Expression of Clu and Tgfb1 during murine tooth development: effects of in-vivo transfection with anti-miR-214

Exploring microRNAs in craniofacial regenerative medicine

microRNAs (miRs) have been reported over the decades as important regulators in bone development and bone regeneration. They play important roles in maintaining the stem cell signature as well as regulating stem cell fate decisions. Thus, delivering miRs and miR inhibitors to the defect site is a potential treatment towards craniofacial bone defects. However, there are challenges in translation of basic research to clinics, including the efficiency, specificity, and efficacy of miR manipulation methods and the safety of miR delivery systems. In this review, we will compare miR oligonucleotides, mimics and antagomirs as therapeutic reagents to treat disease and regenerate tissues. Newer technology will be discussed as well as the efficiency and efficacy of using these technologies to express or inhibit miRs in treating and repairing oral tissues. Delivery of these molecules using extracellular vesicles and nanoparticles can achieve different results and depending on their composition will elicit specific effects. We will highlight the specificity, toxicity, stability, and effectiveness of several miR systems in regenerative medicine.

Exploring craniofacial and dental development with microRNAs

microRNAs (miRs) are small RNA molecules that regulate many cellular and developmental processes. They control gene expression pathways during specific developmental time points and are required for tissue homeostasis and stem cell maintenance. miRs as therapeutic reagents in tissue regeneration and repair hold great promise and new technologies are currently being designed to facilitate their expression or inhibition. Due to the large amount of miR research in cells and cancer many cellular processes and gene networks have been delineated however, their in vivo response can be different in complex tissues and organs. Specifically, this report will discuss animal developmental models to understand the role of miRs as well as xenograft, disease, and injury models. We will discuss the role of miRs in clinical studies including their diagnostic function, as well as their potential ability to correct craniofacial diseases.

Tgfbr2 in Dental Pulp Cells Guides Neurite Outgrowth in Developing Teeth

Transforming growth factor β (TGFβ) plays an important role in tooth morphogenesis and mineralization. During postnatal development, the dental pulp (DP) mesenchyme secretes neurotrophic factors that guide trigeminal nerve fibers into and throughout the DP. This process is tightly linked with dentin formation and mineralization. Our laboratory established a mouse model in which Tgfbr2 was conditionally deleted in DP mesenchyme using an Osterix promoter-driven Cre recombinase (Tgfbr2 ^cko ). These mice survived postnatally with significant defects in bones and teeth, including reduced mineralization and short roots. Hematoxylin and eosin staining revealed reduced axon-like structures in the mutant mice. Reporter imaging demonstrated that Osterix-Cre activity within the tooth was active in the DP and derivatives, but not in neuronal afferents. Immunofluorescence staining for β3 tubulin (neuronal marker) was performed on serial cryosections from control and mutant molars on postnatal days 7 and 24 (P7, P24). Confocal imaging and pixel quantification demonstrated reduced innervation in Tgfbr2 ^cko first molars at both stages compared to controls, indicating that signals necessary to promote neurite outgrowth were disrupted by Tgfbr2 deletion. We performed mRNA-Sequence (RNA-Seq) and gene onotology analyses using RNA from the DP of P7 control and mutant mice to investigate the pathways involved in Tgfbr2-mediated tooth development. These analyses identified downregulation of several mineralization-related and neuronal genes in the Tgfbr2 ^cko DP compared to controls. Select gene expression patterns were confirmed by quantitative real-time PCR and immunofluorescence imaging. Lastly, trigeminal neurons were co-cultured atop Transwell filters overlying primary Tgfbr2 ^f/f DP cells. Tgfbr2 in the DP was deleted via Adenovirus-expressed Cre recombinase. Confocal imaging of axons through the filter pores showed increased axonal sprouting from neurons cultured with Tgfbr2-positive DP cells compared to neurons cultured alone. Axon sprouting was reduced when Tgfbr2 was knocked down in the DP cells. Immunofluorescence of dentin sialophosphoprotein in co-cultured DP cells confirmed reduced mineralization potential in cells with Tgfbr2 deletion. Both our proteomics and RNA-Seq analyses indicate that axonal guidance cues, particularly semaphorin signaling, were disrupted by Tgfbr2 deletion. Thus, Tgfbr2 in the DP mesenchyme appears to regulate differentiation and the cells' ability to guide neurite outgrowth during tooth mineralization and innervation.

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.

Sox21 Regulates Anapc10 Expression and Determines the Fate of Ectodermal Organ

The transcription factor Sox21 is expressed in the epithelium of developing teeth. The present study aimed to determine the role of Sox21 in tooth development. We found that disruption of Sox21 caused severe enamel hypoplasia, regional osteoporosis, and ectopic hair formation in the gingiva in Sox21 knockout incisors. Differentiation markers were lost in ameloblasts, which formed hair follicles expressing hair keratins. Molecular analysis and chromatin immunoprecipitation sequencing indicated that Sox21 regulated Anapc10, which recognizes substrates for ubiquitination-mediated degradation, and determined dental-epithelial versus hair follicle cell fate. Disruption of either Sox21 or Anapc10 induced Smad3 expression, accelerated TGF-β1-induced promotion of epithelial-to-mesenchymal transition (EMT), and resulted in E-cadherin degradation via Skp2. We conclude that Sox21 disruption in the dental epithelium leads to the formation of a unique microenvironment promoting hair formation and that Sox21 controls dental epithelial differentiation and enamel formation by inhibiting EMT via Anapc10.

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Sox21 was induced by Shh in dental epithelial cells

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Sox21 deficiency in dental epithelium caused differentiation into hair cells

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Sox21 deficiency did not cause differentiation into mature ameloblasts

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Anapc10 induced by Sox21 bound to Fzr1 and regulated EMT via Skp2

Mandible exosomal ssc-mir-133b regulates tooth development in miniature swine via endogenous apoptosis

Signal transduction between different organs is crucial in the normal development of the human body. As an important medium for signal communication, exosomes can transfer important information, such as microRNAs (miRNAs), from donors to receptors. MiRNAs are known to fine-tune a variety of biological processes, including maxillofacial development; however, the underlying mechanism remains largely unknown. In the present study, transient apoptosis was found to be due to the expression of a miniature swine maxillofacial-specific miRNA, ssc-mir-133b. Upregulation of ssc-mir-133b resulted in robust apoptosis in primary dental mesenchymal cells in the maxillofacial region. Cell leukemia myeloid 1 (Mcl-1) was verified as the functional target, which triggered further downstream activation of endogenous mitochondria-related apoptotic processes during tooth development. More importantly, mandible exosomes were responsible for the initial apoptosis signal. An animal study demonstrated that ectopic expression of ssc-mir-133b resulted in failed tooth formation after 12 weeks of subcutaneous transplantation in nude mice. The tooth germ developed abnormally without the indispensable exosomal signals from the mandible.

The delivery of the small regulatory molecule microRNA-133b via extracellular vesicles released from the lower jaw is required for tooth formation in pigs and mice. Several microRNAs have been implicated in tooth development, but their precise roles are poorly understood. Songlin Wang at Capital Medical University, China, and colleagues found that microRNA-133b causes temporary cell death at sites of molar development by reducing the levels of the pro-survival protein myeloid cell leukemia-1. Moreover, they showed that microRNA-133b is delivered from the lower jaw in exosomes and that interrupting this signal prevents tooth development. These findings highlight the importance of cross-talk between jaw and tooth tissue for normal development and reveal a possible mechanism for the prevention and treatment of abnormal tooth formation.

Exploring Biological and Geological Age-related Changes through Variations in Intra- and Intertooth Proteomes of Ancient Dentine

Proteomic analyses are becoming more widely used in archeology not only due to the greater preservation of proteins in ancient specimens than DNA but also because they can offer different information, particularly relating to compositional preservation and potentially a means to estimate biological and geological age. However, it remains unclear to what extent different burial environments impact these aspects of proteome decay. Teeth have to date been much less studied than bone but are ideal to explore how proteins decay with time due to the negligible turnover that occurs in dentine relative to bone. We investigated the proteome variability and deamidation levels of different sections of molar teeth from archeological bovine mandibles as well as their mandibular bone. We obtained a greater yield of proteins from the crown of the teeth but did not find differences between the different molars analyzed within each mandible. We also obtained the best variety of protein from a well-preserved mandible that was not the youngest one in terms of chronological age, showing the influence of the preservation conditions on the final proteomic outcome. Intriguingly, we also noticed an increase in abundance levels of fetuin-A in biologically younger mandibles as reported previously, but the opposite trend in tooth dentine. Interestingly, we observed higher glutamine deamidation levels in teeth from the geologically oldest mandible despite it being the biologically youngest specimen, showing that the archeological age strongly impacts on the level of deamidations observed, much more so than biological aging. This indicates that the glutamine deamidation ratio of selected peptides may act as a good predictor of the relative geochronological age of archeological specimens.

Plasticity within the niche ensures the maintenance of a Sox2+ stem cell population in the mouse incisor

In mice, the incisors grow throughout the animal's life, and this continuous renewal is driven by dental epithelial and mesenchymal stem cells. Sox2 is a principal marker of the epithelial stem cells that reside in the mouse incisor stem cell niche, called the labial cervical loop, but relatively little is known about the role of the Sox2⁺ stem cell population. In this study, we show that conditional deletion of Sox2 in the embryonic incisor epithelium leads to growth defects and impairment of ameloblast lineage commitment. Deletion of Sox2 specifically in Sox2⁺ cells during incisor renewal revealed cellular plasticity that leads to the relatively rapid restoration of a Sox2-expressing cell population. Furthermore, we show that Lgr5-expressing cells are a subpopulation of dental Sox2⁺ cells that also arise from Sox2⁺ cells during tooth formation. Finally, we show that the embryonic and adult Sox2⁺ populations are regulated by distinct signalling pathways, which is reflected in their distinct transcriptomic signatures. Together, our findings demonstrate that a Sox2⁺ stem cell population can be regenerated from Sox2^- cells, reinforcing its importance for incisor homeostasis.

Circadian rhythms and gene expression during mouse molar tooth development

OBJECTIVES

Incremental markings in dental enamel suggest that the circadian clock may influence the molecular underpinnings orchestrating enamel formation. The aim of this study was to investigate whether the genes and microRNAs (miRNAs) oscillate in a circadian pattern during tooth and enamel development.

MATERIAL AND METHODS

Comparative gene and miRNA expression profiling of the first mandibular molar tooth germ isolated at different time-points during the light and night period was performed using microarrays and validated using real-time RT-PCR. Bioinformatic analysis was carried out using Ingenuity Pathway Analysis (IPA), and TargetScan software was used in order to identify computationally predicted miRNA-mRNA target relationships.

RESULTS

In total, 439 genes and 32 miRNAs exhibited significantly different (p < 0.05) levels of expression in the light phase compared with the night phase tooth germs. Genes involved in enamel formation, i.e. Amelx, Ambn, Amtn, and Odam, oscillated in a circadian pattern. Furthermore, the circadian clock genes, in particular Clock and Bmal1, oscillated in mouse molar tooth germ during 24-h intervals. The expression of Clock and Bmal1 was inversely correlated with the expression of miR-182 and miR-141, respectively.

CONCLUSIONS

MiRNAs, including miR-182 and miR-141, are involved in the control of peripheral circadian rhythms in the developing tooth by regulating the expression of genes coding for circadian transcription factors such as CLOCK and BMAL1. Regulation of circadian rhythms may be important for enamel phenotype, and the morphology of dental enamel may vary between individuals due to differences in circadian profiles.

Genetic Disorders of Dental Development: Tales from the Bony Crypt

PURPOSE OF REVIEW

The ebb and flow of genetic influence relative to the understanding of craniofacial and dental disorders has evolved into a tacit acceptance of the current genetic paradigm. This review explores the science behind craniofacial and dental disorders through the lens of recent past and current findings and using tooth agenesis as a model of advances in craniofacial genetics.

RECENT FINDINGS

Contemporary studies of craniofacial biology takes advantage of the technological resources stemming from the genomic and post-genomic eras. Emerging data highlights the role of key genes and the epigenetic landscape controlling these genes, in causing dentofacial abnormalities. We also report here a novel Glu78FS MSX1 mutation in one family segregating an autosomal dominant form of severe tooth agenesis as an illustration of an evolving theme, i.e., different mutations in the same gene can result in a spectrum of dentofacial phenotypic severity. The future of clinical therapeutics will benefit from advances in genetics and molecular biology that refine the genotype-phenotype correlation. Indeed, the past century suggests a continued convergence of genetic science in the practice of clinical dentistry.

Identification of differential microRNA expression during tooth morphogenesis in the heterodont dentition of miniature pigs, SusScrofa

Background

It has been found that microRNAs (miRNAs) play important roles in the regulation of tooth development, and most likely increase the complexity of the genetic network, thus lead to greater complexity of teeth. But there has been no research about the key microRNAs associated with tooth morphogenesis based on miRNAs expression profiles. Compared to mice, the pig model has plentiful types of teeth, which is similar with the human dental pattern. Therefore, we used miniature pigs as large-animal models to investigate differentially expressed miRNAs expression during tooth morphogenesis in the early developmental stages of tooth germ.

Results

A custom-designed miRNA microarray with 742 miRNA gene probes was used to analyze the expression profiles of four types of teeth at three stages of tooth development. Of the 591 detectable miRNA transcripts, 212 miRNAs were continuously expressed in all types of tooth germ, but the numbers of miRNA transcript among the four different types of teeth at each embryonic stage were statistically significant differences (p < 0.01). The hierarchical clustering and principal component analysis results suggest that the miRNA expression was globally altered by types and temporal changes. By clustering analysis, we predicted 11 unique miRNA sequences that belong to mir-103 and mir-107, mir-133a and mir-133b, and mir-127 isomiR families. The results of real-time reverse-transcriptase PCR and in situ hybridization experiments revealed that five representative miRNAs may play important roles during different developmental stages of the incisor, canine, biscuspid, and molar, respectively.

Conclusions

The present study indicated that these five miRNAs, including ssc-miR-103 and ssc-miR-107, ssc-miR-133a and ssc-miR-133b, and ssc-miR-127, may play key regulatory roles in different types of teeth during different stages and thus may play critical roles in tooth morphogenesis during early development in miniature pigs.

Electronic supplementary material

The online version of this article (doi:10.1186/s12861-015-0099-0) contains supplementary material, which is available to authorized users.

miRNA-214: Expression, Therapeutic and Diagnostic Potential in Cancer

MicroRNAs (miRNAs) are small noncoding RNAs that negatively regulate gene expression by binding to the 3' untranslated region of their target mRNAs. Recent work supports a role for miRNAs in the initiation and progression of human cancer. miRNA-214 not only mediates differentiation, senescence, angiogenesis, cell migration and virus replication but also acts as a tumor suppressor gene and oncogene. Increasing evidence indicates that miRNA-214 may serve as a biomarker in some cancer types. The aim of this review is to highlight and clarify the complexity of miRNA-214 activity, emphasizing its significant therapeutic and diagnostic potential.

Regulating Craniofacial Development at the 3' End: MicroRNAs and Their Function in Facial Morphogenesis

Defects in craniofacial development represent a majority of observed human birth defects, occurring at a rate as high as 1:800 live births. These defects often occur due to changes in neural crest cell (NCC) patterning and development and can affect non-NCC-derived structures due to interactions between NCCs and the surrounding cell types. Proper craniofacial development requires an intricate array of gene expression networks that are tightly controlled spatiotemporally by a number of regulatory mechanisms. One of these mechanisms involves the action of microRNAs (miRNAs), a class of noncoding RNAs that repress gene expression by binding to miRNA recognition sequences typically located in the 3' UTR of target mRNAs. Recent evidence illustrates that miRNAs are crucial for vertebrate facial morphogenesis, with changes in miRNA expression leading to facial birth defects, including some in complex human syndromes such as 22q11 (DiGeorge Syndrome). In this review, we highlight the current understanding of miRNA biogenesis, the roles of miRNAs in overall craniofacial development, the impact that loss of miRNAs has on normal development and the requirement for miRNAs in the development of specific craniofacial structures, including teeth. From these studies, it is clear that miRNAs are essential for normal facial development and morphogenesis, and a potential key in establishing new paradigms for repair and regeneration of facial defects.

The effect of hypoxia on the formation of mouse incisor enamel

OBJECTIVE

The permanently growing mouse incisors exhibit all stages of tooth development along their inciso-apical axis at any time. Any disturbance or injury of the ameloblasts during enamel formation or maturation may result in permanent defects in the finished enamel since the enamel does not undergo repair or remodeling after formation. In order to increase our understanding of how hypoxia affects enamel formation, we induced severe acute hypoxia in adult mice and observed its effects on the enamel in incisors.

DESIGN

Incisors from hypoxic mice were obtained 5 and 49 days after the hypoxic insult. Hypoxic and control incisors were dissected out and observed by scanning electron microscopy (SEM). Incisors were subsequently ground longitudinally or transversely, etched, and observed again by SEM. The nature and position of defects were considered in relation to the configuration and dynamics of the incisors.

RESULTS

The effect of hypoxia varied considerably, among mice, among incisors, and among ameloblasts. Affected enamel showed hypoplasia with hypomineralization or hypomineralization without hypoplasia. Vascular endothelial growth factor (VEGF) showed considerably stronger labeling in hypoxic compared to control ameloblasts.

CONCLUSIONS

The present study demonstrates quantitative and qualitative defects in the enamel reflecting the vulnerability of ameloblasts toward severe acute hypoxia in mouse incisors.

MicroRNA 665 Regulates Dentinogenesis through MicroRNA-Mediated Silencing and Epigenetic Mechanisms

Studies of proteins involved in microRNA (miRNA) processing, maturation, and silencing have indicated the importance of miRNAs in skeletogenesis, but the specific miRNAs involved in this process are incompletely defined. Here, we identified miRNA 665 (miR-665) as a potential repressor of odontoblast maturation. Studies with cultured cell lines and primary embryonic cells showed that miR-665 represses the expression of early and late odontoblast marker genes and stage-specific proteases involved in dentin maturation. Notably, miR-665 directly targeted Dlx3 mRNA and decreased Dlx3 expression. Furthermore, RNA-induced silencing complex (RISC) immunoprecipitation and biotin-labeled miR-665 pulldown studies identified Kat6a as another potential target of miR-665. KAT6A interacted physically and functionally with RUNX2, activating tissue-specific promoter activity and prompting odontoblast differentiation. Overexpression of miR-665 reduced the recruitment of KAT6A to Dspp and Dmp1 promoters and prevented KAT6A-induced chromatin remodeling, repressing gene transcription. Taken together, our results provide novel molecular evidence that miR-665 functions in an miRNA-epigenetic regulatory network to control dentinogenesis.

MicroRNA 224 Regulates Ion Transporter Expression in Ameloblasts To Coordinate Enamel Mineralization

Enamel mineralization is accompanied by the release of protons into the extracellular matrix, which is buffered to regulate the pH value in the local microenvironment. The present study aimed to investigate the role of microRNA 224 (miR-224) as a regulator of SLC4A4 and CFTR, encoding the key buffering ion transporters, in modulating enamel mineralization. miR-224 was significantly downregulated as ameloblasts differentiated, in parallel with upregulation of SLC4A4 and CFTR. Overexpression of miR-224 downregulated SLC4A4 and CFTR expression in cultured human epithelial cells. A microRNA luciferase assay confirmed the specific binding of miR-224 to the 3' untranslated regions (UTRs) of SLC4A4 and CFTR mRNAs, thereby inhibiting protein translation. miR-224 agomir injection in mouse neonatal incisors resulted in normal enamel length and thickness, but with disturbed organization of the prism structure and deficient crystal growth. Moreover, the enamel Ca/P ratio and microhardness were markedly reduced after miR-224 agomir administration. These results demonstrate that miR-224 plays a pivotal role in fine tuning enamel mineralization by modulating SLC4A4 and CFTR to maintain pH homeostasis and support enamel mineralization.

Mutations in the latent TGF-beta binding protein 3 (LTBP3) gene cause brachyolmia with amelogenesis imperfecta

Inherited dental malformations constitute a clinically and genetically heterogeneous group of disorders. Here, we report on four families, three of them consanguineous, with an identical phenotype, characterized by significant short stature with brachyolmia and hypoplastic amelogenesis imperfecta (AI) with almost absent enamel. This phenotype was first described in 1996 by Verloes et al. as an autosomal recessive form of brachyolmia associated with AI. Whole-exome sequencing resulted in the identification of recessive hypomorphic mutations including deletion, nonsense and splice mutations, in the LTBP3 gene, which is involved in the TGF-beta signaling pathway. We further investigated gene expression during mouse development and tooth formation. Differentiated ameloblasts synthesizing enamel matrix proteins and odontoblasts expressed the gene. Study of an available knockout mouse model showed that the mutant mice displayed very thin to absent enamel in both incisors and molars, hereby recapitulating the AI phenotype in the human disorder.

Root-like enamel pearl: a case report

Introduction

In general, enamel pearls are found in maxillary molars as a small globule of enamel. However, this case report describes an enamel pearl with a prolate spheroid shape which is 1.8mm wide and 8mm long. The different type of enamel pearl found in my clinic has significantly improved our understanding of enamel pearl etiology and pathophysiology.

Case presentation

A 42-year-old Han Chinese woman with severe toothache received treatment in my Department of Endodontics. She had no significant past medical history. A dental examination revealed extensive distal decay in her left mandibular first molar, tenderness to percussion and palpation of the periradicular zone, and found a deep periodontal pocket on the buccal lateral. Vitality testing was negative. Periapical radiographic images revealed radiolucency around the mesial apex. Cone beam computed tomography detected an opaque enamel pearl in the furcation area with a prolate spheroid shape of 1.8mm wide and 8mm long.

Conclusion

The enamel pearl described in this case report is like a very long dental root. Cone beam computed tomography may be used for evaluating enamel pearls.

The physiological roles of apolipoprotein J/clusterin in metabolic and cardiovascular diseases

Several isoforms of apolipoprotein J/clusterin (CLU) are encoded from a single gene located on chromosome 8 in humans. These isoforms are ubiquitously expressed in the tissues, and have been implicated in aging, neurodegenerative disorders, cancer progression, and metabolic/cardiovascular diseases including dyslipidemia, diabetes, atherosclerosis and myocardial infarction. The conventional secreted form of CLU (sCLU) is thought to be a component of high density lipoprotein-cholesterol. sCLU functions as a chaperone for misfolded proteins and it is thought to promote survival by reducing oxidative stress. Nuclear CLU, a truncated CLU formed by alternative splicing, is responsible for promoting apoptosis via a Bax-dependent pathway. There are putative regulatory sites in the promoter regions of CLU, which are occupied by transcription factors such as transforming growth factor (TGF)-β inhibitory element, activator protein-1, CLU-specific elements, and carbohydrate response element. However, the molecular mechanisms underlying the distinct roles of CLU in a variety of conditions remain unclear. Although the function of CLU in cancer or neurological disease has been studied intensively for three decades, physiological roles of CLU seem unexplored in the cardiovascular system and metabolic diseases. In this review, we will discuss general characteristics and regulations of CLU based on previous literature and assess the recent findings associated with its physiological roles in different tissues including the vasculature, heart, liver, kidney, adipose tissue, and brain.