and muscle plasticity and neovascularization (Vegfa). Taken together, our study shows that ERR? plays a key role in directing transcriptional programs required for optimal mitochondrial oxidative potential and muscle fitness, suggesting that modulation of ERR? activity could be used to manage metabolic myopathies and/or promote the adaptive response to physical exercise.
Project description:Skeletal muscles consist of fibers of differing metabolic activities and contractility, which become remodeled in response to chronic exercise, but the epigenomic basis for muscle identity and adaptation remains poorly understood. Here, we used chromatin immunoprecipitation sequencing of dimethylated histone 3 lysine 4 and acetylated histone 3 lysine 27 as well as transposase-accessible chromatin profiling to dissect cis-regulatory networks across muscle groups. We demonstrate that in vivo enhancers specify muscles in accordance with myofiber composition, show little resemblance to cultured myotube enhancers, and identify glycolytic and oxidative muscle-specific regulators. Moreover, we find that voluntary wheel running and muscle-specific peroxisome proliferator-activated receptor gamma coactivator-1 alpha (Pgc1a) transgenic (mTg) overexpression, which stimulate endurance performance in mice, result in markedly different changes to the epigenome. Exercise predominantly leads to enhancer hypoacetylation, whereas mTg causes hyperacetylation at different sites. Integrative analysis of regulatory regions and gene expression revealed that exercise and mTg are each associated with myocyte enhancer factor (MEF) 2 and estrogen-related receptor (ERR) signaling and transcription of genes promoting oxidative metabolism. However, exercise was additionally associated with regulation by retinoid X receptor (RXR), jun proto-oncogene (JUN), sine oculis homeobox factor (SIX), and other factors. Overall, our work defines the unique enhancer repertoires of skeletal muscles in vivo and reveals that divergent exercise-induced or PGC1?-driven epigenomic programs direct partially convergent transcriptional networks.
Project description:OBJECTIVE:Endurance exercise training remodels skeletal muscle, leading to increased mitochondrial content and oxidative capacity. How exercise entrains skeletal muscle signaling pathways to induce adaptive responses remains unclear. In past studies, we identified Perm1 (PGC-1 and ERR induced regulator, muscle 1) as an exercise-induced gene and showed that Perm1 overexpression elicits similar muscle adaptations as endurance exercise training. The mechanism of action and the role of Perm1 in exercise-induced responses are not known. In this study, we aimed to determine the pathway by which Perm1 acts as well as the importance of Perm1 for acute and long-term responses to exercise. METHODS:We performed immunoprecipitation and mass spectrometry to identify Perm1 associated proteins, and validated Perm1 interactions with the Ca2+/calmodulin-dependent protein kinase II (CaMKII). We also knocked down Perm1 expression in gastrocnemius muscles of mice via AAV-mediated delivery of shRNA and assessed the impact of reduced Perm1 expression on both acute molecular responses to a single treadmill exercise bout and long-term adaptive responses to four weeks of voluntary wheel running training. Finally, we asked whether Perm1 levels are modulated by diet or diseases affecting skeletal muscle function. RESULTS:We show that Perm1 associates with skeletal muscle CaMKII and promotes CaMKII activation. In response to an acute exercise bout, muscles with a knock down of Perm1 showed defects in the activation of CaMKII and p38 MAPK and blunted induction of regulators of oxidative metabolism. Following four weeks of voluntary training, Perm1 knockdown muscles had attenuated mitochondrial biogenesis. Finally, we found that Perm1 expression is reduced in diet-induced obese mice and in muscular dystrophy patients and mouse models. CONCLUSIONS:Our findings identify Perm1 as a muscle-specific regulator of exercise-induced signaling and Perm1 levels as tuners of the skeletal muscle response to exercise. The decreased Perm1 levels in states of obesity or muscle disease suggest that Perm1 may link pathological states to inefficient exercise responses.