AXL-dependent infection of human fetal endothelial cells distinguishes Zika virus from other pathogenic flaviviruses

Abstract

Although a causal relationship between Zika virus (ZIKV) and microcephaly has been established, it remains unclear why ZIKV, but not other pathogenic flaviviruses, causes congenital defects. Here we show that when viruses are produced in mammalian cells, ZIKV, but not the closely related dengue virus (DENV) or West Nile virus (WNV), can efficiently infect key placental barrier cells that directly contact the fetal bloodstream. We show that AXL, a receptor tyrosine kinase, is the primary ZIKV entry cofactor on human umbilical vein endothelial cells (HUVECs), and that ZIKV uses AXL with much greater efficiency than does DENV or WNV. Consistent with this observation, only ZIKV, but not WNV or DENV, bound the AXL ligand Gas6. In comparison, when DENV and WNV were produced in insect cells, they also infected HUVECs in an AXLdependent manner. Our data suggest that ZIKV, when produced from mammalian cells, infects fetal endothelial cells much more efficiently than other pathogenic flaviviruses because it binds Gas6 more avidly, which in turn facilitates its interaction with AXL.Zika virus | Flaviviruses | AXL | placental barrier | fetal endothelial cell Z ika (ZIKV), West Nile (WNV), and dengue (DENV) viruses are closely related, and belong to the Flavivirus genus in the Flaviviridae family. Although a causal relation between ZIKV and microcephaly has been established by human and animal studies (1-7), it remains unclear why only ZIKV, but not other pathogenic flaviviruses, causes congenital diseases. Although WNV is known to infect neuronal cells and results in encephalitis (8), it does not cause microcephaly. DENV is not generally neurotropic and is not linked to congenital defects.To reach the fetal brain, a virus must be transported from the maternal to the fetal circulation, which necessitates crossing of the placental barrier. In the placenta, fetal blood in capillaries is separated from maternal blood by placental barrier cells, namely trophoblasts and fetal endothelial cells. Recent studies indicate that the placenta and its barrier cells are infected by ZIKV, and fetal brain lesions develop in mice, pigtail macaques, and humans (1-6, 9). However, it remains unclear why only ZIKV, and not other neurotropic flaviviruses, results in microcephaly and other congenital disorders.Although bona fide entry receptors for flaviviruses remain unknown, many cell surface-expressed molecules contribute to infection, including C-type lectins dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN) and DC-SIGN-related protein (L-SIGN) (10, 11) and phosphatidylserine (PS) receptors (12-15) . PS receptors, which serve as entry cofactors for flaviviruses, include members of the TIM (T-cell Ig mucin) family and the TAM (TYRO3, AXL, and MERTK) family. TIMfamily receptors bind PS directly (14, 15), whereas TAM-family members bind PS indirectly, through the soluble intermediates Gas6 (growth arrest-specific 6) and protein S present in serum and other bodily fluids (16, 17). Whereas Gas6 binds to all th...

Zika Virus Encoding Nonglycosylated Envelope Protein Is Attenuated and Defective in Neuroinvasion

“…Alternatively, ZIKV may directly infect the endothelial cells or choroid plexus epithelial cells, disrupt the BBB, and enter the CNS. Since the TAM receptor AXL makes endothelial cells susceptible to ZIKV infection (50)(51)(52), access of the mutant ZIKVs encoding nonglycosylated E protein to the CNS might be compromised due to their inability to infect these cells. Since WNV disrupts expression of or signaling by IFN- (53) and also uses the Toll-like receptor 3-dependent immune response (54) to gain entry into the CNS, it is possible that ZIKV may employ similar or yet unknown mechanisms to facilitate its entry into the CNS.…”

Suppression of Zika Virus Infection and Replication in Endothelial Cells and Astrocytes by PKA Inhibitor PKI 14-22

“…In the placenta, the maternal blood and fetal blood are separated by placental barrier cells, including trophoblasts and endothelial cells. Recent studies have demonstrated that fetal endothelial cells or human umbilical vein endothelial cells (HUVEC) are permissive for ZIKV infection, making HUVEC a key cell model for ZIKV studies (23,24).…”

“…Our study demonstrates that PKI potently suppresses ZIKV replication and, hence, is a potential candidate for therapeutic application. [23][24][25]. To confirm that HUVEC were permissive for infection with all the ZIKV strains used in the study, we first evaluated the infectivity and replication of ZIKV in HUVEC.…”

Características de la estructura molecular de las proteínas E del virus Zika y E1 del virus de la rubeola. Posibles implicaciones en el neurotropismo y en las alteraciones del sistema nervioso

“…Considerando que en este trabajo se utilizó el prototipo de proteína E del virus ZIKV (entrada PDB 5I6Z7), y dada la existencia de diferentes aislamientos del ZIKV procedentes de Latinoamérica y Asia, es importante profundizar en las mutaciones o variantes de la secuencia y la estructura molecular del E-ZIKV que modifiquen el dominio hidrofóbico interno, el bucle de fusión u otros elementos estructurales que pueden sufrir modificación posterior a la traducción, incluidos los sitios de glucosilación (53), con lo cual se produciría un efecto en la capacidad de infección del ZIKV a otros tipos de células específicas (2,54,55).…”