Liver X Receptor Agonist Prevents Endothelial Progenitor Cell (EPC) Dysfunction and Diabetic Retinopathy

Abstract

Purpose: : The liver X receptors (LXR) belong to the nuclear receptor superfamily of ligand-activated transcription factors. LXRs serve as cholesterol sensors and regulate cholesterol homeostasis. Activation of LXR results in a) increased bile acid synthesis and excretion of excess cholesterol in the bile, b) increased reverse cholesterol transport and c) decreased cholesterol uptake by LDL. LXRs also modulate macrophage function and have potent anti-inflammatory effects by inhibiting NF-ΚB, inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (Cox-2), interleukin-6 (IL-6), IL-1β, monocyte chemoattractant protein-1 and 3 (MCP-1 and MCP-3) and metalloprotease MMP-9. We hypothesized that these properties of LXR agonists would make them useful for correction of diabetes-associated dyslipidemia, dysfunction of endothelial progenitor cells (EPCs) and also prevent DR.

Methods: : Diabetic mice (db/db (Type 2 DM) & STZ treated DBA/2J (Type 1 DM)) or wild type mice were orally administered the LXR agonist, GW 3965 (10 mg/kg), daily for 4 months. Mice were sacrificed and retina and bone marrow were isolated. Lin-Sca1⁺, c-kit⁺ (LSK) cells from bone marrow were analyzed for ability to migrate and for mRNA components of renin angiotensin system (RAS), iNOS, and inflammatory cytokines by qRT-PCR. Retinas were evaluated for number of acellular capillaries and GFAP immunoreactivity.

Results: : GW3965 significantly increased EPC migration in diabetic mice (p<0.05). GW3965 increased the expression of the Mas1 receptor by 50-fold (p<0.05). Mas1 receptor mediates levels of Ang (1-7), the protective component of RAS. GW3965 also reduced expression of IL-6,IL-1 β, MCP-1, and NOX2 mRNA in EPCs while showing increased AT2R expression (by 7-fold) and increased eNOS mRNA (by 50-fold) compared to EPCs of untreated diabetic mice. GW3965 treatment resulted in a 50% reduction in acellular capillaries (p<0.05) and completely prevented elevated GFAP expression in Muller glial cells in retinas from diabetic animals compared to untreated diabetic animals.

Conclusions: : Our study suggests that LXR receptor agonists are promising pharmacological targets for correcting diabetic retinopathy and EPC dysfunction. The protective effects of GW3965 are mediated in part by their ability to activate the protective arm of RAS and reduce diabetes associated inflammation.

Keywords: diabetic retinopathy • transcription factors • inflammation