Contribution of Oxidative Stress and Inflammation to the Neurogenic Hypertension Induced by Intermittent Hypoxia

Neuronal ferroptosis and ferroptosis-mediated endoplasmic reticulum stress: Implications in cognitive dysfunction induced by chronic intermittent hypoxia in mice

Obstructive sleep apnea, typically characterized by chronic intermittent hypoxia (CIH), is linked to cognitive dysfunction in children. Ferroptosis, a novel form of cell death characterized by lethal iron accumulation and lipid peroxidation, is implicated in neurodegenerative diseases and ischemia-reperfusion injuries. Nevertheless, its contribution to CIH-induced cognitive dysfunction and its interaction with endoplasmic reticulum stress (ERS) remain uncertain. In this study, utilizing a CIH model in 4-week-old male mice, we investigated ferroptosis and its potential involvement in ERS regulation during cognitive dysfunction. Our findings indicate ferroptosis activation in prefrontal cortex neurons, leading to neuron loss, mitochondrial damage, decreased levels of GPX4, SLC7A11, FTL, and FTH, increased levels of reactive oxygen species (ROS), malondialdehyde (MDA), Fe2+, ACSL4, TFRC, along with the activation of ERS-related PERK-ATF4-CHOP pathway. Treatment with the ferroptosis inhibitor liproxstatin-1 (Lip-1) and the iron chelator deferoxamine (DFO) effectively mitigated the neuron injury and cognitive dysfunction induced by CIH, significantly reducing Fe2+ and partly restoring expression levels of ferroptosis-related proteins. Furhermore, the use of Lip-1 and DFO downregulated p-PERK, ATF4 and CHOP, and upregulated Nrf2 expression, suggesting that inhibiting ferroptosis reduce ERS and that the transcription factor Nrf2 is involved in the process. In summary, our findings indicate that cognitive impairment in CIH mice correlates with the induction of neuronal ferroptosis, facilitated by the System xc - GPX4 functional axis, lipid peroxidation, and the iron metabolism pathway, along with ferroptosis-mediated ERS in the prefrontal cortex. Nrf2 has been identified as a potential regulator of ferroptosis and ERS involved in the context of CIH.

Intermittent hypoxia induces Th17/Treg imbalance in a murine model of obstructive sleep apnea

Obstructive sleep apnea (OSA) is characterized by cyclic normoxic and hypoxic conditions (intermittent hypoxia, IH) induced by the repeated closure of the upper-airway respiratory tract. As a pathomechanism of OSA, IH results in various comorbidities via chronic inflammation and related pathways. However, the role of other inflammatory cells, such as lymphocytes, has not been well-explored. This study aimed to examine the effects of IH on the distribution and balance of T cell subsets and other related cytokines, and mechanisms in the immune system. We modified OSA mouse model (male C57BL/6N male) using our customized chamber that controls specific sleep and oxygenic cycles. To induce hypoxia, the IH group was repeatedly exposed to 5% O2 and 21% O2 lasting for 120 s each for 7 h daily for 4 weeks. Mice were then subjected to a recovery period of 4 weeks, in which IH stimulation was ceased. T cells and related cytokines were analyzed using flow cytometry and immunohistochemistry. Compared with the control group, the IH group had significantly lower levels of CD4+CD25+Foxp3+ regulatory T cells but higher levels of Th 17, IL-4, HIF-1, and inflammatory cytokines. After the recovery period, these altered changes in the immune cells were recovered, and we found no significant difference in their levels between the control and recovery groups. This study revealed that the Th17/Treg ratio is increased by intermittent hypoxia, and this imbalance can explain immune-related diseases, including recently reported allergies, autoimmune, and even cancer diseases, arising from OSA.

The effect of microvascular decompression of the CN IX-X root entry/exit zone and the ventrolateral medulla in neurogenic hypertension involving the vertebral/basilar artery

Introduction

Neurogenic hypertension (HTN) is a type of HTN characterized by increased activity of the sympathetic nervous system. Vascular compression is one of the pathogenic mechanisms of neurogenic HTN. Despite Jannetta's solid anatomical and physiological arguments in favor of neurogenic HTN in the 1970's, the treatment for essential HTN by microvascular decompression (MVD) still lacks established selection criteria. Therefore, the subjects selected for our center were limited to patients with primary trigeminal neuralgia (TN) and primary hemifacial spasm (HFS) of the vertebral/basilar artery (VA/BA) responsible vessel type coexisting with neurogenic HTN who underwent MVD of the brainstem to further explore possible indications for MVD in the treatment of neurogenic HTN.

Methods

A retrospective analysis of 63 patients who were diagnosed with neurogenic HTN had symptoms of HFS and TN cranial nerve disease. Patients were treated at our neurosurgery department from January 2018 to January 2023. A preoperative magnetic resonance examination of the patients revealed the presence of abnormally located vascular compression in the rostral ventrolateral medulla (RVLM) and the root entry zone (REZ) of the IX and X cranial nerves (CN IX- X).

Results

There was no significant difference between the two groups in terms of gender, age, course of HFS, course of TN, course of HTN, degree of HTN, or preoperative blood pressure. Based on the postoperative blood pressure levels, nine out of 63 patients were cured (14.28%), eight cases (12.70%) showed a marked effect, 16 cases (25.40%) were effective, and 30 cases were invalid (47.62%). The overall efficacy was 52.38%. However, 39 cases of combined cranial nerve disease were on the left side of the efficacy rate (66.67%) and 24 cases of combined cranial nerve disease were on the right side of the efficacy rate (29.16%).

Discussion

Over the last few decades, many scholars have made pioneering progress in the clinical retrospective study of MVD for neurogenic hypertension, and our study confirms the efficacy of MVD in treating vertebral/basilar artery-type neurogenic hypertension by relieving the vascular pressure of RVLM. In the future, with the development and deepening of pathological mechanisms and clinical observational studies, MVD may become an important treatment for neurogenic hypertension by strictly grasping the surgical indications.

Conclusion

MVD is an effective treatment for neurogenic HTN. Indications may include the following: left-sided TN or HFS combined with neurogenic HTN; VA/BA compression in the left RVLM and REZ areas on MRI; and blood pressure in these patients cannot be effectively controlled by drugs.

The association between flavonoids intake and hypertension in U.S. adults: A cross-sectional study from The National Health and Nutrition Examination Survey

Although in vitro experiments have demonstrated the potential of flavonoid compounds in regulating blood pressure, there is still a lack of evidence from large population studies. We conducted a cross-sectional study using the National Health and Nutrition Examination Survey to investigate the relationship between flavonoid intake levels (natural log transformation) and hypertension events. A total of 15 752 participants aged over 20 years were included, and a weighted multivariable logistic regression analysis was performed to explore the relationship between total flavonoids, five sub types intake, and hypertension events. Smooth curve fitting was used to explore potential nonlinear relationships. Higher total flavonoids intake was associated with a lower risk of hypertension than the lowest group. The adjusted odds ratios (95% CIs) were 0.79 (0.70-0.88) for total flavonoids intake. Elevated total flavonoids intake levels were significantly and linearly associated with a lower risk of hypertension. For each unit increase in the total flavonoids intake level, the adjusted ORs for risk of hypertension decrease by 5% (OR 0.95; 95% CI, 0.92-0.98). In addition, in restricted cubic spline regression, we found that flavan-3-ols, anthocyanidins, and flavonols intake were linearly and negatively related to prevalence of hypertension. Flavones intake showed nonlinear associations with prevalence of hypertension with inflection points of -1.90. Within a certain range, a negative correlation exists between flavonoids intake and hypertension events. This finding provides insights into dietary modifications in the prevention of hypertension.

Inflammation of some visceral sensory systems and autonomic dysfunction in cardiovascular disease

The sensitization and hypertonicity of visceral afferents are highly relevant to the development and progression of cardiovascular and respiratory disease states. In this review, we described the evidence that the inflammatory process regulates visceral afferent sensitivity and tonicity, affecting the control of the cardiovascular and respiratory system. Some inflammatory mediators like nitric oxide, angiotensin II, endothelin-1, and arginine vasopressin may inhibit baroreceptor afferents and contribute to the baroreflex impairment observed in cardiovascular diseases. Cytokines may act directly on peripheral afferent terminals that transmit information to the central nervous system (CNS). TLR-4 receptors, which recognize lipopolysaccharide, were identified in the nodose and petrosal ganglion and have been implicated in disrupting the blood-brain barrier, which can potentiate the inflammatory process. For example, cytokines may cross the blood-brain barrier to access the CNS. Additionally, pro-inflammatory cytokines such as IL-1β, IL-6, TNF-α and some of their receptors have been identified in the nodose ganglion and carotid body. These pro-inflammatory cytokines also sensitize the dorsal root ganglion or are released in the nucleus of the solitary tract. In cardiovascular disease, pro-inflammatory mediators increase in the brain, heart, vessels, and plasma and may act locally or systemically to activate/sensitize afferent nervous terminals. Recent evidence demonstrated that the carotid body chemoreceptor cells might sense systemic pro-inflammatory molecules, supporting the novel proposal that the carotid body is part of the afferent pathway in the central anti-inflammatory reflexes. The exact mechanisms of how pro-inflammatory mediators affects visceral afferent signals and contribute to the pathophysiology of cardiovascular diseases awaits future research.

Carotid body contribution to the physio-pathological consequences of intermittent hypoxia: role of nitro-oxidative stress and inflammation

Obstructive sleep apnoea (OSA), characterized by chronic intermittent hypoxia (CIH), is considered to be an independent risk for hypertension. The pathological cardiorespiratory consequences of OSA have been attributed to systemic oxidative stress, inflammation and sympathetic overflow induced by CIH, but an emerging body of evidence indicates that a nitro-oxidative and pro-inflammatory milieu within the carotid body (CB) is involved in the potentiation of CB chemosensory responses to hypoxia, which contribute to enhance the sympathetic activity. Accordingly, autonomic and cardiovascular alterations induced by CIH are critically dependent on an abnormally heightened CB chemosensory input to the nucleus of tractus solitarius (NTS), where second-order neurons project onto the rostral ventrolateral medulla (RVLM), activating pre-sympathetic neurons that control pre-ganglionic sympathetic neurons. CIH produces oxidative stress and neuroinflammation in the NTS and RVLM, which may contribute to the long-term irreversibility of the CIH-induced alterations. This brief review is mainly focused on the contribution of nitro-oxidative stress and pro-inflammatory molecules on the hyperactivation of the hypoxic chemoreflex pathway including the CB and the brainstem centres, and whether the persistence of autonomic and cardiorespiratory alterations may depend on the glial-related neuroinflammation induced by the enhanced CB chemosensory afferent input.

Chemogenetic inhibition of NTS astrocytes normalizes cardiac autonomic control and ameliorate hypertension during chronic intermittent hypoxia

BACKGROUND

Obstructive sleep apnea (OSA) is characterized by recurrent episodes of chronic intermittent hypoxia (CIH), which has been linked to the development of sympathoexcitation and hypertension. Furthermore, it has been shown that CIH induced inflammation and neuronal hyperactivation in the nucleus of the solitary tract (NTS), a key brainstem region involved in sympathetic and cardiovascular regulation. Since several studies have proposed that NTS astrocytes may mediate neuroinflammation, we aimed to determine the potential contribution of NTS-astrocytes on the pathogenesis of CIH-induced hypertension.

RESULTS

Twenty-one days of CIH induced autonomic imbalance and hypertension in rats. Notably, acute chemogenetic inhibition (CNO) of medullary NTS astrocytes using Designer Receptors Exclusively Activated by Designers Drugs (DREADD) restored normal cardiac variability (LF/HF: 1.1 ± 0.2 vs. 2.4 ± 0.2 vs. 1.4 ± 0.3, Sham vs. CIH vs. CIH + CNO, respectively) and markedly reduced arterial blood pressure in rats exposed to CIH (MABP: 82.7 ± 1.2 vs. 104.8 ± 4.4 vs. 89.6 ± 0.9 mmHg, Sham vs. CIH vs. CIH + CNO, respectively). In addition, the potentiated sympathoexcitation elicit by acute hypoxic chemoreflex activation in rats exposed to CIH was also completely abolished by chemogenetic inhibition of NTS astrocytes using DREADDs.

CONCLUSION

Our results support a role for NTS astrocytes in the maintenance of heightened sympathetic drive and hypertension during chronic exposure to intermittent hypoxia mimicking OSA.

Acute inhibition of nicotinamide adenine dinucleotide phosphate oxidase in the commissural nucleus of the solitary tract reduces arterial pressure and renal sympathetic nerve activity in renovascular hypertension

BACKGROUND

A growing body of evidence suggests that oxidative stress plays a role in the pathophysiology of hypertension. However, the involvement of the reactive oxygen species (ROS) in the commissural nucleus of the solitary tract (commNTS) in development the of hypertension remains unclear.

METHOD

We evaluated the hemodynamic and sympathetic responses to acute inhibition of NADPH oxidase in the commNTS in renovascular hypertensive rats. Under anesthesia, male Holtzman rats were implanted with a silver clip around the left renal artery to induce 2-kidney 1-clip (2K1C) hypertension. After six weeks, these rats were anesthetized and instrumented for recording mean arterial pressure (MAP), renal blood flow (RBF), renal vascular resistance (RVR), and renal sympathetic nerve activity (RSNA) during baseline and after injection of apocynin (nicotinamide adenine dinucleotide phosphate oxidase inhibitor), NSC 23766 (RAC inhibitor) or saline into the commNTS.

RESULTS

Apocynin into the commNTS decreased MAP, RSNA, and RVR in 2K1C rats. NSC 23766 into the commNTS decreased MAP and RSNA, without changing RVR in 2K1C rats.

CONCLUSION

These results demonstrate that the formation of ROS in the commNTS is important to maintain sympathoexcitation and hypertension in 2K1C rats and suggest that NADPH oxidase in the commNTS could be a potential target for therapeutics in renovascular hypertension.

Obstructive Sleep Apnea and Venous Thromboembolism: Unraveling the Emerging Association

Oxidative stress has emerged as a significant contributor to skeletal muscle atrophy, influencing cellular processes that underlie muscle wasting. This review article delves into the intricate interplay between oxidative stress and muscle atrophy, shedding light on its mechanisms and implications. We begin by outlining the fundamental concepts of oxidative stress, delineating reactive oxygen species (ROS) and reactive nitrogen species (RNS), their sources, and the ensuing oxidative damage to cellular components. Subsequently, we delve into skeletal muscle atrophy, elucidating its diverse forms, molecular pathways, key signaling cascades, and the role of inflammation in exacerbating muscle wasting. Bridging these concepts, we explore the connections between oxidative stress and muscle atrophy, unveiling how oxidative stress impacts muscle protein synthesis and breakdown, perturbs cellular signaling pathways, and contributes to mitochondrial dysfunction. The review underscores the complexity of quantifying and interpreting oxidative stress markers, highlighting the challenges posed by the dynamic nature of oxidative stress and the presence of basal ROS levels. Addressing the specificity of oxidative stress markers, we emphasize the importance of selecting markers pertinent to muscle tissue and considering systemic influences. Standardization of experimental protocols emerges as a critical need to ensure consistency and reproducibility across studies. Looking ahead, we discuss the implications of oxidative stress in diverse scenarios, encompassing age-related muscle loss (sarcopenia), muscle wasting in chronic diseases like cancer cachexia, and disuse-induced muscle atrophy. Additionally, we delve into potential therapeutic strategies, including antioxidant supplementation, exercise, pharmacological interventions, nutritional approaches, and lifestyle modifications, as avenues to mitigate oxidative stress-driven muscle atrophy. The review concludes by outlining promising future directions in this field, calling for deeper exploration of specific oxidative stress markers, understanding the temporal dynamics of oxidative stress, validation through translational studies in humans, and the development of targeted therapeutic interventions. By advancing our understanding of the intricate relationship between oxidative stress and skeletal muscle atrophy, this review contributes to paving the way for innovative strategies to address muscle wasting and improve muscle health.

Neurogenic Hypertension, the Blood-Brain Barrier, and the Potential Role of Targeted Nanotherapeutics

Hypertension is a major health concern globally. Elevated blood pressure, initiated and maintained by the brain, is defined as neurogenic hypertension (NH), which accounts for nearly half of all hypertension cases. A significant increase in angiotensin II-mediated sympathetic nervous system activity within the brain is known to be the key driving force behind NH. Blood pressure control in NH has been demonstrated through intracerebrovascular injection of agents that reduce the sympathetic influence on cardiac functions. However, traditional antihypertensive agents lack effective brain permeation, making NH management extremely challenging. Therefore, developing strategies that allow brain-targeted delivery of antihypertensives at the therapeutic level is crucial. Targeting nanotherapeutics have become popular in delivering therapeutics to hard-to-reach regions of the body, including the brain. Despite the frequent use of nanotherapeutics in other pathological conditions such as cancer, their use in hypertension has received very little attention. This review discusses the underlying pathophysiology and current management strategies for NH, as well as the potential role of targeted therapeutics in improving current treatment strategies.

Sulforaphane Attenuates Chronic Intermittent Hypoxia-Induced Brain Damage in Mice via Augmenting Nrf2 Nuclear Translocation and Autophagy

Obstructive sleep apnea–hypopnea syndrome (OSAHS), typically characterized by chronic intermittent hypoxia (CIH), is associated with neurocognitive dysfunction in children. Sulforaphane (SFN), an activator of nuclear factor E2-related factor 2 (Nrf2), has been demonstrated to protect against oxidative stress in various diseases. However, the effect of SFN on OSAHS remains elusive. In this research, we investigated the neuroprotective role of SFN in CIH-induced cognitive dysfunction and underlying mechanisms of regulation of Nrf2 signaling pathway and autophagy. CIH exposures for 4 weeks in mice, modeling OSAHS, contributed to neurocognitive dysfunction, manifested as increased working memory errors (WMEs), reference memory errors (RMEs) and total memory errors (TEs) in the 8-arm radial maze test. The mice were intraperitoneally injected with SFN (0.5 mg/kg) 30 min before CIH exposure everyday. SFN treatment ameliorated neurocognitive dysfunction in CIH mice, which demonstrates less RME, WME, and TE. Also, SFN effectively alleviated apoptosis of hippocampal neurons following CIH by decreased TUNEL-positive cells, downregulated cleaved PARP, cleaved caspase 3, and upregulated Bcl-2. SFN protects hippocampal tissue from CIH-induced oxidative stress as evidenced by elevated superoxide dismutase (SOD) activities and reduced malondialdehyde (MDA). In addition, we found that SFN enhanced Nrf2 nuclear translocation to hold an antioxidative function on CIH-induced neuronal apoptosis in hippocampus. Meanwhile, SFN promoted autophagy activation, as shown by increased Beclin1, ATG5, and LC3II/LC3I. Overall, our findings indicated that SFN reduced the apoptosis of hippocampal neurons through antioxidant effect of Nrf2 and autophagy in CIH-induced brain damage, which highlights the potential of SFN as a novel therapy for OSAHS-related neurocognitive dysfunction.

Carotid Body Inflammation: Role in Hypoxia and in the Anti-inflammatory Reflex

Emergent evidence indicates that the carotid body (CB) chemoreceptors may sense systemic inflammatory molecules, and is an afferent-arm of the anti-inflammatory reflex. Moreover, a pro-inflammatory milieu within the CB is involved in the enhanced CB chemosensory responsiveness to oxygen following sustained and intermittent hypoxia. In this review, we focus on the physio-pathological participation of CBs in inflammatory diseases, such as sepsis and intermittent hypoxia.

Carbamylated form of human erythropoietin normalizes cardiorespiratory disorders triggered by intermittent hypoxia mimicking sleep apnea syndrome

BACKGROUND AND OBJECTIVE

Chronic intermittent hypoxia (CIH), one of the main features of obstructive sleep apnea (OSA), enhances carotid body-mediated chemoreflex and induces hypertension and breathing disorders. The carbamylated form of erythropoietin (cEpo) may have beneficial effects as it retains its antioxidant/anti-inflammatory and neuroprotective profile without increasing red blood cells number. However, no studies have evaluated the potential therapeutic effect of cEpo on CIH-related cardiorespiratory disorders. We aimed to determine whether cEpo normalized the CIH-enhanced carotid body ventilatory chemoreflex, the hypertension and ventilatory disorders in rats.

METHODS

Male Sprague-Dawley rats (250 g) were exposed to CIH (5% O2, 12/h, 8 h/day) for 28 days. cEPO (20 μg/kg, i.p) was administrated from day 21 every other day for one more week. Cardiovascular and respiratory function were assessed in freely moving animals.

RESULTS

Twenty-one days of CIH increased carotid body-mediated chemoreflex responses as evidenced by a significant increase in the hypoxic ventilatory response (FiO2 10%) and triggered irregular eupneic breathing, active expiration, and produced hypertension. cEpo treatment significantly reduced the carotid body--chemoreflex responses, normalizes breathing patterns and the hypertension in CIH. In addition, cEpo treatment effectively normalized carotid body chemosensory responses evoked by acute hypoxic stimulation in CIH rats.

CONCLUSION

Present results strongly support beneficial cardiorespiratory therapeutic effects of cEpo during CIH exposure.

Unlocking mammalian regeneration through hypoxia inducible factor one alpha signaling

Historically, the field of regenerative medicine has aimed to heal damaged tissue through the use of biomaterials scaffolds or delivery of foreign progenitor cells. Despite 30 years of research, however, translation and commercialization of these techniques has been limited. To enable mammalian regeneration, a more practical approach may instead be to develop therapies that evoke endogenous processes reminiscent of those seen in innate regenerators. Recently, investigations into tadpole tail regrowth, zebrafish limb restoration, and the super-healing Murphy Roths Large (MRL) mouse strain, have identified ancient oxygen-sensing pathways as a possible target to achieve this goal. Specifically, upregulation of the transcription factor, hypoxia-inducible factor one alpha (HIF-1α) has been shown to modulate cell metabolism and plasticity, as well as inflammation and tissue remodeling, possibly priming injuries for regeneration. Since HIF-1α signaling is conserved across species, environmental or pharmacological manipulation of oxygen-dependent pathways may elicit a regenerative response in non-healing mammals. In this review, we will explore the emerging role of HIF-1α in mammalian healing and regeneration, as well as attempts to modulate protein stability through hyperbaric oxygen treatment, intermittent hypoxia therapy, and pharmacological targeting. We believe that these therapies could breathe new life into the field of regenerative medicine.

Ketogenic diet effects on inflammatory allodynia and ongoing pain in rodents

Ketogenic diets are very low carbohydrate, high fat, moderate protein diets used to treat medication-resistant epilepsy. Growing evidence suggests that one of the ketogenic diet’s main mechanisms of action is reducing inflammation. Here, we examined the diet’s effects on experimental inflammatory pain in rodent models. Young adult rats and mice were placed on the ketogenic diet or maintained on control diet. After 3–4 weeks on their respective diets, complete Freund’s adjuvant (CFA) was injected in one hindpaw to induce inflammation; the contralateral paw was used as the control. Tactile sensitivity (von Frey) and indicators of spontaneous pain were quantified before and after CFA injection. Ketogenic diet treatment significantly reduced tactile allodynia in both rats and mice, though with a species-specific time course. There was a strong trend to reduced spontaneous pain in rats but not mice. These data suggest that ketogenic diets or other ketogenic treatments might be useful treatments for conditions involving inflammatory pain.

Immunity and the carotid body: implications for metabolic diseases

Neuro-immune communication has gained enormous interest in recent years due to increasing knowledge of the way in which the brain coordinates functional alterations in inflammatory and autoimmune responses, and the mechanisms of neuron-immune cell interactions in the context of metabolic diseases such as obesity and type 2 diabetes. In this review, we will explain how this relationship between the nervous and immune system impacts the pro- and anti-inflammatory pathways with specific reference to the hypothalamus-pituitary-adrenal gland axis and the vagal reflex and will explore the possible involvement of the carotid body (CB) in the neural control of inflammation. We will also highlight the mechanisms of vagal anti-inflammatory reflex control of immunity and metabolism, and the consequences of functional disarrangement of this reflex in settlement and development of metabolic diseases, with special attention to obesity and type 2 diabetes. Additionally, the role of CB in the interplay between metabolism and immune responses will be discussed, with specific reference to the different stimuli that promote CB activation and the balance between sympathetic and parasympathetic in this context. In doing so, we clarify the multivarious neuronal reflexes that coordinate tissue-specific responses (gut, pancreas, adipose tissue and liver) critical to metabolic control, and metabolic disease settlement and development. In the final section, we will summarize how electrical modulation of the carotid sinus nerve may be utilized to adjust these reflex responses and thus control inflammation and metabolic diseases, envisioning new therapeutics horizons.

Autonomic innervation of the carotid body as a determinant of its sensitivity: implications for cardiovascular physiology and pathology

The motivation for this review comes from the emerging complexity of the autonomic innervation of the carotid body (CB) and its putative role in regulating chemoreceptor sensitivity. With the carotid bodies as a potential therapeutic target for numerous cardiorespiratory and metabolic diseases, an understanding of the neural control of its circulation is most relevant. Since nerve fibres track blood vessels and receive autonomic innervation, we initiate our review by describing the origins of arterial feed to the CB and its unique vascular architecture and blood flow. Arterial feed(s) vary amongst species and, unequivocally, the arterial blood supply is relatively high to this organ. The vasculature appears to form separate circuits inside the CB with one having arterial venous anastomoses. Both sympathetic and parasympathetic nerves are present with postganglionic neurons located within the CB or close to it in the form of paraganglia. Their role in arterial vascular resistance control is described as is how CB blood flow relates to carotid sinus afferent activity. We discuss non-vascular targets of autonomic nerves, their possible role in controlling glomus cell activity, and how certain transmitters may relate to function. We propose that the autonomic nerves sub-serving the CB provide a rapid mechanism to tune the gain of peripheral chemoreflex sensitivity based on alterations in blood flow and oxygen delivery, and might provide future therapeutic targets. However, there remain a number of unknowns regarding these mechanisms that require further research that is discussed.

Exploring the Mediators that Promote Carotid Body Dysfunction in Type 2 Diabetes and Obesity Related Syndromes

Carotid bodies (CBs) are peripheral chemoreceptors that sense changes in blood O₂, CO₂, and pH levels. Apart from ventilatory control, these organs are deeply involved in the homeostatic regulation of carbohydrates and lipid metabolism and inflammation. It has been described that CB dysfunction is involved in the genesis of metabolic diseases and that CB overactivation is present in animal models of metabolic disease and in prediabetes patients. Additionally, resection of the CB-sensitive nerve, the carotid sinus nerve (CSN), or CB ablation in animals prevents and reverses diet-induced insulin resistance and glucose intolerance as well as sympathoadrenal overactivity, meaning that the beneficial effects of decreasing CB activity on glucose homeostasis are modulated by target-related efferent sympathetic nerves, through a reflex initiated in the CBs. In agreement with our pre-clinical data, hyperbaric oxygen therapy, which reduces CB activity, improves glucose homeostasis in type 2 diabetes patients. Insulin, leptin, and pro-inflammatory cytokines activate the CB. In this manuscript, we review in a concise manner the putative pathways linking CB chemoreceptor deregulation with the pathogenesis of metabolic diseases and discuss and present new data that highlight the roles of hyperinsulinemia, hyperleptinemia, and chronic inflammation as major factors contributing to CB dysfunction in metabolic disorders.

Chronic intermittent hypoxia vs chronic continuous hypoxia: Effects on vascular endothelial function and myocardial contractility

BACKGROUND AND AIM

Both chronic intermittent hypoxia (CIH) and chronic continuous hypoxia (CCH) are risk factors for cardiovascular disease, which are associated with cardiac systolic function and associated with dysfunction of endothelia and coagulation-fibrinolysis system in the vasculature. However, the different effects of these two hypoxic models are not fully understood. In our study, we systemically compared the effects of CIH and CCH on cardiac function and related factor levels in serum using rat model.

METHODS

Forty-five male Sprague-Dawley rats were randomly divided into the normoxia control (NC), CIH and CCH groups. The rat CIH and CCH models were established, then the blood and tissue samples were collected to analyze the function of endothelium and the coagulation-fibrinolysis system. Also, the ultrasound cardiogram was performed to directly assess myocardial contractility.

RESULTS

Both CIH and CCH significantly decreased the NO, eNOS, P-eNOS and AT-III levels in the rat serum but significantly increased the levels of ET-1, vWF, COX-2, NF-κB, FIB, FVIII and PAI-1 in the rat serum (P < 0.05). The expression of ET-1, VWF and ICAM-1 in CIH group were higher than CCH group (P < 0.05), however, the expression of CD62p was increased in CCH group but not in CIH group. The expression of t-PA in CIH group were lower than CCH group (P < 0.05), but there were no significant differences in CCH group and NC group (P > 0.05). Using transmission electron microscope, we found that the mitochondrial ultrastructure of thoracic aorta endothelial cells in CIH and CCH group were damaged. Moreover, the myocardial contractility in CIH and CCH group were significantly decreased compared with NC group.

CONCLUSION

Our results suggested that CIH and CCH could cause endothelial dysfunction, dysfunction of the coagulation-fibrinolysis system and decreasing of myocardial contractility. Compared with CCH, CIH has greater effect on vasoconstriction and adhesion of vascular endothelial cells, and stronger procoagulant effect.

The impact of damage-associated molecular patterns on the neurotransmitter release and gene expression in the ex vivo rat carotid body

NEW FINDINGS

What is the central question of this study? Are carotid bodies (CBs) modulated by the damage-associated molecular patterns (DAMPs) and humoral factors of aseptic tissue injury? What are the main findings and their importance? DAMPs (HMGB1, S100 A8/A9) and blood plasma from rats subjected to tibia surgery, a model of aseptic injury, stimulate the release of neurotransmitters (ATP, dopamine) and TNF-α from ex vivo rat CBs. All-thiol HMGB1 mediates upregulation of immune-related biological pathways. These data suggest regulation of CB function by endogenous mediators of innate immunity.

ABSTRACT

The glomus cells of carotid bodies (CBs) are the primary sensors of arterial partial O₂ and CO₂ tensions and moreover serve as multimodal receptors responding also to other stimuli, such as pathogen-associated molecular patterns (PAMPs) produced by acute infection. Modulation of CB function by excessive amounts of these immunomodulators is suggested to be associated with a detrimental hyperinflammatory state. We have hypothesized that yet another class of immunomodulators, endogenous danger-associated molecular patterns (DAMPs), released upon aseptic tissue injury and recognized by the same pathogen recognition receptors as PAMPs, might modulate the CB activity in a fashion similar to PAMPs. We have tested this hypothesis by exposing rat CBs to various DAMPs, such as HMGB1 (all-thiol and disulfide forms) and S100 A8/A9 in a series of ex vivo experiments that demonstrated the release of dopamine and ATP, neurotransmitters known to mediate CB homeostatic responses. We observed a similar response after incubating CBs with conditioned blood plasma obtained from the rats subjected to tibia surgery, a model of aseptic injury. In addition, we have investigated global gene expression in the rat CB using an RNA sequencing approach. Differential gene expression analysis showed all-thiol HMGB1-driven upregulation of a number of prominent pro-inflammatory markers including Il1α and Il1β. Interestingly, conditioned plasma had a more profound effect on the CB transcriptome resulting in inhibition rather than activation of the immune-related pathways. These data are the first to suggest potential modulation of CB function by endogenous mediators of innate immunity.

Galectin-3 modulates postnatal subventricular zone gliogenesis

Postnatal subventricular zone (SVZ) neural stem cells generate forebrain glia, namely astrocytes and oligodendrocytes. The cues necessary for this process are unclear, despite this phase of brain development being pivotal in forebrain gliogenesis. Galectin‐3 (Gal‐3) is increased in multiple brain pathologies and thereby regulates astrocyte proliferation and inflammation in injury. To study the function of Gal‐3 in inflammation and gliogenesis, we carried out functional studies in mouse. We overexpressed Gal‐3 with electroporation and using immunohistochemistry surprisingly found no inflammation in the healthy postnatal SVZ. This allowed investigation of inflammation‐independent effects of Gal‐3 on gliogenesis. Loss of Gal‐3 function via knockdown or conditional knockout reduced gliogenesis, whereas Gal‐3 overexpression increased it. Gal‐3 overexpression also increased the percentage of striatal astrocytes generated by the SVZ but decreased the percentage of oligodendrocytes. These novel findings were further elaborated with multiple analyses demonstrating that Gal‐3 binds to the bone morphogenetic protein receptor one alpha (BMPR1α) and increases bone morphogenetic protein (BMP) signaling. Conditional knockout of BMPR1α abolished the effect of Gal‐3 overexpression on gliogenesis. Gain‐of‐function of Gal‐3 is relevant in pathological conditions involving the human forebrain, which is particularly vulnerable to hypoxia/ischemia during perinatal gliogenesis. Hypoxic/ischemic injury induces astrogliosis, inflammation and cell death. We show that Gal‐3 immunoreactivity was increased in the perinatal human SVZ and striatum after hypoxia/ischemia. Our findings thus show a novel inflammation‐independent function for Gal‐3; it is necessary for gliogenesis and when increased in expression can induce astrogenesis via BMP signaling.

Upregulating Nrf2 in the RVLM ameliorates sympatho-excitation in mice with chronic heart failure

Nuclear factor E2-related factor 2 (Nrf2) is a key transcription factor that maintains redox homeostasis by governing a broad array of antioxidant genes in response to oxidant stress. We hypothesized that overexpression of Nrf2 in the rostral ventrolateral medulla (RVLM) ameliorates sympatho-excitation in mice with coronary artery ligation-induced chronic heart failure (CHF). To address this, we overexpressed Nrf2 in the RVLM using an HIV-CamKIIa-Nrf2 lenti virus in C57BL/6 mice. In addition, we used a Lenti-Cre virus in Keap1^flox/flox mice to upregulate Nrf2 non-selectively in the RVLM. Arterial blood pressure (AP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were recorded under conscious and anesthetized conditions, respectively. Protein expression was assayed using western blotting and immunofluorescence staining. We found that (1) Nrf2 and two target proteins, NQO1 and HO-1 in the RVLM were significantly lower in CHF compared to Sham mice. Nrf2 viral transfection of the RVLM upregulated Nrf2 protein. (2) Urinary NE excretion in CHF mice was markedly attenuated following Nrf2 upregulation (812 ± 133 vs 1120 ± 271 ng/24hr mean. ±SE, *p < 0.05, n = 8/group). (3) In the conscious state, CHF mice overexpressing Nrf2 exhibited an enhancement in spontaneous baroreflex gain and in phenylephrine-induced baroreflex control of HR. (4) Acute experiments under anesthetisa revealed a significant decrease in basal RSNA (44.0 ± 6.5 vs 64.7 ± 8.3% of Max. *P < 0.05 n = 8/group) and enhancement in baroreflex sensitivity (Maximal gain -1.8 ± 0.3 vs 1.1 ± 0.2 of mmHg. **p < 0.01. n = 6/group) in CHF mice that were virally transfected with Nrf2 compared with CHF mice transfected with Lenti-GFP. Finally, Lenti-Cre viral overexpression of Nrf2 in Keap1^flox/flox mice reduced Keap1 protein and increased Nrf2, NQO1, and HO-1 in the RVLM of Sham and CHF mice. CHF-Cre mice exhibited a significant decrease in baseline RSNA and plasma NE concentration (8.9 ± 1.1 vs 12.7 ± 0.9 ng/mL *P < 0.05 n = 6/group) as compared with CHF-GFP mice. Based on the above data, we conclude that upregulating Nrf2 selectively in the RVLM attenuates sympatho-excitation in CHF mice. Nrf2 may be an important central target for autonomic modulation in cardiovascular disease and during stress.

Placental oxygen transfer reduces hypoxia-reoxygenation swings in fetal blood in a sheep model of gestational sleep apnea

Obstructive sleep apnea (OSA), characterized by events of hypoxia-reoxygenation, is highly prevalent in pregnancy, negatively affecting the gestation process and particularly the fetus. Whether the consequences of OSA for the fetus and offspring are mainly caused by systemic alterations in the mother or by a direct effect of intermittent hypoxia in the fetus is unknown. In fact, how apnea-induced hypoxemic swings in OSA are transmitted across the placenta remains to be investigated. The aim of this study was to test the hypothesis, based on a theoretical background on the damping effect of oxygen transfer in the placenta, that oxygen partial pressure (Po₂) swings resulting from obstructive apneas mimicking OSA are mitigated in the fetal circulation. To this end, four anesthetized ewes close to term pregnancy were subjected to obstructive apneas consisting of 25-s airway obstructions. Real-time Po₂ was measured in the maternal carotid artery and in the umbilical vein with fast-response fiber-optic oxygen sensors. The amplitudes of Po₂ swings in the umbilical vein were considerably smaller [3.1 ± 1.0 vs. 21.0 ± 6.1 mmHg (mean ± SE); P < 0.05]. Corresponding estimated swings in fetal and maternal oxyhemoglobin saturation tracked Po₂ swings. This study provides novel insights into fetal oxygenation in a model of gestational OSA and highlights the importance of further understanding the impact of sleep-disordered breathing on fetal and offspring development.NEW & NOTEWORTHY This study in an airway obstruction sheep model of gestational sleep apnea provides novel data on how swings in oxygen partial pressure (Po₂) translate from maternal to fetal blood. Real-time simultaneous measurement of Po₂ in maternal artery and in umbilical vein shows that placenta transfer attenuates the magnitude of oxygenation swings. These data prompt further investigation of the extent to which maternal apneas could induce similar direct oxidative stress in fetal and maternal tissues.

Is Aberrant Reno-Renal Reflex Control of Blood Pressure a Contributor to Chronic Intermittent Hypoxia-Induced Hypertension?

Renal sensory nerves are important in the regulation of body fluid and electrolyte homeostasis, and blood pressure. Activation of renal mechanoreceptor afferents triggers a negative feedback reno-renal reflex that leads to the inhibition of sympathetic nervous outflow. Conversely, activation of renal chemoreceptor afferents elicits reflex sympathoexcitation. Dysregulation of reno-renal reflexes by suppression of the inhibitory reflex and/or activation of the excitatory reflex impairs blood pressure control, predisposing to hypertension. Obstructive sleep apnoea syndrome (OSAS) is causally related to hypertension. Renal denervation in patients with OSAS or in experimental models of chronic intermittent hypoxia (CIH), a cardinal feature of OSAS due to recurrent apnoeas (pauses in breathing), results in a decrease in circulating norepinephrine levels and attenuation of hypertension. The mechanism of the beneficial effect of renal denervation on blood pressure control in models of CIH and OSAS is not fully understood, since renal denervation interrupts renal afferent signaling to the brain and sympathetic efferent signals to the kidneys. Herein, we consider the currently proposed mechanisms involved in the development of hypertension in CIH disease models with a focus on oxidative and inflammatory mediators in the kidneys and their potential influence on renal afferent control of blood pressure, with wider consideration of the evidence available from a variety of hypertension models. We draw focus to the potential contribution of aberrant renal afferent signaling in the development, maintenance and progression of high blood pressure, which may have relevance to CIH-induced hypertension.

How does homeostasis happen? Integrative physiological, systems biological, and evolutionary perspectives

Homeostasis is a founding principle of integrative physiology. In current systems biology, however, homeostasis seems almost invisible. Is homeostasis a key goal driving body processes, or is it an emergent mechanistic fact? In this perspective piece, I propose that the integrative physiological and systems biological viewpoints about homeostasis reflect different epistemologies, different philosophies of knowledge. Integrative physiology is concept driven. It attempts to explain biological phenomena by continuous formation of theories that experimentation or observation can test. In integrative physiology, "function" refers to goals or purposes. Systems biology is data driven. It explains biological phenomena in terms of "omics"-i.e., genomics, gene expression, epigenomics, proteomics, and metabolomics-it depicts the data in computer models of complex cascades or networks, and it makes predictions from the models. In systems biology, "function" refers more to mechanisms than to goals. The integrative physiologist emphasizes homeostasis of internal variables such as Pco₂ and blood pressure. The systems biologist views these emphases as teleological and unparsimonious in that the "regulated variable" (e.g., arterial Pco₂ and blood pressure) and the "regulator" (e.g., the "carbistat" and "barostat") are unobservable constructs. The integrative physiologist views systems biological explanations as not really explanations but descriptions that cannot account for phenomena we humans believe exist, although they cannot be observed directly, such as feelings and, ultimately, the conscious mind. This essay reviews the history of the two epistemologies, emphasizing autonomic neuroscience. I predict rapprochement of integrative physiology with systems biology. The resolution will avoid teleological purposiveness, transcend pure mechanism, and incorporate adaptiveness in evolution, i.e., "Darwinian medicine."