Developmental changes and regional localization of Dspp, Mepe, Mimecan and Versican in postnatal developing mouse teeth

The significant role of glycosaminoglycans in tooth development

This review delves into the roles of glycosaminoglycans (GAGs), integral components of proteoglycans, in tooth development. Proteoglycans consist of a core protein linked to GAG chains, comprised of repeating disaccharide units. GAGs are classified into several types, such as hyaluronic acid, heparan sulfate, chondroitin sulfate, dermatan sulfate, and keratan sulfate. Functioning as critical macromolecular components within the dental basement membrane, these GAGs facilitate cell adhesion and aggregation, and play key roles in regulating cell proliferation and differentiation, thereby significantly influencing tooth morphogenesis. Notably, our recent research has identified the hyaluronan-degrading enzyme Transmembrane protein 2 (Tmem2) and we have conducted functional analyses using mouse models. These studies have unveiled the essential role of Tmem2-mediated hyaluronan degradation and its involvement in hyaluronan-mediated cell adhesion during tooth formation. This review provides a comprehensive summary of the current understanding of GAG functions in tooth development, integrating insights from recent research, and discusses future directions in this field.

Apical Papilla Regulates Dental Follicle Fate via the OGN-Hh Pathway

Root apical complex, including Hertwig's epithelial root sheath, apical papilla, and dental follicle (DF), is the germinal center of root development, wherein the DF constantly develops into periodontal tissue. However, whether DF development is regulated by the adjacent apical papilla remains largely unknown. In this study, we employed a transwell coculture system and found that stem cells from the apical papilla (SCAPs) inhibit the differentiation and maintain the stemness of dental follicle stem cells (DFSCs). Meanwhile, partial SCAP differentiation markers were upregulated after DFSC coculture. High-throughput RNA sequencing revealed that the Hedgehog (Hh) pathway was significantly downregulated in DFSCs cocultured with SCAPs. Upregulation or downregulation of the Hh pathway can respectively activate or inhibit the multidirectional differentiation of DFSCs. Osteoglycin (OGN) (previously known as mimecan) is highly expressed in the dental papilla, similarly to Hh pathway factors. By secreting OGN, SCAP regulated the stemness and multidirectional differentiation of DFSCs via the OGN-Hh pathway. Finally, Ogn^-/- mice were established using the CRISPR/Cas9 system. We found that the root length growth rate was accelerated during root development from PN0 to PN30 in Ogn^-/- mice. Moreover, the hard tissues (including dentin and cementum) of the root in Ogn^-/- mice were thicker than those in wild-type mice. These phenotypes were likely due to Hh pathway activation and the increased cell proliferation and differentiation in both the apical papilla and DF. The current work elucidates the molecular regulation of early periodontal tissue development, providing a theoretical basis for future research on tooth root biology and periodontal tissue regeneration.

Characterization of SIBLING Proteins in the Mineralized Tissues

The SIBLING proteins are a family of non-collagenous proteins (NCPs) previously thought to be expressed only in dentin but have been demonstrated in other mineralized and non-mineralized tissues. They are believed to play vital roles in both osteogenesis and dentinogenesis. Since they are tightly regulated lifelong processes and involve a peak of mineralization, three different age groups were investigated. Fifteen wild-type (WT) mice were euthanized at ages 1, 3, and 6 months. Hematoxylin and eosin staining (H&E) was performed to localize various microscopic structures in the mice mandibles and tibias. The immunostaining pattern was compared using antibodies for dentin sialoprotein (DSP), dentin matrix protein 1 (DMP1), bone sialoprotein (BSP), and osteopontin (OPN). Immunostaining of DSP in tibia showed its most noticeable staining in the 3-month age group. DSP was expressed in alveolar bone, cellular cementum, and PDL. A similar expression of DMP1 was seen in the tibia and dentin. BSP was most noticeably detected in the tibia and acellular cementum. OPN was mainly expressed in the bone. A lower level of OPN was observed at all age groups in the teeth. The immunostaining intensity was the least detected for all proteins in the 6-month tibia sample. The expression patterns of the four SIBLING proteins showed variations in their staining intensity and temporospatial patterning concordant with skeletal and dental maturity. These findings suggest some role in this tightly regulated mineralization process.

BMP Signaling Pathway in Dentin Development and Diseases

BMP signaling plays an important role in dentin development. BMPs and antagonists regulate odontoblast differentiation and downstream gene expression via canonical Smad and non-canonical Smad signaling pathways. The interaction of BMPs with their receptors leads to the formation of complexes and the transduction of signals to the canonical Smad signaling pathway (for example, BMP ligands, receptors, and Smads) and the non-canonical Smad signaling pathway (for example, MAPKs, p38, Erk, JNK, and PI3K/Akt) to regulate dental mesenchymal stem cell/progenitor proliferation and differentiation during dentin development and homeostasis. Both the canonical Smad and non-canonical Smad signaling pathways converge at transcription factors, such as Dlx3, Osx, Runx2, and others, to promote the differentiation of dental pulp mesenchymal cells into odontoblasts and downregulated gene expressions, such as those of DSPP and DMP1. Dysregulated BMP signaling causes a number of tooth disorders in humans. Mutation or knockout of BMP signaling-associated genes in mice results in dentin defects which enable a better understanding of the BMP signaling networks underlying odontoblast differentiation and dentin formation. This review summarizes the recent advances in our understanding of BMP signaling in odontoblast differentiation and dentin formation. It includes discussion of the expression of BMPs, their receptors, and the implicated downstream genes during dentinogenesis. In addition, the structures of BMPs, BMP receptors, antagonists, and dysregulation of BMP signaling pathways associated with dentin defects are described.

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.

Follicle-stimulating hormone impairs dental pulp stem cells odontogenic differentiation

In addition to bone, the dentin‐pulp complex is also influenced by menopause, showing a decreased regenerative capacity. High levels of follicle‐stimulating hormone (FSH) during menopause could directly regulate bone metabolism. Here, the role of FSH in the odontogenic differentiation of the dentin‐pulp complex was investigated. Dental pulp stem cells (DPSCs) were isolated. CCK‐8 assays, cell apoptosis assays, Western blotting (WB), real‐time RT‐PCR, alkaline phosphatase activity assays, and Alizarin Red S staining were used to clarify the effects of FSH on the proliferation, apoptosis and odontogenic differentiation of the DPSCs. MAPK pathway‐related factors were explored by WB assays. FSH and its inhibitor were used in OVX rats combined with a direct pulp‐capping model. HE and immunohistochemistry were used to detect reparative dentin formation and related features. The results indicated that FSH significantly decreased the odontogenic differentiation of the DPSCs without affecting cell proliferation and apoptosis. Moreover, FSH significantly activated the JNK signalling pathway, and JNK inhibitor partly rescued the inhibitory effect of FSH on DPSC differentiation. In vivo, FSH treatment attenuated the dentin bridge formation and mineralization‐related protein expression in the OVX rats. Our findings indicated that FSH reduced the odontogenic capacity of the DPSCs and was involved in reparative dentinogenesis during menopause.

The extracellular matrix proteoglycan versican is strongly expressed in the urothelium of healthy rats

Objective: We have previously demonstrated protein expression of the extracellular matrix degrading protein ADAMTS5 in the nuclei of urothelial cells in healthy rats. The proteoglycan versican constitutes one of the main substrates for this protease. In this follow up study we investigated a potential co-localization of versican and ADAMTS5 in the urinary bladder wall.Material and Methods: The study was conducted with archive material (paraffin embedded bladder tissue from our previous study, i.e., 8 male Sprague-Dawley rats). Protein expression of versican was investigated by immunohistochemistry. Furthermore, the occurrence of versican mRNA was examined by in-situ hybridization.Results: Positive immunoreactivity for versican was evident in the urothelium but also, weakly, in the detrusor. This expression was localized only in the cytoplasm, leaving the nuclei devoid of reactivity. Interestingly, versican mRNA was only sparsely observed in the urothelial cells.Conclusions: We found by immunohistochemistry that the substrate for ADAMTS5, versican, was localized in the cytosol of urothelial cells. This demonstrates a difference regarding the expression of ADAMTS5, which was emphasized in the nuclei. This could imply an additional, non-enzymatic, function of ADAMTS5 in the urothelium.

Homozygous Recessive Versican Missense Variation Is Associated With Early Teeth Loss in a Pakistani Family

Only a few genes involved in teeth development and morphology are known to be responsible for tooth abnormalities in Mendelian-inherited diseases. We studied an inbred family of Pakistani origin in which two first-cousin born brothers are affected by early tooth loss with peculiar teeth abnormalities characterized by the absence of cementum formation. Whole exome sequencing revealed a H2665L homozygous sequence variant in the VCAN gene. Dominant splicing mutations in VCAN are known to cause Wagner syndrome or vitreoretinopathy. We explored teeth morphology in these two patients, while versican expression was assessed by western blot analysis. Early signs of vitreoretinopathy were found in the elder brother while the parents were completely negative. Our findings suggest that the homozygous recessive H2665L missense sequence variant impairs the normal morphology of the teeth roots via loss of cementum synthesis, and is also associated with early onset, recessive, Wagner syndrome, thus expanding both the phenotype mutation scenario and the inheritance mode of VCAN mutations.

Expression and localization of Yap and Taz during development of the mandibular first molar in rats

Yes-associated protein (Yap) and transcriptional coactivator with PDZ-binding motif (Taz) are two downstream factors in the Hippo signaling pathway. Yap and Taz participate in regulating organ size, stem cell self-renewal, proliferation and differentiation. We investigated the spatial-temporal expression and relative expression levels of Yap and Taz using immunohistochemistry and real-time polymerase chain reaction. We found Yap and Taz in the oral epithelium and mesenchyme at embryonic (E) day 14.5 (E14.5) and E16.5. By E18.5, Yap and Taz were detected in the dental papilla and the entire enamel organ. At postnatal (P) day 0 (PN0), PN3 and PN7, Yap and Taz expression was localized in ameloblasts, odontoblasts and stratum intermedium. Yap and Taz were expressed in Hertwig's epithelial root sheath (HERS) at PN7. At PN3, PN7 and PN14, Yap was detected in the enamel matrix. From PN21 to PN28, Yap and Taz were absent from differentiated ameloblasts, but they were expressed in odontoblasts. From PN0 to PN10, the Yap and Taz mRNA expression increased, then decreased. We found that Yap and Taz may influence the differentiation of ameloblasts and odontoblasts; they also may contribute to enamel mineralization, crown morphogenesis and root formation.

The diverse functions of osteoglycin: a deceitful dwarf, or a master regulator of disease?

Small leucine-rich proteoglycans are emerging as important regulatory proteins within the extracellular matrix, where they exert both structural and nonstructural functions and hence are modulators of numerous biological processes, such as inflammation, fibrosis, and cell proliferation. One proteoglycan in particular, osteoglycin (OGN), also known as mimecan, shows great structural and functional diversity in normal physiology and in disease states, therefore making it a very interesting candidate for the development of novel therapeutic strategies. Unfortunately, the literature on OGN is confusing, as it has different names, and different transcript and protein variants have been identified. This review will give a clear overview of the different structures and functions of OGN that have been identified to date, portray its central role in pathophysiology, and highlight the importance of posttranslational processing, such as glycosylation, for the diversity of its functions.-Deckx, S., Heymans, S., Papageorgiou, A.-P. The diverse functions of osteoglycin: a deceitful dwarf, or a master regulator of disease?

MEPE Localization in the Craniofacial Complex and Function in Tooth Dentin Formation

Matrix extracellular phosphoglycoprotein (MEPE) is an extracellular matrix protein found in dental and skeletal tissues. Although information regarding the role of MEPE in bone and disorders of phosphate metabolism is emerging, the role of MEPE in dental tissues remains unclear. We performed RNA in situ hybridization and immunohistochemistry analyses to delineate the expression pattern of MEPE during embryonic and postnatal development in craniofacial mineralizing tissues. Mepe RNA expression was seen within teeth from cap through root formation in association with odontoblasts and cellular cementoblasts. More intense expression was seen in the alveolar bone within the osteoblasts and osteocytes. MEPE immunohistochemistry showed biphasic dentin staining in incisors and more intense staining in alveolar bone matrix and in forming cartilage. Analysis of Mepe null mouse molars showed overall mineralized tooth volume and density of enamel and dentin comparable with that of wild-type samples. However, Mepe(-/-) molars exhibited increased thickness of predentin, dentin, and enamel over controls and decreased gene expression of Enam, Bsp, Dmp1, Dspp, and Opnby RT-PCR. In vitro Mepe overexpression in odontoblasts led to significant reductions in Dspp reporter activity. These data suggest MEPE may be instrumental in craniofacial and dental matrix maturation, potentially functioning in the maintenance of non-mineralized matrix.

Expression of cytokeratin 8, vimentin, syndecan-1 and Ki-67 during human tooth development

Spatio-temporal immunolocalizations of cytokeratin 8 (CK8), vimentin, syndecan-1 and Ki-67 were analyzed in ten human incisors and canine tooth germs between the 7th and 20th developmental weeks. CK8 expression was mild to moderate in the epithelial tooth parts, while it shifted from absent or mild in its mesenchymal parts, but few cells, sparsely distributed throughout the tooth germ, strongly expressed CK8. As development progressed, CK8 expression increased to strong in preameloblasts, while expression of vimentin increased to moderate in the epithelial and mesenchymal tooth parts, particularly in the dental papilla and sac. Co-expression of CK8 and vimentin was observed in some parts of the tooth germ, and was increasing in the differentiating preameloblasts and preodontoblasts. Syndecan-1 showed characteristic shift of expression from epithelial to mesenchymal tooth parts, being particularly strong in dental papilla, sac and cervical loops, while co-expression of Ki-67/syndecan-1 was strong in the dental papilla. Our study demonstrated spatio-temporal expression and restricted co-expression of the investigated markers, indicating participation of CK8 and vimentin in cell proliferation and migration, and differentiation of preodontoblasts and preameloblasts. Our data also suggest involvement of syndecan-1 in morphogenesis of the developing tooth crown and cervical loops, and together with CK8 and vimentin in differentiation of preameloblasts and preodontoblasts.

An immunohistochemical study of matrix proteins in the craniofacial cartilage in midterm human fetuses

Immunohistochemical localization of collagen types I, II, and X, aggrecan, versican, dentin matrix protein (DMP)-1, martix extracellular phosphoprotein (MEPE) were performed for Meckel's cartilage, cranial base cartilage, and mandibular condylar cartilage in human midterm fetuses; staining patterns within the condylar cartilage were compared to those within other cartilaginous structures. Mandibular condylar cartilage contained aggrecan; it also had more type I collagen and a thicker hypertrophic cell layer than the other two types of cartilage; these three characteristics are similar to those of the secondary cartilage of rodents. MEPE immunoreactivity was first evident in the cartilage matrix of all types of cartilage in the human fetuses and in Meckel's cartilage of mice and rats. MEPE immunoreactivity was enhanced in the deep layer of the hypertrophic cell layer and in the cartilaginous core of the bone trabeculae in the primary spongiosa. These results indicated that MEPE is a component of cartilage matrix and may be involved in cartilage mineralization. DMP-1 immunoreactivity first became evident in human bone lacunae walls and canaliculi; this pattern of expression was comparable to the pattern seen in rodents. In addition, chondroid bone was evident in the mandibular (glenoid) fossa of the temporal bone, and it had aggrecan, collagen types I and X, MEPE, and DMP-1 immunoreactivity; these findings indicated that chondroid bone in this region has phenotypic expression indicative of both hypertrophic chondrocytes and osteocytes.