Evidence of HIF-1 functional binding activity to caspase-3 promoter after photothrombotic cerebral ischemia

Loss of prolyl hydroxylase 1 and 2 in SM22α-expressing cells prevents Hypoxia-Induced pulmonary hypertension

Pulmonary arterial hypertension (PAH) is a disease characterized by increased vasoconstriction and vascular remodeling. Pulmonary artery smooth muscle cells (PASMCs) highly express the transcription factor hypoxia-inducible factor-1α (HIF-1α), yet the role of PASMC HIF-1α in the development of PAH remains controversial. To study the role of SMC HIF-1α in the pulmonary vascular response to acute and chronic hypoxia, we used a gain-of-function strategy to stabilize HIF-1α in PASMC by generating mice lacking prolyl hydroxylase domain (PHD) 1 and 2 in SM22α-expressing cells. This strategy increased HIF-1α expression and transcriptional activity under conditions of normoxia and hypoxia. Acute hypoxia increased right ventricular systolic pressure (RVSP) in control, but not in SM22α-PHD1/2-/- mice. Chronic hypoxia increased RVSP and vascular remodeling more in control SM22α-PHD1/2+/+ than in SM22α-PHD1/2-/- mice. In vitro studies demonstrated increased contractility and myosin light chain phosphorylation in isolated PHD1/2+/+ compared with PHD1/2-/- PASMC under both normoxic and hypoxic conditions. After chronic hypoxia, there was more p27 and less vascular remodeling in SM22α-PHD1/2-/- compared with SM22α-PHD1/2+/+ mice. Hypoxia increased p27 in PASMC isolated from control patients, but not in cells from patients with idiopathic pulmonary arterial hypertension (IPAH). These findings highlight an SM22α-expressing cell-specific role for HIF-1α in the inhibition of pulmonary vasoconstriction and vascular remodeling. Modulating HIF-1α expression in PASMC may represent a promising preventative and therapeutic strategy for patients with PAH.NEW & NOTEWORTHY In a mouse model wherein hypoxia-inducible factor 1 alpha (HIF-1α) is stabilized in vascular smooth muscle cells, we found that HIF-1α regulates vasoconstriction by limiting phosphorylation of myosin light chain and regulates vascular remodeling through p27 induction. These findings highlight a cell-specific role for HIF-1α in the inhibition of pulmonary vasoconstriction and vascular remodeling.

The Role of the lncRNA-LRCF in Propofol-Induced Oligodendrocyte Damage in Neonatal Mouse

In this study, LRCF, a long noncoding RNA (lncRNA) related to cognitive function, which was first discovered and named by our group, was shown to be involved in the propofol-induced proliferation and apoptosis of oligodendrocytes (OLGs). Our systematic study showed that LRCF expression differs in OLGs of mice of different ages. We found that neonatal mice with a high level of LRCF typically showed greater propofol-induced injury of OLGs. Mechanistic research has shown that LRCF can block the HIF-1α/miR138-5p/Caspase-3 pathway by binding to miR138-5p to form a microRNA (miRNA) sponge and result in cell damage through HIF-1α/Caspase-3 pathway in propofol induced OLGs. This may be the intrinsic reason why neonatal animals with high levels of LRCF tend to develop learning disability and neuro-degeneration more frequently than adults' after exposure to general anesthesia. When LRCF is highly expressed, HIF-1α directly regulates the transcription of the Caspase-3 gene by binding to the transcription factor binding site (TFBS) in its promoter, which induces OLGs apoptosis. LRCF is crucial for the mutual activation of the HIF-1α/miR138-5p/Caspase-3 OLGs survival pathway and the HIF-1α/Caspase-3 OLGs damage pathway. This study is the first to report that up-regulation of HIF-1α in OLGs treated with Propofol can promote apoptosis through HIF-1α/caspase-3 pathway and resist apoptosis through HIF-1α/miR-138-5p/caspase-3 pathway. The effect of HIF-1α on Caspase-3 expression depends on LRCF expression, which provides important theoretical support for gene therapy targeting LRCF. The further significance of this study is points to an involvement of the genetic background with high LRCF expression may serve as an important marker for identifying patients with a high risk of OLGs injury by Propofol. Thus, caution should be taken when administrating propofol in these patients, especially pediatric patients with high level of LRCF.

Sonodynamic Therapy Suppresses Neovascularization in Atherosclerotic Plaques via Macrophage Apoptosis-Induced Endothelial Cell Apoptosis

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DVDMS-SDT reduces neovascularization in late-stage atherosclerotic lesions in both rabbit and mouse models.

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DVDMS-SDT enhances macrophage foam cell apoptosis, which in turn induces neovessel endothelial cell apoptosis and inhibits its proliferation, migration, and tubulogenesis, termed apoptosis-induced apoptosis.

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Mechanistically, DVDMS-SDT induces macrophage foam cell apoptosis via mitochondrial-caspase pathway, which activates caspase 3 to cleave SP-1, leading to the reduction of HIF-1α and VEGF-A.

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In the pilot translational study, DVDMS-SDT reduces plaque angiogenesis and inhibits vessel inflammation.

During atherosclerosis plaque progression, pathological intraplaque angiogenesis leads to plaque rupture accompanied by thrombosis, which is probably the most important cause of arteries complications such as cerebral and myocardial infarction. Even though few treatments are available to mitigate plaque rupture, further investigation is required to develop a robust optimized therapeutic method. In this study using rabbit and mouse atherosclerotic models, sinoporphyrin sodium (DVDMS)-mediated sonodynamic therapy reduced abnormal angiogenesis and plaque rupture. Briefly, DVDMS is injected to animals, and then the plaque was locally exposed to pulse ultrasound for a few minutes. Furthermore, a small size clinical trial was conducted on patients with atherosclerosis. Notably, a significant reduction of arterial inflammation and angiogenesis was recorded following a short period of DVDMS-mediated sonodynamic therapy treatment. This beneficial outcome was almost equivalent to the therapeutic outcome after 3-month intensive statin treatment.

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.

The insights into molecular pathways of hypoxia-inducible factor in the brain

The objectives of this present work were to review recent developments on the role of hypoxia-inducible factor (HIF) in the survival of cells under normoxic versus hypoxic and inflammatory brain conditions. The dual nature of HIF effects appears well established, based on the accumulated evidence of HIF playing both the role of adaptive factor and mediator of cell demise. Cellular HIF responses depend on pathophysiological conditions, developmental phase, comorbidities, and administered medications. In addition, HIF-1α and HIF-2α actions may vary in the same tissues. The multiple roles of HIF in stem cells are emerging. HIF not only regulates expression of target genes and thereby influences resultant protein levels but also contributes to epigenetic changes that may reciprocally provide feedback regulations loops. These HIF-dependent alterations in neurological diseases and its responses to treatments in vivo need to be examined alongside with a functional status of subjects involved in such studies. The knowledge of HIF pathways might be helpful in devising HIF-mimetics and modulating drugs, acting on the molecular level to improve clinical outcomes, as exemplified here by clinical and experimental data of selected brain diseases, occasionally corroborated by the data from disorders of other organs. Because of complex role of HIF in brain injuries, prospective therapeutic interventions need to differentially target HIF responses depending on their roles in the molecular mechanisms of neurologic diseases.

Normalizing JMJD6 Expression in Rat Spinal Dorsal Horn Alleviates Hyperalgesia Following Chronic Constriction Injury

Jumonji domain-containing protein 6 (JMJD6) is a homolog of hypoxia-inducible factor (HIF) asparaginyl hydroxylase, an inhibitor of HIF. HIF-1α is known to participate in neuropathic pain (NPP) during chronic constriction injury (CCI); however, the roles of JMJD6 in NPP have not been systematically investigated. In this study, we examined the temporal distribution and cellular location of JMJD6 in the spinal cord during CCI. In addition, we assessed behavioral changes representative of NPP in rats. Following CCI, lentiviral vectors (LV-JMJD6) were intrathecally administered to observe the changes in the expression of JMJD6, HIF-1α, and its downstream factor caspase-3. Co-immunoprecipitation was used to detect potential interactions between JMJD6 and HIF-1α. We found that JMJD6 was decreased in rats following CCI, which was accompanied by significant NPP–associated behavioral changes. JMJD6 was mainly expressed in neurons. Intrathecal injection of LV-JMJD6 following CCI alleviated the thermal and mechanical hyperalgesia, normalized JMJD6 protein expression, and decreased HIF-1α protein expression with a corresponding reduction in caspase-3 protein expression. Furthermore, the co-immunoprecipitation analyses showed that JMJD6 and HIF-1α protein immunoprecipitated with each other, indicating an interaction between these two proteins. Taken together, the results suggest that JMJD6 may serve as a sensor in neurons of the adult rat spinal cord during the CCI state. Furthermore, JMJD6 may exert its function in NPP by regulating HIF-1α in rats exposed to CCI.

Role of HIF-1a in regulating autophagic cell survival during cerebral ischemia reperfusion in rats

Hypoxia-inducible factor-1a (HIF-1a) plays a beneficial role during cerebral ischemia reperfusion (IR), but the underlying molecular mechanisms are not completely understood. Here, we aimed to investigate the effects and molecular regulation of HIF-1a on brain cell apoptosis and autophagy during IR. We found that augmentation of HIF-1a in re-perfused hematopoietic cells significantly reduced brain damage, alleviated brain edema and improved neural function during IR, seemingly through two HIF-1a target genes BNIP3 and NIX, which were critical regulators for cell apoptosis and autophagic cell survival. in vitro, HIF-1a induced up-regulation of BNIP3 and NIX in human cortical neuron cells, HCN-1A. Inhibition of BNIP3 and NIX significantly attenuated HIF-1a-suppressed cell apoptosis and HIF-1a-induced cell autophagy. Together, these data suggest that HIF-1a may ameliorate brain damages during IR through BNIP3 and NIX -dependent augmentation of autophagic cell survival and reduction in cell apoptosis.

Role of HIF-1α and CASPASE-3 in cystogenesis of odontogenic cysts and tumors

OBJECTIVES

Odontogenic cysts and tumors are the most relevant lesions that affect the gnathic bones. These lesions have in common the formation of cystic areas and this common feature may suggest involvement of similar mechanisms. The hypoxia inducible factor 1 alpha (HIF-1α), a responsive protein to hypoxia and caspase-3, an irreversible apoptosis marker, may contribute to cyst formation. Thus, this study aimed to investigate the immunoexpression of these proteins in odontogenic cysts and tumors.

MATERIAL AND METHODS

Twenty cases of ameloblastoma, keratocystic odontogenic tumor (KOT) (n = 20), radicular cyst (RC) (n = 18), dentigerous cyst (DC) (n = 11), calcifying cystic odontogenic tumor (n = 8), and dental follicle (DF) (n = 10) were used to investigate HIF-1α and caspase-3 expression in sequential serial cuts by immunohistochemistry.

RESULTS

HIF-1α was overexpressed in RC, DC, and ameloblastoma when compared with DF. The basal and sometimes the lower suprabasal layer showed no or very low expression in DC, KOT, and ameloblastoma, the last also showing strong expression in solid epithelial areas and initial cystic formation regions. Caspase-3 was found to be overexpressed in all lesions, with the highest expression in odontogenic cysts compared to tumors. HIF-1α and caspase-3 were localized in similar areas of the same lesions, especially in the epithelium surrounding cystic formations.

CONCLUSIONS

This study showed distinct immunoexpression of HIF-1α and caspase-3 in odontogenic cyst and tumors, with higher expression observed in odontogenic cysts.

CLINICAL RELEVANCE

These findings suggest a possible correlation between hypoxia, apoptosis, and cystogenesis, leading to understand the mechanisms responsible to cystic formation in odontogenic lesions.

The antioxidant and antiapoptotic effects of crocin pretreatment on global cerebral ischemia reperfusion injury induced by four vessels occlusion in rats

AIMS

Cerebral ischemia reperfusion (IR) injury is a process in which oxidative and apoptotic mechanisms play a part. Neuroprotective agents to be found could work out well for the efficient and safe minimization of cerebral IR injury. Crocin is a strong antioxidant agent; however the influence of this agent on the experimental cerebral ischemia model has not been studied extensively and thus it is not well-known. The objective of our study was to investigate the antioxidant, antiapoptotic and protective effects of crocin on the global cerebral IR induced by four-vessel occlusion.

MAIN METHODS

A total of 30 adult female Sprague-Dawley rats were equally and randomly separated into three groups as follows: sham, IR and IR+crocin (40mg/kg/day orally for 10days). 24h after electrocauterization of bilateral vertebral arteries, bilateral common carotid arteries were occluded for 30min and reperfused for 30min. Oxidative stress parameters (TAS, TOS, OSI), haematoxylin and eosin staining, caspase-3 and hypoxia-inducible factor-1 alpha (HIF-1α) expressions and TUNEL methods were investigated.

KEY FINDINGS

There was a significant difference between the IR and sham groups by means of OSI level, histopathological scoring, caspase-3, HIF-1α and TUNEL-positive cell parameters. We have also observed that pre-treatment with crocin reduced these parameter levels back to the baseline.

SIGNIFICANCE

The data obtained from the present study suggest that crocin may exert antiapoptotic, antioxidant and protective effects in IR-mediated brain injury induced by four-vessel occlusion. To the best of our knowledge, this would be the first study to be conducted in this field.

Pre- and posttreatment with edaravone protects CA1 hippocampus and enhances neurogenesis in the subgranular zone of dentate gyrus after transient global cerebral ischemia in rats

Edaravone is clinically used for treatment of patients with acute cerebral infarction. However, the effect of double application of edaravone on neurogenesis in the hippocampus following ischemia remains unknown. In the present study, we explored whether pre- and posttreatment of edaravone had any effect on neural stem/progenitor cells (NSPCs) in the subgranular zone of hippocampus in a rat model of transient global cerebral ischemia and elucidated the potential mechanism of its effects. Male Sprague-Dawley rats were divided into three groups: sham-operated (n = 15), control (n = 15), and edaravone-treated (n = 15) groups. Newly generated cells were labeled by 5-bromo-2-deoxyuridine. Immunohistochemistry was used to detect neurogenesis. Terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling was used to detect cell apoptosis. Reactive oxygen species (ROS) were detected by 2,7-dichlorofluorescien diacetate assay in NSPCs in vitro. Hypoxia-inducible factor-1α (HIF-1α) and cleaved caspase-3 proteins were quantified by western blot analysis. Treatment with edaravone significantly increased the number of NSPCs and newly generated neurons in the subgranular zone (p < .05). Treatment with edaravone also decreased apoptosis of NSPCs (p < .01). Furthermore, treatment with edaravone significantly decreased ROS generation and inhibited HIF-1α and cleaved caspase-3 protein expressions. These findings indicate that pre- and posttreatment with edaravone enhances neurogenesis by protecting NSPCs from apoptosis in the hippocampus, which is probably mediated by decreasing ROS generation and inhibiting protein expressions of HIF-1α and cleaved caspase-3 after cerebral ischemia.

Disturbed flow enhances inflammatory signaling and atherogenesis by increasing thioredoxin-1 level in endothelial cell nuclei

BACKGROUND

Oxidative stress occurs with disturbed blood flow, inflammation and cardiovascular disease (CVD), yet free-radical scavenging antioxidants have shown limited benefit in human CVD. Thioredoxin-1 (Trx1) is a thiol antioxidant protecting against non-radical oxidants by controlling protein thiol/disulfide status; Trx1 translocates from cytoplasm to cell nuclei due to stress signaling, facilitates DNA binding of transcription factors, e.g., NF-κB, and potentiates inflammatory signaling. Whether increased nuclear Trx1 contributes to proatherogenic signaling is unknown.

METHODOLOGY/PRINCIPAL FINDINGS

In vitro and in vivo atherogenic models were used to test for nuclear translocation of Trx1 and associated proinflammatory signaling. Disturbed flow by oscillatory shear stress stimulated Trx1 nuclear translocation in endothelial cells. Elevation of nuclear Trx1 in endothelial cells and transgenic (Tg) mice potentiated disturbed flow-stimulated proinflammatory signaling including NF-κB activation and increased expression of cell adhesion molecules and cytokines. Tg mice with increased nuclear Trx1 had increased carotid wall thickening due to disturbed flow but no significant differences in serum lipids or weight gain compared to wild type mice. Redox proteomics data of carotid arteries showed that disturbed flow stimulated protein thiol oxidation, and oxidation was higher in Tg mice than wild type mice.

CONCLUSIONS/SIGNIFICANCE

Translocation of Trx1 from cytoplasm to cell nuclei plays an important role in disturbed flow-stimulated proatherogenesis with greater cytoplasmic protein oxidation and an enhanced nuclear transcription factor activity. The results suggest that pharmacologic interventions to inhibit nuclear translocation of Trx1 may provide a new approach to prevent inflammatory diseases or progression.

Early expressions of hypoxia-inducible factor 1alpha and vascular endothelial growth factor increase the neuronal plasticity of activated endogenous neural stem cells after focal cerebral ischemia

Endogenous neural stem cells become “activated” after neuronal injury, but the activation sequence and fate of endogenous neural stem cells in focal cerebral ischemia model are little known. We evaluated the relationships between neural stem cells and hypoxia-inducible factor-1α and vascular endothelial growth factor expression in a photothromobotic rat stroke model using immunohistochemistry and western blot analysis. We also evaluated the chronological changes of neural stem cells by 5-bromo-2′-deoxyuridine (BrdU) incorporation. Hypoxia-inducible factor-1α expression was initially increased from 1 hour after ischemic injury, followed by vascular endothelial growth factor expression. Hypoxia-inducible factor-1α immunoreactivity was detected in the ipsilateral cortical neurons of the infarct core and peri-infarct area. Vascular endothelial growth factor immunoreactivity was detected in bilateral cortex, but ipsilateral cortex staining intensity and numbers were greater than the contralateral cortex. Vascular endothelial growth factor immunoreactive cells were easily found along the peri-infarct area 12 hours after focal cerebral ischemia. The expression of nestin increased throughout the microvasculature in the ischemic core and the peri-infarct area in all experimental rats after 24 hours of ischemic injury. Nestin immunoreactivity increased in the subventricular zone during 12 hours to 3 days, and prominently increased in the ipsilateral cortex between 3–7 days. Nestin-labeled cells showed dual differentiation with microvessels near the infarct core and reactive astrocytes in the peri-infarct area. BrdU-labeled cells were increased gradually from day 1 in the ipsilateral subventricular zone and cortex, and numerous BrdU-labeled cells were observed in the peri-infarct area and non-lesioned cortex at 3 days. BrdU-labeled cells rather than neurons, were mainly co-labeled with nestin and GFAP. Early expressions of hypoxia-inducible factor-1α and vascular endothelial growth factor after ischemia made up the microenvironment to increase the neuronal plasticity of activated endogenous neural stem cells. Moreover, neural precursor cells after large-scale cortical injury could be recruited from the cortex nearby infarct core and subventricular zone.

KLF5 promotes hypoxia-induced survival and inhibits apoptosis in non-small cell lung cancer cells via HIF-1α

Transcription factor Krüppel-like factors 5 (KLF5) is overexpressed in a wide range of tumor tissues and acts as a prognostic factor in cancer. However, the role of KLF5 in non-small cell lung cancer is not clear. Hypoxia plays a vital part in the development of cancer via hypoxia-inducible factor 1 (HIF-1). Our study showed that hypoxia (1% O2) increased cell viability, clonality and proliferation and inhibited cell apoptosis in A549 cells. The expression of HIF-1α and KLF5 was increased time-dependently in hypoxia. Using small interfering RNA (siRNA) targeting KLF5 or HIF-1α, we demonstrated that KLF5 or HIF-1α knockdown inhibited hypoxia-induced cell survival and promoted cell apoptosis by actively downregulating cyclin B1, survivin and upregulating caspase-3. Given the similar effect of KLF5 and HIF-1α on cell survival, an attempt was made to investigate the putative interaction of them in hypoxia. KLF5 was revealed to co-immunoprecipitate with HIF-1α and hypoxia increased the amount of KLF5 and HIF-1α complex. Moreover, silencing of KLF5 decreased HIF-1α expression while KLF5 was not affected by HIF-1α inhibition in hypoxia, confirming the effect of KLF5 on upregulation of HIF-1α. In conclusion, this study identified hypoxia as a tumor promoter by triggering KLF5 → HIF-1α → cyclin B1/survivin/caspase-3 in lung cancer cells.

Preconditioning and post-treatment with cobalt chloride in rat model of perinatal hypoxic-ischemic encephalopathy

BACKGROUND

Hypoxia-ischemia (HI)-induced perinatal encephalopathy is a major cause of acute mortality and chronic neurologic morbidities such as cerebral palsy, mental retardation, and epilepsy. As the essential transcription factor for the activation of hypoxia-inducible genes, hypoxia-inducible factor 1 alpha (HIF-1α) plays an important role in the pathophysiological response to the stress of HI brain damage. Whether HIF-1α activation promotes neuroprotection in HI tissues is controversial.

METHODS

The left common carotid artery of rats aged 7days was ligated under anesthesia. The pups were then exposed to hypoxia in a normobaric chamber filled with 8% oxygen and 92% nitrogen for 2.5h. In the sham control group, the left common carotid artery was exposed but was not ligated or exposed to hypoxia. To assess the time window for effective treatment, the HIF-1α inducer cobalt chloride (CoCl2) was injected subcutaneously 1day before surgery, immediately or 1day after surgery. The brain tissues were harvested from the pups of each groups at 1, 2 and 7days after insult for HIF-1α protein ant its target genes expression and for investigating the injury. Morris water maze tests were performed at postnatal 7weeks.

RESULTS

HIF-1α protein levels and its target genes vascular endothelial growth factor, heme oxygenase-1, and insulin-like growth factor 1 were markedly increased after intraperitoneal injection of CoCl2 (60mg/kg). The target gene inducible nitric oxide synthase exhibited a biphasic time course. HI caused apoptosis and reduced capillary density, which were ameliorated by CoCl2. Both preconditioning with CoCl2 24h before HI and administration of CoCl2 24h after HI improved long-term reference memory compared with that in vehicle-injected littermate controls. Administration of CoCl2 immediately after HI did not improve spatial working memory.

CONCLUSIONS

CoCl2 activates HIF-1α and protects against brain damage in vivo. The time of administration could be used to manipulate the activity of HIF-1α pathways and promote recovery.

Ipsilateral versus contralateral spontaneous post-stroke neuroplastic changes: involvement of BDNF?

Stroke is a leading cause of death and disability in industrialized countries. Although surviving patients exhibit a certain degree of restoration of function attributable to brain plasticity, the majority of stroke survivors has to struggle with persisting deficits. In order to potentiate post-stroke recovery, several rehabilitation therapies have been undertaken and many experimental studies have reported that brain-derived neurotrophic factor (BDNF) is central to many facets of neuroplastic processes. However, although BDNF role in brain plasticity is well characterized through strategies that manipulate its content, the involvement of this neurotrophin in spontaneous post-stroke recovery remains to be clarified. Besides, while the neuroplastic role of BDNF is restricted to its mature form, most studies investigating the proper effect of ischemia on post-stroke BDNF metabolism focused on mRNA or total protein expressions. In addition, these studies are mainly performed in brain regions collected either at or around the lesion site. Therefore, the objective of the present study was to investigate in both hemispheres, the long-term expression (up to one month) of both pro- and mature BDNF forms in rats subjected to photothrombotic ischemia. These assessments were performed in the cortex and in the hippocampus, two regions known to subserve functional recovery after stroke and were coupled to the study of synaptophysin expression, a marker of synaptogenesis. Our study reports that stroke induces an early and transient increase (4h) in mature BDNF expression in the cortex of both hemispheres that was associated with a delayed rise (30d) in synaptophysin levels ipsilateraly. In both hippocampal territories, the pattern of mature BDNF expression shows a more delayed increase (from 8 to 30d), which coincides with the evolution of synaptophysin expression. Interestingly, in these hippocampal territories, pro-BDNF levels evolve differently suggesting a differential gene regulation between the two hemispheres. While highlighting the complexity of changes in BDNF metabolism after stroke, our data suggest that BDNF involvement in spontaneous post-stroke plasticity is region-dependent.

Ras family small GTPase-mediated neuroprotective signaling in stroke

Selective neuronal cell death is one of the major causes of neuronal damage following stroke, and cerebral cells naturally mobilize diverse survival signaling pathways to protect against ischemia. Importantly, therapeutic strategies designed to improve endogenous anti-apoptotic signaling appear to hold great promise in stroke treatment. While a variety of complex mechanisms have been implicated in the pathogenesis of stroke, the overall mechanisms governing the balance between cell survival and death are not well-defined. Ras family small GTPases are activated following ischemic insults, and in turn, serve as intrinsic switches to regulate neuronal survival and regeneration. Their ability to integrate diverse intracellular signal transduction pathways makes them critical regulators and potential therapeutic targets for neuronal recovery after stroke. This article highlights the contribution of Ras family GTPases to neuroprotective signaling cascades, including mitogen-activated protein kinase (MAPK) family protein kinase- and AKT/PKB-dependent signaling pathways as well as the regulation of cAMP response element binding (CREB), Forkhead box O (FoxO) and hypoxiainducible factor 1(HIF1) transcription factors, in stroke.

Caspase-3 is a target gene of c-Jun:ATF2 heterodimers during apoptosis induced by activity deprivation in cerebellar granule neurons

Caspase-3, a key executor of neuronal apoptosis, is up-regulated and activated during apoptosis induced by activity deprivation in cerebellar granule neurons (CGNs). However, the transcriptional mechanism regulating caspase-3 during CGN apoptosis remains unknown. Here, we show that the caspase-3 gene is transactivated and its induction is preceded by c-Jun NH(2)-terminal kinase (JNK)/c-Jun:ATF2 pathway activation following activity deprivation in CGNs. We observed that caspase-3 induction is abolished by pharmacological inhibition of the JNK/c-Jun:ATF2 pathway. Destroying c-Jun:ATF2 heterodimers with dominant negative mutants of c-Jun and ATF2 or knockdown by small RNA interference reduced caspase-3 promoter activity and mRNA level. Furthermore, chromatin immunoprecipitation showed increased binding of c-Jun:ATF2 heterodimers to the caspase-3 promoter in response to activity deprivation in vivo. Site-directed mutagenesis of the caspase-3 promoter revealed that caspase-3 transcriptional activation depends primarily on an ATF site -233 to -225 nucleotides upstream of the start site. Taken together, these data demonstrate that caspase-3 is a target gene of c-Jun:ATF2 heterodimers during apoptosis induced by activity deprivation in CGNs.

Hypoxia-inducible factor plays a gut-injurious role in intestinal ischemia reperfusion injury

Gut injury and loss of normal intestinal barrier function are key elements in the paradigm of gut-origin systemic inflammatory response syndrome, acute lung injury, and multiple organ dysfunction syndrome (MODS). As hypoxia-inducible factor (HIF-1) is a critical determinant of the physiological and pathophysiological response to hypoxia and ischemia, we asked whether HIF-1 plays a proximal role in the induction of gut injury and subsequent lung injury. Using partially HIF-1α-deficient mice in an isolated superior mesenteric artery occlusion (SMAO) intestinal ischemia reperfusion (I/R) injury model (45 min SMAO followed by 3 h of reperfusion), we showed a direct relationship between HIF-1 activation and intestinal I/R injury. Specifically, partial HIF-1α deficiency attenuated SMAO-induced increases in intestinal permeability, lipid peroxidation, mucosal caspase-3 activity, and IL-1β mRNA levels. Furthermore, partial HIF-1α deficiency prevented the induction of ileal mucosal inducible nitric oxide synthase (iNOS) protein levels after SMAO and iNOS deficiency ameliorated SMAO-induced villus injury. Resistance to SMAO-induced gut injury was also associated with resistance to lung injury, as reflected by decreased levels of myeloperoxidase, IL-6 and IL-10 in the lungs of HIF-1α(+/-) mice. In contrast, a short duration of SMAO (15 min) followed by 3 h of reperfusion neither induced mucosal HIF-1α protein levels nor caused significant gut and lung injury in wild-type or HIF-1α(+/-) mice. This study indicates that intestinal HIF-1 activation is a proximal regulator of I/R-induced gut mucosal injury and gut-induced lung injury. However, the duration and severity of the gut I/R insult dictate whether HIF-1 plays a gut-protective or deleterious role.

HIF-1 mediates pathogenic inflammatory responses to intestinal ischemia-reperfusion injury

Acute lung injury (ALI) and the development of the multiple organ dysfunction syndrome (MODS) are major causes of death in trauma patients. Gut inflammation and loss of gut barrier function as a consequence of splanchnic ischemia-reperfusion (I/R) have been implicated as the initial triggering events that contribute to the development of the systemic inflammatory response, ALI, and MODS. Since hypoxia-inducible factor (HIF-1) is a key regulator of the physiological and pathophysiological response to hypoxia, we asked whether HIF-1 plays a proximal role in the induction of gut injury and subsequent lung injury. Utilizing partially HIF-1α-deficient mice in a global trauma hemorrhagic shock (T/HS) model, we found that HIF-1 activation was necessary for the development of gut injury and that the prevention of gut injury was associated with an abrogation of lung injury. Specifically, in vivo studies demonstrated that partial HIF-1α deficiency ameliorated T/HS-induced increases in intestinal permeability, bacterial translocation, and caspase-3 activation. Lastly, partial HIF-1α deficiency reduced TNF-α, IL-1β, cyclooxygenase-2, and inducible nitric oxide synthase levels in the ileal mucosa after T/HS whereas IL-1β mRNA levels were reduced in the lung after T/HS. This study indicates that prolonged intestinal HIF-1 activation is a proximal regulator of I/R-induced gut mucosal injury and gut-induced lung injury. Consequently, these results provide unique information on the initiating events in trauma-hemorrhagic shock-induced ALI and MODS as well as potential therapeutic insights.

A novel plant homeodomain finger 10-mediated antiapoptotic mechanism involving repression of caspase-3 in gastric cancer cells

The mechanisms governing tumorigenesis of gastric cancer have been an area of intense investigation. Currently, plant homeodomain (PHD) finger (PHF) proteins have been implicated in both tumor suppression and progression. However, the function of PHF10 has not been well characterized. Here, we show that various levels of PHF10 protein were observed in gastric cancer cell lines. Alteration of PHF10 expression, which is associated with tumor cell growth, may result in apoptosis in gastric cancer cells both in vitro and in vivo. Knockdown of PHF10 expression in gastric cancer cells led to significant induction of caspase-3 expression at both the RNA and protein levels and thus induced alteration of caspase-3 substrates in a time-dependent manner. Moreover, results from luciferase assays indicated that PHF10 acted as a transcriptional repressor when the two PHD domains contained in PHF10 were intact. Combined with previous findings, our data suggest that PHF10 transcriptionally regulates the expression of caspase-3. Finally, by using systematic reporter deletion and chromatin immunoprecipitation assays, we localized a region between nucleotides -270 and -170 in the caspase-3 promoter that was required for the efficient inhibition of caspase-3 promoter activity by PHF10. Collectively, our findings show that PHF10 repressed caspase-3 expression and impaired the programmed cell death pathway in human gastric cancer at the transcriptional level.

Transglutaminase 2 protects against ischemic stroke

Transglutaminase 2 (TG2) is a multifunctional protein that modulates cell survival and death pathways. It is upregulated in numerous ischemic models, and protects primary neurons from oxygen and glucose deprivation. TG2 binds to the hypoxia inducible factor (HIF) 1beta and decreases the upregulation of hypoxic-induced proapoptotic genes. To investigate the role of TG2 in ischemic stroke in vivo, we used the murine, permanent middle cerebral artery (MCA) ligation model. TG2 mRNA levels are increased after MCA ligations, and transgenic mice that express human TG2 in neurons had significantly smaller infarct volumes than wild type littermates. Further, TG2 translocates into the nucleus within 2h post ligation. Nuclear-localized TG2 is also apparent in human stroke cases. TG2 suppressed the upregulation of the HIF-induced, proapoptotic gene, Noxa. The findings of this study indicate that TG2 plays a role in attenuating ischemic-induced cell death possibly by modulating hypoxic-induced transcriptional processes.

Microglial involvement in neuroplastic changes following focal brain ischemia in rats

The pathogenesis of ischemic stroke is a complex sequence of events including inflammatory reaction, for which the microglia appears to be a major cellular contributor. However, whether post-ischemic activation of microglial cells has beneficial or detrimental effects remains to be elucidated, in particular on long term brain plasticity events. The objective of our study was to determine, through modulation of post-stroke inflammatory response, to what extent microglial cells are involved in some specific events of neuronal plasticity, neurite outgrowth and synaptogenesis. Since microglia is a source of neurotrophic factors, the identification of the brain-derived neurophic factor (BDNF) as possible molecular actor involved in these events was also attempted. As a means of down-regulating the microglial response induced by ischemia, 3-aminobenzamide (3-AB, 90 mg/kg, i.p.) was used to inhibit the poly(ADP-ribose) polymerase-1 (PARP-1). Indeed, PARP-1 contributes to the activation of the transcription factor NF-kB, which is essential to the upregulation of proinflammatory genes, in particular responsible for microglial activation/proliferation. Experiments were conducted in rats subjected to photothrombotic ischemia which leads to a strong and early microglial cells activation/proliferation followed by an infiltration of macrophages within the cortical lesion, events evaluated at serial time points up to 1 month post-ictus by immunostaining for OX-42 and ED-1. Our most striking finding was that the decrease in acute microglial activation induced by 3-AB was associated with a long term down-regulation of two neuronal plasticity proteins expression, synaptophysin (marker of synaptogenesis) and GAP-43 (marker of neuritogenesis) as well as to a significant decrease in tissue BDNF production. Thus, our data argue in favour of a supportive role for microglia in brain neuroplasticity stimulation possibly through BDNF production, suggesting that a targeted protection of microglial cells could represent an innovative approach to potentiate post-stroke neuroregeneration.

Prodeath or prosurvival: two facets of hypoxia inducible factor-1 in perinatal brain injury

Hypoxia, which occurs in the brain when oxygen availability drops below the normal level, is a major cause of perinatal hypoxic-ischemic injury (HII). The transcriptional factor hypoxia inducible factor-1 (HIF-1) is a key regulator in the pathophysiological response to the stress of hypoxia. Genes regulated by HIF-1 are involved in energy metabolism, erythropoiesis, angiogenesis, vasodilatation, cell survival and apoptosis. Compared with the adult brain, the neonatal brain is different in physiological structure, function, cellular composition and signaling pathway related gene activation and response after hypoxia. The purpose of this review is to determine if developmental susceptibility of the brain after hypoxic/ischemic injury is related to HIF-1alpha, which also plays a pivotal role in the normal brain development. HIF-1alpha regulates both prosurvival and prodeath responses in the neonatal brain and various mechanisms underlie the apparent contradictory effects, including duration of ischemic injury and severity, cell-types, and/or dependent on the nature of the stimulus after HII. Studies report an excessive induction of HIF-1 in the immature brain, which suggests that a cell death promoting role of HIF may prevail. Inhibition of HIF-1alpha and targeted activation of its prosurvival genes appear as a favorable therapeutic strategy. However, a better understanding of multifaceted HIF-1 function during brain development is required to explore potential targets for further therapeutic interventions in the neonate.

HIF-1alpha inhibition ameliorates neonatal brain injury in a rat pup hypoxic-ischemic model

Hypoxia-inducible factor-1alpha (HIF-1alpha) has been considered as a regulator of both prosurvival and prodeath pathways in the nervous system. The present study was designed to elucidate the role of HIF-1alpha in neonatal hypoxic-ischemic (HI) brain injury. Rice-Vannucci model of neonatal hypoxic-ischemic brain injury was used in seven-day-old rats, by subjecting unilateral carotid artery ligation followed by 2 h of hypoxia (8% O2 at 37 degrees C). HIF-1alpha activity was inhibited by 2-methoxyestradiol (2ME2) and enhanced by dimethyloxalylglycine (DMOG). Results showed that 2ME2 exhibited dose-dependent neuroprotection by decreasing infarct volume and reducing brain edema at 48 h post HI. The neuroprotection was lost when 2ME2 was administered 3 h post HI. HIF-1alpha upregulation by DMOG increased the permeability of the BBB and brain edema compared with HI group. 2ME2 attenuated the increase in HIF-1alpha and VEGF 24 h after HI. 2ME2 also had a long-term effect of protecting against the loss of brain tissue. The study showed that the early inhibition of HIF-1alpha acutely after injury provided neuroprotection after neonatal hypoxia-ischemia which was associated with preservation of BBB integrity, attenuation of brain edema, and neuronal death.

Hypoxia-inducible factor-1alpha is a critical mediator of hypoxia induced apoptosis in cardiac H9c2 and kidney epithelial HK-2 cells

BACKGROUND

Hypoxia inducible factor-1 (HIF-1) is a transcription factor that functions to maintain cellular homeostasis in response to hypoxia. There is evidence that HIF-1 can also trigger apoptosis, possibly when cellular responses are inadequate to meet energy demands under hypoxic conditions.

METHODS

Cardiac derived H9c2 and renal tubular epithelial HK-2 cells expressing either the wild type oxygen regulated subunit of HIF-1 (pcDNA3-Hif-1alpha) or a dominant negative version that lacked both DNA binding and transactivation domains (pcDNA3-DN-Hif-1alpha), were maintained in culture and exposed to hypoxia. An RNA interference approach was also employed to selectively knockdown expression of Hif-1alpha. Apoptosis was analyzed in both H9c2 and HK-2 cells by Hoechst and TUNEL staining, caspase 3 activity assays and activation of pro-apoptotic Bcl2 family member Bax.

RESULTS

Overexpression of pcDNA3-DN-Hif-1alpha led to a significant reduction in hypoxia -induced apoptosis (17 +/- 2%, P < 0.01) in H9c2 cells compared to both control-transfected and wild type Hif-1alpha transfected cells. Moreover, selective ablation of HIF-1alpha protein expression by RNA interference in H9c2 cells led to 55% reduction of caspase 3 activity and 46% reduction in the number of apoptotic cells as determined by Hoechst 33258 staining, after hypoxia. Finally, upregulation of the pro-apoptotic protein, Bax, was found in H9c2 cells overexpressing full-length pcDNA3-HA-HIF-1alpha exposed to hypoxia. In HK-2 cells overexpression of wild-type Hif-1alpha led to a two-fold increase in Hif-1alpha levels during hypoxia. This resulted in a 3.4-fold increase in apoptotic cells and a concomitant increase in caspase 3 activity during hypoxia when compared to vector transfected control cells. HIF-1alpha also induced upregulation of Bax in HK-2 cells. In addition, introduction of dominant negative Hif-1alpha constructs in both H9c2 and HK-2 -cells led to decreased active Bax expression.

CONCLUSION

These data demonstrate that HIF-1alpha is an important component of the apoptotic signaling machinery in the two cell types.

Temporal changes in free iron levels after brain ischemia Relevance to the timing of iron chelation therapy in stroke

Whereas iron chelators have been proposed as therapeutic agents in stroke, changes in free iron levels have never been explored after focal brain ischemia. Therefore, free and total iron levels in cortical tissue and free iron levels in plasma were measured before and after (1, 4 and 24h) photothrombotic occlusion of cortical vessels in rats. Brain ferritin expression and localization were also investigated before and after (24, 72 and 192 h) occlusion. The results showed that free iron remained below detectable levels in plasma and that the lesion exhibited high levels of free and total iron. As compared to contralateral values, free iron levels in ischemic core and penumbra increased (+50%) at 1h and returned to control values at 4h post-occlusion. In contrast, the increase in total iron levels (+20-30%) was long-lasting, but confined to the ischemic core. A time-dependent increase in the expression of both chains of ferritin was detected in regions that previously exhibited free iron accumulation. Finally, ischemic damage was reduced by the liposoluble iron chelator 2,2'-dipyridyl (20 mg/kg, i.p.) when injected 15 min or 1 h post-occlusion, yet not later (4 h). In conclusion, our results show that focal brain ischemia results in an early and transient elevation in free iron levels in the ischemic tissue and suggest that free iron excess does not originate in blood. They also highlight the importance of starting iron chelation therapy as soon as possible after stroke.

Transglutaminase 2 protects against ischemic insult, interacts with HIF1beta, and attenuates HIF1 signaling

Transglutaminase 2 (TG2) is a multifunctional enzyme that has been implicated in the pathogenesis of neurodegenerative diseases, ischemia, and stroke. The mechanism by which TG2 modulates disease progression have not been elucidated. In this study we investigate the role of TG2 in the cellular response to ischemia and hypoxia. TG2 is up-regulated in neurons exposed to oxygen and glucose deprivation (OGD), and increased TG2 expression protects neurons against OGD-induced cell death independent of its transamidating activity. We identified hypoxia inducible factor 1beta (HIF1beta) as a TG2 binding partner. HIF1beta and HIF1alpha together form the heterodimeric transcription factor hypoxia inducible factor 1 (HIF1). TG2 and the transaminase-inactive mutant C277S-TG2 inhibited a HIF-dependent transcription reporter assay under hypoxic conditions without affecting nuclear protein levels for HIF1alpha or HIF1beta, their ability to form the HIF1 heterodimeric transcription factor, or HIF1 binding to its DNA response element. Interestingly, TG2 attenuates the up-regulation of the HIF-dependent proapoptotic gene Bnip3 in response to OGD but had no effect on the expression of VEGF, which has been linked to prosurvival processes. This study demonstrates for the first time that TG2 protects against OGD, interacts with HIF1beta, and attenuates the HIF1 hypoxic response pathway. These results indicate that TG2 may play an important role in protecting against the delayed neuronal cell death in ischemia and stroke.