title: Phospho1 deficiency transiently modifies bone architecture yet produces consistent modification in osteocyte differentiation and vascular porosity with ageing.
abstract: PHOSPHO1 is one of principal proteins involved in initiating bone matrix mineralisation. Recent studies have found that Phospho1 KO mice (Phospho1-R74X) display multiple skeletal abnormalities with spontaneous fractures, bowed long bones, osteomalacia and scoliosis. These analyses have however been limited to young mice and it remains unclear whether the role of PHOSPHO1 is conserved in the mature murine skeleton where bone turnover is limited. In this study, we have used ex-vivo computerised tomography to examine the effect of Phospho1 deletion on tibial bone architecture in mice at a range of ages (5, 7, 16 and 34 weeks of age) to establish whether its role is conserved during skeletal growth and maturation. Matrix mineralisation has also been reported to influence terminal osteoblast differentiation into osteocytes and we have also explored whether hypomineralised bones in Phospho1 KO mice exhibit modified osteocyte lacunar and vascular porosity. Our data reveal that Phospho1 deficiency generates age-related defects in trabecular architecture and compromised cortical microarchitecture with greater porosity accompanied by marked alterations in osteocyte shape, significant increases in osteocytic lacuna and vessel number. Our in vitro studies examining the behaviour of osteoblast derived from Phospho1 KO and wild-type mice reveal reduced levels of matrix mineralisation and modified osteocytogenic programming in cells deficient in PHOSPHO1. Together our data suggest that deficiency in PHOSPHO1 exerts modifications in bone architecture that are transient and depend upon age, yet produces consistent modification in lacunar and vascular porosity. It is possible that the inhibitory role of PHOSPHO1 on osteocyte differentiation leads to these age-related changes in bone architecture. It is also intriguing to note that this apparent acceleration in osteocyte differentiation evident in the hypomineralised bones of Phospho1 KO mice suggests an uncoupling of the interplay between osteocytogenesis and biomineralisation. Further studies are required to dissect the molecular processes underlying the regulatory influences exerted by PHOSPHO1 on the skeleton with ageing.
authors.affiliation: The Royal Veterinary College, London, United Kingdom. Electronic address: bjavaheri@rvc.ac.uk.
authors.forename: B
authors.initials: B
authors.lastname: Javaheri
authors.affiliation: Department of Biomedical Engineering, Florida Institute of Technology Melbourne, FL 32901, USA.
authors.forename: A
authors.initials: A
authors.lastname: Carriero
authors.affiliation: The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: K A
authors.initials: KA
authors.lastname: Staines
authors.affiliation: The Royal Veterinary College, London, United Kingdom.
authors.forename: Y-M
authors.initials: YM
authors.lastname: Chang
authors.affiliation: The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: D A
authors.initials: DA
authors.lastname: Houston
authors.affiliation: The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: K J
authors.initials: KJ
authors.lastname: Oldknow
authors.affiliation: Sanford Children's Health Research Center, Sanford-Burnham Medical Research Institute, La Jolla, CA, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Millan
authors.affiliation: Imperial College, London. United Kingdom.
authors.forename: Bassir N
authors.initials: BN
authors.lastname: Kazeruni
authors.affiliation: Bruker-microCT, Kartuizersweg 3B, 2550 Kontich, Belgium.
authors.forename: P
authors.initials: P
authors.lastname: Salmon
authors.affiliation: Department of Mechanical and Industrial Engineering, Northeastern University, USA.
authors.forename: S
authors.initials: S
authors.lastname: Shefelbine
authors.affiliation: The Roslin Institute and R(D)SVS, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: C
authors.initials: C
authors.lastname: Farquharson
authors.affiliation: The Royal Veterinary College, London, United Kingdom.
authors.forename: A A
authors.initials: AA
authors.lastname: Pitsillides
mesh_terms: D000375:Aging / Q000378:metabolism*; D000818:Animals; D015519:Bone Density / Q000502:physiology*; D002199:Capillary Permeability / Q000502:physiology*; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D010011:Osteocytes / Q000378:metabolism*; D010744:Phosphoric Monoester Hydrolases / Q000172:deficiency*; D016062:Porosity; D013977:Tibia / Q000378:metabolism
chemical_list: C552022:PHOSPHO1 protein, mouse; D010744:Phosphoric Monoester Hydrolases
keywords: MicroCT; Mineralisation; Osteoblast; Osteocyte; PHOSPHO1; Vascular porosity