Abstract:
Early life stress (ELS) can increase vulnerability to psychiatric disorders, but also trigger resilience. FKBP51 has been associated with an increased risk for developing psychiatric disorders, specifically in interaction with ELS exposure. Here, the contribution of FKBP51 in glutamatergic forebrain neurons to the long-term consequences of ELS was investigated in both sexes. In female wild-type Fkbp5(lox/lox) mice, ELS exposure led to an anxiolytic phenotype and improved memory performance in a stressful context, however this ELS effect was absent in Fkbp5(Nex) mice. These interactive FKBP51 x ELS effects in female mice were also reflected in reduced brain region volumes, and on structural and electrophysiological properties of CA1 pyramidal neurons of the dorsal hippocampus. In contrast, the behavioral, structural and functional effects in male ELS mice were less pronounced and independent of FKBP51. RNA sequencing of the hippocampus revealed the transcription factor 4 (TCF4) as a potential regulator of the female interactive effects. Cre-dependent viral overexpression of TCF4 in female Nex-Cre mice led to similar beneficial effects on behavior as the ELS exposure. This study demonstrates a sex-specific role for FKBP51 in mediating the adaptive effects of ELS on emotional regulation, cognition, and neuronal function, implicating TCF4 as a downstream effector.

Abstract:
Early life stress (ELS) can negatively impact health, increasing the risk of stress-related disorders, such as post-traumatic stress disorder (PTSD). Importantly, PTSD disproportionately affects women, emphasizing the critical need to explore how sex differences influence the genetic and metabolic neurobiological pathways underlying trauma-related behaviors. This study uses the limited bedding and nesting (LBN) paradigm to model ELS and investigate its sex-specific effects on fear memory formation. Employing innovative unsupervised behavioral classification, the current study reveals distinct behavioral patterns associated with fear acquisition and retrieval in male and female mice following ELS. Females exposed to LBN display heightened active fear responses, contrasting with males. Furthermore, the study examined the crucial link between behavioral regulation and cellular metabolism in key brain regions involved in fear and stress processing. Sex-specific and stress-dependent alterations were observed in purine, pyrimidine, and glutamate metabolism within the basolateral amygdala, the dorsal hippocampus, and the ventral hippocampus. These findings provide crucial insights into the complex interplay between metabolic pathways, the neurobiological underpinnings of fear memory, and stress responses. Importantly, they emphasize the significance of considering sex-specific metabolic alterations when investigating stress-related disorders, opening potential avenues for the development of targeted interventions.

Abstract:
The co-chaperone FKBP51, encoded by FKBP5 gene, is recognized as a psychiatric risk factor for anxiety and depressive disorders due to its crucial role in the stress response. Another key modulator in stress response regulation is the corticotropin releasing hormone (CRH), which is co-expressed with FKBP51 in many stress-relevant brain-regions and cell-types. Together, they intricately influence the balance of the hypothalamic-pituitary-adrenal (HPA) axis, one of the primary stress response systems. Previous research underscores the potential moderating effects these genes have on the regulation of the stressful life events towards the vulnerability of major depressive disorder (MDD). However, the specific function of FKBP51 in CRH-expressing neurons remains largely unexplored. Here, through deep behavioral phenotyping, we reveal heightened stress effects in mice lacking FKBP51 in CRH co-expressing neurons (CRH(FKBP5-/-)), particularly evident in social contexts. Our findings highlight the importance of considering cell-type specificity and context in comprehending stress responses and advocate for the utilization of machine-learning-driven phenotyping of mouse models. By elucidating these intricacies, we lay down the groundwork for personalized interventions aimed at enhancing stress resilience and individual well-being.

Abstract:
Stress, encompassing psychological, physical, and physiological challenges, is an important factor affecting an individual's well-being and potentially leading to psychiatric, neurodegenerative, immune, and metabolic disorders. However, not everyone exposed to stress develops these conditions, highlighting the concept of resilience. Resilience is a dynamic process categorized into four dimensions: pre-existing resilience capacity, ongoing resilience processes, post-stress resilience outcomes, and recovery from psychopathologies. These dimensions involve genomic, cellular, and systemic interactions influenced by genetic factors, early life experiences, adult life experiences in addition to community/environmental factors, and health behaviors. The biological response to stress encompasses endocrine, autonomic, immunological, and behavioral components, modulated by stressor characteristics and individual traits. Due to the limitations in studying stress and resilience in humans, translational models using rodents and cell cultures are essential. Rodent models include acute, chronic, and traumatic stress paradigms, aiding the study of stress-related behavioral and molecular outcomes. Additionally, early life stress models, such as prenatal stress and maternal separation, provide insights into developmental impacts. In this review, first, rodent models for lifelong stress exposure will be summarized considering their validity, advantages, and limitations. Subsequently, an overview of models designed to enhance resilience capacity and process in rodents, and later the behavioral models employed to study the outcomes of resilience will be given. Lastly, the focus will be shifted to cell culture and iPSCs models. Finally, future considerations focused on improving translational models used to study stress and resilience will be discussed. It is aimed to provide an overview of designs for translational stress and resilience models to access more effective translational biomarkers associated with stress and resilience. Stress and resilience are complex phenomena influenced by various factors, spanning molecular to behavioral levels. Integrating data across dimensions remains crucial for unraveling the complexities of stress-related disorders and resilience.

Abstract:

Abstract:
Adverse events in early life can modulate the response to additional stressors later in life and increase the risk of developing psychiatric disorders. The underlying molecular mechanisms responsible for these effects remain unclear. Here, we uncover that early life adversity (ELA) in mice leads to social subordination. Using single-cell RNA sequencing (scRNA-seq), we identified cell type-specific changes in the transcriptional state of glutamatergic and GABAergic neurons in the ventral hippocampus of ELA mice after exposure to acute social stress in adulthood. These findings were reflected by an alteration in excitatory and inhibitory synaptic transmission induced by ELA in response to acute social stress. Finally, enhancing the inhibitory network function through transient diazepam treatment during an early developmental sensitive period reversed the ELA-induced social subordination. Collectively, this study significantly advances our understanding of the molecular, physiological, and behavioral alterations induced by ELA, uncovering a previously unknown cell type-specific vulnerability to ELA.

Abstract:
Social behavior is naturally occurring in vertebrate species, which holds a strong evolutionary component and is crucial for the normal development and survival of individuals throughout life. Behavioral neuroscience has seen different influential methods for social behavioral phenotyping. The ethological research approach has extensively investigated social behavior in natural habitats, while the comparative psychology approach was developed utilizing standardized and univariate social behavioral tests. The development of advanced and precise tracking tools, together with post-tracking analysis packages, has recently enabled a novel behavioral phenotyping method, that includes the strengths of both approaches. The implementation of such methods will be beneficial for fundamental social behavioral research but will also enable an increased understanding of the influences of many different factors that can influence social behavior, such as stress exposure. Furthermore, future research will increase the number of data modalities, such as sensory, physiological, and neuronal activity data, and will thereby significantly enhance our understanding of the biological basis of social behavior and guide intervention strategies for behavioral abnormalities in psychiatric disorders.

Abstract:
Severe stress exposure increases the risk of stress-related disorders such as major depressive disorder (MDD). An essential characteristic of MDD is the impairment of social functioning and lack of social motivation. Chronic social defeat stress is an established animal model for MDD research, which induces a cascade of physiological and behavioral changes. Current markerless pose estimation tools allow for more complex and naturalistic behavioral tests. Here, we introduce the open-source tool DeepOF to investigate the individual and social behavioral profile in mice by providing supervised and unsupervised pipelines using DeepLabCut-annotated pose estimation data. Applying this tool to chronic social defeat in male mice, the DeepOF supervised and unsupervised pipelines detect a distinct stress-induced social behavioral pattern, which was particularly observed at the beginning of a novel social encounter and fades with time due to habituation. In addition, while the classical social avoidance task does identify the stress-induced social behavioral differences, both DeepOF behavioral pipelines provide a clearer and more detailed profile. Moreover, DeepOF aims to facilitate reproducibility and unification of behavioral classification by providing an open-source tool, which can advance the study of rodent individual and social behavior, thereby enabling biological insights and, for example, subsequent drug development for psychiatric disorders.

Abstract:
Early life stress (ELS) is associated with metabolic, cognitive, and psychiatric diseases and has a very high prevalence, highlighting the urgent need for a better understanding of the versatile physiological changes and identification of predictive biomarkers. In addition to programming the hypothalamic-pituitary-adrenal (HPA) axis, ELS may also affect the gut microbiota and metabolome, opening up a promising research direction for identifying early biomarkers of ELS-induced (mal)adaptation. Other factors affecting these parameters include maternal metabolic status and diet, with maternal obesity shown to predispose offspring to later metabolic disease. The aim of the present study was to investigate the long-term effects of ELS and maternal obesity on the metabolic and stress phenotype of rodent offspring. To this end, offspring of both sexes were subjected to an adverse early-life experience, and their metabolic and stress phenotypes were examined. In addition, we assessed whether a prenatal maternal and an adult high-fat diet (HFD) stressor further shape observed ELS-induced phenotypes. We show that ELS has long-term effects on male body weight (BW) across the lifespan, whereas females more successfully counteract ELS-induced weight loss, possibly by adapting their microbiota, thereby stabilizing a balanced metabolome. Furthermore, the metabolic effects of a maternal HFD on BW are exclusively triggered by a dietary challenge in adult offspring and are more pronounced in males than in females. Overall, our study suggests that the female microbiota protects against an ELS challenge, rendering them more resilient to additional maternal- and adult nutritional stressors than males.

Abstract:
Mental health disorders often arise as a combination of environmental and genetic factors. The FKBP5 gene, encoding the GR co-chaperone FKBP51, has been uncovered as a key genetic risk factor for stress-related illness. However, the exact cell type and region-specific mechanisms by which FKBP51 contributes to stress resilience or susceptibility processes remain to be unravelled. FKBP51 functionality is known to interact with the environmental risk factors age and sex, but so far data on behavioral, structural, and molecular consequences of these interactions are still largely unknown. Here we report the cell type- and sex-specific contribution of FKBP51 to stress susceptibility and resilience mechanisms under the high-risk environmental conditions of an older age, by using two conditional knockout models within glutamatergic (Fkbp5(Nex)) and GABAergic (Fkbp5(Dlx)) neurons of the forebrain. Specific manipulation of Fkbp51 in these two cell types led to opposing effects on behavior, brain structure and gene expression profiles in a highly sex-dependent fashion. The results emphasize the role of FKBP51 as a key player in stress-related illness and the need for more targeted and sex-specific treatment strategies.