Image-based crosstalk analysis of cell-cell interactions during sprouting angiogenesis using blood-vessel-on-a-chip

BACKGROUND

Sprouting angiogenesis is an important mechanism for morphogenetic phenomena, including organ development, wound healing, and tissue regeneration. In regenerative medicine, therapeutic angiogenesis is a clinical solution for recovery from ischemic diseases. Mesenchymal stem cells (MSCs) have been clinically used given their pro-angiogenic effects. MSCs are reported to promote angiogenesis by differentiating into pericytes or other vascular cells or through cell-cell communication using multiple protein-protein interactions. However, how MSCs physically contact and move around ECs to keep the sprouting angiogenesis active remains unknown.

METHODS

We proposed a novel framework of EC-MSC crosstalk analysis using human umbilical vein endothelial cells (HUVECs) and MSCs obtained from mice subcutaneous adipose tissue on a 3D in vitro model, microvessel-on-a-chip, which allows cell-to-tissue level study. The microvessels were fabricated and cultured for 10 days in a collagen matrix where MSCs were embedded.

RESULTS

Immunofluorescence imaging using a confocal laser microscope showed that MSCs smoothed the surface of the microvessel and elongated the angiogenic sprouts by binding to the microvessel's specific microstructures. Additionally, three-dimensional modeling of HUVEC-MSC intersections revealed that MSCs were selectively located around protrusions or roots of angiogenic sprouts, whose surface curvature was excessively low or high, respectively.

CONCLUSIONS

The combination of our microvessel-on-a-chip system for 3D co-culture and image-based crosstalk analysis demonstrated that MSCs are selectively localized to concave-convex surfaces on scaffold structures and that they are responsible for the activation and stabilization of capillary vessels.

Ninjurin1 deletion in neuron-glial antigen 2-positive pericytes prevents microvessel maturation and delays wound healing

The formation of mature vasculature through angiogenesis is essential for adequate wound healing, such that blood-borne cells, nutrients, and oxygen can be delivered to the remodeling skin area. Neovessel maturation is highly dependent on the coordinated functions of vascular endothelial cells and perivascular cells, namely pericytes (PCs). However, the underlying mechanism for vascular maturation has not been completely elucidated, and its role in wound healing remains unclear. In this study, we investigated the role of Ninjurin-1 (Ninj1), a new molecule mediating vascular maturation, in wound healing using an inducible PC-specific Ninj1 deletion mouse model. Ninj1 expression increased temporarily in NG2-positive PCs in response to skin injury. When tamoxifen treatment induced a decreased Ninj1 expression in PCs, the neovessels in the regenerating wound margins were structurally and functionally immature, but the total number of microvessels was unaltered. This phenotypic change is associated with a reduction in PC-associated microvessels. Wound healing was significantly delayed in the NG2-specific Ninj1 deletion mouse model. Finally, we showed that Ninj1 is a crucial molecule that mediates vascular maturation in injured skin tissue through the interaction of vascular endothelial cells and PCs, thereby inducing adequate and prompt wound healing.

VEGF-Independent Angiogenic Factors: Beyond VEGF/VEGFR2 Signaling

Tumors induce angiogenesis to acquire oxygen and nutrition from their adjacent microenvironment. Tumor angiogenesis has been believed to be induced primarily by the secretion of vascular endothelial growth factor-A (VEGF-A) from various tumors. VEGF-A binds to VEGF receptor 2 (VEGFR2), resulting in subsequent activation of cellular substances regulating cell proliferation, survival, and angiogenesis. Antiangiogenic therapies targeting the VEGF-A/VEGFR2 axis, including bevacizumab and ramucirumab, humanized monoclonal antibodies against VEGF-A and VEGFR2, respectively, have been proposed as a promising strategy aimed at preventing tumor growth, invasion, and metastasis. Phase III clinical trials using bevacizumab and ramucirumab have shown that not all tumor patients benefit from such antiangiogenic agents, and that some patients who initially benefit subsequently become less responsive to these antibodies, suggesting the possible existence of VEGF-independent angiogenic factors. In this review, we focus on VEGF-independent and VEGFR2-dependent tumor angiogenesis, as well as VEGFR2-independent tumor angiogenesis. Additionally, we discuss VEGF-independent angiogenic factors which have been reported in previous studies. Various molecular targeting drugs are currently being evaluated as potential antitumor therapies. We expect that precision medicine will permit the development of innovative antiangiogenic therapies targeting individual angiogenic factors selected on the basis of the genetic screening of tumors.

Initial reduction of oxidative stress by angiotensin receptor blocker contributes long term outcomes after percutaneous coronary intervention

BACKGROUND

It remains unclear whether administration of ARB with reactive oxygen species (ROS) scavenging effects improves the prognosis of patients undergoing PCI.

OBJECTIVES

This study investigated whether the pre-intervention antioxidant effect of angiotensin receptor blocker (ARB) affects long-term outcomes in patients after successful percutaneous coronary intervention (PCI) without early adverse events.

METHODS

Fifty-two patients who underwent elective PCI were randomly assigned for treatment with or without ARB, which was administered within 48 hours before PCI. ROS levels in mononuclear cells (MNCs) and serum superoxide dismutase (SOD) activity were measured pre-PCI and 6 months post-PCI. After exclusion of unexpected early adverse events during angiographic follow-up period, the long-term outcome (major adverse cerebro-cardiovascular event; MACCE) was assessed in eligible patients.

RESULTS

Forty-three patients (non-ARB n = 22, ARB n = 21) were followed up in this study. During angiographic follow-up period, ROS formation in MNCs was significantly increased in the non-ARB group (from 29.4 [21.6-35.2] to 37.2 [30.7-45.1] arbitrary units; p = 0.031) compared to that in the ARB group. Meanwhile, SOD activity was significantly impaired in the non-ARB group alone (from 24.0 ± 17.0 to 16.3 ± 13.8%, p = 0.004). During the follow-up period (median, 63.3 months), MACCEs were observed in 6 patients. The cumulative event ratio of MACCE was significantly higher in the non-ARB group than in the ARB group (p = 0.018).

CONCLUSIONS

Concomitant administration of ARB effectively reduced ROS production of PCI patients during angiographic follow-up period. Initial ROS inhibition following ARB administration may contribute to improvement of worse outcomes in patients who have undergone successful PCI.

Impaired glutathione redox system paradoxically suppresses angiotensin II-induced vascular remodeling

BACKGROUND

Angiotensin II (AII) plays a central role in vascular remodeling via oxidative stress. However, the interaction between AII and reduced glutathione (GSH) redox status in cardiovascular remodeling remains unknown.

METHODS

In vivo: The cuff-induced vascular injury model was applied to Sprague Dawley rats. Then we administered saline or a GSH inhibitor, buthionine sulfoximine (BSO, 30 mmol/L in drinking water) for a week, subsequently administered 4 more weeks by osmotic pump with saline or AII (200 ng/kg/minute) to the rats. In vitro: Incorporation of bromodeoxyuridine (BrdU) was measured to determine DNA synthesis in cultured rat vascular smooth muscle cells (VSMCs).

RESULTS

BSO reduced whole blood GSH levels. Systolic blood pressure was increased up to 215 ± 4 mmHg by AII at 4 weeks (p<0.01), which was not affected by BSO. Superoxide production in vascular wall was increased by AII and BSO alone, and was markedly enhanced by AII+BSO. The left ventricular weight to body weight ratio was significantly increased in AII and AII+BSO as compared to controls (2.52 ± 0.08, 2.50 ± 0.09 and 2.10 ± 0.07 mg/g respectively, p<0.05). Surprisingly, the co-treatment of BSO totally abolished these morphological changes. Although the vascular circumferential wall stress was well compensated in AII, significantly increased in AII+BSO. The anti-single-stranded DNA staining revealed increasing apoptotic cells in the neointima of injured arteries in BSO groups. BrdU incorporation in cultured VSMCs with AII was increased dose-dependently. Furthermore it was totally abolished by BSO and was reversed by GSH monoethyl ester.

CONCLUSIONS

We demonstrated that a vast oxidative stress in impaired GSH redox system totally abolished AII-induced vascular, not cardiac remodeling via enhancement of apoptosis in the neointima and suppression of cell growth in the media. The drastic suppression of remodeling may result in fragile vasculature intolerable to mechanical stress by AII.

Nerve growth factor stimulates regeneration of perivascular nerve, and induces the maturation of microvessels around the injured artery

An immature vasa vasorum in the adventitia of arteries has been implicated in induction of the formation of unstable atherosclerotic plaques. Normalization/maturation of the vasa vasorum may be an attractive therapeutic approach for arteriosclerotic diseases. Nerve growth factor (NGF) is a pleotropic molecule with angiogenic activity in addition to neural growth effects. However, whether NGF affects the formation of microvessels in addition to innervation during pathological angiogenesis is unclear. In the present study, we show a new role for NGF in neovessels around injured arterial walls using a novel in vivo angiogenesis assay. The vasa vasorum around arterial walls was induced to grow using wire-mediated mouse femoral arterial injury. When collagen-coated tube (CCT) was placed beside the injured artery for 7-14 days, microvessels grew two-dimensionally in a thin layer on the CCT (CCT-membrane) in accordance with the development of the vasa vasorum. The perivascular nerve was found at not only arterioles but also capillaries in the CCT-membrane. Biodegradable hydrogels containing VEGF and NGF were applied around the injured artery/CCT. VEGF significantly increased the total length and instability of microvessels within the CCT-membrane. In contrast, NGF induced regeneration of the peripheral nerve around the microvessels and induced the maturation and stabilization of microvessels. In an ex vivo nerve-free angiogenesis assay, although NGF potentially stimulated vascular sprouting from aorta tissues, no effects of NGF on vascular maturation were observed. These data demonstrated that NGF had potent angiogenic effects on the microvessels around the injured artery, and especially induced the maturation/stabilization of microvessels in accordance with the regeneration of perivascular nerves.

Apurinic/apyrimidinic endonucelase 1 maintains adhesion of endothelial progenitor cells and reduces neointima formation

Apurinic/apyrimidinic endonuclease 1 (APE1) is a multifunctional protein that processes DNA-repair function and controls cellular response to oxidative stress. Endothelial progenitor cells (EPCs) are recruited to oxidative stress-rich injured vascular walls and positively contribute to vascular repair and endothelialization. We hypothesized that APE1 functions for EPCs-mediated inhibition of neointima formation in injured vasculature. EPCs isolated from bone marrow cells of C57BL6 mice (12-16 wk old) were able to survive in the presence of hydrogen peroxide (H2O2; up to 1,000 μM) due to the highly expressed reactive oxygen species (ROS) scavengers. However, adhesion capacity of EPCs was significantly inhibited by H2O2 (100 μM) even though an intracellular ROS was retained at small level. An APE1-selective inhibitor or RNA interference-mediated knockdown of endogenous APE1 in EPCs aggravated the H2O2-mediated inhibition of EPCs-adhesion. In contrast, when APE1 was overexpressed in EPCs using an adenovirus harboring the APE1 gene (APE-EPCs), adhesion was significantly improved during oxidative stress. To examine in vivo effects of APE1 in EPCs, APE-EPCs were transplanted via the tail vein after wire-mediated injury of the mouse femoral artery. The number of adherent EPCs at injured vascular walls and the vascular repair effect of EPCs were enhanced in APE-EPCs compared with control EPCs. Among the cellular functions of EPCs, adhesion is especially sensitive to oxidative stress. APE1 enhances in vivo vascular repair effects of EPCs in part through the maintenance of adhesion properties of EPCs. APE1 may be a novel and useful target gene for effective cellular transplantation therapy.

Prostacyclin stimulated integrin-dependent angiogenic effects of endothelial progenitor cells and mediated potent circulation recovery in ischemic hind limb model

BACKGROUND

Prostacyclin (PGI2) enhances angiogenesis, especially in cooperation with bone marrow (BM)-derived endothelial progenitor cells (EPCs). However, the mechanisms of PGI2 in EPC-mediated angiogenesis in vivo remain unclear. The purpose of this study was to clarify the role of PGI2 in EPC-mediated angiogenesis using BM-specific IP deletion mice.

METHODS AND RESULTS

Hind limb ischemia (HLI) was induced in wild-type (WT) mice transplanted with IP-deleted BM (WT/BM(IP(-/-)). Recovery of blood flow (RBF) in WT/BM(IP(-/-)) was impaired for 28 days after HLI, whereas RBF in IP(-/-)/BM(WT) was attenuated for up to 7 days compared with WT/BM(WT). The impaired RBF in WT/BM(IP(-/-)) was completely recovered by intramuscular injection of WT EPCs but not IP(-/-) EPCs. The impaired effects of IP(-/-) EPCs were in accordance with reduced formation of capillary and arterioles in ischemic muscle. An ex vivo aortic ring assay revealed that microvessel formation was enhanced by accumulation/adhesion of EPCs to perivascular sites as pericytes. IP(-/-)EPCs, in which expression of integrins was decreased, had impaired production of angiogenic cytokines, adhesion to neovessels and their angiogenic effects. The small-interfering RNA (siRNA)-mediated knockdown of integrin β1 in WT EPCs attenuated adhesion to microvessels and their in vivo and in vitro angiogenic effects.

CONCLUSIONS

PGI2 may induce persistent angiogenic effects in HLI through adhesion of EPCs to perivascular sites of neovessels via integrins in addition to paracrine effects.

Clinical and genetic investigation of a Japanese family with cardiac fabry disease. Identification of a novel α-galactosidase A missense mutation (G195V)

Fabry disease is an X-linked lysosomal storage disorder caused by mutations of the α-galactosidase A gene (GLA), and the disease is a relatively prevalent cause of left ventricular hypertrophy mimicking idiopathic hypertrophic cardiomyopathy. We assessed clinically 5 patients of a three-generation family and also searched for GLA mutations in 10 family members. The proband had left ventricular hypertrophy with localized thinning in the basal posterior wall and late gadolinium enhancement (LGE) in the near-circumferential wall in cardiovascular magnetic resonance images and her sister had vasospastic angina pectoris without organic stenosis of the coronary arteries. LGE notably appeared in parallel with decreased α-galactosidase A activity and increased NT-pro BNP in our patients. We detected a new GLA missense mutation (G195V) in exon 4, resulting in a glycine-to-valine substitution. Of the 10 family members, 5 family members each were positive and negative for this mutation. These new data extend our clinical and molecular knowledge of GLA gene mutations and confirm that a novel missense mutation in the GLA gene is important not only for a precise diagnosis of heterozygous status, but also for confirming relatives who are negative for this mutation.

Abstract 1576: Prostaglandin I2 signaling regulates micro-metastasis in lung cancer

Background: Bone marrow-derived cells (BMDCs) play an important role in the initiation of neo-angiogenesis, and contribute to the diseases including ischemic diseases, retinopathy, and cancer. We have reported that BMDCs express prostaglandin I2 (PGI2) specific receptor, IP and the PGI2-IP signaling system maintains the function of BMDCs. Additionally, we have reported that the PGI2-IP signaling in BMDCs play an important role for tumor growth, by using mouse bone marrow transplanted models and tumor xenograft mouse models.

Objectives: The purpose of this study was to test the hypothesis that PGI2-IP signaling system regulates micro-metastasis in lung cancer.

Methods: In vitro study, 5-bromo-2’-deoxy-uridine (BrdU) cell proliferation assay and clonogenic cell assay were used to clarify the effect on lung cancer cell (A549, PC9) proliferation and cellular form in the existence of IP receptor agonist or antagonist. Human cytokine antibody array was performed to detect the expression of angiogenic cytokines and growth factors secreted by the treated cells.

In vivo study, we employed both a mouse lung metastasis model and a mouse bone marrow transplantation model. We used GFP-labeled or DsRed-labeled lung cancer cells to distinguish cancer cells from BMDCs. Lung cancer cells were injected into the tail vein of mice (ICR nu/nu), which were transplanted with bone marrow cells from GFP-labeled wild-type or IP knockout mice. Real-time RT-PCR was used to quantify lung metastasis of human cancer cells in nude mice, and the expression levels of housekeeping genes (human and mouse GAPDH) in the lungs were measured. Immunofluorescence assay was performed to evaluate angiogenesis in pulmonary metastatic tumors.

Results: In vitro study, PGI2-IP signaling didn't impair proliferation of lung cancer cells and production of angiogenic cytokines secreted by tumors.

In the mice lung metastasis model, micro-metastasis in lung cancer was regulated by PGI2-IP signaling system. RT-PCR assay showed that PGI2-IP signaling changed the expression levels of human lung cancer cells in mice lungs. In the immunofluorescence assay, PGI2-IP signaling influenced the expression of pericyte markers around the tumors.

Conclusions: The present study demonstrated that PGI2-IP signaling system regulates micro-metastasis in lung cancer. These results suggest that PGI2-IP system may become a novel therapeutic target in lung metastasis.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1576. doi:10.1158/1538-7445.AM2011-1576

A case of idiopathic systemic capillary leak syndrome with high serum levels of G-CSF on exacerbation

Systemic capillary leak syndrome (SCLS) is a life-threatening disorder which presents with periodic episodes of hypovolemic shock, due to plasma leakage to the extra-vascular space reflected by accompanying hypoalbuminemia, hemoconcentration and edema often with associated monoclonal gammopathy. We describe a 28-year-old woman with SCLS who required aggressive fluid resuscitation and was successfully treated with corticosteroid, terbutaline, and theophylline. At exacerbation, the levels of serum granulocyte colony-stimulating factor (G-CSF) were increased. Thus, G-CSF might play an important role and can be a useful biomarker for the severity of attacks in SCLS.

Transplanting normal vascular proangiogenic cells to tumor-bearing mice triggers vascular remodeling and reduces hypoxia in tumors

Blood vessels deliver oxygen and nutrients to tissues, and vascular networks are spatially organized to meet the metabolic needs for maintaining homeostasis. In contrast, the vasculature of tumors is immature and leaky, resulting in insufficient delivery of nutrients and oxygen. Vasculogenic processes occur normally in adult tissues to repair "injured" blood vessels, leading us to hypothesize that bone marrow mononuclear cells (BMMNC) may be able to restore appropriate vessel function in the tumor vasculature. Culturing BMMNCs in endothelial growth medium resulted in the early outgrowth of spindle-shaped attached cells expressing CD11b/Flt1/Tie2/c-Kit/CXCR4 with proangiogenic activity. Intravenous administration of these cultured vascular proangiogenic cells (VPC) into nude mice bearing pancreatic cancer xenografts and Pdx1-Cre;LSL-Kras(G12D);p53(lox/+) genetically engineered mice that develop pancreatic ductal adenocarcinoma significantly reduced areas of hypoxia without enhancing tumor growth. The resulting vasculature structurally mimicked normal vessels with intensive pericyte coverage. Increases in vascularized areas within VPC-injected xenografts were visualized with an ultrasound diagnostic system during injection of a microbubble-based contrast agent (Sonazoid), indicating a functional "normalization" of the tumor vasculature. In addition, gene expression profiles in the VPC-transplanted xenografts revealed a marked reduction in major factors involved in drug resistance and "stemness" of cancer cells. Together, our findings identify a novel alternate approach to regulate abnormal tumor vessels, offering the potential to improve the delivery and efficacy of anticancer drugs to hypoxic tumors.

Hedgehog promotes neovascularization in pancreatic cancers by regulating Ang-1 and IGF-1 expression in bone-marrow derived pro-angiogenic cells

Background

The hedgehog (Hh) pathway has been implicated in the pathogenesis of cancer including pancreatic ductal adenocarcinoma (PDAC). Recent studies have suggested that the oncogenic function of Hh in PDAC involves signaling in the stromal cells rather than cell autonomous effects on the tumor cells. However, the origin and nature of the stromal cell type(s) that are responsive to Hh signaling remained unknown. Since Hh signaling plays a crucial role during embryonic and postnatal vasculogenesis, we speculated that Hh ligand may act on tumor vasculature specifically focusing on bone marrow (BM)-derived cells.

Methodology/Principal Findings

Cyclopamine was utilized to inhibit the Hh pathway in human PDAC cell lines and their xenografts. BM transplants, co-culture systems of tumor cells and BM-derived pro-angiogenic cells (BMPCs) were employed to assess the role of tumor-derived Hh in regulating the BM compartment and the contribution of BM-derived cells to angiogenesis in PDAC. Cyclopamine administration attenuated Hh signaling in the stroma rather than in the cancer cells as reflected by decreased expression of full length Gli2 protein and Gli1 mRNA specifically in the compartment. Cyclopamine inhibited the growth of PDAC xenografts in association with regression of the tumor vasculature and reduced homing of BM-derived cells to the tumor. Host-derived Ang-1 and IGF-1 mRNA levels were downregulated by cyclopamine in the tumor xenografts. In vitro co-culture and matrigel plug assays demonstrated that PDAC cell-derived Shh induced Ang-1 and IGF-1 production in BMPCs, resulting in their enhanced migration and capillary morphogenesis activity.

Conclusions/Significance

We identified the BMPCs as alternative stromal targets of Hh-ligand in PDAC suggesting that the tumor vasculature is an attractive therapeutic target of Hh blockade. Our data is consistent with the emerging concept that BM-derived cells make important contributions to epithelial tumorigenesis.

Brugada syndrome case: difficult differentiation between a concealed form and tricyclic antidepressant-induced Brugada sign

We describe a case of Brugada syndrome, in which recurrent syncope with convulsive seizures was induced after antidepressant treatment. The patient had been treated with five kinds of psychotropic drugs. The twelve-lead ECG after the syncope exhibited an RSR'-pattern in the precordial leads, however, a coved type ST-segment elevation was induced by a pilsicainide test. Although ventricular fibrillation was not induced in the electrophysiologic study, an ICD implantation was considered as the recommended therapy since Brugada syndrome unmasked by antidepressants could not be ruled out. The possible contribution of antidepressants to Brugada type ST-segment changes is discussed.

Administration of VEGF receptor tyrosine kinase inhibitor increases VEGF production causing angiogenesis in human small-cell lung cancer xenografts

Angiogenesis is mediated mainly by vascular endothelial growth factor (VEGF), and VEGF causes rapid growth in cancers, including human small-cell lung cancer (SCLC). The anti-angiogenic strategy of treating cancer using VEGF receptor (VEGFR) inhibition is currently of great interest. We tested the effects of the VEGFR2 tyrosine kinase inhibitor (TKI) vandetanib on the proliferation of two kinds of SCLC cell lines: SBC-1 cells, with detectable VEGFR2 expression and MS-1-L cells, without detectable VEGFR2 expression. To evaluate the anti-tumor and anti-angiogenic effects of vandetanib in vivo, we grafted SBC-1 and MS-1-L cells into mice. After a 3-week treatment, we measured the tumor size and histologically evaluated necrosis and apoptosis using H&E and TUNEL staining, respectively. The microvessels in the xenografts were also quantified by immunostaining of CD31. Vandetanib did not affect the proliferation of SBC-1 cells, but stimulated the growth of MS-1-L cells. In the SCLC xenograft model, vandetanib inhibited growth and tumor angiogenesis in a dose-dependent manner in SBC-1 xenografts. Vandetanib inhibited the growth of MS-1-L xenografts at a low dose (<12.5 mg/kg/day), but it did not affect tumor size or change microvessel counts at a higher dose. Interestingly, secretion of VEGF increased significantly in the MS-1-L cell line in the presence of a high dose of vandetanib in vitro. The effects of vandetanib on tumor angiogenesis were different in SBC-1 and MS-1-L cell lines. Production of angiogenic factors such as VEGF by the tumor potentially stimulates tumor angiogenesis and results in the acquisition of resistance to VEGFR TKI.

Disruption of type 5 adenylyl cyclase enhances desensitization of cyclic adenosine monophosphate signal and increases Akt signal with chronic catecholamine stress

BACKGROUND

Desensitization of the cyclic adenosine monophosphate signal protects cardiac myocytes against catecholamine stress, thus preventing the development of apoptosis. Molecular mechanisms of desensitization have been well studied at the level of adrenergic receptors but less so at the level of the effector enzyme, adenylyl cyclase (AC).

METHODS AND RESULTS

When the effects of long-term (1 to 2 weeks) isoproterenol infusion were compared between type 5 AC-null mice (AC5KO) and wild-type controls, we found that the subsequent responses of left ventricular ejection fraction to sudden intravenous isoproterenol challenge were reduced in AC5KO compared with wild-type mice (ie, physiological desensitization was more effective in AC5KO), consistent with enhanced downregulation of AC catalytic activity in AC5KO. One mechanism for the less effective desensitization in wild-type mice was paradoxical upregulation of type 5 AC protein expression. The number of apoptotic myocytes was similar at baseline but was significantly less in AC5KO after infusion. This was accompanied by a 4-fold greater increase in Bcl-2 and a 3-fold greater increase in phospho-Akt in AC5KO. The latter is most likely mediated by increased membrane localization of phosphoinositide-dependent protein kinase 1, which is known to be inhibited by the cyclic adenosine monophosphate signal.

CONCLUSIONS

The absence of type 5 AC results in more effective desensitization after long-term catecholamine stress and protects against the development of myocyte apoptosis and deterioration of cardiac function, potentially elucidating a novel approach to the therapy of heart failure.

Caveolin regulates microtubule polymerization in the vascular smooth muscle cells

Microtubule and caveolin have common properties in intracellular trafficking and the regulation of cellular growth. Overexpression of caveolin in vascular smooth muscle cells increased the polymer form of microtubule without changing in the total amount of tubulin, and downregulation of caveolin decreased the polymer form of microtubule. Fractionation of cellular proteins followed by immunodetection as well as immunostaining of caveolin and microtubule revealed that caveolin and a portion of microtubule were co-localized in caveolar fractions. A caveolin scaffolding domain peptide, which mimics caveolin function, did not alter the polymerization of microtubule in vitro, but dramatically inhibited the depolymerization of microtubule induced by stathmin, a microtubule destabilizing protein, which was also found in caveolar fractions. Accordingly, it is most likely that caveolin increased the polymer form of microtubule through the inhibition of a microtubule destabilizer, stathmin, suggesting a novel role of caveolin in regulating cellular network and trafficking.

Insulin resistance in skeletal muscles of caveolin-3-null mice

Type 2 diabetes is preceded by the development of insulin resistance, in which the action of insulin is impaired, largely in skeletal muscles. Caveolin-3 (Cav3) is a muscle-specific subtype of caveolin, an example of a scaffolding protein found within membranes. Cav is also known as growth signal inhibitor, although it was recently demonstrated that the genetic disruption of Cav3 did not augment growth in mice. We found, however, that the lack of Cav3 led to the development of insulin resistance, as exemplified by decreased glucose uptake in skeletal muscles, impaired glucose tolerance test performance, and increases in serum lipids. Such impairments were markedly augmented in the presence of streptozotocin, a pancreatic beta cell toxin, suggesting that the mice were susceptible to severe diabetes in the presence of an additional risk factor. Insulin-stimulated activation of insulin receptors and downstream molecules, such as IRS-1 and Akt, was attenuated in the skeletal muscles of Cav3 null mice, but not in the liver, without affecting protein expression or subcellular localization. Genetic transfer of Cav3 by needle injection restored insulin signaling in skeletal muscles. Our findings suggest that Cav3 is an enhancer of insulin signaling in skeletal muscles but does not act as a scaffolding molecule for insulin receptors.

Translocation of caveolin regulates stretch-induced ERK activity in vascular smooth muscle cells

Mechanical stress contributes to vascular disease related to hypertension. Activation of ERK is key to mediating cellular proliferation and vascular remodeling in response to stretch stress. However, the mechanism by which stretch mediates ERK activation in the vascular tissue is still unclear. Caveolin, a major component of a flasklike invaginated caveolae, acts as an adaptor protein for an integrin-mediated signaling pathway. We found that cyclic stretch transiently induced translocation of caveolin from caveolae to noncaveolar membrane sites in vascular smooth muscle cells (VSMCs). This translocation of caveolin was determined by detergent solubility, sucrose gradient fractionation, and immunocytochemistry. Cyclic stretch induced ERK activation; the activity peaked at 5 min (the early phase), decreased gradually, but persisted up to 120 min (the late phase). Disruption of caveolae by methyl-beta-cyclodextrin, decreasing the caveolar caveolin and accumulating the noncaveolar caveolin, enhanced ERK activation in both the early and late phases. When endogenous caveolins were downregulated, however, the late-phase ERK activation was subsided completely. Caveolin, which was translocated to noncaveolar sites in response to stretch, is associated with beta1-integrins as well as with Fyn and Shc, components required for ERK activation. Taken together, caveolin in caveolae may keep ERK inactive, but when caveolin is translocated to noncaveolar sites in response to stretch stress, caveolin mediates stretch-induced ERK activation through an association with beta1-integrins/Fyn/Shc. We suggest that stretch-induced translocation of caveolin to noncaveolar sites plays an important role in mediating stretch-induced ERK activation in VSMCs.

Thermal treatment attenuates neointimal thickening with enhanced expression of heat-shock protein 72 and suppression of oxidative stress

BACKGROUND

The beneficial effects of thermal therapy have been reported in several cardiovascular diseases. However, it is unknown whether the thermal treatment has some beneficial roles against the development of atherosclerosis.

METHODS AND RESULTS

The inflammatory arterial lesion was introduced by placement of a polyethylene cuff on femoral arteries of male Sprague-Dawley rats for 4 weeks. Thermal-treated group underwent daily bathing in 41 degrees C hot water for 15 minutes. Neointimal thickening along with immunohistochemical expression of heat-shock proteins (HSPs), monocyte chemoattractant protein-1 (MCP-1), and NADPH oxidase were compared with those of a thermally untreated (Control) group. Morphometric analysis demonstrated a significant suppression of neointimal thickening in thermal-treated group compared with the Control group (intimal/medial area ratios, 0.01+/-0.01 versus 0.31+/-0.04, P<0.01). Expression of MCP-1 and infiltration of ED-positive cells were enhanced in the adventitial layer of Control. More importantly, expression of HSP72 in media was enhanced by thermal treatment. Expression of p22-phox, the major membrane subunit of NADPH oxidase, and MCP-1 was augmented in cuff-injured adventitia of the Control but not the thermal-treated groups.

CONCLUSIONS

Thermal treatment significantly attenuated infiltration of inflammatory cells in adventitia and suppressed neointimal thickening in cuff-injured arteries with the enhancement of HSP72 expression and suppression of oxidative stress.

Nicotinic acetylcholine receptor alpha 7 regulates cAMP signal within lipid rafts

Neuronal nicotinic acetylcholine receptors (nAChRs) are made of multiple subunits with diversified functions. The nAChR alpha 7-subunit has a property of high Ca2+ permeability and may have specific functions and localization within the plasma membrane as a signal transduction molecule. In PC-12 cells, fractionation by sucrose gradient centrifugation revealed that nAChR alpha 7 existed in low-density, cholesterol-enriched plasma membrane microdomains known as lipid rafts where flotillin also exists. In contrast, nAChR alpha 5- and beta2-subunits were located in high-density fractions, out of the lipid rafts. Type 6 adenylyl cyclase (AC6), a calcium-inhibitable isoform, was also found in lipid rafts and was coimmunoprecipitated with nAChR alpha 7. Cholesterol depletion from plasma membranes with methyl-beta-cyclodextrin redistributed nAChR alpha 7 and AC6 diffusely within plasma membranes. Nicotine stimulation reduced forskolin-stimulated AC activity by 35%, and this inhibition was negated by either treatment with alpha-bungarotoxin, a specific antagonist of nAChR alpha 7, or cholesterol depletion from plasma membranes. The effect of cholesterol depletion was negated by the addition of cholesterol. These data suggest that nAChR alpha 7 has a specific membrane localization relative to other nAChR subunits and that lipid rafts are necessary to localize nAChR alpha 7 with AC within plasma membranes. In addition, nAChR alpha 7 may regulate the AC activity via Ca2+ within lipid rafts.

Type 5 adenylyl cyclase disruption alters not only sympathetic but also parasympathetic and calcium-mediated cardiac regulation

In a genetically engineered mouse line with disruption of type 5 adenylyl cyclase (AC5-/-), a major cardiac isoform, there was no compensatory increase in other isoforms of AC in the heart. Both basal and isoproterenol (ISO)-stimulated AC activities were decreased by 30% to 40% in cardiac membranes. The reduced AC activity did not affect cardiac function (left ventricular ejection fraction [LVEF]) at baseline. However, increases in LVEF after ISO were significantly attenuated in AC5-/- (P<0.05, n=11). Paradoxically, conscious AC5-/- mice had a higher heart rate compared with wild-type (WT) mice (613+/-8 versus 523+/-11 bpm, P<0.01, n=14 to 15). Muscarinic agonists decreased AC activity, LVEF, and heart rate more in WT than in AC5-/-. In addition, baroreflex-mediated, ie, neuronally regulated, bradycardia after phenylephrine was also attenuated in AC5-/-. The carbachol-activated outward potassium current (at -40 mV) normalized to cell capacitance in AC5-/- (2.6+/-0.4 pA/pF, n=16) was similar to WT (2.9+/-0.3 pA/pF, n=27), but calcium (Ca2+)-mediated inhibition of AC activity and Ca2+ channel function were diminished in AC5-/-. Thus, AC5-/- attenuates sympathetic responsiveness and also impairs parasympathetic and Ca2+-mediated regulation of the heart, indicating that those actions are not only regulated at the level of the receptor and G-protein but also at the level of type 5 AC.

Disruption of type 5 adenylyl cyclase gene preserves cardiac function against pressure overload

The sympathetic nervous system is designed to respond to stress. Adenylyl cyclase (AC) is the keystone of sympathetic transmission, yet its role in response to acute overload in the heart or in the pathogenesis of heart failure is controversial. We examined the effects of pressure overload, induced by thoracic aortic banding, in mice in which type 5 AC, a major cardiac AC isoform, was disrupted (AC5-/-). Left ventricular weight/tibial length ratio (LVW/TL) was not different between the WT and AC5-/- at baseline and increased progressively and similarly in both groups at 1 and 3 wk after aortic banding. However, LV ejection fraction (LVEF) fell in WT at 3 wk after banding (from 70 +/- 2.8 to 57 +/- 3.9%, P < 0.05), and this decrease was associated with LV dilatation, indicating incipient cardiac failure. In contrast, AC5-/- mice did not exhibit a fall in LVEF from 74 +/- 2.2%. The number of apoptotic myocytes was similar at baseline, but it increased roughly 4-fold in WT at both 1 and 3 wk after banding, and significantly less, P < 0.05, in AC5-/-. Importantly, the increase in apoptosis occurred before the decline in LVEF in WT. The protective mechanism seems to involve Bcl-2, which was up-regulated significantly more in AC5-/- mice with pressure overload. Our findings suggest that limiting type 5 AC plays a protective role in response to pressure overload and the development of heart failure, potentially through limiting the incidence of myocardial apoptosis.

Magnesium reduces myocardial infarct size via enhancement of adenosine mechanism in rabbits

OBJECTIVES

Clinical impact of magnesium (Mg) therapy remains controversial in acute myocardial infarction. We investigated the infarct size limiting effects of Mg and its mechanism in rabbits.

METHODS

Anesthetized rabbits underwent 30 min coronary occlusion and 3 h reperfusion in ten groups: (1) Control, (2) Low Mg, (3) Mg, (4) High Mg, (5) calcium (Ca), (6) Mg+Ca, (7) 8-phenyltheophylline (8PT), an adenosine receptor blockade, (8) 8PT+Mg, (9) alpha, beta-methylene-adenosine diphosphate (AOPCP), a selective inhibitor of ecto-5'-nucleotidase, and (10) AOPCP+Mg groups. Infract size (IS) to area at risk (AR) was measured by triphenyltetrazorium chloride method.

RESULTS

The IS/AR ratio was significantly smaller in Mg, 27+/-3% (P<0.05) and High Mg, 24+/-2% (P<0.05) compared to Control, 50+/-3% and Low Mg, 42+/-4%. The IS limiting effects of Mg were abolished in 8PT+Mg, AOPCP+Mg and Mg+Ca. The IS/AR ratio correlated with neither rate-pressure products nor incidence of arrhythmia.

CONCLUSION

Magnesium administration has an infarct size limiting effect independent of its effects on myocardial oxygen consumption and incidence of arrhythmia in rabbits. The infarct size limiting effect of magnesium is attributable, at least in part, to augmentation of adenosine mechanism.

Downregulation of nitric oxide accumulation by cyclooxygenase-2 induction and thromboxane A2 production in interleukin-1beta-stimulated rat aortic smooth muscle cells

BACKGROUND

Cytokines from inflammatory cells do not produce nitric oxide, but stimulate the production of nitric oxide in vascular smooth muscle cells (VSMC). Thromboxane A2 (TXA2) has been believed to have a key role in atherosclerogenesis and post-angioplasty restenosis.

OBJECTIVE

To determine whether cytokine-induced nitric oxide production is regulated by the TXA2/prostaglandin H2 (PGH2) receptor.

METHODS AND RESULTS

We studied the interleukin-1beta (IL-1beta)-induced production of nitric oxide in rat VSMCs using the TXA2/PGH2 receptor antagonists, seratrodast and Bay-u3405, and an agonist, U-46619. Nitrite formation was measured colorimetrically. IL-1beta increased nitrite formation in a time-dependent manner. The nitrite concentration was 1.7 times greater in the presence of seratrodast than that without it. Nitrite accumulation was increased by Bay-u3405, but was decreased in the presence of U-46619, to 44% of that in its absence. Western and Northern blotting showed that seratrodast increased the levels of expression of inducible nitric oxide synthase (iNOS) protein and mRNA in a dose-dependent manner, whereas U-46619 decreased them. We speculated that VSMCs produced TXA2, thereby decreasing nitric oxide production; therefore we measured the accumulation of TXB2 using an enzyme immunoassay. Untreated VSMCs produced about 20 pg/mg protein of TXB2. This was increased by the addition of IL-1beta, to 152.1 +/- 43.0 pg/mg protein after a 24 h incubation; the expression of cyclooxygenase-2 (COX-2) protein was also increased, but there was no effect on the expression of COX-1 and TXA2 synthase. U-63557A, a TXA2 synthase inhibitor, increased the accumulation of nitrite to 1.3-fold that in its absence.

CONCLUSIONS

These data suggest that the expression of iNOS and the production of nitric oxide are regulated by the TXA2/PGH2 receptor in IL-1beta-stimulated VSMCs. The endogenous production of TXA2 by the induction of COX-2 from IL-1beta-stimulated VSMCs probably downregulated the production of nitric oxide in VSMCs. TXA2/PGH2 receptor inhibitors may contribute to the reduction in formation of atherosclerosis in lesions with vascular injury by enhancing the production of nitric oxide by VSMCs.

Changes in caveolin subtype protein expression in aging rat organs

It is now accepted that caveolin plays a key role in signal transduction by directly binding to and regulating the function of molecules involved in transmembrane signaling, such as ras, suggesting that the amount of caveolin within cells may be an important factor in determining the cellular signaling. We investigated the ontogenic changes in the protein amount of caveolin subtypes, as well as ras protein expression in various organs (the heart, lungs, and muscles) obtained from aging rats (neonates, young and old adults). Our results demonstrated that caveolin protein expression changed ontogenically in a subtype-dependent manner. In lungs, for example, caveolin-1 expression changed in an opposite manner to caveolin-3 expression, while in the heart caveolin-1 and -3 changed in parallel. Ras expression showed an ontogenic increase in lungs and a decrease in muscles, which were both parallel to caveolin-1 expression. Our results suggest that the regulation of transmembrane signaling by caveolin may differ among developmental stages and caveolin subtypes.