Dasatinib Blocks Mesangial Cell Activation by IgA1-Containing Immune Complexes in IgA Nephropathy In Vitro and In Vivo

Background: IgA nephropathy (IgAN) is caused by deposition of circulating immune complexes (IC) consisting of galactose-deficient IgA1 (Gd-IgA1) and anti-Gd-IgA1 autoantibodies. These IC activate mesangial cells (MC) and induce kidney injury but the mechanisms of these effects are unknown. We have identified signaling pathways induced in MC by Gd-IgA1-containing IC and targeted them using dasatinib, a broad-spectrum kinase inhibitor. Methods: IC from sera of patients with IgAN (native IC) or engineered IC formed in vitro from polymeric Gd-IgA1 and recombinant IgG autoantibodies in human serum were isolated by size-exclusion chromatography. IC-depleted samples served as controls. In cultured primary human MC, biological activities of native IC or engineered IC were assessed for their capacity to induce cellular proliferation and activate protein-tyrosine kinases, without or with dasatinib in the culture medium. In our passive mouse model of IgAN, nude mice received an intravenous dose of engineered IC (every other day x 3 doses) without or with dasatinib (30 mg/kg/d by gavage; n=5 in each group). Control mice did not receive any IC. Glomerular cellularity was evaluated by quantitative morphometry. Results: Compared to control samples, native and engineered IC increased proliferation of MC in culture by 4.0±2.2-fold and 2.9±0.7-fold, respectively. Kinomic profiling identified multiple activated signaling pathways. These pathways overlapped and encompassed 20 up-regulated kinases, including signaling pathways involving Src-family kinases and protein-tyrosine kinases in the EGF, VEGF, and PDGF pathways. Several up-regulated kinases, including Syk, Tec, Axl, and Eph, are involved in cellular proliferation or trans-activation of other kinases. Dasatinib inhibited upregulation of these kinases and cellular proliferation. In the mouse model of IgAN, engineered IC increased glomerular cellularity (P<0.0001 vs. control mice); dasatinib prevented these changes (P<0.0001 vs. mice given only engineered IC). Conclusion: Gd-IgA1-containing ICs activated multiple signaling pathways in MC in culture and stimulated cellular proliferation in vitro and in vivo. Dasatinib blocked these effects, suggesting its potential utility for IgAN treatment. Funding: NIDDK Support, Private Foundation Support