[Effects of branched-chain amino acid supplementation on skeletal muscle proteolytic pathways after exercise-induced muscle injury in rats].

Objective: To explore the role of branched-chain amino acid(BCAA) supplementation on muscle damage and the regulation of Krüppel-like factor 15(KLF15) and nuclear factor kappa B(NF-κB) mediated proteolytic pathways after an acute eccentric exercise.

Methods: Male SD rats were divided into placebo group(PLA) and BCAA group(BCAA) randomly, 32 rats per group. Both group were then placed into subgroups: placebo and pre-exercise group(PC), placebo and immediately after exercise group(PE), placebo and 6 h after exercise group(PE6), placebo and 12 h after exercise group(PE12), BCAA and pre-exercise group(BC), BCAA and immediately after exercise group(BE), BCAA and 6 h after exercise group(BE6), BCAA and 12 h after exercise group(BE12), 8 rats per group. Rats in BCAA groups were supplied with BCAA(1 g/(kg·d·BW), 3 days) before the exercise day and placebo groups with equal volume of distilled water. The exercised groups performed a 2 h eccentric exercise on treadmill(16 m/min, -16° slope). Blood and gastrocnemius were collected according to the time points. RT-qPCR was used to measure the mRNA expression of KLF15, NF-κB, FoxO1, Atrogin-1 and MuRF1 in gastrocnemius.

Results: (1) No damage was found in myocytes of BC and PC group. The process of morphological damage in BCAA group was relatively faster. (2) The mRNA expression levels of KLF15, FoXO1, Atrogin-1 and MuRF1 in PE were higher than those in PC(P<0.05, P<0.01), NF-κB and Atrogin-1 in PE12 were higher than those in PC(P<0.05). The mRNA expression levels of FoXO1 in BE were higher than those in BC(P<0.05). Compared with PE, the mRNA expression levels of KLF15, Atrogin-1 and MuRF1 in BE were lower(P<0.05, P<0.01), NF-κB and Atrogin-1 in BE12 were lower than those in PE12(P<0.05). The level of serum 3-MH in PE12 group was higher than that in PC group(P<0.05).

Conclusion: The proteolysis of skeletal muscle after high-intensity eccentric exercise is mediated by two different pathways: KLF15 and NF-κB, whose activation is time-dependent. BCAA may reduce skeletal muscle proteolysis by lowering the level of gene transcription in the KLF15 and NF-κB related protein degradation pathway, which occurs immediately after exercise.