Overview | Background GlialFibrillaryAcidicProtein(GFAP)isaclass-IIIintermediatefilamentuniquelyandubiquitouslyexpressedaspartofthestructuralnetworkinastrocyticglialcells.ThisspecificexpressionmakesGFAPidealasabroadastrocyticMarkerinvertebrates.Astrocytesplayavarietyofkeyrolesinsupporting,guiding,nurturing,andsignalingneuronalarchitectureandactivityinahighlyinterdependentmanner.CurrentunderstandingofCNSstructuresuggeststhatthereareatleastasmanyglialcellsastheestimated100billionneurons,butperhapsupwardsof100timesmore.Thus, thehealthofbothneuronsandastrocytesisoftenaffectedindiseaseandtrauma.GFAPisprovingtobeausefulbiomarkerinthedetectionofneuraldegeneration.AlthoughdefectsinGFAPhavebeenreportedtocausecertainrareconditions,suchasAlexander’sdisease(Brenneretal.,2001),theobservedinterconnectedphysiologyofneuronalandglialcellshasenabledtheuseofGFAPasaneurodegenerationdetectiongauge.Thisrelationshipisbeingexploitedbyresearchersandcliniciansmeasuringavarietyofneurologicalissuesfromcancertotrauma.GFAPhasbeenusedasabiomarkerintheearlydetectionofchemicallyinducedcancer(Capoetal.,1997)andclassicalglioblastomas(Jungetal.,2007).ElevatedlevelsofGFAPhavebeenreportedintraumaticbraininjury(TBI)andappeartodirectlycorrelatewiththeseverityofinjuryandbraintissueoxygenationincombatcasualtycareresearch(CCR,2008)aswellascivilianaccidents(Mondelloetal.,2010).GFAPhasalsobeenidentifiedasagoodbiomarkerinstudiesoftoxininducedacutebraininjury(Liaoetal.,2008),indifferentiationofhemorrhagicvs.ischemicstrokes(Foerchetal.,2006),aswellasincardiacarrest(Kanekoetal.,2009).MilliporenowoffersanELISAassayforsensitivemeasurementofGFAPproteinintissuehomogenatesandBIOLOGicalfluids(serum,plasma,CSF,andserumfreemedia)fromhuman,mouse,andrat.
PrincipalsofProcedure ThisassayisaSandwichELISAbasedsequentiallyon:1)captureofsolubleGFAPproteintothewellsofamicrotiterplatecoatedbyapre-titeredamountofanti-GFAPmonoclonalantibody;2)removalofunboundmaterialbywashing;3)bindingofbiotinylatedanti-GFAPmonoclonalantibodyto thepreviouslycapturedGFAPprotein;4)removalofunboundmaterialbywashing;5)bindingofstreptavidinconjugatedhorserADIshperoxidasetothebiotinylatedantibodies;6)removalofexcessorunboundenzymeconjugatesbywashing;and7)quantificationofimmobilizedantibody-enzyme complexesbymonitoringhorseradishperoxidaseactivityinthepresenceofthesubstrate3,3’,5,5’-tetramethylbenzidine(TMB).Enzymeactivityismeasuredspectrophotometricallybyrecordingabsorbancereadingsat450nm.Increasesinabsorbencyaredirectlyproportionaltotheamountof GFAPproteincapturedfromthesample.ThereforetheproteinconcentrationofunknownscanbederivedbyinterpolationusingastandardcurvegeneratedinthesameassaywithreferencestandardsofknownconcentrationsofGFAP.
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