Search

Intermittent hypoxia induces oxidative stress and alters hepatic metabolism, likely underlying the association of sleep apnea with non-alcoholic fatty liver disease. In male patients with sleep apnea, metabolic or liver diseases, the levels of testosterone are reduced, and in patients with metabolic diseases, low levels of testosterone are associated with oxidative stress. To assess potential interactions between testosterone and IH on hepatic oxidative stress we used sham-operated or orchiectomized (ORX) mice exposed to normoxia (Nx) or IH (6% O2, 12 cycles/h, 12h/day) for 2 weeks. The activity of prooxidant (NADPH oxidase – NOX), antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase – SOD, Cat, GPx), lipid peroxidation (MDA concentration) and the total concentration of glutathione (GSH) were measured in liver. IH induced a prooxidant profile of enzyme activity (lower SOD activity and higher NOX/SOD and NOX/Cat activity ratio) without altering hepatic MDA and GSH content. Using RNA sequencing followed by a pathway enrichment analysis we identified putative hepatic genes underlying the interactions between IH and testosterone. ORX and IH altered the expression of genes involved in oxidoreductase activities, cytochromes dependent pathways, and glutathione metabolism. Among the genes upregulated in ORX-IH mice, the flavin-containing monooxygenases (FMO) are particularly relevant since these are potent hepatic antioxidant that could help prevent overt oxidative stress in ORX-IH mice.Graphical Abstract

In multiple sclerosis (MS), Th17 cells are critical drivers of autoimmune central nervous system (CNS) inflammation and demyelination. Th17 cells exhibit functional heterogeneity fostering both pathogenic and nonpathogenic, tissue-protective functions. Still, the factors that control Th17 pathogenicity remain incompletely defined. Here, using experimental autoimmune encephalomyelitis, an established mouse MS model, we report that therapeutic administration of activin-A ameliorates disease severity and alleviates CNS immunopathology and demyelination, associated with decreased activation of Th17 cells. In fact, activin-A signaling through activin-like kinase-4 receptor represses pathogenic transcriptional programs in Th17-polarized cells, while it enhances antiinflammatory gene modules. Whole-genome profiling and in vivo functional studies revealed that activation of the ATP-depleting CD39 and CD73 ectonucleotidases is essential for activin-A–induced suppression of the pathogenic signature and the encephalitogenic functions of Th17 cells. Mechanistically, the aryl hydrocarbon receptor, along with STAT3 and c-Maf, are recruited to promoter elements on Entpd1 and Nt5e (encoding CD39 and CD73, respectively) and other antiinflammatory genes, and control their expression in Th17 cells in response to activin-A. Notably, we show that activin-A negatively regulates the metabolic sensor, hypoxia-inducible factor-1α, and key inflammatory proteins linked to pathogenic Th17 cell states. Of translational relevance, we demonstrate that activin-A is induced in the CNS of individuals with MS and restrains human Th17 cell responses. These findings uncover activin-A as a critical controller of Th17 cell pathogenicity that can be targeted for the suppression of autoimmune CNS inflammation.

Sleep Apnea Syndrome (SAS) is one of the most common chronic diseases, affecting nearly one billion people worldwide. The repetitive occurrence of abnormal respiratory events generates cyclical desaturation-reoxygenation sequences known as intermittent hypoxia (IH). Among SAS metabolic sequelae, it has been established by experimental and clinical studies that SAS is an independent risk factor for the development and progression of non-alcoholic fatty liver disease (NAFLD). The principal goal of this study was to decrypt the molecular mechanisms at the onset of IH-mediated liver injury. To address this question, we used a unique mouse model of SAS exposed to IH, employed unbiased high-throughput transcriptomics and computed network analysis. This led us to examine hepatic mitochondrial ultrastructure and function using electron microscopy, high-resolution respirometry and flux analysis in isolated mitochondria. Transcriptomics and network analysis revealed that IH reprograms Nuclear Respiratory Factor- (NRF-) dependent gene expression and showed that mitochondria play a central role. We thus demonstrated that IH boosts the oxidative capacity from fatty acids of liver mitochondria. Lastly, the unbalance between oxidative stress and antioxidant defense is tied to an increase in hepatic ROS production and DNA damage during IH. We provide a comprehensive analysis of liver metabolism during IH and reveal the key role of the mitochondria at the origin of development of liver disease. These findings contribute to the understanding of the mechanisms underlying NAFLD development and progression during SAS and provide a rationale for novel therapeutic targets and biomarker discovery.

BackgroundObstructive sleep apnoea and the related intermittent hypoxia (IH) are widely recognised as risk factors for incident cardiovascular diseases. Numerous studies support the deleterious vascular impact of IH in rodents but an overall interpretation is challenging owing to heterogeneity in rodent species investigated and the severity and duration of IH exposure. To clarify this major issue, we conducted a systematic review and meta-analysis to quantify the impact of IH on systemic artery structure and function depending on the different IH exposure designs.MethodsWe searched PubMed, Embase and Web of Science, and included 125 articles in a meta-analysis, among them 112 using wild-type rodents and 13 using apolipoprotein E knockout (ApoE−/−) mice. We used the standardised mean difference (SMD) to compare results between studies.ResultsIH significantly increased mean arterial pressure (+13.90 (95% CI 11.88–15.92) mmHg), and systolic and diastolic blood pressure. Meta-regressions showed that mean arterial pressure change was associated with strain and year of publication. IH altered vasodilation in males but not in females and increased endothelin-1-induced but not phenylephrine-induced vasoconstriction. Intima–media thickness significantly increased upon IH exposure (SMD 1.10 (95% CI 0.58–1.62); absolute values +5.23 (2.81–7.84) µm). This increase was observed in mice but not in rats and was negatively associated with age. Finally, IH increased atherosclerotic plaque size in ApoE−/− mice (SMD 1.08 (95% CI 0.80–1.37)).ConclusionsOur meta-analysis established that IH, independently of other confounders, has a strong effect on vascular structure and physiology. Our findings support the interest of identifying and treating sleep apnoea in routine cardiology practice.

Background Intermittent hypoxia (IH) is the major feature of obstructive sleep apnea syndrome, well‐known to induce cardiometabolic complications. We previously demonstrated that IH induces hyperinsulinemia and associated altered insulin signaling in adipose tissue, liver, and skeletal muscle, but impact of IH on cardiac insulin signaling and functional/structural consequences remains unknown. Therefore, the aims of this study were to investigate in both lean and obese mice the effects of chronic IH on the following: (1) cardiac insulin signaling and (2) cardiac remodeling and function. Methods C57BL/6 J male mice were fed low‐fat (LFD) or high‐fat (HFD) diet for 20 weeks, and exposed to IH (21–5% FiO2, 60 s cycle, 8 h/day) or normoxia (N) for the last 6 weeks. Systemic insulin sensitivity was evaluated by an insulin tolerance test. Cardiac remodeling and contractile function were assessed by cardiac ultrasonography. Ultimately, hearts were withdrawn for biochemical and histological analysis. Results In LFD mice, IH‐induced hyperinsulinemia and systemic insulin resistance that were associated with increased phosphorylations of cardiac insulin receptor and Akt on Tyr1150 and Ser473 residues, respectively. In addition, IH significantly increased cardiac interstitial fibrosis and cardiac contractility. In the HFD group, IH did not exert any additional effect, nor on insulin/Akt signaling, nor on cardiac remodeling and function. Conclusion Our study suggests that, despite systemic insulin resistance, IH exposure mediates an adaptive cardiac response in lean but not in obese mice. Further studies are needed to investigate which specific mechanisms are involved and to determine the long‐term evolution of cardiac responses to IH., Despite systemic insulin resistance, intermittent hypoxia mediates an adaptive cardiac response in lean but not in obese mice. Further studies are needed to investigate which specific mechanisms are involved and to determine the long‐term evolution of cardiac responses to intermittent hypoxia.

BackgroundHaemorheological alterations are reported in obstructive sleep apnoea (OSA) and reversed with continuous positive airway pressure (CPAP), observations potentially explained by intermittent hypoxia (IH)-induced oxidative stress. Our objective was to investigate whether IH causes haemorheological alterations via oxidative stress.MethodsWistar rats were exposed to normoxia (n=7) or IH (n=8) for 14 days. 23 moderate-to-severe OSA patients were assessed at three time-points: baseline, after randomisation to either 2 weeks of nocturnal oxygen (n=13) or no treatment (n=10) and after 1 month of CPAP treatment (n=17). Furthermore, an OSA-free control group (n=13) was assessed at baseline and after time-matched follow-up. We measured haemorheological parameters (haematocrit, blood viscosity, plasma viscosity (rats only), erythrocyte aggregation and deformability (humans only)) and redox balance (superoxide dismutase (SOD), glutathione peroxidase, protein oxidation (advanced oxidation protein products (AOPPs)) and lipid peroxidation (malondialdehyde)). We also tested the haemorheological sensitivity of erythrocytes to reactive oxygen species (ROS) in our human participants using the oxidant t-butyl hydroperoxide (TBHP).ResultsIn rats, IH increased blood viscosity by increasing haematocrit without altering the haemorheological properties of erythrocytes. IH also reduced SOD activity and increased AOPPs. In humans, baseline haemorheological properties were similar between patients and control participants, and properties were unaltered following oxygen and CPAP, except erythrocyte deformability was reduced following oxygen therapy. Redox balance was comparable between patients and control participants. At baseline, TBHP induced a greater reduction of erythrocyte deformability in patients while CPAP reduced TBHP-induced increase in aggregation strength.ConclusionsIH and OSA per se do not cause haemorheological alterations despite the presence of oxidative stress or higher sensitivity to ROS, respectively.

Introduction Sleep apnea syndrome is characterized by intermittent hypoxia (IH), leading to an increase in blood pressure (BP), infarct size (IS), endothelial dysfunction, insulin resistance, and dyslipidemia. Insulin resistance and the metabolic syndrome associated with IH are also accompanied by an alteration in the metabolism of Arginine (Arg) [and its precursor Citrulline (Cit)]. As Arg availability directly impacts nitric oxide (NO) production, we speculate that myocardial Arg deficiency during IH may contribute to cardiovascular alterations induced by IH. Objective Knowing that Cit is a much better precursor of Arg than Arg itself, we propose to use Cit during IH to protect against IH-induced increase in BP and IS. Methods Four groups of rats (n = 8), were submitted to normoxia (N) or IH [14 days (d), 8 h per d, 30 s-O2 21%/30 s-O2 5%] and supplemented or not with Cit (1 g.kg−1.d−1). One normoxic per-feed (NPf) supplementary group was added to assess the impact of anorexia associated with IH. BW and food intake were daily measured. After 14 d, BP was measured by carotid catheterization. Hearts were perfused by the Langendorff method and submitted to global and total ischemia (30 min)-reperfusion (120 min) before measuring IS related to left ventricle area (I/V) by colorimetry and planimetry. Results Irrespective of diet, IH increases both systolic BP (141.3 ± 1.1 vs. 170.6 ± 5.5 mmHg in N and IH respectively, n = 4–8, P = 0.05) and I/V (27.2 ± 4.7% vs. 43.6 ± 4.5% in N and IH, respectively, n = 5–8, P Conclusion Under IH, Cit seems to increase the BP but decrease I/V. After completing groups, further biochemical and histological analyses will be performed to enlighten the mechanisms (NOx, NO synthase, oxidative stress…) potentially involved in the impact of Cit chronic supplementation.

International audience; Introduction: Combining exercise training with hypoxic exposure has been recently proposed as a new therapeutic strategy to improve health status of obese individuals. Whether hypoxic exercise training (HET) provides greater benefits regarding body composition and cardiometabolic parameters than normoxic exercise training (NET) remains, however, unclear. We hypothesized that HET would induce greater improvement in exercise capacity and health status than NET in overweight and obese individuals.Methods: Twenty-three subjects were randomized into 8-wk HET (11 men and 1 woman; age, 52 ± 12 yr; body mass index, 31.2 ± 2.4 kg·m) or NET (eight men and three women; age, 56 ± 11 yr; body mass index, 31.8 ± 3.2 kg·m) programs (three sessions per week; constant-load cycling at 75% of maximal heart rate; target arterial oxygen saturation for HET 80%, FiO2 ~0.13, i.e., ~3700 m a.s.l.). Before and after the training programs, the following evaluations were performed: incremental maximal and submaximal cycling tests, measurements of pulse-wave velocity, endothelial function, fasting glucose, insulin and lipid profile, blood NO metabolites and oxidative stress, and determination of body composition by magnetic resonance imaging.Results: Peak oxygen consumption and maximal power output increased significantly after HET only (peak oxygen consumption HET + 10% ± 11% vs NET + 1% ± 10% and maximal power output HET + 11% ± 7% vs NET + 3% ± 10%, P < 0.05). Submaximal exercise responses improved similarly after HET and NET. Except diastolic blood pressure which decreased significantly after both HET and NET, no change in vascular function, metabolic status and body composition was observed after training. Hypoxic exercise training only increased nitrite and reduced superoxide dismutase concentrations.Conclusions: Combining exercise training and hypoxic exposure may provide some additional benefits to standard NET for obese individual health status.

Aims Obstructive sleep apnea (OSA) characterized by nocturnal intermittent hypoxia (IH) is associated with atherosclerosis and cysteinyl-leukotrienes (CysLT) pathway activation. We aimed to identify the determinants of CysLT pathway activation and the role of CysLT in OSA-related atherosclerosis. Methods and results Determinants of the urinary excretion of LTE4 (U-LTE4) including history of cardiovascular events, polysomnographic and biological parameters were studied in a cohort of 170 OSA patients and 29 controls, and in a subgroup of OSA patients free of cardiovascular event (n = 136). Mechanisms linking IH, the CysLT pathway and atherogenesis were investigated in Apolipoprotein E deficient (ApoE−/−) mice exposed to 8-week IH. In the whole cohort, U-LTE4 was independently influenced by age, minimal oxygen saturation, and a history of cardiovascular events, and correlated significantly with intima-media thickness. In the subgroup of OSA patients free of cardiovascular event, increased U-LTE4 was increased compared to controls and independently related to hypoxia severity and traditional risk factors aggregated in the 10-year cardiovascular risk score of European Society of Cardiology. In IH mice, atherosclerosis lesion size and mRNA levels of 5-lipoxygenase, 5-lipoxygenase activating protein (FLAP) and CysLT1 receptor were significantly increased. This transcriptional activation was associated with the binding of HIF-1 to the FLAP promoter and was strongly associated with atherosclerosis lesion size. CysLT1 receptor antagonism (montelukast) significantly reduced atherosclerosis progression in IH mice. Conclusions IH-related CysLT pathway activation contributes to OSA-induced atherogenesis. In the era of personalized medicine, U-LTE4 may be a useful biomarker to identify OSA patients for whom CysLT1 blockade could represent a new therapeutic avenue for reducing cardiovascular risk.

Background Chronic intermittent hypoxia (IH), the major feature of obstructive sleep apnea (OSA) increases myocardial infarct size. Recent data demonstrate that IH-induced cardiomyocyte susceptibility to infarction could be explained by mitochondrial function and/or dynamics alterations. Moreover, AMP-activated protein kinase (AMPK), a major protein involved in cardiomyocyte metabolism is activated by IH in striated skeletal muscle. However, we recently found that AMPK failed to be activated in myocardium from mice exposed to IH. Objective We aimed at demonstrating whether AMPK activation can be beneficial for ischemia-reperfusion injury following chronic IH exposure. Methods Mice were exposed to 21 days of IH (21-5% FiO2, 60 s-cycles, 8 h/day), or normoxia (N) and treated or not with metformin (300 mg.kg−1.day−1). Infarct size was measured after in vivo ischemia (45 min) and reperfusion (90 min). Mitochondrial function was assessed using oxygraphy and spectrofluorimetry. Mitochondrial dynamics and AMPK activation were assessed by Western blot. An insulin tolerance test was also performed. Results Metformin abolished the IH-induced increase in infarct size whereas it did not improve systemic insulin sensitivity. Metformin activated AMPK and did not impact the decrease in mitochondrial respiration (O2 maximal consumption in complex I and II and respiratory control ratio). However, AMPK activation by Metformin seems to reestablish the distinctive IH impact on mitochondrial dynamics (fission and mitophagy). Conclusion Metformin treatment is protective against ischemia-reperfusion injury induced by IH only. This suggests that metformin could be an alternative treatment to the currently restrictive one for apneic patients with a high CV risk. Ongoing studies will aim to better characterize the mechanisms by which metformin specifically decreases infarct size under IH.

Introduction Obstructive sleep apnea is a growing worldwide health problem. The landmark feature of OSA is a chronic intermittent hypoxia (CIH) responsible for multiple organ damages including heart diseases. CIH profoundly alters both visceral adipose tissue (VAT) and heart structures and functions, but little is known regarding their interactions in the context of CIH. We recently showed that VAT senescence drives myocardial alterations through the release of profibrotic factors in aged mice. Thus, we aim at demonstrating that CIH induces a premature vWAT senescent phenotype, responsible for subsequent heart dysfunction. Methods In a first series of animals, ten-week old C57BL6 male mice (n = 10/group) were exposed to 14 days CIH protocol (8 hours daily, 5–21% cyclic inspired oxygen fraction, 60 seconds per cycle). In another series, mice were submitted to VAT surgical lipectomy or sham-surgery (n = 10/group) and then exposed to the same CIH protocol. VAT and heart were assessed by histology for fibrosis (Sirius red), cell hypertrophy (wheat-germ agglutinin) and reactive oxygen species (ROS) (4-HNE), and markers of senescence (p16, p21, p53), inflammation (CD68, Tnfa, Serpine1), fibrosis (Col1a1) and hypertrophy were also evaluated by RT-qPCR and western blot. Results CIH induced an increased macrophage infiltration in VAT, along with an increased expression of senescence markers, ROS production and gene expression of inflammatory and fibrogenic markers. This was associated with CIH-induced myocardial interstitial fibrosis and upregulation of profibrotic gene expression in myocardium. Interestingly, VAT lipectomy prevented CIH-induced myocardial fibrosis. Conclusion Short-term exposure to CIH is sufficient to induce both VAT remodelling, characterized by oxidative stress, inflammation and fibrosis, and cardiac interstitial fibrosis that was prevented by VAT lipectomy. This strongly suggest a causal crosstalk between CIH-induced VAT senescence and cardiac remodeling.

Obstructive sleep apnoea syndrome is a growing health concern, affecting nearly one billion people worldwide; it is an independent cardiovascular risk factor, associated with incident obesity, insulin resistance, hypertension, arrhythmias, stroke, coronary artery disease and heart failure. Obstructive sleep apnoea-related cardiovascular and metabolic co-morbidities are a major concern for prognosis and the complexity of obstructive sleep apnoea integrated care. Continuous positive airway pressure, the first-line therapy for the treatment of obstructive sleep apnoea, is highly effective at improving symptoms and quality of life, but has limited effect on co-morbidities. Deciphering the molecular pathways involved in obstructive sleep apnoea metabolic and cardiovascular consequences is a priority to make new pharmacological targets available, in combination with or as an alternative to continuous positive airway pressure. Intermittent hypoxia, a landmark feature of obstructive sleep apnoea, is the key intermediary mechanism underlying metabolic and cardiovascular complications. Experimental settings allowing intermittent hypoxia exposure in cells, rodents and healthy humans have been established to dissect the molecular mechanisms of obstructive sleep apnoea-related co-morbidities. The main objective of this review is to recapitulate the molecular pathways, cells and tissue interactions contributing to the cardiometabolic consequences of intermittent hypoxia. Sympathetic activation, low-grade inflammation, oxidative stress and endoplasmic reticulum stress are triggered by intermittent hypoxia and play a role in cardiometabolic dysfunction. The key role of hypoxia-inducible factor-1 transcription factor will be detailed, as well as the underestimated and less described importance of mitochondrial functional changes in the intermittent hypoxia setting.

Obstructive sleep apnea (OSA) is a major risk factor for cardiovascular mortality, and apnea-induced intermittent hypoxia (IH) is known to promote various cardiovascular alterations such as vascular remodeling. However, the mechanisms that underlie IH remain incompletely investigated. We previously demonstrated that the hypoxia-inducible factor-1 (HIF-1) and endothelin-1 (ET-1) are involved in arterial hypertension and myocardial susceptibility to infarction induced by IH. Thus the objective of the present study was to investigate whether both ET-1 and HIF-1 were also involved in the vascular inflammatory remodeling induced by IH. Mice partially deficient for the Hif1α gene (HIF-1α+/−) and their wild-type equivalents, as well as C57BL/6J mice, treated or not with bosentan, a dual endothelin receptor antagonist, were exposed to IH or normoxia for 2 wk, 8 h/day. Splenocyte proliferative and secretory capacities, aortic nuclear factor-κB (NF-κB) and HIF-1 activities, and expression of cytokines and intima-media thickness (IMT) were measured. IH induced a systemic and aortic inflammation characterized by an increase in splenocyte proliferative and secretory capacities, aortic NF-κB activity, and cytokine expression in the aortic wall. This was accompanied by an increase in IMT. These modifications were prevented in HIF-1α+/− and bosentan-treated mice. The results of this study suggest that ET-1 is a major contributor to the vascular inflammatory remodeling induced by OSA-related IH, probably through HIF-1-dependent activation of NF-κB.

Background Patients with sleep disordered breathing (SDB) exhibit poor prognosis after myocardial infarction (MI). Intermittent hypoxia (IH), the hallmark feature of SDB, enhances sympathetic activity, depletes cardiac adrenergic reserve and accelerates cardiac remodeling and dysfunction in a rat model of ischemic cardiomyopathy. In the present study, we aim at investigating whether specific cardiac sympathetic denervation (CSD) counteracts the IH-induced adrenergic reserve depletion and ischemic cardiomyopathy aggravation. Methods MI is induced in male Wistar rats by permanent ligation of the left coronary artery and CSD by ablation of the left middle cervical and stellate ganglions. After surgery, rats are exposed to 6 and 14 weeks IH (21–5% FiO2, 60 s cycle, 8 h/day) or normoxia (N). Cardiac function and remodeling are evaluated by echography. Cardiac sympathetic activity is assessed by spectral analysis of heart rate variability on conscious rats (Etisense). Ultimately, hearts are withdrawn for cardiomyocyte isolation and calcium transient analysis, for assessment of calcium and adrenergic signalling pathways (western blot) and for histological analysis of fibrosis (Sirius red), hypertrophy (WGA) and cardiac sympathetic innervation (Tyrosine-hydroxylase staining). Results CSD prevents the IH-induced blunted cardiomyocyte response to isoproterenol challenge (ISO). ISO-induced cardiomyocyte shortening is about 78% on MI-N group, reduced to 28% in MI-IH and restored to 125% in MI-IH-CSD. Preliminary results on cardiac function indicate that CSD also improve long-term ejection fraction in MI-IH rats. Biochemical and histological analysis are on-going. Conclusion These results suggest that IH-induced sympathetic activity is responsible for adrenergic reserve depletion in our rat model of ischemic cardiomyopathy. Ongoing experiments will confirm if CSD also limits the IH-induced cardiac remodeling and contractile dysfunction.

Objectif L’hypoxie intermittente chronique (HI) est caracteristique des troubles respiratoires du sommeil. Des etudes cliniques soulignent une mortalite plus importante chez les patients apneiques severes apres un infarctus du myocarde (IM). Nos etudes preliminaires ont montre qu’une exposition de 12 semaines a l’HI diminue la fraction d’ejection du ventricule gauche de maniere plus importante, compare a un controle normoxique (N). Associee a cette dysfonction nous observons une hyperactivite sympathique. L’objectif de cette etude est d’evaluer l’impact de l’hyperactivite sympathique causee par l’HI sur le developpement de la cardiopathie ischemique (CI) en s’interessant particulierement aux perturbations de l’homeostasie calcique. Methodes Une ligature permanente de l’artere coronaire gauche permet d’induire la CI chez des rats Wistar males. Une denervation sympathique cardiaque est realisee par l’ablation des ganglions moyens cervical et stellaire gauche. Les animaux sont ensuite exposes a l’HI (21–5 % FiO2, cycle de 60 s, 8 h/jour) ou a la N 6 semaines. Apres l’exposition, les cardiomyocytes de ventricules gauches sont isoles pour l’analyse de transitoires calciques. Resultats L’HI associee a la ligature diminue la reponse des cardiomyocytes isoles suite a une stimulation a l’isoproterenol. La denervation retablie la reserve adrenergique des cardiomyocytes, tant sur le raccourcissement des sarcomeres que sur l’efficacite des transitoires calciques. Conclusion L’impact deletere de l’HI sur la cardiopathie ischemique semble passer par une hyperactivation sympathique.

Background: Chronic intermittent hypoxia (IH), the hallmark feature of obstructive sleep apnoea syndrome, contributes to infarct size enhancement after myocardial ischemia–reperfusion (I/R). Curcumin (Curc), the natural pigment of Curcuma longa, has been demonstrated to be beneficial in the context of myocardial injury. In this study, we assessed the effects of Curc on the maladaptive cardiac response to IH, and particularly on IH-induced hypoxia inducible factor-1 (HIF-1) expression, oxidative stress, inflammation, endoplasmic reticulum (ER) stress and apoptosis. Methods: Swiss/SV129 mice were exposed to normoxia or IH (21–5% FiO2, 60 s cycles, 8 h per day, for 21 days) and treated orally with Curc (100 mg kg−1 day−1, oral gavage) or its vehicle. Mice were then either euthanised for heart sampling in order to perform biochemical and histological analysis, or subjected to an in vivo ischemia-reperfusion protocol in order to measure infarct size. Results: IH increased nuclear HIF-1α expression and superoxide anion (O2.–) production as well as nuclear factor kappa B (NF-kB) p65, glucose-regulated protein (Grp78) and C/EBP homologous protein (CHOP) expression. IH also induced apoptosis and increased infarct size after I/R . The IH-induced HIF-1 activation, oxidative stress, inflammation, ER stress and apoptosis were abolished by chronic Curc treatment. Curc also significantly decreased infarct size only in mice exposed to IH. Conclusion: Curc prevents IH-induced myocardial cell death signalling. Curc might be used as a combined therapy with continuous positive airway pressure in sleep apnoea patients with high cardiovascular risk.

Obstructive sleep apnea syndrome is a highly prevalent disease resulting in transient respiratory arrest and chronic intermittent hypoxia (cIH). cIH is associated with insulin resistance and impaired metabolic homeostasis in rodents and humans, but the exact underlying mechanisms remain unclear. In the current study, we investigated the effects of 2 weeks of cIH (1-min cycle, fraction of inspired oxygen 21–5%, 8 h/day) on whole-body insulin sensitivity and glucose tolerance in lean mice. Although food intake and body weight were reduced compared with normoxia, cIH induced systemic insulin resistance in a hypoxia-inducible factor 1–independent manner and impaired insulin signaling in liver, white adipose tissue, and skeletal muscle. Unexpectedly, cIH improved whole-body glucose tolerance independently of changes in body weight and glucose-induced insulin response. This effect was associated with elevated phosphorylation of Thr172-AMPK and Ser237-TBC1 domain family member 1 (TBC1D1) in skeletal muscle, suggesting a tissue-specific AMPK-dependent increase in TBC1D1-driven glucose uptake. Remarkably, although food intake, body weight, and systemic insulin sensitivity were still affected, the improvement in glucose tolerance by cIH was abolished in muscle-specific AMPKα1α2–deficient mice. We conclude that cIH impairs insulin sensitivity while improving whole-body glucose tolerance by promoting specific activation of the skeletal muscle AMPK pathway.

International audience; Clinical and experimental studies suggest that pharmacological postconditioning with Cyclosporin A (CsA) reduces infarct size in cardiac ischemia and reperfusion. CsA interacts with Cyclophilin D (CypD) preventing opening of the mitochondrial permeability transition pore (mPTP). Tissue kallikrein (TK) and its products kinins are involved in cardioprotection in ischemia. CypD knockout mice are resistant to the cardioprotective effects of both CsA and kinins suggesting common mechanisms of action. Using TK gene knockout mice, we investigated whether the kallikrein-kinin system is involved in the cardioprotective effect of CsA. Homozygote and heterozygote TK deficient mice (TK(-/-), TK(+/-)) and wild type littermates (TK(+/+)) were subjected to cardiac ischemia-reperfusion with and without CsA postconditioning. CsA reduced infarct size in TK(+/+) mice but had no effect in TK(+/-) and TK(-/-) mice. Cardiac mitochondria isolated from TK(-/-) mice had indistinguishable basal oxidative phosphorylation and calcium retention capacity compared to TK(+/+) mice but were resistant to CsA inhibition of mPTP opening. TK activity was documented in mouse heart and rat cardiomyoblasts mitochondria. By proximity ligation assay TK was found in close proximity to the mitochondrial membrane proteins VDAC and Tom22, and CypD. Thus, partial or total deficiency in TK induces resistance to the infarct size reducing effect of CsA in cardiac ischemia in mice, suggesting that TK level is a critical factor for cardioprotection by CsA. TK is required for the mitochondrial action of CsA and may interact with CypD. Genetic variability in TK activity has been documented in man and may influence the cardioprotective effect of CsA.

Introduction et but de l’etude L’apnee du sommeil (AS) est reconnue pour s’accompagner de perturbations des metabolismes glucidique et lipidique [1] , [2] . Mais, de facon etonnante, il n’existe aucune donnee quant a une possible malnutrition associee a cette pathologie. Le but de ce travail est d’evaluer les perturbations nutritionnelles dans un modele murin d’apnee du sommeil. Materiel et methodes Vingt-quatre rats males Wistar ont ete randomises en 3 groupes et suivis pendant 14 jours : un groupe d’animaux sains en normoxie (N), un groupe soumis a une hypoxie intermittente (HI : 21–5 % FiO2, 60 s/cycle, 8 h/j ; un modele valide d’AS) et un groupe en normoxie mais en nutrition appariee au groupe HI (groupe NPF). La prise alimentaire et le poids des animaux ont ete mesures tout au long de l’etude. A la fin de l’etude, les muscles (EDL, Tibialis, Soleus), la muqueuse intestinale (ileon et jejunum), le foie, le cœur, la rate et le thymus ont ete preleves et peses. Les donnees sont representees sous la forme moyenne ± SEM. Resultats et analyse statistique La prise alimentaire cumulee etait diminuee dans le groupe HI (412 ± 24 g vs N : 579 ± 16 ; p Conclusion Ces resultats preliminaires indiquent que l’HI induit specifiquement une perte de poids et une atrophie thymique et hepatique. Une caracterisation plus approfondie des autres parametres nutritionnels (contenus et turnover proteique, albumine etc.) est en cours de realisation.

Background— Under physiological conditions, Ca 2+ transfer from the endoplasmic reticulum (ER) to mitochondria might occur at least in part at contact points between the 2 organelles and involves the VDAC1/Grp75/IP3R1 complex. Accumulation of Ca 2+ into the mitochondrial matrix may activate the mitochondrial chaperone cyclophilin D (CypD) and trigger permeability transition pore opening, whose role in ischemia/reperfusion injury is well recognized. We questioned here whether the transfer of Ca 2+ from ER to mitochondria might play a role in cardiomyocyte death after hypoxia-reoxygenation. Methods and Results— We report that CypD interacts with the VDAC1/Grp75/IP3R1 complex in cardiomyocytes. Genetic or pharmacological inhibition of CypD in both H9c2 cardiomyoblasts and adult cardiomyocytes decreased the Ca 2+ transfer from ER to mitochondria through IP3R under normoxic conditions. During hypoxia-reoxygenation, the interaction between CypD and the IP3R1 Ca 2+ channeling complex increased concomitantly with mitochondrial Ca 2+ content. Inhibition of either CypD, IP3R1, or Grp75 decreased protein interaction within the complex, attenuated mitochondrial Ca 2+ overload, and protected cells from hypoxia-reoxygenation. Genetic or pharmacological inhibition of CypD provided a similar effect in adult mice cardiomyocytes. Disruption of ER-mitochondria interaction via the downregulation of Mfn2 similarly reduced the interaction between CypD and the IP3R1 complex and protected against hypoxia-reoxygenation injury. Conclusions— Our data (1) point to a new role of CypD at the ER-mitochondria interface and (2) suggest that decreasing ER-mitochondria interaction at reperfusion can protect cardiomyocytes against lethal reperfusion injury through the reduction of mitochondrial Ca 2+ overload via the CypD/VDAC1/Grp75/IP3R1 complex.

International audience; Cardiac ischemia is one of the leading causes of death worldwide. It is now well established that natriuretic peptides can attenuate the development of irreversible ischemic injury during myocardial infarction. Lebetin 2 (L2) is a new discovered peptide isolated from Macrovipera lebetina venom with structural similarity to B-type natriuretic peptide (BNP). Our objectives were to define the acute cardioprotective actions of L2 in isolated Langendorff-perfused rat hearts after regional or global ischemia-reperfusion (IR). We studied infarct size, left ventricular contractile recovery, survival protein kinases and mitochondrial permeability transition pore (mPTP) opening in injured myocardium. L2 dosage was determined by preliminary experiments at its ability to induce cyclic guanosine monophosphate (cGMP) release without changing hemodynamic effects in normoxic hearts. L2 was found to be as effective as BNP in reducing infarct size after the induction of either regional or global IR. Both peptides equally improved contractile recovery after regional IR, but only L2 increased coronary flow and reduced severe contractile dysfunction after global ischemia. Cardioprotection afforded by L2 was abolished after isatin or 5-hydroxydecanote pretreatment suggesting the involvement of natriuretic peptide receptors and mitochondrial KATP (mitoKATP) channels in the L2-induced effects. L2 also increased survival protein expression in the reperfused myocardium as evidenced by phosphorylation of signaling pathways PKCε/ERK/GSK3β and PI3K/Akt/eNOS. IR induced mitochondrial pore opening, but this effect was markedly prevented by L2 treatment. These data show that L2 has strong cardioprotective effect in acute ischemia through stimulation of natriuretic peptide receptors. These beneficial effects are mediated, at least in part, by mitoKATP channel opening and downstream activated survival kinases, thus delaying mPTP opening and improving IR-induced mitochondrial dysfunction.

Obesity and diabetes are associated with higher cardiac vulnerability to ischemia-reperfusion (IR). The cardioprotective effect of regular exercise has been attributed to β3-adrenergic receptor (β3AR) stimulation and increased endothelial nitric oxide synthase (eNOS) activation. Here, we evaluated the role of the β3AR-eNOS pathway and NOS isoforms in exercise-induced cardioprotection of C57Bl6 mice fed with high fat and sucrose diet (HFS) for 12 weeks and subjected or not to exercise training during the last 4 weeks (HFS-Ex). HFS animals were more sensitive to in vivo and ex vivo IR injuries than control (normal diet) and HFS-Ex mice. Cardioprotection in HFS-Ex mice was not associated with increased myocardial eNOS activation and NO metabolites storage, possibly due to the β3AR-eNOS pathway functional loss in their heart. Indeed, a selective β3AR agonist (BRL37344) increased eNOS activation and had a protective effect against IR in control, but not in HFS hearts. Moreover, iNOS expression, nitro-oxidative stress (protein s-nitrosylation and nitrotyrosination) and ROS production during early reperfusion were increased in HFS, but not in control mice. Exercise normalized iNOS level and reduced protein s-nitrosylation, nitrotyrosination and ROS production in HFS-Ex hearts during early reperfusion. The iNOS inhibitor 1400 W reduced in vivo infarct size in HFS mice to control levels, supporting the potential role of iNOS normalization in the cardioprotective effects of exercise training in HFS-Ex mice. Although the β3AR-eNOS pathway is defective in the heart of HFS mice, regular exercise can protect their heart against IR by reducing iNOS expression and nitro-oxidative stress.

Mitochondria-associated endoplasmic reticulum membranes (MAMs) are regions of the endoplasmic reticulum (ER) tethered to mitochondria and controlling calcium (Ca(2+)) transfer between both organelles through the complex formed between the voltage-dependent anion channel, glucose-regulated protein 75 and inositol 1,4,5-triphosphate receptor (IP3R). We recently identified cyclophilin D (CYPD) as a new partner of this complex and demonstrated a new role for MAMs in the control of insulin's action in the liver. Here, we report on the mechanisms by which disruption of MAM integrity induces hepatic insulin resistance in CypD (also known as Ppif)-knockout (KO) mice.We used either in vitro pharmacological and genetic inhibition of CYPD in HuH7 cells or in vivo loss of CYPD in mice to investigate ER-mitochondria interactions, inter-organelle Ca(2+) exchange, organelle homeostasis and insulin action.Pharmacological and genetic inhibition of CYPD concomitantly reduced ER-mitochondria interactions, inhibited inter-organelle Ca(2+) exchange, induced ER stress and altered insulin signalling in HuH7 cells. In addition, histamine-stimulated Ca(2+) transfer from ER to mitochondria was blunted in isolated hepatocytes of CypD-KO mice and this was associated with an increase in ER calcium store. Interestingly, disruption of inter-organelle Ca(2+) transfer was associated with ER stress, mitochondrial dysfunction, lipid accumulation, activation of c-Jun N-terminal kinase (JNK) and protein kinase C (PKC)ε and insulin resistance in liver of CypD-KO mice. Finally, CYPD-related alterations of insulin signalling were mediated by activation of PKCε rather than JNK in HuH7 cells.Disruption of IP3R-mediated Ca(2+) signalling in the liver of CypD-KO mice leads to hepatic insulin resistance through disruption of organelle interaction and function, increase in lipid accumulation and activation of PKCε. Modulation of ER-mitochondria Ca(2+) exchange may thus provide an exciting new avenue for treating hepatic insulin resistance.

Obstructive sleep apnea (OSA) is a highly prevalent disease and a risk factor for myocardial infarction expansion in humans. Intermittent hypoxia (IH) is known to be the most important OSA feature in terms of cardiovascular morbi-mortality. Since ER stress and HIF-1 are known to be involved in cardiomyocyte life or death, this study investigates the role of ER stress on HIF-1 activation in myocardial susceptibility to ischemia-reperfusion (I/R) induced by IH.C57Bl6J, HIF-1α(+/-) and their respective control mice were exposed to 14 days of IH (21-5% FiO2, 60 scycle, 8h/day). Myocardial inter-organelle calcium exchanges, ER stress and HIF-1 activity were investigated and in vivo I/R was performed to measure infarct size. In additional groups, tauroursodeoxycholic acid (TUDCA, 75 mg·kg(-1)), an ER stress inhibitor, was administered daily during exposure.In C57Bl6J mice, chronic IH induced an increase in ER-Ca(2+) content, ER stress markers and HIF-1 activity, associated with an enhanced infarct size (33.7 ± 9.4 vs. 61.0 ± 5.6% in N and IH, respectively, p0.05). IH failed to increase infarct size in HIF-1α deficient mice (42.4 ± 2.7 and 24.7 ± 3.4% N and IH, respectively). Finally, TUDCA totally abolished the IH-induced increase in HIF-1 activity (1.3 ± 0.04 vs. 0.14 ± 0.02 fold increase in IH vs. IH-TUDCA respectively, p0.0001) and in infarct size (55.5 ± 7.6 vs. 49.9 ± 3.0 in N-TUDCA and IH-TUDCA, respectively).This novel regulatory mechanism of HIF-1 activity by ER stress should be considered as a potential diagnostic tool for cardiovascular complications in OSA patients as well as a therapeutic target to limit myocardial ischemic damage.

Obesity is associated with local tissue hypoxia and elevated hypoxia-inducible factor 1 alpha (HIF-1α) in metabolic tissues. Prolyl hydroxylases (PHDs) play an important role in regulating HIF-α isoform stability. In the present study, we investigated the consequence of whole-body PHD1 gene (Egln2) inactivation on metabolic homeostasis in mice. At baseline, PHD1−/− mice exhibited higher white adipose tissue (WAT) mass, despite lower body weight and impaired insulin sensitivity and glucose tolerance when compared to age-matched wild-type (WT) mice. When fed a synthetic low-fat diet, PHD1−/− mice also exhibit a higher body weight gain and WAT mass along with glucose intolerance and systemic insulin resistance compared to WT mice. PHD1 deficiency led to increase in glycolytic gene expression, lipogenic proteins ACC and FAS, hepatic steatosis and liver-specific insulin resistance. Furthermore, gene markers of inflammation were also increased in the liver, but not in WAT or skeletal muscle, of PHD1−/− mice. As expected, high-fat diet (HFD) promoted obesity, hepatic steatosis, tissue-specific inflammation and systemic insulin resistance in WT mice but these diet-induced metabolic alterations were not exacerbated in PHD1−/− mice. In conclusion, PHD1 deficiency promotes hepatic steatosis and liver-specific insulin resistance but does not worsen the deleterious effects of HFD on metabolic homeostasis.

International audience; Obstructive sleep apnea (OSA) is now recognized as an independent and important risk factor for cardiovascular diseases such as hypertension, coronary heart disease, heart failure and stroke. Clinical and experimental data have confirmed that intermittent hypoxia is a major contributor to these deleterious consequences. The repetitive occurrence of hypoxia-reoxygenation sequences generates significant amounts of free radicals, particularly in moderate to severe OSA patients. Moreover, in addition to hypoxia, reactive oxygen species (ROS) are potential inducers of the hypoxia inducible transcription factor-1 (HIF-1) that promotes the transcription of numerous adaptive genes some of which being deleterious for the cardiovascular system, such as the endothelin-1 gene. This review will focus on the involvement of the ROS-HIF-1-endothelin signaling pathway in OSA and intermittent hypoxia and discuss current and potential therapeutic approaches targeting this pathway to treat or prevent cardiovascular disease in moderate to severe OSA patients.

Background Chronic intermittent hypoxia (IH) is the hallmark feature of sleep-disordered breathing and clinical studies underlie a poor prognosis in severe apneic patients post-myocardial infarction (MI). Thus, it is necessary to understand specific mechanistic pathways involved in this post-MI aggravation, in order to improve the management of patient. Previous studies showed that IH activates myocardial HIF1-endoplasmic reticulum (ER) stress axis. Thus, we aimed at highlighting: 1 the impact of IH on the development of ischemic cardiomyopathy; 2 to determine the involved mechanisms, in particular the role of IH on HIF1-ER stress axis, sympathetic activation and calcium (Ca2+) homeostasis perturbations. Methods MI was induced by permanent ligation of the left coronary artery in male Wistar rats. Then, rats were exposed to IH (21–5% FiO2, 60 s cycle, 8 h/day) or normoxia (N) for 1 to 12 weeks. Cardiac function was evaluated by ultrasonography and cardiac catheterization. Ultimately, hearts were withdrawn for biochemical and histological analysis, as well as Ca2+ transient imaging after cardiomyocytes isolation. Results We observed more important alterations in ejection fraction, dP/dtmax, and dP/dtmin in IH rats compared to N. These IH rats exhibited sympathetic hyperactivation (i.e. increased LF/HF ratio and adrenal gland hypertrophy), which was associated with an increased HIF1 expression post-MI. Expressions of GRP78, CHOP and caspase 12 proteins were also increased by IH, suggesting a pro apoptotic ER stress. Except from phospholamban that was hyper-phosphorylated, Ca2+ handling protein expressions were not different between N and IH. Finally, Ca2+ transient analysis is ongoing. Conclusion As in severe apneic patients, we showed that IH is deleterious on ischemic cardiomyopathy development. Besides, HIF1, sympathetic activity, ER stress and Ca2+ homeostasis are disturbed. Further studies are needed to better understand the relationship between these mechanisms.