Postnatal loss of hap1 reduces hippocampal neurogenesis and causes adult depressive-like behavior in mice

Mechanistic insights into sevoflurane-induced hippocampal neuronal damage and cognitive dysfunction through the NEAT1/Nrf2 signaling axis in aged rats

The use of anesthetics during surgery can cause severe neurological damage and cognitive dysfunction in elderly patients. However, this health issue currently lacks corresponding therapeutic strategies. This research involved the utilization of single-cell RNA sequencing (scRNA-seq) and transcriptomic assessment to pinpoint crucial cell classifications and molecular pathways, as well as the lncRNA expression profiles, that undergo substantial alterations in aged rats experiencing sevoflurane-induced cognitive impairment. The results of our investigation pointed towards the enrichment of differentially expressed genes in neurons within the Nrf2/ARE signaling pathway, alongside an elevated expression of lncRNA NEAT1. Subsequently, by constructing a rat model to induce neuronal dysfunction with sevoflurane and performing experiments both in vivo and in vitro (including TUNEL staining, H&E staining, immunohistochemistry, immunofluorescence, and flow cytometry to assess apoptosis levels), we confirmed that NEAT1 inhibits the Nrf2/ARE/HO-1 pathway-related factors. Sevoflurane promotes oxidative stress and apoptosis in primary hippocampal neurons through the NEAT1/Nrf2/ARE/HO-1 axis. This study elucidates the molecular mechanism by which sevoflurane induces hippocampal neuronal damage and cognitive decline in elderly rats via the regulation of the lncRNA NEAT1/Nrf2 signaling axis. We discovered that upregulation of NEAT1 suppresses the Nrf2 signaling pathway, further inducing neuronal damage and cognitive dysfunction, furnishing an essential citation to grasp the molecular pathways involved in neuronal harm and devising corresponding treatment methodologies.

GraphCVAE: Uncovering cell heterogeneity and therapeutic target discovery through residual and contrastive learning

Advancements in Spatial Transcriptomics (ST) technologies in recent years have transformed the analysis of tissue structure and function within spatial contexts. However, accurately identifying spatial domains remains challenging due to data sparsity and noise. Traditional clustering methods often fail to capture spatial dependencies, while spatial clustering methods struggle with batch effects and data integration. We introduce GraphCVAE, a model designed to enhance spatial domain identification by integrating spatial and morphological information, correcting batch effects, and managing heterogeneous data. GraphCVAE employs a multi-layer Graph Convolutional Network (GCN) and a variational autoencoder to improve the representation and integration of spatial information. Through contrastive learning, the model captures subtle differences between cell types and states. Extensive testing on various ST datasets demonstrates GraphCVAE's robustness and biological contributions. In the dorsolateral prefrontal cortex (DLPFC) dataset, it accurately delineates cortical layer boundaries. In glioblastoma, GraphCVAE reveals critical therapeutic targets such as TF and NFIB. In colorectal cancer, it explores the role of the extracellular matrix in colorectal cancer. The model's performance metrics consistently surpass existing methods, validating its effectiveness. GraphCVAE's advanced visualization capabilities further highlight its precision in resolving spatial structures, making it a powerful tool for spatial transcriptomics analysis and offering new insights into disease studies.

Research advances in huntingtin-associated protein 1 and its application prospects in diseases

Huntingtin-associated protein 1 (HAP1) was the first protein discovered to interact with huntingtin. Besides brain, HAP1 is also expressed in the spinal cord, dorsal root ganglion, endocrine, and digestive systems. HAP1 has diverse functions involving in vesicular transport, receptor recycling, gene transcription, and signal transduction. HAP1 is strongly linked to several neurological diseases, including Huntington's disease, Alzheimer's disease, epilepsy, ischemic stroke, and depression. In addition, HAP1 has been proved to participate in cancers and diabetes mellitus. This article provides an overview of HAP1 regarding the tissue distribution, cell localization, functions, and offers fresh perspectives to investigate its role in diseases.

Anti-depression-like effect of Mogroside V is related to the inhibition of inflammatory and oxidative stress pathways

Siraitia grosvenorii (SG) is an edible medicinal plant found mainly in Guangxi, China, and Mogroside V (MGV) is the main component of SG extract. Previous research has shown that SG and MGV exert anti-inflammatory, antioxidative and neuroprotective effects. However, it is not clear whether MGV has anti-depression-like effect. In this study, we evaluated the neuroprotective effects and anti-depression-like effect of MGV both in vitro and in vivo. By performing in vitro tests, we evaluated the protective effects of MGV on PC12 cells with corticosterone-induced injury. In vivo tests, we used the chronic unpredictable mild stress (CUMS) depression model. Fluoxetine (10 mg/kg/day) and MGV (10 or 30 mg/kg/day) were administered by gavage for 21 days, and the open field test (OFT), novelty suppressed feeding test (NSFT), Tail suspension test (TST), and forced Swimming test (FST) were used to evaluate the depressive-like behaviors. In addition, we investigated the role of proinflammatory cytokines (IL-1β, IL-6, and TNF-α) and anti-inflammatory cytokine (IL-4) in the hippocampal and cortex tissues. The levels of Superoxide dismutase (SOD), malondialdehyde (MDA), and glutathione peroxidase (GSH-PX) in hippocampal and cortex tissues were also measured. Pathological changes in the hippocampal dentate gyrus and cortex regions were detected by immunofluorescence and Western blotting was used to measure the protein expression of BDNF, TrkB, TNF-α, and AKT. The results showed that MGV had a protective effect on PC12 cells with corticosterone-induced incurred injury. In addition, MGV treatment relieved the depressive symptoms and significantly reduced inflammatory levels (IL-1β, IL-6, and TNF-α). MGV also significantly reduced oxidative stress damage and reduced the levels of apoptosis in hippocampal nerve cells. These results suggested that the anti-depressive effect of MGV may occur through the inhibition of inflammatory and oxidative stress pathways and the BDNF/TrkB/AKT pathway. These findings provide a new concept for the identification of new anti-depressive strategies.

Sodium-Glucose Cotransporter-2 Inhibitors in Depression

ABSTRACT

Novel treatment strategies that refract existing treatment algorithms for depressive disorders are being sought. Abnormal brain bioenergetic metabolism may represent an alternative, therapeutically targetable neurobiological basis for depression. A growing body of research points to endogenous ketones as candidate neuroprotective metabolites with the potential to enhance brain bioenergetics and improve mood. Sodium-glucose cotransporter-2 (SGLT2) inhibitors, originally approved for the treatment of diabetes, induce ketogenesis and are associated with mood improvement in population-based studies. In this column, we highlight the rationale for the hypothesis that ketogenesis induced by SGLT2 inhibitors may be an effective treatment for depressive disorders.

Differential expression and roles of Huntingtin and Huntingtin-associated protein 1 in the mouse and primate brains

Huntingtin-associated protein 1 (HAP1) is the first identified protein whose function is affected by its abnormal interaction with mutant huntingtin (mHTT), which causes Huntington disease. However, the expression patterns of Hap1 and Htt in the rodent brain are not correlated. Here we found that the primate HAP1, unlike the rodent Hap1, is correlatively expressed with HTT in the primate brains. CRISPR/Cas9 targeting revealed that HAP1 deficiency in the developing human neurons did not affect neuronal differentiation and gene expression as seen in the mouse neurons. However, deletion of HAP1 exacerbated neurotoxicity of mutant HTT in the organotypic brain slices of adult monkeys. These findings demonstrate differential HAP1 expression and function in the mouse and primate brains, and suggest that interaction of HAP1 with mutant HTT may be involved in mutant HTT-mediated neurotoxicity in adult primate neurons.

Mettl3-mediated m6 A modification of Lrp2 facilitates neurogenesis through Ythdc2 and elicits antidepressant-like effects

N⁶ -methyladenosine (m⁶ A) is the most abundant mRNA modification affecting diverse biological processes. However, the functions and precise mechanisms of m⁶ A signaling in adult hippocampal neurogenesis and neurogenesis-related depression remain largely enigmatic. We found that depletion of Mettl3 or Mettl14 in neural stem cells (NSCs) dramatically reduced m⁶ A abundance, proliferation, and neuronal genesis, coupled with enhanced glial differentiation. Conversely, overexpressing Mettl3 promoted proliferation and neuronal differentiation. Mechanistically, the m⁶ A modification of Lrp2 mRNA by Mettl3 enhanced its stability and translation efficiency relying on the reader protein Ythdc2, which in turn promoted neurogenesis. Importantly, mice lacking Mettl3 manifested reduced hippocampal neurogenesis, which could contribute to spatial memory decline, and depression-like behaviors. We found that these defective behaviors were notably reversed by Lrp2 overexpression. Moreover, Mettl3 overexpression in the hippocampus of depressive mice rescues behavioral defects. Our findings uncover the biological role of m⁶ A modification in Lrp2-mediated neurogenesis via m⁶ A-binding protein Ythdc2, and propose a rationale that targeting Mettl3-Ythdc2-Lrp2 axis regulation of neurogenesis might serve as a promising antidepressant strategy.

Integrated Multi-Omics Analysis Reveals the Effect of Maternal Gestational Diabetes on Fetal Mouse Hippocampi

Growing evidence suggests that adverse intrauterine environments could affect the long-term health of offspring. Recent evidence indicates that gestational diabetes mellitus (GDM) is associated with neurocognitive changes in offspring. However, the mechanism remains unclear. Using a GDM mouse model, we collected hippocampi, the structure critical to cognitive processes, for electron microscopy, methylome and transcriptome analyses. Reduced representation bisulfite sequencing (RRBS) and RNA-seq in the GDM fetal hippocampi showed altered methylated modification and differentially expressed genes enriched in common pathways involved in neural synapse organization and signal transmission. We further collected fetal mice brains for metabolome analysis and found that in GDM fetal brains, the metabolites displayed significant changes, in addition to directly inducing cognitive dysfunction, some of which are important to methylation status such as betaine, fumaric acid, L-methionine, succinic acid, 5-methyltetrahydrofolic acid, and S-adenosylmethionine (SAM). These results suggest that GDM affects metabolites in fetal mice brains and further affects hippocampal DNA methylation and gene regulation involved in cognition, which is a potential mechanism for the adverse neurocognitive effects of GDM in offspring.

Dexamethasone Protects Against Ischaemic Brain Injury via Inhibiting the pAkt Signalling Pathway Through Increasing Hap1

Dexamethasone has been reported to reduce the infarct volume and protect neurological function after ischaemic injury, but the mechanism of Dex in brain injury is not clear. We aimed to study the mechanism by which dexamethasone protects against ischaemic brain injury. Western blotting was to detected the expression of Hap1,TrkB, Akt and Erk; TTC staining to analyse ischemic volume; neurological deficit evaluation to test degree of ischemic injury; immunofluorescence staining to analyse the distribution of Hap1; and the MCAO model was used to study these processes. All data are expressed as the means ± SEM and were analysed by GraphPad Prism 6. P < 0.05 was considered statistically significant. After dexamethasone (Dex) treatment, Hap1 levels were increased and peaked at 2 days; then, we found that body weight was decreased in Hap1-/+ mice. Further study showed that Dex treatment reduced the ischaemic volume and improved neurological function. Finally, we showed that Hap1 regulated the levels of pTrkB, pAkt and pErk 1/2 in ischaemic injury after Dex treatment. Our data suggest that dexamethasone protects against ischaemic brain injury by inhibiting the pAkt signalling pathway through increasing Hap1.

Huntingtin-associated protein 1 plays an essential role in the pathogenesis of type 2 diabetes by regulating the translocation of GLUT4 in mouse adipocytes

OBJECTIVE

Glucose disposal by insulin-responsive tissues maintains the body glucose homeostasis and insulin resistance leads to a risk of developing type 2 diabetes (T2DM). Insulin stimulates the translocation of glucose transporter isoform 4 (GLUT4) vesicles from intracellular compartments to the plasma membrane to facilitate glucose uptake. However, the underlying mechanisms of GLUT4 vesicle translocation are not well defined. Here we show the role of huntingtin-associated protein 1 (HAP1) in GLUT4 translocation in adipocytes and the pathogenesis of T2DM.

RESEARCH DESIGN AND METHODS

The parameters for glucose metabolism including body weight, glucose tolerance and insulin tolerance were assessed in wild-type (WT) and Hap1^+/- mice. HAP1 protein expression was verified in adipose tissue. Hap1 mRNA and protein expression was monitored in adipose tissue of high-fat diet (HFD)-induced diabetic mice. Insulin-stimulated GLUT4 vesicle translocation and glucose uptake were detected using immunofluorescence techniques and quantified in primary adipocytes from Hap1^-/- mice. The interaction between HAP1 and GLUT4 was assessed by immunofluorescence colocalization and co-immunoprecipitation in HEK293 cells and adipose tissue. The role of sortilin in HAP1 and GLUT4 interaction was approved by co-immunoprecipitation and RNA interference.

RESULTS

The expression of Hap1 mRNA and protein was detected in WT mouse adipose tissue and downregulated in adipose tissue of HFD-induced diabetic mice. Hap1^+/- mice exhibited increased body weight, pronounced glucose tolerance and significant insulin intolerance compared with the WT mice. HAP1 colocalized with GLUT4 in mouse adipocytes and cotransfected HEK293 cells. Furthermore, the insulin-stimulated GLUT4 vesicle translocation and glucose uptake were defective in Hap1^-/- adipocytes. Finally, sortilin mediated the interaction of HAP1 and GLUT4.

CONCLUSIONS

Our study showed that HAP1 formed a protein complex with GLUT4 and sortilin, and played a critical role in insulin-stimulated GLUT4 translocation in adipocytes. Its downregulation may contribute to the pathogenesis of diabetes.

HAP1 is an in vivo UBE3A target that augments autophagy in a mouse model of Angelman syndrome

Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by maternal mutation and paternal imprinting of the gene encoding UBE3A, an E3 ubiquitin ligase. Although several potential target proteins of UBE3A have been reported, how these proteins regulate neuronal development remains unclear. We performed a large-scale quantitative proteomic analysis using stable-isotope labeling of amino acids in mammals (SILAM) in mice with maternal Ube3a mutation. We identified huntingtin (Htt)-associated protein (HAP1), a protein that is involved in Huntington's disease (HD), as a new target of UBE3A. We demonstrate that HAP1 regulates autophagy at the initiation stage by promoting PtdIns3K complex formation and enhancing its activity. HAP1 also co-localized with MAP1LC3 (LC3) and other proteins involved in autophagosome expansion. As a result, HAP1 increased autophagy flux. Strikingly, knocking down of HAP1 alleviated aberrant autophagy in primary neurons from AS mice. Concordantly, treatment of AS neurons with an autophagy inhibitor alleviated the reduction in density of dendritic spines. Furthermore, autophagy inhibition in AS mice partially alleviated a social interaction deficit as shown in open field test. Thus, our results identify HAP1 as an in vivo UBE3A target that contributes to deregulated autophagy and synaptic dysfunction in the central nervous system of AS mouse.

Expression of AHI1 Rescues Amyloidogenic Pathology in Alzheimer's Disease Model Cells

A hallmark of Alzheimer's disease (AD) pathogenesis is the accumulation of extracellular plaques mainly composed of amyloid-β (Aβ) derived from amyloid precursor protein (APP) cleavage. Recent reports suggest that transport of APP in vesicles with huntingtin-associated protein-1 (HAP1) negatively regulates Aβ production. In neurons, HAP1 forms a stable complex with Abelson helper integration site-1 (AHI1), in which mutations cause neurodevelopmental and psychiatric disorders. HAP1 and AHI1 interact with tropomyosin receptor kinases (Trks), which are also associated with APP and mediate neurotrophic signaling. In this study, we hypothesize that AHI1 participates in APP trafficking and processing to rescue AD pathology. Indeed, AHI1 was significantly reduced in mouse neuroblastoma N2a cells expressing human Swedish and Indiana APP (designed as AD model cells) and in 3xTg-AD mouse brain. The AD model cells as well as Ahi1-knockdown cells expressing wild-type APP-695 exhibited a significant reduction in viability. In addition, the AD model cells were reduced in neurite outgrowth. APP C-terminal fragment-β (CTFβ) and Aβ42 were increased in the AD cell lysates and the culture media, respectively. To investigate the mechanism how AHI1 alters APP activities, we overexpressed human AHI1 in the AD model cells. The results showed that AHI1 interacted with APP physically in mouse brain and transfected N2a cells despite APP genotypes. AHI1 expression facilitated intracellular translocation of APP and inhibited APP amyloidogenic process to reduce the level of APP-CTFβ in the total lysates of AD model cells as well as Aβ in the culture media. Consequently, AHI1-APP interactions enhanced neurotrophic signaling through Erk activation and led to restored cell survival and differentiation.

PINK1 deficiency is associated with increased deficits of adult hippocampal neurogenesis and lowers the threshold for stress-induced depression in mice

Parkinson's disease (PD) is characterized by motor impairments and several non-motor features, including frequent depression and anxiety. Stress-induced deficits of adult hippocampal neurogenesis (AHN) have been linked with abnormal affective behavior in animals. It has been speculated that AHN defects may contribute to affective symptoms in PD, but this hypothesis remains insufficiently tested in animal models. Mice that lack the PD-linked kinase PINK1 show impaired differentiation of adult-born neurons in the hippocampus. Here, we examined the relationship between AHN deficits and affective behavior in PINK1^-/- mice under basal (no stress) conditions and after exposure to chronic stress. PINK1 loss and corticosterone negatively and jointly affected AHN, leading to lower numbers of neural stem cells and newborn neurons in the dentate gyrus of corticosterone-treated PINK1^-/- mice. Despite increased basal AHN deficits, PINK1-deficient mice showed normal affective behavior. However, lack of PINK1 sensitized mice to corticosterone-induced behavioral despair in the tail suspension test at a dose where wildtype mice were unaffected. Moreover, after two weeks of chronic restraint stress male PINK1^-/- mice displayed increased immobility in the forced swim test, and protein expression of the glucocorticoid receptor in the hippocampus was reduced. Thus, while impaired AHN as such is insufficient to cause affective dysfunction in this PD model, PINK1 deficiency may lower the threshold for chronic stress-induced depression in PD. Finally, PINK1-deficient mice displayed reduced basal voluntary wheel running but normal rotarod performance, a finding whose mechanisms remain to be determined.

Open chromatin dynamics reveals stage-specific transcriptional networks in hiPSC-based neurodevelopmental model

Chromatin accessibility to transcription factors (TFs) strongly influences gene transcription and cell differentiation. However, a mechanistic understanding of the transcriptional control during the neuronal differentiation of human induced pluripotent stem cells (hiPSCs), a promising cellular model for mental disorders, remains elusive. Here, we carried out additional analyses on our recently published open chromatin regions (OCRs) profiling at different stages of hiPSC neuronal differentiation. We found that the dynamic changes of OCR during neuronal differentiation highlighted cell stage-specific gene networks, and the chromatin accessibility at the core promoter region of a gene correlates with the corresponding transcript abundance. Within the cell stage-specific OCRs, we identified the binding of cell stage-specific TFs and observed a lag of a neuronal TF binding behind the mRNA expression of the corresponding TF. Interestingly, binding footprints of NEUROD1 and NEUROG2, both of which induce high efficient conversion of hiPSCs to glutamatergic neurons, were among those most enriched in the relatively mature neurons. Furthermore, TF network analysis showed that both NEUROD1 and NEUROG2 were present in the same core TF network specific to more mature neurons, suggesting a pivotal mechanism of epigenetic control of neuronal differentiation and maturation. Our study provides novel insights into the epigenetic control of glutamatergic neurogenesis in the context of TF networks, which may be instrumental to improving hiPSC modeling of neuropsychiatric disorders.

Mast cells increase adult neural precursor proliferation and differentiation but this potential is not realized in vivo under physiological conditions

There is growing evidence that both peripheral and resident immune cells play an important part in regulating adult neural stem cell proliferation and neurogenesis, although the contribution of the various immune cell types is still unclear. Mast cells, a population of immune cells known for their role in the allergic response, have been implicated in the regulation of adult hippocampal neurogenesis. Mast cell-deficient c-kit^W-sh/W-sh mice have previously been shown to exhibit significantly decreased adult hippocampal neurogenesis and associated learning and memory deficits. However, given that numerous other cell types also express high levels of c-kit, the utility of these mice as a reliable model of mast cell-specific depletion is questionable. We show here, using a different model of mast cell deficiency (Mcpt5CreR26^DTA/DTA), that precursor proliferation and adult neurogenesis are not influenced by mast cells in vivo. Interestingly, when applied at supraphysiological doses, mast cells can activate latent hippocampal precursor cells and increase subventricular zone precursor proliferation in vitro, an effect that can be blocked with specific histamine-receptor antagonists. Thus, we conclude that while both mast cells and their major chemical mediator histamine have the potential to affect neural precursor proliferation and neurogenesis, this is unlikely to occur under physiological conditions.

A pilot investigation on DNA methylation modifications associated with complex posttraumatic symptoms in elderly traumatized in childhood

OBJECTIVE

Complex posttraumatic stress disorder (CPTSD) is a newly proposed diagnosis in the International Classification of Diseases-version 11, which is currently intensively investigated. Childhood trauma is regarded as main source of CPTSD symptoms, even in later life. Induction of DNA methylation changes by childhood trauma may contribute to its long-lasting adverse health consequences. The current study analyzed the correlation of genome-wide DNA methylation profiles with complex posttraumatic sequelae in buccal epithelial cells from 31 elderly former indentured child laborers (Verdingkinder) using the Infinium Illumina 450k Human DNA methylation chip.

RESULTS

DNA methylation modifications indicated experiment-wide significant associations with the following complex posttraumatic symptom domains: dissociation, tension reduction behavior and dysfunctional sexual behavior. Differentially methylated CpG sites were mapped to the genes huntington associated protein 1 (HAP1), RAN binding protein 2 (RANBP2) and proteasome subunit alpha 4 (PSMA4), respectively. In addition, the methylation of cg07225277 located in carnosine synthase 1 (CARNS1) correlated with trauma symptom complexity. Our pilot data suggest correlation of DNA methylation modifications with complex posttraumatic symptoms in elderly individuals subjected to prolonged and complex childhood trauma. More comprehensive and elaborated studies should be carried out to analyze epigenetic modifications associated with CPTSD.

Behavioral Phenotyping Assays for Genetic Mouse Models of Neurodevelopmental, Neurodegenerative, and Psychiatric Disorders

Animal models offer heuristic research tools to understand the causes of human diseases and to identify potential treatments. With rapidly evolving genetic engineering technologies, mutations identified in a human disorder can be generated in the mouse genome. Phenotypic outcomes of the mutation are then explicated to confirm hypotheses about causes and to discover effective therapeutics. Most neurodevelopmental, neurodegenerative, and psychiatric disorders are diagnosed primarily by their prominent behavioral symptoms. Mouse behavioral assays analogous to the human symptoms have been developed to analyze the consequences of mutations and to evaluate proposed therapeutics preclinically. Here we describe the range of mouse behavioral tests available in the established behavioral neuroscience literature, along with examples of their translational applications. Concepts presented have been successfully used in other species, including flies, worms, fish, rats, pigs, and nonhuman primates. Identical strategies can be employed to test hypotheses about environmental causes and gene × environment interactions.

Synergistic Toxicity of Polyglutamine-Expanded TATA-Binding Protein in Glia and Neuronal Cells: Therapeutic Implications for Spinocerebellar Ataxia 17

Spinocerebellar ataxia 17 (SCA17) is caused by polyglutamine (polyQ) repeat expansion in the TATA-binding protein (TBP) and is among a family of neurodegenerative diseases in which polyQ expansion leads to preferential neuronal loss in the brain. Although previous studies have demonstrated that expression of polyQ-expanded proteins in glial cells can cause neuronal injury via noncell-autonomous mechanisms, these studies investigated animal models that overexpress transgenic mutant proteins. Since glial cells are particularly reactive to overexpressed mutant proteins, it is important to investigate the in vivo role of glial dysfunction in neurodegeneration when mutant polyQ proteins are endogenously expressed. In the current study, we generated two conditional TBP-105Q knock-in mouse models that specifically express mutant TBP at the endogenous level in neurons or in astrocytes. We found that mutant TBP expression in neuronal cells or astrocytes alone only caused mild neurodegeneration, whereas severe neuronal toxicity requires the expression of mutant TBP in both neuronal and glial cells. Coculture of neurons and astrocytes further validated that mutant TBP in astrocytes promoted neuronal injury. We identified activated inflammatory signaling pathways in mutant TBP-expressing astrocytes, and blocking nuclear factor κB (NF-κB) signaling in astrocytes ameliorated neurodegeneration. Our results indicate that the synergistic toxicity of mutant TBP in neuronal and glial cells plays a critical role in SCA17 pathogenesis and that targeting glial inflammation could be a potential therapeutic approach for SCA17 treatment.SIGNIFICANCE STATEMENT Mutant TBP with polyglutamine expansion preferentially affects neuronal viability in SCA17 patients. Whether glia, the cells that support and protect neurons, contribute to neurodegeneration in SCA17 remains mostly unexplored. In this study, we provide both in vivo and in vitro evidence arguing that endogenous expression of mutant TBP in neurons and glia synergistically impacts neuronal survival. Hyperactivated inflammatory signaling pathways, particularly the NF-κB pathway, underlie glia-mediated neurotoxicity. Moreover, blocking NF-κB activity with small chemical inhibitors alleviated such neurotoxicity. Our study establishes glial dysfunction as an important component of SCA17 pathogenesis and suggests targeting glial inflammation as a potential therapeutic approach for SCA17 treatment.

DYRK1A regulates Hap1-Dcaf7/WDR68 binding with implication for delayed growth in Down syndrome

Huntingtin-associated protein 1 (Hap1) is known to be critical for postnatal hypothalamic function and growth. Hap1 forms stigmoid bodies (SBs), unique neuronal cytoplasmic inclusions of unknown function that are enriched in hypothalamic neurons. Here we developed a simple strategy to isolate the SB-enriched fraction from mouse brain. By analyzing Hap1 immunoprecipitants from this fraction, we identified a Hap1-interacting SB component, DDB1 and CUL4 associated factor 7 (Dcaf7)/WD40 repeat 68 (WDR68), whose protein level and nuclear translocation are regulated by Hap1. Moreover, we found that Hap1 bound Dcaf7 competitively in cytoplasm with dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A), a protein implicated in Down syndrome (DS). Depleting Hap1 promoted the DYRK1A-Dcaf7 interaction and increased the DYRK1A protein level. Transgenic DS mice overexpressing DYRK1A showed reduced Hap1-Dcaf7 association in the hypothalamus. Furthermore, the overexpression of DYRK1A in the hypothalamus led to delayed growth in postnatal mice, suggesting that DYRK1A regulates the Hap1-Dcaf7 interaction and postnatal growth and that targeting Hap1 or Dcaf7 could ameliorate growth retardation in DS.

Whole exome sequencing of Rett syndrome-like patients reveals the mutational diversity of the clinical phenotype

Classical Rett syndrome (RTT) is a neurodevelopmental disorder where most of cases carry MECP2 mutations. Atypical RTT variants involve mutations in CDKL5 and FOXG1. However, a subset of RTT patients remains that do not carry any mutation in the described genes. Whole exome sequencing was carried out in a cohort of 21 female probands with clinical features overlapping with those of RTT, but without mutations in the customarily studied genes. Candidates were functionally validated by assessing the appearance of a neurological phenotype in Caenorhabditis elegans upon disruption of the corresponding ortholog gene. We detected pathogenic variants that accounted for the RTT-like phenotype in 14 (66.6 %) patients. Five patients were carriers of mutations in genes already known to be associated with other syndromic neurodevelopmental disorders. We determined that the other patients harbored mutations in genes that have not previously been linked to RTT or other neurodevelopmental syndromes, such as the ankyrin repeat containing protein ANKRD31 or the neuronal acetylcholine receptor subunit alpha-5 (CHRNA5). Furthermore, worm assays demonstrated that mutations in the studied candidate genes caused locomotion defects. Our findings indicate that mutations in a variety of genes contribute to the development of RTT-like phenotypes.

Huntingtin-associated protein 1: Eutherian adaptation from a TRAK-like protein, conserved gene promoter elements, and localization in the human intestine

Background

Huntingtin-associated Protein 1 (HAP1) is expressed in neurons and endocrine cells, and is critical for postnatal survival in mice. HAP1 shares a conserved “HAP1_N” domain with TRAfficking Kinesin proteins TRAK1 and TRAK2 (vertebrate), Milton (Drosophila) and T27A3.1 (C. elegans). HAP1, TRAK1 and TRAK2 have a degree of common function, particularly regarding intracellular receptor trafficking. However, TRAK1, TRAK2 and Milton (which have a “Milt/TRAK” domain that is absent in human and rodent HAP1) differ in function to HAP1 in that they are mitochondrial transport proteins, while HAP1 has emerging roles in starvation response. We have investigated HAP1 function by examining its evolution, and upstream gene promoter sequences. We performed phylogenetic analyses of the HAP1_N domain family of proteins, incorporating HAP1 orthologues (identified by genomic synteny) from 5 vertebrate classes, and also searched the Dictyostelium proteome for a common ancestor. Computational analyses of mammalian HAP1 gene promoters were performed to identify phylogenetically conserved regulatory motifs.

Results

We found that as recently as marsupials, HAP1 contained a Milt/TRAK domain and was more similar to TRAK1 and TRAK2 than to eutherian HAP1. The Milt/TRAK domain likely arose post multicellularity, as it was absent in the Dictyostelium proteome. It was lost from HAP1 in the eutherian lineage, and also from T27A3.1 in C. elegans. The HAP1 promoter from human, mouse, rat, rabbit, horse, dog, Tasmanian devil and opossum contained common sites for transcription factors involved in cell cycle, growth, differentiation, and stress response. A conserved arrangement of regulatory elements was identified, including sites for caudal-related homeobox transcription factors (CDX1 and CDX2), and myc-associated factor X (MAX) in the region of the TATA box. CDX1 and CDX2 are intestine-enriched factors, prompting investigation of HAP1 protein expression in the human duodenum. HAP1 was localized to singly dispersed mucosal cells, including a subset of serotonin-positive enterochromaffin cells.

Conclusion

We have identified eutherian HAP1 as an evolutionarily recent adaptation of a vertebrate TRAK protein-like ancestor, and found conserved CDX1/CDX2 and MAX transcription factor binding sites near the TATA box in mammalian HAP1 gene promoters. We also demonstrated that HAP1 is expressed in endocrine cells of the human gut.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-016-0780-3) contains supplementary material, which is available to authorized users.

Stress-Induced Anxiety- and Depressive-Like Phenotype Associated with Transient Reduction in Neurogenesis in Adult Nestin-CreERT2/Diphtheria Toxin Fragment A Transgenic Mice

Depression and anxiety involve hippocampal dysfunction, but the specific relationship between these mood disorders and adult hippocampal dentate gyrus neurogenesis remains unclear. In both humans with MDD and rodent models of depression, administration of antidepressants increases DG progenitor and granule cell number, yet rodents with induced ablation of DG neurogenesis typically do not demonstrate depressive- or anxiety-like behaviors. The conflicting data may be explained by the varied duration and degree to which adult neurogenesis is reduced in different rodent neurogenesis ablation models. In order to test this hypothesis we examined how a transient–rather than permanent–inducible reduction in neurogenesis would alter depressive- and anxiety-like behaviors. Transgenic Nestin-CreER^T2/floxed diphtheria toxin fragment A (DTA) mice (Cre+DTA+) and littermates (Cre+DTA-; control) were given tamoxifen (TAM) to induce recombination and decrease nestin-expressing stem cells and their progeny. The decreased neurogenesis was transient: 12 days post-TAM Cre+DTA+ mice had fewer DG proliferating Ki67+ cells and fewer DCX+ neuroblasts/immature neurons relative to control, but 30 days post-TAM Cre+DTA+ mice had the same DCX+ cell number as control. This ability of DG neurogenesis to recover after partial ablation also correlated with changes in behavior. Relative to control, Cre+DTA+ mice tested between 12–30 days post-TAM displayed indices of a stress-induced anxiety phenotype–longer latency to consume highly palatable food in the unfamiliar cage in the novelty-induced hypophagia test, and a depression phenotype–longer time of immobility in the tail suspension test, but Cre+DTA+ mice tested after 30 days post-TAM did not. These findings suggest a functional association between adult neurogenesis and stress induced anxiety- and depressive-like behaviors, where induced reduction in DCX+ cells at the time of behavioral testing is coupled with stress-induced anxiety and a depressive phenotype, and recovery of DCX+ cell number corresponds to normalization of these behaviors.

Exosomes as Novel Regulators of Adult Neurogenic Niches

Adult neurogenesis has been convincingly demonstrated in two regions of the mammalian brain: the sub-granular zone (SGZ) of the dentate gyrus (DG) in the hippocampus, and the sub-ventricular zone (SVZ) of the lateral ventricles (LV). SGZ newborn neurons are destined to the granular cell layer (GCL) of the DG, while new neurons from the SVZ neurons migrate rostrally into the olfactory bulb (OB). The process of adult neurogenesis persists throughout life and is supported by a pool of neural stem cells (NSCs), which reside in a unique and specialized microenvironment known as "neurogenic niche". Neurogenic niches are structured by a complex organization of different cell types, including the NSC-neuron lineage, glial cells and vascular cells. Thus, cell-to-cell communication plays a key role in the dynamic modulation of homeostasis and plasticity of the adult neurogenic process. Specific cell-cell contacts and extracellular signals originated locally provide the necessary support and regulate the balance between self-renewal and differentiation of NSCs. Furthermore, extracellular signals originated at distant locations, including other brain regions or systemic organs, may reach the niche through the cerebrospinal fluid (CSF) or the vasculature and influence its nature. The role of several secreted molecules, such as cytokines, growth factors, neurotransmitters, and hormones, in the biology of adult NSCs, has been systematically addressed. Interestingly, in addition to these well-recognized signals, a novel type of intercellular messengers has been identified recently: the extracellular vesicles (EVs). EVs, and particularly exosomes, are implicated in the transfer of mRNAs, microRNAs (miRNAs), proteins and lipids between cells and thus are able to modify the function of recipient cells. Exosomes appear to play a significant role in different stem cell niches such as the mesenchymal stem cell niche, cancer stem cell niche and pre-metastatic niche; however, their roles in adult neurogenic niches remain virtually unexplored. This review focuses on the current knowledge regarding the functional relationship between cellular and extracellular components of the adult SVZ and SGZ neurogenic niches, and the growing evidence that supports the potential role of exosomes in the physiology and pathology of adult neurogenesis.