Juhui Qiu

Biomechanical regulation of vascular smooth muscle cell functions: from in vitro to in vivo understanding

Vascular smooth muscle cells (VSMCs) have critical functions in vascular diseases. Haemodynamic factors are important regulators of VSMC functions in vascular pathophysiology. VSMCs are physiologically active in the three-dimensional matrix and interact with the shear stress sensor of endothelial cells (ECs). The purpose of this review is to illustrate how haemodynamic factors regulate VSMC functions under two-dimensional conditions in vitro or three-dimensional co-culture conditions in vivo. Recent advances show that high shear stress induces VSMC apoptosis through endothelial-released nitric oxide and low shear stress upregulates VSMC proliferation and migration through platelet-derived growth factor released by ECs. This differential regulation emphasizes the need to construct more actual environments for future research on vascular diseases (such as atherosclerosis and hypertension) and cardiovascular tissue engineering.

Substrate stiffness regulates the proliferation, migration, and differentiation of epidermal cells

The aim of this study was to investigate the role of substrate stiffness on the proliferation, migration, and differentiation of epidermal cells. To investigate the effects of substrate stiffness on wound healing, epidermal cells were chosen and inoculated on silicone substrate with different values of Youngs modulus of elasticity. The cell growth curve, MTT method, and cell cycle detection were used to investigate proliferation, and the scratch test was used to investigate cell migration. Fluorescence flow cytometry was used to study epidermal cell differentiation. The proliferation and migration of epidermal cells favoured stiffer surfaces. A highly stiff surface stimulated epidermal cell proliferation and migration and increased re-epithelialisation, but inhibited differentiation. The candidate pathways mediating epidermal cell proliferation and migration are linked to cell anchoring to substrates by integrin-mediated focal adhesion.

Upregulation of SDF-1 is Associated with Atherosclerosis Lesions Induced by LDL Concentration Polarization

Previous numerical simulations on low-density lipoprotein (LDL) concentration polarization in the arterial system indicated that LDL concentration polarization might play an important role in the genesis and development of atherosclerosis. To date, no in vivo experiments have examined this question directly, and the molecular mechanisms are unknown. In this study, ten rabbits were treated with gel–silica loop to develop a defined local stenosis in the straight segment of the left carotid artery. Both numerical simulation and experiment measurements showed that the concentration of LDL was about 35% higher at the blood/arterial wall interface than in the lumen on the distal side of the stenosis. Atherosclerotic lesions with abundant lipid deposits were observed and stromal derived factor-1 (SDF-1) was detected at the distal end of the stenosis, while the straight segment was plaque-free. In vitro studies demonstrated that LDL-induced SDF-1 expression in endothelial cells and increased monocyte adhesion to endothelial cells in a dose-dependent manner. The adhesion was suppressed when endothelial cells were pretreated with SDF-1 antibody. These results suggested LDL concentration polarization contributed to the localization of atherosclerosis and to the expression of SDF-1. In turn, SDF-1 facilitated plaque formation.

High shear stress induces atherosclerotic vulnerable plaque formation through angiogenesis.

Rupture of atherosclerotic plaques causing thrombosis is the main cause of acute coronary syndrome and ischemic strokes. Inhibition of thrombosis is one of the important tasks developing biomedical materials such as intravascular stents and vascular grafts. Shear stress (SS) influences the formation and development of atherosclerosis. The current review focuses on the vulnerable plaques observed in the high shear stress (HSS) regions, which localizes at the proximal region of the plaque intruding into the lumen. The vascular outward remodelling occurs in the HSS region for vascular compensation and that angiogenesis is a critical factor for HSS which induces atherosclerotic vulnerable plaque formation. These results greatly challenge the established belief that low shear stress is important for expansive remodelling, which provides a new perspective for preventing the transition of stable plaques to high-risk atherosclerotic lesions.

Id1-induced inhibition of p53 facilitates endothelial cell migration and tube formation by regulating the expression of beta1-integrin

The Id1 protein is critical for endothelial cell angiogenesis, and this function is particularly relevant to cancer development, cardiovascular disease, and wound healing. We hypothesized that Id1 enhanced migration and tubulogenesis by controlling the expression and function of p53. In this study, we examined cell migration following Id1 overexpression and silencing endothelial cells. The results showed that overexpression of Id1 enhanced cell migration and increased beta1-integrin expression, but inhibition of beta1-integrin blocked motility even in clones overexpressing Id1, suggesting that Id1 regulated motility through beta1-integrin. Further analysis revealed that p53, whose expression and distribution is regulated by Id1, was critical for cell migration, and may be involved in regulating the expression of beta1-integrin. Inhibiting p53 function using PFT-α, a functional inhibitor of p53, increased the expression of beta1-integrin and promoted cell migration even in Id1-silencing endothelial cells, demonstrating that the Id1 knockdowns induced inhibition of endothelial cell migration and the expression of beta1-integrin were controlled by p53. In addition, Id1–p53 pathway regulated the cytoskeleton formation and tubulogenesis. These results demonstrate that Id1-induced beta1-integrin expression in endothelial cells and the function of Id1 in cell migration and tubulogenesis are dependent on p53.

Id1 induces tubulogenesis by regulating endothelial cell adhesion and cytoskeletal organization through β1-integrin and Rho-kinase signalling

The inhibitor of differentiation 1 (Id1) protein is required for tubulogenesis, but the molecular signalling pathways remain unclear. Overexpression (Id1-t) or down-regulation (si-Id1) of Id-1 in cell lines, were used to study the function of Id1. The expression of Id1 and β1-integrin was assessed by Western blotting. Up-regulation of Id1 in human umbilical vascular endothelial cells (HUVECs) activated the expression of β1-integrin and promoted cell adhesion and spreading. Conversely, down-regulation of Id1 suppressed β1-integrin expression and inhibited tubulogenesis. By using a β1-integrin antibody to inhibit β1-integrin function, we demonstrated that Id1-induced cell adhesion and tubulogenesis were mediated by β1-integrin. In addition, HUVECs overexpressing Id1 were able to promote capillary tube formation through cytoskeleton reorganization and cell contraction. Finally, the Rho-kinase inhibitor Y27632 inhibited tubulo-genesis induced by Id1. Our findings provide evidence that Id1 regulates tubulogenesis in vitro through β1-integrin and Rho-kinase signalling.

OxLDL stimulates Id1 nucleocytoplasmic shuttling in endothelial cell angiogenesis via PI3K pathway.

Angiogenesis plays remarkable roles in the development of atherosclerotic rupture plaques. However, its essential mechanism remains unclear. The purpose of the study was to investigate whether inhibitor of DNA binding-1 or inhibitor of differentiation 1 (Id1) promoted angiogenesis when exposed to oxidised low-density lipoprotein (oxLDL), and to determine the molecular mechanism involved. Using aortic ring assay and tube formation assay as a model system, a low concentration of oxLDL was found to induce angiogenic sprouting and capillary lumen formation of endothelial cell. But the Id1 expression was significantly upregulated by oxLDL at low and high concentrations. The Id1 was localised in the nuclei of the human umbilical vein endothelial cells in the control group and in the high-concentration oxLDL group. Id1 was translocated to the cytoplasm at low oxLDL concentrations. The nucleocytoplasmic shuttling at low oxLDL concentration was inhibited by treatment with the nuclear export inhibitor leptomycin B. Protein kinase A (PKA) inhibitor H89 promoted nuclear export of Id1, and phosphatidylinositol-3-kinase (PI3K) inhibitor LY294002 reduced the nuclear export of Id1. PI3K inhibition blocked oxLDL-induced angiogenesis. Low concentrations of oxLDL promoted angiogenic sprouting and capillary formation. And this process depends on nuclear export of Id1, which in turn is controlled by the PI3K pathway. This report presents a new link between oxLDL and Id1 localisation, and may provide a new insight into the interactions of ox-LDL and Id1 in the context of atherosclerosis.

Coordination of Id1 and p53 Activation by Oxidized LDL Regulates Endothelial Cell Proliferation and Migration

Considering that oxidized low-density lipoprotein (ox-LDL) may inhibit endothelial cell (EC) migration and proliferation during endothelialization, we hypothesize that the Id1 protein promotes endothelialization exposed to ox-LDL. Cell proliferation was evaluated by cell counts, and cell migration was evaluated by wound closure assay. The role of Id1 in the cell migration and proliferation was appraised through building Id1 overexpression and silencing ECs. Here, we report that Id1 in human umbilical vascular ECs (HUVECs) was up-regulated by ox-LDL in a dose- and time-dependent manner. Low concentrations of ox-LDL increased the proliferation and migration of EC. High concentrations of ox-LDL suppressed HUVECs proliferation and migration, whose inhibitory effects were abolished by Id1 over-expression. Attenuated proliferation and migration of ECs exposed to high concentrations of ox-LDL may be correlated with the nuclear localization of p53, which was obviously weakened by over-expression of Id1 and strengthened by silencing Id1. Collectively, changes in EC, comprising proliferation and migration, upon exposure to various concentrations of ox-LDL are, at least in part, attributed to the modulatory effect of the Id1 protein, which suggests that manipulating Id1 protein activity may offer therapeutic opportunities to promote re-endothelialization under high concentrations of ox-LDL.

Id1: A novel therapeutic target for patients with atherosclerotic plaque rupture

Plaque neovascularization and inflammation are responsible for plaque destabilization and rupture. However, the precise triggers for inflammation and neovascularization in atherosclerosis are largely unknown. Id1 (inhibitor of DNA-binding) protein is a helix-loop-helix transcription factor and plays an important role in angiogenesis and inflammation. The expression of Id1 can be up-regulated by plaque formation factors such as vascular endothelial growth factor (VEGF), hypoxia, NAD(P)H oxidase, and TNF-alpha. Moreover, Id1 is critical to endothelial progenitor cell (EPC) population formation and angiogenesis. Evidence from diverse sources has suggested that Id1 may affect plaque destabilization through angiogenesis and inflammation. Herein we hypothesize that Id1 is an important protein for the development and progression of atherosclerotic plaque destabilization and hence blocking the expression of Id1 may serve as new targets for antiatherogenic therapy.

ENDOTHELIAL MECHANOTRANSDUCTION MECHANISMS FOR VASCULAR PHYSIOLOGY AND ATHEROSCLEROSIS

Vascular physiology and disease progression, such as atherosclerosis, are mediated by hemodynamic force generated from blood flow. The hemodynamic force exerts on vascular endothelial cells (ECs), which could perceive the mechanical signals and transmit them into cell interior by multiple potential shear sensors, collectively known as mechanotransduction. However, we do not understand completely how these shear-sensitive components orchestrate physiological and atherosclerotic responses to shear stress. In this review, we provide an overview of biomechanical mechanisms underlying vascular physiology and atherosclerotic progression. Additionally, we summarize current evidences to illustrate that atherosclerotic lesions preferentially develop in arterial regions experiencing disturbance in blood flow, during which endothelial dysfunction is the initial event of atherosclerosis, inflammation plays dominant roles in atherosclerotic progression, and angiogenesis emerges as compensatory explanation for atherosclerotic plaque rupture. Especially in the presence of systemic risk factors (e.g., hyperlipidaemia, hypertension and hyperglycemia), the synergy between these systemic risk factors with hemodynamic factors aggravates atherosclerosis by co-stimulating some of these biomechanical events. Given the hemodynamic environment of vasculature, understanding how the rapid shear-mediated signaling, particularly in combination with systemic risk factors, contribute to atherosclerotic progression through endothelial dysfunction, inflammation and angiogenesis helps to elucidate the role for atherogenic shear stress in specifically localizing atherosclerotic lesions in arterial regions with disturbed flow.