IgA1 deposition may induce NLRP3 expression and macrophage transdifferentiation of podocyte in IgA nephropathy

BACKGROUND: The NLRP3 inflammasome plays an important role in mediating podocyte injury in various kidney diseases. The aim of this study was to investigate whether NLRP3 expression associated with podocyte injury was involved in the pathogenesis of IgA nephropathy (IgAN). METHODS: NLRP3 inflammasomes and macrophage marker (F4/80) were detected in the renal tissues of IgAN patients. Association between kidney NLRP3 levels and the clinical feature of IgAN patients was analyzed. Podocytes were incubated with serum containing dys-glycosylated IgA1 protein isolated from IgAN patients. Expression of NLRP3 inflammasomes, F4/80, inflammatory cytokine and renal fibrosis marker were measured using RT-PCR and Western blotting. RESULTS: Renal NLRP3 inflammasome expression was significantly increased in IgAN patients compared to normal control tissues. Moreover, co-expression of NLRP3 and F4/80 could be observed in the podocytes of IgAN patients. Patients with eGFR < 60 ml/min/1.73 m(2) had remarkably higher tubular NLRP3 expression (P < 0.05), while patients with gross proteinuria (≥ 3.5 g/day) had a significantly higher glomerular NLRP3 expression (P < 0.05). Further analysis indicated that dys-glycosylated IgA1 isolated from IgAN patient serum could induce podocyte expression of NLRP3 and the macrophage marker F4/80, which could lead to induction of an inflammatory reaction (increased expression of ICAM-1) and fibrosis (increased expression of α-SMA). CONCLUSION: Dys-glycosylated IgA1 isolated from IgAN patient serum could induce NLRP3 expression in podocytes and initiate podocyte macrophage transdifferentiation (PMT). After PMT, podocytes secrete proinflammatory cytokines that can contribute to the inflammation cascade and renal fibrosis changes associated with IgAN.