• Parkinson’s disease (PD) is a complex age-related neurodegenerative disease associated with dopamine deficiency and both motor and nonmotor deficits. Mutations in leucine-rich repeat kinase 2 (encoded by LRRK2) have been identified in autosomal dominant late-onset PD.
• The exons 1-53 of mouse Lrrk2 gene that encode the whole molecule (ATG to STOP codon), including the promoter, 5’UTR and 3’UTR region were replaced by human counterparts in B-hLRRK2*G2019S mice. The human LRRK2 expression is driven by human LRRK2 promoter, while the transcription and translation of mouse Lrrk2 gene will be disrupted.
• Human LRRK2 mRNA was only detectable in brain from homozygous B-hLRRK2*G2019S mice, and the point mutation was confirmed via Sanger Sequencing. LRRK2 protein were detectable in cortex, hippocampus, mid-brain, thalamus and cerebellum from homozygous B-hLRRK2*G2019S mice. The antibody used showed cross-react with both human and mouse proteins.
• This model is useful in studying the role of LRRK2, and the therapeutic efficacy targeting LRRK2 in PD.

Gene targeting strategy for B-hLRRK2*G2019S mice. The exons 1-53 of mouse Lrrk2 gene that encode the whole molecule (ATG to STOP codon), including the promoter, 5’UTR and 3’UTR region were replaced by human counterparts in B-hLRRK2*G2019S mice. The human LRRK2 expression is driven by human LRRK2 promoter, while the transcription and translation of mouse Lrrk2 gene will be disrupted.

Strain specific analysis of LRRK2 mRNA expression in wild-type C57BL/6JNifdc mice and B-hLRRK2*G2019S by RT-PCR. Brian RNA were isolated from wild-type C57BL/6JNifdc mice (+/+) and homozygous B-hLRRK2*G2019S mice (H/H), then cDNA libraries were synthesized by reverse transcription, followed by PCR with mouse or human LRRK2 primers. Mouse Lrrk2 mRNA was only detectable in wild-type mice, human LRRK2 mRNA was exclusively detectable in homozygous B-hLRRK2*G2019S mice but not in wild-type mice. The point mutation of G2019S was confirmed via Sanger Sequencing.

Strain specific analysis of LRRK2 mRNA expression in wild-type C57BL/6JNifdc mice and B-hLRRK2*G2019S by RT-PCR. Striatum, mid-brain, cortex, hippocampus, lung and kidney RNA were isolated from wild-type C57BL/6JNifdc mice (+/+) and homozygous B-hLRRK2*G2019S mice (H/H, male, 12-week-old), then cDNA libraries were synthesized by reverse transcription, followed by RT-qPCR with mouse or human LRRK2 primers. Mouse Lrrk2 mRNA was only detectable in wild-type mice, human LRRK2 mRNA was exclusively detectable in homozygous B-hLRRK2*G2019S mice but not in wild-type mice. Mouse Gapdh served as an internal reference gene, and LRRK2 expression in other tissues was normalized to that in the mid-brain.

Western blot analysis of LRRK2 protein expression in homozygous B-hLRRK2*G2019S mice. Various tissue were collected from wild-type C57BL/6JNifdc mice (+/+) and homozygous B-hLRRK2*G2019S mice (H/H), and then analyzed by western blot with anti-LRRK2 antibody (Abcam, ab133474). 40 μg total proteins were loaded for western blotting analysis. LRRK2 was detected in both wild-type mice and homozygous B-hLRRK2*G2019S mice, as the antibody is cross-recognized both human and mouse LRRK2.

The inhibitory efficiency of the LRRK2-targeted small nucleic acid drug in homozygous B-hLRRK2*G2019S mice. B-hLRRK2*G2019S mice were randomly divided into 2 groups (n=4, 8-week-old, male). The human LRRK2-targeted nucleic acid drug (Test Article 1, TA1, produced in-house according to a patent) and artificial cerebrospinal fluid (αCSF) were administered to the mice individually. The mice were sacrificed on day 14, and the brains (cortex, hippocampus, mid-brain and striatum) were collected to detect the human LRRK2 expression by qRT-PCR. (A) The schematic diagram of experimental processing. (B) The expression of human LRRK2 mRNA in cortex, hippocampus, mid-brain and striatum. Gapdh served as an internal reference gene, and LRRK2 expression in other tissues was normalized to that in the mid-brain. The human LRRK2 mRNA in the treatment group was significantly reduced compared to the control group. Values are expressed as mean ± SEM. Significance was determined by 2-way ANOVA.  *P < 0.05, **P < 0.01, ***P < 0.001.