Longitudinal analysis of early stage sarcopenia in aging rhesus monkeys.

We present a longitudinal study using the rhesus monkey to determine biochemical and histological changes in vastus lateralis (VL) muscle fibers and whether these changes correlate with muscle mass loss. Dual-energy X-ray absorptiometry (DXA) was used to determine body weight, body fat and to estimate upper leg muscle mass in 12 adult male rhesus monkeys over 12 years. Muscle mass (MM) was evaluated at years 6, 9 and 12 of the study. Concurrently, VL muscle biopsy samples were collected. Muscle tissue was sectioned, stained and individual muscle fibers were analyzed for fiber type, cross-sectional area (CSA) and mitochondrial electron transport system (ETS) enzyme abnormalities. The animals' body weight did not change over time, however a significant increase in DXA-measured percent body fat was observed. Significant MM loss occurred in the upper leg over 12 years. A reduction in muscle fiber CSA significantly contributed to the MM loss observed in the VL of middle-aged rhesus monkeys. An age-dependent increase in muscle fibers developing mitochondrial enzyme abnormalities due to mitochondrial DNA deletion mutations was observed. The longitudinal approach of this study demonstrated that significant muscle changes occurred during middle age in a cohort of aging rhesus monkeys.