Nicotinic acid adenine dinucleotide phosphate activates two-pore channel TPC1 to mediate lysosomal Ca 2+ release in endothelial colony-forming cells.

Nicotinic acid adenine dinucleotide phosphate (NAADP) is the most recently discovered Ca ²⁺ -releasing messenger that increases the intracellular Ca ²⁺ concentration by mobilizing the lysosomal Ca ²⁺ store through two-pore channels 1 (TPC1) and 2 (TPC2). NAADP-induced lysosomal Ca ²⁺ release regulates multiple endothelial functions, including nitric oxide release and proliferation. A sizeable acidic Ca ²⁺ pool endowed with TPC1 is also present in human endothelial colony-forming cells (ECFCs), which represent the only known truly endothelial precursors. Herein, we sought to explore the role of the lysosomal Ca ²⁺ store and TPC1 in circulating ECFCs by harnessing Ca ²⁺ imaging and molecular biology techniques. The lysosomotropic agent, Gly-Phe β-naphthylamide, and nigericin, which dissipates the proton gradient which drives Ca ²⁺ sequestration by acidic organelles, caused endogenous Ca ²⁺ release in the presence of a replete inositol-1,4,5-trisphosphate (InsP ₃ )-sensitive endoplasmic reticulum (ER) Ca ²⁺ pool. Likewise, the amount of ER releasable Ca ²⁺ was reduced by disrupting lysosomal Ca ²⁺ content. Liposomal delivery of NAADP induced a transient Ca ²⁺ signal that was abolished by disrupting the lysosomal Ca ²⁺ store and by pharmacological and genetic blockade of TPC1. Pharmacological manipulation revealed that NAADP-induced Ca ²⁺ release also required ER-embedded InsP ₃ receptors. Finally, NAADP-induced lysosomal Ca ²⁺ release was found to trigger vascular endothelial growth factor-induced intracellular Ca ²⁺ oscillations and proliferation, while it did not contribute to adenosine-5'-trisphosphate-induced Ca ²⁺ signaling. These findings demonstrated that NAADP-induced TPC1-mediated Ca ²⁺ release can selectively be recruited to induce the Ca ²⁺ response to specific cues in circulating ECFCs.
(© 2020 Wiley Periodicals LLC.)