miR-32533 Reduces Cognitive Impairment and Amyloid-β Overload by Targeting CREB5-Mediated Signaling Pathways in Alzheimer's Disease

MicroRNAs (miRNAs) are associated with amyloid-β (Aβ) dysmetabolism, a pivotal factor in the pathogenesis of Alzheimer's disease (AD). This study unveiled a novel miRNA, microRNA-32533 (miR-32533), featuring a distinctive base sequence identified through RNA sequencing of the APPswe/PSEN1dE9 (APP/PS1) mouse brain. Its role and underlying mechanisms were subsequently explored. Bioinformatics and confirmatory experiments revealed that miR-32533 had a novel 23-base sequence with minimal coding potential, functioning within the Drosha ribonuclease III (Drosha)/Dicer 1, ribonuclease III (Dicer)-dependent canonical pathway and identifiable via northern blot. miR-32533 was abundantly brain-distributed and downregulated in diverse AD-related models, including APP/PS1 and five familial AD (5×FAD) mouse brains and AD patient plasma. Overexpression or inhibition of miR-32533 led to improvements or exacerbations in cognitive dysfunction, respectively, by modulating Aβ production, apoptosis, oxidation, and neuroinflammation through targeting cAMP-responsive element binding protein 5 (CREB5), which interacted with α disintegrin and metalloproteinase 10 (ADAM10), beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), and presenilin 1 (PS1) promoters, thereby enhancing Aβ production through BACE1 and PS1 upregulation while suppressing non-amyloidogenic amyloid precursor protein (APP) processing via ADAM10 downregulation. Furthermore, modulation of the miR-32533/CREB5 axis ameliorated or worsened cognitive impairment by inhibiting or amplifying Aβ overproduction through the BACE1-involved amyloidogenic and ADAM10-involved non-amyloidogenic pathways. Overall, the findings suggest miR-32533 as a regulator of Aβ metabolism, oxidative stress, and neuroinflammation, establishing the miR-32533/CREB5 signaling pathways as potential therapeutic targets for combating Aβ accumulation and cognitive deficits in AD.