Perm1 regulates CaMKII activation and shapes skeletal muscle responses to endurance exercise training

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.

NOR-1 Overexpression Elevates Myoglobin Expression via PERM1 and Enhances Mitochondrial Function and Endurance in Skeletal Muscles of Aged Mice

Skeletal muscle health and function deteriorate with age, ultimately leading to impaired mobility and disability. Exercise is among the most effective interventions to mitigate muscle dysfunction in aging and reverse deficits. However, low attrition and an impaired capacity to exercise may limit its utility in improving muscle function in aged persons. Therefore, it is crucial to advance our mechanistic understanding of the molecular transducers of exercise to identify new and innovative drug targets to improve muscle health. Transcriptomic profiling of the human response to exercise has revealed that the nuclear receptor NR4A3 (NOR-1) is among the most responsive genes to acute exercise. Previously, we observed that in vitro knockdown of NOR-1 alters metabolic signaling in C2C12 myotubes. Specifically, we found that expression of PERM1, CKMT2, myoglobin, and mTORC1 signaling were perturbed during the knockdown of NOR-1. Herein, we extend these findings and observe that a NOR-1-PERM1-myoglobin axis regulates myoglobin expression in vitro. Furthermore, we found that aging is associated with reduced skeletal muscle NOR-1 expression. Although it is well known that exercise improves aged muscle function, whether overexpression of the exercise-responsive gene NOR-1 can confer benefits and improve muscle function in an aged context has not been evaluated. We found that the overexpression of NOR-1 in aged muscle results in enhanced muscle endurance, mitochondrial respiration, and elevated expression of NOR-1 responsive genes that we previously identified in loss of function studies. However, we also observed that overexpression of NOR-1 did not improve maximal muscle torque production and resulted in a small but significant loss of muscle wet weight that was concomitant with elevated autophagy signaling. Our data suggest that NOR-1 expression may reduce muscle fatigability and that NOR-1 drives myoglobin expression in a PERM1-dependent manner.

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.

Exercise promotes skeletal muscle growth in adolescents via modulating Mettl3-mediated m6A methylation of MyoD in muscle satellite cells

BACKGROUND

Exercise exerts positive impacts on skeletal muscle health and homeostasis. Emerging evidence suggests that m6A methylation is involved in various physiological processes. However, the impact of exercise on adolescent skeletal muscle growth and the underlying epigenetic mechanisms remain poorly understood.

METHODS

The lower-limb skeletal muscles were harvested from exercise and control groups to compare the skeletal muscle growth in adolescents. mRNA sequencing was conducted to explore the mechanisms underlying enhanced skeletal muscle growth following exercise. The effects and mechanisms of Mettl3-mediated m6A methylation on adolescent skeletal muscle growth were investigated using muscle satellite cell (MuSC)-specific Mettl3 knockout (KO) mice. The potential function of MyoD for skeletal muscle growth in adolescents was explored by phenotypes after overexpression and evaluation of in vivo myogenesis. Additionally, the effects of the methyl donor betaine on adolescent skeletal muscle growth were investigated in vitro and in vivo.

RESULTS

Exercise could promote skeletal muscle growth in adolescents. Sequencing data analysis and confirmation assays uncovered that exercise significantly increased Mettl3-mediated m6A methylation and elevated the expression levels of activation marker MyoD in MuSCs. Establishment of MuSC-specific Mettl3 KO mice further demonstrated that Mettl3-mediated m6A methylation in MyoD contributed to skeletal muscle growth during adolescence. Mettl3-mediated m6A methylation regulated MyoD mRNA stability at the posttranscriptional level in MuSCs, with a functional site at 234 bp A. Increased expression of MyoD could contribute to myogenesis of adolescent MuSCs. Furthermore, the methyl donor betaine could enhance MyoD expression, contributing to MuSCs activation and skeletal muscle growth in adolescents by boosting m6A methylation levels.

CONCLUSIONS

Exercise promoted skeletal muscle growth in adolescents through facilitating MyoD mRNA stability of MuSCs in a Mettl3-mediated m6A-dependent manner. The methyl donor betaine could be a potential alternative to exercise for promoting adolescent skeletal muscle growth by directly augmenting the global levels of m6A methylation. These findings may provide a theoretical foundation for encouraging daily fitness exercise and ensuring healthy growth in adolescents.

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.

Exercise training and changes in skeletal muscle mitochondrial proteins: from blots to "omics"

Mitochondria are essential, membrane-enclosed organelles that consist of ∼1100 different proteins, which allow for many diverse functions critical to maintaining metabolism. Highly metabolic tissues, such as skeletal muscle, have a high mitochondrial content that increases with exercise training. The classic western blot technique has revealed training-induced increases in the relatively small number of individual mitochondrial proteins studied (∼5% of the >1100 proteins in MitoCarta), with some of these changes dependent on the training stimulus. Proteomic approaches have identified hundreds of additional mitochondrial proteins that respond to exercise training. There is, however, surprisingly little crossover in the mitochondrial proteins identified in the published human training studies. This suggests that to better understand the link between training-induced changes in mitochondrial proteins and metabolism, future studies need to move beyond maximizing protein detection to adopting methods that will increase the reliability of the changes in protein abundance observed.

Redox signaling and skeletal muscle adaptation during aerobic exercise

Redox regulation is a fundamental physiological phenomenon related to oxygen-dependent metabolism, and skeletal muscle is mainly regarded as a primary site for oxidative phosphorylation. Several studies have revealed the importance of reactive oxygen and nitrogen species (RONS) in the signaling process relating to muscle adaptation during exercise. To date, improving knowledge of redox signaling in modulating exercise adaptation has been the subject of comprehensive work and scientific inquiry. The primary aim of this review is to elucidate the molecular and biochemical pathways aligned to RONS as activators of skeletal muscle adaptation and to further identify the interconnecting mechanisms controlling redox balance. We also discuss the RONS-mediated pathways during the muscle adaptive process, including mitochondrial biogenesis, muscle remodeling, vascular angiogenesis, neuron regeneration, and the role of exogenous antioxidants.

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.

Glucose restriction enhances oxidative fiber formation: A multi-omic signal network involving AMPK and CaMK2

Skeletal muscle is a highly plastic organ that adapts to different metabolic states or functional demands. This study explored the impact of permanent glucose restriction (GR) on skeletal muscle composition and metabolism. Using Glut4m mice with defective glucose transporter 4, we conducted multi-omics analyses at different ages and after low-intensity treadmill training. The oxidative fibers were significantly increased in Glut4m muscles. Mechanistically, GR activated AMPK pathway, promoting mitochondrial function and beneficial myokine expression, and facilitated slow fiber formation via CaMK2 pathway. Phosphorylation-activated Perm1 may synergize AMPK and CaMK2 signaling. Besides, MAPK and CDK kinases were also implicated in skeletal muscle protein phosphorylation during GR response. This study provides a comprehensive signaling network demonstrating how GR influences muscle fiber types and metabolic patterns. These insights offer valuable data for understanding oxidative fiber formation mechanisms and identifying clinical targets for metabolic diseases.

Native lamin A/C proteomes and novel partners from heart and skeletal muscle in a mouse chronic inflammation model of human frailty

Clinical frailty affects ∼10% of people over age 65 and is studied in a chronically inflamed (Interleukin-10 knockout; "IL10-KO") mouse model. Frailty phenotypes overlap the spectrum of diseases ("laminopathies") caused by mutations in LMNA. LMNA encodes nuclear intermediate filament proteins lamin A and lamin C ("lamin A/C"), important for tissue-specific signaling, metabolism and chromatin regulation. We hypothesized that wildtype lamin A/C associations with tissue-specific partners are perturbed by chronic inflammation, potentially contributing to dysfunction in frailty. To test this idea we immunoprecipitated native lamin A/C and associated proteins from skeletal muscle, hearts and brains of old (21-22 months) IL10-KO versus control C57Bl/6 female mice, and labeled with Tandem Mass Tags for identification and quantitation by mass spectrometry. We identified 502 candidate lamin-binding proteins from skeletal muscle, and 340 from heart, including 62 proteins identified in both tissues. Candidates included frailty phenotype-relevant proteins Perm1 and Fam210a, and nuclear membrane protein Tmem38a, required for muscle-specific genome organization. These and most other candidates were unaffected by IL10-KO, but still important as potential lamin A/C-binding proteins in native heart or muscle. A subset of candidates (21 in skeletal muscle, 30 in heart) showed significantly different lamin A/C-association in an IL10-KO tissue (p < 0.05), including AldoA and Gins3 affected in heart, and Lmcd1 and Fabp4 affected in skeletal muscle. To screen for binding, eleven candidates plus prelamin A and emerin controls were arrayed as synthetic 20-mer peptides (7-residue stagger) and incubated with recombinant purified lamin A "tail" residues 385-646 under relatively stringent conditions. We detected strong lamin A binding to peptides solvent exposed in Lmcd1, AldoA, Perm1, and Tmem38a, and plausible binding to Csrp3 (muscle LIM protein). These results validated both proteomes as sources for native lamin A/C-binding proteins in heart and muscle, identified four candidate genes for Emery-Dreifuss muscular dystrophy (CSRP3, LMCD1, ALDOA, and PERM1), support a lamin A-interactive molecular role for Tmem38A, and supported the hypothesis that lamin A/C interactions with at least two partners (AldoA in heart, transcription factor Lmcd1 in muscle) are altered in the IL10-KO model of frailty.

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.

Transient changes to metabolic homeostasis initiate mitochondrial adaptation to endurance exercise

Endurance exercise is well established to increase mitochondrial content and function in skeletal muscle, a process termed mitochondrial biogenesis. Current understanding is that exercise initiates skeletal muscle mitochondrial remodeling via modulation of cellular nutrient, energetic and contractile stress pathways. These subtle changes in the cellular milieu are sensed by numerous transduction pathways that serve to initiate and coordinate an increase in mitochondrial gene transcription and translation. The result of these acute signaling events is the promotion of growth and assembly of mitochondria, coupled to a greater capacity for aerobic ATP provision in skeletal muscle. The aim of this review is to highlight the acute metabolic events induced by endurance exercise and the subsequent molecular pathways that sense this transient change in cellular homeostasis to drive mitochondrial adaptation and remodeling.

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.

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.

Short-term step reduction reduces CS activity without altering skeletal muscle markers of oxidative metabolism or insulin-mediated signalling in young males

Mitochondria are critical to skeletal muscle contractile function and metabolic health. Short-term periods of step reduction (SR) are associated with alterations in muscle protein turnover and mass. However, the effects of SR on mitochondrial metabolism/muscle oxidative metabolism and insulin-mediated signaling are unclear. We tested the hypothesis that the total and/or phosphorylated protein content of key skeletal muscle markers of mitochondrial/oxidative metabolism, and insulin-mediated signaling would be altered over 7 days of SR in young healthy males. Eleven, healthy, recreationally active males (means ± SE, age: 22 ± 1 yr, BMI: 23.4 ± 0.7 kg·m²) underwent a 7-day period of SR. Immediately before and following SR, fasted-state muscle biopsy samples were acquired and analyzed for the assessment of total and phosphorylated protein content of key markers of mitochondrial/oxidative metabolism and insulin-mediated signaling. Daily step count was significantly reduced during the SR intervention (13,054 ± 833 to 1,192 ± 99 steps·day⁻¹, P < 0.001). Following SR, there was a significant decline in maximal citrate synthase activity (fold change: 0.94 ± 0.08, P < 0.05) and a significant increase in the protein content of p-glycogen synthase (P-GS^S641; fold change: 1.47 ± 0.14, P < 0.05). No significant differences were observed in the total or phosphorylated protein content of other key markers of insulin-mediated signaling, oxidative metabolism, mitochondrial function, or mitochondrial dynamics (all P > 0.05). These results suggest that short-term SR reduces the maximal activity of citrate synthase, a marker of mitochondrial content, without altering the total or phosphorylated protein content of key markers of skeletal muscle mitochondrial metabolism and insulin signaling in young healthy males.

NEW & NOTEWORTHY Short-term (7 day) step reduction reduces the activity of citrate synthase without altering the total or phosphorylated protein content of key markers of skeletal muscle mitochondrial metabolism and insulin signaling in young healthy males.

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.

Chronic exercise training activates histone turnover in mouse skeletal muscle fibers

Epigenetic regulation of skeletal muscle adaptation to exercise is a recent topic for which there is limited information. This study investigated whether exercise training activates histone turnover in the skeletal muscle fibers of mice. Experiments using a tetracycline-inducible H2B-GFP expression model demonstrated that 4 weeks of running training, but not 2 weeks of training, significantly promoted the incorporation of H2B-GFP into nucleosomes and the dissociation of histone H3.3 at both transcriptionally upregulated and nonresponsive loci. Muscle-specific PGC-1α-b-overexpressing mice crossed with H2B-GFP mice showed a slight increase in H2B-GFP incorporation at transcriptionally active loci, but not in the dissociation of H3.3 from nucleosomes. Gene expression responses to a single bout of running were significantly enhanced in 4-week trained mice when compared with those in 2-week trained mice. The most drastic increase in the gene response was found in the expression of Hspa1a and Hspa1b, in which the magnitude of upregulation in response to running was significantly enhanced from 8-fold in 2 week trained mice to 97- and 121-fold in 4 week trained mice, respectively. It was also found that the HSP70 level increased during the training period. In a myonuclear immunohistochemical analysis of chromatin remodelers, we further found that the level of SPT16, an H2A-H2B-specific chaperone, was upregulated after running training. These results revealed that 4 weeks of running training activated histone turnover in skeletal muscle fibers. They also suggested that histone turnover led to loosening of the nucleosomes and enhanced gene responses to exercise.

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.

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.

Effectiveness of HIIE versus MICT in Improving Cardiometabolic Risk Factors in Health and Disease: A Meta-analysis

PURPOSE

We aimed to investigate differences between high-intensity interval exercise (HIIE, including high-intensity interval training and sprint interval training) and moderate-intensity continuous training (MICT) on physical fitness, body composition, blood pressure, blood lipids, insulin and glucose metabolism, inflammation, and endothelial function.

METHODS

Differences between HIIE and MICT were summarized using a random-effects meta-analysis on the effect size (Cohen's d). A meta-regression was conducted using the following subgroups: population, age, training duration, men ratio, exercise type, baseline values (clinical relevant ranges), and type of HIIE. Studies were included if at least one of the following outcomes were reported: maximal oxygen uptake (V˙O2max), flow-mediated dilation (FMD), body mass index (BMI), body mass, percent body fat, systolic and diastolic blood pressure, high-density lipoprotein (HDL), low-density lipoprotein (LDL), triglycerides, total cholesterol, C-reactive protein (CRP), fasting glucose and insulin, glycated hemoglobin (HbA1c), and insulin resistance (HOMA-IR). A total of 55 studies were included.

RESULTS

Overall, HIIE was superior to MICT in improving V˙O2max (d = 0.40, P < 0.001) and FMD (d = 0.54, P < 0.05). Oppositely, MICT was superior to HIIE in improving HbA1c (d = -0.27, P < 0.05). No differences were observed in BMI (d = -0.02), body mass (d = -0.05), percent body fat (d = 0.04), systolic blood pressure (d = -0.04), diastolic blood pressure (d = 0.03), HDL (d = -0.05), LDL (d = 0.08), triglycerides (d = 0.03), total cholesterol (d = 0.14), CRP (d = -0.11), fasting insulin (d = 0.02), fasting glucose (d = 0.02), and HOMA-IR (d = -0.04). Moderator analyses indicated that the difference between HIIE and MICT was affected by different subgroups.

CONCLUSION

Overall, HIIE showed to be more effective in improving cardiovascular health and cardiorespiratory fitness, whereas MICT was superior in improving long-term glucose metabolism. In the process of personalized training counseling, health-enhancing effects of exercise training may be improved by considering the individual risk profiles.

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.

Effect of endurance exercise training on liver gene expression in male and female mice

Chronic endurance exercise is a therapeutic strategy in the treatment of many chronic diseases in humans, including the prevention and treatment of metabolic diseases such as diabetes mellitus. Metabolic, cardiorespiratory, and endocrine pathways targeted by chronic endurance exercise have been identified. In the liver, however, the cellular and molecular pathways that are modified by exercise and have preventive or therapeutic relevance to metabolic disease need to be elucidated. The mouse model used in the current study allows for the quantification of a human-relevant exercise "dosage". In this study we show hepatic gene expression differences between sedentary female and sedentary male mice and that chronic exercise modifies the transcription of hepatic genes related to metabolic disease and steatosis in both male and female mice. Chronic exercise induces molecular pathways involved in glucose tolerance, glycolysis, and gluconeogenesis while producing a decrease in pathways related to insulin resistance, steatosis, fibrosis, and inflammation. Given these findings, this mouse exercise model has potential to dissect the cellular and molecular hepatic changes following chronic exercise with application to understanding the role that chronic exercise plays in preventing human diseases. Novelty: Exercise modifies the hepatic gene expression and hepatic pathways related to metabolic disease in male and female mice. Sex differences were seen in hepatic gene expression between sedentary and exercised mice. The mouse exercise model used in this study allows for application and evaluation of exercise effects in human disease.

Perm1 regulates cardiac energetics as a downstream target of the histone methyltransferase Smyd1

The transcriptional regulatory machinery in mitochondrial bioenergetics is complex and is still not completely understood. We previously demonstrated that the histone methyltransferase Smyd1 regulates mitochondrial energetics. Here, we identified Perm1 (PPARGC-1 and ESRR-induced regulator, muscle specific 1) as a downstream target of Smyd1 through RNA-seq. Chromatin immunoprecipitation assay showed that Smyd1 directly interacts with the promoter of Perm1 in the mouse heart, and this interaction was significantly reduced in mouse hearts failing due to pressure overload for 4 weeks, where Perm1 was downregulated (24.4 ± 5.9% of sham, p<0.05). Similarly, the Perm1 protein level was significantly decreased in patients with advanced heart failure (55.2 ± 13.1% of donors, p<0.05). Phenylephrine (PE)-induced hypertrophic stress in cardiomyocytes also led to downregulation of Perm1 (55.7 ± 5.7% of control, p<0.05), and adenovirus-mediated overexpression of Perm1 rescued PE-induced downregulation of estrogen-related receptor alpha (ERRα), a key transcriptional regulator of mitochondrial energetics, and its target gene, Ndufv1 (Complex I). Pathway enrichment analysis of cardiomyocytes in which Perm1 was knocked-down by siRNA (siPerm1), revealed that the most downregulated pathway was metabolism. Cell stress tests using the Seahorse XF analyzer showed that basal respiration and ATP production were significantly reduced in siPerm1 cardiomyocytes (40.7% and 23.6% of scrambled-siRNA, respectively, both p<0.05). Luciferase reporter gene assay further revealed that Perm1 dose-dependently increased the promoter activity of the ERRα gene and known target of ERRα, Ndufv1 (Complex I). Overall, our study demonstrates that Perm1 is an essential regulator of cardiac energetics through ERRα, as part of the Smyd1 regulatory network.