Failure of caspase inhibition in the double-lesion rat model of striatonigral degeneration (multiple system atrophy)

A progressive dopaminergic phenotype associated with neurotoxic conversion of α-synuclein in BAC-transgenic rats

Conversion of soluble α-synuclein into insoluble and fibrillar inclusions is a hallmark of Parkinson's disease and other synucleinopathies. Accumulating evidence points towards a relationship between its generation at nerve terminals and structural synaptic pathology. Little is known about the pathogenic impact of α-synuclein conversion and deposition at nigrostriatal dopaminergic synapses in transgenic mice, mainly owing to expression limitations of the α-synuclein construct. Here, we explore whether both the rat as a model and expression of the bacterial artificial chromosome construct consisting of human full-length wild-type α-synuclein could exert dopaminergic neuropathological effects. We found that the human promoter induced a pan-neuronal expression, matching the rodent α-synuclein expression pattern, however, with prominent C-terminally truncated fragments. Ageing promoted conversion of both full-length and C-terminally truncated α-synuclein species into insolube and proteinase K-resistant fibres, with strongest accumulation in the striatum, resembling biochemical changes seen in human Parkinson's disease. Transgenic rats develop early changes in novelty-seeking, avoidance and smell before the progressive motor deficit. Importantly, the observed pathological changes were associated with severe loss of the dopaminergic integrity, thus resembling more closely the human pathology.

Models of multiple system atrophy

Multiple system atrophy (MSA) is a predominantly sporadic, adult-onset, fatal neurodegenerative disease of unknown etiology. MSA is characterized by autonomic failure, levodopa-unresponsive parkinsonism, cerebellar ataxia and pyramidal signs in any combination. MSA belongs to a group of neurodegenerative disorders termed α-synucleinopathies, which also include Parkinson's disease and dementia with Lewy bodies. Their common pathological feature is the occurrence of abnormal α-synuclein positive inclusions in neurons or glial cells. In MSA, the main cell type presenting aggregates composed of α-synuclein are oligodendroglial cells . This pathological hallmark, also called glial cytoplasmic inclusions (GCIs) , is associated with progressive and profound neuronal loss in various regions of the brain. The development of animal models of MSA is justified by the limited understanding of the mechanisms of neurodegeneration and GCIs formation, which is paralleled by a lack of therapeutic strategies. Two main types of rodent models have been generated to replicate different features of MSA neuropathology. On one hand, neurotoxin-based models have been produced to reproduce neuronal loss in substantia nigra pars compacta and striatum. On the other hand, transgenic mouse models with overexpression of α-synuclein in oligodendroglia have been used to reproduce GCIs-related pathology. This chapter gives an overview of the atypical Parkinson's syndrome MSA and summarizes the currently available MSA animal models and their relevance for pre-clinical testing of disease-modifying therapies.

Animal models of multiple system atrophy

Multiple system atrophy (MSA) is a fatal neurodegenerative disorder presenting with autonomic failure and motor impairment, primarily comprising L-dopa-resistant parkinsonism but occasionally involving cerebellar ataxia. These features result from progressive multisystem neuronal loss that is associated with oligodendroglial alpha-synuclein inclusions. The growing number of animal models for MSA reflects the search for a preclinical test-bed for elucidating MSA pathogenesis and for developing novel therapeutic interventions. Here, the currently available MSA animal models will be reviewed and leads for future research will be identified.

The role of alpha-synuclein in the pathogenesis of multiple system atrophy

The discovery of glial cytoplasmic inclusions (GCIs) in 1989 helped to define multiple system atrophy (MSA) as a clinicopathological entity, and drew attention to the prominent role played by these inclusions in the pathogenesis of the disorder. Subsequently, GCIs were shown to be highly positive for alpha-synuclein, a neuronal protein that is normally absent in oligodendroglia except during embryonic development. The source of oligodendroglial alpha-synuclein aggregation in MSA is unknown. Since genetic overexpression has been excluded, active uptake from dying neurons remains a possibility. The similar topography of oligodendroglial and neuronal pathology in MSA suggests a fundamental disturbance of the functional unit between oligodendroglia, axon, and neuron. Transgenic MSA mouse models are now available to determine these aspects of cellular disturbance experimentally.