Hannakate Hall

Introduction: Zika Virus is a positive sense, single stranded RNA flavivirus that has attracted worldwide attention within the last 5 years for its transcontinental spread and ability to evoke devastating results within certain patient populations¹. Zika is transmitted by the bite of infected Aedes aegypti mosquitoes⁶, and is now generally included within the list of TORCH agents known to cause fetal damage or abortion. Pregnant women, as well as those planning to become pregnant, are at particular risk for fetal loss or fetal microcephaly if infected. There is no current vaccine available, but researchers are actively seeking to understand Zika Virus’ genome and viremia in order to create one. Understanding the mechanism of neural damage caused by Zika could lay a foundation for the development of a protective and preventive therapeutic intervention. For example, this research hypothesizes that Zika Virus may somehow hijack the cell’s natural apoptotic pathways to artificially cause premature apoptosis in neural stem cells¹. Akt-mTOR is a key molecule known to prevent apoptosis by downstream phosphorylation cascades². If Zika were to block the Akt-mTOR pathway, it could induce apoptosis in fetal neural stem cells, leading to microcephaly and other neural defects. Methods : Immunoblot and neurosphere methods were used. By harvesting colonies of fNSCs, infecting them with Zika, and immunostaining for antibodies to detect levels of Akt-mTOR, researchers determined that the virus played a role in suppressing the pathway⁴. Researchers also analyzed proteins within the Zika Virus genome, isolating and infecting cells with different proteins to determine which products resulted in Akt-mTOR suppression (p<0.05)⁴. Finally, researchers conducted neurosphere experiments in vitro to analyze apoptosis or growth levels post exposure³. Results: Zika Virus efficiently blocks phosphorylation of Akt at a few key sites, thus inhibiting its suppression of apoptosis and creating a pro-apoptotic state within the infected cell⁴. The protein likely responsible for blocking Akt is Non Structural Protein 4A⁵. Neurospheres exposed to the live virus and NS4A (Non Structural Protein 4A) both exhibited apoptosis and limited growth³. Conclusions: By isolating NS4A as a key player in fetal neural stem cell apoptosis, and linking it to microcephaly, researchers can now target it therapeutically. This opens doors to possibilities of a future vaccine, or a prophylactic NS4A blocker to administer to pregnant women at risk of contracting Zika. With further research, Zika Virus’ NS4A could become a point of intervention to prevent microcephaly.

1. Devhare P, Meyer K, Steele R, Ray RB, Ray R. Zika virus infection dysregulates human neural stem cell growth and inhibits differentiation into neuroprogenitor cells. Cell Death & Disease. 2017;8(10):e3106-. doi:10.1038/cddis.2017.517.
2. Ersahin, T., Tuncbag, N., & Cetin-Atalay, R. (2015). The PI3K/AKT/mTOR interactive pathway. Molecular BioSystems, 11(7), 1946-1954. doi:10.1039/c5mb00101c
3. Garcez, P. P., Loiola, E. C., Costa, R. M., Higa, L. M., Trindade, P., Delvecchio, R., . . . Rehen, S. K. (2016). Zika virus impairs growth in human neurospheres and brain organoids. Science, 352(6287), 816-818. doi:10.1126/science.aaf6116
4. Liang, Q., Luo, Z., Zeng, J., Chen, W., Foo, S., Lee, S., . . . Jung, J. (2016). Zika Virus NS4A and NS4B Proteins Deregulate Akt-mTOR Signaling in Human Fetal Neural Stem Cells to Inhibit Neurogenesis and Induce Autophagy. Cell Stem Cell, 19(5), 663-671. doi:10.1016/j.stem.2016.07.019
5. McLean, J. E., Wudzinska, A., Datan, E., Quaglino, D., & Zakeri, Z. (2011). Flavivirus NS4A-induced Autophagy Protects Cells against Death and Enhances Virus Replication. The Journal of Biological Chemistry, 286(25), 22147–22159. http://doi.org.ezproxy.library.tamu.edu/10.1074/jbc.M110.192500
6. Mori, A., Tsuda, Y., Takagi, M., Higa, Y., & Severson, D. W. (2016). Multiple QTL Determine Dorsal Abdominal Scale Patterns in the Mosquito Aedes aegypti . Journal of Heredity, 107(5), 438–444. http://doi.org.ezproxy.library.tamu.edu/10.1093/jhered/esw027