MicroRNA-502-3p Modulates the GABA A Subunits, Synaptic Proteins, and Mitochondrial Morphology in Hippocampal Neurons

MicroRNA-502-3p (MiR-502-3p), a synapse-enriched miRNA, is significantly implicated in Alzheimer's disease (AD). Our previous study revealed a high expression level of miR-502-3p in AD synapses relative to controls. Additionally, miR-502-3p was found to modulate the GABAergic synapse function by modulating the GABA A receptor subunit α-1 (GABRA1) protein. The current study aims to investigate the impact of miR-502-3p on other GABA receptor subunit proteins, synaptic proteins, mitochondrial morphology, and other hippocampal neuron genes. Mouse hippocampal neuronal (HT22) cells were transfected with miR-502-3p overexpression (OE) vector, miR-502-3p suppression (sponge) vector, or scramble control vector. Transfection of miR-502-3p vectors was confirmed by fluorescence microscopy. MiR-502-3p and Gabra1 expressions were confirmed by qRT-PCR and RNAscope-based in situ hybridization analysis. GABA A subunits and synaptic protein levels were analyzed by immunoblotting, and mitochondrial morphology was examined by transmission electron microscopy. Additionally, Affymetrix gene array analysis was performed on miR-502-3p overexpressed and suppressed cells. Our results demonstrate that elevated levels of miR-502-3p negatively regulate the Gabra1 expression. The levels of GABA A subunit and synaptic proteins were reduced upon ectopic expression of miR-502-3p and increased upon miR-502-3p suppression. Mitochondrial morphology was improved in terms of mitochondrial number, length, and mitochondrial area in miR-502-3p suppressed cells. Furthermore, gene array analysis unveiled the modulatory effects of miR-502-3p on several specific genes, especially those that are associated with oxidative stress, immune response, and synaptic function. These findings provide a new insight into the molecular mechanism of miR-502-3p in regulating neuronal function and synaptic activity.