Introduction

Mineral Trioxide aggregate (MTA) is routinely used for pulp capping procedures. However, little is known about its direct interaction with the cells or whether MTA is capable of releasing soluble factors that could help in differentiating cells. There have been no previous studies demonstrating this aspect of MTA. Hence the aim of this study was to determine whether direct contact of the cells with MTA was necessary to help differentiate the pulp cells into odontoblast like cells.

Methods

Human dental pulp cells (DPCs) were cultured on Grey MTA, either in direct contact or away from the cells on a cell culture insert, and the levels of gene expression, secretion of Vascular Endothelial Growth Factor (VEGF) and the rates of cell proliferation were analyzed.

Results

MTA when placed in direct contact with the cells promoted upregulated the expression of important odontoblastic genes like Osteocalcin (OCN) and Dentin Sialoprotein (DSP), thereby demonstrating that direct contact of the cells with the MTA is necessary to promote differentiation of the pulp cells into odontoblast like cells which in turn are responsible for dentin bridge formation. MTA also induced an increase in secretion of VEGF when placed in direct contact with the cells.

Conclusion

Overall our studies support the fact that direct contact of the cells with the MTA is necessary to help differentiate them into odontoblast like cells which in turn will lead to a successful treatment outcome.

Bacterially induced cell death in human lymphocytes is an important virulence factor for pathogenic bacteria. Previously discovered mechanisms of bacterially induced cell death are predominantly based on the transfer of bacterial proteins to the target host cell, such as the toxins secreted through type I, II, and VI secretion systems or effector proteins injected through type III, IV, and Vb secretion systems. Here, we report a mechanism employed by the Gram-negative oral pathogen Fusobacterium nucleatum for cell death induction of human lymphocytes via two outer membrane proteins (OMPs), Fap2 and RadD, which share regions homologous to autotransporter secretion systems (type Va secretion systems). Genetic and physiological studies established that inactivation of the two OMPs led to significantly reduced ability to trigger cell death in Jurkat cells, while the corresponding double mutant was almost completely attenuated. Additional biochemical and molecular analyses demonstrated that cell-free F. nucleatum membranes are sufficient to induce cell death in Jurkat cells, suggesting that no active process or effector protein transfer was necessary to induce eukaryotic cell death.

The aims of this study are to demonstrate the increased lysis of stem cells but not their differentiated counterparts by the NK cells and to determine whether disturbance in cell differentiation is a cause for increased sensitivity to NK cell mediated cytotoxicity. Increased cytotoxicity and augmented secretion of IFN-γ were both observed when PBMCs or NK cells were co-incubated with primary UCLA oral squamous carcinoma stem cells (UCLA-OSCSCs) when compared to differentiated UCLA oral squamous carcinoma cells (UCLA-OSCCs). In addition, human embryonic stem cells (hESCs) were also lysed greatly by the NK cells. Moreover, NK cells were found to lyse human Mesenchymal Stem Cells (hMSCs), human dental pulp stem cells (hDPSCs) and human induced pluripotent stem cells (hiPSCs) significantly more than their differentiated counterparts or parental lines from which they were derived. It was also found that inhibition of differentiation or reversion of cells to a less-differentiated phenotype by blocking NFκB or targeted knock down of COX2 in monocytes significantly augmented NK cell cytotoxicity and secretion of IFN-γ. Taken together, these results suggest that stem cells are significant targets of the NK cell cytotoxicity. However, to support differentiation of a subset of tumor or healthy untransformed primary stem cells, NK cells may be required to lyse a number of stem cells and/or those which are either defective or incapable of full differentiation in order to lose their cytotoxic function and gain the ability to secrete cytokines (split anergy). Therefore, patients with cancer may benefit from repeated allogeneic NK cell transplantation for specific elimination of cancer stem cells.

The mechanisms by which resin based materials induce adverse effects in patients have not been completely elucidated. Here we show that 2-hydroxyethyl methacrylate (HEMA) induces apoptotic cell death in oral keratinocytes. Functional loss and cell death induced by HEMA was significantly inhibited in the presence of N-acetyl cysteine (NAC) treatment. NAC also prevented HEMA mediated decrease in vascular endothelial growth factor secretion. The protective effect of NAC was partly related to its ability to induce NF-κB in the cells, since HEMA mediated inhibition of nuclear NF-κB expression and function was significantly blocked in the presence of NAC treatment. Moreover, blocking of nuclear translocation of NF-κB in oral keratinocytes sensitized these cells to HEMA mediated apoptosis. In addition, since NAC was capable of rescuing close to 50% of NF-κB knockdown cells from HEMA mediated cell death, there is, therefore, an NF-κB independent pathway of protection from HEMA mediated cell death by NAC. NAC mediated prevention of HEMA induced cell death in NF-κB knockdown cells was correlated with a decreased induction of c-Jun N-terminal kinase (JNK) activity since NAC inhibited HEMA mediated increase in JNK levels. Furthermore, the addition of a pharmacologic JNK inhibitor to HEMA treated cells prevented cell death and restored NF-κB knockdown cell function significantly. Therefore, NAC protects oral keratinocytes from the toxic effects of HEMA through NF-κB dependent and independent pathways. Moreover, our data suggest the potential involvement of JNK pathway in NAC mediated protection.

Background

The aim of this paper is to study the function of allogeneic and autologous NK cells against Dental Pulp Stem Cells (DPSCs) and Mesenchymal Stem Cells (MSCs) and to determine the function of NK cells in a three way interaction with monocytes and stem cells.

Methodology/Principal Findings

We demonstrate here that freshly isolated untreated or IL-2 treated NK cells are potent inducers of cell death in DPSCs and MSCs, and that anti-CD16 antibody which induces functional split anergy and apoptosis in NK cells inhibits NK cell mediated lysis of DPSCs and MSCs. Monocytes co-cultured with either DPSCs or MSCs decrease lysis of stem cells by untreated or IL-2 treated NK cells. Monocytes also prevent NK cell apoptosis thereby raising the overall survival and function of NK cells, DPSCs or MSCs. Both total population of monocytes and those depleted of CD16+ subsets were able to prevent NK cell mediated lysis of MSCs and DPSCs, and to trigger an increased secretion of IFN-γ by IL-2 treated NK cells. Protection of stem cells from NK cell mediated lysis was also seen when monocytes were sorted out from stem cells before they were added to NK cells. However, this effect was not specific to monocytes since the addition of T and B cells to stem cells also protected stem cells from NK cell mediated lysis. NK cells were found to lyse monocytes, as well as T and B cells.

Conclusion/Significance

By increasing the release of IFN-γ and decreasing the cytotoxic function of NK cells monocytes are able to shield stem cells from killing by the NK cells, resulting in an increased protection and differentiation of stem cells. More importantly studies reported in this paper indicate that anti-CD16 antibody can be used to prevent NK cell induced rejection of stem cells.

Resin based materials are now widely used in dental restorations. While the use of these materials is aesthetically appealing in patients, they carry the risk of local and systemic adverse effects. The potential risks are direct damage to the cells and induction of immune-based hypersensitivity reactions. Dental Pulp Stromal Cells (DPSCs) and oral keratinocytes are the major cell types which may come in contact with dental resins such as 2-hydroxyethyl methacrylate (HEMA) after dental restorations. Here we show that N-acetyl cysteine (NAC) inhibits HEMA induced apoptotic cell death and restores the function of DPSCs and oral epithelial cells. NAC inhibits HEMA mediated toxicity through induction of differentiation in DPSCs since the genes for dentin sialoprotein (DSP), Osteopontin (OPN), Osteocalcin (OCN), and Alkaline Phosphatase (ALP) which are induced during differentiation are also induced by NAC. Unlike NAC, Vitamin E and C which known anti-oxidant compounds failed to prevent either HEMA mediated cell death or decrease in VEGF secretion by human DPSCs. More importantly, when added either alone or in combination with HEMA Vitamin E and Vitamin C did not increase the gene expression for OPN, and in addition Vitamin E inhibited the protective effect of NAC on DPSCs. NAC inhibited HEMA mediated decrease in NFκB activity thus, providing survival mechanism for the cells. Overall, the studies reported in this paper indicated that undifferentiated DPSCs have exquisite sensitivity to HEMA induced cell death, and their differentiation by NAC resulted in an increased NFκB activity which might have provided the basis for their increased protection from HEMA mediated functional loss and cell death.