Mutations: LRRK2 G2019S
Modification: LRRK2: Transgenic
Disease Relevance: Parkinson's Disease
Strain Name: NTac:SD-Tg(LRRK2*G2019S)571CJLi
Genetic Background: Sprague-Dawley
Availability: Available through Taconic, Cat# 10681, Live.
This transgenic rat model overexpresses mutant Lrrk2. It was originally developed in the laboratory of Chenjian Li and then re-derived at Taconic with the support of the Micheal J. Fox Foundation.
This model expresses high levels of mutant Lrrk2 in the brain. An early study found approximately 20-30x more Lrrk2 in transgenic rats than in nonTg rats. However, as the BAC line stabilized, expression levels have stabilized at about 4fold increase over endogenous levels (Andrew West, pers comm. February 2017). Expression was highest in the striatum and cortex. In contrast to nonTg rats, in which cortical expression is largely restricted to layer V, transgenic rats exhibit expression in layers II-V. In the midbrain, Lrrk2 expression was seen in dopaminergic neurons of the substantia nigra pars compacta (SNpc), but not in the substantia nigra pars reticulata. In the striatum, scattered large neurons were strongly positive for Lrrk2 protein (West et al., 2014).
Another study found Lrrk2 expression levels to be five to eight times greater in transgenic rats than in nonTg rats at eight months of age. Again, clear expression was observed in the cortex and ventral midbrain, including the SNpc. In the midbrain, Lrrk2 expression was highly co-localized with dopaminergic neurons, that is, neurons co-labeling with tyrosine hydroxylase (TH) (Lee et al., 2015).
Despite high levels of Lrrk2 overexpression, these rats do not develop overt loss of dopaminergic neurons in the substantia nigra or striatum out to 12 months of age. Nor do they develop gross changes in cellular morphology, although quantitative morphometric analysis revealed dopaminergic neurons in the SNpc to be abnormally elongated compared with nonTg neurons. Total cell body area was not significantly affected (Lee et al., 2015). Neurodegeneration could be elicited in 10-12 week old rats by intracranial injection of recombinant adeno-association viral vectors (AAV) expressing human α-synuclein. In this paradigm rats expressing G2019S were more vulnerable than control rats to neurodegeneration and inflammation in the substantia nigra (Daher et al., 2015).
Transgenic rats exhibited elevated levels of oxidative and nitrosative stress in the midbrain. Specifically, individual nigral dopaminergic neurons in transgenic rats had a higher ratio of oxidized (S-S) thiols to reduced (SH) thiols compared with nonTg controls. Similarly, levels of nitrotryrosine (3-NT) in dopaminergic neurons of the substantia nigra were increased nearly twofold in transgenic rats. Levels of iNOS expression were elevated in nigral dopaminergic neurons, suggestive of neuroinflammation. However, there were no detectable differences in microglia density in the substantia nigra or in the morphology of IBA-1 positive cells at 12 months of age. Similarly, there was no change in the number of reactive astrocytes as assessed by GFAP staining in the substantia nigra (Lee et al., 2015).
In the striatum, expression of G2019S Lrrk2 in transgenic rats did not induce changes in dopamine levels, nor the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC), or the rate of dopamine turnover in eight- and 12-month-old rats. At 12 months of age transgenic rats exhibited significantly more homovanillic acid (HVA). Serotonin levels in the striatum were unchanged. The density of dopaminergic terminals in the striatum were unchanged (Lee et al., 2015).
Under basal conditions, these rats do not develop α-synuclein inclusions. However, they demonstrated a greater propensity to develop inclusions when α-synuclein fibrils, but not monomers, were injected in the SNpc (Volpicelli-Daley et al., 2016).
Behaviorally, these rats exhibit mild age-specific motor abnormalities. In terms of postural instability, they were comparable to nonTg rats at four and 12 months of age, with slightly more instability at eight months of age. In a rearing test, they reared a comparable number of times to nonTg rats at four and eight months of age, but exhibited significantly more rearing events at 12 months of age than nonTg controls (Lee et al., 2015).
The above description refers to hemizygous rats.
These rats carry a BAC construct carrying the human gene Lrrk2 with the G2019S mutation.
When visualized, these models will distributed over a 18 month timeline demarcated at the following intervals: 1mo, 3mo, 6mo, 9mo, 12mo, 15mo, 18mo+.
- Dopamine Deficiency
- α-synuclein Inclusions
- Neuronal Loss
- Mitochondrial Abnormalities
- Cognitive Dysfunction
Under basal conditions no α-synuclein inclusions were observed. Inclusions could be induced by exogenous α-synuclein (e.g., viral transduction or fibril intracerebral injection). LRRK2 rats were more prone to inclusion formation under these conditions.
No increase in Iba-1 positive microglia or GFAP-positive astrocytes in the substantia nigra at 12 months of age. However, iNOS expression was elevated in nigral dopaminergic neurons.
No change in striatal dopamine levels. No change in 3,4-dihydroxyphenylacetic acid (DOPAC) levels. No change in the rate of dopamine turnover. At 12 months of age transgenic rats exhibited higher levels of striatal homovanillic acid (HVA).
Mild abnormalities in motor behavior. Slightly more postural instability at eight months of age (but not at 4 and 12 months). Slightly more rearing events at 12 months, but not at younger ages.
No overt loss of dopaminergic neurons in the substantia nigra out to 12 months of age.
- 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.
- Lee JW, Tapias V, Di Maio R, Greenamyre JT, Cannon JR. Behavioral, neurochemical, and pathologic alterations in bacterial artificial chromosome transgenic G2019S leucine-rich repeated kinase 2 rats. Neurobiol Aging. 2015 Jan;36(1):505-18. Epub 2014 Jul 15 PubMed.
- Daher JP, Abdelmotilib HA, Hu X, Volpicelli-Daley LA, Moehle MS, Fraser KB, Needle E, Chen Y, Steyn SJ, Galatsis P, Hirst WD, West AB. Leucine-rich Repeat Kinase 2 (LRRK2) Pharmacological Inhibition Abates α-Synuclein Gene-induced Neurodegeneration. J Biol Chem. 2015 Aug 7;290(32):19433-44. Epub 2015 Jun 15 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.
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