Expression status of mRNA for sex hormone receptors in human dental pulp cells and the response to sex hormones in the cells

Use of Dental Defects Associated with Low-Dose di(2-Ethylhexyl)Phthalate as an Early Marker of Exposure to Environmental Toxicants

BACKGROUND

Markers of exposure to environmental toxicants are urgently needed. Tooth enamel, with its unique properties, is able to record certain environmental conditions during its formation. Enamel formation and quality are dependent on hormonal regulation and environmental conditions, including exposure to endocrine disrupting chemicals (EDCs). Among EDCs, phthalates such as di-(2-ethylhexyl) phthalate (DEHP) raise concerns about their contribution to various pathologies, including those of mineralized tissues.

OBJECTIVES

The effects of exposure to low-doses of DEHP on the continually growing incisors were analyzed in mouse males and females.

METHODS

Adult male and female C57BL/6J mice were exposed daily to 0.5, 5, and 50μg/kg per day DEHP for 12 wk and their incisors clinically examined. Incisors of males were further analyzed by scanning electron microscopy (SEM), micro X-ray computed tomography (micro-computed tomography; μCT), and nanoindentation for the enamel, histology and real-time quantitative polymerase chain reaction (RT-qPCR) for the dental epithelium.

RESULTS

Clinical macroscopic observations of incisors showed various dose-dependent dental lesions such as opacities, scratches, and enamel breakdown in 30.5% of males (10 of 34 total incisors across three independent experiments), and 15.6% of females (7 of 46 incisors) at the highest dose, among which 18.1% (6 of 34 total incisors across three independent experiments) and 8.9% (4 of 46 incisors), respectively, had broken incisors. SEM showed an altered enamel surface and ultrastructure in DEHP-exposed male mice. Further characterization of the enamel defects in males by μCT showed a lower mineral density than controls, and nanoindentation showed a lower enamel hardness during all stages of enamel mineralization, with more pronounced alterations in the external part of the enamel. A delay in enamel mineralization was shown by several approaches (μCT, histology, and RT-qPCR).

DISCUSSION

We conclude that DEHP disrupted enamel development in mice by directly acting on dental cells with higher prevalence and severity in males than in females. The time window of DEHP effects on mouse tooth development led to typical alterations of structural, biochemical, and mechanical properties of enamel comparable to other EDCs, such as bisphenol A. The future characterization of dental defects in humans and animals due to environmental toxicants might be helpful in proposing them as early markers of exposure to such molecules. https://doi.org/10.1289/EHP10208.

Conserved and Taxon-Specific Patterns of Phenotypic Modularity in the Mammalian Dentition

Previous genotype:phenotype mapping of the mouse and primate dentition revealed the presence of pre- and post-canine modules in mice and anthropoid primates, as well as molar and premolar submodules in anthropoid primates. We estimated phenotypic correlation matrices for species that sample broadly across Mammalia to test the hypothesis that these modules exist across a broader range of taxa and thereby represent a conserved mammalian trait. We calculated phenotypic correlation matrices from linear dental measurements of 419 individual specimens representing 5 species from 4 mammalian orders: Artiodactyla (Odocoileus hemionus), Carnivora (Canis latrans and Ursus americanus), Didelphimorphia (Didelphis virginiana), and Primates (Colobus guereza). Our results based on hierarchical clustering indicate a generally higher correlation within incisors and among post-canine teeth. However, the post-canine phenotypic correlation matrices do not consistently exhibit the premolar and molar submodularity observed in anthropoid primates. Additionally, we find evidence of sex differences in the Odocoileus phenotypic correlation matrices: Males of this species exhibit overall higher inter-trait correlations compared to females. Our overall findings support the interpretation that incisors and post-canine dentition represent different phenotypic modules, and that this architecture may be a conserved trait for mammals.

Exome array identifies functional exonic biomarkers for pediatric dental caries

BACKGROUND

Pediatric dental caries is common among Arab children, however we are still searching for possible genes and molecular mechanisms that influence caries development.

AIM

To identity genetic predispositions of dental caries among Saudi children with high DMFT (Decayed, Missing, and Filled Teeth).

DESIGN

This case-control study analysed putative functional exonic-variants (n = 243,345) to study the molecular genetics of pediatric caries with high dmft index, 8.75 ± 4.16 on Arab-ancestry subjects with primary dentition (n = 111; 76 cases, dmft>5 and 35 controls, dmft = 0).

RESULTS

Pediatric caries is significantly associated with single nucleotide polymorphisms (SNP) in the GRIN2B-rs4764039C (p-value = 2.03 × 10^-08) and CFH-rs1065489G (p-value = 8.26 × 10^-08) genes, even after Bonferroni correction. Irregular tooth brushing habits (p = 0.0404) and irregular dental visits (p = 0.0050) are significantly associated with caries. Functional enrichment analysis of significant genes is associated with calcium-activated chloride channel, Staphylococcus aureus infection, and N-linked glycosylation.

CONCLUSION

Genetic predispositions are found to be significantly associated with the high prevalence of pediatric caries, which is a disorder of multigene-environment interaction. The significant functional exonic variants identified can be biomarkers for the early diagnosis of pediatric dental caries in Arabs.

Evaluation of odonto/osteogenic differentiation potential from different regions derived dental tissue stem cells and effect of 17β-estradiol on efficiency

Background

The dentin is a tissue, which is formed by odontoblasts at the pulp interface of the teeth that supports the enamel. Odontoblasts, the cranial neural crest cells are derived from ectodermal mesenchymal stem cells (MSCs) and are long and polarized cells. They are present at the outer surface of dentin and play a prominent role about dentin formation. Recently, attention has been focused on induction of odontoblast using various type of MSCs and effects of the 17ß-estradiol supplementation. In this study, we establish an efficient odonto/osteoblast differentiation protocol using 17ß-estradiol supplementation while comparing the odonto/osteoblast ability of various dental MSCs.

Methods

Same donor derived four types of dental MSCs namely dental pulp stem cells (DPSCs), stem cells from apical papilla (SCAP), dental follicle stem cells (DFSCs), and periodontal ligament stem cells (PDLSCs) were evaluated for their stemness characteristics and potency towards odonto/osteoblast (Induced odonto/osteoblast) differentiation. Then 17ß-estradiol supplementation of 0 and 10 µM was applied to the odonto/osteoblast differentiation media for 14 days respectively. Furthermore, mRNA and protein levels of odonto/osteoblast markers were evaluated.

Results

All of the experimental groups displayed stemness characteristics by showing adipocyte and chondrocyte differentiation abilities, expression for cell surface markers and cell proliferation capacity without any significant differences. Moreover, all dental derived MSCs were shown to have odonto/osteoblast differentiation ability when cultured under specific conditions and also showed positive expression for odontoblast markers at both mRNA and protein level. Among all, DPSCs revealed the higher differentiation potential than other dental MSCs. Furthermore, odonto/osteoblast differentiation potential was enhanced by supplementing the differentiation media with 17ß-estradiol (E2).

Conclusions

Thus, DPSCs possess higher odonto/osteogenic potential than the SCAPs, DFSCs, PDLSCs and their differentiation capacity can by further enhanced under E2 supplementation.

Dimorphism in dental tissues: Sex differences in archaeological individuals for multiple tooth types

OBJECTIVES

Dimorphism in the dentition has been observed in human populations worldwide. However, research has largely focused on traditional linear crown measurements. As imaging systems, such as micro-computed tomography (micro-CT), become increasingly more accessible, new dental measurements such as dental tissue size and proportions can be obtained. This research investigates the variation of dental tissues and proportions by sex in archaeological samples.

MATERIALS AND METHODS

Upper and lower first incisor to second premolar tooth rows were obtained from 30 individuals (n = 300), from 3 archaeological samples. The teeth were micro-CT scanned and surface area and volumetric measurements were obtained from the surface meshes extracted. Dental wear was also recorded and differences between sexes determined.

RESULTS

Enamel and crown measurements were found to be larger in females. Conversely, dentine and root measurements were larger in males.

DISCUSSION

The findings support the potential use of dental tissues to estimate sex of individuals from archaeological samples, while also indicating that individuals aged using current dental aging methods may be underaged or overaged due to sex differences in enamel thickness.

Changes in pulp sensitivity across the menstrual cycle in healthy women and women with temporomandibular disorders

BACKGROUND

Menstrual cycle may contribute to experimental pain measures in healthy women and women with chronic pain.

OBJECTIVES

The present study aimed to investigate variation in pulp sensitivity across the menstrual cycle in healthy women and women with temporomandibular disorders (TMD) and to explore the effect of TMD pain and psychosocial variables on the pulp response.

METHODS

This longitudinal study involved 47 regularly menstruating women aged 20-45, 24 healthy and 23 with diagnosed painful TMD. The electric and cold stimuli were performed by electric pulp tester and refrigerant spray, respectively, on mandibular lateral incisors, in five menstrual phases (menstrual, follicular, periovulatory, luteal and premenstrual). Research Diagnostic Criteria for TMD were used to assess TMD, chronic pain, depression and somatisation. Regression analysis was performed to investigate the effect of the predictor variables on the pulp sensitivity.

RESULTS

Significant phase-related differences were observed for pain intensity to cold stimuli. Higher pain sensitivity was reported in menstrual in comparison with luteal phase (P = .019) among healthy women, and in menstrual in comparison with follicular (P = .033), periovulatory (P = .003) and luteal (P = .007) phases in TMD women. No significant differences were recorded for electric stimuli. Regression analysis identified depression as the determinant of cold and electric response in menstrual phase, regardless of age and presence of TMD.

CONCLUSION

Menstrual phase in healthy and TMD women with regular menstrual cycle is characterised with higher pulp sensitivity to cold stimuli. Depressive symptoms independently influence pulp response in this phase.

Oestrogen receptor β (ERβ) regulates osteogenic differentiation of human dental pulp cells

Estradiol (E₂) has many important actions in the tissues of the oral cavity. Disruption of E₂ metabolism or alterations in systemic E₂ concentrations have been associated with compromised periodontal health. In many instances such changes occur secondarily to the well characterised effects of E₂ on bone physiology -especially maintenance of bone mineral density (BMD). Despite these important epidemiological findings, little is known about the mechanism of action of E₂ in oral tissues or the expression and function of oestrogen receptor (ER) isoforms in these tissues. We have isolated human dental pulp cells (hDPCs), which are able to differentiate towards an osteogenic lineage under appropriate culture conditions. We show that hDPCs express ERα, ERβ1, ERβ2 and the cell membrane associated G protein-coupled ER (GPR30). Following osteogenic differentiation of hDPCs, ERβ1 and ERβ2 were up regulated approximately 50-fold while ERα and GPR30 were down regulated, but to a much lesser degree (approximately 2-fold). ERβ was characterised as a 59kDa protein following Western blot analysis with validated antibodies and ERβ was detected in both nuclear and cytoplasmic cell compartments following immunofluorescence (IF) and immunohistochemical (IHC) analysis of cultured cells. Furthermore isoform specific antibodies detected both ERβ1 and ERβ2 in DPC cultures and in situ analysis of ERβ expression in decalcified tooth/pulp sections identified the odontoblast layer of pulp cells juxtaposed to the tooth enamel as strongly reactive for both ERβ isoforms. Finally the use of isoform specific agonists identified ERβ as the main receptor responsible for the pro-osteogenic effect of oestrogenic hormones in this tissue. Our data suggest that oestrogens stimulated osteogenic differentiation in hDPCs and that this action is mediated principally through the ERβ isoform. These findings may have important consequences for the investigation and treatment of oral and periodontal pathologies which are associated with imbalances in oestrogen concentrations and action.

Expression of Steroid Receptors in Ameloblasts during Amelogenesis in Rat Incisors

Endocrine disrupting chemicals (EDCs) play a part in the modern burst of diseases and interfere with the steroid hormone axis. Bisphenol A (BPA), one of the most active and widely used EDCs, affects ameloblast functions, leading to an enamel hypomineralization pattern similar to that of Molar Incisor Hypomineralization (MIH). In order to explore the molecular pathways stimulated by BPA during amelogenesis, we thoroughly investigated the receptors known to directly or indirectly mediate the effects of BPA. The expression patterns of high affinity BPA receptors (ERRγ, GPR30), of ketosteroid receptors (ERs, AR, PGR, GR, MR), of the retinoid receptor RXRα, and PPARγ were established using RT-qPCR analysis of RNAs extracted from microdissected enamel organ of adult rats. Their expression was dependent on the stage of ameloblast differentiation, except that of ERβ and PPARγ which remained undetectable. An additional large scale microarray analysis revealed three main groups of receptors according to their level of expression in maturation-stage ameloblasts. The expression level of RXRα was the highest, similar to the vitamin D receptor (VDR), whereas the others were 13 to 612-fold lower, with AR and GR being intermediate. Immunofluorescent analysis of VDR, ERα and AR confirmed their presence mainly in maturation- stage ameloblasts. These data provide further evidence that ameloblasts express a specific combination of hormonal receptors depending on their developmental stage. This study represents the first step toward understanding dental endocrinology as well as some of the effects of EDCs on the pathophysiology of amelogenesis.

17β-Estradiol induces odontoblastic differentiation via activation of the c-Src/MAPK pathway in human dental pulp cells

The present study is aimed at investigating the effects of the exogenous estrogen 17β-estradiol (E2) on odontoblastic differentiation in human dental pulp cells (HDPCs) immotalized with hTERT gene and their molecular mechanism. Proliferation was detected by BrdU assay, and odontoblast differentiation induction was evaluated by the expression of dentin sialophosphoprotein (DSPP), dentin sialoprotein (DSP) and dentin matrix protein1 (DMP1), and alkaline phosphatase (ALP) activity and mineralization. Estrogen receptor-α (ER-α), c-Src, and mitogen-activated protein kinases (MAPKs) were examined and their inhibitors were used to determine the roles on odontogenic induction. E2 significantly promoted the HDPC proliferation, which was mediated by extracellular signal-related kinase 1/2. E2 upregulated DSPP, DSP, and DMP1 as the odontogenic differentiation markers and enhanced ALP activity and mineralization. E2 increased phosphorylation of ER-α and fulvestrant, an ER downregulator, significantly downregulated DSPP, DMP1, and DSP induced by E2. Moreover, E2 treatment activated c-Src and MAPKs upon odontogenic induction, whereas chemical inhibition of c-Src and MAPKs decreased expression of DSPP, DMP1, and DSP and mineralization augmented by E2. Moreover, fulvestrant reduced E2-induced phosphorylation of c-Src and MAPK and inhibition of c-Src by PP2 attenuated activation of MAPKs during E2-induced odontoblastic differentiation. Taken together, these results indicated that E2 stimulates odontoblastic differentiation of HDPCs via coordinated regulation of ER-α, c-Src, and MAPK signaling pathways, which may play a key role in the regeneration of dentin.

Estradiol induces osteoprotegerin expression by human dental pulp cells

Estrogen deficiency is associated with increased inflammation related periapical bone resorption. The present study aimed to evaluate the effect and intracellular mechanism(s) of estrogen on osteoprotegerin (OPG) and receptor activator of nuclear factor κB ligand (RANKL) expression in human dental pulp cells (HDPs). HDPs were treated with estradiol at a concentration of 0.1-10 μM. The results showed that estradiol induced OPG expression at both the mRNA and protein levels in a dose-dependent manner. However, no influence on RANKL expression was observed. An estrogen receptor (ER) inhibitor failed to attenuate the estradiol-induced OPG expression. Furthermore, ER-α and ER-β agonists did not simulate estradiol's effects on OPG expression by HDPs. However, a significant OPG upregulation was observed in HDPs treated with an estradiol-BSA conjugate or a GPR30 agonist. An ERK inhibitor significantly enhanced estradiol-induced OPG expression, whereas a p38 inhibitor markedly attenuated this expression. In conclusion, OPG expression by HDPs may be regulated by estradiol binding a membrane receptor and the balance between the ERK and p38 signaling pathways.