Department of Medical Education and Research, Kaohsiung Veterans General Hospital, Kaohsiung 813, Taiwan.
Center of General Education, Shu-Zen Junior College of Medicine and Management, Kaohsiung 821, Taiwan.
Int J Mol Sci. 2022 Sep 3;23(17):10072. doi: 10.3390/ijms231710072.
Nonalcoholic fatty liver disease (NAFLD) is a major cause of liver-related morbidities and mortality, and no effective drug treatment currently exists. We aimed to develop a novel treatment strategy to induce the expression of glycine N-methyltransferase (GNMT), which is an important enzyme regulating S-adenosylmethionine metabolism whose expression is downregulated in patients with NAFLD. Because 1,2,3,4,6-pentagalloyl glucose (PGG) is a GNMT inducer, and metformin was shown to upregulate liver mitochondrial GNMT protein expression, the effect of PGG and metformin was evaluated. Biochemical analysis, histopathological examination, immunohistochemical staining, reverse transcription-quantitative PCR (RT-qPCR), Western blotting (WB), proteomic analysis and Seahorse XF Cell Mito Stress Test were performed. The high-fat diet (HFD)-induced NAFLD mice were treated with PGG and metformin. Combination of PGG and metformin nearly completely reversed weight gain, elevation of serum aminotransferases, and hepatic steatosis and steatohepatitis. In addition, the downregulated GNMT expression in liver tissues of HFD-induced NAFLD mice was restored. The GNMT expression was further confirmed by RT-qPCR and WB analysis using both in vitro and in vivo systems. In addition, PGG treatment was shown to increase oxygen consumption rate (OCR) maximum capacity in a dose-dependent manner, and was capable of rescuing the suppression of mitochondrial OCR induced by metformin. Proteomic analysis identified increased expression of glutathione S-transferase mu 4 (GSTM4), heat shock protein 72 (HSP72), pyruvate carboxylase (PYC) and 40S ribosomal protein S28 (RS28) in the metformin plus PGG treatment group. Our findings show that GNMT expression plays an important role in the pathogenesis of NAFLD, and combination of an inducer of GNMT and metformin can be of therapeutic potential for patients with NAFLD.
非酒精性脂肪性肝病 (NAFLD) 是导致肝脏相关发病率和死亡率的主要原因，目前尚无有效的药物治疗方法。我们旨在开发一种新的治疗策略，以诱导甘氨酸 N-甲基转移酶 (GNMT) 的表达，GNMT 是调节 S-腺苷甲硫氨酸代谢的重要酶，其在 NAFLD 患者中的表达下调。由于 1,2,3,4,6-五没食子酰葡萄糖 (PGG) 是 GNMT 的诱导剂，并且二甲双胍被证明上调肝脏线粒体 GNMT 蛋白表达，因此评估了 PGG 和二甲双胍的作用。进行了生化分析、组织病理学检查、免疫组织化学染色、逆转录定量 PCR (RT-qPCR)、Western blot (WB)、蛋白质组学分析和 Seahorse XF 细胞线粒体应激测试。用 PGG 和二甲双胍治疗高脂肪饮食 (HFD) 诱导的 NAFLD 小鼠。PGG 和二甲双胍的联合使用几乎完全逆转了体重增加、血清转氨酶升高以及肝脂肪变性和脂肪性肝炎。此外，还恢复了 HFD 诱导的 NAFLD 小鼠肝组织中下调的 GNMT 表达。通过 RT-qPCR 和 WB 分析，在体外和体内系统中进一步证实了 GNMT 的表达。此外，PGG 处理显示以剂量依赖性方式增加氧消耗率 (OCR) 最大容量，并且能够挽救二甲双胍诱导的线粒体 OCR 抑制。蛋白质组学分析鉴定出在二甲双胍加 PGG 治疗组中，谷胱甘肽 S-转移酶 mu 4 (GSTM4)、热休克蛋白 72 (HSP72)、丙酮酸羧化酶 (PYC) 和 40S 核糖体蛋白 S28 (RS28) 的表达增加。我们的研究结果表明，GNMT 表达在 NAFLD 的发病机制中起重要作用，GNMT 诱导剂和二甲双胍的联合治疗可能对 NAFLD 患者具有治疗潜力。
