Superoxide deficiency protects against Coxsackievirus-induced Type 1 diabetes through dampened macrophage anti-viral responses

Abstract

Abstract Viral infections are highly-suspected environmental triggers of autoimmune Type 1 diabetes (T1D), but the mechanism remains unclear. Many innate immune pro-inflammatory anti-viral factors, including IFN-α/β, TNF-α, CXCL10 and CCL5, are pathogenic in T1D. We recently demonstrated a crucial role for reactive oxygen species (ROS) production in modulating these factors, as Non-Obese Diabetic (NOD) mice deficient in NADPH oxidase (NOX)-derived superoxide (NOD.Ncf1m1J) are highly protected against T1D, partly due to impaired inflammatory macrophage responses. Therefore, we hypothesize that NOD.Ncf1m1J mice will be protected from virus-induced diabetes due to dampened pro-inflammatory anti-viral macrophage responses. Upon infection with Coxsackie B3 (CB3), a suspected diabetogenic virus, NOX-derived superoxide is rapidly generated by NOD macrophages, but is significantly decreased in NOD.Ncf1m1J macrophages. Loss of redox-dependent pro-inflammatory cytokine and chemokine synthesis significantly protected NOD.Ncf1m1J mice from virus accelerated T1D, as infected NOD.Ncf1m1J pancreata revealed significant decreases in Tnf, Cxcl10 and Ccl5 mRNA accumulation. This corresponded with 2.5-fold decreases in TNF-α- and IL-1β-producing pancreas-infiltrating macrophages, despite having no significant defect in CB3 viral clearance. Mechanistically, we determined that MDA5, a viral RNA sensor, was regulated by ROS. CB3-infected NOD.Ncf1m1J macrophages displayed a decrease in MDA5 expression, but was rescued by addition of exogenous ROS. Therefore, our results provide evidence that ROS can synergistically influence anti-viral responses to promote autoimmune diabetes in response to diabetogenic viral infections.