REV-ERBs negatively regulate mineralization of the cementoblasts

Genome wide analysis of dexamethasone stimulated mineralization in human dental pulp cells by RNA sequencing

Human dental pulp cells (hDPCs) contain mesenchymal stem cells and are therefore indispensible for reparative dentin formation. Here, we present a pilot study of transcriptomic profiles of mineralized hDPCs isolated from sound human maxillary third molars. We observed altered gene expression of hDPCs between control (dexamethasone free) and experimental (dexamethasone 1 nm) groups. Differential expression analysis revealed up-regulation of several inflammation and mineralization-related genes in the experimental group. After a Gene Ontology analysis for predicting genes involved in biological process, cellular component and molecular function, we found enrichment of genes related to protein binding. Based on the results of Kyoto Encylopedia of Genes and Genomes pathway analysis, it is suggested up-regulated genes in mineralized hDPCs were mostly enriched in the mitogen-activated protein kinase (MAPK) signaling pathway, fluid shear stress and the atherosclerosis signaling pathway, etc. Importantly, Gene Set Enrichment Analysis revealed dexamethasone was positively related to the Janus kinase/signal transducer and activator of transcription, MAPK and Notch signaling pathway. Moreover, it was suggested that dexamethasone regulates signaling pathway in pluripotency of stem cells. Collectively, our work highlights transcriptome level gene regulation and intercellular interactions in mineralized hDPCs. The database produced in the present study paves the way for further investigations looking to explore genes that are involved in dental pulp cells mineralization.

Clock genes are expressed in cementum and regulate the proliferation and mineralization of cementoblasts

Circadian clock genes are present in the ameloblasts, odontoblasts, and dental pulp cells. The cementum plays a vital role in connecting the roots of teeth to the alveolar bone by anchoring the periodontal ligament. The present study aimed at confirming the existence of clock genes and describing the potential regulatory effects of REV-ERBα in the cementum. The tooth-periodontal ligament-alveolar bone complexes of 6-week-old mice were analyzed using immunohistochemistry. OCCM-30 cells, an immortalized cementoblast cell line, were synchronized with dexamethasone. We used RT-PCR to detect the expression of clock genes in the absence or presence of SR8278, an effective antagonist of REV-ERBα. We performed a cell counting kit-8 (CCK-8) assay to determine the effect of SR8278 on cell proliferation. RT-PCR and Western blot were used to measure the expression of mineralization-related markers in mineralization-induced OCCM-30 cells, with or without SR8278 treatment. Finally, we used Alizarin red staining, and ALP staining and activity to further verify the effect of SR8278 on mineralization of OCCM-30 cells on macro-level. In our study, clock protein expression was confirmed in the murine cementum. Clock genes were shown to oscillate continuously in OCCM-30 cells. SR8278-induced inactivation of REV-ERBα inhibited the proliferation but promoted the mineralization of OCCM-30 cells. The present study confirmed the presence of clock genes in the cementum, where they potentially participate in cell proliferation and mineralization. Our findings may inspire new research directions for periodontal regeneration via clock gene manipulation.

Circadian clock genes as promising therapeutic targets for bone loss

The circadian clock regulates many key physiological processes such as the sleep-wake cycle, hormone release, cardiovascular health, glucose metabolism and body temperature. Recent evidence has suggested a critical role of the circadian system in controlling bone metabolism. Here we review the connection between bone metabolism and the biological clock, and the roles of these mechanisms in bone loss. We also analyze the regulatory effects of clock-related genes on signaling pathways and transcription factors in osteoblasts and osteoclasts. Additionally, osteocytes and endothelial cells (ECs) regulated by the circadian clock are also discussed in our review. Furthermore, we also summarize the regulation of circadian clock genes by some novel modulators, which provides us with a new insight into a potential strategy to prevent and treat bone diseases such as osteoporosis by targeting circadian genes.

The roles of heteromorphic crystals and organic compounds in the formation of the submandibular stones

Objective

The study aimed to analyze the formation process of submandibular stones based on the theory of biological mineralization and inorganic crystal structure variation.

Study design

From January 2021 to December 2021, patients with submandibular stones treated in the Affiliated Hospital of Stomatology, Sun Yat-sen University (Guangzhou, China) were selected. According to the criterion of maximum transverse diameter ≥3 mm, a total of five submandibular stones meeting the requirement were included. After the surface of sample stones were washed, they were cut along the maximum transverse diameter. Next, the study employed Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and polycrystalline X-ray Diffraction (XRD) to analyze the composition and structure of submandibular stones.

Results

Five submandibular stones were included. The organic and inorganic compounds showed a rhythmic or irregular distribution. Submandibular stones were highly occupied with carbon (C), oxygen (O), calcium (Ca), and phosphorus (P). Hydroxyapatite (HAP) was the primary inorganic component. In addition, the precursor of HAP, namely Amorphous Calcium Phosphate (ACP), was also found. Tetrahedral Substitution Index (TSI) and Ca/P ratio reflected the degree of structural variation in HAP crystal, which fluctuated from 5.62-90.71 and 1.10-1.35, respectively.

Conclusions

The development of submandibular stones was influenced by inorganic crystals' chemical and structural variation as well as the organics' regulation towards the inorganic. The isomorphic substitution was accompanied by the occurrence of inorganic crystals, resulting in the crystal structure change. Organics might influence the appearance, aggregation, and mineralization of HAP during its formation.

Circadian clock—A promising scientific target in oral science

The oral and maxillofacial organs play vital roles in chewing, maintaining facial beauty, and speaking. Almost all physiological processes display circadian rhythms that are driven by the circadian clock, allowing organisms to adapt to the changing environment. In recent years, increasing evidence has shown that the circadian clock system participates in oral and maxillofacial physiological and pathological processes, such as jaw and tooth development, salivary gland function, craniofacial malformations, oral carcinoma and other diseases. However, the roles of the circadian clock in oral science have not yet been comprehensively reviewed. Therefore, This paper provides a systematic and integrated perspective on the function of the circadian clock in the fields of oral science, reviews recent advances in terms of the circadian clock in oral and maxillofacial development and disease, dialectically analyzes the importance of the circadian clock system and circadian rhythm to the activities of oral and maxillofacial tissues, and focuses on analyzing the mechanism of the circadian clock in the maintenance of oral health, affecting the common diseases of the oral and maxillofacial region and the process of oral-related systemic diseases, sums up the chronotherapy and preventive measures for oral-related diseases based on changes in tissue activity circadian rhythms, meanwhile, comes up with a new viewpoint to promote oral health and human health.

Fibroblasts Mediate Ectopic Bone Formation of Calcium Phosphate Ceramics

Heterogeneity of fibroblasts directly affects the outcome of tissue regeneration; however, whether bioactive ceramics regulate bone regeneration through fibroblasts is unclear. Ectopic bone formation model with biphasic calcium phosphate (BCP) implantation was used to investigate the temporal and spatial distribution of fibroblasts around ceramics. The effect of BCP on L929 fibroblasts was evaluated by EdU assay, transwell assay, and qRT-PCR. Further, the effect of its conditioned medium on osteogenic differentiation of bone marrow mesenchymal stem cells (BMSCs) was confirmed by ALP staining. SEM and XRD results showed that BCP contained abundant micro- and macro-pores and consisted of hydrogen-apatite (HA) and β-tricalcium phosphate (β-TCP) phases. Subsequently, BCP implanted into mice muscle successfully induced osteoblasts and bone formation. Fibroblasts labelled by vimentin gathered around BCP at 7 days and peaked at 14 days post implantation. In vitro, BCP inhibited proliferation of L929 fibroblast but promoted its migration. Moreover, expression of Col1a1, Bmp2, and Igf1 in L929 treated by BCP increased significantly while expression of Tgfb1 and Acta did not change. ALP staining further showed conditioned media from L929 fibroblasts treated by BCP could enhance osteogenic differentiation of BMSCs. In conclusion, fibroblasts mediate ectopic bone formation of calcium phosphate ceramics.