Abstract
Purpose :
We performed studies to define the role of ACAT1 in vitreoretinal neovascularization (PVR). Lipid loading in macrophages increases intracellular levels of cholesterol esters (CEs) which promotes an inflammatory phenotype. During ischemia, macrophages are exposed to a microenvironment of variably oxidized lipids, cytokines, and growth factors. ACAT1, an enzyme localized in the macrophage endoplasmic reticulum is responsible for cholesterol esterification with fatty acids and formation of CEs. During ischemic stress, macrophages increase their uptake of oxidized low-density lipoprotein cholesterol leading to increased ACAT1 activity and formation of toxic levels of CEs. This promotes expression of inflammatory factors like the amplifier of inflammatory signaling TREM-1 (triggering receptor expressed in myeloid cells-1) and M-CSF (macrophage colony-stimulating factor) and growth factors like VEGF. TREM-1, MCSF, and VEGF are major players PVR but the role of ACAT1 is completely unknown.
Methods :
We examined the role of ACAT1 in PVR using both in vitro and in vivo models. For in vitro studies, human macrophages were subjected to hypoxia (1% O2) or normoxia (21% O2) for 16 hrs and treated with the ACAT inhibitor N-[3-(4-hydroxyphenyl)-1-oxo-2-propenyl]-L-phenylalanine, methyl ester (10µg/ml) or vehicle. Expression of TREM-1, M-CSF, and VEGF was determined by western blot. In vivo studies used a mouse model of oxygen-induced retinopathy (OIR). Neonatal mice were maintained in 75% oxygen from postnatal day 7 (P7) to P12 and normoxia to P17 and treated with the ACAT inhibitor (10 mg/Kg, i.p) or vehicle (PBS) on alternate days from P7 to P16. Eyes were collected at P17 and prepared for retinal flat mount imaging, frozen sectioning, or western blot.
Results :
Hypoxia in vitro or OIR in vivo induced significant increases in TREM-1, M-CSF, and VEGF expression (p<0.05). The latter increases were significantly inhibited by treatment with the ACAT inhibitor (p<0.05). The inhibitor treatment also reduced OIR-induced vitreoretinal neovascularization and improved physiological repair of the avascular zone as compared to the vehicle (p<0.05).
Conclusions :
Hypoxia-induced increases in PVR are associated with increases in the expression of TREM-1, M-CSF, and VEGF require ACAT1 activity. Blockade of this pathway offers a new strategy for treatment and prevention of vascular injury during ischemic retinopathy
This is a 2020 ARVO Annual Meeting abstract.