Role Of Mannose-binding Lectin Pathway In Progression Of IgA Nephropathy

In 1968,IgA nephropathy(IgAN)was firstly discribed by Berger and Hinglais.This disease is characterized by deposition of IgA-IgG in the glomerular mesangium and along capillary loops.Currently,as one of the most common primary glomerulonephritis in the worldwide,the incidence of IgAN is highest in Asia,and lowest in Africa.Its distribution presents the ethnic and regional differences.In the past,IgAN is known as a disease having good prognosis.But,0 to 40%of patients with IgAN reached the end-stage renal failure in 20 years after renal biopsy.As an autoimmune glomerular disease,IgA nephropathy has complex gene background,clinical diversity and no specific treatment.So exploring its pathogenesis and finding new therapeutic targets for prevention is important for us.It has become the focus of current research in this field.The first part of our study is to collect 930 primary IgAN patients diagnosised in our department.By retrospectively analyzing the clincal prognosis and baseline data,the relationship between underweight and renal outcome in this study population was showed.During follow-up time of 100 months,underweight group had the higher ESRD incidence(17.3%)than normal weight(9.6%),overweight(9.0%)and obese group(6.0%).Survival analysis also showed the mean renal ESRD-free time in underweight is lower than the other three groups.Compared to normal weight group,multivariate COX analysis presented that underweight is an independent risk factor for progressin to ESRD in IgAN patients(HR=3.06;95%CI 1.41-6.64;P=0.005).Its hemoglobin,uric acid,triglycerides,cholesterol and lymphocyte counts were lower than normal weight group,suggesting that underweight exacerbate deterioration of renal function by its malnutrition status.Then,via linear correlation analysis,we found that BMI was positively correlated to serum C3(r=0.252,p<0.001)and C4(r=0.157,p<0.001).Univariate COX analysis presented that C3(HR=0.99,95%CI 0.98-1.00,P=0.03)is an independent risk factor for progression to ESRD.Conditional COX regression showed the association between underweight and ESRD was significantly weakened after adjusted by serum C3,which meant underweight may be involved in renal progression by reducing serum complement levels.And the complement activation plays an important effect in IgAN patients with advanced renal disease.Our second part consequently focused on MBL pathway activation in IgAN patients,and its effect on mesangial cells after complement activation in vitro study.55 patients with long follow-up time(the median follow-up time was 39 months)was enrolled,the association between systemic and local activation of MBL with clinical baseline indicators or prognosis were analyzed Compared to patients without MBL renal deposition,the presence of clinical and pathological manifestations in those who with renal tissue deposition were heavier.Although without statistical significance,higher incidence of ESRD was found in MBL positive deposition group(33.3%vs.8.5%,p=0.071).Utilizing the protein purification techniques to purify and separate the polymeric IgAl and monomeric IgAl from human serum,polymeric IgAl from patients was used to stimulate mesangial cells for modeling IgAN disease cell.On this basis,the preliminary study discussed whether pathological deposition of MBL in renal tissue directly affect mesangial cells and exacerbate the kidney damage.It found that low serum level of MBL could promote mesangial cell proliferation,while high concentrations were significantly promote apoptosis.Due to mesangial cells stimulated by high dose of MBL were decreasing the anti-apoptotic protein Bcl-2 expression,so we speculate that apoptosis in vitro mesangial cells was induced by down-regulating the expression of Bcl-2 protein,although the corresponding signaling pathways need study in further.In the third part of our study,we recruited 613 primary IgAN patients with follow-up time more than 12 months.Basing on this large database,we systematically explore the assocaition between lectin pathway molecule(MBL and L-ficolin)gene polymorphism and renal progression,while analyzing relevance between gene polymorphism and their corresponding functional proteins.Firstly,we included 50 cases of patients by deeply sequencing of the above two genes,in order to get the single nucleotide polymorphism in gene coding region,promoter region and junction.Analyzing of association between 16 SNPs in MBL2 gene and circulating MBL protein levels,only rs11003125 and rs1800450,functionally affect the serum concentration of MBL and presented a high frequency(MAF>10%).Further we tested these two SNPs in 286 IgAN patients,and found that only rs 1800450 associated with renal function deterioration.As the other one activate molecule of lectin pathway,structure and function of L-ficolin is similar to MBL.By the same testing methods,we found that 21 snps was located in FCN2,only rs7851696 was associated with serum protein concentration,and this variation is also involved in renal progression.Finally,two SNPs were carried out in all 613 patients,COX regression analysis showed that both of rs1800450(HR=1.74,1.20-2.53,p=0.004)and rs7851696(HR=1.53,1.06-2.19,p=0.022)are the risk factors for ESRD.Adjusted by clinical indicators,rs7851696 loss its significant influence on the prognosis,but rs1800450 still is the independent risk factor for ESRD(HR=2.50,1.43-4.36,p=0.001).Then,based on previously established risk score in our department,combined with rs1800450,we further establish a new integrated risk model to predict the risk of progression to ESRD.Finally,patients were divided into three genotype groups by rs1800450,in order to compare the differences of systemic and local kidney lectin pathway activation among them.Different from the other two genotypes,the development mechanism of patients with AA genotype having poor renal prognosis might because of lacking of MBL complement activation.In summary,the clinical aspects of our study found that underweight may be involved in renal progression by influencing complement levels,suggesting the importance of complement activation in disease development of IgAN patients;we also discovered MBL capable of affecting mesangial cell by activating complement and non-complement pathway(e.g.apoptosis)to aggravate kidney damage;rs1800450 in MBL2 gene is a risk factor of poor prognosis,which is independent of gender,age,clinical indicators and our previously established risk score[1].Significantly decreased serum level of MBL in rs1800450-AA patients suggested that their renal progression was caused by MBL deficiency,which could induce a corresponding lack of MBL pathway activiation.These results indicated that the role of MBL pathway is a "double-edged sword",which means its deactivation and over-activation could cause excessive damage to kidney,eventually leading to renal progression in IgAN patients.