Luo Qiang, Liang Wei, Zhang Zongwei, Zhu Zijing, Chen Zhaowei, Hu Jijia, Yang Keju, Chi Qingjia, Ding Guohua
Division of Nephrology, Renmin Hospital of Wuhan University, Wuhan, Hubei, China; Nephrology and Urology Research Institute of Wuhan University, Wuhan, Hubei, China.
Division of Nephrology, Renmin Hospital of Wuhan University, Wuhan, Hubei, China; Nephrology and Urology Research Institute of Wuhan University, Wuhan, Hubei, China.
Metabolism. 2022 Sep;134:155245. doi: 10.1016/j.metabol.2022.155245. Epub 2022 Jun 30.
Compromised glycolysis in podocytes contributes to the initiation of diabetic kidney disease (DKD). Podocyte injury is characterized by cytoskeletal remodeling and foot process fusion. Compromised glycolysis in diabetes likely leads to switch of energy supply in podocyte. However, the underlying mechanism by which disturbed energy supply in podocytes affects the cytoskeletal structure of podocytes remains unclear.
Metabolomic and transcriptomic analyses were performed on the glomeruli of db/db mice to examine the catabolism of glucose, fatty, and amino acids. Ornithine catabolism was targeted in db/db and podocyte-specific pyruvate kinase M2 knockout (PKM2-podoKO) mice. In vitro, expression of ornithine decarboxylase (ODC1) was modulated to investigate the effect of ornithine catabolism on mammalian target of rapamycin (mTOR) signaling and cytoskeletal remodeling in cultured podocytes.
Multi-omic analyses of the glomeruli revealed that ornithine metabolism was enhanced in db/db mice compared with that in db/m mice under compromised glycolytic conditions. Additionally, ornithine catabolism was exaggerated in podocytes of diabetic PKM2-podoKO mice compared with that in diabetic PKM2 mice. In vivo, difluoromethylornithine (DFMO, inhibitor of ODC1) administration reduced urinary albumin excretion and alleviated podocyte foot process fusion in db/db mice. In vitro, 2-deoxy-d-glucose (2-DG) exposure induced mTOR signaling activation and cytoskeletal remodeling in podocytes, which was alleviated by ODC1-knockdown. Mechanistically, a small GTPase Ras homolog enriched in the brain (Rheb), a sensor of mTOR signaling, was activated by exposure to putrescine, a metabolic product of ornithine catabolism.
These findings demonstrate that compromised glycolysis in podocytes under diabetic conditions enhances ornithine catabolism. The metabolites of ornithine catabolism contribute to mTOR signaling activation via Rheb and cytoskeletal remodeling in podocytes in DKD.
足细胞中糖酵解受损会促使糖尿病肾病（DKD）的发生。足细胞损伤的特征是细胞骨架重塑和足突融合。糖尿病中糖酵解受损可能导致足细胞能量供应的转换。然而，足细胞中能量供应紊乱影响其细胞骨架结构的潜在机制仍不清楚。
对db/db小鼠的肾小球进行代谢组学和转录组学分析，以检测葡萄糖、脂肪酸和氨基酸的分解代谢。在db/db小鼠和足细胞特异性丙酮酸激酶M2基因敲除（PKM2-podoKO）小鼠中靶向鸟氨酸分解代谢。在体外，调节鸟氨酸脱羧酶（ODC1）的表达，以研究鸟氨酸分解代谢对培养的足细胞中雷帕霉素靶蛋白（mTOR）信号传导和细胞骨架重塑的影响。
肾小球的多组学分析显示，在糖酵解受损的条件下，与db/m小鼠相比，db/db小鼠的鸟氨酸代谢增强。此外，与糖尿病PKM2小鼠相比，糖尿病PKM2-podoKO小鼠足细胞中的鸟氨酸分解代谢更为亢进。在体内，给予二氟甲基鸟氨酸（DFMO，ODC1抑制剂）可减少db/db小鼠的尿白蛋白排泄，并减轻足细胞足突融合。在体外，2-脱氧-D-葡萄糖（2-DG）暴露可诱导足细胞中mTOR信号激活和细胞骨架重塑，而ODC1基因敲低可减轻这种情况。机制上，mTOR信号的传感器、富含脑的小GTP酶Ras同源物（Rheb）可被鸟氨酸分解代谢的代谢产物腐胺激活。
这些发现表明，糖尿病条件下足细胞中糖酵解受损会增强鸟氨酸分解代谢。鸟氨酸分解代谢的代谢产物通过Rheb促进DKD中足细胞的mTOR信号激活和细胞骨架重塑。
