Research Models

α-synuclein A53T Mouse (Tg)

Synonyms: G2-3(A53T), PrPsynA53T, A53TαS Tg mice (line G2-3), MoPrP-Huα-Syn(A53T), Hualpha-Syn(A53T), A53T aSyn Tg Mouse (Lee), alpha-synuclein A53T Mouse (Tg)

Species: Mouse
Genes: SNCA
Mutations: SNCA A53T
Modification: SNCA: Transgenic
Disease Relevance: Parkinson's Disease
Strain Name: B6.Cg-2310039L15RikTg(Prnp-SNCA*A53T)23Mkle/J. Formerly: B6.Cg-Tg(Prnp-SNCA*A53T)23Mkle/J
Genetic Background: Established as C3H/HeJ x C57BL6/J hybrids, then maintained by backcrossing to C57Bl6/J.
Availability: Available through The Jackson Laboratory, Stock# 006823, Live.

Summary

These transgenic mice overexpress human α-synuclein with a PD-associated mutation (A53T). Hemizygous mice overexpress mutant α-synuclein in the brain at levels about sixfold higher than endogenous mouse α-synuclein. They develop severe progressive motor impairments around one year of age, but no overt neuronal loss (Lee et al., 2002). The data on this page refer to phenotypes observed in hemizygous animals; homozygous mice from this strain are not viable.

The mouse prion protein (PrP) promotor drives transgene expression in these mice, resulting in widespread neuronal expression. In situ hybridization confirmed expression in neurons of the substantia nigra pars compacta. Expression was also observed in glia cells. Human α-synuclein protein appeared in a punctate pattern in the neuropil, suggesting enrichment at presynaptic terminals.

These transgenic mice exhibit normal levels of activity at five months of age, but become hyperactive by nine months (Unger et al., 2006). Moreover, around 10 months of age they begin to develop severe motor impairments (Lee et al., 2002). Early signs of impairment include wobbling and posturing. Within a few days, total locomotor activity decreases and spontaneous movements slow. Stiffness of the tail was noted. Ultimately, the mice are unable to right themselves and reach end-stage disease, typically within 14–21 days of onset. The motor phenotype is reportedly about 90 percent penetrant, with 10 percent of mice escaping impairment at 16 to 18 months of age (The Jackson Laboratory, Stock # 006823, January 2019). Mice that do not develop motor abnormalities remain hyperactive as late as 19 months (Unger et al., 2006).

Cognitive defects also have been reported. At 11–12 months of age, spatial memory was impaired as assessed by the Barnes circular maze (Teravskis et al., 2018).

Neuropathologically, affected G2-3 mice exhibit accumulation of α-synuclein protein in certain neuronal populations, including the midbrain, cerebellum, brainstem, and spinal cord (including ventral horn motor neurons). In addition, these neurons accumulate ubiquitin and phosphorylated neurofilament-H. The protein aggregates do not resemble Lewy bodies, but are thioflavin-S-positive, indicating a fibrillar structure. These protein accumulations were absent in young mice (two to four months of age) but were detectable in presymptomatic older mice.

Although the transgene is expressed in the substantia nigra, significant pathology was not observed in this region and tyrosine hydroxylase levels were not significantly different from those of wild-type mice. However, levels of LC3-II, a protein involved in autophagy, were reduced (Pupyshev et al., 2018), and increased D1 receptor expression correlated with hyperactivity (Unger et al., 2006).
In the striatum, no significant loss of dopamine, or the dopamine metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) was detected after symptom onset (Lee et al., 2002). However, Pupyshev et al. reported tyrosine hydroxylase levels were reduced at five months (Pupyshev et al., 2018), and Unger et al. found the rate of dopamine uptake in isolated synaptosomes was down by 40 percent (Unger et al., 2006). Moreover, decreased expression of dopamine transporters correlated with hyperactivity in both the striatum and nucleus accumbens. In addition, striatal LC3-II levels were reduced (Pupyshev et al., 2018).

Reactive gliosis is another neuropathological feature of these mice. Compared with age-matched non-transgenic controls, symptomatic G2-3 mice exhibited higher levels of GFAP immunoreactivity in the midbrain, deep cerebellar nuclei, brainstem, and spinal cord. In contrast, GFAP immunoreactivity was comparable to controls in the cortex, hippocampus, thalamus, and caudate/putamen.

Mitochondrial alterations also have been reported. At 11–14 months of age, mitochondria in brainstem neurons were enlarged and their co-localization with the mitochondrial fission protein Drp1 was reduced. In addition, rod-shaped actin inclusions were detected, suggesting reorganization of the actin cytoskeleton may contribute to mitochondrial dysfunction (Ordonez et al., 2018).

Moreover, defects in hippocampal synaptic function appear to surface at an early age (Teravskis et al., 2018). Evoked synaptic responses measured in CA1 pyramidal neurons from hippocampal slices of 3- to 6-month-old mice were comparable to those of non-transgenic animals. However, the amplitude of miniature postsynaptic currents and the ratio of AMPA to NMDA receptor currents were reduced. In addition, long-term potentiation was suppressed.

Hemizygous G2-3 mice are viable and fertile prior to symptom onset, but female carriers do not breed well (The Jackson Laboratory, Stock # 006823, January 2019).

Modification Details

The transgene consists of the human α-synuclein sequence with the A53T mutation driven by the mouse prion protein (PrP) promoter. The transgene inserted at Chr10:95350683-95399000 (Build GRCm38/mm10), causing a 249 Kb deletion that disrupted the 2310039L15Rik gene, which codes for a lincRNA (Goodwin et al., 2017).

Phenotype Characterization

When visualized, these models will distributed over a 18 month timeline demarcated at the following intervals: 1mo, 3mo, 6mo, 9mo, 12mo, 15mo, 18mo+.

Absent

  • Neuronal Loss

No Data

Neuronal Loss

Overt neuronal loss was not reported in these mice.

Dopamine Deficiency

In symptomatic mice, striatal dopamine and metabolites DOPAC and HVA are comparable to wildtype, but at 5 months, striatal tyrosine hydroxylase is reduced.  Increased D1 receptors in the substantia nigra and decreased dopamine transporters in the nucleus accumbens and striatum have been reported.

α-synuclein Inclusions

Prior to motor deficits, these mice develop accumulations of α-synuclein in select neuronal populations, including the midbrain, cerebellum, brainstem, and spinal cord. The protein aggregates do not resemble Lewy bodies, but are thioflavin-S-positive, indicating fibrillar structure.

Neuroinflammation

In symptomatic mice, increased GFAP immunoreactivity was observed in select brain regions, including the dorsal midbrain, deep cerebellar nuclei, brainstem, and spinal cord. Cortex, hippocampus, and substantia nigra did not have increased reactivity compared with non-Tg controls.

Mitochondrial Abnormalities

At 11–14 months, mitochondria in brainstem neurons were enlarged and their co-localization with the mitochondrial fission protein Drp1 was reduced.

Motor Impairment

These mice develop severe motor impairment starting around 9-16 months of age. The deficits start out with mild hyperactivity at 7 months and progress to a wobbling movement, decreased activity, and ultimately paralysis and death.

Cognitive Dysfunction

At 11–12 months, spatial memory was impaired as assessed by the Barnes circular maze.

Last Updated: 08 Feb 2019

COMMENTS / QUESTIONS

  1. This paper rigorously demonstrates that overexpression of one mutant form of alpha-synuclein results in synuclein aggregation, inclusions, and neurological disease while overexpression of wild-type human synuclein and another mutant does not. These mice should be very useful for further studying the pathophysiology of alpha-synucleinopathies.

    View all comments by David Holtzman

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References

Paper Citations

  1. . Human alpha-synuclein-harboring familial Parkinson's disease-linked Ala-53 --> Thr mutation causes neurodegenerative disease with alpha-synuclein aggregation in transgenic mice. Proc Natl Acad Sci U S A. 2002 Jun 25;99(13):8968-73. PubMed.
  2. . A53T Mutant Alpha-Synuclein Induces Tau-Dependent Postsynaptic Impairment Independently of Neurodegenerative Changes. J Neurosci. 2018 Nov 7;38(45):9754-9767. Epub 2018 Sep 24 PubMed.
  3. . Suppression of autophagy in the brain of transgenic mice with overexpression of А53Т-mutant α-synuclein as an early event at synucleinopathy progression. Neurosci Lett. 2018 Apr 13;672:140-144. Epub 2017 Dec 2 PubMed.
  4. . Locomotor hyperactivity and alterations in dopamine neurotransmission are associated with overexpression of A53T mutant human alpha-synuclein in mice. Neurobiol Dis. 2006 Feb;21(2):431-43. Epub 2005 Oct 14 PubMed.
  5. . α-synuclein Induces Mitochondrial Dysfunction through Spectrin and the Actin Cytoskeleton. Neuron. 2018 Jan 3;97(1):108-124.e6. Epub 2017 Dec 14 PubMed.
  6. . Large-scale discovery of mouse transgenic integration sites reveals frequent structural variation and insertional mutagenesis. bioRxiv preprint first posted online Dec. 18, 2017

External Citations

  1. Unger et al., 2006
  2. The Jackson Laboratory, Stock # 006823
  3. The Jackson Laboratory, Stock# 006823

Further Reading