In Vivo Dual RNA-Seq uncovers key toxin-like effectors of epithelial barrier disruption and tissue colonization by an extracellular bacterial pathogen

Disruption of host cell barriers is a fundamental strategy enabling pathogens to establish a paracellular infection. Using dual RNA-Seq, we determined the in vivo host-pathogen transcriptomic landscape upon infection by the extracellular pathogen Leptospira interrogans and uncovered a novel mechanism of cell-cell junction disruption. We demonstrated that, upon infection, an increase in intracellular calcium triggered tight junction destabilization, by activating the calmodulin and myosin light chain kinase signalization. We identified two novel bacterial effectors of the Virulence-Modifying (VM) proteins family, structurally related to toxin-like proteins, that promoted modulation of calcium homeostasis and disruption of cell-cell junctions, thereby allowing Leptospira translocation across epithelium barriers, tissue colonization and pathogenicity. Furthermore, we demonstrated that at least one of these VM proteins was internalized inside 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.