Regulation Of Hypoxia-inducible Factor-1alpha Research Articles

Empagliflozin Protects Against Proximal Renal Tubular Cell Injury Induced by High Glucose via Regulation of Hypoxia-Inducible Factor 1-Alpha.

BackgroundEvidence from both animal and human studies clearly supports the renal beneficial effects of empagliflozin (emp), a sodium glucose co-transporter 2 (SGLT2) inhibitor, but the mechanism in which it exerts its effect is not well understood. In this study, we investigated the capability of emp on reducing hyperglycemia-induced renal proximal tubular epithelial cells injury and we evaluated if the renoprotective effect of emp associates with hypoxia-inducible factor-1α (HIF-1α).Materials and MethodsHuman kidney cell lines (HK-2 cells) were incubated in normoxia, high glucose with or without emp treatment for 72 hours to evaluate the induction of HIF-1α, glucose transporter-1, SGLT2, the fibrosis signal pathway and epithelial–mesenchymal transition (EMT) markers.ResultsHigh glucose (HG) increased expression of Collagen IV, Fibronectin, transforming growth factor-beta1 (TGF-β1). However, emp treatment remarkably decreased expression of TGF-β1, accumulation of extracellular matrix proteins (Fibronectin, Collagen IV), as well as (phosphorylated-smad3) P-smad3. HG increased SGLT2 protein expression compared to normal glucose (NG) while emp significantly decreased SGLT2 expression. Furthermore, emp decreased high glucose-induced alpha-smooth muscle actin (α-SMA) expression and reversed epithelial marker (E-catherin) suppression induced by high glucose. In addition, emp treatment for 72 h increased expression of HIF-1α protein (95% CI: -0.5918 to –0.002338, at 100nM, P < 0.05, 95% CI –0.6631 to –0.07367 at 500nM, P < 0.05) in hyperglycemic normoxic HK-2 cells. Furthermore, we observed increased expression of GLUT-1 protein after emp treatment and remarkably decreased cell proliferation.ConclusionEmp treatment protected proximal renal tubular cells injury induced by high glucose. Induction of HIF-1α expression by emp may play an essential role in the protection of high glucose-induced proximal renal tubular epithelial cells injury.

NPGPx modulates CPEB2-controlled HIF-1α RNA translation in response to oxidative stress.

Non-selenocysteine-containing phospholipid hydroperoxide glutathione peroxidase (NPGPx or GPx7) is an oxidative stress sensor that modulates the antioxidative activity of its target proteins through intermolecular disulfide bond formation. Given NPGPx's role in protecting cells from oxidative damage, identification of the oxidative stress-induced protein complexes, which forms with key stress factors, may offer novel insight into intracellular reactive oxygen species homeostasis. Here, we show that NPGPx forms a disulfide bond with the translational regulator cytoplasmic polyadenylation element-binding protein 2 (CPEB2) that results in negative regulation of hypoxia-inducible factor 1-alpha (HIF-1α) RNA translation. In NPGPx-proficient cells, high oxidative stress that disrupts this bonding compromises the association of CPEB2 with HIF-1α RNA, leading to elevated HIF-1α RNA translation. NPGPx-deficient cells, in contrast, demonstrate increased HIF-1α RNA translation under normoxia with both impaired induction of HIF-1α synthesis and blunted HIF-1α-programmed transcription following oxidative stress. Together, these results reveal a molecular mechanism for how NPGPx mediates CPEB2-controlled HIF-1α RNA translation in a redox-sensitive manner.

Vascular endothelial growth factor (VEGF) regulation by hypoxia inducible factor-1 alpha (HIF1A) starts and peaks during endometrial breakdown, not repair, in a mouse menstrual-like model.

How is vascular endothelial growth factor (VEGF) expression regulated by hypoxia inducible factor 1 alpha (HIF1A) during menstruation? After progesterone (P4) withdrawal, HIF1A was activated and it directly up-regulated VEGF mRNA expression and this regulation was the highest during endometrium breakdown in the mouse menstrual-like model. VEGF, an important angiogenic factor, is known to be essential for endometrial repair, particularly in angiogenesis and re-epithelialization. However, its upstream regulation has not been fully clarified. HIF1 is the first transcription factor response to hypoxia and is closely associated with angiogenesis; it is also an upstream regulator of VEGF mRNA. We investigated the changes in the expression of HIF1A and VEGF after P4 withdrawal and after HIF1A inhibition. The total number of mice used was 62. The treatment duration in the mouse menstrual-like model was 8 days. The mouse menstrual-like model and mouse and human decidual endometrial stromal cells were established to mimic menstruation. Protein and mRNA expressions of HIF1A and VEGF were investigated by immunohistochemistry, Western blot and quantitative PCR. The direct interaction between HIF1A and the Vegf promoter was also investigated by chromatin immunoprecipitation. HIF1A inhibition in vivo and in vitro was achieved by administration of an HIF1A inhibitor and by siRNA knockdown, respectively. HIF1A was translocated to the nucleus from 8 to 16 h after P4 withdrawal, while VEGF mRNA expression was the highest at 12 h. HIF1A directly bound to Vegf promoter during endometrial breakdown, which peaked at 12 h. HIF1A inhibition suppressed VEGF mRNA and protein expression in the mouse menstrual-like model and decidualized stromal cells. Inhibition of HIF1A also suppressed endometrial breakdown. Although HIF1A regulation of VEGF mRNA was confirmed in the mouse menstrual-like model and decidual endometrium stromal cells, the functional regulation of VEGF protein was not further determined. Here, we report that the functional regulation of VEGF was complicate in menstruation. We also report that HIF1A plays a key role in endometrial breakdown. The National Nature Science Foundation of China (No. 30901608), the National Basic Research Program of China (2010CB530403) and the National Science and Technology Support Program (No. 2012BAI32B05). The authors have no conflicts of interest to disclose. This study is not a clinical trial.

Heat-shock-protein 90 protects from downregulation of HIF-1α in calcineurin-induced myocardial hypertrophy

Aim of the studyCapillary/myocyte mismatch is a hallmark of maladaptive myocardial hypertrophy, but the exact mechanisms of this phenomenon remain unknown. We therefore aimed to evaluate the role of calcineurin A in the regulation of hypoxia-inducible factor-1 alpha (HIF-1 alpha) in a calcineurin overexpressing mouse model of myocardial hypertrophy. Methods and resultsMice overexpressing calcineurin A (CnATg) showed persistent upregulation of HIF-1 alpha protein without evidence of a reduction in capillary density despite progressive myocardial hypertrophy. Likewise, overexpression of calcineurin A in isolated cardiomyocytes induced upregulation of HIF-1 alpha protein. In contrast, NFAT-overexpression had no such effect, implying that NFAT-independent mechanisms were responsible for increased HIF-1 alpha levels. In addition, inhibition of HSP90 via the HSP90-inhibitor 17-AAG or siRNA abolished calcineurin A-induced upregulation of HIF-1 alpha. Consequently, upregulation of HIF-1 alpha target genes like VEGF-A, BNIP-3 or PGK-1 was also inhibited by either 17-AAG or siRNA directed against HSP90. Finally, when CnATg mice were treated with 17-AAG, they demonstrated reduced left ventricular function and capillary density. ConclusionsWe describe here for the first time that overexpression of the phosphatase calcineurin A prevents the development of a capillary/myocyte mismatch despite progressive myocardial hypertrophy. This effect was mediated by HSP-90 induced stabilization of HIF-1 alpha. Further work is needed to understand this unexpected cardioprotective effect of calcineurin A.

Abstract 122: 15-lipoxygenase-1 regulation of HIF-1a and angiogenesis

Abstract Expression of 15-lipoxygenase-1(15-LOX-1) is down-regulated in colon and other major human cancer cells. 15-LOX-1 re-expression in cancer cells suppresses colonic tumorigenesis. We recently reported that targeted transgenic 15-LOX-1 expression in murine intestine suppresses colonic tumorigenesis. Nevertheless, the role of 15-LOX-1 loss of expression in cancer epithelial cells in metastases continues to be debated. Hypoxia-inducible factor 1-alpha (HIF-1a) is a transcriptional master regulator that enhances cancer cell survival under hypoxia and the development of various metastatic mechanisms (e.g. upregulation of VEGF to promote angiogenesis). We therefore examined the effects of 15-LOX-1 expression restoration in colon cancer cells on cell survival, migration and invasion, angiogenesis, and HIF-1a expression and stability under hypoxia. We found that 15-LOX-1 re-expression in colon cancer cells inhibited colon cancer cell survival, migration and invasion, VEGF expression, HUVEC cell tubular formation, and HIF-1a protein stability under hypoxia. These findings demonstrate that the loss of 15-LOX-1 significantly contribute to the ability of colon cancer cells to acquire metastasis promoting abilities by increasing a HIF-1 protein stability to up-regulate VEGF production of cancer cells and subsequently angiogenesis. Thus, therapeutic targeting 15-LOX-1 ubiquitous loss in cancer cells has the potential to be used to suppress tumor metastases. Citation Format: Yuanqing Wu, Fei Mao, Xiangsheng Zuo, Micheline J. Moussalli, Elias Elias, Imad Shureiqi. 15-lipoxygenase-1 regulation of HIF-1a and angiogenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 122. doi:10.1158/1538-7445.AM2014-122

Hypoxia Increases the Expression of Stem-Cell Markers and Promotes Clonogenicity in Glioblastoma Neurospheres

Hypoxia promotes the expansion of non-neoplastic stem and precursor cell populations in the normal brain, and is common in malignant brain tumors. We examined the effects of hypoxia on stem-like cells in glioblastoma (GBM). When GBM-derived neurosphere cultures are grown in 1% oxygen, hypoxia-inducible factor 1alpha (HIF1alpha) protein levels increase dramatically, and mRNA encoding other hypoxic response genes, such as those encoding hypoxia-inducible gene-2, lysyl oxidase, and vascular endothelial growth factor, are induced over 10-fold. Hypoxia increases the stem-like side population over fivefold, and the percentage of cells expressing CD133 threefold or more. Notch pathway ligands and targets are also induced. The rise in the stem-like fraction in GBM following hypoxia is paralleled by a twofold increase in clonogenicity. We believe HIF1alpha plays a causal role in these changes, as when oxygen-stable HIF1alpha is expressed in normoxic glioma cells CD133 is induced. We used digoxin, which has been shown to lower HIF protein levels in vitro and in vivo, to inhibit the hypoxic response. Digoxin suppressed HIF1alpha protein expression, HIF1alpha downstream targets, and slowed tumor growth in vivo. In addition, pretreatment with digoxin reduced GBM flank xenograft engraftment of hypoxic GBM cells, and daily intraperitoneal injections of digoxin were able to significantly inhibit the growth of established subcutaneous glioblastoma xenografts, and suppressed expression of vascular endothelial growth factor.

Hypoxia-regulated microRNA-210 modulates mitochondrial function and decreases ISCU and COX10 expression

The mechanisms of compromised mitochondrial function under various pathological conditions, including hypoxia, remain largely unknown. Recent studies have shown that microRNA-210 (miR-210) is induced by hypoxia under the regulation of hypoxia-inducible factor-1alpha and has an important role in cell survival under hypoxic microenvironment. Hence, we hypothesized that miR-210 has a role in regulating mitochondrial metabolism and investigated miR-210 effects on mitochondrial function in cancer cell lines under normal and hypoxic conditions. Our results demonstrate that miR-210 decreases mitochondrial function and upregulates the glycolysis, thus make cancer cells more sensitive to glycolysis inhibitor. miR-210 can also activate the generation of reactive oxygen species (ROS). ISCU (iron-sulfur cluster scaffold homolog) and COX10 (cytochrome c oxidase assembly protein), two important factors of the mitochondria electron transport chain and the tricarboxylic acid cycle have been identified as potential targets of miR-210. The unique means by which miR-210 regulates mitochondrial function reveals an miRNA-mediated link between microenvironmental stress, oxidative phosphorylation, ROS and iron homeostasis.

The effect of alpha-blocker treatment on bladder hypoxia inducible factor-1 alpha regulation during lower urinary tract obstruction

To determine whether alpha1-blocker treatment, in chronic bladder outlet obstruction (BOO), influences bladder tissue ischemia. This prospective study included 60 patients with BOO, of which 40 were under alpha1-blocker medication and 20 without treatment. Patients underwent transurethral resection of the prostate (TURP) or suprapubic prostatectomy (SPP). Ten patients with non-muscle invasive bladder cancer underwent transurethral resection of the bladder tumor and served as the control group. Tissue specimens were immunohistochemically stained for hypoxia inducible factor-1alpha (HIF-1alpha). Bladder tissue from obstructed subjects showed high immunoreactivity to HIF-1alpha. The specimens from the control group, showed no or weak, mainly cytoplasmic immunoreactivity to HIF-1alpha. Patients under alpha -blocker treatment did not differ in the number of HIF-1alpha positive cells compared to subjects with no treatment (median number 86.8 [20-150] and 88.6 [0-175], respectively) (p > 0.05). The lowest bladder pressure at which HIF-1alpha was up regulated, was detected at detrusor pressure Qmax (PdetQmax) = 60 cm H2O. Treatment with alpha-blockers in obstructed patients considered as non-responders, does not result in HIF-1alpha down regulation, thus bladder continues to be under chronic stress.

The regulation of hypoxia inducible factor-1alpha on osteoblast function in postmenopausal osteoporosis

To study the regulation of hypoxia inducible factor-1alpha (HIF-1alpha) on osteoblast function in postmenopausal osteoporosis. From October 2004 to May 2006, Cre-Loxp recombinase was used to create mice which the HIF-1alpha gene in osteoblasts was conditional knock-out, 24 female wild-type (WT) mice and 24 female conditional knock-out (CKO) mice of 3 months old were operated on ovariotomy. At 0,4,8 weeks after operation, bone histomorphometry parameters were measured with computer image analysis in HE stain sections and in tetracycline bone double labeling fluorescence sections; Bone density and the trabecular bone architecture parameters were measured by Micro-CT; The mRNA expression of vascular endothelial growth factors (VEGF), RunX2, OC, ALP were detected with quantitative RT-PCR; The protein expression of VEGF and RunX2 were detected with Western-blotting. In CKO mice, the trabecular number, volume, thickness, bone density, mineral apposition rate (MAR), the expression of VEGF, RunX2, OC, ALP on mRNA level and the expression of VEGF, RunX2 on protein level decreased significantly compared with WT mice especially in 8 weeks after operation. The bone formation ability of osteoblasts in CKO mice was reduced compared with WT mice after ovariotomy. HIF-1alpha can regulate the bone formation ability of osteoblasts in postmenopausal osteoporosis.

Oxidative stress and hypoxia inducible factor-1 alpha regulation

Oxidative stress and hypoxia inducible factor-1 alpha regulation

Thrombin induces angiogenesis and vascular endothelial growth factor expression in human endothelial cells: possible relevance to HIF-1α

The serine protease thrombin present at the site of vascular injury triggers fibrin formation, platelet activation and different cellular responses including angiogenesis. We report a role for thrombin in the human monolayer cultured endothelial cell growth and angiogenesis in 3D collagen gel angiogenesis assay. The angiogenic activity of thrombin is, in part, related to the expression of the vascular endothelial growth factor (VEGF)165 mRNA, assessed by reverse transcriptase-polymerase chain reaction, either in monolayer cultured endothelial cells or in endothelial cells forming capillary-like structures in the 3D collagen gel assay. This expression of VEGF mRNA is associated with a VEGF secretion in the supernatant of thrombin-treated human umbilical vein endothelial cells. The thrombin-induced VEGF165 mRNA expression is associated with the regulation of hypoxia-inducible factor 1alpha, analyzed by Western Blot, in endothelial cells.

Regulation of hypoxia-inducible factor 1alpha is mediated by an O2-dependent degradation domain via the ubiquitin-proteasome pathway.

Hypoxia induces a group of physiologically important genes such as erythropoietin and vascular endothelial growth factor. These genes are transcriptionally up-regulated by hypoxia-inducible factor 1 (HIF-1), a global regulator that belongs to the basic helix-loop-helix PAS family. Although HIF-1 is a heterodimer composed of alpha and beta subunits, its activity is primarily determined by hypoxia-induced stabilization of HIF-1alpha, which is otherwise rapidly degraded in oxygenated cells. We report the identification of an oxygen-dependent degradation (ODD) domain within HIF-1alpha that controls its degradation by the ubiquitin-proteasome pathway. The ODD domain consists of approximately 200 amino acid residues, located in the central region of HIF-1alpha. Because portions of the domain independently confer degradation of HIF-1alpha, deletion of this entire region is required to give rise to a stable HIF-1alpha, capable of heterodimerization, DNA-binding, and transactivation in the absence of hypoxic signaling. Conversely, the ODD domain alone confers oxygen-dependent instability when fused to a stable protein, Gal4. Hence, the ODD domain plays a pivotal role for regulating HIF-1 activity and thereby may provide a means of controlling gene expression by changes in oxygen tension.