Effects of six APOA5 variants, identified in patients with severe hypertriglyceridemia, on in vitro lipoprotein lipase activity and receptor binding.
OBJECTIVE
The purpose of this study was to identify rare APOA5 variants in 130 severe hypertriglyceridemic patients by sequencing, and to test their functionality, since no patient recall was possible.


RESULTS
We studied the impact in vitro on LPL activity and receptor binding of 3 novel heterozygous variants, apoAV-E255G, -G271C, and -H321L, together with the previously reported -G185C, -Q139X, -Q148X, and a novel construct -Delta139 to 147. Using VLDL as a TG-source, compared to wild type, apoAV-G255, -L321 and -C185 showed reduced LPL activation (-25% [P=0.005], -36% [P<0.0001], and -23% [P=0.02]), respectively). ApoAV-C271, -X139, -X148, and Delta139 to 147 had little affect on LPL activity, but apoAV-X139, -X148, and -C271 showed no binding to LDL-family receptors, LR8 or LRP1. Although the G271C proband carried no LPL and APOC2 mutations, the H321L carrier was heterozygous for LPL P207L. The E255G carrier was homozygous for LPL W86G, yet only experienced severe hypertriglyceridemia when pregnant.


CONCLUSIONS
The in vitro determined function of these apoAV variants only partly explains the high TG levels seen in carriers. Their occurrence in the homozygous state, coinheritance of LPL variants or common APOA5 TG-raising variant in trans, appears to be essential for their phenotypic expression.
Dorfmeister
B
B
Department of Medicine, Division of Cardiovascular Genetics, UCL, London, UK.
Zeng
W W
WW
Dichlberger
A
A
Nilsson
S K
SK
Schaap
F G
FG
Hubacek
J A
JA
Merkel
M
M
Cooper
J A
JA
Lookene
A
A
Putt
W
W
Whittall
R
R
Lee
P J
PJ
Lins
L
L
Delsaux
N
N
Nierman
M
M
Kuivenhoven
J A
JA
Kastelein
J J P
JJ
Vrablik
M
M
Olivecrona
G
G
Schneider
W J
WJ
Heeren
J
J
Humphries
S E
SE
Talmud
P J
PJ
D000328:Adult; D000072040:Apolipoprotein A-V; D001054:Apolipoproteins A / Q000235:genetics / Q000378:metabolism*; D004252:DNA Mutational Analysis; D005060:Europe; D005260:Female; D006579:Heterozygote; D006720:Homozygote; D006801:Humans; D006868:Hydrolysis; D015228:Hypertriglyceridemia / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D008071:Lipoprotein Lipase / Q000378:metabolism*; D008079:Lipoproteins, VLDL / Q000378:metabolism; D008297:Male; D008958:Models, Molecular; D020125:Mutation, Missense; D010641:Phenotype; D011247:Pregnancy; D011248:Pregnancy Complications / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D011973:Receptors, LDL / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012720:Severity of Illness Index; D013329:Structure-Activity Relationship; D020349:Surface Plasmon Resonance; D014280:Triglycerides / Q000097:blood
C437704:APOA5 protein, human; D000072040:Apolipoprotein A-V; D001054:Apolipoproteins A; D008079:Lipoproteins, VLDL; D011973:Receptors, LDL; D011994:Recombinant Proteins; D014280:Triglycerides; D008071:Lipoprotein Lipase