Angiotensin II favors subretinal inflammation in a splenic-dependent manner in acute and chronic mouse model of AMD

Abstract

Purpose : We previously showed that the subretinal infiltrate observed in age-related macular degeneration (AMD) invariably contain pathogenic mononuclear phagocytes (MPs) derived from circulating CCR2⁺Monocytes (Mo). In ischemic myocardial inflammation, CCR2⁺Mo recruitment are partly originating from the spleen (SpleMo) and their mobilization is dependant of AngII stimulation. We examined here the role played by AngII and the spleMo in chronic, age related, and acute subretinal inflammation and the mechanism of AngII induced SpleMo mobilization

Methods : Acute model of Subretinal inflammation and choroidal neovascularisation (CNV) was induced by laser-injury (450mW; 250um; 50ms) in eyes of C57Bl6 daily treated or not by intraperitoneal AT1 antagonist Losartan (125mg/kg/day), and carrying or not subcutaneous osmotic pumps releasing systemic Angiotensin II (1ug/kg/min) with or without splenectomy. Chronic model was induced on ApoE2 Ki (TRE2) mice, which develop spontaneously a subretinal inflammation with the age. Mice were treated or not by losartan (drinking water) or were splenectomized to finally be sacrificed 3 month later. In both model, subretinal MPs (IBA1+) were quantified on immune-stained retinal and RPE/choroidal flatmounts. CD11b+ and CD31+ cells were isolated from the spleen and the bone-marrow (BM) by magnetic beads positif selection. RT-qPCR were performed to compare the AT1 mRNA level expression in different splenic and BM cell fractions.

Results : Losartan and splenectomy strongly reduced subretinal MP accumulation similarly, in both acute and chronic disease models. Interestingly, splenectomies abolished the proinflammatory effect of AngII on CNV-induced subretinal MP accumulation. PCR revealed that there is no significant differences in the level expression of AT1 mRNA between BM and Splenic cells fraction except for CD31+ cells: splenic CD31+ cells expressed 20 times more AT1 mRNA than BM CD31+ cells.

Conclusions : AngII plays a critical role in subretinal inflammation in acute and chronic disease models.. AngII’s proinflammatory effect is dependent on the spleen and mediated by the stimulation of its receptor AT1 that is strongly expressed in the spleen by CD31+ cells.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.