Identification of osteo-adipo progenitor cells in fat tissue

Icariin and Icariside II Reciprocally Stimulate Osteogenesis and Inhibit Adipogenesis of Multipotential Stromal Cells through ERK Signaling

Herba Epimedii is a famous Chinese herbal medicine for treating bone diseases. Icariin and icariside II, the main chemical constituents, have attracted great attention from scientists for their potential as antiosteoporosis agents. Our study aimed to evaluate their effects on the lineage commitment of multipotential stromal cells (MSCs). The osteogenesis and adipogenesis of MSCs were assessed by ALP activity, calcium deposition, and adipocyte formation. The expression profiles and levels of osteogenic and adipogenic specific genes were evaluated by cDNA microarray and quantitative real-time PCR. The involvement of extracellular signal-regulated kinase (ERK) signaling was studied by enzyme-linked immunosorbent assay. Icariin and icariside II significantly increased ALP activity and mineralization during osteogenic differentiation of MSCs. Runx2, Col1, and Bmp2 were upregulated in the presence of icariin and icariside II. Meanwhile, they downregulated Pparg, Adipsin, and Cebpb expression during adipogenic differentiation. cDNA microarray revealed 57 differentially expressed genes during lineage commitment of MSCs. In addition, icariin and icariside II enhanced the phosphorylation of ERK, and the above biological effects were blocked by ERK inhibitor U0126. Icariin and icariside II may drive the final lineage commitment of MSCs towards osteogenesis and inhibit adipogenesis through the ERK signaling pathway. Both of them exert multiple osteoprotective effects and deserve more attention for their medicinal and healthcare prospects.

Epigallocatechin-3-gallate enhances the osteoblastogenic differentiation of human adipose-derived stem cells

Purpose

The aim of this study is to investigate the effects of epigallocatechin-3-gallate (EGCG), a major polyphenol extracted from green tea, on the osteoblastogenic differentiation of human adipose-derived stem cells (hASCs).

Patients and methods

hASCs were acquired from human adipose tissue. With informed consent, subcutaneous adipose tissue samples were harvested from periorbital fat pad resections from ten healthy female adults who underwent double eyelid surgery. hASCs were cultured in osteogenic medium with or without EGCG (1 μM, 5 μM, or 10 μM) for 14 days. We evaluated the effects of EGCG by quantifying cell growth, ALP activity (an early osteoblastogenic differentiation marker), BSP, OCN (a late osteoblastogenic differentiation marker), and extracellular matrix mineralization. We also performed Western blots to measure osteoblastogenesis-related proteins such as Runx2 and adipoblastogenesis-related transcription factors, such as STAT3, C/EBP-α, and PPAR-γ.

Results

EGCG at 5 μM resulted in significantly higher cell proliferation and ALP activity than did the control on days 3, 7, and 14. On day 7, 5 μM EGCG significantly enhanced BSP expression. On day 14, EGCG at all concentrations promoted OCN expression. In addition, EGCG at 5 μM resulted in the highest level of extracellular matrix mineralization. On day 3, the expression levels of Runx2 were significantly higher in the 5 μM EGCG group than in the other groups, whereas later, on days 7 and 14, Runx2 expression levels in the EGCG group were significantly lower than those of the control group. EGCG at all three concentrations was associated with significantly lower levels of phosphorylated STAT3, C/EBP-α, and PPAR-γ.

Conclusion

EGCG at 5 μM significantly enhanced the osteoblastogenic differentiation of hASCs.

SeesawPred: A Web Application for Predicting Cell-fate Determinants in Cell Differentiation

Cellular differentiation is a complex process where a less specialized cell evolves into a more specialized cell. Despite the increasing research effort, identification of cell-fate determinants (transcription factors (TFs) determining cell fates during differentiation) still remains a challenge, especially when closely related cell types from a common progenitor are considered. Here, we develop SeesawPred, a web application that, based on a gene regulatory network (GRN) model of cell differentiation, can computationally predict cell-fate determinants from transcriptomics data. Unlike previous approaches, it allows the user to upload gene expression data and does not rely on pre-compiled reference data sets, enabling its application to novel differentiation systems. SeesawPred correctly predicted known cell-fate determinants on various cell differentiation examples in both mouse and human, and also performed better compared to state-of-the-art methods. The application is freely available for academic, non-profit use at http://seesaw.lcsb.uni.lu.

Gene Expression Noise Enhances Robust Organization of the Early Mammalian Blastocyst

A critical event in mammalian embryo development is construction of an inner cell mass surrounded by a trophoectoderm (a shell of cells that later form extraembryonic structures). We utilize multi-scale, stochastic modeling to investigate the design principles responsible for robust establishment of these structures. This investigation makes three predictions, each supported by our quantitative imaging. First, stochasticity in the expression of critical genes promotes cell plasticity and has a critical role in accurately organizing the developing mouse blastocyst. Second, asymmetry in the levels of noise variation (expression fluctuation) of Cdx2 and Oct4 provides a means to gain the benefits of noise-mediated plasticity while ameliorating the potentially detrimental effects of stochasticity. Finally, by controlling the timing and pace of cell fate specification, the embryo temporally modulates plasticity and creates a time window during which each cell can continually read its environment and adjusts its fate. These results suggest noise has a crucial role in maintaining cellular plasticity and organizing the blastocyst.

A critical event in mammalian embryo development is construction of a mass of embryonic stem cells surrounded by a distinct shell that later forms the placenta along with other structures. Despite sustained investigation, multiple hypotheses for what is responsible for this organization persist and it remains unclear what is responsible for the robust organization (remarkable ability for embryos to pattern correctly) of these structures. Here, we utilize multi-scale, stochastic modeling along with fluorescence imaging to investigate the factors that contribute to the incredible robustness of this organizational process. Results point to two factors that contribute to this robustness: 1) the timing and pace of cell fate specification and 2) stochastic gene regulatory effects. The former creates a window of time during which each cell can continually read their environment and adjust their gene expressions (and consequently fate) in response to dynamic rearrangements of cells arising from cell divisions and motions. The latter improves cell plasticity, providing the capability for cells to adjust to changes in their local environment. Fluorescence imaging results demonstrate that the magnitude and structure of gene expression variations match those predicted to promote organizational robustness.

A Generalized Gene-Regulatory Network Model of Stem Cell Differentiation for Predicting Lineage Specifiers

Identification of cell-fate determinants for directing stem cell differentiation remains a challenge. Moreover, little is known about how cell-fate determinants are regulated in functionally important subnetworks in large gene-regulatory networks (i.e., GRN motifs). Here we propose a model of stem cell differentiation in which cell-fate determinants work synergistically to determine different cellular identities, and reside in a class of GRN motifs known as feedback loops. Based on this model, we develop a computational method that can systematically predict cell-fate determinants and their GRN motifs. The method was able to recapitulate experimentally validated cell-fate determinants, and validation of two predicted cell-fate determinants confirmed that overexpression of ESR1 and RUNX2 in mouse neural stem cells induces neuronal and astrocyte differentiation, respectively. Thus, the presented GRN-based model of stem cell differentiation and computational method can guide differentiation experiments in stem cell research and regenerative medicine.

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A network-based method for predicting lineage specifiers and key network motifs

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A computational guidance to stem cell differentiation experiments

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Overexpression of ESR1 in mNSCs induces neuronal differentiation

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Overexpression of RUNX2 in mNSCs induces astrocyte differentiation

Effect of miR-26a-5p on the Wnt/Ca(2+) Pathway and Osteogenic Differentiation of Mouse Adipose-Derived Mesenchymal Stem Cells

Elucidation of the molecular mechanisms that regulate the differentiation of adipose-derived mesenchymal stem cells into osteogenic cells may lead to new methods for bone tissue engineering. We examined the role of miR-26a-5p in the regulation of osteogenic differentiation of mouse adipose-derived mesenchymal stem cells (mADSCs) by using mimics and inhibitors of this microRNA. Our results showed that over-expression of miR-26a-5p inhibited osteogenesis and that suppression of endogenous miR-26a-5p promoted osteogenesis. Four bioinformatics algorithms indicated that the 3'UTR of Wnt5a was a potential target of miR-26a-5p. We confirmed this prediction by use of dual-luciferase reporter assay and GFP/RFP assay. We also examined the molecular mechanisms by which miR-26a-5p regulates osteogenesis. Fura-2AM and Western blot assays after transfection indicated that miR-26a-5p repressed WNT5A, inhibited calcium flux and protein kinase C, and suppressed osteogenic differentiation of mADSCs. By contrast, miR-26a-5p inhibition activated these signal proteins and promoted osteogenic differentiation. Taken together, our results suggest that up-regulation of miR-26a-5p inhibits osteogenic differentiation of mADSCs by directly targeting the 3'UTR of Wnt5a, thereby down-regulating the Wnt/Ca(2+) signaling pathway.

Association of the I264T variant in the sulfide quinone reductase-like (SQRDL) gene with osteoporosis in Korean postmenopausal women

To identify novel susceptibility variants for osteoporosis in Korean postmenopausal women, we performed a genome-wide association analysis of 1180 nonsynonymous single nucleotide polymorphisms (nsSNPs) in 405 individuals with osteoporosis and 722 normal controls of the Korean Association Resource cohort. A logistic regression analysis revealed 72 nsSNPs that showed a significant association with osteoporosis (p<0.05). The top 10 nsSNPs showing the lowest p-values (p = 5.2×10-4-8.5×10-3) were further studied to investigate their effects at the protein level. Based on the results of an in silico prediction of the protein's functional effect based on amino acid alterations and a sequence conservation evaluation of the amino acid residues at the positions of the nsSNPs among orthologues, we selected one nsSNP in the SQRDL gene (rs1044032, SQRDL I264T) as a meaningful genetic variant associated with postmenopausal osteoporosis. To assess whether the SQRDL I264T variant played a functional role in the pathogenesis of osteoporosis, we examined the in vitro effect of the nsSNP on bone remodeling. Overexpression of the SQRDL I264T variant in the preosteoblast MC3T3-E1 cells significantly increased alkaline phosphatase activity, mineralization, and the mRNA expression of osteoblastogenesis markers, Runx2, Sp7, and Bglap genes, whereas the SQRDL wild type had no effect or a negative effect on osteoblast differentiation. Overexpression of the SQRDL I264T variant did not affect osteoclast differentiation of the primary-cultured monocytes. The known effects of hydrogen sulfide (H2S) on bone remodeling may explain the findings of the current study, which demonstrated the functional role of the H2S-catalyzing enzyme SQRDL I264T variant in osteoblast differentiation. In conclusion, the results of the statistical and experimental analyses indicate that the SQRDL I264T nsSNP may be a significant susceptibility variant for osteoporosis in Korean postmenopausal women that is involved in osteoblast differentiation.

Identification of a subpopulation of marrow MSC-derived medullary adipocytes that express osteoclast-regulating molecules: marrow adipocytes express osteoclast mediators

Increased marrow medullary adipogenesis and an associated decrease in bone mineral density, usually observed in elderly individuals, is a common characteristic in senile osteoporosis. In this study we investigated whether cells of the medullary adipocyte lineage have the potential to directly support the formation of osteoclasts, whose activity in bone leads to bone degradation. An in vitro mesenchymal stem cell (MSC)-derived medullary adipocyte lineage culture model was used to study the expression of the important osteoclast mediators RANKL, M-CSF, SDF-1, and OPG. We further assessed whether adipocytes at a specific developmental stage were capable of supporting osteoclast-like cell formation in culture. In vitro MSC-derived medullary adipocytes showed an mRNA and protein expression profile of M-CSF, RANKL, and OPG that was dependent on its developmental/metabolic stage. Furthermore, RANKL expression was observed in MSC-derived adipocytes that were at a distinct lineage stage and these cells were also capable of supporting osteoclast-like cell formation in co-cultures with peripheral blood mononuclear cells. These results suggest a connection between medullary adipocytes and osteoclast formation in vivo and may have major significance in regards to the mechanisms of decreased bone density in senile osteoporosis.

BMP4 promotes vascularization of human adipose stromal cells and endothelial cells in vitro and in vivo

OBJECTIVES

Vascularization is a major obstacle to clinical application of regenerative medicine. Engineered tissues must be able to generate an early vascular network that can quickly connect with the host vasculature. Recent research demonstrates that natural adipose tissues contain abundant stromal cells, which can give rise to pericytes. In this study, we aimed to investigate the application of human adipose stromal cells (ASCs) to vascularization, and the function of BMP4 protein during vascularization.

MATERIALS AND METHODS

Immunofluorescence staining for α-SMA and PDGFR-β were utilized to identify characteristics of ASCs/pericytes. They were then loaded into a collagen-fibronectin gel with endothelial cells to assess their vascularization ability, both in vitro and in vivo.

RESULTS

We showed that the ASCs expressed some of the essential markers of pericytes and they were able to promote vascularization with endothelial cells in 3D culture, both in vitro and in vivo. BMP4 protein further promoted this vascularization.

CONCLUSION

Adipose stromal cells promoted vascularization by endothelial cells and BMP4 protein further enhanced this effect.

Adult stem cells properties in terms of commitment, aging and biological safety of grit-blasted and Acid-etched ti dental implants surfaces

Titanium (Ti) is one of the most widely used biomaterials for manufacturing dental implants. The implant surface properties strongly influence osseointegration. The aim of the present study was to in vitro investigate the characteristics of Ti dental implants in terms of mutagenicity, hemocompatibility, biocompatibility, osteoinductivity and biological safety. The Ames test was used to test the mutagenicity of the Ti dental implants, and the hemolysis assay for evaluating their hemocompatibility. Human adipose - derived stem cells (ADSCs) were then seeded onto these implants in order to evaluate their cytotoxicity. Gene expression analyzing with real-time PCR was carried out to investigate the osteoinductivity of the biomaterials. Finally, the genetic stability of the cells cultured onto dental implants was determined by karyotyping. Our results demonstrated that Ti dental implants are not mutagenic, do not cause hemolysis, and are biocompatible. The MTT assay revealed that ADSCs, seeded on Ti dental implants, proliferate up to 30 days in culture. Moreover, ADSCs loaded on Ti dental implants show a substantial expression of some osteoblast specific markers, such as COL1A1, OPN, ALPL, and RUNX2, as well as chromosomal stability after 30 days of culture in a medium without osteogenic factors. In conclusion, the grit-blasted and acid-etched treatment seems to favor the adhesion and proliferation of ADSCs and improve the osteoinductivity of Ti dental implant surfaces.

The roles of bone morphogenetic proteins and their signaling in the osteogenesis of adipose-derived stem cells

Large-size bone defects can severely compromise both aesthetics and musculoskeletal functions. Adipose-derived stem cells (ASCs)-based bone tissue engineering has recently become a promising treatment strategy for the above situation. As robust osteoinductive cytokines, bone morphogenetic proteins (BMPs) are commonly used to promote the osteogenesis of ASCs. In this process, BMP signaling plays a pivotal role. However, it remains ambiguous how the pleiotrophic BMPs are involved in the commitment of ASCs along osteogenesis instead of other lineages, such as adipogenesis. BMP receptor type-IB, extracellular signal-regulated kinase, and Wnt5a appear to be the main switches controlling the in vitro osteogenic commitment of ASCs. Tumor necrosis factor-alpha, an acute inflammatory cytokine, is reported to play an important role in mediating osteogenic commitment of ASCs in vivo. In addition, various active agents and methods have been used to enhance and accelerate the osteogenesis of ASCs through promoting BMP signaling. In this review, we summarize the current knowledge on the roles of BMPs and their signaling in the osteogenesis of ASCs in vitro and in vivo.

Low-intensity pulsed ultrasound induced enhanced adipogenesis of adipose-derived stem cells

OBJECTIVE

The aim of this study was to investigate effects of low-intensity pulsed ultrasound (LIPUS) on differentiation of adipose-derived stem cells (ASCs), in vitro.

MATERIALS AND METHODS

Murine ASCs were treated with LIPUS for either three or five days, immediately after adipogenic induction, or delayed for 2 days. Expression of adipogenic genes PPAR-γ1, and APN, was examined by real-time PCR. Immunofluorescence (IF) staining was performed to test for PPAR-γ at the protein level.

RESULTS

Our data revealed that specific patterns of LIPUS up-regulated levels of both PPAR-γ1 and APN mRNA, and PPAR-γ protein.

CONCLUSIONS

In culture medium containing adipogenic reagents, LIPUS enhanced ASC adipogenesis.

Regeneration of articular cartilage by adipose tissue derived mesenchymal stem cells: perspectives from stem cell biology and molecular medicine

Adipose-derived stem cells (ASCs) have been discovered for more than a decade. Due to the large numbers of cells that can be harvested with relatively little donor morbidity, they are considered to be an attractive alternative to bone marrow derived mesenchymal stem cells. Consequently, isolation and differentiation of ASCs draw great attention in the research of tissue engineering and regenerative medicine. Cartilage defects cause big therapeutic problems because of their low self-repair capacity. Application of ASCs in cartilage regeneration gives hope to treat cartilage defects with autologous stem cells. In recent years, a lot of studies have been performed to test the possibility of using ASCs to re-construct damaged cartilage tissue. In this article, we have reviewed the most up-to-date articles utilizing ASCs for cartilage regeneration in basic and translational research. Our topic covers differentiation of adipose tissue derived mesenchymal stem cells into chondrocytes, increased cartilage formation by co-culture of ASCs with chondrocytes and enhancing chondrogenic differentiation of ASCs by gene manipulation.

MicroRNA regulation of adipose derived stem cells in aging rats

Background

Perturbations in abdominal fat secreted adipokines play a key role in metabolic syndrome. This process is further altered during the aging process, probably due to alterations in the preadipocytes (aka. stromal vascular fraction cells-SVF cells or adipose derived stem cells-ASCs) composition and/or function. Since microRNAs regulate genes involved both in development and aging processes, we hypothesized that the impaired adipose function with aging is due to altered microRNA regulation of adipogenic pathways in SVF cells.

Methodology and Principal Findings

Alterations in mRNA and proteins associated with adipogenic differentiation (ERK5 and PPARg) but not osteogenic (RUNX2) pathways were observed in SVF cells isolated from visceral adipose tissue with aging (6 to 30 mo) in female Fischer 344 x Brown Norway Hybrid (FBN) rats. The impaired differentiation capacity with aging correlated with altered levels of miRNAs involved in adipocyte differentiation (miRNA-143) and osteogenic pathways (miRNA-204). Gain and loss of function studies using premir or antagomir-143 validated the age associated adipocyte dysfunction.

Conclusions and Significance

Our studies for the first time indicate a role for miRNA mediated regulation of SVF cells with aging. This discovery is important in the light of the findings that dysfunctional adipose derived stem cells contribute to age related chronic diseases.

Association between the SPRY1 gene polymorphism and obesity-related traits and osteoporosis in Korean women

BACKGROUND

Emerging evidence has revealed a close relationship between obesity and osteoporosis. It was reported recently that conditional knockout of the Spry1 gene in mice adipocytes causes an increase in body fat and a decrease in bone mass, and that these phenotypes are rescued by Spry1 overexpression in adipose tissue. In this study, we investigated whether genetic variation in the human SPRY1 gene is associated with obesity-related phenotypes and/or osteoporosis in humans.

METHODS

We performed a candidate gene association analysis between the four single nucleotide polymorphisms (SNPs) and 14 imputed SNPs in the SPRY1 gene and obesity-related traits and osteoporosis in a Korean women cohort (3013 subjects).

RESULTS

All four SPRY1 gene SNPs were significantly associated with either obesity-related traits or osteoporosis. The TGCC haplotype in the SRPY1 gene showed simultaneous association with an increased risk for obesity-related traits, percentage body fat (p=0.0087) and percentage abdominal fat (p=0.047), and osteoporosis (odds ratio=1.50; p=0.025) in the recessive genetic model.

CONCLUSIONS

Our results support a previous finding in conditional Spry1 gene knockout mice and suggest that the SPRY1 gene is an important genetic factor for determining the risk of both obesity and osteoporosis in humans.

Stimulation of sub-sonic vibration promotes the differentiation of adipose tissue-derived mesenchymal stem cells into neural cells

AIMS

Adipose tissue-derived stem cells (AT-MSCs) have been proposed as a new source for nervous tissue damage due to their capacity of neural differentiation potential including neurons, oligodendrocytes and astrocytes. Recently, many studies have demonstrated that sub-sonic vibration (SSV) is an effective cell differentiation method but there have been no studies on the effect of SSV about AT-MSC differentiation into neural-like cells in vitro. Therefore, we examined the effect of SSV on AT-MSCs to investigate the differentiation potential of neural-like cells.

MAIN METHODS

We assessed the changes in AT-MSCs by SSV during 4 days at 10, 20, 30 and 40 Hz (1.0 V). After stimulation, they were analyzed by RT-PCR, Western blot and immunohistological analysis using neural cell type-specific genes and antibodies. Further, to confirm the neural differentiation, we investigated adipogenic genes for RT-PCR analysis. For a mechanism study, we analyzed activation levels in time course of ERK phosphorylation after SSV.

KEY FINDINGS

After 4-day SSV exposure, we observed morphological changes of AT-MSCs. Further, SSV induced gene/protein levels of neural markers while inhibiting adipogenesis and they were mainly upregulated at 30 Hz. In addition, phosphorylated ERK level was increased in a time-dependent manner upon 30 Hz SSV for 6h.

SIGNIFICANCE

These results demonstrated that SSV affects AT-MSCs differentiation potential and 30 Hz SSV affected neural differentiation on AT-MSCs.

Secreted factors from adipose tissue increase adipogenic differentiation of mesenchymal stem cells

OBJECTIVES

Adipose tissue engineering is one of the hottest topics in the field of regenerative medicine. Fat tissue has been considered as an abundant and accessible source of adult stem cells by tissue engineers, since it gives rise to adipose stem cells. However, recent reports have pointed out that adipose tissue, as a secretory and endocrine organ, might secrete cytokines that regulate body functions such as metabolism, infammation and more. In this study, we aim to investigate the adipogenic-inducing factors secreted by fat tissue.

MATERIALS AND METHODS

Conditioned medium were collected by culturing fat tissue fragments in plastic flasks. Mesenchymal stem cells (MSCs) cultured in conditioned medium (CM) to test the adipogenic-inducing factors. Oil red O staining, reverse transcription/polymerase chain reaction and immunocytofluorescent staining were performed to examine the differentiation of MSCs in CM.

RESULTS

MSCs cultured in CM of adipose tissue spontaneously differentiated into adipocytes. Furthermore, supplementation of insulin or dexamethasone to CM accelerated the process of lipid accumulation of differentiated MSCs.

DISCUSSION

Results from this study demonstrated that fat tissues secrete small molecules, which induce adipogenic differentiation of MSCs.

CONCLUSIONS

Our study provides clues for improving adipose tissue engineering by using fragmented adipose tissue as sources of fat-inducing factors.

Mechanical stretch inhibits adipogenesis and stimulates osteogenesis of adipose stem cells

A reciprocal relationships between osteogenesis and adipogenesis has been observed in vitro and in vivo, and mechanical stretch has been believed to be a regulating factor of osteo-adipogenic axis differentiation of mesenchymal stem cells. In this study, rat adipose stem cells (ASCs) were isolated and cultured in adipogenic or normal medium. Their exposure to cyclic mechanical stretch (2000 με, 1 Hz) in the presence of adipogenic medium decreased mRNA and protein level of PPAR-γ, and increased Runx2 mRNA and protein levels as well as Pref-1 mRNA level, compared to static samples. ASCs cultured in normal medium without adipogenic induction did not show any significant change in mRNA expression of PPAR-γ, Runx2, nor Pref-1 irrespective of mechanical loading. Stretching induced phosphorylation of extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) during the induction period. It was concluded that mechanical stretch inhibited adipogenesis and stimulated osteogenesis of these ASCs in the presence of adipogenic medium and that ERK1/2 activation may be involved in the mechanical stress-induced trans-differentiation.

Tissue-specific expression of Sprouty1 in mice protects against high-fat diet-induced fat accumulation, bone loss and metabolic dysfunction

We recently characterised Sprouty1 (Spry1), a growth factor signalling inhibitor as a regulator of marrow progenitor cells promoting osteoblast differentiation at the expense of adipocytes. Adipose tissue-specific Spry1 expression in mice resulted in increased bone mass and reduced body fat, while conditional knockout of Spry1 had the opposite effect with decreased bone mass and increased body fat. Because Spry1 suppresses normal fat development, we tested the hypothesis that Spry1 expression prevents high-fat diet-induced obesity, bone loss and associated lipid abnormalities, and demonstrate that Spry1 has a long-term protective effect on mice fed a high-energy diet. We studied diet-induced obesity in mice with fatty acid binding promoter-driven expression or conditional knockout of Spry1 in adipocytes. Phenotyping was performed by whole-body dual-energy X-ray absorptiometry, microCT, histology and blood analysis. In conditional Spry1-null mice, a high-fat diet increased body fat by 40 %, impaired glucose regulation and led to liver steatosis. However, overexpression of Spry1 led to 35 % (P < 0·05) lower body fat, reduced bone loss and normal metabolic function compared with single transgenics. This protective phenotype was associated with decreased circulating insulin (70 %) and leptin (54 %; P < 0·005) compared with controls on a high-fat diet. Additionally, Spry1 expression decreased adipose tissue inflammation by 45 %. We show that conditional Spry1 expression in adipose tissue protects against high-fat diet-induced obesity and associated bone loss.

Protein Expression of STRO-1 Cells in Response to Different Topographic Features

Human skeletal stem cells (STRO-1 positive) display distinct responses to different topographical features. On a flat surface, skeletal cells spread, and in vitro, they typically display a polarized, fibroblast-like morphology. However, on microgrooved surfaces, these cells prefer to stretch along the grooves forming a similar morphology to in vivo, bipolarized fibroblasts. In contrast, on nanopits, these cells display a polygonal and osteoblastic phenotype. We have examined mechanotransduction events of STRO-1 positive in response to fibroblastic, microgrooved and osteogenic, controlled disorder nanopit, topographies using proteomics after 3 days in culture. Protein expression profiles were analyzed by difference gel electrophoresis to identify proteins that showed modulation of expression in response to different topographic features to assess early decision events in these cells on these discrete topographies. After only 72 hours in culture, STRO-1 positive displayed differential regulations of families of proteins involved in cell migration and proliferation. The current study indicated that osteogenic decision specific events had already occurred. Runx2 was localized in nuclei of the skeletal stem cells on the osteogenic nanopits; however, few signaling pathway changes were observed. This study demonstrated that micro- and nanotopographies activated skeletal stem cells at different times and with distinct mechanotransduction profiles.

Poncirin promotes osteoblast differentiation but inhibits adipocyte differentiation in mesenchymal stem cells

Poncirin, flavanone glycoside, isolated from the fruit of Poncirus trifoliata, has anti-bacterial and anti-inflammatory activities. In this study, the effects of poncirin on the differentiation of mesenchymal stem cells were investigated. The C3H10T1/2 mesenchymal stem cells and primary bone marrow mesenchymal stem cells were studied. In the C3H10T1/2 cells, poncirin prevented adipocyte differentiation, as demonstrated by inhibition of cytoplasm lipid droplet accumulation and peroxisome proliferator-activating receptor-γ (PPAR-γ) and CCAAT-enhancer-binding protein-β (C/EBP-β) mRNA expression. By contrast, poncirin enhanced the expression of the key osteogenic transcription factors, runt-related transcription factor 2 (Runx2) and transcriptional coactivator with PDZ-binding motif (TAZ). Poncirin also enhanced expression of the osteogenic marker genes including alkaline phosphatase (ALP) and osteocalcin (OC). Poncirin increased mineral nodule formation in primary bone marrow mesenchymal stem cells. These results suggest that poncirin prevents adipogenesis and enhances osteoblast differentiation in mesenchymal stem cells.

Dental follicle stem cells and tissue engineering

Adult stem cells are multipotent and can be induced experimentally to differentiate into various cell lineages. Such cells are therefore a key part of achieving the promise of tissue regeneration. The most studied stem cells are those of the hematopoietic and mesenchymal lineages. Recently, mesenchymal stem cells were demonstrated in dental tissues, including dental pulp, periodontal ligament, and dental follicle. The dental follicle is a loose connective tissue that surrounds the developing tooth. Dental follicle stem cells could therefore be a cell source for mesenchymal stem cells. Indeed, dental follicle is present in impacted teeth, which are commonly extracted and disposed of as medical waste in dental practice. Dental follicle stem cells can be isolated and grown under defined tissue culture conditions, and recent characterization of these stem cells has increased their potential for use in tissue engineering applications, including periodontal and bone regeneration. This review describes current knowledge and recent developments in dental follicle stem cells and their application.

Adipose-derived stem cells for clinical applications: a review

The use of stem cells derived from adipose tissue as an autologous and self-replenishing source for a variety of differentiated cell phenotypes, provides a great deal of promise for reconstructive surgery. In this article, we review available literature encompassing methods of extraction of pluripotent adipose stem cells (ASCs) from lipoaspirate locations, their storage, options for culture, growth and differentiation, cryopreservation and its effect on stem cell survival and proliferation, and new technologies involving biomaterials and scaffolds. We will conclude by assessing potential avenues for developing this incredibly promising field.

Native human adipose stromal cells: localization, morphology and phenotype

Objectives:

Beside having roles in energy homeostasis and endocrine modulation, adipose tissue (AT) is now considered a promising source of mesenchymal stromal cells (adipose-derived stromal cells or ASCs) for regenerative medicine. Despite numerous studies on cultured ASCs, native human ASCs are rarely investigated. Indeed, the phenotype of ASCs in their native state, their localization within AT and comparison with bone marrow-derived mesenchymal stromal cells (BM-MSCs) has been poorly investigated.

Design:

To address these issues, the stroma vascular fraction (SVF) of human AT was extracted and native cell subtypes were isolated by immunoselection to study their clonogenic potential in culture. Immunohistology on samples of human AT in combination with reconstruction of confocal sections were performed in order to localize ASCs.

Results:

Compared with BM-MNCs, all native ASCs were found in the CD34⁺ cell fraction of the AT-SVF. Native ASCs expressed classical mesenchymal markers described for BM-MSCs. Interestingly, CD34 expression decreased during ASC cell culture and was negatively correlated with cell proliferation rate. Immunohistological analysis revealed that native ASCs exhibited specific morphological features with protrusions. They were found scattered in AT stroma and did not express in vivo pericytic markers such as NG2, CD140b or alpha-smooth muscle actin, which appeared during the culture process. Finally, ASCs spontaneous commitment to adipocytic lineage was enhanced in AT from obese humans.

Conclusions:

The use of complementary methodological approaches to study native human ASCs revealed their immunophenotype, their specific morphology, their location within AT and their stemness. Furthermore, our data strongly suggest that human ASCs participate in adipogenesis during AT development.

Depot-specific differences in the insulin response of adipose-derived stromal cells

Visceral adiposity is more strongly linked to insulin resistance than subcutaneous adiposity. High insulin levels can be mitogenic or adipogenic to adipocytes, but little is known regarding these effects of insulin on stromal cells from visceral and subcutaneous fat depots. Consequently, we measured adipogenesis and mitosis in response to elevated insulin levels in rat adipose-derived stromal cells (ADSCs) from visceral (perirenal) and subcutaneous depots. Insulin alone, at 10 microM, did not stimulate adipogenesis in naïve perirenal visceral (pvADSCs) or subcutaneous ADSCs (scADSCs), although a significant increase in proliferation occurred in both. Adipogenesis, induced using adipocyte differentiation medium (AM), resulted in greater lipid accumulation in pvADSCs, but the associated decrease in proliferation was less than in scADSCs. Omission of insulin from AM significantly reduced lipid accumulation in pvADSCs, but had little effect in scADSC, whilst proliferation was inhibited more in scADSCs than pvADSCs. Consequently, insulin is more lipogenic and less mitogenic in differentiating pvADSCs compared to scADSCs.

Explant culture: an efficient method to isolate adipose-derived stromal cells for tissue engineering

Enzymatic digestion, the commonly used method of adipose-derived stromal cells isolation, is time consuming and expensive, especially when applied to large volumes of tissue. In the present study, the characteristics of the cells obtained by adipose tissue explant culture were studied. We found that adipose tissue fragments could adhere onto the growth surface of flasks in a very short time after plating and that fibroblast-like cells migrated from the explants and reached confluence. Morphologic analysis and surface markers expression suggested the mesenchymal origin of the cells derived from adipose tissue explants. After in vitro expansion these cells were successfully induced into adipogenic, osteogenic, and chondrogenic lineages, which demonstrated their multipotency. The high growth rate and colony-forming efficiency of explant-derived cells were similar to those of cells obtained by digestion. Furthermore, explant culture gave higher yield of cells than digestion method after primary culture. The experiment of ectopic adipogenesis in nude mice suggested the prospects for tissue engineering of these cells. In conclusion, we obtained multipotent stromal cells from adipose tissue by explant culture, and this method was simple, time saving, and gave a high yield of cells. Therefore, explant culture can be used as an effective way to isolate adipose-derived stromal cells for tissue engineering.

Uniaxial cyclic tensile stretch inhibits osteogenic and odontogenic differentiation of human dental pulp stem cells

As the most important organs of occlusion, teeth are subjected to a variety of mechanical stresses. These stresses are transmitted into the dental pulp tissue and affect the dental pulp stem cells. In this study, human dental pulp stem cells were isolated from human impacted third molars and their multilineage differentiation abilities were tested. Human dental pulp stem cells were then exposed to cyclic tensile stretch. The results showed that the cyclic tensile stretch inhibited the expression of osteogenic marker genes and proteins such as BMP-2, OCN and ALP. Simultaneously, odontogenic marker genes and proteins such as DSPP, DSP and BSP were also inhibited by the mechanical stress. It was concluded that cyclic tensile stretch inhibits the osteogenic and odontogenic differentiation of dental pulp stem cells.

gamma-secretase inhibitor induces adipogenesis of adipose-derived stem cells by regulation of Notch and PPAR-gamma

OBJECTIVE

To determine the inhibitory effect and mechanism of Notch signalling on adipogenesis of mouse adipose-derived stem cells (mASCs).

MATERIALS AND METHODS

Varied concentrations of N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butylester (DAPT) were added to mASCs 3 days before adipogenic induction with insulin-containing differentiation medium. The process of adipogenesis and ability of lipid droplet accumulation were analysed using oil red-O staining. The Notch signalling pathway (Notch-1, -2, -3, -4, Hes-1 and Hey-1) and adipogenesis-related factors (PPAR-gamma, DLK-1/Pref-1 and Acrp) were tested using real-time PCR, Western blot analysis and immunofluorescence staining assays.

RESULTS

We demonstrated that Notch-2-Hes-1 signalling pathway was inhibited dose-dependently by DAPT in mASCs. In addition, transcription of PPAR-gamma was promoted by DAPT before adipogenic induction, while inhibitor of adipogenesis DLK-1/Pref-1 was further depressed. At early stages of differentiation (2-4 days), adipogenesis in mASCs was advanced and significantly enhanced in 5 and 10 mum DAPT pre-treated cases. On day 4, in differentiated mASCs cases with DAPT pre-treatment, we also found promotion of activation of de-PPAR-gamma and depression of HES-1, DLK-1/Pref-1 mRNA and protein expression.

CONCLUSIONS

We conclude that blocking Notch signalling with DAPT enhances adipogenesis of differentiated mASCs at an early stage. It may be due to depression of DLK-1/Pref-1 and promotion of de-PPAR-gamma activation, which work through inhibition of Notch-2-Hes-1 pathway by DAPT.

Cyclic tensile stretch modulates osteogenic differentiation of adipose-derived stem cells via the BMP-2 pathway

INTRODUCTION

Mechanical forces play critical roles in the development and remodelling process of bone. As an alternative cell source for bone engineering, adipose-derived stem cells (ASCs) should be fully investigated for their responses to mechanical stress and the mechanisms responsible for osteogenic induction in response to mechanical signals.

MATERIAL AND METHODS

We hypothesized that appropriate application of uniaxial cyclic tensile strain to ASCs could increase bone morphogenetic protein-2 (BMP-2) expression and improve osteogenesis of ASCs. To test our hypothesis, ASCs from the same flask of the same donor were subjected to tensile strain with different patterns in order to eliminate the difference of donor site and passage. After surface markers investigation, the osteo-induced ASCs were subjected to uniaxial cyclic tensile stretch with the following two loading patterns: long duration continuous pattern (6 h, 1 HZ, 2000 µɛ) and short duration consecutive pattern (17 min every day for 10 consecutive days, 1 HZ, 2000 µɛ). Then osteogenic related genes were analysed by real-time PCR.

RESULTS

The ASCs were positive for the markers STRO-1, CD90 and CD44 and negative for CD34. Cyclic tensile strain of 6 continuous h' duration significantly increased gene expressions of BMP-2 and Runx2, and depressed OCN mRNA expression. In contrast, mechanical loading of 17 min every day did not significantly affect gene expression of BMP-2, Runx2, OCN or ALP.

CONCLUSIONS

We indicate that ASCs may sense mechanical loading in a duration-dependent manner and cyclic tensile stretch may modulate the osteogenic differentiation of ASCs via the BMP-2 signalling pathway.

Sprouty1 is a critical regulatory switch of mesenchymal stem cell lineage allocation

Development of bone and adipose tissue are linked processes arising from a common progenitor cell, but having an inverse relationship in disease conditions such as osteoporosis. Cellular differentiation of both tissues relies on growth factor cues, and we focus this study on Sprouty1 (Spry1), an inhibitor of growth factor signaling. We tested whether Spry1 can modify the development of fat cells through its activity in regulating growth factors known to be important for adipogenesis. We utilized conditional expression and genetic-null mouse models of Spry1 in adipocytes using the fatty acid binding promoter (aP2). Conditional deletion of Spry1 results in 10% increased body fat and decreased bone mass. This phenotype was rescued on Spry1 expression, which results in decreased body fat and increased bone mass. Ex vivo bone marrow experiments indicate Spry1 in bone marrow and adipose progenitor cells favors differentiation of osteoblasts at the expense of adipocytes by suppressing CEBP-beta and PPARgamma while up regulating TAZ. Age and gender-matched littermates expressing only Cre recombinase were used as controls. Spry1 is a critical regulator of adipocyte differentiation and mesenchymal stem cell (MSC) lineage allocation, potentially acting through regulation of CEBP-beta and TAZ.

Bone marrow derived pluripotent cells are pericytes which contribute to vascularization

Pericytes are essential to vascularization, but the purification and characterization of pericytes remain unclear. Smooth muscle actin alpha (alpha-SMA) is one marker [corrected] of pericytes. The aim of this study is to purify the alpha-SMA positive cells from bone marrow and study the characteristics of these cells and the interaction between alpha-SMA positive cells and endothelial cells. The bone marrow stromal cells were harvested from alpha-SMA-GFP transgenic mice, and the alpha-SMA-GFP positive cells were sorted by FACS. The proliferative characteristics and multilineage differentiation ability of the alpha-SMA-GFP positive cells were tested. A 3-D culture model was then applied to test their vascularization by loading alpha-SMA-GFP positive cells and endothelial cells on collagen-fibronectin gel. Results demonstrated that bone marrow stromal cells are mostly alpha-SMA-GFP positive cells which are pluripotent, and these cells expressed alpha-SMA during differentiation. The alpha-SMA-GFP positive cells could stimulate the endothelial cells to form tube-like structures and subsequently robust vascular networks in 3-D culture. In conclusion, the bone marrow derived pluripotent cells include [corrected] pericytes and can contribute to vascularization.

Reprogramming cell fates: reconciling rarity with robustness

The stunning possibility of "reprogramming" differentiated somatic cells to express a pluripotent stem cell phenotype (iPS, induced pluripotent stem cell) and the "ground state" character of pluripotency reveal fundamental features of cell fate regulation that lie beyond existing paradigms. The rarity of reprogramming events appears to contradict the robustness with which the unfathomably complex phenotype of stem cells can reliably be generated. This apparent paradox, however, is naturally explained by the rugged "epigenetic landscape" with valleys representing "preprogrammed" attractor states that emerge from the dynamical constraints of the gene regulatory network. This article provides a pedagogical primer to the fundamental principles of gene regulatory networks as integrated dynamic systems and reviews recent insights in gene expression noise and fate determination, thereby offering a formal framework that may help us to understand why cell fate reprogramming events are inherently rare and yet so robust.

Serum regulates adipogenesis of mesenchymal stem cells via MEK/ERK-dependent PPARgamma expression and phosphorylation

Mesenchymal stem cells (MSCs) provide us an excellent cellular model to uncover the molecular mechanisms underlying adipogenic differentiation of adult stem cells. PPARγ had been considered as an important molecular marker of cells undergoing adipogenic differentiation. Here, we demonstrated that expression and phosphorylation of PPARγ could be found in bone marrow–derived MSCs cultured in expansion medium without any adipogenic additives (dexamethasone, IBMX, insulin or indomethacin). Then, PPARγ was dephosphorylated in MSCs during the process of adipogenic differentiation. We then found that inhibition of MEK activation by specific inhibitor (PD98059) counteracted the PPARγ expression and phosphorylation. However, expression and phosphorylation of PPARγ did not present in MSCs cultured in medium with lower serum concentration. When these MSCs differentiated into adipocytes, no phosphorylation could be detected to accompany the expression of PPARγ. Moreover, exposure of MSCs to higher concentration of serum induced stronger PPARγ expression, and subsequently enhanced their adipogenesis. These data suggested that activation of the MEK/ERK signalling pathway by high serum concentration promoted PPARγ expression and phosphorylation, and subsequently enhanced adipogenic differentiation of MSCs.