Leucine-rich repeat kinase-2 (LRRK2) R1441G knockin mice are more susceptible to rotenone toxicity

Abstract

OBJECTIVE: To assess the susceptibility of LRRK2 R1441G knockin mice against (1) striatal dopamine (DA) uptake deficit, (2) locomotor inactivity and, (3) dopaminergic neuronal cell death, as induced by rotenone (mitochondrial complex-I inhibitor). BACKGROUND: LRRK2 mutations are the commonest genetic risk in Parkinson's disease (PD). LRRK2 is linked to synapse functions. However, the pathogenic mechanism of LRRK2 mutation in striatal DA homeostasis and mitochondria dysfunction is unknown. METHODS: Cell viability of primary DA neurons from R1441G knockin mice and their wild-type littermates were compared after rotenone exposure. Total [3H]-DA uptake in isolated striatal synaptosomes incubated with rotenone, and the locomotor activity in open-field test after chronic (20 weeks) oral gavage of rotenone were also assessed. RESULTS: Without rotenone, R1441G mutant mice show no overt phenotype. However, synaptosomes from young (3-month-old) mutant mice exhibited lower DA uptake when incubated with rotenone (100nM), compared with wild-type controls. Number of tyrosine hydroxylase (TH)-positive neurons in mutant culture after rotenone exposure (5nM) was significantly lower. Also, chronic exposure to rotenone (5mg/kg, twice per week orally) for 20 weeks caused significantly lower locomotor activity in mutant mice compared with the wild-type controls. CONCLUSIONS: Similar to R1441C [1], LRRK2 R1441G mutant mice show no overt phenotype. However, R1441G mutant synaptosomes were more vulnerable to rotenone toxicity as shown by lower DA uptake, indicating that R1441G mutation contributes to mitochondrial dysfunction-induced synaptic dysfunction. Re-uptake of extracellular DA requires mitochondrial ATP for synaptic recycling. Uptake deficits associated with LRRK2 mutation may adversely affects striatal neuronal survival and locomotor activity as observed in our mutant mice. This differential susceptibility against rotenone toxicity of the mutant mice suggests that LRRK2 R1441G mutation may be a predisposing genetic factor in synaptic energy deficiency leading to early striatal synaptic dysfunction [2], and later nigrostriatal DA cell death in LRRK2-associated PD.