Potential of caveolae in the therapy of cardiovascular and neurological diseases

Spatiotemporal Characteristics Determining the Multifaceted Nature of Reactive Oxygen, Nitrogen, and Sulfur Species in Relation to Proton Homeostasis

Significance: Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) act as signaling molecules, regulating gene expression, enzyme activity, and physiological responses. However, excessive amounts of these molecular species can lead to deleterious effects, causing cellular damage and death. This dual nature of ROS, RNS, and RSS presents an intriguing conundrum that calls for a new paradigm. Recent Advances: Recent advancements in the study of photosynthesis have offered significant insights at the molecular level and with high temporal resolution into how the photosystem II oxygen-evolving complex manages to prevent harmful ROS production during the water-splitting process. These findings suggest that a dynamic spatiotemporal arrangement of redox reactions, coupled with strict regulation of proton transfer, is crucial for minimizing unnecessary ROS formation. Critical Issues: To better understand the multifaceted nature of these reactive molecular species in biology, it is worth considering a more holistic view that combines ecological and evolutionary perspectives on ROS, RNS, and RSS. By integrating spatiotemporal perspectives into global, cellular, and biochemical events, we discuss local pH or proton availability as a critical determinant associated with the generation and action of ROS, RNS, and RSS in biological systems. Future Directions: The concept of localized proton availability will not only help explain the multifaceted nature of these ubiquitous simple molecules in diverse systems but also provide a basis for new therapeutic strategies to manage and manipulate these reactive species in neural disorders, pathogenic diseases, and antiaging efforts.

Deciphering the relationship between caveolae-mediated intracellular transport and signalling events

The caveolae-mediated transport across polarized epithelial cell barriers has been largely deciphered in the last decades and is considered the second essential intracellular transfer mechanism, after the clathrin-dependent endocytosis. The basic cell biology knowledge was supplemented recently, with the molecular mechanisms beyond caveolae generation implying the key contribution of the lipid-binding proteins (the structural protein Caveolin and the adapter protein Cavin), along with the bulb coat stabilizing molecules PACSIN-2 and Eps15 homology domain protein-2. The current attention is focused also on caveolae architecture (such as the bulb coat, the neck, the membrane funnel inside the bulb, and the associated receptors), and their specific tasks during the intracellular transport of various cargoes. Here, we resume the present understanding of the assembly, detachment, and internalization of caveolae from the plasma membrane lipid raft domains, and give an updated view on transcytosis and endocytosis, the two itineraries of cargoes transport via caveolae. The review adds novel data on the signalling molecules regulating caveolae intracellular routes and on the transport dysregulation in diseases. The therapeutic possibilities offered by exploitation of Caveolin-1 expression and caveolae trafficking, and the urgent issues to be uncovered conclude the review.

Caveolin-1: A promising therapeutic target for diverse diseases

The plasma membrane of eukaryotic cells contains small flask-shaped invaginations known as caveolae that are involved in the regulation of cellular signaling. Caveolin-1 is a 21-24kDa protein localized in the caveolar membrane. Caveolin-1 (Cav-1) has been considered as a master regulator among the various signaling molecules. It has been emerging as a chief protein regulating cellular events associated with homeostasis, caveolae formation, and caveolae trafficking. In addition to the physiological role of cav-1, it has a complex role in the progression of various diseases. Caveolin-1 has been identified as a prognosticator in patients with cancer and has a dual role in tumorigenesis. The expression of Cav-1 in hippocampal neurons and synapses is related to neurodegeneration, cognitive decline, and aging. Despite the ubiquitous association of caveolin-1 in various pathological processes, the mechanisms associated with these events are still unclear. Caveolin-1 has a significant role in various events of the viral cycle, such as viral entry. This review will summarize the role of cav-1 in the development of cancer, neurodegeneration, glaucoma, cardiovascular diseases, and infectious diseases. The therapeutic perspectives involving clinical applications of Caveolin-1 have also been discussed. The understanding of the involvement of caveolin-1 in various diseased states provides insights into how it can be explored as a novel therapeutic target.

Differential barcoding of opioid receptors trafficking

Over the past several years, studies have highlighted the δ-opioid receptor (DOPr) as a promising therapeutic target for chronic pain management. While exhibiting milder undesired effects than most currently prescribed opioids, its specific agonists elicit effective analgesic responses in numerous animal models of chronic pain, including inflammatory, neuropathic, diabetic, and cancer-related pain. However, as compared with the extensively studied μ-opioid receptor, the molecular mechanisms governing its trafficking remain elusive. Recent advances have denoted several significant particularities in the regulation of DOPr intracellular routing, setting it apart from the other members of the opioid receptor family. Although they share high homology, each opioid receptor subtype displays specific amino acid patterns potentially involved in the regulation of its trafficking. These precise motifs or "barcodes" are selectively recognized by regulatory proteins and therefore dictate several aspects of the itinerary of a receptor, including its anterograde transport, internalization, recycling, and degradation. With a specific focus on the regulation of DOPr trafficking, this review will discuss previously reported, as well as potential novel trafficking barcodes within the opioid and nociceptin/orphanin FQ opioid peptide receptors, and their impact in determining distinct interactomes and physiological responses.

A Cell Membrane-Level Approach to Cicatricial Alopecia Management: Is Caveolin-1 a Viable Therapeutic Target in Frontal Fibrosing Alopecia?

Irreversible destruction of the hair follicle (HF) in primary cicatricial alopecia and its most common variant, frontal fibrosing alopecia (FFA), results from apoptosis and pathological epithelial-mesenchymal transition (EMT) of epithelial HF stem cells (eHFSCs), in conjunction with the collapse of bulge immune privilege (IP) and interferon-gamma-mediated chronic inflammation. The scaffolding protein caveolin-1 (Cav1) is a key component of specialized cell membrane microdomains (caveolae) that regulates multiple signaling events, and even though Cav1 is most prominently expressed in the bulge area of human scalp HFs, it has not been investigated in any cicatricial alopecia context. Interestingly, in mice, Cav1 is involved in the regulation of (1) key HF IP guardians (TGF-β and α-MSH signaling), (2) IP collapse inducers/markers (IFNγ, substance P and MICA), and (3) EMT. Therefore, we hypothesize that Cav1 may be an unrecognized, important player in the pathobiology of cicatricial alopecias, and particularly, in FFA, which is currently considered as the most common type of primary lymphocytic scarring alopecia in the world. We envision that localized therapeutic inhibition of Cav1 in management of FFA (by cholesterol depleting agents, i.e., cyclodextrins/statins), could inhibit and potentially reverse bulge IP collapse and pathological EMT. Moreover, manipulation of HF Cav1 expression/localization would not only be relevant for management of cicatricial alopecia, but FFA could also serve as a model disease for elucidating the role of Cav1 in other stem cell- and/or IP collapse-related pathologies.

Genetic and Proteomic Contributions to the Pathophysiology of Moyamoya Angiopathy and Related Vascular Diseases

Rationale

This literature review describes the pathophysiological mechanisms of the current classes of proteins, cells, genes, and signaling pathways relevant to moyamoya angiopathy (MA), along with future research directions and implementation of current knowledge in clinical practice.

Objective

This article is intended for physicians diagnosing, treating, and researching MA.

Methods and Results

References were identified using a PubMed/Medline systematic computerized search of the medical literature from January 1, 1957, through August 4, 2020, conducted by the authors, using the key words and various combinations of the key words “moyamoya disease,” “moyamoya syndrome,” “biomarker,” “proteome,” “genetics,” “stroke,” “angiogenesis,” “cerebral arteriopathy,” “pathophysiology,” and “etiology.” Relevant articles and supplemental basic science articles published in English were included. Intimal hyperplasia, medial thinning, irregular elastic lamina, and creation of moyamoya vessels are the end pathologies of many distinct molecular and genetic processes. Currently, 8 primary classes of proteins are implicated in the pathophysiology of MA: gene-mutation products, enzymes, growth factors, transcription factors, adhesion molecules, inflammatory/coagulation peptides, immune-related factors, and novel biomarker candidate proteins. We anticipate that this article will need to be updated in 5 years.

Conclusion

It is increasingly apparent that MA encompasses a variety of distinct pathophysiologic conditions. Continued research into biomarkers, genetics, and signaling pathways associated with MA will improve and refine our understanding of moyamoya’s complex pathophysiology. Future efforts will benefit from multicenter studies, family-based analyses, comparative trials, and close collaboration between the clinical setting and laboratory research.

The Old and New Visions of Biased Agonism Through the Prism of Adenosine Receptor Signaling and Receptor/Receptor and Receptor/Protein Interactions

Biased signaling is a concept that has arisen in the G protein-coupled receptor (GCPR) research field, and holds promise for the development of new drug development strategies. It consists of different signaling outputs depending on the agonist's chemical structure. Here we review the most accepted mechanisms for explaining biased agonism, namely the induced fit hypothesis and the key/lock hypothesis, but we also consider how bias can be produced by a given agonist. In fact, different signaling outputs may originate at a given receptor when activated by, for instance, the endogenous agonist. We take advantage of results obtained with adenosine receptors to explain how such mechanism of functional selectivity depends on the context, being receptor-receptor interactions (heteromerization) one of the most relevant and most studied mechanisms for mammalian homeostasis. Considering all the possible mechanisms underlying functional selectivity is essential to optimize the selection of biased agonists in the design of drugs targeting GPCRs.

Energy and Dynamics of Caveolae Trafficking

Caveolae are 70–100 nm diameter plasma membrane invaginations found in abundance in adipocytes, endothelial cells, myocytes, and fibroblasts. Their bulb-shaped membrane domain is characterized and formed by specific lipid binding proteins including Caveolins, Cavins, Pacsin2, and EHD2. Likewise, an enrichment of cholesterol and other lipids makes caveolae a distinct membrane environment that supports proteins involved in cell-type specific signaling pathways. Their ability to detach from the plasma membrane and move through the cytosol has been shown to be important for lipid trafficking and metabolism. Here, we review recent concepts in caveolae trafficking and dynamics. Second, we discuss how ATP and GTP-regulated proteins including dynamin and EHD2 control caveolae behavior. Throughout, we summarize the potential physiological and cell biological roles of caveolae internalization and trafficking and highlight open questions in the field and future directions for study.

The Role of Glycocalyx and Caveolae in Vascular Homeostasis and Diseases

This review highlights recent findings about the role that endothelial glycocalyx and caveolae play in vascular homeostasis. We describe the structure, synthesis, and function of glycocalyx and caveolae in vascular cells under physiological and pathophysiological conditions. Special focus will be given in glycocalyx and caveolae that are associated with impaired production of nitric oxide (NO) and generation of reactive oxygen species (ROS). Such alterations could contribute to the development of cardiovascular diseases, such as atherosclerosis, and hypertension.

LDL receptors, caveolae and cholesterol in endothelial dysfunction: oxLDLs accomplices or victims?

Oxidized LDLs (oxLDLs) and oxysterols play a key role in endothelial dysfunction and the development of atherosclerosis. The loss of vascular endothelium function negatively impacts vasomotion, cell growth, adhesiveness and barrier functions. While for some of these disturbances, a reasonable explanation can be provided from a mechanistic standpoint, for many others, the molecular mediators that are involved are unknown. Caveolae, specific plasma membrane domains, have recently emerged as targets and mediators of oxLDL-induced endothelial dysfunction. Caveolae and their associated protein caveolin-1 (Cav-1) are involved in oxLDLs/LDLs transcytosis, mainly through the scavenger receptor class B type 1 (SR-B1 or SCARB1). In contrast, oxLDLs endocytosis is mediated by the lectin-like oxidized LDL receptor 1 (LOX-1), whose activity depends on an intact caveolae system. In addition, LOX-1 regulates the expression of Cav-1 and vice versa. On the other hand, oxLDLs may affect cholesterol plasma membrane content/distribution thus influencing caveolae architecture, Cav-1 localization and the associated signalling. Overall, the evidence indicate that caveolae have both active and passive roles in oxLDL-induced endothelial cell dysfunction. First, as mediators of lipid uptake and transfer in the subendothelial space and, later, as targets of changes in composition/dynamics of plasma membrane lipids resulting from increased levels of circulating oxLDLs. Gaining a better understanding of how oxLDLs interact with endothelial cells and modulate caveolae-mediated signalling pathways, leading to endothelial dysfunction, is crucial to find new targets for intervention to tackle atherosclerosis and the related clinical entities. LINKED ARTICLES: This article is part of a themed issue on Oxysterols, Lifelong Health and Therapeutics. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.16/issuetoc.

Deciphering the roles of caveolin in neurodegenerative diseases: The good, the bad and the importance of context

Neurodegenerative diseases (NDDs), which contribute to progressive and irreversible impairments of both the structure and function of the nervous system, pose a substantial socioeconomic burden on society. Mitochondrial dysfunction, oxidative stress, membrane damage, DNA damage, and abnormal protein degradation pathways play pivotal roles in the etiology of NDDs. Recently, growing evidence has demonstrated that caveolins are important in the pathology of NDDs due to their cellular functions in signal transduction, endocytosis, transcytosis, cholesterol transport, and lipid homeostasis. Given the significance of caveolins, here we review the literature to clarify their molecular mechanisms and roles in NDDs. We first briefly introduce the general background on caveolins. Next, we focus on the various important functions of caveolins in the brain. Finally, we emphasize recent progress regarding caveolins, especially Cav-1, which exert both benefit and unfavorable effects in NDDs such as AD and PD. Collectively, the data presented here should advance the investigation of caveolins for the future development of innovative strategies for the treatment of NDDs.

Caveolin-1, Ring finger protein 213, and endothelial function in Moyamoya disease

BACKGROUND

Moyamoya disease is a unique cerebrovascular occlusive disease of unknown etiology. Ring finger protein 213 (RNF213) was identified as a susceptibility gene for Moyamoya disease in East Asian countries. However, the pathogenesis of Moyamoya disease remains unclear.

METHODS

We prospectively analyzed clinical data for 139 patients with Moyamoya disease (108 bilateral Moyamoya disease, 31 unilateral Moyamoya disease), 61 patients with intracranial atherosclerotic stroke, and 68 healthy subjects. We compared the genetic (RNF213 variant) and protein biomarkers for caveolae (caveolin-1), angiogenesis (vascular endothelial growth factor (VEGF) and receptor (VEGFR2), and antagonizing cytokine (endostatin)) and endothelial dysfunction (asymmetric dimethylarginine (ADMA), and nitric oxide and its metabolites (nitrite and nitrate)) between patients with Moyamoya disease and intracranial atherosclerotic stroke. We then performed path analysis to evaluate whether a certain protein biomarker mediates the association between genes and Moyamoya disease.

RESULTS

Caveolin-1 level was decreased in patients with Moyamoya disease and markedly decreased in RNF213 variant carriers. Circulating factors such as VEGF and VEGFR2 did not differ among the groups. Markers for endothelial dysfunction were significantly higher in patients with intracranial atherosclerotic stroke but normal in those with Moyamoya disease. Path analysis showed that the presence of the RNF213 variant was associated with caveolin-1 levels that could lead to Moyamoya disease. The level of combined marker of Moyamoya disease (caveolin-1) and intracranial atherosclerotic stroke (ADMA, an endothelial dysfunction marker) predicted Moyamoya disease with good sensitivity and specificity.

CONCLUSION

Our results suggest that Moyamoya disease is a caveolae disorder but is not related to endothelial dysfunction or dysregulation of circulating cytokines.

The Pathophysiology of Moyamoya Disease: An Update

Moyamoya disease (MMD) is a unique cerebrovascular disease characterized by the progressive stenosis of large intracranial arteries and a hazy network of basal collaterals called moyamoya vessels. Because the etiology of MMD is unknown, its diagnosis is based on characteristic angiographic findings. Re-vascularization techniques (e.g., bypass surgery) are used to restore perfusion, and are the primary treatment for MMD. There is no specific treatment to prevent MMD progression. This review summarizes the recent advances in MMD pathophysiology, including the genetic and circulating factors related to disease development. Genetic and environmental factors may play important roles in the development of the vascular stenosis and aberrant angiogenesis in complex ways. These factors include the related changes in circulating endothelial/smooth muscle progenitor cells, cytokines related to vascular remodeling and angiogenesis, and endothelium, such as caveolin which is a plasma membrane protein. With a better understanding of MMD pathophysiology, nonsurgical approaches targeting MMD pathogenesis may be available to stop or slow the progression of this disease. The possible strategies include targeting growth factors, retinoic acid, caveolin-1, and stem cells.

Lipid rafts: integrated platforms for vascular organization offering therapeutic opportunities

Research on the nanoscale membrane structures known as lipid rafts is relevant to the fields of cancer biology, inflammation and ischaemia. Lipid rafts recruit molecules critical to signalling and regulation of the invasion process in malignant cells, the leukocytes that provide immunity in inflammation and the endothelial cells that build blood and lymphatic vessels, as well as the patterning of neural networks. As angiogenesis is a common denominator, regulation of receptors and signalling molecules critical to angiogenesis is central to the design of new approaches aimed at reducing, promoting or normalizing the angiogenic process. The goal of this review is to highlight some of the key issues that indicate the involvement of endothelial cell lipid rafts at each step of so-called 'sprouting angiogenesis', from stimulation of the vascular endothelial growth factor to the choice of tip cells, activation of migratory and invasion pathways, recruitment of molecules that guide axons in vascular patterning and maturation of blood vessels. Finally, the review addresses opportunities for future studies to define how these lipid domains (and their constituents) may be manipulated to stimulate the so-called 'normalization' of vascular networks within tumors, and be identified as the main target, enabling the development of more efficient chemotherapeutics and cancer immunotherapies.