Gut microbial metabolite, sphingosine-1-phosphate (S1P), drives mesangial cell phenotypic transformation and accelerates progression of IgA nephropathy via CCL2-MET-FAK pathway.

INTRODUCTION: IgA nephropathy (IgAN), the most prevalent primary glomerulonephritis subtype, affects many patients worldwide. To identify new therapeutic targets for IgAN, this study aimed to investigate the role and mechanisms of gut microbiota metabolites in mesangial cell proliferation. METHODS: Building on our prior finding of elevated serum sphingosine-1-phosphate (S1P) in IgAN patients versus healthy controls,we established complementary in vivo and in vitro models.Using humanized-gut microbiota mice and IgA1-stimulated mesangial cells, we examined S1P effects via receptor modulation and Chemokine ligand 2(CCL2)-Mesenchymal to epithelial transition factor(MET)-Focal Adhesion Kinase(FAK) pathway analysis, validated in renal biopsies. RESULTS: Treatment of human mesangial cells with aggregated IgA1 (aIgA1) successfully induced an IgAN phenotype, characterized by increased proliferation, reduced apoptosis, and significant intracellular IgA accumulation. This model demonstrated upregulated CCL2 expression, along with increased proportions of cells in S and G2 phases. Western blot analysis further revealed significant upregulation of MET, phosphorylated MET (Tyr1234/1235 and Tyr1349), Proliferating Cell Nuclear Antigen(PCNA), cyclin D1, S1PR1, and S1PR3 protein expression. Targeted intervention using CCL2 siRNA, the CCL2 inhibitor NOX-E36, and the MET inhibitor LY2801653 decreased IgA deposition, p-Met protein expression, and cell proliferation. Furthermore, S1P intervention in IgAN mesangial cell models significantly increased S1PR1, S1PR3, CCL2, and MET protein expression, promoting mesangial cell proliferation. Importantly, the CCL2-MET-FAK signaling pathway was activated in both the mice with an IgAN-like phenotype and IgAN patients. CONCLUSIONS: Disruption of the gut microbiota in IgAN increases CCL2 expression in renal mesangial cells, driven by the metabolite S1P. This, activates the MET/FAK signaling pathway, promoting mesangial cell proliferation and contributing to IgAN progression.Our findings support targeting S1P as a therapeutic strategy for IgAN.