Objective: Inter-species differences between mouse and human α-synuclein (asyn) may influence aggregation and pathology in animal models, highlighting the need for models expressing human asyn. To address this gap, we generated a human asyn knock-in (KI) mouse in which the endogenous mouse asyn coding sequence was replaced with the full-length human sequence.

Background: Lewy body disorders, including Parkinson’s disease (PD), are characterized by pathological aggregation of asyn. In animal studies, species related biological differences can alter aggregation, fibril seeding, and propagation of pathology, potentially limiting how faithfully these models reproduce human disease mechanisms.

Method: Human SNCA cDNA was targeted to the endogenous SNCA locus in C57BL/6 mice using homologous recombination. Heterozygous and homozygous mice were obtained by breeding. Genotyping was confirmed by PCR, and expression of human asyn was assessed biochemically. In addition to health and survival, mice of all genotypes were also challenged with hippocampal injections of human wild-type preformed fibrils (PFFs). Brains were analyzed histologically at 1- and 3-months post-injection (MPI).

Results: PCR and Whole genome sequencing (WGS) confirmed the KI of human SNCA. Comparable expression of human asyn was detected in brains of homozygous KI mice versus mouse asyn in wild-type animals while peripheral expression was lower. Heterozygous mice have reached 20 months and homozygous mice 15 months without adverse health effects thus far. No phosphorylated asyn aggregates were detected at 1 MPI with PFFs; however, Lewy body–like aggregates and neuritic pathology were observed in the dentate gyrus at 3 MPI.

Conclusion: We established a stable SNCA KI C57BL/6 mouse line expressing human asyn under endogenous regulatory control. By exclusively producing human asyn, this model may better recapitulate aspects of human PD pathology, including its slower progression, and provides a biochemically relevant platform for mechanistic studies and preclinical evaluation of therapeutic strategies, including immunotherapies.

References: 1) Koprich, J., Kalia, L. & Brotchie, J. Animal models of α-synucleinopathy for Parkinson disease drug development. Nat Rev Neurosci 18, 515–529 (2017).
2) Luk KC et al. Molecular and Biological Compatibility with Host Alpha-Synuclein Influences Fibril Pathogenicity. Cell Rep. Sep 20;16(12):3373-3387 (2016).
3) Sokratian A et al. Mouse α-synuclein fibrils are structurally and functionally distinct from human fibrils associated with Lewy body diseases. Sci Adv. Nov;10(44):eadq3539 (2024).
4) Fernagut PO, Chesselet MF. Alpha-synuclein and transgenic mouse models. Neurobiology of Disease, 17(2):123-130 (2004).

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MDS Abstracts - https://www.mdsabstracts.org/abstract/human-snca-knock-in-mouse-as-a-model-for-synucleinopathy-research/