Hypoxia-ischemia induces heat shock protein-like (HSP72) immunoreactivity in neonatal rat brain

The role of interleukin-1 in perinatal inflammation and its impact on transitional circulation

Preterm birth is defined as delivery at <37 weeks of gestational age (GA) and exposes 15 million infants worldwide to serious early life diseases. Lowering the age of viability to 22 weeks GA entailed provision of intensive care to a greater number of extremely premature infants. Moreover, improved survival, especially at extremes of prematurity, comes with a rising incidence of early life diseases with short- and long-term sequelae. The transition from fetal to neonatal circulation is a substantial and complex physiologic adaptation, which normally happens rapidly and in an orderly sequence. Maternal chorioamnionitis or fetal growth restriction (FGR) are two common causes of preterm birth that are associated with impaired circulatory transition. Among many cytokines contributing to the pathogenesis of chorioamnionitis-related perinatal inflammatory diseases, the potent pro-inflammatory interleukin (IL)-1 has been shown to play a central role. The effects of utero-placental insufficiency-related FGR and in-utero hypoxia may also be mediated, in part, via the inflammatory cascade. In preclinical studies, blocking such inflammation, early and effectively, holds great promise for improving the transition of circulation. In this mini-review, we outline the mechanistic pathways leading to abnormalities in transitional circulation in chorioamnionitis and FGR. In addition, we explore the therapeutic potential of targeting IL-1 and its influence on perinatal transition in the context of chorioamnionitis and FGR.

Transcriptome Analysis Reveals Molecular Underpinnings of Common Carp (Cyprinus carpio) Under Hypoxia Stress

As an essential environmental factor that affects the economic benefits of aquaculture, hypoxia is one of the urgent problems to be solved in the aquaculture fish breeding industry. Common carp (Cyprinus carpio) is a critical economic fish in China, and at present, there are many breeding strains of common carp with different character advantages in China, including Hebao red carp (C. carpio var wuyuanesis) and Songpu mirror carp (C. carpio var specularis). Even if the environmental adaptation of common carp is generally strong, the genetic background of hypoxia tolerance in different strains of common carp is unclear yet. This study tested the hypoxia tolerance of Songpu minor carp, Hebao red carp, and their hybrid F1 population by an acute hypoxia treatment. Muscle and liver tissues were used for transcriptome sequencing analysis to identify the key factors for hypoxia tolerance and explore the potential genetic mechanism for breeding high hypoxia tolerance in common carp. The comparative transcriptomic analysis revealed abundant hypoxia response-related genes and their differential regulation mechanism in these two tissues of different common carp strains under acute hypoxia, including immune response, cellular stress response, HIFs (hypoxia-inducible factors), MAP kinase, iron ion binding, and heme binding. Our findings will facilitate future investigation on the hypoxia response mechanism and provide a solid theoretical basis for breeding projects in common carp.

Hypothermia decreased the expression of heat shock proteins in neonatal rat model of hypoxic ischemic encephalopathy

Hypothermia (HT) is a well-established neuroprotective strategy against neonatal hypoxic ischemic encephalopathy (HIE). The overexpression of heat shock proteins (HSP) has been shown to provide neuroprotection in animal models of stroke. We aimed to investigate the effect of HT on HSP70 and HSP27 expression in a neonatal rat model of HIE. Seven-day-old rat pups were exposed to hypoxia for 90 min to establish the Rice-Vannucci model and were assigned to the following four groups: hypoxic injury (HI)-normothermia (NT, 36 °C), HI-HT (30 °C), sham-NT, and sham-HT. After temperature intervention for 24 h, the mRNA and protein expression of HSP70 and HSP27 were measured. The association between HSP expression and brain injury severity was also evaluated. The brain infarct size was significantly smaller in the HI-HT group than in the HI-NT group. The mRNA and protein expression of both HSPs were significantly greater in the two HI groups, compared to those in the two sham groups. Moreover, among the rat pups subjected to HI, HT significantly reduced the mRNA and protein expression of both HSPs. The mRNA expression level of the HSPs was proportional to the brain injury severity. Post-ischemic HT, i.e., a cold shock attenuated the expression of HSP70 and HSP27 in a neonatal rat model of HIE. Our study suggests that neither HSP70 nor HSP27 expression is involved in the neuroprotective mechanism through which prolonged HT protects against neonatal HIE.

Tonicity enhancer binding protein (TonEBP) and hypoxia-inducible factor (HIF) coordinate heat shock protein 70 (Hsp70) expression in hypoxic nucleus pulposus cells: role of Hsp70 in HIF-1α degradation

The objective of our study was to examine the regulation of hypoxic expression of heat shock protein 70 (Hsp70) in nucleus pulposus cells and to determine if Hsp70 promoted hypoxia-inducible factor (HIF)-1α degradation. Rat nucleus pulposus cells were maintained in culture in either 21% or 1% oxygen. To determine the regulation of Hsp70 expression by tonicity enhancer binding protein (TonEBP) and HIF-1/2, loss-of-function and gain-of-function experiments and mutational analysis of the Hsp70 promoter were performed. Hypoxia increased Hsp70 expression in nucleus pulposus cells. Noteworthy, hypoxia increased TonEBP transactivation and mutation of TonE motifs blocked hypoxic induction of the Hsp70 promoter. In contrast, mutation of hypoxia response element (HRE) motifs coupled with loss-of-function experiments suggested that HIF-1 and HIF-2 suppressed Hsp70 promoter activity and transcription. Interestingly, HIF-α interferes with TonEBP function and suppresses the inductive effect of TonEBP on the Hsp70 promoter. In terms of Hsp70 function, when treated with Hsp70 transcriptional inhibitor, KNK437, there was an increase in HIF-1α protein stability and transcriptional activity. Likewise, when Hsp70 was overexpressed, the stability of HIF-1α and its transcriptional activity decreased. Hsp70 interacted with HIF-1α under hypoxic conditions and evidenced increased binding when treated with MG132, a proteasomal inhibitor. These results suggest that Hsp70 may promote HIF-1α degradation through the proteasomal pathway in nucleus pulposus cells. In hypoxic and hyperosmolar nucleus pulposus cells, Hsp70, TonEBP, and HIFs form a regulatory loop. We propose that the positive regulation by TonEBP and negative regulation of Hsp70 by HIF-1 and HIF-2 may serve to maintain Hsp70 levels in these cells, whereas Hsp70 may function in controlling HIF-1α homeostasis.

Effects of graded hypothermia on hypoxic-ischemic brain damage in the neonatal rat

OBJECTIVE

To investigate the effect of graded hypothermia on neuropathologic alterations of neonatal rat brain after exposed to hypoxic-ischemic insult at 37°C, 33°C, 31°C, and 28°C, respectively, and to observe the effect of hypothermia on 72-kDa heat shock protein (HSP72) expression after hypoxic-ischemic insult.

METHODS

Seven days old Wistar rats were subjected to unilateral common carotid artery ligation followed by exposure to hypoxia in 8% oxygen for 2 hours at 37°C, 33°C, 31°C, and 28°C, respectively. The brain temperature was monitored indirectly by inserting a mini-thermocouple probe into the temporal muscle during hypoxia. After hypoxia-ischemia their mortality was assessed. Neuronal damage was assessed with HE staining 72 hours after hypoxia. HSP72 expression at 0.5, 24, and 72 hours of recovery was immunohistochemically assessed using a monoclonal antibody to HSP72.

RESULTS

Hypoxia-ischemia caused 10.5% (2/19) of mortality in rat of 37°C group, but no death occurred in 33°C, 31°C or 28°C groups. HE staining showed neuropathologic damage was extensive in rats exposed to hypoxia-ischemia at 37°C (more than 80.0%). The incidence of severe brain damage was significantly decreased in 33°C (53.3%) and 31°C groups (44.4%), and no histologic injury was seen in the 28°C group of rats. Expression of HSP72 was manifest and persistent in the rat brain of 37°C group, but minimum in the rat brain of 28°C group.

CONCLUSION

Mild and moderate hypothermia might prevent cerebral visible neuropathologic damage associated with hypoxic-ischemic injury by decreasing stress response.

Neuron-microglia crosstalk up-regulates neuronal FGF-2 expression which mediates neuroprotection against excitotoxicity via JNK1/2

Glial cells and neurons are in constant reciprocal signalling both under physiological and neuropathological conditions. Microglial activation is often associated with neuronal death during inflammation of the CNS, although microglial cells are also known to exert a neuroprotective role. In this work, we investigated the interplay between cerebellar granule neurons (CGN) and microglia in the perspective of CGN survival to an excitotoxic stimulus, quinolinic acid (QA), a catabolite of the tryptophan degradation pathway. We observed that CGN succumb to QA challenge via extracellular signal regulated kinase 1 and 2 (ERK) activation. Our data with transgenic mice expressing the natural inhibitor of calpains, calpastatin, indicate that together with cathepsins they mediate QA-induced toxicity acting downstream of the mitogen-activated protein kinase kinase-ERK pathway. Microglial cells are not only resistant to QA but can rescue neurons from QA-mediated toxicity when they are mixed in culture with neurons or by using mixed culture-conditioned medium (MCCM). This effect is mediated via fibroblast growth factor-2 (FGF-2) present in MCCM. FGF-2 is transcriptionally up-regulated in neurons and secreted in the MCCM as a result of neuron-microglia crosstalk. The neuroprotection is associated with the retention of cathepsins in the lysosomes and with transactivation of inducible heat-shock protein 70 downstream of FGF-2. Furthermore, FGF-2 upon release by neurons activates c-jun N-terminal kinase 1 and 2 pathway which also contributes to neuronal survival. We suggest that FGF-2 plays a pivotal role in neuroprotection against QA as an outcome of neuron-microglia interaction.

Regional metabolic status of the E-18 rat fetal brain following transient hypoxia/ischemia

Increasing evidence indicates that fetal metabolic stress may result in a variety of post-natal perturbations during brain development. The goal of the study was to determine the duration of hypoxia/ischemia that would elicit a demonstrable regional depression of metabolism in the fetal brain and further to examine several end-points to determine if the metabolic stress affects the developing brain. The uterine artery and uterine branch of the ovarian artery were occluded with aneurysm clamps for a period of 45 min, the clips removed and the metabolites in five regions of the perinatal brain were measured at 0, 2 and 6 h of reflow. Regional P-creatine, ATP and glucose levels were significantly depleted at the end of the 45 min occlusion. The levels of glycogen and glutamate at the end of the occlusion indicated a decreasing trend which was not significant. The concentration of citrate remained essentially unchanged at the end of the occlusion. To ensure that the insult was not lethal to the tissue, the recovery of the metabolites was examined at 2 and 6 h of reflow and generally the concentrations of the high-energy phosphates and glucose were normal or near-normal by 6 h of reperfusion in the five regions of the brain examined. The changes in the metabolites indicate that 45 min of hypoxia/ischemia is an appropriate model for studying neonatal development after fetal metabolic stress.

Pentylenetetrazol-induced status epilepticus up-regulates the expression of glucose transporter mRNAs but not proteins in the immature rat brain

Prolonged pentylenetetrazol (PTZ)-induced seizures increase cerebral energy demands in a region-specific manner. During PTZ seizures, cerebral glucose utilization increases over control levels in all brain regions at 10 days while 21-day-old rats exhibit increases, decreases or no change. To explore the effects of such acute changes in metabolic demand on the expression of glucose transporter proteins mediating glucose delivery to brain, we studied the consequences of PTZ seizures on GLUT1 and GLUT3 mRNAs and proteins between 1 and 72 h after seizure induction. At both ages, seizures induced a rapid up-regulation of GLUT1 and GLUT3 mRNAs which was prominent at 1 and 4 h, and was greater at 10 than at 21 days. By 24 h and 72 h, the levels of the mRNAs of the two transporter returned to control levels or were slightly down-regulated. The levels of GLUT1 and GLUT3 proteins were not affected by the seizures and only scattered decreases in GLUT3 protein were recorded, mainly in midbrain-brainstem areas. These data show that acute pentylenetetrazol seizures induce a rapid up-regulation of the GLUT1 and GLUT3 mRNAs, but do not result in measurable increases in protein levels, suggesting translational regulation.

Mild Intermittent Hypoxia Does Not Induce Stress Responses in the Neonatal Rat Brain

We previously demonstrated that intermittent hypoxia evokes persistent changes in extracellular striatal dopamine, locomotor activity and executive function, using a rodent model emulating apnea of prematurity in which rat pups are exposed to 20-second bursts of hypoxic gas mix containing 10% oxygen (60 events/h; 6 h/day) from postnatal days 7 to 11. To determine whether subtle repetitive hypoxic insults also induce expression of stress-related genes, we employed real-time RT-PCR to assay gene transcription in neonatal rats subjected to the same paradigm. In addition, we also measured expression of stress-induced transcripts in an age-matched cohort following a more severe oxidative stressor: permanent focal ischemia. Four transcripts were elevated following the ischemic insult: heat shock protein 70 (Hsp70), CL100, nurr77, and heme oxygenase-1. In contrast, these transcripts were not regulated in the majority of neonatal rats exposed to an intermittent hypoxia protocol. Hsp70 was strongly induced, and CL100 and nurr77 were slightly induced in only 2 of 11 post-hypoxic rats compared to controls. These data demonstrate that a single ischemic event elicits expression of specific stress-related genes, whereas 5 days of brief intermittent hypoxic insults typically do not. Thus, it is unlikely that the neurochemical and behavioral morbidity observed in juvenile and adult rodents exposed to intermittent hypoxia during a critical period of brain development are related to stress-induced changes in gene expression.

Physical activity alters the brain Hsp72 and IL-1beta responses to peripheral E. coli challenge

Physically active rats have facilitated heat shock protein 72 (Hsp72) responses after stressor exposure in both brain and peripheral tissues compared with sedentary rats. This study verifies that physically active animals do not have elevated Hsp72 levels compared with sedentary animals in the hypothalamus, pituitary, or dorsal vagal complex. We then examined whether 1) physically active rats respond more efficiently than sedentary rats to a bacterial challenge; 2) peripheral immune challenge elicits brain induction of Hsp72; 3) this induction is facilitated by prior freewheel running; and 4) Hsp72 upregulation produced by peripheral immune challenge results in a commensurate decrease in the proinflammatory cytokine IL-1beta. Adult male Fischer 344 rats were housed with either a mobile or locked running wheel. Six weeks later, rats were injected intraperitoneally with saline or Escherichia coli and killed 30 min, 2.5 h, 6 h, and 24 h later. Serum endotoxin and IL-1beta, and peritoneal fluid endotoxin and E. coli colony-forming units (CFUs) were measured. Hsp72 and IL-1beta were measured in hypothalamus, pituitary, and dorsal vagal complex. The results were that physically active rats had a faster reduction in endotoxin and E. coli CFUs and lower levels of circulating endotoxin and cytokines compared with sedentary rats. E. coli challenge elicited significantly greater time-dependent increases of both Hsp72 and IL-1beta in hypothalamus, pituitary, and dorsal vagal complex of physically active animals but not sedentary animals. Contrary to our hypothesis, increases in Hsp72 were positively correlated with IL-1beta. This study extends our findings that physical activity facilitates stress-induced Hsp72 to include immunological stressors such as bacterial challenge and suggests that brain Hsp72 and IL-1beta responses to peripheral immune challenge may contribute to exercise-mediated resistance to long-term sickness.

Hsp70 overexpression sequesters AIF and reduces neonatal hypoxic/ischemic brain injury

Apoptosis is implicated in neonatal hypoxic/ischemic (H/I) brain injury among various forms of cell death. Here we investigate whether overexpression of heat shock protein (Hsp) 70, an antiapoptotic protein, protects the neonatal brain from H/I injury and the pathways involved in the protection. Postnatal day 7 (P7) transgenic mice overexpressing rat Hsp70 (Tg) and their wild-type littermates (Wt) underwent unilateral common carotid artery ligation followed by 30 mins exposure to 8% O(2). Significant neuroprotection was observed in Tg versus Wt mice on both P12 and P21, correlating with a high level of constitutive but not inducible Hsp70 in the Tg. More prominent injury was observed in Wt and Tg mice on P21, suggesting its continuous evolution after P12. Western blot analysis showed that translocation of cytochrome c, but not the second mitochondria-derived activator of caspase (Smac)/DIABLO and apoptosis-inducing factor (AIF), from mitochondria into cytosol was significantly reduced in Tg 24 h after H/I compared with Wt mice. Coimmunoprecipitation detected more Hsp70 bound to AIF in Tg than Wt mice 24 h after H/I, inversely correlating with the amount of nuclear, but not cytosolic, AIF translocation. Our results suggest that interaction between Hsp70 and AIF might have reduced downstream events leading to cell death, including the reduction of nuclear AIF translocation in the neonatal brains of Hsp70 Tg mice after H/I.

Selective neuronal vulnerability and inadequate stress response in superoxide dismutase mutant mice

To understand the role of oxidative stress and mitochondrial defects in the development of neurodegeneration, we examined the age-related pathological changes and corresponding gene expression profiles in homozygous mutant mice deficient in the mitochondrial form of superoxide dismutase (MnSOD, SOD2). These Sod2-/- mice, generated on a B6D2F1 background, developed ataxia at Postnatal Day (P) 11 and progressively deteriorated with frequent seizures by P14. Histopathological examination revealed neurodegenerative changes consistent with the neurological signs. Vacuolar degeneration was observed in neurons and neuropil throughout the brainstem and rostral cortex. The motor trigeminal nucleus in brainstem and the deeper layers of the motor cortex were the earliest regions to degenerate, with the thalamus and hippocampus affected at later stages. Oligonucleotide microarrays were used to compare gene expression profiles in the brainstem and thalamus of Sod2+/+ and -/- mice from birth to P18. Notably, a large set of heat-shock protein genes was transcriptionally down regulated, and this was most likely due to a reduction in the heat-shock transcription factor 1 (HSF1). Other major classes of differentially expressed genes include lipid biosynthesis and ROS metabolism.

Long-term neuroprotection with 2-iminobiotin, an inhibitor of neuronal and inducible nitric oxide synthase, after cerebral hypoxia-ischemia in neonatal rats

The short- and long-term neuroprotective effects of 2-iminobiotin, a selective inhibitor of neuronal and inducible nitric oxide synthase, were studied in 12-day-old rats following hypoxia-ischemia. Hypoxia-ischemia was induced by occlusion of the right carotid artery followed by 90 minutes of hypoxia (FiO2 0.08). Immediately on reoxygenation, 12 and 24 hours later the rats were treated with vehicle or 2-iminobiotin at a dose of 5.5, 10, 30, or 60 mg/kg per day. Histologic analysis of brain damage was performed at 6 weeks after hypoxia-ischemia. To assess early changes of cerebral tissue, levels of HSP70, nitrotyrosine, and cytochrome c were determined 24 hours after reoxygenation. Significant neuroprotection was obtained using a dose of 30 mg/kg per day of 2-iminobiotin. Levels of HSP70 were increased in the ipsilateral hemisphere in both groups (P<0.05), but the increase was significantly (P<0.05) less in the rats receiving the optimal dose of 2-iminobiotin (30 mg/kg per day). Hypoxia-ischemia did not lead to increased levels of nitrotyrosine, nor did 2-iminobiotin influence levels of nitrotyrosine. In contrast, hypoxia-ischemia induced an increase in cytochrome c level that was prevented by 2-iminobiotin. In conclusion, 2-iminobiotin administered after hypoxia-ischemia provides long-term neuroprotection. This neuroprotection is obtained by mechanisms other than a reduction of nitrotyrosine formation in proteins.

Cat exposure induces both intra- and extracellular Hsp72: the role of adrenal hormones

Heat-shock proteins (Hsp) play an important role in stress physiology. Exposure to a variety of stressors will induce intracellular Hsp72, and this induction is believed to be beneficial for cell survival. In contrast, Hsp72 released during stress (extracellular Hsp72; eHsp72) activates pro-inflammatory responses. Clearly, physical stressors such as heat, cold, H(2)O(2), intense exercise and tail shock will induce both intra- and extracellular Hsp72. The current study tested whether a psychological stressor, cat exposure, would also trigger this response. In addition, the potential role of adrenal hormones in the Hsp72 response was examined. Adult, male Sprague Dawley rats were either adrenalectomized (ADX) or sham operated. Ten days post-recovery, rats were exposed to either a cat with no physical contact or control procedures (n = 5-6/group) for 2 h. Levels of intracellular Hsp72 were measured in the brain (frontal cortex, hippocampus, hypothalamus, dorsal vagal complex) and pituitary (ELISA). Levels of eHsp72 (ELISA) and corticosterone (RIA) were measured from serum obtained at the end of the 2-h stress period. Rats that were exposed to a cat had elevated intracellular Hsp72 in hypothalamus and dorsal vagal complex, and elevated eHsp72 and corticosterone in serum. Both the intra- and extracellular Hsp72 responses were blocked or attenuated by ADX. This study demonstrates that cat exposure can stimulate the Hsp72 response and that adrenal hormones contribute to this response.

Glia activation and cytokine increase in rat hippocampus by kainic acid-induced status epilepticus during postnatal development

In adult rats, status epilepticus (SE) induces cytokine production by glia especially when seizures are associated with neuronal injury. This suggests that cytokines may play a role in seizure-induced neuronal damage. As SE-induced injury is age-specific, we used rats of different ages (with distinct susceptibilities to seizure-induced neuronal injury) to elucidate the role of cytokines in this process. Thus, we investigated the activation of microglia and astrocytes, induction of cytokines, and hippocampal neuronal injury 4 and 24 h following kainic acid-induced SE in postnatal day (PN) 9, 15, and 21 rats. At PN9, there was little activation of microglia and astrocytes at any time point studied. Interleukin-1beta (IL), tumor necrosis factor-alpha (TNF), and IL-6 or the naturally occurring IL-1 receptor antagonist (Ra) mRNA expression did not increase. No evidence of cell injury has been detected. At PN15, immunostaining of microglia and astrocytes was enhanced, but only IL-1beta mRNA expression was increased. These changes were observed 4 h after SE. Scattered injured neurons in CA3 and subiculum, but not in any other region, were present 24 h following SE. At PN21, immunostaining of microglia and astrocytes and the mRNA expression of all cytokines studied was significantly increased already 4 h after SE. At 24 h, many injured neurons were present in CA1 and CA3 regions and in 40% of rats in other forebrain areas. These data show that (i) the pattern of glia activation and cytokine gene transcription induced by SE is age-dependent and (ii) neuronal injury in the hippocampus occurs only when cytokines are induced and their synthesis precedes the appearance of neuronal damage. Thus, cytokine expression in immature brain is associated specifically with cell injury rather than with seizures per se, suggesting that proinflammatory cytokines may contribute to the occurence of SE-induced hippocampal damage.

Mechanisms of erythropoietin-induced brain protection in neonatal hypoxia-ischemia rat model

Erythropoietin, a hemotopoietic growth factor, has brain protective actions. This study investigated the mechanisms of Recombinant Human EPO (rhEPO)-induced brain protection in neonates. An established rat hypoxia-ischemia model was used by ligation of the right common carotid artery of 7-day-old pups, followed by 90 minute of hypoxia (8% 02 and 92% N2) at 37 degrees C. Animals were divided into three groups: control, hypoxia-ischemia, and hypoxia-ischemia plus rhEPO treatment. In rhEPO treated pups, 300 units rhEPO was administered intraperitoneally 24 hours before hypoxia. rhEPO treatment (300 units) was administered daily for an additional 2 days. ELISA and immunohistochemistry examined the expression of EPO and EPOR. Brain weight, morphology, TUNEL assay, and DNA laddering evaluated brain protection. rhEPO abolished mortality (from 19% to 0%) during hypoxia insult, increased brain weight from 52% to 88%, reduced DNA fragmentation, and decreased TUNEL-positive cells. Real-time RT-PCR, Western blot, and immunohistochemistry revealed an enhanced expression of heat shock protein 27 (HSP27) in ischemic brain hemisphere. Double labeling of TUNEL with HSP27 showed most HSP27 positive cells were negative to TUNEL staining. rhEPO reduces brain injury, especially apoptotic cell death after neonatal hypoxia-ischemia, partially mediated by the activation of HSP27.

Heat shock inhibits hydrogen peroxide-induced apoptosis in cultured astrocytes

Heat shock proteins (HSPs) have been shown to act as inhibitors of apoptosis, but this anti-apoptotic effect is not known in the central nervous system. Prior heat shock has been demonstrated to protect astrocytes from cell death in a model of reperfusion injury (Brain Res. 735 (1996) 265). The present study examines the mechanism underlying the protective effect of the heat shock. Preincubation of astrocytes at 40 degrees C for 10 min attenuated the hydrogen peroxide (H(2)O(2))-induced decrease in cell viability, DNA ladder formation and nuclear condensation, and these effects were blocked by the protein synthesis inhibitor cycloheximide. The thermal stress inhibited the H(2)O(2)-induced increase in caspase-3 like protease activity, but it did not affect the H(2)O(2)-induced loss of mitochondrial membrane potential. The cytosol prepared from preheated cells did not affect Ca(2+)-induced swelling of mitochondria, a marker of the permeable transition pore. The protective effect of the thermal stress on the H(2)O(2)-induced decrease in cell viability was not affected by the mitogen-activated protein/extracellular signal-regulated kinase kinase inhibitor 2'-amino-3'-methoxyflavone, the phosphatidylinositol-3 kinase inhibitor wortmannin and the NF-kappaB inhibitor pyrrolidinedithiocarbamate. These findings suggest that HSPs inhibit apoptosis via an inhibition of caspase-3 activation without effect on mitochondrial dysfunction.

Heat shock protein 70 expression in neonatal rats after hypoxic stress

OBJECTIVES

The tissue damage due to hypoxia in newborns is to some extent age-dependent; organs of premature babies are more vulnerable to hypoxic insult than full-term neonates. The aim of this immunohistochemical study was to investigate the role of heat shock protein 70 (HSP70), a stress-inducible protein, in developing the response to hypoxia in premature newborns.

METHODS

Postnatal day-7 rats (corresponding to a human fetus of 32-34 weeks' gestation) and day-12 rats (corresponding to a full-term newborn infant) (n = 7) were subjected to mild hypoxia at 33 degrees C. Control rats (n = 7) for each group breathed room air for 4 h. After 4 h of recovery, the animals were killed, and brains, hearts and kidneys were removed for immunohistochemical staining.

RESULTS

Immunohistochemically, HSP70 expression was found to be induced in the hippocampus and myocardium after exposure to hypoxia. The level of HSP70 expression in the hippocampus after hypoxic stress was significantly higher in the 12-day rats than in the 7-day rats (p = 0.03). However, HSP70 expression in the myocardium did not show any significant difference between the two groups. In addition, no significant induction of HSP70 expression was apparent in the kidney of rats exposed to hypoxia or in any organ of the control animals.

CONCLUSIONS

We conclude that diminished HSP70 expression in the hippocampus of premature newborns may play a critical role in developing the response to hypoxic stress. However, HSP70 expression in the heart and the kidney after exposure to hypoxia did not appear to be related to fetal maturity.

Hypoxic preconditioning induces changes in HIF-1 target genes in neonatal rat brain

Hypoxic preconditioning induces tolerance to hypoxic-ischemic injury in neonatal rat brain and is associated with changes in gene expression. Hypoxia-inducible factor-1 (HIF-1) is a transcription factor that is strongly induced by hypoxia or the hypoxia-mimetic compound cobalt chloride (CoCl(2)). Hypoxia-inducible factor-1 modulates the expression of several target genes including the glycolytic enzymes, glucose transporter-1 (GLUT-1), and erythropoietin. Recently, HIF-1 expression was shown to increase after hypoxic and CoCl(2) preconditioning in newborn rat brain. To study the involvement of HIF-1 target genes in neonatal hypoxia-induced ischemic tolerance, the authors examined the brains of newborn rats after exposure to hypoxia (8% O(2) for 3 hours) or injection of CoCl(2) (60 mg/kg). Preconditioning with hypoxia or CoCl(2) 24 hours before hypoxia-ischemia afforded a 96% and 76% brain protection, respectively, compared with littermate control animals. Hypoxic preconditioning increased the expression of GLUT-1 mRNA and protein, and of aldolase, phosphofructokinase, and lactate dehydrogenase proteins but not mRNA. This suggests that the modulation of glucose transport and glycolysis by hypoxia may contribute to the development of hypoxia-induced tolerance. In contrast, preconditioning with CoCl(2) did not produce any change in HIF-1 target gene expression suggesting that different molecular mechanisms may be involved in the induction of tolerance by hypoxia and CoCl(2) in newborn brain.

Molecular and biochemical mechanisms of perinatal brain injury

Hypoxic-ischemic injury to the prenatal and perinatal brain is a major contributor to morbidity and mortality to infants, often leading to mental retardation, seizures, and cerebral palsy. The susceptibility of the immature CNS to hypoxia-ischemia is largely dependent on the temporal and regional status of critical developmental processes, as well as on the regulation of cerebral blood flow and metabolism. The molecular and biochemical mechanisms of acute injury to the neonatal brain in experimental rodent and murine models of hypoxic-ischemic and ischemic injury, including disturbances of intracellular homeostasis, role of glutamate receptors, free radicals and transitional ions, as well as the modifying role of gene expression to cell death/survival will be reviewed in this chapter.

Craniocerebral missile injuries

Gun shot wounds to the brain are among the most devastating causes of morbidity and mortality in the civilian population. The majority of the victims will not survive and for a great number of survivors life becomes an uphill battle with permanent deficits and complications. While the fundamental surgical care of these patients is essentially unchanged, our scientific understanding of the pathophysiological changes and the post-injury care of the victims has been evolving. The purpose of this article is to provide an overview of the current clinical and laboratory advances in understanding and treating gun shot injuries to the brain.

Perinatal brain injury

Perinatal brain damage in the mature fetus is usually brought about by severe intrauterine asphyxia following an acute reduction of the uterine or umbilical circulation. The areas most heavily affected are the parasagittal region of the cerebral cortex and the basal ganglia. The fetus reacts to a severe lack of oxygen with activation of the sympathetic-adrenergic nervous system and a redistribution of cardiac output in favor of the central organs (brain, heart and adrenals). If the asphyxic insult persists, the fetus is unable to maintain circulatory centralization, and the cardiac output and extent of cerebral perfusion fall. Owing to the acute reduction in oxygen supply, oxidative phosphorylation in the brain comes to a standstill. The Na+/K+ pump at the cell membrane has no more energy to maintain the ionic gradients. In the absence of a membrane potential, large amounts of calcium ions flow through the voltage-dependent ion channels, down an extreme extra-/intracellular concentration gradient, into the cell. Current research suggests that the excessive increase in levels of intracellular calcium, so-called calcium overload, leads to cell damage through the activation of proteases, lipases and endonucleases. During ischemia, besides the influx of calcium ions into the cells via voltage-dependent calcium channels, more calcium enters the cells through glutamate-regulated ion channels. Glutamate, an excitatory neurotransmitter, is released from presynaptic vesicles during ischemia following anoxic cell depolarization. The acute lack of cellular energy arising during ischemia induces almost complete inhibition of cerebral protein biosynthesis. Once the ischemic period is over, protein biosynthesis returns to preischemic levels in non-vulnerable regions of the brain, while in more vulnerable areas it remains inhibited. The inhibition of protein synthesis, therefore, appears to be an early indicator of subsequent neuronal cell death. A second wave of neuronal cell damage occurs during the reperfusion phase. This cell damage is thought to be caused by the postischemic release of oxygen radicals, synthesis of nitric oxide (NO), inflammatory reactions and an imbalance between the excitatory and inhibitory neurotransmitter systems. Part of the secondary neuronal cell damage may be caused by induction of a kind of cellular suicide programme known as apoptosis. Interestingly, there is increasing evidence from recent clinical studies that perinatal brain damage is closely associated with ascending intrauterine infection before or during birth. However, a major part of this damage is likely to be of hypoxic-ischemic nature due to LPS-induced effects on fetal cerebral circulation. Knowledge of these pathophysiological mechanisms has enabled scientists to develop new therapeutic strategies with successful results in animal experiments. The potential of such therapies is discussed here, particularly the promising effects of intravenous administration of magnesium or postischemic induction of cerebral hypothermia.

Perinatal expression of heat-shock protein 27 in brain regions and nonneural tissues of the piglet

Important stressful events occur at birth or within the few hours that follow this event. To unravel a possible involvement of stress proteins, it is important to determine their levels of expression. Expression of HSP27 protein was determined by Western blotting in several nonneural tissues and in brain regions of the developing pig (fetal to adult). Maximum levels of expression were observed in heart, liver, and lung. In kidney, the expression was reduced during the first hours of life. Brain parts included whole brain, cerebellum, cortex, hippocampus, hypothalamus, and striatum. HSP27 immunogenicity was observed in all the brain regions studied. In whole brain, cerebellum, cortex, hippocampus, and hypothalamus extracts, the levels of HSP27 were decreased during the first hours of age (4 h to 2 d). In striatum, levels of expression were very low--if detectable--during the early postnatal days of life. Changes in environmental parameters, like temperature and/or hypoxia can be possibly related to differential expressions of HSPs, which can result in severe adverse developmental outcomes. The results are discussed in terms of using the newborn piglet as a model to study different forms of stress on the heat-shock protein postnatal expression.

Endothelial cells downregulate expression of the 70 kDa heat shock protein during hypoxia

Hsp70 is induced by hypoxia in most mammalian cell types and contributes to their ability to survive hypoxic episodes. However, little is known about Hsp70 expression in the hypoxia-tolerant endothelial cells (ECs). We investigated the effect of hypoxia on Hsp70 in human microvascular endothelial HMEC-1 cells. Reduction of pO(2) to 2.5% of normal for 20 h stimulated lactate production and the activity of glycolytic enzymes. This metabolic adaptation to hypoxia was accompanied by a remarkable reduction of Hsp70 on the protein level and on the mRNA level. Approximately 12 h after the hypoxic period Hsp70 expression reached pre-hypoxia levels again. Since ECs are adapted to the low oxygen tension of the vasculature they are confronted with a supraphysiological oxygen level during in vitro culture. We suppose that the high Hsp70 under these conditions reflects a stress response which disappears at the more physiological reduced oxygen tension during hypoxia.

Differential expression of HSC73 and HSP72 mRNA and proteins between young and adult gerbils after transient cerebral ischemia: relation to neuronal vulnerability

This study presents a quantitative comparison of the time courses and regional distribution of both constitutive HSC73 and inducible HSP72 mRNA expression and their respective encoded proteins between young (3-week-old) and adult (3-month-old) gerbil hippocampus after transient global ischemia. The constitutive expression of HSC73 mRNA and protein in the hippocampus of the young sham-operated gerbils was significantly higher than in the adults. The HSC73 mRNA expression after ischemia in the CA1 layer of young gerbils was greater than in adult gerbils. HSC73 immunoreactivity was not significantly changed after ischemia-reperfusion in adult hippocampus, whereas it decreased in young gerbils. Ischemia-reperfusion led to induction of HSP72 mRNA expression throughout the hippocampus of both young and adult gerbils. HSP72 mRNA induction was more intense and sustained in the CA1 subfield of young gerbils; this was associated with a marked induction of HSP72 proteins and neuronal survival. The transient expression of HSP72 mRNA in the CA1 layer of adult gerbils was not associated with a subsequent synthesis of HSP72 protein but was linked to neuronal loss. Expression of HSP72 mRNA was shifted to an earlier period of reflow in CA3 and dentate gyrus (DG) subfields of young animals. These findings suggest that the induction of both HSP72 mRNA and proteins in the CA1 pyramidal neurons of young gerbils, as well as the higher constitutive expression of HSC73, may partially contribute to higher neuronal resistance of young animals to transient cerebral ischemia.

Regional expression of heat shock protein 72 mRNA following mild and severe hypoxia in neonatal piglet brain

The present study examined the effect of hypoxia on expression of 72-kDa heat shock protein (hsp72) mRNA in the newborn brain. The studies were carried out in anesthetized and mechanically ventilated newborn piglets, age 3-5 days. Hypoxic insult was induced by decreasing the fraction of inspired oxygen (FiO2) from 21% to 6% or 10% for 1 h. Oxygen pressure in the microvasculature of the cortex (cortical pO2) was measured by oxygen dependent quenching of the phosphorescence of phosphor dissolved in blood. Following the two hours of normoxic recovery, regional expression of the 72-kDa heat shock protein (hsp72) mRNA was determined using in situ hybridization and autoradiography. Two grades of hypoxia were studied. Mild hypoxia (cortical pO2 = 10-30 mm Hg) induced the expression of hsp72 mRNA predominantly in the subcortical white matter. In individual animals of this group, the extent of expression varied from isolated regions to widespread involvement of the white matter. Severe hypoxia (cortical pO2 = 3-10 mm Hg) induced the expression of hsp72 mRNA in both white and gray matter regions, with strong expression occurring in the cerebral cortex of individual animals. The present results indicate that immature white matter is more sensitive than gray matter to the hypoxia induced expression of hsp72 mRNA. Further, increased expression of hsp72 mRNA may be an indicator of a pathologic degree of hypoxic stress, and the observed increase may indicate that in the newborn brain the immature white matter is particularly sensitive to injury by hypoxia-ischemia and reperfusion.

Important role of 72-kd heat shock protein expression in the endothelial cell in acquisition of hypoxic-ischemic tolerance in the immature rat

OBJECTIVES

Hypoxic-ischemic tolerance can be induced in neonatal rats through hyperthermic preconditioning. The purposes of this study were to determine the interval between hyperthermic preconditioning and a subsequent hypoxic-ischemic insult that would provide optimal neuroprotection against the insult and to examine the relationship between tolerance induction and heat shock protein expression.

STUDY DESIGN

On postnatal day 7 Wistar rat pups were separated into the following 2 groups: a heated group (those exposed to 15 minutes of hyperthermic pretreatment at a brain temperature of 41.5 degrees C-42.0 degrees C) and an unheated control group. At 6, 12, 24, 48, and 72 hours after the hyperthermic stress, rats from both groups were exposed to left carotid artery ligation followed by 2 hours of hypoxia (8% oxygen and 92% nitrogen) at 33 degrees C. Twenty animals from each group were used at each time point. All rats were killed at 1 week after hypoxia-ischemia, at which time the brains were processed and neuronal damage in the cortex and hippocampus was assessed histologically. Another set of 7-day-old rats (n = 30) was studied immunohistochemically at 6, 12, 24, 48, and 72 hours after the same hyperthermic treatment. Expression of 72-kd heat shock protein was measured in neuronal, glial, and vascular endothelial cells.

RESULTS

Hyperthermia-induced hypoxic-ischemic tolerance was observed at 6, 12, and 24 hours but not at 48 and 72 hours after hyperthermic preconditioning. Heat shock protein 72 expression in the vascular endothelial cells, rather than in the glial or neuronal cells, was most strongly associated with hypoxic-ischemic tolerance.

CONCLUSION

These findings suggest that heat shock protein 72 in endothelial cells plays an important role in the acquisition of hypoxic-ischemic tolerance at postnatal day 7, a time when maximal angiogenesis occurs and the blood-brain barrier is still immature.

Stress proteins as molecular markers of neurotoxicity

In response to many environmental and pathophysiologic stressful stimuli, cells undergo a stress response characterized by induction of a variety of proteins, including the heat shock protein family. The inducible heat shock protein 70 (hsp70) is believed to participate in an array of cellular activities, including cytoprotection. Normal brain cells have little detectable hsp70 RNA or protein. However, following a stressful condition hsp70 mRNA and protein are induced in different cell types depending on the severity and the nature of the stimulus. The induction of hsp70 protein correlates with the regional and cellular vulnerability to a particular injury as identified by standard histologic methods. The pattern of hsp70 expression differs in response to various neurotoxic stimuli, including hyperthermia, ischemia, seizures, hemorrhage, and N-methyl-D-aspartate receptor antagonist administration. Hsp70 expression is a useful marker of cellular injury and may help to identify previously unrecognized areas of vulnerability in the nervous system after a neurotoxic stimulus. Hsp70 may also play a neuroprotective role in the brain.

Ischemic "cross" tolerance in hypoxic ischemia of immature rat brain

The phenomenon of ischemic tolerance has been closely associated with the expression of heat shock proteins but recently, stress tolerance not related to hsp72 has been reported. In the present study, we focused on ischemic tolerance induced by hypoxia and hyperthermia in neonatal rat brain and analyzed the expression of hsp72. In a neonatal rat model of hypoxic ischemia (H-I), preconditioning by whole-body hyperthermia or hypoxia was induced 24 h prior to the ischemia. Brain damage was histologically evaluated and the expressions of hsp72 were analyzed. Hyperthermic preconditioning at 41 degrees C for 15 min, as well as hypoxic preconditioning with 8% hypoxia for 3 h, had almost complete neuroprotective effects. However, we failed to detect the expression of hsp72 in any of preconditioning. Only the H-I insult itself induced hsp72 in the dorsal striatum and slightly in the thalamus and the hippocampus. Hyperthermic preconditioning has neuroprotective effects which are comparable to hypoxic preconditioning in immature brain. The expression of hsp72 is not likely necessary for the ischemic tolerance in immature brain.

Pathophysiology of perinatal brain damage

Perinatal brain damage in the mature fetus is usually brought about by severe intrauterine asphyxia following an acute reduction of the uterine or umbilical circulation. The areas most heavily affected are the parasagittal region of the cerebral cortex and the basal ganglia. The fetus reacts to a severe lack of oxygen with activation of the sympathetic-adrenergic nervous system and a redistribution of cardiac output in favour of the central organs (brain, heart and adrenals). If the asphyxic insult persists, the fetus is unable to maintain circulatory centralisation, and the cardiac output and extent of cerebral perfusion fall. Owing to the acute reduction in oxygen supply, oxidative phosphorylation in the brain comes to a standstill. The Na(+)/K(+) pump at the cell membrane has no more energy to maintain the ionic gradients. In the absence of a membrane potential, large amounts of calcium ions flow through the voltage-dependent ion channel, down an extreme extra-/intracellular concentration gradient, into the cell. Current research suggests that the excessive increase in levels of intracellular calcium, so-called calcium overload, leads to cell damage through the activation of proteases, lipases and endonucleases. During ischemia, besides the influx of calcium ions into the cells via voltage-dependent calcium channels, more calcium enters the cells through glutamate-regulated ion channels. Glutamate, an excitatory neurotransmitter, is released from presynaptic vesicles during ischemia following anoxic cell depolarisation. The acute lack of cellular energy arising during ischemia induces almost complete inhibition of cerebral protein biosynthesis. Once the ischemic period is over, protein biosynthesis returns to pre-ischemic levels in non-vulnerable regions of the brain, while in more vulnerable areas it remains inhibited. The inhibition of protein synthesis, therefore, appears to be an early indicator of subsequent neuronal cell death. A second wave of neuronal cell damage occurs during the reperfusion phase. This cell damage is thought to be caused by the post-ischemic release of oxygen radicals, synthesis of nitric oxide (NO), inflammatory reactions and an imbalance between the excitatory and inhibitory neurotransmitter systems. Part of the secondary neuronal cell damage may be caused by induction of a kind of cellular suicide programme known as apoptosis. Knowledge of these pathophysiological mechanisms has enabled scientists to develop new therapeutic strategies with successful results in animal experiments. The potential of such therapies is discussed here, particularly the promising effects of i.v. administration of magnesium or post-ischemic induction of cerebral hypothermia.

Detection of hypoxic cells with the 2-nitroimidazole, EF5, correlates with early redox changes in rat brain after perinatal hypoxia-ischemia

The hypoxia-dependent activation of nitroheterocyclic drugs by cellular nitroreductases leads to the formation of intracellular adducts between the drugs and cellular macromolecules. Because this covalent binding is maximal in the absence of oxygen, detection of bound adducts provides an assay for estimating the degree of cellular hypoxia in vivo. Using a pentafluorintated derivative of etanidazole called EF5, we studied the distribution of EF5 adducts in seven-day-old rats subjected to different treatments which decrease the level of oxygen in the brain. EF5 solution was administered intraperitoneally 30 min prior to each treatment. The effect of acute and chronic hypoxia on EF5 adduct formation (binding) was studied in the brain of newborn rats exposed to global hypoxia (8% O2 for 30, 90 or 150 min) and in the brain of chronically hypoxic rat pups with congenital cardiac defects (Wistar Kyoto). The effect of combined hypoxia-ischemia was investigated in rat pups subjected to right carotid coagulation and concurrent exposure to 8% O2 for 30, 90 or 150 min. Brains were frozen immediately at the end of each treatment. Using a Cy3-conjugated monoclonal mouse antibody (ELK3-51) raised against EF5 adducts, hypoxic cells within brain regions were visualized by fluorescence immunocytochemistry. Brains from controls or vehicle-injected animals showed no EF5 binding. Notably, brains from animals which were chronically hypoxemic as a result of congenital cardiac defects also showed no EF5 binding. A short exposure (30 min) to hypoxia or to combined hypoxia-ischemia resulted in increased background stain and few scattered cells with low-intensity immunostaining. Acute hypoxia exposure of at least 90-150 min, which in this age animal does not result in frank cellular damage, produced patchy areas of low- to moderate-intensity fluorescence scattered throughout the brain. In contrast, 90-150 min of hypoxia-ischemia was associated with intense immunofluorescence in the hemisphere ipsilateral to the carotid occlusion, with a pattern similar to that reported previously for the histological damage seen in this model. This study provides a sensitive method for the evaluation of the level of oxygen depletion in brain tissue after neonatal hypoxia-ischemia at times much earlier than any method demonstrates apoptotic or necrotic cell death Since the level of in vivo formation of macromolecular adducts of EF5 depends on the degree of oxygen depletion in a tissue, intracellular EF5 binding may serve as a useful marker of regional cellular vulnerability and redox state after brain injury resulting from hypoxia-ischemia.

Heat shock protein 72 expression and microtubule-associated protein 2 disappearance after hypoxia-ischemia in the developing rat brain

OBJECTIVE

This study was intended to investigate the temporal changes in heat shock protein 72 expression and microtubule-associated protein 2 disappearance in rat brain at 2 different ages after hypoxic-ischemic insult.

STUDY DESIGN

Both 5-day-old and 14-day-old Wistar rats were subjected to unilateral common carotid artery ligation and hypoxia in 8% oxygen for 2 hours at 33 degrees C. Brain sections were examined sequentially for heat shock protein 72 expression at 0.5, 3, 6, 12, 24, 48, and 72 hours of recovery after hypoxia-ischemia and for microtubule-associated protein 2 disappearance at 0, 24, 48, and 72 hours of recovery and at 7 days of recovery after hypoxia-ischemia. Results of immunohistochemical staining for heat shock protein 72 and microtubule-associated protein 2 were used as markers for detection of early hypoxic-ischemic brain damage. Permanent neuronal damage was assessed with hematoxylin and eosin staining at 7 days after hypoxia.

RESULTS

In 5-day-old rats microtubule-associated protein 2 expression was lost as early as 0 hours after hypoxia-ischemia in the cerebral cortex and hippocampus, with a peak at 48 hours after which expression recovered. Expression of heat shock protein 72 was detected in the ligated hemisphere at 0.5 hours after hypoxia-ischemia and peaked at 6 to 24 hours of recovery. In 14-day-old rats microtubule-associated protein 2 was stained in the cortex at 0 hours after hypoxia-ischemia but gradually disappeared in the cerebral cortex and hippocampus after 24 hours of recovery. The expression of heat shock protein 72 was not detected by 6 hours of recovery in the cerebral cortex and by 3 to 12 hours of recovery in the hippocampus, but heat shock protein 72 was persistently expressed in the cortex and hippocampus after 48 hours of recovery. Neuronal damage was significantly less in 5-day-old rats than in 14-day-old rats.

CONCLUSION

In 5-day-old rats hypoxia-ischemia causes earlier changes in heat shock protein 72 and microtubule-associated protein 2 immunostaining results and causes less severe brain damage than in 14-day-old rats.

Rat model of perinatal hypoxic-ischemic brain damage

To gain insights into the pathogenesis and management of perinatal hypoxic-ischemic brain damage, the authors have used an immature rat model which they developed many years ago. The model entails ligation of one common carotid artery followed thereafter by systemic hypoxia. The insult produces permanent hypoxic-ischemic brain damage limited to the cerebral hemisphere ipsilateral to the carotid artery occlusion. The mini-review describes recently accomplished research pertaining to the use of the immature rat model, specifically, investigations involving energy metabolism, glucose transporter proteins, free radical injury, and seizures superimposed upon cerebral hypoxia-ischemia. Future research will focus on molecular mechanisms of neuronal injury with a continuing focus on therapeutic strategies to prevent or minimize hypoxic-ischemic brain damage.

Role of heat shock protein Hsp25 in the response of the orofacial nuclei motor system to physiological stress

Although expression of the small heat shock protein family member Hsp25 has been previously observed in the central nervous system (CNS), both constitutively and upon induction, its function in the CNS remains far from clear. In the present study we have characterized the spatial pattern of expression of Hsp25 in the normal adult mouse brain as well as the changes in expression patterns induced by subjecting mice to experimental hyperthermia or hypoxia. Immunohistochemical analysis revealed a surprisingly restricted pattern of constitutive expression of Hsp25 in the brain, limited to the facial, trigeminal, ambiguus, hypoglossal and vagal motor nuclei of the brainstem. After hyperthermia or hypoxia treatment, significant increases in the levels of Hsp25 were observed in these same areas and also in fibers of the facial and trigeminal nerve tracts. Immunoblot analysis of protein lysates from brainstem also showed the same pattern of induction of Hsp25. Surprisingly, no other area in the brain showed expression of Hsp25, in either control or stressed animals. The highly restricted expression of Hsp25 implies that this protein may have a specific physiological role in the orofacial motor nuclei, which govern precise coordination between muscles of mastication and the pharynx, larynx, and face. Its rapid induction after stress further suggests that Hsp25 may serve as a specific molecular chaperone in the lower cholinergic motor neurons and along their fibers under conditions of stress or injury.

C-Fos, Jun D and HSP72 immunoreactivity, and neuronal injury following lithium-pilocarpine induced status epilepticus in immature and adult rats

In order to follow the maturation-related evolution of neuronal damage, cellular activation and stress response subsequent to Li-Pilo seizures in the 10- (P10), 21-day-old (P21) and adult rat, we analyzed the expression of the c-Fos protein as a marker of cellular activation, HSP72 immunoreactivity as the stress response and silver staining for the assessment of neuronal damage in 20 selected brain regions. The early wave of c-Fos measured at 2 h after the onset of seizures was present in most structures of the animals at the three ages studied and particularly strong in the cerebral cortex, hippocampus and amygdala. The late wave of c-Fos measured at 24 h after the onset of seizures and that was shown to correlate to neuronal damage was absent from the P10 rat brain, and present mainly in the cerebral cortex and hippocampus of P21 and adult rats. The expression of the stress response, assessed by the immunoreactivity of HSP72 at 24 h after the seizures was absent from the P10 rat brain and present in the entorhinal cortex, amygdala, hippocampus and thalamus of P21 and adult rats. The expression of Jun D at 24 h after the seizures was discrete and present in most brain regions at all ages. Neuronal injury assessed by silver staining at 6 h after the onset of seizures was very discrete in the brain of the P10 rat and limited to a few neurons in the piriform and entorhinal cortices. In older animals, marked neuronal degeneration occurred in the cerebral cortex, amygdala, hippocampus, lateral septum and thalamus. Thus the immediate cell activation induced by lithium-pilocarpine seizures which is present at all ages translates only into a late wave of c-Fos and the expression of HSP72 in P21 and adult animals in which there will be extensive cell damage.

Strain-related brain injury in neonatal mice subjected to hypoxia-ischemia

The development of transgenic mice has led to an increase in the use of mice as models for human disease. We hypothesized that the degree of brain damage sustained by animals in a neonatal mouse model of hypoxia-ischemia depends on the strain used. We compared three strains of mice commonly used to generate transgenic strains (C57Bl/6, 129Sv and CD1), as well as three hybrids of these strains (C57Bl/6x129Sv, CD1xC57Bl/6, and CD1x129Sv). At postnatal day 7 (P7), pups were subjected to a modified Vannucci procedure for hypoxia-ischemia as follows: permanent ligation of right common carotid artery under halothane anesthesia, 2-h recovery period, exposure to 8% oxygen at 37 degreesC for varying durations (30, 60 or 90 min). After 5 days, animals were perfused with 4% paraformaldehyde, brains were removed, postfixed and examined histologically with cresyl violet and Perl's iron stain to assess the degree of damage. Damage was assessed blindly using a score ranging from 0 (none) to 3 (infarct) in eight regions (ant-, mid-, and post- cortex, CA1, CA2, CA3 and dentate gyrus of the hippocampus, and striatum). We found significant differences in susceptibility to brain damage and mortality depending on the strain used. While determining the maximal degree of injury with the least amount of mortality for each strain, it was found that some strains (CD1) are particularly susceptible to brain damage in this model, while others (129Sv) are resistant.

Heat-shock protein 72 expression in excitotoxic versus penetrating injuries of the rodent cerebral cortex

The induction of heat shock protein 72 (hsp72) has been described in various experimental models of brain injury. The present study examined hsp72 expression patterns within the rodent cerebral cortex in experimental paradigms designed to mimic two mechanisms of damage produced by penetration of the cerebral cortex: (1) tissue tearing from the missile track and (2) diffuse excitotoxicity during temporary cavitation and shock wave formation. Adult male Spaque-Dawley rats received controlled penetration (stab) or injection of the NMDA receptor excitotoxin, quinolinic acid (QA), into the frontal cortex and were killed 1-24 h later. Tissue from the lesioned, sham-operated, or contralateral uninjected cortex was processed for Western and immunocytochemical analyses of hsp72 protein expression. By 12 h, both controlled penetration and excitotoxic brain injuries produced significant increases in hsp72 immunoreactivity, which decreased toward control levels at 24 h. However, the severity and regional distribution of hsp72 expression varied between the two models. Specifically, the controlled penetration injury produced many hsp72-expressing cells near the needle track, while immunoreactive cells within the QA-injected cortex were found in the periphery of the lesion site. Morphological assessment of brain sections subjected to dual-labeling procedures demonstrated that cells expressing hsp72 were primarily neuronal in both models of injury. These results suggest that although controlled penetration and diffuse excitotoxicity may induce similar temporal and cellular patterns of hsp72 expression, the spatial location of hsp72-immunoreactive cells may differ between the two models.

Patterns of heat-shock protein 70 biosynthesis following human traumatic brain injury

Heat-shock protein 70 (hsp70) is activated upon cellular stress/injury and participates in the folding and intracellular transport of damaged proteins. The expression of hsp70 following CNS trauma has been speculated to be part of a cellular response which is involved in the repair of damaged proteins. In this study, we measured hsp70 mRNA and protein levels within human cerebral cortex subjected to traumatic brain injury. Specimens were obtained during routine neurosurgery for trauma and processed for Northern mRNA and Western protein analysis. The largest increase in hsp70 mRNA levels was detected in trauma tissue obtained 4-6 h following injury. By 24 h, hsp70 mRNA levels were similar to nontrauma comparison tissues. hsp70 protein expression exhibited its greatest increases at 12-20 h post-injury. Immunocytological techniques revealed hsp70 protein expression in cells with neuronal-like morphology at 12 h after injury. These results suggest a role for hsp70 in human cortex following TBI. Moreover, since the temporal induction pattern of hsp70 biosynthesis is similar to that reported in the rodent, our observations validate the importance of rodent brain injury models in providing useful information directly applicable to human brain injury.

Spatial and temporal evolution of neuronal activation, stress and injury in lithium-pilocarpine seizures in adult rats

In order to follow the spatial and temporal evolution of neuronal damage, cellular activation and stress responses subsequent to lithium-pilocarpine seizures of various durations in the adult rat, we analyzed the expression of Fos protein and local cerebral glucose utilization as markers of cellular activation, HSP72 immunoreactivity and acid fuchsin staining as indicators of cellular stress and injury, and Cresyl violet staining for the assessment of neuronal damage. The expression of Fos appeared very early, 2-30 min after the onset of polyspikes and intensified during the following 4 h. Fos immunoreactivity was especially high in the hippocampus, cerebral cortex, amygdala and anterior olfactory nuclei. Local cerebral glucose utilization measured during the second hour of seizures was largely increased (350-580%) over control levels in cortical areas, amygdala, dentate gyrus, caudate nucleus and mediodorsal thalamus. HSP72 immunoreactivity never appeared earlier than 40-50 min after the onset of polyspikes, and was most prominent in hippocampal CA3 area, cerebral cortex (except the piriform cortex) and anterior olfactory nuclei. Acid fuchsin staining was maximal in the piriform cortex and the polymorphic layer of the dentate gyrus. Staining was moderate in the sensorimotor cortex and the amygdala. Neuronal damage was extensive in the piriform and entorhinal cortices, the hippocampal CA3 area and the polymorphic layer of the dentate gyrus, basal amygdala, mediodorsal thalamus and anterior olfactory nuclei. In conclusion, the present study shows that brain regions with the highest expression of Fos and the largest metabolic activation were also highly stained with acid fuchsin and most heavily damaged. Conversely, there is no clear relationship between HSP72 expression, cellular activation and neuronal damage.

Developmental expression of heme oxygenase-1 (HSP32) in rat brain: an immunocytochemical study

Heme oxygenase (HO) is a microsomal enzyme that oxidatively cleaves heme molecules to produce bile pigments, iron and carbon monoxide. In normal adult rat brain, HO-2 is the most abundant isozyme whereas HO-1 is present at very low levels except in select cell populations. Because its promoter region has NF-kB and AP-1 sites, heat-shock and heme-responsive elements, the HO-1 isozyme can be induced by a variety of stimuli. Since the expression and activity of several transcription factors such as NF-kB, Fos/Jun, and CREB show specific changes during development, we postulated that HO-1 expression may show similar developmental regulation. Using immunocytochemistry and Western blotting, this study demonstrates the development changes of HO-1 protein expression in normal brain from rats at postnatal day 7 (P7), P14, P21, and adult. Brain HO-1 immunoreactivity was highest at P7 in most brain regions including the white matter in areas of myelinogenesis, cerebral cortex, hippocampus, thalamus and hypothalamus and, in the blood vessel endothelial cells throughout the brain. In most regions, the adult pattern was reached by P21 with HO-1 protein localized almost exclusively to the dentate regions of hippocampus, some thalamic and hypothalamic nuclei, with little or no staining of endothelium, white matter and cortex. In a few select areas such as the substantia nigra, globus pallidus, ventromedial hypothalamic nucleus and the lateral preoptic nuclei area, little or no cellular HO-1 staining was observed at P7 whereas increased staining was found with maturation and adulthood. These results show that HO-1 protein expression is regulated in different cell types of specific regions of the rat brain during development.

A model of perinatal hypoxic-ischemic brain damage

In conclusion, our immature rat model has gained wide acceptance as the animal model of choice to study basic physiologic, biochemical, and molecular mechanisms of perinatal hypoxic-ischemic brain damage. In addition, the model has been used extensively to study those physiologic and therapeutic variables which either are deleterious or beneficial to the perinatal brain undergoing hypoxia-ischemia. As therapeutic interventions are tested in the animal setting, the results will provide important information regarding the effect of these agents in the human setting.

Effects of pentylenetetrazol-induced status epilepticus on c-Fos and HSP72 immunoreactivity in the immature rat brain

Pentylenetetrazol (PTZ)-induced status epilepticus (SE) leads to acute and long-term metabolic decreases in specific brain regions of rats at 10 (P10) or 21 days after birth (P21). These decreases are not related to apparent neuronal damage. Therefore, to better understand the neuronal activation and stress response to PTZ in immature rats, we mapped the expression of c-Fos and of the 72 kDa heat-shock protein (HSP72) in the same model of severe SE induced by the repetitive i.p. injections of subconvulsive doses of PTZ. Rats were sacrificed either at 2 or 24 h after the onset of SE in order to reveal c-Fos immunoreactivity, and at 24 and 72 h for HSP72 expression. Hematoxylin-eosin staining was performed at 24, 72 and 144 h after SE. The expression of c-Fos at 2 h after SE was more marked at P21 than at P10 and was prominent at both ages in the hippocampal dentate gyrus, cerebral cortex and amygdala. Some immunoreactivity was also present in the hypothalamus, thalamus and a few brainstem and cerebellar regions at both ages. There was a good relation between the regions expressing c-Fos and those exhibiting acute metabolic decreases at P21. Conversely, PTZ seizures did not lead to any expression of c-Fos at 24 h after SE or of HSP72 at 24 or 72 h at any age. Cell density was not affected by PTZ-induced SE at any age and at any time. These results suggest that c-Fos is a useful marker of neuronal activation induced by severe and prolonged seizures in the immature brain. The lack of HSP72 and of late c-Fos expression likely reflect the absence of neuronal damage in this model of PTZ-induced SE in the immature rat.

Magnesium and the N-methyl-D-aspartate receptor antagonist dizocilpine maleate neither increase glucose use nor induce a 72-kilodalton heat shock protein expression in the immature rat brain

In adult rats N-methyl-D-aspartate receptor (NMDAR) antagonists increase glucose use and induce a 72-kD heat shock protein (HSP72) expression in limbic system areas that later undergo neuronal necrosis, which have limited the clinical development of these drugs. Dizocilpine maleate (MK-801) and magnesium sulfate (MgSO4) reduce hypoxic-ischemic brain injury in immature animals, but the effects on HSP72 expression and glucose use are unknown. Seven-day-old rats received injections of either vehicle (control), 0.5 or 1.0 mg/kg MK-801, or 2 or 4 mmol/kg MgSO4. Glucose utilization was measured with the deoxyglucose method, 30 min, 48 h, and 4 d after injection. HSP72 immunostaining was evaluated 4 or 24 h after injection. Both doses of MK-801 and 4 mmol/kg MgSO4 induced a temporary decrease in glucose use in the posterior cingulate and retrosplenial cortex, the CA1 and CA3 subfields of the hippocampus, the caudoputamen, and the parietal cortex. Doses of 2 mmol/kg MgSO4 did not affect glucose use in any structure. Neuronal HSP72 expression was not found in any drug-treated rats. In conclusion, neither MK-801 nor MgSO4 increased glucose use in the limbic system and did not induce HSP72 expression, suggesting that NMDAR antagonists lack direct neurotoxicity in the immature brain.

Sequence of neuronal responses assessed by immunohistochemistry in the newborn rat brain after hypoxia-ischemia

OBJECTIVE

Our purpose was to study the neuronal responses of heat shock protein-72 (a stress-inducible protein) and microtubule-associated protein-2 (a constitutive protein of the neuronal cytoskeleton) after hypoxia-ischemia and their relationship with permanent damage in the newborn rat brain.

STUDY DESIGN

Seven-day-old rats were exposed to unilateral carotid artery ligation followed by 2 hours of hypoxia (8% oxygen/92% nitrogen) and then killed at time points ranging from 1 to 72 hours after injury. Brains were removed for immunohistochemical and routine staining.

RESULTS

Heat shock protein-72 appearance and microtubule-associated protein-2 disappearance occurred from 1 hour after injury, mainly in the dentate gyrus of the hippocampal formation and the cerebral cortex. Such alterations reached maximal levels at 24 hours for both proteins. Microtubule-associated protein-2 staining recovered in almost all parts of the brain. However, the hippocampal CA3 showed a delay in the responses for both proteins, and microtubule-associated protein-2 did not recover the response to immunostaining. Histologic evaluation at 72 hours after hypoxia by routine methods showed predominant damage in the hippocampal CA3.

CONCLUSION

Our results show that delayed responses of heat shock protein-72 and microtubule-associated protein-2 are related to a high incidence of neuronal cell loss in the hippocampal CA3 region.

The effects of hypoxia-ischemia on expression of c-Fos, c-Jun and Hsp70 in the young rat hippocampus

The expression of c-Fos, c-Jun and Hsp70 was examined in the hippocampus at 6, 12, 24, 48, 72 h, 4, 7 and 42 days following a combination of unilateral common carotid artery ligation and 60 min of systemic hypoxia (8% oxygen, 92% nitrogen) in 25-day-old male rats. While pyknotic cells were not visible in the hippocampus of control animals, pyknosis was evident in the ipsilateral, but not the contralateral hippocampus, of hypoxic-ischemic animals beginning at 24 h post-hypoxia. Immunohistochemical analysis revealed no c-Fos-, c-Jun- or Hsp70-immunoreactivity (IR) in any control animals. However, at 6 h post-hypoxia, Fos- and Jun-IR was evident throughout the injured ipsilateral hippocampus and later appeared throughout the contralateral hippocampus, which never showed signs of pyknosis. In contrast, Hsp70-IR was first observed at 24 h post-hypoxia and was restricted to the injured ipsilateral hippocampus. Hsp70-IR was not, however, limited to dying neurons. H-I/seizure animals did not express these proteins at any time point. These results suggest that, even in irreversibly injured neurons, Fos, Jun and Hsp70 appear to be involved in the aftermath of ischemia but probably do not play a pivotal role in the outcome of H-I compromised cells. Furthermore, compounded injury (H-I/seizure) appears to block the synthesis these proteins.