Mechanistic characterization of novel host and viral factors for therapeutic interventions targeting transplacental transmission of Flaviviruses

"VERTICAL perfectly fits in the PEPR MIE Volet 1 by aiming to produce knowledge on emerging infectious diseases, focusing on Orthoflavivirus vertical transmission during congenital infection. Our primary goal is to stimulate new interventions to alleviate the health burden of Orthoflavivirus congenital infections during likely future outbreaks. Our consortium comprises five partners with complementary expertise in virology, cell biology, molecular biology, in vivo mouse models and drug screening, and includes a private company to potentiate industrial developments. The Zika virus (ZIKV) outbreak in the Americas (2015-2016) revealed the importance of Orthoflavivirus vertical transmission, causing congenital Zika syndrome with severe birth defects, primarily microcephaly. More alarmingly, the threat of vertical transmission extends to other arboviruses like Dengue, West Nile and Usutu virus, emphasizing the need for therapeutic interventions against congenital orthoflaviviral infections. At the heart of the viral congenital infections lies the placenta, which is targeted by several viruses, notably ZIKV, and allows viral replication before virus dissemination to the fetus through transplacental transmission. This transient organ plays a pivotal role throughout pregnancy by regulating maternal-fetal exchanges and defending the fetus against pathogens. Amongst the various factors secreted by the placenta during pregnancy, placental extracellular vesicles (EVs) mediate communication between maternal and fetal compartments. These membranous nanovesicles are abundant and critical during pregnancy and their composition is tightly regulated. Interestingly, they could contribute to viral dissemination and cause fetal damage during congenital infections, as recently observed by Partner 1 upon human cytomegalovirus infection. Other studies also suggest that they can act in a paracrine manner to protect the fetus from viral infections. While ZIKV replication in placental cells has been well described, the role of placental EVs upon ZIKV infection has never been precisely addressed. Our recent data suggests that certain host and viral factors, secreted in EVs, modulate ZIKV vertical transmission. Among these factors, the 46 miRNAs from the C19MC cluster, specific to primate placental cells, show potential antiviral properties. However, their role, particularly in orthoflaviviral infections, remains elusive. On the other hand, a viral non-coding RNA, the subgenomic orthoflaviviral RNA (sfRNA), has been proposed to facilitate vertical transmission. The sfRNA, produced by all Orthoflaviviruses, inhibits immune response to enhance viral infection and dissemination. While our preliminary data suggest that it is packaged in placental EVs, information about sfRNA-EV function in congenital transmission and the associated mechanism is lacking. Leveraging strong preliminary data and a multidisciplinary consortium, VERTICAL will decipher the mechanistic underpinnings of both host and viral factors that influence orthoflaviviral transplacental infections through EVs and apply this knowledge to develop therapeutic interventions targeting vertical transmission of Orthoflaviviruses. VERTICAL is structured around four well delineated work packages, which are described below: Dissect the molecular and cellular actions of C19MC miRNAs upon orthoflaviviral infection; Establish whether C19MC miRNAs act via EV delivery; Determine the function of sfRNA in EVs for Orthoflavivirus transplacental transmission; Develop a high-throughput imaging screening platform for assessing the action of placental EVs. The knowledge acquired upon the completion of our project will help to prepare for potential future Orthoflavivirus outbreaks and promote targeted therapeutic interventions to restrict vertical transmission."