Hypoxia-inducible factor-1alpha mediates hypoxia-induced delayed neuronal death that involves p53

Impact of Prenatal Dietary Soy on Cerebellar Neurodevelopment and Function in Experimental Fetal Alcohol Spectrum Disorder

Background: Prenatal alcohol exposure (PAE) models can cause neurodevelopmental abnormalities like those observed in fetal alcohol spectrum disorder (FASD). Previous studies link experimental PAE effects in the brain to impaired signaling through insulin/IGF and Notch pathways that mediate neuronal survival, growth, migration, energy metabolism, and plasticity. Importantly, concurrent administration of peroxisome proliferator-activated receptor agonists or dietary soy prevented many aspects of FASD due to their insulin-sensitizing, anti-inflammatory, and antioxidant properties. Objective: To determine if dietary soy interventions during pregnancy would be sufficient to normalize central nervous system structure and function, we examined the effects of maternal gestation-limited dietary soy on cerebellar postnatal development, motor function, and critical signaling pathways. Methods: Pregnant Long Evans rats were fed isocaloric liquid diets containing 0% or 26% caloric ethanol with casein or soy isolate as the protein source. The ethanol and soy feedings were discontinued upon delivery. The offspring were subjected to rotarod motor function tests, and on postnatal day 35, they were sacrificed to harvest cerebella for histological and molecular studies. Results: Despite the postnatal cessation of alcohol exposure, chronic gestational exposure reduced brain weight, caused cerebellar hypoplasia, and impaired motor performance. Gestational dietary soy prevented the ethanol-associated reduction in brain weight and largely restored the histological integrity of the cerebellum but failed to normalize motor performance. Ethanol withdrawal abolished the impairments in insulin/IGF signaling that were previously associated with ongoing ethanol exposures, but ethanol's inhibitory effects on Notch and Wnt signaling persisted. Soy significantly increased cerebellar expression of the insulin and IGF-1 receptors and abrogated several ethanol-associated impairments in Notch and Wnt signaling. Conclusions: Although gestation-restricted dietary soy has significant positive effects on neurodevelopment, optimum prevention of FASD's long-term effects will likely require dietary soy intervention during the critical periods of postnatal development, even after alcohol exposures have ceased.

Effect of hypoxia in the post-hatching development of the salmon (Salmo salar L.) spinal cord

Introduction

Hypoxia has a teratogenic effect on the fish during embryonic development. Nevertheless, the effects on the larval stage are not yet known. Therefore, the aim of this study was to assess the effects of hypoxia on the number of neurons and their apoptotic rate in the spinal cord of Salmo salar alevins after hatching.

Methods

We used a total of 400 alevins, establishing both hypoxia and control (normoxia) groups (n = 8), considering post-hatching days 1, 3, 5, and 7, each with 50 individuals. Transversal sections of 50 μm thickness were cut from the alevin body. We performed cresyl-violet staining and counted the spinal cord neurons. Also, immunohistochemistry for HIF-1α and caspase-3 were used. For statistical analysis ANOVA one-way and Tukey's Test were used.

Results

HIF-1α was expressed in spinal neurons in both the hypoxic and normoxic groups, with the former being significantly higher. Both the hypoxic and normoxic groups evidenced the process of neuronal apoptosis, with the hypoxic groups demonstrating a higher significance. The number of neurons in the spinal cord was significantly lower in the hypoxic group.

Discussion

We found that when oxygen levels in the aquatic environment were low in Salmo salar farming alevins post-hatch, the number of spinal neurons dropped by half. These results contribute to increasing our knowledge of the biological development of salmon, in particular the genesis of the spinal cord, and the effects of hypoxic conditions on the development of this structure of the nervous system.

Melatonin Inhibits Hypoxia-Induced Alzheimer's Disease Pathogenesis by Regulating the Amyloidogenic Pathway in Human Neuroblastoma Cells

Stroke and Alzheimer's disease (AD) are prevalent age-related diseases; however, the relationship between these two diseases remains unclear. In this study, we aimed to investigate the ability of melatonin, a hormone produced by the pineal gland, to alleviate the effects of ischemic stroke leading to AD by observing the pathogenesis of AD hallmarks. We utilized SH-SY5Y cells under the conditions of oxygen-glucose deprivation (OGD) and oxygen-glucose deprivation and reoxygenation (OGD/R) to establish ischemic stroke conditions. We detected that hypoxia-inducible factor-1α (HIF-1α), an indicator of ischemic stroke, was highly upregulated at both the protein and mRNA levels under OGD conditions. Melatonin significantly downregulated both HIF-1α mRNA and protein expression under OGD/R conditions. We detected the upregulation of β-site APP-cleaving enzyme 1 (BACE1) mRNA and protein expression under both OGD and OGD/R conditions, while 10 µM of melatonin attenuated these effects and inhibited beta amyloid (Aβ) production. Furthermore, we demonstrated that OGD/R conditions were able to activate the BACE1 promoter, while melatonin inhibited this effect. The present results indicate that melatonin has a significant impact on preventing the aberrant development of ischemic stroke, which can lead to the development of AD, providing new insight into the prevention of AD and potential stroke treatments.

Molecular Mechanisms of Neuroprotection after the Intermittent Exposures of Hypercapnic Hypoxia

The review introduces the stages of formation and experimental confirmation of the hypothesis regarding the mutual potentiation of neuroprotective effects of hypoxia and hypercapnia during their combined influence (hypercapnic hypoxia). The main focus is on the mechanisms and signaling pathways involved in the formation of ischemic tolerance in the brain during intermittent hypercapnic hypoxia. Importantly, the combined effect of hypoxia and hypercapnia exerts a more pronounced neuroprotective effect compared to their separate application. Some signaling systems are associated with the predominance of the hypoxic stimulus (HIF-1α, A1 receptors), while others (NF-κB, antioxidant activity, inhibition of apoptosis, maintenance of selective blood-brain barrier permeability) are mainly modulated by hypercapnia. Most of the molecular and cellular mechanisms involved in the formation of brain tolerance to ischemia are due to the contribution of both excess carbon dioxide and oxygen deficiency (ATP-dependent potassium channels, chaperones, endoplasmic reticulum stress, mitochondrial metabolism reprogramming). Overall, experimental studies indicate the dominance of hypercapnia in the neuroprotective effect of its combined action with hypoxia. Recent clinical studies have demonstrated the effectiveness of hypercapnic-hypoxic training in the treatment of childhood cerebral palsy and diabetic polyneuropathy in children. Combining hypercapnic hypoxia with pharmacological modulators of neuro/cardio/cytoprotection signaling pathways is likely to be promising for translating experimental research into clinical medicine.

PDGFRβ + cell HIF2α is dispensable for white adipose tissue metabolic remodeling and hepatic lipid accumulation in obese mice

BACKGROUND

Obesity is associated with extensive white adipose tissue (WAT) expansion and remodeling. Healthy WAT expansion contributes to the maintenance of energy balance in the liver, thereby ameliorating obesity-related hepatic steatosis. Tissue-resident mesenchymal stromal cell populations, including PDGFRβ + perivascular cells, are increasingly recognized pivotal as determinants of the manner in which WAT expands. However, the full array of regulatory factors controlling WAT stromal cell functions remains to be fully elucidated. Hypoxia-inducible factors (HIFs) are critical regulators in WAT stromal cell populations such as adipocyte precursor cells (APCs). It is revealed that HIF1α activation within PDGFRβ + stromal cells results in the suppression of de novo adipogenesis and the promotion of a pro-fibrogenic cellular program in obese animals. However, the role of HIF2α in PDGFRβ + cells remains undetermined in vivo.

METHODS

New genetic models were employed in which HIF1α (encoded by the Hif1a gene) and HIF2α (encoded by the Epas1 gene) are selectively inactivated in PDGFRβ + cells in an inducible manner using tamoxifen (TAM). With these models, both in vitro and in vivo functional analysis of PDGFRβ + cells lacking HIF proteins were performed. Additionally, comprehensive metabolic phenotyping in diet-induced mouse models were performed to investigate the roles of PDGFRβ + cell HIF proteins in WAT remodeling, liver energy balance and systemic metabolism.

RESULTS

Unlike HIF1α inactivation, the new findings in this study suggest that inducible ablation of HIF2α in PDGFRβ + cells does not cause apparent effects on WAT expansion induced by obesogenic diet. The adipogenic ability of PDGFRβ + APCs is not significantly altered by genetic HIF2α ablation. Moreover, no difference of key parameters associated with healthy WAT remodeling such as improvements of WAT insulin sensitivity, reduction in metabolic inflammation, as well as changes in liver fat accumulation or systemic glucose metabolism, is detected in PDGFRβ + cell Epas1-deficient mice.

CONCLUSION

The new findings in this study support that, in contrast to HIF1α, PDGFRβ + cell HIF2α appears dispensable for WAT metabolic remodeling and the resulting effects on liver metabolic homeostasis in diet-induced obesity, underscoring the isoform-specific roles of HIFα proteins in the regulation of adipose tissue biology.

Biomimetic oxygen-boosted hybrid membrane nanovesicles as the treatment strategy for ischemic stroke with the concept of the neurovascular unit

The pathogenesis of ischemic cerebrovascular disease has revealed that ischemic stroke often leads to deprivation of oxygen, blood-brain barrier (BBB) damage and enhanced inflammatory activation, eventually causing severe brain tissue damage. Herein, we prepared hybrid membrane nanovesicles (YC-1@[RBC-PL] NVs) composed of red blood cell (RBC) membrane and platelet (PL) membrane encapsulating hypoxia inducible factor-1α (HIF-1α) inhibitor YC-1 for contributing to the protection of the neurovascular unit (NVU) in ischemic stroke. YC-1@[RBC-PL] NVs targeted the ischemic brain by the thrombus targeting properties of PL membrane and relieved the hypoxia inside ischemic brain in the presence of YC-1 and catalase in YC-1@[RBC-PL] NVs. Finally, YC-1@[RBC-PL] NVs attenuated ischemic injury to NVU by reducing infarct volume, preserving BBB integrity, and blocking activation of astrocyte and microglia in a middle cerebral artery occlusion/reperfusion (MCAO/R) model.

The upregulation of Nur77 decreases ketamine-induced hippocampal neurons toxicity in rats

Ketamine is clinically used as a narcotic. However, ketamine has certain deficits and produces toxicity to neurons. As a member of the NR4A receptor subfamily, Nur77 decreases neurodegenerative disorders. The study aims to investigate the effects of upregulated Nur77 on ketamine-induced rat hippocampal neurons damage and the active mechanism. Neurons were obtained from rat hippocampal and identified by immunofluorescence assays. The treatment groups contained ketamine group, Nur77 group, ketamine + Nur77 group and ketamine + L-cam group. Neurons apoptosis and reactive oxygen species (ROS) were determined by a related kit using flow cytometry. Enzyme NAD(P)H quinone oxidoreductase 1 (NQO1), enzyme heme oxygenase 1 (HO1), Nur77, the expression of Bax, Bcl-2 and cleaved-caspase-3 and inflammatory cytokines were measured using western blot assays and reverse transcription-quantitative PCR (RT-qPCR) assays. Ketamine-induced neurons apoptosis; however, Nur77 decreased ketamine-induced neurons apoptosis. A low level of ROS was observed in two combination groups. Neurons treated by ketamine only had the lowest levels of Nur77, NQO1 and HO1, compared with other treatment groups. The levels of Bax and cleaved-caspase-3 in two combination groups were lower than those in the ketamine group. Furthermore, the ketamine group had higher levels of tumor necrosis factor alpha, IL-1β and IL-6 but the lowest level of IL-4. Upregulated Nur77 reduced the ketamine-induced toxicity in neurons. The mechanism of Nur77 involved antioxidation, apoptosis signaling pathway and inflammation signaling pathway. Our study provides a novel therapy that could attenuate ketamine-induced toxicity.

Serum hypoxia-inducible factor 1alpha emerges as a prognostic factor for severe traumatic brain injury

BACKGROUND

Hypoxia-inducible factor 1alpha (HIF-1α) is implicated in the cell's response to hypoxia. We investigated whether serum HIF-1α concentrations are correlated with the severity and clinical outcome of severe traumatic brain injury (sTBI).

METHODS

Serum HIF-1α concentrations were quantified in 104 sTBI patients and 80 healthy controls. Trauma severity was assessed using Glasgow coma scale (GCS). Glasgow outcome scale (GOS) score of 1-3 at post-trauma 90 days was defined as a poor outcome. Multivariate analyses were performed to discern the relationship between serum HIF-1α concentrations and outcome.

RESULTS

Patients displayed significantly higher serum HIF-1α concentrations than controls (median, 294.9 versus 102.7 pg/ml). HIF-1α concentrations were intimately related to GCS scores (r = -0.62) and GOS scores (r = -0.64). 48 patients (46.2%) experienced a poor outcome. Serum HIF-1α concentrations > 280.2 pg/ml significantly distinguished patients with the development of poor outcome with 77.1% sensitivity and 69.6% specificity (AUC, 0.750; 95% CI: 0.655-0.829). Serum HIF-1α concentrations > 280.2 pg/ml emerged as an independent predictor for poor outcome (OR: 4.179; 95% CI: 1.024-17.052).

CONCLUSIONS

Serum HIF-1α concentrations are tightly associated with trauma severity and poor 90-day outcome, substantializing serum HIF-1α as a promising prognostic biomarker for sTBI.

Nitric Oxide-Dependent Pathways as Critical Factors in the Consequences and Recovery after Brain Ischemic Hypoxia

Brain ischemia is one of the leading causes of disability and mortality worldwide. Nitric oxide (NO^•), a molecule that is involved in the regulation of proper blood flow, vasodilation, neuronal and glial activity constitutes the crucial factor that contributes to the development of pathological changes after stroke. One of the early consequences of a sudden interruption in the cerebral blood flow is the massive production of reactive oxygen and nitrogen species (ROS/RNS) in neurons due to NO^• synthase uncoupling, which leads to neurotoxicity. Progression of apoptotic or necrotic neuronal damage activates reactive astrocytes and attracts microglia or lymphocytes to migrate to place of inflammation. Those inflammatory cells start to produce large amounts of inflammatory proteins, including pathological, inducible form of NOS (iNOS), which generates nitrosative stress that further contributes to brain tissue damage, forming vicious circle of detrimental processes in the late stage of ischemia. S-nitrosylation, hypoxia-inducible factor 1α (HIF-1α) and HIF-1α-dependent genes activated in reactive astrocytes play essential roles in this process. The review summarizes the roles of NO^•-dependent pathways in the early and late aftermath of stroke and treatments based on the stimulation or inhibition of particular NO^• synthases and the stabilization of HIF-1α activity.

Adiponectin Treatment Attenuates Cerebral Ischemia-Reperfusion Injury through HIF-1α-Mediated Antioxidation in Mice

Adiponectin (ADPN) plays an important role in cerebral ischemia-reperfusion injury. Although previous studies have confirmed that ADPN pretreatment has a protective effect on ischemic stroke, the therapeutic effect of ADPN on ischemic stroke and the underlying mechanism are still unclear. In order to clarify these questions, focal transient cerebral ischemia was induced by middle cerebral artery occlusion (MCAO) in mice and ADPN was administered for three times at 6 h, 24 h, and 48 h after reperfusion. Meanwhile, a virus-delivered HIF-1α siRNA was used before ADPN administration. The infarct volume, neurological score, cellular apoptosis, and oxidative stress were assessed at 72 h after reperfusion. The long-term outcome of mice after stroke was recorded as well. The results indicated that ADPN treatment reduced the infarct volume (P = 0.032), neurological deficits (P = 0.047), cellular apoptosis (P = 0.041), and oxidative responses (P = 0.031) at 72 h after MCAO. Moreover, ADPN increased both the protein level and transcriptional activity of HIF-1α as evidenced by the transcription levels of VEGF (P = 0.046) and EPO (P = 0.043) at 72 h after MCAO. However, knockdown of HIF-1α partially reversed the antioxidant and treatment effect of ADPN after cerebral ischemia. In the observation of long-term outcome after ADPN treatment, it demonstrated that ADPN not only prevented the cerebral atrophy (P = 0.031) and the neurological function decline (P = 0.048), but also promoted angiogenesis (P = 0.028) after stroke. In conclusion, our findings suggest that ADPN is effective in treatment of ischemic stroke which could be attributed to the increased antioxidant capacity regulated by HIF-1α.

Serum Hypoxia-Inducible Factor 1alpha Levels Correlate with Outcomes After Intracerebral Hemorrhage

Background

Serum hypoxia-inducible factor 1alpha (HIF-1α) is a key regulator in hypoxic and ischemic brain injury. We determined the relationship between serum HIF-1α levels and long-term prognosis plus severity of intracerebral hemorrhage (ICH).

Methods

A total of 97 ICH cases and 97 healthy controls were enrolled. Glasgow Coma Scale (GCS) score and hematoma volume were used to assess hemorrhagic severity. Glasgow Outcome Scale (GOS) score of 1–3 at post-stroke 90 days was defined as a poor outcome.

Results

Serum HIF-1α levels of ICH patients were significantly higher than those of healthy controls (median, 218.8 vs 105.4 pg/mL; P<0.001) and were substantially correlated with GCS score (r=−0.485, P<0.001), hematoma volume (r=0.357, P<0.001) and GOS score (r=−0.436, P<0.001). Serum HIF-1α levels >239.4 pg/mL discriminated patients at risk of 90-day poor outcome with sensitivity of 65.9% and specificity of 79.3% (area under the receiver operating characteristic curve, 0.725; 95% confidence interval, 0.625–0.811; P<0.001). Moreover, serum HIF-1α levels >239.4 pg/mL were independently associated with a poor 90-day outcome (odds ratio, 5.133; 95% confidence interval, 1.117–23.593; P=0.036).

Conclusion

Serum HIF-1α, in close correlation with hemorrhagic severity and poor 90-day outcome, may serve as a potential prognostic biomarker for ICH.

Pathologic HIF1α signaling drives adipose progenitor dysfunction in obesity

Adipose precursor cells (APCs) exhibit regional variation in response to obesity, for unclear reasons. Here, we reveal that HIFα-induced PDGFRβ signaling within murine white adipose tissue (WAT) PDGFRβ⁺ cells drives inhibitory serine 112 (S112) phosphorylation of PPARγ, the master regulator of adipogenesis. Levels of PPARγ S112 phosphorylation in WAT PDGFRβ⁺ cells are depot dependent, with levels of PPARγ phosphorylation in PDGFRβ⁺ cells inversely correlating with their capacity for adipogenesis upon high-fat-diet feeding. HIFα suppression in PDGFRβ⁺ progenitors promotes subcutaneous and intra-abdominal adipogenesis, healthy WAT remodeling, and improved metabolic health in obesity. These metabolic benefits are mimicked by treatment of obese mice with the PDGFR antagonist Imatinib, which promotes adipocyte hyperplasia and glucose tolerance in a progenitor cell PPARγ-dependent manner. Our studies unveil a mechanism underlying depot-specific responses of APCs to high-fat feeding and highlight the potential for APCs to be targeted pharmacologically to improve metabolic health in obesity.

Neuroprotective Effect of Brazilian Green Propolis on Retinal Ganglion Cells in Ischemic Mouse Retina

PURPOSE

The current study was undertaken to investigate whether Brazilian green propolis (BGP) can increase the viability of retinal ganglion cells (RGCs) in ischemic mouse retina, and examined the possible mechanisms underlying this neuroprotection.

MATERIALS AND METHODS

C57BL/6J mice were subjected to constant elevation of intraocular pressure for 60 min to establish retinal ischemia-reperfusion injury. Mice then received saline or BGP (200 mg/kg) intraperitoneally once daily until sacrifice. The expression of hypoxia-inducing factor (HIF)-1α and glial fibrillary acidic protein (GFAP) and the level of histone acetylation were assessed at 1, 3, and 7 days after injury. The expression of Bax, Bcl-2, p53, NF-κB, Nrf2, and HO-1 were also analyzed at 3 days after injury. The neuroprotective effect of BGP treatment on RGC survival was evaluated using Brn3a immunohistochemical staining.

RESULTS

The expression of HIF-1α and GFAP was increased and the level of histone acetylation decreased in saline-treated ischemic retinas within 7 days. BGP treatment effectively attenuated the elevated expression of HIF-1α, GFAP, Bax, NF-κB and p53. The expression of Bcl-2, Nrf2, HO-1 and the level of histone acetylation increased by BGP treatment, resulting in a significant difference between BGP-treated and saline-treated retinas. Immunohistochemical staining for Brn3a also revealed that BGP treatment protected against RGC loss in ischemic retina.

CONCLUSIONS

Our results suggest that BGP has a neuroprotective effect on RGCs through the upregulation of histone acetylation, downregulation of apoptotic stimuli, and suppression of NF-κB mediated inflammatory pathway in ischemic retina. These findings suggest that BGP is a potential neuroprotective agent against RGC loss under oxidative stress.

Loss of Regulator of G-Protein Signaling 5 Leads to Neurovascular Protection in Stroke

Background and Purpose- In ischemic stroke, breakdown of the blood-brain barrier (BBB) aggravates brain damage. Pericyte detachment contributes to BBB disruption and neurovascular dysfunction, but little is known about its regulation in stroke. Here, we investigated how loss of RGS5 (regulator of G protein signaling 5) in pericytes affects BBB breakdown in stroke and its consequences. Method- We used RGS5 knockout and control mice and applied a permanent middle cerebral occlusion model. We analyzed pericyte numbers, phenotype, and vessel morphology using immunohistochemistry and confocal microscopy. We investigated BBB breakdown by measuring endothelial coverage, tight junctions, and AQP4 (aquaporin 4) in addition to BBB permeability (fluorescent-conjugated dextran extravasation). Tissue hypoxia was assessed with pimonidazole hydrochloride and neuronal death quantified with the terminal deoxynucleotidyl transferase dUTP nick end labeling assay. Results- We demonstrate that loss of RGS5 increases pericyte numbers and their endothelial coverage, which is associated with higher capillary density and length, and significantly less BBB damage after stroke. Loss of RGS5 in pericytes results in reduced vascular leakage and preserved tight junctions and AQP4, decreased cerebral hypoxia, and partial neuronal protection in the infarct area. Conclusions- Our findings show that loss of RGS5 affects pericyte-related BBB preservation in stroke and identifies RGS5 as an important target for neurovascular protection.

Novel application of amino-acid buffered solution for neuroprotection against ischemia/reperfusion injury

Ischemic neuron loss contributes to brain dysfunction in patients with cardiac arrest (CA). Histidine–tryptophan–ketoglutarate (HTK) solution is a preservative used during organ transplantation. We tested the potential of HTK to protect neurons from severe hypoxia (SH) following CA. We isolated rat primary cortical neurons and induced SH with or without HTK. Changes in caspase-3, hypoxia-inducible factor 1-alpha (HIF-1α), and nicotinamide adenine dinucleotide phosphate oxidase-4 (NOX4) expression were evaluated at different time points up to 72 h. Using a rat asphyxia model, we induced CA-mediated brain damage and then completed resuscitation. HTK or sterile saline was administered into the left carotid artery. Neurological deficit scoring and mortality were evaluated for 3 days. Then the rats were sacrificed for evaluation of NOX4 and H₂O₂ levels in blood and brain. In the in vitro study, HTK attenuated SH- and H₂O₂-mediated cytotoxicity in a volume- and time-dependent manner, associated with persistent HIF-1α expression and reductions in procaspase-3 activation and NOX4 expression. The inhibition of HIF-1α abrogated HTK’s effect on NOX4. In the in vivo study, neurological scores were significantly improved by HTK. H₂O₂ level, NOX4 activity, and NOX4 gene expression were all decreased in the brain specimens of HTK-treated rats. Our results suggest that HTK acts as an effective neuroprotective solution by maintaining elevated HIF-1α level, which was associated with inhibited procaspase-3 activation and decreased NOX4 expression.

Hypoxia Mimetic Agents for Ischemic Stroke

Every year stroke claims more than 6 million lives worldwide. The majority of them are ischemic stroke. Small molecule-based therapeutics for ischemic stroke has attracted a lot of attention, but none has been shown to be clinically useful so far. Hypoxia-inducible factor-1 (HIF-1) plays a crucial role in the transcriptional adaptation of cells to hypoxia. Small molecule-based hypoxia-mimetic agents either stabilize HIF-1α via HIF-prolyl hydroxylases (PHDs) inhibition or through other mechanisms. In both the cases, these agents have been shown to confer ischemic neuroprotection in vitro and in vivo. The agents which act via PHD inhibition are mainly classified into iron chelators, iron competitors, and 2 oxoglutarate (2OG) analogs. This review discusses HIF structure and key players in the HIF-1 degradation pathway as well as the genes, proteins and chemical molecules that are connected to HIF-1 and how they affect cell survival following ischemic injury. Furthermore, this review gives a summary of studies that used PHD inhibitors and other HIF-1α stabilizers as hypoxia-mimetic agents for the treatment of ischemic injury.

HIF-1α is Critical for the Activation of Notch Signaling in Neurogenesis During Acute Epilepsy

Emerging evidence suggests that hypoxia-inducible factors (specifically, HIF-1α) and Notch signaling are involved in epileptogenesis and that cross-coupling exists between HIF-1α and Notch signaling in other diseases, including tumors and ischemia. However, the exact molecular mechanisms by which HIF-1α and Notch signaling affect the development of epilepsy, especially regarding neurogenesis, remain unclear. In the present study, we investigated the role of HIF-1α in neurogenesis and whether Notch signaling is involved in this process during epileptogenesis by assessing hippocampal apoptosis, neuronal injury, and the proliferation and differentiation of neural stem cells (NSCs) in four groups, including control, epilepsy, epilepsy+2-methoxyestradiol (2ME2) and epilepsy+GSI-IX (DAPT) groups. Our data demonstrated that HIF-1α mediated neurogenesis during acute epilepsy, which required the participation of Notch signaling. The immunoprecipitation data illustrated that HIF-1α activated Notch signaling by physically interacting with the Notch intracellular domain (NICD) in epilepsy. In conclusion, our results suggested that HIF-1α-Notch signaling enhanced neurogenesis in acute epilepsy and that neurogenesis during epileptogenesis was reduced once this pathway was blocked; thus, members of this pathway might be potential therapeutic targets for epilepsy.

Interplay between Notch and p53 promotes neuronal cell death in ischemic stroke

Stroke is the world's second leading cause of mortality, with a high incidence of morbidity. Numerous neuronal membrane receptors are activated by endogenous ligands and may contribute to infarct development. Notch is a well-characterized membrane receptor involved in cell differentiation and proliferation, and now shown to play a pivotal role in cell death during ischemic stroke. Blockade of Notch signaling by inhibition of γ-secretase, an enzyme that generates the active form of Notch, is neuroprotective following stroke. We have also identified that Pin1, a peptidyl-prolyl isomerase that regulates p53 transactivation under stress, promotes the pathogenesis of ischemic stroke via Notch signaling. Moreover, Notch can also mediate cell death through a p53-dependent pathway, resulting in apoptosis of neural progenitor cells. The current study has investigated the interplay between Notch and p53 under ischemic stroke conditions. Using pharmacological inhibitors, we have demonstrated that a Notch intracellular domain (NICD)/p53 interaction is involved in transcriptional regulation of genes downstream of p53 and NICD to modify stroke severity. Furthermore, the NICD/p53 interaction confers stability to p53 by rescuing it from ubiquitination. Together, these results indicate that Notch contributes to the pathogenesis of ischemic stroke by promoting p53 stability and signaling.

PI3K/Akt and HIF‑1 signaling pathway in hypoxia‑ischemia (Review)

Hypoxia-ischemia (H-I) is frequently observed in perinatal asphyxia and other diseases. It can lead to serious cardiac injury, cerebral damage, neurological disability and mortality. Previous studies have demonstrated that the phosphatidylinositol-3 kinase (PI3K)/protein kinase B (Akt) signaling pathway, which regulates a wide range of cellular functions, is involved in the resistance response to H-I through the activation of proteins associated with survival and inactivation of apoptosis-associated proteins. It can also regulate the expression of hypoxia-induced factor-1α (HIF-1α). HIF-1α can further regulate the expression of downstream proteins involved in glucose metabolism and angiogenesis, such as vascular endothelial growth factor and erythropoietin, to facilitate ischemic adaptation. Notably, HIF-1α may also induce detrimental effects. The effects of HIF-1 on ischemic outcomes may be dependent on the H-I duration, animal age and species. Thus, further investigation of the PI3K/Akt signaling pathway may provide further insights of the potential targets for treating diseases accompanied by H-I.

CD40-mediated HIF-1α expression underlying microangiopathy in diabetic nerve pathology

To understand the pathology and molecular signatures of microangiopathy in diabetic neuropathy, we systemically and quantitatively examined the morphometry of microvascular and nerve pathologies of sural nerves. In the endoneurium of diabetic nerves, prominent microangiopathy was observed, as evidenced by reduced capillary luminal area, increased capillary basement membrane thickness and increased proportion of fibrin(+) blood vessels. Furthermore, capillary basement membrane thickness and the proportion of fibrin(+) blood vessels were correlated with small myelinated fiber density in diabetic nerves. In diabetic nerves, there was also significant macrophage and T cell infiltration, and cluster of differentiation 40 (CD40) expression was increased. The molecular alterations observed were upregulation of hypoxia-inducible factor-1α (HIF-1α), mitogen-activated protein kinase-activated protein kinase 2 (MK2; MAPKAPK2) and phosphatase and tensin homolog (PTEN). In addition, HIF-1α was correlated with small myelinated fiber density and capillary luminal area, while both MK2 and PTEN were correlated with capillary basement membrane thickness. The molecular cascades were further demonstrated and replicated in a cell model of microangiopathy on human umbilical vein endothelial cells (HUVECs) exposed to high-glucose medium by silencing of CD40, PTEN and HIF-1α in HUVECs using shRNA. These data clarified the hierarchy of the molecular cascades, i.e. upregulation of CD40 leading to HIF-1α expression in endothelium and nerve fibers. In conclusion, this study revealed the association of microangiopathy, thrombosis and inflammatory infiltrates with nerve degeneration in diabetic nerves, demonstrating that CD40 is a key molecule for the upregulation of HIF-1α and PTEN underlying the severity of microangiopathy.

Caffeic acid phenethyl ester protects against photothrombotic cortical ischemic injury in mice

In this study, we aimed to investigate the neuroprotective effects of caffeic acid phenethyl ester (CAPE), an active component of propolis purified from honeybee hives, on photothrombotic cortical ischemic injury in mice. Permanent focal ischemia was achieved in the medial frontal and somatosensory cortices of anesthetized male C57BL/6 mice by irradiation of the skull with cold light laser in combination with systemic administration of rose bengal. The animals were treated with CAPE (0.5–5 mg/kg, i.p.) twice 1 and 6 h after ischemic insult. CAPE significantly reduced the infarct size as well as the expression of tumor necrosis factor-α, hypoxiainducible factor-1α, monocyte chemoattractant protein-1, interleukin-1α, and indoleamine 2,3-dioxygenase in the cerebral cortex ipsilateral to the photothrombosis. Moreover, it induced an increase in heme oxygenase-1 immunoreactivity and interleukin-10 expression. These results suggest that CAPE exerts a remarkable neuroprotective effect on ischemic brain injury via its anti-inflammatory properties, thereby providing a benefit to the therapy of cerebral infarction.

HIF-1alpha and infectious diseases: a new frontier for the development of new therapies

The aim of this review is to show the significant role of HIF-1alpha in inflammatory and infectious diseases. Hypoxia is a physiological characteristic of a wide range of diseases from cancer to infection. Cellular hypoxia is sensed by oxygen-sensitive hydrolase enzymes, which control the protein stability of hypoxia-inducible factor alpha 1 (HIF-1alpha) transcription factors. When stabilized, HIF-1alpha binds with its cofactors to HIF-responsive elements (HREs) in the promoters of target genes to organize a broad ranging transcriptional program in response to the hypoxic environment. HIF-1alpha also plays a regulatory function in response to a diversity of molecular signals of infection and inflammation even under normoxic conditions. HIF-1alpha is stimulated by pro-inflammatory cytokines, growth factors and a wide range of infections. Its induction is a general element of the host response to infection. In this review, we also discuss recent advances in knowledge on HIF-1alpha and inflammatory responses, as well as its direct influence in infectious diseases caused by bacteria, virus, protozoan parasites and fungi.

Preconditioning in neuroprotection: From hypoxia to ischemia

Sublethal hypoxic or ischemic events can improve the tolerance of tissues, organs, and even organisms from subsequent lethal injury caused by hypoxia or ischemia. This phenomenon has been termed hypoxic or ischemic preconditioning (HPC or IPC) and is well established in the heart and the brain. This review aims to discuss HPC and IPC with respect to their historical development and advancements in our understanding of the neurochemical basis for their neuroprotective role. Through decades of collaborative research and studies of HPC and IPC in other organ systems, our understanding of HPC and IPC-induced neuroprotection has expanded to include: early- (phosphorylation targets, transporter regulation, interfering RNA) and late- (regulation of genes like EPO, VEGF, and iNOS) phase changes, regulators of programmed cell death, members of metabolic pathways, receptor modulators, and many other novel targets. The rapid acceleration in our understanding of HPC and IPC will help facilitate transition into the clinical setting.

sMEK1 inhibits endothelial cell proliferation by attenuating VEGFR-2-dependent-Akt/eNOS/HIF-1α signaling pathways

The suppressor of MEK null (sMEK1) protein possesses pro-apoptotic activities. In the current study, we reveal that sMEK1 functions as a novel anti-angiogenic factor by suppressing vascular endothelial growth factor (VEGF)-induced cell proliferation, migration, and capillary-like tubular structure in vitro. In addition, sMEK1 inhibited the phosphorylation of the signaling components up- and downstream of Akt, including phospholipase Cγ1 (PLC-γ1), 3-phosphoinositide-dependent protein kinase 1 (PDK1), endothelial nitric oxide synthetase (eNOS), and hypoxia-inducible factor 1 (HIF-1α) during ovarian tumor progression via binding with vascular endothelial growth factor receptor 2 (VEGFR-2). Furthermore, sMEK1 decreased tumor vascularity and inhibited tumor growth in a xenograft human ovarian tumor model. These results supply convincing evidence that sMEK1 controls endothelial cell function and subsequent angiogenesis by suppressing VEGFR-2-mediated PI3K/Akt/eNOS signaling pathway. Taken together, our results clearly suggest that sMEK1 might be a novel anti-angiogenic and anti-tumor agent for use in ovarian tumor.

Syringaresinol protects against hypoxia/reoxygenation-induced cardiomyocytes injury and death by destabilization of HIF-1α in a FOXO3-dependent mechanism

Hypoxia-inducible factor 1 (HIF-1) is a master regulator of hypoxic response and has been a prime therapeutic target for ischemia/reperfusion (I/R)-derived myocardial dysfunction and tissue damage. There is also increasing evidence that HIF-1 plays a central role in regulating aging, both through interactions with key longevity factors including Sirtuins and mTOR, as well as by directly promoting longevity in Caenorhabditis elegans. We investigated a novel function and the underlying mechanism of syringaresinol, a lignan compound, in modulation of HIF-1 and protection against cellular damage and death in a cardiomyocyte model of I/R injury. Syringaresinol caused destabilization of HIF-1α following H/R and then protected against hypoxia/reoxygenation (H/R)-induced cellular damage, apoptosis, and mitochondrial dysfunction in a dose-dependent manner. Knock-down of FOXO3 by specific siRNAs completely abolished the ability of syringaresinol to inhibit HIF-1 stabilization and apoptosis caused by H/R. Syringaresinol stimulated the nuclear localization and activity of FOXO3 leading to increased expression of antioxidant genes and decreased levels of reactive oxygen species (ROS) following H/R. Our results provide a new mechanistic insight into a functional role of syringaresinol against H/R-induced cardiomyocyte injury and death. The degradation of HIF-1α through activation of FOXO3 is a potential therapeutic strategy for ischemia-related diseases.

GABARBP down-regulates HIF-1α expression through the VEGFR-2 and PI3K/mTOR/4E-BP1 pathways

Human γ-aminobutyrate type A (GABAA) receptor-binding protein (GABARBP), a tumor suppressor protein with apoptotic function, can be inhibited in response to angiogenesis through the PI3K/Akt signaling cascades. Here, we investigated whether GABARBP over-expression could regulate vascular endothelial growth factor (VEGF)/hypoxia-inducible factor-1α (HIF-1α) expression and angiogenic activity in a carcinoma model system. GABARBP dramatically inhibited VEGF-induced endothelial cell proliferation, migration, and tube formation, as well as VEGFR-2 phosphorylation in vitro. At the same time, GABARBP exposed potent anti-angiogenic activity and remarkably down-regulated the levels of VEGF and HIF-1α protein expression, key components for angiogenesis. In addressing its biological molecular mechanism, GABARBP was found to effectively inhibit the phosphorylation of down-stream PI3K components, such as PDK1, Akt, mTOR, TSC-2, p70S6K, and 4E-BP1 by directly binding with VEGFR-2. In contrast, p38/JNK phosphorylation was not suppressed by GABARBP. These findings disclose a novel function of GABARBP in suppressing VEGF and HIF-1α protein expression, which is important for tumor angiogenesis and tumor growth. Thus, our data strongly provides novel biological mechanistic insights into the regulatory function of GABARBP in ovarian tumor progression, and the important of pre-clinical certification of GABARBP as a potential angiogenesis agent targeting ovarian tumorigenesis.

Hyperbaric oxygen for cerebral vasospasm and brain injury following subarachnoid hemorrhage

The impact of acute brain injury and delayed neurological deficits due to cerebral vasospasm (CVS) are major determinants of outcomes after subarachnoid hemorrhage (SAH). Although hyperbaric oxygen (HBO) had been used to treat patients with SAH, the supporting evidence and underlying mechanisms have not been systematically reviewed. In the present paper, the overview of studies of HBO for cerebral vasospasm is followed by a discussion of HBO molecular mechanisms involved in the protection against SAH-induced brain injury and even, as hypothesized, in attenuating vascular spasm alone. Faced with the paucity of information as to what degree HBO is capable of antagonizing vasospasm after SAH, the authors postulate that the major beneficial effects of HBO in SAH include a reduction of acute brain injury and combating brain damage caused by CVS. Consequently, authors reviewed the effects of HBO on SAH-induced hypoxic signaling and other mechanisms of neurovascular injury. Moreover, authors hypothesize that HBO administered after SAH may "precondition" the brain against the detrimental sequelae of vasospasm. In conclusion, the existing evidence speaks in favor of administering HBO in both acute and delayed phase after SAH; however, further studies are needed to understand the underlying mechanisms and to establish the optimal regimen of treatment.

Changes of hypoxia-inducible factor-1 signaling and the effect of cilostazol in chronic cerebral ischemia

Hypoxia-inducible factor-1 and its specific target gene heme oxygenase-1, are involved in acute cerebral ischemia. However, very few studies have examined in detail the changes in the hypoxia-inducible factor-1/heme oxygenase-1 signaling pathway in chronic cerebral ischemia. In this study, a rat model of chronic cerebral ischemia was established by permanent bilateral common carotid artery occlusion, and these rats were treated with intragastric cilostazol (30 mg/kg) for 9 weeks. Morris water maze results showed that cognitive impairment gradually worsened as the cerebral ischemia proceeded. Immunohistochemistry, semi-quantitative PCR and western blot analysis showed that hypoxia-inducible factor-1α and heme oxygenase-1 expression levels increased after chronic cerebral ischemia, with hypoxia-inducible factor-1α expression peaking at 3 weeks and heme oxygenase-1 expression peaking at 6 weeks. These results suggest that the elevated levels of hypoxia-inducible factor-1α may upregulate heme oxygenase-1 expression following chronic cerebral ischemia and that the hypoxia-inducible factor-1/heme oxygenase-1 signaling pathway is involved in the development of cognitive impairment induced by chronic cerebral ischemia. Cilostazol treatment alleviated the cognitive impairment in rats with chronic cerebral ischemia, decreased hypoxia-inducible factor-1α and heme oxygenase-1 expression levels, and reduced apoptosis in the frontal cortex. These findings demonstrate that cilostazol can protect against cognitive impairment induced by chronic cerebral ischemic injury through an anti-apoptotic mechanism.

Selective inhibition of hypoxia-inducible factor 1α ameliorates adipose tissue dysfunction

Hypoxia-inducible factor 1α (HIF1α) induction in adipocytes is a critical component of the "fibrotic response," directly linked to metabolic dysfunction in adipose tissues under hypoxic conditions. We reasoned that inhibition of HIF1α may ameliorate the negative aspects of the obesity-associated fat pad expansion. We used the selective HIF1α inhibitor PX-478, whose effectiveness has previously been established in tumor models. We demonstrate that PX-478 treatment effectively suppresses the high-fat-diet (HFD)-induced HIF1α activation in adipose tissue. HIF1α inhibition causes a reduction of weight gain in mice on an HFD but not on a chow diet. Treatment increases energy expenditure and prompts resistance to HFD-mediated deterioration of metabolic parameters. Moreover, PX-478-treated mice have reduced fibrosis and fewer inflammatory infiltrates in their adipose tissues. We confirm the metabolic effects obtained with PX-478 treatment using an adipose tissue-specific, doxycycline-inducible dominant negative HIF1α mutant (dn-HIF1α). Consistent with the pharmacological results, genetic inhibition of endogenous HIF1α activity prompts similar metabolic improvements in HFD-fed mice. Collectively, our results demonstrate that HIF1α inhibition in the adipocyte leads to significant metabolic improvements, suggesting that selective HIF1α inhibition in adipose tissue may be an effective therapeutic avenue in the context of metabolic dysfunction.

The effect of melatonin on retinal ganglion cell survival in ischemic retina

Our objective was to determine whether melatonin increases retinal ganglion cell (RGC) survival in ischemic mouse retina. Transient retinal ischemia was induced by an acute elevation of intraocular pressure in C57BL/6 mice. To evaluate the effect of melatonin on retinal ischemia, an equal amount of either melatonin or vehicle was intraperitoneally injected into the mice 1 hour before ischemia, at the time of ischemia, and 1 hour after ischemia. Hypoxia inducible factor 1α (HIF-1α) and glial fibrillary acidic protein (GFAP) expression were assessed 6, 12, and 24 hours after ischemia-reperfusion by Western blot. RGC survival was measured 2 weeks after ischemia-reperfusion. The expression of HIF-1α and GFAP peaked 24 hours after ischemia-reperfusion in ischemic retina. The treatment of ischemic retina with melatonin resulted in the inhibition of increased expression of HIF-1α and GFAP. RGC survival was greater in retinas treated with melatonin than in retinas treated with vehicle 2 weeks after ischemia-reperfusion. On the basis of our results, we suggest that melatonin treatment increased RGC survival in ischemic mouse retina. The neuroprotective effect of melatonin is mediated by the inhibition of HIF-1α stabilization and reduced activity of glial cells in ischemic mouse retina.

Hypoxia-inducible factor prolyl hydroxylase inhibition: robust new target or another big bust for stroke therapeutics?

A major challenge in developing stroke therapeutics that augment adaptive pathways to stress has been to identify targets that can activate compensatory programs without inducing or adding to the stress of injury. In this regard, hypoxia-inducible factor prolyl hydroxylases (HIF PHDs) are central gatekeepers of posttranscriptional and transcriptional adaptation to hypoxia, oxidative stress, and excitotoxicity. Indeed, some of the known salutary effects of putative 'antioxidant' iron chelators in ischemic and hemorrhagic stroke may derive from their abilities to inhibit this family of iron, 2-oxoglutarate, and oxygen-dependent enzymes. Evidence from a number of laboratories supports the notion that HIF PHD inhibition can improve histological and functional outcomes in ischemic and hemorrhagic stroke models. In this review, we discuss this evidence and highlight important gaps in our understanding that render HIF PHD inhibition a promising but not yet preclinically validated target for protection and repair after stroke.

Differential expression of BNIP family members of BH3-only proteins during the development and after axotomy in the rat

The BNIPs (BCL2 and adenovirus E1B 19 kDa interacting proteins) are a subfamily of BCL2 family proteins typically containing a single BCL2 homology 3 (BH3) domain. BNIPs exert important roles in two major degradation processes in cells - apoptosis and autophagy. Although it is known that the function of BNIPs is transcriptionally regulated under hypoxic conditions in tumors, their regulation in the developing brain and neurons following the induction of apoptosis/autophagy is largely unknown. In this study, we demonstrate that three members of the BNIP family, BNIP1, BNIP3 and BNIP3L, are expressed in the developing brain with distinct brain region specificity. BNIP3 mRNA was especially enriched in the entorhinal cortex, raising a possibility that it may have additional biological functions in addition to its apoptotic and autophagic functions. Following starvation-induced autophagy induction, BNIP1 mRNA was selectively increased in cultured neurons. However, the apoptogenic chemical staurosporine failed to modulate the expression of BNIPs, which is in contrast to the marked induction of all BNIPs by glucose-oxygen deprivation. Finally, neonatal nerve axotomy, which triggers apoptosis in motoneurons, selectively enhanced BNIP3 mRNA expression. Collectively, these results suggest that the expression of BNIPs is differentially regulated depending on the stimuli, and BNIPs may exert unique biological functions.

Von Hippel-Lindau protein in the RPE is essential for normal ocular growth and vascular development

Molecular oxygen is essential for the development, growth and survival of multicellular organisms. Hypoxic microenvironments and oxygen gradients are generated physiologically during embryogenesis and organogenesis. In the eye, oxygen plays a crucial role in both physiological vascular development and common blinding diseases. The retinal pigment epithelium (RPE) is a monolayer of cells essential for normal ocular development and in the mature retina provides support for overlying photoreceptors and their vascular supply. Hypoxia at the level of the RPE is closely implicated in pathogenesis of age-related macular degeneration. Adaptive tissue responses to hypoxia are orchestrated by sophisticated oxygen sensing mechanisms. In particular, the von Hippel-Lindau tumour suppressor protein (pVhl) controls hypoxia-inducible transcription factor (HIF)-mediated adaptation. However, the role of Vhl/Hif1a in the RPE in the development of the eye and its vasculature is unknown. In this study we explored the function of Vhl and Hif1a in the developing RPE using a tissue-specific conditional-knockout approach. We found that deletion of Vhl in the RPE results in RPE apoptosis, aniridia and microphthalmia. Increased levels of Hif1a, Hif2a, Epo and Vegf are associated with a highly disorganised retinal vasculature, chorioretinal anastomoses and the persistence of embryonic vascular structures into adulthood. Additional inactivation of Hif1a in the RPE rescues the RPE morphology, aniridia, microphthalmia and anterior vasoproliferation, but does not rescue retinal vasoproliferation. These data demonstrate that Vhl-dependent regulation of Hif1a in the RPE is essential for normal RPE and iris development, ocular growth and vascular development in the anterior chamber, whereas Vhl-dependent regulation of other downstream pathways is crucial for normal development and maintenance of the retinal vasculature.

Hypoxia inducible factor-1: its potential role in cerebral ischemia

A divergence in the supply and consumption of oxygen in brain tissue initiates complex cycle of biochemical and molecular events resulting in neuronal death. To overcome such adverse situation, the tissue has to adopt some cellular mechanisms such as induction of various transcription factors, such as hypoxia inducible factor (HIF). It is a transcriptional regulator of oxygen homeostasis and key factor to generate the adaptive responses through upregulation of various target genes involved in the erythropoiesis, angiogenesis as well as glucose metabolism and transport. On the other hand, some studies do suggest that HIF also plays a detrimental role in ischemic reperfusion injury by inducing the pro apoptotic molecules, cytokines such as Nix, BNip3, and IL-20 which cause mitochondrial dysfunction leading to cell death. Hence, modulation of HIF-1 activity seems to provide an innovative therapeutic target to reduce the cellular damage, which arises from ischemic injury. Apart from traditional oxygen dependent HIF regulation, the focus has now shifted toward oxygen independent regulation in cell specific manner through reactive oxygen species involving hypoxia-associated factor, and heat shock protein 90, etc. Therefore, future development of such small molecule regulators for HIF-1 stability and signaling may prove useful to therapeutically target for enhancing recovery and repair in I/R injury.

Sequential activation of hypoxia-inducible factor 1 and specificity protein 1 is required for hypoxia-induced transcriptional stimulation of Abcc8

Cerebral ischemia causes increased transcription of sulfonylurea receptor 1 (SUR1), which forms SUR1-regulated NC(Ca-ATP) channels linked to cerebral edema. We tested the hypothesis that hypoxia is an initial signal that stimulates transcription of Abcc8, the gene encoding SUR1, via activation of hypoxia-inducible factor 1 (HIF1). In the brain microvascular endothelial cells, hypoxia increased SUR1 abundance and expression of functional SUR1-regulated NC(Ca-ATP) channels. Luciferase reporter activity driven by the Abcc8 promoter was increased by hypoxia and by coexpression of HIF1α. Surprisingly, a series of luciferase reporter assays studying the Abcc8 promoter revealed that binding sites for specificity protein 1 (Sp1), but not for HIF, were required for stimulation of Abcc8 transcription by HIF1α. Luciferase reporter assays studying Sp1 promoters of three species, and chromatin immunoprecipitation analysis in rats after cerebral ischemia, indicated that HIF binds to HIF-binding sites on the Sp1 promoter to stimulate transcription of the Sp1 gene. We conclude that sequential activation of two transcription factors, HIF and Sp1, is required to stimulate transcription of Abcc8 following cerebral ischemia. Sequential gene activation in cerebral ischemia provides a plausible molecular explanation for the prolonged treatment window observed for inhibition of the end-target gene product, SUR1, by glibenclamide.

Hypoxia inducible factor-1α is involved in the neurodegeneration induced by isoflurane in the brain of neonatal rats

More and more data show isoflurane, a commonly used volatile anesthetic has dual effects on neuron fate. However, the underlying mechanisms that can explain the apparent paradox are poorly understood. Hypoxia inducible factor (HIF)-1α, a transcription factor, has been found regulating both prosurvival and prodeath pathways in the CNS. Previously, we found that isoflurane can activate HIF-1α under normoxic conditions in vitro and HIF-1α has been found to be involved in the pre-conditioning effect of isoflurane in various organs. Here, we investigated whether HIF-1α is a contributing factor in the neurodegenration in rodent primary cultured neurons and in developing rat brain. Isoflurane dose-dependently induced apoptotic neurodegeneration in neonatal rats as assessed by S100β, cleaved caspase 3 and poly-(ADP-ribose) polymerase (PARP), respectively. Notably, isoflurane up-regulates HIF-1α protein levels in vivo and in vitro during induction of neurodegeneration. Likewise, isoflurane resulted in a significant elevation of cytosonic calcium levels in neuron cultures. Furthermore, knockdown of HIF-1α expression in cultured neurons attenuated isoflurane-induced neurotoxicity. Finally, Morris water maze (MWM) test showed neonatal exposure to isoflurane impaired juvenile learning and memory ability in rats. These findings indicate that HIF-1α is involved in the neurodegeneration induced by isoflurane in the brain of neonatal rats, suggesting HIF-1α may be a candidate for the dual effects of isoflurane on neuron fate.

HIF-1α is neuroprotective during the early phases of mild hypoxia in rat cortical neurons

Hypoxia-inducible factor 1α (HIF-1α) is a transcription factor that plays a key role in regulating the adaptive response to hypoxia. HIF-1α is stabilised during hypoxia and, after dimerisation with hypoxia-inducible factor 1β (HIF-1β), triggers the expression of various genes involved in cell cycle control and energy metabolism associated with cell survival. However, HIF-1α also regulates the expression of proapoptotic genes. The aim of this study was to ascertain the influence of HIF-1α on neurotoxicity evoked by hypoxia in rat cortical neurons. We found that mild hypoxia induces time-dependent neuronal death involving free radical production, mitochondrial depolarisation, cytochrome c release and caspase-3 activation. Lentivirus-mediated HIF-1α knockdown markedly strengthened all of these effects during the initial 24h of hypoxia, which suggests that HIF-1α plays a neuroprotective role in hypoxia-mediated neuronal death. After this initial period, the protective actions of HIF-1α disappeared over the course of the hypoxia-mediated HIF-1α stabilisation. Moreover, lentiviral-mediated overexpression of HIF-1α increased lactate dehydrogenase (LDH) A, one of the target genes for HIF-1α, but did not show protective actions on hypoxia-mediated neuronal death, indicating that the level of endogenous HIF-1α stabilisation achieved during hypoxia was already the maximum required for HIF-1α transcription activities. These results indicate that HIF-1α is neuroprotective in the early phases of hypoxia.

Regional genome transcriptional response of adult mouse brain to hypoxia

BACKGROUND

Since normal brain function depends upon continuous oxygen delivery and short periods of hypoxia can precondition the brain against subsequent ischemia, this study examined the effects of brief hypoxia on the whole genome transcriptional response in adult mouse brain.

RESULT

Pronounced changes of gene expression occurred after 3 hours of hypoxia (8% O(2)) and after 1 hour of re-oxygenation in all brain regions. The hypoxia-responsive genes were predominantly up-regulated in hindbrain and predominantly down-regulated in forebrain - possibly to support hindbrain survival functions at the expense of forebrain cognitive functions. The up-regulated genes had a significant role in cell survival and involved both shared and unshared signaling pathways among different brain regions. Up-regulation of transcriptional signaling including hypoxia inducible factor, insulin growth factor (IGF), the vitamin D3 receptor/retinoid X nuclear receptor, and glucocorticoid signaling was common to many brain regions. However, many of the hypoxia-regulated target genes were specific for one or a few brain regions. Cerebellum, for example, had 1241 transcripts regulated by hypoxia only in cerebellum but not in hippocampus; and, 642 (54%) had at least one hepatic nuclear receptor 4A (HNF4A) binding site and 381 had at least two HNF4A binding sites in their promoters. The data point to HNF4A as a major hypoxia-responsive transcription factor in cerebellum in addition to its known role in regulating erythropoietin transcription. The genes unique to hindbrain may play critical roles in survival during hypoxia.

CONCLUSION

Differences of forebrain and hindbrain hypoxia-responsive genes may relate to suppression of forebrain cognitive functions and activation of hindbrain survival functions, which may coordinately mediate the neuroprotection afforded by hypoxia preconditioning.

Oxidative toxicity in neurodegenerative diseases: role of mitochondrial dysfunction and therapeutic strategies

Besides fluorine, oxygen is the most electronegative element with the highest reduction potential in biological systems. Metabolic pathways in mammalian cells utilize oxygen as the ultimate oxidizing agent to harvest free energy. They are very efficient, but not without risk of generating various oxygen radicals. These cells have good antioxidative defense mechanisms to neutralize these radicals and prevent oxidative stress. However, increased oxidative stress results in oxidative modifications in lipid, protein, and nucleic acids, leading to mitochondrial dysfunction and cell death. Oxidative stress and mitochondrial dysfunction have been implicated in many neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, and stroke-related brain damage. Research has indicated mitochondria play a central role in cell suicide. An increase in oxidative stress causes mitochondrial dysfunction, leading to more production of reactive oxygen species and eventually mitochondrial membrane permeabilization. Once the mitochondria are destabilized, cells are destined to commit suicide. Therefore, antioxidative agents alone are not sufficient to protect neuronal loss in many neurodegenerative diseases. Combinatorial treatment with antioxidative agents could stabilize mitochondria and may be the most suitable strategy to prevent neuronal loss. This review discusses recent work related to oxidative toxicity in the central nervous system and strategies to treat neurodegenerative diseases.

Adaptation to moderate hypoxia protects cortical neurons against ischemia-reperfusion injury and excitotoxicity independently of HIF-1α

Continuous exposure of cultured cortical neurons to moderate hypoxia (1% O(2)) elevates cellular accumulation of hypoxia-inducible factor-1α (HIF-1α) and improves basal survival of cultured cortical neurons. We examined the effects of adaptation to moderate hypoxia on the vulnerability of cultured neurons to the acute injury of simulated ischemia-reperfusion. Cortical neurons cultured continuously in 1% O(2) were markedly protected against simulated ischemia-reperfusion, with protection persisting through 72h after ischemia. Neurons from 1% O(2) conditions were also highly resistant to glutamate-induced NMDA receptor-dependent excitotoxic injury, despite expression of NMDA receptors at levels not significantly changed from controls. Inhibition of prolyl hydroxylase, mimicking cellular signaling effects of hypoxia including HIF-1α stabilization, also protected neurons against simulated ischemia-reperfusion injury. Nevertheless, genetic deletion of HIF-1α expression did not diminish the protection of neurons adapted to 1% O(2) from excitotoxicity or ischemia-reperfusion injury, nor did it prevent the protective effect of prolyl hydroxylase inhibition. We conclude that chronic exposure to moderate hypoxia, through HIF-1α-independent mechanisms, produces strong protective effects against excitotoxic and ischemia-reperfusion related injury.