TSPO Ligands Promote Cholesterol Efflux and Suppress Oxidative Stress and Inflammation in Choroidal Endothelial Cells

Int J Mol Sci. 2018 Nov 24;19(12):3740. doi: 10.3390/ijms19123740.

Abstract

Choroidal endothelial cells supply oxygen and nutrients to retinal pigment epithelial (RPE) cells and photoreceptors, recycle metabolites, and dispose of metabolic waste through the choroidal blood circulation. Death of the endothelial cells of the choroid may cause abnormal deposits including unesterified and esterified cholesterol beneath RPE cells and within Bruch's membrane that contribute to the progression of age-related macular degeneration (AMD), the most prevalent cause of blindness in older people. Translocator protein (TSPO) is a cholesterol-binding protein that is involved in mitochondrial cholesterol transport and other cellular functions. We have investigated the role of TSPO in choroidal endothelial cells. Immunocytochemistry showed that TSPO was localized to the mitochondria of choroidal endothelial cells. Choroidal endothelial cells exposed to TSPO ligands (Etifoxine or XBD-173) had significantly increased cholesterol efflux, higher expression of cholesterol homeostasis genes (LXRα, CYP27A1, CYP46A1, ABCA1 and ABCG1), and reduced biosynthesis of cholesterol and phospholipids from [14C]acetate, when compared to untreated controls. Treatment with TSPO ligands also resulted in reduced production of reactive oxygen species (ROS), increased antioxidant capacity, and reduced release of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α and VEGF) induced by oxidized LDL. These data suggest TSPO ligands may offer promise for the treatment of AMD.

Keywords: TSPO; age-related macular degeneration; cholesterol efflux; choroidal endothelial cells; inflammation; oxidative stress.

MeSH terms

  • ATP Binding Cassette Transporter 1 / genetics
  • ATP Binding Cassette Transporter 1 / metabolism
  • ATP Binding Cassette Transporter, Subfamily G, Member 1 / genetics
  • ATP Binding Cassette Transporter, Subfamily G, Member 1 / metabolism
  • Animals
  • Biological Transport / drug effects
  • Cell Line
  • Cholesterol / metabolism*
  • Choroid / cytology
  • Choroid / drug effects*
  • Choroid / metabolism
  • Cytochrome P-450 Enzyme System / genetics
  • Cytochrome P-450 Enzyme System / metabolism
  • Endothelial Cells / cytology
  • Endothelial Cells / drug effects
  • Endothelial Cells / metabolism
  • Gene Expression Regulation
  • Humans
  • Interleukin-1beta / antagonists & inhibitors
  • Interleukin-1beta / genetics
  • Interleukin-1beta / metabolism
  • Ligands
  • Lipoproteins, LDL / antagonists & inhibitors*
  • Lipoproteins, LDL / pharmacology
  • Liver X Receptors / genetics
  • Liver X Receptors / metabolism
  • Macaca mulatta
  • Mitochondria / drug effects
  • Mitochondria / metabolism
  • Oxazines / pharmacology*
  • Oxidative Stress / drug effects
  • Phospholipids / antagonists & inhibitors
  • Phospholipids / biosynthesis
  • Purines / pharmacology*
  • Reactive Oxygen Species / antagonists & inhibitors*
  • Reactive Oxygen Species / metabolism
  • Receptors, GABA-A / genetics
  • Receptors, GABA-A / metabolism
  • Signal Transduction
  • Vascular Endothelial Growth Factor A / antagonists & inhibitors*
  • Vascular Endothelial Growth Factor A / genetics
  • Vascular Endothelial Growth Factor A / metabolism

Substances

  • ATP Binding Cassette Transporter 1
  • ATP Binding Cassette Transporter, Subfamily G, Member 1
  • Interleukin-1beta
  • Ligands
  • Lipoproteins, LDL
  • Liver X Receptors
  • N-benzyl-N-ethyl-2-(7,8-dihydro-7-methyl-8-oxo-2-phenyl-9H-purin-9-yl)acetamide
  • Oxazines
  • Phospholipids
  • Purines
  • Reactive Oxygen Species
  • Receptors, GABA-A
  • VEGFA protein, human
  • Vascular Endothelial Growth Factor A
  • oxidized low density lipoprotein
  • Cytochrome P-450 Enzyme System
  • Cholesterol
  • etifoxine