Endochondral ossification is a carefully orchestrated process mediated by promoters and inhibitors of mineralization. Experimental evidence has pointed to the presence of hydroxyapatite crystals along collagen fibrils in the extracellular matrix and also within the lumen of chondrocyte- and osteoblast-derived matrix vesicles (MVs). Phosphatases are implicated, but their identities and functions remain unclear. Our work centers on elucidating the concerted action of three phosphatases, PHOSPHO1, tissue-nonspecific alkaline phosphatase (TNAP) and nucleosidetriphosphate pyrophosphohydrolase (NPP1) in establishing a Pi/PPi ratio conducive to controlled physiological skeletal mineralization. Our current model of the mechanisms of initiation of skeletal mineralization implicate intra-vesicular PHOSPHO1 function and Pi influx into MVs in the initiation of mineralization and the functions of TNAP, NPP1 in the extra-vesicular progression of mineralization. This hypothesis-driven competitive renewal application seeks to test crucial aspects of this comprehensive model of initiation of skeletal mineralization that unifies a number of disparate biochemical observations, e.g., intravesicular Pi-generation by PHOSPHO1, Pi-generation versus PPi-degradation by TNAP, the role of Pi- transporters in MVs, the need for locally produced Pi versus systemic Pi, and MV-mediated versus collagen- mediated ECM mineralization. This proposal will also advance significant translational studies into the possible involvement of Phospho1 gene mutations in the development of early-onset scoliosis and osteogenesis imperfecta-like syndrome, the possible compounding effect of Phospho1 gene mutations on the severity of hypophosphatasia, and the putative role of PHOSPHO1 in medial vascular calcification, a condition with high morbidity in end-stage renal disease, obesity, diabetes and aging.

Public Health Relevance

Our work focuses on elucidating the functional interplay of three phosphatases (PHOSPHO1, TNAP and NPP1) during the initiation of skeletal mineralization, a process of fundamental importance to all vertebrate animal species, including mice and humans. Alterations in the function of these phosphatases lead to soft bone conditions, including rickets, osteomalacia, spontaneous fractures, loss of teeth as well as inappropriate calcification of soft tissues in the form of osteoarthritis and arterial calcification. Our work has clear translational applications to rare diseases, such as hypophosphatasia and osteogenesis imperfecta, and also prevalent diseases, including scoliosis, osteoarthritis and medial vascular calcification.

National Institute of Health (NIH)
Research Project (R01)
Project #
Application #
Study Section
Skeletal Biology Development and Disease Study Section (SBDD)
Program Officer
Sharrock, William J
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Sanford-Burnham Medical Research Institute
La Jolla
United States
Zip Code
Bravo, Yalda; Teriete, Peter; Dhanya, Raveendra-Panickar et al. (2014) Design, synthesis and evaluation of benzoisothiazolones as selective inhibitors of PHOSPHO1. Bioorg Med Chem Lett 24:4308-11
Li, Lingyin; Yin, Qian; Kuss, Pia et al. (2014) Hydrolysis of 2'3'-cGAMP by ENPP1 and design of nonhydrolyzable analogs. Nat Chem Biol 10:1043-8
Falanga, Alessia; Stojanovi?, Ozren; Kiffer-Moreira, Tina et al. (2014) Exonic splicing signals impose constraints upon the evolution of enzymatic activity. Nucleic Acids Res 42:5790-8
Yadav, Manisha C; Huesa, Carmen; Narisawa, Sonoko et al. (2014) Ablation of osteopontin improves the skeletal phenotype of phospho1(-/-) mice. J Bone Miner Res 29:2369-81
Kuzynski, Maria; Goss, Morgan; Bottini, Massimo et al. (2014) Dual role of the Trps1 transcription factor in dentin mineralization. J Biol Chem 289:27481-93
Simao, Ana Maria S; Bolean, Mayte; Hoylaerts, Marc F et al. (2013) Effects of pH on the production of phosphate and pyrophosphate by matrix vesicles' biomimetics. Calcif Tissue Int 93:222-32
Hoac, Betty; Kiffer-Moreira, Tina; Millan, Jose Luis et al. (2013) Polyphosphates inhibit extracellular matrix mineralization in MC3T3-E1 osteoblast cultures. Bone 53:478-86
Kiffer-Moreira, Tina; Yadav, Manisha C; Zhu, Dongxing et al. (2013) Pharmacological inhibition of PHOSPHO1 suppresses vascular smooth muscle cell calcification. J Bone Miner Res 28:81-91
Zhu, Dongxing; Mackenzie, Neil C W; Millan, Jose Luis et al. (2013) A protective role for FGF-23 in local defence against disrupted arterial wall integrity? Mol Cell Endocrinol 372:1-11
McKee, M D; Yadav, M C; Foster, B L et al. (2013) Compounded PHOSPHO1/ALPL deficiencies reduce dentin mineralization. J Dent Res 92:721-7

Showing the most recent 10 out of 26 publications