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Comparison of the in vivo induction and transmission of ?-synuclein pathology by mutant ?-synuclein fibril seeds in transgenic mice.

ABSTRACT: Parkinson's disease (PD) is one of many neurodegenerative diseases termed synucleinopathies, neuropathologically defined by inclusions containing aggregated ?-synuclein (?S). ?S gene (SNCA) mutations can directly cause autosomal dominant PD. In vitro studies demonstrated that SNCA missense mutations may either enhance or diminish ?S aggregation but cross-seeding of mutant and wild-type ?S proteins appear to reduce aggregation efficiency. Here, we extended these studies by assessing the effects of seeded ?S aggregation in ?S transgenic mice through intracerebral or peripheral injection of various mutant ?S fibrils. We observed modestly decreased time to paralysis in mice transgenic for human A53T ?S (line M83) intramuscularly injected with H50Q, G51D or A53E ?S fibrils relative to wild-type ?S fibrils. Conversely, E46K ?S fibril seeding was significantly delayed and less efficient in the same experimental paradigm. However, the amount and distribution of ?S inclusions in the central nervous system were similar for all ?S fibril muscle injected mice that developed paralysis. Mice transgenic for human ?S (line M20) injected in the hippocampus with wild-type, H50Q, G51D or A53E ?S fibrils displayed induction of ?S inclusion pathology that increased and spread over time. By comparison, induction of ?S aggregation following the intrahippocampal injection of E46K ?S fibrils in M20 mice was much less efficient. These findings show that H50Q, G51D or A53E can efficiently cross-seed and induce ?S pathology in vivo. In contrast, E46K ?S fibrils are intrinsically inefficient at seeding ?S inclusion pathology. Consistent with previous in vitro studies, E46K ?S polymers are likely distinct aggregated conformers that may represent a unique prion-like strain of ?S.

SUBMITTER: Rutherford NJ

PROVIDER: S-EPMC5886210 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature

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Comparison of the in vivo induction and transmission of α-synuclein pathology by mutant α-synuclein fibril seeds in transgenic mice.

Rutherford Nicola J NJ Dhillon Jess-Karan S JS Riffe Cara J CJ Howard Jasie K JK Brooks Mieu M Giasson Benoit I BI

Human molecular genetics 20171201 24

Parkinson's disease (PD) is one of many neurodegenerative diseases termed synucleinopathies, neuropathologically defined by inclusions containing aggregated α-synuclein (αS). αS gene (SNCA) mutations can directly cause autosomal dominant PD. In vitro studies demonstrated that SNCA missense mutations may either enhance or diminish αS aggregation but cross-seeding of mutant and wild-type αS proteins appear to reduce aggregation efficiency. Here, we extended these studies by assessing the effects o ...[more]

PMID: 29036344

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Project description:Lewy body disorders are characterized by the emergence of α-synucleinopathy in many parts of the central and peripheral nervous systems, including in the telencephalon. Dense α-synuclein+ pathology appears in regio inferior of the hippocampus in both Parkinson's disease and dementia with Lewy bodies and may disturb cognitive function. The preformed α-synuclein fibril model of Parkinson's disease is growing in use, given its potential for seeding the self-propagating spread of α-synucleinopathy throughout the mammalian brain. Although it is often assumed that the spread occurs through neuroanatomical connections, this is generally not examined vis-à-vis the uptake and transport of tract-tracers infused at precisely the same stereotaxic coordinates. As the neuronal connections of the hippocampus are historically well defined, we examined the first-order spread of α-synucleinopathy three months following fibril infusions centered in the mouse regio inferior (CA2+CA3), and contrasted this to retrograde and anterograde transport of the established tract-tracers FluoroGold and biotinylated dextran amines (BDA). Massive hippocampal α-synucleinopathy was insufficient to elicit memory deficits or loss of cells and synaptic markers in this model of early disease processes. However, dense α-synuclein+ inclusions in the fascia dentata were negatively correlated with memory capacity. A modest compensatory increase in synaptophysin was evident in the stratum radiatum of cornu Ammonis in fibril-infused animals, and synaptophysin expression correlated inversely with memory function in fibril but not PBS-infused mice. No changes in synapsin I/II expression were observed. The spread of α-synucleinopathy was somewhat, but not entirely consistent with FluoroGold and BDA axonal transport, suggesting that variables other than innervation density also contribute to the materialization of α-synucleinopathy. For example, layer II entorhinal neurons of the perforant pathway exhibited somal α-synuclein+ inclusions as well as retrogradely labeled FluoroGold+ somata. However, some afferent brain regions displayed dense retrograde FluoroGold label and no α-synuclein+ inclusions (e.g. medial septum/diagonal band), supporting the selective vulnerability hypothesis. The pattern of inclusions on the contralateral side was consistent with specific spread through commissural connections (e.g. stratum pyramidale of CA3), but again, not all commissural projections exhibited α-synucleinopathy (e.g. hilar mossy cells). The topographical extent of inclusions is displayed here in high-resolution images that afford viewers a rich opportunity to dissect the potential spread of pathology through neural circuitry. Finally, the results of this expository study were leveraged to highlight the challenges and limitations of working with preformed α-synuclein fibrils.

Project description:Alpha-synuclein pathology is associated with dopaminergic neuronal loss in the substantia nigra (SN) of Parkinson's patients. Working across human and mouse models, we investigated mechanisms by which the accumulation of soluble α-synuclein oligomers leads to neurodegeneration. Biochemical analysis of the midbrain of α-synuclein overexpressing BAC-transgenic male and female mice revealed age- and region-dependent mitochondrial dysfunction and accumulation of damaged proteins downstream of the RE1 Silencing Transcription Factor (REST). Vulnerable SN dopaminergic neurons displayed low REST levels compared with neighboring protected SN GABAergic neurons, which correlated with the accumulation of α-synuclein oligomers and disrupted mitochondrial morphology. Consistent with a protective role, REST levels were reduced in patient induced pluripotent stem cell-derived dopaminergic neurons carrying the SNCA-Triplication mutation, which accumulated α-synuclein oligomers and mitochondrial damage, and displayed REST target gene dysregulation. Furthermore, CRISPR-mediated REST KO induced mitochondrial dysfunction and impaired mitophagy in vitro Conversely, REST overexpression attenuated mitochondrial toxicity and mitochondrial morphology disruption through the transcription factor PGC-1α. Finally, decreased α-synuclein oligomer accumulation and mitochondrial dysfunction in mice correlated with nuclear REST and PGC-1α in protected SN GABAergic neurons compared with vulnerable dopaminergic neurons. Our findings show that increased levels of α-synuclein oligomers cause dopaminergic neuronal-specific dysfunction through mitochondrial toxicity, which can be attenuated by REST in an early model of Parkinsonian pathology. These findings highlight REST as a mediator of dopaminergic vulnerability in PD.SIGNIFICANCE STATEMENT Understanding early Parkinsonian pathophysiology through studies of advanced preclinical models is fundamental to the translation of disease-modifying therapies. Here we show disease-relevant levels of α-synuclein expression in mice leads to accumulation of α-synuclein oligomers in the absence of overt aggregation, and mitochondrial dysfunction in dopaminergic neurons lacking the RE1 Silencing Transcription Factor. Our findings identify the mechanism of action of RE1 Silencing Transcription Factor and PGC-1α as mediators of dopaminergic vulnerability in α-synuclein BAC-transgenic mice and induced pluripotent stem cell-derived dopaminergic cultures, highlighting their potential as therapeutic targets.

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Dataset Information

Comparison of the in vivo induction and transmission of ?-synuclein pathology by mutant ?-synuclein fibril seeds in transgenic mice.

Publications

Comparison of the in vivo induction and transmission of α-synuclein pathology by mutant α-synuclein fibril seeds in transgenic mice.

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