alpha(1G) T-Type Calcium Channel Determines the Angiogenic Potential of Pulmonary Microvascular Endothelial Cells

Pulmonary microvascular endothelial cells (PMVECs) display a rapid angioproliferative phenotype, essential for maintaining homeostasis in steady-state and promoting vascular repair after injury. Although it has long been established that endothelial cytosolic Ca2+ ([Ca2+](i)) transients are required for proliferation and angiogenesis, mechanisms underlying such regulation and the transmembrane channels mediating the relevant [Ca2+](i) transients remain incompletely understood. In the present study, the functional role of the microvascular endothelial site-specific alpha(1G) T-type Ca2+ channel in angiogenesis was examined. PMVECs intrinsically possess an in vitro angiogenic "network formation" capacity. Depleting extracellular Ca2+ abolishes network formation, whereas blockade of vascular endothelial growth factor receptor or nitric oxide synthase has little or no effect, suggesting that the network formation is a [Ca2+](i)-dependent process. Blockade of the T-type Ca2+ channel or silencing of alpha(1G), the only voltage-gated Ca2+ channel subtype expressed in PMVECs, disrupts network formation. In contrast, blockade of canonical transient receptor potential (TRP) isoform 4 or TRP vanilloid 4, two other Ca2+ permeable channels expressed in PMVECs, has no effect on network formation. T-type Ca2+ channel blockade also reduces proliferation, cell-matrix adhesion, and migration, three major components of angiogenesis in PMVECs. An in vivo study demonstrated that the mice lacking alpha(1G) exhibited a profoundly impaired postinjury cell proliferation in the lungs following lipopolysaccharide challenge. Mechanistically, Ttype Ca2+ channel blockade reduces Akt phosphorylation in a dosedependent manner. Blockade of Akt or its upstream activator, phosphatidylinositol-3-kinase (PI3K), also impairs network formation. Altogether, these findings suggest a novel functional role for the alpha(1G) T-type Ca2+ channel to promote the cell's angiogenic potential via a PI3K-Akt signaling pathway.