Effect of shear stress on 86Rb+ efflux from calf pulmonary artery endothelial cells

Cardiovascular mechanosensitive ion channels-Translating physical forces into physiological responses

Cells and tissues are constantly exposed to mechanical stress. In order to respond to alterations in mechanical stimuli, specific cellular machinery must be in place to rapidly convert physical force into chemical signaling to achieve the desired physiological responses. Mechanosensitive ion channels respond to such physical stimuli in the order of microseconds and are therefore essential components to mechanotransduction. Our understanding of how these ion channels contribute to cellular and physiological responses to mechanical force has vastly expanded in the last few decades due to engineering ingenuities accompanying patch clamp electrophysiology, as well as sophisticated molecular and genetic approaches. Such investigations have unveiled major implications for mechanosensitive ion channels in cardiovascular health and disease. Therefore, in this chapter I focus on our present understanding of how biophysical activation of various mechanosensitive ion channels promotes distinct cell signaling events with tissue-specific physiological responses in the cardiovascular system. Specifically, I discuss the roles of mechanosensitive ion channels in mediating (i) endothelial and smooth muscle cell control of vascular tone, (ii) mechano-electric feedback and cell signaling pathways in cardiomyocytes and cardiac fibroblasts, and (iii) the baroreflex.

System-on-Chip Considerations for Heterogeneous Integration of CMOS and Fluidic Bio-Interfaces

CMOS chips are increasingly used for direct sensing and interfacing with fluidic and biological systems. While many biosensing systems have successfully combined CMOS chips for readout and signal processing with passive sensing arrays, systems that co-locate sensing with active circuits on a single chip offer significant advantages in size and performance but increase the complexity of multi-domain design and heterogeneous integration. This emerging class of lab-on-CMOS systems also poses distinct and vexing technical challenges that arise from the disparate requirements of biosensors and integrated circuits (ICs). Modeling these systems must address not only circuit design, but also the behavior of biological components on the surface of the IC and any physical structures. Existing tools do not support the cross-domain simulation of heterogeneous lab-on-CMOS systems, so we recommend a two-step modeling approach: using circuit simulation to inform physics-based simulation, and vice versa. We review the primary lab-on-CMOS implementation challenges and discuss practical approaches to overcome them. Issues include new versions of classical challenges in system-on-chip integration, such as thermal effects, floor-planning, and signal coupling, as well as new challenges that are specifically attributable to biological and fluidic domains, such as electrochemical effects, non-standard packaging, surface treatments, sterilization, microfabrication of surface structures, and microfluidic integration. We describe these concerns as they arise in lab-on-CMOS systems and discuss solutions that have been experimentally demonstrated.

Rho-kinase as a therapeutic target in vascular diseases: striking nitric oxide signaling

Rho GTPases are a globular, monomeric group of small signaling G-protein molecules. Rho-associated protein kinase/Rho-kinase (ROCK) is a downstream effector protein of the Rho GTPase. Rho-kinases are the potential therapeutic targets in the treatment of cardiovascular diseases. Here, we have primarily discussed the intriguing roles of ROCK in cardiovascular health in relation to nitric oxide signaling. Further, we highlighted the biphasic effects of Y-27632, a ROCK inhibitor under shear stress, which acts as an agonist of nitric oxide production in endothelial cells. The biphasic effects of this inhibitor raised the question of safety of the drug usage in treating cardiovascular diseases.

Fluid Shear Stress Effects on Endothelial Cell Cytosolic pH

Fluid flow can modulate endothelial cell intracellular pH (pH(i)). Venous and arterial shear stresses of 1.4 and 14 dyn/cm2, respectively, induced intracellular acidification. The kinetics of the process and magnitude of acidification were dependent on the level of shear stress. Endothelial cells exposed to a venous shear stress were able to recover from the acidification, whereas cells exposed to an arterial shear stress remained acidic. Addition of SITS (1 mM), a HCO(3) (-)/CI(-) exchange inhibitor, greatly reduced the shear stress induced acidification, suggesting that the HCO(3) (-)/C1(-) exchanger is activated by shear stress. Shear stress may activate the exchanger by lowering the [HCO(3) (-)] at the cell surface via convective mass transfer. Altering the HCO(3) (-) gradient across the cell membrane activates the exchanger and, as a consequence, results in intracellular acidification. Perfusion with media containing ATP (10 microM) altered the kinetics of flow-induced acidification observed at both shear stress levels. ATP modulation of pH(i) may be coupled to the rise in [Ca(2+)](j) known to occur with ATP stimulation. To summarize, media perfusion induces intracellular acidification in endothelial cells, and there is evidence to suggest that pH(i) may serve as a second messenger to modulate flow associated changes in endothelial cell metabolism.

Molecular basis of the effects of shear stress on vascular endothelial cells

Blood vessels are constantly exposed to hemodynamic forces in the form of cyclic stretch and shear stress due to the pulsatile nature of blood pressure and flow. Endothelial cells (ECs) are subjected to the shear stress resulting from blood flow and are able to convert mechanical stimuli into intracellular signals that affect cellular functions, e.g., proliferation, apoptosis, migration, permeability, and remodeling, as well as gene expression. The ECs use multiple sensing mechanisms to detect changes in mechanical forces, leading to the activation of signaling networks. The cytoskeleton provides a structural framework for the EC to transmit mechanical forces between its luminal, abluminal and junctional surfaces and its interior, including the cytoplasm, the nucleus, and focal adhesion sites. Endothelial cells also respond differently to different modes of shear forces, e.g., laminar, disturbed, or oscillatory flows. In vitro studies on cultured ECs in flow channels have been conducted to investigate the molecular mechanisms by which cells convert the mechanical input into biochemical events, which eventually lead to functional responses. The knowledge gained on mechano-transduction, with verifications under in vivo conditions, will advance our understanding of the physiological and pathological processes in vascular remodeling and adaptation in health and disease.

Finite element modelling and simulations in cardiovascular mechanics and cardiology: A bibliography 1993–2004

The paper gives a bibliographical review of the finite element modelling and simulations in cardiovascular mechanics and cardiology from the theoretical as well as practical points of views. The bibliography lists references to papers, conference proceedings and theses/dissertations that were published between 1993 and 2004. At the end of this paper, more than 890 references are given dealing with subjects as: Cardiovascular soft tissue modelling; material properties; mechanisms of cardiovascular components; blood flow; artificial components; cardiac diseases examination; surgery; and other topics.

Flow-dependent increase of ICAM-1 on saphenous vein endothelium is sensitive to apamin

The potassium channel blocker tetraethylammonium blocks the flow-induced increase in endothelial ICAM-1. We have investigated the subtype of potassium channel that modulates flow-induced increased expression of ICAM-1 on saphenous vein endothelium. Cultured human saphenous vein endothelial cells (HSVECs) or intact saphenous veins were perfused at fixed low and high flows in a laminar shear chamber or flow rig, respectively, in the presence or absence of potassium channel blockers. Expression of K(+) channels and endothelial ICAM-1 was measured by real-time polymerase chain reaction and/or immunoassays. In HSVECs, the application of 0.8 N/m(2) (8 dyn/cm(2)) shear stress resulted in a two- to fourfold increase in cellular ICAM-1 within 6 h (P < 0.001). In intact vein a similar shear stress, with pulsatile arterial pressure, resulted in a twofold increase in endothelial ICAM-1/CD31 staining area within 1.5 h (P < 0.001). Both increases in ICAM-1 were blocked by inclusion of 100 nM apamin in the vein perfusate, whereas other K(+) channel blockers were less effective. Two subtypes of small conductance Ca(2+)-activated K(+) channel (selectively blocked by apamin) were expressed in HSVECs and vein endothelium (SK3>SK2). Apamin blocked the upregulation of ICAM-1 on saphenous vein endothelium in response to increased flow to implicate small conductance Ca(2+)-activated K(+) channels in shear stress/flow-mediated signaling pathways.

Endothelial responses to mechanical stress: where is the mechanosensor?

OBJECTIVE

The endothelium is normally subjected to mechanical deformation resulting from shear stress and from strain associated with stretch of the vessel wall. These stimuli are detected by a mechanosensor that initiates a variety of signaling systems responsible for triggering the functional responses. The identity of the mechanosensor has not been established. This article discusses the different mechanisms of mechanosensing that have been proposed and reviews the literature with respect to signaling systems that are activated in response to stress and strain in endothelium.

DATA SOURCES

Published literature related to mechanotransduction, signal transduction pathways initiated by strain in endothelium, and pathophysiologic effects of abnormal shear forces in diseases.

DATA EXTRACTION AND SYNTHESIS

Proposed mechanisms of mechanosensing include stretch-sensitive ion channels, protein kinases associated with the cytoskeleton, integrin-cytoskeletal interactions, cytoskeletal-nuclear interactions, and oxidase systems capable of generating reactive oxygen species. However, the molecular identity of the mechanosensor is not known, nor is it clear whether multiple sensing mechanisms exist.

CONCLUSIONS

Many responses are initiated in cells subjected to mechanical deformation, including alterations in ion channel conductance, activation of signal transduction pathways, and altered expression of specific genes. Future progress in this field will require a critical distinction between cell systems that become activated during mechanical strain and the identity of the cellular mechanosensor that triggers subsequent responses.

Flow-induced pressure differentially regulates endothelin-1, urotensin II, adrenomedullin, and relaxin in pulmonary vascular endothelium

We hypothesized that increased pulmonary vascular pressure--one of the characteristics of congestive heart failure--directly regulates pulmonary endothelial vasoconstrictors (endothelin-1, urotensin II) and vasodilators (adrenomedullin, relaxin). To this end, we subjected pulmonary artery endothelial cells in a novel flow-chamber model to different shear stresses (17, 29, and 46 dyn/cm(2)) at low and elevated levels of downstream pressure (10 and 30 mm Hg). Application of elevated pressure over 16 h increased gene expression and peptide secretion of endothelin-1 at all shear levels, whereas secretion of adrenomedullin rose via decreased expression of its clearance receptor. In contrast, preprourotensin II mRNA and urotensin II peptide decreased in response to elevated pressure, and relaxin remained unaffected. This is the first study to identify pressure as key regulator of mediator synthesis by pulmonary vascular endothelium. Pressure-induced mediator regulation may represent an early event in the development of secondary pulmonary hypertension.

Mechanical force-induced signal transduction in lung cells

The lung is a unique organ in that it is exposed to physical forces derived from breathing, blood flow, and surface tension throughout life. Over the past decade, significant progress has been made at the cellular and molecular levels regarding the mechanisms by which physical forces affect lung morphogenesis, function, and metabolism. With the use of newly developed devices, mechanical forces have been applied to a variety of lung cells including fetal lung cells, adult alveolar epithelial cells, fibroblasts, airway epithelial and smooth muscle cells, pulmonary endothelial and smooth muscle cells, and mesothelial cells. These studies have led to new insights into how cells sense mechanical stimulation, transmit signals intra- and intercellularly, and regulate gene expression at the transcriptional and posttranscriptional levels. These advances have significantly increased our understanding of the process of mechanotransduction in lung cells. Further investigation in this exciting research field will facilitate our understanding of pulmonary physiology and pathophysiology at the cellular and molecular levels.

Fluid shear stress as a regulator of gene expression in vascular cells: possible correlations with diabetic abnormalities

Diabetes mellitus is associated with increased frequency, severity and more rapid progression of cardiovascular diseases. Metabolic perturbations from hyperglycemia result in disturbed endothelium-dependent relaxation, activation of coagulation pathways, depressed fibrinolysis, and other abnormalities in vascular homeostasis. Atherosclerosis is localized mainly at areas of geometric irregularity at which blood vessels branch, curve and change diameter, and where blood is subjected to sudden changes in velocity and/or direction of flow. Shear stress resulting from blood flow is a well known modulator of vascular cell function. This paper presents what is currently known regarding the molecular mechanisms responsible for signal transduction and gene regulation in vascular cells exposed to shear stress. Considering the importance of the hemodynamic environment of vascular cells might be vital to increasing our understanding of diabetes.

Pulsatile shear stress leads to DNA fragmentation in human SH-SY5Y neuroblastoma cell line

1. Using an in vitro model of shear stress-induced cell injury we demonstrate that application of shear to differentiated human SH-SY5Y cells leads to cell death characterized by DNA fragmentation. Controlled shear stress was applied to cells via a modified cone and plate viscometer. 2. We show that pulsatile shear stress leads to DNA fragmentation, as determined via flow cytometry of fluorescein-12-dUTP nick-end labelled cells, in 45 +/- 4 % of cells. No lactate dehydrogenase (LDH) release was observed immediately after injury; however, 24 h after injury significant LDH release was observed. 3. Nitric oxide production by cells subjected to pulsatile shear increased two- to threefold over that in unsheared control cells. 4. Inhibition of protein synthesis, nitric oxide production, Ca2+ entry into cells, and pertussis toxin-sensitive G protein activation attenuated the shear stress-induced cell injury. 5. Our results show for the first time that application of pulsatile shear stress to a neuron-like cell in vitro leads to nitric oxide-dependent cell death.

Novel optical methodologies in studying mechanical signal transduction in mammalian cells

For the last 3 decades evidence has been accumulating that some types of mammalian cells respond to their mechanically active environment by altering their morphology, growth rate, and metabolism. The study of such responses is very important in understanding, physiological and pathological conditions ranging from bone formation to atherosclerosis. Obtaining this knowledge has been the goal for an active research area in bioengineering termed cell mechanotransduction. The advancement of optical methodologies used in cell biology research has given the tools to elucidate cellular mechanisms that would otherwise be impossible to visualize. Combined with molecular biology techniques, they give engineers invaluable tools in understanding the chemical pathways involved in mechanotransduction. Herein we briefly review the current knowledge on mechanical signal transduction in mammalian cells, focusing on the application of novel optical techniques in the ongoing research.

Superoxide and endothelium-dependent constriction to flow in porcine small pulmonary arteries

1. The aim of this study was to determine the response of porcine small pulmonary arteries to intralumenal flow and to identify the cellular mechanisms and potential mediators involved in the response. 2. Porcine small pulmonary arteries were isolated from a branch of the main intrapulmonary artery of the lower lung lobe and studied in a perfusion myograph system that allowed independent control of transmural pressure and intralumenal flow. At a transmural pressure of 20 mmHg, the baseline internal diameter (BID) of the arteries was 251.2+/-16.1 microm (n=16). 3. Under quiescent conditions or during constriction with U46619 to approximately 60% of BID, intralumenal flow caused reversible constriction in arteries with endothelium (in the presence of U46619, flow decreased diameter from 60.0+/-2.5% to 49.5+/-3.0% BID at 10 microl min(-1), n=16, P<0.05) but no change in diameter of arteries without endothelium. 4. In the presence of superoxide dismutase (SOD, 150 u ml(-1)), the response to flow was converted from constriction to vasodilatation (in presence of U46619 and SOD, flow increased diameter from 54.2+/-3.4% to 76.7+/-4.5% BID at 10 microl min(-1), n=10, P<0.05). Inhibition of NO synthase with L-NAME (3 x 10(-5) M) abolished the flow-induced vasodilatation occurring in the presence of SOD and the flow-induced constriction occurring in the absence of SOD. In arteries with endothelium, L-NAME (3 x 10(-5) M) caused significant vasoconstriction, whereas SOD did not alter vasomotor tone. 5. Acetylcholine (10(-8) to 10(-6) M) caused endothelium-dependent relaxation of small pulmonary arteries that was not significantly affected by SOD (150 u ml(-1)) but was inhibited by L-NAME (3 x 10(-5) M). 6. These results suggest that in small, porcine, isolated pulmonary arteries, intralumenal flow increases the production of NO but this is obscured by the generation of superoxide which causes vasoconstriction.

Mechanosensitive Ca2+ oscillations and STOC activation in endothelial cells

Activation of ion channels and the increase in intracellular Ca2+ concentration [Ca2+]i play a key role in endothelial responses to hemodynamic forces and subsequent vasoregulation. In bovine aortic endothelial cells subjected to shear stress in a parallel flow chamber, we demonstrate shear stress activation of hyperpolarizing K+ currents that occur simultaneously with oscillating increases of [Ca2+]i. Oscillating K+ currents, also known as spontaneous transient outward currents (STOC), were regulated in frequency and amplitude by the rate of shear stress in a range from 5 to 18 dyn/cm2. Activation of STOC depended on Ca2+ influx; current depended on the extracellular Ca2+ concentration and was blocked by 50 microM Gd3+. Emptying of Ca2+ stores by BHQ abolished current responses to shear stress. STOC activation was significantly reduced by cell dialysis with ryanodine (20 microM), but not heparin (200 microg/ml). Shear stress-induced STOC activation was also observed in the intact endothelium. The endothelial response to shear stress involves oscillating [Ca2+]i increase and STOC activation, which depend on Ca2+ influx-induced Ca2+ release from ryanodine-sensitive stores, demonstrating a new signaling pathway in endothelial mechanotransduction.

Molecular cloning and expression of a bovine endothelial inward rectifier potassium channel

A 5.1 kb cDNA encoding an inward rectifier K+ channel (BIK) was isolated from a bovine aortic endothelial cell library. The cDNA codes for a 427-amino-acid protein with two putative transmembrane regions. Sequence analysis reveals that BIK is a member of the Kir2.1 family of inward rectifier K+ channels. Expression in Xenopus oocytes showed that BIK is a K+-specific strong inward rectifier channel that is sensitive to extracellular Ba2+, Cs+, and a variety of anti-arrhythmic agents. Northern analysis revealed that endothelial cells express a 5.5 kb BIK mRNA that is sensitive to shear stress.

Cultivation of fall armyworm ovary cells in simulated microgravity

A methodology is presented to culture Fall Armyworm Ovary cells in simulated micrograviy using a novel bioreactor developed by NASA, the High-Aspect Ratio Vessel. In this vessel, the growth and metabolic profile for these insect cells were profoundly different than those obtained in shaker-flask culture. Specifically, stationary phase in the NASA vessel was extended from 24 h to at least 7 d while cell concentration and viability remained in excess of 1 x 10(7) viable cells/ml and 90%, respectively. Measurements of glucose utilization, lactate production, ammonia production, and pH change indicate that simulated microgravity had a twofold effect on cell metabolism. Fewer nutrients were consumed and fewer wastes were produced in stationary phase by as much as a factor of 4 over that achieved in shaker culture. Those nutrients that were consumed in the NASA vessel were directed along different metabolic pathways as evidenced by an extreme shift in glucose utilization from consumption to production in lag phase and a decrease in yield coefficients by one half in stationary phase. These changes reflect a reduction in hydrodynamic forces from over 1 dyne/cm2 in shaker culture to under 0.5 dyne/cm2 in the NASA vessel. These results suggest that cultivation of insect cells in simulated microgravity may reduce production costs of cell-derived biologicals by extending production time and reducing medium requirements.

Spatial relationships in early signaling events of flow-mediated endothelial mechanotransduction

Blood flow interactions with the vascular endothelium represent a specialized example of mechanical regulation of cell function that has important physiological and pathological cardiovascular consequences. The endothelial monolayer in vivo acts as a signal transduction interface for forces associated with flowing blood (hemodynamic forces) in the acute regulation of artery tone and chronic structural remodeling of arteries, including the pathology of atherosclerosis. Mechanisms related to spatial relationships at the cell surfaces and throughout the cell that influence flow-mediated endothelial mechanotransduction are discussed. In particular, flow-mediated ion channel activation and cytoskeletal dynamics are considered in relation to topographic analyses of the luminal and abluminal surfaces of living endothelial cells.

Mechanism of endothelial cell shape change and cytoskeletal remodeling in response to fluid shear stress

Endothelium exposed to fluid shear stress (FSS) undergoes cell shape change, alignment and microfilament network remodeling in the direction of flow by an unknown mechanism. In this study we explore the role of tyrosine kinase (TK) activity, intracellular calcium ([Ca2+]i), mechanosensitive channels and cytoskeleton in the mechanism of cell shape change and actin stress fiber induction in bovine aortic endothelium (BAE). We report that FSS induces beta-actin mRNA in a time- and magnitude-dependent fashion. Treatment with quin2-AM to chelate intracellular calcium release and herbimycin A to inhibit TK activity abolished BAE shape change and actin stress fiber induction by FSS, while inhibition of protein kinase C with chelerythrine had no effect. Altering intermediate filament structure with acrylamide did not affect alignment or F-actin induction by FSS. Examining the role of the BAE cytoskeleton revealed a critical role for microtubules (MT). MT disruption with nocodazole blocked both FSS-induced morphological change and actin stress fiber induction. In contrast, MT hyperpolymerization with taxol attenuated the cell shape change but did not prevent actin stress fiber induction under flow. Mechanosensitive channels were found not to be involved in the FSS-induced shape change. Blocking the shear-activated current (IK.S) with barium and the stretch-activated cation channels (ISA) with gadolinium had no effect on the shear-induced changes in morphology and cytoskeleton. In summary, FSS has a profound effect on endothelial shape and F-actin network by a mechanism which depends on TK activity, intracellular calcium, and an intact microtubule network, but is independent of protein kinase C, intermediate filaments and shear- and stretch-activated mechanosensitive channels.

The development and characterization of an in vitro system to study strain-induced cell deformation in isolated chondrocytes

A model system has been developed to investigate cell deformation of chondrocytes in vitro. Chondrocytes were isolated from bovine articular cartilage by enzymatic digestion and seeded in agarose (type VII) at a final concentration of 2 x 10(6) cells.ml-1 in 3% agarose. Mechanical evaluation of the system showed no change in the tangent modulus of agarose/chondrocyte cultures over a 6-d culture period. The resulting agarose/chondrocyte cultures were subjected to compressive strains ranging from 5-20%. Cell shape was assessed by measuring the dimensions of the cell both perpendicular (x) and parallel (y) to the axis of compression and deformation indices (I = y/x) calculated. Cell deformation increased with the level of strain applied for freshly isolated chondrocytes. The cultures were maintained in medium that inhibits or stimulates matrix production (DMEM and DMEM + 20% FCS, respectively) in order to assess the effect of cartilaginous matrix on chondrocyte deformation. Matrix elaborated by the cells markedly influenced levels of cell deformation, an increase in matrix leading to a decrease in cell deformation. Freshly isolated deep zone chondrocytes were found to deform significantly more than surface zone chondrocytes, although this effect was lost after 6 d in culture. The elaborated matrix also altered the recovery characteristics of the chondrocytes following constant compressive strain of 15% for 24 h. Cells that had elaborated matrix took several hours to return to unloaded shape, while cells without matrix returned to the unloaded shape instantly.

Flow-mediated endothelial mechanotransduction

Mechanical forces associated with blood flow play important roles in the acute control of vascular tone, the regulation of arterial structure and remodeling, and the localization of atherosclerotic lesions. Major regulation of the blood vessel responses occurs by the action of hemodynamic shear stresses on the endothelium. The transmission of hemodynamic forces throughout the endothelium and the mechanotransduction mechanisms that lead to biophysical, biochemical, and gene regulatory responses of endothelial cells to hemodynamic shear stresses are reviewed.

Regulation of vascular tone

The intimal surface of the blood vessel in vivo is subject to shear stress resulting from blood flow, which in most of the circulation, at least at rest, is laminar. Turbulence can occur at bifurcations, especially those of the large arteries, and where vessels curve significantly. Shear stress is a frictional tangential force exerted at the fluid-intimal interface in the long axis of the vessel. It is now known that hemodynamic shear stress can influence a large variety of biological processes in endothelial cells, which vary from those with a short response time, just a few milliseconds, such as the opening of ion channels, to those that change over a period of minutes to several hours, for example, endocytosis and cytoskeleton rearrangement, and those features that alter much more slowly, such as cell shape and stiffness. In addition to these types of changes, there are suggestions that flow acting through shear stress may be responsible for several basic attributes of the vasculature, including the relative size and diameter of the components of a branching vascular system. In this symposium on the flow regulation of the blood vessel, the first presentation dealt with optimality principles that appear to govern the dimensions of the vasculature, in particular the geometry of the arterial branching and the role of shear stress. An optimally designed system is one that requires the least metabolic work to perform its function.(ABSTRACT TRUNCATED AT 250 WORDS)

Shear-dependence of endothelial functions

Endothelial cells are subjected to shear forces which influence important cell functions. Shear stress induces cell elongation and formation of stress fibers, increases permeability, pinocytosis and lipoprotein internalization, is involved in the formation of atherosclerotic lesions, increases the production of tissue plasminogen activator, and enhances von Willebrand factor release and hence platelet aggregation. It decreases adherence of erythrocytes and leukocytes, and increases the release of prostacyclin, endothelium derived relaxing factor, histamine and other compounds, but decreases erythropoietin secretion. The mechanism of signal transduction to the endothelial cell is not known exactly; shear-sensitive ion channels seem to be involved. It is concluded that a better understanding of shear-dependent endothelial functions will influence pathophysiologic concepts and therapeutic interventions.

1992 ALZA Distinguished Lecture: bioengineering and vascular biology

The vascular system is naturally dynamic; fluid mechanics and mass transfer are closely integrated with blood and vascular cell function. We are beginning to understand how local wall shear stress and strain modulate endothelial cell metabolism at the gene level. This knowledge may help explain the focal nature of many vascular pathologies, including atherosclerosis. Understanding mechanical control of gene regulation at the level of specific promoter elements and transcription factors involved will lead to development of novel constructs for localized delivery of specific gene products in regions of high or low shear stress or strain in the vascular system. In addition, recent research has shown how local fluid mechanics can alter receptor specificity in cell-to-cell and cell-to-matrix protein adhesion and aggregation. Knowledge of the specific molecular sequences involved in cell-to-cell recognition will allow development of targeted therapeutics, with applications in thrombosis, inflammation, cancer metastasis, and sickle-cell anemia. Bioengineers are uniquely qualified to be leaders in this field, because advances require a synthesis of cell and molecular biology with systems analysis, transport phenomena, and quantitative modeling. Rapid progress in tissue engineering applications will require this new kind of biomedical engineer, which represents both a challenge and an opportunity for our profession.