Kirtan Patel

Introduction. Systemic Lupus Erythematosis (SLE) is a chronic autoimmune inflammatory disorder in which anti-nuclear antibodies are thought to cause multi-organ damage^2,3,7. Studies have found that plasmacytoid dendritic cells (pDC) are at the center of SLE pathogenesis as they are the prime producers of Interferon-1 (IFN-1)^1,5,6. It has long been known that pDCs are activated by dysfunctional neutrophil extracellular traps (NET) because the process involves extruded DNA out into the extracellular matrix where it can react with anti-nuclear antibodies, and thus promote SLE pathogenesis^3,4. However, the mechanism behind abnormal NETosis has not been explored and could give potential insight into the disease and novel therapeutic treatments. Methods. Blood was isolated from patients with SLE from the NIH. Heparinized blood was layered on Polymorphprep to isolate neutrophils and NETs. NETs were quantified with Sytox Green intensity by plate reader. Reactive Oxygen Species (ROS) were quantified using ROS MitoSOX detection kit. ELISA was performed to quantify oxidized DNA and was visualized with fluorescent microscopy. DNA was immunoprecipitated through supernatant isolation. MRL/lpr mice were used to quantify in-vivo effect of ROS scavengers. Results. Ribonucleoprotein-Immune complex (RNP-IC) mediated NETosis is dependent on mitochondrial ROS³. Furthermore, RNP-IC stimulated mitochondria are shown to become hypopolarized, migrate to the cell surface, and localize with oxidized DNA³. It was subsequently shown that the oxidized DNA is of mitochondrial origin. Another independent study shows that oxidized mtDNA is required to activate plasma-cytoid dendritic cell mediated production of IFN-1¹. It was shown that mitochondrial ROS scavengers suppress lupus-like disease in vivo in murine models of lupus³. Conclusion. Studies have shown that dysfunctional mitochondria promote dysfunction in NETosis – specifically, the role of ROS in promoting oxidized mtDNA in NETosis. Abnormal NETosis has been shown to induce SLE-like pathogenesis. ROS scavengers were shown to potentially reduce SLE-like pathogenesis in murine models of lupus by reducing organ damage and anti-DNA antibody levels. Although a cure is far from discovery, this novel insight into the mechanism behind SLE pathogenesis may show a novel therapeutic route of treatment.

1. Caielli, S., Athale, S., Domic, B., Murat, E., Chandra, M., Banchereau, R., Baisch, J., Phelps, K., Clayton, S., Gong, M., et al. (2016). Oxidized mitochondrial nucleoids released by neutrophils drive type I interferon production in human lupus. The Journal of Experimental Medicine 213, 697–713.
2. Lee, K.H., Kronbichler, A., Park, D.D.-Y., Park, Y., Moon, H., Kim, H., Choi, J.H., Choi, Y., Shim, S., Lyu, I.S., et al. (2017). Neutrophil extracellular traps (NETs) in autoimmune diseases: A comprehensive review. Autoimmunity Reviews 16, 1160–1173.
3. Lood, C., Blanco, L.P., Purmalek, M.M., Carmona-Rivera, C., De Ravin, S.S., Smith, C.K., Malech, H.L., Ledbetter, J.A., Elkon, K.B., and Kaplan, M.J. (2016). Neutrophil extracellular traps enriched in oxidized mitochondrial DNA are interferogenic and contribute to lupus-like disease. Nature Medicine 22, 146–153.
4. Lou, H., and Pickering, M.C. (2018). Extracellular DNA and autoimmune diseases. Cellular and Molecular Immunology.
5. Mackern-Oberti, J.P., Llanos, C., Riedel, C.A., Bueno, S.M., and Kalergis, A.M. (2015). Contribution of dendritic cells to the autoimmune pathology of systemic lupus erythematosus. Immunology 146, 497–507.
6. Psarras, A., Emery, P., and Vital, E.M. (2017). Type I interferon–mediated autoimmune diseases: pathogenesis, diagnosis and targeted therapy. Rheumatology kew431
7. Tsokos, G.C., Lo, M.S., Reis, P.C., and Sullivan, K.E. (2016). New insights into the immunopathogenesis of systemic lupus erythematosus. Nature Reviews Rheumatology 12, 716–730.