Transcriptional suppression of nephrin in podocytes by macrophages: Roles of inflammatory cytokines and involvement of the PI3K/Akt pathway

Abstract 

Expression of nephrin, a crucial component of the glomerular slit diaphragm, is downregulated in patients with proteinuric glomerular diseases. Using conditionally immortalized reporter podocytes, we found that bystander macrophages as well as macrophage-derived cytokines IL-1β and TNF-α markedly suppressed activity of the nephrin gene promoter in podocytes. The cytokine-initiated repression was reversible, observed on both basal and inducible expression, independent of Wilms’ tumor suppressor WT1, and caused in part via activation of the phosphatidylinositol-3-kinase/Akt pathway. These results indicated a novel mechanism by which activated macrophages participate in the induction of proteinuria in glomerular diseases.

Abbreviations: PKC, protein kinase C, SEAP, secreted alkaline phosphatase, FBS, fetal bovine serum, ATRA, all-trans retinoic acid, PI3K, phosphophatidylinositol-3-kinase, TPA, 12-o-tetradecanoylphorbol-13-acetate, MϕCM, macrophage-conditioned medium, LPS, lipopolysaccharide, RT-PCR, reverse transcriptase-polymerase chain reaction, GAPDH, glyceraldehydes-3-phosphate dehydrogenase, REPON, reporter podocytes for nephrin, HGF, hepatocyte growth factor, RAR, retinoic acid receptor, RARE, retinoic acid response element

Keywords: Podocyte, Nephrin, Macrophage, IL-1β, TNF-α, Phosphatidylinositol-3-kinase