doi:10.1182/blood-2004-01-0373Prepublished online March 11, 2004;€€€€R Bornstein, Helmut L Haas, Guido Kobbe, Daniel G Tenen, Rainer Haas and Ralf KronenwettSchroeder, Ulrich P Rohr, Roland Fenk, Slawomir Kliszewski, Christian Maercker, Peter Neubert, Stefan Ulrich Steidl, Simone Bork, Sebastian Schaub, Oliver Selbach, Janette Seres, Manuel Aivado, Thomas€

The promising use of mesenchymal stromal cells (MSC) in regenerative technologies accounts for necessity of detailed study of their physiology. Proliferation and differentiation of multipotent cells often involve changes in their metabolic state. In the present study, we analyzed the expression of ATP-sensitive potassium (KATP) channels in MSC and upon in vitro differentiation. KATP channels are present in many cells and regulate a variety of cellular functions by coupling cell metabolism with membrane potential. Kir6.1, Kir6.2 and SUR2A were expressed in undifferentiated MSC, whereas SUR2B and SUR1 were not detected on cDNA and protein level. Upon adipogenic differentiation Kir6.1 and SUR2A showed a significant reduction of the amount of mRNA by 84% and 95%, respectively, whereas Kir6.2 expression was unchanged. Osteogenic differentiation strongly up-regulated Kir6.2 mRNA (28-fold) whereas Kir6.1 and SUR2A showed no significant change in expression. Quantitative Western blot analysis and immunofluorescence staining confirmed the elevated expression of Kir6.2 upon osteogenic differentiation. Taken together, expression changes of KATP channels may contribute to in vitro differentiation of MSC and represent changes in the metabolic state of the developing tissue.

Epigenetic modifications of cytosine residues in the DNA play a critical role for cellular differentiation and potentially also for aging. In mesenchymal stromal cells (MSC) from human bone marrow we have previously demonstrated age-associated methylation changes at specific CpG-sites of developmental genes. In continuation of this work, we have now isolated human dermal fibroblasts from young (<23 years) and elderly donors (>60 years) for comparison of their DNA methylation profiles using the Infinium HumanMethylation27 assay. In contrast to MSC, fibroblasts could not be induced towards adipogenic, osteogenic and chondrogenic lineage and this is reflected by highly significant differences between the two cell types: 766 CpG sites were hyper-methylated and 752 CpG sites were hypo-methylated in fibroblasts in comparison to MSC. Strikingly, global DNA methylation profiles of fibroblasts from the same dermal region clustered closely together indicating that fibroblasts maintain positional memory even after in vitro culture. 75 CpG sites were more than 15% differentially methylated in fibroblasts upon aging. Very high hyper-methylation was observed in the aged group within the INK4A/ARF/INK4b locus and this was validated by pyrosequencing. Age-associated DNA methylation changes were related in fibroblasts and MSC but they were often regulated in opposite directions between the two cell types. In contrast, long-term culture associated changes were very consistent in fibroblasts and MSC. Epigenetic modifications at specific CpG sites support the notion that aging represents a coordinated developmental mechanism that seems to be regulated in a cell type specific manner.

Human mesenchymal stromal cells (MSC) raise high hopes for tissue engineering and therapeutic -applications. So far, it is not possible to isolate pure fractions from bone marrow and therefore MSC cell preparations notoriously represent heterogeneous mixtures of different cell types. The composition of -subpopulations can already be affected by the initial steps of cell preparation. Usually, isolation of MSC involves density fractionation to separate the mononuclear cells (MNCs) from erythrocytes and -granulocytes. However, this method is difficult to standardize especially under GMP conditions. Here, we describe an alternative approach for isolation of human MSC based on red blood cell (RBC) lysis with ammonium chloride. This results in a slightly higher number of fibroblastic colony forming units (CFU-F), whereas morphological analysis of the CFU-F reveals the same heterogeneous composition of MSC cultures indicating that the proportion of subpopulations is not affected by RBC lysis. Immunophenotype (CD73+, CD90+, CD105+, CD31-, CD34-, CD45-), adipogenic, and osteogenic differentiation potential of MSC were also similar with both methods. In conclusion, RBC lysis comprises an efficient method for the isolation of human MSC from bone marrow aspirate. This technique is faster and can be standardized more easily for clinical application of MSC.

Background Research on mesenchymal stromal cells has created high expectations for a variety of therapeutic applications. Extensive propagation to yield enough mesenchymal stromal cells for therapy may result in replicative senescence and thus hamper long-term functionality in vivo. Highly variable proliferation rates of mesenchymal stromal cells in the course of long-term expansions under varying culture conditions may already indicate different propensity for cellular senescence. We hypothesized that senescence-associated regulated genes differ in mesenchymal stromal cells propagated under different culture conditions.Design and Methods Human bone marrow-derived mesenchymal stromal cells were cultured either by serial passaging or by a two-step protocol in three different growth conditions. Culture media were supplemented with either fetal bovine serum in varying concentrations or pooled human platelet lysate.Results All mesenchymal stromal cell preparations revealed significant gene expression changes upon long-term culture. Especially genes involved in cell differentiation, apoptosis and cell death were up-regulated, whereas genes involved in mitosis and proliferation were down-regulated. Furthermore, overlapping senescence-associated gene expression changes were found in all mesenchymal stromal cell preparations.Conclusions Long-term cell growth induced similar gene expression changes in mesenchymal stromal cells independently of isolation and expansion conditions. In advance of therapeutic application, this panel of genes might offer a feasible approach to assessing mesenchymal stromal cell quality with regard to the state of replicative senescence.

Abstract Abstract 4775 Background: Based on promising experimental studies with mesenchymal stem and progenitor cells (MSPCs) multiple clinical trials have been initiated. In previous studies we have observed genomic stability of MSPCs after efficient short-term expansion in a humanized GMP compliant system with pooled human platelet lysate (pHPL) replacing fetal bovine serum (FBS) as the cell culture supplement (Schallmoser K. and Strunk D., Journal of Visualized Experiments (32) DOI: 10.3791/1523, 2009). Notably, depending on culture protocols, an extensive propagation with highly variable cell culture duration may be necessary to yield enough MSPCs for therapy. The decline in proliferation rates of MSPCs in the course of the different long-term expansion procedures may indicate a propensity for replicative senescence which may hamper long term functionality in vivo. We have therefore initiated a molecular profiling of senescence-associated regulated genes to determine the state of senescence before MSPC transplantation. Methods: Human bone marrow-derived MSPCs were cultured following a highly efficient two-passage protocol (primary culture of unseparated bone marrow and subsequent large scale expansion; Schallmoser K. et al., Tissue Engineering 14:185-196, 2008) compared to conventional serial passaging in three different growth conditions with regularly more then four passages to obtain comparable final cell numbers. Culture media were either supplemented with FBS in different concentrations or pHPL. Gene expression changes were tested by microarray analysis and selected targets were reanalyzed by quantitative real-time PCR. The genomic stability of MSPCs after long-term culture was determined by array comparative genomic hybridization (CGH). Results: Despite high proliferation rate large scale expanded MSPCs showed genomic stability in array CGH. Long-term MSPC growth induced similar gene expression changes in MSPCs irrespective of isolation and expansion conditions. In particular, genes involved in cell differentiation, apoptosis and cell death were up-regulated, whereas genes involved in mitosis and proliferation were down-regulated. Furthermore, overlapping senescence-associated gene expression changes were found in all MSPC preparations. The genomic copy number variations detected in MSPCs of early and late passages in all culture conditions did not coincide with differentially expressed genes. Conclusion: Our data indicate that MSPC expansion can induce gene expression changes independent of isolation and FBS-supplemented as well as FBS-free expansion conditions. A panel of genes will be presented that might offer a practicable approach to assess MSPC quality with regard to the state of replicative senescence in advance of therapeutic application. Determining the impact of senescence acquired during cell expansion on the therapeutic potential of MSCPs for both immune modulation and organ regeneration may help to develop more efficient treatment strategies. Disclosures: No relevant conflicts of interest to declare.

Mesenchymal stromal cells (MSC) are currently tested in a large number of clinical trials and raise high hope in regenerative medicine. These cells have to be expanded in vitro before transplantation and several studies demonstrated that long-term culture evokes continuous changes in MSC: proliferation rate decays, the cell size increases, differentiation potential is affected, chromosomal instabilities may arise and molecular changes are acquired. Long-term culture of cell preparations might also have therapeutic consequences, although this has hardly been addressed in ongoing trials so far. Reliable therapeutic regimens necessitate quality control of cellular products. This research perspective summarizes available methods to track cellular aging of MSC. We have demonstrated that gene expression changes and epigenetic modifications are continuously acquired during replicative senescence. Molecular analysis of a suitable panel of genes might provide a robust tool to assess efficiency and safety of long-term expansion.

Specific cell–cell junctions between hematopoietic stem cells (HSC) and their niche have been shown to regulate stem cell function. N-cadherin was suggested to play a central role in this process, whereas other studies indicated that it did not play an essential role in the murine model. We have analyzed the role of N-cadherin for interaction between hematopoietic progenitor cells (HPC) and supportive mesenchymal stromal cells (MSC) in a human–human setting. Expression of N-cadherin and of cadherin-11 (osteoblast cadherin) was analyzed in HPC by quantitative RT-PCR, Western blot, and flow cytometry. N-cadherin and cadherin-11 were expressed in HPC at a moderate level, whereas they were not detectable in differentiated cells. Confocal laser scanning microscopy revealed that N-cadherin and β-catenin are colocalized at the junction of HPC and MSC. siRNA knockdown of N-cadherin or cadherin-11 as well as treatment with the blocking function antibody decreased adhesive interaction of HPC to MSC. Furthermore, knockdown of N-cadherin or blocking function antibody impaired maintenance of long-term culture-initiating cells (LTC-IC) on coculture of HPC and MSC. These results indicate that N-cadherin is involved in the bidirectional interaction of human HPC with their cellular determinants in the niche.

Long‐term culture of human mesenchymal stromal cells (MSC) has implications on their proliferation and differentiation potential and we have demonstrated that this is associated with up‐regulation of the five microRNAs miR‐29c, miR‐369‐5p, miR‐371, miR‐499, and let‐7f. In this study, we examined the role of these senescence‐associated microRNAs for cellular aging and differentiation of MSC. Proliferation was reduced upon transfection with miR‐369‐5p, miR‐371, and miR‐499. Adipogenic differentiation was impaired by miR‐369‐5p whereas it was highly increased by miR‐371. This was accompanied by respective gene expression changes of some adipogenic key molecules (adiponectin and fatty acid‐binding protein 4 [FABP4]). Furthermore luciferase reporter assay indicated that FABP4 is a direct target of miR‐369‐5p. Microarray analysis upon adipogenic or osteogenic differentiation revealed down‐regulation of several microRNAs albeit miR‐369‐5p and miR‐371 were not affected. Expression of the de novo DNA methyltransferases DNMT3A and DNMT3B was up‐regulated by transfection of miR‐371 whereas expression of DNMT3A was down‐regulated by miR‐369‐5p. In summary, we identified miR‐369‐5p and miR‐371 as antagonistic up‐stream regulators of adipogenic differentiation and this might be indirectly mediated by epigenetic modifications. J. Cell. Physiol. 226: 2226–2234, 2011. © 2010 Wiley‐Liss, Inc.

BACKGROUND AIMS:Culture medium for mesenchymal stromal cells (MSC) is frequently supplemented with fetal calf serum (FCS). FCS can induce xenogeneic immune reactions, transmit bovine pathogens and has a high lot-to-lot variability that hampers reproducibility of results. Several studies have demonstrated that pooled human platelet lysate (HPL) provides an attractive alternative for FCS. However, little is known about the variation between different platelet lysates.METHODS:We compared activities of individual HPL on initial fibroblastoid colony-forming units (CFU-F), proliferation, in vitro differentiation and long-term culture. These data were correlated with chemokine profiles of HPL.RESULTS:Isolation of MSC with either HPL or FCS resulted in similar CFU-F frequency, colony morphology, immunophenotype and adipogenic differentiation potential. Osteogenic differentiation was even more pronounced in HPL than FCS. There were significant differences in MSC proliferation with different HPL, but it was always higher in comparison with FCS. Cell growth correlated with the concentration of platelet-derived growth factor (PDGF) and there was a moderate association with platelet counts. All HPL facilitated expansion for more than 20 population doublings.CONCLUSIONS:Taken together, reliable long-term expansion was possible with all HPL, although there was some variation in platelet lysates of individual units. Therefore the use of donor recipient-matched or autologous HPL is feasible for therapeutic MSC products.

The regenerative potential diminishes with age and this has been ascribed to functional impairments of adult stem cells. Cells in culture undergo senescence after a certain number of cell divisions whereby the cells enlarge and finally stop proliferation. This observation of replicative senescence has been extrapolated to somatic stem cells in vivo and might reflect the aging process of the whole organism. In this study we have analyzed the effect of aging on gene expression profiles of human mesenchymal stromal cells (MSC) and human hematopoietic progenitor cells (HPC). MSC were isolated from bone marrow of donors between 21 and 92 years old. 67 genes were age-induced and 60 were age-repressed. HPC were isolated from cord blood or from mobilized peripheral blood of donors between 27 and 73 years and 432 genes were age-induced and 495 were age-repressed. The overlap of age-associated differential gene expression in HPC and MSC was moderate. However, it was striking that several age-related gene expression changes in both MSC and HPC were also differentially expressed upon replicative senescence of MSC in vitro. Especially genes involved in genomic integrity and regulation of transcription were age-repressed. Although telomerase activity and telomere length varied in HPC particularly from older donors, an age-dependent decline was not significant arguing against telomere exhaustion as being causal for the aging phenotype. These studies have demonstrated that aging causes gene expression changes in human MSC and HPC that vary between the two different cell types. Changes upon aging of MSC and HPC are related to those of replicative senescence of MSC in vitro and this indicates that our stem and progenitor cells undergo a similar process also in vivo.