RESUMEN
Thymocyte differentiation is dependent on the availability and transport of metabolites in the thymus niche. As expression of metabolite transporters is a rate-limiting step in nutrient utilization, cell surface transporter levels generally reflect the cell's metabolic state. The GLUT1 glucose transporter is upregulated on actively dividing thymocytes, identifying thymocytes with an increased metabolism. However, it is not clear whether transporters of essential elements such as phosphate are modulated during thymocyte differentiation. While PiT1 and PiT2 are both phosphate transporters in the SLC20 family, we show here that they exhibit distinct expression profiles on both murine and human thymocytes. PiT2 expression distinguishes thymocytes with high metabolic activity, identifying immature murine double negative (CD4-CD8-) DN3b and DN4 thymocyte blasts as well as immature single positive (ISP) CD8 thymocytes. Notably, the absence of PiT2 expression on RAG2-deficient thymocytes, blocked at the DN3a stage, strongly suggests that high PiT2 expression is restricted to thymocytes having undergone a productive TCRß rearrangement at the DN3a/DN3b transition. Similarly, in the human thymus, PiT2 was upregulated on early post-ß selection CD4+ISP and TCRαß-CD4hiDP thymocytes co-expressing the CD71 transferrin receptor, a marker of metabolic activity. In marked contrast, expression of the PiT1 phosphate importer was detected on mature CD3+ murine and human thymocytes. Notably, PiT1 expression on CD3+DN thymocytes was identified as a biomarker of an aging thymus, increasing from 8.4 ± 1.5% to 42.4 ± 9.4% by 1 year of age (p < 0.0001). We identified these cells as TCRγδ and, most significantly, NKT, representing 77 ± 9% of PiT1+DN thymocytes by 1 year of age (p < 0.001). Thus, metabolic activity and thymic aging are associated with distinct expression profiles of the PiT1 and PiT2 phosphate transporters.
Asunto(s)
Diferenciación Celular , Proteínas de Transporte de Fosfato/metabolismo , Timocitos/metabolismo , Animales , Biomarcadores , Diferenciación Celular/genética , Perfilación de la Expresión Génica , Transportador de Glucosa de Tipo 1/genética , Transportador de Glucosa de Tipo 1/metabolismo , Humanos , Inmunofenotipificación , Subgrupos Linfocitarios/inmunología , Subgrupos Linfocitarios/metabolismo , Ratones , Ratones Noqueados , Proteínas de Transporte de Fosfato/genética , Proteínas Cotransportadoras de Sodio-Fosfato de Tipo III/genética , Proteínas Cotransportadoras de Sodio-Fosfato de Tipo III/metabolismo , Timocitos/citología , Timocitos/inmunología , Timo/citología , Timo/inmunología , Timo/metabolismo , TranscriptomaRESUMEN
T cell activation requires that the cell meet increased energetic and biosynthetic demands. We showed that exogenous nutrient availability regulated the differentiation of naïve CD4(+) T cells into distinct subsets. Activation of naïve CD4(+) T cells under conditions of glutamine deprivation resulted in their differentiation into Foxp3(+) (forkhead box P3-positive) regulatory T (Treg) cells, which had suppressor function in vivo. Moreover, glutamine-deprived CD4(+) T cells that were activated in the presence of cytokines that normally induce the generation of T helper 1 (TH1) cells instead differentiated into Foxp3(+) Treg cells. We found that α-ketoglutarate (αKG), the glutamine-derived metabolite that enters into the mitochondrial citric acid cycle, acted as a metabolic regulator of CD4(+) T cell differentiation. Activation of glutamine-deprived naïve CD4(+) T cells in the presence of a cell-permeable αKG analog increased the expression of the gene encoding the TH1 cell-associated transcription factor Tbet and resulted in their differentiation into TH1 cells, concomitant with stimulation of mammalian target of rapamycin complex 1 (mTORC1) signaling. Together, these data suggest that a decrease in the intracellular amount of αKG, caused by the limited availability of extracellular glutamine, shifts the balance between the generation of TH1 and Treg cells toward that of a Treg phenotype.
Asunto(s)
Diferenciación Celular/inmunología , Glutamina/inmunología , Ácidos Cetoglutáricos/inmunología , Linfocitos T Reguladores/inmunología , Células TH1/inmunología , Animales , Glutamina/metabolismo , Ácidos Cetoglutáricos/metabolismo , Diana Mecanicista del Complejo 1 de la Rapamicina , Ratones , Complejos Multiproteicos/inmunología , Complejos Multiproteicos/metabolismo , Linfocitos T Reguladores/metabolismo , Serina-Treonina Quinasas TOR/inmunología , Serina-Treonina Quinasas TOR/metabolismo , Células TH1/metabolismoRESUMEN
Mitochondrial activity is central to tissue homeostasis. Mitochondria dysfunction constitutes a hallmark of many genetic diseases and plays a key role in tumor progression. The essential role of mitochondria, added to their recently documented capacity to transfer from cell to cell, obviously contributes to their current interest. However, determining the proper role of mitochondria in defined biological contexts was hampered by the lack of suitable experimental tools. We designed a protocol (MitoCeption) to directly and quantitatively transfer mitochondria, isolated from cell type A, to recipient cell type B. We validated and quantified the effective mitochondria transfer by imaging, fluorescence-activated cell sorting (FACS) and mitochondrial DNA analysis. We show that the transfer of minute amounts of mesenchymal stem/stromal cell (MSC) mitochondria to cancer cells, a process otherwise occurring naturally in coculture, results in cancer cell enhanced oxidative phosphorylation (OXPHOS) activity and favors cancer cell proliferation and invasion. The MitoCeption technique, which can be applied to different cell systems, will therefore be a method of choice to analyze the metabolic modifications induced by exogenous mitochondria in host cells.
Asunto(s)
Células Madre Mesenquimatosas/metabolismo , Metabolómica/métodos , Mitocondrias/metabolismo , Neoplasias/metabolismo , Adenosina Trifosfato/biosíntesis , Línea Celular Tumoral , Movimiento Celular , Proliferación Celular , Técnicas de Cocultivo , Citometría de Flujo , Humanos , Reproducibilidad de los Resultados , Imagen de Lapso de TiempoRESUMEN
The metabolic state of quiescent hematopoietic stem cells (HSCs) is an important regulator of self-renewal, but it is unclear whether or how metabolic parameters contribute to HSC lineage specification and commitment. Here, we show that the commitment of human and murine HSCs to the erythroid lineage is dependent upon glutamine metabolism. HSCs require the ASCT2 glutamine transporter and active glutamine metabolism for erythroid specification. Blocking this pathway diverts EPO-stimulated HSCs to differentiate into myelomonocytic fates, altering in vivo HSC responses and erythroid commitment under stress conditions such as hemolytic anemia. Mechanistically, erythroid specification of HSCs requires glutamine-dependent de novo nucleotide biosynthesis. Exogenous nucleosides rescue erythroid commitment of human HSCs under conditions of limited glutamine catabolism, and glucose-stimulated nucleotide biosynthesis further enhances erythroid specification. Thus, the availability of glutamine and glucose to provide fuel for nucleotide biosynthesis regulates HSC lineage commitment under conditions of metabolic stress.
Asunto(s)
Sistema de Transporte de Aminoácidos ASC/metabolismo , Linaje de la Célula , Regulación de la Expresión Génica , Glucosa/metabolismo , Glutamina/metabolismo , Células Madre Hematopoyéticas/citología , ADP-Ribosil Ciclasa 1/metabolismo , Animales , Antígenos CD34/metabolismo , Transporte Biológico , Diferenciación Celular , Cromatografía Liquida , Eritrocitos/citología , Glucólisis , Proteínas Fluorescentes Verdes/metabolismo , Humanos , Espectrometría de Masas , Ratones , Ratones Endogámicos C57BL , Antígenos de Histocompatibilidad Menor , ARN Interferente Pequeño/metabolismoRESUMEN
Cells respond to stress by coordinating proliferative and metabolic pathways. Starvation restricts cell proliferative (glycolytic) and activates energy productive (oxidative) pathways. Conversely, cell growth and proliferation require increased glycolytic and decreased oxidative metabolism levels. E2F transcription factors regulate both proliferative and metabolic genes. E2Fs have been implicated in the G1/S cell-cycle transition, DNA repair, apoptosis, development and differentiation. In pancreatic ß-cells, E2F1 gene regulation facilitated glucose-stimulated insulin secretion. Moreover, mice lacking E2F1 (E2f1(-/-)) were resistant to diet-induced obesity. Here, we show that E2F1 coordinates cellular responses by acting as a regulatory switch between cell proliferation and metabolism. In basal conditions, E2F1 repressed key genes that regulate energy homeostasis and mitochondrial functions in muscle and brown adipose tissue. Consequently, E2f1(-/-) mice had a marked oxidative phenotype. An association between E2F1 and pRB was required for repression of genes implicated in oxidative metabolism. This repression was alleviated in a constitutively active CDK4 (CDK4(R24C)) mouse model or when adaptation to energy demand was required. Thus, E2F1 represents a metabolic switch from oxidative to glycolytic metabolism that responds to stressful conditions.
Asunto(s)
Tejido Adiposo Pardo/metabolismo , Factor de Transcripción E2F1/metabolismo , Metabolismo Energético , Músculo Esquelético/metabolismo , Tejido Adiposo Pardo/citología , Animales , Proliferación Celular , Células Cultivadas , Quinasa 4 Dependiente de la Ciclina/genética , Quinasa 4 Dependiente de la Ciclina/metabolismo , Metilación de ADN , Factor de Transcripción E2F1/genética , Embrión de Mamíferos/citología , Fibroblastos/citología , Fibroblastos/metabolismo , Perfilación de la Expresión Génica , Immunoblotting , Ratones , Ratones Noqueados , Microscopía Fluorescente , Mitocondrias/metabolismo , Fibras Musculares Esqueléticas/citología , Fibras Musculares Esqueléticas/metabolismo , Músculo Esquelético/citología , Músculo Esquelético/ultraestructura , Mioblastos/citología , Mioblastos/metabolismo , Consumo de Oxígeno , Interferencia de ARN , Proteína de Retinoblastoma/genética , Proteína de Retinoblastoma/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa InversaRESUMEN
Increased de novo fatty acid (FA) synthesis is one hallmark of tumor cells, including prostate cancer. We present here our most recent results showing that lipid composition in human prostate cancer is characterized by an increased ratio of monounsaturated FA to saturated FA, compared with normal prostate, and evidence the overexpression of the lipogenic enzyme stearoyl-CoA desaturase 1 (SCD1) in human prostate cancer. As a new therapeutic strategy, we show that pharmacologic inhibition of SCD1 activity impairs lipid synthesis and results in decreased proliferation of both androgen-sensitive and androgen-resistant prostate cancer cells, abrogates the growth of prostate tumor xenografts in nude mice, and confers therapeutic benefit on animal survival. We show that these changes in lipid synthesis are translated into the inhibition of the AKT pathway and that the decrease in concentration of phosphatidylinositol-3,4,5-trisphosphate might at least partially mediate this effect. Inhibition of SCD1 also promotes the activation of AMP-activated kinase and glycogen synthase kinase 3alpha/beta, the latter on being consistent with a decrease in beta-catenin activity and mRNA levels of various beta-catenin growth-promoting transcriptional targets. Furthermore, we show that SCD1 activity is required for cell transformation by Ras oncogene. Together, our data support for the first time the concept of targeting the lipogenic enzyme SCD1 as a new promising therapeutic approach to block oncogenesis and prostate cancer progression.
Asunto(s)
Progresión de la Enfermedad , Lipogénesis , Neoplasias de la Próstata/enzimología , Neoplasias de la Próstata/patología , Transducción de Señal/efectos de los fármacos , Estearoil-CoA Desaturasa/antagonistas & inhibidores , Animales , Línea Celular Transformada , Línea Celular Tumoral , Proliferación Celular/efectos de los fármacos , Supervivencia Celular/efectos de los fármacos , Inhibidores Enzimáticos/farmacología , Ácidos Grasos Monoinsaturados/metabolismo , Fibroblastos/efectos de los fármacos , Fibroblastos/patología , Humanos , Lipogénesis/efectos de los fármacos , Masculino , Ratones , Estearoil-CoA Desaturasa/metabolismo , Proteína p53 Supresora de Tumor/metabolismo , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
BACKGROUND: Micro RNAs are small, non-coding, single-stranded RNAs that negatively regulate gene expression at the post-transcriptional level. Since miR-143 was found to be down-regulated in prostate cancer cells, we wanted to analyze its expression in human prostate cancer, and test the ability of miR-43 to arrest prostate cancer cell growth in vitro and in vivo. RESULTS: Expression of miR-143 was analyzed in human prostate cancers by quantitative PCR, and by in situ hybridization. miR-143 was introduced in cancer cells in vivo by electroporation. Bioinformatics analysis and luciferase-based assays were used to determine miR-143 targets. We show in this study that miR-143 levels are inversely correlated with advanced stages of prostate cancer. Rescue of miR-143 expression in cancer cells results in the arrest of cell proliferation and the abrogation of tumor growth in mice. Furthermore, we show that the effects of miR-143 are mediated, at least in part by the inhibition of extracellular signal-regulated kinase-5 (ERK5) activity. We show here that ERK5 is a miR-143 target in prostate cancer. CONCLUSIONS: miR-143 is as a new target for prostate cancer treatment.
Asunto(s)
MicroARNs/metabolismo , Proteína Quinasa 7 Activada por Mitógenos/metabolismo , Neoplasias de la Próstata/metabolismo , Transducción de Señal , Animales , Línea Celular Tumoral , Biología Computacional/métodos , Progresión de la Enfermedad , Electroporación , Humanos , Hibridación in Situ , Masculino , Ratones , Ratones DesnudosRESUMEN
Prostate cancer metastasis to bone results in mixed osteolytic and osteoblastic lesions associated with high morbidity, and there is mounting evidence that the urokinase-type plasminogen system is causatively involved in the progression of prostate cancer. Adult mesenchymal stem cells (MSCs) are promising tools for cell-mediated gene therapy with the advantage of osteogenic potential, a critical issue in the case of osteolytic metastases. In this study, we evaluated the therapeutic use of engineered murine MSCs for in vivo delivery of the urokinase-type plasminogen antagonist amino-terminal fragment (hATF) to impair osteolytic prostate cancer cell progression in bone and to repair bone lesions. Bioluminescence imaging revealed that both primary MSCs and the MSC line C3H10T1/2 (C3) expressing hATF (MSC-hATF) significantly inhibited intratibial PC-3 Luciferase (Luc) growth following coinjection in SCID mice. Furthermore, microcomputed tomography imaging of vascular network clearly demonstrated a significant decrease in tumor-associated angiogenesis and a protection from tumor-induced osteolysis in MSC-hATF-treated mice. Importantly, the osteogenic potential of MSC-hATF cells was unaffected, and an area of new bone formation was evidenced in 60% of animals. Together, these data support the concept of MSC-based therapy of tumor osteolysis disease, indicating that MSCs may combine properties of vehicle for angiostatic agent with osteogenic potential. Disclosure of potential conflicts of interest is found at the end of this article.
Asunto(s)
Neoplasias Óseas/terapia , Células Madre Mesenquimatosas/citología , Fragmentos de Péptidos/biosíntesis , Neoplasias de la Próstata/terapia , Activador de Plasminógeno de Tipo Uroquinasa/antagonistas & inhibidores , Adenoviridae/genética , Animales , Neoplasias Óseas/irrigación sanguínea , Neoplasias Óseas/secundario , Comunicación Celular , Línea Celular Tumoral , Estudios de Factibilidad , Masculino , Trasplante de Células Madre Mesenquimatosas/métodos , Células Madre Mesenquimatosas/metabolismo , Ratones , Ratones SCID , Neovascularización Patológica/terapia , Osteogénesis , Osteólisis/patología , Osteólisis/terapia , Fragmentos de Péptidos/genética , Neoplasias de la Próstata/irrigación sanguínea , Neoplasias de la Próstata/patología , Receptores del Activador de Plasminógeno Tipo Uroquinasa/metabolismo , Activador de Plasminógeno de Tipo Uroquinasa/metabolismoRESUMEN
Mesenchymal stem cells (MSCs) from post-natal bone marrow possess tremendous potential for cell-mediated gene therapy in several disease processes, and recent reports have broadened the spectrum for therapeutic applications to cancer therapy. The evidence that sites of active tumorigenesis favor the homing of exogenous MSCs have support the rationale for developing engineered MSCs as a tool to track malignant tissues and deliver anticancer agents within the tumor microenvironment. Several reports have proven the efficiency of MSCs as cell carrier for in vivo delivery of various clinically relevant anticancer factors, including cytokines, interferon, pro-drugs or replicative adenovirus, and tumor growth inhibition following engraftment within or in the vicinity of tumor. The enthusiasm for MSCs is further reinforced by the striking observation that unmodified MSCs can exert antitumorigenic activity, and preliminary reports in immunocompetent animals have provided encouraging results for the use of MSCs in cancer immunotherapy. This review highlights recent works and potential clinical applications of MSCs in this field.
Asunto(s)
Terapia Genética/métodos , Trasplante de Células Madre Mesenquimatosas , Células Madre Mesenquimatosas/fisiología , Neoplasias/terapia , Animales , Células de la Médula Ósea/fisiología , Movimiento Celular/fisiología , Marcación de Gen/métodos , Genes Transgénicos Suicidas/fisiología , Vectores Genéticos/fisiología , Humanos , Inmunoterapia/métodos , Células Madre Mesenquimatosas/metabolismo , Neoplasias/genética , Tropismo/fisiologíaRESUMEN
Prostate cancer (CaP) cells possess high affinity for bone marrow and predilection to induce bone metastasis. Although the end result of metastasis is predominantly osteoblastic, most patients present mixed lesions with osteolytic component which could initiate and precede bone formation. A precise characterization of tumor-induced bone resorption is thus necessary for early evaluation of therapeutic efficiency. Herein, we investigate the advantage of combining micro-computed tomography (microCT) and in vivo bioluminescence imaging (BLI) to determine the kinetics of the intraosseous CaP growth and bone lesions appearance in an experimental murine model. To mimic established osteolytic bone metastasis, the left tibiae of SCID mice were injected with the human CaP cell line PC-3 expressing luciferase (PC-3 Luc). Noninvasive monitoring of tumor progression was followed weekly by BLI during 4 weeks and bone morphometric parameters were quantified by microCT. Data were compared with conventional radiological and histological analyses. While BLI monitoring in vivo revealed an exponential growth of PC-3 Luc after 2 weeks, a decrease of bone density and bone mineral content was evidenced by microCT as early as 7 days post-injection, reaching significant values at day 21 (30% and 25% loss, respectively), compared with mock-injected controls. Enhanced osteoclast TRAP activity was observed during the first two weeks, highlighting an active interaction between low proliferative PC-3 cells and osteoclasts at the early stage of tumor establishment in bone. Tumor growth detected by BLI was tightly correlated to the osteolysis assessed by microCT (p<0.05). Our results show that the combination of microCT and BLI applied to this tumor osteolysis murine model allows early measurement of intraosseous tumor growth and bone destruction, as well as correlation between both processes kinetics. This model will help to assess new therapeutic approaches targeting intraosseous tumor growth or tumor/osteoclast crosstalk.
Asunto(s)
Neoplasias Óseas/patología , Neoplasias Óseas/secundario , Osteólisis/patología , Animales , Neoplasias Óseas/diagnóstico por imagen , Línea Celular Tumoral , Femenino , Humanos , Luciferasas/genética , Mediciones Luminiscentes , Masculino , Ratones , Ratones SCID , Trasplante de Neoplasias , Osteólisis/diagnóstico por imagen , Neoplasias de la Próstata , Proteínas Recombinantes/genética , Tomografía Computarizada por Rayos X , Trasplante HeterólogoRESUMEN
Peroxisome proliferator-activated receptor gamma (PPARgamma) might not be permissive to ligand activation in prostate cancer cells. Association of PPARgamma with repressing factors or posttranslational modifications in PPARgamma protein could explain the lack of effect of PPARgamma ligands in a recent randomized clinical trial. Using cells and prostate cancer xenograft mouse models, we demonstrate in this study that a combination treatment using the PPARgamma agonist pioglitazone and the histone deacetylase inhibitor valproic acid is more efficient at inhibiting prostate tumor growth than each individual therapy. We show that the combination treatment impairs the bone-invasive potential of prostate cancer cells in mice. In addition, we demonstrate that expression of E-cadherin, a protein involved in the control of cell migration and invasion, is highly up-regulated in the presence of valproic acid and pioglitazone. We show that E-cadherin expression responds only to the combination treatment and not to single PPARgamma agonists, defining a new class of PPARgamma target genes. These results open up new therapeutic perspectives in the treatment of prostate cancer.
Asunto(s)
Cadherinas/metabolismo , PPAR gamma/metabolismo , Neoplasias de la Próstata/metabolismo , Neoplasias de la Próstata/patología , Animales , Cadherinas/genética , Línea Celular Tumoral , Proliferación Celular/efectos de los fármacos , Modelos Animales de Enfermedad , Progresión de la Enfermedad , Quimioterapia Combinada , Inhibidores Enzimáticos/farmacología , Regulación Neoplásica de la Expresión Génica , Inhibidores de Histona Desacetilasas , Histona Desacetilasas/metabolismo , Humanos , Masculino , Ratones , Invasividad Neoplásica/patología , Trasplante de Neoplasias , PPAR gamma/agonistas , PPAR gamma/genética , Fosforilación/efectos de los fármacos , Pioglitazona , Neoplasias de la Próstata/tratamiento farmacológico , Neoplasias de la Próstata/genética , ARN Mensajero/genética , Proteína de Retinoblastoma/metabolismo , Tiazolidinedionas/uso terapéutico , Ácido Valproico/uso terapéuticoRESUMEN
Neurospheres (NSs) are clonal cellular aggregates composed of neural stem cells and progenitors. A comprehensive description of their proliferation and differentiation regulation is an essential prerequisite for their use in biotherapies. Cytokines are essential molecules regulating cell precursor fate. Using a gene-array strategy, we conducted a descriptive and functional analysis of endogenous cytokines and receptors expressed by spinal cord-derived NSs during their growth or their differentiation into neuronal and glial cells. NSs were found to express approximately 100 receptor subunits and cytokine/secreted developmental factors. Several angiogenic factors and receptors that could mediate neural precursor cell-endothelial cell relationships were detected. Among them, receptor B for endothelins was highly expressed, and endothelins were found to increase NS growth. In contrast, NSs express receptors for ciliary neurotrophic factor (CNTF), bone morphogenetic protein (BMP), interferon (IFN)-gamma, or tumor necrosis factor (TNF)-alpha, which, when added in the growth phase, led to a dramatic growth reduction followed by a reduction or a loss of oligodendrocyte formation on differentiation. In addition, NSs synthesize fibroblast growth factor 2/epidermal growth factor (FGF2/EGF)-regulated endogenous cytokines that participate in their growth and differentiation. Notably, BMP-7 and CNTF were expressed during expansion, but upon differentiation there was a remarkable switch from BMP-7 to BMP-4 and -6 and a sharp increase of CNTF. Reintroduction of growth factors reverses the BMP expression profile, indicating growth factor-BMP cross-regulations. The role of endogenous CNTF was investigated by deriving NSs from CNTF knockout mice. These NSs have an increased growth rate associated with reduction of apoptosis and generate astrocytes with a reduced glial fibulary acidic protein (GFAP) content. These results demonstrate the combined role of endogenous and exogenous cytokines in neural precursor cell growth and differentiation.
Asunto(s)
Proliferación Celular , Factor de Crecimiento Epidérmico/metabolismo , Ganglios Espinales/fisiología , Receptor Tipo 2 de Factor de Crecimiento de Fibroblastos/metabolismo , Células Madre/fisiología , Animales , Diferenciación Celular/efectos de los fármacos , Proliferación Celular/efectos de los fármacos , Células Cultivadas , Factor de Crecimiento Epidérmico/farmacología , Ganglios Espinales/citología , Ratones , Ratones Transgénicos , Neuronas/citología , Neuronas/fisiología , Oligodendroglía/citología , Oligodendroglía/fisiología , Receptor Tipo 2 de Factor de Crecimiento de Fibroblastos/farmacología , Células Madre/citologíaRESUMEN
OBJECTIVE: Adult mesenchymal stem cells (MSCs) represent promising tools for therapeutic applications such as tissue engineering and cellular therapy. Recent data suggest that, due to their immunosuppressive nature, MSCs may be of interest to enhance allogeneic hematopoietic engraftment and prevent graft-versus-host disease. Using a murine model of rheumatoid arthritis (RA), this study investigated whether the immunosuppressive properties of MSCs could be of therapeutic value to inhibit reactive T cells in autoimmune diseases such as RA. METHODS: In mice with collagen-induced arthritis (CIA), we injected various doses of C3 MSCs at the time of immunization or booster injection, and subsequently evaluated the clinical and immunologic parameters. The immunosuppressive properties of MSCs were determined in vitro in mixed lymphocyte reactions with or without the addition of tumor necrosis factor alpha (TNFalpha). RESULTS: In the CIA model of arthritis, MSCs did not confer any benefit. Both the clinical and the immunologic findings suggested that MSCs were associated with accentuation of the Th1 response. Using luciferase-expressing MSCs, we were unable to detect labeled cells in the articular environment of the knee, suggesting that worsening of the symptoms was unlikely due to the homing of MSCs in the joints. Experiments in vitro showed that the addition of TNFalpha was sufficient to reverse the immunosuppressive effect of MSCs on T cell proliferation, and this observation was associated with an increase in interleukin-6 secretion. CONCLUSION: Our data suggest that environmental parameters, in particular those related to inflammation, may influence the immunosuppressive properties of MSCs.