AP2γ controls adult hippocampal neurogenesis and modulates cognitive, but not anxiety or depressive-like behavior

Integrative bioinformatic approach reveals novel melatonin-related biomarkers for Alzheimer's disease

BACKGROUND

Melatonin (MLT) can improve mitophagy, thereby ameliorating cognitive deficits in Alzheimer's disease (AD) patients. Hence, our research focused on the potential value of MLT-related genes (MRGs) in AD through bioinformatic analysis.

METHODS

First, the key cells in the single-cell dataset GSE138852 were screened out based on the proportion of annotated cells and Fisher's test between the AD and control groups. The differentially expressed genes (DEGs) in the key cell and GSE5281 datasets were identified, and the MRGs in GSE5281 were selected via weighted gene coexpression network analysis. After intersecting two sets of DEGs and MRGs, we performed Mendelian randomization analysis to identify the MRGs causally related to AD. Biomarkers were further ascertained through receiver operating characteristic curve (ROC) and expression analysis in GSE5281 and GSE48350. Furthermore, gene set enrichment analysis, immune infiltration analysis and correlation analysis with metabolic pathways were conducted, as well as construction of a regulator network and molecular docking.

RESULTS

According to the Fisher test, oligodendrocytes were regarded as key cells due to their excellent abundance in the GSE138852 dataset, in which there were 281 DEGs between the AD and control groups. After overlapping with 3,490 DEGs and 550 MRGs in GSE5281, four genes were found to be causally related to AD, namely, G protein-coupled receptor, family C, group 5, member B (GPRC5B), Methyltransferase-like protein 7 A (METTL7A), NF-κB inhibitor alpha (NFKBIA) and RAS association domain family 4(RASSF4). Moreover, GPRC5B, NFKBIA and RASSF4 were deemed biomarkers, except for METTL7A, because of their indistinctive expression between the AD and control groups. Biomarkers might be involved in oxidative phosphorylation, adipogenesis and heme metabolism. Moreover, T helper type 17 cells, natural killer cells and CD56dim natural killer cells were significantly correlated with biomarkers. Transcription factors (GATA2, POU2F2, NFKB1, etc.) can regulate the expression of biomarkers. Finally, we discovered that all biomarkers could bind to MLT with a strong binding energy.

CONCLUSION

Our study identified three novel biomarkers related to MLT for AD, namely, GPRC5B, NFKBIA and RASSF4, providing a novel approach for the investigation and treatment of AD patients.

Maternal separation during lactation affects recognition memory, emotional behaviors, hippocampus and gut microbiota composition in C57BL6J adolescent female mice

BACKGROUND

Maternal separation (MS) in rodents is a paradigm of early life events that affects neurological development in depression. Adolescence is a time of dramatic increases in psychological vulnerability, and being female is a depression risk factor. However, data on whether different MS scenarios affect behavioral deficits and the potential mechanisms in adolescent female mice are limited.

METHODS

C57BL/6 J female pups were exposed to different MS (no MS, NMS; MS for 15 min/day, MS15; or 180 min/day, MS180) from postnatal day (PND)1 to PND21 and subjected for behavioral tests during adolescence. Behavioural tests, specifically the open field test (OFT), novel object recognition test (NOR) test and tail suspension test (TST), were performed. The expression of proinflammatory cytokines, hippocampal neurogenesis, neuroinflammation, and gut microbiota were also assessed.

RESULTS

The results showed that MS180 induced emotional behavioral deficits and object recognition memory impairment; however, MS15 promoted object recognition memory in adolescent females. MS180 decreased hippocampal neurogenesis of adolescent females, induced an increase in microgliosis, and increased certain inflammatory factors in the hippocampus, including TNF-α, IL-1β, and IL-6. Furthermore, different MS altered gut microbiota diversity, and alpha diversity in the Shannon index was negatively correlated with the peripheral inflammatory factors TNF-α, IL-1β, and IL-6. Species difference analysis showed that the gut microbiota composition of the phyla Desulfobacterota and Proteobacteria was affected by the MS.

LIMITATIONS

The sex differences in adolescent animal and causality of hippocampal neurogenesis and gut microbiota under different MS need to be further analyzed in depression.

CONCLUSION

This study indicates different MS affect recognition memory and emotional behaviors in adolescent females, and gut microbiota-neuroinflammation and hippocampal neurogenesis may be a potential site of early neurodevelopmental impairment in depression.

Infliximab alleviates memory impairment in rats with chronic pain by suppressing neuroinflammation and restoring hippocampal neurogenesis

Patients with chronic pain commonly report impaired memory. Increasing evidence has demonstrated that inhibition of neurogenesis by neuroinflammation plays a crucial role in chronic pain-associated memory impairments. There is currently a lack of treatment strategies for this condition. An increasing number of clinical trials have reported the therapeutic potential of anti-inflammatory therapies targeting tumour necrosis factor-α (TNF-α) for inflammatory diseases. The present study investigated whether infliximab alleviates chronic pain-associated memory impairments in rats with chronic constriction injury (CCI). We demonstrated that infliximab alleviated spatial memory impairment and hyperalgesia induced by CCI. Furthermore, infliximab inhibited the activation of hippocampal astrocytes and microglia and decreased the release of proinflammatory cytokines in CCI rats. Furthermore, infliximab reversed the decrease in the numbers of newborn neurons and mature neurons in the dentate gyrus (DG) caused by chronic pain. Our data provide evidence that infliximab alleviates chronic pain-associated memory impairments, suppresses neuroinflammation and restores hippocampal neurogenesis in a CCI model. These facts indicate that infliximab may be a potential therapeutic agent for the treatment of chronic pain and associated memory impairments.

Transcriptome analysis reveals genes associated with stem cell activation by physical exercise in the dentate gyrus of aged p16Ink4a knockout mice

Throughout adulthood neural stem cells divide in neurogenic niches-the dentate gyrus of the hippocampus and the subventricular zone-producing progenitor cells and new neurons. Stem cells self-renew, thus preserving their pool. Furthermore, the number of stem/progenitor cells in the neurogenic niches decreases with age. We have previously demonstrated that the cyclin-dependent kinase inhibitor p16Ink4a maintains, in aged mice, the pool of dentate gyrus stem cells by preventing their activation after a neurogenic stimulus such as exercise (running). We showed that, although p16Ink4a ablation by itself does not activate stem/progenitor cells, exercise strongly induced stem cell proliferation in p16Ink4a knockout dentate gyrus, but not in wild-type. As p16Ink4a regulates stem cell self-renewal during aging, we sought to profile the dentate gyrus transcriptome from p16Ink4a wild-type and knockout aged mice, either sedentary or running for 12 days. By pairwise comparisons of differentially expressed genes and by correlative analyses through the DESeq2 software, we identified genes regulated by p16Ink4a deletion, either without stimulus (running) added, or following running. The p16Ink4a knockout basic gene signature, i.e., in sedentary mice, involves upregulation of apoptotic, neuroinflammation- and synaptic activity-associated genes, suggesting a reactive cellular state. Conversely, another set of 106 genes we identified, whose differential expression specifically reflects the pattern of proliferative response of p16 knockout stem cells to running, are involved in processes that regulate stem cell activation, such as synaptic function, neurotransmitter metabolism, stem cell proliferation control, and reactive oxygen species level regulation. Moreover, we analyzed the regulation of these stem cell-specific genes after a second running stimulus. Surprisingly, the second running neither activated stem cell proliferation in the p16Ink4a knockout dentate gyrus nor changed the expression of these genes, confirming that they are correlated to the stem cell reactivity to stimulus, a process where they may play a role regulating stem cell activation.

Neuronal TIMP2 regulates hippocampus-dependent plasticity and extracellular matrix complexity

Functional output of the hippocampus, a brain region subserving memory function, depends on highly orchestrated cellular and molecular processes that regulate synaptic plasticity throughout life. The structural requirements of such plasticity and molecular events involved in this regulation are poorly understood. Specific molecules, including tissue inhibitor of metalloproteinases-2 (TIMP2) have been implicated in plasticity processes in the hippocampus, a role that decreases with brain aging as expression is lost. Here, we report that TIMP2 is highly expressed by neurons within the hippocampus and its loss drives changes in cellular programs related to adult neurogenesis and dendritic spine turnover with corresponding impairments in hippocampus-dependent memory. Consistent with the accumulation of extracellular matrix (ECM) in the hippocampus we observe with aging, we find that TIMP2 acts to reduce accumulation of ECM around synapses in the hippocampus. Moreover, its deletion results in hindrance of newborn neuron migration through a denser ECM network. A novel conditional TIMP2 knockout (KO) model reveals that neuronal TIMP2 regulates adult neurogenesis, accumulation of ECM, and ultimately hippocampus-dependent memory. Our results define a mechanism whereby hippocampus-dependent function is regulated by TIMP2 and its interactions with the ECM to regulate diverse processes associated with synaptic plasticity.

Fibroblast exosomal TFAP2C induced by chitosan oligosaccharides promotes peripheral axon regeneration via the miR-132-5p/CAMKK1 axis

Chitosan and its degradation product, oligosaccharides, have been shown to facilitate peripheral nerve regeneration. However, the underlying mechanisms are not well understood. In this study, we analyzed the protein expression profiles in sciatic nerves after injury using proteomics. A group of proteins related to exosome packaging and transport is up-regulated by chitosan oligosaccharides (COS), implying that exosomes are involved in COS-induced peripheral nerve regeneration. In fact, exosomes derived from fibroblasts (f-EXOs) treated with COS significantly promoted axon extension and regeneration. Exosomal protein identification and functional studies, revealed that TFAP2C is a key factor in neurite outgrowth induced by COS-f-EXOs. Furthermore, we showed that TFAP2C targets the pri-miRNA-132 gene and represses miR-132-5p expression in dorsal root ganglion neurons. Camkk1 is a downstream substrate of miR-132-5p that positively affects axon extension. In rats, miR-132-5p antagomir stimulates CAMKK1 expression and improves axon regeneration and functional recovery in sciatic nerves after injury. Our data reveal the mechanism for COS in axon regeneration, that is COS induce fibroblasts to produce TFAP2C-enriched EXOs, which are then transferred into axons to promote axon regeneration via miR-132-5p/CAMKK1. Moreover, these results show a new facet of fibroblasts in axon regeneration in peripheral nerves.

Transcriptomics in the nucleus accumbens shell reveal sex- and reinforcer-specific signatures associated with morphine and sucrose craving

Incubation of craving is a well-documented phenomenon referring to the intensification of drug craving over extended abstinence. The neural adaptations that occur during forced abstinence following chronic drug taking have been a topic of intense study. However, little is known about the transcriptomic changes occurring throughout this window of time. To define gene expression changes associated with morphine consumption and extended abstinence, male and female rats underwent 10 days of morphine self-administration. Separate drug-naive rats self-administered sucrose in order to compare opioid-induced changes from those associated with natural, non-drug rewards. After one or 30 days of forced abstinence, rats were tested for craving, or nucleus accumbens shell tissue was dissected for RNA sequencing. Morphine consumption was predictive of drug seeking after extended (30 days) but not brief (1 day) abstinence in both sexes. Extended abstinence was also associated with robust sex- and reinforcer-specific changes in gene expression, suggesting sex differences underlying incubation of morphine and sucrose seeking respectively. Importantly, these changes in gene expression occurred without re-exposure to drug-paired cues, indicating that chronic morphine causes long-lasting changes in gene expression that prime the system for increased craving. These findings lay the groundwork for identifying specific therapeutic targets for curbing opioid craving without impacting the natural reward system in males and females.

Potential genetic biomarkers are found to be associated with both cognitive function and blood pressure: A bivariate genome-wide association analysis

A bivariate genome-wide association study was conducted in 137 pairs of twins to explore the shared genetic loci between cognition and blood pressure (BP). Before SNPs imputation, rs72815554 is significantly (P < 5 × 10-8) associated with the cognition-pulse pressure (PP) phenotype, while after imputation, 4 and 9 SNPs are significantly associated with the cognition-SBP phenotype, and cognition-PP phenotype, respectively, including rs72815554. There existed SNPs with highly linkage disequilibrium (LD) of rs10998339, rs72815554, rs11665292, and rs10823231. Besides, rs10998347, rs12153038, and rs10998295 had higher RegulomeDB scores and are located in the transcription factors binding regions. Rs7574283 and rs58113664 are located in the super-enhancer regions which are expressed highly in the adrenal gland, artery, atrial tissue, brain, nerves, etc. There are 1108, 1154, 1071, and 1102 genes associated with cognition-SBP, cognition-DBP, cognition-PP, and cognition-mean arterial pressure (MAP) phenotypes at the suggestive significant association level (P < 0.05), respectively. Furthermore, 641, 630, 900, and 555 pathways are associated with cognition-SBP, cognition-DBP, cognition-PP, and cognition-MAP phenotypes at the suggestive significant association level (P < 0.05), respectively.

Effects of Septin-14 Gene Deletion on Adult Cognitive/Emotional Behavior

While various septin GTPases have been reported for their physiological functions, their roles in orchestrating complex cognitive/emotional functions in adult mammals remained scarcely explored. A comprehensive behavioral test battery was administered to two sexes of 12-week-old Septin-14 (SEPT14) knockout (KO) and wild-type (WT) mice. The sexually dimorphic effects of brain SEPT14 KO on inhibitory avoidance (IA) and hippocampal mGluR5 expression were noticed with greater IA latency and elevated mGluR5 level exclusively in male KO mice. Moreover, SEPT14 KO appeared to be associated with stress-provoked anxiety increase in a stress-related navigation task regardless of animals’ sexes. While male and female WT mice demonstrated comparable cell proliferation in the dorsal and ventral hippocampal dentate gyrus (DG), both sexes of SEPT14 KO mice had increased cell proliferation in the ventral DG. Finally, male and female SEPT14 KO mice displayed dampened observational fear conditioning magnitude and learning-provoked corticosterone secretion as compared to their same-sex WT mice. These results, taken together, prompt us to conclude that male, but not female, mice lacking the Septin-14 gene may exhibit increased aversive emotion-related learning and dorsal/ventral hippocampal mGluR5 expressions. Moreover, deletion of SEPT14 may be associated with elevated ventral hippocampal DG cell proliferation and stress-provoked anxiety-like behavior, while dampening vicarious fear conditioning magnitudes.

Constitutive deficiency of the neurogenic hippocampal modulator AP2γ promotes anxiety-like behavior and cumulative memory deficits in mice from juvenile to adult periods

The transcription factor activating protein two gamma (AP2γ) is an important regulator of neurogenesis both during embryonic development as well as in the postnatal brain, but its role for neurophysiology and behavior at distinct postnatal periods is still unclear. In this work, we explored the neurogenic, behavioral, and functional impact of a constitutive and heterozygous AP2γ deletion in mice from early postnatal development until adulthood. AP2γ deficiency promotes downregulation of hippocampal glutamatergic neurogenesis, altering the ontogeny of emotional and memory behaviors associated with hippocampus formation. The impairments induced by AP2γ constitutive deletion since early development leads to an anxious-like phenotype and memory impairments as early as the juvenile phase. These behavioral impairments either persist from the juvenile phase to adulthood or emerge in adult mice with deficits in behavioral flexibility and object location recognition. Collectively, we observed a progressive and cumulative impact of constitutive AP2γ deficiency on the hippocampal glutamatergic neurogenic process, as well as alterations on limbic-cortical connectivity, together with functional behavioral impairments. The results herein presented demonstrate the modulatory role exerted by the AP2γ transcription factor and the relevance of hippocampal neurogenesis in the development of emotional states and memory processes.

Hippocampal cytogenesis abrogation impairs inter-regional communication between the hippocampus and prefrontal cortex and promotes the time-dependent manifestation of emotional and cognitive deficits

Impaired ability to generate new cells in the adult brain has been linked to deficits in multiple emotional and cognitive behavioral domains. However, the mechanisms by which abrogation of adult neural stem cells (NSCs) impacts on brain function remains controversial. We used a transgenic rat line, the GFAP-Tk, to selectively eliminate NSCs and assess repercussions on different behavioral domains. To assess the functional importance of newborn cells in specific developmental stages, two parallel experimental timeframes were adopted: a short- and a long-term timeline, 1 and 4 weeks after the abrogation protocol, respectively. We conducted in vivo electrophysiology to assess the effects of cytogenesis abrogation on the functional properties of the hippocampus and prefrontal cortex, and on their intercommunication. Adult brain cytogenesis abrogation promoted a time-specific installation of behavioral deficits. While the lack of newborn immature hippocampal neuronal and glial cells elicited a behavioral phenotype restricted to hyperanxiety and cognitive rigidity, specific abrogation of mature new neuronal and glial cells promoted the long-term manifestation of a more complex behavioral profile encompassing alterations in anxiety and hedonic behaviors, along with deficits in multiple cognitive modalities. More so, abrogation of 4 to 7-week-old cells resulted in impaired electrophysiological synchrony of neural theta oscillations between the dorsal hippocampus and the medial prefrontal cortex, which are likely to contribute to the described long-term cognitive alterations. Hence, this work provides insight on how newborn neurons and astrocytes display different functional roles throughout different maturation stages, and establishes common ground to reconcile contrasting results that have marked this field.

Astrocyte-derived TNF and glutamate critically modulate microglia activation by methamphetamine

Methamphetamine (Meth) is a powerful illicit psychostimulant, widely used for recreational purposes. Besides disrupting the monoaminergic system and promoting oxidative brain damage, Meth also causes neuroinflammation, contributing to synaptic dysfunction and behavioral deficits. Aberrant activation of microglia, the largest myeloid cell population in the brain, is a common feature in neurological disorders triggered by neuroinflammation. In this study, we investigated the mechanisms underlying the aberrant activation of microglia elicited by Meth in the adult mouse brain. We found that binge Meth exposure caused microgliosis and disrupted risk assessment behavior (a feature that usually occurs in individuals who abuse Meth), both of which required astrocyte-to-microglia crosstalk. Mechanistically, Meth triggered a detrimental increase of glutamate exocytosis from astrocytes (in a process dependent on TNF production and calcium mobilization), promoting microglial expansion and reactivity. Ablating TNF production, or suppressing astrocytic calcium mobilization, prevented Meth-elicited microglia reactivity and re-established risk assessment behavior as tested by elevated plus maze (EPM). Overall, our data indicate that glial crosstalk is critical to relay alterations caused by acute Meth exposure.

Cell Cycle Regulation of Hippocampal Progenitor Cells in Experimental Models of Depression and after Treatment with Fluoxetine

Changes in adult hippocampal cell proliferation and genesis have been largely implicated in depression and antidepressant action, though surprisingly, the underlying cell cycle mechanisms are largely undisclosed. Using both an in vivo unpredictable chronic mild stress (uCMS) rat model of depression and in vitro rat hippocampal-derived neurosphere culture approaches, we aimed to unravel the cell cycle mechanisms regulating hippocampal cell proliferation and genesis in depression and after antidepressant treatment. We show that the hippocampal dentate gyrus (hDG) of uCMS animals have less proliferating cells and a decreased proportion of cells in the G2/M phase, suggesting a G1 phase arrest; this is accompanied by decreased levels of cyclin D1, E, and A expression. Chronic fluoxetine treatment reversed the G1 phase arrest and promoted an up-regulation of cyclin E. In vitro, dexamethasone (DEX) decreased cell proliferation, whereas the administration of serotonin (5-HT) reversed it. DEX also induced a G1-phase arrest and decreased cyclin D1 and D2 expression levels while increasing p27. Additionally, 5-HT treatment could partly reverse the G1-phase arrest and restored cyclin D1 expression. We suggest that the anti-proliferative actions of chronic stress in the hDG result from a glucocorticoid-mediated G1-phase arrest in the progenitor cells that is partly mediated by decreased cyclin D1 expression which may be overcome by antidepressant treatment.

Unilateral Intrastriatal 6-Hydroxydopamine Lesion in Mice: A Closer Look into Non-Motor Phenotype and Glial Response

Parkinson’s disease (PD) is a prevalent movement disorder characterized by the progressive loss of dopaminergic neurons in substantia nigra pars compacta (SNpc). The 6-hydroxydopamine (6-OHDA) lesion is still one of the most widely used techniques for modeling Parkinson’s disease (PD) in rodents. Despite commonly used in rats, it can be challenging to reproduce a similar lesion in mice. Moreover, there is a lack of characterization of the extent of behavioral deficits and of the neuronal loss/neurotransmitter system in unilateral lesion mouse models. In this study, we present an extensive behavioral and histological characterization of a unilateral intrastriatal 6-OHDA mouse model. Our results indicate significant alterations in balance and fine motor coordination, voluntary locomotion, and in the asymmetry’s degree of forelimb use in 6-OHDA lesioned animals, accompanied by a decrease in self-care and motivational behavior, common features of depressive-like symptomatology. These results were accompanied by a decrease in tyrosine hydroxylase (TH)-labelling and dopamine levels within the nigrostriatal pathway. Additionally, we also identify a marked astrocytic reaction, as well as proliferative and reactive microglia in lesioned areas. These results confirm the use of unilateral intrastriatal 6-OHDA mice for the generation of a mild model of nigrostriatal degeneration and further evidences the recapitulation of key aspects of PD, thereby being suitable for future studies beholding new therapeutical interventions for this disease.

Reproduction-Associated Hormones and Adult Hippocampal Neurogenesis

The levels of reproduction-associated hormones in females, such as estrogen, progesterone, prolactin, and oxytocin, change dramatically during pregnancy and postpartum. Reproduction-associated hormones can affect adult hippocampal neurogenesis (AHN), thereby regulating mothers' behavior after delivery. In this review, we first briefly introduce the overall functional significance of AHN and the methods commonly used to explore this front. Then, we attempt to reconcile the changes of reproduction-associated hormones during pregnancy. We further update the findings on how reproduction-related hormones influence adult hippocampal neurogenesis. This review is aimed at emphasizing a potential role of AHN in reproduction-related brain plasticity and its neurobiological relevance to motherhood behavior.

Melatonin and Melatonergic Influence on Neuronal Transcription Factors: Implications for the Development of Novel Therapies for Neurodegenerative Disorders

Melatonin is a multifunctional signalling molecule that is secreted by the mammalian pineal gland, and also found in a number of organisms including plants and bacteria. Research has continued to uncover an ever-increasing number of processes in which melatonin is known to play crucial roles in mammals. Amongst these functions is its contribution to cell multiplication, differentiation and survival in the brain. Experimental studies show that melatonin can achieve these functions by influencing transcription factors which control neuronal and glial gene expression. Since neuronal survival and differentiation are processes that are important determinants of the pathogenesis, course and outcome of neurodegenerative disorders; the known and potential influences of melatonin on neuronal and glial transcription factors are worthy of constant examination. In this review, relevant scientific literature on the role of melatonin in preventing or altering the course and outcome of neurodegenerative disorders, by focusing on melatonin's influence on transcription factors is examined. A number of transcription factors whose functions can be influenced by melatonin in neurodegenerative disease models have also been highlighted. Finally, the therapeutic implications of melatonin's influences have also been discussed and the potential limitations to its applications have been highlighted.

Tet3 ablation in adult brain neurons increases anxiety-like behavior and regulates cognitive function in mice

TET3 is a member of the ten-eleven translocation (TET) family of enzymes which oxidize 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC). Tet3 is highly expressed in the brain, where 5hmC levels are most abundant. In adult mice, we observed that TET3 is present in mature neurons and oligodendrocytes but is absent in astrocytes. To investigate the function of TET3 in adult postmitotic neurons, we crossed Tet3 floxed mice with a neuronal Cre-expressing mouse line, Camk2a-CreERT2, obtaining a Tet3 conditional KO (cKO) mouse line. Ablation of Tet3 in adult mature neurons resulted in increased anxiety-like behavior with concomitant hypercorticalism, and impaired hippocampal-dependent spatial orientation. Transcriptome and gene-specific expression analysis of the hippocampus showed dysregulation of genes involved in glucocorticoid signaling pathway (HPA axis) in the ventral hippocampus, whereas upregulation of immediate early genes was observed in both dorsal and ventral hippocampal areas. In addition, Tet3 cKO mice exhibit increased dendritic spine maturation in the ventral CA1 hippocampal subregion. Based on these observations, we suggest that TET3 is involved in molecular alterations that govern hippocampal-dependent functions. These results reveal a critical role for epigenetic modifications in modulating brain functions, opening new insights into the molecular basis of neurological disorders.

Neurogenic hypothesis of positive psychology in stress-induced depression: Adult hippocampal neurogenesis, neuroinflammation, and stress resilience

Stress is an important risk factor for depression. Emerging evidence supports the hypothesis that stress-mediated neuroinflammation destroys brain function and leads to anxiety-like and depression-like behaviors. Previous studies of stress-induced depression have mainly focused on pathological damage; however, the rise of positive psychology has attracted the interest of many researchers in environmental enrichment to promote stress resilience. The hippocampus is one of the most severely damaged brain regions in stress-induced depression. In addition, the hippocampus is one of the most unique regions in the brain, as new neurons are produced in the adult hippocampus, a process known as adult hippocampal neurogenesis (AHN). AHN is an important core component of the neurogenic hypothesis and has also become a major innovative breakthrough in positive psychology, in which environmental enrichment mediates stress resilience. Neuroinflammation, by activating microglia and releasing some proinflammatory cytokines, is increasingly shown to be one of the key determinant pathophysiological factors that negatively affects AHNand cognitive reserve. AHN is mainly related to remodeling stress response mechanisms, such as memory clearing, emotional control, and pattern separation, suggesting that a correlation may exist between neuroinflammation and AHN in stress resilience. Therefore, we summarized the previous research results to systematically expound on the relationship between AHN, stress resilience, and neuroinflammation. We hope this neurogenic hypothesis of positive psychology in stress-induced depression will provide a new perspective for the study of depression and antidepressant therapy.

The Role of PAX2 in Neurodevelopment and Disease

In developmental biology, transcription factors are involved in regulating the process of neural development, controlling the differentiation of nerve cells, and affecting the normal functioning of neural circuits. Transcription factors regulate the expression of multiple genes at the same time and have become a key gene category that is recognized to be disrupted in neurodevelopmental disorders such as autism spectrum disorders. This paper briefly introduces the expression and role of PAX2 in neurodevelopment and discusses the neurodevelopmental disorders associated with Pax2 mutations and its possible mechanism. Firstly, mutations in the human Pax2 gene are associated with abnormalities in multiple systems which can result in neurodevelopmental disorders such as intellectual disability, epilepsy and autism spectrum disorders. Secondly, the structure of Pax2 gene and PAX2 protein, as well as the function of Pax2 gene in neural development, was discussed. Finally, a diagram of the PAX2 protein regulatory network was made and a possible molecular mechanism of Pax2 mutations leading to neurodevelopmental disorders from the perspectives of developmental process and protein function was proposed.

Lithium treatment reverses irradiation-induced changes in rodent neural progenitors and rescues cognition

Cranial radiotherapy in children has detrimental effects on cognition, mood, and social competence in young cancer survivors. Treatments harnessing hippocampal neurogenesis are currently of great relevance in this context. Lithium, a well-known mood stabilizer, has both neuroprotective, pro-neurogenic as well as antitumor effects, and in the current study we introduced lithium treatment 4 weeks after irradiation. Female mice received a single 4 Gy whole-brain radiation dose on postnatal day (PND) 21 and were randomized to 0.24% Li2CO₃ chow or normal chow from PND 49 to 77. Hippocampal neurogenesis was assessed on PND 77, 91, and 105. We found that lithium treatment had a pro-proliferative effect on neural progenitors, but neuronal integration occurred only after it was discontinued. Also, the treatment ameliorated deficits in spatial learning and memory retention observed in irradiated mice. Gene expression profiling and DNA methylation analysis identified two novel factors related to the observed effects, Tppp, associated with microtubule stabilization, and GAD2/65, associated with neuronal signaling. Our results show that lithium treatment reverses irradiation-induced loss of hippocampal neurogenesis and cognitive impairment even when introduced long after the injury. We propose that lithium treatment should be intermittent in order to first make neural progenitors proliferate and then, upon discontinuation, allow them to differentiate. Our findings suggest that pharmacological treatment of cognitive so-called late effects in childhood cancer survivors is possible.

Identification of gene targets of developmental neurotoxicity focusing on DNA hypermethylation involved in irreversible disruption of hippocampal neurogenesis in rats

We have previously found that maternal exposure to 6‐propyl‐2‐thiouracil (PTU), valproic acid (VPA), or glycidol (GLY) has a sustained or late effect on hippocampal neurogenesis at the adult stage in rat offspring. Herein, we searched for genes with hypermethylated promoter region and downregulated transcript level to reveal irreversible markers of developmental neurotoxicity. The hippocampal dentate gyrus of male rat offspring exposed maternally to PTU, VPA, or GLY was subjected to Methyl‐Seq and RNA‐Seq analyses on postnatal day (PND) 21. Among the genes identified, 170 were selected for further validation analysis of gene expression on PND 21 and PND 77 by real‐time reverse transcription‐PCR. PTU and GLY downregulated many genes on PND 21, reflecting diverse effects on neurogenesis. Furthermore, genes showing sustained downregulation were found after PTU or VPA exposure, reflecting a sustained or late effect on neurogenesis by these compounds. In contrast, such genes were not observed with GLY, probably because of the reversible nature of the effects. Among the genes showing sustained downregulation, Creb, Arc, and Hes5 were concurrently downregulated by PTU, suggesting an association with neuronal mismigration, suppressed synaptic plasticity, and reduction in neural stem and progenitor cells. Epha7 and Pvalb were also concurrently downregulated by PTU, suggesting an association with the reduction in late‐stage progenitor cells. VPA induced sustained downregulation of Vgf and Dpysl4, which may be related to the aberrations in synaptic plasticity. The genes showing sustained downregulation may be irreversible markers of developmental neurotoxicity.

Hippocampal dentate gyrus of rat offspring exposed maternally to PTU, VPA, or GLY was subjected to global methylation analysis on PND 21. Genes downregulated on PND 77 were examined. PTU concurrently downregulated Creb, Arc, and Hes5, suggesting an association with the diverse effects on neurogenesis. PTU also concurrently downregulated Epha7 and Pvalb, suggesting an association with progenitor cell reduction. VPA downregulated Vgf and Dpysl4, suggesting an association with the aberrant synaptic plasticity. In contrast, GLY did not induce sustained downregulation.

Functional polymorphisms and transcriptional analysis in the 5' region of the human serotonin receptor 1B gene (HTR1B) and their associations with psychiatric disorders

BACKGROUND

The 5-hydroxytryptamine 1B receptor (5-HT1B) plays an essential role in the serotonin (5-HT) system and is widely involved in a variety of brain activities. HTR1B is the gene encoding 5-HT1B. Genome-wide association studies have shown that HTR1B polymorphisms are closely related to multiple mental and behavioral disorders; however, the functional mechanisms underlying these associations are unknown. This study investigated the effect of several HTR1B haplotypes on regulation of gene expression in vitro and the functional sequences in the 5' regulatory region of HTR1B to determine their potential association with mental and behavioral disorders.

METHODS

Six haplotypes consisting of rs4140535, rs1778258, rs17273700, rs1228814, rs11568817, and rs130058 and several truncated fragments of the 5' regulatory region of HTR1B were transfected into SK-N-SH and HEK-293 cells. The relative fluorescence intensities of the different haplotypes and truncated fragments were detected using a dual-luciferase reporter assay system.

RESULTS

Compared to the major haplotype T-G-T-C-T-A, the relative fluorescence intensities of haplotypes C-A-T-C-T-A, C-G-T-C-T-A, C-G-C-A-G-T, and C-G-T-A-T-A were significantly lower, and that of haplotype C-G-C-A-G-A was significantly higher. Furthermore, the effects of the rs4140535T allele, the rs17273700C-rs11568817G linkage combination, and the rs1228814A allele made their relative fluorescence intensities significantly higher than their counterparts at each locus. Conversely, the rs1778258A and rs130058T alleles decreased the relative fluorescence intensities. In addition, we found that regions from - 1587 to - 1371 bp (TSS, + 1), - 1149 to - 894 bp, - 39 to + 130 bp, + 130 to + 341 bp, and + 341 to + 505 bp upregulated gene expression. In contrast, regions - 603 to - 316 bp and + 130 to + 341 bp downregulated gene expression. Region + 341 to + 505 bp played a decisive role in gene transcription.

CONCLUSIONS

HTR1B 5' regulatory region polymorphisms have regulatory effects on gene expression and potential correlate with several pathology and physiology conditions. This study suggests that a crucial sequence for transcription is located in region + 341 ~ + 505 bp. Regions - 1587 to - 1371 bp, - 1149 to - 894 bp, - 603 to - 316 bp, - 39 to + 130 bp, and + 130 to + 341 bp contain functional sequences that can promote or suppress the HTR1B gene expression.

IP3 R2 null mice display a normal acquisition of somatic and neurological development milestones

Astrocytes are key players in the regulation of brain development and function. They sense and respond to the surrounding activity by elevating their intracellular calcium (Ca²⁺ ) levels. These astrocytic Ca²⁺ elevations emerge from different sources and display complex spatio-temporal properties. Ca²⁺ elevations are spatially distributed in global (soma and main processes) and/or focal regions (microdomains). The inositol 1,4,5-trisphosphate receptor type 2 knockout (IP₃ R2 KO) mouse model lacks global Ca²⁺ elevations in astrocytes, and it has been used by different laboratories. However, the constitutive deletion of IP₃ R2 during development may trigger compensating phenotypes, which could bias the results of experiments using developing or adult mice. To address this issue, we performed a detailed neurodevelopmental evaluation of male and female IP₃ R2 KO mice, during the first 21 days of life, as well as an evaluation of motor function, strength and neurological reflexes in adult mice. Our results show that male and female IP₃ R2 KO mice display a normal acquisition of developmental milestones, as compared with wild-type (WT) mice. We also show that IP₃ R2 KO mice display normal motor coordination, strength and neurological reflexes in adulthood. To exclude a potential compensatory overexpression of other IP₃ Rs, we quantified the relative mRNA levels of all 3 subtypes, in brain tissue. We found that, along with the complete deletion of Itpr2, there is no compensatory expression of Itpr1 or Itrp3. Overall, our results show that the IP₃ R2 KO mouse is a reliable model to study the functional impact of global IP₃ R2-dependent astrocytic Ca²⁺ elevations.

Region-specific control of microglia by adenosine A2A receptors: uncoupling anxiety and associated cognitive deficits in female rats

Epidemiologic studies have provided compelling evidence that prenatal stress, through excessive maternal glucocorticoids exposure, is associated with psychiatric disorders later in life. We have recently reported that anxiety associated with prenatal exposure to dexamethasone (DEX, a synthetic glucocorticoid) correlates with a gender-specific remodeling of microglia in the medial prefrontal cortex (mPFC), a core brain region in anxiety-related disorders. Gender differences in microglia morphology, the higher prevalence of anxiety in women and the negative impact of anxiety in cognition, led us to specifically evaluate cognitive behavior and associated circuits (namely mPFC-dorsal hippocampus, dHIP), as well as microglia morphology in female rats prenatally exposed to dexamethasone (in utero DEX, iuDEX). We report that iuDEX impaired recognition memory and deteriorated neuronal synchronization between mPFC and dHIP. These functional deficits are paralleled by microglia hyper-ramification in the dHIP and decreased ramification in the mPFC, showing a heterogeneous remodeling of microglia morphology, both postnatally and at adulthood in different brain regions, that differently affect mood and cognition. The chronic blockade of adenosine A2A receptors (A2A R), which are core regulators of microglia morphology and physiology, ameliorated the cognitive deficits, but not the anxiety-like behavior. Notably, A2A R blockade rectified both microglia morphology in the dHIP and the lack of mPFC-dHIP synchronization, further heralding their role in cognitive function.

Adult Hippocampal Neurogenesis Modulation by the Membrane-Associated Progesterone Receptor Family Member Neudesin

Neudesin (Neuron-derived neurotrophic factor, NENF), a membrane-associated progesterone receptor family (MAPR) member, is a neuron secreted protein with neurotrophic properties during embryonic stages. However, its role in the adult brain is still poorly addressed. In this study we have used neudesin-null (Nenf^−/−) mice and performed a characterization of the proliferation state of the adult neurogenic niches, the adult subventricular zone (SVZ) and the hippocampus subgranular zone (SGZ). Nenf^−/− males did not presented any deficits in proliferation in the SVZ neither in vivo nor in vitro. On the other hand a decrease in cell proliferation in the SGZ was observed, as well as a decrease in the number of newborn neurons in the dentate gyrus (DG) that was accompanied by impaired context discrimination in a contextual fear conditioning (CFC) task. Since NENF neurotrophic action is suggested to occur via the formation of a progesterone stability complex for the activation of non-genomic cascade, we further evaluated progesterone metabolism in the absence of NENF. Interestingly, expression of progesterone catabolic rate-determining enzyme, 5-α-reductase was upregulated in the DG of Nenf^−/−, together with a significant increase in the expression of the δGABA_A receptor gene, involved in DG tonic inhibition. Taken together, these findings add in vivo evidence on the neurotrophic properties of NENF in the adult brain. Furthermore, the mechanism of action of NENF in this process might implicate neurosteroids modulation, at least in the DG.

NFIX-Mediated Inhibition of Neuroblast Branching Regulates Migration Within the Adult Mouse Ventricular–Subventricular Zone

Understanding the migration of newborn neurons within the brain presents a major challenge in contemporary biology. Neuronal migration is widespread within the developing brain but is also important within the adult brain. For instance, stem cells within the ventricular–subventricular zone (V-SVZ) and the subgranular zone of dentate gyrus of the adult rodent brain produce neuroblasts that migrate to the olfactory bulb and granule cell layer of the dentate gyrus, respectively, where they regulate key brain functions including innate olfactory responses, learning, and memory. Critically, our understanding of the factors mediating neuroblast migration remains limited. The transcription factor nuclear factor I X (NFIX) has previously been implicated in embryonic cortical development. Here, we employed conditional ablation of Nfix from the adult mouse brain and demonstrated that the removal of this gene from either neural stem and progenitor cells, or neuroblasts, within the V-SVZ culminated in neuroblast migration defects. Mechanistically, we identified aberrant neuroblast branching, due in part to increased expression of the guanylyl cyclase natriuretic peptide receptor 2 (Npr2), as a factor contributing to abnormal migration in Nfix-deficient adult mice. Collectively, these data provide new insights into how neuroblast migration is regulated at a transcriptional level within the adult brain.

AP2γ: A New Player on Adult Hippocampal Neurogenesis Regulation

Since the recognition that the mammalian brain retains the ability to generate newborn neurons with functional relevance throughout life, the matrix of molecular regulators that govern adult neurogenesis has been the focus of much interest. In a recent study published in Molecular Psychiatry, we demonstrate Activating Protein 2γ (AP2γ), a transcription factor previously implicated in cell fate determination in the developing cortex, as a novel player in the regulation of glutamatergic neurogenesis in the adult hippocampus. Using distinct experimental approaches, we showed that AP2γ is specifically present in a subpopulation of transient amplifying progenitors, where it acts as a crucial promoter of proliferation and differentiation of adult-born glutamatergic granule neurons. Strikingly, deficiency of AP2γ in the adult brain compromises the generation of new glutamatergic neurons, with impact on the function of cortico-limbic circuits. Here, we share our view on how AP2γ integrates the transcriptional orchestration of glutamatergic neurogenesis in the adult hippocampus, and consequently, how it emerges as a novel molecular candidate to study the translation of environmental pressures into alterations of brain neuroplasticity in homeostatic, but also in neuropathological contexts.

Conserved properties of dentate gyrus neurogenesis across postnatal development revealed by single-cell RNA sequencing

The dentate gyrus of the hippocampus is a brain region in which neurogenesis persists into adulthood; however, the relationship between developmental and adult dentate gyrus neurogenesis has not been examined in detail. Here we used single-cell RNA sequencing to reveal the molecular dynamics and diversity of dentate gyrus cell types in perinatal, juvenile, and adult mice. We found distinct quiescent and proliferating progenitor cell types, linked by transient intermediate states to neuroblast stages and fully mature granule cells. We observed shifts in the molecular identity of quiescent and proliferating radial glia and granule cells during the postnatal period that were then maintained through adult stages. In contrast, intermediate progenitor cells, neuroblasts, and immature granule cells were nearly indistinguishable at all ages. These findings demonstrate the fundamental similarity of postnatal and adult neurogenesis in the hippocampus and pinpoint the early postnatal transformation of radial glia from embryonic progenitors to adult quiescent stem cells.

Astrocytic signaling supports hippocampal-prefrontal theta synchronization and cognitive function

Astrocytes interact with neurons at the cellular level through modulation of synaptic formation, maturation, and function, but the impact of such interaction into behavior remains unclear. Here, we studied the dominant negative SNARE (dnSNARE) mouse model to dissect the role of astrocyte-derived signaling in corticolimbic circuits, with implications for cognitive processing. We found that the blockade of gliotransmitter release in astrocytes triggers a critical desynchronization of neural theta oscillations between dorsal hippocampus and prefrontal cortex. Moreover, we found a strong cognitive impairment in tasks depending on this network. Importantly, the supplementation with d-serine completely restores hippocampal-prefrontal theta synchronization and rescues the spatial memory and long-term memory of dnSNARE mice. We provide here novel evidence of long distance network modulation by astrocytes, with direct implications to cognitive function.