Caveolae are involved in mechanotransduction during pulmonary hypertension

Opposite changes in the expression of clathrin and caveolin-1 in normal and cancerous human prostate tissue: putative clathrin-mediated recycling of EGFR

Endocytosis, an important macromolecule uptake process in cells, is known to be dysregulated in cancer. Clathrin and caveolin-1 proteins play a major role in receptor-mediated endocytosis. We have used a quantitative, unbiased and semi-automated method to measure in situ protein expression of clathrin and caveolin-1 in cancerous and paired normal (cancer adjacent, non-cancerous) human prostate tissue. There was a significant (p < 0.0001) increase in the expression of clathrin in prostate cancer samples (N = 29, n = 91) compared to normal tissue (N = 29, n = 67) (N = number of patients, n = number of cores in tissue arrays). Conversely, there was a significant (p < 0.0001) decrease in expression of caveolin-1 in prostate cancer tissue compared to normal prostate tissue. The opposite change in expression of the two proteins was highly correlated to increasing cancer aggressiveness. There was also a concurrent increase in the expression of epidermal growth factor receptor (EGFR), a key receptor in carcinogenesis, with clathrin in prostate cancer tissue, indicating recycling of EGFR through clathrin-mediated endocytosis (CME). These results indicate that in prostate cancer, caveolin-1-mediated endocytosis (CavME) may be acting as a brake and increase in CME may facilitate tumorigenicity and aggressiveness of prostate cancer through recycling of EGFR. Changes in the expression of these proteins can also potentially be used as a biomarker for prostate cancer to aid in diagnosis and prognosis and clinical decision-making.

Mechanosensitivity in Pulmonary Circulation: Pathophysiological Relevance of Stretch-Activated Channels in Pulmonary Hypertension

A variety of cell types in pulmonary arteries (endothelial cells, fibroblasts, and smooth muscle cells) are continuously exposed to mechanical stimulations such as shear stress and pulsatile blood pressure, which are altered under conditions of pulmonary hypertension (PH). Most functions of such vascular cells (e.g., contraction, migration, proliferation, production of extracellular matrix proteins, etc.) depend on a key event, i.e., the increase in intracellular calcium concentration ([Ca²⁺]_i) which results from an influx of extracellular Ca²⁺ and/or a release of intracellular stored Ca²⁺. Calcium entry from the extracellular space is a major step in the elevation of [Ca²⁺]_i, involving a variety of plasmalemmal Ca²⁺ channels including the superfamily of stretch-activated channels (SAC). A common characteristic of SAC is that their gating depends on membrane stretch. In general, SAC are non-selective Ca²⁺-permeable cation channels, including proteins of the TRP (Transient Receptor Potential) and Piezo channel superfamily. As membrane mechano-transducers, SAC convert physical forces into biological signals and hence into a cell response. Consequently, SAC play a major role in pulmonary arterial calcium homeostasis and, thus, appear as potential novel drug targets for a better management of PH.

Electrophysiological and Molecular Mechanisms of Sinoatrial Node Mechanosensitivity

The understanding of the electrophysiological mechanisms that underlie mechanosensitivity of the sinoatrial node (SAN), the primary pacemaker of the heart, has been evolving over the past century. The heart is constantly exposed to a dynamic mechanical environment; as such, the SAN has numerous canonical and emerging mechanosensitive ion channels and signaling pathways that govern its ability to respond to both fast (within second or on beat-to-beat manner) and slow (minutes) timescales. This review summarizes the effects of mechanical loading on the SAN activity and reviews putative candidates, including fast mechanoactivated channels (Piezo, TREK, and BK) and slow mechanoresponsive ion channels [including volume-regulated chloride channels and transient receptor potential (TRP)], as well as the components of mechanochemical signal transduction, which may contribute to SAN mechanosensitivity. Furthermore, we examine the structural foundation for both mechano-electrical and mechanochemical signal transduction and discuss the role of specialized membrane nanodomains, namely, caveolae, in mechanical regulation of both membrane and calcium clock components of the so-called coupled-clock pacemaker system responsible for SAN automaticity. Finally, we emphasize how these mechanically activated changes contribute to the pathophysiology of SAN dysfunction and discuss controversial areas necessitating future investigations. Though the exact mechanisms of SAN mechanosensitivity are currently unknown, identification of such components, their impact into SAN pacemaking, and pathological remodeling may provide new therapeutic targets for the treatment of SAN dysfunction and associated rhythm abnormalities.

Upregulation of Piezo1 (Piezo Type Mechanosensitive Ion Channel Component 1) Enhances the Intracellular Free Calcium in Pulmonary Arterial Smooth Muscle Cells From Idiopathic Pulmonary Arterial Hypertension Patients

[Figure: see text].

Caveolae and lipid sorting: Shaping the cellular response to stress

Caveolae are an abundant and characteristic surface feature of many vertebrate cells. The uniform shape of caveolae is characterized by a bulb with consistent curvature connected to the plasma membrane (PM) by a neck region with opposing curvature. Caveolae act in mechanoprotection by flattening in response to increased membrane tension, and their disassembly influences the lipid organization of the PM. Here, we review evidence for caveolae as a specialized lipid domain and speculate on mechanisms that link changes in caveolar shape and/or protein composition to alterations in specific lipid species. We propose that high membrane curvature in specific regions of caveolae can enrich specific lipid species, with consequent changes in their localization upon caveolar flattening. In addition, we suggest how changes in the association of lipid-binding caveolar proteins upon flattening of caveolae could allow release of specific lipids into the bulk PM. We speculate that the caveolae-lipid system has evolved to function as a general stress-sensing and stress-protective membrane domain.

Caveolin1 Tyrosine-14 Phosphorylation: Role in Cellular Responsiveness to Mechanical Cues

The plasma membrane is a dynamic lipid bilayer that engages with the extracellular microenvironment and intracellular cytoskeleton. Caveolae are distinct plasma membrane invaginations lined by integral membrane proteins Caveolin1, 2, and 3. Caveolae formation and stability is further supported by additional proteins including Cavin1, EHD2, Pacsin2 and ROR1. The lipid composition of caveolar membranes, rich in cholesterol and phosphatidylserine, actively contributes to caveolae formation and function. Post-translational modifications of Cav1, including its phosphorylation of the tyrosine-14 residue (pY14Cav1) are vital to its function in and out of caveolae. Cells that experience significant mechanical stress are seen to have abundant caveolae. They play a vital role in regulating cellular signaling and endocytosis, which could further affect the abundance and distribution of caveolae at the PM, contributing to sensing and/or buffering mechanical stress. Changes in membrane tension in cells responding to multiple mechanical stimuli affects the organization and function of caveolae. These mechanical cues regulate pY14Cav1 levels and function in caveolae and focal adhesions. This review, along with looking at the mechanosensitive nature of caveolae, focuses on the role of pY14Cav1 in regulating cellular mechanotransduction.

Caveolin-1 in oncogenic metabolic symbiosis

Metabolic phenotypes of cancer cells are heterogeneous and flexible as a tumor mass is a hurriedly evolving system capable of constant adaptation to oxygen and nutrient availability. The exact type of cancer metabolism arises from the combined effects of factors intrinsic to the cancer cells and factors proposed by the tumor microenvironment. As a result, a condition termed oncogenic metabolic symbiosis in which components of the tumor microenvironment (TME) promote tumor growth often occurs. Understanding how oncogenic metabolic symbiosis emerges and evolves is crucial for perceiving tumorigenesis. The process by which tumor cells reprogram their TME involves many mechanisms, including changes in intercellular communication, alterations in metabolic phenotypes of TME cells, and rearrangement of the extracellular matrix. It is possible that one molecule with a pleiotropic effect such as Caveolin-1 may affect many of these pathways. Here, we discuss the significance of Caveolin-1 in establishing metabolic symbiosis in TME.

Stretch-activated Piezo1 Channel in Endothelial Cells Relaxes Mouse Intrapulmonary Arteries

In intrapulmonary arteries (IPA), endothelial cells (EC) respond to mechanical stimuli by releasing vasoactive factors to set the vascular tone. Piezo1, a stretch-activated, calcium-permeable channel, is a sensor of mechanical stress in EC. The present study was undertaken to investigate the implication of Piezo1 in the endothelium-dependent regulation of IPA tone and potential involvement of Piezo1 in pulmonary hypertension, the main disease of this circulation. IPA tone was quantified by means of a myograph in control Piezo1^+/+ mice and in mice lacking endothelial Piezo1 (EC-Piezo1^-/-). Endothelial intracellular calcium concentration ([Ca²⁺]_i) and nitric oxide (NO) production were measured, in mouse or human EC, with Fluo-4 or DAF-FM probe, respectively. Immunofluorescent labeling and patch-clamp experiments revealed the presence of Piezo1 channels in EC. Yoda1, a Piezo1 agonist, induced an endothelium-dependent relaxation that was significantly reduced in pulmonary arteries in EC-Piezo1^-/- compared with Piezo1^+/+ mice. Yoda1 as well as mechanical stimulation (by osmotic stress) increased [Ca²⁺]_i in mouse or human EC. Consequently, both stimuli increased the production of NO. NO and [Ca²⁺]_i increases were reduced in EC from Piezo1^-/- mice or in the presence of Piezo1 inhibitors. Furthermore, deletion of Piezo1 increased α-adrenergic agonist-mediated contraction. Finally, in chronically hypoxic mice, a model of pulmonary hypertension, Piezo1 still mediated arterial relaxation, and deletion of this channel did not impair the development of the disease. The present study thus demonstrates that endothelial Piezo1 contributes to intrapulmonary vascular relaxation by controlling endothelial [Ca²⁺]_i and NO production and that this effect is still present in pulmonary hypertension.

The Evolution of Cholesterol-Rich Membrane in Oxygen Adaption: The Respiratory System as a Model

The increase in atmospheric oxygen levels imposed significant environmental pressure on primitive organisms concerning intracellular oxygen concentration management. Evidence suggests the rise of cholesterol, a key molecule for cellular membrane organization, as a cellular strategy to restrain free oxygen diffusion under the new environmental conditions. During evolution and the increase in organismal complexity, cholesterol played a pivotal role in the establishment of novel and more complex functions associated with lipid membranes. Of these, caveolae, cholesterol-rich membrane domains, are signaling hubs that regulate important in situ functions. Evolution resulted in complex respiratory systems and molecular response mechanisms that ensure responses to critical events such as hypoxia facilitated oxygen diffusion and transport in complex organisms. Caveolae have been structurally and functionally associated with respiratory systems and oxygen diffusion control through their relationship with molecular response systems like hypoxia-inducible factors (HIF), and particularly as a membrane-localized oxygen sensor, controlling oxygen diffusion balanced with cellular physiological requirements. This review will focus on membrane adaptations that contribute to regulating oxygen in living systems.

Caveolae-Mediated Activation of Mechanosensitive Chloride Channels in Pulmonary Veins Triggers Atrial Arrhythmogenesis

Background

Atrial fibrillation often occurs in the setting of hypertension and associated atrial dilation with pathologically increased cardiomyocyte stretch. In the setting of atrial dilation, mechanoelectric feedback has been linked to the development of ectopic beats that trigger paroxysmal atrial fibrillation mainly originating from pulmonary veins (PVs). However, the precise mechanisms remain poorly understood.

Methods and Results

We identify mechanosensitive, swelling‐activated chloride ion channels (I_Cl,swell) as a crucial component of the caveolar mechanosensitive complex in rat and human cardiomyocytes. In vitro optical mapping of rat PV, single rat PV, and human cardiomyocyte patch clamp studies showed that stretch‐induced activation of I_Cl,swell leads to membrane depolarization and decreased action potential amplitude, which trigger conduction discontinuities and both ectopic and reentrant activities within the PV. Reverse transcription quantitative polymerase chain reaction, immunofluorescence, and coimmunoprecipitation studies showed that I_Cl,swell likely consists of at least 2 components produced by mechanosensitive ClC‐3 (chloride channel‐3) and SWELL1 (also known as LRRC8A [leucine rich repeat containing protein 8A]) chloride channels, which form a macromolecular complex with caveolar scaffolding protein Cav3 (caveolin 3). Downregulation of Cav3 protein expression and disruption of caveolae structures during chronic hypertension in spontaneously hypertensive rats facilitates activation of I_Cl,swell and increases PV sensitivity to stretch 10‐ to 50‐fold, promoting the development of atrial fibrillation.

Conclusions

Our findings identify caveolae‐mediated activation of mechanosensitive I_Cl,swell as a critical cause of PV ectopic beats that can initiate atrial arrhythmias including atrial fibrillation. This mechanism is exacerbated in the setting of chronically elevated blood pressures.

Mechanical Stretch Redefines Membrane Gαq-Calcium Signaling Complexes

Muscle cells are routinely subjected to mechanical stretch but the impact of stretch on the organization of membrane domains is unknown. In this study, we characterize the effect of stretch on GPCR-Gαq protein signaling. Activation of this pathway leads to an increase in intracellular calcium. In muscle cells, GPCR-Gαq signals are enhanced when these proteins are localized in caveolae membrane domains whose curved structure can flatten with stretch. When we statically stretch rat aortic smooth muscle A10 cells by 1-5%, cellular calcium appears unperturbed as indicated by a calcium indicator. However, when we activate the bradykinin type 2 receptor (B2R)/Gαq pathway, we observe a loss in calcium that appears to be mediated through perturbations in calcium-activated stretch receptors. In contrast, if we apply oscillating stretch, calcium levels are enhanced. We tested whether the observed changes in B2R-Gαq calcium signals were caused by stretch-induced disruption of caveolae using a combination of silencing RNA technology and growth conditions. We find that stretch changes the ability of monoclonal caveolin antibodies to bind caveolae indicating a change in configuration of the domains. This change is seen by the inability of cells to survive stretch cycles when the level of caveolae is significantly reduced. Our studies show that the effect of calcium signals by mechanical stretch is mediated by the type of stretch and the amount of caveolae.

In vitro gentamicin exposure alters caveolae protein profile in cochlear spiral ligament pericytes

Background

The aminoglycoside antibiotic gentamicin is an ototoxic drug and has been used experimentally to investigate cochlear damage induced by noise.We have investigated the changes in the protein profile associated with caveolae in gentamicin treated and untreated spiral ligament (SL) pericytes, specialized cells in the blood labyrinth barrier of the inner ear microvasculature. Pericytes from various microvascular beds express caveolae, protein and cholesterol rich microdomains, which can undergo endocytosis and transcytosis to transport small molecules in and out the cells. A different protein profile in transport-specialized caveolae may induce pathological changes affecting the integrity of the blood labyrinth barrier and ultimately contributing to hearing loss.

Method

Caveolae isolation from treated and untreated cells is achieved through ultracentrifugation of the lysates in discontinuous gradients. Mass spectrometry (LC-MS/MS) analysis identifies the proteins in the two groups. Proteins segregating with caveolae isolated from untreated SL pericytes are then compared to caveolae isolated from SL pericytes treated with the gentamicin for 24 h. Data are analyzed using bioinformatic tools.

Results

The caveolae proteome in gentamicin treated cells shows that 40% of total proteins are uniquely associated with caveolae during the treatment, and 15% of the proteins normally associated with caveolae in untreated cell are suppressed. Bioinformatic analysis of the data shows a decreased expression of proteins involved in genetic information processing, and an increase in proteins involved in metabolism, vesicular transport and signal transduction in gentamicin treated cells. Several Rab GTPases proteins, ubiquitous transporters, uniquely segregate with caveolae and are significantly enriched in gentamicin treated cells.

Conclusion

We report that gentamicin exposure modifies protein profile of caveolae from SL pericytes. We identified a pool of proteins which are uniquely segregating with caveolae during the treatment, mainly participating in metabolic and biosynthetic pathways, in transport pathways and in genetic information processing. Finally, we show for the first time proteins associated with caveolae SL pericytes linked to nonsyndromic hearing loss.

Mitochondrial dysfunction and pulmonary hypertension: cause, effect, or both

Pulmonary hypertension describes a heterogeneous disease defined by increased pulmonary artery pressures, and progressive increase in pulmonary vascular resistance due to pathologic remodeling of the pulmonary vasculature involving pulmonary endothelial cells, pericytes, and smooth muscle cells. This process occurs under various conditions, and although these populations vary, the clinical manifestations are the same: progressive dyspnea, increases in right ventricular (RV) afterload and dysfunction, RV-pulmonary artery uncoupling, and right-sided heart failure with systemic circulatory collapse. The overall estimated 5-yr survival rate is 72% in highly functioning patients, and as low as 28% for those presenting with advanced symptoms. Metabolic theories have been suggested as underlying the pathogenesis of pulmonary hypertension with growing evidence of the role of mitochondrial dysfunction involving the major proteins of the electron transport chain, redox-related enzymes, regulators of the proton gradient and calcium homeostasis, regulators of apoptosis, and mitophagy. There remain more studies needed to characterize mitochondrial dysfunction leading to impaired vascular relaxation, increase proliferation, and failure of regulatory mechanisms. The effects on endothelial cells and resulting interactions with their microenvironment remain uncharted territory for future discovery. Additionally, on the basis of observations that the "plexigenic lesions" of pulmonary hypertension resemble the unregulated proliferation of tumor cells, similarities between cancer pathobiology and pulmonary hypertension have been drawn, suggesting interactions between mitochondria and angiogenesis. Recently, mitochondria targeting has become feasible, which may yield new therapeutic strategies. We present a state-of-the-art review of the role of mitochondria in both the pathobiology of pulmonary hypertension and potential therapeutic targets in pulmonary vascular processes.

Mechanobiology and Vascular Remodeling: From Membrane to Nucleus

Vascular endothelial cells (ECs) and smooth muscle cells (VSMCs) are constantly exposed to hemodynamic forces in vivo, including flow shear stress and cyclic stretch caused by the blood flow. Numerous researches revealed that during various cardiovascular diseases such as atherosclerosis, hypertension, and vein graft, abnormal (pathological) mechanical forces play crucial roles in the dysfunction of ECs and VSMCs, which is the fundamental process during both vascular homeostasis and remodeling. Hemodynamic forces trigger several membrane molecules and structures, such as integrin, ion channel, primary cilia, etc., and induce the cascade reaction processes through complicated cellular signaling networks. Recent researches suggest that nuclear envelope proteins act as the functional homology of molecules on the membrane, are important mechanosensitive molecules which modulate chromatin location and gene transcription, and subsequently regulate cellular functions. However, the studies on the roles of nucleus in the mechanotransduction process are still at the beginning. Here, based on the recent researches, we focused on the nuclear envelope proteins and discussed the roles of pathological hemodynamic forces in vascular remodeling. It may provide new insight into understanding the molecular mechanism of vascular physiological homeostasis and pathophysiological remodeling and may help to develop hemodynamic-based strategies for the prevention and management of vascular diseases.

Mechanobiology in vascular remodeling

Vascular remodeling is a common pathological process in cardiovascular diseases and includes changes in cell proliferation, apoptosis and differentiation as well as vascular homeostasis. Mechanical stresses, such as shear stress and cyclic stretch, play an important role in vascular remodeling. Vascular cells can sense the mechanical factors through cell membrane proteins, cytoskeletons and nuclear envelope proteins to initiate mechanotransduction, which involves intercellular signaling, gene expression, and protein expression to result in functional regulations. Non-coding RNAs, including microRNAs and long non-coding RNAs, are involved in the regulation of vascular remodeling processes. Mechanotransduction triggers a cascade reaction process through a complicated signaling network in cells. High-throughput technologies in combination with functional studies targeting some key hubs and bridging nodes of the network can enable the prioritization of potential targets for subsequent investigations of clinical translation. Vascular mechanobiology, as a new frontier field of biomechanics, searches for principles of stress-growth in vasculature to elucidate how mechanical factors induce biological effects that lead to vascular remodeling, with the goal of understanding the mechanical basis of the pathological mechanism of cardiovascular diseases at the cellular and molecular levels. Vascular mechanobiology will play a unique role in solving the key scientific problems of human physiology and disease, as well as generating important theoretical and clinical results.

Ion channels of the lung and their role in disease pathogenesis

Maintenance of normal epithelial ion and water transport in the lungs includes providing a thin layer of surface liquid that coats the conducting airways. This airway surface liquid is critical for normal lung function in a number of ways but, perhaps most importantly, is required for normal mucociliary clearance and bacterial removal. Preservation of the appropriate level of hydration, pH, and viscosity for the airway surface liquid requires the proper regulation and function of a battery of different types of ion channels and transporters. Here we discuss how alterations in ion channel/transporter function often lead to lung pathologies.

Nitric oxide and hydrogen sulfide: the gasotransmitter paradigm of the vascular system

There are several reviews on NO and hydrogen sulfide (H₂ S) and their role in vascular diseases in the current relevant literature. The aim of this review is to discuss, within the limits of present knowledge, the interconnection between these two gasotransmitters in vascular function. In particular, the review focuses on the role played by the balance between the NO and H₂ S pathways in either physiological or pathological conditions. The distinction between physiology and pathology has been made in order to dissect the molecular basis of this crosstalk, highlighting how and if this balance varies, depending upon the vascular status. Perspectives and possible novel therapeutic approaches are also discussed.

LINKED ARTICLES

This article is part of a themed section on Targeting Inflammation to Reduce Cardiovascular Disease Risk. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.22/issuetoc and http://onlinelibrary.wiley.com/doi/10.1111/bcp.v82.4/issuetoc.