To evaluate the role that HL plays in facilitating the selective uptake of HDL-CE in vivo, we performed a series of autologous HDL-metabolic studies in control C57BL (n=7; TC=60?5, CE=43?4, HDL-C=58?6, apoA- I=76?7, apoA-II=13?1 mg/dL) and HL-deficient (HL-KO) mice (n=7; TC=114?10, CE=86?8, HDL-C=83?9, apoA-I=137?16, apoA-II=47?16 mg/dL). HDL from HL-KO and C57BL were radiolabeled with 3H-CE, as well as 125I- apoAI and 131I-apoAII and injected in HL-KO and C57BL mice, respectively. Kinetic analysis revealed similar catabolism of 125I- apoAI HDL (FCR=2.17?0.15 & 2.16?0.11 d-1,resp; p=0.98) and of 131I- apoAII HDL(FCR=2.59?0.14 & 2.67?0.13 d-1,resp; p=0.72) in HL-KO and C57BL mice. In contrast, despite similar hepatic SR-BI expression determined by immunoblot analysis, the clearance of 3H-CE HDL was delayed in HL-KO compared to C57BL (FCR=4.27?0.01 & 5.6?0.34 d-1,resp; p<0.05) indicating impaired selective uptake of HDL-CE in HL-KO mice. Ten hours after injection, the hepatic accumulation of 3H-CE in HL-KO mice was decreased compared to C57BL mice (60?5% & 78?5% of total; p<0.05) while the 3H-CE remaining in the plasma compartment was increased in HL-KO mice compared to C57BL (19?1% & 13?1% of total; p<0.002). In summary: HL deficiency in mice does not alter the catabolism of apoA-I and apoA-II HDL but delays the plasma clearance of HDL-CE as well as decrease the hepatic uptake of HDL-CE. These findings establish an important in vivo role for HL in facilitating the selective uptake of HDL-CE, and thus modulating reverse cholesterol transport and are consistent with the proposed ligand-binding role of HL in facilitating SR-BI mediated cellular HDL-CE uptake.
