Targeted replacement of mouse apolipoprotein A-I with human ApoA-I or the mutant ApoA-IMilano. Evidence of APOA-IM impaired hepatic secretion.
Despite a pro-atherogenic profile, individuals carrying the molecular variant (R173C) of apolipoprotein (apo)A-I, named apoA-I(Milano) (apoA-I(M)), appear to be at reduced risk for cardiovascular disease. To develop an in vivo system to explore, in a controlled manner, the effects of apoA-I(M) on lipid metabolism, we have used the gene targeting technology, or "gene knock-in" (gene k-in), to replace the murine apoA-I gene with either human apoA-I or apoA-I(M) genes in embryonic stem cells. As in human carriers, mice expressing apoA-I(M) (A-I(M) k-in) are characterized by low concentrations of the human apolipoprotein and reduced high density lipoprotein cholesterol levels, compared with A-I k-in animals. The aim of the present study was to investigate the basic mechanisms of hypoalphalipoproteinemia associated with the apoA-I(M) mutation. ApoA-I and apoA-I(M) mRNA expression, as assessed by Northern blot analysis and quantitative real time reverse transcription-PCR, did not exhibit significant differences in either liver or intestine. Moreover, human apolipoprotein synthesis rates were similar in the k-in lines. When the secretion rate of the human apolipoproteins was assessed in cultured hepatocytes from the mouse lines, secretion from apoA-I(M)-expressing cells was markedly reduced (42% for A-I(M) k-in and 36% for A-I/A-I(M) k-in mice) as compared with that of A-I k-in hepatocytes. These results provide the first evidence that the hypoalphalipoproteinemia in apoA-I(M) human carriers may be partially explained by impaired apoA-I(M) secretion.
Parolini
Cinzia
C
Department of Pharmacological Sciences, University of Milan, 20133 Milan, Italy. cinzia.parolini@unimi.it
Chiesa
Giulia
G
Zhu
Yiwen
Y
Forte
Trudy
T
Caligari
Silvia
S
Gianazza
Elisabetta
E
Sacco
Maria Grazia
MG
Sirtori
Cesare R
CR
Rubin
Edward M
EM
D000818:Animals; D016632:Apolipoprotein A-I / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D005786:Gene Expression Regulation; D006801:Humans; D007009:Hypolipoproteinemias / Q000235:genetics / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism; D008075:Lipoproteins, HDL / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D051379:Mice; D009154:Mutation
D016632:Apolipoprotein A-I; D008075:Lipoproteins, HDL