Correction: Hypoxia-inducible factor 1 upregulation of both VEGF and ANGPTL4 is required to promote the angiogenic phenotype in uveal melanoma.

[This corrects the article DOI: 10.18632/oncotarget.6868.].

Lack of Evidence for Vasoactive and Inflammatory Mediators in the Promotion of Macular Edema Associated with Epiretinal Membranes.

The development of symptoms in patients with epiretinal membranes (ERMs) often corresponds with the accumulation of interstitial fluid in the retina [i.e., the development of macular edema, (ME)]. To explore the potential value of pharmacologic therapeutic options to treat ME in patients with ERMs, we examine here the expression of vasoactive and inflammatory mediators in the vitreous of patients with idiopathic ERMs. We observed that vitreous concentrations of classic vasoactive factors (e.g., vascular endothelial growth factor) were similar in ERM patients with ME compared to controls. Using an array assessing the expression of 102 inflammatory cytokines we similarly did not observe a marked difference in cytokine expression in the vitreous of most ERM patients with ME compared to control patients. While the array data did implicate a group of inflammatory cytokines that were elevated in a subset of ERM patients who had severe ME (central subfield thickness ≥450 µm on spectral domain optical coherence tomography), expression of 3 of these inflammatory cytokines, all previously implicated in the promotion of ME in ischemic retinal disease, were not elevated by quantitative enzyme-linked immunosorbent assay. We conclude that therapies modulating vasoactive mediators or inflammatory cytokines may not affect ME in ERM patients.

Hypoxia-inducible factor 1 upregulation of both VEGF and ANGPTL4 is required to promote the angiogenic phenotype in uveal melanoma.

PURPOSE: Expression of the hypoxia-inducible factor (HIF)-1-regulated gene product, vascular endothelial growth factor (VEGF), correlates with tumor vascularity in patients with uveal melanoma (UM). While the relationship between HIF-1 and VEGF in cancer is well-studied, their relative contribution to the angiogenic phenotype in UM has not previously been interrogated. Here we evaluate the contribution of HIF-1, VEGF, and a second HIF-1-regulated gene product, angiopoietin-like 4 (ANGPTL4), to angiogenesis in UM. EXPERIMENTAL DESIGN: UM cells were examined for expression of HIF-1α, VEGF, and ANGPTL4. Their contribution to the angiogenic potential of UM cells was assessed using the endothelial cell tubule formation and directed in vivo angiogenesis assays. These results were corroborated in tissue from UM animal models and in tissue from patients with UM. RESULTS: Inhibition of VEGF partially reduced tubule formation promoted by conditioned medium from UM cells. Inhibition of ANGPTL4, which was highly expressed in hypoxic UM cells, a UM orthotopic transplant model, a UM tumor array, and vitreous samples from UM patients, inhibited the angiogenic potential of UM cells in vitro and in vivo; this effect was additive to VEGF inhibition. CONCLUSIONS: Targeting both ANGPTL4 and VEGF may be required for the effective inhibition of angiogenesis in UM.

Angiopoietin-like 4 is a potent angiogenic factor and a novel therapeutic target for patients with proliferative diabetic retinopathy.

Diabetic eye disease is the most common cause of severe vision loss in the working-age population in the developed world, and proliferative diabetic retinopathy (PDR) is its most vision-threatening sequela. In PDR, retinal ischemia leads to the up-regulation of angiogenic factors that promote neovascularization. Therapies targeting vascular endothelial growth factor (VEGF) delay the development of neovascularization in some, but not all, diabetic patients, implicating additional factor(s) in PDR pathogenesis. Here we demonstrate that the angiogenic potential of aqueous fluid from PDR patients is independent of VEGF concentration, providing an opportunity to evaluate the contribution of other angiogenic factor(s) to PDR development. We identify angiopoietin-like 4 (ANGPTL4) as a potent angiogenic factor whose expression is up-regulated in hypoxic retinal Müller cells in vitro and the ischemic retina in vivo. Expression of ANGPTL4 was increased in the aqueous and vitreous of PDR patients, independent of VEGF levels, correlated with the presence of diabetic eye disease, and localized to areas of retinal neovascularization. Inhibition of ANGPTL4 expression reduced the angiogenic potential of hypoxic Müller cells; this effect was additive with inhibition of VEGF expression. An ANGPTL4 neutralizing antibody inhibited the angiogenic effect of aqueous fluid from PDR patients, including samples from patients with low VEGF levels or receiving anti-VEGF therapy. Collectively, our results suggest that targeting both ANGPTL4 and VEGF may be necessary for effective treatment or prevention of PDR and provide the foundation for studies evaluating aqueous ANGPTL4 as a biomarker to help guide individualized therapy for diabetic eye disease.

VEGF secreted by hypoxic Müller cells induces MMP-2 expression and activity in endothelial cells to promote retinal neovascularization in proliferative diabetic retinopathy.

In proliferative diabetic retinopathy (PDR), retinal ischemia promotes neovascularization (NV), which can lead to profound vision loss in diabetic patients. Treatment for PDR, panretinal photocoagulation, is inherently destructive and has significant visual consequences. Therapies targeting vascular endothelial growth factor (VEGF) have transformed the treatment of diabetic eye disease but have proven inadequate for treating NV, prompting exploration for additional therapeutic options for PDR patients. In this regard, extracellular proteolysis is an early and sustained activity strictly required for NV. Extracellular proteolysis in NV is facilitated by the dysregulated activity of matrix metalloproteinases (MMPs). Here, we set out to better understand the regulation of MMPs by ischemia in PDR. We demonstrate that accumulation of hypoxia-inducible factor-1α in Müller cells induces the expression of VEGF, which, in turn, promotes increased MMP-2 expression and activity in neighboring endothelial cells (ECs). MMP-2 expression was detected in ECs in retinal NV tissue from PDR patients, whereas MMP-2 protein levels were elevated in the aqueous of PDR patients compared with controls. Our findings demonstrate a complex interplay among hypoxic Müller cells, secreted angiogenic factors, and neighboring ECs in the regulation of MMP-2 in retinal NV and identify MMP-2 as a target for the treatment of PDR.