Caveolin as a potential drug target for cardiovascular protection

Effect of long-term inorganic nitrate administration on myocardial ischemia-reperfusion injury in ovariectomized rats

Introduction: Menopause is associated with reduced nitric oxide (NO) bioavailability and lower tolerance against myocardial ischemia-reperfusion (IR) injury. This study investigated whether long-term nitrate administration provides resistance against myocardial IR injury in ovariectomized (OVX) rats. Method: After ovariectomy, female rats were assigned to the OVX and the OVX + nitrate groups (n = 14/group); the latter group consumed nitrate (100 mg/L) for 9 months. At month 9, each group was divided into two subgroups (n = 7/subgroup), of which one subgroup was exposed to myocardial IR (IR+ hearts) and the other was not exposed (IR- hearts). The hearts of rats were isolated, and NO metabolite (NOx), oxidative stress indices, and mRNA expressions of endothelial (eNOS), inducible (iNOS), and neuronal (nNOS) NO synthases, as well as markers of apoptosis, were measured in the IR- and IR+ hearts. In the IR+ hearts, cardiac function indices (CFI) and the infarct size were also measured. Results: Nitrate increased catalase activity (97%) and eNOS expression (2.94-fold) in the IR- hearts. In the IR+ hearts, nitrate reduced left ventricular (LV) end-diastolic pressure (11.6%) and infarct size (26.2%) and increased recovery of LV developed pressure (44.0%) and peak rate of positive (28.9%) and negative (15.4%) changes in LV pressure. In addition, in the IR+ hearts, nitrate increased eNOS and B-cell lymphoma-2 (Bcl-2) as well as decreased iNOS, Bcl-2 associated X protein (Bax), caspase-3, caspase-8, caspase-9, and tumor necrosis factor-α (TNF-α) expression. Nitrate increased total antioxidant capacity (TAC) and catalase (CAT) activity and decreased malondialdehyde (MDA) levels at month nine in serum and IR+ hearts. Conclusion: The favorable effects of nitrate against IR injury were associated with higher eNOS and Bcl-2 expression, CAT activity, TAC, and lower iNOS, Bax, caspase-3, caspase-8, caspase-9 and TNF-α expression, and MDA in the heart tissue. Nitrate preconditioning alleviated IR-induced myocardial injury in OVX rats; this effect was associated with eNOS upregulation before IR and the blunting of OVX-induced eNOS downregulation, iNOS upregulation, apoptosis, and oxidative stress in heart tissue after IR.

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.

Low Pre-Transplant Caveolin-1 Serum Concentrations Are Associated with Acute Cellular Tubulointerstitial Rejection in Kidney Transplantation

Acute and chronic transplant rejections due to alloreactivity are essential contributors to graft loss. However, the strength of alloreactivity is biased by non-immunological factors such as ischemia reperfusion injury (IRI). Accordingly, protection from IRI could be favorable in terms of limiting graft rejection. Caveolin-1 (Cav-1) is part of the cell membrane and an important regulator of intracellular signaling. Cav-1 has been demonstrated to limit IRI and to promote the survival of a variety of cell types including renal cells under stress conditions. Accordingly, Cav-1 could also play a role in limiting anti-graft immune responses. Here, we evaluated a possible association between pre-transplant serum concentrations of Cav-1 and the occurrence of rejection during follow-up in a pilot study. Therefore, Cav-1-serum concentrations were analyzed in 91 patients at the time of kidney transplantation and compared to the incidence of acute and chronic rejection. Higher Cav-1 levels were associated with lower occurrence of acute cellular tubulointerstitial rejection episodes.

Effects of voluntary exercise duration on myocardial ischaemic tolerance, kinase signaling and gene expression

AIM

Exercise is cardioprotective, though optimal interventions are unclear. We assessed duration dependent effects of exercise on myocardial ischemia-reperfusion (I-R) injury, kinase signaling and gene expression.

METHODS

Responses to brief (2 day; 2EX), intermediate (7 and 14 day; 7EX and 14EX) and extended (28 day; 28EX) voluntary wheel running (VWR) were studied in male C57Bl/6 mice. Cardiac function, I-R tolerance and survival kinase signaling were assessed in perfused hearts.

KEY FINDINGS

Mice progressively increased running distances and intensity, from 2.4 ± 0.2 km/day (0.55 ± 0.04 m/s) at 2-days to 10.6 ± 0.4 km/day (0.72 ± 0.06 m/s) after 28-days. Myocardial mass and contractility were modified at 14-28 days VWR. Cardioprotection was not 'dose-dependent', with I-R tolerance enhanced within 7 days and not further improved with greater VWR duration, volume or intensity. Protection was associated with AKT, ERK1/2 and GSK3β phosphorylation, with phospho-AMPK selectively enhanced with brief VWR. Gene expression was duration-dependent: 7 day VWR up-regulated glycolytic (Pfkm) and down-regulated maladaptive remodeling (Mmp2) genes; 28 day VWR up-regulated caveolar (Cav3), mitochondrial biogenesis (Ppargc1a, Sirt3) and titin (Ttn) genes. Interestingly, I-R tolerance in 2EX/2SED groups improved vs. groups subjected to longer sedentariness, suggesting transient protection on transition to housing with running wheels.

SIGNIFICANCE

Cardioprotection is induced with as little as 7 days VWR, yet not enhanced with further or faster running. This protection is linked to survival kinase phospho-regulation (particularly AKT and ERK1/2), with glycolytic, mitochondrial, caveolar and myofibrillar gene changes potentially contributing. Intriguingly, environmental enrichment may also protect via similar kinase regulation.

Caveolae as Potential Hijackable Gates in Cell Communication

Caveolae are membrane microdomains described in many cell types involved in endocytocis, transcytosis, cell signaling, mechanotransduction, and aging. They are found at the interface with the extracellular environment and are structured by caveolin and cavin proteins. Caveolae and caveolins mediate transduction of chemical messages via signaling pathways, as well as non-chemical messages, such as stretching or shear stress. Various pathogens or signals can hijack these gates, leading to infectious, oncogenic and even caveolin-related diseases named caveolinopathies. By contrast, preclinical and clinical research have fallen behind in their attempts to hijack caveolae and caveolins for therapeutic purposes. Caveolae involvement in human disease is not yet fully explored or understood and, of all their scaffold proteins, only caveolin-1 is being considered in clinical trials as a possible biomarker of disease. This review briefly summarizes current knowledge about caveolae cell signaling and raises the hypothesis whether these microdomains could serve as hijackable “gatekeepers” or “gateways” in cell communication. Furthermore, because cell signaling is one of the most dynamic domains in translating data from basic to clinical research, we pay special attention to translation of caveolae, caveolin, and cavin research into clinical practice.

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.

Postconditioning with Nitrates Protects Against Myocardial Reperfusion Injury: A New Use for an Old Pharmacological Agent

Early reperfusion remains the key therapy to salvage viable myocardium and must be applied as soon as possible following an acute myocardial infarction (AMI) to attenuate the ischemic insult. However, reperfusion injury may develop following reintroduction of blood and oxygen to vulnerable myocytes, which results in more severe cell death than in the preceding ischemic episode. Ischemic postconditioning (I-PostC) provides a cardioprotective effect in combination with pharmacological agents. Although nitrates have been tested in many experimental and clinical studies of acute AMI to evaluate the cardioprotective effect, few investigations have been focused on nitrates postconditioning in patients undergoing percutaneous coronary intervention (PCI). This review presents the manifestations of myocardial reperfusion injury (RI) and potential mechanisms underlying it, and provides the mechanisms involved in the cardioprotection of I-PostC. We also present a new therapeutic approach to attenuate RI by use of an ‘old’ agent – nitrates – in AMI patients.

Cholesteryl α-D-glucoside 6-acyltransferase enhances the adhesion of Helicobacter pylori to gastric epithelium

Helicobacter pylori, the most common etiologic agent of gastric diseases including gastric cancer, is auxotrophic for cholesterol and has to hijack it from gastric epithelia. Upon uptake, the bacteria convert cholesterol to cholesteryl 6′-O-acyl-α-D-glucopyranoside (CAG) to promote lipid raft clustering in the host cell membranes. However, how CAG appears in the host to exert the pathogenesis still remains ambiguous. Herein we identified hp0499 to be the gene of cholesteryl α-D-glucopyranoside acyltransferase (CGAT). Together with cholesteryl glucosyltransferase (catalyzing the prior step), CGAT is secreted via outer membrane vesicles to the host cells for direct synthesis of CAG. This significantly enhances lipid rafts clustering, gathers adhesion molecules (including Lewis antigens and integrins α5, β1), and promotes more bacterial adhesion. Furthermore, the clinically used drug amiodarone was shown as a potent inhibitor of CGAT to effectively reduce the bacterial adhesion, indicating that CGAT is a potential target of therapeutic intervention.

Jan et al. identify cholesteryl α-D- glucopyranoside acyltransferase as a key enzyme in Helicobacter pylori’s synthesis of cholesteryl 6’-O-acyl-α-D-glucopyranoside, which promotes bacterial adhesion. This study provides insights into the H. pylori-induced pathogenesis and therapeutic strategies against it.

Nitric Oxide Induces Cardiac Protection by Preventing Extracellular Matrix Degradation through the Complex Caveolin-3/EMMPRIN in Cardiac Myocytes

Inhibition of Extracellular Matrix degradation by nitric oxide (NO) induces cardiac protection against coronary ischemia/reperfusion (IR). Glycosylation of Extracellular Matrix Metalloproteinase Inducer (EMMPRIN) stimulates enzymatic activation of matrix metalloproteinases (MMPs) in the heart, although the mechanisms leading to EMMPRIN glycosylation are poorly understood. We sought to determine if NO may induce cardiac protection by preventing glycosylation of EMMPRIN in a mouse model of IR. Here we found that Caveolin-3 binds to low glycosylated EMMPRIN (LG-EMMPRIN) in cardiac cells and in the hearts of healthy mice, whereas IR disrupted the complex in nitric oxide synthase 2 (NOS2) knockout (KO) mice. By contrast, the binding was partially restored when mice were fed with an NO donor (DEA-NO) in the drinking water, showing a significant reduction on infarct size (NOS2KO: 34.6±5 vs NOS2KO+DEA-NO: 20.7±9), in expression of matrix metalloproteinases, and cardiac performance was improved (left ventricular ejection fraction (LVEF). NOS2KO: 31±4 vs NOS2KO+DEA-NO: 46±6). The role of Caveolin-3/EMMPRIN in NO-mediated cardiac protection was further assayed in Caveolin-3 KO mice, showing no significant improvement on infarct size (Caveolin-3 KO: 34.8±3 vs Caveolin-3 KO+DEA-NO:33.7±5), or in the expression of MMPs, suggesting that stabilization of the complex Caveolin-3/LG-EMMPRIN may play a significant role in the cardioprotective effect of NO against IR.

PTRF/Cavin-1 Deficiency Causes Cardiac Dysfunction Accompanied by Cardiomyocyte Hypertrophy and Cardiac Fibrosis

Mutations in the PTRF/Cavin-1 gene cause congenital generalized lipodystrophy type 4 (CGL4) associated with myopathy. Additionally, long-QT syndrome and fatal cardiac arrhythmia are observed in patients with CGL4 who have homozygous PTRF/Cavin-1 mutations. PTRF/Cavin-1 deficiency shows reductions of caveolae and caveolin-3 (Cav3) protein expression in skeletal muscle, and Cav3 deficiency in the heart causes cardiac hypertrophy with loss of caveolae. However, it remains unknown how loss of PTRF/Cavin-1 affects cardiac morphology and function. Here, we present a characterization of the hearts of PTRF/Cavin-1-null (PTRF^−/−) mice. Electron microscopy revealed the reduction of caveolae in cardiomyocytes of PTRF^−/− mice. PTRF^−/− mice at 16 weeks of age developed a progressive cardiomyopathic phenotype with wall thickening of left ventricles and reduced fractional shortening evaluated by echocardiography. Electrocardiography revealed that PTRF^−/− mice at 24 weeks of age had low voltages and wide QRS complexes in limb leads. Histological analysis showed cardiomyocyte hypertrophy accompanied by progressive interstitial/perivascular fibrosis. Hypertrophy-related fetal gene expression was also induced in PTRF^−/− hearts. Western blotting analysis and quantitative RT-PCR revealed that Cav3 expression was suppressed in PTRF^−/− hearts compared with that in wild-type (WT) ones. ERK1/2 was activated in PTRF^−/− hearts compared with that in WT ones. These results suggest that loss of PTRF/Cavin-1 protein expression is sufficient to induce a molecular program leading to cardiomyocyte hypertrophy and cardiomyopathy, which is partly attributable to Cav3 reduction in the heart.

Dietary Flaxseed Mitigates Impaired Skeletal Muscle Regeneration: in Vivo, in Vitro and in Silico Studies

BACKGROUND

Diets enriched with n-3 polyunsaturated fatty acids (n-3 PUFAs) have been shown to exert a positive impact on muscle diseases. Flaxseed is one of the richest sources of n-3 PUFA acid α-linolenic acid (ALA). The aim of this study was to assess the effects of flaxseed and ALA in models of skeletal muscle degeneration characterized by high levels of Tumor Necrosis Factor-α (TNF).

METHODS

The in vivo studies were carried out on dystrophic hamsters affected by muscle damage associated with high TNF plasma levels and fed with a long-term 30% flaxseed-supplemented diet. Differentiating C2C12 myoblasts treated with TNF and challenged with ALA represented the in vitro model. Skeletal muscle morphology was scrutinized by applying the Principal Component Analysis statistical method. Apoptosis, inflammation and myogenesis were analyzed by immunofluorescence. Finally, an in silico analysis was carried out to predict the possible pathways underlying the effects of n-3 PUFAs.

RESULTS

The flaxseed-enriched diet protected the dystrophic muscle from apoptosis and preserved muscle myogenesis by increasing the myogenin and alpha myosin heavy chain. Moreover, it restored the normal expression pattern of caveolin-3 thereby allowing protein retention at the sarcolemma. ALA reduced TNF-induced apoptosis in differentiating myoblasts and prevented the TNF-induced inhibition of myogenesis, as demonstrated by the increased expression of myogenin, myosin heavy chain and caveolin-3, while promoting myotube fusion. The in silico investigation revealed that FAK pathways may play a central role in the protective effects of ALA on myogenesis.

CONCLUSIONS

These findings indicate that flaxseed may exert potent beneficial effects by preserving skeletal muscle regeneration and homeostasis partly through an ALA-mediated action. Thus, dietary flaxseed and ALA may serve as a useful strategy for treating patients with muscle dystrophies.

Endothelial nitric oxide synthase in the microcirculation

Endothelial nitric oxide synthase (eNOS, NOS3) is responsible for producing nitric oxide (NO)--a key molecule that can directly (or indirectly) act as a vasodilator and anti-inflammatory mediator. In this review, we examine the structural effects of regulation of the eNOS enzyme, including post-translational modifications and subcellular localization. After production, NO diffuses to surrounding cells with a variety of effects. We focus on the physiological role of NO and NO-derived molecules, including microvascular effects on vessel tone and immune response. Regulation of eNOS and NO action is complicated; we address endogenous and exogenous mechanisms of NO regulation with a discussion of pharmacological agents used in clinical and laboratory settings and a proposed role for eNOS in circulating red blood cells.

Cavin-1: caveolae-dependent signalling and cardiovascular disease

Caveolae are curved lipid raft regions rich in cholesterol and sphingolipids found abundantly in vascular endothelial cells, adipocytes, smooth muscle cells and fibroblasts. They are multifunctional organelles with roles in clathrin-independent endocytosis, cholesterol transport, mechanosensing and signal transduction. Caveolae provide an environment where multiple receptor signalling components are sequestered, clustered and compartmentalized for efficient signal transduction. Many of these receptors, including cytokine signal transducer gp130 (glycoprotein 130), are mediators of chronic inflammation during atherogenesis. Subsequently, disruption of these organelles is associated with a broad range of disease states including cardiovascular disease and cancer. Cavin-1 is an essential peripheral component of caveolae that stabilizes caveolin-1, the main structural/integral membrane protein of caveolae. Caveolin-1 is an essential regulator of eNOS (endothelial nitric oxide synthase) and its disruption leads to endothelial dysfunction which initiates a range of cardiovascular and pulmonary disorders. Although dysfunctional cytokine signalling is also a hallmark of cardiovascular disease, knowledge of caveolae-dependent cytokine signalling is lacking as is the role of cavin-1 independent of caveolae. The present review introduces caveolae, their structural components, the caveolins and cavins, their regulation by cAMP, and their potential role in cardiovascular disease.

Role of nitric oxide in murine conventional outflow physiology

Elevated intraocular pressure (IOP) is the main risk factor for glaucoma. Exogenous nitric oxide (NO) decreases IOP by increasing outflow facility, but whether endogenous NO production contributes to the physiological regulation of outflow facility is unclear. Outflow facility was measured by pressure-controlled perfusion in ex vivo eyes from C57BL/6 wild-type (WT) or transgenic mice expressing human endothelial NO synthase (eNOS) fused to green fluorescent protein (GFP) superimposed on the endogenously expressed murine eNOS (eNOS-GFPtg). In WT mice, exogenous NO delivered by 100 μM S-nitroso-N-acetylpenicillamine (SNAP) increased outflow facility by 62 ± 28% (SD) relative to control eyes perfused with the inactive SNAP analog N-acetyl-d-penicillamine (NAP; n = 5, P = 0.016). In contrast, in eyes from eNOS-GFPtg mice, SNAP had no effect on outflow facility relative to NAP (-9 ± 4%, P = 0.40). In WT mice, the nonselective NOS inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME, 10 μM) decreased outflow facility by 36 ± 13% (n = 5 each, P = 0.012), but 100 μM l-NAME had no detectable effect on outflow facility (-16 ± 5%, P = 0.22). An eNOS-selective inhibitor (cavtratin, 50 μM) decreased outflow facility by 19 ± 12% in WT (P = 0.011) and 39 ± 25% in eNOS-GFPtg (P = 0.014) mice. In the conventional outflow pathway of eNOS-GFPtg mice, eNOS-GFP expression was localized to endothelial cells lining Schlemm's canal and the downstream vessels, with no apparent expression in the trabecular meshwork. These results suggest that endogenous NO production by eNOS within endothelial cells of Schlemm's canal or downstream vessels contributes to the physiological regulation of aqueous humor outflow facility in mice, representing a viable strategy to more successfully lower IOP in glaucoma.

Role of caveolin-1 in asthma and chronic inflammatory respiratory diseases

Caveolin-1 (Cav-1) is the major protein present in invaginations of the plasma membrane of cells known as caveolae. Cav-1 is expressed in numerous resident and inflammatory cells implicated in the pathogenesis of asthma and chronic inflammatory respiratory diseases including chronic obstructive pulmonary disease. A remarkable repertoire of functions has been identified for Cav-1 and these extend to, and have relevance to, asthma and chronic inflammatory respiratory diseases. Important processes influenced by Cav-1 include inflammation, fibrosis, smooth muscle contractility, regulation of apoptosis and cell senescence as well as epithelial barrier function and homeostasis. A better understanding of Cav-1 may be useful in developing new therapies for chronic inflammatory respiratory diseases.

Cardioprotective Role of Caveolae in Ischemia-Reperfusion Injury

Caveolae are flask-like invaginations of the plasma membrane enriched in cholesterol, sphingolipids, the marker protein caveolin and the coat protein cavin. In cardiomyocytes, multiple signaling molecules are concentrated and organized within the caveolae to mediate signaling transduction. Recent studies suggest that caveolae and caveolae-associated signaling molecules play an important role in protecting the myocardium against ischemia-reperfusion injury. For example, cardiac-specific overexpression of caveolin-3 has been shown to lead to protection that mimics ischemic preconditioning, while the knockout of caveolin-3 abolished ischemic preconditioning. In this review, we discuss the molecular mechanisms and signaling pathways that are involved in caveolae-mediated cardioprotection, and examine the potential for caveolae as a therapeutic target for pharmaceutical intervention to treat cardiovascular disease.