Proteolytic degradation and impaired secretion of an apolipoprotein A-I mutant associated with dominantly inherited hypoalphalipoproteinemia.
We have devised a combined in vivo, ex vivo, and in vitro approach to elucidate the mechanism(s) responsible for the hypoalphalipoproteinemia in heterozygous carriers of a naturally occurring apolipoprotein A-I (apoA-I) variant (Leu(159) to Arg) known as apoA-I Finland (apoA-I(FIN)). Adenovirus-mediated expression of apoA-I(FIN) decreased apoA-I and high density lipoprotein cholesterol concentrations in both wild-type C57BL/6J mice and in apoA-I-deficient mice expressing native human apoA-I (hapoA-I). Interestingly, apoA-I(FIN) was degraded in the plasma, and the extent of proteolysis correlated with the most significant reductions in murine apoA-I concentrations. ApoA-I(FIN) had impaired activation of lecithin:cholesterol acyltransferase in vitro compared with hapoA-I, but in a mixed lipoprotein preparation consisting of both hapoA-I and apoA-I(FIN) there was only a moderate reduction in the activation of this enzyme. Importantly, secretion of apoA-I was also decreased from primary apoA-I-deficient hepatocytes when hapoA-I was co-expressed with apoA-I(FIN) following infection with recombinant adenoviruses, a condition that mimics secretion in heterozygotes. Thus, this is the first demonstration of an apoA-I point mutation that decreases LCAT activation, impairs hepatocyte secretion of apoA-I, and makes apoA-I susceptible to proteolysis leading to dominantly inherited hypoalphalipoproteinemia.
McManus
D C
DC
Lipoprotein and Atherosclerosis Research Group, Department of Pathology, University of Ottawa Heart Institute, Ottawa, Ontario K1Y 4W7, Canada.
Scott
B R
BR
Franklin
V
V
Sparks
D L
DL
Marcel
Y L
YL
D019943:Amino Acid Substitution; D000818:Animals; D016632:Apolipoprotein A-I / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism*; D001120:Arginine; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism; D008076:Cholesterol, HDL / Q000097:blood; D000242:Cyclic AMP / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000502:physiology; D005387:Finland; D018014:Gene Transfer Techniques; D014644:Genetic Variation; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D007009:Hypolipoproteinemias / Q000235:genetics*; D007700:Kinetics; D007930:Leucine; D008264:Macrophages / Q000187:drug effects / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D020125:Mutation, Missense; D013873:Thionucleotides / Q000494:pharmacology
D016632:Apolipoprotein A-I; D008076:Cholesterol, HDL; D013873:Thionucleotides; C015929:8-((4-chlorophenyl)thio)cyclic-3',5'-AMP; D001120:Arginine; D002784:Cholesterol; D000242:Cyclic AMP; D007930:Leucine