Remodeling process in bone of aged rats in response to resistance training

We investigate the effects of RT on the mechanical function, gene, and protein expression of key factors involved in bone remodeling during aging. Male rats of 3 and 21 months of age were randomly allocated into four groups (8 per group): young sedentary (YS), young trained (YT), old sedentary (OS), and old trained (OT). RT was performed three times per week (12 weeks). Bone tenacity and stiffness were measured by biomechanical tests and mRNA levels of COL1A1, MEPE, SOST, OPG, BMP-2, PPAR-y, MMP-2-9-13, and TIMP-1 were evaluated by quantitative PCR. COL1A1 protein and MMP-2 activity were detected by western blotting and zymography assays. Aging increased stiffness, while BMP-2, OPG, COL1A1 and MMP-2 mRNA levels reduced (OS vs YS; p ≤ 0.05). RT increased the tenacity of the femur and reduced PPAR-γ regardless of age (YT vs. YS; OT vs. OS; p ≤ 0.05). RT downregulated SOST mRNA levels only in the OT group (vs. OS group, p ≤ 0.05). RT mitigated the age-associated increase in MMP-9 mRNA levels (p ≤ 0.05). In young animals, upregulation in MEPE, MMP-13, TIMP-1 were observed after RT, as well an increase in COL1A1 protein and MMP-2 activity (p ≤ 0.05). RT improved bone tenacity independent of aging, which is relevant for mechanical function, while, at protein levels, RT upregulated MMP-2 activity and collagen 1 only in young rats. This study highlights the importance of exercise on bone health and identifies specific molecular changes in response to RT. Our findings provide insights into the mechanisms involved in age-related changes.