MicroRNAs (miRNAs or miRs) regulate several biological functions, including cell fate determination and differentiation. Although miR-145 has already been described to regulate glioma development, its precise role in neurogenesis has never been addressed. miR-145 represses sexdetermining region Y-box 2 (Sox2), a core transcription factor of embryonic stem cells (ESCs), to inhibit pluripotency and self-renewal in human ESCs. In addition, the Sox2-Lin28/let-7 signaling pathway regulates proliferation and neurogenesis of neural precursors. In this study, we aimed to investigate the precise role of miR-145 in neural stem cell (NSC) fate decision, and the possible involvement of the Sox2-Lin28/let-7 signaling pathway in miR-145 regulatory network. Our results show for the first time that miR-145 expression significantly increased after induction of mouse NSC differentiation, remaining elevated throughout this process. Forced miR-145 downregulation decreased neuronal markers, namely bIII-tubulin, NeuN, and MAP2. Interestingly, throughout NSC differentiation, protein levels of Sox2 and Lin28, a well-known suppressor of let-7 biogenesis, decreased. Of note, neuronal differentiation also resulted in let-7a and let-7b upregulation. Transfection of NSCs with anti-miR-145, in turn, increased both Sox2 and Lin28 protein levels, while decreasing both let-7a and let-7b. More importantly, Sox2 and Lin28 silencing partially rescued the impairment of neuronal differentiation induced by miR-145 downregulation. In conclusion, our results demonstrate a novel role for miR-145 during NSC differentiation, where miR-145 modulation of Sox2-Lin28/let-7 network is crucial for neurogenesis progression. STEM CELLS 2016;34:1386-1395
SIGNIFICANCE STATEMENTNeural stem cells (NSCs) are a potential source of repairing cells. Although neurogenesis occurs in adult mammalian brain, NSCs produce very few neurons during aging or after injury. Thus, the identification of novel players that improve neural plasticity can have a huge impact in age-associated neurogenesis and cognitive decline. Recent evidence suggests that microRNAs (miRNAs or miRs), small noncoding RNA molecules that regulate gene expression, affect NSC fate. However, the underlying molecular mechanisms driving the enhancement of neuroplasticity by miRNAs remain largely unknown. Using in vitro models of mouse NSC, we revealed the molecular mechanisms by which miR-145 drives NSCs toward neuronal differentiation. The results from our study might add significant new information on key players responsible for neuroplasticity enhancement, thus contributing to improve the health and life quality of the aging population.