MicroRNA: Basic concepts and implications for regeneration and repair of neurodegenerative diseases

MicroRNAs (miRNA) are small non-coding molecules that revolutionized our knowledge about the regulation of gene expression. Capable to target a large number of mRNA, miRNA are thought to regulate around 30% of the entire human genome. Therefore, these molecules are able to regulate several biological processes, including neuronal survival, differentiation and regeneration. Additionally, miRNA might act as valuable clinical agents in brain pathological conditions. Their specific expression patterns in the brain parenchyma and/or in circulating fluids have been highlighted as potential biomarkers, while the modulation of their activity may have therapeutic value for several neurodegenerative diseases. In this review, we describe miRNA biogenesis, signaling and regulation as well as the role of miR-9, miR-124, miR-132 and miR-137 in both adult neurogenesis and neurodegeneration, namely in Alzheimer's disease, Parkinson's disease, Huntington's disease and amyotrophic lateral sclerosis. The relationship between miRNA, neurodegeneration and neurogenesis will be highlighted. Moreover, the benefits, outcomes and limitations of therapies using miRNA technology for neurodegenerative disorders will also be discussed.