MicroRNA Profiling in Aging Brain of PSEN1/PSEN2 Double Knockout Mice. 
MicroRNAs are small non-coding RNAs that function as regulators of gene expression.  The altered expression of microRNAs influences the pathogenesis of Alzheimer's disease.  Many researchers have focused on studies based on the relatively distinctive etiology of familial Alzheimer's disease due to the absence of risk factors in the pathogenesis of sporadic Alzheimer's disease.  Although there is a limitation in Alzheimer's disease studies, both Alzheimer's disease types have a common risk factor-aging.  No study to date has examined the aging factor in Alzheimer's disease animal models with microRNAs.  To investigate the effect of aging on the changes in microRNA expressions in the Alzheimer's disease animal model, we selected 37 hippocampal microRNAs whose expression in 12- and 18-month aged mice changed significantly using microRNA microarray.  On the basis of bioinformatics databases, 30 hippocampal microRNAs and their putative targets of PSEN1/PSEN2 double knockout mice were included in 28 pathways such as the wnt signaling pathway and ubiquitin-mediated proteolysis pathway.  Cortical microRNAs and its putative targets involved in pathological aging were included in only four pathways such as the heparin sulfate biosynthesis.  The altered expressions of these hippocampal microRNAs were associated to the imbalance between neurotoxic and neuroprotective functions and seemed to affect neurodegeneration in PSEN1/PSEN2 double knockout mice more severely than in wild-type mice.  This microRNA profiling suggests that microRNAs play potential roles in the normal aging process, as well as in the Alzheimer's disease process.