AbstractIntroduction and AimsAlzheimer's disease (AD) is characterized by the abnormal accumulation of hyperphosphorylated tau proteins and amyloid‐beta (Aβ) peptides. Recent studies have shown that many microRNAs (miRNAs) are dysregulated in AD, and modulation of these miRNAs can influence the development of tau and Aβ pathology. The brain‐specific miRNA miR‐128, encoded byMIR128‐1andMIR128‐2, is important for brain development and dysregulated in AD. In this study, the role of miR‐128 in tau and Aβ pathology as well as the regulatory mechanism underlying its dysregulation were investigated.MethodsThe effect of miR‐128 on tau phosphorylation and Aβ accumulation was examined in AD cellular models through miR‐128 overexpression and inhibition. The therapeutic potential of miR‐128 in AD mouse model was assessed by comparing phenotypes of 5XFAD mice administered with miR‐128‐expressing AAVs with 5XFAD mice administered with control AAVs. Phenotypes examined included behavior, plaque load, and protein expression. The regulatory factor of miR‐128 transcription was identified through luciferase reporter assay and validated by siRNA knockdown and ChIP analysis.ResultsBoth gain‐of‐function and loss‐of‐function studies in AD cellular models reveal that miR‐128 represses tau phosphorylation and Aβ secretion. Subsequent investigations show that miR‐128 directly inhibits the expression of tau phosphorylation kinase GSK3β and Aβ modulators APPBP2 and mTOR. Upregulation of miR‐128 in the hippocampus of 5XFAD mice ameliorates learning and memory impairments, decreases plaque deposition, and enhances autophagic flux. We further demonstrated that C/EBPα transactivatesMIR128‐1transcription, while both C/EBPα and miR‐128 expression are inhibited by Aβ.ConclusionOur findings suggest that miR‐128 suppresses AD pathogenesis, and could be a promising therapeutic target for AD. We also find a possible mechanism underlying the dysregulation of miR‐128 in AD, in which Aβ reduces miR‐128 expression by inhibiting C/EBPα.