Palmitoleate Protects against Zika virus infection-induced Endoplasmic Reticulum Stress and Apoptosis in Neurons

Zika virus (ZIKV) infection during pregnancy is associated with the development of fetal complications such as microcephaly. We have recently demonstrated that palmitoleate protects against ZIKV-induced apoptosis in placental trophoblasts. In the present study, we hypothesize that palmitoleate prevents ZIKV infection-induced endoplasmic reticulum (ER) stress and apoptosis in neurons. Neurons were infected with 0.1-1 multiplicity of infection of recombinant MR766 or PRVABC59 strains of ZIKV for an hour followed by treatment of palmitoleate (100 {micro}M-200 {micro}M) for different post-infection time points. Apoptosis was measured by nuclear morphological changes, caspase 3/7 activity, and immunoblot analysis of pro-apoptotic mediators. Activation of ER stress markers and viral envelope levels were detected using qRT-PCR and immunoblot analysis. Infectious virus particles were measured by using plaque assay. ZIKV infection to neuronal cells showed increased levels of pro-apoptotic markers like cleaved-PARP, cleaved caspase-3, Bim, and Puma, whereas decreased levels of anti-apoptotic markers such as Mcl-1, Bcl-1, and Bcl-xL. Further, we observed activation of three arms of ER stress namely: inositol requiring enzyme 1 alpha (IRE1), protein kinase-like ER kinase (PERK), and activating transcription factor (ATF6) pathways with ZIKV infection. Treatment of palmitoleate dramatically decreased ZIKV infection-induced increase in percent apoptotic nuclei and caspase 3/7 activity. Further, treatment of palmitoleate decreased cleaved PARP and PUMA protein expressions. Treatment of palmitoleate reduced ZIKV-induced ER stress activation as evidenced by decreased levels of phosphorylated forms of IRE1 and eukaryotic initiation factor 2 alpha; decreased expressions of cleaved ATF6, spliced X-box associated protein 1 and C/EBP homologous protein compared to ZIKV infection alone. Further, treatment of palmitoleate attenuated ZIKV envelope levels and infectious titer in SH-SY5Y and primary fetal cortical neurons isolated from humanized STAT2 knockin mice. These data suggest that palmitoleate supplementation protects against ZIKV-induced neuronal ER stress, apoptosis and decreases Zika viral load thereby mitigates neuronal damage.