In vivo regulation of amyloid precursor protein neuronal splicing by microRNAs.

The β-amyloid peptide that accumulate in Alzheimer's disease (AD) brain derive from proteolytic processing of the amyloid precursor protein (APP). Recent evidence suggest that microRNAs (miRNAs) participate in the post-transcriptional regulation of APP expression. Because gene dosage effects of the APP gene can cause genetic AD, dysregulation of the miRNA network could contribute significantly to disease. Here, we present evidence that, besides APP expression regulation, miRNAs are equally involved in the regulation of neuronal APP mRNA alternative splicing. Lack of miRNAs in post-mitotic neurons in vivo is associated with APP exons 7 and 8 inclusion, while ectopic expression of miR-124, an abundant neuronal-specific miRNA, reversed these effects in cultured neurons. Similar results were obtained by depletion of endogenous polypyrimidine tract binding protein 1 (PTBP1) in cells, a recognized miR-124 target gene. Furthermore, PTBP1 levels correlate with the presence of APP exons 7 and 8, while PTBP2 levels correlate with the skipping of these exons during neuronal differentiation. Finally, we show that miR-124 is down-regulated in AD brain. In sum, our results suggest that specific miRNAs are involved in the fine-tuning of APP alternative splicing in neurons. Since abnormal neuronal splicing of APP affects β-amyloid peptide production, these results could contribute to the understanding of the implication of miRNAs in brain health and disease.