Bartonella-induced endothelial cell proliferation is mediated by release of calcium from intracellular stores

The facultative intracellular bacterium Bartonella henselae induces unique angiogenic lesions in immunocompromised hosts. To determine the role of intracellular calcium pools in B. henselae-induced endothelial cell proliferation, we generated B. henselae-conditioned medium (BCM) and tested the ability of these cell-free proteins to induce human umbilical vein endothelial cell (HUVEC) proliferation, CXCL8 production, and intracellular Ca2+ signals. HUVECs incubated with BCM for 3 days had higher cell numbers than controls. In addition, HUVECs produced increased amounts of CXCL8 in response to BCM when compared to medium controls. When BCM was added to HUVECs and the intracellular Ca2+ response measured with the calcium-sensitive dye fura-2/AM, a Ca2+ rise was demonstrated. It was determined that this Ca2+ rise originated from intracellular Ca2+ stores through the use of the Ca2+ ATPase inhibitor thapsigargin. Further, it was demonstrated that BCM enhanced CXCL8 production and HUVEC proliferation in a Ca2+-dependent manner. Conditioned medium from B. henselae causes an intracellular Ca2+ rise in HUVECs, which is involved in B. henselae-induced HUVEC proliferation and CXCL8 production. These results implicate intracellular Ca2+ pools in B. henselae-induced angiogenesis and may lead to increased understanding of the mechanisms of pathogen-induced angiogenesis.