The protective role of Mertk in JEV-induced encephalitis by maintaining the integrity of blood–brain barrier

Japanese encephalitis is an acute infectious disease of the central nervous system caused by neurotropic Japanese encephalitis virus (JEV). As a member of TAM (Tyro3, Axl and Mertk) family, Mertk has involved in multiple biological processes by engaging with its bridging ligands Gas6 and Protein S, including invasion of pathogens, phagocytosis of apoptotic cells, inflammatory response regulation, and the maintenance of blood brain barrier (BBB) integrity. However, its role in encephalitis caused by JEV infection has not been studied in detail. Here, we found that Mertk^-/- mice exhibited higher mortality and more rapid disease progression than wild-type mice after JEV challenge. There were no significant differences in viral load and cytokines expression level in peripheral tissues between Wild type and Mertk^-/- mice. Furthermore, the absence of Mertk had little effect on the inflammatory response and immunopathological damage while it can cause an increased viral load in the brain. For the in vitro model of BBB, Mertk was shown to maintain the integrity of the BBB. In vivo, Mertk^-/- mice exhibited higher BBB permeability and lower BBB integrity. Taken together, our findings demonstrate that Mertk acts as a protective factor in the development of encephalitis induced by JEV infection, which is mainly associated with its beneficial effect on BBB integrity, rather than its regulation of inflammatory response.