Study On The Effect Of Glycosylation And Histone Acetylation On The Pathogenesis Of IgA Nephropathy

IgA nephropathy(IgAN) is the most common glomerular disease worldwide, which is the important cause of renal failure.Its clinical manifestation is diversiform and its pathogenesis is unclear yet.Aberrantly glycosylated IgA1 is found nearly exclusively within immune complexes bound to Ig G or IgA1 antibodies.Synthesis and binding of antibodies directed against galactose-deficient IgA1 are required for formation of immune complexes that accumulate in the glomerular mesangium.These immune complexes activate mesangial cells,inducing proliferation and secretion of extracellular matrix, cytokines and chemokines,which result in renal injury.As a result,the formation of immune complexes containing aberrantly glycosylated IgA1 is the key factor in the pathogenesis of IgAN.IgA1 glycosylation modification is regulated by the two kinds of glycosylation enzymes:C1Gal T1 and ST6GALNAC2.IgAN is a kind of complex diseases affected by multiple genes and environmental factors.Epigenetic mechanism affects the human diseases by adjusting the interaction of genetic and environmental factors.The discordant clinicopathological features of a pair of identical twins with IgA nephropathy suggest that not only genetic factors but also epigenetic differences may be involved in the pathogenesy of IgAN.Histone acetylation modification is one of the histone modification,but its role in the pathogenesis of IgAN is unclear.In this research we studied the role of aberrant IgA1 glycosylation and histone acetylation modification by in vivo and in vitro to explore the pathogenesis and potential therapies of IgAN.In the first part of the research,we found the plasma level of IgA and galactose–deficient IgA1( Gd-IgA1) in IgAN patients were significantly increased compared with the healthy controls(P < 0.0001).With correlation analysis we found that: the plasma level of Gd-IgA1 in IgAN patients was positively correlated with the total amount of 24 h urine protein(r=0.479,P<0.001).C1GALT1 m RNA expression in peripheral blood mononuclear cell(PBMC)of IgAN patients was 0.38±0.07 folds(P<0.01) and ST6GALNAC2 m RNA expression was 2.31±0.48 folds(P<0.05) that in the healthy controls. Increased global H3 acetylation(P<0.05) and H4 acetylation(P<0.01) were observed in PBMC from IgAN patients compared with controls.The m RNA level of histone deacetylases such as HDAC1,HDAC2,HDAC3,HDAC7 and HDAC8 in PBMC from IgAN patients was respectively 2.20±0.18(P<0.001),0.44±0.08 folds(P<0.05), 0.98±0.18 folds(P>0.05),1.02±0.21 folds(P>0.05) and 1.47±0.25 folds(P<0.05) that in heath controls.The m RNA level of the histone acetyltransferases P300 and CREBBP in PBMC from IgAN patients was respectively 2.81±0.39 folds and 2.44±0.27 folds(all P<0.01) that in heath controls.H3 acetylation and H4 acetylation at C1GALT1 and ST6GALNAC2 gene promoter region were elevated in PBMC from IgAN patients compared with health controls.Immune fluorescent results of renal tissue indicated that the HDAC1 protein expression was increased obviously,but H3 Ac protein expression was significantly reduced in the renal tissue.In the second part of the research,we found that protein levels of TNF-α, MCP-1 were significantly increased in the plasma of IgAN patients.The m RNA expression of MCP-1,TNF-α,NF-κB,IL-1β and IL-6 were significantly increased in PBMC of IgAN Patients.We detected the cytokines profile in the supernatant of cultured human mesangial cells(HMC) respectively induced by N-IgA1(normal individual derived IgA1),N-a IgA1(normal individual derived aggregated IgA1),P-IgA1(IgAN patient derived IgA1), P-a IgA1(IgAN patient derived aggregated IgA1) and PBS(control group, i.e. add the same volumn 0.01mol/L PBS) with Ray Bio G-Series Select Human Inflammation Array 3.In P-a IgA1 group,IL-6s R,TNF-α,RANTES,TIMP-1,TIMP-2 and TNFRII were increased significantly.P-a IgA1 can also promote the proliferation of mesangial cell. HDAC1 inhibitors valproic acid(VPA) can decrease the amount of inflammatory factors produced by mesangial cells and inhibit the proliferation of mesangial cell.P-a IgA1 can up-regulated HDAC1 protein expression significantly and downregulated H3 Ac protein expression significantly.In the third part of the research,we found that P-a IgA1 can significantly promote the synthesis of HMC extracellular matrix and increase plasminogen activator inhibitor-1(PAI-1) expression.VPA can significantly reduce the synthesis of extracellular matrix by reducing the expression of HDAC1 and raising the level of histone acetylation in mesangial cells.In conclusion,this study found that IgAN patients were in an abnormal histone acetylation state;IgA1 glycosylation and Histone acetylation take part in the pathogenesis of IgAN.P-a IgA1 has proinflammative and profibrotic effects on human mesangial cells. VPA can inhibit the inflammation and fibrosis induced by P-a IgA1. The results enrich the pathogenesis of IgAN and provide new insights to the treatment of IgAN.