Teng Jiamin, Zhang Ping L, Russell William J, Zheng Lu P, Jones M Lamar, Herrera Guillermo A
Department of Pathology, Louisiana State University Health Sciences Center, Shreveport 71130, USA.
Nephron Physiol. 2003;94(2):p28-38. doi: 10.1159/000071288.
Our previous studies have shown that human mesangial cells (HMCs) incubated with fibrogenic glomerulopathic monoclonal light chains (G-LCs) obtained from the urine of patients with light chain deposition disease produce increased extracellular matrix (ECM) when compared with HMCs not exposed to fibrogenic LCs. This overproduction of ECM proteins is regulated by transforming growth factor-beta (TGF-beta); blocking TGF-beta normalizes the production of ECM proteins. All ECM proteins, after synthesis, have to go through the secretory pathway in the endoplasmic reticulum (ER) and Golgi complex for final maturation and secretion. Blocking the secretory pathway may reduce the accumulation of ECM proteins. We tested the effect of tunicamycin, a specific inhibitor of N-linked glycosylation in the ER which inhibited glycosylation and brefeldin A, an inhibitor of vesicle transport between the endoplasmic reticulum and the Golgi complex, on ECM protein production, both resulting in subsequent upregulation of glucose-regulated protein 78. Overproduction of fibronectin and tenascin by HMCs was normalized by tunicamycin and brefeldin A. Similarly, when HMCs were exposed to exogenous TGF-beta, the increase in fibronectin was reversed by tunicamycin and brefeldin A. Exogenous platelet-derived growth factor-beta (PDGF-beta) did not induce fibronectin overproduction but significantly stimulated proliferation of HMCs. In summary, this study further supports the notion that fibrogenic G-LCs promote the accumulation of ECM proteins, through the actions of TGF-beta. Importantly, the data indicate that altering protein trafficking in the ER results in impairment of secretion of proteins into the ECM. Furthermore, the data also reveal that PDGF-beta and TGF-beta act independently and that PDGF-beta activation by itself cannot increase ECM proteins directly, but only by increasing the number of HMCs.
我们之前的研究表明，与未暴露于致纤维化轻链的人系膜细胞（HMCs）相比，用从轻链沉积病患者尿液中获得的致纤维化肾小球病单克隆轻链（G-LCs）孵育的HMCs产生的细胞外基质（ECM）增加。ECM蛋白的这种过度产生由转化生长因子-β（TGF-β）调节；阻断TGF-β可使ECM蛋白的产生正常化。所有ECM蛋白在合成后都必须通过内质网（ER）和高尔基体中的分泌途径进行最终成熟和分泌。阻断分泌途径可能会减少ECM蛋白的积累。我们测试了衣霉素（一种内质网中N-连接糖基化的特异性抑制剂，可抑制糖基化）和布雷菲德菌素A（一种内质网与高尔基体之间囊泡运输的抑制剂）对ECM蛋白产生的影响，二者均导致随后葡萄糖调节蛋白78的上调。衣霉素和布雷菲德菌素A使HMCs中纤连蛋白和腱生蛋白的过度产生正常化。同样，当HMCs暴露于外源性TGF-β时，衣霉素和布雷菲德菌素A可逆转纤连蛋白的增加。外源性血小板衍生生长因子-β（PDGF-β）不会诱导纤连蛋白过度产生，但会显著刺激HMCs的增殖。总之，本研究进一步支持了致纤维化G-LCs通过TGF-β的作用促进ECM蛋白积累的观点。重要的是，数据表明改变内质网中的蛋白质运输会导致蛋白质向ECM分泌受损。此外，数据还显示PDGF-β和TGF-β独立发挥作用，并且PDGF-β自身激活不能直接增加ECM蛋白，而只能通过增加HMCs的数量来实现。
