Central angiotensin II-enhanced splenic cytokine gene expression is mediated by the sympathetic nervous system

Neuro-immune interactions and immuno-oncology

The nervous system is an important component of the tumor microenvironment (TME), driving tumorigenesis and tumor progression. Neuronal cues (e.g., neurotransmitters and neuropeptides) in the TME cause phenotypic changes in immune cells, such as increased exhaustion and inhibition of effector cells, which promote immune evasion and cancer progression. Two types of immune regulation by tumor-associated nerves are discussed in this review: regulation via neuronal stimuli (i.e., by neural transmission) and checkpoint-mediated neuronal immune regulation. The latter occurs via the expression of immune checkpoints on the membranes of intratumoral nerves and glial cells. Here, we summarize novel findings regarding the neuroimmune circuits in the tumor milieu, while emphasizing the potential targets of new and affordable anticancer therapeutic approaches.

Impact of exercise on brain-bone marrow interactions in chronic stress: potential mechanisms preventing stress-induced hypertension

We examined the effect of chronic restraint stress and the counteractive effects of daily exercise on the molecular basis of the brain-bone marrow (BM) interactions, by especially focusing on the paraventricular nucleus (PVN) of the hypothalamus. Male Wistar rats were assigned into control, restraint stress, and stress + daily spontaneous exercise (SE) groups. BM and hypothalamic gene expression profiles were examined through the undertaking of RT-PCR and microarrays, respectively. The inflammatory blood cell population was investigated through flow cytometry. Through the use of immunohistochemistry, we examined the presence of BM-derived C-C chemokine receptor type 2 (CCR2)-expressing microglial cells in the rat PVN. The gene expression levels of BM inflammatory factors such as those of interleukin 1 beta and CCR2, and the inflammatory blood cell population were found to be significantly higher in both restrained groups compared with control group. Interestingly, chronic restraint stress alone activated the recruitment of BM-derived CCR2-expressing microglial cells into the PVN, whereas daily spontaneous exercise prevented it. A notable finding was that restraint stress upregulated relative gene expression of hypothalamic matrix metalloproteinase 3 (MMP3), which increases the permeability of the blood-brain barrier (BBB), and that exercise managed to normalize it. Moreover, relative expression of some hypothalamic genes directly involved in the facilitation of cell migration was downregulated by daily exercise. Our findings suggest that daily spontaneous exercise can reduce the numbers of BM-derived CCR2-expressing microglial cells into the PVN through the prevention of stress-induced changes in the hypothalamic gene expression.NEW & NOTEWORTHY Chronic restraint stress can upregulate MMP3 gene expression in the rat hypothalamus, whereas daily spontaneous exercise can prevent this stress-induced effect. Stress-induced BM-derived inflammatory cell recruitment into the rat PVN can be prevented by daily spontaneous exercise. Stress-induced increase of hypothalamic MMP3 gene expression may be responsible for BBB injury, thereby allowing for BM-derived inflammatory cells to be recruited and to accumulate in the rat PVN, and to be subsequently involved in the onset of stress-induced hypertension.

The antihypertensive effect of remote ischemic conditioning in spontaneously hypertensive rats

Purpose

Limb remote ischemic conditioning (LRIC) may be an effective method to control hypertension. This study investigated whether LRIC decreases blood pressure by regulating the hypertensive inflammatory response in spontaneously hypertensive rats (SHR).

Method

The SHR and aged-matched Wistar rats with different ages were randomly assigned to the SHR group, SHR+LRIC group, Wistar group, and Wistar + LRIC group. LRIC was conducted by tightening a tourniquet around the upper thigh and releasing it for three cycles daily (10 mins x3 cycles). Blood pressure, the percentage of monocytes and T lymphocytes, and the concentration of pro-inflammatory cytokines in the blood were analyzed.

Results

The blood pressure of SHR was significantly higher than that of age-matched Wistar rats. LRIC decreased blood pressure in SHR at different ages (4, 8, and 16 weeks old), but had no effect on the blood pressure in Wistar rats. Flow cytometry analysis showed that blood monocytes and CD8 T cells of SHR were higher than those of Wistar rats. LRIC significantly decreased the percentage of monocytes and CD8 T cells in SHR. Consistent with the changes of immune cells, the levels of plasma IL-6 and TNF-α in SHR were also higher. And LRIC attenuated the plasma IL-6 and TNF-α levels in SHR.

Conclusion

LRIC may decreased the blood pressure via modulation of the inflammatory response in SHR.

Metabolic syndrome and aberrant immune responses to viral infection and vaccination: Insights from small animal models

This review outlines the propensity for metabolic syndrome (MetS) to induce elevated disease severity, higher mortality rates post-infection, and poor vaccination outcomes for viral pathogens. MetS is a cluster of conditions including high blood glucose, an increase in circulating low-density lipoproteins and triglycerides, abdominal obesity, and elevated blood pressure which often overlap in their occurrence. MetS diagnoses are on the rise, as reported cases have increased by greater than 35% since 1988, resulting in one-third of United States adults currently diagnosed as MetS patients. In the aftermath of the 2009 H1N1 pandemic, a link between MetS and disease severity was established. Since then, numerous studies have been conducted to illuminate the impact of MetS on enhancing virally induced morbidity and dysregulation of the host immune response. These correlative studies have emphasized the need for elucidating the mechanisms by which these alterations occur, and animal studies conducted as early as the 1940s have linked the conditions associated with MetS with enhanced viral disease severity and poor vaccine outcomes. In this review, we provide an overview of the importance of considering overall metabolic health in terms of cholesterolemia, glycemia, triglyceridemia, insulin and other metabolic molecules, along with blood pressure levels and obesity when studying the impact of metabolism-related malignancies on immune function. We highlight the novel insights that small animal models have provided for MetS-associated immune dysfunction following viral infection. Such animal models of aberrant metabolism have paved the way for our current understanding of MetS and its impact on viral disease severity, dysregulated immune responses to viral pathogens, poor vaccination outcomes, and contributions to the emergence of viral variants.

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.

Increased angiotensin II formation in the brain modulates cardiovascular homeostasis and erythropoiesis

In spite of the fact that the modulatory effects of angiotensin II (Ang II) on the sympathetic nerve activity to targeted organs involved in blood pressure (BP) regulation is well acknowledged, the local production of this peptide in the brain and the consequences of enhanced central Ang II beyond the cardiovascular system are not yet well comprehended. In the present study, we generated and validated a new transgenic mouse line overexpressing the rat full-length angiotensinogen (Agt) protein specifically in the brain (Agt-Tg). Adult Agt-Tg mice presented overall increased gene expression of total Agt in the brain including brainstem and hypothalamus. In addition, the excess of Agt led to abundantly detectable brain Ang II levels as well as increased circulating copeptin levels. Agt-Tg displayed raised BP in acute recordings, while long-term telemetrically measured basal BP was indistinguishable from wild-types. Agt-Tg has altered peripheral renin–angiotensin system and vasomotor sympathetic tone homeostasis because renal gene expression analysis, plasma Ang II measurements and ganglionic blockade experiments revealed suppressed renin expression and reduced Ang II and higher neurogenic pressure response, respectively. Plasma and urine screens revealed apparently normal fluid and electrolyte handling in Agt-Tg. Interestingly, hematological analyses showed increased hematocrit in Agt-Tg caused by enhanced erythropoiesis, which was reverted by submitting the transgenic mice to a long-term peripheral sympathectomy protocol. Collectively, our findings suggest that Agt-Tg is a valuable tool to study not only brain Ang II formation and its modulatory effects on cardiovascular homeostasis but also its role in erythropoiesis control via autonomic modulation.

Cholinergic stimulation with pyridostigmine modulates a heart-spleen axis after acute myocardial infarction in spontaneous hypertensive rats

The mechanisms regulating immune cells recruitment into the heart during healing after an acute myocardial infarction (AMI) have major clinical implications. We investigated whether cholinergic stimulation with pyridostigmine, a cholinesterase inhibitor, modulates heart and spleen immune responses and cardiac remodeling after AMI in spontaneous hypertensive rats (SHRs). Male adult SHRs underwent sham surgery or ligation of the left coronary artery and were randomly allocated to remain untreated or to pyridostigmine treatment (40 mg/kg once a day by gavage). Blood pressure and heart rate variability were determined, and echocardiography was performed at day six after MI. The heart and spleen were processed for immunohistochemistry cellular analyses (CD3⁺ and CD4⁺ lymphocytes, and CD68⁺ and CD206⁺ macrophages), and TNF levels were determined at day seven after MI. Pyridostigmine treatment increased the parasympathetic tone and T CD4⁺ lymphocytes in the myocardium, but lowered M1/M2 macrophage ratio towards an anti-inflammatory profile that was associated with decreased TNF levels in the heart and spleen. Treatment with this cholinergic agent improved heart remodeling manifested by lower ventricular diameters and better functional parameters. In summary, cholinergic stimulation by pyridostigmine enhances the parasympathetic tone and induces anti-inflammatory responses in the heart and spleen fostering cardiac recovery after AMI in SHRs.

Impact of aging and comorbidities on ischemic stroke outcomes in preclinical animal models: A translational perspective

Ischemic stroke is a highly complex and devastating neurological disease. The sudden loss of blood flow to a brain region due to an ischemic insult leads to severe damage to that area resulting in the formation of an infarcted tissue, also known as the ischemic core. This is surrounded by the peri-infarct region or penumbra that denotes the functionally impaired but potentially salvageable tissue. Thus, the penumbral tissue is the main target for the development of neuroprotective strategies to minimize the extent of ischemic brain damage by timely therapeutic intervention. Given the limitations of reperfusion therapies with recombinant tissue plasminogen activator or mechanical thrombectomy, there is high enthusiasm to combine reperfusion therapy with neuroprotective strategies to further reduce the progression of ischemic brain injury. Till date, a large number of candidate neuroprotective drugs have been identified as potential therapies based on highly promising results from studies in rodent ischemic stroke models. However, none of these interventions have shown therapeutic benefits in stroke patients in clinical trials. In this review article, we discussed the urgent need to utilize preclinical models of ischemic stroke that more accurately mimic the clinical conditions in stroke patients by incorporating aged animals and animal stroke models with comorbidities. We also outlined the recent findings that highlight the significant differences in stroke outcome between young and aged animals, and how major comorbid conditions such as hypertension, diabetes, obesity and hyperlipidemia dramatically increase the vulnerability of the brain to ischemic damage that eventually results in worse functional outcomes. It is evident from these earlier studies that including animal models of aging and comorbidities during the early stages of drug development could facilitate the identification of neuroprotective strategies with high likelihood of success in stroke clinical trials.

CNS and peripheral immunity in cerebral ischemia: partition and interaction

Stroke elicits excessive immune activation in the injured brain tissue. This well-recognized neural inflammation in the brain is not just an intrinsic organ response but also a result of additional intricate interactions between infiltrating peripheral immune cells and the resident immune cells in the affected areas. Given that there is a finite number of immune cells in the organism at the time of stroke, the partitioned immune systems of the central nervous system (CNS) and periphery must appropriately distribute the limited pool of immune cells between the two domains, mounting a necessary post-stroke inflammatory response by supplying a sufficient number of immune cells into the brain while maintaining peripheral immunity. Stroke pathophysiology has mainly been neurocentric in focus, but understanding the distinct roles of the CNS and peripheral immunity in their concerted action against ischemic insults is crucial. This review will discuss stroke-induced influences of the peripheral immune system on CNS injury/repair and of neural inflammation on peripheral immunity, and how comorbidity influences each.

Brain Angiotensinergic Regulation of the Immune System: Implications for Cardiovascular and Neuroendocrine Responses

OBJECTIVE

The Renin-Angiotensin-Aldosterone System (RAAS) plays a major role in the regulation of cardiovascular functions, water and electrolytic balance, and hormonal responses. We perform a review of the literature, aiming at providing the current concepts regarding the angiotensin interaction with the immune system in the brain and the related implications for cardiovascular and neuroendocrine responses.

METHODS

Appropriate keywords and MeSH terms were identified and searched in Pubmed. Finally, references of original articles and reviews were examined.

RESULTS

Angiotensin II (ANG II), beside stimulating aldosterone, vasopressin and CRH-ACTH release, sodium and water retention, thirst, and sympathetic nerve activity, exerts its effects on the immune system via the Angiotensin Type 1 Receptor (AT 1R) that is located in the brain, pituitary, adrenal gland, and kidney. Several actions are triggered by the binding of circulating ANG II to AT 1R into the circumventricular organs that lack the Blood-Brain-Barrier (BBB). Furthermore, the BBB becomes permeable during chronic hypertension thereby ANG II may also access brain nuclei controlling cardiovascular functions. Subfornical organ, organum vasculosum lamina terminalis, area postrema, paraventricular nucleus, septal nuclei, amygdala, nucleus of the solitary tract and retroventral lateral medulla oblongata are the brain structures that mediate the actions of ANG II since they are provided with a high concentration of AT 1R. ANG II induces also T-lymphocyte activation and vascular infiltration of leukocytes and, moreover, oxidative stress stimulating inflammatory responses via inhibition of endothelial progenitor cells and stimulation of inflammatory and microglial cells facilitating the development of hypertension.

CONCLUSION

Besides the well-known mechanisms by which RAAS activation can lead to the development of hypertension, the interactions between ANG II and the immune system at the brain level can play a significant role.

Neural Control of Immunity in Hypertension: Council on Hypertension Mid Career Award for Research Excellence, 2019

The nervous system and the immune system share the common ability to exert gatekeeper roles at the interfaces between internal and external environment. Although interaction between these 2 evolutionarily highly conserved systems has been recognized for long time, the investigation into the pathophysiological mechanisms underlying their crosstalk has been tackled only in recent decades. Recent work of the past years elucidated how the autonomic nervous system controls the splenic immunity recruited by hypertensive challenges. This review will focus on the neural mechanisms regulating the immune response and the role of this neuroimmune crosstalk in hypertension. In this context, the review highlights the components of the brain-spleen axis with a focus on the neuroimmune interface established in the spleen, where neural signals shape the immune response recruited to target organs of high blood pressure.

Sympathetic activation: a potential link between comorbidities and COVID-19

In coronavirus disease 2019 (COVID-19), higher morbidity and mortality are associated with age, male gender, and comorbidities, such as chronic lung diseases, cardiovascular pathologies, hypertension, kidney diseases, diabetes mellitus, and obesity. All of the above conditions are characterized by increased sympathetic discharge, which may exert significant detrimental effects on COVID-19 patients, through actions on the lungs, heart, blood vessels, kidneys, metabolism, and/or immune system. Furthermore, COVID-19 may also increase sympathetic discharge, through changes in blood gases (chronic intermittent hypoxia, hyperpnea), angiotensin-converting enzyme (ACE)1/ACE2 imbalance, immune/inflammatory factors, or emotional distress. Nevertheless, the potential role of the sympathetic nervous system has not yet been considered in the pathophysiology of COVID-19. In our opinion, sympathetic overactivation could represent a so-far undervalued mechanism for a vicious circle between COVID-19 and comorbidities.

Neuroimmune interactions in cardiovascular diseases

Our body is continuously in contact with external stimuli that need a fine integration with the internal milieu in order to maintain the homoeostasis. Similarly, perturbations of the internal environment are responsible for the alterations of the physiological mechanisms regulating our main functions. The nervous system and the immune system represent the main interfaces between the internal and the external environment. In carrying out these functions, they share many similarities, being able to recognize, integrate, and organize responses to a wide variety of stimuli, with the final aim to re-establish the homoeostasis. The autonomic nervous system, which collectively refers to the ensemble of afferent and efferent neurons that wire the central nervous system with visceral effectors throughout the body, is the prototype system controlling the homoeostasis through reflex arches. On the other hand, immune cells continuously patrol our body against external enemies and internal perturbations, organizing acute responses and forming memory for future encounters. Interesting to notice, the integration of the two systems provides a further unique opportunity for fine tuning of our body's homoeostasis. In fact, the autonomic nervous system guides the development of lymphoid and myeloid organs, as well as the deployment of immune cells towards peripheral tissues where they can affect and control several physiological functions. In turn, every specific immune cell type can contribute to regulate neural circuits involved in cardiovascular function, metabolism, and inflammation. Here, we review current understanding of the cross-regulation between these systems in cardiovascular diseases.

Neuroimmune crosstalk in the pathophysiology of hypertension

Hypertension is an important risk factor for cardiovascular morbidity and mortality and for events such as myocardial infarction, stroke, heart failure and chronic kidney disease and is a major determinant of disability-adjusted life-years. Despite the importance of hypertension, the pathogenesis of essential hypertension, which involves the complex interaction of several mechanisms, is still poorly understood. Evidence suggests that interplay between bone marrow, microglia and immune mediators underlies the development of arterial hypertension, in particular through mechanisms involving cytokines and peptides, such as neuropeptide Y, substance P, angiotensin II and angiotensin-(1-7). Chronic psychological stress also seems to have a role in increasing the risk of hypertension, probably through the activation of neuroimmune pathways. In this Review, we summarize the available data on the possible role of neuroimmune crosstalk in the origin and maintenance of arterial hypertension and discuss the implications of this crosstalk for recovery and rehabilitation after cardiac and cerebral injuries.

Hypertension and Its Impact on Stroke Recovery: From a Vascular to a Parenchymal Overview

Hypertension is the first modifiable vascular risk factor accounting for 10.4 million deaths worldwide; it is strongly and independently associated with the risk of stroke and is related to worse prognosis. In addition, hypertension seems to be a key player in the implementation of vascular cognitive impairment. Long-term hypertension, complicated or not by the occurrence of ischemic stroke, is often reviewed on its vascular side, and parenchymal consequences are put aside. Here, we sought to review the impact of isolated hypertension or hypertension associated to stroke on brain atrophy, neuron connectivity and neurogenesis, and phenotype modification of microglia and astrocytes. Finally, we discuss the impact of antihypertensive therapies on cell responses to hypertension and functional recovery. This attractive topic remains a focus of continued investigation and stresses the relevance of including this vascular risk factor in preclinical investigations of stroke outcome.

Microglia, autonomic nervous system, immunity and hypertension: Is there a link?

Hypertension ranks the most common risk factor for cardiovascular diseases, and it affects almost one third of adult population globally. Emerging evidence indicates that immune activation is highly involved in the entire progress of hypertension and end organ damage. In addition to immunity, autonomic nervous system, particularly sympathetic nervous system, is one of the most conserved systems to maintain body homeostasis. Immune and sympathetic activities are found simultaneously increased in hypertension, suggesting a synergistic action of these two systems in the progression of this disease. Microglia, the primary immune cells in the central nervous system, have been suggested in the regulation of sympathetic outflow; depletion of microglia alters neuroinflammation and pressor responses in hypertensive models. In this review, we firstly updated the current understanding on microglial ontogeny and functions in both steady state and diseases. Then we reviewed on the interaction between autonomic nervous system and peripheral immunity in hypertension. Microglia bridge the central and peripheral inflammation via regulating the sympathetic nerve activity in hypertension. Future exploration of the molecular linkage of this pathway may provide novel therapeutic angel for hypertension and related cardiovascular diseases.

Autonomic regulation of T-lymphocytes: Implications in cardiovascular disease

The nervous and immune systems both serve as essential assessors and regulators of physiological function. Recently, there has been a great interest in how the nervous and immune systems interact to modulate both physiological and pathological states. In particular, the autonomic nervous system has a direct line of communication with immune cells anatomically, and moreover, immune cells possess receptors for autonomic neurotransmitters. This circumstantial evidence is suggestive of a functional interplay between the two systems, and extensive research over the past few decades has demonstrated neurotransmitters such as the catecholamines (i.e. dopamine, norepinephrine, and epinephrine) and acetylcholine have potent immunomodulating properties. Furthermore, immune cells, particularly T-lymphocytes, have now been found to express the cellular machinery for both the synthesis and degradation of neurotransmitters, which suggests the ability for both autocrine and paracrine signaling from these cells independent of the nervous system. The details underlying the functional interplay of this complex network of neuroimmune communication are still unclear, but this crosstalk is suggestive of significant implications on the pathogenesis of a number of autonomic-dysregulated and inflammation-mediated diseases. In particular, it is widely accepted that numerous forms of cardiovascular diseases possess imbalanced autonomic tone as well as altered T-lymphocyte function, but a paucity of literature exists discussing the direct role of neurotransmitters in shaping the inflammatory microenvironment during the progression or therapeutic management of these diseases. This review seeks to provide a fundamental framework for this autonomic neuroimmune interaction within T-lymphocytes, as well as the implications this may have in cardiovascular diseases.

The bidirectional interaction between the sympathetic nervous system and immune mechanisms in the pathogenesis of hypertension

Over the last few years, evidence has accumulated to suggest that hypertension is, at least in part, an immune-mediated inflammatory disorder. Many links between immunity and hypertension have been established and provide a complex framework of mechanistic interactions contributing to the rise in BP. These include immune-mediated inflammatory processes affecting regulatory brain nuclei and interactions with other mediators of cardiovascular regulation such as the sympathetic nervous system. Sympathoexcitation differentially regulates T-cells based upon activation status of the immune cell as well as the resident organ. Exogenous and endogenous triggers activate signalling pathways in innate and adaptive immune cells resulting in pro-inflammatory cytokine production and activation of T-lymphocytes in the cardiovascular and renal regions, now considered major factors in the development of essential hypertension. The inflammatory cascade is sustained and exacerbated by the immune flow via the brain-bone marrow-spleen-gastrointestinal axis and thereby further aggravating immune-mediated pathways resulting in a vicious cycle of established hypertension and target organ damage. This review summarizes the evidence and recent advances in linking immune-mediated inflammation, sympathetic activation and their bidirectional interactions with the development of hypertension. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Increased expression and functionality of the gap junction in peripheral blood lymphocytes is associated with hypertension-mediated inflammation in spontaneously hypertensive rats

BACKGROUND

Imbalances in circulating T lymphocytes play critical roles in the pathogenesis of hypertension-mediated inflammation. Connexins (Cxs) in immune cells are involved in the maintenance of homeostasis of T lymphocytes. However, the association between Cxs in peripheral blood T lymphocytes and hypertension-mediated inflammation remains unknown. This study was designed to investigate the role of Cxs in T lymphocytes in hypertension-mediated inflammation in spontaneously hypertensive rats (SHRs).

METHODS

The systolic blood pressure (SBP) in Wistar-Kyoto (WKY) rats and SHRs was monitored using the tail-cuff method. The serum cytokine level was determined using ELISA. The proportions of different T-lymphocyte subtypes in the peripheral blood, the expressions of Cx40/Cx43 in the T-cell subtypes, and the gap junctional intracellular communication (GJIC) of peripheral blood lymphocytes were measured using flow cytometry (FC). The accumulations of Cx40/Cx43 at the plasma membrane and/or in the cytoplasm were determined using immunofluorescence staining. The in vitro mRNA levels of cytokines and GJIC in the peripheral blood lymphocytes were respectively examined using real-time PCR and FC after treatment with Gap27 and/or concanavalin A (Con A).

RESULTS

The percentage of CD4+ T cells and the CD4+/CD8+ ratio were high, and the accumulation or expressions of Cx40/Cx43 in the peripheral blood lymphocytes in SHRs were higher than in those of WKY rats. The percentage of CD8+ and CD4+CD25+ T cells was lower in SHRs. The serum levels of IL-2, IL-4 and IL-6 from SHRs were higher than those from WKY rats, and the serum levels of IL-2 and IL-6 positively correlated with the expression of Cx40/Cx43 in the peripheral blood T lymphocytes from SHRs. The peripheral blood lymphocytes of SHRs exhibited enhanced GJIC. Cx43-based channel inhibition, which was mediated by Gap27, remarkably reduced GJIC in lymphocytes, and suppressed IL-2 and IL-6 mRNA expressions in Con A stimulated peripheral blood lymphocytes.

CONCLUSIONS

Our data suggest that Cxs may be involved in the regulation of T-lymphocyte homeostasis and the production of cytokines. A clear association was found between alterations in Cxs expression or in Cx43-based GJIC and hypertension-mediated inflammation.

Sympathetic neurotransmission in spleens from aging Brown-Norway rats subjected to reduced sympathetic tone

Senescence of innate and adaptive responses and low-grade inflammation (inflammaging) hallmarks normal aging, which increases vulnerability to infectious diseases, autoimmunity and cancer. In normal aging, sympathetic dysregulation contributes to the dysregulation of innate and adaptive immunity and inflammaging. Sympathetic innervation of immune cells in secondary immune organs regulates immune responses. Previously in Fischer 344 (F344) rats, we reported an age-related increase in sympathetic tone and sympathetic dysfunction in beta-adrenergic receptor (AR) signaling of splenic lymphocytes that contributes to immune senescence, although the responsible mechanisms remains unexplored. In this study, we extend our previous findings using the much longer-lived Brown-Norway (BN) rats, whose behavior and immune response profile differ strikingly from F344 rats. Here, we investigated whether increased sympathetic nerve activity (SNA) in the aging spleen contributes to age-related sympathetic neuropathy and altered neurotransmission in splenic lymphocytes in BN rats. Fifteen-month male BN rats received 0, 0.5 or 1.5 μg/kg/day rilmenidine intraperitoneally for 90 days to lower sympathetic tone. Untreated young and age-matched rats controlled for effects of age. We found that elevated SNA in the aging BN rat spleen does not contribute significantly to sympathetic neuropathy or the aging-induced impairment of canonical β-AR signal transduction. Despite the rilmenidine-induced increase in β-AR expression, splenocyte c-AMP production was comparable with age-matched controls, thus dampening nerve activity had no effect on receptor coupling to adenylate cyclase. Understanding how aging affects neuroimmune regulation in healthy aging rodent models may eventually lead to strategies that improve health in aging populations vulnerable to immunosenescence and low-grade systemic inflammation.

Mechanisms in hypertension and target organ damage: Is the role of the thymus key? (Review)

A variety of cells and cytokines have been shown to be involved in the whole process of hypertension. Data from experimental and clinical studies on hypertension have confirmed the key roles of immune cells and inflammation in the process. Dysfunction of the thymus, which modulates the development and maturation of lymphocytes, has been shown to be associated with the severity of hypertension. Furthermore, gradual atrophy, functional decline or loss of the thymus has been revealed to be associated with aging. The restoration or enhancement of thymus function via upregulation in the expression of thymus transcription factors forkhead box N1 or thymus transplantation may provide an option to halt or reverse the pathological process of hypertension. Therefore, the thymus may be key in hypertension and associated target organ damage, and may provide a novel treatment strategy for the clinical management of patients with hypertension in addition to different commercial drugs. The purpose of this review is to summarize and discuss the advances in our understanding of the impact of thymus function on hypertension from data from animal and human studies, and the potential mechanisms.

Central blockade of NLRP3 reduces blood pressure via regulating inflammation microenvironment and neurohormonal excitation in salt-induced prehypertensive rats

BACKGROUND

Inflammation has been implicated in the development of cardiovascular disease. We determined whether nod-like receptor with pyrin domain containing 3 (NLRP3) involved in the process of prehypertension, central blockade of NLRP3 decreased inflammation reaction, regulated neurohormonal excitation, and delayed the progression of prehypertension.

METHODS

Prehypertensive rats were induced by 8% salt diet. The rats on high-salt diet for 1 month were administered a specific NLRP3 blocker in the hypothalamic paraventricular nucleus (PVN) for 4 weeks. ELISA, western blotting, immunohistochemistry, and flow cytometry were used to measure NLRP3 cascade proteins, pro-inflammation cytokines (PICs), chemokine ligand 2 (CCL2), C-X-C chemokine receptor type 3 (CXCR3), vascular cell adhesion molecule 1 (VCAM-1), neurotransmitters, and leukocytes count detection, respectively.

RESULTS

NLRP3 expression in PVN was increased significantly in prehypertensive rats, accompanied by increased number of microglia, CD4⁺, CD8⁺ T cell, and CD8⁺ microglia. Expressions of PICs, CCL2, CXCR3, and VCAM-1 significantly increased. The balance between 67-kDa isoform of glutamate decarboxylase (GAD67) and tyrosine hydroxylase (TH) was damaged. Plasma norepinephrine (NE) in prehypertensive rats was increased and gamma-aminobutyric acid (GABA) was reduced. NLRP3 blockade significantly decreased blood pressure, reduced PICs, CCL2, VCAM-1 expression in PVN, and restored neurotransmitters. Blood pressure and inflammatory markers were upregulated after termination of central blockage NLRP3.

CONCLUSIONS

Salt-induced prehypertension is partly due to the role of NLRP3 in PVN. Blockade of brain NLRP3 attenuates prehypertensive response, possibly via downregulating the cascade reaction triggered by inflammation and restoring the balance of neurotransmitters.

Macrophages under pressure: the role of macrophage polarization in hypertension

Hypertension is a multifactorial disease involving the nervous, renal, and cardiovascular systems. Macrophages are the most abundant and ubiquitous immune cells, placing them in a unique position to serve as key mediators between these components. The polarization of macrophages confers vast phenotypic and functional plasticity, allowing them to act as proinflammatory, homeostatic, and anti-inflammatory agents. Key differences between the M1 and M2 phenotypes, the 2 subsets at the extremes of this polarization spectrum, place macrophages at a juncture to mediate many mechanisms involved in the pathogenesis of hypertension. Neuronal and non-neuronal regulation of the immune system, that is, the "neuroimmuno" axis, plays an integral role in the polarization of macrophages. In hypertension, the neuroimmuno axis results in synchronization of macrophage mobilization from immune cell reservoirs and their chemotaxis, via increased expression of chemoattractants, to end organs critical in the development of hypertension. This complicated system is largely coordinated by the dichotomous actions of the autonomic neuronal and non-neuronal activation of cholinergic, adrenergic, and neurohormonal receptors on macrophages, leading to their ability to "switch" between phenotypes at sites of active inflammation. Data from experimental models and human studies are in concordance with each other and support a central role for macrophage polarization in the pathogenesis of hypertension.

The immunology of hypertension

Emerging evidence indicates that both innate and adaptive immunity contribute to hypertension. Efforts to understand mechanisms of immune activation in hypertension are defining not only new mechanisms of disease but also new therapeutic options for its treatment.

Although systemic hypertension affects a large proportion of the population, its etiology remains poorly defined. Emerging evidence supports the concept that immune cells become activated and enter target organs, including the vasculature and the kidney, in this disease. Mediators released by these cells, including reactive oxygen species, metalloproteinases, cytokines, and antibodies promote dysfunction of the target organs and cause damage. In vessels, these factors enhance constriction, remodeling, and rarefaction. In the kidney, these mediators increase expression and activation of sodium transporters, and cause interstitial fibrosis and glomerular injury. Factors common to hypertension, including oxidative stress, increased interstitial sodium, cytokine production, and inflammasome activation promote immune activation in hypertension. Recent data suggest that isolevuglandin-modified self-proteins in antigen-presenting cells are immunogenic, promoting cytokine production by the cells in which they are formed and T cell activation. Efforts to prevent and reverse immune activation may prove beneficial in preventing the long-term sequelae of hypertension and its related cardiovascular diseases.

Autonomic regulation of the immune system in cardiovascular diseases

The autonomic nervous system is a powerful regulator of circulatory adjustments to acute hemodynamic stresses. Here we focus on new concepts that emphasize the chronic influence of the sympathetic and parasympathetic systems on cardiovascular pathology. The autonomic neurohumoral system can dramatically influence morbidity and mortality from cardiovascular disease through newly discovered influences on the innate and adaptive immune systems. Specifically, the end-organ damage in heart failure or hypertension may be worsened or alleviated by pro- or anti-inflammatory pathways of the immune system, respectively, that are activated through neurohumoral transmitters. These concepts provide a major new perspective on potentially life-saving therapeutic interventions in the deadliest of diseases.

Salt, Hypertension, and Immunity

The link between inappropriate salt retention in the kidney and hypertension is well recognized. However, growing evidence suggests that the immune system can play surprising roles in sodium homeostasis, such that the study of inflammatory cells and their secreted effectors has provided important insights into salt sensitivity. As part of the innate immune system, myeloid cells have diverse roles in blood pressure regulation, ranging from prohypertensive actions in the kidney, vasculature, and brain, to effects in the skin that attenuate blood pressure elevation. In parallel, T lymphocyte subsets, as key constituents of the adaptive immune compartment, have variable effects on renal sodium handling and the hypertensive response, accruing from the functions of the cytokines that they produce. Conversely, salt can directly modulate the phenotypes of myeloid and T cells, illustrating bidirectional regulatory mechanisms through which sodium and the immune system coordinately impact blood pressure. This review details the complex interplay between myeloid cells, T cells, and salt in the pathogenesis of essential hypertension.

Recent Advances in Immunity and Hypertension

Persistent immune system activation plays an important role in the development of various forms of hypertension. Activation of the innate immune system, inflammation, and subsequent adaptive immune system response causing end-organ injury and dysfunction ultimately leads to hypertension and its associated sequelae including coronary artery disease, heart failure, stroke, and chronic kidney disease. In this review, we will provide updates on the innate and adaptive immune cells involved in hypertension, the current understanding of how the immune system gets activated, and examine the recently discovered mechanisms involved in several forms of experimental hypertension.

Role of the Immune System in Hypertension

High blood pressure is present in more than one billion adults worldwide and is the most important modifiable risk factor of death resulting from cardiovascular disease. While many factors contribute to the pathogenesis of hypertension, a role of the immune system has been firmly established by a large number of investigations from many laboratories around the world. Immunosuppressive drugs and inhibition of individual cytokines prevent or ameliorate experimental hypertension, and studies in genetically-modified mouse strains have demonstrated that lymphocytes are necessary participants in the development of hypertension and in hypertensive organ injury. Furthermore, immune reactivity may be the driving force of hypertension in autoimmune diseases. Infiltration of immune cells, oxidative stress, and stimulation of the intrarenal angiotensin system are induced by activation of the innate and adaptive immunity. High blood pressure results from the combined effects of inflammation-induced impairment in the pressure natriuresis relationship, dysfunctional vascular relaxation, and overactivity of the sympathetic nervous system. Imbalances between proinflammatory effector responses and anti-inflammatory responses of regulatory T cells to a large extent determine the severity of inflammation. Experimental and human studies have uncovered autoantigens (isoketal-modified proteins and heat shock protein 70) of potential clinical relevance. Further investigations on the immune reactivity in hypertension may result in the identification of new strategies for the treatment of the disease.

Oxidative Stress and Hypertensive Diseases

It has become clear that reactive oxygen species (ROS) contribute to the development of hypertension via myriad effects. ROS are essential for normal cell function; however, they mediate pathologic changes in the brain, the kidney, and blood vessels that contribute to the genesis of chronic hypertension. There is also emerging evidence that ROS contribute to immune activation in hypertension. This article discusses these events and how they coordinate to contribute to hypertension and its consequent end-organ damage.

A cholinergic-sympathetic pathway primes immunity in hypertension and mediates brain-to-spleen communication

The crucial role of the immune system in hypertension is now widely recognized. We previously reported that hypertensive challenges couple the nervous drive with immune system activation, but the physiological and molecular mechanisms of this connection are unknown. Here, we show that hypertensive challenges activate splenic sympathetic nerve discharge to prime immune response. More specifically, a vagus-splenic nerve drive, mediated by nicotinic cholinergic receptors, links the brain and spleen. The sympathetic discharge induced by hypertensive stimuli was absent in both coeliac vagotomized mice and in mice lacking α7nAChR, a receptor typically expressed by peripheral ganglionic neurons. This cholinergic-sympathetic pathway is necessary for T cell activation and egression on hypertensive challenges. In addition, we show that selectively thermoablating the splenic nerve prevents T cell egression and protects against hypertension. This novel experimental procedure for selective splenic denervation suggests new clinical strategies for resistant hypertension.

Immune system participates in the development of high blood pressure. Here the authors show that cholinergic-sympathetic pathway mediated by the α7nAChR receptor and the activation of splenic T cells prime immunity during hypertension and that selective splenic denervation protects against the onset of hypertension in mice.

Brain-Gut-Bone Marrow Axis: Implications for Hypertension and Related Therapeutics

Hypertension is the most prevalent modifiable risk factor for cardiovascular disease and disorders directly influencing cardiovascular disease morbidity and mortality, such as diabetes mellitus, chronic kidney disease, obstructive sleep apnea, etc. Despite aggressive attempts to influence lifestyle modifications and advances in pharmacotherapeutics, a large percentage of patients still do not achieve recommended blood pressure control worldwide. Thus, we think that mechanism-based novel strategies should be considered to significantly improve control and management of hypertension. The overall objective of this review is to summarize implications of peripheral- and neuroinflammation as well as the autonomic nervous system-bone marrow communication in hematopoietic cell homeostasis and their impact on hypertension pathophysiology. In addition, we discuss the novel and emerging field of intestinal microbiota and roles of gut permeability and dysbiosis in cardiovascular disease and hypertension. Finally, we propose a brain-gut-bone marrow triangular interaction hypothesis and discuss its potential in the development of novel therapies for hypertension.

Immunological Aspects of Hypertension

Hypertension is a leading cause of morbidity and mortality worldwide, being the major risk factor for stroke, heart failure and kidney diseases. During past decades, several therapies have been developed to afford an optimal regulation of blood pressure levels. However, the prevalence of uncontrolled hypertension still represents an unsolved problem, with a number of patients resistant as well to all ongoing antihypertensive treatments, raising unsolved mechanistic challenges. In the last years, the most attractive novelty in hypertension research postulated that immune system may have a crucial role in blood pressure elevation, as well as in end-organ damage. Here we briefly review the most important contribution revealing the role of innate and adaptive immune system in hypertension. Moreover, we discuss evidence showing that, in the regulation of body hemodynamics, the immune system and the autonomic nervous systems serve as two major sensory organs whose interaction is crucial for blood pressure increase and target organ damage in hypertension.

Dysregulation of T cell subsets in the pathogenesis of hypertension

Essential hypertension (EH) and its complications have had a severe impact on public health. However, the underlying mechanisms of the pathogenesis of EH remain largely unknown. Recent investigations, predominantly in rats and mice, have provided evidence that dysregulation of distinct functions of T lymphocyte subsets is a potentially important mechanism in the pathogenesis of hypertension. We critically reviewed recent findings and propose an alternative explanation on the understanding of dysfunctional T lymphocyte subsets in the pathogenesis of hypertension. The hypothesis is that hypertensive stimuli, directly and indirectly, increase local IL-6 levels in the cardiovascular system and kidney, which may promote peripheral imbalance in the differentiation and ratio of Th17 and T regulatory cells. This results in increased IL-17 and decreased IL-10 in perivascular adipose tissue and adventitia contributing to the development of hypertension in experimental animal models. Further investigation in the field is warranted to inform new translational advances that will promote to understand the pathogenesis of EH and develop novel approaches to prevent and treat EH.

Novel Pathophysiological Mechanisms in Hypertension

Hypertension is the most common disease affecting humans and imparts a significant cardiovascular and renal risk to patients. Extensive research over the past few decades has enhanced our understanding of the underlying mechanisms in hypertension. However, in most instances, the cause of hypertension in a given patient continues to remain elusive. Nevertheless, achieving aggressive blood pressure goals significantly reduces cardiovascular morbidity and mortality, as demonstrated in the recently concluded SPRINT trial. Since a large proportion of patients still fail to achieve blood pressure goals, knowledge of novel pathophysiologic mechanisms and mechanism based treatment strategies is crucial. The following chapter will review the novel pathophysiological mechanisms in hypertension, with a focus on role of immunity, inflammation and vascular endothelial homeostasis. The therapeutic implications of these mechanisms will be discussed where applicable.

Sympathetic-mediated activation versus suppression of the immune system: consequences for hypertension

It is generally well-accepted that the immune system is a significant contributor in the pathogenesis of hypertension. Specifically, activated and pro-inflammatory T-lymphocytes located primarily in the vasculature and kidneys appear to have a causal role in exacerbating elevated blood pressure. It has been proposed that increased sympathetic nerve activity and noradrenaline outflow associated with hypertension may be primary contributors to the initial activation of the immune system early in the disease progression. However, it has been repeatedly demonstrated in many different human and experimental diseases that sympathoexcitation is immunosuppressive in nature. Moreover, human hypertensive patients have demonstrated increased susceptibility to secondary immune insults like infections. Thus, it is plausible, and perhaps even likely, that in diseases like hypertension, specific immune cells are activated by increased noradrenaline, while others are in fact suppressed. We propose a model in which this differential regulation is based upon activation status of the immune cell as well as the resident organ. With this, the concept of global immunosuppression is obfuscated as a viable target for hypertension treatment, and we put forth the concept of focused organ-specific immunotherapy as an alternative option.

Arterial Hypertension Aggravates Innate Immune Responses after Experimental Stroke

Arterial hypertension is not only the leading risk factor for stroke, but also attributes to impaired recovery and poor outcome. The latter could be explained by hypertensive vascular remodeling that aggravates perfusion deficits and blood–brain barrier disruption. However, besides vascular changes, one could hypothesize that activation of the immune system due to pre-existing hypertension may negatively influence post-stroke inflammation and thus stroke outcome. To test this hypothesis, male adult spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto rats (WKYs) were subjected to photothrombotic stroke. One and 3 days after stroke, infarct volume and functional deficits were evaluated by magnetic resonance imaging and behavioral tests. Expression levels of adhesion molecules and chemokines along with the post-stroke inflammatory response were analyzed by flow cytometry, quantitative real-time PCR and immunohistochemistry in rat brains 4 days after stroke. Although comparable at day 1, lesion volumes were significantly larger in SHR at day 3. The infarct volume showed a strong correlation with the amount of CD45 highly positive leukocytes present in the ischemic hemispheres. Functional deficits were comparable between SHR and WKY. Brain endothelial expression of intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), and P-selectin (CD62P) was neither increased by hypertension nor by stroke. However, in SHR, brain infiltrating myeloid leukocytes showed significantly higher surface expression of ICAM-1 which may augment leukocyte transmigration by leukocyte–leukocyte interactions. The expression of chemokines that primarily attract monocytes and granulocytes was significantly increased by stroke and, furthermore, by hypertension. Accordingly, ischemic hemispheres of SHR contain considerably higher numbers of monocytes, macrophages and granulocytes. Exacerbated brain inflammation in SHR may finally be responsible for larger infarct volumes. These findings provide an immunological explanation for the epidemiological observation that existing hypertension negatively affects stroke outcome and mortality.

Renal Denervation Prevents Immune Cell Activation and Renal Inflammation in Angiotensin II-Induced Hypertension

RATIONALE

Inflammation and adaptive immunity play a crucial role in the development of hypertension. Angiotensin II and probably other hypertensive stimuli activate the central nervous system and promote T-cell activation and end-organ damage in peripheral tissues.

OBJECTIVE

To determine if renal sympathetic nerves mediate renal inflammation and T-cell activation in hypertension.

METHODS AND RESULTS

Bilateral renal denervation using phenol application to the renal arteries reduced renal norepinephrine levels and blunted angiotensin II-induced hypertension. Bilateral renal denervation also reduced inflammation, as reflected by decreased accumulation of total leukocytes, T cells, and both CD4+ and CD8+ T cells in the kidney. This was associated with a marked reduction in renal fibrosis, albuminuria, and nephrinuria. Unilateral renal denervation, which partly attenuated blood pressure, only reduced inflammation in the denervated kidney, suggesting that this effect is pressure independent. Angiotensin II also increased immunogenic isoketal-protein adducts in renal dendritic cells (DCs) and increased surface expression of costimulation markers and production of interleukin (IL)-1α, IL-1β, and IL-6 from splenic DCs. Norepinephrine also dose dependently stimulated isoketal formation in cultured DCs. Adoptive transfer of splenic DCs from angiotensin II-treated mice primed T-cell activation and hypertension in recipient mice. Renal denervation prevented these effects of hypertension on DCs. In contrast to these beneficial effects of ablating all renal nerves, renal afferent disruption with capsaicin had no effect on blood pressure or renal inflammation.

CONCLUSIONS

Renal sympathetic nerves contribute to DC activation, subsequent T-cell infiltration and end-organ damage in the kidney in the development of hypertension.

The immune system and hypertension

A powerful interaction between the autonomic and the immune systems plays a prominent role in the initiation and maintenance of hypertension and significantly contributes to cardiovascular pathology, end-organ damage and mortality. Studies have shown consistent association between hypertension, proinflammatory cytokines and the cells of the innate and adaptive immune systems. The sympathetic nervous system, a major determinant of hypertension, innervates the bone marrow, spleen and peripheral lymphatic system and is proinflammatory, whereas the parasympathetic nerve activity dampens the inflammatory response through α7-nicotinic acetylcholine receptors. The neuro-immune synapse is bidirectional as cytokines may enhance the sympathetic activity through their central nervous system action that in turn increases the mobilization, migration and infiltration of immune cells in the end organs. Kidneys may be infiltrated by immune cells and mesangial cells that may originate in the bone marrow and release inflammatory cytokines that cause renal damage. Hypertension is also accompanied by infiltration of the adventitia and perivascular adipose tissue by inflammatory immune cells including macrophages. Increased cytokine production induces myogenic and structural changes in the resistance vessels, causing elevated blood pressure. Cardiac hypertrophy in hypertension may result from the mechanical afterload and the inflammatory response to resident or migratory immune cells. Toll-like receptors on innate immune cells function as sterile injury detectors and initiate the inflammatory pathway. Finally, abnormalities of innate immune cells and the molecular determinants of their activation that include toll-like receptor, adrenergic, cholinergic and AT1 receptors can define the severity of inflammation in hypertension. These receptors are putative therapeutic targets.

Dexmedetomidine and regulation of splenic sympathetic nerve discharge in aged F344 rats

Sedatives influence the immune system and centrally-acting alpha2-adrenergic receptor agonists, including Dexmedetomidine (Dex), modulate sympathetic nerve discharge (SND). Because sedatives are used under medical conditions that include elderly patients, and because advancing age attenuates SND responsivity to various interventions, we tested the hypothesis that splenic sympathoinhibitory responses to Dex would be attenuated in aged compared with young Fischer 344 rats. Dex-mediated reductions in splenic SND were similar in aged and young baroreceptor-intact and -denervated rats, indicating that SND changes to Dex administration occur in an age-independent manner. These findings provide new information regarding interactions between alpha2-adrenergic agonists, advanced age, and SND regulation.

Autonomic nervous system and immune system interactions

The present review assesses the current state of literature defining integrative autonomic-immune physiological processing, focusing on studies that have employed electrophysiological, pharmacological, molecular biological, and central nervous system experimental approaches. Central autonomic neural networks are informed of peripheral immune status via numerous communicating pathways, including neural and non-neural. Cytokines and other immune factors affect the level of activity and responsivity of discharges in sympathetic and parasympathetic nerves innervating diverse targets. Multiple levels of the neuraxis contribute to cytokine-induced changes in efferent parasympathetic and sympathetic nerve outflows, leading to modulation of peripheral immune responses. The functionality of local sympathoimmune interactions depends on the microenvironment created by diverse signaling mechanisms involving integration between sympathetic nervous system neurotransmitters and neuromodulators; specific adrenergic receptors; and the presence or absence of immune cells, cytokines, and bacteria. Functional mechanisms contributing to the cholinergic anti-inflammatory pathway likely involve novel cholinergic-adrenergic interactions at peripheral sites, including autonomic ganglion and lymphoid targets. Immune cells express adrenergic and nicotinic receptors. Neurotransmitters released by sympathetic and parasympathetic nerve endings bind to their respective receptors located on the surface of immune cells and initiate immune-modulatory responses. Both sympathetic and parasympathetic arms of the autonomic nervous system are instrumental in orchestrating neuroimmune processes, although additional studies are required to understand dynamic and complex adrenergic-cholinergic interactions. Further understanding of regulatory mechanisms linking the sympathetic nervous, parasympathetic nervous, and immune systems is critical for understanding relationships between chronic disease development and immune-associated changes in autonomic nervous system function.

CNS inflammation and bone marrow neuropathy in type 1 diabetes

By using pseudorabies virus expressing green fluorescence protein, we found that efferent bone marrow-neural connections trace to sympathetic centers of the central nervous system in normal mice. However, this was markedly reduced in type 1 diabetes, suggesting a significant loss of bone marrow innervation. This loss of innervation was associated with a change in hematopoiesis toward generation of more monocytes and an altered diurnal release of monocytes in rodents and patients with type 1 diabetes. In the hypothalamus and granular insular cortex of mice with type 1 diabetes, bone marrow-derived microglia/macrophages were activated and found at a greater density than in controls. Infiltration of CD45(+)/CCR2(+)/GR-1(+)/Iba-1(+) bone marrow-derived monocytes into the hypothalamus could be mitigated by treatment with minocycline, an anti-inflammatory agent capable of crossing the blood-brain barrier. Our studies suggest that targeting central inflammation may facilitate management of microvascular complications.

The pathophysiology of hypertension in patients with obesity

The combination of obesity and hypertension is associated with high morbidity and mortality because it leads to cardiovascular and kidney disease. Potential mechanisms linking obesity to hypertension include dietary factors, metabolic, endothelial and vascular dysfunction, neuroendocrine imbalances, sodium retention, glomerular hyperfiltration, proteinuria, and maladaptive immune and inflammatory responses. Visceral adipose tissue also becomes resistant to insulin and leptin and is the site of altered secretion of molecules and hormones such as adiponectin, leptin, resistin, TNF and IL-6, which exacerbate obesity-associated cardiovascular disease. Accumulating evidence also suggests that the gut microbiome is important for modulating these mechanisms. Uric acid and altered incretin or dipeptidyl peptidase 4 activity further contribute to the development of hypertension in obesity. The pathophysiology of obesity-related hypertension is especially relevant to premenopausal women with obesity and type 2 diabetes mellitus who are at high risk of developing arterial stiffness and endothelial dysfunction. In this Review we discuss the relationship between obesity and hypertension with special emphasis on potential mechanisms and therapeutic targeting that might be used in a clinical setting.

Dual opposing roles of adaptive immunity in hypertension

Hypertension involves remodelling and inflammation of the arterial wall. Interactions between vascular and inflammatory cells play a critical role in disease initiation and progression. T effector and regulatory lymphocytes, members of the adaptive immune system, play contrasting roles in hypertension. Signals from the central nervous system and the innate immune system antigen-presenting cells activate T effector lymphocytes and promote their differentiation towards pro-inflammatory T helper (Th) 1 and Th17 phenotypes. Th1 and Th17 effector cells, via production of pro-inflammatory mediators, participate in the low-grade inflammation that leads to blood pressure elevation and end-organ damage. T regulatory lymphocytes, on the other hand, counteract hypertensive effects by suppressing innate and adaptive immune responses. The present review summarizes and discusses the adaptive immune mechanisms that participate in the pathophysiology in hypertension.