Abstract
Hydrolysis of intracellular cholesteryl esters (CEs) represents the first step in the removal of cholesterol from lipid-laden foam cells associated with atherosclerotic lesions. Neutral cholesteryl ester hydrolase (CEH) catalyzes this reaction, and we recently cloned the cDNA for the human macrophage CEH and demonstrated increased mobilization of intracellular CE droplets by CEH overexpression. The present study was undertaken to test the hypothesis that for CE hydrolysis, CEH must become associated with the surface of the cytoplasmic lipid droplets. Our data show the redistribution of CEH from cytosol to lipid droplets upon lipid loading of human THP-1 macrophages. Depletion of triacylglycerol (TG) by incubation with the acyl-CoA synthetase inhibitor Triacsin D had no effect on CEH association with the lipid droplets, suggesting that CEH associates with mixed (CE + TG) as well as TG-depleted CE droplets. However, CEH had 2.5-fold higher activity when mixed droplets were used as substrate in an in vitro assay, consistent with the reported higher cholesterol efflux from cells containing mixed isotropic droplets. Perilipin as well as adipophilin, two lipid droplet-associated proteins, were also present on the lipid droplets in THP-1 macrophages. In conclusion, CEH associates with its intracellular substrate (lipid droplets) and hydrolyzes CE more efficiently from mixed droplets.
Highlights
Hydrolysis of intracellular cholesteryl esters (CEs) represents the first step in the removal of cholesterol from lipid-laden foam cells associated with atherosclerotic lesions
The data presented here demonstrate, for the first time, the redistribution of neutral cholesteryl ester hydrolase (CEH) from the cytoplasm to lipid droplets in human monocyte/macrophage THP-1 cells (Figs. 2, 3), thereby confirming the association of CEH with its physiological substrate, an obligatory step toward enzymatic hydrolysis of intracellular CE stored as lipid droplets
Unlike hormone-sensitive lipase, which associates with the lipid droplets in adipocytes after hormonal stimulation [10], the movement of CEH from the cytoplasm to lipid droplets upon lipid loading does not require any additional stimulation and is probably a spontaneous rather than a regulated step
Summary
Hydrolysis of intracellular cholesteryl esters (CEs) represents the first step in the removal of cholesterol from lipid-laden foam cells associated with atherosclerotic lesions. Unregulated uptake of modified LDL by blood monocyte-derived macrophages results in the cytoplasmic accumulation of cholesteryl ester (CE)-rich lipid droplets and the formation of foam cells. The ratelimiting role of this enzyme in intracellular CE mobilization was confirmed by the observed concentration-dependent decrease in intracellular lipid droplets and cellular CE mass after overexpression [8] This enzyme hydrolyzes CEs presented as lipid droplets in vitro and effectively mobilizes intracellular CE droplets, a direct association of CEH with cytoplasmic lipid droplets has not been demonstrated. The presence of neither perilipin nor adipophilin, the human ortholog of ADRP, is described in human blood monocyte-derived macrophages or in THP-1 cells It is not known whether CEH associates with cytoplasmic lipid droplets in a manner similar to hormone-sensitive lipase association with lipid droplets in adipocytes, a process regulated by perilipin A [16]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
