Stress induced neuroendocrine-immune plasticity: A role for the spleen in peripheral inflammatory disease and inflammaging?

Specific Salivary Neuropeptides Shift Synchronously during Acute Stress in Fire Recruits

Once thought of as an immune-privileged site, we now know that the nervous system communicates in a bidirectional manner with the immune system via the neuroimmune axis. Neuropeptides constitute a component of this axis, playing critical roles in the brain and periphery. The function of salivary neuropeptides in the acute stress response is not well understood. The purpose of this study is to investigate salivary neuropeptide levels during acute stress. Salivary samples were collected from fire recruits engaged in a stress training exercise previously shown to induce acute stress, at three separate timepoints during the exercise and levels of oxytocin, neurotensin, Substance P, α-MSH, and β-Endorphin were measured using the Human Neuropeptide 5-Plex Custom Assay Eve Technologies. All neuropeptides increased throughout the acute stress simulation and during the recovery phase. Exploratory factor analysis (EFA) identified one factor contributing to baseline values across five neuropeptides and Pairwise Pearson Correlation Coefficient analysis showed positive correlations >0.9 for almost all neuropeptide combinations at the pre-stress timepoint. Further analysis identified negative and positive correlations between past-life trauma and self-assessed hardiness, respectively. Calculated neuropeptide scores showed an overall positive correlation to self-assessed hardiness. Altogether, our results suggest that salivary neuropeptides increase synchronously during acute stress and higher levels correlate with an increase in self-assessed hardiness. Further study is required to determine if interventions designed to enhance neuropeptide activity can increase stress resilience, especially in high-stress occupations such as firefighting.

Cytotoxic Activity and Lymphocyte Subtypes in Mice Selected for Maximal and Minimal Inflammatory Response after Transplantation of B16F10 and S91 Melanoma Cells

AIRmax and AIRmin mice strains were selected according to the intensity of their acute inflammatory responsiveness. Previous studies have shown that AIR mice differ in their resistance to chemically induced skin tumors and in the development of melanoma metastases, in addition to differences in neutrophil and NK cells activity. In the present work, we aimed to evaluate whether the difference of susceptibility to murine melanoma is associated with NK cytotoxic activity against Yac.1 cells and lymphocyte subsets. Mice were subcutaneously inoculated with B16F10 or S91 melanoma cells. After 7, 14, or 30 days, the animals were euthanized to analyze the number of lymphocyte subsets, cytotoxic activity, and number of cytokine-producing spleen cells. AIRmax mice presented a higher number of CD4⁺/CD25⁺ cells than that of AIRmin mice following inoculation of B16F10 cells, whereas inoculation of S91 cells reduced CD4⁺/CD25⁺ and increased TCD8⁺ cell subsets in the AIRmax mice. AIRmax mice had a higher number of interleukin (IL)-10- and IL-12-producing cells and a lower number of interferon-γ–producing cells than those of AIRmin mice at 30 days. The cytotoxic activity of nonadherent spleen cells was similar in both the AIR strains. These results suggest that melanoma cells can induce different responses in AIR mice, possibly owing to alterations in regulatory mechanisms, such as the action of CD4⁺/CD25⁺ regulatory T cells and IL-10, in AIRmax mice.

Neuroimmune connections between corticotropin-releasing hormone and mast cells: novel strategies for the treatment of neurodegenerative diseases

Corticotropin-releasing hormone is a critical component of the hypothalamic–pituitary–adrenal axis, which plays a major role in the body’s immune response to stress. Mast cells are both sensors and effectors in the interaction between the nervous and immune systems. As first responders to stress, mast cells can initiate, amplify and prolong neuroimmune responses upon activation. Corticotropin-releasing hormone plays a pivotal role in triggering stress responses and related diseases by acting on its receptors in mast cells. Corticotropin-releasing hormone can stimulate mast cell activation, influence the activation of immune cells by peripheral nerves and modulate neuroimmune interactions. The latest evidence shows that the release of corticotropin-releasing hormone induces the degranulation of mast cells under stress conditions, leading to disruption of the blood-brain barrier, which plays an important role in neurological diseases, such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, autism spectrum disorder and amyotrophic lateral sclerosis. Recent studies suggest that stress increases intestinal permeability and disrupts the blood-brain barrier through corticotropin-releasing hormone-mediated activation of mast cells, providing new insight into the complex interplay between the brain and gastrointestinal tract. The neuroimmune target of mast cells is the site at which the corticotropin-releasing hormone directly participates in the inflammatory responses of nerve terminals. In this review, we focus on the neuroimmune connections between corticotropin-releasing hormone and mast cells, with the aim of providing novel potential therapeutic targets for inflammatory, autoimmune and nervous system diseases.

Stress Pathway Modulation Is Detrimental or Ineffective for Functional Recovery after Spinal Cord Injury in Mice

A mounting body of evidence suggests that stress plays a major role in the injury progression after spinal cord injury (SCI). Injury activates the stress systems; this in turn may augment the generation of pro-inflammatory cytokines, stimulate pro-inflammatory immune cells, and alter the balance between the pro- and anti-inflammatory immune response. As a result, it is suggested that stress pathways may augment neuronal damage and loss after SCI. Considering these potential detrimental effects of stress after SCI, we hypothesized that inhibition of stress pathways immediately after SCI may offer protection from damage and improve recovery. To investigate the relevance of stress responses in SCI recovery, we investigated the effects of blocking three well-studied stress response axes in a mouse model of SCI. Propranolol, RU-486, and CP-99994 were administered to inhibit the sympathetic axis, the hypothalamus-pituitary-adrenal axis, and the neuropeptide axis, respectively. Surprisingly, assessing functional recovery by the Basso Mouse Scale revealed that RU-486 and CP-99994 did not affect functional outcome, indicating that these pathways are dispensable for neuroprotection or repair after SCI. Moreover, the beta-blocker propranolol worsened functional outcome in the mouse SCI model. In conclusion, immediate inhibition of three major stress axes has no beneficial effects on functional recovery after SCI in mice. These results suggest that injury-induced stress responses do not interfere with the healing process and hence, pharmacological targeting of stress responses is not a recommended treatment option for SCI. These findings are of great importance for other researchers to avoid unnecessary and potentially futile animal experiments.

Blood biomarkers are associated with brain function and blood flow following sport concussion

BACKGROUND

Secondary injury pathophysiology after sport-related concussion (SRC) is poorly understood. Blood biomarkers may be a useful tool for characterizing these processes, yet there are limitations in their application as a single modality. Combining blood biomarker analysis with advanced neuroimaging may help validate their continued utility in brain injury research by elucidating important secondary injury mechanisms. Hence, the purpose of this study was to evaluate co-modulation between peripheral blood biomarkers and advanced functional brain imaging after SRC.

METHODS

Forty-three university level athletes from 7 sports were recruited (16 recently concussed athletes; 15 healthy athletes with no prior history of concussion; 12 healthy athletes with a history of concussion). Seven blood biomarkers were evaluated: s100B, total tau (T-tau), von Willebrand factor (vWF), brain derived neurotrophic factor (BDNF), peroxiredoxin (PRDX)-6, monocyte chemoattractant protein (MCP)-1 and -4. Resting-state functional MRI was employed to assess global neural connectivity (Gconn), and arterial spin labelling was used to evaluate cerebral blood flow (CBF). We tested for concurrent alterations in blood biomarkers and MRI measures of brain function between athlete groups using a non-parametric, bootstrapped resampling framework.

RESULTS

Compared to healthy athletes, recently concussed athletes showed greater concurrent alterations in several peripheral blood biomarker and MRI measures: a decrease in T-Tau and Gconn, a decrease in T-Tau and CBF, a decrease in Gconn with elevated PRDX-6, a decrease in CBF with elevated PRDX-6, and a decrease in Gconn with elevated MCP-4. In addition, compared to healthy athletes with no concussion history, healthy athletes with a history of concussion displayed greater concurrent alterations in blood biomarkers and Gconn; lower GConn covaried with higher blood levels of s100B and MCP-4.

CONCLUSION

We identified robust relationships between peripheral blood biomarkers and MRI measures in both recently concussed athletes and healthy athletes with a history of concussion. The results from this combinatorial approach further support that human concussion is associated with inflammation, oxidative stress, and cellular damage, and that physiological perturbations may extend chronically beyond recovery. Finally, our results support the continued implementation of blood biomarkers as a tool to investigate brain injury, particularly in a multimodal framework.

Altered Neuroendocrine Immune Responses, a Two-Sword Weapon against Traumatic Inflammation

During the occurrence and development of injury (trauma, hemorrhagic shock, ischemia and hypoxia), the neuroendocrine and immune system act as a prominent navigation leader and possess an inter-system crosstalk between the reciprocal information dissemination. The fundamental reason that neuroendocrinology and immunology could mix each other and permeate toward the field of traumatology is owing to their same biological languages or chemical information molecules (hormones, neurotransmitters, neuropeptides, cytokines and their corresponding receptors) shared by the neuroendocrine and immune systems. The immune system is not only modulated by the neuroendocrine system, but also can modulate the biological functions of the neuroendocrine system. The interactive linkage of these three systems precipitates the complicated space-time patterns for the courses of traumatic inflammation. Recently, compelling evidence indicates that the network linkage pattern that initiating agents of neuroendocrine responses, regulatory elements of immune cells and effecter targets for immune regulatory molecules arouse the resistance mechanism disorders, which supplies the beneficial enlightenment for the diagnosis and therapy of traumatic complications from the view of translational medicine. Here we review the alternative protective and detrimental roles as well as possible mechanisms of the neuroendocrine immune responses in traumatic inflammation.

Health and disease phenotyping in old age using a cluster network analysis

Human ageing is a complex trait that involves the synergistic action of numerous biological processes that interact to form a complex network. Here we performed a network analysis to examine the interrelationships between physiological and psychological functions, disease, disability, quality of life, lifestyle and behavioural risk factors for ageing in a cohort of 3,270 subjects aged ≥55 years. We considered associations between numerical and categorical descriptors using effect-size measures for each variable pair and identified clusters of variables from the resulting pairwise effect-size network and minimum spanning tree. We show, by way of a correspondence analysis between the two sets of clusters, that they correspond to coarse-grained and fine-grained structure of the network relationships. The clusters obtained from the minimum spanning tree mapped to various conceptual domains and corresponded to physiological and syndromic states. Hierarchical ordering of these clusters identified six common themes based on interactions with physiological systems and common underlying substrates of age-associated morbidity and disease chronicity, functional disability, and quality of life. These findings provide a starting point for indepth analyses of ageing that incorporate immunologic, metabolomic and proteomic biomarkers, and ultimately offer low-level-based typologies of healthy and unhealthy ageing.

Connexin 43 in splenic lymphocytes is involved in the regulation of CD4+CD25+ T lymphocyte proliferation and cytokine production in hypertensive inflammation

Chronic inflammation promotes the development of hypertension and is associated with increased T cell infiltration and cytokine production in impaired organs. Gap junction protein connexin 43 (Cx43), is ubiquitously expressed in immune cells and plays an important role in T cell proliferation and activation, and cytokine production. However, the correlation between Cx43 in T cells and the hypertensive inflammatory response remains unknown. Thus, in this study, we wished to examine this correlation. First, our results revealed that hypertension caused significant thickening of the vascular wall, inflammatory cell infiltration into part of the renal interstitium and glomerular atrophy, and it increased the tubular damage scores in the kidneys of spontaneously hypertensive rats (SHRs). Moreover, the SHRs exhibited stenosis in the central artery wall of the spleen with increased serum levels of interleukin (IL)-2 and IL-6 compared with normotensive Wistar-Kyoto (WKY) rats. The spleens of the SHRs exhibited a significantly decreased percentage of CD4⁺CD25⁺ (Treg) T cells. However, the percentages of CD3⁺, CD4⁺ and CD8⁺ T cell and the levels of CD4⁺Cx43 and CD8⁺Cx43 did not differ significantly between the SHRs and WKY rats. In cultured lymphocytes from the SHRs and WKY rats, low percentages of Treg cells and reduced cytokine (IL-2 and IL-6) mRNA expression levels were observed in the lymphocytes obtained from the SHRs and WKY rats treated with the connexin blocker, Gap27, or concanavalin A (ConA) plus Gap27. The effects of ConA and Gap27 differed between the SHRs and WKY rats. On the whole, our findings demonstrate that the splenic Treg cell-mediated suppression in SHRs may be involved in hypertensive inflammatory responses. Cx43 in the gap junctional channel may regulate lymphocyte activation and inflammatory cytokine production.

Stressed skin?--a molecular psychosomatic update on stress-causes and effects in dermatologic diseases

A pathogenetically relevant link between stress, in terms of psychosocial stress, and disease was first described in the 1970s, when it was proven that viral diseases of mucous membranes (such as rhinovirus and Coxsackie virus infections) develop faster and more severe after stress exposure. Since then, there has been an annual increase in the number of publications which investigate this relationship and break it down to the molecular level. Nevertheless, the evidences for the impact of psychosocial stress on chronic inflammatory skin diseases and skin tumors are hardly known. In the present review, we outline current insights into epidemiology, psychoneuroimmunology, and molecular psychosomatics which demonstrate the manifold disease-relevant interactions between the endocrine, nervous, and immune systems. The focus is on stress-induced shifts in immune balance in exemplary disorders such as atopic dermatitis, psoriasis, and malignant melanoma. The objective of this article is to convey basic psychosomatic knowledge with respect to etiology, symptomatology, and therapeutic options for chronic skin diseases. Particular attention is directed towards the underlying molecular relationships, both from a somatic to mental as well as a mental to somatic perspective.

Monocyte trafficking to the brain with stress and inflammation: a novel axis of immune-to-brain communication that influences mood and behavior

HIGHLIGHTSPsychological stress activates neuroendocrine pathways that alter immune responses.Stress-induced alterations in microglia phenotype and monocyte priming leads to aberrant peripheral and central inflammation.Elevated pro-inflammatory cytokine levels caused by microglia activation and recruitment of monocytes to the brain contribute to development and persistent anxiety-like behavior.Mechanisms that mediate interactions between microglia, endothelial cells, and macrophages and how these contribute to changes in behavior are discussed.Sensitization of microglia and re-distribution of primed monocytes are implicated in re-establishment of anxiety-like behavior. Psychological stress causes physiological, immunological, and behavioral alterations in humans and rodents that can be maladaptive and negatively affect quality of life. Several lines of evidence indicate that psychological stress disrupts key functional interactions between the immune system and brain that ultimately affects mood and behavior. For example, activation of microglia, the resident innate immune cells of the brain, has been implicated as a key regulator of mood and behavior in the context of prolonged exposure to psychological stress. Emerging evidence implicates a novel neuroimmune circuit involving microglia activation and sympathetic outflow to the peripheral immune system that further reinforces stress-related behaviors by facilitating the recruitment of inflammatory monocytes to the brain. Evidence from various rodent models, including repeated social defeat (RSD), revealed that trafficking of monocytes to the brain promoted the establishment of anxiety-like behaviors following prolonged stress exposure. In addition, new evidence implicates monocyte trafficking from the spleen to the brain as key regulator of recurring anxiety following exposure to prolonged stress. The purpose of this review is to discuss mechanisms that cause stress-induced monocyte re-distribution in the brain and how dynamic interactions between microglia, endothelial cells, and brain macrophages lead to maladaptive behavioral responses.

Effects of constant light during perinatal periods on the behavioral and neuronal development of mice with or without dietary lutein

Constant light conditions (LL) carry a risk of disrupting the biological clock of developing animals. Our purpose in this study was to investigate what disorders occur in animals receiving an LL stress during the late embryonic and suckling periods as compared with animals housed in dark-light (14 h-10 h) conditions (DL). In addition, we examined ameliorating effects against the disorder by the oral administration of lutein as an antioxidant. LL caused hypertrophy of the spleen and induced a higher expression of serotonin transporter (5HTT) in the corpus striatum and hippocampus in 15-day-old pups. In 9-week-old offspring, LL caused abnormal behavior in the elevated plus-maze test. The expression levels of 5HTT in the brain of the LL group changed to lower than those in DL group. The oral administration of lutein lessened the abnormality in behavior and 5HTT expression in the hippocampus to a certain degree although the expression levels of 5HTT in the corpus striatum were not altered by lutein diet. LL also induced disorders in the maternal brain with lower expression levels of 5HTT and neuregulin 1. These results indicate that LL during the perinatal periods may induce some neuronal abnormalities in both offspring and mothers that may be partially ameliorated by dietary lutein as an antioxidant.