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Abstract. Progressive renal failure is accompanied by uncontrolled accumulation of extracellular matrix in glomeruli and tubulointerstitium, eventually resulting in glomerulosclerosis. Although glomerulosclerosis occurs secondary to various renal diseases, the fact that not all patients develop progressive glomerulosclerosis suggests that genetic factors may underlie the tendency to progress, or not to progress. Identified were two Lewis rat substrains with small genetic differences but with considerable difference in resolution of glomerulonephritis after anti-Thy-1 administration. In the Lewis/Møllegard rat strain, anti-Thy-1 glomerulonephritis spontaneously resolves within 4 wk. In contrast, Lewis/Maastricht rats develop progressive glomerulosclerosis after induction of this disease. The involvement of bone marrowderived cells and kidney cells in the development of glomerulosclerosis was determined. In the first study, exchange of bone marrow between these substrains did not affect the course of anti-Thy-1 nephritis. Lewis/Møllegard rats recovered rapidly, but Lewis/Maastricht rats showed progressive disease regardless of the genotype of the bone marrow they received. In the second study, kidneys were exchanged between the substrains. After transplantation, anti-Thy-1 nephritis was induced and glomerular damage assessed at day 21. Severe damage was observed in Lewis/Maastricht glomeruli independent of whether the kidney had been transplanted or not. Similarly, Lewis/Møllegard glomeruli, whether transplanted or not, revealed no residual histopathologic abnormalities. The inherited differences between the two substrains with regard to their insusceptibility to develop progressive glomerulosclerosis after mesangial injury are governed by genes expressed by the kidney, but not by bone marrow-derived cells.

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Although it is clear that genetic predispositions play a role in progressive glomerulosclerosis, identification of specific genes is difficult because of natural genetic heterogeneity among individuals. We have reported a differential susceptibility to progressive glomerulosclerosis after induction of experimental glomerulonephritis anti-Thy-1 nephritis in Lewis rat substrains. Glomerular lesions in Lewis/Møllegard rats resolve spontaneously, whereas Lewis/Maastricht (Lew/Maa) rats develop progressive glomerulosclerosis. This predisposition for progressive glomerulosclerosis is governed by unknown genes that are expressed by renal cells. Here, differential gene expression analysis using a rat complementary DNA micro array revealed neuronal activity-regulated pentraxin (Narp) as a candidate gene involved in the remodeling or progression of damaged glomeruli. Glomerular Narp mRNA expression was monitored during disease in both Lewis sub strains. Immunohistochemistry revealed that Narp protein is exclusively expressed in Lew/Maa glomeruli 7 and 14 days after induction of anti-Thy-1 nephritis. Double-immunofluorescent staining showed that proliferating mesangial cells and parietal epithelial cells (PECs) at sites of adhesion to podocytes are partially Narp-positive, whereas podocytes fail to express Narp. Immunohistochemistry in nephritic Wistar, unilaterally nephrectomized Wistar and Sprague-Dawley rats showed that Narp protein is present only in strains that develop progressive glomerulosclerosis but never in strains that show remodeling. We conclude that Narp is a predictor for anti-Thy-1 nephritis-induced glomerulosclerosis and its expression by PECs may be involved in the progression to glomerulosclerosis.

IJpelaar DH, Schulz A, Aben J, van der Wal A, Bruijn JA, Kreutz R, de Heer E. Genetic predisposition for glomerulonephritisinduced glomerulosclerosis in rats is linked to chromosome 1.