Tanaka, K.; Chanduri, M. V.; Chen, M.; Prendergast, A.; Mani, A.; Schwartz, M. A.

Fluid shear stress (FSS) from blood flow critically determines vascular stability and remodeling. The Smad1/5 pathway is activated by FSS through the BMP9/10 receptors Alk1 and Endoglin, with a maximal activation occurring at physiological magnitudes of FSS, to promote vascular homeostasis. Here, we report that the adhesion G protein-coupled receptor Latrophilin-2 (Lphn2), previously found to mediate flow activation of the canonical junctional complex, is required for flow-mediated Smad1/5 activation in endothelial cells. Lphn2 localized to endothelial junctions, physically associates with Endoglin, and is required for Smad1/5 activation by laminar shear stress but not soluble BMP9. This regulation was independent of G-protein signaling but required Lphn2s C-terminal PDZ binding motif. Endothelial-specific Lphn2 knockout reduced Smad1/5 activation in mice. In zebrafish embryos, both loss of flow and Lphn2 knockout similarly reduced endothelial Smad1/5 activation, with no additive effect, indicating Lphn2 mediates flow-induced activation in vivo. APEX2 proximity labeling revealed that the PDZ domain-containing scaffold protein Shank3 associated with Lphn2 under flow. Shank3 knockdown blocked flow-induced Smad1/5 activation in vitro and Shank3 knockout mice exhibited reduced endothelial nuclear Smad1/5 in vivo. Our findings demonstrate that Lphn2 mediates G protein independent Smad1/5 activation through Shank3. GWAS data revealed that Shank3 rare variants are associated with low risk of peripheral artery disease, suggesting a role for this pathway in cardiovascular disease.