The overview of channels, transporters, and calcium signaling molecules during amelogenesis

Microspatial distribution of trace elements in feline dental hard tissues: early life exposure to essential and toxic elements

Introduction

Trace elements play a key role in dental tissue development, as dental hard tissues accumulate both essential and toxic trace elements during mineralization. Characterization of the spatial accumulation pattern of trace elements may provide insight into exposure to toxic elements over time and to the nature of disease processes affecting the hard dental tissues. Here, we present the first report of the use of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to map the microspatial distribution of multiple trace elements, essential and toxic, across feline dental hard tissues.

Methods

Eleven teeth were extracted from 8 cats. Nine teeth were from 7 cats diagnosed with idiopathic tooth resorption on intraoral radiographs prior to extraction. Two teeth were included from a cadaver that had no signs of tooth resorption on intraoral radiographs. The normal dental tissue was analyzed from each sample using LA-ICP-MS to map the microspatial distribution of essential and toxic trace elements across feline enamel, dentin, and cementum.

Results

Results showed a higher accumulation of barium and strontium in coronal dentin as compared to root dentin. The timing of the accumulation mirrors nursing timelines seen in teeth from human and non-human primates, consistent with barium and strontium being sourced from maternal milk. Results also showed a higher uptake of lead in the coronal dentin, suggesting this lead exposure was likely passed from mother to offspring.

Discussion

This work characterizes a baseline for elemental distribution in feline teeth linked to early life exposure to toxic elements such as lead and provides a framework for future studies investigating long-term environmental exposures to trace elements, essential and toxic, and their involvement in feline systemic and dental diseases.

Conditional knockout of transient receptor potential melastatin 7 in the enamel epithelium: Effects on enamel formation

Transient receptor potential melastatin 7 (TRPM7) is a unique ion channel connected to a kinase domain. We previously demonstrated that Trpm7 expression is high in mouse ameloblasts and odontoblasts, and that amelogenesis is impaired in TRPM7 kinase-dead mice. Here, we analyzed TRPM7 function during amelogenesis in Keratin 14-Cre;Trpm7^fl/fl conditional knockout (cKO) mice and Trpm7 knockdown cell lines. cKO mice showed lesser tooth pigmentation than control mice and broken incisor tips. Enamel calcification and microhardness were lower in cKO mice. Electron probe microanalysis (EPMA) showed that the calcium and phosphorus contents in the enamel were lower in cKO mouse than in control mice. The ameloblast layer in cKO mice showed ameloblast dysplasia at the maturation stage. The morphological defects were observed in rat SF2 cells with Trpm7 knockdown. Compared with mock transfectants, the Trpm7 knockdown cell lines showed lower levels of calcification with Alizarin Red-positive staining and an impaired intercellular adhesion structures. These findings suggest that TRPM7 is a critical ion channel in enamel calcification for the effective morphogenesis of ameloblasts during amelogenesis.

Equine odontoclastic tooth resorption and hypercementosis (EOTRH): microspatial distribution of trace elements in hypercementosis-affected and unaffected hard dental tissues

Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH) is a common, painful and poorly understood disease. Enamel, dentin and cementum accumulate both essential and toxic trace elements during mineralization. Characterization of the spatial accumulation pattern of trace elements may provide insight into the role that toxic elements play and inform biological processes affecting these hard dental tissues for future research. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to map the distribution of multiple trace elements and heavy metals across equine healthy and diseased (hypercementosis-affected) hard dental tissues among four teeth extracted from horses with EOTRH. Results showed banding patterns of some trace elements (lead, strontium, barium), reflecting the temporal component of accumulation of trace elements during dentin mineralization. Essential elements zinc and magnesium did not show banding patterns. Comparison to the unaffected cementum and dentin adjacent to the hypercementosis region showed that there is an underlying incremental pattern in the uptake of some metals with spatial irregularities. This supports a possible metabolic change involved in hypercementosis lesion development. This represents the first use of LA-ICP-MS to study the microspatial distribution of trace elements in equine teeth, establishing a baseline for elemental distribution in normal and EOTRH impacted dental hard tissue.

Crucial Role of microRNAs as New Targets for Amelogenesis Disorders Detection

INTRODUCTION

Amelogenesis imperfecta (AI) refers to a heterogeneous group of conditions with multiple factors which contribute to the hypomineralisation of enamel. Preventive measures are necessary to predict this pathology. Prospects for preventive medicine are closely related to the search for new informative methods for diagnosing a human disease. MicroRNAs are prominent for the non-invasive diagnostic platform.

THE AIM OF THE STUDY

The aim of the review is to review the heterogeneous factors involved in amelogenesis and to select the microRNA panel associated with the AI type.

METHODS

We used DIANA Tools (algorithms, databases and software) for interpreting and archiving data in a systematic framework ranging from the analysis of expression regulation from deep sequencing data to the annotation of miRNA regulatory elements and targets (https://dianalab. e-ce.uth.gr/). In our study, based on a gene panel associated with the AI types, twenty-four miRNAs were identified for the hypoplastic type (supplement), thirty-five for hypocalcified and forty-- nine for hypomaturation AI. The selection strategy included the microRNA search with multiple targets using the AI type's gene panel.

RESULTS

Key proteins, calcium-dependent and genetic factors were analysed to reveal their role in amelogenesis. The role of extracellular non-coding RNA sequences with multiple regulatory functions seems to be the most attractive. We chose the list of microRNAs associated with the AI genes. We found four microRNAs (hsa-miR-27a-3p, hsa-miR-375, hsa-miR-16-5p and hsamiR- 146a-5p) for the gene panel, associated with the hypoplastic type of AI; five microRNAs (hsa- miR-29c-3p, hsa-miR-124-3p, hsa-miR-1343-3p, hsa-miR-335-5p, and hsa-miR-16-5p - for hypocalcified type of AI, and seven ones (hsa-miR-124-3p, hsa-miR-147a, hsa-miR-16-5p, hsamiR- 429, hsa-let-7b-5p, hsa-miR-146a-5p, hsa-miR-335-5p) - for hypomaturation. It was revealed that hsa-miR-16-5p is included in three panels specific for both hypoplastic, hypocalcified, and hypomaturation types. Hsa-miR-146a-5p is associated with hypoplastic and hypomaturation type of AI, which is associated with the peculiarities of the inflammatory response immune response. In turn, hsa-miR-335-5p associated with hypocalcified and hypomaturation type of AI.

CONCLUSION

Liquid biopsy approaches are a promising way to reduce the economic cost of treatment for these patients in modern healthcare. Unique data exist about the role of microRNA in regulating amelogenesis. The list of microRNAs that are associated with AI genes and classified by AI types has been uncovered. The target gene analysis showed the variety of functions of selected microRNAs, which explains the multiple heterogeneous mechanisms in amelogenesis. Predisposition to mineralisation problems is a programmed event. Many factors determine the manifestation of this problem. Additionally, it is necessary to remember the variable nature of the changes, which reduces the prediction accuracy. Therefore, models based on liquid biopsy and microRNAs make it possible to take into account these factors and their influence on the mineralisation. The found data needs further investigation.

Ift88 regulates enamel formation via involving Shh signaling

OBJECTIVES

The ciliopathies are a wide spectrum of human diseases, which are caused by perturbations in the function of primary cilia. Tooth enamel anomalies are often seen in ciliopathy patients; however, the role of primary cilia in enamel formation remains unclear.

MATERIALS AND METHODS

We examined mice with epithelial conditional deletion of the ciliary protein, Ift88, (Ift88^fl/fl ;K14Cre).

RESULTS

Ift88^fl/fl ;K14Cre mice showed premature abrasion in molars. A pattern of enamel rods which is determined at secretory stage, was disorganized in Ift88 mutant molars. Many amelogenesis-related molecules expressing at the secretory stage, including amelogenin and ameloblastin, enamelin, showed significant downregulation in Ift88 mutant molar tooth germs. Shh signaling is essential for amelogenesis, which was found to be downregulated in Ift88 mutant molar at the secretory stage. Application of Shh signaling agonist at the secretory stage partially rescued enamel anomalies in Ift88 mutant mice.

CONCLUSION

Findings in the present study indicate that the function of the primary cilia via Ift88 is critical for the secretory stage of amelogenesis through involving Shh signaling.

Manifestation and Mechanisms of Abnormal Mineralization in Teeth

Tooth biomineralization is a dynamic and complicated process influenced by local and systemic factors. Abnormal mineralization in teeth occurs when factors related to physiologic mineralization are altered during tooth formation and after tooth maturation, resulting in microscopic and macroscopic manifestations. The present Review provides timely information on the mechanisms and structural alterations of different forms of pathological tooth mineralization. A comprehensive study of these alterations benefits diagnosis and biomimetic treatment of abnormal mineralization in patients.

TRPM7-Mediated Calcium Transport in HAT-7 Ameloblasts

TRPM7 plays an important role in cellular Ca²⁺, Zn²⁺ and Mg²⁺ homeostasis. TRPM7 channels are abundantly expressed in ameloblasts and, in the absence of TRPM7, dental enamel is hypomineralized. The potential role of TRPM7 channels in Ca²⁺ transport during amelogenesis was investigated in the HAT-7 rat ameloblast cell line. The cells showed strong TRPM7 mRNA and protein expression. Characteristic TRPM7 transmembrane currents were observed, which increased in the absence of intracellular Mg²⁺ ([Mg²⁺]_i), were reduced by elevated [Mg²⁺]_i, and were inhibited by the TRPM7 inhibitors NS8593 and FTY720. Mibefradil evoked similar currents, which were suppressed by elevated [Mg²⁺]_i, reducing extracellular pH stimulated transmembrane currents, which were inhibited by FTY720. Naltriben and mibefradil both evoked Ca²⁺ influx, which was further enhanced by the acidic intracellular conditions. The SOCE inhibitor BTP2 blocked Ca²⁺ entry induced by naltriben but not by mibefradil. Thus, in HAT-7 cells, TRPM7 may serves both as a potential modulator of Orai-dependent Ca²⁺ uptake and as an independent Ca²⁺ entry pathway sensitive to pH. Therefore, TRPM7 may contribute directly to transepithelial Ca²⁺ transport in amelogenesis.

Overexpression of miR-1306-5p, miR-3195, and miR-3914 Inhibits Ameloblast Differentiation through Suppression of Genes Associated with Human Amelogenesis Imperfecta

Amelogenesis imperfecta is a congenital form of enamel hypoplasia. Although a number of genetic mutations have been reported in humans, the regulatory network of these genes remains mostly unclear. To identify signatures of biological pathways in amelogenesis imperfecta, we conducted bioinformatic analyses on genes associated with the condition in humans. Through an extensive search of the main biomedical databases, we found 56 genes in which mutations and/or association/linkage were reported in individuals with amelogenesis imperfecta. These candidate genes were further grouped by function, pathway, protein-protein interaction, and tissue-specific expression patterns using various bioinformatic tools. The bioinformatic analyses highlighted a group of genes essential for extracellular matrix formation. Furthermore, advanced bioinformatic analyses for microRNAs (miRNAs), which are short non-coding RNAs that suppress target genes at the post-transcriptional level, predicted 37 candidates that may be involved in amelogenesis imperfecta. To validate the miRNA-gene regulation association, we analyzed the target gene expression of the top seven candidate miRNAs: miR-3195, miR-382-5p, miR-1306-5p, miR-4683, miR-6716-3p, miR-3914, and miR-3935. Among them, miR-1306-5p, miR-3195, and miR-3914 were confirmed to regulate ameloblast differentiation through the regulation of genes associated with amelogenesis imperfecta in AM-1 cells, a human ameloblastoma cell line. Taken together, our study suggests a potential role for miRNAs in amelogenesis imperfecta.