Adenovirus-mediated Bcl-X(L) expression using a neuron-specific synapsin-1 promoter protects against disseminated neuronal injury and brain infarction following focal cerebral ischemia in mice

Truncated Dyrk1A aggravates neuronal apoptosis by inhibiting ASF-mediated Bcl-x exon 2b inclusion

AIM

Aggravated neuronal loss, caused mainly by neuronal apoptosis, is observed in the brain of patients with Alzheimer's disease (AD) and animal models of AD. A truncated form of Dual-specific and tyrosine phosphorylation-regulated protein kinase 1A (Dyrk1A) plays a vital role in AD pathogenesis. Downregulation of anti-apoptotic Bcl-xL is tightly correlated with neuronal loss in AD. However, the molecular regulation of neuronal apoptosis and Bcl-x expression by Dyrk1A in AD remains largely elusive. Here, we aimed to explore the role and molecular mechanism of Dyrk1A in apoptosis.

METHODS

Cell Counting Kit-8 (CCK8), flow cytometry, and TdT-mediated dUTP Nick-End Labeling (TUNEL) were used to check apoptosis. The cells, transfected with Dyrk1A or/and ASF with Bcl-x minigene, were used to assay Bcl-x expression by RT-PCR and Western blots. Co-immunoprecipitation, autoradiography, and immunofluorescence were conducted to check the interaction of ASF and Dyrk1A. Gene set enrichment analysis (GSEA) of apoptosis-related genes was performed in mice overexpressing Dyrk1A (TgDyrk1A) and AD model 5xFAD mice.

RESULTS

Dyrk1A promoted Bcl-xS expression and apoptosis. Splicing factor ASF promoted Bcl-x exon 2b inclusion, leading to increased Bcl-xL expression. Dyrk1A suppressed ASF-mediated Bcl-x exon 2b inclusion via phosphorylation. The C-terminus deletion of Dyrk1A facilitated its binding and kinase activity to ASF. Moreover, Dyrk1a1-483 further suppressed the ASF-mediated Bcl-x exon 2b inclusion and aggravated apoptosis. The truncated Dyrk1A, increased Bcl-xS, and enrichment of apoptosis-related genes was observed in the brain of 5xFAD mice.

CONCLUSIONS

We speculate that increased Dyrk1A and truncated Dyrk1A may aggravate neuronal apoptosis by decreasing the ratio of Bcl-xL/Bcl-xS via phosphorylating ASF in AD.

Apoptotic cell death in disease-Current understanding of the NCCD 2023

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions. Here, the Nomenclature Committee on Cell Death (NCCD) gathered to critically summarize an abundant pre-clinical literature mechanistically linking the core apoptotic apparatus to organismal homeostasis in the context of disease.

Delayed Therapeutic Administration of Melatonin Enhances Neuronal Survival Through AKT and MAPK Signaling Pathways Following Focal Brain Ischemia in Mice

Melatonin has a role in the cell survival signaling pathways as a candidate for secondary stroke prevention. Therefore, in the present study, the coordination of ipsilateral and contralateral hemispheres to evaluate delayed post-acute effect of melatonin was examined on recovery of the cell survival and apoptosis after stroke. Melatonin was administered (4 mg/kg/day) intraperitoneally for 45 days, starting 3 days after 30 min of middle cerebral artery occlusion. The genes and proteins related to the cell survival and apoptosis were investigated by immunofluorescence, western blotting, and RT-PCR techniques after behavioral experiments. Melatonin produced delayed neurological recovery by improving motor coordination on grip strength and rotarod tests. This neurological recovery was also reflected by high level of NeuN positive cells and low level of TUNEL-positive cells suggesting enhanced neuronal survival and reduced apoptosis at the fifty-fifth day of stroke. The increase of NGF, Nrp1, c-jun; activation of AKT; and dephosphorylation of ERK and JNK at the fifty-fifth day showed that cell survival and apoptosis signaling molecules compete to contribute to the remodeling of brain. Furthermore, an increase in the CREB and Atf-1 expressions suggested the melatonin's strong reformative effect on neuronal regeneration. The contralateral hemisphere was more active at the latter stages of the molecular and functional regeneration which provides a further proof of principle about melatonin's action on the promotion of brain plasticity and recovery after stroke.

Evaluation of Gene Therapy as an Intervention Strategy to Treat Brain Injury from Stroke

Stroke is a leading cause of death and disability, with a lack of treatments available to prevent cell death, regenerate damaged cells and pathways, or promote neurogenesis. The extended period of hours to weeks over which tissue damage continues to occur makes this disorder a candidate for gene therapy. This review highlights the development of gene therapy in the area of stroke, with the evolution of viral administration, in experimental stroke models, from pre-injury to clinically relevant timeframes of hours to days post-stroke. The putative therapeutic proteins being examined include anti-apoptotic, pro-survival, anti-inflammatory, and guidance proteins, targeting multiple pathways within the complex pathology, with promising results. The balance of findings from animal models suggests that gene therapy provides a viable translational platform for treatment of ischemic brain injury arising from stroke.

Pair housing reverses post-stroke depressive behavior in mice

Social isolation (SI) has been linked epidemiologically to high rates of morbidity and mortality following stroke. In contrast, strong social support enhances recovery and lowers stroke recurrence. However, the mechanism by which social support influences stroke recovery has not been adequately explored. The goal of this study was to examine the effect of post-stroke pair housing and SI on behavioral phenotypes and chronic functional recovery in mice. Young male mice were paired for 14 days before a 60 min transient middle cerebral artery occlusion (MCAO) or sham surgery and assigned to various housing environments immediately after stroke. Post-stroke mice paired with either a sham or stroke partner showed significantly higher (P<0.05) sociability after MCAO than isolated littermates. Sociability deficits worsened over time in isolated animals. Pair-housed mice showed restored sucrose consumption (P<0.05) and reduced immobility in the tail suspension test compared to isolated cohorts. Pair-housed stroked mice demonstrated significantly reduced cerebral atrophy after 6 weeks (17.5 ± 1.5% in PH versus 40.8 ± 1.3% in SI; P<0.001). Surprisingly, total brain arginase-1, a marker of a M2 "alternatively activated" myeloid cells was higher in isolated mice. However, a more detailed assessment of cellular expression showed a significant increase in the number of microglia that co-labeled with arginase-1 in the peri-infarct region in PH stroke mice compared to SI mice. Pair housing enhances sociability and reduces avolitional and anhedonic behavior. Pair housing reduced serum IL-6 and enhanced peri-infarct microglia arginase-1 expression. Social interaction reduces post-stroke depression and improves functional recovery.

Neuroprotection of neurotrophin-3 against focal cerebral ischemia/reperfusion injury is regulated by hypoxia-responsive element in rats

Exogenous delivery of the neurotrophin-3 (NT-3) gene may provide a potential therapeutic strategy for ischemic stroke. To investigate the neuroprotective effects of NT-3 expression controlled by 5HRE after focal cerebral ischemia, we constructed a recombinant retrovirus vector (RV) with five copies of hypoxia-responsive elements (5HRE or 5H) and NT-3 and delivered it to the rat brain. Three groups of rats received RV-5H-NT3, RV-5H-EGFP or saline injection. Three days after gene transfer, the rats underwent 90min of transient middle cerebral artery occlusion (tMCAO), followed by 1-28days of reperfusion. Three days after tMCAO, brain NT-3 expression was significantly increased in the RV-5H-NT3-transduced animals compared with the RV-5H-EGFP or saline group, and brain infarct volume was smaller in the RV-5H-NT3-transduced group than the RV-5H-EGFP or saline group. The percentage of TUNEL-positive cells was reduced in RV-5H-NT3-transduced brains compared with the RV-5H-EGFP or saline group 3 and 7days after tMCAO. Furthermore, the neurological status of RV-5H-NT3-transduced rats was better than that of RV-5H-EGFP- or saline-transduced animals from 1day to 4weeks after tMCAO. Our results demonstrated that 5HRE could modulate NT-3 expression in the ischemic brain environment and that the up-regulated NT-3 could effectively improve neurological status following tMCAO due to decreased initial damage. To avoid unexpected side effects, 5HRE-controlled gene expression might be a useful tool for gene therapy of ischemic disorders in the central nervous system.

Protective functions of taurine against experimental stroke through depressing mitochondria-mediated cell death in rats

Taurine, an abundant amino acid in the nervous system, is reported to reduce ischemic brain injury in a dose-dependent manner. This study was designed to investigate whether taurine protected brain against experimental stroke through affecting mitochondria-mediated cell death pathway. Rats were subjected to 2-h ischemia by intraluminal filament, and then reperfused for 22 h. It was confirmed again that taurine (50 mg/kg) administered intravenously 1 h after ischemia markedly improved neurological function and decreased infarct volume at 22 h after reperfusion. In vehicle-treated rats, the levels of intracellular ATP and the levels of cytosolic and mitochondrial Bcl-xL in the penumbra and core were markedly reduced, while the levels of cytosolic Bax in the core and mitochondrial Bax in the penumbra and core were enhanced significantly. There was a decrease in cytochrome C in mitochondria and an increase in cytochrome C in the cytosol of the penumbra and core. These changes were reversed by taurine. Furthermore, taurine inhibited the activation of calpain and caspase-3, reduced the degradation of αII-spectrin, and attenuated the necrotic and apoptotic cell death in the penumbra and core. These data demonstrated that preserving the mitochondrial function and blocking the mitochondria-mediated cell death pathway may be one mechanism of taurine's action against brain ischemia.

Transcriptional and post-translational regulatory system for hypoxia specific gene expression using the erythropoietin enhancer and the oxygen-dependent degradation domain

Gene therapy with angiogenic factors is a promising strategy for the treatment of ischemic diseases. However, unregulated expression of an angiogenic factor may induce pathological angiogenesis. In this study, a hypoxia specific gene expression plasmid, pSV-Luc-ODD, was constructed with the oxygen-dependent degradation (ODD) domain for rapid degradation of a target protein under normoxia. In the transfection assay, luciferase activity in the pSV-Luc-ODD transfected cells was much lower under normoxia than that under hypoxia. However, the luciferase mRNA levels under hypoxia and normoxia were not significantly different. Therefore, decrease of luciferase activity under normoxia is not due to pre-translational events such as change of transcription rate or mRNA stability, but to post-translational degradation. For more hypoxia specific gene expression, pEpo-SV-Luc-ODD was constructed with the erythropoietin (Epo) enhancer and the ODD domain. pEpo-SV-Luc-ODD showed more than 1000 times increase of gene expression under hypoxia in Neuro2A cells, compared to normoxia. In addition, reoxygenation studies after hypoxia incubation showed that gene expression was decreased in response to increased oxygen concentration. This highly hypoxia specific gene expression system will be useful for development of targeting gene therapy for ischemic diseases.

Improvement in reproductive parameters in hypogonadal female mice by regulated gene replacement therapy in the central nervous system

One of the challenges of gene targeting is to achieve regulated transgene expression in specific target cells. The hypogonadal (hpg) mice are genetically deficient in hypothalamic gonadotropin-releasing hormone (GnRH) production due to a deletion in the GnRH gene, resulting in hypogonadotropic hypogonadism. Here we show an improvement in reproductive parameters of adult female homozygous hpg mice by direct infusion into the hypothalamic preoptic area (POA) of a herpes simplex virus (HSV)-based amplicon vector containing a 13.5 kb genomic fragment encoding the GnRH gene together with its cognate promoter and regulatory elements. Following vector injection, GnRH-expressing neurons were detected in the POA, and pituitary and plasma gonadotropin levels as well as ovarian and uterine weights increased. In addition, a subset of injected hpg mice demonstrated cyclic estrous changes, consistent with regulated control of GnRH production. Administration of kisspeptin-10 resulted in an increase in plasma luteinizing hormone levels, further supporting appropriate regulation of the introduced GnRH transgene. These findings indicate that delivery of the GnRH gene resulted in selective neuronal expression of GnRH and regulated hypothalamic GnRH release. To our knowledge, this is the first example of the correct targeting of a gene under its cognate promoter to neurons resulting in selective and regulated synthesis of a biologically active peptide, and thus may have a wide range of applications in the treatment of human disorders.

Molecular targets in cerebral ischemia for developing novel therapeutics

Cerebral ischemia (stroke) triggers a complex series of biochemical and molecular mechanisms that impairs the neurologic functions through breakdown of cellular integrity mediated by excitotoxic glutamatergic signalling, ionic imbalance, free-radical reactions, etc. These intricate processes lead to activation of signalling mechanisms involving calcium/calmodulin-dependent kinases (CaMKs) and mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK). The distribution of these transducers bring them in contact with appropriate molecular targets leading to altered gene expression, e.g. ERK and JNK mediated early gene induction, responsible for activation of cell survival/damaging mechanisms. Moreover, inflammatory reactions initiated at the neurovascular interface and alterations in the dynamic communication between the endothelial cells, astrocytes and neurons are thought to substantially contribute to the pathogenesis of the disease. The damaging mechanisms may proceed through rapid nonspecific cell lysis (necrosis) or by active form of cell demise (apoptosis or necroptosis), depending upon the severity and duration of the ischemic insult. A systematic understanding of these molecular mechanisms with prospect of modulating the chain of events leading to cellular survival/damage may help to generate the potential strategies for neuroprotection. This review briefly covers the current status on the molecular mechanisms of stroke pathophysiology with an endeavour to identify potential molecular targets such as targeting postsynaptic density-95 (PSD-95)/N-methyl-d-aspartate (NMDA) receptor interaction, certain key proteins involved in oxidative stress, CaMKs and MAPKs (ERK, p38 and JNK) signalling, inflammation (cytokines, adhesion molecules, etc.) and cell death pathways (caspases, Bcl-2 family proteins, poly (ADP-ribose) polymerase-1 (PARP-1), apoptosis-inducing factor (AIF), inhibitors of apoptosis proteins (IAPs), heat shock protein 70 (HSP70), receptor interacting protein (RIP), etc., besides targeting directly the genes itself. However, selecting promising targets from various signalling cascades, for drug discovery and development is very challenging, nevertheless such novel approaches may lead to the emergence of new avenues for therapeutic intervention in cerebral ischemia.

Virally mediated knock-down of NR2 subunits ipsilateral to the deprived eye blocks ocular dominance plasticity

NMDA receptors (NMDARs) are important in developmental plasticity in the visual cortex. The NR2A and NR2B subunits of this receptor develop with different time courses, suggesting that they play different roles in plasticity. To understand the role of the NR2B subunit, we knocked-down NR2B gene expression in visual cortex by injecting a recombinant adenovirus containing an antisense NR2B oligonucleotide. To assess knock-down, we injected the recombinant adenovirus into the right visual cortex of rats (p22) or mice (p30). Eight days later we perfused the animals and processed the visual cortex for NMDAR subunit immunoreactivity (IR). NR2B-IR was depleted dramatically in the neuropil near the injection. Depletion was more modest in the neuronal somata. Surprisingly, NR2A-IR was also reduced, but NR1-IR was not reduced. To assess the functional effects of depletion, we measured ocular dominance plasticity with monocular deprivation (MD). We compared mice receiving the NR2B antisense virus with mice receiving virus containing only the GFP sequence and mice receiving no injection. All injections were between p26 and p29 in the right cortex and bilateral recordings were performed 6-8 days later. Animals receiving the antisense virus lost plasticity if the right eye was deprived. If the left eye was deprived, the cortex was normally plastic bilaterally. Injection of control virus had no effect on plasticity. The data indicate that ocular dominance plasticity requires normal NMDARs in the hemisphere ipsilateral to the deprived eye but not in the hemisphere contralateral to the deprived eye.

Assessment of CMV, RSV and SYN1 promoters and the woodchuck post-transcriptional regulatory element in adenovirus vectors for transgene expression in cortical neuronal cultures

In order to investigate protein function in rat primary cortical neuronal cultures, we modified an adenoviral vector expression system and assessed the strength and specificity of the cytomegalovirus (CMV), rous sarcoma virus (RSV), and rat and human synapsin 1 (SYN1) promoters to drive DsRed-X expression. We also incorporated the woodchuck post-transcriptional regulatory element (WPRE) and a CMV promoter-enhanced green fluorescent protein (EGFP) reporter cassette. We observed that the RSV promoter activity was strong in neurons and moderate in astrocytes, while the CMV promoter activity was weak-to-moderate in neurons and very strong in astrocytes. The rat and human SYN1 promoters exhibited similar but weak activity in neurons, despite inclusion of the WPRE. We confirmed that the WPRE enhanced RSV promoter-mediated DsRed-X expression in a time-dependent fashion. Interestingly, we observed very weak SYN1-mediated DsRed-X expression in astrocytes and HEK293 cells suggesting incomplete neuronal-restrictive behavior for this promoter. Finally, using our adenoviral expression system, we demonstrated that RSV promoter-mediated Bcl-X(L) overexpression attenuated neuronal death caused by in vitro ischemia and oxidative stress.

TAT-GDNF in neurodegeneration and ischemic stroke

The delivery of proteins across the blood-brain barrier is severely limited by their size and biochemical properties. Numerous peptides have been characterized in recent years that prevent neuronal death in vitro, but cannot be used therapeutically, since they do not cross cell membrane barriers. It has been shown in the 1990s that the HIV TAT protein is able to cross cell membranes even when coupled with larger peptides. It appears, therefore, that TAT fusion proteins may enter the brain, even when used systemically. Indeed, the systemic delivery of a TAT protein linked with glial-derived neurotrophic factor (GDNF) successfully transduced central nervous system (CNS) neurons in mice. When administered after optic nerve transection and focal cerebral ischemia, TAT-GDNF protected retinal ganglion cells and brain neurons from cell death, elevated tissue Bcl-XL levels and attenuated the activity of the executioner caspase-3. These findings demonstrate the in vivo efficacy of fusion proteins in clinically relevant disease models, raising hopes that neuroprotection may become eventually feasible in human patients.

Cultured astrocytes from heme oxygenase-1 knockout mice are more vulnerable to heme-mediated oxidative injury

Hemin, the oxidized form of heme, is released from hemoglobin after CNS hemorrhage and may contribute to injury to surrounding tissue. The heme oxygenase (HO) enzymes catalyze the breakdown of hemin to biliverdin, carbon monoxide, and ferric iron. Although HO-2, the isoform expressed predominantly in neurons, accelerates heme-mediated neuronal injury, inhibitor studies suggest that HO-1 induction has a protective effect on astrocytes. In the present study, we directly compared the vulnerability of cultured HO-1 knockout and wild-type astrocytes to hemin. Consistent with prior observations, exposure of wild-type cultures to hemin for 24 hr resulted in protein carbonylation and concentration-dependent cell death between 10 and 60 microM, as determined by MTT and lactate dehydrogenase release assays. In cultures prepared from mice lacking the HO-1 gene, oxidative cell injury was approximately doubled. Both protein oxidation and cell death in HO-1 knockout astrocytes were significantly reduced by pretreating cultures with an adenovirus encoding the HO-1 gene prior to hemin exposure. HO-2 expression was observed in both knockout and wild-type cultures and was not altered by HO-1 gene deletion. Cell hemin accumulation after 20 hr hemin exposure was 4.7-fold higher in knockout cells. These results support the hypothesis that HO-1 protects astrocytes from heme-mediated oxidative injury. Selectively increasing its expression in astrocytes may be beneficial after hemorrhagic CNS injuries.

Long-term in vivo inhibition of CNS neurodegeneration by Bcl-XL gene transfer

The inherently low regenerative capacity of the CNS demands effective strategies to inhibit neurodegeneration in acute lesions but also in slowly progressive neurological disorders. Therefore, therapeutic targets that can interact with the degeneration cascade to block, not just postpone, neuronal degeneration need to be defined. Bcl-X(L), a protein protecting the integrity of the mitochondrial membrane potential, was investigated for its neuroprotective properties in a long-term in vivo model of neuronal cell death. An AAV-2-based vector was used to express both Bcl-X(L) and EGFP in retinal ganglion cells (RGCs) of the adult rat retina. Transection of the optic nerve results in degeneration of RGCs in control retinae, while Bcl-X(L)-overexpressing ganglion cells were protected from degeneration. At 2 weeks after axotomy, 94% of the transduced RGCs survived the lesion (15% in controls). For the first time, we investigated RGC survival up to 8 weeks after axotomy and detected that 46% of the Bcl-X(L)-overexpressing RGCs still survived, representing significantly increased neuroprotection compared to neurotrophin-based approaches. We could also show that the axons of AAV-Bcl-X(L)-transduced RGCs remained morphologically intact after the lesion, thus providing the basis for regeneration-inducing attempts.

Recent advances in the pharmacology of neurological gene therapy

The choice of vectors, transgenes, regulatory elements, delivery approaches and the capacity to transduce the appropriate target cell type all influence the effectiveness of gene therapy for neurological diseases. Furthermore, even if many strategies are sound and effective in experimental animals, issues relating to side effects of gene therapy, longevity of therapeutic transgene expression and diffusion throughout the brain can limit the clinical potential of gene therapy. During the past 12-18 months, there have been significant advances in the following areas: the capacity to target vectors to predetermined cells types; the development of gene therapy approaches for the treatment of dominant inherited and neurodegenerative diseases; the capacity to achieve systemic delivery of viral vectors to the brain; and the development of viral vectors to model neurological diseases.

The superoxide dismutase1 (sod1) G93A mutation does not promote neuronal injury after focal brain ischemia and optic nerve transection in mice

The superoxide dismutase 1 (SOD1)G93A mouse was recently established as transgenic model of amyotrophic lateral sclerosis. We were interested to know whether the SOD1 G93A mutation promotes neuronal injury after intraluminal middle cerebral artery thread occlusion and/or retinal ganglion cell (RGC) axotomy in mice, which are highly reproducible and clinically relevant in vivo models of acute and subacute neuronal degeneration, respectively. In our experiments, G93A mutant SOD1 neither influenced ischemic injury after 90 or 30 min of focal ischemia, nor had an impact on the severity of RGC degeneration after optic nerve transection, when human SOD1 G93A mutant mice were compared to human wild-type SOD1 mice. Our data indicate that the clinically relevant SOD1 G93A mutation, which leads to amyotrophic lateral sclerosis in humans and mice, does not necessarily worsen neuronal degeneration in other pathologies. Thus, the G93A mutation may be counterbalanced in non-motor neurons of young animals, and region-specific and age-related factors may be necessary so that neurodegeneration is re-enforced.