Journal
JOURNAL OF BIOLOGICAL CHEMISTRY
Volume 280, Issue 42, Pages 35647-35657Publisher
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
DOI: 10.1074/jbc.M507924200
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Funding
- NEI NIH HHS [R01 EY009339, R01 EY09339, R01 EY08123, R01 EY008123] Funding Source: Medline
- NIDDK NIH HHS [R01 DK067512, R01 DK061310, R01 DK068437] Funding Source: Medline
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Lecithin: retinol acyltransferase (LRAT) is believed to be the predominant if not the sole enzyme in the body responsible for the physiologic esterification of retinol. We have studied Lrat-deficient (Lrat(-/-)) mice to gain a better understanding of how these mice take up and store dietary retinoids and to determine whether other enzymes may be responsible for retinol esterification in the body. Although the Lrat(-/-) mice possess only trace amounts of retinyl esters in liver, lung, and kidney, they possess elevated (by 2-3-fold) concentrations of retinyl esters in adipose tissue compared with wild type mice. These adipose retinyl ester depots are mobilized in times of dietary retinoid insufficiency. We further observed an up-regulation (3-4- fold) in the level of cytosolic retinol-binding protein type III (CRBPIII) in adipose tissue of Lrat(-/-) mice. Examination by electron microscopy reveals a striking total absence of large lipid-containing droplets that normally store hepatic retinoid within the hepatic stellate cells of Lrat(-/-) mice. Despite the absence of significant retinyl ester stores and stellate cell lipid droplets, the livers of Lrat(-/-) mice upon histologic analysis appear normal and show no histological signs of liver fibrosis. Lrat(-/-) mice absorb dietary retinol primarily as free retinol in chylomicrons; however, retinyl esters are also present within the chylomicron fraction obtained from Lrat(-/-) mice. The fatty acyl composition of these chylomicron retinyl esters suggests that they are synthesized via an acyl-CoA-dependent process suggesting the existence of a physiologically significant acyl-CoA: retinol acyltransferase.
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