Dimerizer regulation of AADC expression and behavioral response in AAV-transduced 6-OHDA lesioned rats

Recombinant AAV vectors containing a dimerizer-inducible system of transcriptional activation provide a strategy for control of therapeutic gene expression in the CNS. Here we explored this system for regulated expression of human aromatic L-amino acid decarboxylase (hAADC) in a rodent model of Parkinson disease. Expression of hAADC, the enzyme that converts L-dopa to dopamine, was dependent on reconstitution of a functional transcription factor (TF) by the dimerizer rapamycin. Two vectors, AAV-CMV-TF and AAV-Z12-hAADC, were infused into striata of 6-OHDA-lesioned rats. Rapamycin-induced increases in expression of hAADC repeatedly produced robust rotational behavior in response to low doses of L-dopa. Seven weeks after vector infusion, AADC expression in brain was quantitated by both stereology and Western blot analysis following the final rapamycin treatment. While a low level of hAADC was observed in rats that were not induced with rapamycin, this basal expression was not significant enough to elicit a rotational response to L-dopa. This study demonstrated a robust behavioral response of parkinsonian rats to regulated hAADC expression. Recombinant AAV vectors controlled by rapamycin or its analogs show promise as candidates for CNS therapies in which regulation of the transgene is desired.