Adeno-Associated Virus Serotypes 1, 8, and 9 Share Conserved Mechanisms for Anterograde and Retrograde Axonal Transport

Abstract

Adeno-associated virus (AAV) vectors often undergo long-distance axonal transport after brain injection. This leads to transduction of brain regions distal to the injection site, although the extent of axonal transport and distal transduction varies widely among AAV serotypes. The mechanisms driving this variability are poorly understood. This is a critical problem for applications that require focal gene expression within a specific brain region, and also impedes the utilization of vector transport for applications requiring widespread delivery of transgene to the brain. Here, we compared AAV serotypes 1 and 9, which frequently demonstrate distal transduction, with serotype 8, which rarely spreads beyond the injection site. To examine directional AAV transport in vitro, we used a microfluidic chamber to apply dye-labeled AAV to the axon termini or to the cell bodies of primary rat embryonic cortical neurons. All three serotypes were actively transported along axons, with transport characterized by high velocities and prolonged runs in both the anterograde and retrograde directions. Coinfection with pairs of serotypes indicated that AAV1, 8, and 9 share the same intracellular compartments for axonal transport. In vivo, both AAV8 and 9 demonstrated anterograde and retrograde transport within a nonreciprocal circuit after injection into adult mouse brain, with highly similar distributions of distal transduction. However, in mass-cultured neurons, we found that AAV1 was more frequently transported than AAV8 or 9, and that the frequency of AAV9 transport could be enhanced by increasing receptor availability. Thus, while these serotypes share conserved mechanisms for axonal transport both in vitro and in vivo, the frequency of transport can vary among serotypes, and axonal transport can be markedly increased by enhancing vector uptake. This suggests that variability in distal transduction in vivo likely results from differential uptake at the plasma membrane, rather than fundamental differences in transport mechanisms among AAV serotypes.

Evaluation of WGA–Cre-dependent topological transgene expression in the rodent brain

“…It has been reported that some AAV serotypes appear to transduce distal neurons upon cell entry via the fiber terminals in the injection site. Consequent retrograde transfer to the cell body could then result in transduced neurons several mm away (Castle et al 2014). Since this characteristic seems to depend upon the serotype and the region of interest, retrograde transfer could be limited by the use of the right serotype for the application (Aschauer et al 2013;Cearley and Wolfe 2006;Van der Perren et al 2011;Taymans et al 2007).…”

Avian sarcoma leukosis virus receptor-envelope system for simultaneous dissection of multiple neural circuits in mammalian brain

“…Reports about retrograde transduction by AAV vector appear inconsistent; it has been reported as weak or ineffective in some cases (51,52) and effective in others (44,45). In addition to this inconsistency, AAV serotypes 8 and 9, which are known to undergo retrograde axonal transport, also anterogradely transduce second-order neurons in vivo (53). This anterograde transport of AAV vector is not suitable for pathway-specific gene expression.…”

Molecular Mechanisms of Reward and Aversion

“…AAV5 and AAV8 have been demonstrated in a multitude of studies to effectively transduce neurons of these brain areas (Aschauer et al, 2013;Atasoy et al, 2012;Betley et al, 2015;Wang et al, 2015;Witten et al, 2010). Another important aspect to consider for experimental design is that both AAV5 and AAV8-serotypes are capable of axonal transport in both retro-and anterograde directions (Castle et al, 2014). This phenomenon, can be regulated in a dose-dependent manner.…”

“…This phenomenon, can be regulated in a dose-dependent manner. For instance, by using lower doses of AAVs for transduction, axonal transport can be diminished (Castle et al, 2014). In study III, a high dose of AAV8 (600 nl per site of 3x10 12 genome copies/ml) was applied for retrograde transduction from the NAc shell to the ARC, compared to direct targeting of POMC-somas in the ARC (250 nl per site of 3x10 12 genome copies/ml).…”