Skeletal muscle atrophy is a common and debilitating condition that lacks an effective therapy. To address this problem, we used a systems-based discovery strategy to search for a small molecule ...whose mRNA expression signature negatively correlates to mRNA expression signatures of human skeletal muscle atrophy. This strategy identified a natural small molecule from tomato plants, tomatidine. Using cultured skeletal myotubes from both humans and mice, we found that tomatidine stimulated mTORC1 signaling and anabolism, leading to accumulation of protein and mitochondria, and ultimately, cell growth. Furthermore, in mice, tomatidine increased skeletal muscle mTORC1 signaling, reduced skeletal muscle atrophy, enhanced recovery from skeletal muscle atrophy, stimulated skeletal muscle hypertrophy, and increased strength and exercise capacity. Collectively, these results identify tomatidine as a novel small molecule inhibitor of muscle atrophy. Tomatidine may have utility as a therapeutic agent or lead compound for skeletal muscle atrophy.
Skeletal muscle atrophy is a common and serious condition that lacks a pharmacologic therapy.
We used a systems-based strategy to identify tomatidine, a natural compound from tomato plants, as a novel small molecule inhibitor of muscle atrophy.
Tomatidine may have utility as a therapeutic agent or lead compound for muscle atrophy.
These results suggest new therapeutic strategies for muscle atrophy.
Aberrant proliferation of vascular smooth muscle cells (VSMC) is a critical contributor to the pathogenesis of atherosclerosis (AS). Our previous studies have demonstrated that apelin‐13/APJ confers ...a proliferative response in VSMC, however, its underlying mechanism remains elusive. In this study, we aimed to investigate the role of mitophagy in apelin‐13‐induced VSMC proliferation and atherosclerotic lesions in apolipoprotein E knockout (ApoE‐/‐) mice. Apelin‐13 enhances human aortic VSMC proliferation and proliferative regulator proliferating cell nuclear antigen expression in dose and time‐dependent manner, while is abolished by APJ antagonist F13A. We observe the engulfment of damage mitochondria by autophagosomes (mitophagy) of human aortic VSMC in apelin‐13 stimulation. Mechanistically, apelin‐13 increases p‐AMPKα and promotes mitophagic activity such as the LC3I to LC3II ratio, the increase of Beclin‐1 level and the decrease of p62 level. Importantly, the expressions of PINK1, Parkin, VDAC1, and Tom20 are induced by apelin‐13. Conversely, blockade of APJ by F13A abolishes these stimulatory effects. Human aortic VSMC transfected with AMPKα, PINK1, or Parkin and subjected to apelin‐13 impairs mitophagy and prevents proliferation. Additional, apelin‐13 not only increases the expression of Drp1 but also reduces the expressions of Mfn1, Mfn2, and OPA1. Remarkably, the mitochondrial division inhibitor‐1(Mdivi‐1), the pharmacological inhibition of Drp1, attenuates human aortic VSMC proliferation. Treatment of ApoE‐/‐ mice with apelin‐13 accelerates atherosclerotic lesions, increases p‐AMPKα and mitophagy in aortic wall in vivo. Finally, PINK1‐/‐ mutant mice with apelin‐13 attenuates atherosclerotic lesions along with defective in mitophagy. PINK1/Parkin‐mediated mitophagy promotes apelin‐13‐evoked human aortic VSMC proliferation by activating p‐AMPKα and exacerbates the progression of atherosclerotic lesions.
PINK1/Parkin‐mediated mitophagy promotes apelin‐13‐induced human aortic vascular smooth muscle cell proliferation through activating AMPKα in vitro. Mitophagy exacerbates atherosclerotic lesions of ApoE‐/‐ mice with apelin‐13 stimulation in vivo. Apelin‐13 also increases mitochondrial fission and decreases mitochondrial fusion via AMPKα, thus contributing to the regulation of mitochondrial dynamics. PINK1 deficiency results in defective mitophagy and attenuates vascular smooth muscle cells (VSMC) proliferation induced by apelin‐13. AMPKα‐PINK1‐Parkin axis plays a crucial role in apelin‐13‐induced human aortic VSMC proliferation and atherosclerotic plaques in vitro and in vivo, and consequently atherosclerosis.
Muscle satellite cells contribute to muscle regeneration. We have used a Pax3superscript GFP/+ mouse line to directly isolate (Pax3)(green fluorescent protein)-expressing muscle satellite cells, by ...flow cytometry from adult skeletal muscles, as a homogeneous population of small, nongranular, Pax7+, CD34+, CD45-, Sca1- cells. The flow cytometry parameters thus established enabled us to isolate satellite cells from wild-type muscles. Such cells, grafted into muscles of mdx nu/nu mice, contributed both to fiber repair and to the muscle satellite cell compartment. Expansion of these cells in culture before engraftment reduced their regenerative capacity.
The loss of skeletal muscle mass with aging has been attributed to a decline in muscle fiber number and muscle fiber size.
To define to what extent differences in leg muscle cross-sectional area ...(CSA) between young and elderly men are attributed to differences in muscle fiber size.
Quadriceps muscle CSA and type I and type II muscle fiber size were measured in healthy young (n=25; 23±1y) and older (n=26; 71±1y) men. Subsequently, the older subjects performed 6months of resistance type exercise training, after which measurements were repeated. Differences in quadriceps muscle CSA were compared with differences in type I and type II muscle fiber size.
Quadriceps CSA was substantially smaller in older versus young men (68±2 vs 80±2cm2, respectively; P<0.001). Type II muscle fiber size was substantially smaller in the elderly vs the young (29%; P<0.001), with a tendency of smaller type I muscle fibers (P=0.052). Differences in type II muscle fiber size fully explained differences in quadriceps CSA between groups. Prolonged resistance type exercise training in the elderly increased type II muscle fiber size by 24±8% (P<0.01), explaining 100±3% of the increase in quadriceps muscle CSA (from 68±2 to 74±2cm2).
Reduced muscle mass with aging is mainly attributed to smaller type II muscle fiber size and, as such, is unlikely accompanied by substantial muscle fiber loss. In line, the increase in muscle mass following prolonged resistance type exercise training can be attributed entirely to specific type II muscle fiber hypertrophy.
► Age-related differences in muscle size can be attributed to smaller muscle fibers. ► Training-induced increase in muscle size is attributed to muscle fiber hypertrophy. ► Large in muscle fiber numbers changes in aging or after training are unlikely. ► Interventions for sarcopenia should target type II muscle fiber hypertrophy.
The use of human pluripotent stem cells for in vitro disease modelling and clinical applications requires protocols that convert these cells into relevant adult cell types. Here, we report the rapid ...and efficient differentiation of human pluripotent stem cells into vascular endothelial and smooth muscle cells. We found that GSK3 inhibition and BMP4 treatment rapidly committed pluripotent cells to a mesodermal fate and subsequent exposure to VEGF-A or PDGF-BB resulted in the differentiation of either endothelial or vascular smooth muscle cells, respectively. Both protocols produced mature cells with efficiencies exceeding 80% within six days. On purification to 99% via surface markers, endothelial cells maintained their identity, as assessed by marker gene expression, and showed relevant in vitro and in vivo functionality. Global transcriptional and metabolomic analyses confirmed that the cells closely resembled their in vivo counterparts. Our results suggest that these cells could be used to faithfully model human disease.
Short-term muscle disuse has been reported to lower both postabsorptive and postprandial myofibrillar protein synthesis rates. This study assessed the impact of disuse on daily myofibrillar protein ...synthesis rates following short-term (2 and 7 days) muscle disuse under free living conditions. Thirteen healthy young men (age: 20 ± 1 yr; BMI: 23 ± 1 kg/m
) underwent 7 days of unilateral leg immobilization via a knee brace, with the nonimmobilized leg acting as a control. Four days before immobilization participants ingested 400 mL of 70% deuterated water, with 50-mL doses consumed daily thereafter. Upper leg bilateral MRI scans and muscle biopsies were collected before and after 2 and 7 days of immobilization to determine quadriceps volume and daily myofibrillar protein synthesis rates. Immobilization reduced quadriceps volume in the immobilized leg by 1.7 ± 0.3 and 6.7 ± 0.6% after 2 and 7 days, respectively, with no changes in the control leg. Over the 1-wk immobilization period, myofibrillar protein synthesis rates were 36 ± 4% lower in the immobilized (0.81 ± 0.04%/day) compared with the control (1.26 ± 0.04%/day) leg (
< 0.001). Myofibrillar protein synthesis rates in the control leg did not change over time (
= 0.775), but in the immobilized leg they were numerically lower during the 0- to 2-day period (16 ± 6%, 1.11 ± 0.09%/day,
= 0.153) and were significantly lower during the 2- to 7-day period (44 ± 5%, 0.70 ± 0.06%/day,
< 0.001) when compared with the control leg. We conclude that 1 wk of muscle disuse induces a rapid and sustained decline in daily myofibrillar protein synthesis rates in healthy young men.
BACKGROUND:Mechanical ventilation is a life-saving intervention used to provide adequate pulmonary ventilation in patients suffering from respiratory failure. However, prolonged mechanical ...ventilation is associated with significant diaphragmatic weakness resulting from both myofiber atrophy and contractile dysfunction. Although several signaling pathways contribute to diaphragm weakness during mechanical ventilation, it is established that oxidative stress is required for diaphragmatic weakness to occur. Therefore, identifying the site(s) of mechanical ventilation- induced reactive oxygen species production in the diaphragm is important.
OBJECTIVE:These experiments tested the hypothesis that elevated mitochondrial reactive oxygen species emission is required for mechanical ventilation-induced oxidative stress, atrophy, and contractile dysfunction in the diaphragm.
DESIGN:Cause and effect was determined by preventing mechanical ventilation-induced mitochondrial reactive oxygen species emission in the diaphragm of rats using a novel mitochondria-targeted antioxidant (SS-31).
INTERVENTIONS:None.
MEASUREMENTS AND MAIN RESULTS:Compared to mechanically ventilated animals treated with saline, animals treated with SS-31 were protected against mechanical ventilation-induced mitochondrial dysfunction, oxidative stress, and protease activation in the diaphragm. Importantly, treatment of animals with the mitochondrial antioxidant also protected the diaphragm against mechanical ventilation-induced myofiber atrophy and contractile dysfunction.
CONCLUSIONS:These results reveal that prevention of mechanical ventilation-induced increases in diaphragmatic mitochondrial reactive oxygen species emission protects the diaphragm from mechanical ventilation-induced diaphragmatic weakness. This important new finding indicates that mitochondria are a primary source of reactive oxygen species production in the diaphragm during prolonged mechanical ventilation. These results could lead to the development of a therapeutic intervention to impede mechanical ventilation-induced diaphragmatic weakness.
Satellite cells, the predominant stem cell population in adult skeletal muscle, are activated in response to hypertrophic stimuli and give rise to myogenic progenitor cells (MPCs) within the ...extracellular matrix (ECM) that surrounds myofibers. This ECM is composed largely of collagens secreted by interstitial fibrogenic cells, which influence satellite cell activity and muscle repair during hypertrophy and aging. Here we show that MPCs interact with interstitial fibrogenic cells to ensure proper ECM deposition and optimal muscle remodeling in response to hypertrophic stimuli. MPC-dependent ECM remodeling during the first week of a growth stimulus is sufficient to ensure long-term myofiber hypertrophy. MPCs secrete exosomes containing miR-206, which represses Rrbp1, a master regulator of collagen biosynthesis, in fibrogenic cells to prevent excessive ECM deposition. These findings provide insights into how skeletal stem and progenitor cells interact with other cell types to actively regulate their extracellular environments for tissue maintenance and adaptation.
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•Myogenic progenitor cells (MPCs) regulate the muscle extracellular matrix•MPCs regulate skeletal muscle fiber hypertrophy independent of fusion•miR-206 in MPC exosomes regulates fibrogenic cell Rrbp1 and collagen expression•MPCs regulate ECM remodeling within 1 week to facilitate fiber growth
Stem cells interact with the surrounding extracellular environment to facilitate tissue plasticity. Fry and colleagues report that skeletal muscle myogenic progenitor cells (MPCs) secrete exosomes containing miR-206, which regulates fibrogenic cell collagen expression through repression of Rrbp1. MPC-mediated regulation of the muscle extracellular environment is necessary during early myofiber growth.
Scope
In this study, we aim to determine the effects of resveratrol (RSV) on muscle atrophy in streptozocin‐induced diabetic mice and to explore mitochondrial quality control (MQC) as a possible ...mechanism.
Methods and results
The experimental mice were fed either a control diet or an identical diet containing 0.04% RSV for 8 weeks. Examinations were subsequently carried out, including the effects of RSV on muscle atrophy and muscle function, as well as on the signaling pathways related to protein degradation and MQC processes. The results show that RSV supplementation improves muscle atrophy and muscle function, attenuates the increase in ubiquitin and muscle RING‐finger protein‐1 (MuRF‐1), and simultaneously attenuates LC3‐II and cleaved caspase‐3 in the skeletal muscle of diabetic mice. Moreover, RSV treatment of diabetic mice results in an increase in mitochondrial biogenesis and inhibition of the activation of mitophagy in skeletal muscle. RSV also protects skeletal muscle against excess mitochondrial fusion and fission in the diabetic mice.
Conclusion
The results suggest that RSV ameliorates diabetes‐induced skeletal muscle atrophy by modulating MQC.
Diabetes‐mellitus‐induced skeletal muscle atrophy is associated with impaired mitochondrial quality control, greater activation of mitophagy, elevated mitochondrial fusion and fission, and decreased mitochondrial biogenesis in this study. Interestingly, resveratrol supplementation improved defective MQC by increasing mitochondrial biogenesis, suppressing the activation of mitophagy, and giving rise to reduced mitochondrial fission and fusion in skeletal muscle of diabetic mice.
Abstract
Aims
Angiotensin II (AngII) is a potential contributor to the development of abdominal aortic aneurysm (AAA). In aortic vascular smooth muscle cells (VSMCs), exposure to AngII induces ...mitochondrial fission via dynamin-related protein 1 (Drp1). However, pathophysiological relevance of mitochondrial morphology in AngII-associated AAA remains unexplored. Here, we tested the hypothesis that mitochondrial fission is involved in the development of AAA.
Methods and results
Immunohistochemistry was performed on human AAA samples and revealed enhanced expression of Drp1. In C57BL6 mice treated with AngII plus β-aminopropionitrile, AAA tissue also showed an increase in Drp1 expression. A mitochondrial fission inhibitor, mdivi1, attenuated AAA size, associated aortic pathology, Drp1 protein induction, and mitochondrial fission but not hypertension in these mice. Moreover, western-blot analysis showed that induction of matrix metalloproteinase-2, which precedes the development of AAA, was blocked by mdivi1. Mdivi1 also reduced the development of AAA in apolipoprotein E-deficient mice infused with AngII. As with mdivi1, Drp1+/− mice treated with AngII plus β-aminopropionitrile showed a decrease in AAA compared to control Drp1+/+ mice. In abdominal aortic VSMCs, AngII induced phosphorylation of Drp1 and mitochondrial fission, the latter of which was attenuated with Drp1 silencing as well as mdivi1. AngII also induced vascular cell adhesion molecule-1 expression and enhanced leucocyte adhesion and mitochondrial oxygen consumption in smooth muscle cells, which were attenuated with mdivi1.
Conclusion
These data indicate that Drp1 and mitochondrial fission play salient roles in AAA development, which likely involves mitochondrial dysfunction and inflammatory activation of VSMCs.
Graphical Abstract
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