Central TNF inhibition results in attenuated neurohumoral excitation in heart failure: a role for superoxide and nitric oxide

Tumor necrosis factor alpha induces NOX2-dependent reactive oxygen species production in hypothalamic paraventricular nucleus neurons following angiotensin II infusion

There is evidence that tumor necrosis factor alpha (TNFα) influences autonomic processes coordinated within the hypothalamic paraventricular nucleus (PVN), however, the signaling mechanisms subserving TNFα's actions in this brain area are unclear. In non-neuronal cell types, TNFα has been shown to play an important role in canonical NADPH oxidase (NOX2)-mediated production of reactive oxygen species (ROS), molecules also known to be critically involved in hypertension. However, little is known about the role of TNFα in NOX2-dependent ROS production in the PVN within the context of hypertension. Using dual labeling immunoelectron microscopy and dihydroethidium (DHE) microfluorography, we provide structural and functional evidence for interactions between TNFα and NOX2 in the PVN. The TNFα type 1 receptor (TNFR1), the major mediator of TNFα signaling in the PVN, was commonly co-localized with the catalytic gp91phox subunit of NOX2 in postsynaptic sites of PVN neurons. Additionally, there was an increase in dual labeled dendritic profiles following fourteen-day slow-pressor angiotensin II (AngII) infusion. Using DHE microfluorography, it was also shown that TNFα application resulted in a NOX2-dependent increase in ROS in isolated PVN neurons projecting to the spinal cord. Further, TNFα-mediated ROS production was heightened after AngII infusion. The finding that TNFR1 and gp91phox are positioned for rapid interactions, particularly in PVN-spinal cord projection neurons, provides a molecular substrate by which inflammatory signaling and oxidative stress may jointly contribute to AngII hypertension.

Vagus nerve stimulation alleviates cardiac dysfunction and inflammatory markers during heart failure in rats

Vagus nerve stimulation (VNS) is under clinical investigation as a therapy for heart failure with reduced ejection fraction (HFrEF). This study aimed to investigate its therapeutic effects on three main components of heart failure: cardiac function, cardiac remodeling and central neuroinflammation using a pressure overload (PO) rat model. Male Sprague-Dawley rats were divided into four groups: PO, PO + VNS, PO + VNS sham, and controls. All rats, except controls, underwent a PO surgery to constrict the thoracic aorta (~50 %) to induce HFrEF. Open loop VNS therapy was continuously administered to PO + VNS rats at 20 Hz, 1.0 mA for 60 days. Evaluation of cardiac function and structure via echocardiograms showed decreases in stroke volume and relative ejection fraction and increases in the internal diameter of the left ventricle during systole and diastole in PO rats (p < 0.05). However, these PO-induced adverse changes were alleviated with VNS therapy. Additionally, PO rats exhibited significant increases in myocyte cross sectional areas indicating hypertrophy, along with significant increases in myocardial fibrosis and apoptosis, all of which were reversed by VNS therapy (p < 0.05). Furthermore, VNS mitigated microglial activation in two central autonomic nuclei: the paraventricular nucleus of the hypothalamus and locus coeruleus. These findings demonstrate that when VNS therapy is initiated at an early stage of HFrEF progression (<10 % reduction in relative ejection fraction), the supplementation of vagal activity is effective in restoring multi organ homeostasis in a PO model.

The Regulatory Effect of the Paraventricular Nucleus on Hypertension

Hypertension is among the most harmful factors of cardiovascular and cerebrovascular diseases and poses an urgent problem for the development of human society. In addition to previous studies on its pathogenesis focusing on the peripheral sympathetic nervous system, investigating the central causes of high blood pressure involving the neuroendocrine and neuroinflammatory mechanisms of the hypothalamic paraventricular nucleus (PVN) is paramount. This nucleus is considered to regulate the output of neurohormones and sympathetic nerve activity. In this article, we focussed on the neuroendocrine mechanism, primarily exploring the specific contributions and interactions of various neurons and neuroendocrine hormones, including GABAergic and glutamatergic neurons, nitric oxide, arginine vasopressin, oxytocin, and the renin-angiotensin system. Additionally, the neuroinflammatory mechanism in the PVN was discussed, encompassing microglia, reactive oxygen species, inflammatory factors, and pathways, as well as immune connections between the brain and extracerebral organs. Notably, the two central mechanisms involved in the PVN not only exist independently but also communicate with each other, jointly maintaining the hypertensive state of the body. Furthermore, we introduce well-known molecules and signal transduction pathways within the PVN that can play a regulatory role in the two mechanisms to provide a basis and inspire ideas for further research.

Estrogen receptor beta activity contributes to both tumor necrosis factor alpha expression in the hypothalamic paraventricular nucleus and the resistance to hypertension following angiotensin II in female mice

Sex differences in the sensitivity to hypertension and inflammatory processes are well characterized but insufficiently understood. In male mice, tumor necrosis factor alpha (TNFα) in the hypothalamic paraventricular nucleus (PVN) contributes to hypertension following slow-pressor angiotensin II (AngII) infusion. However, the role of PVN TNFα in the response to AngII in female mice is unknown. Using a combination of in situ hybridization, high-resolution electron microscopic immunohistochemistry, spatial-temporal gene silencing, and dihydroethidium microfluorography we investigated the influence of AngII on both blood pressure and PVN TNFα signaling in female mice. We found that chronic (14-day) infusion of AngII in female mice did not impact blood pressure, TNFα levels, the expression of the TNFα type 1 receptor (TNFR1), or the subcellular distribution of TNFR1 in the PVN. However, it was shown that blockade of estrogen receptor β (ERβ), a major hypothalamic estrogen receptor, was accompanied by both elevated PVN TNFα and hypertension following AngII. Further, AngII hypertension following ERβ blockade was attenuated by inhibiting PVN TNFα signaling by local TNFR1 silencing. It was also shown that ERβ blockade in isolated PVN-spinal cord projection neurons (i.e. sympathoexcitatory) heightened TNFα-induced production of NADPH oxidase (NOX2)-mediated reactive oxygen species, molecules that may play a key role in mediating the effect of TNFα in hypertension. These results indicate that ERβ contributes to the reduced sensitivity of female mice to hypothalamic inflammatory cytokine signaling and hypertension in response to AngII.

Reducing brain TACE activity improves neuroinflammation and cardiac function in heart failure rats

Tumor necrosis factor (TNF)-α converting enzyme (TACE) is a key metalloprotease mediating ectodomain shedding of a variety of inflammatory mediators, substrates, and growth factors. We previously reported that TACE-mediated production of TNF-α in the hypothalamic paraventricular nucleus (PVN) contributes to sympathetic excitation in heart failure (HF). Here, we sought to determine whether central interventions in TACE activity attenuate neuroinflammation and improve cardiac function in heart failure. Myocardial infarction-induced HF or sham-operated (SHAM) rats were treated with bilateral paraventricular nucleus microinjection of a TACE siRNA or a 4-week intracerebroventricular (ICV) infusion of the TACE inhibitor TAPI-0. Compared with SHAM rats, scrambled siRNA-treated HF rats had higher TACE levels in the PVN along with increased mRNA levels of TNF-α, TNF-α receptor 1 and cyclooxygenase-2. The protein levels of TNF-α in cerebrospinal fluid and phosphorylated (p-) NF-κB p65 and extracellular signal-regulated protein kinase (ERK)1/2 in the PVN were also elevated in HF rats treated with scrambled siRNA. The expression of these inflammatory mediators and signaling molecules in the PVN of HF rats were significantly attenuated by TACE siRNA. Interestingly, the mRNA level of TNF-α receptor 2 in the PVN was increased in HF treated with TACE siRNA. Moreover, sympathetic excitation, left ventricular end-diastolic pressure, pulmonary congestion, and cardiac hypertrophy and fibrosis were reduced by PVN microinjection of TACE siRNA. A 4-week treatment with intracerebroventricular TAPI-0 had similar effects to ameliorate these variables in HF rats. These data indicate that interventions suppressing TACE activity in the brain mitigate neuroinflammation, sympathetic activation and cardiac dysfunction in HF rats.

Renal denervation based on experimental rationale

Excessive activation of the sympathetic nervous system is one of the pathophysiological hallmarks of hypertension and heart failure. Within the central nervous system, the paraventricular nucleus (PVN) of the hypothalamus and the rostral ventrolateral medulla in the brain stem play critical roles in the regulation of sympathetic outflow to peripheral organs. Information from the peripheral circulation, including serum concentrations of sodium and angiotensin II, is conveyed to the PVN via adjacent structures with a weak blood-brain barrier. In addition, signals from baroreceptors, chemoreceptors and cardiopulmonary receptors as well as afferent input via the renal nerves are all integrated at the level of the PVN. The brain renin-angiotensin system and the balance between nitric oxide and reactive oxygen species in these brain areas also determine the final sympathetic outflow. Additionally, brain inflammatory responses have been shown to modulate these processes. Renal denervation interrupts both the afferent inputs from the kidney to the PVN and the efferent outputs from the PVN to the kidney, resulting in the suppression of sympathetic outflow and eliciting beneficial effects on both hypertension and heart failure.

The heart is lost without the hypothalamus

Neuroanatomic and functional studies show the paraventricular (PVN) of the hypothalamus to have a central role in the autonomic control that supports cardiovascular regulation. Direct and indirect projections from the PVN preautonomic neurons to the sympathetic preganglionic neurons in the spinal cord modulate sympathetic activity. The preautonomic neurons of the PVN adjust their level of activation in response to afferent signals arising from peripheral viscerosensory receptors relayed through the nucleus tractus solitarius. The prevailing sympathetic tone is a balance between excitatory and inhibitory influences that arises from the preautonomic PVN neurons. Under physiologic conditions, tonic sympathetic inhibition driven by a nitric oxide-γ-aminobutyric acid-mediated mechanism is dominant, but in pathologic situation such as heart failure there is a switch from inhibition to sympathoexcitation driven by glutamate and angiotensin II. Angiotensin II, reactive oxygen species, and hypoxia as a result of myocardial infarction/ischemia alter the tightly regulated posttranslational protein-protein interaction of CAPON (carboxy-terminal postsynaptic density protein ligand of neuronal nitric oxide synthase (NOS1)) and PIN (protein inhibitor of NOS1) signaling mechanism. Within the preautonomic neurons of the PVN, the disruption of CAPON and PIN signaling leads to a downregulation of NOS1 expression and reduced NO bioavailability. These data support the notion that CAPON-PIN dysregulation of NO bioavailability is a major contributor to the pathogenesis of sympathoexcitation in heart failure.

Vasopressin & Oxytocin in Control of the Cardiovascular System: An Updated Review

Since the discovery of vasopressin (VP) and oxytocin (OT) in 1953, considerable knowledge has been gathered about their roles in cardiovascular homeostasis. Unraveling VP vasoconstrictor properties and V1a receptors in blood vessels generated powerful hemostatic drugs and drugs effective in the treatment of certain forms of circulatory collapse (shock). Recognition of the key role of VP in water balance via renal V2 receptors gave birth to aquaretic drugs found to be useful in advanced stages of congestive heart failure. There are still unexplored actions of VP and OT on the cardiovascular system, both at the periphery and in the brain that may open new venues in treatment of cardiovascular diseases. After a brief overview on VP, OT and their peripheral action on the cardiovascular system, this review focuses on newly discovered hypothalamic mechanisms involved in neurogenic control of the circulation in stress and disease.

Neuroinflammation in heart failure: new insights for an old disease

Heart failure (HF) is a complex clinical syndrome affecting roughly 26 million people worldwide. Increased sympathetic drive is a hallmark of HF and is associated with disease progression and higher mortality risk. Several mechanisms contribute to enhanced sympathetic activity in HF, but these pathways are still incompletely understood. Previous work suggests that inflammation and activation of the renin-angiotensin system (RAS) increases sympathetic drive. Importantly, chronic inflammation in several brain regions is commonly observed in aged populations, and a growing body of evidence suggests neuroinflammation plays a crucial role in HF. In animal models of HF, central inhibition of RAS and pro-inflammatory cytokines normalizes sympathetic drive and improves cardiac function. The precise molecular and cellular mechanisms that lead to neuroinflammation and its effect on HF progression remain undetermined. This review summarizes the most recent advances in the field of neuroinflammation and autonomic control in HF. In addition, it focuses on cellular and molecular mediators of neuroinflammation in HF and in particular on brain regions involved in sympathetic control. Finally, we will comment on what is known about neuroinflammation in the context of preserved vs. reduced ejection fraction HF.

Tumor necrosis factor alpha mediates orofacial discomfort in an occlusal dental interference model in rats: The role of trigeminal ganglion inflammation

BACKGROUND

Tumor necrosis factor alpha (TNF-α) is a proinflammatory cytokine that plays an important role in the early stages of inflammation. In this study, we investigated its role in orofacial discomfort in rats subjected to occlusal dental interference (ODI).

METHODS

Female Wistar rats (180-200 g) were divided in three groups (n = 30/group): sham group, without ODI, and two experimental groups with ODI pre-treated with 0.1 mL/kg saline (ODI + SAL) or 5 mg/kg infliximab (ODI + INF) and treated every 3 days. The animals were euthanized after 1, 3, and 7 days. The number of bites and scratches and grimace scale scores were determined daily, and the bilateral trigeminal ganglion was histomorphometrically (neuronal body area) analyzed and submitted for immunohistochemistry for TNF-α, nitric oxide synthesis (NOS) neuronal (nNOS) and inducible (iNOS), peroxisome proliferator-activated receptors (PPAR) y (PPARy) and δ/β (PPARδ/β), and glial fibrillary acidic protein (GFAP). One-way/two-way ANOVA/Bonferroni tests were used (P < .05, GraphPad Prism 5.0).

RESULTS

ODI + SAL showed a large number of bites (P = .002), scratches (P = .002), and grimace scores (P < .001) in the firsts days, and ODI + INF partially reduced these parameters. The contralateral and ipsilateral neuronal body area was significantly reduced on day 1 in ODI + SAL, but returned to the basal size on days 3 and 7, by increase in TNF-α, nNOS, PPARy, PPARδ/β, and GFAP immunostaining. The infliximab treatment attenuated these alterations (P < .05). There was no iNOS immunostaining.

CONCLUSION

Occlusal dental interference induced transitory orofacial discomfort by trigeminal inflammatory mediator overexpression, and TNF-α blockage attenuated these processes.

Adipose afferent reflex is enhanced by TNFα in paraventricular nucleus through NADPH oxidase-dependent ROS generation in obesity-related hypertensive rats

BACKGROUND

The adipose afferent reflex (AAR), a sympatho-excitatory reflex, can promote the elevation of sympathetic nerve activity (SNA) and blood pressure (BP). Inflammation in the paraventricular nucleus (PVN) involves sympathetic abnormality in some cardiovascular diseases such as hypertension. This study was designed to explore the effects of tumor necrosis factor alpha (TNFα) in the PVN on the AAR and SNA in rats with obesity-related hypertension (OH) induced by a high-fat diet for 12 weeks.

METHODS

Renal sympathetic nerve activity (RSNA) and mean arterial pressure (MAP) were continuously recorded in anesthetized rats, and their responses to capsaicin (CAP) stimulation of the right inguinal white adipose tissue were used to evaluate the AAR.

RESULTS

Compared to the control rats, the systolic blood pressure (SBP), plasma norepinephrine (NE, indicating SNA) and TNFα levels, TNFα mRNA and protein levels, reactive oxygen species (ROS) content and NADPH oxidase activity in the PVN were significantly elevated in rats with OH. TNFα in the PVN markedly enhanced sympathoexcitation and AAR. Moreover, the enhancement of AAR caused by TNFα can be significantly strengthened by the pretreatment of diethyldithiocarbamate (DETC), a superoxide dismutase inhibitor, but attenuated by TNF-α receptor antagonist R-7050, superoxide scavenger PEG-SOD and NADPH oxidase inhibitor apocynin (Apo) in rats with OH. Acute microinjection of TNF-α into the PVN significantly increased the activity of NADPH oxidase and ROS levels in rats with OH, which were effectively blocked by R-7050. Furthermore, our results also showed that the increased levels of ROS, TNFα and NADPH oxidase subunits mRNA and protein in the PVN of rats with OH were significantly reversed by pentoxifylline (PTX, 30 mg/kg daily ip; in 10% ethanol) application, a cytokine blocker, for a period of 5 weeks. PTX administration also significantly decreased SBP, AAR and plasma NE levels in rats with OH.

CONCLUSIONS

TNFα in the PVN modulates AAR and contributes to sympathoexcitation in OH possibly through NADPH oxidase-dependent ROS generation. TNFα blockade attenuates AAR and sympathoexcitation that unveils TNFα in the PVN may be a possible therapeutic target for the intervention of OH.

Effect of oxidative stress in rostral ventrolateral medulla on sympathetic hyperactivity after traumatic brain injury

Sympathetic hyperactivity occurs in a subgroup of patients after traumatic brain injury (TBI). The rostral ventrolateral medulla (RVLM) is a key region for the activity of sympathetic nervous system. Oxidative stress in the RVLM is proved to be responsible for the increased level of sympathetic activity in animal models of hypertension and heart failure. In this study, we investigated whether oxidative stress in the RVLM contributed to the development of sympathetic hyperactivity after TBI in rats. Model of diffuse axonal injury was induced using Sprague-Dawley rats, and level of mean arterial pressure (MAP) and plasma Norepinephrine (NE) was measured to evaluate the sympathetic activity. For the assessment of oxidative stress, expression of reactive oxygen species (ROS), malondialdehyde (MDA), and superoxide dismutase (SOD) in the RVLM was determined. Microinjection of Tempol into the RVLM was performed to determine the effect of oxidative stress on sympathetic hyperactivity. According to the results, TBI led to elevated MAP and plasma NE in rats. It also induced a significantly increased level of ROS, MDA production and decreased level of SOD in the RVLM. The sympathetic activity, ROS, and MDA in the RVLM decreased significantly after microinjection of Tempol. Therefore, the present results suggested that oxidative stress in the RVLM was involved in the development of sympathetic hyperactivity following TBI.

Brain tumor necrosis factor-α mediates anxiety-like behavior in a mouse model of severe obesity

Although the high prevalence of anxiety in obesity increasingly emerges as significant risk factor for related severe health complications, the underlying pathophysiological mechanisms remain poorly understood. Considering that chronic inflammation is a key component of obesity and is well known to impact brain function and emotional behavior, we hypothesized that it may similarly contribute to the development of obesity-related anxiety. This hypothesis was experimentally tested by measuring whether chronic food restriction, a procedure known to reduce inflammation, or chronic anti-inflammatory treatment with ibuprofen improved anxiety-like behavior and concomitantly decreased peripheral and/or hippocampal inflammation characterizing a model of severe obesity, the db/db mice. In both experiments, reduced anxiety-like behaviors in the open-field and/or elevated plus-maze were selectively associated with decreased hippocampal tumor necrosis factor-α (TNF-α) mRNA expression. Highlighting the causality of both events, chronic central infusion of the TNF-α blocker etanercept was then shown to be sufficient to improve anxiety-like behavior in db/db mice. Lastly, by measuring the impact of ex-vivo etanercept on hippocampal synaptic processes underlying anxiety-like behaviors, we showed that the anxiolytic effect of central TNF-α blockade likely involved modulation of synaptic transmission within the ventral hippocampus. Altogether, these results uphold the role of brain TNF-α in mediating obesity-related anxiety and provide important clues about how it may modulate brain function and behavior. They may therefore help to introduce novel therapeutic strategies to reduce anxiety associated with inflammatory conditions.

Silencing salusin β ameliorates heart failure in aged spontaneously hypertensive rats by ROS-relative MAPK/NF-κB pathways in the paraventricular nucleus

OBJECTIVE

Sustained hypertension is a major cause of heart failure in aging hypertensive patients. Salusin β, a novel bioactive peptide of 20 amino acids, has been reported to participate in various cardiovascular diseases, including hypertension. We therefore hypothesized that central knockdown of salusin β might be effective for hypertension-induced heart failure treatment.

METHODS AND RESULTS

Eighteen-month-old male aged spontaneously hypertensive rats (SHR) with heart failure and WKY rats were microinjected with either a specific adenoviral vector encoding salusin β shRNA (Ad-Sal-shRNA) or a scramble shRNA (Ad-Scr-shRNA) in the hypothalamic paraventricular nucleus (PVN) for 4 weeks. Radiotelemetry and echocardiography were used for measuring blood pressure and cardiac function, respectively. Blood samples and heart were harvested for evaluating plasma norepinephrine, tyrosine hydroxylase, and cardiac morphology, respectively. The mesenteric arteries were separated for measurement of vascular responses. The PVN was analyzed for salusin β, proinflammatory cytokines (PICs), mitogen-activated protein kinase (MAPK), NF-κB, and reactive oxygen species (ROS) levels. Compared with normotensive rats, aging SHR with heart failure had dramatically increased salusin β expression. Silencing salusin β with Ad-Sal-shRNA attenuated arterial pressure and improved autonomic function, cardiac and vascular dysfunction in aging SHR with heart failure, but not in aging WKY rats. Knockdown of salusin β significantly reduced paraventricular nucleus PICs levels, MAPK and NF-κB activity, and ROS levels in aging SHR with heart failure.

CONCLUSION

These data demonstrate that in aging SHR, the heart failure that was developed during the end stage of hypertension could be ameliorated by silencing salusin β.

Ion Channels in the Paraventricular Hypothalamic Nucleus (PVN); Emerging Diversity and Functional Roles

The paraventricular nucleus of the hypothalamus (PVN) is critical for the regulation of homeostatic function. Although also important for endocrine regulation, it has been referred to as the "autonomic master controller." The emerging consensus is that the PVN is a multifunctional nucleus, with autonomic roles including (but not limited to) coordination of cardiovascular, thermoregulatory, metabolic, circadian and stress responses. However, the cellular mechanisms underlying these multifunctional roles remain poorly understood. Neurones from the PVN project to and can alter the function of sympathetic control regions in the medulla and spinal cord. Dysfunction of sympathetic pre-autonomic neurones (typically hyperactivity) is linked to several diseases including hypertension and heart failure and targeting this region with specific pharmacological or biological agents is a promising area of medical research. However, to facilitate future medical exploitation of the PVN, more detailed models of its neuronal control are required; populated by a greater compliment of constituent ion channels. Whilst the cytoarchitecture, projections and neurotransmitters present in the PVN are reasonably well documented, there have been fewer studies on the expression and interplay of ion channels. In this review we bring together an up to date analysis of PVN ion channel studies and discuss how these channels may interact to control, in particular, the activity of the sympathetic system.

Bimodal Function of Anti-TNF Treatment: Shall We Be Concerned about Anti-TNF Treatment in Patients with Rheumatoid Arthritis and Heart Failure?

Treatment with anti-TNF-α (tumor necrosis factor), one of the pivotal cytokines, was introduced to clinical practice at the end of last century and revolutionized the treatment of rheumatoid arthritis (RA) as well as many other inflammatory conditions. Such a treatment may however bring many safety issues regarding infections, tuberculosis, as well as cardiovascular diseases, including heart failure. Given the central role of proinflammatory cytokines in RA, atherosclerosis, and congestive heart failure (CHF), such a treatment might result in better control of the RA process on the one side and improvement of heart function on the other. Unfortunately, at the beginning of this century two randomized controlled trials failed to show any benefit of anti-TNF treatment in patients with heart failure (HF), suggesting direct negative impact of the treatment on morbidity and mortality in HF patients. As a result the anti-TNF treatment is contraindicated in all patients with heart failure and a substantial portion of patients with RA and impaired heart function are not able to benefit from the treatment. The role of TNF in CHF and RA differs substantially with regard to the source and pathophysiological function of the cytokine in both conditions, therefore negative data from CHF studies should be interpreted with caution. At least some of RA patients with heart failure may benefit from anti-TNF treatment, as it results not only in the reduction of inflammation but also contributes significantly to the improvement of cardiac function. The paper addresses the epidemiological data of safety of anti-TNF treatment in RA patients with the special emphasis to basic pathophysiological mechanisms via which TNF may act differently in both diseases.

Implications of disturbances in circadian rhythms for cardiovascular health: A new frontier in free radical biology

Cell autonomous circadian "clock" mechanisms are present in virtually every organ, and generate daily rhythms that are important for normal physiology. This is especially relevant to the cardiovascular system, for example the circadian mechanism orchestrates rhythms in heart rate, blood pressure, cardiac contractility, metabolism, gene and protein abundance over the 24-h day and night cycles. Conversely, disturbing circadian rhythms (e.g. via shift work, sleep disorders) increases cardiovascular disease risk, and exacerbates cardiac remodelling and worsens outcome. Notably, reactive oxygen species (ROS) are important contributors to heart disease, especially the pathophysiologic damage that occurs after myocardial infarction (MI, heart attack). However, little is known about how the circadian mechanism, or rhythm desynchrony, is involved in these key pathologic stress responses. This review summarizes the current knowledge on circadian rhythms in the cardiovascular system, and the implications of rhythm disturbances for cardiovascular health. Furthermore, we highlight how free radical biology coincides with the pathogenesis of myocardial repair and remodelling after MI, and indicate a role for the circadian system in the oxidative stress pathways in the heart and brain after MI. This fusion of circadian biology with cardiac oxidative stress pathways is novel, and offers enormous potential for improving our understanding and treatment of heart disease.

Mitochondrial dysfunction: maternal protein restriction as a trigger of reactive species overproduction and brainstem energy failure in male offspring brainstem

Mitochondria are important organelles in eukaryotic organisms, wherein their capacity to produce energy vary among the tissues depending upon the amounts of oxygen consumed. Part of the oxygen consumed during ATP generation produces reactive oxygen species, which if not efficiently removed can trigger a systemic damage to molecular compounds characterized as oxidative stress. Several studies have demonstrated that mitochondrial dysfunction and oxidative stress in the central nervous system (CNS) are related to a plethora of neural disorders. Herein, we hypothesize that a late autonomic imbalance-induced hypertension might be related to long-lasting effects of protein restriction during the critical period of the CNS development on the mitochondrial function and oxidative stress in the brainstem of adult (i.e. 150 days of age) male Wistar rats. Maternal protein restriction was induced by offering a diet based on 8% of casein from first day of pregnancy until weaning, when the male pups started to receive laboratory chow up to 150 days of life. The protein restriction induced an extended detrimental modulation in mitochondria function, decreasing the phosphorylation capacity with concomitant decrease in the mitochondrial membrane potential, wherein the reactive species overproduction triggered a disruption in proton conductance, which may gradually compromise mitochondria energy conservation. Interestingly, the elevated activity of glutathione-S-transferase and the augmented expression of uncoupling protein 2 are likely protective mechanisms induced by lipid peroxidation products, being feasible molecular changes attempting to deal with oxidative stress-induced ageing.

Blood-borne interleukin-1β acts on the subfornical organ to upregulate the sympathoexcitatory milieu of the hypothalamic paraventricular nucleus

We previously reported that microinjection of the proinflammatory cytokine interleukin-1β (IL-1β) into the subfornical organ (SFO) elicits a pressor response accompanied by increases in inflammation and renin-angiotensin system (RAS) activity in the SFO and hypothalamic paraventricular nucleus (PVN). The present study sought to determine whether blood-borne IL-1β induces similar neurochemical changes in the SFO and PVN and, if so, whether increased inflammation and RAS activity at the SFO level orchestrate the sympathoexcitatory response to circulating IL-1β. In urethane-anesthetized male Sprague-Dawley rats, intravenous injection of IL-1β (500 ng) increased blood pressure, heart rate, renal sympathetic nerve activity, and mRNA for angiotensin-converting enzyme, angiotensin II type 1a receptor, cyclooxygenase-2, tumor necrosis factor-α, and IL-1β, as well as the tumor necrosis factor-α p55 receptor and the IL-1 receptor, in the SFO and PVN. Pretreatment with SFO microinjections of the angiotensin II type 1a receptor blocker losartan (1 µg), the angiotensin-converting enzyme inhibitor captopril (1 µg), or the cyclooxygenase-2 inhibitor NS-398 (2 µg) attenuated expression of these excitatory mediators in the SFO and downstream in the PVN and the IL-1β-induced pressor responses. An SFO lesion minimized the IL-1β-induced expression of inflammatory and RAS components as well as c-Fos, an indicator of neuronal excitation, in the PVN. These studies demonstrate that circulating IL-1β, which increases in cardiovascular disorders such as hypertension and heart failure, acts on the SFO to increase inflammation and RAS activity in the SFO and PVN and that intervening in these neurochemical processes in the SFO can significantly reduce the sympathetic response.

TNF-α receptor 1 knockdown in the subfornical organ ameliorates sympathetic excitation and cardiac hemodynamics in heart failure rats

In systolic heart failure (HF), circulating proinflammatory cytokines upregulate inflammation and renin-angiotensin system (RAS) activity in cardiovascular regions of the brain, contributing to sympathetic excitation and cardiac dysfunction. Important among these is the subfornical organ (SFO), a forebrain circumventricular organ that lacks an effective blood-brain barrier and senses circulating humors. We hypothesized that the tumor necrosis factor-α (TNF-α) receptor 1 (TNFR1) in the SFO contributes to sympathetic excitation and cardiac dysfunction in HF rats. Rats received SFO microinjections of a TNFR1 shRNA or a scrambled shRNA lentiviral vector carrying green fluorescent protein, or vehicle. One week later, some rats were euthanized to confirm the accuracy of the SFO microinjections and the transfection potential of the lentiviral vector. Other rats underwent coronary artery ligation (CL) to induce HF or a sham operation. Four weeks after CL, vehicle- and scrambled shRNA-treated HF rats had significant increases in TNFR1 mRNA and protein, NF-κB activity, and mRNA for inflammatory mediators, RAS components and c-Fos protein in the SFO and downstream in the hypothalamic paraventricular nucleus, along with increased plasma norepinephrine levels and impaired cardiac function, compared with vehicle-treated sham-operated rats. In HF rats treated with TNFR1 shRNA, TNFR1 was reduced in the SFO but not paraventricular nucleus, and the central and peripheral manifestations of HF were ameliorated. In sham-operated rats treated with TNFR1 shRNA, TNFR1 expression was also reduced in the SFO but there were no other effects. These results suggest a key role for TNFR1 in the SFO in the pathophysiology of systolic HF.NEW & NOTEWORTHY Activation of TNF-α receptor 1 in the subfornical organ (SFO) contributes to sympathetic excitation in heart failure rats by increasing inflammation and renin-angiotensin system activity in the SFO and downstream in the hypothalamic paraventricular nucleus. Cytokine receptors in the SFO may be a target for central intervention in cardiovascular conditions characterized by peripheral inflammation.

c-Jun N-terminal Kinase mediates prostaglandin-induced sympathoexcitation in rats with chronic heart failure by reducing GAD1 and GABRA1 expression

AIM

Prostaglandin E2 mediates sympathoexcitation in chronic heart failure (CHF) through EP3 receptors (PTGER3) in the paraventricular nucleus (PVN). The aim of this study was to investigate the role of c-Jun N-terminal kinase (JNK) in expressional regulation of gamma-aminobutyric acid signalling in PVN in CHF rats.

METHODS

Chronic heart failure was induced by left coronary ligation in Wistar rats. Renal sympathetic nerve discharge (RSND) and mean arterial pressure (MAP) responses to the PVN infusion were determined in anaesthetized rats. Osmotic minipumps were used for chronic PVN infusion. PTGER3 expression was examined with immunofluorescence staining, quantitative real-time PCR and Western blot.

RESULTS

Chronic heart failure rats had increased JNK activation and decreased glutamate decarboxylase 1 (GAD1) and GABA_A receptor alpha 1 subunit (GABRA1) expression in the PVN. PVN infusion of the PTGER3 agonist SC-46275 caused sympathoexcitation in sham-operated control (Sham) rats and increased it further in CHF. The PTGER3 antagonist L798106 reduced sympathoexcitation and cardiac dysfunction in CHF. PVN infusion of EP1 receptor antagonist SC-19220, EP2 receptor antagonist AH6809 or EP4 receptor antagonist L-161982 had no effect on sympathoexcitation. The JNK inhibitor SP600125 normalized sympathoexcitation and GAD1 and GABRA1 expression in PVN in CHF rats. Both the p44/42 and p38 mitogen-activated protein kinase inhibitors PD98059 and SB203580 could not prevent the downregulation of GAD1 and GABRA1 expression in PVN in CHF. PTGER3 agonist activated JNK but downregulated GAD1 and GABRA1 expression in NG108 neuronal cells.

CONCLUSION

Prostaglandin signalling through upregulated PTGER3 activates JNK which reduces GAD1 and GABRA1 expression in the PVN, and contributes to sympathoexcitation in CHF.

Inhibitory effects of alpha-lipoic acid on oxidative stress in the rostral ventrolateral medulla in rats with salt-induced hypertension

Oxidative stress in the rostral ventrolateral medulla (RVLM) plays an important role in the pathophysiology of hypertension. Alpha‑lipoic acid (ALA) is widely recognized for its potent superoxide inhibitory properties, and it can safely penetrate deep into the brain. The aim of this study was to explore whether ALA supplementation attenuates hypertensive responses and cardiac hypertrophy by decreasing the NAD(P)H oxidase (NOX)-derived overproduction of reactive oxygen species (ROS) in the mitochondria in the RVLM, and thus attenuating the development of salt‑induced hypertension. For this purpose, male Wistar rats were randomly divided into 2 groups and either fed a high-salt diet or not. After 8 weeks, the rats were either administered ALA or an equal volume of the vehicle for 8 weeks. The rats fed a high‑salt diet exhibited higher mean arterial pressure (MAP) and higher plasma noradrenaline (NE) levels, as well as cardiac hypertrophy, as evidence by the increased whole heart weight/body weight (WHW/BW) ratio, WHW/tibia length (TL) ratio and left‑ventricular weight (LVW)/TL ratio. Compared with the rats in the NS group, the rats in the HS group only exhibited increased levels of superoxide, NOX2, NOX4 and mitochondrial malondialdehyde (MDA), but also decreased levels of copper/zinc (Cu/Zn)-superoxide dismutase (SOD), mitochondrial SOD and glutathione (GSH) in the RVLM. The supplementation of ALA decreased MAP, plasma NE levels and the levels of cardiac hypertrophy indicators. It also decreased the levels of superoxide, NOX2, NOX4 and mitochondrial MDA, and increased the levels of Cu/Zn‑SOD, mitochondrial SOD and GSH in the RVLM compared with the rats fed a high-salt diet and not treated with ALA. On the whole, our findings indicate that long‑term ALA supplementation attenuates hypertensive responses and cardiac hypertrophy by decreasing the expression of NAD(P)H subunits (NOX2 and NOX4), increasing the levels of mitochondrial bioenergetic enzymes, and enhancing the intracellular antioxidant capacity in the RVLM during the development of hypertension.

Renal Denervation Improves Exaggerated Sympathoexcitation in Rats With Heart Failure: A Role for Neuronal Nitric Oxide Synthase in the Paraventricular Nucleus

Renal denervation (RDN) has been postulated to reduce sympathetic drive during heart failure (HF), but the central mechanisms are not completely understood. The purpose of the present study was to assess the contribution of neuronal nitric oxide synthase (nNOS) within the paraventricular nucleus (PVN) in modulating sympathetic outflow in rats with HF that underwent RDN. HF was induced in rats by ligation of the left coronary artery. Four weeks after surgery, bilateral RDN was performed. Rats with HF had an increase in FosB-positive cells in the PVN with a concomitant increase in urinary excretion of norepinephrine, and both of these parameters were ameliorated after RDN. nNOS-positive cells immunostaining, diaphorase staining, and nNOS protein expression were significantly decreased in the PVN of HF rats, findings that were ameliorated by RDN. Microinjection of nNOS inhibitor N(G)-monomethyl l-arginine into the PVN resulted in a blunted increase in lumbar sympathetic nerve activity (11±2% versus 24±2%) in HF than in sham group. This response was normalized after RDN. Stimulation of afferent renal nerves produced a greater activation of PVN neurons in rats with HF. Afferent renal nerve stimulation elicited a greater increase in lumbar sympathetic nerve activity in rats with HF than in sham rats (45±5% versus 22±2%). These results suggest that intact renal nerves contribute to the reduction of nNOS in the PVN, resulting in the activation of the neurons in the PVN of rats with HF. RDN restores nNOS and thus attenuates the sympathoexcitation commonly observed in HF.

A Functional Coupling Between Carbon Monoxide and Nitric Oxide Contributes to Increased Vasopressin Neuronal Activity in Heart Failure rats

Despite the pathophysiological importance of neurohumoral activation in patients with heart failure (HF), the precise underlying mechanisms contributing to elevated vasopressin (VP) activation in HF remains unknown. Carbon monoxide (CO) is a gaseous neurotransmitter in the central nervous system that stimulates VP neuronal firing activity. Recently, we showed that the excitatory effect of CO on VP neurons in the hypothalamic paraventricular nucleus (PVN) was mediated by inhibition of nitric oxide (NO). Given that previous studies showed that VP neuronal activity is enhanced, whereas NO inhibitory signaling is blunted in HF rats, we tested whether an enhanced endogenous CO availability within the PVN contributes to elevated VP neuronal activity and blunted NO signaling in HF rats. We found that both haeme-oxygenase 1 (the CO-synthesizing enzyme) protein and mRNA expression levels were enhanced in the PVN of HF compared with sham rats (∼18% and ∼38%, respectively). We report that in sham rats, bath application of a CO donor (tricarbonyldichlororuthenium dimer) increased the firing activity of identified PVN VP neurons (P < .05), whereas inhibition of endogenous CO production (Tin-protoporphyrin IX [SnPP]) failed to affect neuronal activity. In HF rats, however, SnPP decreased VP activity (P < .05), an effect that was occluded by previous NO synathase blockade NG-nitro-larginine methyl ester. Finally, we found that SnPP increased the mean frequency of γ-aminobutyric acid inhibitory postsynaptic currents in VP neurons in HF (P < .05) but not sham rats. Our results support an enhanced endogenous CO excitatory signaling in VP neurons, which likely contributes to blunted NO and γ-aminobutyric acid inhibitory function in HF rats.

Brain mechanisms of sympathetic activation in heart failure: Roles of the renin‑angiotensin system, nitric oxide and pro‑inflammatory cytokines (Review)

Patients with chronic heart failure (CHF) have an insufficient perfusion to the peripheral tissues due to decreased cardiac output. The compensatory mechanisms are triggered even prior to the occurrence of clinical symptoms, which include activation of the sympathetic nervous system (SNS) and other neurohumoral factors. However, the long‑term activation of the SNS contributes to progressive cardiac dysfunction and has toxic effects on the cardiomyocytes. The mechanisms leading to the activation of SNS include changes in peripheral baroreceptor and chemoreceptor reflexes and the abnormal regulation of sympathetic nerve activity (SNA) in the central nervous system (CNS). Recent studies have focused on the role of brain mechanisms in the regulation of SNA and the progression of CHF. The renin‑angiotensin system, nitric oxide and pro‑inflammatory cytokines were shown to be involved in the abnormal regulation of SNA in the CNS. The alteration of these neurohumoral factors during CHF influences the activity of neurons in the autonomic regions and finally increase the sympathetic outflow. The present review summarizes the brain mechanisms contributing to sympathoexcitation in CHF.

Exercise training in chronic heart failure: improving skeletal muscle O2 transport and utilization

Chronic heart failure (CHF) impairs critical structural and functional components of the O2 transport pathway resulting in exercise intolerance and, consequently, reduced quality of life. In contrast, exercise training is capable of combating many of the CHF-induced impairments and enhancing the matching between skeletal muscle O2 delivery and utilization (Q̇mO2 and V̇mO2 , respectively). The Q̇mO2 /V̇mO2 ratio determines the microvascular O2 partial pressure (PmvO2 ), which represents the ultimate force driving blood-myocyte O2 flux (see Fig. 1). Improvements in perfusive and diffusive O2 conductances are essential to support faster rates of oxidative phosphorylation (reflected as faster V̇mO2 kinetics during transitions in metabolic demand) and reduce the reliance on anaerobic glycolysis and utilization of finite energy sources (thus lowering the magnitude of the O2 deficit) in trained CHF muscle. These adaptations contribute to attenuated muscle metabolic perturbations (e.g., changes in [PCr], [Cr], [ADP], and pH) and improved physical capacity (i.e., elevated critical power and maximal V̇mO2 ). Preservation of such plasticity in response to exercise training is crucial considering the dominant role of skeletal muscle dysfunction in the pathophysiology and increased morbidity/mortality of the CHF patient. This brief review focuses on the mechanistic bases for improved Q̇mO2 /V̇mO2 matching (and enhanced PmvO2 ) with exercise training in CHF with both preserved and reduced ejection fraction (HFpEF and HFrEF, respectively). Specifically, O2 convection within the skeletal muscle microcirculation, O2 diffusion from the red blood cell to the mitochondria, and muscle metabolic control are particularly susceptive to exercise training adaptations in CHF. Alternatives to traditional whole body endurance exercise training programs such as small muscle mass and inspiratory muscle training, pharmacological treatment (e.g., sildenafil and pentoxifylline), and dietary nitrate supplementation are also presented in light of their therapeutic potential. Adaptations within the skeletal muscle O2 transport and utilization system underlie improvements in physical capacity and quality of life in CHF and thus take center stage in the therapeutic management of these patients.

Modulation of angiotensin II signaling following exercise training in heart failure

Sympathetic activation is a consistent finding in the chronic heart failure (CHF) state. Current therapy for CHF targets the renin-angiotensin II (ANG II) and adrenergic systems. Angiotensin converting enzyme (ACE) inhibitors and ANG II receptor blockers are standard treatments along with β-adrenergic blockade. However, the mortality and morbidity of this disease is still extremely high, even with good medical management. Exercise training (ExT) is currently being used in many centers as an adjunctive therapy for CHF. Clinical studies have shown that ExT is a safe, effective, and inexpensive way to improve quality of life, work capacity, and longevity in patients with CHF. This review discusses the potential neural interactions between ANG II and sympatho-excitation in CHF and the modulation of this interaction by ExT. We briefly review the current understanding of the modulation of the angiotensin type 1 receptor in sympatho-excitatory areas of the brain and in the periphery (i.e., in the carotid body and skeletal muscle). We discuss possible cellular mechanisms by which ExT may impact the sympatho-excitatory process by reducing oxidative stress, increasing nitric oxide. and reducing ANG II. We also discuss the potential role of ACE2 and Ang 1-7 in the sympathetic response to ExT. Fruitful areas of further investigation are the role and mechanisms by which pre-sympathetic neuronal metabolic activity in response to individual bouts of exercise regulate redox mechanisms and discharge at rest in CHF and other sympatho-excitatory states.

Proinflammatory cytokines upregulate sympathoexcitatory mechanisms in the subfornical organ of the rat

Our previous work indicated that the subfornical organ (SFO) is an important brain sensor of blood-borne proinflammatory cytokines, mediating their central effects on autonomic and cardiovascular function. However, the mechanisms by which SFO mediates the central effects of circulating proinflammatory cytokines remain unclear. We hypothesized that proinflammatory cytokines act within the SFO to upregulate the expression of excitatory and inflammatory mediators that drive sympathetic nerve activity. In urethane-anesthetized Sprague-Dawley rats, direct microinjection of tumor necrosis factor (TNF)-α (25 ng) or interleukin (IL)-1β (25 ng) into SFO increased mean blood pressure, heart rate, and renal sympathetic nerve activity within 15 to 20 minutes, mimicking the response to systemically administered proinflammatory cytokines. Pretreatment of SFO with microinjections of the angiotensin II type-1 receptor blocker losartan (1 μg), angiotensin-converting enzyme inhibitor captopril (1 μg) or cyclooxygenase-2 inhibitor NS-398 (2 μg) attenuated those responses. Four hours after the SFO microinjection of TNF-α (25 ng) or IL-1β (25 ng), mRNA for angiotensin-converting enzyme, angiotensin II type-1 receptor, TNF-α and the p55 TNF-α receptor, IL-1β and the IL-1R receptor, and cyclooxygenase-2 had increased in SFO, and mRNA for angiotensin-converting enzyme, angiotensin II type-1 receptor, and cyclooxygenase-2 had increased downstream in the hypothalamic paraventricular nucleus. Confocal immunofluorescent images revealed that immunoreactivity for the p55 TNF-α receptor and the IL-1 receptor accessory protein, a subunit of the IL-1 receptor, colocalized with angiotensin-converting enzyme, angiotensin II type-1 receptor-like, cyclooxygenase-2, and prostaglandin E2 EP3 receptor immunoreactivity in SFO neurons. These data suggest that proinflammatory cytokines act within the SFO to upregulate the expression of inflammatory and excitatory mediators that drive sympathetic excitation.

Cardiac sympathetic afferent stimulation induces salt-sensitive sympathoexcitation through hypothalamic epithelial Na+ channel activation

The cardiac sympathetic afferent (CSA), which plays an important role in heart-brain communication for sympathoexcitation, is stimulated in heart failure. Additionally, high salt intake leads to further sympathoexcitation due to activation of hypothalamic epithelial Na(+) channels (ENaCs) in heart failure. In the present study, we stimulated the CSA in adult male mice by epicardial application of capsaicin and using ethanol as a control to determine whether CSA stimulation led to activation of hypothalamic ENaCs, resulting in salt-induced sympathoexcitation. Three days after capsaicin treatment, an upregulation of hypothalamic α-ENaCs, without activation of mineralocorticoid receptors, was observed. We also examined expression levels of the known ENaC activator TNF-α. Hypothalamic TNF-α increased in capsaicin-treated mice, whereas intracerebroventricular infusion of the TNF-α blocker etanercept prevented capsaicin-induced upregulation of α-ENaCs. To examine brain arterial pressure (AP) sensitivity toward Na(+), we performed an intracerebroventricular infusion of high Na(+)-containing (0.2 M) artificial cerebrospinal fluid. AP and heart rate were significantly increased in capsaicin-treated mice compared with control mice. CSA stimulation also caused excitatory responses with high salt intake. Compared with a regular salt diet, the high-salt diet augmented AP, heart rate, and 24-h urinary norepinephrine excretion, which is an indirect marker of sympathetic activity with mineralocorticoid receptor activation, in capsaicin-treated mice but not in ethanol-treated mice. Treatment with etanercept or the ENaC blocker benzamil prevented these salt-induced excitatory responses. In summary, we show that CSA stimulation leads to an upregulation of hypothalamic α-ENaCs mediated via an increase in TNF-α and results in increased salt sensitivity.

Angiotensin II causes imbalance between pro- and anti-inflammatory cytokines by modulating GSK-3β in neuronal culture

BACKGROUND AND PURPOSE

Emerging evidence indicates that the balance between pro-inflammatory cytokines (PICs) and anti-inflammatory cytokines (AICs) within the brain is an important determinant in the outcome of hypertension. However, the mechanism by which this dysregulation occurs is not known. We aimed to investigate whether AngII induces imbalance between PIC and AIC by modulating downstream transcription factors, NFκB and cyclic AMP response element-binding protein (CREB), and whether AngII-induced effects are mediated by glycogen synthase kinase-3β (GSK-3β).

EXPERIMENTAL APPROACH

CATH.a neurons were exposed to AngII (10 nM-1 μM) over a preset time course. In another set of experiments, GSK-3β was knock down by using lentivirus containing short hairpin RNA targeting GSK-3β (L-sh-GSK3β) before AngII exposure. Cell extracts were subjected to RT-PCR, immunoblot and immunoprecipitation.

KEY RESULTS

AngII caused time-dependent increase in PICs (TNF-α and IL-1β) and reduction in AIC (IL-10). AngII exposure caused reduced phosphorylated CREB(Ser-133) and increased p-NFκB(Ser-276) levels, leading to reduced CREB-CBP and increased NFκB-CBP binding. These results were accompanied by increased activation of GSK-3β, as indicated by increased p-GSK3(Tyr-216) to p-GSK3(Ser-9) ratio. In a subsequent study, pretreatment with L-sh-GSK3β attenuated AngII-induced alterations in PICs and IL-10 by augmenting CREB-CBP and attenuating NFκB-CBP binding.

CONCLUSIONS AND IMPLICATIONS

Collectively, these findings are the first to provide direct evidence that AngII-induced dysregulation in cytokines is mediated by GSK-3β-mediated alterations in downstream transcription factors in neuronal cells. Our data also reveal that AngII-induced effects could be alleviated by GSK-3β inhibition, suggesting GSK-3β as an important therapeutic target for hypertension that is characterized by increased PICs and NFκB activation.

Central SDF-1/CXCL12 expression and its cardiovascular and sympathetic effects: the role of angiotensin II, TNF-α, and MAP kinase signaling

The chemokine stromal cell-derived factor-1 (SDF-1/CXCL12) and its receptors are expressed by neurons and glial cells in cardiovascular autonomic regions of the brain, including the hypothalamic paraventricular nucleus (PVN), and contribute to neurohumoral excitation in rats with ischemia-induced heart failure. The present study examined factors regulating the expression of SDF-1 in the PVN and mechanisms mediating its sympatho-excitatory effects. In urethane anesthetized rats, a 4-h intracerebroventricular (ICV) infusion of angiotensin II (ANG II) or tumor necrosis factor-α (TNF-α) in doses that increase mean blood pressure (MBP) and sympathetic drive increased the expression of SDF-1 in PVN. ICV administration of SDF-1 increased the phosphorylation of p44/42 mitogen-activated protein kinase (MAPK), JNK, and p38 MAPK in PVN, along with MBP, heart rate (HR), and renal sympathetic nerve activity (RSNA), but did not affect total p44/42 MAPK, JNK, and p38 MAPK levels. ICV pretreatment with the selective p44/42 MAPK inhibitor PD98059 prevented the SDF-1-induced increases in MBP, HR, and RSNA; ICV pretreatment with the selective JNK and p38 MAPK inhibitors attenuated but did not block these SDF-1-induced excitatory responses. ICV PD98059 also prevented the sympatho-excitatory response to bilateral PVN microinjections of SDF-1. ICV pretreatment with SDF-1 short-hairpin RNA significantly reduced ANG II- and TNF-α-induced phosphorylation of p44/42 MAPK in PVN. These findings identify TNF-α and ANG II as drivers of SDF-1 expression in PVN and suggest that the full expression of their cardiovascular and sympathetic effects depends upon SDF-1-mediated activation of p44/42 MAPK signaling.

Central command dysfunction in rats with heart failure is mediated by brain oxidative stress and normalized by exercise training

Sympathoexcitation elicited by central command, a parallel activation of the motor and autonomic neural circuits in the brain, has been shown to become exaggerated in chronic heart failure (CHF). The present study tested the hypotheses that oxidative stress in the medulla in CHF plays a role in exaggerating central command-elicited sympathoexcitation, and that exercise training in CHF suppresses central command-elicited sympathoexcitation through its antioxidant effects in the medulla. In decerebrate rats, central command was activated by electrically stimulating the mesencephalic locomotor region (MLR) after neuromuscular blockade. The MLR stimulation at a current intensity greater than locomotion threshold in rats with CHF after myocardial infarction (MI) evoked larger (P < 0.05) increases in renal sympathetic nerve activity and arterial pressure than in sham-operated healthy rats (Sham) and rats with CHF that had completed longterm (8–12 weeks) exercise training (MI + TR). In the Sham and MI + TR rats, bilateral microinjection of a superoxide dismutase (SOD) mimetic Tempol into the rostral ventrolateral medulla (RVLM) had no effects on MLR stimulation-elicited responses. By contrast, in MI rats, Tempol treatment significantly reduced MLR stimulation-elicited responses. In a subset of MI rats, treatment with Tiron, another SOD mimetic, within the RVLM also reduced responses. Superoxide generation in the RVLM, as evaluated by dihydroethidium staining, was enhanced in MI rats compared with that in Sham and MI + TR rats. Collectively, these results support the study hypotheses. We suggest that oxidative stress in the medulla in CHF mediates central command dysfunction, and that exercise training in CHF is capable of normalizing central command dysfunction through its antioxidant effects in the medulla.

The central renin-angiotensin system and sympathetic nerve activity in chronic heart failure

CHF (chronic heart failure) is a multifactorial disease process that is characterized by overactivation of the RAAS (renin-angiotensin-aldosterone system) and the sympathetic nervous system. Both of these systems are chronically activated in CHF. The RAAS consists of an excitatory arm involving AngII (angiotensin II), ACE (angiotensin-converting enzyme) and the AT1R (AngII type 1 receptor). The RAAS also consists of a protective arm consisting of Ang-(1-7) [angiotensin-(1-7)], the AT2R (AngII type 2 receptor), ACE2 and the Mas receptor. Sympatho-excitation in CHF is driven, in large part, by an imbalance of these two arms, with an increase in the AngII/AT1R/ACE arm and a decrease in the AT2R/ACE2 arm. This imbalance is manifested in cardiovascular-control regions of the brain such as the rostral ventrolateral medulla and paraventricular nucleus in the hypothalamus. The present review focuses on the current literature that describes the components of these two arms of the RAAS and their imbalance in the CHF state. Moreover, the present review provides additional evidence for the relevance of ACE2 and Ang-(1-7) as key players in the regulation of central sympathetic outflow in CHF. Finally, we also examine the effects of exercise training as a therapeutic strategy and the molecular mechanisms at play in CHF, in part, because of the ability of exercise training to restore the balance of the RAAS axis and sympathetic outflow.

Hypothalamic paraventricular nucleus activation contributes to neurohumoral excitation in rats with heart failure

Heart failure (HF) is a serious cardiovascular disease and is characterized by exaggerated sympathetic activity. In this paper, we review these limited studies, with particular emphasis on examining the role of the paraventricular nucleus (PVN) in the neurohumoral excitation in HF. The PVN is an important neuroendocrine and preautonomic output nucleus, and is considered as the important central site for integration of sympathetic nerve activity. Accumulating evidences demonstrate that a number of neurohumoral processes are involved in the pathophysiology of HF, such as renin-angiotensin system (RAS), proinflammatory cytokines (PICs), neurotransmitters, and reactive oxygen species (ROS). Recent studies about neurohumoral regulation indicate that angiotensin II type1 receptor (AT₁-R) is the important product mediated by cytoplasmic nuclear factor-kappa B (NF-κB) which is up-regulated along with elevated PICs and angiotensin II (ANG II) in the PVN of HF rats. These findings suggest that the NF-κB mediates the cross-talk between RAS and PICs in the PVN in HF. The further studies indicate that the interaction between AT₁-R and NF-κB in the PVN contributes to oxidative stress and sympathoexcitation by modulating neurotransmitters in heart failure, and the superoxide activates NF-κB in the PVN and contributes to neurohumoral excitation. In conclusion, the neurohumoral excitation in HF is based on the interaction of RAS, PICs, ROS, NF-κB and neurotransmitters in the PVN; and the activated NF-κB in the PVN modulates the neurotransmitters and contributes to sympathoexcitation in rats with heart failure.

Inflammation and oxidative stress are elevated in the brain, blood, and adrenal glands during the progression of post-traumatic stress disorder in a predator exposure animal model

This study sought to analyze specific pathophysiological mechanisms involved in the progression of post-traumatic stress disorder (PTSD) by utilizing an animal model. To examine PTSD pathophysiology, we measured damaging reactive oxygen species and inflammatory cytokines to determine if oxidative stress and inflammation in the brain, adrenal glands, and systemic circulation were upregulated in response to constant stress. Pre-clinical PTSD was induced in naïve, male Sprague-Dawley rats via a predator exposure/psychosocial stress regimen. PTSD group rats were secured in Plexiglas cylinders and placed in a cage with a cat for one hour on days 1 and 11 of a 31-day stress regimen. In addition, PTSD group rats were subjected to psychosocial stress whereby their cage cohort was changed daily. This model has been shown to cause heightened anxiety, exaggerated startle response, impaired cognition, and increased cardiovascular reactivity, all of which are common symptoms seen in humans with PTSD. At the conclusion of the predator exposure/psychosocial stress regimen, the rats were euthanized and their brains were dissected to remove the hippocampus, amygdala, and pre-frontal cortex (PFC), the three areas commonly associated with PTSD development. The adrenal glands and whole blood were also collected to assess systemic oxidative stress. Analysis of the whole blood, adrenal glands, and brain regions revealed oxidative stress increased during PTSD progression. In addition, examination of pro-inflammatory cytokine (PIC) mRNA and protein demonstrated neurological inflammatory molecules were significantly upregulated in the PTSD group vs. controls. These results indicate oxidative stress and inflammation in the brain, adrenal glands, and systemic circulation may play a critical role in the development and further exacerbation of PTSD. Thus, PTSD may not be solely a neurological pathology but may progress as a systemic condition involving multiple organ systems.

Effect of naloxone on ischemic acute kidney injury in the mouse

Renal ischemia produces sympathoexcitation, which is responsible for the development of ischemic acute kidney injury. Stimulation of central opioid receptors activates the renal sympathetic nerve. The present study examined the effect of an opioid receptor antagonist naloxone on the ischemia/reperfusion-induced renal dysfunction in mice. Blood urea nitrogen (BUN) and plasma creatinine increased 24 h after the renal ischemia/reperfusion. Intraperitoneal or intracerebroventricular, but not intrathecal, pretreatment with naloxone suppressed the renal ischemia/reperfusion-induced increases in BUN and plasma creatinine. This effect of naloxone was reversed by subcutaneous pretreatment with morphine. Selective MOP receptor antagonist β-funaltrexamine (FNA) also suppressed the renal ischemia/reperfusion-induced increases in BUN and plasma creatinine. Moreover, tyrosine hydroxylase expression in the renal tissue increased 24 h after renal ischemia/reperfusion, which was abolished by intraperitoneal or intracerebroventricular pretreatment with naloxone and FNA. Immunohistochemical experiments revealed a significant increase in the number of the Fos family proteins (c-Fos, FosB, Fra-1, and Fra-2) positive cells in the paraventricular nucleus of hypothalamus and supraoptic nucleus 24 h after the renal ischemia/reperfusion. Intracerebroventricular pretreatment with naloxone attenuated the renal ischemia/reperfusion-induced increase in the number of the Fos family proteins positive cells in these areas. Finally, we observed that i.c.v. pretreatment with antiserum against β-endorphin also suppressed the increased blood urea and plasma creatinine. These results suggest that the blockade of central opioid receptors can attenuate the ischemic acute kidney injury through the inhibition of renal sympathoexcitation. The central opioid receptors may thus be a new target for the treatment of ischemic organ failures.

(Pro)renin receptor mediates both angiotensin II-dependent and -independent oxidative stress in neuronal cells

The binding of renin or prorenin to the (pro)renin receptor (PRR) promotes angiotensin (Ang) II formation and mediates Ang II-independent signaling pathways. In the central nervous system (CNS), Ang II regulates blood pressure via inducing oxidative stress; however, the role of PRR-mediated Ang II-independent signaling pathways in oxidative stress in the CNS remains undefined. To address this question, Neuro-2A cells were infected with control virus or an adeno-associated virus encoding the human PRR. Human PRR over-expression alone increased ROS levels, NADPH oxidase activity, as well as NADPH oxidase (NOX) isoforms 2 and 4 mRNA expression levels and these effects were not blocked by losartan. Moreover, the increase in NOX 2 and NOX 4 mRNA levels, NADPH oxidase activity, and ROS levels induced by PRR over-expression was prevented by mitogen activated protein kinase/extracellular signal-regulated kinase 1 and 2 (MAPK/ERK1/2) inhibition, and phosphoinositide 3 kinase/Akt (IP3/Akt) inhibition, indicating that PRR regulates NOX activity and ROS formation in neuro-2A cells through Ang II-independent ERK1/2 and IP3/Akt activation. Interestingly, at a concentration of 2 nM or higher, prorenin promoted Ang II formation, and thus further increased the ROS levels in cultured Neuro-2A cells via PRR. In conclusion, human PRR over-expression induced ROS production through both angiotensin II-dependent and -independent mechanisms. We showed that PRR-mediated angiotensin II-independent ROS formation is associated with activation of the MAPK/ERK1/2 and PI3/Akt signaling pathways and up-regulation of mRNA level of NOX 2 and NOX4 isoforms in neuronal cells.

Neuronal nitric oxide synthase is indispensable for the cardiac adaptive effects of exercise

Exercise results in beneficial adaptations of the heart that can be directly observed at the ventricular myocyte level. However, the molecular mechanism(s) responsible for these adaptations are not well understood. Interestingly, signaling via neuronal nitric oxide synthase (NOS1) within myocytes results in similar effects as exercise. Thus, the objective was to define the role NOS1 plays in the exercise-induced beneficial contractile effects in myocytes. After an 8-week aerobic interval training program, exercise-trained (Ex) mice had higher VO(2max) and cardiac hypertrophy compared to sedentary (Sed) mice. Ventricular myocytes from Ex mice had increased NOS1 expression and nitric oxide production compared to myocytes from Sed mice. Remarkably, acute NOS1 inhibition normalized the enhanced contraction (shortening and Ca(2+) transients) in Ex myocytes to Sed levels. The NOS1 effect on contraction was mediated via greater Ca(2+) cycling that resulted from increased phospholamban phosphorylation. Intriguingly, a similar aerobic interval training program on NOS1 knockout mice failed to produce any beneficial cardiac adaptations (VO(2max), hypertrophy, and contraction). These data demonstrate that the beneficial cardiac adaptations observed after exercise training were mediated via enhanced NOS1 signaling. Therefore, it is likely that beneficial effects of exercise may be mimicked by the interventions that increase NOS1 signaling. This pathway may provide a potential novel therapeutic target in cardiac patients who are unable or unwilling to exercise.

Exercise training prevents TNF-α induced loss of force in the diaphragm of mice

Rationale

Inflammatory cytokines like tumor necrosis factor alpha (TNF-α) are elevated in congestive heart failure and are known to induce the production of reactive oxygen species as well as to deteriorate respiratory muscle function.

Objectives

Given the antioxidative effects of exercise training, the aim of the present study was to investigate if exercise training is capable of preventing a TNF-α induced loss of diaphragmatic force in mice and, if so, to elucidate the potential underlying mechanisms.

Methods

Prior to intraperitoneal injection of TNF-α or saline, C57Bl6 mice were assigned to four weeks of exercise training or sedentary behavior. Diaphragmatic force and power generation were determined in vitro. Expression/activity of radical scavenger enzymes, enzymes producing reactive oxygen species and marker of oxidative stress were measured in the diaphragm.

Main Results

In sedentary animals, TNF-α reduced specific force development by 42% concomitant with a 2.6-fold increase in the amount of carbonylated α-actin and creatine kinase. Furthermore, TNF-α led to an increased NAD(P)H oxidase activity in both sedentary and exercised mice whereas xanthine oxidase activity and intramitochondrial ROS production was only enhanced in sedentary animals by TNF-α. Exercise training prevented the TNF-α induced force reduction and led to an enhanced mRNA expression and activity of glutathione peroxidase. Carbonylation of proteins, in particular of α-actin and creatine kinase, was diminished by exercise training.

Conclusion

TNF-α reduces the force development in the diaphragm of mice. This effect is almost abolished by exercise training. This may be a result of reduced carbonylation of proteins due to the antioxidative properties of exercise training.

Purinergic signalling in the rostral ventro-lateral medulla controls sympathetic drive and contributes to the progression of heart failure following myocardial infarction in rats

Heart failure may lead to hypoperfusion and hypooxygenation of tissues and this is often exacerbated by central and obstructive sleep apnoeas associated with recurrent episodes of systemic hypoxia which triggers release of ATP within the CNS circuits controlling sympathetic outflow. Using in vitro and in vivo models we tested two hypotheses: (1) activated brainstem astroglia release ATP and via release of ATP activate sympathoexcitatory neurones of the rostral ventrolateral medulla (RVLM); and (2) ATP actions in the RVLM contribute to sympathoexcitation, progression of left ventricular (LV) remodelling and development heart failure secondary to myocardial infarction. In vitro, optogenetic activation of RVLM astrocytes transduced to express light-sensitive channelrhodopsin-2 activated sympathoexcitatory RVLM neurones in ATP-dependent manner. In anaesthetised rats in vivo, similar optogenetic activation of RVLM astrocytes increased sympathetic renal nerve activity, arterial blood pressure and heart rate. To interfere with ATP-mediated signalling by promoting its extracellular breakdown, we developed a lentiviral vector to express an ectonucleotidase—transmembrane prostatic acid phosphatase (TMPAP) on the cellular membranes. In rats with myocardial infarction-induced heart failure, expression of TMPAP bilaterally in the RVLM led to lower plasma noradrenaline concentration, maintained left ventricular end diastolic pressure, attenuated decline in dP/dT_max and shifted the LV pressure–volume relationship curve to the left. These results show that activated RVLM astrocytes are capable of increasing sympathetic activity via release of ATP while facilitated breakdown of ATP in the RVLM attenuates the progression of LV remodelling and heart failure secondary to myocardial infarction.

Chronic exercise modulates RAS components and improves balance between pro- and anti-inflammatory cytokines in the brain of SHR

Recently, exercise has been recommended as a part of lifestyle modification for all hypertensive patients; however, the precise mechanisms of its effects on hypertension are largely unknown. Therefore, this study aimed to investigate the mechanisms within the brain that can influence exercise-induced effects in an animal model of human essential hypertension. Young normotensive WKY rats and SHR were given moderate-intensity exercise for 16 weeks. Blood pressure was measured bi-weekly by tail-cuff method. Animals were then euthanized; paraventricular nucleus (PVN) and rostral ventrolateral medulla (RVLM), important cardiovascular regulatory centers in the brain, were collected and analyzed by real-time RT-PCR, Western blot, EIA, and fluorescent microscopy. Exercise of 16-week duration attenuated systolic, diastolic, and mean arterial pressure in SHR. Sedentary SHR exhibited increased pro-inflammatory cytokines (PICs) and decreased anti-inflammatory IL-10 levels in the PVN and RVLM. Furthermore, SHR(sed) rats exhibited elevated levels of ACE, AT1R, and decreased levels of ACE2 and receptor Mas in the PVN and RVLM. Chronic exercise not only prevented the increase in PICs (TNF-α, IL-1β), ACE, and AT1R protein expression in the brain of SHR, but also dramatically upregulated IL-10, ACE2, and Mas receptor expression in SHR. In addition, these changes were associated with reduced plasma AngII levels, reduced neuronal activity, reduced NADPH-oxidase subunit gp91(phox) and inducible NO synthase in trained SHRs indicating reduced oxidative stress. These results suggest that chronic exercise not only attenuates PICs and the vasoconstrictor axis of the RAS but also improves the anti-inflammatory defense mechanisms and vasoprotective axis of the RAS in the brain, which, at least in part, explains the blood pressure-lowering effects of exercise in hypertension.

Angiotensin II-induced hypertension is modulated by nuclear factor-κBin the paraventricular nucleus

Hypertension is considered a low-grade inflammatory condition, and understanding the role of transcription factors in guiding this response is pertinent. A prominent transcription factor that governs inflammatory responses and has become a focal point in hypertensive research is nuclear factor-κB (NFκB). Within the hypothalamic paraventricular nucleus (PVN), a known brain cardioregulatory center, NFκB becomes potentially even more important in ultimately coordinating the systemic hypertensive response. To definitively demonstrate the role of NFκB in the neurogenic hypertensive response, we hypothesized that PVN NFκB blockade would attenuate angiotensin II-induced hypertension. Twelve-week-old male Sprague-Dawley rats were implanted with radiotelemetry probes for blood pressure measurement and allowed a 7-day recovery. After baseline blood pressure recordings, rats were administered either continuous NFκB decoy oligodeoxynucleotide infusion or microinjection of a serine mutated adenoviral inhibitory-κB vector, or their respective controls, bilaterally into the PVN to inhibit NFκB at two levels of its activation pathway. Simultaneously, rats were implanted subcutaneously with an angiotensin II or saline-filled 14-day osmotic minipump. After the 2-week treatments, rats were euthanized and brain tissues collected for PVN analysis. Bilaterally inhibited NFκB rats had a decrease in blood pressure, NFκB p65 subunit activity, proinflammatory cytokines, and reactive oxygen species, including the angiotensin II type 1 receptor, angiotensin-converting enzyme, tumor necrosis factor, and superoxide in angiotensin II-treated rats. Moreover, after NFκB blockade, key protective antihypertensive renin-angiotensin system components were upregulated. This demonstrates the important role that transcription factor NFκB plays within the PVN in modulating and perpetuating the hypertensive response via renin-angiotensin system modulation.

NF-κB in the paraventricular nucleus modulates neurotransmitters and contributes to sympathoexcitation in heart failure

Findings from our laboratory indicate that proinflammatory cytokines and their transcription factor, nuclear factor-kappaB (NF-κB), are increased in the hypothalamic paraventricular nucleus (PVN) and contribute towards the progression of heart failure. In this study, we determined whether NF-κB activation within the PVN contributes to sympathoexcitation via interaction with neurotransmitters in the PVN during the pathogenesis of heart failure. Heart failure was induced in rats by left anterior descending coronary artery ligation. Sham-operated control (SHAM) or heart failure rats were treated for 4 weeks through bilateral PVN infusion with SN50, SN50M or vehicle via osmotic minipump. Rats with heart failure treated with PVN vehicle or SN50M (inactive peptide for SN50) had increased levels of glutamate, norepinephrine (NE), tyrosine hydroxylase (TH), superoxide, gp91(phox) (a subunit of NAD(P)H oxidase), phosphorylated IKKβ and NF-κB p65 activity, and lower levels of gamma-aminobutyric acid (GABA) and the 67-kDa isoform of glutamate decarboxylase (GAD67) in the PVN compared with those of SHAM rats. Plasma levels of cytokines, norepinephrine, epinephrine and angiotensin II, and renal sympathetic nerve activity (RSNA) were increased in heart failure rats. Bilateral PVN infusion of SN50 prevented the decreases in PVN GABA and GAD67, and the increases in RSNA and PVN glutamate, norepinephrine, TH, superoxide, gp91(phox), phosphorylated IKKβ and NF-κB p65 activity observed in vehicle or SN50M-treated heart failure rats. A same dose of SN50 given intraperitoneally did not affect neurotransmitters concentration in the PVN and was similar to vehicle-treated heart failure rats. These findings suggest that NF-κB activation in the PVN modulates neurotransmitters and contributes to sympathoexcitation in rats with ischemia-induced heart failure.

Tumor necrosis factor receptor 2 signaling limits β-adrenergic receptor-mediated cardiac hypertrophy in vivo

The in vivo role of TNF signaling in the genesis of β-adrenergic receptor (β-AR)-mediated cardiac hypertrophy is unknown. Wild-type (WT), TNF receptor 1 (TNFR1)-/- and TNFR2-/- mice were given isoproterenol (ISO, 12.5 μg/kg/h) or saline (SAL) for 1 or 7 days. In WT mice, 7 days of ISO yielded chamber/myocyte hypertrophy and hyperdynamic function without hypertension or fibrosis. WT ISO hearts exhibited an early (1 day) pro-inflammatory response with significant (p < 0.05) activation of nuclear factor (NF)-κB and activator protein 1 (AP-1) and upregulation of TNF, interleukin (IL)-1β and IL-6, inducible nitric oxide synthase (iNOS) and monocyte chemotactic protein-1 (MCP-1), together with increased anti-inflammatory IL-10. This response diminished markedly by 7 days. As compared with WT ISO mice, TNFR1-/- ISO mice exhibited significantly (p < 0.05) less NF-κB and AP-1 activation, less IL-1β, TNF, iNOS and MCP-1 upregulation, but greater IL-10 at 1 day. However, there were no differences in hypertrophy or contractility at 7 days. In contrast, TNFR2-/- ISO mice exhibited augmented NF-κB and AP-1 activation, increased IL-1β and diminished IL-10 expression at 1 day, and significant exaggeration of hypertrophy and less contractile augmentation at 7 days. Moreover, TNFR2-/- mice exposed to tenfold higher ISO doses displayed significant mortality. TNF signaling contributes to β-AR-mediated cardiac remodeling in vivo in a receptor-specific manner. Unopposed TNFR1 activation is pro-inflammatory, pro-hypertrophic and promotes functional decline. However, co-activation of TNFR2 during β-AR stress is anti-inflammatory and counterbalances these deleterious effects. TNF modulatory strategies that maintain TNFR2 signaling may help prevent the detrimental long-term effects of β-AR stimulation in the heart.