Caspase-3-Dependent and -Independent Apoptosis in Focal Brain Ischemia

A meta-analysis of animal studies evaluating the effect of hydrogen sulfide on ischemic stroke: is the preclinical evidence sufficient to move forward?

Hydrogen sulfide (H2S) is a gasotransmitter that has been studied for its potential therapeutic effects, including its role in the pathophysiology and treatment of stroke. This systematic review and meta-analysis aimed to determine the sufficiency of overall preclinical evidence to guide the initiation of clinical stroke trials with H2S and provide tailored recommendations for their design. PubMed, Web of Science, Scopus, EMBASE, and MEDLINE were searched for studies evaluating the effect of any H2S donor on in vivo animal models of regional ischemic stroke, and 34 publications were identified. Pooling of the effect sizes using the random-effect model revealed that H2S decreased the infarct area by 34.5% (95% confidence interval (CI) 28.2-40.8%, p < 0.0001), with substantial variability among the studies (I2 = 89.8%). H2S also caused a 37.9% reduction in the neurological deficit score (95% CI 29.0-46.8%, p < 0.0001, I2 = 63.8%) and in the brain water content (3.2%, 95% CI 1.4-4.9%, p = 0.0014, I2 = 94.6%). Overall, the studies had a high risk of bias and low quality of evidence (median quality score 5/15, interquartile range 4-9). The majority of the included studies had a "high" or "unclear" risk of bias, and none of the studies overall had a "low" risk. In conclusion, H2S significantly improves structural and functional outcomes in in vivo animal models of ischemic stroke. However, the level of evidence from preclinical studies is not sufficient to proceed to clinical trials due to the low external validity, high risk of bias, and variable design of existing animal studies.

TUNEL-n-DIFL Method for Detection and Estimation of Apoptosis Specifically in Neurons and Glial Cells in Mixed Culture and Animal Models of Central Nervous System Diseases and Injuries

Detection of merely apoptosis does not reveal the type of central nervous system (CNS) cells that are dying in the CNS diseases and injuries. In situ detection and estimation of amount of apoptosis specifically in neurons or glial cells (astrocytes, oligodendrocytes, and microglia) can unveil valuable information for designing therapeutics for protection of the CNS cells and functional recovery. A method was first developed and reported from our laboratory for in situ detection and estimation of amount of apoptosis precisely in neurons and glial cells using in vitro and in vivo models of CNS diseases and injuries. This is a combination of terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) and double immunofluorescent labeling (DIFL) or simply TUNEL-n-DIFL method for in situ detection and estimation of amount of apoptosis in a specific CNS cell type. An anti-digoxigenin (DIG) IgG antibody conjugated with 7-amino-4-methylcoumarin-3-acetic acid (AMCA) for blue fluorescence, fluorescein isothiocyanate (FITC) for green fluorescence, or Texas Red (TR) for red fluorescence can be used for in situ detection of apoptotic cell DNA, which is earlier labeled with TUNEL using alkali-stable DIG-11-dUTP. A primary anti-NeuN (neurons), anti-GFAP (astrocytes), anti-MBP (oligodendrocytes), or anti-OX-42 (microglia) IgG antibody and a secondary IgG antibody conjugated with one of the above fluorophores (other than that of ani-DIG antibody) are used for in situ detection of apoptosis in a specific CNS cell type in the mixed culture and animal models of the CNS diseases and injuries.

The role of the DFF40/CAD endonuclease in genomic stability

Maintenance of genomic stability in cells is primordial for cellular integrity and protection against tumor progression. Many factors such as ultraviolet light, oxidative stress, exposure to chemical reagents, particularly mutagens and radiation, can alter the integrity of the genome. Thus, human cells are equipped with many mechanisms that prevent these irreversible lesions in the genome, as DNA repair pathways, cell cycle checkpoints, and telomeric function. These mechanisms activate cellular apoptosis to maintain DNA stability. Emerging studies have proposed a new protein in the maintenance of genomic stability: the DNA fragmentation factor (DFF). The DFF40 is an endonuclease responsible of the oligonucleosomal fragmentation of the DNA during apoptosis. The lack of DFF in renal carcinoma cells induces apoptosis without oligonucleosomal fragmentation, which poses a threat to genetic information transfer between cancerous and healthy cells. In this review, we expose the link between the DFF and genomic instability as the source of disease development.

TRPM2 ion channel is involved in the aggravation of cognitive impairment and down regulation of epilepsy threshold in pentylenetetrazole-induced kindling mice

Epilepsy is one of the most common neurological conditions. Recent findings suggest that one of the mechanisms promoting its existence is calcium influx. The transient receptor potential melastatin type 2 channel (TRPM2) is a Ca²⁺-permeable cation channel that contributes to cell apoptosis; its possible signaling pathway is the PARP1/BNIP3/AIF/Endo G pathway that may be related to epilepsy. The aim of this study was to investigate the TRPM2 channel's involvement in epilepsy and how it works. We also explored the possible role of the TRPM2 channel on cognitive ability and emotion in epilepsy. To accomplish our goals, we used different animal epilepsy models to study the effect of the TRPM2 channel on epilepsy. The results showed that the knockout (KO) of the TRPM2 gene might play a protective role in epilepsy. Considering the advantages attributed to pentylenetetrazole (PTZ)-induced kindling mouse model, we used the model for the following assessments: 1. to observe changes in cognition and anxiety between wild type (WT) mice and TRPM2-KO mice with the recognition of new things trial and elevated plus-maze; 2. to determine the expression of apoptosis-associated proteins (PARP1, BNIP3, AIF, and Endo G) using Reverse transcription-polymerase chain reaction (RT-PCR) and Western blot; 3. to observe neurons pathologic damages and astrocyte activation in each group. The main findings of our study were: (a) TRPM2-KO had a protective effect on epilepsy; (b) TRPM2-KO improved spatial memory deficits overtime during epilepsy, but it did not improve anxiety; (c) the protective effect probably occurred via the PARP1 downstream signaling pathway; (d) TRPM2-KO could ameliorate epilepsy-induced hippocampal pathological damages and weaken astrocyte activation. These findings may provide a new approach for the treatment of epilepsy and early intervention.

Highlights for Dengue Immunopathogenesis: Antibody-Dependent Enhancement, Cytokine Storm, and Beyond

Infection with dengue virus (DENV) can lead to a wide spectrum of clinical presentations, ranging from asymptomatic infection to death. It is estimated that the disease manifests only in 90 million cases out of the total 390 million yearly infections. Even though research has not yet elucidated which are the precise pathophysiological mechanisms that trigger severe forms of dengue, the infection elicits a critical immune response significant for dengue pathogenesis development. Understanding how the immune response to DENV is established and how it can resolve the infection or turn into an immunopathology is of great importance in DENV research. Currently, studies have extensively debated 2 hypotheses involving immune response: antibody-dependent enhancement and cytokine storm. However, despite its undeniable importance in severe forms of the disease, these 2 hypotheses are based on a primed immune status resulting from previous heterologous infection, abstaining them from explaining the severe forms of dengue in naive immune subjects, for example. Thus, it seems that a more intricate arrangement of causes and conditions must be achieved to severe dengue to occur. Among them, the cytokine network signature elicited, in association with viral aspects deserves special attention regarding the establishment of infection and evolution to pathogenesis. In this work, we intend to shed light on how those elements contribute to severe dengue development.

Simvastatin Induces Apoptosis in Medulloblastoma Brain Tumor Cells via Mevalonate Cascade Prenylation Substrates

Medulloblastoma is a common pediatric brain tumor and one of the main types of solid cancers in children below the age of 10. Recently, cholesterol-lowering “statin” drugs have been highlighted for their possible anti-cancer effects. Clinically, statins are reported to have promising potential for consideration as an adjuvant therapy in different types of cancers. However, the anti-cancer effects of statins in medulloblastoma brain tumor cells are not currently well-defined. Here, we investigated the cell death mechanisms by which simvastatin mediates its effects on different human medulloblastoma cell lines. Simvastatin is a lipophilic drug that inhibits HMG-CoA reductase and has pleotropic effects. Inhibition of HMG-CoA reductase prevents the formation of essential downstream intermediates in the mevalonate cascade, such as farnesyl pyrophosphate (FPP) and gernaylgerany parophosphate (GGPP). These intermediates are involved in the activation pathway of small Rho GTPase proteins in different cell types. We observed that simvastatin significantly induces dose-dependent apoptosis in three different medulloblastoma brain tumor cell lines (Daoy, D283, and D341 cells). Our investigation shows that simvastatin-induced cell death is regulated via prenylation intermediates of the cholesterol metabolism pathway. Our results indicate that the induction of different caspases (caspase 3, 7, 8, and 9) depends on the nature of the medulloblastoma cell line. Western blot analysis shows that simvastatin leads to changes in the expression of regulator proteins involved in apoptosis, such as Bax, Bcl-2, and Bcl-xl. Taken together, our data suggests the potential application of a novel non-classical adjuvant therapy for medulloblastoma, through the regulation of protein prenylation intermediates that occurs via inhibition of the mevalonate pathway.

Neuroprotective effects of human bone marrow mesenchymal stem cells against cerebral ischemia are mediated in part by an anti-apoptotic mechanism

Transplantation of human bone marrow mesenchymal stem cells (hMSCs) stands as a potent stroke therapy, but its exact mechanism remains unknown. This study investigated the anti-apoptotic mechanisms by which hMSCs exert neuroprotective effects on cerebral ischemia. Primary mixed cultures of rat neurons and astrocytes were cultured and exposed to oxygen-glucose deprivation. A two-hour period of "reperfusion" in standard medium and normoxic conditions was allowed and immediately followed by hMSCs and/or Bcl-2 antibody treatment. Cell viability of primary rat neurons and astrocytes was determined by 3-(4,5-dimethylthianol-2-yl)-2,5 diphenyl tetrazolium bromide and trypan blue exclusion methods. hMSC survival and differentiation were characterized by immunocytochemistry, while the concentration of Bcl-2 in the supernatant was measured by enzyme-linked immunosorbent assay to reveal the secretory anti-apoptotic function of hMSCs. Cultured hMSCs expressed embryonic-like stem cell phenotypic markers CXCR4, Oct4, SSEA4, and Nanog, as well as immature neural phenotypic marker Nestin. Primary rat neurons and astrocytes were protected from oxygen-glucose deprivation by hMSCs, which was antagonized by the Bcl-2 antibody. However, Bcl-2 levels in the supernatants did not differ between hMSC- and non-treated cells exposed to oxygen-glucose deprivation. Neuroprotective effects of hMSCs against cerebral ischemia were partially mediated by the anti-apoptotic mechanisms. However, further studies are warranted to fully elucidate this pathway.

Tangeretin protects human brain microvascular endothelial cells against oxygen-glucose deprivation-induced injury

Tangeretin, a citrus flavonoid extracted from the peel of citrus fruits, was reported to possess antiasthmatic, antioxidant, anti-inflammatory, and neuroprotective properties. However, the effect of tangeretin on human brain microvascular endothelial cells (HBMECs) has not been examined. This study was designed to investigate the protective effects of tangeretin on oxygen-glucose deprivation (OGD)-induced injury of HBMECs, and explore the underlying mechanisms. Our results showed that tangeretin improved HBMECs viability in response to OGD. In addition, tangeretin was able to increase the activity of superoxide dismutase and decrease the levels of reactive oxygen species and malondialdehyde (MDA), as well as ameliorate cell apoptosis in OGD-stimulated HBMECs. Mechanistic studies showed that tangeretin prevented the activation of JNK signaling pathway in OGD-stimulated HBMECs. Taken together, our current study demonstrated that tangeretin could ameliorate OGD-induced HBMECs injury through the JNK signaling pathway. Thus, tangeretin might be used as a therapeutic strategy for ischemia-reperfusion brain injury and related diseases.

Whole blood gene expression and white matter Hyperintensities

Background

White matter hyperintensities (WMH) are an important biomarker of cumulative vascular brain injury and have been associated with cognitive decline and an increased risk of dementia, stroke, depression, and gait impairments. The pathogenesis of white matter lesions however, remains uncertain. The characterization of gene expression profiles associated with WMH might help uncover molecular mechanisms underlying WMH.

Methods

We performed a transcriptome-wide association study of gene expression profiles with WMH in 3248 participants from the Framingham Heart Study using the Affymetrix Human Exon 1.0 ST Array.

Results

We identified 13 genes that were significantly associated with WMH (FDR < 0.05) after adjusting for age, sex and blood cell components. Many of these genes are involved in inflammation-related pathways.

Conclusion

Thirteen genes were significantly associated with WMH. Our study confirms the hypothesis that inflammation might be an important factor contributing to white matter lesions. Future work is needed to explore if these gene products might serve as potential therapeutic targets.

Electronic supplementary material

The online version of this article (10.1186/s13024-017-0209-5) contains supplementary material, which is available to authorized users.

Apoptotic Bodies: Selective Detection in Extracellular Vesicles

Normal and dying cells release various types of membrane-bound vesicles including microvesicles, exosomes, and apoptotic bodies. These vesicles play important roles in intercellular communication and signal transduction. However, their diverse forms and subtypes fluctuate in size and other properties. In result current purification approaches do not fully discriminate between different categories of extracellular vesicles. Here, we present a fluorescence technique that specifically identifies apoptotic bodies in preparations of microvesicles, exosomes, and other extracellular vesicles.The approach exclusively labels the vesicles that contain DNA with 5'PO₄ blunt-ended DNA breaks, such as those produced by the apoptotic CAD nuclease during apoptotic DNA degradation. The technique can be useful in studies of apoptosis involving microvesicles and exosomes.

Dual Detection of Nucleolytic and Proteolytic Markers of Lysosomal Cell Death: DNase II-Type Breaks and Cathepsin D

Lysosomes contain hydrolytic enzymes that can degrade proteins and DNA. Leakage of these reactive compounds through a compromised lysosomal membrane causes lysosomal cell death, which can have apoptotic, necrotic, or mixed morphology. Lysosomal cathepsin proteases, such as cathepsin D, and the lysosomal endonuclease, DNase II, have both been implicated in lysosome-related cell death. Here, we present a fluorescence dual-labeling technique for simultaneous visualization of these two markers of lysosomal activity linked to cell death. The approach labels the intracellular distribution of cathepsin D and the sites with DNase II-type breaks in fixed tissue sections. It determines the lysosomal or extra-lysosomal localization of the markers and can be useful in studying pathways and signals of lysosomal cell death.

Synergic Effect of Borneol and Ligustrazine on the Neuroprotection in Global Cerebral Ischemia/Reperfusion Injury: A Region-Specificity Study

The cooperation of ligustrazine (LI) and borneol was proved to be much better than each of them in treating cerebral ischemia. However, the mechanism of their synergic therapy is unclear till now. Moreover, whether their cooperation brought different degrees of protection among different brain regions was also unclear. In the present study, the effects of LI, borneol, and their mixture were observed in global cerebral ischemia-reperfusion (GCIR) injury by detecting microcirculation, expressions of caspase-3 and p53, levels of IL-1β, IL-6, and TNF-α, and contents of SOD, GSH-Px, and MDA in cortex, hippocampus, hypothalamus, and striatum, respectively. Furthermore, Nissl bodies were scored also. Monotherapy of LI or borneol showed obvious improvements in the four regions, specially in cortex and hippocampus. Interestingly, the cooperation of LI and borneol brought some new improvements, specially in hypothalamus and striatum. Thus, the synergic effect of the two drugs showed region-specificity in GCIR injury except the expressions of caspase-3 and p53.

A single intraperitoneal injection of ketamine does not affect spatial working, reference memory or neurodegeneration in adult mice: An animal study

BACKGROUND

Ketamine is an anaesthetic and analgesic drug used in research and clinical practice. Little is known about the effects of different doses of this drug on memory and brain cellular death.

OBJECTIVE

To study the effects of different doses of ketamine on working and reference memory, and neurodegeneration in adult mice.

DESIGN

A randomised study.

SETTINGS

The study was carried out in a basic science laboratory, between March 2011 and August 2012.

ANIMALS

Forty-eight 7-month-old, male C57BL/6 mice were used.

INTERVENTION

Animals received a single intraperitoneal injection of physiological saline solution or one of three doses of ketamine (25, 75 or 150 mg kg(-1)). Each group consisted of 12 animals (seven animals for behavioural tests and five animals for histopathological and immunohistochemical studies). The animals used for histopathology studies were sacrificed 3 h after anaesthesia.

MAIN OUTCOME MEASURES

Working and reference memories were assessed using the radial-maze test over 12 consecutive days. The equilibrium was tested using the vertical pole (4 and 24 h after injection), whereas locomotion was assessed using the open field (24, 48 and 72 h after injection). Histopathological (haematoxylin-eosin staining) and immunohistochemical analyses (procaspase-3 and activated caspase-3 detections) were performed 3 h after injection to assess neurodegeneration in the retrosplenial and visual cortices, pyramidal cell layer of the cornu Ammonis 1 and cornu Ammonis 3 areas of the hippocampus, in the granular layer of the dentate gyrus, in the laterodorsal thalamic nucleus, striatum and accumbens nucleus.

RESULTS

No significant differences were observed between the groups regarding the number of dead cells and cells showing positive immune-reactivity in the different regions of the brain studied. The performance in the vertical pole test and the number of reference and working memory errors in the radial-maze were similar in all groups. Nevertheless, the animals treated with ketamine 75 mg kg(-1) were transiently more active, walking a greater total distance at a greater speed in the open field than other groups (power of 0.96).

CONCLUSION

These data indicate that a single intraperitoneal injection of ketamine at subanaesthetic and anaesthetic doses does not impair working memory, reference memory or neurodegeneration in adult mice, but an intermediate dose of ketamine produces transitory hyperlocomotion.

Injury of the developing cerebellum: a brief review of the effects of endotoxin and asphyxial challenges in the late gestation sheep fetus

The vulnerability of the fetal and newborn brain to events in utero or at birth that cause damage arising from perturbations of cerebral blood flow and metabolism, such as the accumulation of free radicals and excitatory transmitters to neurotoxic levels, has received considerable attention over the last few decades. Attention has usually been on the damage to cerebral structures, particularly, periventricular white matter. The rapid growth of the cerebellum in the latter half of fetal life in species with long gestations, such as the human and sheep, suggests that this may be a particularly important time for the development of cerebellar structure and function. In this short review, we summarize data from recent studies with fetal sheep showing that the developing cerebellum is particularly sensitive to infectious processes, chronic hypoxia and asphyxia. The data demonstrates that the cerebellum should be further studied in insults of this nature as it responds differently to the remainder of the brain. Damage to this region of the brain has implications not only for the development of motor control and posture, but also for higher cognitive processes and the subsequent development of complex behaviours, such as learning, memory and attention.

Mitochondrial BNIP3 upregulation precedes endonuclease G translocation in hippocampal neuronal death following oxygen-glucose deprivation

Background

Caspase-independent apoptotic pathways are suggested as a mechanism for the delayed neuronal death following ischemic insult. However, the underlying signalling mechanisms are largely unknown. Recent studies imply the involvement of several mitochondrial proteins, including endonuclease G (EndoG) and Bcl-2/adenovirus E1B 19 kDa-interacting protein (BNIP3), in the pathway of non-neuronal cells.

Results

In this report, using western blot analysis and immunocytochemistry, we found that EndoG upregulates and translocates from mitochondria to nucleus in a time-dependent manner in cultured hippocampal neurons following oxygen-glucose deprivation (OGD). Moreover, the translocation of EndoG occurs hours before the observable nuclear pyknosis. Importantly, the mitochondrial upregulation of BNIP3 precedes the translocation of EndoG. Forced expression of BNIP3 increases the nuclear translocation of EndoG and neuronal death while knockdown of BNIP3 decreases the OGD-induced nuclear translocation of EndoG and neuronal death.

Conclusion

These results suggest that BNIP3 and EndoG play important roles in hippocampal neuronal apoptosis following ischemia, and mitochondrial BNIP3 is a signal protein upstream of EndoG that can induce neuronal death.

Reduced early hypoxic/ischemic brain damage is associated with increased GLT-1 levels in mice expressing mutant (P301L) human tau

Mutations in tau proteins are associated with a group of neurodegenerative diseases, termed tauopathies. To investigate whether over-expressing human tau with P301L mutation also affects stroke-induced brain damage, we performed hypoxia/ischemia (H/I) in young adult P301L tau transgenic mice. Surprisingly, brain infarct volume was significantly smaller in transgenic mice compared to wild-type mice 24 h after H/I induction. TUNEL staining also revealed less brain apoptosis in transgenic mice following H/I. H/I resulted in a significant increase in tau fragments generated by caspase activation and a marked decrease in tau phosphorylation at residue T231 in cortex of wild-type but not transgenic mice. Activation of calpain and caspase-3 following H/I was also reduced in transgenic compared to wild-type mice, as reflected by lower levels of the specific spectrin breakdown products generated by calpain or caspase-3. Finally, basal levels of the glial glutamate transporter, GLT-1, were higher in brains of transgenic as compared to wild-type mice. These results support the idea that enhanced levels of GLT-1 in transgenic mice are responsible for reducing H/I-induced brain damage by decreasing extracellular glutamate accumulation and subsequent calpain and caspase activation.

Therapeutic potential of AIF-mediated caspase-independent programmed cell death

Resistance to anticancer drugs is often related to deficient cell death execution pathways in cancer cells. Apoptosis, which denotes a form of cell death executed by caspases, was traditionally considered as the only physiological and programmed form of cell death. However, recent evidence indicates that programmed cell death (PCD) can occur in complete absence of caspase activation. Indeed, a large number of caspase-independent models are now defined and a key protein implicated in this type of PCD, apoptosis-inducing factor (AIF), has been identified. AIF is a mitochondrial protein with two faces looking in opposite life/death directions. Recently, the identification of five different isoforms allowed a better characterization of AIFs life/mitochondrial versus death/nuclear functions, as well as definition of its pro-apoptotic region and some of its nuclear partners. Importantly, much work on caspase-independent PCD has revealed that AIF participates in more PCD systems than initially thought. A wider molecular knowledge of AIF, and of the caspase-independent PCDs in which it is involved, are key to provide new insights into the role of PCD. There is no doubt that these insights will lead to the development of more selective and efficient drugs against cancer, degenerative diseases, and other pathological disorders implicating AIF.

Effects of ischemia-reperfusion injury on renal ammonia metabolism and the collecting duct

Acute renal injury induces metabolic acidosis, but its specific effects on the collecting duct, the primary site for urinary ammonia secretion, the primary component of net acid excretion, are incompletely understood. We induced ischemia-reperfusion (I/R) acute renal injury in Sprague-Dawley rats by clamping the renal pedicles bilaterally for 30 min followed by reperfusion for 6 h. Control rats underwent sham surgery without renal pedicle clamping. I/R injury decreased urinary ammonia excretion significantly but did not persistently alter urine volume, Na+, K+, or bicarbonate excretion. Histological examination demonstrated cellular damage in the outer and inner medullary collecting duct, as well as in the proximal tubule and the thick ascending limb of the loop of Henle. A subset of collecting duct cells were damaged and/or detached from the basement membrane; these cells were present predominantly in the outer medulla and were less frequent in the inner medulla. Immunohistochemistry identified that the damaged/detached cells were A-type intercalated cells, not principal cells. Both TdT-mediated dUTP nick-end labeling (TUNEL) staining and transmission electron microscopic examination demonstrated apoptosis but not necrosis. However, immunoreactivity for caspase-3 was observed in the proximal tubule, but not in collecting duct intercalated cells, suggesting that mechanism(s) of collecting duct intercalated cell apoptosis differ from those operative in the proximal tubule. We conclude that I/R injury decreases renal ammonia excretion and is associated with intercalated cell-specific detachment and apoptosis in the outer and inner medullary collecting duct. These effects likely contribute to the metabolic acidosis frequently observed in acute renal injury.

BNIP3 upregulation and EndoG translocation in delayed neuronal death in stroke and in hypoxia

BACKGROUND AND PURPOSE

Delayed neuronal death is a hallmark feature of stroke and the primary target of neuroprotective strategies. Caspase-independent apoptosis pathways are suggested as a mechanism for the delayed neuronal injury. Here we test the hypothesis that one of the caspase-independent apoptosis pathways is activated by BNIP3 and mediated by EndoG.

METHODS

We performed immunohistochemistry, Western blotting, cell transfection, subcellular fractionation, and RNA interfering to analyze the expression and localization of BNIP3 and EndoG in degenerating neurons in models of stroke and hypoxia.

RESULTS

BNIP3 was upregulated in brain neurons in a rat model of stroke and in cultured primary neurons exposed to hypoxia. The expressed BNIP3 was localized to mitochondria. Both forced expression of BNIP3 by plasmid transfection and induced expression of BNIP3 by hypoxia in neurons resulted in mitochondrial release and nuclear translocation of EndoG and neuronal cell death. Knockdown of BNIP3 by RNAi inhibited EndoG translocation and protected against hypoxia-induced neuronal death.

CONCLUSIONS

BNIP3 plays a role in delayed neuronal death in hypoxia and stroke and EndoG is a mediator of the BNIP3-activated neuronal death pathway. The results suggest that BNIP3 may be a new target for neuronal rescue strategies.

Rho mediates calcium-dependent activation of p38alpha and subsequent excitotoxic cell death

Excitotoxic neuronal death contributes to many neurological disorders, and involves calcium influx and stress-activated protein kinases (SAPKs) such as p38alpha. There is indirect evidence that the small Rho-family GTPases Rac and cdc42 are involved in neuronal death subsequent to the withdrawal of nerve growth factor (NGF), whereas Rho is involved in the inhibition of neurite regeneration and the release of the amyloidogenic Abeta(42) peptide. Here we show that Rho is activated in rat neurons by conditions that elevate intracellular calcium and in the mouse cerebral cortex during ischemia. Rho is required for the rapid glutamate-induced activation of p38alpha and ensuing neuronal death. The ability of RhoA to activate p38alpha was not expected, and it was specific to primary neuronal cultures. The expression of active RhoA alone not only activated p38alpha but also induced neuronal death that was sensitive to the anti-apoptotic protein Bcl-2, showing that RhoA was sufficient to induce the excitotoxic pathway. Therefore, Rho is an essential component of the excitotoxic cell death pathway.

Caspase-dependent cell death involved in brain damage after acute subdural hematoma in rats

Traumatic brain injury is associated with acute subdural hematoma (ASDH) that worsens outcome. Although early removal of blood can reduce mortality, patients still die or remain disabled after surgery and additional treatments are needed. The blood mass and extravasated blood induce pathomechanisms such as high intracranial pressure (ICP), ischemia, apoptosis and inflammation which lead to acute as well as delayed cell death. Only little is known about the basis of delayed cell death in this type of injury. Thus, the purpose of the study was to investigate to which extent caspase-dependent intracellular processes are involved in the lesion development after ASDH in rats. A volume of 300microL blood was infused into the subdural space under monitoring of ICP and tissue oxygen concentration. To asses delayed cell death mechanisms, DNA fragmentation was measured 1, 2, 4 and 7 days after ASDH by TUNEL staining, and the effect of the pan-caspase inhibitor zVADfmk on lesion volume was assessed 7 days post-ASDH. A peak of TUNEL-positive cells was found in the injured cortex at day 2 after blood infusion (53.4+/-11.6 cells/mm(2)). zVADfmk (160ng), applied by intracerebroventricular injection before ASDH, reduced lesion volume significantly by more than 50% (vehicle: 23.79+/-7.62mm(3); zVADfmk: 9.06+/-4.08). The data show for the first time that apoptotic processes are evident following ASDH and that caspase-dependent mechanisms play a crucial role in the lesion development caused by the blood effect on brain tissue.

Illuminating the role of caspases during Drosophila oogenesis

Cell death is a prominent feature of animal germline development. In Drosophila, the death of 15 nurse cells is linked to the development of each oocyte. In addition, females respond to poor environmental conditions by inducing egg chamber death prior to yolk uptake by the oocyte. To study these two forms of cell death, we analyzed caspase activity in the germline by expressing a transgene encoding a caspase cleavage site flanked by cyan fluorescent protein and yellow fluorescent protein. When expressed in ovaries undergoing starvation-induced apoptosis, this construct was an accurate reporter of caspase activity. However, dying nurse cells at the end of normal oogenesis showed no evidence of cytoplasmic caspase activity. Furthermore, although expression of the caspase inhibitors p35 or Drosophila inhibitor of apoptosis protein 1 blocked starvation-induced death, it did not affect normal nurse cell death or overall oogenesis in well-fed females. Our data suggest that caspases play no role in developmentally programmed nurse cell death.

Multiparameter Measurement of Caspase 3 Activation and Apoptotic Cell Death in NT2 Neuronal Precursor Cells Using High-Content Analysis

Caspase activation is a component of a number of neurodegenerative disorders, including stroke. In this study, the authors describe a multiplexed assay for caspase 3 activation, nuclear condensation, and cell viability in a neuronal precursor cell line Ntera-2, injuredwith staurosporine and etoposide. Using a high-content screening approach, cells were identified by staining with the nuclear stain Hoechst 33342; cell viability wasmeasured by staining cells with YoPro-1, which is taken up by damaged cells but excluded from healthy cells; and caspase 3/7 activation was detected using the cell-permeable probe PhiPhi-Lux, which becomes fluorescentwhen cleaved by active caspase 3 or 7. These 3 dyeswere detected simultaneously using a 4-band pass filter set on a Cellomics Arrayscan. The authors used peptide-fmk inhibitors selective for a variety of caspases, demonstrating that the injury is mediated primarily through caspase 3 or 7, although other caspases or related proteases may play aminor role. The general caspase inhibitor zVAD-fmkwas able to block cell death and caspase activationwith the highest potency. The caspase 3 selective inhibitor DEVD-fmkwas almost as potent as zVAD-fmk; other peptide caspase inhibitors displayed onlymodest inhibition of cell death. This assay was also used as a high-content screening tool for the evaluation of novel caspase 3 inhibitors for the potential treatment of degenerative disorders.

Cell-cycle regulators are involved in transient cerebral ischemia induced neuronal apoptosis in female rats

Recent evidence indicates that cell-cycle regulating proteins are involved in apoptotic process in post-mitotic neurons. In this study, we examined cell-cycle regulators for G1/S cell-cycle progression after a transient focal cerebral ischemia induced by middle cerebral artery (MCA) occlusion. In the cerebral frontoparietal cortex, we observed a marked induction of Cyclin D1 (a coactivator of Cdks), and proliferating cell nuclear antigen (PCNA), together with upregulated Cdk kinase activities. This process is accompanied with multiple phosphorylation of retinoblastoma (Rb) protein at Cdk phosphorylation sites in neurons from the ischemic cortex. We further examined DNA synthesis by the incorporation of BrdU, a nucleotide analog that incorporates into newly synthesized DNA. Within 24-h of reperfusion after 60-min occlusion, substantial BrdU-positive neurons were observed in the ischemic cortex. Inhibition of Cdk4 activity during this ischemia/reperfusion is highly neuroprotective. These results suggest that ischemia/reperfusion cerebral damage induces signalings at the G1/S cell-cycle transition, and may constitute a critical step in the neuronal apoptotic pathway in ischemia/reperfusion induced neuronal damage.

Delayed cell death related to acute cerebral blood flow changes following subarachnoid hemorrhage in the rat brain

Object. The authors tested the hypotheses that subarachnoid hemorrhage (SAH) leads to delayed cell death with the participation of apoptotic-like mechanisms and is influenced by the degree of acute decrease in the cerebral blood flow (CBF) following hemorrhage.

Methods. Subarachnoid hemorrhage was induced in rats by endovascular perforation of the internal carotid artery or injection of blood into the prechiasmatic cistern. Cerebral blood flow was measured using laser Doppler flowmetry for 60 minutes. Brain sections stained with terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL) showed DNA fragmentation at 2 and 7 days after both methods of inducing SAH in one third to two thirds of the surviving animals in the different experimental groups. More than 80% of the TUNEL-positive cells were neuron-specific nuclear protein—positive (neurons), but immunoreactivity to glial fibrillary acidic protein (astrocytes) and transferrin (oligodendrocytes) were markedly decreased in TUNEL-positive areas. Most of the TUNEL-positive cells displayed chromatin condensation and/or blebs and immunostained for increased Bax; approximately 50% of them were immunoreactive to cleaved caspase-3 and a few to Bcl-2. The duration of the acute CBF decrease below 30% of the baseline level was related to the degree of TUNEL staining.

Conclusions. Subarachnoid hemorrhage resulted in delayed cell death in a large proportion, but not all, of the surviving animals. The acute CBF decrease was related to the degree of subsequent cell death. These findings indicated the relevance of apoptotic-like pathways. There appears to be a temporal therapeutic window during which adequate treatment might reduce the final damage following SAH.

Apoptosis and necrosis in developing cerebellum and brainstem induced after focal cerebral hypoxic-ischemic injury

Focal cerebral hypoxia-ischemia due to isolated vascular insufficiency is well known to cause ipsilateral, but not contralateral, cerebral apoptosis. Hypoxic-ischemic damage to the cerebellum and brainstem in such a model has not been established. This experimental rodent study demonstrates, through deoxyribonucleic acid fragmentation and terminal deoxynucleotidyl transferase-mediated deoxyuridine 5'-triphosphate-digoxigenin nick end labeling analysis, that neuronal cells in these infratentorial regions also suffer mild apoptosis and necrosis after focal cerebral hypoxic-ischemic injury in the newborn rat. These data provide additional insight into the mechanisms of neurological injury in the cerebellum and brainstem areas resulting from a focal cerebral hypoxic-ischemic insult and demonstrate that future therapeutic interventions for hypoxic-ischemic encephalopathy system should deal with the entire central nervous system.

The PSD95-nNOS interface: a target for inhibition of excitotoxic p38 stress-activated protein kinase activation and cell death

The stress-activated protein kinase p38 and nitric oxide (NO) are proposed downstream effectors of excitotoxic cell death. Although the postsynaptic density protein PSD95 can recruit the calcium-dependent neuronal NO synthase (nNOS) to the mouth of the calcium-permeable NMDA receptor, and depletion of PSD95 inhibits excitotoxicity, the possibility that selective uncoupling of nNOS from PSD95 might be neuroprotective is unexplored. The relationship between excitotoxic stress–generated NO and activation of p38, and the significance of the PSD95–nNOS interaction to p38 activation also remain unclear. We find that NOS inhibitors reduce both glutamate-induced p38 activation and the resulting neuronal death, whereas NO donor has effects consistent with NO as an upstream regulator of p38 in glutamate-induced cell death. Experiments using a panel of decoy constructs targeting the PSD95–nNOS interaction suggest that this interaction and subsequent NO production are critical for glutamate-induced p38 activation and the ensuing cell death, and demonstrate that the PSD95–nNOS interface provides a genuine possibility for design of neuroprotective drugs with increased selectivity.

Mild sustained and intermittent hypoxia induce apoptosis in PC-12 cells via different mechanisms

Episodic hypoxia, a characteristic feature of obstructive sleep apnea, induces cellular changes and apoptosis in brain regions associated with neurocognitive function. To investigate whether mild, intermittent hypoxia would induce more extensive neuronal damage than would a similar degree of sustained hypoxia, rat pheochromocytoma PC-12 neuronal cells were subjected to either sustained (5% O(2)) or intermittent (alternating 5% O(2) 35 min, 21% O(2) 25 min) hypoxia for 2 or 4 days. Quantitative assessment of apoptosis showed that while mild sustained hypoxia did not significantly increase cell apoptosis at 2 days (1.31 +/- 0.29-fold, n = 8; P = NS), a significant increase in apoptosis occurred after 4 days (2.25 +/- 0.4-fold, n = 8; P < 0.002), without increased caspase activation. Furthermore, caspase inhibition with the general caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (Z-VAD-FMK) did not modify sustained hypoxia-induced apoptosis. In contrast, mild, intermittent hypoxia induced significant increases in apoptosis at 2 days (3.72 +/- 1.43-fold, n = 8; P < 0.03) and at 4 days (4.57 +/- 0.82-fold, n = 8; P < 0.001) that was associated with enhanced caspase activity and attenuated by Z-VAD-FMK pretreatment. We conclude that intermittent hypoxia induces an earlier and more extensive apoptotic response than sustained hypoxia and that this response is at least partially dependent on caspase-mediated pathways. In contrast, caspases do not seem to play a role in sustained hypoxia-induced apoptosis. These findings suggest that different signaling pathways are involved in sustained and intermittent hypoxia-induced cell injury and may contribute to the understanding of differential brain susceptibility to sustained and intermittent hypoxia.

Distinct requirements for p38alpha and c-Jun N-terminal kinase stress-activated protein kinases in different forms of apoptotic neuronal death

The stress-activated protein kinases c-Jun-activated kinase (JNK) and p38 are implicated in neuronal apoptosis. Early studies in cell lines suggested a requirement for both in the apoptosis induced by withdrawal of nerve growth factor. However, studies in neuronal cells typically implicate JNK but not p38 in apoptosis. In some cases, p38 is implicated, but the role of JNK is undefined. It remains unclear whether p38 and JNK have differing roles dependent on cell type, apoptotic stimulus, or mechanism of cell death or whether they are redundant and each sufficient to induce identical forms of cell death. We investigate the relative roles of these protein kinases in different death mechanisms in a single system, cultured cerebellar granule neurons. Apoptosis induced by withdrawal of trophic support and glutamate are mechanistically different in terms of caspase activation, DNA fragmentation profile, chromatin morphology, and dependence on de novo gene expression. Caspase-independent apoptosis induced by glutamate is accompanied by strong activation of p38, and dominant negatives and inhibitors of the p38 pathway prevent this apoptosis. In contrast, withdrawal of trophic support induces caspase-dependent death accompanied by JNK-dependent phosphorylation of c-Jun, and inhibition of JNK is sufficient to prevent the death induced by withdrawal of trophic support. Inhibition of p38 does not block withdrawal of trophic support-induced death, nor does inhibition of JNK block glutamate-induced death. We propose that mechanistically different forms of apoptosis have differing requirements for p38 and JNK activities in neurons and demonstrate that only inhibition of the appropriate kinase will prevent neurons from undergoing apoptosis.

Cathepsin B mRNA and protein expression following contusion spinal cord injury in rats

We provide the first data that cathepsin B (Cath B), a lysosomal cysteine protease, is up-regulated following contusion-spinal cord injury (SCI). Following T12 laminectomy and moderate contusion, Cath B mRNA and protein expression profiles were examined from 2 to 168 h post-injury in rats using real-time PCR and immunoblots, respectively. Contusion injury significantly increased [mRNA]Cath B in the injury site and adjacent segments over sham injury levels. While the largest [mRNA]Cath B induction (20-fold over naive) was seen in the injury site, the caudal segment routinely yielded [mRNA]Cath B levels greater than 10-fold over naive. Interestingly, sham injury animals also experienced mRNA induction at several time points at the injury site and in segments rostral and caudal to the injury site. Contusion injury also significantly elevated levels of Cath B proenzyme protein (37 kDa) over sham injury in the injury site (48, 72 and 168 h post-injury). Furthermore, significant protein increases of single and double chain Cath B (both active forms) occurred at the injury site at 72 and 168 h post-injury. Similar significant increases in Cath B protein levels were seen in areas adjacent to the injury site. The induction of Cath B mRNA and protein expression following contusion injury is previously undescribed and suggests that Cath B may potentially be involved in the secondary injury cascade, perhaps for as long as 1 week post-injury.

Postnatal apoptosis, development, and sex difference in the lateral septum of rats

To determine whether apoptosis is involved in the formation of the structure and morphological sex difference of the lateral septum (LS), the postnatal developmental changes in the number of apoptotic cells were examined in the LS on postnatal day 1 (PD1 = birth day), 4, 6, 8, 11, 16, and 31 in male and female rats. Apoptotic cells were immunohistochemically detected by antibody against single-stranded DNA (ssDNA) or active caspase-3. The volume of the LS was also measured and was found to increase with age. The number of apoptotic cells detected by anti-ssDNA in the LS increased from PD1 to PD8 but decreased after PD11. Also, the LS was divided into dorsal, intermediate, and ventral parts (LSd, LSi, and LSv), and the volume and number of ssDNA-immunoreactive cells in each part were measured on PD6, 8, 11, 16, and 31. In both sexes, a large number of ssDNA-immunoreactive cells was found in the LSd and LSi on PD8 (but not on PD6) and in the LSv on PD6 and PD8. On PD6, the number of active caspase-3-immunoreactive cells was significantly greater in the LSv than in the LSd or LSi, in both sexes. Only the LSi of males had a high number of ssDNA-immunoreacitve cells on PD16; the number was significantly greater than that of females of the same age. However, there was no significant sex difference in the number of active caspase-3-immunoreacitve cells in the LSi on PD16. On PD31, the volume of the LSi was significantly greater in females than in males. There was no sex difference in volume or number of apoptotic cells in the LSd or LSv. These findings indicate that loss of cells due to apoptosis, which is partially caused by activation of caspase-3, occurs in the LS during postnatal development, with regional differences. They also indicate that sex difference in caspase-3-independent apoptosis contributes to morphological sexual differentiation of the LSi.

Cell death in toxic nephropathies

Toxic nephropathies cause acute and chronic renal failure, primarily as a result of injury to renal tubular epithelium. There is a well-known capacity in the renal nephron for the synchronous occurrence of both apoptosis and necrosis in toxic nephropathies. This has engendered interest in the differing or complementary roles of these modes of cell death. Once thought to be mutually exclusive in incidence and morphologic and biochemical features, recent evidence in renal and other diseases indicates some blurring in the features of apoptosis and necrosis, particularly in the situations in which they are identified, in their molecular pathways, and in the role of inflammation in the processes. Definition of the heterogenic pathophysiologic response of the nephron should provide information useful for promoting the health of the kidney after injury, particularly in relation to controlling the extent and modalities of cell death via the associated renal-specific molecular features. This article indicates the significance and some problems of defining the types of cell death in toxic nephropathies.