Molecular and cellular mechanism regulating innate immunity and inflammation during pattern recognition receptor activation and respiratory virus infection

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Innate immunity constitutes pro-inflammatory response to initiate inflammation for adaptive immune response required for virus clearance. Pro-inflammatory (and inflammation) response need to be “tightly” regulated during virus infection since exaggerated inflammation contributes to inflammatory diseases. Activation of Pattern Recognition Receptors (PRRs) is critical for triggering innate immunity and inflammation during infection with human respiratory syncytial virus (RSV) and influenza A virus (IAV). Therefore, it is important to study the underlying cellular/molecular mechanism involved in transducing optimal innate immunity and inflammatory (and pro-inflammatory) response upon PRR activation. We have surprisingly identified a novel signaling network that is required for optimal pro-inflammatory response following PRR activation. Our preliminary result suggested that an oxysterol (a bioactive lipid) 25-hydroxycholesterol (25HC) play an important role in magnifying and intensifying pro-inflammatory response following activation of PRRs and during virus (RSV, IAV) infection. Surprisingly we observed interaction of 25HC with cell surface integrins and further preliminary studies suggested a possible mechanism. Mechanistically, we postulate that 25HC released from PRR activated (and virus infected) cells act as an extracellular soluble mediator to activate 25HC--- integrin (51, V3 integrins)---FAK (focal adhesion kinase)---NFB pathway for optimal pro-inflammatory response. Thus, we envision that extracellular 25HC serve as a “linker” (via autocrine/paracine mechanism) to bridge PRR pathway with integrin pathway for optimal pro-inflammatory response. We hypothesize that - a) extracellular 25HC links PRR pathway with integrin pathway; b) PRR---25HC---integrin---FAK---NFB signaling network magnifies pro-inflammatory response and inflammation; and c) 25HC--- integrin---FAK signaling pathway contributes to exaggerated inflammation during RSV and IAV infection, thus leading to development of exacerbated airway diseases like pneumonia and bronchiolitis. In the current proposal we have selected a membrane bound PRR (i.e. toll-like receptor 3 or TLR3) and a cytosolic PRR (i.e. Nod2) along with two clinically important respiratory viruses (RSV, IAV) to elucidate the role of 25HC---integrin---FAK---NFB pathway in promoting optimal and maximal pro-inflammatory response. In aim-1 we will investigate interaction of 25HC with integrins leading to activation of integrin---FAK---NFB pathway and subsequent pro- inflammatory response in macrophages. In aim-2 we will examine the role of 25HC---integrin---FAK---NFB pathway in triggering optimal pro-inflammatory response in macrophages following PRR (TLR3, Nod2) activation and virus (RSV, IAV) infection. Finally, in aim-3 we will utilize knockout mice to study physiological in vivo role of 25HC---integrin---FAK pathway during PRR (Nod2, TLR3) activation and virus (RSV, IAV) infection. Significance –Our current proposal has wide implication in development of therapeutics against RSV, IAV and other pathogens that activate PRRs.