Treatment with an activator of hypoxia-inducible factor 1, DMOG provides neuroprotection after traumatic brain injury

The Hypoxia Response Pathway: A Potential Intervention Target in Parkinson's Disease?

Parkinson's disease (PD) is a progressive neurodegenerative disorder for which only symptomatic treatments are available. Both preclinical and clinical studies suggest that moderate hypoxia induces evolutionarily conserved adaptive mechanisms that enhance neuronal viability and survival. Therefore, targeting the hypoxia response pathway might provide neuroprotection by ameliorating the deleterious effects of mitochondrial dysfunction and oxidative stress, which underlie neurodegeneration in PD. Here, we review experimental studies regarding the link between PD pathophysiology and neurophysiological adaptations to hypoxia. We highlight the mechanistic differences between the rescuing effects of chronic hypoxia in neurodegeneration and short-term moderate hypoxia to improve neuronal resilience, termed "hypoxic conditioning". Moreover, we interpret these preclinical observations regarding the pharmacological targeting of the hypoxia response pathway. Finally, we discuss controversies with respect to the differential effects of hypoxia response pathway activation across the PD spectrum, as well as intervention dosing in hypoxic conditioning and potential harmful effects of such interventions. We recommend that initial clinical studies in PD should focus on the safety, physiological responses, and mechanisms of hypoxic conditioning, as well as on repurposing of existing pharmacological compounds. © 2023 International Parkinson and Movement Disorder Society.

Construction of Rapid Extracellular Matrix-Deposited Small-Diameter Vascular Grafts Induced by Hypoxia in a Bioreactor

Cardiovascular disease has become one of the most globally prevalent diseases, and autologous or vascular graft transplantation has been the main treatment for the end stage of the disease. However, there are no commercialized small-diameter vascular graft (SDVG) products available. The design of SDVGs is promising in the future, and SDVG preparation using an in vitro bioreactor is a favorable method, but it faces the problem of long-term culture of >8 weeks. Herein, we used different oxygen (O₂) concentrations and mechanical stimulation to induce greater secretion of extracellular matrix (ECM) from cells in vitro to rapidly prepare SDVGs. Culturing with 2% O₂ significantly increased the production of the ECM components and growth factors of human dermal fibroblasts (hDFs). To accelerate the formation of ECM, hDFs were seeded on a polycaprolactone (PCL) scaffold and cultured in a flow culture bioreactor with 2% O₂ for only 3 weeks. After orthotopic transplantation in rat abdominal aorta, the cultured SDVGs (PCL-decellularized ECM) showed excellent endothelialization and smooth muscle regeneration. The vascular grafts cultured with hypoxia and mechanical stimulation could accelerate the reconstruction speed and obtain an improved therapeutic effect and thereby provide a new research direction for improving the production and supply of SDVGs.

HIF-1α participates in secondary brain injury through regulating neuroinflammation

A deeper understanding of the underlying biological mechanisms of secondary brain injury induced by traumatic brain injury (TBI) will greatly advance the development of effective treatments for patients with TBI. Hypoxia-inducible factor-1 alpha (HIF-1α) is a central regulator of cellular response to hypoxia. In addition, growing evidence shows that HIF-1α plays the important role in TBI-induced changes in biological processes; however, detailed functional mechanisms are not completely known. The aim of the present work was to further explore HIF-1α-mediated events after TBI. To this end, next-generation sequencing, coupled with cellular and molecular analysis, was adopted to interrogate vulnerable events in a rat controlled cortical impact model of TBI. The results demonstrated that TBI induced accumulation of HIF-1α at the peri-injury site at 24 h post-injury, which was associated with neuronal loss. Moreover, gene set enrichment analysis unveiled that neuroinflammation, especially an innate inflammatory response, was significantly evoked by TBI, which could be attenuated by the inhibition of HIF-1α. Furthermore, the inhibition of HIF-1α could mitigate the activation of microglia and astrocytes. Taken together, all these data implied that HIF-1α might contribute to secondary brain injury through regulating neuroinflammation.

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.

Exosomes Secreted by Adipose-Derived Stem Cells Following FK506 Stimulation Reduce Autophagy of Macrophages in Spine after Nerve Crush Injury

Macrophages emerge in the milieu around innervated neurons after nerve injuries. Following nerve injury, autophagy is induced in macrophages and affects the regulation of inflammatory responses. It is closely linked to neuroinflammation, while the immunosuppressive drug tacrolimus (FK506) enhances nerve regeneration following nerve crush injury and nerve allotransplantation with additional neuroprotective and neurotrophic functions. The combined use of FK506 and adipose-derived stem cells (ADSCs) was employed in cell therapy for organ transplantation and vascularized composite allotransplantation. This study aimed to investigate the topical application of exosomes secreted by ADSCs following FK506 treatment (ADSC-F-exo) to the injured nerve in a mouse model of sciatic nerve crush injury. Furthermore, isobaric tags for relative and absolute quantitation (iTRAQ) were used to profile the potential exosomal proteins involved in autophagy. Immunohistochemical analysis revealed that nerve crush injuries significantly induced autophagy in the dorsal root ganglia and dorsal horn of the spinal segments. Locally applied ADSC-F-exo significantly reduced autophagy of macrophages in the spinal segments after nerve crush injury. Proteomic analysis showed that of the 22 abundant exosomal proteins detected in ADSC-F-exo, heat shock protein family A member 8 (HSPA8) and eukaryotic translation elongation factor 1 alpha 1 (EEF1A1) are involved in exosome-mediated autophagy reduction.

HIF-1α is a negative regulator of interferon regulatory factors: Implications for interferon production by hypoxic monocytes

Patients with severe COVID-19 infection exhibit a low level of oxygen in affected tissue and blood. To understand the pathophysiology of COVID-19 infection, it is therefore necessary to understand cell function during hypoxia. We investigated aspects of human monocyte activation under hypoxic conditions. HMGB1 is an alarmin released by stressed cells. Under normoxic conditions, HMGB1 activates interferon regulatory factor (IRF)5 and nuclear factor-κB in monocytes, leading to expression of type I interferon (IFN) and inflammatory cytokines including tumor necrosis factor α, and interleukin 1β, respectively. When hypoxic monocytes are activated by HMGB1, they produce proinflammatory cytokines but fail to produce type I IFN. Hypoxia-inducible factor-1α, induced by hypoxia, functions as a direct transcriptional repressor of IRF5 and IRF3. As hypoxia is a stressor that induces secretion of HMGB1 by epithelial cells, hypoxia establishes a microenvironment that favors monocyte production of inflammatory cytokines but not IFN. These findings have implications for the pathogenesis of COVID-19.

HIF-1α aggravated traumatic brain injury by NLRP3 inflammasome-mediated pyroptosis and activation of microglia

Hypoxia inducible factor 1 alpha (HIF-1α) is involved in regulating the biological functions of neuronal death after traumatic brain injury (TBI), and attaches importance in the inflammatory response, but its potential mechanism is still unknown. Our study aimed to explore the regulatory mechanism between HIF-1α and NLRP3 inflammasome after TBI. Male mice underwent controlled cortical impact (CCI) or sham-operated procedures. Brain water content and blood-brain barrier permeability were measured at the indicated time after TBI. The behavioral performance, ELISA, immunofluorescence, and western blot analysis were used to determine whether HIF-1α specifically targeted TBI-induced pyroptosis. We discovered that TBI-induced brain injury caused by external mechanical forces is characterized by edema and blood-brain barrier disorder, and the release of IL-1β, IL-18, and LDH and upregulation of HIF-1α expression, reaching the peak on the third day post-TBI. In addition, HIF-1α accumulated NLRP3 inflammasome-mediated pyroptosis and activation of microglia. The protein expressions of NLRP3, GSDMD, GSDMD-N, pro-caspase 1, and cleaved caspase 1 were markedly increased in the injured cortex, which were restored to normal levels by the interference of HIF-1α. The inactivation of HIF-1α conferred neuroprotection and alleviated brain injury after TBI. HIF-1α was implicated in TBI-induced brain injury, aggravated NLRP3 inflammasome -mediated pyroptosis, and the activation of microglia, which provided a potential target for treating TBI.

The effect of hypoxia-mimicking responses on improving the regeneration of artificial vascular grafts

Cellular transition to hypoxia following tissue injury, has been shown to improve angiogenesis and regeneration in multiple tissues. To take advantage of this, many hypoxia-mimicking scaffolds have been prepared, yet the oxygen access state of implanted artificial small-diameter vascular grafts (SDVGs) has not been investigated. Therefore, the oxygen access state of electrospun PCL grafts implanted into rat abdominal arteries was assessed. The regions proximal to the lumen and abluminal surfaces of the graft walls were normoxic and only the interior of the graft walls was hypoxic. In light of this differential oxygen access state of the implanted grafts and the critical role of vascular regeneration on SDVG implantation success, we investigated whether modification of SDVGs with HIF-1α stabilizer dimethyloxalylglycine (DMOG) could achieve hypoxia-mimicking responses resulting in improving vascular regeneration throughout the entirety of the graft wall. Therefore, DMOG-loaded PCL grafts were fabricated by electrospinning, to support the sustained release of DMOG over two weeks. In vitro experiments indicated that DMOG-loaded PCL mats had significant biological advantages, including: promotion of human umbilical vein endothelial cells (HUVECs) proliferation, migration and production of pro-angiogenic factors; and the stimulation of M2 macrophage polarization, which in-turn promoted macrophage regulation of HUVECs migration and smooth muscle cells (SMCs) contractile phenotype. These beneficial effects were downstream of HIF-1α stabilization in HUVECs and macrophages in normoxic conditions. Our results indicated that DMOG-loaded PCL grafts improved endothelialization, contractile SMCs regeneration, vascularization and modulated the inflammatory reaction of grafts in abdominal artery replacement models, thus promoting vascular regeneration.

Discoveries for Long Non-Coding RNA Dynamics in Traumatic Brain Injury

Simple Summary

The biomedical studies of traumatic brain injury (TBI) can lead to insight for treatment clinically. However, TBIs are occurred by various risk factors and showing heterogeneity that make difficult to accurate diagnosis for initiation treatment of patients. Therefore, identification of biomarkers requires to prediction and therapeutics for TBI treatment. The canonical function of the long non-coding RNAs (lncRNAs) have been recently shown to promote transcription, post-transcription, and protein activity in many different conditions. Therefore, understanding the molecular mechanisms that are altered by the expression of lncRNAs will allow the design of novel therapeutic strategies. Here, we review the molecular process of lncRNA as new targets and approaches in TBIs treatment.

Abstract

In recent years, our understanding of long non-coding RNAs (lncRNAs) has been challenged with advances in genome sequencing and the widespread use of high-throughput analysis for identifying novel lncRNAs. Since then, the characterization of lncRNAs has contributed to the establishment of their molecular roles and functions in transcriptional regulation. Although genetic studies have so far explored the sequence-based primary function of lncRNAs that guides the expression of target genes, recent insights have shed light on the potential of lncRNAs for widening the identification of biomarkers from non-degenerative to neurodegenerative diseases. Therefore, further advances in the genetic characteristics of lncRNAs are expected to lead to diagnostic accuracy during disease progression. In this review, we summarized the latest studies of lncRNAs in TBI as a non-degenerative disease and discussed their potential limitations for clinical treatment.

HIF-1α Mediates TRAIL-Induced Neuronal Apoptosis via Regulating DcR1 Expression Following Traumatic Brain Injury

Background: Neuronal apoptosis involved in secondary injury following traumatic brain injury (TBI) significantly contributes to the poor outcomes of patients with TBI. The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can selectively induce apoptosis of tumor cells. Hypoxia factor (HIF) 1α is a controversial factor that mediates the neuronal apoptotic pathway. Herein, we hypothesize that HIF-1α may mediate the TRAIL-induced neuronal apoptosis after TBI.

Methods: We used Western blots and immunofluorescence to study the expression and cell localization of TRAIL and death receptor 5 (DR5) after TBI in rats. Soluble DR5 (sDR5) administration was used to block the TRAIL-induced neuronal death and neural deficits. HIF-1α inhibitor 2ME and agonist DMOG were used to study the role of HIF-1α in TRAIL-induced neuronal death. Meanwhile, HIF-1α siRNA was used to investigate the role of HIF-1α in TRAIL-induced neuronal death in vitro.

Results: The expressions of microglia-located TRAIL and neuron-located DR5 were significantly upregulated after TBI. sDR5 significantly attenuated TRAIL-induced neuronal apoptosis and neurological deficits. 2ME decreased neuronal apoptosis, lesion area, and brain edema and improved neurological function via increased expression of TRAIL decoy receptor 1 (DcR1), which inhibited TRAIL-induced apoptosis after TBI. The administration of DMOG produced the opposite effect than did 2ME. Similarly, HIF-1α siRNA attenuated TRAIL-induced neuronal death via increased DcR1 expression in vitro.

Conclusion: Our findings suggested that the TRAIL/DR5 signaling pathway plays an important role after neuronal apoptosis after TBI. HIF-1α mediates TRAIL-induced neuronal apoptosis by regulating DcR1 expression following TBI.

Sex-dependent effects of GPER activation on neuroinflammation in a rat model of traumatic brain injury

The G protein-coupled estrogen receptor (GPER) plays a role in estrogen-mediated neuroprotection and has been considered a potential therapeutic target for treating various neurological diseases. It is increasingly recognized that sex is a biological variable affecting treatment outcomes and efficacy, and that neuroinflammation is a key secondary injury mechanism following brain injury, though it is unknown whether the neuroprotective effects exerted by GPER involve modulation of inflammatory processes. The aim of this study was to investigate whether activation of GPER has a sex-dependent effect on neuroinflammation following traumatic brain injury (TBI), a sexually dimorphic disease. In male and ovariectomized (OVX) female rats, the GPER agonist, G1, inhibited the upregulated expression of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α), increased the expression of the anti-inflammatory cytokine IL-4, and shifted microglia/macrophage polarization toward the M2 phenotype. In gonadally-intact females, G1 caused more pro-inflammatory (IL-6 and TNF-α) and less anti-inflammatory cytokine (IL-4) production, without altering microglia/macrophage polarization. Estradiol supplementation blocked the effects of G1 in OVX females. We also found that post-injury GPER expression was increased in males and OVX females but not in intact females. G1 administration increased Akt phosphorylation in males and OVX females, but had no significant effect in intact females, while Akt inhibition blocked the effects of G1 in males and OVX females. These results indicate that G1 exerts anti-inflammatory effects in males and OVX females but not in intact females; these sex-specific effects are dependent on circulating estrogen levels and are partially mediated through Akt signaling. Future studies are needed to elucidate the relevant molecular mechanisms, especially in females. A better understanding of the sex differences in treatment efficacy with GPER agonists may help improve personalized therapeutic strategies for males and pre- and postmenopausal females with TBI.

HIF-1α/SDF-1/CXCR4 axis reduces neuronal apoptosis via enhancing the bone marrow-derived mesenchymal stromal cell migration in rats with traumatic brain injury

Mesenchymal stromal injection is a promising therapy for traumatic brain injury (TBI). The aim of this study was to explore the effects of the HIF-1α/SDF-1/CXCR4 axis on neuron repair in TBI rats through improving the bone marrow-derived mesenchymalstromal cells (BMSCs) migration. TBI rat models were established. The rats were treated with exogenous SDF-1, and then the neuronal apoptosis in TBI rats was measured. BMSCs from rats were collected, and the roles of NF-κB p65 expression in nuclei, overexpression of SDF-1 and HIF-1α, as well as downregulation of CXCR4 in BMSC migration were identified. HIF-1α- and SDF-1- treated BMSCs were transplanted into TBI rats, after which the neuronal apoptosis and activity of the HIF-1α/SDF-1/CXCR4 axis were detected. Consequently, we found SDF-1 elevated the HIF-1α/SDF-1/CXCR4 activity and presented protective roles in TBI rat hippocampal neurons with reduced neuronal apoptosis. SDF-1 promoted BMSC migration in vitro, and co-effects of SDF-1 and HIF-1α showed strong promotion, while CXCR4 inhibition suppressed BMSC migration. BMSC transplantation activated the HIF-1α/SDF-1/CXCR4 axis and reduced neuronal apoptosis in TBI rats. To conclude, our study demonstrated that the HIF-1α/SDF-1/CXCR4 axis could enhance BMSC migration and alleviate neuronal damage and apoptosis in TBI rats. This study provided novel options for TBI therapy.

Targeting immunometabolism as an anti-inflammatory strategy

The growing field of immunometabolism has taught us how metabolic cellular reactions and processes not only provide a means to generate ATP and biosynthetic precursors, but are also a way of controlling immunity and inflammation. Metabolic reprogramming of immune cells is essential for both inflammatory as well as anti-inflammatory responses. Four anti-inflammatory therapies, DMF, Metformin, Methotrexate and Rapamycin all work by affecting metabolism and/or regulating or mimicking endogenous metabolites with anti-inflammatory effects. Evidence is emerging for the targeting of specific metabolic events as a strategy to limit inflammation in different contexts. Here we discuss these recent developments and speculate on the prospect of targeting immunometabolism in the effort to develop novel anti-inflammatory therapeutics. As accumulating evidence for roles of an intricate and elaborate network of metabolic processes, including lipid, amino acid and nucleotide metabolism provides key focal points for developing new therapies, we here turn our attention to glycolysis and the TCA cycle to provide examples of how metabolic intermediates and enzymes can provide potential novel therapeutic targets.

Acute Methylmercury Exposure and the Hypoxia-Inducible Factor-1α Signaling Pathway under Normoxic Conditions in the Rat Brain and Astrocytes in Vitro

BACKGROUND

As a ubiquitous environmental pollutant, methylmercury (MeHg) induces toxic effects in the nervous system, one of its main targets. However, the exact mechanisms of its neurotoxicity have not been fully elucidated. Hypoxia-inducible factor- 1 α (HIF- 1 α ), a transcription factor, plays a crucial role in adaptive and cytoprotective responses in cells and is involved in cell survival, proliferation, apoptosis, inflammation, angiogenesis, glucose metabolism, erythropoiesis, and other physiological activities.

OBJECTIVES

The aim of this study was to explore the role of HIF- 1 α in response to acute MeHg exposure in rat brain and primary cultured astrocytes to improve understanding of the mechanisms of MeHg-induced neurotoxicity and the development of effective neuroprotective strategies.

METHODS

Primary rat astrocytes were treated with MeHg (0 - 10 μ M ) for 0.5 h . Cell proliferation and cytotoxicity were assessed with a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl diphenyltetrazolium bromide (MTT) assay and a lactate dehydrogenase (LDH) release assay, respectively. Reactive oxygen species (ROS) levels were analyzed to assess the level of oxidative stress using 2',7'-dichlorofluorescin diacetate (DCFH-DA) fluorescence. HIF- 1 α , and its downstream proteins, glucose transporter 1 (GLUT-1), erythropoietin (EPO), and vascular endothelial growth factor A (VEGF-A) were analyzed by means of Western blotting. Real-time PCR was used to detect the expression of HIF- 1 α mRNA. Pretreatment with protein synthesis inhibitor (CHX), proteasome inhibitor (MG132), or proline hydroxylase inhibitor (DHB) were applied to explore the possible mechanisms of HIF- 1 α inhibition by MeHg. To investigate the role of HIF- 1 α in MeHg-induced neurotoxicity, cobalt chloride (CoC l 2 ), 2-methoxyestradiol (2-MeOE2), small interfering RNA (siRNA) transfection and adenovirus overexpression were used. Pretreatment with N-acetyl-L-cysteine (NAC) and vitamin E (Trolox) were used to investigate the putative role of oxidative stress in MeHg-induced alterations in HIF- 1 α levels. The expression of HIF- 1 α and related downstream proteins was detected in adult rat brain exposed to MeHg (0 - 10 mg / kg ) for 0.5 h in vivo.

RESULTS

MeHg caused lower cell proliferation and higher cytotoxicity in primary rat astrocytes in a time- and concentration-dependent manner. In comparison with the control cells, exposure to 10 μ M MeHg for 0.5 h significantly inhibited the expression of astrocytic HIF- 1 α , and the downstream genes GLUT-1, EPO, and VEGF-A (p < 0.05 ), in the absence of a significant decrease in HIF- 1 α mRNA levels. When protein synthesis was inhibited by CHX, MeHg promoted the degradation rate of HIF- 1 α . MG132 and DHB significantly blocked the MeHg-induced decrease in HIF- 1 α expression (p < 0.05 ). Overexpression of HIF- 1 α significantly attenuated the decline in MeHg-induced cell proliferation, whereas the inhibition of HIF- 1 α significantly increased the decline in cell proliferation (p < 0.05 ). NAC and Trolox, two established antioxidants, reversed the MeHg-induced decline in HIF- 1 α protein levels and the decrease in cell proliferation (p < 0.05 ). MeHg suppressed the expression of HIF- 1 α and related downstream target proteins in adult rat brain.

DISCUSSION

MeHg induced a significant reduction in HIF- 1 α protein by activating proline hydroxylase (PHD) and the ubiquitin proteasome system (UPS) in primary rat astrocytes. Additionally, ROS scavenging by antioxidants played a neuroprotective role via increasing HIF- 1 α expression in response to MeHg toxicity. Moreover, we established that up-regulation of HIF- 1 α might serve to mitigate the acute toxicity of MeHg in astrocytes, affording a novel therapeutic target for future exploration. https://doi.org/10.1289/EHP5139.

Aberrant ER Stress Induced Neuronal-IFNβ Elicits White Matter Injury Due to Microglial Activation and T-Cell Infiltration after TBI

Persistent endoplasmic reticulum (ER) stress in neurons is associated with activation of inflammatory cells and subsequent neuroinflammation following traumatic brain injury (TBI); however, the underlying mechanism remains elusive. We found that induction of neuronal-ER stress, which was mostly characterized by an increase in phosphorylation of a protein kinase R-like ER kinase (PERK) leads to release of excess interferon (IFN)β due to atypical activation of the neuronal-STING signaling pathway. IFNβ enforced activation and polarization of the primary microglial cells to inflammatory M1 phenotype with the secretion of a proinflammatory chemokine CXCL10 due to activation of STAT1 signaling. The secreted CXCL10, in turn, stimulated the T-cell infiltration by serving as the ligand and chemoattractant for CXCR3⁺ T-helper 1 (Th1) cells. The activation of microglial cells and infiltration of Th1 cells resulted in white matter injury, characterized by impaired myelin basic protein and neurofilament NF200, the reduced thickness of corpus callosum and external capsule, and decline of mature oligodendrocytes and oligodendrocyte precursor cells. Intranasal delivery of CXCL10 siRNA blocked Th1 infiltration but did not fully rescue microglial activation and white matter injury after TBI. However, impeding PERK-phosphorylation through the administration of GSK2656157 abrogated neuronal induction of IFNβ, switched microglial polarization to M2 phenotype, prevented Th1 infiltration, and increased Th2 and Treg levels. These events ultimately attenuated the white matter injury and improved anxiety and depressive-like behavior following TBI.SIGNIFICANCE STATEMENT A recent clinical study showed that human brain trauma patients had enhanced expression of type-1 IFN; suggests that type-1 IFN signaling may potentially influence clinical outcome in TBI patients. However, it was not understood how TBI leads to an increase in IFNβ and whether induction of IFNβ has any influence on neuroinflammation, which is the primary reason for morbidity and mortality in TBI. Our study suggests that induction of PERK phosphorylation, a characteristic feature of ER stress is responsible for an increase in neuronal IFNβ, which, in turn, activates microglial cells and subsequently manifests the infiltration of T cells to induce neuroinflammation and subsequently white matter injury. Blocking PERK phosphorylation using GSK2656157 (or PERK knockdown) the whole cascade of neuroinflammation was attenuated and improved cognitive function after TBI.

Carnosine and L-arginine attenuate the downregulation of brain monoamines and gamma aminobutyric acid; reverse apoptosis and upregulate the expression of angiogenic factors in a model of hemic hypoxia in rats

PURPOSE

The purpose of the present study was to investigate the preventive effect of L-arginine (ARG) and carnosine (CAR) on hypoxia-induced neurotoxicity in rats. The impact on neuro-inflammation, apoptosis, angiogenesis, and the brain levels of monoamines and GABA were investigated.

METHODS

Rats were divided into the following: normal control, hypoxia model induced by sodium nitrite (75 mg/kg s.c), and hypoxic rats pre-treated with CAR (250 mg/kg), ARG (200 mg/kg), and their combination.

RESULTS

Data revealed that hypoxia induced significant elevation of hypoxia inducible factor-1α (HIF-1α), vascular endothelial growth factor (VEGF), and its receptor reflecting the stimulation of angiogenesis. Hypoxia also resulted in increased inflammatory mediators-including nuclear factor kappa B (NF-κB), tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6). In addition, hypoxia initiates cerebral apoptosis as revealed by increased caspase-3 and BAX with reduced Bcl-2. These changes were associated with reduced brain levels of GABA and monoamines including noradrenaline (NADR), dopamine (DOP), and serotonin (SER). Pre-treatment with ARG and/or CAR significantly mitigated the neural changes induced by hypoxia and attenuated the elevated levels of NF-κB, TNF-α, IL-6, caspase-3, and BAX, while ameliorated the reduced levels of Bcl-2, NADR, DOP, SER, and GABA, with the best improvement observed with the combination. Further elevation of the angiogenic markers was observed indicating their role in boosting oxygen delivery to brain.

CONCLUSION

CAR, ARG, and, importantly, their combination could effectively protect against hypoxia-induced neurotoxicity, via their angiogenic, anti-inflammatory, and anti-apoptotic properties in addition to reversing the effect on GABA and monoamines.

HIF-1α/PDK4/autophagy pathway protects against advanced glycation end-products induced vascular smooth muscle cell calcification

Osteogenic differentiation of VSMC is one of the main causes of diabetic vascular calcification, and AGEs accumulation accelerates the calcification of VSMCs in diabetic patients. Autophagy has also been found to play an important role in the process of vascular calcification. However, the potential link between AGEs, autophagy and vascular calcification is still unclear and was investigated in this study. Primary VSMCs were isolated from the thoracic aorta of Sprague Dawley rats and cultured with AGEs-BSA to induce osteogenic differentiation. VSMCs calcification was evaluated by measuring the calcium content, RUNX2 protein levels, and by Alizarin red S staining. We demonstrated that treatment of VSMCs with AGE-BSA increased the expression of HIF-1α and PDK4. AGE-BSA treatment increased LC3-II and decreased p62 protein levels. AGE-BSA exposure enhanced autophagic flux determined by mRFP-GFP-LC3 adenovirus, induced co-localization of LC3-II and LAMP-1, and increased the number of autophagasome under TEM. HIF-1α/PDK4 pathway was activated during AGEs-induced autophagy of VSMCs. In addition, autophagy played a protective role during AGE-induced calcification of VSMCs. In conclusion, AGEs enhance autophagy via the HIF-1α/PDK4 signaling pathway, and autophagy helps attenuate AGE-induced calcification of VSMCs.

Histone Deacetylase 4 Downregulation Elicits Post-Traumatic Psychiatric Disorders through Impairment of Neurogenesis

An enduring deficit in neurogenesis largely contributes to the development of severe post-traumatic psychiatric disorders such as anxiety, depression, and memory impairment following traumatic brain injury (TBI); however, the mechanism remains obscure. Here we have shown that an imbalance in the generation of γ-aminobutyric acid (GABA)ergic and glutamatergic neurons due to aberrant induction of vesicular glutamate transporter 1 (vGlut1)-positive glutamatergic cells is responsible for impaired neuronal differentiation in the hippocampus following TBI. To elucidate the molecular mechanism, we found that TBI activates a transcription factor, Pax3, by increasing its acetylation status, and subsequently induces Ngn2 transcription. This event, in turn, augments the vGlut1-expressing glutamatergic neurons and accumulation of excess glutamate in the hippocampus that can affect neuronal differentiation. In our study the acetylation of Pax3 was increased due to loss of its interaction with a deacetylase, histone deacetylase 4 (HDAC4), which was downregulated after TBI. TBI-induced activation of GSK3β was responsible for the degradation of HDAC4. We also showed that overexpression of HDAC4 before TBI reduces Pax3 acetylation by restoring an interaction between HDAC4 and Pax3 in the hippocampus. This event prevents the aberrant induction of vGlut1-positive glutamatergic neurons by decreasing the Ngn2 level and subsequently reinforces the balance between GABAergic and glutamatergic neurons following TBI. Further, we found that overexpression of HDAC4 in the hippocampus improves anxiety, depressive-like behavior, and memory functions following TBI.

Dimethyloxalylglycine (DMOG) and the Caspase Inhibitor "Ac-LETD-CHO" Protect Neuronal ND7/23 Cells of Gluocotoxicity

It well known that long-lasting hyperglycaemia disrupts neuronal function and leads to neuropathy and other neurodegenerative diseases. The α-ketoglutarate analogue (DMOG) and the caspase-inhibitor "Ac-LETD-CHO are potential neuroprotective molecules. Whether their protections may also extend glucotoxicity-induced neuropathy is not known. Herein, we evaluated the possible cell-protective effects of DMOG and Ac-LETD-CHO against hyperglycaemia-induced reactive oxygen species and apoptosis in ND7/23 neuronal cells. The impact of glucotoxicity on the expression of HIF-1α and a panel of micro-RNAs of significance in hyperglycaemia and apoptosis was also investigated.ND7/23 cells cultured under hyperglycaemic conditions showed decreased cell viability and elevated levels of ROS production in a dose- and time-dependent manner. However, presence DMOG (500 µM) and/or Ac-LETD-CHO (50 µM) counteracted this effect and increase cell viability concomitant with reduction in ROS production, DNA damage and apoptosis. AcLETD-CHO suppressed hyperglycaemia-induced caspase 3 activation in ND7/23 cells. Both DMOG and Ac-LETD-CHO increased HIF-1α expression paralleled with the suppression of miR-126-5p, miR-128-3p and miR-181 expression and upregulation of miR-26b, 106a-5p, 106b-5p, 135a-5p, 135b-5p, 138-5p, 199a-5p, 200a-3p and 200c-3p expression.We demonstrate a mechanistic link for the DMOG and Ac-LETD-CHO protection against hyperglycaemia-induced neuronal dysfunction, DNA damage and apoptosis and thereby propose that pharmacological agents mimicking these effects may represent a promising novel therapy for the hyperglycaemia-induced neuropathy.

An augmentation in histone dimethylation at lysine nine residues elicits vision impairment following traumatic brain injury

Traumatic Brain Injury (TBI) affects more than 1.7 million Americans each year and about 30% of TBI-patients having visual impairments. The loss of retinal ganglion cells (RGC) in the retina and axonal degeneration in the optic nerve have been attributed to vision impairment following TBI; however, the molecular mechanism has not been elucidated. Here we have shown that an increase in histone di-methylation at lysine 9 residue (H3K9Me2), synthesized by the catalytic activity of a histone methyltransferase, G9a is responsible for RGC loss and axonal degeneration in the optic nerve following TBI. To elucidate the molecular mechanism, we found that an increase in H3K9Me2 results in the induction of oxidative stress both in the RGC and optic nerve by decreasing the mRNA level of antioxidants such as Superoxide dismutase (sod) and catalase through impairing the transcriptional activity of Nuclear factor E2-related factor 2 (Nrf2) via direct interaction. The induction of oxidative stress is associated with death in RGC and oligodendrocyte precursor cells (OPCs). The death in OPCs is correlated with a reduction in myelination, and the expression of myelin binding protein (MBP) in association with degeneration of neurofilaments in the optic nerve. This event allied to an impairment of the retrograde transport of axons and loss of nerve fiber layer in the optic nerve following TBI. An administration of G9a inhibitor, UNC0638 attenuates the induction of H3K9Me2 both in RGC and optic nerve and subsequently activates Nrf2 to reduce oxidative stress. This event was concomitant with the rescue in the loss of retinal thickness, attenuation in optic nerve degeneration and improvement in the retrograde transport of axons following TBI.

Working with Hypoxia

A hypoxic environment can be defined as a region of the body or the whole body that is deprived of oxygen. Hypoxia is a feature of many diseases, such as cardiovascular disease, tissue trauma, stroke, and solid cancers. A loss of oxygen supply usually results in cell death; however, when cells gradually become hypoxic, they may survive and continue to thrive as described for conditions that promote metastatic growth. The role of hypoxia in these pathogenic pathways is therefore of great interest, and understanding the effect of hypoxia in regulating these mechanisms is fundamentally important. This chapter gives an extensive overview of these mechanisms. Moreover, given the challenges posed by tumor hypoxia we describe the current methods to simulate and detect hypoxic conditions followed by a discussion on current and experimental therapies that target hypoxic cells.

Upregulation of miR-335 ameliorates myocardial ischemia reperfusion injury via targeting hypoxia inducible factor 1-alpha subunit inhibitor

MicroRNA-335 (miR-335) is implicated in several pathophysiological processes, including tumorigenesis, lipid metabolism and ischemic stroke; however, whether miR-335 plays a role in modulating myocardial ischemia reperfusion injury (MIRI) is still unknown. This study is aimed to explore the role and mechanism of miR-335 in the pathophysiological process of MIRI. Specifically, miR-335 mimics or a chemically modified agomiR-335 were transfected or injected into H9c2 cells and Wistar rats to upregulate miR-335 expression in vitro and in vivo, respectively. The effects of miR-335 overexpression on hypoxia/reoxygenation (H/R)-treated cardiomyocytes and ischemia/reperfusion (I/R)-exposed heart samples were investigated by a Cell Counting Kit-8 assay, flow cytometry, TTC staining and a TUNEL assay. The target of miR-335 was identified using a luciferase reporter assay. The expression of heme oxygenase 1 (HO-1) and inducible nitric oxide synthase (iNOS) was detected by reverse transcription-quantitative polymerase chain reaction and western blotting. The results showed that miR-335 expression in cardiomyocytes and the myocardium was downregulated during MIRI but was induced by hypoxic/ischemic postconditioning. MiR-335 overexpression led to an increase in cell viability and a reduction in the apoptosis of H/R-treated cardiomyocytes. Meanwhile, myocardial infarct size and the apoptosis of I/R-exposed heart tissues were decreased in response to miR-335 upregulation. Furthermore, we identified that hypoxia inducible factor 1-alpha subunit inhibitor (HIF1AN), a suppressor of hypoxia inducible factor 1-alpha (HIF-1α) stabilization and transcriptional activity, is a novel target of miR-335. MiR-335 overexpression enhanced the transcriptional activity of HIF-1α, increased the expression of HO-1 and iNOS, and inhibited mitochondrial permeability transition pore (MPTP) opening. In conclusion, we are the first to demonstrate that upregulation of miR-335 ameliorates MIRI by targeting HIF1AN. Thus, miR-335 may be a new therapeutic target for the treatment of MIRI.

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.

Advanced glycation end products accelerate calcification in VSMCs through HIF-1α/PDK4 activation and suppress glucose metabolism

Arterial media calcification is associated with diabetes mellitus. Previous studies have shown that advanced glycation end products (AGEs) are responsible for vascular smooth muscle cell (VSMC) calcification, but the underlying mechanisms remain unclear. Hypoxia-inducible factor-1α (HIF-1α), one of the major factors during hypoxia, and pyruvate dehydrogenase kinase 4 (PDK4), an important mitochondrial matrix enzyme in cellular metabolism shift, have been reported in VSMC calcification. The potential link among HIF-1α, PDK4, and AGEs-induced vascular calcification was investigated in this study. We observed that AGEs elevated HIF-1α and PDK4 expression levels in a dose-dependent manner and that maximal stimulation was attained at 24 h. Two important HIF-1α-regulated genes, vascular endothelial growth factor A (VEGFA) and glucose transporter 1 (GLUT-1), were significantly increased after AGEs exposure. Stabilization or nuclear translocation of HIF-1α increased PDK4 expression. PDK4 inhibition attenuated AGEs-induced VSMC calcification, which was evaluated by measuring the calcium content, alkaline phosphatase (ALP) activity and runt-related transcription factor 2 (RUNX2) expression levels and by Alizarin red S staining. In addition, the glucose consumption, lactate production, key enzymes of glucose metabolism and oxygen consumption rate (OCR) were decreased during AGEs-induced VSMC calcification. In conclusion, this study suggests that AGEs accelerate vascular calcification partly through the HIF-1α/PDK4 pathway and suppress glucose metabolism.

Activation of cyclin D1 affects mitochondrial mass following traumatic brain injury

Cell cycle activation has been associated with varying types of neurological disorders including brain injury. Cyclin D1 is a critical modulator of cell cycle activation and upregulation of Cyclin D1 in neurons contributes to the pathology associated with traumatic brain injury (TBI). Mitochondrial mass is a critical factor to maintain the mitochondrial function, and it can be regulated by different signaling cascades and transcription factors including NRF1. However, the underlying mechanism of how TBI leads to impairment of mitochondrial mass following TBI remains obscure. Our results indicate that augmentation of CyclinD1 attenuates mitochondrial mass formation following TBI. To elucidate the molecular mechanism, we found that Cyclin D1 interacts with a transcription factor NRF1 in the nucleus and prevents NRF1's interaction with p300 in the pericontusional cortex following TBI. As a result, the acetylation level of NRF1 was decreased, and its transcriptional activity was attenuated. This event leads to a loss of mitochondrial mass in the pericontusional cortex following TBI. Intranasal delivery of Cyclin D1 RNAi immediately after TBI rescues transcriptional activation of NRF1 and recovers mitochondrial mass after TBI.

Effects of over-expression of HIF-1alpha in bone marrow-derived mesenchymal stem cells on traumatic brain injury

Mesenchymal stem cells (MSCs) have been shown to play therapeutic effect in traumatic brain injury (TBI). To augment the therapeutic effect, MSCs could be engineered to over-express genes that are beneficial for treatment. In the present study, we over-expressed hypoxia inducible factor (HIF)-1alpha in bone marrow derived MSCs (BM-MSCs) and sought to investigate whether HIF-1alpha could enhance the therapeutic effect of MSCs in a mouse model of TBI. Balb/c mice were subjected to controlled cortical impact injury and MSCs were transplanted intravenously at 6 h after injury. The lesion volume and brain water content were measured and the neurological function was assessed by modified neurologic severity score tests. Double-labeled immunofluorescence for BrdU and NeuU was performed to determine angiogenesis and neurogenesis. The expression of erythropoietin (EPO) and vascular endothelial growth factor (VEGF) was measured by quantitative RT-PCR and western blotting. After TBI, mice received BM-MSCs over-expressing HIF-1alpha showed significantly more functional recovery, reduced brain damage, increased angiogenesis and neurogenesis and increased expression of VEGF and EPO, compared with control mice or mice treated with non-transduced BM-MSCs. Over-expression of HIF-1alpha enhanced BM-MSCs induced improvement of neurological recovery after TBI, by stimulating angiogenesis and neurogenesis.

Nitrosylation of GAPDH augments pathological tau acetylation upon exposure to amyloid-β

Acetylation of the microtubule-associated protein tau promotes its polymerization into neurofibrillary tangles that are implicated in the pathology of Alzheimer's disease (AD). The gaseous neurotransmitter nitric oxide (NO) regulates cell signaling through the nitrosylation of proteins. We found that NO production and tau acetylation at Lys²⁸⁰ occurred in the brain tissue in mice and in cultured mouse cortical neurons in response to exposure to amyloid-β_1-42 (Aβ_1-42), a peptide that is also implicated in AD. An increased abundance of NO facilitated the S-nitrosylation (SNO) of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). S-nitrosylated GAPDH (GAPDH-SNO) promoted the acetylation and activation of the acetyltransferase p300 and facilitated the nitrosylation and inactivation of the deacetylase sirtuin 1 (SIRT1). The abundance of GAPDH-SNO was increased in postmortem brain samples from AD patients. Preventing the increase in GAPDH-SNO abundance in both cultured neurons and mice, either by overexpression of the nitrosylation mutant of GAPDH (GAPDH C150S) or by treatment with the GAPDH nitrosylation inhibitor CGP3466B (also known as omigapil), abrogated Aβ_1-42-induced tau acetylation, memory impairment, and locomotor dysfunction in mice, suggesting that this drug might be repurposed to treat patients with AD.

HIF-1α stabilization reduces retinal degeneration in a mouse model of retinitis pigmentosa

Retinitis pigmentosa (RP) is a group of inherited retinal dystrophies characterized by progressive and irreversible loss of vision due to rod and cone degeneration. Evidence suggests that an inappropriate oxygen level could contribute to its pathogenesis. Rod cell death could increase oxygen concentration, reduce hypoxia-inducible factor 1 (HIF-1α) and contribute to cone cell death. The purposes of this study were: 1) to analyze the temporal profile of HIF-1α, its downstream effectors VEGF, endothelin-1 (ET-1), iNOS, and glucose transporter 1 (GLUT1), and neuroinflammation in retinas of the murine model of rd10 ( retinal degeneration 10) mice with RP; 2) to study oxygen bioavailability in these retinas; and 3) to investigate how stabilizing HIF-1α proteins with dimethyloxaloglycine (DMOG), a prolyl hydroxylase inhibitor, affects retinal degeneration, neuroinflammation, and antioxidant response in rd10 mice. A generalized down-regulation of HIF-1α and its downstream targets was detected in parallel with reactive gliosis, suggesting high oxygen levels during retinal degeneration. At postnatal d 18, DMOG treatment reduced photoreceptor cell death and glial activation. In summary, retinas of rd10 mice seem to be exposed to a hyperoxic environment even at early stages of degeneration. HIF-1α stabilization could have a temporal neuroprotective effect on photoreceptor cell survival, glial activation, and antioxidant response at early stages of RP.-Olivares-González, L., Martínez-Fernández de la Cámara, C., Hervás, D., Millán, J. M., Rodrigo, R. HIF-1α stabilization reduces retinal degeneration in a mouse model of retinitis pigmentosa.

HIF-1α-l-PGDS-PPARγ regulates hypoxia-induced ANP secretion in beating rat atria

Lipocalin-type prostaglandin D synthase (L-PGDS) and peroxisome proliferator activated receptor γ (PPARγ) play important roles in cardiovascular diseases. Nevertheless, effects of hypoxia-inducible factor 1α (HIF-1α) on L-PGDS and PPARγ protein levels and its role in hypoxia-induced atrial natriuretic peptide (ANP) secretion are unclear. In perfused beating rat atria, we observed that hypoxia significantly increased HIF-1α protein levels and stimulated ANP secretion, while upregulating L-PGDS. Hypoxia-induced ANP secretion was clearly attenuated by HIF-1α antagonist 2-methoxyestradiol, downregulating both HIF-1α and L-PGDS protein levels. It was also attenuated by L-PGDS antagonists, AT-56 and HQL-49, downregulating L-PGDS protein levels. In addition, hypoxia-induced ANP secretion was accompanied by increased PPARγ protein levels and was strongly attenuated by PPARγ antagonist GW9662. Hypoxia-induced increase in atrial PPARγ protein levels were dramatically inhibited by both 2-methoxyestradiol and AT-56. These results indicated that hypoxia promotes ANP secretion, at least in part, by activating HIF-1α-l-PGDS-PPARγ signaling in beating rat atria.

Manipulation of neural progenitor fate through the oxygen sensing pathway

Neural progenitor cells hold significant promise in a variety of clinical settings. While both the brain and spinal cord harbor endogenous neural progenitor or stem cells, they typically are not capable of repopulating neural populations in case of injury or degenerative disease. In vitro systems for the culture of neural progenitors has come a long ways due to advances in the method development. Recently, many groups have shown that manipulation of the oxygen-sensing pathway leading to activation of hypoxia inducible factors (HIFs) that can influence the proliferation, differentiation or maturation of neural progenitors. Moreover, different oxygen concentrations appear to affect lineage specification of neural progenitors upon their differentiation in vitro. Here we summarize some of these studies in an attempt to direct effort towards implementation of best methods to advance the use of neural progenitors from basic development towards clinical application.

Activation of PERK Elicits Memory Impairment through Inactivation of CREB and Downregulation of PSD95 After Traumatic Brain Injury

The PKR-like ER kinase (PERK), a transmembrane protein, resides in the endoplasmic reticulum (ER). Its activation serves as a key sensor of ER stress, which has been implicated in traumatic brain injury (TBI). The loss of memory is one of the most common symptoms after TBI, but the precise role of PERK activation in memory impairment after TBI has not been well elucidated. Here, we have shown that blocking the activation of PERK using GSK2656157 prevents the loss of dendritic spines and rescues memory deficits after TBI. To elucidate the molecular mechanism, we found that activated PERK phosphorylates CAMP response element binding protein (CREB) and PSD95 directly at the S129 and T19 residues, respectively. Phosphorylation of CREB protein prevents its interaction with a coactivator, CREB-binding protein, and subsequently reduces the BDNF level after TBI. Conversely, phosphorylation of PSD95 leads to its downregulation in pericontusional cortex after TBI in male mice. Treatment with either GSK2656157 or overexpression of a kinase-dead mutant of PERK (PERK-K618A) rescues BDNF and PSD95 levels in the pericontusional cortex by reducing phosphorylation of CREB and PSD95 proteins after TBI. Similarly, administration of either GSK2656157 or overexpression of PERK-K618A in primary neurons rescues the loss of dendritic outgrowth and number of synapses after treatment with a PERK activator, tunicamycin. Therefore, our study suggests that inhibition of PERK phosphorylation could be a potential therapeutic target to restore memory deficits after TBI.SIGNIFICANCE STATEMENT Traumatic brain injury (TBI) is the leading cause of death and disability around the world and affects 1.7 million Americans each year. Here, we have shown that TBI-activated PKR-like ER kinase (PERK) is responsible for memory deficiency, which is the most common problem in TBI patients. A majority of PERK's biological activities have been attributed to its function as an eIF2α kinase. However, our study suggests that activated PERK mediates its function via increasing phosphorylation of CAMP response element binding protein (CREB) and PSD95 after TBI. Blocking PERK phosphorylation rescues spine loss and memory deficits independently of phosphorylation of eIF2α. Therefore, our study suggests that CREB and PSD95 are novel substrates of PERK, so inhibition of PERK phosphorylation using GSK2656157 would be beneficial against memory impairment after TBI.

Erythropoietin: Endogenous Protection of Ischemic Brain

The human brain requires uninterrupted delivery of blood-borne oxygen and nutrients to sustain its function. Focal ischemia, particularly, ischemic stroke, and global ischemia imposed by cardiac arrest disrupt the brain's fuel supply. The resultant ATP depletion initiates a complex injury cascade encompassing intracellular Ca²⁺ overload, glutamate excitotoxicity, oxido-nitrosative stress, extracellular matrix degradation, and inflammation, culminating in neuronal and astroglial necrosis and apoptosis, neurocognitive deficits, and even death. Unfortunately, brain ischemia has proven refractory to pharmacological intervention. Many promising treatments afforded brain protection in animal models of focal and global ischemia, but failed to improve survival and neurocognitive recovery of stroke and cardiac arrest patients in randomized clinical trials. The culprits are the blood-brain barrier (BBB) that limits transferral of medications to the brain parenchyma, and the sheer complexity of the injury cascade, which presents a daunting array of targets unlikely to respond to monotherapies. Erythropoietin is a powerful neuroprotectant capable of interrupting multiple aspects of the brain injury cascade. Preclinical research demonstrates erythropoietin's ability to suppress glutamate excitotoxicity and intracellular Ca²⁺ overload, dampen oxidative stress and inflammation, interrupt the apoptotic cascade, and preserve BBB integrity. However, the erythropoietin dosages required to traverse the BBB and achieve therapeutically effective concentrations in the brain parenchyma impose untoward side effects. Recent discoveries that hypoxia induces erythropoietin production within the brain and that neurons, astroglia, and cerebrovascular endothelium harbor membrane erythropoietin receptors, raise the exciting prospect of harnessing endogenous erythropoietin to protect the brain from the ravages of ischemia-reperfusion.

Hypoxia inducible factor-1 alpha stabilization for regenerative therapy in traumatic brain injury

Mild traumatic brain injury (TBI), also called concussion, initiates sequelae leading to motor deficits, cognitive impairments and subtly compromised neurobehaviors. While the acute phase of TBI is associated with neuroinflammation and nitroxidative burst, the chronic phase shows a lack of stimulation of the neurorepair process and regeneration. The deficiency of nitric oxide (NO), the consequent disturbed NO metabolome, and imbalanced mechanisms of S-nitrosylation are implicated in blocking the mechanisms of neurorepair processes and functional recovery in the both phases. Hypoxia inducible factor-1 alpha (HIF-1α), a master regulator of hypoxia/ischemia, stimulates the process of neurorepair and thus aids in functional recovery after brain trauma. The activity of HIF-1α is regulated by NO via the mechanism of S-nitrosylation of HIF-1α. S-nitrosylation is dynamically regulated by NO metabolites such as S-nitrosoglutathione (GSNO) and peroxynitrite. GSNO stabilizes, and peroxynitrite destabilizes HIF-1α. Exogenously administered GSNO was found not only to stabilize HIF-1α and to induce HIF-1α-dependent genes but also to stimulate the regeneration process and to aid in functional recovery in TBI animals.

Hypoxia and HIF-1 activation in bacterial infections

For most of the living beings, oxygen is one of the essential elements required to sustain life. Deprivation of oxygen causes tissue hypoxia and this severely affects host cell and organ functions. Tissue hypoxia is a prominent microenvironmental condition occurring in infections and there is a body of evidence that hypoxia and inflammation are interconnected with each other. The primary key factor mediating the mammalian hypoxic response is hypoxia inducible factor (HIF)-1, which regulates oxygen homeostasis on cellular, tissue and organism level. Recent studies show that HIF-1 plays a central role in angiogenesis, cancer and cardiovascular disease but also in bacterial infections. Activation of HIF-1 depends on the nature of the pathogen and the characteristics of infections in certain hosts. Up to date, it is not completely clear whether the phenomenon of HIF-1 activation in infections has a protective or detrimental effect on the host. In this review, we give an overview of whether and how hypoxia and HIF-1 affect the course of infections.

GSNO promotes functional recovery in experimental TBI by stabilizing HIF-1α

Traumatic brain injury (TBI) causes sustained disability due to compromised neurorepair mechanisms. Crucial to neurorepair and functional recovery following both TBI and stroke is hypoxia-inducible factor-1 alpha (HIF-1α). Based on reports that HIF-1α could be stabilized via S-nitrosylation, we tested the hypothesis that the S-nitrosylating agent S-nitrosoglutathione (GSNO) would stabilize HIF-1α, thereby stimulating neurorepair mechanisms and aiding in functional recovery. TBI was induced by controlled cortical impact (CCI) in adult rats. GSNO (0.05mg/kg) was administered at two hours after CCI. The treatment was repeated daily until the 14th day after CCI. Functional recovery was assessed by motor and cognitive functions, and the recovery was compared with the expression of HIF-1α. The mechanisms of GSNO-mediated S-nitrosylation of HIF-1α were determined using brain endothelial cells. While non-treated TBI animals showed sustained neurobehavioral deficits, GSNO treatment of TBI improved neurobehavioral functions. GSNO also increased the expression of HIF-1α and VEGF. The beneficial effects of GSNO on neurobehavioral functions in TBI animals were blocked by treatment with the HIF-1α inhibitor 2-methoxyestradiol (2-ME). The stimulatory effect of GSNO on VEGF was reversed not only by 2-ME but also by the denitrosylating agent dithiothreitol, confirming our hypothesis that GSNO's benefits are mediated by the stabilization of HIF-1α via S-nitrosylation. GSNO's S-nitrosylation of HIF-1α was further confirmed using a biotin switch assay in endothelial cells. The data provide evidence that GSNO treatment of TBI aids functional recovery through stabilizing HIF-1α via S-nitrosylation. GSNO is a natural component of the human brain/body, and its exogenous administration has not shown adverse effects in humans. Therefore, the translational potential of GSNO therapy in TBI is high.

Aberrant expression of miR-153 is associated with overexpression of hypoxia-inducible factor-1α in refractory epilepsy

Evidence suggest that overexpression of hypoxia-inducible factor-1α (HIF-1α) is linked to multidrug resistance of epilepsy. Here we explored whether aberrant expression of HIF-1α is regulated by miRNAs. Genome-wide microRNA expression profiling was performed on temporal cortex resected from mesial temporal lobe epilepsy (mTLE) patients and age-matched controls. miRNAs that are putative regulator of HIF-1α were predicted via target scan and confirmed by real-time quantitative polymerase chain reaction (RT-qPCR). Mimics or miRNA morpholino inhibitors were transfected in astrocytes and luciferase reporter assay was applied to detect HIF-11α expression. Microarray profiling identified down-regulated miR-153 as a putative regulator of HIF-1α in temporal cortex resected from surgical mTLE patients. RT-qPCR confirmed down-regulation of miR-153 in plasma of mTLE patients in an independent validation cohort. Knockdown of miR-153 significantly enhanced expression of HIF-1α while forced expression of miR-153 dramatically inhibited HIF-1α expression in pharmacoresistant astrocyte model. Luciferase assay established that miR-153 might inhibit HIF-1α expression via directly targeting two binding sites in the 3′UTR region of HIF-1α transcript. These data suggest that down-regulation of miR-153 may contribute to enhanced expression of HIF-1α in mTLE and serve as a novel biomarker and treatment target for epilepsy.