Abstract 144: A20 Inhibits Pathologic Interferon-? Signaling in Smooth Muscle Cells to Prevent Atherosclerotic Vascular Disease

Abstract

The pleiotropic cytokine Interferon-γ (IFNγ), best known for its anti-viral and immunomodulatory activities, also demonstrates pro-atherogenic effects. Implication of IFNγ in the pathogenesis of atherosclerosis results in part from the upregulation of a number of pro-inflammatory interferon stimulated genes (ISGs) in vascular smooth muscle cells (SMC). Hence, strategies to reduce IFNγ signaling are of particular interest to reduce or prevent pathologic vascular remodeling associated with atherosclerotic disease, for instance transplant arteriosclerosis. We discovered that the anti-inflammatory and vasculoprotective protein A20 inhibits IFNγ signaling and thus the expression of ISG in vitro in human coronary artery SMC, and in vivo in vascular allografts. The aim of this study was to unveil the mechanism(s) of A20 mediated inhibition of IFNγ signaling. Adenovirus-mediated overexpression of A20 in SMC significantly decreased mRNA and protein levels of signal transducer and activator of transcription 1 (STAT1), the key mediator of IFNγ signaling, as a result of lower transcription. Moreover, overexpression of A20 in SMC also efficiently inhibited activating Y701 phosphorylation of STAT1, through a mechanism possibly implicating A20 binding to STAT1, as confirmed by co-immunoprecipitation. As expected, overexpression of A20 also inhibited NF-κB activation in SMC, which is required for full-blown IFNγ responses. Indeed, we confirmed that inhibition of NF-κB by overexpression of its inhibitor, IκBα also quenched upregulation of ISGs in SMC, albeit without down-regulating STAT1. Overall, our results identify A20 as a potent inhibitor of IFNγ signaling in SMC through several non-mutually exclusive mechanisms. This novel function of A20 in SMC further qualifies its atheroprotective properties and supports the pursuit of A20-based therapies for the cure of atherosclerotic vascular disease.