Department of Medicine, Center for Human Nutrition, Washington University in St. Louis, United States.
Department of Biomedical Sciences, Western Michigan University School of Medicine, Kalamazoo, MI, Cirius Therapeutics, Kalamazoo, MI, United States.
Mol Metab. 2023 Apr;70:101694. doi: 10.1016/j.molmet.2023.101694. Epub 2023 Feb 18.
The mitochondrial pyruvate carrier (MPC) has emerged as a therapeutic target for treating insulin resistance, type 2 diabetes, and nonalcoholic steatohepatitis (NASH). We evaluated whether MPC inhibitors (MPCi) might correct impairments in branched chain amino acid (BCAA) catabolism, which are predictive of developing diabetes and NASH.
Circulating BCAA concentrations were measured in people with NASH and type 2 diabetes, who participated in a recent randomized, placebo-controlled Phase IIB clinical trial to test the efficacy and safety of the MPCi MSDC-0602K (EMMINENCE; NCT02784444). In this 52-week trial, patients were randomly assigned to placebo (n = 94) or 250 mg MSDC-0602K (n = 101). Human hepatoma cell lines and mouse primary hepatocytes were used to test the direct effects of various MPCi on BCAA catabolism in vitro. Lastly, we investigated how hepatocyte-specific deletion of MPC2 affects BCAA metabolism in the liver of obese mice and MSDC-0602K treatment of Zucker diabetic fatty (ZDF) rats.
In patients with NASH, MSDC-0602K treatment, which led to marked improvements in insulin sensitivity and diabetes, had decreased plasma concentrations of BCAAs compared to baseline while placebo had no effect. The rate-limiting enzyme in BCAA catabolism is the mitochondrial branched chain ketoacid dehydrogenase (BCKDH), which is deactivated by phosphorylation. In multiple human hepatoma cell lines, MPCi markedly reduced BCKDH phosphorylation and stimulated branched chain keto acid catabolism; an effect that required the BCKDH phosphatase PPM1K. Mechanistically, the effects of MPCi were linked to activation of the energy sensing AMP-dependent protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) kinase signaling cascades in vitro. BCKDH phosphorylation was reduced in liver of obese, hepatocyte-specific MPC2 knockout (LS-Mpc2-/-) mice compared to wild-type controls concomitant with activation of mTOR signaling in vivo. Finally, while MSDC-0602K treatment improved glucose homeostasis and increased the concentrations of some BCAA metabolites in ZDF rats, it did not lower plasma BCAA concentrations.
These data demonstrate novel cross talk between mitochondrial pyruvate and BCAA metabolism and suggest that MPC inhibition leads to lower plasma BCAA concentrations and BCKDH phosphorylation by activating the mTOR axis. However, the effects of MPCi on glucose homeostasis may be separable from its effects on BCAA concentrations.
线粒体丙酮酸载体（MPC）已成为治疗胰岛素抵抗、2 型糖尿病和非酒精性脂肪性肝炎（NASH）的治疗靶点。我们评估了 MPC 抑制剂（MPCi）是否可能纠正支链氨基酸（BCAA）分解代谢的损伤，这种损伤可预测糖尿病和 NASH 的发生。
在最近一项随机、安慰剂对照的 2 期 B 期临床试验中，评估了患有 NASH 和 2 型糖尿病的人的循环 BCAA 浓度，该试验旨在测试 MPCi MSDC-0602K（EMMINENCE；NCT02784444）的疗效和安全性。在这项为期 52 周的试验中，患者被随机分配至安慰剂（n=94）或 250mg MSDC-0602K（n=101）组。我们使用人肝癌细胞系和小鼠原代肝细胞来测试各种 MPCi 在体外对 BCAA 分解代谢的直接作用。最后，我们研究了肝细胞特异性敲除 MPC2 如何影响肥胖小鼠肝脏中的 BCAA 代谢以及 MSDC-0602K 对 Zucker 糖尿病肥胖（ZDF）大鼠的影响。
在患有 NASH 的患者中，MSDC-0602K 治疗可显著改善胰岛素敏感性和糖尿病，与基线相比，血浆中 BCAAs 的浓度降低，而安慰剂则没有影响。BCAA 分解代谢的限速酶是线粒体支链酮酸脱氢酶（BCKDH），其磷酸化失活。在多种人肝癌细胞系中，MPCi 显著降低 BCKDH 磷酸化并刺激支链酮酸分解代谢；这种作用需要 BCKDH 磷酸酶 PPM1K。在体外，MPCi 的作用机制与能量感应 AMP 依赖性蛋白激酶（AMPK）和雷帕霉素（mTOR）激酶信号通路的激活有关。与野生型对照相比，肥胖、肝细胞特异性 MPC2 敲除（LS-Mpc2-/-）小鼠肝脏中的 BCKDH 磷酸化降低，同时体内 mTOR 信号通路被激活。最后，虽然 MSDC-0602K 治疗改善了葡萄糖稳态并增加了 ZDF 大鼠中一些 BCAA 代谢物的浓度，但并未降低血浆 BCAA 浓度。
这些数据证明了线粒体丙酮酸和 BCAA 代谢之间存在新的交叉对话，并表明 MPC 抑制通过激活 mTOR 轴导致较低的血浆 BCAA 浓度和 BCKDH 磷酸化。然而，MPCi 对葡萄糖稳态的影响可能与其对 BCAA 浓度的影响是分开的。
