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Background: Arpin was discovered as an inhibitor of the Arp2/3 complex in the lamellipodial tip of fibroblasts, where it regulated migration steering. Recently, we described that arpin stabilized the epithelial barrier in an Arp2/3-dependent manner. However, expression of arpin in endothelial cells (EC) and its role in the regulation of endothelial barrier functions has not yet been described. Methods: Arpin expression in EC was analyzed by qRT-PCR, Western blot, and confocal microscopy under basal and inflammatory conditions. Arpin-depleted human umbilical vein EC (HUVEC) were generated to perform permeability assays and to analyze changes in endothelial junctions and the actin cytoskeleton by confocal microscopy. To elucidate arpin functions in vivo, we generated and characterized arpin-deficient mice. Results: Arpin mRNA and protein were expressed in EC and downregulated by pro-inflammatory cytokines. Arpin depletion in HUVEC caused junction destabilization and the formation of actomyosin stress fibers leading to increased permeability in an Arp2/3-independent manner. In contrast to the Arp2/3 inhibitor CK666, inhibitors of kinases involved in the generation of stress fibers, namely ROCK1 and ZIPK, were able to normalize the loss-of-arpin effects on actin filaments and permeability. Arpin-deficient mice were viable but showed a characteristic vascular phenotype in the lung including edema, microhemorrhage and vascular congestion that was accompanied by increased F-actin levels and vascular permeability. Conclusions: Our data show that apart from being an Arp2/3 inhibitor, arpin is also a regulator of actomyosin contractility and endothelial barrier integrity in vitro and in vivo. Therefore, this study will pave the way for future investigations on the role of arpin in vascular and inflammatory diseases.

BACKGROUNDZika virus (ZIKV) is highly teratogenic, in contrast with dengue virus (DENV) or the yellow fever virus vaccine (YFV-17D). The mechanisms employed by ZIKV to cross the placenta need to be elucidated.METHODSParallel infections with ZIKV, DENV and YFV-17D were compared in terms of efficiency, activation of mTOR pathways and cytokine secretion profile in human cytotrophoblastic HTR8 cells (CTB), and monocytic U937 cells, differentiated to M2 macrophages (M2-MØ).RESULTSIn CTB, ZIKV replication was significantly more efficient than DENV or YFV-17D. In M2-MØ, ZIKV replication continued to be more efficient, although differences between strains were reduced. Significantly greater activation of Phospho-S6r and Phospho-AKT/Ser473 fractions in CTB infected with ZIKV than with DENV or YFV-17D, was observed. CTB treated with the mTOR inhibitors rapamycin or AZD8055, showed a 20-fold-reduction in ZIKV yield, versus 5 and 3.5-fold for DENV and YFV-17D, respectively. Finally, we detected that ZIKV infection, but not DENV or YFV-17D, efficiently inhibited the interferon response of CTB cells.CONCLUSIONSThese results suggest that CTB cells are permissive and act favoring ZIKV entry into the placental stroma, over DENV and YFV-17D and that the mTOR complex is a switch that enhances the replication of ZIKV in CTB cells.