Expression of the full-length human mutant (G2019S) LRRK2 protein, HA-tagged, under the control of a CMV enhancer and platelet-derived growth factor beta (PDGF).
Endogenous LRRK2: yes
Corresponding human genotype: The G2019S substitution in the LRRK2 gene is believed to be the most common mutation associated with Parkinson’s disease. It is located in the kinase domain of the protein.
Targeted gene: LRRK2
- 2-3 months: Expression of human G2019S LRRK2 is 2.7 fold higher than the level of the endogenous LRRK2. LRRK2G2019S is expressed in various part of the brain but mRNA levels are particularly high in the striatum, substantia nigra (SN), olfactory bulb, cortex, hippocampus and cerebellum.
- 10 months: Transgene is expressed in the SN in 70% of the dopaminergic cells (TH positive). It is also express in the cortex and cerebellum.
- 8-9 months: No differences in the number of TH-positive cells in the SN compared to control littermates. Similarly, the availability of striatal vesicular monoamine transporter 2 (VMAT2) remains unchanged.
- 12-16 months: A significant and progressive decrease in the number of TH-positive cells and TH positive fibres is observed respectively in the SN and striatum of transgenic animals compared to control littermates. A separate study reports no loss of striatal fibres after 20 months.
No degeneration can be observed in the cortex, hippocampus or striatum (NeuN immunostaining).
- 19-21 months: A 14-17% loss of TH-positive cells is observed in the SN of the transgenic mice compared to their non-transgenic littermates.
- 12 months: The availability of dopamine transporters (DAT) is significantly lower in transgenic animals compared to control littermates.
- 14-15 months: Normal levels of DA) and its metabolites (DOPAC, HVA) is measured in the striatum of transgenic mice. Similarly, the rate of DA turnover is unaltered. However, a drop in the levels of DOPAC and HVA can be observed in the olfactory bulb.
- 12 months: Accumulation of phosphorylated tau proteins is observed in the SN but not in the cerebellum, cortex or striatum of transgenic mice.
- Up to 23-24 months: No abnormalities can be seen on alpha-synuclein, phosphorylated alpha-synuclein, tau, phosphorylated tau or ubiquitin stained brain sections.
- Up to 16 months: Contradictory results have been reported. Transgenic animals show a significant reduction in spontaneous ambulatory activity (activity cages and open field) and altered performances on the pole test when compared to control littermates (12-16 months; Chen 2012), or do not display any significant impairment in motor abilities (open field, 6 and 15 months; Ramonet 2011).
- Response to dopaminergic treatment
- 8-9 months: L-DOPA treatment restores ambulatory activity in activity cages.
- 12 months: L-DOPA treatment reverses hypokinesia observed in the open field.
- 6 and 15 months: No impairment can be observed in the sensorimotor gating abilities of the transgenic animals.
- 8 months: Transgenic animals show a reduction of nigral dopaminergic neurons spontaneous firing rates, as well as an impaired striatal evoked dopamine release and long-term depression of corticostriatal glutamatergic transmission, compared to control littermates. However, membrane properties of DA neurons remain comparable to those of control animal (membrane capacitance, input resistance, action potential etc.)
- up to 23-24 months: No abnormalities can be seen using astrocyte marker GFAP in the striatum, midbrain or cortex.