白蛋白超载诱导近端肾小管上皮细胞表达α-平滑肌肌动蛋白

目的：探讨白蛋白超载是否可以诱导近端肾小管上皮细胞（PTCs）向成肌纤维细胞转化（EMT）。方法：大鼠近端肾小管上皮细胞株NRK52E培养至70％融合或完全融合时，用不同浓度（0-30 g/L）去脂牛血清白蛋白(dBSA)超载144 h。NRK52E形态和结构改变用光镜和电镜观测。上皮细胞标记抗原E-钙黏蛋白和β-连环蛋白，以及成肌纤维细胞标记抗原α-平滑肌肌动蛋白（α-SMA）表达用免疫荧光和Western 印迹法检测。结果：dBSA超载可诱导未完全融合NRK52E表达α-SMA，少数细胞变为长梭形，但α-SMA 的表达不呈剂量依赖性。dBSA超载处理不能诱导完全融合的NRK52E表达α-SMA，细胞形态也无改变。dBSA超载完全或未完全融合NRK52E均不能抑制E-钙黏蛋白和β-连环蛋白表达，电镜显示这些细胞仍保持上皮细胞结构，包括微绒毛和紧密连接。结论：白蛋白超载可以诱导PTCs表达α-SMA，促进EMT，但不能诱导PTCs完全转化为成肌纤维细胞，细胞完全融合可抑制白蛋白超载诱导PTCs表达α-SMA。

Albumin overload induces α-smooth muscle actin expression in proximal tubular epithelial cells

AIM: To study whether albumin overload in proximal tubular epithelial cells (PTCs) induces epithelial to myofibroblast transdifferentiation (EMT). METHODS: Rat renal proximal tubular cell line NRK52E was cultured on 6 well plates. When the cells reached 70% confluens or complete confluens, cells were serum starved for 24 h. Different concentrations of delipidated bovine serum albumin (dBSA), ranging from 0-30 g/L, were then added to the cells. The media was changed every 48 h until the end of 144 h. Cell shapes were monitored by light microscope during experiment. Cell structures were detected by electron microscopy. Epithelial cell markers: E-cadherin, β-catenin, and myofibroblast marker: α-smooth muscle actin (α-SMA) were detected by immunofluorescent microscopy and Western blotting. RESULTS: dBSA overload induced the expression of α-SMA in sub-confluent NRK52E, and a few cells elongated, but the induced expression of α-SMA was not in a dose dependent manner. dBSA overload did not induce the expression of α-SMA in complete confluent NRK52E, cell shape did not change either. dBSA overload did not inhibit expression of E-cadherin or β-catenin both in sub-confluent and complete confluent NRK52E. The electron microscope showed that these cells retained epithelial phenotype, with microvilli and tight junction. CONCLUSION: Albumin overload induces PTCs expressing myofibroblast marker α-SMA and promotes EMT. However, complete EMT does not achieve. Complete confluens (cell-cell contacts) inhibits albumin induced α-SMA expression in PTCs.