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THE EFFECT OF LEUCINE SUPPLEMENTATION ON ATROGENES IN AGED MALE MICE AT THE ONSET OF MUSCLE REGENERATION.

Abstract

INTRODUCTION: Skeletal muscle regeneration is a crucial biological process that restores muscle tissue following injury. However, aging significantly diminishes the capacity for muscle repair, leading to delayed recovery in older individuals. This diminished regenerative capacity is associated with dysregulated protein turnover, characterized by increased expression of genes associated with protein degradation, called atrogenes. Leucine, a branched-chain amino acid, has shown promise in altering protein turnover. Previous work by our group demonstrated that independent of leucine supplementation, injury-induced atrogene expression in female mice. PURPOSE: To investigate the effects of leucine supplementation on gene expression of atrogenes in aged male mice at the onset of muscle regeneration. METHODS: Experiments were conducted exclusively on aged male C57/BL6 mice (24 months old), which were divided into four groups: uninjured without leucine (UNL), uninjured with leucine (UL), injured without leucine (INL), and injured with leucine (IL). Muscle injury was induced in the tibialis anterior (TA) muscles using bupivacaine injections, while uninjured groups received phosphate-buffered saline (PBS). Leucine supplementation (1.5%) was administered ad libitum via drinking water. TA muscles were harvested three days post-injection, and quantitative PCR was performed to assess gene expression changes. Data was analyzed by two-way ANOVA and significance was established at (p > 0.05). RESULTS: There were no differences in body mass between UNL, INL, UL, and IL (P>0.05). There was no difference in the TA mass across the 4 groups (46.2 mg ± 2.6, 51.7 mg ± 1.7, 51.5 mg ± 1.2, 49.2 mg ± 1.0) (P>0.05). There were no fold differences in atrogenes mRNA abundance of atrogenes Foxo3, Foxo1, Atrogin, and Murf1 (P>0.05). CONCLUSION: Leucine was not sufficient to alter atrogene expression at the onset of muscle regeneration in male mice. In contrast to our published data in female mice, male mice did not increase atrogene expression in response to injury. This could partially explain the biological sex differences seen during aged skeletal muscle regeneration.

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