Sam Ramin, Wanna Linda, Gudehithlu Krishnamurthy P, Garber Sandra L, Dunea George, Arruda Jose A L, Singh Ashok K
Division of Nephrology, Stroger Hospital of Cook County, Chicago, Ill, USA.
Transl Res. 2006 Sep;148(3):142-8. doi: 10.1016/j.trsl.2006.04.003.
Studies were carried out to determine whether epithelial-mesenchymal transformation (EMT), well described in renal tubular epithelial cells, also occurs in glomerular epithelial cells and whether it is reversible. To this effect, cultured glomerular epithelial cells were incubated with TGF-beta(1) and their transformation into myofibroblasts was studied. At 4 days, the cells altered their phenotype, as shown by a change in shape, an increase in intracellular staining for alpha-smooth muscle actin (alpha-SMA), a decrease in membrane staining for cytokeratin, and an increase in matrix deposition. Changing the medium after 4 days by excluding TGF-beta(1) and adding fetal bovine serum (FBS) [as a source of epidermal growth factor (EGF) and other growth factors] caused the cells to revert to their original epithelial phenotype. By contrast, when the medium was changed in the same manner after 8 days of exposure to TGF-beta(1), the cells did not revert but remained myofibroblastic. Staining the cells for expression of EGF receptor before and after exposure to TGF-beta(1) caused this receptor, originally present on the plasma membrane, to become partly intracellular after 4 days of TGF-beta(1) exposure and completely intracellular after 8 days of TGF-beta(1) exposure. Kidney sections from 2 models of renal mass reduction were stained. Loss of the epithelial marker (podocalyxin) staining and the acquisition of alpha-SMA staining was observed in the glomeruli. It is concluded that EMT takes place in glomerular epithelial cells in vivo and in vitro. In cultured glomerular epithelial cells, the process can be reversed by early, but not late intervention. It seems that TGF-beta(1) exposure progressively downregulates the EGF receptor on the membrane, rendering the cell refractory to EGF signals critical for maintaining the epithelial phenotype.
开展了多项研究，以确定在肾小管上皮细胞中被充分描述的上皮-间质转化（EMT）是否也发生在肾小球上皮细胞中，以及它是否可逆。为此，将培养的肾小球上皮细胞与转化生长因子-β1（TGF-β1）一起孵育，并研究其向肌成纤维细胞的转化。在第4天，细胞改变了其表型，表现为形态改变、α-平滑肌肌动蛋白（α-SMA）的细胞内染色增加、细胞角蛋白的膜染色减少以及基质沉积增加。在第4天后更换培养基，去除TGF-β1并添加胎牛血清（FBS）[作为表皮生长因子（EGF）和其他生长因子的来源]，可使细胞恢复到原来的上皮表型。相比之下，在暴露于TGF-β1 8天后以相同方式更换培养基时，细胞没有恢复，而是保持肌成纤维细胞状态。在暴露于TGF-β1前后对细胞进行EGF受体表达染色，发现该受体最初存在于质膜上，在暴露于TGF-β1 4天后部分进入细胞内，在暴露于TGF-β1 8天后完全进入细胞内。对2个肾实质减少模型的肾脏切片进行染色。在肾小球中观察到上皮标志物（足突蛋白）染色缺失和α-SMA染色增加。结论是，EMT在体内和体外的肾小球上皮细胞中均会发生。在培养的肾小球上皮细胞中，该过程可通过早期而非晚期干预逆转。似乎暴露于TGF-β1会逐渐下调膜上的EGF受体，使细胞对维持上皮表型至关重要的EGF信号产生抗性。
