Pigment epithelium-derived factor inhibits retinal microvascular dysfunction induced by 12/15-lipoxygenase-derived eicosanoids

Abstract

We recently demonstrated that 12/15-lipoxygenase (LOX) derived metabolites, hydroxyeicosatetraenoic acids (HETEs), contribute to diabetic retinopathy (DR) via NADPH oxidase (NOX) and disruption of the balance in retinal levels of the vascular endothelial growth factor (VEGF) and Pigment Epithelium-Derived Factor (PEDF). Here, we test whether PEDF ameliorates retinal vascular injury induced by HETEs and the underlying mechanisms. Furthermore, we pursue the causal relationship between LOX-NOX system and regulation of PEDF expression during DR. For these purposes, we used an experimental eye model in which normal mice were injected intravitreally with 12/15HETE with/without PEDF. Thereafter, Fluorescein Angiography (FA) was used to evaluate the vascular leakage, followed by Optical coherence tomography (OCT) to assess the presence of angiogenesis. FA and OCT reported an increased vascular leakage and pre-retinal neovascularization, respectively, in response to 12-HETE that were not observed in PEDF-treated group. Moreover, PEDF significantly attenuated the increased levels of vascular cell and intercellular adhesion molecules, VCAM-1 and ICAM-1, elicited by 12-HETE injection. Accordingly, the direct relationship between HETE and PEDF has been explored through in-vitro studies using Müller cells (rMCs) and human retinal endothelial cells (HRECs). The results showed that HETEs triggered the secretion of TNF-α and IL-6, as well as activation of NFκB in rMCs and significantly increased permeability and reduced zonula occludens protein-1 (ZO-1) immunoreactivity in HRECs. All these effects were prevented in PEDF-treated cells. Furthermore, interest in PEDF regulation during DR has been expanded to include NOX system. Retinal PEDF was significantly restored in diabetic mice treated with NOX inhibitor, apocynin, or lacking NOX2 up to 80% of the control level. Collectively, our findings suggest that interfering with LOX-NOX signaling opens up a new direction for treating DR by restoring endogenous PEDF that carries out multilevel vascular protective functions.

A journey into the retina: Müller glia commanding survival and death

“…The secretion of PEDF by MGCs is known to activate the NF‐κB signalling pathway, which avoids ganglion cell apoptosis in oxygen deprivation conditions (Unterlauft et al., ). At the vascular level, PEDF is able to prevent the formation of neovessels towards the vitreous cavity and the breakdown of the BRB by upregulating the proteins that constitute the tight junctions between ECs, including zonula occludens‐1 (Ibrahim et al., ). Moreover, PEDF is able to reduce VEGF levels in a significant manner, thereby contributing to the restoration of vascular homoeostasis.…”

Targeting of 12/15-Lipoxygenase in retinal endothelial cells, but not in monocytes/macrophages, attenuates high glucose-induced retinal leukostasis

“…Additionally, we have reported a reduction in diabetes-induced retinal ICAM-1 expression by the pharmacological inhibition of 12/15-LO [21]. Furthermore, our very recent studies have demonstrated the ability of intravitreally injected 12-HETE to compromise endothelial barrier function in the retina associated with the induction of a pro-inflammatory phenotype (increased in retinal ICAM-1 expression and leukocyte adhesion) [22, 23]. As a further support for the role of 12/15-LO in early DR, we have shown by using fluorescein angiography (FA) and retinal albumin leakage assay a significant reduction in retinal barrier dysfunction in diabetic mice lacking global expression of 12/15-LO compared to diabetic wild type (WT) mice [22].…”

Bioactive lipids and pathological retinal angiogenesis

“…This was supported by in vitro studies in which the endothelial, rather than the leucocytic, 12/15‐LO was involved in hyperglycaemia‐induced dysfunction of retinal endothelial cell (RECs) (Ibrahim et al ., ). Treatment of Müller cells with HETEs, metabolites of 12/15‐LO, up‐regulated the proangiogenic and proinflammatory factors VEGF, IL6 and TNFα but suppressed the expression of the angiostatic and neurotrophic factor PEDF (Al‐Shabrawey et al ., ; Ibrahim et al ., ). On the other hand, they induced ER stress, NADPH‐oxidase‐derived ROS and adhesion molecules in RECs (Ibrahim et al ., ; Elmasry et al ., ).…”