Unusual transduction response of progenitor-derived and mature endothelial cells exposed to laminar pulsatile shear stress

Treatment strategy of different enhanced external counterpulsation frequencies for coronary heart disease and cerebral ischemic stroke: A hemodynamic numerical simulation study

BACKGROUND AND OBJECTIVES

Currently, enhanced external counterpulsation (EECP) devices mainly produce one counterpulsation per cardiac cycle. However, the effect of other frequencies of EECP on the hemodynamics of coronary and cerebral arteries is still unclear. It should be investigated whether one counterpulsation per cardiac cycle leads to the optimal therapeutic effect in patients with different clinical indications. Therefore, we measured the effects of different frequencies of EECP on the hemodynamics of coronary and cerebral arteries to determine the optimal counterpulsation frequency for the treatment of coronary heart disease and cerebral ischemic stroke.

METHODS

We established 0D/3D geometric multi-scale hemodynamics model of coronary and cerebral arteries in two healthy individuals, and performed clinical trials of EECP to verify the accuracy of the multi-scale hemodynamics model. The pressure amplitude (35 kPa) and pressurization duration (0.6 s) were fixed. The global and local hemodynamics of coronary and cerebral arteries were studied by changing counterpulsation frequency. Three frequency modes, including one counterpulsation in one, two and three cardiac cycles, were applied. Global hemodynamic indicators included diastolic / systolic blood pressure (D/S), mean arterial pressure (MAP), coronary artery flow (CAF), and cerebral blood flow (CBF), whereas local hemodynamic effects included area-time-averaged wall shear stress (ATAWSS) and oscillatory shear index (OSI). The optimal counterpulsation frequency was verified by analyzing the hemodynamic effects of different frequency modes of counterpulsation cycles and full cycles.

RESULTS

In the full cycle, CAF, CBF and ATAWSS of coronary and cerebral arteries were the highest when one counterpulsation per cardiac cycle was applied. However, in the counterpulsation cycle, the global and local hemodynamic indicators of coronary and cerebral artery reached the highest when one counterpulsation in one cardiac cycle or two cardiac cycles was applied.

CONCLUSIONS

For clinical application, the results of global hemodynamic indicators in the full cycle have more clinical practical significance. Combined with the comprehensive analysis of local hemodynamic indicators, it can be concluded that for coronary heart disease and cerebral ischemic stroke, applying one counterpulsation per cardiac cycle may provide the optimal benefit.

Model-based evaluation of local hemodynamic effects of enhanced external counterpulsation

BACKGROUND AND OBJECTIVES

The treatment benefits of enhanced external counterpulsation (EECP) heavily depends on hemodynamics. Global hemodynamics of EECP can cause blood flow redistribution in the circulatory system whereas local hemodynamic effects act on vascular endothelial cells (VECs). Local hemodynamic effects of EECP on VECs are important in the treatment of atherosclerosis, but currently cannot be not evaluated. Herein we aim to establish evaluation models of local hemodynamic effects based on the global hemodynamic indicators.

METHODS

We established 0D/3D geometric multi-scale hemodynamic models of the coronary and cerebral artery of two healthy individuals to calculate the global hemodynamic indicators and the local hemodynamic effects. Clinical EECP trials were performed to verify the accuracy of the multi-scale hemodynamic model. The global hemodynamic indicators included diastolic blood pressure/systolic blood pressure (Q = D/S), mean arterial pressure (MAP), internal carotid artery flow (ICAF) and cerebral blood flow (CBF), whereas local hemodynamic effects focused on time-averaged wall shear stress (TAWSS). The correlation between these indicators was analyzed via Pearson correlation coefficient. Significantly related indicators were selected for curve-fitting to establish evaluation models of the coronary and cerebral artery. Moreover, clinical data of a coronary heart disease patient and a cerebral ischemic stroke patient were collected to verify the effectiveness of the application of the established evaluation models to real patients.

RESULTS

For coronary artery, TAWSS was correlated to Q = D/S and ICAF (P < 0.05), whereas for cerebral artery, TAWSS was correlated to MAP and CBF (P < 0.05). The mean square error (MSE) between the evaluated values using evaluation model and the calculated values using 0D/3D model of TAWSS of the coronary and cerebral artery were 5.4% and 1.0%, respectively. The MSE of evaluation model applied to real patients was greater than that applied to healthy individuals, but within an acceptable range.

CONCLUSIONS

The presented error demonstrated validity and accuracy of the evaluation models in clinical patients. Based on the evaluation models, global hemodynamic indicators could be used to evaluate the local hemodynamic effects under the current counterpulsation mode. With TAWSS range of 4-7 Pa as the target range, EECP strategies can further be optimized.

Long-term hemodynamic mechanism of enhanced external counterpulsation in the treatment of coronary heart disease: a geometric multiscale simulation

Enhanced external counterpulsation (EECP) is a noninvasive treatment method for coronary artery atherosclerosis that acts on the vascular endothelial cells. The intracoronary hemodynamic parameters that influence long-term treatment effect are the fundamental factors for the inhibition of intimal hyperplasia, which cannot be measured in real time. In order to optimize the long-term treatment effect of coronary heart disease, it is necessary to establish a method for quantified calculation of intracoronary hemodynamic parameters during counterpulsation to research the long-term hemodynamic mechanism of EECP. A geometric multiscale model coupled by the zero-dimensional (0D) lumped parameter model and the three-dimensional (3D) model of narrow coronary artery was established for the simulation of intracoronary hemodynamic environment. The 3D model was used to calculate the hemodynamic parameters such as wall shear stress (WSS) and oscillatory shear index (OSI), while the 0D model was used to simulate the blood circulatory system. Sequential pressure was applied to calves, thighs, and buttocks module in 0D model with the consideration of vessel collapse. Hemodynamic performance was compared with clinical reports to verify the effectiveness of the method. There were significant increases of the diastolic blood pressure (DBP), coronary flow, and the area-averaged WSS during application of EECP, while OSI behind stenosis has some decrease. The waveforms of coronary flow has good similarity with the clinical measured waveforms, and the differences between calculated mean arterial pressures (MAPs) and clinical measurements were within 1%. The fundamental factor in the cure of coronary heart disease by EECP is the improvement of WSS and the decrease of OSI. Comparing with the clinical reports, the immediate hemodynamic changes demonstrate the effectiveness of model. Intracoronary hemodynamic parameters during EECP could be acquired and the method could be used to simulate the long-term treatment effect of EECP. Graphical abstract.

Shear stress: An essential driver of endothelial progenitor cells

The blood flow through vessels produces a tangential, or shear, stress sensed by their innermost layer (i.e., endothelium) and representing a major hemodynamic force. In humans, endothelial repair and blood vessel formation are mainly performed by circulating endothelial progenitor cells (EPCs) characterized by a considerable expression of vascular endothelial growth factor receptor 2 (VEGFR2), CD34, and CD133, pronounced tube formation activity in vitro, and strong reendothelialization or neovascularization capacity in vivo. EPCs have been proposed as a promising agent to induce reendothelialization of injured arteries, neovascularization of ischemic tissues, and endothelialization or vascularization of bioartificial constructs. A number of preconditioning approaches have been suggested to improve the regenerative potential of EPCs, including the use of biophysical stimuli such as shear stress. However, in spite of well-defined influence of shear stress on mature endothelial cells (ECs), articles summarizing how it affects EPCs are lacking. Here we discuss the impact of shear stress on homing, paracrine effects, and differentiation of EPCs. Unidirectional laminar shear stress significantly promotes homing of circulating EPCs to endothelial injury sites, induces anti-thrombotic and anti-atherosclerotic phenotype of EPCs, increases their capability to form capillary-like tubes in vitro, and enhances differentiation of EPCs into mature ECs in a dose-dependent manner. These effects are mediated by VEGFR2, Tie2, Notch, and β1/3 integrin signaling and can be abrogated by means of complementary siRNA/shRNA or selective pharmacological inhibitors of the respective proteins. Although the testing of sheared EPCs for vascular tissue engineering or regenerative medicine applications is still an unaccomplished task, favorable effects of unidirectional laminar shear stress on EPCs suggest its usefulness for their preconditioning.

A bilayer small diameter in vitro vascular model for evaluation of drug induced vascular injury

In pre-clinical safety studies, drug-induced vascular injury (DIVI) is defined as an adverse response to a drug characterized by degenerative and hyperplastic changes of endothelial cells and vascular smooth muscle cells. Inflammation may also be seen, along with extravasation of red blood cells into the smooth muscle layer (i.e., hemorrhage). Drugs that cause DIVI are often discontinued from development after considerable cost has occurred. An in vitro vascular model has been developed using endothelial and smooth muscle cells in co-culture across a porous membrane mimicking the internal elastic lamina. Arterial flow rates of perfusion media within the endothelial chamber of the model induce physiologic endothelial cell alignment. Pilot testing with a drug known to cause DIVI induced extravasation of red blood cells into the smooth muscle layer in all devices with no extravasation seen in control devices. This engineered vascular model offers the potential to evaluate candidate drugs for DIVI early in the discovery process. The physiologic flow within the co-culture model also makes it candidate for a wide variety of vascular biology investigations.

Adiponectin enhances bone marrow mesenchymal stem cell resistance to flow shear stress through AMP-activated protein kinase signaling

Adiponectin has been demonstrated to protect the cardiovascular system and bone marrow mesenchymal stem cells (BMSCs). However, it is unclear whether adiponectin can protect BMSCs against flow shear stress (FSS). In this study, our aim was to explore the effects of adiponectin on BMSCs and to explore the role of AMP-activated protein kinase (AMPK) signaling in this process. Shear stress significantly inhibits the survival and increases the apoptosis of BMSCs in an intensity-dependent manner. The expression levels of TGF-β, bFGF, VEGF, PDGF, and Bcl2 are simultaneously reduced, and the phosphorylation levels of AMPK and ACC, as well as the expression level of Bax, are increased. Supplementation with adiponectin promotes the survival of BMSCs; reverses the changes in the expression levels of TGF-β, bFGF, VEGF, PDGF, Bcl2, and Bax; and further amplifies the phosphorylation of AMPK and ACC. Furthermore, the protective effects of adiponectin can be partially neutralized by AMPK siRNA. In summary, we have demonstrated for the first time that adiponectin can effectively protect BMSCs from FSS and that this effect depends, at least in part, on the activation of AMPK signaling.

Packed Bed Bioreactor for the Isolation and Expansion of Placental-Derived Mesenchymal Stromal Cells

Large numbers of Mesenchymal stem/stromal cells (MSCs) are required for clinical relevant doses to treat a number of diseases. To economically manufacture these MSCs, an automated bioreactor system will be required. Herein we describe the development of a scalable closed-system, packed bed bioreactor suitable for large-scale MSCs expansion. The packed bed was formed from fused polystyrene pellets that were air plasma treated to endow them with a surface chemistry similar to traditional tissue culture plastic. The packed bed was encased within a gas permeable shell to decouple the medium nutrient supply and gas exchange. This enabled a significant reduction in medium flow rates, thus reducing shear and even facilitating single pass medium exchange. The system was optimised in a small-scale bioreactor format (160 cm²) with murine-derived green fluorescent protein-expressing MSCs, and then scaled-up to a 2800 cm² format. We demonstrated that placental derived MSCs could be isolated directly within the bioreactor and subsequently expanded. Our results demonstrate that the closed system large-scale packed bed bioreactor is an effective and scalable tool for large-scale isolation and expansion of MSCs.

Blood flow and stem cells in vascular disease

It is well known that the altered blood flow is related to vascular diseases, including atherosclerosis, restenosis, and arteriosclerosis, which preferentially located at areas with the disturbed blood flow, suggesting that altered biomechanical stress may exert their effect on the vascular disease. Recent evidence indicated the presence of abundant stem/progenitor cells in the vessel wall, in which laminar shear stress can stimulate these cells to differentiate towards endothelial lineage, while cyclic strain results in smooth muscle differentiation. In line with this, it was evidenced that altered biomechanical stress in stented vessels may lead to 'wrong' direction of vascular stem cell differentiation resulting in restenosis. However, the underlying mechanisms are not well understood. In this article, we will give an overview of the effect of the local flow pattern on stem/progenitor cell differentiation and the possible mechanism on how the blood flow influences stem cell behaviours in the development of vascular diseases.

Fluid shear stress induces differentiation of circulating phenotype endothelial progenitor cells

Endothelial progenitor cells (EPCs) are mobilized from bone marrow to peripheral blood, and contribute to angiogenesis in tissue. In the process, EPCs are exposed to shear stress generated by blood flow and tissue fluid flow. Our previous study showed that shear stress induces differentiation of mature EPCs in adhesive phenotype into mature endothelial cells and, moreover, arterial endothelial cells. In this study we investigated whether immature EPCs in a circulating phenotype differentiate into mature EPCs in response to shear stress. When floating-circulating phenotype EPCs derived from ex vivo expanded human cord blood were exposed to controlled levels of shear stress in a flow-loading device, the bioactivities of adhesion, migration, proliferation, antiapoptosis, tube formation, and differentiated type of EPC colony formation increased. The surface protein expression rate of the endothelial markers VEGF receptor 1 (VEGF-R1) and -2 (VEGF-R2), VE-cadherin, Tie2, VCAM1, integrin α(v)/β(3), and E-selectin increased in shear-stressed EPCs. The VEGF-R1, VEGF-R2, VE-cadherin, and Tie2 protein increases were dependent on the magnitude of shear stress. The mRNA levels of VEGF-R1, VEGF-R2, VE-cadherin, Tie2, endothelial nitric oxide synthase, matrix metalloproteinase 9, and VEGF increased in shear-stressed EPCs. Inhibitor analysis showed that the phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signal transduction pathway is a potent activator of adhesion, proliferation, tube formation, and differentiation in response to shear stress. Western blot analysis revealed that shear stress activated the VEGF-R2 phosphorylation in a ligand-independent manner. These results indicate that shear stress increases differentiation, adhesion, migration, proliferation, antiapoptosis, and vasculogenesis of circulating phenotype EPCs by activation of VEGF-R2 and the PI3K/Akt/mTOR signal transduction pathway.

Dynamic compression promotes proliferation and neovascular networks of endothelial progenitor cells in demineralized bone matrix scaffold seed

Neovascularization is required for bone formation and successful fracture healing. In the process of neovascularization, endothelial progenitor cells (EPCs) play an important role and finish vascular repair through reendothelialization to promote successful fracture healing. In this study, we found that dynamic compression can promote the proliferation and capillary-like tube formation of EPCs in the demineralized bone matrix (DBM) scaffold seed. EPCs isolated from the bone marrow of rats have been cultured in DBM scaffolds before dynamic compression and then seeded in the DBM scaffolds under dynamic conditions. The cells/scaffold constructs were subjected to cyclic compression with 5% strain and at 1 Hz for 4 h/day for 7 consecutive days. By using MTT and real-time PCR, we found that dynamic compression can significantly induce the proliferation of EPCs in three-dimensional culture with an even distribution of cells onto DBM scaffolds. Both in vitro and in vivo, the tube formation assays in the scaffolds showed that the loaded EPCs formed significant tube-like structures. These findings suggest that dynamic compression promoted the vasculogenic activities of EPCs seeded in the scaffolds, which would benefit large bone defect tissue engineering.

Laminar shear stress delivers cell cycle arrest and anti-apoptosis to mesenchymal stem cells

Biomechanical forces are emerging as critical regulators of cell function and fluid flow is a potent mechanical stimulus. Although the mechanisms of osteoblasts and osteocytes responding to fluid flow are being elucidated, little is known about how the osteoprogenitors, mesenchymal stem cells (MSCs), respond to fluid flow. Here, we examined the effects of laminar shear stress (LSS) on MSCs in vitro. MSCs from bone marrow of Sprague-Dawley rats were isolated, purified, and subjected to physiological levels of LSS. DNA synthesis and cell cycle were measured through [(3)H]thymidine and by flow cytometry, respectively, to detect the cellular proliferation. Annexin V immunostaining and Bcl-2/Bax mRNA expression were evaluated to determine the effect of LSS on MSCs apoptosis. Results showed that fluid shear stress caused a dose-related reduction of MSCs' proliferation rate with the majority of cells being arrested in the G(0) or G(1) phase. Moreover, it was found that physiological levels of LSS exerted a potent suppression effect on MSC apoptosis. In summary, these data revealed a critical role of LSS in maintaining the quiescence of MSCs.

Human progenitor-derived endothelial cells vs. venous endothelial cells for vascular tissue engineering: an in vitro study

The isolation of endothelial progenitor cells from human peripheral blood generates a great hope in vascular tissue engineering because of particular benefit when compared with mature endothelial cells. We explored the capability of progenitor-derived endothelial cells (PDECs) to line fibrin and collagen scaffolds in comparison with human saphenous and umbilical cord vein endothelial cells (HSVECs and HUVECs): (a) in a static situation, allowing definition of the optimal cell culture conditions with different media and cell-seeding densities to check cell behaviour; (b) under shear stress conditions (flow chambers or tubular vascular constructs), allowing investigation of cell response and mRNA expression on both substrates by oligonucleotide microarray analysis and quantitative real-time PCR. Well characterized PDECs: (a) could not be expanded adequately with the usual mature ECs culture media; (b) were able to colonize and grow on fibrin glue; (c) exhibited higher resistance to oxidative stress than HSVECs and HUVECs; (d) withstood physiological shear stress when lining both substrates in flow chambers, and their gene expression was regulated; (e) colonized a collagen-impregnated vascular prosthesis and were able to sense mechanical forces. Our results provide an improved qualification of PDECs for vascular tissue engineering.

Responsiveness of human bone marrow stromal cells to shear stress

We examined the hypothesis that human mesenchymal stem cells detect physiological mechanical signals. Human bone marrow stromal cells (HBMSCs) were exposed to fluid shear stress of 12 dynes/cm(2) and analysed for their ability to express osteoblast-specific markers and associated signalling pathways. HBMSCs showed a significant increase in alkaline phosphatase (ALP) gene expression and a marked decrease in type I collagen, while no effect on Cbfa1/Runx2 was detected. This regulation is related to p38 and ERK1/2 activation, although the use of specific inhibitors to these two MAP kinases suggests that ALP mRNA induction is especially dependent on p38 activity, while type I collagen downregulation is ERK1/2-dependent. Interestingly, the expression of connexin43, which is involved in cell-to-cell communication of osteoblastic cells through gap junction formation, and its distribution through the cells, were modified by fluid flow (FF). HBMSCs are sensitive to shear stress and it appears essential to take their responsiveness into consideration before associating these regenerative cells with a bioactive biomaterial in a new bone tissue-engineering strategy.

Capability of human umbilical cord blood progenitor-derived endothelial cells to form an efficient lining on a polyester vascular graft in vitro

One of the goals of vascular tissue engineering is to create functional conduits for small-diameter bypass grafting. The present biocompatibility study was undertaken to check the ability of cord blood progenitor-derived endothelial cells (PDECs) to take the place of endothelial cells in vascular tissue engineering. After isolation, culture and characterization of endothelial progenitor cells, the following parameters were explored, with a commercial knitted polyester prosthesis (Polymaille C, Laboratoires Pérouse, France) impregnated with collagen: cell adhesion and proliferation, colonization, cell retention on exposure to flow, and the ability of PDECs to be regulated by arterial shear stress via mRNA levels. PDECs were able to adhere to commercial collagen-coated vascular grafts in serum-free conditions, and were maintained but did not proliferate when seeded at 2.0 x 10(5) cm(-2). Cellularized conduits were analyzed by histology and histochemical staining, demonstrating collagen impregnation and the endothelial characteristics of the colonizing cells. Thirty-six hours after cell seeding the grafts were maintained for 6 h of either static conditions (controls) or application of pulsatile laminar shear stress, which restored the integrity of the monolayer. Finally, quantitative real-time RT-PCR analysis performed at 4 and 8 h from cells lining grafts showed that MMP1 mRNA only was increased at 4h whereas vWF, VE-cadherin and KDR were not significantly modified at 4 and 8 h. Our results show that human cord blood PDECs are capable of forming an efficient lining and to withstand shear stress.