A critical role for the protein apoptosis repressor with caspase recruitment domain in hypoxia-induced pulmonary hypertension.

BACKGROUND: Pulmonary hypertension (PH) is a lethal syndrome associated with the pathogenic remodeling of the pulmonary vasculature and the emergence of apoptosis-resistant cells. Apoptosis repressor with caspase recruitment domain (ARC) is an inhibitor of multiple forms of cell death known to be abundantly expressed in striated muscle. We show for the first time that ARC is expressed in arterial smooth muscle cells of the pulmonary vasculature and is markedly upregulated in several experimental models of PH. In this study, we test the hypothesis that ARC expression is essential for the development of chronic hypoxia-induced PH. METHODS AND RESULTS: Experiments in which cells or mice were rendered ARC-deficient revealed that ARC not only protected pulmonary arterial smooth muscle cells from hypoxia-induced death, but also facilitated growth factor-induced proliferation and hypertrophy and hypoxia-induced downregulation of selective voltage-gated potassium channels, the latter a hallmark of the syndrome in humans. Moreover, ARC-deficient mice exhibited diminished vascular remodeling, increased apoptosis, and decreased proliferation in response to chronic hypoxia, resulting in marked protection from PH in vivo. Patients with PH have significantly increased ARC expression not only in remodeled vessels but also in the lumen-occluding lesions associated with severe disease. CONCLUSIONS: These data show that ARC, previously unlinked to pulmonary hypertension, is a critical determinant of vascular remodeling in this syndrome.

An Adam15 amplification loop promotes vascular endothelial growth factor-induced ocular neovascularization.

Proteins with a disintegrin and a metalloproteinase domain (ADAMs) are a family of membrane-bound proteinases that bind integrins through their disintegrin domain. In this study, we have found modest expression of ADAM15 in pericytes in normal retina and strong up-regulation of ADAM15 in retinal vascular endothelial cells in ischemic retina. Increased expression of vascular endothelial growth factor (VEGF) in the retina in the absence of ischemia also increased ADAM15 levels, and knockdown of Vegf mRNA in ischemic retina reduced Adam15 mRNA. Mice deficient in ADAM15 showed a significant reduction in ischemia-induced retinal neovascularization, choroidal neovascularization at rupture sites in Bruch's membrane, and VEGF-induced subretinal neovascularization. ADAM15-deficient mice also showed reduced levels of VEGF(164), VEGF receptor 1, and VEGF receptor 2 in ischemic retina. These data suggest that ADAM15 and VEGF participate in an amplification loop; VEGF increases expression of ADAM15, which in turn increases expression of VEGF and its receptors. Perturbation of the loop by elimination of ADAM15 suppresses ocular neovascularization in 3 different model systems, and thus ADAM15 provides a new therapeutic target for diseases complicated by neovascularization.

MicroRNAs regulate ocular neovascularization.

In this study, we used ischemia-induced retinal neovascularization (NV) as a model to investigate the possible role of microRNAs in a clinically important disease process. Microarray analysis demonstrated seven microRNAs (miR-106a, -146, -181, -199a, -214, -424, and -451) that were substantially increased and three microRNAs (miR-31, -150, and -184) that were substantially decreased in ischemic retina. Potential targets for the upregulated microRNAs were not identified, but bioinformatic analysis suggested target genes for the downregulated microRNAs, and these were confirmed using a luciferase reporter assay. Real-time reverse transcriptase PCR confirmed that the substantial levels of miR-31, -150, and -184 present in normal retina were significantly reduced in ischemic retina. Interestingly, constitutive levels of miR-31 and -184 are high in the cornea and lens, two avascular tissues. Intraocular injection of pre-miR-31, -150, or -184 significantly reduced ischemia-induced retinal NV, and injection of pre-miR-31 or -150 also significantly reduced choroidal NV. These data suggest that alteration of microRNA levels contributes to two types of ocular NV, and that injection or enhanced expression of microRNAs is a potential therapeutic strategy.

In vivo immunostaining demonstrates macrophages associate with growing and regressing vessels.

PURPOSE: The purpose of this study was to identify ways to improve qualitative and quantitative assessments of retinal vessels and neovascularization (NV). METHODS: At postnatal day (P) 17, mice with oxygen-induced ischemic retinopathy were injected intravitreously with one of a variety of FITC-labeled or unlabeled antibodies and humanely killed 12 hours later. Retinas were flat mounted (retinas from eyes injected with labeled antibodies) or incubated with secondary antibody and then flat mounted (retinas from eyes injected with unlabeled antibodies). RESULTS: Retinas from eyes injected with labeled anti-platelet endothelial cell adhesion molecule 1 (PECAM1) showed good resolution of the fine structure of retinal NV, including filopodia at the tips of sprouts. New vessels originated from superficial retinal vessels, something that is widely recognized, but they also arose from deep retinal capillaries and from large retinal vessels, which is not generally known. Retinas from eyes injected with unlabeled anti-PECAM1 antibody and then incubated with labeled secondary antibody showed selective staining of retinal NV with little or no background, greatly facilitating identification and quantification of the NV by image analysis software. Double labeling with anti-PECAM1 antibody and one of three other antibodies--anti-CD45, F4/80, or anti-CXCR4--showed exquisite localization of various populations of bone marrow-derived cells with respect to the vasculature and demonstrated close association of macrophages with NV and regressing vessels. Double labeling with anti-PECAM1 antibody and anti-placental growth factor (PlGF) showed high levels of PlGF in growing and regressing vessels but no detectable signal elsewhere in the retina. CONCLUSIONS: This study describes techniques that facilitate measurements and detailed structural analysis of retinal NV and that allow identification and quantification of populations of bone marrow-derived cells and support the view that macrophages contribute to the growth and regression of vessels in the eye.

Differential sensitivity of cones to iron-mediated oxidative damage.

PURPOSE: In this study, the hypothesis that increased intraocular levels of iron cause oxidative damage to the retina was tested. METHODS: Adult C57BL/6 mice were given an intravitreous injection of saline or 0.10, 0.25, or 0.50 mM FeSO(4). Scotopic electroretinograms (ERGs) were performed 3, 7, and 14 days after injection, and photopic ERGs were performed on day 14. Hydroethidine was used to identify superoxide radicals and lipid peroxidation was visualized by staining for hydroxynonenal (HNE). Retinal cell death was evaluated by TUNEL and measurement of inner nuclear layer (INL) and outer nuclear layer (ONL) thickness. Levels of rhodopsin and cone-opsin mRNA were measured by quantitative real time RT-PCR. Cone density was assessed by peanut agglutinin staining and confocal microscopy. RESULTS: Compared with retinas in saline-injected eyes, retinas from eyes injected with FeSO(4) showed greater fluorescence after intravenous injection of hydroethidine due to superoxide radicals in photoreceptors, greater photoreceptor staining for HNE, a marker of lipid peroxidation, and increased expression of Heme oxygenase 1, an indicator of oxidative stress. ERG b-wave amplitudes were reduced (photopic > scotopic) in FeSO(4)-injected eyes compared with those in saline-injected eyes. Numerous TUNEL-stained nuclei were seen along the outer border of the ONL, the location of cone cell nuclei, at 1 and 2 days after injection of FeSO(4). In FeSO(4)-injected eyes, the thickness of the ONL, but not the INL, was significantly reduced, and 17 days after injection, there were 3.8- and 2.6-fold reductions in the mRNAs for M-cone and S-cone opsin, respectively, whereas there was no significant difference in rhodopsin mRNA. Confocal microscopy of peanut agglutinin-stained sections showed dose-dependent FeSO(4)-induced cone drop out. CONCLUSIONS: Increased intraocular levels of FeSO(4) cause oxidative damage to photoreceptors with greater damage to cones than rods. This finding suggests that the oxidative defense system of cones differs from that of rods and other retinal cells, and that cones are more susceptible to damage from the type of oxidative stress imposed by iron.