Parkinson’s disease (PD) is a complex neurodegenerative disorder that affects millions of people worldwide. Different experimental models recapitulate distinct pathophysiological features of PD. Selecting the most appropriate model for a specific research question is crucial to advancing targeted PD treatments.
Both in vitro and in vivo models have been generated to study different aspects of the disease, enabling research toward the development of novel therapeutics. Here, we discuss the applicability and potential limitations of the most commonly used PD models.
Modelling Parkinson’s disease in vitro & ex vivo
On the cellular level, the intracellular formation of Lewy bodies consisting predominantly of alpha-synuclein aggregates is one of the characteristic hallmarks of PD. Modeling PD in vitro serves as an efficient method to facilitate the selection of the most promising lead compounds.
Culturing of neuronal and glial cells is a useful, cost-effective, and quick tool for basic linear kinetic studies during the drug discovery process. At InnoSer, we observe that treating immortalized human microglial cells (HMC3) with α-synuclein fibrils modulates microglial function by significantly increasing the phagocytic capacity (Figure 1A). Similarly, treating microglial cells with glutamate induces microglial cell death, reflective of glutamate-induced excitotoxicity that is frequently observed in PD patients (Figure 1B). Other in vitro assays such as analysis of neuroinflammation and reactive oxygen species (ROS) production allow further investigation of the putative therapeutic effect of the investigational compound on specific neurological pathways.
The use of ex vivo brain slice culture overcomes many of the difficulties inherent to cell lines, such as recapitulating the complex cellular organization of the CNS. This allows researchers to further examine any possible therapeutic effects beyond cell lines, namely in the complex brain environment. We offer flexible research options and readouts including live cell imaging, cell-cell interaction, examination of neuro-inflammation and neuroprotection as well as analysis of de- and re-myelination in ex vivo models of PD.
FIGURE 1. Modelling Parkinson’s disease in vitro. (A) Treating microglial cells (HMC3 cell line) with alpha-synuclein fibrils modulates microglial function by significantly increasing the phagocytic capacity (*P<0.05; ****P<0.0001). (B) Treating HMC3 cells with glutamate induces microglial cell death, reflective of glutamate-induced excitotoxicity frequently observed in PD patients. Microglial cell death was assessed by MTT.
Modelling dopaminergic cell loss: MPTP-Based Inducible Models & 6-OHDA model
Degeneration of dopaminergic cells in the substantia nigra (SN) is the primary cause of motor symptoms in PD. This can be modelled in vivo by the administration of neurotoxins, such as MPTP and Oxidopamine (6-OHDA).
MPTP is a pro-drug for MPP+, which selectively kills dopamine-producing neurons in the SN. InnoSer offers acute and chronic MPTP exposure models. Acute MPTP administration leads to dysfunction of dopaminergic neurons, leading to impaired motor function, which is partly reversible with treatment (Figure 2). Following MPTP administration, we observe neuroinflammation in the SN (e.g., NLRP3 inflammasome activation) (Figure 3). Chronic MPTP administration leads to an irreversible loss of dopaminergic neurons. Similarly, unilateral stereotaxic injection of 6-OHDA into the SN or the medial forebrain bundle selectively kills dopamine-producing neurons and is a particularly robust model in rats.
FIGURE 2. MPTP administration induces Parkinson’s disease-like phenotype in vivo. MPTP administration leads to motor deficits which can be rescued following treatment with a neuroprotectant. The activity of mice was tracked in their automated home cage (PhenoTyper™) before and after acute MPTP administration. Acute MPTP administration leads to a decrease in activity in the following days, which is partially reversible by co-administration of a neuroprotectant.
Figure 3. MPTP administration leads to NLRP3 inflammasome activation in the substantia nigra, as detected by fluorescence immunohistochemistry (IHC). Iba1 signal (red) shows microgliosis. Asc signal (green) staining shows NLRP3 inflammasome activation. Asc signal co-localizes with Iba1-positive microglia (overlay). Nuclei (blue) were detected by DAPI.
Modelling alpha-synuclein formation and spreading: Alpha-Synuclein Models (Transgenic or Seeding Models)
Alpha-synuclein is a key protein involved in PD pathogenesis that forms abnormal aggregates that deposit into cellular inclusions, known as Lewy bodies. Lewy bodies lead to neuronal dysfunction and neurodegeneration. Models that recapitulate alpha-synuclein pathology – either by overexpression or seeding – are thus a valuable research tool.
Transgenic alpha-synuclein models
The transgenic alpha-synuclein models at InnoSer overexpress the human alpha-synuclein gene, recapitulating the formation of Lewy bodies and the development of PD-like symptoms. These models are useful for studying the role of alpha-synuclein in PD pathogenesis and testing potential therapies to target alpha-synuclein aggregation. They can also be used to study the effects downstream of alpha-synuclein pathology, such as neuroinflammation and neurodegeneration.
Seeding alpha-synuclein models
Recent evidence indicates that the progression of PD and alpha-synuclein pathology is not restricted exclusively to the SN region and that the sequential development of Lewy bodies can be found in different brain regions. The alpha-synuclein seeding model at InnoSer is a rapid model that allows researchers to study the spread of alpha-synuclein pathology.
In this model, recombinant alpha-synuclein fibrils or brain extracts from PD patients are injected into the brains of transgenic or wild-type mice, leading to the formation of Lewy bodies. Alpha-synuclein seeding models are especially useful to investigate the spreading of alpha-synuclein pathology to different brain regions and if this can be inhibited by novel targeted therapeutics.
Modelling PD (intra)cellular pathways: GBA Model and LRRK2 (MIJFF) model
GBA and LRRK2 Models
Mutations in the glucocerebrosidase (GBA) and leucine-rich repeat kinase 2 (LRRK2) genes are associated with an increased risk of PD. Mouse models that express GBA and LRRK2 with PD-associated mutations represent attractive models for target engagement studies, targeting the downstream and upstream pathways controlled by the affected proteins.
The GBA model can also be used to investigate the effects of different GBA mutations on PD development and the interaction between GBA mutations that contribute to PD. We have a profound experience with repeated or chronic intra-ventricular infusions to test novel therapies, including enzyme replacement therapies (ERT) in the GBA mouse model.
Similarly, the inhibition of LRRK2 is increasingly pursued as a therapeutic strategy in PD. Mouse models overexpressing the mutated LRKK2 gene such as LRRK2-G2019S and LRRK2-R1441C are useful for testing potential therapies that target LRRK2-related pathways.
Thanks to our continuous ongoing research and development of novel in vitro and in vivo models, we aim to gain a better understanding of the underlying mechanisms of PD and in turn, help industry innovators develop effective therapies to treat and/or cure this devastating disease.
The key to clinical success is thorough preclinical research and generating relevant and translatable results with carefully selected readouts. InnoSer’s neurology expert team is readily equipped and knowledgeable to consult with you to determine the best model together with readout customization to meet your specific needs and goals.