New pharmacological targets for the treatment of diabetic retinopathy

Diabetic retinopathy (DR) is a secondary complication of diabetes mellitus and represent the most common cause of irreversible vision loss in working aged people in industrialized countries. DR is generally considered as microvascular complication of diabetes, although during the last decade several other etiopathogenic mechanisms have been proposed for this disease. The main cause of the vision loss in diabetic patients with proliferative diabetic retinopathy (PDR) is diabetic macular edema (DME), mainly caused by neovascularization, vessel leakage and blood retinal barrier (BRB) breakdown in the macula. Angiogenesis, a hallmark of the advanced stage of DR (proliferative diabetic retinopathy, PDR), occurs at the vitreoretinal interface and is often associated with tractional retinal detachment and vitreous hemorrhage. Neovascularization is basically driven by pro-angiogenic factors (e.g. VEGF-A, PlGF), inflammatory mediators (TNF-α, interleukins, chemokines) and oxidative stress-related elements. Chronic hyperglycemia is the primary causative factor of DR, however, etiopathogenesis of DR due to poor glycemic control is still unclear. Many other factors are involved during the early stages of DR such as the hypoxic microenvironment, which leads to the upregulation of pro-angiogenic and inflammatory mediators, indeed retinal hypoxia is a well-known trigger of VEGF release in diabetic retinopathy. Up to now therapies provided for DR, among laser photocoagulation or vitrectomy (only for PDR patients) are intravitreal anti-VEGF and corticosteroids. However, a key issue in the treatment of retinal disease in general is the heterogeneity of response to both these therapies, indeed various novel pharmacological targets are also being assessed in order to reduce these limitations. Therefore, retinal microvascular complications must be deeply investigated to better understand the pathophysiology of retinal degeneration during in DR, in order to search and discover new pharmacological targets for treatment of diabetic retinopathy. To this purpose I focused my research project on PlGF and growth factors modulated during retinal hypoxia. Particularly, I have studied in-vitro and in-vivo the role of PlGF in modulation of angiogenic and inflammatory pathways in diabetic retinopathy. I have found that aflibercept (a decoy receptor for VEGFA and PlGF) and an anti-PlGF could be endowed of anti-inflammatory activity, blocking the ERK pathway and its consequential production of inflammatory mediators, such as TNF-α. Together with the demonstration of anti-inflammatory molecular action of aflibercept, I have found that PlGF can be considered a target for the treatment of DR, along with VEGFA. Moreover, considering that hypoxia is one of the main factors triggering neovascularization, I have also analyzed the modulation of growth factors and miRNAs, previously found to be linked to diabetic retinopathy, in an in-vitro model of retinal hypoxia (primary retinal endothelial cells (HRECs) treated with CoCl2). In this context we hypothesized that specific dysregulated miRNA in diabetic retinopathy could be linked to hypoxia-induced damage in HRECs. Therefore, I have investigated the effects of chemical hypoxia on the expression of HIF-1α, VEGF, PlGF, and pattern expression of a focused set of miRNAs (miR-20a-5p, miR-20b-5p, miR-27a-3p, miR-27b-3p, miR-206-3p, miR-381-3p). Our results demonstrated that pattern expression of the above mentioned miRNAs correlated also with expression of VEGFA and TGFβ signaling pathway genes, but not with PlGF expression. We propose that retinal angiogenesis by HIF-1α nuclear translocation could be promoted also by up-regulation of PlGF and other factors such as miRNAs and their target genes of VEGF and TGFβ1 signaling pathways.