Clinical Research of Oral Connective Tissue Program

项目a：确定遗传易感性和促进特发性牙根吸收的免疫病理机制

Project A. Determine genetic susceptibility and immunopathological mechanisms contributing to idiopathic tooth root resorption Background: Previously, we reported that BSP KO mice exhibit a tooth root resorption phenotype. Based on this finding, we sought to identify human subjects exhibiting multiple idiopathic cervical root resorption (MICRR), a familial pattern of MICRR with suggested genetic susceptibility. Following IRB approval from the University of Detroit Mercy School of Dentistry and NIH, dental/medical histories, x-rays, saliva samples, and extracted teeth were collected from a kindred (4 affected and 4 unaffected members) exhibiting MICRR. Whole exome sequencing using saliva identified a mutation in the c-terminal region of IRF8 responsible for overactive osteoclast function. Results were published in JBMR, 2019 and this project transitioned to University Maryland with Dr. Thumbigere-Math (K99/R00 recipient). Ongoing: We continue to collaborate with Dr. Thumbigere-Math as the lead on the IRF8 project, with other NIH collaborators, Drs. Ozato and Holland, with a publication in Bone, 2020 (see below). Collaborations were established with other clinicians: Dr. Steve Russo (Chicago, IL), Dr. Thomas Schneider (New Jersey), and Dr. Janina Golob Deeb (VCU), who have seen patients with rapid MICRR. Dr. Golob Deeb noticed a potential association with MICRR and cessation of denosumab, leading us to collaborate with Drs. Alison Boyce and Marie Kao-Hseih (NIDCR) to conduct dental exams on patients taking denosumab for fibrous dysplasia. We have also set up a collaboration with an expert in microbial analyses, Dr. Purnima Kumar (Ohio State University), to determine the microbial profile of plaque samples from Russos patient. Further, we analyzed teeth obtained from Dr. Betty Hajishengallis (U. Penn), from a patient with missing ossicles and idiopathic root resorption, diagnosed with familial expansile osteolysis (age 10, mutations in the TNFRSF11 gene encoding RANK protein, over expression) and noted cementum defects. Project B. Disorders of mineralization: In collaboration with NIDCR clinical researchers and other IC clinicians, we have been examining individuals with mineralized tissue metabolism disorders for alterations in tissues/cells of the DOC complex. 1. Mutations in key regulators of Pi/PPi. Mineralization of skeleton and teeth is tightly regulated by levels of extracellular inorganic phosphate (Pi) and pyrophosphate (PPi). Three regulators that control pericellular concentrations of Pi and PPi include tissue-nonspecific alkaline phosphatase (TNAP), progressive ankylosis protein (ANK), and ectonucleotide pyrophosphatase/phosphodiesterase 1 (ENPP1). Inactivation of these factors results in mineralization disorders affecting teeth and their supporting structures. We examined the effect of decreased PPi on development and maturation of teeth in human subjects (4) with generalized arterial calcification of infancy (GACI), who harbor loss-of-function mutations in ENPP1. Subjects reported a history of infraocclusion or over-retained primary teeth,poor orthodontic tooth movement, suggesting altered mineral metabolism as a contributing factor. Micro-CT analyses of extracted primary teeth from GACI subjects revealed marked increase cervical cementum thickness and density vs. age-matched healthy control teeth. There were no differences in enamel and dentin densities between GACI and control teeth. Histology revealed dramatically expanded cervical cementum in GACI teeth, including cementocyte-like cells and unusual patterns of cementum resorption and repair. Micro-CT analysis of Enpp1 knock-out mouse molars revealed a marked increase in acellular cementum thickness and volume. Collectively, these findings report a novel dental phenotype in GACI and further support our hypothesis that Pi/PPi modulation is as a key mechanism for regulating cementogenesis across species. Thumbigere-Math V et al., JDR, 2018. Ongoing: We have continued to examine patients with Pi/PPi disorders at NIH CRC as well as analyzing exfoliated or extracted teeth from patients with Pi/PPi disorders. We have also included patients with ABCC6 (ATP Binding Cassette Subfamily C Member 6), which is associated with some cases of GACI. We have also been examining teeth from patients with disorders associated with skeletal disturbances, e.g., human familial tumoral calcinosis (collaborators: Dr. Michael Collins, manuscript submitted July 2020) , patients with Hypoxia-inducible factor 2a mutations (collaborators: Drs. Pacak, Rosenblum, and Zhuang). For controls, in collaboration with North Carolina State University and Duke under the Newborn Epigenetics Study, we are obtaining exfoliated primary teeth from healthy individuals.