Overexpression of the type 1 adenylyl cyclase in the forebrain leads to deficits of behavioral inhibition

Ca2+-stimulated adenylyl cyclases as therapeutic targets for psychiatric and neurodevelopmental disorders

As the main secondary messengers, cyclic AMP (cAMP) and Ca2+ trigger intracellular signal transduction cascade and, in turn, regulate many aspects of cellular function in developing and mature neurons. The group I adenylyl cyclase (ADCY, also known as AC) isoforms, including ADCY1, 3, and 8 (also known as AC1, AC3, and AC8), are stimulated by Ca2+ and thus functionally positioned to integrate cAMP and Ca2+ signaling. Emerging lines of evidence have suggested the association of the Ca2+-stimulated ADCYs with bipolar disorder, schizophrenia, major depressive disorder, post-traumatic stress disorder, and autism. In this review, we discuss the molecular and cellular features as well as the physiological functions of ADCY1, 3, and 8. We further discuss the recent therapeutic development to target the Ca2+-stimulated ADCYs for potential treatments of psychiatric and neurodevelopmental disorders.

Physiological roles of mammalian transmembrane adenylyl cyclase isoforms

Adenylyl cyclases (ACs) catalyze the conversion of ATP to the ubiquitous second messenger cAMP. Mammals possess nine isoforms of transmembrane ACs, dubbed AC1-9, that serve as major effector enzymes of G protein-coupled receptors (GPCRs). The transmembrane ACs display varying expression patterns across tissues, giving the potential for them to have a wide array of physiological roles. Cells express multiple AC isoforms, implying that ACs have redundant functions. Furthermore, all transmembrane ACs are activated by Gαs, so it was long assumed that all ACs are activated by Gαs-coupled GPCRs. AC isoforms partition to different microdomains of the plasma membrane and form prearranged signaling complexes with specific GPCRs that contribute to cAMP signaling compartments. This compartmentation allows for a diversity of cellular and physiological responses by enabling unique signaling events to be triggered by different pools of cAMP. Isoform-specific pharmacological activators or inhibitors are lacking for most ACs, making knockdown and overexpression the primary tools for examining the physiological roles of a given isoform. Much progress has been made in understanding the physiological effects mediated through individual transmembrane ACs. GPCR-AC-cAMP signaling pathways play significant roles in regulating functions of every cell and tissue, so understanding each AC isoform's role holds potential for uncovering new approaches for treating a vast array of pathophysiological conditions.

Uncaria rhynchophylla ameliorates unpredictable chronic mild stress-induced depression in mice via activating 5-HT1A receptor: Insights from transcriptomics

BACKGROUND

Depression is a pervasive or persistent mental disorder that causes mood, cognitive and memory deficits. Uncaria rhynchophylla has been widely used to treat central nervous system diseases for a long history, although its efficacy and potential mechanism are still uncertain.

PURPOSE

The present study aimed to investigate anti-depression effect and potential mechanism of U. rhynchophylla extract (URE).

STUDY DESIGN AND METHODS

A mouse depression model was established using unpredictable chronic mild stress (UCMS). Effects of URE on depression-like behaviours, neurotransmitters, and neuroendocrine hormones were investigated in UCMS-induced mice. The potential target of URE was analyzed by transcriptomics and bioinformatics methods and validated by RT-PCR and Western blot. The agonistic effect on 5-HT1A receptor was assayed by dual-luciferase reporter system.

RESULTS

URE ameliorated depression-like behaviours, and modulated levels of neurotransmitters and neuroendocrine hormones, including 5-hydroxytryptamine (5-HT), 5-hydroxyindole acetic acid (5-HIAA), dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), corticosterone (CORT), corticotropin-releasing hormone (CRH), and adrenocorticotropic hormone (ACTH), in UCMS-induced mice. Transcriptomics and bioinformatics results indicated that URE could regulate glutamatergic, cholinergic, serotonergic, and GABAergic systems, especially neuroactive ligand-receptor and cAMP signaling pathways, revealing that Htr1a encoding 5-HT1A receptor was a potential target of URE. The expression levels of downstream proteins of 5-HT1A signaling pathway 5-HT1A, CREB, BDNF, and PKA were increased in UCMS-induced mice after URE administration, and URE also displayed an agonistic effect against 5-HT1A receptor with an EC50 value of 17.42 μg/ml.

CONCLUSION

U. rhynchophylla ameliorated depression-like behaviours in UCMS-induced mice through activating 5-HT1A receptor.

Carbamazepine Restores Neuronal Signaling, Protein Synthesis, and Cognitive Function in a Mouse Model of Fragile X Syndrome

Fragile X syndrome (FXS) is a leading genetic disorder of intellectual disability caused by the loss of the functional fragile X mental retardation protein (FMRP). To date, there is no efficacious mechanism-based medication for FXS. With regard to potential disease mechanisms in FXS, it is widely accepted that the lack of FMRP causes elevated protein synthesis and deregulation of neuronal signaling. Abnormal enhancement of the ERK½ (extracellular signal-regulated kinase ½) and PI3K-Akt (Phosphoinositide 3 kinase-protein kinase B) signaling pathways has been identified in both FXS patients and FXS mouse models. In this study, we show that carbamazepine, which is an FDA-approved drug and has been mainly used to treat seizure and neuropathic pain, corrects cognitive deficits including passive avoidance and object location memory in FXS mice. Carbamazepine also rescues hyper locomotion and social deficits. At the cellular level, carbamazepine dampens the elevated level of ERK½ and Akt signaling as well as protein synthesis in FXS mouse neurons. Together, these results advocate repurposing carbamazepine for FXS treatment.

B-vitamin supplementation ameliorates anxiety- and depression-like behavior induced by gestational urban PM2.5 exposure through suppressing neuroinflammation in mice offspring

PM_2.5 exposure is an emerging environmental concern and severe health insult closely related to psychological conditions such as anxiety and depression in adolescence. Adolescence is a critical period for neural system development characterized by continuous brain maturation, especially in the prefrontal cortex. The etiology of these adolescent conditions may derive from fetal origin, probably attributed to the adverse effects induced by intrauterine environmental exposure. Anxiety- and depression-like behavior can be induced by gestational exposure to PM_2.5 in mice offspring which act as a useful model system. Recent studies show that B-vitamin may alleviate PM_2.5-induced hippocampal neuroinflammation- and function-related spatial memory impairment in adolescent mice offspring. However, cortical damage and related neurobehavioral defects induced by gestational PM_2.5 exposure, as well as the potential reversibility by interventions in mice offspring require to be elucidated. Here, we aimed to investigate whether B-vitamin would protect mice offspring from the adverse effects derived from gestational exposure to urban PM_2.5 on cortical areas to which anxiety and depression are closely related. Pregnant mice were divided into three groups: control group (treated with PBS alone), model group (treated with both PM_2.5 and PBS), and intervention group (treated with both PM_2.5 and B-vitamin), respectively. The mice offspring were then applied to comprehensive neurobehavioral, ultrastructural, biochemical, and molecular biological analyses. Interestingly, we observed that gestational PM_2.5 exposure led to neurobehavioral defects including anxiety- and depression-like behavior. In addition, neuroinflammation, oxidative damage, increased apoptosis, and caspase-1-mediated inflammasome activation in the prefrontal cortex were observed. Notably, both behavioral and molecular changes could be significantly alleviated by B-vitamin treatment. In summary, our results suggest that the anxiety- and depression-like behavior induced by gestational PM_2.5 exposure in mice offspring can be ameliorated by B-vitamin supplementation, probably through the suppression of apoptosis, oxidative damage, neuroinflammation, and caspase-1-mediated inflammasome activation.

Forebrain overexpression of type 1 adenylyl cyclase promotes molecular stability and behavioral resilience to physical stress

The ability to cope with stress is essential for emotional stability and mental health. It is also hypothesized that factors promoting resilience to stress may offer treatment strategies for maladaptive disorders such as anxiety and depression. Here, we find that physical restraint reduces the expression of type 1 adenylyl cyclase (Adcy1), a neurospecific synaptic enzyme that positively regulates the cAMP signaling cascade. Conversely, an increase of forebrain Adcy1 expression in transgenic mouse (i.e., Adcy1 ^tg mouse) predisposes individuals to molecular stability and behavioral resilience. Transgenic overexpression of Adcy1 prevents the physical restraint-induced down-regulation of brain-derived neurotrophic factor (BDNF) and neuropeptide Y (NPY). Further, Adcy1 ^tg mice maintain regular locomotive activity in novelty exploration and voluntary wheel running following physical restraint. Adcy1 ^tg mice show higher corticosterone and lower basal glucocorticoid receptor (GR) expression, along with a higher MR (mineralocorticoid receptor) to GR ratio in the hippocampus. Further, Adcy1 ^tg mice show reduced immobility under acute physical stress conditions in the forced swimming test and are more sensitive to the antidepressant desipramine. Our results demonstrate a novel function of Adcy1 in stress coping and suggest Adcy1 as a potential target to antagonize stress vulnerability and promote antidepressant efficacy.

Neonatal sevoflurane exposure induces impulsive behavioral deficit through disrupting excitatory neurons in the medial prefrontal cortex in mice

Sevoflurane, in particular multiple exposures, has been reported to cause the abnormal neurological development including attention-deficit/hyperactivity disorder (ADHD). This study is to investigate ADHD-like impulsivity in adult mice after repeated sevoflurane exposures at the neonatal stage. Six-day-old pups were exposed to 60% oxygen in the presence or absence of 3% sevoflurane for 2 h and the treatment was administrated once daily for three consecutive days. To assess the impulsivity, the cliff avoidance reaction (CAR) was carried out at the 8th week. Our results showed that repeated sevoflurane treatment increased the number of jumps and shortened the jumping latency in the CAR test. The cortices were harvested for immunostaining to detect c-Fos and calmodulin-dependent protein kinase IIα (CaMKIIα) expression in the medial prefrontal cortex (mPFC). We found that mPFC neurons, especially excitatory neurons, were highly activated and related to impulsive behavior. The activation viruses (AAV-CaMKIIα-hM3Dq) were injected to evaluate the effects of specific activation of mPFC excitatory neurons on impulsive behavior in the presence of clozapine-N-oxide (CNO). Likewise, the inhibitory viruses (AAV-CaMKIIα-hM4Di) were injected in the sevoflurane group to explore whether the mPFC excitatory neuronal inhibition reduced the impulsivity. Our results revealed that chemogenetic activation of mPFC excitatory neurons induced impulsive behavior whereas inhibition of mPFC excitatory neurons partially rescued the deficit. These results indicate that repeated sevoflurane exposures at the critical time induce impulsive behavior accompanied with overactivation of mPFC excitatory neurons in adult stages. This work may further extend to understand the ADHD-like impulsive behavior of the anesthetic neurotoxicity.

Induction of activity synchronization among primed hippocampal neurons out of random dynamics is key for trace memory formation and retrieval

Memory is thought to be encoded by sparsely distributed neuronal ensembles in memory‐related regions. However, it is unclear how memory‐eligible neurons react during learning to encode trace fear memory and how they retrieve a memory. We implemented a fiber‐optic confocal fluorescence endomicroscope to directly visualize calcium dynamics of hippocampal CA1 neurons in freely behaving mice subjected to trace fear conditioning. Here we report that the overall activity levels of CA1 neurons showed a right‐skewed lognormal distribution, with a small portion of highly active neurons (termed Primed Neurons) filling the long‐tail. Repetitive training induced Primed Neurons to shift from random activity to well‐tuned synchronization. The emergence of activity synchronization coincided with the appearance of mouse freezing behaviors. In recall, a partial synchronization among the same subset of Primed Neurons was induced from random dynamics, which also coincided with mouse freezing behaviors. Additionally, training‐induced synchronization facilitated robust calcium entry into Primed Neurons. In contrast, most CA1 neurons did not respond to tone and foot shock throughout the training and recall cycles. In conclusion, Primed Neurons are preferably recruited to encode trace fear memory and induction of activity synchronization among Primed Neurons out of random dynamics is critical for trace memory formation and retrieval.

Gestational B-vitamin supplementation alleviates PM2.5-induced autism-like behavior and hippocampal neurodevelopmental impairment in mice offspring

Gestational exposure to PM_2.5 is a worldwide environmental issue associated with long-lasting behavior abnormalities and neurodevelopmental impairments in the hippocampus of offspring. PM_2.5 may induce hippocampus injury and lead to autism-like behavior such as social communication deficits and stereotyped repetitive behavior in children through neuroinflammation and neurodegeneration. Here, we investigated the preventive effect of B-vitamin on PM_2.5-induced deleterious effects by focusing on anti-inflammation, antioxidant, synaptic remodeling and neurodevelopment. Pregnant mice were randomly divided into three groups including control group (mice subject to PBS only), model group (mice subject to both 30 μL PM_2.5 of 3.456 μg/μL and 10 mL/(kg·d) PBS), and intervention group (mice subject to both 30 μL PM_2.5 of 3.456 μg/μL and 10 mL/(kg·d) B-vitamin supplementation (folic acid, vitamin B6 and vitamin B12 with concentrations at 0.06, 1.14 and 0.02 mg/mL, respectively)). In the current study B-vitamin significantly alleviated neurobehavioral impairment reflected in reduced social communication disorders, stereotyped repetitive behavior, along with learning and spatial memory impairment in PM_2.5-stimulated mice offspring. Next, B-vitamin corrected synaptic loss and reduced mitochondrial damage in hippocampus of mice offspring, demonstrated by normalized synapse quantity, synaptic cleft, postsynaptic density (PSD) thickness and length of synaptic active area. Furthermore, significantly down-regulated expression of pro-inflammatory cytokines including NF-κB, TNF-α and IL-1β, and lipid peroxidation were found. We observed elevated levels of oxidant-related genes (SOD, GSH and GSH-Px). Moreover, decreased cleaved caspase-3 and TUNEL-positive cells suggested inhibited PM_2.5-induced apoptosis by B-vitamin. Furthermore, B-vitamin increased neurogenesis by increasing EdU-positive cells in the subgranular zone (SGZ) of offspring. Collectively, our results suggest that B-vitamin supplementation exerts preventive effect on autism-like behavior and neurodevelopmental impairment in hippocampus of mice offspring gestationally exposed to PM_2.5, to which alleviated mitochondrial damage, increased anti-inflammatory and antioxidant capacity and synaptic efficiency, reduced neuronal apoptosis and improved hippocampal neurogenesis may contribute.

Socially dominant mice in C57BL6 background show increased social motivation

A series of behavioral tests measuring social dominance, social motivation, and non-social motivation are examined in adult male C57BL6 mice. By using the well-known tube dominance test to determine social dominance and rank, we find that, in the absence of competition for resource and mating, group-housed mouse cage-mates display stable and mostly linear and transitive social hierarchies. Mice with top and bottom social ranks are subjected to a three-chamber social interaction test to measure social motivation. The top ranked mice spend more time interacting with a stranger mouse than the bottom ranked mice, suggesting that social dominance may positively influence social motivation. When subjected to a novel environment, mice with different social ranks show similar locomotion and exploring activity in the open field test, suggesting no detectable difference in certain aspects of non-social motivation. These results demonstrate a behavioral correlation between social dominance and social motivation.

Role of circadian rhythm and REM sleep for memory consolidation

Although sleep is strongly implicated in memory consolidation, the molecular basis for the role of sleep in memory is not known. It has been established that the consolidation of hippocampus-dependent memory depends on the activation of the Erk1,2 MAP kinase (MAPK) pathway which activates de novo CRE-mediated transcription and translation, two processes required for memory consolidation pathway. The activation of MAPK during memory formation and its nuclear translocation both depend upon cAMP signals generated by the calmodulin-stimulated adenylyl cyclases, type 1 and type 8 (AC1 and AC8). This signaling pathway undergoes a circadian oscillation in the hippocampus with maximal activation during REM sleep. This data supports the hypothesis that the persistence of long-term memory traces may depend upon the reactivation and circadian oscillation of the cAMP/MAP kinase/CRE transcriptional pathway in tagged neurons which reaches a maximum during REM sleep.

International Union of Basic and Clinical Pharmacology. CI. Structures and Small Molecule Modulators of Mammalian Adenylyl Cyclases

Adenylyl cyclases (ACs) generate the second messenger cAMP from ATP. Mammalian cells express nine transmembrane AC (mAC) isoforms (AC1-9) and a soluble AC (sAC, also referred to as AC10). This review will largely focus on mACs. mACs are activated by the G-protein Gαs and regulated by multiple mechanisms. mACs are differentially expressed in tissues and regulate numerous and diverse cell functions. mACs localize in distinct membrane compartments and form signaling complexes. sAC is activated by bicarbonate with physiologic roles first described in testis. Crystal structures of the catalytic core of a hybrid mAC and sAC are available. These structures provide detailed insights into the catalytic mechanism and constitute the basis for the development of isoform-selective activators and inhibitors. Although potent competitive and noncompetitive mAC inhibitors are available, it is challenging to obtain compounds with high isoform selectivity due to the conservation of the catalytic core. Accordingly, caution must be exerted with the interpretation of intact-cell studies. The development of isoform-selective activators, the plant diterpene forskolin being the starting compound, has been equally challenging. There is no known endogenous ligand for the forskolin binding site. Recently, development of selective sAC inhibitors was reported. An emerging field is the association of AC gene polymorphisms with human diseases. For example, mutations in the AC5 gene (ADCY5) cause hyperkinetic extrapyramidal motor disorders. Overall, in contrast to the guanylyl cyclase field, our understanding of the (patho)physiology of AC isoforms and the development of clinically useful drugs targeting ACs is still in its infancy.

Enhanced expression of ADCY1 underlies aberrant neuronal signalling and behaviour in a syndromic autism model

Fragile X syndrome (FXS), caused by the loss of functional FMRP, is a leading cause of autism. Neurons lacking FMRP show aberrant mRNA translation and intracellular signalling. Here, we identify that, in Fmr1 knockout neurons, type 1 adenylyl cyclase (Adcy1) mRNA translation is enhanced, leading to excessive production of ADCY1 protein and insensitivity to neuronal stimulation. Genetic reduction of Adcy1 normalizes the aberrant ERK1/2- and PI3K-mediated signalling, attenuates excessive protein synthesis and corrects dendritic spine abnormality in Fmr1 knockout mice. Genetic reduction of Adcy1 also ameliorates autism-related symptoms including repetitive behaviour, defective social interaction and audiogenic seizures. Moreover, peripheral administration of NB001, an experimental compound that preferentially suppresses ADCY1 activity over other ADCY subtypes, attenuates the behavioural abnormalities in Fmr1 knockout mice. These results demonstrate a connection between the elevated Adcy1 translation and abnormal ERK1/2 signalling and behavioural symptoms in FXS.

Fragile X syndrome (FXS) is a leading cause of autism and neurons lacking FMRP show aberrant mRNA translation and intracellular signalling. Here, the authors show that neurons from Fmr1 knockout mice have increased levels of ADCY1 protein, producing abnormal ERK1/2 signalling, dysregulated protein synthesis and behavioural symptoms associated with FXS.

Ablation of Type III Adenylyl Cyclase in Mice Causes Reduced Neuronal Activity, Altered Sleep Pattern, and Depression-like Phenotypes

BACKGROUND

Although major depressive disorder (MDD) has low heritability, a genome-wide association study in humans has recently implicated type 3 adenylyl cyclase (AC3; ADCY3) in MDD. Moreover, the expression level of AC3 in blood has been considered as a MDD biomarker in humans. Nevertheless, there is a lack of supporting evidence from animal studies.

METHODS

We employed multiple approaches to experimentally evaluate if AC3 is a contributing factor for major depression using mouse models lacking the Adcy3 gene.

RESULTS

We found that conventional AC3 knockout (KO) mice exhibited phenotypes associated with MDD in behavioral assays. Electroencephalography/electromyography recordings indicated that AC3 KO mice have altered sleep patterns characterized by increased percentage of rapid eye movement sleep. AC3 KO mice also exhibit neuronal atrophy. Furthermore, synaptic activity at cornu ammonis 3-cornu ammonis 1 synapses was significantly lower in AC3 KO mice, and they also exhibited attenuated long-term potentiation as well as deficits in spatial navigation. To confirm that these defects are not secondary responses to anosmia or developmental defects, we generated a conditional AC3 floxed mouse strain. This enabled us to inactivate AC3 function selectively in the forebrain and to inducibly ablate it in adult mice. Both AC3 forebrain-specific and AC3 inducible knockout mice exhibited prodepression phenotypes without anosmia.

CONCLUSIONS

This study demonstrates that loss of AC3 in mice leads to decreased neuronal activity, altered sleep pattern, and depression-like behaviors, providing strong evidence supporting AC3 as a contributing factor for MDD.

Type 3 adenylyl cyclase: a key enzyme mediating the cAMP signaling in neuronal cilia

Cilia are rigid, centriole-derived, microtubule-based organelles present in a majority of vertebrate cells including neurons. They are considered the cellular "antennae" attuned for detecting a range of extracellular signals including photons, odorants, morphogens, hormones and mechanical forces. The ciliary microenvironment is distinct from most actin-based subcellular structures such as microvilli or synapses. In the nervous system, there is no evidence that neuronal cilia process any synaptic structure. Apparently, the structural features of neuronal cilia do not allow them to harbor any synaptic connections. Nevertheless, a large number of G protein-coupled receptors (GPCRs) including odorant receptors, rhodopsin, Smoothened, and type 6 serotonin receptor are found in cilia, suggesting that these tiny processes largely depend on metabotropic receptors and their tuned signals to impact neuronal functions. The type 3 adenylyl cyclase (AC3), widely known as a cilia marker, is highly and predominantly expressed in olfactory sensory cilia and primary cilia throughout the brain. We discovered that ablation of AC3 in mice leads to pleiotropic phenotypes including anosmia, failure to detect mechanical stimulation of airflow, cognitive deficit, obesity, and depression-like behaviors. Multiple lines of human genetic evidence also demonstrate that AC3 is associated with obesity, major depressive disorder (MDD), sarcoidosis, and infertility, underscoring its functional importance. Here we review recent progress on AC3, a key enzyme mediating the cAMP signaling in neuronal cilia.

Voluntary running depreciates the requirement of Ca2+-stimulated cAMP signaling in synaptic potentiation and memory formation

Mental health and cognitive functions are influenced by both genetic and environmental factors. Although having active lifestyle with physical exercise improves learning and memory, how it interacts with the specific key molecular regulators of synaptic plasticity is largely unknown. Here, we examined the effects of voluntary running on long-term potentiation (LTP) and memory formation in mice lacking type 1 adenylyl cyclase (AC1), a neurospecific synaptic enzyme that contributes to Ca(2+)-stimulated cAMP production. Following 1 mo of voluntary running-wheel exercise, the impaired LTP and object recognition memory in AC1 knockout (KO) mice were significantly attenuated. Running up-regulated exon II mRNA level of BDNF (brain-derived neurotrophic factor), though it failed to increase exon I and IV mRNAs in the hippocampus of AC1 KO mice. Intrahippocampal infusion of recombinant BDNF was sufficient to rescue LTP and object recognition memory defects in AC1 KO mice. Therefore, voluntary running and exogenous BDNF application overcome the defective Ca(2+)-stimulated cAMP signaling. Our results also demonstrate that alteration in Ca(2+)-stimulated cAMP can affect the molecular outcome of physical exercise.