Takahisa Murata

Direct evidence for the role of caveolin-1 and caveolae in mechanotransduction and remodeling of blood vessels

Caveolae in endothelial cells have been implicated as plasma membrane microdomains that sense or transduce hemodynamic changes into biochemical signals that regulate vascular function. Therefore we compared long- and short-term flow-mediated mechanotransduction in vessels from WT mice, caveolin-1 knockout (Cav-1 KO) mice, and Cav-1 KO mice reconstituted with a transgene expressing Cav-1 specifically in endothelial cells (Cav-1 RC mice). Arterial remodeling during chronic changes in flow and shear stress were initially examined in these mice. Ligation of the left external carotid for 14 days to lower blood flow in the common carotid artery reduced the lumen diameter of carotid arteries from WT and Cav-1 RC mice. In Cav-1 KO mice, the decrease in blood flow did not reduce the lumen diameter but paradoxically increased wall thickness and cellular proliferation. In addition, in isolated pressurized carotid arteries, flow-mediated dilation was markedly reduced in Cav-1 KO arteries compared with those of WT mice. This impairment in response to flow was rescued by reconstituting Cav-1 into the endothelium. In conclusion, these results showed that endothelial Cav-1 and caveolae are necessary for both rapid and long-term mechanotransduction in intact blood vessels.

Reexpression of caveolin-1 in endothelium rescues the vascular, cardiac, and pulmonary defects in global caveolin-1 knockout mice

Caveolin-1 (Cav-1) is the principal structural component of caveolae organelles in smooth muscle cells, adipocytes, fibroblasts, epithelial cells, and endothelial cells (ECs). Cav-1–deficient (Cav-1 knockout [KO]) mice are viable and show increases of nitric oxide (NO) production in vasculature, cardiomyopathy, and pulmonary dysfunction. In this study, we generated EC-specific Cav-1–reconstituted (Cav-1 RC) mice and reexamined vascular, cardiac, and pulmonary phenotypes. Cav-1 KO pulmonary arteries had decreased smooth muscle contractility and increased endothelial NO synthase activation and hypotension; the latter two effects were rescued completely in Cav-1 RC mice. Cav-1 KO mice exhibited myocardial hypertrophy, pulmonary hypertension, and alveolar cell hyperproliferation caused by constitutive activation of p42/44 mitogen-activated protein kinase and Akt. Interestingly, in Cav-1 RC mice, cardiac hypertrophy and pulmonary hypertension were completely rescued, whereas alveolar hyperplasia was partially recovered because of the lack of rescue of Cav-1 in bronchiolar epithelial cells. These results provide clear physiological evidence supporting the important role of cell type–specific Cav-1 expression governing multiple phenotypes in the vasculature, heart, and lung.

Anti‐inflammatory effects of phytosteryl ferulates in colitis induced by dextran sulphate sodium in mice

We have recently reported that phytosteryl ferulates isolated from rice bran inhibit nuclear factor‐κB (NF‐κB) activity in macrophages. In the present study, we investigated the effect of γ‐oryzanol (γ‐ORZ), a mixture of phytosteryl ferulates, cycloartenyl ferulate (CAF), one of the components of γ‐ORZ, and ferulic acid (FA), a possible metabolite of γ‐ORZ in vivo, on a model of colitis in mice.

Genetic evidence supporting caveolae microdomain regulation of calcium entry in endothelial cells

Various cellular signals initiate calcium entry into cells, and there is evidence that lipid rafts and caveolae may concentrate proteins that regulate transmembrane calcium fluxes. Here, using mice deficient in caveolin-1 (Cav-1) and Cav-1 knock-out reconstituted with endothelium-specific Cav-1, we show that Cav-1 is essential for calcium entry in endothelial cells and governs the localization and protein-protein interactions between transient receptor channels C4 and C1. Thus, Cav-1 is required for calcium entry in vascular endothelial cells and perhaps other specialized cell types containing caveolae.

The phosphorylation state of eNOS modulates vascular reactivity and outcome of cerebral ischemia in vivo

NO plays critical roles in vascular function. We show that modulation of the eNOS serine 1179 (S1179) phosphorylation site affects vascular reactivity and determines stroke size in vivo. Transgenic mice expressing only a phosphomimetic (S1179D) form of eNOS show greater vascular reactivity, develop less severe strokes, and have improved cerebral blood flow in a middle cerebral artery occlusion model than mice expressing an unphosphorylatable (S1179A) form. These results provide a molecular mechanism by which multiple diverse cardiovascular risks, such as diabetes and obesity, may be centrally integrated by eNOS phosphorylation in vivo to influence blood flow and cardiovascular disease. They also demonstrate the in vivo relevance of posttranslational modification of eNOS in vascular function.

Caveolin-1-deficient mice have increased tumor microvascular permeability, angiogenesis, and growth.

Caveolin-1 (Cav-1) is a major structural protein that is essential to the formation of the organelle, caveolae. Cav-1 knockout (KO) mice were observed to be completely devoid of caveolae yet they exhibit a hyperpermeable vasculature. Given the nature of the hyperpermeable Cav-1 KO endothelium, we sought to investigate if tumors grown in Cav-1 KO mice would be leaky and grow faster. Indeed, Lewis lung carcinoma cells implanted into Cav-1 KO mice had increased tumor vascular permeability, measured by Evans blue extravasation and fibrinogen deposition compared with tumors implanted into wild-type (WT) mice. Cav-1 KO mice also had significantly higher tumor growth rates, attributable to increased tumor angiogenesis and decreased tumor cell death. Furthermore, administration of an antipermeability peptide, cavtratin, was able to correct the tumor hyperpermeability as well as attenuate the increased tumor growth. Mechanistically, endothelial cells isolated from Cav-1 KO mice exhibited increased tyrosine phosphorylation on vascular endothelial growth factor (VEGF) receptor-2 (VEGFR-2) and decreased association with the adherens junction protein, VE-cadherin. Thus, the loss of Cav-1 increases tumor permeability and growth and that may relate to enhanced VEGF signaling due to lack of Cav-1 inhibition of VEGFR-2 or decreased VE-cadherin mediated VEGFR-2 phosphorylation.

Lipopolysaccharide induces macrophage migration via prostaglandin D(2) and prostaglandin E(2).

Lipopolysaccharide (LPS) produces prostaglandins (PGs) concomitant to eliciting macrophage migration. We evaluated the role of PGs in initiating the migration of macrophages, especially focusing on PGD2 and PGE2. In RAW264.7 macrophages, cyclooxygenase (COX)-2 inhibitor, CAY10404 [3-(4-methylsulphonylphenyl)-4-phenyl-5-trifluoromethylisoxazole], completely inhibited LPS-mediated migration at 4 h (early phase) but only partially inhibited the migration at 8 h (late phase), suggesting the presence of PG-dependent and -independent pathways. In the early phase, LPS up-regulated mRNA expressions of COX-2, hematopoietic PGD synthase (H-PGDS), and microsomal-PGE synthase 1, increasing PGD2 and PGE2 substantially. The chemoattractant receptor-homologous molecule expressed on Th2 lymphocytes (CRTH2) agonist, DK-PGD2 (13–14-dihydro-15-keto-PGD2), and the EP4 agonist, ONO-AE1-329 (16-{3-methoxymethyl}phenyl-ω-tetranor-3,7-dithia-prostaglandin E1), but not selective agonists of D prostanoid receptor, E prostanoid receptor (EP) 2, or EP3, stimulated random migration (chemokinesis). In peritoneal macrophages from CRTH2-deficient and H-PGDS-deficient mice, LPS-mediated migration was significantly inhibited at either early or late phases of the migration. The H-PGDS inhibitor, HQL-79 [4-(diphenylmethoxy)-1-[3-(1H-tetrazol-5-yl)propyl-piperidine]], partially inhibited the migration of the RAW264.7 macrophage in both phases. These results suggest the importance of the PGD2/CRTH2 pathway in LPS-mediated migration of macrophages. In the late phase of migration, LPS up-regulated monocyte chemoattractant protein (MCP)-1 mRNA. The CC chemokine receptor (CCR2) antagonist, RS102895 [1′-[2-[4-(trifluoromethyl)phenyl]ethyl]-spiro[4H-3,1-benzoxazine-4,4′-piperidin]-2(1H)-one], inhibited LPS-mediated migration in the late phase without affecting the early phase. ONO-AE1-329, but not DK-PGD2, up-regulated MCP-1 mRNA. Taken together, LPS stimulation of chemokinesis or chemotaxis, or both, occurs in macrophages via PGD2 and PGE2 in tandem arrangement; i.e., 1) LPS stimulates prostaglandin signaling, initiating early migration through the PGD2/CRTH2 and PGE2/EP4 signaling pathways; and 2) LPS leads induction of MCP-1, which contributes to later phase migration of the macrophages through the PGE2/EP4 pathway.

Statin Protects Endothelial Nitric Oxide Synthase Activity in Hypoxia-Induced Pulmonary Hypertension

Objective—We investigated the effects of fluvastatin on hypoxia-induced (1 to 3 weeks, 10% O2) pulmonary hypertension with focus on endothelial nitric oxide synthase (eNOS) activity. Methods and Results—Oral fluvastatin treatment (1 mg/kg daily) prevented the causing and progression of pulmonary hypertension as determined by the right ventricular pressure, right ventricular hypertrophy, and muscularization of pulmonary artery. We also revealed that fluvastatin treatments prevented the hypoxia-induced decrease in cGMP production in the rat lung and restored the endothelium-dependent relaxation in the pulmonary artery. We revealed that this beneficial effect was not dependent on the increase in eNOS mRNA or protein expression, but was dependent on the inhibition of the eNOS-tight coupling with caveolin-1, the eNOS dissociation from heat shock protein 90, and the decrease in eNOS Ser1177–phosphorylation induced by hypoxia. Furthermore, in a whole-mount immunostaining the hypoxia-induced eNOS protein condensation with caveolin-1 of pulmonary endothelial cells was restored by the fluvastatin-treatment. Conclusion—These results suggest that the fluvastatin exerts beneficial effects on chronic hypoxia-induced pulmonary hypertension by protecting against the eNOS activity at the post-transcriptional level.

Neuronal stimulation with 5-hydroxytryptamine 4 receptor induces anti-inflammatory actions via α7nACh receptors on muscularis macrophages associated with postoperative ileus

Background The main symptom of postoperative ileus (POI) is an intestinal motility disorder in which monocytes/macrophages and neutrophils play crucial roles. Prokinetic 5-hydroxytryptamine 4 receptor (5-HT4R) agonists and dopamine receptor antagonists are potential therapeutic agents for directly ameliorating the motility disorder associated with POI. Aim To determine the effects of the 5-HT4R agonists mosapride citrate (MOS) and CJ-033466 on intestinal smooth muscle contractility relative to immune reactions after POI. Methods Intestinal manipulation (IM) was applied to the rat distal ileum. Both MOS (0.3 and 1 mg/kg, s.c.) and CJ-033466 (1 mg/kg, s.c.) were administered to the animals before and after IM. At 24 h after IM, isolated intestinal smooth muscle contractile activity in vitro, gastrointestinal transit in vivo, inflammatory mediator expression and leucocyte infiltration were measured. Results After IM, ileal circular muscle contractility in vitro and gastrointestinal transit in vivo were reduced and the number of macrophages and neutrophils increased in the inflamed muscle layer, resulting in the induction of inflammatory mediators such as interleukin 1 β (IL-1β), IL-6, tumour necrosis factor α (TNFα), monocyte chemoattractant protein 1 (MCP-1) and inducible nitric oxide synthase (iNOS). Both MOS and CJ-033466 significantly attenuated not only the intestinal motility dysfunction but also the leucocyte infiltration and inflammatory mediator expression after IM. The autonomic ganglionic blocker hexamethonium (1 mg/kg, i.p.) and the α7-nicotinic acetylcholine receptor (α7nAChR) antagonist methyl lycaconitine citrate (0.087 mg/kg, i.p.) blocked MOS-mediated ameliorative actions. Immunohistochemically, α7nAChR is expressed by monocytes/macrophages but not by neutrophils in the inflamed intestine. Conclusion Stimulating the 5-HT4R accelerates acetyl choline (ACh) release from cholinergic myenteric neurons, which subsequently activates α7nAChR on activated monocytes/macrophages to inhibit their inflammatory reactions in the muscle layer. In addition to their gastroprokinetic action, 5-HT4R agonists might serve as novel therapeutic agents for POI characterised by anti-inflammatory potency.

The Akt1-eNOS Axis Illustrates the Specificity of Kinase-Substrate Relationships in Vivo

Akt mediates postnatal angiogenesis through eNOS signaling. Defining the Critical Relationship Many protein kinases have multiple potential substrates and, in turn, many substrate sites can be phosphorylated by multiple kinases. Thus, determining which of many possible kinase-substrate pairs mediate a particular response can be challenging. Here, Schleicher et al. used lines of mice that both lacked the protein kinase Akt1 and carried mutations in the Akt1 substrate endothelial nitric oxide synthase (eNOS) that either mimicked or abolished Akt1 phosphorylation to tease out the physiological functions of Akt1-eNOS signaling. Although various phenotypes associated with loss of Akt1 were unaffected by the eNOS mutations—indicating that these Akt1 functions were mediated through other substrates—defects in postnatal reparative angiogenesis associated with the loss of Akt1 were rescued by the phosphomimetic mutant. Further analysis indicated that Akt1 signaled through eNOS to regulate the hypoxia-inducible factor 1α (HIF-1α)–mediated angiogenic response to ischemia. Thus, the authors conclude that Akt1 regulates postnatal angiogenesis largely through eNOS phosphorylation. Akt1 is critical for many in vivo functions; however, the cell-specific substrates responsible remain to be defined. Here, we examine the importance of endothelial nitric oxide synthase (eNOS) as an Akt1 substrate by generating Akt1-deficient mice (Akt1−/− mice) carrying knock-in mutations (serine to aspartate or serine to alanine substitutions) of the critical Akt1 phosphorylation site on eNOS (serine 1176) that render the enzyme “constitutively active” or “less active.” The eNOS mutations did not influence several phenotypes in Akt1−/− mice; however, the defective postnatal angiogenesis characteristic of Akt1−/− mice was rescued by crossing the Akt1−/− mice with mice carrying the constitutively active form of eNOS, but not by crossing with mice carrying the less active eNOS mutant. This genetic rescue resulted in the stabilization of hypoxia-inducible factor 1α (HIF-1α) and increased production of HIF-1α–responsive genes in vivo and in vitro. Thus, Akt1 regulates angiogenesis largely through phosphorylation of eNOS and NO-dependent signaling.