Cortical Neurons Derived from Equine Induced Pluripotent Stem Cells Are Susceptible to Neurotropic Flavivirus Infection and Replication: An In Vitro Model for Equine Neuropathic Diseases.

Horses are susceptible to a number of neurotropic viruses, including West Nile virus (WNV), which is a pathogen of global significance in both horses and humans. However, there are no in vitro models with which to study infectious neuropathic diseases in the horse. In an effort to redress this, we have generated neurons from equine induced pluripotent stem cells (equiPSCs) that express a range of cortical neuron-specific markers, in addition to the membrane-bound ligand ephrin B3, which plays an important role in axon guidance as well as functioning as the receptor through which henipaviruses, such as Hendra virus, enter mammalian neurons. EquiPSC-derived neurons spontaneously depolarize with waves of depolarization conducted unidirectionally to adjacent neurons. We sought to confirm that equiPSC-derived neurons are a possible in vitro model for viral neuropathic diseases in the horse by examining their susceptibility to infection with flaviviruses that are known to be neurotropic in horses, including WNV and Murray Valley encephalitis virus (MVEV), and to compare these to nonpathogenic flaviviruses such as Fitzroy River virus (FRV) and Bamaga virus (BgV). All three strains of WNV tested in this study grew to high titres in the equiPSC-derived neurons, inducing a strong cytopathic effect (cpe), as did MVEV. In contrast, FRV showed restricted replication, and no cpe, which is consistent with the observation that FRV infects, but does not cause disease, in horses. BgV, which is thought to infect only marsupials, did not replicate in the equiPSC-derived neurons. Hence, our equiPSC-derived neurons display virus-specific differences in terms of viral titre and cpe that are similar to observations made in vivo, thus supporting their use as an in vitro model for neurotropic viral infection in horses.