Apolipoprotein E is secreted by cultured lipocytes of the rat liver.
Hepatic lipocytes, the retinoid-storing cells of the liver, share several characteristics with vascular smooth muscle cells. To determine whether they also share the characteristic of apolipoprotein E secretion, we have compared the relative mRNA expression and protein secretion of apolipoprotein E, apolipoprotein A-I, and apolipoprotein A-IV in early primary cultures of lipocytes, hepatocytes, and Kupffer cells. Expression of apolipoprotein mRNAs was detected using the polymerase chain reaction and oligonucleotide primers specific for apolipoprotein E, apolipoprotein A-I, and apolipoprotein A-IV. Cellular mRNA concentrations were compared by dot blot analysis, and apolipoprotein secretion was assessed by immunoblot analysis of culture media. Apolipoprotein E mRNA was found in all three cell types, whereas apolipoprotein A-I and A-IV mRNAs were detected only in hepatocytes. Hepatocyte, lipocyte, and Kupffer cell media all contained a Mr approximately 36,000 protein identified by an antibody specific for rat apolipoprotein E. The relative concentration of apolipoprotein E mRNA per microgram of total cellular RNA in lipocytes, hepatocytes, and Kupffer cells was 1.0, 3.0, and 1.6, respectively. The relative secretion of apolipoprotein E per cell was also lowest in lipocytes, being twofold greater in hepatocytes and 1.4-fold greater in Kupffer cells. The secretion of apolipoprotein E by lipocytes is not only an additional smooth muscle cell-like characteristic of the hepatic lipocyte, but also raises the possibility of retinol mobilization upon apolipoprotein secretion.
Friedman
G
G
Gladstone Foundation Laboratories for Cardiovascular Disease, Cardiovascular Research Institute, University of California, San Francisco 94140-0608.
Liu
L M
LM
Friedman
S L
SL
Boyles
J K
JK
D000818:Animals; D001054:Apolipoproteins A / Q000378:metabolism; D001057:Apolipoproteins E / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002478:Cells, Cultured; D004247:DNA; D015151:Immunoblotting; D008099:Liver / Q000166:cytology* / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D009841:Oligonucleotides; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
D001054:Apolipoproteins A; D001057:Apolipoproteins E; D009841:Oligonucleotides; D012333:RNA, Messenger; D004247:DNA