Kdm3b haploinsufficiency impairs the consolidation of cerebellum-dependent motor memory in mice.

Histone modifications are a key mechanism underlying the epigenetic regulation of gene expression, which is critically involved in the consolidation of multiple forms of memory. However, the roles of histone modifications in cerebellum-dependent motor learning and memory are not well understood. To test whether changes in histone methylation are involved in cerebellar learning, we used heterozygous Kdm3b knockout (Kdm3b+/-) mice, which show reduced lysine 9 on histone 3 (H3K9) demethylase activity. H3K9 di-methylation is significantly increased selectively in the granule cell layer of the cerebellum of Kdm3b+/- mice. In the cerebellum-dependent optokinetic response (OKR) learning, Kdm3b+/- mice show deficits in memory consolidation, whereas they are normal in basal oculomotor performance and OKR acquisition. In addition, RNA-seq analyses revealed that the expression levels of several plasticity-related genes were altered in the mutant cerebellum. Our study suggests that active regulation of histone methylation is critical for the consolidation of cerebellar motor memory.

Reduced chronic restraint stress in mice overexpressing hyperactive proteasomes in the forebrain.

While chronic restraint stress (CRS) results in depression-like behaviors possibly through oxidative stress in the brain, its molecular etiology and the development of therapeutic strategies remain elusive. Since oxidized proteins can be targeted by the ubiquitin-proteasome system, we investigated whether increased proteasome activity might affect the stress response in mice. Transgenic mice, expressing the N-terminally deleted version of α3 subunit (α3ΔN) of the proteasome, which has been shown to generate open-gated mutant proteasomes, in the forebrain were viable and fertile, but showed higher proteasome activity. After being challenged with CRS for 14 d, the mutant mice with hyperactive proteasomes showed significantly less immobility time in the forced swimming test compared with their wild-type littermates, suggesting that the α3ΔN transgenic mice are resistant to CRS. The accumulation of ER stress markers, such as polyubiquitin conjugates and phospho-IRE1α, was also significantly delayed in the hippocampus of the mutants. Notably, α3ΔN mice exhibited little deficits in other behavioral tasks, suggesting that stress resilience is likely due to the degradation of misfolded proteins by the open-gated proteasomes. These data strongly indicate that not only is the proteasome a critical modulator of stress response in vivo but also a possible therapeutic target for reducing chronic stress.

Molecular and functional signatures in a novel Alzheimer's disease mouse model assessed by quantitative proteomics.

BACKGROUND: Alzheimer's disease (AD), the most common neurodegenerative disorder, is characterized by the deposition of extracellular amyloid plaques and intracellular neurofibrillary tangles. To understand the pathological mechanisms underlying AD, developing animal models that completely encompass the main features of AD pathologies is indispensable. Although mouse models that display pathological hallmarks of AD (amyloid plaques, neurofibrillary tangles, or both) have been developed and investigated, a systematic approach for understanding the molecular characteristics of AD mouse models is lacking. METHODS: To elucidate the mechanisms underlying the contribution of amyloid beta (Aß) and tau in AD pathogenesis, we herein generated a novel animal model of AD, namely the AD-like pathology with amyloid and neurofibrillary tangles (ADLPAPT) mice. The ADLPAPT mice carry three human transgenes, including amyloid precursor protein, presenilin-1, and tau, with six mutations. To characterize the molecular and functional signatures of AD in ADLPAPT mice, we analyzed the hippocampal proteome and performed comparisons with individual-pathology transgenic mice (i.e., amyloid or neurofibrillary tangles) and wild-type mice using quantitative proteomics with 10-plex tandem mass tag. RESULTS: The ADLPAPT mice exhibited accelerated neurofibrillary tangle formation in addition to amyloid plaques, neuronal loss in the CA1 area, and memory deficit at an early age. In addition, our proteomic analysis identified nearly 10,000 protein groups, which enabled the identification of hundreds of differentially expressed proteins (DEPs) in ADLPAPT mice. Bioinformatics analysis of DEPs revealed that ADLPAPT mice experienced age-dependent active immune responses and synaptic dysfunctions. CONCLUSIONS: Our study is the first to compare and describe the proteomic characteristics in amyloid and neurofibrillary tangle pathologies using isobaric label-based quantitative proteomics. Furthermore, we analyzed the hippocampal proteome of the newly developed ADLPAPT model mice to investigate how both Aß and tau pathologies regulate the hippocampal proteome. Because the ADLPAPT mouse model recapitulates the main features of AD pathogenesis, the proteomic data derived from its hippocampus has significant utility as a novel resource for the research on the Aß-tau axis and pathophysiological changes in vivo.

p53-dependent SIRT6 expression protects Aß42-induced DNA damage.

Alzheimer's disease (AD) is the most common type of dementia and age-related neurodegenerative disease. Elucidating the cellular changes that occur during ageing is an important step towards understanding the pathogenesis and progression of neurodegenerative disorders. SIRT6 is a member of the mammalian sirtuin family of anti-aging genes. However, the relationship between SIRT6 and AD has not yet been elucidated. Here, we report that SIRT6 protein expression levels are reduced in the brains of both the 5XFAD AD mouse model and AD patients. Aß42, a major component of senile plaques, decreases SIRT6 expression, and Aß42-induced DNA damage is prevented by the overexpression of SIRT6 in HT22 mouse hippocampal neurons. Also, there is a strong negative correlation between Aß42-induced DNA damage and p53 levels, a protein involved in DNA repair and apoptosis. In addition, upregulation of p53 protein by Nutlin-3 prevents SIRT6 reduction and DNA damage induced by Aß42. Taken together, this study reveals that p53-dependent SIRT6 expression protects cells from Aß42-induced DNA damage, making SIRT6 a promising new therapeutic target for the treatment of AD.

Aß-induced degradation of BMAL1 and CBP leads to circadian rhythm disruption in Alzheimer's disease.

BACKGROUND: Patients with Alzheimer's disease (AD) frequently experience disruption of their circadian rhythms, but whether and how circadian clock molecules are perturbed by AD remains unknown. AD is an age-related neurological disorder and amyloid-ß (Aß) is one of major causative molecules in the pathogenesis of AD. RESULTS: In this study, we investigated the role of Aß in the regulation of clock molecules and circadian rhythm using an AD mouse model. These mice exhibited altered circadian behavior, and altered expression patterns of the circadian clock genes, Bmal1 and Per2. Using cultured cells, we showed that Aß induces post-translational degradation of the circadian clock regulator CBP, as well as the transcription factor BMAL1, which forms a complex with the master circadian transcription factor CLOCK. Aß-induced degradation of BMAL1 and CBP correlated with the reduced binding of transcription factors to the Per2 promoter, which in turn resulted in disruptions to PER2 protein expression and the oscillation of Per2 mRNA levels. CONCLUSIONS: Our results elucidate the underlying mechanisms for disrupted circadian rhythm in AD.