Molecular and Immunological Basis of Tubulo-Interstitial Injury in Lupus Nephritis: a Comprehensive Review

Lupus nephritis is an important cause of kidney failure in patients of Asian, African, or Hispanic descent. Its etiology and pathogenesis are multifactorial and remain to be elucidated. Accumulating evidence suggests that anti-double-stranded DNA (dsDNA) antibodies play a critical role in the pathogenesis, through its direct binding to cross-reactive antigens on resident renal cells or indirect binding through chromatin material to extracellular matrix components, resulting in complement activation, cell activation and proliferation, and induction of inflammatory and fibrotic processes. While tubulo-interstitial damage portends poor long-term renal prognosis, the mechanisms leading to tubulo-interstitial injury in lupus nephritis has received relatively less attention to date. Immune deposition along the tubular basement membrane is often observed in lupus nephritis and correlates with tubulo-interstitial infiltration of immune cells and interstitial fibrosis. Anti-dsDNA antibodies bind to resident renal cells, including proximal renal tubular epithelial cells, and contribute to renal inflammation and fibrosis. There is emerging evidence that epigenetic influence such as DNA methylation, histone modification, and microRNAs (miRs) also contribute to kidney fibrosis. Overexpression of miR-150 is observed in renal biopsies from patients with lupus nephritis and correlates with kidney fibrosis and chronicity score. Mycophenolate mofetil (MMF) is an established and effective standard-of-care therapy for patients with lupus nephritis. Accumulating data suggest that in addition to its immunosuppressive actions on lymphocyte proliferation, mycophenolic acid (MPA), the active metabolite of MMF, can exert a direct effect on nonimmune cells. Mediators of inflammation and fibrosis induced by anti-dsDNA antibodies in cultured proximal renal tubular epithelial cells are ameliorated by the addition of MPA, suggesting that in addition to its immunosuppressive actions, MPA may also have a beneficial effect in improving tubulo-interstitial inflammation and fibrosis through its direct action on proximal renal tubular epithelial cells.