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Mesenchymal Stem Cells Cooperate with Bone Marrow Cells in Therapy of Diabetes

Several recent studies have suggested that the adult bone marrow harbors cells that can influence β‐cell regeneration in diabetic animals. Other reports, however, have contradicted these findings. To address this issue, we used an animal model of type 1 diabetes in which the disease was induced with streptozotocin in mice. Freshly prepared sex‐mismatched bone marrow cells (BMCs) and syngeneic or allogeneic mesenchymal stem cells (MSCs) were concomitantly administrated into sublethally irradiated diabetic mice. Blood glucose and serum insulin concentrations rapidly returned to normal levels, accompanied by efficient tissue regeneration after a single injection of a mixture of 106 BMCs per 105 MSCs. Neither BMC nor MSC transplantation was effective alone. Successful treatment of diabetic animals was not due to the reconstitution of the damaged islet cells from the transplant, since no donor‐derived β‐cells were found in the recovered animals, indicating a graft‐initiated endogenous repair process. Moreover, MSC injection caused the disappearance of β‐cell‐specific T lymphocytes from diabetic pancreas. Therefore, we suggest that two aspects of this successful treatment regimen operate in parallel and synergistically in our model. First, BMCs and MSCs induce the regeneration of recipient‐derived pancreatic insulin‐secreting cells. Second, MSCs inhibit T‐cell‐mediated immune responses against newly formed β‐cells, which, in turn, are able to survive in this altered immunological milieu. Thus, the application of this therapy in human patients suffering from diabetes and/or other tissue destructive autoimmune diseases may be feasible.

Biphasic Effect of Recombinant Galectin‐1 on the Growth and Death of Early Hematopoietic Cells

Galectin‐1 is a member of the family of β‐galactoside binding animal lectins, galectins. Its presence in the bone marrow has been detected; however, its role in the regulation of hematopoiesis is unknown. In the present study, we have evaluated the effect of recombinant human galectin‐1 on the proliferation and survival of murine and human hematopoietic stem and progenitor cells. We show that low amount of galectin‐1 (10 ng/ml) increases the formation of granulocyte‐macrophage and erythroid colonies and the frequencies of day‐7 cobblestone area–forming cells on a lactose‐inhibitable fashion. In contrast, high amount of galectin‐1 (10 μg/ml) dramatically reduces the growth of the committed blood‐forming progenitor cells as well as the much younger, lineage‐negative hematopoietic cells (day‐28 to −35 cobblestone area–forming cells). This inhibition is not blocked by lactose and, therefore, is largely independent of the β‐galactoside–binding site of the lectin. Furthermore, assays to detect apoptosis render it likely that the high amount of galectin‐1 acts as a classical proapoptotic factor for the premature hematopoietic cells.

Soluble Jagged-1 is able to inhibit the function of its multivalent form to induce hematopoietic stem cell self-renewal in a surrogate in vitro assay

Stem cells reside in customized microenvironments (niches) that contribute to their unique ability to divide asymmetrically to give rise to self and to a daughter cell with distinct properties. Notch receptors and their ligands are highly conserved and have been shown to regulate cell‐fate decisions in multiple developmental systems through local cell interactions. To assess whether Notch signaling may regulate hematopoiesis to maintain cells in an immature state, we examined the functional role of the recombinant, secreted form of the Notch ligand Jagged‐1 during mouse hematopoietic stem cell (HSC) and progenitor cell proliferation and maturation. We found that ligand immobilization on stromal layer or on Sepharose‐4B beads is required for the induction of self‐renewing divisions of days 28–35 cobblestone area‐forming cell. The free, soluble Jagged‐1, however, has a dominant‐negative effect on self‐renewal in the stem‐cell compartment. In contrast, free as well as immobilized Jagged‐1 promotes growth factor‐induced colony formation of committed hematopoietic progenitor cells. Therefore, we propose that differences in Jagged‐1 presentation and developmental stage of the Notch receptor‐bearing cells influence Notch ligand‐binding results toward activation or inhibition of downstream signaling. Moreover, these results suggest potential clinical use of recombinant Notch ligands for expanding human HSC populations in vitro.

Inappropriate notch activity and limited mesenchymal stem cell plasticity in the bone marrow of patients with myelodysplastic syndromes

Myelodysplastic syndromes (MDSs) are a heterogeneous group of hematological disorders characterized by ineffective hematopoiesis, enhanced bone marrow apoptosis and frequent progression to acute myeloid leukemia. Several recent studies suggested that, besides the abnormal development of stem cells, microenvironmental alterations are also present in the MDS bone marrow. In this study, we have examined the relative frequencies of stem and progenitor cell subsets of MDS and normal hematopoietic cells growing on stromal cell layers established from MDS patients and from normal donors. When hematopoietic cells from MDS patients were co-cultured with normal stromal cells, the frequency of either early or late cobblestone area-forming cells (CAFC) was significantly lower compared to the corresponding normal control values in 4 out of 8 patients. In the opposite situation, when normal hematopoietic cells were incubated on MDS stromal cells, the CAFC frequencies were decreased in 5 out of 6 patients, compared to normal stromal layer-containing control cultures. Moreover, a soluble Notch ligand (Jagged-1 protein) was an inhibitor of day-35-42 CAFC when normal hematopoietic cells were cultured with normal or MDS stromal cells, but was unable to inhibit MDS stem and early progenitor cell growth (day-35-42 CAFC) on pre-established stromal layers. These findings suggest that in early hematopoietic cells isolated from MDS patients the Notch signal transduction pathway is disrupted. Furthermore, there was a marked reduction in the plasticity of mesenchymal stem cells of MDS patients compared with those of normal marrow donors, in neurogenic and adipogenic differentiation ability and hematopoiesis supporting capacityin vitro. These results are consistent with the hypothesis that when alterations are present in the myelodysplastic stroma environment along with intrinsic changes in a hematopoietic stem/progenitor cell clone, both factors might equally contribute to the abnormal hematopoiesis in MDS.

In vitro expansion of long-term repopulating hematopoietic stem cells in the presence of immobilized Jagged-1 and early acting cytokines.

There is an increasing body of evidence that suggests that genes involved in cell fate decisions and pattern formation during development also play a key role in the continuous cell fate decisions made by adult tissue stem cells. Here we show that prolonged in vitro culture (14 days) of murine bone marrow lineage negative cells in medium supplemented with three early acting cytokines (stem cell factor, Flk‐2/Flt‐3 ligand, thrombopoietin) and with immobilized Notch ligand, Jagged‐1, resulted in robust expansion of serially transplantable hematopoietic stem cells with long‐term repopulating ability. We found that the absolute number of marrow cells was increased ∼8 to 14‐fold in all cultures containing recombinant growth factors. However, the frequency of high quality stem cells was markedly reduced at the same time, except in cultures containing growth factors and Jagged‐1‐coated Sepharose‐4B beads. The absolute number of hematopoietic cells with long‐term repopulating ability was increased ∼10 to 20‐fold in the presence of multivalent Notch ligand. These results support a role for combinatorial effects by Notch and cytokine‐induced signaling pathways in regulating hematopoietic stem cell fate and to a potential role for Notch ligand in increasing cell numbers in clinical stem cell transplantation.

Transcriptional characterization of the Notch signaling pathway in rodent multipotent adult progenitor cells

The Notch signaling pathway is a multifunctional, evolutionarily conserved pathway, which plays an important role in development as well as stem cell biology. Multipotent adult progenitor cells (MAPCs) represent a unique stem cell population, which is capable of differentiating into cell types of the ectodermal, mesodermal and endodermal lineages in vitro, and contribute to most somatic cell types in vivo. Our aim was to characterize the gene expression of Notch signaling elements in rodent MAPCs. We show that transcripts for Notch-receptors, ligands, regulatory molecules of the pathway and the Hairy/Enhancer of Split-1 (HES-1) target gene are present in mouse and rat low-Oct4 MAPCs. We found that mouse Notch3 and rat Notch1 transcripts increased when cells were cultured at high density for 48 to 96 hours. HES-1 and HES-related transcription factor-1 (HERP-1), transcriptional targets of Notch-signaling, were both elicited by immobilized Delta1 ligand. In addition, mRNA for Notch1 and Notch3 was also induced by Notch-signaling, suggesting the presence of regulatory feedback loops. Slight differences between mouse and rat derived MAPCs suggest that the exact function, transcriptional regulation and the fine-tuning of the signal may be species specific. Taken together, we characterized the gene expression profile of the Notch pathway in rodent low-Oct4-MAPCs, and showed that the pathway is functional and can be modulated. Our results provide an additional tool and a further basis for a better understanding of stem cell biology.

The scaffold protein Tks4 is required for the differentiation of mesenchymal stromal cells (MSCs) into adipogenic and osteogenic lineages.

The commitment steps of mesenchymal stromal cells (MSCs) to adipogenic and other lineages have been widely studied but not fully understood. Therefore, it is critical to understand which molecules contribute to the conversion of stem cells into differentiated cells. The scaffold protein Tks4 plays a role in podosome formation, EGFR signaling and ROS production. Dysfunction of Tks4 causes a hereditary disease called Frank-ter Haar syndrome with a variety of defects concerning certain mesenchymal tissues (bone, fat and cartilage) throughout embryogenic and postnatal development. In this study, we aimed to analyze how the mutation of Tks4 affects the differentiation potential of multipotent bone marrow MSCs (BM-MSCs). We generated a Tks4 knock-out mouse strain on C57Bl/6 background, and characterized BM-MSCs isolated from wild type and Tks4−/− mice to evaluate their differentiation. Tks4−/− BM-MSCs had reduced ability to differentiate into osteogenic and adipogenic lineages compared to wild type. Studying the expression profile of a panel of lipid-regulated genes during adipogenic induction revealed that the expression of adipogenic transcription factors, genes responsible for lipid droplet formation, sterol and fatty acid metabolism was delayed or reduced in Tks4−/− BM-MSCs. Taken together, these results establish a novel function for Tks4 in the regulation of MSC differentiation.

A mesenchymalis őssejtek és az immunrendszer – immunszuppresszió gyógyszerek nélkül?@@@Mesenchymal stem cells and the immune system – Immunosuppression without drugs

Mesenchymal stem cells (MSC) - isolated from various tissues in humans and other species - are one of the most promising adult stem cell types due to their availability and the relatively simple requirements for in vitro expansion. They have the capacity to differentiate into several tissues, including bone, cartilage, tendon, muscle and adipose, and produce growth factors and cytokines that promote hematopoietic cell expansion and differentiation. In vivo, MSCs are able to repair damaged tissue from kidney, heart, liver, pancreas and gastrointestinal tract. Furthermore, they also have anti-proliferative, immunomodulatory and anti-inflammatory effects, but evoke only little immune reactivity. Although the mechanism underlying the immunosuppressive effects of MSCs has not been clearly defined, their immunosuppressive properties have already been exploited in the clinical setting. Therefore, in the future, MSCs might have implications for treatment of allograft rejection, graft-versus-host disease, rheumatoid arthritis, autoimmune inflammatory bowel disease and other disorders in which immunomodulation and tissue repair are required. The aim of this review is to critically analyze the field of MSC biology, particularly with respect to their immunomodulatory properties and potential clinical use in the future.

A mesenchymalis ôssejtek és az immunrendszer - immunszuppresszió gyógyszerek nélkül?

Mesenchymal stem cells (MSC) - isolated from various tissues in humans and other species - are one of the most promising adult stem cell types due to their availability and the relatively simple requirements for in vitro expansion. They have the capacity to differentiate into several tissues, including bone, cartilage, tendon, muscle and adipose, and produce growth factors and cytokines that promote hematopoietic cell expansion and differentiation. In vivo, MSCs are able to repair damaged tissue from kidney, heart, liver, pancreas and gastrointestinal tract. Furthermore, they also have anti-proliferative, immunomodulatory and anti-inflammatory effects, but evoke only little immune reactivity. Although the mechanism underlying the immunosuppressive effects of MSCs has not been clearly defined, their immunosuppressive properties have already been exploited in the clinical setting. Therefore, in the future, MSCs might have implications for treatment of allograft rejection, graft-versus-host disease, rheumatoid arthritis, autoimmune inflammatory bowel disease and other disorders in which immunomodulation and tissue repair are required. The aim of this review is to critically analyze the field of MSC biology, particularly with respect to their immunomodulatory properties and potential clinical use in the future.

Alternative views of tissue stem cell plasticity.

Stem cells have traditionally been characterized as either embryonic (pluripotent) or tissue-specific (multipotent). Thus, tissue-specific stem cells generate the cell types comprising a particular tissue in embryos and, in some cases, adults. A recent series of studies, however, has challenged the notion of lineage restriction in multipotent stem cells. These experiments have been interpreted as evidence that stem cells from one tissue can be induced to differentiate into cells of other organs, either in vitro or after transplantation in vivo. This paper reviews the current evidence for stem cell plasticity. Some of the potential caveats to the current work are also discussed and, finally, the potential underlying mechanisms of stem cell plasticity are examined.