Hypoxia-inducible Factor 1 Beta Research Articles

Advances in Hypoxia-Inducible Factor 1-Alpha and Ischemic Heart Disease

Ischemic heart disease, resulting from ischemic and anoxic cardiomyocytes, can lead to the abnormal metabolic activity which is able to result in some serious diseases including cardiac failure, thrombus and other deadly disease and it is also the bad factor to the health of human. Besides, oxidative stress resulting from ischemic heart disease is one of the most serious factors of this disease which can destroy the healthy tissue, protein and so on. Hypoxia, as a signal, is able to launch hypoxia-inducible factor 1-alpha which lives in cytoplasm. It transfers to cell nucleus to achieve its aim, which means hypoxia-inducible factor 1-alpha is going to bind to hypoxia-inducible factor 1-beta first, then start some downstream promoters to facilitate several target genes such as vascular endothelial growth factor, inducible nitric oxide synthase, necessary enzyme of glycolysis and erythropoietin. Reactive oxygen species has also been proved that, it can start hypoxia-inducible factor 1-alpha as the second messenger. At the moment, hypoxia-inducible factor 1-alpha has been proved that, it is influential for ischemic heart disease through some pathways such as the increased angiogenesis, promoting glycolysis and the decreased reactive oxygen species. In this review, we discussed the advances in hypoxiainducible factor 1-alpha and ischemic heart disease.

Low-Load Resistance Exercise with Blood Flow Restriction Increases Hypoxia-Induced Angiogenic Genes Expression.

The aim of the study was to determine whether low-load exercise (LL) with blood flow restriction (LL-BFR) would induce similar changes in expression of genes involved in hypoxia and angiogenesis compared to LL and high-load exercise (HL). Twenty-four males (age: 21.3 ± 1.9 years, body height: 1.74 ± 0.8 m, body mass: 73 ± 1.8 kg) were allocated into three groups: low-load exercise (LL), low-load exercise with blood-flow restriction (LL-BFR), and high-load exercise (HL). For the LL-BFR group a pneumatic cuff was inflated at 80% of the arterial occlusion pressure. All participants performed bilateral knee extension exercise, twice a week, for 8 weeks. LL and LL-BFR groups performed 3-4 sets of 15 reps at 20% 1RM, whilst the HL group performed 3-4 sets of 8-10 reps at 80% 1RM with a 60-s rest interval between sets. The hypoxia-inducible factor-1 alpha (HIF-1α) and beta (HIF-1β), vascular endothelial growth factor (VEGF), neuronal (nNOS), and inducible nitric oxide synthase (iNOS) genes expression were assessed before and after training. HIF-1α and HIF-1β mRNA levels significantly increased in the LL-BFR group and exceeded those elicited by HL and LL groups (p < .0001). VEGF gene expression was increased in both LL-BFR and HL groups, however, LL-BFR elicited a greater increase than LL (p < .0001). nNOS and iNOS genes expression significantly increased in all groups with greatest increases being observed in the LL-BFR group (p < .0001). The findings suggest that LL-BFR induces greater increases in genes expression related to hypoxia and angiogenesis than traditional resistance training.

Myoblast differentiation of C2C12 cell may related with oxidative stress.

Muscle is a contractile tissue responsible for maintaining posture and the movement of all parts of the body. Prolonged oxidizative stress can lead to the damage of cells, tissues, and organs. In this study, we investigated the possibility of oxidative stress in the process of myoblast differentiation of C2C12 cells. First, the myoblast differentiation model of C2C12 cells was constructed and verified by Giemsa staining. The expression of hypoxia inducible factor1-alpha (HIF1-α), hypoxia inducible factor1-beta (HIF1-β), Von Hippel-Lindau (VHL), lysyl oxidase (Lox), EGL-9 family hypoxia-inducible factor 1 (EGLN1), proline 4-hydroxylase alpha 1 (P4HA1) and heme oxygenase-1 (HOMX1) in the process of myoblast differentiation was verified by in vitro experiments and Gene Expression Omnibus (GEO) bioinformatic analysis. We found that with the increased expression of myogenic factor 5 (MYF5), myogenic differentiation 1 (MYOD1), and Desmin, myotube fusion became more obvious during the process of C2C12 cell differentiation. Both experimental and GEO analysis indicated that the expression of HIF1-α, HIF1-β, VHL, LOX, EGLN1 and P4HA1 increased, and the expression of HOMX1 decreased during myogenic differentiation. Therefore, we suggest that the myoblast differentiation of C2C12 cells may be related to oxidative stress. Their possible relationship was proposed, though further studies are needed.

Hypoxic Gene Signature of Primary and Metastatic Melanoma Cell Lines: Focusing on HIF-1β and NDRG-1

Background:Hypoxia is an important microenvironmental factor significantly affecting tumor proliferation and progression. The importance of hypoxia is, however, not well known in oncogenesis of malignant melanoma.Aims:To evaluate the difference of hypoxic gene expression signatures in primary melanoma cell lines and metastatic melanoma cell lines and to find the expression changes of hypoxia-related genes in primary melanoma cell lines at experimental hypoxic conditions.Study Design:Cell study.Methods:The mRNA expression levels of hypoxia-related genes in primary melanoma cell lines and metastatic melanoma cell lines and at experimental hypoxic conditions in primary melanoma cell lines were evaluated by using real-time polymerase chain reaction. Depending on the experimental data, we focused on two genes/proteins, the hypoxia-inducible factor-1 beta and the N-myc downstream regulated gene-1. The expression levels of the two proteins were investigated by immunohistochemistry methods in 16 primary and metastatic melanomas, 10 intradermal nevi, and a commercial tissue array comprised of 208 cores including 192 primary and metastatic malignant melanomas.Results:The real-time polymerase chain reaction study showed that hypoxic gene expression signature was different between metastatic melanoma cell lines and primary melanoma cell lines. Hypoxic experimental conditions significantly affected the hypoxic gene expression signature. In immunohistochemical study, N-myc downstream regulated gene-1 expression was found to be lower in primary cutaneous melanoma compared to in intradermal nevi (p=0.001). In contrast, the cytoplasmic expression of hypoxia-inducible factor-1 beta was higher in primary cutaneous melanoma than in intradermal nevi (p=0.001). We also detected medium/strong significant correlations between the two proteins studied in the study groups.Conclusion:Hypoxic response consists of closely related proteins in more complex pathways. These findings will shed light on hypoxic processes in melanoma and unlock a Pandora’s box for development of new therapeutic strategies.

Activation of hypoxia-inducible factor\xa01 attenuates periapical inflammation and bone loss

Hypoxia (low oxygen level) is an important feature during infections and affects the host defence mechanisms. The host has evolved specific responses to address hypoxia, which are strongly dependent on the activation of hypoxia-inducible factor 1 (HIF-1). Hypoxia interferes degradation of HIF-1 alpha subunit (HIF-1α), leading to stabilisation of HIF-1α, heterodimerization with HIF-1 beta subunit (HIF-1β) and subsequent activation of HIF-1 pathway. Apical periodontitis (periapical lesion) is a consequence of endodontic infection and ultimately results in destruction of tooth-supporting tissue, including alveolar bone. Thus far, the role of HIF-1 in periapical lesions has not been systematically examined. In the present study, we determined the role of HIF-1 in a well-characterised mouse periapical lesion model using two HIF-1α-activating strategies, dimethyloxalylglycine (DMOG) and adenovirus-induced constitutively active HIF-1α (CA-HIF1A). Both DMOG and CA-HIF1A attenuated periapical inflammation and tissue destruction. The attenuation in vivo was associated with downregulation of nuclear factor-κappa B (NF-κB) and osteoclastic gene expressions. These two agents also suppressed NF-κB activation and subsequent production of proinflammatory cytokines by macrophages. Furthermore, activation of HIF-1α by DMOG specifically suppressed lipopolysaccharide-stimulated macrophage differentiation into M1 cells, increasing the ratio of M2 macrophages against M1 cells. Taken together, our data indicated that activation of HIF-1 plays a protective role in the development of apical periodontitis via downregulation of NF-κB, proinflammatory cytokines, M1 macrophages and osteoclastogenesis.

Abstract 306: Endothelial Arnt Mediates Cardiac Remodeling After Ischemia Reperfusion Injury Through an MMP Pathway

Background: Prevention of myocardial injury following heart attack is a challenge due to lack of effective treatments and the potential to develop chronic heart failure (HF). Impaired endothelial function is thought to contribute to the progression of HF after cardiac ischemia-reperfusion injury (IR). However, the underlying mechanisms are unknown. Aryl Hydrocarbon Receptor Nuclear Translocator (ARNT), also known as hypoxia-inducible factor 1-beta (HIF1-β), plays a major role in vascular endothelial function and is implicated in ischemic diseases. We hypothesize that endothelial ARNT mediates cardiac remodeling following IR. Methods and Results: We generated inducible endothelial specific ARNT knockout mice (ecARNT -/- ) by crossing mice with loxP sequences flanking exon 6 of ARNT with Cre ERT2 mice under the VE-cadherin promoter. A 90% deletion of ecARNT was achieved following two weeks of oral tamoxifen administration. ecARNT -/- mice exhibit severe cardiac blood vessel leakage and impaired cardiac function after IR. Following 1 month of IR, ecARNT -/- mice had a 50% mortality rate, while no mortality was observed in the control group (ARNTf/f mice treated with tamoxifen). To determine the underlying mechanisms by which ARNT regulates endothelial function, we performed DNA sequencing on cardiac microvascular endothelial cells (CMECs) isolated from control and ecARNT -/- hearts. Data suggest a significant increase in the matrix metalloproteinases (MMP) family of proteins following ARNT knockdown. An increase in MMP activity in the serum of ecARNT -/- CMECs after IR was also detected. Moreover, use of an MMP inhibitor in vivo rescues heart failure induced by IR in ecARNT -/- mice. Taken together, these results suggest that ecARNT may mediate heart failure during IR through an MMP pathway. Conclusion: Endothelial ARNT is a critical regulator of endothelial function and could potentially serve as a therapeutic target for HF in response to IR injury.

Possible role for HIF-1?/ARNT in the regulation of vascular function in diabetes and cardiovascular disease

Aryl hydrocarbon receptor nuclear translocator (ARNT), also known as hypoxia-inducible factor-1 beta (HIF-1β), is a transcription factor that functions as a master regulator of glucose homeostasis. We have previously demonstrated that ARNT expression is highest in the heart, where it is required for maintaining normal cardiac metabolism and cardiac function. Diabetes is associated with a loss of ARNT, although the specific role of ARNT in the diabetic heart is still unknown. Diabetes is also characterized by endothelial dysfunction. Thus, investigating the role of endothelial ARNT in diabetic cardiovascular disease could lead to new therapies for treatment or prevention.

Silencing of hypoxia-inducible factor-1β induces anti-tumor effects in hepatoma cell lines under tumor hypoxia.

Dimerization of hypoxia-inducible factor-1 beta (HIF-1β) [aryl hydrocarbon receptor nuclear translocator (ARNT)] with HIF-1α is involved in various aspects of cancer biology, including proliferation and survival under hypoxic conditions. We investigated the in vitro mechanism by which silencing of HIF-1β leads to the suppression of tumor cell growth and cellular functions. Various hepatocellular carcinoma (HCC) cell lines (Huh-7, Hep3B, and HepG2) were transfected with small interfering RNA (siRNA) against HIF-1β (siHIF-1β) and cultured under hypoxic conditions (1% O2 for 24 h). The expression levels of HIF-1β, HIF-1α, and growth factors were examined by immunoblotting. Tumor growth was measured using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, and tumor activity was measured by terminal deoxynucleotidyl transferase dUTP nick end labeling, tumor cell invasion, and migration assays. Under hypoxic conditions, silencing of HIF-1β expression suppressed tumor cell growth and regulated the expression of tumor growth-related factors, such as vascular endothelial growth factor, epidermal growth factor, and hepatocyte growth factor. Suppression of tumor cell invasion and migration was also demonstrated in HIF-1β-silenced HCC cell lines. Silencing of HIF-1β expression may induce anti-tumor effects under hypoxic conditions in HCC cell lines.

Differential distribution of hypoxia-inducible factor 1-beta (ARNT or ARNT2) in mouse substantia nigra and ventral tegmental area

Hypoxia has been proposed as a mechanism underlying gene–environment interactions in the neurodevelopmental model of schizophrenia, and hypoxia-inducible factor 1 (HIF-1) could mediate the interactions. In the current study, we analyzed the HIF-1 beta subunit, as formed by aryl hydrocarbon receptor nuclear translocator (ARNT) or ARNT2, in the mouse substantia nigra (SN) and the ventral tegmental area (VTA). We performed immunohistochemical studies of ARNT and ARNT2 in the adult mouse brain, and colocalization analyses, with specific emphasis on dopaminergic cells, i.e. tyrosine hydroxylase (TH) immunoreactive cells. Bioinformatic analyses identified shared protein partners for ARNT and ARNT2. ARNT immunoreactivity showed widespread neuronal labeling without overt regional specificity. We observed co-localization of ARNT and TH in the SN compacta and VTA. Nuclei strongly labeled for ARNT2 were observed in the SN reticulata, while only weak immunoreactivity for ARNT2 was found in TH-immunoreactive neurons in SN compacta and VTA. Stereological analysis showed that ARNT was preferentially expressed in dopaminergic neurons in SN compacta and VTA. Nuclei strongly labeled for ARNT2 were present in neocortex and CA1 of hippocampus. Differential expression of ARNT and ARNT2 in dopaminergic neurons may relate to the vulnerability of distinct dopaminergic projections to hypoxia and to functional vulnerability in schizophrenia and other neuropsychiatric disorders.

713: Impaired fetoplacental angiogenesis in fetal growth restriction is mediated by hypoxia inducible factor 1-beta (HIF1β)

Fetal growth restriction with abnormal umbilical artery Doppler velocimetry (FGRadv) increases risk for adverse perinatal outcome. Impaired branching angiogenesis in the second half of pregnancy contributes to this phenotype. Low oxygen tension is one key mediator of angiogenesis, and physiologic pO2 within the fetoplacental circulation is more hypoxemic than that of postnatal life, suggesting that hypoxia may be one regulator of fetoplacental angiogenesis. We sought to determine whether there was an intrinsic defect within fetoplacental endothelium and to delineate the molecular mechanisms by which branching angiogenesis was deficient.

Abstract 16841: Cardiac Deletion of Aryl Hydrocarbon Nuclear Translocator (Hypoxia Inducible Factor 1-beta) in the Adult Heart Leads to Cardiomyopathy Due to Lipid Accumulation via Peroxisome Proliferator Activated Receptor Activation

Background: Aryl hydrocarbon receptor nuclear translocator (ARNT), also known as hypoxia-inducible factor 1-beta (HIF1-beta), serves as a binding partner for numerous basic helix-loop-helix Per/ARNT/Sim proteins, including HIF1alpha. Although HIF1alpha is known to be required for normal cardiac development, the role of ARNT in basal cardiac function in the adult is not known. We hypothesized that ARNT is required for normal cardiac physiology, and that ARNT deletion in the adult heart results in cardiomyopathy. Methods and Results: Cardiac-specific ARNT deletion was achieved by crossing ARNT flox/flox with αMHC-MCM (tamoxifen-inducible heart specific Cre) transgenic mice, followed by oral administration of tamoxifen. MCM/ARNT +/+ (WT) littermates were used as a control. Echocardiography of the ARNT knockout (KO) mice showed enlarged left ventricle with a reduction in ejection fraction (KO vs. WT: 35.8 ± 3.6% vs. 61.2 ± 2.8%, n=12, p&lt;0.01). Closed-chest catheterization indicated that +dP/dt (KO vs. WT: 4355 ± 538 vs. 9426 ± 180 mmHg, p&lt;0.01) was reduced in KO mice but not in WT mice. Electron microscopy revealed lipid droplets in ARNT KO heart tissues that were confirmed by oil-red staining. Furthermore, genes involved in fatty acid oxidation were up-regulated in KO hearts, as shown by microarray analysis and qRT-PCR. We further confirmed these results in vitro with siRNA-mediated knock down of ARNT in H9c2 cardiac myoblasts. Compared to control siRNA transfection, ARNT knockdown led to increases in PPAR-alpha (1.7-fold, p&lt;0.001), fatty acid translocase (1.4-fold, P&lt;0.01), and acyl-coenzyme A dehydrogenase (1.6-fold, p&lt;0.0001) mRNA levels and to enhanced triglyceride accumulation (p&lt;0.05). Moreover, insulin resistance was noted in ARNT knockdown cells, as demonstrated by significantly reduced glucose uptake in response to insulin stimulation. These results suggest that impaired fatty acid oxidation leads to lipid accumulation in response to a reduction in ARNT levels. Conclusion: ARNT is essential for normal cardiac function, and a reduction in ARNT levels leads to cardiomyopathy by increasing triglyceride accumulation through a PPAR-alpha pathway.

Burn wound homing of bone marrow-derived angiogenic cells is impaired by conditional knock out of the hypoxia-inducible factor 1beta gene

Burn wound homing of bone marrow-derived angiogenic cells is impaired by conditional knock out of the hypoxia-inducible factor 1beta gene

Single nucleotide polymorphisms in the hypoxia‐inducible factor‐1 gene and colorectal cancer risk

With an incidence of about 300 000 new cases colorectal cancer (CRC) is the second leading cause of cancer-related death in Europe and the United States. Environmental and genetic factors influence CRC risk. Hypoxia-inducible factor-1 (HIF-1), a heterodimeric protein composed of two subunits, HIF-1 alpha and HIF-1 beta, plays a critical role in oxygen homeostasis and is involved in angiogenesis and cell proliferation. The gene for the HIF-1 alpha subunit (HIF1A) carries two common missense mutations-P582S (rs11549465) and A588T (rs11549467)-which both have been related to increased trans-activation capacity of HIF1A. In our case-control study we investigated the association between these polymorphisms and CRC risk. We investigated 381 patients with histologically confirmed CRC and 2156 control subjects. HIF1A genotypes were determined by exonuclease (TaqMan) assays. For determination of microvessel density (MVD) tumor sections were stained using a mouse monoclonal antibody recognizing the pan-endothelial marker CD31. In a multivariate logistic regression analysis including age and sex neither the HIF1A 582S allele (Odds ratio: 1.204; 95% confidence interval 0.911-1.592; P = 0.193) nor the 588T allele was significantly associated with CRC (Odds ratio: 0.851; 95% confidence interval 0.444-1.631; P = 0.626). However, in an exploratory analysis, the HIF1A 588T allele was associated with tumor localization (P = 0.016) and tumor size (P = 0.003). MVD was similar in tumors of patients carrying HIF1A 588T allele and patients without this rare allele. We conclude that functional polymorphisms in the HIF1A gene do not modify CRC risk but maybe associated with clinic-pathological features of the disease.

Significance of p27kip1as potential biomarker for intracellular oxidative status

Our previous proteomic study demonstrated that oxidative stress and antioxidant delphinidin regulated the cellular level of p27kip1 (referred to as p27) as well as some heat shock proteins in human colon cancer HT 29 cells. Current study was conducted to validate and confirm the regulation of these proteins using both in vitro and in vivo systems. The level of p27 was decreased by hydrogen peroxide in a dose-dependent manner in human colon carcinoma HCT 116 (p53-positive) cells while it was increased upon exposure to hydrogen peroxide in HT 29 (p53-negative) cells. However, high concentration of hydrogen peroxide (100 µM) downregulated p27 in both cell lines, but delphindin, one of antioxidative anthocyanins, enhanced the level of p27 suppressed by 100 µM hydrogen peroxide. ICR mice were injected with varying concentrations of hydrogen peroxide, delphinidin and both. Western blot analysis for the mouse large intestinal tissue showed that the expression of p27 was upregulated by 25 mg/kg BW hydrogen peroxide. To investigate the association of p27 regulation with hypoxia-inducible factor 1-beta (HIF-1β), the level of p27 was analyzed in wild-type mouse hepatoma hepa1c1c7 and Aryl Hydrocarbon Nuclear Translocator (arnt, HIF-1β)-defective mutant BPRc1 cells in the absence and presence of hydrogen peroxide and delphinidin. While the level of p27 was responsive to hydrogen peroxide and delphinidin, it remained unchanged in BPRc1, suggesting that the regulation of p27 requires functional HIF-1β. We also found that hydrogen peroxide and delphinidin affected PI3K/Akt/mTOR signaling pathway which is one of upstream regulators of HIFs. In conclusion, hydrogen peroxide and antioxidant delphinidin seem to regulate intracellular level of p27 through regulating HIF-1 level which is, in turn, governed by its upstream regulators comprising of PI3K/Akt/mTOR signaling pathway. The results should also encourage further study for the potential of p27 as a biomarker for intracellular oxidative or antioxidant status.

Aryl hydrocarbon nuclear translocator (hypoxia inducible factor 1β) activity is required more during early than late tumor growth

c4 is a derivative of the mouse hepatoma cell line, Hepa-1, that harbors a mutation in the aryl hydrocarbon receptor nuclear translocator gene (Arnt, or hypoxia inducible factor 1beta [HIF-1beta]) leading to loss of activity. Clone 3 cells were generated by introducing a doxycycline-repressible Arnt expression vector into c4 cells. Clone 3 cells were injected subcutaneously into immunosuppressed mice, which were treated with doxycyline (a) throughout the growth of the subsequent tumor xenografts, or (b) from day 7 through to the end of the experiment (day 30), or not treated (c). Tumors in all groups grew exponentially between days 14 and 30, and at rates that were indistinguishable from each other. However, tumors in group a were smaller than those of the other two groups throughout the measurable growth period, while tumor volumes in groups b and c were not significantly different from each other. The degrees of vascularity and apoptosis did not correlate with the differences in degrees of growth between the different groups. Thus, Arnt is required during the early stages of growth of the tumors but less in later stages. Since Arnt does not detectably effect the growth kinetics of Hepa-1 cells either during hypoxia or normoxia, this requirement is unlikely to reflect a direct effect of Arnt on cell proliferation, and is therefore probably a consequence of altered interaction(s) between the tumor cells and the host. These studies suggest that Arnt (and HIF-1alpha/HIF-2alpha) inhibitors will be particularly effective against smaller tumors, including micrometastases.

Effects of Radix et Rhizoma Rhodiolae Kirilowii on expressions of von Willebrand factor, hypoxia-inducible factor 1 and vascular endothelial growth factor in myocardium of rats with acute myocardial infarction

To investigate the effects of Radix et Rhizoma Rhodiolae Kirilowii on angiogenesis and expressions of hypoxia-inducible factor 1alpha (HIF-1alpha), hypoxia-inducible factor 1beta (HIF-1beta) and vascular endothelial growth factor (VEGF) in myocardium of rats with acute myocardial infarction (AMI), to elucidate the possible mechanism of Radix et Rhizoma Rhodiolae Kirilowii in promoting angiogenesis, and to investigate that whether or not salidroside could be considered as the effective component of Radix et Rhizoma Rhodiolae Kirilowii with regard to the effects mentioned above. Thirty-six male Wistar rats had the anterior descending branch of coronary artery ligated as AMI model. Rats were fed with normal saline (untreated group), Radix et Rhizoma Rhodiolae Kirilowii solution (Radix et Rhizoma Rhodiolae Kirilowii group) or salidroside solution (salidroside group) from 7 days before until 7 days after the operation, with twelve rats in each group. All rats were sacrificed 7 days after the operation. Immunohistochemical assay (IHC) was used for detecting the expression of von Willebrand factor (vWF); TaqMan real-time quantitative polymerase chain reaction (PCR) assay was employed for detection of the levels of HIF-1alpha, HIF-1beta and VEGF mRNAs; Western blot analysis was used for detection of the corresponding protein levels. Results of IHC index showed that both at infarct border zone and non-infarct zone, the expressions of vWF were significantly increased in Radix et Rhizoma Rhodiolae Kirilowii group as compared with the untreated group (P<0.05). The expressions of HIF-1alpha, HIF-1beta and VEGF mRNAs and the expressions of HIF-1alpha and VEGF proteins were significantly increased in the Radix et Rhizoma Rhodiolae Kirilowii group as compared with the untreated group (P<0.01). The level of HIF-1beta protein in the Radix et Rhizoma Rhodiolae Kirilowii group was also higher than that in the untreated group but the difference was not statistically significant (P>0.05). All the expression levels, including those of vWF, HIF-1alpha, HIF-1beta and VEGF, in the salidroside group were higher than those in the untreated group while lower than those in the Radix et Rhizoma Rhodiolae Kirilowii group. Radix et Rhizoma Rhodiolae Kirilowii may promote angiogenesis in myocardium of rats with AMI through elevating the expressions of HIF-1alpha, HIF-1beta, and VEGF. Salidroside may be one of the effective components in Radix et Rhizoma Rhodiolae Kirilowii, which increases the expressions of HIF-1alpha, HIF-1beta and VEGF during ischemia or hypoxia.

Transglutaminase 2 protects against ischemic insult, interacts with HIF1β, and attenuates HIF1 signaling

Transglutaminase 2 (TG2) is a multifunctional enzyme that has been implicated in the pathogenesis of neurodegenerative diseases, ischemia, and stroke. The mechanism by which TG2 modulates disease progression have not been elucidated. In this study we investigate the role of TG2 in the cellular response to ischemia and hypoxia. TG2 is up-regulated in neurons exposed to oxygen and glucose deprivation (OGD), and increased TG2 expression protects neurons against OGD-induced cell death independent of its transamidating activity. We identified hypoxia inducible factor 1beta (HIF1beta) as a TG2 binding partner. HIF1beta and HIF1alpha together form the heterodimeric transcription factor hypoxia inducible factor 1 (HIF1). TG2 and the transaminase-inactive mutant C277S-TG2 inhibited a HIF-dependent transcription reporter assay under hypoxic conditions without affecting nuclear protein levels for HIF1alpha or HIF1beta, their ability to form the HIF1 heterodimeric transcription factor, or HIF1 binding to its DNA response element. Interestingly, TG2 attenuates the up-regulation of the HIF-dependent proapoptotic gene Bnip3 in response to OGD but had no effect on the expression of VEGF, which has been linked to prosurvival processes. This study demonstrates for the first time that TG2 protects against OGD, interacts with HIF1beta, and attenuates the HIF1 hypoxic response pathway. These results indicate that TG2 may play an important role in protecting against the delayed neuronal cell death in ischemia and stroke.

Loss of Mcl-1 protein and inhibition of electron transport chain together induce anoxic cell death.

How cells die in the absence of oxygen (anoxia) is not understood. Here we report that cells deficient in Bax and Bak or caspase-9 do not undergo anoxia-induced cell death. However, the caspase-9 null cells do not survive reoxygenation due to the generation of mitochondrial reactive oxygen species. The individual loss of Bim, Bid, Puma, Noxa, Bad, caspase-2, or hypoxia-inducible factor 1beta, which are potential upstream regulators of Bax or Bak, did not prevent anoxia-induced cell death. Anoxia triggered the loss of the Mcl-1 protein upstream of Bax/Bak activation. Cells containing a mitochondrial DNA cytochrome b 4-base-pair deletion ([rho(-)] cells) and cells depleted of their entire mitochondrial DNA ([rho(0)] cells) are oxidative phosphorylation incompetent and displayed loss of the Mcl-1 protein under anoxia. [rho(0)] cells, in contrast to [rho(-)] cells, did not die under anoxia. However, [rho(0)] cells did undergo cell death in the presence of the Bad BH3 peptide, an inhibitor of Bcl-X(L)/Bcl-2 proteins. These results indicate that [rho(0)] cells survive under anoxia despite the loss of Mcl-1 protein due to residual prosurvival activity of the Bcl-X(L)/Bcl-2 proteins. Collectively, these results demonstrate that anoxia-induced cell death requires the loss of Mcl-1 protein and inhibition of the electron transport chain to negate Bcl-X(L)/Bcl-2 proteins.

The homozygous P582S mutation in the oxygen‐dependent degradation domain of HIF‐1α is associated with increased risk for prostate cancer

The heterodimeric transcription factor HIF-1 (hypoxia-inducible factor 1), consisting of a critically regulated HIF-1 alpha subunit and a constitutively expressed HIF-1 beta subunit, is a master regulator of genes involved in adaptation and survival under low-oxygen conditions. Increased levels of HIF-1 activity are associated with increased tumor aggressiveness, therapeutic resistance, and mortality. We studied 402 prostate cancer patients for the presence of the 1772C > T (P582S) and 1790G > A (A588T) mutations within the oxygen-dependent domain of HIF-1 alpha. Homozygosity for the P582S mutation was fourfold greater among prostate cancer patients compared to controls (OR = 4.10 [C.I. 95% 1.11 < OR < 17.87], P = 0.018). The existence of this mutation in prostate cancer patients was not associated with any of the clinical or pathological characteristics of the disease. No significant differences were found between the frequencies of A588T mutation in prostate cancer patients and controls. Our data suggest that homozygous HIF1A P582S mutation confers significant susceptibility to prostate cancer.

Hypoxia and angiogenesis in rheumatoid arthritis

Angiogenesis is a prominent feature of rheumatoid synovitis. Although new blood vessels deliver oxygen to the augmented inflammatory cell mass, the neovascular network is dysfunctional and fails to restore tissue oxygen homeostasis, so that the rheumatoid joint remains a markedly hypoxic environment. The purpose of this review is to discuss the role of hypoxia and angiogenesis in the pathogenesis of rheumatoid arthritis. Vascular pathologic change, in the form of angiogenesis, is important in the perpetuation of rheumatoid arthritis and, in the form of endothelial dysfunction, contributes to associated cardiovascular comorbidity. Recent data suggest that tumor necrosis factor-alpha blockade may modify the vascular pathologic changes in rheumatoid arthritis. Angiogenesis is a prominent feature of rheumatoid synovitis. Emerging evidence based on ultrasonographic vascular imaging and angiogenic biomarkers implicates angiogenesis in the active phase of erosive disease. Many factors contribute to the profoundly hypoxic environment that can arise within the joint affected by rheumatoid arthritis. At a cellular level, hypoxia is detected by a mechanism that regulates cytoplasmic concentrations of hypoxia-inducible factor-1alpha. After translocation to the nucleus, hypoxia-inducible factor-1alpha binds its partner hypoxia-inducible factor-1beta to form a heterodimeric, functional transcription factor, hypoxia-inducible factor-1, which activates a gene program associated with angiogenesis, glycolysis, and adaptation to pH. Despite the luxuriant vasculature associated with rheumatoid arthritis synovitis, the joint affected by rheumatoid arthritis is hypoxic. Repetitive cycles of hypoxia and reoxygenation together with oxidants produced by phagocytic cells promote chronic oxidative stress within the microenvironment of the affected joint, leading to the generation of reactive oxygen species with the potential to contribute to tissue damage.