HIF Alpha Research Articles

Gliflozins, Erythropoietin, and Erythrocytosis: Is It Renal Normoxia- or Hypoxia-Driven?

The introduction of gliflozins in the management of type 2 diabetes mellitus leads to a better control of hyperglycemia, obesity, hypertension, dyslipidemia, and fluid retention. Most importantly, it also improves renal survival and reduces major cardiovascular events and mortality. Gliflozins were also found to induce erythropoietin (EPO) synthesis, leading to reticulocytosis and erythropoiesis. The mechanism(s) by which gliflozins induce erythropoiesis is a matter of debate. Although the canonical pathway of triggering EPO synthesis is through renal tissue hypoxia, it has been suggested that improved renal oxygenation may facilitate EPO synthesis via non-canonical routes. The latter proposes that the recovery of peritubular interstitial fibroblasts producing erythropoietin (EPO) is responsible for enhanced erythropoiesis. According to this hypothesis, enhanced glucose/sodium re-uptake by proximal tubules in uncontrolled diabetes generates cortical hypoxia, with injury to these cells. Once transport workload declines with the use of SGLT2i, they recover and regain their capacity to produce EPO. In this short communication, we argue that this hypothesis may be wrong and propose that gliflozins likely induce EPO through the documented intensification of renal hypoxia at the corticomedullary junction, related to the translocation of tubular transport from cortical segments to medullary thick ascending limbs. We propose that gliflozins, through intensified hypoxia in this region, trigger local EPO synthesis in peritubular interstitial cells via the canonical pathway of blocking HIF-prolyl hydroxylases (that initiate HIF alpha degradation), with the consequent stabilization of HIF-2 signal and an apocrinic induction of EPO in these same cells.

Integrated Datasets of Proteomic and Metabolomic Biomarkers to Predict Its Impacts on Comorbidities of Type 2 Diabetes Mellitus.

ObjectiveThe objective of the current study is to accomplish a relative exploration of the biological roles of differentially dysregulated genes (DRGs) in type 2 diabetes mellitus (T2DM). The study aimed to determine the impact of these DRGs on the biological pathways and networks that are related to the associated disorders and complications in T2DM and to predict its role as prospective biomarkers.MethodsDatasets obtained from metabolomic and proteomic profiling were used for investigation of the differential expression of the genes. A subset of DRGs was integrated into IPA software to explore its biological pathways, related diseases, and their regulation in T2DM. Upon entry into the IPA, only 94 of the DRGs were recognizable, mapped, and matched within the database.ResultsThe study identified networks that explore the dysregulation of several functions; cell components such as degranulation of cells; molecular transport process and metabolism of cellular proteins; and inflammatory responses. Top disorders associated with DRGs in T2DM are related to organ injuries such as renal damage, connective tissue disorders, and acute inflammatory disorders. Upstream regulator analysis predicted the role of several transcription factors of interest, such as STAT3 and HIF alpha, as well as many kinases such as JAK kinases, which affects the gene expression of the dataset in T2DM. Interleukin 6 (IL6) is the top regulator of the DRGs, followed by leptin (LEP). Monitoring the dysregulation of the coupled expression of the following biomarkers (TNF, IL6, LEP, AGT, APOE, F2, SPP1, and INS) highlights that they could be used as potential prognostic biomarkers.ConclusionThe integration of data obtained by advanced metabolomic and proteomic technologies has made it probable to advantage in understanding the role of these biomarkers in the identification of significant biological processes, pathways, and regulators that are associated with T2DM and its comorbidities.

Dysregulated expression of hypoxia-inducible factors augments myofibroblasts differentiation in idiopathic pulmonary fibrosis

BackgroundIdiopathic pulmonary fibrosis (IPF) is an age-related, progressive and lethal disease, whose pathogenesis is associated with fibroblasts/myofibroblasts foci that produce excessive extracellular matrix accumulation in lung parenchyma. Hypoxia has been described as a determinant factor in its development and progression. However, the role of distinct members of this pathway is not completely described.MethodsBy western blot, quantitative PCR, Immunohistochemistry and Immunocitochemistry were evaluated, the expression HIF alpha subunit isoforms 1, 2 & 3 as well, as their role in myofibroblast differentiation in lung tissue and fibroblast cell lines derived from IPF patients.ResultsHypoxia signaling pathway was found very active in lungs and fibroblasts from IPF patients, as demonstrated by the abundance of alpha subunits 1 and 2, which further correlated with the increased expression of myofibroblast marker αSMA. In contrast, HIF-3α showed reduced expression associated with its promoter hypermethylation.ConclusionsThis study lends further support to the involvement of hypoxia in the pathogenesis of IPF, and poses HIF-3α expression as a potential negative regulator of these phenomena.

Assessment of hypoxia and TNF-alpharesponse by a vector with HRE and NF-kappaB response elements.

Hypoxia and inflammatory cytokine activation (H&I) are common processes in many acute and chronic diseases. Thus, a single vector that responds to both hypoxia and inflammatory cytokines, such as TNF-alpha, is useful for assesing the severity of such diseases. Adaptation to hypoxia is regulated primarily by hypoxia inducible transcription factor (HIF alpha) nuclear proteins that engage genes containing a hypoxia response element (HRE). Inflammation activates a multitude of cytokines, including TNF-alpha, that invariably modulate activation of the nuclear factor kappa B (NF-kB) transcription factor. We constructed a vector that encompassed both a hypoxia response element (HRE), and a NF-kappaB responsive element. We show that this vector was functionally responsive to both hypoxia and TNF-alpha, in vitro and in vivo. Thus, this vector might be suitable for the detection and assessment of hypoxia or TNF-alpha.

Transcriptional divergence of the duplicated hypoxia-inducible factor alpha genes in zebrafish

Oxygen availability has been a major force in shaping the physiological evolution of animals. Under reduced oxygen availability (hypoxia) major changes in gene expression are mediated by hypoxia-inducible factors (HIF alphas). Tetrapods have three hif alpha genes, whereas zebrafish (Danio rerio) and other cyprinids have six due to a teleost lineage-specific genome duplication. We studied the transcriptional divergence of the six teleost-specific hif alphas by inspecting the tissue-specific transcription patterns in adult zebrafish and by monitoring the early developmental transcription of normoxia- and hypoxia-grown zebrafish embryos. Overall we observed the highest hif alpha mRNA levels in tissues that are important for hypoxic survival, including the brain, gill and heart. Of the paralogs that have not previously received attention (hif alpha-1A, hif alpha-2B and hif alpha-3B) especially the hif alpha-2B transcription levels suggest functional relevance. The hif alpha-1A/B paralogs that have considerable coding sequence divergence displayed more overall transcriptional divergence than the hif alpha-2A/B paralog pair. The hif alpha-2A/B paralogs that are similarly conserved in coding sequence had a divergent transcription pattern during early development. When zebrafish grown in modest hypoxia were compared to normoxia grown fish, only hif alpha-3A transcription was significantly altered. These results suggest that, in zebrafish, the evolutionary retention of each hif alpha paralog pair has involved unique patterns of coding sequence divergence, adult tissue-specific transcriptional divergence or developmental transcriptional divergence.

Molecular analysis in breast cancer subtypes and correlation with pathologic complete response (pCR) to neoadjuvant chemotherapy.

e22119 Background: Although it is know that pCR following neoadjuvant chemotherapy is more frequent in some subtypes of breast cancer such as Triple Negative (TN) or erb2 tumors, the predictive role of gene expression and mutation status is not well defined in this setting. Methods: We analyzed samples from 41 patients (p) prospectively treated with neoadjuvant chemotherapy (sequential AC followed by weekly TXL, or inverse sequence, plus trastuzumab for erb2 positive p). Pathologic response (PR) was classified according to Miller-Payne and RCB criteria. Radiologic evaluation was performed by ultrasonography, dynamic MR and PET-TAC after each chemotherapy sequence. We performed expression analysis of AXL, BRCA1, RAP80, BIM, EZH2, ROR1, FGFR1, PTPN12, YAP, GAS6, beta-TRCP, HIF1 alpha and ZNF217 by RT-PCR, and mutational status of p53 and PI3K genes in pretreatment biopsies. Statistical analysis was performed using Mann-Whitney U and Pearson’s chi-squared tests. Results: pCR was detected in 5 p (3TN, 2 erb2) of 25 p (9 luminal A, 5 luminal B, 6 erb2 and 5 TN) evaluated for PR at time of submitting this abstract. TN tumors had lower levels of RAP80 (p=.0013), PTPN12 (p=.003), beta TRCP (p=.001), ZNF217 (p=.014) and YAP (p=.097). Luminal B tumors had low levels of YAP and the highest levels of FGFR1 (p=.09) and ZNF217 (p=.014). Luminal A tumors had high levels of beta-TRCP (p=.003). We found no differences in BRCA1, AXL, BIM, EZH2, ROR1, GAS6 and HIF1 levels by breast cancer subtype. P with low levels of FGFR1 (p=.087), HIF1alpha (p=.07) or EZH2 (p=.005) had higher probability of pCR. No pCR was observed in p with higher levels of AXL, EZH2, RAP80, GAS6, beta TRCP, HIF alpha. Four p had p53 mutations (1 luminal B, 1 erb2 and 2 TN) and 4 p had PI3K mutations (2 luminal A, 1 erb2, 1 luminal B). There was no correlation between p53 status and PR. P with PI3K mutations did not achieve pCR vs 46% of p with wild type PI3K (p=.23). Conclusions: Gene expression profile varies by breast cancer subtype. Chemosensitivity could be higher in tumors with lower levels of FGFR1, HIF1alpha or EZH2. Further results will be presented.

SUBFUNCTIONALIZATION OF CYPRINID HYPOXIA-INDUCIBLE FACTORS FOR ROLES IN DEVELOPMENT AND OXYGEN SENSING

Among vertebrates, teleost fishes have evolved the most impressive adaptations to variable oxygen tensions in water (Shoubridge and Hochachka 1980; Nilsson and Randall 2010). Under conditions of oxygen deprivation (hypoxia), major changes in gene expression are mediated by hypoxia-inducible factors (HIF alpha). Here we show that hif alpha genes were duplicated in the teleost specific whole-genome duplication. Although one of each paralogous gene pair was lost in most teleosts, both copies were retained in cyprinids. Computational analyses suggest that these duplicates have become subfunctionalized with complementary changes in coding and regulatory sequences within each paralogous gene pair. We tested our predictions with comparisons of hif alpha transcription in zebrafish, a cyprinid, and sturgeon, an outgroup that diverged from teleosts before the duplication event. Our experiments revealed distinct transcriptional profiles in the cyprinid duplicates: while one of each paralogous pair maintained the ancestral developmental response, the other was more sensitive to changes in oxygen tension. These results demonstrate the subfunctionalization of cyprinid hif alpha paralogs for specialized roles in development and the hypoxic stress response.

Phosphorylation of von Hippel-Lindau protein by checkpoint kinase 2 regulates p53 transactivation

von-Hippel Lindau protein (pVHL) suppresses tumorigenesis in the kidney, in part through regulation of hypoxia-inducible factor alpha (HIF alpha). However, HIF has been proposed to be necessary but insufficient for renal tumorigenesis. p53 was implicated as a transcription factor that is regulated by pVHL, but the molecular mechanism by which pVHL regulates p53 on DNA damage is unknown. We demonstrated that checkpoint kinase-2 (Chk2) binds to the beta-domain of pVHL and phosphorylates Ser 111 on DNA damage. Notably, this modification enhances pVHL-mediated transactivation of p53 by recruiting p300 and Tip60 to the chromatin of p53 target gene. Further, the naturally occurring pVHL mutants pVHL-S111R and pVHL-S111C showed diminished binding to coactivators, ultimately retarding p53-mediated growth arrest and apoptosis. In this study, we determined the molecular mechanism by which pVHL transactivates p53 on DNA damage and demonstrated that p53-related pVHL subtype mutants regulate tumorigenecity in VHL diseases.

Abstract 2064: Regulation of the VHL tumor suppressor protein in hypoxia and through the cell cycle

Abstract The von Hippel-Lindau (VHL) gene is a classical tumor suppressor and is inactivated in patients with von Hippel-Lindau disease, as well as the majority of patients with sporadic clear cell renal carcinoma (RCC). The VHL protein (pVHL) is an E3 ubiquitin ligase with many functions, including regulating the hypoxia response as well as microtubule stability. While the involvement of pVHL in targeting of HIF alpha subunits for ubiquitin-mediated degradation is well documented, less is understood about regulation of pVHL itself. We determined pVHL levels under normoxic (room air, 21% oxygen) and hypoxic (1% oxygen) conditions and found that pVHL levels decreased in hypoxia. VHL protein half-life was similar in cells cultured in normoxia or hypoxia, suggesting that pVHL expression is regulated through a post-transcriptional mechanism. Down regulation of pVHL in hypoxia suggests a novel and complementary mechanism to account for stabilization of HIF alpha subunits. While pVHL-negative RCC cells progress through the cell cycle when cultured in hypoxia, isogenic pVHL-expressing RCC exhibited hypoxia-induced arrest in G1 phase of the cell cycle. We also determined pVHL levels during cell cycle progression and found that pVHL levels were decreased levels during mitosis and G1. The anaphase promoting complex/cyclosome (APC/C) is an E3 ubiquitin ligase that is active during late M phase and G1 through the association with the activators, Cdh1 and Cdc20. Cdh1 and Cdc20 bind to APC/C target proteins through recognition of Destruction box consensus sequences. Such sequences are found in pVHL, suggesting that pVHL may be a target for APC/C ubiquitylation. We found that pVHL physically bound to Cdh1, that Cdh1 knockdown was associated with increased pVHL levels, that Cdh1 overexpression was associated with decreased pVHL levels and increased polyubiquitylation pVHL, and that these activities were dependent on pVHL Destruction box sequences. Our results indicate that pVHL is a novel substrate of APC/C-Cdh1. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2064. doi:10.1158/1538-7445.AM2011-2064

Astrocyte hypoxic response is essential for pathological but not developmental angiogenesis of the retina

Vascular/parenchymal crosstalk is increasingly recognized as important in the development and maintenance of healthy vascularized tissues. The retina is an excellent model in which to study the role of cell type-specific contributions to the process of blood vessel and neuronal growth. During retinal vascular development, glial cells such as astrocytes provide the template over which endothelial cells migrate to form the retinal vascular network, and hypoxia-regulated vascular endothelial growth factor (VEGF) has been demonstrated to play a critical role in this process as well as pathological neovascularization. To investigate the nature of cell-specific contributions to this process, we deleted VEGF and its upstream regulators, the hypoxia-inducible transcription factors HIF-1 alpha and HIF-2 alpha, and the negative regulator of HIF alpha, von Hippel-Lindau protein (VHL), in astrocytes. We found that loss of hypoxic response and VEGF production in astrocytes does not impair normal development of retinal vasculature, indicating that astrocyte-derived VEGF is not essential for this process. In contrast, using a model of oxygen-induced ischemic retinopathy, we show that astrocyte-derived VEGF is essential for hypoxia-induced neovascularization. Thus, we demonstrate that astrocytes in the retina have highly divergent roles during developmental, physiological angiogenesis, and ischemia-driven, pathological neovascularization.

HIF signaling during molting in Crustacea

Increasing evidence has demonstrated HIF regulation of gene activity in response to both hypoxia and non‐hypoxic stimuli. Normoxic upregulation of vertebrate HIF alpha has been reported during tissue reconstruction, vascularization, and the immune response, events also integral to the crustacean molt cycle. This study investigated the potential role of HIF alpha in mobilizing genes during molting in normoxic crabs. In premolt, the epidermis underlying the exoskeleton hypertrophies, hemocytes and reserve cells proliferate, cryptocyanin increases, and selected muscle proteins atrophy. New exoskeleton secretion occurs from premolt through postmolt. Tissue growth, vascularization and sclerotization begin in postmolt. A cohort of juvenile Dungeness crab Cancer magister was sampled daily for an entire molt cycle. Analysis of HIF alpha, arthrodial membrane protein 6, anti‐lipopolysaccharide factor, cryptocyanin 2 and B‐actin mRNA expression was carried out via real‐time quantitative PCR using SYBR GreenER qPCR SuperMix, ABI Prism 7700 instrumentation (Applied Biosystems) and non‐degenerate primers. Each gene showed a specific pattern of translational upregulation consistent with its putative role in molting. The changes in HIF alpha transcript support the hypothesis that HIF alpha is upregulated in normoxic crabs to coordinate gene expression during molting. Supported by MDIBL NIA (NBT).

The hypoxia-inducible factor α pathway couples angiogenesis to osteogenesis during skeletal development

Skeletal development and turnover occur in close spatial and temporal association with angiogenesis. Osteoblasts are ideally situated in bone to sense oxygen tension and respond to hypoxia by activating the hypoxia-inducible factor alpha (HIF alpha) pathway. Here we provide evidence that HIF alpha promotes angiogenesis and osteogenesis by elevating VEGF levels in osteoblasts. Mice overexpressing HIF alpha in osteoblasts through selective deletion of the von Hippel-Lindau gene (Vhl) expressed high levels of Vegf and developed extremely dense, heavily vascularized long bones. By contrast, mice lacking Hif1a in osteoblasts had the reverse skeletal phenotype of that of the Vhl mutants: long bones were significantly thinner and less vascularized than those of controls. Loss of Vhl in osteoblasts increased endothelial sprouting from the embryonic metatarsals in vitro but had little effect on osteoblast function in the absence of blood vessels. Mice lacking both Vhl and Hif1a had a bone phenotype intermediate between those of the single mutants, suggesting overlapping functions of HIFs in bone. These studies suggest that activation of the HIF alpha pathway in developing bone increases bone modeling events through cell-nonautonomous mechanisms to coordinate the timing, direction, and degree of new blood vessel formation in bone.

Vascular biology and bone formation: hints from HIF

In this issue of the JCI, Wang, Clemens, and colleagues demonstrate that hypoxia-inducible factor alpha (HIF alpha) signaling in bone-building osteoblasts is central to the coupling of angiogenesis and long bone development in mice (see the related article beginning on page 1616). They show that bone formation controlled by osteoblast HIF alpha signaling is not cell autonomous but is coupled to skeletal angiogenesis dependent upon VEGF signaling. Thus, strategies that promote HIF alpha signaling in osteoblasts may augment bone formation and accelerate fracture repair.

Tumor cell invasion of von Hippel Lindau renal cell carcinoma cells is mediated by membrane type-1 matrix metalloproteinase

BackgroundMetastatic renal cell carcinoma (RCC) remains the leading cause of mortality in patients with clear cell RCC arising from mutations in the von Hippel Lindau (VHL) tumor suppressor. Successful RCC tumor suppression by VHL requires the negative regulation of hypoxia inducible factor alpha (HIF alpha) protein and its downstream targets. Thus, identification of HIF target genes responsible for RCC tumor progression will aid in the development of therapies for this disease. We previously identified membrane type-1 matrix metalloproteinase (MT1-MMP) as a transcriptional target of HIF-2alpha in RCC cells null for VHL and showed that MT1-MMP is overexpressed in these cells. MT1-MMP is a key regulator of tumor progression through its functions as a matrix-degrading enzyme, as well as its ability to cleave factors, such as adhesion molecules and other MMPs. The aim of this study was to investigate the contribution of MT1-MMP to the invasive potential of RCC cells using in vitro type I collagen degradation and invasion assays.ResultsWe evaluated RCC cells wild-type (WT8) and null (pRc-9) for VHL for invasive characteristics and showed that the pRc-9 cells demonstrated a greater propensity for both invasion and degradation of a type I collagen matrix. Furthermore, overexpression of either HIF-2alpha or MT1-MMP in the poorly invasive cell line, WT8, promoted collagen degradation and invasion of these cells. Finally, using RNAi, we show that inhibition of MT1-MMP suppresses tumor cell invasion of RCC cells.ConclusionOur results suggest that MT1-MMP is a major mediator of tumor cell invasiveness and type I collagen degradation by VHL RCC cells that express either MT1-MMP or HIF-2alpha. As such, MT1-MMP may represent a novel target for anti-invasion therapy for this disease.