Correction of Hypophosphatasia-Associated Mineralization Deficiencies In Vitro by Phosphate/Pyrophosphate Modulation in Periodontal Ligament Cells

Author(s)

Rodrigues, Thaisangela L. ^[1] ; Foster, Brian L. ^{[2, 3]} ; Silverio, Karina G. ^[1] ; Martins, Luciane ^[1] ; Casati, Marcio Z. ^[1] ; Sallum, Enilson A. ^[1] ; Somerman, Martha J. ^{[2, 3]} ; Nociti, Jr., Francisco H. ^{[2, 1]}

Affiliation

^[1] Univ Estadual Campinas, Dept Prosthodont & Periodont, Div Periodont, Sch Dent, Sao Paulo - Brazil

^[2] Univ Washington, Sch Dent, Dept Periodont, Seattle, WA 98195 - USA

^[3] Univ Washington, Sch Dent, Dept Oral Biol, Seattle, WA 98195 - USA

• Document type: Journal article
• Source: Journal of Periodontology; v. 83, n. 5, p. 653-663, MAY 2012.
• Web of Science Citations: 5

Abstract

Background: Mutations in the liver/bone/kidney alkaline phosphatase (ALPL) gene in hypophosphatasia (HPP) reduce the function of tissue non-specific alkaline phosphatase (ALP), resulting in increased pyrophosphate (PPi) and a severe deficiency in acellular cementum. We hypothesize that exogenous phosphate (P-i) would rescue the in vitro mineralization capacity of periodontal ligament (PDL) cells harvested from HPP-diagnosed patients, by correcting the P-i/PPi ratio and modulating expression of genes involved with P-i/PPi metabolism. Methods: Ex vivo and in vitro analyses were used to identify mechanisms involved in HPP-associated PDL/tooth root deficiencies. Constitutive expression of PPi-associated genes was contrasted in PDL versus pulp tissues obtained from healthy individuals. Primary PDL cell cultures from patients with HPP (monozygotic twin males) were established to assay ALP activity, in vitro mineralization, and gene expression. Exogenous P-i was provided to correct the P-i/PPi ratio. Results: PDL tissues obtained from healthy individuals featured higher basal expression of key PPi regulators, genes ALPL, progressive ankylosis protein (ANKH), and ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1), versus paired pulp tissues. A novel ALPL mutation was identified in the twin patients with HPP enrolled in this study. Compared to controls, HPP-PDL cells exhibited significantly reduced ALP and mineralizing capacity, which were rescued by addition of 1 mM P-i. Dysregulated expression of PPi regulatory genes ALPL, ANKH, and ENPP1 was also corrected by adding P-i, although other matrix markers evaluated in our study remained downregulated. Conclusion: These findings underscore the importance of controlling the P-i/PPi ratio toward development of a functional periodontal apparatus and support P-i/PPi imbalance as the etiology of HPP-associated cementum defects. J Periodontol 2012;83:653-663. (AU)

• FAPESP's process: 08/00534-7 - Regulation of dentin-pulp and periodontal ligament cells in healthy individuals and with hypophosphatasia
• Grantee: Márcio Zaffalon Casati
• Support Opportunities: Regular Research Grants
• FAPESP's process: 07/08192-5 - Regulation of dentin-pulp and periodontal ligament cells in HELTHY individuals and with hypophosphatasia
• Grantee: Thaisângela Rodrigues Lopes e Silva Gomes
• Support Opportunities: Scholarships in Brazil - Doctorate