Targeting proteolytic cleavage of Toll-Like receptors by alpha-1 antitrypsin inhibited dendritic cells activation and function

Abstract

Abstract Toll-like receptors (TLRs) on dendritic cells (DC) interact with self-antigens and play a critical role in systemic lupus erythematosus (SLE) pathogenesis. TLR3, TLR7/8, or TLR9 are endosomal receptors that require proteolytic processing in the endolysosome to initiate signaling in response to DNA, single-stranded RNA, and double-stranded RNA. Targeting this proteolytic processing may represent a novel strategy for inhibiting TLR mediated pathogenesis. Human alpha 1 antitrypsin (hAAT) is a protease inhibitor with anti-inflammatory and immunoregulatory properties. However, the effect of hAAT on TLRs is not clear. In this study we first tested the effect of hAAT on DCs. We showed that hAAT treatment inhibited TLR7/8 and TLR9 agonists induced DC expressions of CD80, CD86 and MHC-II and significantly reduced the productions of IL-12, IFN-α and CXCL-10. Mechanistically, hAAT lowered the expression of interferon signature genes (MX-I, Isg-15, IRF-7, Il-12p40 and TNF-α). Importantly, western blot analysis showed that hAAT treatment reduced the active form (cleaved) of TLR9 in DCs indicating a novel mechanism of hAAT function in the immune system. Our in vivo studies in mouse models also showed that hAAT attenuated TLR agonist-induced pathogenesis. These data demonstrated that hAAT inhibited TLR7/8 and TLR9 signaling pathways in DCs, which are critical for lupus development. These findings not only advanced the current knowledge of hAAT biology, but also implied an insight for clinical application of hAAT.