Functional role of Rho-kinase in ameloblast differentiation

Ameloblastin and its multifunctionality in amelogenesis: A review

Extracellular matrix proteins play crucial roles in the formation of mineralized tissues like bone and teeth via multifunctional mechanisms. In tooth enamel, ameloblastin (Ambn) is one such multifunctional extracellular matrix protein implicated in cell signaling and polarity, cell adhesion to the developing enamel matrix, and stabilization of prismatic enamel morphology. To provide a perspective for Ambn structure and function, we begin this review by describing dental enamel and enamel formation (amelogenesis) followed by a description of enamel extracellular matrix. We then summarize the established domains and motifs in Ambn protein, human amelogenesis imperfecta cases, and genetically engineered mouse models involving mutated or null Ambn. We subsequently delineate in silico, in vitro, and in vivo evidence for the amphipathic helix in Ambn as a proposed cell-matrix adhesive and then more recent in vitro evidence for the multitargeting domain as the basis for dynamic interactions of Ambn with itself, amelogenin, and membranes. The multitargeting domain facilitates tuning between Ambn-membrane interactions and self/co-assembly and supports a likely overall role for Ambn as a matricellular protein. We anticipate that this review will enhance the understanding of multifunctional matrix proteins by consolidating diverse mechanisms through which Ambn contributes to enamel extracellular matrix mineralization.

Critical roles of adherens junctions in diseases of the oral mucosa

The oral cavity is directly exposed to a variety of environmental stimuli and contains a diverse microbiome that continuously interacts with the oral epithelium. Therefore, establishment and maintenance of the barrier function of the oral mucosa is of paramount importance for its function and for the body's overall health. The adherens junction is a cell-cell adhesion complex that is essential for epithelial barrier function. Although a considerable body of work has associated barrier disruption with oral diseases, the molecular underpinnings of these associations have not been equally investigated. This is critical, since adherens junction components also possess significant signaling roles in the cell, in addition to their architectural ones. Here, we summarize current knowledge involving adherens junction components in oral pathologies, such as cancer and oral pathogen-related diseases, while we also discuss gaps in the knowledge and opportunities for future investigation of the relationship between adherens junctions and oral diseases.

The effects of 4-Phenylbutyric acid on ER stress during mouse tooth development

Introduction: During tooth development, proper protein folding and trafficking are significant processes as newly synthesized proteins proceed to form designated tissues. Endoplasmic reticulum (ER) stress occurs inevitably in tooth development as unfolded and misfolded proteins accumulate in ER. 4-Phenylbutyric acid (4PBA) is a FDA approved drug and known as a chemical chaperone which alleviates the ER stress. Recently, several studies showed that 4PBA performs therapeutic effects in some genetic diseases due to misfolding of proteins, metabolic related-diseases and apoptosis due to ER stress. However, the roles of 4PBA during odontogenesis are not elucidated. This study revealed the effects of 4PBA during molar development in mice. Methods: We employed in vitro organ cultivation and renal transplantation methods which would mimic the permanent tooth development in an infant period of human. The in vitro cultivated tooth germs and renal calcified teeth were examined by histology and immunohistochemical analysis. Results and Discussion: Our results revealed that treatment of 4PBA altered expression patterns of enamel knot related signaling molecules, and consequently affected cellular secretion and patterned formation of dental hard tissues including dentin and enamel during tooth morphogenesis. The alteration of ER stress by 4PBA treatment during organogenesis would suggest that proper ER stress is important for pattern formation during tooth development and morphogenesis, and 4PBA as a chemical chaperone would be one of the candidate molecules for dental and hard tissue regeneration.

Energy metabolic shift contributes to the phenotype modulation of maturation stage ameloblasts

Maturation stage ameloblasts (M-ABs) are responsible for terminal enamel mineralization in teeth and undergo characteristic cyclic changes in both morphology and function between ruffle-ended ameloblasts (RA) and smooth-ended ameloblasts (SA). Energy metabolism has recently emerged as a potential regulator of cell differentiation and fate decisions; however, its implication in M-ABs remains unclear. To elucidate the relationship between M-ABs and energy metabolism, we examined the expression pattern of energy metabolic enzymes in M-ABs of mouse incisors. Further, using the HAT7 cell line with M-AB characteristics, we designed experiments to induce an energy metabolic shift by changes in oxygen concentration. We revealed that RA preferentially utilizes oxidative phosphorylation, whereas SA depends on glycolysis-dominant energy metabolism in mouse incisors. In HAT7 cells, hypoxia induced an energy metabolic shift toward a more glycolytic-dominant state, and the energy metabolic shift reduced alkaline phosphatase (ALP) activity and calcium transport and deposition with a change in calcium-related gene expression, implying a phenotype shift from RA to SA. Taken together, these results indicate that the energy metabolic state is an important determinant of the RA/SA phenotype in M-ABs. This study sheds light on the biological significance of energy metabolism in governing M-ABs, providing a novel molecular basis for understanding enamel mineralization and elucidating the pathogenesis of enamel hypomineralization.

Inhibition of ROCK ameliorates pulmonary fibrosis by suppressing M2 macrophage polarisation through phosphorylation of STAT3

BACKGROUND

Emerging evidence provides mechanistic insights into the pathogenesis of pulmonary fibrosis (PF), and rare anti-PF therapeutic method has promising effect in its treatment. Rho-associated coiled-coil kinases (ROCK) inhibition significantly ameliorates bleomycin-induced PF and decreases macrophage infiltration, but the mechanism remains unclear. We established bleomycin and radiation-induced PF to identify the activity of WXWH0265, a newly designed unselective ROCK inhibitor in regulating macrophages.

METHODS

Bleomycin-induced PF was induced by intratracheal instillation and radiation-induced PF was induced by bilateral thoracic irradiation. Histopathological techniques (haematoxylin and eosin, Masson's trichrome and immunohistochemistry) and hydroxyproline were used to evaluate PF severity. Western blot, quantitative real-time reverse transcription-polymerase chain reaction and flow cytometry were performed to explore the underlying mechanisms. Bone marrow-derived macrophages (BMDMs) were used to verify their therapeutic effect. Clodronate liposomes were applied to deplete macrophages and to identify the therapeutic effect of WXWH0265.

RESULTS

Therapeutic administration of ROCK inhibitor ameliorates bleomycin-induced PF by inhibiting M2 macrophages polarisation. ROCK inhibitor showed no significant anti-fibrotic effect in macrophages-depleted mice. Treatment with WXWH0265 demonstrated superior protection effect in bleomycin-induced PF compared with positive drugs. In radiation-induced PF, ROCK inhibitor effectively ameliorated PF. Fibroblasts co-cultured with supernatant from various M2 macrophages phenotypes revealed that M2 macrophages stimulated by interleukin-4 promoted extracellular matrix production. Polarisation of M2 macrophages was inhibited by ROCK inhibitor treatment in vitro. The p-signal transducer and activator of transcription 3 (STAT3) in lung tissue and BMDMs was significantly decreased in PF in vivo and vitro after treated with ROCK inhibitors.

CONCLUSION

Inhibiting ROCK could significantly attenuate bleomycin- and radiation-induced PF by regulating the macrophages polarisation via phosphorylation of STAT3. WXWH0265 is a kind of efficient unselective ROCK inhibitor in ameliorating PF. Furthermore, the results provide empirical evidence that ROCK inhibitor, WXWH0265 is a potential drug to prevent the development of PF.

Response of TGF-β isoforms in epithelial-mesenchymal transition of enamel epithelial cells

OBJECTIVE

During enamel formation, transforming growth factor-beta (TGF-β) isoforms exhibit different activities for gene expression, apoptosis, and endocytosis. This study aimed to investigate the differential response of TGF-β isoforms to epithelial-mesenchymal transition (EMT) in enamel epithelial cells.

DESIGN

Using a mouse enamel epithelial cell line (mHAT9d) cultured in the presence of each TGF-β isoform, (1) the morphological changes in EMT were explored, (2) EMT-related genes were analyzed by next-generation sequencing (NGS), (3) TGF-β pathway for EMT was identified by inhibition experiments, and (4) the expression of the TGF-β receptor gene in response to the binding affinity of the TGF-β isoform were analyzed.

RESULTS

EMT was observed in mHAT9d cultured in the presence of TGF-β1 and β3 but not TGF-β2. The expression of both epithelial and mesenchymal marker genes was observed in mHAT9d exhibiting EMT. NGS analysis suggested extracellular signal-regulated kinase (ERK) and Rho pathways as TGF-β signaling pathways associated with EMT. However, EMT in mHAT9d cultured in the presence of TGF-β1 or β3 occurred even in presence of an ERK1/2 inhibitor and was suppressed by Rho-kinase inhibitor. The expression of co-receptors for TGF-β signaling in mHAT9d cells reduced following stimulation with each TGF-β isoform. In contrast, endoglin levels increased following TGF-β1 or β3 stimulation, but no change was noted in response to TGF-β2.

CONCLUSIONS

We propose that in TGF-β-stimulated enamel epithelial cells, EMT mainly occurred via the Rho signaling pathway, and the differences in response across TGF-β isoforms were due to their endoglin-mediated binding affinity for the TGF-β receptor.

Inhibition of RhoA/MRTF-A signaling alleviates nucleus pulposus fibrosis induced by mechanical stress overload

PURPOSE/AIM

: Intervertebral disc degeneration (IDD) is the leading cause of lower back pain, and clinically useful drugs for IDD are unavailable. Mechanical stress overload-induced fibrosis plays a critical role in IDD. RhoA/MRTF-A signaling is known to regulate tissue fibrosis; however, the effect of RhoA/MRTF-A on the development of IDD is unclear.

MATERIALS AND METHODS

: The expression of aggrecan, collagen I, collagen II, MMP-12, CTGF, and MRTF-A in nucleus pulposus (NP) samples from IDD patients and controls was detected by immunohistochemical staining. Primary nucleus pulposus cells (NPCs) were isolated and cultured to establish an overload strain model treated with or without CCG-1423. The protein levels of RhoA, ROCK2, MRTF-A, CTGF, and MMP-12 as well as fibrosis-associated proteins were detected by western blotting and immunofluorescence.

RESULTS

: Collagen I, MMP-12, and CTGF were significantly upregulated, and aggrecan and collagen II were significantly downregulated in the IDD samples. The cellular localization of MRTF-A was associated with intervertebral disc (IVD) degeneration. Overloaded strain enhanced the nuclear translocation of MRTF-A and changed the NPC morphology from spindle-shaped to long strips. Additional experiments showed that RhoA, ROCK2, MRTF-A, SRF, MMP-12, and CTGF were upregulated; however, aggrecan and collagen II were downregulated in NPCs under overload strain. CCG-1423, a RhoA/MRTF-A pathway inhibitor, reversed strain-induced fibrosis.

CONCLUSION

: Mechanical stress activates RhoA/MRTF-A signaling to promote extracellular matrix (ECM) degeneration in the NP, which is associated with the development of IDD. Our findings suggest that the RhoA/MRTF-A inhibitor CCG-1423 can alleviate NPC degeneration caused by overload stress and has potential as a therapeutic agent for IDD.

Signaling Modulation by miRNA-221-3p During Tooth Morphogenesis in Mice

miRNAs are conserved short non-coding RNAs that play a role in the modulation of various biological pathways during tissue and organ morphogenesis. In this study, the function of miRNA-221-3p in tooth development, through its loss or gain in function was evaluated. A variety of techniques were utilized to evaluate detailed functional roles of miRNA-221-3p during odontogenesis, including in vitro tooth cultivation, renal capsule transplantation, in situ hybridization, real-time PCR, and immunohistochemistry. Two-day in vitro tooth cultivation at E13 identified altered cellular events, including cellular proliferation, apoptosis, adhesion, and cytoskeletal arrangement, with the loss and gain of miRNA-221-3p. qPCR analysis revealed alterations in gene expression of tooth-related signaling molecules, including β-catenin, Bmp2, Bmp4, Fgf4, Ptch1, and Shh, when inhibited with miRNA-221-3p and mimic. Also, the inhibition of miRNA-221-3p demonstrated increased mesenchymal localizations of pSMAD1/5/8, alongside decreased expression patterns of Shh and Fgf4 within inner enamel epithelium (IEE) in E13 + 2 days in vitro cultivated teeth. Moreover, 1-week renal transplantation of in vitro cultivated teeth had smaller tooth size with reduced enamel and dentin matrices, along with increased cellular proliferation and Shh expression along the Hertwig epithelial root sheath (HERS), within the inhibitor group. Similarly, in 3-week renal calcified teeth, the overexpression of miRNA-221-3p did not affect tooth phenotype, while the loss of function resulted in long and slender teeth with short mesiodistal length. This study provides evidence that a suitable level of miRNA-221-3p is required for the modulation of major signaling pathways, including Wnt, Bmp, and Shh, during tooth morphogenesis.

Constitutive activation of β-catenin in odontoblasts induces aberrant pulp calcification in mouse incisors

During dentin formation, odontoblast polarization ensures that odontoblasts directionally secrete dentin matrix protein, leading to tubular dentin formation; however, little is known about the major features and regulatory mechanisms of odontoblast polarization. In a study of epithelial cell polarization, β-catenin was shown to serve as a structural component of cadherin-based adherens junctions to initiate cell polarity. However, the role of β-catenin in odontoblast polarization has not been well investigated. In this study, we explored whether β-catenin participated in odontoblast polarization to regulate the secretion of mineralization proteins. We established Col1-CreErt2; β-catenin exon3fl/fl (CA-β-catenin) mice, which constitutively activate β-catenin in odontoblasts. CA-β-catenin mice exhibited disorganization and depolarization of incisor odontoblasts. Moreover, the incisor dentin was hypomineralized, and ectopic calcification was found in mouse incisor pulp. In addition, by constitutive activation of β-catenin, the expression levels of the core polarity molecule Cdc42 and its downstream polarity protein complex Par3-Par6-aPKC were decreased in the incisors of CA-β-catenin mice. These findings suggest that β-catenin plays an essential role in dentin formation by regulating odontoblast polarization.

Oxygen regulates epithelial stem cell proliferation via RhoA-actomyosin-YAP/TAZ signal in mouse incisor

Stem cells are maintained in specific niches that strictly regulate their proliferation and differentiation for proper tissue regeneration and renewal. Molecular oxygen (O₂) is an important component of the niche microenvironment, but little is known about how O₂ governs epithelial stem cell (ESC) behavior. Here, we demonstrate that O₂ plays a crucial role in regulating the proliferation of ESCs using the continuously growing mouse incisors. We have revealed that slow-cycling cells in the niche are maintained under relatively hypoxic conditions compared with actively proliferating cells, based on the blood vessel distribution and metabolic status. Mechanistically, we have demonstrated that, during hypoxia, HIF1α upregulation activates the RhoA signal, thereby promoting cortical actomyosin and stabilizing the adherens junction complex, including merlin. This leads to the cytoplasmic retention of YAP/TAZ to attenuate cell proliferation. These results shed light on the biological significance of blood-vessel geometry and the signaling mechanism through microenvironmental O₂ to orchestrate ESC behavior, providing a novel molecular basis for the microenvironmental O₂-mediated stem cell regulation during tissue development and renewal.

Signaling Modulations of miR-206-3p in Tooth Morphogenesis

MicroRNAs (miRNAs) are a class of naturally occurring small non-coding RNAs that post-transcriptionally regulate gene expression in organisms. Most mammalian miRNAs influence biological processes, including developmental changes, tissue morphogenesis and the maintenance of tissue identity, cell growth, differentiation, apoptosis, and metabolism. The miR-206-3p has been correlated with cancer; however, developmental roles of this miRNA are unclear. In this study, we examined the expression pattern and evaluated the developmental regulation of miR-206-3p during tooth morphogenesis using ex-vivo culture method. The expression pattern of miR-206-3p was examined in the epithelium and mesenchyme of developing tooth germ with stage-specific manners. Perturbation of the expression of miR-206-3p clearly altered expression patterns of dental-development-related signaling molecules, including Axin2, Bmp2, Fgf4, Lef1 and Shh. The gene expression complemented with change in cellular events including, apoptosis and proliferation which caused altered crown and pulp morphogenesis in renal-capsule-calcified teeth. Especially, mislocalization of β-Catenin and SMAD1/5/8 were observed alongside dramatic alterations in the expression patterns of Fgf4 and Shh. Overall, our data suggest that the miR-206-3p regulate the cellular physiology during tooth morphogenesis through modulation of the Wnt, Bmp, Fgf, and Shh signaling pathways to form proper tooth pulp and crown.

[Polarity of ameloblasts and odontoblasts and their related regulators]

The polarity of ameloblasts and odontoblasts is crucial for their differentiation and function. Polarity-related molecules play an important role in this process. This review summarizes the process of polarity formation of ameloblasts and odontoblasts and their related regulators.

Potential function of TGF-β isoforms in maturation-stage ameloblasts

OBJECTIVES

To investigate potential functions of transforming growth factor-beta (TGF-β) isoforms in maturation-stage ameloblasts during amelogenesis.

METHODS

In vivo activation of TGF-β was characterized by using matrix metalloproteinase 20 null (Mmp20^-/-) and wild-type (Mmp20^+/+) mice. Using mHAT9d cells cultured in the presence of each TGF-β isoform, (1) cell proliferation was determined by MTS assay, (2) immunostaining with anti-cleaved caspase-3 monoclonal antibody was performed and apoptotic indices were measured, (3) gene expression was analyzed by RT-qPCR, and (4) the uptake of amelogenin into mHAT9d cells was directly observed using a fluorescence microscope.

RESULTS

TGF-β1 and TGF-β3 were present in the enamel matrix of developing teeth which were activated by MMP20 in vivo. A genetic study revealed that the three TGF-β isoforms upregulate kallikrein 4 (KLK4) mRNA levels but downregulate carbonic anhydrase II. Moreover, TGF-β1 and TGF-β2 significantly upregulated the mRNA level of amelotin, whereas TGF-β3 dramatically downregulated the mRNA levels of odontogenic ameloblast-associated protein (ODAM), family with sequence similarity 83 member H (FAM83H), and alkaline phosphatase (ALP). Immunostaining analysis showed that the apoptosis of mHAT9d cells is induced by three TGF-β isoforms, with TGF-β3 being most effective. Both TGF-β1 and TGF-β3 induced endocytosis of amelogenin.

CONCLUSIONS

We propose that TGF-β is regulated in an isoform-specific manner to perform multiple biological functions such as gene expression related to the structure of basal lamina/ameloblasts, mineral ion transport, apoptosis, and endocytosis in maturation-stage ameloblasts.

Early development of porcine parthenogenetic embryos and reduced expression of primed pluripotent marker genes under the effect of lysophosphatidic acid

To further promote the early development of porcine embryos and capture "naïve" pluripotent state within blastocyst, the experiment explored the effects of lysophosphatidic acid (LPA) on the early development of porcine parthenogenetic embryos and the expression of pluripotency relevant genes. The results showed that the addition of 50 μM LPA significantly improved parthenogenetic embryo cleavage rate (82.7% vs. 74.7%, p < 0.05), blastocyst rate (24.5% vs. 11.3%, p < 0.05) and blastocyst cell count (56 ± 7.9 vs. 42 ± 1.0, p < 0.05) than that of the control group. In addition, immunostaining experiment determined that the fluorescence intensity of OCT4 was also significantly higher than that of the control group. The quantitative real-time polymerase chain reaction (qRT-PCR) test revealed that addition of 50 μM LPA could significantly enhance the expression level of pluripotent gene OCT4 and trophoblast marker genes CDX2, however, decrease the expression of primitive hypoblast marker gene GATA4. The results also indicated that LPA might decrease the expression of GATA4 through the ROCK signalling pathway. For further investigating the effect of the addition of LPA on the expression of "primed" and "naïve" genes, we also detected the expression of those pluripotency-related genes by qRT-PCR. The results showed addition of LPA had no significant effect on the expression of "naïve" pluripotent genes, but it was able to significantly decrease the expression of "primed" pluripotent genes, NODAL and Activin-A; furthermore, it also could significantly improve the expression of OCT4 and c-Myc which act as two important ES cell renewal factors. Above all, the addition of LPA can facilitate the early development of porcine parthenogenetic embryos, which may be able to benefit for capturing "naïve" pluripotency in vitro through inhibiting "primed" pluripotency.

Loss of Stemness, EMT, and Supernumerary Tooth Formation in Cebpb-/-Runx2+/- Murine Incisors

Adult Cebpb KO mice incisors present amelogenin-positive epithelium pearls, enamel and dentin allopathic hyperplasia, fewer Sox2-positive cells in labial cervical loop epitheliums, and reduced Sox2 expression in enamel epithelial stem cells. Thus, Cebpb acts upstream of Sox2 to regulate stemness. In this study, Cebpb KO mice demonstrated cementum-like hard tissue in dental pulp, loss of polarity by ameloblasts, enamel matrix in ameloblastic layer, and increased expression of epithelial-mesenchymal transition (EMT) markers in a Cebpb knockdown mouse enamel epithelial stem cell line. Runx2 knockdown in the cell line presented a similar expression pattern. Therefore, the EMT enabled disengaged odontogenic epithelial stem cells to develop supernumerary teeth. Cebpb and Runx2 knockdown in the cell line revealed higher Biglycan and Decorin expression, and Decorin-positive staining in the periapical region, indicating their involvement in supernumerary tooth formation. Cebpb and Runx2 acted synergistically and played an important role in the formation of supernumerary teeth in adult incisors.

Modulation of microenvironment for controlling the fate of periodontal ligament cells: the role of Rho/ROCK signaling and cytoskeletal dynamics

Cells behave in a variety of ways when they perceive changes in their microenvironment; the behavior of cells is guided by their coordinated interactions with growth factors, niche cells, and extracellular matrix (ECM). Modulation of the microenvironment affects the cell morphology and multiple gene expressions. Rho/Rho-associated coiled-coil-containing protein kinase (ROCK) signaling is one of the key regulators of cytoskeletal dynamics and actively and/or passively determines the cell fate, such as proliferation, migration, differentiation, and apoptosis, by reciprocal communication with the microenvironment. During periodontal wound healing, it is important to recruit the residential stem cells into the defect site for regeneration and homeostasis of the periodontal tissue. Periodontal ligament (PDL) cells contain a heterogeneous fibroblast population, including mesenchymal stem cells, and contribute to the reconstruction of tooth-supporting tissues. Therefore, bio-regeneration of PDL cells has been the ultimate goal of periodontal therapy for decades. Recent stem cell researches have shed light on intrinsic ECM properties, providing paradigm shifts in cell fate determination. This review focuses on the role of ROCK activity and the effects of Y-27632, a specific inhibitor of ROCK, in the modulation of ECM-microenvironment. Further, it presents the current understanding of how Rho/ROCK signaling affects the fate determination of stem cells, especially PDL cells. In addition, we have also discussed in detail the underlying mechanisms behind the reciprocal response to the microenvironment.

Deciphering defective amelogenesis using in vitro culture systems

The conventional two-dimensional (2D) in vitro culture system is frequently used to analyze the gene expression with or without extracellular signals. However, the cells derived from primary culture and cell lines frequently deviate the gene expression profile compared to the corresponding in vivo samples, which sometimes misleads the actual gene regulation in vivo. To overcome this gap, we developed the comparative 2D and 3D in vitro culture systems and applied them to the genetic study of amelogenesis imperfecta (AI) as a model. Recently, we found specificity protein 6 (Sp6) mutation in an autosomal-recessive AI rat that was previously named AMI. We constructed 3D structure of ARE-B30 cells (AMI-derived rat dental epithelial cells) or G5 (control wild type cells) combined with RPC-C2A cells (rat pulp cell line) separated by the collagen membrane, while in 2D structure, ARE-B30 or G5 was cultured with or without the collagen membrane. Comparative analysis of amelogenesis-related gene expression in ARE-B30 and G5 using our 2D and 3D in vitro systems revealed distinct expression profiles, showing the causative outcomes. Bone morphogenetic protein 2 and follistatin were reciprocally expressed in G5, but not in ARE-B30 cells. All-or-none expression of amelotin, kallikrein-related peptidase 4, and nerve growth factor receptor was observed in both cell types. In conclusion, our in vitro culture systems detected the phenotypical differences in the expression of the stage-specific amelogenesis-related genes. Parallel analysis with 2D and 3D culture systems may provide a platform to understand the molecular basis for defective amelogenesis caused by Sp6 mutation.

GSK3β regulates ameloblast differentiation via Wnt and TGF-β pathways

Wnt and TGF-β signaling pathways participate in regulating a variety of cell fates during organogenesis, including tooth development. Despite well-documented, the specific mechanisms, especially how these two pathways act coordinately in regulating enamel development, remain unknown. In this study, we identified Glycogen Synthase Kinase 3 beta (GSK3β), a negative regulator of Wnt signal pathway, participated in ameloblast differentiation via Wnt and TGF-β pathways during enamel development. In vitro rat mandible culture treated with specific GSK3β inhibitor SB415286 displayed enamel defects, accompanied by disrupted ameloblasts polarization, while odontoblasts and dentin appeared to be unaffected. Moreover, after GSK3β knockdown by lentivirus-mediated RNA silencing, HAT-7 cells displayed abnormal cell polarity and cell adhesion, and failed to synthesize appreciable amounts of ameloblast-specific proteins. More importantly, inactivation of GSK3β caused upregulated Wnt and downregulated TGF-β pathway, while reactivation of TGF-β signaling or suppression of Wnt signaling partially rescued the differentiation defects of ameloblasts caused by the GSK3β knock-down. Taken together, these results suggested that GSK3β was essential for ameloblasts differentiation, which might be indirectly mediated through Wnt and TGF-β signaling pathways.

The Semaphorin 4D-RhoA-Akt Signal Cascade Regulates Enamel Matrix Secretion in Coordination With Cell Polarization During Ameloblast Differentiation

During tooth development, oral epithelial cells differentiate into ameloblasts in order to form the most mineralized tissue in the vertebrate body: enamel. During this process, ameloblasts directionally secrete enamel matrix proteins and morphologically change from low columnar cells to polarized tall columnar cells, both of which are essential for the proper formation of enamel. In this study, we elucidated the molecular mechanism that integrates ameloblast function and morphology. Immunohistochemistry revealed that the restricted expression of semaphorin 4D (Sema4D) and RhoA activation status are closely associated with ameloblast differentiation in mouse incisors. In addition, in vitro gain-of-function and loss-of-function experiments demonstrated that Sema4D acts upstream of RhoA to regulate cell polarity and amelogenin expression via the Plexin B1/Leukemia-associated RhoGEF (LARG) complex during ameloblast differentiation. Experiments in transgenic mice demonstrated that expression of a dominant-negative form of RhoA in dental epithelium hindered ameloblast differentiation and subsequent enamel formation, as well as perturbing the establishment of polarized cell morphology and vectorial amelogenin expression. Finally, we showed that spatially restricted Akt mediates between Sema4D-RhoA signaling and these downstream cellular events. Collectively, our results reveal a novel signaling network, the Sema4D-RhoA-Akt signal cascade, that coordinates cellular function and morphology and highlights the importance of specific spatiotemporally restricted components of a signaling pathway in the regulation of ameloblast differentiation. © 2016 American Society for Bone and Mineral Research.

Quantitative Imaging of Cell Membrane-associated Effective Mass Density Using Photonic Crystal Enhanced Microscopy (PCEM)

Adhesion is a critical cellular process that contributes to migration, apoptosis, differentiation, and division. It is followed by the redistribution of cellular materials at the cell membrane or at the cell-surface interface for cells interacting with surfaces, such as basement membranes. Dynamic and quantitative tracking of changes in cell adhesion mass redistribution is challenging because cells are rapidly moving, inhomogeneous, and nonequilibrium objects, whose physical and mechanical properties are difficult to measure or predict. Here, we report a novel biosensor based microscopy approach termed Photonic Crystal Enhanced Microscopy (PCEM) that enables the movement of cellular materials at the plasma membrane of individual live cells to be dynamically monitored and quantitatively imaged. PCEM utilizes a photonic crystal biosensor surface, which can be coated with arbitrary extracellular matrix materials to facilitate cellular interactions, within a modified brightfield microscope with a low intensity non-coherent light source. Benefiting from the high sensitivity, narrow resonance peak, and tight spatial confinement of the evanescent field atop the photonic crystal biosensor, PCEM enables label-free live cell imaging with high sensitivity and high lateral and axial spatial-resolution, thereby allowing dynamic adhesion phenotyping of single cells without the use of fluorescent tags or stains. We apply PCEM to investigate adhesion and the early stage migration of different types of stem cells and cancer cells. By applying image processing algorithms to analyze the complex spatiotemporal information generated by PCEM, we offer insight into how the plasma membrane of anchorage dependent cells is dynamically organized during cell adhesion. The imaging and analysis results presented here provide a new tool for biologists to gain a deeper understanding of the fundamental mechanisms involved with cell adhesion and concurrent or subsequent migration events.

Antagonistic Functions of USAG-1 and RUNX2 during Tooth Development

Supernumerary teeth and tooth agenesis are common morphological anomalies in humans. We previously obtained evidence that supernumerary maxillary incisors form as a result of the successive development of the rudimentary maxillary incisor tooth germ in Usag-1 null mice. The development of tooth germs is arrested in Runx2 null mice, and such mice also exhibit lingual epithelial buds associated with the upper molars and incisors. The aim of this study is to investigate the potential crosstalk between Usag-1 and Runx2 during tooth development. In the present study, three interesting phenomena were observed in double null Usag-1^-/-/Runx2^-/- mice: the prevalence of supernumerary teeth was lower than in Usag-1 null mice; tooth development progressed further compared than in Runx2 null mice; and the frequency of molar lingual buds was lower than in Runx2 null mice. Therefore, we suggest that RUNX2 and USAG-1 act in an antagonistic manner. The lingual bud was completely filled with odontogenic epithelial Sox2-positive cells in the Usag-1^+/+/Runx2^-/- mice, whereas almost no odontogenic epithelial Sox2-positive cells contributed to supernumerary tooth formation in the rudimentary maxillary incisors of the Usag-1^-/-/Runx2^+/+ mice. Our findings suggest that RUNX2 directly or indirectly prevents the differentiation and/or proliferation of odontogenic epithelial Sox2-positive cells. We hypothesize that RUNX2 inhibits the bone morphogenetic protein (BMP) and/or Wnt signaling pathways regulated by USAG-1, whereas RUNX2 expression is induced by BMP signaling independently of USAG-1.

Sp6 regulation of Rock1 promoter activity in dental epithelial cells

Sp6 is a transcription factor of the SP/KLF family and an indispensable regulator of the morphological dynamics of ameloblast differentiation during tooth development. However, the underlying molecular mechanisms remain unclear. We have previously identified one of the Sp6 downstream genes, Rock1, which is involved in ameloblast polarization. In this study, we investigated the transcriptional regulatory mechanisms of Rock1 by Sp6. First, we identified the transcription start sites (TSS) and cloned the 5'-flanking region of Rock1. Serial deletion analyses identified a critical region for Rock1 promoter activity within the 249-bp upstream region of TSS, and chromatin immunoprecipitation assays revealed Sp6-binding to this region. Subsequent transient transfection experiments showed that Rock1 promoter activity is enhanced by Sp6, but reduced by Sp1. Treatment of dental epithelial cells with the GC-selective DNA binding inhibitor, mithramycin A, affected Rock1 promoter activity in loss of enhancement by Sp6, but not repression by Sp1. Further site-directed mutagenesis indicated that the region from -206 to -150 contains responsive elements for Sp6. Taken together, we conclude that Sp6 positively regulates Rock1 transcription by direct binding to the Rock1 promoter region from -206 to -150, which functionally distinct from Sp1.

Rho GTPases in ameloblast differentiation

During tooth development, ameloblasts differentiate from inner enamel epithelial cells to enamel-forming cells by modulating the signal pathways mediating epithelial–mesenchymal interaction and a cell-autonomous gene network. The differentiation process of epithelial cells is characterized by marked changes in their morphology and polarity, accompanied by dynamic cytoskeletal reorganization and changes in cell–cell and cell–matrix adhesion over time. Functional ameloblasts are tall, columnar, polarized cells that synthesize and secrete enamel-specific proteins. After deposition of the full thickness of enamel matrix, ameloblasts become smaller and regulate enamel maturation. Recent significant advances in the fields of molecular biology and genetics have improved our understanding of the regulatory mechanism of the ameloblast cell life cycle, mediated by the Rho family of small GTPases. They act as intracellular molecular switch that transduce signals from extracellular stimuli to the actin cytoskeleton and the nucleus. In our review, we summarize studies that provide current evidence for Rho GTPases and their involvement in ameloblast differentiation. In addition to the Rho GTPases themselves, their downstream effectors and upstream regulators have also been implicated in ameloblast differentiation.

β catenin in health: A review

β catenin belongs to the armadillo family of proteins. It plays a crucial role in developmental and homeostatic processes. Wnts are a family of 19 secreted glycoproteins that transduce multiple signaling cascades, including the canonical Wnt/β catenin pathway, Wnt/Ca(2+) pathway and the Wnt/polarity pathway. This is a review on β catenin, Wnt proteins and their secretion, the signaling pathway, the associated factors and the crucial role of β catenin in odontogenesis.

ODAM inhibits RhoA-dependent invasion in breast cancer

Odontogenic ameloblast-associated protein (ODAM) contributes to cell adhesion. In human cancer, ODAM is down-regulated, and the overexpression of ODAM results in a favourable prognosis; however, the molecular mechanisms underlying ODAM-mediated inhibition of cancer invasion and metastasis remain unclear. Here, we identify a critical role for ODAM in inducing cancer cell adhesion. ODAM induced RhoA activity and the expression of downstream factors, including Rho-associated kinase (ROCK). ODAM-mediated RhoA signalling resulted in actin filament rearrangement by activating PTEN and inhibiting the phosphorylation of AKT. When ODAM is overexpressed in MCF7 breast cancer cells and AGS gastric cancer cells that activate RhoA at high levels, it decreases motility, increases adhesion and inhibits the metastasis of MCF7 cells. Conversely, depletion of ODAM in cancer cells inhibits Rho GTPase activation, resulting in increased cancer migration and invasion. These results suggest that ODAM expression in cells maintains their adhesion, resulting in the prevention of their metastasis via the regulation of RhoA signalling in breast cancer cells. SIGNIFICANCE Breast cancer represents the first most frequent cancer, and the ratio of mortality is high in women. Of utmost importance for reducing risk by breast cancer are their anti-invasion mechanisms, particularly in the non-invasive cancer cells because metastasis is the principal cause of death among cancer patients. ODAM induced RhoA activity. ODAM-mediated RhoA signalling resulted in actin filament rearrangement, increased cell adhesion and inhibited the migration/invasion of MCF7 cells. These results suggest that ODAM expression maintains their adhesion, resulting in the prevention of their metastasis via the regulation of RhoA signalling in breast cancer cells.

CXCR4/CXCL12 signaling impacts enamel progenitor cell proliferation and motility in the dental stem cell niche

Dental stem cells are located at the proximal ends of rodent incisors. These stem cells reside in the dental epithelial stem cell niche, termed the apical bud. We focused on identifying critical features of a chemotactic signal in the niche. Here, we report that CXCR4/CXCL12 signaling impacts enamel progenitor cell proliferation and motility in dental stem cell niche cells. We report cells in the apical bud express CXCR4 mRNA at high levels while expression is restricted in the basal epithelium (BE) and transit-amplifying (TA) cell regions. Furthermore, the CXCL12 ligand is present in mesenchymal cells adjacent to the apical bud. We then performed gain- and loss-of-function analyses to better elucidate the role of CXCR4 and CXCL12. CXCR4-deficient mice contain epithelial cell aggregates, while cell proliferation in mutant incisors was also significantly reduced. We demonstrate in vitro that dental epithelial cells migrate toward sources of CXCL12, whereas knocking down CXCR4 impaired motility and resulted in formation of dense cell colonies. These results suggest that CXCR4 expression may be critical for activation of enamel progenitor cell division and that CXCR4/CXCL12 signaling may control movement of epithelial progenitors from the dental stem cell niche.

Cytoskeletal Reorganization Drives Mesenchymal Condensation and Regulates Downstream Molecular Signaling

Skeletal condensation occurs when specified mesenchyme cells self-organize over several days to form a distinctive cartilage template. Here, we determine how and when specified mesenchyme cells integrate mechanical and molecular information from their environment, forming cartilage condensations in the pharyngeal arches of chick embryos. By disrupting cytoskeletal reorganization, we demonstrate that dynamic cell shape changes drive condensation and modulate the response of the condensing cells to Fibroblast Growth Factor (FGF), Bone Morphogenetic Protein (BMP) and Transforming Growth Factor beta (TGF-β) signaling pathways. Rho Kinase (ROCK)-driven actomyosin contractions and Myosin II-generated differential cell cortex tension regulate these cell shape changes. Disruption of the condensation process inhibits the differentiation of the mesenchyme cells into chondrocytes, demonstrating that condensation regulates the fate of the mesenchyme cells. We also find that dorsal and ventral condensations undergo distinct cell shape changes. BMP signaling is instructive for dorsal condensation-specific cell shape changes. Moreover, condensations exhibit ventral characteristics in the absence of BMP signaling, suggesting that in the pharyngeal arches ventral morphology is the ground pattern. Overall, this study characterizes the interplay between cytoskeletal dynamics and molecular signaling in a self-organizing system during tissue morphogenesis.

The role of APCDD1 in epithelial rearrangement in tooth morphogenesis

Adenomatosis polyposis coli downregulated 1 (APCDD1), a negative regulator of Wnt signaling, was examined to understand detailed mechanisms underlying Wnt signaling tooth development. In situ hybridization showed that Apcdd1 was expressed in the condensed mesenchyme at the bud stage, and in the inner enamel epithelium (IEE), including enamel knot (EK) at the cap stage. In vitro organ cultivation by using Apcdd1 antisense oligodeoxynucleotides was performed at E13.5 for 2 days to define the developmental functions of APCDD1 during tooth development. Analysis of histogenesis and cellular events such as cell adhesion, proliferation, apoptosis and epithelial rearrangement after Apcdd1 knockdown showed altered morphogenesis of the tooth germ with decreased cell proliferation and altered localization of cell adhesion molecules. Actin filament staining and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) labeling of IEE cells showed that Apcdd1 knockdown enhanced epithelial rearrangement in the IEE and EK. To understand the precise signaling regulations of Apcdd1, we evaluated the altered expression patterns of signaling molecules, related with Wnt and enamel knot signalings using RT-qPCR. Tooth germs at cap stage were transplanted into the kidney capsules and were allowed to develop into calcified teeth for 3 weeks. Apcdd1 knockdown increased the number of ectopic cusps on the mesial side of the tooth. Our results suggested that APCDD1 modulates the gene expression of Wnt- and EK-related signaling molecules at the cap stage of tooth development, and is involved in tooth cusp patterning by modulating the epithelial rearrangement in the IEE.

Distinct roles of ROCK1 and ROCK2 during development of porcine preimplantation embryos

Cell-to-cell contact mediated by cell adhesion is fundamental to the compaction process that ensures blastocyst quality during embryonic development. In this study, we first showed that Rho-associated coiled-coil protein kinases (ROCK1 and ROCK2) were expressed both in porcine oocytes and IVF preimplantation embryos, playing different roles in oocytes maturation and embryo development. The amount of mRNA encoding ROCK1 and the protein concentration clearly increased between the eight-cell and morula stages, but decreased significantly when blastocysts were formed. Conversely, ROCK2 was more abundant in the blastocyst compared with other embryonic stages. Moreover, immunostaining showed that ROCK1 protein distribution changed as the embryo progressed through cleavage and compaction to the morula stage. Initially, the protein was predominantly associated with the plasma membrane but later became cytoplasmic. By contrast, ROCK2 protein was localized in both the cytoplasm and the spindle rotation region during oocyte meiosis, but in the cytoplasm and nucleus as the embryo developed. In addition, ROCK2 was present in the trophectoderm cells of the blastocyst. Treatment with 15 μM Y27632, a specific inhibitor of ROCKs, completely blocked further development of early four-cell stage embryos. Moreover, we did not detect the expression ofROCK1but did detectROCK2expression in blastocysts. Moreover, lysophosphatidic acid an activator of ROCKs significantly improved the rates of blastocyst formation. These data demonstrate that ROCKs are required for embryo development to the blastocyst stage. Together, our results indicate that ROCK1 and ROCK2 may exert different biological functions during the regulation of compaction and in ensuring development of porcine preimplantation embryos to the blastocyst stage.

Angular distribution of cross-sectioned cell boundaries at the distal terminal web in differentiating preameloblasts, inner enamel secretory ameloblasts and outer enamel secretory ameloblasts

The cross-sectioned profiles of differentiating preameloblasts, inner enamel secretory ameloblasts and outer enamel secretory ameloblasts at the distal terminal web were quantitatively compared. First, the angles of each line constituting the sectioned cell polygons were measured, and the patterns of angular distribution histograms were compared. Second, all groups of line angles from one differentiating preameloblast population, two inner enamel secretory ameloblast and one outer enamel secretory ameloblast populations at the distal terminal web were compared statistically by the χ(2)-test using the multiple comparison method. The results showed that cell shapes between differentiating preameloblasts and inner enamel secretory ameloblasts were similar, but that those between differentiating preameloblasts and outer enamel secretory ameloblasts and between inner enamel secretory ameloblasts and outer enamel secretory ameloblasts were significantly different. Third, F-actin fluorescence microscopy in the distal terminal web was performed and was consistent with the angular distribution. These results suggest that cell shapes of inner enamel secretory ameloblasts and differentiating preameloblasts at the distal terminal web are specialized for sideways cell movement during decussating tooth enamel formation.

Photonic crystal enhanced microscopy for imaging of live cell adhesion

A form of microscopy that utilizes a photonic crystal biosensor surface as a substrate for cell attachment enables label-free, quantitative, submicron resolution, time-resolved imaging of cell-surface interactions without cytotoxic staining agents or temporally-unstable fluorophores. Other forms of microscopy do not provide this direct measurement of live cell-surface attachment localization and strength that includes unique, dynamic morphological signatures critical to the investigation of important biological phenomena such as stem cell differentiation, chemotaxis, apoptosis, and metastasis. Here, we introduce Photonic Crystal Enhanced Microscopy (PCEM), and apply it to the study of murine dental stem cells to image the evolution of cell attachment and morphology during chemotaxis and drug-induced apoptosis. PCEM provides rich, dynamic information about the evolution of cell-surface attachment profiles over biologically relevant time-scales. Critically, this method retains the ability to monitor cell behavior with spatial resolution sufficient for observing both attachment footprints of filopodial extensions and intracellular attachment strength gradients.

Ameloblasts require active RhoA to generate normal dental enamel

RhoA plays a fundamental role in regulation of the actin cytoskeleton, intercellular attachment, and cell proliferation. During amelogenesis, ameloblasts (which produce the enamel proteins) undergo dramatic cytoskeletal changes and the RhoA protein level is up-regulated. Transgenic mice were generated that express a dominant-negative RhoA transgene in ameloblasts using amelogenin gene-regulatory sequences. Transgenic and wild-type (WT) molar tooth germs were incubated with sodium fluoride (NaF) or sodium chloride (NaCl) in organ culture. Filamentous actin (F-actin) stained with phalloidin was elevated significantly in WT ameloblasts treated with NaF compared with WT ameloblasts treated with NaCl or with transgenic ameloblasts treated with NaF, thereby confirming a block in the RhoA/Rho-associated protein kinase (ROCK) pathway in the transgenic mice. Little difference in quantitative fluorescence (an estimation of fluorosis) was observed between WT and transgenic incisors from mice provided with drinking water containing NaF. We subsequently found reduced transgene expression in incisors compared with molars. Transgenic molar teeth had reduced amelogenin, E-cadherin, and Ki67 compared with WT molar teeth. Hypoplastic enamel in transgenic mice correlates with reduced expression of the enamel protein, amelogenin, and E-cadherin and cell proliferation are regulated by RhoA in other tissues. Together these findings reveal deficits in molar ameloblast function when RhoA activity is inhibited.

Dpysl4 is involved in tooth germ morphogenesis through growth regulation, polarization and differentiation of dental epithelial cells

Dihydropyrimidinase-related protein 4 (Dpysl4) is a known regulator of hippocampal neuron development. Here, we report that Dpysl4 is involved in growth regulation, polarization and differentiation of dental epithelial cells during tooth germ morphogenesis. A reduction in Dpysl4 gene expression in the tooth germ produced a loss of ameloblasts, resulting in the decrease of synthesis and secretion of enamel. The inhibition of Dpysl4 gene expression led to promotion of cell proliferation of inner enamel epithelial cells and inhibition of the differentiation of these cells into pre-ameloblasts, which was confirmed by analyzing cell polarization, columnar cell structure formation and the expression of ameloblast marker genes. By contrast, overexpression of Dpysl4 in dental epithelial cells induces inhibition of growth and increases the expression of the inner enamel epithelial cell marker gene, Msx2. These findings suggest that Dpysl4 plays essential roles in tooth germ morphogenesis through the regulation of dental epithelial cell proliferation, cell polarization and differentiation.

Adenosine A2A receptor: a target for regulating renal interstitial fibrosis in obstructive nephropathy

Renal interstitial fibrosis (RIF) is the common pathological process of chronic kidney diseases leading inevitably to renal function deterioration. RIF and its preceding epithelial-mesenchymal transition (EMT) are commonly triggered by an early occurring renal inflammation. However, an effective approach to prevent EMT and RIF is still lacking and of urgent need. Recently, the adenosine A_2A receptor (A_2AR) emerges as a novel inflammation regulator, therefore manipulation of A_2AR may suppress the EMT process and as such protect against RIF. To test this hypothesis we applied a unilateral ureteral obstruction (UUO) model of RIF on A_2AR knockout mice and their wild-type littermates, combined with the intervention of a selective A_2AR agonist, CGS 21680. On days 3, 7 and 14 post-UUO we evaluated the effects of A_2AR manipulation on the molecular pathological progresses of RIF, including the cellular component of interstitial infiltration, expression of profibrotic factors, cellular biomarkers of EMT, and collagen deposition of extracellular matrix. Our data demonstrated that activation of A_2AR significantly suppressed the deposition of collagen types I and III, reduced the infiltration of CD4+ T lymphocytes, and attenuated the expression of TGF-β1 and ROCK1, which in turn inhibited and postponed the EMT progress. Conversely, genetic inactivation of A_2AR exacerbated the aforementioned pathological processes of UUO-induced RIF. Together, activation of A_2AR effectively alleviated EMT and RIF in mice, suggesting A_2AR as a potential therapeutic target for the treatment of RIF.

Planar cell polarity protein localization in the secretory ameloblasts of rat incisors

The localization of the planar cell polarity proteins Vang12, frizzled-3, Vang11, and Celsr1 in the rat incisors was examined using immunocytochemistry. The results showed that Vang12 was localized at two regions of the Tomes' processes of inner enamel-secretory ameloblasts in rat incisors: a proximal and a distal region. In contrast, frizzled-3 was localized at adherens junctions of the proximal and distal areas of inner enamel- and outer enamel-secretory ameloblasts, where N-cadherin and β-catenin were localized. frizzled-3 was also localized in differentiating inner enamel epithelial cells. Vang11 was localized sparsely in differentiating preameloblasts and extensively at the cell boundary of stratum intermedium. Celsr1 was not localized in ameloblasts but localized in odontoblasts extensively. These results suggest the involvement of planar cell polarity proteins in odontogenesis.

Possible linkage of SP6 transcriptional activity with amelogenesis by protein stabilization

Ameloblasts produce enamel matrix proteins such as amelogenin, ameloblastin, and amelotin during tooth development. The molecular mechanisms of ameloblast differentiation (amelogenesis) are currently not well understood. SP6 is a transcription factor of the Sp/KLF family that was recently found to regulate cell proliferation in a cell-type-specific manner. Sp6-deficient mice demonstrate characteristic tooth anomalies such as delayed eruption of the incisors and supernumerary teeth with disorganized amelogenesis. However, it remains unclear how Sp6 controls amelogenesis. In this study, we used SP6 high producer cells to identify SP6 target genes. Based on the observations that long-term culture of SP6 high producer cells reduced SP6 protein expression but not Sp6 mRNA expression, we found that SP6 is short lived and specifically degraded through a proteasome pathway. We established an in vitro inducible SP6 expression system coupled with siRNA knockdown and found a possible linkage between SP6 and amelogenesis through the regulation of amelotin and Rock1 gene expression by microarray analysis. Our findings suggest that the regulation of SP6 protein stability is one of the crucial steps in amelogenesis.