Background Podocyte injury probably plays important roles in the pathogenesis of IgA nephropathy (IgAN). We studied intra-renal and urinary messenger RNA (mRNA) expression of podocyte-associated molecules in patients with IgAN. Methods We studied 43 consecutive patients with biopsy-proven IgAN. Intra-renal and urinary expression of mRNAs was determined and compared to that of 20 patients with nephrectomy for kidney cancer and 12 normal subjects. Results Intra-renal mRNA expression levels of nephrin, podocin and synaptopodin were significantly lower in patients with IgAN than that of controls. In contrast, their urinary mRNA expression levels were similar. Intra-renal gene expression of nephrin inversely correlated with proteinuria (r = –0.620, P 0.001), GFR (r = 0.538, P 0.001), and the degree of tubulointerstitial scarring (r = –0.423, P = 0.013). After followed for an average of 33.4 ? 12.6 months, intra-renal nephrin expression significantly correlated with the rate of GFR decline (r = 0.324, P = 0.041). Conclusions Intra-renal mRNA expression of podocyte associated molecules was down-regulated in patients with IgAN, and the degree of down- regulation of nephrin correlated with disease severity and the rate of progression. Our result supports the hypothesis that podocyte injury is an important component in the pathophysiology of IgAN.
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