Characterisation of a novel rat model of Parkinson's disease involving a small-molecule inducer of α-synuclein oligomerisation and a viral mimetic

L. Olsen¹, A. Cairns², J. Aden², N. Moriarty¹, S. Cabre¹, V. Alamilla¹, F. Almqvist², E. Dowd¹, D. McKernan¹. ¹Pharmacology & Therapeutics, National University of Ireland, Galway, Galway, Ireland, ²Chemistry, Umea University, Umeå, Sweden.

Introduction: Current animal models of Parkinson’s disease (PD) are limited and not ideal for drug screening. Studies suggest that viral infections may increase the incidence of developing PD.¹ We report a novel dual-hit model combining viral-mediated neuroinflammation and α-synuclein aggregation.

Methods: Male Sprague Dawley (SD) rats (n=7-8 per group) received unilateral intra-nigral injections of poly I:C (30μg), a synthetic mimetic of viral dsRNA or saline followed two weeks later by unilateral intra-nigral injection of synthetic FN075 (1.93μg)² used to produce α-synuclein aggregates or vehicle. Stepping and Whisker behavioural tests³ were conducted for seven weeks post-surgery (n=7-8). Post-mortem immunohistochemical analysis quantified neuronal (tyrosine hydroxylase), astrocytic (GFAP) and microglial (OX42) markers in the substantia nigra (SN) (n=3-4). In vitro E14 ventral mesencephalic SD rat cell cultures⁴ treated with poly I:C (20 μg/ml for 24 hours) and/or FN075 (25 μM for 48 hour) (n=6-9) were assessed for synaptic (PSD95 & synaptophysin) and autophagy (p62) protein changes using immunocytochemistry. Data were analysed using Two-way ANOVA or Three-way Repeated Measures ANOVA, followed by appropriate post-hoc tests.

Results: The poly I:C+FN075 combination rat group had significantly fewer steps in the Stepping (S) and Whisker (W) tests at five and seven weeks post-surgery compared to all other groups (S: p<0.01, W: p<0.001). At eight weeks post-surgery, aggregate-specific α-synuclein protein was increased at least 3-fold in the SN for the FN075 (p<0.05) and combination groups (p<0.01) compared to the vehicle. Also, the number of astrocytes was increased by 50% (p<0.01), while the number of TH+ neurons was decreased by 50% (p<0.05) in the SN of the combination group (vs. vehicle). Qualitative staining for OX42 revealed activated SN microglia in the combination group. In vitro, aggregate-specific α-synuclein protein was increased after FN075 treatment (p<0.05 vs. control). FN075 alone increased p62 punctate in E14 rat cells (p<0.001 vs. all other groups), but priming with poly I:C before FN075 treatment suppressed this effect (p>0.05).

Conclusion: This novel model of PD successfully recapitulates the motor deficits, α-synuclein aggregation, neuroinflammation, and TH+ neuronal loss in the SN making it more suitable for future drugs testing.

References:

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2. Horvath I et al. (2012) J. Am. Chem. Soc. 134: 3439-3444.

3. Concannon et al (2016) Exp. Neurol. 283: 204-12.

4. Clayton KB and Sullivan AM (2007). Neurosci Lett. 427: 132-137.