Transgene expression and effective gene silencing in vagal afferent neurons in vivo using recombinant adeno-associated virus vectors

Vagal afferent fibres innervating thoracic structures such as the respiratory tract and oesophagus are diverse, comprising several subtypes of functionally distinct C-fibres and A-fibres. Both morphological and functional studies of these nerve subtypes would be advanced by selective, effective and long-term transduction of vagal afferent neurons with viral vectors. Here we addressed the hypothesis that vagal sensory neurons can be transduced with adeno-associated virus (AAV) vectors in vivo, in a manner that would be useful for morphological assessment of nerve terminals, using enhanced green fluorescent protein (eGFP), as well as for the selective knock-down of specific genes of interest in a tissue-selective manner. We found that a direct microinjection of AAV vectors into the vagal nodose ganglia in vivo leads to selective, effective and long-lasting transduction of the vast majority of primary sensory vagal neurons without transduction of parasympathetic efferent neurons. The transduction of vagal neurons by pseudoserotype AAV2/8 vectors in vivo is sufficiently efficient such that it can be used to functionally silence TRPV1 gene expression using short hairpin RNA (shRNA). The eGFP encoded by AAV vectors is robustly transported to both the central and peripheral terminals of transduced vagal afferent neurons allowing for bright imaging of the nerve endings in living tissues and suitable for structure-function studies of vagal afferent nerve endings. Finally, the AAV2/8 vectors are efficiently taken up by the vagal nerve terminals in the visceral tissue and retrogradely transported to the cell body, allowing for tissue-specific transduction. Vagal sensory neurons play a central role in communication between visceral organs and the central nervous system. Research into the physiology of these neurons would be advanced by techniques that could deliver molecular biological tools allowing for the manipulation of selected genes. We investigated whether adeno-associated virus (AAV) vectors can be used to such ends. We found that certain AAV vectors can deliver the gene for green fluorescent protein (eGFP) resulting in robust production of eGFP that is then transported peripherally to the nerve terminals in the visceral organs of innervation and centrally to the brain, where their morphology can readily be visualized. We also found that AAV vectors can effectively deliver shRNA allowing for efficient silencing of genes of interest in the vagal sensory nerves. A combination of AAV transfection with available techniques will probably advance understanding of the structure and function of vagal sensory nerves.