Study On The Mechanism Of Differentially Activation Of The Innate Immune Pathway In Astrocytes By Wild-type Or Lab-attenuated Rabies Virus

Rabies is an ancient disease which remains endemic in many countries of the world and causes approximately 59,000 deaths annually.The mechanism through which the causative agent,rabies virus(RABV),evades the host immune response and infects the host central nervous system(CNS)has not been completely elucidated yet.Our previous studies have shown that lab-attenuated,but not wild-type(wt),RABV could activate the innate immune response in mouse and dog models.The astrocyte has been widely proved to limit the pathogens from invading into the CNS by inducing innate immune response and regulating the BBB permeability,which is important to protect the CNS from infection.In the present study,we focus on investigating the role of astrocytes in the context of rabies virus infection.Firstly,mice were infected with wild-type(wt)strain DRV-AH08(DRV for short thereafter)or lab-attenuated strain B2 c to verify the characteristics of DRV as a wt RABV.As expected,mice infected with DRV succumbed to rabies earlier than those infected with B2 c,and less inflammation and peripheral immune cells invasion were observed in the CNS of mice infected with DRV than that in B2 c infected mice,suggesting that DRV own the typical characteristics of wt RABV.Next,the primary astrocytes were isolated,pured and cultured from mouse brain,and infected with wt DRV or lab-attenuated B2 c subsequently.It was found that wt,but not lab-attenuated,RABV could persistently replicate in primary astrocytes.Then the activation of the mitochondrial antiviral-signaling protein(MAVS)signaling pathway in different RABV infected primary astrocyte was analyzed,the results suggested that B2 c could enhance the expression of key proteins involved in MAVS signaling,which was proved to be related with the RNA produced during viral transcription.Furthermore,we found that the level of double-stranded RNA(ds RNA)produced after B2 c infection was significantly higher than that after DRV infection.Moreover,the MAVS-/-and TLR7-/-mice were introduced into our study,and it was observed that B2 c could replicate in a manner identical to that of wt RABV in astrocytes isolated from MAVS-/-mice rather than in that isolated form TLR7-/-mice.In addition,it was also found that lab-attenuated,but not wt,RABV could induce the expression of inflammatory cytokines via the MAVS-/p38/NF-?B signaling pathway.These inflammatory cytokines subsequently increased the blood-brain barrier(BBB)permeability in transwell model,and the culture supernatant of B2 c infected primary astrocytes could decrease the level of tight-junction protein ZO-1.Together,in this study,we found that the astrocyte play an important role in limiting the lab-attenuated RABV infection in CNS through producing IFN and ISGs by activating MAVS signaling pathway,and inducing inflammatory factors to enhance BBB permeability to facilitate RABV clearance in CNS.In contrast,wt RABV could restrict ds RNA production and thus inhibit the activation of MAVS signaling pathway in astrocytes to avoid form clearing by immune response in CNS.These findings could lay a foundation for the elucidation of mechanism of innate immune evasion by wt RABV,and provide a new clue for clinical therapy of rabies.