Propagated but Topologically Distributed Forebrain Neurons Expressing Alpha-Synuclein in Aged Macaques

Increased Expression of Alpha-, Beta-, and Gamma-Synucleins in Brainstem Regions of a Non-Human Primate Model of Parkinson’s Disease

Parkinson’s disease (PD) is characterized by cell loss in the substantia nigra and the presence of alpha-synuclein (α-syn)-containing neuronal Lewy bodies. While α-syn has received major interest in the pathogenesis of PD, the function of beta- and gamma-synucleins (β-syn and γ-syn, respectively) is not really known. Yet, these proteins are members of the same family and also concentrated in neuronal terminals. The current preclinical study investigated the expression levels of α-, β-, and γ-synucleins in brainstem regions involved in PD physiopathology. We analyzed synuclein expression in the substantia nigra, raphe nuclei, pedunculopontine nucleus, and locus coeruleus from control and parkinsonian (by MPTP) macaques. MPTP-intoxicated monkeys developed a more or less severe parkinsonian score and were sacrificed after a variable post-MPTP period ranging from 1 to 20 months. The expression of the three synucleins was increased in the substantia nigra after MPTP, and this increase correlates positively, although not very strongly, with cell loss and motor score and not with the time elapsed after intoxication. In the dorsal raphe nucleus, the expression of the three synucleins was also increased, but only α- and γ-Syn are linked to the motor score and associated cell loss. Finally, although no change in synuclein expression was demonstrated in the locus coeruleus after MPTP, we found increased expression levels of γ-Syn, which are only correlated with cell loss in the pedunculopontine nucleus. Altogether, our data suggest that these proteins may play a key role in brainstem regions and mesencephalic tegmentum. Given the involvement of these brain regions in non-motor symptoms of PD, these data also strengthen the relevance of the MPTP macaque model of PD, which exhibits pathological changes beyond nigral DA cell loss and α-synucleinopathy.

Co-editing PINK1 and DJ-1 Genes Via Adeno-Associated Virus-Delivered CRISPR/Cas9 System in Adult Monkey Brain Elicits Classical Parkinsonian Phenotype

Whether direct manipulation of Parkinson's disease (PD) risk genes in the adult monkey brain can elicit a Parkinsonian phenotype remains an unsolved issue. Here, we used an adeno-associated virus serotype 9 (AAV9)-delivered CRISPR/Cas9 system to directly co-edit PINK1 and DJ-1 genes in the substantia nigras (SNs) of two monkey groups: an old group and a middle-aged group. After the operation, the old group exhibited all the classic PD symptoms, including bradykinesia, tremor, and postural instability, accompanied by key pathological hallmarks of PD, such as severe nigral dopaminergic neuron loss (>64%) and evident α-synuclein pathology in the gene-edited SN. In contrast, the phenotype of their middle-aged counterparts, which also showed clear PD symptoms and pathological hallmarks, were less severe. In addition to the higher final total PD scores and more severe pathological changes, the old group were also more susceptible to gene editing by showing a faster process of PD progression. These results suggested that both genetic and aging factors played important roles in the development of PD in the monkeys. Taken together, this system can effectively develop a large number of genetically-edited PD monkeys in a short time (6-10 months), and thus provides a practical transgenic monkey model for future PD studies.

A New Rise of Non-Human Primate Models of Synucleinopathies

Synucleinopathies are neurodegenerative diseases characterized by the presence of α-synuclein-positive intracytoplasmic inclusions in the central nervous system. Multiple experimental models have been extensively used to understand better the mechanisms involved in the pathogenesis of synucleinopathy. Non-human primate (NHP) models are of interest in neurodegenerative diseases as they constitute the highest relevant preclinical model in translational research. They also contribute to bringing new insights into synucleinopathy’s pathogenicity and help in the quest and validation of therapeutical strategies. Here, we reviewed the different NHP models that have recapitulated key characteristics of synucleinopathy, and we aimed to highlight the contribution of NHP in mechanistic and translational approaches for synucleinopathies.

Phosphorylated α-Synuclein Accumulations and Lewy Body-like Pathology Distributed in Parkinson's Disease-Related Brain Areas of Aged Rhesus Monkeys Treated with MPTP

Phosphorylation of α-synuclein at serine 129 (P-Ser 129 α-syn) is involved in the pathogenesis of Parkinson's disease (PD) and Lewy body (LB) formation. However, there is no clear evidence indicates the quantitative relation of P-Ser 129 α-syn accumulation and dopaminergic cell loss, LBs pathology and the affected brain areas in PD monkeys. Here, pathological changes in the substantia nigra (SN) and PD-related brain areas were measured in aged monkeys treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) utilizing a modeling-recovery-remodeling strategy. Compared to age-matched controls, the MPTP-treated monkeys showed significantly reduced tyrosine hydroxylase (TH)-positive neurons and increased P-Ser 129 α-syn-positive aggregations in the SN. Double-labeling Immunofluorescence found some TH-positive neurons to be co-localized with P-Ser129 α-syn in the SN, suggesting the inverse correlation between P-Ser 129 α-syn aggregations and dopaminergic cell loss in the SN may represent an interactive association related to the progression of the PD symptoms in the model. P-Ser 129 α-syn aggregations or LB-like pathology was also found in the midbrain and the neocortex, specifically in the oculomotor nucleus (CN III), temporal cortex (TC), prefrontal cortex (PFC) and in cells surrounding the third ventricle. Notably, the occipital cortex (OC) was P-Ser 129 α-syn negative. The findings of LB-like pathologies, dopaminergic cell loss and the stability of the PD symptoms in this model suggest that the modeling-recovery-remodeling strategy in aged monkeys may provide a new platform for biomedical investigations into the pathogenesis of PD and potential therapeutic development.