Insights into mechanisms responsible for mesangial alterations associated with fibrogenic glomerulopathic light chains.
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.
Teng
Jiamin
J
Department of Pathology, Louisiana State University Health Sciences Center, Shreveport 71130, USA.
Zhang
Ping L
PL
Russell
William J
WJ
Zheng
Lu P
LP
Jones
M Lamar
ML
Herrera
Guillermo A
GA
D000911:Antibodies, Monoclonal / Q000494:pharmacology / Q000652:urine; D020126:Brefeldin A / Q000494:pharmacology / Q000633:toxicity; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D005353:Fibronectins / Q000096:biosynthesis*; D005920:Glomerular Mesangium / Q000737:chemistry / Q000187:drug effects / Q000276:immunology* / Q000473:pathology*; D006801:Humans; D007147:Immunoglobulin Light Chains / Q000494:pharmacology / Q000652:urine; D007678:Kidney Glomerulus / Q000276:immunology; D007684:Kidney Tubules / Q000276:immunology; D020574:Proto-Oncogene Proteins c-sis / Q000096:biosynthesis / Q000494:pharmacology; D016212:Transforming Growth Factor beta / Q000096:biosynthesis / Q000494:pharmacology; D014415:Tunicamycin / Q000494:pharmacology / Q000633:toxicity
D000911:Antibodies, Monoclonal; D005353:Fibronectins; D007147:Immunoglobulin Light Chains; D020574:Proto-Oncogene Proteins c-sis; D016212:Transforming Growth Factor beta; D014415:Tunicamycin; D020126:Brefeldin A