Dyslipidemia-associated activation of monocyte-derived macrophages in diabetic retinopathy

Abstract

Purpose : Diabetic retinopathy (DR) is a common cause of irreversible blindness. Besides hyperglycemia, dyslipidemia is an often-disregarded risk factor of DR. DR is associated with monocyte (Mo) infiltration and ocular inflammation. We hypothesized that Mos exposure to systemic diabetic environment may promote their differentiation into infiltrating pro-inflammatory macrophages (MPs). We thus analyzed the differentiation of Mos from a cohort of DR patients and compared it to the differentiation of naive Mos exposed to high glucose and/or high lipid concentration.

Methods : We isolated circulating Mos from (i) controls (n=15), (ii) T2DM patients with no sign of DR (n=26) (iii) patients with non-proliferative DR (NPDR) (n=22), and (iv) patients with proliferative DR (PDR) (n=9) and allowed them to differentiate in vitro into MPs for 18 h. High CRP level, renal dysfunction or anti-inflammatory medication donors were excluded from the study. Naive Mos were differentiated in different glucose concentrations (low glucose (LG): 2.5 mM; nomo glucose (NG): 5 mM; or high glucose (HG) 25 mM), or in a combination of glucose/palmitic acid (PA) (LG, NG or HG; PA 500 µM). The cytokine expression was quantified by RT-qPCR. Secretome of PA-treated (or control BSA-treated) MPs was tested for angiogenic activity in rat aortic rings model.

Results : IL-6 and IL-8 expression is elevated in MPs from the 3 diabetic groups compared to control donors. MPs from DR groups (NPDR and PDR) exhibited an elevated level of VEGF and CCL2 expression compared to T2DM. Naive MPs differentiated in LG, NG or HG conditions shown no difference in cytokine expression. Control MPs differentiated under PA exposure demonstrated an elevated expression of all pro-inflammatory cytokines tested, but no for VEGF expression. HG/PA cotreatment increased even more the expression of IL-6 and CCL2. PA-treated MPs secretome had a potent anti-angiogenic effect on rat aortic rings model showing a decrease of 90% (+/- 2 SEM, p<0,01) of sprout numbers.

Conclusions : MPs differentiated from DR patients exhibited a specific inflammatory pattern when compared to control or diabetic patients. PA, but not HG, treatment of naive Mos can partly replicate this specific differentiation. Secretome from PA-treated MPs has a potent anti-angiogenic effect. Our data suggest that Mos/MPs polarized by dyslipidemia are key players in the initial retinal vessel loss.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.