Supplementary Material for: Taurine Supplementation Reverses Diabetes-Induced Podocytes Injury via Modulation of the CSE/TRPC6 Axis and Improvement of Mitochondrial Function

Background: The protective effects of taurine supplementation on diabetic kidney disease (DKD) have been defined, but the mechanisms are not quite clear yet. TRPC6 has been shown to function in the homeostasis of podocytes, but whether TRPC6-modulated mitochondrial dysfunctions participating in taurine-induced renal protection during diabetes are unclear. Methods: A DKD model was constructed using streptozocin (STZ), and an immortalized mouse podocytes cell line MPC-5 was used. Renal histology and western blot were used to analyze the expression levels of certain proteins. Cell proliferation assays, apoptosis assays, calcium influx, and mitochondrial functions were evaluated. Results: In this study, taurine intervention improved STZ-induced DKD injuries, while it decreased both 24-h urinary protein and podocytes apoptosis. In detail, this study showed that taurine treatment decreased mitochondrial ROS productions by suppressing calcium overload and improving mitochondrial respiratory functions. Furthermore, the upregulation of TRPC6 is partially responsible for the calcium overload during high glucose treatment, whereas taurine treatment inhibited TRPC6 expression and partially attenuated high glucose-induced podocytes injuries. In addition, we demonstrated that taurine could upregulate CSE expression and inhibits TRPC6 expression via promoting the synthesis of H2S. Conclusion: Our study reveals that taurine intervention could partially attenuate the lesions of DKD by modulating the CSE/TRPC6 axis.

研究背景：补充牛磺酸（taurine）对糖尿病肾病（diabetic kidney disease, DKD）的保护作用已得到证实，但其具体分子机制尚未完全阐明。瞬时受体电位阳离子通道6（TRPC6）已被证实参与足细胞（podocytes）的稳态调控，但在糖尿病状态下，TRPC6调控的线粒体功能障碍是否参与牛磺酸介导的肾脏保护作用，目前仍不明确。
研究方法：本研究采用链脲佐菌素（streptozocin, STZ）构建糖尿病肾病模型，并使用永生化小鼠足细胞系MPC-5开展实验。通过肾脏组织学检测与蛋白质印迹（western blot）分析特定蛋白的表达水平，同时开展细胞增殖实验、细胞凋亡实验、钙内流检测及线粒体功能评估。
研究结果：本研究显示，牛磺酸干预可改善链脲佐菌素诱导的糖尿病肾病损伤，同时降低24小时尿蛋白水平与足细胞凋亡率。具体而言，牛磺酸处理可通过抑制钙超载、改善线粒体呼吸功能，减少线粒体活性氧（reactive oxygen species, ROS）的生成。进一步研究发现，高糖处理下TRPC6的上调是导致钙超载的部分原因，而牛磺酸处理可抑制TRPC6的表达，进而部分减轻高糖诱导的足细胞损伤。此外，本研究证实牛磺酸可通过促进硫化氢（H2S）的合成，上调胱硫醚γ裂解酶（CSE）的表达并抑制TRPC6的表达。
研究结论：本研究揭示，牛磺酸干预可通过调控CSE/TRPC6信号轴，部分减轻糖尿病肾病的组织损伤。