Pleiotropic effects of YC-1 selectively inhibit pathological retinal neovascularization and promote physiological revascularization in a mouse model of oxygen-induced retinopathy

Hypoxia-Dependent Upregulation of VEGF Relies on β3-Adrenoceptor Signaling in Human Retinal Endothelial and Müller Cells

β-adrenoceptors (BARs) are involved in vascular endothelial growth factor (VEGF) production during retinal neovascularization. Here, using human retinal endothelial and Müller cells (hRECs and MIO-M1, respectively), we evaluated the effects exerted by hypoxia on BARs, hypoxia-inducible factor-1α subunit (HIF-1α) and VEGF, as well as the involvement of BAR3 and nitric oxide synthase (NOS) enzymes in hypoxia-induced VEGF production. We altered oxygen availability through a hypoxic incubator. BARs, HIF-1 α and VEGF levels were evaluated. Cells were treated with the BAR3 antagonist SR59230A, different NOS inhibitors or the NO donor SNAP. The influence of the BAR3/NOS axis on hypoxic VEGF production was assessed. Hypoxia upregulated BAR3, HIF-1α and VEGF in hRECs and MIO-M1 cells. SR59230A counteracted hypoxia-dependent VEGF increase in both cell lines, exerting no effect on HIF-1α upregulation. Treatments with NOS inhibitors prevented the hypoxia-dependent VEGF increase, while SNAP abrogated the effect of SR59230A in reducing hypoxia-induced VEGF upregulation. The present results corroborate the hypothesis that in the hypoxic retina, BAR3 influence on VEGF production is mediated by NO and suggest that, at least in endothelial and Müller cells, BAR3 activity is necessary to allow the HIF-1-mediated VEGF upregulation.

The role of hypoxic microenvironment in autoimmune diseases

The hypoxic microenvironment, characterized by significantly reduced oxygen levels within tissues, has emerged as a critical factor in the pathogenesis and progression of various autoimmune diseases (AIDs). Central to this process is the hypoxia-inducible factor-1 (HIF-1), which orchestrates a wide array of cellular responses under low oxygen conditions. This review delves into the multifaceted roles of the hypoxic microenvironment in modulating immune cell function, particularly highlighting its impact on immune activation, metabolic reprogramming, and angiogenesis. Specific focus is given to the mechanisms by which hypoxia contributes to the development and exacerbation of diseases such as rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), multiple sclerosis (MS), and dermatomyositis (DM). In these conditions, the hypoxic microenvironment not only disrupts immune tolerance but also enhances inflammatory responses and promotes tissue damage. The review also discusses emerging therapeutic strategies aimed at targeting the hypoxic pathways, including the application of HIF-1α inhibitors, mTOR inhibitors, and other modulators of the hypoxic response. By providing a comprehensive overview of the interplay between hypoxia and immune dysfunction in AIDs, this review offers new perspectives on the underlying mechanisms of these diseases and highlights potential avenues for therapeutic intervention.

An allosteric peptide inhibitor of HIF-1α regulates hypoxia-induced retinal neovascularization

Retinal neovascularization (NV), a leading cause of vision loss, results from localized hypoxia that stabilizes the hypoxia-inducible transcription factors HIF-1α and HIF-2α, enabling the expression of angiogenic factors and genes required to maintain homeostasis under conditions of oxygen stress. HIF transcriptional activity depends on the interaction between its intrinsically disordered C-terminal domain and the transcriptional coactivators CBP/p300. Much effort is currently directed at disrupting protein-protein interactions between disease-associated transcription factors like HIF and their cellular partners. The intrinsically disordered protein CITED2, a direct product of HIF-mediated transcription, functions as a hypersensitive negative regulator that attenuates the hypoxic response by competing allosterically with HIF-1α for binding to CBP/p300. Here, we show that a peptide fragment of CITED2 is taken up by retinal cells and efficiently regulates pathological angiogenesis in murine models of ischemic retinopathy. Both vaso-obliteration (VO) and NV were significantly inhibited in an oxygen-induced retinopathy (OIR) model following intravitreal injection of the CITED2 peptide. The CITED2 peptide localized to retinal neurons and glia, resulting in decreased expression of HIF target genes. Aflibercept, a commonly used anti-VEGF therapy for retinal neovascular diseases, rescued NV but not VO in OIR. However, a combination of the CITED2 peptide and a reduced dose of aflibercept significantly decreased both NV and VO. In contrast to anti-VEGF agents, the CITED2 peptide can rescue hypoxia-induced retinal NV by modulating the hypoxic response through direct competition with HIF for CBP/p300, suggesting a dual targeting strategy for treatment of ischemic retinal diseases and other neovascular disorders.

Pharmacologic Targeting of Hypoxia-Inducible Factors

Hypoxia-inducible factors (HIFs) control transcriptional responses to reduced O₂ availability. HIFs are heterodimeric proteins composed of an O₂-regulated HIF-α subunit and a constitutively expressed HIF-1β subunit. HIF-α subunits are subject to prolyl hydroxylation, which targets the proteins for degradation under normoxic conditions. Small molecule prolyl hydroxylase inhibitors, which stabilize the HIF-α subunits and increase HIF-dependent expression of erythropoietin, are in phase III clinical trials for the treatment of anemia in patients with chronic kidney disease. HIFs contribute to the pathogenesis of many cancers, particularly the clear cell type of renal cell carcinoma in which loss of function of the von Hippel-Lindau tumor suppressor blocks HIF-2α degradation. A small molecule inhibitor that binds to HIF-2α and blocks dimerization with HIF-1β is in clinical trials for the treatment of renal cell carcinoma. Targeting HIFs for stabilization or inhibition may improve outcomes in diseases that are common causes of mortality in the US population.

Vascular and Neuronal Protection in the Developing Retina: Potential Therapeutic Targets for Retinopathy of Prematurity

Retinopathy of prematurity (ROP) is a common retinal disease in preterm babies. To prolong the lives of preterm babies, high oxygen is provided to mimic the oxygen level in the intrauterine environment for postnatal organ development. However, hyperoxia-hypoxia induced pathological events occur when babies return to room air, leading to ROP with neuronal degeneration and vascular abnormality that affects retinal functions. With advances in neonatal intensive care, it is no longer uncommon for increased survival of very-low-birth-weight preterm infants, which, therefore, increased the incidence of ROP. ROP is now a major cause of preventable childhood blindness worldwide. Current proven treatment for ROP is limited to invasive retinal ablation, inherently destructive to the retina. The lack of pharmacological treatment for ROP creates a great need for effective and safe therapies in these developing infants. Therefore, it is essential to identify potential therapeutic agents that may have positive ROP outcomes, especially in preserving retinal functions. This review gives an overview of various agents in their efficacy in reducing retinal damages in cell culture tests, animal experiments and clinical studies. New perspectives along the neuroprotective pathways in the developing retina are also reviewed.

Müller cells in pathological retinal angiogenesis

Müller cells are the major glial cells spanning the entire layer of the retina and maintaining retinal structure. Under pathological conditions, Müller cells are involved in retinal angiogenesis, a process of growing new blood vessels from pre-existing capillaries. In response to hypoxia, high glucose, and inflammation conditions, multiple signaling pathways are activated in Müller cells, followed by the increased production of proangiogenic factors including vascular endothelial growth factor, basic fibroblast growth factor, matrix metalloproteinases, Netrin-4, and angiopoietin-like 4. Expression of antiangiogenic factors is also downregulated in Müller cells. Besides, proliferation and dedifferentiation of Müller cells facilitates retinal angiogenesis. In this review, we summarized molecular mechanisms of Müller cells-related retinal angiogenesis. The potential of Müller cells as a therapeutic target for retinal angiogenesis was also discussed.

Intracellular calcium and NF-kB regulate hypoxia-induced leptin, VEGF, IL-6 and adiponectin secretion in human adipocytes

AIMS

Hypoxia-induced adipokine release has been attributed mainly to HIF-1α. Here we investigate the role of intracellular calcium and NF-kB in the hypoxia-dependent release of leptin, VEGF, IL-6 and the hypoxia-induced inhibition of adiponectin release in human adipocytes.

MAIN METHODS

We used intracellular calcium imaging to compare calcium status in preadipocytes and in adipocytes. We subjected both cell types to hypoxic conditions and measured the release of adipokines induced by hypoxia in the presence and absence of HIF-1α inhibitor YC-1, NF-_κB inhibitor SN50 and intracellular calcium chelator BAPTA-AM.

KEY FINDINGS

We demonstrate reduced intracellular calcium oscillations and increased oxidative stress as the cells transitioned from preadipocytes to adipocytes. We show that differentiation of preadipocytes to adipocytes is associated with distinct morphological changes in the mitochondria. We also show that hypoxia-induced secretion of leptin, VEGF, IL-6 and hypoxia-induced inhibition of adiponectin secretion are independent of HIF-1α expression. The hypoxia-induced leptin, VEGF and IL-6 release are [Ca⁺⁺]_i dependent whereas adiponectin is NF-_kB dependent.

SIGNIFICANCE

Our work suggests a major role for [Ca⁺⁺]_i in preadipocyte differentiation to adipocytes and that changes in mitochondrial morphology in the adipocytes might underlie the reduced calcium oscillations observed in the adipocytes. It also demonstrates that multiple signaling pathways are associated with the hypoxia-induced adipokine secretion.

Therapeutic window for YC‑1 following glutamate‑induced neuronal damage and transient focal cerebral ischemia

3-(5′-Hydroxymethyl-2′-furyl)-1-benzylindazole (YC-1), has been demonstrated to inhibit platelet aggregation, vascular contraction and hypoxia-inducible factor 1 activity in vitro and in vivo. The present study investigated the neuroprotective efficacy of YC-1 in cultured neurons exposed to glutamate-induced excitotoxicity and in an animal model of stroke. In a cortical neuronal culture model, YC-1 demonstrated neurotoxicity at a concentration >100 µM, and YC-1 (10–30 µM) achieved potent cytoprotection against glutamate-induced neuronal damage. Additionally, YC-1 (30 µM) effectively attenuated the increase in intracellular Ca²⁺ levels. Delayed treatment of YC-1 (30 µM) also protected against glutamate-induced neuronal damage and cell swelling in cultured neurons, though only at 4 h post-treatment. In addition, immediate treatment of YC-1 (30 µM) following the exposure of cortical neurons to glutamate (300 µM) produced a marked reduction in intracellular pH. Delayed treatment of YC-1 (25 mg/kg) protected against ischemic brain damage in vivo, though only when administered at 3 h post-insult. Thus, YC-1 exhibited neuroprotection against glutamate-induced neuronal damage and in mice subjected to transient focal cerebral ischemia. This neuroprotection may be mediated via its ability to limit the glutamate-induced excitotoxicity. However, the neuroprotective therapeutic window of YC-1 is only at 3 h in vivo and 4 h in vitro, which may, at least in part, be attributed to its ability to reduce the intracellular pH in the early phase of ischemic stroke. Although YC-1 provided the potential for clinical therapy, the treatment time point must be carefully evaluated following ischemia.

HIF-1α Dependent Wound Healing Angiogenesis In Vivo Can Be Controlled by Site-Specific Lentiviral Magnetic Targeting of SHP-2

Hypoxia promotes vascularization by stabilization and activation of the hypoxia inducible factor 1α (HIF-1α), which constitutes a target for angiogenic gene therapy. However, gene therapy is hampered by low gene delivery efficiency and non-specific side effects. Here, we developed a gene transfer technique based on magnetic targeting of magnetic nanoparticle-lentivirus (MNP-LV) complexes allowing site-directed gene delivery to individual wounds in the dorsal skin of mice. Using this technique, we were able to control HIF-1α dependent wound healing angiogenesis in vivo via site-specific modulation of the tyrosine phosphatase activity of SHP-2. We thus uncover a novel physiological role of SHP-2 in protecting HIF-1α from proteasomal degradation via a Src kinase dependent mechanism, resulting in HIF-1α DNA-binding and transcriptional activity in vitro and in vivo. Excitingly, using targeting of MNP-LV complexes, we achieved simultaneous expression of constitutively active as well as inactive SHP-2 mutant proteins in separate wounds in vivo and hereby specifically and locally controlled HIF-1α activity as well as the angiogenic wound healing response in vivo. Therefore, magnetically targeted lentiviral induced modulation of SHP-2 activity may be an attractive approach for controlling patho-physiological conditions relying on hypoxic vessel growth at specific sites.

Effects of Histone Deacetylase Inhibitor (Valproic Acid) on the Expression of Hypoxia-inducible Factor-1 Alpha in Human Retinal Müller Cells

Purpose

To evaluate the effects of valproic acid (VPA), a histone deacetylase inhibitor (HDACI), on the expression of hypoxia-inducible factor-1 alpha (HIF-1α) and vascular endothelial growth factor (VEGF) in human retinal Müller cells under hypoxic conditions.

Methods

Chemical hypoxia was induced in human retinal Müller cells (MIO-M1) by treatment with increasing concentrations of cobalt(II) chloride (CoCl₂). Müller cells were also treated with a set concentration of CoCl₂, along with various concentrations of VPA. The expression of HIF-1α and VEGF in the treated Müller cells was determined by enzyme-linked immunosorbent assay.

Results

Exposure of human retinal Müller cells to increasing concentrations of CoCl₂ produced a dose-dependent increase in HIF-1α expression. The addition of increasing concentrations of VPA lead to a dose-dependent decrease in expression of HIF-1α and VEGF in Müller cells exposed to a set concentration of CoCl₂.

Conclusions

HDACI VPA downregulated the expressions of HIF-1α and VEGF in human retinal Müller cells under hypoxic conditions. Using HDACI to target HIF-1α expression in Müller cells could be a new therapeutic strategy for the treatment of retinal vascular diseases.

Inhibition of Hypoxia-Induced Retinal Angiogenesis by Specnuezhenide, an Effective Constituent of Ligustrum lucidum Ait., through Suppression of the HIF-1α/VEGF Signaling Pathway

Specnuezhenide (SPN), one of the main ingredients of Chinese medicine "Nü-zhen-zi", has anti-angiogenic and vision improvement effects. However, studies of its effect on retinal neovascularization are limited so far. In the present study, we established a vascular endothelial growth factor A (VEGFA) secretion model of human acute retinal pigment epithelial-19 (ARPE-19) cells by exposure of 150 μM CoCl₂ to the cells and determined the VEGFA concentrations, the mRNA expressions of VEGFA, hypoxia inducible factor-1α (HIF-1α) & prolyl hydroxylases 2 (PHD-2), and the protein expressions of HIF-1α and PHD-2 after treatment of 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1, 1.0 μg/mL) or SPN (0.2, 1.0 and 5.0 μg/mL). Furthermore, rat pups with retinopathy were treated with SPN (5.0 and 10.0 mg/kg) in an 80% oxygen atmosphere and the retinal avascular areas were assessed through visualization using infusion of ADPase and H&E stains. The results showed that SPN inhibited VEGFA secretion by ARPE-19 cells under hypoxia condition, down-regulated the mRNA expressions of VEGFA and PHD-2 slightly, and the protein expressions of VEGFA, HIF-1α and PHD-2 significantly in vitro. SPN also prevented hypoxia-induced retinal neovascularization in a rat model of oxygen-induced retinopathy in vivo. These results indicate that SPN ameliorates retinal neovascularization through inhibition of HIF-1α/VEGF signaling pathway. Therefore, SPN has the potential to be developed as an agent for the prevention and treatment of diabetic retinopathy.

Aloe-emodin suppresses hypoxia-induced retinal angiogenesis via inhibition of HIF-1α/VEGF pathway

Background: Aloe-emodin (AE) has been reported to possess the antiangiogenic effect on laser induced choroidal neovascularization. AE inhibits the vessel formation in the zebrafish embryos. However, it is still unclear whether AE can alleviate neovascularization. Here, we investigated the inhibitory effect of AE on the hypoxia-induced retinal neovascularization and the possible mechanisms. Methods: We established a vascular endothelial growth factor (VEGF) secretion model under chemical induced hypoxia by exposure of 150 µM CoCl₂ to the ARPE-19 cells, then treated the cells with different concentrations of AE (0.2, 1.0 and 5.0 µg/mL) or a special hypoxia-inducible factor 1α (HIF-1α) inhibitor [3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole, YC-1, 1.0 µg/mL]. The cellular supernatants were collected 48 h later to measure the VEGFA concentrations by human VEGFA enzyme-linked immunosorbent assay (ELISA) kits, the mRNA expressions of VEGFA, HIF-1α and prolyl hydroxylase-2 (PHD-2) by quantitative reverse transcription-PCR (qRT-PCR) and the protein expressions of HIF-1α and PHD-2 by Western blots. For in vivo study, the rat pups with oxygen-induced retinopathy were treated with Conbercept ophthalmic injection (1.0 mg/kg) or AE (5.0 and 10.0 mg/kg) for five days, then the retinal avascular areas were assessed via visualization of the retinal vasculature with ADPase and hematoxylin & eosin (H&E) stains. Results: AE inhibits the VEGFA secretion of ARPE-19 cells under hypoxia condition, decreases the mRNA expressions of VEGFA and PHD-2 and the protein expressions of VEGFA, HIF-1α and PHD-2 in vitro and prevents hypoxia-induced retinal neovascularization in vivo.Conclusions: AE ameliorates retinal neovascularization throuth inhibition of the HIF-1α/VEGF signaling pathway. AE may be developed as a potential drug for the prevention and treatment of diabetic retinopathy.

Formononetin, an active compound of Astragalus membranaceus (Fisch) Bunge, inhibits hypoxia-induced retinal neovascularization via the HIF-1α/VEGF signaling pathway

BACKGROUND

It has been reported that formononetin (FMN), one of the main ingredients from famous traditional Chinese medicine "Huang-qi" (Astragalus membranaceus [Fisch] Bunge) for Qi-tonifying, exhibits the effects of immunomodulation and tumor growth inhibition via antiangiogenesis. Furthermore, A. membranaceus may alleviate the retinal neovascularization (NV) of diabetic retinopathy. However, the information of FMN on retinal NV is limited so far. In the present study, we investigated the effects of FMN on the hypoxia-induced retinal NV and the possible related mechanisms.

MATERIALS AND METHODS

The VEGF secretion model of acute retinal pigment epithelial-19 (ARPE-19) cells under chemical hypoxia was established by the exposure of cells to 150 μM CoCl₂ and then cells were treated with 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1, a potent HIF-1α inhibitor, 1.0 μg/mL) or different concentrations of FMN (0.2 μg/mL, 1.0 μg/mL, and 5.0 μg/mL). The supernatants of cells were collected 48 hours later to measure the VEGF concentrations, following the manufacturer's instruction. The mRNA expressions of VEGF, HIF-1α, PHD-2, and β-actin were analyzed by quantitative reverse transcription polymerase chain reaction, and the protein expressions of HIF-1α and PHD-2 were determined by Western blot analysis. Furthermore, the rats with retinopathy were treated by intraperitoneal administration of conbercept injection (1.0 mg/kg) or FMN (5.0 mg/kg and 10.0 mg/kg) in an 80% oxygen atmosphere. The retinal avascular areas were assessed through visualization of the retinal vasculature by adenosine diphosphatase staining and hematoxylin and eosin staining.

RESULTS

FMN can indeed inhibit the VEGF secretion of ARPE-19 cells under hypoxia, downregulate the mRNA expression of VEGFA and PHD-2, and decrease the protein expression of VEGF, HIF-1α, and PHD-2 in vitro. Furthermore, FMN can prevent hypoxia-induced retinal NV in vivo.

CONCLUSION

FMN can ameliorate retinal NV via the HIF-1α/VEGF signaling pathway, and it may become a potential drug for the prevention and treatment of diabetic retinopathy.

Evaluation of anti-HIF and anti-angiogenic properties of honokiol for the treatment of ocular neovascular diseases

Pathological activation of the hypoxia-inducible-factor (HIF) pathway leading to expression of pro-angiogenic genes, such as vascular endothelial growth factor (VEGF), is the fundamental cause of neovascularization in ocular ischemic diseases and cancers. We have shown that pure honokiol inhibits the HIF pathway and hypoxia-mediated expression of pro-angiogenic genes in a number of cancer and retinal pigment epithelial (RPE) cell lines. The crude extracts, containing honokiol, from Magnolia plants have been used for thousands of years in the traditional oriental medicine for a number of health benefits. We have recently demonstrated that daily intraperitoneal injection of honokiol starting at postnatal day (P) 12 in an oxygen induced retinopathy mouse model significantly reduced retinal neovascularization at P17. Here, we evaluate the mechanism of HIF inhibition by honokiol in RPE cells. Using chromatin immunoprecipitation experiments, we demonstrate that honokiol inhibits binding of HIF to hypoxia-response elements present on VEGF promoter. We further show using a number of in vitro angiogenesis assays that, in addition to anti-HIF effect, honokiol manifests potent anti-angiogenic effect on human retinal micro vascular endothelial cells. Our results suggest that honokiol possesses potent anti-HIF and anti-angiogenic properties. These properties of honokiol make it an ideal therapeutic agent for the treatment of ocular neovascular diseases and solid tumors.

Candesartan stimulates reparative angiogenesis in ischemic retinopathy model: role of hemeoxygenase-1 (HO-1)

Ischemic diseases such as stroke and proliferative retinopathy are characterized by hypoxia-driven release of angiogenic factors such as vascular endothelial growth factor (VEGF). However, revascularization of the ischemic areas is inadequate, resulting in impaired neuro-vascular function. We aim to examine the vascular protective effects of candesartan, an angiotensin receptor blocker, in an ischemic retinopathy mouse model. Vascular density, number of tip cells, and perfusions of capillaries were assessed. Activation of Muller glial cells and levels of peroxynitrite, VEGF, VEGFR2, inducible nitric oxide synthase, hemeoxygenase-1 (HO-1) were assessed. Proangiogenic effects of candesartan were examined in human endothelial cells (EC) that were cultured in normoxia or hypoxia and transduced with siRNA against HO-1. Candesartan (1 mg/kg) and (10 mg/kg) decreased hypoxia-induced neovascularization by 67 and 70%, respectively. Candesartan (10 mg/kg) significantly stimulated the number of tip cells and physiological revascularization of the central retina (45%) compared with untreated pups. The effects of candesartan coincided with reduction of hypoxia-induced Muller glial activation, iNOS expression and restoration of HO-1 expression with no significant change in VEGF levels. In vitro, silencing HO-1 expression blunted the ability of candesartan to induce VEGF expression under normoxia and VEGFR2 activation and angiogenic response under both normoxia and hypoxia. These findings suggest that candesartan improved reparative angiogenesis and hence prevented pathological angiogenesis by modulating HO-1 and iNOS levels in ischemic retinopathy. HO-1 is required for VEGFR2 activation and proangiogenic action of candesartan in EC. Candesartan, an FDA-approved drug, could be repurposed as a potential therapeutic agent for the treatment of ischemic diseases.

Nuclear factor kappa-B signaling is integral to ocular neovascularization in ischemia-independent microenvironment

Retinal ischemia promotes the upregulation of VEGF expression and accounts for most pathological features of retinal neovascularization (NV). Paradoxically, VEGF remains the pivotal stimulator of ocular NV, despite the absence of ischemia. Therefore, the central question arises as to how the various molecular mechanisms interplay in ischemia-independent NV. It's been suggested that NFκB plays a crucial role in the pathogenesis of diabetic vasculopathies. Here, we dissected the molecular mechanism of ocular NV in the rho/VEGF transgenic mouse model, which develops subretinal NV in ischemia-independent microenvironment. Furthermore, we examined whether intravitreal administration of YC-1, a HIF-1 inhibitor, can modulate the activation of NFκB and its downstream angiogenic signaling in the mouse retina. We demonstrated that YC-1 inhibited retinal NFκB/p65 DNA binding activity and downregulated NFκB/p65, FAK, α5β1, EPO, ET-1, and MMP-9 expression at the message and the protein levels. In addition, YC-1 significantly inhibited subretinal NV by reducing the number of neovascular lesions, the area of each lesion and the total area of NV per retina. We further investigated the influence of VEGF signaling pathway on HIF-1α transcriptional activity to substantiate that this mouse model develops subretinal NV in an ischemia-independent microenvironment. Our data demonstrated that VEGF overexpression didn't have any impact on HIF-1α transcriptional activity, whereas treatment with YC-1 significantly inhibited endogenous HIF-1 activity. Our study suggests that retinal NFκB transcriptional activity is pivotal to ischemia-independent mechanisms, which lead to the local activation of angiogenic cascades. Our data also indicate that the nexus between VEGF and NFκB is implicated in triggering the angiogenic cascade that promotes retinal NV. Hence, targeting the VEGF/NFκB axis may act in a negative feedback loop to suppress ocular NV. This study suggests that inhibition of NFκB activation may be a means of turning off a “master switch” responsible for initiating and perpetuating these ocular pathologies.

Erythropoietin inhibits HIF-1α expression via upregulation of PHD-2 transcription and translation in an in vitro model of hypoxia-ischemia

Hypoxia inducible factor (HIF)-1α is the central transcriptional factor for the regulation of oxygen-associated genes in response to hypoxia. Erythropoietin (EPO), a hematopoietic growth factor, increases oxygen availability during hypoxia/ischemia and is associated with neuroprotection following hypoxia-ischemia in laboratory models of stroke. However, EPO has failed to translate in a clinical setting. Thus, it is critical to elucidate the key players in EPO-induced neuroprotection. Our preliminary studies have shown that EPO, as a downstream gene of HIF, inhibits HIF-1α in a dose-dependent manner in an in vitro model of hypoxia-ischemia. This study is designed to elucidate the primary mediator of EPO-induced HIF-1α inhibition and subsequent cell survival/neuroprotection. Oxygen and glucose deprivation (OGD) of nerve growth factor-differentiated rat pheochromocytoma (PC-12) cells were used to model hypoxia-ischemia in an in vitro environment. The profile of HIF-1α, HIF-2α and prolyl hydroxylase domain 2 (PHD-2) expression; HIF-1α and prolyl hydroxylase (PHD-2) mRNA levels; matrix metalloproteinase (MMP)-9; and cell death was evaluated in the presence and absence of either EPO or PHD-2 inhibitor during OGD. Our findings showed that EPO treatment resulted in an increase in PHD-2 transcription and translation, inhibition of HIF-1α expression, reactive oxygen species formation, and MMP-9 activity, resulting in increased cell survival after OGD. We also observed that EPO-induced cell survival/neuroprotection was reversed by siRNA silencing of PHD-2. This led to the conclusion that PHD-2 is a key mediator of EPO-induced HIF-1α inhibition and subsequent neuroprotection in an in vitro model of hypoxia-ischemia.

Ritonavir inhibits HIF-1α-mediated VEGF expression in retinal pigment epithelial cells in vitro

PURPOSE

Retinal hypoxia-mediated activation of the hypoxia-inducible factor (HIF pathway) leading to angiogenesis is a major signaling mechanism underlying a number of sight-threatening diseases. Inhibiting this signaling mechanism with an already approved therapeutic molecule may have promising anti-angiogenic role with fewer side effects. Hence, the primary objective of this study was to examine the expression of HIF-1α and VEGF in human retinal pigment epithelial cells treated with ritonavir under hypoxic and normoxic conditions.

METHODS

ARPE-19 and D407 cells were cultured in normoxic or hypoxic conditions, alone or in the presence of ritonavir. Quantitative real-time polymerase chain reaction, immunoblot analysis, sandwich ELISA, endothelial cell proliferation, and cytotoxicity were performed.

RESULTS

A 12-h hypoxic exposure resulted in elevated mRNA expression levels of both HIF-1α and VEGF in ARPE-19 and D407 cells. Hence, this time point was selected for subsequent experiments. Presence of ritonavir in the culture medium strongly inhibited VEGF expression in a concentration-dependent manner under hypoxic conditions. Immunoblot analysis demonstrated a substantially reduced protein expression of HIF-1α in the presence of ritonavir. Further, hypoxic exposure-induced VEGF secretion was also inhibited by ritonavir, as demonstrated using ELISA. Finally, ritonavir significantly diminished the proliferation of choroid-retinal endothelial (RF/6A) cells demonstrating potential anti-angiogenic activity. Cytotoxicity studies showed that ritonavir is non-toxic to RPE cells.

CONCLUSIONS

This study demonstrates for the first time that ritonavir can inhibit HIF-1α and VEGF in ARPE-19 and D407 cells. Such inhibition may form a platform for application of ritonavir in the treatment of various ocular diseases.

Honokiol inhibits pathological retinal neovascularization in oxygen-induced retinopathy mouse model

Aberrant activation of the hypoxia inducible factor (HIF) pathway is the underlying cause of retinal neovascularization, one of the most common causes of blindness worldwide. The HIF pathway also plays critical roles during tumor angiogenesis and cancer stem cell transformation. We have recently shown that honokiol is a potent inhibitor of the HIF pathway in a number of cancer and retinal pigment epithelial cell lines. Here we evaluate the safety and efficacy of honokiol, digoxin, and doxorubicin, three recently identified HIF inhibitors from natural sources. Our studies show that honokiol has a better safety to efficacy profile as a HIF inhibitor than digoxin and doxorubicin. Further, we show for the first time that daily intraperitoneal injection of honokiol starting at postnatal day (P) 12 in an oxygen-induced retinopathy (OIR) mouse model significantly reduced retinal neovascularization at P17. Administration of honokiol also prevents the oxygen-induced central retinal vaso-obliteration, characteristic feature of the OIR model. Additionally, honokiol enhanced physiological revascularization of the retinal vascular plexuses. Since honokiol suppresses multiple pathways activated by HIF, in addition to the VEGF signaling, it may provide advantages over current treatments utilizing specific VEGF antagonists for ocular neovascular diseases and cancers.

The nexus between VEGF and NFκB orchestrates a hypoxia-independent neovasculogenesis

Nuclear Factor-Kappa B [NFκB] activation triggers the elevation of various pro-angiogenic factors that contribute to the development and progression of diabetic vasculopathies. It has been demonstrated that vascular endothelial growth factor [VEGF] activates NFκB signaling pathway. Under the ischemic microenvironments, hypoxia-inducible factor-1 [HIF-1] upregulates the expression of several proangiogenic mediators, which play crucial roles in ocular pathologies. Whereas YC-1, a soluble guanylyl cyclase [sGC] agonist, inhibits HIF-1 and NFκB signaling pathways in various cell and animal models. Throughout this investigation, we examined the molecular link between VEGF and NFκB under a hypoxia-independent microenvironment in human retinal microvascular endothelial cells [hRMVECs]. Our data indicate that VEGF promoted retinal neovasculogenesis via NFκB activation, enhancement of its DNA-binding activity, and upregulating NFκB/p65, SDF-1, CXCR4, FAK, αVβ3, α5β1, EPO, ET-1, and MMP-9 expression. Conversely, YC-1 impaired the activation of NFκB and its downstream signaling pathways, via attenuating IκB kinase phosphorylation, degradation and activation, and thus suppressing p65 phosphorylation, nuclear translocation, and inhibiting NFκB-DNA binding activity. We report for the first time that the nexus between VEGF and NFκB is implicated in coordinating a scheme that upregulates several pro-angiogenic molecules, which promotes retinal neovasculogenesis. Our data may suggest the potential use of YC-1 to attenuate the deleterious effects that are associated with hypoxia/ischemia-independent retinal vasculopathies.

Role of the retinal vascular endothelial cell in ocular disease

Retinal endothelial cells line the arborizing microvasculature that supplies and drains the neural retina. The anatomical and physiological characteristics of these endothelial cells are consistent with nutritional requirements and protection of a tissue critical to vision. On the one hand, the endothelium must ensure the supply of oxygen and other nutrients to the metabolically active retina, and allow access to circulating cells that maintain the vasculature or survey the retina for the presence of potential pathogens. On the other hand, the endothelium contributes to the blood-retinal barrier that protects the retina by excluding circulating molecular toxins, microorganisms, and pro-inflammatory leukocytes. Features required to fulfill these functions may also predispose to disease processes, such as retinal vascular leakage and neovascularization, and trafficking of microbes and inflammatory cells. Thus, the retinal endothelial cell is a key participant in retinal ischemic vasculopathies that include diabetic retinopathy and retinopathy of prematurity, and retinal inflammation or infection, as occurs in posterior uveitis. Using gene expression and proteomic profiling, it has been possible to explore the molecular phenotype of the human retinal endothelial cell and contribute to understanding of the pathogenesis of these diseases. In addition to providing support for the involvement of well-characterized endothelial molecules, profiling has the power to identify new players in retinal pathologies. Findings may have implications for the design of new biological therapies. Additional progress in this field is anticipated as other technologies, including epigenetic profiling methods, whole transcriptome shotgun sequencing, and metabolomics, are used to study the human retinal endothelial cell.

Zinc transporter 8 (ZnT8) expression is reduced by ischemic insults: a potential therapeutic target to prevent ischemic retinopathy

The zinc (Zn⁺⁺) transporter ZnT8 plays a crucial role in zinc homeostasis. It’s been reported that an acute decrease in ZnT8 levels impairs β cell function and Zn⁺⁺ homeostasis, which contribute to the pathophysiology of diabetes mellitus (DM). Although ZnT8 expression has been detected in the retinal pigment epithelium (RPE), its expression profile in the retina has yet to be determined. Furthermore, the link between diabetes and ischemic retinopathy is well documented; nevertheless, the molecular mechanism(s) of such link has yet to be defined. Our aims were to; investigate the expression profile of ZnT8 in the retina; address the influence of ischemia on such expression; and evaluate the influence of YC-1; (3-(50-hydroxymethyl-20-furyl)-1-benzyl indazole), a hypoxia inducible factor-1 (HIF-1) inhibitor, on the status of ZnT8 expression. We used real-time RT-PCR, immunohistochemistry, and Western blot in the mouse model of oxygen-induced retinopathy (OIR) and Müller cells to evaluate the effects of ischemia/hypoxia and YC-1 on ZnT8 expression. Our data indicate that ZnT8 was strongly expressed in the outer nuclear layer (ONL), outer plexiform layer (OPL), ganglion cell layer (GCL), and nerve fiber layer (NFL), whereas the photoreceptor layer (PRL), inner nuclear layer (INL) and inner plexiform layer (IPL) showed moderate ZnT8 immunoreactivity. Furthermore, we demonstrate that retinal ischemic insult induces a significant downregulation of ZnT8 at the message and protein levels, YC-1 rescues the injured retina by restoring the ZnT8 to its basal homeostatic levels in the neovascular retinas. Our data indicate that ischemic retinopathy maybe mediated by aberrant Zn⁺⁺ homeostasis caused by ZnT8 downregulation, whereas YC-1 plays a neuroprotective role against ischemic insult. Therefore, targeting ZnT8 provides a therapeutic strategy to combat neovascular eye diseases.

Candesartan, an angiotensin II type 1 receptor antagonist, inhibits pathological retinal neovascularization by downregulating VEGF receptor-2 expression

Several studies have examined the anti-angiogenic effects of angiotensin II type 1 (AT(1)) receptor antagonists; however, the mechanisms underlying these effects are currently unclear. In the present study, we examined the efficacy and the mechanism of candesartan, an AT(1) receptor antagonist, in suppressing pathological retinal neovascularization. We used an in vivo murine oxygen-induced retinopathy (OIR) model and also studied the in vitro proliferation and migration of human retinal microvascular endothelial cells (HRMECs) induced by vascular endothelial growth factor (VEGF)-A. The regulation of angiogenesis-associated genes such as hypoxia-inducible factor (HIF-1α), VEGF-A, VEGF receptor-1, and VEGF receptor-2 was evaluated with real-time RT-PCR in the OIR model. In the OIR model, candesartan suppressed the pathological neovascularization in a dose-dependent manner, but did not prevent the physiological angiogenesis. However, candesartan did not inhibit VEGF-A-induced proliferation or migration in HRMECs in the in vitro study. When administered interperitoneally in the OIR model, candesartan reduced the upregulation of VEGF receptor-2 in the retina, but had no effects in the other angiogenesis-related genes, such as HIF-1α, VEGF-A, and VEGF receptor-1. These findings indicate that candesartan inhibited the retinal pathological neovascularization, at least in part, by suppressing the expression of VEGF receptor-2, independent of VEGF signaling cascade. Therefore, candesartan may be a useful therapeutic target for the inhibition of retinal neovascularization that has a low risk of serious side effects.

Hypoxia--a key regulator of angiogenesis and inflammation in rheumatoid arthritis

The importance of inflammation in rheumatoid arthritis (RA) is well understood. This knowledge has resulted in the development of anti-inflammatory therapies--either broadly acting (such as steroids) or more specific approaches (such as antibodies against TNF)--with biologic therapies (including TNF inhibitors) revolutionizing the treatment of RA. However, what is less well appreciated in RA are the links between inflammation, blood-vessel formation (angiogenesis) and cellular responses to changes in oxygen tension. Inadequate oxygenation, termed hypoxia, is thought to drive the increase in synovial angiogenesis that occurs in RA, through expression of hypoxia-inducible molecules, including vascular endothelial growth factor (VEGF). This process promotes further infiltration of inflammatory cells and production of inflammatory mediators, perpetuating synovitis. This Review highlights the molecular pathways activated by hypoxia, and how these pathways might interact with inflammatory signaling to promote and maintain synovitis in RA, with a particular focus on the response of macrophages to hypoxia in the context of RA. Successful treatment of RA, for example with anti-TNF antibodies, reduces levels of proangiogenic factors, including VEGF, and leads to normalization of the vasculature. These processes emphasise the close links between hypoxia, angiogenesis and inflammation in this disease and supports the concept that angiogenesis blockade could be of therapeutic benefit in RA.

Hypoxia-regulated retinal glial cell-specific promoter for potential gene therapy in disease

PURPOSE

Retinal Müller cells span the retina and secrete several trophic factors and represent the functional link between blood vessels and neurons, making them attractive targets for gene therapy. Therefore, a hypoxia-regulated, retinal glial cell-specific vector was constructed and tested for its response to hypoxia.

METHODS

A hybrid promoter containing domains of human glial fibrillary acidic protein (GFAP) and several hypoxia-responsive and aerobically silenced elements (HRSE) was incorporated separately into plasmid vectors for generation of self-complementary adeno-associated virus. Müller cells trasfected with plasmids or virus were compared with other cell lines using standard

METHODS

The mouse model of oxygen-induced retinopathy (OIR) was used to analyze retinas from mice exposed to high oxygen or room air to evaluate the induction of the regulated promoter.

RESULTS

The regulated promoter was silenced under aerobic conditions in comparison with unregulated promoter in Müller cells. Hypoxia induced a 12-fold and 16-fold increase in promoter activity in primary Müller cells and human Müller cell lines, respectively. In the OIR model, intravitreal injection of the regulated promoter at postnatal day 7 (P7) resulted in high levels of green fluorescent protein expression only in retinal Müller cells at P17. GFP expression was absent in retinas of mice only exposed to room air. In vivo studies confirm normoxia silencing, hypoxic induction, and cell specificity of the regulated promoter in the mouse retina.

CONCLUSIONS

This hypoxia-regulated, retinal glial cell-specific AAV vector provides a platform for gene therapy within regions of retinal hypoxia which are found in diabetic retinopathy and age-related macular degeneration.

Mediators involved in retinopathy of prematurity and emerging therapeutic targets

Retinopathy of prematurity (ROP) is a potentially blinding disease of premature infants and despite timely treatment some infants develop retinal detachment and sight loss. Current treatment utilises laser therapy which causes destruction of treated retinal tissue resulting in field loss. There is considerable research work ongoing on neovascular eye disease which is likely to result in antiangiogenic approaches that will arrest the development of ROP by specifically targeting the involved molecular mediators. Some of these new therapeutic interventions have entered clinical trials. This article reviews new information available on the molecular pathogenesis of ROP which may result in novel treatments for ROP; it does not discuss the well-known role of oxygen in the development of ROP.

A novel composition for in vitro and in vivo regeneration of skin and connective tissues

The particular combination of polydeoxyribonucleotides, l-carnitine, calcium ions, proteolytic enzyme and other ingredients acts in a synergetic way in the regeneration of skin and connective tissues. This new formulation of active principles was tested in vitro as a cell and tissue culture medium and in vivo for various preparations in support of tissue regeneration. In vitro, the new blend allowed the maintenance of skin biopsies for more than 1 year in eutrophic conditions. Immunocytochemical analyses of fibroblasts isolated from these biopsies confirmed a significant increase of the epidermal and connective wound-healing markers such as collagen type I, collagen type IV, cytokeratin 1 (CK1), CK5, CK10 and CK14 versus controls. To examine the effects of the new compound in vivo, we studied impaired wound healing in genetically diabetic db/db mice. At day 18, diabetic mice treated with the new composition showed 100% closure of wounds and faster healing than mice treated with the other solutions. This complex of vital continuity factors or life-keeping factors could be used as a tissue-preserving solution or a cosmetic/drug/medical device to accelerate wound healing in the treatment of patients with deficient wound repair to promote the regeneration of cutaneous and connective tissues (injuries-wound, dermatitis) and prevent the recurrent relapses.

YC-1 attenuates hypoxia-induced pulmonary arterial hypertension in mice

BACKGROUND

Pulmonary arterial hypertension (PAH) is characterized by a progressive increase in pulmonary vascular resistance and elevation of pulmonary arterial pressure, leading to right ventricular failure and eventual death. Currently, no curative therapy for PAH is available, and the overall prognosis is very poor. Recently, direct activators of soluble guanylyl cyclase (sGC) have been tested as a novel therapeutic modality in experimental models of pulmonary arterial hypertension (PAH).

OBJECTIVE

In this study, we used in vitro and in vivo models to evaluate the therapeutic potential of 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1), a dual functioning chemical, as a direct activator of guanylyl cyclase and an inhibitor of hypoxia-inducible factor-1.

METHODS

We analyzed the effects of YC-1 on cell proliferation and the levels of p21 and p53 in human pulmonary artery smooth muscle cells (HPASMCs) under hypoxia. We also determined the effects of YC-1 on expression of endothelin-1 (ET-1) and phosphorylation status of endothelial nitric oxide synthase (eNOS) at Ser(1179) in human pulmonary artery endothelial cells (HPAECs) under hypoxia. In mice, hypoxic PAH was induced by exposure to normobaric hypoxic conditions for 28 days. To assess preventive or therapeutic effects, randomized mice were subjected to once daily i.p. injections of YC-1 for the entire hypoxic period (5 mg/kg) or for the last seven days of a 28-day hypoxic period (5 and 10 mg/kg). On day 28, we measured the right ventricular systolic pressure (RVSP) and determined the degrees of right ventricular hypertrophy (RVH) and vascular remodeling.

RESULTS

In HPASMCs, YC-1 inhibited hypoxia-induced proliferation and induction of p53 and p21 in a concentration-dependent manner. Also, YC-1 suppressed the hypoxia-induced expression of ET-1 mRNA and dephosphorylation of eNOS at Ser(1179) in HPAECs. In the preventive in vivo model, a daily dose of 5 mg/kg YC-1 significantly prevented the elevation of RVSP, development of RVH, and pulmonary vascular remodeling, which were caused by hypoxic exposure. In the therapeutic model, YC-1 at daily doses of 5 and 10 mg/kg alleviated RVH and pulmonary vascular remodeling but did not prevent the elevation of RVSP.

CONCLUSIONS

Our results indicate that YC-1 prevents the development of hypoxia-induced PAH in a preventive model and alleviates RVH and pulmonary vascular remodeling in a therapeutic model. Therefore, these data imply that YC-1 has therapeutic potential for use in a single or combination therapy for PAH.

Blockade of hypoxia-inducible factor-1α by YC-1 attenuates interferon-γ and tumor necrosis factor-α-induced intestinal epithelial barrier dysfunction

Proinflammatory cytokines play vital roles in intestinal barrier function disruption. YC-1 has been reported to have potent anti-inflammatory properties, and to be a potential agent for sepsis treatment. Here, we investigated the protective effect of YC-1 against intestinal barrier dysfunction caused by interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α). To assess the protective effect of YC-1 on intestinal barrier function, Caco-2 monolayers treated with simultaneous IFN-γ and TNF-α were used to measure transepithelial electrical resistance (TER) and paracellular permeability. To determine the mechanisms involved in the protective action of YC-1, expression and distribution of tight junction proteins ZO-1 and occludin in Caco-2 monolayers challenged with simultaneous IFN-γ and TNF-α were analyzed by Western blot and immunofluorescence, respectively. Expressions of phosphorylated myosin light chain (MLC), MLC kinase (MLCK) and hypoxia-inducible factor-1α (HIF-1α) were analyzed by Western blot in IFN-γ and TNF-α-treated Caco-2 monolayers. It was found that YC-1 attenuated barrier dysfunction caused by IFN-γ and TNF-α, and also prevented IFN-γ and TNF-α-induced morphological redistribution of tight junction proteins ZO-1 and occludin in Caco-2 monolayers. In addition, YC-1 suppressed IFN-γ and TNF-α-induced upregulation of MLC phosphorylation and MLCK protein expression. Furthermore, enhanced expression of HIF-1α in Caco-2 monolayers treated with IFN-γ and TNF-α was also suppressed by YC-1. It is suggested that YC-1, by downregulating MLCK expression, attenuates intestinal barrier dysfunction induced by IFN-γ and TNF-α, in which HIF-1α inhibition, at least in part, might by involved. YC-1 may be a potential agent for treatment of intestinal barrier disruption in inflammation.

Inhibition of reactive gliosis prevents neovascular growth in the mouse model of oxygen-induced retinopathy

Retinal neovascularization (NV) is a major cause of blindness in ischemic retinopathies. Previous investigations have indicated that ischemia upregulates GFAP and PDGF-B expression. GFAP overexpression is a hallmark of reactive gliosis (RG), which is the major pathophysiological feature of retinal damage. In addition, PDGF-B has been implicated in proliferative retinopathies. It was the aim of this study to gain insights on the possible pharmacological interventions to modulate PDGF-B and GFAP expression, and its influence on RG and NV. We used an array of assays to evaluate the effects of YC-1, a small molecule inhibitor of HIF-1 and a novel NO-independent activator of soluble guanylyl cyclase (sGC), on RG and NV, in vivo and in vitro. When compared to the DMSO-treated retinas, dual-intravitreal injections of YC-1, in vivo: (1) suppressed the development and elongation of neovascular sprouts in the retinas of the oxygen-induced retinopathy (OIR) mouse model; and (2) reduced ischemia-induced overexpression of GFAP and PDGF-B at the message (by 64.14±0.5% and 70.27±0.04%) and the protein levels (by 65.52±0.02% and 57.59±0.01%), respectively. In addition, at 100 µM, YC-1 treatment downregulated the hypoxia-induced overexpression of GFAP and PDGF-B at the message level in rMC-1 cells (by 71.42±0.02% and 75±0.03%), and R28 cells (by 58.62±0.02% and 50.00±0.02%), respectively; whereas, the protein levels of GFAP and PDGF-B were reduced (by 78.57±0.02% and 77.55±0.01%) in rMC-1 cells, and (by 81.44±0.02% and 79.16±0.01%) in R28 cells, respectively. We demonstrate that YC-1 reversed RG during ischemic retinopathy via impairing the expression of GFAP and PDGF-B in glial cells. This is the first investigation that delves into the reversal of RG during ischemic retinal vasculopathies. In addition, the study reveals that YC-1 may exert promising therapeutic effects in the treatment of retinal and neuronal pathologies.

Ischaemia-induced retinal neovascularisation and diabetic retinopathy in mice with conditional knockout of hypoxia-inducible factor-1 in retinal Müller cells

AIMS/HYPOTHESIS

Retinal Müller cells are known to produce inflammatory and angiogenic cytokines, which play important roles in diabetic retinopathy. Hypoxia-inducible factor (HIF)-1 has been shown to play a crucial role in retinal inflammation and neovascularisation. We sought to determine the role of Müller cell-derived HIF-1 in oxygen-induced retinopathy (OIR) and diabetic retinopathy using conditional Hif-1α (also known as Hif1a) knockout (KO) mice.

METHODS

Conditional Hif-1α KO mice were generated by crossing mice expressing cyclisation recombinase (cre, also known as P1_gp003) in Müller cells with floxed Hif-1α mice and used for OIR and streptozotocin-induced diabetes to induce retinal neovascularisation and inflammation, respectively. Abundance of HIF-1α and pro-angiogenic and pro-inflammatory factors was measured by immunoblotting and immunohistochemistry. Retinal neovascularisation was visualised by angiography and quantified by counting pre-retinal nuclei. Retinal inflammation was evaluated by leucostasis and vascular leakage.

RESULTS

While the Hif-1α KO mice showed significantly decreased HIF-1α levels in the retina, they exhibited no apparent histological or visual functional abnormalities under normal conditions. Compared with wild-type counterparts, Hif-1α KO mice with OIR demonstrated attenuated overproduction of vascular endothelial growth factor (VEGF) and intercellular adhesion molecule (ICAM)-1, reduced vascular leakage and alleviated neovascularisation in the retina. Under diabetes conditions, disruption of Hif-1α in Müller cells attenuated the increases of retinal vascular leakage and adherent leucocytes, as well as the overproduction of VEGF and ICAM-1.

CONCLUSIONS/INTERPRETATION

Müller cell-derived HIF-1α is a key mediator of retinal neovascularisation, vascular leakage and inflammation, the major pathological changes in diabetic retinopathy. Müller cell-derived HIF-1α is therefore a promising therapeutic target for diabetic retinopathy.

Hypoxia-inducible factor-1-dependent mechanisms of vascularization and vascular remodelling

The vascular system delivers oxygen and nutrients to every cell in the vertebrate organism. Hypoxia-inducible factor 1 (HIF-1) is a master regulator of hypoxic/ischaemic vascular responses, driving transcriptional activation of hundreds of genes involved in vascular reactivity, angiogenesis, arteriogenesis, and the mobilization and homing of bone marrow-derived angiogenic cells. This review will focus on the pivotal role of HIF-1 in vascular homeostasis, the involvement of HIF-1 in vascular diseases, and recent advances in targeting HIF-1 for therapy in preclinical models.