The interaction between epithelial and mesenchymal tissues plays a critical role in the development of organs such as teeth, lungs, and hair. During tooth development, fibroblast growth factor (FGF) ...signaling is critical for regulating reciprocal epithelial and mesenchymal interactions. FGF signaling requires FGF ligands and their receptors (FGFRs). In this study, we investigated the role of epithelial FGF signaling in tooth development, using the Cre-loxp system to create tissue-specific inactivation of Fgfr1 in mice. In K14-Cre;Fgfr1
fl/fl
mice, the apical sides of enamel-secreting ameloblasts failed to adhere properly to each other, although ameloblast differentiation was unaffected at early stages. Prior to eruption, enamel structure was compromised in the K14-Cre;Fgfr1
fl/fl
mice and displayed severe enamel defects that mimic amelogenesis imperfecta (AI), with a rough, irregular enamel surface. These results suggest that there is a cell-autonomous requirement for FGF signaling in the dental epithelium during enamel formation. Loss of Fgfr1 affects ameloblast organization at the enamel-secretory stage and, hence, the formation of enamel.
The quality and quantity of mandibular bone are essential prerequisites for osseointegrated implants. Only the Hounsfield unit on preoperative computed tomography is currently used as a clinical ...index. Nevertheless, a considerable mismatch occurs between bone quality and the Hounsfield unit. Loss of bone toughness during aging has been accepted based on empirical evidence, but this concept is unlikely evidence based at the level of mechanical properties. Nonenzymatic bone matrix cross-links associated with advanced glycation end products predominate as a consequence of aging. Thus, loss of tissue integrity could diminish the bone toughening mechanism. Here, we demonstrate an impaired bone toughening mechanism caused by mimicking aging in rabbits on a methionine-rich diet, which enabled an enhanced nonenzymatically cross-linked bone matrix. A 3-point bending test revealed a greater reduction in femoral fracture resistance in rabbits on a methionine-rich diet, despite higher maximum and normalized breaking forces (287.3 N and 88.1%, respectively), than in rabbits on a normal diet (262.2 N and 79.7%, respectively). In situ nanoindentation on mandibular cortical bone obtained from rabbits on a methionine-rich diet did not enable strain rate–dependent stiffening and consequent large-dimensional recovery during rapid loading following constant displacement after a rapid-load indentation test as compared with those in rabbits on a normal diet. Such nanoscale structure-function relationships dictate resistance to cracking propagation at the material level and allow for the overall bone toughening mechanism to operate under large external stressors. The strain-dependent stiffening was likely associated with strain-energy transfer to the superior cross-linked bone matrix network of the normal diet, while the reduction in the enzymatically cross-linked matrix in bone samples from rabbits on a methionine-rich diet likely diminished the intrinsic bone toughening mechanism. The present study also provides a precise protocol for evaluating bone mechanical properties at the material level based on observations from a series of nanoindentation experiments.
Abstract Objective Cevimeline and pilocarpine (muscarinic receptor agonists) are used as sialogogues in xerostomia treatment. It is important to know the different effects on their salivary ...mechanisms and the side effects. The aim of the present study was to clarify and compare the comprehensive effects of cevimeline to pilocarpine on salivary, cardiovascular and central mechanisms in rats. Design Under anaesthesia, whole saliva secretion, parotid blood flow and blood pressure were measured following intra-peritoneal administrations of the sialogogues. In digested parotid cells, intracellular Ca2+ concentrations were measured after the sialogogue application. In the conscious condition, changes in angiotensin II-induced water intake were observed after cevimeline administration. In the subfornical organ, which is a thirst-related central nucleus, the effect of cevimeline on the neuronal activity was electrophysiologically investigated. Results Cevimeline at 80 μmol kg−1 showed slowly increasing and lasting salivation, a similar blood flow increment in the parotid gland and higher pressor response when compared to pilocarpine at 4 μmol kg−1 . In parotid cells, cevimeline increased the intracellular Ca2+ concentration in a similar manner to pilocarpine, but at a higher concentration than pilocarpine. Cevimeline inhibited angiotensin II-induced water intake and neuronal activity in the subfornical organ, which is in contrast to reported effects of pilocarpine. Conclusions Cevimeline activates common salivary mechanism with pilocarpine but has a slower onset of activation, longer duration of salivation and an increased pressor response at higher doses. The anti-dipsogenic effect of cevimeline is due to the inhibitory neuronal effect on the thirst-related central nuclei.
Hydroxyapatite (HA) is an osteoconductive implant material. We previously demonstrated that RGD peptides regulate the spreading of HOS cells on HA but not on titanium, speculating that the ...osteoconductivity of HA might be attributed to this RGD domain-dependent spreading of osteoblasts. To confirm this hypothesis, the molecules which regulate the spreading of HOS cells on HA and on titanium were investigated. The 50% effective dose (ED
50) of RGD peptide for the spreading on HA was five fold lower comparing to titanium. Anti-
αV integrin antibody, vitronectin, and fibronectin inhibited the spreading on HA but not on titanium. In Western blot analysis, vitronectin and fibronectin were found in components adsorbed to HA but not to titanium. Taken together, the spreading of HOS cells on HA but not on titanium requires the interaction of
αV integrin and its ligands. The ED
50 of the RGD peptides on titanium but not on HA was remarkably reduced by neuraminidase treatment, that by itself could not inhibit the spreading on both materials. This phenomenon suggests that RGD domain and sialic acid cooperatively but not independently mediate the spreading of HOS cells on titanium. Collectively, the molecules regulating the spreading on HA are apparently different from those on titanium. The spreading of osteoblasts mediated by RGD domain of vitronectin and fibronectin might contribute to the osteoconductive ability of HA.
Statement of problem. Partially stabilized zirconia implants placed by a 1-stage procedure have been previously shown to obtain initial osseointegration under clinically unloaded condition. However, ...it is unknown whether freestanding and tooth-connected partially stabilized zirconia implants can maintain a long-term direct bone-implant interface.
Purpose. This study examined the possibility of the long-term stability of osseointegration around partially stabilized zirconia implants with a 1-stage procedure with different loading designs.
Material And Methods. Thirty-two partially stabilized zirconia implants were placed into the mandibles of 8 monkeys. Three months after implant placement, 3 types of superstructure were provided in each animal to obtain different concepts of support as (1) single freestanding implant support, (2) connected freestanding implant support, and (3) a combination of implant and tooth support. At 12 and 24 months after loading, clinical, histologic, and histomorphometric evaluations of peri-implant tissues were performed on 28 implants.
Results. No clear difference in clinical features was observed among the different types of support. Direct bone apposition to the implant was generally seen in all groups. Histometrically, bone contact ratio ranged between 66% and 81%, and bone area ratio varied between 49% and 78% at 24 months after loading. These values showed almost no difference among single freestanding, connected freestanding, and implant-tooth supports of partially stabilized zirconia implants.
Conclusion. In a primate model, partially stabilized zirconia implants placed with a 1-stage procedure achieve long-term stability of osseointegration with the use of single freestanding, connected freestanding, and implant-tooth supports. (J Prosthet Dent 1998;80:551-8.)
The mechanism by which enhanced external counterpulsation therapy exerts its beneficial effects on chronic and symptomatic stable angina is largely unknown. To clarify the mechanism of action of ...enhanced external counterpulsation, we used(13)N-ammonia positron emission tomography to evaluate myocardial perfusion.
This was not a randomized controlled study. Eleven patients (eight male, age: 61.6+/-9.7) with angina pectoris underwent enhanced external counterpulsation therapy for 35 1 h sessions. They underwent a treadmill exercise test and(13)N-ammonia positron emission tomography, both at rest and with dipyridamole, before and after enhanced external counterpulsation therapy. Neurohumoral factors and nitric oxide were also evaluated. Myocardial perfusion increased at rest after therapy (0.69+/-0.27 to 0.85+/-0.47 ml x min(-1) x g(-1), P<0.05). In ischaemic regions, particularly the anterior region, myocardial perfusion at rest and with dipyridamole and coronary flow reserve improved significantly after therapy (at rest: 0.71+/-0.26 to 0.86+/-0.31;P<0.05, with dipyridamole: 1.26+/-0.65 to 1.84+/-0.94;P<0.02, coronary flow reserve: 1.75+/-0.24 to 2.08+/-0.28;P<0.04). Exercise time was prolonged and the time to 1-mm ST depression improved markedly (P<0.01). After therapy, nitric oxide levels increased (P<0.02) and neurohumoral factors decreased.
Enhanced external counterpulsation therapy improved myocardial perfusion at rest and with dipyridamole and was associated with an increased exercise tolerance with(13)N-ammonia positron emission tomography and increased nitric oxide levels. These results suggest that one of the enhanced external counterpulsation mechanisms is development and recruitment of collateral vessels.
TGF-β3 mediates epithelial-mesenchymal transformation during normal fusion of lip and
palate, but how TGF-β3 functions during cleft lip repair remains unexplored. We
hypothesize that TGF-β3 promotes ...fetal cleft lip repair and fusion by increasing the
availability of mesenchymal cells. In this investigation, we demonstrated that cleft
lips in mouse fetuses were repaired by fetal surgery, producing scarless fusion. At
the site of the operation, we first observed an infusion of platelets expressing
TGF-β3, followed by increased expression of cyclin D1 and tenascin-C, and coupled
with increased mesenchymal cell proliferation. In an ex vivo
serumless culture system, cleft lip explants fused in the presence of exogenous
TGF-β3. Cultured lips also showed up-regulation in cyclin D1 and tenascin-C
expression. These findings suggest that microsurgical repair of cleft lip in the
fetus that produced scarless fusion is mediated by TGF-β3 regulation of mesenchymal
cell proliferation and migration at the site of repair.
Cleft lip is a common congenital malformation, and labioplasty performed on infants to repair such defects often results in severe scar formation. Since TGF-β3 has been implicated in wound healing, ...we therefore hypothesized that TGF-β3 functions to reduce scarring after cleft lip repair. In this investigation, we demonstrated that exogenous TGF-β3 reduced scar formation in an incised and sutured mouse lip in vivo. During labioplasty, endogenous TGF-β3 expression was also elevated. In vitro experiments showed that exogenous TGF-β3 reduced type I collagen accumulation. Furthermore, TGF-β3 inhibited alpha-smooth-muscle actin expression, a marker for myofibroblasts. In tandem, TGF-β3 induced the expression and activity of MMP-9. Analysis of our data suggests that TGF-β3 is normally secreted following labioplastic wound healing. An elevated level of TGF-β3 reduces type I collagen deposition by restricting myofibroblast differentiation and thereby collagen synthesis, and by promoting collagen degradation by MMP-9. In combination, these events lead to TGF-β3-mediated reduced scar formation.
Hydroxyapatite (HA) is a bioactive dental implant material which accelerates bone formation on its surface. The mechanism of this acceleration is not clear. The elucidation of the cell adhesion might ...be the key to the understanding of the bioactive mechanism of HA. In this study, we analyzed the adhesion of HOS human osteoblasts onto HA and titanium to find the particular adhesion to HA. In short-term cultures in fetal bovine serum-pre-coated materials, a significantly higher number of cells adhered to HA than to titanium. In addition, serum-free conditions with phosphate-buffered saline pre-coating or bovine serum albumin pre-coating materials were tested. The results were nearly the same among all pre-coating conditions, suggesting that the quantity of cell adhesion was not affected by serum components. However, in the morphological observations by SEM, the form of adhesion was found to differ among pre-coating conditions. The osteoblasts tightly adhered and spread onto both HA and titanium with serum pre-coating, whereas the cells loosely adhered and did not spread without serum. To evaluate the Arg-Gly-Asp (RGD) sequence-specific adhesion, we used synthetic RGD peptides for a competitive inhibition test. The results showed that RGD peptides remarkably inhibited the tight adhesion and spreading of osteoblasts onto HA, whereas they did not strongly inhibit adhesion and spreading onto titanium. These results demonstrate that the regulation of cell adhesion to HA is different from that to titanium. Our study suggests that the RGD-containing serum proteins might have a major role in regulating the specific adhesion of osteoblasts to HA, and in inducing enhanced cell growth and differentiation.
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