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

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.

TSPO Ligands PK11195 and Midazolam Reduce NLRP3 Inflammasome Activation and Proinflammatory Cytokine Release in BV-2 Cells

“…TSPO plays an important role in regulating inflammation (McNeela et al, 2018 ). Under normal physiological conditions, TSPO expression is low in brain glial cells but is significantly increased in brain injury and inflammation, a feature that makes it particularly suitable for assessing active glial cells (Biswas et al, 2018 ; Werry et al, 2019 ). Significant increases in TSPO expression were found in many neurodegenerative diseases, such as Alzheimer’s disease (AD; Metaxas et al, 2019 ), Parkinson’s disease (PD; Gerhard, 2016 ), and Huntington’s disease (HD; Metaxas et al, 2019 ).…”

Diazepam Promotes Translocation of Human Constitutive Androstane Receptor (CAR) via Direct Interaction with the Ligand-Binding Domain

“…The endogenous metabolism genes Fasn and G6pase revealed non-significant down-regulation trends. However, these genes might be co-regulated by diazepam through a translocator protein [34] ( Figure 6B). Furthermore, the proliferation and apoptosis-related genes Mki67, Foxm1, Gadd45b, and Pcna were regulated neither by diazepam nor CITCO ( Figure 6C).…”

Age-Related Macular Degeneration Revisited: From Pathology and Cellular Stress to Potential Therapies

“…In vitro studies using a monkey choroidal endothelial cell line (RF6A) exposed to sirtuin inhibitors points to a significant increase in reactive oxygen species production ( Balaiya et al, 2017 ). Translocator protein (TSPO), a cholesterol-binding protein involved in mitochondrial cholesterol transport has been found to be expressed in the mitochondria of choroidal endothelial cells ( Biswas et al, 2018 ). When exposed to TSPO ligands, production of reactive oxygen species by choroidal endothelial cells are reduced and there is an increase in antioxidant capacity, and reduction of pro-inflammatory cytokines induced by oxidized low-density lipoproteins, suggesting TSPO may be a potential therapeutic means to reduce oxidative stress in the choroidal endothelial cells.…”