Overlapping functions of bone sialoprotein and pyrophosphate regulators in directing cementogenesis

Abstract

Although acellular cementum is essential for tooth attachment, factors directing its development and regeneration remain poorly understood. Inorganic pyrophosphate (PPi), a mineralization inhibitor, is a key regulator of cementum formation: tissue-nonspecific alkaline phosphatase (Alpl/TNAP) null mice (increased PPi) feature deficient cementum, while progressive ankylosis protein (Ank/ANK) null mice (decreased PPi) feature increased cementum. Bone sialoprotein (Bsp/BSP) and osteopontin (Spp1/OPN) are multifunctional extracellular matrix components of cementum proposed to have direct and indirect effects on cell activities and mineralization. Studies on dentoalveolar development of Bsp knockout (Bsp−/−) mice revealed severely reduced acellular cementum, however underlying mechanisms remain unclear. The similarity in defective cementum phenotypes between Bsp−/− mice and Alpl−/− mice (the latter featuring elevated PPi and OPN), prompted us to examine whether BSP is operating by modulating PPi-associated genes. Genetic ablation of Bsp caused a 2-fold increase in circulating PPi, altered mRNA expression of Alpl, Spp1, and Ank, and increased OPN protein in the periodontia. Generation of a Bsp knock-out (KO) cementoblast cell line revealed significantly decreased mineralization capacity, 50% increased PPi in culture media, and increased Spp1 and Ank mRNA expression. While addition of 2 μg/ml recombinant BSP altered Spp1, Ank, and Enpp1 expression in cementoblasts, changes resulting from this dose were not dependent on the integrin-binding RGD motif or by genetic ablation of Ank on the Bsp−/− MAPK/ERK signaling pathway. Decreasing PPi mouse background reestablished cementum formation, allowing more than 3-fold increased acellular cementum volume compared to WT. However, deleting Ank did not fully compensate for the absence of BSP. Bsp−/−;Ank−/− double-deficient mice exhibited mean 20–27% reduced cementum thickness and volume compared to Ank−/− mice. From these data, we conclude that the perturbations in PPi metabolism are not solely driving the cementum pathology in Bsp−/− mice, and that PPi is more potent than BSP as a cementum regulator, as shown by the ability to override loss of BSP by lowering PPi. We propose that BSP and PPi work in concert to direct mineralization in cementum and likely other mineralized tissues.

M2 Macrophages Enhance the Cementoblastic Differentiation of Periodontal Ligament Stem Cells via the Akt and JNK Pathways

“…Although the actual specificity of CAP and CEMP-1 for the cementum remains to be explored, CAP and CEMP-1 are commonly used as cementogenesis-related markers in cellular investigations [45][46][47]. In addition, BSP and OCN are initiators of mineral formation, and BSP has been demonstrated to be an adhesion molecule that maintains appropriate cells at the tooth root surface [47][48][49][50]. Therefore, CAP, CEMP-1, BSP, and OCN were used as markers for cementogenic differentiation in our study, and an appropriate induction time (a 7-day incubation duration) for detecting the above cementoblastic markers was determined (Supporting Information Fig.…”

Basic fibroblast growth factor regulates phosphate/pyrophosphate regulatory genes in stem cells isolated from human exfoliated deciduous teeth

“…Induction of Ank was also achieved by addition of 5 mM P i to OCCM.30 murine cementoblast cells, hypothesized to be a response to pro-mineralization conditions and a sort of negative feedback to compensate the overabundance of extracellular P i and to balance P i /PP i ratio, and regulate the pace of mineralization [ 22 ]. Loss of function of Ank/ANKH leads to decreased PP i and increased and sometimes ectopic mineralization, and Ank mutant or knockout mice feature skeletal differences and massively increased acellular cementum [ 12 , 14 , 17 , 59 ]. These potent effects of ANK/ANKH on mineralized tissue development in vivo justify further investigation of the interactions of bFGF, ANKH , PP i , and mineralization in SHEDs.…”

How To Build a Bone: PHOSPHO1, Biomineralization, and Beyond

“…PHOSPHO1 was found to show expression in osteoblasts and cementoblasts of alveolar bone and cementum, respectively, during their mineralization phases where osteoid accumulation was evident in the bone and was accompanied by delayed mineralization of the cellular cementum in Phospho1 –/– animals . Intriguingly, acellular cementum formation was normal, despite downregulation of Phospho1 –/– in a bone sialoprotein knockout model in this region . PHOSPHO1 is therefore an enzyme critical for the integrity of the periodontal tissue interface, along with normal development of these hard tissues.…”

“…(45) Intriguingly, acellular cementum formation was normal, despite downregulation of Phospho1 -/in a bone sialoprotein knockout model in this region. (46) PHOSPHO1 is therefore an enzyme critical for the integrity of the periodontal tissue interface, along with normal development of these hard tissues. In enamel, Phospho1 -/mice exhibited a 25% increase in tissue volume, with a significantly reduced level of mineralization.…”