Podocyte injuries exacerbate mesangial proliferative glomerulonephritis

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Abstract. The present histopathologic study of anti-Thy-1.1 models of mesangioproliferative glomerulonephritis in rats provides a structural analysis of damage development and of pathways to recovery and to nephron loss. As long as the disease remains confined to the endocapillary compartment, the damage may be resolved or recover with a mesangial scar. Irreversible lesions with loss of nephrons emerge from extracapillary processes with crucial involvement of podocytes, leading to tuft adhesions to Bowman's capsule (BC) and subsequent crescent formation. Two mechanisms appeared to be responsible: (1) Epithelial cell proliferation at BC and the urinary orifice and (2) misdirected filtration and filtrate spreading on the outer aspect of the nephron. Both may lead to obstruction of the tubule, disconnection from the glomerulus, and subsequent degeneration of the entire nephron. No evidence emerged to suggest that the kind of focal interstitial proliferation associated with the degeneration of injured nephrons was harmful to a neighboring healthy nephron.Glomerular diseases starting with mesangiolysis have a high probability of recovery. However, not all nephrons recover; some always undergo destruction; we therefore raised the following questions: (1) what is the crucial stage of damage that determines the subsequent recovery or progression and (2) what are the sequences of events leading either to the restitution or to the degeneration of the respective nephron? Thus, our primary question was not why a nephron degenerated or recovered but how these outcomes were achieved. A glomerulus, and all the more a nephron, are both complex structures; we therefore wanted to analyze to which extent the loss and, on the other hand, the reestablishment of the higher order structure were decisive for damage progression and recovery, respectively.The most common models used to study mesangiolysis and damage development starting therefrom are those that induce mesangial cell lysis with antibodies against the Thy 1.1 antigen of mesangial cells; the resulting disease is generally referred to as anti-Thy-1 nephritis. The classical experiments were performed either with polyclonal antibodies (1,2) or with the monoclonal antibody OX-7 (3). More recently, the monoclonal antibody 1-22-3 (4) has been shown to produce more severe damage. Administration of these antibodies in rats leads to a brisk complement-dependent lysis of the mesangial cells followed by the development of a mesangioproliferative glomerulonephritis.We used both the OX-7 and the 1-22-3 antibodies in two originally separate studies. Because disease development was more or less identical in both models, we combined both studies. This permitted us to analyze complete pathways of damage development and to provide step-by-step sequences of events leading from mesangiolysis via various intermediate stages to either the recovery or loss of a nephron. We think that these results are of considerable general interest when asking how nephrons degenerate in chronic renal disease. M...

Section: Relevance Of Tubulointerstitial Processessupporting

confidence: 92%

Pathways to Recovery and Loss of Nephrons in Anti-Thy-1 Nephritis

Kriz¹,

Hähnel²,

Hosser³

et al. 2003

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“…Preceding minor podocyte injury to this model leads to irreversible mesangial alteration (8), demonstrating the importance of podocytes for the glomerular recovery in this model. These findings suggest that podocytes contribute to maintenance and recovery of the glomerular structure by counteracting the hydrostatic force on the glomerular filtration barrier mechanically.…”

mentioning

confidence: 74%

“…One study showed that minor podocyte injury with puromycin preceding Thy-1 GN induction results in irreversible mesangial lesions (8). Another report demonstrated that mice deficient of podocyte-specific mole- cule CD2-associated protein exhibit mesangial cell proliferation and mesangial matrix expansion (32).…”

Section: Discussionmentioning

confidence: 99%

Angiogenic Protein Cyr61 is Expressed by Podocytes in Anti-Thy-1 Glomerulonephritis

Sawai¹,

Mori²,

Mukoyama³

et al. 2003

Abstract. Dynamic recovery of glomerular structure occurs after severe glomerular damage in anti-Thy-1 glomerulonephritis (Thy-1 GN), but its mechanism remains to be investigated. To identify candidate genes possibly involved in glomerular reconstruction, screening was performed for genes that are specifically expressed by podocytes and are upregulated in glomeruli of Thy-1 GN. Among them, cysteine-rich protein 61 (Cyr61 or CCN1), a soluble angiogenic protein belonging to the CCN family, was identified. By Northern blot analysis, Cyr61 mRNA was markedly upregulated in glomeruli of Thy-1 GN from day 3 through day 7, when mesangial cell migration was most prominent. By in situ hybridization and immunohistochemistry, Cyr61 mRNA and protein were expressed by proximal straight tubules and afferent and efferent arterioles in normal rat kidneys and were intensely upregulated at podocytes in Thy-1 GN. Platelet-derived growth factor-BB (PDGF-BB) and transforming growth factor-␤1 (TGF-␤1), of which the gene expression in the glomeruli of Thy-1 GN was upregulated in similar time course as Cyr61, induced Cyr61 mRNA expression in cultured podocytes. Furthermore, supernatant of Cyr61-overexpressing cells inhibited PDGF-induced mesangial cell migration. In conclusion, it is shown that Cyr61 is strongly upregulated at podocytes in Thy-1 GN possibly by PDGF and TGF-␤. Cyr61 may be involved in glomerular remodeling as a factor secreted from podocytes to inhibit mesangial cell migration.

“…Second, podocyte injury impairs mesangial structure and function. In anti-Thy-1 glomerulonephritis, a reversible self-limiting model in itself, preceding minor podocyte injury with PAN pretreatment results in irreversible mesangial alteration (48). We showed recently that cysteine-rich protein 61 (Cyr61), a potent angiogenic protein that belongs to the CCN family of matrix-associated secreted protein family, is expressed in podocytes and upregulated in anti-Thy-1 glomerulonephritis (20).…”

Section: Discussionmentioning

confidence: 99%

Role of p38 Mitogen-Activated Protein Kinase Activation in Podocyte Injury and Proteinuria in Experimental Nephrotic Syndrome

Koshikawa¹,

Mukoyama²,

Mori³

et al. 2005

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158

145

Podocytes play an important role in maintaining normal glomerular function and structure, and podocyte injury leads to proteinuria and glomerulosclerosis. The family of mitogen-activated protein kinases (MAPK; extracellular signal-regulated kinase [ERK], c-Jun N-terminal kinase, and p38) may be implicated in the progression of various glomerulopathies, but the role of MAPK in podocyte injury remains elusive. This study examined phosphorylation of p38 MAPK in clinical glomerulopathies with podocyte injury, as well as in rat puromycin aminonucleoside (PAN) nephropathy and mouse adriamycin (ADR) nephropathy. The effect of treatment with FR167653, an inhibitor of p38 MAPK, was also investigated in rodent models. In human podocyte injury diseases, the increased phosphorylation of p38 MAPK was observed at podocytes. In PAN and ADR nephropathy, the phosphorylation of p38 MAPK and ERK was marked but transient, preceding overt proteinuria. Pretreatment with FR167653 (day ؊2 to day 14, subcutaneously) to PAN or ADR nephropathy completely inhibited p38 MAPK activation and attenuated ERK phosphorylation, with complete suppression of proteinuria. Electron microscopy and immunohistochemistry for nephrin and connexin43 revealed that podocyte injury was markedly ameliorated by FR167653. Furthermore, early treatment with FR167653 effectively prevented glomerulosclerosis and renal dysfunction in the chronic phase of ADR nephropathy. In cultured podocytes, PAN or oxidative stress induced the phosphorylation of p38 MAPK along with actin reorganization, and FR167653 inhibited such changes. These findings indicate that the activation of MAPK is necessary for podocyte injury, suggesting that p38 MAPK and, possibly, ERK should become a potential target for therapeutic intervention in proteinuric glomerulopathies.