The emerging role of AMPK in the regulation of breathing and oxygen supply

SubSol-HIe is an AMPK-dependent hypoxia-responsive subnucleus of the nucleus tractus solitarius that coordinates the hypoxic ventilatory response and protects against apnoea in mice

Functional magnetic resonance imaging (fMRI) suggests that the hypoxic ventilatory response is facilitated by the AMP-activated protein kinase (AMPK), not at the carotid bodies, but within a subnucleus (Bregma -7.5 to -7.1 mm) of the nucleus tractus solitarius that exhibits right-sided bilateral asymmetry. Here, we map this subnucleus using cFos expression as a surrogate for neuronal activation and mice in which the genes encoding the AMPK-α1 (Prkaa1) and AMPK-α2 (Prkaa2) catalytic subunits were deleted in catecholaminergic cells by Cre expression via the tyrosine hydroxylase promoter. Comparative analysis of brainstem sections, relative to controls, revealed that AMPK-α1/α2 deletion inhibited, with right-sided bilateral asymmetry, cFos expression in and thus activation of a neuronal cluster that partially spanned three interconnected anatomical nuclei adjacent to the area postrema: SolDL (Bregma -7.44 mm to -7.48 mm), SolDM (Bregma -7.44 mm to -7.48 mm) and SubP (Bregma -7.48 mm to -7.56 mm). This approximates the volume identified by fMRI. Moreover, these nuclei are known to be in receipt of carotid body afferent inputs, and catecholaminergic neurons of SubP and SolDL innervate aspects of the ventrolateral medulla responsible for respiratory rhythmogenesis. Accordingly, AMPK-α1/α2 deletion attenuated hypoxia-evoked increases in minute ventilation (normalised to metabolism), reductions in expiration time, and increases sigh frequency, but increased apnoea frequency during hypoxia. The metabolic response to hypoxia in AMPK-α1/α2 knockout mice and the brainstem and spinal cord catecholamine levels were equivalent to controls. We conclude that within the brainstem an AMPK-dependent, hypoxia-responsive subnucleus partially spans SubP, SolDM and SolDL, namely SubSol-HIe, and is critical to coordination of active expiration, the hypoxic ventilatory response and defence against apnoea.

Intelligent alert system for predicting invasive mechanical ventilation needs via noninvasive parameters: employing an integrated machine learning method with integration of multicenter databases

The use of invasive mechanical ventilation (IMV) is crucial in rescuing patients with respiratory dysfunction. Accurately predicting the demand for IMV is vital for clinical decision-making. However, current techniques are invasive and challenging to implement in pre-hospital and emergency rescue settings. To address this issue, a real-time prediction method utilizing only non-invasive parameters was developed to forecast IMV demand in this study. The model introduced the concept of real-time warning and leveraged the advantages of machine learning and integrated methods, achieving an AUC value of 0.935 (95% CI 0.933-0.937). The AUC value for the multi-center validation using the AmsterdamUMCdb database was 0.727, surpassing the performance of traditional risk adjustment algorithms (OSI(oxygenation saturation index): 0.608, P/F(oxygenation index): 0.558). Feature weight analysis demonstrated that BMI, Gcsverbal, and age significantly contributed to the model's decision-making. These findings highlight the substantial potential of a machine learning real-time dynamic warning model that solely relies on non-invasive parameters to predict IMV demand. Such a model can provide technical support for predicting the need for IMV in pre-hospital and disaster scenarios.

Anti-adipogenic action of a novel oxazole derivative through activation of AMPK pathway

Obesity is a chronic disorder with multifactorial etiology, including genetic, medical, dietary and other environmental factors. Both natural and synthetic heterocyclic compounds, especially oxazoles, represent an interesting group of compounds and have gained much attention due to their remarkable biological activities. Therefore, a library of 3,3-DMAH (3,3-dimethylallylhalfordinol) inspired N-alkylated oxazole bromide salts with varied substitutions were prepared and screened using the 3T3-L1 model of adipogenesis and HFD-induced obesity model in Syrian golden hamsters. Several compounds in the synthesized series displayed remarkable anti-adipogenic potential on the differentiation of 3T3-L1 preadipocytes. Compound 19e, displayed the most potent activity of all and selected for further studies. Compound 19e inhibited mitotic clonal expansion of 3T3-L1 cells and enhanced the mitochondrial oxygen consumption rate of the cells during early phase of differentiation via AMPK activation. 19e also improved the dyslipidaemia in high calorie diet fed Syrian Golden Hamsters. Therefore, compound 19e can serve as a potential lead against adipogenesis and dyslipidaemia models and could be further investigated to affirm its significance as a drug candidate.

AMPK facilitates the hypoxic ventilatory response through non-adrenergic mechanisms at the brainstem

We recently demonstrated that the hypoxic ventilatory response (HVR) is facilitated by the AMP-activated protein kinase (AMPK) in catecholaminergic neural networks that likely lie downstream of the carotid bodies within the caudal brainstem. Here, we further subcategorise the neurons involved, by cross-comparison of mice in which the genes encoding the AMPK-α1 (Prkaa1) and AMPK-α2 (Prkaa2) catalytic subunits were deleted in catecholaminergic (TH-Cre) or adrenergic (PNMT-Cre) neurons. As expected, the HVR was markedly attenuated in mice with AMPK-α1/α2 deletion in catecholaminergic neurons, but surprisingly was modestly augmented in mice with AMPK-α1/α2 deletion in adrenergic neurons when compared against a variety of controls (TH-Cre, PNMT-Cre, AMPK-α1/α2 floxed). Moreover, AMPK-α1/α2 deletion in catecholaminergic neurons precipitated marked hypoventilation and apnoea during poikilocapnic hypoxia, relative to controls, while mice with AMPK-α1/α2 deletion in adrenergic neurons entered relative hyperventilation with reduced apnoea frequency and duration. We conclude, therefore, that AMPK-dependent modulation of non-adrenergic networks may facilitate increases in ventilatory drive that shape the classical HVR, whereas AMPK-dependent modulation of adrenergic networks may provide some form of negative feedback or inhibitory input to moderate HVR, which could, for example, protect against hyperventilation-induced hypocapnia and respiratory alkalosis.

Flaxseed Polysaccharide Alters Colonic Gene Expression of Lipid Metabolism and Energy Metabolism in Obese Rats

Obesity is one of the most serious public health challenges. Recently, we found that flaxseed polysaccharides (FPs) had an anti-obesity effect through promoting lipid metabolism, but the obesity-inhibiting pathway of FP is still unclear. In this study, after FP intervention in an obese rat model, a transcriptome study was performed to further investigate how FP intervention alters the gene expression of colonic epithelial tissues (CETs). The results showed that there were 3785 genes differentially expressed due to the FP intervention, namely 374 downregulated and 3411 upregulated genes. After analyzing all the differentially expressed genes, two classical KEGG pathways were found to be related to obesity, namely the PPAR-signaling pathway and energy metabolism, involving genes Fabp1–5, Lpl, Gyk, Qqp7, Pparg, Rxrg, Acsl1, Acsl4, Acsl6, Cpt1c, Car1–4, Ca5b, Car8, Car12–14, Cps1, Ndufa4l2, Cox6b2, Atp6v1g2, Ndufa4l2 and Cox4i2. QRT-PCR results showed a consistent expression trend. Our results indicate that FP promotes lipid metabolism by changing the expression of some key genes of CETs, thus inhibiting obesity.

Chemoreflex Control as the Cornerstone in Immersion Water Sports: Possible Role on Breath-Hold

Immersion water sports involve long-term apneas; therefore, athletes must physiologically adapt to maintain muscle oxygenation, despite not performing pulmonary ventilation. Breath-holding (i.e., apnea) is common in water sports, and it involves a decrease and increases PaO₂ and PaCO₂, respectively, as the primary signals that trigger the end of apnea. The principal physiological O₂ sensors are the carotid bodies, which are able to detect arterial gases and metabolic alterations before reaching the brain, which aids in adjusting the cardiorespiratory system. Moreover, the principal H⁺/CO₂ sensor is the retrotrapezoid nucleus, which is located at the brainstem level; this mechanism contributes to detecting respiratory and metabolic acidosis. Although these sensors have been characterized in pathophysiological states, current evidence shows a possible role for these mechanisms as physiological sensors during voluntary apnea. Divers and swimmer athletes have been found to displayed longer apnea times than land sports athletes, as well as decreased peripheral O₂ and central CO₂ chemoreflex control. However, although chemosensitivity at rest could be decreased, we recently found marked sympathoexcitation during maximum voluntary apnea in young swimmers, which could activate the spleen (which is a reservoir organ for oxygenated blood). Therefore, it is possible that the chemoreflex, autonomic function, and storage/delivery oxygen organ(s) are linked to apnea in immersion water sports. In this review, we summarized the available evidence related to chemoreflex control in immersion water sports. Subsequently, we propose a possible physiological mechanistic model that could contribute to providing new avenues for understanding the respiratory physiology of water sports.

Gene panel diagnostics reveals new pathogenic variants in pulmonary arterial hypertension

Background

A genetic predisposition can lead to the rare disease pulmonary arterial hypertension (PAH). Most mutations have been identified in the gene BMPR2 in heritable PAH. However, as of today 15 further PAH genes have been described. The exact prevalence across these genes particularly in other PAH forms remains uncertain. We present the distribution of mutations across PAH genes identified at the largest German referral centre for genetic diagnostics in PAH over a course of > 3 years.

Methods

Our PAH-specific gene diagnostics panel was used to sequence 325 consecutive PAH patients from March 2017 to October 2020. For the first year the panel contained thirteen PAH genes: ACVRL1, BMPR1B, BMPR2, CAV1, EIF2AK4, ENG, GDF2, KCNA5, KCNK3, KLF2, SMAD4, SMAD9 and TBX4.These were extended by the three genes ATP13A3, AQP1 and SOX17 from March 2018 onwards following the genes’ discovery.

Results

A total of 79 mutations were identified in 74 patients (23%). Of the variants 51 (65%) were located in the gene BMPR2 while the other 28 variants were found in ten further PAH genes. We identified disease-causing variants in the genes AQP1, KCNK3 and SOX17 in families with at least two PAH patients. Mutations were not only detected in patients with heritable and idiopathic but also with associated PAH.

Conclusions

Genetic defects were identified in 23% of the patients in a total of 11 PAH genes. This illustrates the benefit of the specific gene panel containing all known PAH genes.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-01987-x.

Novel oxygen sensing mechanism in the spinal cord involved in cardiorespiratory responses to hypoxia

As blood oxygenation decreases (hypoxemia), mammals mount cardiorespiratory responses, increasing oxygen to vital organs. The carotid bodies are the primary oxygen chemoreceptors for breathing, but sympathetic-mediated cardiovascular responses to hypoxia persist in their absence, suggesting additional high-fidelity oxygen sensors. We show that spinal thoracic sympathetic preganglionic neurons are excited by hypoxia and silenced by hyperoxia, independent of surrounding astrocytes. These spinal oxygen sensors (SOS) enhance sympatho-respiratory activity induced by CNS asphyxia-like stimuli, suggesting they bestow a life-or-death advantage. Our data suggest the SOS use a mechanism involving neuronal nitric oxide synthase 1 (NOS1) and nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX). We propose NOS1 serves as an oxygen-dependent sink for NADPH in hyperoxia. In hypoxia, NADPH catabolism by NOS1 decreases, increasing availability of NADPH to NOX and launching reactive oxygen species-dependent processes, including transient receptor potential channel activation. Equipped with this mechanism, SOS are likely broadly important for physiological regulation in chronic disease, spinal cord injury, and cardiorespiratory crisis.

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

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

Effect of exercise on sleep and cardiopulmonary parameters in patients with pulmonary artery hypertension

BACKGROUND

Pulmonary arterial hypertension (PAH) is considered to be a rare progressive disease resulting from restricted flow through the pulmonary arterial circulation resulting ultimately in right-sided heart failure. Most patients with PAH suffer from sleep disorders, reduced aerobic fitness, and mortality risk despite optimized medical treatment. This study investigated the effect of 12 weeks of aerobic training on sleep quality, sleep efficiency, right ventricular systolic pressure (RVSP), and aerobic fitness in patients with PAH.

METHODS

Thirty patients with PAH were randomized to two equal groups, training group (A) and control group (B). The Pittsburg sleep quality index (PSQI) questionnaire and a wrist-worn actigraph were used for the assessment of sleep quality and sleep efficiency respectively. RVSP was measured using echocardiography. Cardiopulmonary exercise testing (CPET) assessed maximal heart rate and VO2max. All were measured before and after the study period for both groups. Exercise training was conducted on a bicycle ergometer as an individually-tailored moderate-intensity aerobic training session (60 to 70% of the maximal heart rate reached during the initial exercise test) for 30 to 45 min/day, 3 sessions/week for 12 weeks (36 sessions).

RESULTS

Sleep scores and RVSP showed significant reductions and VO2max-representing the aerobic fitness-showed a significant increase in the group (A) compared with group (B).

CONCLUSION

These results suggest that aerobic training has a positive effect on three risk factors for mortality in patients with PAH, namely sleep quality, decline in exercise capacity, and right ventricular remodeling.

CLINICAL TRIALS REGISTRATION

Clinical trial registered in ClinicalTrials.gov , ID: NCT04337671.

AMPK and the Need to Breathe and Feed: What's the Matter with Oxygen?

We live and to do so we must breathe and eat, so are we a combination of what we eat and breathe? Here, we will consider this question, and the role in this respect of the AMP-activated protein kinase (AMPK). Emerging evidence suggests that AMPK facilitates central and peripheral reflexes that coordinate breathing and oxygen supply, and contributes to the central regulation of feeding and food choice. We propose, therefore, that oxygen supply to the body is aligned with not only the quantity we eat, but also nutrient-based diet selection, and that the cell-specific expression pattern of AMPK subunit isoforms is critical to appropriate system alignment in this respect. Currently available information on how oxygen supply may be aligned with feeding and food choice, or vice versa, through our motivation to breathe and select particular nutrients is sparse, fragmented and lacks any integrated understanding. By addressing this, we aim to provide the foundations for a clinical perspective that reveals untapped potential, by highlighting how aberrant cell-specific changes in the expression of AMPK subunit isoforms could give rise, in part, to known associations between metabolic disease, such as obesity and type 2 diabetes, sleep-disordered breathing, pulmonary hypertension and acute respiratory distress syndrome.

Metformin accelerates myelin recovery and ameliorates behavioral deficits in the animal model of multiple sclerosis via adjustment of AMPK/Nrf2/mTOR signaling and maintenance of endogenous oligodendrogenesis during brain self-repairing period

BACKGROUND

Multiple sclerosis (MS) is a devastating autoimmune disorder characterized by oligodendrocytes (OLGs) loss and demyelination. In this study, we have examined the effects of metformin (MET) on the oligodendrogenesis, redox signaling, apoptosis, and glial responses during a self-repairing period (1-week) in the animal model of MS.

METHODS

For induction of demyelination, C57BL/6 J mice were fed a 0.2% cuprizone (CPZ) for 5 weeks. Thereafter, CPZ was removed for 1-week and molecular and behavioral changes were monitored in the presence or absence of MET (50 mg/kg body weight/day).

RESULTS

MET remarkably increased the localization of precursor OLGs (NG2⁺/O4⁺ cells) and subsequently the renewal of mature OLGs (MOG⁺ cells) in the corpus callosum via AMPK/mammalian target of rapamycin (mTOR) pathway. Moreover, we observed a significant elevation in the antioxidant responses, especially in mature OLGs (MOG⁺/nuclear factor erythroid 2-related factor 2 (Nrf2⁺) cells) after MET intervention. MET also reduced brain apoptosis markers and lessened motor dysfunction in the open-field test. While MET was unable to decrease active astrogliosis (GFAP mRNA), it reduced microgliosis by down-regulation of Mac-3 mRNA a marker of pro-inflammatory microglia/macrophages. Molecular modeling studies, likewise, confirmed that MET exerts its effects via direct interaction with AMPK.

CONCLUSIONS

Altogether, our study reveals that MET effectively induces lesion reduction and elevated molecular processes that support myelin recovery via direct activation of AMPK and indirect regulation of AMPK/Nrf2/mTOR pathway in OLGs. These findings facilitate the development of new therapeutic strategies based on AMPK activation for MS in the near future.

The impact of preterm adversity on cardiorespiratory function

NEW FINDINGS

What is the topic of this review? We review the influence of prematurity on the cardiorespiratory system and examine the common sequel of alterations in oxygen tension, and immune activation in preterm infants. What advances does it highlight? The review highlights neonatal animal models of intermittent hypoxia, hyperoxia and infection that contribute to our understanding of the effect of stress on neurodevelopment and cardiorespiratory homeostasis. We also focus on some of the important physiological pathways that have a modulatory role on the cardiorespiratory system in early life.

ABSTRACT

Preterm birth is one of the leading causes of neonatal mortality. Babies that survive early-life stress associated with immaturity have significant prevailing short- and long-term morbidities. Oxygen dysregulation in the first few days and weeks after birth is a primary concern as the cardiorespiratory system slowly adjusts to extrauterine life. Infants exposed to rapid alterations in oxygen tension, including exposures to hypoxia and hyperoxia, have altered redox balance and active immune signalling, leading to altered stress responses that impinge on neurodevelopment and cardiorespiratory homeostasis. In this review, we explore the clinical challenges posed by preterm birth, followed by an examination of the literature on animal models of oxygen dysregulation and immune activation in the context of early-life stress.

Acute oxygen sensing by the carotid body: a rattlebag of molecular mechanisms

The molecular underpinnings of the oxygen sensitivity of the carotid body Type I cells are becoming better defined as research begins to identify potential interactions between previously separate theories. Nevertheless, the field of oxygen chemoreception still presents the general observer with a bewildering array of potential signalling pathways by which a fall in oxygen levels might initiate Type I cell activation. The purpose of this brief review is to address five of the current oxygen sensing hypotheses: the lactate-Olfr 78 hypothesis of oxygen chemotransduction; the role mitochondrial ATP and metabolism may have in chemotransduction; the AMP-activated protein kinase hypothesis and its current role in oxygen sensing by the carotid body; reactive oxygen species as key transducers in the oxygen sensing cascade; and the mechanisms by which H2 S, reactive oxygen species and haem oxygenase may integrate to provide a rapid oxygen sensing transduction system. Over the previous 15 years several lines of research into acute hypoxic chemotransduction mechanisms have focused on the integration of mitochondrial and membrane signalling. This review places an emphasis on the subplasmalemmal-mitochondrial microenvironment in Type I cells and how theories of acute oxygen sensing are increasingly dependent on functional interaction within this microenvironment.

Nimodipine represses AMPK phosphorylation and excessive autophagy after chronic cerebral hypoperfusion in rats

Chronic cerebral hypofusion (CCH) after bilateral carotid artery occlusion (2VO) causes cognitive damage and neuronal degeneration in the cortex and hippocampal CA1 area, and influences the oxygen and glucose supply in the brain which often results in metabolic alterations and oxidative stress. AMP-activated protein kinase (AMPK) phosphorylation, a sensor of cellular energy status, directs metabolic adaptation to support cellular growth and survival after CCH. Autophagy is also likely to be involved in metabolic adaptation and plays an important role in neuronal deterioration and cognitive decline after CCH. Nimodipine, an L-type calcium channel antagonist, has been reported to exert neuroprotective effects. However, the potential role of nimodipine in autophagy and the energy sensing AMPK signal is not well understood. In addition, little is known about the relationship between autophagy and AMPK signal. Here, we designed a way to evaluate these issues. Adult male Wistar rats were subjected to 2VO and randomly divided into three groups: the Vehicle (2VO), Nimodipine (2VO + nimodipine 10 mg/kg) groups. A third group served as sham controls. Each group was investigated at 2 and 4 weeks post gavage and tested using the Morris water maze. The activities of LC3B and AMPK signal were examined using immunohistochemistry and western blotting. Nimodipine significantly alleviated spatial learning and memory impairments and the number of lesion neurons. At 2 weeks of durg administration, these drug effects, suppressing AMPK activation and excessive autophagy, were more pronounced at the cortex than at hippocampal CA1 area. The effects of nimodipine were significant in the hippocampal CA1 area after 4 weeks of administration. Furthermore, nimodipine inhibited expression of eIF2α/ATF4 signaling related to energy deficit stress in 2VO rats. These results suggest that excessive autophagy has promoted neuronal and tissue injury after 2VO in rats. Nimodipine protected the brain from CCH by inhibiting the autophagy activity. The p-AMPK and eIF2α/ATF4 pathway is likely part of an integrated pro-autophagy signaling network after CCH.

The emerging role of AMP-activated protein kinase in cholestatic liver diseases

AMP-activated protein kinase (AMPK), recognized as an energy sensor with three heterotrimeric subunits (α, β and γ), not only maintains basal intracellular adenosine triphosphate levels but also regulates energy-intensive pathological responses, such as neurodegenerative and metabolic diseases, through multiple signaling pathways. Recent studies open a new direction for AMPK research and demonstrate that AMPK is a critical player in the pathogenesis of cholestatic liver injury and plays paradoxical roles in the regulation of different pathological processes, including the disruption of bile acid homeostasis and the regulation of hepatic polarity, inflammation and fibrosis. In the present review, we summarize recent findings that implicate AMPK-mediated signaling pathways in the pathogenesis of cholestatic liver injury. These findings provide novel insight regarding the potential use of AMPK as a therapeutic target for the treatment of cholestatic liver injury.

A paradigm shift in oxygen sensing with a twist in the tale!

AMP-activated protein kinase (AMPK) is pivotal to metabolic homoeostasis in eukaryotes, serving as a critical energy sensor. Increased AMPK activity during oxygen deprivation (hypoxia) protects against potentially catastrophic deficits in ATP supply. Although the nervous system circuitry for elaboration of the complex cardiorespiratory response to hypoxia has been understood in some detail for many decades, there is continued and considerable interest in the molecular machinery underpinning the mechanism(s) of oxygen sensing. In this issue of the Biochemical Journal, Evans et al. [(2016) Biochem. J.] review their recent work, which points to a pivotal role for AMPK in the transduction of cellular hypoxic stress to integrated ventilatory behaviour, critical in the defence of whole-body oxygen homoeostasis. Of great surprise, there is profound blunting of the hyperventilatory response to hypoxic stress in AMPK deficient mice, with resultant dysregulated breathing arising in spite of normal peripheral oxygen sensing and appropriate sensory input to the brain! Their pointedly provocative review challenges current dogma, and in doing so raises intriguing questions that probe fundamental aspects of our understanding of the mammalian ventilatory response to hypoxic stress. The engaging review by Evans et al. [(2016) Biochem. J.] is an interesting read that is sure to encourage colourful debate.