Celiac Vagus Nerve Stimulation Recapitulates Angiotensin II-Induced Splenic Noradrenergic Activation, Driving Egress of CD8 Effector Cells

Immune and inflammatory mechanisms in hypertension

Hypertension is a global health problem, with >1.3 billion individuals with high blood pressure worldwide. In this Review, we present an inflammatory paradigm for hypertension, emphasizing the crucial roles of immune cells, cytokines and chemokines in disease initiation and progression. T cells, monocytes, macrophages, dendritic cells, B cells and natural killer cells are all implicated in hypertension. Neoantigens, the NLRP3 inflammasome and increased sympathetic outflow, as well as cytokines (including IL-6, IL-7, IL-15, IL-18 and IL-21) and a high-salt environment, can contribute to immune activation in hypertension. The activated immune cells migrate to target organs such as arteries (especially the perivascular fat and adventitia), kidneys, the heart and the brain, where they release effector cytokines that elevate blood pressure and cause vascular remodelling, renal damage, cardiac hypertrophy, cognitive impairment and dementia. IL-17 secreted by CD4+ T helper 17 cells and γδ T cells, and interferon-γ and tumour necrosis factor secreted by immunosenescent CD8+ T cells, exert crucial effector roles in hypertension, whereas IL-10 and regulatory T cells are protective. Effector mediators impair nitric oxide bioavailability, leading to endothelial dysfunction and increased vascular contractility. Inflammatory effector mediators also alter renal sodium and water balance and promote renal fibrosis. These mechanisms link hypertension with obesity, autoimmunity, periodontitis and COVID-19. A comprehensive understanding of the immune and inflammatory mechanisms of hypertension is crucial for safely and effectively translating the findings to clinical practice.

Brain-Splenic Immune System Interactions in Hypertension: Cellular and Molecular Mechanisms

Hypertension represents a major worldwide cause of death and disability, and it is becoming increasingly clear that available therapies are not sufficient to reduce the risk of major cardiovascular events. Various mechanisms contribute to blood pressure increase: neurohormonal activation, autonomic nervous system imbalance, and immune activation. Of note, the brain is an important regulator of blood pressure levels; it recognizes the peripheral perturbation and organizes a reflex response by modulating immune system and hormonal release to attempt at restoring the homeostasis. The connection between the brain and peripheral organs is mediated by the autonomic nervous system, which also modulates immune and inflammatory responses. Interestingly, an increased autonomic nervous system activity has been correlated with an altered immune response in cardiovascular diseases. The spleen is the largest immune organ exerting a potent influence on the cardiovascular system during disease and is characterized by a dense noradrenergic innervation. Taken together, these aspects led to hypothesize a key role of neuroimmune mechanisms in the onset and progression of hypertension. This review discusses how the nervous and splenic immune systems interact and how the mechanisms underlying the neuroimmune cross talk influence the disease progression.

Vagus nerve-dependent effects of fluoxetine on anxiety- and depression-like behaviors in mice

The vagus nerve is a major pathway in the body that is responsible for regulating the activity of the parasympathetic nervous system, which plays an important role in mood disorders including anxiety and depression. Fluoxetine, also known as Prozac, is widely used to treat depression. Nevertheless, there are few studies on the vagus nerve-mediated action of fluoxetine. In this study, we aimed to investigate the vagus nerve-dependent actions of fluoxetine in mice with restraint stress-induced or antibiotics-induced anxiety- and depression-like behaviors. Compared to sham operation, vagotomy alone did not exhibit significant effects on behavioral changes and serotonin-related biomarkers in mice not exposed to stress, antibiotics, or fluoxetine. Oral administration of fluoxetine significantly alleviated anxiety- and depression-like behaviors. However, celiac vagotomy significantly attenuated the anti-depressive effects of fluoxetine. The vagotomy also inhibited the effect of fluoxetine to attenuate restraint stress- or cefaclor-induced reduction in serotonin levels and Htr1a mRNA expression in the hippocampus. These findings suggest that the vagus nerve may regulate the efficacy of fluoxetine for depression.

Small fish, big discoveries: zebrafish shed light on microbial biomarkers for neuro-immune-cardiovascular health

Zebrafish (Danio rerio) have emerged as a powerful model to study the gut microbiome in the context of human conditions, including hypertension, cardiovascular disease, neurological disorders, and immune dysfunction. Here, we highlight zebrafish as a tool to bridge the gap in knowledge in linking the gut microbiome and physiological homeostasis of cardiovascular, neural, and immune systems, both independently and as an integrated axis. Drawing on zebrafish studies to date, we discuss challenges in microbiota transplant techniques and gnotobiotic husbandry practices. We present advantages and current limitations in zebrafish microbiome research and discuss the use of zebrafish in identification of microbial enterotypes in health and disease. We also highlight the versatility of zebrafish studies to further explore the function of human conditions relevant to gut dysbiosis and reveal novel therapeutic targets.

Cardiovascular Brain Circuits

The cardiovascular system is hardwired to the brain via multilayered afferent and efferent polysynaptic axonal connections. Two major anatomically and functionally distinct though closely interacting subcircuits within the cardiovascular system have recently been defined: The artery-brain circuit and the heart-brain circuit. However, how the nervous system impacts cardiovascular disease progression remains poorly understood. Here, we review recent findings on the anatomy, structures, and inner workings of the lesser-known artery-brain circuit and the better-established heart-brain circuit. We explore the evidence that signals from arteries or the heart form a systemic and finely tuned cardiovascular brain circuit: afferent inputs originating in the arterial tree or the heart are conveyed to distinct sensory neurons in the brain. There, primary integration centers act as hubs that receive and integrate artery-brain circuit-derived and heart-brain circuit-derived signals and process them together with axonal connections and humoral cues from distant brain regions. To conclude the cardiovascular brain circuit, integration centers transmit the constantly modified signals to efferent neurons which transfer them back to the cardiovascular system. Importantly, primary integration centers are wired to and receive information from secondary brain centers that control a wide variety of brain traits encoded in engrams including immune memory, stress-regulating hormone release, pain, reward, emotions, and even motivated types of behavior. Finally, we explore the important possibility that brain effector neurons in the cardiovascular brain circuit network connect efferent signals to other peripheral organs including the immune system, the gut, the liver, and adipose tissue. The enormous recent progress vis-à-vis the cardiovascular brain circuit allows us to propose a novel neurobiology-centered cardiovascular disease hypothesis that we term the neuroimmune cardiovascular circuit hypothesis.

Preclinical models and evaluation criteria of prostatitis

Prostatitis is a common urological condition that affects almost half of all men at some point in their life. The prostate gland has a dense nerve supply that contributes to the production of fluid to nourish sperm and the mechanism to switch between urination and ejaculation. Prostatitis can cause frequent urination, pelvic pain, and even infertility. Long-term prostatitis increases the risk of prostate cancer and benign prostate hyperplasia. Chronic non-bacterial prostatitis presents a complex pathogenesis, which has challenged medical research. Experimental studies of prostatitis require appropriate preclinical models. This review aimed to summarize and compare preclinical models of prostatitis based on their methods, success rate, evaluation, and range of application. The objective of this study is to provide a comprehensive understanding of prostatitis and advance basic research.

Noninvasive ultrasound stimulation to treat myocarditis through splenic neuro-immune regulation

BACKGROUND

The cholinergic anti-inflammatory pathway (CAP) has been widely studied to modulate the immune response. Current stimulating strategies are invasive or imprecise. Noninvasive low-intensity pulsed ultrasound (LIPUS) has become increasingly appreciated for targeted neuronal modulation. However, its mechanisms and physiological role on myocarditis remain poorly defined.

METHODS

The mouse model of experimental autoimmune myocarditis was established. Low-intensity pulsed ultrasound was targeted at the spleen to stimulate the spleen nerve. Under different ultrasound parameters, histological tests and molecular biology were performed to observe inflammatory lesions and changes in immune cell subsets in the spleen and heart. In addition, we evaluated the dependence of the spleen nerve and cholinergic anti-inflammatory pathway of low-intensity pulsed ultrasound in treating autoimmune myocarditis in mice through different control groups.

RESULTS

The echocardiography and flow cytometry of splenic or heart infiltrating immune cells revealed that splenic ultrasound could alleviate the immune response, regulate the proportion and function of CD4+ Treg and macrophages by activating cholinergic anti-inflammatory pathway, and finally reduce heart inflammatory injury and improve cardiac remodeling, which is as effective as an acetylcholine receptor agonists GTS-21. Transcriptome sequencing showed significant differential expressed genes due to ultrasound modulation.

CONCLUSIONS

It is worth noting that the ultrasound therapeutic efficacy depends greatly on acoustic pressure and exposure duration, and the effective targeting organ was the spleen but not the heart. This study provides novel insight into the therapeutic potentials of LIPUS, which are essential for its future application.

Brief periods of transcutaneous auricular vagus nerve stimulation improve autonomic balance and alter circulating monocytes and endothelial cells in patients with metabolic syndrome: a pilot study

BACKGROUND

There is emerging evidence that the nervous system regulates immune and metabolic alterations mediating Metabolic syndrome (MetS) pathogenesis via the vagus nerve. This study evaluated the effects of transcutaneous auricular vagus nerve stimulation (TAVNS) on key cardiovascular and inflammatory components of MetS.

METHODS

We conducted an open label, randomized (2:1), two-arm, parallel-group controlled trial in MetS patients. Subjects in the treatment group (n = 20) received 30 min of TAVNS with a NEMOS® device placed on the cymba conchae of the left ear, once weekly. Patients in the control group (n = 10) received no stimulation. Hemodynamic, heart rate variability (HRV), biochemical parameters, and monocytes, progenitor endothelial cells, circulating endothelial cells, and endothelial micro particles were evaluated at randomization, after the first TAVNS treatment, and again after 8 weeks of follow-up.

RESULTS

An improvement in sympathovagal balance (HRV analysis) was observed after the first TAVNS session. Only patients treated with TAVNS for 8 weeks had a significant decrease in office BP and HR, a further improvement in sympathovagal balance, with a shift of circulating monocytes towards an anti-inflammatory phenotype and endothelial cells to a reparative vascular profile.

CONCLUSION

These results are of interest for further study of TAVNS as treatment of MetS.

Cardiovascular Response to Intraneural Right Vagus Nerve Stimulation in Adult Minipig

OBJECTIVE

This study explored intraneural stimulation of the right thoracic vagus nerve (VN) in sexually mature male minipigs to modulate safe heart rate and blood pressure response.

MATERIAL AND METHODS

We employed an intraneural electrode designed for the VN of pigs to perform VN stimulation (VNS). This was delivered using different numbers of contacts on the electrode and different stimulation parameters (amplitude, frequency, and pulse width), identifying the most suitable stimulation configuration. All the parameter ranges had been selected from a computational cardiovascular system model.

RESULTS

Clinically relevant responses were observed when stimulating with low current intensities and relatively low frequencies delivered with a single contact. Selecting a biphasic, charge-balanced square wave for VNS with a current amplitude of 500 μA, frequency of 10 Hz, and pulse width of 200 μs, we obtained heart rate reduction of 7.67 ± 5.19 beats per minute, systolic pressure reduction of 5.75 ± 2.59 mmHg, and diastolic pressure reduction of 3.39 ± 1.44 mmHg.

CONCLUSION

Heart rate modulation was obtained without inducing any observable adverse effects, underlining the high selectivity of the intraneural approach.

Heart development and regeneration-a multi-organ effort

Development of the heart, from early morphogenesis to functional maturation, as well as maintenance of its homeostasis are tasks requiring collaborative efforts of cardiac tissue and different extra-cardiac organ systems. The brain, lymphoid organs, and gut are among the interaction partners that can communicate with the heart through a wide array of paracrine signals acting at local or systemic level. Disturbance of cardiac homeostasis following ischemic injury also needs immediate response from these distant organs. Our hearts replace dead muscles with non-contractile fibrotic scars. We have learned from animal models capable of scarless repair that regenerative capability of the heart does not depend only on competency of the myocardium and cardiac-intrinsic factors but also on long-range molecular signals originating in other parts of the body. Here, we provide an overview of inter-organ signals that take part in development and regeneration of the heart. We highlight recent findings and remaining questions. Finally, we discuss the potential of inter-organ modulatory approaches for possible therapeutic use.

Autonomic nervous system and cardiac neuro-signaling pathway modulation in cardiovascular disorders and Alzheimer's disease

The heart is a functional syncytium controlled by a delicate and sophisticated balance ensured by the tight coordination of its several cell subpopulations. Accordingly, cardiomyocytes together with the surrounding microenvironment participate in the heart tissue homeostasis. In the right atrium, the sinoatrial nodal cells regulate the cardiac impulse propagation through cardiomyocytes, thus ensuring the maintenance of the electric network in the heart tissue. Notably, the central nervous system (CNS) modulates the cardiac rhythm through the two limbs of the autonomic nervous system (ANS): the parasympathetic and sympathetic compartments. The autonomic nervous system exerts non-voluntary effects on different peripheral organs. The main neuromodulator of the Sympathetic Nervous System (SNS) is norepinephrine, while the principal neurotransmitter of the Parasympathetic Nervous System (PNS) is acetylcholine. Through these two main neurohormones, the ANS can gradually regulate cardiac, vascular, visceral, and glandular functions by turning on one of its two branches (adrenergic and/or cholinergic), which exert opposite effects on targeted organs. Besides these neuromodulators, the cardiac nervous system is ruled by specific neuropeptides (neurotrophic factors) that help to preserve innervation homeostasis through the myocardial layers (from epicardium to endocardium). Interestingly, the dysregulation of this neuro-signaling pathway may expose the cardiac tissue to severe disorders of different etiology and nature. Specifically, a maladaptive remodeling of the cardiac nervous system may culminate in a progressive loss of neurotrophins, thus leading to severe myocardial denervation, as observed in different cardiometabolic and neurodegenerative diseases (myocardial infarction, heart failure, Alzheimer's disease). This review analyzes the current knowledge on the pathophysiological processes involved in cardiac nervous system impairment from the perspectives of both cardiac disorders and a widely diffused and devastating neurodegenerative disorder, Alzheimer's disease, proposing a relationship between neurodegeneration, loss of neurotrophic factors, and cardiac nervous system impairment. This overview is conducive to a more comprehensive understanding of the process of cardiac neuro-signaling dysfunction, while bringing to light potential therapeutic scenarios to correct or delay the adverse cardiovascular remodeling, thus improving the cardiac prognosis and quality of life in patients with heart or neurodegenerative disorders.

Neuroimmune cardiovascular interfaces control atherosclerosis

Atherosclerotic plaques develop in the inner intimal layer of arteries and can cause heart attacks and strokes¹. As plaques lack innervation, the effects of neuronal control on atherosclerosis remain unclear. However, the immune system responds to plaques by forming leukocyte infiltrates in the outer connective tissue coat of arteries (the adventitia)^2-6. Here, because the peripheral nervous system uses the adventitia as its principal conduit to reach distant targets^7-9, we postulated that the peripheral nervous system may directly interact with diseased arteries. Unexpectedly, widespread neuroimmune cardiovascular interfaces (NICIs) arose in mouse and human atherosclerosis-diseased adventitia segments showed expanded axon networks, including growth cones at axon endings near immune cells and media smooth muscle cells. Mouse NICIs established a structural artery-brain circuit (ABC): abdominal adventitia nociceptive afferents^10-14 entered the central nervous system through spinal cord T₆-T₁₃ dorsal root ganglia and were traced to higher brain regions, including the parabrachial and central amygdala neurons; and sympathetic efferent neurons projected from medullary and hypothalamic neurons to the adventitia through spinal intermediolateral neurons and both coeliac and sympathetic chain ganglia. Moreover, ABC peripheral nervous system components were activated: splenic sympathetic and coeliac vagus nerve activities increased in parallel to disease progression, whereas coeliac ganglionectomy led to the disintegration of adventitial NICIs, reduced disease progression and enhanced plaque stability. Thus, the peripheral nervous system uses NICIs to assemble a structural ABC, and therapeutic intervention in the ABC attenuates atherosclerosis.

Neuroimmune axis of cardiovascular control: mechanisms and therapeutic implications

Cardiovascular diseases (CVDs) make a substantial contribution to the global burden of disease. Prevention strategies have succeeded in reducing the effect of acute CVD events and deaths, but the long-term consequences of cardiovascular risk factors still represent the major cause of disability and chronic illness, suggesting that some pathophysiological mechanisms might not be adequately targeted by current therapies. Many of the underlying causes of CVD have now been recognized to have immune and inflammatory components. However, inflammation and immune activation were mostly regarded as a consequence of target-organ damage. Only more recent findings have indicated that immune dysregulation can be pathogenic for CVD, identifying a need for novel immunomodulatory therapeutic strategies. The nervous system, through an array of afferent and efferent arms of the autonomic nervous system, profoundly affects cardiovascular function. Interestingly, the autonomic nervous system also innervates immune organs, and neuroimmune interactions that are biologically relevant to CVD have been discovered, providing the foundation to target neural reflexes as an immunomodulatory therapeutic strategy. This Review summarizes how the neural regulation of immunity and inflammation participates in the onset and progression of CVD and explores promising opportunities for future therapeutic strategies.

Brain Areas Involved in Modulating the Immune Response Participating in Hypertension and Its Target Organ Damage

Significance: Hypertension is a multifactorial disease ensuing from the continuous challenge imposed by several risk factors on the cardiovascular system. Classically known pathophysiological alterations associated with hypertension comprise neurogenic mechanisms dysregulating the autonomic nervous system (ANS), vascular dysfunction, and excessive activation of the renin angiotensin system. During the past few years, a considerable number of studies indicated that immune activation and inflammation also have an important role in the onset and maintenance of hypertension. Critical Issues: On these premises, it has been necessary to reconsider the pathophysiological mechanisms underlying hypertension development, taking into account the potential interactions established between classically known determinants of high blood pressure and the immune system. Recent Advances: Interestingly, central nervous system areas controlling cardiovascular functions are enriched with Angiotensin II receptors. Observations showing that these brain areas are crucial for mediating peripheral ANS and immune responses were suggestive of a critical role of neuroimmune interactions in hypertension. In fact, the ANS, characterized by an intricate network of afferent and efferent fibers, represents an intermediate between the brain and peripheral responses that are essential for blood pressure regulation. Future Directions: In this review, we will summarize studies showing how specific brain areas can modulate immune responses that are involved in hypertension. Antioxid. Redox Signal. 35, 1515-1530.

Therapeutic targeting of inflammation in hypertension: from novel mechanisms to translational perspective

Both animal models and human observational and genetic studies have shown that immune and inflammatory mechanisms play a key role in hypertension and its complications. We review the effects of immunomodulatory interventions on blood pressure, target organ damage, and cardiovascular risk in humans. In experimental and small clinical studies, both non-specific immunomodulatory approaches, such as mycophenolate mofetil and methotrexate, and medications targeting T and B lymphocytes, such as tacrolimus, cyclosporine, everolimus, and rituximab, lower blood pressure and reduce organ damage. Mechanistically targeted immune interventions include isolevuglandin scavengers to prevent neo-antigen formation, co-stimulation blockade (abatacept, belatacept), and anti-cytokine therapies (e.g. secukinumab, tocilizumab, canakinumab, TNF-α inhibitors). In many studies, trial designs have been complicated by a lack of blood pressure-related endpoints, inclusion of largely normotensive study populations, polypharmacy, and established comorbidities. Among a wide range of interventions reviewed, TNF-α inhibitors have provided the most robust evidence of blood pressure lowering. Treatment of periodontitis also appears to deliver non-pharmacological anti-hypertensive effects. Evidence of immunomodulatory drugs influencing hypertension-mediated organ damage are also discussed. The reviewed animal models, observational studies, and trial data in humans, support the therapeutic potential of immune-targeted therapies in blood pressure lowering and in hypertension-mediated organ damage. Targeted studies are now needed to address their effects on blood pressure in hypertensive individuals.

Activation of Yes-Associated Protein/PDZ-Binding Motif Pathway Contributes to Endothelial Dysfunction and Vascular Inflammation in AngiotensinII Hypertension

Yes-associated protein (YAP) and its associated coactivator of PDZ-binding motif (TAZ) are co-transcriptional regulators and down effectors of the Hippo signaling pathway. Recent studies have shown that the Hippo/YAP signaling pathway may play a role in mediating vascular homeostasis. This study investigated the role of YAP/TAZ in endothelial dysfunction and vascular inflammation in angiotensin (Ang)II hypertensive mice. The infusion of AngII (1.1 mg/kg/day by mini-pump) for 3 weeks induced the activation of YAP/TAZ, manifested by decreased cytosolic phosphor-YAP and phosphor-TAZ, and increased YAP/TAZ nuclear translocation, which were prevented by YAP/TAZ inhibitor verteporfin. AngII significantly increased systolic blood pressure (SBP), macrophage infiltration, and expressions of proinflammatory cytokines, and impaired endothelial function in the aorta of the mice. Treatment with verteporfin improved endothelial function and reduced vascular inflammation with a mild reduction in SBP. AngII also induced YAP/TAZ activation in human umbilical vein endothelial cells in vitro, which were prevented by LB-100, an inhibitor of protein phosphatase 2A (PP2A, a major dephosphorylase). Treatment with LB-100 reversed AngII-induced proinflammatory cytokine expression and impairment of phosphor-eNOS expression in vitro. Our results suggest that AngII induces YAP/TAZ activation via PP2A-dependent dephosphorylation, which may contribute to the impairment of endothelial function and the induction of vascular inflammation in hypertension. YAP/TAZ may be a new target for hypertensive vascular injury.

A Focused Review of Neural Recording and Stimulation Techniques With Immune-Modulatory Targets

The complex interactions established between the nervous and immune systems have been investigated for a long time. With the advent of small and portable devices to record and stimulate nerve activity, researchers from many fields began to be interested in how nervous activity can elicit immune responses and whether this activity can be manipulated to trigger specific immune responses. Pioneering works demonstrated the existence of a cholinergic inflammatory reflex, capable of controlling the systemic inflammatory response through a vagus nerve-mediated modulation of the spleen. This work inspired many different areas of technological and conceptual advancement, which are here reviewed to provide a concise reference for the main works expanding the knowledge on vagus nerve immune-modulatory capabilities. In these works the enabling technologies of peripheral nervous activity recordings were implemented and embody the current efforts aimed at controlling neural activity with modulating functions in immune response, both in experimental and clinical contexts.