Neuronal deficiency of HIF prolyl 4-hydroxylase 2 in mice improves ischemic stroke recovery in an HIF dependent manner

PHD1-3 oxygen sensors in vivo-lessons learned from gene deletions

Oxygen sensors enable cells to adapt to limited oxygen availability (hypoxia), affecting various cellular and tissue responses. Prolyl-4-hydroxylase domain 1-3 (PHD1-3; also called Egln1-3, HIF-P4H 1-3, HIF-PH 1-3) proteins belong to the Fe2+- and 2-oxoglutarate-dependent dioxygenase superfamily and utilise molecular oxygen (O2) alongside 2-oxoglutarate as co-substrate to hydroxylate two proline residues of α subunits of the dimeric hypoxia inducible factor (HIF) transcription factor. PHD1-3-mediated hydroxylation of HIF-α leads to its degradation and inactivation. Recently, various PHD inhibitors (PHI) have entered the clinics for treatment of renal anaemia. Pre-clinical analyses indicate that PHI treatment may also be beneficial in numerous other hypoxia-associated diseases. Nonetheless, the underlying molecular mechanisms of the observed protective effects of PHIs are only partly understood, currently hindering their translation into the clinics. Moreover, the PHI-mediated increase of Epo levels is not beneficial in all hypoxia-associated diseases and PHD-selective inhibition may be advantageous. Here, we summarise the current knowledge about the relevance and function of each of the three PHD isoforms in vivo, based on the deletion or RNA interference-mediated knockdown of each single corresponding gene in rodents. This information is crucial for our understanding of the physiological relevance and function of the PHDs as well as for elucidating their individual impact on hypoxia-associated diseases. Furthermore, this knowledge highlights which diseases may best be targeted by PHD isoform-selective inhibitors in case such pharmacologic substances become available.

Recent Advances and Therapeutic Implications of 2-Oxoglutarate-Dependent Dioxygenases in Ischemic Stroke

Ischemic stroke is a common disease with a high disability rate and mortality, which brings heavy pressure on families and medical insurance. Nowadays, the golden treatments for ischemic stroke in the acute phase mainly include endovascular therapy and intravenous thrombolysis. Some drugs are used to alleviate brain injury in patients with ischemic stroke, such as edaravone and 3-n-butylphthalide. However, no effective neuroprotective drug for ischemic stroke has been acknowledged. 2-Oxoglutarate-dependent dioxygenases (2OGDDs) are conserved and common dioxygenases whose activities depend on O2, Fe2+, and 2OG. Most 2OGDDs are expressed in the brain and are essential for the development and functions of the brain. Therefore, 2OGDDs likely play essential roles in ischemic brain injury. In this review, we briefly elucidate the functions of most 2OGDDs, particularly the effects of regulations of 2OGDDs on various cells in different phases after ischemic stroke. It would also provide promising potential therapeutic targets and directions of drug development for protecting the brain against ischemic injury and improving outcomes of ischemic stroke.

Expression of hypoxia-inducing factor-1α and matrix metalloproteinase-9 in the recipient parasylvian cortical arteries with different hemodynamic sources in adult moyamoya disease

Objective

In our latest research, we have demonstrated that the recipient parasylvian cortical arteries (PSCAs) with hemodynamic sources from the middle cerebral artery (M-PSCAs) has a higher risk of postoperative cerebral hyperperfusion (CHP) syndrome than those from non-M-PSCAs in adult moyamoya disease (MMD) patient. However, whether there are differences between M-PSCAs and non-M-PSCAs in vascular specimens characteristics has not been studied. In this study, we further investigate the vascular specimen of recipient PSCAs by histological and immunohistochemical methods.

Methods

50 vascular specimens of recipient PSCAs were obtained from 50 adult MMD patients during the combined bypass surgeries in our departments of Zhongnan hospital. 4 recipient PSCAs samples were also obtained in the same way from the middle cerebral artery occlusion patients. The samples were received the pathological sectioning, hematoxylin and eosin staining, and immunohistochemistry, then the vascular wall thickness, matrix metalloproteinase-9 (MMP-9) and hypoxia-inducing factor-1α (HIF-1α) were analyzed.

Results

M-PSCAs adult MMD patients had a thinner intima than non-M-PSCAs in the recipient PSCAs specimens. In recipient non-M-PSCAs vascular specimens, the immunoreactivity indicating HIF-1α and matrix metalloproteinase-9 (MMP-9) was significantly higher than M-PSCAs groups. The logistic regression analyses showed that the M-PSCAs was an independent risk factor of postoperative cerebral hyperperfusion (CHP) syndrome (OR 6.235, 95% CI1.018-38.170, P = 0.048) in MMD.

Conclusion

Our results indicate that M-PSCAs adult MMD patients had thinner intima than non-MCAs adult MMD patients in the PSCAs. More importantly, HIF-1α and MMP-9 were overexpressed in non-M-PSCAs vascular specimens.

Inactivation of mouse transmembrane prolyl 4-hydroxylase increases blood brain barrier permeability and ischemia-induced cerebral neuroinflammation

Hypoxia-inducible factor prolyl 4-hydroxylases (HIF-P4Hs) regulate the hypoxic induction of >300 genes required for survival and adaptation under oxygen deprivation. Inhibition of HIF-P4H-2 has been shown to be protective in focal cerebral ischemia rodent models, while that of HIF-P4H-1 has no effects and inactivation of HIF-P4H-3 has adverse effects. A transmembrane prolyl 4-hydroxylase (P4H-TM) is highly expressed in the brain and contributes to the regulation of HIF, but the outcome of its inhibition on stroke is yet unknown. To study this, we subjected WT and P4htm^−/− mice to permanent middle cerebral artery occlusion (pMCAO). Lack of P4H-TM had no effect on lesion size following pMCAO, but increased inflammatory microgliosis and neutrophil infiltration was observed in the P4htm^−/− cortex. Furthermore, both the permeability of blood brain barrier and ultrastructure of cerebral tight junctions were compromised in P4htm^−/− mice. At the molecular level, P4H-TM deficiency led to increased expression of proinflammatory genes and robust activation of protein kinases in the cortex, while expression of tight junction proteins and the neuroprotective growth factors erythropoietin and vascular endothelial growth factor was reduced. Our data provide the first evidence that P4H-TM inactivation has no protective effect on infarct size and increases inflammatory microgliosis and neutrophil infiltration in the cortex at early stage after pMCAO. When considering HIF-P4H inhibitors as potential therapeutics in stroke, the current data support that isoenzyme-selective inhibitors that do not target P4H-TM or HIF-P4H-3 would be preferred.

Inhibition or Deletion of Hydroxylases-Prolyl-4-Hydroxyases 3 Alleviates Lipopolysaccharide-induced Neuroinflammation and Neurobehavioral Deficiency

It is well known that neuroinflammation plays a key role in neurodegenerative diseases. Hypoxia-inducible factor (HIF) and its hydroxylases-Prolyl-4-hydroxyases (PHDs) have been found to modulate the inflammatory processes. Here, the effects of PHDs enzyme onlipopolysaccharide-induced neuroinflammation and neurocognitive deficits were investigated. BV2 microglia cells were stimulated by LPS (1 μg/ml) as neuroinflammation model in vitro. Dimethyloxalylglycine (DMOG, 100 μM) and PHD3-siRNA were used to suppress the expression of PHD3. In vivo, mice received consecutive intraperitoneal injection of LPS (500 μg/kg) for 7 days, and intraperitoneal injection of DMOG (100 mg/kg) was applied 1 h before LPS at the same days. Several neurobehavioral tests (Open field, Novel object recognition and Morris water maze) were used to measure cognitive function. RT-qPCR and Western blotting were used to investigate the expression of inflammatory cytokines, HIF-PHDs protein. Metabolic reprogramming was measured by seahorse method. The results revealed that LPS induced neuroinflammation and PHD3 expression in vivo and vitro. DMOG and PHD3knockout decreased expression of inflammatory cytokines and improved the metabolic reprogramming caused by LPS treatment. Furthermore, pretreatment of DMOG reversed learning and memory deficits in systemic LPS-exposed mice through anti-neuroinflammation, which is independent of DMOG angiogenesis. These findings suggested that PHD3 may mediate LPS-induced microglial activation and neuroinflammation-associated neurobehavioral deficits.

HIF‑1α in cerebral ischemia (Review)

Cerebral ischemic injury may lead to a series of serious brain diseases, death or different degrees of disability. Hypoxia-inducible factor-1α (HIF-1α) is an oxygen-sensitive transcription factor, which mediates the adaptive metabolic response to hypoxia and serves a key role in cerebral ischemia. HIF-1α is the main molecule that responds to hypoxia. HIF-1α serves an important role in the development of cerebral ischemia by participating in numerous processes, including metabolism, proliferation and angiogenesis. The present review focuses on the endogenous protective mechanism of cerebral ischemia and elaborates on the role of HIF-1α in cerebral ischemia. In addition, it focuses on cerebral ischemia interventions that act on the HIF-1α target, including biological factors, non-coding RNA, hypoxic-ischemic preconditioning and drugs, and expands upon the measures to strengthen the endogenous compensatory response to support HIF-1α as a therapeutic target, thus providing novel suggestions for the treatment of cerebral ischemia.

Hypoxia Tolerant Species: The Wisdom of Nature Translated into Targets for Stroke Therapy

Human neurons rapidly die after ischemia and current therapies for stroke management are limited to restoration of blood flow to prevent further brain damage. Thrombolytics and mechanical thrombectomy are the available reperfusion treatments, but most of the patients remain untreated. Neuroprotective therapies focused on treating the pathogenic cascade of the disease have widely failed. However, many animal species demonstrate that neurons can survive the lack of oxygen for extended periods of time. Here, we reviewed the physiological and molecular pathways inherent to tolerant species that have been described to contribute to hypoxia tolerance. Among them, Foxo3 and Eif5A were reported to mediate anoxic survival in Drosophila and Caenorhabditis elegans, respectively, and those results were confirmed in experimental models of stroke. In humans however, the multiple mechanisms involved in brain cell death after a stroke causes translation difficulties to arise making necessary a timely and coordinated control of the pathological changes. We propose here that, if we were able to plagiarize such natural hypoxia tolerance through drugs combined in a pharmacological cocktail it would open new therapeutic opportunities for stroke and likely, for other hypoxic conditions.

Hypoxia-Inducible Factor (HIF) in Ischemic Stroke and Neurodegenerative Disease

Hypoxia is one of the most common pathological conditions, which can be induced by multiple events, including ischemic injury, trauma, inflammation, tumors, etc. The body's adaptation to hypoxia is a highly important phenomenon in both health and disease. Most cellular responses to hypoxia are associated with a family of transcription factors called hypoxia-inducible factors (HIFs), which induce the expression of a wide range of genes that help cells adapt to a hypoxic environment. Basic mechanisms of adaptation to hypoxia, and particularly HIF functions, have being extensively studied over recent decades, leading to the 2019 Nobel Prize in Physiology or Medicine. Based on their pivotal physiological importance, HIFs are attracting increasing attention as a new potential target for treating a large number of hypoxia-associated diseases. Most of the experimental work related to HIFs has focused on roles in the liver and kidney. However, increasing evidence clearly demonstrates that HIF-based responses represent an universal adaptation mechanism in all tissue types, including the central nervous system (CNS). In the CNS, HIFs are critically involved in the regulation of neurogenesis, nerve cell differentiation, and neuronal apoptosis. In this mini-review, we provide an overview of the complex role of HIF-1 in the adaptation of neurons and glia cells to hypoxia, with a focus on its potential involvement into various neuronal pathologies and on its possible role as a novel therapeutic target.

Discovery of neuroprotective agents that inhibit human prolyl hydroxylase PHD2

Prolyl hydroxylase (PHD) enzymes play a critical role in the cellular responses to hypoxia through their regulation of the hypoxia inducible factor α (HIF-α) transcription factors. PHD inhibitors show promise for the treatment of diseases including anaemia, cardiovascular disease and stroke. In this work, a pharmacophore-based virtual high throughput screen was used to identify novel potential inhibitors of human PHD2. Two moderately potent new inhibitors were discovered, with IC50 values of 4 μM and 23 μM respectively. Cell-based studies demonstrate that these compounds exhibit protective activity in neuroblastoma cells, suggesting that they have the potential to be developed into clinically useful neuroprotective agents.

Hypoxia-inducible factor prolyl hydroxylase domain (PHD) inhibition after contusive spinal cord injury does not improve locomotor recovery

Traumatic spinal cord injury (SCI) is a devastating neurological condition that involves both primary and secondary tissue loss. Various cytotoxic events including hypoxia, hemorrhage and blood lysis, bioenergetic failure, oxidative stress, endoplasmic reticulum (ER) stress, and neuroinflammation contribute to secondary injury. The HIF prolyl hydroxylase domain (PHD/EGLN) family of proteins are iron-dependent, oxygen-sensing enzymes that regulate the stability of hypoxia inducible factor-1α (HIF-1α) and also mediate oxidative stress caused by free iron liberated from the lysis of blood. PHD inhibition improves outcome after experimental intracerebral hemorrhage (ICH) by reducing activating transcription factor 4 (ATF4)-driven neuronal death. As the ATF4-CHOP (CCAAT-enhancer-binding protein homologous protein) pathway plays a role in the pathogenesis of contusive SCI, we examined the effects of PHD inhibition in a mouse model of moderate T9 contusive SCI in which white matter damage is the primary driver of locomotor dysfunction. Pharmacological inhibition of PHDs using adaptaquin (AQ) moderately lowers acute induction of Atf4 and Chop mRNAs and prevents the acute decline of oligodendrocyte (OL) lineage mRNAs, but does not improve long-term recovery of hindlimb locomotion or increase chronic white matter sparing. Conditional genetic ablation of all three PHD isoenzymes in OLs did not affect Atf4, Chop or OL mRNAs expression levels, locomotor recovery, and white matter sparing after SCI. Hence, PHDs may not be suitable targets to improve outcomes in traumatic CNS pathologies that involve acute white matter injury.

Hypoxia-inducible Factor 2α Exerts Neuroprotective Effects by Promoting Angiogenesis via the VEGF/Notch Pathway after Intracerebral Hemorrhage Injury in Rats

Angiogenesis after intracerebral hemorrhage (ICH) injury can effectively alleviate brain damage and improve neurological function. Hypoxia-inducible factor 2α (HIF-2α) is an important angiogenic regulator and exhibits protective effects in several neurological diseases; however, its role in ICH has not yet been reported. Hence, in the present study, we explored whether HIF-2α reduces ICH injury by promoting angiogenesis. In addition, we explored the role of the vascular endothelial growth factor (VEGF)/Notch pathway in HIF-2α-mediated angiogenesis. We injected 50 μL of autologous blood taken from the femoral artery into the right striatum of healthy male adult Sprague-Dawley rats to create an autologous-blood-induced rat model of ICH. Lentiviral vectors were injected to both overexpress and knock down HIF-2α expression. VEGF receptor 2 (VEGFR2) and Notch-specific inhibitors were injected intraperitoneally to block VEGFR2- and Notch-mediated signaling after lentiviral injections. Our data showed that HIF-2α overexpression reduced neurological-damage scores and brain-water content, suggesting it had a protective effect on ICH injury. In addition, overexpression of HIF-2α promoted angiogenesis, increased focal cerebral blood flow (CBF), and reduced neuronal damage, whereas HIF-2α knockdown resulted in the opposite effects. Furthermore, we found that HIF-2α-mediated angiogenesis was blocked by a Notch-specific inhibitor. Likewise, the HIF-2α-mediated increase in phospho-VEGFR-2, cleaved-Notch1 and Notch1 expression was reversed via a VEGFR2-specific inhibitor. Taken together, our results indicate that HIF-2α promotes angiogenesis via the VEGF/Notch pathway to attenuate ICH injury. Moreover, our findings may contribute to the development of a novel strategy for alleviating ICH injury via HIF-2α-mediated upregulation of angiogenesis.

Efficacy of an Oncolytic Adenovirus Driven by a Chimeric Promoter and Armed with Decorin Against Renal Cell Carcinoma

Virus-targeted therapy for tumors can effectively prolong the survival rate of patients and has become a new trend for cancer biotherapy. Oncolytic adenovirus (OAd) can specifically replicate in tumor cells, allowing the therapeutic genes carried to be rapidly copied. As known, solid tumors are always hypoxic, and researchers often overlook a key point, the replication of OAd depends not only on its own activity but also on the cellular hypoxic environment in which the virus replicates. In this study, we constructed an OAd carrying Decorin, HRE-Ki67-Decorin, combining the Ki67 promoter upstreamed with hypoxia-response element (HRE) sequences to drive adenoviral E1A. The OAd HRE-Ki67-Decorin had better replication ability under hypoxic conditions, downregulated cellular immunosuppressed growth factor TGF-β. In addition, HRE-Ki67-Decorin was potent in suppressing tumor growth and participated in the assembly of tumor extracellular matrix by expressing Decorin in subcutaneous renal cancer cell tumor models. Tumor sections from HRE-Ki67-Decorin-treated tissues had less collagen fibers and more spread of virus among tumor tissues. These results indicated that chimeric HRE-Ki67 promoter-regulated OAd carrying Decorin might be an effective anticancer treatment strategy.

Inhibition of Endothelial PHD2 Suppresses Post-Ischemic Kidney Inflammation through Hypoxia-Inducible Factor-1

BACKGROUND

Prolyl-4-hydroxylase domain-containing proteins 1-3 (PHD1 to PHD3) regulate the activity of the hypoxia-inducible factors (HIFs) HIF-1 and HIF-2, transcription factors that are key regulators of hypoxic vascular responses. We previously reported that deficiency of endothelial HIF-2 exacerbated renal ischemia-reperfusion injury, whereas inactivation of endothelial PHD2, the main oxygen sensor, provided renoprotection. Nevertheless, the molecular mechanisms by which endothelial PHD2 dictates AKI outcomes remain undefined.

METHODS

To investigate the function of the endothelial PHD2/HIF axis in ischemic AKI, we examined the effects of endothelial-specific ablation of PHD2 in a mouse model of renal ischemia-reperfusion injury. We also interrogated the contribution of each HIF isoform by concurrent endothelial deletion of both PHD2 and HIF-1 or both PHD2 and HIF-2.

RESULTS

Endothelial deletion of Phd2 preserved kidney function and limited transition to CKD. Mechanistically, we found that endothelial Phd2 ablation protected against renal ischemia-reperfusion injury by suppressing the expression of proinflammatory genes and recruitment of inflammatory cells in a manner that was dependent on HIF-1 but not HIF-2. Persistence of renoprotective responses after acute inducible endothelial-specific loss of Phd2 in adult mice ruled out a requirement for PHD2 signaling in hematopoietic cells. Although Phd2 inhibition was not sufficient to induce detectable HIF activity in the kidney endothelium, in vitro experiments implicated a humoral factor in the anti-inflammatory effects generated by endothelial PHD2/HIF-1 signaling.

CONCLUSIONS

Our findings suggest that activation of endothelial HIF-1 signaling through PHD2 inhibition may offer a novel therapeutic approach against ischemic AKI.

Exosomal miRNAs in central nervous system diseases: biomarkers, pathological mediators, protective factors and therapeutic agents

Exosomes are small bilipid layer-enclosed extracellular vesicles that can be found in tissues and biological fluids. As a key cell-to-cell and distant communication mediator, exosomes are involved in various central nervous system (CNS) diseases, potentially through transferring their contents such as proteins, lipids and nucleic acids to the target cells. Exosomal miRNAs, which are small non-coding RNAs in the exosomes, are known to be more stable than free miRNAs and therefore have lasting effects on disease-related gene expressions. There are distinct profiles of exosomal miRNAs in different types of CNS diseases even before the onset of irreversible neurological damages, indicating that exosomal miRNAs within tissues and biological fluids could serve as promising biomarkers. Emerging evidence has also demonstrated the pathological effects of several exosomal miRNAs in CNS diseases via specific modulation of disease-related factors. Moreover, exosomes carry therapeutically beneficial miRNAs across the blood-brain-barrier, which can be exploited as a powerful drug delivery tool to help alleviating multiple CNS diseases. In this review, we summarize the recent progress made in understanding the biological roles of exosomal miRNAs as potential diagnostic biomarkers, pathological regulators, and therapeutic targets/drugs for CNS diseases. A comprehensive discussion of the main concerns and challenges for the applications of exosomal miRNAs in the clinical setting is also provided.

The neuronal oxygen-sensing pathway controls postnatal vascularization of the murine brain

The contribution of neurons to growth and refinement of the microvasculature during postnatal brain development is only partially understood. Tissue hypoxia is the physiologic stimulus for angiogenesis by enhancing angiogenic mediators partly through activation of hypoxia-inducible factors (HIFs). Hence, we investigated the HIF oxygen-sensing pathway in postmitotic neurons for physiologic angiogenesis in the murine forebrain during postnatal development by using mice lacking the HIF suppressing enzyme prolyl-4-hydroxylase domain (PHD)2 and/or HIF-1/2α in postmitotic neurons. Perinatal activation or inactivation of the HIF pathway in neurons inversely modulated brain vascularization, including endothelial cell number and proliferation, density of total and perfused microvessels, and vascular branching. Accordingly, several angiogenesis-related genes were up-regulated in vivo and in primary neurons derived from PHD2-deficient mice. Among them, only VEGF and adrenomedullin (Adm) promoted angiogenic sprouting of brain endothelial cells. VEGF and Adm additively enhanced endothelial sprouting through activation of multiple pathways. PHD2 deficiency in neurons caused HIF-α stabilization and increased VEGF mRNA levels not only in neurons but unexpectedly also in astrocytes, suggesting a new mechanism of neuron-to-astrocyte signaling. Collectively, our results identify the PHD-HIF pathway in neurons as an important determinant for vascularization of the brain during postnatal development.-Nasyrov, E., Nolan, K. A., Wenger, R. H., Marti, H. H., Kunze, R. The neuronal oxygen-sensing pathway controls postnatal vascularization of the murine brain.

Sex differences in neonatal mouse brain injury after hypoxia-ischemia and adaptaquin treatment

Hypoxia-inducible factor prolyl 4-hydroxylases (HIF-PHDs) are important targets against oxidative stress. We hypothesized that inhibition HIF-PHD by adaptaquin reduces hypoxic-ischemic brain injury in a neonatal mouse model. The pups were treated intraperitoneally immediately with adaptaquin after hypoxia-ischemia (HI) and then every 24 h for 3 days. Adaptaquin treatment reduced infarction volume by an average of 26.3% at 72 h after HI compared to vehicle alone, and this reduction was more pronounced in males (34.8%) than in females (11.7%). The protection was also more pronounced in the cortex. The subcortical white matter injury as measured by tissue loss volume was reduced by 24.4% in the adaptaquin treatment group, and this reduction was also more pronounced in males (28.4%) than in females (18.9%). Cell death was decreased in the cortex as indicated by Fluoro-Jade labeling, but not in other brain regions with adaptaquin treatment. Furthermore, in the brain injury area, adaptaquin did not alter the number of cells positive for caspase-3 activation or translocation of apoptosis-inducing factor to the nuclei. Adaptaquin treatment increased glutathione peroxidase 4 mRNA expression in the cortex but had no impact on 3-nitrotyrosine, 8-hydroxy-2 deoxyguanosine, or malondialdehyde production. Hif1α mRNA expression increased after HI, and adaptaquin treatment also stimulated Hif1α mRNA expression, which was also more pronounced in males than in females. However, nuclear translocation of HIF1α protein was decreased after HI, and adaptaquin treatment had no influence on HIF1α expression in the nucleus. These findings demonstrate that adaptaquin treatment is neuroprotective, but the potential mechanisms need further investigation. Read the Editorial Highlight for this article on page 645.

Dual Effects of Chinese Herbal Medicines on Angiogenesis in Cancer and Ischemic Stroke Treatments: Role of HIF-1 Network

Hypoxia-inducible factor-1 (HIF-1)–induced angiogenesis has been involved in numerous pathological conditions, and it may be harmful or beneficial depending on the types of diseases. Exploration on angiogenesis has sparked hopes in providing novel therapeutic approaches on multiple diseases with high mortality rates, such as cancer and ischemic stroke. The HIF-1 pathway is considered to be a major regulator of angiogenesis. HIF-1 seems to be involved in the vascular formation process by synergistic correlations with other proangiogenic factors in cancer and cerebrovascular disease. The regulation of HIF-1–dependent angiogenesis is related to the modulation of HIF-1 bioactivity by regulating HIF-1α transcription or protein translation, HIF-1α DNA binding, HIF-1α and HIF-1α dimerization, and HIF-1 degradation. Traditional Chinese herbal medicines have a long history of clinical use in both cancer and stroke treatments in Asia. Growing evidence has demonstrated potential proangiogenic benefits of Chinese herbal medicines in ischemic stroke, whereas tumor angiogenesis could be inhibited by the active components in Chinese herbal medicines. The objective of this review is to provide comprehensive insight on the effects of Chinese herbal medicines on angiogenesis by regulating HIF-1 pathways in both cancer and ischemic stroke.

Angioneurins - Key regulators of blood-brain barrier integrity during hypoxic and ischemic brain injury

The loss of blood-brain barrier (BBB) integrity leading to vasogenic edema and brain swelling is a common feature of hypoxic/ischemic brain diseases such as stroke, but is also central to the etiology of other CNS disorders. In the past decades, numerous proteins, belonging to the family of angioneurins, have gained increasing attention as potential therapeutic targets for ischemic stroke, but also other CNS diseases attributed to BBB dysfunction. Angioneurins encompass mediators that affect both neuronal and vascular function. Recently, increasing evidence has been accumulated that certain angioneurins critically determine disease progression and outcome in stroke among others through multifaceted effects on the compromised BBB. Here, we will give a concise overview about the family of angioneurins. We further describe the most important cellular and molecular components that contribute to structural integrity and low permeability of the BBB under steady-state conditions. We then discuss BBB alterations in ischemic stroke, and highlight underlying cellular and molecular mechanisms. For the most prominent angioneurin family members including vascular endothelial growth factors, angiopoietins, platelet-derived growth factors and erythropoietin, we will summarize current scientific literature from experimental studies in animal models, and if available from clinical trials, on the following points: (i) spatiotemporal expression of these factors in the healthy and hypoxic/ischemic CNS, (ii) impact of loss- or gain-of-function during cerebral hypoxia/ischemia for BBB integrity and beyond, and (iii) potential underlying molecular mechanisms. Moreover, we will highlight novel therapeutic strategies based on the activation of endogenous angioneurins that might improve BBB dysfuntion during ischemic stroke.

EphB2-dependent signaling promotes neuronal excitotoxicity and inflammation in the acute phase of ischemic stroke

Local cerebral hypoperfusion causes ischemic stroke while driving multiple cell-specific responses including inflammation, glutamate-induced neurotoxicity mediated via NMDAR, edema formation and angiogenesis. Despite the relevance of these pathophysiological mechanisms for disease progression and outcome, molecular determinants controlling the onset of these processes are only partially understood. In this context, our study intended to investigate the functional role of EphB2, a receptor tyrosine kinase that is crucial for synapse function and binds to membrane-associated ephrin-B ligands.

Cerebral ischemia was induced in Ephb2^−/− mice by transient middle cerebral artery occlusion followed by different times (6, 12, 24 and 48 h) of reperfusion. Histological, neurofunctional and transcriptome analyses indicated an increase in EphB2 phosphorylation under these conditions and attenuated progression of stroke in Ephb2^−/− mice. Moreover, while infiltration of microglia/macrophages and astrocytes into the peri-infarct region was not altered, expression of the pro-inflammatory mediators MCP-1 and IL-6 was decreased in these mice. In vitro analyses indicated that binding of EphB2 to astrocytic ephrin-B ligands stimulates NF-κB-mediated cytokine expression via the MAPK pathway. Further magnetic resonance imaging of the Ephb2^−/− ischemic brain revealed a lower level of cytotoxic edema formation within 6 h upon onset of reperfusion. On the mechanistic level, absence of neuronal EphB2 decreased the mitochondrial Ca²⁺ load upon specific activation of NMDAR but not during synaptic activity. Furthermore, neuron-specific loss of ephrin-B2 reduced the extent of cerebral tissue damage in the acute phase of ischemic stroke.

Collectively, EphB2 may promote the immediate response to an ischemia-reperfusion event in the central nervous system by (i) pro-inflammatory activation of astrocytes via ephrin-B-dependent signaling and (ii) amplification of NMDA-evoked neuronal excitotoxicity.

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.

Prolyl hydroxylase domain inhibitors: can multiple mechanisms be an opportunity for ischemic stroke?

Stroke and cerebrovascular disease are now the fifth most common cause of death behind other diseases such as heart, cancer and respiratory disease and accounts for approximately 40-50 fatalities per 100,000 people each year in the United States. Currently the only therapy for acute stroke, is intravenous administration of tissue plasminogen activator which was approved in 1996 by the FDA. Surprisingly no new treatments have come on the market since, although endovascular mechanical thrombectomy is showing promising results in trials. Recently focus has shifted towards a preventative therapy rather than trying to reverse or limit the amount of damage occurring following stroke onset. During one of the components of ischemia, hypoxia, a number of physiological changes occur within neurons which include the stabilization of hypoxia-inducible factors. The activity of these proteins is regulated by O₂, Fe²⁺, 2-OG and ascorbate-dependant hydroxylases which contain prolyl-4-hydroxylase domains (PHDs). PHD inhibitors are capable of pharmacologically activating the body's own endogenous adaptive response to low levels of oxygen and have therefore become an attractive therapeutic target for treating ischemia. They have been widely used in the periphery and have been shown to have a preconditioning and protective effect against a later and more severe ischemic insult. Currently there are a number of these agents in phase 1, 2 and 3 clinical trials for the treatment of anemia. In this review we assess the neuroprotective effects of PHD inhibitors, including dimethyloxalylglycine and deferoxamine and suggest that not all of their effects in the CNS are HIF-dependent. Unravelling new roles and a better understanding of the function of PHD inhibitors in the CNS may be of great benefit especially when investigating their use in the treatment of stroke and other ischemic diseases.

Reactive Oxygen Species Formation in the Brain at Different Oxygen Levels: The Role of Hypoxia Inducible Factors

Hypoxia inducible factor (HIF) is the master oxygen sensor within cells and is central to the regulation of cell responses to varying oxygen levels. HIF activation during hypoxia ensures optimum ATP production and cell integrity, and is associated both directly and indirectly with reactive oxygen species (ROS) formation. HIF activation can either reduce ROS formation by suppressing the function of mitochondrial tricarboxylic acid cycle (TCA cycle), or increase ROS formation via NADPH oxidase (NOX), a target gene of HIF pathway. ROS is an unavoidable consequence of aerobic metabolism. In normal conditions (i.e., physioxia), ROS is produced at minimal levels and acts as a signaling molecule subject to the dedicated balance between ROS production and scavenging. Changes in oxygen concentrations affect ROS formation. When ROS levels exceed defense mechanisms, ROS causes oxidative stress. Increased ROS levels can also be a contributing factor to HIF stabilization during hypoxia and reoxygenation. In this review, we systemically review HIF activation and ROS formation in the brain during hypoxia and hypoxia/reoxygenation. We will then explore the literature describing how changes in HIF levels might provide pharmacological targets for effective ischaemic stroke treatment. HIF accumulation in the brain via HIF prolyl hydroxylase (PHD) inhibition is proposed as an effective therapy for ischaemia stroke due to its antioxidation and anti-inflammatory properties in addition to HIF pro-survival signaling. PHD is a key regulator of HIF levels in cells. Pharmacological inhibition of PHD increases HIF levels in normoxia (i.e., at 20.9% O₂ level). Preconditioning with HIF PHD inhibitors show a neuroprotective effect in both in vitro and in vivo ischaemia stroke models, but post-stroke treatment with PHD inhibitors remains debatable. HIF PHD inhibition during reperfusion can reduce ROS formation and activate a number of cellular survival pathways. Given agents targeting individual molecules in the ischaemic cascade (e.g., antioxidants) fail to be translated in the clinic setting, thus far, HIF pathway targeting and thereby impacting entire physiological networks is a promising drug target for reducing the adverse effects of ischaemic stroke.

Knockdown of HIF-1α impairs post-ischemic vascular reconstruction in the brain via deficient homing and sprouting bmEPCs

Although the critical role of hypoxia inducible factor-1α (HIF-1α) in cerebral neovascularization after stroke has been well characterized, the details regarding the regulation of endothelial progenitor cell (EPC)-dependent neovascularization by HIF-1α are not completely understood. Using lentiviral shRNA to knockdown HIF-1α, we showed that HIF-1α plays a central role in bone marrow-derived EPC (bmEPC) homing and sprouting in the post-acute stage of ischemic Sprague Dawley (SD) rat brains. First, knockdown of HIF-1α decreased the homing of both endogenous and exogenous bmEPCs to the ischemic brain. Additionally, the knockdown impaired the incorporation and sprouting of bmEPCs in the ischemic brain. In vitro, knockdown of HIF-1α inhibited the spheroid sprouting and tube formation of bmEPCs. Mechanically, the HIF-1α-dependent recruitment of bmEPCs to the ischemic brain was relative to the CXCL12/CXCR4 axis and HMGB1, which were relative to astrocytes. In addition, the loss of HIF-1α resulted in deficient expression levels of VEGF-A, Flk-1, NRP1, and Dll4 in the ischemic brains, bmEPCs, and astrocytes. These findings suggested that HIF-1α implicates in bmEPC homing via CXCL12/CXCR4 and HMGB1 and that it promotes bmEPC sprouting via VEGF-A/flk1-NRP1/Dll4.

Role of Nitric Oxide and Hydrogen Sulfide in Ischemic Stroke and the Emergent Epigenetic Underpinnings

Nitric oxide (NO) and hydrogen sulfide (H₂S) are the key gasotransmitters with an imperious role in the maintenance of cerebrovascular homeostasis. A decline in their levels contributes to endothelial dysfunction that portends ischemic stroke (IS) or cerebral ischemia/reperfusion (CI/R). Nevertheless, their exorbitant production during CI/R is associated with exacerbation of cerebrovascular injury in the post-stroke epoch. NO-producing nitric oxide synthases are implicated in IS pathology and their activity is regulated, inter alia, by various post-translational modifications and chromatin-based mechanisms. These account for heterogeneous alterations in NO production in a disease setting like IS. Interestingly, NO per se has been posited as an endogenous epigenetic modulator. Further, there is compelling evidence for an ingenious crosstalk between NO and H₂S in effecting the canonical (direct) and non-canonical (off-target collateral) functions. In this regard, NO-mediated S-nitrosylation and H₂S-mediated S-sulfhydration of specific reactive thiols in an expanding array of target proteins are the principal modalities mediating the all-pervasive influence of NO and H₂S on cell fate in an ischemic brain. An integrated stress response subsuming unfolded protein response and autophagy to cellular stressors like endoplasmic reticulum stress, in part, is entrenched in such signaling modalities that substantiate the role of NO and H₂S in priming the cells for stress response. The precis presented here provides a comprehension on the multifarious actions of NO and H₂S and their epigenetic underpinnings, their crosstalk in maintenance of cerebrovascular homeostasis, and their "Janus bifrons" effect in IS milieu together with plausible therapeutic implications.

Shengui Sansheng San extraction is an angiogenic switch via regulations of AKT/mTOR, ERK1/2 and Notch1 signal pathways after ischemic stroke

BACKGROUND

As a traditional Chinese herbal formula, Shengui Sansheng San (SSS) has been employed for stroke treatment more than 300 years.

PURPOSE

We hypothesize that SSS extraction is an angiogenic switch in penumbra post-stroke, and corresponding mechanisms are investigated.

METHODS

In present study, rats were subjected to permanent middle cerebral artery occlusion model (MCAo) and were treated with low, middle and high doses of SSS extraction. We assessed neurological function and survival rate, and measured infarct volume by 2,3,5-triphenyltetrazolium chloride staining on day 7 after ischemia. von Willebrand factor (vWF), stromal cell-derived factor-1 alpha (SDF-1α) /chemokine (C-X-C motif) receptor 4 (CXCR4) axis, vascular endothelial growth factor (VEGF)/VEGF receptor 2 (VEGFR2) as well as protein kinase B (AKT)/mammalian target of rapamycin (mTOR) /hypoxia-inducible factor-1 alpha (HIF-1α), extracellular signal-regulated kinase 1/2 (ERK1/2) and Notch1 signaling pathways were respectively investigated by immunofluorescence assay or western blotting in vivo and oxygen-glucose-deprived (OGD) brain microvascular endothelial cells (BMECs); simultaneously, wound healing of BMECs and tube formation assay were administrated.

RESULTS

Compared to MCAo group, SSS extraction could significantly improve neurological functional scores, survival rate and cerebral infarct volume, enhance vWF⁺ vascular density and perimeter, SDF-1α/CXCR4 axis, VEGF expression, as well as activate AKT/mTOR/HIF-1α and ERK1/2 and inhibit Notch1 pathways in penumbra. In vitro, containing SSS extraction serum increased BMEC migration, capillary formation and VEGF expression via up-regulations of AKT/mTOR and ERK1/2 pathways in OGD BMECs, but ERK inhibitor (U0126) reversed the result of VEGF expression in high dose of SSS group. Additionally, VEGFR2 and Notch1 expressions were suppressed by containing SSS extraction serum. All results were in dose dependent manner.

CONCLUSION

Our study firstly demonstrates that SSS extraction is an angiogenic switch. Due to suppressed VEGFR2/Notch1 cascades and activated AKT/mTOR and ERK1/2 signals in BMECs, a feedback loop of angiogenic homeostasis is established. Furthermore, the comprehensive mediations of SDF-1α/CXCR4 axis, AKT/mTOR/HIF-α, ERK1/2 and Notch1 pathways in penumbra contribute to the improvements of neurological function, survival rate and infarct volume post-stroke.

Expression of Hypoxia Inducible Factor 1alpha Is Protein Kinase A-dependent in Primary Cortical Astrocytes Exposed to Severe Hypoxia

The hypoxia inducible factor 1 (HIF-1) and the cyclic AMP-responsive element binding protein (CREB) are two transcription factors that have been studied in the context of neuronal survival and neurodegeneration. HIF-1 upregulation and CREB activation have been observed not only in neurons but also in astrocytes under conditions of hypoxia. We hypothesized that activation of CREB regulate HIF-1α expression in the nucleus of cortical astrocytes under in vitro ischemic condition. To test the hypothesis, we determined the effects of inhibiting the CREB activation pathway on the expression of HIF-1α protein in astrocytes exposed to CoCl₂ and severe hypoxia (near anoxia, 0.1% O₂). The results demonstrated that inhibition of CaMKII and CaMKIV had no effect on both HIF-1α and pCREB expression in cortical astrocytes exposed to CoCl₂ and anoxia. In contrast, PKA inhibition lowered the expression of HIF-1α and pCREB expression. Furthermore, the inhibition of PKA but not CaMKII or CaMKIV increased cell death of astrocytes exposed to near anoxia. The results suggest that PKA plays an important role in the cell survival signaling pathways in astrocytes.

Differential regulation of angiogenesis in the developing mouse brain in response to exogenous activation of the hypoxia-inducible transcription factor system

Angiogenesis due to hypoxic-ischemic (HI) injury represents a crucial compensatory mechanism of the developing brain that is mainly regulated by hypoxia-inducible transcription factors (HIF). Pharmacological stimulation of HIF is suggested as a neuroprotective option, however, studies of its effects on vascular development are limited. We analyzed the influence of the prolyl-4-hydroxylase inhibitor (PHI), FG-4497, and erythropoietin (rhEPO) on post-hypoxic angiogenesis (angiogenic growth factors, vessel structures) in the developing mouse brain (P7) assessed after a regeneration period of 72 h. Exposure to systemic hypoxia (8% O₂, 6 h) was followed by treatment (i.p.) with rhEPO (2500/5000 IU/kg) at 0, 24 and 48 h or FG-4497 (60/100 mg/kg) compared to controls. In response to FG-4497 treatment cortical and hippocampal vessel area and branching were significantly increased compared to controls. This was associated with elevated ANGPT-2 as well as decreased ANGPT-1 and TIE-2 mRNA levels. In response to rhEPO, mildly increased angiogenesis was associated with elevated ANGPT-2 but also TIE-2 mRNA levels in comparison to controls. In conclusion, present data demonstrate a differential regulation of the angiopoietin/TIE-2 system in response to PHI and rhEPO in the post-hypoxic developing brain pointing to potential functional consequences for vascular regeneration and vessel development.

Preferential activation of HIF-2α adaptive signalling in neuronal-like cells in response to acute hypoxia

Stroke causes severe neuronal damage as disrupted cerebral blood flow starves neurons of oxygen and glucose. The hypoxia inducible factors (HIF-1α and HIF-2α) orchestrate oxygen homeostasis and regulate specific aspects of hypoxic adaptation. Here we show the importance of HIF-2α dependant signalling in neuronal adaptation to hypoxic insult. PC12 and NT2 cells were differentiated into neuronal-like cells using NGF and retinoic acid, and exposed to acute hypoxia (1% O₂). Gene and protein expression was analysed by qPCR and immunoblotting and the neuronal-like phenotype was examined. PC12 and NT2 differentiation promoted neurite extension and expression of neuronal markers, NSE and KCC2. Induction of HIF-1α mRNA or protein was not detected in hypoxic neuronal-like cells, however marked induction of HIF-2α mRNA and protein expression was observed. Induction of HIF-1α target genes was also not detected in response to acute hypoxia, however significant induction of HIF-2α transcriptional targets was clearly evident. Furthermore, hypoxic insult dramatically reduced both neurite number and length, and attenuated expression of neuronal markers, NSE and KCC2. This correlated with an increase in expression of the neural progenitor and stem cell-like markers, CD44 and vimentin, suggesting HIF-2α molecular mechanisms could potentially promote regression of neuronal-like cells to a stem-like state and trigger neuronal recovery following ischaemic insult. Our findings suggest the HIF-2α pathway predominates over HIF-1α signalling in neuronal-like cells following acute hypoxia.

Acute cardiac support with intravenous milrinone promotes recovery from early brain injury in a murine model of severe subarachnoid haemorrhage

Early brain injury/ischaemia (EBI) is a serious complication early after subarachnoid haemorrhage (SAH) that contributes to development of delayed cerebral ischaemia (DCI). This study aimed to determine the role of inotropic cardiac support using milrinone (MIL) on restoring acute cerebral hypoperfusion attributable to EBI and improving outcomes after experimental SAH. Forty-three male C57BL/6 mice were assigned to either sham surgery (SAH-sham), SAH induced by endovascular perforation plus postconditioning with 2% isoflurane (Control), or SAH plus isoflurane combined with MIL with and without hypoxia-inducible factor inhibitor (HIF-I) pretreatment. Cardiac output (CO) during intravenous MIL infusion (0.25-0.75 μg/kg/min) between 1.5 and 2.5 hours after SAH induction was monitored with Doppler echocardiography. Magnetic resonance imaging (MRI)-continuous arterial spin labelling was used for quantitative cerebral blood flow (CBF) measurements. Neurobehavioral function was assessed daily by neurological score and open field test. DCI was analyzed 3 days later by determining infarction on MRI. Mild reduction of cardiac output (CO) and global cerebral blood flow (CBF) depression were notable early after SAH. MIL increased CO in a dose-dependent manner (P<.001), which was accompanied by improved hypoperfusion, incidence of DCI and functional recovery than Control (P<.05). The neuroprotective effects afforded by MIL or Control were attenuated by hypoxia-inducible factor (HIF) inhibition (P<.05). These results suggest that MIL improves acute hypoperfusion by its inotropic effect, leading to neurobehavioral improvement in mice after severe SAH, in which HIF may be acting as a critical mediator.

Relative Contribution of Prolyl Hydroxylase-Dependent and -Independent Degradation of HIF-1alpha by Proteasomal Pathways in Cerebral Ischemia

Hypoxia inducible factor-1 (HIF-1) is a key regulator in hypoxia and can determine the fate of brain cells during ischemia. However, the mechanism of HIF-1 regulation is still not fully understood in ischemic brains. We tested a hypothesis that both the 26S and the 20S proteasomal pathways were involved in HIF-1α degradation under ischemic conditions. Using in vitro ischemic model (oxygen and glucose deprivation) and a mouse model of middle cerebral artery occlusion, we tested effects of inhibitors of proteasomes and prolyl hydroxylase (PHD) on HIF-1α stability and brain injury in cerebral ischemia. We observed that 30 and 60 min of oxygen-glucose deprivation significantly increased the 20S proteasomal activity. We demonstrated that proteasome inhibitors increased HIF-1α stabilization and cell viability and were more effective than PHD inhibitors in primary cultured cortical neurons exposed to oxygen and glucose deprivation. Furthermore, the administration of the proteasome inhibitor, epoxomicin, to mice resulted in smaller infarct size and brain edema than a PHD inhibitor. Our results indicate that 20S proteasomes are involved in HIF-1α degradation in ischemic neurons and that proteasomal inhibition provides more HIF-1α stabilization and neuroprotection than PHD inhibition in cerebral ischemia.

Lyophilized Powder of Catalpol and Puerarin Protected Cerebral Vessels from Ischemia by Its Anti-apoptosis on Endothelial Cells

Catalpol and puerarin are two monomers of Rehmannia glutinosa and Lobed Kudzuvine Root, which are two herbs commonly used together in ancient prescriptions of traditional Chinese medicine for cerebral ischemia. Our previous study shows that the lyophilized powder of the two monomers improved the outcome of cerebral ischemia excellently in rodents. However, if it protects vessels from ischemia is unknown. The present research studied the protection of lyophilized powder of catalpol and puerarin (CP) on endothelial cells and the relative mechanism in vivo and in vitro. Middle cerebral artery occlusion (MCAO) rats were used to study the improvement of CP on neurological deficiency, regional cerebral blood flow (rCBF), and infarct volume. The morphology of vessels and the apoptosis of brain vascular endothelial cells (BVECs) were observed and detected by immunohistochemistry approaches. To study how CP protected primary BVECs (pBVECs) from ischemic penumbra, oxygen glucose deprivation (OGD)-damaged pBVECs were cultured in the condition of insufficient nutrition and low oxygen which recapitulate the low perfusion of ischemic penumbra. Using the cell model, the mechanism by which CP protected pBVECs was studied by shRNA and pathway inhibitors. CP at the dose of 65.4 mg/kg increased regional cerebral blood flow (rCBF), reduced infarct volume, protected vessel integrity and inhibited endothelial cell apoptosis in vivo. But it only improved rCBF, vessel integrity and BVECs apoptosis at the dose of 32.7 mg/kg. In vitro, the protection of CP on pBVECs was proved to be ERK/HIF-1a- and PI3K/AKT/mTOR/HIF-1a-dependent. This study indicates a possibility of CP being a new drug for cerebral ischemia. Besides, this research provides an alternative cell model for penumbra ECs study.

Clinical significance of changes in serum neuroglobin and HIF-1α concentrations during the early-phase of acute ischemic stroke

BACKGROUND

Neuroglobin (NGB) has been described as a neuroprotective agent in cerebral ischemia, hypoxia inducible factor (HIF) has shown an important role in modulating hypoxic and ischemic injury, and therefore they have the potential to impact outcomes after acute ischemic stroke (AIS). Thus, we investigated early changes in the concentrations of serum NGB and HIF-1α after AIS and evaluated the relations of both NGB and HIF-1α to stroke severity and prognosis.

METHODS

We prospectively measured the serum concentrations of NGB and HIF-1α in 40 patients with AIS at 24, 48, 72, and 96h after stroke. Correlation combined with infarct size and National Institutes of Health Stroke Scale (NIHSS) score of the patients was analyzed. Receiver operating characteristic (ROC) curve was used to appraise their value in predicting the 90-day outcome after AIS.

RESULTS

Serum NGB concentrations increased and peaked at 72h after AIS, whereas serum concentrations of HIF-1α increased for 48h. Peak serum NGB concentration correlated significantly with both infarct size (R²=0.484, p<0.001) and admission NIHSS score (R²=0.578, p<0.001), while serum HIF-1α concentration was only correlated to a patient's infarct size (R²=0.394, p<0.001). ROC curve analysis suggested that the serum NGB concentration had a significantly better predictive power for poor outcome.

CONCLUSIONS

NGB level increased in serum after AIS accompanied by increases in serum HIF-1α, and was suggested as a predictor of stroke severity and poor prognosis.

Role of HIF-1α in the hypoxia inducible expression of the thiamine transporter, SLC19A3

Ensuring continuous intracellular supply of thiamine is essential to maintain metabolism. Cellular homeostasis requires the function of the membrane bound thiamine transporters THTR1 and THTR2. In the absence of increased dietary intake of thiamine, varying intracellular levels to meet metabolic demands during pathophysiological stressors, such as hypoxia, requires adaptive regulatory mechanisms to increase thiamine transport capacity. Previous work has established the up-regulation of SLC19A3 (THTR2) gene expression and activity during hypoxic stress through the activity of the hypoxia inducible transcription factor 1 alpha (HIF-1α). However, it is unknown whether HIF-1α acts directly or indirectly to trans-activate expression of SLC19A3. This work utilized the breast cancer cell line BT-474 treated with 1% O2 or a hypoxia chemical mimetic deferoxamine to determine the minimal promoter region of SLC19A3 responsible for hypoxia responsiveness. In silico sequence analysis determined two contiguous hypoxia responsive elements in close proximity to the transcriptional start site of the SLC19A3 gene. Using a HIF-1α transcriptional factor ELISA assay, HIF-1α was capable of binding to a dsDNA construct of the SLC19A3 minimal promoter. Chromatin immunoprecipitation assay established that SP1 was bound to the SLC19A3 minimal promoter region under normoxic conditions. However, HIF-1α binding to the minimal promoter region occurred during hypoxic treatments, while no SP1 binding was observed under these conditions. This work demonstrates the direct binding and activation of SLC19A3 expression by HIF-1α during hypoxic stress, suggesting an important adaptive regulatory role for HIF-1α in maintaining thiamine homeostasis.

Inotropic support against early brain injury improves cerebral hypoperfusion and outcomes in a murine model of subarachnoid hemorrhage

Early brain injury/ischemia is a recent therapeutic target that contributes to triggering delayed cerebral ischemia (DCI) in the setting of subarachnoid hemorrhage (SAH). This study aimed to determine the role of dobutamine for inotropic cardiac support in improving cerebral blood flow (CBF) and outcomes after experimental SAH, mediated by hypoxia-inducible factor (HIF). Thirty-one mice were subjected to SAH by endovascular perforation, and assigned to either 2% isoflurane postconditioning performed between 1 and 2.5h after SAH induction or concomitant intravenous dobutamine infusion (15μg/kg/min) with or without HIF inhibitor 2-methoxyestradiol (2ME2) (10mg/kg) administered intraperitoneally. Neurobehavioral function was assessed daily by neurological scores and open field testing. DCI was defined 3days later by detecting a new infarction on MRI. Global CBF depression was notable early after SAH, but dobutamine showed significant improvement in CBF, lower incidence of DCI, and better recovery of neuroscores and open field test variables compared with isoflurane postconditioning (P<0.05). CBF over the entire brain on day 1 predicted DCI with a cut-off of 36.5ml/100g/min (80% specificity and 67% sensitivity), with a better area under the curve (0.83 versus 0.75) than the hemispheric CBF measured on the perforated side. The dobutamine-mediated outcomes were attenuated (P<0.05) by 2ME2 pretreatment. The data suggest that cardiac support with dobutamine improves global CBF depression induced by early brain injury, leading to reduced prevalence of DCI and better functional outcomes after experimental SAH, in which HIF may be acting as a critical mediator.

Neuronal prolyl-4-hydroxylase 2 deficiency improves cognitive abilities in a murine model of cerebral hypoperfusion

Episodes of cerebral hypoxia/ischemia increase the risk of dementia, which is associated with impaired learning and memory. Previous studies in rodent models of dementia indicated a favorable effect of the hypoxia-inducible factor (HIF) targets VEGF (vascular endothelial growth factor) and erythropoietin (Epo). In the present study we thus investigated whether activation of the entire adaptive HIF pathway in neurons by cell-specific deletion of the HIF suppressor prolyl-4-hydroxylase 2 (PHD2) improves cognitive abilities in young (3months) and old (18-28months) mice suffering from chronic brain hypoperfusion. Mice underwent permanent occlusion of the left common carotid artery, and cognitive function was assessed using the Morris water navigation task. Under conditions of both normal and decreased brain perfusion, neuronal PHD2 deficiency resulted in improved and faster spatial learning in young mice, which was preserved to some extent also in old animals. The loss of PHD2 in neurons resulted in enhanced hippocampal mRNA and protein levels of Epo and VEGF, but did not alter local microvascular density, dendritic spine morphology, or expression of synaptic plasticity-related genes in the hippocampus. Instead, better cognitive function in PHD2 deficient animals was accompanied by an increased number of neuronal precursor cells along the subgranular zone of the dentate gyrus. Overall, our current pre-clinical findings indicate an important role for the endogenous oxygen sensing machinery, encompassing PHDs, HIFs and HIF target genes, for proper cognitive function. Thus, pharmacological compounds affecting the PHD-HIF axis might well be suited to treat cognitive dysfunction and neurodegenerative processes.