Abstract
Purpose :
Lipid metabolism is crucial for maintaining retinal homeostasis. Defects in lipid metabolism underlie a variety of severe retinal diseases such as age-related macular degeneration and glaucoma. Lipe encodes for the enzyme hormone-sensitive lipase (HSL) which plays a key role in the hydrolysis of cholesteryl esters (CEs), retinyl esters (REs), triacylglycerols (TAGs), and diacylglycerols (DAGs) in multiple tissues. While hormone sensitive lipase is expressed in the retina, its function and relevance in the retina-RPE-choroid environment is not known. We recently generated Lipe-/- mice; they develop a retinal degeneration. Our objective here is to study the role of Lipe/HSL in retinal lipid metabolism by analyzing the lipid composition in the retina and RPE/choroid of Lipe-/- vs Lipe+/+ mice.
Methods :
To prevent the decomposition of retinoids, all procedures and analyses were performed under dim red light. Retina and RPE/Choroid tissue specimens were isolated from Lipe+/+ (n=40 eyes) and Lipe-/- mice (n=40 eyes) using a dissection microscope. The tissues were then combined (8 eyes/sample) into 5 pooled retina samples and 5 pooled RPE/Choroid samples for each genotype. Each pooled sample was placed in a glass vial with chloroform/methanol = 2/1 (vol:vol). Lipids were extracted thrice from all tissue samples. Free cholesterol, CEs, REs, TAGs, and DAGs were analyzed using ultra-high-performance liquid chromatography/high-resolution mass spectrometry. Chemical standards of CEs, REs, and TAGs were used to identify the compounds in retina and RPE/choroid samples.
Results :
Untargeted multivariate statistical analysis demonstrated clear differences in the lipid composition between Lipe+/+ and Lipe-/- mouse retina and RPE/choroid. The abundance of CEs, REs, and TAGs was affected. There was a three-fold increase in CEs (e.g. C16:1-CE) in the Lipe-/- mouse retina (p=0.008). Surprisingly, while the amount of retinyl palmitate (RetPalm) in Lipe-/- specimens was three times higher than that in their wild-type littermates (p=0.016), there was only a minimal, statistically insignificant increase in RetPalm in Lipe-/- RPE/choroid (p=0.124).
Conclusions :
Lipe deficiency in the retina leads to a decline in the hydrolysis of various ester lipids and the accumulation of TAGs, DAGs and retinyl esters, including retinyl palmitate. These findings help to better understand the pathophysiology of the retinal degeneration we previously reported in Lipe-/- mice.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.