Hypoxic Stimulus Research Articles

Stabilization of HIF-1α in Human Retinal Endothelial Cells Modulates Expression of miRNAs and Proangiogenic Growth Factors.

Retinal hypoxia is one of the causative factors of diabetic retinopathy and is also one of the triggers of VEGF release. We hypothesized that specific dysregulated miRNAs in diabetic retinopathy could be linked to hypoxia-induced damage in human retinal endothelial cells (HRECs). We investigated in HRECs the effects of chemical (CoCl2) hypoxia on the expression of HIF-1α, VEGF, PlGF, and of a focused set of miRNAs. We found that miR-20a-5p, miR-20b-5p, miR-27a-3p, miR-27b-3p, miR-206-3p, miR-381-3p correlated also with expression of TGFβ signaling pathway genes in HRECs, challenged with chemical hypoxic stimuli. In conclusion, our data suggest that retinal angiogenesis would be promoted, at least under HIF-1α activation, by upregulation of PlGF and other factors such as miRNAs, VEGFA, and TGFβ1.

"Take My Bone Away?" Hypoxia and bone: A narrative review.

To maintain normal cellular and physiological function, sufficient oxygen is required. Recently, evidence has suggested that hypoxia, either pathological or environmental, may influence bone health. It appears that bone cells are distinctly responsive to hypoxic stimuli; for better or worse, this is still yet to be elucidated. Hypoxia has been shown to offer potentially therapeutic effects for bone by inducing an osteogenic-angiogenic response, although, others have noted excessive osteoclastic bone resorption instead. Much evidence suggests that the hypoxic-inducible pathway is integral in mediating the changes in bone metabolism. Furthermore, many factors associated with hypoxia including changes in energy metabolism, acid-base balance and the increased generation of reactive oxygen species, are known to influence bone metabolism. This review aims to examine some of the putative mechanisms responsible for hypoxic-induced alterations of bone metabolism, with regard to osteoclasts and osteoblasts, both positive and negative.

β-arrestin1 inhibits hypoxic injury-induced autophagy in human pulmonary artery endothelial cells via the Akt/mTOR signaling pathway.

Autophagy has been greatly implicated in injured endothelial cells during pulmonary arterial hypertension (PAH). β-arrestin1, a multifunctional cytoplasmic protein, has attracted considerable attention as an essential protective factor in PAH. However, its role in autophagy of injured pulmonary arterial endothelial cells (PAECs) remains to be determined. Here, we investigated the potential effects of β-arrestin1 on autophagy and apoptosis in human PAECs (hPAECs) under hypoxic stress. Hypoxic stimuli increases autophagy and decreases the level of β-arrestin1 in hPAECs. Furthermore, pathologic changes, namely increased proliferation, migration, and apoptosis resistance, are observed after hypoxia exposure. These are reversed after β-arrestin1 overexpression (β-arrestin1-OV) or treatment with 3-MA, an autophagy inhibitor. Finally, β-arrestin1 suppresses the increase in autophagy and apoptosis resistance of hypoxic hPAECs. Mechanistically, β-arrestin1 upregulates the activity of the Akt/mTOR signaling pathway and downregulates the expression of BNIP3 and Nix after hypoxic stress. Collectively, we have demonstrated, for the first time, that β-arrestin1 reduces excessive autophagy and apoptosis resistance by activating the Akt/mTOR axis in hypoxic hPAECs. This knowledge suggests a promising therapeutic target for PAH.

Different subpopulations of kidney interstitial cells produce erythropoietin and factors supporting tissue oxygenation in response to hypoxia in vivo

Genetic induction of hypoxia signaling by deletion of the von Hippel-Lindau (Vhl) protein in mesenchymal PDGFR-β+ cells leads to abundant HIF-2 dependent erythropoietin (EPO) expression in the cortex and outer medulla of the kidney. This rather unique feature of kidney PDGFR-β+ cells promote questions about their special characteristics and general functional response to hypoxia. To address these issues, we characterized kidney PDGFR-β+ EPO expressing cells based on additional cell markers and their gene expression profile in response to hypoxia signaling induced by targeted deletion of Vhl or exposure to low oxygen and carbon monoxide respectively, and after unilateral ureteral obstruction. CD73+, Gli1+, tenascin C+ and interstitial SMMHC+ cells were identified as zonally distributed subpopulations of PDGFR-β+ cells. EPO expression could be induced by Vhl deletion in all PDGFR-β+ subpopulations. Under hypoxemic conditions, recruited EPO+ cells were mostly part of the CD73+ subpopulation. Besides EPO production, expression of adrenomedullin and regulator of G-protein signaling 4 was upregulated in PDGFR-β+ subpopulations in response to the different hypoxic stimuli. Thus, different kidney interstitial PDGFR-β+ subpopulations exist, capable of producing EPO in response to different stimuli. Activation of hypoxia signaling in these cells also induces factors likely contributing to improved kidney interstitial tissue oxygenation.

Causes of, and countermeasures to, increased ventilatory drive in tetraplegia.

Causes of, and countermeasures to, increased ventilatory drive in tetraplegia.

The miR-590-3p/VEGFA axis modulates secretion of VEGFA from adipose-derived stem cells, which acts as a paracrine regulator of human dermal microvascular endothelial cell angiogenesis.

The paracrine secretion of angiogenic cytokines from adipose-derived stem cells (ADSCs) might promote endothelial cell angiogenesis, therefore promoting wound healing in injured tissues. Hypoxia is one of the common occurrence in injured tissues, during which angiogenesis is enhanced to improve the oxygen supply. In the present study, miR-590-3p, an anti-angiogenic miRNA, was predicted to target VEGFA, a key factor that can be transcriptionally upregulated by HIF1A during ADSC proliferation and tubule formation in response to hypoxic stimulation. Herein, we found that in response to hypoxic stimuli, HIF1A and VEGFA protein expressions were remarkably induced. In addition, ADSC viability was promoted. Incubation with conditioned medium from ADSCs stimulated by hypoxia significantly enhanced the angiogenic ability of human dermal microvascular endothelial cells (HDMECs), while the conditioned medium from VEGFA-silenced ADSCs significantly reversed the angiogenic ability of HDMECs. Regarding the molecular mechanism, it was verified that miR-590-3p binds to VEGFA; miR-590-3p inhibited VEGFA to affect the paracrine regulation by ADSCs, subsequently hindering the HDMEC angiogenesis. More importantly, the consequences of miR-590-3p-overexpressing conditioned medium on HDMEC angiogenesis were partially reversed by VEGFA-overexpressing conditioned medium. In conclusion, miR-590-3-5p/VEGFA axis modulates the paracrine secretion of VEGFA by ADSCs to affect the angiogenesis of HDMECs.

INTEGRATED EFFECTS OF NORMOBARIC HYPOXIA AND METABOREFLEX ACTIVATION ON HEMODYNAMICS

IntroductionBoth metaboreflex activity and hypoxia affect hemodynamics. In particular, metaboreflex induces an augmentation in stroke volume (SV), systemic vascular resistance (SVR), and blood pressure (BP) by activating the sympathetic nervous system (SNS). In contrast, hypoxia produces a heart rate (HR)‐mediated increase in cardiac output (CO), while its effect on SVR is variable as it increases SNS activity but, at the same time, it triggers nitric oxide (NO) production in the endothelium, thus inducing venous and arteriolar dilation. Since studies on the possible interaction between metaboreflex and hypoxia are still lacking, our investigation aimed to study their combined effects on hemodynamics.Methods11 male subjects underwent a preliminary cardiopulmonary exercise test (CPET) on a cycle ergometer to assess their aerobic fitness. Then, a metaboreflex activation protocol in normoxia and normobaric hypoxia (fraction of inspired oxygen – FiO2 – of 13.5%) was conducted on separate days. Hypoxia was induced using a hypoxic gas generator (Everest Summit II Generator, Hypoxico, USA) connected to the subjects by a facemask. The metaboreflex activation protocol consisted of two randomly assigned sessions: one of post‐exercise muscle ischemia (PEMI) and one of control exercise recovery (CER). PEMI comprised a 3‐minute exercise bout pedaling at 30% of the maximum workload reached during the CPET followed by 3 minutes of vascular occlusion using an inflatable thigh cuff to stimulate the metaboreflex. CER was similar, but no occlusion was applied after the exercise session. SV, HR, CO, ventricular filling rate (VFR), and ventricular ejection rate (VER) were measured through impedance cardiography while mean blood pressure (MBP) was assessed using manual sphygmomanometer. SVR was calculated indirectly from CO and MBP according to Poiseuille’s law. Near‐infrared spectroscopy was employed to measure cerebral oxygenation (COX) and peripheral hemoglobin saturation (SPO2) to control the level of tissue hypoxia. Two‐way ANOVA and paired sample t‐test were utilized when appropriate.ResultsCO was increased during metaboreflex activation in normoxia (p= 0.013) but not in hypoxia. SV, CO, and VFR responses to metaboreflex (measured as the difference PEMI‐CER at the third minute after exercise) were reduced when the hypoxic stimulus was applied (p=0.02; p=0.02; p=0.003 respectively). Moreover, SVR response showed a nearly significant (p=0.07) increase in hypoxia, with MBP response being unchanged. COX and SPO2 confirmed that the hypoxic stimulus was effective.DiscussionResults demonstrated that hypoxia impaired the hemodynamic response to metaboreflex. Specifically, SV was reduced during metaboreflex in hypoxia because of a reduction in preload as a consequence of two mechanisms: 1) a reduction in venous return probably induced by NO‐mediated vasodilation of the venous bed; 2) an increase in right ventricle afterload likely produced by the pulmonary arterial system vasoconstriction. Of note, baroreflex successfully defended MBP response despite the reduced CO during hypoxia.

Cerebral Blood Flow and Cerebral Tissue Oxygen Responses to Inspiratory Resistance Breathing During Hypoxia

Increasing resistance to inspiration further decreases intrathoracic and intracranial pressures, leading to increases in venous return, stroke volume, and consequently, arterial pressure and cerebral perfusion pressure. Accordingly, inspiratory resistance breathing may be of therapeutic interest for clinical conditions associated with decreased delivery of blood and oxygen to the brain. Previous studies in healthy humans have investigated the effect of inspiratory resistance breathing on the cerebral circulation, by studying blood velocity within intracranial vessels (via transcranial Doppler (TCD) ultrasound), with equivocal results. The aim of this study was to investigate the effect of inspiratory resistance breathing on blood flow through the internal carotid artery (ICA), and cerebral tissue oxygenation during hypoxia. We hypothesized that inspiratory resistance breathing would increase ICA blood flow, and improve cerebral tissue oxygenation during a mild hypoxic stimulus.MethodsSix healthy human subjects (5M/1F) completed two 10‐min protocols in randomized order: 1) breathing a hypoxic gas mix (16% O2, balance N2), and 2) breathing a hypoxic gas mix (16% O2, balance N2) with inspiratory resistance of −7 cmH2O. ICA blood flow was derived from simultaneous measurements of blood velocity and diameter measured by duplex ultrasound, middle cerebral artery velocity (MCAv) was recorded continuously by TCD ultrasound, and cerebral tissue oxygenation (ScO2) was recorded by near‐infrared spectroscopy. Arterial oxygen saturation (SpO2) was measured by pulse oximetry, and end‐tidal O2 (etO2) was measured by a gas analyzer. Data were analyzed from the last 1‐min of baseline and each protocol with a linear mixed model.ResultsThe hypoxic stimulus decreased SpO2 and etO2 (P<0.0001), and inspiratory resistance breathing did not protect against these responses (P≥0.21). ICA diameter increased with hypoxia under both conditions (P=0.002), regardless of resistance breathing (P=0.56). ICA velocity (23.6 ± 1.6 cm/s vs. 25.7 ± 1.1 cm/s) and flow (298.8 ± 36.6 ml/min vs. 328.8 ± 39.5 ml/min) were lower with hypoxia and inspiratory resistance breathing compared with hypoxia alone (P≤0.07), while mean MCAv was not affected by either hypoxia or resistance breathing (P≥0.15). ScO2 decreased under both conditions (P=0.0009; hypoxia: −2.7 ± 0.9 %; hypoxia + resistance breathing: −3.6 ± 0.8 %), with no effect of inspiratory resistance breathing (P=0.90).ConclusionThese preliminary data demonstrate that, contrary to our hypothesis, inspiratory resistance breathing did not increase ICA blood flow, nor improve cerebral tissue oxygenation during a mild hypoxic stimulus. Rather, ICA blood flow decreased with inspiratory resistance breathing during hypoxia, primarily due to a reduction in ICA blood velocity. Further studies are required to elucidate whether inspiratory resistance breathing may be of therapeutic interest for clinical conditions affecting cerebral blood flow and tissue oxygenation.

Tibetans resident at intermediate altitude (1300 m, 4327 ft) show similar hypoxic ventilatory responses but blunted heart rate responses to poikilocapnic hypoxia

Population living at high altitudes for hundreds of generations exhibit distinct respiratory and cardiovascular responses to hypoxia relative to other populations. The extent of these differences at intermediate altitude is less understood and could provide important insight into ancestry specific physiological responses in the absence of hypoxia. We hypothesized that Tibetans living at intermediate altitude (1300 m, 4327 ft) exhibit an increased hypoxic ventilatory response (HVR) and an elevated hypoxic heart rate response (HHR) compared to Han Chinese examined at the same altitude. To estimate O2 sensitivity, we measured ventilation (VI), heart rate (HR) and O2 saturation (Sat) under hyperoxic conditions (30% O2) and then during a hypoxic stimulus (10% minimum desaturation) keeping end‐tidal CO2 (EtCO2) levels constant (isocapnia) or allowing changes in the EtCO2 (poikilocapnia). We quantified HVR and HHR as change in VI and HR between hyperoxia and hypoxia standardized per the change in O2 Sat (ΔVI/ΔSat and ΔHR/ΔSat respectively). To estimate CO2 sensitivity, we measured changes in VI and HR responses between poikilocapnic and isocapnic hypoxia and standardized these changes per change in EtCO2 (ΔVI/ΔEtCO2 and ΔHR/ΔEtCO2 respectively). We did not find significant differences in ΔVI/ΔSat and ΔVI/ΔEtCO2 between Tibetan and Han Chinese during isocapnic and poikilocapnic hypoxia. The ΔHR/ΔSat between populations during isocapnic hypoxia was also not significantly different. However, Tibetans exhibited a blunted ΔHR/ΔSat during poikilocapnic hypoxia compared to Han Chinese (35.8% decrease, p < 0.02) with a significant ancestry effect in women (37.6% decrease, p < 0.009). The mean value of ΔHR/ΔEtCO2 was positive in the Han Chinese group but negative in Tibetan (169% difference, p < 0.02), indicating that Tibetans had a blunted HR response when CO2 is not controlled. Our results show that HVR responses in Tibetan individuals with high‐altitude ancestry is not different than Han Chinese residents at comparable intermediate altitude, but the HHR to hypoxia during poikilocapnia is blunted in individuals with Tibetan ancestry. These results suggest that, at intermediate altitude, individuals with Tibetan ancestry exhibit an attenuated heart rate response to hypoxia due to an increased contribution of the CO2 chemosensory response.Support or Funding InformationSupported by NIH 1RO1HL145470 and R01 HL‐081823.

Sildenafil reverses the right ventricular hypertrophy induced by hypoxia but does not bring down the expression of MHC‐β to normal value

IntroductionMyosin is the major player in structure and function of cardiac muscle. There are two sub‐types of myosin heavy chain in cardiac muscle; myosin heavy chain‐α (MHC‐α) and myosin heavy chain‐β (MHC‐β). The contractile properties of the cardiac muscle are determined largely by types and the expression of the myosin heavy chain (MHC) which is altered by many physiological and pathological conditions.ObjectivesIn this study we investigated the effect of hypoxia and sildenafil treatment on myosin heavy chain isoform in hy poxia ‐ induced hypertrophied right ventricle.MethodsRight ventricular hypertrophy was induced in 45 mice by exposing them to hypoxic stimulus (11% ambient oxygen) in normobaric chamber for 20 days. The animals were distributed randomly into three groups: first group served as control (CO), second group exposed to hypoxia for 20 days without sildenafil treatment (HY) and third group was given sildenafil orally at dose of 30 mg.Kg−1.day−1 plus exposure to hypoxia for 20 days (HS). MHC isoforms were calculated using two ELISA kits containing antibodies against α and β MHC and by SDS‐PAGE (Mybiosource‐USA). The HY group in comparison with CO group, showed a significant increase in right ventricle weight/left ventricle plus septum ratio (Fulton’s ratio). HS group showed significant decrease in Fulton’s ratio compared with HY but not with CO. Expression of MHC‐β isoform was significantly increased in HY group compared with CO. There was no significant difference in MHC‐β between HY group and HS group. Expression of more beta myosin heavy in hypoxic group is beneficial to the heart since hearts with more MHC‐β have more economic contraction.Conclusionsildenafil reversed the right ventricular hypertrophy induced by hypoxia but did not bring down the expression of MHC‐β to normal value.Support or Funding InformationDeanship of research at Jordan University of Science & TechnologyEffects of hypoxia and hypoxia with sildenafil on myosin heavy chain isoforms.Expression of cardiac myosin heavy chains in different groups: Hypoxia caused expression of more MHC‐β and sildenafil failed in revering the changes caused by hypoxia. Control (CO), hypoxia for 20 days without treatment (HY) and hypoxia for 20 days plus treatment with sildenafil (HS). *** P < 0.01 HY and HS vs COFigure 1

Increased Vasoconstriction of the Pulmonary Vasculature in Response to a Hypoxic Challenge in Swine Exposed to Hypoxia in the Neonatal Period

IntroductionAdvances in neonatal care improved the survival of very prematurely born infants. Exposure to high oxygen is often necessary to ensure adequate oxygen uptake in these infants, leading to halted development and oxidative injury of the pulmonary vasculature which is often accompanied by increased pulmonary arterial pressure (PAP). Although pressures normalize in school age childhood, various stressors as hypoxia and exercise may unmask increased pulmonary vasoreactivity. Furthermore, now that these infants reach adulthood, it is increasingly recognized that this large, preterm born adult cohort has a less favorable cardiopulmonary risk profile. Particularly male subjects were shown to respond with a higher increase in PAP upon re‐exposure to hypoxia, which might be a predisposition to pulmonary vascular disease later in life. Pathophysiological risk factors causing this predisposition are unidentified and challenging to investigate in the human population.ObjectiveTo assess if swine with perinatal oxidative injury of the pulmonary vasculature respond differently to re‐exposure to a hypoxic stimulus compared to healthy swine.Methods6 male swine were exposed to 10–12% hypoxia in the neonatal period (NH‐swine) for a maximum of 4 weeks to interfere with normal lung development, while 5 male control pigs (healthy swine) were raised in normoxic conditions. In the NH‐swine, a symptom‐guided method (echocardiographic changes and clinical symptoms) orchestrated timing of the return to normoxic conditions. At the age of 8 weeks, NH and healthy swine were chronically instrumented. In week 10, hemodynamics were evaluated at rest and during exposure to 14–15% oxygen for 20 minutes.ResultsNH‐swine were exposed to a 23±5 days of hypoxia. 2 NH‐swine passed away as a consequence of heart failure before chronic instrumentation. At the age of 10 weeks, baseline PAP (14.6±2 vs 13.8±1 mmHg) and pulmonary vascular resistance (PVR, 4.1±0.7 vs 2.8±0.4 WU) at rest was not different in NH‐swine compared to healthy swine. During the hypoxic challenge, oxygen saturation decreased similarly in both groups compared to baseline measurements. PAP increased upon exposure to hypoxia due to an increase in PVR. The increases in PAP and PVR showed a transient peak after two minutes, which were larger in in NH‐swine compared to healthy swine. PAP and ΔPVR stabilized between 10 and 20 minutes of hypoxia exposure at levels that were not different between groups.ConclusionsInterfering with normal lung development in the first weeks of life induces a transiently exaggerated increase in PAP and PVR during a hypoxic challenge at the age of ten weeks. Normalization of PAP and PVR suggests effective counter mechanisms to reduce cardiac work and increase arterial oxygen saturation. The increased response to hypoxia of the pulmonary circulation suggest long‐term structural and/or functional changes that possibly predisposes the pulmonary circulation to adult pulmonary vascular disease.Support or Funding InformationErasmusMC M‐RACEHypoxic challenge data in 10 week old swine exposed to neonatal hypoxia (NH‐swine) compared to healthy swine. A: Arterial oxygen saturation (sO2), B: Pulmonary arterial pressure (PAP), C: Difference in pulmonary vascular resistance compared to baseline values (ΔPVR). BL ‐ baseline, WU ‐ Wood units. *=p<0.05 between groups, †=p<0.05 compared to baseline valuesFigure 1

An Updated Panorama of "Living Low-Training High" Altitude/Hypoxic Methods.

With minimal costs and travel constraints for athletes, the “living low-training high” (LLTH) approach is becoming an important intervention for modern sport. The popularity of the LLTH model of altitude training is also associated with the fact that it only causes a slight disturbance to athletes' usual daily routine, allowing them to maintain their regular lifestyle in their home environment. In this perspective article, we discuss the evolving boundaries of the LLTH paradigm and its practical applications for athletes. Passive modalities include intermittent hypoxic exposure at rest (IHE) and Ischemic preconditioning (IPC). Active modalities use either local [blood flow restricted (BFR) exercise] and/or systemic hypoxia [continuous low-intensity training in hypoxia (CHT), interval hypoxic training (IHT), repeated-sprint training in hypoxia (RSH), sprint interval training in hypoxia (SIH) and resistance training in hypoxia (RTH)]. A combination of hypoxic methods targeting different attributes also represents an attractive solution. In conclusion, a growing number of LLTH altitude training methods exists that include the application of systemic and local hypoxia stimuli, or a combination of both, for performance enhancement in many disciplines.

Enhanced glycolysis and HIF-1\u03b1 activation in adipose tissue macrophages sustains local and systemic interleukin-1\u03b2 production in obesity

During obesity, macrophages infiltrate the visceral adipose tissue and promote inflammation that contributes to type II diabetes. Evidence suggests that the rewiring of cellular metabolism can regulate macrophage function. However, the metabolic programs that characterize adipose tissue macrophages (ATM) in obesity are poorly defined. Here, we demonstrate that ATM from obese mice exhibit metabolic profiles characterized by elevated glycolysis and oxidative phosphorylation, distinct from ATM from lean mice. Increased activation of HIF-1α in ATM of obese visceral adipose tissue resulted in induction of IL-1β and genes in the glycolytic pathway. Using a hypoxia-tracer, we show that HIF-1α nuclear translocation occurred both in hypoxic and non-hypoxic ATM suggesting that both hypoxic and pseudohypoxic stimuli activate HIF-1α and its target genes in ATM during diet-induced obesity. Exposure of macrophages to the saturated fatty acid palmitate increased glycolysis and HIF-1α expression, which culminated in IL-1β induction thereby simulating pseudohypoxia. Using mice with macrophage-specific targeted deletion of HIF-1α, we demonstrate the critical role of HIF-1α-derived from macrophages in regulating ATM accumulation, and local and systemic IL-1β production, but not in modulating systemic metabolic responses. Collectively, our data identify enhanced glycolysis and HIF-1α activation as drivers of low-grade inflammation in obesity.

Icariin alleviates hypoxia-induced damage in MC3T3-E1 cells by downregulating TALNEC2.

Osteonecrosis is a harmful musculoskeletal disease. We aim to detect the effects of icariin (ICA) in MC3T3-E1 cell. MC3T3-E1 cell was pretreated with ICA and was subjected to hypoxia stimuli. The tumor-associated long noncoding RNA expressed on chromosome 2 (TALNEC2) overexpression or silencing vectors (pTALNEC2 or si-TALNEC2) was utilized for MC3T3-E1 cell transfection. Viability and apoptosis rate were individually tested by cell counting kit-8 and Annexin V-fluorescein isothiocyanate/propidium iodide kit untied with flow cytometry. The alkaline phosphatase activity (ALP) activity was tested through ALP assay. The quantitative reverse transcription PCR or Western blot was performed for elements detection at the RNA or protein level. Hypoxia treatment induced viability inhibition and CyclinD1 reduction, but elevation of p53 and p16. It also promoted apoptosis by increasing apoptotic cells, Bax, and cleaved-poly ADP-ribose polymerase but decreasing Bcl-2. Also, hypoxia stimuli restrained ALP activity, and osteopontin, osteocalcin, and Runt-related transcription factor 2 expression. Those effects caused by hypoxia stimuli were all reversed by ICA. TALNEC2 was downregulated by ICA, whose impacts were subsequently abolished by pTALNEC2. Silencing TALNEC2 displayed similar effects with ICA. But the apoptosis was not affected by si-TALNEC2. ICA blocked ste20-related proline/alanine-rich kinase/c-Jun N-terminal kinase (SPAK/JNK) but triggered phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway in MC3T3-E1 cell by suppressing TALNEC2. ICA relieved hypoxia-stimulated damage by restraining TALNEC2 through blocking SPAK/JNK and triggering PI3K/AKT/mTOR in the MC3T3-E1 cell.

Hypoxic-inflammatory responses under acute hypoxia: In Vitro experiments and prospective observational expedition trial.

Induction of hypoxia-inducible-factor-1α (HIF-1α) pathway and HIF-target genes allow adaptation to hypoxia and are associated with reduced incidence of acute mountain sickness (AMS). Little is known about HIF-pathways in conjunction with inflammation or exercise stimuli under acute hypobaric hypoxia in non-acclimatized individuals. We therefore tested the hypotheses that (1) both hypoxic and inflammatory stimuli induce hypoxic-inflammatory signaling pathways in vitro, (2) similar results are seen in vivo under hypobaric hypoxia, and (3) induction of HIF-dependent genes is associated with AMS in 11 volunteers. In vitro, peripheral blood mononuclear cells (PBMCs) were incubated under hypoxic (10%/5% O2) or inflammatory (CD3/CD28) conditions. In vivo, Interleukin 1β (IL-1β), C-X-C Chemokine receptor type 4 (CXCR-4), and C-C Chemokine receptor type 2 (CCR-2) mRNA expression, cytokines and receptors were analyzed under normoxia (520 m above sea level (a.s.l.)), hypobaric hypoxia (3883 m a.s.l.) before/after exercise, and after 24 h under hypobaric hypoxia. In vitro, isolated hypoxic (p = 0.004) or inflammatory (p = 0.006) stimuli induced IL-1β mRNA expression. CCR-2 mRNA expression increased under hypoxia (p = 0.005); CXCR-4 mRNA expression remained unchanged. In vivo, cytokines, receptors, and IL-1β, CCR-2 and CXCR-4 mRNA expression increased under hypobaric hypoxia after 24 h (all p ≤ 0.05). Of note, proinflammatory IL-1β and CXCR-4 mRNA expression changes were associated with symptoms of AMS. Thus, hypoxic-inflammatory pathways are differentially regulated, as combined hypoxic and exercise stimulus was stronger in vivo than isolated hypoxic or inflammatory stimulation in vitro.

Pluripotent hematopoietic stem cells augment α-adrenergic receptor-mediated contraction of pulmonary artery and contribute to the pathogenesis of pulmonary hypertension.

Pulmonary hypertension (PH) is a multicellular and progressive disease with a high mortality rate. Among many cell types, hematopoietic stem cells (HSCs) are incriminated in the pathogenesis of PH. However, our understanding of the mechanisms that increase HSCs in blood and lungs of hypertensive animals or patients and the role played by HSCs in the pathogenesis of PH remains elusive. Studies suggest that glycolysis is critical for the survival and growth of HSCs. In various cell types from hypertensive lungs of animals and patients, glycolysis and the glucose-6-phosphate dehydrogenase (G6PD) activity are increased. Herein, we demonstrated in mice that chronic hypoxia increased HSCs (CD34+, CD117+, CD133+, CD34+/CD117+, and CD34+/CD133+) in bone marrow and blood and around hypertensive pulmonary arteries in a time-dependent manner. Intriguingly, we found fewer CD133+ cells in the bone marrow of C57BL/6 mice compared with Sv129J mice, and C57BL mice developed less severe chronic hypoxia-elicited PH and heart failure than Sv129J mice. Similarly, the numbers of CD34+ and CD117+ cells in blood of patients with pulmonary arterial hypertension (PAH) were higher (>3-fold) compared with healthy individuals. By allogeneic bone marrow transplantation, we found that GFP+ bone marrow cells infiltrated the lungs and accumulated around the pulmonary arteries in lungs of hypoxic mice, and these cells contributed to increased α-adrenergic receptor-mediated contraction of the pulmonary artery cultured in hypoxia. Inhibition of G6PD activity with (3β,5α)-3,21-dihydroxypregnan-20-one, a novel and potent G6PD inhibitor, decreased HSCs in bone marrow, blood, and lungs of hypoxic mice and reduced α-agonist-induced contraction of the pulmonary artery and established hypoxia-induced PH. We did not observe CD133+ cells around the pulmonary arteries in the lungs of chronically hypoxic G6PD-deficient mice. Furthermore, knockdown of G6PD and inhibition of G6PD activity: 1) downregulated canonical and noncanonical Wnt and Fzd receptors genes; 2) upregulated Bmpr1a; 3) decreased Cxcl12, and 4) reduced HSC (CD117+ and CD133+) numbers. In all, our findings demonstrate unexpected function for bone marrow-derived HSCs in augmenting α-adrenergic receptor-mediated contraction of pulmonary arteries and remodeling of pulmonary arteries that contribute to increase pulmonary vascular resistance in PAH patients and hypoxic mice and suggest that G6PD, by regulating expression of genes in the WNT and BMPR signaling, contributed to increase and release of HSCs from the bone marrow in response to hypoxic stimuli.

Role of IP3 Receptors in Shaping the Carotid Chemoreceptor Response to Hypoxia But Not to Hypercapnia in the Rat Carotid Body: An Evidence Review.

This article addresses the disparity in the transduction pathways for hypoxic and hypercapnic stimuli in carotid body glomus cells. We investigated and reviewed the experimental evidence showing that the response to hypoxia, but not to hypercapnia, is mediated by 1,4,5-inositol triphosphate receptors (IP3R/s) regulating the intracellular calcium content [Ca2+]c in glomus cells. The rationale was based on the past observations that inhibition of oxidative phosphorylation leads to the explicit inhibition of the hypoxic chemoreflex. [Ca2+]c changes were measured using cellular Ca2+-sensitive fluorescent probes, and carotid sinus nerve (CSN) sensory discharge was recorded with bipolar electrodes in in vitro perfused-superfused rat carotid body preparations. The cell-permeant, 2-amino-ethoxy-diphenyl-borate (2-APB; 100μM) and curcumin (50μM) were used as the inhibitors of IP3R/s. These agents suppressed the [Ca2+]c, and CSN discharge increases in hypoxia but not in hypercapnia, leading to the conclusion that only the hypoxic effects were mediated via modulation of IP3R/s. The ATP-induced Ca2+ release from intracellular stores in a Ca2+-free medium was blocked with 2-APB, supporting this conclusion.

Effects of strength training under hypoxic conditions on muscle performance, body composition and haematological variables.

The addition of a hypoxic stimulus during resistance training is suggested to increase the metabolic responses, enhancing hypertrophy and muscle strength. The purpose of this study was to investigate the effects of resistance training performed at submaximal intensities combined with normobaric hypoxia on muscular performance, body composition and haematological parameters. Thirty-two untrained subjects participated in this study (weight: 74.68±12.89 kg; height: 175±0.08 cm; BMI: 24.28±3.80 kg/m2). They were randomized to two groups: hypoxia (FiO2 = 13%) or normoxia (FiO2 = 20.9%). The training programme lasted 7 weeks (3 d/w) and several muscle groups were exercised (3 sets x 65−80% 1RM to failure). Measurements were taken before, after the training and after a 3-week detraining period. Body composition and muscle mass were assessed through skinfolds and muscle girths. Muscle strength was evaluated by the 1RM estimated test. Finally, haemoglobin and haematocrit were taken from the antecubital vein. Both groups improved their strength performance and muscle perimeters, but the hypoxia group obtained a greater increase in muscle mass (hypoxia: +1.80% vs. normoxia: +0.38%; p<0.05) and decrease in fat mass (hypoxia: -6.83% vs. normoxia: +1.26%; p<0.05) compared to the normoxia group. Additionally, haematocrit values were also higher for the hypoxia group after the detraining period (hypoxia: +2.20% vs. normoxia: -2.22%; p<0.05). In conclusion, resistance training under hypoxic conditions could increase muscle mass and decrease fat mass more effectively than training performed in normoxia, but without contributing to greater muscle strength.

Isometric Exercise with Large Muscle Mass Improves Redox Balance and Blood Pressure in Hypertensive Adults.

The aim of this study was to investigate the hemodynamic, oxidative stress (OS), and nitric oxide (NO) responses to a submaximal isometric exercise session (IES) involving large muscle mass. Fourteen hypertensive (HTG: age = 35.9 ± 8.1 yr, height = 1.73 ± 0.10 m, total body mass = 78.0 ± 15.8 kg) and 10 normotensive (NTG: age = 41.1 ± 9.4 yr, height = 1.71 ± 0.12 m, total body mass = 82.3 ± 22.4 kg) participants performed two experimental sessions in the leg press and bench press: (i) control session and (ii) 8 sets × 1 min contraction at 30% maximal voluntary isometric contraction with 2-min rest interval. Blood pressure (BP) was measured at rest and during 60 min postexercise. Blood samples were collected at rest, immediately after the session, and 60 min postexercise. NO was obtained through the Griess reaction method. OS parameters were analyzed using commercial kits. A repeated-measures ANOVA with Bonferroni post hoc test was used to analyze all dependent variables. A significant decrease in systolic BP was observed only for HTG at 45 and 60 min postexercise (baseline vs 45 min: P = 0.03, Δ% = 4.44%; vs 60 min: P = 0.018, Δ% = 5.58%). NO increased immediately postexercise only for HTG (P = 0.008, Δ% = 16.44%). Regarding OS parameters, thiobarbituric acid reactive substances presented a significant reduction 60 min after the IES for NTG and HTG; catalase increased in both groups. The data showed that only 8 min of IES with a large muscle mass elicits an elevated pro-oxidant activity leading to a greater NO bioavailability, increases antioxidant reaction, and consequently reduces BP in hypertensive patients.

MicroRNA-146a protects against myocardial ischaemia reperfusion injury by targeting Med1

BackgroundMyocardial ischaemia reperfusion injury (MIRI) is a difficult problem in clinical practice, and it may involve various microRNAs. This study investigated the role that endogenous microRNA-146a plays in myocardial ischaemia reperfusion and explored the possible target genes.MethodsMIRI models were established in microRNA-146a deficient (KO) and wild type (WT) mice. MicroRNA-146a expression was evaluated in the myocardium of WT mice after reperfusion. The heart function, area of myocardium infarction and in situ apoptosis were compared between the KO and WT mice. Microarray was used to explore possible target genes of microRNA-146a, while qRT-PCR and dual luciferase reporter assays were used for verification. Western blotting was performed to detect the expression levels of the target gene and related signalling molecules. A rescue study was used for further testing.ResultsMicroRNA-146a was upregulated 1 h after reperfusion. MicroRNA-146a deficiency decreased heart function and increased myocardial infarction and apoptosis. Microarray detected 19 apoptosis genes upregulated in the KO mice compared with the WT mice. qRT-PCR and dual luciferase verified that Med1 was one target gene of microRNA-146a. TRAP220, encoded by Med1 in the KO mice, was upregulated, accompanied by an amplified ratio of Bax/Bcl2 and increased cleaved caspase-3. Inhibition of microRNA-146a in H9C2 cells caused increased TRAP220 expression and more apoptosis under the stimulus of hypoxia and re-oxygenation, while knockdown of the increased TRAP220 expression led to decreased cell apoptosis.ConclusionsMicroRNA-146a exerts a protective effect against MIRI, which might be partially mediated by the target gene Med1 and related to the apoptosis signalling pathway.