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Background and Objectives Periodontitis is a chronic inflammatory disease of periodontal supporting tissues. The persistent inflammatory reaction depends on the release of chemokines to continuously recruit inflammation cells. GATA‐binding protein 4 (GATA4) exerts effects on senescence and inflammation, while its role in periodontitis is far from clear. The present study aims to address the effect of GATA4 on regulating chemokines and the chemotaxis in periodontitis. Material and Methods Periodontitis rat models were constructed to detect the expression of GATA4 and the chemokine monocyte chemoattractant protein‐1 (MCP‐1) by immunohistochemistry. Lipopolysaccharide (LPS)‐stimulated human periodontal ligament (PDL) cells and GATA4‐knockdown by siRNA transient transfection PDL cells were used to explore the correlation between GATA4 and chemokines. Transwell assay was performed to detect the role of GATA4 for the recruitment effect of chemokines on macrophages. Mitogen‐activated protein kinase (MAPK) inhibitors were scheduled to intervene in LPS‐stimulated PDL cells to examine the association between MAPK signaling pathways and GATA4. The expression of GATA4, chemokines, or MAPK signaling molecules was determined by quantitative real‐time polymerase chain reaction, western blotting, or cell immunofluorescence. Results The expression of GATA4 and MCP‐1 was significantly increased in periodontitis rat models and in LPS‐stimulated PDL cells. Knockdown GATA4 inhibited the expression of GATA4 and MCP‐1 as well as suppressed the recruitment of macrophage in LPS‐stimulated PDL cells. Inhibitors of p38 and ERK1/2 signaling pathways significantly downregulated the increased expression of GATA4 and MCP‐1 induced by LPS in PDL cells. Conclusions GATA‐binding protein 4 could act as an upstream regulator of MCP‐1 and as a downstream regulator of p38 and ERK1/2 signaling pathways to initiate inflammation response and regulate chemotaxis during the progression of periodontitis.

Circadian rhythm is involved in the development and diseases of many tissues. However, as an essential environmental regulating factor, its effect on amelogenesis has not been fully elucidated. The present study aims to investigate the correlation between circadian rhythm and ameloblast differentiation and to explore the mechanism by which circadian genes regulate ameloblast differentiation. Circadian disruption models were constructed in mice for in vivo experiments. An ameloblast-lineage cell (ALC) line was used for in vitro studies. As essential molecules of the circadian system, Bmal1 and Per2 exhibited circadian expression in ALCs. Circadian disruption mice showed reduced amelogenin (AMELX) expression and enamel matrix secretion and downregulated expression of BMAL1, PER2, PPARγ, phosphorylated AKT1 and β-catenin, cytokeratin-14 and F-actin in ameloblasts. According to previous findings and our study, BMAL1 positively regulated PER2. Therefore, the present study focused on PER2-mediated ameloblast differentiation and enamel formation. Per2 knockdown decreased the expression of AMELX, PPARγ, phosphorylated AKT1 and β-catenin, promoted nuclear β-catenin accumulation, inhibited mineralization and altered the subcellular localization of E-cadherin in ALCs. Overexpression of PPARγ partially reversed the above results in Per2-knockdown ALCs. Furthermore, in in vivo experiments, the length of incisor eruption was significantly decreased in the circadian disturbance group compared to that in the control group, which was rescued by using a PPARγ agonist in circadian disturbance mice. In conclusion, through regulation of the PPARγ/AKT1/β-catenin signalling axis, PER2 played roles in amelogenin expression, cell junctions and arrangement, enamel matrix secretion and mineralization during ameloblast differentiation, which exert effects on enamel formation.

During periodontitis progression, PPARγ could inhibit inflammation, prevent bone resorption within a short time, while the long-term PPARγ activation would lead to increased bone resorption, and PPARγ repression by antagonist would enhance alveolar bone formation.

Amelogenesis imperfecta is a group of disorders causing abnormalities in enamel formation in various phenotypes. Many mutations in the FAM83H gene have been identified to result in autosomal dominant hypocalcified amelogenesis imperfecta in different populations. However, the structure and function of FAM83H and its pathological mechanism have yet to be further explored. Evolutionary analysis is an alternative for revealing residues or motifs that are important for protein function. In the present study, we chose 50 vertebrate species in public databases representative of approximately 230 million years of evolution, including 1 amphibian, 2 fishes, 7 sauropsidas and 40 mammals, and we performed evolutionary analysis on the FAM83H protein. By sequence alignment, conserved residues and motifs were indicated, and the loss of important residues and motifs of five special species (Malayan pangolin, platypus, minke whale, nine-banded armadillo and aardvark) was discovered. A phylogenetic time tree showed the FAM83H divergent process. Positive selection sites in the C-terminus suggested that the C-terminus of FAM83H played certain adaptive roles during evolution. The results confirmed some important motifs reported in previous findings and identified some new highly conserved residues and motifs that need further investigation. The results suggest that the C-terminus of FAM83H contain key conserved regions critical to enamel formation and calcification.