Yufang Shi

Molecular definitions of cell death subroutines: recommendations of the Nomenclature Committee on Cell Death 2012

In 2009, the Nomenclature Committee on Cell Death (NCCD) proposed a set of recommendations for the definition of distinct cell death morphologies and for the appropriate use of cell death-related terminology, including ‘apoptosis’, ‘necrosis’ and ‘mitotic catastrophe’. In view of the substantial progress in the biochemical and genetic exploration of cell death, time has come to switch from morphological to molecular definitions of cell death modalities. Here we propose a functional classification of cell death subroutines that applies to both in vitro and in vivo settings and includes extrinsic apoptosis, caspase-dependent or -independent intrinsic apoptosis, regulated necrosis, autophagic cell death and mitotic catastrophe. Moreover, we discuss the utility of expressions indicating additional cell death modalities. On the basis of the new, revised NCCD classification, cell death subroutines are defined by a series of precise, measurable biochemical features.

Mesenchymal Stem Cell-Mediated Immunosuppression Occurs via Concerted Action of Chemokines and Nitric Oxide

Mesenchymal stem cells (MSCs) can become potently immunosuppressive through unknown mechanisms. We found that the immunosuppressive function of MSCs is elicited by IFNgamma and the concomitant presence of any of three other proinflammatory cytokines, TNFalpha, IL-1alpha, or IL-1beta. These cytokine combinations provoke the expression of high levels of several chemokines and inducible nitric oxide synthase (iNOS) by MSCs. Chemokines drive T cell migration into proximity with MSCs, where T cell responsiveness is suppressed by nitric oxide (NO). This cytokine-induced immunosuppression was absent in MSCs derived from iNOS(-/-) or IFNgammaR1(-/-) mice. Blockade of chemokine receptors also abolished the immunosuppression. Administration of wild-type MSCs, but not IFNgammaR1(-/-) or iNOS(-/-) MSCs, prevented graft-versus-host disease in mice, an effect reversed by anti-IFNgamma or iNOS inhibitors. Wild-type MSCs also inhibited delayed-type hypersensitivity, while iNOS(-/-) MSCs aggravated it. Therefore, proinflammatory cytokines are required to induce immunosuppression by MSCs through the concerted action of chemokines and NO.

The end of the (cell) line: Methods for the study of apoptosis in vitro

Publisher Summary This chapter describes techniques commonly used to study cell death using in vitro cell culture systems. These techniques include a range of simple dye exclusion assays that give crude information on cell viability but do not necessarily discriminate between apoptotic or necrotic modes of cell death. The chapter describes cell death assays that are based on the observation that apoptosis is accompanied by DNA fragmentation, either into the classical “ladder” pattern of 200 bp integer multiples, 50kb fragments, or single-stranded DNA cleavage. Assays used to measure this fragmentation include gel electrophoresis of total DNA, quantification of the release of radioactively labeled DNA, examination of cell cycle profile, and in situ nick translation. Because apoptotic cells are morphologically highly distinctive and are easily distinguishable from both viable and necrotic cells, most cell death assays should be coupled with direct morphological evaluation of the cell population under study to define with certainty the mode of cell death that is occurring.

Species Variation in the Mechanisms of Mesenchymal Stem Cell‐Mediated Immunosuppression

Bone marrow‐derived mesenchymal stem cells (MSCs) hold great promise for treating immune disorders because of their immunoregulatory capacity, but the mechanism remains controversial. As we show here, the mechanism of MSC‐mediated immunosuppression varies among different species. Immunosuppression by human‐ or monkey‐derived MSCs is mediated by indoleamine 2,3‐dioxygenase (IDO), whereas mouse MSCs utilize nitric oxide, under the same culture conditions. When the expression of IDO and inducible nitric oxide synthase (iNOS) were examined in human and mouse MSCs after stimulation with their respective inflammatory cytokines, we found that human MSCs expressed extremely high levels of IDO, and very low levels of iNOS, whereas mouse MSCs expressed abundant iNOS and very little IDO. Immunosuppression by human MSCs was not intrinsic, but was induced by inflammatory cytokines and was chemokine‐dependent, as it is in mouse. These findings provide critical information about the immunosuppression of MSCs and for better application of MSCs in treating immune disorders. STEM CELLS 2009;27:1954–1962

Mesenchymal stem cells derived from human gingiva are capable of immunomodulatory functions and ameliorate inflammation-related tissue destruction in experimental colitis

Aside from the well-established self-renewal and multipotent differentiation properties, mesenchymal stem cells exhibit both immunomodulatory and anti-inflammatory roles in several experimental autoimmune and inflammatory diseases. In this study, we isolated a new population of stem cells from human gingiva, a tissue source easily accessible from the oral cavity, namely, gingiva-derived mesenchymal stem cells (GMSCs), which exhibited clonogenicity, self-renewal, and multipotent differentiation capacities. Most importantly, GMSCs were capable of immunomodulatory functions, specifically suppressed peripheral blood lymphocyte proliferation, induced expression of a wide panel of immunosuppressive factors including IL-10, IDO, inducible NO synthase (iNOS), and cyclooxygenase 2 (COX-2) in response to the inflammatory cytokine, IFN-γ. Cell-based therapy using systemic infusion of GMSCs in experimental colitis significantly ameliorated both clinical and histopathological severity of the colonic inflammation, restored the injured gastrointestinal mucosal tissues, reversed diarrhea and weight loss, and suppressed the overall disease activity in mice. The therapeutic effect of GMSCs was mediated, in part, by the suppression of inflammatory infiltrates and inflammatory cytokines/mediators and the increased infiltration of regulatory T cells and the expression of anti-inflammatory cytokine IL-10 at the colonic sites. Taken together, GMSCs can function as an immunomodulatory and anti-inflammatory component of the immune system in vivo and is a promising cell source for cell-based treatment in experimental inflammatory diseases.

Mesenchymal stem cells: a new trend for cell therapy

Mesenchymal stem cells (MSCs), the major stem cells for cell therapy, have been used in the clinic for approximately 10 years. From animal models to clinical trials, MSCs have afforded promise in the treatment of numerous diseases, mainly tissue injury and immune disorders. In this review, we summarize the recent opinions on methods, timing and cell sources for MSC administration in clinical applications, and provide an overview of mechanisms that are significant in MSC-mediated therapies. Although MSCs for cell therapy have been shown to be safe and effective, there are still challenges that need to be tackled before their wide application in the clinic.

Plasticity of mesenchymal stem cells in immunomodulation: pathological and therapeutic implications

Mesenchymal stem cells (MSCs) are multipotent stromal cells that exist in many tissues and are capable of differentiating into several different cell types. Exogenously administered MSCs migrate to damaged tissue sites, where they participate in tissue repair. Their communication with the inflammatory microenvironment is an essential part of this process. In recent years, much has been learned about the cellular and molecular mechanisms of the interaction between MSCs and various participants in inflammation. Depending on their type and intensity, inflammatory stimuli confer on MSCs the ability to suppress the immune response in some cases or to enhance it in others. Here we review the current findings on the immunoregulatory plasticity of MSCs in disease pathogenesis and therapy.

Immunobiology of mesenchymal stem cells

Mesenchymal stem cells (MSCs) can be isolated from almost all tissues and effectively expanded in vitro. Although their true in situ properties and biological functions remain to be elucidated, these in vitro expanded cells have been shown to possess potential to differentiate into specific cell lineages. It is speculated that MSCs in situ have important roles in tissue cellular homeostasis by replacing dead or dysfunctional cells. Recent studies have demonstrated that in vitro expanded MSCs of various origins have great capacity to modulate immune responses and change the progression of different inflammatory diseases. As tissue injuries are often accompanied by inflammation, inflammatory factors may provide cues to mobilize MSCs to tissue sites with damage. Before carrying out tissue repair functions, MSCs first prepare the microenvironment by modulating inflammatory processes and releasing various growth factors in response to the inflammation status. In this review, we focus on the crosstalk between MSCs and immune responses and their potential clinical applications, especially in inflammatory diseases.

Inflammatory Cytokine-Induced Intercellular Adhesion Molecule-1 and Vascular Cell Adhesion Molecule-1 in Mesenchymal Stem Cells Are Critical for Immunosuppression

Cell–cell adhesion mediated by ICAM-1 and VCAM-1 is critical for T cell activation and leukocyte recruitment to the inflammation site and, therefore, plays an important role in evoking effective immune responses. However, we found that ICAM-1 and VCAM-1 were critical for mesenchymal stem cell (MSC)-mediated immunosuppression. When MSCs were cocultured with T cells in the presence of T cell Ag receptor activation, they significantly upregulated the adhesive capability of T cells due to the increased expression of ICAM-1 and VCAM-1. By comparing the immunosuppressive effect of MSCs toward various subtypes of T cells and the expression of these adhesion molecules, we found that the greater expression of ICAM-1 and VCAM-1 by MSCs, the greater the immunosuppressive capacity that they exhibited. Furthermore, ICAM-1 and VCAM-1 were found to be inducible by the concomitant presence of IFN-γ and inflammatory cytokines (TNF-α or IL-1). Finally, MSC-mediated immunosuppression was significantly reversed in vitro and in vivo when the adhesion molecules were genetically deleted or functionally blocked, which corroborated the importance of cell–cell contact in immunosuppression by MSCs. Taken together, these findings reveal a novel function of adhesion molecules in immunoregulation by MSCs and provide new insights for the clinical studies of antiadhesion therapies in various immune disorders.

Mesenchymal stem cells： a new strategy for immunosuppression and tissue repair

Mesenchymal stem cells (MSCs) have great potential for treating various diseases, especially those related to tissue damage involving immune reactions. Various studies have demonstrated that MSCs are strongly immunosuppressive in vitro and in vivo. Our recent studies have shown that un-stimulated MSCs are indeed incapable of immunosuppression; they become potently immunosuppressive upon stimulation with the supernatant of activated lymphocytes, or with combinations of IFN-γ with TNF-α, IL-1α or IL-1β. This observation revealed that under certain circumstances, inflammatory cytokines can actually become immunosuppressive. We showed that there is a species variation in the mechanisms of MSC-mediated immunosuppression: immunosuppression by cytokine-primed mouse MSCs is mediated by nitric oxide (NO), whereas immunosuppression by cytokine-primed human MSCs is executed through indoleamine 2, 3-dioxygenase (IDO). Additionally, upon stimulation with the inflammatory cytokines, both mouse and human MSCs secrete several leukocyte chemokines that apparently serve to attract immune cells into the proximity with MSCs, where NO or IDO is predicted to be most active. Therefore, immunosuppression by inflammatory cytokine-stimulated MSCs occurs via the concerted action of chemokines and immune-inhibitory NO or IDO produced by MSCs. Thus, our results provide novel information about the mechanisms of MSC-mediated immunosuppression and for better application of MSCs in treating tissue injuries induced by immune responses.