Differential engagement of inhibitory and excitatory cardiopulmonary reflexes by capsaicin and phenylbiguanide in C57BL/6 mice

The Bezold-Jarisch reflex is a powerful inhibitory reflex initiated by activation of cardiopulmonary vagal nerves during myocardial ischemia, hemorrhage, and orthostatic stress leading to bradycardia, vasodilation, hypotension, and vasovagal syncope. This clinically relevant reflex has been studied by measuring heart rate (HR) and mean arterial pressure (MAP) responses to injections of a variety of chemical compounds. We hypothesized that reflex responses to different compounds vary due to differential activation of vagal afferent subtypes and/or variable coactivation of excitatory afferents. HR and MAP responses to intravenous injections of the transient receptor potential vanilloid-1 (TRPV1) agonist capsaicin and the serotonin 5-HT3 receptor agonist phenylbiguanide (PBG) were measured in anesthetized C57BL/6 mice before and after bilateral cervical vagotomy. Capsaicin and PBG evoked rapid dose-dependent decreases in HR and MAP followed by increases in HR and MAP above baseline. Bezold-Jarisch reflex responses were abolished after vagotomy, whereas the delayed tachycardic and pressor responses to capsaicin and PBG were differentially enhanced. The relative magnitude of bradycardic versus depressor responses (↓HR/↓MAP) in vagus-intact mice was greater with capsaicin. In contrast, after vagotomy, the magnitude of excitatory tachycardic versus pressor responses (↑HR/↑MAP) was greater with PBG. Although capsaicin-induced increases in MAP and HR postvagotomy were strongly attenuated or abolished after administration of the ganglionic blocker hexamethonium, PBG-induced increases in MAP and HR were mildly attenuated and unchanged, respectively. We conclude that responses to capsaicin and PBG differ in mice, with implications for delineating the role of endogenous agonists of TRPV1 and 5-HT3 receptors in evoking cardiopulmonary reflexes in pathophysiological states.

Plasticity of cerebral microvascular structure and mechanics during hypertension and following recovery of arterial pressure

Changes in vascular structure contribute to vascular events and loss of brain health. We examined changes in cerebral arterioles at the onset of hypertension and the hypothesis that alterations during hypertension would recover with the return of mean arterial pressure (MAP) to normal. MAP was measured with radiotelemetry in awake male C57BL/6J mice at baseline and during infusion of vehicle or angiotensin II (ANG II, 1.4 mg/kg/day using osmotic pumps) for 28 days, followed by a 28-day recovery. With ANG II treatment, MAP increased through day 28. On day 30, MAP began to recover, reaching levels not different from vehicle on day 37. We measured intravascular pressure, diameter, wall thickness (WT), wall:lumen ratio (W:L), cross-sectional area (CSA), and slope of the tangential elastic modulus (ET) in maximally dilated arterioles. Variables were similar in both groups at day 1, with no significant change with vehicle treatment. With ANG II treatment, CSA, WT, and W:L increased on days 7-28. Internal and external diameter was reduced at 14 and 28 days. ET versus wall stress was reduced on days 7-28. During recovery, the diameter remained at days 14 and 28 values, whereas other variables returned partly or completely to normal. Thus, CSA, WT, W:L, and ET versus wall stress changed rapidly during hypertension and recovered with MAP. In contrast, inward remodeling developed slowly and did not recover. This lack of recovery has mechanistic implications for the long-term impact of hypertension on vascular determinants of brain health.NEW & NOTEWORTHY Changes in vascular structure contribute to vascular events and loss of brain health. We examined the inherent structural plasticity of cerebral arterioles during and after a period of hypertension. Arteriolar wall thickness, diameter, wall-to-lumen ratio, and biological stiffness changed rapidly during hypertension and recovered with blood pressure. In contrast, inward remodeling developed slowly and did not recover. This lack of recovery of arteriolar diameter has implications for the long-term impact of hypertension on vascular determinants of brain health.

Research Opportunities in Autonomic Neural Mechanisms of Cardiopulmonary Regulation: A Report From the National Heart, Lung, and Blood Institute and the National Institutes of Health Office of the Director Workshop

This virtual workshop was convened by the National Heart, Lung, and Blood Institute, in partnership with the Office of Strategic Coordination of the Office of the National Institutes of Health Director, and held September 2 to 3, 2020. The intent was to assemble a multidisciplinary group of experts in basic, translational, and clinical research in neuroscience and cardiopulmonary disorders to identify knowledge gaps, guide future research efforts, and foster multidisciplinary collaborations pertaining to autonomic neural mechanisms of cardiopulmonary regulation. The group critically evaluated the current state of knowledge of the roles that the autonomic nervous system plays in regulation of cardiopulmonary function in health and in pathophysiology of arrhythmias, heart failure, sleep and circadian dysfunction, and breathing disorders. Opportunities to leverage the Common Fund's SPARC (Stimulating Peripheral Activity to Relieve Conditions) program were characterized as related to nonpharmacologic neuromodulation and device-based therapies. Common themes discussed include knowledge gaps, research priorities, and approaches to develop novel predictive markers of autonomic dysfunction. Approaches to precisely target neural pathophysiological mechanisms to herald new therapies for arrhythmias, heart failure, sleep and circadian rhythm physiology, and breathing disorders were also detailed.

Altering Early Life Gut Microbiota Has Long-Term Effect on Immune System and Hypertension in Spontaneously Hypertensive Rats

Hypertension is regulated by immunological components. Spontaneously hypertensive rats (SHR) display a large population of proinflammatory CD161 + immune cells. We investigated the effect of early post-natal gut microbiota on the development of the immune system and resulting hypertension in the SHR. We first examined the microbial populations in the fecal samples of SHR and normotensive control WKY using 16S rDNA sequencing. We found that in the newborn SHR (1-week old) the gut microbiota was qualitatively and quantitatively different from the newborns of normotensive WKY. The representation of the predominant bacterial phylum Proteobacteria was significantly less in 1-week old SHR pups than in WKY (94.5% Proteobacteria in WKY vs. 65.2% in SHR neonates). Even within the phylum Proteobacteria, the colonizing genera in WKY and SHR differed dramatically. Whereas WKY microbiota was predominantly comprised of Escherichia-Shigella, SHR microbiota was represented by other taxa of Enterobacteriaceae and Pasteurellaceae. In contrast, the representation of phylum Firmicutes in the neonatal SHR gut was greater than WKY. Cross-fostering newborn SHR pups by lactating WKY dams caused a dramatic shift in 1-week old cross-fostered SHR gut microbiota. The two major bacterial taxa of phylum Proteobacteria, Enterobacteriaceae and Pasteurellaceae as well as Lactobacillus intestinalis, Proteus, Romboustia and Rothia were depleted after cross-fostering and were replaced by the predominant genera of WKY (Escherichia-Shigella). A proinflammatory IL-17F producing CD161 + immune cell population in the spleen and aorta of cross-fostered SHR was also reduced (30.7% in self-fostered SHR vs. 12.6% in cross-fostered SHR at 30 weeks of age) as was the systolic blood pressure in adult cross-fostered SHR at 10 weeks of age. Thus, altered composition of gut microbiota of SHR toward WKY at early neonatal age had a long-lasting effect on immune system by reducing proinflammatory immune cells and lowering systolic blood pressure.

Carotid body chemoreceptors: physiology, pathology, and implications for health and disease

The carotid body (CB) is the main peripheral chemoreceptor for arterial respiratory gases O2 and CO2 and pH, eliciting reflex ventilatory, cardiovascular, and humoral responses to maintain homeostasis. This review examines the fundamental biology underlying CB chemoreceptor function, its contribution to integrated physiological responses, and its role in maintaining health and potentiating disease. Emphasis is placed on 1) transduction mechanisms in chemoreceptor (type I) cells, highlighting the role played by the hypoxic inhibition of O2-dependent K+ channels and mitochondrial oxidative metabolism, and their modification by intracellular molecules and other ion channels; 2) synaptic mechanisms linking type I cells and petrosal nerve terminals, focusing on the role played by the main proposed transmitters and modulatory gases, and the participation of glial cells in regulation of the chemosensory process; 3) integrated reflex responses to CB activation, emphasizing that the responses differ dramatically depending on the nature of the physiological, pathological, or environmental challenges, and the interactions of the chemoreceptor reflex with other reflexes in optimizing oxygen delivery to the tissues; and 4) the contribution of enhanced CB chemosensory discharge to autonomic and cardiorespiratory pathophysiology in obstructive sleep apnea, congestive heart failure, resistant hypertension, and metabolic diseases and how modulation of enhanced CB reactivity in disease conditions may attenuate pathophysiology.

Human papillomavirus (HPV) vaccine and autonomic disorders: a position statement from the American Autonomic Society

INTRODUCTION

Human papillomavirus (HPV) vaccination has been anecdotally connected to development of dysautonomia, chronic fatigue, complex regional pain syndrome and postural tachycardia syndrome.

OBJECTIVES

To critically evaluate a potential connection between HPV vaccination and above noted conditions.

METHODS

We reviewed the literature containing the biology of the virus, pathophysiology of infection, epidemiology of associated cancers, indications of HPV vaccination, safety surveillance data and published reports linking HPV vaccination to autonomic disorders.

RESULTS

At this time the American Autonomic Society finds that there are no data to support a causal relationship between HPV vaccination and CRPS, chronic fatigue, POTS or other forms of dysautonomia.

CONCLUSIONS

Certain conditions are prevalent in the same patient populations that are vaccinated with the HPV vaccine (peri-pubertal males and females). This association, however, is insufficient proof of causality.

Neurohormones in Vasovagal Syncope: Are They Important?

See Article Torabi et al

Increased receptor activity-modifying protein 1 in the nervous system is sufficient to protect against autonomic dysregulation and hypertension

Calcitonin gene-related peptide (CGRP) can cause migraines, yet it is also a potent vasodilator that protects against hypertension. Given the emerging role of CGRP-targeted antibodies for migraine prevention, an important question is whether the protective actions of CGRP are mediated by vascular or neural CGRP receptors. To address this, we have characterized the cardiovascular phenotype of transgenic nestin/hRAMP1 mice that have selective elevation of a CGRP receptor subunit in the nervous system, human receptor activity-modifying protein 1 (hRAMP1). Nestin/hRAMP1 mice had relatively little hRAMP1 RNA in blood vessels and intravenous injection of CGRP caused a similar blood pressure decrease in transgenic and control mice. At baseline, nestin/hRAMP1 mice exhibited similar mean arterial pressure, heart rate, baroreflex sensitivity, and sympathetic vasomotor tone as control mice. We previously reported that expression of hRAMP1 in all tissues favorably improved autonomic regulation and attenuated hypertension induced by angiotensin II (Ang II). Similarly, in nestin/hRAMP1 mice, hypertension caused by Ang II or phenylephrine was greatly attenuated, and associated autonomic dysregulation and increased sympathetic vasomotor tone were diminished or abolished. We conclude that increased expression of neuronal CGRP receptors is sufficient to induce a protective change in cardiovascular autonomic regulation with implications for migraine therapy.

TMEM16B determines cholecystokinin sensitivity of intestinal vagal afferents of nodose neurons

The satiety effects and metabolic actions of cholecystokinin (CCK) have been recognized as potential therapeutic targets in obesity for decades. We identified a potentially novel Ca2+-activated chloride (Cl-) current (CaCC) that is induced by CCK in intestinal vagal afferents of nodose neurons. The CaCC subunit Anoctamin 2 (Ano2/TMEM16B) is the dominant contributor to this current. Its expression is reduced, as is CCK current activity in obese mice on a high-fat diet (HFD). Reduced expression of TMEM16B in the heterozygote KO of the channel in sensory neurons results in an obese phenotype with a loss of CCK sensitivity in intestinal nodose neurons, a loss of CCK-induced satiety, and metabolic changes, including decreased energy expenditure. The effect on energy expenditure is further supported by evidence in rats showing that CCK enhances sympathetic nerve activity and thermogenesis in brown adipose tissue, and these effects are abrogated by a HFD and vagotomy. Our findings reveal that Ano2/TMEM16B is a Ca2+-activated chloride channel in vagal afferents of nodose neurons and a major determinant of CCK-induced satiety, body weight control, and energy expenditure, making it a potential therapeutic target in obesity.

Angiotensin II-induced hypertension and cardiac hypertrophy are differentially mediated by TLR3- and TLR4-dependent pathways

Toll-like receptors (TLR) are key components of the innate immune system that elicit inflammatory responses through the adaptor proteins myeloid differentiation protein 88 (MyD88) and Toll-interleukin receptor domain-containing adaptor protein-inducing interferon-β (TRIF). Previously, we demonstrated that TRIF mediates the signaling of angiotensin II (ANG II)- induced hypertension and cardiac hypertrophy. Since TRIF is activated selectively by TLR3 and TLR4, our goals in this study were to determine the roles of TLR3 and TLR4 in mediating ANG II-induced hypertension and cardiac hypertrophy, and associated changes in proinflammatory gene expression in heart and kidney. In wild-type (WT) mice, ANG II infusion (1,000 ng·kg^-1·min^-1 for 3 wk) increased systolic blood pressure and caused cardiac hypertrophy. In ANG II-infused TLR4-deficient mice (Tlr4^del), hypertrophy was significantly attenuated despite a preserved or enhanced hypertensive response. In contrast, in TLR3-deficient mice (Tlr3^-/-), both ANG II-induced hypertension and hypertrophy were abrogated. In WT mice, ANG II increased the expression of several proinflammatory genes in hearts and kidneys that were attenuated in both TLR4- and TLR3-deficient mice compared with WT. We conclude that ANG II activates both TLR4-TRIF and TLR3-TRIF pathways in a nonredundant manner whereby hypertension is dependent on activation of the TLR3-TRIF pathway and cardiac hypertrophy is dependent on both TLR3-TRIF and TLR4-TRIF pathways. NEW & NOTEWORTHY Angiotensin II (ANG II)-induced hypertension is dependent on the endosomal Toll-like receptor 3 (TLR3)-Toll-interleukin receptor domain-containing adaptor protein-inducing interferon-β (TRIF) pathway of the innate immune system but not on cell membrane localized TLR4. However, ANG II-induced cardiac hypertrophy is regulated by both TLR4-TRIF and TLR3-TRIF pathways. Thus, ANG II-induced rise in systolic blood pressure is independent of TLR4-TRIF effect on cardiac hypertrophy. The TLR3-TRIF pathway may be a potential target of therapeutic intervention.

PIEZOs mediate neuronal sensing of blood pressure and the baroreceptor reflex

Activation of stretch-sensitive baroreceptor neurons exerts acute control over heart rate and blood pressure. Although this homeostatic baroreflex has been described for more than 80 years, the molecular identity of baroreceptor mechanosensitivity remains unknown. We discovered that mechanically activated ion channels PIEZO1 and PIEZO2 are together required for baroreception. Genetic ablation of both Piezo1 and Piezo2 in the nodose and petrosal sensory ganglia of mice abolished drug-induced baroreflex and aortic depressor nerve activity. Awake, behaving animals that lack Piezos had labile hypertension and increased blood pressure variability, consistent with phenotypes in baroreceptor-denervated animals and humans with baroreflex failure. Optogenetic activation of Piezo2-positive sensory afferents was sufficient to initiate baroreflex in mice. These findings suggest that PIEZO1 and PIEZO2 are the long-sought baroreceptor mechanosensors critical for acute blood pressure control.

Abstract P202: Targeting the Cardiac Sympathetic Afferent Reflex in Hypertrophic Cardiomyopathy

Sarcomere gene mutations cause hypertrophic cardiomyopathy (HCM). Hallmark features include cardiac hypertrophy, fibrosis, excessive cardiac sympathetic tone, and increased risk of arrhythmias and sudden death. The mechanism(s) of increased sympathetic tone is poorly understood. We hypothesized that cardiac spinal (sympathetic) afferents are sensitized by metabolites (e.g., H+) produced during myocyte energy depletion in HCM, resulting in an enhanced cardiac sympathetic afferent reflex (CSAR). We studied mice with cardiac-specific expression of mutated alpha-tropomyosin (Glu180Gly), an established model of HCM. The CSAR was assessed by measuring mean arterial pressure (MAP) and heart rate (HR) responses to epicardial application of the TRPV1 agonist capsaicin (2.5mM, 2μL) to the left ventricle in anesthetized, ventilated HCM (n=5) and wild-type (WT) littermate control (n=5) mice. Pressor and tachycardic responses to capsaicin were markedly enhanced in HCM mice (Table). Blocking the tonic influence of cardiac afferent activity by epicardial application of the local anesthetic lidocaine (2%) caused small, significant decreases in MAP in both groups of mice; but decreased HR markedly in HCM mice only (n=5) (Table). mRNA expression (qPCR) of acid-sensing ion channel 3 was increased by 2-fold in dorsal root ganglia (T1-T9) of HCM vs. WT mice (n=6 each, P<0.05), suggesting a mechanism for sensitization of cardiac sympathetic afferents in HCM. We conclude that the CSAR is enhanced in HCM mice and speculate that increased activity of cardiac ‘sympathetic’ afferent nerves contributes to increased sympathetic tone, arrhythmias and disease progression in HCM.

Abstract P341: Renal Denervation Prevents Cholinergic Mediated Hypertension and Renal Macrophage Infiltration

In vivo cholinergic activation with nicotine induces renal infiltration of M1 inflammatory CD161a+/CD68+ macrophages and the development of hypertension. Renal denervation has been proposed as a treatment for essential hypertension. Based on this we hypothesized that the renal sympathetic nerves play a role in these processes. Bilateral renal denervation was performed surgically in 3-4 week old Spontaneously Hypertensive Rats (SHR), a genetic model of essential hypertension. Following one week recovery, animals received subcutaneous infusion of nicotine (15mg/kg/day) via osmotic pumps for 2 weeks. Blood pressure was measured by tail-cuff and kidneys harvested on completion of infusion. Prior to nicotine infusion, at baseline, there was no difference between the systolic blood pressures of the sham treated (n=7) and renal denervation (n=10) groups, 132 ± 4 vs 128 ± 3 mmHg, respectively (p>0.05). In contrast, nicotine infusion significantly raised the systolic blood pressure in the sham treated group (159 ± 3mmHg), but not in the renal denervation group (135 ± 5 mmHg) (p<0.001). Moreover, nicotine infusion induced a significantly greater infiltration of inflammatory CD161a+ immune cells and CD161a+/CD68+ inflammatory macrophages into the renal medulla of the sham treated group (n=4) (13 ± 2 cells/hpf and 5 ±1 cells/hpf, respectively), compared to renal denervation(n=4) (2 ± 1 cells/hpf and 2 ± 1 cells/hpf) (p<0.001). We conclude that renal sympathetic innervation is required for the nicotine-induced migration of inflammatory CD161a+ immune cells and CD161a+/CD68+ inflammatory macrophages into the renal medulla and that renal denervation prevents the cholinergic-induced renal inflammation and hypertension in this model.

Abstract 030: Angiotensin II-induced Hypertension and Cardiac Hypertrophy are Mediated Differentially by TLR3- and TLR4-dependent Pathways

The innate immune system plays a key role in onset and maintenance of hypertension. We showed that the toll-like receptor (TLR) adaptor protein TRIF (toll interleukin receptor domain-containing adaptor-inducing interferon-b), but not MyD88 (myeloid differentiation 88), is required for angiotensin II (Ang II) induced hypertension in mice. TRIF transduces signals from TLR3 and TLR4, to induce inflammatory gene expression. In this study, we sought to determine which TLR is responsible for TRIF-mediated hypertensive effects of Ang II. We used a TLR4 deficient mice (TLR4-del) that have TLR4 gene deleted and the wild type (WT) control strain (C57BL/10). We also used a TLR3-knockout mice (TLR3ko) that have the exon 1 of the Tlr3 gene deleted. Saline or Ang II (1000 ng/kg/min) was infused subcutaneously for 3 weeks using mini-osmotic pumps and systolic blood pressure (SBP) was measured by tail cuff. Ang II increased peak SBP in WT (from 108 ± 1.3 mmHg to 136.0 ± 12.7 mmHg, n= 3) and TLR4-del (from 115.6 ± 2.7 mmHg to 154.4 ± 3.3 mmHg, n=3) mice. In contrast, peak SBP was not increased significantly with Ang II infusion in TLR3ko mice (from 111.3 ± 4.5 to 122.2 ± 18.6 mmHg, n=6) nor was it increased in WT mice after selective inhibition of TLR3 signaling with CU CPT 4a. Thus, the TLR3/TRIF, but not TLR4, pathway is essential for Ang II hypertension. In parallel with the pressure responses to Ang II, renal expression of Nox4 was significantly decreased in TLR3ko mice but was unchanged in TLR4-del and WT mice.

In contrast to Ang II-induced hypertension, AngII-induced cardiac hypertrophy, measured as heart weight to body weight ratio, after 3 weeks of Ang II infusion was reduced in both TLR4-del (5.38 ± 0.19 mg/g) and TLR3ko (4.99 ± 0.15 mg/g) compared to WT (7.14 ± 0.49 mg/g). Thus, cardiac hypertrophy is abrogated in TLR4-del despite a robust pressor response to Ang II. The cardiac pro-inflammatory gene expression of tumor necrosis factor alpha ( Tnfa ), NADPH oxidase 4 ( Nox4 ), and matrix metalloproteinase 9 ( Mmp9 ) was increased in WT heart but attenuated in both TLR4-del and TLR3ko hearts. The results indicate a selective dependence of Ang II hypertension on TLR3/TRIF pathway whereas Ang II-induced cardiac hypertrophy depends on both TLR3 and TLR4, likely through the common TRIF adaptor protein.

Abstract 020: Heterozygote Knockout of TMEM16B in Intestinal Vagal Afferents Causes Cholecystokinin Insensitivity and Obesity in Male but Not Female Mice

Cholecystokinin (CCK) is a well-known satiety peptide that inhibits food intake. The CCK induced satiety signal in intestinal vagal afferents is attenuated in mice on a High Fat Diet (HFD). We have shown that down regulation of a Ca 2+ -activated Cl - channel (CaCC) downstream of CCK receptors is responsible for the neuronal insensitivity to CCK. We also found that the CaCC subunit Ano2/TMEM16B is essential for the CCK-induced current in nodose neurons. In this study we tested the hypothesis that reduction of this subunit in vivo contributes to weight gain. One allele of the Ano2/TMEM16B was knocked out in sensory neurons by crossing the ano2 fl/ fl mice with Nav1.8Cre mice to generate the Nav1.8Cre;ano2 fl /wt mice. The Cre negative littermates were used as control. We found that CCK-induced suppression of food intake is eliminated in male Nav1.8Cre;ano2 fl /wt mice. Food intake measured over 4 hours was 1.21±0.11g (n=5) in male wild type (wt) mice injected with saline and was reduced to 0.77±0.18 g (n=7, p<0.05) in mice injected with CCK-8 (3μg/kg). Those values were 0.63±0.15 g (n=6) in saline injected and 0.91±0.13 g (n=7, p>0.05) in CCK injected male Nav1.8Cre;ano2 fl /wt mice. However, the CCK injection did not affect food intake in either female wt or Nav1.8Cre;ano2 fl /wt mice. The male Nav1.8/ano2 fl/wt mice were on the average 5.5g heavier than wt mice at 40 weeks of age (39.8±1.4 g, n=13 vs 34.3±1.4 g, n=14, p<0.01). Body weight of females was significantly lower than in males but was not different between wt and Nav1.8Cre;ano2 fl /wt mice (30.4±1.0 g, n=14 vs 28.5±1.0 g, n=11, p=0.20 respectively). Single cell mRNA level of Ano2 and CCK-induced TMEM16 currents in nodose neurons were reduced significantly in male Nav1.8Cre;ano2 fl/wt mice compared to Cre negative controls, but such changes were not seen in female mice. We conclude that heterozygote knockout of Ano2/TMEM16B specifically in sensory neurons causes neuronal insensitivity to CCK and excessive weight gain in male but not female mice. Reduction of this subunit may contribute to the HFD induced obesity. The reason for the phenotype and allele expression variability between sexes is unclear.

The volume-regulated anion channel (LRRC8) in nodose neurons is sensitive to acidic pH

The leucine rich repeat containing protein 8A (LRRC8A), or SWELL1, is an essential component of the volume-regulated anion channel (VRAC) that is activated by cell swelling and ionic strength. We report here for the first time to our knowledge its expression in a primary cell culture of nodose ganglia neurons and its localization in the soma, neurites, and neuronal membrane. We show that this neuronal VRAC/SWELL1 senses low external pH (pH_o) in addition to hypoosmolarity. A robust sustained chloride current is seen in 77% of isolated nodose neurons following brief exposures to extracellular acid pH. Its activation involves proton efflux, intracellular alkalinity, and an increase in NOX-derived H₂O_2. The molecular identity of both the hypoosmolarity-induced and acid pH_o-conditioned VRAC as LRRC8A (SWELL1) was confirmed by Cre-flox-mediated KO, shRNA-mediated knockdown, and CRISPR/Cas9-mediated LRRC8A deletion in HEK cells and in primary nodose neuronal cultures. Activation of VRAC by low pH_o reduces neuronal injury during simulated ischemia and N-methyl-D-aspartate-induced (NMDA-induced) apoptosis. These results identify the VRAC (LRRC8A) as a dual sensor of hypoosmolarity and low pH_o in vagal afferent neurons and define the mechanisms of its activation and its neuroprotective potential.

Nicotine Mediates CD161a+ Renal Macrophage Infiltration and Premature Hypertension in the Spontaneously Hypertensive Rat

RATIONALE

Renal inflammation contributes to the pathophysiology of hypertension. CD161a+ immune cells are dominant in the (SHR) spontaneously hypertensive rat and expand in response to nicotinic cholinergic activation.

OBJECTIVE

We aimed to phenotype CD161a+ immune cells in prehypertensive SHR after cholinergic activation with nicotine and determine if these cells are involved in renal inflammation and the development of hypertension.

METHODS AND RESULTS

Studies used young SHR and WKY (Wistar-Kyoto) rats. Splenocytes and bone marrow cells were exposed to nicotine ex vivo, and nicotine was infused in vivo. Blood pressures, kidney, serum, and urine were obtained. Flow cytometry, Luminex/ELISA, immunohistochemistry, confocal microscopy, and Western blot were used. Nicotinic cholinergic activation induced proliferation of CD161a+/CD68+ macrophages in SHR-derived splenocytes, their renal infiltration, and premature hypertension in SHR. These changes were associated with increased renal expression of MCP-1 (monocyte chemoattractant protein-1) and VLA-4 (very-late antigen-4). LLT1 (lectin-like transcript 1), the ligand for CD161a, was overexpressed in SHR kidney, whereas vascular cellular and intracellular adhesion molecules were similar to those in WKY. Inflammatory cytokines were elevated in SHR kidney and urine after nicotine infusion. Nicotine-mediated renal macrophage infiltration/inflammation was enhanced in denervated kidneys, not explained by angiotensin II levels or expression of angiotensin type-1/2 receptors. Moreover, expression of the anti-inflammatory α7-nAChR (α7-nicotinic acetylcholine receptor) was similar in young SHR and WKY rats.

CONCLUSIONS

A novel, inherited nicotinic cholinergic inflammatory effect exists in young SHR, measured by expansion of CD161a+/CD68+ macrophages. This leads to renal inflammation and premature hypertension, which may be partially explained by increased renal expression of LLT-1, MCP-1, and VLA-4.

Chronic vagal nerve stimulation prevents high-salt diet-induced endothelial dysfunction and aortic stiffening in stroke-prone spontaneously hypertensive rats

Parasympathetic activity is often reduced in hypertension and can elicit anti-inflammatory mechanisms. Thus we hypothesized that chronic vagal nerve stimulation (VNS) may alleviate cardiovascular end-organ damage in stroke-prone spontaneously hypertensive rats. Vagal nerve stimulators were implanted, a high-salt diet initiated, and the stimulators turned on (VNS, n = 10) or left off (sham, n = 14) for 4 wk. Arterial pressure increased equally in both groups. After 4 wk, endothelial function, assessed by in vivo imaging of the long posterior ciliary artery (LPCA) after stimulation (pilocarpine) and inhibition (N(ω)-nitro-l-arginine methyl ester) of endothelial nitric oxide synthase (eNOS), had significantly declined (-2.3 ± 1.2 μm, P < 0.05) in sham, but was maintained (-0.7 ± 0.8 μm, nonsignificant) in VNS. Furthermore, aortic eNOS activation (phosphorylated to total eNOS protein content ratio) was greater in VNS (0.83 ± 0.07) than in sham (0.47 ± 0.08, P < 0.05). After only 3 wk, ultrasound imaging of the aorta demonstrated decreased aortic strain (-9.7 ± 2.2%, P < 0.05) and distensibility (-2.39 ± 0.49 1,000/mmHg, P < 0.05) and increased pulse-wave velocity (+2.4 ± 0.7 m/s, P < 0.05) in sham but not in VNS (-3.8 ± 3.8%, -0.70 ± 1.4 1,000/mmHg, and +0.1 ± 0.7 m/s, all nonsignificant). Interleukin (IL)-6 serum concentrations tended to be higher in VNS than in sham (34.3 ± 8.3 vs. 16.1 ± 4.6 pg/ml, P = 0.06), and positive correlations were found between NO-dependent relaxation of the LPCA and serum levels of IL-6 (r = +0.70, P < 0.05) and IL-10 (r = +0.56, P < 0.05) and between aortic eNOS activation and IL-10 (r = +0.48, P < 0.05). In conclusion, chronic VNS prevents hypertension-induced endothelial dysfunction and aortic stiffening in an animal model of severe hypertension. We speculate that anti-inflammatory mechanisms may contribute to these effects.

Fibrotic Aortic Valve Stenosis in Hypercholesterolemic/Hypertensive Mice

OBJECTIVE

Hypercholesterolemia and hypertension are associated with aortic valve stenosis (AVS) in humans. We have examined aortic valve function, structure, and gene expression in hypercholesterolemic/hypertensive mice.

APPROACH AND RESULTS

Control, hypertensive, hypercholesterolemic (Apoe(-/-)), and hypercholesterolemic/hypertensive mice were studied. Severe aortic stenosis (echocardiography) occurred only in hypercholesterolemic/hypertensive mice. There was minimal calcification of the aortic valve. Several structural changes were identified at the base of the valve. The intercusp raphe (or seam between leaflets) was longer in hypercholesterolemic/hypertensive mice than in other mice, and collagen fibers at the base of the leaflets were reoriented to form a mesh. In hypercholesterolemic/hypertensive mice, the cusps were asymmetrical, which may contribute to changes that produce AVS. RNA sequencing was used to identify molecular targets during the developmental phase of stenosis. Genes related to the structure of the valve were identified, which differentially expressed before fibrotic AVS developed. Both RNA and protein of a profibrotic molecule, plasminogen activator inhibitor 1, were increased greatly in hypercholesterolemic/hypertensive mice.

CONCLUSIONS

Hypercholesterolemic/hypertensive mice are the first model of fibrotic AVS. Hypercholesterolemic/hypertensive mice develop severe AVS in the absence of significant calcification, a feature that resembles AVS in children and some adults. Structural changes at the base of the valve leaflets include lengthening of the raphe, remodeling of collagen, and asymmetry of the leaflets. Genes were identified that may contribute to the development of fibrotic AVS.

Abstract P053: Nicotine-induced Renal Inflammation in Genetic Hypertension is Not Dependent on Renal Sympathetic Nerve Activity

We recently demonstrated that cholinergic stimulation with nicotine in vivo leads to renal inflammation and premature development of hypertension in Spontaneously Hypertensive Rats (SHR), but not in Wistar Kyoto (WKY) controls. Nicotine can stimulate immune cells directly and influence inflammation indirectly by increasing sympathetic nerve activity (SNA). We hypothesized that increased renal SNA contributes to nicotine-induced renal inflammation in SHR. We tested this hypothesis by measuring the number of CD68+ macrophages in kidneys of prehypertensive SHR (3-5 weeks old, n=7) and age-matched WKY rats (n=3) after subcutaneous infusion of nicotine via osmotic mini-pump (625 mcg/kg/hr) for 24 hours. Each rat was subjected to unilateral renal nerve denervation (RND) and sham surgery on the contralateral kidney 1 week before implanting the mini-pump. RND failed to abrogate nicotine-induced renal inflammation, actually increasing CD68+ macrophage infiltration in renal tubulointerstitium of SHR (110 ± 3 vs. 89 ± 1 cells/unit area in denervated vs. contralateral intact kidneys, respectively, p<0.001). RND had no effect on the number of infiltrating CD68+ macrophages in the tubulointerstitium of WKY controls (83 ± 3 vs. 79 ± 2 cells/unit area in denervated vs. intact kidneys, respectively, p>0.05). Renal norepinephrine content was measured by ELISA to confirm RND. We conclude that nicotine-induced renal macrophage infiltration in SHR is not dependent on renal SNA, and speculate that renal SNA may be anti-inflammatory in this model.

Abstract 072: TRIF-Pathway of Innate Immune Responses Mediates Angiotensin II Hypertension

We tested the role of two distinct adaptors of toll-like receptor (TLR) signaling on Ang II-induced hypertension and cardiac hypertrophy. These TLR adaptors, myeloid differentiation protein 88 (MyD88) and TIR domain-containing adaptor inducing interferon β (TRIF) facilitate distinct inflammatory signaling pathways. In an earlier study, we reported that MyD88-/- mice are protected from cardiac hypertrophy and pro-inflammatory gene expression after myocardial infarction. Our current results with 3 weeks infusion of Ang II (3000 ng/kg/min) vs. saline indicate that in MyD88-/- mice, the pressor response to Ang II and cardiac hypertrophy were increased more than in wild type (WT) mice. In Ang II-infused WT, systolic blood pressure (SBP) peaked at 147 ± 4 mmHg whereas in Ang II-infused MyD88-/- mice SBP reached a peak value of 163 ± 6 mmHg. However, in mice with non-functional TRIF adaptor mutant (Trifmut), SBP did not increase during Ang II infusion and remained similar to the SBP in saline-infused mice (115 ± 3 mmHg). Baseline SBP was not different among WT, MyD88-/- and Trifmut mice. The increase in heart weight to body weight ratio (HW/BW) between saline and Ang II-infused mice was greater in MyD88-/- mice than WT mice (60% increase in MyD88-/- vs. 40% increase in WT), whereas it was less in Trifmut mice (22% increase). Accordingly, expression of several inflammatory genes (Tnfa, Nox4 and Agtr1a) was significantly greater (P< 0.05) in the heart and kidney of Ang II-infused MyD88-/- mice compared with Ang II-infused WT mice, whereas expression of these genes in Trifmut mice was either unchanged or reduced. We conclude that- (1) Ang II-induced hypertension, cardiac hypertrophy and inflammatory gene expression are mediated by activation of a TRIF-dependent pathway, but not by the MyD88-dependent pathways, and (2) Enhanced Ang II effects on SBP and hypertrophy in MyD88-/- mice suggest that MyD88 may serve as a negative regulator of the TRIF pathway in Ang II-induced hypertension. Selective targeting of these adaptor proteins may have significant therapeutic implications.

Dual Activation of TRIF and MyD88 Adaptor Proteins by Angiotensin II Evokes Opposing Effects on Pressure, Cardiac Hypertrophy, and Inflammatory Gene Expression

Hypertension is recognized as an immune disorder whereby immune cells play a defining role in the genesis and progression of the disease. The innate immune system and its component toll-like receptors are key determinants of the immunologic outcome through their proinflammatory response. Toll-like receptor-activated signaling pathways use several adaptor proteins of which adaptor proteins myeloid differentiation protein 88 (MyD88) and toll-interleukin receptor domain-containing adaptor protein-inducing interferon-β (TRIF) define 2 major inflammatory pathways. In this study, we compared the contributions of MyD88 and TRIF adaptor proteins to angiotensin II (Ang II)-induced hypertension and cardiac hypertrophy in mice. Deletion of MyD88 did not prevent cardiac hypertrophy and the pressor response to Ang II tended to increase. Moreover, the increase in inflammatory gene expression (Tnfa, Nox4, and Agtr1a) was significantly greater in the heart and kidney of MyD88-deficient mice when compared with wild-type mice. Thus, pathways involving MyD88 may actually restrain the inflammatory responses. However, in mice with nonfunctional TRIF (Trif(mut) mice), Ang II-induced hypertension and cardiac hypertrophy were abrogated, and proinflammatory gene expression in heart and kidneys was unchanged or decreased. Our results indicate that Ang II induces activation of a proinflammatory innate immune response, causing hypertension and cardiac hypertrophy. These effects require functional adaptor protein TRIF-mediated pathways. However, the common MyD88-dependent signaling pathway, which is also activated simultaneously by Ang II, paradoxically exerts a negative regulatory influence on these responses.

Calcium/calmodulin-dependent kinase II inhibition in smooth muscle reduces angiotensin II-induced hypertension by controlling aortic remodeling and baroreceptor function

Background

Multifunctional calcium/calmodulin-dependent kinase II (CaMKII) is activated by angiotensin II (Ang II) in cultured vascular smooth muscle cells (VSMCs), but its function in experimental hypertension has not been explored. The aim of this study was to determine the impact of CaMKII inhibition selectively in VSMCs on Ang II hypertension.

Methods and Results

Transgenic expression of a CaMKII peptide inhibitor in VSMCs (TG SM-CaMKIIN model) reduced the blood pressure response to chronic Ang II infusion. The aortic depressor nerve activity was reset in hypertensive versus normotensive wild-type animals but not in TG SM-CaMKIIN mice, suggesting that changes in baroreceptor activity account for the blood pressure difference between genotypes. Accordingly, aortic pulse wave velocity, a measure of arterial wall stiffness and a determinant of baroreceptor activity, increased in hypertensive versus normotensive wild-type animals but did not change in TG SM-CaMKIIN mice. Moreover, examination of blood pressure and heart rate under ganglionic blockade revealed that VSMC CaMKII inhibition abolished the augmented efferent sympathetic outflow and renal and splanchnic nerve activity in Ang II hypertension. Consequently, we hypothesized that VSMC CaMKII controls baroreceptor activity by modifying arterial wall remodeling in Ang II hypertension. Gene expression analysis in aortas from normotensive and Ang II–infused mice revealed that TG SM-CaMKIIN aortas were protected from Ang II–induced upregulation of genes that control extracellular matrix production, including collagen. VSMC CaMKII inhibition also strongly altered the expression of muscle contractile genes under Ang II.

Conclusions

CaMKII in VSMCs regulates blood pressure under Ang II hypertension by controlling structural gene expression, wall stiffness, and baroreceptor activity.

Angiotensin-dependent autonomic dysregulation precedes dilated cardiomyopathy in a mouse model of muscular dystrophy

NEW FINDINGS

What is the central question of this study? Is autonomic dysregulation in a mouse model of muscular dystrophy dependent on left ventricular systolic dysfunction and/or activation of the renin-angiotensin system (RAS) and does it predict development of dilated cardiomyopathy (DCM)? What is the main finding and its importance? The results demonstrate that autonomic dysregulation precedes and predicts left ventricular dysfunction and DCM in sarcoglycan-δ-deficient (Sgcd-/-) mice. The autonomic dysregulation is prevented by treatment of young Sgcd-/- mice with the angiotensin II type 1 receptor blocker losartan. Measurements of RAS activation and autonomic dysregulation may predict risk of DCM, and therapies targeting the RAS and autonomic dysregulation at a young age may slow disease progression in patients. Sarcoglycan mutations cause muscular dystrophy. Patients with muscular dystrophy develop autonomic dysregulation and dilated cardiomyopathy (DCM), but the temporal relationship and mechanism of autonomic dysregulation are not well understood. We hypothesized that activation of the renin-angiotensin system (RAS) causes autonomic dysregulation prior to development of DCM in sarcoglycan-δ-deficient (Sgcd-/-) mice and that the severity of autonomic dysfunction at a young age predicts the severity of DCM at older ages. At 10-12 weeks of age, when left ventricular function assessed by echocardiography remained normal, Sgcd-/- mice exhibited decreases in arterial pressure, locomotor activity, baroreflex sensitivity and cardiovagal tone and increased sympathetic tone compared with age-matched C57BL/6 control mice (P < 0.05). Systemic and skeletal muscle RAS were activated, and angiotensin II type 1 receptor (AT1 R) expression, superoxide and fibrosis were increased in dystrophic skeletal muscle (P < 0.05). Treatment with the AT1 R blocker losartan for 7-9 weeks beginning at 3 weeks of age prevented or strongly attenuated the abnormalities in Sgcd-/- mice (P < 0.05). Repeated assessment of phenotypes between 10 and 75 weeks of age demonstrated worsening of autonomic function, progressive cardiac dysfunction and DCM and increased mortality in Sgcd-/- mice. High sympathetic tone predicted subsequent left ventricular dysfunction. We conclude that activation of the RAS causes severe autonomic dysregulation in young Sgcd-/- mice, which portends a worse long-term prognosis. Therapeutic targeting of the RAS at a young age may improve autonomic function and slow disease progression in muscular dystrophy.

Habituation of parasympathetic-mediated heart rate responses to recurring acoustic startle

Startle habituation is a type of implicit and automatic emotion regulation. Diminished startle habituation is linked to several psychiatric or neurological disorders. Most previous studies quantified startle habituation by assessing skin conductance response (SCR; reflecting sympathetic-mediated sweating), eye-blink reflex, or motor response. The habituation of parasympathetic-mediated heart rate responses to recurrent startle stimuli is not well understood. A variety of methods and metrics have been used to quantify parasympathetic activity and its effects on the heart. We hypothesized that these different measures reflect unique psychological and physiological processes that may habituate differently during repeated startle stimuli. We measured cardiac inter-beat intervals (IBIs) to recurring acoustic startle probes in 75 eight year old children. Eight acoustic stimuli of 500 ms duration were introduced at intervals of 15-25 s. Indices of parasympathetic effect included: (1) the initial rapid decrease in IBI post-startle mediated by parasympathetic inhibition (PI); (2) the subsequent IBI recovery mediated by parasympathetic reactivation (PR); (3) rapid, beat-to-beat heart rate variability (HRV) measured from the first seven IBIs following each startle probe. SCR and motor responses to startle were also measured. Results showed that habituation of PR (IBI recovery and overshoot) and SCRs were rapid and robust. In addition, changes in PR and SCR were significantly correlated. In contrast, habituation of PI (the initial decrease in IBI) was slower and relatively modest. Measurement of rapid HRV provided an index reflecting the combination of PI and PR. We conclude that different measures of parasympathetic-mediated heart rate responses to repeated startle probes habituate in a differential manner.

Autocrine/paracrine modulation of baroreceptor activity after antidromic stimulation of aortic depressor nerve in vivo

Activation of the sensory nerve endings of non-myelinated C-fiber afferents evokes release of autocrine/paracrine factors that cause localized vasodilation, neurogenic inflammation, and modulation of sensory nerve activity. The aims of this study were to determine the effect of antidromic electrical stimulation on afferent baroreceptor activity in vivo, and investigate the role of endogenous prostanoids and hydrogen peroxide (H2O2) in mediating changes in nerve activity. Baroreceptor activity was recorded from the left aortic depressor nerve (ADN) in anesthetized rats before and after stimulating the ADN for brief (5–20 s) periods. The rostral end of the ADN was crushed or sectioned beforehand to prevent reflex changes in blood pressure. Antidromic stimulation of ADN using parameters that activate both myelinated A-fibers and non-myelinated C-fibers caused pronounced and long-lasting (> 1 min) inhibition of baroreceptor activity (n = 9, P < 0.05), with the magnitude and duration of inhibition dependent on the duration of the stimulation period (n = 5). Baroreceptor activity was only transiently inhibited after selective stimulation of A-fibers. The inhibition of activity after antidromic stimulation of A and C fibers was prolonged after administration of the cyclooxygenase inhibitor indomethacin (5 mg/kg, IV, n = 7) and abolished after administration of PEG-catalase (104 units/kg, IV, n = 7), an enzyme that catalyzes the decomposition of H2O2 to water and oxygen. The results demonstrate a long-lasting inhibition of baroreceptor activity after antidromic stimulation of ADN and suggest that endogenous prostanoids and H2O2 oppose and mediate the inhibition, respectively. These mechanisms may contribute to rapid baroreceptor resetting during acute hypertension and be engaged during chronic baroreceptor activation therapy in patients with hypertension.

Abstract 003: Cholinergic Expansion of an Inflammatory Macrophage Population in the Pre-Hypertensive Spontaneously Hypertensive Rat

Our laboratory previously identified an abnormally elevated CD161a+ immune cell population in splenocytes of the pre-hypertensive Spontaneously Hypertensive Rat (SHR) that was abnormally expanded following cholinergic activation with nicotine . In the present study, we tested the hypothesis that the expanded CD161a+ cell population represents an activated monocyte/macrophage population and are present in the bone marrow (BM). We isolated cells from the spleen and BM of pre-hypertensive (4-5 week old) SHR (n=3) and age-matched normotensive Wistar Kyoto (WKY, n=3) rats. Isolated cells were stained with a fluorochrome conjugated anti-rat CD161a monoclonal antibody and analyzed by flow cytometry. CD161a+ cells were more prevalent in splenocytes and BM of the pre-hypertensive SHR, compared to WKY (8.7 ± 1.4% vs 1.2 ± 0.6% and 12.6 ± 1.8% vs 1.7 ± 0.8%, respectively, p<0.001). BM cells and splenocytes were cultured for 36-48 hours in the presence or absence of nicotine (10μM) and then stained with fluorochrome conjugated anti-rat CD161a and CD68 antibodies. CD68 is a well accepted pan-macrophage marker that is up-regulated on activated monocytes/macrophages. The CD161+/CD68+ macrophages were comparable between the WKY and SHR in freshly isolated cells from the spleen (0.3 ± 0.2% vs 0.9 ± 0.5%, respectively) and BM (0.6 ± 0.4% vs 0.7 ± 0.2%, respectively). However, nicotine strongly expanded the CD161a+/CD68+ macrophage population in the BM of the SHR (1.1 ± 0.15% to 11.9 ± 3.45%, p<0.001) and WKY (1.7 ± 0.17% to 11.0 ± 1.9%, p<0.001). In contrast, the response of splenocytes to nicotine was strong in SHR (1.8 ± 0.40% to 10.7 ± 1.1%, p<0.001), but not significant in WKY (1.9 ± 0.4% to 3.1 ± 0.6%, p>0.05). Nicotine had no effect on the CD161a+/CD68- cell population in either splenocytes or BM cells of the SHR or WKY. Thus, an activated monocyte/macrophage population (CD161a+/CD68+) is expanded by cholinergic activation in both the BM and spleen of SHR, but only in the BM and not spleen of the WKY. Since, the pro-inflammatory nicotinic response present in the BM of the WKY is abrogated in the peripheral spleen, we conclude that the retention of this response in the SHR may contribute to the development of hypertension.

Blood pressure regulation XI: overview and future research directions

While the importance of regulating arterial blood pressure within a 'normal' range is widely appreciated, the definition of 'normal' and the means by which humans and other species regulate blood pressure under various conditions remain hotly debated. The effects of diverse physiological, pathological and environmental challenges on blood pressure and the mechanisms that attempt to maintain it at an optimal level are reviewed and critically analyzed in a series of articles published in this themed issue of the European Journal of Applied Physiology. We summarize here the major points made in these reviews, with emphasis on unifying concepts of regulatory mechanisms and future directions for research.

Autonomic, locomotor and cardiac abnormalities in a mouse model of muscular dystrophy: targeting the renin-angiotensin system

New Findings What is the topic of this review? This symposium report summarizes autonomic, cardiac and skeletal muscle abnormalities in sarcoglycan-δ-deficient mice (Sgcd-/-), a mouse model of limb girdle muscular dystrophy, with emphasis on the roles of autonomic dysregulation and activation of the renin-angiotensin system at a young age. What advances does it highlight? The contributions of the autonomic nervous system and the renin-angiotensin system to the pathogenesis of muscular dystrophy are highlighted. Results demonstrate that autonomic dysregulation precedes and predicts later development of cardiac dysfunction in Sgcd-/- mice and that treatment of young Sgcd-/- mice with the angiotensin type 1 receptor antagonist losartan or with angiotensin-(1-7) abrogates the autonomic dysregulation, attenuates skeletal muscle pathology and increases spontaneous locomotor activity. Muscular dystrophies are a heterogeneous group of genetic muscle diseases characterized by muscle weakness and atrophy. Mutations in sarcoglycans and other subunits of the dystrophin-glycoprotein complex cause muscular dystrophy and dilated cardiomyopathy in animals and humans. Aberrant autonomic signalling is recognized in a variety of neuromuscular disorders. We hypothesized that activation of the renin-angiotensin system contributes to skeletal muscle and autonomic dysfunction in mice deficient in the sarcoglycan-δ (Sgcd) gene at a young age and that this early autonomic dysfunction contributes to the later development of left ventricular (LV) dysfunction and increased mortality. We demonstrated that young Sgcd-/- mice exhibit histopathological features of skeletal muscle dystrophy, decreased locomotor activity and severe autonomic dysregulation, but normal LV function. Autonomic regulation continued to deteriorate in Sgcd-/- mice with age and was accompanied by LV dysfunction and dilated cardiomyopathy at older ages. Autonomic dysregulation at a young age predicted later development of LV dysfunction and higher mortality in Sgcd-/- mice. Treatment of Sgcd-/- mice with the angiotensin type 1 receptor blocker losartan for 8-9 weeks, beginning at 3 weeks of age, decreased fibrosis and oxidative stress in skeletal muscle, increased locomotor activity and prevented autonomic dysfunction. Chronic infusion of the counter-regulatory peptide angiotensin-(1-7) resulted in similar protection. We conclude that activation of the renin-angiotensin system, at a young age, contributes to skeletal muscle and autonomic dysfunction in muscular dystrophy. We speculate that the latter is mediated via abnormal sensory nerve and/or cytokine signalling from dystrophic skeletal muscle to the brain and contributes to age-related LV dysfunction, dilated cardiomyopathy, arrhythmias and premature death. Therefore, correcting the early autonomic dysregulation and renin-angiotensin system activation may provide a novel therapeutic approach in muscular dystrophy.

Abstract 13: Central Sympathoinhibition Abrogates Skeletal Muscle Fibrosis, Oxidative Stress and Autonomic Dysregulation in a Mouse Model of Muscular Dystrophy

Sarcoglycan mutations cause muscular dystrophy in humans. We recently demonstrated that sarcoglycan delta deficient (Sgcd-/-) mice with muscular dystrophy exhibit autonomic dysregulation [Hypertension 2010]. We hypothesized that excessive sympathetic activity contributes to skeletal muscle pathology, decreased locomotor activity and autonomic dysregulation in young (10-12 wks) Sgcd-/- mice. The centrally-acting sympathoinhibitory drug rilmenidine (RIL) was infused into the brain of control C57BL6 and Sgcd-/- mice by osmotic pump for 7-9 wks beginning at 3 wks of age (42 ng/g/hr, ICV). Separate groups of mice were infused with saline vehicle (VEH). Blood pressure (BP), heart rate (HR) and locomotor activity were measured by telemetry. Cardiac (HR responses to propranolol) and vasomotor (BP response to ganglionic blockade) sympathetic tone were increased in VEH-treated Sgcd-/- mice, and normalized by RIL (Table). The RIL-induced sympathoinhibition in Sgcd-/- mice was accompanied by increases in baroreflex sensitivity (BRS, sequence technique), cardiovagal tone (HR response to atropine) and activity, with no change in BP (Table). RIL also decreased oxidative stress (superoxide) by 56% and fibrosis in Sgcd-/- skeletal muscle. RIL did not affect measured variables in control mice (Table). In summary, RIL-induced sympathoinhibition decreased skeletal muscle pathology, increased locomotor activity and improved autonomic regulation in young Sgcd-/- mice. The results implicate increased sympathetic activity in the pathogenesis of muscular dystrophy, and suggest that targeting the brain to inhibit sympathetic activity may provide a novel therapeutic approach.

Abstract 394: Angiotensin II Mediated Increase in Hypertension and Cardiac Hypertrophy in MyD88 Knockout Mice

Toll-like receptors (TLR) are a class of pattern-recognizing receptors (PRR) that play a central role in the innate immune response during infection and sterile injury. MyD88 is an adapter protein that mediates the majority of TLR responses. Since inflammation is a coexisting condition in several cardiovascular diseases, TLRs are thought to play a major role in these conditions. We have previously shown that indeed post-MI survival was significantly improved and cardiac fibrosis and hypertrophy were reduced in MyD88-/- mice (Singh et al. 2012. JMCC). In this study we tested whether angiotensin II (AngII) hypertension and cardiac hypertrophy depended on TLR signaling pathways mediated by MyD88. Male MyD88-/- mice and C57BL/6 mice of 10 to 12 weeks of age were subcutaneously implanted with osmotic minipumps (Alzet) eluting saline or AngII (Sigma, 733 ng/kg/min). Tailcuff pressures were measured with BP2000 (Visitech Systems). Mice were sacrificed after 3 weeks of AngII infusion and hearts were collected for weighing and gene expression analyses. In control WT mice, mean arterial pressure (MAP) remained near baseline levels during the first week of infusion averaging 71± 2 mm Hg and then increased to an average of 100 ± 3 mm Hg and 102 ± 2 mm Hg during the 2nd and 3rd weeks of infusions, respectively. In MyD88-/- mice, MAP increased from a baseline of 84 ± 3 to a high of 120 ± 7 mm Hg during the first week and then declined to 109 ± 6 and 91 ± 9 mm Hg during the 2nd and 3rd weeks. The heart weight to body weight ratios (HW/BW x 1000) after 3 weeks of AngII infusion were not significantly different between WT (5.23 ± 0.15) and MyD88-/- (4.76 ± 0.16). Increases in cardiac hypertrophic marker gene Acta1 were up 4-fold in both WT and MyD88-/- mice, and increases in proinflammatory TNF-alpha, IL-1β, and Nox4 were seen in both genotypes, but the increase in TNF-alpha was significantly greater in MyD88-/- mice.

We conclude that unlike post- MI cardiac hypertrophy, the AngII cardiac hypertrophy is not MyD88 -dependent, yet the delayed Ang II pressor response is abrogated in the absence of MyD88. The delayed pressor response to AngII infusion is likely dependent on the immune system.

Testing the autonomic nervous system

Autonomic testing is used to define the role of the autonomic nervous system in diverse clinical and research settings. Because most of the autonomic nervous system is inaccessible to direct physiological testing, in the clinical setting the most widely used techniques entail the assessment of an end-organ response to a physiological provocation. The noninvasive measures of cardiovascular parasympathetic function involve the assessment of heart rate variability while the measures of cardiovascular sympathetic function assess the blood pressure response to physiological stimuli. Tilt-table testing, with or without pharmacological provocation, has become an important tool in the assessment of a predisposition to neurally mediated (vasovagal) syncope, the postural tachycardia syndrome, and orthostatic hypotension. Distal, postganglionic, sympathetic cholinergic (sudomotor) function may be evaluated by provoking axon reflex mediated sweating, e.g., the quantitative sudomotor axon reflex (QSART) or the quantitative direct and indirect axon reflex (QDIRT). The thermoregulatory sweat test provides a nonlocalizing measure of global pre- and postganglionic sudomotor function. Frequency domain analyses of heart rate and blood pressure variability, microneurography, and baroreflex assessment are currently research tools but may find a place in the clinical assessment of autonomic function in the future.

Responses of glomus cells to hypoxia and acidosis are uncoupled, reciprocal and linked to ASIC3 expression: selectivity of chemosensory transduction

Carotid body glomus cells are the primary sites of chemotransduction of hypoxaemia and acidosis in peripheral arterial chemoreceptors. They exhibit pronounced morphological heterogeneity. A quantitative assessment of their functional capacity to differentiate between these two major chemical signals has remained undefined. We tested the hypothesis that there is a differential sensory transduction of hypoxia and acidosis at the level of glomus cells. We measured cytoplasmic Ca(2+) concentration in individual glomus cells, isolated in clusters from rat carotid bodies, in response to hypoxia ( mmHg) and to acidosis at pH 6.8. More than two-thirds (68%) were sensitive to both hypoxia and acidosis, 19% were exclusively sensitive to hypoxia and 13% exclusively sensitive to acidosis. Those sensitive to both revealed significant preferential sensitivity to either hypoxia or to acidosis. This uncoupling and reciprocity was recapitulated in a mouse model by altering the expression of the acid-sensing ion channel 3 (ASIC3) which we had identified earlier in glomus cells. Increased expression of ASIC3 in transgenic mice increased pH sensitivity while reducing cyanide sensitivity. Conversely, deletion of ASIC3 in the knockout mouse reduced pH sensitivity while the relative sensitivity to cyanide or to hypoxia was increased. In this work, we quantify functional differences among glomus cells and show reciprocal sensitivity to acidosis and hypoxia in most glomus cells. We speculate that this selective chemotransduction of glomus cells by either stimulus may result in the activation of different afferents that are preferentially more sensitive to either hypoxia or acidosis, and thus may evoke different and more specific autonomic adjustments to either stimulus.

Abstract 168: Abnormal Pro-inflammatory Regulation of the Innate Immune System in Genetic Hypertension

Immune cells from patients with essential hypertension are hyper-responsive to activation of toll-like receptor (TLR) 4 with lipopolysaccharide. Activation of the alpha7 nicotinic cholinergic receptor exerts an anti-inflammatory effect on innate immune cells. We hypothesized that this anti-inflammatory cholinergic response is lacking in the Spontaneously Hypertensive Rat (SHR) and recently reported that nicotine suppresses TLR7 and TLR9 mediated IL-6 secretion by isolated splenocytes of WKY rats; whereas, it dramatically enhances IL-6 secretion in SHR. Here we aimed to confirm these effects in vivo and identify potential cellular mediators of the observed immune responses. Flow cytometry on splenocytes revealed a greater number of CD3-/CD8dim innate immune cells in SHR (4.0±0.56%), compared to WKY (2.97±0.6%)(n=3, p<0.05). Using CD161, a cell surface marker of natural kille/dendritic cells and activated macrophages, we show that the CD3-/CD8dim+/CD161+ and CD3-/ CD8-/CD161+ innate immune cells are increased in SHR (5±0.5% and 4.6±0.85, respectively), compared to WKY (0.8±0.3% and 1.0±0.5%, respectively) (n=3, p<0.05). Moreover, nicotine expanded both cell populations in the SHR to 6.4% and 6.0%, respectively, but had no effect in WKY, where the populations remained at 1.1% and 1.2%, respectively. In vivo, we infused saline or nicotine (15mg/kg/day) over 24 hours using subcutaneous pumps. At 20 hrs, animals received an intraperitoneal injection of a TLR7 ligand (Clo97). Serum was collected at the end of the 24 hr infusion. Similar to previous in vitro results, nicotine suppressed the serum IL-6 response to i.p. Clo97 from 108±28 pg/ml in WKY (n=4) to 12±7 pg/ml (p<0.05) in 4-5 week old WKY, but dramatically enhanced the IL-6 response in SHR (n=4), following i.p. Clo97, from 58±20 pg/ml to 187±38 pg/ml (p<0.05). We conclude that there is a dominant innate immune cell population in SHR prior to the development of hypertension that expands with cholinergic stimulation and may contribute to the pronounced pro-inflammatory increase in IL-6 following cholinergic stimulation. We speculate that this abnormality in the pre-hypertensive state contributes to the development of genetic hypertension and may play a role in human essential hypertension.

Abstract 398: Angiotensin-[1-7] Infusion Reduces Skeletal Muscle Fibrosis and Restores Locomotor Activity and Sympathovagal Balance in a Mouse Model of Muscular Dystrophy

Muscular dystrophy is a catastrophic, fatal neuromuscular disease in need of new therapies. Angiotensin II binding to AT 1 receptors (AT 1 R) contributes to fibrosis in dystrophic skeletal muscle and AT 1 R blockers are currently being tested in clinical trials. Recently, we reported that autonomic dysregulation precedes and predicts development of cardiomyopathy in sarcoglycan delta deficient (Sgcd-/-) mice with muscular dystrophy (Clin Auton Res, 2010 ). We hypothesized that infusion of the angiotensin peptide Ang-[1-7] will rescue skeletal muscle, locomotor, and autonomic nervous system phenotypes in young Sgcd-/- mice. Control and Sgcd-/- mice were infused with Ang-[1-7] (300 ng/kg/min) for 8 wks beginning at 3 wks of age. Blood pressure (BP), heart rate (HR) and activity were recorded by telemetry in treated and untreated mice. Baroreflex sensitivity (BRS, sequence technique) and resting cardiac vagal and sympathetic tone (HR responses to atropine and propranolol) were measured. BP, activity, BRS and vagal tone were lower in Sgcd-/- vs. control mice, whereas sympathetic tone was higher (Table). Ang-[1-7] normalized activity, BRS, and sympathovagal balance in Sgcd-/- mice without affecting BP, and did not influence any variable in control mice. Skeletal muscle fibrosis present in Sgcd-/- mice (18±1%, n=9) was markedly reduced by Ang-[1-7] (3±1%, n=5). We conclude that Ang-[1-7] reduces skeletal muscle fibrosis and restores locomotor activity and sympathovagal balance in Sgcd-/- mice, without lowering BP. Ang-[1-7] and/or enhancement of its endogenous production may provide a novel therapeutic approach to muscular dystrophy.

Abstract 199: Hydrogen Peroxide Mediates the pH Conditioned Chloride Conductance in Nodose Ganglia Neurons

pH sensitivity has been rarely studied in vagal afferents of nodose ganglia (NG) neurons. Using whole-cell patch-clamp technique in isolated NG neurons, we recently identified a pH-conditioned Cl - current (pH-I) that was evoked following 2 or 3 brief (10s) exposures to low extracellular pH (7.0-6.0) in 16 of 22 (70%) cells (FASEB J, 2012). The current is large (904.3±159.9pA) and prolonged, lasting 10∼15 minutes, and causes significant depolarization (Δ35.2±4.4mV). In the present study, we tested the hypothesis that reactive oxygen species (ROS) mediates this pH-conditioned Cl - conductance. We found that the rate of increase in fluorescence [(F-F 0 )/F 0 ] of NG neurons loaded with dihydroethidine (ROS dye) rose dramatically following the brief exposures to pH 6.0 from a control of 0.04±0.01 to 0.12±0.02 units/min over 10∼15 minutes (n=31 neurons, p<0.01). Moreover superfusion of neurons with H 2 O 2 induced currents that mimicked the pH conditioned currents. Because of similarities between the pH-conditioned Cl - conductance and the previously described “swell-activated” Cl - current induced with hypoosmotic solutions, we superfused the NG neurons with the H 2 O 2 scavenger PEG-catalase (1000 units/ml). PEG-catalase blocked significantly (p<0.01) the “swell” response to 210 mOsm from 23.3±6.3pA/pF to 0.57±0.39 pA/pF (n=4) as well as the pH-conditioned response from 25.7±6.5pA/pF (n=6) to 6.9±1.4 pA/pF (n=12). The superoxide scavenger PEG-SOD did not affect the current. These results indicate that both pH-conditioned and swell-induced responses are mediated by H 2 O 2 . Opening of these outward Cl - conductances that cause sustained depolarization of vagal afferents may induce a beneficial reflex sympathoinhibition during myocardial ischemia/acidosis or initiate a gastro-intestinal post-prandial satiety reflex.

Neurohormonal modulation of the innate immune system is proinflammatory in the prehypertensive spontaneously hypertensive rat, a genetic model of essential hypertension

RATIONALE

Inflammation and autonomic dysfunction contribute to the pathophysiology of hypertension. Cholinergic stimulation suppresses innate immune responses. Angiotensin II (Ang II) induces hypertension and is associated with proinflammatory immune responses.

OBJECTIVE

Our goal was to define the innate immune response in a model of genetic hypertension and the influences of cholinergic stimulation and Ang II.

METHODS AND RESULTS

Studies were conducted on 4- to 5-week-old prehypertensive spontaneously hypertensive rats (SHRs) and age-matched normotensive control, Wistar Kyoto (WKY) rats. Isolated splenocytes were preexposed to nicotine or Ang II before Toll-like receptor (TLR) activation. Culture supernatants were tested for cytokines (tumor necrosis factor-α, interleukin [IL]-10, and IL-6). TLR-mediated cytokine responses were most pronounced with TLR7/8 and TLR9 activation and similar between WKY rats and SHRs. Nicotine and Ang II enhanced this TLR-mediated IL-6 response in prehypertensive SHR splenocytes. In contrast, nicotine suppressed the TLR-mediated IL-6 response in WKY rats, whereas Ang II had no effect. In vivo, nicotine enhanced plasma levels of TLR7/8-mediated IL-6 and IL-1β responses in prehypertensive SHRs but suppressed these responses in WKY rats. Flow cytometry revealed an increase in a CD161+ innate immune cell population, which was enhanced by nicotine in the prehypertensive SHR spleen but not in WKY.

CONCLUSIONS

There is a pronounced anti-inflammatory nicotinic/cholinergic modulation of the innate immune system in WKY rats, which is reversed in prehypertensive SHRs. The results support the novel concept that neurohormonal regulation of the innate immune system plays a role in the pathogenesis of genetic hypertension and provide putative molecular targets for treatment of hypertension.