Adenine Nucleotides and Inhibition of Protein Synthesis in Isolated Hepatocytes Incubated under Different pO2 Levels

Lefebvre, Véronique; Vansteenbrugge, M.; Beckers, Véronique; Roberfroid, Marcel; Buc-Calderon, Pedro

doi:10.1006/abbi.1993.1357

Cited by 46 publications

(26 citation statements)

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“…This suggestion is supported by the findings of Wolff et al, 36 who reported that stationary culture conditions lead to cellular anoxia. This explanation would account for the discrepancy between our data and those of Lefebvre et al 34 Interestingly, the use of chemical hypoxia to model severe hypoxia had an unexpected effect on Na ϩ ,K ϩ -ATPase activity, with rates of the pump being more depressed when cells were incubated under normoxic conditions in the presence of myxothiazol than when cells were incubated under severe hypoxia. Additionally, intracellular ATP concentrations were more depressed under these conditions.…”

Section: Are Energy-consuming Pathways Downregulated In Response To Econtrasting

confidence: 96%

“…This suggestion is in agreement with results obtained by Lefebvre et al, 34 who found that rates of protein and RNA synthesis were reduced when isolated preparations of hepatocytes were exposed to reduced oxygen concentrations. However, this group overlooked the link between metabolic downregulation and energetic stress, despite showing that ATP concentrations were decreased and ADP concentrations were increased under these conditions.…”

Section: Are Energy-consuming Pathways Downregulated In Response To Esupporting

confidence: 93%

“…However, this group overlooked the link between metabolic downregulation and energetic stress, despite showing that ATP concentrations were decreased and ADP concentrations were increased under these conditions. It was surprising to note that in the study by Lefebvre et al, 34 hepatocytes exhibited decreased rates of energy consumption and signs of energetic stress at oxygen concentrations as high as 100 mol/L, inasmuch as ATP concentrations usually fall only when isolated cardiomyocytes are exposed to near-anoxic oxygen concentrations. 22,35 We believe that despite being exposed to a gas mixture containing 100 mol/L O 2 , the oxygen concentration at the cell level was probably Ͻ0.5 mol/L because of the presence of oxygen diffusion gradients.…”

Section: Are Energy-consuming Pathways Downregulated In Response To Ementioning

confidence: 95%

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Hypoxia Causes Downregulation of Protein and RNA Synthesis in Noncontracting Mammalian Cardiomyocytes

Casey

Pakay

Guppy

et al. 2002

Circulation Research

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Abstract-The aim was to identify energy-consuming processes, other than contraction, downregulated during moderate hypoxia (Ϸ5 mol/L, 0.5% O 2 ) and severe hypoxia (Ͻ0.5 mol/L, Ͻ0.05% O 2 ) in isolated neonatal cardiomyocytes. The metabolic response of cardiomyocytes to moderate and severe hypoxia was assessed by measuring rates of energy consumption and energetic status of cells maintained under these conditions. We found that the rates of energy production were decreased during both forms of hypoxia. Decreased rates of energy production under moderate hypoxia were associated with reduced energy wastage through a downregulation of proton leak in the mitochondria. Cellular protein synthesis and RNA synthesis, major energy-consuming pathways, were downregulated only during severe hypoxia, when oxygen concentrations were low enough to induce energetic stress (quantitatively defined as being any situation in which phosphocreatine concentrations had fallen by Ն40% 3 has also been demonstrated experimentally in a variety of animal models. 4,5 These studies collectively suggest that hibernating cardiomyocytes maintain metabolic stability by reducing their rates of energy utilization to levels that match rates of energy production. It is not clear whether contraction is the only process downregulated during myocardial hibernation or whether any of the other energy-using processes are also shut down.The response of isolated contracting cardiomyocytes 6,7 to hypoxia (Ϸ8 to Ϸ29 mol/L, 0.8% to 3% O 2 ) is similar to the phenomenon observed in hibernating regions of myocardium, in that contractile activity is reduced and recovers with reoxygenation. We have previously shown that isolated noncontracting cardiomyocytes are also capable of reversibly downregulating metabolic activity during hypoxia (Ͻ5 mol/L, Ͻ0.5% O 2 ). 8 In the present study, we have assessed the effect of hypoxia on cellular energy consumption not associated with contraction by measuring the rates of protein synthesis, RNA synthesis, Na ϩ ,K ϩ -ATPase activity, and proton leak. Whereas hibernation was previously thought to be due only to reduced rates of contractile activity, 4 -7 in the present study, we show that rates of protein synthesis, RNA synthesis, and proton leak are also downregulated by noncontracting cardiomyocytes exposed to reduced oxygen availability.

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Section: Are Energy-consuming Pathways Downregulated In Response To Econtrasting

confidence: 96%

Section: Are Energy-consuming Pathways Downregulated In Response To Esupporting

confidence: 93%

Section: Are Energy-consuming Pathways Downregulated In Response To Ementioning

confidence: 95%

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Hypoxia Causes Downregulation of Protein and RNA Synthesis in Noncontracting Mammalian Cardiomyocytes

Casey

Pakay

Guppy

et al. 2002

Circulation Research

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“…Translation is the second largest consumer of ATP (22) in the cell, and its coordinated shutdown may be one strategy to ensure energy conservation in the cell when ATP levels are limiting. It has been well established that hypoxic stress results in a profound inhibition in translation (30,33,43), thereby causing the majority of mRNA transcripts to experience diminished translational efficiencies. Our microarray analysis revealed that 95% of cellular mRNA species that do not change or decrease in abundance during hypoxia experience a decrease in their translational efficiency.…”

Section: Discussionmentioning

confidence: 99%

Activating Transcription Factor 4 Is Translationally Regulated by Hypoxic Stress

Blais

Filipenko

et al. 2004

Molecular and Cellular Biology

397

347

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Hypoxic stress results in a rapid and sustained inhibition of protein synthesis that is at least partially mediated by eukaryotic initiation factor 2␣ (eIF2␣) phosphorylation by the endoplasmic reticulum (ER) kinase PERK. Here we show through microarray analysis of polysome-bound RNA in aerobic and hypoxic HeLa cells that a subset of transcripts are preferentially translated during hypoxia, including activating transcription factor 4 (ATF4), an important mediator of the unfolded protein response. Changes in mRNA translation during the unfolded protein response are mediated by PERK phosphorylation of the translation initiation factor eIF2␣ at Ser-51. Similarly, PERK is activated and is responsible for translational regulation under hypoxic conditions, while inducing the translation of ATF4. The overexpression of a C-terminal fragment of GADD34 that constitutively dephosphorylates eIF2␣ was able to attenuate the phosphorylation of eIF2␣ and severely inhibit the induction of ATF4 in response to hypoxic stress. These studies demonstrate the essential role of ATF4 in the response to hypoxic stress, define the pathway for its induction, and reveal that GADD34, a target of ATF4 activation, negatively regulates the eIF2␣-mediated inhibition of translation. Taken with the concomitant induction of additional ER-resident proteins identified by our microarray analysis, this study suggests an important integrated response between ER signaling and the cellular adaptation to hypoxic stress.Mammalian cells have the ability to alter their gene expression in order to adapt to a variety of environmental stresses, including nutrient depletion, oxidative stress, UV irradiation, reductive stress, exposure to toxins, and hypoxia, although the exact molecular events controlling the stress response have not been fully elucidated.Hypoxic stress plays a pivotal role in normal human development and physiology, including embryogenesis and wound repair, and has been well studied for its importance in the pathogenesis of several human diseases, namely, heart disease, stroke, diabetes, and cancer (for a detailed review, see reference 52). Hypoxia results when oxygen availability does not meet the demand of the surrounding tissue, resulting in decreased oxygen tension. In cancer this is initiated by the rapid proliferation of tumor cells, which gives rise to abnormal and chaotic vasculature, leading to the development of occlusions, blind ends, and vesicular shunts (4). The presence of hypoxic cells in solid tumors is well documented, and both clinical and experimental evidence suggests that the hypoxic microenvironment of a tumor helps to produce a more aggressive phenotype (62) by functioning as a selective pressure for the clonal expansion of apoptotically insensitive cells (16). The presence of hypoxic regions in solid tumors also correlates with a poor prognosis and has been shown to limit the efficacy of standard anticancer treatments, such as radiotherapy and chemotherapy (5). A key element to cellular survival and adaptation during hypo...

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“…In preliminary titration experiments the effect of the cycloheximide concentration on the rate of oxygen consumption was established (data not shown). We incubated cells with 35.5·µmol·l -1 (Lefebvre et al, 1993), 0.7·mmol·l -1 and 1·mmol·l -1 (Wieser and Krumschnabel, 2001) cycloheximide. The measured reduction of oxygen consumption rate did not increase with increased inhibitor concentrations above the value obtained at 35.5·µmol·l -1 cycloheximide.…”

Section: Inhibition Of Protein Biosynthesis By Cycloheximidementioning

confidence: 99%

Energy budget of hepatocytes from Antarctic fish (Pachycara brachycephalumandLepidonotothen kempi) as a function of ambient CO2: pH-dependent limitations of cellular protein biosynthesis?

Langenbuch

Pörtner

2003

Journal of Experimental Biology

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SUMMARYScenarios of rising CO2 concentration in surface waters due to atmospheric accumulation of anthropogenic CO2, or in the deep sea due to anticipated industrial dumping of CO2, suggest that hypercapnia (elevated partial pressure of CO2) will become a general stress factor in aquatic environments, with largely unknown effects on species survival and well being, especially in cold and deep waters. For an analysis of CO2 effects at the cellular level, isolated hepatocytes were prepared from two representatives of the Antarctic fish fauna, Pachycara brachycephalum and Lepidonotothen kempi. Correlated changes in energy and protein metabolism were investigated by determining the rates of oxygen consumption at various levels of PCO2, of intra- and extracellular pH, and after inhibition of protein synthesis by cycloheximide. A decrease in extracellular pH (pHe) from control levels (pHe 7.90) to pHe 6.50 caused a reduction in aerobic metabolic rate of 34-37% under both normocapnic and hypercapnic conditions. Concomitantly, protein biosynthesis was inhibited by about 80%under conditions of severe acidosis in hepatocytes from both species. A parallel drop in intracellular pH probably mediates this effect. In conclusion, the present data indicate that elevated PCO2 may limit the functional integrity of the liver due to a pronounced depression in protein anabolism. This process may contribute to the limits of whole-animal tolerance to raised CO2levels.

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Adenine Nucleotides and Inhibition of Protein Synthesis in Isolated Hepatocytes Incubated under Different pO2 Levels

Cited by 46 publications

References 0 publications

Hypoxia Causes Downregulation of Protein and RNA Synthesis in Noncontracting Mammalian Cardiomyocytes

Hypoxia Causes Downregulation of Protein and RNA Synthesis in Noncontracting Mammalian Cardiomyocytes

Activating Transcription Factor 4 Is Translationally Regulated by Hypoxic Stress

Energy budget of hepatocytes from Antarctic fish (Pachycara brachycephalumandLepidonotothen kempi) as a function of ambient CO2: pH-dependent limitations of cellular protein biosynthesis?

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