Intramuscular gene transfer of apolipoprotein E (ApoE) to reverse hyperlipidaemia and atherosclerosis in ApoE-deficient mice

• Main Author: Evans, Vanessa
• Published: University College London (University of London) 2007
• Subjects: 616.1
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.498138

Plasma ApoE has multiple atheroprotective actions, including clearance of cholesterol-rich remnant lipoproteins, and is an attractive gene therapy candidate to treat atherosclerosis. Here, I focus on the single intramuscular injection of an ApoE-expressing vector, non-viral DNA (plasmid) or adeno-associated virus (AAV), as a safe and effective treatment to alleviate hypercholesterolaemia and atherosclerosis in ApoE-deficient (ApoE" ") mice. Firstly, I constructed expression plasmids harbouring human ApoE3 cDNA, driven by two muscle-specific (CK6 and C512) and one ubiquitous (CAG) promoter. The CAG-driven plasmid was injected into tibialis anterior muscles, pre-treated with hyaluronidase, of young ApoE"'" mice and, provided the injection site was electropulsed, gave strong local expression of ApoE3 protein at 1 week (13.38 7.46jig ApoE3 per muscle). This amount was much greater than the CK6- and C512-driven plasmids (0.61 0.38 and 0.45 0.38/ig, respectively), but in all mice plasma ApoE3 levels were below the detection limit (<15ng/ml) and did not ameliorate the hyperlipidaemia. Next, I generated both single-stranded (ss) and self- complementary (sc) AAV2/7 vectors. At 1, 2 and 4 weeks, ApoE was readily measured in the plasma of ApoE'" mice injected with the ssAAV2/7.CAG vector, reaching levels of 1.4/ig/ml, whereas plasma ApoE was again undetected after administration of the CAG-driven plasmid . By contrast, both ssAAV2/7 and scAAV2/7 vectors driven by the muscle-specific promoters performed poorly and ApoE could not be detected in plasma. Therefore, for my final experiment I pseudotyped the ssAAV2.CAG.ApoE3 vector with the robust serotypes 8 and 9, and directly compared their efficiency with ssAAV2/7.CAG.ApoE3 in ApoE"" mice. After 1 week plasma ApoE had reached 2ug/ml in ssAAV2/7 and ssAAV2/8-treated animals, and persisted at l-2ug/ml throughout the 13 week study, whereas the ssAAV2/9 vector was less effective and gave only 0.5ug ApoE/ml. Disappointingly, however, these concentrations of plasma ApoE were still insufficient to have hypolipidaemic effects or to inhibit plaque development in the brachiocephalic artery. In conclusion, although electropulsation enhanced plasmid-mediated transgene expression from skeletal muscle, rAAV was a more efficient gene transfer vector and modest additional optimisation should provide therapeutic levels of ApoE3 in plasma.