Tolerance to ischemia - an increasingly complex biology

Endogenous neuroprotective mechanism of ATP2B1 in transcriptional regulation of ischemic preconditioning

Ischemic stroke is the main cause of disability and mortality in the world. Clinical studies have shown that patients who undergo mild transient ischemic attack (TIA) before more severe ischemic stroke have lower clinical severity of stroke and better functional prognosis. This phenomenon is called ischemic preconditioning (IPC). IPC is a powerful intrinsic protection of the brain against ischemic injury, but the underlying mechanism of IPC-mediated endogenous protection of the brain is not clear.

METHODS

Using transcriptome method, we sequenced the serum of 3 stroke patients with progenitor TIA and 3 stroke patients without prodromal TIA. We explored the expression profiles of miRNAs and mRNAs in response to IPC, and predicted the regulatory pathway of IPC related genes and their expression in cerebral neurons. The methylation consistent expression of IPC-related gene ATP2B1 in blood and brain and alternative polyadenylate (APA) analysis were used to identify the pathway and molecular mechanism of endogenous neuroprotection of IPC.

RESULTS

We found that the brain protective effect of IPC was related to platelet homeostasis and Ca²⁺ concentration. IPC-related gene ATP2B1 was highly expressed in γ-aminobutyric acid (GABA)-containing neurons in the brain. From the mechanism, we speculated that ATP2B1 was representative of the same methylation in blood and brain and was affected by alternative polyadenylation.

CONCLUSION

We speculate that IPC can induce alternative polyadenylation of ATP2B1 and trigger the mechanism of brain endogenous neuroprotection by regulating the decrease of Ca²⁺ concentration in platelet homeostasis pathway and the activation of GABAB receptor.

Magnesium induces preconditioning of the neonatal brain via profound mitochondrial protection

Magnesium sulphate (MgSO4) given to women in preterm labor reduces cerebral palsy in their offspring but the mechanism behind this protection is unclear, limiting its effective, safe clinical implementation. Previous studies suggest that MgSO4 is not neuroprotective if administered during or after the insult, so we hypothesised that MgSO4 induces preconditioning in the immature brain. Therefore, we administered MgSO4 at various time-points before/after unilateral hypoxia-ischemia (HI) in seven-day-old rats. We found that MgSO4 treatment administered as a bolus between 6 days and 12 h prior to HI markedly reduced the brain injury, with maximal protection achieved by 1.1 mg/g MgSO4 administered 24 h before HI. As serum magnesium levels returned to baseline before the induction of HI, we ascribed this reduction in brain injury to preconditioning. Cerebral blood flow was unaffected, but mRNAs/miRNAs involved in mitochondrial function and metabolism were modulated by MgSO4. Metabolomic analysis (H+-NMR) disclosed that MgSO4 attenuated HI-induced increases in succinate and prevented depletion of high-energy phosphates. MgSO4 pretreatment preserved mitochondrial respiration, reducing ROS production and inflammation after HI. Therefore, we propose that MgSO4 evokes preconditioning via induction of mitochondrial resistance and attenuation of inflammation.

SUMOylation participates in induction of ischemic tolerance in mice

A group of proteins, small ubiquitin-like modifier (SUMO) proteins, has been shown to play a major role in rodent cerebral ischemia. Here, we proved that transient global cerebral ischemia induces a marked increase in protein sumo2/3 conjugation levels, we also find that global sumo2/3 conjugation is involved in ischemic tolerance in mice. Mice preconditioned by sublethal ischemia were less vulnerable to severe ischemia than non-preconditioned mice. Five-minute BCCAO precondition decreased the levels of SUMO2/3-conjugated proteins induced by MCAO. These findings suggest that maintenance of a globally decreased SUMO2/3 (and maybe SUMO-2/3) conjugation level as revealed by immunoblot assays is a component of ischemic tolerance.

Further application of hyperbaric oxygen in prostate cancer

Hyperbaric oxygen therapy (HBOT) has been used as an adjuvant treatment for multiple pathological states, which involves hypoxic conditions. Over the past 50 years, HBOT has been recommended and used in a wide variety of medical conditions, clinically in the treatment of ischemic or nonhealing wounds and radiation-injured tissue, and in the treatment of malignancy. The mechanism of this treatment is providing oxygen under pressure which is higher than the atmosphere thus increasing tissue oxygen concentration. When cells get enough oxygen in the microenvironment, they become active and replicate effectively. Prostate cancer is the second most common cancer and the fifth leading cause of cancer death among male around the world. It is estimated that more than 29,000 men died from metastatic prostate cancer in 2014. With the development of the prostate-specific antigen-based screening technology, prostate cancer incidence has increased markedly over time. According to the survey, the morbidity and mortality of prostate cancer have surpassed bladder cancer and renal carcinoma, becoming the most common cancer in urology in Chinese adults. Nowadays, the main solution to deal with prostate cancer is still the surgical ways, including laparoscopic radical prostatectomy and robot-assisted radical prostatectomy. Nevertheless, the complications of the surgical treatment have not been completely avoided. HBOT has gained great clinical recognition over the decade. It has been demonstrated that HBOT has considerable effects on carcinoma, especially on decreasing complications and improving mortality. So, it is important to combine the HBOT with patients who suffer from prostate cancer. This review illuminates the effect and underlying mechanism of the HBOT in prostate cancer for further clinical application.

Magnesium sulphate induces preconditioning in preterm rodent models of cerebral hypoxia-ischemia

BACKGROUND

Brain injury in preterm infants represents a substantial clinical problem associated with development of motor impairment, cognitive deficits and psychiatric problems. According to clinical studies, magnesium sulphate (MgSO₄) given to women in preterm labor reduces the risk of cerebral palsy in the offspring but the mechanisms behind its neuroprotective effects are still unclear. Our aim was to explore whether MgSO₄ induces tolerance (preconditioning) in the preterm rodent brain. For this purpose we established a model of perinatal hypoxia-ischemia (HI) in postnatal day 4 rats and also applied a recently developed postnatal day 5 mouse model of perinatal brain injury.

METHODS

Postnatal day 4 Wistar rats were exposed to unilateral carotid artery ligation followed by 60, 70 or 80 min of hypoxia (8% O₂). On postnatal day 11, brains were collected and macroscopically visible damage as well as white and grey matter injury was examined using immunohistochemical staining. Once the model had been established, a possible preconditioning protection induced by a bolus MgSO₄ injection prior to 80 min HI was examined 7 days after the insult. Next, a MgSO₄ bolus was injected in C57Bl6 mice on PND 4 followed by exposure to unilateral carotid artery ligation and hypoxia, (10% O₂) for 70 min on PND 5. Brains were collected 7 days after the insult and examined with immunohistochemistry for grey and white matter injury.

RESULTS

In rats, a 60 min period of hypoxia resulted in very few animals with brain injury and although 70 min of hypoxia resulted in a higher percentage of injured animals, the brains were marginally damaged. An 80 min exposure of hypoxia caused cortical tissue damage combined with hippocampal atrophy and neuronal loss in the C3 hippocampal layer. In the rat model, MgSO₄ (1.1 mg/g administered i.p. 24 h prior to the induction of HI, resulting in a transient serum Mg²⁺ concentration elevation to 4.1 ± 0.2 mmol/l at 3 h post i.p. injection) reduced brain injury by 74% in grey matter and 64% in white matter. In the mouse model, MgSO₄ (0.92 mg/g) i.p. injection given 24 h prior to the HI insult resulted in a Mg²⁺ serum concentration increase reaching 2.7 ± 0.3 mmol/l at 3 h post injection, which conferred a 40% reduction in grey matter injury.

CONCLUSIONS

We have established a postnatal day 4 rat model of HI for the study of preterm brain injury. MgSO₄ provides a marked preconditioning protection both in postnatal day 4 rats and in postnatal day 5 mice.

Regulation of gene expression in ischemic preconditioning in the brain

Stroke is the third leading cause of death and the leading cause of long-term disability, with very few effective treatments and limited progress in the effort to search for novel therapeutic approaches. The phenomenon that a sublethal ischemic insult induces protection against a subsequent severe ischemia, termed ischemic preconditioning (IPC), represents an endogenous protective approach against ischemic brain injury, and may direct a breakthrough to future therapeutic strategies. It is broadly accepted that new protein synthesis is required for IPC-mediated long-term neuroprotection; however, their relative regulatory mechanisms are poorly understood. In the present review, we summarize genomic-based studies on alterations in gene expression and protein synthesis, particularly categorizing potential pathways regulated by IPC. We also review the role of epigenetics, an inheritable genetic regulatory mechanism without changes in DNA sequence, in IPC-mediated neuroprotection.

Neuroprotective effects of 2,4-dinitrophenol in an acute model of Parkinson's disease

Neurons depend on mitochondria for homeostasis and survival, and thus, mitochondrial dysfunction has been implicated in neurodegenerative diseases, including Parkinson's disease (PD). Increasing evidence indicates the mitochondrial uncoupler, 2,4-dinitrophenol (DNP), protects neurons against neurodegeneration and enhances neural plasticity. Here, the authors evaluated the protective effects of intraperitoneally (i.p.) administered low dose DNP in an acute mouse model of PD. Mice were administered DNP (1 or 5mg/kg) for 12 consecutive days, and then on day 13, MPTP (20mg/kg, i.p.) was administered four times (with 2h intervals between injections) to induce PD. It was found that MPTP-induced motor dysfunction was ameliorated in the DNP-treated mice versus vehicle-treated controls. Additionally, DNP effectively attenuated dopaminergic neuronal loss observed in MPTP treated mice. Moreover, in primary cultured neurons, DNP at 10μM, but not at 100μM, prevented MPP⁺-induced cell death and mitochondrial membrane potential (MMP) reduction. In addition, DNP was observed to cause the nuclear translocation of Nrf2 in primary neurons. Taken together, these findings of the present study suggest that DNP protects dopaminergic neurons against neurodegeneration and maintains MMP integrity in PD by activating adaptive stress responses.

The mitochondrial uncoupler DNP triggers brain cell mTOR signaling network reprogramming and CREB pathway up-regulation

Mitochondrial metabolism is highly responsive to nutrient availability and ongoing activity in neuronal circuits. The molecular mechanisms by which brain cells respond to an increase in cellular energy expenditure are largely unknown. Mild mitochondrial uncoupling enhances cellular energy expenditure in mitochondria and can be induced with 2,4-dinitrophenol (DNP), a proton ionophore previously used for weight loss. We found that DNP treatment reduces mitochondrial membrane potential, increases intracellular Ca(2+) levels and reduces oxidative stress in cerebral cortical neurons. Gene expression profiling of the cerebral cortex of DNP-treated mice revealed reprogramming of signaling cascades that included suppression of the mammalian target of rapamycin (mTOR) and insulin--PI3K - MAPK pathways, and up-regulation of tuberous sclerosis complex 2, a negative regulator of mTOR. Genes encoding proteins involved in autophagy processes were up-regulated in response to DNP. CREB (cAMP-response element-binding protein) signaling, Arc and brain-derived neurotrophic factor, which play important roles in synaptic plasticity and adaptive cellular stress responses, were up-regulated in response to DNP, and DNP-treated mice exhibited improved performance in a test of learning and memory. Immunoblot analysis verified that key DNP-induced changes in gene expression resulted in corresponding changes at the protein level. Our findings suggest that mild mitochondrial uncoupling triggers an integrated signaling response in brain cells characterized by reprogramming of mTOR and insulin signaling, and up-regulation of pathways involved in adaptive stress responses, molecular waste disposal, and synaptic plasticity. Physiological bioenergetic challenges such as exercise and fasting can enhance neuroplasticity and protect neurons against injury and neurodegeneration. Here, we show that the mitochondrial uncoupling agent 2,4-dinitrophenol (DNP) elicits adaptive signaling responses in the cerebral cortex involving activation of Ca(2+) -CREB and autophagy pathways, and inhibition of mTOR and insulin signaling pathways. The molecular reprogramming induced by DNP, which is similar to that of exercise and fasting, is associated with improved learning and memory, suggesting potential therapeutic applications for DNP.

Remote Limb Ischemic Preconditioning: A Neuroprotective Technique in Rodents

Sublethal ischemia protects tissues against subsequent, more severe ischemia through the upregulation of endogenous mechanisms in the affected tissue. Sublethal ischemia has also been shown to upregulate protective mechanisms in remote tissues. A brief period of ischemia (5-10 min) in the hind limb of mammals induces self-protective responses in the brain, lung, heart and retina. The effect is known as remote ischemic preconditioning (RIP). It is a therapeutically promising way of protecting vital organs, and is already under clinical trials for heart and brain injuries. This publication demonstrates a controlled, minimally invasive method of making a limb - specifically the hind limb of a rat - ischemic. A blood pressure cuff developed for use in human neonates is connected to a manual sphygmomanometer and used to apply 160 mmHg pressure around the upper part of the hind limb. A probe designed to detect skin temperature is used to verify the ischemia, by recording the drop in skin temperature caused by pressure-induced occlusion of the leg arteries, and the rise in temperature which follows release of the cuff. This method of RIP affords protection to the rat retina against bright light-induced damage and degeneration.

Dynamic changes in DNA methylation in ischemic tolerance

Epigenetic mediators of gene expression are hypothesized to regulate transcriptomic responses to preconditioning ischemia and ischemic tolerance. Here, we utilized a methyl-DNA enrichment protocol and sequencing (ChIP-seq) to identify patterns of DNA methylation in an established model of ischemic tolerance in neuronal cultures (oxygen and glucose deprivation: OGD). We observed an overall decrease in global DNA methylation at 4 h following preconditioning ischemia (30 min OGD), harmful ischemia (120 min OGD), and in ischemic tolerant neuronal cultures (30 min OGD, 24 h recovery, 120 min OGD). We detected a smaller cohort of hypermethylated regions following ischemic conditions, which were further analyzed revealing differential chromosomal localization of methylation, and a differential concentration of methylation on genomic regions. Together, these data show that the temporal profiles of DNA methylation with respect to chromatin hyper- and hypo-methylation following various ischemic conditions are highly dynamic, and may reveal novel targets for neuroprotection.

A critical review of mechanisms regulating remote preconditioning-induced brain protection

Remote preconditioning (rPC) is the phenomenon whereby brief organ ischemia evokes an endogenous response such that a different (remote) organ is protected against subsequent, normally injurious ischemia. Experiments show rPC to be effective at evoking cardioprotection against ischemic heart injury and, more recently, neuroprotection against brain ischemia. Such is the enthusiasm for rPC that human studies have been initiated. Clinical trials suggest rPC to be safe (phase II trial) and effective in reducing stroke incidence in a population with high stroke risk. However, despite the therapeutic potential of rPC, there is a large gap in knowledge regarding the effector mechanisms of rPC and how it might be orchestrated to improve outcome after stroke. Here we provide a critical review of mechanisms that are directly attributable to rPC-induced neuroprotection in preclinical trials of rPC.

Oxygen and glucose deprivation induces widespread alterations in mRNA translation within 20 minutes

Background

Oxygen and glucose metabolism play pivotal roles in many (patho)physiological conditions. In particular, oxygen and glucose deprivation (OGD) during ischemia and stroke results in extensive tissue injury and cell death.

Results

Using time-resolved ribosome profiling, we assess gene expression levels in a neural cell line, PC12, during the first hour of OGD. The most substantial alterations are seen to occur within the first 20 minutes of OGD. While transcription of only 100 genes is significantly altered during one hour of OGD, the translation response affects approximately 3,000 genes. This response involves reprogramming of initiation and elongation rates, as well as the stringency of start codon recognition. Genes involved in oxidative phosphorylation are most affected. Detailed analysis of ribosome profiles reveals salient alterations of ribosome densities on individual mRNAs. The mRNA-specific alterations include increased translation of upstream open reading frames, site-specific ribosome pauses, and production of alternative protein isoforms with amino-terminal extensions. Detailed analysis of ribosomal profiles also reveals six mRNAs with translated ORFs occurring downstream of annotated coding regions and two examples of dual coding mRNAs, where two protein products are translated from the same long segment of mRNA, but in two different frames.

Conclusions

These findings uncover novel regulatory mechanisms of translational response to OGD in mammalian cells that are different from the classical pathways such as hypoxia inducible factor (HIF) signaling, while also revealing sophisticated organization of protein coding information in certain genes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-015-0651-z) contains supplementary material, which is available to authorized users.

Ischemic conditioning-induced endogenous brain protection: Applications pre-, per- or post-stroke

In the area of brain injury and neurodegenerative diseases, a plethora of experimental and clinical evidence strongly indicates the promise of therapeutically exploiting the endogenous adaptive system at various levels like triggers, mediators and the end-effectors to stimulate and mobilize intrinsic protective capacities against brain injuries. It is believed that ischemic pre-conditioning and post-conditioning are actually the strongest known interventions to stimulate the innate neuroprotective mechanism to prevent or reverse neurodegenerative diseases including stroke and traumatic brain injury. Recently, studies showed the effectiveness of ischemic per-conditioning in some organs. Therefore the term ischemic conditioning, including all interventions applied pre-, per- and post-ischemia, which spans therapeutic windows in 3 time periods, has recently been broadly accepted by scientific communities. In addition, it is extensively acknowledged that ischemia-mediated protection not only affects the neurons but also all the components of the neurovascular network (consisting of neurons, glial cells, vascular endothelial cells, pericytes, smooth muscle cells, and venule/veins). The concept of cerebroprotection has been widely used in place of neuroprotection. Intensive studies on the cellular signaling pathways involved in ischemic conditioning have improved the mechanistic understanding of tolerance to cerebral ischemia. This has added impetus to exploration for potential pharmacologic mimetics, which could possibly induce and maximize inherent protective capacities. However, most of these studies were performed in rodents, and the efficacy of these mimetics remains to be evaluated in human patients. Several classical signaling pathways involving apoptosis, inflammation, or oxidation have been elaborated in the past decades. Newly characterized mechanisms are emerging with the advances in biotechnology and conceptual renewal. In this review we are going to focus on those recently reported methodological and mechanistic discoveries in the realm of ischemic conditioning. Due to the varied time differences of ischemic conditioning in different animal models and clinical trials, it is important to define optimal timing to achieve the best conditioning induced neuroprotection. This brings not only an opportunity in the treatment of stroke, but challenges as well, as data is just becoming available and the procedures are not yet optimized. The purpose of this review is to shed light on exploiting these ischemic conditioning modalities to protect the cerebrovascular system against diverse injuries and neurodegenerative disorders.

Enhanced Retinal Ganglion Cell Survival in Glaucoma by Hypoxic Postconditioning After Disease Onset

The neuroprotective efficacy of adaptive epigenetics, wherein beneficial gene expression changes are induced by nonharmful "conditioning" stimuli, is now well established in several acute, preclinical central nervous system injury models. Recently, in a mouse model of glaucoma, we demonstrated retinal ganglion cell (RGC) protection by repetitively "preconditioning" with hypoxia prior to disease onset, indicating an epigenetic approach may also yield benefits in chronic neurodegenerative disease. Herein, we determined whether presenting the repetitive hypoxic stimulus after disease initiation [repetitive hypoxic "postconditioning" (RH-Post)] could afford similar functional and morphologic protection against glaucomatous RGC injury. Chronic elevations in intraocular pressure (IOP) were induced unilaterally in adult male C57BL/6 mice by episcleral vein ligation. Mice were randomized to an RH-Post [1 h of systemic hypoxia (11% oxygen) every other day, starting 4 days after IOP elevation] or an untreated control group. After 3 weeks of experimental glaucoma, the 21-27% reduction and 5-25% prolongation in flash visual-evoked potential amplitudes and latencies, respectively, and the 30% impairment in visual acuity were robustly improved in RH-Post-treated mice, as was the 17% loss in RGC soma number and 20% reduction in axon integrity. These protective effects were observed without RH-Post affecting IOP. The present findings demonstrate that functional and morphologic protection of RGCs can be realized by stimulating epigenetic responses during the early stages of disease, and thus constitute a new conceptual approach to glaucoma therapeutics.

Extending injury- and disease-resistant CNS phenotypes by repetitive epigenetic conditioning

Significant reductions in the extent of acute injury in the CNS can be achieved by exposure to different preconditioning stimuli, but the duration of the induced protective phenotype is typically short-lasting, and thus is deemed as limiting its clinical applicability. Extending the period over which such adaptive epigenetic changes persist – in effect, expanding conditioning’s “therapeutic window” – would significantly broaden the potential applications of such a treatment approach in patients. The frequency of the conditioning stimulus may hold the key. While transient (1–3 days) protection against CNS ischemic injury is well established preclinically following a single preconditioning stimulus, repetitively presenting preconditioning stimuli extends the duration of ischemic tolerance by many weeks. Moreover, repetitive intermittent postconditioning enhances post-ischemic recovery metrics and improves long-term survival. Intermittent conditioning is also efficacious for preventing or delaying injury in preclinical models of chronic neurodegenerative disease, and for promoting long-lasting functional improvements in a number of other pathologies as well. Although the detailed mechanisms underlying these protracted kinds of neuroplasticity remain largely unstudied, accumulating empirical evidence supports the contention that all of these adaptive phenotypes are epigenetically mediated. Going forward, additional preclinical demonstrations of the ability to induce sustained beneficial phenotypes that reduce the burden of acute and chronic neurodegeneration, and experimental interrogations of the regulatory constructs responsible for these epigenetic responses, will accelerate the identification of not only efficacious but also practical, adaptive epigenetics-based treatments for individuals with neurological disease.

In vitro ischemia decreases histone H4K16 acetylation in neural cells

Inhibitors of histone deacetylases are frequently used against ischemia-induced injury, but the specific mechanisms of their action are poorly understood. Here, we report that following a 5-7-h oxygen-glucose deprivation (OGD) acetylation of histone H4 at residue K16 (H4K16Ac) decreases by 40-80% in both PC12 cells and primary neurons. This effect can be reverted by treatment with trichostatin A, or by supplementation with acetyl-CoA. A decrease in H4K16Ac levels can affect the expression of mitochondrial uncoupling protein 2 (UCP2), huntingtin-interacting protein 1 (HIP1) and Notch-pathway genes in a cell-specific manner. Thus, H4K16 acetylation is important for responses to ischemia and cell energy stress, and depends on both cytosolic and mitochondrial acetyl-CoA.

Role of hypoxia-inducible factor-1α in preconditioning-induced protection of retinal ganglion cells in glaucoma

PURPOSE

We recently demonstrated in a mouse model of glaucoma that endogenous epigenetic mechanisms can be activated by a repetitive hypoxic preconditioning (RHP) stimulus to provide robust retinal ganglion cell (RGC) protection. Although we also provided evidence that RHP prevents or delays the apoptotic demise of the RGC soma, the mechanisms responsible for signaling this epigenetic response, as well as the effectors of the glaucoma-tolerant phenotype at the somatic and axonal levels, remain unidentified. In the present study, we used conditional mutant mice lacking hypoxia-inducible factor-1α (HIF-1α) in RGCs (HIF-1α RGC-knockout [KO] mice) to test the hypothesis that RHP-mediated activation of this transcription factor in these cells protects them from glaucomatous injury.

METHODS

Adult HIF-1α RGC-KO mice, generated by mating floxed HIF-1α mice with math5-Cre mice, were used. Experimental glaucoma was induced unilaterally in the HIF-1α RGC-KO mice and matched wild-types by elevating the intraocular pressure to 16-20 mmHg for 3 consecutive weeks, secondary to episcleral vein ligation. Mice of each genotype were randomized to either an RHP protocol (six total exposures to systemic hypoxia [11% oxygen], interspersed over a 2-week period, completed 3 days before ligation surgery) or to an untreated group. RGC soma and axon injury was quantified with Neuronal Nuclei (NeuN) immunohistochemistry in retinal flat mounts and SMI32 immunohistochemistry in cross sections of the post-laminar optic nerve, respectively.

RESULTS

HIF-1α RGC-KO mice exhibited normal retinal function and morphology, and crosses of math5-Cre mice with floxed ROSA26 reporter mice confirmed Cre recombinase activity was confined to the RGC axons and soma. Untreated wild-type mice exhibited a 30±2% loss of RGC soma and a 31±3% loss of RGC axons after 3 weeks of intraocular hypertension (both p<0.05 versus fellow eye). The 90% and 81% improvement in soma and axon survival, respectively, observed in the wild-type mice treated with RHP (both p<0.05 versus the glaucoma eye in the untreated mice) was still observed to a near identical extent in the RHP-treated HIF-1α RGC-KO mice. RHP had no effect on the magnitude of intraocular pressure elevation in either the KO or wild-type groups, indicating that protection was realized in both genotypes in the face of ongoing intraocular hypertension.

CONCLUSIONS

These findings indicate that the robust, glaucomatous protection of the RGC soma and axons induced by RHP does not require HIF-1α-mediated transcription of survival genes and other adaptive responses within the RGCs themselves. Rather, we infer that RGC survival is augmented secondary to the activation of other hypoxia-sensitive transcription factors in RGCs and/or the action of diffusible HIF-1α target gene proteins released from neighboring retinal cells. Ideally, the involvement of such autocrine- and/or paracrine-based mechanisms would be confirmed in future studies, but distinct components of the integrated, pleiotropic, and multicellular basis of this endogenous epigenetic response may prove difficult to demonstrate experimentally, as we found in the present study.

All's well that transcribes well: non-coding RNAs and post-stroke brain damage

The mammalian genome is replete with various classes of non-coding (nc) RNA genes. Many of them actively transcribe, and their relevance to CNS diseases is just beginning to be understood. CNS is one of the organs in the body that shows very high ncRNAs activity. Recent studies demonstrated that cerebral ischemia rapidly changes the expression profiles of different classes of ncRNAs: including microRNA, long noncoding RNA and piwi-interacting RNA. Several studies further showed that post-ischemic neuronal death and/or plasticity/regeneration can be altered by modulating specific microRNAs. These studies are of interest for therapeutic development as they may contribute to identifying new ncRNA targets that can be modulated to prevent secondary brain damage after stroke.

Neuroglobin: neuroprotection and neurogenesis

Globins, such as hemoglobin, serve as oxygen sensors. Neuroglobin is the globin in brain. It is induced by ischemia and is protective in modeled stroke. Here, Haines et al. describe an additional property of neuroglobin, its expression in progenitor cell populations in brain during development. A physiologic role is offered but other data show progenitor cells response to injury and their neurotropic properties in ischemic brain.