N‐Acetyl Cysteine Regulates TNF‐α‐Inhibited Differentiation in ROS 17/2.8 Osteoblasts

Mechanisms of N-acetyl cysteine-mediated protection from 2-hydroxyethyl methacrylate-induced apoptosis

Resin-based materials are now commonly used in dentistry in restorative materials as well as in endodontic sealers. These materials have been shown to be cytotoxic. The mechanisms by which resin-based materials mediate their adverse effects have not been completely elucidated. Here we show that 2-hydroxyethyl methacrylate (HEMA) induces apoptotic cell death in oral keratinocytes and immune cells through the intrinsic cell death pathway. Functional loss and cell death induced by HEMA was significantly inhibited in the presence of N-acetyl cysteine (NAC) treatment. In addition, HEMA induced a decrease in mitochondrial membrane potential, and an increase in cleaved caspases was potently inhibited in the presence of NAC treatment. Overall, the results reported in this article indicate that NAC is an effective chemoprotectant that can safely be used to protect the pulp and the surrounding tissues from adverse effects of dental restorative and endodontic materials.

Role of MyD88 in TLR agonist-induced functional alterations of human adipose tissue-derived mesenchymal stem cells

Toll-like receptors (TLRs) sense microorganism components and are critical host mediators of inflammation during infection. Recently, TLRs have been reported to be involved in cell proliferation and differentiation. We previously reported that TLR agonists might affect proliferation and differentiation of human adipose tissue-derived mesenchymal stem cells (hASCs). In this study, we sought to determine whether TLR signaling is dependent on MyD88 in hASCs. The hASCs were downregulated using LV-GFP-miR-MyD88, a lentiviral construct inserted siRNA against human MyD88 that significantly inhibited cell proliferation. MyD88 downregulation reduced NF-kappaB activation and enhancement of osteogenic differentiation induced by peptidoglycan (PGN) more significantly than that induced by lipopolysaccharide (LPS). Although LPS- and PGN-induced cytokine secretions were decreased greatly by MyD88 downregulation, IFN-gamma-induced protein-10 (IP10) and IFNbeta expression were enhanced by LPS irrespective of the downregulation of MyD88. These results suggest that TLR signaling is mediated via MyD88-independent pathways as well as MyD88-dependent pathways in hASCs and that MyD88 contributes to the regulation of cell proliferation and differentiation in hASCs.

Toll-like receptors and their ligands control mesenchymal stem cell functions

Mesenchymal stem cells (MSCs) are widespread in adult organisms and may be involved in tissue maintenance and repair as well as in the regulation of hematopoiesis and immunologic responses. Thus, it is important to discover the factors controlling MSC renewal and differentiation. Here we report that adult MSCs express functional Toll-like receptors (TLRs), confirmed by the responses of MSCs to TLR ligands. Pam3Cys, a prototypic TLR-2 ligand, augmented interleukin-6 secretion by MSC, induced nuclear factor kappa B (NF-kappaB) translocation, reduced MSC basal motility, and increased MSC proliferation. The hallmark of MSC function is the capacity to differentiate into several mesodermal lineages. We show herein that Pam3Cys inhibited MSC differentiation into osteogenic, adipogenic, and chondrogenic cells while sparing their immunosuppressive effect. Our study therefore shows that a TLR ligand can antagonize MSC differentiation triggered by exogenous mediators and consequently maintains the cells in an undifferentiated and proliferating state in vitro. Moreover, MSCs derived from myeloid factor 88 (MyD88)-deficient mice lacked the capacity to differentiate effectively into osteogenic and chondrogenic cells. It appears that TLRs and their ligands can serve as regulators of MSC proliferation and differentiation and might affect the maintenance of MSC multipotency.