| Alzheimer’s disease (AD) is a progressive, neurodegenerative brain disease of the elderly characterized by memory loss, cognition, and behavioral abnormalities. Aging is the single most important risk factor and there is no proven therapy. Aging invariably decreases sensory stimuli and impacts on the thalamocortical system and its connectivity to key brain regions. Memory dysfunction in senescence and early AD is becoming the world wide problem. The incidence of the disease doubles every five years after 65 years of age.The two hallmark histopathological changes in AD patients are amyloid plaques and neurofibrillary tangles (NFTs). The amyloidβpeptide (Aβ), an inaccurately cleaved product of the amyloid precursor protein (APP), contributes to the core element of plaques, and the hyperphosphorylated microtubule binding protein tau makes up of the core of the tangles.Endogenous mature microRNAs (miRNAs) of 20 to 25 nt have been implicated as critical regulators in the expression and function of eukaryotic genomes. Translational repression or degradation of mRNA occurs when miRNAs bind to the RNA-induced silencing complex (RISC). One miRNA could potentially regulate large numbers of target genes synchronously, which implies that miRNAs may be important sculptors of transcriptional networks. As such, they are attractive candidates for regulating development and pathological changes. miRNAs are also implicated in cell fate determination, senescence, apoptosis, proliferation and stress. Recent studies of mammals have suggested a role for miRNAs in neurodegenerative diseases.One of the senescence-accelerated mouse (SAM) strains, SAM prone 8 (SAMP8), shows aging features. It has been demonstrated SAMP8 mice has deficits in age-related learning and memory and could be a plausible model to investigate the fundamental mechanism of early-onset AD. APP accumulation occurs around the hippocampal area with increased age, and plaques also appear when the SAMP8 mice acquisition deficits but not in normal aging SAMR1 mice. Thus, we chose the SAMP8 strain as a mouse model and the SAMR1 strain as a control to explore AD-associated pathogenesis and the links between miRNAs and AD.Because abnormal APP enrichment in the brain could actually increase the risk of AD and is known to be one of the characteristic features of AD, therefore, we first examined the post-transcriptional regulation mechanism of APP. The trend of APP mRNA and protein were different and we focused on the post-transcription regulation of APP. Base on the bioinformatics results and Real-time PCR result, we performed dual luciferase assay and confirmed that miR-16 could target APP 3’UTR through specific sites.The protein levels of APP were examined by western blot analysis in Neuro-2a and NIH3T3 murine cells transfected with the miR-16 overexpression plasmid and controls. APP protein level was reduced with overexpressed miR-16 in the two cell lines.We infused the miR-16 mimics or scrambled oligodeoxynucleotides (mimics negative control) into the lateral ventricle of 8-month-old SAMP8 mice, respectively. APP expression in hippocampus was substantially decreased with an exogenous miR-16 overexpression. Furthermore, miR-16 and APP displayed complementary expression patterns in SAMP8 mice and BALb/c mice embryos. Taken together, APP is a target of miR-16 and the abnormally low expression of miR-16 could potentially lead to APP protein accumulation in AD mice.As above, combined with our results, miRNAs have been implied to play important role in AD-associated progress; therefore, we attempted to explore other miRNAs which might involve in the learning and memory deficits with aging. We performed microRNAs microarray to figure out the change of miRNAs expression with age in SAMP8 and SAMR1 mice. And we tested the high-throughput results with Real-time PCR and in situ hybridization. We then gained a batch of miRNAs that might participate in regulation of learning and memory. After summary of the microarray data, we first analyzed miR-9 and miR-9* which have been widely reported in nervous system and shown signicant differences of expression between SAMP8 and SAMR1 mice, and found they might regulate MAP3K3 and CDKnlc, respectively. Taken together, we provide new evidence for addressing the network of miRNAs and their targets affected learning and memory loss in aged SAMP8 mice. |
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