Store-independent Orai1/3 channels activated by intracrine leukotriene C4: role in neointimal hyperplasia

Rationale: Through largely unknown mechanisms, Ca 2+ signaling plays important roles in vascular smooth muscle cell (VSMC) remodeling. Orai1-encoded store-operated Ca 2+ entry has recently emerged as an important player in VSMC remodeling. However, the role of the exclusively mammalian Orai3 protein in native VSMC Ca 2+ entry pathways, its upregulation during VSMC remodeling, and its contribution to neointima formation remain unknown. Objective: The goal of this study was to determine the agonist-evoked Ca 2+ entry pathway contributed by Orai3; Orai3 potential upregulation and role during neointima formation after balloon injury of rat carotid arteries. Methods and Results: Ca 2+ imaging and patch-clamp recordings showed that although the platelet-derived growth factor activates the canonical Ca 2+ release-activated Ca 2+ channels via store depletion in VSMC, the pathophysiological agonist thrombin activates a distinct Ca 2+ -selective channel contributed by Orai1, Orai3, and stromal interacting molecule1 in the same cells. Unexpectedly, Ca 2+ store depletion is not required for activation of Orai1/3 channel by thrombin. Rather, the signal for Orai1/3 channel activation is cytosolic leukotrieneC 4 produced downstream thrombin receptor stimulation through the catalytic activity of leukotrieneC 4 synthase. Importantly, Orai3 is upregulated in an animal model of VSMC neointimal remodeling, and in vivo Orai3 knockdown inhibits neointima formation. Conclusions: These results demonstrate that distinct native Ca 2+ -selective Orai channels are activated by different agonists/pathways and uncover a mechanism whereby leukotrieneC 4 acts through hitherto unknown intracrine mode to elicit store-independent Ca 2+ signaling that promotes vascular occlusive disease. Orai3 and Orai3-containing channels provide novel targets for control of VSMC remodeling during vascular injury or disease.