Mutations: LRRK2 G2019S
Modification: LRRK2: Transgenic
Disease Relevance: Parkinson's Disease
Strain Name: B6.Cg-Tg(Lrrk2*G2019S)2Yue/J
Genetic Background: A BAC construct was injected into B6C3 F1 oocytes. Founder line 2 was established and maintained by breeding to C57BL/6J inbred mice.
Availability: Available through The Jackson Lab, Stock# 012467, Live.
This transgenic mouse overexpresses a mutant form of Lrrk2 in the brain using a bacterial artificial chromosome (BAC) (Li et al., 2010). Transgene expression is driven by the mouse Lrrk2 promoter sequence. Hemizygous mice develop an age-associated decrease in striatal dopamine, but no loss of dopaminergic neurons or behavioral motor deficits.
Hemizygous mice are viable, fertile, and do not have any overt brain abnormalities, at least out to 18 months of age. Immunoblots of whole-brain lysate indicate that the mutant protein is present at levels about sixfold above endogenous levels (Li et al., 2010) or as much as 20-30-fold (West et al., 2014). Lrrk2 expression is observed in the cerebral cortex, striatum, substantia nigra, internal capsule, and hippocampus (Li et al., 2010). The highest expression levels were observed in the cortex and striatum with clear expression in the substantia nigra pars compacta, but not in the substantia nigra pars reticulata. Overall, the pattern of Lrrk2 expression in this transgenic is consistent with the distribution of Lrrk2 protein observed in nonTg mice (West et al., 2014).
Overexpression of mutant Lrrk2 in this model did not alter motor performance in hemizygous mice. They performed like wild-type controls in the open-field test and in a test of motor coordination involving walking across a beam (Li et al., 2010).
Hemizygous mice displayed no signs of neuronal or other cell death in any brain region, including the cortex, striatum, and hippocampus. There was no difference in the number of dopaminergic neurons in the substantia nigra compared to littermate controls at six or 12 months. In addition, nigrostriatal terminals appeared normal at six and 12 months. Lrrk2-G2019S protein purified from transgenic brains had higher kinase activity than wild-type Lrrk2 (Li et al., 2010).
The brains of BAC-Lrrk2-G2019S mice showed no evidence of α-synuclein aggregation or deposits (Li et al., 2010).
Hemizygous BAC-Lrrk2-G2019S mice develop an age-related decline in striatal dopamine content. Levels were not different from littermate controls at six months of age, but by 12 months of age, mutant mice had 25 percent less dopamine and less homovanillic acid (HVA), a dopamine metabolite. Levels of tyrosine hydroxylase in the striatum were comparable to controls at 10 months of age; likewise, enzymatic activity levels were unchanged.
In striatal slices taken from mice at one year of age, the peak amount of evoked dopamine was lower in BAC-Lrrk2-G2019S mice than in littermate controls. This effect was not seen at six months of age. In addition, the decrease in evoked dopamine was accompanied by a decrease in dopamine reuptake, which may be a compensatory response (Li et al., 2010).
Electrophysiological studies in acute hippocampal slices have shown impaired synaptic plasticity in BAC-Lrrk2-G2019S mice. Specifically, LRRK2-G2019S mice showed a profound deficit in synaptically induced long-term depression whereas mice expressing wild-type Lrkk2 did not. Long-term potentiation was not affected. In terms of basal synaptic transmission, mutant mice had higher basal efficiency than mice expressing wild-type Lrrk2. These changes were observed in aged mice (8-12 months) but not in young mice (3-6 months). Presynaptic function appeared intact as assessed by measuring paired-pulse facilitation, post-tetanic potentiation, and the response to a train of stimuli (Sweet et al., 2015).
Lrrk2 protein levels were reported to be 10-12 fold higher in cultured mutant neurons compared to nonTg neurons. Mutant neurons also had increased levels of α-synuclein protein (about 1.5 fold higher than nonTg neurons). Furthermore, 18 days after exposure to exogenous α-synuclein fibrils, the mutant neurons developed more α-synuclein inclusions than nonTg neurons. The inclusions generally colocalized with tau along axons, but were also seen in the cell body (Volpicelli-Daley et al., 2016). Inclusions were absent from neurons not exposed to fibrils.
There were no overt morphological differences in cultured neurons from Lrkk2-G2019S mice and nonTg neurons and quantification of confocal images revealed no significant differences in the abundance of axons, dendrites, or total cells numbers in culture (Volpicelli-Daley et al., 2016). Although the mutant neurons develop elaborate arbors, their growth rate was found to be somewhat reduced compared to nonTg neurons and time lapse imaging revealed reduced neurite motility (Sepulveda et al., 2013)
The description above refers to hemizygous mice. Homozygous mice are viable and have higher levels of mutant protein expression (personal communication, Zhenyu Yue, January 2017). They have not yet been phenotypically characterized.
This model was generated using a bacterial artificial chromosome (BAC) containing the entire mouse Lrrk2 gene was modified to include the G2019S mutation. The BAC (~240 kb) contained the murine Lrrk2 promoter region (~35 kb) and a FLAG-tag downstream of the start codon. The transgene inserted at Chr18:44968085 (Build GRCm38/mm10), where it does not affect any known genes (Goodwin et al., 2017).
When visualized, these models will distributed over a 18 month timeline demarcated at the following intervals: 1mo, 3mo, 6mo, 9mo, 12mo, 15mo, 18mo+.
- α-synuclein Inclusions
- Motor Impairment
- Neuronal Loss
- Mitochondrial Abnormalities
- Cognitive Dysfunction
No evidence of α-synuclein inclusions up to 18 months of age.
Age-related decline in striatal dopamine content. Levels were decreased at 12 months of age, but not significantly different from controls at six months of age. Also, decreased dopamine metabolite homovanillic acid (HVA).
Behavior in hemizygous mice was comparable to littermate controls in terms of activity levels (open-field test) and coordination (beam-walk test) at 6 and 12 months.
No evidence of neuronal or other cell death in any brain region, including the cortex, striatum, and hippocampus. There was no difference in the number of dopaminergic neurons in the substantia nigra compared to littermate controls at six or 12 months.
- Li X, Patel JC, Wang J, Avshalumov MV, Nicholson C, Buxbaum JD, Elder GA, Rice ME, Yue Z. Enhanced striatal dopamine transmission and motor performance with LRRK2 overexpression in mice is eliminated by familial Parkinson's disease mutation G2019S. J Neurosci. 2010 Feb 3;30(5):1788-97. PubMed.
- West AB, Cowell RM, Daher JP, Moehle MS, Hinkle KM, Melrose HL, Standaert DG, Volpicelli-Daley LA. Differential LRRK2 expression in the cortex, striatum, and substantia nigra in transgenic and nontransgenic rodents. J Comp Neurol. 2014 Aug 1;522(11):2465-80. Epub 2014 Apr 12 PubMed.
- Sweet ES, Saunier-Rebori B, Yue Z, Blitzer RD. The Parkinson's Disease-Associated Mutation LRRK2-G2019S Impairs Synaptic Plasticity in Mouse Hippocampus. J Neurosci. 2015 Aug 12;35(32):11190-5. PubMed.
- Volpicelli-Daley LA, Abdelmotilib H, Liu Z, Stoyka L, Daher JP, Milnerwood AJ, Unni VK, Hirst WD, Yue Z, Zhao HT, Fraser K, Kennedy RE, West AB. G2019S-LRRK2 Expression Augments α-Synuclein Sequestration into Inclusions in Neurons. J Neurosci. 2016 Jul 13;36(28):7415-27. PubMed.
- Sepulveda B, Mesias R, Li X, Yue Z, Benson DL. Short- and long-term effects of LRRK2 on axon and dendrite growth. PLoS One. 2013;8(4):e61986. Print 2013 PubMed.
- Goodwin LO, Splinter E, Davis TL, Urban R, He H, Braun RE, Chesler EJ, Kumar V, van Min M, Ndukum J, Philip VM, Reinholdt LG, Svenson K, White JK, Sasner M, Lutz C, Murray SA. Large-scale discovery of mouse transgenic integration sites reveals frequent structural variation and insertional mutagenesis. bioRxiv preprint first posted online Dec. 18, 2017
No Available Further Reading