The role of human SLE causal variant NCF1.pR90H in promoting kidney damage

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Abstract: Systemic lupus erythematosus (SLE) is a heterogeneous autoimmune disease with diverse manifestations characterized by the presence of autoantibodies to nuclear autoantigens and upregulated expression of type I interferon (IFN-I) stimulated genes. Epidemiology studies show that the strongest driver for the development of SLE is heritability, and SLE manifests when an environmental exposure of a genetically predisposed individual exceeds a liability threshold. We identified a p.Arg90His (p.R90H, rs201802880) substitution in neutrophil cytosolic factor (NCF1), encoding a hypofunctional, essential subunit of the phagocyte NADPH oxidase complex 2 (NOX2), as the strongest common risk variant associated with SLE in multiple ancestries, and showed association of the risk variant NCF1-H90 with kidney damage (defined by the presence of proteinuria >3.5g/24h, estimated glomerular filtration rate <50%, or end stage kidney disease [ESKD]) in SLE patients of Asian and African American ancestries. Lupus nephritis (LN) is a common severe manifestation of SLE that is initiated by glomerular accumulation of immune complexes that could incite inflammation in the glomeruli and tubulointerstitium (TI). TI inflammation -and not glomerulonephritis (GN)- on kidney biopsy predicts progression to ESKD in LN, one of the most important predictors of mortality in SLE. The primary target of the SLE-associated TI lesions relates to pathological remodeling in proximal tubule epithelial cells (PTEC); however, the underlying mechanisms and treatment targets remain unclear. To study the functional effects of the NCF1-H90 variant, we established a knock-in (KI) H90 variant in a non-autoimmune C57BL/6 (B6) background. Young naïve KI mice developed spontaneous autoimmunity, and pristane treatment induced proliferative GN and proteinuria, exhibiting increased follicular humoral responses and IgG autoantibody production, demonstrating the causality of this risk variant. The NCF1-H90 variant impaired apoptotic cell (AC) clearance by macrophages in B6 mice and SLE patients and expanded Tfh2 cells in a CD40 dependent manner, suggesting dysregulated mechanisms identified in Ncf1-H90 KI mice could be confirmed in NCF1-H90 expressing SLE patients. We observed exacerbated TI lesions induced by nephrotoxic serum (NTS) in Ncf1-H90 KI mice by systemic exposure to AC in B6 mice expressing another SLE risk variant. We hypothesize that imbalanced oxidative stress mediated by Ncf1-H90 could induce ferroptosis contributing to TI nephropathy. We will assess genotypic and sex effects in NTS or AC-induced nephritis to establish an LN-like TI nephropathy model to investigate if the Ncf1-H90 genotype affects iron homeostasis, lipid peroxidation and ferroptosis contributing to TI injury by altering transcriptomic profiles of renal infiltrated leukocytes and kidney resident cell subsets using single cell (sc) RNA-seq of CD45+ cells and kidney cells isolated from either NTS- or AC-treated WT and KI kidneys. Our findings will provide new insights into underlying mechanisms to identify potential therapeutic targets that could benefit LN patients carrying this common causal variant.