低氧预适应的脑机制

A concept ot tissue adaptation to hypoxia( i.e. hypoxic preconditioning) was developed and its corresponding animal models were reproduced in 1966s. The methods of model reproduction in rat, rabbit, and mouse in particular and the main results are brifly introduced in this review. The tolerance to hypoxia o{ preconditioned animals is significantly increased. Regular changes in animals‘ behavior, neurophysiology, respiratory and circulatory physiology, neuromorphology in vivo and {unction of brain and spinal cord in vitro are briefly demonstrated. The protective effects in vivo and in vitro of homogenate extract taken from the brain o{ preconditioned animals, neurochemcals and molecular neurobiolcgical alterations are briefly presented. The essence and significance of tissue adaption to hypoxia/hypoxic preconditioning are discussed in the review in terms of evolution and practical implication.     

Fasting promotes acute hypoxic adaptation by suppressing mTOR-mediated pathways

Rapid adaptation to a hypoxic environment is an unanswered question that we are committed to exploring. At present, there is no suitable strategy to achieve rapid hypoxic adaptation. Here, we demonstrate that fasting preconditioning for 72 h reduces tissue injuries and maintains cardiac function, consequently significantly improving the survival rates of rats under extreme hypoxia, and this strategy can be used for rapid hypoxic adaptation. Mechanistically, fasting reduces blood glucose and further suppresses tissue mTOR activity. On the one hand, fasting-induced mTOR inhibition reduces unnecessary ATP consumption and increases ATP reserves under acute hypoxia as a result of decreased protein synthesis and lipogenesis; on the other hand, fasting-induced mTOR inhibition improves mitochondrial oxygen utilization efficiency to ensure ATP production under acute hypoxia, which is due to the significant decrease in ROS generation induced by enhanced mitophagy. Our findings highlight the important role of mTOR in acute hypoxic adaptation, and targeted regulation of mTOR could be a new strategy to improve acute hypoxic tolerance in the body.Subject terms: Autophagy, Metabolism     

Phosphoproteome profiling of substantia nigra and cortex regions of Alzheimer's disease patients

The induction of ischemic tolerance by preconditioning provides a platform to elucidate endogenous mechanisms of stroke protection. In these studies, we characterize the relationship between hypoxia‐inducible factor (HIF), sphingosine kinase 2 (SphK2), and chemokine (C–C motif) ligand 2 (CCL2) in models of hypoxic or pharmacological preconditioning‐induced ischemic tolerance. A genetics‐based approach using SphK2‐ and CCL2‐null mice showed both SphK2 and CCL2 to be necessary for the induction of ischemic tolerance following preconditioning with hypoxia, the hypoxia‐mimetic cobalt chloride, or the sphingosine‐1‐phosphate (S1P) agonist FTY720. A pharmacological approach confirmed the necessity of HIF signaling for all three preconditioning stimuli, and showed that the SphK/S1P pathway transduces tolerance via the S1P₁ receptor. In addition, our data suggest significant cross‐talk between HIF and SphK2‐produced S1P signaling, which together act to up‐regulate CCL2 expression. Overall, HIF, SphK, S1P, and CCL2 participate in a signaling cascade to induce the gene expression responsible for the stroke‐tolerant phenotype established by hypoxic and FTY720 preconditioning. The identification of these common molecular mediators involved in signaling the genomic response to multiple preconditioning stimuli provides several targets for therapeutic manipulation.     

间歇性低氧适应的心脏保护

间歇性低氧（intermittent hypoxia,IH）是指一定时间间断地暴露于低氧环境,而其余时间处于常氧环境。IH是机体某种生理和病理状态下的低氧形式。研究表明：间歇性低氧适应（IHadaptation）,类似缺血预适应（ischemic preconditioning,IPC）和长期高原低氧适应（long-termhigh-altitude hypoxic adaptation,LHA）,具有明显的心脏保护作用,表现为增强心肌对缺血／再灌注损伤的耐受性、限制心肌梗死面积和形态学改变、抗细胞凋亡、促进缺血／再灌注心脏舒缩功能的恢复,以及抗心律失常。尽管IH对心脏的保护作用不容质疑,但其作用机制远未阐明。IH心脏保护作用可能涉及氧的运输、能量代谢、神经体液调节、抗氧化酶、应激蛋白、腺苷系统、ATP敏感钾通道、线粒体及其钙调控、一氧化氮和蛋白激酶等多方面机制,并受低氧处理方式、动物年龄和性别等因素影响。IH心脏保护持续时间明显长于IPC,而对机体的不良影响远小于LHA,具有潜在的应用价值。     

Changes of adenosine and its A(1) receptor in hypoxic preconditioning.

Effects of hypoxic preconditioning on adenosine (ADO) and its A(1) receptor were studied in Kunming mice. The ADO content and its metabolites in the brain were measured by a specific enzymatic method; a radioligand binding method was used to study the ADO A(1) receptor. The ADO content of the hippocampus in group C (exposure to 4 runs of hypoxia) was markedly higher than that in group A (control, without exposure to hypoxia and B (exposure to 1 run of hypoxia), showing that the ADO content could be cumulatively increased in the hippocampus, which was more sensitive to ischemia and hypoxia, during acute and repeated exposure to hypoxia. A(1) receptor density in group C was significantly lower than in group A and no difference was seen between groups B and C; A(1) receptor affinity in the hippocampus, pons and medula oblongata in group C was significantly higher than in group A, implying that during hypoxic preconditioning there might be some mechanisms preventing A(1) receptor density from decreasing further and making A(1) receptor affinity increase in some brain regions. These results indicate that cumulatively increased ADO in the hippocampus via A(1) receptor may play a neuroprotective role in the CNS as an inhibitory neuromodulator and thus contribute to the formation and development of acute hypoxic adaptation or tolerance.     

The effect of preceding mild hypoxia on the alteration of acquisition and retention of the conditioned passive avoidance behavior caused by severe hypobaric hypoxia in rats

The purpose of this study was to determine whether mild hypobaric hypoxic preconditioning provides protection against learning deficit caused by subsequent more severe hypoxia insult. Learning was examined using a passive avoidance task. Three groups of Wistar male rats: the intact and exposed to either severe hypoxia (160 Torr, exposition 3 h) or mild hypobaric hypoxic preconditioning (360 Torr, exposition 2 h, repeated three or six times daily) followed by severe hypoxia, were included in this study. In experiment 1 a passive avoidance response was acquired in 15 min immediately after hypoxia. In experiment 2 rats were exposed to hypoxia in 60 min after the acquisition of passive avoidance response. The mild hypobaric hypoxic preconditioning significantly attenuated the hypoxia-induced learning deficit in rats in Experiments 1 and 2. In experiment 1 the mild hypobaric hypoxic preconditioning repeated six times was more effective in protection against learning deficit in hypoxia exposed rats than in the case of triple mild hypobaric hypoxic preconditioning. The amount of rats suffered irreversible respiratory arrest was also assessed in this study. It was found that 50% of rats exposed to severe hypoxia died in consequence of this pathology, whereas in rats preconditioned before the severe hypoxia only 15% died for this reason. The overall results indicate that the mild hypobaric hypoxic preconditioning significantly increases CNS resistance to severe hypoxia in rats.     

Adaptive effects of hypoxic preconditioning in brain neurons

A preventive short-term hypoxia (preconditioning) increases neuronal resistance against subsequent strong hypoxic effects. Literature review and authors' own data on molecular-cellular mechanisms of the hypoxic preconditioning, are presented. Participation of intracellular signal transduction, genome, stress-proteins, and neuromodulating peptides in this process, is discussed. The role of glutamatergic as well as calcium and phosphoinositide regulatory systems and neuromodulating factors as the components of a "volume" signal transmission are analyzed in hypoxic precondition-associated induction of functional tolerance mechanisms against acute harmful effects in neurones of olfactory slices.     

Priming adult stem cells by hypoxic pretreatments for applications in regenerative medicine

The efficiency of regenerative medicine can be ameliorated by improving the biological performances of stem cells before their transplantation. Several ex-vivo protocols of non-damaging cell hypoxia have been demonstrated to significantly increase survival, proliferation and post-engraftment differentiation potential of stem cells. The best results for priming cultured stem cells against a following, otherwise lethal, ischemic stress have been obtained with brief intermittent episodes of hypoxia, or anoxia, and reoxygenation in accordance with the extraordinary protection afforded by the conventional maneuver of ischemic preconditioning in severely ischemic organs. These protocols of hypoxic preconditioning can be rather easily reproduced in a laboratory; however, more suitable pharmacological interventions inducing stem cell responses similar to those activated in hypoxia are considered among the most promising solutions for future applications in cell therapy. Here we want to offer an up-to-date review of the molecular mechanisms translating hypoxia into beneficial events for regenerative medicine. To this aim the involvement of epigenetic modifications, microRNAs, and oxidative stress, mainly activated by hypoxia inducible factors, will be discussed. Stem cell adaptation to their natural hypoxic microenvironments (niche) in healthy and neoplastic tissues will be also considered.     

低氧预适应增强大鼠海马神经元的耐缺氧能力

本研究对整体大鼠进行了模拟不同海拔高度（3000、5000m）的低氧预适应,然后观察了急性致死性缺氧对这些大鼠海马脑片诱发群锋电位的影响。结果显示,经低氧预适应的大鼠其海马脑片在给予急性缺氧后,CA1区缺氧损伤电位（hypoxic injury potential,HIP）出现时间以及突触前排放（presynaptic volley,PV）消失时间均明显延迟;其中5000m预适应组的延迟程度比3000m组明显。复氧后,PV的恢复率在3000m和5000m低氧预适应组均明显高于对照组。本研究结果提示,整体动物的低氧预适应可以增强离体海马脑片神经元的耐缺氧能力。     

Hypoxic preconditioning-induced mitochondrial protection is not disrupted in a cell model of mtDNA T8993G mutation-induced F1F0-ATP synthase defect: the role of mitochondrial permeability transition

Transient opening of the mitochondrial permeability transition pore plays a crucial role in hypoxic preconditioning-induced protection. Recently, the cyclophilin-D component of the mitochondrial permeability transition pore has been shown to interact with and regulate the F1F0-ATP synthase. However, the precise role of the F1F0-ATP synthase and the interaction between cyclophilin-D and F1F0-ATP synthase in the mitochondrial permeability transition pore and hypoxic preconditioning remain uncertain. Here we found that a 1-h hypoxic preconditioning delayed apoptosis and improved cell survival after stimulation with various apoptotic inducers including H₂O₂, ionomycin, and arachidonic acid in mitochondrial DNA T8993G mutation (NARP) osteosarcoma 143B cybrids, an F1F0-ATP synthase defect cell model. This hypoxic preconditioning protected NARP cybrid cells against focal laser irradiation-induced oxidative stress by suppressing reactive oxygen species formation and preventing the depletion of cardiolipin. Furthermore, the protective functions of transient opening of the mitochondrial permeability transition pore in both NARP cybrids and wild-type 143B cells can be augmented by hypoxic preconditioning. Disruption of the interaction between cyclophilin-D and F1F0-ATP synthase by cyclosporin A attenuated the mitochondrial protection induced by hypoxic preconditioning in both NARP cybrids and wild-type 143B cells. Our results demonstrate that the interaction between cyclophilin-D and F1F0-ATP synthase is important in the hypoxic preconditioning-induced cell protection. This finding improves our understanding of the mechanism of mitochondrial permeability transition pore opening in cells in response to hypoxic preconditioning, and will be helpful in further developing new pharmacological agents targeting hypoxia–reoxygenation injury and mitochondria-mediated cell death     

Chronic and intermittent hypoxia induce different degrees of myocardial tolerance to hypoxia-induced dysfunction

Chronic hypoxia (CH) is believed to induce myocardial protection, but this is in contrast with clinical evidence. Here, we test the hypothesis that repeated brief reoxygenation episodes during prolonged CH improve myocardial tolerance to hypoxia-induced dysfunction. Male 5-week-old Sprague-Dawley rats (n = 7-9/group) were exposed for 2 weeks to CH (F(I)O(2) = 0.10), intermittent hypoxia (IH, same as CH, but 1 hr/day exposure to room air), or normoxia (N, F(I)O(2) = 0.21). Hearts were isolated, Langendorff perfused for 30 min with hypoxic medium (Krebs-Henseleit, PO(2) = 67 mmHg), and exposed to hyperoxia (PO(2) = 670 mm Hg). CH hearts displayed higher end-diastolic pressure, lower rate x pressure product, and higher vascular resistance than IH. During hypoxic perfusion, anaerobic mechanisms recruitment was similar in CH and IH hearts, but less than in N. Thus, despite differing only for 1 hr daily exposure to room air, CH and IH induced different responses in animal homeostasis, markers of oxidative stress, and myocardial tolerance to reoxygenation. We conclude that the protection in animals exposed to CH appears conferred by the hypoxic preconditioning due to the reoxygenation rather than by hypoxia per se.     

Molecular mechanisms of cardiac protection by adaptation to chronic hypoxia

Effective protection of the heart against ischemia/reperfusion injury is one of the most important goals of experimental and clinical research in cardiology. Besides ischemic preconditioning as a powerful temporal protective phenomenon, adaptation to chronic hypoxia also increases cardiac tolerance to all major deleterious consequences of acute oxygen deprivation such as myocardial infarction, contractile dysfunction and ventricular arrhythmias. Although many factors have been proposed to play a potential role, the detailed mechanism of this long-term protection remains poorly understood. This review summarizes current limited evidence for the involvement of ATP-sensitive potassium channels, reactive oxygen species, nitric oxide and various protein kinases in cardioprotective effects of chronic hypoxia.     

Hypoxic preconditioning improves spatial cognitive ability in mice

Although it has been reported in a lot of studies that hypoxic preconditioning could protect the brain from hypoxic/ischemic injury, it is not clear whether hypoxic preconditioning could affect brain functions such as cognitive ability. This work aims at investigating the effect of hypoxic preconditioning on spatial cognitive ability in mice after acute and repeated hypoxic exposures. The mice were randomly divided into 3 groups: a control group in which mice were not exposed to hypoxia (H0) and experimental groups in which mice encountered hypoxia either once (H1) or 4 times (H4). Neural cell adhesion molecule (NCAM) expression, long-term potentiation (LTP) recording and Morris water maze test were used to measure the animals' cognitive ability. The tolerance time was progressively prolonged as exposure went on. The expression of both NCAM mRNA and NCAM protein as well as the LTP induction rate decreased in group H1, but recovered to control level in group H4. The performance of mice in the maze test was improved in H4 in comparison with that in both H1 and H0. These findings may indicate that spatial cognitive ability is improved in adult mice by their hypoxic preconditioning.     

Role of excitatory amino acids in hypoxic preconditioning.

We examined the effects of the extrinsic ionotropic NMDA receptor agonist (aspartate) and antagonist (ketamine) on the hypoxic preconditioning of mice and the concentration changes of intrinsic excitatory amino acids (EAAs), aspartate and glutamate, in the whole brain and different brain regions during preconditioning by an HPLC method. Our results showed that aspartate and ketamine significantly prolonged and shortened the standard tolerance time of mice during preconditioning and survival time in hypobaric chambers, respectively. After the 1st exposure, EAA concentrations in the whole brain and brain regions were increased. After run 4, they were decreased or maintained. It is suggested that the activation and suppression of ionotropic NMDA receptors is harmful and beneficial to hypoxic preconditioning, respectively. Degradation and/or inactivation of EAAs might be beneficial to the tolerance of mice to hypoxia.     

Underlying mechanism of hypoxic preconditioning decreasing apoptosis induced by anoxia in cultured hippocampal neurons

It is known that hypoxic preconditioning (HP, a brief period of sublethal hypoxia) provides neuroprotection against subsequent severe anoxia, but the mechanisms of this increased tolerance have not been fully elucidated. A hypoxic preconditioning model was established by exposing a 4-day hippocampal culture to 1% O(2) for 20 min/day for 8 days. The preconditioning significantly decreased the number of apoptotic neurons at reoxygenation 24 h after 4 h of severe anoxia (0% O(2)). Further study demonstrated that the degradation of mitochondrial membrane potential (MMP) was greatly inhibited and the expression of B-cell lymphoma protein-2 (Bcl-2) was increased considerably after severe anoxia in the HP groups. These results indicate that the increased anoxic tolerance, which is induced by HP in cultured hippocampal cells, may be correlated with Bcl-2 overexpression and enhanced stability of MMP, which ultimately reduces apoptosis 24 h after reoxygenation.     

Protein binding of NADH on chemical preconditioning

Chemical preconditioning, an emerging neuroprotective strategy described in recent years, results in preserved energy metabolism during hypoxia via yet unknown mechanisms. The hypoxic increase of NADH content is attenuated by preconditioning. The goal of the present study was to investigate whether attenuation of the hypoxic NADH increase is due to a shift between free and protein-bound NADH. NADH in solution has a fluorescence maximum at 469.2 nm. In untreated mouse hippocampal slices, lambda(control onset) is 456.2 +/- 5.3 nm in CA1 (mean +/- SD; p < 0.01 vs. solution) and 454.6 +/- 6.1 nm in CA3 [p < 0.01 vs. solution, not significant (NS) to lambda(control onset) in CA1]. In slices prepared from animals pretreated in vivo with 20 mg/kg 3-nitropropionate, lambda(preconditioning onset) is 439.2 +/- 5.0 nm (p < 0.001 vs. control) in CA1 and 434.2 +/- 6.4 nm in CA3 (p < 0.001 vs. control; NS to lambda(preconditioning onset) in CA1). In controls, the fluorescence maximum shifts to lambda(control hypoxia) 458.2 +/- 1.3 nm in CA1 (NS vs. onset) and 456.0 +/- 3.6 nm in CA3 (NS vs. onset). On preconditioning with 3-nitropropionate, lambda(preconditioning hypoxia) shifts to 446.4 +/- 4.3 nm in CA1 (p < 0.03 vs. onset) and 438.6 +/- 6.9 nm in CA3 (p < 0.03 vs. onset). Posthypoxic decay of free and protein-bound NADH is diminished after preconditioning. We conclude that the free NADH level is reduced on an increase of hypoxic tolerance by chemical preconditioning. Reduction of free NADH content is maintained during hypoxia after preconditioning.     

缺氧诱导因子-1α在缺氧预处理预防心肌细胞损伤中的作用

本工作旨在研究缺氧预处理(hypoxic preconditioning,HPC)对于心肌细胞外信号调节激酶(extracellular signal-regulated proteinkinases,ERK)活性、缺氧诱导因子-1α(hypoxia-inducible factor-1α,HIF-1α)表达的影响,及其在缺氧复氧诱导心肌细胞损伤中的作用。通过在培养的SD乳鼠心肌细胞缺氧／复氧(H／R)模型上,观察HPC对于24h后H／R诱导心肌细胞损伤的影响,以台盼蓝排斥实验检测心肌细胞存活率、以TUNEL法检测细胞凋亡、并用荧光素染料Hoechst33258测定心肌细胞凋亡率：制备心肌细胞蛋白提取物,以磷酸化的ERK1／2抗体测定ERK1／2活性,以抗HIF-1α抗体检测HIF-1α的表达,并观察ERKs的上游激酶(MEK1／2)抑制剂PD98059对于HPC诱导的ERKs磷酸化、HIF-1α表达以及心肌细胞保护作用的影响,并分析细胞损伤与ERK1／2活性、HIF-1α表达量之间的相互关系。结果 显示缺氧复氧造成心肌细胞损伤,HPC可以增加心肌细胞H／R后存活率,降低凋亡率,并激活ERKll2,诱导HIF-1α表达：细胞凋亡与ERKs活性、HIF-1α表达量之间存在负相关,即ERKs活化、HIF-1α表达与预防细胞损伤有关：而ERKs活性与HIF-1α表达量之间存在正相关,ERKs的上游激酶MEK抑制剂PD98059可以消除HPC诱导的ERKs磷酸化、HIF-1α表达和心肌细胞保护作用。由此得出的结论是HPC可以提高乳鼠心肌细胞对于H／R的耐受性,其机制涉及ERKs介导的HIF-1α表达。     

Changes of superoxide dismutase, glutathione perioxidase and lipid peroxides in the brain of mice preconditioned by hypoxia.

We have developed an animal model of hypoxic preconditioning and assumed that oxygen radicals and their endogenous scavenging enzymes may play an important role in the preconditioning. To test this hypothesis, activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and the content of lipid peroxides (LPO) were measured during the preconditioning. Compared with unpreconditioned control animals, in animals exposed to hypoxia only once, the activities of SOD and GSH-Px in whole brain were found to be significantly decreased while the LPO content in the hippocampus significantly increased. However, those in animals exposed to 4 runs of hypoxia tended to return to control levels and were lower than those in animals exposed to 1 and 2 runs of hypoxia. Our results indicate that the oxygen radicals and their specific scavenging enzymes seem to be involved in the development of tolerance to hypoxia.