Adeno-associated virus Serotype 3 (AAV3) was originally isolated from humans. Similar to AAV2, this serotype uses HSPG, FGFR1 and LR receptors as well as human HGFR (hHGFR) receptors. Iodixanol gradient ultracentrifugation and ion exchange chromatography have been used for AAV3 purification. Post-translational modifications (PTMs) of rAAV3 capsid include acetylation, phosphorylation and glycosylation.
Due to its insufficient transduction efficiency in vitro and in murine cell lines, AAV3 has been mostly overlooked as an option for gene therapy. However, due to its later discovery that it uses hHGFR as a coreceptor, it has shown extremely efficient transduction of human hepatoma cells as well as human and NHP hepatocytes. Since the discovery of this selective tropism of AAV3, various studies have been aimed at optimizing strategies to generate rAAV3 vectors with higher transduction efficiency. The strategies developed have proposed different approaches, mainly the capsid modification of AAV3 vectors and the modification of hHGFR expression levels, as well as the tyrosine kinase activity associated with it. AAV3 was also found to have a specific tropism for cochlear inner hair cells and exhibited high in vivo transduction efficiency in a mouse model.
PCSK9 (proprotein convertase subtilisin/kexin type 9) plays an important role in lipoprotein metabolism by regulating LDL receptor homeostasis. Gain-of-function mutations in the human PCSK9 protein are associated with autosomal dominant hypercholesterolemia. Two research groups used an adeno-associated virus (AAV)-mediated gene transfer approach to investigate the effects of a well-characterized gain-of-function mutation in humans, D374Y, on atherosclerosis in mice. This approach resulted in a rapid increase in plasma cholesterol concentrations in C57BL/6 mice via a single injection of AAV containing the human PCSK9D374Y mutation or its mouse equivalent, the D377Y mutation. Thus, this single injection accelerated atherosclerosis in mice. In this study, the researchers demonstrated that the AAV-delivered mouse PCSK9D377Y mutation rapidly enhanced AngII-induced AAA in male C57BL/6 mice.
To evaluate the expression efficiency and stability of the AAV vectors, the researchers measured plasma PCSK9 concentrations at week 0 (before AAV injection) and at 2 and 6 weeks after AAV injection. Plasma PCSK9 concentrations were lower and remained unchanged in C57BL/6 mice that received an AAV vector containing a null insert (Figure 1A). In C57BL/6 mice infected with an AAV vector expressing the PCSK9D377Y mutation, plasma PCSK9 concentrations were significantly elevated 2 weeks after injection and remained high during 6 weeks of Western diet feeding. There was no difference in plasma PCSK9 concentrations between mice infected with 10×1010 and 30×1010 genome copies (Figure 1A). Consistent with the increase in plasma PCSK9 concentrations, plasma cholesterol concentrations increased significantly and consistently during 6 weeks of Western diet feeding (Figure 1B). All three dose groups of PCSK9D377Y.AAV increased atherosclerotic lesions (Figure 1C), while only the medium and high doses of PCSK9D377Y mutant groups resulted in an increase in AngII-induced AAA (Figure 1D).
Figure 1. Dose-response curve of AAV vector infection with PCSK9 gain-of-function mutation in C57BL/6 mice. (Lu H, et al., 2016)
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