Abstract
Age-related skeletal muscle decline, or sarcopenia, is characterised by the progressive loss of muscle mass and function with age, resulting in increased morbidity and reduced quality of life. This study explores the role of short, non-coding strands of RNA called microRNA (miRNA) in the progression of age-related muscle loss. In recent years, miRNAs have gained traction in research due to their pivotal roles in regulating normal cell physiology. This growing recognition of miRNA's importance in cellular function culminated in Victor Ambros and Gary Ruvkun winning the esteemed Nobel Prize in 2024 for their work in elucidating the role of miRNA in regulating gene activity. As such, the role of miRNA-1, -126 and -133a was evaluated. miRNA-1 and -133a play different yet complementary roles in muscle regeneration, with miRNA-133a mediating satellite cell proliferation while subsequent differentiation is mediated by miRNA-1. miRNA-126 was evaluated for its role in angiogenesis. Therefore, we aimed to elucidate the role of these miRNAs and their target proteins in the development of sarcopenia.
Using qRT-PCR analysis, expression profiles for the miRNA in the gastrocnemius of male and female mice aged 12, 24, 36, 48, 60 and 72 weeks were determined. Following PCR, western blotting was used to determine the protein expression of SRF and SPRED-1, the direct targets of miRNA-133a and -126, respectively. Finally, the functional effect of miRNA-protein changes was determined through endothelial cells and α-smooth muscle actin staining to evaluate capillary and arteriole density changes.
Our results indicated that miRNA-1, -126 and -133a are sex-specifically differentially expressed with ageing. miRNA-1 was downregulated in males but upregulated in females. Comparatively, miRNA-126 and -133a showed no significant changes in males but were upregulated in females. Furthermore, expressing miRNA-1 and -133a as a ratio showed no significant differences in males but a significant increase in females. SRF expression showed sex-specific differences but no changes with age, while SPRED-1 was markedly decreased in female mice with age. Histology showed increased capillary density regardless of sex, while arteriole density was only increased in males.
This study proved that miRNA-1, -126 and -133a are sex-specifically dysregulated with ageing. Changes in miRNA-1/-133a ratios suggest that in males, the regenerative process is not dysfunctional but dysfunctional in females. Furthermore, miRNA-126-SPRED-1 and miRNA 133a-SRF expression discrepancies were identified. We identified that miRNA-126 and miRNA-133a expression is not reflected in SPRED-1 and SRF expression, respectively. This suggests that in ageing skeletal muscle, miRNA-126 and -133a target other pathways to exert their effect. This is especially true with miRNA-126, as increased capillary density and the expected effect of increased miRNA-126 expression were observed.
This study provides novel insights into the molecular mechanisms underlying sarcopenia. Our study was the first longitudinal study to determine temporal miRNA expression changes in a sex-specific manner. This highlights the divergent roles of miRNAs in male and female skeletal muscle ageing. While candidate biomarkers and therapeutic targets were not identifiable in this study, our study provides a framework for future sarcopenia studies that could elucidate specific pathways involved.