Zhang Yao, Li Yufei, Zhang Lin, Li Zhaoqing, Lin Keqin, Huang Kai, Yang Zhaoqing, Ma Shaohui, Sun Hao, Zhang Xiaochao
School of Pharmaceutical Sciences, Yunnan Key Laboratory of Pharmacology for Natural Products, Kunming Medical University, Kunming, China.
Department of Medical Genetics, Institute of Medical Biology, Chinese Academy of Medical Sciences & Peking Union Medical College, Kunming, China.
Animal Model Exp Med. 2025 Jun 24. doi: 10.1002/ame2.70047.
Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disease marked by significant clinical and genetic heterogeneity, primarily caused by expanded CAG mutations in the ATXN2 gene. The unstable expansion of CAG repeats disrupts the genetic stability of animal models, which is detrimental to disease research.
In this study, we established a mouse model in which CAG repeats do not undergo microsatellite instability (MSI) across generations. A humanized ATXN2 cDNA with four CAA interruptions within 73 CAG expansions was inserted into the Rosa26 locus of C57BL/6J mice. A 23 CAG control mouse model was also generated to verify ATXN2 integration and expression.
In our model, the number of CAG repeats remained stable during transmission, with no CAG repeat expansion observed in 64 parent-to-offspring transmissions. Compared with SCA2-Q23 mice, SCA2-Q73 mice exhibited progressive motor impairment, reduced Purkinje cell count and volume (indicative of cell atrophy), and muscle atrophy. These observations in the mice suggest that the behavioral and neuropathological phenotypes may reflect the features of SCA2 patients. RNA-seq analysis of the gastrocnemius muscle in SCA2-Q73 mice showed significant changes in muscle differentiation and development gene expression at 56 weeks, with no significant differences at 16 weeks compared to SCA2-Q23 mice. The expression level of the Myf6 gene significantly changed in the muscles of aged mice.
In summary, the establishment of this model not only provides a stable animal model for studying CAG transmission in SCA2 but also indicates that the lack of long-term neural stimulation leads to muscle atrophy.
2型脊髓小脑共济失调（SCA2）是一种神经退行性疾病，具有显著的临床和遗传异质性，主要由ATXN2基因中的CAG突变扩增引起。CAG重复序列的不稳定扩增破坏了动物模型的遗传稳定性，不利于疾病研究。
在本研究中，我们建立了一个小鼠模型，其中CAG重复序列在代际间不发生微卫星不稳定性（MSI）。将在73个CAG扩增中有四个CAA中断的人源化ATXN2 cDNA插入C57BL/6J小鼠的Rosa26位点。还构建了一个含有23个CAG的对照小鼠模型，以验证ATXN2的整合和表达。
在我们的模型中，CAG重复序列的数量在传递过程中保持稳定，在64次亲代到子代的传递中未观察到CAG重复序列的扩增。与SCA2-Q23小鼠相比，SCA2-Q73小鼠表现出进行性运动障碍、浦肯野细胞数量和体积减少（表明细胞萎缩）以及肌肉萎缩。小鼠中的这些观察结果表明，行为和神经病理表型可能反映了SCA2患者的特征。对SCA2-Q73小鼠腓肠肌的RNA测序分析显示，在56周时肌肉分化和发育基因表达有显著变化，与SCA2-Q23小鼠相比，在16周时无显著差异。Myf6基因的表达水平在老年小鼠的肌肉中显著变化。
总之，该模型的建立不仅为研究SCA2中CAG传递提供了一个稳定的动物模型，还表明长期缺乏神经刺激会导致肌肉萎缩。
