title: Overexpression of GTP cyclohydrolase 1 feedback regulatory protein is protective in a murine model of septic shock.
abstract: Overproduction of nitric oxide (NO) by inducible NO synthase contributes toward refractory hypotension, impaired microvascular perfusion, and end-organ damage in septic shock patients. Tetrahydrobiopterin (BH4) is an essential NOS cofactor. GTP cyclohydrolase 1 (GCH1) is the rate-limiting enzyme for BH4 biosynthesis. Under inflammatory conditions, GCH1 activity and hence BH4 levels are increased, supporting pathological NOS activity. GCH1 activity can be controlled through allosteric interactions with GCH1 feedback regulatory protein (GFRP). We investigated whether overexpression of GFRP can regulate BH4 and NO production and attenuate cardiovascular dysfunction in sepsis. Sepsis was induced in mice conditionally overexpressing GFRP and wild-type littermates by cecal ligation and puncture. Blood pressure was monitored by radiotelemetry, and mesenteric blood flow was quantified by laser speckle contrast imaging. Blood biochemistry data were obtained using an iSTAT analyzer, and BH4 levels were measured in plasma and tissues by high-performance liquid chromatography. Increased BH4 and NO production and hypotension were observed in all mice, but the extents of these pathophysiological changes were attenuated in GFRP OE mice. Perturbations in blood biochemistry were similarly attenuated in GFRP OE compared with wild-type controls. These results suggest that GFRP overexpression regulates GCH1 activity during septic shock, which in turn limits BH4 bioavailability for iNOS. We conclude that the GCH1-GFRP axis is a critical regulator of BH4 and NO production and the cardiovascular derangements that occur in septic shock.
authors.affiliation: *Pharmacology and Therapeutics Group, Institute of Pharmaceutical Science, School of Biomedical Sciences, King's College London; and †MRC Clinical Sciences Centre, Faculty of Medicine, Imperial College London, London; and ‡British Heart Foundation Centre of Research Excellence, Division of Cardiovascular Medicine, University of Oxford, John Radcliffe Hospital, Oxford, United Kingdom.
authors.forename: Anna
authors.initials: A
authors.lastname: Starr
authors.forename: Claire A
authors.initials: CA
authors.lastname: Sand
authors.forename: Lamia
authors.initials: L
authors.lastname: Heikal
authors.forename: Peter D
authors.initials: PD
authors.lastname: Kelly
authors.forename: Domenico
authors.initials: D
authors.lastname: Spina
authors.forename: Mark
authors.initials: M
authors.lastname: Crabtree
authors.forename: Keith M
authors.initials: KM
authors.lastname: Channon
authors.forename: James M
authors.initials: JM
authors.lastname: Leiper
authors.forename: Manasi
authors.initials: M
authors.lastname: Nandi
mesh_terms: D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives / Q000096:biosynthesis / Q000378:metabolism; D002352:Carrier Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000502:physiology; D004195:Disease Models, Animal; D005786:Gene Expression Regulation / Q000502:physiology; D006439:Hemodynamics / Q000502:physiology; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009569:Nitric Oxide / Q000096:biosynthesis / Q000378:metabolism; D012772:Shock, Septic / Q000378:metabolism* / Q000503:physiopathology; D013152:Splanchnic Circulation / Q000502:physiology
chemical_list: D001708:Biopterins; D002352:Carrier Proteins; D009569:Nitric Oxide; C000592576:GCHFR protein, mouse; C003402:sapropterin