A requirement for Gch1 and tetrahydrobiopterin in embryonic development

摘要

IntroductionGTPcyclohydrolaseI(GTPCH)catalysesthefirstandrate-limitingreactioninthesynthesisoftheenzymaticcofactor,tetrahydrobiopterin(BH4).LossoffunctionmutationsintheGCH1geneleadtocongenitalneurologicaldiseasessuchasDOPA-responsivedystoniaandhyperphenylalaninemia.However,littleisknownabouthowGTPCHandBH4affectsembryonicdevelopmentinutero,andinparticularwhethermetabolicreplacementorsupplementationinpregnancyissufficienttorescuegeneticGTPCHdeficiencyinthedevelopingembryo.MethodsandresultsGch1deficientmiceweregeneratedbytheinsertionofloxPsitesflankingexons2–3oftheGch1gene.Gch1fl/flmicewerebredwithSox2cremicetogeneratemicewithglobalGch1deficiency.GeneticablationofGch1causedembryoniclethalitybyE13.5.DespitelossofGch1mRNAandGTPCHenzymaticactivity,wholeembryoBH4levelsweremaintaineduntilE11.5,indicatingsufficientmaternaltransferofBH4toreachthisstageofdevelopment.AfterE11.5,Gch1−/−embryosweredeficientinBH4,butanunbiasedmetabolomicscreenindicatedthatthelethalitywasnotduetoagrossdisturbanceinmetabolicprofile.EmbryoniclethalityinGch1−/−embryoswasnotcausedbystructuralabnormalities,butwasassociatedwithsignificantbradycardiaatE11.5.EmbryoniclethalitywasnotrescuedbymaternalsupplementationofBH4,butwaspartiallyrescued,uptoE15.5,bymaternalsupplementationofBH4andl-DOPA.ConclusionThesefindingsdemonstratearequirementforGch1inembryonicdevelopmentandhaveimportantimplicationsfortheunderstandingofpathogenesisandtreatmentofgeneticBH4deficiencies,aswellastheidentificationofnewpotentialrolesforBH4.