PI3K-AKT-FOXO1 pathway targeted by skeletal muscle microRNA to suppress proteolytic gene expression in response to carbohydrate intake during aerobic exercise

Muscle-enriched microRNA-486-mediated regulation of muscular atrophy and exercise

The objectives of this review were to understand the impact of microRNA-486 on myogenesis and muscle atrophy, and the change of microRNA-486 following exercise, and provide valuable information for improving muscle atrophy based on exercise intervention targeting microRNA-486. Muscle-enriched microRNAs (miRNAs), also referred to as myomiRs, control various processes in skeletal muscles, from myogenesis and muscle homeostasis to different responses to environmental stimuli such as exercise. MicroRNA-486 is a miRNA in which a stem-loop sequence is embedded within the ANKYRIN1 (ANK1) locus and is strictly conserved across mammals. MicroRNA-486 is involved in the development of muscle atrophy caused by aging, immobility, prolonged exposure to microgravity, or muscular and neuromuscular disorders. PI3K/AKT signaling is a positive pathway, as it increases muscle mass by increasing protein synthesis and decreasing protein degradation. MicroRNA-486 can activate this pathway by inhibiting phosphatase and tensin homolog (PTEN), it may also indirectly inhibit the HIPPO signaling pathway to promote cell growth. Exercises regulate microRNA-486 expression both in blood and muscle. This review focused on the recent elucidation of sarcopenia regulation by microRNA-486 and its effects on pathological states, including primary muscular disease, secondary muscular disorders, and age-related sarcopenia. Additionally, the role of exercise in regulating skeletal muscle-enriched microRNA-486 was highlighted, along with its physiological significance. Growing evidence indicates that microRNA-486 significantly impacts the development of muscle atrophy. MicroRNA-486 has great potential to become a therapeutic target for improving muscle atrophy through exercise intervention.

Resveratrol Reverses Myogenic Induction Suppression Caused by High Glucose Through Activating the SIRT1/AKT/FOXO1 Pathway

Background

Differentiated bone marrow mesenchymal stem cells (BMSCs) may be a therapeutic strategy to treat sarcopenia caused by high glucose. The effects of resveratrol in the myogenic induction of BMSCs under high glucose are unknown. We evaluated the effects and possible mechanisms of high glucose and resveratrol on myogenic induction of rat BMSCs.

Methods

Primary rat BMSCs were isolated and purified from Sprague-Dawley rats aged between 3 and 4 weeks. Rat BMSCs were differentiated into myogenic cells using conditioned medium and treated with glucose and/or resveratrol along with EX527 (a specific silent information regulator 1 [SIRT1] inhibitor). The expressions of MyoD1 and Myogenin were measured. The reactive oxygen species (ROS) level, superoxide dismutase (SOD) activity, and the expressions of FOXO1 and p-AKT/AKT during myogenic induction were also examined.

Results

High glucose decreased cell viability, cell proliferation, and SOD activity, increased intracellular ROS levels, and inhibited the AKT/FOXO1. Resveratrol reversed myogenic induction suppression caused by high glucose, partly through restoring cell proliferation and viability, reducing peroxidative damage, and activating the AKT/FOXO1 pathway; this effect was eliminated by EX527.

Conclusion

Our results indicate that resveratrol promoted myogenic induction and partially reversed the suppression of myogenic induction caused by high glucose through activating the SIRT1/AKT/FOXO1 pathway.

Carbohydrate intake in recovery from aerobic exercise differentiates skeletal muscle microRNA expression

Posttranscriptional regulation by microRNA (miRNA) facilitates exercise and diet-induced skeletal muscle adaptations. However, the impact of diet on miRNA expression during postexercise recovery remains unclear. The objective of this study was to examine the effects of consuming carbohydrate or a nutrient-free control on skeletal muscle miRNA expression during 3 h of recovery from aerobic exercise. Using a randomized, crossover design, seven men (means ± SD, age: 21 ± 3 yr; body mass: 83 ± 13 kg; V̇o2peak: 43 ± 2 mL/kg/min) completed two-cycle ergometry glycogen depletion trials followed by 3 h of recovery while consuming either carbohydrate (CHO: 1 g/kg/h) or control (CON: nutrient free). Muscle biopsy samples were obtained under resting fasted conditions at baseline and at the end of the 3-h recovery (REC) period. miRNA expression was determined using unbiased RT-qPCR microarray analysis. Trials were separated by 7 days. Twenty-five miRNAs were different (P < 0.05) between CHO and CON at REC, with Let7i-5p and miR-195-5p being the most predictive of treatment. In vitro overexpression of Let7i-5p and miR-195-p5 in C2C12 skeletal muscle cells decreased (P < 0.05) the expression of protein breakdown (Foxo1, Trim63, Casp3, and Atf4) genes, ubiquitylation, and protease enzyme activity compared with control. Energy sensing (Prkaa1 and Prkab1) and glycolysis (Gsy1 and Gsk3b) genes were lower (P < 0.05) with Let7i-5p overexpression compared with miR-195-5p and control. Fat metabolism (Cpt1a, Scd1, and Hadha) genes were lower (P < 0.05) in miR-195-5p than in control. These data indicate that consuming CHO after aerobic exercise alters miRNA profiles compared with CON, and these differences may govern mechanisms facilitating muscle recovery.NEW & NOTEWORTHY Results provide novel insight into effects of carbohydrate intake on the expression of skeletal muscle microRNA during early recovery from aerobic exercise and reveal that Let7i-5p and miR-195-5p are important regulators of skeletal muscle protein breakdown to aid in facilitating muscle recovery.

miR-486 is essential for muscle function and suppresses a dystrophic transcriptome

miR-486 is a muscle-enriched microRNA, or "myomiR," that has reduced expression correlated with Duchenne muscular dystrophy (DMD). To determine the function of miR-486 in normal and dystrophin-deficient muscles and elucidate miR-486 target transcripts in skeletal muscle, we characterized mir-486 knockout mice (mir-486 KO). mir-486 KO mice developed disrupted myofiber architecture, decreased myofiber size, decreased locomotor activity, increased cardiac fibrosis, and metabolic defects were exacerbated in mir-486 KO:mdx 5cv (DKO) mice. To identify direct in vivo miR-486 muscle target transcripts, we integrated RNA sequencing and chimeric miRNA eCLIP sequencing to identify key transcripts and pathways that contribute towards mir-486 KO and dystrophic disease pathologies. These targets included known and novel muscle metabolic and dystrophic structural remodeling factors of muscle and skeletal muscle contractile transcript targets. Together, our studies identify miR-486 as essential for normal muscle function, a driver of pathological remodeling in dystrophin-deficient muscle, a useful biomarker for dystrophic disease progression, and highlight the use of multiple omic platforms to identify in vivo microRNA target transcripts.

MiR-29a Family as a Key Regulator of Skeletal Muscle Dysplasia in a Porcine Model of Intrauterine Growth Retardation

MicroRNAs (miRNAs) play an essential role in many biological processes. In this study, miRNAs in the skeletal muscle of normal and intrauterine growth retardation (IUGR) neonatal piglets were identified by sequencing, and canonical miRNAs were functionally validated in vitro. A total of 403 miRNAs were identified in neonatal piglet skeletal muscle, among them 30 and 46 miRNAs were upregulated and downregulated in IUGR pigs, respectively. Upregulated miRNAs were mainly enriched in propanoate metabolism, endocytosis, beta-Alanine metabolism, gap junction, and tumor necrosis factor signaling pathway. Down-regulated miRNAs were mainly enriched in chemical carcinogenesis—receptor activation, endocytosis, MAPK signaling pathway, insulin resistance, and EGFR tyrosine kinase inhibitor resistance. Co-expression network analysis of umbilical cord blood and skeletal muscle miRNAs showed that the miR-29 family is an essential regulator of IUGR pigs. The dual-luciferase reporter system showed that IGF1 and CCND1 were target genes of the miR-29 family. Transfection of IUGR pig umbilical cord blood exosomes and miR-29a mimic significantly inhibited cell proliferation and promoted the expression of cellular protein degradation marker genes Fbxo32 and Trim63. In summary, these results enrich the regulatory network of miRNAs involved in skeletal muscle development in IUGR animals.

Circulating and skeletal muscle microRNA profiles are more sensitive to sustained aerobic exercise than energy balance in males

KEY POINTS

Circulating and skeletal muscle miRNA profiles are more sensitive to high levels of aerobic exercise-induced energy expenditures compared to energy status Changes in circulating miRNA in response to high levels of daily sustained aerobic exercise are not reflective of changes in skeletal muscle miRNA.

ABSTRACT

MicroRNA (miRNA) regulate molecular processes governing muscle metabolism. Physical activity and energy balance influence both muscle anabolism and metabolism, but whether circulating and skeletal muscle miRNA mediate those effects remains unknown. This study assessed the impact of sustained physical activity with participants in energy balance (BAL) or deficit (DEF) on circulating and skeletal muscle miRNA. Using a randomized cross-over design, 10 recreational active healthy males (mean ± SD; 22±5 yrs, 87±11 kg) completed 72 hours of high aerobic exercise-induced energy expenditures in BAL (689±852 kcal/d) or DEF (-2047±920 kcal/d). Blood and muscle samples were collected under rested/fasted conditions before (PRE) and immediately after 120-min load carriage exercise bout at the end (POST) of the 72 hours. Trials were separated by 7 days. Circulating and skeletal muscle miRNA were measured using microarray RT-qPCR. Independent of energy status, 36 circulating miRNA decreased (P<0.05), while 10 miRNA increased and 3 miRNA decreased in skeletal muscle (P<0.05) at POST compared to PRE. Of these, miR-122-5p, miR-221-3p, miR-222-3p, and miR-24-3p decreased in circulation and increased in skeletal muscle. Two circulating (miR-145-5p and miR-193a-5p) and 4 skeletal muscle (miR-21-5p, miR-372-3p, miR-34a-5p, and miR-9-5p) miRNA had time-by-treatment effects (P<0.05). These data suggest that changes in miRNA profiles are more sensitive to increased physical activity compared to energy status, and that changes in circulating miRNA in response to high levels of daily aerobic exercise are not reflective of changes in skeletal muscle miRNA. Graphical abstract legend In response to 72 hours of high aerobic exercise, circulating miRNA decreased and miRNA in skeletal muscle primarily increased. The changes in miRNA occurred independent of energy status (i.e., exercise-induced energy defcit or exercise plus increased energy intake to achieve energy balance), and circulating miRNA did not refect changes in skeletal muscle. This article is protected by copyright. All rights reserved.

MicroRNA-100 Reduced Fetal Bovine Muscle Satellite Cell Myogenesis and Augmented Intramuscular Lipid Deposition by Modulating IGF1R

Previously, microRNA-100 (miR-100) and its putative mRNA target, insulin-like growth factor receptor-1 (IGF1R) were identified as differentially and inversely expressed in bovine longissimus dorsi (LD) muscles with divergent intramuscular fat (IMF) content by our group. While IGF1R signaling is implicated in myogenesis and muscle lipid metabolism, the underlying regulatory mechanisms are poorly understood. In the present study, we aimed to investigate the regulation of IGF1R by miR-100 during bovine muscle satellite cell (BMSC) myogenesis and lipid deposition. MiR-100 was confirmed to target the IGF1R 3′-untranslated region (3′-UTR) by luciferase reporter assay. Furthermore, expression of miR-100 and IGF1R was reciprocal during BMSC differentiation, suggesting a crosstalk between the two. Correspondingly, miR-100 mimic (agomiR) suppressed the levels of IGF1R, PI3K/AKT pathway signaling, myogenic gene MYOG, muscle structural components MYH7 and MYH8, whereas the inhibitor (antagomiR) had no clear stimulating effects. The IGF1R inhibitor (BMS-754807) curtailed receptor levels and triggered atrophy in muscle myotubes but did not influence miR-100 expression. AgomiR increased oleic acid-induced lipid deposition in BMSC myotubes supporting its involvement in intramuscular fat deposition, while antagomiR had no effect. Moreover, mitochondrial beta-oxidation and long-chain fatty acid synthesis-related genes were modulated by agomiR addition. Our results demonstrate modulatory roles of miR-100 in BMSC development, lipid deposition, and metabolism and suggest a role of miR-100 in marbling characteristics of meat animals and fat oxidation in muscle.

The dependency of autophagy and ubiquitin proteasome system during skeletal muscle atrophy

Among the four proteolytic systems in the cell, autophagy and the ubiquitin-proteasome system (UPS) are the main proteolytic events that allow for the removal of cell debris and proteins to maintain cellular homeostasis. Previous studies have revealed that these systems perform their functions independently of each other. However, recent studies indicate the existence of regulatory interactions between these proteolytic systems via ubiquitinated tags and a reciprocal regulation mechanism with several crosstalk points. UPS plays an important role in the elimination of short-lived/soluble misfolded proteins, whereas autophagy eliminates defective organelles and persistent insoluble protein aggregates. Both of these systems seem to act independently; however, disruption of one pathway affects the activity of the other pathway and contributes to different pathological conditions. This review summarizes the recent findings on direct and indirect dependencies of autophagy and UPS and their execution at the molecular level along with the important drug targets in skeletal muscle atrophy.

Moringa oleifera leaf extracts protect BMSC osteogenic induction following peroxidative damage by activating the PI3K/Akt/Foxo1 pathway

Objective

We aimed to investigate the therapeutic effects of Moringa oleifera leaf extracts on osteogenic induction of rat bone marrow mesenchymal stem cells (BMSCs) following peroxidative damage and to explore the underlying mechanisms.

Methods

Conditioned medium was used to induce osteogenic differentiation of BMSCs, which were treated with H₂O₂, Moringa oleifera leaf extracts-containing serum, or the phosphatidyl inositol-3 kinase (PI3K) inhibitor wortmannin, alone or in combination. Cell viability was measured using the MTT assay. Cell cycle was assayed using flow cytometry. Expression levels of Akt, phosphorylated (p)Akt, Foxo1, and cleaved caspase-3 were analyzed using western blot analysis. The mRNA levels of osteogenesis-associated genes, including alkaline phosphatase (ALP), collagen І, osteopontin (OPN), and Runx2, were detected using qRT-PCR. Reactive oxygen species (ROS) and malondialdehyde (MDA) levels, as well as superoxide dismutase (SOD), glutathione peroxidase (GSH-PX), and ALP activity were detected using commercially available kits. Osteogenic differentiation capability was determined using alizarin red staining.

Results

During osteogenic induction of rat BMSCs, H₂O₂ reduced cell viability and proliferation, inhibited osteogenesis, increased ROS and MDA levels, and decreased SOD and GSH-PX activity. H₂O₂ significantly reduced pAkt and Foxo1 expression, and increased cleaved caspase-3 levels in BMSCs. Additional treatments with Moringa oleifera leaf extracts partially reversed the H₂O₂-induced changes. Wortmannin partially attenuated the effects of Moringa oleifera leaf extracts on protein expression of Foxo1, pAkt, and cleaved caspase-3, as well as mRNA levels of osteogenesis-associated genes.

Conclusion

Moringa oleifera leaf extracts ameliorate peroxidative damage and enhance osteogenic induction of rat BMSCs by activating the PI3K/Akt/Foxo1 pathway.

Non-Coding RNAs in the Transcriptional Network That Differentiates Skeletal Muscles of Sedentary from Long-Term Endurance- and Resistance-Trained Elderly

In a previous study, the whole transcriptome of the vastus lateralis muscle from sedentary elderly and from age-matched athletes with an exceptional record of high-intensity, life-long exercise training was compared-the two groups representing the two extremes on a physical activity scale. Exercise training enabled the skeletal muscle to counteract age-related sarcopenia by inducing a wide range of adaptations, sustained by the expression of protein-coding genes involved in energy handling, proteostasis, cytoskeletal organization, inflammation control, and cellular senescence. Building on the previous study, we examined here the network of non-coding RNAs participating in the orchestration of gene expression and identified differentially expressed micro- and long-non-coding RNAs and some of their possible targets and roles. Unsupervised hierarchical clustering analyses of all non-coding RNAs were able to discriminate between sedentary and trained individuals, regardless of the exercise typology. Validated targets of differentially expressed miRNA were grouped by KEGG analysis, which pointed to functional areas involved in cell cycle, cytoskeletal control, longevity, and many signaling pathways, including AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR), which had been shown to be pivotal in the modulation of the effects of high-intensity, life-long exercise training. The analysis of differentially expressed long-non-coding RNAs identified transcriptional networks, involving lncRNAs, miRNAs and mRNAs, affecting processes in line with the beneficial role of exercise training.

Thioredoxin mitigates H2 O2 -induced inhibition of myogenic differentiation of rat bone marrow mesenchymal stem cells by enhancing AKT activation

Thioredoxin (Trx) is a hydrogen acceptor of ribonucleotide reductase and a regulator of some enzymes and receptors. It has been previously shown that significantly elevated levels of Trx expression are associated with the osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs), but it is not clear how Trx regulates the effects of hydrogen peroxide (H₂O₂) on myogenic differentiation of BMSCs. Here, we report that rat BMSCs treated with a high dose (150 µm) of H₂O₂ exhibited a significant reduction in viability, cell cycling, and superoxide dismutase and glutathione peroxidase levels, and an increase in reactive oxygen species and malondialdehyde levels, which was accompanied by reductions in protein kinase B activation and forkhead Box O1, myogenic differentiation 1 and myogenin expression during myogenic differentiation. Furthermore, treatment with recombinant human Trx significantly mitigated the effects of H₂O₂ on the myogenic differentiation of BMSCs, and this was abrogated by cotreatment with wortmannin [a specific phosphatidylinositol 3‐kinase inhibitor]. In summary, our results suggest that treatment with recombinant human Trx mitigates H₂O₂‐induced oxidative stress and may promote myogenic differentiation of rat BMSCs by enhancing phosphatidylinositol 3‐kinase/protein kinase B/forkhead Box O1 signaling.

Molecular Mechanisms Mediating Adaptation to Exercise

Several experimental and human studies documented the preventive and therapeutic effects of exercise on the normal physiological function of different body systems during aging as well as various diseases. Recent studies using cellular and molecular (biochemical, proteomics, and genomics) techniques indicated that exercise modifies intracellular and extracellular signaling and pathways. In addition, in vivo or in vitro experiments, particularly, using knockout and transgenic animals, helped to mimic physiological conditions during and after exercise. According to the findings of these studies, some important signaling pathways modulated by exercise are Ca2+-dependent calcineurin/activated nuclear factor of activated T-cells, mammalian target of rapamycin, myostatin/Smad, and AMP-activated protein kinase regulation of peroxisome proliferator-activated receptor-gamma coactivator 1-alpha. Such modulations contribute to cell adaptation and remodeling of muscle fiber type in response to exercise. Despite great improvement in this field, there are still several unanswered questions as well as unfixed issues concerning clinical trials' biases and limitations. Nevertheless, designing multicenter standard clinical trials while considering individual variability and the exercise modality and duration will improve the perspective we have on the mechanisms mediating adaptation to exercise and final outcomes.

Prostaglandin receptor EP4 expression by Th17 cells is associated with high disease activity in ankylosing spondylitis

BACKGROUND

Th17 cells are involved in the pathogenesis of ankylosing spondylitis (AS). However, the mechanism underlying enhanced Th17 cell accumulation in AS remains unknown. The prostaglandin E₂ receptor EP2/EP4 signaling pathway plays a critical role in the development of autoimmune Th17 cells. Interestingly, recent genome-wide association studies (GWAS) have identified five risk alleles for AS in PTGER4, the gene encoding for EP4. The aim of this study was to reveal a possible link between EP4 and disease activity in patients with AS.

METHODS

Th17 cells from patients with AS were analyzed for the transcriptional expression of prostaglandin receptor genes by quantitative RT-PCR. Th17 cells from patients with rheumatoid arthritis (RA) and from healthy individuals served as controls. EP4 receptor expression in Th17 cells was assessed ex vivo by flow cytometry and by western blot. Functional analysis using EP4-specific agonists was performed to reveal how EP4 regulates Th17 cells.

RESULTS

EP4 is significantly overexpressed in Th17 cells from patients with AS compared to Th17 cells from healthy individuals or patients with RA or psoriatic arthritis (PsA). EP4 upregulation is unique to Th17 cells and is not found in other CD4⁺ T cell subsets. Specific activation of EP4 drives Th17 cell development and promotes EP4 expression in a positive feedback loop in AS but not in RA or PsA. Mechanistically, EP4 acts via upregulation of the interleukin-23 receptor (IL-23R), by suppressing the RORγt inhibitor FoxO1 and by enhancing STAT3 phosphorylation. Increased EP4 expression levels in Th17 cells from AS patients correlate with high disease activity as defined by a Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) score ≥ 4 (r = 0.7591, p = 0.0016).

CONCLUSIONS

EP4 is a potential marker of disease activity in patients with AS. Aberrant EP4 expression might contribute to pathogenic Th17 cell accumulation and represent a new target for the treatment of AS.