Downregulation of E3 ubiquitin ligases and mitophagy-related genes in skeletal muscle of physically inactive, frail older women: A cross-sectional comparison

Abstract

Background and Objectives. 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. Methods. 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. Results. 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