Role Of Human Mesangial-tubular Crosstalk In Secretory IgA-induced IgA Nephropathy

BackgroundIgA nephropathy(IgAN),a common primary glomerular disease with a complex pathological mechanism,is the leading cause of kidney failure.In China,the incidence of IgAN is approximately 45.3%in those with primary glomerulonephritis,30-40%of patients with IgAN progress to renal failure within 10-25 years.Currently,it is thought that aberrant glycosylated IgA,genetic factors and mucosal immunity are involved in the pathogenesis of IgAN,but the exact pathogenesis remains uncertain.Recently,many studies have shown that mucosal immunity,especially antibody-secretory IgA(SIgA),has a vital role in IgAN.Our previous research also confirmed that SIgA deposited in the mesangium was pathogenic in IgAN patients.SIgA stimulated the proliferation and activation of mesangial cells to release various cytokines and participated in kidney damage.Therefore,SIgA is closely related to the development of IgAN.IgAN was previously considered a mesangial proliferative glomerular disease,but studies suggested that tubulointerstitial damage correlated more closely with disease progression than glomerular injury.A subgroup of IgAN with severe tubulointerstitial damage usually progress faster to kidney failure.The severity of tubulointerstitial damage is related to decreased renal function and long-term prognosis of glomerular diseases including IgAN,and tubular atrophy/interstitial fibrosis is an independent risk predictor for disease progression in IgAN patients.Previous studies showed that tumor necrosis factor-?(TNF-?)released from mesangial cells after IgA deposition activated renal tubular cells through glomerulo-tubular communication.Aldosterone and angiotensin II secreted by IgA-activated mesangial cells regulated oxidative damage and induced apoptosis in tubular epithelial cells via glomerulo-tubular communication.We previously documented that approximately one-third of IgAN patients had SIgA deposition in the mesangium,two-third of them had IgA deposition,and some of them with SIgA deposition had tubulointerstitial damage.Therefore,we hypothesized that SIgA could mediate tubulointerstitial damage in IgAN through mesangial-tubular crosstalk as IgA.The aim of this study is to explore the mechanism of SIgA in renal injury of IgAN from the perspective of mesangial-tubular communication.ObjectiveTo explore whether SIgA can mediate IgAN tubulointerstitial damage through mesangial-tubular crosstalk by combination of in vivo experiments and coculturing HRMC and human proximal tubular epithelial cells(HK-2)in vitro,and provide a new idea for the treatment of IgAN.MethodsNinety-six patients with renal-biopsy-proven IgAN,from the Renal Division,First Affiliated Hospital of Zhengzhou University from September 2017 to September 2018,were enrolled in this study.We excluded patients with Henoch Schonlein purpura,systemic lupus erythematosus and diabetes,active hepatitis,cirrhosis,severe metabolic syndrome and other diseases that may cause secondary IgAN.Ten cases of normal renal tissue adjacent to kidney cancer were recruited as normal controls.(1)The deposition of SIgA in renal tissues of IgAN patients was detected by immunofluorescence;(2)SIgA of IgAN patients and normal controls in saliva were separated and purified by affinity chromatography,which were represented as P-SIgA and N-SIgA;(3)The binding rate of SIgA to HRMC and human proximal tubular epithelial cells(HK-2)were detected by flow cytometry;(4)HRMC and HK-2 were stimulated by SIgA(400?g/ml),and HK-2 cells were co-cultured with HRMC timulated by SIgA for 24 hours.The protein synthesis and mRNA expression of TNF-?,TGF-?1 and MCP-1 were detected by ELISA and PCR.(5)Immunohistochemistry was used to detect the expression of the above inflammatory factors in renal tissues of IgAN patients with SIgA deposition,and the correlation between the expression of above cytokines and tubulointerstitial injury of IgAN patients was analyzed.ResultsSignificant mesangial area SIgA deposits were detected in 29 patients(30.21%).No significant deposition of SIgA was observed in the renal tubular area.The binding rate of SIgA to HRMC was up to 81.6%,which was significantly higher than that of SIgA to HK-2(less than 3%).Our in vitro co-culture experiment showed that,the protein synthesis and mRNA expression of TNF-?,TGF-?1 and MCP-1 were up-regulated in SIgA-stimulated HRMC,but no obvious changes in the expression of above cytokines were observed in SIgA-stimulated HK-2.After cocultivation,the protein and mRNA expression of TNF-?,TGF-?1 and MCP-1 were significantly higher than those in SIgA-HRMC group and SIgA-HK-2 group.Furthermore,in renal tissues,we found that TNF-?,TGF-?1 and MCP-1 were mainly expressed in the tubulointerstitium of IgAN patients with SIgA deposition,and the expression of these factors was positively correlated with tubulointerstitial injury.ConclusionThe inflammatory mediators,which secreted by mesangial cells with SIgA stimulation,may further induced the release of inflammatory factors in tubular epithelial cells via the mesangial-tubular communication,thus mediating the tubulointerstitial injury in IgAN.