Biphasic expression of the fos and jun families of transcription factors following transient forebrain ischaemia in the rat. Effect of hypothermia

Pharmacokinetics during therapeutic hypothermia in neonates: from pathophysiology to translational knowledge and physiologically-based pharmacokinetic (PBPK) modeling

INTRODUCTION

Perinatal asphyxia (PA) still causes significant morbidity and mortality. Therapeutic hypothermia (TH) is the only effective therapy for neonates with moderate to severe hypoxic-ischemic encephalopathy after PA. These neonates need additional pharmacotherapy, and both PA and TH may impact physiology and, consequently, pharmacokinetics (PK) and pharmacodynamics (PD).

AREAS COVERED

This review provides an overview of the available knowledge in PubMed (until November 2022) on the pathophysiology of neonates with PA/TH. In vivo pig models for this setting enable distinguishing the effect of PA versus TH on PK and translating this effect to human neonates. Available asphyxia pig models and methodological considerations are described. A summary of human neonatal PK of supportive pharmacotherapy to improve neurodevelopmental outcomes is provided.

EXPERT OPINION

To support drug development for this population, knowledge from clinical observations (PK data, real-world data on physiology), preclinical (in vitro and in vivo (minipig)) data, and molecular and cellular biology insights can be integrated into a predictive physiologically-based PK (PBPK) framework, as illustrated by the I-PREDICT project (Innovative physiology-based pharmacokinetic model to predict drug exposure in neonates undergoing cooling therapy). Current knowledge, challenges, and expert opinion on the future directions of this research topic are provided.

Transient expression of thyrotropin releasing hormone peptide and mRNA in the rat hippocampus following global cerebral ischemia/reperfusion injury

INTRODUCTION

The role of extra-hypothalamic thyrotropin-releasing hormone (TRH) has been investigated by pharmacological studies using TRH or its analogues and found to produce a wide array of effects in the central nervous system.

METHODS

Immunofluorescence, In situ labeling of DNA (TUNEL), in situ hybridization chain reaction and quantitative real-time polymerase chain reaction were used in this study.

RESULTS

We found that the granular cells of the dentate gyrus expressed transiently a significant amount of TRH-like immunoreactivity and TRH mRNA during the 6-24 h period following global cerebral ischemia/reperfusion injury. TUNEL showed that apoptosis of neurons in the CA1 region occurred from 48 h and almost disappeared at 7 days. TRH administration 30 min before or 24 h after the injury could partially inhibit neuronal loss, and improve the survival of neurons in the CA1 region.

CONCLUSION

These data suggest that endogenous TRH expressed transiently in the dentate gyrus of the hippocampus may play an important role in the survival of neurons during the early stage of ischemia/reperfusion injury and that delayed application of TRH still produced neuroprotection. This delayed application of TRH has a promising therapeutic significance for clinical situations.

Therapeutic Hypothermia and Neuroprotection in Acute Neurological Disease

Therapeutic hypothermia has consistently been shown to be a robust neuroprotectant in many labs studying different models of neurological disease. Although this therapy has shown great promise, there are still challenges at the clinical level that limit the ability to apply this routinely to each pathological condition. In order to overcome issues involved in hypothermia therapy, understanding of this attractive therapy is needed. We review methodological concerns surrounding therapeutic hypothermia, introduce the current status of therapeutic cooling in various acute brain insults, and review the literature surrounding the many underlying molecular mechanisms of hypothermic neuroprotection. Because recent work has shown that body temperature can be safely lowered using pharmacological approaches, this method may be an especially attractive option for many clinical applications. Since hypothermia can affect multiple aspects of brain pathophysiology, therapeutic hypothermia could also be considered a neuroprotection model in basic research, which would be used to identify potential therapeutic targets. We discuss how research in this area carries the potential to improve outcome from various acute neurological disorders.

Hypothermia and brain inflammation after cardiac arrest

The cessation (ischemia) and restoration (reperfusion) of cerebral blood flow after cardiac arrest (CA) induce inflammatory processes that can result in additional brain injury. Therapeutic hypothermia (TH) has been proven as a brain protective strategy after CA. In this article, the underlying pathophysiology of ischemia-reperfusion brain injury with emphasis on the role of inflammatory mechanisms is reviewed. Potential targets for immunomodulatory treatments and relevant effects of TH are also discussed. Further studies are needed to delineate the complex pathophysiology and interactions among different components of immune response after CA and identify appropriate targets for clinical investigations.

Therapeutic hypothermia for ischemic stroke; pathophysiology and future promise

Therapeutic hypothermia, or cooling of the body or brain for the purposes of preserving organ viability, is one of the most robust neuroprotectants at both the preclinical and clinical levels. Although therapeutic hypothermia has been shown to improve outcome from related clinical conditions, the significance in ischemic stroke is still under investigation. Numerous pre-clinical studies of therapeutic hypothermia has suggested optimal cooling conditions, such as depth, duration, and temporal therapeutic window for effective neuroprotection. Several studies have also explored mechanisms underlying the mechanisms of neuroprotection by therapeutic hypothermia. As such, it appears that cooling affects multiple aspects of brain pathophysiology, and regulates almost every pathway involved in the evolution of ischemic stroke. This multifaceted mechanism is thought to contribute to its strong neuroprotective effect. In order to carry out this therapy in optimal clinical settings, methodological and pathophysiological understanding is crucial. However, more investigation is still needed to better understand the underlying mechanisms of this intervention, and to overcome clinical barriers which seem to preclude the routine use therapeutic hypothermia in stroke. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Hypothermia during Carotid Endarterectomy: A Safety Study

Background

CEA is associated with peri-operative risk of brain ischemia, due both to emboli production caused by manipulation of the plaque and to potentially noxious reduction of cerebral blood flow by carotid clamping. Mild hypothermia (34–35°C) is probably the most effective approach to protect brain from ischemic insult. It is therefore a substantial hypothesis that hypothermia lowers the risk of ischemic brain damage potentially associated with CEA. Purpose of the study is to test whether systemic endovascular cooling to a target of 34.5–35°C, initiated before and maintained during CEA, is feasible and safe.

Methods

The study was carried out in 7 consecutive patients referred to the Vascular Surgery Unit and judged eligible for CEA. Cooling was initiated 60–90 min before CEA, by endovascular approach (Zoll system). The target temperature was maintained during CEA, followed by passive, controlled rewarming (0.4°C/h). The whole procedure was carried out under anesthesia.

Results

All the patients enrolled had no adverse events. Two patients exhibited a transient bradycardia (heart rate 30 beats/min). There were no significant differences in the clinical status, laboratory and physiological data measured before and after CEA.

Conclusions

Systemic cooling to 34.5–35.0°C, initiated before and maintained during carotid clamping, is feasible and safe.

Trial Registration

ClinicalTrials.gov NCT02629653

Anesthesia-induced hypothermia mediates decreased ARC gene and protein expression through ERK/MAPK inactivation

Several anesthetics have been reported to suppress the transcription of a number of genes, including Arc, also known as Arg3.1, an immediate early gene that plays a significant role in memory consolidation. The purpose of this study was to explore the mechanism of anesthesia-mediated depression in Arc gene and protein expression. Here, we demonstrate that isoflurane or propofol anesthesia decreases hippocampal Arc protein expression in rats and mice. Surprisingly, this change was secondary to anesthesia-induced hypothermia. Furthermore, we confirm in vivo and in vitro that hypothermia per se is directly responsible for decreased Arc protein levels. This effect was the result of the decline of Arc mRNA basal levels following inhibition of ERK/MAPK by hypothermia. Overall, our results suggest that anesthesia-induced hypothermia leads to ERK inhibition, which in turns decreases Arc levels. These data give new mechanistic insights on the regulation of immediate early genes by anesthesia and hypothermia.

Long-term effects of gestational nicotine exposure and food-restriction on gene expression in the striatum of adolescent rats

Gestational exposure to environmental toxins such as nicotine may result in detectable gene expression changes in later life. To investigate the direct toxic effects of prenatal nicotine exposure on later brain development, we have used transcriptomic analysis of striatal samples to identify gene expression differences between adolescent Lister Hooded rats exposed to nicotine in utero and controls. Using an additional group of animals matched for the reduced food intake experienced in the nicotine group, we were also able to assess the impact of imposed food-restriction on gene expression profiles. We found little evidence for a role of gestational nicotine exposure on altered gene expression in the striatum of adolescent offspring at a significance level of p<0.01 and |log2 fold change >0.5|, although we cannot exclude the possibility of nicotine-induced changes in other brain regions, or at other time points. We did, however, find marked gene expression differences in response to imposed food-restriction. Food-restriction resulted in significant group differences for a number of immediate early genes (IEGs) including Fos, Fosb, Fosl2, Arc, Junb, Nr4a1 and Nr4a3. These genes are associated with stress response pathways and therefore may reflect long-term effects of nutritional deprivation on the development of the stress system.

Role of inflammation and its mediators in acute ischemic stroke

Inflammation plays an important role in the pathogenesis of ischemic stroke and other forms of ischemic brain injury. Increasing evidence suggests that inflammatory response is a double-edged sword, as it not only exacerbates secondary brain injury in the acute stage of stroke but also beneficially contributes to brain recovery after stroke. In this article, we provide an overview on the role of inflammation and its mediators in acute ischemic stroke. We discuss various pro-inflammatory and anti-inflammatory responses in different phases after ischemic stroke and the possible reasons for their failures in clinical trials. Undoubtedly, there is still much to be done in order to translate promising pre-clinical findings into clinical practice. A better understanding of the dynamic balance between pro- and anti-inflammatory responses and identifying the discrepancies between pre-clinical studies and clinical trials may serve as a basis for designing effective therapies.

Molecular and cellular pathways as a target of therapeutic hypothermia: pharmacological aspect

Induced therapeutic hypothermia is the one of the most effective tools against brain injury and inflammation. Even though its beneficial effects are well known, there are a lot of pitfalls to overcome, since the potential adverse effects of systemic hypothermia are still troublesome. Without the knowledge of the precise mechanisms of hypothermia, it will be difficult to tackle the application of hypothermia in clinical fields. Better understanding of the characteristics and modes of hypothermic actions may further extend the usage of hypothermia by developing novel drugs based on the hypothermic mechanisms or by combining hypothermia with other therapeutic modalities such as neuroprotective drugs. In this review, we describe the potential therapeutic targets for the development of new drugs, with a focus on signal pathways, gene expression, and structural changes of cells. Theapeutic hypothermia has been shown to attenuate neuroinflammation by reducing the production of reactive oxygen species and proinflammatory mediators in the central nervous system. Along with the mechanism-based drug targets, applications of therapeutic hypothermia in combination with drug treatment will also be discussed in this review.

MicroRNA expression changes in the hippocampi of rats subjected to global ischemia

The hippocampus is particularly vulnerable to ischemia, which is accompanied by substantial alterations in gene expression. Recent studies show that microRNAs extensively mediate post-transcriptional gene expression. However, the regulatory mechanisms in the hippocampus that microRNAs participate in remain unclear. Here, we used microarray analysis to characterize the microRNA expression profile in rat hippocampus and to identify changes in expression after 20 minutes of global ischemia followed by either 30 minutes or 24 hours of reperfusion. In the normal hippocampus, we detected 286 microRNAs, of which the let-7 family accounted for 32%. After ischemia followed by 30 minutes of reperfusion, 23 microRNAs were upregulated and 32 were downregulated; after 24 hours of reperfusion 40 were upregulated and 31 were downregulated. These results suggest that several microRNAs may be involved in regulating the normal physiological activity of the hippocampus and its response to ischemia and reperfusion.

Global profiling of influence of intra-ischemic brain temperature on gene expression in rat brain

Mild to moderate differences in brain temperature are known to greatly affect the outcome of cerebral ischemia. The impact of brain temperature on ischemic disorders has been mainly evaluated through pathological analysis. However, no comprehensive analyses have been conducted at the gene expression level. Using a high-density oligonucleotide microarray, we screened 24000 genes in the hippocampus under hypothermic (32 degrees C), normothermic (37 degrees C), and hyperthermic (39 degrees C) conditions in a rat ischemia-reperfusion model. When the ischemic group at each intra-ischemic brain temperature was compared to a sham-operated control group, genes whose expression levels changed more than three-fold with statistical significance could be detected. In our screening condition, thirty-three genes (some of them novel) were obtained after screening, and extensive functional surveys and literature reviews were subsequently performed. In the hypothermic condition, many neuroprotective factor genes were obtained, whereas cell death- and cell damage-associated genes were detected as the brain temperature increased. At all intra-ischemic brain temperatures, multiple molecular chaperone genes were obtained. The finding that intra-ischemic brain temperature affects the expression level of many genes related to neuroprotection or neurotoxicity coincides with the different pathological outcomes at different brain temperatures, demonstrating the utility of the genetic approach.

General versus specific actions of mild-moderate hypothermia in attenuating cerebral ischemic damage

Mild or moderate hypothermia is generally thought to block all changes in signaling events that are detrimental to ischemic brain, including ATP depletion, glutamate release, Ca(2+) mobilization, anoxic depolarization, free radical generation, inflammation, blood-brain barrier permeability, necrotic, and apoptotic pathways. However, the effects and mechanisms of hypothermia are, in fact, variable. We emphasize that, even in the laboratory, hypothermic protection is limited. In certain models of permanent focal ischemia, hypothermia may not protect at all. In cases where hypothermia reduces infarct, some studies have overemphasized its ability to maintain cerebral blood flow and ATP levels, and to prevent anoxic depolarization, glutamate release during ischemia. Instead, hypothermia may protect against ischemia by regulating cascades that occur after reperfusion, including blood-brain barrier permeability and the changes in gene and protein expressions associated with necrotic and apoptotic pathways. Hypothermia not only blocks multiple damaging cascades after stroke, but also selectively upregulates some protective genes. However, most of these mechanisms are addressed in models with intraischemic hypothermia; much less information is available in models with postischemic hypothermia. Moreover, although it has been confirmed that mild hypothermia is clinically feasible for acute focal stroke treatment, no definite beneficial effect has been reported yet. This lack of clinical protection may result from suboptimal criteria for patient entrance into clinical trials. To facilitate clinical translation, future efforts in the laboratory should focus more on the protective mechanisms of postischemic hypothermia, as well as on the effects of sex, age and rewarming during reperfusion on hypothermic protection.

Cardiopulmonary bypass management and neurologic outcomes: an evidence-based appraisal of current practices

Neurologic complications after cardiac surgery are of growing importance for an aging surgical population. In this review, we provide a critical appraisal of the impact of current cardiopulmonary bypass (CPB) management strategies on neurologic complications. Other than the use of 20-40 microm arterial line filters and membrane oxygenators, newer modifications of the basic CPB apparatus or the use of specialized equipment or procedures (including hypothermia and "tight" glucose control) have unproven benefit on neurologic outcomes. Epiaortic ultrasound can be considered for ascending aorta manipulations to avoid atheroma, although available clinical trials assessing this maneuver are limited. Current approaches for managing flow, arterial blood pressure, and pH during CPB are supported by data from clinical investigations, but these studies included few elderly or high-risk patients and predated many other contemporary practices. Although there are promising data on the benefits of some drugs blocking excitatory amino acid signaling pathways and inflammation, there are currently no drugs that can be recommended for neuroprotection during CPB. Together, the reviewed data highlight the deficiencies of the current knowledge base that physicians are dependent on to guide patient care during CPB. Multicenter clinical trials assessing measures to reduce the frequency of neurologic complications are needed to develop evidence-based strategies to avoid increasing patient morbidity and mortality.

Cold as a therapeutic agent

The use of cold as a therapeutic agent has a long and colorful history. The Edwin Smith Papyrus, the most ancient medical text known, dated 3500 B.C., made numerous references to the use of cold as therapy. Baron de Larrey, a French army surgeon during Napoleon's Russian campaign, packed the limbs in ice prior to amputations to render the procedures painless. In the early twentieth century, a neurosurgeon, Temple Fay, pioneered "human refrigeration" as a treatment for malignancies and head injuries. In 1961, Irving Cooper developed the first closed cryoprobe system and ushered in the modern era of cryogenic surgery with his imperturbable convictions. Fay's early work fell victim to the disruptive sequel of the World War II. The Nazis confiscated his data (presented before the Third International Cancer Congress in 1939) forwarded to Belgium for publication and brutally applied his refrigeration techniques experimentally without any benefit of anesthesia in the concentration camps, especially Dachau. Hypothermia became associated in the public mind with the atrocities exposed at the war trials in Nürnberg. After lying dormant for decades, the interest was rekindled in the late 80s when mild hypothermia was shown to confer dramatic neuroprotection in a number of experimental models of brain injury. With several large multi-center clinical studies currently under way, hypothermia is receiving unprecedented attention from the medical and scientific communities.

Comprehensive regional and temporal gene expression profiling of the rat brain during the first 24 h after experimental stroke identifies dynamic ischemia-induced gene expression patterns, and reveals a biphasic activation of genes in surviving tissue

In order to identify biological processes relevant for cell death and survival in the brain following stroke, the postischemic brain transcriptome was studied by a large-scale cDNA array analysis of three peri-infarct brain regions at eight time points during the first 24 h of reperfusion following middle cerebral artery occlusion in the rat. K-means cluster analysis revealed two distinct biphasic gene expression patterns that contained 44 genes (including 18 immediate early genes), involved in cell signaling and plasticity (i.e. MAP2K7, Sprouty2, Irs-2, Homer1, GPRC5B, Grasp). The first gene induction phase occurred at 0-3 h of reperfusion, and the second at 9-15 h, and was validated by in situ hybridization. Four gene clusters displayed a progressive increase in expression over time and included 50 genes linked to cell motility, lipid synthesis and trafficking (i.e. ApoD, NPC1, G3P-dehydrogenase1, and Choline kinase) or cell death-regulating genes such as mitochondrial CLIC. We conclude that a biphasic transcriptional up-regulation of the brain-derived neurotrophic factor (BDNF)-G-protein coupled receptor (GPCR)-mitogen-activated protein (MAP) kinase signaling pathways occurs in surviving tissue, concomitant with a progressive and persistent activation of cell proliferation signifying tissue regeneration, which provide the means for cell survival and postischemic brain plasticity.

Effect of Cyclosporin A on Immediate Early Gene in Rat Global Ischemia and Its Neuroprotection

The expressions of the immediate early genes, c-fos and c-jun, and their product proteins C-FOS, C-JUN, and P-JUN were examined in the hippocampal CA1 subfield after global ischemia and reperfusion in rats treated with cyclosporin A. More than 90% neuronal cell death was seen in hippocampal CA1 7 days after global ischemia in control animals, but only 5% cell death after ischemia was seen in the CsA-treated animals. The expressions of c-fos and c-jun mRNA in the control animals were detected with an increase from 1 to 48 h after ischemia. On the other hand, they showed significant suppression in the CsA-treated animals. Increased expressions of C-FOS were found 1, 24, and 48 h after reperfusion in the control animals. In the CsA-treated animals C-FOS expression was found to increase, but the expression level reduced to a statistically insignificant level within 48 h after the ischemia. C-JUN and P-JUN expressions increased in control animals, but were almost completely suppressed in the CsA-treated animals. The present study demonstrated that the suppressant effects of CsA on IEGs and their products might have causal relationship to the dramatic protecting effect of the drug against delayed neuronal cell death.

The effect of therapeutic hypothermia on the expression of inflammatory response genes following moderate traumatic brain injury in the rat

Traumatic brain injury (TBI) initiates a cascade of cellular and molecular responses including both pro- and anti-inflammatory. Although post-traumatic hypothermia has been shown to improve outcome in various models of brain injury, the underlying mechanisms responsible for these effects have not been clarified. In this study, inflammation cDNA arrays and semi-quantitative RT-PCR were used to detect genes that are differentially regulated after TBI. In addition, the effect of post-traumatic hypothermia on the expression of selective genes was also studied. Rats (n = 6-8 per group) underwent moderate fluid-percussion (F-P) brain injury with and without hypothermic treatment (33 degrees C/3 h). RNA from 3-h or 24-h survival was analyzed for the expression of IL1-beta, IL2, IL6, TGF-beta2, growth-regulated oncogene (GRO), migration inhibitory factor (MIF), and MCP (a transcription factor). The interleukins IL-1beta, IL-2, and IL-6 and TGF-beta and GRO were strongly upregulated early and transiently from 2- to 30-fold over sham at 3 h, with normalization by 24 h. In contrast, the expressions of MIF and MCP were both reduced by TBI compared to sham. Post-traumatic hypothermia had no significant effect on the acute expression of the majority of genes investigated. However, the expression of TGF-beta2 at 24 h was significantly reduced by temperature manipulation. The mechanism by which post-traumatic hypothermia is protective may not involve a general genetic response of the inflammatory genes. However, specific genes, including TGF-beta2, may be altered and effect cell death mechanisms after TBI. Hypothermia differentially regulates certain genes and may target more delayed responses underlying the secondary damage following TBI.

Regional expression of constitutive and inducible transcription factors following transient focal ischemia in the neonatal rat: influence of hypothermia

Ischemia is a potent modulator of gene expression. Differential expression of transcription factors after focal ischemia may reflect the potential for neuronal recovery in peri-ischemic regions. Previously, we demonstrated that hypothermia reduces the volume of damage in a model of neonatal focal ischemia. In the present study, immunocytochemistry was used to assess the temporal and spatial profiles of the transcription factors Fos and pCREB under normal and hypothermic conditions in this neonatal model of focal ischemia. At 7 days of age, rat pups underwent a permanent middle cerebral artery occlusion (MCAo) coupled with a temporary 1-h occlusion of the common carotid artery (CCAo). They were maintained at 37 degrees C throughout ischemia and reperfusion (Normothermic), or given 1 h of hypothermic conditions (28 degrees C) either during the occlusion (Intraischemic Hypothermia) or during the second hour of reperfusion (postischemic hypothermia). In normothermic pups, Fos immunoreactivity peaked at early time points (4-8 h post-ischemia) in a narrow band in peri-ischemic regions. By later stages of reperfusion (12-24 h), there was a more widespread induction in peri-ischemic regions including the ipsilateral cortex. In contrast with Fos, the constitutive transcription factor pCREB was reduced in core regions at all time points examined. Both the c-fos induction in peri-ischemic regions and the reduction of pCREB in the core were attenuated by intraischemic hypothermia. Postischemic hypothermia altered the distribution of Fos immunoreactivity without significantly changing the number of Fos- and pCREB-immunoreactive cells compared to normothermic rats. Both intra- and postischemic hypothermia reduced the number of caspase-immunoreactive cells. Thus, focal ischemia in the P7 rat produces different distributions of Fos and pCREB than what has been observed in adult rats subjected to focal ischemia, and expression of these transcription factors can be altered by hypothermia.

Quantitative PCR analysis of FosB mRNA expression after short duration oxygen and light stress

Quantitative polymerase chain reaction (QPCR) was used to examine changes in FosB mRNA expression in models of oxygen and light stress to the retina. C57BL/6 mice or Sprague-Dawley (SD) albino rats were subjected to several experimental paradigms: short-term light or oxygen stress, extended hyperoxia (75% oxygen), or a model of oxygen-induced retinopathy (OIR). Control animals were subjected to room air and 5 lux cyclic light. FosB expression dramatically increases in response to light stress as well as in a model of OIR, but not in response to sustained 75% oxygen. These data suggest that both hypoxia and light stress induce expression of FosB in the retina.

Temporal and regional expression of Fos-related proteins in response to ischemic injury

The AP-1 transcription factor family has been widely studied in the response to ischemic brain injury. The data to date have demonstrated a complex involvement that depends on stimulus, subunit composition and brain region. One member in particular, the Fos-related antigen FRA-2, has demonstrated a potential for controlling neuroprotective gene expression. This study characterized the temporal and regional expression of a variety of proteins following ischemic injury induced by occlusion of the middle cerebral artery in rats. The results demonstrated upregulation of both c-Fos and FRA-2 in penumbral regions that preceded upregulation of the classic injury-associated proteins expressed by astrocytes and microglia and, in the case of FRA-2, appeared to correlate with neuronal survival. A further, previously undescribed, expression of FRA-2 in endothelial cells of the core ischemic region was also demonstrated.

Hypothermia prolongs activation of NF-kappaB and augments generation of inflammatory cytokines

While moderate hypothermia is protective against ischemic cardiac and brain injury, it is associated with much higher mortality in patients with sepsis. We previously showed that in vitro exposure to moderate hypothermia (32 degrees C) delays the induction and prolongs the duration of TNF-alpha and IL-1beta secretion by lipopolysaccharide (LPS)-stimulated human mononuclear phagocytes. In the present study, we extended these observations by showing that moderate hypothermia exerts effects on TNF-alpha and IL-1beta generation in the human THP-1 monocyte cell line that are similar to those that we previously found in primary cultured monocytes; that hypothermia causes comparable changes in cytokine generation stimulated by zymosan, toxic shock syndrome toxin-1, and LPS; and that hypothermia causes similar changes in TNF-alpha and IL-1beta mRNA accumulation. TNF-alpha mRNA half-life, determined after transcriptional arrest with actinomycin D, was not significantly prolonged by lowering incubation temperature from 37 to 32 degrees C, suggesting that hypothermia modifies TNF-alpha gene transcription. This finding was further supported by reporter gene studies showing a threefold increase in activity of the human TNF-alpha promoter at 32 vs. 37 degrees C. Electrophoretic mobility shift assay revealed that hypothermia prolonged NF-kappaBeta activation, identifying a potential role for this transcription factor in mediating the effects of hypothermia on TNF-alpha and IL-1beta production. Delayed reexpression of the inhibitor IkappaBalpha, shown by Northern blotting and immunoblotting, may account in part for the prolonged NF-kappaBeta activation at 32 degrees C. Augmentation of NF-kappaBeta-dependent gene expression during prolonged exposure to hypothermia may be a common mechanism leading to increased lethality in sepsis, late-onset systemic inflammatory response syndrome after accidental hypothermia, and neuroprotection after ischemia.

Hypothermia and stroke: the pathophysiological background

Hypothermia to mitigate ischemic brain tissue damage has a history of about six decades. Both in clinical and experimental studies of hypothermia, two principal arbitrary patterns of core temperature lowering have been defined: mild (32-35 degrees C) and moderate hypothermia (30-33 degrees C). The neuroprotective effectiveness of postischemic hypothermia is typically viewed with skepticism because of conflicting experimental data. The questions to be resolved include the: (i) postischemic delay; (ii) depth; and (iii) duration of hypothermia. However, more recent experimental data have revealed that a protected reduction in brain temperature can provide sustained behavioral and histological neuroprotection, especially when thermoregulatory responses are suppressed by sedation or anesthesia. Conversely, brief or very mild hypothermia may only delay neuronal damage. Accordingly, protracted hypothermia of 32-34 degrees C may be beneficial following acute cerebral ischemia. But the pathophysiological mechanism of this protection remains yet unclear. Although reduction of metabolism could explain protection by deep hypothermia, it does not explain the robust protection connected with mild hypothermia. A thorough understanding of the experimental data of postischemic hypothermia would lead to a more selective and effective clinical therapy. For this reason, we here summarize recent experimental data on the application of hypothermia in cerebral ischemia, discuss problems to be solved in the experimental field, and try to draw parallels to therapeutic potentials and limitations.

Hypothermia protects against gut ischemia/reperfusion-induced impaired intestinal transit by inducing heme oxygenase-1

PURPOSE

Gut ischemia/reperfusion (I/R) elicits an inflammatory response that impairs intestinal transit. We have previously shown that regional intraischemic hypothermia (IH) protects against moderate gut I/R-induced mucosal injury, is associated with decreased NF-kappaB activity and inducible nitric oxide synthase induction and preserves heme oxygenase-1 (HO-1) expression. HO-1 provides cytoprotection in various models of oxidant stress. We, therefore, tested the hypothesis that IH protects against gut I/R-induced impaired intestinal transit via HO-1 induction.

MATERIALS AND METHODS

At laparotomy (lap), Sprague-Dawley rats had duodenal catheters placed followed by sham or gut I/R (superior mesenteric artery occlusion for 75 min) with or without regional IH (15 degrees C). Each animal was placed on a heating blanket maintaining systemic normothermia (37 degrees C). At 12 or 24 h of reperfusion, small intestinal transit was determined by quantitating the distribution of a tracer (FITC dextran) in the intestine 30 min after instillation (expressed as geometric center of distribution). Ileal samples were obtained for histology and HO-1 expression, assessed by Western immunoblot at 12 and 24 h of reperfusion. In separate experiments, rats were pretreated with an HO-1 inhibitor Sn protoporphyrin IX (25 mumol/kg, ip), 1 h before superior mesenteric artery occlusion and transit measured as above.

RESULTS

Rats treated with I/R had increased histological injury and impaired intestinal transit at both 12 and 24 h compared with sham. Rats treated with I/R+IH exhibited histological injury and transit comparable with sham controls. I/R induced HO-1 expression at 12 and 24 h of reperfusion and IH augmented this I/R-induced HO-1 expression. Sn protoporphyrin IX abrogated IH protection against histological injury and impaired transit.

CONCLUSION

We conclude that intraischemic regional hypothermia protects against histological injury and impaired intestinal transit caused by severe gut I/R injury. Hypothermic protection under these conditions is in part due to HO-1 expression.

Regional hypothermia reduces mucosal NF-kappaB and PMN priming via gut lymph during canine mesenteric ischemia/reperfusion

BACKGROUND

Mesenteric ischemia/reperfusion (I/R) activates pro-inflammatory mediators that exacerbate gut reperfusion injury and prime circulating neutrophils that cause remote organ injury. We have shown that regional intraischemic hypothermia protects the intestinal mucosa during I/R in rats. In this study, we examined the effects of regional hypothermia on I/R-induced transvascular protein clearance, NF-kappaB DNA binding activity, and polymorphonuclear neutrophil (PMN) priming via gut lymph in a canine mesenteric lymphatic fistula model.

MATERIALS AND METHODS

Conditioned dogs underwent 60 min of mesenteric ischemia, with or without regional intraischemic hypothermia, and 3 h reperfusion. A mesenteric lymphatic fistula model was used to measure transvascular protein clearance and harvest lymph. Biopsies of distal ileum were obtained at baseline and 0, 180 min of reperfusion for NF-kappaB DNA binding activity using electrophoretic mobility shift assay (EMSA). A kinetic spectrophotometric assay was used to determine fMLP stimulated PMN superoxide production after priming by gut lymph obtained at baseline and 180 min reperfusion.

RESULTS

Transvascular protein clearance increased during reperfusion compared to baseline, and hypothermia had no significant effect on this I/R-induced protein clearance. NF-kappaB activity increased three-fold at the end of ischemia and hypothermia prevented this early activation. PMN superoxide production increased 19-fold during I/R (0.06 +/- 0.04 versus 1.14 +/- 0.50 nmol O(2), P < 0.05), but only 2.5-fold during I/R + hypothermia (0.28 +/- 0.09 versus 0.70 +/- 0.32 nmol O(2), P = 0.2).

CONCLUSIONS

Regional intraischemic hypothermia prevented early intestinal NF-kappaB activation, partially abrogated PMN priming via gut lymph, but had no significant effect on increased transvascular protein clearance during mesenteric I/R in dogs.

Effect of intra-ischemic hypothermia on the expression of c-Fos and c-Jun, and DNA binding activity of AP-1 after focal cerebral ischemia in rat brain

It is unknown whether immediate early gene (IEG) induction and subsequent late gene regulation after ischemia is beneficial or deleterious. The aim of this study was to examine the effect of hypothermia on expression of c-Fos and c-Jun, and AP-1 DNA binding activity, after transient focal cerebral ischemia in rat brain, and clarify the role of IEGs and AP-1 after insults. Male Wistar rats underwent right middle cerebral artery occlusion for 1 h with the intraluminal suture method. During ischemia, animals were assigned to either normothermic (NT) or hypothermic (HT) groups. In the NT group, brain temperature was observed to spontaneously increase to 40 degrees C during ischemia. In the HT group, brain temperature decreased to 30 degrees C. Infarct volume in cortex was decreased in the HT group, compared with that in the NT group (P<0.001). Increased c-Fos immunoreactivity in the cortex was observed at 3 h after reperfusion in the HT, but not the NT group, while c-Jun expression was not affected by HT treatment. There was also a significant increase in AP-1 DNA binding activity at 3 h in the HT group when compared to the NT group (P<0.01). In conclusion, hypothermia decreased cerebral infarction in association with early increases in c-Fos expression and AP-1 DNA binding activity in peri-infarct cortex. It remains to be established whether such responses are a cause or consequence of cell survival, but these results clearly establish that altered transcription is a key feature of tissue spared following hypothermic focal ischemia.

Intraischemic hypothermia differentially modulates oxidative stress proteins during mesenteric ischemia/reperfusion

BACKGROUND

Thoracoabdominal aortic aneurysm repair requires obligatory mesenteric ischemia/reperfusion (I/R), eliciting an inflammatory response resulting in gut dysfunction and remote organ injury. Therapeutic hypothermia has been advocated for organ protection (ie, brain, spinal cord, and kidneys) during extensive aortic operation, and it has also been shown to differentially modulate proinflammatory gene transcription in the central nervous system. In other I/R models, nuclear factor Kappa-B (NF-(kappa)B) and inducible nitric oxide synthase (iNOS) worsen while heme oxygenase-1 (HO-1) protects against injury. We examined the effects of regional intraischemic hypothermia on mesenteric I/R-induced mucosal injury, NF-kappaB activation, and expression of iNOS and HO-1.

METHODS

Sprague-Dawley rats underwent sham laparotomy or superior mesenteric artery occlusion for 45 minutes with or without topical hypothermia (15 degrees -20 degrees C). Intestinal epithelial permeability to (14)C inulin was assessed at 6 hours of reperfusion. In a separate set of experiments, biopsies of the ileum were obtained at 6 hours of reperfusion for: 1) mucosal histologic injury assessed by a blinded observer; 2) NF-kappaB activation by electrophoretic mobility shift assay; and 3) iNOS and HO-1 protein expression by immunoblot.

RESULTS

Mesenteric I/R significantly increased intestinal permeability to (14)C inulin, histologic injury, activation of NF-kappaB, and iNOS and HO-1 expression when compared with sham control rats. In contrast, rats treated with intraischemic topical hypothermia exhibited intestinal permeability comparable with sham control rats, and reduced histologic injury. In addition, hypothermia prevented the activation of NF-kappaB and iNOS expression, but had no effect on HO-1 expression.

CONCLUSIONS

On the basis of these observations, we conclude that therapeutically applied intraischemic hypothermia protects the gut during mesenteric I/R. In addition, hypothermia prevented NF-kappaB activation while differentially modulating expression of the oxidative stress proteins iNOS and HO-1 in response to mesenteric I/R.

Mild hypothermia increases Bcl-2 protein expression following global cerebral ischemia

Mild hypothermia protects the brain against experimental ischemia, but the reasons are not well known. We examined whether the protective effects of mild hypothermia could be correlated with alterations in expression of Bcl-2, an anti-apoptotic protein in a rat model of transient global ischemia. Following 10 min of forebrain ischemia, hippocampal neurons were examined 72 h later for survival, expression of Bcl-2 family proteins and apoptosis. Intraischemic mild hypothermia was applied for 3 h (33 degrees C, isch-33) or normal body temperature was maintained (37 degrees C, isch-37). Survival of CA1 neurons was significantly improved in the isch-33 group compared to the isch-37 group (90 vs. 53% survival; P<0.01). The proportion of Bcl-2-positive cells among surviving CA1 neurons in the isch-33 group was increased compared to that of sham and isch-37 groups (P<0.01). Bax expression in CA1 was no different between sham and isch-33 groups, but was significantly decreased in isch-37 (P<0.05). TUNEL staining was positive in many isch-37 CA1 neurons, but absent in isch-33. Utilizing electron microscopy, more cells meeting criteria for apoptosis were observed in the isch-37 than isch-33. These data suggest that mild hypothermia attenuates apoptotic death, and that this protection may be related to increases in Bcl-2.

Cell death in the choroid plexus following transient forebrain global ischemia in the rat

Following a complete disruption of blood flow to the brain, cerebral ischemia, a specific neuronal population, namely the CA1 pyramidal neurons in the hippocampus, will die a delayed type of cell death. This is often referred to as "delayed neuronal death" (DND). It is not known why it takes around 48 hours for these cells to die. It is very often speculated that events, intrinsic to the CA1 neurons, regulate their demise, whereas it is less often considered that extrinsic mechanisms also could play an important role for the development of DND. We discovered that in addition to the CA1 pyramidal neurons, cells in the choroid plexus were TUNEL (terminaldeoxynucleotidyl-mediated biotin-dUTP nick-end labeling)-positive following transient forebrain global ischemia. The time course and the number of TUNEL-positive cells were determined. A dramatic increase in the number of TUNEL-positive cells in the choroid plexus was seen at 18, 24, and at 36 hours of recovery, but not at 48 hours of recovery following 15 minutes of transient forebrain global ischemia. No TUNEL-positive cells were seen at 24 hours of recovery in the CA1 region. The cell death in the choroid plexus thus preceded the occurrence of cell death in the CA1 region. Massive cell death in the choroid plexus will inevitably lead to a leaky blood-CSF barrier, which in turn will allow substances to enter the ventricular system and from there reach the brain parenchyma. We, therefore, conclude that choroid plexus cell death may adversely affect the outcome of CA1 pyramidal neurons following transient forebrain global ischemia, through, e.g., a disruption of the blood-cerebro spinal fluid barrier. Alternatively, the choroid plexus may produce factors, which can affect the outcome of neurons.

Is light-regulated AP-1 binding in the rat suprachiasmatic nucleus gated by the circadian clock?

In mammals, photic entrainment of circadian rhythms likely involves light- and clock-dependent expression of immediate early genes, including fos-like and jun-like genes, in the rat suprachiasmatic nucleus. Using an electrophoretic mobility shift assay, we evaluated whether the photic regulation of DNA-binding activity and composition of activating protein-1 (AP-1) complexes in the suprachiasmatic nucleus is also dependent on circadian phase. Phase-dependent light inducibility in the expression of fra-2 and c-fos genes and in immunoreactive Fra-2 and c-Fos protein expression was also evaluated, by in situ hybridization and immunocytochemistry. Light's effects on AP-1 DNA-binding differed both qualitatively and quantitatively according to the circadian phase at which light was applied. This phase dependence accounted for by both compartmentalization of proteins involved in constitutive AP-1 complexes within the nucleus or cytoplasm and control of the extent to which the expression of specific complexes was induced. It was then shown that the mechanisms by which the circadian clock gates the photic induction of AP-1 components differed according to the nature of the protein.

Mild hypothermia decreases the incidence of transient ADC reduction detected with diffusion MRI and expression of c-fos and hsp70 mRNA during acute focal ischemia in rats

The effects of mild hypothermia on the apparent diffusion coefficient of water (ADC) and expression of c-fos and hsp70 mRNA were examined during acute focal cerebral ischemia. Young adult rats were subjected to 60-min middle cerebral artery occlusion under either normothermia (37.5 degrees C) or hypothermia (33 degrees C). Diffusion-weighted echo-planar magnetic resonance imaging was used to monitor changes in ADC throughout the ischemic period. Perfusion MRI with dysprosium contrast was used at the end of the ischemic period to verify that the occlusion was successful. C-fos and hsp70 mRNA expression were examined with in situ hybridization at the end of the ischemic period. The results indicate that the size of the region that exhibited reduced ADC was smaller during hypothermia than during normothermia. Hypothermia also decreased the frequency of occurrence of transient ADC reductions, especially in dorsal aspects of cortex. Expression of both c-fos and hsp70 mRNA were markedly reduced by hypothermia. Transient ADC reduction and c-fos expression are associated with spreading depression, which is believed to contribute to lesion expansion during acute focal ischemia. The results suggest that part of the neuroprotective effect of hypothermia may be due to a reduced incidence of spreading depression.

Subcellular distribution and autophosphorylation of calcium/calmodulin-dependent protein kinase II-alpha in rat hippocampus in a model of ischemic tolerance

A brief period of sublethal ischemia induces resistance to a subsequent, otherwise lethal, ischemic insult, a process named ischemic tolerance or preconditioning. A persistently disturbed cell signaling during reperfusion after cerebral ischemia has been proposed to contribute to ischemic cell death. Here, we report on the effect of ischemic preconditioning on the levels of the regulatory alpha-subunit of calcium/calmodulin protein kinase II and its phosphorylation in the hippocampal CA1 region. We found that during and following lethal cerebral ischemia, calcium/calmodulin protein kinase II-alpha is persistently translocated to cell membranes, where it becomes phosphorylated at threonine 286. In contrast, in the preconditioned brains the translocation and phosphorylation are transient and return to preischemic values after one day of reperfusion. At this time of reperfusion, the total level of calcium/calmodulin protein kinase II-alpha is significantly lower in preconditioned animals compared to the sham and non-conditioned animals. After one day of reperfusion, the level of calcium/calmodulin protein kinase II-alpha messenger RNA decreases in the non-conditioned brains, whereas it is unchanged in preconditioned brains. We conclude that, during and after ischemia, calcium/calmodulin protein kinase II-alpha is translocated to cell membranes and becomes phosphorylated at threonine 286. This could detrimentally influence cell survival by changing receptor function and ion channel conductance. Ischemic preconditioning prevents the persistent presence of calcium/calmodulin protein kinase II-alpha at cell membranes, presumably by enhancing its degradation, which could be part of a neuroprotective mechanism of ischemic tolerance.

Hypothermia modulates induction of hsp70 and c-jun mRNA in the rat brain after subarachnoid hemorrhage

We investigated expression of hsp70 and c-jun mRNA with in situ hybridization for evaluating hypothermia effect on the brain exposed to subarachnoid hemorrhage (SAH). SAH was induced in Wistar rats with endovascular perforation. Animals were divided arbitrarily into normothermic and hypothermic groups, and they were sacrificed at 3 h or 12 h after SAH. The SAH induced hsp70 and c-jun mRNAs in the cerebral cortex, hippocampus, thalamus, hypothalamus, and caudoputamen. Mild hypothermia depressed hsp70 mRNA expression in the cortex, thalamus, and hippocampus. The c-jun mRNA expression was reduced by hypothermia in the cortex, thalamus, and CA1 of the hippocampus. Based on these findings, we speculate that hypothermia protects the brain exposed to SAH by reducing this stress response. Although it is yet difficult to employ hypothermia in the clinical settings, this study suggests its utility to those patients sustaining severe subarachnoid hemorrhage.

AP1 transcriptional factor activation and its relation to apoptosis of hippocampal CA1 pyramidal neurons after transient ischemia in gerbils

The cellular processes with a potential to lead to delayed death of neurons following transient (5 min) ischemia in gerbil hippocampus were evaluated. Neuronal apoptosis, visualized by the terminal transferase dUTP nick-end labelling (TUNEL) reaction, selectively appeared in the CA1 region of the pyramidal cell layer between the third and fourth days after the insult. Concomitantly, an enhanced immunoreactivity to anti-cJun/AP1 (N) antibody as a major component of activator protein 1 (AP1) transcriptional factor was observed in CA1 neurons. In contrast, in the early postischemic phase, the cJun/AP1 reaction was noticed in numerous neurons and glia-like cells of the CA2/CA3 region, hilus of the dentate gyrus, and region of mossy fiber terminals. In parallel, hippocampal protein binding to AP1, measured by the electrophoretic mobility shift assay (EMSA), showed biphasic enhancement at 3 and then 72-120 hours after ischemia. Supershifts, with antibodies against c-Fos and phospho-c-Jun constituencies of the AP1 dimer, revealed an increased amount of phosphorylated c-Jun in the late postischemic phase. Collectively, these results suggest diversity of AP1 complex function, regulated by its dimer composition as well as time and place of expression during postischemic reperfusion. The early, survival-supporting AP1 response, located mainly in ischemia-resistant areas of CA2/3, is followed by the delayed phase, characteristic of massive neuronal apoptosis in CA1 with concomitant increase of phospho-c-Jun in AP1 dimer.

The time-course of DNA fragmentation in the choroid plexus and the CA1 region following transient global ischemia in the rat brain. The effect of intra-ischemic hypothermia

The time-course of DNA fragmentation in the CA1 region of the hippocampus and the choroid plexus was studied following induction of transient forebrain ischemia under lethal normothermic (37 degrees C), or sublethal hypothermic (33 degrees C) conditions. Oligonucleosomal- and high-molecular-weight DNA fragmentation were analysed by conventional agarose gel electrophoresis and pulsed-field gel electrophoresis, respectively. DNA breaks were visualized by the terminal deoxynucleotidyl transferase-mediated biotin-deoxyuridinetriphosphate nick-end labeling method. At 48 h of recovery following normothermic ischemia, in situ labeling of DNA breaks were widespread in medial CA1 and high-molecular-weight DNA cleavage was seen. In contrast, at the same time-point in lateral CA1, many pyknotic but few cells displaying in situ labeling of DNA breaks were observed. Major oligonucleosomal DNA fragmentation was not seen until 72 h of recovery. Following hypothermic ischemia, DNA fragmentation was absent in CA1. DNA fragmentation was seen in the choroid plexus at 24 h of recovery following normothermic ischemia, which was diminished by 48 h of recovery. In conclusion, oligonucleosomal and high-molecular-weight DNA fragmentation at 10-50 kilobase pairs, occur in CA1 after morphological signs, and acidophilia signifying neurodegeneration appear. DNA fragmentation and cell death in the choroid plexus precede neuronal death in CA1 and may play a causative role.

Neuroprotective effect of mild hypothermia cannot be explained in terms of a reduction of glutamate release during ischemia

An exogenous glutamate injection into the hypothermic hippocampal CA1 during 5-min ischemia produced the same extent of extracellular glutamate levels as observed in the normothermic CA1 during 5-min ischemia; however, neuronal death was not induced in the hypothermic CA1. Glutamate is released excessively into the extracellular space during ischemia, and is thought to induce brain injury by its neurotoxicity. It has been reported that the massive glutamate release is reduced by mild hypothermia, and it has been proposed that the reduction of ischemia-induced glutamate release exerts the neuroprotective effect on postischemic neuronal death. In the present study, to determine whether the neuroprotective effect of mild hypothermia on postischemic hippocampal CA1 neuronal death is due to the reduction of ischemia-induced glutamate release, gerbils were subjected to 5-min ischemia under hypothermic condition at 31 degrees C and were simultaneously injected exogenously with L-glutamate, so that the hypothermic CA1 around a microdialysis probe was exposed to the same extracellular glutamate levels as seen during normothermic ischemia, and the histological outcome was examined. An injection with 1 mM L-glutamate into the hypothermic CA1 during 5-min ischemia produced a similar extent of increased glutamate (17-fold increase) to that observed in the normothermic CA1 during 5-min ischemia (16-fold increase). However, neuronal death was not induced in the hypothermic CA1. This result indicates that the neuroprotective effect of mild hypothermia cannot be explained in terms of a reduction of glutamate release during ischemia.

Neuronal death and survival in two models of hypoxic-ischemic brain damage

Two unilateral hypoxic-ischemia (HI) models (moderate and severe) in immature rat brain have been used to investigate the role of various transcription factors and related proteins in delayed neuronal death and survival. The moderate HI model results in an apoptotic-like neuronal death in selectively vulnerable regions of the brain while the more severe HI injury consistently produces widespread necrosis resulting in infarction, with some necrosis resistant cell populations showing evidence of an apoptotic type death. In susceptible regions undergoing an apoptotic-like death there was not only a prolonged induction of the immediate early genes, c-jun, c-fos and nur77, but also of possible target genes amyloid precursor protein (APP751) and CPP32. In contrast, increased levels of BDNF, phosphorylated CREB and PGHS-2 were found in cells resistant to the moderate HI insult suggesting that these proteins either alone or in combination may be of importance in the process of neuroprotection. An additional feature of both the moderate and severe brain insults was the rapid activation and/or proliferation of glial cells (microglia and astrocytes) in and around the site of damage. The glial response following HI was associated with an upregulation of both the CCAAT-enhancer binding protein alpha (microglia only) and NFkappaB transcription factors.

Overexpression of thioredoxin in transgenic mice attenuates focal ischemic brain damage

Thioredoxin (TRX) plays important biological roles both in intra- and extracellular compartments, including in regulation of various intracellular molecules via thiol redox control. We produced TRX overexpressing mice and confirmed that there were no anatomical and physiological differences between wild-type (WT) mice and TRX transgenic (Tg) mice. In the present study we subjected mice to focal brain ischemia to shed light on the role of TRX in brain ischemic injury. At 24 hr after middle cerebral artery occlusion, infarct areas and volume were significantly smaller in Tg mice than in WT mice. Moreover neurological deficit was ameliorated in Tg mice compared with WT mice. Protein carbonyl content, a marker of cellular protein oxidation, in Tg mice showed less increase than did that of WT mice after the ischemic insult. Furthermore, c-fos expression in Tg mice was stronger than in WT mice 1 hr after ischemia. Our results suggest that transgene expression of TRX decreased ischemic neuronal injury and that TRX and the redox state modified by TRX play a crucial role in brain damage during stroke.

The tumor suppressor p53 and its response gene p21WAF1/Cip1 are not markers of neuronal death following transient global cerebral ischemia

The tumor suppressor protein p53 is implicated in cell cycle arrest and DNA repair as well as in apoptosis. In the CNS, p53 has been associated with neuronal cell death following various insults, including cerebral ischemia. We investigated the expression of p53 messenger RNA and protein, and the messenger RNA expression of the p53-responsive gene p21(WAF1/CiP1, in specific hippocampal regions following 15 min of normothermic and neuroprotective hypothermic (33 degrees C) global forebrain ischemia in the rat. Both p53 and p21WAF1/Cip1 messenger RNAs were transiently induced in ischemia resistant regions following normo- and hypothermic ischemia. In the ischemia sensitive CA1 region, p53 and p21WAF1/Cip1 messenger RNAs were up-regulated throughout reperfusion following the normothermic insult. The p53 protein levels increased following the insult, most markedly in ischemia-resistant CA3 neurons after normothermic ischemia, and in the CA1 neurons following hypothermic ischemia. Concomitantly, the protein was translocated to nuclei. These findings indicate that p53 and p21WAF1/Cip1 are not markers of neuronal death following global cerebral ischemia. Their rapid and transient induction correlates with cell survival, and suggests a possible role in DNA repair.

Persistent phosphorylation of cyclic AMP responsive element-binding protein and activating transcription factor-2 transcription factors following transient cerebral ischemia in rat brain

The transcription factors cyclic AMP responsive element-binding protein (CREB) and activating transcription factor-2 were studied in rat brains subjected to 15 min ischemia followed by varied periods of reperfusion using western blot and immunocytochemical analyses. The total amounts of both CREB and activating transcription factor-2 were not altered in the hippocampus after ischemia. In contrast, levels of the phosphorylated forms of both transcription factors decreased during ischemia but rebounded following reperfusion. The phospho-forms of CREB and activating transcription factor-2 showed regional and temporal differences in their expression. Phospho-CREB was increased relative to control levels at 30 min, and continued to increase for at least three days postischemia, mainly in dentate granule cells. The level of phospho-activating transcription factor-2 appeared to be higher in CAI pyramidal cells than in dentate granule cells after ischemia. The present findings suggest that the signaling pathways for phosphorylation of CREB may be neuroprotective for dentate cells, which are relatively resistant to ischemic insults. The increased phospho-activating transcription factor-2 may reflect increased stresses in these neurons. The more modest activation of CREB pathways in CA1 neurons may not be enough to overcome the increased stresses in these neurons, contributing to delayed neuronal death.

Fra-1 immunoreactivity in the rat brain during normal postnatal development and after injury in adulthood

Fra-1 is a member of the Fos family whose functional role in the central nervous system is little understood. In the present study, Fra-1 immunoreactivity is examined in the rat brain during normal development and after different injuries in adulthood, by using Western blotting and immunohistochemistry. Western blots show a band at p35 which corresponds to the molecular weight of Fra-1. During postnatal development, Fra-1 immunoreactivity is observed in nerve fibers of all the main fiber tracts in the cerebrum, whereas Fra-1 immunoreactivity in adult rats is restricted to the hippocampus, mainly the molecular layer of the dentate gyrus and the mossy fiber layer. After administration of colchicine, an axonal transport inhibitor, Fra-1 immunoreactivity accumulates in the perikarya of many cerebral neurons, including those of the dentate gyrus, hippocampus, cerebral cortex, amygdala and thalamus. Fra-1 immunoreactivity is also found in the nuclei of reactive astrocytes, as revealed with double-labeling immunohistochemistry to Fra-1 and GFAP, following either intraperitoneal injection of kainic acid at convulsant doses, intrastriatal injection of quinolinic acid, or intraventricular injection of colchicine. These results suggest a cytoplasmic role for Fra-1 in the neurons, whereas the localization of Fra-1 in the nuclei of reactive astrocytes suggests a participation of this transcription factor in the activation of the AP-1 sequence of selected genes in the early glial response after different brain lesions.

Sequential activation of activator protein-1-related transcription factors and JNK protein kinases may contribute to apoptotic death induced by transient hypoxia in developing brain neurons

Previous studies have demonstrated that transient hypoxia (6 h) induces apoptotic death in cultured neurons isolated from the fetal rat forebrain. Since activation of c-Jun N-terminal kinases (JNKs) and subsequent phosphorylation of c-Jun are suspected to be involved in the apoptotic pathway in several cell types, the time course of activator protein-1 (AP-1) DNA-binding, in line with induction of the AP-1 components and JNK activation, was examined during hypoxia/reoxygenation in the same model. Gel shift analysis depicted the presence of functional AP-1 transcription factors in both control and hypoxic neurons. One hour after the onset of hypoxia, all AP-1 components were markedly overexpressed. They include c-Jun, Jun B, Jun D, c-Fos and Fos-related antigens. Whereas, only c-Jun remained elevated for up to 96 h post-reoxygenation, time at which neurons were injured, other gene products showed patterned induction/repression as hypoxia progressed and then during the post-reoxygenation period, with Fos-related antigens being finally induced at 96 h. Only JNK1 was constitutively detected in cultured neurons, and its expression was inhibited during hypoxia. Nonetheless, both JNK1 and JNK3 were markedly, but transiently, induced at 48 h post-reoxygenation, when apoptosis-related morphological features became apparent. These data support the hypothesis that transient hypoxia, independently of ischemia, may trigger apoptosis through JNK signaling pathway in developing brain neurons.

The effect of hypothermia on the expression of neurotrophin mRNA in the hippocampus following transient cerebral ischemia in the rat

The expression of the mRNAs of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT3) and the neurotrophin receptor, TrkB, was studied in the rat hippocampus by in situ hybridization following normothermic (37 degreesC) and protective hypothermic (33 degreesC) transient cerebral ischemia of 15 min duration. In the resistant dentate gyrus, normothermic ischemia transiently induced NGF mRNA at around 8 h of recovery, while the NT3 mRNA levels were depressed over at least a 24-h recovery period. The levels of BDNF and TrkB were transiently and markedly elevated with a maximal expression at 24 h of recovery. Intraischemic hypothermia reduced the induction of NGF mRNA, while the increase of BDNF mRNA expression occurred earlier during recovery, and the post-ischemic NT3 mRNA depression was not affected. Also, the expression of TrkB mRNA was enhanced, and occurred concomitantly with the elevation of BDNF mRNA. In contrast, there were no changes in neurotrophin and TrkB mRNA in the CA3 and CA1 regions. The expression of BDNF mRNA at 24 h after normothermic ischemia, was attenuated by intraischemic hypothermia. We conclude that, the expressions of NGF, BDNF, NT3 or TrkB mRNA in ischemia-sensitive hippocampal subregions are not increased by protective hypothermia. In contrast, hypothermia induces neurotrophin mRNA alterations in the ischemia-resistant dentate gyrus that may convey protection to sensitive regions.

Inducible and constitutive transcription factors in the mammalian nervous system: control of gene expression by Jun, Fos and Krox, and CREB/ATF proteins

This article reviews findings up to the end of 1997 about the inducible transcription factors (ITFs) c-Jun, JunB, JunD, c-Fos, FosB, Fra-1, Fra-2, Krox-20 (Egr-2) and Krox-24 (NGFI-A, Egr-1, Zif268); and the constitutive transcription factors (CTFs) CREB, CREM, ATF-2 and SRF as they pertain to gene expression in the mammalian nervous system. In the first part we consider basic facts about the expression and activity of these transcription factors: the organization of the encoding genes and their promoters, the second messenger cascades converging on their regulatory promoter sites, the control of their transcription, the binding to dimeric partners and to specific DNA sequences, their trans-activation potential, and their posttranslational modifications. In the second part we describe the expression and possible roles of these transcription factors in neural tissue: in the quiescent brain, during pre- and postnatal development, following sensory stimulation, nerve transection (axotomy), neurodegeneration and apoptosis, hypoxia-ischemia, generalized and limbic seizures, long-term potentiation and learning, drug dependence and withdrawal, and following stimulation by neurotransmitters, hormones and neurotrophins. We also describe their expression and possible roles in glial cells. Finally, we discuss the relevance of their expression for nervous system functioning under normal and patho-physiological conditions.

Mild hypothermia--a revived countermeasure against ischemic neuronal damages

Although hypothermia as a means of cerebral protection against and resuscitation from ischemic damage has a history of approximately six decades, extensive studies, both in basic and clinical fields, on the mechanisms, effects and methods of mild hypothermia at temperatures no less than 31 degrees C have started only in the last decade. In experiments on rodents, hypothermia in the postischemic period that is introduced up to several hours after reperfusion and is maintained for one day followed by a slow rewarming, significantly protects hippocampal neurons against damage. The mode of action of hypothermia is apparently non-specific and multi-focal in widely progressing cascade reactions in ischemic cells; namely, suppressing: (1) glutamate surge followed by; (2) intraneuronal calcium mobilization; (3) sustained activation of glutamate receptors; (4) dysfunction of blood brain barrier; (5) proliferation of microglial cells; and (6) production of superoxide anions and nitric oxide. In addition, mild hypothermia modulates processes in ischemic condition at the level of cell nucleus, such as the binding of transcription factor AP-1 to DNA, and ameliorates the depression of protein synthesis. This non-specific and widely affecting manner might explain why hypothermia is superior to any medicine developed. Recent clinical trials of mild hypothermia in various individual institutions have revealed significantly beneficial outcomes in some cases, along with an accumulation of practical knowledge of techniques and treatments. Large scale randomized studies involving multiple institutions as well as exchange of informations and ideas are needed for further development of hypothermia treatment.

Changes in proliferating cell nuclear antigen, a protein involved in DNA repair, in vulnerable hippocampal neurons following global cerebral ischemia

Proliferating cell nuclear antigen (PCNA) is required for completion of the DNA synthesis step of DNA replication as well as nucleotide excision repair (NER) of damaged DNA. We investigated the expression of PCNA mRNA and the levels of PCNA protein in the adult rat hippocampus following normo- and hypothermic global forebrain ischemia. Hypothermia protected the CA1 neurons from ischemic damage. A constitutive expression of PCNA mRNA and protein was detected in all hippocampal subfields, as well as in other brain regions. During reperfusion, PCNA mRNA levels were up-regulated in the vulnerable CA1 subfield at 36 h following normothermic ischemia. In hypothermia, this induction appeared already after 18 h. Following normothermic ischemia, nuclear PCNA immunoreactivity was largely abolished during reperfusion in the vulnerable CA1 neurons, prior to cell death. In contrast, total PCNA protein content of this region, as measured by Western blotting, remained largely unchanged. In the CA3 region, a transient decrease in nuclear PCNA immunoreactivity was observed. In the dentate gyrus region, no down-regulation of nuclear or total PCNA protein was observed during reperfusion. Following hypothermic ischemia, the PCNA protein levels did not decrease in any of the hippocampal subregions. In contrast, no change in the levels of Ref-1, a protein involved in base excision DNA repair (BER), was observed following normo- or hypothermic ischemia. Our findings indicate an altered functional state of PCNA protein in the ischemia-sensitive CA1 neurons suggesting that DNA repair processes are affected in these post-mitotic cells following ischemia. Impaired DNA repair may play a role in the development of postischemic neuronal damage.