The Characteristics Of Oral Microbiome And Its Relationship With The Pathogenesis Of IgA Nephropathy

BackgroundIgA nephropathy(IgAN)is the most common primary glomerulonephritis in the world,which occurs in people aged 20-40 years.Among them,20%-40%of IgA nephropathy patients will progress to end-stage renal disease within 20 years.The diagnosis of IgAN must be based on immunopathology,which is characterized by the deposition of IgA dominated immune complexes in glomerular mesangial area and/or glomerular capillary loops under immunofluorescence.At present,it is believed that genetic factors,glycosylated IgA molecules and mucosal immunity are involved in the occurrence of IgAN,but the exact pathogenesis remains unclear.Patients with IgAN usually have gross hematuria,proteinuria or deterioration of renal function after upper respiratory tract or intestinal mucosal infection,suggesting that microbial mucosal infection may be closely related to the occurrence and development of IgAN,but the exact role and mechanism are not clear.A series of previous studies at home and abroad suggest that human oral,intestinal and other micro ecosystems are closely related to kidney disease.The dynamic balance of intestinal flora plays an important role in promoting the digestion and absorption of nutrients,maintaining the normal physiological function of the intestine,regulating the body’s immunity,and fighting against pathogenic microorganisms.The microbes in the mouth and intestine interact with each other to a certain extent.Bacteria in the mouth are ingested into the stomach through food and eventually reach the intestine.Studies have shown that,similar to intestinal flora,the disruption of oral flora homeostasis is closely related to the occurrence of autoimmune diseases,and oral microbial antigens may participate in the occurrence and development of IgAN.Watanabe h found that IgAN and recurrent tonsillitis patients had similar bacterial composition,in which Prevotella,fusobacteria and Sphingomonas were more abundant.The tonsillar infection caused by Staphylococcus aureus and Haemophilus parainfluenzae was positively correlated with IgA nephropathy.Haemophilus parainfluenzae,as an oral innate strain,can stimulate the proliferation of tonsil monocytes and produce IgA molecules in vitro.However,most of the current studies focus on the relationship between intestinal microflora and the pathogenesis of IgAN.There are few reports on the characteristics of oral microbiome and the role of excessive mucosal immune response caused by oral microbial mucosal infection in the occurrence and development of IgAN.Only a few studies have observed the composition of oral microbiome in IgAN patients,and the characteristics of oral microbiome have not been systematically described.Therefore,a clear understanding of the composition of oral microbiota and its changes in IgAN patients can provide new ideas for the pathogenesis,early diagnosis and treatment of IgAN.Therefore,the purpose of this study is to explore the relationship between oral microbiome composition,gene function and metabolic pathway and IgAN.ObjectiveBy sequencing 16S rRNA gene,the composition and distribution of oral flora in IgAN patients were discussed,the significant differences between IgAN patients and healthy people were analyzed,and the relationship between gene function,metabolic pathway and IgAN was studied,so as to provide new ideas for the pathogenesis of IgAN.MethodsMethods:a total of 40 patients with primary IgA and negative immunofluorescence IgM(excluding the interference of secretory IgM)diagnosed by renal biopsy in our hospital were collected.The secondary IgA deposition in mesangial region was excluded in all patients.16S rRNA gene sequencing was used to determine the difference of oral flora between IgAN patients and healthy people.Saliva samples of 20 healthy people were collected as control.(1)16S rRNA gene sequencing:the total DNA of microbiome was extracted,the target fragment was amplified by PCR,the amplified product was purified by magnetic beads,the amplified product was quantified by fluorescence,the sequencing library was prepared,and the highthroughput sequencing was carried out on the computer.(2)Species composition spectrum analysis:To explore the composition and distribution of oral flora in IgAN patients by species abundance difference analysis and rarefaction sparse curve.(3)Alpha and beta diversity analysis:through alpha diversity index analysis,PCA principal component analysis,Bray Curtis PCoA principal coordinate analysis,non metric multi-dimensional scale analysis(NMDS)and other methods,the flora richness and diversity were discussed.(4)Gene function prediction and function annotation:through the analysis of relative abundance distribution,relative abundance difference,common/unique KEGG metabolic pathway,KEGG metabolic pathway enrichment,the relationship between the dominant gene function and metabolic pathway and IgAN was studied.(5)Subgroup analysis of oral microflora distribution:IgAN patients were divided into renal SIgA deposition positive group and SIgA deposition negative group by immunofluorescence technique,and the structural characteristics of oral microflora among subgroups were further analyzed.ResultsCompared with healthy controls,oral flora richness and diversity of IgAN patients are decreased.The abundance of Prevotella,Veillonella and Clostridia in saliva samples of IgAN patients was significantly higher than that of healthy controls,while the abundance of Actinobacillus,Gemellaceae,Bacilli and Firmicute in saliva samples of IgAN patients was significantly lower than that of healthy controls.In IgAN group,AMPK signaling pathway,arachidonic acid metabolism,inositol phosphate metabolism,phenylpropanoid biosynthesis and pentose and gluconate interconversion were the most abundant genes.Subgroup analysis of IgAN patients showed that the abundance of Prevotella in IgAN patients with positive SIgA deposition was significantly higher than that in IgAN patients with negative SIgA deposition.ConclusionThe abundance and diversity of oral microorganisms in IgAN patients decreased,and the structure and composition of oral flora changed significantly,which may be involved in the pathogenesis of IgAN by affecting the material metabolism and related metabolic pathways.