[Expressions of matrix metalloproteinase-1 and tissue inhibitor of metalloproteinases 1 in skeletal muscles of aged rats with sarcopenia].

OBJECTIVE: To investigate the changes of skeletal muscle mass and strength and the expressions of matrix metalloproteinase-1 (MMP-1), tissue inhibitor of metalloproteinases-1 (TIMP-1) and collagen-1 in the skeletal muscle of aged rats with sarcopenia.
METHODS: With 11 young (6-month-old) SD rats as control group, 18 aged (25-month-old) SD rats were divided into two groups (n=9) according to the relative lean mass determined dual X-ray absorptiometry (DXA), namely aged control group and aged sarcopenia group (the relative lean mass was 2SD higher in aged control than in aged sarcopenia group. The forelimb grip strength of the rats was measured using an electronic grip strength meter. The extracellular matrix (ECM) of the rat's gastrocnemius was observed with HE staining and sirius Red staining, and the protein expressions of collagen-1, MMP-1, and TIMP-1 in the muscular tissues were detected with Western blotting.
RESULTS: Compared with the young rats, the aged control rats had significantly lower relative grip strength (P < 0.01) and increased expressions of collagen-1 and TIMP-1 (P < 0.05) and ECM content in the skeletal muscles, but the relative lean mass and MMP-1 protein expression were comparable between the two groups (P>0.05). Compared with the aged control rats, the aged sarcopenic rats had significantly lowered relative lean mass (P < 0.01) and MMP-1 expressions of (P < 0.05) and increased expressions of collagen-1 and TIMP-1 proteins and ECM content in the muscular tissues (P < 0.05) without significant changes in the relative grip strength (P>0.05).
CONCLUSIONS: MMP-1/TIMP-1 imbalance in the skeletal muscle during aging affects ECM metabolism and leads to increased collagen fibers, which in turn affects the skeletal muscle mass and function and contribute to the onset of sarcopenia.