Emerging Role of Plasma Membranes in Vascular Endothelial Mechanosensing

Cancer cell response to extrinsic and intrinsic mechanical cue: opportunities for tumor apoptosis strategies

Increasing studies have revealed the importance of mechanical cues in tumor progression, invasiveness and drug resistance. During malignant transformation, changes manifest in either the mechanical properties of the tissue or the cellular ability to sense and respond to mechanical signals. The major focus of the review is the subtle correlation between mechanical cues and apoptosis in tumor cells from a mechanobiology perspective. To begin, we focus on the intracellular force, examining the mechanical properties of the cell interior, and outlining the role that the cytoskeleton and intracellular organelle-mediated intracellular forces play in tumor cell apoptosis. This article also elucidates the mechanisms by which extracellular forces guide tumor cell mechanosensing, ultimately triggering the activation of the mechanotransduction pathway and impacting tumor cell apoptosis. Finally, a comprehensive examination of the present status of the design and development of anti-cancer materials targeting mechanotransduction is presented, emphasizing the underlying design principles. Furthermore, the article underscores the need to address several unresolved inquiries to enhance our comprehension of cancer therapeutics that target mechanotransduction.

Dietary (poly)phenols as modulators of the biophysical properties in endothelial cell membranes: its impact on nitric oxide bioavailability in hypertension

Hypertension is a major contributor to premature death, owing to the associated increased risk of damage to the heart, brain and kidneys. Although hypertension is manageable by medication and lifestyle changes, the risk increases with age. In an increasingly aged society, the incidence of hypertension is escalating, and is expected to increase the prevalence of (cerebro)vascular events and their associated mortality. Adherence to plant-based diets improves blood pressure and vascular markers in individuals with hypertension. Food flavonoids have an inhibitory effect towards angiotensin-converting enzyme (ACE1) and although this effect is greatly diminished upon metabolization, their microbial metabolites have been found to improve endothelial nitric oxide synthase (eNOS) activity. Considering the transmembrane location of ACE1 and eNOS, the ability of (poly)phenols to interact with membrane lipids modulate the cell membrane's biophysical properties and impact on nitric oxide (· NO) synthesis and bioavailability, remain poorly studied. Herein, we provide an overview of the current knowledge on the lipid remodeling of endothelial membranes with age, its impact on the cell membrane's biophysical properties and · NO permeability across the endothelial barrier. We also discuss the potential of (poly)phenols and other plant-based compounds as key players in hypertension management, and address the caveats and challenges in adopted methodologies.

Endothelial cells differentially sense laminar and disturbed flows by altering the lipid order of their plasma and mitochondrial membranes

Endothelial cells (ECs) experience two different blood flow patterns: laminar and disturbed flow. Their responses to laminar flow contribute to vascular homeostasis, whereas their responses to disturbed flow result in EC dysfunction and vascular diseases. However, it remains unclear how ECs differentially sense laminar and disturbed flow and trigger signaling that elicits different responses. Here, we showed that ECs differentially sense laminar and disturbed flows by altering the lipid order of their plasma and mitochondrial membranes in opposite directions. This results in distinct changes in mitochondrial function, namely, increased adenosine triphosphate (ATP) production for laminar flow and increased hydrogen peroxide (H2O2) release for disturbed flow, leading to ATP- and H2O2-mediated signaling, respectively. When cultured human aortic ECs were subjected to laminar or disturbed flow in flow-loading devices, the lipid order of their plasma membranes immediately decreased in response to laminar flow and increased in response to disturbed flow. Laminar flow also decreased the lipid order of mitochondrial membranes and increased mitochondrial ATP production. In contrast, disturbed flow increased the lipid order of mitochondrial membranes and increased the release of H2O2 from the mitochondria. The addition of cholesterol to the cells increased the lipid order of both membranes and abrogated laminar flow-induced ATP production, while treatment of the cells with a cholesterol-depleting reagent, methyl-β cyclodextrin, decreased the lipid order of both membranes and abolished disturbed flow-induced H2O2 release, indicating that changes in the membrane lipid order and/or cholesterol content are closely linked to flow-induced changes in mitochondrial functions.NEW & NOTEWORTHY How vascular endothelial cells (ECs) differentially sense laminar and disturbed flows and trigger intracellular signaling remains unclear. Here, we show that EC plasma membranes act as mechanosensors to discriminate between laminar and disturbed flows by undergoing opposite changes in their lipid order. Similar lipid order changes occur simultaneously in the mitochondrial membranes, which are linked to changes in mitochondrial function, that is, increased ATP production for laminar flow and increased H2O2 release for disturbed flow.

Cells immersed in collagen matrices show a decrease in plasma membrane fluidity as the matrix stiffness increases

Cells are constantly adapting to maintain their identity in response to the surrounding media's temporal and spatial heterogeneity. The plasma membrane, which participates in the transduction of external signals, plays a crucial role in this adaptation. Studies suggest that nano and micrometer areas with different fluidities at the plasma membrane change their distribution in response to external mechanical signals. However, investigations linking fluidity domains with mechanical stimuli, specifically matrix stiffness, are still in progress. This report tests the hypothesis that the stiffness of the extracellular matrix can modify the equilibrium of areas with different order in the plasma membrane, resulting in changes in overall membrane fluidity distribution. We studied the effect of matrix stiffness on the distribution of membrane lipid domains in NIH-3 T3 cells immersed in matrices of varying concentrations of collagen type I, for 24 or 72 h. The stiffness and viscoelastic properties of the collagen matrices were characterized by rheometry, fiber sizes were measured by Scanning Electron Microscopy (SEM) and the volume occupied by the fibers by second harmonic generation imaging (SHG). Membrane fluidity was measured using the fluorescent dye LAURDAN and spectral phasor analysis. The results demonstrate that an increase in collagen stiffness alters the distribution of membrane fluidity, leading to an increasing amount of the LAURDAN fraction with a high degree of packing. These findings suggest that changes in the equilibrium of fluidity domains could represent a versatile and refined component of the signal transduction mechanism for cells to respond to the highly heterogeneous matrix structural composition. Overall, this study sheds light on the importance of the plasma membrane's role in adapting to the extracellular matrix's mechanical cues.

Vascular mechanotransduction

This review aims to survey the current state of mechanotransduction in vascular smooth muscle cells (VSMCs) and endothelial cells (ECs), including their sensing of mechanical stimuli and transduction of mechanical signals that result in the acute functional modulation and longer-term transcriptomic and epigenetic regulation of blood vessels. The mechanosensors discussed include ion channels, plasma membrane-associated structures and receptors, and junction proteins. The mechanosignaling pathways presented include the cytoskeleton, integrins, extracellular matrix, and intracellular signaling molecules. These are followed by discussions on mechanical regulation of transcriptome and epigenetics, relevance of mechanotransduction to health and disease, and interactions between VSMCs and ECs. Throughout this review, we offer suggestions for specific topics that require further understanding. In the closing section on conclusions and perspectives, we summarize what is known and point out the need to treat the vasculature as a system, including not only VSMCs and ECs but also the extracellular matrix and other types of cells such as resident macrophages and pericytes, so that we can fully understand the physiology and pathophysiology of the blood vessel as a whole, thus enhancing the comprehension, diagnosis, treatment, and prevention of vascular diseases.

The mechanical cell - the role of force dependencies in synchronising protein interaction networks

The role of mechanical signals in the proper functioning of organisms is increasingly recognised, and every cell senses physical forces and responds to them. These forces are generated both from outside the cell or via the sophisticated force-generation machinery of the cell, the cytoskeleton. All regions of the cell are connected via mechanical linkages, enabling the whole cell to function as a mechanical system. In this Review, we define some of the key concepts of how this machinery functions, highlighting the critical requirement for mechanosensory proteins, and conceptualise the coupling of mechanical linkages to mechanochemical switches that enables forces to be converted into biological signals. These mechanical couplings provide a mechanism for how mechanical crosstalk might coordinate the entire cell, its neighbours, extending into whole collections of cells, in tissues and in organs, and ultimately in the coordination and operation of entire organisms. Consequently, many diseases manifest through defects in this machinery, which we map onto schematics of the mechanical linkages within a cell. This mapping approach paves the way for the identification of additional linkages between mechanosignalling pathways and so might identify treatments for diseases, where mechanical connections are affected by mutations or where individual force-regulated components are defective.

The Importance of the Plasma Membrane in Atherogenesis

Atherosclerotic cardiovascular diseases are an important medical problem due to their high prevalence, impact on quality of life and prognosis. The pathogenesis of atherosclerosis is an urgent medical and social problem, the solution of which may improve the quality of diagnosis and treatment of patients. Atherosclerosis is a complex chain of events, which proceeds over many years and in which many cells in the bloodstream and the vascular wall are involved. A growing body of evidence suggests that there are complex, closely linked molecular mechanisms that occur in the plasma membranes of cells involved in atherogenesis. Lipid transport, innate immune system receptor function, and hemodynamic regulation are linked to plasma membranes and their biophysical properties. A better understanding of these interrelationships will improve diagnostic quality and treatment efficacy.

Diversity of Lipid Function in Atherogenesis: A Focus on Endothelial Mechanobiology

Atherosclerosis is one of the most important problems in modern medicine. Its high prevalence and social significance determine the need for a better understanding of the mechanisms of the disease's development and progression. Lipid metabolism and its disorders are one of the key links in the pathogenesis of atherosclerosis. Lipids are involved in many processes, including those related to the mechanoreception of endothelial cells. The multifaceted role of lipids in endothelial mechanobiology and mechanisms of atherogenesis are discussed in this review. Endothelium is involved in ensuring adequate vascular hemodynamics, and changes in blood flow characteristics are detected by endothelial cells and affect their structure and function.

Mechanosensitive molecular interactions in atherogenic regions of the arteries: development of atherosclerosis

A terrible disease of the cardiovascular system, atherosclerosis, develops in the areas of bends and branches of arteries, where the direction and modulus of the blood flow velocity vector change, and consequently so does the mechanical effect on endothelial cells in contact with the blood flow. The review focuses on topical research studies on the development of atherosclerosis – mechanobiochemical events that transform the proatherogenic mechanical stimulus of blood flow – low and low/oscillatory arterial wall shear stress in the chains of biochemical reactions in endothelial cells, leading to the expression of specific proteins that cause the progression of the pathological process. The stages of atherogenesis, systemic risk factors for atherogenesis and its important hemodynamic factor, low and low/oscillatory wall shear stress exerted by blood flow on the endothelial cells lining the arterial walls, have been described. The interactions of cell adhesion molecules responsible for the development of atherosclerosis under low and low/oscillating shear stress conditions have been demonstrated. The activation of the regulator of the expression of cell adhesion molecules, the transcription factor NF-κB, and the factors regulating its activation under these conditions have been described. Mechanosensitive signaling pathways leading to the expression of NF-κB in endothelial cells have been described. Studies of the mechanobiochemical signaling pathways and interactions involved in the progression of atherosclerosis provide valuable information for the development of approaches that delay or block the development of this disease. Key words: atherogenesis; shear stress; transcription factor NF-κB; RelA expression; mechanosensitive receptors; cell adhesion molecules; signaling pathways; mechanotransduction.

Effects of shear stress on differentiation of stem cells into endothelial cells

Stem cell transplantation is an appealing potential therapy for vascular diseases and an indispensable key step in vascular tissue engineering. Substantial effort has been made to differentiate stem cells toward vascular cell phenotypes, including endothelial cells (ECs) and smooth muscle cells. The microenvironment of vascular cells not only contains biochemical factors that influence differentiation but also exerts hemodynamic forces, such as shear stress and cyclic strain. More recently, studies have shown that shear stress can influence the differentiation of stem cells toward ECs. A deep understanding of the responses and underlying mechanisms involved in this process is essential for clinical translation. This review highlights current data supporting the role of shear stress in stem cell differentiation into ECs. Potential mechanisms and signaling cascades for transducing shear stress into a biological signal are proposed. Further study of stem cell responses to shear stress will be necessary to apply stem cells for pharmacological applications and cardiovascular implants in the realm of regenerative medicine.

Hemodynamic Forces, Endothelial Mechanotransduction, and Vascular Diseases

Cells in the tissues and organs of a living body are subjected to mechanical forces, such as pressure, friction, and tension from their surrounding environment. Cells are equipped with a mechanotransduction mechanism by which they perceive mechanical forces and transmit information into the cell interior, thereby causing physiological or pathogenetic mechano-responses. Endothelial cells (ECs) lining the inner surface of blood vessels are constantly exposed to shear stress caused by blood flow and a cyclic strain caused by intravascular pressure. A number of studies have shown that ECs are sensitive to changes in these hemodynamic forces and alter their morphology and function, sometimes by modifying gene expression. The mechanism of endothelial mechanotransduction has been elucidated, and the plasma membrane has recently been shown to act as a mechanosensor. The lipid order and cholesterol content of plasma membranes change immediately upon the exposure of ECs to hemodynamic forces, resulting in a change in membrane fluidity. These changes in a plasma membrane's physical properties affect the conformation and function of various ion channels, receptors, and microdomains (such as caveolae and primary cilia), thereby activating a wide variety of downstream signaling pathways. Such endothelial mechanotransduction works to maintain circulatory homeostasis; however, errors in endothelial mechanotransduction can cause abnormalities in vascular physiological function, leading to the initiation and progression of various vascular diseases, such as hypertension, thrombosis, aneurysms, and atherosclerosis. Recent advances in detailed imaging technology and computational fluid dynamics analysis have enabled us to evaluate the hemodynamic forces acting on vascular tissue accurately, contributing greatly to our understanding of vascular mechanotransduction and the pathogenesis of vascular diseases, as well as the development of new therapies for vascular diseases.

Fluid shear stress-mediated mechanotransduction in circulating leukocytes and its defect in microvascular dysfunction

Leukocytes (neutrophils, monocytes) in the active circulation exhibit multiple phenotypic indicators for a low level of cellular activity, like lack of pseudopods and minimal amounts of activated, cell-adhesive integrins on their surfaces. In contrast, before these cells enter the circulation in the bone marrow or when they recross the endothelium into extravascular tissues of peripheral organs they are fully activated. We review here a multifaceted mechanism mediated by fluid shear stress that can serve to deactivate leukocytes in the circulation. The fluid shear stress controls pseudopod formation via the FPR receptor, the same receptor responsible for pseudopod projection by localized actin polymerization. The bioactivity of macromolecular factors in the blood plasma that interfere with receptor stimulation by fluid flow, such as proteolytic cleavage in the extracellular domain of the receptor or the membrane actions of cholesterol, leads to a defective ability to respond to fluid shear stress by actin depolymerization. The cell reaction to fluid shear involves CD18 integrins, nitric oxide, cGMP and Rho GTPases, is attenuated in the presence of inflammatory mediators and modified by glucocorticoids. The mechanism is abolished in disease models (genetic hypertension and hypercholesterolemia) leading to an increased number of activated leukocytes in the circulation with enhanced microvascular resistance and cell entrapment. In addition to their role in binding to biochemical agonists/antagonists, membrane receptors appear to play a second role: to monitor local fluid shear stress levels. The fluid shear stress control of many circulating cell types such as lymphocytes, stem cells, tumor cells remains to be elucidated.

3D-Bioprinting Strategies Based on In Situ Bone-Healing Mechanism for Vascularized Bone Tissue Engineering

Over the past decades, a number of bone tissue engineering (BTE) approaches have been developed to address substantial challenges in the management of critical size bone defects. Although the majority of BTE strategies developed in the laboratory have been limited due to lack of clinical relevance in translation, primary prerequisites for the construction of vascularized functional bone grafts have gained confidence owing to the accumulated knowledge of the osteogenic, osteoinductive, and osteoconductive properties of mesenchymal stem cells and bone-relevant biomaterials that reflect bone-healing mechanisms. In this review, we summarize the current knowledge of bone-healing mechanisms focusing on the details that should be embodied in the development of vascularized BTE, and discuss promising strategies based on 3D-bioprinting technologies that efficiently coalesce the abovementioned main features in bone-healing systems, which comprehensively interact during the bone regeneration processes.

Early events in endothelial flow sensing

Responses of vascular and lymphatic endothelial cells (ECs) to fluid shear stress (FSS) from blood or lymphatic fluid flow govern the development, physiology, and diseases of these structures. Extensive research has characterized the signaling, gene expression and cytoskeletal pathways that mediate effects on EC phenotype and vascular morphogenesis. But the primary mechanisms by which ECs transduce the weak forces from flow into biochemical signals are less well understood. This review covers recent advances in our understanding of the immediate mechanisms of FSS mechanotransduction, integrating results from different disciplines, addressing their roles in development, physiology and disease, and suggesting important questions for future work.

Functional lipidomics of vascular endothelial cells in response to laminar shear stress

Laminar shear stress generated by blood flow stimulates endothelial cells and activates signal transduction, which plays an important role in vascular homeostasis. Several lines of evidence indicate that membrane and intracellular lipids are involved in the signal transduction of biomechanical stresses. In this study, we performed global profiling of cellular lipids from human pulmonary artery endothelial cells (HPAEC) exposed to laminar shear stress. A total of 761 species of lipids were successfully annotated, with 198 of these species significantly changed in response to shear stress for 24 hours. Ether-linked lipids containing an alkyl moiety with a medium chain length (C11-C14) were uniquely upregulated, and the administration of their biosynthetic precursor 1-O-dodecyl-rac-glycerol attenuated phorbol 12-myristate 13-acetate (PMA) induced vascular cell adhesion molecule-1 (VCAM-1) expression. Given the pro-inflammatory and atherogenic roles of VCAM-1, our findings suggest that the induction of a specific group of lipids (ie, ether-linked lipids with medium length alkyl side chain) may confer atheroprotective and anti-inflammatory roles to vascular endothelial cells under flow conditions.

Shear stress activates mitochondrial oxidative phosphorylation by reducing plasma membrane cholesterol in vascular endothelial cells

The mechanotransduction of shear stress in vascular endothelial cells is still not completely understood. We show a pathway of shear stress signal transduction mediated by plasma membrane cholesterol-dependent mitochondrial oxidative phosphorylation. The latest imaging technology using domain 4 mutant-derived cholesterol biosensors and a fluorescence resonance energy transfer-based adenosine triphosphate (ATP) biosensor revealed that shear stress rapidly decreases cholesterol levels in the plasma membrane via both efflux and internalization, and reduction in plasma membrane cholesterol was linked to the activation of mitochondrial ATP production. The addition of cholesterol blocked these shear stress effects. Increased mitochondrial ATP production led to ATP release from the endothelial cells, thereby activating purinoceptors in the plasma membrane and leading to purinergic Ca²⁺ signaling in response to shear stress.

Vascular endothelial cells (ECs) sense and respond to hemodynamic shear stress, which is critical for circulatory homeostasis and the pathophysiology of vascular diseases. The mechanisms of shear stress mechanotransduction, however, remain elusive. We previously demonstrated a direct role of mitochondria in the purinergic signaling of shear stress: shear stress increases mitochondrial adenosine triphosphate (ATP) production, triggering ATP release and Ca²⁺ signaling via EC purinoceptors. Here, we showed that shear stress rapidly decreases cholesterol in the plasma membrane, thereby activating mitochondrial ATP production. Imaging using domain 4 mutant-derived cholesterol biosensors showed that the application of shear stress to cultured ECs markedly decreased cholesterol levels in both the outer and inner plasma membrane bilayers. Flow cytometry showed that the cholesterol levels in the outer bilayer decreased rapidly after the onset of shear stress, reached a minimum (around 60% of the control level) at 10 min, and plateaued thereafter. After the shear stress ceased, the decreased cholesterol levels returned to those seen in the control. A biochemical analysis showed that shear stress caused both the efflux and the internalization of plasma membrane cholesterol. ATP biosensor imaging demonstrated that shear stress significantly increased mitochondrial ATP production. Similarly, the treatment of cells with methyl-β-cyclodextrin (MβCD), a membrane cholesterol-depleting agent, increased mitochondrial ATP production. The addition of cholesterol to cells inhibited the increasing effects of both shear stress and MβCD on mitochondrial ATP production in a dose-dependent manner. These findings indicate that plasma membrane cholesterol dynamics are closely coupled to mitochondrial oxidative phosphorylation in ECs.

Physicochemical Tools for Visualizing and Quantifying Cell-Generated Forces

To discern how mechanical forces coordinate biological outcomes, methods that map cell-generated forces in a spatiotemporal manner, and at cellular length scales, are critical. In their native environment, whether it be within compact multicellular three-dimensional structures or sparsely populated fibrillar networks of the extracellular matrix, cells are constantly exposed to a slew of physical forces acting on them from all directions. At the same time, cells exert highly localized forces of their own on their surroundings and on neighboring cells. Together, the generation and transmission of these forces can control diverse cellular activities and behavior as well as influence cell fate decisions. To thoroughly understand these processes, we must first be able to characterize and measure such forces. However, our experimental needs and technical capabilities are in discord-while it is apparent that we should study cell-generated forces within more biologically relevant 3D environments, this goal remains challenging because of caveats associated with complex "sensing-transduction-readout" modalities. In this Review, we will discuss the latest techniques for measuring cell-generated forces. We will highlight recent advances in traction force microscopy and examine new alternative approaches for quantifying cell-generated forces, both of individual cells and within 3D tissues. Finally, we will explore the future direction of novel cellular force-sensing tools in the context of mechanobiology and next-generation biomaterials design.

Mechanoresponse of stem cells for vascular repair

Stem cells have shown great potential in vascular repair. Numerous evidence indicates that mechanical forces such as shear stress and cyclic strain can regulate the adhesion, proliferation, migration, and differentiation of stem cells via serious signaling pathways. The enrichment and differentiation of stem cells play an important role in the angiogenesis and maintenance of vascular homeostasis. In normal tissues, blood flow directly affects the microenvironment of vascular endothelial cells (ECs); in pathological status, the abnormal interactions between blood flow and vessels contribute to the injury of vessels. Next, the altered mechanical forces are transduced into cells by mechanosensors to trigger the reformation of vessels. This process occurs when signaling pathways related to EC differentiation are initiated. Hence, a deep understanding of the responses of stem cells to mechanical stresses and the underlying mechanisms involved in this process is essential for clinical translation. In this the review, we provide an overview of the role of stem cells in vascular repair, outline the performance of stem cells under the mechanical stress stimulation, and describe the related signaling pathways.

Force Sensing by Piezo Channels in Cardiovascular Health and Disease

Mechanical forces are fundamental in cardiovascular biology, and deciphering the mechanisms by which they act remains a testing frontier in cardiovascular research. Here, we raise awareness of 2 recently discovered proteins, Piezo1 and Piezo2, which assemble as transmembrane triskelions to combine exquisite force sensing with regulated calcium influx. There is emerging evidence for their importance in endothelial shear stress sensing and secretion, NO generation, vascular tone, angiogenesis, atherosclerosis, vascular permeability and remodeling, blood pressure regulation, insulin sensitivity, exercise performance, and baroreceptor reflex, and there are early suggestions of relevance to cardiac fibroblasts and myocytes. Human genetic analysis points to significance in lymphatic disease, anemia, varicose veins, and potentially heart failure, hypertension, aneurysms, and stroke. These channels appear to be versatile force sensors, used creatively to inform various force-sensing situations. We discuss emergent concepts and controversies and suggest that the potential for new important understanding is substantial.

Endothelial Cell Biomechanical Responses are Dependent on Both Fluid Shear Stress and Tensile Strain

Introduction

The goal of this study was to investigate how concurrent shear stress and tensile strain affect endothelial cell biomechanical responses.

Methods

Human coronary artery endothelial cells were exposed to concurrent pulsatile shear stress and cyclic tensile strain in a programmable shearing and stretching device. Three shear stress-tensile strain conditions were used: (1) pulsatile shear stress at 1 Pa and cyclic tensile strain at 7%, simulating normal stress/strain conditions in a healthy coronary artery; (2) shear stress at 3.7 Pa and tensile strain at 3%, simulating pathological stress/strain conditions near a stenosis; (3) shear stress at 0.7 Pa and tensile strain at 5%, simulating pathological stress/strain conditions in a recirculation zone. Cell morphology was quantified using immunofluorescence microscopy. Cell surface PECAM-1 phosphorylation, ICAM-1 expression, ERK1/2 and NF-κB activation were measured using ELISA or Western blot.

Results

Simultaneous stimulation from pulsatile shear stress and cyclic tensile strain induced a significant increase in cell area, compared to that induced by shear stress or tensile strain alone. The combined stimulation caused significant increases in PECAM-1 phosphorylation. The combined stimulation also significantly enhanced EC surface ICAM-1 expression (compared to that under shear stress alone) and transcriptional factor NF-κB activation (compared to that under control conditions).

Conclusion

Pulsatile shear stress and cyclic tensile strain could induce increased but not synergistic effect on endothelial cell morphology or activation. The combined mechanical stimulation can be relayed from cell membrane to nucleus. Therefore, to better understand how mechanical conditions affect endothelial cell mechanotransduction and cardiovascular disease development, both shear stress and tensile strain need to be considered.

Mechanosensitive ATP release in the lungs: New insights from real-time luminescence imaging studies

Extracellular ATP and other nucleotides are important autocrine/paracrine mediators that stimulate purinergic receptors and regulate diverse processes in the normal lungs. They are also associated with pathogenesis of a number of respiratory diseases and clinical complications including acute respiratory distress syndrome and ventilator induced lung injury. Mechanical forces are major stimuli for cellular ATP release but precise mechanisms responsible for this release are still debated. The present review intends to provide the current state of knowledge of the mechanisms of ATP release in the lung. Putative pathways of the release, including the contribution of cell membrane injury and cell lysis are discussed addressing their strength, weaknesses and missing evidence that requires future study. We also provide an overview of the recent technical advances in studying cellular ATP release in vitro and ex vivo. Special attention is given to new insights into lung ATP release obtained with the real-time luminescence ATP imaging. This includes recent data on stretch-induced mechanosensitive ATP release in a model and primary cells of lung alveoli in vitro as well as inflation-induced ATP release in airspaces and pulmonary blood vessels of lungs, ex vivo.