Altered gene expression during hypoxia and reoxygenation of the heart

Hypoxia and re-oxygenation effects on human cardiomyocytes cultured on polycaprolactone and polyurethane nanofibrous mats

Heart diseases are caused mainly by chronic oxygen insufficiency (hypoxia), leading to damage and apoptosis of cardiomyocytes. Research into the regeneration of a damaged human heart is limited due to the lack of cellular models that mimic damaged cardiac tissue. Based on the literature, nanofibrous mats affect the cardiomyocyte morphology and stimulate the growth and differentiation of cells cultured on them; therefore, nanofibrous materials can support the production of in vitro models that faithfully mimic the 3D structure of human cardiac tissue. Nanofibrous mats were used as scaffolds for adult primary human cardiomyocytes (HCM) and immature human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). This work focuses on understanding the effects of hypoxia and re-oxygenation on human cardiac cells cultured on polymer nanofibrous mats made of poly(ε-caprolactone) (PCL) and polyurethane (PU). The expression of selected genes and proteins in cardiomyocytes during hypoxia and re-oxygenation were evaluated. In addition, the type of cell death was analyzed. To the best of our knowledge, there are no studies on the effects of hypoxia on cardiomyocyte cells cultured on nanofibrous mats. The present study aimed to use nanofiber mats as scaffolds that structurally could mimic cardiac extracellular matrix. Understanding the impact of 3D structural properties in vitro cardiac models on different human cardiomyocytes is crucial for advancing cardiac tissue engineering and regenerative medicine. Observing how 3D scaffolds affect cardiomyocyte function under hypoxic conditions is necessary to understand the functioning of the entire human heart.

Effects of chronic hypoxia on the gene expression profile in the embryonic heart in three Chinese indigenous chicken breeds (Gallus gallus)

Hypoxia exposure (HE) has adverse impacts on the embryonic development of chicken, whereas the mechanism underlying the response of the heart to HE during embryo development in birds is still unclear. Therefore, our study was designed to reveal the hub genes and the signaling pathways linked to chronic hypoxia stress. Thus, the gene expression microarray GSE12675, downloaded from the GEO database, included 12 embryonic heart samples in hypoxia and normoxia of three Chinese indigenous chicken breeds [Shouguang (SG), Tibetan (TB), and Dwarf Recessive White (DRW) chickens]. A total of 653 to 714 breed-specific differentially expressed genes (DEGs) were detected in each pairwise comparison. Gene ontology (GO) showed that the DEGs were mainly involved in biological processes, including vasoconstriction, cell differentiation, and the positive regulation of vasoconstriction. KEGG enrichment revealed that the DEGs were mainly enriched in MAPK, PPAR, insulin, adrenergic signaling in cardiomyocytes, etc. Moreover, 48 genes (e.g., SGCD, DHRS9, HELQ, MCMDC2, and ESCO2) might contribute to the response of the heart to HE. Taken together, the current study provides important clues for understanding the molecular mechanism of the heart's response to HE during the embryonic period of chicken.

Myocardial ER chaperone activation and protein degradation occurs due to synergistic, not individual, cold and hypoxic stress

Environmental stress at high altitude affects the myocardium at the physiological and molecular level. Characterized by hypobaric hypoxia and low temperatures, the cumulative impact of these stressors on the protein folding homeostasis in the heart is yet unexplored. The present study evaluates the collective effect of cold and hypoxia on the myocardial protein oxidation and activation of the endoplasmic reticulum (ER) stress response. Adult rats were exposed to either a singular acute stress of cold (10 °C; C), hypobaric hypoxia (7620 m; H) or simultaneously to both cold and hypobaric hypoxia (CH) for 6 h. Hypoxic stress amplified the free radical generation in H and CH groups, leading to enhanced HIF-1α expression. Coupled to cold stress, reduced oxygen availability caused substantial protein oxidative modifications, as well as cardiac tissue injury and matrix remodeling, evident in the histological staining. Presence of oxidized proteins caused a significant upregulation in expression of ER chaperones GRP78 and PDI in the cold hypoxia exposed animals. Enhanced proteolytic activity signaled the removal of misfolded proteins. Linked intricately to cellular stress response, cell survival kinases were expressed higher in CH group; however apoptotic CHOP (C/EBP homologous protein) expression remained unaltered. Administration of ER stress inducer, tunicamycin along with cold hypoxic stress, caused a discernible increase in protein oxidation and GRP78 expression, along with a significant elevation in proteasome and apoptotic activity. Highlighting the significance of a synergistic, rather than individual, effect of low oxygen and temperature on the protein folding machinery, our study provides evidence for the activation of ER stress response in the myocardium under acute high altitude stress.

Cytotoxicity, anti-angiogenic, apoptotic effects and transcript profiling of a naturally occurring naphthyl butenone, guieranone A

Background

Malignant diseases are responsible of approximately 13% of all deaths each year in the world. Natural products represent a valuable source for the development of novel anticancer drugs. The present study was aimed at evaluating the cytotoxicity of a naphtyl butanone isolated from the leaves of Guiera senegalensis, guieranone A (GA).

Results

The results indicated that GA was active on 91.67% of the 12 tested cancer cell lines, the IC₅₀ values below 4 μg/ml being recorded on 83.33% of them. In addition, the IC₅₀ values obtained on human lymphoblastic leukemia CCRF-CEM (0.73 μg/ml) and its resistant subline CEM/ADR5000 (1.01 μg/ml) and on lung adenocarcinoma A549 (0.72 μg/ml) cell lines were closer or lower than that of doxorubicin. Interestingly, low cytotoxicity to normal hepatocyte, AML12 cell line was observed. GA showed anti-angiogenic activity with up to 51.9% inhibition of the growth of blood capillaries on the chorioallantoic membrane of quail embryo. Its also induced apotosis and cell cycle arrest. Ingenuity Pathway Analysis identified several pathways in CCRF-CEM cells and functional group of genes regulated upon GA treatment (P < 0.05), the Cell Cycle: G2/M DNA Damage Checkpoint Regulation and ATM Signaling pathways being amongst the four most involved functional groups.

Conclusion

The overall results of this work provide evidence of the cytotoxic potential of GA and supportive data for its possible use in cancer chemotherapy.

Variation of NDRG2 and c-Myc expression in rat heart during the acute stage of ischemia/reperfusion injury

N-Myc downstream regulated gene 2 (NDRG2), a Myc-repressed gene, is highly expressed in heart tissue. NDRG2 increases in response to hypoxia-induced stress and is involved in hypoxia-induced radioresistance. However, little is known about the expression changes and possible roles of NDRG2 in the heart under hypoxia condition. Here, the authors show that NDRG2, mainly localized in cardiomyocyte cytoplasm, was significantly reduced in myocardial tissue after acute ischemia/reperfusion (I/R) injury. Meanwhile, c-Myc was up-regulated following acute I/R injury, and the expression of c-Myc was significantly inversely correlated with that of NDRG2. In addition, overexpression of c-Myc in primary cultured cardiomyocyte repressed NDRG2 expression. Furthermore, the increase of cardiomyocyte apoptosis was correlated with the decrease of NDRG2 protein during the acute phase of reperfusion. These data suggested for the first time that I/R injury-induced up-regulation of pro-apoptotic c-Myc expression may contribute to the down-regulation of anti-apoptotic NDRG2. This stress response might be involved in the novel mechanism of myocardial apoptosis induced by I/R injury in rat.

Flexibility in energy metabolism supports hypoxia tolerance in Drosophila flight muscle: metabolomic and computational systems analysis

The fruitfly Drosophila melanogaster offers promise as a genetically tractable model for studying adaptation to hypoxia at the cellular level, but the metabolic basis for extreme hypoxia tolerance in flies is not well known. Using ¹H NMR spectroscopy, metabolomic profiles were collected under hypoxia. Accumulation of lactate, alanine, and acetate suggested that these are the major end products of anaerobic metabolism in the fly. A constraint-based model of ATP-producing pathways was built using the annotated genome, existing models, and the literature. Multiple redundant pathways for producing acetate and alanine were added and simulations were run in order to find a single optimal strategy for producing each end product. System-wide adaptation to hypoxia was then investigated in silico using the refined model. Simulations supported the hypothesis that the ability to flexibly convert pyruvate to these three by-products might convey hypoxia tolerance by improving the ATP/H⁺ ratio and efficiency of glucose utilization.

Heat shock proteins, end effectors of myocardium ischemic preconditioning?

The purpose of this study was to investigate (1) whether ischemia-reperfusion increased the content of heat shock protein 72 (Hsp72) transcripts and (2) whether myocardial content of Hsp72 is increased by ischemic preconditioning so that they can be considered as end effectors of preconditioning. Twelve male minipigs (8 protocol, 4 sham) were used, with the following ischemic preconditioning protocol: 3 ischemia and reperfusion 5-minute alternative cycles and last reperfusion cycle of 3 hours. Initial and final transmural biopsies (both in healthy and ischemic areas) were taken in all animals. Heat shock protein 72 messenger ribonucleic acid (mRNA) expression was measured by a semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) method using complementary DNA normalized against the housekeeping gene cyclophilin. The identification of heat shock protein 72 was performed by immunoblot. In our "classic" preconditioning model, we found no changes in mRNA hsp72 levels or heat shock protein 72 content in the myocardium after 3 hours of reperfusion. Our experimental model is valid and the experimental techniques are appropriate, but the induction of heat shock proteins 72 as end effectors of cardioprotection in ischemic preconditioning does not occur in the first hours after ischemia, but probably at least 24 hours after it, in the so-called "second protection window."

Angiotensin-II Receptor Blocker Exerts Cardioprotection in Diabetic Rats Exposed to Hypoxia

BACKGROUND

Hypoxia caused by sleep apnea might be associated with an increased risk of cardiovascular events in subjects with metabolic syndrome. The aim of this study was to examine the effect of hypoxia on the left ventricular (LV) myocardium and evaluate the cardioprotective effect of an angiotensin-II receptor blocker (ARB) in diabetic rats.

METHODS AND RESULTS

Male Otsuka Long-Evans Tokushima Fatty (OLETF) rats at 30 weeks of age (n=30) were divided into 2 groups that were treated with vehicle or candesartan 0.2 mg x kg(-1) x day (-1). The animals were housed in a hypoxic gas chamber (oxygen, 10.0+/-0.5%, mean +/- standard deviation) for 2 weeks. Hypoxia increased right ventricular (RV) systolic pressure (hypoxia; 78+/-14 mmHg vs control; 22+/-5, p<0.05), but did not increase LV systolic pressure (131+/-23 mmHg vs 121+/-10). Hypoxia exacerbated the degeneration of cardiomyocytes, and accelerated the expression of hypoxia inducible factor-1alpha (HIF-1 alpha) and vascular endothelial growth factor (VEGF) in the myocardium. Treatment with ARB decreased RV and LV pressures (46+/-7 and 100+/-18 mmHg, respectively), suppressed the expression of HIF-1alpha and VEGF, and preserved the fine structure of the LV myocardium.

CONCLUSIONS

ARB exhibited cardioprotection under hypoxia, in part through the reduction of blood pressure and cytokine expression, in OLETF rats. Thus, ARB might be a potent agent for the treatment of diabetic patients with the complication of sleep apnea.

Hypoxia/reoxygenation reduces microvascular endothelial cell coupling by a tyrosine and MAP kinase dependent pathway

Communication of electrical signals along the microvascular endothelium plays a key role in integrating microvascular function required for local regulation of blood flow. The aim of the present study was to examine the effect of a short-term hypoxia (0.1% O(2), 1 h) plus reoxygenation (H/R) on electrical coupling in cultured monolayers of microvascular endothelial cells (rat skeletal muscle origin). To assess coupling, we used a current injection technique and a Bessel function model to compute the intercellular resistance (an inverse measure of coupling) and cell membrane resistivity (a measure of resistance to current leakage across the cell membrane). H/R resulted in rapid (within 4 min after reoxygenation) and sustained (up to 100 min) reduction in intercellular coupling, but it did not alter membrane resistivity. H/R did not alter gap junction protein connexin 43 expression nor its tyrosine phosphorylation as determined by immunoblot and immunoprecipitation analyses. Inhibition of mitochondrial respiration (1 mM NaCN) did not mimic the effect of H/R. However, pre-treatment of monolayers with tyrphostin A48 (1.5 microM), PP2 (10 nM) (tyrosine kinase inhibitors), U 0126 (20 microM), and PD 98059 (5 microM) (MEK1/2 inhibitors) inhibited the H/R-induced reduction in coupling. These results indicate that endothelial cell coupling was reduced quickly after reoxygenation, via activation of a tyrosine and MAP kinase dependent pathway. We predict that a short-term H/R can rapidly compromise microvascular function in terms of reduced cellular communication along the vascular wall.

Impact of a novel cardioprotective agent on the ischaemia-reperfusion-induced Akt kinase activation

Cardioprotective effect of a free radical-scavenging compound (HO-3073) was examined during ischaemia-reperfusion (IR) in isolated heart perfusion system and its influence on the pro-survival Akt signalling pathway was addressed. Rat hearts were perfused according to the Langendorff method and subjected to a global 25-min ischaemia and 15, 45 and 90-min reperfusion either untreated or treated with HO-3073 (2, 5 and 10 microM) and/or wortmannin (100 nM, inhibitor of phosphatidylinositol-3-kinase). HO-3073 facilitated the recovery of myocardial energy metabolism as assessed by 31P NMR spectroscopy (creatine phosphate recovery in reperfusion was 76+/-5%, while in untreated hearts 32+/-4%). Functional performance of the hearts followed by a left ventricular balloon manometer was also markedly improved by HO-3073 administration (recovery of rate-pressure product related to normoxia was 47+/-3%, while in untreated hearts 12+/-3%). HO-3073 diminished the infarct size measured by TTC staining (29+/-6% as opposed to 64+/-7% in untreated ischaemia-reperfusion). HO-3073 also significantly attenuated lipid peroxidation (thiobarbituric acid reactive substances) and protein oxidation (protein carbonyl content) compared to untreated hearts. HO-3073 enhanced the ischaemia-reperfusion-triggered phosphorylation of Akt-1 (activation) and glycogen synthase kinase-3 beta (inactivation) as evidenced by Western blot analysis. Wortmannin co-administration neutralised the beneficial effects of HO-3073 on cardiac energetics, contractile function, infarct size, as well as Akt signalling. Our results first display that a radical-scavenging molecule possesses the ability to intensify the pro-survival functioning of phosphatidylinositol-3-kinase/Akt pathway, which is presumed to play an additive role in the cardioprotective properties of HO-3073.

Akt activation induced by an antioxidant compound during ischemia-reperfusion

Molecular mechanisms of cardioprotection afforded by modified mexiletine compounds were investigated during ischemia-reperfusion (IR) in Langendorff perfused hearts. Rat hearts were subjected to a global 25 min ischemia followed by reperfusion, either untreated or treated with mexiletine, or three substituted mexiletine derivates (5 muM). A modified mexiletine derivative (H-2693) promoted best the recovery of myocardial energy metabolism (assessed by (31)P NMR spectroscopy) compared to untreated and mexiletine-treated hearts. H-2693 also preserved cardiac contractile function and attenuated the IR-induced lipid peroxidation (TBARS formation) and protein oxidation (carbonyl content). Western blot revealed that H-2693 propagated the phosphorylation of Akt (activation) and its downstream substrate glycogen synthase kinase-3beta (GSK-3beta, inactivation) compared to untreated IR. Parallel treatment with the phosphatidylinositol-3-kinase (upstream activator of Akt) inhibitor wortmannin (100 nM) abolished the beneficial effects of H-2693 on energetics and function, and reduced Akt and GSK-3beta phosphorylation. As a result of the antiapoptotic impacts of Akt activation, H-2693 decreased caspase-3 activity, which was neutralized by wortmannin. Here we first demonstrated that a free radical-entrapping compound could activate the prosurvival Akt pathway beyond its proven ability to scavenge reactive oxygen species. In conclusion, the favorable influence of H-2693 on signaling events during IR may have considerably contributed to its cardioprotective effect.

The graft response to transplantation: a gene expression profile analysis

Little is known regarding the graft response to transplantation injury. This study investigates the posttransplantation response of genes that are constitutively expressed in the heart. Constitutive heart and lymph node tissue-restricted gene expression was first analyzed with DNA microarrays. To demonstrate changes following transplantation in genes constitutively expressed in the heart, we performed vascularized murine heart transplants in allogeneic (BALB/c to B6), syngeneic (B6 to B6), and alymphoid (BALB/c-RAG2-/- to B6-RAG1-/-) experimental groups. Temporal induction of genes posttransplant relative to constitutive expression was evaluated with DNA microarrays. Dendrograms and self-organizing maps were generated to determine the dissimilarity between the experimental groups and to identify subsets of differentially expressed genes within the groups, respectively. Expression patterns of selected genes were confirmed by real-time PCR. Biological processes were assigned to genes induced posttransplant using the AnnBuilder package via the Gene Ontology Database. Post-transplant, a shift was noted in genes classified as defense, communication, and metabolism. Our results identify novel components of the graft response to transplantation injury and rejection.

Hypoxia-induced switches of myosin heavy chain iso-gene expression in rat heart

Cardiac hypertrophy and atrophy increase expression of fetal iso-genes. A common factor is a decrease in cellular oxygen tension. To test the hypothesis that hypoxia changes cardiac MHC iso-gene expression Wistar rats were exposed to 24 and 48 h of hypobaric hypoxia (11% oxygen) and mRNA was isolated from the left ventricle. In addition, neonatal rat cardiomyocytes were incubated for up to 48 h in a hypoxic chamber. Transcript levels of MHCalpha (adult isoform), MHCbeta (fetal isoform), and Nkx2.5, the earliest known marker for cardiogenesis, were measured by real-time quantitative RT-PCR and normalized to levels of 18S rRNA. Expression of the transcription factor Nkx2.5 increased with hypoxia. Hypoxia decreased MHCalpha and increased MHCbeta transcript levels, both in vivo and in vitro. We conclude that hypoxia per se induces a pattern of isoform gene expression associated with early cardiac development.

Obstructive sleep apnoea syndrome--an oxidative stress disorder

Obstructive sleep apnoea syndrome (OSA) is associated with increased cardiovascular morbidity and mortality. However, the underlying mechanisms are not entirely understood. This review will summarize the evidence that substantiates the notion that the repeated apnoea-related hypoxic events in OSA, similarly to hypoxia/reperfusion injury, initiate oxidative stress. Thus, affecting energy metabolism, redox-sensitive gene expression, and expression of adhesion molecules. A limited number of studies substantiate this hypothesis directly by demonstrating increased free radical production in OSA leukocytes and increased plasma-lipid peroxidation. A great number of studies, however, support this hypothesis indirectly. Increase in circulating levels of adenosine and urinary uric acid in OSA are implicated with increased production of reactive oxygen species (ROS). Activation of redox-sensitive gene expression is suggested by the increase in some protein products of these genes, including VEGF, erythropoietin, endothelin-1, inflammatory cytokines and adhesion molecules. These implicate the participation of redox-sensitive transcription factors as HIF-1 AP-1 and NFkappaB. Finally, adhesion molecule-dependent increased avidity of OSA monocytes to endothelial cells, combined with diminished NO bioavailability, lead to exaggerated endothelial cell damage and dysfunction. Cumulatively, these processes may exacerbate atherogenic sequelae in OSA.

A functional activating protein 1 (AP-1) site regulates matrix metalloproteinase 2 (MMP-2) transcription by cardiac cells through interactions with JunB-Fra1 and JunB-FosB heterodimers

Enhanced synthesis of a specific matrix metalloproteinase, MMP-2, has been demonstrated in experimental models of ventricular failure and in cardiac extracts from patients with ischaemic cardiomyopathy. Cultured neonatal rat cardiac fibroblasts and myocytes were used to analyse the determinants of MMP-2 synthesis, including the effects of hypoxia. Culture of rat cardiac fibroblasts for 24 h in 1% oxygen enhanced MMP-2 synthesis by more than 5-fold and augmented the MMP-2 synthetic responses of these cells to endothelin-1, angiotensin II and interleukin 1beta. A series of MMP-2 promoter-luciferase constructs were used to map the specific enhancer element(s) that drive MMP-2 transcription in cardiac cells. Deletion studies mapped a region of potent transactivating function within the 91 bp region from -1433 to -1342 bp, the activity of which was increased by hypoxia. Oligonucleotides from this region were cloned in front of a heterologous simian-virus-40 (SV40) promoter and mapped the enhancer activity to a region between -1410 and -1362 bp that included a potential activating protein 1 (AP-1)-binding sequence, C(-1394)CTGACCTCC. Site-specific mutagenesis of the core TGAC sequence (indicated in bold) eliminated the transactivating activity within the -1410 to -1362 bp sequence. Electrophoretic mobility shift assays (EMSAs) using the -1410 to -1362 bp oligonucleotide and rat cardiac fibroblast nuclear extracts demonstrated specific nuclear-protein binding that was eliminated by cold competitor oligonucleotide, but not by the AP-1-mutated oligonucleotide. Antibody-supershift EMSAs of nuclear extracts from normoxic rat cardiac fibroblasts demonstrated Fra1 and JunB binding to the -1410 to -1362 bp oligonucleotide. Nuclear extracts isolated from hypoxic rat cardiac fibroblasts contained Fra1, JunB and also included FosB. Co-transfection of cardiac fibroblasts with Fra1-JunB and FosB-JunB expression plasmids led to significant increases in transcriptional activity. These studies demonstrate that a functional AP-1 site mediates MMP-2 transcription in cardiac cells through the binding of distinctive Fra1-JunB and FosB-JunB heterodimers. The synthesis of MMP-2 is widely considered, in contrast with many members of the MMP gene family, to be independent of the AP-1 transcriptional complex. This report is the first demonstration that defined members of the Fos and Jun transcription-factor families specifically regulate this gene under conditions relevant to critical pathophysiological processes.

Tissue-specific expression of inducible and constitutive Hsp70 isoforms in the western painted turtle

Expression of Hsp73 and Hsp72 in four tissues of the naturally anoxia-tolerant western painted turtle (Chrysemys picta) was investigated in response to a 24 h forced dive and following 1 h recovery. Of the tissues examined, brain and liver displayed approximately threefold and sevenfold higher basal Hsp73 expression than heart and skeletal muscle. Basal Hsp72 expression was relatively low in all tissues examined. After the 24 h forced dive and 1 h recovery, Hsp73 expression did not differ significantly from basal expression with the exception of liver, where expression decreased significantly after 1 h recovery. Hsp72 expression was unchanged in liver following a 24 h dive; however, it increased twofold in brain and threefold in heart and skeletal muscle. Dive-induced Hsp72 expression was found to correlate inversely with basal Hsp73 expression. Following 1 h recovery, Hsp72 expression was significantly elevated in all tissues above levels in dived animals. These data indicate a tissue-specific pattern of Hsp73 and Hsp72 expression in the western painted turtle during both unstressed and stressed conditions.

Hypoxia up-regulates expression of peroxisome proliferator-activated receptor gamma angiopoietin-related gene (PGAR) in cardiomyocytes: role of hypoxia inducible factor 1alpha

Peroxisome proliferator-activated receptors (PPAR), especially the PPARalpha and PPARgamma, are associated with an extraordinary diverse spectrum of cardiovascular diseases including hypertension, angiogenesis, cardiac hypertrophy, and atherosclerosis. PGAR (for PPAR gamma angiopoietin-related gene) is a recently identified PPAR target gene which is associated with adipose differentiation, systemic lipid metabolism, energy homeostasis, and possibly angiogenesis. We report here that WY-14643, a selective PPARalpha ligand up-regulated PGAR expression in neonatal rat cardiomyocytes. In parallel to activating the expression of vascular endothelial growth factor and glucose transporter-4, hypoxia increased PGAR mRNA levels. PGAR expression was also increased by desferrioxamine and CoCl(2), but not by sodium cyanide, results consistent with the pharmacological features of hypoxia-responsive genes. These studies are the first to demonstrate that hypoxia increases the mRNA levels of a PPAR target gene in cardiomyocytes. Furthermore, infection with adenoviral vectors encoding the wild-type or a hybrid form of HIF-1alpha highly increased PGAR mRNA levels. In contrast, neither hypoxia nor overexpression of HIF-1alpha affected the mRNA levels of PPARalpha, PPAR gamma, and muscle carnitine palmitoyltransferase, a known PPARalpha target gene. These results suggest that hypoxic activation of PGAR expression is likely mediated by HIF-1 but not the PPARalpha/RXR pathway.

Hypoxia-inducible factor-1alpha accumulation in the brain after experimental intracerebral hemorrhage

Hypoxia-inducible factor-1 (HIF-1), a transcription factor composed of HIF-1alpha and HIF-1beta protein subunits, has been implicated in cellular protection and cell death in cerebral ischemia. The extent to which HIF-1 plays a role in brain pathology during intracerebral hemorrhage (ICH) is unknown. This study determined whether HIF-1alpha is upregulated at different time points in a rat model of ICH and the role of thrombin and red blood cell lysis in upregulation. Recently, thrombin has been implicated as a nonhypoxic regulator of HIF-1alpha in cultured smooth-muscle cells. Male Sprague-Dawley rats received intracerebral infusions of saline, autologous whole blood, blood plus hirudin, thrombin, thrombin plus hirudin, or lysed erythrocytes. Rats were killed at different time points for Western blot analysis, immunohistochemistry, immunofluorescent double staining, and reverse transcription polymerase chain reaction measurements of HIF-1alpha. HIF-1alpha protein levels increased without changing HIF-1alpha messenger RNA levels after intracerebral infusions of blood, thrombin, and lysed erythrocytes. HIF-1alpha positive cells, which proved to be neurons, were found in the brain after ICH. Hirudin, a specific thrombin inhibitor, reduced HIF-1alpha upregulation in response to both thrombin and blood. This study demonstrates that perihematomal HIF-1alpha protein is upregulated after ICH. This phenomenon is an early response of brain parenchyma to the clot. Thrombin and erythrocyte lysate are involved in HIF-1alpha upregulation through reducing HIF-1alpha degradation.

l-carnosine and verapamil inhibit hypoxia-induced expression of hypoxia inducible factor (HIF-1 alpha) in H9c2 cardiomyoblasts

Contractile failure of myocardial cells is a common cause of mortality in ischemic heart disease. In response to hypoxic conditions, cells upregulate the activity of hypoxia-inducible factor 1 (HIF-1) and express a number of genes encoding proteins that either enhance O (2)delivery or increase cellular ATP levels. HIF-1 is a heterodimer of bHLH-PAS proteins, HIF-1 alpha and HIF-1 beta. Both subunits are constitutively expressed under normoxic conditions, but HIF-1 alpha levels are kept low by proteolytic degradation, then stabilized under conditions of low O (2)by a mechanism that is poorly understood. Here we tested the hypothesis that expression of HIF-1 alpha in cardiac cells may be affected by two known cardioprotective agents. We tested l-carnosine, a naturally occurring dipeptide which has been shown to improve myocardial contractility during hypoxia, and verapamil, a calcium channel blocker frequently prescribed for the treatment of heart disease. The levels of HIF-1 alphamRNA remained relatively stable during time course hypoxia (1% O (2)) in H9c2 cardiomyoblasts, then increased slightly after 24 h. In cells pretreated with 1 microM carnosine, the levels of mRNA were transiently reduced, but then increased after 24 h similar to the controls. The levels of HIF-1 alpha protein increased rapidly in H9c2 cells within 30 min of hypoxia, but this induction was significantly reduced in cells treated with either carnosine or verapamil. In addition, treatment of cells with these agents further reduced the low levels of HIF-1 under normoxic conditions. These results suggest that l-carnosine and verapamil may affect the regulated proteolytic degradation of HIF-1 alpha in heart cells during hypoxia.

Evaluation of preconditioning treatments to protect near-pure cortical neuronal cultures from in vitro ischemia induced acute and delayed neuronal death

We evaluated the efficacy of cycloheximide, heat stress, NMDA receptor blockade (MK801/AP-5), oxygen--glucose deprivation, hypoxia, hypothermia and TNFalpha preconditioning to protect cortical neurons from in vitro ischemic insults that result in acute necrotic and delayed apoptotic neuronal death. Preconditioning treatments were performed 22--24 h before in vitro ischemia. In vitro ischemia was carried out in 96-well microtitre strip-plates by washing neuronal cultures with a balanced salt solution containing 25 mM 2-deoxy-D-glucose and incubating in an anaerobic chamber. Glutamate receptor blockers were present during in vitro ischemia to induce delayed neuronal death. Cycloheximide, heat stress, MK801 and oxygen--glucose deprivation preconditioning were neuroprotective in both acute and delayed in vitro ischemic neuronal death models. AP-5 preconditioning and a 12 h post-MK801 preconditioning interval protected neurons from acute ischemic neuronal death only. Hypoxia, TNFalpha and hypothermic preconditioning provided no neuronal protection in the in vitro ischemia models. This study has confirmed for the first time that several preconditioning treatments can protect neurons from in vitro ischemia induced acute necrotic and delayed apoptotic neuronal death. In addition, a unique feature of this study is the finding that preconditioning could be induced in near-pure primary cortical neuronal cultures, thus confirming that ischemic tolerance is an intrinsic property of neurons and provides a simplified culture system for identifying neuroprotective proteins.

Gene expression profiles in human cardiac cells subjected to hypoxia or expressing a hybrid form of HIF-1 alpha

The cellular response to hypoxia depends on rapid posttranslational modifications of proteins as well as regulation of gene expression. We performed serial analysis of gene expression (SAGE) on human cardiac cells under normoxia, subjected to hypoxia, or infected with Ad2/HIF-1alpha/VP16 (an adenoviral vector expressing a stable hybrid form of hypoxia-inducible factor 1alpha) or Ad2/CMVEV (an empty vector). Of the 97,646 SAGE tags that were sequenced, 27% matched GenBank entries, while an additional 32% matched expressed sequence tags (ESTs) in UniGene. We analyzed 161 characterized genes or ESTs with a putative identification. Expression of 35, 11, and 46 genes was increased by hypoxia, infection with Ad2/EVCMV, or infection with Ad2/HIF-1alpha/VP16, respectively, compared with normoxia; conversely, 20, 11, 38 genes, respectively, were expressed at lower levels. Genes regulated by hypoxia were associated with transcription, biosynthesis, extracellular matrix formation, glycolysis, energy production, cell survival, and cell stress. Changes following infection with Ad2/HIF-1alpha/VP16 mimicked the hypoxic response to a certain extent. Infection with Ad2/CMVEV affected expression of genes that were associated with extracellular matrix formation and membrane trafficking. Differential expression of select genes was confirmed using TaqMan in additional human cardiac cells and rat neonatal ventricular myocytes. These data provide insight into gene expression underlying the diverse and complex cellular response to hypoxia, expression of HIF-1alpha/VP16, or adenoviral infection.

Hypoxia in vivo decreases peroxisome proliferator-activated receptor alpha-regulated gene expression in rat heart

We tested the hypothesis that hypoxia decreases PPARalpha-regulated gene expression in heart muscle in vivo. In two rat models of systemic hypoxia (cobalt chloride treatment and iso-volemic hemodilution), transcript levels of PPARalpha and PPARalpha-regulated genes (pyruvate dehydrogenase kinase 4 (PDK4), muscle carnitine palmitoyltransferase-I (mCPT-I), and malonyl-CoA decarboxylase (MCD)) were measured using real-time quantitative RT-PCR. Data were normalized to the housekeeping gene beta-actin. Atrial natriuretic factor (ANF) and pyruvate dehydrogenase kinase 2 (PDK2), which are not regulated by PPARalpha, served as controls. CoCl(2) treatment decreased PPARalpha, PDK4, mCPT-I, and MCD mRNA levels. Iso-volemic anemia also caused a significant decrease in PPARalpha, PDK4, and MCD mRNA levels. Transcript levels of mCPT-I showed a slight, but not significant decrease (P = 0.08). Gene expression of beta-actin, ANF, and PDK2 did not change with either CoCl(2) treatment nor with anemia. Myocardial PPARalpha-regulated gene expression is decreased in two models of hypoxia in vivo. These results suggest a transcriptional mechanism for decreased fatty oxidation and increased reliance of the heart for glucose during hypoxia.

Hypoxic upregulation of TNF receptor type 2 expression involves NF-IL-6 and is independent of HIF-1 or HIF-2

Tumor necrosis factor (TNF) exerts its biologic activity via two distinct membrane receptors, TNF receptor type 1 (p55TNFR) and TNF receptor type 2 (p75TNFR). Whereas the p55TNFR gene is rather constitutively expressed, transcription of p75TNFR is strongly modulated by a number of stimulatory agents. Experimental evidence suggested the involvement of p75TNFR in endothelial cell activation. Therefore, we have tested the transcriptional activity of p75TNFR under conditions of hypoxia and reoxygenation. Northern blot analysis revealed that p75TNFR mRNA is upregulated in NIH3T3 cells under hypoxia and reoxygenation. This observation directly originates from transcriptional activation of the p75TNFR gene, as shown by reporter gene analysis. Cotransfection experiments clearly showed that the transcriptional induction of the p75TNFR gene is independent of the hypoxia-induced factors, HIF-1alpha and HIF-2alpha. Using deletion mutants of the 5'-flanking region of the p75TNFR gene, we were able to identify a putative DNA binding site for the transcription factor nuclear factor-interleukin-6 (NF-IL-6) to be responsible for the transcriptional upregulation of the p75TNFR gene under conditions of hypoxia and reoxygenation.