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Altered glomerular extracellular matrix synthesis in experimental membranous nephropathy
J Floege1, R J Johnson, K Gordon
1Department of Medicine, University of Washington, Seattle.
Abstract:
Chronic progressive membranous nephropathy (MN) in humans is characterized by thickening of the glomerular basement membrane (GBM) with formation of spikes which contain laminin and other extracellular matrix (ECM) proteins. We have utilized two models of MN in the rat (active and passive Heymann nephritis, AICN, PHN) to define the sequential changes in composition of GBM as they relate to changes in glomerular gene expression for ECM components, altered permeability and morphological changes. Renal biopsies obtained during the course of AICN and PHN were immunostained for various ECM proteins and total glomerular RNA was hybridized with cDNA probes specific for laminin B2-chain, s-laminin, and types I and IV collagen. In addition, the ability of anti-glomerular epithelial cell (GEC) antibody and complement on rat GEC in culture to induce laminin release or laminin and s-laminin mRNA expression was determined. The results demonstrate that at weeks 12, 16, and 20 of AICN, immunostaining for laminin, s-laminin, fibronectin, entactin, and heparan sulfate proteoglycan increased in the GBM in a spike-like pattern. Concomitantly, glomerular mRNA levels of laminin B2-chain and of s-laminin increased. Type IV collagen protein and gene expression remained unchanged or decreased. No glomerular immunostaining for type I collagen occurred during AICN despite increased expression of mRNA for this collagen type. In contrast to AICN, in PHN no pronounced changes of the glomerular ECM occurred, except for transient expression of type I collagen mRNA in whole glomerular RNA and type I collagen protein the GEC cytoplasm. Stimulation of GEC in culture with anti-GEC antibody and complement also failed to induce transcription of laminin or s-laminin mRNA or the release of laminin protein. These findings suggest that the polyantigenic expansion of GBM which occurs in chronic experimental MN may be stimulated by factors different from the C5b-9 mediated processes that cause the initial proteinuria.
Insights
Chronic membranous nephropathy (MN) involves glomerular basement membrane (GBM) thickening. Experimental models show increased laminin and s-laminin in GBM during active Heymann nephritis (AHCN), suggesting distinct stimuli for GBM expansion.
Area of Science:
- Nephrology
- Molecular Biology
- Pathology
Background:
- Chronic progressive membranous nephropathy (MN) is characterized by glomerular basement membrane (GBM) thickening and spike formation.
- The composition of the GBM and its gene expression in MN are not fully understood.
- Experimental models are crucial for dissecting the molecular mechanisms of MN.
Purpose of the Study:
- To investigate sequential changes in GBM composition and glomerular gene expression in experimental MN models.
- To determine the role of glomerular epithelial cells (GECs) in GBM changes during MN.
- To identify potential stimuli driving GBM expansion in chronic MN.
Main Methods:
- Utilized active and passive Heymann nephritis (AHCN, PHN) rat models of MN.
- Performed immunostaining of renal biopsies for extracellular matrix (ECM) proteins.
- Analyzed glomerular gene expression of ECM components using cDNA probes.
- Investigated GEC response to anti-GEC antibody and complement in vitro.
Main Results:
- AHCN showed increased GBM immunostaining for laminin, s-laminin, fibronectin, entactin, and heparan sulfate proteoglycan in a spike-like pattern.
- Glomerular mRNA levels of laminin B2-chain and s-laminin increased in AHCN.
- Type IV collagen expression was unchanged or decreased; type I collagen showed increased mRNA but no protein in GBM during AHCN.
- PHN exhibited minimal ECM changes, with transient type I collagen expression in GECs.
- In vitro studies failed to induce laminin or s-laminin mRNA expression or laminin release in GECs.
Conclusions:
- Polyantigenic expansion of GBM in chronic experimental MN is stimulated by factors distinct from C5b-9 mediated processes.
- Increased laminin and s-laminin in GBM during AHCN suggest specific molecular responses.
- GECs may not directly mediate the transcriptional changes of laminin/s-laminin in response to complement activation.