Involvement of caspase-3 in cell death after hypoxia-ischemia declines during brain maturation

Delayed, long-term administration of the caspase inhibitor Q-VD-OPh reduced brain injury induced by neonatal hypoxia-ischemia

Apoptosis contributes greatly to the morphological and biochemical features of cell death after neonatal cerebral hypoxia-ischemia (HI), making this mode of cell death a promising therapeutic target. We previously showed that 10 mg/kg of the caspase inhibitor Q-VD-OPh at the onset of and immediately after HI on postnatal day 9 reduced brain infarct volume. In this study, delayed administration of Q-VD-OPh, 12 and 36 h after HI, decreased HI-induced caspase-3 activity (DEVD cleavage) by 23% and diminished the levels of the proinflammatory chemokines CCL2 (MCP-1) and CCL3 (MIP-1α) by 29.3 and 29.1%, respectively, but not the levels of the anti-inflammatory cytokines IL-4 and IL-10. Long-term administration of Q-VD-OPh initiated at 12 h after HI, and continued at 24-hour intervals for 2 weeks, reduced total brain tissue loss by 31.3% from 41.5±3.1 mm3 in the vehicle group to 28.5±3.0 mm3 in the Q-VD-OPh group when evaluated 16 weeks after HI (p=0.004). Q-VD-OPh treatment also ameliorated the loss of sensorimotor function, as evaluated by a cylinder rearing test (Q-VD-OPh: 30.8±4.3% vs. vehicle: 59.7±6.3% in nonimpaired forepaw preference) 3 weeks after HI, and reduced HI-induced hyperactivity, as measured in an open field test (Q-VD-OPh: 4,062±198 cm vs. vehicle: 4,792±205 cm in distance moved) 7 weeks after the insult. However, the functional protection was no longer observed when analyzed again at later time points. The mechanisms underlying the discrepancy between sustained morphological protection and transient functional protection remain to be elucidated.

Protein misfolding, aggregation, and autophagy after brain ischemia

Ischemic brain injury is a common disorder linked to a variety of diseases. Significant progress has been made in our understanding of the underlying mechanisms. Previous studies show that protein misfolding, aggregation, and multiple organelle damage are major pathological events in postischemic neurons. The autophagy pathway is the chief route for bulk degradation of protein aggregates and damaged organelles. The latest studies suggest that impairment of autophagy contributes to abnormal protein aggregation and organelle damages after brain ischemia. This article reviews recent studies of protein misfolding, aggregation, and impairment of autophagy after brain ischemia.

Differential roles for caspase-mediated and calpain-mediated cell death in 1- and 3-week-old rat cortical cultures

Necrosis and apoptosis are well established as two primary cell death pathways. Mixed neuroglial cultures are commonly used to study cell death mechanisms in neural cells. However, the ages of these cultures vary across studies and little attention has been paid to how cell death processes may change as the cultures mature. To clarify whether neuroglial culture age affects cell death mechanisms, we treated 1- and 3-week-old neuroglial cultures with either the excitotoxic stimulus, N-methyl-D-aspartate (NMDA), or with the oxidative stressor, hydrogen peroxide (H2O2). Although NMDA is known to be toxic only in cultures that are at least 2 weeks old, H2O2 is toxic in cultures of all ages. Here, we confirm that, in 1-week-old neuroglial cultures, NMDA does not induce toxicity, whereas H2O2 induces both calpain-mediated and caspase-mediated neuronal death. In 3-week-old cultures, both NMDA and H2O2 trigger calpain-mediated, but not caspase-mediated, neuronal death. Further, we observed a decrease in caspase-3 levels and an increase in calpain levels in untreated neuroglial cultures as they aged. The findings presented here show that neuronal cell death mechanisms vary with culture age and highlight the necessity of considering culture age when interpreting neural cell culture data.

Cell death atlas of the postnatal mouse ventral forebrain and hypothalamus: effects of age and sex

Naturally occurring cell death is essential to the development of the mammalian nervous system. Although the importance of developmental cell death has been appreciated for decades, there is no comprehensive account of cell death across brain areas in the mouse. Moreover, several regional sex differences in cell death have been described for the ventral forebrain and hypothalamus, but it is not known how widespread the phenomenon is. We used immunohistochemical detection of activated caspase-3 to identify dying cells in the brains of male and female mice from postnatal day (P) 1 to P11. Cell death density, total number of dying cells, and regional volume were determined in 16 regions of the hypothalamus and ventral forebrain (the anterior hypothalamus, arcuate nucleus, anteroventral periventricular nucleus, medial preoptic nucleus, paraventricular nucleus, suprachiasmatic nucleus, and ventromedial nucleus of the hypothalamus; the basolateral, central, and medial amygdala; the lateral and principal nuclei of the bed nuclei of the stria terminalis; the caudate-putamen; the globus pallidus; the lateral septum; and the islands of Calleja). All regions showed a significant effect of age on cell death. The timing of peak cell death varied between P1 to P7, and the average rate of cell death varied tenfold among regions. Several significant sex differences in cell death and/or regional volume were detected. These data address large gaps in the developmental literature and suggest interesting region-specific differences in the prevalence and timing of cell death in the hypothalamus and ventral forebrain.

Brain development in rodents and humans: Identifying benchmarks of maturation and vulnerability to injury across species

Hypoxic-ischemic and traumatic brain injuries are leading causes of long-term mortality and disability in infants and children. Although several preclinical models using rodents of different ages have been developed, species differences in the timing of key brain maturation events can render comparisons of vulnerability and regenerative capacities difficult to interpret. Traditional models of developmental brain injury have utilized rodents at postnatal day 7-10 as being roughly equivalent to a term human infant, based historically on the measurement of post-mortem brain weights during the 1970s. Here we will examine fundamental brain development processes that occur in both rodents and humans, to delineate a comparable time course of postnatal brain development across species. We consider the timing of neurogenesis, synaptogenesis, gliogenesis, oligodendrocyte maturation and age-dependent behaviors that coincide with developmentally regulated molecular and biochemical changes. In general, while the time scale is considerably different, the sequence of key events in brain maturation is largely consistent between humans and rodents. Further, there are distinct parallels in regional vulnerability as well as functional consequences in response to brain injuries. With a focus on developmental hypoxic-ischemic encephalopathy and traumatic brain injury, this review offers guidelines for researchers when considering the most appropriate rodent age for the developmental stage or process of interest to approximate human brain development.

Mature neurons: equipped for survival

Neurons completely transform how they regulate cell death over the course of their lifetimes. Developing neurons freely activate cell death pathways to fine-tune the number of neurons that are needed during the precise formation of neural networks. However, the regulatory balance between life and death shifts as neurons mature beyond early development. Mature neurons promote survival at all costs by employing multiple, often redundant, strategies to prevent cell death by apoptosis. This dramatic shift from permitting cell death to ensuring cellular survival is critical, as these post-mitotic cells must provide neuronal circuitry for an organism's entire lifetime. Importantly, as many neurodegenerative diseases afflict adult neuronal populations, the survival mechanisms in mature neurons are likely to be either reversed or circumvented during neurodegeneration. Examining the adaptations for inhibiting apoptosis during neuronal maturation is key to comprehending not just how neurons survive long term, but may also provide insight for understanding how neuronal toxicity in various neurodegenerative diseases may ultimately lead to cell death.

Biomarkers for the clinical differential diagnosis in traumatic brain injury--a systematic review

Rapid triage and decision-making in the treatment of traumatic brain injury (TBI) present challenging dilemma in "resource poor" environments such as the battlefield and developing areas of the world. There is an urgent need for additional tools to guide treatment of TBI. The aim of this review is to establish the possible use of diagnostic TBI biomarkers in (1) identifying diffuse and focal brain injury and (2) assess their potential for determining outcome, intracranial pressure (ICP), and responses to therapy. At present, there is insufficient literature to support a role for diagnostic biomarkers in distinguishing focal and diffuse injury or for accurate determination of raised ICP. Presently, neurofilament (NF), S100β, glial fibrillary acidic protein (GFAP), and ubiquitin carboxyl terminal hydrolase-L1 (UCH-L1) seemed to have the best potential as diagnostic biomarkers for distinguishing focal and diffuse injury, whereas C-tau, neuron-specific enolase (NSE), S100β, GFAP, and spectrin breakdown products (SBDPs) appear to be candidates for ICP reflective biomarkers. With the combinations of different pathophysiology related to each biomarker, a multibiomarker analysis seems to be effective and would likely increase diagnostic accuracy. There is limited research focusing on the differential diagnostic properties of biomarkers in TBI. This fact warrants the need for greater efforts to innovate sensitive and reliable biomarkers. We advocate awareness and inclusion of the differentiation of injury type and ICP elevation in further studies with brain injury biomarkers.

Dexamethasone induces apoptosis of progenitor cells in the subventricular zone and dentate gyrus of developing rat brain

The use of dexamethasone in premature infants to prevent and/or treat bronchopulmonary dysplasia adversely affects neurocognitive development and is associated with cerebral palsy. The underlying mechanisms of these effects are multifactorial and likely include apoptosis. The objective of this study was to confirm whether dexamethasone causes apoptosis in different regions of the developing rat brain. On postnatal day 2, pups in each litter were randomly divided into the dexamethasone-treated (n = 91) or vehicle-treated (n = 92) groups. Rat pups in the dexamethasone group received tapering doses of dexamethasone on postnatal days 3-6 (0.5, 0.25, 0.125, and 0.06 mg/kg/day, respectively). Dexamethasone treatment significantly decreased the gain of body and brain weight and increased brain caspase-3 activity, DNA fragments, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, and cleaved caspse-3-positive cells at 24 hr after treatment. Dexamethasone increased cleaved caspse-3-positive cells in the cortex, thalamus, hippocampus, cerebellum, dentate gyrus, and subventricular zone. Double-immunofluorescence studies show that progenitor cells in the subventricular zone and dentate gyrus preferentially undergo apoptosis following dexamethasone exposure. These results indicate that dexamethasone-induced apoptosis in immature cells in developing brain is one of the mechanisms of its neurodegenerative effects in newborn rats.

Neuroprotective effects of hypothermia and erythropoietin after perinatal asphyxia in newborn rats

OBJECTIVE

Evaluation of neuroprotective effects of hypothermia, erythropoietin and their simultaneous use after perinatal asphyxia in newborn rats.

METHOD

Hysterectomy was performed to Wistar female rats on the last day of gestation. Perinatal asphyxia was induced by submersion of uterus containing pups in saline for 15 min. After resuscitation, pups were randomized into 4 groups, 15 animals in each: G1 - asphyxia; G2 - asphyxia + hypothermia (rectal temperature 33 °C for 1 h); G3 - asphyxia + erythropoietin (Darbepoetin-α 2.5 μg, intraperitoneally) and G4 - asphyxia + erythropoietin + hypothermia. Pups were sacrificed on 7th day of life and histopathological analysis of hippocampus was performed.

RESULTS

Measure of damage to dorsal, ventral and entire hippocampus was significantly lower in groups G2, G3 and G4 than in group G1 (p ~ 0.00; respectively). Measure of damage to hippocampus in group G4 was significantly lower than in group G2 (p = 0.029).

CONCLUSIONS

This study demonstrates that simultaneous use of hypothermia and erythropoietin has more expressed neuroprotective effects than sole use of hypothermia after perinatal asphyxia in newborn rats.

Fluoxetine-induced cortical adult neurogenesis

Adult neurogenesis in the hippocampal subgranular zone (SGZ) and the anterior subventricular zone (SVZ) is regulated by multiple factors, including neurotransmitters, hormones, stress, aging, voluntary exercise, environmental enrichment, learning, and ischemia. Chronic treatment with selective serotonin reuptake inhibitors (SSRIs) modulates adult neurogenesis in the SGZ, the neuronal area that is hypothesized to mediate the antidepressant effects of these substances. Layer 1 inhibitory neuron progenitor cells (L1-INP cells) were recently identified in the adult cortex, but it remains unclear what factors other than ischemia affect the neurogenesis of L1-INP cells. Here, we show that chronic treatment with an SSRI, fluoxetine (FLX), stimulated the neurogenesis of γ-aminobutyric acid (GABA)ergic interneurons from L1-INP cells in the cortex of adult mice. Immunofluorescence and genetic analyses revealed that FLX treatment increased the number of L1-INP cells in all examined cortical regions in a dose-dependent manner. Furthermore, enhanced Venus reporter expression driven by the synapsin I promoter demonstrated that GABAergic interneurons were derived from retrovirally labeled L1-INP cells. In order to assess if these new GABAergic interneurons possess physiological function, we examined their effect on apoptosis surrounding areas following ischemia. Intriguingly, the number of neurons expressing the apoptotic marker, active caspase-3, was significantly lower in adult mice pretreated with FLX. Our findings indicate that FLX stimulates the neurogenesis of cortical GABAergic interneurons, which might have, at least, some functions, including a suppressive effect on apoptosis induced by ischemia.

Acute diagnostic biomarkers for spinal cord injury: review of the literature and preliminary research report

OBJECTIVE

Many efforts have been made to create new diagnostic technologies for use in the diagnosis of central nervous system injury. However, there is still no consensus for the use of biomarkers in clinical acute spinal cord injury (SCI). The aims of this review are (1) to evaluate the current status of neurochemical biomarkers and (2) to discuss their potential acute diagnostic role in SCI by reviewing the literature.

METHODS

PubMed (http://www.ncbi.nlm.nih.gov/pubmed) was searched up to 2012 to identify publications concerning diagnostic biomarkers in SCI. To support more knowledge, we also checked secondary references in the primarily retrieved literature.

RESULTS

Neurofilaments, cleaved-Tau, microtubule-associated protein 2, myelin basic protein, neuron-specific enolase, S100β, and glial fibrillary acidic protein were identified as structural protein biomarkers in SCI by this review process. We could not find reports relating ubiquitin C-terminal hydrolase-L1 and α-II spectrin breakdown products, which are widely researched in other central nervous system injuries. Therefore, we present our preliminary data relating to these two biomarkers. Some of biomarkers showed promising results for SCI diagnosis and outcome prediction; however, there were unresolved issues relating to accuracy and their accessibility.

CONCLUSION

Currently, there still are not many reports focused on diagnostic biomarkers in SCI. This fact warranted the need for greater efforts to innovate sensitive and reliable biomarkers for SCI.

Over-expression of X-linked inhibitor of apoptosis protein modulates multiple aspects of neuronal Ca2+ signaling

X-linked inhibitor of apoptosis (XIAP) protects and preserves the function of neurons in both in vitro and in vivo models of excitotoxicity. Since calcium (Ca(2+)) overload is a pivotal event in excitotoxic neuronal cell death, we have determined whether XIAP over-expression influences Ca(2+)-signaling in primary cultures of mouse cortical neurons. Using cortical neuron cultures derived from wild-type (Wt) mice transiently transfected with XIAP or from transgenic mice that over-express XIAP, we show that XIAP opposes the rise in intracellular Ca(2+) concentration by a variety of triggers. Relative to control neurons, XIAP over-expression produced a slight, but significant, elevation of resting Ca(2+) concentrations. By contrast, the rise in intracellular Ca(2+) concentrations produced by N-methyl-D-aspartate receptor stimulation and voltage gated Ca(2+) channel activation were markedly attenuated by XIAP over-expression. The release of Ca(2+) from intracellular stores induced by the sarco/endoplasmic reticulum Ca(2+) ATPase inhibitor thapsigargin was also inhibited in neurons transiently transfected with XIAP. The pan-caspase inhibitor zVAD did not, however, diminish the rise in intracellular Ca(2+) concentrations elicited by L-glutamate suggesting that XIAP influences Ca(2+) signaling in a caspase-independent manner. Taken together, these findings demonstrate that the ability of XIAP to block excessive rises in intracellular Ca(2+) by a variety of triggers may contribute to the neuroprotective effects of this anti-apoptotic protein.

Genetic deletion of CD36 enhances injury after acute neonatal stroke

OBJECTIVE

The scavenger receptor CD36 is injurious in acute experimental focal stroke and neurodegenerative diseases in the adult. We investigated the effects of genetic deletion of CD36 (CD36ko) on acute injury, and oxidative and inflammatory signaling after neonatal stroke.

METHODS

Postnatal day 9 CD36ko and wild-type (WT) mice were subjected to a transient middle cerebral artery occlusion (MCAO). Injury, phagocytosis of dying cells, and CD36 inflammatory signaling were determined.

RESULTS

While the volume of tissue at risk by diffusion-weighted magnetic resonance imaging during MCAO was similar in neonatal CD36ko and WT mice, by 24 hours after reperfusion, injury was more severe in CD36ko and was associated with increased caspase-3 cleavage and reduced engulfment of neurons expressing cleaved caspase-3 by activated microglia. No significant superoxide generation was observed in activated microglia in injured WT, whereas increased superoxide production in vessels and nuclear factor (NF)-κB activation induced by MCAO were unaffected by lack of CD36. Lyn expression was higher in injured CD36ko, and cell type-specific patterns of Lyn expression were altered; Lyn was expressed in endothelial cells and microglia in WT but predominantly in dying neurons in CD36ko.

INTERPRETATION

Lack of CD36 results in poorer short-term outcome from neonatal focal stroke due to lack of attenuation of NF-κB-mediated inflammation and diminished removal of apoptotic neuronal debris. Although inhibition of CD36 does not seem to be a good therapeutic target for protection after acute neonatal stroke, as it is after adult stroke, seeking better understanding of CD36 signaling in particular cell populations may reveal important therapeutic targets for neonatal stroke.

Clinical utility of serum levels of ubiquitin C-terminal hydrolase as a biomarker for severe traumatic brain injury

BACKGROUND

Brain damage markers released in cerebrospinal fluid (CSF) and blood may provide valuable information about diagnosis and outcome prediction after traumatic brain injury (TBI).

OBJECTIVE

To examine the concentrations of ubiquitin C-terminal hydrolase-L1 (UCH-L1), a novel brain injury biomarker, in CSF and serum of severe TBI patients and their association with clinical characteristics and outcome.

METHODS

This case-control study enrolled 95 severe TBI subjects (Glasgow Coma Scale [GCS] score, 8). Using sensitive UCH-L1 sandwich ELISA, we studied the temporal profile of CSF and serum UCH-L1 levels over 7 days for severe TBI patients.

RESULTS

Comparison of serum and CSF levels of UCH-L1 in TBI patients and control subjects shows a robust and significant elevation of UCH-L1 in the acute phase and over the 7-day study period. Serum and CSF UCH-L1 receiver-operating characteristic curves further confirm strong specificity and selectivity for diagnosing severe TBI vs controls, with area under the curve values in serum and CSF statistically significant at all time points up to 24 hours (P < .001). The first 12-hour levels of both serum and CSF UCH-L1 in patients with GCS score of 3 to 5 were also significantly higher than those with GCS score of 6 to 8. Furthermore, UCH-L1 levels in CSF and serum appear to distinguish severe TBI survivors from nonsurvivors within the study, with nonsurvivors having significantly higher and more persistent levels of serum and CSF UCH-L1. Cumulative serum UCH-L1 levels > 5.22 ng/mL predicted death (odds ratio, 4.8).

CONCLUSION

Serum levels of UCH-L1 appear to have potential clinical utility in diagnosing TBI, including correlating to injury severity and survival outcome.

Rescuing the neonatal brain from hypoxic injury with autologous cord blood

Brain injury resulting from perinatal hypoxic-ischemic encephalopathy (HIE) is a major cause of acute mortality in infants and chronic neurologic disability in surviving children. Recent multicenter clinical trials demonstrated the effectiveness of hypothermia initiated within the first 6 postnatal hours to reduce the risk of death or major neurological disabilities among neonates with HIE. However, in these trials, approximately 40% of cooled infants died or survived with significant impairments. Therefore, adjunct therapies are required to improve the outcome in neonates with HIE. Cord blood (CB) is a rich source of stem cells. Administration of human CB cells in animal models of HIE has generally resulted in improved outcomes and multiple mechanisms have been suggested including anti-inflammation, release of neurotrophic factors and stimulation of endogenous neurogenesis. Investigators at Duke are conducting studies of autologous CB infusion in neonates with HIE and in children with cerebral palsy. These pilot studies indicate no added risk from the regimens used, but results of ongoing placebo-controlled trials are needed to assess efficacy. Meanwhile, further investigations are warranted to determine the best strategies, that is, timing, dosing, route of delivery, choice of stem cells and ex vivo modulations, to attain long-term benefits of CB stem cell therapy.

Apoptosis-inducing factor downregulation increased neuronal progenitor, but not stem cell, survival in the neonatal hippocampus after cerebral hypoxia-ischemia

BACKGROUND

A considerable proportion of all newly generated cells in the hippocampus will die before becoming fully differentiated, both under normal and pathological circumstances. The caspase-independent apoptosis-inducing factor (AIF) has not been investigated previously in this context.

RESULTS

Postnatal day 8 (P8) harlequin (Hq) mutant mice, expressing lower levels of AIF, and wild type littermates were injected with BrdU once daily for two days to label newborn cells. On P10 mice were subjected to hypoxia-ischemia (HI) and their brains were analyzed 4 h, 24 h or 4 weeks later. Overall tissue loss was 63.5% lower in Hq mice 4 weeks after HI. Short-term survival (4 h and 24 h) of labeled cells in the subgranular zone was neither affected by AIF downregulation, nor by HI. Long-term (4 weeks) survival of undifferentiated, BLBP-positive stem cells was reduced by half after HI, but this was not changed by AIF downregulation. Neurogenesis, however, as judged by BrdU/NeuN double labeling, was reduced by half after HI in wild type mice but preserved in Hq mice, indicating that primarily neural progenitors and neurons were protected. A wave of cell death started early after HI in the innermost layers of the granule cell layer (GCL) and moved outward, such that 24 h after HI dying cells could be detected in the entire GCL.

CONCLUSIONS

These findings demonstrate that AIF downregulation provides not only long-term overall neuroprotection after HI, but also protects neural progenitor cells, thereby rescuing hippocampal neurogenesis.

Genetic inhibition of caspase-2 reduces hypoxic-ischemic and excitotoxic neonatal brain injury

OBJECTIVE

Perinatal brain injury is a major cause of neurodevelopmental handicaps. Multiple pathways of oxidant stress, inflammation, and excitotoxicity lead to cell damage and death, including caspase-dependent apoptosis. Caspase-2 (Casp2; Nedd-2, Ich-1) is a developmentally regulated initiator caspase, which poorly cleaves other caspases but can initiate mitochondrial outer membrane permeabilization. We have investigated if Casp2 could mediate perinatal ischemic brain damage.

METHODS

Casp2 expression in human neonatal brains and developmental patterns in rats and mice were evaluated. Casp2-deficient (Casp2(-/-)), wild-type (WT), and heterozygous (Casp2(+/-)) newborn C57BL/6 mice were subjected to hypoxia-ischemia (unilateral carotid occlusion + exposure to 10% oxygen for 50 minutes) or intracerebral injection of the excitotoxic N-methyl-D-aspartate-receptor agonist ibotenate. In addition, Casp2 specific siRNAs were preinjected into the brain of WT newborn mice 24 hours before ibotenate treatment. Brain tissues were examined by immunohistochemical staining (cresyl violet, MAP2, NF68, Casp2, Casp3) and Western blotting. Lesion volumes and injury in the cortical plates and white matter were quantified together with activated Casp3.

RESULTS

Casp2 is highly expressed in the neonatal brain. Casp2-deficient mice subjected to hypoxia-ischemia at postnatal day 9 present significantly lower cerebral infarction, reduced white matter injury, and reduced Casp3 activation in the thalamus and hippocampus. Both Casp2(-/-) mice and siRNA-administered WT mice conferred reduction of gray and white matter injury after excitotoxic insult at postnatal day 5. Casp3 activation was also found reduced in Casp2-deficient mice subjected to excitotoxicity.

INTERPRETATION

These data suggest for the first time a role of Casp2 in neonatal brain damage.

Comparison of carbamylated erythropoietin-FC fusion protein and recombinant human erythropoietin during porcine aortic balloon occlusion-induced spinal cord ischemia/reperfusion injury

PURPOSE

Recombinant human erythropoietin (rhEPO) attenuated ischemia/reperfusion (I/R) injury-induced spinal cord damage. Since carbamylated EPO derivatives are stated to be devoid of rhEPO side effects, we tested the hypothesis that a newly developed carbamylated EPO-FC fusion protein (cEPO-FC) would compare favorably with rhEPO.

METHODS

Anesthetized and mechanically ventilated pigs randomly received cEPO-FC (50 μg kg(-1)), rhEPO (5,000 IU kg(-1)) or vehicle (n = 9 per group) 30 min prior to 30 min of aortic occlusion and over the 4 h of reperfusion. During aortic occlusion, mean arterial pressure (MAP) was maintained at 80-120% of baseline values by esmolol, nitroglycerin, and adenosine-5'-triphosphate (ATP). During reperfusion, noradrenaline was titrated to keep MAP at pre-ischemic levels. Spinal cord function was assessed by motor evoked potentials (MEP) and lower limb reflexes. Tissue damage was evaluated using hematoxylin and eosin, Nissl, and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) staining. Plasma levels of interleukin-6, tumor necrosis factor-α, and 8-isoprostanes were measured as markers of systemic inflammation and oxidative stress.

RESULTS

While only cEPO-FC restored MEP amplitude to values close to pre-occlusion levels, both cEPO-FC and rhEPO comparably restored lower limb reflexes and reduced the percentage of damaged neurons. Infiltration of mononuclear inflammatory cells was moderate without intergroup difference; positive TUNEL staining was barely detectable in any group. I/R injury increased blood cytokine levels without intergroup difference, whereas both cEPO-FC and rhEPO significantly lowered 8-isoprostane levels.

CONCLUSIONS

In a porcine model of aortic balloon occlusion-induced spinal cord I/R injury, cEPO-FC and rhEPO comparably protected against ischemic spinal cord dysfunction and neuronal damage. This effect coincided with attenuated oxidative stress.

Diffusion characteristics associated with neuronal injury and glial activation following hypoxia-ischemia in the immature brain

To identify quantitative MRI indices of injury in the brain following neonatal hypoxic-ischemic brain injury, we subjected mouse pups to hypoxia-ischemia on postnatal day 7 and obtained conventional and diffusion-weighted in vivo images of the brain 24 h later followed by histological assessment. T(2)-weighted images showed increased signal intensity in the CA1 and CA2 regions of the hippocampus ipsilateral to the injury and adjacent white matter. In contrast, diffusion imaging showed reduced apparent diffusion coefficient (ADC) values in CA1 and CA2, but increased values in the adjacent white matter. Histological analysis showed widespread gliosis with degenerating oligodendrocytes in the ipsilateral hippocampus. In addition, white matter areas that were abnormal by MRI showed an increase in the number of activated microglia (CD45 positive cells). Activated caspase-3 immunostaining showed a marked increase in neurons in the hippocampal regions corresponding to those with reduced ADC, and a quantitative measure of staining showed a statistically significant correlation with the ADC. In contrast, ADC was higher in adjacent white matter, where histology showed activation of microglia and reactive oligodendrocytes but not caspase-3 activation. These results suggest that the ADC response differs between areas of neuronal injury as compared with those showing glial changes without marked cell death.

Death and survival of neuronal and astrocytic cells in ischemic brain injury: a role of autophagy

Autophagy is a highly regulated cellular mechanism that leads to degradation of long-lived proteins and dysfunctional organelles. The process has been implicated in a variety of physiological and pathological conditions relevant to neurological diseases. Recent studies show the existence of autophagy in cerebral ischemia, but no consensus has yet been reached regarding the functions of autophagy in this condition. This article highlights the activation of autophagy during cerebral ischemia and/or reperfusion, especially in neurons and astrocytes, as well as the role of autophagy in neuronal or astrocytic cell death and survival. We propose that physiological levels of autophagy, presumably caused by mild to modest hypoxia or ischemia, appear to be protective. However, high levels of autophagy caused by severe hypoxia or ischemia and/or reperfusion may cause self-digestion and eventual neuronal and astrocytic cell death. We also discuss that oxidative and endoplasmic reticulum (ER) stresses in cerebral hypoxia or ischemia and/or reperfusion are potent stimuli of autophagy in neurons and astrocytes. In addition, we review the evidence suggesting a considerable overlap between autophagy on one hand, and apoptosis, necrosis and necroptosis on the other hand, in determining the outcomes and final morphology of damaged neurons and astrocytes.

Lipopolysaccharide-induced preconditioning against ischemic injury is associated with changes in toll-like receptor 4 expression in the rat developing brain

Lipopolysaccharide (LPS) preconditioning reduces ischemic injury in adult brain by activating Toll-like receptor 4 (TLR-4). We sought to investigate the effect of brain maturity on the efficacy of LPS preconditioning against hypoxic-ischemic (HI) injury in the developing rat brain. Rat pups at the specified age were randomly assigned to LPS-treated (0.1 mg/kg) or saline-treated groups. HI injury was induced 48 h later by occluding the right common carotid artery followed by transient hypoxia. Brains were removed 1 wk after HI injury, and infarct volumes were compared between the two groups. TLR-4 expression was also compared among different ages. We found that LPS treated P7, P9, and P14 rat pups had significantly smaller infarct volume compared with saline-treated pups (p = 0.006, 0.03, and 0.01, respectively). This significant reduction in infarct volume was not observed in P3 and P5 rats. TLR-4 expression was significantly higher in older rats compared with P3 and P5 rats (p < 0.01). These findings indicate that LPS-induced preconditioning is a robust neuroprotective phenomenon in the ischemic developing brain that is age dependent. Pattern of TLR-4 expression is also affected by brain maturity and likely to be responsible for differences in the efficacy of LPS preconditioning.

In vivo contributions of BH3-only proteins to neuronal death following seizures, ischemia, and traumatic brain injury

The Bcl-2 homology (BH) domain 3-only proteins are a proapoptotic subgroup of the Bcl-2 gene family, which regulate cell death via effects on mitochondria. The BH3-only proteins react to various cell stressors and promote cell death by binding and inactivating antiapoptotic Bcl-2 family members and direct activation of proapoptotic multi-BH domain proteins such as Bax. Here, we review the in vivo evidence for their involvement in the pathophysiology of status epilepticus and contrast it to ischemia and traumatic brain injury. Seizures in rodents activate three potent proapoptotic BH3-only proteins: Bid, Bim, and Puma. Analysis of damage after seizures in mice singly deficient for each BH3-only protein supports a causal role for Puma and to a lesser extent Bim but, surprisingly, not Bid. In ischemia and trauma, where core aspects of the pathophysiology of cell death overlap, multiple BH3-only proteins are also activated and Bid has been shown to be required for neuronal death. The findings suggest that while each neurologic insult activates multiple BH3-only proteins, there may be specificity in their functional contribution. Future challenges include evaluating the remaining BH3-only proteins, explaining different causal contributions, and, if possible, exploring neurologic outcomes in mouse models deficient for multiple BH3-only proteins.

Neuronal cell death in neonatal hypoxia-ischemia

Perinatal hypoxic-ischemic encephalopathy (HIE) is a significant cause of mortality and morbidity in infants and young children. Therapeutic opportunities are very limited for neonatal and pediatric HIE. Specific neural systems and populations of cells are selectively vulnerable in HIE; however, the mechanisms of degeneration are unresolved. These mechanisms involve oxidative stress, excitotoxicity, inflammation, and the activation of several different cell death pathways. Decades ago the structural and mechanistic basis of the cellular degeneration in HIE was thought to be necrosis. Subsequently, largely due to advances in cell biology and to experimental animal studies, emphasis has been switched to apoptosis or autophagy mediated by programmed cell death (PCD) mechanisms as important forms of degeneration in HIE. We have conceptualized based on morphological and biochemical data that this degeneration is better classified according to an apoptosis-necrosis cell death continuum and that programmed cell necrosis has prominent contribution in the neurodegeneration of HIE in animal models. It is likely that neonatal HIE evolves through many cell death chreodes influenced by the dynamic injury landscape. The relevant injury mechanisms remain to be determined in human neonatal HIE, though preliminary work suggests a complexity in the cell death mechanisms greater than that anticipated from experimental animal models. The accurate identification of the various cell death chreodes and their mechanisms unfolding within the immature brain matrix could provide fresh insight for developing meaningful therapies for neonatal and pediatric HIE.

Effect of hypoxia on expression of selected proteins involved in regulation of apoptotic activity in striatum of newborn piglets

The levels of selected neuroregulatory proteins that inhibit or promote apoptotic cell death were measured in the striatum of piglets subjected to precisely controlled 1 h hypoxic insult followed by 0, 2 and 4 h recovery and compared to sham operated animals. The anti-apoptotic proteins: there were increases in Survivin at 0 (157%, P = 0.031) and 4 h (171%, P = 0.033), in Bcl-XL at 0 (138%, P = 0.028) and 4 h (143%, P = 0.007), in VEGF at 4 h (185%, P = 0.019) and Hsp27 at 2 h (144%, P = 0.05) and 4 h (143%, P = 0.05). The pro-apoptotic proteins: caspases-1 and 7 increased at 4 h (135%, P = 0.05) and (129%, P = 0.038), respectively. Bim increased after 4 h (115%, P = 0.028), Apoptosis Inducing Factor after 2 h (127%, P = 0.048) and Calpain after 4 h (143% of control, P = 0.04). Hypoxia causes increase in levels of both anti- and pro-apoptotic proteins. Their relative activity determines the outcome in terms of cell damage and neuronal deficit.

Resuscitation of newborn piglets. short-term influence of FiO2 on matrix metalloproteinases, caspase-3 and BDNF

BACKGROUND

Perinatal hypoxia-ischemia is a major cause of mortality and cerebral morbidity, and using oxygen during newborn resuscitation may further harm the brain. The aim was to examine how supplementary oxygen used for newborn resuscitation would influence early brain tissue injury, cell death and repair processes and the regulation of genes related to apoptosis, neurodegeneration and neuroprotection.

METHODS AND FINDINGS

Anesthetized newborn piglets were subjected to global hypoxia and then randomly assigned to resuscitation with 21%, 40% or 100% O(2) for 30 min and followed for 9 h. An additional group received 100% O(2) for 30 min without preceding hypoxia. The left hemisphere was used for histopathology and immunohistochemistry and the right hemisphere was used for in situ zymography in the corpus striatum; gene expression and the activity of various relevant biofactors were measured in the frontal cortex. There was an increase in the net matrix metalloproteinase gelatinolytic activity in the corpus striatum from piglets resuscitated with 100% oxygen vs. 21%. Hematoxylin-eosin (HE) staining revealed no significant changes. Nine hours after oxygen-assisted resuscitation, caspase-3 expression and activity was increased by 30-40% in the 100% O(2) group (n = 9/10) vs. the 21% O(2) group (n = 10; p<0.04), whereas brain-derived neurotrophic factor (BDNF) activity was decreased by 65% p<0.03.

CONCLUSIONS

The use of 100% oxygen for resuscitation resulted in increased potentially harmful proteolytic activities and attenuated BDNF activity when compared with 21%. Although there were no significant changes in short term cell loss, hyperoxia seems to cause an early imbalance between neuroprotective and neurotoxic mechanisms that might compromise the final pathological outcome.

Uncx regulates proliferation of neural progenitor cells and neuronal survival in the olfactory epithelium

Uncx (Phd1, Chx4) is a paired homeobox transcription factor gene. It and its probable functional partners, Tle co-repressors, were expressed by neurally-fated basal progenitor cells and olfactory sensory neurons of the olfactory epithelium. Uncx expression was rare in olfactory epithelia of Ascl1(-/-) mice, but common in Neurog1(-/-) mice. In Uncx(-/-) mice olfactory progenitor cell proliferation, progenitor cell number, olfactory sensory neuron survival, and Umodl1 and Kcnc4 mRNAs were reduced. Evidence of sensory neuron activity and functional connections to the olfactory bulb argue that decreased neuronal survival was not due to loss of trophic support or activity-dependent mechanisms. These data suggest that UNCX acts downstream of neural determination factors to broadly control transcriptional mechanisms used by neural progenitor cells to specify neural phenotypes.

Mechanisms of hypothermic neuroprotection

There is now compelling clinical evidence that prolonged, moderate cerebral hypothermia initiated within a few hours after severe hypoxia-ischemia and continued until resolution of the acute phase of delayed cell death can reduce subsequent neuronal loss and improve behavioral recovery in term infants and adults after cardiac arrest. Perhaps surprisingly, the specific mechanisms of hypothermic neuroprotection remain unclear, at least in part because hypothermia suppresses a broad range of potential injurious factors. In the present review we critically examine proposed mechanisms in relation to the known window of opportunity for effective protection with hypothermia. Better knowledge of the mechanisms of hypothermia is critical to help guide the rational development of future combination treatments to augment neuroprotection with hypothermia, and to identify those most likely to benefit from it.

Hairless expression attenuates apoptosis in a mouse model and the COS cell line; involvement of p53

BACKGROUND

Neurons are more likely to die through apoptosis in the immature brain after injury whereas adult neurons in the mature brain die by necrosis. Several studies have suggested that this maturational change in the mechanism of cell death is regulated, in part, by thyroid hormone. We examined the involvement of the hairless (Hr) gene which has been suspected of having a role in cell cycle regulation and apoptosis in the hair follicle and is strongly regulated by the thyroid hormone in the brain.

METHODOLOGY

Forced expression of Hr by transfection decreased the number of apoptotic nuclei, levels of caspase-3 activity, and cytosolic cytochrome C in COS cells exposed to staurosporine and tunicamycin. Similarly, caspase-3 activity was lower and the decrease in mitochondrial membrane potential was smaller in cultures of adult cerebellar granule neurons from wild type mice compared to Hr knockout mice induced to undergo apoptosis. In vivo, apoptosis as detected by positive TUNEL labeling and caspase 3 activity was lower in wild-type mice compared to Hr knockouts after exposure to trimethyltin. Hr expression lowered levels of p53, p53 mediated reporter gene activity, and lower levels of the pro-apoptotic Bcl2 family member Bax in COS cells. Finally, Hr expression did not attenuate apoptosis in mouse embryonic fibroblasts from p53 knockout mice but was effective in mouse embryonic fibroblasts from wild type mice.

CONCLUSIONS/SIGNIFICANCE

Overall, our studies demonstrate that Hr evokes an anti-apoptotic response by repressing expression of p53 and pro-apoptotic events regulated by p53.

Lithium reduces apoptosis and autophagy after neonatal hypoxia-ischemia

Lithium is used in the treatment of bipolar mood disorder. Reportedly, lithium can be neuroprotective in models of adult brain ischemia. The purpose of this study was to evaluate the effects of lithium in a model of neonatal hypoxic-ischemic brain injury. Nine-day-old male rats were subjected to unilateral hypoxia-ischemia (HI) and 2 mmol/kg lithium chloride was injected i.p. immediately after the insult. Additional lithium injections, 1 mmol/kg, were administered at 24-h intervals. Pups were killed 6, 24 or 72 h after HI. Lithium reduced the infarct volume from 24.7±2.9 to 13.8±3.3 mm(3) (44.1%) and total tissue loss (degeneration + lack of growth) from 67.4±4.4 to 38.4±5.9 mm(3) (43.1%) compared with vehicle at 72 h after HI. Injury was reduced in the cortex, hippocampus, thalamus and striatum. Lithium reduced the ischemia-induced dephosphorylation of glycogen synthase kinase-3β and extracellular signal-regulated kinase, the activation of calpain and caspase-3, the mitochondrial release of cytochrome c and apoptosis-inducing factor, as well as autophagy. We conclude that lithium could mitigate the brain injury after HI by inhibiting neuronal apoptosis. The lithium doses used were in the same range as those used in bipolar patients, suggesting that lithium might be safely used for the avoidance of neonatal brain injury.

Nuclear translocation and calpain-dependent reduction of Bcl-2 after neonatal cerebral hypoxia-ischemia

Apoptosis-related mechanisms are important in the pathophysiology of hypoxic-ischemic injury in the neonatal brain. Caspases are the major executioners of apoptosis, but there are a number of upstream players that influence the cell death pathways. The Bcl-2 family proteins are important modulators of mitochondrial permeability, working either to promote or prevent apoptosis. In this study we focused on the anti-apoptotic Bcl-2 protein after neonatal cerebral hypoxia-ischemia (HI) in 8-day-old rats. Bcl-2 translocated to nuclei and accumulated there over the first 24h of reperfusion after HI, as judged by immunohistochemistry and immuno-electron microscopy. We also found that the total level of Bcl-2 decreased after HI in vivo and after ionophore challenge in cultured human neuroblastoma (IMR-32) cells in vitro. Furthermore, the Bcl-2 reduction was calpain-dependent, because it could be prevented by the calpain inhibitor CX295 both in vivo and in vitro, suggesting cross-talk between excitotoxic and apoptotic mechanisms.

Chemical stress induces the unfolded protein response in olfactory sensory neurons

More than any other neuron, olfactory sensory neurons are exposed to environmental insults. Surprisingly, their only documented response to damaging stress is apoptosis and subsequent replacement by new neurons. However, they expressed unfolded protein response genes, a transcriptionally regulated defense mechanism activated by many types of insults. The unfolded protein response transcripts Xbp1, spliced Xbp1, Chop (Ddit3), and BiP (Hspa5) were decreased when external access of stressors was reduced by blocking a nostril (naris occlusion). These transcripts and Nrf2 (Nfe2l2) were increased by systemic application of tunicamycin or the selective olfactotoxic chemical methimazole. Methimazole's effects overcame naris occlusion, and the unfolded protein response was independent of odor-evoked neuronal activity. Chemical stress is therefore a major and chronic activator of the unfolded protein response in olfactory sensory neurons. Stress-dependent repression of the antiapoptotic gene Bcl2 was absent, however, suggesting a mechanism for disconnecting the UPR from apoptosis and tolerating a chronic unfolded protein response. Environmental stressors also affect both the sustentacular cells that support the neurons and the respiratory epithelia, because naris occlusion decreased expression of the xenobiotic chemical transformation enzyme Cyp2a5 in sustentacular cells, and both naris occlusion and methimazole altered the abundance of the antibacterial lectin Reg3g in respiratory epithelia.

Hypothermia for hypoxic-ischemic encephalopathy

Moderate to severe hypoxic-ischemic injury in newborn infants, manifested as encephalopathy immediately or within hours after birth, is associated with a high risk of either death or a lifetime with disability. In recent multicenter clinical trials, hypothermia initiated within the first 6 postnatal hours has emerged as a therapy that reduces the risk of death or impairment among infants with hypoxic-ischemic encephalopathy. Prior to hypothermia, no therapies directly targeting neonatal encephalopathy secondary to hypoxic-ischemic injury had convincing evidence of efficacy. Hypothermia therapy is now becoming increasingly available at tertiary centers. Despite the deserved enthusiasm for hypothermia, obstetric and neonatology caregivers, as well as society at large, must be reminded that in the clinical trials more than 40% of cooled infants died or survived with impairment. Although hypothermia is an evidence-based therapy, additional discoveries are needed to further improve outcome after HIE. In this article, we briefly present the epidemiology of neonatal encephalopathy due to hypoxic-ischemic injury, describe the rationale for the use of hypothermia therapy for hypoxic-ischemic encephalopathy, and present results of the clinical trials that have demonstrated the efficacy of hypothermia. We also present findings noted during and after these trials that will guide care and direct research for this devastating problem.

Fate of marginal neuroblasts in the vomeronasal epithelium of adult mice

Chemical stimuli are sensed through the olfactory and vomeronasal epithelia, and the sensory cells of both systems undergo neuronal turnover during adulthood. In the vomeronasal epithelium, stem cells adjacent to the basal lamina divide and migrate to replace two classes of sensory neurons: apical neurons that express G(i2alpha)-linked V1R vomeronasal receptors and project to the anterior accessory olfactory bulb, and basal neurons that express G(oalpha)-linked V2R receptors and project to the posterior accessory olfactory bulb. Most of the dividing cells are present in the margins of the epithelium and only migrate locally. Previous studies have suggested that these marginal cells may participate in growth, sensory cell replacement or become apoptotic before maturation; however, the exact fate of these cells have remained unclear. In this work we investigated the fate of these marginal cells by analyzing markers of neurogenesis (bromodeoxyuridine incorporation), apoptosis (caspase-3), and neuronal maturation (olfactory marker protein and Neurotrace Nissl stain). Our data reveal a pool of dividing cells in the epithelial margins that predominantly give rise to mature neurons and only rarely undergo apoptosis. Newly generated cells are several times more numerous than apoptotic cells. These marginal neuroblasts could therefore constitute a net neural addition zone during adulthood.

Ubiquitin C-terminal hydrolase is a novel biomarker in humans for severe traumatic brain injury

OBJECTIVE

Ubiquitin C-terminal hydrolase (UCH-L1), also called neuronal-specific protein gene product (PGP 9.3), is highly abundant in neurons. To assess the reliability of UCH-L1 as a potential biomarker for traumatic brain injury (TBI) this study compared cerebrospinal fluid (CSF) levels of UCH-L1 from adult patients with severe TBI to uninjured controls; and examined the relationship between levels with severity of injury, complications and functional outcome.

DESIGN

This study was designed as prospective case control study.

PATIENTS

This study enrolled 66 patients, 41 with severe TBI, defined by a Glasgow coma scale (GCS) score of < or =8, who underwent intraventricular intracranial pressure monitoring and 25 controls without TBI requiring CSF drainage for other medical reasons.

SETTING

: Two hospital system level I trauma centers.

MEASUREMENTS AND MAIN RESULTS

Ventricular CSF was sampled from each patient at 6, 12, 24, 48, 72, 96, 120, 144, and 168 hrs following TBI and analyzed for UCH-L1. Injury severity was assessed by the GCS score, Marshall Classification on computed tomography and a complicated postinjury course. Mortality was assessed at 6 wks and long-term outcome was assessed using the Glasgow outcome score 6 months after injury. TBI patients had significantly elevated CSF levels of UCH-L1 at each time point after injury compared to uninjured controls. Overall mean levels of UCH-L1 in TBI patients was 44.2 ng/mL (+/-7.9) compared with 2.7 ng/mL (+/-0.7) in controls (p <.001). There were significantly higher levels of UCH-L1 in patients with a lower GCS score at 24 hrs, in those with postinjury complications, in those with 6-wk mortality, and in those with a poor 6-month dichotomized Glasgow outcome score.

CONCLUSIONS

These data suggest that this novel biomarker has the potential to determine injury severity in TBI patients. Further studies are needed to validate these findings in a larger sample.

Traumatic injury activates MAP kinases in astrocytes: mechanisms of hypothermia and hyperthermia

Hyperthermia is common following traumatic brain injury (TBI) and has been associated with poor neurologic outcome, and hypothermia has emerged as a potentially effective therapy for TBI, although its mechanism is still unclear. In this study we investigated the effects of temperature modulations on astrocyte survival following traumatic injury and the involved MAPK pathways. Trauma was produced by scratch injury of a monolayer of confluent astrocytes in culture, followed by incubation at hypothermia (308 degree C), normothermia (378 degree C), or hyperthermia (398 degree C). The activation of MAPK pathways including extracellular signal-regulated protein kinase (ERK), c-Jun NH(2)-terminal kinase ( JNK), and p38 MAPK were measured at 0, 15, 30, 60, and 120 min after traumatic injury followed by temperature modulation. Apoptosis of astrocytes was assessed by quantitation of cleaved caspase-3 expression 24 h after injury. Our findings showed that only JNK activation at 15 min after trauma was reduced by hypothermia, and this was associated with a marked reduction in apoptosis. Hyperthermia activated both ERK and JNK and increased apoptosis. The specific JNK inhibitor, SP60025, markedly reduced JNK-induced apoptosis at normothermia and hyperthermia, and showed a dose-dependent effect. In conclusion, the JNK pathway appears to mediate traumatic injury-induced apoptosis in astrocytes. Prolonged hyperthermia as a secondary insult worsens apoptosis by increasing JNK activation. Hypothermia protects against traumatic injury via early suppression on JNK activation and subsequent prevention of apoptosis. Manipulation of the JNK pathway in astrocytes may represent a therapeutic target for ameliorating the devastating progression of tissue injury and cell death after TBI.

Neuroprotection in the newborn infant

Neonatal brain injury is an important cause of death and disability, with pathways of oxidant stress, inflammation, and excitotoxicity that lead to damage that progresses over a long period of time. Therapies have classically targeted individual pathways during early phases of injury, but more recent therapies such as growth factors may also enhance cell proliferation, differentiation, and migration over time. More recent evidence suggests combined therapy may optimize repair, decreasing cell injury while increasing newly born cells.

Calpain 1 and Calpastatin expression is developmentally regulated in rat brain

Calpains and caspases are cysteine endopeptidases which share many similar substrates. Caspases are essential for caspase-dependent apoptotic death where calpains may play an augmentive role, while calpains are strongly implicated in necrotic cell death morphologies. Previous studies have demonstrated a down-regulation in the expression of many components of the caspase-dependent cell death pathway during CNS development. We therefore sought to determine if there is a corresponding upregulation of calpains. The major CNS calpains are the mu-and m-isoforms, composed of the unique 80 kDa calpain 1 and 2 subunits, respectively, and the shared 28 kDa small subunit. In rat brain, relative protein and mRNA levels of calpain 1, calpain 2, caspase 3, and the endogenous calpain inhibitor-calpastatin, were evaluated using western blot and real-time RT-PCR. The developmental time points examined ranged from embryonic day 18 until postnatal day 90. Calpain 1 and calpastatin protein and mRNA levels were low at early developmental time points and increased dramatically by P30. Conversely, caspase-3 expression was greatest at E18, and was rapidly downregulated by P30. Calpain 2 protein and mRNA levels were relatively constant throughout the E18-P90 age range examined. The inverse relationship of calpain 1 and caspase 3 levels during CNS development is consistent with the shift from caspase-dependent to caspase-independent cell death mechanisms following CNS injury in neonatal vs. adult rat brain.

Neuroprotection against hypoxic-ischemic brain injury by inhibiting the apoptotic protease activating factor-1 pathway

BACKGROUND AND PURPOSE

Emerging evidence suggests that mitochondrial damage-mediated neuronal apoptosis is a major contributor to neonatal hypoxic-ischemic (H-I) brain injury. This study was performed to determine whether targeted inhibition of the apoptotic protease activating factor-1 (Apaf-1) signaling pathway downstream of mitochondrial damage confers neuroprotection in rodent models of neonatal H-I.

METHODS

H-I was induced in 7-day-old (P7) transgenic mice overexpressing the specific Apaf-1-inhibitory protein AIP. Apaf-1 inhibition was also achieved in P7 rats by protein transduction-enhanced delivery of recombinant AIP. Pups were euthanized 6 to 24 hours after H-I for assessing caspase activation and mitochondrial release of cytochrome c and AIF, and 7 days after H-I for analyzing brain tissue damage. Sensorimotor functions were assessed in rats up to 4 weeks after H-I.

RESULTS

Transgenic overexpression of AIP protected against H-I brain injury, resulting in attenuated activation of caspase-9 and caspase-3, and attenuated brain tissue loss. In neonatal H-I rats, intraperitoneal injection of TAT-AIP, but not the control proteins TAT-GFP or AIP, decreased caspase activation and brain damage and improved neurological functions. Neuroprotection conferred by AIP was also associated with significantly reduced release of cytochrome c and AIF from mitochondria.

CONCLUSIONS

The Apaf-1 signaling pathway, which transmits cell death signals after mitochondrial damage to effector caspases, may be a legitimate therapeutic target for the treatment of neonatal H-I brain injury.

Endoplasmic reticulum stress, inflammation, and perinatal brain damage

Inflammation seems to play a role in the pathogenesis of perinatal brain damage in fetuses/infants born much before term. We raise the possibility that noninflammatory phenomena induce endoplasmic reticulum stress, which, in turn, leads to the unfolded protein response, which is followed by apoptosis-promoting processes and inflammation. Perhaps by these events, noninflammatory stimuli lead to perinatal brain damage.

Apoptotic mechanisms in the immature brain: involvement of mitochondria

Brain injury after hypoxic-ischemic encephalopathy often develops with delayed appearance, opening a therapeutic window. Clinical studies in newborns show that post-hypoxic-ischemic hypothermia improves outcome. This has generated renewed interest in the molecular mechanisms of hypoxic-ischemic brain injury. In this brief review, we propose that mitochondrial permeabilization is crucial for injury to advance beyond the point of no return. We suggest that excitatory amino acids, nitric oxide, inflammation, trophic factor withdrawal, and an increased pro- versus antiapoptotic Bcl-2 protein ratio will trigger Bax-dependent mitochondrial outer membrane permeabilization. Mitochondrial outer membrane permeabilization, in turn, elicits mitochondrial release of cytochrome C, apoptosis-inducing factor, second mitochondria-derived activator of caspase/Diablo, and HtrA2/Omi. Cytochrome C efflux activates caspase-9/-3, leading to DNA fragmentation. Apoptosis-inducing factor interacts with cyclophilin A and induces chromatinolysis. Blockage of mitochondrial outer membrane permeabilization holds promise as a strategy for perinatal brain protection.

Mitochondrial mechanisms of cell death and neuroprotection in pediatric ischemic and traumatic brain injury

There are several forms of acute pediatric brain injury, including neonatal asphyxia, pediatric cardiac arrest with global ischemia, and head trauma, that result in devastating, lifelong neurologic impairment. The only clinical intervention that appears neuroprotective is hypothermia initiated soon after the initial injury. Evidence indicates that oxidative stress, mitochondrial dysfunction, and impaired cerebral energy metabolism contribute to the brain cell death that is responsible for much of the poor neurologic outcome from these events. Recent results obtained from both in vitro and animal models of neuronal death in the immature brain point toward several molecular mechanisms that are either induced or promoted by oxidative modification of macromolecules, including consumption of cytosolic and mitochondrial NAD(+) by poly-ADP ribose polymerase, opening of the mitochondrial inner membrane permeability transition pore, and inactivation of key, rate-limiting metabolic enzymes, e.g., the pyruvate dehydrogenase complex. In addition, the relative abundance of pro-apoptotic proteins in immature brains and neurons, and particularly within their mitochondria, predisposes these cells to the intrinsic, mitochondrial pathway of apoptosis, mediated by Bax- or Bak-triggered release of proteins into the cytosol through the mitochondrial outer membrane. Based on these pathways of cell dysfunction and death, several approaches toward neuroprotection are being investigated that show promise toward clinical translation. These strategies include minimizing oxidative stress by avoiding unnecessary hyperoxia, promoting aerobic energy metabolism by repletion of NAD(+) and by providing alternative oxidative fuels, e.g., ketone bodies, directly interfering with apoptotic pathways at the mitochondrial level, and pharmacologic induction of antioxidant and anti-inflammatory gene expression.

The effects of indomethacin on caspases, glutathione level and lipid peroxidation in the newborn rats with hypoxic-ischemic cerebral injury

Activation of phospholipase A(2), degradation of membrane phospholipids resulting in tissue accumulation of arachidonic acid, and the activation of cyclooxygenase that leads to the formation of prostaglandin and free radicals may occur after hypoxic-ischemic damage. The aim of this study was to investigate the effects of indomethacin, a nonselective cyclooxygenase inhibitor, on caspase activity, glutathione levels and lipid peroxidation in newborn rats with hypoxic-ischemic encephalopathy. The effects of indomethacin were evaluated by measuring caspase-3 and caspase-8 activities and glutathione levels. Lipid peroxidation was evaluated by measuring concentrations of malondialdehyde in rat brains. Seven-day-old rat pups with the Levine-Rice model of hypoxic-ischemic cerebral injury were randomly divided into three study groups. In the indomethacin-treated group, rats were administered three doses of indomethacin, at a dose of 2 mg/kg every 12 h. Sham and the hypoxic-ischemic group of rats were given physiologic saline. The sham group underwent all surgical procedures except for arterial ligation. After 72 hours, the rats were decapitated and brain tissues were evaluated. Caspase-3 and caspase-8 activities and glutathione and malondialdehyde levels were evaluated in all groups. There was an obvious decrease in caspase-3 and caspase-8 activities and depleted glutathione levels were reversed in the indomethacin-treated group compared to the hypoxic-ischemia group (p<0.001). As indomethacin was unable to prevent lipid peroxidation, malondialdehyde concentrations increased to ischemia-induced levels. In conclusion, indomethacin administration after hypoxic-ischemic encephalopathy injury has a neuroprotective effect since it inhibits caspase activity and reverses the depletion of glutathione. However, it also aggravates lipid peroxidation-induced ischemia.

Developmental shift of cyclophilin D contribution to hypoxic-ischemic brain injury

Cyclophilin D (CypD), a regulator of the mitochondrial membrane permeability transition pore (PTP), enhances Ca(2+)-induced mitochondrial permeabilization and cell death in the brain. However, the role of CypD in hypoxic-ischemic (HI) brain injury at different developmental ages is unknown. At postnatal day (P) 9 or P60, littermates of CypD-deficient [knock-out (KO)], wild-type (WT), and heterozygous mice were subjected to HI, and brain injury was evaluated 7 d after HI. CypD deficiency resulted in a significant reduction of HI brain injury at P60 but worsened injury at P9. After HI, caspase-dependent and -independent cell death pathways were more induced in P9 CypD KO mice than in WT controls, and apoptotic activation was minimal at P60. The PTP had a considerably higher induction threshold and lower sensitivity to cyclosporin A in neonatal versus adult mice. On the contrary, Bax inhibition markedly reduced caspase activation and brain injury in immature mice but was ineffective in the adult brain. Our findings suggest that CypD/PTP is critical for the development of brain injury in the adult, whereas Bax-dependent mechanisms prevail in the immature brain. The role of CypD in HI shifts from a predominantly prosurvival protein in the immature to a cell death mediator in the adult brain.