B henselae is in humans the aetiologic agent of cat-scratch disease and of the vasculoproliferative disorders bacillary angiomatosis and bacillary peliosis. Although endothelial cells are crucial in the pathogenesis other cell types function as reservoir and contribute to pathological angiogenesis. Among them, mesenchymal stromal cells (MSCs) can sense pathogens and mount an appropriate cytokine/chemokine response through different Pattern Recognition Receptors (PRRs). MSCs exert direct antimicrobial effector function but may also shelter bacteria such as M. tuberculosis. Methods
Adipose-derived MSCs were infected with B. henselae and analyzed for bacterial persistence by gentamicin protection assay, immunohistochemistry and immunofluorescence. Involvement of PRRs in bacterial infection was evaluated through gene and protein expression analysis. The effect of infection on MSC proliferation, apoptosis and release of soluble factors was assessed. The role of infected-MSC conditioned medium in promoting Bartonella infection of endothelial cells and angiogenesis was demonstrated using respectively gentamicin protection assay and different pro-angiogenic assays including spheroid, wound healing and morphogenesis.
B. henselae can readily infect MSCs and survive in perinuclear bound vacuoles for up to 8 days. Bartonella infection stimulates MSC proliferation and upregulation of EGFR and of the two pattern recognition receptors (PRRs) TLR2 and NOD1. Specific inhibition of EGFR reduces bacterial internalization and treatment with anti-TLR2 neutralizing antibody or EGFR/NOD1 inhibitors significantly downmodulates CXCL8 production. Secretome analysis shows that, in addition to CXCL8, infected MSCs secrete higher levels of the proangiogenic factors VEGF, FGF-7, MMP-9, PIGF, serpin E1, TSP-1, uPA, IL-6, CCL5 and PDGF-D. Importantly, supernatants from B. henselae-infected MSCs increase the susceptibility of ECs to B. henselae infection while enhancing EC proangiogenic potential.
Altogether, these findings indicate that MSCs constitute a novel niche for B. henselae, which favors the persistence of vascular proliferative disorders.