HSV-mediated delivery of virally derived anti-apoptotic genes protects the rat hippocampus from damage following excitotoxicity, but not metabolic disruption

Inflammation-induced mitochondrial and metabolic disturbances in sensory neurons control the switch from acute to chronic pain

Pain often persists in patients with an inflammatory disease, even when inflammation has subsided. The molecular mechanisms leading to this failure in pain resolution and the transition to chronic pain are poorly understood. Mitochondrial dysfunction in sensory neurons links to chronic pain, but its role in resolution of inflammatory pain is unclear. Transient inflammation causes neuronal plasticity, called hyperalgesic priming, which impairs resolution of pain induced by a subsequent inflammatory stimulus. We identify that hyperalgesic priming in mice increases the expression of a mitochondrial protein (ATPSc-KMT) and causes mitochondrial and metabolic disturbances in sensory neurons. Inhibition of mitochondrial respiration, knockdown of ATPSCKMT expression, or supplementation of the affected metabolite is sufficient to restore resolution of inflammatory pain and prevents chronic pain development. Thus, inflammation-induced mitochondrial-dependent disturbances in sensory neurons predispose to a failure in resolution of inflammatory pain and development of chronic pain.

Macrophages transfer mitochondria to sensory neurons to resolve inflammatory pain

The current paradigm is that inflammatory pain passively resolves following the cessation of inflammation. Yet, in a substantial proportion of patients with inflammatory diseases, resolution of inflammation is not sufficient to resolve pain, resulting in chronic pain. Mechanistic insight into how inflammatory pain is resolved is lacking. Here, we show that macrophages actively control resolution of inflammatory pain remotely from the site of inflammation by transferring mitochondria to sensory neurons. During resolution of inflammatory pain in mice, M2-like macrophages infiltrate the dorsal root ganglia that contain the somata of sensory neurons, concurrent with the recovery of oxidative phosphorylation in sensory neurons. The resolution of pain and the transfer of mitochondria requires expression of CD200 receptor (CD200R) on macrophages and the non-canonical CD200R-ligand iSec1 on sensory neurons. Our data reveal a novel mechanism for active resolution of inflammatory pain.

SGK1.1 limits brain damage after status epilepticus through M current-dependent and independent mechanisms

Epilepsy is a neurological condition associated to significant brain damage produced by status epilepticus (SE) including neurodegeneration, gliosis and ectopic neurogenesis. Reduction of these processes constitutes a useful strategy to improve recovery and ameliorate negative outcomes after an initial insult. SGK1.1, the neuronal isoform of the serum and glucocorticoids-regulated kinase 1 (SGK1), has been shown to increase M-current density in neurons, leading to reduced excitability and protection against seizures. For this study, we used 4-5 months old male transgenic C57BL/6 J and FVB/NJ mice expressing near physiological levels of a constitutively active form of the kinase controlled by its endogenous promoter. Here we show that SGK1.1 activation potently reduces levels of neuronal death (assessed using Fluoro-Jade C staining) and reactive glial activation (reported by GFAP and Iba-1 markers) in limbic regions and cortex, 72 h after SE induced by kainate, even in the context of high seizure activity. This neuroprotective effect is not exclusively through M-current activation but is also directly linked to decreased apoptosis levels assessed by TUNEL assays and quantification of Bim and Bcl-x_L by western blot of hippocampal protein extracts. Our results demonstrate that this newly described antiapoptotic role of SGK1.1 activation acts synergistically with the regulation of cellular excitability, resulting in a significant reduction of SE-induced brain damage in areas relevant to epileptogenesis.

Cell-specific gene therapy driven by an optimized hypoxia-regulated vector reduces choroidal neovascularization

Aberrant growth of blood vessels in the choroid layer of the eye, termed choroidal neovascularization (CNV), is the pathological hallmark of exudative age-related macular degeneration (AMD), causing irreversible blindness among the elderly. Co-localization of proangiogenic factors and hypoxia inducible factors (HIF) in neovascular membranes from AMD eyes suggests the role of hypoxia in pathogenesis of CNV. In order to utilize hypoxic conditions in RPE for therapeutic purposes, we developed an optimized hypoxia regulated, RPE cell-specific gene therapy to inhibit choroidal neovascularization. An adeno-associated virus (AAV2) vector comprising a RPE-specific promoter and HIF-1 response elements (HRE) was designed to regulate production of human endostatin (a powerful angiostatic protein) in RPE. The vector was tested in a mouse model of laser-induced CNV using subretinal delivery. Spectral domain optical coherence tomography (SD-OCT) images from live mice and confocal images from lectin stained RPE flat mount sections demonstrated reduction in CNV areas by 80% compared to untreated eyes. Quantitative real-time polymerase chain reaction (qPCR) confirmed exogenous endostatin mRNA expression from the regulated vector that was significantly elevated 3, 7, and 14 days following laser treatment, but its expression was completely shut off after 45 days. Thus, RPE-specific, hypoxia-regulated delivery of anti-angiogenic proteins could be a valuable therapeutic approach to treat neovascular AMD at the time and in the ocular space where it arises.

KEY POINTS

An optimized gene therapy vector targeting hypoxia and tissue-specific expression has been designed. The inhibitory role of gene therapy vector was tested in a mouse model of laser-induced CNV. An 80% reduction in choroidal neovascularization was achieved by the optimized vector. The expression of endostatin was limited to retinal pigment epithelium and regulated by hypoxia.

Identification of FAM173B as a protein methyltransferase promoting chronic pain

Chronic pain is a debilitating problem, and insights in the neurobiology of chronic pain are needed for the development of novel pain therapies. A genome-wide association study implicated the 5p15.2 region in chronic widespread pain. This region includes the coding region for FAM173B, a functionally uncharacterized protein. We demonstrate here that FAM173B is a mitochondrial lysine methyltransferase that promotes chronic pain. Knockdown and sensory neuron overexpression strategies showed that FAM173B is involved in persistent inflammatory and neuropathic pain via a pathway dependent on its methyltransferase activity. FAM173B methyltransferase activity in sensory neurons hyperpolarized mitochondria and promoted macrophage/microglia activation through a reactive oxygen species–dependent pathway. In summary, we uncover a role for methyltransferase activity of FAM173B in the neurobiology of pain. These results also highlight FAM173B methyltransferase activity as a potential therapeutic target to treat debilitating chronic pain conditions.

Pain is an evolutionarily conserved physiological phenomenon necessary for survival. Yet, pain can become pathological when it occurs independently of noxious stimuli. The molecular mechanisms of pathological pain are still poorly understood, limiting the development of highly needed novel analgesics. Recently, genetic variations in the genomic region encoding FAM173B—a functionally uncharacterized protein—have been linked to chronic pain in humans. In this study, we identify the role and function of FAM173B in the development of pathological pain. We used genetic, biochemical, and behavioral approaches in mice to show that FAM173B is a mitochondrial lysine methyltransferase—a protein that transfers methyl group to donor proteins. By genetically silencing or overexpressing FAM173B in sensory neurons, we showed that FAM173B methyltransferase activity promotes the development of chronic pain. In addition, we discovered that FAM173B methyltransferase activity in the mitochondria of sensory neurons promotes chronic pain via a pathway that depends on the production of reactive oxygen species and on the engagement of spinal cord microglia—engulfing cells of the central nervous system. These data point to an essential role of FAM173B in the regulation of pathological pain.

Follow-Up of Peripheral IL-1β and IL-6 and Relation with Apoptotic Death in Drug-Resistant Temporal Lobe Epilepsy Patients Submitted to Surgery

Increasing amounts of evidence support the role of inflammation in epilepsy. This study was done to evaluate serum follow-up of IL-1β and IL-6 levels, as well as their concentration in the neocortex, and the relationship of central inflammation with NF-κB and annexin V in drug-resistant temporal lobe epileptic (DRTLE) patients submitted to surgical treatment. Peripheral and central levels of IL-1β and IL-6were measured by ELISA in 10 DRTLE patients. The sera from patients were taken before surgery, and 12 and 24 months after surgical treatment. The neocortical expression of NF-κB was evaluated by western blotting and annexin V co-localization with synaptophysin by immunohistochemistry. The neocortical tissues from five patients who died by non-neurological causes were used as control. Decreased serum levels of IL-1 and IL-6 were observed after surgery; at this time, 70% of patients were seizure-free. No values of IL-1 and IL-6 were detected in neocortical control tissue, whereas cytokine levels were evidenced in DRTLE. Increased NF-κB neocortex expression was found and the positive annexin V neurons were more obvious in the DRTLE tissue, correlating with IL-6 levels. The follow-up study confirmed that the inflammatory alterations disappeared one year after surgery, when the majority of patients were seizure-free, and the apoptotic death process correlated with inflammation.

Decreased interaction between FoxO3a and Akt correlates with seizure-induced neuronal death

Status epilepticus (SE) leads to neurodegeneration which likely contributes to the development of chronic temporal lobe epilepsy (TLE). Therefore, neuroprotection following SE is considered as a promising strategy for preventing chronic TLE, but molecular changes that occur following SE still remain unclear. The Forkhead homeobox type O (FoxO) family of Forkhead transcription factors mediates cell death in several pathological conditions, but the role of FoxO in the excitotoxic effects of kainic acid (KA) remains largely unknown. The present study examined how FoxO3a and its interaction with other proteins changed in response to excitotoxic stimuli in the mouse hippocampus after SE. Mice were given intraperitoneal injection of kainate and seizure behavior was monitored for 2h to ensure SE. Western blot analyses, co-immunoprecipitation experiments, sub-cellular fractionation and double immunofluorescence analyses were used to determine changes in levels of FoxO3a, Akt, Bim, cleaved caspase-3 and phospho-FoxO3a or phospho-Akt, and their interactions at 6 or 24h after KA treatment. We found that SE activated FoxO3a and increased levels of Bim or cleaved caspase-3, and decreased levels of phospho-FoxO3a or phospho-Akt in the hippocampus. In addition, we noted extensive hippocampal cell death at 24h after KA treatment, evidenced by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling (TUNEL), fluoro-jade B or anti-active caspase-3 staining. Furthermore, co-immunoprecipitation experiments revealed that phospho-Akt interaction with FoxO3a was significantly lowered in the hippocampus at 24h after KA treatment, paralleling enhanced Bim levels and Bim interaction with Bcl-xL. Moreover, double immunofluorescence analyses showed increased co-localization of FoxO3a or Bim and TUNEL in the hippocampi at 24h after KA treatment. Identifying molecular mechanism underlying SE-induced neuronal death can provide a novel strategy to protect against seizure-induced neuronal injury. We found that Akt-FoxO3a signaling relates to seizure-induced neuronal death, providing insight into neuroprotection following SE.

Increased Cdk5/p35 activity in the dentate gyrus mediates depressive-like behaviour in rats

Depression is one of the most pervasive and debilitating psychiatric diseases, and the molecular mechanisms underlying the pathophysiology of depression have not been elucidated. Cyclin-dependent kinase 5 (Cdk5) has been implicated in synaptic plasticity underlying learning, memory, and neuropsychiatric disorders. However, whether Cdk5 participates in the development of depressive diseases has not been examined. Using the chronic mild stress (CMS) procedure, we examined the effects of Cdk5/p35 activity in the hippocampus on depressive-like behaviour in rats. We found that CMS increased Cdk5 activity in the hippocampus, accompanied by translocation of neuronal-specific activator p35 from the cytosol to the membrane in the dentate gyrus (DG) subregion. Inhibition of Cdk5 in DG but not in the cornu ammonis 1 (CA1) or CA3 hippocampal subregions inhibited the development of depressive-like symptoms. Overexpression of p35 in DG blocked the antidepressant-like effect of venlafaxine in the CMS model. Moreover, the antidepressants venlafaxine and mirtazapine, but not the antipsychotic aripiprazole, reduced Cdk5 activity through the redistribution of p35 from the membrane to the cytosol in DG. Our results showed that the development of depressive-like behaviour is associated with increased Cdk5 activity in the hippocampus and that the Cdk5/p35 complex plays a key role in the regulation of depressive-like behaviour and antidepressant actions.

Evidence for caspase effects on release of cytochrome c and AIF in a model of ischemia in cortical neurons

Neuronal apoptosis following ischemia can be mediated by a caspase-dependent pathway, which involves the mitochondrial release of cytochrome c that initiates a cascade of caspase activation. In addition, there is a caspase-independent pathway, which is mediated by the release of apoptosis-inducing factor (AIF). Using caspase inhibitor gene therapy, we investigated the roles of caspases on the mitochondrial release of cyt c and the release of AIF. Specifically, we used herpes simplex virus-1 amplicon vectors to ectopically express a viral caspase inhibitor (crmA or p35) in mixed cortical cultures exposed to oxygen/glucose deprivation. Overexpression of either crmA or p35 (but not the caspase-3 inhibitor DEVD) inhibited the release of AIF; this suggests that there can be cross-talk between the caspase-dependent and the ostensibly caspase-independent pathway. In addition, both crmA overexpression and DEVD inhibited cyt c release, suggesting a positive feedback loop involving activated caspases stimulating cyt c release.

SK2 potassium channel overexpression in basolateral amygdala reduces anxiety, stress-induced corticosterone secretion and dendritic arborization

The basolateral amygdala is critical for generation of anxiety. In addition, exposure to both stress and glucocorticoids induces anxiety. Demonstrated ability of the amygdala to change in response to stress and glucocorticoids could thus be important therapeutic target for anxiety management. Several studies have reported a relationship between anxiety and dendritic arborization of the amygdaloid neurons. In this study we employed a gene therapeutic approach to reduce anxiety and dendritic arborization of the amygdala neurons. Specifically, we overexpressed SK2 potassium channel in the basolateral amygdala using a herpes simplex viral system. Our choice of therapeutic cargo was guided by the indications that activation of the amygdala might underlie anxiety and that SK2 could reduce neuronal activation by exerting inhibitory influence on action potentials. We report that SK2 overexpression reduced anxiety and stress-induced corticosterone secretion at a systemic level. SK2 overexpression also reduced dendritic arborization of the amygdala neurons. Hence, SK2 is a potential gene therapy candidate molecule that can be used against stress-related neuropsychiatric disorders such as anxiety.

Modulators of neuronal cell death in epilepsy

Experimental and human data have shown that certain seizures cause damage to brain. Such neuronal loss may result in cognitive impairments and perhaps contribute to the development or phenotype of emergent epilepsy. Recent work using genetically modified mice, Tat protein transduction, and viral vectors has shown functional effects of manipulating Bcl-2 and Bcl-w, heat shock proteins, caspases, and their regulators and endonucleases on neuronal death in models of status epilepticus. Ancillary effects on seizure induction and excitability thresholds have emerged for several genes suggesting additional properties of therapeutic potential. Differing hippocampal expression of certain Bcl-2 family genes, elevated endoplasmic reticulum stress chaperones, and death receptor pathway modulation in epilepsy patients support clinical relevance of this focus. These findings may yield potentially valuable adjunctive neuroprotective or anti-epileptogenic strategies.

Viral caspase inhibitor p35, but not crmA, is neuroprotective in the ischemic penumbra following experimental stroke

Apoptosis, a predominant cause of neuronal death after stroke, can be executed in a caspase-dependent or apoptosis inducing factor (AIF)-dependent manner. Herpes simplex virus (HSV) vectors expressing caspase inhibitors p35 and crmA have been shown to be neuroprotective against various excitotoxic insults. Here we further evaluated the possible neuroprotective role of p35 and crmA in a rat stroke model. Overexpression of p35, but not crmA, significantly increased neuronal survival. Results of double immunofluorescence staining indicate that compared with neurons infected with crmA or control vectors, p35-infected neurons had less active caspase-3 expression, cytosolic cytochrome c and nuclear AIF translocation.

Activation of the caspase 8 pathway mediates seizure-induced cell death in cultured hippocampal neurons

In response to harmful stresses, cells induce programmed cell death (PCD) or apoptosis. Seizures can induce neural damage and activate biochemical pathways associated with PCD. Since seizures trigger intracellular calcium overload, it has been presumed that the intrinsic cell death pathway mediated by mitochondrial dysfunction would modulate cell death following seizures. However, previous work suggests that the extrinsic cell death pathway may initiate the damage program. Here we investigate intrinsic versus extrinsic cell death pathway activation using caspase cleavage as a marker for activation of these pathways in a rat in vitro model of seizures. Hippocampal cells, chronically treated with kynurenic acid, had kynurenic acid withdrawn to induce seizure-like activity for 40 min. Subjecting rat hippocampal cultures to seizures increased cell death and apoptosis-like DNA fragmentation using TUNEL staining. Seizure-induced cell death was blocked by both MK801 (10 microM) and CNQX (40 microM), which suggests multiple glutamate receptors regulate seizure-induced cell death. Cleavage of the initiator caspases, caspase 8 and 12 were increased 4h following seizure, and cleavage of the quintessential executioner caspase, caspase 3 was increased 4h following seizure. In contrast, caspase 9 cleavage only increased 24h following seizure. Using an affinity labeling approach to trap activated caspases in situ, we show that caspase 8 is the apical caspase activated following seizures. Finally, we show that the caspase 8 inhibitor Ac-IETD-CHO was more effective at blocking seizure-induced cell death than the caspase 9 inhibitor Ac-LEHD-CHO. Taken together, our data suggests the extrinsic cell death pathway-associated caspase 8 is activated following seizures in vitro.

Epilepsy and apoptosis pathways

Epilepsy is a common, chronic neurologic disorder characterized by recurrent unprovoked seizures. Experimental modeling and clinical neuroimaging of patients has shown that certain seizures are capable of causing neuronal death. Such brain injury may contribute to epileptogenesis, impairments in cognitive function or the epilepsy phenotype. Research into cell death after seizures has identified the induction of the molecular machinery of apoptosis. Here, the authors review the clinical and experimental evidence for apoptotic cell death pathway function in the wake of seizure activity. We summarize work showing intrinsic (mitochondrial) and extrinsic (death receptor) apoptotic pathway function after seizures, activation of the caspase and Bcl-2 families of cell death modulators and the acute and chronic neuropathologic impact of intervening in these molecular cascades. Finally, we describe evolving data on nonlethal roles for these proteins in neuronal restructuring and cell excitability that have implications for shaping the epilepsy phenotype. This review highlights the work to date on apoptosis pathway signaling during seizure-induced neuronal death and epileptogenesis, and speculates on how emerging roles in brain remodeling and excitability have enriched the number of therapeutic strategies for protection against seizure-damage and epileptogenesis.

Bim regulation may determine hippocampal vulnerability after injurious seizures and in temporal lobe epilepsy

Programmed cell death pathways have been implicated in the mechanism by which neurons die following brief and prolonged seizures, but the significance of proapoptotic Bcl-2 family proteins in the process remains poorly defined. Expression of the death agonist Bcl-2-interacting mediator of cell death (Bim) is under the control of the forkhead in rhabdomyosarcoma (FKHR) transcription factors. This prompted us to examine the response of this pathway to experimental seizures and in hippocampi from patients with intractable temporal lobe epilepsy. A short period of status epilepticus in rats that damaged the hippocampus activated FKHR/FKHRL-1 and induced a significant increase in expression of Bim. Blocking of FKHR/FKHRL-1 dephosphorylation after seizures improved hippocampal neuronal survival in vivo, and Bim antisense oligonucleotides were neuroprotective against seizures in vitro. Inhibition of Akt increased the FKHR/Bim response and DNA fragmentation within the normally resistant cortex. Analysis of hippocampi from patients with intractable epilepsy revealed that Bim levels were significantly lower than in controls and FKHR was inhibited; we were able to reproduce these results experimentally in rats by evoking multiple brief, noninjurious electroshock seizures. We conclude that Bim expression may be a critical determinant of whether seizures damage the brain, and that its control may be neuroprotective in status epilepticus and epilepsy.

Bcl-2 family regulation of neuronal development and neurodegeneration

Neuronal cell death is a key feature of both normal nervous system development and neuropathological conditions. The Bcl-2 family, via its regulation of both caspase-dependent and caspase-independent cell death pathways, is uniquely positioned to critically control neuronal cell survival. Targeted gene disruptions of specific bcl-2 family members and the generation of transgenic mice overexpressing anti- or pro-apoptotic Bcl-2 family members have confirmed the importance of the Bcl-2 family in the nervous system. Data from studies of human brain tissue and experimental animal models of neuropathological conditions support the hypothesis that the Bcl-2 family regulates cell death in the mature nervous system and suggest that pharmacological manipulation of Bcl-2 family action could prove beneficial in the treatment of human neurological conditions such as stroke and neurodegenerative diseases.

Death-associated protein kinase expression in human temporal lobe epilepsy

Experimental and human data suggest programmed (active) cell death may contribute to the progressive hippocampal atrophy seen in patients with refractory temporal lobe epilepsy. Death-associated protein (DAP) kinase is a novel calcium/calmodulin-activated kinase that functions in apoptosis mediated by death receptors. Because seizure-induced neuronal death involves both death receptor activation and calcium, we examined DAP kinase expression, localization, and interactions in hippocampal resections from patients with intractable temporal lobe epilepsy (n = 10) and autopsy controls (n = 6). Expression and phosphorylation of DAP kinase was significantly increased in epilepsy brain compared with control. DAP kinase and DAP kinase-interacting protein 1 (DIP-1) localized to mitochondria in control brain, whereas levels of both were increased in the cytoplasm and microsomal (endoplasmic reticulum) fraction in epilepsy samples. Coimmunoprecipitation analysis showed increased DAP kinase binding to calmodulin, DIP-1, and the Fas-associated protein with death domain (FADD) in epilepsy samples. Finally, immunohistochemistry determined DAP kinase was coexpressed with DIP-1 in neurons. This study provides the first description of DAP kinase and DIP-1 in human brain and suggests DAP kinase is a novel molecular regulator of neuronal death in epilepsy.

To die or not to die for neurons in ischemia, traumatic brain injury and epilepsy: a review on the stress-activated signaling pathways and apoptotic pathways

After a severe episode of ischemia, traumatic brain injury (TBI) or epilepsy, it is typical to find necrotic cell death within the injury core. In addition, a substantial number of neurons in regions surrounding the injury core have been observed to die via the programmed cell death (PCD) pathways due to secondary effects derived from the various types of insults. Apart from the cell loss in the injury core, cell death in regions surrounding the injury core may also contribute to significant losses in neurological functions. In fact, it is the injured neurons in these regions around the injury core that treatments are targeting to preserve. In this review, we present our cumulated understanding of stress-activated signaling pathways and apoptotic pathways in the research areas of ischemic injury, TBI and epilepsy and that gathered from concerted research efforts in oncology and other diseases. However, it is obvious that our understanding of these pathways in the context of acute brain injury is at its infancy stage and merits further investigation. Hopefully, this added research effort will provide a more detailed knowledge from which better therapeutic strategies can be developed to treat these acute brain injuries.