Abstract
Purpose :
Genome-wide association studies (GWAS) revealed that low-expression variants of the human hepatic lipase (LIPC) gene are highly associated with reduced risk of age-related macular degeneration (AMD); however, the biological mechanism underlying this protective role of LIPC in AMD development is still unclear. In this work, we investigated possible mechanisms by which LIPC protects against AMD.
Methods :
LIPC suppresses the expression of scavenger receptor BI (SR-BI), and LIPC inhibition increases SR-BI expression in rodent adrenal glands. To determine whether reduced expression of LIPC increases SR-BI in the eye, we first investigated the expression and distribution of LIPC and SR-BI in the monkey and mouse eyes using western blots and IHC; we then examined the expression of SR-BI in cultured ARPE-19 cells treated with and without small-interference RNA (siRNA) of LIPC using real-time RT-PCR and western blots. SR-BI is a major carotenoid transporter and also facilitates cholesterol efflux from macrophage cells to the bloodstream. Next, we further investigated if LIPC knockdown increases the uptake of antioxidant carotenoids and cholesterol efflux. ARPE-19 cells were cultured to 70 to 80% confluency, then transfected with plasmids expressing short-hairpin RNA against LIPC (LIPC shRNA) and control shRNA. 48-h after transfection, cells were used for carotenoid and cholesterol assays. The contents of carotenoid and cholesterol were detected by HPLC and GC/MS, respectively.
Results :
IHC and western data demonstrated that LIPC and SR-BI are expressed robustly in the RPE of the monkeys and mice. The expression of these two proteins is weak in the monkey retina but not detected in the mouse retina. 40% suppression of LIPC by siRNA resulted in a 35% increase of SR-BI in cultured ARPE-19 cells. LIPC knockdown by shRNA in ARPE-19 cells led to a 1.3 times increase in carotenoid uptake and a 1.5 times increase in cholesterol efflux.
Conclusions :
Our data suggest that LIPC may be involved in the uptake of antioxidant carotenoids and the efflux of toxic cholesterol. Reduced expression of LIPC may increase SR-BI expression in the RPE, thereby increasing the retinal carotenoid influx and cholesterol efflux, which may protect against the progression of AMD.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.