RIPK3 Promotes JEV Replication in Neurons via Downregulation of IFI44L.

Japanese encephalitis virus (JEV), the leading cause of viral encephalitis in Asia, is neurovirulent and neuroinvasive. Neurons are the main target of JEV infection and propagation. Receptor interacting serine/threonine-protein kinase 3 (RIPK3) has been reported to contribute to neuroinflammation and neuronal death in many central nervous system diseases. In this study, we found that the progression of JE was alleviated in RIPK3-knockout (RIPK3-/-) mice in both peripheral and intracerebral infection. RIPK3-knockdown (RIPK3-RNAi) neuro2a cells showed higher cell viability during JEV infection. Moreover, the JEV load was significantly decreased in RIPK3-/- mouse-derived primary neurons and RIPK3-RNAi neuro2a cells compared with wild-type neurons, but this was not observed in microglia. Furthermore, RNA sequencing of brain tissues showed that the level of the interferon (IFN)-induced protein 44-like gene (IFI44L) was significantly increased in JEV-infected RIPK3-/- mouse brains, RIPK3-/- neurons, and RIPK3-RNAi-neuro2a cells. Then, it was demonstrated that the propagation of JEV was inhibited in IFI44L-overexpressing neuro2a cells and enhanced in IFI44L and RIPK3 double knockdown neuro2a cells. Taken together, our results showed that the increased expression of RIPK3 following JEV infection played complicated roles. On the one hand, RIPK3 participated in neuroinflammation and neuronal death during JEV infection. On the other hand, RIPK3 inhibited the expression of IFI44L to some extent, leading to the propagation of JEV in neurons, which might be a strategy for JEV to evade the cellular innate immune response.

Lipoteichoic acid modulates inflammatory response in macrophages after phagocytosis of titanium particles through Toll-like receptor 2 cascade and inflammasomes.

Toll-like receptor 2 (TLR2) and nucleotide-binding and oligomerization domain-like receptors with a pyrin domain 3 (NLRP3) inflammasomes have been presumed to participate in the pathogenesis of aseptic implant loosening. The aim of this study is to analyze the cellular localization of TLR2 and NLRP3 inflammasomes in the periprosthetic tissue from aseptically loose hip implants as well as the expression of these molecules in macrophages stimulated in vitro with titanium particles (Ti) coated with lipoteichoic acid (LTA). Using immunohistochemistry, immunoreactivity of TLR2 and NLRP3 inflammasomes was found in macrophages within the foreign body granulomatosis. Using RAW264.7 cells, stimulation with Ti increased the messenger RNA (mRNA) levels of TLR2 and TNF-α. Stimulation with LTA-coated Ti enhanced mRNA levels of NLRP3 and IL-1ß, whereas reinforced secretion of IL-1ß was not detected in spite of marked release of TNF-α. Finally, the same cells with silenced Irak2, an adaptor protein in the TLR2 cascade, suppressed this NLRP3 upregulation. This study suggests that TLR2 and NLRP3 inflammasomes are factors involved in cross-talk mediating the foreign body type response to wear particles. In addition, discrepant behavior in the release between TNF-α and IL-1ß release may explain the variable pathomechanisms of aseptic implant loosening without acute inflammatory reactions.