title: Regulation of plasma cholesterol esterification by sphingomyelin: effect of physiological variations of plasma sphingomyelin on lecithin-cholesterol acyltransferase activity.
abstract: Although sphingomyelin (SM) is the most abundant phospholipid in the plasma, next to phosphatidylcholine (PC), its physiological function in plasma is unclear. Here we employed plasma from various genetic models of mice which naturally differ in their plasma SM/PC ratios, to study the role of SM as a modulator of LCAT, the enzyme responsible for HDL maturation and the synthesis of cholesteryl esters (CE) in normal plasma. Serine palmitoyltransferase deficient mice, and SM synthase deficient mice, both of which have below normal SM/PC ratios, showed significantly elevated LCAT activities when assayed with the endogenous substrates. On the other hand, LDL receptor knockout mice, and apo E knockout mice, both of which have high SM/PC ratios, had markedly reduced (-80%) LCAT activities. The LCAT levels in plasma, as assayed with an exogenous substrate, were similar in all groups, except for a 45% decrease in apo E knockout mice. Plasma samples with high SM/PC ratios had lower percentage of 20:4, 22:5, and 22:6 CE all of which are formed by LCAT, and a higher percentage of the atherogenic 18:1 CE which is mainly derived from the action of liver ACAT, showing that in vivo, the contribution of LCAT to plasma CE is reduced while that of liver ACAT is increased. These results show that SM is a physiological modulator of LCAT activity as well as plasma CE composition, and this may contribute to the previously reported pro-atherogenic effect of high plasma SM levels.
authors.affiliation: Department of Medicine, University of Illinois at Chicago, Chicago, IL 60612, USA. psubbaia@uic.edu
authors.forename: Papasani Venkata
authors.initials: PV
authors.lastname: Subbaiah
authors.forename: Xian-Cheng
authors.initials: XC
authors.lastname: Jiang
authors.forename: Natalia A
authors.initials: NA
authors.lastname: Belikova
authors.forename: Buzulagu
authors.initials: B
authors.lastname: Aizezi
authors.forename: Zhi Hua
authors.initials: ZH
authors.lastname: Huang
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Reardon
mesh_terms: D000818:Animals; D001057:Apolipoproteins E / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D002784:Cholesterol / Q000097:blood / Q000378:metabolism*; D002788:Cholesterol Esters / Q000097:blood / Q000378:metabolism*; D004951:Esterification; D008055:Lipids / Q000097:blood; D013058:Mass Spectrometry; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D007862:Phosphatidylcholine-Sterol O-Acyltransferase / Q000097:blood / Q000378:metabolism*; D010713:Phosphatidylcholines / Q000097:blood / Q000378:metabolism; D011973:Receptors, LDL / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D051102:Serine C-Palmitoyltransferase / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D013109:Sphingomyelins / Q000097:blood / Q000378:metabolism*; D013379:Substrate Specificity; D017855:Transferases (Other Substituted Phosphate Groups) / Q000172:deficiency / Q000235:genetics / Q000378:metabolism
chemical_list: D001057:Apolipoproteins E; D002788:Cholesterol Esters; D008055:Lipids; D010713:Phosphatidylcholines; D011973:Receptors, LDL; D013109:Sphingomyelins; D002784:Cholesterol; D007862:Phosphatidylcholine-Sterol O-Acyltransferase; D051102:Serine C-Palmitoyltransferase; C495090:Sptlc2 protein, mouse; D017855:Transferases (Other Substituted Phosphate Groups); C543123:Sgms2 protein, mouse