Osteopontin Overproduction Is Associated with Progression of Glomerular Fibrosis in a Rat Model of Anti-Glomerular Basement Membrane Glomerulonephritis

Abstract

Background: Glomerular fibrosis is the common end result of glomerulonephritis (GN) regardless of etiology. In our rat model for anti-glomerular basement membrane GN, severe fibrosis follows glomerular inflammation. We investigated the association between expression of extracellular matrix (ECM) proteins and progression of glomerular fibrosis. Methods: Expression of ECM genes in glomeruli was determined at RNA and protein levels. Immunofluorescence was applied to identify cell sources for the molecules. Results: DNA microarray for ECM genes, quantitative RT-PCR and Western blot revealed significant upregulation of osteopontin (OPN), a multifunctional molecule, in the glomeruli only after onset of glomerular fibrosis. Two-dimensional electrophoresis showed that the expressed OPN was in three major isoforms. Immunofluorescence showed that fibrotic tissues in glomeruli accumulated massive deposits of extracellular OPN. Both in vivo and in vitro experiments showed that a novel population of multinucleated α-smooth muscle actin⁺CD90^– myofibroblast-like cells, which surrounded fibrotic tissue, was the main source of OPN during progression of fibrosis. Since senescence-associated β-galactosidase activity was detected in those cells both in vitro and in vivo, these cells probably were terminally differentiated senescent myofibroblasts. Conclusion: OPN has been implicated in fibrosis in several organs. Our results suggest potential roles of OPN and its main source, the senescent myofibroblasts, in glomerular fibrosis.

Blockade of Osteopontin Inhibits Glomerular Fibrosis in a Model of Anti-Glomerular Basement Membrane Glomerulonephritis

“…However, our antibody blockage experiments were not able to provide direct evidence to support this possibility. We have shown previously a massive deposition of OPN on fibrotic tissue at the mid to late stage of fibrosis [26] . Binding of antibody to OPN may disturb the architecture of fibrotic tissue.…”

“…The animals undergo two distinct overlapping stages after disease induction: (1) CD4+ T cell-mediated glomerular inflammation followed by (2) severe glomerular fibrosis. We have previously reported upregulation of OPN in a novel multinucleated myofibrobalsts in the glomeruli and massive deposition of OPN on the fibrotic tissue during fibrotic stage [26] . In the present study, we investigated whether blockage of OPN activity at late inflammatory/early fibrotic stage would alter fibrosis progress in our model.…”

Natural Recovery from Antiglomerular Basement Membrane Glomerulonephritis Is Associated with Glomeruli-Infiltrating CD8α+CD11c+MHC Class II+ Cells

“…We have developed a rat model for this disease, which is induced by the well-defined T cell epitope pCol(28–40) of autoantigen collagen 4α3 chain. GN-prone Wistar Kyoto (WKY) rats develop severe glomerular inflammation, which eventually is terminated and replaced by progressive fibrosis [16,17,18]. In fact, it is fibrosis rather than inflammation that leads to end-stage renal disease.…”

Osteopontin Bridging Innate and Adaptive Immunity in Autoimmune Diseases

“…Interestingly, OPN in kidneys may also be secreted by senescent myofibroblasts and drive glomerular fibrosis [116]. OPN is required for myofibroblasts differentiation, and it regulates the molecules involved in tissue fibrosis.…”

“…OPN is required for myofibroblasts differentiation, and it regulates the molecules involved in tissue fibrosis. High levels of glomerular OPN are associated with macrophage accumulation and progressive renal injury in an antiglomerular basement membrane (GBM) glomerulonephritis (GN) model [116, 117]. OPN may modulate also angiotensin-II- (AII-) induced inflammation, oxidative stress, and fibrosis of the kidney [118].…”