FHL2 Regulates Proliferation Differentiation and Autophagy of Bovine Skeletal Muscle Satellite Cells Through Wnt/β-catenin Signaling Pathway

The mechanism of physiological regulation of bovine skeletal muscle development is a complex process, and FHL2 has been studied in association with β-catenin activity and has previously been reported to play a role in skeletal muscle.However the mechanism of FHL2 action in regulating skeletal muscle development in bovine skeletal myosatellite is unclear. Here, we report that FHL2 can both promote the proliferation and differentiation of bovine myosatellite cells through the wnt signaling pathway and bovine skeletal muscle satellite cells through cellular autophagy. The results of western blotting, rt-qPCT, cell transfection assay showed that FHL2 gene expression was enhanced during the proliferation of skeletal muscle satellite cells, and FHL2 knockdown inhibited the proliferation and differentiation of bovine satellite cells and promoted the atrophy of myotubes. Furthermore, immunoprecipitation assays yielded that FHL2 knockdown decreased β-catenin activity in BMSCs and activated β-catenin-mediated wnt signaling pathway in combination with DVL-2, and that FHL2 knockdown induced autophagy in bovine satellite cells. Therefore, the FHL2 gene is a key gene in the regulation of bovine satellite cells.

EFFECT OF LOW-FREQUENCY ELECTROMAGNETICS (LFE) ON MUSCLE SATELLITE CELLS DIFFERENTIATION AND IMMUNE SYSTEM IN RAT

Spinal cord injury (SCI) is a severe neurological disease. Although surgery within 8[Formula: see text]h after SCI can substantially reduce paraplegia, most patients still suffer from hypomusculariasis after neuron recovery, which results in insufficient lower limb muscles to support bodyweight. Currently, there is no effective method to prevent muscle atrophy. Previous studies have shown that low-frequency electromagnetics (LFE) can stimulate the differentiation, proliferation and fusion of muscle satellite cells, however, the optimal electromagnetic strength and effects on the immune system have not been established. Here, we investigated the influence of LFE at different electromagnetic strengths on muscle cell recovery and assessed the impact of chronic LFE on the immune system of SCI rats. The rat immune system was rapidly activated after SCI. High-energy LFE provoked intensive immune responses, while low-energy LFE did not affect immune responses. Simultaneously, LFE effectively prevented myotube reduction and atrophy in SCI rats. The mRNA and protein levels of Pax7 and MyoD were increased after LFE at both high and low electromagnetic strengths, with the latter leading to more robust increases. Indeed, LFE remarkably induced muscle cell fusion. Together, our results demonstrated that LFE activates muscle satellite cells via stimulating myogenic factors. Chronic low-energy LFE is a safe therapy with no adverse impact on the immune system of SCI rats. LFE with 1.5 mT energy should be considered as an optimal therapeutic strategy.

Extraordinarily rapid proliferation of cultured muscle satellite cells from migratory birds

Migratory birds experience bouts of muscle growth and depletion as they prepare for, and undertake prolonged flight. Our studies of migratory bird muscle physiology in vitro led to the discovery that sanderling ( Calidris alba ) muscle satellite cells proliferate more rapidly than other normal cell lines. Here we determined the proliferation rate of muscle satellite cells isolated from five migratory species (sanderling; ruff, Calidris pugnax ; western sandpiper, Calidris mauri ; yellow-rumped warbler, Setophaga coronata ; Swainson's thrush, Catharus ustulatus ) from two families (shorebirds and songbirds) and with different migratory strategies. Ruff and sanderling satellite cells exhibited rapid proliferation, with population doubling times of 9.3 ± 1.3 and 11.4 ± 2 h, whereas the remaining species' cell doubling times were greater than or equal to 24 h. The results indicate that the rapid proliferation of satellite cells is not associated with total migration distance but may be related to flight bout duration and interact with lifespan.

A Novel miRNA Y-56 Mediates the Proliferation of Porcine Skeletal Muscle Satellite Cells by Targeting the IGF-1R-mediated AKT and ERK Pathways

Background: The skeletal muscle phenotype of the Bama Xiang pig (BM) is significantly different from the Landrace pig (LP). Uncovering the mechanism of porcine skeletal muscle growth will be of great significance to elucidate the mechanism of the different formation. As the key post-transcriptional regulators, miRNAs play an indispensable role in skeletal muscle development. The proliferation of skeletal muscle satellite cells not only maintain the muscle stem cell population, but also provide a large number of muscle derived cells. Thus, the goal of this study is to explore the effects of a novel miRNA Y-56 on the porcine skeletal muscle satellite cells (PSCs). Results: Firstly, we found that Y-56 was highly expressed in porcine muscle tissues, and its expression was higher in the BM than the LP. The EdU staining and CCK-8 assays results showed that increased levels of Y-56 suppressed cell proliferation, whereas decreased levels of Y-56 resulted in the opposite consequences. Furthermore, flow cytometry results showed that overexpression of Y-56 significantly reduced the percentage of S-phase cells, and the qRT-PCR and western blotting results showed that the expression levels of cyclin dependent kinase 2 (CDK4), proliferating cell nuclear antigen (PCNA) and Cyclin D1 were significantly inhibited. Moreover, downregulation of Y-56 increased the number of S-phase cells and the expression of CDK, PCNA and Cyclin D1. Furtherly, we identified that insulin like growth factor-1 receptor (IGF-1R) was a direct target of Y-56. Consistently, overexpression of IGF-1R promoted the cell proliferation of the PSCs, and increased the number of S-phase cells, as well as up-regulated the expressions of CDK4, PCNA and Cyclin D1. Meanwhile, knock-down of IGF-1R was associated with the opposite tend. What’s more, overexpression of IGF-1R partially reversed the inhibition of cell proliferation of the PSCs, the decrease of the percentage of S-phase cells and down-regulation of the expression levels of CDK4, PCNA and Cyclin D1, which caused by overexpression of Y-56. Finally, there was a significant decrease in the expression level of p-AKT and p-ERK with transfecting Y-56 mimics in the PSCs, and overexpression of IGF-1R reversed the decrease. Conclusion: Collectively, our findings suggested that Y-56 represses proliferation and cell cycle process of the PSCs through targeting IGF-1R that activated the AKT and ERK pathways.