Role of modulators of Pi/PPi in cementum formation and regeneration

摘要

ABSTRACT Proper pyrophosphate regulation is critical in mineralization processes. Pyrophosphate (PPi) is a direct inhibitor of hydroxyapatite crystal growth, thus inhibiting mineralization. A main source of PPi is ATP, which is hydrolyzed by ectonucleotide pyrophosphatase phosphodiesterases (ENPP), including ENPP1. ENPP1 is expressed in bone along with progressive ankylosis protein (ANK), which transports intracellular PPi to extracellular spaces. While ANK and ENPP1 increase extracellular PPi, tissue non-specific alkaline phosphatase (TNAP, encoded by ALPL), hydrolyzes PPi into inorganic phosphate (Pi), thus decreasing PPi in extracellular spaces. Although the specifics of direct or indirect interactions between ANK, ENPP1, and TNAP are unknown, loss of any of these factors has dramatic effects on mineralized tissue. The studies proposed here were developed to elucidate functions of pyrophosphate regulators with the ultimate goal of developing therapies targeted toward mineralization disorders. Abnormal PPi regulation (as exhibited by individuals with ENPP1, ANK or ALPL mutations) can lead to alterations in the periodontium (cementum, periodontal ligament, alveolar bone), specifically cementum. Alterations include excessive cementum formation (ENPP1, ANK) or deficient cementum formation leading to premature tooth exfoliation (ALPL), an adverse sequelae of untreated periodontal disease. Periodontal disease, a global burden with significant psychosocial and financial consequences, features destruction of the periodontium. Existing regenerative therapies are unpredictable and do not target cementum regeneration. To investigate roles of Ank and Enpp1 during cementogenesis, I, along with my colleagues, developed Ank, Enpp1 double mutant mice. In preliminary studies, we noted a more dramatic hypercementosis phenotype in 8wk old Ank, Enpp1 double mutants versus single mutants. Additionally, we noted distinct differences between single and double mutants within the PDL region/cementum in gene/protein expression of SIBLING proteins, known modulators of the mineralization process. Three aims were developed to define ANK and ENPP1 roles in periodontal development and maintenance, identify mechanistic pathways in which ANK and ENPP1 regulate cementogenesis (e.g. focused on direct and indirect ability to modulate SIBLINGs), and determine the feasibility of using Enpp1 inhibitors to regenerate periodontaltissues. As a clinician scientist, my ultimate goal is to conduct productive research that provides scientific insights into periodontal disease pathogenesis and translate this knowledge into tangible clinical applications (e.g. diagnostic/prognostic tests, prevention strategies, and therapeutic interventions). My career development plan has been tailored toward this goal with solid mentorship, collaborations, and training opportunities in research and clinical settings. In conjunction with institutional support, I am confident studies/activities outlined in my application will help build upon my existing skillset and facilitate my transition into an independent investigator.