Defects of the LDL receptor in WHHL transgenic rabbits lead to a marked accumulation of plasma lipoprotein[a].
In this study, we created LDL receptor (LDLr) defective (WHHL) transgenic rabbits expressing human apo[a] to examine whether LDLr mediates the Lp[a] clearance from the plasma. By crossbreeding WHHL rabbits with human apo[a] transgenic rabbits, we obtained two groups of human apo[a] transgenic rabbits with defective LDLr functions: apo[a](1/0) WHHL heterozygous (LDLr(+/-) and apo[a](+/0) WHHL homozygous (LDLr(-/-) rabbits. The lipid and lipoprotein levels of human apo[a] WHHL rabbits were compared to those of human apo[a] transgenic rabbits with normal LDLr functions (LDLr(+/+). The apo[a] production rate was evaluated by analyzing apo[a] mRNA expression in the liver, the major site for apo[a] synthesis in transgenic rabbits. We found that pre-beta lipoproteins were markedly increased accompanied by a 2-fold increase in the plasma Lp[a] in apo[a](+/0)/LDLr(+/-) rabbits and a 4.2-fold increase in apo[a](+/0)/LDLr(-/-) rabbits compared with that in apo[a](+/0) rabbits with normal LDLr function. In apo[a](+/0)/LDLr(-/-) rabbits, there was a marked increase in plasma total cholesterol and triglycerides, as was found in their counterpart non-transgenic WHHL rabbits. Northern blot analysis revealed that hepatic apo[a] expression in WHHL transgenic rabbits was similar to that in LDLr(+/+) transgenic rabbits, suggesting the accumulation of plasma Lp[a] in WHHL transgenic rabbits was not due to increased apo[a] synthesis. In conclusion, absence of a functional LDLr leads to a marked accumulation of plasma Lp[a] in human apo[a] transgenic WHHL rabbits and LDLr may participate in the catabolism of Lp[a] in rabbits.
Fan
J
J
Department of Pathology, Institute of Basic Medical Sciences, University of Tsukuba, Tsukuba, 305-8575 Japan.
Challah
M
M
Shimoyamada
H
H
Shiomi
M
M
Marcovina
S
S
Watanabe
T
T
D000818:Animals; D030801:Animals, Genetically Modified; D006801:Humans; D017270:Lipoprotein(a) / Q000097:blood / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011817:Rabbits; D011973:Receptors, LDL / Q000235:genetics*
D017270:Lipoprotein(a); D012333:RNA, Messenger; D011973:Receptors, LDL