Theiler's virus-induced apoptosis in cerebrovascular endothelial cells.

Abstract

Theiler's murine encephalomyelitis virus (TMEV) is classified as a Cardiovirus in the Picornaviridae family. An enteric virus, TMEV, spreads within the mouse population by the fecal-oral route. The neurovirulent GDVII strain of Theiler's virus causes a fatal encephalitis in all strains of mice following intra-cranial infection of the virus. Persistent BeAn strain of Theiler's virus causes a demyelinating disease in susceptible strains of mice, which is similar to the human disease - Multiple Sclerosis (MS). Although a well-recognized model for MS, the route of entry of the virus into the central nervous system (CNS) following natural infection has not been well understood. One of the proposed portals of entry includes the blood-brain barrier (BBB). This report indicates the ability of both the neurovirulent and the persistent strains of Theiler's virus to induce apoptosis in the functional units of the BBB - the cerebrovascular endothelial cells (CVE) both in vitro and in vivo. Induction of apoptosis in CVE was demonstrated by Annexin staining, electron microscopy, DNA fragmentation assay, Hoechst staining and by caspase-3 staining. Corresponding to results by other authors, GDVII is a stronger inducer of apoptosis in CVE compared to BeAn. Induction of apoptosis is dependent on the MOI of the virus. UV-inactivated virus is not capable of inducing apoptosis and induction of apoptosis appears to be an internal event not requiring activation of death receptors. Determining the pathway of induction of apoptosis by TMEV in CVE indicated the involvement of a Ca2+ dependent pathway for apoptosis - the calpain pathway. Involvement of calpain in apoptosis has been reported in MS. Induction of apoptosis in CVE in vivo was also demonstrated following the intra-peritoneal inoculation of Theiler's virus. Induction of apoptosis in CVE following Theiler' virus infection could lead to a breach of the BBB and entry of inflammatory cells as well as virus into the central nervous system. This finding could aid understanding the neuropathogenesis of Theiler's virus.