Publications by authors named "Roger P Simon"

101 Publications

GPR68 Is a Neuroprotective Proton Receptor in Brain Ischemia.

Stroke 2020 12 16;51(12):3690-3700. Epub 2020 Oct 16.

Department of Physiology and Cell Biology (T.W., G.Z., M.H., Yuanyuan Xu, X.-m.Z.), University of South Alabama College of Medicine, Mobile.

Background And Purpose: Brain acidosis is prevalent in stroke and other neurological diseases. Acidosis can have paradoxical injurious and protective effects. The purpose of this study is to determine whether a proton receptor exists in neurons to counteract acidosis-induced injury.

Methods: We analyzed the expression of proton-sensitive GPCRs (G protein-coupled receptors) in the brain, examined acidosis-induced signaling in vitro, and studied neuronal injury using in vitro and in vivo mouse models.

Results: GPR68, a proton-sensitive GPCR, was present in both mouse and human brain, and elicited neuroprotection in acidotic and ischemic conditions. GPR68 exhibited wide expression in brain neurons and mediated acidosis-induced PKC (protein kinase C) activation. PKC inhibition exacerbated pH 6-induced neuronal injury in a GPR68-dependent manner. Consistent with its neuroprotective function, GPR68 overexpression alleviated middle cerebral artery occlusion-induced brain injury.

Conclusions: These data expand our knowledge on neuronal acid signaling to include a neuroprotective metabotropic dimension and offer GPR68 as a novel therapeutic target to alleviate neuronal injuries in ischemia and multiple other neurological diseases.
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http://dx.doi.org/10.1161/STROKEAHA.120.031479DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7678672PMC
December 2020

Deletion of a Neuronal Drp1 Activator Protects against Cerebral Ischemia.

J Neurosci 2020 04 6;40(15):3119-3129. Epub 2020 Mar 6.

Department of Neuroscience and Pharmacology and Iowa Neuroscience Institute, University of Iowa, Iowa City, Iowa 52242,

Mitochondrial fission catalyzed by dynamin-related protein 1 (Drp1) is necessary for mitochondrial biogenesis and maintenance of healthy mitochondria. However, excessive fission has been associated with multiple neurodegenerative disorders, and we recently reported that mice with smaller mitochondria are sensitized to ischemic stroke injury. Although pharmacological Drp1 inhibition has been put forward as neuroprotective, the specificity and mechanism of the inhibitor used is controversial. Here, we provide genetic evidence that Drp1 inhibition is neuroprotective. Drp1 is activated by dephosphorylation of an inhibitory phosphorylation site, Ser637. We identify Bβ2, a mitochondria-localized protein phosphatase 2A (PP2A) regulatory subunit, as a neuron-specific Drp1 activator Bβ2 KO mice of both sexes display elongated mitochondria in neurons and are protected from cerebral ischemic injury. Functionally, deletion of Bβ2 and maintained Drp1 Ser637 phosphorylation improved mitochondrial respiratory capacity, Ca homeostasis, and attenuated superoxide production in response to ischemia and excitotoxicity and Last, deletion of Bβ2 rescued excessive stroke damage associated with dephosphorylation of Drp1 S637 and mitochondrial fission. These results indicate that the state of mitochondrial connectivity and PP2A/Bβ2-mediated dephosphorylation of Drp1 play a critical role in determining the severity of cerebral ischemic injury. Therefore, Bβ2 may represent a target for prophylactic neuroprotective therapy in populations at high risk of stroke. With recent advances in clinical practice including mechanical thrombectomy up to 24 h after the ischemic event, there is resurgent interest in neuroprotective stroke therapies. In this study, we demonstrate reduced stroke damage in the brain of mice lacking the Bβ2 regulatory subunit of protein phosphatase 2A, which we have shown previously acts as a positive regulator of the mitochondrial fission enzyme dynamin-related protein 1 (Drp1). Importantly, we provide evidence that deletion of Bβ2 can rescue excessive ischemic damage in mice lacking the mitochondrial PKA scaffold AKAP1, apparently via opposing effects on Drp1 S637 phosphorylation. These results highlight reversible phosphorylation in bidirectional regulation of Drp1 activity and identify Bβ2 as a potential pharmacological target to protect the brain from stroke injury.
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http://dx.doi.org/10.1523/JNEUROSCI.1926-19.2020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7141887PMC
April 2020

Distinct plasma proteomic changes in male and female African American stroke patients.

Int J Physiol Pathophysiol Pharmacol 2019 15;11(2):12-20. Epub 2019 Apr 15.

Neuroscience Institute, Morehouse School of Medicine Atlanta, Georgia.

Background: Stroke occurs more often and results in more severe brain injury in African Americans than in Caucasians. The former also exhibit different responses to thrombolytic therapy than the latter do. There is an imminent need for stroke biomarkers for African Americans, who have been underrepresented in biomarker research for stroke diagnosis and prognosis. Proteomics offers sources for protein biomarkers that are not available by other Omics approaches. In this pilot study, plasma proteomes of African American stroke patients were analyzed and compared to that of hypertensive, non-stroke controls.

Methods: Plasma samples were prepared from whole blood specimens that were collected from stroke patients admitted to Grady Memorial Hospital in Atlanta, and their age- and sex-matched, hypertensive controls from the outpatient clinic. Samples were pooled according to patient groups and sex. Plasma proteins were analyzed with quantitative mass spectrometry. The identified and quantified proteins were compared between stroke and control patients of each sex. Proteins that showed changes in abundances in stroke patients were further analyzed with the assistance of bioinformatics tools for their known biological functions or potential implications in stroke.

Results: A total of 128 annotated proteins were identified. Results of bioinformatic analysis of plasma proteins whose levels were increased in stroke patients showed, as expected, their association with blood coagulation and inflammation processes. Interestingly, a number of proteins showed different or even opposing changes in male and female stroke patients, notably those involved in IL-4 and IL-6 signaling, complement activation, and blood coagulation disorders. For a few proteins that were increased in female but unchanged or decreased in male stroke patients, an association with fibromuscular dysplasia was recognized.

Conclusion: Plasma proteins that differ in quantities between stroke patients and controls were readily detected using a simple proteomic approach. Sex-dependent changes and changes that have not been reported for African American stroke patients offer potentially novel biomarkers for stroke in this underserved population.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6526384PMC
April 2019

Enhancing and Extending Biological Performance and Resilience.

Dose Response 2018 Jul-Sep;16(3):1559325818784501. Epub 2018 Aug 15.

ScitoVation LLC, Research Triangle Park, NC, USA.

Human performance, endurance, and resilience have biological limits that are genetically and epigenetically predetermined but perhaps not yet optimized. There are few systematic, rigorous studies on how to raise these limits and reach the true maxima. Achieving this goal might accelerate translation of the theoretical concepts of conditioning, hormesis, and stress adaptation into technological advancements. In 2017, an Air Force-sponsored conference was held at the University of Massachusetts for discipline experts to display data showing that the amplitude and duration of biological performance might be magnified and to discuss whether there might be harmful consequences of exceeding typical maxima. The charge of the workshop was "to examine and discuss and, if possible, recommend approaches to control and exploit endogenous defense mechanisms to enhance the structure and function of biological tissues." The goal of this white paper is to fulfill and extend this workshop charge. First, a few of the established methods to exploit endogenous defense mechanisms are described, based on workshop presentations. Next, the white paper accomplishes the following goals to provide: (1) synthesis and critical analysis of concepts across some of the published work on endogenous defenses, (2) generation of new ideas on augmenting biological performance and resilience, and (3) specific recommendations for researchers to not only examine a wider range of stimulus doses but to also systematically modify the temporal dimension in stimulus inputs (timing, number, frequency, and duration of exposures) and in measurement outputs (interval until assay end point, and lifespan). Thus, a path forward is proposed for researchers hoping to optimize protocols that support human health and longevity, whether in civilians, soldiers, athletes, or the elderly patients. The long-term goal of these specific recommendations is to accelerate the discovery of practical methods to conquer what were once considered intractable constraints on performance maxima.
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http://dx.doi.org/10.1177/1559325818784501DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6096685PMC
August 2018

Assessing the accuracy of blood RNA profiles to identify patients with post-concussion syndrome: A pilot study in a military patient population.

PLoS One 2017 1;12(9):e0183113. Epub 2017 Sep 1.

Neuroscience Institute, Morehouse School of Medicine, Atlanta, Georgia, United States of America.

Mild traumatic brain injury (mTBI) is a complex, neurophysiological condition that can have detrimental outcomes. Yet, to date, no objective method of diagnosis exists. Physical damage to the blood-brain-barrier and normal waste clearance via the lymphatic system may enable the detection of biomarkers of mTBI in peripheral circulation. Here we evaluate the accuracy of whole transcriptome analysis of blood to predict the clinical diagnosis of post-concussion syndrome (PCS) in a military cohort. Sixty patients with clinically diagnosed chronic concussion and controls (no history of concussion) were recruited (retrospective study design). Male patients (46) were split into a training set comprised of 20 long-term concussed (> 6 months and symptomatic) and 12 controls (no documented history of concussion). Models were validated in a testing set (control = 9, concussed = 5). RNA_Seq libraries were prepared from whole blood samples for sequencing using a SOLiD5500XL sequencer and aligned to hg19 reference genome. Patterns of differential exon expression were used for diagnostic modeling using support vector machine classification, and then validated in a second patient cohort. The accuracy of RNA profiles to predict the clinical diagnosis of post-concussion syndrome patients from controls was 86% (sensitivity 80%; specificity 89%). In addition, RNA profiles reveal duration of concussion. This pilot study shows the potential utility of whole transcriptome analysis to establish the clinical diagnosis of chronic concussion syndrome.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0183113PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5581162PMC
October 2017

Sleep Is Critical for Remote Preconditioning-Induced Neuroprotection.

Sleep 2016 Nov 1;39(11):2033-2040. Epub 2016 Nov 1.

Circadian Rhythms and Sleep Disorders Program, Department of Neurobiology, Morehouse School of Medicine, Atlanta GA.

Study Objectives: Episodes of brief limb ischemia (remote preconditioning) in mice induce tolerance to modeled ischemic stroke (focal brain ischemia). Since stroke outcomes are in part dependent on sleep-wake history, we sought to determine if sleep is critical for the neuroprotective effect of limb ischemia.

Methods: EEG/EMG recording electrodes were implanted in mice. After a 24 h baseline recording, limb ischemia was induced by tightening an elastic band around the left quadriceps for 10 minutes followed by 10 minutes of release for two cycles. Two days following remote preconditioning, a second 24 h EEG/EMG recording was completed and was immediately followed by a 60-minute suture occlusion of the middle cerebral artery (modeled ischemic stroke). This experiment was then repeated in a model of circadian and sleep abnormalities ( knockout [KO] mice sleep 2 h more than wild-type littermates). Brain infarction was determined by vital dye staining, and sleep was assessed by trained identification of EEG/EMG recordings.

Results: Two days after limb ischemia, wild-type mice slept an additional 2.4 h. This additional sleep was primarily comprised of non-rapid eye movement (NREM) sleep during the middle of the light-phase (i.e., naps). Repeating the experiment but preventing increases in sleep after limb ischemia abolished tolerance to ischemic stroke. In knockout mice, remote preconditioning did not increase daily sleep nor provide tolerance to subsequent focal ischemia.

Conclusions: These results suggest that sleep induced by remote preconditioning is both sufficient and necessary for its neuroprotective effects on stroke outcome.
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http://dx.doi.org/10.5665/sleep.6238DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5070757PMC
November 2016

Modulation of Acid-sensing Ion Channel 1a by Intracellular pH and Its Role in Ischemic Stroke.

J Biol Chem 2016 08 8;291(35):18370-83. Epub 2016 Jul 8.

the Department of Neurobiology, Neuroscience Institute, Morehouse School of Medicine, Atlanta, Georgia 30310, and

An important contributor to brain ischemia is known to be extracellular acidosis, which activates acid-sensing ion channels (ASICs), a family of proton-gated sodium channels. Lines of evidence suggest that targeting ASICs may lead to novel therapeutic strategies for stroke. Investigations of the role of ASICs in ischemic brain injury have naturally focused on the role of extracellular pH in ASIC activation. By contrast, intracellular pH (pHi) has received little attention. This is a significant gap in our understanding because the ASIC response to extracellular pH is modulated by pHi, and activation of ASICs by extracellular protons is paradoxically enhanced by intracellular alkalosis. Our previous studies show that acidosis-induced cell injury in in vitro models is attenuated by intracellular acidification. However, whether pHi affects ischemic brain injury in vivo is completely unknown. Furthermore, whereas ASICs in native neurons are composed of different subunits characterized by distinct electrophysiological/pharmacological properties, the subunit-dependent modulation of ASIC activity by pHi has not been investigated. Using a combination of in vitro and in vivo ischemic brain injury models, electrophysiological, biochemical, and molecular biological approaches, we show that the intracellular alkalizing agent quinine potentiates, whereas the intracellular acidifying agent propionate inhibits, oxygen-glucose deprivation-induced cell injury in vitro and brain ischemia-induced infarct volume in vivo Moreover, we find that the potentiation of ASICs by quinine depends on the presence of the ASIC1a, ASIC2a subunits, but not ASIC1b, ASIC3 subunits. Furthermore, we have determined the amino acids in ASIC1a that are involved in the modulation of ASICs by pHi.
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http://dx.doi.org/10.1074/jbc.M115.713636DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5000083PMC
August 2016

Blood transcriptome changes after stroke in an African American population.

Ann Clin Transl Neurol 2016 02 15;3(2):70-81. Epub 2016 Jan 15.

Translational Stroke Program Neuroscience Institute Morehouse School of Medicine Atlanta Georgia; Grady Memorial Hospital Atlanta Georgia.

Objective: Molecular diagnostic medicine holds much promise to change point of care treatment. An area where additional diagnostic tools are needed is in acute stroke care, to assist in diagnosis and prognosis. Previous studies using microarray-based gene expression analysis of peripheral blood following stroke suggests this approach may be effective. Next-generation sequencing (NGS) approaches have expanded genomic analysis and are not limited to previously identified genes on a microarray chip. Here, we report on a pilot NGS study to identify gene expression and exon expression patterns for the prediction of stroke diagnosis and prognosis.

Methods: We recruited 28 stroke patients and 28 age- and sex-matched hypertensive controls. RNA was extracted from 3 mL blood samples, and RNA-Seq libraries were assembled and sequenced.

Results: Bioinformatical analysis of the aligned RNA data reveal exonic (30%), intronic (36%), and novel RNA components (not currently annotated: 33%). We focused our study on patients with confirmed middle cerebral artery occlusion ischemic stroke (n = 17). On the basis of our observation of differential splicing of gene transcripts, we used all exonic RNA expression rather than gene expression (combined exons) to build prediction models using support vector machine algorithms. Based on model building, these models have a high predicted accuracy rate >90% (spec. 88% sen. 92%). We further stratified outcome based on the improvement in NIHss scores at discharge; based on model building we observe a predicted 100% accuracy rate.

Interpretation: NGS-based exon expression analysis approaches have a high potential for patient diagnosis and outcome prediction, with clear utility to aid in clinical patient care.
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http://dx.doi.org/10.1002/acn3.272DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4748310PMC
February 2016

Amiloride Analogs as ASIC1a Inhibitors.

CNS Neurosci Ther 2016 06 18;22(6):468-76. Epub 2016 Feb 18.

Neuroscience Institute, Morehouse School of Medicine, Atlanta, GA, USA.

Background: ASIC1a, the predominant acid-sensing ion channels (ASICs), is implicated in neurological disorders including stroke, traumatic spinal cord injury, and ALS. Potent ASIC1a inhibitors should have promising therapeutic potential for ASIC1a-related diseases.

Aims: We examined the inhibitory effects of a number of amiloride analogs on ASIC1a currents, aimed at understanding the structure-activity relationship and identifying potent ASIC1a inhibitors for stroke intervention.

Methods: Whole-cell patch-clamp techniques and a mouse model of middle cerebral artery occlusion (MCAO)-induced focal ischemia were used. Surflex-Dock was used to dock the analogs into the pocket with default parameters.

Results: Amiloride and its analogs inhibit ASIC1a currents expressed in Chinese hamster ovary cells with a potency rank order of benzamil > phenamil > 5-(N,N-dimethyl)amiloride (DMA) > amiloride > 5-(N,N-hexamethylene)amiloride (HMA) ≥ 5-(N-methyl-N-isopropyl)amiloride (MIA) > 5-(N-ethyl-N-isopropyl)amiloride (EIPA). In addition, amiloride and its analogs inhibit ASIC currents in cortical neurons with the same potency rank order. In mice, benzamil and EIPA decreased MCAO-induced infarct volume. Similar to its effect on the ASIC current, benzamil showed a much higher potency than EIPA.

Conclusion: Addition of a benzyl group to the terminal guanidinyl group resulted in enhanced inhibitory activity on ASIC1a. On the other hand, the bulky groups added to the 5-amino residues slightly decreased the activity. Among the tested amiloride analogs, benzamil is the most potent ASIC1a inhibitor.
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http://dx.doi.org/10.1111/cns.12524DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4996284PMC
June 2016

Region specific contribution of ASIC2 to acidosis-and ischemia-induced neuronal injury.

J Cereb Blood Flow Metab 2017 Feb 21;37(2):528-540. Epub 2016 Jul 21.

1 Department of Physiology and Cell Biology, University of South Alabama, Mobile, USA.

Acidosis in the brain plays a critical role in neuronal injury in neurological diseases, including brain ischemia. One key mediator of acidosis-induced neuronal injury is the acid-sensing ion channels (ASICs). Current literature has focused on ASIC1a when studying acid signaling. The importance of ASIC2, which is also widely expressed in the brain, has not been appreciated. We found here a region-specific effect of ASIC2 on acid-mediated responses. Deleting ASIC2 reduced acid-activated current in cortical and striatal neurons, but had no significant effect in cerebellar granule neurons. In addition, we demonstrated that ASIC2 was important for ASIC1a expression, and that ASIC2a but not 2b facilitated ASIC1a surface trafficking in the brain. Further, we showed that ASIC2 deletion attenuated acidosis/ischemia-induced neuronal injury in organotypic hippocampal slices but had no effect in organotypic cerebellar slices. Consistent with an injurious role of ASIC2, we showed that ASIC2 deletion significantly protected the mouse brain from ischemic damage in vivo. These data suggest a critical region-specific contribution of ASIC2 to neuronal injury and reveal an important functional difference between ASIC2a and 2b in the brain.
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http://dx.doi.org/10.1177/0271678X16630558DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5381448PMC
February 2017

Epigenetic modulation of gene expression governs the brain's response to injury.

Authors:
Roger P Simon

Neurosci Lett 2016 06 29;625:16-9. Epub 2015 Dec 29.

Translational Stroke Program, Neuroscience Institute, Morehouse School of Medicine, Atlanta, GA, USA; Grady Memorial Hospital, Atlanta, GA, USA. Electronic address:

Mild stress from ischemia, seizure, hypothermia, or infection can produce a transient neuroprotected state in the brain. In the neuroprotected state, the brain responds differently to a severe stress and sustains less injury. At the genomic level, the response of the neuroprotected brain to a severe stress is characterized by widespread differential regulation of genes with diverse functions. This reprogramming of gene expression observed in the neuroprotected brain in response to a stress is consistent with an epigenetic model of regulation mediated by changes in DNA methylation and histone modification. Here, we summarize our evolving understanding of the molecular basis for endogenous neuroprotection and review recent findings that implicate DNA methylation and protein mediators of histone modification as epigenetic regulators of the brain's response to injury.
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http://dx.doi.org/10.1016/j.neulet.2015.12.024DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4903900PMC
June 2016

Dynamic changes in DNA methylation in ischemic tolerance.

Front Neurol 2015 15;6:102. Epub 2015 May 15.

Translational Stroke Program, Neuroscience Institute, Morehouse School of Medicine , Atlanta, GA , USA ; Grady Memorial Hospital , Atlanta, GA , USA.

Epigenetic mediators of gene expression are hypothesized to regulate transcriptomic responses to preconditioning ischemia and ischemic tolerance. Here, we utilized a methyl-DNA enrichment protocol and sequencing (ChIP-seq) to identify patterns of DNA methylation in an established model of ischemic tolerance in neuronal cultures (oxygen and glucose deprivation: OGD). We observed an overall decrease in global DNA methylation at 4 h following preconditioning ischemia (30 min OGD), harmful ischemia (120 min OGD), and in ischemic tolerant neuronal cultures (30 min OGD, 24 h recovery, 120 min OGD). We detected a smaller cohort of hypermethylated regions following ischemic conditions, which were further analyzed revealing differential chromosomal localization of methylation, and a differential concentration of methylation on genomic regions. Together, these data show that the temporal profiles of DNA methylation with respect to chromatin hyper- and hypo-methylation following various ischemic conditions are highly dynamic, and may reveal novel targets for neuroprotection.
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http://dx.doi.org/10.3389/fneur.2015.00102DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4432797PMC
June 2015

A critical review of mechanisms regulating remote preconditioning-induced brain protection.

J Appl Physiol (1985) 2015 Nov 7;119(10):1135-42. Epub 2015 May 7.

Translational Stroke Program, Neuroscience Institute, Morehouse School of Medicine, Atlanta, Georgia; and Grady Memorial Hospital, Atlanta, Georgia.

Remote preconditioning (rPC) is the phenomenon whereby brief organ ischemia evokes an endogenous response such that a different (remote) organ is protected against subsequent, normally injurious ischemia. Experiments show rPC to be effective at evoking cardioprotection against ischemic heart injury and, more recently, neuroprotection against brain ischemia. Such is the enthusiasm for rPC that human studies have been initiated. Clinical trials suggest rPC to be safe (phase II trial) and effective in reducing stroke incidence in a population with high stroke risk. However, despite the therapeutic potential of rPC, there is a large gap in knowledge regarding the effector mechanisms of rPC and how it might be orchestrated to improve outcome after stroke. Here we provide a critical review of mechanisms that are directly attributable to rPC-induced neuroprotection in preclinical trials of rPC.
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http://dx.doi.org/10.1152/japplphysiol.00169.2015DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4816414PMC
November 2015

Transcriptional Response of Polycomb Group Genes to Status Epilepticus in Mice is Modified by Prior Exposure to Epileptic Preconditioning.

Front Neurol 2015 10;6:46. Epub 2015 Mar 10.

Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland , Dublin , Ireland.

Exposure of the brain to brief, non-harmful seizures can activate protective mechanisms that temporarily generate a damage-refractory state. This process, termed epileptic tolerance, is associated with large-scale down-regulation of gene expression. Polycomb group (PcG) proteins are master controllers of gene silencing during development that are re-activated by injury to the brain. Here, we explored the transcriptional response of genes associated with polycomb repressive complex (PRC) 1 (Ring1A, Ring1B, and Bmi1) and PRC2 (Ezh1, Ezh2, and Suz12), as well as additional transcriptional regulators Sirt1, Yy1, and Yy2, in a mouse model of status epilepticus (SE). Findings were contrasted to changes after SE in mice previously given brief seizures to evoke tolerance. Real-time quantitative PCR showed SE prompted an early (1 h) increase in expression of several genes in PRC1 and PRC2 in the hippocampus, followed by down-regulation of many of the same genes at later times points (4, 8, and 24 h). Spatio-temporal differences were found among PRC2 genes in epileptic tolerance, including increased expression of Ezh2, Suz12, and Yy2 relative to the normal injury response to SE. In contrast, PRC1 complex genes including Ring 1B and Bmi1 displayed differential down-regulation in epileptic tolerance. The present study characterizes PcG gene expression following SE and shows prior seizure exposure produces select changes to PRC1 and PRC2 composition that may influence differential gene expression in epileptic tolerance.
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http://dx.doi.org/10.3389/fneur.2015.00046DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4354380PMC
March 2015

Acid-sensing ion channels in mouse olfactory bulb M/T neurons.

J Gen Physiol 2014 Jun 12;143(6):719-31. Epub 2014 May 12.

Department of Neurobiology, Neuroscience Institute, Morehouse School of Medicine, Atlanta, GA 30310

The olfactory bulb contains the first synaptic relay in the olfactory pathway, the sensory system in which odorants are detected enabling these chemical stimuli to be transformed into electrical signals and, ultimately, the perception of odor. Acid-sensing ion channels (ASICs), a family of proton-gated cation channels, are widely expressed in neurons of the central nervous system. However, no direct electrophysiological and pharmacological characterizations of ASICs in olfactory bulb neurons have been described. Using a combination of whole-cell patch-clamp recordings and biochemical and molecular biological analyses, we demonstrated that functional ASICs exist in mouse olfactory bulb mitral/tufted (M/T) neurons and mainly consist of homomeric ASIC1a and heteromeric ASIC1a/2a channels. ASIC activation depolarized cultured M/T neurons and increased their intracellular calcium concentration. Thus, ASIC activation may play an important role in normal olfactory function.
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http://dx.doi.org/10.1085/jgp.201310990DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4035746PMC
June 2014

Nascent proteomes in peripheral blood mononuclear cells as a novel source for biomarker discovery in human stroke.

Stroke 2014 Apr 20;45(4):1177-9. Epub 2014 Feb 20.

From the Department of Neurobiology (F.B., R.P.S., Y.L., A.Z.), and Clinical Research Center (J.W.), Morehouse School of Medicine, Atlanta, GA; Marcus Stroke and Neuroscience Center, Grady Memorial Hospital, Atlanta, GA (R.P.S., M.F.); Department of Biochemistry, Oregon Health Science University, Portland (L.D.); and Department of Neurology, Emory University, Atlanta, GA (C.L.H., M.F.).

Background And Purpose: The proteome of newly synthesized proteins (nascent proteome) in peripheral blood mononuclear cells (PBMCs) can be a novel source of stroke biomarkers. Changes in the PBMC nascent proteome after stroke reflect the dynamic response-in-action not detectable in the total proteome (all existing proteins) in blood. Here, we test the application of nascent proteomics as a novel approach for stroke biomarker discovery.

Methods: The PBMC nascent proteome in human blood was determined by metabolic labeling of fresh PBMC cultures with azidohomoalanine (an azide-containing methionine surrogate), followed by mass spectrometry detection and quantification of azidohomoalanine-labeled proteins. The PBMC nascent and total proteomes were compared between patients with stroke and matched controls.

Results: Both PBMC nascent and total proteomes showed differences between stroke patients and controls. Results of hierarchical clustering analysis of proteomic data revealed greater changes in the nascent than in the total PBMC proteomes, supporting the usefulness of the PBMC nascent proteome as a novel source of stroke biomarkers.

Conclusions: Nascent proteomes in PBMC can be a novel source for biomarker discovery in human stroke.
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http://dx.doi.org/10.1161/STROKEAHA.113.004576DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3992918PMC
April 2014

Racial and sex differences in associations between activities of daily living and cognition in community-dwelling older adults.

J Am Geriatr Soc 2013 Dec;61(12):2174-2180

Division of Gerontology, Geriatrics, and Palliative Care, University of Alabama at Birmingham, Birmingham, Alabama.

Objectives: To examine the association between function measured according to activities of daily living (ADLs), instrumental activ1ities of daily living (IADLs), and cognition assessed according to Mini-Mental State Examination (MMSE) scores of older African-American and non-Hispanic white community-dwelling men and women.

Design: Cross-sectional study assessing associations between self-reported ADL and IADL difficulty and MMSE scores for race- and sex-specific groups.

Setting: Homes of community-dwelling older adults.

Participants: A random sample of 974 African-American and non-Hispanic white Medicare beneficiaries aged 65 and older living in west-central Alabama and participating in the University of Alabama at Birmingham Study of Aging, excluding those with reported diagnoses of dementia or with missing data.

Measurements: Function, based on self-reported difficulty in performing ADLs and IADLs, and cognition, using the MMSE. Multivariable linear regression models were used to test the association between function and cognition in race- and sex-specific groups after adjusting for covariates.

Results: Mini-Mental State Examination scores were modestly correlated with ADL and IADL difficulty in all four race- and sex-specific groups, with Pearson correlation coefficients ranging from −0.189 for non-Hispanic white women to −0.429 for African-American men. Correlations between MMSE and ADL or IADL difficulty in any of the race- and sex-specific groups were no longer significant after controlling for sociodemographic factors and comorbidities.

Conclusion: Mini-Mental State Examination was not significantly associated with functional difficulty in older African-American and non-Hispanic white men and women after adjusting for sociodemographic factors and comorbidities, suggesting a mediating role in the relationship between cognition and function.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3909884PMC
http://dx.doi.org/10.1111/jgs.12543DOI Listing
December 2013

Explicit consideration of baseline factors to assess recombinant tissue-type plasminogen activator response with respect to race and sex.

Stroke 2013 Jun 14;44(6):1525-31. Epub 2013 May 14.

Stroke Outcomes Laboratory, Department of Neurology, Baylor College of Medicine, The Michael E. DeBakey VA Medical Center, 2002 Holcombe Blvd (127), Houston, TX 77030, USA.

Background And Purpose: Sex and race reportedly influence outcome after recombinant tissue-type plasminogen activator (rtPA). It is, however, unclear whether baseline imbalances (eg, stroke severity) or lack of response to thrombolysis is responsible. We applied balancing methods to test the hypothesis that race and sex influence outcome after rtPA independent of baseline conditions.

Methods: We mapped group outcomes from the National Institute of Neurological Disorders and Stroke (NINDS) dataset based on race and sex onto a surrogate-control function to assess differences from expected outcomes at their respective National Institutes of Health Stroke Scale and age. Outcomes were also compared for subjects matched individually on key baseline factors using NINDS and 2 recent datasets from southeastern United States.

Results: At similar National Institutes of Health Stroke Scale and age, 90-day good outcomes (modified Rankin Score, 0-2) in NINDS were similarly improved after rtPA for white men and women. There was a strong trend for improvement in black men. Conversely, black women treated with rtPA showed response rates no different from the controls. After baseline matching, there were nonsignificant trends in outcomes except for significantly fewer good outcomes in black versus matched white women (37% versus 63%; P=0.027). Pooling the 3 datasets showed a similar trend for poorer short-term outcome for black women (P=0.054; modified Rankin Score, 0-1).

Conclusions: Matching for key baseline factors indicated that race and sex influence outcome most strikingly in black women who demonstrated poorest outcomes after rtPA. This finding supports the hypothesis that poor response to rtPA, rather than differences in baseline conditions, contributes to the worse outcome. This finding requires prospective confirmation.
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http://dx.doi.org/10.1161/STROKEAHA.113.001116DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5535075PMC
June 2013

Tolerance to ischemia - an increasingly complex biology.

Transl Stroke Res 2013 Feb 11;4(1):40-50. Epub 2013 Jan 11.

Neuroscience Institute, Morehouse School of Medicine, 720 Westview Drive SW, Atlanta, GA, 30310-1495 ; Department of Neurobiology, Morehouse School of Medicine, 720 Westview Drive SW, Atlanta, GA, 30310-1495 ; Department of Pharmacology, Morehouse School of Medicine, 720 Westview Drive SW, Atlanta, GA, 30310-1495.

In this review we identify and discuss some of the genomics studies of preconditioning and the ischemic tolerance phenomenon. Such studies have been attempted in multiple species, using different array technologies and with different preconditioning and tolerance models. In addition, studies are starting to reveal epigenetic mechanisms and modifiers of tolerance and preconditioning. Together these studies are starting to reveal some of the immense complexity of the ischemic tolerance phenomenon, yet further studies await to be performed.
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http://dx.doi.org/10.1007/s12975-012-0246-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3596882PMC
February 2013

Expression profiling the microRNA response to epileptic preconditioning identifies miR-184 as a modulator of seizure-induced neuronal death.

Exp Neurol 2012 Oct 5;237(2):346-54. Epub 2012 Jul 5.

Department of Physiology & Medical Physics, Royal College of Surgeons in Ireland, Dublin 2, Ireland.

Brief seizures (epileptic/seizure preconditioning) are capable of activating endogenous protective pathways in the brain which can temporarily generate a damage-refractory state against subsequent and otherwise harmful episodes of prolonged seizures (tolerance). Altered expression of microRNAs, a class of non-coding RNAs that function post-transcriptionally to regulate mRNA translation has recently been implicated in the molecular mechanism of epileptic tolerance. Here we characterized the effect of seizure preconditioning induced by low-dose systemic kainic acid on microRNA expression in the hippocampus of mice. Seizure preconditioning resulted in up-regulation of 25 mature microRNAs in the CA3 subfield of the mouse hippocampus, with the highest levels detected for miR-184. This finding was supported by real time PCR and in situ hybridization showing increased neuronal miR-184 levels and a reduction in protein levels of a miR-184 target. Inhibiting miR-184 expression in vivo resulted in the emergence of neuronal death after preconditioning seizures and increased seizure-induced neuronal death following status epilepticus in previously preconditioned animals, without altered electrographic seizure durations. The present study suggests miRNA up-regulation after preconditioning may contribute to development of epileptic tolerance and identifies miR-184 as a novel contributor to neuronal survival following both mild and severe seizures.
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http://dx.doi.org/10.1016/j.expneurol.2012.06.029DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3485639PMC
October 2012

Reduced mature microRNA levels in association with dicer loss in human temporal lobe epilepsy with hippocampal sclerosis.

PLoS One 2012 15;7(5):e35921. Epub 2012 May 15.

Department of Physiology and Medical Physics, Royal College of Surgeons in Ireland, Dublin, Ireland.

Hippocampal sclerosis (HS) is a common pathological finding in patients with temporal lobe epilepsy (TLE) and is associated with altered expression of genes controlling neuronal excitability, glial function, neuroinflammation and cell death. MicroRNAs (miRNAs), a class of small non-coding RNAs, function as post-transcriptional regulators of gene expression and are critical for normal brain development and function. Production of mature miRNAs requires Dicer, an RNAase III, loss of which has been shown to cause neuronal and glial dysfunction, seizures, and neurodegeneration. Here we investigated miRNA biogenesis in hippocampal and neocortical resection specimens from pharmacoresistant TLE patients and autopsy controls. Western blot analysis revealed protein levels of Dicer were significantly lower in certain TLE patients with HS. Dicer levels were also reduced in the hippocampus of mice subject to experimentally-induced epilepsy. To determine if Dicer loss was associated with altered miRNA processing, we profiled levels of 380 mature miRNAs in control and TLE-HS samples. Expression of nearly 200 miRNAs was detected in control human hippocampus. In TLE-HS samples there was a large-scale reduction of miRNA expression, with 51% expressed at lower levels and a further 24% not detectable. Primary transcript (pri-miRNAs) expression levels for several tested miRNAs were not different between control and TLE-HS samples. These findings suggest loss of Dicer and failure of mature miRNA expression may be a feature of the pathophysiology of HS in patients with TLE.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0035921PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3352899PMC
September 2012

Cell cycle arrest associated with anoxia-induced quiescence, anoxic preconditioning, and embryonic diapause in embryos of the annual killifish Austrofundulus limnaeus.

J Comp Physiol B 2012 Oct 9;182(7):909-20. Epub 2012 May 9.

Department of Biology, Portland State University, P.O. Box 751, Portland, OR 97207-0751, USA.

Embryos of the annual killifish Austrofundulus limnaeus can enter into dormancy associated with diapause and anoxia-induced quiescence. Dormant embryos are composed primarily of cells arrested in the G(1)/G(0) phase of the cell cycle based on flow cytometry analysis of DNA content. In fact, most cells in developing embryos contain only a diploid complement of DNA, with very few cells found in the S, G(2), or M phases of the cell cycle. Diapause II embryos appear to be in a G(0)-like state with low levels of cyclin D1 and p53. However, the active form of pAKT is high during diapause II. Exposure to anoxia causes an increase in cyclin D1 and p53 expression in diapause II embryos, suggesting a possible re-entry into the cell cycle. Post-diapause II embryos exposed to anoxia or anoxic preconditioning have stable levels of cyclin D1 and stable or reduced levels of p53. The amount of pAKT is severely reduced in 12 dpd embryos exposed to anoxia or anoxic preconditioning. This study is the first to evaluate cell cycle control in embryos of A. limnaeus during embryonic diapause and in response to anoxia and builds a foundation for future research on the role of cell cycle arrest in supporting vertebrate dormancy.
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http://dx.doi.org/10.1007/s00360-012-0672-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3448833PMC
October 2012

Toll-like receptor 7 preconditioning induces robust neuroprotection against stroke by a novel type I interferon-mediated mechanism.

Stroke 2012 May 8;43(5):1383-9. Epub 2012 Mar 8.

Department of Molecular Microbiology and Immunology, Oregon Health & Science University, Portland, OR 97239, USA.

Background And Purpose: Systemic administration of Toll-like receptor (TLR) 4 and TLR9 agonists before cerebral ischemia have been shown to reduce ischemic injury by reprogramming the response of the brain to stroke. Our goal was to explore the mechanism of TLR-induced neuroprotection by determining whether a TLR7 agonist also protects against stroke injury.

Methods: C57Bl/6, TNF(-/-), interferon (IFN) regulatory factor 7(-/-), or type I IFN receptor (IFNAR)(-/-) mice were subcutaneously administered the TLR7 agonist Gardiquimod (GDQ) 72 hours before middle cerebral artery occlusion. Infarct volume and functional outcome were determined after reperfusion. Plasma cytokine responses and induction of mRNA for IFN-related genes in the brain were measured. IFNAR(-/-) mice also were treated with the TLR4 agonist (lipopolysaccharide) or the TLR9 agonist before middle cerebral artery occlusion and infarct volumes measured.

Results: The results show that GDQ reduces infarct volume as well as functional deficits in mice. GDQ pretreatment provided robust neuroprotection in TNF(-/-) mice, indicating that TNF was not essential. GDQ induced a significant increase in plasma IFNα levels and both IRF7(-/-) and IFNAR(-/-) mice failed to be protected, implicating a role for IFN signaling in TLR7-mediated protection.

Conclusions: Our studies provide the first evidence that TLR7 preconditioning can mediate neuroprotection against ischemic injury. Moreover, we show that the mechanism of protection is unique from other TLR preconditioning ligands in that it is independent of TNF and dependent on IFNAR.
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http://dx.doi.org/10.1161/STROKEAHA.111.641522DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3943206PMC
May 2012

Can genes modify stroke outcome and by what mechanisms?

Stroke 2012 Jan 8;43(1):286-91. Epub 2011 Dec 8.

The Neuroscience Institute, Morehouse Medical School, 720 Westview Dr, SW, Atlanta, GA, 30310-1495, USA.

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http://dx.doi.org/10.1161/STROKEAHA.111.622225DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3282466PMC
January 2012

miRNA Expression profile after status epilepticus and hippocampal neuroprotection by targeting miR-132.

Am J Pathol 2011 Nov 23;179(5):2519-32. Epub 2011 Sep 23.

Department of Physiology & Medical Physics, Royal College of Surgeons in Ireland, Dublin, Ireland.

When an otherwise harmful insult to the brain is preceded by a brief, noninjurious stimulus, the brain becomes tolerant, and the resulting damage is reduced. Epileptic tolerance develops when brief seizures precede an episode of prolonged seizures (status epilepticus). MicroRNAs (miRNAs) are small, noncoding RNAs that function as post-transcriptional regulators of gene expression. We investigated how prior seizure preconditioning affects the miRNA response to status epilepticus evoked by intra-amygdalar kainic acid in mice. The miRNA was extracted from the ipsilateral CA3 subfield 24 hours after focal-onset status epilepticus in animals that had previously received either seizure preconditioning (tolerance) or no preconditioning (injury), and mature miRNA levels were measured using TaqMan low-density arrays. Expression of 21 miRNAs was increased, relative to control, after status epilepticus alone, and expression of 12 miRNAs was decreased. Increased miR-132 levels were matched with increased binding to Argonaute-2, a constituent of the RNA-induced silencing complex. In tolerant animals, expression responses of >40% of the injury-group-detected miRNAs differed, being either unchanged relative to control or down-regulated, and this included miR-132. In vivo microinjection of locked nucleic acid-modified oligonucleotides (antagomirs) against miR-132 depleted hippocampal miR-132 levels and reduced seizure-induced neuronal death. Thus, our data strongly suggest that miRNAs are important regulators of seizure-induced neuronal death.
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http://dx.doi.org/10.1016/j.ajpath.2011.07.036DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3204080PMC
November 2011

Suppression of TNF receptor-1 signaling in an in vitro model of epileptic tolerance.

Int J Physiol Pathophysiol Pharmacol 2011 13;3(2):120-32. Epub 2011 Jun 13.

Tumor necrosis factor-α (TNFα) is a pleiotropic cytokine that can regulate cell survival, inflammation or, under certain circumstances, trigger cell death. Previous work in rat seizure models and analysis of temporal lobe samples from epilepsy patients has suggested seizures activate TNF receptor 1 (TNFR1). Here we explored the activation and functional significance of TNFR1 signaling in the mouse hippocampus using in vitro and in vivo models of seizure-induced neuronal injury. Focal-onset status epilepticus in mice upregulated TNFR1 levels and led to formation of TNFR1-TNFR-associated death domain (TRADD) and TRADD-Fas-associated death domain (FADD) binding. Seizure-like injury modeled in vitro by removal of chronic excitatory blockade in mouse hippocampal neurons also activated this TNFR1 signaling pathway. Prior exposure of hippocampal neurons to a non-harmful seizure episode, via NMDA receptor blockade, 24 h prior to injurious seizures significantly reduced cell death and modeled epileptic tolerance in vitro. TNFR1 complex formation with TRADD and TRADD-FADD binding were reduced in tolerant cells. Finally, TNFR1 signaling and cell death were reduced by PKF-242-484, a dual matrix metaloproteinase/TNFα converting enzyme inhibitor. The present study shows that TNFR1 signaling is activated in mouse seizure models and may contribute to neuropathology in vitro and in vivo while suppression of this pathway may underlie neuroprotection in epileptic tolerance.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3134006PMC
November 2011

Multiple preconditioning paradigms converge on interferon regulatory factor-dependent signaling to promote tolerance to ischemic brain injury.

J Neurosci 2011 Jun;31(23):8456-63

Department of Molecular Microbiology and Immunology, Oregon Health & Science University, Portland, Oregon 97239, USA.

Ischemic tolerance can be induced by numerous preconditioning stimuli, including various Toll-like receptor (TLR) ligands. We have shown previously that systemic administration of the TLR4 ligand LPS or the TLR9 ligand unmethylated CpG oligodeoxynucleotide before transient brain ischemia in mice confers substantial protection against ischemic damage. To elucidate the molecular mechanisms of preconditioning, we compared brain genomic profiles in response to preconditioning with these TLR ligands and with preconditioning via exposure to brief ischemia. We found that exposure to the TLR ligands and brief ischemia induced genomic changes in the brain characteristic of a TLR pathway-mediated response. Interestingly, all three preconditioning stimuli resulted in a reprogrammed response to stroke injury that converged on a shared subset of 13 genes not evident in the genomic profile from brains that were subjected to stroke without prior preconditioning. Analysis of the promoter region of these shared genes showed sequences required for interferon regulatory factor (IRF)-mediated transcription. The importance of this IRF gene network was tested using mice deficient in IRF3 or IRF7. Our data show that both transcription factors are required for TLR-mediated preconditioning and neuroprotection. These studies are the first to discover a convergent mechanism of neuroprotection induced by preconditioning--one that potentially results in reprogramming of the TLR-mediated response to stroke and requires the presence of IRF3 and IRF7.
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http://dx.doi.org/10.1523/JNEUROSCI.0821-11.2011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3130521PMC
June 2011

Expression of neurogenesis genes in human temporal lobe epilepsy with hippocampal sclerosis.

Int J Physiol Pathophysiol Pharmacol 2011 15;3(1):38-47. Epub 2010 Dec 15.

Both evoked and spontaneous seizures have been reported to increase neurogenesis in animal models. Less is known about whether neurogenesis and markers thereof are aberrantly expressed in human temporal lobe epilepsy (TLE) with hippocampal sclerosis. In the present study we measured protein levels of multiple neurogenesis marker genes using Western blotting. Tissue homogenates from sclerotic hippocampus surgically resected from patients with pharmacoresistantTLE (n = 7) were compared to hippocampal samples from a group of age- and gender-matched autopsy controls (n = 6). Expression of the mature neuron marker NeuN was significantly lower in TLE samples compared to controls. In contrast, levels of neurogenesis-associated genes including TUC-4, doublecortin, Neu-roD and Numb, were all similarly expressed in TLE and control hippocampus samples. The present study suggests hippocampal expression levels of proteins associated with neurogenesis are not notably different in human TLE, implying the sclerotic hippocampus may retain neurogenic potential.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3068852PMC
July 2011

Identification of a novel Bcl-2-interacting mediator of cell death (Bim) E3 ligase, tripartite motif-containing protein 2 (TRIM2), and its role in rapid ischemic tolerance-induced neuroprotection.

J Biol Chem 2011 Jun 8;286(22):19331-9. Epub 2011 Apr 8.

Neuroscience Institute, Morehouse School of Medicine, Atlanta, Georgia 30310-1495, USA.

We have previously shown that the cell death-promoting protein Bcl-2-interacting mediator of cell death (Bim) is ubiquitinated and degraded following a neuroprotection-conferring episode of brief ischemia (preconditioning). Here, we identify the E3 ligase that ubiquitinates Bim in this model, using a proteomics approach. Using phosphorylated GST-Bim as bait, we precipitated and identified by mass spectrometry tripartite motif protein 2 (TRIM2), a RING (really interesting new gene) domain-containing protein. The reaction between TRIM2 and Bim was confirmed using co-immunoprecipitation followed by immunoblotting. We show that TRIM2 binds to Bim when it is phosphorylated by p42/p44 MAPK but does not interact with a nonphosphorylatable Bim mutant (3ABim). 12-O-tetradecanoylphorbol-13-acetate activation of p42/p44 MAPK drives Bim ubiquitination in mouse embryonic fibroblast cells and is associated with an increased interaction between TRIM2 and Bim. One hour following preconditioning ischemia, the binding of Bim to TRIM2 increased, consistent with the time window of enhanced Bim degradation. Blocking p42/p44 MAPK activation following preconditioning ischemia with U0126 or using the nonphosphorylatable 3ABim reduced the binding between Bim and TRIM2. Immunodepletion of TRIM2 from cell lysates prepared from preconditioned cells reduced Bim ubiquitination. Finally, suppression of TRIM2 expression, using lentivirus transduction of shRNAmir, stabilized Bim protein levels and blocked neuroprotection observed in rapid ischemic tolerance. Taken together, these data support a role for TRIM2 in mediating the p42/p44 MAPK-dependent ubiquitination of Bim in rapid ischemic tolerance.
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http://dx.doi.org/10.1074/jbc.M110.197707DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3103311PMC
June 2011

Inhibition of acid sensing ion channel currents by lidocaine in cultured mouse cortical neurons.

Anesth Analg 2011 Apr 8;112(4):977-81. Epub 2011 Mar 8.

Department of Anesthesiology, SUNY Downstate Medical Center, 450 Clarkson Ave., Box 6, Brooklyn, NY 11203, USA.

Background: Lidocaine is a local anesthetic that has multiple pharmacological effects including antiarrhythmia, antinociception, and neuroprotection. Acid sensing ion channels (ASICs) are proton-gated cation channels that belong to the epithelial sodium channel/degenerin superfamily. Activation of ASICs by protons results in sodium and calcium influx. ASICs have been implicated in various physiological processes including learning/memory, nociception, and in acidosis-mediated neuron injury. In this study, we examined the effect of lidocaine on ASICs in cultured mouse cortical neurons.

Methods: ASIC currents were activated and recorded using a whole-cell patch-clamp technique in cultured mouse cortical neurons. The effects of lidocaine at different concentrations were examined. To determine whether the inhibition of lidocaine on ASIC currents is subunit specific, we examined the effect of lidocaine on homomeric ASIC1a and ASIC2a currents expressed in Chinese hamster ovary cells.

Results: Lidocaine significantly inhibits the ASIC currents in mouse cortical neurons. The inhibition was reversible and dose dependent. A detectable effect was noticed at a concentration of 0.3 mM lidocaine. At 30 mM, ASIC current was inhibited by approximately 90%. Analysis of the complete dose-response relationship yielded a half-maximal inhibitory concentration of 11.79 ± 1.74 mM and a Hill coefficient of 2.7 ± 0.5 (n = 10). The effect is rapid and does not depend on pH. In Chinese hamster ovary cells expressing different ASIC subunits, lidocaine inhibits the ASIC1a current without affecting the ASIC2a current.

Conclusion: ASIC currents are significantly inhibited by lidocaine. Our finding reveals a new pharmacological effect of lidocaine in neurons.
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http://dx.doi.org/10.1213/ANE.0b013e31820a511cDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3387555PMC
April 2011
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