Abstract
Age-related Macular Degeneration (AMD) is regarded as the major cause of blindness to elderly people in the developed nations. It is predicted the number of AMD patients will be increased from 196 million in 2020 to 288 million in 2040, due to an ageing population . There are two types of AMD: dry and wet AMD. Dry AMD (atrophic) is the more common type, characterized by abnormal deposits called drusen underneath the retinal pigment epithelial (RPE) layer that impedes the flow of nutrients between the RPE and choroidal circulation; wet AMD is more serious given that it happens rapidly through choroidal neovascularization (CNV), the formation of abnormal new blood vessels. Cholesterol-rich extracellular lesions are the hallmark features of early and intermediate-stage AMD. Cholesterol, apolipoprotein and cholesteryl ester deposits have been detected in drusen of AMD patients, implicating abnormal cholesterol transport in this disease progression. There are several cholesterol-related genes that have been identified by genome-wide association studies as risk factors for AMD, including cholesteryl ester transfer protein (CETP), ATP-binding cassette (ABC) transporter 1 (ABCA1), Apolipoprotein E (ApoE) and hepatic lipase C (LI PC). Reverse cholesterol transport (RCT) pathway is the process of removing excess cholesterol from peripheral cells to the liver for storage as cholesteryl ester droplets or for excretion in bile. The formation of abnormal cholesterol deposits in AMD retinas may cause dysfunctional RCT that could play an important role in the pathogenesis of AMD. The 18 kDa translocator protein (TSPO), a mitochondrial outer membrane protein, is involved in the cholesterol efflux pathway and the removal of cholesterol from cells.The current study aims to investigate the functional role of TSPO in cholesterol homeostasis in choroidal endothelial cells (RF/6A) and in Tspo knockout mice. We found that TSPO specific ligands significantly increased cholesterol efflux and upregulated the expression of genes involved in cholesterol trafficking and metabolism in choroidal endothelial (RF/6A) cells. Furthermore, the TSPO ligands decreased the production of pro-inflammatory cytokines and increased the antioxidative capacity by increasing activities of SOD and CAT, and the levels of GPX and GSH, and reducing production of reactive oxygen species. Additionally, the TSPO ligands reduced lipid accumulation in RF/GA cells.
In Tspo knockout (KO) mouse model our results from light microscopy demonstrated that deletion ofTSPO did not affect retinal morphology. However, there was defective cholesterol efflux in Tspo KO mouse RPE and increased levels of cholesterol, triglyceride and phospholipids in Tspo KO mouse RPE, retina, brain and liver. Production of inflammatory cytokines was also significantly increased in Tspo KO mouse RPE, retina, brain and liver. Additionally, the deletion of TSPO resulted in microglial activation in Tspo KO mouse retina. These findings suggest that TSPO regulates cholesterol homeostasis in the RPE, retina, brain and liver and that TSPO ligands may have therapeutic potential for AMD patients.
| Date of Award | 2021 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Xinhua Shu (Supervisor) |