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Wagner W.,Aachen University Medical School | Ho A.D.,University of Heidelberg | Zenke M.,Aachen University Medical School
Tissue Engineering - Part B: Reviews | Year: 2010

Mesenchymal stem cells (MSCs) have to be culture expanded to gain relevant cell numbers for therapeutic applications. However, within 2-3 months the proliferation rate of MSCs decays until they ultimately reach a senescent state. This is accompanied by enlarged morphology, reduced expression of surface markers, and decreased differentiation potential. So far it is only scarcely understood how long-term culture affects MSC preparations, and five processes seem to be involved: (1) MSCs are composed of different sub-populations, and due to different proliferation rates the heterogeneity changes in the course of in vitro expansion; (2) cells in culture acquire mutations and other stochastic cellular defects; (3) self-renewal of MSCs may be impaired under culture conditions, leading to gradual differentiation; (4) the number of cell divisions might be restricted (e.g., by loss of telomeres), and (5) replicative senescence might be associated with the aging process of the organism. There is a growing perception that long-term culture has to be taken into account-especially for clinical applications. On the other hand, the state of replicative senescence is poorly defined by the number of population doublings or even by the number of passages. Reliable molecular measures for cellular aging are urgently needed. © 2010 Mary Ann Liebert, Inc. Source

Scholtes F.,University of Liege | Theunissen E.,Hasselt University | Phan-Ba R.,University of Liege | Adriaensens P.,Hasselt University | And 5 more authors.
Spinal Cord | Year: 2011

Study design:This was an experimental study.Objectives:White matter sparing influences locomotor recovery after traumatic spinal cord injury (SCI). The objective of the present post-mortem magnetic resonance imaging (MRI) investigation was to assess the potential of a simple inversion recovery (IR) sequence in combination with high-resolution proton density (PD) images to selectively depict spared white matter after experimental SCI in the rat.Setting:This study was conducted at University of Liège and Centre Hospitalier Universitaire, Liège, Belgium and Hasselt University, Diepenbeek, Belgium.Methods:Post-mortem 9.4 tesla (T) MRI was obtained from five excised rat spines 2 months after compressive SCI. The locomotor recovery had been followed weekly using the standardized Basso-Beattie-Bresnahan scale. IR MRI was used to depict normal white matter as very hypo-intense. Preserved white matter, cord atrophy and lesion volume were assessed, and histology was used to confirm MRI data.Results:MRI showed lesion severity and white matter sparing in accordance with the degree of locomotor recovery. IR MRI enhanced detection of spared and injured white matter by selectively altering the signal of spared white matter. Even subtle white matter changes could be detected, increasing diagnostic accuracy as compared to PD alone. MRI accuracy was confirmed by histology.Conclusion:High-resolution IR-supported PD MRI provides useful micro-anatomical information about white matter damage and sparing in the post-mortem assessment of chronic rat SCI. © 2011 International Spinal Cord Society. All rights reserved. Source

Teschendorff A.E.,University College London | Menon U.,University College London | Gentry-Maharaj A.,University College London | Ramus S.J.,University College London | And 17 more authors.
Genome Research | Year: 2010

Polycomb group proteins (PCGs) are involved in repression of genes that are required for stem cell differentiation. Recently, it was shown that promoters of PCG target genes (PCGTs) are 12-fold more likely to be methylated in cancer than non-PCGTs. Age is the most important demographic risk factor for cancer, and we hypothesized that its carcinogenic potential may be referred by irreversibly stabilizing stem cell features. To test this, we analyzed the methylation status of over 27,000 CpGs mapping to promoters of ∼14,000 genes in whole blood samples from 261 postmenopausal women. We demonstrate that stem cell PCGTs are far more likely to become methylated with age than non-targets (odds ratio = 5.3 [3.8-7.4], P < 10-10), independently of sex, tissue type, disease state, and methylation platform. We identified a specific subset of 69 PCGT CpGs that undergo hypermethylation with age and validated this methylation signature in seven independent data sets encompassing over 900 samples, including normal and cancer solid tissues and a population of bone marrow mesenchymal stem/stromal cells (P < 10-5). We find that the age-PCGT methylation signature is present in preneoplastic conditions and may drive gene expression changes associated with carcinogenesis. These findings shed substantial novel insights into the epigenetic effects of aging and support the view that age may predispose to malignant transformation by irreversibly stabilizing stem cell features. © 2010 by Cold Spring Harbor Laboratory Press. Source

Bork S.,University of Heidelberg | Bork S.,Heidelberg Academy of science and Humanities | Pfister S.,Heidelberg Academy of science and Humanities | Pfister S.,University of Heidelberg | And 10 more authors.
Aging Cell | Year: 2010

Within 2-3 months of in vitro culture-expansion, mesenchymal stromal cells (MSC) undergo replicative senescence characterized by cell enlargement, loss of differentiation potential and ultimate growth arrest. In this study, we have analyzed DNA methylation changes upon long-term culture of MSC by using the HumanMethylation27 BeadChip microarray assessing 27 578 unique CpG sites. Furthermore, we have compared MSC from young and elderly donors. Overall, methylation patterns were maintained throughout both long-term culture and aging but highly significant differences were observed at specific CpG sites. Many of these differences were observed in homeobox genes and genes involved in cell differentiation. Methylation changes were verified by pyrosequencing after bisulfite conversion and compared to gene expression data. Notably, methylation changes in MSC were overlapping in long-term culture and aging in vivo. This supports the notion that replicative senescence and aging represent developmental processes that are regulated by specific epigenetic modifications. © 2009 The Authors. Journal compilation © Blackwell Publishing Ltd/Anatomical Society of Great Britain and Ireland 2009. Source

Schellenberg A.,Aachen University Medical School | Stiehl T.,The Interdisciplinary Center | Stiehl T.,Heidelberg Academy of science and Humanities | Horn P.,Heidelberg Academy of science and Humanities | And 5 more authors.
Cytotherapy | Year: 2012

Background aims. Mesenchymal stromal cells (MSC) are heterogeneous and only a subset possesses multipotent differentiation potential. It has been proven that long-term culture has functional implications for MSC. However, little is known how the composition of subpopulation changes during culture expansion. Methods. We addressed the heterogeneity of MSC using limiting-dilution assays at subsequent passages. In addition, we used a cellular automaton model to simulate population dynamics under the assumption of mixed numbers of remaining cell divisions until replicative senescence. The composition of cells with adipogenic or osteogenic differentiation potential during expansion was also determined at subsequent passages. Results. Not every cell was capable of colony formation upon passaging. Notably, the number of fibroblastoid colony-forming units (CFU-f) decreased continuously, with a rapid decay within early passages. Therefore the CFU-f frequency might be used as an indicator of the population doublings remaining before entering the senescent state. Predictions of the cellular automaton model suited the experimental data best if most cells were already close to their replicative limit by the time of culture initiation. Analysis of differentiated clones revealed that subsets with very high levels of adipogenic or osteogenic differentiation capacity were only observed at early passages. Conclusions. These data support the notion of heterogeneity in MSC, and also with regard to replicative senescence. The composition of subpopulations changes during culture expansion and clonogenic subsets, especially those with the highest differentiation capacity, decrease already at early passages. © 2012 Informa Healthcare. Source

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