Adult hippocampal neural (HCN) stem cells promptly undergo irreversible autophagic cell death (ACD) if deprived of insulin in culture. Small, non-coding microRNAs (miRNA) play an important role in regulating biological processes, including proliferation and cell death. However, there have been no reports thus far regarding miRNA involvement in the induction of adult HCN stem cell death under insulin-deprived conditions, for which we performed a microarray-based analysis to examine the expression signature of miRNAs in adult rat HCN stem cells. Three independent specimens per culture condition either with or without insulin were prepared and a miRNA microarray analysis carried out. A total of 12 exhibited significantly altered expression levels upon cell death due to the absence of insulin when compared to HCN stem cells cultured with insulin present (cut-off limit; p < 0.05 and fold-change >1.3) The resulting volcano plot showed that, among these miRNAs, seven were upregulated and five were downregulated. The upregulated miRNAs were capable of modulating HCN stem cell death. Caspase-3 activity analysis, LC3 conversion, and TEM of autophagosome formation consistently suggested that ACD, not apoptosis, was most likely the mechanism affecting HCN cell death. As such, we have come to term these miRNAs, "HCN stem cell-specific autophagic cell death regulators." Taken together, our data suggest that the miRNA expression profile of HCN stem cells is altered during ACD occurring due to insulin deprivation and that differentially expressed miRNAs are involved in HCN stem cell viability. Detailed explorations of the underlying mechanisms regarding HCN stem cell viability modulation by these miRNAs would be beneficial in further understanding the physiological features of adult HCN stem cells and are currently being investigated.
Keywords: Apoptosis; Autophagy; Cell death; Hippocampal neural stem cell; Neurodegenerative disease; miRNA.
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