Dysregulated ac4C modification of mRNA in a mouse model of early-stage Alzheimer's disease.

Background: The identification and intervention of Alzheimer's Disease (AD) in its early-stage allows for the timely implementation of lifestyle modifications and therapeutic strategies. Although dysregulation of protein expression has been reported in the brain from AD patients and AD animal models, the underlying mechanisms remain poorly understood. N4-acetylcytidine (ac4C), the only known form of RNA acetylation in eukaryotes, has recently been shown to regulate mRNA stability and translation efficiency. However, the dysregulation of ac4C associated with abnormal protein expression levels in the brain of early-stage mouse models of AD remains to be elucidated.

Methods: This study investigated ac4C modifications, mRNA and protein expression in the hippocampus of 3 and 6-month-old 5×FAD mice, a mouse model of AD, and wild-type (WT) littermates. The multi-omics analysis was performed: acetylated RNA immunoprecipitation followed by next-generation sequencing (acRIP-seq) to identify ac4C mRNAs, deep RNA sequencing (RNA-seq) to quantify mRNA abundance, and label-free quantitative proteomics to assess protein expression levels. In addition, we used acRIP-qPCR, regular qPCR and western blots to verify the ac4C, mRNA and protein levels of some key genes that were identified by the high-throughput assays.

Results: Proteomic analysis revealed significant change of protein expression in the hippocampus of 3-months-old 5×FAD mice, compared with WT littermates. In contrast, RNA-seq analysis indicated that there were no substantial alterations in mRNA expression levels in the hippocampus of 3-months-old 5×FAD mice, compared to WT littermates. Strikingly, acRIP-seq revealed notable variations in ac4C modification on mRNAs, particularly those associated with synaptic structure and function, in the hippocampus of 3-months-old 5×FAD mice, compared with WT littermates. The ac4C modifications were found to be correlated with protein expression changes. Genes that are essential for synaptic function and cognition, including GRIN1, MAP2, and DNAJC6, exhibited reduced ac4C and protein levels in 3-months-old 5×FAD mice, without any corresponding changes in the mRNA levels, compared with WT littermates. Moreover, only a small part of dysregulated ac4C mRNAs identified in the 3-month-old 5×FAD mice were found in the 6-month-old 5×FAD mice.

Conclusions: Altogether these results identified abnormal ac4C modification of mRNAs that may contribute to the dysregulation of protein synthesis in the hippocampus from an early-stage mouse model of AD.