Impaired myogenesis in estrogen-related receptor γ (ERRγ)-deficient skeletal myocytes due to oxidative stress

Compound Z526 alleviates chemotherapy-induced cachectic muscle loss by ameliorating oxidative stress-driven protein metabolic imbalance and apoptosis

Chemotherapy is one of the primary and indispensable intervention against cancers though it is always accompanied by severe side effects especially cachexia. Cachexia is a fatal metabolic disorder syndrome, mainly characterized by muscle loss. Oxidative stress is the key factor that trigger cachectic muscle loss by inducing imbalance in protein metabolism and apoptosis. Here, we showed an oral compound (Z526) exhibited potent alleviating effects on C2C12 myotube atrophy induced by various chemotherapeutic agents in vitro as well as mice muscle loss and impaired grip force induced by oxaliplatin in vivo. Furthermore, Z526 also could ameliorate C2C12 myotube atrophy induced by the combination of chemotherapeutic agents with conditioned medium of various tumor cells in vitro as well as mice muscle atrophy of C26 tumor-bearing mice treated with oxaliplatin. The pharmacological effects of Z526 were based on its potency in reducing oxidative stress in cachectic myocytes and muscle tissues, which inhibited the activation of NF-κB and STAT3 to decrease Atrogin-1-mediated protein degradation, activated the AKT/mTOR signaling pathway to promote protein synthesis, regulated Bcl-2/BAX ratio to reduce Caspase-3-triggered apoptosis. Our work suggested Z526 to be an optional strategy for ameliorating cachexia muscle atrophy in the multimodality treatment of cancers.

Metabolic regulator ERRγ governs gastric stem cell differentiation into acid-secreting parietal cells

Parietal cells (PCs) produce gastric acid to kill pathogens and aid digestion. Dysregulated PC census is common in disease, yet how PCs differentiate is unclear. Here, we identify the PC progenitors arising from isthmal stem cells, using mouse models and human gastric cells, and show that they preferentially express cell-metabolism regulator and orphan nuclear receptor Estrogen-related receptor gamma (Esrrg, encoding ERRγ). Esrrg expression facilitated the tracking of stepwise molecular, cellular, and ultrastructural stages of PC differentiation. EsrrgP2ACreERT2 lineage tracing revealed that Esrrg expression commits progenitors to differentiate into mature PCs. scRNA-seq indicated the earliest Esrrg+ PC progenitors preferentially express SMAD4 and SP1 transcriptional targets and the GTPases regulating acid-secretion signal transduction. As progenitors matured, ERRγ-dependent metabolic transcripts predominated. Organoid and mouse studies validated the requirement of ERRγ for PC differentiation. Our work chronicles stem cell differentiation along a single lineage in vivo and suggests ERRγ as a therapeutic target for PC-related disorders.

Nuclear receptors as potential therapeutic targets in peripheral arterial disease and related myopathy

Peripheral arterial disease (PAD) is a prevalent cardiovascular complication of limb vascular insufficiency, causing ischemic injury, mitochondrial metabolic damage and functional impairment in the skeletal muscle, and ultimately leading to immobility and mortality. While potential therapies have been mostly focussed on revascularization, none of the currently available pharmacological treatments are fully effective in PAD, often leading to amputations, particularly in chronic metabolic diseases. One major limitation of focussed angiogenesis and revascularization as a therapeutic strategy is a limited effect on metabolic restoration and muscle regeneration in the affected limb. Therefore, additional preclinical investigations are needed to discover novel treatment options for PAD preferably targeting multiple aspects of muscle recovery. In this review, we propose nuclear receptors expressed in the skeletal muscle as potential candidates for ischemic muscle repair in PAD. We review classic steroid and orphan receptors that have been reported to be involved in the regulation of paracrine muscle angiogenesis, oxidative metabolism, mitochondrial biogenesis and muscle regeneration, and discuss how these receptors could be critical for recovery from ischemic muscle damage. Furthermore, we identify existing gaps in our understanding of nuclear receptor signalling in the skeletal muscle and propose future areas of research that could be instrumental in exploring nuclear receptors as therapeutic candidates for treating PAD.

Estrogen-Related Receptor Gamma Gene Therapy Promotes Therapeutic Angiogenesis and Muscle Recovery in Preclinical Model of PAD

Background Peripheral arterial disease and critical limb ischemia are cardiovascular complications associated with vascular insufficiency, oxidative metabolic dysfunction, and myopathy in the limbs. Estrogen-related receptor gamma (ERRγ) has emerged as a dual regulator of paracrine angiogenesis and oxidative metabolism through transgenic mouse studies. Here our objective was to investigate whether postischemic intramuscular targeting of ERRγ via gene therapy promotes ischemic recovery in a preclinical model of peripheral arterial disease/critical limb ischemia. Methods and Results Adeno-associated virus 9 (AAV9) Esrrg gene delivery vector was developed and first tested via intramuscular injection in murine skeletal muscle. AAV9-Esrrg robustly increased ERRγ protein expression, induced angiogenic and oxidative genes, and boosted capillary density and succinate dehydrogenase oxidative metabolic activity in skeletal muscles of C57Bl/6J mice. Next, hindlimb ischemia was induced via unilateral femoral vessel ligation in mice, followed by intramuscular AAV9-Esrrg (or AAV9-green fluorescent protein) gene delivery 24 hours after injury. ERRγ overexpression increased ischemic neoangiogenesis and markers of endothelial activation, and significantly improved ischemic revascularization measured using laser Doppler flowmetry. Moreover, ERRγ overexpression restored succinate dehydrogenase oxidative metabolic capacity in ischemic muscle, which correlated with increased mitochondrial respiratory complex protein expression. Most importantly, myofiber size to number quantification revealed that AAV9-Esrrg restores myofibrillar size and mitigates ischemia-induced myopathy. Conclusions These results demonstrate that intramuscular AAV9-Esrrg delivery rescues ischemic pathology after hindlimb ischemia, underscoring that Esrrg gene therapy or pharmacological activation could be a promising strategy for the management of peripheral arterial disease/critical limb ischemia.

Estrogen-related Receptor Signaling in Skeletal Muscle Fitness

Skeletal muscle is a highly plastic tissue that can alter its metabolic and contractile features, as well as regenerative potential in response to exercise and other conditions. Multiple signaling factors including metabolites, kinases, receptors, and transcriptional factors have been studied in the regulation of skeletal muscle plasticity. Recently, estrogen-related receptors (ERRs) have emerged as a critical transcriptional hub in control of skeletal muscle homeostasis. ERRα and ERRγ - the two highly expressed ERR sub-types in the muscle respond to various extracellular cues such as exercise, hypoxia, fasting and dietary factors, in turn regulating gene expression in the skeletal muscle. On the other hand, conditions such as diabetes and muscular dystrophy suppress expression of ERRs in the skeletal muscle, likely contributing to disease progression. We highlight key functions of ERRs in the skeletal muscle including the regulation of fiber type, mitochondrial metabolism, vascularization, and regeneration. We also describe how ERRs are regulated in the skeletal muscle, and their interaction with important muscle regulators (e. g. AMPK and PGCs). Finally, we identify critical gaps in our understanding of ERR signaling in the skeletal muscle, and suggest future areas of investigation to advance ERRs as potential targets for function promoting therapeutics in muscle diseases.

microRNA-501 controls myogenin+/CD74+ myogenic progenitor cells during muscle regeneration

OBJECTIVE

Skeletal muscle regeneration is markedly impaired during aging. How adult muscle stem cells contribute to this decrease in regenerative capacity is incompletely understood. We investigated mechanisms of age-related changes in myogenic progenitor cells using the tissue-specific microRNA 501.

METHODS

Young and old C57Bl/6 mice were used (3 months or 24 months of age, respectively) with or without global or tissue-specific genetic deletion of miR-501. Muscle regeneration was induced using intramuscular cardiotoxin injection or treadmill exercise and analysed using single cell and bulk RNA sequencing, qRT-PCR and immunofluorescence. Muscle fiber damage was assessed with Evan`s blue dye (EBD). In vitro analysis was performed in primary muscle cells obtained from mice and humans.

RESULTS

Single cell sequencing revealed myogenic progenitor cells in miR-501 knockout mice at day 6 after muscle injury that are characterized by high levels of myogenin and CD74. In control mice these cells were less in number and already downregulated after day 3 of muscle injury. Muscle from knockout mice had reduced myofiber size and reduced myofiber resilience to injury and exercise. miR-501 elicits this effect by regulating sarcomeric gene expression through its target gene estrogen-related receptor gamma (Esrrg). Importantly, in aged skeletal muscle where miR-501 was significantly downregulated and its target Esrrg significantly upregulated, the number of myog+/CD74+ cells during regeneration was upregulated to similar levels as observed in 501 knockout mice. Moreover, myog+/CD74+-aged skeletal muscle exhibited a similar decrease in the size of newly formed myofibers and increased number of necrotic myofibers after injury as observed in mice lacking miR-501.

CONCLUSIONS

miR-501 and Esrrg are regulated in muscle with decreased regenerative capacity and loss of miR-501 is permissive to the appearance of CD74+ myogenic progenitors. Our data uncover a novel link between the metabolic transcription factor Esrrg and sarcomere formation and demonstrate that stem cell heterogeneity in skeletal muscle during aging is under miRNA control. Targeting Esrrg or myog+/CD74+ progenitor cells might improve fiber size and myofiber resilience to exercise in aged skeletal muscle.

Enrichment of miR-17-5p enhances the protective effects of EPC-EXs on vascular and skeletal muscle injury in a diabetic hind limb ischemia model

BACKGROUND/AIMS

Diabetes mellitus (DM) is highly susceptible to diabetic hind limb ischemia (DHI). MicroRNA (MiR)-17-5p is downregulated in DM and plays a key role in vascular protection. Endothelial progenitor cell (EPC)-released exosomes (EPC-EXs) contribute to vascular protection and ischemic tissue repair by transferring their contained miRs to target cells. Here, we investigated whether miR-17-5p-enriched EPC-EXs (EPC-EXs^miR-17-5p) had conspicuous effects on protecting vascular and skeletal muscle in DHI in vitro and in vivo.

METHODS

EPCs transfected with scrambled control or miR-17-5p mimics were used to generate EPC-EXs and EPC-EXs^miR-17-5p. Db/db mice were subjected to hind limb ischemia. After the surgery, EPC-EXs and EPC-EXs^miR-17-5p were injected into the gastrocnemius muscle of the hind limb once every 7 days for 3 weeks. Blood flow, microvessel density, capillary angiogenesis, gastrocnemius muscle weight, structure integrity, and apoptosis in the hind limb were assessed. Vascular endothelial cells (ECs) and myoblast cells (C2C12 cells) were subjected to hypoxia plus high glucose (HG) and cocultured with EPC-EXs and EPC-EXs^miR-17-5p. A bioinformatics assay was used to analyze the potential target gene of miR-17-5p, the levels of SPRED1, PI3K, phosphorylated Akt, cleaved caspase-9 and cleaved caspase-3 were measured, and a PI3K inhibitor (LY294002) was used for pathway analysis.

RESULTS

In the DHI mouse model, miR-17-5p was markedly decreased in hind limb vessels and muscle tissues, and infusion of EPC-EXs^miR-17-5p was more effective than EPC-EXs in increasing miR-17-5p levels, blood flow, microvessel density, and capillary angiogenesis, as well as in promoting muscle weight, force production and structural integrity while reducing apoptosis in gastrocnemius muscle. In Hypoxia plus HG-injured ECs and C2C12 cells, we found that EPC-EXs^miR-17-5p could deliver their carried miR-17-5p into target ECs and C2C12 cells and subsequently downregulate the target protein SPRED1 while increasing the levels of PI3K and phosphorylated Akt. EPC-EXs^miR-17-5p were more effective than EPC-EXs in decreasing apoptosis and necrosis while increasing viability, migration, and tube formation in Hypoxia plus HG-injured ECs and in decreasing apoptosis while increasing viability and myotube formation in C2C12 cells. These effects of EPC-EXs^miR-17-5p could be abolished by a PI3K inhibitor (LY294002).

CONCLUSION

Our results suggest that miR-17-5p promotes the beneficial effects of EPC-EXs on DHI by protecting vascular ECs and muscle cell functions.

In Vivo Dissection of Chamber-Selective Enhancers Reveals Estrogen-Related Receptor as a Regulator of Ventricular Cardiomyocyte Identity

BACKGROUND

Cardiac chamber-selective transcriptional programs underpin the structural and functional differences between atrial and ventricular cardiomyocytes (aCMs and vCMs). The mechanisms responsible for these chamber-selective transcriptional programs remain largely undefined.

METHODS

We nominated candidate chamber-selective enhancers (CSEs) by determining the genome-wide occupancy of 7 key cardiac transcription factors (GATA4, MEF2A, MEF2C, NKX2-5, SRF, TBX5, TEAD1) and transcriptional coactivator P300 in atria and ventricles. Candidate enhancers were tested using an adeno-associated virus-mediated massively parallel reporter assay. Chromatin features of CSEs were evaluated by performing assay of transposase accessible chromatin sequencing and acetylation of histone H3 at lysine 27-HiChIP on aCMs and vCMs. CSE sequence requirements were determined by systematic tiling mutagenesis of 29 CSEs at 5 bp resolution. Estrogen-related receptor (ERR) function in cardiomyocytes was evaluated by Cre-loxP-mediated inactivation of ERRα and ERRγ in cardiomyocytes.

RESULTS

We identified 134 066 and 97 506 regions reproducibly occupied by at least 1 transcription factor or P300, in atria or ventricles, respectively. Enhancer activities of 2639 regions bound by transcription factors or P300 were tested in aCMs and vCMs by adeno-associated virus-mediated massively parallel reporter assay. This identified 1092 active enhancers in aCMs or vCMs. Several overlapped loci associated with cardiovascular disease through genome-wide association studies, and 229 exhibited chamber-selective activity in aCMs or vCMs. Many CSEs exhibited differential chromatin accessibility between aCMs and vCMs, and CSEs were enriched for aCM- or vCM-selective acetylation of histone H3 at lysine 27-anchored loops. Tiling mutagenesis of 29 CSEs identified the binding motif of ERRα/γ as important for ventricular enhancer activity. The requirement of ERRα/γ to activate ventricular CSEs and promote vCM identity was confirmed by loss of the vCM gene profile in ERRα/γ knockout vCMs.

CONCLUSIONS

We identified 229 CSEs that could be useful research tools or direct therapeutic gene expression. We showed that chamber-selective multi-transcription factor, P300 occupancy, open chromatin, and chromatin looping are predictive features of CSEs. We found that ERRα/γ are essential for maintenance of ventricular identity. Finally, our gene expression, epigenetic, 3-dimensional genome, and enhancer activity atlas provide key resources for future studies of chamber-selective gene regulation.

Innately expressed estrogen-related receptors in the skeletal muscle are indispensable for exercise fitness

Transcriptional determinants in the skeletal muscle that govern exercise capacity, while poorly defined, could provide molecular insights into how exercise improves fitness. Here, we have elucidated the role of nuclear receptors, estrogen-related receptor alpha and gamma (ERRα/γ) in regulating myofibrillar composition, contractility, and exercise capacity in skeletal muscle. We used muscle-specific single or double (DKO) ERRα/γ knockout mice to investigate the effect of ERRα/γ deletion on muscle and exercise parameters. Individual knockout of ERRα/γ did not have a significant impact on the skeletal muscle. On the other hand, DKO mice exhibit pale muscles compared to wild-type (WT) littermates. RNA-seq analysis revealed a predominant decrease in expression of genes linked to mitochondrial and oxidative metabolism in DKO versus WT muscles. DKO muscles exhibit marked repression of oxidative enzymatic capacity, as well as mitochondrial number and size compared to WT muscles. Mitochondrial function is also impaired in single myofibers isolated from DKO versus WT muscles. In addition, mutant muscles exhibit reduced angiogenic gene expression and decreased capillarity. Consequently, DKO mice have a significantly reduced exercise capacity, further reflected in poor fatigue resistance of DKO mice in in vivo contraction assays. These results show that ERRα and ERRγ together are a critical link between muscle aerobic capacity and exercise tolerance. The ERRα/γ mutant mice could be valuable for understanding the long-term impact of impaired mitochondria and vascular supply on the pathogenesis of muscle-linked disorders.

Targeting Estrogen Signaling in the Radiation-induced Neurodegeneration: A Possible Role of Phytoestrogens

Radiation for medical use is a well-established therapeutic method with an excellent prognosis rate for various cancer treatments. Unfortunately, a high dose of radiation therapy comes with its own share of side effects, causing radiation-induced non-specific cellular toxicity; consequently, a large percentage of treated patients suffer from chronic effects during the treatment and even after the post-treatment. Accumulating data evidenced that radiation exposure to the brain can alter the diverse cognitive-related signaling and cause progressive neurodegeneration in patients because of elevated oxidative stress, neuroinflammation, and loss of neurogenesis. Epidemiological studies suggested the beneficial effect of hormonal therapy using estrogen in slowing down the progression of various neuropathologies. Despite its primary function as a sex hormone, estrogen is also renowned for its neuroprotective activity and could manage radiation-induced side effects as it regulates many hallmarks of neurodegenerations. Thus, treatment with estrogen and estrogen-like molecules or modulators, including phytoestrogens, might be a potential approach capable of neuroprotection in radiation-induced brain degeneration. This review summarized the molecular mechanisms of radiation effects and estrogen signaling in the manifestation of neurodegeneration and highlighted the current evidence on the phytoestrogen mediated protective effect against radiationinduced brain injury. This existing knowledge points towards a new area to expand to identify the possible alternative therapy that can be taken with radiation therapy as adjuvants to improve patients' quality of life with compromised cognitive function.

c-Abl tyrosine kinase inhibition attenuate oxidative stress-induced pancreatic β-Cell dysfunction via glutathione antioxidant system

Chronic oxidative stress, which is caused by aberrant non-receptor tyrosine kinase (c-Abl) signaling, plays a key role in the progression of β-cell loss in diabetes mellitus. Recent studies, however, have linked ferroptotic-like death to the β-cell loss in diabetes mellitus. Here, we report that oxidative stress-driven reduced/oxidized glutathione (GSH/GSSG) loss and proteasomal degradation of glutathione peroxidase 4 (GPX4) promote ferroptotic-like cell damage through increased lipid peroxidation. Mechanistically, treatment with GNF2, a non-ATP competitive c-Abl kinase inhibitor, selectively preserves β-cell function by inducing the orphan nuclear receptor estrogen-related receptor gamma (ERRγ). ERRγ-driven glutaminase 1 (GLS1) expression promotes the elevation of the GSH/GSSG ratio, and this increase leads to the inhibition of lipid peroxidation by GPX4. Strikingly, pharmacological inhibition of ERRγ represses the expression of GLS1 and reverses the GSH/GSSG ratio linked to mitochondrial dysfunction and increased lipid peroxidation mediated by GPX4 degradation. Inhibition of GLS1 suppresses the ERRγ agonist DY131-induced GSH/GSSG ratio linked to ferroptotic-like death owing to the loss of GPX4. Furthermore, immunohistochemical analysis showed enhanced ERRγ and GPX4 expression in the pancreatic islets of GNF2-treated mice compared to that in streptozotocin-treated mice. Altogether, our results provide the first evidence that the orphan nuclear receptor ERRγ-induced GLS1 expression augments the glutathione antioxidant system, and its downstream signaling leads to improved β-cell function and survival under oxidative stress conditions.

ADRA1A-Gαq signalling potentiates adipocyte thermogenesis through CKB and TNAP

Noradrenaline (NA) regulates cold-stimulated adipocyte thermogenesis1. Aside from cAMP signalling downstream of β-adrenergic receptor activation, how NA promotes thermogenic output is still not fully understood. Here, we show that coordinated α1-adrenergic receptor (AR) and β3-AR signalling induces the expression of thermogenic genes of the futile creatine cycle2,3, and that early B cell factors, oestrogen-related receptors and PGC1α are required for this response in vivo. NA triggers physical and functional coupling between the α1-AR subtype (ADRA1A) and Gαq to promote adipocyte thermogenesis in a manner that is dependent on the effector proteins of the futile creatine cycle, creatine kinase B and tissue-non-specific alkaline phosphatase. Combined Gαq and Gαs signalling selectively in adipocytes promotes a continual rise in whole-body energy expenditure, and creatine kinase B is required for this effect. Thus, the ADRA1A-Gαq-futile creatine cycle axis is a key regulator of facultative and adaptive thermogenesis.

Estrogen-related receptor alpha is an AMPK-regulated factor that promotes ischemic muscle revascularization and recovery in diet-induced obese mice

Obesity and type II diabetes are leading causes of peripheral arterial disease (PAD), which is characterized by vascular insufficiency and ischemic damage in the limb skeletal muscle. Glycemic control is not sufficient to prevent progression of PAD, and molecular targets that can promote muscle neo-angiogenesis in obesity and diabetes remain poorly defined. Here, we have investigated whether nuclear receptor estrogen-related receptor alpha (ERRα) can promote ischemic revascularization in the skeletal muscles of diet-induced obese (DIO) mice. Using muscle-specific ERRα transgenic mice, we found that ERRα overexpression promotes revascularization, marked by increased capillary staining and muscle perfusion in DIO mice after hindlimb ischemic injury. Furthermore, ERRα facilitates repair and restoration of skeletal muscle myofiber size after limb ischemia in DIO mice. The ameliorative effects of ERRα overexpression did not involve the prevention of weight gain, hyperglycemia or glucose/insulin intolerance, suggesting a direct role for ERRα in promoting angiogenesis. Interestingly, levels of endogenous ERRα protein are suppressed in the skeletal muscles of DIO mice compared to lean controls, coinciding with the suppression of angiogenic gene expression, and reduced AMPK signaling in the DIO skeletal muscles. Upon further investigating the link between AMPK and ERRα, we found that AMPK activation increases the expression and recruitment of ERRα protein to specific angiogenic gene promoters in muscle cells. Further, the induction of angiogenic factors by AMPK activators in muscle cells is blocked by repressing ERRα. In summary, our results identify an AMPK/ERRα-dependent angiogenic gene program in the skeletal muscle, which is repressed by DIO, and demonstrate that forced ERRα activation can promote ischemic revascularization and muscle recovery in obesity.

Estrogen-related receptor gamma regulates mitochondrial and synaptic genes and modulates vulnerability to synucleinopathy

Many studies implicate mitochondrial dysfunction as a key contributor to cell loss in Parkinson disease (PD). Previous analyses of dopaminergic (DAergic) neurons from patients with Lewy-body pathology revealed a deficiency in nuclear-encoded genes for mitochondrial respiration, many of which are targets for the transcription factor estrogen-related receptor gamma (Esrrg/ERRγ). We demonstrate that deletion of ERRγ from DAergic neurons in adult mice was sufficient to cause a levodopa-responsive PD-like phenotype with reductions in mitochondrial gene expression and number, that partial deficiency of ERRγ hastens synuclein-mediated toxicity, and that ERRγ overexpression reduces inclusion load and delays synuclein-mediated cell loss. While ERRγ deletion did not fully recapitulate the transcriptional alterations observed in postmortem tissue, it caused reductions in genes involved in synaptic and mitochondrial function and autophagy. Altogether, these experiments suggest that ERRγ-deficient mice could provide a model for understanding the regulation of transcription in DAergic neurons and that amplifying ERRγ-mediated transcriptional programs should be considered as a strategy to promote DAergic maintenance in PD.

N-acetyl cysteine prevents arecoline-inhibited C2C12 myoblast differentiation through ERK1/2 phosphorylation

Arecoline is known to induce reactive oxygen species (ROS). Our previous studies showed that arecoline inhibited myogenic differentiation and acetylcholine receptor cluster formation of C2C12 myoblasts. N-acetyl-cysteine (NAC) is a known ROS scavenger. We hypothesize that NAC scavenges the excess ROS caused by arecoline. In this article we examined the effect of NAC on the inhibited myoblast differentiation by arecoline and related mechanisms. We found that NAC less than 2 mM is non-cytotoxic to C2C12 by viability analysis. We further demonstrated that NAC attenuated the decreased number of myotubes and nuclei in each myotube compared to arecoline treatment by H & E staining. We also showed that NAC prevented the decreased expression level of the myogenic markers, myogenin and MYH caused by arecoline, using immunocytochemistry and western blotting. Finally, we found that NAC restored the decreased expression level of p-ERK1/2 by arecoline. In conclusion, our results indicate that NAC attenuates the damage of the arecoline-inhibited C2C12 myoblast differentiation by the activation/phosphorylation of ERK. This is the first report to demonstrate that NAC has beneficial effects on skeletal muscle myogenesis through ERK1/2 upon arecoline treatment. Since defects of skeletal muscle associates with several diseases, NAC can be a potent drug candidate in diseases related to defects in skeletal muscle myogenesis.

Long non-coding RNA Tug1 modulates mitochondrial and myogenic responses to exercise in skeletal muscle

BACKGROUND

Mitochondria have an essential role in regulating metabolism and integrate environmental and physiological signals to affect processes such as cellular bioenergetics and response to stress. In the metabolically active skeletal muscle, mitochondrial biogenesis is one important component contributing to a broad set of mitochondrial adaptations occurring in response to signals, which converge on the biogenesis transcriptional regulator peroxisome proliferator-activated receptor coactivator 1-alpha (PGC-1α), and is central to the beneficial effects of exercise in skeletal muscle. We investigated the role of long non-coding RNA (lncRNA) taurine-upregulated gene 1 (TUG1), which interacts with PGC-1α in regulating transcriptional responses to exercise in skeletal muscle.

RESULTS

In human skeletal muscle, TUG1 gene expression was upregulated post-exercise and was also positively correlated with the increase in PGC-1α gene expression (PPARGC1A). Tug1 knockdown (KD) in differentiating mouse myotubes led to decreased Ppargc1a gene expression, impaired mitochondrial respiration and morphology, and enhanced myosin heavy chain slow isoform protein expression. In response to a Ca2+-mediated stimulus, Tug1 KD prevented an increase in Ppargc1a expression. RNA sequencing revealed that Tug1 KD impacted mitochondrial Ca2+ transport genes and several downstream PGC-1α targets. Finally, Tug1 KD modulated the expression of ~300 genes that were upregulated in response to an in vitro model of exercise in myotubes, including genes involved in regulating myogenesis.

CONCLUSIONS

We found that TUG1 is upregulated in human skeletal muscle after a single session of exercise, and mechanistically, Tug1 regulates transcriptional networks associated with mitochondrial calcium handling, muscle differentiation and myogenesis. These data demonstrate that lncRNA Tug1 exerts regulation over fundamental aspects of skeletal muscle biology and response to exercise stimuli.

Enrichment of the exocytosis protein STX4 in skeletal muscle remediates peripheral insulin resistance and alters mitochondrial dynamics via Drp1

Mitochondrial dysfunction is implicated in skeletal muscle insulin resistance. Syntaxin 4 (STX4) levels are reduced in human diabetic skeletal muscle, and global transgenic enrichment of STX4 expression improves insulin sensitivity in mice. Here, we show that transgenic skeletal muscle-specific STX4 enrichment (skmSTX4tg) in mice reverses established insulin resistance and improves mitochondrial function in the context of diabetogenic stress. Specifically, skmSTX4tg reversed insulin resistance caused by high-fat diet (HFD) without altering body weight or food consumption. Electron microscopy of wild-type mouse muscle revealed STX4 localisation at or proximal to the mitochondrial membrane. STX4 enrichment prevented HFD-induced mitochondrial fragmentation and dysfunction through a mechanism involving STX4-Drp1 interaction and elevated AMPK-mediated phosphorylation at Drp1 S637, which favors fusion. Our findings challenge the dogma that STX4 acts solely at the plasma membrane, revealing that STX4 localises at/proximal to and regulates the function of mitochondria in muscle. These results establish skeletal muscle STX4 enrichment as a candidate therapeutic strategy to reverse peripheral insulin resistance.

Muscle-specific deletion of Arid5b causes metabolic changes in skeletal muscle that affect adipose tissue and liver

Emerging evidence suggests that AT-Rich Interaction Domain 5b (Arid5b) may play a role in energy metabolism in various tissues. To study the metabolic function of Arid5b in skeletal muscle, we generated skeletal muscle-specific Arid5b knockout (Arid5b MKO) mice. We found that Arid5b MKO skeletal muscles preferentially utilized fatty acids for energy generation with a corresponding increase in FABP4 expression. Interestingly, in Arid5b MKO mice, the adipose tissue weight decreased significantly. One possible mechanism for the decrease in adipose tissue weight could be the increase in phospho-HSL and HSL expression in white adipose tissue. While glucose uptake increased in an insulin-independent manner in Arid5b MKO skeletal muscle, glucose oxidation was reduced in conjunction with downregulation of the mitochondrial pyruvate carrier (MPC). We found that glucose was diverted into the pentose phosphate pathway as well as converted into lactate through glycolysis for export to the bloodstream, fueling the Cori cycle. Our data show that muscle-specific deletion of Arid5b leads to changes in fuel utilization in skeletal muscle that influences metabolism in other tissues. These results suggest that Arid5b regulates systemic metabolism by modulating fuel selection.

Estrogen-Related Receptor γ Agonist DY131 Ameliorates Lipopolysaccharide-Induced Acute Liver Injury

Sepsis-associated liver dysfunction remains a challenge in clinical practice with high mortality and limited specific therapies. DY131 is a pharmacological agonist of the orphan receptor estrogen-related receptor (ERR) γ which plays a crucial role in regulating energy generation, oxidative metabolism, cell apoptosis, inflammatory responses, etc. However, its role in acute liver injury is unknown. In this study, we evaluated the effect of DY131 on lipopolysaccharide (LPS)-induced liver injury. Mice were pretreated with DY131 through intraperitoneal injection at a dose of 5 mg/kg/day for 3 days prior to LPS challenge (10 mg/kg). 24 h later, they were anesthetized and sacrificed. Blood and liver tissues were collected for further studies. In a separate experiment, mice were treated with saline (vehicle) or DY131 for 3 days to evaluate the toxicity of DY131. We found that ERRγ was downregulated in the liver tissues from LPS-treated mice. Pretreatment with DY131 ameliorated LPS-induced liver injury as demonstrated by reduced liver enzyme release (ALT, AST, and LDH), improved liver morphological damage, and attenuated oxidative stress, inflammation and apoptosis. Meanwhile, DY131 had no significant side effects on hepatic and renal functions in mice. Finally, transcriptomics analysis revealed that the dysregulated pathways associated with inflammation and metabolism were significantly reversed by DY131 in LPS-treated mice, providing more evidence in favor of the protective effect of DY131 against LPS-induced liver injury. Altogether, these findings highlighted the protective effect of DY131 on LPS-induced hepatotoxicity possibly via suppressing oxidative stress, inflammation, and apoptosis.

Characterization of mitochondrial respiratory complexes involved in the regulation of myoblast differentiation

During myoblast differentiation, mitochondria undergo numerous changes that are necessary for the progression of the myogenic program. Notably, we previously showed that alteration in mitochondrial activity was able to control the expression of keys regulator of cell cycle withdrawal and terminal differentiation. Here, we assessed whether inhibition of one of the respiratory complexes was a key factor in the regulation of myogenic differentiation in C2C12 cells, and was associated with alteration in reactive oxygen species (ROS) production. C2C12 cells were treated from proliferation to differentiation with specific inhibitors of mitochondrial complexes at a concentration that were inhibiting respiration but not altering cell morphology. Proliferation was significantly repressed with inhibition of complexes I, II, and III, or mitochondrial protein synthesis (using Chloramphenicol treatment), while complex IV inhibition did not alter myoblast proliferation compared to control cells. Moreover, inhibition of complexes I and II altered cell cycle regulators, with p21 protein expression upregulated since proliferation and p27 protein expression reduced at differentiation. Myotubes formation and myogenin expression were blunted with complexes I and II inhibitors while MyoD protein expression was maintained, suggesting an alteration in its transcriptional activity. Finally, a decrease in overall ROS production was observed with continuous inhibition of mitochondrial complexes I-IV. In summary, our data provide evidence that complexes I and II may be the primary regulators of C2C12 myogenic differentiation. This occurs through specific regulation of myogenic rather than cell cycle regulators expression and ROS production at mitochondrial rather than cell level.

Transcriptional Regulation of ROS Homeostasis by the ERR Subfamily of Nuclear Receptors

Reactive oxygen species (ROS) such as superoxide anion (O₂^•-) and hydrogen peroxide (H₂O₂) are generated endogenously by processes such as mitochondrial oxidative phosphorylation, or they may arise from exogenous sources like bacterial invasion. ROS can be beneficial (oxidative eustress) as signaling molecules but also harmful (oxidative distress) to cells when ROS levels become unregulated in response to physiological, pathological or pharmacological insults. Indeed, abnormal ROS levels have been shown to contribute to the etiology of a wide variety of diseases. Transcriptional control of metabolic genes is a crucial mechanism to coordinate ROS homeostasis. Therefore, a better understanding of how ROS metabolism is regulated by specific transcription factors can contribute to uncovering new therapeutic strategies. A large body of work has positioned the estrogen-related receptors (ERRs), transcription factors belonging to the nuclear receptor superfamily, as not only master regulators of cellular energy metabolism but, most recently, of ROS metabolism. Herein, we will review the role played by the ERRs as transcriptional regulators of ROS generation and antioxidant mechanisms and also as ROS sensors. We will assess how the control of ROS homeostasis by the ERRs can be linked to physiology and disease and the possible contribution of manipulating ERR activity in redox medicine.

Estrogen-related receptors are targetable ROS sensors

Excessive reactive oxygen species (ROS) can cause oxidative stress and consequently cell injury contributing to a wide range of diseases. Addressing the critical gaps in our understanding of the adaptive molecular events downstream ROS provocation holds promise for the identification of druggable metabolic vulnerabilities. Here, we unveil a direct molecular link between the activity of two estrogen-related receptor (ERR) isoforms and the control of glutamine utilization and glutathione antioxidant production. ERRα down-regulation restricts glutamine entry into the TCA cycle, while ERRγ up-regulation promotes glutamine-driven glutathione production. Notably, we identify increased ERRγ expression/activation as a hallmark of oxidative stress triggered by mitochondrial disruption or chemotherapy. Enhanced tumor antioxidant capacity is an underlying feature of human breast cancer (BCa) patients that respond poorly to treatment. We demonstrate that pharmacological inhibition of ERRγ with the selective inverse agonist GSK5182 increases antitumor efficacy of the chemotherapeutic paclitaxel on poor outcome BCa tumor organoids. Our findings thus underscore the ERRs as novel redox sensors and effectors of a ROS defense program and highlight the potential therapeutic advantage of exploiting ERRγ inhibitors for the treatment of BCa and other diseases where oxidative stress plays a central role.

Effects of In Ovo Supplementation with Nanonutrition (L-Arginine Conjugated with Ag NPs) on Muscle Growth, Immune Response and Heat Shock Proteins at Different Chicken Embryonic Development Stages

Simple Summary

In this study, we have analyzed the effects of in ovo supplementation of inorganic and organic synthesized silver nanoparticles (Ag NPs) conjugated with L-arginine (L-Arg) that were injected in chicken embryo at three different embryonic development stages (8th d, 14th d and 18th d). We investigated the effects of both conjugated Ag NPs on the survival, hatchability and body weight on hatching day (1 d old chicks). The expression of muscle growth related proteins, mainly myoblast determination protein (myoD), myogenin and heat-shock proteins (HSPs) were analyzed in pectoral muscles. The serum level of immunoglobulin M (IgM), serum glutamate oxaloacetate transaminase (SGOT) and serum glutamate pyruvate transaminase (SGPT) were also examined. Our study shows that 14th day of injection of both types of conjugated Ag NPs promoted survival rate and hatching rate at 8 d and 18 d from injection. The immunoglobulin (IgM) levels in serum and the expression of muscle growth related proteins (myoD and myogenin) were dramatically improved; in addition, HSP-60 and HSP-70 expression were declined at 14th d of injection. The serum levels of SGOT and SGPT were decreased at 14d injection when compared to 8 d and 18 d injection. Hence, the 14th day would be suitable day for injection of L-Arg with Ag NPs to promote the survival rate, hatching rate, immune system and muscle growth. Our results illustrated that plant mediated synthesis of Ag NPs at 1000 μg and chemically synthesized Ag NPs at 100 μg concentration would be a better choice to make nanonutrition with L-Arg (100 μg) to carry the nutrients without any toxicity at 14 d injection.

Abstract

The aim of the study was to analyze the in ovo injection of inorganic and organic synthesized silver nanoparticles (Ag NPs) using Brassica oleracea L. var. capitate F. rubra (BOL) conjugation with L-Arginine (L-Arg) on the immune, muscle growth, survivability and hatchability of broiler chickens. The conjugation of L-Arg (100 μg) with 1000 µg of Ag NPs synthesized by (BOL)-extract and L-Arg (100 μg) conjugated with 100 µg of Ag NPs inorganic synthesized were injected into fertile eggs at 8 d, 14 d and 18 d of incubation. Survival and hatching rate were significantly improved in the dose of L-Arg (100 μg) with 1000 µg (BOL-Ag NPs) and L-Arg (100 μg) with 100 µg (C-Ag NPs) on 14 d injection whereas it was decreased on 8 d or 18 d injection. Moreover, the protein expression of muscle development markers such as myogenin and myoD were significantly uprelated in 14 d of incubation whereas the heat shock proteins (HSPs), such as HSP-60 and HSP-70, were significantly upregulated in 18 d incubation. In addition, the liver function marker of serum glutamate oxaloacetate transaminase (SGOT) and serum glutamate pyruvate transaminase (SGPT) were significantly decreased and the immunoglobulin (IgM) levels were increased in a 14 d incubation period in serum at the same concentration.

ERRγ is downregulated in injured motor neuron subpopulations following brachial plexus root avulsion

Estrogen-related receptor γ (ERRγ) is a member of a small group of orphan nuclear receptor transcription factors that have been implicated in several physiological and pathological processes, including placental development, regulation of metabolic genes or disease. The pattern of expression of ERRγ, its role in neuronal injury and its co-localization with other transcription factors in the spinal cord of rats with brachial plexus injury has not been determined. The expression profile of ERRγ and its co-localization with RNA binding protein fox-1 homolog 3 (NeuN) or cyclic AMP-dependent transcription factor 3 (ATF-3) in the motor neurons of rats that underwent brachial plexus root avulsion were assessed using western blot analysis, immunohistochemistry and immunofluorescence. Fluorogold (FG) was used to mark neurons whose axons were severed. ATF-3 was expressed in the nuclei of motor neurons whose axons were severed by root avulsion. On day 3 post-avulsion, FG and ATF-3 were all co-localized in the injured motor neurons. The level of ERRγ protein in the ipsilateral half of injured spinal cords was significantly decreased compared with that in the contralateral half on days 3, 14 and 28 post-avulsion (all P<0.05). The numbers of ERRγ-positive motor neurons (ERRγ^on) were also notably decreased in the ipsilateral side compared with that in the contralateral side on days 14 and 28 post-avulsion, implying that the expression occurred in α motor neurons that were progressively being lost, a phenomenon that was expected post-brachial plexus avulsion. Almost all large and small ERRγ-positive motor neurons were also NeuN-positive (NeuN^on). However, a few of these were ERRγ^on/NeuN^off (no NeuN signal). Therefore, these results suggested that ERRγ is a non-specific marker of γ motor neurons in rats, and therefore, this specific transcriptional program cannot be used to define functionally distinct motor neuron sub-populations. However, its downregulation on the injured side suggests that it is an important component of the response to injury in motor neurons.

Oncostatin M induces C2C12 myotube atrophy by modulating muscle differentiation and degradation

Oncostatin M (OSM) is a cytokine of the interleukin-6 family and plays a role in various disorders such as cancer and inflammatory diseases, which are often accompanied by skeletal muscle atrophy, or sarcopenia. However, the role of OSM in the regulation of skeletal muscle mass remains to be identified. In this study, we investigated the effect of OSM on C2C12 myotube formation in vitro. C2C12 myoblasts were induced to differentiate into myotubes for 3 days and then treated with OSM for 24 or 48 h. The diameter of differentiated C2C12 myotubes were reduced by 18.7% and 23.3% compared to control cells after treatment with OSM for 24 and 48 h, respectively. The expression levels of MyoD and myogenin were decreased, while those of atrogin-1, CCAAT/enhancer binding protein δ, and OSM receptor were increased in C2C12 myotubes treated with OSM for 24 h compared to control cells. Furthermore, the inhibitory effect of OSM on myotube formation was significantly attenuated by pretreatment with an inhibitor of signal transducer and activator of transcription (STAT) 3 or by knockdown of Stat3. Finally, the OSM-induced changes in the expression levels of MyoD, myogenin, and atrogin-1 were reversed by pretreatment with an inhibitor of STAT3 or by Stat3 knockdown in C2C12 myotubes. In conclusion, OSM induces C2C12 myotube atrophy by inhibiting myogenic differentiation and activating muscle degradation in a STAT3-dependent manner.

Effect of In Ovo Injection of L-Arginine in Different Chicken Embryonic Development Stages on Post-Hatchability, Immune Response, and Myo-D and Myogenin Proteins

Simple Summary

In the current study, we hypothesized that the in ovo injection of L-arginine (L-Arg) at different stages of embryonic development, which would have positive effects on the survival rate, hatching rate, immunoglobulin M (IgM) levels, heat shock proteins (HSPs) such as HSP-47, HSP-60, and HSP-70, and muscle development markers as well: Mainly, myoblast determination protein (myoD) and myogenin in pectoral muscles. As indicated, the in ovo injection of L-Arg resulted in an increased hatch rate and weight, survival rate, higher levels of IgM, and myogenin and MyoD expression in the muscles. At the same time, a decrease in the level of HSP-47, HSP-60, and HSP-70 expressions in the tissues was observed on the 14th day of injection compared to the eighth and 18th day of the injection period. In addition, the in ovo injection of L-Arg decreased the serum glutamate oxaloacetate transaminase (SGOT) and serum glutamate pyruvate transaminase (SGPT) concentration in serum as well micronuclei and nuclear abnormality in the blood on the 14th day of the incubation period. Hence, the 14th day would be a suitable day for the injection of L-Arg to promote the hatching rate and muscle growth of broiler chickens.

Abstract

The aim of this study was to evaluate the effect of in ovo injection with different ratios of L-arginine (L-Arg) into Ross broiler eggs at three different embryonic developmental stages (eighth day (d), 14th day, and 18th day) on the survival, hatchability, and body weight (BW) of one-day-old hatched chicks. Additionally, we have analyzed the levels of serum glutamate oxaloacetate transaminase (SGOT) and serum glutamate pyruvate transaminase (SGPT), the protein expression of heat shock proteins (HSPs), and we have also determined micronuclei (MN) and nuclear abnormality (NA). In addition, the genotoxic effect was observed in peripheral blood cells such as the presence of micronuclei and nuclear abnormalities in the experimental groups. The results showed that survival and hatching rates as well as body weight were increased on the 14th day of incubation compared to the eighth and 18th day of incubation at lower concentrations of L-Arg. Moreover, the levels of SGOT and SGPT were also significantly (p < 0.05) increased on the 14th day of incubation at the same concentration (100 μg/μL/egg) of injection. In addition, immunoglobulin (IgM) levels were increased on the 14th day of incubation compared to other days. The protein expressions of HSP-47, HSP-60, and HSP-70 in the liver were significantly down-regulated, whereas the expression of myogenin and myoblast determination protein (MyoD) were significantly up-regulated on the 14th day after incubation when treated with all different doses such as 100 μg, 1000 μg, and 2500 μg/μL/egg, namely 3T1, 3T2, and 3T3, respectively. However, the treatment with low doses of L-Arg down-regulated the expression levels of those proteins on the 14th day of incubation. Histopathology of the liver by hematoxylin and eosin (H&E) staining showed that the majority of liver damage, specifically intracytoplasmic vacuoles, were observed in the 3T1, 3T2, and 3T3 groups. The minimum dose of 100 μg/mL/egg on the 14th day of incubation significantly prevented intracytoplasmic vacuole damages. These results demonstrate that in ovo administration of L-Arg at (100 μg/μL/egg) may be an effective method to increase chick BW, hatch rate, muscle growth-related proteins, and promote the immune response through increasing IgM on the 14th day of the incubation period.

Establishment of stably expandable induced myogenic stem cells by four transcription factors

Life-long regeneration of healthy muscle by cell transplantation is an ideal therapy for patients with degenerative muscle diseases. Yet, obtaining muscle stem cells from patients is very limited due to their exhaustion in disease condition. Thus, development of a method to obtain healthy myogenic stem cells is required. Here, we showed that the four transcription factors, Six1, Eya1, Esrrb, and Pax3, converts fibroblasts into induced myogenic stem cells (iMSCs). The iMSCs showed effective differentiation into multinucleated myotubes and also higher proliferation capacity than muscle derived stem cells both in vitro and in vivo. The iMSCs do not lose their proliferation capacity though the passaging number is increased. We further isolated CD106-negative and α7-integrin-positive iMSCs (sort-iMSCs) showing higher myogenic differentiation capacity than iMSCs. Moreover, genome-wide transcriptomic analysis of iMSCs and sort-iMSCs, followed by network analysis, revealed the genes and signaling pathways associated with enhanced proliferation and differentiation capacity of iMSCs and sort-iMSCs, respectively. The stably expandable iMSCs provide a new source for drug screening and muscle regenerative therapy for muscle wasting disease.

ERRγ: a Junior Orphan with a Senior Role in Metabolism

Estrogen-related receptor (ERR)γ is an orphan nuclear hormone receptor that belongs to the ERR subfamily of transcription factors. No endogenous ligand has been identified to date. ERRγ possesses ligand-independent transcriptional activity that is regulated by co-regulator interactions, and post-translational modifications (PTMs). Recent data from animal models have established ERRγ as a crucial mediator of multiple endocrine and metabolic signals. ERRγ plays important roles in pathological conditions such as insulin resistance, alcoholic liver injury, and cardiac hypertrophy, and controls energy metabolism in the heart, skeletal muscle, and pancreatic β cells. These findings corroborate the importance of ERRγ in metabolic homeostasis, and suggest that ERRγ is a good target for the treatment of metabolic diseases.

Identification of novel inverse agonists of estrogen-related receptors ERRγ and ERRβ

Estrogen-related receptors (ERRs, α, β, and γ) are orphan nuclear receptors most closely related in sequence to estrogen receptors (ERα and ERβ). Much attention has been paid recently to the functions of ERRs for their potential roles as new therapeutic targets implicated in the etiology of metabolic disorders. While no endogenous ligand has been identified for any of the ERR isoforms to date, the potential for using synthetic small molecules to modulate their activity has been demonstrated. In the present study, a series of novel inverse agonists of ERRγ and ERRβ were synthesized using regio- and stereo-specific direct substitution of triarylethylenes. These compounds were evaluated for their ability to modulate the activities of ERRs. The rational directed substitution approach and extensive SAR studies resulted in the discovery of compound 4a (DY40) as the most potent ERRγ inverse agonist described to date with mixed ERRγ/ERRβ functional activities, which potently suppressed the transcriptional functions of ERRγ with IC₅₀=0.01μM in a cell-based reporter gene assay and antagonized ERRγ with a potency approximately 60 times greater than its analog Z-4-OHT (Z-4-hydroxytamoxifen). In addition, compound 3h (DY181) was identified as the most potent synthetic inverse agonist for the ERRβ that exhibited excellent selectivity over ERRα/γ in functional assays. This selectivity was also supported by computational docking models that suggest DY181 forms more extensive hydrogen bound network with ERRβ which should result in higher binding affinity on ERRβ over ERRγ.

PGC-1α modulates necrosis, inflammatory response, and fibrotic tissue formation in injured skeletal muscle

Background

Skeletal muscle tissue has an enormous regenerative capacity that is instrumental for a successful defense against muscle injury and wasting. The peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) exerts therapeutic effects in several muscle pathologies, but its role in damage-induced muscle regeneration is unclear.

Methods

Using muscle-specific gain- and loss-of-function models for PGC-1α in combination with the myotoxic agent cardiotoxin (CTX), we explored the role of this transcriptional coactivator in muscle damage and inflammation.

Results

Interestingly, we observed PGC-1α-dependent effects at the early stages of regeneration, in particular regarding macrophage accumulation and polarization from the pro-inflammatory M1 to the anti-inflammatory M2 type, a faster resolution of necrosis and protection against the development of fibrosis after multiple CTX-induced injuries.

Conclusions

PGC-1α exerts beneficial effects on muscle inflammation that might contribute to the therapeutic effects of elevated muscle PGC-1α in different models of muscle wasting.

Electronic supplementary material

The online version of this article (doi:10.1186/s13395-016-0110-x) contains supplementary material, which is available to authorized users.

Estrogen-Related Receptors and the control of bone cell fate

Bone loss is naturally occurring in aging males and females and exacerbated in the latter after menopause, altogether leading to cumulative skeleton fragility and increased fracture risk. Two types of therapeutic strategies can be envisioned to counteract age- or menopause-associated bone loss, aiming at either reducing bone resorption exerted by osteoclasts or, alternatively, promoting bone formation by osteoblasts. We here summarize data suggesting that inhibition of the Estrogen-Related Receptors α and/or γ could promote bone formation and compensate for bone loss induced by ageing or estrogen-deficiency.

Effects of Sunphenon and Polyphenon 60 on proteolytic pathways, inflammatory cytokines and myogenic markers in H2O2-treated C2C12 cells

The effect of Sunphenon and Polyphenon 60 in oxidative stress response, myogenic regulatory factors, inflammatory cytokines, apoptotic and proteolytic pathways on H2O2-induced myotube atrophy was addressed. Cellular responses of H2O2-induced C2C12 cells were examined, including mRNA expression of myogenic regulatory factors, such as MyoD and myogenin, inflammatory pathways, such as TNF-α and NF-kB, as well as proteolytic enzymes, such as μ-calpain and m-calpain. The pre-treatment of Sunphenon (50 μg/mL)/Polyphenon 60 (50 μg/mL) on H2O2-treated C2C12 cells significantly down-regulated the mRNA expression of myogenin and MyoD when compared to those treated with H2O2-induced alone. Additionally, the mRNA expression of μ-calpain and m-calpain were significantly(p<0.05) increased in H2O2-treated C2C12 cells, whereas pre-treatment with Sunphenon/Polyphenon significantly down-regulated the above genes, namely μ-calpain and m-calpain. Furthermore, the mRNA expression of TNF-α and NF-kB were significantly increased in H2O2-treated C2C12 cells, while pre-treatment with Sunphenon (50 μg/mL)/Polyphenon 60 (50 μg/mL) significantly (p<0.05) down-regulated it when compared to the untreated control group.Subsequent analysis of DNA degeneration and caspase activation revealed that Sunphenon (50 μg/mL)/Polyphenon 60 (50 μg/mL) inhibited activation of caspase-3 and showed an inhibitory effect on DNA degradation. From this result, we know that, in stress conditions, μ-calpain may be involved in the muscle atrophy through the suppression of myogenin and MyoD. Moreover, Sunphenon may regulate the skeletal muscle genes/promote skeletal muscle recovery by the up-regulation of myogenin and MyoD and suppression of μ-calpain and inflammatory pathways and may regulate the apoptosis pathways. Our findings suggest that dietary supplementation of Sunphenon might reduce inflammatory events in muscle-associated diseases, such as myotube atrophy.

Regulation of skeletal muscle mitochondrial function by nuclear receptors: implications for health and disease

Skeletal muscle metabolism is highly dependent on mitochondrial function, with impaired mitochondrial biogenesis associated with the development of metabolic diseases such as insulin resistance and type 2 diabetes. Mitochondria display substantial plasticity in skeletal muscle, and are highly sensitive to levels of physical activity. It is thought that physical activity promotes mitochondrial biogenesis in skeletal muscle through increased expression of genes encoded in both the nuclear and the mitochondrial genome; however, how this process is co-ordinated at the cellular level is poorly understood. Nuclear receptors (NRs) are key signalling proteins capable of integrating environmental factors and mitochondrial function, thereby providing a potential link between exercise and mitochondrial biogenesis. The aim of this review is to highlight the function of NRs in skeletal muscle mitochondrial biogenesis and discuss the therapeutic potential of NRs for the management and treatment of chronic metabolic disease.

Constitutive activities of estrogen-related receptors: Transcriptional regulation of metabolism by the ERR pathways in health and disease

The estrogen-related receptors (ERRs) comprise a small group of orphan nuclear receptor transcription factors. The ERRα and ERRγ isoforms play a central role in the regulation of metabolic genes and cellular energy metabolism. Although less is known about ERRβ, recent studies have revealed the importance of this isoform in the maintenance of embryonic stem cell pluripotency. Thus, ERRs are essential to many biological processes. The development of several ERR knockout and overexpression models and the application of advanced functional genomics have allowed rapid advancement of our understanding of the physiology regulated by ERR pathways. Moreover, it has enabled us to begin to delineate the distinct programs regulated by ERRα and ERRγ that have overlapping effects on metabolism and growth. The current review primarily focuses on the physiologic roles of ERR isoforms related to their metabolic regulation; therefore, the ERRα and ERRγ are discussed in the greatest detail. We emphasize findings from gain- and loss-of-function models developed to characterize ERR control of skeletal muscle, heart and musculoskeletal physiology. These models have revealed that coordinating metabolic capacity with energy demand is essential for seemingly disparate processes such as muscle differentiation and hypertrophy, innate immune function, thermogenesis, and bone remodeling. Furthermore, the models have revealed that ERRα- and ERRγ-deficiency in mice accelerates progression of pathologic processes and implicates ERRs as etiologic factors in disease. We highlight the human diseases in which ERRs and their downstream metabolic pathways are perturbed, including heart failure and diabetes. While no natural ligand has been identified for any of the ERR isoforms, the potential for using synthetic small molecules to modulate their activity has been demonstrated. Based on our current understanding of their transcriptional mechanisms and physiologic relevance, the ERRs have emerged as potential therapeutic targets for treatment of osteoporosis, muscle atrophy, insulin resistance and heart failure in humans.

The multiple universes of estrogen-related receptor α and γ in metabolic control and related diseases

The identification of the estrogen-related receptors (ERRs) as the first orphan nuclear receptors ignited a new era in molecular endocrinology, which led to the discovery of new ligand-dependent response systems. Although ERR subfamily members have yet to be associated with a natural ligand, the characterization of these orphan receptors has demonstrated that they occupy a strategic node in the transcriptional control of cellular energy metabolism. In particular, ERRs are required for the response to various environmental challenges that require high energy levels by the organism. As central regulators of energy homeostasis, ERRs may also be implicated in the etiology of metabolic disorders, such as type 2 diabetes and metabolic syndrome. Here, we review the recent evidence that further highlights the role of ERRs in metabolic control, particularly in liver and skeletal muscle, and their likely involvement in metabolic diseases. Consequently, we also explore the promises and pitfalls of ERRs as potential therapeutic targets.

Trophoblast syncytialisation necessitates mitochondrial function through estrogen-related receptor-γ activation

Human pregnancy needs a correct placentation which depends on adequate cytotrophoblast proliferation, differentiation and invasion. In this study, using specific mitochondrial respiratory chain inhibitors, we observed a decrease of hormone production (hCG and leptin) and cell fusion of human primary villous cytotrophoblasts (CT). These results demonstrated that mitochondria are involved in the control of CT differentiation process. Moreover, we also observed a decrease of mitochondrial mass associated with an increase of mitochondrial DNA during CT differentiation. Furthermore, lactate production increased during CT differentiation suggesting that anaerobic metabolism was enhanced in differentiated CTs, and that the role of mitochondria in CT fusion is not only related to its energetic function. Otherwise, the orphan nuclear receptor, estrogen-related receptor γ (ERRγ) is known to orchestrate transcriptional control of energy metabolism genes. In this study, using RNA knockdown and transcriptional activation with DY131 (an ERRγ agonist), we clearly demonstrated that ERRγ promotes hormone production and cell fusion indicating that ERRγ is a key positive transcriptional factor involved in CT differentiation. Finally, we showed that ERRγ promotes mitochondrial biogenesis and function during CT differentiation, and that the role of ERRγ during trophoblast differentiation is mainly mediated by the control of mitochondrial functions.

Estrogen-related receptor-α (ERRα) deficiency in skeletal muscle impairs regeneration in response to injury

The estrogen-related receptor-α (ERRα) regulates mitochondrial biogenesis and glucose and fatty acid oxidation during differentiation in skeletal myocytes. However, whether ERRα controls metabolic remodeling during skeletal muscle regeneration in vivo is unknown. We characterized the time course of skeletal muscle regeneration in wild-type (M-ERRαWT) and muscle-specific ERRα(-/-) (M-ERRα(-/-)) mice after injury by intramuscular cardiotoxin injection. M-ERRα(-/-) 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-ERRαWT. Transcript levels of mitochondrial transcription factor A, nuclear respiratory factor-2a, and peroxisome proliferator-activated receptor (PPAR)-γ coactivator (PGC)-1β, were downregulated in the M-ERRα(-/-) muscles at the onset of myogenesis. Furthermore, coincident with delayed myofiber recovery, we observed reduced muscle ATP content (-45% vs. M-ERRαWT) and enhanced AMP-activated protein kinase (AMPK) activation in M-ERRα(-/-) muscle. We subsequently demonstrated that pharmacologic postinjury AMPK activation was sufficient to delay muscle regeneration in WT mice. AMPK activation induced ERRα transcript expression in M-ERRαWT muscle and in C2C12 myotubes through induction of the Esrra promoter, indicating that ERRα may control gene regulation downstream of the AMPK pathway. Collectively, these results suggest that ERRα deficiency during muscle regeneration impairs recovery of mitochondrial energetic capacity and perturbs AMPK activity, resulting in delayed myofiber repair.

Muscle ERRγ mitigates Duchenne muscular dystrophy via metabolic and angiogenic reprogramming

Treatment of Duchenne muscular dystrophy (DMD) by replacing mutant dystrophin or restoring dystrophin-associated glycoprotein complex (DAG) has been clinically challenging. Instead, identifying and targeting muscle pathways deregulated in DMD will provide new therapeutic avenues. We report that the expression of nuclear receptor estrogen-related receptor-γ (ERRγ), and its metabolic and angiogenic targets are down-regulated (50-85%) in skeletal muscles of mdx mice (DMD model) vs. wild-type mice. Corelatively, oxidative myofibers, muscle vasculature, and exercise tolerance (33%) are decreased in mdx vs. wild-type mice. Overexpressing ERRγ selectively in the dystrophic muscles of the mdx mice restored metabolic and angiogenic gene expression compared with control mdx mice. Further, ERRγ enhanced muscle oxidative myofibers, vasculature, and blood flow (by 33-66%) and improved exercise tolerance (by 75%) in the dystrophic mice. Restoring muscle ERRγ pathway ameliorated muscle damage and also prevented DMD hallmarks of postexercise muscle damage, hypoxia, and fatigue in mdx mice. Notably, ERRγ did not restore sarcolemmal DAG complex, which is thus dispensable for antidystrophic effects of ERRγ. In summary, ERRγ-dependent metabolic and angiogenic gene program is defective in DMD, and we demonstrate that its restoration is a potential strategy for treating muscular dystrophy.