Beta-adrenergic signaling and T-lymphocyte-produced catecholamines are necessary for interleukin 17A synthesis.

Background: Post-traumatic stress disorder (PTSD) is a debilitating psychological disorder that also presents with neuroimmune irregularities. Patients display elevated sympathetic tone and are at an increased risk of developing secondary autoimmune diseases. Previously, using a preclinical model of PTSD, we demonstrated that elimination of sympathetic signaling to T-lymphocytes specifically limited their ability to produce pro-inflammatory interleukin 17A (IL-17A); a cytokine implicated in the development of many autoimmune disorders. However, the mechanism linking sympathetic signaling to T-lymphocyte IL-17A production remained unclear. Methods: Using a modified version of repeated social defeat stress (RSDS) that allows for both males and females, we assessed the impact of adrenergic receptor blockade (genetically and pharmacologically) and catecholamine depletion on T-lymphocyte IL-17A generation. Additionally, we explored the impact of adrenergic signaling and T-lymphocyte-produced catecholamines on both CD4+ and CD8+ T-lymphocytes polarized to IL-17A-producing phenotypes ex vivo. Results: Only pharmacological inhibition of the beta 1 and 2 adrenergic receptors (ß1/2) significantly decreased circulating IL-17A levels after RSDS, but did not impact other pro-inflammatory cytokines (e.g., IL-6, TNF-α, and IL-10). This finding was confirmed using RSDS with both global ß1/2 receptor knock-out mice, as well as by adoptively transferring ß1/2 knock-out T-lymphocytes into immunodeficient hosts. Furthermore, ex vivo polarized T-lymphocytes produced significantly less IL-17A with the blockade of ß1/2 signaling, even in the absence of exogenous sympathetic neurotransmitter supplementation, which suggested T-lymphocyte-produced catecholamines may be involved in IL-17A production. Indeed, pharmacological depletion of catecholamines both in vivo and ex vivo abrogated T-lymphocyte IL-17A production demonstrating the importance of immune-generated neurotransmission in pro-inflammatory cytokine generation. Conclusions: Our data depict a novel role for ß1/2 adrenergic receptors and autologous catecholamine signaling during T-lymphocyte IL-17A production. These findings provide a new target for pharmacological therapy in both psychiatric and autoimmune diseases associated with IL-17A-related pathology.

Innate and adaptive immune system consequences of post-traumatic stress disorder.

In the field of psychiatry, biological markers are rarely, if ever, used in the diagnosis of mental health disorders. Clinicians rely primarily on patient histories and behavioral symptoms to identify specific psychopathologies, which makes diagnosis highly subjective. Moreover, therapies for mental health disorders are aimed specifically at attenuating behavioral manifestations, which overlooks the pathophysiological indices of the disease. This is highly evident in posttraumatic stress disorder (PTSD) where inflammation and immune system perturbations are becoming increasingly described. Further, patients with PTSD possess significantly elevated risks of developing comorbid inflammatory diseases such as autoimmune and cardiovascular diseases, which are likely linked (though not fully proven) to the apparent dysregulation of the immune system after psychological trauma. To date, there is little to no evidence that demonstrates current PTSD therapies are able to reverse the increased risk for psychological trauma-induced inflammatory diseases, which suggests the behavioral and somatic consequences of PTSD may not be tightly coupled. This observation provides an opportunity to explore unique mechanisms outside of the brain that contribute to the long-term pathology of PTSD. Herein, we provide an overview of neuroimmune mechanisms, describe what is known regarding innate and adaptive immunity in PTSD, and suggest new directions that are needed to advance the understanding, diagnosis, and treatment of PTSD moving forward.

S100a9 Protects Against the Effects of Repeated Social Defeat Stress.

Background: Posttraumatic stress disorder, a consequence of psychological trauma, is associated with increased inflammation and an elevated risk of developing comorbid inflammatory diseases. However, the mechanistic link between this mental health disorder and inflammation remains elusive. We previously found that S100a8 and S100a9 messenger RNA, genes that encode the protein calprotectin, were significantly upregulated in T lymphocytes and positively correlated with inflammatory gene expression and the mitochondrial redox environment in these cells. Therefore, we hypothesized that genetic deletion of calprotectin would attenuate the inflammatory and redox phenotype displayed after psychological trauma. Methods: We used a preclinical mouse model of posttraumatic stress disorder known as repeated social defeat stress (RSDS) combined with pharmacological and genetic manipulation of S100a9 (which functionally eliminates calprotectin). A total of 186 animals (93 control, 93 RSDS) were used in these studies. Results: Unexpectedly, we observed worsening of behavioral pathology, inflammation, and the mitochondrial redox environment in mice after RSDS compared with wild-type animals. Furthermore, loss of calprotectin significantly enhanced the metabolic demand on T lymphocytes, suggesting that this protein may play an undescribed role in mitochondrial regulation. This was further supported by single-cell RNA sequencing analysis demonstrating that RSDS and loss of S100a9 primarily altered genes associated with mitochondrial function and oxidative phosphorylation. Conclusions: These data demonstrate that the loss of calprotectin potentiates the RSDS-induced phenotype, which suggests that its observed upregulation after psychological trauma may provide previously unexplored protective functions.

Repeated social defeat stress leads to immunometabolic shifts in innate immune cells of the spleen.

Psychosocial stress has been shown to prime peripheral innate immune cells, which take on hyper-inflammatory phenotypes and are implicated in depressive-like behavior in mouse models. However, the impact of stress on cellular metabolic states that are thought to fuel inflammatory phenotypes in immune cells are unknown. Using single cell RNA-sequencing, we investigated mRNA enrichment of immunometabolic pathways in innate immune cells of the spleen in mice subjected to repeated social defeat stress (RSDS) or no stress (NS). RSDS mice displayed a significant increase in the number of splenic macrophages and granulocytes (p < 0.05) compared to NS littermates. RSDS-upregulated genes in macrophages, monocytes, and granulocytes significantly enriched immunometabolic pathways thought to play a role in myeloid-driven inflammation (glycolysis, HIF-1 signaling, MTORC1 signaling) as well as pathways related to oxidative phosphorylation (OXPHOS) and oxidative stress (p < 0.05 and FDR<0.1). These results suggest that the metabolic enhancement reflected by upregulation of glycolytic and OXPHOS pathways may be important for cellular proliferation of splenic macrophages and granulocytes following repeated stress exposure. A better understanding of these intracellular metabolic mechanisms may ultimately help develop novel strategies to reverse the impact of stress and associated peripheral immune changes on the brain and behavior.

Mitochondrial-related effects of pentabromophenol, tetrabromobisphenol A, and triphenyl phosphate on murine BV-2 microglia cells.

The predominant reliance on bromated flame retardants (BFRs) is diminishing with expanded use of alternative organophosphate flame retardants. However, exposure related issues for susceptible populations, the developing, infirmed, or aged, remain given environmental persistence and home-environment detection. In this regard, reports of flame retardant (FR)-related effects on the innate immune system suggest process by which a spectrum of adverse health effects could manifest across the life-span. As representative of the nervous system innate immune system, the current study examined changes in microglia following exposure to representative FRs, pentabromophenol (PBP), tetrabromobisphenol A (2,2',6,6',-tetrabromo-4,4'-isopropylidine diphenol; TBBPA) and triphenyl phosphate (TPP). Following 18hr exposure of murine BV-2 cells, at dose levels resulting in ≥80% viability (10 and 40 µM), limited alterations in pro-inflammatory responses were observed however, changes were observed in mitochondrial respiration. Basal respiration was altered by PBP; ATP-linked respiration by PBP and TBBPA, and maximum respiration by all three FRs. Basal glycolytic rate was altered by PBP and TBBPA and compensatory glycolysis by all three. Phagocytosis was decreased for PBP and TBBPA. NLRP3 inflammasome activation was assessed using BV-2-ASC (apoptosis-associated speck-like protein containing a CARD) reporter cells to visualize aggregate formation. PBP, showed a direct stimulation of aggregate formation and properties as a NLRP3 inflammasome secondary trigger. TBBPA showed indications of possible secondary triggering activity while no changes were seen with TPP. Thus, the data suggests an effect of all three FRs on mitochondria metabolism yet, different functional outcomes including, phagocytic capability and NLRP3 inflammasome activation.