Histiocytic sarcoma of the spleen without thrombocytopenia.

One case of histiocytic sarcoma of the spleen is reported. The patient, a 54-year-old female, presented with a huge soft tissue mass with a clear border and pseudo capsule in the splenic parenchyma on CT. The density of the mass was uneven, multifocal cystic necrosis and irregular bleeding were observed inside, but no calcification could be seen. On contrast-enhancement scan, the solid component of tumor exhibited moderate progressive enhancement, and area of cystic necrosis exhibited no enhancement. In MRI, T1WI showed mixed low signal, and T2WI showed mixed slightly high signal. The pathological diagnosis was histiocytic sarcoma.

Carotid body hypersensitivity in intermittent hypoxia and obtructive sleep apnoea.

Carotid bodies are the principal sensory organs for detecting changes in arterial blood oxygen concentration, and the carotid body chemoreflex is a major regulator of the sympathetic tone, blood pressure and breathing. Intermittent hypoxia is a hallmark manifestation of obstructive sleep apnoea (OSA), which is a widespread respiratory disorder. In the first part of this review, we discuss the role of carotid bodies in heightened sympathetic tone and hypertension in rodents treated with intermittent hypoxia, and the underlying cellular, molecular and epigenetic mechanisms. We also present evidence for hitherto-uncharacterized role of carotid body afferents in triggering cellular and molecular changes induced by intermittent hypoxia. In the second part of the review, we present evidence for a contribution of a hypersensitive carotid body to OSA and potential therapeutic intervention to mitigate OSA in a murine model.

Role of olfactory receptor78 in carotid body-dependent sympathetic activation and hypertension in murine models of chronic intermittent hypoxia.

Chronic intermittent hypoxia (CIH) is a hallmark manifestation of obstructive sleep apnea (OSA), a widespread breathing disorder. CIH-treated rodents exhibit activation of the sympathetic nervous system and hypertension. Heightened carotid body (CB) activity has been implicated in CIH-induced hypertension. CB expresses high abundance of olfactory receptor (Olfr) 78, a G-protein coupled receptor. Olfr 78 null mice exhibit impaired CB sensory nerve response to acute hypoxia. Present study examined whether Olfr78 participates in CB-dependent activation of the sympathetic nervous system and hypertension in CIH-treated mice and in hemeoxygenase (HO)-2 null mice experiencing CIH as a consequence of naturally occurring OSA. CIH-treated wild-type (WT) mice showed hypertension, biomarkers of sympathetic nerve activation, and enhanced CB sensory nerve response to hypoxia and sensory long-term facilitation (sLTF), and these responses were absent in CIH-treated Olfr78 null mice. HO-2 null mice showed higher apnea index (AI) (58 ± 1.2 apneas/h) than WT mice (AI = 8 ± 0.8 apneas/h) and exhibited elevated blood pressure (BP), elevated plasma norepinephrine (NE) levels, and heightened CB sensory nerve response to hypoxia and sLTF. The magnitude of hypertension correlated with AI in HO-2 null mice. In contrast, HO-2/Olfr78 double null mice showed absence of elevated BP and plasma NE levels and augmented CB response to hypoxia and sLTF. These results demonstrate that Olfr78 participates in sympathetic nerve activation and hypertension and heightened CB activity in two murine models of CIH.NEW & NOTEWORTHY Carotid body (CB) sensory nerve activation is essential for sympathetic nerve excitation and hypertension in rodents treated with chronic intermittent hypoxia (CIH) simulating blood O2 profiles during obstructive sleep apnea (OSA). Here, we report that CIH-treated mice and hemeoxygenase (HO)-2-deficient mice, which show OSA phenotype, exhibit sympathetic excitation, hypertension, and CB activation. These effects are absent in Olfr78 null and Olfr78/HO-2 double null mice.

Gaseous transmitter regulation of hypoxia-evoked catecholamine secretion from murine adrenal chromaffin cells.

Emerging evidence suggests that gaseous molecules, carbon monoxide (CO), and hydrogen sulfide (H2S) generated by heme oxygenase (HO)-2 and cystathionine γ-lyase (CSE), respectively, function as transmitters in the nervous system. Present study examined the roles of CO and H2S in hypoxia-induced catecholamine (CA) release from adrenal medullary chromaffin cells (AMCs). Studies were performed on AMCs from adult (≥6 wk of age) wild-type (WT), HO-2 null, CSE null, and HO-2/CSE double null mice of either gender. CA secretion was determined by carbon fiber amperometry and [Ca2+]i by microflurometry using Fura-2. HO-2- and CSE immunoreactivities were seen in WT AMC, which were absent in HO-2 and CSE null mice. Hypoxia (medium Po2 30-38 mmHg) evoked CA release and elevated [Ca2+]i. The magnitude of hypoxic response was greater in HO-2 null mice and in HO inhibitor-treated WT AMC compared with controls. H2S levels were elevated in HO-2 null AMC. Either pharmacological inhibition or genetic deletion of CSE prevented the augmented hypoxic responses of HO-2 null AMC and H2S donor rescued AMC responses to hypoxia in HO-2/CSE double null mice. CORM3, a CO donor, prevented the augmented hypoxic responses in WT and HO-2 null AMC. CO donor reduced H2S levels in WT AMC. The effects of CO donor were blocked by either ODQ or 8pCT, inhibitors of soluble guanylyl cyclase (SGC) or protein kinase G, respectively. These results suggest that HO-2-derived CO inhibits hypoxia-evoked CA secretion from adult murine AMC involving soluble guanylyl cyclase (SGC)-protein kinase G (PKG)-dependent regulation of CSE-derived H2S.NEW & NOTEWORTHY Catecholamine secretion from adrenal chromaffin cells is an important physiological mechanism for maintaining homeostasis during hypoxia. Here, we delineate carbon monoxide (CO)-sensitive hydrogen sulfide (H2S) signaling as an important mediator of hypoxia-induced catecholamine secretion from murine adrenal chromaffin cells. Heme oxygenase-2 derived CO is a physiological inhibitor of catcholamince secretion by hypoxia and the effects of CO involve inhibition of cystathionine γ-lyase-derived H2S production through soluble guanylyl cyclase-protein kinase G signaling cascade.

Risk of Malnutrition Is Common in Patients with Coronavirus Disease 2019 (COVID-19) in Wuhan, China: A Cross-sectional Study.

BACKGROUND: The coronavirus disease 2019 (COVID-19) has quickly spread across the world. However, the nutritional status of COVID-19 patients has not yet been extensively examined. OBJECTIVES: The aim of this study was to evaluate the nutritional status of COVID-19 patients and to identify factors independently associated with malnutrition risk. METHODS: In this single-center, cross-sectional study, we analyzed data from 760 hospitalized COVID-19 patients between 29 January 2020 and 15 March 2020. Based on the Nutrition Risk Screening (NRS) 2002 score, we divided patients into the normal nutrition group (NRS score <3) and the malnutrition risk group (NRS score ≥3). The associations of age, gender, symptoms, comorbidities, BMI, serum albumin and prealbumin concentrations, disease severity, activities of daily living (ADL) score, and clinical outcomes with malnutrition risk were analyzed. Multivariable logistic regression analysis was used to identify independent factors associated with malnutrition risk. RESULTS: Of patients with COVID-19, 82.6% were at risk of malnutrition. There were statistical differences in the age, incidence of fever, BMI, serum albumin and prealbumin concentrations, ADL score, and disease severity between the 2 groups. Multivariable logistic regression analysis revealed that age ≥65 y (vs. <65 y; OR: 5.40; P < 0.001), serum albumin <35 g/L (vs. ≥35 g/L; OR: 3.61; P < 0.001), serum prealbumin <150 mg/L (vs. ≥150 mg/L; OR: 2.88; P = 0.042), critical cases (vs. moderate cases; OR: 4.46; P < 0.001), ADL score 41-60 (vs. ADL score 100; OR: 4.50; P = 0.012), and ADL score ≤40 (vs. ADL score 100; OR: 9.49; P < 0.001) were significantly associated with the risk of malnutrition in COVID-19 patients. CONCLUSIONS: This study showed that prevalence of malnutrition risk was high in COVID-19 patients. Older age, low serum albumin and prealbumin concentrations, ADL score <60, and disease severity were independent factors associated with malnutrition risk.

Olfactory receptor 78 participates in carotid body response to a wide range of low O2 levels but not severe hypoxia.

The role of olfactory receptor 78 (Olfr78) in carotid body (CB) response to hypoxia was examined. BL6 mice with global deletion of Olfr78 manifested an impaired hypoxic ventilatory response (HVR), a hallmark of the CB chemosensory reflex, CB sensory nerve activity, and reduced intracellular Ca2+ concentration ([Ca2+]i) response of glomus cells to hypoxia (Po2 ~ 40 mmHg). In contrast, severe hypoxia (Po2 ~ 10 mmHg) depressed breathing and produced a very weak CB sensory nerve excitation but robust elevation of [Ca2+]i in Olfr78 null glomus cells. CB sensory nerve excitation evoked by Olfr78 ligands, lactate, propionate, acetate, and butyrate were unaffected in mutant mice and were smaller than that evoked by hypoxia (Po2 ~ 40mmHg). Similar results were obtained in Olfr78 null mice on a JAX genetic background. These results demonstrate a role for Olfr78 in CB responses to a wide range of hypoxia, but not severe hypoxia, and do not require either lactate or any other short-chain fatty acids.NEW & NOTEWORTHY The current study demonstrates that olfactory receptor 78 (Olfr78), a G protein-coupled receptor, is an integral component of the hypoxic sensing mechanism of the carotid body to a wide range of low oxygen levels, but not severe hypoxia, and that Olfr78 participation does not require either lactate or any other short-chain fatty acids, proposed ligands of Olfr78.

Complementary roles of gasotransmitters CO and H2S in sleep apnea.

Sleep apnea, which is the periodic cessation of breathing during sleep, is a major health problem affecting over 10 million people in the United States and is associated with several sequelae, including hypertension and stroke. Clinical studies suggest that abnormal carotid body (CB) activity may be a driver of sleep apnea. Because gaseous molecules are important determinants of CB activity, aberrations in their signaling could lead to sleep apnea. Here, we report that mice deficient in heme oxygenase-2 (HO-2), which generates the gaseous molecule carbon monoxide (CO), exhibit sleep apnea characterized by high apnea and hypopnea indices during rapid eye movement (REM) sleep. Similar high apnea and hypopnea indices were also noted in prehypertensive spontaneously hypertensive (SH) rats, which are known to exhibit CB hyperactivity. We identified the gaseous molecule hydrogen sulfide (H2S) as the major effector molecule driving apneas. Genetic ablation of the H2S-synthesizing enzyme cystathionine-γ-lyase (CSE) normalized breathing in HO-2-/- mice. Pharmacologic inhibition of CSE with l-propargyl glycine prevented apneas in both HO-2-/- mice and SH rats. These observations demonstrate that dysregulated CO and H2S signaling in the CB leads to apneas and suggest that CSE inhibition may be a useful therapeutic intervention for preventing CB-driven sleep apnea.

Long-term facilitation of catecholamine secretion from adrenal chromaffin cells of neonatal rats by chronic intermittent hypoxia.

In neonates, catecholamine (CA) secretion from adrenal medullary chromaffin cells (AMC) is an important mechanism for maintaining homeostasis during hypoxia. Nearly 90% of premature infants experience chronic intermittent hypoxia (IH) because of high incidence of apnea of prematurity, which is characterized by periodic stoppage of breathing. The present study examined the effects of repetitive hypoxia, designed to mimic apnea of prematurity, on CA release from AMC of neonatal rats. Neonatal rats were exposed to either control conditions or chronic intermittent hypoxia (IH) from ages postnatal days 0-5 (P0-P5), and CA release from adrenal medullary slices was measured after challenge with repetitive hypoxia (5 episodes of 30-s hypoxia, Po2 ~35 mmHg). In response to repetitive hypoxia, chronic IH-treated AMC exhibited sustained CA release, and this phenotype was not seen in control AMC. The sustained CA release was associated with long-lasting elevation of intracellular Ca2+ concentration ([Ca2+]i), which was due to store-operated Ca2+ entry (SOCE). 2-Aminoethoxydiphenyl borate, an inhibitor of SOCE, prevented the long-lasting [Ca2+]i elevation and CA release. Repetitive hypoxia increased H2O2 abundance, and polyethylene glycol (PEG)-catalase, a scavenger of H2O2 blocked this effect. PEG-catalase also prevented repetitive hypoxia-induced SOCE activation, sustained [Ca2+]i elevation, and CA release. These results demonstrate that repetitive hypoxia induces long-term facilitation of CA release in chronic IH-treated neonatal rat AMC through sustained Ca2+ influx mediated by SOCE.NEW & NOTEWORTHY Apnea of prematurity and the resulting chronic intermittent hypoxia are major clinical problems in neonates born preterm. Catecholamine release from adrenal medullary chromaffin cells maintains homeostasis during hypoxia in neonates. Our results demonstrate that chronic intermittent hypoxia induces a hitherto uncharacterized long-term facilitation of catecholamine secretion from neonatal rat chromaffin cells in response to repetitive hypoxia, simulating hypoxic episodes encountered during apnea of prematurity. The sustained catecholamine secretion might contribute to cardiovascular morbidities in infants with apnea of prematurity.

DNA methylation in the central and efferent limbs of the chemoreflex requires carotid body neural activity.

KEY POINTS: The mechanisms underlying long-term (30 days) intermittent hypoxia (LT-IH)-evoked DNA methylation of anti-oxidant enzyme (AOE) gene repression in the carotid body (CB) reflex pathway were examined. LT-IH-treated rats showed increased reactive oxygen species (ROS) levels in the CB reflex pathway. Administration of a ROS scavenger or CB ablation blocked LT-IH-evoked DNA methylation and AOE gene repression in the central and efferent limbs of the CB reflex. LT-IH increased DNA methyltransferase (Dnmt) activity through upregulation of Dnmt1 and 3b proteins by ROS-dependent inactivation of glycogen synthase kinase 3ß (GSK3ß) by Akt. A pan-Akt inhibitor prevented LT-IH-induced GSK3ß inactivation, elevated Dnmt protein expression and activity, AOE gene methylation, sympathetic activation and hypertension. ABSTRACT: Long-term exposure to intermittent hypoxia (LT-IH; 30 days), simulating blood O2 profiles during sleep apnoea, has been shown to repress anti-oxidant enzyme (AOE) gene expression by DNA methylation in the carotid body (CB) reflex pathway, resulting in persistent elevation of plasma catecholamine levels and blood pressure. The present study examined the mechanisms by which LT-IH induces DNA methylation. Adult rats exposed to LT-IH showed elevated reactive oxygen species (ROS) in the CB, nucleus tractus solitarius (nTS) and rostroventrolateral medulla (RVLM) and adrenal medulla (AM), which represent the central and efferent limbs of the CB reflex, respectively. ROS scavenger treatment during the first ten days of IH exposure prevented ROS accumulation, blocked DNA methylation, and normalized AOE gene expression, suggesting that ROS generated during the early stages of IH activate DNA methylation. CB ablation prevented the ROS accumulation, normalized AOE gene expression in the nTS, RVLM, and AM and blocked DNA methylation, suggesting that LT-IH-induced DNA methylation in the central and efferent limbs of the CB reflex is indirect and requires CB neural activity. LT-IH increased DNA methyl transferase (Dnmt) activity through upregulation of Dnmt1 and 3b protein expression due to ROS-dependent inactivation of glycogen synthase kinase 3ß (GSK3ß) by protein kinase B (Akt). Treating rats with the pan-Akt inhibitor GSK690693 blocked the induction of Dnmt activity, Dnmt protein expression, and DNA methylation, leading to normalization of AOE gene expression as well as plasma catecholamine levels and blood pressure.

Reactive oxygen radicals and gaseous transmitters in carotid body activation by intermittent hypoxia.

Sleep apnea is a prevalent respiratory disease characterized by periodic cessation of breathing during sleep causing intermittent hypoxia (IH). Sleep apnea patients and rodents exposed to IH exhibit elevated sympathetic nerve activity and hypertension. A heightened carotid body (CB) chemoreflex has been implicated in causing autonomic abnormalities in IH-treated rodents and in sleep apnea patients. The purpose of this article is to review the emerging evidence showing that interactions between reactive oxygen species (ROS) and gaseous transmitters as a mechanism cause hyperactive CB by IH. Rodents treated with IH exhibit markedly elevated ROS in the CB, which is due to transcriptional upregulation of pro-oxidant enzymes by hypoxia-inducible factor (HIF)-1 and insufficient transcriptional regulation of anti-oxidant enzymes by HIF-2. ROS, in turn, increases cystathionine γ-lyase (CSE)-dependent H2S production in the CB. Blockade of H2S synthesis prevents IH-evoked CB activation. However, the effects of ROS on H2S production are not due to direct effects on CSE enzyme activity but rather due to inactivation of heme oxygenase-2 (HO-2), a carbon monoxide (CO) producing enzyme. CO inhibits H2S production through inactivation of CSE by PKG-dependent phosphorylation. During IH, reduced CO production resulting from inactivation of HO-2 by ROS releases the inhibition of CO on CSE thereby increasing H2S. Inhibiting H2S synthesis prevented IH-evoked sympathetic activation and hypertension.

Therapeutic Targeting of the Carotid Body for Treating Sleep Apnea in a Pre-clinical Mouse Model.

Sleep apnea with periodic cessation of breathing during sleep is a highly prevalent respiratory disorder affecting an estimated 10% of adults. Patients with sleep apnea exhibit several co-morbidities including hypertension, stroke, disrupted sleep, and neurocognitive and metabolic complications. Emerging evidence suggests that a hyperactive carotid body (CB) chemo reflex is an important driver of apneas in sleep apnea patients. Gasotransmitters carbon monoxide (CO) and hydrogen sulfide (H2S) play important roles in oxygen sensing by the CB. We tested the hypothesis that an augmented CB chemo reflex stemming from disrupted CO-H2S signaling may lead to sleep apnea. This possibility was tested in mice deficient in hemeoxygenase-2 (HO-2), an enzyme involved in CO synthesis, which were shown to exhibit hyperactive CB activity due to high H2S levels. We found that HO-2-/- mice exhibit a high incidence of apneas during sleep compared to wild type mice. Blocking the CB hyperactivity with L-propargylglycine, an inhibitor of cystathionine-γ-lyase (CSE), which catalyzes H2S synthesis, prevented apneas in HO-2-/- mice. These findings suggest that targeting CB with inhibitors of CSE might be a novel therapeutic strategy for preventing sleep apnea.

Antibodies from combinatorial libraries use functional receptor pleiotropism to regulate cell fates.

To date, most antibodies from combinatorial libraries have been selected purely on the basis of binding. However, new methods now allow selection on the basis of function in animal cells. These selected agonist antibodies have given new insights into the important problem of signal transduction. Remarkably, when some antibodies bind to a given receptor they induce a cell fate that is different than that induced by the natural agonist to the same receptor. The fact that receptors can be functionally pleiotropic may yield new insights into the important problem of signal transduction.

Epigenetic regulation of redox state mediates persistent cardiorespiratory abnormalities after long-term intermittent hypoxia.

KEY POINTS: The effects of short-term (ST; 10 days) and long-term (LT; 30 days) intermittent hypoxia (IH) on blood pressure (BP), breathing and carotid body (CB) chemosensory reflex were examined in adult rats. ST- and LT-IH treated rats exhibited hypertension, irregular breathing with apnoea and augmented the CB chemosensory reflex, with all these responses becoming normalized during recovery from ST- but not from LT-IH. The persistent cardiorespiratory responses to LT-IH were associated with elevated reactive oxygen species (ROS) levels in the CB and adrenal medulla, which were a result of DNA methylation-dependent suppression of genes encoding anti-oxidant enzymes (AOEs). Treating rats with decitabine either during LT-IH or during recovery from LT-IH prevented DNA methylation of AOE genes, normalized the expression of AOE genes and ROS levels, reversed the heightened CB chemosensory reflex and hypertension, and also stabilized breathing. ABSTRACT: Rodents exposed to chronic intermittent hypoxia (IH), simulating blood O2 saturation profiles during obstructive sleep apnoea (OSA), have been shown to exhibit a heightened carotid body (CB) chemosensory reflex and hypertension. CB chemosensory reflex activation also results in unstable breathing with apnoeas. However, the effect of chronic IH on breathing is not known. In the present study, we examined the effects of chronic IH on breathing along with blood pressure (BP) and assessed whether the autonomic responses are normalized after recovery from chronic IH. Studies were performed on adult, male, Sprague-Dawley rats exposed to either short-term (ST; 10 days) or long-term (LT, 30 days) IH. Rats exposed to either ST- or LT-IH exhibited hypertension, irregular breathing with apnoeas, an augmented CB chemosensory reflex as indicated by elevated CB neural activity and plasma catecholamine levels, and elevated reactive oxygen species (ROS) levels in the CB and adrenal medulla (AM). All these effects were normalized after recovery from ST-IH but not from LT-IH. Analysis of the molecular mechanisms underlying the persistent effects of LT-IH revealed increased DNA methylation of genes encoding anti-oxidant enzymes (AOEs). Treatment with decitabine, a DNA methylation inhibitor, either during LT-IH or during recovery from LT-IH, prevented DNA methylation, normalized the expression of AOE genes, ROS levels, CB chemosensory reflex and BP, and also stabilized breathing. These results suggest that persistent cardiorespiratory abnormalities caused by LT-IH are mediated by epigenetic re-programming of the redox state in the CB chemosensory reflex pathway.

An agonist antibody that blocks autoimmunity by inducing anti-inflammatory macrophages.

We have devised a method of using intracellular combinatorial libraries to select antibodies that control cell fates. Many agonist antibodies have been selected with this method, and the process appears to be limited only by the availability of a phenotypic selection system. We demonstrate the utility of this approach to discover agonist antibodies that engage an unanticipated target and regulate macrophage polarization by selective induction of anti-inflammatory M2 macrophages. This antibody was used therapeutically to block autoimmunity in a classic mouse model of spontaneous systemic lupus erythematosus.

Oxygen Sensing by the Carotid Body: Past and Present.

It is now well established that carotid bodies are sensory organs for monitoring arterial blood oxygen levels and trigger reflexes that are critical for maintaining homeostasis during hypoxemia. This review article provides a brief account of the early studies leading to the discovery of the carotid body as a sensory receptor and addresses current views of O2 sensing mechanism(s) in the carotid body and their physiological importance.

Inherent variations in CO-H2S-mediated carotid body O2 sensing mediate hypertension and pulmonary edema.

Oxygen (O2) sensing by the carotid body and its chemosensory reflex is critical for homeostatic regulation of breathing and blood pressure. Humans and animals exhibit substantial interindividual variation in this chemosensory reflex response, with profound effects on cardiorespiratory functions. However, the underlying mechanisms are not known. Here, we report that inherent variations in carotid body O2 sensing by carbon monoxide (CO)-sensitive hydrogen sulfide (H2S) signaling contribute to reflex variation in three genetically distinct rat strains. Compared with Sprague-Dawley (SD) rats, Brown-Norway (BN) rats exhibit impaired carotid body O2 sensing and develop pulmonary edema as a consequence of poor ventilatory adaptation to hypobaric hypoxia. Spontaneous Hypertensive (SH) rat carotid bodies display inherent hypersensitivity to hypoxia and develop hypertension. BN rat carotid bodies have naturally higher CO and lower H2S levels than SD rat, whereas SH carotid bodies have reduced CO and greater H2S generation. Higher CO levels in BN rats were associated with higher substrate affinity of the enzyme heme oxygenase 2, whereas SH rats present lower substrate affinity and, thus, reduced CO generation. Reducing CO levels in BN rat carotid bodies increased H2S generation, restoring O2 sensing and preventing hypoxia-induced pulmonary edema. Increasing CO levels in SH carotid bodies reduced H2S generation, preventing hypersensitivity to hypoxia and controlling hypertension in SH rats.

CaV3.2 T-type Ca2+ channels mediate the augmented calcium influx in carotid body glomus cells by chronic intermittent hypoxia.

Chronic intermittent hypoxia (CIH) is a hallmark manifestation of sleep apnea. A heightened carotid body activity and the resulting chemosensory reflex mediate increased sympathetic nerve activity by CIH. However, the mechanisms underlying heightened carotid body activity by CIH are not known. An elevation of intracellular calcium ion concentration ([Ca(2+)]i) in glomus cells, the primary oxygen-sensing cells, is an essential step for carotid body activation by hypoxia. In the present study, we examined the effects of CIH on the glomus cell [Ca(2+)]i response to hypoxia and assessed the underlying mechanisms. Glomus cells were harvested from adult rats or wild-type mice treated with 10 days of either room air (control) or CIH (alternating cycles of 15 s of hypoxia and 5 min of room air; 9 episodes/h; 8 h/day). CIH-treated glomus cells exhibited an enhanced [Ca(2+)]i response to hypoxia, and this effect was absent in the presence of 2-(4-cyclopropylphenyl)-N-((1R)-1-[5-[(2,2,2-trifluoroethyl)oxo]-pyridin-2-yl]ethyl)acetamide (TTA-A2), a specific inhibitor of T-type Ca(2+) channels, and in voltage-gated calcium channel, type 3.2 (CaV3.2), null glomus cells. CaV3.2 knockout mice exhibited an absence of CIH-induced hypersensitivity of the carotid body. CIH increased reactive oxygen species (ROS) levels in glomus cells. A ROS scavenger prevented the exaggerated TTA-A2-sensitive [Ca(2+)]i response to hypoxia. CIH had no effect on CaV3.2 mRNA levels. CIH augmented Ca(2+) currents and increased CaV3.2 protein in plasma membrane fractions of human embryonic kidney-293 cells stably expressing CaV3.2, and either a ROS scavenger or brefeldin-A, an inhibitor of protein trafficking, prevented these effects. These findings suggest that CIH leads to an augmented Ca(2+) influx via ROS-dependent facilitation of CaV3.2 protein trafficking to the plasma membrane.

Mutual antagonism between hypoxia-inducible factors 1α and 2α regulates oxygen sensing and cardio-respiratory homeostasis.

Breathing and blood pressure are under constant homeostatic regulation to maintain optimal oxygen delivery to the tissues. Chemosensory reflexes initiated by the carotid body and catecholamine secretion from the adrenal medulla are the principal mechanisms for maintaining respiratory and cardiovascular homeostasis; however, the underlying molecular mechanisms are not known. Here, we report that balanced activity of hypoxia-inducible factor-1 (HIF-1) and HIF-2 is critical for oxygen sensing by the carotid body and adrenal medulla, and for their control of cardio-respiratory function. In Hif2α(+/-) mice, partial HIF-2α deficiency increased levels of HIF-1α and NADPH oxidase 2, leading to an oxidized intracellular redox state, exaggerated hypoxic sensitivity, and cardio-respiratory abnormalities, which were reversed by treatment with a HIF-1α inhibitor or a superoxide anion scavenger. Conversely, in Hif1α(+/-) mice, partial HIF-1α deficiency increased levels of HIF-2α and superoxide dismutase 2, leading to a reduced intracellular redox state, blunted oxygen sensing, and impaired carotid body and ventilatory responses to chronic hypoxia, which were corrected by treatment with a HIF-2α inhibitor. None of the abnormalities observed in Hif1α(+/-) mice or Hif2α(+/-) mice were observed in Hif1α(+/-);Hif2α(+/-) mice. These observations demonstrate that redox balance, which is determined by mutual antagonism between HIF-α isoforms, establishes the set point for hypoxic sensing by the carotid body and adrenal medulla, and is required for maintenance of cardio-respiratory homeostasis.

CaV3.2 T-type Ca²âº channels in H2S-mediated hypoxic response of the carotid body.

Arterial blood O2 levels are detected by specialized sensory organs called carotid bodies. Voltage-gated Ca(2+) channels (VGCCs) are important for carotid body O2 sensing. Given that T-type VGCCs contribute to nociceptive sensation, we hypothesized that they participate in carotid body O2 sensing. The rat carotid body expresses high levels of mRNA encoding the α1H-subunit, and α1H protein is localized to glomus cells, the primary O2-sensing cells in the chemoreceptor tissue, suggesting that CaV3.2 is the major T-type VGCC isoform expressed in the carotid body. Mibefradil and TTA-A2, selective blockers of the T-type VGCC, markedly attenuated elevation of hypoxia-evoked intracellular Ca(2+) concentration, secretion of catecholamines from glomus cells, and sensory excitation of the rat carotid body. Similar results were obtained in the carotid body and glomus cells from CaV3.2 knockout (Cacna1h(-/-)) mice. Since cystathionine-γ-lyase (CSE)-derived H2S is a critical mediator of the carotid body response to hypoxia, the role of T-type VGCCs in H2S-mediated O2 sensing was examined. Like hypoxia, NaHS, a H2S donor, increased intracellular Ca(2+) concentration and augmented carotid body sensory nerve activity in wild-type mice, and these effects were markedly attenuated in Cacna1h(-/-) mice. In wild-type mice, TTA-A2 markedly attenuated glomus cell and carotid body sensory nerve responses to hypoxia, and these effects were absent in CSE knockout mice. These results demonstrate that CaV3.2 T-type VGCCs contribute to the H2S-mediated carotid body response to hypoxia.