Impact of aging on type I collagen and transforming growth factor-beta1 (TGF-beta1) mRNA expression during muscle degeneration
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We tested the hypothesis that type I collagen mRNA expression would be lower in injured skeletal muscle from senescent rats compared with young and middle-aged rats, and that this decrease would be associated with a decreased expression of TGF-β1 mRNA. Type I collagen and TGF-β1 transcript levels were examined in control and injured skeletal muscle from young (4-5 month old), adult (12 month), and senescent (24 month) F344 rats (4-6 animals per time point). Skeletal muscle injury was induced by injecting bupivacaine into the extensor digitorum longus (EDL) muscles, which were harvested 24-, 36-, and 72-hours later. Consistent with other studies, type I collagen transcript increased post-injury, but only reached statistically significant at 72 hours. At 72 hours, type I collagen mRNA expression in the injured muscle was significantly lower in senescent rats compared with young and middle aged rats. TGF-β1 mRNA expression significantly increased in the injured muscle at all time points, but there was no age effect. Our results indicated that although aging results in down-regulation of type I collagen mRNA expression 72 hours following bupivacaine-induced muscle damage, it is not associated with an age-related change in TGF-β1 mRNA expression. Future study should examine the effect of age on other inflammatory cytokines, e.g. FGF and TNF-α.