Genetic and pharmacologic modulation of cementogenesis via pyrophosphate regulators.

Abstract

Pyrophosphate (PPi) serves as a potent and physiologically important regulator of mineralization, with systemic and local concentrations determined by several key regulators, including: tissue-nonspecific alkaline phosphatase (ALPL gene; TNAP protein), the progressive ankylosis protein (ANKH; ANK), and ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1; ENPP1). Results to date have indicated important roles for PPi in cementum formation, and we addressed several gaps in knowledge by employing genetically edited mouse models where PPi metabolism was disrupted and pharmacologically modulating PPi in a PPi-deficient mouse model. We demonstrate that acellular cementum growth is inversely proportional to PPi levels, with reduced cementum in Alpl KO (increased PPi levels) mice and excess cementum in Ank KO mice (decreased PPi levels). Moreover, simultaneous ablation of Alpl and Ank results in reestablishment of functional cementum in dKO mice. Additional reduction of PPi by dual deletion of Ank and Enpp1 does not further increase cementogenesis, and PDL space is maintained in part through bone modeling/remodeling by osteoclasts. Our results provide insights into cementum formation and expand our knowledge of how PPi regulates cementum. We also demonstrate for the first time that pharmacologic manipulation of PPi through an ENPP1-Fc fusion protein can regulate cementum growth, supporting therapeutic interventions targeting PPi metabolism.