Glomus Cells Research Articles

Effect of Mild Acidosis on CA2+ Signaling in Rat Carotid Body Chemoreceptor Cells: Role of CAV, ASIC, and Task

Carotid body (CB) glomus cells serve as peripheral chemoreceptors that detect changes in arterial O2 pressure (pO2) and pH, and adjust the level of ventilation to help maintain a normal level of blood pO2 and pH. Severe levels of hypoxia and acidosis are well known to cause sustained rise in cytosolic Ca2+ concentration ([Ca2+]c) in CB glomus cells. We showed recently that isolated gloms cells exhibit spontaneous [Ca2+]c oscillations and that mild levels of hypoxia increase the frequency and amplitude of Ca2+oscillations to augment the secretory response. To understand how mild levels of acidosis regulate Ca2+signaling in glomus cells, we studied the effects of small changes in extracellular pH (pHo) on the kinetics of Ca2+oscillations and the roles of Cav, ASIC and TASK. A decrease in pHo from 7.4 to 7.3 (mild acidosis) and 7.2 (moderate acidosis) produced significant increases in the frequency and amplitude of Ca2+ oscillations without affecting the resting basal [Ca2+]c. These effects on Ca2+ oscillations were not blocked by 0.1 mM amiloride (an ASIC inhibitor) that blocked Na‐H exchange in glomus cells. Mild acidosis was associated with a small but significant inhibition of TASK current and cell depolarization. The increase in Ca2+oscillations produced by mild acidosis was strongly inhibited by nifedipine (1 µM; L‐type Cav inhibitor), as well as by TTA‐P2 (20 µM; T‐type Cav inhibitor). Mild acidosis (0.1 pH unit decrease) and mild hypoxia (~5% O2) produced similar levels of change in the kinetics of Ca2+oscillations and produced an additive effect on Ca2+oscillations. Our study shows that mild to moderate levels of acidosis inhibit TASK to increase Ca2+ influx via both L‐ and T‐type Cav, resulting in increased frequency and amplitude of Ca2+ oscillations. Our study also indicate that ASICs are not involved in the stimulatory effects of mild acidosis on Ca2+oscillations.

Blockade of Trpm7 in the Carotid Body area attenuated intermittent hypoxia‐induced Hypertension

RATIONALEObesity leads to high cardiovascular morbidity and mortality via multiple mechanisms including obstructive sleep apnea (OSA) and hypertension. Intermittent hypoxia (IH), a hallmark manifestation of OSA, is an established cause of hypertension. The carotid body (CB) has been implicated in the pathogenesis of hypertension in IH and obesity. We discovered that obesity‐induced hypertension is mediated via the transient receptor potential melastatin 7 (TRPM7) channel in the glomus cells of CB. Here, we investigate the relevance of TRPM7 signaling in CB for the pathogenesis of hypertension by IH. We developed a novel technique allowing continuous sustained release of the TRPM7 inhibitor FTY720 into the CB area using a hydrogel formulation with a single injection abolishing hypertension in obesity for 3 weeks. We hypothesize that IH causes hypertension acting on CB TRPM7.METHODSC57BL/6J male mice (n = 9) were implanted with telemetry in the left femoral artery for continuous blood pressure monitoring and exposed to IH for 5 days. IH was administered by decreasing O2 levels from 21% to 6%, 60 cycles/hr, during the light phase, 9AM ‐9PM. FTY720 hydrogel (n = 5) or control hydrogel (N = 4) were applied locally to the CB region. Blood pressure was recorded at baseline and during IH and the measurement was repeated 2 weeks after hydrogel application.RESULTIH increased mean arterial pressure from 103.8±1.2 mmHg to 114.3±1.4 mmHg on Day 1 of IH and to 113.0±0.6 mmHg on Day 5 of IH respectively. FTY720 hydrogel abolished IH‐induced hypertension by decreasing blood pressure to 106.6±1.6 mmHg (p<0.005) on Day 1 of IH and to 101.5±1.6 mmHg (p<0.001) on Day 5 of IH. In contrast, control hydrogel had no effect on IH‐induced hypertension.CONCLUSIONOur study has shown that inhibition of TRPM7in the carotid bodies abolished IH‐induced hypertension.

Mitochondrial Redox Signaling in O2-Sensing Chemoreceptor Cells.

Significance: Acute responses to hypoxia are essential for the survival of mammals. The carotid body (CB), the main arterial chemoreceptor, contains glomus cells with oxygen (O2)-sensitive K+ channels, which are inhibited during hypoxia to trigger adaptive cardiorespiratory reflexes. Recent Advances: In this review, recent advances in molecular mechanisms of acute O2 sensing in CB glomus cells are discussed, with a special focus on the signaling role of mitochondria through regulating cellular redox status. These advances have been achieved thanks to the use of genetically engineered redox-sensitive green fluorescent protein (roGFP) probes, which allowed us to monitor rapid changes in ROS production in real time in different subcellular compartments during hypoxia. This methodology was used in combination with conditional knockout mice models, pharmacological approaches, and transcriptomic studies. We have proposed a mitochondria-to-membrane signaling model of acute O2 sensing in which H2O2 released in the mitochondrial intermembrane space serves as a signaling molecule to inhibit K+ channels on the plasma membrane. Critical Issues: Changes in mitochondrial reactive oxygen species (ROS) production during acute hypoxia are highly compartmentalized in the submitochondrial regions. The use of redox-sensitive probes targeted to specific compartments is essential to fully understand the role of mitochondrial ROS in acute O2 sensing. Future Directions: Further studies are needed to specify the ROS and to characterize the target(s) of ROS in chemoreceptor cells during acute hypoxia. These data may also contribute to a more complete understanding of the implication of ROS in acute responses to hypoxia in O2-sensing cells in other organs. Antioxid. Redox Signal. 37, 274-289.

Computed tomography features and clinicopathological characteristics of gastric glomus tumor

BackgroundGastric glomus tumor (GGT) is a rare neoplasm that is difficult to distinguish from other gastric submucosal tumors due to a lack of diagnostic experience. The goal of this study was to better understand GGT by looking at its clinicopathological features, computed tomography (CT) features, and differential diagnosis.MethodsThe clinical data and CT findings of 21 pathologically confirmed GGT patients were examined. The clinical characteristics and CT findings of benign GGT were compared to gastric stromal tumors (GST) (n = 30) and heterotopic pancreas (n = 30).ResultsThe 21 cases included six males and fifteen females ranging in age from 42 to 64 years. The lesions were found in the gastric body in four cases and the antrum in seventeen. GGT was diagnosed as benign in 20 cases and malignant in one. In benign cases, the glomus cells were small, uniform, showed perivascular hemangiopericytoma‑like or solid nest‑like structures. Obvious mitotic figures were observed in the malignant case. SMA staining was positive in the tumor cells. A quasi-round or round solid mass protruded into the gastric cavity in 20 benign cases, with a clear and smooth edge. The long to short diameter ratio was 1.01 ± 0.15. All of the benign cases had obvious enhancement, with homogeneous enhancement in ten cases and heterogeneous enhancement in ten cases, as well as central filling enhancement in 12 cases. The ratio of CT value of lesion to abdominal aorta in arterial phase and venous phase were (0.41 ± 0.11) and (0.81 ± 0.20), which were significantly higher than GST and heterotopic pancreas. The irregular mass broke through the gastric wall and invaded liver with poorly defined boundary and internal necrosis, heterogeneous persistent moderate enhancement with thickening blood supply arteries was seen in one malignant case with a long diameter of 150 mm and a thick diameter of 30 mm.ConclusionsCT enhancement usually shows persistent obvious enhancement, especially in arterial phase, which provides important value for the diagnosis. CT findings can help in the differential diagnosis of GGT and other submucosal tumors.

SDHB knockout and succinate accumulation are insufficient for tumorigenesis but dual SDHB/NF1 loss yields SDHx-like pheochromocytomas.

SUMMARYInherited pathogenic succinate dehydrogenase (SDHx) gene mutations cause the hereditary pheochromocytoma and paraganglioma tumor syndrome. Syndromic tumors exhibit elevated succinate, an oncometabolite that is proposed to drive tumorigenesis via DNA and histone hypermethylation, mitochondrial expansion, and pseudohypoxia-related gene expression. To interrogate this prevailing model, we disrupt mouse adrenal medulla SDHB expression, which recapitulates several key molecular features of human SDHx tumors, including succinate accumulation but not 5hmC loss, HIF accumulation, or tumorigenesis. By contrast, concomitant SDHB and the neurofibromin 1 tumor suppressor disruption yields SDHx-like pheochromocytomas. Unexpectedly, in vivo depletion of the 2-oxoglutarate (2-OG) dioxygenase cofactor ascorbate reduces SDHB-deficient cell survival, indicating that SDHx loss may be better tolerated by tissues with high antioxidant capacity. Contrary to the prevailing oncometabolite model, succinate accumulation and 2-OG-dependent dioxygenase inhibition are insufficient for mouse pheochromocytoma tumorigenesis, which requires additional growth-regulatory pathway activation.

The sympathetic nervous system exacerbates carotid body sensitivity in hypertension.

The carotid bodies (CBs) of spontaneously hypertensive (SH) rats exhibit hypertonicity and hyperreflexia contributing to heightened peripheral sympathetic outflow. We hypothesized that CB hyperexcitability is driven by its own sympathetic innervation. To test this, the chemoreflex was activated (NaCN 50-100 µL, 0.4 µg/µL) in SH and Wistar rats in situ before and after: (i) electrical stimulation (ES; 30 Hz, 2 ms, 10 V) of the superior cervical ganglion (SCG), which innervates the CB; (ii) unilateral resection of the SCG (SCGx); (iii) CB injections of an α1-adrenergic receptor agonist (phenylephrine, 50 µL, 1 mmol/L), and (iv) α1-adrenergic receptor antagonist prazosin (40 µL, 1 mmol/L) or tamsulosin (50 µL, 1 mmol/L). ES of the SCG enhanced CB-evoked sympathoexcitation by 40-50% (P < 0.05) with no difference between rat strains. Unilateral SCGx attenuated the CB-evoked sympathoexcitation in SH (62%; P < 0.01) but was without effect in Wistar rats; it also abolished the ongoing firing of chemoreceptive petrosal neurones of SH rats, which became hyperpolarized. In Wistar rats, CB injections of phenylephrine enhanced CB-evoked sympathoexcitation (33%; P < 0.05), which was prevented by prazosin (26%; P < 0.05) in SH rats. Tamsulosin alone reproduced the effects of prazosin in SH rats and prevented the sensitizing effect of the SCG following ES. Within the CB, α1A- and α1B-adrenoreceptors were co-localized on both glomus cells and blood vessels. In conscious SH rats instrumented for recording blood pressure (BP), the CB-evoked pressor response was attenuated after SCGx, and systolic BP fell by 16 ± 4.85 mmHg. The sympathetic innervation of the CB is tonically activated and sensitizes the CB of SH but not Wistar rats. Furthermore, sensitization of CB-evoked reflex sympathoexcitation appears to be mediated by α1-adrenoceptors located either on the vasculature and/or glomus cells. The SCG is novel target for controlling CB pathophysiology in hypertension.

Chapter 3 - Neurobiology of the carotid body

The carotid body (CB) is a bilateral arterial chemoreceptor located in the carotid artery bifurcation with an essential role in cardiorespiratory homeostasis. It is composed of highly perfused cell clusters, or glomeruli, innervated by sensory fibers. Glomus cells, the most abundant in each glomerulus, are neuron-like multimodal sensory elements able to detect and integrate changes in several physical and chemical parameters of the blood, in particular O2 tension, CO2 and pH, as well as glucose, lactate, or blood flow. Activation of glomus cells (e.g., during hypoxia or hypercapnia) stimulates the afferent fibers which impinge on brainstem neurons to elicit rapid compensatory responses (hyperventilation and sympathetic activation). This chapter presents an updated view of the structural organization of the CB and the mechanisms underlying the chemosensory responses of glomus cells, with special emphasis on the molecular processes responsible for acute O2 sensing. The properties of the glomus cell-sensory fiber synapse as well as the organization of CB output are discussed. The chapter includes the description of recently discovered CB stem cells and progenitor cells, and their role in CB growth during acclimatization to hypoxemia. Finally, the participation of the CB in the mechanisms of disease is briefly discussed.

Chapter 4 - Adaptive cardiorespiratory changes to chronic continuous and intermittent hypoxia

This chapter reviews cardiorespiratory adaptations to chronic hypoxia (CH) experienced at high altitude and cardiorespiratory pathologies elicited by chronic intermittent hypoxia (CIH) occurring with obstructive sleep apnea (OSA). Short-term CH increases breathing (ventilatory acclimatization to hypoxia) and blood pressure (BP) through carotid body (CB) chemo reflex. Hyperplasia of glomus cells, alterations in ion channels, and recruitment of additional excitatory molecules are implicated in the heightened CB chemo reflex by CH. Transcriptional activation of hypoxia-inducible factors (HIF-1 and 2) is a major molecular mechanism underlying respiratory adaptations to short-term CH. High-altitude natives experiencing long-term CH exhibit blunted hypoxic ventilatory response (HVR) and reduced BP due to desensitization of CB response to hypoxia and impaired processing of CB sensory information at the central nervous system. Ventilatory changes evoked by long-term CH are not readily reversed after return to sea level. OSA patients and rodents subjected to CIH exhibit heightened CB chemo reflex, increased hypoxic ventilatory response, and hypertension. Increased generation of reactive oxygen species (ROS) is a major cellular mechanism underlying CIH-induced enhanced CB chemo reflex and the ensuing cardiorespiratory pathologies. ROS generation by CIH is mediated by nontranscriptional, disrupted HIF-1 and HIF-2-dependent transcriptions as well as epigenetic mechanisms.

Science, Medicine, and the Anesthesiologist

Science, Medicine, and the Anesthesiologist

Tumeur glomique intracardiaque : une tumeur péricytaire (périvasculaire) de localisation inhabituelle

Glomus tumor are rare mesenchymal neoplasm, belonging to the pericytic (perivascular) tumor family, witch recent molecular characterization has allowed highlight recurrent molecular abnormalities. In fact, glomus tumor involves frequent MIR143-NOTCH gene fusion whereas others pericytic tumor (myopericytoma and myofibroma) involve mutations of PDGFRB gene. Glomus tumor are usually developed in superficial localization. However visceral locations have been described. Cardiac location is exceptional with only one case reported in literature. Here, we report the case of cardiac glomus tumor (glomangiomyoma) developed in the left ventricle in a 34 year-old patient, diagnosed after chest pain. The length of tumor was 4cm in greatest dimension. Histologically, the tumor concerned both round glomus cells and smooth muscle cells with prominent branching thin-walled vessels. By immunohistochemistry, these two contingents exhibited diffuse expression of smooth muscle actin and heterogeneous expression of H-caldesmone whereas cytokeratins, melanocytic markers and chomogranine were negative. Next Generation molecular analysis using RNA sequencing highlighted the characteristic MIR143-NOTCH gene fusion witch supports the diagnosis of glomus tumor. In this observation, we recall histological and immunohistochemistry features of glomus tumor and we make a synthesis concerning the molecular data recently described in sporadic glomus tumor.

Lack of influence of dexmedetomidine on rat glomus cell response to hypoxia, and on mouse acute hypoxic ventilatory response.

Background and Aims:There is a lack of basic science data on the effect of dexmedetomidine on the hypoxic chemosensory reflex with both depression and stimulation suggested. The primary aim of this study was to assess if dexmedetomidine inhibited the cellular response to hypoxia in rat carotid body glomus cells, the cells of the organs mediating acute hypoxic ventilatory response (AHVR). Additionally, we used a small sample of mice to assess if there was any large influence of subsedative doses of dexmedetomidine on AHVR.Material and Methods:In the primary study, glomus cells isolated from neonatal rats were used to study the effect of 0.1 nM (n = 9) and 1 nM (n = 13) dexmedetomidine on hypoxia-elicited intracellular calcium [Ca2%]i influx using ratiometric fluorimetry. Secondarily, whole animal unrestrained plethysmography was used to study AHVR in a total of 8 age-matched C57BL6 mice, divided on successive days into two groups of four mice randomly assigned to receive sub-sedative doses of 5, 50, or 500 μg.kg-1 dexmedetomidine versus control in a crossover study design (total n = 12 exposures to drug with n = 12 controls).Results:There was no effect of dexmedetomidine on the hypoxia-elicited increase in [Ca2%]i in glomus cells (a mean ± SEM increase of 95 ± 32 nM from baseline with control hypoxia, 124 ± 41 nM with 0.1 nM dexmedetomidine; P = 0.514). In intact mice, dexmedetomidine had no effect on baseline ventilation during air-breathing (4.01 ± 0.3 ml.g-1.min-1 in control and 2.99 ± 0.5 ml.g-1.min-1 with 500 μg.kg-1 dexmedetomidine, the highest dose; P = 0.081) or on AHVR (136 ± 19% increase from baseline in control, 152 ± 46% with 500 μg.kg-1 dexmedetomidine, the highest dose; P = 0.536).Conclusion:Dexmedetomidine had no effect on the cellular responses to hypoxia. We conclude that it unlikely acts via inhibition of oxygen sensing at the glomus cell. The respiratory chemoreflex effects of this drug remain an open question. In our small sample of intact mice, hypoxic chemoreflex responses and basal breathing were preserved.

27933 A rare case of familial generalized multiple glomangiomas in an 11-year-old boy

Glomus tumors are benign vascular neoplasms made up of specialized perivascular modified smooth muscle cells, glomus cells, that present clinically as violaceous-to-blue papules and nodules often on the distal fingers and toes, including the nail bed. Glomus tumors can be histologically classified into 3 variants: solid glomus tumors, glomangiomas, also known as glomuvenous malformations, and glomangiomyomas. We present the case of an 11-year-old boy who presented with multiple blueish lesions on the bilateral arms, trunk, and buttocks, present for 2-3 years. Of note, the patient’s brother reportedly has many similar lesions that developed around the same age. Physical exam revealed solitary and clustered tender, blue, nonblanching vascular papulonodules on the trunk, arms, and back. Biopsy of a lesion on the right arm was performed and histopathology revealed many dilated vascular channels surrounded by sheets of uniform round-to-cuboidal cells with oval nuclei, consistent with a diagnosis of glomangioma. Given the patient’s clinical presentation with multiple glomangiomas and a first degree relative with similar lesions, a diagnosis of familial generalized multiple glomangiomas (FGMG) was made. FGMG is a rare clinical variant present in less than 10% of all glomus tumor cases. FGMG is thought to be caused by mutations in Glomulin (GLMN) and exhibits autosomal dominant inheritance with incomplete penetrance and variable expressivity. Though glomus tumors are benign, they are typically persistent and may be tender. When desired, treatments with reported efficacy include sclerotherapy, local excision and electron beam radiation.

Fast growing myopericytoma of the hand: Case report and literature review.

Introduction and importanceMyopericytoma (MPC) is a rare benign soft tissue neoplasm that arises from perivascular smooth muscle-like myoid cells that share features of both glomus and smooth muscle cells. It usually slow growing solitary tumor that might mimic aggressive sarcoma.Case presentation45 years old male, with unremarkable medical history, presented with fast growing mass on the left 1st webspace that was noticed 6 months prior to presentation. Investigations with US and MRI showed highly vascular solid mass that was worrisome for malignant lesion. Surgical excision was done and histopathology confirmed the diagnosis of myopericytoma.Clinical discussionMPC is a rare perivascular neoplasm that’s reported mainly in the extremities with lower limbs are most affected sites. Usually it presents as solid painless slowly growing mass. However, Multiple papers reported different rare presentations like multiple, painful and some with malignant transformation.ConclusionMPC is a benign tumor that might mimic aggressive sarcoma. Such cases should be approached with high suspicion and proper investigation and management should be followed promptly.

Lactate sensing mechanisms in arterial chemoreceptor cells

Classically considered a by-product of anaerobic metabolism, lactate is now viewed as a fundamental fuel for oxidative phosphorylation in mitochondria, and preferred over glucose by many tissues. Lactate is also a signaling molecule of increasing medical relevance. Lactate levels in the blood can increase in both normal and pathophysiological conditions (e.g., hypoxia, physical exercise, or sepsis), however the manner by which these changes are sensed and induce adaptive responses is unknown. Here we show that the carotid body (CB) is essential for lactate homeostasis and that CB glomus cells, the main oxygen sensing arterial chemoreceptors, are also lactate sensors. Lactate is transported into glomus cells, leading to a rapid increase in the cytosolic NADH/NAD+ ratio. This in turn activates membrane cation channels, leading to cell depolarization, action potential firing, and Ca2+ influx. Lactate also decreases intracellular pH and increases mitochondrial reactive oxygen species production, which further activates glomus cells. Lactate and hypoxia, although sensed by separate mechanisms, share the same final signaling pathway and jointly activate glomus cells to potentiate compensatory cardiorespiratory reflexes.

Glomangioma: Rare presentation over the back

Glomangiomas are a rare benign variant of glomus tumors. They are cutaneous venous malformation that show glomus cells along the venous vasculature. Glomus tumors are most commonly found in digits of hands and feet. Extradigital locations are rare. We are presenting a case with a rare presentation over the back. As per the literature ours is the 6th case reported over back.

IMMUNOHISTOPATHOLOGIC VARIATION OF ORAL MYOPERICYTOMA

<h3>Objective</h3> Myopericytoma (MP) is a rare soft tissue neoplasm infrequently arising in the oral cavity. We aimed to clarify the clinicopathologic characteristics of oral MP based on histologic and immunohistochemical findings. <h3>Methods</h3> We reviewed myogenic neoplasms in our archives and selected 6 cases of MP. Immunostainings were performed using antibodies for smooth muscle actin (SMA), calponin, h-Caldesmon, muscle-specific actin (MSA), desmin, and type IV collagen antibody. <h3>Results</h3> Our patients were predominantly female, and the mean age and size were 57.5 years and 10.8 mm, respectively. Histologically, 3 of 6 cases were well circumscribed but others showed ill-defined borders. Three cases were classic but others were angioleiomatous and myofibromatous cases with a mostly fascicular pattern. Myxoid change appeared in 2 cases. Hyalinized nodules (vascular balls) were found in both classic and nonclassic types. Only one case partially comprised small round cells mimicking glomus cells, but these lacked peculiar type IV collagen expression. Two angioleiomatous cases harbored dilated blood vessels. Two cases partially showed a staghorn and indistinct biphasic pattern but a myofibromatous type demonstrated neither. Immunohistochemically, all cases that tested were positive or focally positive for SMA, MSA, and calponin but negative tumor cells were noted in part. However, h-Caldesmon was only detected in 2 out of 5 cases examined. Desmin was constant-negative except for 1 classic case with focally positive reaction. <h3>Conclusion</h3> Oral MPs are morphologically and phenotypically heterogeneous neoplasms that can sometimes mimic angioleiomyoma or glomangioma. It is necessary to recognize the presence of cases showing varied myogenic natures.

La glomangiomatose médiastinale postérieure : localisation exceptionnelle d’une tumeur rare. À propos d’un cas

Glomangiomatosis is a benign tumour proliferation which develops from the glomus cells in the wall of a vessel, and which contains abnormal venous capillaries. Its usual location is dermal at the extremities, mediastinal presentation is exceptional. A 63-year-old patient, followed for scoliosis, was admitted for a spontaneous haemothorax. The CT scan found hypervascularized left paravertebral masses. Thoracoscopy with biopsy provided the diagnosis of a glomus tumour. Given that its diffuse nature makes surgical excision difficult and the risk of intraoperative bleeding very high, treatment with interleukin alpha 2 was proposed to the patient. After a 3-year course, we did not observe any evolutionary change in the lesions. Glomangiomatosis is an insidiously evolving vascular tumour which must be considered in the presence of vascular lesions. The reference treatment is surgical excision when possible. On the other hand, hasty surgery in diffuse forms remains dangerous given the haemorrhagic nature of this tumour.

Electrical stimulation of the cervical sympathetic chain decreases upper airway resistance and increases central respiratory drive in conscious Sprague‐Dawley Rats

Background The cervical sympathetic chains (CSC) provide sympathetic drive to carotid sinus baroreceptor afferents and chemoreceptive glomus cells within the carotid bodies. We have previously demonstrated that CSC stimulation improves airway patency in anesthetized Sprague Dawley rats. It is unclear whether a paradigm of CSC stimulation in consecutive days would alter respiratory drive. Aim We sought to investigate (1) whether electrical stimulation of the cervical sympathetic chain in conscious Sprague Dawley rats will lead to decrease in specific airway resistance, (2) whether intermittent stimulation over 5 days would alter central inspiratory drive. Methods In Sprague-Dawley rats (n=10), both CSC were implanted with cuff electrodes, which were trocared to a headcap cemented on the skull. Two weeks after recovery, the rats (n=10) were placed in a double chambered plethysmography (DCP) chamber where CSC were electrically stimulated (0.8 mA, 7.5 Hz, and 0.2 ms) and both specific airway resistance and central respiratory drive (tidal volume/ inspiratory time) were assessed. A day later, the animals were placed in whole body plethysmography (WBP) where a stimulation protocol (intermittent (60s on/60s off for 15 min)) was performed over 8 hours a day for 5 days to assess long term efficacy on airway resistance and respiratory drive. Results We present two novel findings. First, bilateral CSC stimulation reduced upper airway resistance by 25 ± 5%. Second, WBP showed that inspiratory drive increased progressively to a maximum of 35 ± 13% change by day 5. Conclusions For the first time, we have demonstrated that CSC stimulation reduces upper airway resistance in conscious Sprague Dawley rats and progressively increases inspiratory drive over 5 consecutive days.

Leptin Induces Epigenetic Regulation of Transient Receptor Potential Melastatin 7 in Rat Adrenal Pheochromocytoma Cells.

Obesity elevates the plasma level of leptin, which has been associated with hypertension. Our recent studies in mice demonstrated that leptin increases blood pressure by activating the carotid sinus nerve, which transmits the chemosensory input from carotid bodies (CBs) to the medullary centers, and that the effect of leptin is mediated via Trpm7 (TRP [transient receptor potential] melastatin 7) channels in CB glomus cells. We also found that Trpm7 overexpression and Trpm7 promoter demethylation in CBs correlate positively with the hyperleptinemia and leptin receptor overexpression in CBs. Hence, we postulated that leptin epigenetically regulates Trpm7 expression in CBs. We addressed our hypothesis by using rat adrenal pheochromocytoma (PC12) cells as a model of CB glomus cells. PC12 cells expressing LEPRb (long, active form of leptin receptor) showed dramatic induction of the promoter activity and expression of Trpm7 upon leptin treatment. The increased Trpm7 expression coincided with the reduction of CpG site-specific methylation and trimethylation of H3K27 (H3 [histone 3] K27 [lysine 27]) and the increase of acetylation of H3K27 and trimethylation of H3K4 (H3 lysine 4) at the Trpm7 promoter. The inhibitor of STAT3 (signal transducer and activator of transcription 3) signaling, SD1008, reversed the leptin-induced Trpm7 promoter activity via modulations of the binding of pSTAT3 (phosphorylated STAT3) and DNMT3B (DNA methyltransferase 3B) and modifications of H3K27 and H3K4 at the Trpm7 promoter. Our results suggest that leptin-activated pSTAT3 epigenetically regulates the transcription of Trpm7 through DNA methylation and histone modifications. Because epigenetic changes are reversible, targeting epigenetic modifications of Trpm7 may serve as a new therapeutic approach for the treatment of hypertension in obesity.

Loss of Cervical Sympathetic Chain Input to the Superior Cervical Ganglia Affects the Ventilatory Responses to Hypoxic Challenge in Freely-Moving C57BL6 Mice.

The cervical sympathetic chain (CSC) innervates post-ganglionic sympathetic neurons within the ipsilateral superior cervical ganglion (SCG) of all mammalian species studied to date. The post-ganglionic neurons within the SCG project to a wide variety of structures, including the brain (parenchyma and cerebral arteries), upper airway (e.g., nasopharynx and tongue) and submandibular glands. The SCG also sends post-ganglionic fibers to the carotid body (e.g., chemosensitive glomus cells and microcirculation), however, the function of these connections are not established in the mouse. In addition, nothing is known about the functional importance of the CSC-SCG complex (including input to the carotid body) in the mouse. The objective of this study was to determine the effects of bilateral transection of the CSC on the ventilatory responses [e.g., increases in frequency of breathing (Freq), tidal volume (TV) and minute ventilation (MV)] that occur during and following exposure to a hypoxic gas challenge (10% O2 and 90% N2) in freely-moving sham-operated (SHAM) adult male C57BL6 mice, and in mice in which both CSC were transected (CSCX). Resting ventilatory parameters (19 directly recorded or calculated parameters) were similar in the SHAM and CSCX mice. There were numerous important differences in the responses of CSCX and SHAM mice to the hypoxic challenge. For example, the increases in Freq (and associated decreases in inspiratory and expiratory times, end expiratory pause, and relaxation time), and the increases in MV, expiratory drive, and expiratory flow at 50% exhaled TV (EF50) occurred more quickly in the CSCX mice than in the SHAM mice, although the overall responses were similar in both groups. Moreover, the initial and total increases in peak inspiratory flow were higher in the CSCX mice. Additionally, the overall increases in TV during the latter half of the hypoxic challenge were greater in the CSCX mice. The ventilatory responses that occurred upon return to room-air were essentially similar in the SHAM and CSCX mice. Overall, this novel data suggest that the CSC may normally provide inhibitory input to peripheral (e.g., carotid bodies) and central (e.g., brainstem) structures that are involved in the ventilatory responses to hypoxic gas challenge in C57BL6 mice.