Synthetic Melanocortin Agonist NDP-MSH Ameliorates THSD7A-Associated Membranous Nephropathy in Mice

Membranous nephropathy (MN) is a leading cause of nephrotic syndrome, with THSD7A-associated MN representing a distinct autoimmune subtype. Current treatments often involve immunosuppressants with significant side effects. While melanocortin-based therapies have shown promise in experimental MN, prior evidence was limited to passive immunization models, which lack the direct human-like autoimmune involvement crucial for translational relevance. This gap necessitates a more clinically representative model to accurately assess melanocortin efficacy and mechanisms, especially concerning autoimmune B cell responses and autoantibody production, which are central to the pathogenesis of THSD7A-associated MN.

Researchers established a novel active immunization mouse model of THSD7A-associated MN by immunizing mice with recombinant THSD7A antigen. This model was designed to recapitulate key features of human MN, including insidious onset and progressive proteinuria. Following disease establishment, mice received rescue treatment with the pan-melanocortin receptor agonist NDP-MSH. The study assessed primary endpoints including proteinuria levels, glomerular damage, podocyte injury, and histopathological changes. Additionally, ex vivo experiments were conducted on primed B cells isolated from diseased mice to investigate direct cellular mechanisms, specifically focusing on plasma cell differentiation and autoantibody production.

The active immunization model successfully replicated cardinal features of human MN, including progressive proteinuria, subepithelial immune deposition, complement fixation, glomerular basement membrane thickening, and podocyte injury. Rescue treatment with NDP-MSH yielded significant therapeutic benefits. NDP-MSH significantly reduced proteinuria and mitigated glomerular damage and podocyte injury. This improvement was accompanied by a marked reduction in circulating anti-THSD7A autoantibody levels, reduced glomerular immune deposition, and diminished complement activation. Mechanistically, ex vivo treatment of primed B cells from diseased mice demonstrated that NDP-MSH directly inhibited plasma cell differentiation and autoantibody production. This suppression was linked to increased expression of microphthalmia-associated transcription factor (MITF) and downregulation of interferon regulatory factor 4 (IRF4), indicating activation of the MITF/IRF4 signaling axis. This pathway is known to negatively regulate B cell differentiation.

NDP-MSH treatment significantly reduced proteinuria and mitigated glomerular damage, while also directly inhibiting B cell differentiation and autoantibody production via the MITF/IRF4 axis.