The involvement of genes related to bile secretion pathway in rat tooth germ development

Dynamic expression of Mage-D1 in rat dental germs and potential role in mineralization of ectomesenchymal stem cells

Mage-D1 (MAGE family member D1) is involved in a variety of cell biological effects. Recent studies have shown that Mage-D1 is closely related to tooth development, but its specific regulatory mechanism is unclear. The purpose of this study was to investigate the expression pattern of Mage-D1 in rat dental germ development and its differential mineralization ability to ectomesenchymal stem cells (EMSCs), and to explore its potential mechanism. Results showed that the expression of Mage-D1 during rat dental germ development was temporally and spatially specific. Mage-D1 promotes the proliferation ability of EMSCs but inhibits their migration ability. Under induction by mineralized culture medium, Mage-D1 promotes osteogenesis and tooth-forming ability. Furthermore, the expression pattern of Mage-D1 at E19.5 d rat dental germ is similar to p75 neurotrophin receptor (p75NTR), distal-less homeobox 1 (Dlx1) and msh homeobox 1 (Msx1). In addition, Mage-D1 is binding to p75NTR, Dlx1, and Msx1 in vitro. These findings indicate that Mage-D1 is play an important regulatory role in normal mineralization of teeth. p75NTR, Dlx1, and Msx1 seem to be closely related to the underlying mechanism of Mage-D1 action.

A potential role of p75NTR in the regulation of circadian rhythm and incremental growth lines during tooth development

Objective: Tooth morphogenesis and the formation of hard tissues have been reported to be closely related to circadian rhythms. This study investigates the spatiotemporal expression and relationship of p75NTR with core clock genes, mineralization-related or odontogenesis-related genes, and aims to derive the potential role of p75NTR in regulating circadian rhythm and incrementality growth line formation during tooth development.

Materials and methods: The dynamic morphology of the rat dental germ was observed at seven stages (E14.5 d, E16.5 d, E18.5 d, P.N. 4 d, P.N. 7 d, P.N. 10 d, and P.N. 15 d). Next, the expressions of p75NTR and other target factors were traced. The ectomesenchymal stem cells (EMSCs) were isolated from the E18.5d rat dental germs and synchronized using 50% of fetal bovine serum. Then, they were cultured in light/light (L.L.), dark/dark (D.D.), and light/dark (L.D.) conditions for 48 h. The total RNA was collected every 4 h, and the circadian rhythm dynamics of target factors were observed. To reveal the mechanism further, p75NTR was down-regulated in p75NTR^ExIII−/− mice and up-regulated in immortalized mouse dental apical papilla progenitor cells. The change tendencies of other target factors were also detected.

Results: The clock genes Bmal1, Clock, Per1, and Per2 were all expressed in tooth germs before the formation of dental hard tissues and demonstrated a regular oscillating expression pattern in EMSCs from dental germs. Their expression was affected by the L.D. stimulus, and most of them were promoted by D.D. conditions. p75NTR presented a similar expression pattern and a positive or negative relationship with most clock genes, mineralization-related and odontogenesis-related factors, such as brain and muscle ARNT-like protein-1 (Bmal1), runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), MSH-like 1 (MSX1), dentin matrix acidic phosphoprotein 1 (Dmp1), and dentin sialophosphoprotein (Dspp). Moreover, the arrangement, morphology, and even boundary in pre-odontoblast/pre-ameloblast layers were disordered in the p75NTR^ExIII−/− mice.

Conclusion: Circadian rhythm was found to affect tooth development. p75NTR might play a crucial role in regulating clock genes in the mineralization and formation of the dental hard tissues. p75NTR is actively involved in the odontoblast-ameloblast junction and cell polarity establishment during tooth morphogenesis.

Association Study Between Polymorphic Loci in Cholesterol Metabolism Pathway and Gallstone in the Tibetan Population

Background: The incidence of gallstones in the Tibetan population is increasing rapidly. Previous studies indicated that genetic variation located in the cholesterol metabolism pathway may be associated with the incidence of gallstones.

Methods: By recruiting 132 Tibetan gallstone patients and 52 normal Tibetan controls, we performed next-generation sequencing for 508 genes in the cholesterol metabolism pathway. Additionally, by integrating the sequence data of 41 normal Tibetan subjects in the public database, we finally obtained 93 normal Tibetan controls. Single nucleotide polymorphisms (SNPs) calling were performed by using the GATK pipeline. The quality control criteria for SNPs were: missing rate <0.05; minor allele frequency (MAF) > 0.01; and p value >0.001 in the Hardy-Weinberg Equilibrium (HWE) test. To eliminate the influence of population heterogeneity, Principal Component Analysis (PCA) was carried out by using the smartpca software. Association analyses were performed by Plink software. Multiple tests were adjusted by the false discovery rate (FDR) method.

Results: A total of 2,401 SNPs were obtained by analyzing 508 genes, and 2,011 SNPs left after quality control. After adjusting the eigen vectors, we found that 10 SNPs (SNV05997, rs80145081, rs80005560, rs79074685, rs748546375, rs201880593, rs142559357, rs750769471, rs869789 and rs4072341) were significantly associated with gallstone. Subsequently, by comparing the case group with our control group and the public database control group separately, we further found that the SNP rs869789 was consistently significantly associated with gallstone (p = 9.04 × 10^–3 in cases vs. our controls and 5.73 × 10^–3 in cases vs. public controls, respectively).

Conclusion: By systematically analyzed SNPs in the cholesterol metabolism pathway, we identified one polymorphic locus rs869789 significantly associated with the pathogenesis of gallstone in the Tibetan population. This study will provide clue for further mechanism study of gallstone in the Tibetan population.

The Genes Involved in Dentinogenesis

The development and repair of dentin are strictly regulated by hundreds of genes. Abnormal dentin development is directly caused by gene mutations and dysregulation. Understanding and mastering this signal network is of great significance to the study of tooth development, tissue regeneration, aging, and repair and the treatment of dental diseases. It is necessary to understand the formation and repair mechanism of dentin in order to better treat the dentin lesions caused by various abnormal properties, whether it is to explore the reasons for the formation of dentin defects or to develop clinical drugs to strengthen the method of repairing dentin. Molecular biology of genes related to dentin development and repair are the most important basis for future research.

Age-Related Metabolic Pathways Changes in Dental Follicles: A Pilot Study

Aging is not a matter of choice; it is our fate. The “time-dependent functional decline that affects most living organisms” is coupled with several alterations in cellular processes, such as cell senescence, epigenetic alterations, genomic instability, stem cell exhaustion, among others. Age-related morphological changes in dental follicles have been investigated for decades, mainly motivated by the fact that cysts and tumors may arise in association with unerupted and/or impacted teeth. The more we understand the physiology of dental follicles, the more we are able to contextualize biological events that can be associated with the occurrence of odontogenic lesions, whose incidence increases with age. Thus, our objective was to assess age-related changes in metabolic pathways of dental follicles associated with unerupted/impacted mandibular third molars from young and adult individuals. For this purpose, a convenience sample of formalin-fixed paraffin-embedded (FFPE) dental follicles from young (<16 y.o., n = 13) and adult (>26 y.o., n = 7) individuals was selected. Samples were analyzed by high-performance liquid chromatography-mass spectrometry (HPLC-MS)-based untargeted metabolomics. Multivariate and univariate analyses were conducted, and the prediction of altered pathways was performed by mummichog and Gene Set Enrichment Analysis (GSEA) approaches. Dental follicles from young and older individuals showed differences in pathways related to C21-steroid hormone biosynthesis, bile acid biosynthesis, galactose metabolism, androgen and estrogen biosynthesis, starch and sucrose metabolism, and lipoate metabolism. We conclude that metabolic pathways differences related to aging were observed between dental follicles from young and adult individuals. Our findings support that similar to other human tissues, dental follicles associated with unerupted tooth show alterations at a metabolic level with aging, which can pave the way for further studies on oral pathology, oral biology, and physiology.