Analysis of West Nile virus neuroinvasion using in vitro blood-brain barrier models

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1. The pathway used by West Nile virus (WNV) to leave the bloodstream and invade the central nervous system is poorly understood. To investigate how WNV cross the blood-brain barrier (BBB), we used confluent human umbilical vein endothelial cells (HUVEC) cultures on transwell inserts as an in vitro BBB model.2. The structural protein genes (C-PrM-E region) of WNV 6-LP strain and Eg 101 strain were cloned into the pCMV expression vector. Sequential transfection of WNV sub-genomic replicon having an EGFP expression cassette and the vector that expressed the structural proteins led to the secretion of virus-like particles (VLPs). VLPs established a single-round of infection without production of progeny, and the physical structure of the VLPs was similar to that of infectious virions.3. In vitro BBB model was infected with VLPs having structural proteins of high vilulent 6LP strain (6LP-VLPs) or VLPs having structural proteins of low vilurent Eg 101 strain (Eg-VLPs). By 24 h after infection, 10% of 6LP-VLPs had crossed in vitro BBB, whereas no Eg-VLPs seemd to traverse. Thus, the ability of WNV to cross BBB may correlate at least in part with viral virulence. Exposure of HUVEC to 6LP strain did not alter the localization of tight junction protein ZO-1, indicating that the passage of WNV across the BBB is not caused by the disruption of tight junction. On the other hand, infection of HUVEC with 6LP strain was inhibited by Chlorpromazine, an inhibitor of clathrin-coated pit formation at the plasma membrane. These results suggest the possibility that WNV may cross BBB by transcytosis via a clathrin-mediated endocytic pathway.