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LEUCINE SUPPLEMENTATION DOES NOT ALTER CELL CYCLE REGULATORS AT THE ONSET OF REGENERATION IN AGED MUSCLE

Abstract

INTRODUCTION: Skeletal muscle regeneration is a vital biological process enabling the repair of damaged muscle tissue following injury. However, with aging, the capacity for muscle regeneration declines, resulting in slower recovery from injuries in older individuals. This diminished regenerative ability is closely linked to dysregulated protein turnover, characterized by increased protein degradation, and reduced protein synthesis. Leucine, a branch chain amino acid, has demonstrated significant potential for enhancing protein synthesis, proliferation, and differentiation. Nevertheless, the impact of leucine supplementation on age-related loss of muscle regenerative capacity remains insufficiently explored and warrants further investigation. PURPOSE: Investigate the impact of leucine supplementation on the muscle specific cell cycle regulators expression at the onset of skeletal muscle regeneration in the aged male mice. METHODS: Aged Male C57/BL6 mice (24 months) were divided into four experimental groups: uninjured, uninjured + leucine, injured, and injured +leucine. To induce muscle damage, bupivacaine was injected into the tibialis anterior (TA) muscles of mice, while the uninjured groups received phosphate-buffered saline (PBS) injections as a control. Following injection, the leucine groups were given drinking water with 1.5% leucine. Three days after injection, the TA was collected, and quantitative PCR was performed to analyze gene expression. Two-way ANOVA was run, and significance was established at (p > 0.05). RESULTS: The ratio of TA mass to body weight (BW) revealed no significant differences (p > 0.05) across groups. A significant main effect was observed in injured groups, with a 15-fold increase in cyclin D1 (p = 0.0064), a ~1.5-fold increase in MyoD (p = 0.0306), and a ~5-fold increase in MyoG (p = 0.0084) mRNA abundance compared to uninjured groups independent of leucine supplementation. CONCLUSION: Aged male mice had increased expression of cell cycle regulators at the onset of muscle regeneration independent of leucine supplementation. It appears that the delayed regenerative response associated with aging is not due to dysregulated myoblast proliferation and differentiation at the onset of muscle regeneration.

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