Development of basic techniques for the liver-directed gene therapy

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Liver-directed gene therapy may be an ultimate therapy for many genetic diseases such as familial hypercholesterolemia (FH). Direct introduction of low density lipoprotein receptor (LDLR) expression into null type of FH may potentially cause antibody formation against the introduced protein, and mitigate the therapeutic effects. To circumbent this problem, we have tested the feasibility of using non- LDLR proteins such as lipoprotein lipase (LPL) and apoliporptein E (apoE). Both proteins may function as ligands for the non-LDLR pathway for hepatic lipoprotein catabolism. We have generated two types of mice : i) LDLR knockout mice overexpressiong LPL under the control of CAG promoter (LPLTg ; LDLRKO), ii) LDLR knockout mice overexpressiong rat apoE under the control of methanotionein promoter (ETg ; LDLRKO). In both animals, cholesterol-lowering effects were observed. More importantly, diet-induced atherosclerosis was significantly suppressed in these animals. These results suggest that LPL or apoE are promising candidate genes as a surrogate for LDLR.The other approach is ex vivo gene therapy. However, its limitation is that the hepatocytes transplanted to the recipient liver do not regenerate to the level which is enough to rescue the metabolic defects. As an experimental tool to investigate the recipient hepatocyte-specific cell ablation, we have generated mice lacking asialoglycoprotein receptor (ASGPR). In the current study, HL1, a major component of ASGPR, has been disrupted. HSL-/- mice lack both HL1 and HL2 in the liver. Plasma clearance of ASGP was almost completely blocked.