Caveolin regulation of endothelial function

Review: molecular pathogenesis of blood-brain barrier breakdown in acute brain injury

Historically, the blood-brain barrier (BBB) was considered to be at the level of cerebral endothelium. Currently, the interaction of endothelium with other components of the vessel wall and with neurones and glial cells is considered to constitute a functional unit, termed the neurovascular unit that maintains cerebral homeostasis in steady states and brain injury. The emphasis of this review is on cerebral endothelium, the best-studied component of the neurovascular unit, and its permeability mechanisms in health and acute brain injury. Major advances have been made in unravelling the molecular structure of caveolae and tight junctions, both of which are components of the structural barrier to the entry of plasma proteins into brain. Time course studies suggest that caveolar changes precede junctional changes in acute brain injury. Additional factors modulating BBB permeability in acute brain injury are matrix metalloproteinases-2 and 9 and angiogenic factors, the most notable being vascular endothelial growth factor-A and angiopoietins (Ang) 1 and 2. Vascular endothelial growth factor-A and Ang2 have emerged as potent inducers of BBB breakdown while Ang1 is a potent anti-leakage factor. These factors have the potential to modulate permeability in acute brain injury and this is an area of ongoing research. Overall, a combination of haemodynamic, structural and molecular alterations affecting brain endothelium results in BBB breakdown in acute brain injury.

Morphology and properties of brain endothelial cells

The molecular advances in various aspects of brain endothelial cell function in steady states are considerable and difficult to summarize in one chapter. Therefore, this chapter focuses on endothelial permeability mechanisms in steady states and disease namely vasogenic edema. The morphology and properties of caveolae and tight junctions that are involved in endothelial permeability to macromolecules are reviewed. Endothelial transport functions are briefly reviewed. Diseases with alterations of endothelial permeability are mentioned and details are provided of the molecular alterations in caveolae and tight junctions in vasogenic edema. Other factors involved in increased endothelial permeability such as the matrix metalloproteinases are briefly discussed. Of the modulators of endothelial permeability, angioneurins such as the vascular endothelial growth factors and angiopoietins are discussed. The chapter concludes with a brief discussion on delivery of therapeutic substances across endothelium.

Vascular endothelial growth factor increases permeability of the blood-tumor barrier via caveolae-mediated transcellular pathway

The first goal of this study was to determine the effect of vascular endothelial growth factor (VEGF) on permeability of the blood-tumor barrier (BTB). The second goal was to determine possible cellular mechanisms by which VEGF increases permeability of the BTB. In the rat C6 glioma model, the permeability of the BTB was significantly increased after VEGF injection at dose of 0.05 ng/g and reached its peak at 45 min. Meanwhile, we observed that the density of pinocytotic vesicles of brain microvascular endothelial cells (BMECs) in the BTB increased dramatically by transmission electron microscopy. The immunohistochemistry and western blot analysis revealed that the expression level of caveolae structure proteins caveolin-1 and caveolin-2 in BMECs was increased after VEGF injection, peaked at 45 min, and then decreased to the untreated level. The time peak of expression level of caveolin-1 and caveolin-2 was identical with the peak time of permeability of the BTB and the density of pinocytotic vesicles. All of these results strongly indicated that VEGF increased permeability of the BTB caused by enhancement of the density of pinocytotic vesicles, and the molecular mechanism might be associated with upregulated expression of caveolin-1 and caveolin-2.

Endogenous adipocyte apolipoprotein E is colocalized with caveolin at the adipocyte plasma membrane

Apolipoprotein (apo)E is well established as a secreted protein that plays an important role in systemic lipoprotein metabolism and vascular wall homeostasis. Recently, endogenous expression of apoE in adipocytes has been shown to play an important role in adipocyte lipoprotein metabolism and gene expression consistent with a nonsecreted cellular itinerary for apoE. We designed studies to evaluate if adipocyte apoE was retained as a constituent protein in adipocytes and to identify a cellular retention compartment. Using confocal microscopy, coimmunoprecipitation, and sucrose density cellular fractionation, we establish that endogenous apoE shares a cellular itinerary with the constituent protein caveolin-1. Altering adipocyte caveolar number by modulating cellular cholesterol flux or altering caveolin expression regulates the distribution of cellular apoE between cytoplasmic and plasma membrane compartments. A mechanism for colocalization of apoE with caveolin was established by demonstrating a noncovalent interaction between an aromatic amino acid-enriched apoE N-terminal domain with the caveolin scaffolding domain. Absent apoE expression in adipocytes alters caveolar lipid composition. These observations provide evidence for an interaction between two proteins involved in cellular lipid metabolism in a cell specialized for lipid storage and flux, and rationalize a biological basis for the impact of adipocyte apoE expression on adipocyte lipoprotein metabolism.

Selective concomitant inhibition of mTORC1 and mTORC2 activity in estrogen receptor negative breast cancer cells by BN107 and oleanolic acid

Hormonal, targeted and chemotherapeutic strategies largely depend on the expression of their cognate receptors and are often accompanied by intolerable toxicities. Effective and less toxic therapies for estrogen receptor negative (ER-) breast cancers are urgently needed. Here, we present the potential molecular mechanisms mediating the selective pro-apoptotic effect induced by BN107 and its principle terpene, oleanolic acid (OA), on ER- breast cancer cells. A panel of breast cancer cell lines was examined and the most significant cytotoxic effect was observed in ER- breast lines. Apoptosis was the major cellular pathway mediating the cytotoxicity of BN107. We demonstrated that sensitivity to BN107 was correlated to the status of ERalpha. Specifically, the presence of functional ERalpha protected cells from BN107-induced apoptosis and absence of ERalpha increased the sensitivity. BN107, an extract rich in OA derivatives, caused rapid alterations in cholesterol homeostasis, presumably by depleting cholesterol in lipid rafts (LRs), which subsequently interfered with signaling mediated by LRs. We showed that BN107 or OA treatment in ER- breast cancer cells resulted in rapid and specific inhibition of LR-mediated survival signaling, namely mTORC1 and mTORC2 activities, by decreasing the levels of the mTOR/FRAP1, RAPTOR and RICTOR. Cotreatment with cholesterol abolished the proapoptotic effect and restored the disrupted mTOR activities. This is the first report demonstrating possible concomitant inhibition of both mTORC1 and mTORC2 activities by modulating the levels of protein constituents present in these signaling complexes, and thus provides a basis for future development of OA-based mTOR inhibitors.

High-molecular-weight hyaluronan is a novel inhibitor of pulmonary vascular leakiness

Endothelial cell (EC) barrier dysfunction results in increased vascular permeability, a perturbation observed in inflammatory states, tumor angiogenesis, atherosclerosis, and both sepsis and acute lung injury. Therefore, agents that enhance EC barrier integrity have important therapeutic implications. We observed that binding of high-molecular-weight hyaluronan (HMW-HA) to its cognate receptor CD44 within caveolin-enriched microdomains (CEM) enhances human pulmonary EC barrier function. Immunocytochemical analysis indicated that HMW-HA promotes redistribution of a significant population of CEM to areas of cell-cell contact. Quantitative proteomic analysis of CEM isolated from human EC demonstrated HMW-HA-mediated recruitment of cytoskeletal regulatory proteins (annexin A2, protein S100-A10, and filamin A/B). Inhibition of CEM formation [caveolin-1 small interfering RNA (siRNA) and cholesterol depletion] or silencing (siRNA) of CD44, annexin A2, protein S100-A10, or filamin A/B expression abolished HMW-HA-induced actin cytoskeletal reorganization and EC barrier enhancement. To confirm our in vitro results in an in vivo model of inflammatory lung injury with vascular hyperpermeability, we observed that the protective effects of HMW-HA on LPS-induced pulmonary vascular leakiness were blocked in caveolin-1 knockout mice. Furthermore, targeted inhibition of CD44 expression in the mouse pulmonary vasculature significantly reduced HMW-HA-mediated protection from LPS-induced hyperpermeability. These data suggest that HMW-HA, via CD44-mediated CEM signaling events, represents a potentially useful therapeutic agent for syndromes of increased vascular permeability.

Vasostatin 1 activates eNOS in endothelial cells through a proteoglycan-dependent mechanism

Accumulating evidences point to a significant role for the chromogranin A (CgA)-derived peptide vasostatin 1 (VS-1) in the protective modulation of the cardiovascular activity, because of its ability to counteract the adrenergic signal. We have recently shown that VS-1 induces a PI3K-dependent-nitric oxide (NO) release by endothelial cells, contributing to explain the mechanism of its cardio-suppressive and vasodilator properties. However, the cellular processes upstream the eNOS activation exerted by this peptide are still unknown, as typical high-affinity receptors have not been identified. Here we hypothesize that in endothelial cells VS-1 acts, on the basis of its cationic and amphipathic properties, as a cell penetrating peptide, binding to heparan sulfate proteoglycans (HSPGs) and activating eNOS phosphorylation (Ser1179) through a PI3K-dependent, endocytosis-coupled mechanism. In bovine aortic endothelial cells (BAE-1 cells) endocytotic vesicles trafficking was quantified by confocal microscopy with a water-soluble membrane dye; caveolin 1 (Cav1) shift from plasma membrane was studied by immunofluorescence staining; VS-1-dependent eNOS phosphorylation was assessed by immunofluorescence and immunoblot analysis. Our experiments demonstrate that VS-1 induces a marked increase in the caveolae-dependent endocytosis, (115 +/- 23% endocytotic spots/cell/field in VS-1-treated cells with respect to control cells), that is significantly reduced by both heparinase III (HEP, 17 +/- 15% above control) and Wortmannin (Wm, 7 +/- 22% above control). Heparinase, Wortmannin, and methyl-beta-cyclodextrin (MbetaCD) abolish the VS-1-dependent eNOS phosphorylation (P(Ser1179)eNOS). These results suggest a novel signal transduction pathway for endogenous cationic and amphipathic peptides in endothelial cells: HSPGs interaction and caveolae endocytosis, coupled with a PI3K-dependent eNOS phosphorylation.

A novel role for caveolin-1 in regulating endothelial nitric oxide synthase activation in response to H2O2 and shear stress

Previous studies have shown that acute increases in oxidative stress induced by the addition of hydrogen peroxide (H(2)O(2)) can increase endothelial nitric oxide synthase (eNOS) catalytic activity via an increase in the phosphorylation of eNOS at serine 1177. However, it is unclear how increased H(2)O(2) affects nitric oxide (NO) signaling when endothelial cells are exposed to biomechanical forces. Thus, the purpose of this study was to evaluate the acute effects of H(2)O(2) on NO signaling in the presence or absence of laminar shear stress. We found that acute sustained increases in cellular H(2)O(2) levels in bovine aortic endothelial cells did not alter basal NO generation but the NO produced in response to shear stress was significantly increased. This amplification in NO signaling was found to correlate with an H(2)O(2)-induced increase in eNOS localized to the plasma membrane and an increase in total caveolin-1 protein levels. We further demonstrated that overexpressing caveolin-1 increased eNOS localized to the plasma membrane again without altering total eNOS protein levels. We also found that caveolin-1 overexpression increased NO generation in response to shear stress but only in the presence of H(2)O(2). Conversely, depleting caveolin-1 with an siRNA decreased eNOS localized to the plasma membrane and abolished the enhanced NO generation. Finally, we found that expressing a caveolin-1 binding-site deletion mutant of eNOS in COS-7 cells decreased its plasma membrane localization and resulted in attenuated NO production in response to calcium activation. In conclusion, we have identified a new role for caveolin-1 in enhancing eNOS trafficking to the plasma membrane that seems to be involved in priming eNOS for flow-mediated activation under conditions of oxidative stress. To our knowledge, this is the first report that H(2)O(2) modulates eNOS activity by altering its subcellular location and that caveolin-1 can play a stimulatory role in NO signaling.

Reduced expression of angiotensin I-converting enzyme in caveolin-1 knockout mouse lungs

Reduced lung capillary expression of angiotensin I-converting enzyme (ACE), a key enzyme in cardiovascular pathophysiology, and of caveolin-1, an important regulator of endothelial cell signalling, has been demonstrated in various models of pulmonary arterial hypertension (PAH). We addressed the relationship between PAH and ACE expression in caveolin-1 knockout mice (Cav1(-/-)), which have moderate PAH. Tissue ACE activity was reduced by 50% in lungs from 3-month-old Cav1(-/-) mice compared to wild type (WT). A similar reduction in lung endothelial ACE expression was observed by measuring the lung uptake of (125)I-labeled monoclonal anti-ACE antibody and by quantitative immunohistochemistry. These alterations in ACE are limited to capillary segments of the pulmonary circulation. Functionally, the increase in pulmonary artery pressure (PAP) in response to ACE conversion of angiotensin I to angiotensin II in isolated, perfused mouse lungs was reduced significantly in Cav1(-/-) mice compared to WT. Thus, these complementary approaches demonstrate the dependence of lung microvascular endothelial cell ACE protein expression on caveolin-1 expression and underscore the vital role of caveolin-1-regulated pulmonary vascular homeostasis on endothelial ACE expression and activity. In summary, we have revealed a novel role of caveolin-1 in the regulation of ACE expression in pulmonary capillary endothelial cells. Further understanding of the mechanism by which reduced caveolin-1 expression leads altered pulmonary vascular development, PAH, and reduced ACE expression may have important clinical implications in patients with these severe lung diseases.

Peroxynitrite induces destruction of the tetrahydrobiopterin and heme in endothelial nitric oxide synthase: transition from reversible to irreversible enzyme inhibition

Endothelial nitric oxide synthase (eNOS) is an important regulator of vascular and cardiac function. Peroxynitrite (ONOO(-)) inactivates eNOS, but questions remain regarding the mechanisms of this process. It has been reported that inactivation is due to oxidation of the eNOS zinc-thiolate cluster, rather than the cofactor tetrahydrobiopterin (BH(4)); however, this remains highly controversial. Therefore, we investigated the mechanisms of ONOO(-)-induced eNOS dysfunction and their dose dependence. Exposure of human eNOS to ONOO(-) resulted in a dose-dependent loss of activity with a marked destabilization of the eNOS dimer. HPLC analysis indicated that both free and eNOS-bound BH(4) were oxidized during exposure to ONOO(-); however, full oxidation of protein-bound biopterin required higher ONOO(-) levels. Additionally, ONOO(-) triggered changes in the UV/visible spectrum and heme content of the enzyme. Preincubation of eNOS with BH(4) decreased dimer destabilization and heme alteration. Addition of BH(4) to the ONOO(-)-destabilized eNOS dimer only partially rescued enzyme function. In contrast to ONOO(-) treatment, incubation with the zinc chelator TPEN with removal of enzyme-bound zinc did not change the eNOS activity or stability of the SDS-resistant eNOS dimer, demonstrating that the dimer stabilization induced by BH(4) does not require zinc occupancy of the zinc-thiolate cluster. While ONOO(-) treatment was observed to induce loss of Zn binding, this cannot account for the loss of enzyme activity. Therefore, ONOO(-)-induced eNOS inactivation is primarily due to oxidation of BH(4) and irreversible destruction of the heme/heme center.

Host-cell lipid rafts: a safe door for micro-organisms?

The lipid raft hypothesis proposed that these microdomains are small (10-200 nM), highly dynamic and enriched in cholesterol, glycosphingolipids and signalling phospholipids, which compartmentalize cellular processes. These membrane regions play crucial roles in signal transduction, phagocytosis and secretion, as well as pathogen adhesion/interaction. Throughout evolution, many pathogens have developed mechanisms to escape from the host immune system, some of which are based on the host membrane microdomain machinery. Thus lipid rafts might be exploited by pathogens as signalling and entry platforms. In this review, we summarize the role of lipid rafts as players in the overall invasion process used by different pathogens to escape from the host immune system.

Sensitivity of NOS-dependent vascular relaxation pathway to mineralocorticoid receptor blockade in caveolin-1-deficient mice

Endothelial caveolin-1 (cav-1) is an anchoring protein in plasma membrane caveolae where it binds endothelial nitric oxide synthase (eNOS) and limits its activation, particularly in animals fed a high salt (HS) diet. Cav-1 also interacts with steroid receptors such as the mineralocorticoid receptor (MR). To test the hypothesis that vascular reactivity is influenced by an interplay between MR and cav-1 during HS diet, we examined the effects of MR blockade on NOS-mediated vascular relaxation in normal and cav-1-deficient mice. Wild-type (WT) and cav-1 knockout mice (cav-1(-/-)) were fed for 14 days a HS (4% NaCl) diet with and without the MR antagonist eplerenone (Epl; 100 mg x kg(-1) x day(-1)). After systolic blood pressure (BP) was measured, the thoracic aorta was isolated for measurement of vascular reactivity, and the aorta and heart were used for measurement of eNOS and MR expression. BP was not different between WT + Epl and WT, but was higher in cav-1(-/-) + Epl than in cav-1(-/-) mice. Phenylephrine (Phe)-induced vascular contraction was less in cav-1(-/-) than WT, and significantly enhanced in cav-1(-/-) + Epl than in cav-1(-/-), but not in WT + Epl compared with WT. Endothelium removal and NOS blockade by N(omega)-nitro-l-arginine methyl ester (l-NAME) enhanced Phe contraction in cav-1(-/-), but not cav-1(-/-) + Epl. ACh-induced aortic relaxation was reduced in cav-1(-/-) + Epl versus cav-1(-/-), but not in WT + Epl compared with WT. Endothelium removal, l-NAME, and the guanylate cyclase inhibitor ODQ abolished the large ACh-induced relaxation in cav-1(-/-) and the remaining relaxation in the cav-1(-/-) + Epl but had similar inhibitory effect in WT and WT + Epl. Real-time RT-PCR indicated decreased eNOS mRNA expression in the aorta and heart, and Western blots revealed decreased total eNOS in the heart of cav-1(-/-) + Epl compared with cav-1(-/-). Vascular and cardiac MR expression was less in cav-1(-/-) than WT, but not in cav-1(-/-) + Epl compared with cav-1(-/-). Plasma aldosterone (Aldo) was not different between WT and cav-1(-/-) mice nontreated or treated with Epl. Thus in cav-1 deficiency states and HS diet MR blockade is associated with increased BP, enhanced vasoconstriction, and decreased NOS-mediated vascular relaxation and eNOS expression. The data suggest that, in the absence of cav-1, MR activation plays a beneficial role in regulating eNOS expression/activity and, consequently, the vascular function during HS diet.

Fatty acids and signalling in endothelial cells

The endothelium is critical for the maintenance of a proper vessel function. Disturbances of endothelial function, called endothelial dysfunction, have serious implications, and lead to the development of atherosclerosis. It is well established that the risk for atherosclerosis development is influenced by nutritional factors such as the intake of certain fatty acids. Due to the fundamental role of the endothelium for atherosclerosis development, it is, therefore, likely that fatty acids directly influence the function of endothelial cells. The present review aims to explain the divergent effects of different types of fatty acids on cardiovascular disease risk by summarizing in vitro-data on the effects of fatty acids on (1) important signalling pathways involved in the modulation of endothelial cell function, and (2) endothelial cell functional properties, namely vasoactive mediator release and mononuclear cell recruitment, both of which are typically dysregulated during endothelial dysfunction.

The endothelial saga: the past, the present, the future

Endothelium-dependent changes in vasomotor tone, whether evoked by vasoactive agents or physical forces, are recognized as essential for the local hemodynamic control in various normal and pathological circumstances. They are based on a complex signaling network within the vascular wall. In recent years, substantial efforts have been made to analyze how such signals are generated and used in the endothelium-dependent control of vascular smooth muscle. The underlying mechanisms vary with species, age, sex, hormonal status, vascular bed studied, caliber of the blood vessels, triggering stimuli, pre-existing vascular tone, oxidative stress, and pathology. Such aspects and many others will be addressed specifically by the authors contributing to this volume.

Regulation of epithelial sodium channel trafficking by ubiquitination

Amiloride-sensitive epithelial sodium (Na(+)) channels (ENaC) play a crucial role in Na(+) transport and fluid reabsorption in the kidney, lung, and colon. The magnitude of ENaC-mediated Na(+) transport in epithelial cells depends on the average open probability of the channels and the number of channels on the apical surface of epithelial cells. The number of channels in the apical membrane, in turn, depends upon a balance between the rate of ENaC insertion and the rate of removal from the apical membrane. ENaC is made up of three homologous subunits, alpha, beta, and gamma. The C-terminal domain of all three subunits is intracellular and contains a proline rich motif (PPxY). Mutations or deletion of this PPxY motif in the beta and gamma subunits prevent the binding of one isoform of a specific ubiquitin ligase, neural precursor cell expressed developmentally down-regulated protein (Nedd4-2) to the channel in vitro and in transfected cell systems, thereby impeding ubiquitin conjugation of the channel subunits. Ubiquitin conjugation would seem to imply that ENaC turnover is determined by the ubiquitin-proteasome system, but when MDCK cells are transfected with ENaC, ubiquitin conjugation apparently leads to lysosomal degradation. However, in untransfected epithelial cells (A6) expressing endogenous ENaC, ENaC appears to be degraded by the ubiquitin-proteasome system. Nonetheless, in both transfected and untransfected cells, the rate of ENaC degradation is apparently controlled by the rate of Nedd4-2-mediated ENaC ubiquitination. Controlling the rate of degradation is apparently important enough to have multiple, redundant pathways to control Nedd4-2 and ENaC ubiquitination.

Alterations in the activity and expression of endothelial NO synthase in aged human endothelial cells

This study was to investigate factors underlying the age-related decrease in NO production in vascular endothelial cells. The age-related changes in NO production, the activity and expression level of eNOS, and eNOS binding proteins, were studied in HUVECs. NO production in HUVECs significantly decreased in an age-dependent manner. The potentiation of NO production by L-Arg was significantly suppressed by L-NIO (eNOS-specific inhibitor) in young HUVECs and was suppressed by 1400W (iNOS-specific inhibitor) in aged HUVECs. The aged HUVECs had lower eNOS protein levels than young cells. eNOS phosphorylation at Ser-1177 (active) decreased gradually from PDL 23 through 40, and eNOS phosphorylation at Thr-495 (inactive) increased in aged cells. Changes of intracellular eNOS binding proteins, such as caveolin-1, pAkt, and Hsp90, as well as interaction between eNOS and eNOS binding proteins, indicated decreasing enzyme activity in aged HUVECs. Aging might decrease the activity as well as expression level of eNOS in HUVECs. And the decrease in eNOS activity probably implicated to the alterations in the regulatory binding proteins. For further study, it needs to be confirmed that the age-related change in the intracellular distribution of eNOS and the relative contribution of eNOS and iNOS on vascular dysfunction in aged endothelial cells.

Size and dynamics of caveolae studied using nanoparticles in living endothelial cells

Caveolae are plasma membrane invaginations prominent in all endothelial cells lining blood vessels. Caveolae characteristically bud to form free cytoplasmic vesicles capable of transporting carrier proteins such as albumin through the cell. However, caveolae size distribution and dynamics in living endothelial cells and ability of caveolae to internalize nanoparticles are not well understood. We demonstrate here the design of a dual-color nanoparticle pair to measure noninvasively caveolae size and dynamics. First, we coated nanoparticles with BSA (bovine serum albumin) to address whether albumin promoted their delivery. Albumin has been shown to bind to protein on endothelial cell surface localized in caveolae and activate albumin endocytosis. Imaging of BSA-coated nanoparticles varying from 20 to 100 nm in diameter in endothelial cells demonstrated that caveolae-mediated nanoparticle uptake was dependent on albumin coating of particles. We also showed that caveolae could accommodate up to 100 nm diameter nanoparticles, a size larger than the diameter of typical caveolae, suggesting compliant property of caveolae. Together, our results show the feasibility of tracking multicolored nanoparticles in living endothelial cells and potential usefulness for designing therapeutic nanoparticle cargo to cross the limiting vessel wall endothelial barrier.

Gangliosides and beta1-integrin are required for caveolae and membrane domains

Caveolae are plasma membrane domains involved in the uptake of certain pathogens and toxins. Internalization of some cell surface integrins occurs via caveolae suggesting caveolae may play a crucial role in modulating integrin-mediated adhesion and cell migration. Here we demonstrate a critical role for gangliosides (sialo-glycosphingolipids) in regulating caveolar endocytosis in human skin fibroblasts. Pretreatment of cells with endoglycoceramidase (cleaves glycosphingolipids) or sialidase (modifies cell surface gangliosides and glycoproteins) selectively inhibited caveolar endocytosis by >70%, inhibited the formation of plasma membrane domains enriched in sphingolipids and cholesterol ('lipid rafts'), reduced caveolae and caveolin-1 at the plasma membrane by approximately 80%, and blunted activation of beta1-integrin, a protein required for caveolar endocytosis in these cells. These effects could be reversed by a brief incubation with gangliosides (but not with asialo-gangliosides or other sphingolipids) at 10 degrees C, suggesting that sialo-lipids are critical in supporting caveolar endocytosis. Endoglycoceramidase treatment also caused a redistribution of focal adhesion kinase, paxillin, talin, and PIP Kinase Igamma away from focal adhesions. The effects of sialidase or endoglycoceramidase on membrane domains and the distribution of caveolin-1 could be recapitulated by beta1-integrin knockdown. These results suggest that both gangliosides and beta1-integrin are required for maintenance of caveolae and plasma membrane domains.

The emerging role of symmetric dimethylarginine in vascular disease

Asymmetric dimethylarginine (ADMA), an endogenous methylated form of the amino acid L-arginine, inhibits the activity of the enzyme endothelial nitric oxide synthase (eNOS), with consequent reduced synthesis of nitric oxide (NO). An increased synthesis and/or a reduced catabolism of ADMA might contribute to the onset and progression of atherosclerosis and thrombosis. The detrimental effects of ADMA on endothelial function, cardiovascular homeostasis, and cardiovascular outcomes have been extensively investigated. However, little attention has been paid to another methylated form of L-arginine, symmetric dimethylarginine (SDMA), as a potential modulator of vascular homeostasis and vascular disease. The first part of this chapter discusses the synthesis, transport, and metabolism of ADMA and SDMA and summarizes the evidence linking ADMA with vascular disease and adverse cardiovascular outcomes. The second part describes the results of recent studies highlighting the important role of SDMA in modulating vascular homeostasis and vascular damage. Suggestions for future research directions on SDMA are also discussed.

Filamin A regulates caveolae internalization and trafficking in endothelial cells

Transcytosis via caveolae is critical for maintaining vascular homeostasis by regulating the tissue delivery of macromolecules, hormones, and lipids. In the present study, we test the hypothesis that interactions between F-actin cross-linking protein filamin A and caveolin-1 facilitate the internalization and trafficking of caveolae. Small interfering RNA-mediated knockdown of filamin A, but not filamin B, reduced the uptake and transcytosis of albumin by approximately 35 and 60%, respectively, without altering the actin cytoskeletal structure or cell-cell adherens junctions. Mobility of both intracellular caveolin-1-green fluorescent protein (GFP)-labeled vesicles measured by fluorescence recovery after photobleaching and membrane-associated vesicles measured by total internal reflection-fluorescence microscopy was decreased in cells with reduced filamin A expression. In addition, in melanoma cells that lack filamin A (M2 cells), the majority of caveolin-1-GFP was localized on the plasma membrane, whereas in cells in which filamin A expression was reconstituted (A7 cells and M2 cells transfected with filamin A-RFP), caveolin-1-GFP was concentrated in intracellular vesicles. Filamin A association with caveolin-1 in endothelial cells was confirmed by cofractionation of these proteins in density gradients, as well as by coimmunoprecipitation. Moreover, this interaction was enhanced by Src activation, associated with increased caveolin-1 phosphorylation, and blocked by Src inhibition. Taken together, these data suggest that filamin A association with caveolin-1 promotes caveolae-mediated transport by regulating vesicle internalization, clustering, and trafficking.

Molecular mechanisms of clathrin-independent endocytosis

There is good evidence that, in addition to the canonical clathrin-associated endocytic machinery, mammalian cells possess multiple sets of proteins that are capable of mediating the formation of endocytic vesicles. The identity, mechanistic properties and function of these clathrin-independent endocytic pathways are currently under investigation. This Commentary briefly recounts how the field of clathrin-independent endocytosis has developed to date. It then highlights recent progress in identifying key proteins that might define alternative types of endocytosis. These proteins include CtBP (also known as BARS), flotillins (also known as reggies) and GRAF1. We argue that a combination of information about pathway-specific proteins and the ultrastructure of endocytic invaginations provides a means of beginning to classify endocytic pathways.

Erythropoietin attenuates hypertrophy of neonatal rat cardiac myocytes induced by angiotensin-II in vitro

OBJECTIVE

Erythropoietin (EPO) is a haematopoietic hormone that has been confirmed as a novel cardioprotective agent. In this study, we test the hypothesis that EPO inhibits angiotensin-II (Ang-II)-induced hypertrophy in cultured neonatal rat cardiomyocytes.

MATERIAL AND METHODS

Cultured neonatal rat cardiomyocytes were used to evaluate the effects of EPO on Ang-II-induced hypertrophy in vitro. The surface area and mRNA expression of atrial natriuretic (ANF) myocytes were employed to detect cardiac hypertrophy. A phosphatidylinositol 3'-kinase (PI3K) inhibitor LY294002 and an endothelial nitric oxide synthase (eNOS) inhibitor L-NAME were also employed to detect the underlying mechanism of EPO. Intracellular signal molecules, such as Akt (PKB), phosphorylated Akt, eNOS and transforming growth factor-beta1 (TGF-beta1) protein expression were determined by Western blot. Nitric oxide (NO) levels in the supernatant of cultured cardiomyocytes were assayed using an NO assay kit.

RESULTS

The results indicate that EPO significantly attenuates Ang-II-induced hypertrophy shown as inhibition of increases in cell surface area and ANF mRNA levels. NO production was also increased proportionally in the EPO-treated group. EPO enhanced Akt activation and eNOS protein expression, whereas LY294002 or L-NAME partially abolished the anti-hypertrophic effect of EPO, accompanied by a decrease in Akt activation, eNOS protein expression and/or a reduction of NO production. EPO also down-regulated the protein expression of TGF-beta1.

CONCLUSION

We conclude that EPO attenuates cardiac hypertrophy via activation of the PI3K-Akt-eNOS-NO pathway and the down-regulation of TGF-beta1.

Polyphenol-containing azuki bean (Vigna angularis) extract attenuates blood pressure elevation and modulates nitric oxide synthase and caveolin-1 expressions in rats with hypertension

BACKGROUND AND AIMS

Azuki beans (Vigna angularis) contain polyphenols such as proanthocyanidins that exhibit potential radical scavenging activities. We herein investigated the effects of polyphenol-containing azuki bean extract (ABE) on elevated blood pressure, nitric oxide (NO) production, and expressions of endothelial NO synthase (eNOS), inducible NOS (iNOS), and caveolin-1 proteins in the aorta and kidney of chronically hypertensive rats.

METHODS AND RESULTS

Spontaneously hypertensive rats (SHRs/Izm) with approximately 200 mm Hg systolic blood pressure (SBP) were randomly divided into 2 groups fed either 0% or 0.9% ABE-containing diet. Age-matched normotensive Wistar-Kyoto rats were used as the control. The content of 24-h urinary nitrate/nitrite (NOx) excretion was measured to evaluate NO production. After 8 weeks of treatment, the eNOS, iNOS, and caveolin-1 protein expressions in the aorta and kidney were analyzed by western blotting. The SBP of the ABE-treated SHR was significantly lower than that of the untreated SHR. The level of 24-h urinary NOx excretion was significantly higher in the ABE-treated SHR than in the untreated SHR. The eNOS and iNOS expressions in the aorta and kidney were remarkably upregulated in the untreated SHR but suppressed in the ABE-treated SHR. The vascular and renal caveolin-1 expressions were upregulated in the ABE-treated SHR.

CONCLUSIONS

ABE reduced the elevated blood pressure and increased NO production in long-term treatment. It may be associated with the modulation of eNOS and iNOS protein expressions in the aorta and kidney during the development of hypertension.

Phosphorylation of caveolin-1 regulates oxidant-induced pulmonary vascular permeability via paracellular and transcellular pathways

RATIONALE

Oxidants are important signaling molecules known to increase endothelial permeability, although the mechanisms underlying permeability regulation are not clear.

OBJECTIVE

To define the role of caveolin-1 in the mechanism of oxidant-induced pulmonary vascular hyperpermeability and edema formation.

METHODS AND RESULTS

Using genetic approaches, we show that phosphorylation of caveolin-1 Tyr14 is required for increased pulmonary microvessel permeability induced by hydrogen peroxide (H(2)O(2)). Caveolin-1-deficient mice (cav-1(-/-)) were resistant to H(2)O(2)-induced pulmonary vascular albumin hyperpermeability and edema formation. Furthermore, the vascular hyperpermeability response to H(2)O(2) was completely rescued by expression of caveolin-1 in cav-1(-/-) mouse lung microvessels but was not restored by the phosphorylation-defective caveolin-1 mutant. The increase in caveolin-1 phosphorylation induced by H(2)O(2) was dose-dependently coupled to both increased (125)I-albumin transcytosis and decreased transendothelial electric resistance in pulmonary endothelial cells. Phosphorylation of caveolin-1 following H(2)O(2) exposure resulted in the dissociation of vascular endothelial cadherin/beta-catenin complexes and resultant endothelial barrier disruption.

CONCLUSIONS

Caveolin-1 phosphorylation-dependent signaling plays a crucial role in oxidative stress-induced pulmonary vascular hyperpermeability via transcellular and paracellular pathways. Thus, caveolin-1 phosphorylation may be an important therapeutic target for limiting oxidant-mediated vascular hyperpermeability, protein-rich edema formation, and acute lung injury.

Pathology and new players in the pathogenesis of brain edema

Brain edema continues to be a major cause of mortality after diverse types of brain pathologies such as major cerebral infarcts, hemorrhages, trauma, infections and tumors. The classification of edema into vasogenic, cytotoxic, hydrocephalic and osmotic has stood the test of time although it is recognized that in most clinical situations there is a combination of different types of edema during the course of the disease. Basic information about the types of edema is provided for better understanding of the expression pattern of some of the newer molecules implicated in the pathogenesis of brain edema. These molecules include the aquaporins, matrix metalloproteinases and growth factors such as vascular endothelial growth factors A and B and the angiopoietins. The potential of these agents in the treatment of edema is discussed. Since many molecules are involved in the pathogenesis of brain edema, effective treatment cannot be achieved by a single agent but will require the administration of a "magic bullet" containing a variety of agents released at different times during the course of edema in order to be successful.

Persistent eNOS activation secondary to caveolin-1 deficiency induces pulmonary hypertension in mice and humans through PKG nitration

Pulmonary hypertension (PH) is an unremitting disease defined by a progressive increase in pulmonary vascular resistance leading to right-sided heart failure. Using mice with genetic deletions of caveolin 1 (Cav1) and eNOS (Nos3), we demonstrate here that chronic eNOS activation secondary to loss of caveolin-1 can lead to PH. Consistent with a role for eNOS in the pathogenesis of PH, the pulmonary vascular remodeling and PH phenotype of Cav1-/- mice were absent in Cav1-/-Nos3-/- mice. Further, treatment of Cav1-/- mice with either MnTMPyP (a superoxide scavenger) or l-NAME (a NOS inhibitor) reversed their pulmonary vascular pathology and PH phenotype. Activation of eNOS in Cav1-/- lungs led to the impairment of PKG activity through tyrosine nitration. Moreover, the PH phenotype in Cav1-/- lungs could be rescued by overexpression of PKG-1. The clinical relevance of the data was indicated by the observation that lung tissue from patients with idiopathic pulmonary arterial hypertension demonstrated increased eNOS activation and PKG nitration and reduced caveolin-1 expression. Together, these data show that loss of caveolin-1 leads to hyperactive eNOS and subsequent tyrosine nitration-dependent impairment of PKG activity, which results in PH. Thus, targeting of PKG nitration represents a potential novel therapeutic strategy for the treatment of PH.

Persistent eNOS activation secondary to caveolin-1 deficiency induces pulmonary hypertension in mice and humans through PKG nitration

Pulmonary hypertension (PH) is an unremitting disease defined by a progressive increase in pulmonary vascular resistance leading to right-sided heart failure. Using mice with genetic deletions of caveolin 1 (Cav1) and eNOS (Nos3), we demonstrate here that chronic eNOS activation secondary to loss of caveolin-1 can lead to PH. Consistent with a role for eNOS in the pathogenesis of PH, the pulmonary vascular remodeling and PH phenotype of Cav1-/- mice were absent in Cav1-/-Nos3-/- mice. Further, treatment of Cav1-/- mice with either MnTMPyP (a superoxide scavenger) or l-NAME (a NOS inhibitor) reversed their pulmonary vascular pathology and PH phenotype. Activation of eNOS in Cav1-/- lungs led to the impairment of PKG activity through tyrosine nitration. Moreover, the PH phenotype in Cav1-/- lungs could be rescued by overexpression of PKG-1. The clinical relevance of the data was indicated by the observation that lung tissue from patients with idiopathic pulmonary arterial hypertension demonstrated increased eNOS activation and PKG nitration and reduced caveolin-1 expression. Together, these data show that loss of caveolin-1 leads to hyperactive eNOS and subsequent tyrosine nitration-dependent impairment of PKG activity, which results in PH. Thus, targeting of PKG nitration represents a potential novel therapeutic strategy for the treatment of PH.

Caveolin-1 Expression and Hemodynamics in COPD Patients

Caveolin-1 is a regulator of both intracellular calcium homeostasis and endothelial nitric oxide synthase and may play a pathogenetic role in pulmonary hypertension. In the present study, we aimed to investigate the correlations between pulmonary hemodynamics and vessel morphology including the expression of Caveolin-1 in pulmonary arterioles from patients with chronic obstructive pulmonary disease (COPD) who underwent lung-volume reduction surgery. Staining and subsequent analysis was performed on paraffin-embedded lung tissue from COPD patients (n = 12). Pulmonary arteries with an external diameter of 100-500µm were analysed. Immunhistochemistry with antibodies against caveolin-1 was performed and intensity was assessed. Morphometric data were obtained by using computer-assisted imaging software. The findings were quantified and correlated to hemodynamic data obtained by right-heart catheterization. In COPD patients with pulmonary hypertension (n = 5), the expression of caveolin-1 within the medial smooth muscle cell layer was found to be increased, whereas the intimal caveolin-1 was more prominently expressed in COPD patients with normal pulmonary pressures (n = 7). The ratio between these expression patterns was positively correlated to the mean pulmonary artery pressure. Similar findings were observed for the ratio between intimal and medial thickness as well as for the expression of smooth muscle actin (SMA).

Taken together, the expression of caveolin-1 within medial smooth muscle cells of pulmonary arteries in patients with COPD is associated with pulmonary hypertension. Our results thus emphasize a potential novel player in the pathogenesis of COPD-associated pulmonary hypertension.

Possible mechanisms involved in the discrepancy of hepatic and aortic endothelial nitric oxide synthases during the development of cirrhosis in rats

BACKGROUND/AIM

In cirrhosis, systemic nitric oxide (NO) overproduction and hepatic NO hypoproduction lead to arterial vasodilatation and portal hypertension. The mechanisms involved in these alterations in endothelial NO synthase (eNOS)-derived NO production in hepatic and systemic vasculature remain unknown. The aim of this study was to evaluate the regulation of eNOS and its major modulators in the liver and aorta during the development of cirrhosis in rats.

METHODS

Activated eNOS and Akt and expressions, and caveolin-1 (Cav-1) and scavenger receptor class B type I (SR-BI) expressions were measured before and 1, 2, 3 and 4 weeks after bile duct ligation. Plasma high-density lipoprotein (HDL) levels were measured.

RESULTS

Activated aortic eNOS increased at week 1, whereas it began to decrease at week 3 in the liver. Aortic expression of Cav-1 decreased at week 3 while hepatic expression increased by four-fold. Activated aortic Akt increased progressively while in the liver it gradually decreased during the development of cirrhosis. HDL levels decreased during the first week and decreased thereafter. The hepatic expression of SR-BI decreased.

CONCLUSION

This study shows that the modulation of Akt and Cav-1 is inverted in the liver and the aorta during the development of cirrhosis. In addition, decreased HDL levels may play a role in reduced hepatic eNOS activity.

Albumin-bound formulation of paclitaxel (Abraxane ABI-007) in the treatment of breast cancer

Breast cancer is the most common type of malignancy diagnosed in women. In the metastatic setting this disease is still uncurable. Taxanes represent an important class of antitumor agents which have proven to be fundamental in the treatment of advanced and early-stage breast cancer, but the clinical advances of taxanes have been limited by their highly hydrophobic molecular status. To overcome this poor water solubility, lipid-based solvents have been used as a vehicle, and new systemic formulations have been developed, mostly for paclitaxel, which are Cremophor-free and increase the circulation time of the drug. ABI-007 is a novel, albumin-bound, 130-nm particle formulation of paclitaxel, free from any kind of solvent. It has been demonstrated to be superior to an equitoxic dose of standard paclitaxel with a significantly lower incidence of toxicities in a large, international, randomized phase III trial. The availability of new drugs, such as Abraxane, in association with other traditional and non-traditional drugs (new antineoplastic agents and targeted molecules), will give the oncologist many different effective treatment options for patients in this setting.

Three-dimensional organization of fenestrae labyrinths in liver sinusoidal endothelial cells

BACKGROUND/AIMS

Liver sinusoidal endothelial cell (LSEC) fenestrae are membrane-bound pores that are grouped in sieve plates and act as a bidirectional guardian in regulating transendothelial liver transport. The high permeability of the endothelial lining is explained by the presence of fenestrae and by various membrane-bound transport vesicles. The question as to whether fenestrae relate to other transport compartments remains unclear and has been debated since their discovery almost 40 years ago.

METHODS

In this study, novel insights concerning the three-dimensional (3D) organization of the fenestrated cytoplasm were built on transmission electron tomographical observations on isolated and cultured whole-mount LSECs. Classical transmission electron microscopy and atomic force microscopy imaging was performed to accumulate cross-correlative structural evidence.

RESULTS AND CONCLUSIONS

The data presented here indicate that different arrangements of fenestrae have to be considered: i.e. open fenestrae that lack any structural obstruction mainly located in the thin peripheral cytoplasm and complexes of multifolded fenestrae organized as labyrinth-like structures that are found in the proximity of the perinuclear area. Fenestrae in labyrinths constitute about one-third of the total LSEC porosity. The 3D reconstructions also revealed that coated pits and small membrane-bound vesicles are exclusively interspersed in the non-fenestrated cytoplasmic arms.

Microfilament and microtubule assembly is required for the propagation of inositol trisphosphate receptor-induced Ca2+ waves in bovine aortic endothelial cells

Ca2+ is a highly versatile second messenger that plays a key role in the regulation of numerous cell processes. One-way cells ensure the specificity and reliability of Ca2+ signals is by organizing them spatially in the form of waves that propagate throughout the cell or within a specific subcellular region. In non-excitable cells, the inositol 1,4,5-trisphosphate receptor (IP3R) is responsible for the release of Ca2+ from the endoplasmic reticulum. The spatial aspect of the Ca2+ signal depends on the organization of various elements of the Ca2+ signaling toolkit and varies from tissue to tissue. Ca2+ is implicated in many of endothelium functions that thus depend on the versatility of Ca2+ signaling. In the present study, we showed that the disruption of caveolae microdomains in bovine aortic endothelial cells (BAEC) with methyl-beta-cyclodextrin was not sufficient to disorganize the propagation of Ca2+ waves when the cells were stimulated with ATP or bradykinin. However, disorganizing microfilaments with latrunculin B and microtubules with colchicine both prevented the formation of Ca2+ waves. These results suggest that the organization of the Ca2+ waves mediated by IP3R channels does not depend on the integrity of caveolae in BAEC, but that microtubule and microfilament cytoskeleton assembly is crucial.

Enhanced caveolae-mediated endocytosis by diagnostic ultrasound in vitro

The modulation of cellular endothelial permeability is a desirable goal for targeted delivery of labels and therapeutic macromolecules; the underlying mechanisms, however, remains poorly understood. Here, we hypothesize that a higher endothelial permeability may result as an outcome of selective enhancement of caveolar endocytosis by ultrasound (US), in the frequency and intensity range of current clinical diagnostic use. To assess the role of free radicals in this phenomenon, we exposed confluent human endothelial cells to pulsed diagnostic US for 30 min, with a mechanical index (MI) of 0.5 and 1.2, using a 1.6-MHz cardiac US scan, and endothelial cells not exposed to US were used as control. Here we show that pulsed diagnostic US with a MI of 1.2 (high mechanical index ultrasound [HMIUS]) were able to selectively enhance endothelial caveolar internalization of recombinant glutathione-S-transferase (GST)-Tat11-EGFP fusion protein (26 +/- 1 vs. 11.6 +/- 1 A.U, p < 0.001 vs. control), without disruption of plasma membrane integrity. Moreover, pulsed diagnostic US with a MI of 0.5 (low mechanical index ultrasound) did not increase caveolar endocytosis compared with control (11.4 +/- 1.2 vs. 11.6 +/- 1). Free-radical generation inhibitors, such as catalase and superoxide dismutase, reduced the HMIUS-induced caveolar internalization by a 49.29% factor; finally, HMIUS-induced caveolar endocytosis was found to be associated with a significant increase in the phosphorylation of tyr-14-caveolin1, ser1177-eNOS and Thr202/Tyr204-ERK(1/2) compared with control. These findings show how HMIUS irradiation of human endothelial cells cause a selective enhancement of caveolar-dependent permeability, partially mediated by free radicals generation, inducing a marked increase of phosphorylation of caveolar-related proteins. Thus, the use of diagnostic US could potentially be used as an adjuvant to drive caveolar traffic of extracellular peptides by using a higher level of US energy.

Expression of endothelial phosphorylated caveolin-1 is increased in brain injury

AIMS

Increased endothelial caveolae leading to transcytosis of plasma proteins is associated with blood-brain barrier (BBB) breakdown and cerebral oedema in brain injury. Increased expression of caveolin-1alpha (Cav-1), an integral caveolar membrane protein, was reported in endothelium of arterioles and veins with BBB breakdown to fibronectin post injury. In this study the phosphorylation state of Cav-1 and its association with BBB breakdown was determined in the rat cortical cold injury model over a period of days 0.5-6 post lesion.

METHODS

Expression of phosphorylated Cav-1 was determined by immunoblotting and dual labelling immunofluorescence for phosphorylated caveolin-1 and fibronectin, a marker of BBB breakdown. A phospho-specific monoclonal antibody that selectively recognizes only tyrosine 14-phosphorylated Cav-1 (PY14Cav-1) was used.

RESULTS

Immunoblots showed constitutive expression of PY14Cav-1 in cortex of control rats and a significant increase in PY14Cav-1 expression at the lesion site up to day 4 post lesion. PY14Cav-1 immunostaining was observed in the endothelium of lesion vessels at days 0.5-4 post lesion, in neutrophils at days 0.5 and 2 and in macrophages at day 6 post lesion. Dual labelling showed that 100% of vessels with BBB breakdown to fibronectin showed endothelial PY14Cav-1 on day 0.5, the percentage decreasing to 62% on day 4. On day 6, none of the vessels showed endothelial phosphorylated Cav-1.

CONCLUSIONS

The presence of phosphorylated Cav-1 in endothelium of vessels showing BBB breakdown suggests that phosphorylated Cav-1 signalling may be one of the factors associated with early BBB breakdown and brain oedema in brain injury.

S-nitrosylated human serum albumin-mediated cytoprotective activity is enhanced by fatty acid binding

Binding of oleate to S-nitrosylated human serum albumin (SNO-HSA) enhances its cytoprotective effect on liver cells in a rat ischemia/reperfusion model. It enhances the antiapoptotic effect of SNO-HSA on HepG2 cells exposed to anti-Fas antibody. To identify some of the reasons for the increased cytoprotective effects, additional experiments were performed with glutathione and HepG2 cells. As indicated by 5,5'-dithiobis-2-nitrobenzoic acid binding, the addition of oleate increased the accessibility of the single thiol group of albumin. Binding of increasing amounts of oleate resulted in increasing and more rapid S-transnitrosation of glutathione. Likewise, binding of oleate, or of a mixture of endogenous fatty acids, improved S-denitrosation of SNO-HSA by HepG2 cells. Oleate also enhanced S-transnitrosation by HepG2 cells, as detected by intracellular fluorescence of diaminofluorescein-FM. All of the S-transnitrosation caused by oleate binding was blocked by filipin III. Oleate also increased, in a dose-dependent manner, the binding of SNO-HSA labeled with fluorescein isothiocyanate to the surface of the hepatocytes. A model in two parts was worked out for S-transnitrosation, which does not involve low molecular weight thiols. Fatty acid binding facilitates S-denitrosation of SNO-HSA, increases its binding to HepG2 cells and greatly increases S-transnitrosation by hepatocytes in a way that is sensitive to filipin III. A small nitric oxide transfer takes place in a slow system, which is unaffected by fatty acid binding to SNO-HSA and not influenced by filipin III. Thus, fatty acids could be a novel type of mediator for S-transnitrosation.

Imaging hemodynamics

Microvascular permeability is a pharmacologic indicator of tumor response to therapy, and it is expected that this biomarker will evolve into a clinical surrogate endpoint and be integrated into protocols for determining patient response to antiangiogenic or antivascular therapies. This review discusses the physiological context of vessel permeability in an imaging setting, how it is affected by active and passive transport mechanisms, and how it is described mathematically for both theoretical and complex dynamic microvessel membranes. Many research groups have established dynamic-enhanced imaging protocols for estimating this important parameter. This review discusses those imaging modalities, the advantages and disadvantages of each, and how they compare in terms of their ability to deliver information about therapy-associated changes in microvessel permeability in humans. Finally, this review discusses future directions and improvements needed in these areas.

[Expression of caveolin in hepatocellular carcinoma: association with unpaired artery formation and radiologic findings]

BACKGROUND/AIMS

Hepatocellular carcinoma (HCC) is becoming one of the common malignant tumors worldwide, and it is characterized by its high vascularity. Caveolin is the major structural protein in caveolae, which are small omega-shaped invaginations within the plasma membrane. Caveolin has been implicated in mitogenic signaling, oncogenesis and angiogenesis. The expression of caveolin-1 and -2 in HCC and its potential relationship with angiogenesis has not been examined.

METHODS

Paraffin sections of 35 HCC specimens were immunostained with caveolin-1, caveolin-2, alpha-smooth muscle actin, and CD34 antibodies. In addition, the expression of caveolin-1 and -2 mRNA in HCC was examined. The relationship between the radiological findings and the number of unpaired arteries and microvessel density (MVD) was also investigated.

RESULTS

Caveolin-1 and -2 were expressed in the sinusoidal endothelial cells in 20 out of 35, and 18 out of 35 HCC specimens, respectively. Caveolin-1 and -2 were also expressed in the smooth muscle cells of the unpaired arteries in 26 out of 35, and 18 out of 35 HCC specimens, respectively. Increased expression of caveolin-1 and -2 mRNA was detected in 26.7% and 33.3% of the tumor specimens, respectively, compared with the corresponding non-tumorous adjacent liver tissues. There was a significant correlation between expression of caveolin-1, -2 in the smooth muscle cells of unpaired arteries and the number of unpaired arteries. The number of unpaired arteries in HCCs was found to be associated with the degree of contrast enhancement in the arterial phase imaging. However, it did not correlate with the degree of MVD.

CONCLUSIONS

These findings suggest that the expression of caveolin-1, -2 is associated with the formation of unpaired arteries in HCC. In addition, there is a correlation between the degree of contrast enhancement of the HCC in the arterial phase image and the number of unpaired arteries.

Small GTPases in mechanosensitive regulation of endothelial barrier

Alterations in vascular permeability are defining feature of diverse processes including atherosclerosis, inflammation, ischemia/reperfusion injury, and ventilator-induced lung injury. Clinical observations and experimental studies support an essential role of mechanical forces in pathophysiologic regulation of lung barrier. Accumulating data demonstrate that decreased levels of blood flow and increased cyclic stretch of lung tissues associated with lung mechanical ventilation at high tidal volumes increase vascular permeability, activate inflammatory cytokine production, alveolar flooding, leukocyte infiltration, and hypoxemia, and increase morbidity and mortality. Potential synergism between pathologic mechanical stimulation and inflammatory molecules resulting in vascular leak and lung injury becomes increasingly recognized. This review will discuss a role of Rho family of small GTPases in the mechanochemical regulation of pulmonary endothelial permeability associated with ventilator induced lung injury.

Molecular imaging with nanoparticles: giant roles for dwarf actors

Molecular imaging, first developed to localise antigens in light microscopy, now encompasses all imaging modalities including those used in clinical care: optical imaging, nuclear medical imaging, ultrasound imaging, CT, MRI, and photoacoustic imaging. Molecular imaging always requires accumulation of contrast agent in the target site, often achieved most efficiently by steering nanoparticles containing contrast agent into the target. This entails accessing target molecules hidden behind tissue barriers, necessitating the use of targeting groups. For imaging modalities with low sensitivity, nanoparticles bearing multiple contrast groups provide signal amplification. The same nanoparticles can in principle deliver both contrast medium and drug, allowing monitoring of biodistribution and therapeutic activity simultaneously (theranostics). Nanoparticles with multiple bioadhesive sites for target recognition and binding will be larger than 20 nm diameter. They share functionalities with many subcellular organelles (ribosomes, proteasomes, ion channels, and transport vesicles) and are of similar sizes. The materials used to synthesise nanoparticles include natural proteins and polymers, artificial polymers, dendrimers, fullerenes and other carbon-based structures, lipid-water micelles, viral capsids, metals, metal oxides, and ceramics. Signal generators incorporated into nanoparticles include iron oxide, gadolinium, fluorine, iodine, bismuth, radionuclides, quantum dots, and metal nanoclusters. Diagnostic imaging applications, now appearing, include sentinal node localisation and stem cell tracking.

Regulation of endothelial junctional permeability

The endothelium is a semi-permeable barrier that regulates the flux of liquid and solutes, including plasma proteins, between the blood and surrounding tissue. The permeability of the vascular barrier can be modified in response to specific stimuli acting on endothelial cells. Transport across the endothelium can occur via two different pathways: through the endothelial cell (transcellular) or between adjacent cells, through interendothelial junctions (paracellular). This review focuses on the regulation of the paracellular pathway. The paracellular pathway is composed of adhesive junctions between endothelial cells, both tight junctions and adherens junctions. The actin cytoskeleton is bound to each junction and controls the integrity of each through actin remodeling. These interendothelial junctions can be disassembled or assembled to either increase or decrease paracellular permeability. Mediators, such as thrombin, TNF-alpha, and LPS, stimulate their respective receptor on endothelial cells to initiate signaling that increases cytosolic Ca2+ and activates myosin light chain kinase (MLCK), as well as monomeric GTPases RhoA, Rac1, and Cdc42. Ca2+ activation of MLCK and RhoA disrupts junctions, whereas Rac1 and Cdc42 promote junctional assembly. Increased endothelial permeability can be reversed with "barrier stabilizing agents," such as sphingosine-1-phosphate and cyclic adenosine monophosphate (cAMP). This review provides an overview of the mechanisms that regulate paracellular permeability.

Endothelial pathomechanisms in acute lung injury

Acute lung injury (ALI) and its most severe extreme the acute respiratory distress syndrome (ARDS) refer to increased-permeability pulmonary edema caused by a variety of pulmonary or systemic insults. ALI and in particular ARDS, are usually accompanied by refractory hypoxemia and the need for mechanical ventilation. In most cases, an exaggerated inflammatory and pro-thrombotic reaction to an initial stimulus, such as systemic infection, elicits disruption of the alveolo-capillary membrane and vascular fluid leak. The pulmonary endothelium is a major metabolic organ promoting adequate pulmonary and systemic vascular homeostasis, and a main target of circulating cells and humoral mediators under injury; pulmonary endothelium is therefore critically involved in the pathogenesis of ALI. In this review we will discuss mechanisms of pulmonary endothelial dysfunction and edema generation in the lung with special emphasis on the interplay between the endothelium, the immune and hemostatic systems, and highlight how these principles apply in the context of defined disorders and specific insults implicated in ALI pathogenesis.

Activation of protease calpain by oxidized and glycated LDL increases the degradation of endothelial nitric oxide synthase

Oxidation and glycation of low-density lipoprotein (LDL) promote vascular injury in diabetes; however, the mechanisms underlying this effect remain poorly defined. The present study was conducted to determine the effects of ‘heavily oxidized’ glycated LDL (HOG-LDL) on endothelial nitric oxide synthase (eNOS) function. Exposure of bovine aortic endothelial cells with HOG-LDL reduced eNOS protein levels in a concentration- and time-dependent manner, without altering eNOS mRNA levels. Reduced eNOS protein levels were accompanied by an increase in intracellular Ca²⁺, augmented production of reactive oxygen species (ROS) and induction of Ca²⁺-dependent calpain activity. Neither eNOS reduction nor any of these other effects were observed in cells exposed to native LDL. Reduction of intracellular Ca²⁺ levels abolished eNOS reduction by HOG-LDL, as did pharmacological or genetic through calcium channel blockers or calcium chelator BAPTA or inhibition of NAD(P)H oxidase (with apocynin) or inhibition of calpain (calpain 1-specific siRNA). Consistent with these results, HOG-LDL impaired acetylcholine-induced endothelium-dependent vasorelaxation of isolated mouse aortas, and pharmacological inhibition of calpain prevented this effect. HOG-LDL may impair endothelial function by inducing calpain-mediated eNOS degradation in a ROS- and Ca²⁺-dependent manner.

Tyrosine phosphorylation-dependence of caveolae-mediated endocytosis

Caveolae are flask-shaped plasma membrane invaginations that mediate endocytosis and transcytosis of plasma macromolecules, such as albumin, insulin and low-density lipoprotein (LDL), as well as certain viruses, bacteria and bacterial toxins. Caveolae-mediated transcytosis of macromolecules is critical for maintaining vascular homeostasis by regulating the oncotic pressure gradient and tissue delivery of drugs, vitamins, lipids and ions. Entrapment of cargo within caveolae induces activation of signalling cascades leading to caveolae fission and internalization. Activation of Src tyrosine kinase is an early and essential step that triggers detachment of loaded caveolae from the plasma membrane. In this review, we examine how Src-mediated phosphorylation regulates caveolae-mediated transport by orchestrating the localization and activity of essential proteins of the endocytic machinery to regulate caveolae formation and fission.