NMDA Receptors&

Stroke Therapies

Ajay Chahal

Vivian Tang

Anushya Vijayaraghevan

Chelsea Geen

PHM142 Fall 2014Coordinator: Dr. Jeffrey HendersonInstructor: Dr. David Hampson

Stroke

• Caused by lack of blood flow to brain

• Variety of effects

– Partial paralysis, vision loss, dizzyness ect.

• Risk factors are:

– hypertension obesity, diabetes, excessive alcohol

consumption, smoking and stress.(Heart and Stroke Foundation, 2014)

NMDA Receptor

• N-methyl-D-aspartate Receptor

• Found in synaptic cleft

• Glutamate-gated ion channel

– Calcium

– Sodium

• Activation: ligand binding and depolarization

(Li & Tsien, 2009)

NMDA Receptor: Mechanism of Action

• At resting potential, the channel is blocked

by a Mg2+ http://www.sumanasinc.com/webcontent/animations/content/receptors.html

(Blanke & VanDongen, 2009)

NMDA Receptor: Mechanism of Action

• Electrical stimulation of presynaptic neurons

releases glutamate into the synaptic cleft. The

glutamate binds to the receptor.http://www.sumanasinc.com/webcontent/animations/content/receptors.html

glutamate

(Blanke & VanDongen, 2009)

NMDA Receptor: Mechanism of Action

• Receptor does not activate because

insufficient depolarization http://www.sumanasinc.com/webcontent/animations/content/receptors.html

(Blanke & VanDongen, 2009)

NMDA Receptor: Mechanism of Action

• During sufficient depolarization, the Mg2+ is

dislodged from channel and activateshttp://www.sumanasinc.com/webcontent/animations/content/receptors.html

Mg2

+

(Blanke & VanDongen, 2009)

NMDA Receptor: Mechanism of Action

• Activated channel results in influx of Ca2+

Acts as a secondary messenger to activate

intracellular signaling cascade(Blanke & VanDongen, 2009)http://www.sumanasinc.com/webcontent/animations/content/

receptors.html

Mechanism of Ischemic Cell Death

(Breton and Rodriguez, 2012)

Effects of High Ca2+ Concentration in Neurons after Ischemia

Rama

(Breton and Rodriguez, 2012)

Excitotoxic Signaling by Overstimulation of NMDA Receptor

(Breton and Rodriguez, 2012)

(R&D Systems, 2012)

NMDA & Stroke: Therapeutic Attempts

Only therapy currently

available:

thrombolytic recombinant tissue

plasminogen activator (rt-PA)

• give within 3 hrs

– most patients (95%) don’t

receive (eg delay to hospital)

– increases intracranial

haemorrhage risk(Reviewed in Green and Shuaib, 2006)Image http://www.thetimes.co.uk/tto/news/uk/scotland/article3796905.ece

Neuroprotective AgentsAnother approach!

– attempt to interfere with ischaemic cascade

mechanisms and decrease tissue damage

– have been studied

• but every one to reach clinical trials…

(Reviewed in Green and Shuaib, 2006)Image http://fightingclean.com/2014/07/kevin-casey-robert-drysdale-fail-post-fight-drug-tests/

Failed Attempts…

Table 1: Compounds that have failed clinical trials for acute ischaemic stroke treatment (Green and Shuaib, 2006).

There is still hope!

• New

neuroprotective

compounds

being

investigated

– But none

currently on

market

(Reviewed in Green and Shuaib, 2006)

Example: DAPK1 and NMDA

• DAPK1: death-associated protein kinase 1

– Found to be important part of neuron death

signaling cascade downstream of NMDA

– Could be a target for neuroprotective drug

development!

(Reviewed in Martin and Wang, 2010)

Mechanism of Potential Therapeutic Action

(Reviewed in Martin and Wang, 2010)

Normal synapse:

Activate NMDA receptor neuronal survival signaling complex (SSC)

(Reviewed in Martin and Wang, 2010)

Increase Ca2+ influx through NMDA receptors activates DAPK promotes DAPK bind and phosphorylation of NR2B

Activated DAPK promotes neuron death signal complex (DSC) that shuts off SSC 

Using an NR2B interference peptide inhibit aDAPK binding to NR2B blocks phosphorylation, decrease DSC activation avoid exitotoxic damage induced by stroke!

STROKECONDITIONS:

http://www.today.com/id/7466911/ns/today-today_entertainment/t/darth-vader-lives/#.VE8mIYvF9-g

Darth Vader = DAPKLightsaber = Ca2+

Darth Vader + Lightsaber = activated DAPK

Darth Vader + Lightsaber:

gives into anger (phosphorylation) and joins the dark side (binds NR2B)

promotes neuron death signal complex (DSC) shutting off survival signal complex (SSC)

Luke Skywalker = NR2B interference peptide

Luke Skywalker stops Darth Vader and his lightsaber (aDAPK) from joining the dark side (binding NR2B), blocking Darth Vader’s anger (phosphorylation)

Since Darth Vader is no longer angry, death signal complex (DSC) is decreased

http://www.comicvine.com/forums/battles-7/anakin-skywalker-vs-luke-skywalker-read-op-576670/

SummarySTROKE• Caused by an event that limits or stops blood flow to the brain

– ischemia or hemorrhaging– 2 kinds of ischemic stroke:

1) Thrombotic stroke: blood clot in an artery leading directly to brain2) Embolic stroke: clot forming somewhere else in the body, travels through blood stream to the brain.

• Risk factors: hypertension, obesity, diabetes, excessive alcohol consumption, smoking and stress

NMDA RECEPTOR• A glutamate-gated ion channel - activated when both glutamate is bound to

receptor and adequate depolarization occurs• Results in Ca2+ ion influx

• NMDA receptors excessively activated resulting in increased Ca2+ influx – after ischemia, cytoplasmic Ca2+ levels rise and can trigger many downstream

neurotoxic cascades including the activation and overstimulation– the results include activation of several signalling pathways mainly causing an

overproduction of free radicals, dysfunction of mitochondria, cell membrane disruption and DNA fragmentation, which together induce neuron death

THERAPY• Currently only rt-PA for ischaemic stroke (within 3 hours)• Neuroprotective agents still being investigated, although most have failed

clinical trials

ReferencesBlanke, M. L., and VanDongen, A.M.J. (2009). "Activation Mechanisms of the NMDA Receptor." Biology of the

NMDA Receptor. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK5274/.

Breton, R.R., and Rodriguez, J.C.G. (2012). Excitotoxicity and oxidative stress in acute ischemic stroke. Stroke, 8, 9. http://cdn.intechopen.com/pdfs/26258.pdf.

Green, A.R., and Shuaib, A. (2006). Therapeutic strategies for the treatment of stroke. Drug Discovery Today, 11:15/16. doi:10.1016/j.drudis.2006.06.001.

Heart and Stroke Foundation. (2014). “Stroke.” Web. 27 Oct. 2014. Retrieved from http://www.heartandstroke.com/site/c.ikIQLcMWJtE/b.3483933/.

Li, F, and Tsien J.Z. (2009). Memory and the NMDA receptors. New England Journal of Medicine, 361(3): 302-3. doi: 10.1056/NEJMcibr0902052.

Martin, H.G.S., and Wang, Y.T. (2010). Blocking the deadly effects of the NDMA receptor in stroke. Cell, 140: 174-176. DOI 10.1016/j.cell.2010.01.014.

R&D Systems. “Neuronal Death by Glutamate Excitotoxicity: Protein Mediators & Strategies for Inhibition.” (2012). Retrieved from http://www.rndsystems.com/mini_review_detail_objectname_neuronal_death_by_glutamate_excitotoxicity_article.aspx.