Stress phase angle regulates differentiation of human adipose-derived stem cells toward endothelial phenotype

The influence of microenvironment stiffness on endothelial cell fate: Implication for occurrence and progression of atherosclerosis

Atherosclerosis, the primary cause of cardiovascular diseases (CVDs), is characterized by phenotypic changes in fibrous proliferation, chronic inflammation and lipid accumulation mediated by vascular endothelial cells (ECs) and vascular smooth muscle cells (SMCs) which are correlated with the stiffening and ectopic remodeling of local extracellular matrix (ECM). The native residents, ECs and SMCs, are not only affected by various chemical factors including inflammatory mediators and chemokines, but also by a range of physical stimuli, such as shear stress and ECM stiffness, presented in the microenvironmental niche. Especially, ECs, as a semi-selective barrier, can sense mechanical forces, respond quickly to changes in mechanical loading and provide context-specific adaptive responses to restore homeostasis. However, blood arteries undergo stiffening and lose their elasticity with age. Reports have shown that the ECM stiffening could influence EC fate by changing the cell adhesion, spreading, proliferation, cell to cell contact, migration and even communication with SMCs. The cell behaviour changes mediated by ECM stiffening are dependent on the activation of a signaling cascade of mechanoperception and mechanotransduction. Although the substantial evidence directly indicates the importance of ECM stiffening on the native ECs, the understanding about this complex interplay is still largely limited. In this review, we systematically summarize the roles of ECM stiffening on the behaviours of endothelial cells and elucidate the underlying details in biological mechanism, aiming to provide the process of how ECs integrate ECM mechanics and the highlights for bioaffinity of tissue-specific engineered scaffolds.

A Bilayered, Electrospun Poly(Glycerol-Sebacate)/Polyurethane-Polyurethane Scaffold for Engineering of Endothelial Basement Membrane

In the cardiovascular system, heart valves and vessels are subjected to continuous cyclic mechanical loadings due to the pulsatile nature of blood flow. Hence, in leveraging tissue engineering (TE) strategies to regenerate such a system, the candidate scaffold should not only be biocompatible with the desired biodegradation rate, but it should also be mechanically competent to provide a supportive structure for facilitating stem cells retention, growth, and differentiation. To this end, herein, we introduced a novel scaffold composed of poly(glycerol-sebacate) (PGS) and polyurethane (PU), which comprises of two layers: an electrospun pure PU layer beneath another electrospun PGS/PU layer with a different ratio of PGS to PU (3:2, 1:1, 2:3 Wt:Wt). The electrospun PGS/PU-PU scaffold was mechanically competent and showed intended hydrophilicity and a good biodegradation rate. Moreover, the PGS/PU-PU scaffold indicated cell viability and proliferation within ten days of in vitro cell culture and upon 7 day vascular endothelial growth factor (VEGF) stimulation, supported endothelial differentiation of mesenchymal stem cells by significant overexpression of platelet-endothelial cell adhesion molecule-1, von Willebrand factor, and VEGF receptor 2. The results of this study could be implemented in cardiovascular TE strategies when regeneration of blood vessel or heart valve is desired.

Geometry and Flow Properties Affect the Phase Shift between Pressure and Shear Stress Waves in Blood Vessels

The phase shift between pressure and wall shear stress (WSS) has been associated with vascular diseases such as atherosclerosis and aneurysms. The present study aims to understand the effects of geometry and flow properties on the phase shift under the stiff wall assumption, using an immersed-boundary-lattice-Boltzmann method. For pulsatile flow in a straight pipe, the phase shift is known to increase with the Womersley number, but is independent of the flow speed (or the Reynolds number). For a complex geometry, such as a curved pipe, however, we find that the phase shift develops a strong dependence on the geometry and Reynolds number. We observed that the phase shift at the inner bend of the curved vessel and in the aneurysm dome is larger than that in a straight pipe. Moreover, the geometry affects the connection between the phase shift and other WSS-related metrics, such as time-averaged WSS (TAWSS). For straight and curved blood vessels, the phase shift behaves qualitatively similarly to and can thus be represented by the TAWSS, which is a widely used hemodynamic index. However, these observables significantly differ in other geometries, such as in aneurysms. In such cases, one needs to consider the phase shift as an independent quantity that may carry additional valuable information compared to well-established metrics.

Contribution of atherosclerotic plaque location and severity to the near-wall hemodynamics of the carotid bifurcation: an experimental study and FSI modeling

Atherosclerosis is initiated by endothelial injury that is related to abnormal values of hemodynamic parameters such as wall shear stress (WSS), oscillatory shear index (OSI) and stress phase angle (SPA), which are more common in arterial bifurcations due to the complex structure. An experimental model of human carotid bifurcation with accurate geometrical and mechanical features was set up, and using realistic pulsatile flow rates, the inlet and outlet pressure pulses were measured for normal and stenosed models with 40% and 80% severities at common carotid (CCA), internal carotid (ICA) and external carotid (ECA) arteries. Based on the obtained experimental data, fluid-structure models were developed to obtain WSS, OSI, and SPA and evaluate pathological consequences at different locations. Mild severity had minor impact, however, inducing severe 80% stenosis in each branch led to considerable localized changes of hemodynamic parameters both in the stenosis site and other locations. This included sharp increases in WSS values accompanied by very low values close to zero before and after the peaks. Severe stenosis not only caused significant changes in the local artery, but also in other branches. OSI and SPA were less sensitive to stenosis, although high peaks were observed on bifurcation site for the stenosis at ECA. The interconnection of arteries at carotid bifurcation results in altered pressure/flow patterns in all branches when a stenosis is applied in any site. Such effect confirms pathological findings that atherosclerotic plaques are observed simultaneously in different carotid branches, although with different degrees of plaque growth and severity.

The influence of hemodynamics on graft patency prediction model based on support vector machine

In the existing patency prediction model of coronary artery bypass grafting (CABG), the characteristics are based on graft flow, but no researchers selected hemodynamic factors as the characteristics. The purpose of this paper is to study whether the introduction of hemodynamic factors will affect the performance of the prediction model. Transit time flow-meter (TTFM) waveforms and 1-year postoperative patency results were obtained from 50 internal mammary arterial grafts (LIMA) and 82 saphenous venous grafts (SVG) in 60 patients. Taking TTFM waveforms as the boundary conditions, the CABG ideal models were constructed to obtain hemodynamic factors in grafts. Based on clinical characteristics and combination of clinical and hemodynamic characteristics, patency prediction models based on support vector machine (SVM) were constructed respectively. For LIMA, after the introduction of hemodynamic factors, the accuracy, sensitivity and specificity of the prediction model increased from 70.35%, 50% and 74.17% to 78.02%, 70% and 78.89%, respectively. For SVG, the accuracy, sensitivity and specificity of the prediction model increased from 63.24%, 40% and 76.91% to 74.41%, 60.1% and 82.73%, respectively. The performance of the prediction model can be improved by introducing hemodynamic factors into the characteristics of the model. The accuracy, sensitivity and specificity of the prediction results are higher with the addition of hemodynamic characteristics.

Regulation of von Willebrand Factor Gene in Endothelial Cells That Are Programmed to Pluripotency and Differentiated Back to Endothelial Cells

Endothelial cells play a central role in physiological function and pathophysiology of blood vessels in health and disease. However, the molecular mechanism that establishes the endothelial phenotype, and contributes to its signature cell type-specific gene expression, is not yet understood. We studied the regulation of a highly endothelial-specific gene, von Willebrand factor (VWF), in induced pluripotent stem cells generated from primary endothelial cells (human umbilical vein endothelial cells [HUVEC] into a pluripotent state [HiPS]) and subsequently differentiated back into endothelial cells. This allowed us to explore how VWF expression is regulated when the endothelial phenotype is revoked (endothelial cells to HiPS), and re-established (HiPS back to endothelial cells [EC-Diff]). HiPS were generated from HUVECs, their pluripotency established, and then differentiated back to endothelial cells. We established phenotypic characteristics and robust angiogenic function of EC-Diff. Gene array analyses, VWF chromatin modifications, and transacting factors binding assays were performed on the three cell types (HUVEC, HiPS, and EC-Diff). The results demonstrated that generally cohorts of transacting factors that function as transcriptional activators, and those that contribute to histone acetylation and DNA demethylation, were significantly decreased in HiPS compared with HUVECs and EC-Diff. In contrast, there were significant increases in the gene expression levels of epigenetic modifiers that function as methyl transferases in HiPS compared with endothelial cells. The results demonstrated that alterations in chromatin modifications of the VWF gene, in addition to expression and binding of transacting factors that specifically function as activators, are responsible for establishing endothelial specific regulation of the VWF gene. Stem Cells 2019;37:542-554.