Numerical Simulation and Experimental Study on Vascular Mechanical Properties of Coronary Degradable Stent Intervention / 医用生物力学

Objective To explore the effect of vascular stress changes on endothelial function recovery and vascular restenosis inhibition in dynamic degradation process of the degradable stent. Methods The material parameters of the hyper-elastic vascular constitutive relationship was fitted, and the stress distribution on the intima of the blood vessel before stent implantation and during dynamic degradation was calculated by numerical simulation. In vitro culture experiments were carried out, and the stretch ratios of the silicon chambers were 0%, 5%, 10% and 15%, respectively, to simulate the mechanical environment at different degradation stages, and to explore the effects of different stretch ratios on growth state of the endothelial cells （ECs）. Results After the stent was completely degraded, the circumferential intimal stress and strain of the vessel were restored to 0.137 MPa and 5.5%, which were close to the physiological parameters (0.122 MPa, 4.8%) before stent implantation. In vitro experiments showed that the survival rate of ECs was the highest under the condition of 0.1 MPa circumferential stress and 5% strain, and adhesion growth could be achieved. Conclusions With the occurrence of stent degradation process, the circumferential stress and strain of the intima were restored to a range close to physiological parameters, which promoted the growth of ECs. The recovery of intimal function could effectively inhibit the process of vascular restenosis. The results can provide the theoretical basis and experimental platform for studying coronary intervention for the treatment of vascular restenosis.

The effect of concentration ratio on tumor cell adhesion in shear flow / 医用生物力学

Objective To study the different effects from different concentration ratios of polymorphonuclear neutrophil (PMN) to tumor cell (TC) on the process of tumor cell adhesion to endothelial cell (EC) in shear flow. Methods PMNs and TCs with different concentration ratios (PMN-TC ratio) were added into the parallel plate flow chamber, and changes in the numbers of transient and accumulative adhered TCs on ECs at different shear rates (50 s-1，100 s-1，200 s-1) were analyzed. Results The transient and accumulative adhesion of TCs on ECs at PMN-TC ratio of 3︰1 significantly increased as compared to that at PMN-TC ratio of 1︰1, especially under high shear flow condition (100 s-1 and 200 s-1). Moreover, in the 5 minute-observation period, the effect of PMN-TC ratio on TC adhered to ECs occurred earlier when the shear rate increased. Conclusions The increase of PMN-TC concentration ratio can promote TC adhesion to ECs in shear flow, and the research findings provide significant references for studying TC metastasis in blood vessels and the target therapy of tumors.

TNF-α promotes the quantity and ICAM-1 expression of endothelial microparticles / 医用生物力学

Objective To study the role of cyclic strain-modulated tumor necrosis factor-α (TNF-α) played in the quantity and intercellular cell adhesion molecule-1(ICAM-1) expression of endothelial microparticles (EMPs). Methods The endothelial cells (ECs) primarily cultured from rat aorta were applied with 5% cyclic strain (to simulate normal physiological condition) and 18% cyclic strain (to simulate hyper-tension condition), respectively, by using FX-4000T cyclic stain loading system for 24 hours at the loading frequency of 1.25 Hz. The mRNA expression of TNF-α under different amplitudes of cyclic strain was determined by real time-PCR. The TNF-α was then used to stimulate the ECs from rat aorta, and the supernatants were collected and ultracentrifuged to get endothelial microparticles (EMPs), which were then identified by lipophilic styryl membrane staining and transmission electron microscope for morphological identification. The quantities of Annexin V positive EMPs under TNF-α stimulation were counted by flow cytometer and ICAM-1 expression on EMPs was detected as well. Results Compared with the 5% normal cyclic strain, under 18% high cyclic strain condition,the mRNA expression of TNF-α in ECs increased significantly. TNF-α could then significantly up-regulate the production of Annexin V positive EMPs and promote the expression of ICAM-1 on EMPs. Conclusions The over-expression of TNF-α in ECs under high cyclic strain might mediate the high production of EMPs and over-expression of ICAM-1 on EMPs. The research findings will provide new experiment evidence for further studying the role of EPCs in the mechanobiological mechanism of vascular remodeling.

Interactions between vascular endothelial cells and smooth muscle cells under shear stress / 医用生物力学

Endothelial cells (ECs) and smooth muscle cells (SMCs) are the most crucial components of the vascular wall, and the interactions between them are essential for the maintenance of normal vascular physiology, as well as the initiation and development of cardiovascular diseases. Various typical co-culture models have been developed to simulate the location and growth situation of ECs and SMCs in vivo. In this review, the co-culture systems combined with the device applying fluid shear stress were introduced with discussion on the strengths and limitations of each system. The influences of ECs-SMCs interaction on the phenotype and alignment of ECs and SMCs, growth and migration of SMCs, and adhesion molecules expression of ECs under shear stress were briefly reviewed. The established evidence indicates that nitric oxide (NO), cytokines and microRNA are the most important signal molecules mediating the interactions between ECs and SMCs.

Effects of ghost red blood cells on tumor cell adhesion in shear flow / 医用生物力学

Objective To study the effect of ghost red blood cells (GRBCs) on white blood cell (WBC)-mediated adhesion of tumor cells (TCs) on endothelial cells (ECs) in shear flow. Methods GRBCs with hematocrit (Hct) of 20% were added in the parallel plate flow chamber to observe changes in the number of tethered WBCs on ECs, the collision between TCs and adhesive WBCs, and the number of firmly adhered TCs at different shear rates of 62.5, 100, 200 s-1, respectively. Results GRBCs could increase the number of adhered WBCs on ECs and the collision between TCs and adhesive WBCs, and finally enhance the adhesion of TCs on ECs, especially at high shear rate (200 s-1). However, the adhesion efficiency of TCs was not significantly influenced by GRBCs. Conclusions GRBCs in shear flow can promote TC adhesion on ECs, and the research finding will provide a theoretical basis for cancer therapy.

The role of microRNA-34a in low shear stress- induced proliferation of vascular smooth muscle cells / 医用生物力学

Objective To investigate the role of microRNA-34a (miR-34a) in the proliferation of vascular smooth muscle cells (VSMCs) induced by low shear stress (LowSS). Methods Using co-culture parallel plate flow chamber system, endothelial cells (ECs) and VSMCs were co-cultured and applied with normal shear stress (1.5 Pa) and LowSS (0.5 Pa) for 12 h. The expression of proliferating cell nuclear antigen (PCNA) in the co-cultured VSMCs was detected by Western blotting to determine the proliferation capacity of VSMCs. Real-time PCR was used to examine the miR levels of miR-34a in the co-cultured VSMCs. The target proteins of miR-34a were predicted by TargetScan, miRWalk and some other websites. Western blotting was used to detect expression of Forkhead box j2 (Foxj2) in the co-cultured VSMCs. Mimics and inhibitor were used to up-regulate or inhibit the expression of miR-34a, and then the expression of Foxj2 and PCNA was detected by Western blotting to verify the regulation relationship between miR 34a and Foxj2. Results Compared with NSS, LowSS promoted the PCNA expression and significantly up-regulated the miR-34a expression in the co-cultured VSMCs. Foxj2 was predicted to be the downstream target protein of miR-34a by TargetScan, miRWalk and some other websites. Foxj2 expression decreased significantly in the co-cultured VSMCs under LowSS application. Under static condition, the expression of Foxj2 obviously decreased and the expression of PCNA obviously increased by up-regulating miR-34a expression in VSMCs. While inhibiting the expression of miR-34a in VSMCs would result in a significant increase in the expression of Foxj2 and a significant decrease in the expression of PCNA. Conclusions LowSS can promote the proliferation of VSMCs by regulating miR-34a and target protein Foxj2 in the co-cultured VSMCs. This research finding will provide new mechanobiological experimental reference for further illustrating the pathogenesis of atherosclerosis and finding the therapeutic targets for drugs.

Shear stress modulates the proliferation of vascular smooth muscle cells via receptor for activated C kinase 1 / 医用生物力学

Objective To investigate the role of receptor for activated C kinase 1 (RACK1) in vascular smooth muscle cells (VSMCs) proliferation modulated by co-cultured endothelial cells (ECs) and shear stress. Methods Using EC/VSMC co-cultured parallel plate flow chamber system, two levels of shear stress, i.e. low shear stress (LowSS, 0.5 Pa) and normal shear stress (NSS, 1.5 Pa), were applied for 12 h. BrdU ELISA was used to detect the proliferation of VSMCs, and Western blot was used to detect the protein expressions of RACK1 and phosphor-Akt. Under the static condition, RNA interference was used to suppress the expression of RACK1 in VSMCs, and then the proliferation of VSMCs and expressions of RACK1 and phosphor-Akt were detected. By using co-culture model (ECs/VSMCs) and separated culture model (ECs//VSMCs), the effect of ECs on expressions of RACK1 and phosphor-Akt in VSMCs was further analyzed. Results Comparative proteomic analysis revealed that LowSS increased the expression of RACK1 in rat aorta. In vitro experiments showed that LowSS induced the proliferation, expressions of RACK1 and phospho Akt in VSMCs co-cultured with ECs. Target RNA interference of RACK1 significantly decreased the proliferation of VSMCs, and the phosphorylation of Akt. In comparison with ECs//VSMCs (separated culture) group, the expression of RACK1 and phosphor-Akt were both up-regulated in the VSMCs co-cultured with ECs (ECs/VSMCs group). Conclusions The expression of RACK1 in VSMCs was modulated by shear stress and neighboring ECs, which might induce cellular proliferation via PI3K/Akt pathway. The investigation on VSMC proliferation and the involved biomechanical mechanism will contribute to understanding and help preventing the pathogenesis and progress of atherosclerosis.

Role of focal adhesion kinases in adhesion and migration of endothelial cells / 医用生物力学

Objective To investigate the effect of focal adhesion kinases (FAK) inhibitor with different concentration on the adhesion and migration of endothelial cells (ECs) and the expression of downstream Rac1 protein, and to explore the role of FAK in adhesion and migration of ECs by using FAK inhibitor to inhibit the phosphorylation of Y397 site of FAK. Method Scratch wound migration assay was performed to examine the effect of FAK inhibitor with different concentration (from 0 nmol/mL to 250 nmol/mL) on ECs migration at 2, 4, 8 and 24 h, respectively. Western blot combined with immunofluorescence analysis were performed to determine the effect of FAK inhibitor with different concentration on distribution and expression of Rac1 protein. Results With the concentration of FAK inhibitor increased, ECs migration distance and the Rac1 protein expression decreased. Conclusions The inhibition of FAK phosphorylation could inhibit cell adhesion and migration with the decrease in downstream Rac1 protein, and ECs adhesion/migration was related to FAK Rho GTPases signaling pathways.

Effect from different pore sizes of co-culture inserts on the permeability of platelet derived growth factor / 医用生物力学

Objective To investigate the effect from different pore sizes of co culture inserts on the permeability of biomacromolecules through polyethylene terephthalate (PET) membrane so as to solve the key technology problem in mechanobiology experiment on vascular cells. Methods Inserts with 0.4 μm and 1.0 μm pores on the PET membrane were studied using flow chamber system. Low shear stress was subjected to the co-cultured system of endothelial cell (EC)/vascular smooth muscle cell (VSMC) and the concentration of platelet-derived growth factor BB (PDGF-BB) was detected by ELISA. Under the static condition, vascular cells were cultured on the plate (with no cell on PET membrane), on the outer side of PET membrane, and on the both sides of PET membrane, respectively. Then the recombinants PDGF-BB (rPDGF-BB) were added on the different sides of PET membrane. Western blotting was used to detect the change in expressions of p-ERK1/2, p-Akt and Lamin after cells were stimulated by rPGDF BB. Results After low shear stress subjection for 12 h, the concentration of PDGF-BB in the medium from VSMC side was significantly higher than that from EC-side. rPDGF-BB passed through 0.4 μm and 1.0 μm pores on the PET membrane and modulated expressions of p-ERK1/2, p-Akt and Lamin A in cells cultured on the opposite side of PET membrane and cells cultured on the plate separately. When cells were cultured on the both sides of PET membrane, rPDGF-BB only stimulated cells cultured on the same side of 0.4 μm pores on PET membrane, but had no specific effect on cells cultured on the opposite side. Conclusions PET membrane with both 0.4 μm and 1.0 μm pores was permeable to PDGF-BB, and cells cultured on the membrane could affect the permeability. The efficiency of PDGF BB passing through 0.4 μm pores was significantly repressed with cells cultured on the both sides, which was more similar to that in vivo.