A novel molecular class that recruits HDAC/MECP2 complexes to PU.1 motifs reduces neuroinflammation.

Pervasive neuroinflammation occurs in many neurodegenerative diseases, including Alzheimer's disease (AD). SPI1/PU.1 is a transcription factor located at a genome-wide significant AD-risk locus and its reduced expression is associated with delayed onset of AD. We analyzed single-cell transcriptomic datasets from microglia of human AD patients and found an enrichment of PU.1-binding motifs in the differentially expressed genes. In hippocampal tissues from transgenic mice with neurodegeneration, we found vastly increased genomic PU.1 binding. We then screened for PU.1 inhibitors using a PU.1 reporter cell line and discovered A11, a molecule with anti-inflammatory efficacy and nanomolar potency. A11 regulated genes putatively by recruiting a repressive complex containing MECP2, HDAC1, SIN3A, and DNMT3A to PU.1 motifs, thus representing a novel mechanism and class of molecules. In mouse models of AD, A11 ameliorated neuroinflammation, loss of neuronal integrity, AD pathology, and improved cognitive performance. This study uncovers a novel class of anti-inflammatory molecules with therapeutic potential for neurodegenerative disorders.

HDAC1 modulates OGG1-initiated oxidative DNA damage repair in the aging brain and Alzheimer's disease.

DNA damage contributes to brain aging and neurodegenerative diseases. However, the factors stimulating DNA repair to stave off functional decline remain obscure. We show that HDAC1 modulates OGG1-initated 8-oxoguanine (8-oxoG) repair in the brain. HDAC1-deficient mice display age-associated DNA damage accumulation and cognitive impairment. HDAC1 stimulates OGG1, a DNA glycosylase known to remove 8-oxoG lesions that are associated with transcriptional repression. HDAC1 deficiency causes impaired OGG1 activity, 8-oxoG accumulation at the promoters of genes critical for brain function, and transcriptional repression. Moreover, we observe elevated 8-oxoG along with reduced HDAC1 activity and downregulation of a similar gene set in the 5XFAD mouse model of Alzheimer's disease. Notably, pharmacological activation of HDAC1 alleviates the deleterious effects of 8-oxoG in aged wild-type and 5XFAD mice. Our work uncovers important roles for HDAC1 in 8-oxoG repair and highlights the therapeutic potential of HDAC1 activation to counter functional decline in brain aging and neurodegeneration.

S-nitrosylation of E3 ubiquitin-protein ligase RNF213 alters non-canonical Wnt/Ca+2 signaling in the P301S mouse model of tauopathy.

Mutations in the MAPT gene, which encodes the tau protein, are associated with several neurodegenerative diseases, including frontotemporal dementia (FTD), dementia with epilepsy, and other types of dementia. The missense mutation in the Mapt gene in the P301S mouse model of FTD results in impaired synaptic function and microgliosis at three months of age, which are the earliest manifestations of disease. Here, we examined changes in the S-nitrosoproteome in 2-month-old transgenic P301S mice in order to detect molecular events corresponding to early stages of disease progression. S-nitrosylated (SNO) proteins were identified in two brain regions, cortex and hippocampus, in P301S and Wild Type (WT) littermate control mice. We found major changes in the S-nitrosoproteome between the groups in both regions. Several pathways converged to show that calcium regulation and non-canonical Wnt signaling are affected using GO and pathway analysis. Significant increase in 3-nitrotyrosine was found in the CA1 and entorhinal cortex regions, which indicates an elevation of oxidative stress and nitric oxide formation. There was evidence of increased Non-Canonical Wnt/Ca++ (NC-WCa) signaling in the cortex of the P301S mice; including increases in phosphorylated CaMKII, and S-nitrosylation of E3 ubiquitin-protein ligase RNF213 (RNF-213) leading to increased levels of nuclear factor of activated T-cells 1 (NFAT-1) and FILAMIN-A, which further amplify the NC-WCa and contribute to the pathology. These findings implicate activation of the NC-WCa pathway in tauopathy and provide novel insights into the contribution of S-nitrosylation to NC-WCa activation, and offer new potential drug targets for treatment of tauopathies.

Epigenome-wide study uncovers large-scale changes in histone acetylation driven by tau pathology in aging and Alzheimer's human brains.

Accumulation of tau and amyloid-ß are two pathologic hallmarks of Alzheimer's disease. We conducted an epigenome-wide association study using the histone 3 lysine 9 acetylation (H3K9ac) mark in 669 aged human prefrontal cortices; in contrast with amyloid-ß, tau protein burden had a broad effect on the epigenome, affecting 5,990 of 26,384 H3K9ac domains. Tau-related alterations aggregated in large genomic segments reflecting spatial chromatin organization, and the magnitude of these effects correlated with the segment's nuclear lamina association. Functional relevance of these chromatin changes was demonstrated by (1) consistent transcriptional changes in three independent datasets and (2) similar findings in two mouse models of Alzheimer's disease. Finally, we found that tau overexpression in induced pluripotent stem cell-derived neurons altered chromatin structure and that these effects could be blocked by a small molecule predicted to reverse the tau effect. Thus, we report broad tau-driven chromatin rearrangements in the aging human brain that may be reversible with heat-shock protein 90 (Hsp90) inhibitors.

APOE4 Causes Widespread Molecular and Cellular Alterations Associated with Alzheimer's Disease Phenotypes in Human iPSC-Derived Brain Cell Types.

The apolipoprotein E4 (APOE4) variant is the single greatest genetic risk factor for sporadic Alzheimer's disease (sAD). However, the cell-type-specific functions of APOE4 in relation to AD pathology remain understudied. Here, we utilize CRISPR/Cas9 and induced pluripotent stem cells (iPSCs) to examine APOE4 effects on human brain cell types. Transcriptional profiling identified hundreds of differentially expressed genes in each cell type, with the most affected involving synaptic function (neurons), lipid metabolism (astrocytes), and immune response (microglia-like cells). APOE4 neurons exhibited increased synapse number and elevated Aß42 secretion relative to isogenic APOE3 cells while APOE4 astrocytes displayed impaired Aß uptake and cholesterol accumulation. Notably, APOE4 microglia-like cells exhibited altered morphologies, which correlated with reduced Aß phagocytosis. Consistently, converting APOE4 to APOE3 in brain cell types from sAD iPSCs was sufficient to attenuate multiple AD-related pathologies. Our study establishes a reference for human cell-type-specific changes associated with the APOE4 variant. VIDEO ABSTRACT.

The Transcription Factor Sp3 Cooperates with HDAC2 to Regulate Synaptic Function and Plasticity in Neurons.

The histone deacetylase HDAC2, which negatively regulates synaptic gene expression and neuronal plasticity, is upregulated in Alzheimer's disease (AD) patients and mouse models. Therapeutics targeting HDAC2 hold promise for ameliorating AD-related cognitive impairment; however, attempts to generate HDAC2-specific inhibitors have failed. Here, we take an integrative genomics approach to identify proteins that mediate HDAC2 recruitment to synaptic plasticity genes. Functional screening revealed that knockdown of the transcription factor Sp3 phenocopied HDAC2 knockdown and that Sp3 facilitated recruitment of HDAC2 to synaptic genes. Importantly, like HDAC2, Sp3 expression was elevated in AD patients and mouse models, where Sp3 knockdown ameliorated synaptic dysfunction. Furthermore, exogenous expression of an HDAC2 fragment containing the Sp3-binding domain restored synaptic plasticity and memory in a mouse model with severe neurodegeneration. Our findings indicate that targeting the HDAC2-Sp3 complex could enhance cognitive function without affecting HDAC2 function in other processes.

Histone deacetylase 3 associates with MeCP2 to regulate FOXO and social behavior.

Mutations in MECP2 cause the neurodevelopmental disorder Rett syndrome (RTT). The RTT missense MECP2R306C mutation prevents MeCP2 from interacting with the NCoR/histone deacetylase 3 (HDAC3) complex; however, the neuronal function of HDAC3 is incompletely understood. We found that neuronal deletion of Hdac3 in mice elicited abnormal locomotor coordination, sociability and cognition. Transcriptional and chromatin profiling revealed that HDAC3 positively regulated a subset of genes and was recruited to active gene promoters via MeCP2. HDAC3-associated promoters were enriched for the FOXO transcription factors, and FOXO acetylation was elevated in Hdac3 knockout (KO) and Mecp2 KO neurons. Human RTT-patient-derived MECP2R306C neural progenitor cells had deficits in HDAC3 and FOXO recruitment and gene expression. Gene editing of MECP2R306C cells to generate isogenic controls rescued HDAC3-FOXO-mediated impairments in gene expression. Our data suggest that HDAC3 interaction with MeCP2 positively regulates a subset of neuronal genes through FOXO deacetylation, and disruption of HDAC3 contributes to cognitive and social impairment.

Activity-Induced DNA Breaks Govern the Expression of Neuronal Early-Response Genes.

Neuronal activity causes the rapid expression of immediate early genes that are crucial for experience-driven changes to synapses, learning, and memory. Here, using both molecular and genome-wide next-generation sequencing methods, we report that neuronal activity stimulation triggers the formation of DNA double strand breaks (DSBs) in the promoters of a subset of early-response genes, including Fos, Npas4, and Egr1. Generation of targeted DNA DSBs within Fos and Npas4 promoters is sufficient to induce their expression even in the absence of an external stimulus. Activity-dependent DSB formation is likely mediated by the type II topoisomerase, Topoisomerase IIß (Topo IIß), and knockdown of Topo IIß attenuates both DSB formation and early-response gene expression following neuronal stimulation. Our results suggest that DSB formation is a physiological event that rapidly resolves topological constraints to early-response gene expression in neurons.

Conserved epigenomic signals in mice and humans reveal immune basis of Alzheimer's disease.

Alzheimer's disease (AD) is a severe age-related neurodegenerative disorder characterized by accumulation of amyloid-ß plaques and neurofibrillary tangles, synaptic and neuronal loss, and cognitive decline. Several genes have been implicated in AD, but chromatin state alterations during neurodegeneration remain uncharacterized. Here we profile transcriptional and chromatin state dynamics across early and late pathology in the hippocampus of an inducible mouse model of AD-like neurodegeneration. We find a coordinated downregulation of synaptic plasticity genes and regulatory regions, and upregulation of immune response genes and regulatory regions, which are targeted by factors that belong to the ETS family of transcriptional regulators, including PU.1. Human regions orthologous to increasing-level enhancers show immune-cell-specific enhancer signatures as well as immune cell expression quantitative trait loci, while decreasing-level enhancer orthologues show fetal-brain-specific enhancer activity. Notably, AD-associated genetic variants are specifically enriched in increasing-level enhancer orthologues, implicating immune processes in AD predisposition. Indeed, increasing enhancers overlap known AD loci lacking protein-altering variants, and implicate additional loci that do not reach genome-wide significance. Our results reveal new insights into the mechanisms of neurodegeneration and establish the mouse as a useful model for functional studies of AD regulatory regions.

Integrative analysis of 111 reference human epigenomes.

The reference human genome sequence set the stage for studies of genetic variation and its association with human disease, but epigenomic studies lack a similar reference. To address this need, the NIH Roadmap Epigenomics Consortium generated the largest collection so far of human epigenomes for primary cells and tissues. Here we describe the integrative analysis of 111 reference human epigenomes generated as part of the programme, profiled for histone modification patterns, DNA accessibility, DNA methylation and RNA expression. We establish global maps of regulatory elements, define regulatory modules of coordinated activity, and their likely activators and repressors. We show that disease- and trait-associated genetic variants are enriched in tissue-specific epigenomic marks, revealing biologically relevant cell types for diverse human traits, and providing a resource for interpreting the molecular basis of human disease. Our results demonstrate the central role of epigenomic information for understanding gene regulation, cellular differentiation and human disease.

Phosphorylation of the SQ H2A.X motif is required for proper meiosis and mitosis in Tetrahymena thermophila.

Phosphorylation of the C terminus SQ motif that defines H2A.X variants is required for efficient DNA double-strand break (DSB) repair in diverse organisms but has not been studied in ciliated protozoa. Tetrahymena H2A.X is one of two similarly expressed major H2As, thereby differing both from mammals, where H2A.X is a quantitatively minor component, and from Saccharomyces cerevisiae where it is the only type of major H2A. Tetrahymena H2A.X is phosphorylated in the SQ motif in both the mitotic micronucleus and the amitotic macronucleus in response to DSBs induced by chemical agents and in the micronucleus during prophase of meiosis, which occurs in the absence of a synaptonemal complex. H2A.X is phosphorylated when programmed DNA rearrangements occur in developing macronuclei, as for immunoglobulin gene rearrangements in mammals, but not during the DNA fragmentation that accompanies breakdown of the parental macronucleus during conjugation, correcting the previous interpretation that this process is apoptosis-like. Using strains containing a mutated (S134A) SQ motif, we demonstrate that phosphorylation of this motif is important for Tetrahymena cells to recover from exogenous DNA damage and is required for normal micronuclear meiosis and mitosis and, to a lesser extent, for normal amitotic macronuclear division; its absence, while not lethal, leads to the accumulation of DSBs in both micro- and macronuclei. These results demonstrate multiple roles of H2A.X phosphorylation in maintaining genomic integrity in different phases of the Tetrahymena life cycle.