Peroxisome proliferator-activated receptor γ coactivator 1 (PGC-1)- and estrogen-related receptor (ERR)-induced regulator in muscle 1 (Perm1) is a tissue-specific regulator of oxidative capacity in skeletal muscle cells

TGFBI R124H mutant allele silencing in granular corneal dystrophy type 2 using topical siRNA delivery

In recent years, success has been achieved in treating several eye conditions with oligonucleotide-based therapies. Herein, we outline the experimentation involved in progressing selection and development of a lead therapeutic siRNA for R124H mutation of TGFBI gene which causes Granular Corneal Dystrophy Type 2 (GCD2/Avellino CD). Firstly, a series of siRNA designs, generated by a gene walk across the R124H TGFBI mutation site, were tested and a lead siRNA identified. The lead siRNA was delivered into an immortalised human corneal epithelial cell line to assess on-target efficacy and off-target effects. The in vivo efficacy of the lead R124H TGFBI siRNA, complexed with Bio-Courier technology, silicon stabilized hybrid lipid nanoparticles (sshLNP), was assessed in a mouse model of GCD2 which expressed the human R124H TGFBI transgene. Following topical siRNA application for 5 consecutive days, expression of the R124H mutant TGFBI transgene was measured and shown to be reduced by 22.4 % (± 15.7 %, p < 0.05). We investigated gene expression in the mouse cornea and showed expression of murine Tgfbi was 20-fold lower than TGFBI in human cornea, and expression of the mutant TGFBI transgene was a further 3-fold lower. This estimated 60-fold lower mutant transgene expression may explain the low frequency of corneal deposits observed in this mouse model, limiting its usefulness to test whether siRNA silencing is capable of phenotypic improvement or regression of GCD2/Avellino corneal dystrophy. We assessed WT TGFBI silencing in human primary corneal epithelial cells (PCEC) derived from human corneal limbal biopsy material, which express TGFBI at a similar level to human corneal biopsy. We demonstrated that a single 100 nM siRNA treatment, delivered by the sshLNP to the primary human corneal epithelial cells, gave 26.6 % (± 6.6 %, p < 0.001) reduction in TGFBI mRNA and a 15.4 % (±10.5 %, p < 0.05 %) reduction in TGFBi protein after 48 h. In consideration of the mutant gene expression levels in existing models of GCD2 disease, an ex vivo model of mutation-expressing primary corneal epithelial cells generated from corneal limbal biopsies from GCD2 patients would be more suitable than existing transgenic mouse models for future pre-clinical work in the development of gene silencing therapies for corneal dystrophies.

Molecular insights into human soleus muscle atrophy development: long-term dry immersion effects on the transcriptomic profile and posttranslational signaling

Muscle disuse results in complex signaling alterations followed by structural and functional changes, such as atrophy, force decrease, and slow-to-fast fiber-type shift. Little is known about human skeletal muscle signaling alterations under long-term muscle disuse. In this study, we describe the effects of 21-day dry immersion on human postural soleus muscle. We performed both transcriptomic analysis and Western blots to describe the states of the key signaling pathways regulating soleus muscle fiber size, fiber type, and metabolism. Twenty-one-day dry immersion resulted in both slow-type and fast-type myofibers atrophy, downregulation of rRNA content, and mTOR signaling. Twenty-one-day dry immersion also leads to slow-to-fast fiber-type and gene expression shift, upregulation of p-eEF2, p-CaMKII, p-ACC content and downregulation of NFATc1 nuclear content. It also caused massive gene expression alterations associated with calcium signaling, cytoskeletal parameters, and downregulated mitochondrial signaling (including fusion, fission, and marker of mitochondrial density).NEW & NOTEWORTHY The main findings of our study are as follows: 1) The soleus slow fibers atrophy after 21-day dry immersion (DI) does not exceed that after 7-day DI; 2) The soleus ubiquitin ligases expression after 21-day DI returns to its initial level; 3) The soleus slow fibers atrophy after 21-day DI is accompanied by a mitochondrial apparatus structural markers decrease; 4) The soleus fibers signaling pathways restructuring process during 21-day DI is carried out in a complex manner.

Oestrogen Receptor Alpha in Myocyte Maintains Muscle Regeneration in Duchenne Muscular Dystrophy

BACKGROUND

Oestrogen receptor alpha (ERα) plays an important role in maintaining mitochondrial function and regulating metabolism in skeletal muscle. However, its alterations and potential mechanisms in Duchenne muscular dystrophy (DMD) remain incompletely understood. In this study, we demonstrated the protective role of ERα in myocyte for skeletal muscle regeneration in mdx mice and explored the therapeutic effects of oestrogen receptor modulators on DMD.

METHODS

DMD patients' biopsies were obtained for histological analysis to explore the expression of ERα. The phenotype of muscle was analysed by histology and molecular biology. The therapeutical effect of different oestrogen receptor modulators was examined in mdx mice treated with fulvestrant (FVT, 20 mg/kg once a week) or oestradiol (E2, 1 mg/kg per day) for 4 weeks. The protective effect of ERα was performed on mdx mice after conditional knockout of ERα in skeletal muscle (ERαmKO mdx mice). Evidence of activation of ERα/oestrogen-related receptor alpha (ERRα)/myogenic differentiation 1 (MyoD) signalling pathway was inspected in the primary myoblasts isolated from mice, and C2C12 cells received intervention with E2/FVT/Esr1-siRNA/Esrra overexpression plasmid.

RESULTS

The ERα expression was increased in DMD patients' triceps (p < 0.05) and mdx mice muscles (p < 0.05). FVT reduced ERα levels in the mdx mice muscles (p < 0.01) but had no significant effect on skeletal muscle regeneration on mdx mice. Compared with mdx mice, E2 reduced the levels of creatine kinase (CK) and lactic dehydrogenase (LDH) (p < 0.001) in serum, enhanced skeletal muscle function, alleviated skeletal muscle atrophy and fibre loss and upregulated the expression of ERα in GAS (p < 0.001) and TA (p < 0.05). The myogenic factors such as myosin heavy chain (MyHC, p < 0.001), myogenin (MyoG, p < 0.05), MyoD (p < 0.05) and ERRα (p < 0.001) were increased in mdx mice GAS with E2. But E2 had no effect on ERαmKO mdx mice. The primary myoblasts and C2C12 were treated with E2 displayed an increased-on myocyte fusion index (p < 0.05), ERα MyoD and ERRα expressions (p < 0.05). The myocytes' fusion index (p < 0.05) and ERα, MyoD and ERRα expression (p < 0.05) were decreased in si-Esr1-transfected C2C12 cells and increased in OE-Esrra-transfected C2C12 cells.

CONCLUSION

We demonstrated that ERα in myocyte exerted a protective effect on skeletal muscle regeneration in DMD patients and mdx mice through the ERα-ERRα-MyoD pathway, which has potential implications for DMD therapy strategies.

Estrogen-related receptor gamma is a regulator of mitochondrial, autophagy, and immediate-early gene programs in spiny projection neurons: Relevance for transcriptional changes in Huntington disease

Mitochondrial dysfunction, transcriptional dysregulation, and protein aggregation are hallmarks of multiple neurodegenerative disorders, including Huntington's disease (HD). Strategies are needed to counteract these processes to restore neuronal health and function in HD. Recent evidence indicates that the transcription factor estrogen-related receptor gamma (ERRγ/Esrrg) is required for normal expression of mitochondrial, synaptic, and autophagy genes in neurons. Further, overexpression of Esrrg in dopaminergic neurons reduces synuclein load in the pre-formed fibril model of synucleinopathy. For these reasons, we sought to understand ERRγ's role in transcriptional regulation in spiny projection neurons (SPNs), one of the neuronal populations vulnerable to transcriptional dysregulation, mitochondrial dysfunction, and protein aggregation in HD. Here, we demonstrate that developmental deletion of Esrrg selectively in SPNs causes a transcriptional pattern consistent with a reduction of Drd1 and Drd2-positive neurons in the mouse dorsolateral striatum. To avoid effects of developmental deletion and explore Esrrg's role within adult SPN populations, we deleted or overexpressed Esrrg in adult SPNs. While overexpression was sufficient to increase the expression of mitochondrial and lysosome-related transcripts, Esrrg deletion surprisingly caused increased expression of immediate-early genes and genes with enrichment of binding sites for transcriptional repressors. In contrast, these genes were downregulated by Esrrg overexpression. Concordantly, Esrrg-deficient mice exhibited lack of amphetamine-induced hyperactivity and further upregulation of immediate-early genes. To determine whether the alterations observed with ERRγ modulation have any relevance for understanding transcriptional changes in SPNs in neurodegeneration, we measured Esrrg and its responsive genes in two mouse models of HD. We found an increase in Esrrg expression in HD models, accompanied by a transcriptional profile with similarities to that observed with Esrrg overexpression, suggesting the existence of an ERRγ-dependent, stress-related response. Altogether, these studies suggest that ERRγ is a key activator of mitochondrial and lysosomal transcripts in SPNs with a potential bi-functional role as a mediator of immediate-early gene repression. Ongoing studies are investigating mechanisms underlying ERRγ's roles in transcriptional activation and repression in SPNs to inform strategies to promote neuroprotective actions of ERRγ in SPNs in HD.

Rostellularia procumbens (L) Nees. extract attenuates adriamycin-induced nephropathy by maintaining mitochondrial dynamics balance via SIRT1/PGC-1α signaling pathway activation

ETHNOPHARMACOLOGICAL RELEVANCE

Rostellularia procumbens (L) Nees. (R. procumbens) is a classical Chinese herbal medicine that has been used for effective treatment of kidney disease for nearly a thousand years in China. Recently, significant progress has been achieved in understanding the abnormal mitochondrial structure and function from chronic kidney disease (CKD). However, the regulatory mechanisms underlying R. procumbens treatment for CKD and its association with dysfunctional mitochondrial function remain elusive.

AIM OF THE STUDY

To study the protective effect of N-butanol extract from R. procumbens (J-NE) on chronic glomerulonephritis (CGN) mice using a mice model and mitochondrial function-related experiments.

MATERIALS AND METHODS

A renal injury mouse model was developed using a single tail vein injection of adriamycin (9 mg/kg). Renal pathology was analyzed through hematoxylin-eosin (HE) staining and transmission electron microscopy (TEM). Cell apoptosis in kidney tissues was analyzed using TUNEL staining. Protein levels were measured via immunohistochemistry (HIF-1α, FN, α-SMA, and Collagen I) and Western blot (Mn-SOD, p-Drp-S637, MFN1, MFN2, OPA1, TFAM, Nrf1, ATP6, SIRT1, and PGC-1α) analysis. UHPLC-MS/MS was used to analyze the presence of bioactive phytocompounds in J-NE.

RESULTS

The results reported that the levels of kidney injury markers (urinary protein, glomerular atrophy, and renal cell apoptosis), mitochondrial dysfunction markers (mitochondrial ultrastructure, Mn-SOD, HIF-1α, FN and α-SMA),mitochondrial dynamic imbalance markers (p-Drp-S637, MFN1, MFN2 and OPA1) and SIRT1/PGC-1α signaling pathway markers (TFAM, Nrf1, ATP6, SIRT1, and PGC-1α) were settled to a significant improvement by the oral administration of J-NE.

CONCLUSIONS

In conclusion, R. procumbens could be able to protect the kidneys from podocyte injury caused mitochondrial dynamics and energy metabolism dysregulation by modulating the SIRT1/PGC-1α signaling pathway.

PERM1 regulates mitochondrial energetics through O-GlcNAcylation in the heart

PERM1 was initially identified as a new downstream target of PGC-1α and ERRs that regulates mitochondrial bioenergetics in skeletal muscle. Subsequently, we and other groups demonstrated that PERM1 is also a positive regulator of mitochondrial bioenergetics in the heart. However, the exact mechanisms of regulatory functions of PERM1 remain poorly understood. O-GlcNAcylation is a post-translational modification of proteins that are regulated by two enzymes: O-GlcNAc transferase (OGT) that adds O-GlcNAc to proteins; O-GlcNAcase (OGA) that removes O-GlcNAc from proteins. O-GlcNAcylation is a powerful signaling mechanism mediating cellular responses to stressors and nutrient availability, which, among other targets, may influence cardiac metabolism. We hypothesized that PERM1 regulates mitochondrial energetics in cardiomyocytes through modulation of O-GlcNAcylation. We found that overexpression of PERM1 decreased the total levels of O-GlcNAcylated proteins, concomitant with decreased OGT and increased OGA expression levels. Luciferase gene reporter assay showed that PERM1 significantly decreases the promoter activity of Ogt without changing the promoter activity of Oga. The downregulation of OGT by PERM1 overexpression was mediated through its interaction with E2F1, a known transcription repressor of Ogt. A deliberate increase of O-GlcNAcylation through Oga silencing in cardiomyocytes decreased the basal and maximal mitochondrial respiration and ATP production rates, all of which were completely restored by PERM1 overexpression. Furthermore, excessive O-GlcNAcylation caused by the loss of PERM1 led to the increase of O-GlcNAcylated PGC-1α, a master regulator of mitochondrial bioenergetics, concurrent with the dissociation of PGC-1α from PPARα, a well-known transcription factor that regulates fatty acid β-oxidation. We conclude that PERM1 positively regulates mitochondrial energetics, in part, via suppressing O-GlcNAcylation in cardiac myocytes.

Metabolic Activity in Human Intermuscular Adipose Tissue Directs the Response of Resident PPARγ+ Macrophages to Fatty Acids

Background/Objectives: Peroxisome proliferator-activated receptor gamma (PPARγ) is a fatty acid-binding transcription activator of the adipokine chemerin. The key role of PPARγ in adipogenesis was established by reports on adipose tissue-resident macrophages that express PPARγ. The present study examined PPARγ+ macrophages in human skeletal muscle tissues, their response to fatty acid (FA) species, and their correlations with age, obesity, adipokine expression, and an abundance of other macrophage phenotypes. Methods: An ex vivo human skeletal muscle model with surgical specimens that were maintained without or with FAs for up to 11 days was utilized. Immunofluorescence analysis was used to detect macrophage phenotypes and mitochondrial activity. Preconfigured arrays were used to detect the expression of 34 different adipokines and chemokines. Results: Data from 14 adults revealed that PPARγ+ macrophages exclusively reside in intermuscular adipose tissue (IMAT), and their abundance correlates with the metabolic status of surrounding adipocytes during tissue maintenance in vitro for 9-11 days. Elevated fatty acid levels lead to significant increases in PPARγ+ populations, which are correlated with the donor's body mass index (BMI). Conclusions: PPARγ+ macrophages represent a distinctly specialized population of regulatory cells that reside within human IMATs in accordance with their metabolic status. Thus, future in-depth studies on IMAT-resident PPARγ+ macrophage action mechanisms will elucidate the role of skeletal muscle in the pathogenesis of human metabolic dysfunction.

PERM1-An Emerging Transcriptional Regulator of Mitochondrial Biogenesis: A Systematic Review

BACKGROUND/OBJECTIVES

This systematic review aims to explore the role of PERM1 across different organisms, tissues, and cellular functions, with a particular focus on its involvement in regulating skeletal muscle mitochondrial biogenesis.

METHODS

This systematic review follows The PRISMA 2020 Statement. We used the Covidence systematic review software for abstract/title screening, full-text review, and data extraction. The review included studies that examined PERM1 expression or activity in skeletal muscle, heart, and adipose tissue and/or cells, from mice, rats, and humans, and involved exercise or disease models. Risk of bias was assessed using the Cochrane Collaboration tool, and the data were extracted and synthesized qualitatively, with bioinformatic analyses performed using the MetaMEx database.

RESULTS

Twenty-one studies were included in our data extraction process, where 10 studies involved humans, 21 involved mice, four involved rats, and 11 involved cells.

CONCLUSIONS

PERM1 in skeletal muscle increases with endurance exercise, affecting muscle function and oxidative metabolism, but its role in humans is not well understood. In cardiac tissue, PERM1 is vital for function and mitochondrial biogenesis purposes, but decreases with disease and pressure overload. Our review synthesizes the current understanding of PERM1's function, raises awareness of its role in mitochondrial regulation, and identifies key areas for future research in the field.

Adeno-associated virus-mediated gene delivery of Perm1 enhances cardiac contractility in mice

Reduced muscle contractility and mitochondrial bioenergetics are the hallmarks of systolic heart failure. There is currently no therapy targeting both. Here, we show that gene delivery of Perm1 via adeno-associated virus (AAV) simultaneously enhances cardiac contractility and mitochondrial biogenesis in C57BL6 mice. Moreover, we found that PERM1 interacts with troponin C (TnC), a key contractile protein in striated muscle, and that AAV-Perm1 led to the upregulation of TnC. This study suggests that gene delivery of Perm1 may be a novel therapeutic approach to treat systolic heart failure by simultaneously restoring cardiac contractility and mitochondrial bioenergetics.NEW & NOTEWORTHY Perm1 gene delivered with AAV9 enhances cardiac contractility in mice, and it is concomitant with the increase of mitochondrial bioenergetics and upregulation of TnC. This is the first study showing that PERM1, previously known as a striated muscle-specific mitochondrial regulator, also positively regulates cardiac contractility.

Unraveling the differential mechanisms of revascularization promoted by MSCs & ECFCs from adipose tissue or umbilical cord in a murine model of critical limb-threatening ischemia

BACKGROUND

Critical limb-threatening ischemia (CLTI) constitutes the most severe manifestation of peripheral artery disease, usually induced by atherosclerosis. CLTI patients suffer from high risk of amputation of the lower extremities and elevated mortality rates, while they have low options for surgical revascularization due to associated comorbidities. Alternatively, cell-based therapeutic strategies represent an effective and safe approach to promote revascularization. However, the variability seen in several factors such as cell combinations or doses applied, have limited their success in clinical trials, being necessary to reach a consensus regarding the optimal "cellular-cocktail" prior further application into the clinic. To achieve so, it is essential to understand the mechanisms by which these cells exert their regenerative properties. Herein, we have evaluated, for the first time, the regenerative and vasculogenic potential of a combination of endothelial colony forming cells (ECFCs) and mesenchymal stem cells (MSCs) isolated from adipose-tissue (AT), compared with ECFCs from umbilical cord blood (CB-ECFCs) and AT-MSCs, in a murine model of CLTI.

METHODS

Balb-c nude mice (n:32) were distributed in four different groups (n:8/group): control shams, and ischemic mice (after femoral ligation) that received 50 µl of physiological serum alone or a cellular combination of AT-MSCs with either CB-ECFCs or AT-ECFCs. Follow-up of blood flow reperfusion and ischemic symptoms was carried out for 21 days, when mice were sacrificed to evaluate vascular density formation. Moreover, the long-term molecular changes in response to CLTI and both cell combinations were analyzed in a proteomic quantitative approach.

RESULTS

AT-MSCs with either AT- or CB-ECFCs, promoted a significant recovery of blood flow in CLTI mice 21 days post-ischemia. Besides, they modulated the inflammatory and necrotic related processes, although the CB group presented the slowest ischemic progression along the assay. Moreover, many proteins involved in the repairing mechanisms promoted by cell treatments were identified.

CONCLUSIONS

The combination of AT-MSCs with AT-ECFCs or with CB-ECFCs promoted similar revascularization in CLTI mice, by restoring blood flow levels, together with the modulation of the inflammatory and necrotic processes, and reduction of muscle damage. The protein changes identified are representative of the molecular mechanisms involved in ECFCs and MSCs-induced revascularization (immune response, vascular repair, muscle regeneration, etc.).

Transcriptional control of cardiac energy metabolism in health and disease: Lessons from animal models

Cardiac ATP production is tightly regulated in order to satisfy the evolving energetic requirements imposed by different cues during health and pathological conditions. In order to sustain high ATP production rates, cardiac cells are endowed with a vast mitochondrial network that is essentially acquired during the perinatal period. Nevertheless, adult cardiac cells also adapt their mitochondrial mass and oxidative function to changes in energy demand and substrate availability by fine-tuning the pathways and mitochondrial machinery involved in energy production. The reliance of cardiac cells on mitochondrial metabolism makes them particularly sensitive to alterations in proper mitochondrial function, so that deficiency in energy production underlies or precipitates the development of heart diseases. Mitochondrial biogenesis is a complex process fundamentally controlled at the transcriptional level by a network of transcription factors and co-regulators, sometimes with partially redundant functions, that ensure adequate energy supply to the working heart. Novel uncovered regulators, such as RIP140, PERM1, MED1 or BRD4 have been recently shown to modulate or facilitate the transcriptional activity of the PGC-1s/ERRs/PPARs regulatory axis, allowing cardiomyocytes to adapt to a variety of physiological or pathological situations requiring different energy provision. In this review, we summarize the current knowledge on the mechanisms that regulate cardiac mitochondrial biogenesis, highlighting the recent discoveries of new transcriptional regulators and describing the experimental models that have provided solid evidence of the relevant contribution of these factors to cardiac function in health and disease.

Mitochondrial quality control in human health and disease

Mitochondria, the most crucial energy-generating organelles in eukaryotic cells, play a pivotal role in regulating energy metabolism. However, their significance extends beyond this, as they are also indispensable in vital life processes such as cell proliferation, differentiation, immune responses, and redox balance. In response to various physiological signals or external stimuli, a sophisticated mitochondrial quality control (MQC) mechanism has evolved, encompassing key processes like mitochondrial biogenesis, mitochondrial dynamics, and mitophagy, which have garnered increasing attention from researchers to unveil their specific molecular mechanisms. In this review, we present a comprehensive summary of the primary mechanisms and functions of key regulators involved in major components of MQC. Furthermore, the critical physiological functions regulated by MQC and its diverse roles in the progression of various systemic diseases have been described in detail. We also discuss agonists or antagonists targeting MQC, aiming to explore potential therapeutic and research prospects by enhancing MQC to stabilize mitochondrial function.

Mapping drug biology to disease genetics to discover drug impacts on the human phenome

Motivation

Medications can have unexpected effects on disease, including not only harmful drug side effects, but also beneficial drug repurposing. These effects on disease may result from hidden influences of drugs on disease gene networks. Then, discovering how biological effects of drugs relate to disease biology can both provide insight into the mechanism of latent drug effects, and can help predict new effects.

Results

Here, we develop Draphnet, a model that integrates molecular data on 429 drugs and gene associations of nearly 200 common phenotypes to learn a network that explains drug effects on disease in terms of these molecular signals. We present evidence that our method can both predict drug effects, and can provide insight into the biology of unexpected drug effects on disease. Using Draphnet to map a drug's known molecular effects to downstream effects on the disease genome, we put forward disease genes impacted by drugs, and we suggest a new grouping of drugs based on shared effects on the disease genome. Our approach has multiple applications, including predicting drug uses and learning drug biology, with implications for personalized medicine.

Availability and implementation

Code to reproduce the analysis is available at https://github.com/RDMelamed/drug-phenome.

Cardiac maturation

The heart undergoes a dynamic maturation process following birth, in response to a wide range of stimuli, including both physiological and pathological cues. This process entails substantial re-programming of mitochondrial energy metabolism coincident with the emergence of specialized structural and contractile machinery to meet the demands of the adult heart. Many components of this program revert to a more "fetal" format during development of pathological cardiac hypertrophy and heart failure. In this review, emphasis is placed on recent progress in our understanding of the transcriptional control of cardiac maturation, encompassing the results of studies spanning from in vivo models to cardiomyocytes derived from human stem cells. The potential applications of this current state of knowledge to new translational avenues aimed at the treatment of heart failure is also addressed.

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.

Mitochondrial DNA Copy Number Drives the Penetrance of Acute Intermittent Porphyria

No published study has investigated the mitochondrial count in patients suffering from acute intermittent porphyria (AIP). In order to determine whether mitochondrial content can influence the pathogenesis of porphyria, we measured the mitochondrial DNA (mtDNA) copy number in the peripheral blood cells of 34 patients and 37 healthy individuals. We found that all AIP patients had a low number of mitochondria, likely as a result of a protective mechanism against an inherited heme synthesis deficiency. Furthermore, we identified a close correlation between disease penetrance and decreases in the mitochondrial content and serum levels of PERM1, a marker of mitochondrial biogenesis. In a healthy individual, mitochondrial count is usually modulated to fit its ability to respond to various environmental stressors and bioenergetic demands. In AIP patients, coincidentally, the phenotype only manifests in response to endogenous and exogenous triggers factors. Therefore, these new findings suggest that a deficiency in mitochondrial proliferation could affect the individual responsiveness to stimuli, providing a new explanation for the variability in the clinical manifestations of porphyria. However, the metabolic and/or genetic factors responsible for this impairment remain to be identified. In conclusion, both mtDNA copy number per cell and mitochondrial biogenesis seem to play a role in either inhibiting or promoting disease expression. They could serve as two novel biomarkers for porphyria.

Myoglobin in Brown Adipose Tissue: A Multifaceted Player in Thermogenesis

Brown adipose tissue (BAT) plays an important role in energy homeostasis by generating heat from chemical energy via uncoupled oxidative phosphorylation. Besides its high mitochondrial content and its exclusive expression of the uncoupling protein 1, another key feature of BAT is the high expression of myoglobin (MB), a heme-containing protein that typically binds oxygen, thereby facilitating the diffusion of the gas from cell membranes to mitochondria of muscle cells. In addition, MB also modulates nitric oxide (NO•) pools and can bind C16 and C18 fatty acids, which indicates a role in lipid metabolism. Recent studies in humans and mice implicated MB present in BAT in the regulation of lipid droplet morphology and fatty acid shuttling and composition, as well as mitochondrial oxidative metabolism. These functions suggest that MB plays an essential role in BAT energy metabolism and thermogenesis. In this review, we will discuss in detail the possible physiological roles played by MB in BAT thermogenesis along with the potential underlying molecular mechanisms and focus on the question of how BAT-MB expression is regulated and, in turn, how this globin regulates mitochondrial, lipid, and NO• metabolism. Finally, we present potential MB-mediated approaches to augment energy metabolism, which ultimately could help tackle different metabolic disorders.

Peroxisom proliferator-activated receptor-γ coactivator-1α in neurodegenerative disorders: A promising therapeutic target

Neurodegenerative disorders (NDDs) are characterized by progressive loss of selectively vulnerable neuronal populations and myelin sheath, leading to behavioral and cognitive dysfunction that adversely affect the quality of life. Identifying novel therapies that attenuate the progression of NDDs would be of significance. Peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α), a widely expressed transcriptional regulator, modulates the expression of genes engaged in mitochondrial biosynthesis, metabolic regulation, and oxidative stress (OS). Emerging evidences point to the strong connection between PGC-1α and NDDs, suggesting its positive impaction on the progression of NDDs. Therefore, it is urgent to gain a deeper and broader understanding between PGC-1α and NDDs. To this end, this review presents a comprehensive overview of PGC-1α, including its basic characteristics, the post-translational modulations, as well as the interacting transcription factors. Secondly, the pathogenesis of PGC-1α in various NDDs, such as Alzheimer's (AD), Parkinson's (PD), and Huntington's disease (HD) is briefly discussed. Additionally, this study summarizes the underlying mechanisms that PGC-1α is neuroprotective in NDDs via regulating neuroinflammation, OS, and mitochondrial dysfunction. Finally, we briefly outline the shortcomings of current NDDs drug therapy, and summarize the functions and potential applications of currently available PGC-1α modulators (activator or inhibitors). Generally, this review updates our insight of the important role of PGC-1α on the development of NDDs, and provides a promising therapeutic target/ drug for the treatment of NDDs.

The role of IGF-1 in exercise to improve obesity-related cognitive dysfunction

Obesity is an important factor that threatens human health. The occurrence of many chronic diseases is related to obesity, and cognitive function decline often occurs with the onset of obesity. With the further prevalence of obesity, it is bound to lead to a wider range of cognitive dysfunction (ORCD). Therefore, it is crucial to suppress ORCD through intervention. In this regard, exercise has been shown to be effective in preventing obesity and improving cognitive function as a non-drug treatment. There is sufficient evidence that exercise has a regulatory effect on a growth factor closely related to cognitive function-insulin-like growth factor 1 (IGF-1). IGF-1 may be an important mediator in improving ORCD through exercise. This article reviews the effects of obesity and IGF-1 on cognitive function and the regulation of exercise on IGF-1. It analyzes the mechanism by which exercise can improve ORCD by regulating IGF-1. Overall, this review provides evidence from relevant animal studies and human studies, showing that exercise plays a role in improving ORCD. It emphasizes the importance of IGF-1, which helps to understand the health effects of exercise and promotes research on the treatment of ORCD.

Loss of NOR-1 represses muscle metabolism through mTORC1-mediated signaling and mitochondrial gene expression in C2C12 myotubes

Gene expression of the NR4A nuclear orphan receptor NOR-1 is reduced in obesity and in human skeletal muscle during disuse. It has been well established that NOR-1 is highly responsive to both aerobic and resistance exercise and NOR-1 overexpression is coincident with a plethora of metabolic benefits. However, it is unclear whether loss of NOR-1 contributes to inappropriate metabolic signaling in skeletal muscle that could lead to insulin resistance. The purpose of this study was to elucidate the impact of NOR-1 deficiency on C2C12 metabolic signaling. Changes in gene expression after siRNA-mediated NOR-1 knockdown in C2C12 myotubes were determined by qPCR and bioinformatic analysis of RNA-Seq data. Our RNA-Seq data identified several metabolic targets regulated by NOR-1 and implicates NOR-1 as a modulator of mTORC1 signaling via Akt-independent mechanisms. Furthermore, pathway analysis revealed NOR-1 knockdown perturbs the insulin resistance and insulin sensitivity pathways. Taken together, these data suggest skeletal muscle NOR-1 deficiency may contribute to altered metabolic signaling that is consistent with metabolic disease. We postulate that strategies that improve NOR-1 may be important to offset the negative impact that inactivity, obesity, and type 2 diabetes have on mitochondria and muscle metabolism.

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.

Pathological implications of cellular stress in cardiovascular diseases

Cellular stress has been a key factor in the development of cardiovascular diseases. Major types of cellular stress such as mitochondrial stress, endoplasmic reticulum stress, hypoxia, and replicative stress have been implicated in clinical complications of cardiac patients. The heart is the central regulator of the body by supplying oxygenated blood throughout the system. Impairment of cellular function could lead to heart failure, myocardial infarction, ischemia, and even stroke. Understanding the effect of these distinct types of cellular stress on cardiac function is crucial for the scientific community to understand and develop novel therapeutic approaches. This review will comprehensively explain the different mechanisms of cellular stress and the most recent findings related to stress-induced cardiac dysfunction.

The Role of Mitophagy in Skeletal Muscle Damage and Regeneration

Mitochondria are cellular organelles that play an essential role in generating the chemical energy needed for the biochemical reactions in cells. Mitochondrial biogenesis, i.e., de novo mitochondria formation, results in enhanced cellular respiration, metabolic processes, and ATP generation, while autophagic clearance of mitochondria (mitophagy) is required to remove damaged or useless mitochondria. The balance between the opposing processes of mitochondrial biogenesis and mitophagy is highly regulated and crucial for the maintenance of the number and function of mitochondria as well as for the cellular homeostasis and adaptations to metabolic demands and extracellular stimuli. In skeletal muscle, mitochondria are essential for maintaining energy homeostasis, and the mitochondrial network exhibits complex behaviors and undergoes dynamic remodeling in response to various conditions and pathologies characterized by changes in muscle cell structure and metabolism, such as exercise, muscle damage, and myopathies. In particular, the involvement of mitochondrial remodeling in mediating skeletal muscle regeneration following damage has received increased attention, as modifications in mitophagy-related signals arise from exercise, while variations in mitochondrial restructuring pathways can lead to partial regeneration and impaired muscle function. Muscle regeneration (through myogenesis) following exercise-induced damage is characterized by a highly regulated, rapid turnover of poor-functioning mitochondria, permitting the synthesis of better-functioning mitochondria to occur. Nevertheless, essential aspects of mitochondrial remodeling during muscle regeneration remain poorly understood and warrant further characterization. In this review, we focus on the critical role of mitophagy for proper muscle cell regeneration following damage, highlighting the molecular mechanisms of the mitophagy-associated mitochondrial dynamics and network reformation.

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.

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.

Resveratrol-Mediated Regulation of Mitochondria Biogenesis-associated Pathways in Neurodegenerative Diseases: Molecular Insights and Potential Therapeutic Applications

Neurodegenerative disorders include different neurological conditions that affect nerve cells, causing the progressive loss of their functions and ultimately leading to loss of mobility, coordination, and mental functioning. The molecular mechanisms underpinning neurodegenerative disease pathogenesis are still unclear. Nonetheless, there is experimental evidence to demonstrate that the perturbation of mitochondrial function and dynamics play an essential role. In this context, mitochondrial biogenesis, the growth, and division of preexisting mitochondria, by controlling mitochondria number, plays a vital role in maintaining proper mitochondrial mass and function, thus ensuring efficient synaptic activity and brain function. Mitochondrial biogenesis is tightly associated with the control of cell division and variations in energy demand in response to extracellular stimuli; therefore, it may represent a promising therapeutic target for developing new curative approaches to prevent or counteract neurodegenerative disorders. Accordingly, several inducers of mitochondrial biogenesis have been proposed as pharmacological targets for treating diverse central nervous system conditions. The naturally occurring polyphenol resveratrol has been shown to promote mitochondrial biogenesis in various tissues, including the nervous tissue, and an ever-growing number of studies highlight its neurotherapeutic potential. Besides preventing cognitive impairment and neurodegeneration through its antioxidant and anti-inflammatory properties, resveratrol has been shown to be able to enhance mitochondria biogenesis by acting on its main effectors, including PGC-1α, SIRT1, AMPK, ERRs, TERT, TFAM, NRF-1 and NRF-2. This review aims to present and discuss the current findings concerning the impact of resveratrol on the machinery and main effectors modulating mitochondrial biogenesis in the context of neurodegenerative diseases.

PERM1 regulates energy metabolism in the heart via ERRα/PGC-1α axis

Aims

PERM1 is a striated muscle-specific regulator of mitochondrial bioenergetics. We previously demonstrated that PERM1 is downregulated in the failing heart and that PERM1 positively regulates metabolic genes known as targets of the transcription factor ERRα and its coactivator PGC-1α in cultured cardiomyocytes. The aims of this study were to determine the effect of loss of PERM1 on cardiac function and energetics using newly generated Perm1-knockout (Perm1 -/-) mice and to investigate the molecular mechanisms of its transcriptional control.

Methods and results

Echocardiography showed that ejection fraction and fractional shortening were lower in Perm1 -/- mice than in wild-type mice (both p < 0.05), and the phosphocreatine-to-ATP ratio was decreased in Perm1 -/- hearts (p < 0.05), indicating reduced contractile function and energy reserves of the heart. Integrated proteomic and metabolomic analyses revealed downregulation of oxidative phosphorylation and upregulation of glycolysis and polyol pathways in Perm1 -/- hearts. To examine whether PERM1 regulates energy metabolism through ERRα, we performed co-immunoprecipitation assays, which showed that PERM1 bound to ERRα in cardiomyocytes and the mouse heart. DNA binding and reporter gene assays showed that PERM1 was localized to and activated the ERR target promoters partially through ERRα. Mass spectrometry-based screening in cardiomyocytes identified BAG6 and KANK2 as potential PERM1's binding partners in transcriptional regulation. Mammalian one-hybrid assay, in which PERM1 was fused to Gal4 DNA binding domain, showed that the recruitment of PERM1 to a gene promoter was sufficient to activate transcription, which was blunted by silencing of either PGC-1α, BAG6, or KANK2.

Conclusion

This study demonstrates that PERM1 is an essential regulator of cardiac energetics and function and that PERM1 is a novel transcriptional coactivator in the ERRα/PGC-1α axis that functionally interacts with BAG6 and KANK2.

Identification of evolutionarily conserved regulators of muscle mitochondrial network organization

Mitochondrial networks provide coordinated energy distribution throughout muscle cells. However, pathways specifying mitochondrial networks are incompletely understood and it is unclear how they might affect contractile fiber-type. Here, we show that natural energetic demands placed on Drosophila melanogaster muscles yield native cell-types among which contractile and mitochondrial network-types are regulated differentially. Proteomic analyses of indirect flight, jump, and leg muscles, together with muscles misexpressing known fiber-type specification factor salm, identified transcription factors H15 and cut as potential mitochondrial network regulators. We demonstrate H15 operates downstream of salm regulating flight muscle contractile and mitochondrial network-type. Conversely, H15 regulates mitochondrial network configuration but not contractile type in jump and leg muscles. Further, we find that cut regulates salm expression in flight muscles and mitochondrial network configuration in leg muscles. These data indicate cell type-specific regulation of muscle mitochondrial network organization through evolutionarily conserved transcription factors cut, salm, and H15.

PERM1 regulates genes involved in fatty acid metabolism in the heart by interacting with PPARα and PGC-1α

PERM1 (PGC-1/ERR-induced regulator in muscle 1) is a muscle-specific protein induced by PGC-1 and ERRs. Previous studies have shown that PERM1 promotes mitochondrial biogenesis and metabolism in cardiomyocytes in vitro. However, the role of endogenous PERM1 in the heart remains to be investigated with loss-of-function studies in vivo. We report the generation and characterization of systemic Perm1 knockout (KO) mice. The baseline cardiac phenotype of the homozygous Perm1 KO mice appeared normal. However, RNA-sequencing and unbiased pathway analyses showed that homozygous downregulation of PERM1 leads to downregulation of genes involved in fatty acid and carbohydrate metabolism in the heart. Transcription factor binding site analyses suggested that PPARα and PGC-1α are involved in changes in the gene expression profile. Chromatin immunoprecipitation assays showed that PERM1 interacts with the proximal regions of PPAR response elements (PPREs) in endogenous promoters of genes involved in fatty acid oxidation. Co-immunoprecipitation and reporter gene assays showed that PERM1 promoted transcription via the PPRE, partly in a PPARα and PGC-1α dependent manner. These results suggest that endogenous PERM1 is involved in the transcription of genes involved in fatty acid oxidation through physical interaction with PPARα and PGC-1α in the heart in vivo.

Preconditioning intensive training ameliorates reduction of transcription biofactors of PGC1α-pathway in paretic muscle due to cerebral ischemia

Exercise training increases fibronectin type III domain-containing protein 5 (FNDC5/irisin) via the peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α)-pathway. The PGC1α pathway induced FNDC5/irisin changes in response to exercise training and ischemic stroke are not entirely understood. We investigated the relation of the PGC-1α/FNDC5/irisin pathway to exercise training and to the pathophysiology of ischemic stroke in paretic muscles of stroke-induced rat models. We induced cerebral ischemia following completion of high-intensity interval training (HIIT) to evaluate PGC1α-pathway biofactors in paretic muscles. To define the underlying molecular mechanisms for improvement in paretic muscles following cerebral ischemia, we evaluated PCG-1α-pathway factors using immunofluorescence tracking and enzyme-linked immunosorbent assay (ELISA) immunoassay. We found that HIIT for 3 weeks produced increased expression and release of PGC-1α-pathway biomarkers in both the serum and paretic muscle of stroke-induced rats. We also found a close relation between the expression of PCG-1α-pathway factors in skeletal muscle and their concentration in blood. We found that PGC-1α-pathway biomarkers cause irisin up-regulation following induction of cerebral ischemia. The reduction in neurofunctional deficits following increased PGC-1α-pathway biomarkers suggests that these factors may act as markers of improvement in paretic muscle healing following cerebral ischemia.

miR-378 affects metabolic disturbances in the mdx model of Duchenne muscular dystrophy

Although Duchenne muscular dystrophy (DMD) primarily affects muscle tissues, the alterations to systemic metabolism manifested in DMD patients contribute to the severe phenotype of this fatal disorder. We propose that microRNA-378a (miR-378) alters carbohydrate and lipid metabolism in dystrophic mdx mice. In our study, we utilized double knockout animals which lacked both dystrophin and miR-378 (mdx/miR-378^-/-). RNA sequencing of the liver identified 561 and 194 differentially expressed genes that distinguished mdx versus wild-type (WT) and mdx/miR-378^-/- versus mdx counterparts, respectively. Bioinformatics analysis predicted, among others, carbohydrate metabolism disorder in dystrophic mice, as functionally proven by impaired glucose tolerance and insulin sensitivity. The lack of miR-378 in mdx animals mitigated those effects with a faster glucose clearance in a glucose tolerance test (GTT) and normalization of liver glycogen levels. The absence of miR-378 also restored the expression of genes regulating lipid homeostasis, such as Acly, Fasn, Gpam, Pnpla3, and Scd1. In conclusion, we report for the first time that miR-378 loss results in increased systemic metabolism of mdx mice. Together with our previous finding, demonstrating alleviation of the muscle-related symptoms of DMD, we propose that the inhibition of miR-378 may represent a new strategy to attenuate the multifaceted symptoms of DMD.

Transcription Factor Movement and Exercise-Induced Mitochondrial Biogenesis in Human Skeletal Muscle: Current Knowledge and Future Perspectives

In response to exercise, the oxidative capacity of mitochondria within skeletal muscle increases through the coordinated expression of mitochondrial proteins in a process termed mitochondrial biogenesis. Controlling the expression of mitochondrial proteins are transcription factors-a group of proteins that regulate messenger RNA transcription from DNA in the nucleus and mitochondria. To fulfil other functions or to limit gene expression, transcription factors are often localised away from DNA to different subcellular compartments and undergo rapid movement or accumulation only when required. Although many transcription factors involved in exercise-induced mitochondrial biogenesis have been identified, numerous conflicting findings and gaps exist within our knowledge of their subcellular movement. This review aims to summarise and provide a critical analysis of the published literature regarding the exercise-induced movement of transcription factors involved in mitochondria biogenesis in skeletal muscle.

Comparative study on molecular mechanism of diabetic myopathy in two different types of streptozotocin-induced diabetic models

AIMS

Streptozotocin (STZ)-induced diabetic animal models have been widely used to study diabetic myopathy; however, non-specific cytotoxic effects of high-dose STZ have been discussed. The purpose of this study was to compare diabetic myopathy in a high-STZ model with another well-established STZ model with reduced cytotoxicity (high-fat diet (HFD) and low-dose STZ) and to identify mechanistic insights underlying diabetic myopathy in STZ models that can mimic perturbations observed in human patients with diabetic myopathy.

MAIN METHODS

Male C57BL6 mice were injected with a single high dose of STZ (180 mg/kg, High-STZ) or were given HFD plus low-dose STZ injection (STZ, 55 mg/kg/day, five consecutive days, HFD/STZ). We characterized diabetic myopathy by histological and immunochemical analyses and conducted gene expression analysis.

KEY FINDINGS

The high-STZ model showed a significant reduction in tibialis anterior myofiber size along with decreased satellite cell content and downregulation of inflammation response and collagen gene expression. Interestingly, blood corticosteroid levels were significantly increased in the high-STZ model, which was possibly related to lowered inflammation response-related gene expression. Further analyses using the HFD/STZ model showed downregulation of gene expression related to mitochondrial functions accompanied by a significant decrease in ATP levels in the muscles.

SIGNIFICANCE

The high-STZ model is suitable for studies regarding not only severe diabetic myopathy with excessive blood glucose but also negative impact of glucocorticoids on skeletal muscles. In contrast, the HFD/STZ model is characterized by higher immune responses and lower ATP production, which also reflects the pathologies observed in human diabetic patients.

Astaxanthin as a Novel Mitochondrial Regulator: A New Aspect of Carotenoids, beyond Antioxidants

Astaxanthin is a member of the carotenoid family that is found abundantly in marine organisms, and has been gaining attention in recent years due to its varied biological/physiological activities. It has been reported that astaxanthin functions both as a pigment, and as an antioxidant with superior free radical quenching capacity. We recently reported that astaxanthin modulated mitochondrial functions by a novel mechanism independent of its antioxidant function. In this paper, we review astaxanthin’s well-known antioxidant activity, and expand on astaxanthin’s lesser-known molecular targets, and its role in mitochondrial energy metabolism.

Effects of Metformin in Heart Failure: From Pathophysiological Rationale to Clinical Evidence

Type 2 diabetes mellitus (T2DM) is a worldwide major health burden and heart failure (HF) is the most common cardiovascular (CV) complication in affected patients. Therefore, identifying the best pharmacological approach for glycemic control, which is also useful to prevent and ameliorate the prognosis of HF, represents a crucial issue. Currently, the choice is between the new drugs sodium/glucose co-transporter 2 inhibitors that have consistently shown in large CV outcome trials (CVOTs) to reduce the risk of HF-related outcomes in T2DM, and metformin, an old medicament that might end up relegated to the background while exerting interesting protective effects on multiple organs among which include heart failure. When compared with other antihyperglycemic medications, metformin has been demonstrated to be safe and to lower morbidity and mortality for HF, even if these results are difficult to interpret as they emerged mainly from observational studies. Meta-analyses of randomized controlled clinical trials have not produced positive results on the risk or clinical course of HF and sadly, large CV outcome trials are lacking. The point of force of metformin with respect to new diabetic drugs is the amount of data from experimental investigations that, for more than twenty years, still continues to provide mechanistic explanations of the several favorable actions in heart failure such as, the improvement of the myocardial energy metabolic status by modulation of glucose and lipid metabolism, the attenuation of oxidative stress and inflammation, and the inhibition of myocardial cell apoptosis, leading to reduced cardiac remodeling and preserved left ventricular function. In the hope that specific large-scale trials will be carried out to definitively establish the metformin benefit in terms of HF failure outcomes, we reviewed the literature in this field, summarizing the available evidence from experimental and clinical studies reporting on effects in heart metabolism, function, and structure, and the prominent pathophysiological mechanisms involved.

The mitochondrial protein Opa1 promotes adipocyte browning that is dependent on urea cycle metabolites

White to brown/beige adipocytes conversion is a possible therapeutic strategy to tackle the current obesity epidemics. While mitochondria are key for energy dissipation in brown fat, it is unknown if they can drive adipocyte browning. Here, we show that the mitochondrial cristae biogenesis protein optic atrophy 1 (Opa1) facilitates cell-autonomous adipocyte browning. In two cohorts of patients with obesity, including weight discordant monozygotic twin pairs, adipose tissue OPA1 levels are reduced. In the mouse, Opa1 overexpression favours white adipose tissue expandability as well as browning, ultimately improving glucose tolerance and insulin sensitivity. Transcriptomics and metabolomics analyses identify the Jumanji family chromatin remodelling protein Kdm3a and urea cycle metabolites, including fumarate, as effectors of Opa1-dependent browning. Mechanistically, the higher cyclic adenosine monophosphate (cAMP) levels in Opa1 pre-adipocytes activate cAMP-responsive element binding protein (CREB), which transcribes urea cycle enzymes. Flux analyses in pre-adipocytes indicate that Opa1-dependent fumarate accumulation depends on the urea cycle. Conversely, adipocyte-specific Opa1 deletion curtails urea cycle and beige differentiation of pre-adipocytes, and is rescued by fumarate supplementation. Thus, the urea cycle links the mitochondrial dynamics protein Opa1 to white adipocyte browning.

Sulforaphane improves mitochondrial metabolism in fibroblasts from patients with fragile X-associated tremor and ataxia syndrome

CGG expansions between 55 and 200 in the 5'-untranslated region of the fragile-X mental retardation gene (FMR1) increase the risk of developing the late-onset debilitating neuromuscular disease Fragile X-Associated Tremor/Ataxia Syndrome (FXTAS). While the science behind this mutation, as a paradigm for RNA-mediated nucleotide triplet repeat expansion diseases, has progressed rapidly, no treatment has proven effective at delaying the onset or decreasing morbidity, especially at later stages of the disease. Here, we demonstrated the beneficial effect of the phytochemical sulforaphane (SFN), exerted through NRF2-dependent and independent manner, on pathways relevant to brain function, bioenergetics, unfolded protein response, proteosome, antioxidant defenses, and iron metabolism in fibroblasts from FXTAS-affected subjects at all disease stages. This study paves the way for future clinical studies with SFN in the treatment of FXTAS, substantiated by the established use of this agent in clinical trials of diseases with NRF2 dysregulation and in which age is the leading risk factor.

PERM1 interacts with the MICOS-MIB complex to connect the mitochondria and sarcolemma via ankyrin B

Skeletal muscle subsarcolemmal mitochondria (SSM) and intermyofibrillar mitochondria subpopulations have distinct metabolic activity and sensitivity, though the mechanisms that localize SSM to peripheral areas of muscle fibers are poorly understood. A protein interaction study and complexome profiling identifies PERM1 interacts with the MICOS-MIB complex. Ablation of Perm1 in mice reduces muscle force, decreases mitochondrial membrane potential and complex I activity, and reduces the numbers of SSM in skeletal muscle. We demonstrate PERM1 interacts with the intracellular adaptor protein ankyrin B (ANKB) that connects the cytoskeleton to the plasma membrane. Moreover, we identify a C-terminal transmembrane helix that anchors PERM1 into the outer mitochondrial membrane. We conclude PERM1 functions in the MICOS-MIB complex and acts as an adapter to connect the mitochondria with the sarcolemma via ANKB.

Tissue-Specific Splicing and Dietary Interaction of a Mutant As160 Allele Determine Muscle Metabolic Fitness in Rodents

Ethnic groups are physiologically and genetically adapted to their diets. Inuit bear a frequent AS160^R684X mutation that causes type 2 diabetes. Whether this mutation evolutionarily confers adaptation in Inuit and how it causes metabolic disorders upon dietary changes are unknown due to limitations in human studies. Here, we develop a genetically modified rat model bearing an orthologous AS160^R693X mutation, which mimics human patients exhibiting postprandial hyperglycemia and hyperinsulinemia. Importantly, a sugar-rich diet aggravates metabolic abnormalities in AS160^R693X rats. The AS160^R693X mutation diminishes a dominant long-variant AS160 without affecting a minor short-variant AS160 in skeletal muscle, which suppresses muscle glucose utilization but induces fatty acid oxidation. This fuel switch suggests a possible adaptation in Inuit who traditionally had lipid-rich hypoglycemic diets. Finally, induction of the short-variant AS160 restores glucose utilization in rat myocytes and a mouse model. Our findings have implications for development of precision treatments for patients bearing the AS160^R684X mutation.

Perm1 promotes cardiomyocyte mitochondrial biogenesis and protects against hypoxia/reoxygenation-induced damage in mice

Normal contractile function of the heart depends on a constant and reliable production of ATP by cardiomyocytes. Dysregulation of cardiac energy metabolism can result in immature heart development and disrupt the ability of the adult myocardium to adapt to stress, potentially leading to heart failure. Further, restoration of abnormal mitochondrial function can have beneficial effects on cardiac dysfunction. Previously, we identified a novel protein termed Perm1 (PGC-1 and estrogen-related receptor (ERR)-induced regulator, muscle 1) that is enriched in skeletal and cardiac-muscle mitochondria and transcriptionally regulated by PGC-1 (peroxisome proliferator-activated receptor gamma coactivator 1) and ERR. The role of Perm1 in the heart is poorly understood and is studied here. We utilized cell culture, mouse models, and human tissue, to study its expression and transcriptional control, as well as its role in transcription of other factors. Critically, we tested Perm1's role in cardiomyocyte mitochondrial function and its ability to protect myocytes from stress-induced damage. Our studies show that Perm1 expression increases throughout mouse cardiogenesis, demonstrate that Perm1 interacts with PGC-1α and enhances activation of PGC-1 and ERR, increases mitochondrial DNA copy number, and augments oxidative capacity in cultured neonatal mouse cardiomyocytes. Moreover, we found that Perm1 reduced cellular damage produced as a result of hypoxia and reoxygenation-induced stress and mitigated cell death of cardiomyocytes. Taken together, our results show that Perm1 promotes mitochondrial biogenesis in mouse cardiomyocytes. Future studies can assess the potential of Perm1 to be used as a novel therapeutic to restore cardiac dysfunction induced by ischemic injury.

On the potential role of globins in brown adipose tissue: a novel conceptual model and studies in myoglobin knockout mice

Myoglobin (Mb) regulates O₂ bioavailability in muscle and heart as the partial pressure of O₂ (Po₂) drops with increased tissue workload. Globin proteins also modulate cellular NO pools, "scavenging" NO at higher Po₂ and converting NO₂^- to NO as Po₂ falls. Myoglobin binding of fatty acids may also signal a role in fat metabolism. Interestingly, Mb is expressed in brown adipose tissue (BAT), but its function is unknown. Herein, we present a new conceptual model that proposes links between BAT thermogenic activation, concurrently reduced Po₂, and NO pools regulated by deoxy/oxy-globin toggling and xanthine oxidoreductase (XOR). We describe the effect of Mb knockout (Mb^-/-) on BAT phenotype [lipid droplets, mitochondrial markers uncoupling protein 1 (UCP1) and cytochrome C oxidase 4 (Cox4), transcriptomics] in male and female mice fed a high-fat diet (HFD, 45% of energy, ∼13 wk), and examine Mb expression during brown adipocyte differentiation. Interscapular BAT weights did not differ by genotype, but there was a higher prevalence of mid-large sized droplets in Mb^-/-. COX4 protein expression was significantly reduced in Mb^-/- BAT, and a suite of metabolic/NO/stress/hypoxia transcripts were lower. All of these Mb^-/--associated differences were most apparent in females. The new conceptual model, and results derived from Mb^-/- mice, suggest a role for Mb in BAT metabolic regulation, in part through sexually dimorphic systems and NO signaling. This possibility requires further validation in light of significant mouse-to-mouse variability of BAT Mb mRNA and protein abundances in wild-type mice and lower expression relative to muscle and heart.NEW & NOTEWORTHY Myoglobin confers the distinct red color to muscle and heart, serving as an oxygen-binding protein in oxidative fibers. Less attention has been paid to brown fat, a thermogenic tissue that also expresses myoglobin. In a mouse knockout model lacking myoglobin, brown fat had larger fat droplets and lower markers of mitochondrial oxidative metabolism, especially in females. Gene expression patterns suggest a role for myoglobin as an oxygen/nitric oxide-sensor that regulates cellular metabolic and signaling pathways.

Skeletal Muscle Metabolism: Origin or Prognostic Factor for Amyotrophic Lateral Sclerosis (ALS) Development?

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive and selective loss of motor neurons, amyotrophy and skeletal muscle paralysis usually leading to death due to respiratory failure. While generally considered an intrinsic motor neuron disease, data obtained in recent years, including our own, suggest that motor neuron protection is not sufficient to counter the disease. The dismantling of the neuromuscular junction is closely linked to chronic energy deficit found throughout the body. Metabolic (hypermetabolism and dyslipidemia) and mitochondrial alterations described in patients and murine models of ALS are associated with the development and progression of disease pathology and they appear long before motor neurons die. It is clear that these metabolic changes participate in the pathology of the disease. In this review, we summarize these changes seen throughout the course of the disease, and the subsequent impact of glucose–fatty acid oxidation imbalance on disease progression. We also highlight studies that show that correcting this loss of metabolic flexibility should now be considered a major goal for the treatment of ALS.

Random errors in protein synthesis activate an age-dependent program of muscle atrophy in mice

Random errors in protein synthesis are prevalent and ubiquitous, yet their effect on organismal health has remained enigmatic for over five decades. Here, we studied whether mice carrying the ribosomal ambiguity (ram) mutation Rps2-A226Y, recently shown to increase the inborn error rate of mammalian translation, if at all viable, present any specific, possibly aging-related, phenotype. We introduced Rps2-A226Y using a Cre/loxP strategy. Resulting transgenic mice were mosaic and showed a muscle-related phenotype with reduced grip strength. Analysis of gene expression in skeletal muscle using RNA-Seq revealed transcriptomic changes occurring in an age-dependent manner, involving an interplay of PGC1α, FOXO3, mTOR, and glucocorticoids as key signaling pathways, and finally resulting in activation of a muscle atrophy program. Our results highlight the relevance of translation accuracy, and show how disturbances thereof may contribute to age-related pathologies.

By introducing a ribosomal ambiguity mutation into mice, Moore et al. establish an in-vivo model to investigate how age-related diseases are related to decreasing accuracy in protein synthesis. Their findings potentially offer new insights into the pathological changes observed in age-related diseases, such as muscle atrophy

Distinct peripheral blood monocyte and neutrophil transcriptional programs following intracerebral hemorrhage and different etiologies of ischemic stroke

Understanding cell-specific transcriptome responses following intracerebral hemorrhage (ICH) and ischemic stroke (IS) will improve knowledge of the immune response to brain injury. Transcriptomic profiles of 141 samples from 48 subjects with ICH, different IS etiologies, and vascular risk factor controls were characterized using RNA-seq in isolated neutrophils, monocytes and whole blood. In both IS and ICH, monocyte genes were down-regulated, whereas neutrophil gene expression changes were generally up-regulated. The monocyte down-regulated response to ICH included innate, adaptive immune, dendritic, NK cell and atherosclerosis signaling. Neutrophil responses to ICH included tRNA charging, mitochondrial dysfunction, and ER stress pathways. Common monocyte and neutrophil responses to ICH included interferon signaling, neuroinflammation, death receptor signaling, and NFAT pathways. Suppressed monocyte responses to IS included interferon and dendritic cell maturation signaling, phagosome formation, and IL-15 signaling. Activated neutrophil responses to IS included oxidative phosphorylation, mTOR, BMP, growth factor signaling, and calpain proteases-mediated blood-brain barrier (BBB) dysfunction. Common monocyte and neutrophil responses to IS included JAK1, JAK3, STAT3, and thrombopoietin signaling. Cell-type and cause-specific approaches will assist the search for future IS and ICH biomarkers and treatments.

Quantitative phosphoproteomic analysis unveil the effect of marketable ages on meat quality in geese

The quality of poultry goose meat is closely related to its marketable ages, with meat quality varying with increasing marketable age. Geese of two marketable ages (70-day and 120-day) were selected to understand the mechanisms behind this effect. Darker and redder meat; chewier and higher water-holding capacity (WHC) as well as greater protein and intramuscular fat (IMF) content were observed in the breast muscle (BM) of 120-day-old geese as compared to 70-day-old geese. Quantitative phosphoproteomics revealed up-regulated phosphorylated myofibrillar proteins and glycolytic enzymes in 120BM contributed to chewier meat with higher WHC. Redder meat might be attributed to phosphorylated mitochondrial proteins interacting with glycolytic enzymes in energy metabolism. Additionally, phosphorylation of PLIN1 and PERM1 might positively affect IMF deposition. Taken together, these data provided a phosphoproteomics perspective for the effect of marketable ages on meat quality and a theoretical strategy for improving meat quality in geese of younger marketable age.

Mitochondrial network remodeling: an important feature of myogenesis and skeletal muscle regeneration

The remodeling of the mitochondrial network is a critical process in maintaining cellular homeostasis and is intimately related to mitochondrial function. The interplay between the formation of new mitochondria (biogenesis) and the removal of damaged mitochondria (mitophagy) provide a means for the repopulation of the mitochondrial network. Additionally, mitochondrial fission and fusion serve as a bridge between biogenesis and mitophagy. In recent years, the importance of these processes has been characterised in multiple tissue- and cell-types, and under various conditions. In skeletal muscle, the robust remodeling of the mitochondrial network is observed, particularly after injury where large portions of the tissue/cell structures are damaged. The significance of mitochondrial remodeling in regulating skeletal muscle regeneration has been widely studied, with alterations in mitochondrial remodeling processes leading to incomplete regeneration and impaired skeletal muscle function. Needless to say, important questions related to mitochondrial remodeling and skeletal muscle regeneration still remain unanswered and require further investigation. Therefore, this review will discuss the known molecular mechanisms of mitochondrial network remodeling, as well as integrate these mechanisms and discuss their relevance in myogenesis and regenerating skeletal muscle.

The MicroRNA miR-696 is regulated by SNARK and reduces mitochondrial activity in mouse skeletal muscle through Pgc1α inhibition

OBJECTIVE

MicroRNAs (miRNA) are known to regulate the expression of genes involved in several physiological processes including metabolism, mitochondrial biogenesis, proliferation, differentiation, and cell death.

METHODS

Using "in silico" analyses, we identified 219 unique miRNAs that potentially bind to the 3'UTR region of a critical mitochondrial regulator, the peroxisome proliferator-activated receptor gamma coactivator (PGC) 1 alpha (Pgc1α). Of the 219 candidate miRNAs, miR-696 had one of the highest interactions at the 3'UTR of Pgc1α, suggesting that miR-696 may be involved in the regulation of Pgc1α.

RESULTS

Consistent with this hypothesis, we found that miR-696 was highly expressed in the skeletal muscle of STZ-induced diabetic mice and chronic high-fat-fed mice. C2C12 muscle cells exposed to palmitic acid also exhibited a higher expression of miR-696. This increased expression corresponded with a reduced expression of oxidative metabolism genes and reduced mitochondrial respiration. Importantly, reducing miR-696 reversed decreases in mitochondrial activity in response to palmitic acid. Using C2C12 cells treated with the AMP-activated protein kinase (AMPK) activator AICAR and skeletal muscle from AMPKα2 dominant-negative (DN) mice, we found that the signaling mechanism regulating miR-696 did not involve AMPK. In contrast, overexpression of SNF1-AMPK-related kinase (SNARK) in C2C12 cells increased miR-696 transcription while knockdown of SNARK significantly decreased miR-696. Moreover, muscle-specific transgenic mice overexpressing SNARK exhibited a lower expression of Pgc1α, elevated levels of miR-696, and reduced amounts of spontaneous activity.

CONCLUSIONS

Our findings demonstrate that metabolic stress increases miR-696 expression in skeletal muscle cells, which in turn inhibits Pgc1α, reducing mitochondrial function. SNARK plays a role in this process as a metabolic stress signaling molecule inducing the expression of miR-696.

Muscle Transcriptome Analysis Reveals Molecular Pathways Related to Oxidative Phosphorylation, Antioxidant Defense, Fatness and Growth in Mangalitsa and Moravka Pigs

This work was aimed at evaluating loin transcriptome and metabolic pathway differences between the two main Serbian local pig breeds with divergent characteristics regarding muscle growth and fatness, as well as exploring nutrigenomic effects of tannin supplementation in Mangalitsa (MA) pigs. The study comprised 24 Mangalitsa and 10 Moravka (MO) males, which were kept under identical management conditions. Mangalitsa animals were divided in two nutritional groups (n = 12) receiving a standard (control) or tannin-supplemented diet (1.5%; MAT). Moravka pigs were fed the standard mixture. All animals were slaughtered at a similar age; 120 kg of average live weight (LW) and loin tissue was used for RNA-seq analysis. Results showed 306 differentially expressed genes (DEGs) according to breed, enriched in genes involved in growth, lipid metabolism, protein metabolism and muscle development, such as PDK4, FABP4, MYOD1 and STAT3, as well as a relevant number of genes involved in mitochondrial respiratory activity (MT-NDs, NDUFAs among others). Oxidative phosphorylation was the most significantly affected pathway, activated in Mangalitsa muscle, revealing the basis of a different muscle metabolism. Also, many other relevant pathways were affected by breed and involved in oxidative stress response, fat accumulation and development of skeletal muscle. Results also allowed the identification of potential regulators and causal networks such as those controlled by FLCN, PPARGC1A or PRKAB1 with relevant regulatory roles on DEGs involved in mitochondrial and lipid metabolism, or IL3 and TRAF2 potentially controlling DEGs involved in muscle development. The Tannin effect on transcriptome was small, with only 23 DEGs, but included interesting ones involved in lipid deposition such as PPARGC1B. The results indicate a significant effect of the breed on muscle tissue gene expression, affecting relevant biological pathways and allowing the identification of strong regulatory candidate genes to underlie the gene expression and phenotypic differences between the compared groups.

Phosphoproteomics of the developing heart identifies PERM1 - An outer mitochondrial membrane protein

Heart development relies on PTMs that control cardiomyocyte proliferation, differentiation and cardiac morphogenesis. We generated a map of phosphorylation sites during the early stages of cardiac postnatal development in mice; we quantified over 10,000 phosphorylation sites and 5000 proteins that were assigned to different pathways. Analysis of mitochondrial proteins led to the identification of PGC-1- and ERR-induced regulator in muscle 1 (PERM1), which is specifically expressed in skeletal muscle and heart tissue and associates with the outer mitochondrial membrane. We demonstrate PERM1 is subject to rapid changes mediated by the UPS through phosphorylation of its PEST motif by casein kinase 2. Ablation of Perm1 in mice results in reduced protein expression of lipin-1 accompanied by accumulation of specific phospholipid species. Isolation of Perm1-deficient mitochondria revealed significant downregulation of mitochondrial transport proteins for amino acids and carnitines, including SLC25A12/13/29/34 and CPT2. Consistently, we observed altered levels of various lipid species, amino acids, and acylcarnitines in Perm1^-/- mitochondria. We conclude that the outer mitochondrial membrane protein PERM1 regulates homeostasis of lipid and amino acid metabolites in mitochondria.