Chronic stress is a burden of modern societies and is known to be a risk factor for numerous somatic and affective disorders, including cardiovascular dysfunction, inflammatory bowel disease, gastric ulceration, general and/ or social anxiety- and depression-related diseases, as well as systemic immunological dysfunctions. Although many of these disorders are paralleled by either hypocorticism, glucocorticoid (GC) resistance, or a combination of both, resulting in a decreased GC signalling, the underlying aetiology of these disorders is still poorly understood, at least partly due to a lack of appropriate and clinically relevant animal models.

Importantly, not all people are equally affected by chronic stressors. While some individuals subjected to severe adverse life events develop pathologies, others do not. But again, the underlying mechanisms engendering resilience and vulnerability are also far from being understood and, thus, the possibility to clinically benefit from these observations is currently still limited.

A failure of immunoregulation, attributable to reduced exposure to the microbial environment within which the mammalian immune system evolved ("Old friends hypothesis"), is thought to be one factor contributing to recent increases in stress-related chronic inflammatory disorders, as well as mood disorders for which chronic low-grade inflammation is a risk factor ("cytokine theory of depression") (Lowry et al., 2016 Curr Environ Health Rep; Reber et al., 2016 PNEC).

Therefore, the main research aims of the Laboratory for Molecular Psychosomatics are to extend the current knowledge on the mechanisms underlying 1i) stressor-induced development of somatic and mental pathologies and 1ii) individual differences in stress resilience and 2) to use this mechanistic knowledge for the development of novel strategies in terms of stress protection (Fig. 1).

Funding Identity of the Laboratory for Molecular Psychosomatics

Facilitating stress resilience by "Old friends": Immunization with Mycobacterium vaccae prevents the negative effects of early life stress on chronic stress vulnerability during adulthood. (German Research Foundation, RE 2911/21-1; successfully applied for by S.O. Reber)

Facilitating resilience to repeated hits of psychosocial traumatization by "Old friend" organisms – a closer look at the influence of the intestinal microbiome. (Collaborative Research Consortium (CRC) 1149/ German Research Foundation; successfully applied for by D. Langgartner)

Effects of psychosocial trauma on bone homeostasis and fracture healing. (German Research Foundation, Project B06 within the CRC 1149, INST 40/599-1; successfully applied for by S.O. Reber Ulm and M. Haffner-Luntzer (Co-PI, Institute of Orthopaedic Research and Biomechanics, Ulm University)

Ph.D. stipend for Sandra Förtsch from April to December 2018. (International Graduate School in Molecular Medicine of Ulm University; successfully applied for by S.O. Reber)

Promotion of stress resilience by non-invasive immunoregulatory approaches.' (Office of Naval Research Global, N00014-17-S-B001; Grant12274897; successfully applied for by S.O.Reber)

Additive effects of multiple psychosocial traumatic life experiences on subsequent blunt thorax trauma. ("Bausteinprogramm" of the medical faculty of the Ulm University; successfully applied for by D. Langgartner)

Danger response and regeneration following musculoskeletal trauma: interdisciplinary approach to link physical and psychological injuries. (Innovation fond of the medical faculty of the Ulm University; successfully applied for by S.O. Reber)

Mechanisms underlying CSC-induced breakdown of HPA axis functions. (German Research Foundation, RE 2911/5-1; successfully applied for by S.O. Reber)

Effects of psychosocial stress on intestinal homeostasis – mechanisms underlying stress-induced colitis. (German Research Foundation, RE 2911/2-1; successfully applied for by S.O. Reber)

Research Profile of the Laboratory for Molecular Psychosomatics

To investigate our research hypotheses stated above, we employ several preclinically validated rodent models of chronic psychosocial stress and study in detail their effects on behavioral, physiological, neuroendocrine, and immunological parameters, thereby considering individual differences in the stress coping strategy. Our main paradigm in this context to induce chronic psychosocial stress during adulthood is the chronic subordinate colony housing (CSC) paradigm (Reber et al., 2007 PNEC; Reber, 2012 PNEC; Langgartner et al., 2015 Frontiers in Psychiatry; Reber et al., 2016 PNEC). The CSC model is based on repeated psychosocial traumatization (social defeat, Days 1, 8, and 15) and prolonged (19 d) social subordination of male experimental mice to a larger dominant male and results in many behavioral, endocrine and immunological changes known from posttraumatic stress disorders patients (for review see Reber et al., 2016 PNEC). The value and clinical relevance of this stress model has recently been acknowledged with the "Curt P. Richter Award" by the International Society for Psychoneuroendocrinology (ISPNE). To induce chronic psychosocial stress in mice during early life we employ the maternal separation (MS) paradigm (Veenema et al., 2008 Endocrinology). Here, the pubs are separated from the mother for 3h per day between postnatal days (PND) 1-14. MS negatively affects the behavior (i.e. increases anxiety-related behavior), alters HPA axis (re)activity, and promotes immune activation, which is in line with what has been reported in humans exposed to early life trauma/stress.

To induce acute psychosocial stress in human volunteers under standard laboratory conditions for investigating its effects on mood, physiology and the immune system, we employ a slightly modified version of the "Trier Social Stress Test (TSST)", originally described earlier (Kirschbaum et al., 1993 Neuropsychobiology). TSST exposure reliably activates the two main stress axes, namely the sympathetic nervous system (SNS) and the hypothalamus-pituitary-adrenal (HPA) axis, as well as the cardiovascular and the immune system.


Current Research Projects

Project 1

Immunoregulatory approaches to promote stress resistance.

It is the major aim of this Project, in collaboration with the lab of Prof. Dr. Christopher Lowry (University of Colorado, Boulder, USA), to promote resilience against stress-related somatic and affective pathologies by treating mice either prior to or following/during stress/psychosocial trauma exposure with a heat-killed preparation of immunoregulatory "old friends from mud and soil", including Mycobacterium vaccae (NCTC 11659; Fig. 3 left panel; taken from Reber et al., 2016 PNAS Figure S2A), and to reveal the underlying mechanisms. Our mouse data so far support a strategy of "re-introducing" humans to their "old friends" in order to promote optimal health and stress/trauma resilience. In detail, this is based on the fact that M. vaccae pre-immunization causes a shift from passive towards active stress coping during CSC exposure, has anxiolytic effects, and prevents development of spontaneous and aggravation of chemically-induced colitis (Reber et al., 2016 PNAS). Effects on anxiety and colitis, but not on "stress coping", were mediated via Treg cell induction. Consistent with the finding, that Treg cells and IL-10 secretion play an important role in the stress/trauma-protective effects of M. vaccae, CSC-induced promotion of a colitogenic gut micromilieu was not corrected by pre-immunization with this "old friends" (Fig. 3 right panel; taken from 2016 PNAS Figure S6M).

We are currently investigating whether i) p.o. or i.n. application of M. vaccae is stress protective as well, ii) M. vaccae immunization is able to treat already existing stress-related disorders, iii) other "old friends" have a comparable potential to prevent stress-associated disorders.

Funding: Office of Naval Research Global, N00014-17-S-B001; Grant12274897 (M. vaccae) & university intern budget (other "old friends")

Project 2

EPSS (Effects of Pets on Social Stress)

A failure of immunoregulation, attributable to reduced exposure to the microbial environment within which the mammalian immune system evolved ("Old friends hypothesis"), is thought to be one factor contributing to recent increases in stress-related chronic inflammatory disorders, as well as psychiatric disorders for which chronic, low-grade inflammation is a risk factor ("cytokine theory of mood disorders").

It is the major aim of this project to assess the stress reactivity in healthy human volunteers raised in an urban environment either in the presence or absence of  pets  towards the standardized Trier Social Stress Test (TSST). Interesting in this context is the fact that people raised in environments offering a narrow relativ to a wide range of biodiversity show an increased prevalence of both somatic and affective disorders.

Funding: University intern budget

Project 3

Chronic psychosocial stress and HPA axis function

Exposure to acute stressful stimuli leads to the activation of both the sympathetic nervous system and the hypothalamus-pituitary-adrenal (HPA) axis and, consequently, to the systemic release of catecholamines and glucocorticoids (GCs). These stress hormones, in turn, trigger physiological alterations enabling an organism to adjust to the new situation and to show an adequate behavioural response. However, if the stress systems are activated over a prolonged period of time, chronically-elevated levels of plasma GC can promote development of somatic and affective disorders. Thus, it is adaptive for an individual to habituate possibly fast to prolonged and non-life-threatening homotypic stressors, but to stay responsive to novel and possibly dangerous challenges.

Interestingly, mice exposed to 19 days of chronic subordinate colony housing (CSC) seem to exactly implement this principle at the level of the adrenal glands. CSC mice show unaffected basal morning corticosterone (CORT) levels despite a pronounced increase in adrenal mass (Reber et al., 2007 PNEC), likely mediated by an attenuation of adrenal corticotrophin (ACTH) responsiveness. The latter was indicated by a reduction of adrenal in vitro CORT secretion in response to various concentrations of ACTH (Reber et al., 2007 PNEC; Uschold-Schmidt et al., 2012 PNEC; Reber et al., 2016 PNAS; Langgartner et al., 2016 BBI). However, in contrast to the in vitro situation, CSC mice show an even more pronounced CORT response to an acute heterotypic stressor exposure (elevated platform, EPF; Uschold-Schmidt et al., 2012 PNEC) compared with respectively treated SHC mice. This is in line with recent data showing an increased availability and mobilization capacity of the CORT precursor molecule cholesterol in CSC compared with SHC mice, possibly contributing to their increased in vivo CORT response during acute heterotypic stressor exposure (Füchsl et al., 2013 Stress). Together, these data clearly argue against a breakdown of adrenal functioning during CSC, but support the hypothesis that a reduction of adrenal ACTH responsiveness during times of chronic stress prevents prolonged hypercorticism and, thus, is adaptive and beneficial. Of note, CSC mice do not develop any signs of depressive-like behaviour (Slattery et al., 2012 PNEC), which can be induced by chronically treating rodents with CORT.

The value and clinical relevance of this project has recently been acknowledged with the "Ernst and Berta Scharrer Prize (German Society of Endocrinology: 'This price awards outstanding original studies in the field of neuroendocrinology.').

Unravelling the underlying mechanisms might help to preventively or therapeutically facilitate stress resilience. We are currently investigating whether i) an additional factor present during heterotypic stressor exposure, and not during in vitro stimulation, rescues adrenal ACTH sensitivity, or itself acts as CORT secretagogue in chronically stressed CSC mice, ii) what this factor might be, and iii) whether or not these HPA axis changes depend on the coping strategy during CSC exposure.

Funding: University intern budget; previously funded by the DFG grant RE-2911/5-1

Project 4

Chronic psychosocial stress and colitis

Inflammatory disorders, such as Crohn's Disease (CD) and Ulcerative Colitis (UC) represent a major health concern, particularly in Western societies, with a life-time prevalence of approximately 0.1%. In addition to limiting quality of life due to abdominal cramps and pain, diarrhea, bloody stools, ulceration, fever, tiredness and other socially-unacceptable symptoms, inflammatory bowel disorders (IBD) are further linked to an increased risk for developing inflammation-related colorectal cancer (CRC).

The pathogenesis of IBD is still not completely understood. It is generally accepted that IBD has a complex and multi-factorial etiology, involving genetic and environmental factors, which are in turn associated with a dysregulation of the mucosal immune system. One environmental factor that is often discussed in this context during the last decades is the perceived level of life stress. Interestingly, available data suggest IBD to be rather associated with hypocortisolism than hypercortisolism.

In line with this hypothesis, we could already show that 19 days of chronic subordinate colony housing (CSC) not only result in basal evening hypocorticism but also reliably induce spontaneous colonic inflammation (Reber et al., 2007 PNEC; Reber et al., 2008 Stress; Reber et al., 2011 BBI; Reber, 2012 PNEC; Reber, 2016 PNAS; Fig. 5). The latter is causally mediated by a pronounced rise in CORT during the initial phase of CSC, preceding later development of hypocorticism and GC resistance, as well as by an increased bacterial translocation as consequence of disturbed colonic barrier functions. CSC-induced colitis is indicated by an increased histological damage score (Fig. 5), which is first detectable after 14 d of CSC, and increased numbers of colonic macrophages, dendritic and Th cells, and cytokine secretion from isolated lamina propria mononuclear and mesenteric lymph node cells, the latter lasting at least until day 8 following CSC termination. In addition, CSC mice show a pronounced reduction in the percentage of Treg cells in peripheral lymphoid organs (Schmidt et al., 2010 BBI), likely contributing to an overall increased inflammatory state and, consequently, to spontaneous colitis development.

Intriguingly, we just recently could show that CSC results in a pronounced expansion of enterohepatic helicobacter species (EHS) in the intestinal microbiome (Reber et al., 2016 PNAS) and that CSC-induced colitis does not develop under specific-pathogen-free (SPF) conditions (Langgartner et al., 2016 BBI), suggesting that translocation of certain pathobionts instead of commensal gut bacteria is critically required for development of stress-induced intestinal pathologies. Of note, stress-protective effects of M.vaccae pre-immunization were not mediated by preventing the colitogenic shift in the intestinal microbiome following CSC, but by inducing intestinal Treg cells, which in turn prevented that the colitogenic microbiome translates into colonic inflammation and tissue damage. Importantly, our data further indicate that CSC-induced HPA axis changes (i.e. hypocorticism) is not critically involved in CSC-induced colitis development (Reber et al., 2016 PNAS; Langgartner et al., 2016 BBI).

The value and clinical relevance of this interdisciplinary project has been acknowledged with the "Ismar-Boas Preis 2007" for excellent work in the field of gastroenterology from the "Deutsche Gesellschaft für Visceralchirurgie (DGVS)".

Currently we are investigating whether i) CSC-induced spontaneous colitis is causally involved in the increased anxiety state detected following CSC exposure and ii) colitis severity depends on the coping strategy of an individual shown during CSC exposure.

Funding: University intern budget; previously funded by the DFG grant RE-2911/2-1

Project 5

Chronic psychosocial stress and long-term effects on anxiety: the role of the autonomic nervous system and of the visual contact

Chronic stress, in particular chronic psychosocial stress, is a risk factor in the etiology of various psychopathologies including general and social anxiety-related disorders. However, despite substantial research efforts in the last decades, the etiology of such stress-associated disorders remains poorly understood. As we previously have shown that CSC exposure increases both general- and social anxiety-related behavior (Slattery et al., 2012 PNEC), we have an animal model in hands allowing us to investigate in detail the underlying mechanisms. Thereby we focus the autonomic nervous system by using telemetry (Fig. 6 right panel), as well as on the assessment of neuro-inflammatory processes by Taqman PCR and immunohistochemistry. Interestingly, while the CSC-induced increase in general anxiety was long-lasting and still detectable 10 days following termination of CSC, social deficits were only transient, suggesting different neuronal mechanisms to be involved in these behavioral stress consequences. As accumulating evidence supports the idea that the sensory, in particular the visual, contact to a rodent conspecific during/following stressor exposure is able to induce a stress response in the observer animal, we also consider different sensory contact modalities to the stressor (last dominant mouse during CSC) following termination of the physical stressor exposure (Fig. 6 left and middle panel).

Funding: University intern Budget

Project 6

Effects of repeated psychosocial traumatisation/chronic psychoscial stress on bone metabolism

Although a strong association between psychiatric and somatic disorders is generally accepted, little is known regarding the interrelation between mental and skeletal health. While depressive disorders were shown to be strongly associated with osteoporosis and increased fracture risk, evidence from post-traumatic stress disorder (PTSD) patients is less consistent. Given that the CSC paradigm induces a behavioural, physiological and immunological phenotype closely related to what is known from PTSD patients, we hold a stress model in hand allowing us to investigate the possible mechanisms underlying disturbance of bone metaolism in PTSD patients.

Therefore, in collaboration with the group of Prof. Anita Ignatius (Institute of Orthopedic Research and Biomechanics, University Medical Center Ulm), here mainly with Dr. Melanie Haffner-Luntzer, we are investigating in male mice whether and how chronic psychosocial stress induced by the chronic subordinate colony housing (CSC) model influences bone metabolism and fracture healing. Besides typical physiological stress consequences, like increased adrenal weight, decreased thymus weight and increased anxiety-related behaviour, our findings indicate a disturbed long bone development as well as compromized fracture healing in chronically stressed compared to unstressed control mice, which are both likely to be at least in part mediated by disturbance of endochondral ossification processes (Förtsch et al., 2017 DMM; Haffner-Luntzer et al., 2019 PNAS). These findings offer possibilities for clinical translation in patients suffering from PTSD and fracture.

The value and clinical relevance of this interdisciplinary project has been acknowledged with the "ORS Travel Award 2018" from the "Deutsche Gesellschaft für Orthopädie und Unfallchirurgie  (DGOU, Germany Scoiety for Orthopaedics and Trauma)" and the "ISFR Award 2019" from the "Orthopaedic Research Society (ORS) for Dr. Melanie Haffner-Luntzer (Institute of Orthopedic Research and Biomechanics, Prof. A. Ignatius, University Medical Center Ulm).

Funding: German Research Foundation, Project B06 within the CRC 1149, INST 40/599-1, PIs  Prof. Dr. Stefan Reber Ulm and Dr. Melanie Haffner-Luntzer;  Gender Equality Funding of Dr. Melanie Haffner-Luntzer provided by the DFG-funded CRC1149; University intern budget of SOR; previously funded by the Innovation fond of the medical faculty of the Ulm University.


Project 7

Second hit hypothesis: additive effects of early life stress and chronic psychosocial stress on physical Trauma

Negative early childhood experiences disrupt normal adaptive HPA axis responses to subsequent stressors during life, and promote chronic low-grade inflammation. Accordingly, child maltreatment is a well-known risk factor for the development of stress-associated somatic and mood disorders, including e.g. anxiety- and depression-related diseases as well as inflammatory bowel diseases. Combining the MS and CSC paradigm, our group previously showed that early life stress and chronic psychosocial stress during adulthood have additive effects on HPA axis disturbances and intestinal pathology following DSS-treatment (Veenema et al., 2008Endocrinology). In the current project we are investigating in collaboration with Prof. Dr. Markus Huber-Lang (Clinic for Trauma, Hand, Plastic, and Reconstructive Surgery, University Ulm) whether MS and CSC also have additive effects in terms of favoring complications following a subsequently-induced thorax trauma (TXT), and how this is mediated.

Funding: 'Bausteinprogramm' of the medical faculty of Ulm University

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Profilbild von Prof. Dr. rer. nat. Stefan Reber

Prof. Dr. rer. nat. Stefan Reber

Head of Laboratory for Molecular Psychosomatics