Renal podocytes and their slit diaphragms ensure the integrity of the renal basement membrane that forms the barrier to urinary protein loss. A putative disruption of the slit diaphragm and its main protein components, nephrin and podocin, may be implicated in the pathogenesis of lupus nephritis (LN). We studied the glomerular protein expression of nephrin and podocin in NZB/W LN mice by Western blot and immunofluorescence; mRNA levels were measured by real-time PCR. Human kidney biopsies of class II (n = 5), IV (n = 4), V (n = 7) LN were evaluated for nephrin expression by immunohistochemistry. Glomerular protein expression of nephrin and podocin were significantly reduced in NZB/W LN, starting from the earlier stages (mild mesangial LN) and becoming pronounced at advanced histological forms (focal and diffuse proliferative LN). Nephrin and podocin mRNA levels were substantially decreased in diffuse proliferative disease. Decreased expression of both proteins correlated with electron microscopy findings of distorted slit diaphragms. In patients with LN, nephrin was decreased particularly in diffuse proliferative LN. The main slit diaphragm proteins, nephrin and podocin, are affected from the earlier stages of LN and their expression correlates with disease histology. Our findings suggest a novel role of podocytes and their structures in immune-mediated nephritis.

Renal podocytes and their slit diaphragms ensure the integrity of renal basement membrane and prevent urinary protein loss. We have previously reported that decreases of the podocyte slit diaphragm proteins nephrin and podocin represent early events in the podocytopathy of lupus nephritis (LN). We asked whether immunosuppressive agents such as glucocorticoids and cyclophosphamide may have direct effects on podocytes. We assessed in New Zealand Black/New Zealand White (NZB/W) F1 LN mice glomerular nephrin and podocin expression and localization by the use of Western blot and immunofluorescence; mRNA levels were measured by real-time polymerase chain reaction (PCR) and renal histology by light and electron microscopy. Early treatment with glucocorticoids and cyclophosphamide halted the histologic alterations associated with LN, preserving podocyte foot processes. Nephrin and podocin protein expression significantly increased in both glucocorticoid and cyclophosphamide groups as early as after three months of therapy. Real-time PCR revealed similar enhancement in nephrin and podocin mRNA levels after three to six months of treatment. This study documents that early treatment in experimental LN with glucocorticoids or cyclophosphamide preserves slit diaphragm proteins in podocytes and halts histological changes of the glomeruli, thus raising the possibility of a direct protective effect of these drugs on podocytes.