Compound 2a is a novel pharmacological stabilizer of the retromer complex, an evolutionary conserved heteropentameric protein cargo. Mutations of the VPS35 gene, which encodes for a subunit of the retromer, are associated with familial PD. The retromer is involved in α-synuclein (αSyn) clearance. αSyn accumulation represents a pathogenetic event for the loss of dopaminergic (DA) neurons in the substantia nigra (SN) of PD patients.

We injected the right SN in WT mice with adenovirus expressing human αSyn A53T (AVV1/2 A53T). 2a (or saline control) was administrated by daily intraperitoneal (IP) injections for 100 days. We assessed motor function with the rotarod and cylinder tests and evaluated the potential neuroprotective impact of 2a in the SN by assessing αSyn pathology in the SN and quantifying tyrosine hydroxylase immunoreactive (TH+) neurons and levels of striatal dopamine and its metabolites.

The rotarod test exhibited a 0.5-fold decrease (p<0.002) in the latency to fall for AAV-A53T-αSyn mice treated daily with 2a compared to saline control mice (p=0.0001). The cylinder test demonstrated 2a-mediated rescue of the asymmetrical defects in forelimb use in the AAV-A53TαSyn mice. 2a administration in AAV-A53T-αSyn mice significantly reduces DA (TH+) neuronal loss (p<0.0384) and attenuates pathological phospho-Serine 129 αSyn accumulation (p<0.0001). Western blots confirmed 2a-induced clearance of αSyn aggregates in the soluble (p<0.0001) and insoluble fractions (p<0.0001). Lastly, treatment with 2a prevented αSyn-induced loss of striatal dopamine (p<0.0068) and the decline of dopamine metabolites DOPAC (p=0.034) and HVA (p=0.0147). 

2a led to protection against behavioral deficits, reduction in αSyn aggregates, and rescue of nigral dopaminergic fibers and striatal monoamines loss, demonstrating protective effects in this mouse model of PD.