Overexpression of miR-455-3p enhances mitophagy, synaptic and mitochondrial proteins in Alzheimer's disease.

MicroRNAs (miRNAs) are small non-coding RNAs that post-transcriptionally regulate gene expression, neural development and plasticity in Alzheimer's disease (AD). Our lab recently discovered molecular links between miR-455-3p and AD. miR-455-3p is known to regulate APP expression, thereby influencing amyloid beta (Aβ) generation. Using pronuclear injection and CRISPR/Cas9 technologies, we created miR-455-3p transgenic (TG) and knockout (KO) mice. Remarkably, the miR-455-3p TG mice displayed an extended lifespan (by approximately 5 months) compared to wild-type (WT) mice, whereas miR-455-3p KO mice had a reduced lifespan (by 4 months). Behaviorally, miR-455-3p TG mice outperformed cognitive tasks such as the Morris water maze and Y-maze, indicating improved spatial memory and learning. To explore miR-455-3p's role in AD progression, we crossed miR-455-3p TG and miR-455-3p KO mice with the humanized amyloid beta knock-in (hAbKI) mouse model, which mimics late-onset AD features. The resulting experimental groups included WT, miR-455-3p TG, miR-455-3p KO, hAbKI, miR-455-3p TG X hAbKI, and miR-455-3p KO X hAbKI. In the current study, we investigated mitochondrial dynamics, mitochondrial biogenesis, mitophagy and synaptic proteins in all six groups of 12-month-old male and female mice. We focused on examining the expression of, mitophagy regulators (PINK1, Parkin), and synaptic markers (PSD95, Synaptophysin), mitochondrial biogenesis regulators (PGC1α, NRF1, TFAM) and dynamic proteins (DRP1, FIS1, Mfn1/2, OPA1) in the cortex of 12-month-old animals using western blot and immunofluorescence analyses. We also studied spine density in hippocampal sections for the mice groups in a Golgi-cox staining assay. We found miR-455-3p overexpression enhances mitophagy, mitochondrial biogenesis, dynamics proteins and spine density, in hAbKI mice. Depleted miR-455-3p exacerbates mitochondrial defects, defective mitophagy and synaptic loss in hAbKI mice. Our findings highlight miR-455-3p as a promising therapeutic target that modulates multiple pathological pathways in AD. This is the first genetic crossing study of miR-455-3p TG/KO mice with late onset AD, hAbKI mice.