ZFYVE21 promotes endothelial nitric oxide signaling and vascular barrier function in the kidney during aging

ZFYVE21 is an ancient, endosome-associated protein that is highly expressed in endothelial cells (ECs) but whose function(s) in vivo are undefined. Here, we identified ZFYVE21 as an essential regulator of vascular barrier function in the aging kidney. ZFYVE21 levels significantly decline in ECs in aged human and mouse kidneys. To investigate attendant effects, we generated EC-specific Zfyve21-/- reporter mice. These knockout mice developed accelerated aging phenotypes including reduced endothelial nitric oxide (ENOS) activity, failure to thrive, and kidney insufficiency. Kidneys from Zfyve21 EC-/- mice showed interstitial edema and glomerular EC injury. ZFYVE21-mediated phenotypes were not programmed developmentally as loss of ZFYVE21 in ECs during adulthood phenocopied its loss prenatally, and a nitric oxide donor normalized kidney function in adult hosts. Using live cell imaging and human kidney organ cultures, we found that in a GTPase Rab5- and protein kinase Akt-dependent manner, ZFYVE21 reduced vesicular levels of inhibitory caveolin-1 and promoted transfer of Golgi-derived ENOS to a perinuclear Rab5+ vesicular population to functionally sustain ENOS activity. Thus, our work defines a ZFYVE21- mediated trafficking mechanism sustaining ENOS activity and demonstrates the relevance of this pathway for maintaining kidney function with aging.

Hitting the Sweet Spot: How Glucose Metabolism Is Orchestrated in Space and Time by Phosphofructokinase-1

Glycolysis is the central metabolic pathway across all kingdoms of life. Intensive research efforts have been devoted to understanding the tightly orchestrated processes of converting glucose into energy in health and disease. Our review highlights the advances in knowledge of how metabolic and gene networks are integrated through the precise spatiotemporal compartmentalization of rate-limiting enzymes. We provide an overview of technically innovative approaches that have been applied to study phosphofructokinase-1 (PFK1), which represents the fate-determining step of oxidative glucose metabolism. Specifically, we discuss fast-acting chemical biology and optogenetic tools that have delineated new links between metabolite fluxes and transcriptional reprogramming, which operate together to enact tissue-specific processes. Finally, we discuss how recent paradigm-shifting insights into the fundamental basis of glycolytic regulatory control have shed light on the mechanisms of tumorigenesis and could provide insight into new therapeutic vulnerabilities in cancer.

Caveolae-mediated endocytosis pathway regulates endothelial fenestra homeostasis in the rat pituitary

Endothelial fenestrae are transcellular pores separated by diaphragms formed by plasmalemma vesicle-associated proteins (PLVAP) and function as channels for peptide hormones and other substances. Caveola, a key regulator of clathrin-independent endocytosis, may be involved in the invagination and fusion of plasma membranes, which are essential for fenestra formation. In this study, we first found that caveolin-1 and -2, the major components of caveolae, was localized in fenestrated endothelial cells in the anterior lobe of the rat pituitary by immunohistochemistry. As we also observed caveolae in the endothelial cells of the anterior lobe of the rat pituitary by transmission electron microscopy, we studied the relationship between the caveolae-mediated endocytosis pathway and fenestrae structure in cultured endothelial cells isolated from the anterior lobe of the rat pituitary (CECAL) by immunofluorescence staining and scanning electron microscopy. The inhibition of caveolae-mediated endocytosis by genistein enlarged the PLVAP-positive oval-shaped structure that represented the sieve plate and induced the formation of a doughnut-shaped bulge around the fenestra in CECAL. In contrast, the acceleration of caveolae-mediated endocytosis by okadaic acid induced the diffusion of PLVAP-positive signals in the cytoplasm and reduced the number of fenestrae in CECAL. These results indicate that the caveolae-mediated endocytosis pathway is involved in the fenestra homeostasis in the fenestrated endothelial cells of the rat pituitary.

Structural analysis of the P132L disease mutation in caveolin-1 reveals its role in the assembly of oligomeric complexes

Caveolin-1 (CAV1) is a membrane-sculpting protein that oligomerizes to generate flask-shaped invaginations of the plasma membrane known as caveolae. Mutations in CAV1 have been linked to multiple diseases in humans. Such mutations often interfere with oligomerization and the intracellular trafficking processes required for successful caveolae assembly, but the molecular mechanisms underlying these defects have not been structurally explained. Here, we investigate how a disease-associated mutation in one of the most highly conserved residues in CAV1, P132L, affects CAV1 structure and oligomerization. We show that P132 is positioned at a major site of protomer-protomer interactions within the CAV1 complex, providing a structural explanation for why the mutant protein fails to homo-oligomerize correctly. Using a combination of computational, structural, biochemical, and cell biological approaches, we find that despite its homo-oligomerization defects P132L is capable of forming mixed hetero-oligomeric complexes with WT CAV1 and that these complexes can be incorporated into caveolae. These findings provide insights into the fundamental mechanisms that control the formation of homo- and hetero-oligomers of caveolins that are essential for caveolae biogenesis, as well as how these processes are disrupted in human disease.

Arterial myogenic response and aging

The arterial myogenic response is an inherent property of resistance arteries. Myogenic tone is crucial for maintaining a relatively constant blood flow in response to changes in intraluminal pressure and protects delicate organs from excessive blood flow. Although this fundamental physiological phenomenon has been extensively studied, the underlying molecular mechanisms are largely unknown. Recent studies identified a crucial role of mechano-activated angiotensin II type 1 receptors (AT1R) in this process. The development of myogenic response is affected by aging. In this review, we summarize recent progress made to understand the role of AT1R and other mechanosensors in the control of arterial myogenic response. We discuss age-related alterations in myogenic response and possible underlying mechanisms and implications for healthy aging.

Emerging Insights into the Molecular Architecture of Caveolin-1

Caveolins are an unusual family of membrane proteins whose primary biological function is to build small invaginated membrane structures at the surface of cells known as caveolae. Caveolins and caveolae regulate numerous signaling pathways, lipid homeostasis, intracellular transport, cell adhesion, and cell migration. They also serve as sensors and protect the plasma membrane from mechanical stress. Despite their many important functions, the molecular basis for how these 50-100 nm "little caves" are assembled and regulate cell physiology has perplexed researchers for 70 years. One major impediment to progress has been the lack of information about the structure of caveolin complexes that serve as building blocks for the assembly of caveolae. Excitingly, recent advances have finally begun to shed light on this long-standing question. In this review, we highlight new developments in our understanding of the structure of caveolin oligomers, including the landmark discovery of the molecular architecture of caveolin-1 complexes using cryo-electron microscopy.

Caveolar disruption with methyl-β-cyclodextrin causes endothelium-dependent contractions in Wistar rat carotid arteries

Caveolae are organizing centers for cellular signal transduction in endothelial cells (ED) and smooth muscle cells (SMCs) in the blood vessels. Myography was used to investigate the effects of a caveolar disruption using methyl-β-cyclodextrin (MBCD) on maxi-K channels in rat carotid arteries. Incubation of carotid segments with MBCD augmented contractions in response to BaK (chemical channel agonist) but not those induced by depolarizing high potassium physiological saline (KPSS). In contrast, incubation with cholesterol-saturated MBCD (Ch-MBCD) abolished the effects of MBCD. Mechanical removal of endothelial cells by MBCD triggered a small contraction in response to BaK. Incubation with nitroarginine methyl ester (L-NAME) inhibited nitric oxide (NO) release, causing increased contractions in response to BaK, and this effect was reversed by pretreatment with MBCD. These results suggest that MBCD inhibits endothelial NO release. Contrastingly, inhibition of maxi-K channels with iberiotoxin enhanced contractions in response to BaK. Likewise, L-NAME decreased the contractile effect of iberiotoxin, as in the ED-denuded arteries. Transmission electron microscopy (TEM) showed the presence and absence of caveolae in intact blood vessels before and after MBCD treatment, respectively, whereas histology confirmed ED removal after the treatment. Caveolar disruption using MBCD impairs ED-dependent relaxation by inhibiting the release of NO from the ED and altered the contractility of SMCs independent of the ED due to reduced contribution of maxi-K channels to the SMC membrane potential, causing depolarization and increasing carotid artery contraction. These findings might help to understand the physiological role of the maxi-K channels in rat carotid arteries.

A review of genetically-driven rodent models of pulmonary hypertension

An increasing number of models used to examine the role of particular signaling pathways in vasculature and the development of pulmonary hypertension (PH) are based on animals with different genetic modifications. The present study explores the severity of PH-related lesions that can be provided by a genetic particular model in accordance to the most common non-genetic PH inducers such as chronic exposure to hypoxia or single injection of monocrotaline. A review of 516 interventions on a variety of animal models was performed. It examined the advantages of various genetically-driven procedures intended to develop spontaneous PH, and the effects of combining such procedures with common PH models or other stimuli ('second-hit') with the aim of exacerbating pulmonary artery remodeling, right ventricle hypertrophy and hemodynamics or animal mortality. A wide range of genetically-modified rodents are used for pre-clinical studies on PH, with different response to the genetic modification as compared to the most common non-genetic stimuli. Nevertheless, they could highlight the mechanisms and pathways that contribute to the expression of pathophysiological features of the disease, and they could be helpful in the identification of additional targets for new drugs.

EHD2 modulates Dll4 endocytosis during blood vessel development

OBJECTIVE

Despite the absolute requirement of Delta/Notch signaling to activate lateral inhibition during early blood vessel development, many mechanisms remain unclear about how this system is regulated. Our objective was to determine the involvement of Epsin 15 Homology Domain Containing 2 (EHD2) in delta-like ligand 4 (Dll4) endocytosis during Notch activation.

APPROACH AND RESULTS

Using both in vivo and in vitro models, we demonstrate that EHD2 is a novel modulator of Notch activation in endothelial cells through controlling endocytosis of Dll4. In vitro, EHD2 localized to plasma membrane-bound Dll4 and caveolae. Chemical disruption of caveolae complexes resulted in EHD2 failing to organize around Dll4 as well as loss of Dll4 internalization. Reduced Dll4 internalization blunted Notch activation in endothelial cells. In vivo, EHD2 is primarily expressed in the vasculature, colocalizing with junctional marker VE-cadherin and Dll4. Knockout of EHD2 in zebrafish produced a significant increase in dysmorphic sprouts in zebrafish intersomitic vessels during development and a reduction in downstream Notch signaling.

CONCLUSIONS

Overall, we demonstrate that EHD2 is necessary for Dll4 transcytosis and downstream Notch activation.

Generalized lipoatrophy syndromes

Generalized lipodystrophy (GL) syndromes are a group of rare heterogenous disorders, characterized by total subcutaneous fat loss. The frequency of GL is currently assessed as approximately 0,23 cases per million of the population, in Europe - as 0,96 cases per million of the population. They can be congenital (CGL) or acquired (AGL) depending on the etiology and the time of the onset of fat loss. Both CGL and AGL are often associated with different metabolic complications, such as hypertriglyceridemia, insulin resistance and lipoatrophic diabetes mellitus, metabolically associated FLD, arterial hypertension, proteinuria, reproductive system disorders. In this review we aimed to summarize the information on all forms of generalized lipodystrophy, especially the ones of genetic etiology, their clinical manifestations and complications, the perspectives for diagnostics, treatment and further research.

Endothelial Cell Receptors in Tissue Lipid Uptake and Metabolism

Lipid uptake and metabolism are central to the function of organs such as heart, skeletal muscle, and adipose tissue. Although most heart energy derives from fatty acids (FAs), excess lipid accumulation can cause cardiomyopathy. Similarly, high delivery of cholesterol can initiate coronary artery atherosclerosis. Hearts and arteries-unlike liver and adrenals-have nonfenestrated capillaries and lipid accumulation in both health and disease requires lipid movement from the circulation across the endothelial barrier. This review summarizes recent in vitro and in vivo findings on the importance of endothelial cell receptors and uptake pathways in regulating FAs and cholesterol uptake in normal physiology and cardiovascular disease. We highlight clinical and experimental data on the roles of ECs in lipid supply to tissues, heart, and arterial wall in particular, and how this affects organ metabolism and function. Models of FA uptake into ECs suggest that receptor-mediated uptake predominates at low FA concentrations, such as during fasting, whereas FA uptake during lipolysis of chylomicrons may involve paracellular movement. Similarly, in the setting of an intact arterial endothelial layer, recent and historic data support a role for receptor-mediated processes in the movement of lipoproteins into the subarterial space. We conclude with thoughts on the need to better understand endothelial lipid transfer for fuller comprehension of the pathophysiology of hyperlipidemia, and lipotoxic diseases such as some forms of cardiomyopathy and atherosclerosis.

Eating behaviour in contrasting adiposity phenotypes: Monogenic obesity and congenital generalized lipodystrophy

Most known types of nonsyndromic monogenic obesity are caused by rare mutations in genes of the leptin-melanocortin pathway controlling appetite and adiposity. In contrast, congenital generalized lipodystrophy represents the most extreme form of leanness in humans caused by recessive mutations in four genes involved in phospholipid/triglyceride synthesis and lipid droplet/caveolae structure. In this disease, the inability to store triglyceride in adipocytes results in hypoleptinemia and ectopic hepatic and muscle fat accumulation leading to fatty liver, hypertriglyceridemia and severe insulin resistance. As a result of hypoleptinemia, patients with lipodystrophy show alterations in eating behaviour characterized by constant increased energy intake. As it occurs in obesity caused by genetic leptin deficiency, exogenous leptin rapidly reduces hunger scores in patients with congenital generalized lipodystrophy, with additional beneficial effects on glucose homeostasis and metabolic profile normalization. The melanocortin-4 receptor agonist setmelanotide has been used in the treatment of monogenic obesities. There is only one report on the effect of setmelanotide in a patient with partial lipodystrophy resulting in mild reductions in hunger scores, with no improvements in metabolic status. The assessment of contrasting phenotypes of obesity/leanness represents an adequate strategy to understand the pathophysiology and altered eating behaviour associated with adipose tissue excessive accumulation/paucity.

Cavin3 Suppresses Breast Cancer Metastasis via Inhibiting AKT Pathway

Objective

Cavin3 is a putative tumor suppressor protein. However, its molecular action on tumor regulation is largely unknown. The aim of the current study is to explore the implication of cavin3 alteration, its clinical significance, and any potential molecular mechanisms in the regulation of breast cancer (BC).

Methods

TCGA (The Cancer Genome Atlas) and GTEx (Genotype-Tissue Expression) data bases, and 17 freshly paired BC and adjacent normal tissues were analyzed for mRNA levels of Cavin3. Furthermore, cavin3 protein expression from 407 primary BC samples were assessed by immunohistochemistry (IHC) and measured by H-score. The clinical significance of cavin3 expression was explored by Kaplan-Meier analysis and the Cox regression method. In vitro biological assays were performed to elucidate the function and underlying mechanisms of cavin 3 in BC cell lines.

Results

Cavin3 mRNA was dramatically down-regulated in BC compared with the negative control. The median H-score of cavin3 protein by IHC was 50 (range 0-270). There were 232 (57%) and 175 (43%) cases scored as low (H-score≤50) and high (H-score >50) levels of cavin3, respectively. Low cavin3 was correlated with a higher T and N stage, and worse distant metastasis-free survival (DMFS) and overall survival (OS). Multivariate survival analysis revealed low cavin3 was an independent fact for worse DMFS. In BC cells, an overexpression of cavin3 could inhibit cell migration and invasion, and significantly decreased the level of p-Akt. Knockout of cavin3, meanwhile, promoted cell invasion ability and increased the level of p-AKT.

Conclusion

Cavin3 expression is significantly lower in BC and is correlated with distant metastasis and worse survival. Cavin3 functions as a metastasis suppressor via inhibiting the AKT pathway, suggesting cavin3 as a potential prognostic biomarker and a target for BC treatment.

Expression of a Human Caveolin-1 Mutation in Mice Drives Inflammatory and Metabolic Defect-Associated Pulmonary Arterial Hypertension

Background: In 2012, mutations in Cav1 were found to be the driving mutation in several cases of heritable pulmonary arterial hypertension (PAH). These mutations replaced the last 21 amino acids of Cav1 with a novel 22-amino-acid sequence. Because previously only Cav1 knockouts had been studied in the context of PAH, examining the in vivo effects of this novel mutation holds promise for new understanding of the role of Cav1 in disease etiology.

Methods: The new 22 amino acids created by the human mutation were knocked into the native mouse Cav1 locus. The mice underwent hemodynamic, energy balance, and inflammatory measurements, both at baseline and after being stressed with either a metabolic or an inflammatory challenge [low-dose lipopolysaccharide (LPS)]. To metabolically challenge the mice, they were injected with streptozotocin (STZ) and fed a high-fat diet for 12 weeks.

Results: Very little mutant protein was found in vivo (roughly 2% of wild-type by mass spectrometry), probably because of degradation after failure to traffic from the endoplasmic reticulum. The homozygous mutants developed a mild, low-penetrance PAH similar to that described previously in knockouts, and neither baseline nor metabolic nor inflammatory stress resulted in pressures above normal in heterozygous animals. The homozygous mutants had increased lean mass and worsened oral glucose tolerance, as previously described in knockouts. Novel findings include the preservation of Cav2 and accessory proteins in the liver and the kidney, while they are lost with homozygous Cav1 mutation in the lungs. We also found that the homozygous mutants had a significantly lower tolerance to voluntary spontaneous exercise than the wild-type mice, with the heterozygous mice at an intermediate level. The mutants also had higher circulating monocytes, with both heterozygous and homozygous animals having higher pulmonary MCP1 and MCP5 proteins. The heterozygous animals also lost weight at an LPS challenge level at which the wild-type mice continued to gain weight.

Conclusions: The Cav1 mutation identified in human patients in 2012 is molecularly similar to a knockout of Cav1. It results in not only metabolic deficiencies and mild pulmonary hypertension, as expected, but also an inflammatory phenotype and reduced spontaneous exercise.

Estrogen Induces Selective Transcription of Caveolin1 Variants in Human Breast Cancer through Estrogen Responsive Element-Dependent Mechanisms

The estrogen receptor (ER) signaling regulates numerous physiological processes mainly through activation of gene transcription (genomic pathways). Caveolin1 (CAV1) is a membrane-resident protein that behaves as platform to enable different signaling molecules and receptors for membrane-initiated pathways. CAV1 directly interacts with ERs and allows their localization on membrane with consequent activation of ER-non-genomic pathways. Loss of CAV1 function is a common feature of different types of cancers, including breast cancer. Two protein isoforms, CAV1α and CAV1β, derived from two alternative translation initiation sites, are commonly described for this gene. However, the exact transcriptional regulation underlying CAV1 expression pattern is poorly elucidated. In this study, we dissect the molecular mechanism involved in selective expression of CAV1β isoform, induced by estrogens and downregulated in breast cancer. Luciferase assays and Chromatin immunoprecipitation demonstrate that transcriptional activation is triggered by estrogen-responsive elements embedded in CAV1 intragenic regions and DNA-binding of estrogen-ER complexes. This regulatory control is dynamically established by local chromatin changes, as proved by the occurrence of histone H3 methylation/demethylation events and association of modifier proteins as well as modification of H3 acetylation status. Thus, we demonstrate for the first time, an estrogen-ERs-dependent regulatory circuit sustaining selective CAV1β expression.

Host Lipid Rafts as the Gates for Listeria monocytogenes Infection: A Mini-Review

Listeria monocytogenes is a Gram-positive foodborne bacterial pathogen capable of interacting and crossing the intestinal barrier, blood–brain barrier, and placental barrier to cause deadly infection with high mortality. L. monocytogenes is an intracellular pathogen characterized by its ability to enter non-phagocytic cells. Expression of the cytolysin listeriolysin O has been shown to be the main virulence determinant in vitro and in vivo in mouse models. L. monocytogenes can also perform cell-to-cell spreading using actin-rich membrane protrusions to infect neighboring cells, which also constitutes an important strategy for infection. These events including entry into host cells, interaction between listeriolysin O and host plasma membrane, and bacterial cell-to-cell spreading have been demonstrated to implicate the cholesterol-rich lipid rafts or molecules in these microdomains in the host plasma membrane in vitro with tissue culture models. Here we review the contribution of lipid rafts on plasma membrane to L. monocytogenes infection.

Genotype-phenotype correlations of Berardinelli-Seip congenital lipodystrophy and novel candidate genes prediction

BACKGROUND

Berardinelli-Seip congenital lipodystrophy (BSCL) is a heterogeneous autosomal recessive disorder characterized by an almost total lack of adipose tissue in the body. Mutations in the AGPAT2, BSCL2, CAV1 and PTRF genes define I-IV subtype of BSLC respectively and clinical data indicate that new causative genes remain to be discovered. Here, we retrieved 341 cases from 60 BSCL-related studies worldwide and aimed to explore genotype-phenotype correlations based on mutations of AGPAT2 and BSCL2 genes from 251 cases. We also inferred new candidate genes for BSCL through protein-protein interaction and phenotype-similarity.

RESULTS

Analysis results show that BSCL type II with earlier age of onset of diabetes mellitus, higher risk to suffer from premature death and mental retardation, is a more severe disorder than BSCL type I, but BSCL type I patients are more likely to have bone cysts. In BSCL type I, females are at higher risk of developing diabetes mellitus and acanthosis nigricans than males, while in BSCL type II, males suffer from diabetes mellitus earlier than females. In addition, some significant correlations among BSCL-related phenotypes were identified. New candidate genes prediction through protein-protein interaction and phenotype-similarity was conducted and we found that CAV3, EBP, SNAP29, HK1, CHRM3, OBSL1 and DNAJC13 genes could be the pathogenic factors for BSCL. Particularly, CAV3 and EBP could be high-priority candidate genes contributing to pathogenesis of BSCL.

CONCLUSIONS

Our study largely enhances the current knowledge of phenotypic and genotypic heterogeneity of BSCL and promotes the more comprehensive understanding of pathogenic mechanisms for BSCL.

Caveolin-1 gene therapy inhibits inflammasome activation to protect from bleomycin-induced pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a devastating and fatal disease and characterized by increased deposition of extracellular matrix proteins and scar formation in the lung, resulting from alveolar epithelial damage and accumulation of inflammatory cells. Evidence suggests that Caveolin-1 (Cav-1), a major component of caveolae which regulates cell signaling and endocytosis, is a potential target to treat fibrotic diseases, although the mechanisms and responsible cell types are unclear. We show that Cav-1 expression was downregulated both in alveolar epithelial type I cells in bleomycin-injured mouse lungs and in lung sections from IPF patients. Increased expression of IL-1β and caspase-1 has been observed in IPF patients, indicating inflammasome activation associated with IPF. Gene transfer of a plasmid expressing Cav-1 using transthoracic electroporation reduced infiltration of neutrophils and monocytes/macrophages and protected from subsequent bleomycin-induced pulmonary fibrosis. Overexpression of Cav-1 suppressed bleomycin- or silica-induced activation of caspase-1 and maturation of pro-IL-1β to secrete cleaved IL-1β both in mouse lungs and in primary type I cells. These results demonstrate that gene transfer of Cav-1 downregulates inflammasome activity and protects from subsequent bleomycin-mediated pulmonary fibrosis. This indicates a pivotal regulation of Cav-1 in inflammasome activity and suggests a novel therapeutic strategy for patients with IPF.

Transforming Growth Factor-β Receptor Internalization via Caveolae Is Regulated by Tubulin-β2 and Tubulin-β3 during Endothelial-Mesenchymal Transition

Fibrotic disorders, which are caused by long-term inflammation, are observed in numerous organs. These disorders are regulated mainly through transforming growth factor (TGF)-β family proteins by a fundamental cellular mechanism, known as the endothelial-mesenchymal transition. Therefore, there is a pressing need to identify the mechanisms and potential therapeutic targets that enable the inhibition of endothelial transdifferentiation. This study is the first to demonstrate that glycosylation of tubulin-β2 and tubulin-β3 in microtubules enhances sensitivity to TGF-β1 stimulation in human microvascular endothelial cells. We observed that the microtubules enriched in glycosylated tubulin-β2 and tubulin-β3 were necessary for caveolae-dependent TGF-β receptor internalization. Post-translational modulation is critical for the generation of myofibroblasts through endothelial-mesenchymal transition during fibrosis development. We suggest that microtubule glycosylation may become the target of new effective therapies for patients with recognized fibrotic diseases.

Targeting the Mitochondrial Potassium Channel Kv1.3 to Kill Cancer Cells: Drugs, Strategies, and New Perspectives

Cancer is the consequence of aberrations in cell growth or cell death. In this scenario, mitochondria and ion channels play a critical role in regard to cell proliferation, malignant angiogenesis, migration, and metastasis. In this review, we focus on Kv1.3 and specifically on mitoKv1.3, which showed an aberrant expression in cancer cells compared with healthy tissues and which is involved in the apoptotic pathway. In recent years, mitoKv1.3 has become an oncological target since its pharmacological modulation has been demonstrated to reduce tumor growth and progression both in vitro and in vivo using preclinical mouse models of different types of tumors.

Interaction Between Pannexin 1 and Caveolin-1 in Smooth Muscle Can Regulate Blood Pressure

Objective- Sympathetic nerve innervation of vascular smooth muscle cells (VSMCs) is a major regulator of arteriolar vasoconstriction, vascular resistance, and blood pressure. Importantly, α-adrenergic receptor stimulation, which uniquely couples with Panx1 (pannexin 1) channel-mediated ATP release in resistance arteries, also requires localization to membrane caveolae. Here, we test whether localization of Panx1 to Cav1 (caveolin-1) promotes channel function (stimulus-dependent ATP release and adrenergic vasoconstriction) and is important for blood pressure homeostasis. Approach and Results- We use in vitro VSMC culture models, ex vivo resistance arteries, and a novel inducible VSMC-specific Cav1 knockout mouse to probe interactions between Panx1 and Cav1. We report that Panx1 and Cav1 colocalized on the VSMC plasma membrane of resistance arteries near sympathetic nerves in an adrenergic stimulus-dependent manner. Genetic deletion of Cav1 significantly blunts adrenergic-stimulated ATP release and vasoconstriction, with no direct influence on endothelium-dependent vasodilation or cardiac function. A significant reduction in mean arterial pressure (total=4 mm Hg; night=7 mm Hg) occurred in mice deficient for VSMC Cav1. These animals were resistant to further blood pressure lowering using a Panx1 peptide inhibitor Px1IL2P, which targets an intracellular loop region necessary for channel function. Conclusions- Translocalization of Panx1 to Cav1-enriched caveolae in VSMCs augments the release of purinergic stimuli necessary for proper adrenergic-mediated vasoconstriction and blood pressure homeostasis.

A disease-associated frameshift mutation in caveolin-1 disrupts caveolae formation and function through introduction of a de novo ER retention signal

Heterozygous mutations in caveolin-1 (CAV1) have been linked to pulmonary arterial hypertension (PAH), but their impact on caveolae is unclear. We show that a PAH-associated frameshift mutation introduces an endoplasmic reticulum retention signal in CAV1 that partially disrupts caveolae assembly and interferes with their ability to serve as membrane buffers.

Caveolin-1 (CAV1) is an essential component of caveolae and is implicated in numerous physiological processes. Recent studies have identified heterozygous mutations in the CAV1 gene in patients with pulmonary arterial hypertension (PAH), but the mechanisms by which these mutations impact caveolae assembly and contribute to disease remain unclear. To address this question, we examined the consequences of a familial PAH-associated frameshift mutation in CAV1, P158PfsX22, on caveolae assembly and function. We show that C-terminus of the CAV1 P158 protein contains a functional ER-retention signal that inhibits ER exit and caveolae formation and accelerates CAV1 turnover in Cav1^–/– MEFs. Moreover, when coexpressed with wild-type (WT) CAV1 in Cav1^–/– MEFs, CAV1-P158 functions as a dominant negative by partially disrupting WT CAV1 trafficking. In patient skin fibroblasts, CAV1 and caveolar accessory protein levels are reduced, fewer caveolae are observed, and CAV1 complexes exhibit biochemical abnormalities. Patient fibroblasts also exhibit decreased resistance to a hypo-osmotic challenge, suggesting the function of caveolae as membrane reservoir is compromised. We conclude that the P158PfsX22 frameshift introduces a gain of function that gives rise to a dominant negative form of CAV1, defining a new mechanism by which disease-associated mutations in CAV1 impair caveolae assembly.

Aberrant CpG Island Shore Region Methylation of CAV1 Is Associated with Tumor Progression and Poor Prognosis in Gastric Cardia Adenocarcinoma

BACKGROUND AND AIMS

Caveolin-1 (CAV1) is a multifunctional scaffolding protein and plays an important role in tumorigenesis. However, the epigenetic changes of CAV1 in gastric cardia adenocarcinoma (GCA) have not been investigated so far. The purpose of this study was to clarify the contribution of critical CpG sites in CAV1 to progression/prognosis of GCA and to further elucidate the effect of critical CpG sites on the ectopic expression of β-catenin in GCA.

METHODS

Methylation-specific polymerase chain reaction (MSP) and bisulfite genomic sequencing (BGS) methods were, respectively, applied to examine the methylation status of CAV1. RT-PCR and immunohistochemistry methods were used to determine the mRNA and protein expression of CAV1 and β-catenin.

RESULTS

Decreased mRNA and protein expression of CAV1 were observed in GCA tumor tissues and were associated with hypermethylation of CpG island shore and transcription start site (TSS) regions in CAV1. Hypermethylation of the other two regions within CpG islands in CAV1 was observed both in tumor and corresponding adjacent tissues but was not related to the transcriptional inhibition of CAV1. The methylation status of CpG island shore region in CAV1 was associated with the ectopic expression of β-catenin and was independently associated with survival in GCA patients.

CONCLUSIONS

Hypermethylation of CpG island shore and TSS regions is cancer specific and is closely associated with reduced expression of CAV1. The CpG island shore methylation of CAV1 may play an important role in progression of GCA and may serve as a prognostic methylation biomarker for GCA patients.

Caveolin 1 and G-Protein-Coupled Receptor Kinase-2 Coregulate Endothelial Nitric Oxide Synthase Activity in Sinusoidal Endothelial Cells

Liver injury leads to a vasculopathy in which post-translational modifications of endothelial nitric oxide synthase (eNOS) lead to impaired nitric oxide synthesis. We hypothesized that caveolin 1 (CAV1), a well-known eNOS interactor, regulates eNOS activity in sinusoidal endothelial cells (SECs) via its interaction with G-protein-coupled receptor kinase-2 (GRK2) that also post-translationally modifies eNOS. Liver injury with portal hypertension was established using bile duct ligation in rats. CAV1 function was modified using a CAV1 scaffolding domain construct and cDNAs encoding wild-type CAV1, and CAV1 phosphorylation was increased in injured SECs, resulting in increased GRK2-CAV1 interaction and decreased eNOS activity. In injured SECs, endothelin-1 blocked CAV1 phosphorylation induced by CAV1 scaffolding domain, indicating that CAV1 interaction with GRK2 is inversely regulated by endothelin-1 and CAV1 scaffolding domain after liver injury. In addition, after transduction with DNA encoding wild-type CAV1 into SECs isolated from Cav1-deficient mice, GRK2 association with CAV1 was evident, whereas transduction with a dominant negative CAV1 mutated at tyrosine 14 reduced the interaction. Finally, isoproterenol-induced GRK2 phosphorylation enhanced CAV1-GRK2 interaction and reduced eNOS activity. Our data suggest a novel mechanism and model in which CAV1 phosphorylation facilitates CAV1 scaffolding and GRK2-CAV1 interaction, thus clustering eNOS within a complex that inhibits eNOS activity. This process takes place in injured, but not in normal, SECs.

Differential roles of caveolin-1 in ouabain-induced Na+/K+-ATPase cardiac signaling and contractility

Binding of ouabain to cardiac Na+/K+-ATPase initiates cell signaling and causes contractility in cardiomyocytes. It is widely accepted that caveolins, structural proteins of caveolae, have been implicated in signal transduction. It is known that caveolae play a role in Na+/K+-ATPase functions. Regulation of caveolin-1 in ouabain-mediated cardiac signaling and contractility has never been reported. The aim of this study is to compare ouabain-induced cardiac signaling and contractility in wild-type (WT) and caveolin-1 knockout (cav-1 KO) mice. In contrast with WT cardiomyocytes, ouabain-induced signaling e.g., activation of phosphoinositide 3-kinase-α/Akt and extracellular signal-regulated kinases (ERK)1/2, and hypertrophic growth were significantly reduced in cav-1 KO cardiomyocytes. Interactions of the Na+/K+-ATPase α1-subunit with caveolin-3 and the Na+/K+-ATPase α1-subunit with PI3K-α were also decreased in cav-1 KO cardiomyocytes. The results from cav-1 KO mouse embryonic fibroblasts also proved that cav-1 significantly attenuated ouabain-induced ERK1/2 activation without alteration in protein and cholesterol distribution in caveolae/lipid rafts. Intriguingly, the effect of ouabain induced positive inotropy in vivo (via transient infusion of ouabain, 0.48 nmol/g body wt) was not attenuated in cav-1 KO mice. Furthermore, ouabain (1-100 μM) induced dose-dependent contractility in isolated working hearts from WT and cav-1 KO mice. The effects of ouabain on contractility between WT and cav-1 KO mice were not significantly different. These results demonstrated differential roles of cav-1 in the regulation of ouabain signaling and contractility. Signaling by ouabain, in contrast to contractility, may be a redundant property of Na+/K+-ATPase.

rBmαTX14 Increases the Life Span and Promotes the Locomotion of Caenorhabditis Elegans

The scorpion has been extensively used in various pharmacological profiles or as food supplies. The exploration of scorpion venom has been reported due to the presence of recombinant peptides. rBmαTX14 is an α-neurotoxin extracted from the venom gland of the East Asian scorpion Buthus martensii Karsch and can affect ion channel conductance. Here, we investigated the functions of rBmαTX14 using the Caenorhabditis elegans model. Using western blot analysis, rBmαTX14 was shown to be expressed both in the cytoplasm and inclusion bodies in the E.coli Rosetta (DE3) strain. Circular dichroism spectroscopy analysis demonstrated that purified rBmαTX14 retained its biological structures. Next, feeding nematodes with E.coli Rosetta (DE3) expressing rBmαTX14 caused extension of the life span and promoted the locomotion of the nematodes. In addition, we identified several genes that play various roles in the life span and locomotion of C. elegans through microarray analysis and quantitative real-time PCR. Furthermore, if the amino acid site H₁₅ of rBmαTX14 was mutated, rBmαTX14 no longer promoted the C. elegans life span. In conclusion, the results not only demonstrated the functions and mechanism of rBmαTX14 in C. elegans, but also provided the new sight in the utility of recombinant peptides from scorpion venom.

Assembly and Turnover of Caveolae: What Do We Really Know?

In addition to containing highly dynamic nanoscale domains, the plasma membranes of many cell types are decorated with caveolae, flask-shaped domains enriched in the structural protein caveolin-1 (Cav1). The importance of caveolae in numerous cellular functions and processes has become well-recognized, and recent years have seen dramatic advances in our understanding of how caveolae assemble and the mechanisms control the turnover of Cav1. At the same time, work from our lab and others have revealed that commonly utilized strategies such as overexpression and tagging of Cav1 have unexpectedly complex consequences on the trafficking and fate of Cav1. Here, we discuss the implications of these findings for current models of caveolae biogenesis and Cav1 turnover. In addition, we discuss how disease-associated mutants of Cav1 impact caveolae assembly and outline open questions in this still-emerging area.

From embryonic development to human diseases: The functional role of caveolae/caveolin

Caveolae, an almost ubiquitous, structural component of the plasma membrane, play a critical role in many functions essential for proper cell function, including membrane trafficking, signal transduction, extracellular matrix remodeling, and tissue regeneration. Three main types of caveolin proteins have been identified from caveolae since the discovery of caveolin-1 in the early 1990s. All three (Cav-1, Cav-2, and Cav-3) play crucial roles in mammalian physiology, and can effect pathogenesis in a wide range of human diseases. While many biological activities of caveolins have been uncovered since its discovery, their role and regulation in embryonic develop remain largely poorly understood, although there is increasing evidence that caveolins may be linked to lung and brain birth defects. Further investigations are clearly needed to decipher how caveolae/caveolins mediate cellular functions and activities of normal embryogenesis and how their perturbations contribute to developmental disorders.

Membrane-mediated regulation of vascular identity

Vascular diseases span diverse pathology, but frequently arise from aberrant signaling attributed to specific membrane-associated molecules, particularly the Eph-ephrin family. Originally recognized as markers of embryonic vessel identity, Eph receptors and their membrane-associated ligands, ephrins, are now known to have a range of vital functions in vascular physiology. Interactions of Ephs with ephrins at cell-to-cell interfaces promote a variety of cellular responses such as repulsion, adhesion, attraction, and migration, and frequently occur during organ development, including vessel formation. Elaborate coordination of Eph- and ephrin-related signaling among different cell populations is required for proper formation of the embryonic vessel network. There is growing evidence supporting the idea that Eph and ephrin proteins also have postnatal interactions with a number of other membrane-associated signal transduction pathways, coordinating translation of environmental signals into cells. This article provides an overview of membrane-bound signaling mechanisms that define vascular identity in both the embryo and the adult, focusing on Eph- and ephrin-related signaling. We also discuss the role and clinical significance of this signaling system in normal organ development, neoplasms, and vascular pathologies.

DT(270-326) , a Truncated Diphtheria Toxin, Increases Blood-Tumor Barrier Permeability by Upregulating the Expression of Caveolin-1

AIM

The nontoxic mutant of diphtheria toxin (DT) has been demonstrated to act as a receptor-specific carrier protein to delivery drug into brain. Recent research showed that the truncated "receptorless" DT was still capable of being internalized into cells. This study investigated the effects and potential mechanisms of DT(270-326) , a truncated "receptorless" DT, on the permeability of the blood-tumor barrier (BTB).

METHODS

BTB and GECs were subjected to DT(270-326) treatment. HRP flux assays, immunofluorescent, co-immunoprecipitation, Western blot, CCK-8, and Flow cytometry analysis were used to evaluate the effects of DT(270-326) administration.

RESULTS

Our results revealed that 5 μM of DT(270-326) significantly increased the permeability of BTBin vitro, which reached its peak at 6 h. The permeability was reduced by pretreatment with filipinIII. DT(270-326) co-localized and interacted with caveolin-1 via its caveolin-binding motif. The mRNA and protein expression levels of caveolin-1 were identical with the changes of BTB permeability. The upregulated expression of caveolin-1 was associated with Src kinase-dependent tyrosine phosphorylation of caveolin-1, which subsequently induced phosphorylation and inactivation of the transcription factor Egr-1. The combination of DT(270-326) with doxorubicin significantly enhanced the loss of cell viability and apoptosis of U87 glioma cells in contrast to doxorubicin alone.

CONCLUSIONS

DT(270-326) might provide a novel strategy to increase the delivery of macromolecular therapeutic agents across the BTB.

Non-canonical roles for caveolin in regulation of membrane repair and mitochondria: implications for stress adaptation with age

Many different theories of ageing have been proposed but none has served the unifying purpose of defining a molecular target that can limit the structural and functional decline associated with age that ultimately leads to the demise of the organism. We propose that the search for a molecule with these unique properties must account for regulation of the signalling efficiency of multiple cellular functions that degrade with age due to a loss of a particular protein. We suggest caveolin as one such molecule that serves as a regulator of key processes in signal transduction. We define a particular distinction between cellular senescence and ageing and propose that caveolin plays a distinct role in each of these processes. Caveolin is traditionally thought of as a membrane-localized protein regulating signal transduction via membrane enrichment of specific signalling molecules. Ultimately we focus on two non-canonical roles for caveolin - membrane repair and regulation of mitochondrial function - which may be novel features of stress adaptation, especially in the setting of ageing. The end result of preserving membrane structure and mitochondrial function is maintenance of homeostatic signalling, preserving barrier function, and regulating energy production for cell survival and resilient ageing.

Congenital generalized lipodystrophies--new insights into metabolic dysfunction

Congenital generalized lipodystrophy (CGL) is a heterogeneous autosomal recessive disorder characterized by a near complete lack of adipose tissue from birth and, later in life, the development of metabolic complications, such as diabetes mellitus, hypertriglyceridaemia and hepatic steatosis. Four distinct subtypes of CGL exist: type 1 is associated with AGPAT2 mutations; type 2 is associated with BSCL2 mutations; type 3 is associated with CAV1 mutations; and type 4 is associated with PTRF mutations. The products of these genes have crucial roles in phospholipid and triglyceride synthesis, as well as in the formation of lipid droplets and caveolae within adipocytes. The predominant cause of metabolic complications in CGL is excess triglyceride accumulation in the liver and skeletal muscle owing to the inability to store triglycerides in adipose tissue. Profound hypoleptinaemia further exacerbates metabolic derangements by inducing a voracious appetite. Patients require psychological support, a low-fat diet, increased physical activity and cosmetic surgery. Aside from conventional therapy for hyperlipidaemia and diabetes mellitus, metreleptin replacement therapy can dramatically improve metabolic complications in patients with CGL. In this Review, we discuss the molecular genetic basis of CGL, the pathogenesis of the disease's metabolic complications and therapeutic options for patients with CGL.

Whole exome sequencing identifies de novo heterozygous CAV1 mutations associated with a novel neonatal onset lipodystrophy syndrome

Despite remarkable progress in identifying causal genes for many types of genetic lipodystrophies in the last decade, the molecular basis of many extremely rare lipodystrophy patients with distinctive phenotypes remains unclear. We conducted whole exome sequencing of the parents and probands from six pedigrees with neonatal onset of generalized loss of subcutaneous fat with additional distinctive phenotypic features and report de novo heterozygous null mutations, c.424C>T (p.Q142*) and c.479_480delTT (p.F160*), in CAV1 in a 7-year-old male and a 3-year-old female of European origin, respectively. Both the patients had generalized fat loss, thin mottled skin and progeroid features at birth. The male patient had cataracts requiring extraction at age 30 months and the female patient had pulmonary arterial hypertension. Dermal fibroblasts of the female patient revealed negligible CAV1 immunofluorescence staining compared to control but there were no differences in the number and morphology of caveolae upon electron microscopy examination. Based upon the similarities in the clinical features of these two patients, previous reports of CAV1 mutations in patients with lipodystrophies and pulmonary hypertension, and similar features seen in CAV1 null mice, we conclude that these variants are the most likely cause of one subtype of neonatal onset generalized lipodystrophy syndrome.

Recent progress in the topology, structure, and oligomerization of caveolin: a building block of caveolae

Caveolae are cholesterol-rich plasma membrane invaginations that are found in a plethora of cell types. They play many roles including signal transduction, endocytosis, and mechanoprotection. The most critical protein in caveolae is the integral membrane protein, caveolin, which has been shown to be necessary for caveolae formation, and governs the major functions attributed to caveolae. Caveolin is postulated to act as a scaffold in the high molecular weight striated coat that surrounds the caveolar bulb, stabilizing it. Caveolin interacts, both directly and indirectly, with a large number of signaling molecules, and presides over the endocytosis of molecular cargo by caveolae. However, many of the key biophysical aspects of the caveolin protein, its structure, topology, and oligomeric behavior, are just beginning to come to light. Herein is an up-to-date summary and critique of the progress that has been made in understanding caveolin on a molecular and atomic level.

Cavin3 interacts with cavin1 and caveolin1 to increase surface dynamics of caveolae

Caveolae are invaginations of the cell surface thought to regulate membrane tension, signalling, adhesion and lipid homeostasis owing to their dynamic behaviour ranging from stable surface association to dynamic rounds of fission and fusion with the plasma membrane. The caveolae coat is generated by oligomerisation of the membrane protein caveolin and the family of cavin proteins. Here, we show that cavin3 (also known as PRKCDBP) is targeted to caveolae by cavin1 (also known as PTRF) where it interacts with the scaffolding domain of caveolin1 and promote caveolae dynamics. We found that the N-terminal region of cavin3 binds a trimer of the cavin1 N-terminus in competition with a homologous cavin2 (also known as SDPR) region, showing that the cavins form distinct subcomplexes through their N-terminal regions. Our data shows that cavin3 is enriched at deeply invaginated caveolae and that loss of cavin3 in cells results in an increase of stable caveolae and a decrease of caveolae that are only present at the membrane for a short time. We propose that cavin3 is recruited to the caveolae coat by cavin1 to interact with caveolin1 and regulate the duration time of caveolae at the plasma membrane.

Caveolin-1 limits human influenza A virus (H1N1) propagation in mouse embryo-derived fibroblasts

Caveolin expression supports the multiplication of retro-, ortho- and paramyxoviruses in susceptible cells. However, human influenza A virus (IAV), an orthomyxovirus, does not multiply efficiently in mouse embryo fibroblasts (MEFs), which are abundant in caveolin-1 (Cav-1). Surprisingly, the absence of Cav-1 in a MEF cell line removed the block for IAV replication and raised the infectious titer 250-fold, whereas the re-introduction of Cav-1 reversed the effect. The monitoring of cellular pathways revealed that Cav-1 loss considerably increased activities of p53. Furthermore, infection of MEF Cav-1 (-/-) induced reactive oxygen species (ROS) and pronounced apoptosis in the late phase of viral multiplication, but no type I IFN response. Strikingly, pharmacological inactivation showed that the elevated levels of ROS together with apoptosis caused the increase of virus yield. Thus, Cav-1 represents a new negative regulator of IAV infection in MEF that diminishes IAV infectious titer by controlling virus-supportive pathways.

Interactions of caveolin-1 scaffolding and intramembrane regions containing a CRAC motif with cholesterol in lipid bilayers

Caveolin-1 is a major structural protein of caveolae and specifically binds cholesterol (Chol). The caveolin scaffolding domain is thought to be involved in caveolin-Chol interaction through the sequence V94-T-K-Y-W-F-Y-R101, a motif that matches a cholesterol recognition amino-acid consensus (CRAC). In the present work, three CRAC-containing peptides, corresponding to caveolin-1 94-101, 82-101 and 93-126, were tested to study the role of the CRAC motif in the caveolin-Chol interaction in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers using differential scanning calorimetry (DSC), fluorescence and circular dichroism (CD). The Y97I substituents of the three peptides and one peptide segment corresponding to caveolin-1 101-126 that excludes the CRAC motif were also tested for comparison. Our results showed the potency of these CRAC-containing peptides in sequestering Chol into domains and the enhanced role of the intramembrane domain and scaffolding domain for the potency. Of the three CRAC-containing peptides, the peptide 93-126 was particularly effective in promoting Chol segregation, while the peptide 82-101 was less potent in promoting the formation of domains than the peptide 93-126, but was more potent than the peptide 94-101. The domain partition of DPPC/Chol bilayers was not observed in the presence of the peptide 101-126, in contrast to the case in the presence of the peptide 93-126 at the same concentrations of peptide and Chol. The potency of the CRAC motif in Chol segregation was lowered by the Y97I mutation. The difference in structure may be a factor that contributes to different effects of these peptides on the distribution of Chol in the lipid membrane.

Regulation of intracellular signaling and function by caveolin

Caveolae, flask-like invaginations of the plasma membrane, were discovered nearly 60 years ago. Originally regarded as fixation artifacts of electron microscopy, the functional role for these structures has taken decades to unravel. The discovery of the caveolin protein in 1992 (by the late Richard G.W. Anderson) accelerated progress in defining the contribution of caveolae to cellular physiology and pathophysiology. The three isoforms of caveolin (caveolin-1, -2, and -3) are caveolae-resident structural and scaffolding proteins that are critical for the formation of caveolae and their localization of signaling entities. A PubMed search for "caveolae" reveals ∼280 publications from their discovery in the 1950s to the early 1990s, whereas a search for "caveolae or caveolin" after 1990, identifies ∼7000 entries. Most work on the regulation of biological responses by caveolae and caveolin since 1990 has focused on caveolae as plasma membrane microdomains and the function of caveolin proteins at the plasma membrane. By contrast, our recent work and that of others has explored the localization of caveolins in multiple cellular membrane compartments and in the regulation of intracellular signaling. Cellular organelles that contain caveolin include mitochondria, nuclei and the endoplasmic reticulum. Such intracellular localization allows for a complexity of responses to extracellular stimuli by caveolin and the possibility of novel organelle-targeted therapeutics. This review focuses on the impact of intracellular localization of caveolin on signal transduction and cell regulation.

Temporal evolution in caveolin 1 methylation levels during human esophageal carcinogenesis

Background

Esophageal cancer ranks eighth among frequent cancers worldwide. Our aim was to investigate whether and at which neoplastic stage promoter hypermethylation of CAV1 is involved in human esophageal carcinogenesis.

Methods

Using real-time quantitative methylation-specific PCR (qMSP), we examined CAV1 promoter hypermethylation in 260 human esophageal tissue specimens. Real-time RT-PCR and qMSP were also performed on OE33 esophageal cancer cells before and after treatment with the demethylating agent, 5-aza-2’-deoxycytidine (5-Aza-dC).

Results

CAV1 hypermethylation showed highly discriminative ROC curve profiles, clearly distinguishing esophageal adenocarcinomas (EAC) and esophageal squamous cell carcinomas (ESCC) from normal esophagus (NE) (EAC vs. NE, AUROC = 0.839 and p < 0.0001; ESCC vs. NE, AUROC = 0.920 and p < 0.0001). Both CAV1 methylation frequency and normalized methylation value (NMV) were significantly higher in Barrett’s metaplasia (BE), low-grade and high-grade dysplasia occurring in BE (D), EAC, and ESCC than in NE (all p < 0.01, respectively). Meanwhile, among 41 cases with matched NE and EAC or ESCC, CAV1 NMVs in EAC and ESCC (mean = 0.273) were significantly higher than in corresponding NE (mean = 0.146; p < 0.01, Student’s paired t-test). Treatment of OE33 EAC cells with 5-Aza-dC reduced CAV1 methylation and increased CAV1 mRNA expression.

Conclusions

CAV1 promoter hypermethylation is a frequent event in human esophageal carcinomas and is associated with early neoplastic progression in Barrett’s esophagus.

Impact of the loss of caveolin-1 on lung mass and cholesterol metabolism in mice with and without the lysosomal cholesterol transporter, Niemann-Pick type C1

Caveolin-1 (Cav-1) is a major structural protein in caveolae in the plasma membranes of many cell types, particularly endothelial cells and adipocytes. Loss of Cav-1 function has been implicated in multiple diseases affecting the cardiopulmonary and central nervous systems, as well as in specific aspects of sterol and lipid metabolism in the liver and intestine. Lungs contain an exceptionally high level of Cav-1. Parameters of cholesterol metabolism in the lung were measured, initially in Cav-1-deficient mice (Cav-1(-/-)), and subsequently in Cav-1(-/-) mice that also lacked the lysosomal cholesterol transporter Niemann-Pick C1 (Npc1) (Cav-1(-/-):Npc1(-/-)). In 50-day-old Cav-1(-/-) mice fed a low- or high-cholesterol chow diet, the total cholesterol concentration (mg/g) in the lungs was marginally lower than in the Cav-1(+/+) controls, but due to an expansion in their lung mass exceeding 30%, whole-lung cholesterol content (mg/organ) was moderately elevated. Lung mass (g) in the Cav-1(-/-):Npc1(-/-) mice (0.356±0.022) markedly exceeded that in their Cav-1(+/+):Npc1(+/+) controls (0.137±0.009), as well as in their Cav-1(-/-):Npc1(+/+) (0.191±0.013) and Cav-1(+/+):Npc1(-/-) (0.213±0.022) littermates. The corresponding lung total cholesterol contents (mg/organ) in mice of these genotypes were 6.74±0.17, 0.71±0.05, 0.96±0.05 and 3.12±0.43, respectively, with the extra cholesterol in the Cav-1(-/-):Npc1(-/-) and Cav-1(+/+):Npc1(-/-) mice being nearly all unesterified (UC). The exacerbation of the Npc1 lung phenotype and increase in the UC level in the Cav-1(-/-):Npc1(-/-) mice imply a regulatory role of Cav-1 in pulmonary cholesterol metabolism when lysosomal sterol transport is disrupted.

Sex-dependent expression of caveolin 1 in response to sex steroid hormones is closely associated with development of obesity in rats

Caveolin-1 (CAV1) is a conserved group of structural membrane proteins that form special cholesterol and sphingolipid-rich compartments, especially in adipocytes. Recently, it has been reported that CAV1 is an important target protein in sex hormone-dependent regulation of various metabolic pathways, particularly in cancer and diabetes. To clarify distinct roles of CAV1 in sex-dependent obesity development, we investigated the effects of high fat diet (HFD) and sex steroid hormones on CAV1 expression in adipose tissues of male and female rats. Results of animal experiments revealed that estrogen (17-β-estradiol, E2) and androgen (dihydrotestosterone, DHT) had opposite effects on body weight gain as well as on the regulation of CAV1, hormone sensitive lipase (HSL) and uncoupling protein 1 (UCP1) in adipose tissues. Furthermore, sex hormone receptors and aromatase were differentially expressed in a sex-dependent manner in response to E2 and DHT treatments. In vivo data were confirmed using 3T3-L1 and HIB1B cell lines, where Cav1 knock down stimulated lipogenesis but suppressed sex hormone receptor signaling proteins. Most importantly, co-immunoprecipitation enabled the identification of previously unrecognized CAV1-interacting mitochondrial or lipid oxidative pathway proteins in adipose tissues. Taken together, current data showed that CAV1 may play important preventive role in the development of obesity, with more prominent effects in females, and proved to be an important target protein for the hormonal regulation of adipose tissue metabolism by manipulating sex hormone receptors and mitochondrial oxidative pathways. Therefore, we can report, for the first time, the molecular mechanism underlying the effects of sex steroid hormones in the sex-dimorphic regulation of CAV1.

Overexpression of aquaporin-1 and caveolin-1 in the rat urinary bladder urothelium following bladder outlet obstruction

PURPOSE

This study was designed to investigate the effect of detrusor overactivity induced by partial bladder outlet obstruction (BOO) on the expression of aquaporin 1 (AQP1) and caveolin 1 (CAV1) in the rat urinary bladder, and to determine the role of these molecules in detrusor overactivity.

METHODS

Female Sprague-Dawley rats were divided into control (n=30) and experimental (n=30) groups. The BOO group underwent partial BOO, and the control group underwent a sham operation. After 4 weeks, an urodynamic study was performed to measure the contraction interval and contraction pressure. The expression and cellular localization of AQP1 and CAV1 were determined by western blot and immunofluorescence experiments in the rat urinary bladder.

RESULTS

In cystometrograms, the contraction interval was significantly lower in the BOO group (2.9±1.5 minutes) than in the control group (6.7±1.0 minutes) (P<0.05). Conversely, the average contraction pressure was significantly higher in the BOO group (21.2±3.3 mmHg) than in the control group (13.0±2.5 mmHg) (P<0.05). AQP1 and CAV1 were coexpressed in the capillaries, arterioles, and venules of the suburothelial layer. AQP1 and CAV1 protein expression was significantly increased in the BOO rats compared to the control rats (P<0.05).

CONCLUSIONS

Detrusor overactivity induced by BOO causes a significant increase in the expression of AQP1 and CAV1, which were coexpressed in the suburothelial microvasculature. This finding suggests that AQP1 and CAV1 might be closely related to bladder signal activity and may have a functional role in BOO-associated detrusor overactivity.

The role of caveolae in the pathophysiology of lung diseases

Caveolae are flask-shaped plasma membrane invaginations formed by constitutive caveolin proteins and regulatory cavin proteins. Caveolae harbor a range of signaling components such as receptors, ion channels and regulatory molecules. There is now increasing evidence that caveolins and cavins play an important role in a variety of diseases. However, the mechanisms by which these caveolar proteins affect lung health and disease are still under investigation, with emerging data suggesting complex roles in disease pathophysiology. This review summarizes the current state of understanding of how caveolar proteins contribute to lung structure and function and how their altered expression and/or function can influence lung diseases.

Prokineticin receptor-1 is a new regulator of endothelial insulin uptake and capillary formation to control insulin sensitivity and cardiovascular and kidney functions

Background

Reciprocal relationships between endothelial dysfunction and insulin resistance result in a vicious cycle of cardiovascular, renal, and metabolic disorders. The mechanisms underlying these impairments are unclear. The peptide hormones prokineticins exert their angiogenic function via prokineticin receptor‐1 (PKR1). We explored the extent to which endothelial PKR1 contributes to expansion of capillary network and the transcapillary passage of insulin into the heart, kidney, and adipose tissues, regulating organ functions and metabolism in a specific mice model.

Methods and Results

By combining cellular studies and studies in endothelium‐specific loss‐of‐function mouse model (ec‐PKR1^−/−), we showed that a genetically induced PKR1 loss in the endothelial cells causes the impaired capillary formation and transendothelial insulin delivery, leading to insulin resistance and cardiovascular and renal disorders. Impaired insulin delivery in endothelial cells accompanied with defective expression and activation of endothelial nitric oxide synthase in the ec‐PKR1^−/− aorta, consequently diminishing endothelium‐dependent relaxation. Despite having a lean body phenotype, ec‐PKR1^−/− mice exhibited polyphagia, polydipsia, polyurinemia, and hyperinsulinemia, which are reminiscent of human lipodystrophy. High plasma free fatty acid levels and low leptin levels further contribute to the development of insulin resistance at the later age. Peripheral insulin resistance and ectopic lipid accumulation in mutant skeletal muscle, heart, and kidneys were accompanied by impaired insulin‐mediated Akt signaling in these organs. The ec‐PKR1^−/− mice displayed myocardial fibrosis, low levels of capillary formation, and high rates of apoptosis, leading to diastolic dysfunction. Compact fibrotic glomeruli and high levels of phosphate excretion were found in mutant kidneys. PKR1 restoration in ec‐PKR1^−/− mice reversed the decrease in capillary recruitment and insulin uptake and improved heart and kidney function and insulin resistance.

Conclusions

We show a novel role for endothelial PKR1 signaling in cardiac, renal, and metabolic functions by regulating transendothelial insulin uptake and endothelial cell proliferation. Targeting endothelial PKR1 may serve as a therapeutic strategy for ameliorating these disorders.

Balancing the fat: lipid droplets and human disease

Lipid droplets (LDs) are dynamic, cytosolic lipid-storage organelles found in nearly all cell types. Too many or too few LDs during excess or deficient fat storage lead to many different human diseases. Recent insights into LD biology and LD protein functions shed new light on mechanisms underlying those metabolic pathologies. These findings will likely provide opportunities for treatment of diseases associated with too much or too little fat.

Caveolin-1 as a promoter of tumour spreading: when, how, where and why

Caveolae are non-clathrin invaginations of the plasma membrane in most cell types; they are involved in signalling functions and molecule trafficking, thus modulating several biological functions, including cell growth, apoptosis and angiogenesis. The major structural protein in caveolae is caveolin-1, which is known to act as a key regulator in cancer onset and progression through its role as a tumour suppressor. Caveolin-1 can also promote cell proliferation, survival and metastasis as well as chemo- and radioresistance. Here, we discuss recent findings and novel concepts that support a role for caveolin-1 in cancer development and its distant spreading. We also address the potential application of caveolin-1 in tumour therapy and diagnosis.