Expression, distribution et fonction du récepteur B1 des kinines dans la rétine lors du diabète et de la néovascularisation choroïdienne chez le rat

Kinins are potent peptide autacoids involved in different physiological functions associated to enhanced vascular permeability, vascular tone and the expression of proinflammatory cytokines. Numerous studies have demonstrated the role of the kinin B1 receptor (B1R) in systemic and retinal inflammation. Inflammation plays a major role in diabetic retinopathy (DR) and age-related macular degeneration (AMD), two pathologies that represent the leading causes of blindness in the working and the retired population. The main objective of this thesis is to evaluate the involvement of B1R in these two ocular pathologies. Specific objectives are defined as follows: 1) to study the inflammatory effect of B1R and the consequent vascular alterations in retina of animal models of diabetes and choroidal neovascularization; 2) to specify the cellular localization of B1R in these retinas; 3) to evaluate the possibility of treating these pathologies by an B1R antagonist; 4) to investigate the possible interaction between B1R and vascular endothelial growth factor (VEGF), known for its key role in choroidal neovascularization. Our results confirm the detrimental role of B1R in the acute and advanced phases of diabetic retinopathy in streptozotocin-induced type 1 diabetes in rats. B1R is highly localized on endothelial cells, glial and ganglion cells in the STZ retina. The mRNAs expression of kinin B1 and B2 receptors, VEGF and VEGF-R2 are significantly elevated at 2 and 6 weeks in the STZ retina compared to control retina. B1R mRNA levels remain increased at 6 months. The expression of the B1 (mRNA and immunodetection) and B2 (mRNA) receptors is amplified by the intravitreal injection of a B1R agonist (R-838). In contrast, intravitreal inhibition of B1R (siRNA-RB1) inhibits gene expression of both kinin receptors, VEGF and VEGF-R2 in the STZ retina (Article 1). The results of the second article highlight the contribution of B1R in choroidal neovascularization (CNV) in a rat model of age-related macular degeneration. B1R is detected by immunofluorescence on endothelial and glial cells and co-located with VEGF-R2 on blood vessels of CNV retinas. The effect of topical application of B1R antagonist (R-954) or intravitreal injection of anti-VEGF was studied on the overexpression of several inflammatory iv mediators involved in CNV. These two treatments significantly reduce the overexpression (mRNA) of the B1 and B2 receptors of kinins, TNF-α and ICAM-1 in the CNV retina. Anti- VEGF also blocks the overexpression of VEGF, VEGF-R2, HIF-1, MCP-1 and VCAM-1, while R-954 inhibits the expression of inflammatory mediators IL-1β and COX-2. It is important to note that topical treatment with R-954 blocks vascular hyperpermeability and leukocyte infiltration in models of diabetic retinopathy and AMD and decreases the size of CNV. In a third article, we studied the morphological alterations of retinal vascular bed in a hereditary type 2 diabetes model, the Goto-Kakizaki rat (GK). We observed an accumulation of lipids in the retina and choroid associated with overexpression of B1R and VEGF, macrophage production and microglia reactivity. Collectively, these studies support a deleterious role for B1R in diabetic retinopathy and AMD and for which the topical application of an antagonist of this receptor (R-954) may be a new therapeutic approach.

Keyphrases: VEGF, Kinin B1 receptor, diabetic retinopathy, age-related macular degeneration, microglia