Ablation of Pyrophosphate Regulators Promotes Periodontal Regeneration.

Biomineralization is regulated by inorganic pyrophosphate (PP), a potent physiological inhibitor of hydroxyapatite crystal growth. Progressive ankylosis protein (ANK) and ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1) act to increase local extracellular levels of PP, inhibiting mineralization. The periodontal complex includes 2 mineralized tissues, cementum and alveolar bone (AB), both essential for tooth attachment. Previous studies demonstrated that loss of function of ANK or ENPP1 (reducing PP) resulted in increased cementum formation, suggesting PP metabolism may be a target for periodontal regenerative therapies. To compare the effects of genetic ablation of , and both factors concurrently on cementum and AB regeneration, mandibular fenestration defects were created in knockout ( KO), mutant (), and double KO (dKO) mice. Genetic ablation of , or both factors increased cementum regeneration compared to controls at postoperative days (PODs) 15 and 30 ( KO: 8-fold, 3-fold; : 7-fold, 3-fold; dKO: 11-fold, 4-fold, respectively) associated with increased fluorochrome labeling and expression of mineralized tissue markers, dentin matrix protein 1 (/DMP1), osteopontin (/OPN), and bone sialoprotein (/BSP). Furthermore, dKO mice featured increased cementum thickness compared to single KOs at POD15 and KO at POD30. No differences were noted in AB volume between genotypes, but osteoblast/osteocyte markers were increased in all KOs, partially mineralized osteoid volume was increased in dKO versus controls at POD15 (3-fold), and mineral density was decreased in and dKOs at POD30 (6% and 9%, respectively). Increased numbers of osteoclasts were present in regenerated AB of all KOs versus controls. These preclinical studies suggest PP modulation as a potential and novel approach for cementum regeneration, particularly targeting ENPP1 and/or ANK. Differences in cementum and AB regeneration in response to reduced PP conditions highlight the need to consider tissue-specific responses in strategies targeting regeneration of the entire periodontal complex.