Targeting the p53 pathway to protect the neonatal ischemic brain

Oxygen regulates molecular mechanisms of cancer progression and metastasis

Oxygen is the basic molecule which supports life and it truly is "god's gift to life." Despite its immense importance, research on "oxygen biology" has never received the light of the day and has been limited to physiological and biochemical studies. It seems that in modern day biology, oxygen research is summarized in one word "hypoxia." Scientists have focused on hypoxia-induced transcriptomics and molecular-cellular alterations exclusively in disease models. Interestingly, the potential of oxygen to control the basic principles of biology like homeostatic maintenance, transcription, replication, and protein folding among many others, at the molecular level, has been completely ignored. Here, we present a perspective on the crucial role played by oxygen in regulation of basic biological phenomena. Our conclusion highlights the importance of establishing novel research areas like oxygen biology, as there is great potential in this field for basic science discoveries and clinical benefits to the society.

Mechanisms of chemotherapy-induced behavioral toxicities

While chemotherapeutic agents have yielded relative success in the treatment of cancer, patients are often plagued with unwanted and even debilitating side-effects from the treatment which can lead to dose reduction or even cessation of treatment. Common side effects (symptoms) of chemotherapy include (i) cognitive deficiencies such as problems with attention, memory and executive functioning; (ii) fatigue and motivational deficit; and (iii) neuropathy. These symptoms often develop during treatment but can remain even after cessation of chemotherapy, severely impacting long-term quality of life. Little is known about the underlying mechanisms responsible for the development of these behavioral toxicities, however, neuroinflammation is widely considered to be one of the major mechanisms responsible for chemotherapy-induced symptoms. Here, we critically assess what is known in regards to the role of neuroinflammation in chemotherapy-induced symptoms. We also argue that, based on the available evidence, neuroinflammation is unlikely the only mechanism involved in the pathogenesis of chemotherapy-induced behavioral toxicities. We evaluate two other putative candidate mechanisms. To this end we discuss the mediating role of damage-associated molecular patterns (DAMPs) activated in response to chemotherapy-induced cellular damage. We also review the literature with respect to possible alternative mechanisms such as a chemotherapy-induced change in the bioenergetic status of the tissue involving changes in mitochondrial function in relation to chemotherapy-induced behavioral toxicities. Understanding the mechanisms that underlie the emergence of fatigue, neuropathy, and cognitive difficulties is vital to better treatment and long-term survival of cancer patients.

The role of inflammation in perinatal brain injury

Inflammation is increasingly recognized as being a critical contributor to both normal development and injury outcome in the immature brain. The focus of this Review is to highlight important differences in innate and adaptive immunity in immature versus adult brain, which support the notion that the consequences of inflammation will be entirely different depending on context and stage of CNS development. Perinatal brain injury can result from neonatal encephalopathy and perinatal arterial ischaemic stroke, usually at term, but also in preterm infants. Inflammation occurs before, during and after brain injury at term, and modulates vulnerability to and development of brain injury. Preterm birth, on the other hand, is often a result of exposure to inflammation at a very early developmental phase, which affects the brain not only during fetal life, but also over a protracted period of postnatal life in a neonatal intensive care setting, influencing critical phases of myelination and cortical plasticity. Neuroinflammation during the perinatal period can increase the risk of neurological and neuropsychiatric disease throughout childhood and adulthood, and is, therefore, of concern to the broader group of physicians who care for these individuals.

p53 signalling mediates acupuncture-induced neuroprotection in Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder associated with a selective loss of dopamine (DA) neurons in the substantia nigra of the midbrain. Recently, it has been demonstrated that acupuncture treatment has protective effects in PD. However, to date, the molecular mechanisms underlying acupuncture's effect on DA neuronal protection are largely unknown. In this study, we report that p53 signalling mediates the protective effects of acupuncture treatment in a mouse model of PD. We found that the acupuncture treatment in the mouse PD model results in significant recovery to the normal in the context of behaviour and molecular signatures. We found that the gene network associated with p53 signalling is closely involved in the protective effects of acupuncture treatment in PD. Consistent with this idea, we demonstrated that specific knockout of the p53 gene in the midbrain DA neurons abrogates the acupuncture induced protective effects in the mouse model of PD. Thus, these data suggest that p53 signalling mediates the protective effects of acupuncture treatment in PD.

Forebrain neuronal specific ablation of p53 gene provides protection in a cortical ischemic stroke model

Cerebral ischemic injury involves death of multiple cell types at the ischemic sites. As a key regulator of cell death, the p53 gene has been implicated in the regulation of cell loss in stroke. Less focal damage is found in stroke animals pre-treated with a p53 inhibitor or in traditional p53 knockout (ko) mice. However, whether the p53 gene plays a direct role in regulating neuronal cell death is unknown. In this study, in contrast to the global inhibition of p53 function by pharmacological inhibitors and in traditional p53 ko mice, we utilized a neuronal specific conditional ko mouse line (CamcreTRP53(loxP/loxP)) to achieve forebrain neuronal specific deletion of p53 and examined the role of the p53 gene in ischemia-induced cell death in neurons. Expression of p53 after stroke is examined using the immunohistochemical method and the outcome of stroke is examined by analysis of infarction size and behavioral deficits caused by stroke. Our data showed that p53 expression is upregulated in the ischemic region in neuronal cells in wildtype (wt) mice but not in CamcreTRP53(loxP/loxP) ko mice. Deletion of the p53 gene in forebrain neurons results in a decreased infarction area in ko mice. Locomotor behavior, measured in automated activity chambers, showed that CamcreTRP53(loxP/loxP) ko mice have less locomotor deficits compared to wt mice after middle cerebral artery occlusion (MCAo). We conclude that manipulation of p53 expression in neurons may lead to unique therapeutic development in stroke.

Role of mitochondria in apoptotic and necroptotic cell death in the developing brain

Hypoxic–ischemic encephalopathy induces secondary brain injury characterized by delayed energy failure. Currently, therapeutic hypothermia is the sole treatment available after severe intrapartum asphyxia in babies and acts to attenuate secondary loss of high energy phosphates improving both short- and long-term outcome. In order to develop the next generation of neuroprotective therapies, we urgently need to understand the underlying molecular mechanisms leading to cell death. Hypoxia–ischemia creates a toxic intracellular environment including accumulation of reactive oxygen/nitrosative species and intracellular calcium after the insult, inducing mitochondrial impairment. More specifically mitochondrial respiration is suppressed and calcium signaling is dysregulated. At a certain threshold, Bax-dependent mitochondrial permeabilization will occur leading to activation of caspase-dependent and apoptosis-inducing factor-dependent apoptotic cell death. In addition, hypoxia–ischemia induces inflammation, which leads to the release of TNF-α, TRAIL, TWEAK, FasL and Toll-like receptor agonists that will activate death receptors on neurons and oligodendroglia. Death receptors trigger apoptotic death via caspase-8 and necroptotic cell death through formation of the necrosome (composed of RIP1, RIP3 and MLKL), both of which converge at the mitochondria.

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Hypoxic-ischemic encephalopathy induces secondary brain injury characterized by delayed energy failure and excitotoxicity.

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Hypoxia-ischemia triggers accumulation of reactive oxygen species andintracellular calcium, which induces mitochondrial dysfunction.

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Mitochondrial impairment can cause Bax-dependent mitochondrial permeabilization, which triggers release of pro-apoptotic proteins and cell death.

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During the recovery phase, Inflammation is produced leading to death receptor activation and induction of necroptosis.

Intrauterine ischemic reperfusion switches the fetal transcriptional pattern from HIF-1α- to P53-dependent regulation in the murine brain

Ischemic reperfusion (IR) during the perinatal period is a known causative factor of fetal brain damage. So far, both morphologic and histologic evidence has shown that fetal brain damage can be observed only several hours to days after an IR insult has occurred. Therefore, to prevent fetal brain damage under these circumstances, a more detailed understanding of the underlying molecular mechanisms involved during an acute response to IR is necessary. In the present work, pregnant mice were exposed to IR on day 18 of gestation by clipping one side of the maternal uterine horn. Simultaneous fetal electrocardiography was performed during the procedure to verify that conditions resulting in fetal brain damage were met. Fetal brain sampling within 30 minutes after IR insult revealed molecular evidence that a fetal response was indeed triggered in the form of inhibition of the Akt-mTOR-S6 synthesis pathway. Interestingly, significant changes in mRNA levels for both HIF-1α and p53 were apparent and gene regulation patterns were observed to switch from a HIF-1α-dependent to a p53-dependent process. Moreover, pre-treatment with pifithrin-α, a p53 inhibitor, inhibited protein synthesis almost completely, revealing the possibility of preventing fetal brain damage by prophylactic pifithrin-α treatment.

Anti-inflammatory and antiapoptotic effects of mesenchymal stem cells transplantation in rat brain with cerebral ischemia

BACKGROUND

Excessive inflammation and apoptosis contribute to the pathogenesis of ischemic brain damage. Nuclear factor-kappa B (NF-κB) is considered to be a key protein complex involved in this cascade of events. The aim of the present study was to clarify the protection mechanism of the mesenchymal stem cells (MSCs).

METHODS

Lewis rats (N = 90) were randomly assigned to three groups: (1) the sham-operated group; (2) the saline group, in which the animals underwent rat transient middle cerebral artery occlusion (tMCAO, for 2 hours) and were treated with saline through the tail vein; and (3) the MSCs group, in which the animals underwent tMCAO (for 2 hours) and were infused with cultured human MSCs (4 × 10(6)/0.4 ml PBS) through the tail vein. At days 1 and 3 post-MSCs infusion, real-time PCR, and Western blot, immunohistochemical analyses were applied for tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β) and P-IKKβ, p53, and B-cell lymphoma 2 (Bcl-2) expression levels.

RESULTS

TNF-α, IL-1β messenger RNA (mRNA) and P-IκB-α, P-IKKβ, p53 protein expression levels were significantly increased in the saline group compared with the sham group. However, IκB-α and Bcl-2 protein expression levels were markedly decreased in the saline group. After injection of BrdU(+) MSCs, the expression levels of TNF-α, IL-1β mRNA and P-IκB-α, P-IKKβ, p53 protein were significantly decreased. Contrary to these findings, IκB-α, Bcl-2 protein expression levels were markedly increased. In addition, we found that infarct area was significantly reduced in MSCs group.

CONCLUSIONS

These results suggest that MSCs' neuroprotection is attributable to its anti-inflammatory and antiapoptotic effect through inhibition of NF-κB.

Inhibition of mitochondrial p53 abolishes the detrimental effects of social isolation on ischemic brain injury

BACKGROUND AND PURPOSE

Social isolation (SI) increases stroke incidence and delays poststroke recovery. Women may be at greater risk from the negative consequences of SI, but few studies have examined both sexes in experimental models, and none have evaluated the effects of isolation initiated after stroke. The effects of poststroke SI in men and women were examined, and the role of mitochondrial P53 was evaluated.

METHODS

C57Bl6 mice were pair-housed (PH; male and ovariectomized female) for 2 weeks, subjected to stroke and then assigned to a housing condition (isolated or PH). The effects of housing on infarct volume and recovery were examined. Changes in Bcl-2 and mitochondrial p53 were assessed by Western blot. A mitochondrial p53 inhibitor (pifithrin-μ) was given to mice of both sexes.

RESULTS

Compared with pair-housed mice, poststroke SI significantly increased infarct size in both sexes; SI mice also had worse neurological deficits. The detrimental effects of SI paralleled increases in mitochondrial p53 levels. Pharmacological inhibition of mitochondrial p53 using pifithrin-μ abolished the detrimental effects of SI and reduced cell death.

CONCLUSIONS

Poststroke SI results in increased ischemic injury in both sexes. The effect of housing on infarct was more pronounced in women. Targeting the mitochondrial P53 pathway could minimize the detrimental effects of isolation after stroke.

Drp1 stabilizes p53 on the mitochondria to trigger necrosis under oxidative stress conditions in vitro and in vivo

Oxidative-stress-induced necrosis is considered to be one of the main pathological mediators in various neurological disorders, such as brain ischaemia. However, little is known about the mechanism by which cells modulate necrosis in response to oxidative stress. In the present study, we showed that Drp1 (dynamin-related protein 1), a primary mitochondrial fission protein, stabilizes the well-known stress gene p53 and is required for p53 translocation to the mitochondria under conditions of oxidative stress. We found that Drp1 binding to p53 induced mitochondria-related necrosis. In contrast, inhibition of Drp1 hyperactivation by Drp1 siRNA reduced necrotic cell death in cell cultures exposed to oxidative stress. Most significantly, we demonstrated that inhibition of Drp1 by the Drp1 peptide inhibitor P110, which was developed recently by our group, abolished p53 association with the mitochondria and reduced brain infarction in rats subjected to brain ischaemia/reperfusion injury. Taken together, these findings reveal a novel mechanism of Drp1 hyperactivation in the induction of mitochondrial damage and subsequent cell death. We propose that a Drp1 inhibitor such as P110 is a possible therapeutic agent for diseases in which hyperactivated Drp1 contributes to the pathology.

Inhibition of cytoplasmic p53 differentially modulates Ca(2+) signaling and cellular viability in young and aged striata

The p53 protein, a transcription factor with many gene targets, can also trigger apoptosis in the cytoplasm. The disruption of cell homeostasis, such as Ca(2+) signaling and mitochondrial respiration, contributes to the loss of viability and ultimately leads to cell death. However, the link between Ca(2+) signaling and p53 signaling remains unclear. During aging, there are alterations in cell physiology that are commonly associated with a reduced adaptive stress response, thus increasing cell vulnerability. In this work, we examined the effects of a cytoplasmic p53 inhibitor (pifithrin μ) in the striatum of young and aged rats by evaluating Ca(2+) signaling, mitochondrial respiration, apoptotic protein expression, and tissue viability. Our results showed that pifithrin μ differentially modulated cytoplasmic and mitochondrial Ca(2+) in young and aged rats. Cytoplasmic p53 inhibition appeared to reduce the mitochondrial respiration rate in both groups. In addition, p53 phosphorylation and Bax protein levels were elevated upon cytoplasmic p53 inhibition and could contribute to the reduction of tissue viability. Following glutamate challenge, pifithrin μ improved cell viability in aged tissue, reduced reactive oxygen species (ROS) generation, and reduced mitochondrial membrane potential (ΔΨm). Taken together, these results indicate that cytoplasmic p53 may have a special role in cell viability by influencing cellular Ca(2+) homeostasis and respiration and may produce differential effects in the striatum of young and aged rats.

Piracetam ameliorated oxygen and glucose deprivation-induced injury in rat cortical neurons via inhibition of oxidative stress, excitatory amino acids release and P53/Bax

Our previous work has demonstrated that piracetam inhibited the decrease in amino acid content induced by chronic hypoperfusion, ameliorated the dysfunction of learning and memory in a hypoperfusion rat model, down-regulated P53, and BAX protein, facilitated the synaptic plasticity, and may be helpful in the treatment of vascular dementia. To explore the precise mechanism, the present study further evaluated effects of piracetam on Oxygen and glucose deprivation (OGD)-induced neuronal damage in rat primary cortical cells. The addition of piracetam to the cultured cells 12 h before OGD for 4 h significantly reduced neuronal damage as determined by MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and lactate dehydrogenase release experiments. Piracetam also lowered the levels of malondialdehyde, nitrogen monoxidum, and xanthine oxidase which was increased in the OGD cells, and enhanced the activities of superoxide dismutase and glutathione peroxidase, which were decreased in the OGD cells. We also demonstrated that piracetam could decrease glutamate and aspartate release when cortical cells were subjected to OGD. Furthermore, Western blot study demonstrated that piracetam attenuated the increased expression of P53 and BAX protein in OGD cells. These observations demonstrated that piracetam reduced OGD-induced neuronal damage by inhibiting the oxidative stress and decreasing excitatory amino acids release and lowering P53/Bax protein expression in OGD cells.

Mitochondrial death functions of p53

The p53 tumor suppressor network plays a fundamental surveillance role in both homeostatic and adaptive cell biology. p53 is one of the most important barriers against malignant derailment of normal cells, orchestrating growth arrest, senescence, or cell death by linking many different pathways in response to genotoxic and non-genotoxic insults. p53 is the key broadband sensor for numerous cellular stresses such as DNA damage, hypoxia, oxidative stress, oncogenic signaling, and nucleolar stress. The crucial tumor suppressive and tissue homeostasis activity of p53 is its ability to activate cell death via multiple different pathways. A well-characterized biochemical function of p53 in the regulation of apoptosis is its role as a potent transcriptional regulator. p53 activates a panel of proapoptotic genes from the mitochondrial apoptotic and death receptor programs while repressing antiapoptotic Bcl2 family genes. In addition, over the last 10 y a growing body of evidence has also defined direct extranuclear non-transcriptional p53 activities within mitochondria-mediated cell death pathways that are based on p53 protein accumulation in cytosolic and mitochondrial compartments and protein-protein interactions. To date, transcription-independent p53-mediated cell death regulation has been described for apoptosis, necrosis, and autophagy. Because mitochondrial dysregulation is central to the development of a number of pathologic processes such as cancer and neurodegenerative and age-related diseases, understanding the direct roles of p53 protein in mitochondria has high translational impact and could facilitate the development of novel drug targets to combat these diseases. In this review we will mainly focus on mechanisms of p53-mediated transcription-independent cell death pathways at mitochondria.

Mitochondria: hub of injury responses in the developing brain

Progress in the field of mitochondrial biology in the past few years has shown that mitochondrial activities go beyond bioenergetics. These new aspects of mitochondrial physiology and pathophysiology have important implications for the immature brain. A picture emerges in which mitochondrial biogenesis, mitophagy, migration, and morphogenesis are crucial for brain development and synaptic pruning, and play a part in recovery after acute insults. Mitochondria also affect brain susceptibility to injury, and mitochondria-directed interventions can make the immature brain highly resistant to acute injury. Finally, the mitochondrion is a platform for innate immunity, contributes to inflammation in response to infection and acute damage, and participates in antiviral and antibacterial defence. Understanding of these new aspects of mitochondrial function will provide insights into brain development and neurological disease, and enable discovery and development of new strategies for treatment.

The mechanisms and treatment of asphyxial encephalopathy

Acute post-asphyxial encephalopathy occurring around the time of birth remains a major cause of death and disability. The recent seminal insight that allows active neuroprotective treatment is that even after profound asphyxia (the “primary” phase), many brain cells show initial recovery from the insult during a short “latent” phase, typically lasting approximately 6 h, only to die hours to days later after a “secondary” deterioration characterized by seizures, cytotoxic edema, and progressive failure of cerebral oxidative metabolism. Although many of these secondary processes are potentially injurious, they appear to be primarily epiphenomena of the “execution” phase of cell death. Animal and human studies designed around this conceptual framework have shown that moderate cerebral hypothermia initiated as early as possible but before the onset of secondary deterioration, and continued for a sufficient duration to allow the secondary deterioration to resolve, has been associated with potent, long-lasting neuroprotection. Recent clinical trials show that while therapeutic hypothermia significantly reduces morbidity and mortality, many babies still die or survive with disabilities. The challenge for the future is to find ways of improving the effectiveness of treatment. In this review, we will dissect the known mechanisms of hypoxic-ischemic brain injury in relation to the known effects of hypothermic neuroprotection.

p53 and mitochondrial function in neurons

The p53 tumor suppressor plays a central role in dictating cell survival and death as a cellular sensor for a myriad of stresses including DNA damage, oxidative and nutritional stress, ischemia and disruption of nucleolar function. Activation of p53-dependent apoptosis leads to mitochondrial apoptotic changes via the intrinsic and extrinsic pathways triggering cell death execution most notably by release of cytochrome c and activation of the caspase cascade. Although it was previously believed that p53 induces apoptotic mitochondrial changes exclusively through transcription-dependent mechanisms, recent studies suggest that p53 also regulates apoptosis via a transcription-independent action at the mitochondria. Recent evidence further suggests that p53 can regulate necrotic cell death and autophagic activity including mitophagy. An increasing number of cytosolic and mitochondrial proteins involved in mitochondrial metabolism and respiration are regulated by p53, which influences mitochondrial ROS production as well. Cellular redox homeostasis is also directly regulated by p53 through modified expression of pro- and anti-oxidant proteins. Proper regulation of mitochondrial size and shape through fission and fusion assures optimal mitochondrial bioenergetic function while enabling adequate mitochondrial transport to accommodate local energy demands unique to neuronal architecture. Abnormal regulation of mitochondrial dynamics has been increasingly implicated in neurodegeneration, where elevated levels of p53 may have a direct contribution as the expression of some fission/fusion proteins are directly regulated by p53. Thus, p53 may have a much wider influence on mitochondrial integrity and function than one would expect from its well-established ability to transcriptionally induce mitochondrial apoptosis. However, much of the evidence demonstrating that p53 can influence mitochondria through nuclear, cytosolic or intra-mitochondrial sites of action has yet to be confirmed in neurons. Nonetheless, as mitochondria are essential for supporting normal neuronal functions and in initiating/propagating cell death signaling, it appears certain that the mitochondria-related functions of p53 will have broader implications than previously thought in acute and progressive neurological conditions, providing new therapeutic targets for treatment.

The rodent endovascular puncture model of subarachnoid hemorrhage: mechanisms of brain damage and therapeutic strategies

Subarachnoid hemorrhage (SAH) represents a considerable health problem. To date, limited therapeutic options are available. In order to develop effective therapeutic strategies for SAH, the mechanisms involved in SAH brain damage should be fully explored. Here we review the mechanisms of SAH brain damage induced by the experimental endovascular puncture model. We have included a description of similarities and distinctions between experimental SAH in animals and human SAH pathology. Moreover, several novel treatment options to diminish SAH brain damage are discussed.SAH is accompanied by cerebral inflammation as demonstrated by an influx of inflammatory cells into the cerebral parenchyma, upregulation of inflammatory transcriptional pathways and increased expression of cytokines and chemokines. Additionally, various cell death pathways including cerebral apoptosis, necrosis, necroptosis and autophagy are involved in neuronal damage caused by SAH.Treatment strategies aiming at inhibition of inflammatory or cell death pathways demonstrate the importance of these mechanisms for survival after experimental SAH. Moreover, neuroregenerative therapies using stem cells are discussed as a possible strategy to repair the brain after SAH since this therapy may extend the window of treatment considerably. We propose the endovascular puncture model as a suitable animal model which resembles the human pathology of SAH and which could be applied to investigate novel therapeutic therapies to combat this debilitating insult.

The endogenous regenerative capacity of the damaged newborn brain: boosting neurogenesis with mesenchymal stem cell treatment

Neurogenesis continues throughout adulthood. The neurogenic capacity of the brain increases after injury by, e.g., hypoxia-ischemia. However, it is well known that in many cases brain damage does not resolve spontaneously, indicating that the endogenous regenerative capacity of the brain is insufficient. Neonatal encephalopathy leads to high mortality rates and long-term neurologic deficits in babies worldwide. Therefore, there is an urgent need to develop more efficient therapeutic strategies. The latest findings indicate that stem cells represent a novel therapeutic possibility to improve outcome in models of neonatal encephalopathy. Transplanted stem cells secrete factors that stimulate and maintain neurogenesis, thereby increasing cell proliferation, neuronal differentiation, and functional integration. Understanding the molecular and cellular mechanisms underlying neurogenesis after an insult is crucial for developing tools to enhance the neurogenic capacity of the brain. The aim of this review is to discuss the endogenous capacity of the neonatal brain to regenerate after a cerebral ischemic insult. We present an overview of the molecular and cellular mechanisms underlying endogenous regenerative processes during development as well as after a cerebral ischemic insult. Furthermore, we will consider the potential to use stem cell transplantation as a means to boost endogenous neurogenesis and restore brain function.

Multiple interacting cell death mechanisms in the mediation of excitotoxicity and ischemic brain damage: a challenge for neuroprotection

There is currently no approved neuroprotective pharmacotherapy for acute conditions such as stroke and cerebral asphyxia. One of the reasons for this may be the multiplicity of cell death mechanisms, because inhibition of a particular mechanism leaves the brain vulnerable to alternative ones. It is therefore essential to understand the different cell death mechanisms and their interactions. We here review the multiple signaling pathways underlying each of the three main morphological types of cell death--apoptosis, autophagic cell death and necrosis--emphasizing their importance in the neuronal death that occurs during cerebral ischemia and hypoxia-ischemia, and we analyze the interactions between the different mechanisms. Finally, we discuss the implications of the multiplicity of cell death mechanisms for the design of neuroprotective strategies.

Oxidative stress, DNA damage, and the telomeric complex as therapeutic targets in acute neurodegeneration

Oxidative stress has been identified as an important contributor to neurodegeneration associated with acute CNS injuries and diseases such as spinal cord injury (SCI), traumatic brain injury (TBI), and ischemic stroke. In this review, we briefly detail the damaging effects of oxidative stress (lipid peroxidation, protein oxidation, etc.) with a particular emphasis on DNA damage. Evidence for DNA damage in acute CNS injuries is presented along with its downstream effects on neuronal viability. In particular, unchecked oxidative DNA damage initiates a series of signaling events (e.g. activation of p53 and PARP-1, cell cycle re-activation) which have been shown to promote neuronal loss following CNS injury. These findings suggest that preventing DNA damage might be an effective way to promote neuronal survival and enhance neurological recovery in these conditions. Finally, we identify the telomere and telomere-associated proteins (e.g. telomerase) as novel therapeutic targets in the treatment of neurodegeneration due to their ability to modulate the neuronal response to both oxidative stress and DNA damage.

Mitochondrial JNK phosphorylation as a novel therapeutic target to inhibit neuroinflammation and apoptosis after neonatal ischemic brain damage

Neonatal encephalopathy is associated with high mortality and life-long developmental consequences. Therapeutic options are very limited. We assessed the effects of D-JNKi, a small peptide c-Jun N-terminal kinase (JNK) MAP kinase inhibitor, on neuroinflammation, mitochondrial integrity and neuronal damage in a neonatal rat model of ischemic brain damage. Hypoxic-ischemic (HI) brain injury was induced in postnatal-day 7 rats by unilateral carotid artery occlusion and hypoxia, and was followed by intraperitoneal D-JNKi treatment. We demonstrate here for the first time that a single intraperitoneal injection with D-JNKi directly after HI strongly reduces neonatal brain damage by >85% with a therapeutic window of at least 6h. D-JNKi treatment also restored cognitive and motor function as analyzed at 9weeks post-insult. Neuroprotective D-JNKi treatment inhibited phosphorylation of nuclear c-Jun (P-c-Jun), and consequently reduced activity of the AP-1 transcription factor and production of cerebral cytokines/chemokines as determined at 3 and 24h post-HI. Inhibition of P-c-Jun by D-JNKi is thought to be mediated via inhibition of the upstream phosphorylation of cytosolic and nuclear JNK and/or by preventing the direct interaction of phosphorylated (P-)JNK with c-Jun. Surprisingly, however, HI did not induce a detectable increase in P-JNK in cytosol or nucleus. Notably, we show here for the first time that HI induces P-JNK only in the mitochondrial fraction, which was completely prevented by D-JNKi treatment. The hypothesis that mitochondrial JNK activation is key to HI brain injury was supported by data showing that treatment of rat pups with SabKIM1 peptide, a specific mitochondrial JNK inhibitor, is also neuroprotective. Inhibition of HI-induced mitochondrial JNK activation was associated with preservation of mitochondrial integrity as evidenced by prevention of ATP loss and inhibition of lipid peroxidation. The HI-induced increase in apoptotic markers (cytochrome c release and caspase 3 activation) as analyzed at 24h post-HI were also strongly reduced by D-JNKi and the mitochondrial anti-apoptotic proteins Bcl-2 and Bcl-xL were upregulated. Neuroprotection was lost after repeated 0+3h D-JNKi treatment which was associated with complete inhibition of the second peak of AP-1 activity and disability to upregulate mitochondrial Bcl-2 and Bcl-xL. We show here for the first time that D-JNKi treatment efficiently protects the neonatal brain against ischemic brain damage and subsequent cognitive and motor impairment. We propose that inhibition of phosphorylation of mitochondrial JNK is a pivotal step in preventing early loss of mitochondrial integrity leading to reduced neuroinflammation and inhibition of apoptotic neuronal loss. Moreover we show the crucial role of upregulation of mitochondrial anti-apoptotic proteins to maintain neuroprotection.

Pifithrin-μ increases mitochondrial COX biogenesis and MnSOD activity in skeletal muscle of middle-aged mice

We investigated the biogenesis and mitochondrial antioxidant capacity of cytochrome c oxidase (COX) within the skeletal muscle under the treatments of p53 inhibitors (pifithrin, PFTα and PFTμ). Significantly, PFTμ increased mtDNA content and COX biogenesis. These changes coincided with increases in the activity and expression of manganese superoxide dismutase (MnSOD), the key antioxidant enzyme in mitochondria. Conversely, PFTα caused muscle loss, increased oxidative damage and decreased MnSOD activity in intermyofibrillar (IMF) mitochondria. Mechanically, PFTμ inhibited p53 translocation to mitochondria and thus increased its transcriptional activity for expression of synthesis of cytochrome c oxidase 2 (SCO2), an important assembly protein for COX. This study provides in vivo evidence that PFTμ, superior to PFTα, preserves muscle mass and increases mitochondrial antioxidant activity.

Effects of oxygen-glucose deprivation on microglial mobility and viability in developing mouse hippocampal tissues

As brain-resident immune cells, microglia (MG) survey the brain parenchyma to maintain homeostasis during development and following injury. Research in perinatal stroke, a leading cause of lifelong disability, has implicated MG as targets for therapeutic intervention during stroke. Although MG responses are complex, work in developing rodents suggests that MG limit brain damage after stroke. However, little is known about how energy-limiting conditions affect MG survival and mobility (motility and migration) in developing brain tissues. Here, we used confocal time-lapse imaging to monitor MG viability and mobility during hypoxia or oxygen-glucose deprivation (OGD) in hippocampal tissue slices derived from neonatal GFP-reporter mice (CX3CR1(GFP/+) ). We found that MG remain viable for at least 6 h of hypoxia but begin to die after 2 h of OGD, while both hypoxia and OGD reduce MG motility. Unexpectedly, some MG retain or recover motility during OGD and can engulf dead cells. Additionally, MG from younger neonates (P2-P3) are more resistant to OGD than those from older ones (P6-P7), indicating increasing vulnerability with developmental age. Finally, transient (2 h) OGD also increases MG death, and although motility is rapidly restored after transient OGD, it remains below control levels for many hours. Together, these results show that MG in neonatal mouse brain tissues are vulnerable to both transient and sustained OGD, and many MG die within hours after onset of OGD. Preventing MG death may, therefore, provide a strategy for promoting tissue restoration after stroke.

Programmed Necrosis: A Prominent Mechanism of Cell Death following Neonatal Brain Injury

Despite the introduction of therapeutic hypothermia, neonatal hypoxic ischemic (HI) brain injury remains a common cause of developmental disability. Development of rational adjuvant therapies to hypothermia requires understanding of the pathways of cell death and survival modulated by HI. The conceptualization of the apoptosis-necrosis “continuum” in neonatal brain injury predicts mechanistic interactions between cell death and hydrid forms of cell death such as programmed or regulated necrosis. Many of the components of the signaling pathway regulating programmed necrosis have been studied previously in models of neonatal HI. In some of these investigations, they participate as part of the apoptotic pathways demonstrating clear overlap of programmed death pathways. Receptor interacting protein (RIP)-1 is at the crossroads between types of cellular death and survival and RIP-1 kinase activity triggers formation of the necrosome (in complex with RIP-3) leading to programmed necrosis. Neuroprotection afforded by the blockade of RIP-1 kinase following neonatal HI suggests a role for programmed necrosis in the HI injury to the developing brain. Here, we briefly review the state of the knowledge about the mechanisms behind programmed necrosis in neonatal brain injury recognizing that a significant proportion of these data derive from experiments in cultured cell and some from in vivo adult animal models. There are still more questions than answers, yet the fascinating new perspectives provided by the understanding of programmed necrosis in the developing brain may lay the foundation for new therapies for neonatal HI.

Mitochondria and perinatal brain injury

Secondary brain injury after hypoxia-ischemia is associated with delayed loss of high energy phosphates implicating bioenergetic mitochondrial failure at least partly related to deregulation of the energy sensor adenosine monophosphate-activated protein kinase. Furthermore, the toxic intracellular environment (accumulation of reactive oxygen/nitrosative species and intracellular calcium) during post-ischemic reperfusion triggers Bax-dependent mitochondrial permeabilization (MP) leading to activation of caspase-dependent and apoptosis-inducing factor dependent cell death. We still do not understand how MP is induced but some data suggest that mitochondrial fusion/fission as well as migration play a critical role. Mitochondrial dynamics also seem critical for brain development as genetic deficiency of proteins involved in mitochondrial fusion and fission results in malformations including microcephaly, abnormal brain development and dysmyelination. In this brief review, we update the critical role of mitochondria in brain development and the decision of cell fate after hypoxia-ischemia in the immature CNS.

Molecular mechanisms of neonatal brain injury

Fetal/neonatal brain injury is an important cause of neurological disability. Hypoxia-ischemia and excitotoxicity are considered important insults, and, in spite of their acute nature, brain injury develops over a protracted time period during the primary, secondary, and tertiary phases. The concept that most of the injury develops with a delay after the insult makes it possible to provide effective neuroprotective treatment after the insult. Indeed, hypothermia applied within 6 hours after birth in neonatal encephalopathy reduces neurological disability in clinical trials. In order to develop the next generation of treatment, we need to know more about the pathophysiological mechanism during the secondary and tertiary phases of injury. We review some of the critical molecular events related to mitochondrial dysfunction and apoptosis during the secondary phase and report some recent evidence that intervention may be feasible also days-weeks after the insult.

Prevention of neonatal oxygen-induced brain damage by reduction of intrinsic apoptosis

Within the last decade, it became clear that oxygen contributes to the pathogenesis of neonatal brain damage, leading to neurocognitive impairment of prematurely born infants in later life. Recently, we have identified a critical role for receptor-mediated neuronal apoptosis in the immature rodent brain. However, the contribution of the intrinsic apoptotic pathway accompanied by activation of caspase-2 under hyperoxic conditions in the neonatal brain still remains elusive. Inhibition of caspases appears a promising strategy for neuroprotection. In order to assess the influence of specific caspases on the developing brain, we applied a recently developed pentapeptide-based group II caspase inhibitor (5-(2,6-difluoro-phenoxy)-3(R,S)-(2(S)-(2(S)-(3-methoxycarbonyl-2(S)-(3-methyl-2(S)-((quinoline-2-carbonyl)-amino)-butyrylamino)propionylamino)3-methylbutyrylamino)propionylamino)-4-oxo-pentanoic acid methyl ester; TRP601). Here, we report that elevated oxygen (hyperoxia) triggers a marked increase in active caspase-2 expression, resulting in an initiation of the intrinsic apoptotic pathway with upregulation of key proteins, namely, cytochrome c, apoptosis protease-activating factor-1, and the caspase-independent protein apoptosis-inducing factor, whereas BH3-interacting domain death agonist and the anti-apoptotic protein B-cell lymphoma-2 are downregulated. These results coincide with an upregulation of caspase-3 activity and marked neurodegeneration. However, single treatment with TRP601 at the beginning of hyperoxia reversed the detrimental effects in this model. Hyperoxia-mediated neurodegeneration is supported by intrinsic apoptosis, suggesting that the development of highly selective caspase inhibitors will represent a potential useful therapeutic strategy in prematurely born infants.

Moderate dietary restriction reduces p53-mediated neurovascular damage and microglia activation after hypoxic ischemia in neonatal brain

BACKGROUND AND PURPOSE

Neurovascular damage, including neuronal apoptosis and blood-brain barrier (BBB) damage, and microglia activation account for the hypoxic-ischemia (HI) susceptibility in neonatal brain. The p53 upregulation is involved in apoptosis, endothelial cell damage, and microglia activation. We hypothesized that underweight induced by dietary restriction (DR) protects against HI in rat pups by attenuating p53-mediated neurovascular damage.

METHODS

Male rat pups were grouped as normal litter (NL) size (12 pups/dam), DR (18 pups/dam), and extreme DR (24 pups/dam) from postnatal day 1 and subjected to HI on postnatal day 7. Immunohistochemistry and immunoblotting were used to determine p53, phospho-murine double minute-2, caspases, BBB damage and microglia activation, and immunofluorescence to determine the cellular distribution of p53. Pharmacological approaches were used to regulate p53.

RESULTS

The NL, DR, and extreme DR pups had similar TUNEL-positive cells and caspases on postnatal day 7 and comparable learning performance at adulthood. After HI, the DR-HI, but not extreme DR-HI, pups had significantly lower p53, higher phospho-murine double minute-2, lower cleaved caspases, less BBB damage and microglia activation, and less brain volume loss than NL-HI pups. In NL-HI pups, p53 expression was located mainly in the neurons, endothelial cells, and microglia. The p53 blockage by pifithrin-α in NL-HI pups decreased apoptosis, BBB damage, and microglia activation, and was neuroprotective. In contrast, upregulating p53 by nutlin-3 in DR-HI pups increased apoptosis, BBB damage, and microglia activation, and worsened brain damage.

CONCLUSIONS

Moderate DR, but not extreme DR, reduces p53-mediated neurovascular damage after HI and confers long-term protection in neonatal brain.