IgA nephropathy: gut microbiome regulates the production of hypoglycosilated IgA1 via the TLR4 signaling pathway

Abstract

Background IgA nephropathy (IgAN) is a major cause of primary glomerulonephritis characterized by mesangial deposits of galactose-deficient IgA1 (Gd-IgA1). Toll-like receptors (TLRs), particularly TLR4 are involved in the pathogenesis of IgAN. The role of gut microbiota on IgAN patients was recently investigated. However, whether gut microbial modifications of Gd-IgA1 through TLR4 play a role in IgAN remains unclear. Methods We recruited subjects into four groups, including 48 patients with untreated IgAN, 22 treated IgAN patients (IgANIT), 22 primary membranous nephropathy (MN), and 31 healthy controls (HCs). Fecal samples were collected to analyze changes in gut microbiome. Gd-IgA1 levels, expression of TLR4, B-cell stimulators, and intestinal barrier function were evaluated in all subjects. C57BL/6 mice were treated with a broad-spectrum antibiotic cocktail to deplete the gut microbiota and then gavaged with fecal microbiota transplanted fromclinical subjects of every group. Gd-IgA1 and TLR4 pathway were detected in peripheral blood mononuclear cells (PBMCs) from IgAN and HCs co-incubated with Lipopolysaccharide (LPS) and TLR4 inhibitor. Results Compared with other three groups, different compositions and decreased diversity demonstrated gut dysbiosis in un-treated IgAN, especially the enrichment of Escherichia -Shigella. Elevated Gd-IgA1 levels were found in un-treated IgAN patients and correlated with gut dysbiosis, TLR4, B-cell stimulators, indexes of intestinal barrier damage, and proinflammatory cytokines. In vivo, mice colonized with gut microbiota from IgAN and IgANIT patients, copied the IgAN phenotype with the activation of TLR4/MyD88/NF-κB pathway, B-cell stimulators in the intestine, and complied with enhanced proinflammatory cytokines. In vitro, LPS activated TLR4/MyD88/NF-κB pathway, B-cell stimulators and proinflammatory cytokines in the PBMCs from IgAN patients, which resulted in overproduction of Gd-IgA1 and inhibited by TLR4 inhibitor. Conclusions Our results illustrated that gut-kidney axis was involved in the pathogenesis of IgAN. Gut dysbiosis could stimulate the overproduction of Gd-IgA1 by TLR4 signaling pathway production and B-cell stimulators.