Sathish Kumar Natarajan
Date of this Version
Zika virus (ZIKV) infection in pregnant women causes congenital Zika syndrome which involves birth defects such as intrauterine growth restriction (IUGR), retinal defects and microcephaly in the fetus. ZIKV infection results in placental pathology which plays a crucial role in disease transmission from mother to fetus. Currently, there is no Food and Drug Administration (FDA) approved vaccine or therapeutic drug against ZIKV. In this thesis, we have elucidated the cell signaling pathways connected to ZIKV-induced apoptosis in trophoblasts and also the protective effect of palmitoleate against ZIKV-induced apoptosis. First, we demonstrated the molecular mechanism behind ZIKV-induced apoptosis using an in vitro model with JEG-3, JAR and HTR-8 cells. We found that persistent endoplasmic reticulum stress (ER stress) causes activation of c-Jun N-terminal kinase (JNK), a stress kinase that leads to trophoblast apoptosis. Next, we studied the protective role of the nutrient compound palmitoleate, an omega-7 monounsaturated fatty acid, in ZIKV infected trophoblasts. Palmitoleate has been shown to have lipokine activity and significant positive effects on metabolism. Palmitoleate treatment post-infection showed a significant decrease in the percentage of apoptotic nuclei and caspase 3/7 activity when compared to ZIKV-infected cells without palmitoleate treatment. Moreover, quantification of viral RNA revealed that there was a notable decrease in viral load in palmitoleate-treated cells. To substantiate the protective role of palmitoleate against ZIKV-induced apoptosis, we treated trophoblasts with palmitate, a 16-carbon saturated fatty acid. Interestingly, we observed that palmitate did not show any protection against ZIKV-induced ER stress and apoptosis. In contrast, palmitoleate treatment enhanced survivability coupled with a non-significant reduction in plaque-forming units/mL of cell culture supernatant. Further, we observed high lipid droplet accumulation along with a significant reduction in IL-1β expression with palmitoleate treatment in infected cells. In conclusion, palmitoleate treatment is protective against ZIKV-induced ER stress and apoptosis in trophoblasts. Palmitoleate can be used as a nutrient compound to prevent placental pathology in ZIKV infected pregnant women and adverse birth defects in the fetus; nevertheless, further studies are necessary.
Adviser: Sathish Kumar Natarajan