BMP receptor-integrin interaction mediates responses of vascular endothelial smad1/5 and proliferation to disturbed flow

[[abstract]]BACKGROUND: Vascular endothelial cells (ECs) are constantly exposed to blood flow-induced shear stress. Our previous study demonstrated that disturbed flow with low and oscillatory shear stress (OSS) induces bone morphogenetic protein receptor (BMPR)-specific Smad1/5 activation in ECs, but the underlying mechanisms and the in vivo functional role of Smad1/5 remain unclear. OBJECTIVES: Here we elucidated the molecular mechanisms by which OSS activates EC Smad1/5 and its in vivo functional role. METHODS: Lentiviral Smad5-specific short hairpin RNA (Lenti-shSmad5) was constructed and intraarterially injected into the lumen of stenosed abdominal aorta in bromodeoxyuridine-infused rats. Co-immunoprecipitation and in situ proximity ligation assays were performed on ECs exposed to OSS (0.5+/-4 dynes/cm(2) ) in a parallel-plate flow chamber to investigate BMPR-integrin interactions and their regulatory role in OSS-activation of EC Smad1/5. RESULTS: Intraarterial administration of Lenti-shSmad5 inhibited bromodeoxyuridine uptake of ECs at post-stenotic sites, where disturbed flow with OSS occurs. OSS induced sustained BMPRIB-alpha(v) beta(3) integrin association in ECs, which was mediated by the intracytoplasmic kinase domain of BMPRII and subsequently activated the Shc/focal adhesion kinase (FAK)/extracellular signal-regulated kinase (ERK) cascade, leading to Smad1/5 activation. This OSS-activation of Smad1/5 induced its association with and activation of runt-related transcription factor-2 (Runx2), leading to activations of mammalian target of rapamycin (mTOR) and p70S6 kinase (p70S6K), a pathway critical for EC proliferation in response to OSS. CONCLUSIONS: OSS induces synergistic interactions between specific BMPRs and integrin to activate Smad1/5 through the Shc/FAK/ERK pathway, which leads to the activation of the Runx2/mTOR/p70S6K pathway to promote EC proliferation