School of Kinesiology and Health Science and Muscle Health Research Centre, York University, Toronto, ON, Canada.
J Nutr Sci. 2024 Oct 18;13:e66. doi: 10.1017/jns.2024.66. eCollection 2024.
Plasma levels of branched-chain amino acids (BCAA) and their metabolites, branched-chain ketoacids (BCKA), are increased in insulin resistance. We previously showed that ketoisocaproic acid (KIC) suppressed insulin-stimulated glucose transport in L6 myotubes, especially in myotubes depleted of branched-chain ketoacid dehydrogenase (BCKD), the enzyme that decarboxylates BCKA. This suggests that upregulating BCKD activity might improve insulin sensitivity. We hypothesised that increasing BCAA catabolism would upregulate insulin-stimulated glucose transport and attenuate insulin resistance induced by BCKA. L6 myotubes were either depleted of BCKD kinase (BDK), the enzyme that inhibits BCKD activity, or treated with BT2, a BDK inhibitor. Myotubes were then treated with KIC (200 μM), leucine (150 μM), BCKA (200 μM), or BCAA (400 μM) and then treated with or without insulin (100 nM). BDK depletion/inhibition rescued the suppression of insulin-stimulated glucose transport by KIC/BCKA. This was consistent with the attenuation of IRS-1 (Ser612) and S6K1 (Thr389) phosphorylation but there was no effect on Akt (Ser473) phosphorylation. The effect of leucine or BCAA on these measures was not as pronounced and BT2 did not influence the effect. Induction of the mTORC1/IRS-1 (Ser612) axis abolished the attenuating effect of BT2 treatment on glucose transport in cells treated with KIC. Surprisingly, rapamycin co-treatment with BT2 and KIC further reduced glucose transport. Our data suggests that the suppression of insulin-stimulated glucose transport by KIC/BCKA in muscle is mediated by mTORC1/S6K1 signalling. This was attenuated by upregulating BCAA catabolic flux. Thus, interventions targeting BCAA metabolism may provide benefits against insulin resistance and its sequelae.
血浆支链氨基酸（BCAA）及其代谢物支链酮酸（BCKA）水平在胰岛素抵抗中升高。我们之前的研究表明，酮异己酸（KIC）抑制 L6 肌管中的胰岛素刺激葡萄糖转运，特别是在缺乏支链酮酸脱氢酶（BCKD）的肌管中，BCKD 是脱羧 BCKA 的酶。这表明上调 BCKD 活性可能改善胰岛素敏感性。我们假设增加 BCAA 分解代谢会上调胰岛素刺激的葡萄糖转运，并减轻 BCKA 引起的胰岛素抵抗。L6 肌管要么耗尽 BCKD 激酶（BDK），BDK 是抑制 BCKD 活性的酶，要么用 BT2（BDK 抑制剂）处理。然后用 KIC（200 μM）、亮氨酸（150 μM）、BCKA（200 μM）或 BCAA（400 μM）处理肌管，然后用或不用胰岛素（100 nM）处理。BDK 耗竭/抑制挽救了 KIC/BCKA 对胰岛素刺激的葡萄糖转运的抑制作用。这与 IRS-1（Ser612）和 S6K1（Thr389）磷酸化的减弱一致，但对 Akt（Ser473）磷酸化没有影响。亮氨酸或 BCAA 的作用不那么明显，BT2 也没有影响。mTORC1/IRS-1（Ser612）轴的诱导消除了 BT2 处理对 KIC 处理细胞葡萄糖转运的减弱作用。令人惊讶的是，雷帕霉素与 BT2 和 KIC 共同处理进一步降低了葡萄糖转运。我们的数据表明，KIC/BCKA 对肌肉中胰岛素刺激的葡萄糖转运的抑制作用是由 mTORC1/S6K1 信号介导的。这通过上调 BCAA 分解代谢通量得到缓解。因此，针对 BCAA 代谢的干预措施可能有益于对抗胰岛素抵抗及其后果。
