| Objective: IgA nephropathy(IgAN)is one of the most prevalent primary glomerulonephritis in the world,within 20 to 25 years,30 to 40 percent of individuals advance to end-stage renal disease.Presently,IgAN can only be treated with symptomatic assistance;hence,research into disease-specific therapies is necessary.Large amount of IgA deposits in the glomeruli and the proliferation of mesangial cells are the primary characteristics of IgAN.Degradation of IgA in the glomeruli could be used as a targeted treatment for IgAN.In this study,peripheral blood mononuclear cells(PBMC)and kidney biopsy samples from IgAN patients were sequenced,and the bioinformatics analysis revealed that the triple motif containing protein-21(TRIM21)is the hug gene of the IgAN’s differential expression genes network.In patients with IgAN,the expression of TRIM21 is up-regulated in the glomeruli.TRIM21 functions as an E3 ubiquitin ligase and is one of the most affinity antibody receptors in mammals.Cells’ cytoplasms exhibit significant levels of TRIM21 expression,which takes part in intracellular IgA identification,degradation,and downstream proliferative signal transduction.The precise function and mechanism of TRIM21 in IgAN are unknown,though.The objective of this research is to investigate the molecular mechanism of TRIM21 in mesangial cells degrading IgA and controlling mesangial cell proliferation,and so give a theoretical basis for degrading glomerular IgA and suppressing mesangial proliferation in IgAN.Method:(1)The differential expression genes in IgAN patients’ peripheral blood mononuclear cells(PBMC)were sequenced,and a network of differential expression genes was built,followed by validation of the network’s hub gene,TRIM21.(2)Measure the quantitative expression of TRIM21 in the glomerulus of IgAN patients and IgAN mice using kidney biopsy samples.The relationship between glomerular mesangial cells,IgA deposition,and the expression and localization of the TRIM21 protein was studied.Investigations were made on the relationships between TRIM21 expression level,pathological damage,renal function,and IgAN disease development.(3)TRIM21 knock-out mice were utilized to investigate the effects of TRIM21 on IgA deposition,pathological changes,and renal function in IgAN mouse models.The effect of TRIM21 knocking down or overexpression on the proliferation of poly-IgA1(a IgA1)stimulated human mesangial cells(HMC)were investigated.(4)To explore the mechanism of a IgA1 degradation by TRIM21 in HMC,proteasome inhibitor MG132 was utilized.Through immunoprecipitation and a laser scanning confocal microscope,the interaction between TRIM21 and IgA in HMC was discovered.TNF-,IL-6,c GAS,and STING mRNA levels in HMC were investigated by TRIM21 knockdown or overexpression.Results:(1)The network of IgAN’s differentially expressed genes was successfully built,and it was discovered and confirmed that TRIM21,the hub gene of the network,exhibited high expression characteristics in the glomeruli of IgAN patients and IgAN mice.In IgAN,TRIM21 can colocalize with PDGFRB,a marker of mesangial cells,and its level of expression is positively connected with IgAN patients’ higher SCr levels.The worse e GFR is associated with the co-localization intensity of TRIM21 and IgA,whereas patients with significant TRIM21 positive expression had a better prognosis for e GFR following 18 months of follow-up.(2)IgAN-like phenotypes of glomerular IgA deposition and mesangial proliferation were discovered to spontaneously manifest in TRIM21-deficient mice.Next,an oral immunization IgAN model was developed in TRIM21-deficient mice.IgA was the main immunoglobulin deposit in the mesangial area,and mesangial cell proliferation and expansion were even worse.In vitro,TRIM21 overexpression decreased a IgA1-stimulated HMC proliferation while TRIM21 knockdown boosted it.(3)Both the Co-IP detection and the fluorescence confocal analysis demonstrate that TRIM21 can co-localize with IgA1 in the HMC.In HMC,reducing TRIM21 expression and using the proteasome inhibitor MG132 can inhibit a IgA1 from being degraded and enhance STING transcription.Raising TRIM21 expression in HMC increased a IgA1 degradation and decreased TNF-,IL-6,c GAS,and STING mRNA transcription levels.Conclusion:(1)TRIM21 is the hub gene of the IgAN differential expression gene network and is strongly expressed in the mesangial region of IgAN patients.In patients with IgAN,the binding of TRIM2 and IgA in the mesangial area is related to impaired glomerular filtration function.The high expression of TRIM21 is also related to a better prognosis of e GFR,suggesting that the high expression of TRIM21 may have a protective effect on the damaged glomerulus.(2)The lack of TRIM21 causes spontaneous IgA deposition and mesangial cell proliferation in mice,and the IgA deposition,mesangial proliferation,and mesangial expansion in TRIM21 knockout mice are made worse by oral mucosal immunization with the IgAN model,suggesting that the lack of TRIM21 may impair IgA degradation.(3)TRIM21 interacts with a IgA1 in the cytoplasm of HMC and facilitates a IgA1 degradation via the ubiquitin proteasome pathway.Inhibiting TRIM21 expression prevents a IgA1 from being degraded and may promote the growth of HMC by boosting STING expression.Enhanced TRIM21 expression increases a IgA1 degradation and inhibits HMC proliferation by lowering TNF-,IL-6,c GAS,and STING expression.In conclusion,TRIM21 protects against IgAN by degrading IgA in mesangial cells and preventing its proliferation.To degrade IgA in mesangial cells and prevent mesangial proliferation in the future,increasing the expression of TRIM21 may be a possible therapeutic target for IgAN. |
