Longitudinal characterization of behavioral, morphological and transcriptomic changes in a tauopathy mouse model.

Neurodegenerative disorders, such as Alzheimer's disease (AD), have the gradual onset of neurobiological changes preceding clinical diagnosis by decades. To elucidate how brain dysfunction proceeds in neurodegenerative disorders, we performed longitudinal characterization of behavioral, morphological, and transcriptomic changes in a tauopathy mouse model, P301S transgenic mice. P301S mice exhibited cognitive deficits as early as 3 months old, and deficits in social preference and social cognition at 5-6 months. They had a significant decrease of arborization in basal dendrites of hippocampal pyramidal neurons from 3 months and apical dendrites of PFC pyramidal neurons at 9 months. Transcriptomic analysis of genome-wide changes revealed the enrichment of synaptic gene upregulation at 3 months of age, while most of these synaptic genes were downregulated in PFC and hippocampus of P301S mice at 9 months. These time-dependent changes in gene expression may lead to progressive alterations of neuronal structure and function, resulting in the manifestation of behavioral symptoms in tauopathies.

Inhibition of histone methyltransferase Smyd3 rescues NMDAR and cognitive deficits in a tauopathy mouse model.

Pleiotropic mechanisms have been implicated in Alzheimer's disease (AD), including transcriptional dysregulation, protein misprocessing and synaptic dysfunction, but how they are mechanistically linked to induce cognitive deficits in AD is unclear. Here we find that the histone methyltransferase Smyd3, which catalyzes histone H3 lysine 4 trimethylation (H3K4me3) to activate gene transcription, is significantly elevated in prefrontal cortex (PFC) of AD patients and P301S Tau mice, a model of tauopathies. A short treatment with the Smyd3 inhibitor, BCI-121, rescues cognitive behavioral deficits, and restores synaptic NMDAR function and expression in PFC pyramidal neurons of P301S Tau mice. Fbxo2, which encodes an E3 ubiquitin ligase controlling the degradation of NMDAR subunits, is identified as a downstream target of Smyd3. Smyd3-induced upregulation of Fbxo2 in P301S Tau mice is linked to the increased NR1 ubiquitination. Fbxo2 knockdown in PFC leads to the recovery of NMDAR function and cognitive behaviors in P301S Tau mice. These data suggest an integrated mechanism and potential therapeutic strategy for AD.

A convergent mechanism of high risk factors ADNP and POGZ in neurodevelopmental disorders.

ADNP and POGZ are two top-ranking risk factors for autism spectrum disorder and intellectual disability, but how they are linked to these neurodevelopmental disorders is largely unknown. Both ADNP and POGZ are chromatin regulators, which could profoundly affect gene transcription and cellular function in the brain. Using post-mortem tissue from patients with autism spectrum disorder, we found diminished expression of ADNP and POGZ in the prefrontal cortex, a region highly implicated in neurodevelopmental disorders. To understand the functional role of these neurodevelopmental disorder risk factors, we used viral-based gene transfer to investigate how Adnp or Pogz deficiency in mouse prefrontal cortex affects behavioural, transcriptomic and synaptic function. Mice with prefrontal cortex deficiency of Adnp or Pogz exhibited specific impairment of cognitive task performance. RNA-sequencing revealed that Adnp or Pogz deficiency induced prominent upregulation of overlapping genes enriched in neuroinflammation, similar to the elevation of pro-inflammatory genes in humans with neurodevelopmental disorders. Concomitantly, Adnp or Pogz deficiency led to the significant increase of pro-phagocytic microglial activation in prefrontal cortex, as well as the significant decrease of glutamatergic transmission and postsynaptic protein expression. These findings have uncovered the convergent functions of two top risk factors for autism spectrum disorder and intellectual disability in prefrontal cortex, providing a mechanism linking chromatin, transcriptional and synaptic dysregulation to cognitive deficits associated with neurodevelopmental disorders.

Targeting histone demethylase LSD1 for treatment of deficits in autism mouse models.

Large-scale genetic studies have revealed that the most prominent genes disrupted in autism are chromatin regulators mediating histone methylation/demethylation, suggesting the central role of epigenetic dysfunction in this disorder. Here, we show that histone lysine 4 dimethylation (H3K4me2), a histone mark linked to gene activation, is significantly decreased in the prefrontal cortex (PFC) of autistic human patients and mutant mice with the deficiency of top-ranking autism risk factor Shank3 or Cul3. A brief treatment of the autism models with highly potent and selective inhibitors of the H3K4me2 demethylase LSD1 (KDM1A) leads to the robust rescue of core symptoms of autism, including social deficits and repetitive behaviors. Concomitantly, LSD1 inhibition restores NMDA receptor function in PFC and AMPA receptor-mediated currents in striatum of Shank3-deficient mice. Genome-wide RNAseq and ChIPseq reveal that treatment of Shank3-deficient mice with the LSD1 inhibitor restores the expression and H3K4me2 occupancy of downregulated genes enriched in synaptic signaling and developmental processes. The immediate early gene tightly linked to neuronal plasticity, Egr1, is on the top list of rescued genes. The diminished transcription of Egr1 is recapitulated in PFC of autistic human patients. Overexpression of Egr1 in PFC of Shank3-deficient mice ameliorates social preference deficits. These results have for the first time revealed an important role of H3K4me2 abnormality in ASD pathophysiology, and the therapeutic potential of targeting H3K4me2 demethylase LSD1 or the downstream molecule Egr1 for ASD.

Deficiency of autism risk factor ASH1L in prefrontal cortex induces epigenetic aberrations and seizures.

ASH1L, a histone methyltransferase, is identified as a top-ranking risk factor for autism spectrum disorder (ASD), however, little is known about the biological mechanisms underlying the link of ASH1L haploinsufficiency to ASD. Here we show that ASH1L expression and H3K4me3 level are significantly decreased in the prefrontal cortex (PFC) of postmortem tissues from ASD patients. Knockdown of Ash1L in PFC of juvenile mice induces the downregulation of risk genes associated with ASD, intellectual disability (ID) and epilepsy. These downregulated genes are enriched in excitatory and inhibitory synaptic function and have decreased H3K4me3 occupancy at their promoters. Furthermore, Ash1L deficiency in PFC causes the diminished GABAergic inhibition, enhanced glutamatergic transmission, and elevated PFC pyramidal neuronal excitability, which is associated with severe seizures and early mortality. Chemogenetic inhibition of PFC pyramidal neuronal activity, combined with the administration of GABA enhancer diazepam, rescues PFC synaptic imbalance and seizures, but not autistic social deficits or anxiety-like behaviors. These results have revealed the critical role of ASH1L in regulating synaptic gene expression and seizures, which provides insights into treatment strategies for ASH1L-associated brain diseases.

Epigenetic treatment of behavioral and physiological deficits in a tauopathy mouse model.

Epigenetic abnormality is implicated in neurodegenerative diseases associated with cognitive deficits, such as Alzheimer's disease (AD). A common feature of AD is the accumulation of neurofibrillary tangles composed of hyperphosphorylated tau. Transgenic mice expressing mutant P301S human tau protein develop AD-like progressive tau pathology and cognitive impairment. Here, we show that the euchromatic histone-lysine N-methyltransferase 2 (EHMT2) is significantly elevated in the prefrontal cortex (PFC) of P301S Tau mice (5-7 months old), leading to the increased repressive histone mark, H3K9me2, which is reversed by treatment with the selective EHMT inhibitor UNC0642. Behavioral assays show that UNC0642 treatment induces the robust rescue of spatial and recognition memory deficits in P301S Tau mice. Concomitantly, the diminished PFC neuronal excitability and glutamatergic synaptic transmission in P301S Tau mice are also normalized by UNC0642 treatment. In addition, EHMT inhibition dramatically attenuates the hyperphosphorylated tau level in PFC of P301S Tau mice. Transcriptomic analysis reveals that UNC0642 treatment of P301S Tau mice has normalized a number of dysregulated genes in PFC, which are enriched in cytoskeleton and extracellular matrix organization, ion channels and transporters, receptor signaling, and stress responses. Together, these data suggest that targeting histone methylation enzymes to adjust gene expression could be used to treat cognitive and synaptic deficits in neurodegenerative diseases linked to tauopathies.

Transcriptomic analysis of human brains with Alzheimer's disease reveals the altered expression of synaptic genes linked to cognitive deficits.

Alzheimer's disease is a progressive neurodegenerative disorder associated with memory loss and impaired executive function. The molecular underpinnings causing cognitive deficits in Alzheimer's disease are loosely understood. Here, we performed cross-study large-scale transcriptomic analyses of postmortem prefrontal cortex derived from Alzheimer's disease patients to reveal the role of aberrant gene expression in this disease. We identified that one of the most prominent changes in prefrontal cortex of Alzheimer's disease humans was the downregulation of genes in excitatory and inhibitory neurons that are associated with synaptic functions, particularly the SNARE-binding complex, which is essential for vesicle docking and neurotransmitter release. Comparing genomic data of Alzheimer's disease with proteomic data of cognitive trajectory, we found that many of the lost synaptic genes in Alzheimer's disease encode hub proteins whose increased abundance is required for cognitive stability. This study has revealed potential molecular targets for therapeutic intervention of cognitive decline associated with Alzheimer's disease.

Targeting histone K4 trimethylation for treatment of cognitive and synaptic deficits in mouse models of Alzheimer's disease.

Epigenetic aberration is implicated in aging and neurodegeneration. Using postmortem tissues from patients with Alzheimer's disease (AD) and AD mouse models, we have found that the permissive histone mark H3K4me3 and its catalyzing enzymes are significantly elevated in the prefrontal cortex (PFC). Inhibiting H3K4-specific methyltransferases with the compound WDR5-0103 leads to the substantial recovery of PFC synaptic function and memory-related behaviors in AD mice. Among the up-regulated genes reversed by WDR5-0103 treatment in PFC of AD mice, many have the increased H3K4me3 enrichment at their promoters. One of the identified top-ranking target genes, Sgk1, which encodes serum and glucocorticoid-regulated kinase 1, is also significantly elevated in PFC of patients with AD. Administration of a specific Sgk1 inhibitor reduces hyperphosphorylated tau protein, restores PFC glutamatergic synaptic function, and ameliorates memory deficits in AD mice. These results have found a novel epigenetic mechanism and a potential therapeutic strategy for AD and related neurodegenerative disorders.

A structural and functional comparison of gap junction channels composed of connexins and innexins.

Methods such as electron microscopy and electrophysiology led to the understanding that gap junctions were dense arrays of channels connecting the intracellular environments within almost all animal tissues. The characteristics of gap junctions were remarkably similar in preparations from phylogenetically diverse animals such as cnidarians and chordates. Although few studies directly compared them, minor differences were noted between gap junctions of vertebrates and invertebrates. For instance, a slightly wider gap was noted between cells of invertebrates and the spacing between invertebrate channels was generally greater. Connexins were identified as the structural component of vertebrate junctions in the 1980s and innexins as the structural component of pre-chordate junctions in the 1990s. Despite a lack of similarity in gene sequence, connexins and innexins are remarkably similar. Innexins and connexins have the same membrane topology and form intercellular channels that play a variety of tissue- and temporally specific roles. Both protein types oligomerize to form large aqueous channels that allow the passage of ions and small metabolites and are regulated by factors such as pH, calcium, and voltage. Much more is currently known about the structure, function, and structure-function relationships of connexins. However, the innexin field is expanding. Greater knowledge of innexin channels will permit more detailed comparisons with their connexin-based counterparts, and provide insight into the ubiquitous yet specific roles of gap junctions. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 522-547, 2017.