Cellular oxygen sensing in health and disease

Effects of high-altitude hypoxia on embryonic developmental potential in women undergoing IVF/ICSI procedures

PURPOSE

In this study we examined the effects of long-term adaptation to hypoxia on embryonic developmental potential of oocytes collected from women who underwent IVF/ICSI procedures.

METHODS

We selected young infertile women who lived in a low-altitude normoxic environment (n = 80, altitude < 500 m) or high-altitude hypoxic environment (n = 100, altitude > 2500 m) for a lengthy period of time and who planned to undergo IVF/ICSI procedures. We then determined the baseline reproductive hormone levels, gonadotropin (Gn) dose and Gn treatment duration during controlled ovarian hyperstimulation (COH), number of oocytes retrieved, number of mature oocytes, oocyte maturation rate, fertilization rate, normal fertilization rate, day (D3) embryo-formation rate, blastocyst formation rate, good-quality formation rate, D5 blastocyst formation rate, and D6 blastocyst formation rate between the two groups.

RESULTS

Compared with the low-altitude normoxic group, the various reproductive hormone markers of women in the high-altitude hypoxia group were lower, with LH and T levels significantly reduced (P < 0.05) at 72.29 and 72.44% of the normoxic group, respectively (normoxic group vs. hypoxic group, 5.24 ± 1.61 vs. 3.79 ± 1.21; 0.61 ± 0.18 vs. 0.42 ± 0.15; P < 0.05). During ovarian hyperstimulation, a greater Gn dose and longer Gn treatment duration were required for the hypoxic group to complete COH (normoxic group vs. hypoxic group, 2152.08 IU ± 52.76 vs. 2622.09 IU ± 123.28; 9.96 days ± 1.27 vs. 11.54 days ± 1.34, respectively; P < 0.05). The fertilization, cleavage, and D3 embryo-formation rates tended to be higher in the normoxic group than in the hypoxic group (P > 0.05); while the normal fertilization rate tended to lower than in the hypoxic group (P > 0.05). When we conducted an analysis of blastocyst formation rates at different timepoints, we ascertained that the blastocyst formation rate, usable blastocyst rate, and good-quality blastocyst rate of the hypoxic group were all lower than in the normoxic group, with the difference in usable blastocyst rate the most highly significant (normoxic group vs. hypoxic group, 75.31 ± 5.53 vs. 56.04 ± 6.10%, respectively; P < 0.05). In addition, the D5 and D6 blastocyst-formation rates in the normoxic group were slightly higher than in the hypoxic group, revealing that not only were fewer blastocysts formed in the hypoxic group but that there was also a delay in blastocyst formation.

CONCLUSION

In young women undergoing IVF/ICSI treatment, long-term hypoxic adaptation required augmented Gn dose and Gn treatment duration during COH, and blastocyst developmental potential was also attenuated.

Relationship between Hypoxic and Immune Pathways Activation in the Progression of Neuroinflammation: Role of HIF-1α and Th17 Cells

Neuroinflammation is a common event in degenerative diseases of the central and peripheral nervous system, triggered by alterations in the immune system or inflammatory cascade. The pathophysiology of these disorders is multifactorial, whereby the therapy available has low clinical efficacy. This review propounds the relationship between the deregulation of T helper cells and hypoxia, mainly Th17 and HIF-1α molecular pathways, events that are involved in the occurrence of the neuroinflammation. The clinical expression of neuroinflammation is included in prevalent pathologies such as multiple sclerosis, Guillain-Barré syndrome, and Alzheimer's disease, among others. In addition, therapeutic targets are analyzed in relation to the pathways that induced neuroinflammation.

Impact of Hypoxia over Human Viral Infections and Key Cellular Processes

Oxygen is essential for aerobic cells, and thus its sensing is critical for the optimal maintenance of vital cellular and tissue processes such as metabolism, pH homeostasis, and angiogenesis, among others. Hypoxia-inducible factors (HIFs) play central roles in oxygen sensing. Under hypoxic conditions, the α subunit of HIFs is stabilized and forms active heterodimers that translocate to the nucleus and regulate the expression of important sets of genes. This process, in turn, will induce several physiological changes intended to adapt to these new and adverse conditions. Over the last decades, numerous studies have reported a close relationship between viral infections and hypoxia. Interestingly, this relation is somewhat bidirectional, with some viruses inducing a hypoxic response to promote their replication, while others inhibit hypoxic cellular responses. Here, we review and discuss the cellular responses to hypoxia and discuss how HIFs can promote a wide range of physiological and transcriptional changes in the cell that modulate numerous human viral infections.

Role of Hypoxia in the Control of the Cell Cycle

The cell cycle is an important cellular process whereby the cell attempts to replicate its genome in an error-free manner. As such, mechanisms must exist for the cell cycle to respond to stress signals such as those elicited by hypoxia or reduced oxygen availability. This review focuses on the role of transcriptional and post-transcriptional mechanisms initiated in hypoxia that interface with cell cycle control. In addition, we discuss how the cell cycle can alter the hypoxia response. Overall, the cellular response to hypoxia and the cell cycle are linked through a variety of mechanisms, allowing cells to respond to hypoxia in a manner that ensures survival and minimal errors throughout cell division.

Intrarenal Renin–Angiotensin System Involvement in the Pathogenesis of Chronic Progressive Nephropathy—Bridging the Informational Gap Between Disciplines

Chronic progressive nephropathy (CPN) is the most commonly encountered spontaneous background finding in laboratory rodents. Various theories on its pathogenesis have been proposed, but there is a paucity of data regarding specific mechanisms or physiologic pathways involved in early CPN development. The current CPN mechanism of action for tumorigenesis is largely based on its associated increase in tubular cell proliferation without regard to preceding subcellular degenerative changes. Combing through the published literature from multiple biology disciplines provided insight into the preceding cellular events. Mechanistic pathways involved in the progressive age-related decline in rodent kidney function and several key inflexion points have been identified. These critical pathway factors were then connected using data from renal models from multiple rodent strains, other species, and mechanistic work in humans to form a cohesive picture of pathways and protein interactions. Abundant data linked similar renal pathologies to local events involving hypoxia (hypoxia-inducible factor 1α), altered intrarenal renin–angiotensin system (RAS), oxidative stress (nitric oxide), and pro-inflammatory pathways (transforming growth factor β), with positive feedback loops and downstream effectors amplifying the injury and promoting scarring. Intrarenal RAS alterations seem to be central to all these events and may be critical to CPN development and progression.

Energy Producing Metabolic Pathways in Functional Regulation of the Hematopoietic Stem Cells

The hematopoietic system has a very well-studied hierarchy with the long-term (LT) hematopoietic stem cells (HSCs) taking the top position. The pool of quiescent adult LT-HSCs generated during the fetal and early postnatal life acts as a reservoir to supply all the blood cells. Therefore, the maintenance of this stem cell pool is pivotal to maintaining homeostasis in hematopoietic system. It has long been known that external cues, along with the internal genetic factors influence the status of HSCs in the bone marrow (BM). Hypoxia is one such factor that regulates the vascular as well as hematopoietic ontogeny from a very early time point in development. The metabolic outcomes of a hypoxic microenvironment play important roles in functional regulation of HSCs, especially in case of adult BM HSCs. Anaerobic metabolic pathways therefore perform prominent role in meeting energy demands. Increased oxidative pathways on the other hand result in loss of stemness. Recent studies have attributed the functional differences in HSCs across different life stages to their metabolic phenotypes regulated by respective niches. Indicating thus, that various energy production pathways could play distinct role in regulating HSC function at different developmental/physiological states. Here, we review the current status of our understanding over the role that energy production pathways play in regulating HSC stemness. © 2018 IUBMB Life, 70(7):612-624, 2018.

Cobalt treatment does not prevent glomerular morphological alterations in type 1 diabetic rats

Early renal morphological alterations including glomerular hypertrophy and mesangial expansion occur in diabetic kidney disease and correlate with various clinical manifestations of diabetes. The present study was designed to investigate the influence of pharmacological modulation of HIF-1α (hypoxia inducible factor-1 alpha) protein levels, on these glomerular changes in rodent model of type 1 diabetes. Male wistar rats were made diabetic (Streptozotocin 45 mg/kg; i.p.) and afterwards treated with HIF activator cobalt chloride for 4 weeks. Renal function was assessed by serum creatinine, albumin, proteinuria levels, oxidative stress: reduced glutathione levels and catalase activity, and renal tissue HIF-1α protein levels were determined by ELISA assay. Histological analysis of kidney sections was done by haematoxylin and eosin (glomeruli diameter), periodic acid Schiff (mesangial expansion and glomerulosclerosis) and sirius red (fibrosis, tubular dilation) staining. Diabetes rats displayed reduced serum albumin levels, marked proteinuria, lower kidney reduced glutathione content, glomerular hypertrophy, glomerulosclerosis, mesangial expansion, tubular dilation and renal fibrosis. Cobalt chloride treatment normalised renal HIF-1α protein levels, reduced development of proteinuria and tubulo-interstitial fibrosis, but the glomerular morphological alterations such as glomerulosclerosis, mesangial expansion, increased glomerular diameter and tubular vacoulations were not abrogated in diabetic kidneys. Glomerular morphological abnormalities might precede the development of proteinuria and renal fibrosis in experimental model of type 1 diabetes. Pharmacological modulation of renal HIF-1α protein levels does not influence glomerular and tubular dilatory changes in diabetic kidney disease.

Hypoxia-induced long non-coding RNA Malat1 is dispensable for renal ischemia/reperfusion-injury

Renal ischemia-reperfusion (I/R) injury is a major cause of acute kidney injury (AKI). Non-coding RNAs are crucially involved in its pathophysiology. We identified hypoxia-induced long non-coding RNA Malat1 (Metastasis Associated Lung Adenocarcinoma Transcript 1) to be upregulated in renal I/R injury. We here elucidated the functional role of Malat1 in vitro and its potential contribution to kidney injury in vivo. Malat1 was upregulated in kidney biopsies and plasma of patients with AKI, in murine hypoxic kidney tissue as well as in cultured and ex vivo sorted hypoxic endothelial cells and tubular epithelial cells. Malat1 was transcriptionally activated by hypoxia-inducible factor 1-α. In vitro, Malat1 inhibition reduced proliferation and the number of endothelial cells in the S-phase of the cell cycle. In vivo, Malat1 knockout and wildtype mice showed similar degrees of outer medullary tubular epithelial injury, proliferation, capillary rarefaction, inflammation and fibrosis, survival and kidney function. Small-RNA sequencing and whole genome expression analysis revealed only minor changes between ischemic Malat1 knockout and wildtype mice. Contrary to previous studies, which suggested a prominent role of Malat1 in the induction of disease, we did not confirm an in vivo role of Malat1 concerning renal I/R-injury.

Endothelial cells modified by adenovirus vector containing nine copies hypoxia response elements and human vascular endothelial growth factor as the novel seed cells for bone tissue engineering

Vascularization is one of the hotspots during the development of new therapeutic strategies for bone tissue engineering, which can alleviate hypoxic circumstance and prevent transplant failure. Vascular endothelial growth factor (VEGF) gene transfection using recombinant adenovirus (Ad) vector can effectively promote angiogenesis, but uncontrolled long-term continuous expression of VEGF brings safety concern. Here we constructed a recombinant Ad vector containing nine copies of HRE promoter and the hVEGF165 gene, which conserved the oxygen sensitivity of hypoxia-inducible factor-1/hypoxia response elements (HIF-1/HRE). After transfection into human umbilical vein endothelial cells (HUVEC), the hVEGF165 mRNA and protein levels were much higher in response to hypoxia, as revealed by RT-PCR and ELISA, respectively. Furthermore, Ad-9HRE-hVEGF165 vector effectively promoted proliferation, migration and tube formation of HUVEC under hypoxic conditions. Thus we believe that the Ad-9HRE-hVEGF165 vector can contribute to the regulation of vascularization, which may provide a new approach for a better control of the expression of hVEGF165 during bone tissue engineering.

KDM2 Family Members are Regulated by HIF-1 in Hypoxia

Hypoxia is not only a developmental cue but also a stress and pathological stimulus in many human diseases. The response to hypoxia at the cellular level relies on the activity of the transcription factor family, hypoxia inducible factor (HIF). HIF-1 is responsible for the acute response and transactivates a variety of genes involved in cellular metabolism, cell death, and cell growth. Here, we show that hypoxia results in increased mRNA levels for human lysine (K)-specific demethylase 2 (KDM2) family members, KDM2A and KDM2B, and also for Drosophila melanogaster KDM2, a histone and protein demethylase. In human cells, KDM2 family member's mRNA levels are regulated by HIF-1 but not HIF-2 in hypoxia. Interestingly, only KDM2A protein levels are significantly induced in a HIF-1-dependent manner, while KDM2B protein changes in a cell type-dependent manner. Importantly, we demonstrate that in human cells, KDM2A regulation by hypoxia and HIF-1 occurs at the level of promoter, with HIF-1 binding to the KDM2A promoter being required for RNA polymerase II recruitment. Taken together, these results demonstrate that KDM2 is a novel HIF target that can help coordinate the cellular response to hypoxia. In addition, these results might explain why KDM2 levels are often deregulated in human cancers.

Kinetic Investigations of the Role of Factor Inhibiting Hypoxia-inducible Factor (FIH) as an Oxygen Sensor

The hypoxia-inducible factor (HIF) hydroxylases regulate hypoxia sensing in animals. In humans, they comprise three prolyl hydroxylases (PHD1-3 or EGLN1-3) and factor inhibiting HIF (FIH). FIH is an asparaginyl hydroxylase catalyzing post-translational modification of HIF-α, resulting in reduction of HIF-mediated transcription. Like the PHDs, FIH is proposed to have a hypoxia-sensing role in cells, enabling responses to changes in cellular O2 availability. PHD2, the most important human PHD isoform, is proposed to be biochemically/kinetically suited as a hypoxia sensor due to its relatively high sensitivity to changes in O2 concentration and slow reaction with O2. To ascertain whether these parameters are conserved among the HIF hydroxylases, we compared the reactions of FIH and PHD2 with O2. Consistent with previous reports, we found lower Km(app)(O2) values for FIH than for PHD2 with all HIF-derived substrates. Under pre-steady-state conditions, the O2-initiated FIH reaction is significantly faster than that of PHD2. We then investigated the kinetics with respect to O2 of the FIH reaction with ankyrin repeat domain (ARD) substrates. FIH has lower Km(app)(O2) values for the tested ARDs than HIF-α substrates, and pre-steady-state O2-initiated reactions were faster with ARDs than with HIF-α substrates. The results correlate with cellular studies showing that FIH is active at lower O2 concentrations than the PHDs and suggest that competition between HIF-α and ARDs for FIH is likely to be biologically relevant, particularly in hypoxic conditions. The overall results are consistent with the proposal that the kinetic properties of individual oxygenases reflect their biological capacity to act as hypoxia sensors.

In vivo experiments reveal the good, the bad and the ugly faces of sFlt-1 in pregnancy

Objective

Soluble fms-like tyrosine kinase (sFlt)-1-e15a, a primate-specific sFlt-1-isoform most abundant in the human placenta in preeclampsia, can induce preeclampsia in mice. This study compared the effects of full-length human (h)sFlt-1-e15a with those of truncated mouse (m)sFlt-1(1-3) used in previous preeclampsia studies on pregnancy outcome and clinical symptoms in preeclampsia.

Methods

Mice were injected with adenoviruses or fiber-mutant adenoviruses overexpressing hsFlt-1-e15a, msFlt-1(1-3) or control GFP under the CMV or CYP19A1 promoters on gestational day 8 (GD8) and GD11. Placentas and pups were delivered by cesarean section, and dams were monitored postpartum. Blood pressure was telemetrically recorded. Urine samples were collected with cystocentesis and examined for albumin/creatinine ratios. Tissue specimens were evaluated for transgene as well as endogenous mFlt-1 and msFlt-1-i13 expression. H&E-, Jones- and PAS-stained kidney sections were histopathologically examined. Placental GFP expression and aortic ring assays were investigated with confocal microscopy.

Results

Mean arterial blood pressure (MAP) was elevated before delivery in hsFlt-1-e15a-treated mice compared to controls (GD18: ΔMAP = 7.8 mmHg, p = 0.009), while ΔMAP was 12.8 mmHg (GD18, p = 0.005) in msFlt-1(1-3)-treated mice. Urine albumin/creatinine ratio was higher in hsFlt-1-e15a-treated mice than in controls (GD18, p = 0.04; PPD8, p = 0.03), and msFlt-1(1-3)-treated mice had marked proteinuria postpartum (PPD8, p = 4×10⁻⁵). Focal glomerular changes were detected in hsFlt-1-e15a and msFlt-1(1-3)-treated mice. Aortic ring microvessel outgrowth was decreased in hsFlt-1-e15a (p = 0.007) and msFlt-1(1-3)-treated (p = 0.02) mice. Full-length msFlt-1-i13 expression was unique for the placenta. In hsFlt-1-e15a-treated mice, the number of pups (p = 0.046), total weight of living pups (p = 0.04) and maternal weights (p = 0.04) were higher than in controls. These differences were not observed in truncated msFlt-1(1-3)-treated mice.

Conclusions

Truncated msFlt-1(1-3) simulated the preeclampsia-promoting effects of full-length hsFlt-1. MsFlt-1(1-3) had strong effect on maternal endothelium but not on placentas and embryos. In contrast, hsFlt-1-e15a induced preeclampsia-like symptoms; however, it also increased litter size. In accord with the predominant placental expression of hsFlt-1-e15a and msFlt-1-i13, full-length sFlt-1 may have a role in the regulation of embryonic development. These observations point to the difference in the biological effects of full-length and truncated sFlt-1 and the changes in the effect of full-length sFlt-1 during pregnancy, and may have important implications in the management of preeclampsia.

Chromatin and oxygen sensing in the context of JmjC histone demethylases

Responding appropriately to changes in oxygen availability is essential for multicellular organism survival. Molecularly, cells have evolved intricate gene expression programmes to handle this stressful condition. Although it is appreciated that gene expression is co-ordinated by changes in transcription and translation in hypoxia, much less is known about how chromatin changes allow for transcription to take place. The missing link between co-ordinating chromatin structure and the hypoxia-induced transcriptional programme could be in the form of a class of dioxygenases called JmjC (Jumonji C) enzymes, the majority of which are histone demethylases. In the present review, we will focus on the function of JmjC histone demethylases, and how these could act as oxygen sensors for chromatin in hypoxia. The current knowledge concerning the role of JmjC histone demethylases in the process of organism development and human disease will also be reviewed.

CoCl2-induced biochemical hypoxia down regulates activities and expression of super oxide dismutase and catalase in cerebral cortex of mice

Hypoxia-induced oxidative stress is one of the major hallmark reasons underlying brain dysfunction. In the present manuscript, we have used CoCl2-induced hypoxic mice to investigate alterations in the activities of chief antioxidative stress enzymes- superoxide dismutase (SOD) and catalase (CAT) and expression of their genes Sod1 and Cat in the cerebral cortex as this model has not been routinely used for carrying out such study. Hypoxia mimetic mice model was accordingly developed by oral CoCl2 administration to mice and validated by analyzing alterations in the expression of the hypoxia inducible factor gene Hif-1α and its immediate responsive genes. Our Western blot data demonstrated that a dose of 40 mg/kg BW of CoCl2 was able to generate hypoxia like condition in mice in which Hif-1α and its immediate responsive genes-glutamate transporter-1 (Slc2a1) and erythropoietin (Epo) expression were up regulated. Our in-gel assay data indicated that SOD and CAT activities significantly declined and it was associated with significant down regulation of Sod1 and Epo expression as evident from our semi quantitative RT-PCR and Western blot data, which might be correlated with up regulation of Hif-1α expression in the cerebral cortex of the CoCl2-treated hypoxic mice. Our findings suggest that CoCl2-induced hypoxic mouse model is useful for studying alterations in the anti oxidative enzymes and biochemical/molecular/neurobiological analysis of hypoxia-induced alterations in brain function.

Marginal effects of glucose, insulin and insulin-like growth factor on chemotherapy response in endothelial and colorectal cancer cells

Resistance to chemotherapy is a major clinical issue for patients with colorectal cancer. Obesity has been associated with a poorer outcome and is a possible mechanism of resistance. The aim of the present study was to investigate the effect of obesity-related factors on the cell response to standard chemotherapy in stromal and colorectal cancer cells. Viability was measured following the treatment of colorectal cancer cell lines (WiDr and SW620) and stromal cells (human microvascular endothelial cells) in vitro with 5-fluorouracil, irinotecan and oxaliplatin under obesity-related conditions [elevated levels of insulin, insulin-like growth factor-1 (IGF-1) and glucose] and compared with non-elevated conditions. Obesity-related conditions alone increased cell viability and in selected cases, accumulation of the transcription factor, hypoxia-inducible factor-1. However, these conditions did not consistently increase resistance to the chemotherapy agents tested. The combination of IGF-1 and extremely low-dose chemotherapy significantly induced cell viability in WiDr colorectal cancer cells. These in vitro results may have clinical importance in an environment of increasing rates of obesity and colorectal cancer, and the frequent under-dosing of obese cancer patients.

Genetic basis of congenital erythrocytosis: mutation update and online databases

Congenital erythrocytosis (CE), or congenital polycythemia, represents a rare and heterogeneous clinical entity. It is caused by deregulated red blood cell production where erythrocyte overproduction results in elevated hemoglobin and hematocrit levels. Primary congenital familial erythrocytosis is associated with low erythropoietin (Epo) levels and results from mutations in the Epo receptor gene (EPOR). Secondary CE arises from conditions causing tissue hypoxia and results in increased Epo production. These include hemoglobin variants with increased affinity for oxygen (HBB, HBA mutations), decreased production of 2,3-bisphosphoglycerate due to BPGM mutations, or mutations in the genes involved in the hypoxia sensing pathway (VHL, EPAS1, and EGLN1). Depending on the affected gene, CE can be inherited either in an autosomal dominant or recessive mode, with sporadic cases arising de novo. Despite recent important discoveries in the molecular pathogenesis of CE, the molecular causes remain to be identified in about 70% of the patients. With the objective of collecting all the published and unpublished cases of CE the COST action MPN&MPNr-Euronet developed a comprehensive Internet-based database focusing on the registration of clinical history, hematological, biochemical, and molecular data (http://www.erythrocytosis.org/). In addition, unreported mutations are also curated in the corresponding Leiden Open Variation Database.

Metabolomic analysis of anti-hypoxia and anti-anxiety effects of Fu Fang Jin Jing Oral Liquid

Background

Herba Rhodiolae is a traditional Chinese medicine used by the Tibetan people for treating hypoxia related diseases such as anxiety. Based on the previous work, we developed and patented an anti-anxiety herbal formula Fu Fang Jin Jing Oral Liquid (FJJOL) with Herba Rhodiolae as a chief ingredient. In this study, the anti-hypoxia and anti-anxiety effects of FJJOL in a high altitude forced-swimming mouse model with anxiety symptoms will be elucidated by NMR-based metabolomics.

Methods

In our experiments, the mice were divided randomly into four groups as flatland group, high altitude saline-treated group, high altitude FJJOL-treated group, and high altitude diazepam-treated group. To cause anxiety effects and hypoxic defects, a combination use of oxygen level decreasing (hypobaric cabin) and oxygen consumption increasing (exhaustive swimming) were applied to mice. After a three-day experimental handling, aqueous metabolites of mouse brain tissues were extracted and then subjected to NMR analysis. The therapeutic effects of FJJOL on the hypobaric hypoxia mice with anxiety symptoms were verified.

Results

Upon hypoxic exposure, both energy metabolism defects and disorders of functional metabolites in brain tissues of mice were observed. PCA, PLS-DA and OPLS-DA scatter plots revealed a clear group clustering for metabolic profiles in the hypoxia versus normoxia samples. After a three-day treatment with FJJOL, significant rescue effects on energy metabolism were detected, and levels of ATP, fumarate, malate and lactate in brain tissues of hypoxic mice recovered. Meanwhile, FJJOL also up-regulated the neurotransmitter GABA, and the improvement of anxiety symptoms was highly related to this effect.

Conclusions

FJJOL ameliorated hypobaric hypoxia effects by regulating energy metabolism, choline metabolism, and improving the symptoms of anxiety. The anti-anxiety therapeutic effects of FJJOL were comparable to the conventional anti-anxiety drug diazepam on the hypobaric hypoxia mice. FJJOL might serve as an alternative therapy for the hypoxia and anxiety disorders.

The endothelium in diabetic nephropathy

The long-term complications of diabetes are characterized by pathologic changes in both the microvasculature and conduit vessels. Although the fenestrated glomerular endothelium classically has been viewed as providing little in the way of an impediment to macromolecular flow, increasing evidence illustrates that this is not the case. Rather, hyperglycemia-mediated endothelial injury may predispose to albuminuria in diabetes both through direct effects and through bidirectional communication with neighboring podocytes. Although neo-angiogenesis of the glomerular capillaries may be a feature of early diabetes, particularly in the experimental setting, loss of capillaries in the glomerulus and in the interstitium are key events that each correlate closely with declining glomerular filtration rate in patients with diabetic nephropathy. The hypoxic milieu that follows the microvascular rarefaction provides a potent stimulus for fibrogenesis, leading to the glomerulosclerosis and tubulointerstitial fibrosis that characterize advanced diabetic kidney disease. Given the pivotal role the endothelium plays in both the development and the progression of diabetic nephropathy we need effective strategies that prevent its loss or accelerate its regeneration. Such advances likely will lead not only to improved tissue oxygenation and reduced fibrosis, but also to improved long-term renal function.

Decreased VEGF expression and microvascular density, but increased HIF-1 and 2α accumulation and EPO expression in chronic moderate hyperoxia in the mouse brain

Normal brain function is dependent on continuous and controlled oxygen delivery. Chronic moderate hypoxia leads to angiogenesis, suggesting a modulatory role for oxygen in determining capillary density. The objective of this study was to determine physiologic and brain angiogenic adaptational changes during chronic moderate normobaric hyperoxia in mice. Four-month old C56BL/6J mice were kept in a normobaric chamber at 50% O(2) for up to 3 weeks. Normoxic littermates were kept in the same room outside the chamber. Freshly collected or fixed brain specimens were analyzed by RT-PCR, Western blot analysis and immunohistochemistry. Results show accumulation of hypoxia inducible factors 1 and 2α (HIF-1 and 2α), and increased expression of erythropoietin (EPO), cyclooxygenase-2 (COX-2) and angiopoietin-2 (Ang-2). Conversely, vascular endothelial growth factor (VEGF), and VEGF receptor-2 (KDR/Flk-1), Peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α) and prolylhydroxylase-2 (PHD-2) expressions were decreased. VEGF mRNA level was diminished but there was no change in HIF-1α mRNA and von Hippel Lindau E3 ubiquitin ligase (VHL) protein expression. Microvascular density was significantly diminished by the end of the 3rd week of hyperoxia. Overall, our results are: (1) increased expression of the potent neuroprotective molecule, EPO; (2) diminished expression of the potent angiogenic factor, VEGF; and (3) decreased microvascular density. We can, therefore, conclude that brain microvascular density can be controlled by HIF-independent mechanisms, and that brain capillary density is a continuously adjusted variable with tissue oxygen availability as one of the controlling modulators.

MicroRNA 107 partly inhibits endothelial progenitor cells differentiation via HIF-1β

Endothelial progenitor cells (EPCs) play an important role in tissue repair after ischemic heart disease. In particular, the recovery of endothelial function is reliant on the ability and rate of EPCs differentiate into mature endothelial cells. The present study evaluated the effect of microRNA 107 (miR-107) on the mechanism of EPCs differentiation. EPCs were isolated from rats' bone marrow and miR-107 expression of EPCs in hypoxic and normoxic conditions were measured by real-time qualitative PCR. CD31 was analyzed by flow cytometry and eNOS was examined by real-time qualitative PCR and western blotting and these were used as markers of EPC differentiation. In order to reveal the mechanism, we used miR107 inhibitor and lentiviral vector expressing a short hairpin RNA (shRNA) that targets miR-107 and hypoxia-inducible factor-1 β (HIF-1β) to alter miR107 and HIF-1β expression. MiR-107 expression were increased in EPCs under hypoxic conditions. Up-regulation of miR-107 partly suppressed the EPCs differentiation induced in hypoxia, while down-regulation of miR-107 promoted EPC differentiation. HIF-1β was the target. This study indicated that miR-107 was up-regulated in hypoxia to prevent EPCs differentiation via its target HIF-1β. The physiological mechanisms of miR-107 must be evaluated if it is to be used as a potential anti-ischemia therapeutic regime.

Protein arginine methyltransferase 5 is an essential component of the hypoxia-inducible factor 1 signaling pathway

Protein arginine methyltransferase 5 (PRMT5) is an enzyme that transfers one or two methyl groups to the arginine residues of histones or non-histone proteins, and that plays critical roles in cellular processes as diverse as receptor signaling and gene expression. Furthermore, PRMT5 is highly expressed in tumors, where it may be associated with tumor growth. Although much research has been conducted on PRMT5, little is known regarding its role in adaption to hypoxia. As hypoxia-inducible factor 1 (HIF-1) is a key player in hypoxic response, we examined the possible involvement of PRMT5 in the HIF-1 signaling pathway. Of the siRNAs targeting PRMT1-8, only PRMT5 siRNA attenuated the hypoxic induction of HIF-1α in A549 cells, and this result was reproducible in all three cancer cell lines examined. PRMT5 knock-down also repressed the promoter activities and the transcript levels of HIF-1-governed genes. Mechanistically, de novo synthesis of HIF-1α protein was reduced in PRMT5-knocked-down A549 cells, and this was rescued by PRMT5 restoration. In contrast, HIF-1α transcription, RNA processing, and protein stability were unaffected by PRMT5 knock-down. Furthermore, PRMT5 was found to be essential for the HIF-1α translation initiated by the 5' UTR of HIF-1α mRNA. Given our results and previous reports, we believe that PRMT5 probably promotes tumor growth by stimulating cell proliferation and by participating in the construction of a tumor-favorable microenvironment via HIF-1 activation.

Lipopolysaccharide and hypoxia-induced HIF-1 activation in human gingival fibroblasts

BACKGROUND

We previously reported that chronic periodontal inflammation causes the accumulation of the transcriptional activator hypoxia-inducible factor-1α (HIF-1α) in human gingival fibroblasts (HGFs) in vivo. Here, evidence is provided that bacterial lipopolysaccharides (LPS) and cellular hypoxia, both associated with periodontitis, can individually, or in combination, lead to the accumulation and activation of HIF-1 in HGF in vitro.

METHODS

Primary gingival fibroblasts were cultured from human gingival biopsies. HIF-1α peptide from HGFs treated with Escherichia coli LPS under normoxia or hypoxia was detected by nuclear protein extraction, immunoprecipitation, immunoblotting, and immunocytofluorescence. HIF-1α transcripts were detected using reverse transcription polymerase chain reaction (PCR). The transcript expression levels of vascular endothelial growth factor-A (VEGF-A), a downstream gene of HIF-1α, were assessed by quantitative real-time PCR.

RESULTS

Two HIF-1α splicing transcription variants were found to be constitutively expressed in HGFs. E. coli LPS induced a dose- and time-dependent nuclear accumulation of HIF-1α peptide in HGFs. This accumulation could be attenuated by treatment with a Toll-like receptor 4 (TLR4)-neutralizing antibody. Under hypoxia, LPS further increased HIF-1α accumulation in HGFs. VEGF-A transcript expression was upregulated by LPS under both normoxia and hypoxia but was downregulated by pretreatment with TLR4-neutralizing antibody or the specific HIF-1α inhibitor 3-(5'-hydroxymethyl-2'-furyl)-1-benzyl indazole.

CONCLUSION

LPS induces the nuclear accumulation of HIF-1α in HGFs and induces HIF-1 biologic activity under normoxia or hypoxia possibly through TLR4.

CITED2 controls the hypoxic signaling by snatching p300 from the two distinct activation domains of HIF-1α

HIF-1α plays a central role in cellular adaptation to hypoxia, and is closely related to the pathogeneses of life-threatening disorders. HIF-1α induces the expressions of numerous hypoxia-induced genes through two transactivation domains; N-terminal TAD (NAD) and C-terminal TAD (CAD). Furthermore, p300 is known to boost CAD-dependent transactivation, and CBP/p300-interacting transactivator with an ED-rich tail 2 (CITED2) inhibits HIF-1α-driven gene expression by interfering with the interaction between CAD and p300. However, few researches have focused on the role of CITED2 in the regulation of NAD activity, and thus, we addressed this point. CITED2 was found to attenuate the hypoxic activations of NAD-dependent and CAD-dependent genes, suggesting that CITED2 negatively regulates both CAD and NAD. Immunoprecipitation analyses showed that NAD interacts with the Cystein/Histidine region (CH) 1 and CH3 domains of p300. Moreover, CH1 and CH3 both were required for NAD-dependent transactivation. Furthermore, CITED2 was found to inactivate NAD by interfering with NAD binding to CH1, but not to CH3. These results indicate that CITED2 inactivates HIF-1α by blocking p300 recruitment by both NAD and CAD. We also found that pVHL inhibits NAD activity regardless of NAD degradation by blocking the interaction between p300 and NAD. Summarizing, NAD was activated by binding to p300, and this was blocked by either CITED2 or pVHL. We propose that pVHL controls NAD during normoxia and that CITED2 controls NAD during hypoxia. Our results provide a new strategy for controlling HIF-1α.

Acute Vhl gene inactivation induces cardiac HIF-dependent erythropoietin gene expression

Von Hippel Lindau (Vhl) gene inactivation results in embryonic lethality. The consequences of its inactivation in adult mice, and of the ensuing activation of the hypoxia-inducible factors (HIFs), have been explored mainly in a tissue-specific manner. This mid-gestation lethality can be also circumvented by using a floxed Vhl allele in combination with an ubiquous tamoxifen-inducible recombinase Cre-ER^T2. Here, we characterize a widespread reduction in Vhl gene expression in Vhl^floxed-UBC-Cre-ER^T2 adult mice after dietary tamoxifen administration, a convenient route of administration that has yet to be fully characterized for global gene inactivation. Vhl gene inactivation rapidly resulted in a marked splenomegaly and skin erythema, accompanied by renal and hepatic induction of the erythropoietin (Epo) gene, indicative of the in vivo activation of the oxygen sensing HIF pathway. We show that acute Vhl gene inactivation also induced Epo gene expression in the heart, revealing cardiac tissue to be an extra-renal source of EPO. Indeed, primary cardiomyocytes and HL-1 cardiac cells both induce Epo gene expression when exposed to low O₂ tension in a HIF-dependent manner. Thus, as well as demonstrating the potential of dietary tamoxifen administration for gene inactivation studies in UBC-Cre-ER^T2 mouse lines, this data provides evidence of a cardiac oxygen-sensing VHL/HIF/EPO pathway in adult mice.

Hypoxia-mediated drug resistance: novel insights on the functional interaction of HIFs and cell death pathways

Resistance towards chemotherapy, either primary or acquired, represents a major obstacle in clinical oncology. Three basic categories underlie most cases of chemotherapy failure: Inadequate pharmacokinetic properties of the drug, tumor cell intrinsic factors such as the expression of drug efflux pumps and tumor cell extrinsic conditions present in the tumor microenvironment, characterized by such hostile conditions as hypoxia, acidosis, nutrient starvation and increased interstitial pressure. Tumor hypoxia has been known to negatively affect therapy outcome for decades. Hypoxia inhibits tumor cell proliferation and induces cell cycle arrest, ultimately conferring chemoresistance since anticancer drugs preferentially target rapidly proliferating cells. However, this knowledge has been largely neglected while screening for anti-proliferative substances in vitro, resulting in hypoxia-mediated failure of most newly identified substances in vivo. To achieve a tangible therapeutic benefit from this knowledge, the mechanisms that drive tumoral responses to hypoxia need to be identified and exploited for their validity as innovative therapy targets. The HIF family of hypoxia-inducible transcription factors represents the main mediator of the hypoxic response and is widely upregulated in human cancers. HIF-1α and to a lesser extent HIF-2α, the oxygen-regulated HIF isoforms, have been associated with chemotherapy failure and interference with HIF function holds great promise to improve future anticancer therapy. In this review we summarize recent findings on the molecular mechanisms that underlie the role of the HIFs in drug resistance. Specifically, we will highlight the multifaceted interaction of HIF with apoptosis, senescence, autophagy, p53 and mitochondrial activity and outline how these are at the heart of HIF-mediated therapy failure.

Redox control of protein-DNA interactions: from molecular mechanisms to significance in signal transduction, gene expression, and DNA replication

Protein-DNA interactions play a key role in the regulation of major cellular metabolic pathways, including gene expression, genome replication, and genomic stability. They are mediated through the interactions of regulatory proteins with their specific DNA-binding sites at promoters, enhancers, and replication origins in the genome. Redox signaling regulates these protein-DNA interactions using reactive oxygen species and reactive nitrogen species that interact with cysteine residues at target proteins and their regulators. This review describes the redox-mediated regulation of several master regulators of gene expression that control the induction and suppression of hundreds of genes in the genome, regulating multiple metabolic pathways, which are involved in cell growth, development, differentiation, and survival, as well as in the function of the immune system and cellular response to intracellular and extracellular stimuli. It also discusses the role of redox signaling in protein-DNA interactions that regulate DNA replication. Specificity of redox regulation is discussed, as well as the mechanisms providing several levels of redox-mediated regulation, from direct control of DNA-binding domains through the indirect control, mediated by release of negative regulators, regulation of redox-sensitive protein kinases, intracellular trafficking, and chromatin remodeling.

The future of toxicity testing: a focus on in vitro methods using a quantitative high-throughput screening platform

The US Tox21 collaborative program represents a paradigm shift in toxicity testing of chemical compounds from traditional in vivo tests to less expensive and higher throughput in vitro methods to prioritize compounds for further study, identify mechanisms of action and ultimately develop predictive models for adverse health effects in humans. The NIH Chemical Genomics Center (NCGC) is an integral component of the Tox21 collaboration owing to its quantitative high-throughput screening (qHTS) paradigm, in which titration-based screening is used to profile hundreds of thousands of compounds per week. Here, we describe the Tox21 collaboration, qHTS-based compound testing and the various Tox21 screening assays that have been validated and tested at the NCGC to date.

Glycine pretreatment ameliorates liver injury after partial hepatectomy in the rat

BACKGROUND

Living donor liver transplantation subjects the donor to a major hepatectomy. Pharmacological or nutritive protection of the liver during the procedure is desirable to ensure that the remnant is able to maintain sufficient function. The aim of our study was to analyze the effects of pretreatments with alpha-tocopherol (vitamin E), the flavonoid silibinin and/or the amino acid L-glycine on the donor in a rat model.

METHODS

Male Wistar rats were pretreated with L-glycine (5% in chow, 5 days), alpha-tocopherol (100 mg/kg body weight by gavage, 3 days) and/or silibinin (100 mg/kg body weight, i.p., 5 days). Thereafter, 90% partial hepatectomy was performed without portal vein clamping.

RESULTS

Glycine pretreatment markedly decreased transaminase release (AST, 12 hr: glycine 1292 +/- 192 U/L, control 2311 +/- 556 U/L, p < .05; ALT, 12 hr: glycine 1013 +/- 278 U/L, control 2038 +/- 500 U/L, p < .05), serum ALP activity and serum bilirubin levels (p < .05). Prothrombin time was reduced, and histologically, liver injury was also decreased in the glycine group. Silibinin pretreatment was less advantageous and pretreatment with alpha-tocopherol at this very high dose showed some adverse effects. Combined, i.e., triple pretreatment was less advantageous than glycine alone. Liver resection induced HIF-1alpha accumulation and HIF-1alpha accumulation was also decreased by glycine pretreatment.

CONCLUSION

The decrease of liver injury and improvement of liver function after pretreatment with glycine suggests that glycine pretreatment might be beneficial for living liver donors as well as for patients subjected to partial hepatectomy for other reasons.

Deletion of von Hippel-Lindau in glomerular podocytes results in glomerular basement membrane thickening, ectopic subepithelial deposition of collagen {alpha}1{alpha}2{alpha}1(IV), expression of neuroglobin, and proteinuria

Vascular endothelial growth factor, which is critical for blood vessel formation, is regulated by hypoxia inducible transcription factors (HIFs). A component of the E3 ubiquitin ligase complex, von Hippel-Lindau (VHL) facilitates oxygen-dependent polyubiquitination and proteasomal degradation of HIFalpha subunits. Hypothesizing that deletion of podocyte VHL would result in HIFalpha hyperstabilization, we crossed podocin promoter-Cre transgenic mice, which express Cre recombinase in podocytes beginning at the capillary loop stage of glomerular development, with floxed VHL mice. Vascular patterning and glomerular development appeared unaltered in progeny lacking podocyte VHL. However, urinalysis showed increased albumin excretion by 4 weeks when compared with wild-type littermates with several sever cases (>1000 microg/ml). Many glomerular ultrastructural changes were seen in mutants, including focal subendothelial delamination and widespread podocyte foot process broadening, and glomerular basement membranes (GBMs) were significantly thicker in 16-week-old mutants compared with controls. Moreover, immunoelectron microscopy showed ectopic deposition of collagen alpha1alpha2alpha1(IV) in GBM humps beneath podocytes. Significant increases in the number of Ki-67-positive mesangial cells were also found, but glomerular WT1 expression was significantly decreased, signifying podocyte death and/or de-differentiation. Indeed, expression profiling of mutant glomeruli suggested a negative regulatory feedback loop involving the HIFalpha prolyl hydroxylase, Egln3. In addition, the brain oxygen-binding protein, Neuroglobin, was induced in mutant podocytes. We conclude that podocyte VHL is required for normal maintenance of podocytes, GBM composition and ultrastructure, and glomerular barrier properties.

Identification of small molecule compounds that inhibit the HIF-1 signaling pathway

Background

Hypoxia-inducible factor-1 (HIF-1) is the major hypoxia-regulated transcription factor that regulates cellular responses to low oxygen environments. HIF-1 is composed of two subunits: hypoxia-inducible HIF-1α and constitutively-expressed HIF-1β. During hypoxic conditions, HIF-1α heterodimerizes with HIF-1β and translocates to the nucleus where the HIF-1 complex binds to the hypoxia-response element (HRE) and activates expression of target genes implicated in cell growth and survival. HIF-1α protein expression is elevated in many solid tumors, including those of the cervix and brain, where cells that are the greatest distance from blood vessels, and therefore the most hypoxic, express the highest levels of HIF-1α. Therapeutic blockade of the HIF-1 signaling pathway in cancer cells therefore provides an attractive strategy for development of anticancer drugs. To identify small molecule inhibitors of the HIF-1 pathway, we have developed a cell-based reporter gene assay and screened a large compound library by using a quantitative high-throughput screening (qHTS) approach.

Results

The assay is based upon a β-lactamase reporter under the control of a HRE. We have screened approximate 73,000 compounds by qHTS, with each compound tested over a range of seven to fifteen concentrations. After qHTS we have rapidly identified three novel structural series of HIF-1 pathway Inhibitors. Selected compounds in these series were also confirmed as inhibitors in a HRE β-lactamase reporter gene assay induced by low oxygen and in a VEGF secretion assay. Three of the four selected compounds tested showed significant inhibition of hypoxia-induced HIF-1α accumulation by western blot analysis.

Conclusion

The use of β-lactamase reporter gene assays, in combination with qHTS, enabled the rapid identification and prioritization of inhibitors specific to the hypoxia induced signaling pathway.

Morg1 heterozygous mice are protected from acute renal ischemia-reperfusion injury

Renal ischemia and reperfusion injury leads to acute renal failure when proinflammatory and apoptotic processes in the kidney are activated. The increase in hypoxia-inducible transcription factor-alpha (HIF-alpha), an important transcription factor for several genes, can attenuate ischemic renal injury. We recently identified a novel WD-repeat protein designated Morg1 (MAPK organizer 1) that interacts with prolyl hydroxylase 3 (PHD3), an important enzyme involved in the regulation of HIF-1alpha and HIF-2alpha expression. While homozygous Morg1 -/- mice are embryonic lethal, heterozygous Morg1 +/- mice have a normal phenotype. We show here that Morg1 +/- were partially protected from renal ischemia-reperfusion injury compared with wild-type Morg1 +/+ animals. Morg1 +/- mice compared with wild-type animals revealed a stronger increase in HIF-1alpha and HIF-2alpha expression in the ischemic-reperfused kidney associated with enhanced serum erythropoietin levels. However, no significant expression of HIF-1alpha and HIF-2alpha was found in nonischemic kidneys without any difference between Morg1 +/- and Morg1 +/+ mice. Ischemic kidneys of Morg1 +/- mice expressed more erythropoietin mRNA than ischemic kidneys from wild-type animals. Renal ischemia in Morg1 +/- mice resulted in a decrease in renal inflammation and reduction of proinflammatory cytokines (MCP-1, IP-10, MIP-2) compared with wild-type mice. Furthermore, there was significantly less apoptosis and tubular damage in Morg1 +/- kidneys after ischemia-reperfusion, and this was also reflected in significantly improved renal function compared with wild-type. Thus Morg1 may be a novel therapeutic target to limit renal injury after ischemia-reperfusion.

Identification of chemical compounds that induce HIF-1alpha activity

Cellular metabolism depends on the availability of oxygen and the major regulator of oxygen homeostasis is hypoxia-inducible factor 1 (HIF-1), a highly conserved transcription factor that plays an essential role in cellular and systemic homeostatic responses to hypoxia. HIF-1 is a heterodimeric transcription factor composed of hypoxia-inducible HIF-1alpha and constitutively expressed HIF-1beta. Under hypoxic conditions, the two subunits dimerize, allowing translocation of the HIF-1 complex to the nucleus where it binds to hypoxia-response elements (HREs) and activates expression of target genes implicated in angiogenesis, cell growth, and survival. The HIF-1 pathway is essential to normal growth and development, and is involved in the pathophysiology of cancer, inflammation, and ischemia. Thus, there is considerable interest in identifying compounds that modulate the HIF-1 signaling pathway. To assess the ability of environmental chemicals to stimulate the HIF-1 signaling pathway, we screened a National Toxicology Program collection of 1408 compounds using a cell-based beta-lactamase HRE reporter gene assay in a quantitative high-throughput screening (qHTS) format. Twelve active compounds were identified. These compounds were tested in a confirmatory assay for induction of vascular endothelial growth factor, a known hypoxia target gene, and confirmed compounds were further tested for their ability to mimic the effect of a reduced-oxygen environment on hypoxia-regulated promoter activity. Based on this testing strategy, three compounds (o-phenanthroline, iodochlorohydroxyquinoline, cobalt sulfate heptahydrate) were confirmed as hypoxia mimetics, whereas two compounds (7-diethylamino-4-methylcoumarin and 7,12-dimethylbenz(a)anthracence) were found to interact with HIF-1 in a manner different from hypoxia. These results demonstrate the effectiveness of qHTS in combination with secondary assays for identification of HIF-1alpha inducers and for distinguishing among inducers based on their pattern of activated hypoxic target genes. Identification of environmental compounds having HIF-1alpha activation activity in cell-based assays may be useful for prioritizing chemicals for further testing as hypoxia-response inducers in vivo.

Enhanced leukocyte HIF-1alpha and HIF-1 DNA binding in humans after rapid ascent to 4300 m

Hypoxia plays a crucial role in the pathogenesis of a multitude of diseases and clinical conditions such as cancer, diabetes, cardiovascular disease, stroke, pulmonary disease, inflammation, organ transplant, and wound healing. Investigations into the role of hypoxia-inducible transcription factor (HIF) in disease development have been conducted with the basic premise that HIF is activated in vivo during hypoxia in humans, yet this basic physiologic premise has never verified. Thus, we hypothesized that HIF-1 DNA binding would be enhanced in vivo in humans in response to acute global hypoxia. Fourteen human subjects were exposed to normoxia (1600 m) and hypoxia (4300 m, approximately 12% O(2)) in a hypobaric hypoxic chamber (8 h). HIF-1 DNA binding and HIF-1alpha protein were evaluated in circulating leukocytes. Oxidative markers were evaluated by plasma metabolomics using nuclear magnetic resonance and by urinary 15-F(2t)-isoprostane concentrations. Leukocyte HIF-1 DNA binding was increased (p=0.007) and HIF-1alpha was greater during hypoxia compared to normoxia. Circulating total glutathione was reduced by 35% (p=0.001), and lactate and succinate were increased by 29 and 158%, respectively (p=0.007 and 0.001), as were urinary 15-F(2t)-isoprostanes (p=0.037). HIF-1 DNA binding and HIF-1alpha were elevated in vivo in leukocytes of healthy human subjects exposed to 12% oxygen, in association with plasma and urinary markers of hypoxic stress.