Sarcopenia refers to gradual and progressive functional limitations and deterioration in muscle strength and endurance. (Greenlund and Nair 2003; Mühlberg and Sieber 2004) Aging is a major factor in this disease by affecting physical activity capability and the molecular basis for the loss of muscle mass. (Goyns et al. 1998; Starling et al. 1999) To understand the underlying biology of sarcopenia and discover an effective intervention that can improve muscle function, it is necessary to monitor gene expression changes in a genome-wide study. Bioinformatics analyses including extended previous data are based on screening genetic alterations of gene expression.(Mullighan et al. 2007)
By identifying the key expression genes and miRNAs of disease including mRNA-miRNA interactions, many helpful disease control strategies can be acquired. To identify more optimal core genes of muscle weakness involved in aging, this study used two profile datasets (GSE8479 and GSE1428) based on bioinformatics methods. Twenty-five aged muscle specimens and twenty-two young muscle specimens were used in the research. Via imaGEO online analysis, a total of 81 commonly changed DEGs including 4 upregulated and 77 downregulated DEGs were revealed. After that, the Metascape online tool was used for functional and pathway enrichment analysis. DEGs were enriched in the category of 1) Reactome gene sets including the TCA cycle and respiratory electron transport and mitochondrial protein import; 2) GO biological processes including mitochondrion organization, monocarboxylic acid metabolic processes, midbrain development, and the regulation of oxidoreductase activity and cold-induced thermogenesis; 3) the KEGG pathway including cardiac muscle contraction, carbon metabolism, and the citrate cycle; and 4) CORUM including the mitochondrial 55S ribosome. Particularly, 23 DEGs including the citric acid (TCA) cycle, respiratory electron transport, and mitochondrial protein import were identified in the Reactome gene sets. In GO biological process and KEGG pathway analyses, mitochondrion organization and cardiac muscle contraction were most associated in each category. Next, a PPI network complex of the DEGs was constructed, which was composed of 79 nodes and 186 edges via Cytoscape using the STRING database. Three vital clusters were obtained by MCODE analysis including 1) cluster one of 12 nodes (COX7B, COX4I1, COX5A, COX7A2, ATP5J, ATP5G1, ATP5G3, NDUFB2, NDUFB3, NDUFB5, UQCRQ, and UQCRFS1) and 66 edges; 2) cluster two of four nodes (CS, APOO, SUCLG1, and PDHA1) and five edges; and 3) cluster three of three nodes (MRPL2, MRPL12, and MRPL34) and three edges. In CytoHubba, a Cytoscape plugin, 20 hub genes (COX5A, UQCRFS1, UQCRQ, COX4I1, COX7A2, NDUFB2, COX7B, ATP5G1, ATP5G3, NDUFB5, ATP5J, NDUFB3, COX7A1, SUCLG1, CS, APOO, C14orf2, PDHA1, and TIMM8A) were clarified. Seven DE-MiRNAs (hsa-miR-450a-5p, hsa-miR-127-3p, hsa-miR-24-2-5p, hsa-miR-378a-5p, hsa-miR-532-5p, hsa-miR-487b-5p, and has-miR-487b-3p) based on one profile dataset (GSE23527) were identified and the Venn diagram web tool was used for the target genes. Finally, we found six target genes (COX7A1, NDUFB5, COX7B, PDHA1, TIMM8A, and CS) and miRNAs that could be considered novel effective targets to treat patients with age-related sarcopenia.
The present study showed that most genes were related to mitochondrial function and energy-producing capabilities. Skeletal muscle mitochondrial capacity is an important factor and is well-studied.(Coen et al. 2013; Gonzalez-Freire et al. 2018) Human aging generally results in lower mitochondrial function.(Tonkonogi et al. 2003; Lanza et al. 2008; Porter et al. 2015) There are close links between muscle mass and mitochondrial energetics including reduced ATP(Romanello et al. 2010) and increased ROS generation.(Kavazis et al. 2009; Min et al. 2011) ROS produced in aged muscle results in proteolytic degradation (proteasome system) and energetic stress, leading to reduced muscle mass. (Jang et al. 2010) If muscle mitochondria fail to provide sufficient ATP, the cells choose either growth or somatic maintenance, and this results in the disruption of proteostasis equilibrium.(Hou 2013)
Because miRNAs are very competitive therapeutic molecules, our findings of miRNAs regulating mitochondrial function-related genes could be used in strategies for recovering the muscle atrophy of patients with age-related sarcopenia.(van Rooij et al. 2012) A recent clinical trial indicated that specific inhibitors of miRNAs called anti-miR compounds represented potential drugs for incurable diseases(Chakraborty et al. 2017), and our study showed a new approach to treating sarcopenia, which remains a challenging muscle disorder.