Guixue Wang

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.

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.

Rear actomyosin contractility-driven directional cell migration in three-dimensional matrices: a mechano-chemical coupling mechanism

Cell migration is of vital importance in many biological processes, including organismal development, immune response and development of vascular diseases. For instance, migration of vascular smooth muscle cells from the media to intima is an essential part of the development of atherosclerosis and restenosis after stent deployment. While it is well characterized that cells use actin polymerization at the leading edge to propel themselves to move on two-dimensional substrates, the migration modes of cells in three-dimensional matrices relevant to in vivo environments remain unclear. Intracellular tension, which is created by myosin II activity, fulfils a vital role in regulating cell migration. We note that there is compelling evidence from theoretical and experimental work that myosin II accumulates at the cell rear, either isoform-dependent or -independent, leading to three-dimensional migration modes driven by posterior myosin II tension. The scenario is not limited to amoeboid migration, and it is also seen in mesenchymal migration in which a two-dimensional-like migration mode based on front protrusions is often expected, suggesting that there may exist universal underlying mechanisms. In this review, we aim to shed some light on how anisotropic myosin II localization induces cell motility in three-dimensional environments from a biomechanical view. We demonstrate an interesting mechanism where an interplay between mechanical myosin II recruitment and biochemical myosin II activation triggers directional migration in three-dimensional matrices. In the case of amoeboid three-dimensional migration, myosin II first accumulates at the cell rear to induce a slight polarization displayed as a uropod-like structure under the action of a tension-dependent mechanism. Subsequent biochemical signalling pathways initiate actomyosin contractility, producing traction forces on the adhesion system or creating prominent motile forces through blebbing activity, to drive cells to move. In mesenchymal three-dimensional migration, cells can also take advantage of the elastic properties of three-dimensional matrices to move. A minor myosin isoform, myosin IIB, is retained by relatively stiff three-dimensional matrices at the posterior side, then activated by signalling cascades, facilitating prominent cell polarization by establishing front–back polarity and creating cell rear. Myosin IIB initiates cell polarization and coordinates with the major isoform myosin IIA-assembled stress fibres, to power the directional migration of cells in the three-dimensional matrix.

Contractions Reverse Stress Softening in Rat Esophagus

Strain/stress induced tissue softening is usually referred to irreversible softening. The aim of this study was to investigate whether stress softening in rat esophagus is reversible after potassium chloride (KCl) induced contraction. Three series of inflation–deflation loadings were carried out on esophageal specimens obtained from 20 Wistar rats. All specimens were subjected to the first two series in Ca2+-free Krebs solution(Krebs−) and then incubated in Ca2+-containing Krebs solution (Krebs+) for 1xa0h. Ten specimens were distended to pressure 1.0xa0kPa and activated with KCl for 3xa0min. The other ten specimens, however, were distended to 1.0xa0kPa without KCl activation. Subsequently, after incubation in Krebs− for 1xa0h, all 20 specimens were subjected to the third series testing. The stored energy in the esophageal tissues (hysteresis loop area) and the esophageal wall stiffness were compared between two groups within the three series loadings. Results indicated that incubation in Krebs+ cannot recover the stress softening induced energy and stiffness loss, but in contrast, these loss were recovered markedly (pxa0<xa00.05) after KCl activation. In conclusion, stress softening in rat esophagus is reversible after the activation of KCl-induced contractions. This mechanism could be related to regeneration of tissue properties in rat esophagus.

Important role of TNF-α in inhibitory effects of Radix Sophorae Flavescentis extract on vascular restenosis in a rat carotid model of balloon dilatation injury.

The aim of this study was to determine the molecular mechanism underlying the inhibition of vascular restenosis by Radix Sophorae Flavescentis (RSF) extract after balloon dilatation injury. In a rat carotid model of balloon dilatation injury, the RSF extract showed a significant inhibitory effect on vascular restenosis. Immunohistochemistry showed that the expression of tumor necrosis factor-alpha (TNF-alpha) in the vascular focus was markedly reduced upon treatment with the RSF extract, whereas the expression of proliferating cell nuclear antigens (PCNA) was mostly unaffected. Colorimetric assays of methylene blue incorporation demonstrated that the proliferation of cultured vascular smooth muscle cells (VSMCs) was not inhibited with serum from rats treated with RSF extract. However, the expression of TNF-alpha in cultured VSMCs was significantly downregulated by serum from rats treated with RSF extract. These results suggested that RSF extract has an inhibitory effect on vascular restenosis after balloon dilatation injury which might be, in part, attributable to its inhibition of TNF-alpha expression.

Penetration of blood–brain barrier and antitumor activity and nerve repair in glioma by doxorubicin-loaded monosialoganglioside micelles system

For the treatment of glioma and other central nervous system diseases, one of the biggest challenges is that most therapeutic drugs cannot be delivered to the brain tumor tissue due to the blood–brain barrier (BBB). The goal of this study was to construct a nanodelivery vehicle system with capabilities to overcome the BBB for central nervous system administration. Doxorubicin as a model drug encapsulated in ganglioside GM1 micelles was able to achieve up to 9.33% loading efficiency and 97.05% encapsulation efficiency by orthogonal experimental design. The in vitro study demonstrated a slow and sustainable drug release in physiological conditions. In the cellular uptake studies, mixed micelles could effectively transport into both human umbilical vein endothelial cells and C6 cells. Furthermore, biodistribution imaging of mice showed that the DiR/GM1 mixed micelles were accumulated sustainably and distributed centrally in the brain. Experiments on zebrafish confirmed that drug-loaded GM1 micelles can overcome the BBB and enter the brain. Among all the treatment groups, the median survival time of C6-bearing rats after administering DOX/GM1 micelles was significantly prolonged. In conclusion, the ganglioside nanomicelles developed in this work can not only penetrate BBB effectively but also repair nerves and kill tumor cells at the same time.

Intestinal Mechanomorphological Remodeling Induced by Long-Term Low-Fiber Diet in Rabbits

Short-term feeding with low-fiber diet remodels the mechanomorphological properties in the rabbit small intestine. The aims were to study the effect of feeding low-fiber diet for 5xa0months on mechanomorphological properties including the collagen fraction in the rabbit intestines. Fifteen rabbits were divided into an Intervention group (IG, nxa0=xa010) fed a low-fiber diet and a Control group (CG, nxa0=xa05) fed a normal diet for 5 months. Five months later, four 10-cm-long segments obtained from the duodenum, jejunum, ileum and large intestine were used for histological and mechanical analysis, respectively. The wall thickness, wall area, mucosa and muscle layer thickness decreased whereas the submucosa layer thickness increased in the IG (pxa0<xa00.05). The collagen fraction decreased in all layers and segments in the IG (pxa0<xa00.05). The opening angle increased in the large intestine and decreased in the ileum in the IG (pxa0<xa00.05). The intestinal stress–strain curves for IG shifted to the right, indicating softening. The creep did not change in the four segments. The wall stiffness was associated with wall thickness and collagen fraction in the submucosa layer. Long-term low-fiber diet in rabbits induced histomorphometric and biomechanical remodelling of the intestines.

The Change of Local Wall Shear Stress Accelerates Intima Hyperplasia and Atherosclerosis

The aim of this study was to create a novel animal model for local change of hemodynamics and analyze the arterial wall response to plaque-prone hemodynamic environments. A stenosis is modeled by a ring placed around the wall of the left common carotid artery. Numerical simulation of blood flow in the stenotic artery was performed to obtain the distribution of flow field and wall shear stress. Rabbits were fed with normal diet and sacrificed at 4 weeks after the operation. Plasma total cholesterol (TQ) high-density lipoprotein cholesterol (HDL-C), and triglycerides (TG) were determined by commercially enzymatic methods. The pathological slides were prepared and stained for optical microscopic observation. Results showed that in the immediate proximal and distal vicinity of stenosis, blood flow was disturbed significantly. The shear stress at the proximal part of ringer was obviously increased (>6Pa), while it was reduced (0~0.3Pa) at the axifugal part. At the end of 4 weeks, plasma total cholesterol, HDL cholesterol and triglyceride increased in high fat/high cholesterol rabbits. Two groups of rabbits had obviously plaque both at the proximal part and backend of ringer, but the proximal parties was more severity than the backend. Lipid deposited at neointima, elasticity fiber was derangement, and partly intima broken. Common carotid arteries by ringer can induce neointima hyperplasia successfully. Hemodynamics was changed by ringer attributed to the hyperplasia, while the gradient of shear stress plays the critic role.

Stress-strain analysis of duodenal contractility in response to flow and ramp distension in rabbits fed low-fiber diet

Previously we demonstrated that low‐fiber diet in rabbits affects the passive mechanomorphological properties in the small intestine, resulting in reduced intestinal wall thickness and collagen content, as well as intestinal wall softening. The aim of the present study was to evaluate the contractility in rabbits on long‐term low‐fiber diet and specifically to compare the contraction threshold, the frequency, and the amplitude of flow‐induced and distension‐induced contractions in the duodenum between rabbits on normal diet and on long‐term low‐fiber diet.

Reversible stress softening in layered rat esophagus in vitro after potassium chloride activation

Significant stress softening recovery after potassium chloride (KCl) administration was previously demonstrated in the intact rat esophageal wall. The aim of this study is to investigate the effect of KCl activation on stress softening recovery in the separated mucosa–submucosa layer and muscle layer of rat esophagus. Three series of loading–unloading distensions were carried out on 10 rat esophagi where the two separated layers were distended at luminal pressure levels 0.5, 1.0 and 2.0 kPa. Numerous distension cycles were done in