Miyano Takashi, Sera Toshihiro, Sakamoto Naoya
Department of Medical and Robotic Engineering Design, Tokyo University of Science, Tokyo, Japan; Department of Mechanical Systems Engineering, Graduate School of Systems Design, Tokyo Metropolitan University, Tokyo, Japan.
Department of Medical and Robotic Engineering Design, Tokyo University of Science, Tokyo, Japan.
Biochem Biophys Res Commun. 2025 Mar 1;750:151432. doi: 10.1016/j.bbrc.2025.151432. Epub 2025 Feb 1.
Proximal tubular epithelial cells (PTECs) are central to maintaining kidney homeostasis. Under pathological conditions, such as ischemia or inflammation, PTECs promote profibrotic signals, including transforming growth factor (TGF)-β, and undergo epithelial-mesenchymal transition (EMT). EMT is characterized by decreased epithelial markers (e.g., E-cadherin) and increased mesenchymal markers (e.g., α-smooth muscle actin [α-SMA]), which promote myofibroblast activation and fibrosis progression. We previously demonstrated that hyperosmotic stress, characterized by elevated extracellular solute concentrations, induces EMT in PTECs. However, we observed that hyperosmotic stress simultaneously activates autophagy, a cellular process that has antagonistic effects on EMT, primarily mediated by transient receptor potential mucolipin 1 (TRPML1). However, the interplay between hyperosmotic stress-induced EMT and autophagy remains unclear. This study examined whether enhancing autophagy via TRPML1 activation could modulate EMT under hyperosmotic stress. Using the TRPML1 agonist ML-SA1, we observed a significantly increased autophagic flux, indicated by elevated LC3-II levels, without cytotoxic effects. Under hyperosmotic conditions, ML-SA1 further amplified autophagic flux in PTECs compared to hyperosmotic stress alone. Notably, this enhanced autophagy suppressed EMT by maintaining E-cadherin expression and reducing α-SMA levels. Furthermore, the ML-SA1-mediated autophagy enhancement attenuated EMT and profibrotic factor production in TGF-β-treated cells, suggesting a broader protective role beyond hyperosmotic stress. These findings reveal a novel interaction between hyperosmotic stress-induced autophagy and EMT, emphasizing TRPML1 activation's therapeutic potential to mitigate PTEC injury and fibrosis progression.
近端肾小管上皮细胞（PTECs）对于维持肾脏内环境稳定至关重要。在诸如缺血或炎症等病理条件下，PTECs会促进包括转化生长因子（TGF）-β在内的促纤维化信号，并经历上皮-间质转化（EMT）。EMT的特征是上皮标志物（如E-钙黏蛋白）减少，间充质标志物（如α-平滑肌肌动蛋白[α-SMA]）增加，这会促进肌成纤维细胞活化和纤维化进展。我们之前证明，以细胞外溶质浓度升高为特征的高渗应激会诱导PTECs发生EMT。然而，我们观察到高渗应激同时激活了自噬，这是一个对EMT具有拮抗作用的细胞过程，主要由瞬时受体电位黏脂蛋白1（TRPML1）介导。然而，高渗应激诱导的EMT与自噬之间的相互作用仍不清楚。本研究探讨了通过激活TRPML1增强自噬是否能在高渗应激下调节EMT。使用TRPML1激动剂ML-SA1，我们观察到自噬通量显著增加，表现为LC3-II水平升高，且无细胞毒性作用。在高渗条件下，与单独的高渗应激相比，ML-SA1进一步放大了PTECs中的自噬通量。值得注意的是，这种增强的自噬通过维持E-钙黏蛋白表达和降低α-SMA水平抑制了EMT。此外，ML-SA1介导的自噬增强减弱了TGF-β处理细胞中的EMT和促纤维化因子产生，表明其在高渗应激之外具有更广泛的保护作用。这些发现揭示了高渗应激诱导的自噬与EMT之间的一种新的相互作用，强调了激活TRPML1在减轻PTEC损伤和纤维化进展方面的治疗潜力。
