In vivo dual RNA-Seq uncovers key effectors of epithelial barrier disruption by an extracellular pathogen.

Disruption of host cell barriers is a fundamental strategy enabling pathogens to establish a paracellular infection. Here, using dual RNA-Seq, we determine the in vivo host-pathogen transcriptomic landscape upon infection by the extracellular pathogen Leptospira interrogans and uncover a mechanism of cell-cell junction disruption. We demonstrate that, upon infection, an increase in intracellular calcium triggers tight junction destabilization, by activating the calmodulin and myosin light chain kinase signalization. We identify two bacterial effectors of the Virulence-Modifying (VM) proteins family, structurally related to toxin-like proteins, that promote modulation of calcium homeostasis and disruption of cell-cell junctions, thereby allowing Leptospira translocation across epithelium barriers, tissue colonization and pathogenicity. Furthermore, we demonstrate that at least one of these VM proteins is secreted and associates with host cells. Altogether, these findings reveal a unique strategy by which an extracellular pathogen secretes toxin-like proteins to exploit host calcium signaling for breaching epithelial barriers.