H. Han et al., A novel mutant, apoA-I Nichinan (Glu235 -> 0), is associated with low HDL cholesterol levels and decreased cholesterol efflux from cells, ART THROM V, 19(6), 1999, pp. 1447-1455
A novel Variant of apolipoprotein (apo) A-I associated with low high densit
y lipoprotein (HDL) cholesterolemia has been identified in a Japanese famil
y during screening for apoA-I variants by isoelectric focusing (IEF) gel an
alysis. ApoA-I (Glu235-->0) Nichinan was caused by a 3-bp deletion of nucle
otides 1998 through 2000 in exon 4 of the apoA-I gene. Four subjects in the
family were heterozygous carriers for this mutation; the mean plasma conce
ntrations of apoA-I and HDL cholesterol of affected family members were 30%
and 32% lower, respectively, than those of unaffected family members. Ther
e were no differences in the levels of very low density lipoprotein and low
density lipoprotein cholesterol, triglycerides, and other apolipoproteins
between the carriers and the noncarrier family members. In the proband, pla
sma lecithin:cholesterol acyltransferase activity was normal. Functional co
nsequences of the mutation were examined by expressing the mutated and wild
-type proapoA-I cDNAs in Escherichia coli. Cholesterol efflux to recombinan
t proapoA-I Nichinan from mouse peritoneal macrophages loaded with [H-3]cho
lesterol-labeled acetylated low density lipoprotein was decreased by 54% wh
en compared that of normal recombinant proapoA-I, In vivo turnover studies
in normal rabbits demonstrated that the recombinant proapoA-I Nichinan was
rapidly cleared (22% faster) compared with normal recombinant proapoA-I. We
conclude that apoA-I (Glu235-->0) Nichinan induced a critical structural c
hange in the carboxyl-terminal domain of apoA-I for cellular cholesterol ef
flux and increased the catabolism of apoA-I, resulting in low HDL cholester
ol levels.