A number of microRNAs (miRNAs, miRs) have been shown to play a role in skeletal muscle atrophy, but their role is not completely understood. Here we show that miR-29b promotes skeletal muscle atrophy in response to different atrophic stimuli in cells and in mouse models. miR-29b promotes atrophy of myotubes differentiated from C2C12 or primary myoblasts, and conversely, its inhibition attenuates atrophy induced by dexamethasone (Dex), TNF-α and H2O2 treatment. Targeting of IGF-1 and PI3K(p85α) by miR-29b is required for induction of muscle atrophy. In vivo, miR-29b overexpression is sufficient to promote muscle atrophy while inhibition of miR-29b attenuates atrophy induced by denervation and immobilization. These data suggest that miR-29b contributes to multiple types of muscle atrophy via targeting of IGF-1 and PI3K(p85α), and that suppression of miR-29b may represent a therapeutic approach for muscle atrophy induced by different stimuli.
ObjectivesExtracellular microRNAs represent functional biomarkers for obesity and related disorders; we investigated plasma microRNAs in insulin resistance phenotypes in obesity.Methods175 microRNA were analysed in females with (insulin sensitivity n=11; insulin resistance n=19; Type-II diabetes n=15) and without (n=12) obesity. Correlations between microRNA level and clinical parameters, and levels of 15 microRNA in a murine obesity model were investigated.Results106 microRNA were significantly (adjusted P≤0.05) different between controls and at least one obesity phenotype, including microRNAs with: previously reported roles in obesity and altered circulating levels (e.g. miR-122, miR-192); known roles in obesity but no reported changes in circulating level (e.g. miR-378a); no current reported role in, or association, with obesity (e.g. miR-28-5p, miR-374b, miR-32). miRNA in the latter group were found to be associated with extracellular vesicles. 48 microRNA showed significant correlations with clinical parameters; stepwise regression retained let-7b, miR-144-5p, miR-34a, and miR-532-5p in a model predictive of insulin resistance (R2 = 0.57, P=7.5 × 10-8). miR-378a and miR-122 were perturbed in metabolically relevant tissues in a murine model of obesity.ConclusionsThis study expands on the role of extracellular miRNA in insulin resistant phenotypes of obesity and identifies candidate miRNA not previously associated with obesity.
Rationale: Previous translational studies implicate plasma extracellular microRNA-30d (miR-30d) as a biomarker in left ventricular (LV) remodeling and clinical outcome in heart failure (HF) patients, though precise mechanisms remain obscure. Objective: To investigate the mechanism of miR-30d-mediated cardioprotection in HF. Methods and Results: In rat and mouse models of ischemic HF, we show that miR-30d gain of function (genetic, lentivirus or agomiR-mediated) improves cardiac function, decreases myocardial fibrosis, and attenuates cardiomyocyte (CM) apoptosis. Genetic or locked nucleic acid (LNA)-based knock-down of miR-30d expression potentiates pathological LV remodeling, with increased dysfunction, fibrosis, and CM death. RNA-seq of in vitro miR-30d gain and loss of function, together with bioinformatic prediction and experimental validation in cardiac myocytes and fibroblasts, were used to identify and validate direct targets of miR-30d. miR-30d expression is selectively enriched in CMs, induced by hypoxic stress and is acutely protective, targeting mitogen-associate protein kinase (MAP4K4) to ameliorate apoptosis. Moreover, miR-30d is secreted primarily in extracellular vesicles by CMs and inhibits fibroblast proliferation and activation by directly targeting integrin α5 in the acute phase via paracrine signaling to cardiac fibroblasts. In the chronic phase of ischemic remodeling, lower expression of miR-30d in the heart and plasma EVs is associated with adverse remodeling in rodent models and human subjects, and is linked to whole blood expression of genes implicated in fibrosis and inflammation, consistent with observations in model systems. Conclusions: These findings provide the mechanistic underpinning for the cardioprotective association of miR-30d in human HF. More broadly, our findings support an emerging paradigm involving intercellular communication of EV-contained miRNAs to trans regulate distinct signaling pathways across cell types. Functionally validated RNA biomarkers and their signaling networks may warrant further investigation as novel therapeutic targets in HF.
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