Inflammatory cytokines upregulate nephrin expression in human embryonic kidney epithelial cells and podocytes

Nephrin is an important regulator of the glomerular filtration barrier and its malfunction is associated with severe proteinuria. In this study we show that exposure of human embryonic kidney epithelial A293 cells to the proinflammatory cytokine interleukin-1beta (IL-1beta) causes a dose-dependent upregulation of nephrin mRNA level. Time-course analyses reveal first significant increases in nephrin mRNA levels after 4h of stimulation. Furthermore, nephrin protein is also elevated by IL-1beta treatment. Tumor necrosis factor-alpha (TNFalpha) exerted a comparable effect on nephrin mRNA and protein expression. The IL-1beta-induced upregulation of nephrin expression occurs independently of nitric oxide (NO) generation, since the NO-synthase inhibitor N(G)-monomethyl-L-arginine does not block the IL-1beta effect. Mechanistically, we found that the IL-1beta-induced response does not involve protein kinase C, protein kinase A, the classical mitogen-activated protein kinase (MAPK), the stress-activated p38-MAPK, or the NF-kappaB cascade, since selective inhibitors of these pathways were unable to alter the IL-1beta response. Moreover, neither unselective cyclooxygenase (COX) inhibitors, like indomethacin, nor COX-2-selective inhibitors, like flosulide and NS 398, nor the anti-inflammatory glucocorticoid dexamethasone were able to alter IL-1beta-induced nephrin expression. The only inhibitor that was able to block IL-1beta- and TNFalpha-induced nephrin upregulation was rottlerin, which has been suggested to act as a selective PKCdelta inhibitor. However, concerning cytokine-triggered nephrin expression, rottlerin action involved inhibition of another still to be identified protein kinase. Importantly, cytokine-induced upregulation of nephrin expression was also confirmed in primary human podocytes. In summary, these data show for the first time that inflammatory cytokines like IL-1beta or TNFalpha can upregulate nephrin expression and this mechanistically involves a rottlerin-sensitive protein kinase.