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.
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.
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|Bolean, MaytÃª; SimÃ£o, Ana Maria S; Kiffer-Moreira, Tina et al. (2015) Proteoliposomes with the ability to transport Ca(2+) into the vesicles and hydrolyze phosphosubstrates on their surface. Arch Biochem Biophys 584:79-89|
|Orriss, Isabel R; Key, Michelle L; Hajjawi, Mark O R et al. (2015) Acidosis is a key regulator of osteoblast ecto-nucleotidase pyrophosphatase/phosphodiesterase 1 (NPP1) expression and activity. J Cell Physiol 230:3049-56|
|Zweifler, Laura E; Patel, Mudita K; Nociti Jr, Francisco H et al. (2015) Counter-regulatory phosphatases TNAP and NPP1 temporally regulate tooth root cementogenesis. Int J Oral Sci 7:27-41|
|Huesa, Carmen; Staines, Katherine A; MillÃ¡n, Jose Luis et al. (2015) Effects of etidronate on the Enpp1â»/â» mouse model of generalized arterial calcification of infancy. Int J Mol Med 36:159-65|
|Huesa, Carmen; Houston, Dean; Kiffer-Moreira, Tina et al. (2015) The Functional co-operativity of Tissue-Nonspecific Alkaline Phosphatase (TNAP) and PHOSPHO1 during initiation of Skeletal Mineralization. Biochem Biophys Rep 4:196-201|
|Rodriguez-Florez, Naiara; Garcia-Tunon, Esther; Mukadam, Quresh et al. (2015) An investigation of the mineral in ductile and brittle cortical mouse bone. J Bone Miner Res 30:786-95|
|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|
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