Adenoviral 15-lipoxygenase-1 gene transfer inhibits hypoxia-induced proliferation of retinal microvascular endothelial cells in vitro

Emerging cellular functions of the lipid metabolizing enzyme 15-Lipoxygenase-1

The oxygenation of polyunsaturated fatty acids such as arachidonic and linoleic acid through lipoxygenases (LOXs) and cyclooxygenases (COXs) leads to the production of bioactive lipids that are important both in the induction of acute inflammation and its resolution. Amongst the several isoforms of LOX that are expressed in mammals, 15-LOX-1 was shown to be important both in the context of inflammation, being expressed in cells of the immune system, and in epithelial cells where the enzyme has been shown to crosstalk with a number of important signalling pathways. This review looks into the latest developments in understanding the role of 15-LOX-1 in different disease states with emphasis on the emerging role of the enzyme in the tumour microenvironment as well as a newly re-discovered form of cell death called ferroptosis. We also discuss future perspectives on the feasibility of use of this protein as a target for therapeutic interventions.

A Critical Analysis of the Available In Vitro and Ex Vivo Methods to Study Retinal Angiogenesis

Angiogenesis is a biological process with a central role in retinal diseases. The choice of the ideal method to study angiogenesis, particularly in the retina, remains a problem. Angiogenesis can be assessed through in vitro and in vivo studies. In spite of inherent limitations, in vitro studies are faster, easier to perform and quantify, and typically less expensive and allow the study of isolated angiogenesis steps. We performed a systematic review of PubMed searching for original articles that applied in vitro or ex vivo angiogenic retinal assays until May 2017, presenting the available assays and discussing their applicability, advantages, and disadvantages. Most of the studies evaluated migration, proliferation, and tube formation of endothelial cells in response to inhibitory or stimulatory compounds. Other aspects of angiogenesis were studied by assessing cell permeability, adhesion, or apoptosis, as well as by implementing organotypic models of the retina. Emphasis is placed on how the methods are applied and how they can contribute to retinal angiogenesis comprehension. We also discuss how to choose the best cell culture to implement these methods. When applied together, in vitro and ex vivo studies constitute a powerful tool to improve retinal angiogenesis knowledge. This review provides support for researchers to better select the most suitable protocols in this field.

CCN1/Cyr61-PI3K/AKT signaling promotes retinal neovascularization in oxygen-induced retinopathy

Retinal neovascularization (RNV) is a characteristic pathological finding of retinopathy of prematurity (ROP). Cysteine-rich 61 [Cyr61, also known as CCN family member 1 (CCN1)] has been reported to mediate angiogenesis. The aim of the present study was to investigate the mechanisms of CCN1/Cyr61-phosphoinositide 3-kinase (PI3K)/AKT signaling in ROP. The contribution of CCN1 to human umbilical vein endothelial cell (HUVEC) proliferation and apoptosis under hypoxic conditions was determined using a cell counting kit-8 (CCK-8) and Annexin V/propidium iodide (PI) staining, respectively, as well as using siRNA targeting CCN1 (CCN1 siRNA). The cells exposed to hypoxia were also treated with the PI3K/AKT inhibitor, LY294002. In addition, mouse pups with oxygen-induced retinopathy (OIR) were administered an intravitreal injection of CCN1 siRNA. RNV was assessed by magnesium-activated adenosine diphosphatease (ADPase) staining. RT-qPCR, western blot analysis, immunofluorescence staining and immunohistochemistry were used to detect the distribution and expression of CCN1, PI3K and AKT. Exposure to hypoxia increased the neovascularization clock hour scores (from 1.23±0.49 to 5.60±0.73, P<0.05) and the number of preretinal neovascular cells, as well as the mRNA and protein expression levels of CCN1, PI3K and AKT (all P<0.05). The injection of CCN1 siRNA decreased the neovascularization clock hour scores and the number of preretinal neovascular cells (1.53±0.72 vs. 4.76±1.04; 12.0±2.8 vs. 31.4±2.6, respectively, both P<0.05), as well as the mRNA and protein expression levels of CCN1, PI3K and AKT (protein, −45.3, −22.5 and −28.4%; mRNA, −43.7, −58.7 and −42.9%, respectively, all P<0.05) compared to the administration of scrambled siRNA under hypoxic conditions. Treatment with LY294002 decreased the mRNA and protein expression levels of CCN1 in the cells exposed to hypoxia (both P<0.05). The administration of CCN1 siRNA resulted in less severe neovascularization in the eyes of the the mouse pups with OIR. Thus, out data suggest that CCN1 plays an important role in RNV in ROP, and may thus be a potential target for the prevention and treatment of ROP.

15-LOX-1 suppression of hypoxia-induced metastatic phenotype and HIF-1α expression in human colon cancer cells

The expression of 15-lipoxygenase-1 (15-LOX-1) is downregulated in colon cancer and other major cancers, and 15-LOX-1 reexpression in cancer cells suppresses colonic tumorigenesis. Various lines of evidence indicate that 15-LOX-1 expression suppresses premetastatic stages of colonic tumorigenesis; nevertheless, the role of 15-LOX-1 loss of expression in cancer epithelial cells in metastases continues to be debated. Hypoxia, a common feature of the cancer microenvironment, promotes prometastatic mechanisms such as the upregulation of hypoxia-inducible factor (HIF)-1α, a transcriptional master regulator that enhances cancer cell metastatic potential, angiogenesis, and tumor cell invasion and migration. We have, therefore, tested whether restoring 15-LOX-1 in colon cancer cells affects cancer cells' hypoxia response that promotes metastasis. We found that 15-LOX-1 reexpression in HCT116, HT29LMM, and LoVo colon cancer cells inhibited survival, vascular endothelial growth factor (VEGF) expression, angiogenesis, cancer cell migration and invasion, and HIF-1α protein expression and stability under hypoxia. These findings demonstrate that 15-LOX-1 expression loss in cancer cells promotes metastasis and that therapeutically targeting ubiquitous 15-LOX-1 loss in cancer cells has the potential to suppress metastasis.

Enzyme 15-lipoxygenase 1 promotes hypoxia-inducible factor 1α turnover and reduces vascular endothelial growth factor expression: implications for angiogenesis

Hypoxia-inducible factor 1α (HIF-1α) is the regulatory subunit of the heterodimeric HIF-1 that plays a critical role in transcriptional regulation of genes in angiogenesis and hypoxic adaptation, while fatty acid metabolism mediated by lipoxygenases has been implicated in a variety of pathogeneses, including cancers. In this study, we report that 15-lipoxygenase 1 (15-LO1), a key member of the lipoxygenase family, promotes HIF-1α ubiquitination and degradation. Altering the level of 15-LO1 yields inverse changes in HIF-1α and HIF-1 transcriptional activity, under both normoxia and hypoxia, and even in CoCl₂-treated cells where HIF-1α has been artificially elevated. The antagonistic effect of 15-LO1 is mediated by the Pro⁵⁶⁴/hydroxylation/26S proteasome system, while both the enzymatic activity and the intracellular membrane-binding function of 15-LO1 appear to contribute to HIF-1α suppression. Our findings provide a novel mechanism for HIF-1α regulation, in which oxygen-dependent HIF-1 activity is modulated by an oxygen-insensitive lipid metabolic enzyme.

Targeting Neovascularization in Ischemic Retinopathy: Recent Advances

Pathological retinal neovascularization (RNV) is a common micro-vascular complication in several retinal diseases including retinopathy of prematurity, diabetic retinopathy, age-related macular degeneration and central vein occlusion. The current therapeutic modalities of RNV are invasive and although they may slow or halt the progression of the disease they are unlikely to restore normal acuity. Therefore, there is an urgent need to develop treatment modalities, which are less invasive and therefore associated with fewer procedural complications and systemic side effects. This review article summarizes our understanding of the pathophysiology and current treatment of RNV in ischemic retinopathies; lists potential therapeutic targets; and provides a framework for the development of future treatment modalities.