Interdisciplinary approaches are fundamental to decode the biology of adversity.

The COVID-19 pandemic has highlighted structural inequalities and racism promoting health disparities among communities of color. Taking cardiovascular disease as an example, we provide a framework for multidisciplinary efforts leveraging translational and epidemiologic approaches to decode the biological impacts of inequalities and racism and develop targeted interventions that promote health equity.

Optogenetic activation of local colonic sympathetic innervations attenuates colitis by limiting immune cell extravasation.

The sympathetic nervous system is composed of an endocrine arm, regulating blood adrenaline and noradrenaline, and a local arm, a network of fibers innervating immune organs. Here, we investigated the impact of the local arm of the SNS in an inflammatory response in the colon. Intra-rectal insertion of an optogenetic probe in mice engineered to express channelrhodopsin-2 in tyrosine hydroxylase cells activated colonic sympathetic fibers. In contrast to systemic application of noradrenaline, local activation of sympathetic fibers attenuated experimental colitis and reduced immune cell abundance. Gene expression profiling showed decreased endothelial expression of the adhesion molecule MAdCAM-1 upon optogenetic stimulation; this decrease was sensitive to adrenergic blockers and 6-hydroxydopamine. Antibody blockade of MAdCAM-1 abrogated the optogenetic effect on immune cell extravasation into the colon and the pathology. Thus, sympathetic fibers control colonic inflammation by regulating immune cell extravasation from circulation, a mechanism likely relevant in multiple organs.

Adrenergic regulation of the vasculature impairs leukocyte interstitial migration and suppresses immune responses.

The sympathetic nervous system (SNS) controls various physiological functions via the neurotransmitter noradrenaline. Activation of the SNS in response to psychological or physical stress is frequently associated with weakened immunity. Here, we investigated how adrenoceptor signaling influences leukocyte behavior. Intravital two-photon imaging after injection of noradrenaline revealed transient inhibition of CD8+ and CD4+ T cell locomotion in tissues. Expression of ß-adrenergic receptor in hematopoietic cells was not required for NA-mediated inhibition of motility. Rather, chemogenetic activation of the SNS or treatment with adrenergic receptor agonists induced vasoconstriction and decreased local blood flow, resulting in abrupt hypoxia that triggered rapid calcium signaling in leukocytes and halted cell motility. Oxygen supplementation reversed these effects. Treatment with adrenergic receptor agonists impaired T cell responses induced in response to viral and parasitic infections, as well as anti-tumor responses. Thus, stimulation of the SNS impairs leukocyte mobility, providing a mechanistic understanding of the link between adrenergic receptors and compromised immunity.

The ß1-adrenergic receptor links sympathetic nerves to T cell exhaustion.

CD8+ T cells are essential components of the immune response against viral infections and tumours, and are capable of eliminating infected and cancerous cells. However, when the antigen cannot be cleared, T cells enter a state known as exhaustion1. Although it is clear that chronic antigen contributes to CD8+ T cell exhaustion, less is known about how stress responses in tissues regulate T cell function. Here we show a new link between the stress-associated catecholamines and the progression of T cell exhaustion through the ß1-adrenergic receptor ADRB1. We identify that exhausted CD8+ T cells increase ADRB1 expression and that exposure of ADRB1+ T cells to catecholamines suppresses their cytokine production and proliferation. Exhausted CD8+ T cells cluster around sympathetic nerves in an ADRB1-dependent manner. Ablation of ß1-adrenergic signalling limits the progression of T cells towards the exhausted state in chronic infection and improves effector functions when combined with immune checkpoint blockade (ICB) in melanoma. In a pancreatic cancer model resistant to ICB, ß-blockers and ICB synergize to boost CD8+ T cell responses and induce the development of tissue-resident memory-like T cells. Malignant disease is associated with increased catecholamine levels in patients2,3, and our results establish a connection between the sympathetic stress response, tissue innervation and T cell exhaustion. Here, we uncover a new mechanism by which blocking ß-adrenergic signalling in CD8+ T cells rejuvenates anti-tumour functions.

Transcription factor Nr4a1 couples sympathetic and inflammatory cues in CNS-recruited macrophages to limit neuroinflammation.

The molecular mechanisms that link the sympathetic stress response and inflammation remain obscure. Here we found that the transcription factor Nr4a1 regulated the production of norepinephrine (NE) in macrophages and thereby limited experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Lack of Nr4a1 in myeloid cells led to enhanced NE production, accelerated infiltration of leukocytes into the central nervous system (CNS) and disease exacerbation in vivo. In contrast, myeloid-specific deletion of tyrosine hydroxylase (TH), the rate-limiting enzyme in catecholamine biosynthesis, protected mice against EAE. Furthermore, we found that Nr4a1 repressed autocrine NE production in macrophages by recruiting the corepressor CoREST to the Th promoter. Our data reveal a new role for macrophages in neuroinflammation and identify Nr4a1 as a key regulator of catecholamine production by macrophages.

Human-relevant near-organ neuromodulation of the immune system via the splenic nerve.

Neuromodulation of immune function by stimulating the autonomic connections to the spleen has been demonstrated in rodent models. Consequently, neuroimmune modulation has been proposed as a new therapeutic strategy for the treatment of inflammatory conditions. However, demonstration of the translation of these immunomodulatory mechanisms in anatomically and physiologically relevant models is still lacking. Additionally, translational models are required to identify stimulation parameters that can be transferred to clinical applications of bioelectronic medicines. Here, we performed neuroanatomical and functional comparison of the mouse, rat, pig, and human splenic nerve using in vivo and ex vivo preparations. The pig was identified as a more suitable model of the human splenic innervation. Using functional electrophysiology, we developed a clinically relevant marker of splenic nerve engagement through stimulation-dependent reversible reduction in local blood flow. Translation of immunomodulatory mechanisms were then assessed using pig splenocytes and two models of acute inflammation in anesthetized pigs. The pig splenic nerve was shown to locally release noradrenaline upon stimulation, which was able to modulate cytokine production by pig splenocytes. Splenic nerve stimulation was found to promote cardiovascular protection as well as cytokine modulation in a high- and a low-dose lipopolysaccharide model, respectively. Importantly, splenic nerve-induced cytokine modulation was reproduced by stimulating the efferent trunk of the cervical vagus nerve. This work demonstrates that immune responses can be modulated by stimulation of spleen-targeted autonomic nerves in translational species and identifies splenic nerve stimulation parameters and biomarkers that are directly applicable to humans due to anatomical and electrophysiological similarities.

Sympathetic Nerves Positively Regulate Eosinophil-Driven Allergic Conjunctivitis via α1-Adrenergic Receptor Signaling.

Eosinophils are a major cause of tissue injury in allergic conjunctivitis. The biological nature of eosinophils in the conjunctiva and the mechanisms that control eosinophils' responses in allergic conjunctivitis are currently not completely understood. This study reports that conjunctival eosinophils comprise two populations-Siglec-Fint and Siglec-Fhi-in different life stages. Siglec-Fint eosinophils partly expressed CD34 and were in the immature (or steady) state. Siglec-Fhi eosinophils did not express CD34, sharply increased in number after short ragweed (SRW) pollen challenge, and were in the mature (or activated) state. Moreover, chemical sympathectomy by 6-hydroxydopamine reduced the recruitment and activation of eosinophils, whereas the activation of the sympathetic nerve system (SNS) with restraint stress accelerated the recruitment and activation of eosinophils in SRW-induced conjunctivitis. It was also found that two eosinophil populations expressed alpha-1a-adrenergic receptors (α1a-ARs); in SRW-induced conjunctivitis, treatment with an α1a-AR antagonist decreased eosinophil responses, whereas treatment with an α1a-AR agonist aggravated eosinophil responses. Thus, eosinophil responses in conjunctivitis are regulated by the SNS via α1a-AR signaling. SNS inputs or α1a-AR function may be potential targets for the treatment of allergic conjunctivitis.

Adrenergic nerves govern circadian leukocyte recruitment to tissues.

The multistep sequence leading to leukocyte migration is thought to be locally regulated at the inflammatory site. Here, we show that broad systemic programs involving long-range signals from the sympathetic nervous system (SNS) delivered by adrenergic nerves regulate rhythmic recruitment of leukocytes in tissues. Constitutive leukocyte adhesion and migration in murine bone marrow (BM) and skeletal-muscle microvasculature fluctuated with circadian peak values at night. Migratory oscillations, altered by experimental jet lag, were implemented by perivascular SNS fibers acting on ß-adrenoreceptors expressed on nonhematopoietic cells and leading to tissue-specific, differential circadian oscillations in the expression of endothelial cell adhesion molecules and chemokines. We showed that these rhythms have physiological consequences through alteration of hematopoietic cell recruitment and overall survival in models of septic shock, sickle cell vaso-occlusion, and BM transplantation. These data provide unique insights in the leukocyte adhesion cascade and the potential for time-based therapeutics for transplantation and inflammatory diseases.

Gut microbiota and neuroinflammation in pathogenesis of hypertension: A potential role for hydrogen sulfide.

Inflammation and gut dysbiosis are hallmarks of hypertension (HTN). Hydrogen sulfide (H2S) is an important freely diffusing molecule that modulates the function of neural, cardiovascular and immune systems, and circulating levels of H2S are reduced in animals and humans with HTN. While most research to date has focused on H2S produced endogenously by the host, H2S is also produced by the gut bacteria and may affect the host homeostasis. Here, we review an association between neuroinflammation and gut dysbiosis in HTN, with special emphasis on a potential role of H2S in this interplay.

Surgical stress and cancer progression: the twisted tango.

Surgical resection is an important avenue for cancer treatment, which, in most cases, can effectively alleviate the patient symptoms. However, accumulating evidence has documented that surgical resection potentially enhances metastatic seeding of tumor cells. In this review, we revisit the literature on surgical stress, and outline the mechanisms by which surgical stress, including ischemia/reperfusion injury, activation of sympathetic nervous system, inflammation, systemically hypercoagulable state, immune suppression and effects of anesthetic agents, promotes tumor metastasis. We also propose preventive strategies or resolution of tumor metastasis caused by surgical stress.

Loss of intestinal sympathetic innervation elicits an innate immune driven colitis.

BACKGROUND: Both the parasympathetic and sympathetic nervous system exert control over innate immune responses. In inflammatory bowel disease, sympathetic innervation in intestinal mucosa is reduced. Our aim was to investigate the role of sympathetic innervation to the intestine on regulation of the innate immune responses. METHODS: In lipopolysaccharide (LPS)-stimulated macrophages, we evaluated the effect of adrenergic receptor activation on cytokine production and metabolic profile. In vivo, the effect of sympathetic denervation on mucosal innate immune responses using 6-hydroxydopamine (6-OHDA), or using surgical transection of the superior mesenteric nerve (sympathectomy) was tested in Rag1-/- mice that lack T- and B-lymphocytes. RESULTS: In murine macrophages, adrenergic ß2 receptor activation elicited a dose-dependent reduction of LPS-induced cytokines, reduced LPS-induced glycolysis and increased maximum respiration. Sympathectomy led to a significantly decreased norepinephrine concentration in intestinal tissue. Within 14 days after sympathectomy, mice developed clinical signs of colitis, colon oedema and excess colonic cytokine production. Both 6-OHDA and sympathectomy led to prominent goblet cell depletion and histological damage of colonic mucosa. CONCLUSIONS: We conclude that the sympathetic nervous system plays a regulatory role in constraining innate immune cell reactivity towards microbial challenges, likely via the adrenergic ß2 receptor.

Elevated bone marrow sympathetic drive precedes systemic inflammation in angiotensin II hypertension.

Increased sympathetic nervous system activity is a hallmark of hypertension (HTN), and it is implicated in altered immune system responses in its pathophysiology. However, the precise mechanisms of neural-immune interaction in HTN remain elusive. We have previously shown an association between elevated sympathetic drive to the bone marrow (BM) and activated BM immune cells in rodent models of HTN. Moreover, microglial-dependent neuroinflammation is also seen in rodent models of HTN. However, the cause-effect relationship between central and systemic inflammatory responses and the sympathetic drive remains unknown. These observations led us to hypothesize that increase in the femoral BM sympathetic nerve activity (fSNA) initiates a cascade of events leading to increase in blood pressure (BP). Here, we investigated the temporal relationship between the BM sympathetic drive, activation of the central and peripheral immune system, and increase in BP in the events leading to established HTN. The present study demonstrates that central infusion of angiotensin II (ANG II) induces early microglial activation in the paraventricular nucleus of hypothalamus, which preceded increase in the fSNA. In turn, activation of fSNA correlated with the timing of increased production and release of CD4+.IL17+ T cells and other proinflammatory cells into circulation and elevation in BP, whereas infiltration of CD4+ cells to the paraventricular nucleus marked establishment of ANG II HTN. This study identifies cellular and molecular mechanisms involved in neural-immune interactions in early and established stages of rodent ANG II HTN. NEW & NOTEWORTHY Early microglia activation in paraventricular nucleus precedes sympathetic activation of the bone marrow. This leads to increased bone marrow immune cells and their release into circulation and an increase in blood pressure. Infiltration of CD4+ T cells into paraventricular nucleus paraventricular nucleus marks late hypertension.

From early adversities to immune activation in psychiatric disorders: the role of the sympathetic nervous system.

Increased peripheral levels of cytokines and central microglial activation have been reported in patients with psychiatric disorders. The degree of both innate and adaptive immune activation is also associated with worse clinical outcomes and poor treatment response in these patients. Understanding the possible causes and mechanisms leading to this immune activation is therefore an important and necessary step for the development of novel and more effective treatment strategies for these patients. In this work, we review the evidence of literature pointing to childhood trauma as one of the main causes behind the increased immune activation in patients with psychiatric disorders. We then discuss the potential mechanisms linking the experience of early life adversity (ELA) to innate immune activation. Specifically, we focus on the innervation of the bone marrow from sympathetic nervous system (SNS) as a new and emerging mechanism that has the potential to bridge the observed increases in both central and peripheral inflammatory markers in patients exposed to ELA. Experimental studies in laboratory rodents suggest that SNS activation following early life stress exposure causes a shift in the profile of innate immune cells, with an increase in proinflammatory monocytes. In turn, these cells traffic to the brain and influence neural circuitry, which manifests as increased anxiety and other relevant behavioural phenotypes. To date, however, very few studies have been conducted to explore this candidate mechanism in humans. Future research is also needed to clarify whether these pathways could be partially reversible to improve prevention and treatment strategies in the future.

Acute Traumatic Brain Injury Induces CD4+ and CD8+ T Cell Functional Impairment by Upregulating the Expression of PD-1 via the Activated Sympathetic Nervous System.

OBJECTIVE: Traumatic brain injury (TBI) induces immunosuppression in the acute phase, and the activation of the sympathetic nervous system (SNS) might play a role in this process, but the mechanism involved is unknown. Herein, we explored the impact of acute (a)TBI on the peripheral immune system and its correlation with the SNS and the T cell exhaustion marker, PD-1 (programmed cell death-1). METHODS: Flow cytometry (FCM) was performed to analyze the expression of T cell markers and intracellular cytokines, interferon-γ and tumor necrosis factor-α, and the T cell exhaustion marker, PD-1, in the peripheral blood mononuclear cells (PBMCs) of TBI rats. Enzyme-linked immunosorbent assay (ELISA) was performed to analyze the concentration of norepinephrine (NE) in the serum. Propranolol was administrated to block the SNS in vivo and NE stimulation was used to imitate the activation of the SNS in vitro. RESULTS: We found that the concentration of NE was significantly elevated after TBI, and the dysfunction of CD4+ and CD8+ T cells was reversed by the SNS blocker propranolol in vivo and imitated by the SNS neurotransmitter NE in vitro. The expression of PD-1 on CD4+ and CD8+ T cells was upregulated after aTBI, which was reversed by propranolol administration in vivo and imitated by NE stimulation in vitro. Furthermore, the PD-1 blocker reversed the dysfunction of CD4+ and CD8+T cells in vitro. CONCLUSION: Our findings demonstrated that aTBI activated the SNS, and further upregulated the expression of PD-1 on CD4+ and CD8+ T cells, which, in turn, impaired their function and contributed to immunosuppression.

Neuroendocrine Modulation of IL-27 in Macrophages.

Heterodimeric IL-27 (p28/EBV-induced gene 3) is an important member of the IL-6/IL-12 cytokine family. IL-27 is predominantly synthesized by mononuclear phagocytes and exerts immunoregulatory functional activities on lymphocytic and nonlymphocytic cells during infection, autoimmunity or neoplasms. There is a great body of evidence on the bidirectional interplay between the autonomic nervous system and immune responses during inflammatory disorders, but so far IL-27 has not been defined as a part of these multifaceted neuroendocrine networks. In this study, we describe the role of catecholamines (as mediators of the sympathetic nervous system) related to IL-27 production in primary mouse macrophages. Noradrenaline and adrenaline dose-dependently suppressed the release of IL-27p28 in LPS/TLR4-activated macrophages, which was independent of α1 adrenoceptors. Instead, ß2 adrenoceptor activation was responsible for mediating gene silencing of IL-27p28 and EBV-induced gene 3. The ß2 adrenoceptor agonists formoterol and salbutamol mediated suppression of IL-27p28 production, when triggered by zymosan/TLR2, LPS/TLR4, or R848/TLR7/8 activation, but selectively spared the polyinosinic-polycytidylic acid/TLR3 pathway. Mechanistically, ß2 adrenergic signaling reinforced an autocrine feedback loop of macrophage-derived IL-10 and this synergized with inhibition of the JNK pathway for limiting IL-27p28. The JNK inhibitors SP600125 and AEG3482 strongly decreased intracellular IL-27p28 in F4/80+CD11b+ macrophages. In endotoxic shock of C57BL/6J mice, pharmacologic activation of ß2 adrenoceptors improved the severity of shock, including hypothermia and decreased circulating IL-27p28. Conversely, IL-27p28 was 2.7-fold increased by removal of the catecholamine-producing adrenal glands prior to endotoxic shock. These data suggest a novel role of the sympathetic neuroendocrine system for the modulation of IL-27-dependent acute inflammation.

Complex regional pain syndrome: a focus on the autonomic nervous system.

PURPOSE: Although autonomic features are part of the diagnostic criteria for complex regional pain syndrome (CRPS), the role of the autonomic nervous system in CRPS pathophysiology has been downplayed in recent years. The purpose of this review is to redress this imbalance. METHODS: We focus in this review on the contribution of the autonomic nervous system to CRPS pathophysiology. In particular, we discuss regional sympathetic and systemic autonomic disturbances in CRPS and the mechanisms which may underlie them, and consider links between these mechanisms, immune disturbances and pain. RESULTS: The focused literature research revealed that immune reactions, alterations in receptor populations (e.g., upregulation of adrenoceptors and reduced cutaneous nerve fiber density) and central changes in autonomic drive seem to contribute to regional and systemic disturbances in sympathetic activity and to sympathetically maintained pain in CRPS. CONCLUSIONS: We conclude that alterations in the sympathetic nervous system contribute to CRPS pathology. Understanding these alterations may be an important step towards providing appropriate treatments for CRPS.

ß-arrestin2 functions as a key regulator in the sympathetic-triggered immunodepression after stroke.

BACKGROUND: Stroke-induced immunodeficiency syndrome (SIDS) is regarded as a protective mechanism for secondary inflammatory injury as well as a contributor to infection complications. Although stroke-induced hyperactivation of the sympathetic system is proved to facilitate SIDS, the involved endogenous factors and pathways are largely elusive. In this study, we aim to investigate the function of beta-arrestin-2 (ARRB2) in the sympathetic-mediated SIDS. METHODS: Splenic ARRB2 expression and the sympathetic system activity were detected after establishing transient models of middle cerebral artery occlusion (MCAO). In addition, a correlation between ARRB2 expression and the sympathetic system activity was analyzed using a linear correlation analysis. Any SIDS reflected in monocyte dysfunction was investigated by measuring inflammatory cytokine secretion and neurological deficit scores and infarct volume were tested to assess neurological outcome. Further, ARRB2 expression in the monocytes was knocked down in vitro by siRNAs. Following the stimulation of noradrenaline and lipopolysaccharide, cytokine secretion and the nuclear factor-κB (NF-κB) pathway were evaluated to gain insight into the mechanisms related to the contribution of ARRB2 to adrenergic-induced monocyte dysfunction. RESULTS: Splenic ARRB2 expression was significantly increased after stroke and also showed a significant positive correlation with the sympathetic system activity. Stroke-induced monocyte dysfunction resulted in an increase of the interleukin-10 (IL-10) level as well as a decrease of the interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α) and interleukin-1ß (IL-1ß) levels. Also, blockade of adrenergic-activity significantly reversed these cytokine levels, and blockade of adrenergic-activity improved stroke-induced neurological results. However, the improved neurological results had no significant correlation with ARRB2 expression. Furthermore, the in vitro results showed that the deficiency of ARRB2 dramatically repealed adrenergic-induced monocyte dysfunction and the inhibition of NF-κB signaling phosphorylation activity. CONCLUSIONS: ARRB2 is implicated in the sympathetic-triggered SIDS, in particular, monocyte dysfunction after stroke. Accordingly, ARRB2 may be a promising therapeutic target for the immunological management of stroke in a clinic.

Macrophages in obesity.

Obesity is a worldwide public health concern yet no safe therapies are currently available. The activity of sympathetic neurons is necessary and sufficient for fat mass reduction, via norepinephrine (NE) signaling. Macrophage accumulation in the adipose tissue is thought to play the central role in the onset of obesity, yet their relation to NE has been controversial. We have identified a population of sympathetic neuron-associated macrophages (SAMs) that control obesity via the uptake and clearing of NE. Here we focus on the neuro-immune regulation of obesity by discussing the genetic, cellular and functional signatures of SAMs vis-a-vis adipose tissue macrophages (ATMs).

Exosomes: an emerging factor in stress-induced immunomodulation.

Cells constitutively release small (40-100 nm) vesicles known as exosomes, but their composition and function changes in response to a variety of physiological challenges, such as injury, infection, and disease. Advances in our understanding of the immunological relevance of exosomes have been made, however, few studies have explored their role in stress physiology. Exposure to a variety of acute stressors facilitates the efficacy of innate immune responses, but the mechanisms for these effects are not fully understood. Since exosomes are emerging as important inflammatory mediators, they likely exhibit a similar role when an organism is exposed to an acute stressor. Here, we review our current knowledge of the basic properties and immunological functions of exosomes and provide emerging data supporting the role of stress-modified exosomes in regulating the innate immune response, potentially enabling long-distance cellular communication and obviating the need for direct cell-to-cell contact.