Transient global ischemia triggers expression of the DNA damage-inducible gene GADD45 in the rat brain

GADD45A: With or without you

The growth arrest and DNA damage inducible (GADD)45 family includes three small and ubiquitously distributed proteins (GADD45A, GADD45B, and GADD45G) that regulate numerous cellular processes associated with stress signaling and injury response. Here, we provide a comprehensive review of the current literature investigating GADD45A, the first discovered member of the family. We first depict how its levels are regulated by a myriad of genotoxic and non-genotoxic stressors, and through the combined action of intricate transcriptional, posttranscriptional, and even, posttranslational mechanisms. GADD45A is a recognized tumor suppressor and, for this reason, we next summarize its role in cancer, as well as the different mechanisms by which it regulates cell cycle, DNA repair, and apoptosis. Beyond these most well-known actions, GADD45A may also influence catabolic and anabolic pathways in the liver, adipose tissue and skeletal muscle, among others. Not surprisingly, GADD45A may trigger AMP-activated protein kinase activity, a master regulator of metabolism, and is known to act as a transcriptional coregulator of numerous nuclear receptors. GADD45A has also been reported to display a cytoprotective role by regulating inflammation, fibrosis and oxidative stress in several organs and tissues, and is regarded an important contributor for the development of heart failure. Overall data point to that GADD45A may play an important role in metabolic, neurodegenerative and cardiovascular diseases, and also autoimmune-related disorders. Thus, the potential mechanisms by which dysregulation of GADD45A activity may contribute to the progression of these diseases are also reviewed below.

GADD34 activates p53 and may have utility as a marker of atherosclerosis

We previously identified growth arrest and DNA-damage-inducible gene 34 (GADD34) as a marker of ischemic stroke. In the present study, serum levels of anti-GADD34 antibodies were found to be significantly higher in patients with acute ischemic stroke or chronic kidney disease compared to healthy donors. We then examined the biological function of GADD34 by transfection into U2OS human osteosarcoma and U87 human glioblastoma cells. Knockdown of GADD34 by siRNA resulted in enhanced cell proliferation, which was reversed by co-knockdown of MDM2. Luciferase reporter assays revealed that the transactivation ability of p53 enhanced by genotoxic anticancer drugs such as camptothecin and etoposide was further potentiated by enforced expression of GADD34 but attenuated by co-transfection with p53 shRNA expression plasmids. Western blotting demonstrated increased p53 protein levels after treatment with camptothecin, which was also potentiated by GADD34 but suppressed by GADD34 siRNA, ATM siRNA, and ATM inhibitor wortmannin. GADD34 levels also increased in response to treatment with camptothecin or adriamycin, and this increase was attenuated by MDM2 siRNA. Immunoprecipitation with anti-GADD34 antibody followed by Western blotting with anti-MDM2 antibodies indicated ubiquitination of GADD34 is mediated by MDM2. Accordingly, GADD34 may function as a ubiquitination decoy to reduce p53 ubiquitination and increase p53 protein levels. Increased neuronal cell death due to activation of p53 by GADD34 may account for the elevated serum levels of anti-GADD34 antibodies observed in patients with acute ischemic stroke.

The role of Gadd45b in neurologic and neuropsychiatric disorders: An overview

Growth arrest and DNA damage-inducible beta (Gadd45b) is directly intertwined with stress-induced DNA repair, cell cycle arrest, survival, and apoptosis. Previous research on Gadd45b has focused chiefly on non-neuronal cells. Gadd45b is extensively expressed in the nervous system and plays a critical role in epigenetic DNA demethylation, neuroplasticity, and neuroprotection, according to accumulating evidence. This article provided an overview of the preclinical and clinical effects of Gadd45b, as well as its hypothesized mechanisms of action, focusing on major psychosis, depression, autism, stroke, seizure, dementia, Parkinson’s disease, and autoimmune diseases of the nervous system.

Gadd45 in Neuronal Development, Function, and Injury

The growth arrest and DNA damage-inducible (Gadd) 45 proteins have been associated with numerous cellular mechanisms including cell cycle control, DNA damage sensation and repair, genotoxic stress, neoplasia, and molecular epigenetics. The genes were originally identified in in vitro screens of irradiation- and interleukin-induced transcription and have since been implicated in a host of normal and aberrant central nervous system processes. These include early and postnatal development, injury, cancer, memory, aging, and neurodegenerative and psychiatric disease states. The proteins act through a variety of molecular signaling cascades including the MAPK cascade, cell cycle control mechanisms, histone regulation, and epigenetic DNA demethylation. In this review, we provide a comprehensive discussion of the literature implicating each of the three members of the Gadd45 family in these processes.

A Mouse Brain-based Multi-omics Integrative Approach Reveals Potential Blood Biomarkers for Ischemic Stroke

Stroke remains a leading cause of death and disability worldwide. Despite continuous advances, the identification of key molecular signatures in the hyper-acute phase of ischemic stroke is still a primary interest for translational research on stroke diagnosis, prognosis, and treatment. Data integration from high-throughput -omics techniques has become crucial to unraveling key interactions among different molecular elements in complex biological contexts, such as ischemic stroke. Thus, we used advanced data integration methods for a multi-level joint analysis of transcriptomics and proteomics data sets obtained from mouse brains at 2 h after cerebral ischemia. By modeling net-like correlation structures, we identified an integrated network of genes and proteins that are differentially expressed at a very early stage after stroke. We validated 10 of these deregulated elements in acute stroke, and changes in their expression pattern over time after cerebral ischemia were described. Of these, CLDN20, GADD45G, RGS2, BAG5, and CTNND2 were next evaluated as blood biomarkers of cerebral ischemia in mice and human blood samples, which were obtained from stroke patients and patients presenting stroke-mimicking conditions. Our findings indicate that CTNND2 levels in blood might potentially be useful for distinguishing ischemic strokes from stroke-mimicking conditions in the hyper-acute phase of the disease. Furthermore, circulating GADD45G content within the first 6 h after stroke could also play a key role in predicting poor outcomes in stroke patients. For the first time, we have used an integrative biostatistical approach to elucidate key molecules in the initial stages of stroke pathophysiology and highlight new notable molecules that might be further considered as blood biomarkers of ischemic stroke.

Elevated levels of autoantibodies against EXD2 and PHAX in the sera of patients with chronic thromboembolic pulmonary hypertension

While circulating autoantibodies have been detected in patients with several cardiovascular diseases, such studies have not been performed for chronic thromboembolic pulmonary hypertension (CTEPH) and pulmonary arterial hypertension (PAH). Here we investigated the production of certain auto-antibodies in CTEPH patients. Initial screening was performed in 5 CTEPH patients and 5 healthy donors (HDs) using a ProtoArray Human Protein Microarray v5.1 containing 9,375 human proteins, and we selected 34 antigens recognized by IgG antibodies more strongly in the sera of CTEPH patients than in the sera of HDs. In subsequent second/third analyses, we validated the auto-antibody level using amplified luminescent proximity homogeneous assay-linked immunosorbent assay (AlphaLISA) in 96 CTEPH patients and 96 HDs as follows: At the second screening, we used 63 crude peptides derived from those selected 34 antigens and found that the serum levels of autoantibodies for 4 peptides seemed higher in CTEPH patients than in HDs. In third analysis, we used the purified peptides of those selected in second screening and found that serum antibodies against peptides derived from exonuclease 3'-5' domain-containing 2 (EXD2) and phosphorylated adaptor for RNA export (PHAX) were significantly higher in CTEPH patients than in HDs. The serum antibody levels to these antigens were also elevated in PAH patients. The titers against EXD2 peptide decreased after surgical treatment in CTEPH patients. These autoantibodies may be useful as biomarkers of CTEPH and PAH, and further investigations may provide novel insight into the etiology.

Silencing Huwe1 reduces apoptosis of cortical neurons exposed to oxygen-glucose deprivation and reperfusion

HECT, UBA and WWE domain-containing 1 (Huwe1), an E3 ubiquitin ligase involved in the ubiquitin-proteasome system, is widely expressed in brain tissue. Huwe1 is involved in the turnover of numerous substrates, including p53, Mcl-1, Cdc6 and N-myc, thereby playing a critical role in apoptosis and neurogenesis. However, the role of Huwe1 in brain ischemia and reperfusion injury remains unclear. Therefore, in this study, we investigated the role of Huwe1 in an in vitro model of ischemia and reperfusion injury. At 3 days in vitro, primary cortical neurons were transduced with a control or shRNA-Huwe1 lentiviral vector to silence expression of Huwe1. At 7 days in vitro, the cells were exposed to oxygen-glucose deprivation for 3 hours and reperfusion for 24 hours. To examine the role of the c-Jun N-terminal kinase (JNK)/p38 pathway, cortical neurons were pretreated with a JNK inhibitor (SP600125) or a p38MAPK inhibitor (SB203508) for 30 minutes at 7 days in vitro, followed by ischemia and reperfusion. Neuronal apoptosis was assessed by TUNEL assay. Protein expression levels of JNK and p38MAPK and of apoptosis-related proteins (p53, Gadd45a, cleaved caspase-3, Bax and Bcl-2) were measured by western blot assay. Immunofluorescence labeling for cleaved caspase-3 was performed. We observed a significant increase in neuronal apoptosis and Huwe1 expression after ischemia and reperfusion. Treatment with the shRNA-Huwe1 lentiviral vector markedly decreased Huwe1 levels, and significantly decreased the number of TUNEL-positive cells after ischemia and reperfusion. The silencing vector also downregulated the pro-apoptotic proteins Bax and cleaved caspase-3, and upregulated the anti-apoptotic proteins Gadd45a and Bcl-2. Silencing Huwe1 also significantly reduced p-JNK levels and increased p-p38 levels. Our findings show that downregulating Huwe1 affects the JNK and p38MAPK signaling pathways as well as the expression of apoptosis-related genes to provide neuroprotection during ischemia and reperfusion. All animal experiments and procedures were approved by the Animal Ethics Committee of Sichuan University, China in January 2018 (approval No. 2018013).

Elevation of Autoantibody in Patients with Ischemic Stroke

Recent clinical research has revealed a significant correlation between atherosclerosis, one of the primary etiologies of ischemic stroke, and the immune system. Assuming that "disease-specific autoantibodies are produced in the sera of patients with ischemic stroke," we investigated multiple arteriosclerosis-related antibodies using the serological identification of antigens by recombinant cDNA expression cloning (SEREX), an established method for identifying antigenic proteins. We either screened a human aortic endothelial cell cDNA library or conducted protein array screening using the sera from patients with ischemic stroke, such as carotid artery stenosis or transient ischemic attack (TIA). Next, we measured serum antibody levels using amplified luminescent proximity homogeneous assay-linked immunosorbent assay (AlphaLISA) in patient/healthy donor (HD) cohorts and identified several antigens, the antibody levels of which were significantly higher in patients with ischemic stroke than in HDs. This review introduced the method of identifying antigens by the SEREX and protein microarray and summarized antigenic proteins. In particular, it focused on anti-replication protein A2 antibody and anti-programmed cell death 11 antibody, which are significantly related to atherosclerotic plaque and ischemic brain tissue, respectively, and proposed the mechanism of elevated autoantibody levels against them. Furthermore, this review suggests a possibility of clinical application as an atherosclerotic disease diagnostic marker for TIA or cerebral infarction.

Neuron-specific SUMO knockdown suppresses global gene expression response and worsens functional outcome after transient forebrain ischemia in mice

Small ubiquitin-like modifier (SUMO) conjugation (SUMOylation) plays key roles in neurologic function in health and disease. Neuronal SUMOylation is essential for emotionality and cognition, and this pathway is dramatically activated in post-ischemic neurons, a neuroprotective response to ischemia. It is also known from cell culture studies that SUMOylation modulates gene expression. However, it remains unknown how SUMOylation regulates neuronal gene expression in vivo, in the physiologic state and after ischemia, and modulates post-ischemic recovery of neurologic function. To address these important questions, we used a SUMO1-3 knockdown (SUMO-KD) mouse in which a Thy-1 promoter drives expression of 3 distinct microRNAs against SUMO1-3 to silence SUMO expression specifically in neurons. Wild-type and SUMO-KD mice were subjected to transient forebrain ischemia. Microarray analysis was performed in hippocampal CA1 samples, and neurologic function was evaluated. SUMOylation had opposite effects on neuronal gene expression before and after ischemia. In the physiological state, most genes regulated by SUMOylation were up-regulated in SUMO-KD compared to wild-type mice. Brain ischemia/reperfusion significantly modulated the expression levels of more than 400 genes in wild-type mice, with a majority of those genes upregulated. The extent of this post-ischemic transcriptome change was suppressed in SUMO-KD mice. Moreover, SUMO-KD mice exhibited significantly worse functional outcome. This suggests that suppression of global gene expression response in post-ischemic brain due to SUMO knockdown has a negative effect on post-ischemic neurologic function. Together, our data provide a basis for future studies to mechanistically link SUMOylation to neurologic function in health and disease.

Targeting type-2 metabotropic glutamate receptors to protect vulnerable hippocampal neurons against ischemic damage

Background

To examine whether metabotropic glutamate (mGlu) receptors have any role in mechanisms that shape neuronal vulnerability to ischemic damage, we used the 4-vessel occlusion (4-VO) model of transient global ischemia in rats. 4-VO in rats causes a selective death of pyramidal neurons in the hippocampal CA1 region, leaving neurons of the CA3 region relatively spared. We wondered whether changes in the expression of individual mGlu receptor subtypes selectively occur in the vulnerable CA1 region during the development of ischemic damage, and whether post-ischemic treatment with drugs targeting the selected receptor(s) affords neuroprotection.

Results

We found that 4-VO caused significantly reduction in the transcript of mGlu2 receptors in the CA1 region at times that preceded the anatomical evidence of neuronal death. Down-regulation of mGlu2 receptors was associated with reduced H3 histone acetylation at the Grm2 promoter. The transcripts of other mGlu receptor subtypes were unchanged in the CA1 region of 4-VO rats. Ischemia did not cause changes in mGlu2 receptor mRNA levels in the resistant CA3 region, which, interestingly, were lower than in the CA1 region. Targeting the mGlu2 receptors with selective pharmacologic ligands had profound effects on ishemic neuronal damage. Post-ischemic oral treatment with the selective mGlu2 receptor NAM (negative allosteric modulator), ADX92639 (30 mg/kg), was highly protective against ischemic neuronal death. In contrast, s.c. administration of the mGlu2 receptor enhancer, LY487379 (30 mg/kg), amplified neuronal damage in the CA1 region and extended the damage to the CA3 region.

Conclusion

These findings suggest that the mGlu2 receptor is an important player in mechanisms regulating neuronal vulnerability to ischemic damage, and that mGlu2 receptor NAMs are potential candidates in the experimental treatments of disorders characterized by brain hypoperfusion, such as hypovolemic shock and cardiac arrest.

Identification of stroke-associated-antigens via screening of recombinant proteins from the human expression cDNA library (SEREX)

Background

Because circulating antibodies against a variety of antigens have been detected in patients with coronary heart disease, carotid atherosclerosis and those who have suffered a stroke, it is suspected that immune response may be one of the mechanisms of atherogenesis The objective of this study is to identify novel antibodies in ischemic stroke patients by screening the expressed recombinant proteins using a human cDNA library (SEREX).

Methods

To identify the candidate antigens, cDNA library was screened by SEREX using plasma from ten patients with ischemic stroke. Subsequently, via ELISA using recombinant proteins and synthetic peptides, the serum antibody levels were measured in two independent patient/healthy donor (HD) cohorts (142 and 78 in the 2nd screening and a validation cohort, respectively).

Results

The initial screening resulted in the identification of six candidate antigens. Of these antigens, replication protein A2 (RPA2) was determined to be the antigen associated with stroke (P < 0.05) by ELISA with 2nd screening and validation cohort. Multifactorial logistic regression analysis showed that the increased levels of the RPA2 antibodies (RPA2-Abs) associated with stroke independent of other risk factors for stroke (P < 0.05). Receiver operating curve analysis demonstrated that the area under the curve from ELISA using GST fusion RPA2 and synthetic peptides (bRPA2-132) were 0.867 (95% CI: 0.798-0.936) and 0.971 (95% CI: 0.940-1.00), respectively. If the cut-off value of the bRPA2-132-Ab level was determined to be 0.334, the sensitivity and specificity of the antibody level as the diagnostic marker for stroke were 0.323 (95% CI: 0.209-0.453) and 1.00 (95% CI: 0.713-1.00), respectively.

Conclusions

SEREX identified RPA2 as the antigen associated with ischemic stroke and serum auto-antibodies against RPA2 elevates in stroke patients. RPA2-Abs could become a biomarker for the evaluation of ischemic stroke at risk.

Epigenetic mechanisms of neuroplasticity and the implications for stroke recovery

Ischemic stroke is a devastating brain injury and an important cause of neurologic disability worldwide and across the lifespan. Despite the physical, social, and economic burdens of this disease there is only a single approved medicine for the treatment of acute stroke, and its use is unfortunately limited to the small fraction of patients presenting within the narrow therapeutic window. Following stroke, there is a period of plasticity involving cell genesis, axon growth, and synaptic modulation that is essential to spontaneous recovery. Treatments focusing on neuroprotection and enhancing recovery have been the focus of intense preclinical studies, but translation of these treatments into clinical use has been disappointing thus far. The important role of epigenetic mechanisms in disease states is becoming increasingly apparent, including in ischemic stroke. These regulators of gene expression are poised to be critical mediators of recovery following stroke. In this review we discuss evidence for the role of epigenetics in neuroplasticity and the implications for stroke recovery.

Electrical stimulation of cerebellar fastigial nucleus: mechanism of neuroprotection and prospects for clinical application against cerebral ischemia

For around two decades, electrical fastigial nucleus stimulation (FNS) has been demonstrated to induce neuroprotection involving multiple mechanisms. In this review, we summarize the protective effects of FNS against cerebral ischemia through the inhibition of electrical activity around the lesion, excitotoxic damage on neurons, and brain inflammatory response, as well as apoptosis. Moreover, FNS has been reported to promote nerve tissue repair, reconstruction, and neurological rehabilitation and improve stroke-related complications including poststroke cognitive dysfunction, depression, and abnormal heart rate variability. We thus further discuss the potential of FNS for clinical applications. Given the absence of any risk of inducing sublethal damage, FNS may offer a new approach to preconditioned neuroprotection against cerebral ischemia.

Endogenous brain protection: what the cerebral transcriptome teaches us

Despite efforts to reduce mortality caused by stroke and perinatal asphyxia, these are still the 2nd largest cause of death worldwide in the age groups they affect. Furthermore, survivors of cerebral hypoxia-ischemia often suffer neurological morbidities. A better understanding of pathophysiological mechanisms in focal and global brain ischemia will contribute to the development of tailored therapeutic strategies. Similarly, insight into molecular pathways involved in preconditioning-induced brain protection will provide possibilities for future treatment. Microarray technology is a great tool for investigating large scale gene expression, and has been used in many experimental studies of cerebral ischemia and preconditioning to unravel molecular (patho-) physiology. However, the amount of data across microarray studies can be daunting and hard to interpret which is why we aim to provide a clear overview of available data in experimental rodent models. Findings for both injurious ischemia and preconditioning are reviewed under separate subtopics such as cellular stress, inflammation, cytoskeleton and cell signaling. Finally, we investigated the transcriptome signature of brain protection across preconditioning studies in search of transcripts that were expressed similarly across studies. Strikingly, when comparing genes discovered by single-gene analysis we observed only 15 genes present in two studies or more. We subjected these 15 transcripts to DAVID Annotation Clustering analysis to derive their shared biological meaning. Interestingly, the MAPK signaling pathway and more specifically the ERK1/2 pathway geared toward cell survival/proliferation was significantly enriched. To conclude, we advocate incorporating pathway analysis into all microarray data analysis in order to improve the detection of similarities between independently derived datasets.

Phycocyanobilin promotes PC12 cell survival and modulates immune and inflammatory genes and oxidative stress markers in acute cerebral hypoperfusion in rats

Since the inflammatory response and oxidative stress are involved in the stroke cascade, we evaluated here the effects of Phycocyanobilin (PCB, the C-Phycocyanin linked tetrapyrrole) on PC12 cell survival, the gene expression and the oxidative status of hypoperfused rat brain. After the permanent bilateral common carotid arteries occlusion (BCCAo), the animals were treated with saline or PCB, taking samples 24h post-surgery. Global gene expression was analyzed with GeneChip Rat Gene ST 1.1 from Affymetrix; the expression of particular genes was assessed by the Fast SYBR Green RT-PCR Master Mix and Bioplex methods; and redox markers (MDA, PP, CAT, SOD) were evaluated spectrophotometrically. The PCB treatment prevented the H2O2 and glutamate induced PC12 cell injury assessed by the MTT assay, and modulated 190 genes (93 up- and 97 down-regulated) associated to several immunological and inflammatory processes in BCCAo rats. Furthermore, PCB positively modulated 19 genes mostly related to a detrimental pro-inflammatory environment and counteracted the oxidative imbalance in the treated BCCAo animals. Our results support the view of an effective influence of PCB on major inflammatory mediators in acute cerebral hypoperfusion. These results suggest that PCB has a potential to be a treatment for ischemic stroke for which further studies are needed.

Growth arrest and DNA-damage-inducible, beta (GADD45b)-mediated DNA demethylation in major psychosis

Aberrant neocortical DNA methylation has been suggested to be a pathophysiological contributor to psychotic disorders. Recently, a growth arrest and DNA-damage-inducible, beta (GADD45b) protein-coordinated DNA demethylation pathway, utilizing cytidine deaminases and thymidine glycosylases, has been identified in the brain. We measured expression of several members of this pathway in parietal cortical samples from the Stanley Foundation Neuropathology Consortium (SFNC) cohort. We find an increase in GADD45b mRNA and protein in patients with psychosis. In immunohistochemistry experiments using samples from the Harvard Brain Tissue Resource Center, we report an increased number of GADD45b-stained cells in prefrontal cortical layers II, III, and V in psychotic patients. Brain-derived neurotrophic factor IX (BDNF IXabcd) was selected as a readout gene to determine the effects of GADD45b expression and promoter binding. We find that there is less GADD45b binding to the BDNF IXabcd promoter in psychotic subjects. Further, there is reduced BDNF IXabcd mRNA expression, and an increase in 5-methylcytosine and 5-hydroxymethylcytosine at its promoter. On the basis of these results, we conclude that GADD45b may be increased in psychosis compensatory to its inability to access gene promoter regions.

BRCA1 is an essential regulator of heart function and survival following myocardial infarction

The tumour suppressor BRCA1 is mutated in familial breast and ovarian cancer but its role in protecting other tissues from DNA damage has not been explored. Here we show a new role for BRCA1 as a gatekeeper of cardiac function and survival. In mice, loss of BRCA1 in cardiomyocytes results in adverse cardiac remodelling, poor ventricular function and higher mortality in response to ischaemic or genotoxic stress. Mechanistically, loss of cardiomyocyte BRCA1 results in impaired DNA double-strand break repair and activated p53-mediated pro-apoptotic signalling culminating in increased cardiomyocyte apoptosis, whereas deletion of the p53 gene rescues BRCA1-deficient mice from cardiac failure. In human adult and fetal cardiac tissues, ischaemia induces double-strand breaks and upregulates BRCA1 expression. These data reveal BRCA1 as a novel and essential adaptive response molecule shielding cardiomyocytes from DNA damage, apoptosis and heart dysfunction. BRCA1 mutation carriers, in addition to risk of breast and ovarian cancer, may be at a previously unrecognized risk of cardiac failure.

The tumour suppressor BRCA1 is mutated in familial breast and ovarian cancer. Now, Shukla et al. demonstrate that mice lacking BRCA1 in cardiomyocytes are more sensitive to ischaemia than control mice, and that BRCA1 is elevated in human tissues exposed to ischaemia, suggesting a cardioprotective role for BRCA1.

GADD45A protects against cell death in dorsal root ganglion neurons following peripheral nerve injury

A significant loss of neurons in the dorsal root ganglia (DRG) has been reported in animal models of peripheral nerve injury. Neonatal sensory neurons are more susceptible than adult neurons to axotomy- or nerve growth factor (NGF) withdrawal-induced cell death. To develop therapies for preventing irreversible sensory cell loss, it is essential to understand the molecular mechanisms responsible for DRG cell death and survival. Here we describe how the expression of the growth arrest- and DNA damage-inducible gene 45α (GADD45A) is correlated with neuronal survival after axotomy in vivo and after NGF withdrawal in vitro. GADD45A expression is low at birth and does not change significantly after spinal nerve ligation (SNL). In contrast, GADD45A is robustly up-regulated in the adult rat DRG 24 hr after SNL, and this up-regulation persists as long as the injured fibers are prevented from regenerating. In vitro delivery of GADD45A protects neonatal rat DRG neurons from NGF withdrawal-induced cytochrome c release and cell death. In addition, in vivo knockdown of GADD45A expression in adult injured DRG by small hairpin RNA increased cell death. Our results indicate that GADD45A protects neuronal cells from SNL-induced cell death.

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

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

The functional genome of CA1 and CA3 neurons under native conditions and in response to ischemia

BACKGROUND

The different physiological repertoire of CA3 and CA1 neurons in the hippocampus, as well as their differing behaviour after noxious stimuli are ultimately based upon differences in the expressed genome. We have compared CA3 and CA1 gene expression in the uninjured brain, and after cerebral ischemia using laser microdissection (LMD), RNA amplification, and array hybridization.

RESULTS

Profiling in CA1 vs. CA3 under normoxic conditions detected more than 1000 differentially expressed genes that belong to different, physiologically relevant gene ontology groups in both cell types. The comparison of each region under normoxic and ischemic conditions revealed more than 5000 ischemia-regulated genes for each individual cell type. Surprisingly, there was a high co-regulation in both regions. In the ischemic state, only about 100 genes were found to be differentially expressed in CA3 and CA1. The majority of these genes were also different in the native state. A minority of interesting genes (e.g. inhibinbetaA) displayed divergent expression preference under native and ischemic conditions with partially opposing directions of regulation in both cell types.

CONCLUSION

The differences found in two morphologically very similar cell types situated next to each other in the CNS are large providing a rational basis for physiological differences. Unexpectedly, the genomic response to ischemia is highly similar in these two neuron types, leading to a substantial attenuation of functional genomic differences in these two cell types. Also, the majority of changes that exist in the ischemic state are not generated de novo by the ischemic stimulus, but are preexistant from the genomic repertoire in the native situation. This unexpected influence of a strong noxious stimulus on cell-specific gene expression differences can be explained by the activation of a cell-type independent conserved gene-expression program. Our data generate both novel insights into the relation of the quiescent and stimulus-induced transcriptome in different cells, and provide a large dataset to the research community, both for mapping purposes, as well as for physiological and pathophysiological research.

Novel roles for metallothionein-I + II (MT-I + II) in defense responses, neurogenesis, and tissue restoration after traumatic brain injury: Insights from global gene expression profiling in wild-type and MT-I + II knockout mice

Traumatic injury to the brain is one of the leading causes of injury-related death or disability, especially among young people. Inflammatory processes and oxidative stress likely underlie much of the damage elicited by injury, but the full repertoire of responses involved is not well known. A genomic approach, such as the use of microarrays, provides much insight in this regard, especially if combined with the use of gene-targeted animals. We report here the results of one of these studies comparing wild-type and metallothionein-I + II knockout mice subjected to a cryolesion of the somatosensorial cortex and killed at 0, 1, 4, 8, and 16 days postlesion (dpl) using Affymetrix genechips/oligonucleotide arrays interrogating approximately 10,000 different murine genes (MG_U74Av2). Hierarchical clustering analysis of these genes readily shows an orderly pattern of gene responses at specific times consistent with the processes involved in the initial tissue injury and later regeneration of the parenchyma, as well as a prominent effect of MT-I + II deficiency. The results thoroughly confirmed the importance of the antioxidant proteins MT-I + II in the response of the brain to injury and opened new avenues that were confirmed by immunohistochemistry. Data in KO, MT-I-overexpressing, and MT-II-injected mice strongly suggest a role of these proteins in postlesional activation of neural stem cells.

Brain response to traumatic brain injury in wild-type and interleukin-6 knockout mice: a microarray analysis

Traumatic injury to the brain is one of the leading causes of injury-related death or disability. Brain response to injury is orchestrated by cytokines, such as interleukin (IL)-6, but the full repertoire of responses involved is not well known. We here report the results obtained with microarrays in wild-type and IL-6 knockout mice subjected to a cryolesion of the somatosensorial cortex and killed at 0, 1, 4, 8 and 16 days post-lesion. Overall gene expression was analyzed by using Affymetrix genechips/oligonucleotide arrays with approximately 12,400 probe sets corresponding to approximately 10,000 different murine genes (MG_U74Av2). A robust, conventional statistical method (two-way anova) was employed to select the genes significantly affected. An orderly pattern of gene responses was clearly detected, with genes being up- or down-regulated at specific timings consistent with the processes involved in the initial tissue injury and later regeneration of the parenchyma. IL-6 deficiency showed a dramatic effect in the expression of many genes, especially in the 1 day post-lesion timing, which presumably underlies the poor capacity of IL-6 knockout mice to cope with brain damage. The results highlight the importance of IL-6 controlling the response of the brain to injury as well as the suitability of microarrays for identifying specific targets worthy of further study.

Induced hippocampal neuron protection in an optimized gerbil ischemia model: insult thresholds for tolerance induction and altered gene expression defined by ischemic depolarization

Preconditioning of hippocampal CA1 neurons was evaluated in a gerbil model of transient global ischemia using extracellular recording of DC potential shifts characteristic of ischemic depolarization to precisely define the duration of both priming and test insults. Brief ischemia resulting in depolarizations of 2.5 to 3.5 minutes consistently induced maximal tolerance (95% protection) against subsequent challenges 2 days later with an approximate doubling of the insult duration required for complete CA1 neuron loss from 6 to 12 minutes depolarization when evaluated 1 week after the test insult. Significant protection persisted at 2 months survival, although the apparent injury threshold regressed to approximately 8 minutes, indicating delayed progression of injury after longer test insults. In situ hybridization was used to evaluate depolarization thresholds for induction of mRNAs encoding the 70 kDa heat shock/stress protein, hsp72, as well as several immediate-early genes (c-fos, c-jun, junB, and junD). Immediate-early genes were prominently expressed after short insults inducing tolerance, whereas appreciable hsp72 induction only occurred after insults approaching the threshold for neuron injury. These results establish an ischemic preconditioning model with the predictability needed for mechanistic studies and demonstrate that prior transcriptional activation of the postischemic heat shock response is not required for expression of delayed tolerance.

Inducible repair of oxidative DNA lesions in the rat brain after transient focal ischemia and reperfusion

To determine the role of oxidative DNA damage and repair in brain injury after focal ischemia and reperfusion, the authors investigated DNA base damage and DNA base excision repair (BER) capacity, the predominant repair mechanism for oxidative DNA lesions, in the rat model of temporary middle cerebral artery occlusion. Contents of 8-hydroxyl-2'-deoxyguanosine (8-oxodG) and apurinic/apyrimidinic abasic site (AP site), hallmarks of oxidative DNA damage, were quantitatively measured in nuclear DNA extracts from brains 0.25 to 72 hours after 1 hour of middle cerebral artery occlusion. In parallel to the detection of DNA lesions, the capacity for 8-oxodG- or AP site-dependent DNA repair synthesis was measured in nuclear protein extracts using specific in vitro DNA repair assays. After postischemic reperfusion, the levels of 8-oxodG and AP sites were markedly increased in ischemic tissues. In frontal/parietal cortex, regions that survived ischemia, 8-oxodG and AP sites were efficiently repaired during reperfusion. However, in the caudate, a region that was destined to infarct, the DNA lesions were poorly repaired. In consistent with the patterns of endogenous lesion repair, a markedly induced and long-lasting (at least 72 hours) BER activity was detected in the cortex but not in the caudate after ischemia. The induced BER activity in ischemic cortex was attributed to the upregulation of gene expression and activation of selective BER enzymes, particularly DNA polymerase-beta and OGG1. These results strongly suggest that inducible DNA BER constitutes an important endogenous mechanism that protects brain against ischemia-induced oxidative neuronal injury.

Selective up-regulation of the growth arrest DNA damage-inducible gene Gadd45 alpha in sensory and motor neurons after peripheral nerve injury

The growth arrest and DNA damage-inducible gene 45 alpha (Gadd45a) was one of 240 genes found previously by high density oligonucleotide microarray analysis to be regulated in the rat L4 and L5 dorsal root ganglia 3 days after transection of the sciatic nerve (>four-fold up-regulation). The Gadd45a mRNA expression profile investigated by northern blot, RNase protection assay and in situ hybridization in the rat shows negligible constitutive mRNA levels in embryonic, neonatal or adult intact dorsal root ganglia. Within 24 h of a sciatic nerve injury, a very large induction is found that persists for as long as regeneration of injured fibres is prevented by peripheral nerve ligation. When axons are allowed to regrow following sciatic nerve crush injury, Gadd45a expression is terminated at later time points, when levels of other markers of injury return towards normal. Colocalization with activating transcription factor 3-LI and c-jun mRNA implies that all peripherally injured primary sensory and motor neurons express Gadd45a mRNA. Injury to the central axons of dorsal root ganglion neurons produces only a minimal induction of Gadd45a while peripheral inflammation is without effect. Gadd45a is a specific marker of the presence of peripheral axonal injury in adult primary sensory and motor neurons.

Gene profiling in spinal cord injury shows role of cell cycle in neuronal death

Spinal cord injury causes secondary biochemical changes leading to neuronal cell death. To clarify the molecular basis of this delayed injury, we subjected rats to spinal cord injury and identified gene expression patterns by high-density oligonucleotide arrays (8,800 genes studied) at 30 minutes, 4 hours, 24 hours, or 7 days after injury (total of 26 U34A profiles). Detailed analyses were limited to 4,300 genes consistently expressed above background. Temporal clustering showed rapid expression of immediate early genes (30 minutes), followed by genes associated with inflammation, oxidative stress, DNA damage, and cell cycle (4 and 24 hours). Functional clustering showed a novel pattern of cell cycle mRNAs at 4 and 24 hours after trauma. Quantitative reverse transcription polymerase chain reaction verified mRNA changes in this group, which included gadd45a, c-myc, cyclin D1 and cdk4, pcna, cyclin G, Rb, and E2F5. Changes in their protein products were quantified by Western blot, and cell-specific expression was determined by immunocytochemistry. Cell cycle proteins showed an increased expression 24 hours after injury and were, in part, colocalized in neurons showing morphological evidence of apoptosis. These findings suggest that cell cycle-related genes, induced after spinal cord injury, are involved in neuronal damage and subsequent cell death.

Extensive oligonucleotide microarray transcriptome analysis of the rat cerebral artery and arachnoid tissue

Cerebral vessels have certain distinct anatomical and developmental characteristics which are well known, but their characteristic genetic expression profile remains as yet only poorly understood. We investigated gene expression in the rat cerebral artery in comparison with the rat descending aorta, two locations which have obviously different anatomical and developmental characteristics. Since the contamination of cerebral small arteries by arachnoid tissue is to a certain extent inevitable, we also performed a gene expression analysis of arachnoid tissue as a background. In an effort to obtain the necessary quality and quantity of total RNA, a novel freeze-fracture apparatus minimizing the time required for the entire procedure from tissue separation to RNA preparation was used. With the material obtained, a group of genes highly expressed in each tissue was detected by oligonucleotide microarray analysis. In the circle of Willis, peptide-19 (PEP-19), connexin-37 (CXN-37), growth arrest-and DNA damage-inducible gene (GADD45), and the putative G protein coupled receptor RA1c, Notch-1, and jagged-1 were predominantly expressed. In arachnoid tissue, bone morphologic protein (BMP)-7, BMP-6, beta defensin-1, neuroendocrine protein 7B2, thiol-specific antioxidant protein, IL-18, beta-chain clathrin-associated protein complex AP-1, and angiopoietin-2 were highly expressed. In the aorta, most of the abundantly expressed genes related to lipid metabolism. By means of oligonucleotide microarray analysis, the distinct gene expression profiles in the circle of Willis arachnoid tissue, and aorta were made evident. From these findings it is reasonable to conclude that a functional interaction exists between the circle of Willis and arachnoid tissue.

Replicate high-density rat genome oligonucleotide microarrays reveal hundreds of regulated genes in the dorsal root ganglion after peripheral nerve injury

BACKGROUND

Rat oligonucleotide microarrays were used to detect changes in gene expression in the dorsal root ganglion (DRG) 3 days following sciatic nerve transection (axotomy). Two comparisons were made using two sets of triplicate microarrays, naïve versus naïve and naïve versus axotomy.

RESULTS

Microarray variability was assessed using the naïve versus naïve comparison. These results support use of a P < 0.05 significance threshold for detecting regulated genes, despite the large number of hypothesis tests required. For the naïve versus axotomy comparison, a 2-fold cut off alone led to an estimated error rate of 16%; combining a >1.5-fold expression change and P < 0.05 significance reduced the estimated error to 5%. The 2-fold cut off identified 178 genes while the combined >1.5-fold and P < 0.05 criteria generated 240 putatively regulated genes, which we have listed. Many of these have not been described as regulated in the DRG by axotomy. Northern blot, quantitative slot blots and in situ hybridization verified the expression of 24 transcripts. These data showed an 83% concordance rate with the arrays; most mismatches represent genes with low expression levels reflecting limits of array sensitivity. A significant correlation was found between actual mRNA differences and relative changes between microarrays (r2 = 0.8567). Temporal patterns of individual genes regulation varied.

CONCLUSIONS

We identify parameters for microarray analysis which reduce error while identifying many putatively regulated genes. Functional classification of these genes suggest reorganization of cell structural components, activation of genes expressed by immune and inflammatory cells and down-regulation of genes involved in neurotransmission.

Genomic responses of the brain to ischemic stroke, intracerebral haemorrhage, kainate seizures, hypoglycemia, and hypoxia

RNA expression profiles in rat brain were examined 24 h after ischemic stroke, intracerebral haemorrhage, kainate-induced seizures, insulin-induced hypoglycemia, and hypoxia and compared to sham- or untouched controls. Rat oligonucleotide microarrays were used to compare expression of over 8000 transcripts from three subjects in each group (n = 27). Of the somewhat less than 4000 transcripts called 'present' in normal or treated cortex, 5-10% of these were up-regulated 24 h after ischemia (415), haemorrhage (205), kainate (187), and hypoglycemia (302) with relatively few genes induced by 6 h of moderate (8% oxygen) hypoxia (15). Of the genes induced 24 h after ischemia, haemorrhage, and hypoglycemia, approximately half were unique for each condition suggesting unique components of the responses to each of the injuries. A significant component of the responses involved immune-process related genes likely to represent responses to dying neurons, glia and vessels in ischemia; to blood elements in haemorrhage; and to the selectively vulnerable neurons that die after hypoglycemia. All of the genes induced by kainate were also induced either by ischemia, haemorrhage or hypoglycemia. This strongly supports the concept that excitotoxicity not only plays an important role in ischemia, but is an important mechanism of brain injury after intracerebral haemorrhage and hypoglycemia. In contrast, there was only a single gene that was down-regulated by all of the injury conditions suggesting there is not a common gene down-regulation response to injury.

Caspase-activated DNase/DNA fragmentation factor 40 mediates apoptotic DNA fragmentation in transient cerebral ischemia and in neuronal cultures

Nuclear changes, including internucleosomal DNA fragmentation, are characteristic features of neuronal apoptosis resulting from transient cerebral ischemia and related brain insults for which the molecular mechanism has not been elucidated. Recent studies suggest that a caspase-3-mediated mechanism may be involved in the process of nuclear degradation in ischemic neurons. In this study, we cloned from rat brain a homolog cDNA encoding caspase-activated deoxyribonuclease (CAD)/DNA fragmentation factor 40 (DFF40), a 40 kDa nuclear enzyme that is activated by caspase-3 and promotes apoptotic DNA degradation. Subsequently, we investigated the role of CAD/DFF40 in the induction of internucleosomal DNA fragmentation in the hippocampus in a rat model of transient global ischemia and in primary neuronal cultures under ischemia-like conditions. At 8-72 hr after ischemia, CAD/DFF40 mRNA and protein were induced in the degenerating hippocampal CA1 neurons. CAD/DFF40 formed a heterodimeric complex in the nucleus with its natural inhibitor CAD (ICAD) and was activated after ischemia in a delayed manner (>24 hr) by caspase-3, which translocated into the nucleus and cleaved ICAD. Furthermore, an induced CAD/DFF40 activity was detected in nuclear extracts in both in vivo and in vitro models, and the DNA degradation activity of CAD/DFF40 was inhibited by purified ICAD protein. These results strongly suggest that CAD/DFF40 is the endogenous endonuclease that mediates caspase-3-dependent internucleosomal DNA degradation and related nuclear alterations in ischemic neurons.

Neuronal death is an active, caspase-dependent process after moderate but not severe DNA damage

Mild insults to neurons caused by ischemia or glutamate induce apoptosis, whereas severe insults induce non apoptotic death, such as necrosis. The molecular targets that are damaged by these insults and ultimately induce cell death are not fully established. To determine if DNA damage can induce apoptotic or non apoptotic death depending on the severity, neurons were treated with up to 128 Gy of ionizing radiation. Such treatment induced a dose-related increase in DNA single-strand breaks but no immediate membrane disruption or lipid peroxidation. Following moderate doses of < or = 32 Gy, neuronal death had many characteristics of apoptosis including nuclear fragmentation and DNA laddering. Nuclear fragmentation and membrane breakdown after moderate DNA damage could be blocked by inhibition of active protein synthesis with cycloheximide and by inhibition of caspases. In contrast, cell death after doses of > 32 Gy was not blocked by cycloheximide or caspase inhibitors, and membrane breakdown occurred relatively early in the cell death process. These data suggest that cell death after high dose irradiation and severe DNA damage can occur by non apoptotic mechanisms and that blocking apoptotic pathways may not prevent death after severe damage.

Mechanisms underlying hypoxia-induced neuronal apoptosis

In vivo models of cerebral hypoxia-ischemia have shown that neuronal death may occur via necrosis or apoptosis. Necrosis is, in general, a rapidly occurring form of cell death that has been attributed, in part, to alterations in ionic homeostasis. In contrast, apoptosis is a delayed form of cell death that occurs as the result of activation of a genetic program. In the past decade, we have learned considerably about the mechanisms underlying apoptotic neuronal death following cerebral hypoxia-ischemia. With this growth in knowledge, we are coming to the realization that apoptosis and necrosis, although morphologically distinct, are likely part of a continuum of cell death with similar operative mechanisms. For example, following hypoxia-ischemia, excitatory amino acid release and alterations in ionic homeostasis contribute to both necrotic and apoptotic neuronal death. However, apoptosis is distinguished from necrosis in that gene activation is the predominant mechanism regulating cell survival. Following hypoxic-ischemic episodes in the brain, genes that promote as well as inhibit apoptosis are activated. It is the balance in the expression of pro- and anti-apoptotic genes that likely determines the fate of neurons exposed to hypoxia. The balance in expression of pro- and anti-apoptotic genes may also account for the regional differences in vulnerability to hypoxic insults. In this review, we will examine the known mechanisms underlying apoptosis in neurons exposed to hypoxia and hypoxia-ischemia.

Overexpression of the cell death suppressor Bcl-w in ischemic brain: implications for a neuroprotective role via the mitochondrial pathway

Bcl-w is a newly described cell death suppressor member of the Bcl-2 gene family. As these genes may have a role in the outcome of ischemic brain injury, the regional expression of Bcl-w protein in rat brain was examined at 6 to 72 hours after 90 minutes of transient middle cerebral artery occlusion. Bcl-w protein, although constitutively expressed at low levels in nonischemic brain, was found to be overexpressed in ischemic brain at all time points studied. Up-regulation of Bcl-w protein was particularly abundant in the penumbral region of the cortex and mainly in cells lacking DNA fragmentation. In the cortical penumbra, Bcl-w protein was detected predominantly in neurons and showed mitochondrial localization, as determined using double-label immunohistochemistry. Bcl-w expression was also detectable, to a lesser extent, in reactive astrocytes in the infarct border zone and in microvessel walls in the infarct regions. At the mechanistic level, incubation of isolated brain mitochondria with the addition of recombinant Bax or high concentration of calcium resulted in release of cytochrome c from the mitochondria. In the presence of recombinant Bcl-w protein, however, the release of cytochrome c induced by Bax or calcium was largely inhibited. Further, recombinant Bcl-w protein inhibited calcium-induced loss of mitochondrial transmembrane potential, indicative of permeability transition, in a dose-dependent manner. These results suggest that Bcl-w may be an endogenous neuroprotectant against ischemic neuronal death and that, like its analogues such as Bcl-2 and Bcl-x-long, Bcl-w may achieve this protection via the mitochondrial death-regulatory pathway.

DNA damage in human leukocytes after ischemia/reperfusion injury

Leukocytes have been shown to play an important role in the development of tissue injury after ischemia and reperfusion (I/R). In the present study, the effects of tourniquet-ischemia on induction of DNA damage in peripheral leukocytes and on respiratory burst of neutrophils in humans were examined. The DNA damage was measured as increased migration of DNA using the single-cell gel-electrophoresis technique (comet assay). Intracellular production of reactive oxygen species by neutrophils was measured flow-cytometrically using dihydrorhodamine 123 as indicator. Postischemic, significantly increased migration of DNA was found in leukocytes of 20 patients (tourniquet-ischemia of the lower limb for 65-130 min, anterior-cruciate-ligament-reconstruction) and in 10 experiments (1 volunteer, repeated tourniquet-ischemia of the upper limb for 60 min, no operation). DNA effects were most pronounced 5-30 min after tourniquet release, and then declined over a 2 h period, but did not return to preischemic baseline values. A similar time course showed the oxidative status of unstimulated granulocytes during reperfusion. Simultaneously, opposing changes were measured in formyl peptide (f-MLP)- or phorbol ester (PMA)-stimulated granulocytes, which showed a significantly declined respiratory burst reaction after tourniquet-release indicating preactivation of neutrophils by IR. Our data suggest that IR induces genotoxic effects in human leukocytes presumably in response to oxidative stress during reperfusion.

Relationship between seizure-induced transcription of the DNA damage-inducible gene GADD45, DNA fragmentation, and neuronal death in focally evoked limbic epilepsy

We investigated the temporal and spatial profile of mRNA transcription for the growth arrest and DNA damage-inducible gene GADD45, DNA fragmentation, and neuronal death in rat brain following focally evoked limbic seizures. GADD45 mRNA was detected by in situ hybridization, whereas fragmented DNA was detected using in situ nick end-labeling by the large (Klenow) fragment of DNA polymerase I. Kainic acid (0.1 microg) was injected into the right amygdala of rats to induce seizures for 45 min, after which diazepam (30 mg/kg) was administered. GADD45 mRNA, DNA fragmentation, and cell death were quantified bilaterally within six limbic brain regions 0-96 h following seizure cessation. All animals underwent seizures of equivalent severity and duration as determined electrographically. In situ hybridization detected bilateral up-regulation of GADD45 mRNA throughout the CA1, CA3, and dentate gyrus of the hippocampus, the piriform and retrosplenial cortices, and the thalamus within 1 h of seizure termination. GADD45 mRNA levels remained elevated for up to 6 h, declining to baseline within all structures by 16 h. Klenow-positive cells were only found within the CA3 pyramidal layer of the ipsilateral hippocampus and appeared 16-72 h following seizure cessation. Morphologic cell death was also restricted to the CA3 subfield. These data demonstrate that focally evoked limbic seizures trigger early bihemispheric GADD45 mRNA transcription within connected limbic structures, whereas subsequent DNA fragmentation and cell death are restricted to selectively vulnerable brain regions.

DNA damage and DNA damage-inducible protein Gadd45 following ischemia in the P7 neonatal rat

Cerebral ischemia in adult rodents leads to the production of several types of lesions in the genomic DNA, followed by the activation of the damage-response indicator Gadd45. Our purpose was to investigate the structural changes that occur in chromatin DNA and repair processes after ischemic injury in neonatal brain. Neonatal ischemia was induced by the permanent left MCA occlusion in association with 1 h occlusion of the left common carotid artery in 7-day-old Wistar pups. Oligonucleosome fragments that are recognized as the characteristic DNA ladder was observed in a delayed fashion. Double-strand breaks result in high molecular weight fragments of 50- and 300-kbp as demonstrated by pulsed-field gel electrophoresis, and visualized by the TUNEL assay at 24 h of recovery. In contrast, DNA single-strand breaks, shown by the use of DNA polymerase I-mediated biotin-dATP nick translation were not so abundant. Gadd45 immunoreactivity was sequentially increased in vulnerable neurons in the infarct (4 to 24 h) and in sublethally injured neurons in the penumbra (24-48 h). Taken together, these findings suggest that Gadd45 responds to DNA damage following neonatal ischemia. Furthermore, repairing processes seem to be more active in the penumbra and therefore Gadd45 could have also a protective role in cerebral ischemia.

Identification of beta-amyloid-responsive genes by RNA differential display: early induction of a DNA damage-inducible gene, gadd45

Alzheimer's disease is a neurodegenerative disorder characterized by the extracellular deposition in the brain of amyloid beta-peptide (A beta), presumed to play a pathogenic role. However, the precise molecular mechanisms of its neurotoxicity are not fully understood. Recent studies have suggested that it may exert its toxic effect via activation of transcription factors. We investigated A beta-responsive genes in human preneuron NT2 cells, at early stages of A beta (25-35) exposure, by RNA differential display. A beta induced the expression of (i) the growth arrest and DNA damage-inducible gene (gadd45) implicated in the DNA excision-repair process; (ii) a stress-signaling kinase gene encoding the mitogen-activated protein kinase/Erk kinase kinase-1 (MEKK1); (iii) a new growth factor-inducible immediate-early gene, CYR61, the product of which functions as an extracellular matrix signaling molecule; (iv) other immediate-early genes, such as c-jun and c-fos; (v) the gene encoding the basic fibroblast growth factor (bFGF); (vi) a gene encoding a constituent of the mitochondrial pyruvate dehydrogenase complex, the dihydrolipoamide dehydrogenase-binding protein (E3-BP); and (vii) an unidentified human gene (KIAA0099). A beta not only activates but also respresses genes: (i) the gene encoding "hinge" protein, a subunit of the mitochondrial cytochrome-c reductase and (ii) the SRp55 gene encoding a splicing factor involved in constitutive pre-mRNA splicing and alternative splice site selection. Our results underscored A beta-responsive genes that play key roles in the response (damage/recovery) of neuron cells to A beta exposure. In particular, the strong upregulation of gadd45, indicating DNA damage, was detected early in A beta cytotoxicity. This suggests that DNA strand breaks occurred rapidly in cells exposed to A beta, which may be a critical event in A beta neurotoxicity.

Pixel-based image analysis of HSP70, GADD45 and MAP2 mRNA expression after focal cerebral ischemia: hemodynamic and histological correlates

Gene expression studies with in situ hybridization after focal brain ischemia indicate a variety of distinct anatomical patterns. An important question is to what extent such reactive gene expression correlates with neuronal damage or survival. To study these questions, we focused on two stressed-induced genes, heat shock protein 70 (HSP70) and growth-arrest and DNA damage-inducible gene (GADD) 45 mRNA, and we compared reactive changes in mRNA to loss of the constitutive signal for microtubule-associated protein 2 (MAP2) mRNA. A pixel-based image analysis of mRNA signals was carried out using a highly reproducible model of focal brain ischemia. A poly-l-lysine coated filament was used to occlude the origin of the middle cerebral artery (MCA) for 2 h in ventilated, normothermic rats. Brains were collected after 0, 1, 3 and 6 h, and 1, 3 and 7 days. In situ hybridization analysis was carried out for HSP70 mRNA, GADD45 mRNA and MAP2 mRNA. Autoradiographic data sets were averaged and co-mapped into a common template of the rat brain. These data sets were then compared on a pixel-by-pixel basis with previously acquired image data sets derived from quantitative studies of local cerebral blood flow (LCBF) (obtained at the end of 2-h ischemia) of and infarctive histopathology (obtained at 3 days) in the same focal ischemia model. HSP70 mRNA and GADD45 mRNA were grossly elevated in the hemisphere subjected to ischemia during the first day. Pixel-based analysis showed a strong correlation between HSP70 mRNA signals, the degree of early blood-flow reduction and the probability of histological infarction. GADD45 mRNA was expressed in a more variable fashion. Decreases in MAP2 mRNA signals at 1, 3 and 7 days correlated strongly with histological infarction. These co-mapping procedures allow us to conclude that HSP70 mRNA is a robust indicator of ischemic stress and histological outcome after 2 h of focal brain ischemia. The topographic features of GADD45 expression suggest its possible role in conferring resistance to ischemic injury. Finally, our results indicate that local decreases in constitutive MAP2 expression at 1 day and beyond may be used as a robust marker of tissue regions having a high probability of focal infarction.

Induction of caspase-3-like protease may mediate delayed neuronal death in the hippocampus after transient cerebral ischemia

Delayed neuronal death after transient cerebral ischemia may be mediated, in part, by the induction of apoptosis-regulatory gene products. Caspase-3 is a newly characterized mammalian cysteine protease that promotes cell death during brain development, in neuronal cultures, and in other cell types under many different conditions. To determine whether caspase-3 serves to regulate neuronal death after cerebral ischemia, we have (1) cloned a cDNA encoding the rat brain caspase-3; (2) examined caspase-3 mRNA and protein expression in the brain using in situ hybridization, Northern and Western blot analyses, and double-labeled immunohistochemistry; (3) determined caspase-3-like activity in brain cell extracts; and (4) studied the effect of caspase-3 inhibition on cell survival and DNA fragmentation in the hippocampus in a rat model of transient global ischemia. At 8-72 hr after ischemia, caspase-3 mRNA and protein were induced in the hippocampus and caudate-putamen (CPu), accompanied by increased caspase-3-like protease activity. In the hippocampus, caspase-3 mRNA and protein were predominantly increased in degenerating CA1 pyramidal neurons. Proteolytic activation of the caspase-3 precursor was detected in hippocampus and CPu but not in cortex at 4-72 hr after ischemia. Double-label experiments detected DNA fragmentation in the majority of CA1 neurons and selective CPu neurons that overexpressed caspase-3. Furthermore, ventricular infusion of Z-DEVD-FMK, a caspase-3 inhibitor, decreased caspase-3 activity in the hippocampus and significantly reduced cell death and DNA fragmentation in the CA1 sector up to 7 d after ischemia. These data strongly suggest that caspase-3 activity contributes to delayed neuronal death after transient ischemia.