The Histone Demethylase PHF8 Is Essential for Endothelial Cell Migration

Epigenetic marks critically control gene expression and thus the cellular activity state. The functions of many epigenetic modifiers in the vascular system have not yet been studied. We screened for histone modifiers in endothelial cells and observed a fairly high expression of the histone plant homeodomain finger protein 8 (PHF8). Given its high expression, we hypothesize that this histone demethylase is important for endothelial cell function. Overexpression of PHF8 catalyzed the removal of methyl-groups from histone 3 lysine 9 (H3K9) and H4K20, whereas knockdown of the enzyme increased H3K9 methylation. Knockdown of PHF8 by RNAi also attenuated endothelial proliferation and survival. As a functional readout endothelial migration and tube formation was studied. PHF8 siRNA attenuated the capacity for migration and developing of capillary-like structures. Given the impact of PHF8 on cell cycle genes, endothelial E2F transcription factors were screened, which led to the identification of the gene repressor E2F4 to be controlled by PHF8. Importantly, PHF8 maintains E2F4 but not E2F1 expression in endothelial cells. Consistently, chromatin immunoprecipitation revealed that PHF8 reduces the H3K9me2 level at the E2F4 transcriptional start site, demonstrating a direct function of PHF8 in endothelial E2F4 gene regulation. Conclusion: PHF8 by controlling E2F4 expression maintains endothelial function.

Continuous and long-term treatment is more important than dosage for the protective effect of thiazide use on bone metabolism and fracture risk

BACKGROUND

Data from observational studies have suggested that thiazide diuretics protect against fractures. Few studies have investigated time frames from initiation of treatment to fracture occurrence.

OBJECTIVE

To evaluate the time to spinal, hip, femur, wrist and upper extremity fracture occurrence before and after thiazide exposure.

METHODS

A matched retrospective cohort study of patient information from national Danish patient databases was conducted. Patients with reimbursed prescriptions for noncompounded thiazide diuretics with potassium supplementation (Anatomical Therapeutic Chemical classification system code C03AB) between 1996 and 2011 were matched with nonexposed control subjects by date of birth and gender. Weekly odds ratios (ORs) of fracture occurrence and total incidence rates (IRs) and incidence rate ratios (IRRs) of fracture risk were calculated for the periods before treatment initiation, weeks 1-42 and weeks 43-780.

RESULTS

A total of 1,602,141 'thiazide exposure periods' (46,8271 individuals) and 1,530,233 'nonexposure periods' (655,399 individuals) were included in the analysis. Thiazide use was associated with factors of increased de novo fracture risk. Weekly adjusted fracture risk between exposure and nonexposure was increased prior to commencing thiazide therapy, further increasing from weeks 1-42 weeks and then decreasing gradually from weeks 43-780. There was a decreasing trend in total age-adjusted risk during these periods: IRR [95% confidence interval 1.44 [1.42; 1.47], 1.27 [1.24; 1.29] and 1.14 [1.11; 1.18], respectively. Prescription patterns showed several treatment breaks amongst thiazide users.

CONCLUSIONS

It appears that thiazides reduce the background risk of fracture that is increased prior to commencing therapy. Long duration and continuity of thiazide exposure seems to be important to obtain this protective effect on fracture risk, but we have found in this study that this approach is not always used in clinical practice.

The NADPH oxidase Nox4 has anti-atherosclerotic functions

AIMS

Oxidative stress is thought to be a risk for cardiovascular disease and NADPH oxidases of the Nox family are important producers of reactive oxygen species. Within the Nox family, the NADPH oxidase Nox4 has a unique position as it is constitutively active and produces H2O2 rather than [Formula: see text] . Nox4 is therefore incapable of scavenging NO and its low constitutive H2O2 production might even be beneficial. We hypothesized that Nox4 acts as an endogenous anti-atherosclerotic enzyme.

METHODS AND RESULTS

Tamoxifen-induced Nox4-knockout mice were crossed with ApoE⁻/⁻ mice and spontaneous atherosclerosis under regular chow as well as accelerated atherosclerosis in response to partial carotid artery ligation under high-fat diet were determined. Deletion of Nox4 resulted in increased atherosclerosis formation in both models. Mechanistically, pro-atherosclerotic and pro-inflammatory changes in gene expression were observed prior to plaque development. Moreover, inhibition of Nox4 or deletion of the enzyme in the endothelium but not in macrophages resulted in increased adhesion of macrophages to the endothelial surface.

CONCLUSIONS

The H2O2-producing NADPH oxidase Nox4 is an endogenous anti-atherosclerotic enzyme. Nox4 inhibitors, currently under clinical evaluation, should be carefully monitored for cardiovascular side-effects.

Polarity Protein Scrib Facilitates Endothelial Inflammatory Signaling

OBJECTIVE

The polarity protein Scrib is highly expressed in endothelial cells and is required for planar cell polarity. Scrib also facilitates recycling of integrin α5 to the plasma membrane. Because integrin α5 signals the presence of the inflammatory matrix protein fibronectin, we hypothesized that Scrib contributes to endothelial inflammatory signaling.

APPROACH AND RESULTS

Cytokine treatment of human umbilical vein endothelial cells induced an inflammatory response as evident by the induction of vascular cell adhesion molecule-1 (VCAM-1). Downregulation of Scrib greatly attenuated this effect. In endothelial-specific conditional Scrib knockout mice, in vivo lipopolysaccharide treatment resulted in an impaired VCAM-1 induction. These effects were functionally relevant because Scrib small interfering RNAs in human umbilical vein endothelial cells attenuated the VCAM-1-mediated leukocyte adhesion in response to tumor necrosis factor-α. In vivo, tamoxifen-induced endothelial-specific deletion of Scrib resulted in a reduced VCAM-1-mediated leukocyte adhesion in response to tumor necrosis factor-α in the mouse cremaster model. This effect was specific for Scrib and not mediated by other polarity proteins. Moreover, it did not involve integrin α5 or classic pathways supporting inflammatory signaling, such as nuclear factor κ light chain enhancer of activated B-cells or MAP kinases. Co-immunoprecipitation/mass spectrometry identified the zinc finger transcription factor GATA-like protein-1 as a novel Scrib interacting protein. Small interfering RNA depletion of GATA-like protein-1 decreased the tumor necrosis factor-α-stimulated VCAM-1 induction to a similar extent as loss of Scrib did. Silencing of Scrib reduced GATA-like protein-1 protein, but not mRNA abundance.

CONCLUSIONS

Scrib is a novel proinflammatory regulator in endothelial cells, which maintains the protein expression of GATA-like protein-1.

Nox4 supports proper capillary growth in exercise and retina neo-vascularization

KEY POINTS

We provide evidence for two distinct functions of the NADPH oxidase Nox4 in angiogenesis using Nox4 knockout mice. First, Nox4 maintains vascular endothelial growth factor expression and prevents an increase in angiopoietin 1 expression, thereby contributing to angiogenesis in exercise. Second, deletion of Nox4, via an enhanced angiopoietin 1 expression, contributes to stabilization of new formed vessels and prevents an exacerbated neo-angiogenesis in oxygen-induced retinopathy. By contrast, Nox4 does not influence developmental angiogenesis.

ABSTRACT

By producing H2 O2 , the NADPH oxidase Nox4 is involved in hypoxia-induced angiogenesis, as present in vascular remodelling of the hypertrophic heart or blood flow recovery after hind limb ischaemia. In the present study, we hypothesized that Nox4 contributes to proper capillary growth in the retina and in exercised muscles and investigated this in wild-type and Nox4(-/-) mice. Exercise, as induced by voluntary running in a running wheel or forced running on a treadmill, stimulated capillary growth in wild-type but not Nox4(-/-) mice. As an underlying mechanism, we identified both vascular endothelial growth factor (VEGF) expression to be reduced and angiopoietin 1 (Ang1) expression to be increased in response to Nox4 knockout. To differentiate the two factors, oxygen-induced retinopathy was investigated. In this model, deletion of Nox4 protected from neo-angiogenesis and stabilized the network of regrown vessels, which is a typical feature of Ang1. However the angiogenesis in the developing retina was similar between Nox4(-/-) and wild-type mice. Thus, Nox4 contributes to exercise- and hypoxia-induced angiogenesis through a dual mechanism of maintaining VEGF and preventing Ang-1 expression, whereas the developmental angiogenesis is Nox4 independent.

Hyponatremia and osteoporosis: insights from the Danish National Patient Registry

The association between hyponatremia and osteoporosis was evaluated in humans. A significant association was found between low sodium levels, lower bone mineralization in the hip, and with several common conditions. Hyponatremia could be used as a marker of osteoporosis and systemic disease.

INTRODUCTION

The objective of this study was to evaluate the association between hyponatremia and osteoporosis in humans through a cross-sectional study.

METHODS

Patient information was gathered from regional and national Danish patient databases, both in- and outpatient settings, from 2004 to 2011. Patients with dual-energy x-ray absorptiometry (DXA) scans performed within this time were included if accompanied [Na+] was measured within 14 days prior or past the scan date. A total of 1575 patients were included.

RESULTS

A total of 104 patients were hyponatremic (6.6 %). Total hip and lumbar spine bone mineral content (BMC) and densities (BMD) and T-scores were all significantly lower with hyponatremia. The odds ratio (OR) of osteoporosis significantly increased among hyponatremic patients at both total hip (unadjusted OR = 2.17, 95% CI = [1.40-3.34], p < .05) and lumbar spine (unadjusted OR = 1.83, 95% CI = [1.20-2.80], p < .05) regions. Dose-response found between increasing [Na+] and increasing total hip BMC (slope .174, adjusted p < .05), BMD (slope .004, adjusted p < .05), and T-score (slope .034, adjusted p < .05). Systemic disease was more prevalent in hyponatremia.

CONCLUSION

The presence of hyponatremia increases the risk of concurrent osteoporosis at both the total hip and lumbar spine in humans. Hyponatremia could be used a screening tool and marker of secondary osteoporosis.

Vitamin D promotes vascular regeneration

BACKGROUND

Vitamin D deficiency in humans is frequent and has been associated with inflammation. The role of the active hormone 1,25-dihydroxycholecalciferol (1,25-dihydroxy-vitamin D3; 1,25-VitD3) in the cardiovascular system is controversial. High doses induce vascular calcification; vitamin D3 deficiency, however, has been linked to cardiovascular disease because the hormone has anti-inflammatory properties. We therefore hypothesized that 1,25-VitD3 promotes regeneration after vascular injury.

METHODS AND RESULTS

In healthy volunteers, supplementation of vitamin D3 (4000 IU cholecalciferol per day) increased the number of circulating CD45-CD117+Sca1+Flk1+ angiogenic myeloid cells, which are thought to promote vascular regeneration. Similarly, in mice, 1,25-VitD3 (100 ng/kg per day) increased the number of angiogenic myeloid cells and promoted reendothelialization in the carotid artery injury model. In streptozotocin-induced diabetic mice, 1,25-VitD3 also promoted reendothelialization and restored the impaired angiogenesis in the femoral artery ligation model. Angiogenic myeloid cells home through the stromal cell-derived factor 1 (SDF1) receptor CXCR4. Inhibition of CXCR4 blocked 1,25-VitD3-stimulated healing, pointing to a role of SDF1. The combination of injury and 1,25-VitD3 increased SDF1 in vessels. Conditioned medium from injured, 1,25-VitD3-treated arteries elicited a chemotactic effect on angiogenic myeloid cells, which was blocked by SDF1-neutralizing antibodies. Conditional knockout of the vitamin D receptor in myeloid cells but not the endothelium or smooth muscle cells blocked the effects of 1,25-VitD3 on healing and prevented SDF1 formation. Mechanistically, 1,25-VitD3 increased hypoxia-inducible factor 1-α through binding to its promoter. Increased hypoxia-inducible factor signaling subsequently promoted SDF1 expression, as revealed by reporter assays and knockout and inhibitory strategies of hypoxia-inducible factor 1-α.

CONCLUSIONS

By inducing SDF1, vitamin D3 is a novel approach to promote vascular repair.

Deuterium Quadrupole Coupling Constants of Deuterohalogenoacetylens

Employing the high resolution of microwave Fourier transform spectroscopy, we investigated the lowest rotational transitions of fluoro-, bromo-, and iodoacetylene-d. Along with the rotational, centrifugal distortion, halogen nuclear quadrupole, and halogen spin-rotation coupling constants, we determined the deuterium quadrupole coupling constants of bromo-and iodoacetylene-d. For fluoroacetylene-d, we redetermined the deuterium nuclear quadrupole coupling constants with higher accuracy.

The polarity protein Scrib is essential for directed endothelial cell migration

RATIONALE

Polarity proteins are involved in the apico-basal orientation of epithelial cells, but relatively little is known regarding their function in mesenchymal cells.

OBJECTIVE

We hypothesized that polarity proteins also contribute to endothelial processes like angiogenesis.

METHODS AND RESULTS

Screening of endothelial cells revealed high expression of the polarity protein Scribble (Scrib). On fibronectin-coated carriers Scrib siRNA (siScrib) blocked directed but not random migration of human umbilical vein endothelial cells and led to an increased number and disturbed orientation of cellular lamellipodia. Coimmunoprecipitation/mass spectrometry and glutathione S-transferase (GST) pulldown assays identified integrin α5 as a novel Scrib interacting protein. By total internal reflection fluorescence (TIRF) microscopy, Scrib and integrin α5 colocalize at the basal plasma membrane of endothelial cells. Western blot and fluorescence activated cell sorting (FACS) analysis revealed that silencing of Scrib reduced the protein amount and surface expression of integrin α5 whereas surface expression of integrin αV was unaffected. Moreover, in contrast to fibronectin, the ligand of integrin α5, directional migration on collagen mediated by collagen-binding integrins was unaffected by siScrib. Mechanistically, Scrib supported integrin α5 recycling and protein stability by blocking its interaction with Rab7a, its translocation into lysosomes, and its subsequent degradation by pepstatin-sensitive proteases. In siScrib-treated cells, reinduction of the wild-type protein but not of PSD95, Dlg, ZO-1 (PDZ), or leucine rich repeat domain mutants restored integrin α5 abundance and directional cell migration. The downregulation of Scrib function in Tg(kdrl:EGFP)(s843) transgenic zebrafish embryos delayed the angiogenesis of intersegmental vessels.

CONCLUSIONS

Scrib is a novel regulator of integrin α5 turnover and sorting, which is required for oriented cell migration and sprouting angiogenesis.

Nox4 is a protective reactive oxygen species generating vascular NADPH oxidase

RATIONALE

The function of Nox4, a source of vascular H(2)O(2), is unknown. Other Nox proteins were identified as mediators of endothelial dysfunction.

OBJECTIVE

We determined the function of Nox4 in situations of increased stress induced by ischemia or angiotensin II with global and tamoxifen-inducible Nox4(-/-) mice.

METHODS AND RESULTS

Nox4 was highly expressed in the endothelium and contributed to H(2)O(2) formation. Nox4(-/-) mice exhibited attenuated angiogenesis (femoral artery ligation) and PEG-catalase treatment in control mice had a similar effect. Tube formation in cultured Nox4(-/-) lung endothelial cells (LECs) was attenuated and restored by low concentrations of H(2)O(2,) whereas PEG-catalase attenuated tube formation in control LECs. Angiotensin II infusion was used as a model of oxidative stress. Compared to wild-type, aortas from inducible Nox4-deficient animals had development of increased inflammation, media hypertrophy, and endothelial dysfunction. Mechanistically, loss of Nox4 resulted in reduction of endothelial nitric oxide synthase expression, nitric oxide production, and heme oxygenase-1 (HO-1) expression, which was associated with apoptosis and inflammatory activation. HO-1 expression is controlled by Nrf-2. Accordingly, Nox4-deficient LECs exhibited reduced Nrf-2 protein level and deletion of Nox4 reduced Nrf-2 reporter gene activity. In vivo treatment with hemin, an inducer of HO-1, blocked the vascular hypertrophy induced by Nox4 deletion in the angiotensin II infusion model and carbon monoxide, the product of HO-1, blocked the Nox4-deletion-induced apoptosis in LECs.

CONCLUSION

Endogenous Nox4 protects the vasculature during ischemic or inflammatory stress. Different from Nox1 and Nox2, this particular NADPH oxidase therefore may have a protective vascular function.

Optical properties of photonic molecules and elliptical pillars made of ZnSe-based microcavities

The influence of the geometric shape of optically confining structures on the emission properties of ZnSe-based microcavities is studied. Elliptical as well as coupled circular structures were fabricated with quantum wells or quantum dots as optical active material. For the elliptical pillars a lifting of the polarization degeneracy of the resonator modes is observed as it is favorable to control the polarization state of the emitted photons. The influence of the ellipticity on the polarization splitting of the fundamental mode as well as on the quality factor of the sample is discussed. For the coupled pillar microcavities the effect of their distance on the energy splitting of the fundamental resonator mode is analyzed. Furthermore, detailed measurements of the spatial mode distribution in elliptically shaped pillars and photonic molecules are performed. By comparing these results to the calculated mode distribution their analogy to a diatomic molecule is illustrated. It turns out that the observed mode splitting into localized bonding and delocalized antibonding states in ZnSe-based microcavities is more pronounced for elliptical geometries. The realization of delocalized mode profiles is favorable for the coupling of spatially separated quantum dots.