The epigenetic modifiers 5-aza-2'-deoxycytidine and trichostatin A influence adipocyte differentiation in human mesenchymal stem cells

Conservative Hypomethylation of Mesenchymal Stem Cells and Their Secretome Restored the Follicular Development in Cisplatin-Induced Premature Ovarian Failure Mice

Premature ovarian failure (POF) is one of the main causes of infertility in women under the age of 40 years. Recently, epigenetic reprogramming, particularly DNA hypomethylation, has emerged as a promising strategy to enhance the therapeutic potential of mesenchymal stem cells (MSCs). Thus, it is crucial to elucidate how far global hypomethylation of MSCs genome can maintain their pluripotency and viability and improve their therapeutic effect in chemotherapy-induced POF mice. Herein, the genomic DNA of bone marrow-derived MSCs (BM-MSCs) was hypomethylated by the DNA methyltransferase inhibitor (5-Aza-dC), and the degree of global hypomethylation was assessed by methylation-sensitive HepII/MspI restriction analysis. Next, mildly hypomethylated cells and their secretome were independently transplanted (or infused) in POF mice, established via cisplatin-mediated gonadotoxicity. We found that conservative global hypomethylation of BM-MSCs genome with low doses of 5-Aza-dC (≤0.5 μM) has maintained cell viability and MSCs-specific clusters of differentiation (CD). Engraftment of mildly hypomethylated cells in POF mice, or infusion of their secretome, improved the concentrations of estradiol (E2), follicle-stimulating hormone (FSH), and anti-Mullerian hormone (AMH). Furthermore, mice restored their normal body weight, ovarian size, and ovarian follicle count. This was associated with improved follicular development, where the populations of healthy primordial, primary, secondary, and tertiary follicles were significantly ameliorated, relative to mice transplanted with normally methylated cells. This observational study suggests that transplantation of mildly hypomethylated BM-MSCs cells and their secretome can restore the structural and functional integrity of the damaged ovaries in POF mice. Also, it presents conservative hypomethylation of BM-MSCs and their secretome as a promising alternative to MSCs transplantation.

How mesenchymal stem cells transform into adipocytes: Overview of the current understanding of adipogenic differentiation

Mesenchymal stem cells (MSCs) are stem/progenitor cells capable of self-renewal and differentiation into osteoblasts, chondrocytes and adipocytes. The transformation of multipotent MSCs to adipocytes mainly involves two subsequent steps from MSCs to preadipocytes and further preadipocytes into adipocytes, in which the process MSCs are precisely controlled to commit to the adipogenic lineage and then mature into adipocytes. Previous studies have shown that the master transcription factors C/enhancer-binding protein alpha and peroxisome proliferation activator receptor gamma play vital roles in adipogenesis. However, the mechanism underlying the adipogenic differentiation of MSCs is not fully understood. Here, the current knowledge of adipogenic differentiation in MSCs is reviewed, focusing on signaling pathways, noncoding RNAs and epigenetic effects on DNA methylation and acetylation during MSC differentiation. Finally, the relationship between maladipogenic differentiation and diseases is briefly discussed. We hope that this review can broaden and deepen our understanding of how MSCs turn into adipocytes.

Epigenetics: Novel crucial approach for osteogenesis of mesenchymal stem cells

Bone has a robust regenerative potential, but its capacity to repair critical-sized bone defects is limited. In recent years, stem cells have attracted significant interest for their potential in tissue engineering. Applying mesenchymal stem cells (MSCs) for enhancing bone regeneration is a promising therapeutic strategy. However, maintaining optimal cell efficacy or viability of MSCs is limited by several factors. Epigenetic modification can cause changes in gene expression levels without changing its sequence, mainly including nucleic acids methylation, histone modification, and non-coding RNAs. This modification is believed to be one of the determinants of MSCs fate and differentiation. Understanding the epigenetic modification of MSCs can improve the activity and function of stem cells. This review summarizes recent advances in the epigenetic mechanisms of MSCs differentiation into osteoblast lineages. We expound that epigenetic modification of MSCs can be harnessed to treat bone defects and promote bone regeneration, providing potential therapeutic targets for bone-related diseases.

Inhibiting DNA methylation as a strategy to enhance adipose-derived stem cells differentiation: Focus on the role of Akt/mTOR and Wnt/β-catenin pathways on adipogenesis

Adipose-derived mesenchymal stem cells (ASCs) represent a valid therapeutic option for clinical application in several diseases, due to their ability to repair damaged tissues and to mitigate the inflammatory/immune response. A better understanding of the underlying mechanisms regulating ASC biology might represent the chance to modulate their in vitro characteristics and differentiation potential for regenerative medicine purposes. Herein, we investigated the effects of the demethylating agent 5-azacytidine (5-aza) on proliferation, clonogenicity, migration, adipogenic differentiation and senescence of ASCs, to identify the molecular pathways involved. Through functional assays, we observed a detrimental effect of 5-aza on ASC self-renewal capacity and migration, accompanied by actin cytoskeleton reorganization, with decreased stress fibers. Conversely, 5-aza treatment enhanced ASC adipogenic differentiation, as assessed by lipid accumulation and expression of lineage-specific markers. We analyzed the involvement of the Akt/mTOR, MAPK and Wnt/β-catenin pathways in these processes. Our results indicated impairment of Akt and ERK phosphorylation, potentially explaining the reduced cell proliferation and migration. We observed a 5-aza-mediated inhibition of the Wnt signaling pathway, this potentially explaining the pro-adipogenic effect of the drug. Finally, 5-aza treatment significantly induced ASC senescence, through upregulation of the p53/p21 axis. Our data may have important translational implications, by helping in clarifying the potential risks and advantages of using epigenetic treatment to improve ASC characteristics for cell-based clinical approaches.

Chaetocin Promotes Osteogenic Differentiation via Modulating Wnt/Beta-Catenin Signaling in Mesenchymal Stem Cells

Mesenchymal stemXin cells (MSCs) are a great cell source for bone regeneration. Although combining MSCs with growth factors and scaffolds provides a useful clinical strategy for bone tissue engineering, the efficiency of MSC osteogenic differentiation remains to be improved. Epigenetic modification is related to the differentiation ability of MSCs during osteogenic induction. In this study, we evaluate the effect of Chaetocin, an inhibitor of lysine-specific histone methyltransferases, on the differentiation of MSCs. We found that MSCs treated with Chaetocin demonstrated increased osteogenic ability and reduced adipogenic ability. The expression of osteogenic markers (Runx2 and OPN) was induced in MSCs by Chaetocin during osteogenic induction. Moveover, treatment of Chaetocin in MSCs improves Wnt/β-catenin signaling pathways and its downstream targets. Finally, we showed increased bone formation of MSC and Wnt/β-catenin signaling activity by treatment of Chaetocin using in vivo bone formation assays. Our data uncovered a critical role of Chaetocin in MSC osteogenic differentiation and provide new insights into bone tissue regeneration and repair.

Effect of the Addition Frequency of 5-Azacytidine in Both Micro- and Macroscale Cultures

INTRODUCTION

Human mesenchymal stem cells (hMSCs) have a great clinical potential for tissue regeneration purposes due to its multilineage capability. Previous studies have reported that a single addition of 5-azacytidine (5-AzaC) causes the differentiation of hMSCs towards a myocardial lineage. The aim of this work was to evaluate the effect of 5-AzaC addition frequency on hMSCs priming (i.e., indicating an early genetic differentiation) using two culture environments.

METHODS

hMSCs were supplemented with 5-AzaC while cultured in well plates and in microfluidic chips. The impact of 5-AzaC concentration (10 and 20 μM) and addition frequency (once, daily or continuously), as well as of culture period (2 or 5 days) on the genetic upregulation of PPARγ (adipocytes), PAX3 (myoblasts), SOX9 (chondrocytes) and RUNX2 (osteoblasts) was evaluated.

RESULTS

Daily delivering 5-AzaC caused a higher upregulation of PPARγ, SOX9 and RUNX2 in comparison to a single dose delivery, both under static well plates and dynamic microfluidic cultures. A particularly high gene expression of PPARγ (tenfold-change) could indicate priming of hMSCs towards adipocytes.

CONCLUSIONS

Both macro- and microscale cultures provided results with similar trends, where addition frequency of 5-AzaC was a crucial factor to upregulate several genes. Microfluidics technology was proven to be a suitable platform for the continuous delivery of a drug and could be used for screening purposes in tissue engineering research.

Epigenetic Regulators of White Adipocyte Browning

Adipocytes play an essential role in maintaining energy homeostasis in mammals. The primary function of white adipose tissue (WAT) is to store energy; for brown adipose tissue (BAT), primary function is to release fats in the form of heat. Dysfunctional or excess WAT can induce metabolic disorders such as dyslipidemia, obesity, and diabetes. Preadipocytes or adipocytes from WAT possess sufficient plasticity as they can transdifferentiate into brown-like beige adipocytes. Studies in both humans and rodents showed that brown and beige adipocytes could improve metabolic health and protect from metabolic disorders. Brown fat requires activation via exposure to cold or β-adrenergic receptor (β-AR) agonists to protect from hypothermia. Considering the fact that the usage of β-AR agonists is still in question with their associated side effects, selective induction of WAT browning is therapeutically important instead of activating of BAT. Hence, a better understanding of the molecular mechanisms governing white adipocyte browning is vital. At the same time, it is also essential to understand the factors that define white adipocyte identity and inhibit white adipocyte browning. This literature review is a comprehensive and focused update on the epigenetic regulators crucial for differentiation and browning of white adipocytes.

Epigenetic Control of Osteogenic Lineage Commitment

Within the eukaryotic nucleus the genomic DNA is organized into chromatin by stably interacting with the histone proteins as well as with several other nuclear components including non-histone proteins and non-coding RNAs. Together these interactions distribute the genetic material into chromatin subdomains which can exhibit higher and lower compaction levels. This organization contributes to differentially control the access to genomic sequences encoding key regulatory genetic information. In this context, epigenetic mechanisms play a critical role in the regulation of gene expression as they modify the degree of chromatin compaction to facilitate both activation and repression of transcription. Among the most studied epigenetic mechanisms we find the methylation of DNA, ATP-dependent chromatin remodeling, and enzyme-mediated deposition and elimination of post-translational modifications at histone and non-histone proteins. In this mini review, we discuss evidence that supports the role of these epigenetic mechanisms during transcriptional control of osteoblast-related genes. Special attention is dedicated to mechanisms of epigenetic control operating at the Runx2 and Sp7 genes coding for the two principal master regulators of the osteogenic lineage during mesenchymal stem cell commitment.

Epigenetic Regulation of Neuregulin-1 Tunes White Adipose Stem Cell Differentiation

Expansion of subcutaneous adipose tissue by differentiation of new adipocytes has been linked to improvements in metabolic health. However, an expandability limit has been observed wherein new adipocytes cannot be produced, the existing adipocytes become enlarged (hypertrophic) and lipids spill over into ectopic sites. Inappropriate ectopic storage of these surplus lipids in liver, muscle, and visceral depots has been linked with metabolic dysfunction. Here we show that Neuregulin-1 (NRG1) serves as a regulator of adipogenic differentiation in subcutaneous primary human stem cells. We further demonstrate that DNA methylation modulates NRG1 expression in these cells, and a 3-day exposure of stem cells to a recombinant NRG1 peptide fragment is sufficient to reprogram adipogenic cellular differentiation to higher levels. These results define a novel molecular adipogenic rheostat with potential implications for the expansion of adipose tissue in vivo.

Concise Review: The Regulatory Mechanism of Lysine Acetylation in Mesenchymal Stem Cell Differentiation

Nowadays, the use of MSCs has attracted considerable attention in the global science and technology field, with the self-renewal and multidirectional differentiation potential for diabetes, obesity treatment, bone repair, nerve repair, myocardial repair, and so on. Epigenetics plays an important role in the regulation of mesenchymal stem cell differentiation, which has become a research hotspot in the medical field. This review focuses on the role of lysine acetylation modification on the determination of MSC differentiation direction. During this progress, the recruitment of lysine acetyltransferases (KATs) and lysine deacetylases (KDACs) is the crux of transcriptional mechanisms in the dynamic regulation of key genes controlling MSC multidirectional differentiation.

The role of epigenetic modifications in the osteogenic differentiation of adipose-derived stem cells

Over the last decade, stem cells have drawn extensive attention from scientists due to their full potential in tissue engineering, gene therapy, and cell therapy. Adipose-derived stem cells (ADSCs), which represent one type of mesenchymal stem cell (MSC), hold great promise in bone tissue engineering due to their painless collection procedure, their ability to self-renew and their multi-lineage differentiation properties. Major epigenetic mechanisms, which involve DNA methylation, histone modifications and RNA interference (RNAi), are known to represent one of the determining factors of ADSC fate and differentiation. Understanding the epigenetic modifications of ADSCs may provide a clue for improving stem cell therapy in bone repair and regeneration. The aim of this review is to present the recent advances in understanding the epigenetic mechanisms that facilitate ADSC differentiation into an osteogenic lineage, in addition to the characteristics of the main epigenetic modifications.

Direct conversion of fibroblasts to osteoblasts as a novel strategy for bone regeneration in elderly individuals

Mortality caused by age-related bone fractures or osteoporosis is steadily increasing worldwide as the population ages. The pace of the development of bone regeneration engineering to treat bone fractures has consequently increased in recent years. A range of techniques for bone regeneration, such as immunotherapy, allografts, and hydrogel therapy, have been devised. Cell-based therapies using bone marrow-derived mesenchymal stem cells and induced pluripotent stem cells derived from somatic cells are considered to be suitable approaches for bone repair. However, these cell-based therapies suffer from a number of limitations in terms of efficiency and safety. Somatic cells can also be directly differentiated into osteoblasts by several transcription factors. As osteoblasts play a central role in the process of bone formation, the direct reprogramming of fibroblasts into osteoblasts may hence be a new way to treat bone fractures in elderly individuals. Here, we review recent developments regarding the therapeutic potential of the direct reprogramming of cells for bone regeneration.

Reprogramming cells that produce connective tissue to form bone instead could help prevent fractures in the elderly. Bones weaken with age, and fractures are a significant health risk in ageing populations. Most current bone regeneration treatments use stem cells, which can differentiate into any type of cell and have infinite capacity to divide; however, they are difficult to source and can lead to tumor formation. Jongpil Kim at Dongguk University in South Korea and coworkers have reviewed a new method that uses genetic signals to transform connective tissue-forming cells into bone-producing cells. The reprogrammed cells have been shown to generate new bone at the desired site, and because they have already lost their capacity for infinite division, tumor formation risk is greatly reduced. This method shows promise to expand treatment options for fractures and osteoporosis.

Paradoxical effects of the epigenetic modifiers 5-aza-deoxycytidine and suberoylanilide hydroxamic acid on adipogenesis

Adipogenesis is an important biological process that is linked to obesity and metabolic disorders. On the other hand, fat regeneration is crucial as a restorative approach following mastectomy or severe burn injury. Furthermore, optimizing an in-vitro model of adipogenesis, which would help in understanding the possible effects and/or side effects of fat-soluble drugs and anti-obesity remedies, in addition to the developmental studies. Epigenetic is an important factor that is involved in cellular differentiation and commitment. This study aimed at investigating the effect of DNA methylation and histone deactylases inhibitors, 5-Aza-deoxycytidine (5-Aza-dC) and Suberoylanilide hydroxamic acid (SAHA), on the adipogenic differentiation process. The two modifiers were applied according to our previously published protocol, followed by three cycles of a classical, two-step adipogenesis protocol. The cells pretreated with SAHA showed enhanced expression of the many adipogenic genes, including peroxisome proliferator-activated receptor-γ as well as the accumulation of intracytoplasmic fat as shown by oil red and Nile red staining and the secretion of adipokines, such as MCP-1 and IP-10. On contrary, 5-Aza-dC inhibited all these markers. In conclusion, adding the reported step with SAHA to the differentiation protocols could have an impact on the progress of the in-vitro fat regenerative approach. The possible role of 5-Aza-dC in the inhibition of adipogenesis can be of clinical interest and will need further characterization in the future.

In vivo and in vitro bisphenol A exposure effects on adiposity

In utero exposure to the ubiquitous plasticizer, bisphenol A (BPA) is associated with offspring obesity. As adipogenesis is a critical factor contributing to obesity, we determined the effects of in vivo maternal BPA and in vitro BPA exposure on newborn adipose tissue at the stem-cell level. For in vivo studies, female rats received BPA before and during pregnancy and lactation via drinking water, and offspring were studied for measures of adiposity signals. For in vitro BPA exposure, primary pre-adipocyte cell cultures from healthy newborns were utilized. We studied pre-adipocyte proliferative and differentiation effects of BPA and explored putative signal factors which partly explain adipose responses and underlying epigenetic mechanisms mediated by BPA. Maternal BPA-induced offspring adiposity, hypertrophic adipocytes and increased adipose tissue protein expression of pro-adipogenic and lipogenic factors. Consistent with in vivo data, in vitro BPA exposure induced a dose-dependent increase in pre-adipocyte proliferation and increased adipocyte lipid content. In vivo and in vitro BPA exposure promotes the proliferation and differentiation of adipocytes, contributing to an enhanced capacity for lipid storage. These findings reinforce the marked effects of BPA on adipogenesis and highlight the susceptibility of stem-cell populations during early life with long-term consequence on metabolic homeostasis.

An epigenetic bioactive composite scaffold with well-aligned nanofibers for functional tendon tissue engineering

Poor tendon repair is often a clinical challenge due to the lack of ideal biomaterials. Electrospun aligned fibers, resembling the ultrastructure of tendon, have been previously reported to promote tenogenesis. However, the underlying mechanism is unclear and the aligned fibers alone are not capable enough to commit teno-differentiation of stem cells. Here, based on our observation of reduced expression of histone deacetylases (HDACs) in tendon stem/progenitor cells (TSPCs) cultured on aligned fibers, we proposed a strategy to enhance the tenogenesis effect of aligned fibers by using a small molecule Trichostatin A (TSA), an HDAC inhibitor. Such a TSA-laden poly (l-lactic acid) (PLLA) aligned fiber (A-TSA) scaffold was successfully fabricated by a stable jet electrospinning method, and demonstrated its sustained capability in releasing TSA. We found that TSA incorporated aligned fibers of PLLA had an additive effect in directing tenogenic differentiation. Moreover, the in situ implantation study in rat model further confirmed that A-TSA scaffold promoted the structural and mechanical properties of the regenerated Achilles tendon. This study demonstrated that HDAC was involved in the teno-differentiation with aligned fiber topography, and the combination of HDAC with aligned topography might be a more efficient strategy to promote tenogenesis of stem cells.

STATEMENT OF SIGNIFICANCE

Electrospun aligned fibers, resembling the ultrastructure of tendon, have been previously reported to promote tenogenesis. However, the underlying mechanism is unclear and the aligned fibers alone are not capable enough to commit teno-differentiation of stem cells. The uniqueness of our studies are as follows, based on our observation of reduced expression of histone deacetylases (HDACs) in tendon stem/progenitor cells (TSPCs) cultured on aligned fibers, we proposed a strategy to enhance the tenogenesis effect of aligned fibers by using a small molecule Trichostatin A (TSA), a HDAC inhibitor. Such a TSA-laden poly (l-lactic acid) (PLLA) aligned fiber (A-TSA) scaffold was successfully fabricated by a stable jet electrospinning method, and demonstrated its sustained capability in releasing TSA. The incorporation and subsequent release of bioactive small molecule TSA into electrospun aligned fibers allows a controllable manner for both biochemical and physical regulation of tenogenesis of stem cells both in vitro and in vivo. Collectively, the present study provides a model of "translating the biological knowledge learned from cell-material interaction into optimizing biomaterials (from Biomat-to-Biomat)".

Reflections on Cancer in the Bone Marrow: Adverse Roles of Adipocytes

This review highlights the recent advances in our understanding of adipocyte contributions to carcinogenesis or cancer disease progression for cancers in the bone.

Purpose

In this review, we aim to describe bone marrow adipose tissue and discuss the soluble adipocyte-derived cytokines (adipokines) or endocrine factors, adipocyte-derived lipids, and the actual or putative juxtacrine signaling between bone marrow adipocytes and tumor cells in the bone marrow. This relationship likely affects tumor cell initiation, proliferation, metastasis, and/or drug resistance.

Recent Findings

Bone marrow adipose may affect tumor proliferation, drug resistance, or cancer-induced bone disease and hence may be a new target in the fight against cancer.

Summary

Overall, evidence is mixed regarding the role of bone marrow adipose and adipocytes in cancer progression, and more research in this arena is necessary to determine how these bone marrow microenvironmental cells contribute to malignancies in the marrow to identify novel, potentially targetable pathways.

Pharmacologic concentrations of linezolid modify oxidative phosphorylation function and adipocyte secretome

The oxidative phosphorylation system is important for adipocyte differentiation. Therefore, xenobiotics inhibitors of the oxidative phosphorylation system could affect adipocyte differentiation and adipokine secretion. As adipokines impact the overall health status, these xenobiotics may have wide effects on human health. Some of these xenobiotics are widely used therapeutic drugs, such as ribosomal antibiotics. Because of its similarity to the bacterial one, mitochondrial translation system is an off-target for these compounds. To study the influence of the ribosomal antibiotic linezolid on adipokine production, we analyzed its effects on adipocyte secretome. Linezolid, at therapeutic concentrations, modifies the levels of apolipoprotein E and several adipokines and proteins related with the extracellular matrix. This antibiotic also alters the global methylation status of human adipose tissue-derived stem cells and, therefore, its effects are not limited to the exposure period. Besides their consequences on other tissues, xenobiotics acting on the adipocyte oxidative phosphorylation system alter apolipoprotein E and adipokine production, secondarily contributing to their systemic effects.

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Linezolid decreases oxidative phosphorylation system capacity.

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Linezolid reduces adipocyte differentiation from human adipose-derived stem cells.

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Linezolid modifies APOE, adipokine and extracellular matrix proteins levels.

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Linezolid changes DNA methylation of human adipose tissue-derived stem cells.

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Xenobiotics, acting on adipocyte oxidative phosphorylation, affect human health.

Adipocyte nuclei captured from VAT and SAT

Background

Obesity-related comorbidities are thought to result from the reprogramming of the epigenome in numerous tissues and cell types, and in particular, mature adipocytes within visceral and subcutaneous adipose tissue, VAT and SAT. The cell-type specific chromatin remodeling of mature adipocytes within VAT and SAT is poorly understood, in part, because of the difficulties of isolating and manipulating large fragile mature adipocyte cells from adipose tissues.

Methods

We constructed MA-INTACT (Mature Adipocyte-Isolation of Nuclei TAgged in specific Cell Types) mice using the adiponectin (ADIPOQ) promoter (ADNp) to tag the surface of mature adipocyte nuclei with a reporter protein. The SUN1mRFP1Flag reporter is comprised of a fragment of the nuclear transmembrane protein SUN1, the fluorescent protein mRFP1, and three copies of the Flag epitope tag.

Results

Mature adipocyte nuclei were rapidly and efficiently immuno-captured from VAT and SAT (MVA and MSA nuclei, respectively), of MA-INTACT mice. MVA and MSA nuclei contained 1,000 to 10,000-fold higher levels of adipocyte-specific transcripts, ADIPOQ, PPARg2, EDNRB, and LEP, relative to uncaptured nuclei, while the latter expressed higher levels of leukocyte and endothelial cell markers IKZF1, RETN, SERPINF1, SERPINE1, ILF3, and TNFA. MVA and MSA nuclei differentially expressed several factors linked to adipogenesis or obesity-related health risks including CEBPA, KLF2, RETN, SERPINE1, and TNFA. The various nuclear populations dramatically differentially expressed transcripts encoding chromatin remodeler proteins regulating DNA cytosine methylation and hydroxymethylation (TETs, DNMTs, TDG, GADD45s) and nucleosomal histone modification (ARID1A, KAT2B, KDM4A, PRMT1, PRMT5, PAXIP1). Remarkably, MSA and MVA nuclei expressed 200 to 1000-fold higher levels of thermogenic marker transcripts PRDM16 and UCP1.

Conclusions

The MA-INTACT mouse enables a simple way to perform cell-type specific analysis of highly purified mature adipocyte nuclei from VAT and SAT and increases the statistical significance of data collected on adipocytes. Isolated VAT and SAT adipocyte nuclei expressed distinct patterns of transcripts encoding chromatin remodeling factors and proteins relevant to diabetes, cardiovascular disease, and thermogenesis. The MA-INTACT mouse is an useful model to test the impact of caloric intake, dietary nutrients, exercise, and pharmaceuticals on the epigenome-induced health risks of obesity.

Electronic supplementary material

The online version of this article (doi:10.1186/s40608-016-0112-6) contains supplementary material, which is available to authorized users.

Subsets of Visceral Adipose Tissue Nuclei with Distinct Levels of 5-Hydroxymethylcytosine

The reprogramming of cellular memory in specific cell types, and in visceral adipocytes in particular, appears to be a fundamental aspect of obesity and its related negative health outcomes. We explored the hypothesis that adipose tissue contains epigenetically distinct subpopulations of adipocytes that are differentially potentiated to record cellular memories of their environment. Adipocytes are large, fragile, and technically difficult to efficiently isolate and fractionate. We developed fluorescence nuclear cytometry (FNC) and fluorescence activated nuclear sorting (FANS) of cellular nuclei from visceral adipose tissue (VAT) using the levels of the pan-adipocyte protein, peroxisome proliferator-activated receptor gamma-2 (PPARg2), to distinguish classes of PPARg2-Positive (PPARg2-Pos) adipocyte nuclei from PPARg2-Negative (PPARg2-Neg) leukocyte and endothelial cell nuclei. PPARg2-Pos nuclei were 10-fold enriched for most adipocyte marker transcripts relative to PPARg2-Neg nuclei. PPARg2-Pos nuclei showed 2- to 50-fold higher levels of transcripts encoding most of the chromatin-remodeling factors assayed, which regulate the methylation of histones and DNA cytosine (e.g., DNMT1, TET1, TET2, KDM4A, KMT2C, SETDB1, PAXIP1, ARID1A, JMJD6, CARM1, and PRMT5). PPARg2-Pos nuclei were large with decondensed chromatin. TAB-seq demonstrated 5-hydroxymethylcytosine (5hmC) levels were remarkably dynamic in gene bodies of various classes of VAT nuclei, dropping 3.8-fold from the highest quintile of expressed genes to the lowest. In short, VAT-derived adipocytes appear to be more actively remodeling their chromatin than non-adipocytes.

Histone modifications interact with DNA methylation at the GATA4 promoter during differentiation of mesenchymal stem cells into cardiomyocyte-like cells

OBJECTIVES

A previous study of ours confirmed that Islet-1 specifically induces differentiation of MSCs into cardiomyocytes, and that one of the mechanisms underlying that process is regulation of histone acetylation. Here, we further explore the mechanism of MSC differentiation into cardiomyocytes from the perspective of interactions between epigenetic modifications.

MATERIALS AND METHODS

We used lentiviral vectors to overexpress Islet-1 in MSCs, and ChIP-qPCR, MSP and BSP were performed to detect levels of histone acetylation/methylation and DNA methylation in the GATA4 and Nkx2.5 promoters. To further explore relationships between these epigenetic modifications, we used 5-aza or TSA to interfere with DNA methylation and histone acetylation, respectively, and detected effects on the other two modifications.

RESULTS

Histone acetylation level increased and its methylation level decreased at GATA4 and Nkx2.5 promoters; DNA methylation level was reduced at the GATA4 promoter but did not change at the Nkx2.5 promoter. Furthermore, 5-aza increased histone acetylation level and reduced its methylation level at the GATA4 promoter but had no effect on the Nkx2.5 promoter; TSA reduced histone methylation and DNA methylation levels at the GATA4 promoter, but it only reduced histone methylation level at the Nkx2.5 promoter.

CONCLUSIONS

Histone acetylation/methylation and DNA methylation were both involved in regulating GATA4 expression, but Nkx2.5 expression was not regulated by DNA methylation. These three modifications had high correlation with each other during regulation of GATA4 and produced a regulation loop at the GATA4 promoter.

Short-chain fatty acids enhance adipocyte differentiation in the stromal vascular fraction of porcine adipose tissue

BACKGROUND

Short-chain fatty acids (SCFAs), including acetate, propionate, and butyrate, are the main products of microbial fermentation in the gut and might mediate some of the effects of gut microbiota and nutrition on development, metabolism, and pathogenesis of obesity and other diseases.

OBJECTIVE

The objective of this study was to determine the effects of SCFAs on adipocyte differentiation and the underlying mechanism.

METHODS

The stromal vascular fraction (SVF) of the porcine subcutaneous fat was used as the preadipocyte model. Adipocyte differentiation was assessed by Oil Red O staining and gene expression analysis of adipocyte markers. Chromatin immunoprecipitation was used to assess the histone acetylation amounts at the peroxisome proliferator-activated receptor γ (PPARG) and CCAAT/enhancer binding protein α (CEBPA) promoters.

RESULTS

Compared with control, propionate and butyrate enhanced the formation of adipocytes by 10-20% and mRNA expression of adipocyte markers by 20-200% in porcine SVF undergoing adipocyte differentiation. Compared with control, short-term treatment of propionate and butyrate enhanced PPARG and CEBPA mRNA expression in porcine SVF by 50-100%. Neither free fatty acid receptor (FFAR) 2 nor FFAR3 mRNA was detectable in porcine SVF before or during differentiation. Neither a cAMP analogue nor an activator of AMP-activated protein kinase (AMPK) affected propionate- or butyrate-enhanced expression of PPARG or CEBPA mRNA. Trichostatin A, a specific inhibitor of histone deacetylases (HDACs), enhanced the formation of adipocytes in porcine SVF by nearly 100% and the expression of PPARG and CEBPA mRNAs by 150% and 50%, respectively. Butyrate increased whereas propionate had no significant effect on histone H3 acetylation at the CEBPA promoter in porcine SVF.

CONCLUSIONS

Propionate and butyrate enhance adipocyte differentiation in porcine SVF. These effects are unlikely mediated through FFAR2, FFAR3, cAMP, or AMPK. The effect of butyrate may be partially mediated by its HDAC inhibitory activity, whereas that of propionate is independent of its HDAC inhibitory activity.

Association of DNA Methylation Levels with Tissue-specific Expression of Adipogenic and Lipogenic Genes in Longissimus dorsi Muscle of Korean Cattle

Epigenetic factors, such as DNA methylation status, may regulate adipogenesis and lipogenesis, thus affecting intramuscular fat (IMF) deposition in longissimus dorsi muscle (LM) of beef cattle. In Korean cattle steers, the LM consists mainly of muscle tissue. However, the LM tissue also contains IMF. We compared the gene expression levels between the IMF and muscle portions of the LM after tissue separation. Real-time polymerase chain reaction analysis showed that the mRNA levels of both adipogenic peroxisome proliferator-activated receptor gamma isoform 1 (PPARG1) and lipogenic fatty acid binding protein 4 (FABP4) were higher (p<0.01) in the IMF than in the muscle portion of the LM. We determined DNA methylation levels of regulatory regions of the PPARG1 and FABP4 genes by pyrosequencing of genomic DNA. DNA methylation levels of two of three CpG sites in the PPARG1 gene promoter region were lower (p<0.05) in the IMF than in the muscle portion of the LM. DNA methylation levels of all five CpG sites from the FABP4 gene promoter region were also lower (p<0.001) in the IMF than in the muscle portion. Thus, mRNA levels of both PPARG1 and FABP4 genes were inversely correlated with DNA methylation levels in regulatory regions of CpG sites of the corresponding gene. Our findings suggest that DNA methylation status regulates tissue-specific expression of adipogenic and lipogenic genes in the IMF and muscle portions of LM tissue in Korean cattle.

Polysome profiling shows the identity of human adipose-derived stromal/stem cells in detail and clearly distinguishes them from dermal fibroblasts

Although fibroblasts and multipotent stromal/stem cells, including adipose-derived stromal cells (ADSCs), have been extensively studied, they cannot be clearly distinguished from each other. We, therefore, investigated the cellular and molecular characteristics of ADSCs and fibroblasts. ADSCs and fibroblasts share several morphological similarities and surface markers, but were clearly found to be different types of cells. Contrary to previous reports, fibroblasts were not able to differentiate into adipocytes, osteoblasts, or chondrocytes. Polysome-bound mRNA profiling revealed that ∼ 1,547 genes were differentially expressed (DE) in the two cell types; the genes were related to cell adhesion, the extracellular matrix, differentiation, and proliferation. These findings were confirmed by functional analyses showing that ADSCs had a greater adhesion capacity than fibroblasts; the proliferation rate of fibroblasts was also higher than that of ADSCs. Importantly, 185 DE genes were integral to the plasma membrane and, thus, candidate markers for ADSC isolation and manipulation. We also observed that an established marker of fibroblasts and ADSCs, CD105, was overexpressed in ADSCs at both mRNA and protein levels. CD105 expression seemed to be related to differentiation capacity, at least for adipogenesis. This study shows that ADSCs and fibroblasts are distinct cell types. These findings should be taken into account when using these two cell types in basic and therapeutic studies.