Porcine reproductive and respiratory syndrome virus induces interleukin-1β through MyD88/ERK/AP-1 and NLRP3 inflammasome in microglia

Porcine reproductive and respiratory syndrome virus (PRRSV) infection which caused severe reproductive failure and respiratory disorders in swine is accompanied with severe nervous symptoms. Our previous studies demonstrated that microglia, the resident innate immune cells in central nervous system (CNS), could support PRRSV infection and replication in vitro. And PRRSV infection led to the increased expressions of large amounts of proinflammatory cytokines and chemokines which contributed to neuropathogenesis of PRRSV. Interleukin-1 beta (IL-1 beta) is one of the increased proinflammatory cytokines, which possesses diverse functions in immune response upon virus infection, including activation of innate immune and modulation of adaptive immune responses. Importantly, considerable evidences indicated that IL-1 beta is involved in neuronal injury. Here, we demonstrated that PRRSV infection up-regulated IL-1 beta expression at both the mRNA and protein levels in microglia in a dose-dependent manner. Myeloid differentiation primary response gene 88 (MyD88), extracellular signal-regulated kinase1/2 (ERK) and activator protein 1 (AP-1) were involved in PRRSV induced IL-1 beta production in microglia. Moreover, NOD-like receptor protein 3 (NLRP3) inflammasome is activated by PRRSV in microglia, which is required for IL-1 beta secretion. Taken together, our data indicated that PRRSV infection could induce IL-1 beta up-regulation, which was likely mediated by MyD88/ERK/AP-1 and NLRP3 inflammasome. These findings will provide new insights into the molecular mechanisms of IL-1 beta production and some implications for neuropathogenesis of PRRSV.