Human Vaginal Epithelial Cells are Susceptible to the Zika Virus: Implications for Zika Vaginal Transmission

Abstract

The Zika Virus (ZIKV) is an emerging RNA virus that cause congenital birth defects and neurological compilations among infected individuals. Since the 2015 ZIKV outbreak in Brazil, the Centers for Disease Control, and Prevention (CDC) reports over 35,000 cases ZIKV disease cases within the United States (US) and US territories. Although ZIKV is primarily transmitted through an infected Aedes mosquito, recent studies demonstrate this pathogenic virus can be transmitted via sexual contact with an infected partner. CDC confirmed multiple clinical cases of infected patients acquired ZIKV through sexual transmission within the US. Additionally, mounting evidence from animal and cell studies demonstrate that the female reproductive tract supports ZIKV replication following intravaginal exposure. Despite the growing evidence associating ZIKV to sexual transmission, the underlying molecular mechanism involving vaginal transmission remains elusive. The overarching goal is to examine the role of the vaginal tract in ZIKV sexual transmission on a molecular level. The vaginal tract has multiple layers of epithelial cells that constitutes as the first line of defense against foreign pathogens. Given the capacity of sexual intercourse, we hypothesize that the initial event for ZIKV vaginal transmission is most likely through direct viral uptake at the outermost epithelial layer of the vaginal tract. We aim to test our hypothesis by (1) characterizing the replication kinetics of ZIKV in human vaginal epithelial cells (hVECs) in vitro and (2) determining the functional role of the putative ZIKV entry receptor, AXL, in hVECs. Our recent findings indicate hVECs is a permissive cell target for local ZIKV replication and production. Vaginal infection resulted in de novo replication of the ZIKV RNA genome, active production of the viral envelope protein, and steady release of infectious viral particles. Cell viability studies further indicate that hVECs do not exhibit significant cytopathic effect following ZIKV exposure. Additional studies show that the flaviviral entry receptor AXL is endogenously expressed in hVECs on a protein, mRNA level, and surface level. When expression patterns were compared between Vero and 293T cell lines, our results show similar protein levels of endogenous AXL in both Vero and VK2E6E7 cell lines, which may suggest that ZIKV entry via AXL‐mediated pathway and the dynamics of viral growth act independently of one another during sexual transmission. Our AXL knockdown and overexpression studies validate that this tyrosine receptor kinase is involved in ZIKV vaginal entry. In the future, kinase inhibitory studies will be performed to further validate whether downstream signaling contributes to ZIKV replication and production in hVECs. The outcome of this research will provide further insight into host‐virus interactions on a molecular level, which can lead to devising therapeutic agents aimed at interfering with the pathology caused by the virus.Support or Funding Information• T32 Grant: NIH National Heart, Lung, and Blood Institute, Research Training in Cardiovascular Biology at Meharry