The PMN-MDSC - A key player in glucocorticoid resistance following combined physical and psychosocial trauma

Early life adversity promotes a milieu in favor of catabolic bone turnover in females: Mycobacterium vaccae NCTC 11659 proofs protective in preclinical studies

Despite early clinical studies supporting the hypothesis that early life adversity (ELA) negatively affects the bone and despite typical ELA-associated disorders, including post-traumatic stress disorder (PTSD) and major depressive disorder (MD), are associated with osteoporosis and increased bone fracture risk, preclinical studies do not support this association. However, previous studies were only performed using male and not female mice. In the current study we showed that ELA, induced by the classical maternal separation (MS) paradigm, facilitated femoral osteoclast activity specifically in female but not male mice. This was associated with a transient decline in both intestinal alpha diversity and Firmicutes/Bacteroidetes ratio, suggesting that the microbiome-gut-bone axis is involved in these effects. Moreover, ELA long-lastingly increased the femoral mRNA expression of the proinflammatory cytokine Interleukin-6 (IL-6) and the osteoclastic markers Cathepsin K and RANKL. Importantly, all sex-specific ELA effects on bone were absent in female mice administered with M. vaccae NCTC 11659 following ELA exposure. Finally, our clinical data indicate strong associations between ELA and development of an osteopenic/osteoporotic bone phenotype in postmenopausal women undergoing bone diagnostics. Together, our preclinical and clinical findings indicate that i) ELA negatively affects the bone, ii) these effects are specific for female sex, iii) the negative effects of ELA on female bone are associated with transient changes in the composition of the intestinal microbiome followed by long-lasting activation of the immune system and the HPA axis, together setting the stage for a facilitated catabolic bone turnover and development of an osteopenic/osteoporotic bone phenotype, iv) developing immunoregulatory approaches, such as repeated s.c. administrations with immunoregulatory microorganisms, have potential for prevention/treatment of ELA-related bone disorders.

The Sex-Specific Effects of Early Life Adversity and Chronic Psychosocial Stress during Adulthood on Bone Are Mitigated by Mycobacterium vaccae NCTC 11659 in Mice

INTRODUCTION

Chronic stress is a major burden in our society and increases the risk for various somatic and mental diseases, in part via promoting chronic low-grade inflammation. Interestingly, the vulnerability for chronic stress during adulthood varies widely among individuals, with some being more resilient than others. For instance, women, relative to men, are at higher risk for developing typical stress-related diseases, including depression and post-traumatic stress disorder (PTSD). Moreover, the experience of early life adversity (ELA) may increase an individuals' vulnerability for chronic stress during adulthood (CAS), possibly due to its association with chronic inflammation. Because severe consequences of stress-induced immune activation are a dysregulated endochondral ossification, delayed long-bone growth, and bone regeneration following fracture, the aim of this study was to investigate the sex-specific effects of ELA alone or in combination with CAS on bone. As enhancement of an individuals' immunoregulatory potential by repeated administrations of a heat-inactivated preparation of Mycobacterium vaccae NCTC (National Collection of Type Cultures) 11659 has been shown to promote stress resilience in mice, we further aimed to investigate if M. vaccae NCTC 11659 also protects against the negative effects of ELA/CAS on bone.

METHODS

Male and female C57BL/6N mice were subjected to ELA using a maternal separation (MS) model. CAS was induced by either using the chronic subordinate colony housing (CSC) paradigm in males or the social instability paradigm (SIP) in females. The effects on bone were evaluated by µCT, histological, and gene expression analysis. M. vaccae NCTC 11659 was administered repeatedly s.c. prior to CAS.

RESULTS

No cumulative impact of ELA and CAS on bone could be detected. Female mice seem to be more susceptible to ELA while male mice to CAS. Importantly, repeated M. vaccae NCTC 11659 administrations were able to mitigate the negative consequences of stress on bone in both sexes.

CONCLUSION

Our results support the hypotheses that the negative effects of ELA and CAS on bone are highly sex-dependent. Moreover, repeated s.c. administrations with immunoregulatory microorganisms might be a future therapeutic option for stress-related bone disorders.

Git2 deficiency promotes MDSCs recruitment in intestine via NF-κB-CXCL1/CXCL12 pathway and ameliorates necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a severe gastrointestinal disease in preterm infants and the most common cause of neonatal death, whereas the molecular mechanism of intestinal injury remains unclear accompanied by deficiency of effective therapeutic approaches. GIT2 (G-protein-coupled receptor kinase interacting proteins 2) can affect innate and adaptive immunity and has been involved in multiple inflammatory disorders. In this study, we investigated whether GIT2 participates in the pathogenesis of NEC. Here we found that intestinal Git2 gene expression was significantly increased in NEC patients and NEC mice, which positively correlated with the tissue damage severity, and Git2 deficiency could potently protect against NEC development in mice. Mechanistically, Git2 gene knockout dramatically increased the recruitment of MDSCs in the intestine, and in vivo depletion of MDSCs almost completely abrogated the protective effect of Git2 deficiency on NEC. Moreover, Git2 deficiency induced MDSCs intestinal accumulation mainly relied on CXCL1/CXCL12 signaling, as evidenced by the significant increment of CXCL1 and CXCL12 levels in intestinal epithelium of Git2-/- mice and dramatically decrease of MDSCs accumulation in intestine as well as increase of NEC severity upon treatment of CXCL1/CXCL12 pathway inhibitors. In addition, Git2 deficiency induced up-regulation of CXCL1 and CXCL12 is at least partially mediated through activating NF-κB signaling. Thus, our findings suggest that GIT2 is involved in the pathogenesis of NEC, and targeting GIT2 may be a potential preventive and therapeutic approach for NEC.

Interactions between MDSCs and the Autonomic Nervous System: Opportunities and Challenges in Cancer Neuroscience

Myeloid-derived suppressor cells (MDSC) are a population of heterogeneous immune cells that are involved in precancerous conditions and neoplasms. The autonomic nervous system (ANS), which is composed of the sympathetic nervous system and the parasympathetic nervous system, is an important component of the tumor microenvironment that responds to changes in the internal and external environment mainly through adrenergic and cholinergic signaling. An abnormal increase of autonomic nerve density has been associated with cancer progression. As we discuss in this review, growing evidence indicates that sympathetic and parasympathetic signals directly affect the expansion, mobilization, and redistribution of MDSCs. Dysregulated autonomic signaling recruits MDSCs to form an immunosuppressive microenvironment in chronically inflamed tissues, resulting in abnormal proliferation and differentiation of adult stem cells. The two components of the ANS may also be responsible for the seemingly contradictory behaviors of MDSCs. Elucidating the underlying mechanisms has the potential to provide more insights into the complex roles of MDSCs in tumor development and lay the foundation for the development of novel MDSC-targeted anticancer strategies.

Chronic sensory contact with subordinated conspecifics promotes splenic glucocorticoid resistance in experimentally wounded C57BL/6N male mice

Chronic psychosocial stress induced by the chronic subordinate colony housing (CSC, 19 Days) paradigm promotes functional splenic in vitro glucocorticoid (GC) resistance, but only if associated with significant bite wounding or prior abdominal transmitter implantation. Moreover, sensory contact to social defeat of conspecifics represents a social stressor for the observer individual. As the occurence and severity of bite wounding is not adequately controllable, the present study aimed to develop an animal model, allowing a bite wound-independent, more reliable generation of chronically-stressed mice characterized by functional splenic in vitro GC resistance. Therefore, male C57BL/6N mice received a standardized sterile intraperitoneal (i.p.) incision surgery or SHAM treatment one week prior to 19-days of (i) CSC, (ii) witnessing social defeat during CSC exposure in sensory contact (SENS) or (iii) single-housing for control (SHC), before assessing basal and LPS-induced splenic in vitro cell viability and GC resistance. Our results indicate that individually-housed SENS but not CSC mice develop mild signs of splenic in vitro GC resistance, when undergoing prior i.p.-wounding. Taken together and considering that future studies are warranted, our findings support the hypothesis that the combination of repeated standardized i.p.-wounding with chronic sensory stress exposure represents an adequate tool to induce functional splenic in vitro GC resistance independent of the occurrence of uncontrollable bite wounds required in social stress paradigms to induce a comparable phenotype.

Subcutaneous Mycobacterium vaccae ameliorates the effects of early life adversity alone or in combination with chronic stress during adulthood in male and female mice

Chronic psychosocial stress is a burden of modern society and poses a clear risk factor for a plethora of somatic and affective disorders, of which most are associated with an activated immune status and chronic low-grade inflammation. Preclinical and clinical studies further suggest that a failure in immunoregulation promotes an over-reaction of the inflammatory stress response and, thus, predisposes an individual to the development of stress-related disorders. Therefore, all genetic (i.e., sex) and environmental (i.e., early life adversity; ELA) factors facilitating an adult's inflammatory stress response are likely to increase their stress vulnerability. In the present study we investigated whether repeated subcutaneous (s.c.) administrations with a heat-killed preparation of Mycobacterium vaccae (M. vaccae; National Collection of Type Cultures (NCTC) 11659), an abundant soil saprophyte with immunoregulatory properties, are protective against negative behavioral, immunological and physiological consequences of ELA alone or of ELA followed by chronic psychosocial stress during adulthood (CAS) in male and female mice. ELA was induced by the maternal separation (MS) paradigm, CAS was induced by 19 days of chronic subordinate colony housing (CSC) in males and by a 7-week exposure to the social instability paradigm (SIP) in females. Our data indicate that ELA effects in both sexes, although relatively mild, were to a great extent prevented by subsequent s.c. M. vaccae administrations. Moreover, although the use of different paradigms for males and females impedes a direct comparison, male mice seemed to be more susceptible to CAS than females, with only females benefitting slightly from the stress protective effects of s.c. M. vaccae administrations when given prior to CAS alone. Finally, our data support the hypothesis that female mice are more vulnerable to the additive effects of ELA and CAS than male mice and that s.c. M. vaccae administrations subsequent to ELA but prior to CAS are protective in both sexes. Taken together and considering the limitation that CAS in males and females was induced by different paradigms, our findings are consistent with the hypotheses that murine stress vulnerability during different phases of life is strongly sex dependent and that developing immunoregulatory approaches, such as repeated s.c. administrations with immunoregulatory microorganisms, have potential for prevention/treatment of stress-related disorders.

Mycobacterium vaccae protects against glucocorticoid resistance resulting from combined physical and psychosocial trauma in mice

Stress-related somatic and psychiatric disorders are often associated with a decline in regulatory T cell (Treg) counts and chronic low-grade inflammation. Recent preclinical evidence suggests that the latter is at least partly mediated by stress-induced upregulation of toll-like receptor (TLR)2 in newly generated neutrophils and polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs), as well as glucocorticoid (GC) resistance in predominantly PMN-MDSCs following stress-induced upregulation of TLR4 expression. Here we show in mice exposed to the chronic subordinate colony housing (CSC) paradigm that repeated intragastric (i.g.) administrations of a heat-killed preparation of Mycobacterium vaccae NCTC 11659, a saprophytic microorganism with immunoregulatory properties, protected against the stress-induced reduction in systemic Tregs, increase in basal and LPS-induced in vitro splenocyte viability, as well as splenic in vitro GC resistance. Our findings further support the hypothesis that i.g. M. vaccae protects against CSC-associated splenic GC resistance via directly affecting the myeloid compartment, thereby preventing the CSC-induced upregulation of TLR4 in newly generated PMN-MDSCs. In contrast, the protective effects of i.g. M. vaccae on the CSC-induced upregulation of TLR2 in neutrophils and the subsequent increase in basal and LPS-induced in vitro splenocyte viability seems to be indirectly mediated via the Treg compartment. These data highlight the potential for use of oral administration of M. vaccae NCTC 11659 to prevent stress-induced exaggeration of inflammation, a risk factor for development of stress-related psychiatric disorders.