Publications by authors named "Michelle Aarts"

21 Publications

  • Page 1 of 1

mRNA expression of transient receptor potential melastatin (TRPM) channels 2 and 7 in perinatal brain development.

Int J Dev Neurosci 2018 Oct 26;69:23-31. Epub 2018 May 26.

Department of Biological Sciences, University of Toronto Scarborough, Ontario, Canada.

TRPM7 and TRPM2 are non-specific cation channels of the Transient Receptor Potential channel superfamily. Each channel has gained attention for their potential to mediate oxidative and anoxic cell death (Rama and García, 2016; Nazıroğlu, 2011a; Abiria et al., 2017; Sun, 2017), however their physiological expression and roles in the developing brain remain poorly defined. We employed real-time reverse transcription PCR to examine mRNA expression of TRPM7 and TRPM2 in the developing rat brain and brain-specific cell types. We determined the temporal and spatial expression patterns at four developmental time points (postnatal day 7, 14, 21, and 90) in four critical regions of the brain (cortex, hippocampus, striatum, and cerebellum) and examined gene expression in neuronal, astrocytic, and microglial primary cell cultures. Our results revealed that TRPM7 mRNA expression peaks in the cortex at 2-weeks after birth, and thus correlates most closely with a period of rat brain development associated with neurite outgrowth, which is heightened at 2-weeks after birth. Our cell-specific gene expression assays revealed that TRPM7 was expressed at equivalent levels in neurons, astrocytes, and microglia. Conversely, TRPM2 was most highly expressed in microglia with little expression in neurons and astrocytes. In the hippocampus and striatum, the expression profile of TRPM2 parallels the perinatal expression timeline for microglial infiltration and maturation in the rat brain. Microglial maturation is highest from the time of birth, up to 7-days, but subsequently declines. The latter developmental expression profiles indicate a role for TRPM2 in microglial activation.
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http://dx.doi.org/10.1016/j.ijdevneu.2018.05.008DOI Listing
October 2018

Differential expression of sirtuin family members in the developing, adult, and aged rat brain.

Front Aging Neurosci 2014 18;6:333. Epub 2014 Dec 18.

Division of Genetics and Development, Toronto Western Research Institute Toronto, ON, Canada ; Department of Physiology, University of Toronto Toronto, ON, Canada ; Institute of Medical Sciences, University of Toronto Toronto, ON, Canada ; Department of Surgery (Neurosurgery), University of Toronto Toronto, ON, Canada.

The sirtuins are NAD(+)-dependent protein deacetylases and/or ADP-ribosyltransferases that play roles in metabolic homeostasis, stress response and potentially aging. This enzyme family resides in different subcellular compartments, and acts on a number of different targets in the nucleus, cytoplasm and in the mitochondria. Despite their recognized ability to regulate metabolic processes, the roles played by specific sirtuins in the brain-the most energy demanding tissue in the body-remains less well investigated and understood. In the present study, we examined the regional mRNA and protein expression patterns of individual sirtuin family members in the developing, adult, and aged rat brain. Our results show that while each sirtuin is expressed in the brain at each of these different stages, they display unique spatial and temporal expression patterns within the brain. Further, for specific members of the family, the protein expression profile did not coincide with their respective mRNA expression profile. Moreover, using primary cultures enriched for neurons and astrocytes respectively, we found that specific sirtuin members display preferential neural lineage expression. Collectively, these results provide the first composite illustration that sirtuin family members display differential expression patterns in the brain, and provide evidence that specific sirtuins could potentially be targeted to achieve cell-type selective effects within the brain.
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http://dx.doi.org/10.3389/fnagi.2014.00333DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4270178PMC
January 2015

Uncoupling PSD-95 interactions leads to rapid recovery of cortical function after focal stroke.

J Cereb Blood Flow Metab 2013 Dec 11;33(12):1937-43. Epub 2013 Sep 11.

Institute of Medical Sciences, University of Toronto, Toronto, Ontario, Canada.

Since the most significant ischemic sequelae occur within hours of stroke, it is necessary to understand how neuronal function changes during this time. While histologic and behavioral models show the extent of stroke-related damage, only in vivo recordings can illustrate changes in brain activity during stroke and validate effectiveness of neuroprotective compounds. Spontaneous and evoked field potentials (fEPs) were recorded in the deep layers of the cortex with a linear microelectrode array for 3 hours after focal stroke in anesthetized rats. Tat-NR2B9c peptide, which confers neuroprotection by uncoupling the PSD-95 protein from N-methyl-D-aspartate receptor (NMDAR), was administered 5 minutes before ischemia. Evoked field potentials were completely suppressed within 3 minutes of infarct in all ischemic groups. Evoked field potential recovery after stroke in rats treated with Tat-NR2B9c (83% of baseline) was greater compared with stroke-only (61% of baseline) or control peptide (Tat-NR2B-AA; 67% of baseline) groups (P<0.001). Electroencephalography (EEG) power was higher in Tat-NR2B9c-treated animals at both 20 minutes and 1 hour (50% and 73% of baseline, respectively) compared with stroke-only and Tat-NR2B-AA-treated rats (P<0.05). Tat-NR2B9c significantly reduces stroke-related cortical dysfunction as evidenced by greater recovery of fEPs and EEG power; illustrating the immediate effects of the compound on poststroke brain function.
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http://dx.doi.org/10.1038/jcbfm.2013.153DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3851903PMC
December 2013

High-frequency cortical activity associated with postischemic epileptiform discharges in an in vivo rat focal stroke model.

J Neurosurg 2013 May 15;118(5):1098-106. Epub 2013 Feb 15.

Institute of Medical Sciences, University of Toronto, Toronto, Canada.

Object: The postischemic brain has greater susceptibility to epileptogenic activity than physiologically healthy tissue. Epileptiform discharges are thought to exacerbate postischemic brain function. The aim of this study was to develop an in vivo focal stroke model in rats to characterize epileptiform activity.

Methods: The authors developed a parasagittal 8-channel intracortical microelectrode array to obtain recordings of cortical oscillations of local field potentials following partial middle and anterior cerebral artery occlusion. All experiments were done in urethane-anesthetized Sprague-Dawley rats.

Results: Theta runs (TRs), ranging in duration from 5 seconds to 5 minutes, were observed in 62% of animals within 1 hour of occlusion. High-frequency oscillations (HFOs) in the high gamma range (80-120 Hz) were observed 5-15 seconds before each TR and terminated at the onset of the discharge. Periodic epileptiform discharges (PEDs) were detected in 54% of rats following ischemia. The PEDs consisted of an early negative slow wave, a high-amplitude positive spike, and a short negative slow wave. Transient HFOs in the low gamma range (30-70 Hz) occurred during the first negative wave and the rising phase of the positive spike of the PED.

Conclusions: These recordings provide the first intracortical evidence of a high-frequency component that could be an important element for diagnosis and intervention in postischemic epileptogenic activity. The early onset also suggests that HFOs could serve as a reliable method of detecting small epileptiform events and could be used as a consideration in deciding whether antiepileptic medications are appropriate as part of a patient's poststroke care.
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http://dx.doi.org/10.3171/2013.1.JNS121059DOI Listing
May 2013

Calmodulin kinase IV-dependent CREB activation is required for neuroprotection via NMDA receptor-PSD95 disruption.

J Neurochem 2013 Jul 3;126(2):274-87. Epub 2013 Mar 3.

Department of Biological Sciences, University of Toronto, Scarborough, Ontario, Canada.

NMDA-type glutamate receptors mediate both trophic and excitotoxic signalling in CNS neurons. We have previously shown that blocking NMDAR- post-synaptic density-95 (PSD95) interactions provides significant protection from excitotoxicity and in vivo ischaemia; however, the mechanism of neuroprotection is unclear. Here, we report that blocking PSD-95 interactions with the Tat-NR2B9c peptide enhances a Ca²⁺-dependent protective pathway converging on cAMP Response Element binding protein (CREB) activation. We provide evidence that Tat-NR2B9c neuroprotection from oxygen glucose deprivation and NMDA toxicity occurs in parallel with the activation of calmodulin kinase signalling and is dependent on a sustained phosphorylation of the CREB transcription factor and its activator CaMKIV. Tat-NR2B9c-dependent neuroprotection and CREB phosphorylation are blocked by coapplication of CaM kinase (KN93 and STO-609) or CREB (KG-501) inhibitors, and by siRNA knockdown of CaMKIV. These results are mirrored in vivo in a rat model of permanent focal ischaemia. Tat-NR2B9c application significantly reduces infarct size and causes a selective and sustained elevation in CaMKIV phosphorylation; effects which are blocked by coadministration of KN93. Thus, calcium-dependent nuclear signalling via CaMKIV and CREB is critical for neuroprotection via NMDAR-PSD95 blockade, both in vitro and in vivo. This study highlights the importance of maintaining neuronal function following ischaemic injury. Future stroke research should target neurotrophic and pro-survival signal pathways in the development of novel neuroprotective strategies.
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http://dx.doi.org/10.1111/jnc.12176DOI Listing
July 2013

TRPM7, the cytoskeleton and neuronal death.

Channels (Austin) 2013 Jan 17;7(1):6-16. Epub 2012 Dec 17.

Department of Biological Sciences, University of Toronto, Scarborough, ON, Canada.

Ischemic stroke is one of the leading causes of disability and death in the world. Elucidation of the underlying mechanisms associated with neuronal death during this detrimental process has been of significant interest in the field of research. One principle component vital to the maintenance of cellular integrity is the cytoskeleton. Studies suggest that abnormalities at the level of this fundamental structure are directly linked to adverse effects on cellular well-being, including cell death. In recent years, evidence has also emerged regarding an imperative role for the transient receptor potential (TRP) family member TRPM7 in the mediation of excitotoxic-independent neuronal demise. In this review, we will elaborate on the current knowledge and unique properties associated with the functioning of this structure. In addition, we will deliberate the involvement of distinct mechanistic pathways during TRPM7-dependent cell death, including modifications at the level of the cytoskeleton.
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http://dx.doi.org/10.4161/chan.22824DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3589284PMC
January 2013

A double TRPtych: six views of transient receptor potential channels in disease and health.

J Neurosci 2008 Nov;28(46):11778-84

Department of Anatomy and Cell Biology, Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA.

At the 2008 Annual Meeting of the Society for Neuroscience, a Mini-Symposium entitled "Contributions to TRP Channels to Neurological Disease" included talks from six heads of newly established laboratories, each with a unique research focus, model system, and set of experimental tools. Some of the questions addressed in these talks include the following. What is the role of transient receptor potential (TRP) channels in pain perception? How do normally functioning TRP channels contribute to cell death pathways? What are the characteristics of TRPpathies, disease states that result from overactive or underactive TRP channels? How are TRP channels regulated by signal transduction cascades? This review summarizes recent results from those laboratories and provides six perspectives on the subject of TRP channels and disease.
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http://dx.doi.org/10.1523/JNEUROSCI.3929-08.2008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2775540PMC
November 2008

Specific targeting of pro-death NMDA receptor signals with differing reliance on the NR2B PDZ ligand.

J Neurosci 2008 Oct;28(42):10696-710

Centres for Integrative Physiology and Neuroscience Research, University of Edinburgh, Edinburgh EH8 9XD, United Kingdom.

NMDA receptors (NMDARs) mediate ischemic brain damage, for which interactions between the C termini of NR2 subunits and PDZ domain proteins within the NMDAR signaling complex (NSC) are emerging therapeutic targets. However, expression of NMDARs in a non-neuronal context, lacking many NSC components, can still induce cell death. Moreover, it is unclear whether targeting the NSC will impair NMDAR-dependent prosurvival and plasticity signaling. We show that the NMDAR can promote death signaling independently of the NR2 PDZ ligand, when expressed in non-neuronal cells lacking PSD-95 and neuronal nitric oxide synthase (nNOS), key PDZ proteins that mediate neuronal NMDAR excitotoxicity. However, in a non-neuronal context, the NMDAR promotes cell death solely via c-Jun N-terminal protein kinase (JNK), whereas NMDAR-dependent cortical neuronal death is promoted by both JNK and p38. NMDAR-dependent pro-death signaling via p38 relies on neuronal context, although death signaling by JNK, triggered by mitochondrial reactive oxygen species production, does not. NMDAR-dependent p38 activation in neurons is triggered by submembranous Ca(2+), and is disrupted by NOS inhibitors and also a peptide mimicking the NR2B PDZ ligand (TAT-NR2B9c). TAT-NR2B9c reduced excitotoxic neuronal death and p38-mediated ischemic damage, without impairing an NMDAR-dependent plasticity model or prosurvival signaling to CREB or Akt. TAT-NR2B9c did not inhibit JNK activation, and synergized with JNK inhibitors to ameliorate severe excitotoxic neuronal loss in vitro and ischemic cortical damage in vivo. Thus, NMDAR-activated signals comprise pro-death pathways with differing requirements for PDZ protein interactions. These signals are amenable to selective inhibition, while sparing synaptic plasticity and prosurvival signaling.
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http://dx.doi.org/10.1523/JNEUROSCI.1207-08.2008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2602846PMC
October 2008

Effectiveness of PSD95 inhibitors in permanent and transient focal ischemia in the rat.

Stroke 2008 Sep 10;39(9):2544-53. Epub 2008 Jul 10.

Toronto Western Hospital Research Institute, Suite 4W-435, 399 Bathurst Street, Toronto, Ontario, Canada.

Background And Purpose: Postsynaptic density-95 inhibitors reduce ischemic brain damage without inhibiting excitatory neurotransmission, circumventing the negative consequences of glutamatergic inhibition. However, their efficacy in permanent ischemia and in providing permanent neuroprotection and neurobehavioral improvement in a practical therapeutic window is unproven. These were tested here under conditions that included fever, which is a common occurrence in clinical stroke.

Methods: Six studies were performed in unfasted Sprague-Dawley rats. Two involved permanent pial vessel occlusion in male and female rats. Two involved permanent middle cerebral artery occlusion, which induced severe hyperthermia, and 2 involved transient middle cerebral artery occlusion. Animals were treated with a single intravenous injection of postsynaptic density-95 inhibitors (Tat-NR2B9c([SDV]) or Tat-NR2B9c([TDV])) 1 hour or 3 hours after stroke. Infarct volumes and neurobehavior were assessed in a blinded manner at 24 hours (pial vessel occlusion and permanent middle cerebral artery occlusion) or at 62 days (transient middle cerebral artery occlusion).

Results: Postsynaptic density-95 inhibitors dramatically reduced infarct size in male and female animals exposed to pial vessel occlusion (>50%), in hyperthermic animals with fever exceeding 39 degrees C exposed to permanent middle cerebral artery occlusion (approximately 50%), and at 62 days poststroke in animals exposed to transient middle cerebral artery occlusion (approximately 80%). Effectiveness of postsynaptic density-95 inhibitors was achieved without the drugs affecting body temperature. In transient middle cerebral artery occlusion, a single dose of postsynaptic density-95 inhibitor given 3 hours after stroke onset permanently maintained reduced infarct size and improved neurobehavior.

Conclusions: Postsynaptic density-95 inhibitors administrated 3 hours after stroke onset reduced infarct volumes and improved long-term neurobehavioral functions in a wide therapeutic window. This raises the possibility that they may have future clinical usefulness.
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http://dx.doi.org/10.1161/STROKEAHA.107.506048DOI Listing
September 2008

NMDA receptor subunits have differential roles in mediating excitotoxic neuronal death both in vitro and in vivo.

J Neurosci 2007 Mar;27(11):2846-57

Brain Research Centre, Vancouver Coastal Health Research Institute and University of British Columbia, Vancouver, British Columbia, Canada V6T 2B5.

Well-documented experimental evidence from both in vitro and in vivo models of stroke strongly supports the critical involvement of NMDA receptor-mediated excitotoxicity in neuronal damage after stroke. Despite this, the results of clinical trials testing NMDA receptor antagonists as neuroprotectants after stroke and brain trauma have been discouraging. Here, we report that in mature cortical cultures, activation of either synaptic or extrasynaptic NR2B-containing NMDA receptors results in excitotoxicity, increasing neuronal apoptosis. In contrast, activation of either synaptic or extrasynaptic NR2A-containing NMDA receptors promotes neuronal survival and exerts a neuroprotective action against both NMDA receptor-mediated and non-NMDA receptor-mediated neuronal damage. A similar opposing action of NR2B and NR2A in mediating cell death and cell survival was also observed in an in vivo rat model of focal ischemic stroke. Moreover, we found that blocking NR2B-mediated cell death was effective in reducing infarct volume only when the receptor antagonist was given before the onset of stroke and not 4.5 h after stroke. In great contrast, activation of NR2A-mediated cell survival signaling with administration of either glycine alone or in the presence of NR2B antagonist significantly attenuated ischemic brain damage even when delivered 4.5 h after stroke onset. Together, the present work provides a molecular basis for the dual roles of NMDA receptors in promoting neuronal survival and mediating neuronal damage and suggests that selective enhancement of NR2A-containing NMDA receptor activation with glycine may constitute a promising therapy for stroke.
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http://dx.doi.org/10.1523/JNEUROSCI.0116-07.2007DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6672582PMC
March 2007

TRPMs and neuronal cell death.

Pflugers Arch 2005 Oct 26;451(1):243-9. Epub 2005 Jul 26.

Applied and Interventional Research and Division of Neurosurgery, Toronto Western Research Institute, W4-325, 399 Bathurst Street, Toronto, ON M5T 2S8, Canada.

Death of CNS neurons during acute injury occurs as a result of a complex combination of excitotoxicity, necrosis, apoptosis, oedema and inflammatory reactions. Neuroprotection via glutamate receptor blockade or antioxidant or anti-inflammatory therapy have not proven effective in the clinical treatment of brain damage due to narrow therapeutic windows, poor pharmacokinetics or blockade of the signalling essential for normal excitatory neurotransmission and neuronal survival. Recent work in neuronal biochemistry, genomics and proteomics has increased understanding of the molecular organization of the excitatory synapse and the neuronal postsynaptic density. Transient receptor potential (TRP) channels are an exciting new family of cation channels that are highly expressed in the brain. Several members can be induced by oxidative stress and oxygen free radicals, both of which play important roles in neurodegeneration. Recent work has indicated that members of the melastatin subfamily (TRPM) of TRP proteins, particularly TRPM7 and TRPM2, may play key roles in neuronal death that is activated by oxidative stress and downstream from excitotoxic signal pathways. This discovery provides an exiting new avenue for research into the pathophysiology and treatment of acute neurodegeneration.
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http://dx.doi.org/10.1007/s00424-005-1439-xDOI Listing
October 2005

TRPM7 and ischemic CNS injury.

Neuroscientist 2005 Apr;11(2):116-23

Applied and Interventional Research and Division of Neurosurgery, Toronto Western Research Institute, 399 BathurstStreet, Toronto, Ontario M5T 2S8, Canada.

Ischemic brain damage represents a major source of morbidity and mortality in westernized society and poses a significant financial burden on the health care system. To date, few effective therapies have been realized to treat stroke and once promising avenues such as antiexcitotoxic therapy with NMDA receptor antagonists have not proven clinically useful. Thus, we need to identify new targets for research and therapeutic intervention of the neurodegeneration caused by stroke. Transient receptor potential (TRP) channels are an exciting new family of cation channels that respond to intracellular and extracellular stimuli. Indeed, several members can be induced by oxidative stress and oxygen free radicals. We have recently demonstrated that one member, TRPM7, is an essential mediator of anoxic neuronal death that is activated by oxidative stress, in parallel to excitotoxic signal pathways. Thus, future treatment of ischemic brain injury may need to include strategies that inhibit or modulate TRPM7 activity. Further investigation of the physiology and pathophysiology of TRPM7 and other TRP family members is needed to provide both pharmacological targets and a better understanding of ischemic brain disorders.
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http://dx.doi.org/10.1177/1073858404272966DOI Listing
April 2005

Vulnerability of central neurons to secondary insults after in vitro mechanical stretch.

J Neurosci 2004 Sep;24(37):8106-23

Toronto Western Hospital Research Institute, Toronto, Ontario, M5T 2S8 Canada,.

Mild traumatic brain injuries are of major public health significance. Neurons in such injuries often survive the primary mechanical deformation only to succumb to subsequent insults. To study mechanisms of vulnerability of injured neurons to secondary insults, we used an in vitro model of sublethal mechanical stretch. Stretch enhanced the vulnerability of the neurons to excitotoxic insults, causing nuclear irregularities, DNA fragmentation, and death suggestive of apoptosis. However, the DNA degradation was not attributable to classical (caspase mediated) or caspase-independent apoptosis. Rather, it was associated with profound stretch-induced mitochondrial dysfunction and the overproduction of reactive oxygen species (ROS). Sublethally stretched neurons produced surprisingly high levels of ROS, but these in isolation were insufficient to kill the cells. To be lethal, the ROS also needed to combine with nitric oxide (NO) to form the highly reactive species peroxynitrite. Peroxynitrite was not produced after stretch alone and arose only after combining stretch with an insult capable of stimulating NO production, such as NMDA or an NO donor. This explained the exquisite sensitivity of sublethally stretched neurons to a secondary NMDA insult. ROS scavengers and NO synthase (NOS) inhibitors prevented cell death and DNA degradation. Moreover, inhibiting neuronal NOS activation by NMDA using peptides that perturb NMDA receptor-postsynaptic density-95 interactions also reduced protein nitration and cell death, indicating that the reactive nitrogen species produced were neuronal in origin. Our data explain the mechanism of enhanced vulnerability of sublethally injured neurons to secondary excitotoxic insults and highlight the importance of secondary mechanisms to the ultimate outcome of neurons in mild neurotrauma.
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http://dx.doi.org/10.1523/JNEUROSCI.1362-04.2004DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6729801PMC
September 2004

Molecular mechanisms underlying specificity of excitotoxic signaling in neurons.

Curr Mol Med 2004 Mar;4(2):137-47

Toronto Western Research Institute, McPav 11-416, 399 Bathurst Street, Toronto, Ontario, Canada.

The central role of glutamate receptors in mediating excitotoxic neuronal death in stroke, epilepsy and trauma has been well established. Glutamate is the major excitatory amino acid transmitter within the CNS and it's signaling is mediated by a number of postsynaptic ionotropic and metabotropic receptors. Although calcium ions are considered key regulators of excitotoxicity, new evidence suggests that specific second messenger pathways rather than total Ca(2+) load, are responsible for mediating neuronal degeneration. Glutamate receptors are found localized at the synapse within electron dense structures known as the postsynaptic density (PSD). Localization at the PSD is mediated by binding of glutamate receptors to submembrane proteins such as actin and PDZ containing proteins. PDZ domains are conserved motifs that mediate protein-protein interactions and self-association. In addition to glutamate receptors PDZ-containing proteins bind a multitude of intracellular signal molecules including nitric oxide synthase. In this way PDZ proteins provide a mechanism for clustering glutamate receptors at the synapse together with their corresponding signal transduction proteins. PSD organization may thus facilitate the individual neurotoxic signal mechanisms downstream of receptors during glutamate overactivity. Evidence exists showing that inhibiting signals downstream of glutamate receptors, such as nitric oxide and PARP-1 can reduce excitotoxic insult. Furthermore we have shown that uncoupling the interaction between specific glutamate receptors from their PDZ proteins protects neurons against glutamate-mediated excitotoxicity. These findings have significant implications for the treatment of neurodegenerative diseases using therapeutics that specifically target intracellular protein-protein interactions.
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http://dx.doi.org/10.2174/1566524043479202DOI Listing
March 2004

Novel concepts in excitotoxic neurodegeneration after stroke.

Expert Rev Mol Med 2003 Dec 16;5(30):1-22. Epub 2003 Dec 16.

Division of Cellular and Molecular Biology, Toronto Western Research Institute, Toronto Western Hospital, Suite 4W-435, 399 Bathurst Street, Toronto, ON, M5T 2S8, Canada.

Brain injury following cerebral ischaemia (stroke) involves a complex combination of pathological processes, including excitotoxicity and inflammation leading to necrotic and apoptotic forms of cell death. At the cellular level, excitotoxicity is mediated by glutamate and its cognate receptors, resulting in increased intracellular calcium and free radical production, and eventual cell death. Recent evidence suggests that scaffolding molecules that associate with glutamate receptors at the postsynaptic density allow coupling of receptor activity to specific second messengers capable of mediating excitotoxicity. These findings have important implications in the search for effective neuroprotective therapies in treating stroke.
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http://dx.doi.org/10.1017/S1462399403007087DOI Listing
December 2003

Enhanced vulnerability to NMDA toxicity in sublethal traumatic neuronal injury in vitro.

J Neurotrauma 2003 Dec;20(12):1377-95

Toronto Western Hospital Research Institute, Toronto, Ontario, Canada.

Traumatic brain injury causes neuronal disruption and triggers secondary events leading to additional neuronal death. To study injuries triggered by secondary events, we exposed cultured cortical neurons to sublethal mechanical stretch, thus eliminating confounding death from primary trauma. Sublethally stretched neurons maintained cell membrane integrity, viability, and electrophysiological function. However, stretching induced in the cells a heightened vulnerability to subsequent challenges with L-glutamate or NMDA. This heightened vulnerability was specifically mediated by NMDA receptors (NMDARs), as stretched neurons did not become more vulnerable to either kainate toxicity or to that induced by the Ca(2+) ionophore A23187. Stretch-enhanced vulnerability to NMDA occurred independently of endogenous glutamate release, but required Ca(2+) and Na(+) influx through NMDARs. Stretch did not affect the electrophysiological properties of NMDARs nor excitatory synaptic activity, indicating that specificity of enhanced vulnerability to NMDA involves postsynaptic mechanisms downstream from NMDARs. To test whether this specificity requires physical interactions between NMDARs and cytoskeletal elements, we perturbed actin filaments and microtubules, both of which are linked to NMDARs. This had no effect on the stretch-induced vulnerability to NMDA, suggesting that sublethal stretch does not affect cell survival through the cytoskeleton. Our data illustrate that sublethal in vitro stretch injury triggers distinct signaling pathways that lead to secondary injury, rather than causing a generalized increase in vulnerability to secondary insults.
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http://dx.doi.org/10.1089/089771503322686166DOI Listing
December 2003

A key role for TRPM7 channels in anoxic neuronal death.

Cell 2003 Dec;115(7):863-77

Toronto Western Hospital Research Institute, 11-416 MC-PAV, 399 Bathurst Street, Toronto, Ontario M5T-2S8 Canada.

Excitotoxicity in brain ischemia triggers neuronal death and neurological disability, and yet these are not prevented by antiexcitotoxic therapy (AET) in humans. Here, we show that in neurons subjected to prolonged oxygen glucose deprivation (OGD), AET unmasks a dominant death mechanism perpetuated by a Ca2+-permeable nonselective cation conductance (IOGD). IOGD was activated by reactive oxygen/nitrogen species (ROS), and permitted neuronal Ca2+ overload and further ROS production despite AET. IOGD currents corresponded to those evoked in HEK-293 cells expressing the nonselective cation conductance TRPM7. In cortical neurons, blocking IOGD or suppressing TRPM7 expression blocked TRPM7 currents, anoxic 45Ca2+ uptake, ROS production, and anoxic death. TRPM7 suppression eliminated the need for AET to rescue anoxic neurons and permitted the survival of neurons previously destined to die from prolonged anoxia. Thus, excitotoxicity is a subset of a greater overall anoxic cell death mechanism, in which TRPM7 channels play a key role.
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http://dx.doi.org/10.1016/s0092-8674(03)01017-1DOI Listing
December 2003

Peptide action in stroke therapy.

Expert Opin Biol Ther 2003 Oct;3(7):1093-104

Toronto Western Hospital, Suite 4W-435, 399 Bathurst Street, Toronto, Ontario, M5T 2S8, Canada.

Glutamate receptor antagonists, although effective in preventing in vitro excitotoxic death, also block the glutamatergic signalling that is essential for normal excitatory neurotransmission and neuronal survival. This has contributed to the failure of clinical trials employing glutamate receptor antagonists as stroke therapeutics. However, recent years have seen an increased understanding of the molecular organisation of glutamate receptors in the neuronal postsynaptic density. This and a dissection of their associated intracellular signalling cascades has allowed the identification of distinct pathways responsible for excitotoxicity. It has become possible to uncouple toxic signalling cascades from glutamate receptors by targeting the interactions of membrane receptors with downstream proteins. Toxic signalling can be effectively uncoupled from glutamate receptors using targeted, cell-permeable peptides to disrupt specific protein-protein interactions. This approach does not block essential excitatory neurotransmission, but attenuates neurotoxic signals specifically and reduces stroke damage. This novel approach to blocking excitotoxic signalling in cerebral ischaemia may constitute a practical approach to stroke therapy.
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http://dx.doi.org/10.1517/14712598.3.7.1093DOI Listing
October 2003

Novel treatment of excitotoxicity: targeted disruption of intracellular signalling from glutamate receptors.

Biochem Pharmacol 2003 Sep;66(6):877-86

Toronto Western Research Institute, McPav 11-416, 399 Bathurst Street, Toronto, Ont., Canada M5T 2S8.

Glutamate signalling plays key physiological roles in excitatory neurotransmission and CNS plasticity, but also mediates excitotoxicity, the process responsible for triggering neurodegeneration through glutamate receptor overactivation. Excitotoxicity is thought to be a key neurotoxic mechanism in neurological disorders, including brain ischemia, CNS trauma and epilepsy. However, treating excitotoxicity using glutamate receptor antagonists has not proven clinically viable, necessitating more sophisticated approaches. Increasing knowledge of the composition of the postsynaptic density at glutamatergic synapses has allowed us to extend our understanding of the molecular mechanisms of excitotoxicity and to dissect out the distinct signalling pathways responsible for excitotoxic damage. Key molecules in these pathways are physically linked to the cytoplasmic face of glutamate receptors by scaffolding proteins that exhibit binding specificity for some receptors over others. This imparts specificity to physiological and pathological glutamatergic signalling. Recently, we have capitalized on this knowledge and, using targeted peptides to selectively disrupt intracellular interactions linked to glutamate receptors, have blocked excitotoxic signalling in neurones. This therapeutic approach circumvents the negative consequences of blocking glutamate receptors, and may be a practical strategy for treating neurological disorders that involve excitotoxicity.
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http://dx.doi.org/10.1016/s0006-2952(03)00297-1DOI Listing
September 2003

Treatment of ischemic brain damage by perturbing NMDA receptor- PSD-95 protein interactions.

Science 2002 Oct;298(5594):846-50

Toronto Western Hospital Research Institute, 11-416 MC-PAV, 399 Bathurst Street, Toronto, Ontario M5T 2S8, Canada.

N-methyl-D-aspartate receptors (NMDARs) mediate ischemic brain damage but also mediate essential neuronal excitation. To treat stroke without blocking NMDARs, we transduced neurons with peptides that disrupted the interaction of NMDARs with the postsynaptic density protein PSD-95. This procedure dissociated NMDARs from downstream neurotoxic signaling without blocking synaptic activity or calcium influx. The peptides, when applied either before or 1 hour after an insult, protected cultured neurons from excitotoxicity, reduced focal ischemic brain damage in rats, and improved their neurological function. This approach circumvents the negative consequences associated with blocking NMDARs and may constitute a practical stroke therapy.
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http://dx.doi.org/10.1126/science.1072873DOI Listing
October 2002

1Alpha,25-dihydroxyvitamin D3 promotes vascularization of the chondro-osseous junction by stimulating expression of vascular endothelial growth factor and matrix metalloproteinase 9.

J Bone Miner Res 2002 Sep;17(9):1604-12

Department of Physiology, McGill University, Montreal, Quebec, Canada.

Vitamin D deficiency results in defects in endochondral bone development characteristic of rickets, which include elongation of the cartilaginous growth plates and disorganization of the primary spongiosa. These defects are caused in part by impaired cartilage mineralization and vascularization of the chondro-osseous junction. Blood vessel invasion of mineralized cartilage is an essential step in endochondral ossification, providing access for cells that degrade cartilage as well as those that form bone. Vascular endothelial growth factor (VEGF) was shown to be a key regulator of this process when infusion of a dominant negative VEGF receptor effectively blocked vascular invasion and endochondral ossification in the growth plates of juvenile mice. Here, we show that the active metabolite of vitamin D 1alpha,25-dihydroxyvitamin D3 [1alpha,25(OH)2D3] directly stimulates transcription of mRNAs encoding VEGF121 and -165 isoforms in the CFK2 chondrogenic cell line. Enhanced VEGF expression also was evident in growth plate chondrocytes and osteoblasts in the tibia of juvenile mice treated systemically with 1alpha,25(OH)2D3. This was seen in conjunction with enhanced expression of matrix metalloproteinase (MMP) 9, which activates VEGF stored in the cartilage matrix, in osteoclastic cells adjacent to the chondro-osseous junction. The alterations in VEGF and MMP-9 expression were accompanied by enhanced vascular invasion of mineralized cartilage, as assessed by CD31 immunoreactivity. These results provide evidence that 1alpha,25(OH)2D3 signaling stimulates VEGF and MMP-9 gene expression and promotes neovascularization of the epiphyseal growth plate in vivo through increased availability of active growth factor.
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http://dx.doi.org/10.1359/jbmr.2002.17.9.1604DOI Listing
September 2002
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