Jakob Hartmann

FK506 binding protein 5 shapes stress responsiveness: modulation of neuroendocrine reactivity and coping behavior.

BACKGROUND The Hsp90 cochaperone FK506 binding protein 5 (FKBP5) is an established regulator of the glucocorticoid receptor (GR), and numerous genetic studies have linked it to stress-related diseases such as major depression or posttraumatic stress disorder. However, translational studies including genetic animal models are lacking. METHODS Mice deficient of FKBP5 were generated and analyzed in comparison with wildtype littermates. They were subjected to several test paradigms characterizing their emotionality, stress reactivity, and coping behavior as well as hypothalamus-pituitary-adrenal axis function and regulation. Moreover, protein expression of GR and FKBP5 was determined in different brain structures 8 days after stress exposure. The combined dexamethasone/corticotropin-releasing hormone test was performed both in mice and healthy human subjects of different FKBP5 genotypes. The GR function was evaluated by reporter gene assays. RESULTS Under basal conditions, deletion of FKBP5 did not change exploratory drive, locomotor activity, anxiety-related behavior, stress-coping, or depression-like behavior. After exposure to different acute stressors of sufficient intensity, however, it led to a more active coping behavior. Moreover, loss of FKBP5 decreased hypothalamus-pituitary-adrenal axis reactivity and GR expression changes in response to stressors. In mice and humans, the FKBP5 genotype also determined the outcome of the dexamethasone/corticotropin-releasing hormone test. CONCLUSIONS This study in mice and humans presents FKBP5 as a decisive factor for the physiological stress response, shaping neuroendocrine reactivity as well as coping behavior. This lends strong support to the concept emerging from human studies of FKBP5 as important factor governing gene-environment interactions relevant for the etiology of affective disorders.

Nectin-3 links CRHR1 signaling to stress-induced memory deficits and spine loss

Stress impairs cognition via corticotropin-releasing hormone receptor 1 (CRHR1), but the molecular link between abnormal CRHR1 signaling and stress-induced cognitive impairments remains unclear. We investigated whether the cell adhesion molecule nectin-3 is required for the effects of CRHR1 on cognition and structural remodeling after early-life stress exposure. Postnatally stressed adult mice had decreased hippocampal nectin-3 levels, which could be attenuated by CRHR1 inactivation and mimicked by corticotropin-releasing hormone (CRH) overexpression in forebrain neurons. Acute stress dynamically reduced hippocampal nectin-3 levels, which involved CRH-CRHR1, but not glucocorticoid receptor, signaling. Suppression of hippocampal nectin-3 caused spatial memory deficits and dendritic spine loss, whereas enhancing hippocampal nectin-3 expression rescued the detrimental effects of early-life stress on memory and spine density in adulthood. Our findings suggest that hippocampal nectin-3 is necessary for the effects of stress on memory and structural plasticity and indicate that the CRH-CRHR1 system interacts with the nectin-afadin complex to mediate such effects.

Selective inhibitors of the FK506-binding protein 51 by induced fit

The FK506-binding protein 51 (FKBP51, encoded by the FKBP5 gene) is an established risk factor for stress-related psychiatric disorders such as major depression. Drug discovery for FKBP51 has been hampered by the inability to pharmacologically differentiate against the structurally similar but functional opposing homolog FKBP52, and all known FKBP ligands are unselective. Here, we report the discovery of the potent and highly selective inhibitors of FKBP51, SAFit1 and SAFit2. This new class of ligands achieves selectivity for FKBP51 by an induced-fit mechanism that is much less favorable for FKBP52. By using these ligands, we demonstrate that selective inhibition of FKBP51 enhances neurite elongation in neuronal cultures and improves neuroendocrine feedback and stress-coping behavior in mice. Our findings provide the structural and functional basis for the development of mechanistically new antidepressants.

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.

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.

Neuropeptide Y mediates the initial hypothalamic-pituitary-adrenal response to maternal separation in the neonatal mouse

The function of the hypothalamic-pituitary-adrenal (HPA) axis of the neonatal mouse or rat is characterized by a period of quiescence, where mild stimuli are unable to elicit a pronounced increase in circulating corticosterone. A disruption of this period by maternal separation has been shown to result in a variety of long-term consequences, including neuroendocrine and behavioral disturbances. We have recently shown that peripheral metabolic markers like glucose or ghrelin are altered by maternal separation and that these changes precede the effects on corticosterone secretion. In the current study, we investigated whether the initial activation of the HPA axis is mediated via neuropeptide Y (NPY). To test this hypothesis, we studied the effects of an 8 h maternal separation in NPY-deficient mice. In addition, we compared the effect of the genotype with the previously described pharmacological effect of a ghrelin receptor antagonist. We could show that the peripheral response to maternal separation is decreased in NPY heterozygous and homozygous animals. In addition, maternal separation effects on corticotropin releasing hormone and glucocorticoid receptor expression in the brain were prevented in NPY-deficient pups. These effects were similar to a pharmacological ghrelin receptor blockade. We conclude that metabolic signals via an NPY-mediated pathway play a crucial role in activating the stress system of the neonatal mouse.

Fkbp52 heterozygosity alters behavioral, endocrine and neurogenetic parameters under basal and chronic stress conditions in mice

Aversive life events represent one of the main risk factors for the development of many psychiatric diseases, but the interplay between environmental factors and genetic predispositions is still poorly understood. One major finding in many depressed patients is an impaired regulation of the hypothalamic-pituitary-adrenal (HPA) axis. The negative feedback loop of the HPA axis is mediated via the glucocorticoid receptor (GR) and the mineralocorticoid receptor. The co-chaperones FK506-binding protein 51 (FKBP51) and FK506-binding protein 52 (FKBP52) are components of the heat shock protein 90-receptor-heterocomplex and are functionally divergent regulators of both receptors. Here, we characterized heterozygous Fkbp52 knockout (Fkbp52(+/-)) mice under basal or chronic social defeat stress (CSDS) conditions with regard to physiological, neuroendocrine, behavioral and mRNA expression alterations. Fkbp52(+/-) mice displayed symptoms of increased stress sensitivity in a subset of behavioral and neuroendocrine parameters. These included increased anxiety-related behavior in the elevated plus-maze and an enhanced neuroendocrine response to a forced swim test (FST), possibly mediated by reduced GR sensitivity. At the same time, Fkbp52(+/-) mice also demonstrated signs of stress resilience in other behavioral and neuroendocrine aspects, such as reduced basal corticosterone levels and more active stress-coping behavior in the FST following CSDS. These contrasting results are in line with previous reports showing that FKBP52 is not involved in all branches of GR signaling, but rather acts in a gene-specific manner to regulate GR transcriptional activation.

Chaperoning epigenetics: FKBP51 decreases the activity of DNMT1 and mediates epigenetic effects of the antidepressant paroxetine

Chaperone switching at the kinase CDK5 mediates epigenetic effects of antidepressants. Antidepressants chaperone DNA methylation Epigenetic changes are associated with depression. Some depressed patients have increased DNA methylation and decreased expression of the gene encoding BDNF, a secreted factor important for synaptic plasticity. Rein et al. found that some antidepressants inhibit epigenetic changes by causing a switch in chaperone binding to the DNA methyltransferase DNMT1. The chaperones FKBP51 and FKBP52 competed for binding to CDK5, a kinase that activates DNMT1. The authors found that cells from depressed patients or cultured mouse astrocytes exposed to the antidepressant paroxetine favored the FKBP51-CDK5 interaction, resulting in reduced activity of DNMT1 and DNA methylation, and increased the expression of BDNF. These effects of paroxetine on patient blood cells isolated before therapy correlated with a positive clinical response to antidepressants, suggesting that a simple blood test may aid in personalizing treatment for depression. Epigenetic processes, such as DNA methylation, and molecular chaperones, including FK506-binding protein 51 (FKBP51), are independently implicated in stress-related mental disorders and antidepressant drug action. FKBP51 associates with cyclin-dependent kinase 5 (CDK5), which is one of several kinases that phosphorylates and activates DNA methyltransferase 1 (DNMT1). We searched for a functional link between FKBP51 (encoded by FKBP5) and DNMT1 in cells from mice and humans, including those from depressed patients, and found that FKBP51 competed with its close homolog FKBP52 for association with CDK5. In human embryonic kidney (HEK) 293 cells, expression of FKBP51 displaced FKBP52 from CDK5, decreased the interaction of CDK5 with DNMT1, reduced the phosphorylation and enzymatic activity of DNMT1, and diminished global DNA methylation. In mouse embryonic fibroblasts and primary mouse astrocytes, FKBP51 mediated several effects of paroxetine, namely, decreased the protein-protein interactions of DNMT1 with CDK5 and FKBP52, reduced phosphorylation of DNMT1, and decreased the methylation and increased the expression of the gene encoding brain-derived neurotrophic factor (Bdnf). In human peripheral blood cells, FKBP5 expression inversely correlated with both global and BDNF methylation. Peripheral blood cells isolated from depressed patients that were then treated ex vivo with paroxetine revealed that the abundance of BDNF positively correlated and phosphorylated DNMT1 inversely correlated with that of FKBP51 in cells and with clinical treatment success in patients, supporting the relevance of this FKBP51-directed pathway that prevents epigenetic suppression of gene expression.

An adverse early life environment can enhance stress resilience in adulthood

Chronic stress is a major risk factor for depression. Interestingly, not all individuals develop psychopathology after chronic stress exposure. In contrast to the prevailing view that stress effects are cumulative and increase stress vulnerability throughout life, the match/mismatch hypothesis of psychiatric disorders. The match/mismatch hypothesis proposes that individuals who experience moderate levels of early life psychosocial stress can acquire resilience to renewed stress exposure later in life. Here, we have tested this hypothesis by comparing the developmental effects of 2 opposite early life conditions, when followed by 2 opposite adult environments. Male Balb/c mice were exposed to either adverse early life conditions (limited nesting and bedding material) or a supportive rearing environment (early handling). At adulthood, the animals of each group were either housed with an ovariectomized female (supportive environment) or underwent chronic social defeat stress (socially adverse environment) for 3 weeks. At the end of the adult manipulations, all of the animals were returned to standard housing conditions. Then, we compared the neuroendocrine, behavioral and molecular effects of the interaction between early and adult environment. Our study shows that early life adversity does not necessarily result in increased vulnerability to stress. Specific endophenotypes, like hypothalamic-pituitary-adrenal axis activity, anxiety-related behavior and glucocorticoid receptor expression levels in the hippocampus were not significantly altered when adversity is experienced during early life and in adulthood, and are mainly affected by either early life or adult life adversity alone. Overall our data support the notion that being raised in a stressful environment prepares the offspring to better cope with a challenging adult environment and emphasize the role of early life experiences in shaping adult responsiveness to stress.