Sonic hedgehog delivered by an adeno-associated virus protects dopaminergic neurones against 6-OHDA toxicity in the rat

Direct intracerebral administration of sonic hedgehog (SHH) reduces 6-OHDA and MPTP toxicity to nigral dopaminergic cells in rats and primates. To determine whether transfection of the DNA sequence for SHH using viral vectors also protects against 6-OHDA toxicity, a type 2 adeno-associated virus (AAV) incorporating 600 base pairs of N-terminal SHH DNA was generated to induce SHH expression in rat striatum.
AAV-SHH was injected into the striatum, 3 weeks prior to the initiation of an unilateral partial 6-OHDA nigro-striatal lesion. Animals receiving 4 x 10(7) viral particles of AAV-SHH showed a reduction in (+)-amphetamine induced ipsilateral turning over 4 weeks, when compared to animals receiving vehicle or a LacZ encoding vector. Following vehicle or AAV-LacZ administration, 6-OHDA caused a marked loss of striatal dopamine content and nigral tyrosine hydroxylase (TH) immunopositive cells. Following treatment with 4 x 10(7) viral particles of AAV-SHH the loss of striatal dopamine content was reduced and there was marked preservation of nigral dopaminergic cells. However, administration of 4 x 10(8) particles of AAV-SHH did not cause a significant change in (+)-amphetamine-induced rotation, striatal dopamine levels or the number of nigral TH immunoreactive cells following 6-OHDA lesioning compared to vehicle or AAV-LacZ treated animals.
The results show that SHH delivered via a viral vector can protect dopaminergic neurons against 6-OHDA toxicity and suggest that this could be developed into a novel treatment for PD. However, the effects maybe dose limited due to uncoupling of hedgehog receptor signalling at higher levels of SHH expression.