Atrophic skeletal muscle fibre-derived small extracellular vesicle miR-690 inhibits satellite cell differentiation during ageing

BACKGROUND

Sarcopenia is a common and progressive skeletal muscle disorder characterized by atrophic muscle fibres and contractile dysfunction. Accumulating evidence shows that the number and function of satellite cells (SCs) decline and become impaired during ageing, which may contribute to impaired regenerative capacity. A series of myokines/small extracellular vesicles (sEVs) released from muscle fibres regulate metabolism in muscle and extramuscular tissues in an autocrine/paracrine/endocrine manner during muscle atrophy. It is still unclear whether myokines/sEVs derived from muscle fibres can affect satellite cell function during ageing.

METHODS

Aged mice were used to investigate changes in the myogenic capacity of SCs during ageing-induced muscle atrophy. The effects of atrophic myotube-derived sEVs on satellite cell differentiation were investigated by biochemical methods and immunofluorescence staining. Small RNA sequencing was performed to identify differentially expressed sEV microRNAs (miRNAs) between the control myotubes and atrophic myotubes. The target genes of the miRNA were predicted by bioinformatics analysis and verified by luciferase activity assays. The effects of identified miRNA on the myogenic capacity of SCs in vivo were investigated by intramuscular injection of adeno-associated virus (AAV) to overexpress or silence miRNA in skeletal muscle.

RESULTS

Our study showed that the myogenic capacity of SCs was significantly decreased (50%, n = 6, P < 0.001) in the tibialis anterior muscle of aged mice. We showed that atrophic myotube-derived sEVs inhibited satellite cell differentiation in vitro (n = 3, P < 0.001) and in vivo (35%, n = 6, P < 0.05). We also found that miR-690 was the most highly enriched miRNA among all the screened sEV miRNAs in atrophic myotubes [Log₂ (Fold Change) = 7, P < 0.001], which was verified in the atrophic muscle of aged mice (threefold, n = 6, P < 0.001) and aged men with mean age of 71 ± 5.27 years (2.8-fold, n = 10, P < 0.001). MiR-690 can inhibit myogenic capacity of SCs by targeting myocyte enhancer factor 2, including Mef2a, Mef2c and Mef2d, in vitro (n = 3, P < 0.05) and in vivo (n = 6, P < 0.05). Specific silencing of miR-690 in the muscle can promote satellite cell differentiation (n = 6, P < 0.001) and alleviate muscle atrophy in aged mice (n = 6, P < 0.001).

CONCLUSIONS

Our study demonstrated that atrophic muscle fibre-derived sEV miR-690 may inhibit satellite cell differentiation by targeting myocyte enhancer factor 2 during ageing.

MiR-690 treatment causes decreased fibrosis and steatosis and restores specific Kupffer cell functions in NASH

Nonalcoholic steatohepatitis (NASH) is a liver disease associated with significant morbidity. Kupffer cells (KCs) produce endogenous miR-690 and, via exosome secretion, shuttle this miRNA to other liver cells, such as hepatocytes, recruited hepatic macrophages (RHMs), and hepatic stellate cells (HSCs). miR-690 directly inhibits fibrogenesis in HSCs, inflammation in RHMs, and de novo lipogenesis in hepatocytes. When an miR-690 mimic is administered to NASH mice in vivo, all the features of the NASH phenotype are robustly inhibited. During the development of NASH, KCs become miR-690 deficient, and miR-690 levels are markedly lower in mouse and human NASH livers than in controls. KC-specific KO of miR-690 promotes NASH pathogenesis. A primary target of miR-690 is NADK mRNA, and NADK levels are inversely proportional to the cellular miR-690 content. These studies show that KCs play a central role in the etiology of NASH and raise the possibility that miR-690 could emerge as a therapeutic for this condition.

MiR-690, an exosomal-derived miRNA from M2-polarized macrophages, improves insulin sensitivity in obese mice

Insulin resistance is a major pathophysiologic defect in type 2 diabetes and obesity, while anti-inflammatory M2-like macrophages are important in maintaining normal metabolic homeostasis. Here, we show that M2 polarized bone marrow-derived macrophages (BMDMs) secrete miRNA-containing exosomes (Exos), which improve glucose tolerance and insulin sensitivity when given to obese mice. Depletion of their miRNA cargo blocks the ability of M2 BMDM Exos to enhance insulin sensitivity. We found that miR-690 is highly expressed in M2 BMDM Exos and functions as an insulin sensitizer both in vivo and in vitro. Expressing an miR-690 mimic in miRNA-depleted BMDMs generates Exos that recapitulate the effects of M2 BMDM Exos on metabolic phenotypes. Nadk is a bona fide target mRNA of miR-690, and Nadk plays a role in modulating macrophage inflammation and insulin signaling. Taken together, these data suggest miR-690 could be a new therapeutic insulin-sensitizing agent for metabolic disease.

Role of microRNA 690 in Mediating Angiotensin II Effects on Inflammation and Endoplasmic Reticulum Stress

Overactivation of the renin–angiotensin system (RAS) during obesity disrupts adipocyte metabolic homeostasis and induces endoplasmic reticulum (ER) stress and inflammation; however, underlying mechanisms are not well known. We propose that overexpression of angiotensinogen (Agt), the precursor protein of RAS in adipose tissue or treatment of adipocytes with Angiotensin II (Ang II), RAS bioactive hormone, alters specific microRNAs (miRNA), that target ER stress and inflammation leading to adipocyte dysfunction. Epididymal white adipose tissue (WAT) from B6 wild type (Wt) and transgenic male mice overexpressing Agt (Agt-Tg) in adipose tissue and adipocytes treated with Ang II were used. Small RNA sequencing and microarray in WAT identified differentially expressed miRNAs and genes, out of which miR-690 and mitogen-activated protein kinase kinase 3 (MAP2K3) were validated as significantly up- and down-regulated, respectively, in Agt-Tg, and in Ang II-treated adipocytes compared to respective controls. Additionally, the direct regulatory role of miR-690 on MAP2K3 was confirmed using mimic, inhibitors and dual-luciferase reporter assay. Downstream protein targets of MAP2K3 which include p38, NF-κB, IL-6 and CHOP were all reduced. These results indicate a critical post-transcriptional role for miR-690 in inflammation and ER stress. In conclusion, miR-690 plays a protective function and could be a useful target to reduce obesity.

MiR-690, a Runx2-targeted miRNA, regulates osteogenic differentiation of C2C12 myogenic progenitor cells by targeting NF-kappaB p65

BACKGROUND

The runt-related transcription factor 2 (Runx2) is a cell-fate-determining factor that controls osteoblast differentiation and bone formation. It has been previously demonstrated that microRNAs (miRNAs) play important roles in osteogenesis. However, the Runx2-regulated miRNAs that have been reported thus far are limited. In this study, we pursued to identify these miRNAs in Tet-on stable C2C12 cell line (C2C12/Runx2(Dox) subline).

RESULTS

Microarray analysis revealed that alterations in miRNA expression occur with 54 miRNAs. Among these miRNAs, miR-690 was identified as a positive regulator of Runx2-induced osteogenic differentiation of C2C12 cells through gain- and loss-of-function assays. Expression of miR-690 is induced by Runx2, which binds directly to the putative promoter of mir-690 (Mirn690). The miR-690 proceeds to inhibit translation of the messenger RNA encoding the nuclear factor kappa B (NF-κB) subunit p65 whose overexpression inhibits Runx2-induced osteogenic differentiation of C2C12 cells. Interleukin-6 (IL-6), a downstream target of NF-κB pathway, is upregulated by p65 overexpression but significantly downregulated during this differentiation process. Furthermore, overexpression of IL-6 impedes the expression of osteocalcin, a defined marker of late osteoblast differentiation.

CONCLUSIONS

Together, our results suggest that the miR-690 transactivated by Runx2 acts as a positive regulator of Runx2-induced osteogenic differentiation by inactivating the NF-κB pathway via the downregulation of the subunit p65.