Finding druggable pathways affected by the R90H-NCF1 SLE risk variants
Dr. Betty Tsao found a mutation in a specific gene, NCF1, that predicts increased risk for several autoimmune diseases, including lupus. The mutation causes a reduction in the amount of reactive oxygen species (ROS), small chemicals that contain oxygen and other elements that are formed as a normal byproduct of the body’s metabolism. Hydrogen peroxide is one example of an ROS. Interestingly, ROS are normally thought of as troublemakers in the body, causing stress and tissue damage that contribute to many diseases, as well as signs of aging. To understand why a reduction in ROS might lead to lupus, Dr. Tsao will create an animal model with the mutated NCF1 gene. This model will allow her to understand how reduced ROS affects immune system cell function.
What this study means to people with lupus
Ultimately, Dr. Tsao expects to find new targets in the NCF1/ROS pathway for drug development to prevent or treat lupus.
SLE is a heterogeneous autoimmune disease with a strong genetic predisposition. Recently, we have identified a missense mutation (p.R90H) in NCF1, encoding p47phox subunit of the phagocyte NADPH oxidase (NOX2) complex, as the putative underlying causal variant that drives a strong SLE-associated signal detected by ImmunoChip at the GTF2IRD1-GTF2I region on 7q11.23 with a complex genomic structure. We show that R90H, which is reported to cause reduced reactive oxygen species (ROS) production, predisposes to SLE (odds ratio [OR]=3.47 in Asians [Pmeta=3.1×10-104], OR=2.61 in European Americans, OR=2.02 in African Americans) and other autoimmune diseases including primary Sjögren’s syndrome (OR=2.45 in Chinese, OR=2.35 in European Americans) and rheumatoid arthritis (OR=1.65 in Koreans). Additionally, decreased and increased copy numbers of NCF1 predispose to and protect against SLE, respectively. Our data highlights the pathogenic role of reduced NOX2-derived ROS level in autoimmune diseases, which supports previous publications that reduced ROS production by the SLE-risk missense mutation H389Q NCF2, encoding another NOX2 subunit p67phox, and Nox2 deficiency exacerbates lupus features in MRL.Faslpr mice. The consistent and robust genetic evidence suggests activating the NOX2 complex to restore ROS homeostasis have therapeutic potential in treating multiple autoimmune diseases, especially SLE. As a proof of concept, compounds that increase NOX2-dependent ROS production have shown efficacy in treating existing conditions of animal models of autoimmune diseases. However, NOX2-derived ROS has diverse roles in immunity, which makes it critical to develop drugs targeting underpinning cellular and molecular mechanisms linking this strong genetic risk to lupus manifestations. The high homology between mouse and human NCF1 and the lack of NCF1B/1C pseudogenes led us to propose establishing a C57BL/6 (B6) mouse model with a R90H point mutation in Ncf1 locus by CRISPR/Cas genome editing. In Aim 1, we will compare 90H B6 knockin (KI) and wildtype 90R.B6 mice for R90H genotypic effects on ROS production in various immune cell types, and the development of autoantibodies and lupus-like kidney disease in the presence or absence of an environmental trigger pristine to induce (if a single gene variant is insufficient to produce lupus-like phenotypes) or amplify murine lupus features. In Aim 2, we will assess 90H genotypic effect on LC3-associated phagocytosis and clearance of dying cells as well as effector functions of dendritic cells, B- and T-cells contributing to murine lupus. In Aim 3, we will conduct RNA-seq and bioinformatics to identify differentially expressed transcripts and affected molecular pathways in relevant immune cell types. Results from these studies will provide new insights to select drugs to target the pivotal cellular and/ or molecular pathways responsible for R90H-mediated risk for consideration of lupus therapies.