N-acetylcysteine treatment prevents the up-regulation of MnSOD in chronically hypoxic rat hearts

HIF-1α limits myocardial infarction by promoting mitophagy in mouse hearts adapted to chronic hypoxia

AIM

The transcriptional factor HIF-1α is recognized for its contribution to cardioprotection against acute ischemia/reperfusion injury. Adaptation to chronic hypoxia (CH) is known to stabilize HIF-1α and increase myocardial ischemic tolerance. However, the precise role of HIF-1α in mediating the protective effect remains incompletely understood.

METHODS

Male wild-type (WT) mice and mice with partial Hif1a deficiency (hif1a +/-) were exposed to CH for 4 weeks, while their respective controls were kept under normoxic conditions. Subsequently, their isolated perfused hearts were subjected to ischemia/reperfusion to determine infarct size, while RNA-sequencing of isolated cardiomyocytes was performed. Mitochondrial respiration was measured to evaluate mitochondrial function, and western blots were performed to assess mitophagy.

RESULTS

We demonstrated enhanced ischemic tolerance in WT mice induced by adaptation to CH compared with their normoxic controls and chronically hypoxic hif1a +/- mice. Through cardiomyocyte bulk mRNA sequencing analysis, we unveiled significant reprogramming of cardiomyocytes induced by CH emphasizing mitochondrial processes. CH reduced mitochondrial content and respiration and altered mitochondrial ultrastructure. Notably, the reduced mitochondrial content correlated with enhanced autophagosome formation exclusively in chronically hypoxic WT mice, supported by an increase in the LC3-II/LC3-I ratio, expression of PINK1, and degradation of SQSTM1/p62. Furthermore, pretreatment with the mitochondrial division inhibitor (mdivi-1) abolished the infarct size-limiting effect of CH in WT mice, highlighting the key role of mitophagy in CH-induced cardioprotection.

CONCLUSION

These findings provide new insights into the contribution of HIF-1α to cardiomyocyte survival during acute ischemia/reperfusion injury by activating the selective autophagy pathway.

The effect of adaptation to hypoxia on cardiac tolerance to ischemia/reperfusion

The acute myocardial infarction (AMI) and sudden cardiac death (SCD), both associated with acute cardiac ischemia, are one of the leading causes of adult death in economically developed countries. The development of new approaches for the treatment and prevention of AMI and SCD remains the highest priority for medicine. A study on the cardiovascular effects of chronic hypoxia (CH) may contribute to the development of these methods. Chronic hypoxia exerts both positive and adverse effects. The positive effects are the infarct-reducing, vasoprotective, and antiarrhythmic effects, which can lead to the improvement of cardiac contractility in reperfusion. The adverse effects are pulmonary hypertension and right ventricular hypertrophy. This review presents a comprehensive overview of how CH enhances cardiac tolerance to ischemia/reperfusion. It is an in-depth analysis of the published data on the underlying mechanisms, which can lead to future development of the cardioprotective effect of CH. A better understanding of the CH-activated protective signaling pathways may contribute to new therapeutic approaches in an increase of cardiac tolerance to ischemia/reperfusion.

Nitration of MnSOD in the Carotid Body and Adrenal Gland Induced by Chronic Intermittent Hypoxia

Chronic intermittent hypoxia (CIH), main feature of obstructive sleep apnea, produces nitro-oxidative stress, which contributes to potentiate carotid body (CB) chemosensory discharges and sympathetic-adrenal-axis activity, leading to hypertension. The MnSOD enzymatic activity, a key enzyme on oxidative stress control, is reduced by superoxide-induced nitration. However, the effects of CIH-induced nitration on MnSOD enzymatic activity in the CB and adrenal gland are not known. We studied the effects of CIH on MnSOD protein and immunoreactive (MnSOD-ir) levels in the CB, adrenal gland and superior cervical ganglion (SCG), and on 3-nitrotyrosine (3-NT-ir), CuZnSOD (CuZnSOD-ir), MnSOD nitration, and its enzymatic activity in the CB and adrenal gland from male Sprague-Dawley rats exposed to CIH for 7 days. CIH increased 3-NT-ir in CB and adrenal gland, whereas MnSOD-ir increased in the CB and in adrenal cortex, but not in the whole adrenal medulla or SCG. CIH nitrated MnSOD in the CB and adrenal medulla, but its activity decreased in the adrenal gland. CuZnSOD-ir remained unchanged in both tissues. All changes observed were prevented by ascorbic acid treatment. Present results show that CIH for 7 days produced MnSOD nitration, but failed to reduce its activity in the CB, because of the increased protein level.

Reactive Oxygen Species as Intracellular Signaling Molecules in the Cardiovascular System

BACKGROUND

Redox signaling plays an important role in the lives of cells. This signaling not only becomes apparent in pathologies but is also thought to be involved in maintaining physiological homeostasis. Reactive Oxygen Species (ROS) can activate protein kinases: CaMKII, PKG, PKA, ERK, PI3K, Akt, PKC, PDK, JNK, p38. It is unclear whether it is a direct interaction of ROS with these kinases or whether their activation is a consequence of inhibition of phosphatases. ROS have a biphasic effect on the transport of Ca2+ in the cell: on one hand, they activate the sarcoplasmic reticulum Ca2+-ATPase, which can reduce the level of Ca2+ in the cell, and on the other hand, they can inactivate Ca2+-ATPase of the plasma membrane and open the cation channels TRPM2, which promote Ca2+-loading and subsequent apoptosis. ROS inhibit the enzyme PHD2, which leads to the stabilization of HIF-α and the formation of the active transcription factor HIF.

CONCLUSION

Activation of STAT3 and STAT5, induced by cytokines or growth factors, may include activation of NADPH oxidase and enhancement of ROS production. Normal physiological production of ROS under the action of cytokines activates the JAK/STAT while excessive ROS production leads to their inhibition. ROS cause the activation of the transcription factor NF-κB. Physiological levels of ROS control cell proliferation and angiogenesis. ROS signaling is also involved in beneficial adaptations to survive ischemia and hypoxia, while further increases in ROS can trigger programmed cell death by the mechanism of apoptosis or autophagy. ROS formation in the myocardium can be reduced by moderate exercise.

Enhancement of Glucose Metabolism via PGC-1α Participates in the Cardioprotection of Chronic Intermittent Hypobaric Hypoxia

Background and Aims: Previous studies demonstrated that energy metabolism disturbance impairs cardiac function and chronic intermittent hypobaric hypoxia (CIHH) protects heart against ischemia/reperfusion injury. The present study aimed to test the hypothesis that CIHH protects the heart against ischemia/reperfusion (I/R) injury via improvement of cardiac glucose metabolism.

Methods: Male Sprague-Dawley rats received CIHH treatment simulating 5000-m altitude for 28 days, 6 h per day in a hypobaric chamber or no treatment (control). Body weight, fasting blood glucose, blood lipid and glucose tolerance were measured. The left ventricular function of isolated hearts was evaluated during 30 min of ischemia and 60 min of reperfusion using Langendorff method. The mRNA and protein expression involved in cardiac energy metabolism was determined using quantitative PCR and Western blot techniques.

Results: 1. There was no difference of body weight, fast blood glucose, blood lipid and glucose tolerance between control and CIHH rats under baseline condition (p > 0.05). 2. The recovery of left ventricular function after I/R was improved significantly in CIHH rats compared to control rats (p < 0.05). 3. The expression of cardiac GLUT4 and PGC-1α was increased but PDK4 gene expression was decreased by CIHH treatment at both mRNA and protein level. Also p-AMPK/AMPK ratio was increased in CIHH rats (p < 0.05).

Conclusion: CIHH ameliorates I/R injury through improving cardiac glucose metabolism via upregulation of GLUT4, p-AMPK, and PGC-1α expressions, but downregulation of cardiacPDK4 expression.

Cardioprotective adaptation of rats to intermittent hypobaric hypoxia is accompanied by the increased association of hexokinase with mitochondria

Chronic hypoxia increases the myocardial resistance to acute ischemia-reperfusion injury by affecting the mitochondrial redox balance. Hexokinase (HK) bears a high potential to suppress the excessive formation of reactive oxygen species because of its increased association with mitochondria, thereby inhibiting the membrane permeability transition pore opening and preventing cell death. The purpose of this study was to determine the effect of severe intermittent hypobaric hypoxia (7,000 m, 8 h/day, 5 wk) on the function and colocalization of HK isoforms with mitochondria in the left (LV) and right ventricles of rat myocardium. The real-time RT-PCR, Western blot, enzyme coupled assay, and quantitative immunofluorescence techniques were used. Our results showed significantly elevated expression of HK isoforms (HK1 and HK2) in the hypoxic LV. In addition, intermittent hypoxia increased the total HK activity and the association of HK isoforms with mitochondria in both ventricles. These findings suggest that HK may contribute to the cardioprotective phenotype induced by adaptation to severe intermittent hypobaric hypoxia.

Cardioprotective and nonprotective regimens of chronic hypoxia diversely affect the myocardial antioxidant systems

It has been documented that adaptation to hypoxia increases myocardial tolerance to ischemia-reperfusion (I/R) injury depending on the regimen of adaptation. Reactive oxygen species (ROS) formed during hypoxia play an important role in the induction of protective cardiac phenotype. On the other hand, the excess of ROS can contribute to tissue damage caused by I/R. Here we investigated the relationship between myocardial tolerance to I/R injury and transcription activity of major antioxidant genes, transcription factors, and oxidative stress in three different regimens of chronic hypoxia. Adult male Wistar rats were exposed to continuous normobaric hypoxia (FiO2 0.1) either continuously (CNH) or intermittently for 8 h/day (INH8) or 23 h/day (INH23) for 3 wk period. A control group was kept in room air. Myocardial infarct size was assessed in anesthetized open-chest animals subjected to 20 min coronary artery occlusion and 3 h reperfusion. Levels of mRNA transcripts and the ratio of reduced and oxidized glutathione (GSH/GSSG) were analyzed by real-time RT-PCR and by liquid chromatography, respectively. Whereas CNH as well as INH8 decreased infarct size, 1 h daily reoxygenation (INH23) abolished the cardioprotective effect and decreased GSH/GSSG ratio. The majority of mRNAs of antioxidant genes related to mitochondrial antioxidant defense (manganese superoxide dismutase, glutathione reductase, thioredoxin/thioredoxin reductase, and peroxiredoxin 2) were upregulated in both cardioprotective regimens (CNH, INH8). In contrast, INH23 increased only PRX5, which was not sufficient to induce the cardioprotective phenotype. Our results suggest that the increased mitochondrial antioxidant defense plays an important role in cardioprotection afforded by chronic hypoxia.

Tumour necrosis factor-α contributes to improved cardiac ischaemic tolerance in rats adapted to chronic continuous hypoxia

AIM

It has been demonstrated that tumour necrosis factor-alpha (TNF-α) via its receptor 2 (TNFR2) plays a role in the cardioprotective effects of preconditioning. It is also well known that chronic hypoxia is associated with activation of inflammatory response. With this background, we hypothesized that TNF-α signalling may contribute to the improved ischaemic tolerance of chronically hypoxic hearts.

METHODS

Adult male Wistar rats were kept either at room air (normoxic controls) or at continuous normobaric hypoxia (CNH; inspired O2 fraction 0.1) for 3 weeks; subgroups of animals were treated with infliximab (monoclonal antibody against TNF-α; 5 mg kg(-1), i.p., once a week). Myocardial levels of oxidative stress markers and the expression of selected signalling molecules were analysed. Infarct size (tetrazolium staining) was assessed in open-chest rats subjected to acute coronary artery occlusion/reperfusion.

RESULTS

CNH increased myocardial TNF-α level and expression of TNFR2; this response was abolished by infliximab treatment. CNH reduced myocardial infarct size from 50.8 ± 4.3% of the area at risk in normoxic animals to 35.5 ± 2.4%. Infliximab abolished the protective effect of CNH (44.9 ± 2.0%). CNH increased the levels of oxidative stress markers (3-nitrotyrosine and malondialdehyde), the expression of nuclear factor κB and manganese superoxide dismutase, while these effects were absent in infliximab-treated animals. CNH-elevated levels of inducible nitric oxide synthase and cyclooxygenase 2 were not affected by infliximab.

CONCLUSION

TNF-α plays a role in the induction of ischaemia-resistant cardiac phenotype of CNH rats, possibly via the activation of protective redox signalling.

Ω3 Supplementation and intermittent hypobaric hypoxia induce cardioprotection enhancing antioxidant mechanisms in adult rats

Intermittent hypobaric hypoxia (IH) is linked with oxidative stress, impairing cardiac function. However, early IH also activate cardio-protective mechanisms. Omega 3 fatty acids (Ω3) induce cardioprotection by reducing infarct size and reinforcing antioxidant defenses. The aim of this work was to determine the combined effects of IH and Ω3 on cardiac function; oxidative balance and inflammatory state. Twenty-eight rats were randomly divided into four groups: normobaric normoxia (N); N + Ω3 (0.3 g·kg⁻¹·day⁻¹); IH; and IH + Ω3. IH was induced by 4 intercalate periods of hypoxia (4 days)—normoxia (4 days) in a hypobaric chamber during 32 days. At the end of the exposure, hearts were mounted in a Langendorff system and subjected to 30 min of ischemia followed by 120 min of reperfusion. In addition, we determined HIF-1α and ATP levels, as well as oxidative stress by malondialdehyde and nitrotyrosine quantification. Further, the expression of the antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase was determined. NF-kappaB and myeloperoxidase levels were assessed in the hearts. Relative to N hearts, IH improved left ventricular function (Left ventricular developed pressure: N; 21.8 ± 3.4 vs. IH; 42.8 ± 7.1 mmHg; p < 0.05); reduced oxidative stress (Malondialdehyde: N; 14.4 ± 1.8 vs. IH; 7.3 ± 2.1 μmol/mg prot.; p < 0.05); and increased antioxidant enzymes expression. Supplementation with Ω3 induces similar responses as IH group. Our findings suggest that both, IH and Ω3 in an independent manner, induce functional improvement by antioxidant and anti-inflammatory mechanisms, establishing cardio-protection.

Resveratrol alleviates lung ischemia and reperfusion-induced pulmonary capillary injury through modulating pulmonary mitochondrial metabolism

OBJECTIVE

Lung ischemia and reperfusion (I/R) injury is one of the major causes of postoperative pulmonary dysfunction after cardiopulmonary surgery and thoracic organ transplantation. Recent studies suggest that lung I/R injury may be associated with defects in pulmonary mitochondrial function, in addition to damage from reactive oxygen species. In this study, we examined effects of one lung I/R injury on the other lung, and the protective efficacy of resveratrol on mitochondrial biogenesis in lungs.

METHODS

Studies were performed in male Sprague-Dawley rats in 3 groups: sham-operated, lung I/R injury, and treated with resveratrol before lung I/R injury (20 mg/kg/d, orally). Lung ischemia was established by occluding the lung left hilum for 60 minutes, followed by releasing the occlusion and closing the chest. Four days after ischemia, we assessed the lung water content and protein concentration in lung lavage of the nonischemic lung; lung inflammation and pulmonary oxidative stress were assessed by leukocyte counts and tissue content of malondialdehyde (MDA), respectively. The level of mitochondrial biogenesis was determined according to PGC1-α mRNA expression.

RESULTS

The left lung I/R injury significantly suppressed right lung PGC1-α mRNA expression, increasing pulmonary oxidative stress, lung water content, and lavage leukocyte count and protein concentration (P < .05). Resveratrol treatment attenuated lung injury as well as increasing PGC1-α mRNA expression.

CONCLUSIONS

Resveratrol treatment protects lung against I/R injury through improving mitochondrial biogenesis and reducing oxidative stress and leukocyte infiltration.

Fatty acid synthase inhibitors induce apoptosis in non-tumorigenic melan-a cells associated with inhibition of mitochondrial respiration

The metabolic enzyme fatty acid synthase (FASN) is responsible for the endogenous synthesis of palmitate, a saturated long-chain fatty acid. In contrast to most normal tissues, a variety of human cancers overexpress FASN. One such cancer is cutaneous melanoma, in which the level of FASN expression is associated with tumor invasion and poor prognosis. We previously reported that two FASN inhibitors, cerulenin and orlistat, induce apoptosis in B16-F10 mouse melanoma cells via the intrinsic apoptosis pathway. Here, we investigated the effects of these inhibitors on non-tumorigenic melan-a cells. Cerulenin and orlistat treatments were found to induce apoptosis and decrease cell proliferation, in addition to inducing the release of mitochondrial cytochrome c and activating caspases-9 and -3. Transfection with FASN siRNA did not result in apoptosis. Mass spectrometry analysis demonstrated that treatment with the FASN inhibitors did not alter either the mitochondrial free fatty acid content or composition. This result suggests that cerulenin- and orlistat-induced apoptosis events are independent of FASN inhibition. Analysis of the energy-linked functions of melan-a mitochondria demonstrated the inhibition of respiration, followed by a significant decrease in mitochondrial membrane potential (ΔΨm) and the stimulation of superoxide anion generation. The inhibition of NADH-linked substrate oxidation was approximately 40% and 61% for cerulenin and orlistat treatments, respectively, and the inhibition of succinate oxidation was approximately 46% and 52%, respectively. In contrast, no significant inhibition occurred when respiration was supported by the complex IV substrate N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD). The protection conferred by the free radical scavenger N-acetyl-cysteine indicates that the FASN inhibitors induced apoptosis through an oxidative stress-associated mechanism. In combination, the present results demonstrate that cerulenin and orlistat induce apoptosis in non-tumorigenic cells via mitochondrial dysfunction, independent of FASN inhibition.

Modulation of cardiac mitochondrial permeability transition and apoptotic signaling by endurance training and intermittent hypobaric hypoxia

BACKGROUND

Modulation of the mitochondrial permeability transition pore (MPTP) and inhibition of the apoptotic signaling are critically associated with the cardioprotective phenotypes afforded by both intermittent hypobaric-hypoxia (IHH) and endurance-training (ET). We recently proposed that IHH and ET improve cardiac function and basic mitochondrial capacity, although without showing addictive effects. Here we investigate whether a combination of IHH and ET alters cardiac mitochondrial vulnerability to MPTP and related apoptotic signaling.

METHODS

Male Wistar rats were divided into normoxic-sedentary (NS), normoxic-exercised (NE, 1h/day/5 week treadmill-running), hypoxic-sedentary (HS, 6000 m, 5h/day/5 weeks) and hypoxic-exercised (HE) to study susceptibility to calcium-induced cardiac MPTP opening. Mitochondrial cyclophilin D (CypD), adenine nucleotide translocator (ANT), Bax and Bcl-2 protein contents were semi-quantified by Western blotting. Cardiac caspase 3-, 8- and 9-like activities were measured. Mitochondrial aconitase and superoxide dismutase (MnSOD) activity and malondialdehyde (MDA) and sulphydryl group (-SH) content were determined.

RESULTS

Susceptibility to MPTP decreased in NE and HS vs. NS and even further in HE. The ANT content increased in HE vs. NS. Bcl-2/Bax ratio increased in NE and HS compared to NS. Decreased activities in tissue caspase 3-like (HE vs. NS) and caspase 9-like (HS and HE vs. NS) were observed. Mitochondrial aconitase increased in NE and HS vs. NS. No alterations between groups were observed for caspase 8-like activity, MnSOD, CypD, MDA and -SH.

CONCLUSIONS

Data confirm that IHH and ET modulate cardiac mitochondria to a protective phenotype characterized by decreased MPTP induction and apoptotic signaling, although without visible addictive effects as initially hypothesized.

Normobaric, intermittent hypoxia conditioning is cardio- and vasoprotective in rats

Favorable versus detrimental cardiovascular responses to intermittent hypoxia conditioning (IHC) are heavily dependent on experimental or pathological conditions, including the duration, frequency and intensity of the hypoxia exposures. Recently, we demonstrated that a program of moderate, normobaric IHC (FIO2 9.5-10% for 5-10 min/cycle, with intervening 4 min normoxia, 5-8 cycles/day for 20 days) in dogs afforded robust cardioprotection against infarction and arrhythmias induced by coronary artery occlusion-reperfusion, but this protection has not been verified in other species. Accordingly, in this investigation cardio- as well as vasoprotection were examined in male Wistar rats completing the normobaric IHC program or a sham program in which the rats continuously breathed atmospheric air. Myocardial ischemia and reperfusion (IR) was imposed by occlusion and reperfusion of the left anterior descending coronary artery in in situ experiments and by subjecting isolated, perfused hearts to global ischemia-reperfusion. Cardiac arrhythmias and myocardial infarct size were quantified in in situ experiments. Endothelial function was evaluated from the relaxation to acetylcholine of norepinephrine-precontracted aortic rings taken from in situ IR experiments, and from the increase in coronary flow produced by acetylcholine in isolated hearts. IHC sharply reduced cardiac arrhythmias during ischemia and decreased infarct size by 43% following IR. Endothelial dysfunction in aorta was marked after IR in sham rats, but not significant in IHC rats. Similar findings were found for the coronary circulations of isolated hearts. These findings support the hypothesis that moderate, normobaric IHC is cardio- and vasoprotective in a rat model of IR.

Computational classification of mitochondrial shapes reflects stress and redox state

Dynamic variations in mitochondrial shape have been related to function. However, tools to automatically classify and enumerate mitochondrial shapes are lacking, as are systematic studies exploring the relationship of such shapes to mitochondrial stress. Here we show that during increased generation of mitochondrial reactive oxygen species (mtROS), mitochondria change their shape from tubular to donut or blob forms, which can be computationally quantified. Imaging of cells treated with rotenone or antimycin, showed time and dose-dependent conversion of tubular forms to donut-shaped mitochondria followed by appearance of blob forms. Time-lapse images showed reversible transitions from tubular to donut shapes and unidirectional transitions between donut and blob shapes. Blobs were the predominant sources of mtROS and appeared to be related to mitochondrial-calcium influx. Mitochondrial shape change could be prevented by either pretreatment with antioxidants like N-acetyl cysteine or inhibition of the mitochondrial calcium uniporter. This work represents a novel approach towards relating mitochondrial shape to function, through integration of cellular markers and a novel shape classification algorithm.

Gene expression profile of hepatopancreas from grass shrimp Palaemonetes pugio exposed to cyclic hypoxia

Estuarine organisms often experience periods of cyclic hypoxia characterized by hypoxia in the early morning and normoxia in the afternoon. Here we examine the genomic responses of grass shrimp, Palaemonetes pugio, exposed to cyclic hypoxia in the laboratory. Differentially expressed genes in the hepatopancreas were determined in cyclic hypoxic vs. normoxic control groups after 1, 2, 5 and 10 days of exposure to cyclic hypoxia using microarrays printed with 661 annotated transcripts obtained from multiple EST (expressed sequence tag) libraries. Sampling on each day was conducted at two different time series, one in the morning (representing low concentration of dissolved oxygen (DO), designated C-AM) and one in the afternoon (representing high DO concentration, designated C-PM). Distinct differences were observed between the number and identity of specific genes that were significantly down- or up-regulated in shrimp collected at the low DO and high DO points of the cyclic DO cycle. However, cluster analysis showed that the overall response patterns of high (C-PM) and low DO (C-AM) exposures were in the same cluster at 1, 2, and 5 days. In contrast, the response patterns on different days were in different clusters. Day 1 was characterized by up-regulation of 17 unknown genes in the morning and a transient down-regulation of several hemocyanin genes, which returned to normoxic control levels in the afternoon. Days 2 and 5 showed significant down-regulation of 10 (C-AM) and 15 (C-PM) unknown genes, respectively. On day 10 the high DO samples showed a dramatic increase in the number of up-regulated genes, including several distinct hemocyanin genes, and this profile did not cluster with any of the other treatment groups. Vitellogenin, cathepsin L, cytochrome c oxidase subunit III, and fatty acid binding protein 10 were the signature down-regulated genes at day 10 (C-AM). According to GO annotation, the most abundant group of genes for both cyclic low (C-AM) and high (C-PM) DO exposure was associated with transport, defense response, and metabolic process. The differentially expressed genes were mapped to KEGG metabolic and regulatory pathways according to the gene distribution in Drosophila pathway database. Cyclic high (C-PM) DO affected a broad range of pathways compared to cyclic low (C-AM) DO.