PET imaging of dopaminergic changes in the rodent brain after AAV-mediated overexpression of human α-synuclein

ABSTRACT – YRLS 2018 

Acknowledgements
This project has been funded by the European Union Horizon 2020 Programme (H2020-MSCA-ITN-2015) under the Marie Skłodowska-Curie Innovative Training Network and Grant Agreement No. 676408.

Abstract
Parkinson’s disease (PD) is the second most prevalent age-related neurodegenerative disorder, resulting in a dopamine (DA) deficiency in the striatum [10.1016/S0896-6273(03)00568-3]. We developed two rodent PD models overexpressing either WT or mutant (A53T) human alpha-synuclein protein (α-syn) in the substantia nigra (SN) [Cresto et al., unpublished]. Our aims are to evaluate the DA changes and neuronal loss in these models by two different presynaptic PET tracers and correlate these results with behaviour and histological data.

Two groups of rats were unilateral injected in the SN with an AAV-viral vector overexpressing WT-α-syn or mutant α-syn (A53T-α-syn) and were studied using cylinder test and PET imaging at 12 weeks post injection, and subsequently sacrificed for stereological counting after tyrosine hydroxylase staining. PET imaging was performed using 6-[18F]fluoro-L-m-tyrosine [10.1111/jnc.14016](“FMT”), or [18F]-LBT999 [10.1016/j.nucmedbio.2013.09.007](“LBT").

We did not observed decreased AADC activity in ipsilateral striata with FMT for the WT-α-syn (n=3, p=0.255) nor A53T-α-syn rats (n=2, p=0.336). LBT showed decreased DA transporter (DAT) binding in the ipsilateral striata of A53T-α-syn animals (n=4, p=0.003), and a trend towards decreased DAT binding in the WT-α-syn group (n=3, p=0.051). These results are in concordance with the behavioural observations, showing roughly only 30% use of the contralateral forepaw for A53T-α-syn (n=8, p=0.045), while the WT-α-syn rats showed no significant difference (n=7, p=0.949). All counts using stereological methods and comparisons, are still ongoing.

We have shown, using in vivo PET imaging and behavioural analysis, that the A53T-α-syn vector induces stronger dopaminergic pathology than the WT-α-syn vector. This model is interesting to evaluate therapeutic strategies for PD by in vivo imaging. Additionally we have defined DAT transporter imaging, as more sensitive and robust as compared to AADC substrate imaging.