Bone is continuously remodeled by bone resorption and formation. The bone metabolism is tightly regulated to maintain homeostasis. Deviation from the normal conditions of bone resorption would result in bone diseases. Lipid rafts are specialized plasma membrane microdomains enriched with glycosphingolipids, sphingomyelin and cholesterol. Lipid rafts are important for the transport of selected membranes and relay stations in intracellular signaling. To investigate the role of lipid rafts in RAW264 cell signaling, lipid rafts were disrupted by depleting cholesterol with lysenin. We found that RANKL-induced differentiation into osteoclasts was markedly inhibited by lysenin in a dose-dependent manner. Lysenin abolished RANKL-induced phosphorylation of PLCγ2, Gab2, AKT, ERK1/2, p38. These data suggest that a crucial role for cholesterol in the regulation of the RANKL-mediated signaling pathway and osteoclast differentiation in RAW264 cells, which reflects its importance in the formation of plasma membrane lipid rafts.
A biocompatible, bioactive agent that rapidly induces reparative dentin formation is required to improve the clinical success of vital pulp therapy. Recently, enamel matrix derivative (EMD) has been evaluated as having high potential as a pulp-capping material in vivo. The objective of the present study was to investigate mRNA expression of dentin-related protein in human dental pulp cells (hDPCs) stimulated by amelogenin, the major constituent of EMD, using quantitative real-time RT-PCR in vitro. As our results, the expressions of BMP-4 and osteopontin mRNA were enhanced in hDPCs by addition of 50 ng/mL amelogenin for 24 hours. Furthermore, the expression of DMP-1 mRNA, which is a specific marker of dentin, was promoted intensively by addition of 10 ng/mL and 50 ng/mL amelogenin for 24 hours, while hDPCs did not express DMP-1 mRNA without amelogenin. Despite the limitations of our experimental system in the present study, our findings indicate that amelogenin stimulates the differentiation of hDPCs into odontoblastic cells in vitro. Moreover, it is essential to elucidate the function and mechanism of action of amelogenin in dental pulp cells.
Many studies have investigated the relationship between periodontal and cardiovascular diseases, particulaly myocardial infartiction (MI) and stroke. Pathological sympathetic overactivation and vagal withdrawal are thought to reduce the survival rate after acute MI (AMI). Electrical stimulation of aortic depressor nerve (ADN) decreases sympathetic nerve activity and increases vagal nerve activity via the arterial baroreflex pathway. We tested whether ADN stimulation improved the survival rate after AMI in rats. AMI was induced by ligating the left coronary artery. Two minutes after the ligation, 10-Hz stimulation of the intact left ADN was started and continued for 30-min in the treatment group, whereas no stimulation was performed in control group. The survival rate at 60 min after AMI was only 6.7 % in the control group, whereas it increased to 76.5 % in the treatment group. ADN stimulation markedly improved the survival rate of rats following AMI.
Pluripotent embryonic stem cells have the potential to differentiate to all fetal and adult cell types and might represent a useful cell source for tissue regeneration. Moreover, the applicable of an embryonic stem cell can be used not only to the tissue regenerative field but also to in vitro embryotoxicity field. The influences of biomaterials on human reproduction and development are still unclear. Their influences on the next or future generations are also unknown. Although many biomaterials have already been used, many people have concerns over them. Regarding long-term embryotoxicity associated with biomaterial exposure, even the presence or absence of risks is unclear. Spielmann et al. suggested that embryotoxicity could be estimated based on influences on ES cell differentiation. In 1997, Spielmann et al. proposed the first in vitro embryotoxicity test (EST) protocol using ES and 3T3 cells. The EST protocol has achieved global attention as an in vitro means to screen the embryotoxicity of chemical substances. The EST protocol should be further improved as a useful method of utilizing an embryonic stem cells.