Evaluation of the role of lipoprotein metabolism genes in systemic cationic liposome-mediated gene transfer in vivo

Germ line gene disruption and gene insertion are often used to study the fu nction of selected genes in vivo. We used selected knockout and transgenic mouse models to attempt to identify lipoprotein-related genes and gene prod ucts that regulate the process of intravenous cationic liposome-DNA complex (CLDC)-based gene delivery. Several observations suggested that proteins i nvolved in lipoprotein metabolism might be important in influencing the del ivery and/or expression of CLDC. First, in vitro transfection of either K56 2 or CHO cells by CLDCs was enhanced by the presence of a functional low-de nsity lipoprotein receptor (LDLR). Second, pretreatment of mice with 4-amin opyrazolopyrimidine (4APP), an agent that alters lipoprotein profiles in mi ce, significantly decreased expression of luciferase (luc) after intravenou s injection of CLDC-luc complexes in mice. Therefore, we tested mouse model systems either deficient for, or overexpressing, selected genes involved i n lipoprotein metabolism, for their potential to regulate intravenous, CLDC -based gene delivery. Although homozygous knockout mutation in the apoE gen e caused a significant decrease in gene expression in many tissues of apoE- deficient mice, mice with homozygous deletion of both the apoE and LDLR gen es showed wild-type levels of gene transfer efficiency. Thus, a secondary e vent, produced by homozygous deletion of apoE, but compensated for by the c oncomitant deletion of LDLR, and/or effects resulting from strain-related, genetic background differences, appeared to play a significant role in medi ating intravenous, CLDC-based gene delivery. Secondary alterations resultin g from germ line knockouts, as well as epigenetic effects produced by strai n differences, may limit the ability to assign specific, gene transfer-rela ted functions to the deleted gene.