Advanced Magnetic Resonance Imaging to Define the Microvascular Injury Driven by Neuroinflammation in the Brain of a Mouse Model of Hypertension.

BACKGROUND: Hypertension is one of the main risk factors for dementia and cognitive impairment. METHODS: We used the model of transverse aortic constriction to induce chronic pressure overload in mice. We characterized brain injury by advanced translational applications of magnetic resonance imaging. In parallel, we analyzed peripheral target organ damage induced by chronic pressure overload by ultrasonography. Microscopical characterization of brain vasculature was performed as well, together with the analysis of immune and inflammatory markers. RESULTS: We identified a specific structural, microstructural, and functional brain injury. In particular, we highlighted a regional enlargement of the hypothalamus, microstructural damage in the white matter of the fimbria, and a reduction of the cerebral blood flow. A parallel analysis performed by confocal microscopy revealed a correspondent tissue damage evidenced by a reduction of cerebral capillary density, paired with loss of pericyte coverage. We assessed cognitive impairment and cardiac damage induced by hypertension to perform correlation analyses with the brain injury severity. At the mechanistic level, we found that CD8+T cells, producing interferon-γ, infiltrated the brain of hypertensive mice. By neutralizing this proinflammatory cytokine, we obtained a rescue of the phenotype, demonstrating their crucial role in establishing the microvascular damage. CONCLUSIONS: Overall, we have used translational tools to comprehensively characterize brain injury in a mouse model of hypertension induced by chronic pressure overload. We have identified early cerebrovascular damage in hypertensive mice, sustained by CD8+IFN-γ+T lymphocytes, which fuel neuroinflammation to establish the injury of brain capillaries.

Mouse models of cerebral injury and cognitive impairment in hypertension.

Hypertension is a major risk factor for dementia, including both vascular and neurodegenerative etiologies. With the original aim of studying the effect of blood pressure elevation on canonical target organs of hypertension as the heart, the vasculature or the kidneys, several experimental models of hypertension have sprouted during the years. With the more recent interest of understanding the cerebral injury burden caused by hypertension, it is worth understanding how the main models of hypertension or localized cerebral hypertension stand in the field of hypertension-induced cerebral injury and cognitive impairment. With this review we will report main genetic, pharmacological and surgical models of cognitive impairment induced by hypertension, summarizing how each specific category and model can improve our understanding of the complex phenomenon of cognitive loss of vascular etiology.

Interferon-γ drives macrophage reprogramming, cerebrovascular remodelling, and cognitive dysfunction in a zebrafish and a mouse model of ion imbalance and pressure overload.

AIMS: Dysregulated immune response contributes to inefficiency of treatment strategies to control hypertension and reduce the risk of end-organ damage. Uncovering the immune pathways driving the transition from the onset of hypertensive stimulus to the manifestation of multi-organ dysfunction are much-needed insights for immune targeted therapy. METHODS AND RESULTS: To aid visualization of cellular events orchestrating multi-organ pathogenesis, we modelled hypertensive cardiovascular remodelling in zebrafish. Zebrafish larvae exposed to ion-poor environment exhibited rapid angiotensinogen up-regulation, followed by manifestation of arterial hypertension and cardiac remodelling that recapitulates key characteristics of incipient heart failure with preserved ejection fraction. In the brain, time-lapse imaging revealed the occurrence of cerebrovascular regression through endothelial retraction and migration in response to the ion-poor treatment. This phenomenon is associated with macrophage/microglia-endothelial contacts and endothelial junctional retraction. Cytokine and transcriptomic profiling identified systemic up-regulation of interferon-γ and interleukin 1ß and revealed altered macrophage/microglia transcriptional programme characterized by suppression of innate immunity and vasculo/neuroprotective gene expression. Both zebrafish and a murine model of pressure overload-induced brain damage demonstrated that the brain pathology and macrophage/microglia phenotypic alteration are dependent on interferon-γ signalling. In zebrafish, interferon-γ receptor 1 mutation prevents cerebrovascular remodelling and dysregulation of macrophage/microglia transcriptomic profile. Supplementation of bone morphogenetic protein 5 identified from the transcriptomic approach as a down-regulated gene in ion-poor-treated macrophages/microglia that is rescued by interferon-γ blockage, mitigated cerebral microvessel loss. In mice subjected to transverse aortic constriction-induced pressure overload, typically developing cerebrovascular injury, neuroinflammation, and cognitive dysfunction, interferon-γ neutralization protected them from blood-brain barrier disruption, cerebrovascular rarefaction, and cognitive decline. CONCLUSIONS: These findings uncover cellular and molecular players of an immune pathway communicating hypertensive stimulus to structural and functional remodelling of the brain and identify anti-interferon-γ treatment as a promising intervention strategy capable of preventing pressure overload-induced damage of the cerebrovascular and nervous systems.

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 targets7-9, 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 afferents10-14 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.

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.

Chronic 3D Vascular-Immune Interface Established by Coculturing Pressurized Resistance Arteries and Immune Cells.

[Figure: see text].

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.

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

Angiotensin II (AngII) is a peptide hormone that affects the cardiovascular system, not only through typical effects on the vasculature, kidneys, and heart, but also through less understood roles mediated by the brain and the immune system. Here, we address the hard-wired neural connections within the autonomic nervous system that modulate splenic immunity. Chronic AngII infusion triggers burst firing of the vagus nerve celiac efferent, an effect correlated with noradrenergic activation in the spleen and T cell egress. Bioelectronic stimulation of the celiac vagus nerve, in the absence of other challenges and independently from afferent signals to the brain, evokes the noradrenergic splenic pathway to promote release of a growth factor mediating neuroimmune crosstalk, placental growth factor (PlGF), and egress of CD8 effector T cells. Our findings also indicate that the neuroimmune interface mediated by PlGF and necessary for transducing the neural signal into an effective immune response is dependent on α-adrenergic receptor signaling.

Loss of EMILIN-1 Enhances Arteriolar Myogenic Tone Through TGF-ß (Transforming Growth Factor-ß)-Dependent Transactivation of EGFR (Epidermal Growth Factor Receptor) and Is Relevant for Hypertension in Mice and Humans.

Objective- EMILIN-1 (elastin microfibrils interface located protein-1) protein inhibits pro-TGF-ß (transforming growth factor-ß) proteolysis and limits TGF-ß bioavailability in vascular extracellular matrix. Emilin1-/- null mice display increased vascular TGF-ß signaling and are hypertensive. Because EMILIN-1 is expressed in vessels from embryonic life to adulthood, we aimed at unravelling whether the hypertensive phenotype of Emilin1-/- null mice results from a developmental defect or lack of homeostatic role in the adult. Approach and Results- By using a conditional gene targeting inactivating EMILIN-1 in smooth muscle cells of adult mice, we show that increased blood pressure in mice with selective smooth muscle cell ablation of EMILIN-1 depends on enhanced myogenic tone. Mechanistically, we unveil that higher TGF-ß signaling in smooth muscle cells stimulates HB-EGF (heparin-binding epidermal growth factor) expression and subsequent transactivation of EGFR (epidermal growth factor receptor). With increasing intraluminal pressure in resistance arteries, the cross talk established by TGF-ß and EGFR signals recruits TRPC6 (TRP [transient receptor potential] classical type 6) and TRPM4 (TRP melastatin type 4) channels, lastly stimulating voltage-dependent calcium channels and potentiating myogenic tone. We found reduced EMILIN-1 and enhanced myogenic tone, dependent on increased TGF-ß-EGFR signaling, in resistance arteries from hypertensive patients. Conclusions- Taken together, our findings implicate an unexpected role of the TGF-ß-EGFR pathway in hypertension with current translational perspectives.

The Interactions of the Immune System and the Brain in Hypertension.

PURPOSE OF REVIEW: Hypertension still represents a huge health problem, causing death and disability and rising at epidemic levels worldwide. The availability of a vast array of antihypertensive therapeutic strategies still fails to adequately treat significant fractions of refractory patients. The possible explanation to this disappointing evidence should be ascribed to the fact that myriad of mechanisms contribute to onset and maintenance of hypertension. Although we have been able to develop strategies aimed at counteracting the single mechanisms identified as master regulators of blood pressure, we still lack strategies capable to approach at the complex interactions established among the different pathophysiological mechanisms. RECENT FINDINGS: One of the most intriguing pathophysiological interactions in hypertension emerged in the very last years is the one established between the autonomic nervous system and immunity. Here we briefly review the most important contributions revealing neural modulation of immunity in hypertension and how this novel concept is integrated in the already known multitude of regulations exerted by the autonomic nervous system in typical organs involved in blood pressure regulation.

Effects of a new nutraceutical combination on cognitive function in hypertensive patients.

BACKGROUND: Chronic increased arterial blood pressure has been associated with executive dysfunction, slowing of attention and mental processing speed, and later with memory deficits. Due to the absence of a concrete therapeutic approach to this pathophysiological process, in the last decades there has been an increasing interest in the use of nutraceuticals, especially those with antioxidant properties, which own strong neuroprotective potential, that may help to improve cognitive function and to delay the onset of dementia. RESULTS: We evaluated the effects of the treatment with a new nutraceutical preparation containing different molecules with potent antioxidant properties (AkP05, IzzeK®) and placebo on a cohort of thirty-six hypertensive patients. At baseline, neuropsychological evaluation, arterial stiffness and biochemical parameters of the subjects were comparable. After 6 months of treatment, there was a significant reduction of the augmentation index in the AkP05-treated group. Moreover, the measurement of cognitive function, evaluated with MoCA test and Word Match Testing, showed a significant improvement in patients receiving the active treatment. In addition, the group treated with nutraceutical reached a better Stroop test score, while subjects that received placebo did not showed any improvement. Finally, a positive relationship between SBP variation and the psychometric assessment with the EQ-VAS scale was observed only in the active treatment group. CONCLUSIONS: In this study, we demonstrated that the therapy with a new nutraceutical preparation is able to significantly increase the scores of important neuropsychological tests in hypertensive patients already on satisfactory blood pressure control. Although future studies are needed to better characterize the molecular mechanisms involved, these results candidate the new nutraceutical combination as a possible therapeutic strategy to support the cerebrovascular functions and delay the onset of dementia in hypertensive patients.

Deoxycorticosterone acetate-salt hypertension activates placental growth factor in the spleen to couple sympathetic drive and immune system activation.

AIMS: Chronic increase of mineralocorticoids obtained by administration of deoxycorticosterone acetate (DOCA) results in salt-dependent hypertension in animals. Despite the lack of a generalized sympathoexcitation, DOCA-salt hypertension has been also associated to overdrive of peripheral nervous system in organs typically targeted by blood pressure (BP), as kidneys and vasculature. Aim of this study was to explore whether DOCA-salt recruits immune system by overactivating sympathetic nervous system in lymphoid organs and whether this is relevant for hypertension. METHODS AND RESULTS: To evaluate the role of the neurosplenic sympathetic drive in DOCA-salt hypertension, we challenged splenectomized mice or mice with left coeliac ganglionectomy with DOCA-salt, observing that they were both unable to increase BP. Then, we evaluated by immunofluorescence and ELISA levels of the placental growth factor (PlGF) upon DOCA-salt challenge, which significantly increased the growth factor expression, but only in the presence of an intact neurosplenic sympathetic drive. When PlGF KO mice were subjected to DOCA-salt, they were significantly protected from the increased BP observed in WT mice under same experimental conditions. In addition, absence of PlGF hampered DOCA-salt mediated T cells co-stimulation and their consequent deployment towards kidneys where they infiltrated tissue and provoked end-organ damage. CONCLUSION: Overall, our study demonstrates that DOCA-salt requires an intact sympathetic drive to the spleen for priming of immunity and consequent BP increase. The coupling of nervous system and immune cells activation in the splenic marginal zone is established through a sympathetic-mediated PlGF release, suggesting that this pathway could be a valid therapeutic target for hypertension.

Targeting Interleukin-1ß Protects from Aortic Aneurysms Induced by Disrupted Transforming Growth Factor ß Signaling.

Aortic aneurysms are life-threatening conditions with effective treatments mainly limited to emergency surgery or trans-arterial endovascular stent grafts, thus calling for the identification of specific molecular targets. Genetic studies have highlighted controversial roles of transforming growth factor ß (TGF-ß) signaling in aneurysm development. Here, we report on aneurysms developing in adult mice after smooth muscle cell (SMC)-specific inactivation of Smad4, an intracellular transducer of TGF-ß. The results revealed that Smad4 inhibition activated interleukin-1ß (IL-1ß) in SMCs. This danger signal later recruited innate immunity in the adventitia through chemokine (C-C motif) ligand 2 (CCL2) and modified the mechanical properties of the aortic wall, thus favoring vessel dilation. SMC-specific Smad4 deletion in Il1r1- or Ccr2-null mice resulted in milder aortic pathology. A chronic treatment with anti-IL-1ß antibody effectively hampered aneurysm development. These findings identify a mechanistic target for controlling the progression of aneurysms with compromised TGF-ß signaling, such as those driven by SMAD4 mutations.

The Spleen: A Hub Connecting Nervous and Immune Systems in Cardiovascular and Metabolic Diseases.

Metabolic disorders have been identified as major health problems affecting a large portion of the world population. In addition, obesity and insulin resistance are principal risk factors for the development of cardiovascular diseases. Altered immune responses are common features of both hypertension and obesity and, moreover, the involvement of the nervous system in the modulation of immune system is gaining even more attention in both pathophysiological contexts. For these reasons, during the last decades, researches focused their efforts on the comprehension of the molecular mechanisms connecting immune system to cardiovascular and metabolic diseases. On the other hand, it has been reported that in these pathological conditions, central neural pathways modulate the activity of the peripheral nervous system, which is strongly involved in onset and progression of the disease. It is interesting to notice that neural reflex can also participate in the modulation of immune functions. In this scenario, the spleen becomes the crucial hub allowing the interaction of different systems differently involved in metabolic and cardiovascular diseases. Here, we summarize the major findings that dissect the role of the immune system in disorders related to metabolic and cardiovascular dysfunctions, and how this could also be influenced by neural reflexes.

The Multifaceted Roles of PI3Kγ in Hypertension, Vascular Biology, and Inflammation.

PI3Kγ is a multifaceted protein, crucially involved in cardiovascular and immune systems. Several studies described the biological and physiological functions of this enzyme in the regulation of cardiovascular system, while others stressed its role in the modulation of immunity. Although PI3Kγ has been historically investigated for its role in leukocytes, the last decade of research also dedicated efforts to explore its functions in the cardiovascular system. In this review, we report an overview recapitulating how PI3Kγ signaling participates in the regulation of vascular functions involved in blood pressure regulation. Moreover, we also summarize the main functions of PI3Kγ in immune responses that could be potentially important in the interaction with the cardiovascular system. Considering that vascular and immune mechanisms are increasingly emerging as intertwining players in hypertension, PI3Kγ could be an intriguing pathway acting on both sides. The availability of specific inhibitors introduces a perspective of further translational research and clinical approaches that could be exploited in hypertension.

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.

Hypertension and Dementia: Epidemiological and Experimental Evidence Revealing a Detrimental Relationship.

Hypertension and dementia represent two major public health challenges worldwide, notably in the elderly population. Although these two conditions have classically been recognized as two distinct diseases, mounting epidemiological, clinical and experimental evidence suggest that hypertension and dementia are strictly intertwined. Here, we briefly report how hypertension profoundly affects brain homeostasis, both at the structural and functional level. Chronic high blood pressure modifies the cerebral vasculature, increasing the risk of Aß clearance impairment. The latter, excluding genetic etiologies, is considered one of the main causes of Aß deposition in the brain. Studies have shown that hypertension induces cerebral arterial stiffening and microvascular dysfunction, thus contributing to dementia pathophysiology. This review examines the existing and the updated literature which has attempted to explain and clarify the relationship between hypertension and dementia at the pathophysiological level.

Pathophysiological Links Among Hypertension and Alzheimer's Disease.

Genetic Alzheimer's disease (AD) accounts for only few AD cases and is almost exclusively associated to increased amyloid production in the brain. Instead, the majority of patients is affected with the AD sporadic form with typical alterations of clearance mechanisms of the brain. Most studies use engineered animal models that mimic genetic AD. Since it is emerging the existence of a pathophysiological link between cardiovascular risk factors and AD etiology, the strategy to develop animal models of vascular related AD pathology could be the key toward developing novel successful therapies. On this issue, we have demonstrated that mice that have been chronically subjected to high blood pressure show deposition of amyloid aggregates, the main histological feature of AD, and loss of memory in specific tasks. More importantly, we have identified that the hypertensive challenge increases the expression of the receptor for advanced glycated end products (RAGE), leading to beta-amyloid (Aß) deposition and learning impairment. Here, we review different murine models of hypertension, induced either pharmacologically or mechanically, leading in the long time to plaque formation in the brain parenchyma and around blood vessels. The major findings obtained till now in this particular experimental setting allow us to suggest that this appears to be a unique possibility to study the pathogenetic mechanisms of sporadic AD triggered by vascular risk factors.