<scp>HSP70</scp> governs permeability and mechanotransduction in primary human endothelial cells

Vascular barrier disruption is a hallmark of diseases such as cardiovascular disease, stroke, hypertension, pulmonary disorders, infections, and cancer. Endothelium permeability is tightly regulated by shear stress, allowing tissue perfusion, while disturbed flow leads to increased permeability. Cell-cell junctional proteins, including platelet/endothelial cell adhesion molecule-1 (PECAM-1)/CD31 and VE-cadherin, play significant roles in mechanotransduction and barrier integrity. The 70 kDa heat shock protein HSP70 has a well-established cytoprotective function in cardiovascular physiology. Here, we hypothesized that HSP70 interacts with and regulates these junctional proteins. We found that PECAM-1 and VE-cadherin co-immunoprecipitate with endogenous HSP70, and both proteins exhibited positive proximity ligation assay signals in the endothelial monolayers. HSP70 loss of function leads to disassembly of VE-cadherin and PECAM-1 at the cell surface and selectively decreases PECAM-1 steady-state expression. Consistent with its vascular protective role, HSP70 inhibition also reduced endothelial nitric oxide synthase (eNOS) levels. Furthermore, HSP70 was essential for maintaining normal paracellular flux in primary vein (HUVEC) and coronary artery endothelial cells (HCAEC) monolayers, as well as for promoting natural cell alignment under physiological laminar shear stress in HUVEC. These results demonstrate that HSP70 regulates the quality control of interendothelial adherens junctions, mediates responses to hemodynamic forces, and maintains monolayer barrier function across vascular beds. Our findings advance the mechanistic understanding of how human HSP70 mediates vascular homeostasis through endothelium responses to blood flow and permeability in addition to HSP70 role in migration, proliferation, and angiogenesis.