title: Altered bone development and an increase in FGF-23 expression in Enpp1(-/-) mice.
abstract: Nucleotide pyrophosphatase phosphodiesterase 1 (NPP1) is required for the conversion of extracellular ATP into inorganic pyrophosphate (PP(i)), a recognised inhibitor of hydroxyapatite (HA) crystal formation. A detailed phenotypic assessment of a mouse model lacking NPP1 (Enpp1(-/-)) was completed to determine the role of NPP1 in skeletal and soft tissue mineralization in juvenile and adult mice. Histopathological assessment of Enpp1(-/-) mice at 22 weeks of age revealed calcification in the aorta and kidney and ectopic cartilage formation in the joints and spine. Radiographic assessment of the hind-limb showed hyper-mineralization in the talocrural joint and hypo-mineralization in the femur and tibia. MicroCT analysis of the tibia and femur disclosed altered trabecular architecture and bone geometry at 6 and 22 weeks of age in Enpp1(-/-) mice. Trabecular number, trabecular bone volume, structure model index, trabecular and cortical thickness were all significantly reduced in tibiae and femurs from Enpp1(-/-) mice (P<0.05). Bone stiffness as determined by 3-point bending was significantly reduced in Enpp1(-/-) tibiae and femurs from 22-week-old mice (P<0.05). Circulating phosphate and calcium levels were reduced (P<0.05) in the Enpp1(-/-) null mice. Plasma levels of osteocalcin were significantly decreased at 6 weeks of age (P<0.05) in Enpp1(-/-) mice, with no differences noted at 22 weeks of age. Plasma levels of CTx (Ratlaps™) and the phosphaturic hormone FGF-23 were significantly increased in the Enpp1(-/-) mice at 22 weeks of age (P<0.05). Fgf-23 messenger RNA expression in cavarial osteoblasts was increased 12-fold in Enpp1(-/-) mice compared to controls. These results indicate that Enpp1(-/-) mice are characterized by severe disruption to the architecture and mineralization of long-bones, dysregulation of calcium/phosphate homeostasis and changes in Fgf-23 expression. We conclude that NPP1 is essential for normal bone development and control of physiological bone mineralization.
authors.affiliation: The Roslin Institute and Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Midlothian, Scotland, United Kingdom.
authors.forename: Neil Charles Wallace
authors.initials: NC
authors.lastname: Mackenzie
authors.forename: Dongxing
authors.initials: D
authors.lastname: Zhu
authors.forename: Elspeth M
authors.initials: EM
authors.lastname: Milne
authors.forename: Rob
authors.initials: R
authors.lastname: van 't Hof
authors.forename: Aline
authors.initials: A
authors.lastname: Martin
authors.forename: Leigh
authors.initials: L
authors.lastname: Darryl Quarles
authors.forename: Darryl Leigh
authors.initials: DL
authors.lastname: Quarles
authors.forename: José Luis
authors.initials: JL
authors.lastname: Millán
authors.forename: Colin
authors.initials: C
authors.lastname: Farquharson
authors.forename: Vicky Elisabeth
authors.initials: VE
authors.lastname: MacRae
mesh_terms: D000818:Animals; D001846:Bone Development / Q000187:drug effects*; D002113:Calcification, Physiologic; D002118:Calcium / Q000378:metabolism; D000089703:Fibroblast Growth Factor-23; D005346:Fibroblast Growth Factors / Q000096:biosynthesis*; D051379:Mice; D018345:Mice, Knockout; D010006:Osteoblasts; D010710:Phosphates / Q000378:metabolism; D010727:Phosphoric Diester Hydrolases / Q000172:deficiency* / Q000502:physiology; D011755:Pyrophosphatases / Q000172:deficiency* / Q000502:physiology; D012333:RNA, Messenger / Q000096:biosynthesis
chemical_list: C000717428:Fgf23 protein, mouse; D010710:Phosphates; D012333:RNA, Messenger; D005346:Fibroblast Growth Factors; D000089703:Fibroblast Growth Factor-23; D010727:Phosphoric Diester Hydrolases; C065962:ectonucleotide pyrophosphatase phosphodiesterase 1; D011755:Pyrophosphatases; D002118:Calcium