Dieckol induces vasodilation via endothelial–smooth muscle crosstalk in co-culture and in vivo zebrafish models

Dieckol (DK), a phlorotannin isolated from Ecklonia cava, has been suggested to exert vasodilatory effects through endothelial signaling. In this study, the endothelial-smooth muscle signaling pathway involved in DK-mediated vasodilation was recapitulated using a multistep experimental system that integrates a co-culture of human coronary artery endothelial cells (HCAEC) and human coronary artery Smooth Muscle Cells (HCASMC) with an in vivo zebrafish model. DK activated calcium-dependent signaling pathways in HCAEC, notably via muscarinic acetylcholine receptor M3 (AChM3R) and voltage-dependent calcium channels (VDCC), resulting in increased intracellular calcium levels and nitric oxide (NO) production. These effects were confirmed using specific antagonists. NO produced by HCAEC was subsequently transferred to adjacent HCASMC, leading to reduced expression of contractile proteins such as phosphorylated myosin light chain (p-MLC) and calmodulin (CaM), thereby promoting smooth muscle relaxation. Moreover, DK counteracted phenylephrine-induced vasoconstriction in zebrafish by reinforcing vascular integrity and regulating blood flow dynamics, ultimately restoring vascular patency and hemodynamic homeostasis. Collectively, these results demonstrate that DK induces vasodilation by activating AChM3R- and VDCC-mediated calcium signaling and NO production in endothelial cells, with downstream effects on vascular smooth muscle cells. This study highlights the therapeutic potential of DK for improving vascular function through modulation of endothelial-smooth muscle signaling.