Transgenerational impairment of hippocampal Akt-mTOR signaling and behavioral deficits in the offspring of mice that experience postpartum depression-like illness

Deciphering the role of siRNA in anxiety and depression

Anxiety and depression are central nervous system illnesses that are among the most prevalent medical concerns of the twenty-first century. Patients with this condition and their families bear psychological, financial, and societal hardship. There are currently restrictions when utilizing the conventional course of treatment. RNA interference is expected to become an essential approach in anxiety and depression due to its potent and targeted gene silencing. Silencing of genes by post-transcriptional modification is the mechanism of action of small interfering RNA (siRNA). The suppression of genes linked to disease is typically accomplished by siRNA molecules in an efficient and targeted manner. Unfavourable immune responses, off-target effects, naked siRNA instability, nuclease vulnerability, and the requirement to create an appropriate delivery method are some of the challenges facing the clinical application of siRNA. This review focuses on the use of siRNA in the treatment of anxiety and depression.

Antidepressant effects of esketamine via the BDNF/AKT/mTOR pathway in mice with postpartum depression and their offspring

Postpartum depression (PPD) is a serious mental health problem that can negatively affect future generations. BDNF/AKT/mTOR signaling in the frontal lobe and hippocampus in mice is associated with depression, but its role in mice with PPD and their offspring is unknown. This study was aimed at investigating the effects of esketamine (ESK), a drug approved for treatment of refractory depression, on the BDNF/AKT/mTOR pathway in mice with PPD and their offspring. A model of chronic unpredictable mild stress with pregnancy was used. ESK was injected into postpartum mice, and behavioral tests were conducted to predict the severity of symptoms at the end of lactation and in the offspring after adulthood. Both mice with PPD and their offspring showed significant anxiety- and depression-like behaviors that were ameliorated with the ESK intervention. ESK enhanced exploratory behavior in unfamiliar environments, increased the preference for sucrose, and ameliorated the impaired BDNF/AKT/mTOR signaling in the frontal and hippocampal regions in mice. Thus, ESK may have great potential in treating PPD and decreasing the incidence of depression in offspring.

Ketamine causes poor maternal care in rats with postpartum depression and leads to few behavioral and neurochemical alterations on male offspring

Ketamine is an anesthetic drug that also has antidepressant properties, with quick action. Despite the great number of studies showing its effectiveness as a treatment for major depression, there is little information about its effects on postpartum depression, as pharmacological treatments bring risks to the health of both mother and child. Thus, this study aimed to evaluate the effects of prolonged treatment with subanesthetic doses of ketamine in a rat model of postpartum depression. Female dams were induced to postpartum depression by the maternal separation model from lactating day (LD) 2-12. They were divided into four groups: one control and three experimental groups, which were treated with different doses of ketamine (5, 10 or 20 mg/kg) from LD 2-21 i.p. Maternal studies were conducted from LD5 to LD21 and the offspring studies from postnatal day 2 through 90. Ketamine causes poor maternal care, with few neurochemical alterations. However, the highest dose used in this study had an antidepressant effect. Regarding the male offspring, indirect exposure to ketamine through breast milk caused few behavioral changes during infancy, but they were not permanent, as they faded in adulthood. Nevertheless, this exposure was able to cause alterations in their monoaminergic neurotransmission systems that were found in both infancy and adulthood periods.

Differential susceptibility of male and female germ cells to glucocorticoid-mediated signaling

While physiologic stress has long been known to impair mammalian reproductive capacity through hormonal dysregulation, mounting evidence now suggests that stress experienced prior to or during gestation may also negatively impact the health of future offspring. Rodent models of gestational physiologic stress can induce neurologic and behavioral changes that persist for up to three generations, suggesting that stress signals can induce lasting epigenetic changes in the germline. Treatment with glucocorticoid stress hormones is sufficient to recapitulate the transgenerational changes seen in physiologic stress models. These hormones are known to bind and activate the glucocorticoid receptor (GR), a ligand-inducible transcription factor, thus implicating GR-mediated signaling as a potential contributor to the transgenerational inheritance of stress-induced phenotypes. Here, we demonstrate dynamic spatiotemporal regulation of GR expression in the mouse germline, showing expression in the fetal oocyte as well as the perinatal and adult spermatogonia. Functionally, we find that fetal oocytes are intrinsically buffered against changes in GR signaling, as neither genetic deletion of GR nor GR agonism with dexamethasone altered the transcriptional landscape or the progression of fetal oocytes through meiosis. In contrast, our studies revealed that the male germline is susceptible to glucocorticoid-mediated signaling, specifically by regulating RNA splicing within the spermatogonia, although this does not abrogate fertility. Together, our work suggests a sexually dimorphic function for GR in the germline, and represents an important step towards understanding the mechanisms by which stress can modulate the transmission of genetic information through the germline.

Differential susceptibility of male and female germ cells to glucocorticoid-mediated signaling

While physiologic stress has long been known to impair mammalian reproductive capacity through hormonal dysregulation, mounting evidence now suggests that stress experienced prior to or during gestation may also negatively impact the health of future offspring. Rodent models of gestational physiologic stress can induce neurologic and behavioral changes that persist for up to three generations, suggesting that stress signals can induce lasting epigenetic changes in the germline. Treatment with glucocorticoid stress hormones is sufficient to recapitulate the transgenerational changes seen in physiologic stress models. These hormones are known to bind and activate the glucocorticoid receptor (GR), a ligand-inducible transcription factor, thus implicating GR-mediated signaling as a potential contributor to the transgenerational inheritance of stress-induced phenotypes. Here we demonstrate dynamic spatiotemporal regulation of GR expression in the mouse germline, showing expression in the fetal oocyte as well as the perinatal and adult spermatogonia. Functionally, we find that fetal oocytes are intrinsically buffered against changes in GR signaling, as neither genetic deletion of GR nor GR agonism with dexamethasone altered the transcriptional landscape or the progression of fetal oocytes through meiosis. In contrast, our studies revealed that the male germline is susceptible to glucocorticoid-mediated signaling, specifically by regulating RNA splicing within the spermatogonia, although this does not abrogate fertility. Together, our work suggests a sexually dimorphic function for GR in the germline, and represents an important step towards understanding the mechanisms by which stress can modulate the transmission of genetic information through the germline.

Dysregulation of AMPK-mTOR signaling leads to comorbid anxiety in Dip2a KO mice

Autism is often comorbid with other psychiatric disorders. We have previously shown that Dip2a knockout (KO) induces autism-like behaviors in mice. However, the role of Dip2a in other psychiatric disorders remains unclear. In this paper, we revealed that Dip2a KO mice had comorbid anxiety. Dip2a KO led to a reduction in the dendritic length of cortical and hippocampal excitatory neurons. Molecular mechanism studies suggested that AMPK was overactivated and suppressed the mTOR cascade, contributing to defects in dendritic morphology. Deletion of Dip2a in adult-born hippocampal neurons (Dip2a conditional knockout (cKO)) increased susceptibility to anxiety upon acute stress exposure. Application of (2R,6R)-hydroxynorketamine (HNK), an inhibitor of mTOR, rescued anxiety-like behaviors in Dip2a KO and Dip2a cKO mice. In addition, 6 weeks of high-fat diet intake alleviated AMPK-mTOR signaling and attenuated the severity of anxiety in both Dip2a KO mice and Dip2a cKO mice. Taken together, these results reveal an unrecognized function of DIP2A in anxiety pathophysiology via regulation of AMPK-mTOR signaling.

Interleukin-1 receptor-associated kinase 4 (IRAK4) in the nucleus accumbens regulates opioid-seeking behavior in male rats

Opioid addiction remains a severe health problem. While substantial insights underlying opioid addiction have been yielded from neuron-centric studies, the contribution of non-neuronal mechanisms to opioid-related behavioral adaptations has begun to be recognized. Toll-like receptor 4 (TLR4), a pattern recognition receptor, has been widely suggested in opioid-related behaviors. Interleukin-1 receptor-associated kinase 4 (IRAK4) is a kinase essential for TLR4 responses, However, the potential role of IRAK4 in opioid-related responses has not been examined. Here, we explored the role of IRAK4 in cue-induced opioid-seeking behavior in male rats. We found that morphine self-administration increased the phosphorylation level of IRAK4 in the nucleus accumbens (NAc) in rats; the IRAK4 signaling remained activated after morphine extinction and cue-induced reinstatement test. Both systemic and local inhibition of IRAK4 in the NAc core attenuated cue-induced morphine-seeking behavior without affecting the locomotor activity and cue-induced sucrose-seeking. In addition, inhibition of IRAK4 also reduced the cue-induced reinstatement of fentanyl-seeking. Our findings suggest an important role of IRAK4 in opioid relapse-like behaviors and provide novel evidence in the association between innate immunity and drug addiction.

mTOR Knockdown in the Infralimbic Cortex Evokes A Depressive-like State in Mouse

Fast and sustained antidepressant effects of ketamine identified the mammalian target of rapamycin (mTOR) signaling pathway as the main modulator of its antidepressive effects. Thus, mTOR signaling has become integral for the preclinical evaluation of novel compounds to treat depression. However, causality between mTOR and depression has yet to be determined. To address this, we knocked down mTOR expression in mice using an acute intracerebral infusion of small interfering RNAs (siRNA) in the infralimbic (IL) or prelimbic (PrL) cortices of the medial prefrontal cortex (mPFC), and evaluated depressive- and anxious-like behaviors. mTOR knockdown in IL, but not PrL, cortex produced a robust depressive-like phenotype in mice, as assessed in the forced swimming test (FST) and the tail suspension test (TST). This phenotype was associated with significant reductions of mTOR mRNA and protein levels 48 h post-infusion. In parallel, decreased brain-derived neurotrophic factor (BDNF) expression was found bilaterally in both IL and PrL cortices along with a dysregulation of serotonin (5-HT) and glutamate (Glu) release in the dorsal raphe nucleus (DRN). Overall, our results demonstrate causality between mTOR expression in the IL cortex and depressive-like behaviors, but not in anxiety.

Rapid and Prolonged Antidepressant-like Effect of Crocin Is Associated with GHSR-Mediated Hippocampal Plasticity-related Proteins in Mice Exposed to Prenatal Stress

Prenatal stress (PNS) has a prolonged and adverse effect on offspring, leading to a significantly increased vulnerability to developing depression in their later life. Traditional therapies have delayed onset and limited efficacy; thus, it remains an urgent need to find novel medications with fast-onset and high-efficacy potentials. Crocin, with its structure clearly examined, has shown antidepressant-like effects. However, few studies extensively investigated its effect especially in mice exposed to PNS. Using an established PNS model, we tested whether crocin could have a rapid and persistent antidepressant-like effect in PNS mice. Growth hormone secretagogue receptor (GHSR) and phosphoinositide 3-kinase (PI3K) inhibitors were used to test their effects in antidepressant-like effect of crocin. Hippocampal GHSR-PI3K signaling was examined both in PNS mice treated with a single dose of crocin and in combination of GHSR inhibitor. PNS mice showed depression-like behaviors at juvenile and adulthood, and crocin induced an instant and persistent antidepressant-like response in PNS mice in a dose-dependent manner. Moreover, crocin increased the expression of hippocampal synaptic plasticity-associated proteins through the restoration of GHSR-PI3K signaling. Inhibitions of both GHSR and PI3K abolished the effect of crocin in alleviating depressive-like behaviors. More importantly, GHSR inhibitor JMV2959 blocked the enhanced expression of hippocampal plasticity-related proteins induced by crocin. The present study demonstrated that crocin induced a fast-onset and prolonged antidepressant effect in PNS mice and suggested that GHSR-PI3K signaling may play a key role in crocin's effect at least partially by a restoration of hippocampal synaptic plasticity-associated proteins.

Rodent ketamine depression-related research: Finding patterns in a literature of variability

Discovering that the anesthetic drug ketamine has rapidly acting antidepressant effects in many individuals with major depression is one of the most important findings in clinical psychopharmacology in recent decades. The initial report of these effects in human subjects was based on a foundation of rodent preclinical studies carried out in the 1990s, and subsequent investigation has included both further studies in individuals with depression, as well as reverse translational experiments in animal models, especially rodents. While there is general agreement in the rodent literature that ketamine has rapidly-acting, and generally sustained, antidepressant-like properties, there are also points of contention across studies, including the precise mechanism of action of this drug. In this review, we briefly summarize prominent yet variable findings regarding the mechanism of action. We also discuss a combination of similarities and variances in the rodent literature in the antidepressant-like effects of ketamine as a function of dose, species and strain, test, stressor, and presumably sex of the experimenter. We then present previously unpublished mouse strain comparison data suggesting that subanesthetic ketamine does not have robust antidepressant-like properties in unstressed animals, and may actually promote depression-like behavior, in contrast to widely reported findings. We conclude that the data best support the notion of ketamine action principally via NMDA receptor antagonism, transiently boosting glutamatergic (and possibly other) signaling in diverse brain circuits. We also suggest that future studies should address in greater detail the extent to which antidepressant-like properties of this drug are stress-sensitive, in an effort to better model major depression present in humans.

Transgenerational deep sequencing revealed hypermethylation of hippocampal mGluR1 gene with altered mRNA expression of mGluR5 and mGluR3 associated with behavioral changes in Sprague Dawley rats with history of prolonged febrile seizure

The impact of febrile seizure has been shown to transcend immediate generation with the alteration of glutamatergic pathway being implicated. However, transgenerational effects of this neurological disorder particularly prolonged febrile seizure (PFS) on neurobehavioral study and methylation profile is unknown. We therefore hypothesized that transgenerational impact of prolonged febrile seizure is dependent on methylation of hippocampal mGluR1 gene. Prolonged febrile seizure was induced on post-natal day (PND) 14, by injecting lipopolysaccharide (LPS; 217μg/kg ip) and kainic acid (KA; 1.83 mg/kg ip). Sucrose preference test (SPT) and Forced swim test (FST) were carried out in the first generation (F0) of animals at PND37 and PND60. The F0 rats were decapitated at PND 14, 37 and 60 which corresponded to childhood, adolescent and adulthood respectively and their hippocampal tissue collected. The second generation (F1) rats were obtained by mating F0 generation at PND 60 across different groups, F1 rats were subjected to SPT and FST test on PND 37 only. Decapitation of F1rats and collection of hippocampal tissues were done on PND 14 and 37. Assessment of mGluR5 and mGluR3 mRNA was done with PCR while mGluR1 methylation profile was assessed with the Quantitative MassARRAY analysis. Results showed that PFS significantly leads to decreased sucrose consumption in the SPT and increased immobility time in the FST in both generations of rats. It also leads to significant decrease in mGluR5 mRNA expression with a resultant increased expression of mGluR3 mRNA expression and hypermethylation of mGluR1 gene across both generations of rats. This study suggested that PFS led to behavioral changes which could be transmitted on to the next generation in rats.

Augmentation effect of ketamine by guanosine in the novelty-suppressed feeding test is dependent on mTOR signaling pathway

The ketamine's potential for the treatment of refractory depression and anxiety has been considered one the most important discoveries in the last years, however, repeated use of ketamine is limited due to its side/adverse effects. Therefore, the search for effective augmentation strategies that may reduce ketamine doses is welcome. Therefore, this study sought to augment the effect of ketamine by guanosine in the novelty-suppressed feeding (NSF) test, a behavioral paradigm able to detect depression/anxiety-related behavior. Acute administration of guanosine (0.05 mg/kg, p.o.), similar to ketamine (1 mg/kg, i.p.), produced a rapid behavioral response in mice submitted to NSF test. Moreover, the coadministration of sub-effective doses of guanosine (0.01 mg/kg, p.o.) and ketamine (0.1 mg/kg, i.p.) was effective in mice submitted to NSF test. Subsequently, the intracellular mechanism underpinning the augmentation effect of ketamine by guanosine was investigated. Our results suggest that augmentation response of ketamine by guanosine in the NSF test probably involves the activation of mTOR signaling, since the treatment with rapamycin (0.2 nmol/site, i.c.v., a selective mTOR inhibitor) completely abolished this effect. This augmentation strategy also increased mTOR phosphorylation (Ser²⁴⁴⁸) in the hippocampus, reinforcing the role of mTOR in this augmentation response. However, no changes in the p70S6K, PSD-95, GluA1, and synapsin immunocontents were found in the hippocampus of ketamine plus guanosine-treated mice. Overall, results provide evidence that guanosine is able to augment the effect of ketamine in the NSF test via mTOR activation, a finding that might have therapeutic implications for the management of depression/anxiety.

Loss of Glutamate Decarboxylase 67 in Somatostatin-Expressing Neurons Leads to Anxiety-Like Behavior and Alteration in the Akt/GSK3β Signaling Pathway

Major depressive disorder (MDD) is a highly prevalent psychiatric disorder worldwide. Several lines of evidence suggest that the dysfunction of somatostatin (SOM) neurons is associated with the pathophysiology of MDD. Importantly, most SOM neurons are γ-aminobutyric acid (GABA) interneurons. However, whether the dysfunction of GABAergic neurotransmission from SOM neurons contributes to the pathophysiology of MDD remains elusive. To address this issue, we investigated the emotional behaviors and relevant molecular mechanism in mice lacking glutamate decarboxylase 67 (GAD67), an isoform of GABA-synthesizing enzyme, specifically in SOM neurons (SOM-GAD67 mice). The SOM-GAD67 mice exhibited anxiety-like behavior in the open-field test without an effect on locomotor activity. The SOM-GAD67 mice showed depression-like behavior in neither the forced swimming test nor the sucrose preference test. In addition, the ability to form contextual fear memory was normal in the SOM-GAD67 mice. Furthermore, the plasma corticosterone level was normal in the SOM-GAD67 mice both under baseline and stress conditions. The expression ratios of p-Akt^Ser473/Akt and p-GSK3β^Ser9/GSK3β were decreased in the frontal cortex of SOM-GAD67 mice. Taken together, these data suggest that the loss of GAD67 from SOM neurons may lead to the development of anxiety-like but not depression-like states mediated by modification of Akt/GSK3β activities.

Transgenerational Epigenetics of Traumatic Stress

Traumatic stress is a type of environmental experience that can modify behavior, cognition and physiological functions such as metabolism, in mammals. Many of the effects of traumatic stress can be transmitted to subsequent generations even when individuals from these generations are not exposed to any traumatic stressor. This book chapter discusses the concept of epigenetic/non-genomic inheritance of such traits involving the germline in mammals. It includes a comprehensive review of animal and human studies on inter- and transgenerational inheritance of the effects of traumatic stress, some of the epigenetic changes in the germline currently known to be associated with traumatic stress, and possible mechanisms for their induction and maintenance during development and adulthood. We also describe some experimental interventions that attempted to prevent the transmission of these effects, and consider the evolutionary importance of transgenerational inheritance and future outlook of the field.

Human and animal evidence of potential transgenerational inheritance of health effects: An evidence map and state-of-the-science evaluation

BACKGROUND

An increasing number of reports suggest early life exposures result in adverse effects in offspring who were never directly exposed; this phenomenon is termed "transgenerational inheritance." Given concern for public health implications for potential effects of exposures transmitted to subsequent generations, it is critical to determine how widespread and robust this phenomenon is and to identify the range of exposures and possible outcomes.

OBJECTIVES

This scoping report examines the evidence for transgenerational inheritance associated with exposure to a wide range of stressors in humans and animals to identify areas of consistency, uncertainty, data gaps, and to evaluate general risk of bias issues for the transgenerational study design.

METHODS

A protocol was developed to collect and categorize the literature into a systematic evidence map for transgenerational inheritance by health effects, exposures, and evidence streams following the Office of Health Assessment and Translation (OHAT) approach for conducting literature-based health assessments.

RESULTS

A PubMed search yielded 63,758 unique records from which 257 relevant studies were identified and categorized into a systematic evidence map by evidence streams (46 human and 211 animal), broad health effect categories, and exposures. Data extracted from the individual studies are available in the Health Assessment Workspace Collaborative (HAWC) program. There are relatively few bodies of evidence where multiple studies evaluated the same exposure and the same or similar outcomes. Studies evaluated for risk of bias generally had multiple issues in design or conduct.

CONCLUSIONS

The evidence mapping illustrated that risk of bias, few studies, and heterogeneity in exposures and endpoints examined present serious limitations to available bodies of evidence for assessing transgenerational effects. Targeted research is suggested to addressed inconsistencies and risk of bias issues identified, and thereby establish more robust bodies of evidence to critically assess transgenerational effects - particularly by adding data on exposure-outcome pairs where there is some evidence (i.e., reproductive, metabolic, and neurological effects).

Transcriptomic analysis reveals transgenerational effect of hypoxia on the neural control of testicular functions

There are over 400 hypoxic zones in the ocean worldwide. Both laboratory and field studies have shown that hypoxia causes endocrine disruption and reproductive impairments in vertebrates. More importantly, our recent study discovered that parental (F0) hypoxia exposure resulted in the transgenerational impairment of sperm quality in the F2 generation through the epigenetic regulation of germ cells. In the present study, we aim to test the hypothesis that the brain, as the major regulator of the brain-pituitary-gonad (BPG) axis, is also involved in the observed transgenerational effect. Using comparative transcriptomic analysis on brain tissues of marine medaka Oryzias melastigma, 45 common differentially expressed genes caused by parental hypoxia exposure were found in the hypoxic group of the F0 and F2 generations, and the transgenerational groups of the F2 generation. The bioinformatic analysis on this deregulated gene cluster further highlighted the possible involvement of the brain in the transgenerational effect of hypoxia on testicular structure, including abnormal morphologies of the epididymis and the seminal vesicle, and degeneration of the seminiferous tubule. This finding is concordant to the result of hematoxylin and eosin staining, which showed the reduction of testicular lobular diameter in the F0 and F2 generations. Our study demonstrated for the first time the involvement of the brain in the transgenerational effect of hypoxia.

Serotonin transporter immunoreactivity is modulated during development and after fluoxetine treatment in the rodent visual system

The serotonin transporter (5-HTT) regulates serotonin homeostasis and has been used as a target for different drugs in depression treatment. Although the serotonergic system has received a lot of attention, little is known about the effects of these drugs over serotonin transporters. In this work, we investigated the expression pattern of 5-HTT during development of the visual system and the influence of fluoxetine on different signaling pathways. Our data showed that the expression of 5-HTT has a gradual increase from postnatal day 0 until 42 and decrease afterwards. Moreover, chronic fluoxetine treatment both in childhood and adolescence induces down regulation of 5-HTT expression and phosphorylation of ERK and AKT signaling pathways. Together these data suggest that the levels of 5-HTT protein could be important for the development of the central nervous system and suggest that the ERK and AKT are involved in the molecular pathways of antidepressants drugs, acting in concert to improve serotonergic signaling.

Chronic stress prior to pregnancy potentiated long-lasting postpartum depressive-like behavior, regulated by Akt-mTOR signaling in the hippocampus

Postpartum depression (PPD) affects over 10% of new mothers and adversely impacts the health of offspring. One of the greatest risk factors for PPD is prepregnancy stress but the underlying biological mechanism is unknown. Here we constructed an animal model which recapitulated prepregnancy stress induced PPD and tested the role of Akt-mTOR signaling in the hippocampus. Female virgin Balb/c mice received chronic restraint stress, followed by co-housing with a normal male mouse. We found that the chronic stress led to a transient depressive-like condition that disappeared within two weeks. However, prepregnantly stressed females developed long-term postpartum depressive-like (PPD-like) symptoms as indicated by deficient performance in tests of sucrose preference, forced swim, and novelty-suppressed feeding. Chronic stress induced transient decrease in Akt-mTOR signaling and altered expressions of glutamate receptor subunits NR1 and GluR1, in contrast to long-term deficits in Akt-mTOR signaling, GluR1/NR1 ratio, and hippocampal neurogenesis in PPD-like mice. Acute ketamine improved the molecular signaling abnormality, and reversed the behavioral deficits in PPD-like mice in a rapid and persistent manner, in contrast to ineffectiveness by chronic fluoxetine treatment. Taken together, we find that chronic prepregnancy stress potentiates a long-term PPD, in which Akt-mTOR signaling may play a crucial role.