Histone deacetylase 2 (HDAC2) plays a major role in the epigenetic regulation of gene expression. Previous studies have shown that HDAC2 expression is strongly increased in Alzheimer's disease (AD), a major neurodegenerative disorder and the most common form of dementia. Moreover, previous studies have linked HDAC2 to Ab overproduction in AD; however, its involvement in tau pathology and other memoryrelated functions remains unclear. Here, we show that increased HDAC2 levels strongly correlate with phosphorylated tau in a mouse model of AD. HDAC2 overexpression induced AD-like tau hyperphosphorylation and aggregation, which were accompanied by a loss of dendritic complexity and spine density. The ectopic expression of HDAC2 resulted in the deacetylation of the hepatocyte nuclear factor 4a (HNF-4A) transcription factor, which disrupted its binding to the miR-101b promoter. The suppression of miR-101b caused an upregulation of its target, AMP-activated protein kinase (AMPK). The introduction of miR-101b mimics or small interfering RNAs (siRNAs) against AMPK blocked HDAC2-induced tauopathy and dendritic impairments in vitro. Correspondingly, miR-101b mimics or AMPK siRNAs rescued tau pathology, dendritic abnormalities, and memory deficits in AD mice. Taken together, the current findings implicate the HDAC2/miR-101/AMPK pathway as a critical mediator of AD pathogenesis. These studies also highlight the importance of epigenetics in AD and provide novel therapeutic targets.

MicroRNAs have been implicated in diverse physiological and pathological processes. We previously reported that aberrant microRNA‐124 (miR‐124)/non‐receptor–type protein phosphatase 1 (PTPN1) signaling plays an important role in the synaptic disorders associated with Alzheimer's disease (AD). In this study, we further investigated the potential role of miR‐124/PTPN1 in the tau pathology of AD. We first treated the mice with intra‐hippocampal stereotactic injections. Then, we used quantitative real‐time reverse transcription PCR (qRT‐PCR) to detect the expression of microRNAs. Western blotting was used to measure the level of PTPN1, the level of tau protein, the phosphorylation of tau at AD‐related sites, and alterations in the activity of glycogen synthase kinase 3β (GSK‐3β) and protein phosphatase 2 (PP2A). Immunohistochemistry was also used to detect changes in tau phosphorylation levels at AD‐related sites and somadendritic aggregation. Soluble and insoluble tau protein was separated by 70% formic acid (FA) extraction to examine tau solubility. Finally, behavioral experiments (including the Morris water maze, fear conditioning, and elevated plus maze) were performed to examine learning and memory ability and emotion‐related behavior. We found that artificially replicating the abnormalities in miR‐124/PTPN1 signaling induced AD‐like tau pathology in the hippocampus of wild‐type mice, including hyperphosphorylation at multiple sites, insolubility and somadendritic aggregation, as well as learning/memory deficits. We also found that disruption of miR‐124/PTPN1 signaling was caused by the loss of RE1‐silencing transcription factor protein, which can be initiated by Aβ insults or oxidative stress, as observed in the brains of P301S mice. Correcting the deregulation of miR‐124/PTPN1 signaling rescued the tau pathology and learning/memory impairments in the P301S mice. We also found that miR‐124/PTPN1 abnormalities induced activation of glycogen synthase kinase 3 (GSK‐3) and inactivation of protein phosphatase 2A (PP2A) by promoting tyrosine phosphorylation, implicating an imbalance in tau kinase/phosphatase. Thus, targeting the miR‐124/PTPN1 signaling pathway is a promising therapeutic strategy for AD. image

Impairments of dendritic trees and spines have been found in many neurodegenerative diseases, including Alzheimer's disease (AD), in which the deficits of melatonin signal pathway were reported. Melatonin receptor 2 (MT2) is widely expressed in the hippocampus and mediates the biological functions of melatonin. It is known that melatonin application is protective to dendritic abnormalities in AD. However, whether MT2 is involved in the neuroprotection and the underlying mechanisms are not clear. Here, we first found that MT2 is dramatically reduced in the dendritic compartment upon the insult of oligomer Aβ. MT2 activation prevented the Aβ‐induced disruption of dendritic complexity and spine. Importantly, activation of MT2 decreased cAMP, which in turn inactivated transcriptional factor CCAAT/enhancer‐binding protein α(C/EBPα) to suppress miR‐125b expression and elevate the expression of its target, GluN2A. In addition, miR‐125b mimics fully blocked the protective effects of MT2 activation on dendritic trees and spines. Finally, injection of a lentivirus containing a miR‐125b sponge into the hippocampus of APP/PS1 mice effectively rescued the dendritic abnormalities and learning/memory impairments. Our data demonstrated that the cAMP‐C/EBPα/miR‐125b/GluN2A signaling pathway is important to the neuroprotective effects of MT2 activation in Aβ‐induced dendritic injuries and learning/memory disorders, providing a novel therapeutic target for the treatment of AD synaptopathy.

DNA double-strand breaks (DSBs) are common events that were recognized as one of the most toxic lesions in eukaryotic cells. DSBs are widely involved in many physiological processes such as V(D)J recombination, meiotic recombination, DNA replication and transcription. Deregulation of DSBs has been reported in multiple diseases in human beings, such as the neurodegenerative diseases, with which the underlying mechanisms are needed to be illustrated. Here, we reviewed the recent insights into the dysfunction of DSB formation and repair, contributing to the pathogenesis of neurodegenerative disorders including Alzheimer’s disease (AD), amyotrophic lateral sclerosis (ALS), Huntington’s disease (HD) and ataxia telangiectasia (A-T).

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative diseases that is characterized by progressive memory loss and two main pathological hallmarks, including the extracellular amyloid plaques and intracellular neurofibrillary tangles. The microtubule-related protein tau is involved in the pathogenesis of many neurological diseases commonly known as tauopathies and is found to be abnormally hyperphosphorylated in AD and accumulated in neurons. Besides hyperphosphorylation, tau also undergoes abnormal glycosylation, ubiquitination, glycation, and other posttranslational modifications. These abnormalities lead to the aberrant aggregation of tau in the synaptic loci in AD. In this review, we highlighted the most recent studies about how tau is abnormally regulated and how those abnormalities play important roles in the pathogenesis of AD.