Normoxic induction of cerebral HIF-1α by acetazolamide in rats: Role of acidosis (original) (raw)
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HIF1α and physiological responses to hypoxia are correlated in mice but not in rats
Journal of Experimental Biology, 2016
We previously reported that rats and mice that have been raised for more than 30 generations in La Paz, Bolivia (3600m), display divergent physiological responses to high altitude (HA), including improved respiratory and metabolic control in mice. In the present study we asked whether these traits would also be present in response to hypoxia at sea level (SL). To answer this question, we exposed rats (SD) and mice (FVB) to normoxia (21% O2) or hypoxia (15 and 12% O2) for 6 hours and measured ventilation and metabolic rate (whole body plethysmography), and expression of the transcription factor HIF-1α (ELISA and Mass Spectrometry) and other proteins whose expression are regulated by hypoxia (Glucose Transporter 1, Pyruvate Dehydrogenase Kinase 1, and Angiopoietin 2 - Mass Spectrometry) in the brainstem. In response to hypoxia, compared with rats, mice had higher minute ventilation, lower metabolic rate, and higher expression of HIF-1α in the brainstem. In mice the expression level of...
Hypoxic stress-induced changes in adrenergic function: role � of HIF1a
J Neurochem, 2009
Sustaining epinephrine-elicited behavioral and physiological responses during stress requires replenishment of epinephrine stores. Egr-1 and Sp1 contribute by stimulating the gene encoding the epinephrine-synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT), as shown for immobilization stress in rats in adrenal medulla and for hypoxic stress in adrenal medulla-derived PC12 cells. Hypoxia (5% O 2) also activates hypoxia inducible factor (HIF) 1a, increasing mRNA, nuclear protein and nuclear protein/hypoxia response element binding complex formation. Hypoxia and HIF1a over-expression also elevate PNMT promoter-driven luciferase activity in PC12 cells. Hypoxia may be limiting as HIF1a over-expression increases luciferase expression to no greater extent than oxygen reduction alone. HIF1a inducers CoCl 2 or deferoxamine elevate luciferase as well. PC12 cells harboring a HIF1a expression construct show markedly higher levels of Egr-1 and Sp1 mRNA and nuclear protein and PNMT mRNA and cytoplasmic protein. Inactivation of Egr-1 and Sp1 binding sites in the proximal)893 bp of PNMT promoter precludes HIF1a stimulation while a potential hypoxia response element ()282 bp) in the promoter shows weak HIF1a affinity at best. These findings are the first to suggest that hypoxia activates the proximal rat PNMT promoter primarily via HIF1a induction of Egr-1 and Sp1 rather than by co-activation by Egr-1, Sp1 and HIF1a. In addition, the rise in HIF1a protein leading to Egr-1 and Sp1 stimulation of PNMT appears to include HIF1a gene activation rather than simply prevention of HIF1a proteolytic degradation.
HIF-1α is neuroprotective during the early phases of mild hypoxia in rat cortical neurons
Experimental Neurology, 2012
Hypoxia-inducible factor 1α (HIF-1α) is a transcription factor that plays a key role regulating the adaptive response to hypoxia. HIF-1α is stabilised during hypoxia and, after dimerization with HIF-1β, triggers the expression of different genes involved in cell cycle control and energy metabolism associated with cell survival. However, HIF-1α also regulates the expression of proapoptotic genes. The aim of this work is to ascertain the influence of HIF-1α on neurotoxicity evoked by hypoxia in rat cortical neurons. We found that mild hypoxia induces a time-dependent neuronal death that involves free radical production, mitochondrial depolarization, cytochrome c release and caspase 3 activation. Lentiviral mediated knockdown of HIF-1α markedly potentiated all these effects during the initial 24 hours of hypoxia suggesting that HIF-1α plays a neuroprotective role on hypoxia-mediated neuronal death. After this period, the protective actions of HIF-1α disappeared in agreement with the time-course of hypoxia-mediated HIF-1α stabilization. On the other hand, lentiviral mediated over expression of HIF-1α increased lactate dehydrogenase A, one of the target genes for HIF-1α, but did not show protective actions on hypoxia-mediated neuronal death indicating that the level of endogenous HIF-1α stabilization achieved during hypoxia is already the maximal required for the transcription activities of HIF-1α. These results indicate that HIF-1α is neuroprotective in the early phases of hypoxia.
Polycythemic responses to hypoxia: molecular and genetic mechanisms of chronic mountain sickness
Journal of applied physiology (Bethesda, Md. : 1985), 1998
We examined erythropoietin (EPO) gene expression and EPO production during hypoxia in two Sprague-Dawley rat strains with divergent polycythemic responses to hypoxia. Hilltop (H) rats develop severe polycythemia, severe hypoxemia, and pulmonary artery hypertension. The H rats often die from a syndrome indistinguishable from chronic mountain sickness (CMS) in humans. Madison (M) rats develop polycythemia and pulmonary artery hypertension that is modest and suffer no excess mortality. We tested the hypothesis that these rat strains have different stimulus-response characteristics governing EPO production. Rats of each strain were exposed to hypoxia (0.5 atm, 73 Torr inspired PO2), and renal tissue EPO mRNA and EPO levels, plasma EPO, ventilation, arterial and renal venous blood gases, and indexes of renal function were measured at fixed times during a 30-day hypoxic exposure. During extended hypoxic exposure, H rats had significantly elevated renal EPO mRNA, renal EPO, and plasma EPO ...
Nrf2 activation: A potential strategy for the prevention of acute mountain sickness
Free Radical Biology and Medicine, 2013
Reactive oxygen species (ROS) formed during acute high altitude exposure contribute to cerebral vascular leak and development of acute mountain sickness (AMS). Nuclear factor (erythroid-derived 2)-related factor 2 (Nrf2) is a transcription factor that regulates expression of greater than 90% of antioxidant genes, but prophylactic treatment with Nrf2 activators has not yet been tested as an AMS therapy. We hypothesized that prophylactic activation of the antioxidant genome with Nrf2 activators would attenuate high-altitude-induced ROS formation and cerebral vascular leak and that some drugs currently used to treat AMS symptoms have an additional trait of Nrf2 activation. Drugs commonly used to treat AMS were screened with a luciferase reporter cell system for their effectiveness to activate Nrf2, as well as being tested for their ability to decrease high altitude cerebral vascular leak in vivo. Compounds that showed favorable results for Nrf2 activation from our screen and attenuated high altitude cerebral vascular leak in vivo were further tested in brain microvascular endothelial cells (BMECs) to determine if they attenuated hypoxia-induced ROS production and monolayer permeability. Of nine drugs tested, with the exception of dexamethasone, only drugs that showed the ability to activate Nrf2 (Protandim, methazolamide, nifedipine, amlodipine, ambrisentan, and sitaxentan) decreased high-altitude-induced cerebral vascular leak in vivo. In vitro, Nrf2 activation in BMECs before 24 h hypoxia exposure attenuated hypoxic-induced hydrogen peroxide production and permeability. Prophylactic Nrf2 activation is effective at reducing brain vascular leak from acute high altitude exposures. Compared to acetazolamide, methazolamide may offer better protection against AMS. Nifedipine, in addition to its known vasodilatory activities in the lung and protection against high altitude pulmonary edema, may provide protection against brain vascular leak as well.
American Journal of Respiratory and Critical Care Medicine, 2007
Rationale: Acute mountain sickness (AMS) may affect individuals who (rapidly) ascend to altitudes higher than 2,000-3,000 m. A more serious consequence of rapid ascent may be high-altitude pulmonary edema, a hydrostatic edema associated with increased pulmonary capillary pressures. Acetazolamide is effective against AMS, possibly by increasing ventilation and cerebral blood flow (CBF). In animals, it inhibits hypoxic pulmonary vasoconstriction. Objectives: We examined the influence of acetazolamide on the response to hypoxia of ventilation, CBF, and pulmonary vascular resistance (PVR).
High altitude medicine & biology, 2007
van Patot. Acute hypobaric hypoxia (5486 m) induces greater pulmonary HIF-1 activation in hilltop compared to Madison rats. High Alt. Med. Biol. 8:312-321, 2007.-Compared to Madison strain Sprague-Dawley rats, the Hilltop strain is resistant to acute hypoxic pulmonary vasoconstriction and pulmonary leak, a pathology resembling high altitude pulmonary edema (HAPE) in humans. Hypoxia inducible transcription factor-1 (HIF-1) mediates transcription of proteins that can "rescue" tissue from hypoxia, including vasoactive and angiogenic proteins such as inducible nitric oxide synthase (iNOS) and vascular endothelial growth factor (VEGF). Because these proteins have theoretical relevance to the etiology of HAPE, we hypothesized that hypoxia-resistant Hilltop rats acutely exposed to high altitude would have greater HIF-1 activity and expression of iNOS and VEGF as compared to hypoxia-sensitive Madison rats. Animals were exposed to normobaric normoxia or hypobaric hypoxia (18 h at 5486 m). The presence of nuclear HIF-1 heterodimer subunits, HIF-1-DNA binding, and iNOS and VEGF protein expression were determined in lung tissue. Hypoxic HIF-1 expression, HIF-1-DNA binding, and iNOS and VEGF expression were greater in Hilltop than in Madison rats. After 18-h hypobaric hypoxia, HIF-1 activity and HIF-mediated protein expression were elevated in Hilltop rats, but not in Madison rats. To our knowledge, this is the first report of differing HIF-1 activation between two strains of animals with clearly divergent physiological responses to identical hypoxic conditions.
Neuropharmacology, 2018
High-altitude hypoxia (HH) causes a spectrum of pathophysiological effects, including headaches, gliovascular dysfunction, and cognitive slowing. Previous studies have shown arachidonic acid (AA) metabolism due to cyclooxygenase (COX) activity before clinical manifestations in many diseases. AA metabolites, including COXs and prostaglandin E2 (PGE2), are well known immunomodulators. However, the relative contribution of COX-2 and COX-1 isoforms in the downstream proinflammatory responses and cognitive deficit in HH remains unknown. In the present study, AA metabolism via the COX pathway was investigated in Sprague Dawley rats after 0, 1, 3, and 7 days of HH exposure. Furthermore, we investigated the inflammatory response and cell-type-specific induction of both COXs. Our data revealed that AA metabolites peaked on day 3 of HH exposure. Interestingly, we observed endothelial and microglial activation on day 1, accompanied by an increase in the levels of proinflammatory cytokines, followed by astrocyte activation on day 3. We showed that the increase in COX activity during HH culminated in a significant increase in hippocampal inflammation, concomitant with spatial memory impairment and neuronal injury at day 7 of HH. We showed HH induced distinct COX-1 expression in endothelial and microglial cells, whereas it induced COX-2 expression predominantly in neurons, endothelial cells, and astrocytes. Notably, our data showed that the inhibition of COX-1 using valeryl salicylate had a prominent role in containing hippocampal inflammation by reducing microglial activation. COX-2 inhibition using celecoxib, along with COX-1 inhibition, ameliorated spatial memory impairment, astrocyte activation, and neurodegeneration after HH exposure.
European Journal of Neuroscience, 2001
Under severe oxygen deprivation, all cells are able to express the transcription factor HIF-1, which activates a wide range of genes. Under tolerable hypoxia, chemosensory inputs are integrated in brainstem areas, which control cardiorespiratory responses. However, the molecular mechanisms of this functional acclimatization are unknown. We investigated when and where the inducible HIF-1a subunit is expressed in the rat brainstem in vivo, under physiological hypoxia. The regional localization of HIF-1a mRNA and protein was determined by in situ hybridization and immunocytochemistry in adult male rats exposed to moderate hypoxia (10% O 2 ) for 1±6 h. HIF-1a protein was found in cell types identi®ed by immunocytochemistry as catecholaminergic neurons. Hypoxia induced HIF-1a mRNA and protein in only some parts of the brainstem located dorsomedially and ventrolaterally, which are those involved in the cardiorespiratory control. No labelling was detected under normoxia. The protein was detected in glia and neurons after 1 and 6 h of hypoxia, respectively. A subset of A2C2 and A1C1 catecholaminergic neurons colocalized tyrosine hydroxylase and HIF-1a proteins under hypoxia, but no HIF-1a was detected in more rostral catecholaminergic areas. In contrast to cardiorespiratory areas, HIF-1a protein was already present under normoxia in glial cells of brainstem tracts but was not overexpressed under hypoxia, although HIF-1a mRNA was up-regulated. In conclusion, there appear to be two regulatory mechanisms for HIF-1a expression in the brainstem: hypoxic induction of HIF-1a protein in cardiorespiratory-related areas and constitutive protein expression unaffected by hypoxia in brainstem tracts.
Induction of HIF-1a in response to hypoxia is instantaneous
The FASEB Journal, 2001
Despite the pivotal role the hypoxia-inducible factor 1␣ (HIF-1␣) plays in physiological and pathological processes, little is known regarding the time frame and mechanisms involved in its regulation. The aim of this study was to gain insight into the sequential events occurring in the nucleus immediately after hypoxic exposure and reoxygenation by determining the kinetics of HIF-1␣ induction and degradation, and comparison with its dimerization partner ARNT (aryl hydrocarbon receptor nuclear translocator) and nuclear levels of NF-B (nuclear factor kappa B), c-Fos, c-Jun, Ref-1 (redox factor 1), and Trx (thioredoxin) over a range of pathophysiological oxygen concentrations.