A transcriptomics study of differentiated C2C12 myoblasts identified novel functional responses to 17β-estradiol

Transcriptome sequencing promotes insights on the molecular mechanism of SKP-SC-EVs mitigating denervation-induced muscle atrophy

BACKGROUND

Complex pathophysiological changes accompany denervation-induced skeletal muscle atrophy, but no effective treatment strategies exist. Our previous study indicated that extracellular vesicles derived from skin-derived precursors-derived Schwann cells (SKP-SC-EVs) can effectively mitigate denervation-induced muscle atrophy. However, the specific molecular mechanism remains unclear.

METHODS AND RESULTS

In this study, we used bioinformatics methods to scrutinize the impact of SKP-SC-EVs on gene expression in denervation-induced skeletal muscle atrophy. We found that SKP-SC-EVs altered the expression of 358 genes in denervated skeletal muscles. The differentially expressed genes were predominantly participated in biological processes, including cell cycle, inflammation, immunity, and adhesion, and signaling pathways, such as FoxO and PI3K.Using the Molecular Complex Detection (MCODE) plugin, we identified the two clusters with the highest score: cluster 1 comprised 37 genes, and Cluster 2 consisted of 24 genes. Then, fifty hub genes were identified using CytoHubba. The intersection of Hub genes and genes obtained by MCODE showed that all 23 genes related to the cell cycle in Cluster 1 were hub genes, and 5 genes in Cluster 2 were hub genes and associated with inflammation.

CONCLUSIONS

Overall, the differentially expressed genes in denervated skeletal muscle following SKP-SC-EVs treatment are primarily linked to the cell cycle and inflammation. Consequently, promoting proliferation and inhibiting inflammation may be the critical process in which SKP-SC-EVs delay denervation-induced muscle atrophy. Our findings contribute to a better understanding of the molecular mechanism of SKP-SC-EVs delaying denervation-induced muscle atrophy, offering a promising new avenue for muscle atrophy treatment.

Down-regulated Smyd1 participated in the inhibition of myoblast differentiation induced by cigarette smoke extract

The histone methyltransferase Smyd1 is essential for muscle development; however, its role in smoking-induced skeletal muscle atrophy and dysfunction has not been investigated thus far. In this study, Smyd1 was overexpressed or knocked down in C2C12 myoblasts by an adenovirus vector and cultured in differentiation medium containing 5% cigarette smoke extract (CSE) for 4 days. CSE exposure resulted in inhibition of C2C12 cell differentiation and downregulation of Smyd1 expression, whereas Smyd1 overexpression reduced the degree of inhibition of myotube differentiation caused by CSE exposure. CSE exposure activated P2RX7-mediated apoptosis and pyroptosis, caused increased intracellular reactive oxygen species (ROS) levels, and impaired mitochondrial biogenesis and increased protein degradation by downregulating PGC1α, whereas Smyd1 overexpression partially restored the altered protein levels caused by CSE exposure. Smyd1 knockdown alone produced a phenotype similar to CSE exposure, and Smyd1 knockdown during CSE exposure aggravated the degree of inhibition of myotube differentiation and the degree of activation of P2RX7. CSE exposure suppressed H3K4me2 expression, and chromatin immunoprecipitation confirmed the transcriptional regulation of P2rx7 by H3K4me2 modification. Our findings suggest that CSE exposure mediates C2C12 cell apoptosis and pyroptosis through the Smyd1-H3K4me2-P2RX7 axis, and inhibits PGC1α expression to impair mitochondrial biosynthesis and increase protein degradation by inhibiting Smyd1 expression, ultimately leading to abnormal C2C12 myoblasts differentiation and impaired myotube formation.

Trichostatin A inhibits skeletal muscle atrophy induced by cigarette smoke exposure in mice

AIMS

It is well known that cigarette smoke (CS) is the main risk factor for chronic obstructive pulmonary disease (COPD) accompanied by skeletal muscle atrophy. Histone deacetylases (HDACs) that remove acetyl groups from target proteins are necessary for the muscle atrophy associated with skeletal muscle disuse. However, the role of HDACs and trichostatin A (TSA), a HDAC inhibitor, in skeletal muscle atrophy caused by CS exposure remains poorly understood.

MAIN METHODS

Female mice were exposed to CS twice daily for 40 days and TSA injected intraperitoneally into CS-exposed mice on alternate days. Skeletal muscles were weighed and gastrocnemius (Gas) muscle histomorphology examined by hematoxylin and eosin staining. Histone deacetylases 1 and 2 (HDAC1/2), and markers of ubiquitin degradation, muscle differentiation, apoptosis, pyroptosis, and the cytoskeletal proteins were assessed by western blot and immunohistochemistry in Gas.

KEYFINDINGS

CS exposure decreased body and skeletal muscle weights and triggered an increase in the percentage of fiber with centralized nuclei in Gas. HDAC1/2 proteins were upregulated in the Gas of mice exposed to CS, while TSA effectively inhibited HDAC1/2 protein levels and attenuated the loss of body weight and skeletal muscle wet weight induced by CS exposure. Markers for ubiquitin degradation, muscle differentiation, cytoskeletal proteins, apoptosis and pyroptosis were all upregulated following CS exposure and effectively restored by TSA.

SIGNIFICANCE

TSA may inhibit skeletal muscle atrophy and histomorphological alterations induced by CS exposure by downregulating markers of ubiquitin degradation, muscle fiber differentiation, cytoskeletal proteins, apoptosis and pyroptosis via HDAC1/2 inhibition.