Christiana Labermaier

Early‐life stress‐induced anxiety‐related behavior in adult mice partially requires forebrain corticotropin‐releasing hormone receptor 1

Early‐life stress may lead to persistent changes in central corticotropin‐releasing hormone (CRH) and the CRH receptor 1 (CRHR1) system that modulates anxiety‐related behavior. However, it remains unknown whether CRH–CRHR1 signaling is involved in early‐life stress‐induced anxiety‐related behavior in adult animals. In the present study, we used conditional forebrain CRHR1 knockout (CRHR1‐CKO) mice and examined the potential role of forebrain CRHR1 in the anxiogenic effects of early‐life stress. As adults, wild‐type mice that received unstable maternal care during the first postnatal week showed reduced body weight gain and increased anxiety levels in the open field test, which were prevented in stressed CRHR1‐CKO mice. In the light–dark box test, control CRHR1‐CKO mice were less anxious, but early‐life stress increased anxiety levels in both wild‐type and CRHR1‐CKO mice. In the elevated plus maze test, early‐life stress had only subtle effects on anxiety‐related behavior. Moreover, early‐life stress did not alter the basal home cage activity and gene expression levels of key hypothalamic‐pituitary‐adrenal axis regulators in adult wild‐type and CRHR1‐CKO mice, but enhanced neuroendocrine reactivity to acute immobilization stress in CRHR1‐CKO mice. Our findings highlight the importance of forebrain CRHR1 in modulating some of the anxiogenic effects of early‐life stress, and suggest that other neural circuits are also involved in the programming effects of early‐life stress on anxiety‐related behavior.

Evidence supporting the match/mismatch hypothesis of psychiatric disorders

Chronic stress is one of the predominant environmental risk factors for a number of psychiatric disorders, particularly for major depression. Different hypotheses have been formulated to address the interaction between early and adult chronic stress in psychiatric disease vulnerability. The match/mismatch hypothesis of psychiatric disease states that the early life environment shapes coping strategies in a manner that enables individuals to optimally face similar environments later in life. We tested this hypothesis in female Balb/c mice that underwent either stress or enrichment early in life and were in adulthood further subdivided in single or group housed, in order to provide aversive or positive adult environments, respectively. We studied the effects of the environmental manipulation on anxiety-like, depressive-like and sociability behaviors and gene expression profiles. We show that continuous exposure to adverse environments (matched condition) is not necessarily resulting in an opposite phenotype compared to a continuous supportive environment (matched condition). Rather, animals with mismatched environmental conditions behaved differently from animals with matched environments on anxious, social and depressive like phenotypes. These results further support the match/mismatch hypothesis and illustrate how mild or moderate aversive conditions during development can shape an individual to be optimally adapted to similar conditions later in life.

Interplay between diet-induced obesity and chronic stress in mice: potential role of FKBP51

While it is known that stress promotes obesity, the effects of stress within an obesogenic context are not so clear and molecular targets at the interface remain elusive. The FK506-binding protein 51 (FKBP51, gene: Fkbp5) has been identified as a target gene implicated in the development of stress-related psychiatric disorders and is a possible candidate for involvement in stress and metabolic regulation. The aims of the current study are to investigate the interaction between chronic stress and an obesogenic context and to additionally examine whether FKBP51 is involved in this interaction. For this purpose, male C57BL/6 mice were exposed to a high-fat diet for 8 weeks before being challenged with chronic social defeat stress. Herein, we demonstrate that chronic stress induces hypophagia and weight loss, ultimately improving features arising from an obesogenic context, including glucose tolerance and levels of insulin and leptin. We show that Fkbp5 expression is responsive to diet and stress in the hypothalamus and hippocampus respectively. Furthermore, under basal conditions, higher levels of hypothalamic Fkbp5 expression were related to increased body weight gain. Our data indicate that Fkbp5 may represent a novel target in metabolic regulation.

Biomarkers predicting antidepressant treatment response: how can we advance the field?

Major depression, affecting an estimated 350 million people worldwide, poses a serious social and economic threat to modern societies. There are currently two major problems calling for innovative research approaches, namely, the absence of biomarkers predicting antidepressant response and the lack of conceptually novel antidepressant compounds. Both, biomarker predicting a priori whether an individual patient will respond to the treatment of choice as well as an early distinction of responders and nonresponders during antidepressant therapy can have a significant impact on improving this situation. Biosignatures predicting antidepressant response a priori or early in treatment would enable an evidence-based decision making on available treatment options. However, research to date does not identify any biologic or genetic predictors of sufficient clinical utility to inform the selection of specific antidepressant compound for an individual patient. In this review, we propose an optimized translational research strategy to overcome some of the major limitations in biomarker discovery. We are confident that early transfer and integration of data between both species, ideally leading to mutual supportive evidence from both preclinical and clinical studies, are most suitable to address some of the obstacles of current depression research.

Differences in FKBP51 Regulation Following Chronic Social Defeat Stress Correlate with Individual Stress Sensitivity: Influence of Paroxetine Treatment

Various clinical studies have identified FK506-binding protein 51 (FKBP51) as a target gene involved in the development of psychiatric disorders such as depression. Furthermore, FKBP51 has been shown to affect glucocorticoid receptor signaling by sensitivity modulation and it is implicated in stress reactivity as well as in molecular mechanisms of stress vulnerability and resilience. We investigated the physiological, behavioral, and neuroendocrine parameters in an established chronic stress model both directly after stress and after a recovery period of 3 weeks and also studied the efficacy of paroxetine in this model. We then examined FKBP51 mRNA levels in the dorsal and ventral part of the hippocampus and correlated the expression to behavioral and endocrine parameters. We show robust chronic stress effects in physiological, behavioral, and neuroendocrine parameters, which were only slightly affected by paroxetine treatment. On the contrary, paroxetine led to a disruption of the neuroendocrine system. FKBP51 expression was significantly increased directly after the stress period and correlated with behavioral and neuroendocrine parameters. Taken together, we were able to further elucidate the role of FKBP51 in the mechanisms of stress resilience and vulnerability, especially with respect to behavioral and neuroendocrine parameters. These findings strongly support the concept of FKBP51 as a marker for glucocorticoid receptor sensitivity and its involvement in the development of psychiatric disorders.

Time-dependent metabolomic profiling of Ketamine drug action reveals hippocampal pathway alterations and biomarker candidates

Ketamine, an N-methyl-D-aspartate receptor (NMDAR) antagonist, has fast-acting antidepressant activities and is used for major depressive disorder (MDD) patients who show treatment resistance towards drugs of the selective serotonin reuptake inhibitor (SSRI) type. In order to better understand Ketamine’s mode of action, a prerequisite for improved drug development efforts, a detailed understanding of the molecular events elicited by the drug is mandatory. In the present study we have carried out a time-dependent hippocampal metabolite profiling analysis of mice treated with Ketamine. After a single injection of Ketamine, our metabolomics data indicate time-dependent metabolite level alterations starting already after 2 h reflecting the fast antidepressant effect of the drug. In silico pathway analyses revealed that several hippocampal pathways including glycolysis/gluconeogenesis, pentose phosphate pathway and citrate cycle are affected, apparent by changes not only in metabolite levels but also connected metabolite level ratios. The results show that a single injection of Ketamine has an impact on the major energy metabolism pathways. Furthermore, seven of the identified metabolites qualify as biomarkers for the Ketamine drug response.

Homer1/mGluR5 Activity Moderates Vulnerability to Chronic Social Stress

Stress-induced psychiatric disorders, such as depression, have recently been linked to changes in glutamate transmission in the central nervous system. Glutamate signaling is mediated by a range of receptors, including metabotropic glutamate receptors (mGluRs). In particular, mGluR subtype 5 (mGluR5) is highly implicated in stress-induced psychopathology. The major scaffold protein Homer1 critically interacts with mGluR5 and has also been linked to several psychopathologies. Yet, the specific role of Homer1 in this context remains poorly understood. We used chronic social defeat stress as an established animal model of depression and investigated changes in transcription of Homer1a and Homer1b/c isoforms and functional coupling of Homer1 to mGluR5. Next, we investigated the consequences of Homer1 deletion, overexpression of Homer1a, and chronic administration of the mGluR5 inverse agonist CTEP (2-chloro-4-((2,5-dimethyl-1-(4-(trifluoromethoxy)phenyl)-1H-imidazol-4-yl)ethynyl)pyridine) on the effects of chronic stress. In mice exposed to chronic stress, Homer1b/c, but not Homer1a, mRNA was upregulated and, accordingly, Homer1/mGluR5 coupling was disrupted. We found a marked hyperactivity behavior as well as a dysregulated hypothalamic–pituitary–adrenal axis activity in chronically stressed Homer1 knockout (KO) mice. Chronic administration of the selective and orally bioavailable mGluR5 inverse agonist, CTEP, was able to recover behavioral alterations induced by chronic stress, whereas overexpression of Homer1a in the hippocampus led to an increased vulnerability to chronic stress, reflected in an increased physiological response to stress as well as enhanced depression-like behavior. Overall, our results implicate the glutamatergic system in the emergence of stress-induced psychiatric disorders, and support the Homer1/mGluR5 complex as a target for the development of novel antidepressant agents.

The stress-inducible actin-interacting protein DRR1 shapes social behavior

Understanding the molecular mechanisms by which stress is translated into changes in complex behavior may help to identify novel treatment strategies for stress-associated psychiatric disorders. The tumor suppressor gene down-regulated in renal cell carcinoma 1 (DRR1) was recently characterized as a new molecular link between stress, synaptic efficacy and behavioral performance, most likely through its ability to modulate actin dynamics. The lateral septum is one of the brain regions prominently involved in the stress response. This brain region features high DRR1 expression in adult mice, even under basal conditions. We therefore aimed to characterize and dissect the functional role of septal DRR1 in modulating complex behavior. DRR1 protein expression was shown to be expressed in both neurons and astrocytes of the lateral septum of adult mice. Septal DRR1 mRNA expression increased after acute defeat stress and glucocorticoid receptor activation. To mimic the stress-induced DRR1 increase in the lateral septum of mice, we performed adenovirus-mediated region-specific overexpression of DRR1 and characterized the behavior of these mice. Overexpression of DRR1 in the septal region increased sociability, but did not change cognitive, anxiety-like or anhedonic behavior. The observed changes in social behavior did not involve alterations of the expression of vasopressin or oxytocin receptors, the canonical social neuropeptidergic circuits of the lateral septum. In summary, our data suggest that the stress-induced increase of DRR1 expression in the lateral septum could be a protective mechanism to buffer or counterbalance negative consequences of stress exposure on social behavior.

Forebrain glutamatergic, but not GABAergic, neurons mediate anxiogenic effects of the glucocorticoid receptor

Anxiety disorders constitute a major disease and social burden worldwide; however, many questions concerning the underlying molecular mechanisms still remain open. Besides the involvement of the major excitatory (glutamate) and inhibitory (gamma aminobutyric acid (GABA)) neurotransmitter circuits in anxiety disorders, the stress system has been directly implicated in the pathophysiology of these complex mental illnesses. The glucocorticoid receptor (GR) is the major receptor for the stress hormone cortisol (corticosterone in rodents) and is widely expressed in excitatory and inhibitory neurons, as well as in glial cells. However, currently it is unknown which of these cell populations mediate GR actions that eventually regulate fear- and anxiety-related behaviors. In order to address this question, we generated mice lacking the receptor specifically in forebrain glutamatergic or GABAergic neurons by breeding GRflox/flox mice to Nex-Cre or Dlx5/6-Cre mice, respectively. GR deletion specifically in glutamatergic, but not in GABAergic, neurons induced hypothalamic–pituitary–adrenal axis hyperactivity and reduced fear- and anxiety-related behavior. This was paralleled by reduced GR-dependent electrophysiological responses in the basolateral amygdala (BLA). Importantly, viral-mediated GR deletion additionally showed that fear expression, but not anxiety, is regulated by GRs in glutamatergic neurons of the BLA. This suggests that pathological anxiety likely results from altered GR signaling in glutamatergic circuits of several forebrain regions, while modulation of fear-related behavior can largely be ascribed to GR signaling in glutamatergic neurons of the BLA. Collectively, our results reveal a major contribution of GRs in the brain’s key excitatory, but not inhibitory, neurotransmitter system in the regulation of fear and anxiety behaviors, which is crucial to our understanding of the molecular mechanisms underlying anxiety disorders.

SLC6A15, a novel stress vulnerability candidate, modulates anxiety and depressive-like behavior: involvement of the glutamatergic system

Abstract Major depression is a multifactorial disease, involving both environmental and genetic risk factors. Recently, SLC6A15 – a neutral amino acid transporter mainly expressed in neurons – was proposed as a new candidate gene for major depression and stress vulnerability. Risk allele carriers for a single nucleotide polymorphism (SNP) in a SLC6A15 regulatory region display altered hippocampal volume, glutamate levels, and hypothalamus-pituitary-adrenal axis activity, all markers associated with major depression. Despite this genetic link between SLC6A15 and depression, its functional role with regard to the development and maintenance of depressive disorder is still unclear. The aim of the current study was therefore to characterize the role of mouse slc6a15 in modulating brain function and behavior, especially in relation to stress as a key risk factor for the development of mood disorders. We investigated the effects of slc6a15 manipulation using two mouse models, a conventional slc6a15 knock-out mouse line (SLC-KO) and a virus-mediated hippocampal slc6a15 overexpression (SLC-OE) model. Mice were tested under basal conditions and following chronic social stress. We found that SLC-KO animals displayed a similar behavioral profile to wild-type littermates (SLC-WT) under basal conditions. Interestingly, following chronic social stress SLC-KO animals showed lower levels of anxiety- and depressive-like behavior compared to stressed WT littermates. In support of these findings, SLC-OE animals displayed increased anxiety-like behavior already under basal condition. We also provide evidence that GluR1 expression in the dentate gyrus, but not GluR2 or NR1, are regulated by slc6a15 expression, and may contribute to the difference in stress responsiveness observed between SLC-KO and SLC-WT animals. Taken together, our data demonstrate that slc6a15 plays a role in modulating emotional behavior, possibly mediated by its impact on glutamatergic neurotransmission.