title: Novel lipid droplet-associated serine hydrolase regulates macrophage cholesterol mobilization.
abstract: OBJECTIVE
  Lipid-laden macrophages or foam cells are characterized by massive cytosolic lipid droplet (LD) deposition containing mostly cholesterol ester (CE) derived from the lipoproteins cleared from the arterial wall. Cholesterol efflux from foam cells is considered to be atheroprotective. Because cholesterol is effluxed as free cholesterol, CE accumulation in LDs may limit free cholesterol efflux. Our objective was to identify proteins that regulate cholesterol trafficking through LDs.
  
  
  RESULTS
  In a proteomic analysis of the LD fraction of RAW 264.7 macrophages, we identified an evolutionarily conserved protein with a canonical GXSXG lipase catalytic motif and a predicted α/β-hydrolase fold, the RIKEN cDNA 1110057K04 gene, which we named LD-associated hydrolase (LDAH). LDAH association with LDs was confirmed by immunoblotting and immunocytochemistry. LDAH was labeled with a probe specific for active serine hydrolases. LDAH showed relatively weak in vitro CE hydrolase activity. However, cholesterol measurements in intact cells supported a significant role of LDAH in CE homeostasis because LDAH upregulation and downregulation decreased and increased, respectively, intracellular cholesterol and CE in human embryonic kidney-293 cells and RAW 264.7 macrophages. Mutation of the putative nucleophilic serine impaired active hydrolase probe binding, in vitro CE hydrolase activity, and cholesterol-lowering effect in cells, whereas this mutant still localized to the LD. LDAH upregulation increased CE hydrolysis and cholesterol efflux from macrophages, and, interestingly, LDAH is highly expressed in macrophage-rich areas within mouse and human atherosclerotic lesions.
  
  
  CONCLUSIONS
  The data identify a candidate target to promote reverse cholesterol transport from atherosclerotic lesions.
authors.affiliation: From the Center for Cardiovascular Sciences, Albany Medical College, NY (Y.-H.G., S.-H.S., A.P.); and the Institute for Vascular Health and Disease, Albany, NY (P.B.K.).
authors.forename: Young-Hwa
authors.initials: YH
authors.lastname: Goo
authors.forename: Se-Hee
authors.initials: SH
authors.lastname: Son
authors.forename: Paul B
authors.initials: PB
authors.lastname: Kreienberg
authors.forename: Antoni
authors.initials: A
authors.lastname: Paul
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001057:Apolipoproteins E / Q000172:deficiency / Q000235:genetics; D050197:Atherosclerosis / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D001692:Biological Transport; D002784:Cholesterol / Q000378:metabolism*; D002788:Cholesterol Esters / Q000378:metabolism; D004195:Disease Models, Animal; D005487:Foam Cells / Q000201:enzymology* / Q000473:pathology; D015971:Gene Expression Regulation, Enzymologic; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D006868:Hydrolysis; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D058226:Plaque, Atherosclerotic; D040901:Proteomics / Q000379:methods; D034622:RNA Interference; D057057:Serine Proteases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity; D013997:Time Factors; D014162:Transfection
chemical_list: D001057:Apolipoproteins E; D002788:Cholesterol Esters; D002784:Cholesterol; C587070:LD-associated hydrolase, mouse; D057057:Serine Proteases
keywords: atherosclerosis; foam cells