An article by Federico Martinón-Torres, Irene Rivero Calle, Alberto Gómez Carballa, Antonio Salas and Francesco Bonfante
Knowledge of the molecular mechanisms behind the trans-placental Zika virus infection is one of the most challenging aspects concerning Zika virus congenital disease. Although it is well known that other flaviviruses can occasionally infect the fetus after crossing the placenta, none has the same impact as congenital Zika infection. Zika infection in pregnant women can not only affect the placenta, producing fetal growth problems or fetal demise, but also the fetus itself, resulting in the apoptosis of neural cell precursors affecting the development of fetal brain and leading to microcephaly and other malformations.
Understanding the interplay between Zika and the placental interface is particularly challenging given the limited translatability of animal and in vitro models for vertical transmission. To address this issue, we have developed an ex vivo placental model to simulate a maternal Zika virus infection using explants of 2-3 mm3 from placental cotyledons. After producing an artificial infection of the placental explants we are currently measuring the gene expression in the placental tissue, at different time points, to unravel the host immune response and searching for specific genes and pathways involved. Ex vivo infections will be compared to in vitro infections using immortalized trophoblast and primary macrophage cell lines.
For this purpose, we rely on the ultra-precise n-counter technology from Nanostring to carry out a multiplex gene expression analysis in the placental tissue of more than 500 genes related to the host immune response to infectious diseases. This technology requires small sample inputs to accurately detect the real number of mRNA molecules through direct hybridization-based digital counting of the genes of interest, eliminating the need to use technical replicates. In addition, sample amplification is not required, leading to an unbiased mRNA quantification, obtaining highly precise results and saving time and efforts.
With this approach we try to address several important points regarding congenital Zika infection such as: a) differences in local immune response after placental infection; b) differences in transcriptomic response in placental immune-related genes upon infection with the African and the Asian Zika lineages; c) study to what extent culture conditions affect explant gene expression and d) investigate how the host immune response evolves over time.
Overall, this study will help to elucidate the immune system pathways that are being altered during congenital Zika infection and/or the gene sets that are over-represented, shedding some light on the transplacental infection mechanism from the host perspective, helping to understand how the maternal-fetal infection develops.
Note on the authors: Federico Martinón-Torres and Irene Rivero Calle are pediatricians working at Hospital Clinico Universitario de Santiago de Compostela in Spain.
Alberto Gómez Carballa and Antonio Salas are researchers working at the Genetics, Vaccines, Infectious Diseases and Pediatrics research group (GENVIP) in Santiago de Compsotela Spain. All members of the ZIKAction consortium as SERGAS, contributing to Work Package 2, 3 and 4 with genetic and transcriptomic host studies.
Francesco Bonfante is a veterinary virologist working with the Istituto Zooprofilattico Sperimentale delle Venezie (IZSVe) in Padova, Italy. He is a member of the ZIKAction consortium and one of the leaders of Work Package 3 (ZIKA-PATHO).
