TLR4 and Myd88/TRIF signaling serve as novel immune sensor and adapters of SARS-CoV-2-membrane (M) protein induced immune response 2730

Abstract Description Severe COVID-19 is associated with excessive lung inflammation and impaired antiviral response. SARS-CoV-2 structural spike (S), nucleocapsid (N), and envelope (E) proteins are key mediators of excessive inflammation. The immune sensors and signaling pathways for S-, N-, and E-proteins are well described. However, the role of M-protein in SARS-CoV-2-induced immunity, and the immune sensor and downstream pathways promoting M protein-induced immunity are not well defined. Here, we stimulated murine bone marrow derived macrophages (BMDMs) with M-protein and examined host response, identified immune sensor, and defined key adapter molecules that facilitated excessive inflammation and impaired antiviral response. We show that M-protein elicits robust inflammation and suppresses antiviral immunity. Using wild-type and knock-out BMDMs, we identified TLR4 as primary immune sensor, while Myd88 and TRIF facilitated M-protein-induced inflammation via both NFkB and MAPK activation. Interestingly, M-protein suppressed antiviral interferon (IFN) response via ERK1/2 activation, while blocking M-protein-induced ERK1/2 activity reduced inflammation while improving IFN-I response. Collectively, we defined the role of M-protein in SARS-CoV-2-induced inflammation and identified TLR4 and Myd88/TRIF as key molecules orchestrating dysregulated immunity largely via the ERK1/2 pathway; specifically targeting these pathways may mitigate SARS-CoV-2-mediated dysregulated immunity and severe disease. Funding Sources Supported by NIH R21AI186028; NIH P20GM103648; P30GM149368; SRTP OSU-CVM; FFAR Veterinary Student Research Fellowship. Topic Categories Viral Immunology (VIR)