Angiogenesis, the formation of new blood vessels, is a key physiological event in organ development and tissue responses to hypoxia but is also involved in pathophysiologies such as tumour growth and retinopathies. Understanding the molecular mechanisms involved is important to design strategies for therapeutic intervention. One important regulator of angiogenesis is transforming growth factor-1 (TGF-1). In addition, reactive oxygen species (ROS) and the ROS-forming NADPH oxidase type 4 (Nox4) have been implicated as additional regulators such as during hypoxia. Here, we show that both processes are indeed mechanistically linked. TGF-1-stimulated Nox4 expression and ROS formation in endothelial cells. In cells from Nox4-deficient mice, TGF-1-induced cell proliferation, migration and tube formation were abolished. In vivo, TGF-1 stimulated growth of blood vessels into sponges implanted subcutaneously, and this angiogenesis was markedly reduced in Nox4 knockout mice. Thus, endothelial cells are regulated by a TGF-1 signalling pathway involving Nox4-derived ROS to promote angiogenesis. In order to abrogate pathological angiogenesis triggered by a multitude of factors, such as TGF-1 and hypoxia, Nox4 may thus be an ideal therapeutic target.

The anti-inflammatory peptide annexin-1 binds to formyl peptide receptors (FPR) but little is known about its mechanism of action in the vasculature. Here we investigate the effect of annexin peptide Ac2-26 on NADPH oxidase activity induced by tumour necrosis factor alpha (TNFα) in human endothelial cells. Superoxide release and intracellular reactive oxygen species (ROS) production from NADPH oxidase was measured with lucigenin-enhanced chemiluminescence and 2′,7′-dichlorodihydrofluorescein diacetate, respectively. Expression of NADPH oxidase subunits and intracellular cell adhesion molecule (ICAM-1) and vascular cell adhesion molecule (VCAM-1) were determined by real-time PCR and Western blot analysis. Promoter activity of nuclear factor kappa B (NFκB) was measured by luciferase activity assay. TNFα stimulated NADPH-dependent superoxide release, total ROS formation and expression of ICAM-1and VCAM-1. Pre-treatment with N-terminal peptide of annexin-1 (Ac2-26, 0.5–1.5 µM) reduced all these effects, and the inhibition was blocked by the FPRL-1 antagonist WRW4. Furthermore, TNFα-induced NFκB promoter activity was attenuated by both Ac2-26 and NADPH oxidase inhibitor diphenyliodonium (DPI). Surprisingly, Nox4 gene expression was reduced by TNFα whilst expression of Nox2, p22phox and p67phox remained unchanged. Inhibition of NADPH oxidase activity by either dominant negative Rac1 (N17Rac1) or DPI significantly attenuated TNFα-induced ICAM-1and VCAM-1 expression. Ac2-26 failed to suppress further TNFα-induced expression of ICAM-1 and VCAM-1 in N17Rac1-transfected cells. Thus, Ac2-26 peptide inhibits TNFα-activated, Rac1-dependent NADPH oxidase derived ROS formation, attenuates NFκB pathways and ICAM-1 and VCAM-1 expression in endothelial cells. This suggests that Ac2-26 peptide blocks NADPH oxidase activity and has anti-inflammatory properties in the vasculature which contributes to modulate in reperfusion injury inflammation and vascular disease.

Histone deacetylase (HDAC) inhibitors are known to suppress abnormal development of blood vessels. Angiogenic activity in endothelial cells depends upon NADPH oxidase 4 (Nox4)‐dependent redox signalling. We set out to study whether the HDAC inhibitor trichostatin A (TSA) affects Nox4 expression and angiogenesis. Nox4 expression was measured by real time PCR and Western blot analysis in endothelial cells. Hydrogen peroxide (H₂O₂) was measured by amplex^® red assay in endothelial cells. Nox4 was knocked down by Nox4 shRNA. In vitro angiogenic activities such migration and tubulogenesis were assessed using wound healing and Matrigel assays, respectively. In vivo angiogenic activity was assessed using subcutaneous sponge assay in C57Bl/6 and Nox4‐deficient mice. Trichostatin A reduced Nox4 expression in a time‐ and concentration‐dependent manner. Both TSA and Nox4 silencing decreased Nox4 protein and H₂O₂. Mechanistically, TSA reduced expression of Nox4 via ubiquitination of p300‐ histone acetyltransferase (p300‐HAT). Thus, blocking of the ubiquitination pathway using an inhibitor of ubiquitin‐activating enzyme E1 (PYR‐41) prevented TSA inhibition of Nox4 expression. Trichostatin A also reduced migration and tube formation, and these effects were not observed in Nox4‐deficient endothelial cells. Finally, transforming growth factor beta1 (TGFβ1) enhanced angiogenesis in sponge model in C57BL/6 mice. This response to TGFβ1 was substantially reduced in Nox4‐deficient mice. Similarly intraperitoneal infusion of TSA (1 mg/kg) also suppressed TGFβ1‐induced angiogenesis in C57BL/6 mice. Trichostatin A reduces Nox4 expression and angiogenesis via inhibition of the p300‐HAT‐dependent pathway. This mechanism might be exploited to prevent aberrant angiogenesis in diabetic retinopathy, complicated vascular tumours and malformations.

Purpose: Fibrotic scarring after ocular surgeries and chemical burn injuries can impede clarity of the cornea and cause vision impairment. Transforming growth factor β (TGFβ) signaling pathway is known to mediate fibrotic scarring, and NADPH oxidase–derived reactive oxygen species has been shown to be an effector molecule that facilitates TGFβ1-mediated responses. The present study explores the expression profile and functional importance of NADPH oxidase (Nox) in conjunctival fibroblasts. In addition, the effect of curcumin on the TGFβ1-induced NADPH oxidase expression and collagen synthesis was also investigated. Methods: The mRNA expression of Nox isoforms in rabbit conjunctival fibroblasts was measured by real-time PCR. The production of hydrogen peroxide (H₂O₂) and total collagen by these cells was measured by Amplex Red assay and Picro-Sirius red assay, respectively. Nox4 was knocked down by adenovirus-mediated siRNA targeting Nox4 (Adv-Nox4i). Results: We describe for the first time that conjunctival fibroblasts express mRNA encoding for Nox2, Nox3, Nox4, and Nox5. TGFβ1 was found to induce Nox4 mRNA expression and total collagen release by these cells (P < 0.05; n = 4), and both responses are blocked by Smad3 inhibitor SIS3. Suppressing Nox4 gene transcription with Adv-Nox4i completely attenuated TGFβ1-stimulated H₂O₂ release and collagen production by conjunctival fibroblasts (P < 0.05; n = 4–6). Similarly, curcumin also inhibited TGFβ1-induced Smad3 phosphorylation, Nox4-derived H₂O₂ production, and total collagen synthesis by conjunctival fibroblasts (P < 0.05; n = 4–6). Conclusions: The present study suggests that TGFβ1-mediated production of collagen by conjunctival fibroblasts involves Nox4-derived H₂O₂ pathway and this effect of Nox4 is abrogated by curcumin. This mechanism might be exploited to prevent fibrotic scarring after surgeries and chemical burn injuries in the eye.

Introduction: Endothelial progenitor cells (EPCs) display a unique ability to promote angiogenesis and restore endothelial function in injured blood vessels. NADPH oxidase 4 (NOX4)-derived hydrogen peroxide (H2O2) serves as a signalling molecule and promotes endothelial cell proliferation and migration as well as protecting against cell death. However, the role of NOX4 in EPC function is not completely understood. Methods: EPCs were isolated from human saphenous vein and mammary artery discarded during bypass surgery. NOX4 gene and protein expression in EPCs were measured by real time-PCR and Western blot analysis respectively. NOX4 gene expression was inhibited using an adenoviral vector expressing human NOX4 shRNA (Ad-NOX4i). H2O2 production was measured by Amplex red assay. EPC migration was evaluated using a transwell migration assay. EPC proliferation and viability were measured using trypan blue counts. Results: Inhibition of NOX4 using Ad-NOX4i reduced Nox4 gene and protein expression as well as H2O2 formation in EPCs. Inhibition of NOX4-derived H2O2 decreased both proliferation and migration of EPCs. Interestingly, pro-inflammatory cytokine tumour necrosis factor alpha (TNFα) decreased NOX4 expression and reduced survival of EPCs. However, the survival of EPCs was further diminished by TNF-α in NOX4-knockdown cells, suggesting that NOX4 has a protective role in EPCs. Conclusion: These findings suggest that NOX4-type NADPH oxidase is important for proliferation and migration functions of EPCs and protects against pro-inflammatory cytokine induced EPC death. These properties of NOX4 may facilitate the efficient function of EPCs which is vital for successful neovascularization.