Defects of the LDL receptor in WHHL transgenic rabbits lead to a marked accumulation of plasma lipoprotein[a]

Abstract

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]+/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-β 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.

Keywords

• lipoprotein[a]
• WHHL rabbit
• apolipoprotein[a]
• LDL receptor
• transgenic rabbit
• metabolism