Yu Sugawara

Connexin 43 Is Necessary for Salivary Gland Branching Morphogenesis and FGF10-induced ERK1/2 Phosphorylation

Cell-cell interaction via the gap junction regulates cell growth and differentiation, leading to formation of organs of appropriate size and quality. To determine the role of connexin43 in salivary gland development, we analyzed its expression in developing submandibular glands (SMGs). Connexin43 (Cx43) was found to be expressed in salivary gland epithelium. In ex vivo organ cultures of SMGs, addition of the gap junctional inhibitors 18α-glycyrrhetinic acid (18α-GA) and oleamide inhibited SMG branching morphogenesis, suggesting that gap junctional communication contributes to salivary gland development. In Cx43−/− salivary glands, submandibular and sublingual gland size was reduced as compared with those from heterozygotes. The expression of Pdgfa, Pdgfb, Fgf7, and Fgf10, which induced branching of SMGs in Cx43−/− samples, were not changed as compared with those from heterozygotes. Furthermore, the blocking peptide for the hemichannel and gap junction channel showed inhibition of terminal bud branching. FGF10 induced branching morphogenesis, while it did not rescue the Cx43−/− phenotype, thus Cx43 may regulate FGF10 signaling during salivary gland development. FGF10 is expressed in salivary gland mesenchyme and regulates epithelial proliferation, and was shown to induce ERK1/2 phosphorylation in salivary epithelial cells, while ERK1/2 phosphorylation in HSY cells was dramatically inhibited by 18α-GA, a Cx43 peptide or siRNA. On the other hand, PDGF-AA and PDGF-BB separately induced ERK1/2 phosphorylation in primary cultured salivary mesenchymal cells regardless of the presence of 18α-GA. Together, our results suggest that Cx43 regulates FGF10-induced ERK1/2 phosphorylation in salivary epithelium but not in mesenchyme during the process of SMG branching morphogenesis.

PDGFs regulate tooth germ proliferation and ameloblast differentiation

OBJECTIVE The purpose of this study was to elucidate the effects of platelet-derived growth factors (PDGFs) during tooth development, as well as the mechanisms underlying the interactions of growth factors with PDGF signalling during odontogenesis. DESIGN We used an ex vivo tooth germ organ culture system and two dental cell lines, SF2 cells and mDP cells, as models of odontogenesis. AG17, a tyrosine kinase inhibitor, was utilised for blocking PDGF receptor signalling. To analyse the expressions of PDGFs, reverse transcriptase (RT)-PCR and immunohistochemistry were performed. Proliferation was examined using a BrdU incorporation assay for the organ cultures and a cell counting kit for the cell lines. The expressions of Fgf2 and ameloblastin were analysed by real-time RT-PCR. RESULTS The PDGF ligands PDGF-A and PDGF-B, and their receptors, PDGFRalpha and PDGFRbeta, were expressed throughout the initial stages of tooth development. In the tooth germ organ cultures, PDGF-AA, but not PDGF-BB, accelerated cusp formation. Conversely, AG17 suppressed both growth and cusp formation of tooth germs. Exogenous PDGF-BB promoted mDP cell proliferation. Furthermore, PDGF-AA decreased Fgf2 expression and increased that of ameloblastin, a marker of differentiated ameloblasts. CONCLUSION Our results indicate that PDGFs are involved in initial tooth development and regulate tooth size and shape, as well as ameloblast differentiation.

Improvement of Pitting Corrosion Resistance of Type 316L Stainless Steel by Potentiostatic Removal of Surface MnS Inclusions

The beneficial effect of the removal of MnS inclusions on the pitting of stainless steels has been demonstrated in two ways. (1) High-purity Type 316L stainless steel with no inclusions was used as a specimen in the measurement of anodic polarization curves in 0.5 M NaCl and (2) commercial Type 316L stainless steel with MnS and slag-related inclusions was first polarized at different potentials for 30 min in 1 M Na2SO4 of pH 3 and then anodic polarization measurements were taken in 0.5 M NaCl. Pitting did not occur in the passive or transpassive region of the high-purity steel. The polarization treatment dissolved MnS and some oxide inclusions (CaO and SiO2) on the surface of the commercial steel. An increase in pitting potential of the commercial steel was noted after treatment at potentials above 0.2 V. At the same time, the number of current spikes due to metastable pits decreased significantly. These results are more likely due to the beneficial effect of removing MnS inclusions from the steel surface rather than the modification effect of the chemical composition of passive films on the surface.

Expressions and functions of neurotrophic factors in tooth development

Neurotrophic factors are soluble growth factors predominantly expressed in vertebrate nervous systems and have been well-characterized for their critical roles in neural tissues. Recent studies have revealed that neurotrophin factors and their receptors are also expressed in multiple non-neural tissues, and play a role in a wide range of biological functions, such as regulation of cellular proliferation, survival, migration, and differentiation. The neurotrophic factor family is defined by its structural and functional similarities to 4 ligands; nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), and neurotrophin-4 (NT-4, also known as NT-5). They activate 2 different receptors, trk tyrosine kinase and p75, the latter of which is a member of the tumor necrosis factor receptor superfamily. During tooth development, observations of dynamic changes of specific expression patterns of neurotrophic factors and their receptors imply their important functions in odontogenic processes. In addition, our recent study demonstrated that NT-4 regulates proliferation and differentiation of dental epithelium, and promotes the production of enamel matrixes. In this review, we describe the expression patterns and functions of neurotrophic factors in the tooth germ, and discuss the relationships with tooth development.

Nanoporous Copper Dealloyed from a Nanocrystallized Ticu Alloy

Nanoporous copper (NPC) was fabricated through dealloying nanocrystallized TiSubscript text50Cu50 ribbon alloy under a free immersion condition in HF solutioSubscript textns at 25 °C. Multimodal nanoporous structure was formed due to the presence of Ti3Cu4 phase, which was co-precipitated with Ti2Cu during the heat treatment at T = 400 °C (Italic textTSubscript textg Italic textT Subscript textx). The presence of multiphases in tItalic texthe starting material caused the different behavior in the evolution of nanoporosity. In 0.03 mol/L HF solution, the bimodal nanoporous copper with a pore size of 54 nm and 184 nm was obtained in different regions where the composition differed. The ligament scale lengths in two regions were confirmed to be 54 nm and 203 nm, respectively. In 0.13 mol/L HF solution, the difference in the pore size and phase separation became weak, accompanying with the evolution of larger pores and smaller ligaments. The residue after dealloying was confirmed to be fcc Cu, indicated by the presence of Cu (111), (200), (220) and (311) in XRD patterns and TEM selective area diffraction pattern. The microstructure of the starting materials for dealloying, such as intermetallic phases, played a key role in the formation of the final multimodal nanoporous structure.

Formation of Pt Skin Layer on Ordered and Disordered Pt-Co Alloys and Corrosion Resistance in Sulfuric Acid

AbstractThe formation of the Pt-enriched layer (Pt skin layer) formed at the surface of the ordered and disordered Pt-Co alloy specimens by a dealloying treatment and its corrosion resistance under potential cycling in sulfuric acid were examined to clarify the dissolution behavior of the Pt skin layer in polymer electrolyte fuel cell-operating conditions. The ordered and disordered Pt-Co specimens were obtained by heat treatment at 1073 and 1473 K, respectively. Co at the alloy surfaces dramatically dissolved in an early phase of the dealloying treatment in naturally aerated 0.5 M H2SO4 at 298 K, and Pt skin layers were formed. Pt skin layers ca. 2 monolayer in thickness were formed on the Pt-Co alloy specimens by the dealloying treatment in 0.5 M H2SO4. The cyclic voltammetry measurements of the Pt-Co specimens showed the existence of Pt skin layers after the dealloying treatment and the inhibition of the Pt oxide formation on the Pt skin layers. The Pt oxide formation for ordered Pt-Co was more suppressed than that for the disordered Pt-Co. The Pt skin layers on the Pt-Co specimens exhibited a higher corrosion resistance than pure Pt, and the dissolution of the Pt skin layer for ordered Pt-Co was more inhibited than that for disordered Pt-Co under potential cycling in the potential range of 0.6–1.4 V in 0.5 M H2SO4 (dissolution test). A thin, continuous Pt skin layer remained at the surface of the ordered Pt-Co specimen after the dissolution test. The formation of a uniform Pt skin layer seems to provide high oxidation resistance to the surface, leading to high corrosion resistance. Graphical AbstractThe dissolution of Pt skin layer for the ordered Pt-Co was highly suppressed compared with that for the disordered Pt-Co and pure Pt. The suppression of Pt-O formation seems to be the main reason for the high corrosion resistance. The formation of a thin and continuous Pt skin layer is important to prevent the dissolution of Pt.

Microelectrochemistry of Sulfide Inclusions and Pit Initiation Mechanisms of Stainless Steels

Stainless steels suffer from pitting corrosion in chloride-containing environments. Sulfide inclusions, such as MnS, are known to act as the initiation sites of pitting. The pit initiation mechanism at MnS inclusions in chloride-containing environments is as follows : 1) dissolution of MnS inclusions leads to the deposition of elemental sulfur on and around the inclusions ; 2) the coexistence of elemental sulfur and chloride ions results in the dissolution of the steel matrix, forming the trenches at the boundaries between the inclusions and the steel matrix, 3) rapid active dissolution occurs locally at the bottom of the trenches, because of the decrease of pH due to the hydrolysis reaction of Cr and the electrode potential decrease at the bottom of the trench due to the solution resistance. Dissolution behavior of sulfide inclusions is of key importance in pit initiation process. Insoluble sulfide inclusions, such as CrS, TiS, and Ti4C2S2, are unlikely to act as the pit initiation sites. Cr-or Ti-oxide films on the inclusions act as a barrier against inclusion dissolution. An applied stress causes micro-cracks on MnS inclusions, which promotes pit initiation of stainless steels. The micro-crack initiation is closely related to oxide film formation on MnS inclusions.

Epithelial-mesenchymal interaction reduces inhibitory effects of fluoride on proliferation and enamel matrix expression in dental epithelial cells

Abstract Aim Fluoride, well known as a specific and effective caries prophylactic agent, also affects the differentiation and function of ameloblasts. High dose sodium fluoride (NaF) induces enamel hypoplasia, also called enamel fluorosis, whereas the size and form of teeth except the enamel are not changed with its treatment. We examined the effects of fluoride on dental epithelium proliferation and differentiation using co-cultures of dental epithelial and mesenchymal cells. Methods Cultures of the dental epithelial cell line SF2 and dental mesenchymal cell line mDP were performed, as well as co-cultures. Enamel matrix expression in SF2 cells treated with NaF was analyzed by RT-PCR, while cell proliferation was examined using a trypan blue dye exclusion method and BrdU incorporation findings. The effects of NaF on NT-4-induced ERK1/2 phosphorylation were analyzed by western immunoblotting. Results Neurotrophic factor NT-4 induced enamel matrix expression, which was inhibited in the presence of NaF. Similar results were observed in regard to SF2 cell proliferation, but not with mDP cells. The levels of proliferation and ameloblastin expression in SF2-GFP cells co-cultured with mDP in the presence of NaF were lower as compared to those in SF2 cells cultured alone. Conclusion Our results indicate that dental epithelial cells co-cultured with dental mesenchymal cells are resistant to the inhibitory effects of NaF on proliferation and ameloblastin expression. They also suggest that the dental fluorosis phenotype may affect enamel, but not tooth size or shape, because of rescue of the inhibitory effects of NaF by culturing with dental mesenchymal cells.