Oxidative stress and inflammation are mediated via aryl hydrocarbon receptor signalling in idiopathic membranous nephropathy

Abstract

Membranous nephropathy (MN) patients are diagnosed by the presence of phospholipase A₂ receptor (PLA2R) before they progress to renal failure. However, the subepithelium-like immunocomplex deposit-mediated downstream molecular pathways are poorly understood. The aryl hydrocarbon receptor (AHR), NF-ƙB and Nrf2 pathways play central roles in the pathogenesis and progression of chronic kidney disease. However, their mutual effects on MN require further examination. Thus, we investigated the effect of AHR signalling on the NF-ƙB and Nrf2 pathways in IMN patients, cationic bovine serum albumin (CBSA)-injected rats and zymosan activation serum (ZAS)-treated podocytes. IMN patients show significantly decreased serum total protein and albumin levels, increased urine protein levels and intrarenal IgG₄ and PLA2R protein expression in glomeruli compared with controls. IMN patients exhibited increased mRNA expression of intrarenal AHR and its target genes, including CYP1A1, CYP1A2, CYP1B1 and COX-2. This increase was accompanied by significantly upregulated protein expression of CD3, NF-ƙB p65 and COX-2 and significantly downregulated Nrf2 and HO-1 expression. Similarly, CBSA-induced rats showed severe proteinuria and activated intrarenal AHR signalling. This was accompanied by significantly upregulated protein expression of intrarenal p-IκBα, NF-κB p65 and its gene products, including COX-2, MCP-1, iNOS, 12-LOX, p47^phox and p67^phox, and significantly downregulated protein expression of Nrf2 and its gene products, including HO-1, catalase, GCLC, GCLM, MnSOD and NQO1. These results were further verified in ZAS-induced podocytes. Treatment with the AHR antagonist CH223191 and AHRsiRNA significantly preserved podocyte-specific protein expression and improved the NF-ƙB and Nrf2 pathways in ZAS-induced podocytes. In contrast, similar results were obtained in ZAS-induced podocytes treated with the NF-ƙB inhibitor BAY 11-7082 and NF-κBp65 siRNA. However, neither method had a significant effect on AHR signalling. Collectively, these results indicate that the NF-ƙB pathway is a downstream target of AHR signalling. Our findings suggest that blocking AHR signalling inhibits oxidative stress and inflammation, thereby improving proteinuria and renal injury.

Keywords: Aryl hydrocarbon receptor; Cationic bovine serum albumin; Idiopathic membranous nephropathy; Nrf2; Nuclear factor kappa B; Oxidative stress and inflammation.