miR-34a deficiency in APP/PS1 mice promotes cognitive function by increasing synaptic plasticity via AMPA and NMDA receptors.

MicroRNA (miR)-34a was recently determined to contribute to the pathological development of Alzheimer's disease (AD). miR-34a deficiency significantly attenuates cognitive deficits in amyloid precursor protein (APP)/presenilin 1 (PS1) mice; however, its role in early AD pathology and the underlying mechanisms remain elusive. Here, we confirmed that the increase of miR-34a expression in APP/PS1 mice was earlier than the relevant AD pathological characteristics, such as amyloid-β production, amyloid plaque deposition, and cognitive deficits. Furthermore, because predicted miR-34a target genes were broadly linked to α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-d-aspartate (NMDA) receptors, we evaluated synaptic plasticity by investigating high-frequency conditioning tetanus-induced excitatory postsynaptic potential, which revealed that synaptic plasticity was promoted in miR-34a knockout/APP/PS1 mice. Therefore, we assessed the expression of the presynaptic components synaptophysin and postsynaptic density protein 95 (PSD95) and found that synaptophysin and PSD95 were not altered by miR-34a deficiency. Additionally, the synaptic strength (vesicular fusion, vesicular docking, and transporting) was either not significantly changed. We also evaluated the levels of AMPA and NMDA receptors, which showed that the expression of AMPA and NMDA receptors was markedly upregulated in APP/PS1 mice with miR-34a deficiency. We conclude that miR-34a is involved in synaptic deficits in AD pathological development, which was, at least in part, due to the inhibition of NMDA (by miR-34a-5p) and AMPA (by miR-34a-3p) receptor expression.

Xu Y ，Chen P ，Wang X ，Yao J ，Zhuang S ... -  《-》

Over-expression of miR-34a induces rapid cognitive impairment and Alzheimer's disease-like pathology.

Autosomal dominant Alzheimer disease (AD) is caused by rare mutations in one of three specific genes. This is in contrast to idiopathic, late-onset AD (LOAD), which has a more polygenetic risk profile and represents more than 95% of cases. Previously, we have demonstrated that increased expression of microRNA (miRNA)-34a (miR-34a) in AD brain targets genes linked to synaptic plasticity, energy metabolism, and resting state network activity. Here we report the generation of a heterozygous, conditional miR-34a overexpression mouse (miR-34a+/-(TetR-TetO-miR-34a) Transgenic Mice). Doxycycline-treated mice of either sex exhibited profound behavioral impairment compared to untreated groups with only 1-2 months of over-expression of miR-34a. Cognitive impairment of individual mice in T- and Y-maze tasks correlated with elevated miR-34a expression in many parts of the brain including the hippocampus and prefrontal cortex, regions which are known to be involved in this task and implicated in LOAD dysfunction. Immunocytochemistry of brain sections from mice show high amyloid β and phosphorylated tau-specific staining in the hippocampus and cortex. Analysis of protein samples from these mice revealed that miR-34a targets specific genes involved in memory formation, amyloid precursor protein (APP) metabolism and phosphorylation-dephosphorylation of tau. Thus, our results suggest that the polygenetic dysfunction caused by miR-34a may occur in LOAD and disclose miR-34a as a potential therapeutic target. SIGNIFICANCE STATEMENT: Late-onset Alzheimer disease (LOAD) is associated with multiple gene alleles, a polygenetic profile of risk factors that is difficult to model in animals. Our approach to modeling LOAD was to produce a conditional over-expressing, miR-34a mouse using doxycycline-induction to activate expression. We observed that miR-34a over-expression results in a rapid cognitive impairment, associated with accumulation of intracellular Aβ and tau hyperphosphorylation in multiple brain regions. Targets for miR-34a, including ADAM10, NMDAR 2B, and SIRT1 RNAs, were profoundly reduced by miR-34a over-expression. Collectively, these results indicate that a rapid, profound cognitive decline and Alzheimer's disease neuropathology can be induced with miR-34a over-expression, suggesting that this animal model may represent a polygenetic risk factor model for LOAD.

Sarkar S ，Engler-Chiurazzi EB ，Cavendish JZ ，Povroznik JM ，Russell AE ，Quintana DD ，Mathers PH ，Simpkins JW ... -  《-》

Disrupted Maturation of Prefrontal Layer 5 Neuronal Circuits in an Alzheimer's Mouse Model of Amyloid Deposition.

Mutations in genes encoding amyloid precursor protein (APP) and presenilins (PSs) cause familial forms of Alzheimer's disease (AD), a neurodegenerative disorder strongly associated with aging. It is currently unknown whether and how AD risks affect early brain development, and to what extent subtle synaptic pathology may occur prior to overt hallmark AD pathology. Transgenic mutant APP/PS1 over-expression mouse lines are key tools for studying the molecular mechanisms of AD pathogenesis. Among these lines, the 5XFAD mice rapidly develop key features of AD pathology and have proven utility in studying amyloid plaque formation and amyloid β (Aβ)-induced neurodegeneration. We reasoned that transgenic mutant APP/PS1 over-expression in 5XFAD mice may lead to neurodevelopmental defects in early cortical neurons, and performed detailed synaptic physiological characterization of layer 5 (L5) neurons from the prefrontal cortex (PFC) of 5XFAD and wild-type littermate controls. L5 PFC neurons from 5XFAD mice show early APP/Aβ immunolabeling. Whole-cell patch-clamp recording at an early post-weaning age (P22-30) revealed functional impairments; although 5XFAD PFC-L5 neurons exhibited similar membrane properties, they were intrinsically less excitable. In addition, these neurons received smaller amplitude and frequency of miniature excitatory synaptic inputs. These functional disturbances were further corroborated by decreased dendritic spine density and spine head volumes that indicated impaired synapse maturation. Slice biotinylation followed by Western blot analysis of PFC-L5 tissue revealed that 5XFAD mice showed reduced synaptic AMPA receptor subunit GluA1 and decreased synaptic NMDA receptor subunit GluN2A. Consistent with this, patch-clamp recording of the evoked L23>L5 synaptic responses revealed a reduced AMPA/NMDA receptor current ratio, and an increased level of AMPAR-lacking silent synapses. These results suggest that transgenic mutant forms of APP/PS1 overexpression in 5XFAD mice leads to early developmental defects of cortical circuits, which could contribute to the age-dependent synaptic pathology and neurodegeneration later in life.

Chen C ，Wei J ，Ma X ，Xia B ，Shakir N ，Zhang JK ，Zhang L ，Cui Y ，Ferguson D ，Qiu S ，Bai F ... -  《-》

Folic acid deficiency enhances abeta accumulation in APP/PS1 mice brain and decreases amyloid-associated miRNAs expression.

Recent efforts have revealed the microRNA (miRNA) pathways in the pathogenesis of Alzheimer's disease (AD). Epidemiological studies have revealed an association between folic acid deficiency and AD risk. However, the effects of folic acid deficiency on miRNA expression in AD animals have not been observed. We aimed to find if folic acid deficiency may enhance amyloid-β (Aβ) peptide deposition and regulate amyloid-associated miRNAs and their target genes expression in APP/PS1 mice. APP/PS1 mice and N2a cells were treated with folic acid-deficient diet or medium. Cognitive function of mice was assessed using the Morris water maze. miRNA profile was tested by polymerase chain reaction (PCR) array. Different expressional miRNAs were validated by real-time PCR. The deposition of Aβ plaques was evaluated by immunohistochemistry and enzyme-linked immunosorbent assay. APP and BACE1 proteins in mice brain and N2a cells were determined by Western blot. Folic acid deficiency aggravated amyloid pathology in AD mice. The AD+FD group showed shorter time spent in the target zone during the probe test. Analysis of miRNAs predicted to target these genes revealed several miRNA candidates that were differentially modulated by folic acid deficiency. In APP/PS1 mice brains and N2a cells with folic acid-deficient treatment, miR-106a-5p, miR-200b-3p and miR-339-5p were down-regulated, and their target genes APP and BACE1 were up-regulated. In conclusion, folic acid deficiency can enhance Aβ accumulation in APP/PS1 mice brain and decrease amyloid-associated miRNAs expression.

Liu H ，Tian T ，Qin S ，Li W ，Zhang X ，Wang X ，Gao Y ，Huang G ... -  《-》

MicroRNA-574 is involved in cognitive impairment in 5-month-old APP/PS1 mice through regulation of neuritin.

Alzheimer's disease (AD) is the most common form of dementia in the elderly. The recent evidence in AD research suggests that alterations in the microRNA (miRNA) could contribute to risk for the disease. However, little is understood about the roles of miRNAs in cognitive impairment of early Alzheimer's disease (AD). Here, we used 5-month-old APP/PS1 mice, which mimic many of the salient features of the early stage of AD pathological process, to further investigate the roles of miRNAs in synaptic loss involved in learning and memory. We used miRNA expression microarrays on RNA extracted from the hippocampus of 5-month-old APP/PS1 mice and wild type mice. Real-time reverse transcription PCR was conducted to verify the candidate miRNAs discovered by microarray analysis. The data showed that miR-574 was increased significantly in the hippocampus of 5-month-old APP/PS1 mice, which were concomitant with that APP/PS1 mice at the same age displayed a significant synaptic loss and cognitive deficits. Bioinformatic analysis predicted that neuritin (Nrn1) mRNA is targeted by miR-574. Overexpression of miR-574 lowers the levels of neuritin and synaptic proteins expression in primary hippocampal neurons damage induced by Aβ25-35. And the expression of miR-574 was also up-regulated in the hippocampal neurons from APP/PS1 mice compared with WT littermates. In contrast, suppression of miR-574 by miR-574 inhibitor significantly results in higher levels of neuritin and synaptic proteins expression. Taken together, miR-574 is involved in cognitive impairment in 5-month-old APP/PS1 mice through regulation of neuritin.

Li F ，Wei G ，Bai Y ，Li Y ，Huang F ，Lin J ，Hou Q ，Deng R ，Zhou JH ，Zhang SX ，Chen DF ... -  《-》