Species: Mouse
Genes: Gba1
Modification: Gba1: Knock-In
Disease Relevance: Parkinson's Disease
Strain Name: C57BL/6N-Gba1^tm1.1Mjff/J
Genetic Background: Mixed C57BL/6J and C57BL/6N background.
Availability: Available through The Jackson Laboratory, Stock# 019106, Cryopreserved.

Summary

This knock-in (KI) mouse model was generated by introducing a D427V point mutation into exon 10 of the mouse Gba1 (glucosidase, beta, acid 1) gene, which corresponds to the human D409V mutation (The Jackson Laboratory; Polinski et al., 2021). The GBA1 protein is the lipid-degrading lysosomal enzyme glucocerebrosidase (GCase), and mutations in the human GBA1 gene are a common risk factor for Parkinson’s disease and are present in up to 10% of patients (Farfel-Becker et al., 2019). Although the D409V mutation, specifically, is not usually found in patients with Parkinson’s disease, this mutation leads to reduced GCase activity, which can be associated with α-synuclein aggregation.

Heterozygous (het) and homozygous (hom) KI mice are viable and fertile, with normal litter sizes, weaning behavior, and development (Polinski et al., 2021). Body weight does not differ between KI (hom) and wild-type mice at 4, 8, or 12 months of age (Polinski et al., 2022).

Compared to wild-type controls, 4-month-old KI mice (het and hom), did not exhibit differences in Gba1 mRNA nor in GCase protein levels in frontal cortex and forebrain samples, respectively (Polinski et al., 2021). Protein levels of GBA1 also did not differ in the hippocampus and cortex of 12-month-old KI mice in a separate study (Clarke et al., 2019). However, activity of the GCase enzyme was significantly decreased in KI (hom) mouse brain and liver versus wild-type control mice at 4, 8, and 12 months of age (Polinski et al., 2021). Accordingly, this decrease in activity corresponded to increases in levels of the GCase substrate glucosylsphingosine in the brain and liver at these same ages in KI (hom) mice. Levels of another GCase substrate, glucosylceramide, were also increased at 12 months of age, but not at younger ages (4 and 8 months). With regard to het KI mice (5-month-old), they had significantly decreased GCase activity versus wild-type controls, but this decrease was not as extensive as in hom KI mice, and the only substrate that was increased compared to control mice was glucosylsphingosine in the brain. In a different study of het and hom KI mice, reduced GBA1 GCase activity was observed in the hippocampus and cortex at 12 months of age (Clarke et al., 2019). This study also examined GBA2 GCase activity, finding that it was reduced in the hippocampus, but not in the cortex. At 15 months of age, another study found that KI (het) mice have decreased GCase activity in the cerebral cortex, but levels of glucosylceramide and glucosylsphingosine were similar to wild-type controls (Ikuno et al., 2019).

Motor Behavior

In the primary analysis of this KI model, a functional observational battery was conducted to assess a range of mouse behaviors, including neuromuscular function, and no differences were observed between KI and wild-type mice (Polinski et al., 2021). In other studies, for the most part, D409V KI (hom) mice also displayed motor behavior (open-field activity and grip strength) that is similar to wild-type controls at 4, 8, and 12 months of age (Polinski et al., 2022). Differences between genotypes were observed only at 12 months in grip strength, with KI mice exhibiting greater force, and in the open-field assay, transiently at 8 months of age, with KI mice having more locomotor activity. In another study, no perturbations were observed in KI (het) mice on Rotarod performance or distance travelled in an open field at 12 months of age (Clarke et al., 2019). This study also assessed swim velocity (in the context of a Morris water maze assay), which did not differ between wild-type and KI (het) mice at 3, 6, 9, or 12 months of age.

Non-Motor Behaviors

Cognitive performance was assessed by the Morris water maze, and deficits in KI (het) mouse performance appeared at 12 months of age compared to wild-type mice; such deficits were not observed at 3, 6, or 9 months of age (Clarke et al., 2019). Cognitive impairment was also indicated by a reduction in spontaneous alternation in the Y-maze at 12 months of age in KI (het) mice, but not at 3, 6, or 9, months of age. Anxiety-like behavior, which was measured by time spent in the perimeter of an open field did not differ at 12 months of age in KI (het) mice versus wild-type controls.

Neuropathology

No differences in the number of dopaminergic neurons in the substantia nigra pars compacta were found between KI (hom) mice and wild-type mice at 4, 8, and 12 months of age, using unbiased stereology for quantification (Polinski et al., 2021; Polinski et al., 2022).

Dopamine neurotransmitter levels and dopamine metabolites were measured in the striata of KI (hom) mice at 4, 8, and 12 months of age (Polinski et al., 2021). Dopamine levels themselves did not differ, but dopamine turnover (as measured by the ratio of dopamine metabolites DOPAC and HVA to dopamine) tended to increase, though the increase was only significant at 12 months of age. This effect at 12 months of age went away when the dataset was analyzed in a separate study with additional groups included for comparison (Polinski et al., 2022).

Differences in striatal serotonin (5-HT) levels were found at 12, but not at 4 or 8, months of age, with KI mice having lower levels than wild-type controls (Polinski et al., 2022).

Levels of α-synuclein and its pathologic phosphorylated form pS129 did not differ in the striatum or substantia nigra of KI (hom) mice compared to that in wild-type mice, as measured by immunohistochemistry at 12 months of age (Polinski et al., 2021). In a separate study, there were also no differences observed in pS129 between wild-type and KI (hom) mice at 4 and 8 months of age, as well as in the cortex and hippocampus (Polinski et al., 2022). No significant differences between KI (het) and wild-type mice were observed in Lewy body deposition or soluble monomeric α-synuclein levels in the hippocampus at 12 months of age (Clarke et al., 2019). In KI (hom) mice, however, soluble monomeric α-synuclein levels were significantly increased in the hippocampus compared to that in KI (het) and wild-type mice.

Significant cholinergic deficits were observed in KI (het) mice at 12 months of age in the dentate gyrus, with KI mice exhibiting reduced vesicular acetylcholine transporter and increased choline acetyltransferase levels compared to wild-type mice, based on immunofluorescence (Clarke et al., 2019). Of note, these findings did not significantly bear out in semi-quantitative western blot analyses, but they did at the mRNA level, with reductions in Slc18a3 and Chat gene expression.

Neuroinflammation

Microgliosis and astrogliosis (as measured by Iba-1 and GFAP immunostaining, respectively) did not differ between KI (hom) and wild-type mice in the striatum and substantia nigra at 4, 8, or 12 months of age (Polinski et al., 2021). One exception in a separate study was a decrease observed in GFAP signaling in the substantia nigra of KI (hom) mice versus wild-type mice at 12 months of age, but not at younger ages (4 and 8 months; Polinski et al., 2022). In contrast to the above, a third study found that in the hippocampus, KI (het) mice had elevated GFAP and Iba-1 immunostaining compared to wild-type controls at 12 months of age (Clarke et al., 2019). 

Endocytic Pathway

Levels of lysosome-associated protein 1 (Lamp1) protein, a marker of lysosomal integrity, were similar between wild-type and KI (hom) mice in brain and liver samples at 4, 8, or 12 months of age (Polinski et al., 2021).

Ocular Function

Ocular pathology has been investigated in KI (hom) mice (Weber et al., 2021). KI mice have a smaller pupil diameter, which is evident by 17 months of age, but not at 2 months of age, compared to wild-type controls. Moreover, cracks and holes appear in the iris by 17 months of age, suggesting age-dependent ocular damage. Additional pathology (iris atrophy) was also observed to some extent even in younger (3-month-old) mice. Older mice (17 months of age), however, had more severe pathology, including pigment dispersion, loss of iris pigmented epithelial cells, diminished iris stroma, posterior synechia, and cataracts, among other features.

Related Models

These D409V Gba1 KI mice are also available as a cross with the Tg(Thy1-SNCA)15Mjff transgenic mouse line (The Jackson Laboratory).

Phenotype Characterization

Q&A with Model Creator

Q&A with Ying Sun

What would you say are the unique advantages of this model?

• This D409V KI model produces viable mice. Both male and female mice are fertile, making it easy to maintain the colony.
• The model has been characterized by their neurological phenotypes, brain pathology, and α-synuclein and dopaminergic neuron-related phenotypes.

What do you think this model is best used for?

• Studying the interplay of modifiers on modulating Gaucher disease and Parkinson’s disease.
• Due to the low GCase activity and mild phenotype, this model can be transformed into a severe GD model through chemical induction using CBE for testing new therapies that are not GCase-based.

What caveats are associated with this model?

• The mild phenotype and delayed disease progression will make the study costly.
• The mixed phenotypes create challenges in accurately assessing disease outcomes and therapeutic effects.

Anything else useful or particular about this model you think our readers would like to know?

• Choose appropriate controls, such as strain background, age, and sex, and use reliable reagents and protocols for your study.

COMMENTS / QUESTIONS

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References

Paper Citations

1. Polinski NK, Martinez TN, Gorodinsky A, Gareus R, Sasner M, Herberth M, Switzer R, Ahmad SO, Cosden M, Kandebo M, Drolet RE, Buckett PD, Shan W, Chen Y, Pellegrino LJ, Ellsworth GD, Dungan LB, Hirst WD, Clark SW, Dave KD. Decreased glucocerebrosidase activity and substrate accumulation of glycosphingolipids in a novel GBA1 D409V knock-in mouse model. PLoS One. 2021;16(6):e0252325. Epub 2021 Jun 9 PubMed.
2. Farfel-Becker T, Do J, Tayebi N, Sidransky E. Can GBA1-Associated Parkinson Disease Be Modeled in the Mouse?. Trends Neurosci. 2019 Sep;42(9):631-643. Epub 2019 Jul 6 PubMed.
3. Polinski NK, Martinez TN, Ramboz S, Sasner M, Herberth M, Switzer R, Ahmad SO, Pelligrino LJ, Clark SW, Marcus JN, Smith SM, Dave KD, Frasier MA. The GBA1 D409V mutation exacerbates synuclein pathology to differing extents in two alpha-synuclein models. Dis Model Mech. 2022 Jun 1;15(6) Epub 2022 May 25 PubMed.
4. Clarke E, Jantrachotechatchawan C, Buhidma Y, Broadstock M, Yu L, Howlett D, Aarsland D, Ballard C, Francis PT. Age-related neurochemical and behavioural changes in D409V/WT GBA1 mouse: Relevance to lewy body dementia. Neurochem Int. 2019 Oct;129:104502. Epub 2019 Jul 9 PubMed.
5. Ikuno M, Yamakado H, Akiyama H, Parajuli LK, Taguchi K, Hara J, Uemura N, Hatanaka Y, Higaki K, Ohno K, Tanaka M, Koike M, Hirabayashi Y, Takahashi R. GBA haploinsufficiency accelerates alpha-synuclein pathology with altered lipid metabolism in a prodromal model of Parkinson's disease. Hum Mol Genet. 2019 Jun 1;28(11):1894-1904. PubMed.

External Citations

1. The Jackson Laboratory
2. The Jackson Laboratory
3. The Jackson Laboratory, Stock# 019106
4. The Jackson Laboratory

Further Reading