Department of Laboratory Medicine, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, 430030, China.
Departments of Pathophysiology, Guangxi Medical University, Nanning, 530021, China.
Transl Neurodegener. 2023 Nov 28;12(1):53. doi: 10.1186/s40035-023-00386-6.
Synaptic degeneration occurs in the early stage of Alzheimer's disease (AD) before devastating symptoms, strongly correlated with cognitive decline. Circular RNAs (circRNAs) are abundantly enriched in neural tissues, and aberrant expression of circRNAs precedes AD symptoms, significantly correlated with clinical dementia severity. However, the direct relationship between circRNA dysregulation and synaptic impairment in the early stage of AD remains poorly understood.
Hippocampal whole-transcriptome sequencing was performed to identify dysregulated circRNAs and miRNAs in 4-month-old wild-type and APP/PS1 mice. RNA antisense purification and mass spectrometry were utilized to unveil interactions between circRIMS2 and methyltransferase 3, N6-adenosine-methyltransferase complex catalytic subunit (METTL3). The roles of circRIMS2/miR-3968 in synaptic targeting of UBE2K-mediated ubiquitination of GluN2B subunit of NMDA receptor were evaluated via numerous lentiviruses followed by morphological staining, co-immunoprecipitation and behavioral testing. Further, a membrane-permeable peptide was used to block the ubiquitination of K1082 on GluN2B in AD mice.
circRIMS2 was significantly upregulated in 4-month-old APP/PS1 mice, which was mediated by METTL3-dependent N6-methyladenosine (m6A) modification. Overexpression of circRIMS2 led to synaptic and memory impairments in 4-month-old C57BL/6 mice. MiR-3968/UBE2K was validated as the downstream of circRIMS2. Elevated UBE2K induced synaptic dysfunction of AD through ubiquitinating K1082 on GluN2B. Silencing METTL3 or blocking the ubiquitination of K1082 on GluN2B with a short membrane-permeable peptide remarkably rescued synaptic dysfunction in AD mice.
In conclusion, our study demonstrated that m6A-modified circRIMS2 mediates the synaptic and memory impairments in AD by activating the UBE2K-dependent ubiquitination and degradation of GluN2B via sponging miR-3968, providing novel therapeutic strategies for AD.
在阿尔茨海默病（AD）出现破坏性症状之前，突触退化就已经发生，这与认知能力下降密切相关。环状 RNA（circRNA）在神经组织中大量富集，circRNA 的异常表达先于 AD 症状出现，与临床痴呆严重程度显著相关。然而，circRNA 失调与 AD 早期突触损伤之间的直接关系仍知之甚少。
对 4 月龄野生型和 APP/PS1 小鼠的海马全转录组进行测序，以鉴定失调的 circRNA 和 miRNA。利用 RNA 反义纯化和质谱技术揭示了 circRIMS2 与甲基转移酶 3、N6-腺苷甲基转移酶复合物催化亚基（METTL3）之间的相互作用。通过多种慢病毒转染，评估 circRIMS2/miR-3968 对 UBE2K 介导的 NMDA 受体 GluN2B 亚基泛素化的突触靶向作用，并用形态学染色、共免疫沉淀和行为测试进行评价。此外，还使用一种膜通透肽来阻断 AD 小鼠中 GluN2B 上 K1082 的泛素化。
circRIMS2 在 4 月龄 APP/PS1 小鼠中显著上调，这是由 METTL3 依赖性 N6-甲基腺苷（m6A）修饰介导的。circRIMS2 的过表达导致 4 月龄 C57BL/6 小鼠的突触和记忆损伤。MiR-3968/UBE2K 被验证为 circRIMS2 的下游靶点。UBE2K 的升高通过泛素化 GluN2B 上的 K1082 导致 AD 中的突触功能障碍。沉默 METTL3 或用一种短的膜通透肽阻断 GluN2B 上 K1082 的泛素化，可显著挽救 AD 小鼠的突触功能障碍。
总之，本研究表明，m6A 修饰的 circRIMS2 通过激活 UBE2K 依赖性泛素化和降解 GluN2B，通过海绵 miR-3968 介导 AD 中的突触和记忆损伤，为 AD 提供了新的治疗策略。
