Zika virus (ZIKV) infection to a pregnant woman can be vertically transmitted to the fetus via the placenta leading to Congenital Zika syndrome. This is characterized by microcephaly, retinal defects, and intrauterine growth retardation. ZIKV induces placental trophoblast apoptosis leading to severe abnormalities in the growth and development of the fetus. However, the molecular mechanism behind ZIKV-induced apoptosis in placental trophoblasts remains unclear. We hypothesize that ZIKV infection induces endoplasmic reticulum (ER) stress in the trophoblasts, and sustained ER stress results in apoptosis. HTR-8 (HTR-8/SVneo), a human normal immortalized trophoblast cell and human choriocarcinoma-derived cell lines (JEG-3 and JAR) were infected with ZIKV. Biochemical and structural markers of apoptosis like caspase 3/7 activity and percent apoptotic nuclear morphological changes, respectively were assessed. ZIKV infection in placental trophoblasts showed an increase in the levels of CHOP mRNA and protein expression, which is an inducer of apoptosis. Next, we also observed increased levels of ER stress markers such as phosphorylated forms of inositol-requiring transmembrane kinase/endoribonuclease 1α (P-IRE1α), and its downstream target, the spliced form of XBP1 mRNA, phosphorylated eukaryotic initiation factor 2α (P-eIF2α), and activation of cJun N-terminal Kinase (JNK) and p38 mitogen activated protein kinase (MAPK) after 16–24 h of ZIKV infection in trophoblasts. Inhibition of JNK or pan-caspases using small molecule inhibitors significantly prevented ZIKV-induced apoptosis in trophoblasts. Further, JNK inhibition also reduced XBP1 mRNA splicing and viral E protein staining in ZIKV infected cells. In conclusion, the mechanism of ZIKV-induced placental trophoblast apoptosis involves the activation of ER stress and JNK activation, and the inhibition of JNK dramatically prevents ZIKV-induced trophoblast apoptosis.
Introduction Obesity during pregnancy increases the risk for maternal complications like gestational diabetes, preeclampsia, and maternal inflammation. Maternal obesity also increases the risk of childhood obesity, intrauterine growth restriction (IUGR) and diabetes to the offspring. Increased circulating free fatty acids (FFAs) in obesity due to adipose tissue lipolysis induces lipoapoptosis to hepatocytes, cholangiocytes, and pancreatic-β-cells. During the third trimester of human pregnancy, there is an increase in maternal lipolysis and release of FFAs into the circulation. It is currently unknown if increased FFAs during gestation as a result of maternal obesity cause placental cell lipoapoptosis. Increased exposure of FFAs during maternal obesity has been shown to result in placental lipotoxicity. The objective of the present study is to determine saturated FFA-induced trophoblast lipoapoptosis and also to test the protective role of monounsaturated fatty acids against FFA-induced trophoblast lipoapoptosis using in vitro cell culture model. Here, we hypothesize that saturated FFAs induce placental trophoblast lipoapoptosis, which was prevented by monounsaturated fatty acids. Methods Biochemical and structural markers of apoptosis by characteristic nuclear morphological changes with DAPI staining, and caspase 3/7 activity was assessed. Cleaved PARP and cleaved caspase 3 were examined by western blot analysis. Results Treatment of trophoblast cell lines, JEG-3 and JAR cells with palmitate (PA) or stearate (SA) induces trophoblast lipoapoptosis as evidenced by a significant increase in apoptotic nuclear morphological changes and caspase 3/7 activity. We observed that saturated FFAs caused a concentration-dependent increase in placental trophoblast lipoapoptosis. We also observed that monounsaturated fatty acids like palmitoleate and oleate mitigates placental trophoblast lipoapoptosis caused due to PA exposure. Conclusion We show that saturated FFAs induce trophoblast lipoapoptosis. Co-treatment of monounsaturated fatty acids like palmitoleate and oleate protects against FFA-induced trophoblast lipoapoptosis.
Zika virus (ZIKV) infection in pregnant woman can be vertically transmitted to the fetus via the placenta leading to Congenital Zika syndrome (CZS). CZS is characterized by microcephaly, retinal defects and intrauterine growth retardation. ZIKV also causes placental pathology leading to severe compromise in the growth and development of the fetus. Further, the molecular mechanism behind ZIKV‐induced apoptosis in placental trophoblasts is unknown. We hypothesize that accumulation of viral proteins in the endoplasmic reticulum could lead to sustained endoplasmic reticulum stress (ER stress) and trigger apoptotic events. Methods HTR‐8, a human normal immortalized trophoblast cell and human choriocarcinoma derived cell lines (JEG‐3 and JAR) were infected with 0.1–1MOI ZIKV. Apoptosis was assessed by characteristic nuclear morphology staining with DAPI and caspase 3/7 activity. Results We observed an increase in the mRNA levels of CHOP and the spliced form of XBP1 gene, 16–24h post infection in trophoblast. We also observed an increase in the levels of ER stress markers such as p‐IRE1α, p‐eif2α, and activation of c‐Jun N‐terminal Kinase (JNK) and p38 mitogen‐activated protein kinase (MAPK) after 16–24h of ZIKV infection in trophoblast. As prolonged ER stress can cause apoptosis, we observed a dramatic increase in trophoblast apoptosis 48h post infection. Mechanistically, inhibition of JNK by SP600125 or pan caspase by Z‐VAD‐FMK significantly blocked ZIKV‐induced apoptosis in trophoblast. In conclusion, the mechanism of ZIKV‐induced placental trophoblast apoptosis involves the activation of ER stress and MAPK activation. Support or Funding Information NIH: P20GM104320, Layman Seed award, UNL, Food for Health Research Initiative, UNL
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