Dynamics of adipogenic promoter DNA methylation during clonal culture of human adipose stem cells to senescence

Dnmt3b deficiency in adipocyte progenitor cells ameliorates obesity in female mice

Obesity arises from chronic energy imbalance where energy intake exceeds energy expenditure. Emerging evidence supports a key role of DNA methylation in the regulation of adipose tissue development and metabolism. We recently discovered a key role of DNA methylation, catalyzed by DNA methyltransferase 1 or 3a (Dnmt1 or 3a), in the regulation of adipocyte differentiation and metabolism. Here, we aimed to investigate the role of adipocyte progenitor cell Dnmt3b, an enzyme mediating de novo DNA methylation, in energy metabolism and obesity. We generated a genetic model with Dnmt3b knockout in adipocyte progenitor cells (PD3bKO) by crossing Dnmt3b -floxed mice with platelet-derived growth factor receptor alpha (Pdgfrα)-Cre mice. Dnmt3b gene deletion in adipocyte progenitors enhanced thermogenic gene expression in brown adipose tissue, increased overall energy expenditure, and mitigated high-fat diet (HFD)-induced obesity in female mice. PD3bKO mice also displayed a lower respiratory exchange ratio (RER), indicative of a metabolic shift favoring fat utilization as an energy source. Furthermore, female PD3bKO mice exhibited improved insulin sensitivity alongside their lean phenotype. In contrast, male PD3bKO mice showed no changes in body weight but demonstrated decreased insulin sensitivity, revealing a sexually dimorphic metabolic response to Dnmt3b deletion in adipocyte progenitor cells. These findings underscore the critical role of Dnmt3b in regulating energy homeostasis, body weight, and metabolic health, with significant implications for understanding sex-specific mechanisms of obesity and metabolism.

JAK-STAT signaling mediates the senescence of cartilage-derived stem/progenitor cells

Aging is a major risk factor for degenerative joint diseases, such as osteoarthritis (OA). Previous studies have confirmed the link between senescent mesenchymal stem cells (MSCs) and OA. Cartilage-derived stem/progenitor cells (CSPCs) with MSCs properties have been extracted from a variety of species. We inferred that the senescence of CSPCs may promote the development of osteoarthritis. However, the cellular and molecular mechanisms of CSPCs senescence remains unknown. In this study, we investigated the role of JAK-STAT signaling pathway in a replicative senescence model of CSPCs. We showed that the late CSPCs (> 15th passage) exhibited distinct senescent phenotypes, including increased proportion of β-gal positive senescent cells and F-actin content, as well as cell cycle arrest. In late CSPCs, the activity of JAK-STAT signaling pathway was significantly increased. Activation of JAK-STAT signaling pathway promoted cell senescence in early CSPCs (< 6th passage). Conversely, pharmacological inhibition or genetic knockdown of JAK-STAT signaling pathway attenuated cell senescence in late CSPCs. In conclusion, our results demonstrated the critical role of JAK-STAT signaling pathway in CSPCs senescence.

Comparative analysis of mesenchymal stem cells cultivated in serum free media

Stem cells are attractive candidates for the regeneration of tissue and organ. Mesenchymal stem cells (MSCs) have been extensively investigated for their potential applications in regenerative medicine and cell therapy. For developing effective stem cell therapy, the mass production of consistent quality cells is required. The cell culture medium is the most critical aspect of the mass production of qualified stem cells. Classically, fetal bovine serum (FBS) has been used as a culture supplement for MSCs. Due to the undefined and heterologous composition of animal origin components in FBS, efforts to replace animal-derived components with non-animal-derived substances led to safe serum free media (SFM). Adipose derived mesenchymal stem cells (ADSCs) cultivated in SFM provided a more stable population doubling time (PDT) to later passage and more cells in a shorter time compared to FBS containing media. ADSCs cultivated in SFM had lower cellular senescence, lower immunogenicity, and higher genetic stability than ADSCs cultivated in FBS containing media. Differential expression analysis of mRNAs and proteins showed that the expression of genes related with apoptosis, immune response, and inflammatory response were significantly up-regulated in ADSCs cultivated in FBS containing media. ADSCs cultivated in SFM showed similar therapeutic efficacy in an acute pancreatitis mouse model to ADSCs cultivated in FBS containing media. Consideration of clinical trials, not only pre-clinical trial, suggests that cultivation of MSCs using SFM might offer more safe cell therapeutics as well as repeated administration due to low immunogenicity.

DNA Methylation Modulates Aging Process in Adipocytes

Aging has been recognized to be a highly complex biological health problem with a high risk of chronic diseases, including type 2 diabetes, atherosclerosis, chronic bronchitis or emphysema, cancer and Alzheimer's disease. Particularly, age-related turnover in adipose tissue is a major contributor to metabolic syndromes and shortened lifespan. Adipocytes undergo senescence in early stage, which results in adipose tissue metabolic dysfunction, redistribution, and inflammation. The well-established association between DNA methylation (DNAm) and aging has been observed in the past few decades. Indeed, age-related alteration in DNAm is highly tissue-specific. This review intends to summarize the advancements how DNAm changes coupled with aging process in adipose tissue, by which DNAm regulates cellular senescence, metabolic function, adipokine secretion and beiging process in adipocytes. Elucidation of the effect of DNAm on adipose aging would have great potential to the development of epigenetic therapeutic strategies against aging-related diseases in clinical settings.

Brown Fat Dnmt3b Deficiency Ameliorates Obesity in Female Mice

Obesity results from a chronic energy imbalance due to energy intake exceeding energy expenditure. Activation of brown fat thermogenesis has been shown to combat obesity. Epigenetic regulation, including DNA methylation, has emerged as a key regulator of brown fat thermogenic function. Here we aimed to study the role of Dnmt3b, a DNA methyltransferase involved in de novo DNA methylation, in the regulation of brown fat thermogenesis and obesity. We found that the specific deletion of Dnmt3b in brown fat promotes the thermogenic and mitochondrial program in brown fat, enhances energy expenditure, and decreases adiposity in female mice fed a regular chow diet. With a lean phenotype, the female knockout mice also exhibit increased insulin sensitivity. In addition, Dnmt3b deficiency in brown fat also prevents diet-induced obesity and insulin resistance in female mice. Interestingly, our RNA-seq analysis revealed an upregulation of the PI3K-Akt pathway in the brown fat of female Dnmt3b knockout mice. However, male Dnmt3b knockout mice have no change in their body weight, suggesting the existence of sexual dimorphism in the brown fat Dnmt3b knockout model. Our data demonstrate that Dnmt3b plays an important role in the regulation of brown fat function, energy metabolism and obesity in female mice.

Chronological Age Affects MSC Senescence In Vitro-A Systematic Review

The use of mesenchymal stromal cells (MSCs) in regenerative medicine and tissue engineering is well established, given their properties of self-renewal and differentiation. However, several studies have shown that these properties diminish with age, and understanding the pathways involved are important to provide regenerative therapies in an ageing population. In this PRISMA systematic review, we investigated the effects of chronological donor ageing on the senescence of MSCs. We identified 3023 studies after searching four databases including PubMed, Web of Science, Cochrane, and Medline. Nine studies met the inclusion and exclusion criteria and were included in the final analyses. These studies showed an increase in the expression of p21, p53, p16, ROS, and NF-κB with chronological age. This implies an activated DNA damage response (DDR), as well as increased levels of stress and inflammation in the MSCs of older donors. Additionally, highlighting the effects of an activated DDR in cells from older donors, a decrease in the expression of proliferative markers including Ki67, MAPK pathway elements, and Wnt/β-catenin pathway elements was observed. Furthermore, we found an increase in the levels of SA-β-galactosidase, a specific marker of cellular senescence. Together, these findings support an association between chronological age and MSC senescence. The precise threshold for chronological age where the reported changes become significant is yet to be defined and should form the basis for further scientific investigations. The outcomes of this review should direct further investigations into reversing the biological effects of chronological age on the MSC senescence phenotype.

Quality by design to define critical process parameters for mesenchymal stem cell expansion

Stem cell-based therapeutic products could be the key to treat the deadliest current pathologies, ranging from neuro-degenerative to respiratory diseases. However, in order to bring these innovative therapeutics to a commercialization stage, reproducible manufacturing of high quality cell products is required. Although advances in cell culture techniques have led to more robust production processes and dramatically accelerated the development of early-phase clinical studies, challenges remain before regulatory approval, particularly to define and implement science-based quality standards (essential pre-requisites for national health agencies). In this regard, using new methodologies, such as Quality By Design (QBD), to build the production process around drug quality, could significantly reduce the chance of product rejection. This review-based work aims to perform a QBD approach to Mesenchymal Stem Cell (MSC) manufacturing in standard two-dimensional flasks, using published studies which have determined the impact of individual process parameters on defined Critical Quality Attributes (CQA). Along with this bibliographic analysis, parameter criticality was determined during the two main manufacturing stages (cell extraction and cell amplification) along with an overall classification in view of identifying the Critical Process Parameters (CPP). The analysis was performed in view of an improved standardization between research teams, and should contribute to reduce the gap towards compliant Good Manufacturing Practice (cGMP) manufacturing.

DNMT3B Is an Oxygen-Sensitive De Novo Methylase in Human Mesenchymal Stem Cells

The application of physiological oxygen (physoxia) concentrations is becoming increasingly commonplace within a mammalian stem cell culture. Human mesenchymal stem cells (hMSCs) attract widespread interest for clinical application due to their unique immunomodulatory, multi-lineage potential, and regenerative capacities. Descriptions of the impact of physoxia on global DNA methylation patterns in hMSCs and the activity of enzymatic machinery responsible for its regulation remain limited. Human bone marrow-derived mesenchymal stem cells (BM-hMSCs, passage 1) isolated in reduced oxygen conditions displayed an upregulation of SOX2 in reduced oxygen conditions vs. air oxygen (21% O2, AO), while no change was noted for either OCT-4 or NANOG. DNA methylation marks 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) showed decreases in 2% O2 environment (workstation) (2% WKS). DNMT3B (DNA methyltransferase 3B) and TET1 (Ten-eleven translocation enzyme 1) displayed reduced transcription in physoxia. Consistent with transcriptional downregulation, we noted increased promoter methylation levels of DNMT3B in 2% WKS accompanied by reduced DNMT3B and TET1 protein expression. Finally, a decrease in HIF1A (Hypoxia-inducible factor 1A) gene expression in 2% WKS environment correlated with protein levels, while HIF2A was significantly higher in physoxia correlated with protein expression levels vs. AO. Together, these data have demonstrated, for the first time, that global 5mC, 5hmC, and DNMT3B are oxygen-sensitive in hMSCs. Further insights into the appropriate epigenetic regulation within hMSCs may enable increased safety and efficacy development within the therapeutic ambitions.

Adipose-Derived Mesenchymal Stromal Cells in Regenerative Medicine: State of Play, Current Clinical Trials, and Future Prospects

Significance: Wound healing is a complex process involving pain and inflammation, where innervation plays a central role. Managing wound healing and pain remains an important issue, especially in pathologies such as excessive scarring (often leading to fibrosis) or deficient healing, leading to chronic wounds. Recent Advances: Advances in therapies using mesenchymal stromal cells offer new insights for treating indications that previously lacked options. Adipose-derived mesenchymal stromal cells (AD-MSCs) are now being used to a much greater extent in clinical trials for regenerative medicine. However, to be really valid, these randomized trials must imperatively follow strict guidelines such as consolidated standards of reporting trials (CONSORT) statement. Indeed, AD-MSCs, because of their paracrine activities and multipotency, have potential to cure degenerative and/or inflammatory diseases. Combined with their relatively easy access (from adipose tissue) and proliferation capacity, AD-MSCs represent an excellent candidate for allogeneic treatments. Critical Issues: The success of AD-MSC therapy may depend on the robustness of the biological functions of AD-MSCs, which requires controlling source heterogeneity and production processes, and development of biomarkers that predict desired responses. Several studies have investigated the effect of AD-MSCs on innervation, wound repair, or pain management separately, but systematic evaluation of how those effects could be combined is lacking. Future Directions: Future studies that explore how AD-MSC therapy can be used to treat difficult-to-heal wounds, underlining the need to thoroughly characterize the cells used, and standardization of preparation processes are needed. Finally, how this a priori easy-to-use cell therapy treatment fits into clinical management of pain, improvement of tissue healing, and patient quality of life, all need to be explored.

Characterization and comparative DNA methylation profiling of four adipogenic genes in adipose-derived stem cells and dedifferentiated fat cells from aging subjects

Adipose-derived stem cells (ASCs) and dedifferentiated fat (DFAT) cells are alternative cell sources in tissue engineering and regeneration because they are easily obtained and exhibit multilineage differentiation. However, aging may attenuate their regenerative potential and metabolic functions. Reports characterizing DFAT cells derived from aging donors are rare, and comparisons of DNA methylation profiles between aging ASCs and DFAT cells are poorly understood. Therefore, this study aimed to characterize DFAT cells relative to ASCs derived from aging subjects and compare the DNA methylation profiles of four adipogenic genes in these cells. ASCs and DFAT cells from aging donors exhibited characteristics similar to those of stem cells, including colony formation, proliferation, and multilineage differentiation abilities. However, compared with ASCs, DFAT cells exhibited increased proliferation, smooth muscle actin alpha (SMA-α) expression and decreased cellular senescence. DNA methylation profiling of ASCs and DFAT cells by combined bisulfite restriction analysis (COBRA) demonstrated hypermethylation patterns in three potent adipogenic genes—peroxisome proliferator-activated receptor gamma 2 (PPARγ2), fatty acid-binding protein 4 (FABP4), and lipoprotein lipase (LPL)—but hypomethylation of CCAAT/enhancer binding protein alpha (C/EBPα) in the aging group. Statistically significant differences were observed between the aging group and the young group. Epigenetic regulation maintains the stability of ASCs and DFAT cells in an age-dependent manner. Our findings suggested that although the DNA methylation patterns of three adipogenic genes correlated with hypermethylation and aging, ASCs and DFAT cells exhibited cellular stability and several stem cell characteristics, offering further opportunities for personalized regeneration and energy maintenance by adipogenesis during aging.

Regulation of Adipocyte Differentiation by METTL4, a 6 mA Methylase

As one of the most abundant DNA methylation form in prokaryotes, N⁶-methyladenine nucleotide (6 mA) was however only recently identified in eukaryotic genomes. To explore the implications of N⁶-adenine methylation in adipogenesis, genomic N⁶-adenine methylation was examined across adipocyte differentiation stages of 3T3-L1 cells. When the N⁶-adenine methylation profiles were analyzed and compared with the levels of gene expression, a positive correlation between the density of promoter 6 mA and gene expression level was uncovered. By means of in vitro methylation and gene knockdown assay, METTL4, a homologue of Drosophila methylase CG14906 and C. elegans methylase DAMT-1, was demonstrated to be a mammalian N⁶-adenine methylase that functions in adipogenesis. Knockdown of Mettl4 led to altered adipocyte differentiation, shown by defective gene regulation and impaired lipid production. We also found that the effects of N⁶-adenine methylation on lipid production involved the regulation of INSR signaling pathway, which promotes glucose up-taking and lipid production in the terminal differentiation stage.

DNA methylation of the PLIN1 promoter downregulates expression in chicken lines

Evidence suggests that Perilipin-1 (PLIN1) is subject to functional regulation by epigenetic modifications in women with obesity. However, whether chicken PLIN1 expression is regulated by DNA methylation is unknown. Here, Sequenom MassARRAY and real-time polymerase chain reaction (PCR) were conducted to analyze the promoter methylation status and expression of the PLIN1 gene in Northeast Agricultural University broiler lines divergently selected for abdominal fat content. We found that chicken PLIN1 expression was significantly higher in adipose tissue of fat-line broilers than in lean lines at 1-7 weeks of age, and was significantly positively correlated with abdominal fat percentage (AFP) in chicken adipose development (Pearson's r = 0.627 , P < 0.001 ). The region analyzed for DNA methylation was from - 12 to - 520  bp upstream of the translation start codon ATG, and had five CpG sites, where only the DNA methylation levels of CpG5 located at position - 490  bp were significantly higher in lean compared to fat chickens at 5 and 6 weeks ( P < 0.05 ) and were significantly negatively correlated with PLIN1 mRNA levels and AFP ( P < 0.05 ). These results shed new light on the regulation of hypertrophic growth in chicken adipose development.

DNA methylation profile of different clones of human adipose stem cells does not allow to predict their differentiation potential

Human adipose stem cells can differentiate into various mesodermic lineages, including adipogenic, osteogenic, chondrogenic, myogenic and endothelial pathways. In addition, these cells types possess immunomodulatory properties, potentially useful for autoimmune and autoinflammatory diseases. However, single-cell expanded clones have shown that the cells can present a variety of differentiation potential, which may be partly due to epigenetic differences among them. The objective of this study was to assess if DNA methylation plays a role in the differentiation potential observed between different cell clones obtained from the same donor. To this end, the methylation profile of five clonal cell lines of human adipose stem cells obtained by liposuction from two donors was analyzed. Previous reports demonstrated that cell lines 1.7 and 1.22 from Donor 1 and 3.5 from Donor 3 were adipogenic-osteogenic, but not cell lines 1.10 and 3.10. The genes analyzed were neuronal, endothelial, myogenic, osteogenic, adipogenic, extracellular matrix, cell cycle, cytoskeleton and metabolic enzymes. All clones analyzed in this study displayed a similar pattern of methylation in most of the gene families: 85.5% were hypomethylated genes and 14.5% hypermethylated. In conclusion, the methylation pattern of the 1113 genes studied in this report was not a consistent tool to identify the differentiation potential of human adipose stem cells.

DNA methylation microarray uncovers a permissive methylome for cardiomyocyte differentiation in human mesenchymal stem cells

Differentiation of Wharton's Jelly-Mesenchymal Stem cells (WJ-MSCs) into cardiomyocytes (CMs) in vitro has been reported widely although contradictions remain regarding the maturation of differentiated MSCs into fully functioning CMs. Studies suggest that use of epigenetic modifiers like 5'Azacytidine (5-AC) in MSCs de-methylates DNA and results in expression of cardiac-specific genes (CSGs). However, only partial expression of the CSG set leads to incomplete differentiation of WJ-MSCs to CMs. We used the Agilent 180 K human DNA methylation microarray on WJ-MSCs, 5-AC treated WJ-MSCs and human cardiac tissue (hCT) to analyze differential DNA methylation profiles which were then validated by bisulfite sequencing PCR (BSP). BSP confirmed that only a limited number of CSGs were de-methylated by 5-AC in WJ-MSCs. It also revealed that hCT displays a methylation profile similar to promoter regions of CSG in untreated WJ-MSCs. Thus, the presence of hypo-methylated CSGs indicates that WJ-MSCs are ideal cell types for cardiomyogenic differentiation.

Molecular Insight into the Interaction between Epigenetics and Leptin in Metabolic Disorders

Nowadays, it is well-known that the deregulation of epigenetic machinery is a common biological event leading to the development and progression of metabolic disorders. Moreover, the expression level and actions of leptin, a vast adipocytokine regulating energy metabolism, appear to be strongly associated with epigenetics. Therefore, the aim of this review was to summarize the current knowledge of the epigenetic regulation of leptin as well as the leptin-induced epigenetic modifications in metabolic disorders and associated phenomena. The collected data indicated that the deregulation of leptin expression and secretion that occurs during the course of metabolic diseases is underlain by a variation in the level of promoter methylation, the occurrence of histone modifications, along with miRNA interference. Furthermore, leptin was proven to epigenetically regulate several miRNAs and affect the activity of the histone deacetylases. These epigenetic modifications were observed in obesity, gestational diabetes, metabolic syndrome and concerned various molecular processes like glucose metabolism, insulin sensitivity, liver fibrosis, obesity-related carcinogenesis, adipogenesis or fetal/early postnatal programming. Moreover, the circulating miRNA profiles were associated with the plasma leptin level in metabolic syndrome, and miRNAs were found to be involved in hypothalamic leptin sensitivity. In summary, the evidence suggests that leptin is both a target and a mediator of epigenetic changes that develop in numerous tissues during metabolic disorders.

Bone marrow mononuclear cells versus mesenchymal stem cells from adipose tissue on bone healing in an Old World primate: can this be extrapolated to humans?

ABSTRACT In veterinary medicine, the cell therapy is still unexplored and there are many unanswered questions that researchers tend to extrapolate to humans in an attempt to treat certain injuries. Investigating this subject in nonhuman primates turns out to be an unparalleled opportunity to better understand the dynamics of stem cells against some diseases. Thus, we aimed to compare the efficiency of bone marrow mononuclear cells (BMMCs) and mesenchymal stem cells (MSCs) from adipose tissue of Chlorocebus aethiops in induced bone injury. Ten animals were used, male adults subjected, to bone injury the iliac crests. The MSCs were isolated by and cultured. In an autologous manner, the BMMCs were infused in the right iliac crest, and MSCs from adipose tissue in the left iliac crest. After 4.8 months, the right iliac crests fully reconstructed, while left iliac crest continued to have obvious bone defects for up to 5.8 months after cell infusion. The best option for treatment of injuries with bone tissue loss in old world primates is to use autologous MSCs from adipose tissue, suggesting we can extrapolate the results to humans, since there is phylogenetic proximity between species.

Identification of senescent cells in multipotent mesenchymal stromal cell cultures: Current methods and future directions

Regardless of their tissue of origin, multipotent mesenchymal stromal cells (MSCs) are commonly expanded in vitro for several population doublings to achieve a sufficient number of cells for therapy. Prolonged MSC expansion has been shown to result in phenotypical, morphological and gene expression changes in MSCs, which ultimately lead to the state of senescence. The presence of senescent cells in therapeutic MSC batches is undesirable because it reduces their viability, differentiation potential and trophic capabilities. Additionally, senescent cells acquire senescence-activated secretory phenotype, which may not only induce apoptosis in the neighboring host cells following MSC transplantation, but also trigger local inflammatory reactions. This review outlines the current and promising new methodologies for the identification of senescent cells in MSC cultures, with a particular emphasis on non-destructive and label-free methodologies. Technologies allowing identification of individual senescent cells, based on new surface markers, offer potential advantage for targeted senescent cell removal using new-generation senolytic agents, and subsequent production of therapeutic MSC batches fully devoid of senescent cells. Methods or a combination of methods that are non-destructive and label-free, for example, involving cell size and spectroscopic measurements, could be the best way forward because they do not modify the cells of interest, thus maximizing the final output of therapeutic-grade MSC cultures. The further incorporation of machine learning methods has also recently shown promise in facilitating, automating and enhancing the analysis of these measured data.

Effects of Cyclocarya paliurus polysaccharide on lipid metabolism-related genes DNA methylation in rats

The present study was conducted to evaluate the effect of CPP on the DNA methylation and expressions of lipid metabolism-related genes (leptin and MTTP) in hyperlipidemic rats. After 8 weeks intervention of CPP, the abdominal wall fat index, liver weight, the serum concentrations of TC, TG and LDL-C were significantly decreased, while HDL was increased. In addition, DNA methylation was analyzed by bisulfite sequencing method, and the mRNA expression levels of leptin and MTTP were detected by Q-PCR. The results showed that CPP could considerably decrease DNA methylation levels of leptin (regions from -694 ~ -370 bp contains 14 CpGs and -324 ~ -29 bp contains 18 CpGs) and MTTP (region from -350 ~ -1 bp contains 11 CpGs) promoters in the liver with the maximum decrease rate of 43.2%, 40.2% and 7.7%, respectively. In parallel, the mRNA contents of leptin and MTTP were dramatically down-regulated. In conclusion, the present findings demonstrated that CPP can regulate the level of mRNA by controlling DNA methylation levels in the liver, thereby reducing blood lipids.

A comprehensive study on donor-matched comparisons of three types of mesenchymal stem cells-containing cells from human dental tissue

BACKGROUND AND OBJECTIVE

Mesenchymal stem cells (MSCs) have been widely used in tissue engineering, such as for regenerating the supporting structures of teeth destroyed by periodontal diseases. In recent decades, dental tissue-derived MSCs have drawn much attention owing to their accessibility, plasticity and applicability. Dental pulp stem cells (DPSCs), periodontal ligament stem cells (PDLSCs) and gingival MSCs (GMSCs) are the most readily available MSCs among all types of dental MSCs. The purpose of this study was to comprehensively compare the characteristics of MSCs from dental pulp (DP), periodontal ligament (PDL) and gingiva (G) in vitro and thus provide insight into optimizing the performance of cells and seed cell selection strategies for tissue regeneration.

MATERIALS AND METHODS

In this study, patient-matched (n = 5) cells derived from DP, PDL and G which, respectively, contained DPSCs, PDLSCs and GMSCs were evaluated using multiple methods in terms of their proliferation, senescence, apoptosis, multilineage differentiation and stemness maintenance after long-term passage.

RESULTS

Mesenchymal stem cells-containing cells from G (MSCs/GCs) showed superior proliferation capability, whereas patient-matched MSCs-containing cells from PDL (MSCs/PDLCs) exhibited excellent osteogenic and adipogenic differentiation ability; MSCs-containing cells from DP (MSCs/DPCs) achieved mediocre results in both aspects. In addition, MSCs/GCs were the least susceptible to senescence, while MSCs/PDLCs were the most prone to ageing. Furthermore, the biological properties of these three types of cells were all affected after long-term in vitro culture.

CONCLUSION

These three types of dental MSCs showed different biological characteristics. MSCs/PDLCs are the best candidate cells for bone regeneration, but the application of MSCs/PDLCs might be limited to certain number of passages. Improving the differentiation of MSCs/GCs remains the key issue regarding their application in tissue engineering.

Aging- and Senescence-associated Changes of Mesenchymal Stromal Cells in Myelodysplastic Syndromes

Hematopoietic stem and progenitor cells reside within the bone marrow (BM) microenvironment. By a well-balanced interplay between self-renewal and differentiation, they ensure a lifelong supply of mature blood cells. Physiologically, multiple different cell types contribute to the regulation of stem and progenitor cells in the BM microenvironment by cell-extrinsic and cell-intrinsic mechanisms. During the last decades, mesenchymal stromal cells (MSCs) have been identified as one of the main cellular components of the BM microenvironment holding an indispensable role for normal hematopoiesis. During aging, MSCs diminish their functional and regenerative capacities and in some cases encounter replicative senescence, promoting inflammation and cancer progression. It is now evident that alterations in specific stromal cells that comprise the BM microenvironment can contribute to hematologic malignancies, and there is growing interest regarding the contribution of MSCs to the pathogenesis of myelodysplastic syndromes (MDSs), a clonal hematological disorder, occurring mostly in the elderly, characterized by ineffective hematopoiesis and increased tendency to acute myeloid leukemia evolution. The pathogenesis of MDS has been associated with specific genetic and epigenetic events occurring both in hematopoietic stem cells (HSCs) and in the whole BM microenvironment with an aberrant cross talk between hematopoietic elements and stromal compartment. This review highlights the role of MSCs in MDS showing functional and molecular alterations such as altered cell-cycle regulation with impaired proliferative potential, dysregulated cytokine secretion, and an abnormal gene expression profile. Here, the current knowledge of impaired functional properties of both aged MSCs and MSCs in MDS have been described with a special focus on inflammation and senescence induced changes in the BM microenvironment. Furthermore, a better understanding of aberrant BM microenvironment could improve future potential therapies.

Analysis of DNA modifications in aging research

As geroscience research extends into the role of epigenetics in aging and age-related disease, researchers are being confronted with unfamiliar molecular techniques and data analysis methods that can be difficult to integrate into their work. In this review, we focus on the analysis of DNA modifications, namely cytosine methylation and hydroxymethylation, through next-generation sequencing methods. While older techniques for modification analysis performed relative quantitation across regions of the genome or examined average genome levels, these analyses lack the desired specificity, rigor, and genomic coverage to firmly establish the nature of genomic methylation patterns and their response to aging. With recent methodological advances, such as whole genome bisulfite sequencing (WGBS), bisulfite oligonucleotide capture sequencing (BOCS), and bisulfite amplicon sequencing (BSAS), cytosine modifications can now be readily analyzed with base-specific, absolute quantitation at both cytosine-guanine dinucleotide (CG) and non-CG sites throughout the genome or within specific regions of interest by next-generation sequencing. Additional advances, such as oxidative bisulfite conversion to differentiate methylation from hydroxymethylation and analysis of limited input/single-cells, have great promise for continuing to expand epigenomic capabilities. This review provides a background on DNA modifications, the current state-of-the-art for sequencing methods, bioinformatics tools for converting these large data sets into biological insights, and perspectives on future directions for the field.

On the origin and impact of mesenchymal stem cell heterogeneity: new insights and emerging tools for single cell analysis

Mesenchymal stem cells (MSCs) display substantial cell-to-cell variation. This heterogeneity manifests among donors, among tissue sources, and within cell populations. Such pervasive variability complicates the use of MSCs in regenerative applications and may limit their therapeutic efficacy. Most conventional assays measure MSC properties in bulk and, as a consequence, mask this cell-to-cell variation. Recent studies have identified extensive variability amongst and within clonal MSC populations, in dimensions including functional differentiation capacity, molecular state (e.g. epigenetic, transcriptomic, and proteomic status), and biophysical properties. While the origins of these variations remain to be elucidated, potential mechanisms include in vivo micro-anatomical heterogeneity, epigenetic bistability, and transcriptional fluctuations. Emerging tools for single cell analysis of MSC gene and protein expression may yield further insight into the mechanisms and implications of single cell variation amongst these cells, and ultimately improve the clinical utility of MSCs in tissue engineering and regenerative medicine applications. This review outlines the dimensions across which MSC heterogeneity is present, defines some of the known mechanisms that govern this heterogeneity, and highlights emerging technologies that may further refine our understanding and improve our clinical application of this unique cell type.

Peroxisome Proliferator-Activated Receptor Gamma in Obesity and Colorectal Cancer: the Role of Epigenetics

Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor that is deregulated in obesity. PPARγ exerts diverse antineoplastic effects. Attempting to determine the clinical relevance of the epigenetic mechanisms controlling the expression PPARγ and susceptibility to colorectal cancer (CRC) in obese subjects, this study investigated the role of some microRNAs and DNA methylation on the deregulation of PPARγ. Seventy CRC patients (34 obese and 36 lean), 22 obese and 24 lean healthy controls were included. MicroRNA levels were measured in serum. PPARγ promoter methylation was evaluated in peripheral blood mononuclear cells (PBMC). PPARγ level was evaluated by measuring mRNA level in PBMC and protein level in serum. The tested microRNAs (miR-27b, 130b and 138) were significantly upregulated in obese and CRC patients. Obese and CRC patients had significantly low levels of PPARγ. A significant negative correlation was found between PPARγ levels and the studied microRNAs. There was a significant PPARγ promoter hypermethylation in CRC patients that correlated to low PPARγ levels. Our results suggest that upregulation of microRNAs 27b, 130b and 138 is associated with susceptibility to CRC in obese subjects through PPARγ downregulation. Hypermethylation of PPARγ gene promoter is associated with CRC through suppression of PPARγ regardless of BMI.

Dynamic changes of epigenetic signatures during chondrogenic and adipogenic differentiation of mesenchymal stem cells

Extensive studies have been performed to clarify the processes during which mesenchymal stem cells (MSCs) differentiate into their lineage fates. In vitro differentiation of MSCs into distinct lineages have attracted the focus of a large number of clinical investigations. Although the gene expression profiling during differentiation of MSC toward bone, cartilage, and adipocytes is well established, the master regulators by which MSC fate can be controlled are not entirely determined. During differentiation of MSCs into a special cell fate, epigenetic mechanisms considered as the primary mediators that suppress the irrelevant genes and activate the genes required for a specific cell lineage. This review dedicated to addressing the changes of various epigenetic mechanisms, including DNA methylation, histone modifications, and micro-RNAs during chondrogenic and adipogenic differentiation of MSC.

Proteasome activation enhances stemness and lifespan of human mesenchymal stem cells

The age-associated decline of adult stem cell function contributes to the physiological failure of homeostasis during aging. The proteasome plays a key role in the maintenance of proteostasis and its failure is associated with various biological phenomena including senescence and aging. Although stem cell biology has attracted intense attention, the role of proteasome in stemness and its age-dependent deterioration remains largely unclear. By employing both Wharton's-Jelly- and Adipose-derived human adult mesenchymal stem cells (hMSCs), we reveal a significant age-related decline in proteasome content and peptidase activities, accompanied by alterations of proteasomal complexes. Additionally, we show that senescence and the concomitant failure of proteostasis negatively affects stemness. Remarkably, the loss of proliferative capacity and stemness of hMSCs can be counteracted through proteasome activation. At the mechanistic level, we demonstrate for the first time that Oct4 binds at the promoter region of β2 and β5 proteasome subunits and thus possibly regulates their expression. A firm understanding of the mechanisms regulating proteostasis in stem cells will pave the way to innovative stem cell-based interventions to improve healthspan and lifespan.

Senescence-associated DNA methylation is stochastically acquired in subpopulations of mesenchymal stem cells

Replicative senescence has a major impact on function and integrity of cell preparations. This process is reflected by continuous DNA methylation (DNAm) changes at specific CpG dinucleotides in the course of in vitro culture, and such modifications can be used to estimate the state of cellular senescence for quality control of cell preparations. Still, it is unclear how senescence‐associated DNAm changes are regulated and whether they occur simultaneously across a cell population. In this study, we analyzed global DNAm profiles of human mesenchymal stem cells (MSCs) and human umbilical vein endothelial cells (HUVECs) to demonstrate that senescence‐associated DNAm changes are overall similar in these different cell types. Subsequently, an Epigenetic‐Senescence‐Signature, based on six CpGs, was either analyzed by pyrosequencing or by bar‐coded bisulfite amplicon sequencing. There was a good correlation between predicted and real passage numbers in bulk populations of MSCs (R² = 0.67) and HUVECs (R² = 0.97). However, when we analyzed the Epigenetic‐Senescence‐Signature in subclones of MSCs, the predictions revealed high variation and they were not related to the adipogenic or osteogenic differentiation potential of the subclones. Notably, in clonally derived subpopulations, the DNAm levels of neighboring CpGs differed extensively, indicating that these genomic regions are not synchronously modified during senescence. Taken together, senescence‐associated DNAm changes occur in a highly reproducible manner, but they are not synchronously co‐regulated. They rather appear to be acquired stochastically—potentially evoked by other epigenetic modifications.

Potential drawbacks in cell-assisted lipotransfer: A systematic review of existing reports (Review)

Cell-assisted lipotransfer (CAL) has been widely used in various clinical applications, including breast augmentation following mammectomy, soft-tissue reconstruction and wound healing. However, the clinical application of CAL has been restricted due to the transplanted fat tissues being readily liquefied and absorbed. The present review examines 57 previously published studies involving CAL, including fat grafting or fat transfer with human adipose-stem cells in all known databases. Of these 57 articles, seven reported the clinical application of CAL. In the 57 studies, the majority of the fat tissues were obtained from the abdomen via liposuction of the seven clinical studies, four were performed in patients requiring breast augmentation, one in a patient requiring facial augmentation, one in a patient requiring soft tissue augmentation/reconstruction and one in a patient requiring fat in their upper arms. Despite the potential risks, there has been an increased demand for CAL in in cosmetic or aesthetic applications. Thus, criteria and guidelines are necessary for the clinical application of CAL technology.

Effect of mild heat stress on the proliferative and differentiative ability of human mesenchymal stromal cells

BACKGROUND AIMS

Mesenchymal stromal cells (MSCs) are an attractive candidate for autologous cell therapy, but regenerative potential can be compromised with extensive in vitro cell passaging. Development of viable cell therapies must address the effect of in vitro passaging to maintain overall functionality of expanded MSCs.

METHODS

We examined the effect of repeated mild heat shock on the proliferation and differentiation capability of human adipose-derived MSCs. Adipose tissue MSCs were characterized by means of fluorescence activated cell sorting analysis for expression of CD3, CD14, CD19, CD34, CD44, CD45, CD73, CD90 and CD105. Similarly, the expression of SIRT-1, p16(INK4a) and p21 was determined by means of polymerase chain reaction. Measurements of population doubling, doubling time and superoxide dismutase activity were also determined. Differentiation of expanded MSCs into bone and adipose were analyzed qualitatively and quantitatively.

RESULTS

The strategy led to an increase in expression of SIRT-1 concomitant with enhanced viability, proliferation and delayed senescence. The stressed MSCs showed better differentiation into osteoblasts and adipocytes.

CONCLUSIONS

The results indicate that mild heat shock could be used to maintain MSC proliferative and differentiation potential.

Mitochondrial transfer from Wharton's jelly-derived mesenchymal stem cells to mitochondria-defective cells recaptures impaired mitochondrial function

Adult mesenchymal stem cell (MSC)-conducted mitochondrial transfer has been recently shown to rescue cellular bioenergetics and prevent cell death caused by mitochondrial dysfunction. Wharton's jelly-derived MSCs (WJMSCs) harvested from postpartum umbilical cords are an accessible and abundant source of stem cells. This study aimed to determine the capability of WJMSCs to transfer their own mitochondria and rescue impaired oxidative phosphorylation (OXPHOS) and bioenergetics caused by mitochondrial DNA defects. To do this, WJMSCs were co-cultured with mitochondrial DNA (mtDNA)-depleted ρ(0) cells and the recapture of mitochondrial function was evaluated. WJMSCs were shown to be capable of transferring their own mitochondria into ρ(0) cells and underwent interorganellar mixture within these cells. Permissive culture media (BrdU-containing and pyruvate- and uridine-free) sieved out a survival cell population from the co-cultured WJMSCs (BrdU-sensitive) and ρ(0) cells (pyruvate/uridine-free). The survival cells had mtDNA identical to that of WJMSCs, whereas they expressed cellular markers identical to that of ρ(0) cells. Importantly, these ρ(0)-plus -WJMSC-mtDNA (ρ(+W)) cells recovered the expression of mtDNA-encoded proteins and exhibited functional oxygen consumption and respiratory control, as well as the activity of electron transport chain (ETC) complexes I, II, III and IV. In addition, ETC complex V-inhibitor-sensitive ATP production and metabolic shifting were also recovered. Furthermore, cellular behaviors including attachment-free proliferation, aerobic viability and OXPHOS-reliant cellular motility were also regained after mitochondrial transfer by WJMSCs. The therapeutic effect of WJMSCs-derived mitochondrial transfer was able to stably sustain for at least 45 passages. In conclusion, this study suggests that WJMSCs may serve as a potential therapeutic strategy for diseases linked to mitochondrial dysfunction through the donation of healthy mitochondria to cells with genetic mitochondrial defects.

An analysis of DNA methylation in human adipose tissue reveals differential modification of obesity genes before and after gastric bypass and weight loss

Background

Environmental factors can influence obesity by epigenetic mechanisms. Adipose tissue plays a key role in obesity-related metabolic dysfunction, and gastric bypass provides a model to investigate obesity and weight loss in humans.

Results

Here, we investigate DNA methylation in adipose tissue from obese women before and after gastric bypass and significant weight loss. In total, 485,577 CpG sites were profiled in matched, before and after weight loss, subcutaneous and omental adipose tissue. A paired analysis revealed significant differential methylation in omental and subcutaneous adipose tissue. A greater proportion of CpGs are hypermethylated before weight loss and increased methylation is observed in the 3′ untranslated region and gene bodies relative to promoter regions. Differential methylation is found within genes associated with obesity, epigenetic regulation and development, such as CETP, FOXP2, HDAC4, DNMT3B, KCNQ1 and HOX clusters. We identify robust correlations between changes in methylation and clinical trait, including associations between fasting glucose and HDAC4, SLC37A3 and DENND1C in subcutaneous adipose. Genes investigated with differential promoter methylation all show significantly different levels of mRNA before and after gastric bypass.

Conclusions

This is the first study reporting global DNA methylation profiling of adipose tissue before and after gastric bypass and associated weight loss. It provides a strong basis for future work and offers additional evidence for the role of DNA methylation of adipose tissue in obesity.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-014-0569-x) contains supplementary material, which is available to authorized users.

EZH2 and KDM6A act as an epigenetic switch to regulate mesenchymal stem cell lineage specification

The methyltransferase, Enhancer of Zeste homology 2 (EZH2), trimethylates histone 3 lysine 27 (H3K27me3) on chromatin and this repressive mark is removed by lysine demethylase 6A (KDM6A). Loss of these epigenetic modifiers results in developmental defects. We demonstrate that Ezh2 and Kdm6a transcript levels change during differentiation of multipotential human bone marrow-derived mesenchymal stem cells (MSC). Enforced expression of Ezh2 in MSC promoted adipogenic in vitro and inhibited osteogenic differentiation potential in vitro and in vivo, whereas Kdm6a inhibited adipogenesis in vitro and promoted osteogenic differentiation in vitro and in vivo. Inhibition of EZH2 activity and knockdown of Ezh2 gene expression in human MSC resulted in decreased adipogenesis and increased osteogenesis. Conversely, knockdown of Kdm6a gene expression in MSC leads to increased adipogenesis and decreased osteogenesis. Both Ezh2 and Kdm6a were shown to affect expression of master regulatory genes involved in adipogenesis and osteogenesis and H3K27me3 on the promoters of master regulatory genes. These findings demonstrate an important epigenetic switch centered on H3K27me3 which dictates MSC lineage determination.

Matrix elasticity, replicative senescence and DNA methylation patterns of mesenchymal stem cells

Matrix elasticity guides differentiation of mesenchymal stem cells (MSCs) but it is unclear if these effects are only transient - while the cells reside on the substrate - or if they reflect persistent lineage commitment. In this study, MSCs were continuously culture-expanded in parallel either on tissue culture plastic (TCP) or on polydimethylsiloxane (PDMS) gels of different elasticity to compare impact on replicative senescence, in vitro differentiation, gene expression, and DNA methylation (DNAm) profiles. The maximal number of cumulative population doublings was not affected by matrix elasticity. Differentiation towards adipogenic and osteogenic lineage was increased on soft and rigid biomaterials, respectively - but this propensity was no more evident if cells were transferred to TCP. Global gene expression profiles and DNAm profiles revealed relatively few differences in MSCs cultured on soft or rigid matrices. Furthermore, only moderate DNAm changes were observed upon culture on very soft hydrogels of human platelet lysate. Our results support the notion that matrix elasticity influences cellular behavior while the cells reside on the substrate, but it does not have major impact on cell-intrinsic lineage determination, replicative senescence or DNAm patterns.

Adipocytes under assault: environmental disruption of adipose physiology

The burgeoning obesity epidemic has placed enormous strains on individual and societal health mandating a careful search for pathogenic factors, including the contributions made by endocrine disrupting chemicals (EDCs). In addition to evidence that some exogenous chemicals have the capacity to modulate classical hormonal signaling axes, there is mounting evidence that several EDCs can also disrupt metabolic pathways and alter energy homeostasis. Adipose tissue appears to be a particularly important target of these metabolic disruptions. A diverse array of compounds has been shown to alter adipocyte differentiation, and several EDCs have been shown to modulate adipocyte physiology, including adipocytic insulin action and adipokine secretion. This rapidly emerging evidence demonstrating that environmental contaminants alter adipocyte function emphasizes the potential role that disruption of adipose physiology by EDCs may play in the global epidemic of metabolic disease. Further work is required to better characterize the molecular targets responsible for mediating the effects of EDCs on adipose tissue. Improved understanding of the precise signaling pathways altered by exposure to environmental contaminants will enhance our understanding of which chemicals pose a threat to metabolic health and how those compounds synergize with lifestyle factors to promote obesity and its associated complications. This knowledge may also improve our capacity to predict which synthetic compounds may alter energy homeostasis before they are released into the environment while also providing critical evidentiary support for efforts to restrict the production and use of chemicals that pose the greatest threat to human metabolic health. This article is part of a Special Issue entitled: Modulation of Adipose Tissue in Health and Disease.

PPARγ-induced PARylation promotes local DNA demethylation by production of 5-hydroxymethylcytosine

Recent studies have shown that DNA demethylation goes through the conversion of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC) by Tet proteins. However, it is still unclear how the target regions for demethylation are distinguished within their genomic context. Here we show that the nuclear receptor peroxisome proliferator-activated receptor-γ (PPARγ) has the ability to direct local demethylation around its binding sites, the PPAR response elements (PPREs), during adipocyte differentiation. PPARγ is a key regulator of the differentiation process that forms a PPARγ co-activator complex on PPREs and activates the expression of adipocyte-specific genes. The complex is poly(ADP-ribosyl)ated (PARylated) on PPREs, and Tet proteins catalyse the conversion of 5mC to 5hmC locally by their ability to bind to the PAR polymer, thereby inducing region-specific demethylation. Our study demonstrates that a sequence-dependent transcription factor complex can, through its post-translational modification, serve for Tet proteins as a landmark to identify sites of DNA demethylation.

DNA methylation of leptin and adiponectin promoters in children is reduced by the combined presence of obesity and insulin resistance

OBJECTIVE

Epigenetic alterations have been suggested to be associated with obesity and related metabolic disorders. Here we examined the correlation between obesity and insulin resistance with the methylation frequency of the leptin (LEP) and adiponectin (ADIPOQ) promoters in obese adolescents with the aim to identify epigenetic markers that might be used as tools to predict and follow up the physiological alterations associated with the development of the metabolic syndrome.

SUBJECTS

One hundred and six adolescents were recruited and classified according to body mass index and homeostasis model of assessment-insulin resistance index. The circulating concentrations of leptin, adiponectin and of several metabolic markers of obesity and insulin resistance were determined by standard methods. The methylation frequency of the LEP and ADIPOQ promoters was determined by methylation-specific PCR (MS-PCR) in DNA obtained from peripheral blood samples.

RESULTS

Obese adolescents without insulin resistance showed higher and lower circulating levels of, respectively, leptin and adiponectin along with increased plasmatic concentrations of insulin and triglycerides. They also exhibited the same methylation frequency than lean subjects of the CpG sites located at -51 and -31 nt relative to the transcription start site of the LEP gene. However, the methylation frequency of these nucleotides dropped markedly in obese adolescents with insulin resistance. We found the same inverse relationship between the combined presence of obesity and insulin resistance and the methylation frequency of the CpG site located at -283 nt relative to the start site of the ADIPOQ promoter.

CONCLUSIONS

These observations sustain the hypothesis that epigenetic modifications might underpin the development of obesity and related metabolic disorders. They also validate the use of blood leukocytes and MS-PCR as a reliable and affordable methodology for the identification of epigenetic modifications that could be used as molecular markers to predict and follow up the physiological changes associated with obesity and insulin resistance.

DNA Methylation Changes during In Vitro Propagation of Human Mesenchymal Stem Cells: Implications for Their Genomic Stability?

Mesenchymal stem cells (MSCs) hold great promise for the treatment of numerous diseases. A major problem for MSC therapeutic use is represented by the very low amount of MSCs which can be isolated from different tissues; thus ex vivo expansion is indispensable. Long-term culture, however, is associated with extensive morphological and functional changes of MSCs. In addition, the concern that they may accumulate stochastic mutations which lead the risk of malignant transformation still remains. Overall, the genome of human MSCs (hMSCs) appears to be apparently stable throughout culture, though transient clonal aneuploidies have been detected. Particular attention should be given to the use of low-oxygen environment in order to increase the proliferative capacity of hMSCs, since data on the effect of hypoxic culture conditions on genomic stability are few and contradictory. Furthermore, specific and reproducible epigenetic changes were acquired by hMSCs during ex vivo expansion, which may be connected and trigger all the biological changes observed. In this review we address current issues on long-term culture of hMSCs with a 360-degree view, starting from the genomic profiles and back, looking for an epigenetic interpretation of their genetic stability.

Assay validation for the assessment of adipogenesis of multipotential stromal cells--a direct comparison of four different methods

Background aims

Mesenchymal stromal cells (MSCs) are regenerative and immuno-privileged cells that are used for both tissue regeneration and treatment of severe inflammation-related disease. For quality control of manufactured MSC batches in regard to mature fat cell contamination, a quantitative method for measuring adipogenesis is needed.

Methods

Four previously proposed methods were validated with the use of bone marrow (BM) MSCs during a 21-day in vitro assay. Oil red staining was scored semiquantitatively; peroxisome proliferator activated receptor-γ and fatty acid binding protein (FABP)4 transcripts were measured by quantitative real-time polymerase chain reaction; FABP4 protein accumulation was evaluated by flow cytometry; and Nile red/4′,6-diamidino-2-phenylindole (DAPI) ratios were measured in fluorescent microplate assay. Skin fibroblasts and MSCs from fat pad, cartilage and umbilical cord were used as controls.

Results

Oil red staining indicated considerable heterogeneity between BM donors and individual cells within the same culture. FABP4 transcript levels increased 100- to 5000-fold by day 21, with large donor variability observed. Flow cytometry revealed increasing intra-culture heterogeneity over time; more granular cells accumulated more FABP4 protein and Nile red fluorescence compared with less granular cells. Nile red increase in day-21 MSCs was ∼5- and 4-fold, measured by flow cytometry or microplate assay, respectively. MSC proliferation/apoptosis was accounted through the use of Nile red/DAPI ratios; adipogenesis levels in day-21 BM MSCs increased ∼13-fold, with significant correlations with oil red scoring observed for MSC from other sources.

Conclusions

Flow cytometry permits the study of MSC differentiation at the single-cell level and sorting more and less mature cells from mixed cell populations. The microplate assay with the use of the Nile red/DAPI ratio provides rapid quantitative measurements and could be used as a low-cost, high-throughput method to quality-control MSC batches from different tissue sources.

Epigenetics and early life origins of chronic noncommunicable diseases

In light of the increasing threats of chronic noncommunicable diseases in developing countries, the growing recognition of the early life origins of chronic disease, and innovative breakthroughs in biomedical research and technology, it is imperative that we harness cutting-edge data to improve health promotion and maintenance. It is well recognized that chronic diseases are complex traits affected by a wide range of environmental and genetic factors; however, the role of epigenetic factors, particularly with regard to early life origins, remains largely unexplored. Given the unique properties of the epigenome-functionality during critical time windows, such as the intrauterine period, heritability, and reversibility-enhancing our understanding of epigenetic mechanisms may offer new opportunities for the development of novel early prediction and prevention paradigms. This may present an unparalleled opportunity to offer maternal and child health professionals important tools with the translational value to predict, detect, and prevent disease at an early age, long before its clinical occurrence, and as such, break lifelong and transgenerational cycles of disease. In doing so, modern technology can be leveraged to make great contributions to population health, quality of life, and reducing the burdensome economic costs of noncommunicable diseases in developing countries.

Genome-scale DNA methylation pattern profiling of human bone marrow mesenchymal stem cells in long-term culture

Human bone marrow mesenchymal stem cells (MSCs) expanded in vitro exhibit not only a tendency to lose their proliferative potential, homing ability and telomere length but also genetic or epigenetic modifications, resulting in senescence. We compared differential methylation patterns of genes and miRNAs between early-passage [passage 5 (P5)] and late-passage (P15) cells and estimated the relationship between senescence and DNA methylation patterns. When we examined hypermethylated genes (methylation peak ≥ 2) at P5 or P15, 2,739 genes, including those related to fructose and mannose metabolism and calcium signaling pathways, and 2,587 genes, including those related to DNA replication, cell cycle and the PPAR signaling pathway, were hypermethylated at P5 and P15, respectively. There was common hypermethylation of 1,205 genes at both P5 and P15. In addition, genes that were hypermethylated at P5 (CPEB1, GMPPA, CDKN1A, TBX2, SMAD9 and MCM2) showed lower mRNA expression than did those hypermethylated at P15, whereas genes that were hypermethylated at P15 (MAML2, FEN1 and CDK4) showed lower mRNA expression than did those that were hypermethylated at P5, demonstrating that hypermethylation at DNA promoter regions inhibited gene expression and that hypomethylation increased gene expression. In the case of hypermethylation on miRNA, 27 miRNAs were hypermethylated at P5, whereas 44 miRNAs were hypermethylated at P15. These results show that hypermethylation increases at genes related to DNA replication, cell cycle and adipogenic differentiation due to long-term culture, which may in part affect MSC senescence.

Tracking of replicative senescence in mesenchymal stem cells by colony-forming unit frequency

Long-term culture of mesenchymal stem cells (MSC) has major impact on cellular characteristics and differentiation potential. Numerous clinical trials raise high hopes in regenerative medicine and this necessitates reliable quality control of the cellular products-also with regard to replicative senescence. The maximum number of population doublings before entering the senescent state depends on the cell type, tissue of origin, culture medium as well as cell culture methods. Therefore, it would be valuable to predict the remaining proliferative potential in the course of culture expansion. Here, we describe a refined fibroblastic colony forming unit (CFU-f) assay which can be performed at any passage during culture expansion with simple cell culture techniques. This method is based on limiting dilutions in the 96-well format to determine the proportion of highly proliferative and clonogenic cells. The number of CFU-f declines rapidly during culture expansion. Especially at higher passages the CFU-f frequency correlates very well with the remaining cumulative population doublings. This approach can be used as quality measure to estimate the remaining proliferative potential of MSC in culture.

Epigenetic reprogramming of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent stem cells of mesodermal origin that can be isolated from various sources and induced into different cell types. Although MSCs possess immune privilege and are more easily obtained than embryonic stem cells, their propensity to tumorigenesis has not been fully explored. Epigenomic changes in DNA methylation and chromatin structure have been hypothesized to be critical in the determination of lineage-specific differentiation and tumorigenesis of MSCs, but this has not been formally proven. We applied a targeted DNA methylation method to methylate a Polycomb group protein-governed gene, Trip10, in MSCs, which accelerated the cell fate determination of MSCs. In addition, targeted methylation of HIC1 and RassF1A, both tumor suppressor genes, transformed MSCs into tumor stem cell-like cells. This new method will allow better control of the differentiation of MSCs and their use in downstream applications.

Functional comparison of chronological and in vitro aging: differential role of the cytoskeleton and mitochondria in mesenchymal stromal cells

Mesenchymal stromal cells (MSCs) are of high relevance for the regeneration of mesenchymal tissues such as bone and cartilage. The promising role of MSCs in cell-based therapies and tissue engineering appears to be limited due to a decline of their regenerative potential with increasing donor age, their limited availability in human tissues and the need of in vitro expansion prior to treatment. We therefore aimed to determine to which degree in vitro aging and chronological aging may be similar processes or if in vitro culture-related changes at the cellular and molecular level are at least altered as a function of donor age. For that purpose we established MSCs cultures from young (yMSCs) and aged (aMSCs) rats that were cultured for more than 100 passages. These long-term MSCs cultures were non-tumorigenic and exhibited similar surface marker patterns as primary MSCs of passage 2. During in vitro expansion, but not during chronological aging, MSCs progressively lose their progenitor characteristics, e.g., complete loss of osteogenic differentiation potential, diminished adipogenic differentiation, altered cell morphology and increased susceptibility towards senescence. Transcriptome analysis revealed that long-term in vitro MSCs cultivation leads to down-regulation of genes involved in cell differentiation, focal adhesion organization, cytoskeleton turnover and mitochondria function. Accordingly, functional analysis demonstrated altered mitochondrial morphology, decreased antioxidant capacities and elevated ROS levels in long-term cultivated yMSCs as well as aMSCs. Notably, only the MSC migration potential and their antioxidative capacity were altered by in vitro as well as chronological aging. Based on specific differences observed between the impact of chronological and in vitro MSC aging we conclude that both are distinct processes.