ERRγ Promotes Angiogenesis, Mitochondrial Biogenesis, and Oxidative Remodeling in PGC1α/β-Deficient Muscle

Genetic mechanisms of multiciliated cell development: from fate choice to differentiation in zebrafish and other models

Multiciliated cells (MCCS) form bundles of cilia and their activities are essential for the proper development and physiology of many organ systems. Not surprisingly, defects in MCCs have profound consequences and are associated with numerous disease states. Here, we discuss the current understanding of MCC formation, with a special focus on the genetic and molecular mechanisms of MCC fate choice and differentiation. Furthermore, we cast a spotlight on the use of zebrafish to study MCC ontogeny and several recent advances made in understanding MCCs using this vertebrate model to delineate mechanisms of MCC emergence in the developing kidney.

International Union of Basic and Clinical Pharmacology CXIII: Nuclear Receptor Superfamily-Update 2023

The NR superfamily comprises 48 transcription factors in humans that control a plethora of gene network programs involved in a wide range of physiologic processes. This review will summarize and discuss recent progress in NR biology and drug development derived from integrating various approaches, including biophysical techniques, structural studies, and translational investigation. We also highlight how defective NR signaling results in various diseases and disorders and how NRs can be targeted for therapeutic intervention via modulation via binding to synthetic lipophilic ligands. Furthermore, we also review recent studies that improved our understanding of NR structure and signaling. SIGNIFICANCE STATEMENT: Nuclear receptors (NRs) are ligand-regulated transcription factors that are critical regulators of myriad physiological processes. NRs serve as receptors for an array of drugs, and in this review, we provide an update on recent research into the roles of these drug targets.

Development and pharmacological evaluation of a new chemical series of potent pan-ERR agonists, identification of SLU-PP-915

Estrogen-related receptors (ERR) are an orphan nuclear receptor sub-family that play a critical role in regulating gene transcription for several physiological processes including mitochondrial function, cellular energy utilization and homeostasis. They have also been implicated to play a role in several pathological conditions. Herein, we report the identification, synthesis, structure-activity relationships and pharmacological evaluation of a new chemical series of potent pan-ERR agonists. This template was designed for ERRγ starting from the known acyl hydrazide template and compounds such as agonist GSK-4716 employing a structure-based drug design approach. This led to the preparation of a series of 2,5-disubstituted thiophenes from which several were found to be potent agonists of ERRγ in cell-based co-transfection assays. Additionally, direct binding to ERRγ was established through 1H NMR protein-ligand binding experiments. Compound optimization revealed that the phenolic or aniline groups could be replaced with a boronic acid moiety, which was able to maintain activity and demonstrated improved metabolic stability in microsomal in vitro assays. Further pharmacological evaluation of these compounds showed that they had roughly equivalent agonist activity on ERR isoforms α and β representing an ERR pan-agonist profile. One potent agonist, SLU-PP-915 (10s), which contained a boronic acid moiety was profiled in gene expression assays and found to significantly upregulate the expression of ERR target genes such as peroxisome-proliferator activated receptor γ co-activators-1α, lactate dehydrogenase A, DNA damage inducible transcript 4 and pyruvate dehydrogenase kinase 4 both in vitro and in vivo.

Mitochondrial Properties in Skeletal Muscle Fiber

Mitochondria are the primary source of energy production and are implicated in a wide range of biological processes in most eukaryotic cells. Skeletal muscle heavily relies on mitochondria for energy supplements. In addition to being a powerhouse, mitochondria evoke many functions in skeletal muscle, including regulating calcium and reactive oxygen species levels. A healthy mitochondria population is necessary for the preservation of skeletal muscle homeostasis, while mitochondria dysregulation is linked to numerous myopathies. In this review, we summarize the recent studies on mitochondria function and quality control in skeletal muscle, focusing mainly on in vivo studies of rodents and human subjects. With an emphasis on the interplay between mitochondrial functions concerning the muscle fiber type-specific phenotypes, we also discuss the effect of aging and exercise on the remodeling of skeletal muscle and mitochondria properties.

Interaction between poly-A binding protein PABPC4 and nuclear receptor corepressor NCoR1 modulates a metabolic stress response

Mitochondria are organelles known primarily for generating ATP via the oxidative phosphorylation process. Environmental signals are sensed by whole organisms or cells and markedly affect this process, leading to alterations in gene transcription and, consequently, changes in mitochondrial function and biogenesis. The expression of mitochondrial genes is finely regulated by nuclear transcription factors, including nuclear receptors and their coregulators. Among the best-known coregulators is the nuclear receptor corepressor 1 (NCoR1). Muscle-specific knockout of NCoR1 in mice induces an oxidative phenotype, improving glucose and fatty acid metabolism. However, the mechanism by which NCoR1 is regulated remains elusive. In this work, we identified the Poly A Binding Protein (PABPC4) as a new NCoR1 interactor. Unexpectedly, we found that silencing of PABPC4 induced an oxidative phenotype in both C2C12 and MEF cells as indicated by increased oxygen consumption, mitochondria content, and reduced lactate production. Mechanistically, we demonstrated that PABPC4 silencing increased the ubiquitination and consequent degradation of NCoR1, leading to the derepression of PPAR-regulated genes. As a consequence, cells with PABPC4 silencing had a greater capacity to metabolize lipids, reduced intracellular lipid droplets and reduced cell death. Interestingly, in conditions known to induce mitochondrial function and biogenesis, both mRNA expression and PABPC4 protein content were markedly reduced. Our study, therefore, suggests that the lowering of PABPC4 expression may represent an adaptive event required to induce mitochondrial activity in response to metabolic stress in skeletal muscle cells. As such, the NCoR1-PABPC4 interface might be a new road to the treatment of metabolic diseases.

Adult skeletal muscle peroxisome proliferator-activated receptor γ -related coactivator 1 is involved in maintaining mitochondrial content

The peroxisome proliferator-activated receptor γ coactivator-1 (PGC-1) family of transcriptional coactivators are regulators of mitochondrial oxidative capacity and content in skeletal muscle. Many of these conclusions are based primarily on gain-of-function studies using muscle-specific overexpression of PGC1s. We have previously reported that genetic deletion of both PGC-1α and PGC-1β in adult skeletal muscle resulted in a significant reduction in oxidative capacity with no effect on mitochondrial content. However, the contribution of PGC-1-related coactivator (PRC), the third PGC-1 family member, in regulating skeletal muscle mitochondria is unknown. Therefore, we generated an inducible skeletal muscle-specific PRC knockout mouse (iMS-PRC-KO) to assess the contribution of PRC in skeletal muscle mitochondrial function. We measured mRNA expression of electron transport chain (ETC) subunits as well as markers of mitochondrial content in the iMS-PRC-KO animals and observed an increase in ETC gene expression and mitochondrial content. Furthermore, the increase in ETC gene expression and mitochondrial content was associated with increased expression of PGC-1α and PGC-1β. We therefore generated an adult-inducible PGC-1 knockout mouse in which all PGC-1 family members are deleted (iMS-PGC-1TKO). The iMS-PGC-1TKO animals exhibited a reduction in ETC mRNA expression and mitochondrial content. These data suggest that in the absence of PRC alone, compensation occurs by increasing PGC-1α and PGC-1β to maintain mitochondrial content. Moreover, the removal of all three PGC-1s in skeletal muscle results in a reduction in both ETC mRNA expression and mitochondrial content. Taken together, these results suggest that PRC plays a role in maintaining baseline mitochondrial content in skeletal muscle.

LSD1 defines the fiber type-selective responsiveness to environmental stress in skeletal muscle

Skeletal muscle exhibits remarkable plasticity in response to environmental cues, with stress-dependent effects on the fast-twitch and slow-twitch fibers. Although stress-induced gene expression underlies environmental adaptation, it is unclear how transcriptional and epigenetic factors regulate fiber type-specific responses in the muscle. Here, we show that flavin-dependent lysine-specific demethylase-1 (LSD1) differentially controls responses to glucocorticoid and exercise in postnatal skeletal muscle. Using skeletal muscle-specific LSD1-knockout mice and in vitro approaches, we found that LSD1 loss exacerbated glucocorticoid-induced atrophy in the fast fiber-dominant muscles, with reduced nuclear retention of Foxk1, an anti-autophagic transcription factor. Furthermore, LSD1 depletion enhanced endurance exercise-induced hypertrophy in the slow fiber-dominant muscles, by induced expression of ERRγ, a transcription factor that promotes oxidative metabolism genes. Thus, LSD1 serves as an 'epigenetic barrier' that optimizes fiber type-specific responses and muscle mass under the stress conditions. Our results uncover that LSD1 modulators provide emerging therapeutic and preventive strategies against stress-induced myopathies such as sarcopenia, cachexia, and disuse atrophy.

Roles of Estrogen, Estrogen Receptors, and Estrogen-Related Receptors in Skeletal Muscle: Regulation of Mitochondrial Function

Estrogen is an essential sex steroid hormone that functions primarily in female reproductive system, as well as in a variety of tissues and organs with pleiotropic effects, such as in cardiovascular, nervous, immune, and musculoskeletal systems. Women with low estrogen, as exemplified by those in postmenopause, are therefore prone to suffer from various disorders, i.e., cardiovascular disease, dementia, metabolic syndrome, osteoporosis, sarcopenia, frailty, and so on. Estrogen regulates the expression of its target genes by binding to its cognate receptors, estrogen receptors (ERs) α and β. Notably, the estrogen-related receptors (ERRs) α, β, and γ are originally identified as orphan receptors that share substantial structural homology and common transcriptional targets with ERs. Accumulating evidence suggests that ERs and ERRs play crucial roles in skeletal muscles, such as muscle mass maintenance, muscle exercise physiology, and muscle regeneration. In this article, we review potential regulatory roles of ERs and ERRs in muscle physiology, particularly with regard to mitochondrial function and metabolism.

DN200434, an orally available inverse agonist of estrogen-related receptor γ, induces ferroptosis in sorafenib-resistant hepatocellular carcinoma

Sorafenib, originally identified as an inhibitor of multiple oncogenic kinases, induces ferroptosis in hepatocellular carcinoma (HCC) cells. Several pathways that mitigate sorafenib-induced ferroptosis confer drug resistance; thus strategies that enhance ferroptosis increase sorafenib efficacy. Orphan nuclear receptor estrogen-related receptor γ (ERRγ) is upregulated in human HCC tissues and plays a role in cancer cell proliferation. The aim of this study was to determine whether inhibition of ERRγ with DN200434, an orally available inverse agonist, can overcome resistance to sorafenib through induction of ferroptosis. Sorafenib-resistant HCC cells were less sensitive to sorafenibinduced ferroptosis and showed significantly higher ERRγ levels than sorafenib-sensitive HCC cells. DN200434 induced lipid peroxidation and ferroptosis in sorafenib-resistant HCC cells. Mechanistically, DN200434 increased mitochondrial ROS generation by reducing glutathione/glutathione disulfide levels, which subsequently reduced mTOR activity and GPX4 levels. DN200434 induced amplification of the antitumor effects of sorafenib was confirmed in a tumor xenograft model. The present results indicate that DN200434 may be a novel therapeutic strategy to re-sensitize HCC cells to sorafenib. [BMB Reports 2022; 55(11): 547-552].

DN200434, an orally available inverse agonist of estrogen-related receptor γ, induces ferroptosis in sorafenib-resistant hepatocellular carcinoma

Sorafenib, originally identified as an inhibitor of multiple oncogenic kinases, induces ferroptosis in hepatocellular carcinoma (HCC) cells. Several pathways that mitigate sorafenib-induced ferroptosis confer drug resistance; thus strategies that enhance ferroptosis increase sorafenib efficacy. Orphan nuclear receptor estrogen-related receptor γ (ERRγ) is upregulated in human HCC tissues and plays a role in cancer cell proliferation. The aim of this study was to determine whether inhibition of ERRγ with DN200434, an orally available inverse agonist, can overcome resistance to sorafenib through induction of ferroptosis. Sorafenib-resistant HCC cells were less sensitive to sorafenibinduced ferroptosis and showed significantly higher ERRγ levels than sorafenib-sensitive HCC cells. DN200434 induced lipid peroxidation and ferroptosis in sorafenib-resistant HCC cells. Mechanistically, DN200434 increased mitochondrial ROS generation by reducing glutathione/glutathione disulfide levels, which subsequently reduced mTOR activity and GPX4 levels. DN200434 induced amplification of the antitumor effects of sorafenib was confirmed in a tumor xenograft model. The present results indicate that DN200434 may be a novel therapeutic strategy to re-sensitize HCC cells to sorafenib. [BMB Reports 2022; 55(11): 547-552].

DN200434 Inhibits Vascular Smooth Muscle Cell Proliferation and Prevents Neointima Formation in Mice after Carotid Artery Ligation

BACKGRUOUND

Excessive proliferation and migration of vascular smooth muscle cells (VSMCs), which contributes to the development of occlusive vascular diseases, requires elevated mitochondrial oxidative phosphorylation to meet the increased requirements for energy and anabolic precursors. Therefore, therapeutic strategies based on blockade of mitochondrial oxidative phosphorylation are considered promising for treatment of occlusive vascular diseases. Here, we investigated whether DN200434, an orally available estrogen receptor-related gamma inverse agonist, inhibits proliferation and migration of VSMCs and neointima formation by suppressing mitochondrial oxidative phosphorylation.

METHODS

VSMCs were isolated from the thoracic aortas of 4-week-old Sprague-Dawley rats. Oxidative phosphorylation and the cell cycle were analyzed in fetal bovine serum (FBS)- or platelet-derived growth factor (PDGF)-stimulated VSMCs using a Seahorse XF-24 analyzer and flow cytometry, respectively. A model of neointimal hyperplasia was generated by ligating the left common carotid artery in male C57BL/6J mice.

RESULTS

DN200434 inhibited mitochondrial respiration and mammalian target of rapamycin complex 1 activity and consequently suppressed FBS- or PDGF-stimulated proliferation and migration of VSMCs and cell cycle progression. Furthermore, DN200434 reduced carotid artery ligation-induced neointima formation in mice.

CONCLUSION

Our data suggest that DN200434 is a therapeutic option to prevent the progression of atherosclerosis.

Balanced Free Essential Amino Acids and Resistance Exercise Training Synergistically Improve Dexamethasone-Induced Impairments in Muscle Strength, Endurance, and Insulin Sensitivity in Mice

Our previous study shows that an essential amino acid (EAA)-enriched diet attenuates dexamethasone (DEX)-induced declines in muscle mass and strength, as well as insulin sensitivity, but does not affect endurance. In the present study, we hypothesized that the beneficial effects will be synergized by adding resistance exercise training (RET) to EAA, and diet-free EAA would improve endurance. To test hypotheses, mice were randomized into the following four groups: control, EAA, RET, and EAA+RET. All mice except the control were subjected to DEX treatment. We evaluated the cumulative rate of myofibrillar protein synthesis (MPS) using ²H₂O labeling and mass spectrometry. Neuromuscular junction (NMJ) stability, mitochondrial contents, and molecular signaling were demonstrated in skeletal muscle. Insulin sensitivity and glucose metabolism using ¹³C₆-glucose tracing during oral glucose tolerance tests were analyzed. We found that EAA and RET synergistically improve muscle mass and/or strength, and endurance capacity, as well as insulin sensitivity, and glucose metabolism in DEX-treated muscle. These improvements are accomplished, in part, through improvements in myofibrillar protein synthesis, NMJ, fiber type preservation, and/or mitochondrial biogenesis. In conclusion, free EAA supplementation, particularly when combined with RET, can serve as an effective means that counteracts the adverse effects on muscle of DEX that are found frequently in clinical settings.

Exercise improves high-fat diet-induced metabolic disorder by promoting HDAC5 degradation through the ubiquitin-proteasome system in skeletal muscle

Histone deacetylase 4/5 are essential for regulating metabolic gene expression, AMPKα2 regulates HDAC4/5 activity and the expression of MuRF1 during exercise. In this study, we used wild type and AMPKα2-/- mice to explore the potential regulatory relationship between AMPKα2 and HDAC4/5 expression during exercise. Firstly, we fed C57BL/6J mice with high-fat diet for eight-week to assess the effects of high-fat diet on skeletal muscle metabolism and HDAC4/5 expression. We then performed a six-week treadmill exercise on both wild type and AMPKα2-/- mice. After exercise, the expressions of HDAC4/5 were examined in both gastrocnemius and soleus. The citrate synthase activity and proteins involved in skeletal muscle oxidative process were assessed. To determine the relationship of HDAC4/5 and skeletal muscle oxidative capacity, citrate synthase activity was assessed after silencing HDAC4/5. Moreover, HDAC5 ubiquitination and the association of MuRF1 to HDAC5 were also investigated. Our results showed that six-week exercise increased the skeletal muscle oxidative capacity and decreased HDAC4/5 expression only in soleus. HDAC5 silencing increased C2C12 cells oxidative capacity. Proteasome inhibition by MG132 abolished exercise-induced HDAC5 degradation mediated by MuRF1-ubiquitin-proteasome system. However, the UPS did not dominantly account for exercise-induced HDAC4 degradation. Exercise up-regulated MuRF1-HDAC5 association in wild type mice but not in AMPKα2-/- mice. Our results revealed that six-week exercise increased the skeletal muscle oxidative capacity and promoted HDAC5 degradation in soleus through the UPS, MuRF1 mediated HDAC5 ubiquitination. Although AMPKα2 played partial role in regulating MuRF1 expression and HDAC5 ubiquitination, exercise-induced HDAC5 degradation did not fully depend on AMPKα2.

Estrogen-Related Receptor γ Maintains Pancreatic Acinar Cell Function and Identity by Regulating Cellular Metabolism

BACKGROUND & AIMS

Mitochondrial dysfunction disrupts the synthesis and secretion of digestive enzymes in pancreatic acinar cells and plays a primary role in the etiology of exocrine pancreas disorders. However, the transcriptional mechanisms that regulate mitochondrial function to support acinar cell physiology are poorly understood. Here, we aim to elucidate the function of estrogen-related receptor γ (ERRγ) in pancreatic acinar cell mitochondrial homeostasis and energy production.

METHODS

Two models of ERRγ inhibition, GSK5182-treated wild-type mice and ERRγ conditional knock-out (cKO) mice, were established to investigate ERRγ function in the exocrine pancreas. To identify the functional role of ERRγ in pancreatic acinar cells, we performed histologic and transcriptome analysis with the pancreas isolated from ERRγ cKO mice. To determine the relevance of these findings for human disease, we analyzed transcriptome data from multiple independent human cohorts and conducted genetic association studies for ESRRG variants in 2 distinct human pancreatitis cohorts.

RESULTS

Blocking ERRγ function in mice by genetic deletion or inverse agonist treatment results in striking pancreatitis-like phenotypes accompanied by inflammation, fibrosis, and cell death. Mechanistically, loss of ERRγ in primary acini abrogates messenger RNA expression and protein levels of mitochondrial oxidative phosphorylation complex genes, resulting in defective acinar cell energetics. Mitochondrial dysfunction due to ERRγ deletion further triggers autophagy dysfunction, endoplasmic reticulum stress, and production of reactive oxygen species, ultimately leading to cell death. Interestingly, ERRγ-deficient acinar cells that escape cell death acquire ductal cell characteristics, indicating a role for ERRγ in acinar-to-ductal metaplasia. Consistent with our findings in ERRγ cKO mice, ERRγ expression was significantly reduced in patients with chronic pancreatitis compared with normal subjects. Furthermore, candidate locus region genetic association studies revealed multiple single nucleotide variants for ERRγ that are associated with chronic pancreatitis.

CONCLUSIONS

Collectively, our findings highlight an essential role for ERRγ in maintaining the transcriptional program that supports acinar cell mitochondrial function and organellar homeostasis and provide a novel molecular link between ERRγ and exocrine pancreas disorders.

Beneficial and Detrimental Roles of Heme Oxygenase-1 in the Neurovascular System

Heme oxygenase (HO) has both beneficial and detrimental effects via its metabolites, including carbon monoxide (CO), biliverdin or bilirubin, and ferrous iron. HO-1 is an inducible form of HO that is upregulated by oxidative stress, nitric oxide, CO, and hypoxia, whereas HO-2 is a constitutive form that regulates vascular tone and homeostasis. In brains injured by trauma, ischemia-reperfusion, or Alzheimer’s disease (AD), the long-term expression of HO-1 can be detected, which can lead to cytotoxic ferroptosis via iron accumulation. In contrast, the transient induction of HO-1 in the peri-injured region may have regenerative potential (e.g., angiogenesis, neurogenesis, and mitochondrial biogenesis) and neurovascular protective effects through the CO-mediated signaling pathway, the antioxidant properties of bilirubin, and the iron-mediated ferritin synthesis. In this review, we discuss the dual roles of HO-1 and its metabolites in various neurovascular diseases, including age-related macular degeneration, ischemia-reperfusion injury, traumatic brain injury, Gilbert’s syndrome, and AD.

Adapting Physiology in Functional Human Islet Organogenesis

Generation of three-dimensional (3D)-structured functional human islets is expected to be an alternative cell source for cadaveric human islet transplantation for the treatment of insulin-dependent diabetes. Human pluripotent stem cells (hPSCs), such as human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSCs), offer infinite resources for newly synthesized human islets. Recent advancements in hPSCs technology have enabled direct differentiation to human islet-like clusters, which can sense glucose and secrete insulin, and those islet clusters can ameliorate diabetes when transplanted into rodents or non-human primates (NHPs). However, the generated hPSC-derived human islet-like clusters are functionally immature compared with primary human islets. There remains a challenge to establish a technology to create fully functional human islets in vitro, which are functionally and transcriptionally indistinguishable from cadaveric human islets. Understanding the complex differentiation and maturation pathway is necessary to generate fully functional human islets for a tremendous supply of high-quality human islets with less batch-to-batch difference for millions of patients. In this review, I summarized the current progress in the generation of 3D-structured human islets from pluripotent stem cells and discussed the importance of adapting physiology for in vitro functional human islet organogenesis and possible improvements with environmental cues.

软骨细胞线粒体生物发生在骨关节炎发病机制中的作用

OBJECTIVE

To summarize the role of chondrocytes mitochondrial biogenesis in the pathogenesis of osteoarthritis (OA), and analyze the applications in the treatment of OA.

METHODS

A review of recent literature was conducted to summarize the changes in mitochondrial biogenesis in the course of OA, the role of major signaling molecules in OA chondrocytes, and the prospects for OA therapeutic applications.

RESULTS

Recent studies reveales that mitochondria are significant energy metabolic centers in chondrocytes and its dysfunction has been considered as an essential mechanism in the pathogenesis of OA. Mitochondrial biogenesis is one of the key processes maintaining the normal quantity and function of mitochondria, and peroxisome proliferator-activated receptor-gamma coactivator 1 alpha (PGC-1α) is the central regulator of this process. A regulatory network of mitochondrial biogenesis with PGC-1α as the center, adenosine monophosphate-activated protein kinase, sirtuin1/3, and cyclic adenosine monophosphate response element-binding protein as the main upstream regulatory molecules, and nuclear respiratory factor 1, estrogen-related receptor α, and nuclear respiratory factor 2 as the main downstream regulatory molecules has been reported. However, the role of mitochondrial biogenesis in OA chondrocytes still needs further validation and in-depth exploration. It has been demonstrated that substances such as puerarin and omentin-1 can retard the development of OA by activating the damaged mitochondrial biogenesis in OA chondrocytes, which proves the potential to be used in the treatment OA.

CONCLUSION

Mitochondrial biogenesis in chondrocytes plays an important role in the pathogenesis of OA, and further exploring the related mechanisms is of great clinical significance.

Mitochondrial repair as potential pharmacological target in cerebral ischemia

Cerebral ischemia and its consequences like transient ischemic attack, aneurysm and stroke are the common and devastating conditions which remain the leading cause of mortality after coronary heart disease in developed countries and are the greatest cause of disability, leaving 50% of survivors permanently disabled. Despite recognition of risk factors and mechanisms involved in the pathology of the disease, treatment of ischemic disorders is limited to thrombolytic drugs like recombinant tissue plasminogen activator (rt-PA) and clinical rendition of the neuroprotective agents have not been so successful. Recent studies evidenced the role of mitochondrial dysfunction in neuronal damage that occurred after cerebral ischemia. This review article will focus on the various fundamental mechanisms responsible for neuronal damage because of mitochondrial dysfunction including cell signaling pathways, autophagy, apoptosis/necrosis, generation of reactive oxygen species, calcium overload, the opening of membrane permeability transition pore (mPTP), mitochondrial dynamics and biogenesis. Recent studies have concerned the significant role of mitochondrial biogenesis in mitochondrial repair and transfer of healthy mitochondria from astrocytes to the damaged neurons, providing neuroprotection and neural recovery following ischemia. Novel and influential studies have evidenced the significant role of mitochondria transfer and mitochondrial transplantation in reviving cell energy and in replacement of impaired or dysfunctional mitochondria with healthy mitochondria after ischemic episode. This review article will focus on recent advances in mitochondrial interventions and exogenous therapeutic modalities like mitochondria transfer technique, employment of stem cells, mitochondrial transplantation, miRNA inhibition and mitochondrial-targeted Sirtuin1 activator for designing novel and promising treatment for cerebral ischemia induced pathological states.

Molecular targets of exercise mimetics and their natural activators

Physical exercise can be effective in preventing or ameliorating various diseases, including diabetes, cardiovascular diseases, neurodegenerative diseases, and cancer. However, not everyone may be able to participate in exercise due to illnesses, age-related frailty, or difficulty in long-term behavior change. An alternative option is to utilize pharmacological interventions that mimic the positive effects of exercise training. Recent studies have identified signaling pathways associated with the benefits of physical activity and discovered exercise mimetics that can partially simulate the systemic impact of exercise. This review describes the molecular targets for exercise mimetics and their effect on skeletal muscle and other tissues. We will also discuss the potential advantages of using natural products as a multi-targeting agent for mimicking the health-promoting effects of exercise.

Muscle-secreted neurturin couples myofiber oxidative metabolism and slow motor neuron identity

Endurance exercise promotes skeletal muscle vascularization, oxidative metabolism, fiber-type switching, and neuromuscular junction integrity. Importantly, the metabolic and contractile properties of the muscle fiber must be coupled to the identity of the innervating motor neuron (MN). Here, we show that muscle-derived neurturin (NRTN) acts on muscle fibers and MNs to couple their characteristics. Using a muscle-specific NRTN transgenic mouse (HSA-NRTN) and RNA sequencing of MN somas, we observed that retrograde NRTN signaling promotes a shift toward a slow MN identity. In muscle, NRTN increased capillary density and oxidative capacity and induced a transcriptional reprograming favoring fatty acid metabolism over glycolysis. This combination of effects on muscle and MNs makes HSA-NRTN mice lean with remarkable exercise performance and motor coordination. Interestingly, HSA-NRTN mice largely recapitulate the phenotype of mice with muscle-specific expression of its upstream regulator PGC-1ɑ1. This work identifies NRTN as a myokine that couples muscle oxidative capacity to slow MN identity.

Ontogeny of Carbon Monoxide-Related Gene Expression in a Deep-Diving Marine Mammal

Marine mammals such as northern elephant seals (NES) routinely experience hypoxemia and ischemia-reperfusion events to many tissues during deep dives with no apparent adverse effects. Adaptations to diving include increased antioxidants and elevated oxygen storage capacity associated with high hemoprotein content in blood and muscle. The natural turnover of heme by heme oxygenase enzymes (encoded by HMOX1 and HMOX2) produces endogenous carbon monoxide (CO), which is present at high levels in NES blood and has been shown to have cytoprotective effects in laboratory systems exposed to hypoxia. To understand how pathways associated with endogenous CO production and signaling change across ontogeny in diving mammals, we measured muscle CO and baseline expression of 17 CO-related genes in skeletal muscle and whole blood of three age classes of NES. Muscle CO levels approached those of animals exposed to high exogenous CO, increased with age, and were significantly correlated with gene expression levels. Muscle expression of genes associated with CO production and antioxidant defenses (HMOX1, BVR, GPX3, PRDX1) increased with age and was highest in adult females, while that of genes associated with protection from lipid peroxidation (GPX4, PRDX6, PRDX1, SIRT1) was highest in adult males. In contrast, muscle expression of mitochondrial biogenesis regulators (PGC1A, ESRRA, ESRRG) was highest in pups, while genes associated with inflammation (HMOX2, NRF2, IL1B) did not vary with age or sex. Blood expression of genes involved in regulation of inflammation (IL1B, NRF2, BVR, IL10) was highest in pups, while HMOX1, HMOX2 and pro-inflammatory markers (TLR4, CCL4, PRDX1, TNFA) did not vary with age. We propose that ontogenetic upregulation of baseline HMOX1 expression in skeletal muscle of NES may, in part, underlie increases in CO levels and expression of genes encoding antioxidant enzymes. HMOX2, in turn, may play a role in regulating inflammation related to ischemia and reperfusion in muscle and circulating immune cells. Our data suggest putative ontogenetic mechanisms that may enable phocid pups to transition to a deep-diving lifestyle, including high baseline expression of genes associated with mitochondrial biogenesis and immune system activation during postnatal development and increased expression of genes associated with protection from lipid peroxidation in adulthood.

Effects of dietary ferulic acid supplementation on growth performance and skeletal muscle fiber type conversion in weaned piglets

BACKGROUND

Ferulic acid (FA) is a common polyphenolic compound. The purpose of this study was to explore the effect of dietary FA supplementation on growth performance and muscle fiber type conversion in weaned piglets. In this study, eighteen 21-day-old DLY (Duroc × Landrace × Yorkshire) weaned piglets were randomly divided into control, 0.05% FA, and 0.45% FA groups.

RESULTS

Our study showed that dietary FA supplementation had no effect on growth performance, but it could upregulate the expression of slow myosin heavy chain (MyHC) protein, increase the activities of succinic dehydrogenase and malate dehydrogenase, and downregulate the expression of fast MyHC protein. Dietary FA supplementation also increased the expression levels of phosphorylated AMP-activated protein kinase, sirtuin 1 (Sirt1), peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α), myocyte enhancer factor 2C, and troponin I-SS, increased the proportion of slow-twitch fiber, and decreased the proportion of fast-twitch fiber. In addition, our results showed that dietary FA supplementation increased the messenger RNA abundance of mitochondrial nuclear transcription genes, including ATP synthase membrane subunit c locus 1, cytochrome oxidase subunit 1, nuclear respiratory factor 1, mitochondrial transcription factor A, mitochondrial transcription factor B1, and cytochrome c.

CONCLUSION

We provided the first evidence that FA could promote muscle fiber type conversion from fast-twitch to slow-twitch via the Sirt1/AMP-activated protein kinase/PGC-1α signaling pathway and could improve the mitochondrial function in weaned piglets. This means that FA can be used as a dietary supplement to improve the quality of pork. © 2021 Society of Chemical Industry.

Allostatic hypermetabolic response in PGC1α/β heterozygote mouse despite mitochondrial defects

Aging, obesity, and insulin resistance are associated with low levels of PGC1α and PGC1β coactivators and defective mitochondrial function. We studied mice deficient for PGC1α and PGC1β [double heterozygous (DH)] to investigate their combined pathogenic contribution. Contrary to our hypothesis, DH mice were leaner, had increased energy dissipation, a pro-thermogenic profile in BAT and WAT, and improved carbohydrate metabolism compared to wild types. WAT showed upregulation of mitochondriogenesis/oxphos machinery upon allelic compensation of PGC1α4 from the remaining allele. However, DH mice had decreased mitochondrial OXPHOS and biogenesis transcriptomes in mitochondria-rich organs. Despite being metabolically healthy, mitochondrial defects in DH mice impaired muscle fiber remodeling and caused qualitative changes in the hepatic lipidome. Our data evidence first the existence of organ-specific compensatory allostatic mechanisms are robust enough to drive an unexpected phenotype. Second, optimization of adipose tissue bioenergetics is sufficient to maintain a healthy metabolic phenotype despite a broad severe mitochondrial dysfunction in other relevant metabolic organs. Third, the decrease in PGC1s in adipose tissue of obese and diabetic patients is in contrast with the robustness of the compensatory upregulation in the adipose of the DH mice.

Identifying Codium fragile extract components and their effects on muscle weight and exercise endurance

Codium fragile (CF) is a type of green algae consumed as kimchi in Asia. UPLC-QTOF-MS/MS analysis showed that CF contain lysophosphatidyl choline, canthaxanthin, retinoic acid, α-tocopherol, and unsaturated fatty acids, which reportedly improve skeletal muscle health. However, the effect of CF on skeletal muscle mass and function remains to be elucidated. In mice fed with CF extracts, exercise endurance and muscle weight increased. CF extracts enhanced protein synthesis and myogenic differentiation through the mTORC1 pathway. CF extracts also promoted oxidative muscle fiber formation and mitochondrial biogenesis through the PGC-1α-related signaling pathway. Upregulation of PGC-1α by CF extracts was abolished by EX527 SIRT1 inhibitor treatment. Changed signaling molecules in the CF extracts were partially regulated by canthaxanthin, a new compound in CF extracts, suggesting that canthaxanthin contribute synergistically to the effect of CF extracts. Therefore, CF is a potential food source for sport nutrition or prevention of sarcopenia.

Sesamol promotes browning of white adipocytes to ameliorate obesity by inducing mitochondrial biogenesis and inhibition mitophagy via β3-AR/PKA signaling pathway

Background

Obesity is defined as an imbalance between energy intake and expenditure, and it is a serious risk factor of non-communicable diseases. Recently many studies have shown that promoting browning of white adipose tissue (WAT) to increase energy consumption has a great therapeutic potential for obesity. Sesamol, a lignan from sesame oil, had shown potential beneficial functions on obesity treatment.

Objective

In this study, we used C57BL/6J mice and 3T3-L1 adipocytes to investigate the effects and the fundamental mechanisms of sesamol in enhancing the browning of white adipocytes to ameliorate obesity.

Methods

Sixteen-week-old C57BL/6J male mice were fed high-fat diet (HFD) for 8 weeks to establish the obesity models. Half of the obese mice were administered with sesamol (100 mg/kg body weight [b.w.]/day [d] by gavage for another 8 weeks. Triacylglycerol (TG) and total cholesterol assay kits were used to quantify serum TG and total cholesterol (TC). Oil red O staining was used to detect lipid droplet in vitro. Mito-Tracker Green was used to detect the mitochondrial content. Quantitative reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the levels of beige-specific genes. Immunoblotting was used to detect the proteins involved in beige adipocytes formation.

Results

Sesamol decreased the content of body fat and suppressed lipid accumulation in HFD-induced obese mice. In addition, sesamol significantly upregulated uncoupling protein-1 (UCP1) protein in adipose tissue. Further research found that sesamol also significantly activated the browning program in mature 3T3-L1 adipocytes, manifested by the increase in beige-specific genes and proteins. Moreover, sesamol greatly increased mitochondrial biogenesis, as proved by the upregulated protein levels of mitochondrial biogenesis, and the inhibition of the proteins associated with mitophagy. Furthermore, β3-adrenergic receptor (β3-AR), protein kinase A-C (PKA-C) and Phospho-protein kinase A (p-PKA) substrate were elevated by sesamol, and these effects were abolished by the pretreatment of antagonists β3-AR.

Conclusion

Sesamol promoted browning of white adipocytes by inducing mitochondrial biogenesis and inhibiting mitophagy through the β3-AR/PKA pathway. This preclinical data promised the potential to consider sesamol as a metabolic modulator of HFD-induced obesity.

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.

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.

Upstream Regulator Analysis of Wooden Breast Myopathy Proteomics in Commercial Broilers and Comparison to Feed Efficiency Proteomics in Pedigree Male Broilers

In an effort to understand the apparent trade-off between the continual push for growth performance and the recent emergence of muscle pathologies, shotgun proteomics was conducted on breast muscle obtained at ~8 weeks from commercial broilers with wooden breast (WB) myopathy and compared with that in pedigree male (PedM) broilers exhibiting high feed efficiency (FE). Comparison of the two proteomic datasets was facilitated using the overlay function of Ingenuity Pathway Analysis (IPA) (Qiagen, CA, USA). We focused on upstream regulator analysis and disease-function analysis that provides predictions of activation or inhibition of molecules based on (a) expression of downstream target molecules, (b) the IPA scientific citation database. Angiopoeitin 2 (ANGPT2) exhibited the highest predicted activation Z-score of all molecules in the WB dataset, suggesting that the proteomic landscape of WB myopathy would promote vascularization. Overlaying the FE proteomics data on the WB ANGPT2 upstream regulator network presented no commonality of protein expression and no prediction of ANGPT2 activation. Peroxisome proliferator coactivator 1 alpha (PGC1α) was predicted to be inhibited, suggesting that mitochondrial biogenesis was suppressed in WB. PGC1α was predicted to be activated in high FE pedigree male broilers. Whereas RICTOR (rapamycin independent companion of mammalian target of rapamycin) was predicted to be inhibited in both WB and FE datasets, the predictions were based on different downstream molecules. Other transcription factors predicted to be activated in WB muscle included epidermal growth factor (EGFR), X box binding protein (XBP1), transforming growth factor beta 1 (TGFB1) and nuclear factor (erythroid-derived 2)-like 2 (NFE2L2). Inhibitions of aryl hydrocarbon receptor (AHR), AHR nuclear translocator (ARNT) and estrogen related receptor gamma (ESRRG) were also predicted in the WB muscle. These findings indicate that there are considerable differences in upstream regulators based on downstream protein expression observed in WB myopathy and in high FE PedM broilers that may provide additional insight into the etiology of WB myopathy.

Cybrid Model Supports Mitochondrial Genetic Effect on Pig Litter Size

In pigs, mitochondrial DNA (mtDNA) polymorphism and the correlation to reproductive performance across breeds and individuals have been largely reported, however, experimental proof has never been provided. In this study, we analyzed 807 sows for correlation of total number born (TNB) and mitotype, which presented the maximum of 1.73 piglets for mtDNA contribution. Cybrid models representing different mitotypes were generated for identification of the mtDNA effect. Results indicated significant differences on cellular and molecular characteristics among cybrids, including energy metabolic traits, mtDNA copy numbers and transcriptions, mRNA and protein expressions on mitochondrial biogenesis genes and reproduction-related genes. Referring to mitotypes, the cybrids with prolific mitotypes presented significantly higher oxygen consumption rate (OCR) productions, mtDNA transcriptions and copy numbers than those with common mitotypes, while both mRNA and protein expressions of PPARA, TFAM, ER1, ER2, and ESRRG in prolific cybrids were significantly higher than those with common mitotypes. Cybrid models reflected the mtDNA effect on pig litter size, suggesting the potential application of mtDNA polymorphism in pig selection and breeding practices.

Mitochondrial rewiring through mitophagy and mitochondrial biogenesis in cancer stem cells: A potential target for anti-CSC cancer therapy

Cancer stem cells (CSCs) are distinct subpopulations of cancer cells with stem cell-like abilities and are more resilient to chemotherapy, causing tumor relapse. Mitophagy, a selective form of autophagy, removes damaged unwanted mitochondria from cells through a lysosome-based degradation pathway to maintain cellular homeostasis. CSCs use mitophagy as a chief survival response mechanism for their growth, propagation, and tumorigenic ability. Mitochondrial biogenesis is a crucial cellular event replacing damaged mitochondria through the coordinated regulation of several transcription factors to achieve the bioenergetic demands of the cell. Because of the high mitochondrial content in CSCs, mitochondrial biogenesis is an interesting target to address the resistance mechanisms of anti-CSC therapy. However, to what extent both mitophagy and mitochondrial biogenesis are vital in promoting stemness, metabolic reprogramming, and drug resistance in CSCs has yet to be established. Therefore, in this review, we focus on understanding the interesting aspects of mitochondrial rewiring that involve mitophagy and mitochondrial biogenesis in CSCs. We also discuss their coordinated regulation in the elimination of CSCs, with respect to stemness and differentiation of the CSC phenotype, and the different aspects of tumorigenesis such as cancer initiation, progression, resistance, and tumor relapse. Finally, we address several other unanswered questions relating to targeted anti-CSC cancer therapy, which improves patient survival.

Regulation of the expression of the estrogen related receptors (ERRs)

Estrogen related receptors (ERRα, β and γ in mammals) are orphan members of the nuclear receptor superfamily acting as transcription factors. ERRs are expressed in several tissues and cells and they display various physiological and pathological functions, controlling, amongst others and depending on the receptor, bone homeostasis, energy metabolism, embryonic stem cell pluripotency, and cancer progression. In contrast to classical nuclear receptors, the activities of the ERRs are not controlled by a natural ligand. Regulation of their activities thus rely on other means such as post-translational modification or availability of transcriptional co-regulators. In addition, regulation of their mere expression under given physiological or pathological conditions is a particularly important level of control. Here we discuss the mechanisms involved in the regulation of ERRs expression and the reported means to impact on it using pharmacological approaches.

Carnitine palmitoyltransferase 1C reverses cellular senescence of MRC-5 fibroblasts via regulating lipid accumulation and mitochondrial function

Cellular senescence, a state of growth arrest, is involved in various age-related diseases. We previously found that carnitine palmitoyltransferase 1C (CPT1C) is a key regulator of cancer cell proliferation and senescence, but it is unclear whether CPT1C plays a similar role in normal cells. Therefore, this study aimed to investigate the role of CPT1C in cellular proliferation and senescence of human embryonic lung MRC-5 fibroblasts and the involved mechanisms. The results showed that CPT1C could reverse the cellular senescence of MRC-5 fibroblasts, as evidenced by reduced senescence-associated β-galactosidase activity, downregulated messenger RNA (mRNA) expression of senescence-associated secretory phenotype factors, and enhanced bromodeoxyuridine incorporation. Lipidomics analysis further revealed that CPT1C gain-of-function reduced lipid accumulation and reversed abnormal metabolic reprogramming of lipids in late MRC-5 cells. Oil Red O staining and Nile red fluorescence also indicated significant reduction of lipid accumulation after CPT1C gain-of-function. Consequently, CPT1C gain-of-function significantly reversed mitochondrial dysfunction, as evaluated by increased adenosine triphosphate synthesis and mitochondrial transmembrane potential, decreased radical oxygen species, upregulated respiratory capacity and mRNA expression of genes related to mitochondrial function. In summary, CPT1C plays a vital role in MRC-5 cellular proliferation and can reverse MRC-5 cellular senescence through the regulation of lipid metabolism and mitochondrial function, which supports the role of CPT1C as a novel target for intervention into cellular proliferation and senescence and suggests CPT1C as a new strategy for antiaging.

Polyphenols as Caloric Restriction Mimetics Regulating Mitochondrial Biogenesis and Mitophagy

The tight coordination between mitochondrial biogenesis and mitophagy can be dysregulated during aging, critically influencing whole-body metabolism, health, and lifespan. To date, caloric restriction (CR) appears to be the most effective intervention strategy to improve mitochondrial turnover in aging organisms. The development of pharmacological mimetics of CR has gained attention as an attractive and potentially feasible approach to mimic the CR phenotype. Polyphenols, ubiquitously present in fruits and vegetables, have emerged as well-tolerated CR mimetics that target mitochondrial turnover. Here, we discuss the molecular mechanisms that orchestrate mitochondrial biogenesis and mitophagy, and we summarize the current knowledge of how CR promotes mitochondrial maintenance and to what extent different polyphenols may mimic CR and coordinate mitochondrial biogenesis and clearance.

A Critical Role for Estrogen-Related Receptor Signaling in Cardiac Maturation

RATIONALE

The heart undergoes dramatic developmental changes during the prenatal to postnatal transition, including maturation of cardiac myocyte energy metabolic and contractile machinery. Delineation of the mechanisms involved in cardiac postnatal development could provide new insight into the fetal shifts that occur in the diseased heart and unveil strategies for driving maturation of stem cell-derived cardiac myocytes.

OBJECTIVE

To delineate transcriptional drivers of cardiac maturation.

METHODS AND RESULTS

We hypothesized that ERR (estrogen-related receptor) α and γ, known transcriptional regulators of postnatal mitochondrial biogenesis and function, serve a role in the broader cardiac maturation program. We devised a strategy to knockdown the expression of ERRα and γ in heart after birth (pn-csERRα/γ [postnatal cardiac-specific ERRα/γ]) in mice. With high levels of knockdown, pn-csERRα/γ knockdown mice exhibited cardiomyopathy with an arrest in mitochondrial maturation. RNA sequence analysis of pn-csERRα/γ knockdown hearts at 5 weeks of age combined with chromatin immunoprecipitation with deep sequencing and functional characterization conducted in human induced pluripotent stem cell-derived cardiac myocytes (hiPSC-CM) demonstrated that ERRγ activates transcription of genes involved in virtually all aspects of postnatal developmental maturation, including mitochondrial energy transduction, contractile function, and ion transport. In addition, ERRγ was found to suppress genes involved in fibroblast activation in hearts of pn-csERRα/γ knockdown mice. Disruption of Esrra and Esrrg in mice during fetal development resulted in perinatal lethality associated with structural and genomic evidence of an arrest in cardiac maturation, including persistent expression of early developmental and noncardiac lineage gene markers including cardiac fibroblast signatures. Lastly, targeted deletion of ESRRA and ESRRG in hiPSC-CM derepressed expression of early (transcription factor 21 or TCF21) and mature (periostin, collagen type III) fibroblast gene signatures.

CONCLUSIONS

ERRα and γ are critical regulators of cardiac myocyte maturation, serving as transcriptional activators of adult cardiac metabolic and structural genes, an.d suppressors of noncardiac lineages including fibroblast determination.

Undaria pinnatifida extract feeding increases exercise endurance and skeletal muscle mass by promoting oxidative muscle remodeling in mice

Dietary habits can alter the skeletal muscle performance and mass, and Undaria pinnatifida extracts are considered a potent candidate for improving the muscle mass and function. Therefore, in this study, we aimed to assess the effect of U pinnatifida extracts on exercise endurance and skeletal muscle mass. C57BL/6 mice were fed a 0.25% U pinnatifida extract-containing diet for 8 weeks. U pinnatifida extract-fed mice showed increased running distance, total running time, and extensor digitorum longus and gastrocnemius muscle weights. U pinnatifida extract supplementation upregulated the expression of myocyte enhancer factor 2C, oxidative muscle fiber markers such as myosin heavy chain 1 (MHC1), and oxidative biomarkers in the gastrocnemius muscles. Compared to the controls, U pinnatifida extract-fed mice showed larger mitochondria and increased gene and protein expression of molecules involved in mitochondrial biogenesis and oxidative phosphorylation, including nuclear respiratory factor 2 and mitochondrial transcription factor A. U pinnatifida extract supplementation also increased the mRNA expression of angiogenesis markers, including VEGFa, VEGFb, FGF1, angiopoietin 1, and angiopoietin 2, in the gastrocnemius muscles. Importantly, U pinnatifida extracts upregulated the estrogen-related receptor γ and peroxisome proliferator-activated receptor gamma co-activator 1-alpha (PGC-1α)/AMP-activated protein kinase (AMPK)/sirtuin 1 (SIRT1) networks, which are partially increased by fucoxanthin, hesperetin, and caffeic acid treatments. Collectively, U pinnatifida extracts enhance mitochondrial biogenesis, increase oxidative muscle fiber, and promote angiogenesis in skeletal muscles, resulting in improved exercise capacity and skeletal muscle mass. These effects are attributable to fucoxanthin, hesperetin, and caffeic acid, bioactive components of U pinnatifida extracts.

Natural products, PGC-1 , and Duchenne muscular dystrophy

Peroxisome proliferator-activated receptor γ (PPARγ) is a transcriptional coactivator that binds to a diverse range of transcription factors. PPARγ coactivator 1 (PGC-1) coactivators possess an extensive range of biological effects in different tissues, and play a key part in the regulation of the oxidative metabolism, consequently modulating the production of reactive oxygen species, autophagy, and mitochondrial biogenesis. Owing to these findings, a large body of studies, aiming to establish the role of PGC-1 in the neuromuscular system, has shown that PGC-1 could be a promising target for therapies targeting neuromuscular diseases. Among these, some evidence has shown that various signaling pathways linked to PGC-1α are deregulated in muscular dystrophy, leading to a reduced capacity for mitochondrial oxidative phosphorylation and increased reactive oxygen species (ROS) production. In the light of these results, any intervention aimed at activating PGC-1 could contribute towards ameliorating the progression of muscular dystrophies. PGC-1α is influenced by different patho-physiological/pharmacological stimuli. Natural products have been reported to display modulatory effects on PPARγ activation with fewer side effects in comparison to synthetic drugs. Taken together, this review summarizes the current knowledge on Duchenne muscular dystrophy, focusing on the potential effects of natural compounds, acting as regulators of PGC-1α.

Recent advances in acute kidney injury and its consequences and impact on chronic kidney disease

PURPOSE OF REVIEW

Acute kidney injury (AKI) remains a major unmet medical need and associates with high morbidity, mortality, and healthcare costs. Among survivors, long-term outcomes of AKI can include development of chronic kidney disease (CKD) or progression of preexisting CKD. In this review, we focus on ongoing efforts by the AKI community to understand the human AKI to CKD continuum, with an emphasis on the cellular stress responses that underlie AKI and the maladaptive responses that persist in the acute-to-chronic phase. The emphasis is on work that has been published in the past year in this rapidly expanding field.

RECENT FINDINGS

Recent studies in preclinical models highlight the importance of mitochondrial dysfunction, cell death, and inflammation on the underlying pathogenesis of AKI. These pathogenic mechanisms can resolve with adaptive kidney repair but persist in maladaptive repair that leads to progressive chronic disease. The complexity and interconnections of these pathways involve cross-talk between the tubular epithelium, endothelium, and interstitial compartments.

SUMMARY

Approaches which lessen or counteract these cellular responses represent novel strategies to prevent AKI and stop or slow down the progression to CKD.

Regulation of PGC-1α expression by a GSK-3β-TFEB signaling axis in skeletal muscle

OBJECTIVE

In muscle cells, the peroxisome proliferator-activated receptor γ co-activator 1 (PGC-1) signaling network, which has been shown to be disturbed in the skeletal muscle in several chronic diseases, tightly controls mitochondrial biogenesis and oxidative substrate metabolism. Previously, we showed that inactivation of glycogen synthase kinase (GSK)-3β potently increased Pgc-1α abundance and oxidative metabolism in skeletal muscle cells. The current study aims to unravel the molecular mechanism driving the increase in Pgc-1α mediated by GSK-3β inactivation.

METHODS

GSK-3β was inactivated genetically or pharmacologically in C2C12 myotubes and the requirement of transcription factors known to be involved in Pgc-1α transcription for increases in Pgc-1α abundance mediated by inactivation of GSK-3β was examined.

RESULTS

Enhanced PGC-1α promoter activation after GSK-3β inhibition suggested a transcriptionally-controlled mechanism. While myocyte enhancer factor (MEF)2 transcriptional activity was unaltered, GSK-3β inactivation increased the abundance and activity of the transcription factors estrogen-related receptor (ERR)α and ERRγ. Pharmacological inhibition or knock-down of ERRα and ERRγ however failed to prevent increases in Pgc-1α mRNA mediated by GSK-3β inactivation. Interestingly, GSK-3β inactivation activated transcription factor EB (TFEB), evidenced by decreased phosphorylation and enhanced nuclear localization of the TFEB protein. Moreover, knock-down of TFEB completely prevented increases in Pgc-1α gene expression, PGC-1α promoter activity and PGC-1α protein abundance induced by GSK-3β inactivation. Furthermore, mutation of a specific TFEB binding site on the PGC-1α promoter blocked promoter activation upon inhibition of GSK-3β.

CONCLUSIONS

In skeletal muscle, GSK-3β inactivation causes dephosphorylation and nuclear translocation of TFEB resulting in TFEB-dependent induction of Pgc-1α expression.

The impact of acute and chronic exercise on Nrf2 expression in relation to markers of mitochondrial biogenesis in human skeletal muscle

PURPOSE

To examine the relationship between changes in nuclear factor erythroid 2-related factor 2 (Nrf2) expression and markers of mitochondrial biogenesis in acutely and chronically exercised human skeletal muscle.

METHODS

The impact of acute submaximal endurance (END) and supramaximal interval (Tabata) cycling on the upregulation of Nrf2 (and its downstream targets), nuclear respiratory factor-1 (NRF-1) and mitochondrial transcription factor A (TFAM) mRNA expression was examined in healthy young males (n = 10). The relationship between changes in citrate synthase (CS) maximal activity and the protein content of Nrf2, heme oxygenase 1 (HO-1), NRF-1, and TFAM was also investigated following 4 weeks of Tabata in a separate group of males (n = 21).

RESULTS

Nrf2, NRF-1, and HO-1 mRNA expression increased after acute exercise (p < 0.05), whereas the increase in superoxide dismutase 2 (SOD2) mRNA expression approached significance (p = 0.08). Four weeks of Tabata increased CS activity and Nrf2, NRF-1, and TFAM protein content (p < 0.05), but decreased HO-1 protein content (p < 0.05). Training-induced changes in Nrf2 protein were strongly correlated with NRF-1 (r = 0.63, p < 0.01). When comparing protein content changes between individuals with the largest (HI: + 23%) and smallest (LO: - 1%) observed changes in CS activity (n = 8 each), increases in Nrf2 and TFAM protein content were apparent in the HI group only (p < 0.02) with medium-to-large effect sizes for between-group differences in changes in Nrf2 (η_p²₌0.15) and TFAM (η_p² = 0.12) protein content.

CONCLUSION

Altogether, our findings support a potential role for Nrf2 in exercise-induced mitochondrial biogenesis in human skeletal muscle.

The 5-hydroxytryptamine receptor 1F stimulates mitochondrial biogenesis and angiogenesis in endothelial cells

A hallmark of acute kidney injury (AKI) is vascular rarefication and mitochondrial dysfunction. Promoting vascular recovery following AKI could facilitate kidney repair as the vasculature is responsible for oxygen and nutrient delivery to extravascular tissues. Little is known about mitochondrial biogenesis (MB) in endothelial cells, and the role of 5-HT1F receptor signaling in MB has only been studied in epithelial cells. Our laboratory has shown that stimulating MB through the 5-HT1F receptor promotes recovery from AKI and that 5-HT1F receptor knockout mice have decreased MB and poor renal recovery. We hypothesized that the 5-HT1F receptor plays a role in vascular homeostasis and mediates MB in renal endothelial cells. 5-HT1F receptor knockout mice had decreased renal vascular content, as evidenced by decreased CD31+ endothelial cells and αSMA+ vessels. Human glomerular endothelial cells (HEC) and mouse glomerular endothelial cells (MEC) expressed the 5-HT1F receptor. Treatment of HEC and MEC with 5-HT1F receptor agonists LY344864 or lasmiditan (0-500 nM) induced MB as evidenced by maximal mitochondrial respiration, a marker of MB. HEC and MEC treated with lasmiditan or LY344864 also had increased nuclear- and mitochondrial-encoded proteins (PGC1α, COX-1, and VDAC), and mitochondrial number, confirming MB. Treatment of HEC with LY344864 or lasmiditan enhanced endothelial branching morphogenesis and migration, indicating a role for 5-HT1F receptor stimulation in angiogenic pathways. We propose that stimulation of 5-HT1F receptor is involved in MB in endothelial cells and that treatment with 5-HT1F receptor agonists could restore stimulate repair and recovery following kidney injury.

Genome-Wide Analysis of Low Dose Bisphenol-A (BPA) Exposure in Human Prostate Cells

Endocrine disrupting compounds (EDCs) have the potential to cause adverse effects on wild-life and human health. Two important EDCs are the synthetic estrogen 17α-ethynylestradiol (EE2) and bisphenol-A (BPA) both of which are xenoestrogens (XEs) as they bind the estrogen receptor and dis-rupt estrogen physiology in mammals and other vertebrates. In the recent years the influence of XEs on oncogenes, specifically in relation to breast and prostate cancer has been the subject of considerable study.

Dynamic enhancers control skeletal muscle identity and reprogramming

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 PGC1α-driven epigenomic programs direct partially convergent transcriptional networks.

Effects of long-term feeding of rapeseed meal on skeletal muscle transcriptome, production efficiency and meat quality traits in Norwegian Landrace growing-finishing pigs

This study was performed to investigate the effects of dietary inclusion of 20% rapeseed meal (RSM) as an alternative to soybean meal (SBM) in a three-month feeding experiment with growing finishing pigs. Dietary alteration affected growth performance, several carcass traits and transcriptional responses in the skeletal muscle, but did not affect measured meat quality traits. In general, pigs fed the RSM test diet exhibited reduced growth performance compared to pigs on SBM control diet. Significant transcriptional changes in the skeletal muscle of growing pigs fed RSM diet were likely the consequence of an increased amount of fiber and higher polyunsaturated fatty acids, and presence of bioactive phytochemicals, such as glucosinolates. RNAseq pipeline using Tophat2-Cuffdiff identified 57 upregulated and 63 downregulated genes in RSM compared to SBM pigs. Significantly enriched among downregulated pathways was p53-mediated signalling involved in cellular proliferation, while activation of negative growth regulators (IER5, KLF10, BTG2, KLF11, RETREG1, PRUNE2) in RSM fed pigs provided further evidence for reduced proliferation and increased cellular death, in accordance with the observed reduction in performance traits. Upregulation of well-known metabolic controllers (PDK4, UCP3, ESRRG and ESRRB), involved in energy homeostasis (glucose and lipid metabolism, and mitochondrial function), suggested less available energy and nutrients in RSM pigs. Furthermore, several genes supported more pronounced proteolysis (ABTB1, OTUD1, PADI2, SPP1) and reduced protein synthesis (THBS1, HSF4, AP1S2) in RSM muscle tissue. In parallel, higher levels of NR4A3, PDK4 and FGF21, and a drop in adropin, ELOVL6 and CIDEC/FSP27 indicated increased lipolysis and fatty acid oxidation, reflective of lower dressing percentage. Finally, pigs exposed to RSM showed greater expression level of genes responsive to oxidative stress, indicated by upregulation of GPX1, GPX2, and TXNIP.

Looking beyond PGC-1α: emerging regulators of exercise-induced skeletal muscle mitochondrial biogenesis and their activation by dietary compounds

Despite its widespread acceptance as the "master regulator" of mitochondrial biogenesis (i.e., the expansion of the mitochondrial reticulum), peroxisome proliferator-activated receptor (PPAR) gamma coactivator-1 alpha (PGC-1α) appears to be dispensable for the training-induced augmentation of skeletal muscle mitochondrial content and respiratory function. In fact, a number of regulatory proteins have emerged as important players in skeletal muscle mitochondrial biogenesis and many of these proteins share key attributes with PGC-1α. In an effort to move past the simplistic notion of a "master regulator" of mitochondrial biogenesis, we highlight the regulatory mechanisms by which nuclear factor erythroid 2-related factor 2 (Nrf2), estrogen-related receptor gamma (ERRγ), PPARβ, and leucine-rich pentatricopeptide repeat-containing protein (LRP130) may contribute to the control of skeletal muscle mitochondrial biogenesis. We also present evidence supporting/refuting the ability of sulforaphane, quercetin, and epicatechin to promote skeletal muscle mitochondrial biogenesis and their potential to augment mitochondrial training adaptations. Targeted activation of specific pathways by these compounds may allow for greater mechanistic insight into the molecular pathways controlling mitochondrial biogenesis in human skeletal muscle. Dietary activation of mitochondrial biogenesis may also be useful in clinical populations with basal reductions in mitochondrial protein content, enzyme activities, and/or respiratory function as well as individuals who exhibit a blunted skeletal muscle responsiveness to contractile activity. Novelty The existence of redundant pathways leading to mitochondrial biogenesis refutes the simplistic notion of a "master regulator" of mitochondrial biogenesis. Dietary activation of specific pathways may provide greater mechanistic insight into the exercise-induced mitochondrial biogenesis in human skeletal muscle.

The PGC-1/ERR network and its role in precision oncology

Transcriptional regulators include a superfamily of nuclear proteins referred to as co-activators and co-repressors, both of which are involved in controlling the functions of several nuclear receptors (NRs). The Nuclear Receptor Signaling Atlas (NURSA) has cataloged the composition of NRs, co-regulators, and ligands present in the human cell and their effort has been identified in more than 600 potential molecules. Given the importance of co-regulators in steroid, retinoid, and thyroid hormone signaling networks, hypothesizing that NRs/co-regulators are implicated in a wide range of pathologies are tempting. The co-activators known as peroxisome proliferator-activated receptor gamma co-activator 1 (PGC-1) and their key nuclear partner, the estrogen-related receptor (ERR), are emerging as pivotal transcriptional signatures that regulate an extremely broad repertoire of mitochondrial and metabolic genes, making them very attractive drug targets for cancer. Several studies have provided an increased understanding of the functional and structural biology of nuclear complexes. However, more comprehensive work is needed to create different avenues to explore the therapeutic potential of NRs/co-activators in precision oncology. Here, we discuss the emerging data associated with the structure, function, and molecular biology of the PGC-1/ERR network and address how the concepts evolving from these studies have deepened our understanding of how to develop more effective treatment strategies. We present an overview that underscores new biological insights into PGC-1/ERR to improve cancer outcomes against therapeutic resistance. Finally, we discuss the importance of exploiting new technologies such as single-particle cryo-electron microscopy (cryo-EM) to develop a high-resolution biological structure of PGC-1/ERR, focusing on novel drug discovery for precision oncology.

Metabolic regulation of exercise-induced angiogenesis

Skeletal muscle relies on an ingenious network of blood vessels, which ensures optimal oxygen and nutrient supply. An increase in muscle vascularization is an early adaptive event to exercise training, but the cellular and molecular mechanisms underlying exercise-induced blood vessel formation are not completely clear. In this review, we provide a concise overview on how exercise-induced alterations in muscle metabolism can evoke metabolic changes in endothelial cells (ECs) that drive muscle angiogenesis. In skeletal muscle, angiogenesis can occur via sprouting and splitting angiogenesis and is dependent on vascular endothelial growth factor (VEGF) signaling. In the resting muscle, VEGF levels are controlled by the estrogen-related receptor γ (ERRγ). Upon exercise, the transcriptional coactivator peroxisome-proliferator-activated receptor-γ coactivator-1α (PGC1α) orchestrates several adaptations to endurance exercise within muscle fibers and simultaneously promotes transcriptional activation of Vegf expression and increased muscle capillary density. While ECs are highly glycolytic and change their metabolism during sprouting angiogenesis in development and disease, a similar role for EC metabolism in exercise-induced angiogenesis in skeletal muscle remains to be elucidated. Nonetheless, recent studies have illustrated the importance of endothelial hydrogen sulfide and sirtuin 1 (SIRT1) activity for exercise-induced angiogenesis, suggesting that EC metabolic reprogramming may be fundamental in this process. We hypothesize that the exercise-induced angiogenic response can also be modulated by metabolic crosstalk between muscle and the endothelium. Defining the underlying molecular mechanisms responsible for skeletal muscle angiogenesis in response to exercise will yield valuable insight into metabolic regulation as well as the determinants of exercise performance.