Oxygen sensing and signaling: impact on the regulation of physiologically important genes

Advances in kidney disease: pathogenesis and therapeutic targets

Chronic kidney disease (CKD) is a global public health issue characterized by progressive loss of kidney function, of which end-stage kidney disease (ESKD) is the last stage. The global increase in the prevalence of CKD is linked to the increasing prevalence of traditional risk factors, including obesity, hypertension, and diabetes mellitus, as well as metabolic factors, particularly insulin resistance, dyslipidemia, and hyperuricemia. Mortality and comorbidities, such as cardiovascular complications, rise steadily as kidney function deteriorates. Patients who progress to ESKD require long-term kidney replacement therapy, such as transplantation or hemodialysis/peritoneal dialysis. It is currently understood that a crucial aspect of CKD involves persistent, low-grade inflammation. In addition, increased oxidative and metabolic stress, endothelial dysfunction, vascular calcification from poor calcium and phosphate metabolism, and difficulties with coagulation are some of the complex molecular pathways underlying CKD-related and ESKD-related issues. Novel mechanisms, such as microbiome dysbiosis and apolipoprotein L1 gene mutation, have improved our understanding of kidney disease mechanisms. High kidney disease risk of Africa has been linked to APOL1 high-risk alleles. The 3-fold increased risk of ESKD in African Americans compared to European Americans is currently mainly attributed to variants in the APOL1 gene in the chromosome 22q12 locus. Additionally, the role of new therapies such as SGLT2 inhibitors, mineralocorticoid receptor antagonists, and APOL1 channel function inhibitors offers new therapeutic targets in slowing down the progression of chronic kidney disease. This review describes recent molecular mechanisms underlying CKD and emerging therapeutic targets.

Oxygen is an essential gasotransmitter directly sensed via protein gasoreceptors

The current restrictive criteria for gasotransmitters exclude oxygen (O2) as a gasotransmitter in vertebrates. In this manuscript, I propose a revision of gasotransmitter criteria to include O2 per se as a signaling molecule and 'essential gasotransmitter' for vertebrates. This revision would enable us to search for protein-based O2-binding sensors (gasoreceptors) in all cells in the brain or other tissues rather than specialized tissues such as the carotid body or gills. If microorganisms have protein-based O2-binding sensors or gasoreceptors such as DosP or FixL or FNR with diverse signaling domains, then eukaryotic cells must also have O2-binding sensors or gasoreceptors. Just as there are protein-based receptor(s) for nitric oxide (GUCY1A, GUCY1B, CLOCK, NR1D2) in cells of diverse tissues, it is reasonable to consider that there are protein-based receptors for O2 in cells of diverse tissues as well. In mammals, O2 must be acting as a gasotransmitter or gaseous signaling molecule via protein-based gasoreceptors such as androglobin that very likely mediate acute sensing of O2. Accepting O2 as an essential gasotransmitter will enable us to search for gasoreceptors not only for O2 but also for other nonessential gasotransmitters such as hydrogen sulfide, ammonia, methane, and ethylene. It will also allow us to investigate the role of environment-derived metal ions in acute gas (or solute) sensing within and between organisms. Finally, accepting O2 per se as a signaling molecule acting via gasoreceptors will open up the field of gasocrinology.

Downregulation of miR-337-3p in hypoxia/reoxygenation neuroblastoma cells increases KCTD11 expression

Neurodegeneration is linked to the progressive loss of neural function and is associated with several diseases. Hypoxia is a hallmark in many of these diseases, and several therapies have been developed to treat this disease, including gene expression therapies that should be tightly controlled to avoid side effects. Cells experiencing hypoxia undergo a series of physiological responses that are induced by the activation of various transcription factors. Modulation of microRNA (miRNA) expression to alter transcriptional regulation has been demonstrated to be beneficial in treating multiple diseases, and in this study, we therefore explored potential miRNA candidates that could influence hypoxia-induced nerve cell death. Our data suggest that in mouse neuroblasts Neuro-2a cells with hypoxia/reoxygenation (H/R), miR-337-3p is downregulated to increase the expression of Potassium channel tetramerization domain containing 11 (KCTD11) and subsequently promote apoptosis. Here, we demonstrate for the first time that KCTD11 plays a role in the cellular response to hypoxia, and we also provide a possible regulatory mechanism by identifying the axis of miR-337-3p/KCTD11 as a promising candidate modulator of nerve cell survival after H/R exposure.

Oxalic acid secretion alleviates saline-alkali stress in alfalfa by improving photosynthetic characteristics and antioxidant activity

Saline-alkali stress significantly affects the growth and yield of alfalfa (Medicago sativa L.). Organic acid secretion is crucial in alleviating abiotic stress-induced damage in plants. In this study, we evaluated the contents of the major organic acids secreted by the roots of tolerant (ZD) and sensitive (LYL) varieties of alfalfa under saline-alkali stress and investigated the effects of these organic acids on the growth, and physiological functions of alfalfa. Our results indicated that the oxalic acid (OA) content was the highest among the organic acids secreted from alfalfa roots under saline-alkali stress, and oxalic acid content was the most significantly different between the two varieties, ZD and LYL, compared to the contents of the other organic acids. Oxalic acid alleviated the inhibition of alfalfa growth caused by saline-alkali stress, improved photosynthetic characteristics, reduced the accumulation of reactive oxygen species, and increased the activity of antioxidant enzymes and content of osmoregulatory substances. Furthermore, oxalic acid resulted in significantly increased expression of genes involved in photosynthesis and antioxidant system in alfalfa under saline-alkali stress. This study revealed the effects of oxalic acid secreted by the root system on stress-related physiological processes, providing valuable insights into the functions of root secretions in plant saline-alkali resistance.

The Role of Mitochondrial Enzymes, Succinate-Coupled Signaling Pathways and Mitochondrial Ultrastructure in the Formation of Urgent Adaptation to Acute Hypoxia in the Myocardium

The effect of a single one-hour exposure to three modes of hypobaric hypoxia (HBH) differed in the content of O₂ in inhaled air (FiO₂-14%, 10%, 8%) in the development of mitochondrial-dependent adaptive processes in the myocardium was studied in vivo. The following parameters have been examined: (a) an urgent reaction of catalytic subunits of mitochondrial enzymes (NDUFV2, SDHA, Cyt b, COX2, ATP5A) in the myocardium as an indicator of the state of the respiratory chain electron transport function; (b) an urgent activation of signaling pathways dependent on GPR91, HIF-1α and VEGF, allowing us to assess their role in the formation of urgent mechanisms of adaptation to hypoxia in the myocardium; (c) changes in the ultrastructure of three subpopulations of myocardial mitochondria under these conditions. The studies were conducted on two rat phenotypes: rats with low resistance (LR) and high resistance (HR) to hypoxia. The adaptive and compensatory role of the mitochondrial complex II (MC II) in maintaining the electron transport and energy function of the myocardium in a wide range of reduced O₂ concentrations in the initial period of hypoxic exposure has been established. The features of urgent reciprocal regulatory interaction of NAD- and FAD-dependent oxidation pathways in myocardial mitochondria under these conditions have been revealed. The data indicating the participation of GPR91, HIF-1a and VEGF in this process have been obtained. The ultrastructure of the mitochondrial subpopulations in the myocardium of LR and HR rats differed in normoxic conditions and reacted differently to hypoxia of varying severity. The parameters studied together are highly informative indicators of the quality of cardiac activity and metabolic biomarkers of urgent adaptation in various hypoxic conditions.

Crystal and solution structure of NDRG1, a membrane-binding protein linked to myelination and tumour suppression

N-myc downstream-regulated gene 1 (NDRG1) is a tumour suppressor involved in vesicular trafficking and stress response. NDRG1 participates in peripheral nerve myelination, and mutations in the NDRG1 gene lead to Charcot-Marie-Tooth neuropathy. The 43-kDa NDRG1 is considered as an inactive member of the α/β hydrolase superfamily. In addition to a central α/β hydrolase fold domain, NDRG1 consists of a short N terminus and a C-terminal region with three 10-residue repeats. We determined the crystal structure of the α/β hydrolase domain of human NDRG1 and characterised the structure and dynamics of full-length NDRG1. The structure of the α/β hydrolase domain resembles the canonical α/β hydrolase fold with a central β sheet surrounded by α helices. Small-angle X-ray scattering and CD spectroscopy indicated a variable conformation for the N- and C-terminal regions. NDRG1 binds to various types of lipid vesicles, and the conformation of the C-terminal region is modulated upon lipid interaction. Intriguingly, NDRG1 interacts with metal ions, such as nickel, but is prone to aggregation in their presence. Our results uncover the structural and dynamic features of NDRG1, as well as elucidate its interactions with metals and lipids, and encourage studies to identify a putative hydrolase activity of NDRG1. DATABASES: The coordinates and structure factors for the crystal structure of human NDRG1 were deposited to PDB (PDB ID: 6ZMM).

Pheochromocytoma

Pheochromocytomas are rare tumors originating in the adrenal medulla. They may be sporadic or in the context of a hereditary syndrome. A considerable number of pheochromocytomas carry germline or somatic gene mutations, which are inherited in the autosomal dominant way. All patients should undergo genetic testing. Symptoms are due to catecholamines over production or to a mass effect. Diagnosis is confirmed by raised plasma or urine metanephrines or normetanephrines. Radiology assists in the tumor location and any local invasion or metastasis. All the patients should have preoperative preparation with α-blockers and/or other medications to control hypertension, arrhythmia, and volume expansion. Surgery is the definitive treatment. Follow up should be life-long.

Egr-1 functions as a master switch regulator of remote ischemic preconditioning-induced cardioprotection

Despite improved treatment options myocardial infarction (MI) is still a leading cause of mortality and morbidity worldwide. Remote ischemic preconditioning (RIPC) is a mechanistic process that reduces myocardial infarction size and protects against ischemia reperfusion (I/R) injury. The zinc finger transcription factor early growth response-1 (Egr-1) is integral to the biological response to I/R, as its upregulation mediates the increased expression of inflammatory and prothrombotic processes. We aimed to determine the association and/or role of Egr-1 expression with the molecular mechanisms controlling the cardioprotective effects of RIPC. This study used H9C2 cells in vitro and a rat model of cardiac ischemia reperfusion (I/R) injury. We silenced Egr-1 with DNAzyme (ED5) in vitro and in vivo, before three cycles of RIPC consisting of alternating 5 min hypoxia and normoxia in cells or hind-limb ligation and release in the rat, followed by hypoxic challenge in vitro and I/R injury in vivo. Post-procedure, ED5 administration led to a significant increase in infarct size compared to controls (65.90 ± 2.38% vs. 41.00 ± 2.83%, p < 0.0001) following administration prior to RIPC in vivo, concurrent with decreased plasma IL-6 levels (118.30 ± 4.30 pg/ml vs. 130.50 ± 1.29 pg/ml, p < 0.05), downregulation of the cardioprotective JAK-STAT pathway, and elevated myocardial endothelial dysfunction. In vitro, ED5 administration abrogated IL-6 mRNA expression in H9C2 cells subjected to RIPC (0.95 ± 0.20 vs. 6.08 ± 1.40-fold relative to the control group, p < 0.05), resulting in increase in apoptosis (4.76 ± 0.70% vs. 2.23 ± 0.34%, p < 0.05) and loss of mitochondrial membrane potential (0.57 ± 0.11% vs. 1.0 ± 0.14%-fold relative to control, p < 0.05) in recipient cells receiving preconditioned media from the DNAzyme treated donor cells. This study suggests that Egr-1 functions as a master regulator of remote preconditioning inducing a protective effect against myocardial I/R injury through IL-6-dependent JAK-STAT signaling.

Intracellular processing of silica-coated superparamagnetic iron nanoparticles in human mesenchymal stem cells

Silica-coated superparamagnetic iron nanoparticles (SiMAGs) are an exciting biomedical technology capable of targeted delivery of cell-based therapeutics and disease diagnosis. However, in order to realise their full clinical potential, their intracellular fate must be determined. The analytical techniques of super-resolution fluorescence microscopy, particle counting flow cytometry and pH-sensitive nanosensors were applied to elucidate mechanisms of intracellular SiMAG processing in human mesenchymal stem cell (hMSCs). Super-resolution microscopy showed SiMAG fluorescently-tagged nanoparticles are endocytosed and co-localised within lysosomes. When exposed to simulated lysosomal conditions SiMAGs were solubilised and exhibited diminishing fluorescence emission over 7 days. The in vitro intracellular metabolism of SiMAGs was monitored in hMSCs using flow cytometry and co-localised pH-sensitive nanosensors. A decrease in SiMAG fluorescence emission, which corresponded to a decrease in lysosomal pH was observed, mirroring ex vivo observations, suggesting SiMAG lysosomal exposure degrades fluorescent silica-coatings and iron cores. These findings indicate although there is a significant decrease in intracellular SiMAG loading, sufficient particles remain internalised (>50%) to render SiMAG treated cells amenable to long-term magnetic cell manipulation. Our analytical approach provides important insights into the understanding of the intracellular fate of SiMAG processing, which could be readily applied to other particle therapeutics, to advance their clinical translation.

Hypoxic preconditioned bone mesenchymal stem cells ameliorate spinal cord injury in rats via improved survival and migration

The unique hypoxic inflammatory microenvironment observed in the spinal cord following spinal cord injury (SCI) limits the survival and efficacy of transplanted bone mesenchymal stem cells (BMSCs). The aim of the present study was to determine whether hypoxic preconditioning (HP) increased the therapeutic effects of BMSC on SCI. BMSCs were pretreated with cobalt chloride (CoCl2) in vitro, and the proliferative apoptotic and migratory abilities of these hypoxic BMSCs (H‑BMSCs) were assessed. BMSCs and H‑BMSCs derived from green fluorescent protein (GFP) rats were transplanted into SCI rats in vivo. The neurological function, histopathology, inflammation, and number and migration of transplanted cells were examined. HP significantly enhanced BMSC migration (increased hypoxia inducible factor 1α and C‑X‑C motif chemokine receptor 4 expression) and tolerance to apoptotic conditions (decreased caspase‑3 and increased B‑cell lymphoma 2 expression) in vitro. In vivo, H‑BMSC transplantation significantly improved neurological function, decreased spinal cord damage and suppressed the inflammatory response associated with microglial activation. The number of GFP‑positive cells in the SCI core and peripheral region of H‑BMSC animals was increased compared with that in those of BMSC animals, suggesting that HP may increase the survival and migratory abilities of BMSCs and highlights their therapeutic potential for SCI.

Integrated phosphorescence-based photonic biosensor (iPOB) for monitoring oxygen levels in 3D cell culture systems

Physiological processes, such as respiration, circulation, digestion, and many pathologies alter oxygen concentration in the blood and tissue. When designing culture systems to recapitulate the in vivo oxygen environment, it is important to integrate systems for monitoring and controlling oxygen concentration. Herein, we report the design and engineering of a system to remotely monitor and control oxygen concentration inside a device for 3D cell culture. We integrate a photonic oxygen biosensor into the 3D tissue scaffold and regulate oxygen concentration via the control of purging gas flow. The integrated phosphorescence-based oxygen biosensor employs the quenching of palladium-benzoporphyrin by molecular oxygen to transduce the local oxygen concentration in the 3D tissue scaffold. The system is validated by testing the effects of normoxic and hypoxic culture conditions on healthy and tumorigenic breast epithelial cells, MCF-10A cells and BT474 cells, respectively. Under hypoxic conditions, both cell types exhibited upregulation of downstream target genes for the hypoxia marker gene, hypoxia-inducible factor 1α (HIF1A). Lastly, by monitoring the real-time fluctuation of oxygen concentration, we illustrated the formation of hypoxic culture conditions due to limited diffusion of oxygen through 3D tissue scaffolds.

Transplantation of Hypoxic-Preconditioned Bone Mesenchymal Stem Cells Retards Intervertebral Disc Degeneration via Enhancing Implanted Cell Survival and Migration in Rats

OBJECTIVE

Special hypoxic and hypertonic microenvironment in intervertebral discs (IVDs) decreases the treatment effect of cell transplantation. We investigated the hypothesis that hypoxic preconditioning (HP) could improve the therapeutic effect of bone mesenchymal stem cells (BMSCs) to IVD degeneration.

METHODS

BMSCs from green fluorescent protein-transgenic rats were pretreated with cobalt chloride (CoCl2, 100 μM, 24 h) for hypoxic conditions in vitro. Apoptosis (related pathways of caspase-3 and bcl-2) and migration (related pathways of HIF-1α and CXCR4) were detected in BMSCs. In vivo, BMSCs and HP BMSCs (H-BMSCs) were injected into the rat model of IVD degeneration. The IVD height, survival, migration, and differentiation of transplanted BMSCs and matrix protein expression (collagen II, aggrecan, and MMP-13) were tested.

RESULTS

H-BMSCs could extensively decrease IVD degeneration by increasing IVD height and collagen II and aggrecan expressions when compared with BMSCs. Significantly, more GFP-positive BMSCs were observed in the nucleus pulposus and annulus fibrosus regions of IVD. HP could significantly decrease BMSC apoptosis (activating bcl-2 and inhibiting caspase-3) and improve BMSC migration (increasing HIF-1α and CXCR4) in vitro.

CONCLUSION

HP could significantly enhance the capacity of BMSCs to repair DDD by increasing the survival and migration of implanted cells and increasing matrix protein expression.

Enhancing cell and gene therapy manufacture through the application of advanced fluorescent optical sensors (Review)

Cell and gene therapies (CGTs) are examples of future therapeutics that can be used to cure or alleviate the symptoms of disease, by repairing damaged tissue or reprogramming defective genetic information. However, despite the recent advancements in clinical trial outcomes, the path to wide-scale adoption of CGTs remains challenging, such that the emergence of a "blockbuster" therapy has so far proved elusive. Manufacturing solutions for these therapies require the application of scalable and replicable cell manufacturing techniques, which differ markedly from the existing pharmaceutical incumbent. Attempts to adopt this pharmaceutical model for CGT manufacture have largely proved unsuccessful. The most significant challenges facing CGT manufacturing are process analytical testing and quality control. These procedures would greatly benefit from improved sensory technologies that allow direct measurement of critical quality attributes, such as pH, oxygen, lactate and glucose. In turn, this would make manufacturing more robust, replicable and standardized. In this review, the present-day state and prospects of CGT manufacturing are discussed. In particular, the authors highlight the role of fluorescent optical sensors, focusing on their strengths and weaknesses, for CGT manufacture. The review concludes by discussing how the integration of CGT manufacture and fluorescent optical sensors could augment future bioprocessing approaches.

Neuroprotective effect of electroacupuncture and upregulation of hypoxia-inducible factor-1α during acute ischaemic stroke in rats

BACKGROUND

Acupuncture is a traditional method that has been widely used in various fields of medicine with therapeutic effect. However, evidence of effectiveness to support the application of electroacupuncture (EA) during the process of ischaemia is scarce.

OBJECTIVES

To investigate dynamic changes in hypoxia-inducible factor (HIF)-1α expression as well as its association with neurological status in rats subjected to acute ischaemic stroke and EA intervention.

METHODS

Forty adult male rats were randomly divided into three groups that received sham surgery (Control group, n=10) or underwent middle cerebral artery occlusion and EA (MCAO+EA group, n=15) or minimal acupuncture as a control treatment (MCAO+MA group, n=15). The rats in the MCAO+EA and MCAO+MA groups received EA or acupuncture without any electrical current, respectively, during 90 min of ischaemia. Rats in the Control group received the same surgical procedure but without MCAO. EA involved electrical stimulation of needles inserted into the quadriceps at 50 Hz frequency and 3 mA current intensity. Neurological status was evaluated on postoperative day 1, and cerebral infarction volume (IV) and HIF-1α expression 24 hours later.

RESULTS

Neurological scores were improved and cerebral IV was decreased in the MCAO+EA group compared to the MCAO+MA group (both p<0.05). Moreover, HIF-1α expression was higher in the MCAO+EA group versus the MCAO+MA group (p<0.05).

CONCLUSIONS

EA enhanced recovery of neurological function, decreased cerebral IV and increased HIF-1α expression in ischaemic rats. Further research is needed to determine whether EA is effective for stroke treatment through the stimulation of muscle contraction.

Oxidative stress: a key regulator of leiomyoma cell survival

OBJECTIVE

To determine the effects of attenuating oxidative stress with the use of dichloroacetate (DCA) on the expression of key redox enzymes myeloperoxidase (MPO) and inducible nitric oxide synthase (iNOS) as well as on apoptosis.

DESIGN

Prospective experimental study.

SETTING

University medical center.

PATIENT(S)

Cells established from myometrium and uterine fibroid from the same patients.

INTERVENTION(S)

Cells were exposed to normal (20% O₂) or hypoxic (2% O₂) conditions for 24 hours with or without DCA (20 μg/mL), a metabolic modulator that shifts anaerobic to aerobic metabolism.

MAIN OUTCOME MEASURE(S)

Nitrate/nitrite (iNOS activity indicator), iNOS, Bcl-2/Bax ratio, MPO, and caspase-3 activities and levels were determined by means of Greiss assay, real-time reverse-transcription polymerase chain reaction, and ELISA. Data were analyzed with the use of SPSS by means of one-way analysis of variance with Tukey post hoc analysis and independent t tests.

RESULT(S)

MPO, iNOS, and nitrate/nitrite expression were higher in leiomyoma than in myometrial cells, and they were further enhanced by hypoxia in myometrial cells. Treatment with the use of DCA decreased MPO, iNOS, and nitrate/nitrite levels and negated the effect of hypoxia in both types of cells. Leiomyoma cells showed less apoptosis, as indicated by both caspase-3 activity and the Bcl-2/Bax ratio, than myometrial cells. Hypoxia further decreased apoptosis in myometrial cells with no further effect on leiomyoma cells. Treatment with DCA resulted in increased apoptosis in both types of cells, even in the presence of hypoxia.

CONCLUSION(S)

Shifting anaerobic to aerobic metabolism with the use of DCA resulted in an increase in apoptosis in leiomyoma cells and protected myometrial cells from the acquisition of the leiomyoma-like phenotype.

Molecular targeting of hypoxia in radiotherapy

Hypoxia (low O₂) is an essential microenvironmental driver of phenotypic diversity in human solid cancers. Hypoxic cancer cells hijack evolutionarily conserved, O₂- sensitive pathways eliciting molecular adaptations that impact responses to radiotherapy, tumor recurrence and patient survival. In this review, we summarize the radiobiological, genetic, epigenetic and metabolic mechanisms orchestrating oncogenic responses to hypoxia. In addition, we outline emerging hypoxia- targeting strategies that hold promise for individualized cancer therapy in the context of radiotherapy and drug delivery.

Negative Impact of Hypoxia on Tryptophan 2,3-Dioxygenase Function

Tryptophan is an essential amino acid for hosts and pathogens. The liver enzyme tryptophan 2,3-dioxygenase (TDO) provokes, by its ability to degrade tryptophan to N-formylkynurenine, the precursor of the immune-relevant kynurenines, direct and indirect antimicrobial and immunoregulatory states. Up to now these TDO-mediated broad-spectrum effector functions have never been observed under hypoxia in vitro, although physiologic oxygen concentrations in liver tissue are low, especially in case of infection. Here we analysed recombinant expressed human TDO and ex vivo murine TDO functions under different oxygen conditions and show that TDO-induced restrictions of clinically relevant pathogens (bacteria, parasites) and of T cell proliferation are abrogated under hypoxic conditions. We pinpointed the loss of TDO efficiency to the reduction of TDO activity, since cell survival and TDO protein levels were unaffected. In conclusion, the potent antimicrobial as well as immunoregulatory effects of TDO were substantially impaired under hypoxic conditions that pathophysiologically occur in vivo. This might be detrimental for the appropriate host immune response towards relevant pathogens.

Light-Responsive Biodegradable Nanomedicine Overcomes Multidrug Resistance via NO-Enhanced Chemosensitization

Multidrug resistance (MDR) is responsible for the relatively low effectiveness of chemotherapeutics. Herein, a nitric oxide (NO) gas-enhanced chemosensitization strategy is proposed to overcome MDR by construction of a biodegradable nanomedicine formula based on BNN6/DOX coloaded monomethoxy(polyethylene glycol)-poly(lactic-co-glycolic acid) (mPEG-PLGA). On one hand, the nanomedicine features high biocompatibility due to the high density of PEG and biodegradable PLGA. On the other hand, the nanoformula exhibits excellent stability under physiological conditions but exhibits stimuli-responsive decomposition of BNN6 for NO gas release upon ultraviolet-visible irradiation. More importantly, after NO release is triggered, gas molecules are generated that break the nanoparticle shell and lead to the release of doxorubicin. Furthermore, NO was demonstrated to reverse the MDR of tumor cells and enhance the chemosensitization for doxorubicin therapy.

Cross regulation between hypoxia-inducible transcription factor-1α (HIF-1α) and transforming growth factor (TGF)-ß1 mediates nickel oxide nanoparticles (NiONPs)-induced pulmonary fibrosis

Numerous analyses including in vivo and in vitro experiments have demonstrated that inhalation exposure of NiONPs can result in pulmonary fibrosis. However, the potential mechanisms of this pathological process remain elusive. Here, we investigate the role of HIF-1α and TGF-ß1 in NiONPs-induced pulmonary fibrosis with a focus on the interplay of the above two proteins. In vivo, male Sprague&Dawley rats were exposed to NiONPs and pulmonary fibrosis was demonstrated using H&E staining and immunochemistry of αSMA. In vitro, NiONPs contributed to cell proliferation and increased expressions of collagen-1 and αSMA in human fetal lung fibroblasts. Both HIF-1α and TGF-ß1 were upregulated by NiONPs treatment. Inhibition of HIF-1α reduced TGF-ß1 expression and downregulation of TGF-ß1 reduced HIF-1α protein level. Mechanism investigation revealed that TGF-ß1 affects nuclear translocation activity of HIF-1α. Taken together, these finding provide evidence that HIF-1α and TGF-ß1 act in synergy to foster NiONPs-induced pulmonary fibrosis, and the cross talk between them is a pivotal mechanism of pulmonary fibrosis.

Mitochondria-controlled signaling mechanisms of brain protection in hypoxia

The article is focused on the role of the cell bioenergetic apparatus, mitochondria, involved in development of immediate and delayed molecular mechanisms for adaptation to hypoxic stress in brain cortex. Hypoxia induces reprogramming of respiratory chain function and switching from oxidation of NAD-related substrates (complex I) to succinate oxidation (complex II). Transient, reversible, compensatory activation of respiratory chain complex II is a major mechanism of immediate adaptation to hypoxia necessary for (1) succinate-related energy synthesis in the conditions of oxygen deficiency and formation of urgent resistance in the body; (2) succinate-related stabilization of HIF-1α and initiation of its transcriptional activity related with formation of long-term adaptation; (3) succinate-related activation of the succinate-specific receptor, GPR91. This mechanism participates in at least four critical regulatory functions: (1) sensor function related with changes in kinetic properties of complex I and complex II in response to a gradual decrease in ambient oxygen concentration; this function is designed for selection of the most efficient pathway for energy substrate oxidation in hypoxia; (2) compensatory function focused on formation of immediate adaptive responses to hypoxia and hypoxic resistance of the body; (3) transcriptional function focused on activated synthesis of HIF-1 and the genes providing long-term adaptation to low pO2; (4) receptor function, which reflects participation of mitochondria in the intercellular signaling system via the succinate-dependent receptor, GPR91. In all cases, the desired result is achieved by activation of the succinate-dependent oxidation pathway, which allows considering succinate as a signaling molecule. Patterns of mitochondria-controlled activation of GPR-91- and HIF-1-dependent reaction were considered, and a possibility of their participation in cellular-intercellular-systemic interactions in hypoxia and adaptation was proved.

Advances in the Pathogenesis of Adhesion Development: The Role of Oxidative Stress

Over the past several years, there has been increasing recognition that pathogenesis of adhesion development includes significant contributions of hypoxia induced at the site of surgery, the resulting oxidative stress, and the subsequent free radical production. Mitochondrial dysfunction generated by surgically induced tissue hypoxia and inflammation can lead to the production of reactive oxygen and nitrogen species as well as antioxidant enzymes such as superoxide dismutase, catalase, and glutathione peroxidase which when optimal have the potential to abrogate mitochondrial dysfunction and oxidative stress, preventing the cascade of events leading to the development of adhesions in injured peritoneum. There is a significant cross talk between the several processes leading to whether or not adhesions would eventually develop. Several of these processes present avenues for the development of measures that can help in abrogating adhesion formation or reformation after intraabdominal surgery.

Hypoxia and cytoplasmic alkalinization upregulate growth hormone expression in lymphocytes

We report here that culture of lymphoid cells under hypoxic conditions showed an increase in both luciferase expression from a GH-promoter luciferase construct and the levels of lymphocyte GH. The effect was mimicked by treatment of cells with cobalt chloride consistent with a specific oxygen-sensing mechanism. We identified a putative hypoxia response element (HRE) in the GH promoter at the region -176 bp to -172 bp that contains a copy of the hypoxia-inducible factor-1 (Hif-1) binding motif (5'-ACGTG-3'). The results also showed that culture of primary rat spleen cells with different doses of TMA induced a dose-dependent increase in lymphocyte GH by Western blot analysis. Greater levels of GH are induced in T cell-enriched populations compared to B cell-enriched populations after treatment with CoCl(2) or TMA. Our results suggest that the stressful cellular conditions likely to occur at sites of inflammation or tumor growth may induce the synthesis of lymphocyte GH.

Rescuing iron-overloaded macrophages by conservative relocation of the accumulated metal

BACKGROUND AND PURPOSE

Systemic iron deficiency concomitant with macrophage iron retention is characteristic of iron-refractory anaemias associated with chronic disease. The systemic misdistribution of iron, which is further exacerbated by parenteral iron supplementation, is mainly attributable to iron retention exerted on resident macrophages by hepcidin-mediated down-regulation of the iron exporter ferroportin. We aimed at developing an experimental macrophage-based cell model that recapitulates pathophysiological features of iron misdistribution found in chronic disorders and use it as a screening platform for identifying agents with the potential for relocating the accumulated metal and restoring affected functions.

EXPERIMENTAL APPROACH

A raw macrophage subline was selected as cell model of iron retention based on their capacity to take up polymeric iron or aged erythrocytes excessively, resulting in a demonstrable increase of cell labile iron pools and oxidative damage that are aggravated by hepcidin.

KEY RESULTS

This model provided a three-stage high throughput screening platform for identifying agents with the combined ability to: (i) scavenge cell iron and thereby rescue macrophage cells damaged by iron-overload; (ii) bypass the ferroportin blockade by conveying the scavenged iron to other iron-starved cells in co-culture via transferrin but (iii) without promoting utilization of the scavenged iron by intracellular pathogens. As test agents we used chelators in clinical practice and found the oral chelator deferiprone fulfilled essentially all of the three criteria.

CONCLUSIONS AND IMPLICATIONS

We provide a proof of principle for conservative iron relocation as complementary therapeutic approach for correcting the misdistribution of iron associated with chronic disease and exacerbated by parenteral iron supplementation.

Anemia of renal disease: what it is, what to do and what's new

PATIENT GROUP

It is estimated that 15-30% of geriatric cats will develop chronic kidney disease (CKD), and that 30-65% of these cats will develop anemia as their renal disease worsens. Anemia of renal disease is multifactorial in its pathogenesis, but the main cause is reduced production of erythropoietin, a renal hormone that controls the bone marrow's production of red blood cells, as kidney disease progresses.

PRACTICAL RELEVANCE

It is important to recognize the presence of anemia of renal disease so that adequate treatment may be instituted to improve quality of life and metabolic function. Erythrocyte-stimulating agents (ESAs), such as epoetin alfa, epoetin beta and darbepoetin alfa, have been developed to counteract the effects of decreased erythropoietin production by the kidneys. These treatments, which are the focus of this review, have 83% similarity in amino acid sequence to the feline hormone. On average, the target packed cell volume (>25%) is reached within 3-4 weeks of ESA therapy.

CLINICAL CHALLENGES

The use of ESAs has been associated with a number of complications, such as iron deficiency, hypertension, arthralgia, fever, seizures, polycythemia and pure red cell aplasia (PRCA). Darbepoetin has a prolonged half-life compared with epoetin and thus can be given only once a week, instead of three times a week. The incidence of PRCA appears to be decreased with darbepoetin use when compared with epoetin use in cats.

EVIDENCE BASE

There is limited published evidence to date to underpin the use of ESAs in cats. This review draws on the relevant publications that currently exist, and the authors' personal experience of using these therapies for over 5 years.

Postoperative adhesion development following cesarean and open intra-abdominal gynecological operations: a review

In this review, we discuss the pathophysiology of adhesion development, the impact of physiological changes associated with pregnancy on markers of adhesion development, and the clinical implications of adhesion development following cesarean delivery (CD). Although peritoneal adhesions develop after the overwhelming majority of intra-abdominal and pelvic surgery, there is evidence in the literature that suggests that patients having CD may develop adhesions less frequently. However, adhesions continue to be a concern after CD, and are likely significant, albeit on average less than after gynecological operations, but with potential to cause significant delay in the delivery of the baby with serious, lifelong consequences. Appreciation of the pathophysiology of adhesion development described herein should allow a more informed approach to the rapidly evolving field of intra-abdominal adhesions and should serve as a reference for an evidence-based approach to consideration for the prevention and treatment of adhesions.

Exposure to polychlorinated biphenyls enhances lipid peroxidation in human normal peritoneal and adhesion fibroblasts: a potential role for myeloperoxidase

Nitric oxide, superoxide, and lipid peroxidation (LPO) produced under oxidative stress may contribute to the development of postoperative adhesions. The objective of this study was to determine the effects of polychlorinated biphenyls (PCBs) on LPO, superoxide dismutase, myeloperoxidase (MPO), and nitrite/nitrate in human normal peritoneal and adhesion fibroblasts. PCB treatment reduced inducible nitric oxide synthase (iNOS) expression as well as levels of nitrite/nitrate in both cell lines. Although there was no difference in iNOS expression between the two cell lines, adhesion fibroblasts manifested lower basal levels of MPO compared to normal peritoneal fibroblasts. There was a reduction in MPO expression and its activity in response to PCB treatment in normal peritoneal fibroblasts; however, this effect was minimal in adhesion fibroblasts. Moreover, adhesion fibroblasts manifested higher levels of LPO compared to normal peritoneal fibroblasts, whereas PCB treatment increased LPO levels in both cell types. We conclude that PCBs promote the development of the adhesion phenotype by generating an oxidative stress environment. This is evident by lower iNOS, MPO, and nitrite/nitrate and a simultaneous increase in LPO. Loss of MPO activity, possibly through a mechanism involving MPO heme depletion and free iron release, is yet another source of oxidative stress.

Effects of glutathione depletion on hypoxia-induced erythropoietin production in rats

In vitro studies have indicated that reactive oxygen species modifying cellular redox status are involved in hypoxia-induced erythropoietin (EPO) production. However, the effects of redox balance on hypoxia-induced EPO production in vivo are still not fully understood. To investigate the effect of the change in cellular redox status on EPO generation, we determined whether glutathione (GSH) depletion has a significant influence on hypoxia-induced EPO production in rats. For the inhibition of GSH synthesis, DL-buthionine-[S,R]-sulfoximine (BSO) was employed by intraperitoneal injection. Twenty male rats were assigned to one of four experimental groups: (1) normoxic placebo, (2) normoxic BSO, (3) hypoxic placebo, and (4) hypoxic BSO. Hypoxic groups were exposed to a simulated normobaric hypoxic condition (4,500 m above sea level) for 12 hours. BSO treatment resulted in a significant depletion of total GSH levels in kidney and plasma in both conditions. However, the hypoxia-induced elevation in serum EPO concentration was not completely affected by the inhibition of GSH synthesis. These data demonstrate that GSH depletion in the kidney is not involved in the increase in serum EPO concentration in response to systemic hypoxia. It is also conceivable that the cellular redox changes could not function as a primary regulator of hypoxia-induced renal erythropoietin formation in vivo.

Hypoxia targeting gene expression for breast cancer gene therapy

Gene therapy is a promising strategy to treat various inherited and acquired diseases. However, targeting gene expression to specific tissue is required to minimize side effects of gene therapy. Hypoxia is present in the microenvironment of solid tumors such as breast tumors. A hypoxic tumor targeting gene expression system has been developed for cancer gene therapy. In hypoxic tissues, hypoxia inducible factor (HIF)-1alpha is accumulated and stimulates transcription of the genes that have hypoxia response elements (HREs) in their promoters. Therefore, transcriptional regulation with a hypoxia inducible promoter is the most widely used strategy for hypoxic tumors targeting gene therapy. In breast cancer gene therapy, breast tumor specific promoters in combination with HREs have been used to induce gene expression in hypoxic breast tumors. Post-transcriptional regulation using an untranslated region (UTR) is also a useful strategy to increase gene expression in hypoxic tumor tissue. In addition, post-translational regulation with the oxygen-dependent degradation (ODD) domain is effective to eliminate therapeutic gene products and reduce side effects in normal tissue. In combination with the breast tumor specific promoters, hypoxic tumor targeting strategies will be useful for the development of a safe breast cancer gene therapy.

Nonhematological Mechanisms of Improved Sea-Level Performance after Hypoxic Exposure

Altitude training has been used regularly for the past five decades by elite endurance athletes, with the goal of improving performance at sea level. The dominant paradigm is that the improved performance at sea level is due primarily to an accelerated erythropoietic response due to the reduced oxygen available at altitude, leading to an increase in red cell mass, maximal oxygen uptake, and competitive performance. Blood doping and exogenous use of erythropoietin demonstrate the unequivocal performance benefits of more red blood cells to an athlete, but it is perhaps revealing that long-term residence at high altitude does not increase hemoglobin concentration in Tibetans and Ethiopians compared with the polycythemia commonly observed in Andeans. This review also explores evidence of factors other than accelerated erythropoiesis that can contribute to improved athletic performance at sea level after living and/or training in natural or artificial hypoxia. We describe a range of studies that have demonstrated performance improvements after various forms of altitude exposures despite no increase in red cell mass. In addition, the multifactor cascade of responses induced by hypoxia includes angiogenesis, glucose transport, glycolysis, and pH regulation, each of which may partially explain improved endurance performance independent of a larger number of red blood cells. Specific beneficial nonhematological factors include improved muscle efficiency probably at a mitochondrial level, greater muscle buffering, and the ability to tolerate lactic acid production. Future research should examine both hematological and nonhematological mechanisms of adaptation to hypoxia that might enhance the performance of elite athletes at sea level.

Hypoxia and Reoxygenation Augment Bone-Resorbing Factor Production From Human Periodontal Ligament Cells

BACKGROUND

Oxygen deficiency caused by occlusal trauma and smoking may be associated with bone resorption in periodontitis. In the present study, the effects of hypoxia and reoxygenation on the production of bone-resorbing factors by cultured human periodontal ligament (PDL) cells were examined.

METHODS

Human PDL cells were cultured in 1% O(2) (hypoxia), 20% O(2) (normal oxygen tension [normoxia]), or an oxygen concentration that went from 1% to 20% (reoxygenation). The concentrations of bone-resorbing factors, i.e., vascular endothelial growth factor (VEGF), interleukin (IL)-6 and -1beta, tumor necrosis factor-alpha (TNF-alpha), and prostaglandin E(2) (PGE(2)), in the cell culture supernatants were determined by enzyme-linked immunosorbent assay. Expression of the corresponding mRNAs was detected by reverse transcription-polymerase chain reaction.

RESULTS

Significantly higher extracellular concentrations of VEGF and IL-6 were detected along with greater corresponding mRNA expression in the hypoxia group compared to the normoxia group. The protein production and mRNA expression of IL-1beta were observed only in the hypoxia group. Neither TNF-alpha nor PGE(2) was detectable in samples from either group, whereas cyclooxygenase-2 mRNA was detected. However, PGE(2) was detected after reoxygenation. Furthermore, VEGF and IL-6 and -1beta production also tended to increase in extracellular concentration and mRNA level after reoxygenation.

CONCLUSION

Hypoxia and reoxygenation may stimulate the PDL to produce VEGF, IL-6 and -1beta, and PGE2, which could result in the resorption of alveolar bone in periodontitis.

Transcriptional and post-translational regulatory system for hypoxia specific gene expression using the erythropoietin enhancer and the oxygen-dependent degradation domain

Gene therapy with angiogenic factors is a promising strategy for the treatment of ischemic diseases. However, unregulated expression of an angiogenic factor may induce pathological angiogenesis. In this study, a hypoxia specific gene expression plasmid, pSV-Luc-ODD, was constructed with the oxygen-dependent degradation (ODD) domain for rapid degradation of a target protein under normoxia. In the transfection assay, luciferase activity in the pSV-Luc-ODD transfected cells was much lower under normoxia than that under hypoxia. However, the luciferase mRNA levels under hypoxia and normoxia were not significantly different. Therefore, decrease of luciferase activity under normoxia is not due to pre-translational events such as change of transcription rate or mRNA stability, but to post-translational degradation. For more hypoxia specific gene expression, pEpo-SV-Luc-ODD was constructed with the erythropoietin (Epo) enhancer and the ODD domain. pEpo-SV-Luc-ODD showed more than 1000 times increase of gene expression under hypoxia in Neuro2A cells, compared to normoxia. In addition, reoxygenation studies after hypoxia incubation showed that gene expression was decreased in response to increased oxygen concentration. This highly hypoxia specific gene expression system will be useful for development of targeting gene therapy for ischemic diseases.

Oxyl radicals, redox-sensitive signalling cascades and antioxidants

Oxidative stress is an increase in the reduction potential or a large decrease in the reducing capacity of the cellular redox couples. A particularly destructive aspect of oxidative stress is the production of reactive oxygen species (ROS), which include free radicals and peroxides. Some of the less reactive of these species can be converted by oxidoreduction reactions with transition metals into more aggressive radical species that can cause extensive cellular damage. In animals, ROS may influence cell proliferation, cell death (either apoptosis or necrosis) and the expression of genes, and may be involved in the activation of several signalling pathways, activating cell signalling cascades, such as those involving mitogen-activated protein kinases. Most of these oxygen-derived species are produced at a low level by normal aerobic metabolism and the damage they cause to cells is constantly repaired. The cellular redox environment is preserved by enzymes and antioxidants that maintain the reduced state through a constant input of metabolic energy. This review summarizes current studies that have been regarding the production of ROS and the general redox-sensitive targets of cell signalling cascades.

Protein kinase C beta/early growth response-1 pathway: a key player in ischemia, atherosclerosis, and restenosis

Atherosclerosis, restenosis, and the consequences of ischemia are the major causes of morbidity and mortality worldwide. Elucidation of key contributing pathways in animal models of ischemia-reperfusion injury, atherosclerosis, and restenosis consequent to vascular injury may lead to great interest in determining if blocking these pathways could prevent vascular disease in human subjects. This review details the evidence that the protein kinase C (PKC) beta/early growth response-1 axis plays a central role in the response to both acute and chronic vascular stresses in animal models and also indicates the clinical implications of a specific inhibitor of PKCbeta, ruboxistaurin (LY333531).

Ocular oxygenation and the treatment of diabetic retinopathy

Retinal photocoagulation and vitrectomy both reduce diabetic macular edema and neovascularization in diabetic retinopathy. We suggest that this clinical effect is based on the effect these treatment modalities have on retinal oxygenation, and we present a theory to explain why retinal photocoagulation and vitrectomy influence edema and neovascularization in diabetic and other ischemic retinopathies.

A novel chimeric promoter that is highly responsive to hypoxia and metals

To develop a potent hypoxia-inducible promoter, we evaluated the usefulness of chimeric combinations of the (Egr-1)-binding site (EBS) from the Egr-1 gene, the metal-response element (MRE) from the metallothionein gene, and the hypoxia-response element (HRE) from the phosphoglycerate kinase 1 gene. In transient transfection assays, combining three copies of HRE (3 x HRE) with either EBS or MRE significantly increased hypoxia responsiveness. When a three-enhancer combination was tested, the EBS-MRE-3 x HRE (E-M-H) gave a hypoxia induction ratio of 69. The expression induced from E-M-H-pGL3 was 2.4-fold higher than that induced from H-pGL3 and even surpassed the expression from a human cytomegalovirus promoter-driven vector. The high inducibility of E-M-H was confirmed by validation studies in different cells and by expressing other cDNAs. Gel shift assays together with functional overexpression studies suggested that increased levels of hypoxia-inducible factor 1alpha, metal transcription factor-1 and Egr-1 may be associated with the high inducibility of the E-M-H chimeric promoter. E-M-H was also induced by hypoxia mimetics such as Co2+ and deferoxamine (DFX) and by hydrogen peroxide. Gene expression from the E-M-H was reversible as shown by the reduced expression of the transgene upon removal of inducers such as hypoxia and DFX. In vivo evaluation of the E-M-H in ischemic muscle revealed that erythropoietin secretion and luciferase and LacZ expression were significantly higher in the E-M-H group than in a control or H group. With its high induction capacity and versatile means of modulation, this novel chimeric promoter should find wide application in the treatment of ischemic diseases and cancer.

Xanthine oxidase-dependent regulation of hypoxia-inducible factor in cancer cells

During chemical hypoxia induced by cobalt chloride (CoCl2), hypoxia-inducible factor 1alpha (HIF1-alpha) mediates the induction of a variety of genes including erythropoietin and vascular endothelial growth factor. We used glioma cells with oxidative phosphorylation-dependent (D54-MG) and glycolytic-dependent (U251-MG) phenotypes to monitor HIF1-alpha regulation in association with redox responsiveness to CoCl2 treatment. We showed that CoCl2 increased xanthine oxidase (XO)-derived reactive oxygen species (ROS), which causes accumulation of HIF1-alpha protein in U251-MG cells. Under these conditions, blockade of XO activity by pharmacologic (N-acetyl-L-cysteine or allopurinol) or molecular (by small interfering RNA) approaches significantly attenuated HIF1-alpha expression. Exogenous H2O2 stabilizes HIF1-alpha protein. XO was present in these cells and was the primary source of free radicals. We also showed higher XO activity in cells exposed to CoCl2 compared with cells grown in normoxia. From the experiments shown here, we concluded that ROS were indeed generated in D54-MG cells exposed to CoCl2 but it was unlikely that ROS participated in the hypoxic signal transduction pathways in this cell type. Possibly, cell type-dependent and stimulus-dependent factors may control ROS dependency or redox sensitivity of HIF1-alpha and thus HIF1-alpha activation either directly or by induction of specific signaling cascades. Our findings reveal that XO-derived ROS is a novel and critical component of HIF1-alpha regulation in U251-MG cells, pointing toward a more general role of this transcription factor in tumor progression.

Hypoxic preconditioning: a novel intrinsic cytoprotective strategy

A concept of tissue-cell adaptation to hypoxia (hypoxic preconditioning) is raised and its corresponding animal model is introduced. A significantly strengthened tolerance to hypoxia and a protective effect of the brain extracts from the preconditioned animals are presented. Changes in animals' behavior, neuromorphology, neurophysiology, neurochemistry and molecular neurobiology during preconditioning are described. Energy saving, hypometabolism, and cerebral protection in particular are thought to be involved in the development of hypoxic tolerance and tissue-cell protection. The essence and significance of the hypoxic tissue-cell adaptation or preconditioning are discussed in terms of biological evolution and practical implication.

Mitochondrial reactive oxygen species are required for hypoxic HIF alpha stabilization

Multicellular organisms initiate adaptive responses when oxygen (O2) availability decreases. The underlying mechanisms of O2 sensing remain unclear. Mitochondria have been implicated in many hypoxia-inducible factor (HIF) -dependent and -independent hypoxic responses. However, the role of mitochondria in mammalian cellular O2 sensing has remained controversial, particularly regarding the use pharmacologic agents to effect hypoxic HIF alpha stabilization, which has produced conflicting data in the literature. Using murine embryonic cells lacking cytochrome c, we show that mitochondrial reactive O2 species (ROS) are essential for O2 sensing and subsequent HIF alpha stabilization at 1.5% O2. In the absence of this signal, HIF alpha subunits continue to be hydroxylated and degraded via the proteasome. Importantly, exogenous treatment with H2O2 and severe O2 deprivation is sufficient to stabilize HIF alpha even in the absence of functional mitochondrial. These results demonstrate that mitochondria function as O2 sensors and signal hypoxic HIF alpha stabilization by releasing ROS to the cytoplasm. The cytochrome c mutant embryonic cells provide a unique reagent to further dissect the role of mitochondria in O2 mediated-intracellular events.