Downregulation of E3 Ubiquitin Ligases and Mitophagy-Related Genes in Skeletal Muscle of Physically Inactive, Frail Older Women: A Cross-Sectional Comparison

Reduced lean mass and physical function is a characteristic of frailty. However, it is currently unknown if proteolysis through the E3 ubiquitin ligases and the autophagic lysosomal pathway is dysregulated in inactive frail older women. The purpose of this study was to determine the expression of key markers of ubiquitin-mediated and autophagic lysosomal proteolysis in inactive (N = 7) compared with active (N = 7) older women. Strength, mobility, leg lean mass, and physical activity assessment were used to characterize activity levels and frailty in older women. Vastus lateralis biopsies were collected after an overnight fast and were assessed for gene and protein targets related to E3 ubiquitin ligases and the autophagic lysosomal system. We found that AMP-activated protein kinase alpha (Thr172) was increased (p = .045), and forkhead box O3A (FOXO3A) gene expression (p = .047) was lower in inactive frail older women. Foxo3a (Ser253), Beclin1 (Ser93/96), and class III phosphatidylinositol-3-kinase (VPS34) protein expression were not different between the groups (p > .05). Neural precursor cell-expressed developmentally downregulated protein 4, muscle ring finger 1, muscle atrophy F-box, and the autophagy/mitophagy gene expression markers, Beclin1, autophagy-related-7, BCL2/adenovirus E1B 19kDa interacting protein 3 (BNIP3), dynamin-related protein 1, and Parkinson protein 2 (PARKIN) were lower in inactive frail older women (p < .05). Autophagy/mitophagy markers were positively correlated with the 6-minute walk and leg lean mass (p < .05). We conclude that physical inactivity in frail older women is associated with a downregulation of ubiquitin-mediated and autophagic lysosomal skeletal muscle gene expression, perhaps related to low muscle mass and poor physical function.