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Plasminogen activator inhibitor-1 (PAI-1) is the primary physiological inhibitor of both tissue-type and urokinase-type plasminogen activators. The balance between plasminogen activators and PAI-1 plays an important role in several physiological and pathophysiological processes such as atherosclerosis or thrombosis. Because these conditions are associated with hypoxia, it was the aim of the present study to investigate the influence of low O(2) tension on the expression of PAI-1 mRNA and protein using primary cultured rat hepatocytes as a model system. We found that PAI-1 mRNA and protein were induced by mild hypoxia (8% O(2)). The hypoxia-dependent PAI-1 mRNA induction was transcriptionally regulated because it was inhibited by actinomycin D (ActD). Luciferase (LUC) reporter gene constructs driven by about 800 bp of the 5'-flanking region of the rat PAI-1 gene were transiently transfected into primary rat hepatocytes; mild hypoxia caused a 3-fold induction, which was mediated by the PAI-1 promoter region -175/-158 containing 2 putative hypoxia response elements (HRE) binding the hypoxia-inducible factor (HIF-1). Mutation of the HRE-1 (-175/-168) or HRE-2 (-165/-158) also abolished the induction by mild hypoxia. Cotransfection of a HIF-1alpha vector and the PAI-1-LUC constructs, as well as gel shift assays, showed that the HRE-2 of the PAI-1 promoter was most critical for induction by hypoxia and HIF-1 binding. Thus, PAI-1 induction by mild hypoxia via a HIF-1 binding HRE in the rat PAI-1 promoter appears to be the mechanism causing the increase in PAI-1 in many clinical conditions associated with O(2) deficiency.
Hypoxia-inducible factor-1 (HIF-1) is a transcriptional complex that is activated in response to hypoxia and growth factors. HIF-1 plays a central role in tumor progression, invasion, and metastasis. Overexpression of the HIF-1alpha subunit has been observed in many human cancers and is associated with a poor prognostic outcome with conventional treatments. Targeting HIF-1 using novel small molecule inhibitors is, therefore, an attractive strategy for therapeutic development. We have generated U2OS human osteosarcoma cells stably expressing a luciferase reporter construct under the control of a hypoxia response element (U2OS-HRE-luc). The U2OS-HRE-luc cells were robustly and reproducibly sensitive to hypoxic stress in a HIF-1-dependent manner. We developed an automated U2OS-HRE-luc cell-based assay that was used in a high-throughput screen to identify compounds that inhibited HIF-1 activity induced by treatment with the hypoxia mimetic, deferoxamine mesylate. We performed a pilot screen of the National Cancer Institute Diversity Set of 2,000 compounds. We identified eight hit compounds, six of these were also identified by Rapisarda et al. in an independent hypoxia screen. However, there were two novel hit compounds, NSC-134754 and NSC-643735, that did not significantly inhibit constitutive luciferase activity in U2OS cells (U2OS-luc). We showed that both NSC-134754 and NSC-643735 significantly inhibited HIF-1 activity and HIF-1alpha protein induced by deferoxamine mesylate. Interestingly, NSC-134754 but not NCS-643735 inhibited HIF-1 activity and HIF-1alpha protein induced by hypoxia and significantly inhibited Glut-1 expression. Finally, we showed that both NCS-134754 and NCS-643735 inhibited HIF-1alpha protein induced by insulin-like growth factor-1. Our cell-based assay approach has successfully identified novel compounds that differentially target hypoxia and/or growth factor-mediated induction of HIF-1alpha.
Hypoxia has been recognised as an important tumoral feature related to resistance to radiotherapy since 1933. Recent advances in biological research have revealed important aspects on the cellular response to hypoxic stimuli and on the role of hypoxia pathways in the metabolism, growth and progression of cancer. The hypoxia-inducible factors (HIF-1a and HIF-2a) have been identified as key proteins that directly respond to hypoxic stress. Following hypoxia, stabilisation and nuclear binding of HIFs triggers the expression of a variety of genes related to erythropoiesis, glycolysis and angiogenesis. This review reports on and discusses the biology of the hypoxia pathways, the studies performed on the expression of HIFs in human cancer and the implications of hypoxia pathways in cancer therapy.
Poor outcome of treatment in advanced cervix carcinoma has been shown to be associated with poor oxygenation of the primary tumour. Hypoxia may cause radiation resistance and promote lymph-node metastasis. The purpose of the study reported here was to investigate whether hypoxia-induced treatment failure in advanced cervix carcinoma is primarily a result of hypoxia-induced radiation resistance or the presence of hypoxia-induced lymph-node metastases at the start of treatment. Thirty-two patients with squamous cell carcinoma of the uterine cervix were included in the study. Radiation therapy was given with curative intent as combined external irradiation and endocavitary brachytherapy. The oxygenation status of the primary tumour was measured prior to treatment using the Eppendorf PO2 Histograph. Pelvic and para-aortal lymph-node metastases were detected by magnetic resonance imaging at the time of initial diagnosis. The primary tumours of the patients with metastases (n = 18) were significantly more poorly oxygenated than those of the patients without metastases (n = 14). Multivariate Cox regression analyses involving biological and clinical parameters identified the tumour subvolume having PO2 values below 5 mmHg (HSV (pO2 < 5 mmHg) as the only significant, independent prognostic factor for locoregional control, disease-free survival and overall survival. The probabilities of locoregional control, disease-free survival and overall survival were significantly lower for the patients with HSV (PO2 < 5 mmHg) above the median value than for those with HSV (PO2 < 5 mmHg) below the median value. On the other hand, the outcome of treatment was not significantly different for the patients with metastases and the patients without metastases at the start of treatment, irrespective of clinical end-point. Consequently, treatment failure was primarily a result of hypoxia-induced radiation resistance rather than hypoxia-induced lymph-node metastasis, suggesting that novel treatment strategies aiming at improving tumour oxygenation or enhancing the radiation sensitivity of hypoxic tumour cells may prove beneficial in attempts to improve the radiation therapy of advanced cervix carcinoma.
Many signals involved in pathophysiology are controlled by hypoxia-inducible factors (HIFs), transcription factors that induce expression of hypoxia-responsive genes. HIFs are post-translationally regulated by a family of O2-dependent HIF hydroxylases: four prolyl 4-hydroxylases and an asparaginyl hydroxylase. Most of these enzymes are abundant in resting liver, which is itself unique because of its physiological O2 gradient, and they can exist in both nuclear and cytoplasmic pools. In this study, we analyzed the cellular localization of endogenous HIFs and their regulatory hydroxylases in primary rat hepatocytes cultured under hypoxia-reoxygenation conditions. In hepatocytes, hypoxia targeted HIF-1alpha to the peroxisome, rather than the nucleus, where it co-localized with von Hippel-Lindau tumor suppressor protein and the HIF hydroxylases. Confocal immunofluorescence microscopy demonstrated that the HIF hydroxylases translocated from the nucleus to the cytoplasm in response to hypoxia, with increased accumulation in peroxisomes on reoxygenation. These results were confirmed via immunotransmission electron microscopy and Western blotting. Surprisingly, in resting liver tissue, perivenous localization of the HIF hydroxylases was observed, consistent with areas of low pO2. In conclusion, these studies establish the peroxisome as a highly relevant site of subcellular localization and function for the endogenous HIF pathway in hepatocytes.
SCR-hypoxia test is based on the possible recovery by treatments tested of the SCR depressed through hypoxia. All drugs were administered intraperitoneally to male and female Swiss Orl mice randomized into groups of 10. SCR is measured with a palmar skin conductance-meter, in response to a photostimulus. This apparatus takes place in a cell allowing working in a definite hypoxic atmosphere, at a normal pressure. 15 drugs clinically used in various pathological states related to hypoxia are tested. SCR magnitude is recovered by the "antihypoxic" drugs. Specificity, sensitivity and quantifying value of the test are discussed leading to propose the SCR-hypoxia test in the design of new potentially antihypoxic drugs.
AIM: Analysis of radioprotective effect of respiratory hypoxia on hemopoietic tissue and enhancement of this effect by hemopoietic activation. MATERIAL AND METHODS: In mice breathing hypoxic gas mixture during total body gamma irradiation the recovery of pluripotent and committed granulocyte-macrophage progenitor cells and animal lethality were determined. RESULTS: In mice forced to breathe 10% O2 and 8% O2 during irradiation, the oxygen tension in the spleen decreased to 40% and 20%, respectively, of control values. Hypoxia mitigated the lethal effect of gamma-rays and improved the recovery of hemopoiesis in compartments of pluripotent and committed progenitor cells. Enhancement of the proliferative activity in hemopoietic tissue by a cytokine (rmGM-CSF) or an immunomodulator (dextran sulfate) increased the effect of hypoxic radioprotection, while elimination of proliferative cells by hydroxyurea decreased the radioprotective effect. Adaptation of experimental animals to hypoxic conditions was found to reduce the radioprotective effect without influencing tissue partial oxygen pressure lowered by hypoxic conditions. CONCLUSION: The data presented confirm the radioprotective effect of 10% and 8% O2 respiratory hypoxia on hemopoiesis. These findings may represent a way out for further experimental and clinical research aimed at considering differential protection of various tissues by hypoxia.
IGFBP-1 is elevated in fetuses with long-term, chronic hypoxia and intrauterine growth restriction. We investigated the hypothesis that hypoxia regulates IGFBP-1 in the human fetus in vivo and IGFBP-1 gene expression and protein in vitro. Umbilical artery IGFBP-1 levels (mean +/- SEM) from term babies with respiratory acidosis (acute hypoxia), normal babies, and those with mixed respiratory/metabolic acidosis (more profound and prolonged hypoxia) were measured using an immunoradiometric assay. IGFBP-1 levels were similar in normal (n = 12) and acutely hypoxic (n = 6) babies (189.1 +/- 71.8 vs. 175.8 +/- 45.9 ng /ml, respectively, P = 0.789). However, with more profound and prolonged hypoxia (n = 19), IGFBP-1 levels were markedly elevated (470.6 +/- 80.0 ng /ml, P = 0.044). To investigate IGFBP-1 regulation by hypoxia in vitro, HepG2 cells were incubated under hypoxia (pO2 = 2%) and normoxia (pO2 = 20%). IGFBP-1 protein and mRNA increased 8- and 12-fold, respectively, under hypoxic conditions. Hypoxia did not affect protein or mRNA levels of IGFBP-2 or -4. IGFBP-5 and -6 mRNAs, undetectable in control cells, were not induced by hypoxia, whereas minimally expressed IGFBP-3 mRNA increased twofold. Investigation into IGFBP-1 gene structure revealed three potential consensus sequences for the hypoxia response element (HRE) in the first intron. To investigate functionality, a 372-bp fragment of IGFBP-1 intron 1, containing putative HREs, was placed 5' to a heterologous hsp70 promoter in a plasmid using luciferase as a reporter gene. Under hypoxia, reporter gene activity increased up to 30-fold. Mutations in the middle HRE abolished reporter activity in response to hypoxia, suggesting that this HRE is functional in the IGFBP-1 hypoxia response. Cotransfection of HRE reporter genes with a constitutively expressing hypoxia-inducible factor 1 plasmid in HepG2 cells resulted in a fourfold induction of reporter activity, suggesting a role for hypoxia-inducible factor 1 in hypoxia induction of IGFBP-1 gene expression. These data support the hypothesis that hypoxia regulation of IGFBP-1 may be a mechanism operating in the human fetus to restrict insulin-like growth factor-mediated growth in utero under conditions of chronic hypoxia and limited substrate availability.
The present study was undertaken to investigate the dynamic expression of hypoxia inducible factor-1alpha (HIF-1alpha) and transforming growth factor-beta1 (TGF-beta1) in hypoxia-induced pulmonary hypertension of rats. It was found that mean pulmonary arterial pressure (mPAP) increased significantly after 7 d of hypoxia. Pulmonary artery remodeling index and right ventricular hypertrophy became evident after 14 d of hypoxia. HIF-1alpha mRNA staining was less positive in the control, hypoxia for 3 d and hypoxia for 7 d, but began to enhance significantly after 14 d of hypoxia, then remained stable. Expression of HIF-1alpha protein in the control was less positive, but was up-regulated in pulmonary arterial tunica intima of all hypoxic rats. TGF-beta1 mRNA expression in pulmonary arterial walls was increased significantly after 14 d of hypoxia, but showed no obvious changes after 3 or 7 d of hypoxia. In pulmonary tunica adventitia and tunica media, TGF-beta1 protein staining was less positive in control rats, but was markedly enhanced after 3 d of hypoxia, reaching its peak after 7 d of hypoxia, and then weakening after 14 and 21?d of hypoxia. Western blotting showed that HIF-1alpha protein levels increased significantly after 7 d of hypoxia and then remained at a high level. TGF-beta1 protein level was markedly enhanced after 3 d of hypoxia, reaching its peak after 7 d of hypoxia, and then decreasing after 14 and 21?d of hypoxia. Linear correlation analysis showed that HIF-1alpha mRNA, TGF-beta1 mRNA, TGF-beta1 protein were positively correlated with mPAP, vessel morphometry and right ventricular hypertrophy index. TGF-beta1 protein (tunica adventitia) was negatively correlated with HIF-1alpha mRNA. Taken together, our results suggest that changes in HIF-1alpha and TGF-beta1 expression after hypoxia play an important role in hypoxia-induced pulmonary hypertension of rats.
Our primary hypothesis was that the acute ventilatory response to carbon dioxide in the presence of sustained hypoxia {VRCO2 (hypoxia)} or hyperoxia {VRCO2 (hyperoxia)} would increase in subjects with obstructive sleep apnea (OSA) after exposure to episodic hypoxia. Secondarily, we hypothesized that chronic (i.e. years) exposure to episodic hypoxia, a hallmark of OSA, would facilitate persistent augmentation of respiratory activity (i.e. long-term facilitation) after acute (i.e. minutes) exposure to episodic hypoxia. Nine healthy males with OSA that were healthy otherwise completed a series of rebreathing trials before and after exposure to eight 4 min episodes of hypoxia. On a separate occasion, the rebreathing trials were repeated before and after exposure to atmospheric air for a duration equivalent to the episodic hypoxia protocol (i.e. sham episodic hypoxia). During the rebreathing trials, subjects initially hyperventilated to reduce the partial pressure of carbon dioxide (P(ET)CO2) below 25 Torr. Subjects then rebreathed from a bag containing a normocapnic (42 Torr), low (50 Torr) or high oxygen gas mixture (140 Torr). During the trials, P(ET)CO2 increased while the selected level of oxygen was maintained. The point at which ventilation began to rise in a linear fashion as P(ET)CO2 increased was the ventilatory threshold. The ventilatory response below and above the threshold was determined. The results showed that the VRCO2 (hypoxia) and the VRCO2 (hyperoxia) was increased after exposure to episodic hypoxia {VRCO2 (hypoxia): 7.9 +/- 1.3 versus 10.5 +/- 1.3, VRCO2 (hyperoxia): 5.9 +/- 1.1 versus 6.7 +/- 1.1 L/min/Torr}. However, only the increase in the VRCO2 (hypoxia) after episodic hypoxia was greater than the increase measured after exposure to sham episodic hypoxia. Long-term facilitation of ventilation, tidal volume and breathing frequency was not evident after episodic hypoxia. We conclude that the VRCO2 (hypoxia) is enhanced after exposure to acute episodic hypoxia and that enhancement of the VRCO2 (hypoxia) occurs even though long-term facilitation is not evident.
To test the hypothesis that hypoxia inducible factor-1 alpha (HIF-1alpha) up-regulated the expression of heme oxygenase-1 (HO-1) gene in pulmonary arteries of rats with hypoxia-induced pulmonary hypertension, 8 male Wistar rats in each of 5 groups were exposed to hypoxia for 0, 3, 7, 14 or 21 d, respectively. Mean pulmonary arterial pressure (mPAP), vessel morphometry and right ventricle hypertrophy index were measured. Lungs were inflation fixed for immunohistochemistry, in situ hybridization; frozen for later measurement of HO-1 enzyme activity. mPAP increased significantly after 7 d of hypoxia [(18.4 +/- 0.4) mmHg, P<0.05], reaching its peak after 14 d of hypoxia, then remained stable. Pulmonary artery remodeling became to develop significantly after 14 d of hypoxia. HIF-1alpha protein in control was poorly positive (0.05 +/- 0.01), but was up-regulated in pulmonary arterial tunica intima of all hypoxic rats. In pulmonary arterial tunica media, the levels of HIF-1alpha protein were markedly up-regulated after 3 d and 7 d of hypoxia (0.20 +/- 0.02; 0.22 +/- 0.02, P<0.05), then declined after 14 d and 21 d of hypoxia. HIF-1alpha mRNA staining was poorly positive in control, hypoxia for 3 and 7 d, but enhanced significantly after 14 d of hypoxia (0.20 +/- 0.02, P<0.05), then remained stable. HO-1 protein increased after 7 d of hypoxia (0.10 +/- 0.01, P<0.05), reaching its peak after 14 d of hypoxia (0.21 +/- 0.02, P<0.05), then remained stable. HO-1 mRNA increased after 3 d of hypoxia, reaching its peak after 7 d of hypoxia (0.17 +/- 0.01, P<0.05), then declined. Linear correlation analysis showed that HIF-1alpha mRNA, HO-1 protein and mPAP were associated with pulmonary remodeling. HIF-1alpha protein (tunica intima) was conversely correlated with HIF-1alpha mRNA (r=0.921,P<0.01), HO-1 protein was conversely correlated with HIF-1alpha protein (tunica intima) (r=0.821, P<0.01). HIF-1alpha and HO-1 were both involved in the pathogenesis of hypoxia-induced pulmonary hypertension in rat. Hypoxia inducible factor-1 alpha correlated the expression of heme oxygenase 1 gene in pulmonary arteries of rat with hypoxia-induced pulmonary hypertension.
Hypoxia preconditioning and subsequent tolerance to hypoxia-ischemia damage is a well-known phenomenon and has significant implications in clinical medicine. In this investigation, we tested the hypothesis that the transcriptional activation of IGF-I is one of the underlying mechanisms for hypoxia-induced neuroprotection. In a rodent model of hypoxia-ischemia, hypoxia preconditioning improved neuronal survival as demonstrated by decreased hypoxia-ischemia-induced neuronal apoptosis. To study the role of IGF-I in hypoxia tolerance, we used in situ hybridization to examine IGF-I mRNA distribution on adjacent tissue sections. In cerebral cortex and hippocampus, hypoxia preconditioning resulted in an increase in neuronal IGF-I mRNA levels with or without hypoxia-ischemia. To test its direct effects, we added IGF-I to primary neuronal culture under varying oxygen concentrations. As oxygen concentration decreased, neuronal survival also decreased, which could be reversed by IGF-I, especially at the lowest oxygen concentration. Interestingly, IGF-I treatment resulted in an activation of hypoxia-inducible factor 1alpha (HIF-1alpha), a master transcription factor for hypoxia-induced metabolic adaptation. To evaluate whether IGF-I transcriptional activation correlates with HIF-1alpha activity, we studied the time course of HIF-1alpha DNA binding activity in the same rat model of hypoxia-ischemia. After hypoxia-ischemia, there was an increase in HIF-1alpha DNA binding activity in cortical tissues, with the highest increase around 24 h. Like IGF-I mRNA levels, hypoxia preconditioning increased HIF-1alpha DNA binding activity alone or with subsequent hypoxia ischemia. Overall, our results suggest that IGF-I transcriptional activation is one of the metabolic adaptive responses to hypoxia, which is likely mediated by a direct activation of HIF-1alpha.
PURPOSE OF REVIEW: The transcription factor hypoxia-inducible factor is activated by low oxygen to promote the expression of target genes that allow cellular, tissue, and organismal adaptation to low oxygen. Hypoxia-inducible factor is activated not only by hypoxia but also as a consequence of genetic mutations in a variety of tumors. This review summarizes recent studies on hypoxia-inducible factor-alpha functions in development and tumorigenesis. RECENT FINDINGS: Deficiency of the tumor suppressor von Hippel-Lindau leads to constitutively active hypoxia-inducible factor and hypoxia-inducible factor target gene expression. Other genetic lesions, however, e.g. in JunD, can also result in elevated hypoxia-inducible factor levels. The specific functions of hypoxia-inducible factor-1alpha and hypoxia-inducible factor-2alpha during development and tumor growth remain incompletely understood. Whereas hypoxia-inducible factor-2alpha seems to be the critical hypoxia factor in renal cell carcinoma, hypoxia-inducible factor-1alpha plays a significant role in the growth of tumors in other tissues. Loss of von Hippel-Lindau is not sufficient for neoplastic transformation, suggesting that hypoxia-inducible factor does not act alone to cause tumors. SUMMARY: It will be important to further characterize the specific roles of hypoxia-inducible factor-1alpha and hypoxia-inducible factor-2alpha during tumorigenesis to design therapies targeting the relevant isoform for specific diseases. It is also necessary to investigate the effect of reducing hypoxia-inducible factor levels on other angiogenic factors.
OBJECTIVE: To investigate the dynamic expression of hypoxia inducible factor 1alpha (HIF-1alpha) and vascular endothelial growth factor (VEGF) in pulmonary arteries of rats with hypoxia-induced pulmonary hypertension. METHODS: Forty male adult Wistar rats were randomly divided into five groups: a control group (C group) and groups with hypoxia for 3, 7, 14 and 21 days (H(3), H(7), H(14) and H(21) group), eight rats per group. Mean pulmonary pressure (mPAP), vessel morphometry and right ventricle hypertrophy index (RVHI) were measured. Lungs were inflation fixed for in situ hybridization and immunohistochemistry. RESULTS: mPAP increased significantly after 7-day of hypoxia [(18.41 +/- 0.37) mm Hg, P < 0.05], reaching its peak after 14-day of hypoxia, then remained on the high level. Pulmonary artery remodeling index (outer diameter 100 - 150 micro m) and RVHI became evident after 14-day of hypoxia. Expression of HIF-1alpha protein in control group was poorly positive, but was up-regulated in pulmonary arterial tunica intima of all hypoxic rats. In pulmonary arterial tunica media, the levels of HIF-1alpha protein was markedly up-regulated after 3-day (0.178 +/- 0.017, P < 0.05), reaching its peak after 7-day of hypoxia (0.221 +/- 0.021, P < 0.05), then tended to decline after 14-day and 21-day of hypoxia. HIF-1alpha mRNA staining was poorly positive in control, hypoxia for 3 days and hypoxia for 7 days, but began to increase significantly after 14-day of hypoxia (0.203 +/- 0.024, P < 0.05), then remained stable. Expression of VEGF protein began to increase after 7-day of hypoxia (0.074 +/- 0.022, P < 0.05), reaching its peak after 14-day of hypoxia (0.147 +/- 0.017, P < 0.05), then remained on the high level. VEGF mRNA in control and hypoxia for 3 days was poorly positive, but began to increase after 7-day of hypoxia (0.138 +/- 0.010, P < 0.05), and remained on the high level thereafter. VEGF mRNA located mainly in tunica intima and tunica media, whereas VEGF protein located predominantly in tunica intima. Linear correlation analysis showed that HIF-1alpha mRNA, VEGF, and mPAP were correlated with vessel morphometry and RVHI (P < 0.01). HIF-1alpha protein (tunica intima) was positively correlated with VEGF mRNA and protein (P < 0.01). CONCLUSIONS: HIF-1alpha and VEGF are both involved in the pathogenesis of hypoxia-induced pulmonary hypertension in rats. HIF-1alpha protein may regulate the expression of VEGF gene by transcriptional activation, resulting in the occurrence and development of hypoxic pulmonary hypertension.
A close relationship exists between hypoxia-inducible factor (HIF)-1alpha and pulmonary hypertension. The present study was carried out to explore if there are temporal alterations in HIF-1alpha levels during prolonged hypoxia and after monocrotaline (MCT) treatment. First, young Wistar rats were divided into 5 groups: control, hypoxia-1, hypoxia-2, hypoxia-3 and hypoxia-4. Hypoxic rats were placed in a closed hypobaric chamber (380 mm Hg) for a 1-week (hypoxia-1), 2-week (hypoxia-2), 3-week (hypoxia-3) or 5-week (hypoxia-4) period. Second, other young Wistar rats were divided into 4 groups: control, MCT-1, MCT-2 and MCT-3. MCT-treated rats were injected subcutaneously once with MCT (60 mg/kg) for a 1-week (MCT-1), 2-week (MCT-2) or 3-week (MCT-3) period. Subsequently, pulmonary arterial pressure (Ppa) and the weight ratio of the right ventricle to the left ventricle plus the septum [RV/(LV + S)] were measured, and lungs were obtained for the determination of HIF-1alpha via Western blot analysis. Both hypoxia and MCT induced temporal increases in the Ppa, the ratio RV/(LV + S) and HIF-1alpha levels. A close relationship between the Ppa and HIF-1alpha level was found in both hypoxia- and MCT-treated animals. In addition, the PaO(2) level significantly decreased in rats 1-3 weeks after MCT treatment. These results, along with previous data in the literature, suggest that both chronic hypoxia- and MCT-induced lung hypoxia activate an increase in the production of HIF-1alpha, and result in vascular remodeling and pulmonary hypertension.
In aquatic environments, natural and anthropogenic factors commonly reduce dissolved oxygen (DO) and trigger hypoxia, which threatens the health and survival of aquatic organisms. As an important economic fish species in China, pikeperch (Sander lucioperca) is extremely sensitive to hypoxia. However, there are relatively few reports on how hypoxia and reoxygenation affect its intestinal physiology and microbial community. Three treatment groups were set for pikeperch: normoxia (DO = 8.5 ± 0.5 mg/L), 48 h hypoxia (DO = 2.5 ± 0.1 mg/L), and reoxygenation (48 h hypoxia followed by 6 h reoxygenation at normal DO), to evaluate alterations in intestinal histopathology, tight junction gene expression, oxidative stress, hypoxia signaling molecules and intestinal microbiota composition. The results showed that hypoxia significantly decreased muscularis thickness by approximately 32.5% and reduced the expression of tight junction genes (Occludin, Claudin2, and ZO-2). Moreover, hypoxia significantly increased oxidative stress index levels (GSH-Px, CAT, and MDA), markedly upregulated the expression of Bax, Caspase3, and HIF-1α, while significantly downregulating the expression of Bcl-2, Egln1, and Egln2. Notably, reoxygenation elicited partial compensatory effects against these hypoxia-induced changes. 16S rRNA sequencing analysis revealed that hypoxic stress altered the intestinal microbial community composition of pikeperch and increased its diversity. In the hypoxia group, the abundance of the phylum Bacillota, along with the genera Halomonas and Acinetobacter, was significantly elevated, whereas in the reoxygenation group, the genus Lactobacillus increased approximately 180-fold. The results indicated that hypoxia caused intestinal oxidative damage, cell apoptosis, and intestinal microbiota dysbiosis in pikeperch, while short-term reoxygenation achieved partial recovery from these hypoxia-triggered intestinal injuries. The present research provides valuable references for in-depth exploration of the molecular mechanisms behind the response of pikeperch to acute hypoxia and reoxygenation stress, while also offering a novel perspective to understand the mechanism by which hypoxia impacts intestinal health in fish.
Acute hypoxia increases the endogenous release of nitric oxide (NO) in rat carotid body and the expression of nitric oxide synthases is modulated by chronic hypoxia. The aim of the study was to examine hypoxia-induced NO generation in rat carotid body adapted to chronic hypoxia with inspired oxygen at 10% for 4 weeks. The concentration of NO was measured electrochemically with a Pt/Nafion/Pd-IrOx/POAP modified electrode inserted into the isolated carotid body superfused with bicarbonate-buffer saline at 35 degrees C. Acute hypoxia increased the concentration of NO by 471.3+/-71.4 nM in the carotid body of chronically hypoxic (CH) rats. The amount of NO release induced by hypoxia was significantly augmented when compared with that of the normoxic control (87.6+/-15.9 nM). The hypoxia-induced NO generation was markedly attenuated by pretreatment with L- NG-nitroarginine methylester (L-NAME; 500 microM), a non-selective nitric oxide synthase (NOS) inhibitor and also by removal of extracellular calcium with the calcium chelator EGTA (5 mM). Additionally, NO generation during hypoxia was reduced by 30% in the CH carotid body treated with S-methylisothiourea (SMT; 50 microM), a specific blocker of inducible NOS (iNOS). Immunohistochemical study revealed that positive iNOS protein immunoreactivity was detected in clusters of glomus cells in the carotid bodies of CH rats, but not in the normoxic group. Thus, chronic hypoxia enhances hypoxia-induced NO generation mediated by calcium-dependent NOSs and iNOS in the carotid body. Extracellular recording of sinus nerve activity of CH carotid bodies showed that L-NAME treatment enhanced the afferent discharge in response to hypoxia, confirming that the generation of NO suppresses the activities of carotid chemoreceptors. Taken together, our results suggest that hypoxia-induced NO production increases in the rat carotid body adapted to chronic hypoxia and that constitutive and inducible NOSs are involved in the NO generation. The enhancement of NO generation may play a physiological role in blunting the hypoxic chemosensitivity during chronic hypoxia.