Human adipose tissue-derived multipotent stem cells differentiate in vitro and in vivo into osteocyte-like cells

Epidermal growth factor signalling pathway in endochondral ossification: an evidence-based narrative review

During endochondral bone development, a complex process that leads to the formation of the majority of skeletal elements, mesenchymal cells condense, differentiating into chondrocytes and producing the foetal growth plate. Chondrocytes progressively hypertrophy, induce angiogenesis and are then gradually replaced by bone. Epidermal Growth Factor (EGF), one of many growth factors, is the prototype of the EGF-ligand family, which comprises several proteins involved in cell proliferation, migration and survival. In bone, EGF pathway signalling finely tunes the first steps of chondrogenesis by maintaining mesenchymal cells in an undifferentiated stage, and by promoting hypertrophic cartilage replacement. Moreover, EGF signalling modulates bone homeostasis by stimulating osteoblast and osteoclast proliferation, and by regulating osteoblast differentiation under specific spatial and temporal conditions. This evidence-based narrative review describes the EGF pathway in bone metabolism and endochondral bone development. This comprehensive description may be useful in light of possible clinical applications in orthopaedic practice. A deeper knowledge of the role of EGF in bone may be useful in musculoskeletal conditions which may benefit from the modulation of this signalling pathway.Key messagesThe EGF pathway is involved in bone metabolism.EGF signalling is essential in the very early stages of limb development by maintaining cells in an undifferentiated stage.EGF pathway positively regulates chondrocyte proliferation, negatively modulates hypertrophy, and favours cartilage replacement by bone.EGF and EGF-like proteins finely tune the proliferation and differentiation of bone tissue cells, and they also regulate the initial phases of endochondral ossification.

HAND2 is a novel obesity-linked adipogenic transcription factor regulated by glucocorticoid signalling

AIMS/HYPOTHESIS

Adipocytes are critical cornerstones of energy metabolism. While obesity-induced adipocyte dysfunction is associated with insulin resistance and systemic metabolic disturbances, adipogenesis, the formation of new adipocytes and healthy adipose tissue expansion are associated with metabolic benefits. Understanding the molecular mechanisms governing adipogenesis is of great clinical potential to efficiently restore metabolic health in obesity. Here we investigate the role of heart and neural crest derivatives-expressed 2 (HAND2) in adipogenesis.

METHODS

Human white adipose tissue (WAT) was collected from two cross-sectional studies of 318 and 96 individuals. In vitro, for mechanistic experiments we used primary adipocytes from humans and mice as well as human multipotent adipose-derived stem (hMADS) cells. Gene silencing was performed using siRNA or genetic inactivation in primary adipocytes from loxP and or tamoxifen-inducible Cre-ERT2 mouse models with Cre-encoding mRNA or tamoxifen, respectively. Adipogenesis and adipocyte metabolism were measured by Oil Red O staining, quantitative PCR (qPCR), microarray, glucose uptake assay, western blot and lipolysis assay. A combinatorial RNA sequencing (RNAseq) and ChIP qPCR approach was used to identify target genes regulated by HAND2. In vivo, we created a conditional adipocyte Hand2 deletion mouse model using Cre under control of the Adipoq promoter (Hand2AdipoqCre) and performed a large panel of metabolic tests.

RESULTS

We found that HAND2 is an obesity-linked white adipocyte transcription factor regulated by glucocorticoids that was necessary but insufficient for adipocyte differentiation in vitro. In a large cohort of humans, WAT HAND2 expression was correlated to BMI. The HAND2 gene was enriched in white adipocytes compared with brown, induced early in differentiation and responded to dexamethasone (DEX), a typical glucocorticoid receptor (GR, encoded by NR3C1) agonist. Silencing of NR3C1 in hMADS cells or deletion of GR in a transgenic conditional mouse model results in diminished HAND2 expression, establishing that adipocyte HAND2 is regulated by glucocorticoids via GR in vitro and in vivo. Furthermore, we identified gene clusters indirectly regulated by the GR-HAND2 pathway. Interestingly, silencing of HAND2 impaired adipocyte differentiation in hMADS and primary mouse adipocytes. However, a conditional adipocyte Hand2 deletion mouse model using Cre under control of the Adipoq promoter did not mirror these effects on adipose tissue differentiation, indicating that HAND2 was required at stages prior to Adipoq expression.

CONCLUSIONS/INTERPRETATION

In summary, our study identifies HAND2 as a novel obesity-linked adipocyte transcription factor, highlighting new mechanisms of GR-dependent adipogenesis in humans and mice.

DATA AVAILABILITY

Array data have been submitted to the GEO database at NCBI (GSE148699).

Synergistic interaction of hTGF-β3 with hBMP-6 promotes articular cartilage formation in chitosan scaffolds with hADSCs: implications for regenerative medicine

Background

Human TGF-β₃ has been used in many studies to induce genes coding for typical cartilage matrix components and accelerate chondrogenic differentiation, making it the standard constituent in most cultivation media used for the assessment of chondrogenesis associated with various stem cell types on carrier matrices. However, in vivo data suggests that TGF-β₃ and its other isoforms also induce endochondral and intramembranous osteogenesis in non-primate species to other mammals. Based on previously demonstrated improved articular cartilage induction by a using hTGF-β₃ and hBMP-6 together on hADSC cultures and the interaction of TGF- β with matrix in vivo, the present study investigates the interaction of a chitosan scaffold as polyanionic polysaccharide with both growth factors. The study analyzes the difference between chondrogenic differentiation that leads to stable hyaline cartilage and the endochondral ossification route that ends in hypertrophy by extending the usual panel of investigated gene expression and stringent employment of quantitative PCR.

Results

By assessing the viability, proliferation, matrix formation and gene expression patterns it is shown that hTGF-β₃ + hBMP-6 promotes improved hyaline articular cartilage formation in a chitosan scaffold in which ACAN with Col2A1 and not Col1A1 nor Col10A1 where highly expressed both at a transcriptional and translational level. Inversely, hTGF-β₃ alone tended towards endochondral bone formation showing according protein and gene expression patterns.

Conclusion

These findings demonstrate that clinical therapies should consider using hTGF-β₃ + hBMP-6 in articular cartilage regeneration therapies as the synergistic interaction of these morphogens seems to ensure and maintain proper hyaline articular cartilage matrix formation counteracting degeneration to fibrous tissue or ossification. These effects are produced by interaction of the growth factors with the polysaccharide matrix.

Loss of G protein pathway suppressor 2 in human adipocytes triggers lipid remodeling by upregulating ATP binding cassette subfamily G member 1

OBJECTIVE

Adipogenesis is critical for adipose tissue remodeling during the development of obesity. While the role of transcription factors in the orchestration of adipogenic pathways is already established, the involvement of coregulators that transduce regulatory signals into epigenome alterations and transcriptional responses remains poorly understood. The aim of our study was to investigate which pathways are controlled by G protein pathway suppressor 2 (GPS2) during the differentiation of human adipocytes.

METHODS

We generated a unique loss-of-function model by RNAi depletion of GPS2 in human multipotent adipose-derived stem (hMADS) cells. We thoroughly characterized the coregulator depletion-dependent pathway alterations during adipocyte differentiation at the level of transcriptome (RNA-seq), epigenome (ChIP-seq H3K27ac), cistrome (ChIP-seq GPS2), and lipidome. We validated the in vivo relevance of the identified pathways in non-diabetic and diabetic obese patients.

RESULTS

The loss of GPS2 triggers the reprogramming of cellular processes related to adipocyte differentiation by increasing the responses to the adipogenic cocktail. In particular, GPS2 depletion increases the expression of BMP4, an important trigger for the commitment of fibroblast-like progenitors toward the adipogenic lineage and increases the expression of inflammatory and metabolic genes. GPS2-depleted human adipocytes are characterized by hypertrophy, triglyceride and phospholipid accumulation, and sphingomyelin depletion. These changes are likely a consequence of the increased expression of ATP-binding cassette subfamily G member 1 (ABCG1) that mediates sphingomyelin efflux from adipocytes and modulates lipoprotein lipase (LPL) activity. We identify ABCG1 as a direct transcriptional target, as GPS2 depletion leads to coordinated changes of transcription and H3K27 acetylation at promoters and enhancers that are occupied by GPS2 in wild-type adipocytes. We find that in omental adipose tissue of obese humans, GPS2 levels correlate with ABCG1 levels, type 2 diabetic status, and lipid metabolic status, supporting the in vivo relevance of the hMADS cell-derived in vitro data.

CONCLUSION

Our study reveals a dual regulatory role of GPS2 in epigenetically modulating the chromatin landscape and gene expression during human adipocyte differentiation and identifies a hitherto unknown GPS2-ABCG1 pathway potentially linked to adipocyte hypertrophy in humans.

Mineral deposition and vascular invasion of hydroxyapatite reinforced collagen scaffolds seeded with human adipose-derived stem cells

Background

Collagen-based scaffolds reinforced with hydroxyapatite (HA) are an attractive choice for bone tissue engineering because their composition mimics that of bone. We previously reported the development of compression-molded collagen-HA scaffolds that exhibited high porosity, interconnected pores, and mechanical properties that were well-suited for surgical handling and fixation. The objective of this study was to investigate these novel collagen-HA scaffolds in combination with human adipose-derived stem cells (hASCs) as a template for bone formation in a subcutaneous athymic mouse model.

Methods

Collagen-HA scaffolds and collagen-only scaffolds were fabricated as previously described, and a clinically approved bone void filler was used as a control for the material. Constructs were seeded with hASCs and were pre-treated with either control or osteogenic media. A cell-free group was also included. Scaffolds were implanted subcutaneously in the backs of athymic nude mice for 8 weeks. Mineral deposition was quantified via micro-computed tomography. Histological and immunofluorescence images of the explants were used to analyze their vascular invasion, remodeling and cellularity.

Results

Cell-free collagen-HA scaffolds and those that were pre-seeded with osteogenically differentiated hASCs supported mineral deposition and vascular invasion at comparable rates, while cell-seeded constructs treated with the control medium showed lower mineralization after implantation. HA-reinforcement allowed collagen constructs to maintain their shape, provided improved cell-tissue-scaffold integration, and resulted in a more organized tissue when pre-treated in an osteogenic medium. Scaffold type and pre-treatment also determined osteoclast activity and therefore potential remodeling of the constructs.

Conclusions

The results of this study cumulatively indicate that treatment medium and scaffold composition direct mineralization and angiogenic tissue formation in an ectopic model. The data suggest that it may be necessary to match the scaffold with a particular cell type and cell-specific pre-treatment to achieve optimal bone formation.

Induction of Articular Chondrogenesis by Chitosan/Hyaluronic-Acid-Based Biomimetic Matrices Using Human Adipose-Derived Stem Cells

Cartilage repair using tissue engineering is the most advanced clinical application in regenerative medicine, yet available solutions remain unsuccessful in reconstructing native cartilage in its proprietary form and function. Previous investigations have suggested that the combination of specific bioactive elements combined with a natural polymer could generate carrier matrices that enhance activities of seeded stem cells and possibly induce the desired matrix formation. The present study sought to clarify this by assessing whether a chitosan-hyaluronic-acid-based biomimetic matrix in conjunction with adipose-derived stem cells could support articular hyaline cartilage formation in relation to a standard chitosan-based construct. By assessing cellular development, matrix formation, and key gene/protein expressions during in vitro cultivation utilizing quantitative gene and immunofluorescent assays, results showed that chitosan with hyaluronic acid provides a suitable environment that supports stem cell differentiation towards cartilage matrix producing chondrocytes. However, on the molecular gene expression level, it has become apparent that, without combinations of morphogens, in the chondrogenic medium, hyaluronic acid with chitosan has a very limited capacity to stimulate and maintain stem cells in an articular chondrogenic state, suggesting that cocktails of various growth factors are one of the key features to regenerate articular cartilage, clinically.

In Vitro Models for Study of Brown Adipocyte Biology

Brown adipocytes are the key cell type in brown adipose tissue (BAT) that express the genes required for heat production through the process of thermogenesis. Brown adipocyte cell culture models are important for researching the molecular pathways that control cell autonomous processes. In vitro tools for the study of brown adipocytes include BAT explant cultures and BAT primary cultures that are first proliferated and then differentiated. A number of stable brown preadipocyte cell lines have been generated by the expression transforming factors such as SV40 T antigen. The application of these cell lines reduces the requirement for animal tissue which is needed for primary culture and explants. Furthermore, brown adipocyte cell lines that effectively recapitulate the properties of brown adipocytes permit large-scale experimental procedures that are generally unfeasible with primary cultures that undergo a restricted number of cell divisions. Cell lines are valuable for applications such as large-scale endogenous protein expression, ChIP assay, and procedures requiring antibiotic selection over several cell divisions including stable exogenous gene expression and CRISR/Cas9 gene editing.

Osteoblastic differentiation potential of human amniotic fluid-derived mesenchymal stem cells in different culture conditions

Osteoporosis is a bone degenerative disease characterized by a decrease in bone strength and an alteration in the osseous micro-architecture causing an increase in the risk of fractures. These diseases usually happen in post-menopausal women and elderly men. The most common treatment involves anti-resorptive agent drugs. However, the inhibition of bone resorption alone is not adequate for recovery in patients at the severe stage of osteoporosis who already have a fracture. Therefore, the combination of utilizing osteoblast micro mimetic scaffold in cultivation with the stimulation of osteoblastic differentiations to regain bone formation is a treatment strategy of considerable interest. The aims of this current study are to investigate the osteoblastic differentiation potential of mesenchymal stem cells derived from human amniotic fluid and to compare the monolayer culture and scaffold culture conditions. The results showed the morphology of cells in human amniotic fluid as f-type, which is a typical cell shape of mesenchymal stem cells. In addition, the proliferation rate of cells in human amniotic fluid reached the highest peak after 14 days of culturing. After which time, the growth rate slowly decreased. Moreover, the positive expression of specific mesenchymal cell surface markers including CD44, CD73, CD90, and also HLA-ABC (MHC class I) were recorded. On the other hand, the negative expressions of the endothelial stem cells markers (CD31), the hematopoietic stem cells markers (CD34, 45), the amniotic stem cells markers (CD117), and also the HLA-DR (MHC class II) were also recorded. The expressions of osteoblastogenic related genes including OCN, COL1A1, and ALP were higher in the osteogenic-induced group when compared to the control group. Interestingly, the osteoblastogenic related gene expressions that occurred under scaffold culture conditions were superior to the monolayer culture conditions. Additionally, higher ALP activity and greater calcium deposition were recorded in the extracellular matrix in the osteogenic-induced group than in the culture in the scaffold group. In summary, the mesenchymal stem cells derived from human amniotic fluid can be induced to be differentiated into osteoblastic-like cells and can promote osteoblastic differentiation using the applied scaffold.

Function of microRNAs in the Osteogenic Differentiation and Therapeutic Application of Adipose-Derived Stem Cells (ASCs)

Traumatic wounds with segmental bone defects represent substantial reconstructive challenges. Autologous bone grafting is considered the gold standard for surgical treatment in many cases, but donor site morbidity and associated post-operative complications remain a concern. Advances in regenerative techniques utilizing mesenchymal stem cell populations from bone and adipose tissue have opened the door to improving bone repair in the limbs, spine, and craniofacial skeleton. The widespread availability, ease of extraction, and lack of immunogenicity have made adipose-derived stem cells (ASCs) particularly attractive as a stem cell source for regenerative strategies. Recently it has been shown that small, non-coding miRNAs are involved in the osteogenic differentiation of ASCs. Specifically, microRNAs such as miR-17, miR-23a, and miR-31 are expressed during the osteogenic differentiation of ASCs, and appear to play a role in inhibiting various steps in bone morphogenetic protein-2 (BMP2) mediated osteogenesis. Importantly, a number of microRNAs including miR-17 and miR-31 that act to attenuate the osteogenic differentiation of ASCs are themselves stimulated by transforming growth factor β-1 (TGFβ-1). In addition, transforming growth factor β-1 is also known to suppress the expression of microRNAs involved in myogenic differentiation. These data suggest that preconditioning strategies to reduce TGFβ-1 activity in ASCs may improve the therapeutic potential of ASCs for musculoskeletal application. Moreover, these findings support the isolation of ASCs from subcutaneous fat depots that tend to have low endogenous levels of TGFβ-1 expression.

Inferior In Vivo Osteogenesis and Superior Angiogenesis of Human Adipose‐Derived Stem Cells Compared with Bone Marrow‐Derived Stem Cells Cultured in Xeno‐Free Conditions

The possibility of using adipose tissue-derived stromal cells (ATSC) as alternatives to bone marrow-derived stromal cells (BMSC) for bone repair has garnered interest due to the accessibility, high cell yield, and rapid in vitro expansion of ATSC. For clinical relevance, their bone forming potential in comparison to BMSC must be proven. Distinct differences between ATSC and BMSC have been observed in vitro and comparison of osteogenic potential in vivo is not clear to date. The aim of the current study was to compare the osteogenesis of human xenofree-expanded ATSC and BMSC in vitro and in an ectopic nude mouse model of bone formation. Human MSC were implanted with biphasic calcium phosphate biomaterials in subcutis pockets for 8 weeks. Implant groups were: BMSC, ATSC, BMSC and ATSC mixed together in different ratios, as well as MSC primed with either osteogenic supplements (250 μM ascorbic acid, 10 mM β-glycerolphosphate, and 10 nM dexamethasone) or 50 ng/ml recombinant bone morphogenetic protein 4 prior to implantation. In vitro results show osteogenic gene expression and differentiation potentials of ATSC. Despite this, ATSC failed to form ectopic bone in vivo, in stark contrast to BMSC, although osteogenic priming did impart minor osteogenesis to ATSC. Neovascularization was enhanced by ATSC compared with BMSC; however, less ATSC engrafted into the implant compared with BMSC. Therefore, in the content of bone regeneration, the advantages of ATSC over BMSC including enhanced angiogenesis, may be negated by their lack of osteogenesis and prerequisite for osteogenic differentiation prior to transplantation. Stem Cells Translational Medicine 2017;6:2160-2172.

Biological characteristics of muscle-derived satellite cells isolated from rats at different postnatal days

This study investigated the in vitro growth characteristics and differential potential of muscle-derived satellite cells (MDSCs) derived from rats at different postnatal (P) stages, in order to expand the range of source material for tissue engineering. Rat MDSCs were isolated from P5, P10, P15, P21 and P42 rat skeletal muscles using double enzyme digestion and differential adherent culture. Neurogenic, osteogenic and myogenic induction media were used to induce directed differentiation. Differentiated nerve cells, osteoblasts and myotubes were identified by their morphology and immunohistochemical staining. Most cells transformed into spindle-shaped mononuclear cells after 48 h and proliferated rapidly. MDSCs were difficult to isolate from P42 rats. After neurogenesis, four groups MDSCs formed neuron-specific enolase positive polygonal-shaped dendritic cells. After osteogenesis, P5, P10, P15 and P21 MDSCs formed Alizarin red- and osteocalcin-positive bone nodules. After myogenesis, myotubes were formed and were fast muscle myosin-positive. MDSCs derived from P5, P10, P15 and P21 rat skeletal muscle are easy to isolate, culture and amplify in vitro, which increases the range of source material available for tissue engineering.

Visceral abdominal obesity is associated with an increased risk of irritable bowel syndrome

OBJECTIVES

There are several studies considering obesity as the risk factor for various lower gastrointestinal symptoms. But the relationship between visceral abdominal obesity and the incidence of irritable bowel syndrome (IBS) is not studied yet. The aim of this study was to investigate the association between visceral adipose tissue (VAT) and the risk of IBS.

METHODS

This is a case-control study comparing the VAT area between subjects with IBS (IBS group) and controls without IBS (non IBS group), who underwent abdomen computerized tomography (CT) for routine health checkup from January 2012 to August 2013 in a health promotion center. A telephone survey was retrospectively conducted to diagnose IBS by Rome III criteria. The association between IBS and abdominal obesity was evaluated by measuring VAT, subcutaneous adipose tissue (SAT), VAT/SAT ratio, body mass index (BMI) and waist circumference (WC).

RESULTS

The prevalence of IBS was 19.9% (67/336) among all enrolled subjects. In the univariate analysis, VAT area, VAT/SAT ratio, waist circumference, the presence of reflux esophagitis and the ratio of females were significantly higher in the IBS group than in the non IBS group. However, a higher BMI or a higher SAT area is not associated with an increased risk of IBS. In the multivariate analysis, a higher VAT area (odds ratio (OR)=9.42, 95% confidence interval (CI): 2.90-30.64, highest tertile vs. lowest tertile, P=0.001), VAT/SAT ratio (OR=10.15, 95% CI: 3.05-33.58, highest tertile vs. lowest tertile, P=0.001) and waist circumference (OR=7.81, 95% CI: 2.13-28.66, highest tertile vs. lowest tertile, P=0.002) were independently associated with a risk of IBS. Only in the IBS-D group, not in the IBS-C, visceral adiposity was associated with an increased risk of IBS.

CONCLUSIONS

Visceral adiposity measured by VAT, VAT/SAT, and waist circumference is associated with an increased risk of IBS, especially of IBS-D. However, neither SAT nor BMI are associated with an increased risk of IBS.

MicroRNA-26 family is required for human adipogenesis and drives characteristics of brown adipocytes

Adipose tissue contains thermogenic adipocytes (i.e., brown and brite/beige) that oxidize nutrients at exceptionally high rates via nonshivering thermogenesis. Its recent discovery in adult humans has opened up new avenues to fight obesity and related disorders such as diabetes. Here, we identified miR-26a and -26b as key regulators of human white and brite adipocyte differentiation. Both microRNAs are upregulated in early adipogenesis, and their inhibition prevented lipid accumulation while their overexpression accelerated it. Intriguingly, miR-26a significantly induced pathways related to energy dissipation, shifted mitochondrial morphology toward that seen in brown adipocytes, and promoted uncoupled respiration by markedly increasing the hallmark protein of brown fat, uncoupling protein 1. By combining in silico target prediction, transcriptomics, and an RNA interference screen, we identified the sheddase ADAM metallopeptidase domain 17 (ADAM17) as a direct target of miR-26 that mediated the observed effects on white and brite adipogenesis. These results point to a novel, critical role for the miR-26 family and its downstream effector ADAM17 in human adipocyte differentiation by promoting characteristics of energy-dissipating thermogenic adipocytes.

Periodontal tissue regeneration by transplantation of rat adipose-derived stromal cells in combination with PLGA-based solid scaffolds

Regeneration of damaged periodontium is challenging due to its multi-tissue composition. Mesenchymalstem cell-based approaches using adipose-derived stromal cells (ASCs) may contribute to periodontal reconstruction, particularly when combined with the use of scaffolds to maintain a space for new tissue growth. The aim of this study was to assess the regenerative potential of ASCs derived from inbred or outbred rats in combination with novel solid scaffolds composed of PLGA (Poly D,L-lactic-co-glycolic acid) (PLGA-scaffolds). Cultured ASCs seeded onto PLGA scaffolds (ASCs/PLGA) or PLGA-scaffolds (PLGA) alone were transplanted into periodontal fenestration defects created in F344 or Sprague Dawley (SD) rats. Micro-CT analysis showed a significantly higher percentage of bone growth in the ASCs/PLGA groups compared with the PLGA-alone groups at five weeks after surgery. Similarly, histomorphometric analysis demonstrated thicker growth of periodontal ligament and cementum layers in the ASCs/PLGA-groups compared with the PLGA-alone groups. In addition, transplanted DiI-labeled ASCs were observed in the periodontal regenerative sites. The present investigation demonstrated the marked ability of ASCs in combination with PLGA scaffolds to repair periodontal defects.

Adipose-Derived Stem Cells: Isolation, Characterization, and Differentiation Potential

In mammals, the two main types of adipose tissues, white and brown adipose tissues, exert different physiological functions. White adipose tissue (WAT) is for storing energy, while brown adipose tissue (BAT) is for energy consumption. Adipose-derived stem cells (ADSCs) are abundant in WAT and BAT, have multipotent characteristics, and are easily extracted. ADSCs can be differentiated into several cell lineages, including adipocytes, osteoblasts, chondrocytes (cartilage cells), myocytes, and neuronal cells. Therefore, ADSC could be considered as a strategy for future regenerative medicine and tissue engineering.

Material-driven differentiation of induced pluripotent stem cells in neuron growth factor-grafted poly(ε-caprolactone)-poly(β-hydroxybutyrate) scaffolds

The potential of constructs comprising induced pluripotent stem (iPS) cells and biopolymers can be high for neurological surgery practice, if the systematic activity of neuronal regeneration is clarified. This study shows a guided differentiation of iPS cells toward neurons in neuron growth factor (NGF)-grafted poly(ε-caprolactone) (PCL)-poly(β-hydroxybutyrate) (PHB) scaffolds. The porosity of PCL-PHB scaffolds enhanced with increasing the concentration of salt particles (porogen) and the weight percentage of PCL. An increase in the graft concentration of NGF elevated the atomic ratios of N/C and O/C on the surface of NGF-grafted PCL-PHB scaffolds. In addition, incorporating heparin and NGF promoted the adhesion and viability of iPS cells in constructs. When the weight percentage of PCL increased, the viability of iPS cells reduced; however, more PCL in constructs benefited the adhesion of iPS cells. Under the influence of heparin and NGF, a high weight percentage of PCL and a long inductive period improved iPS cells to differentiate into neuron-like cells carrying βIII tubulin and inhibited other differentiation(s). The material-driven differentiation in NGF-grafted PCL-PHB constructs can be promising in guiding iPS cells to produce neurons for nerve tissue engineering.

Activation of protein kinase A and exchange protein directly activated by cAMP promotes adipocyte differentiation of human mesenchymal stem cells

Human mesenchymal stem cells are primary multipotent cells capable of differentiating into several cell types including adipocytes when cultured under defined in vitro conditions. In the present study we investigated the role of cAMP signaling and its downstream effectors, protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac) in adipocyte conversion of human mesenchymal stem cells derived from adipose tissue (hMADS). We show that cAMP signaling involving the simultaneous activation of both PKA- and Epac-dependent signaling is critical for this process even in the presence of the strong adipogenic inducers insulin, dexamethasone, and rosiglitazone, thereby clearly distinguishing the hMADS cells from murine preadipocytes cell lines, where rosiglitazone together with dexamethasone and insulin strongly promotes adipocyte differentiation. We further show that prostaglandin I₂ (PGI₂) may fully substitute for the cAMP-elevating agent isobutylmethylxanthine (IBMX). Moreover, selective activation of Epac-dependent signaling promoted adipocyte differentiation when the Rho-associated kinase (ROCK) was inhibited. Unlike the case for murine preadipocytes cell lines, long-chain fatty acids, like arachidonic acid, did not promote adipocyte differentiation of hMADS cells in the absence of a PPARγ agonist. However, prolonged treatment with the synthetic PPARδ agonist L165041 promoted adipocyte differentiation of hMADS cells in the presence of IBMX. Taken together our results emphasize the need for cAMP signaling in concert with treatment with a PPARγ or PPARδ agonist to secure efficient adipocyte differentiation of human hMADS mesenchymal stem cells.

β₁-Adrenergic receptors increase UCP1 in human MADS brown adipocytes and rescue cold-acclimated β₃-adrenergic receptor-knockout mice via nonshivering thermogenesis

With the finding that brown adipose tissue is present and negatively correlated to obesity in adult man, finding the mechanism(s) of how to activate brown adipose tissue in humans could be important in combating obesity, type 2 diabetes, and their complications. In mice, the main regulator of nonshivering thermogenesis in brown adipose tissue is norepinephrine acting predominantly via β(3)-adrenergic receptors. However, vast majorities of β(3)-adrenergic agonists have so far not been able to stimulate human β(3)-adrenergic receptors or brown adipose tissue activity, and it was postulated that human brown adipose tissue could be regulated instead by β(1)-adrenergic receptors. Therefore, we have investigated the signaling pathways, specifically pathways to nonshivering thermogenesis, in mice lacking β(3)-adrenergic receptors. Wild-type and β(3)-knockout mice were either exposed to acute cold (up to 12 h) or acclimated for 7 wk to cold, and parameters related to metabolism and brown adipose tissue function were investigated. β(3)-knockout mice were able to survive both acute and prolonged cold exposure due to activation of β(1)-adrenergic receptors. Thus, in the absence of β(3)-adrenergic receptors, β(1)-adrenergic receptors are effectively able to signal via cAMP to elicit cAMP-mediated responses and to recruit and activate brown adipose tissue. In addition, we found that in human multipotent adipose-derived stem cells differentiated into functional brown adipocytes, activation of either β(1)-adrenergic receptors or β(3)-adrenergic receptors was able to increase UCP1 mRNA and protein levels. Thus, in humans, β(1)-adrenergic receptors could play an important role in regulating nonshivering thermogenesis.

Small RNA sequencing reveals miR-642a-3p as a novel adipocyte-specific microRNA and miR-30 as a key regulator of human adipogenesis

BACKGROUND

In severe obesity, as well as in normal development, the growth of adipose tissue is the result of an increase in adipocyte size and numbers, which is underlain by the stimulation of adipogenic differentiation of precursor cells. A better knowledge of the pathways that regulate adipogenesis is therefore essential for an improved understanding of adipose tissue expansion. As microRNAs (miRNAs) have a critical role in many differentiation processes, our study aimed to identify the role of miRNA-mediated gene silencing in the regulation of adipogenic differentiation.

RESULTS

We used deep sequencing to identify small RNAs that are differentially expressed during adipogenesis of adipose tissue-derived stem cells. This approach revealed the un-annotated miR-642a-3p as a highly adipocyte-specific miRNA. We then focused our study on the miR-30 family, which was also up-regulated during adipogenic differentiation and for which the role in adipogenesis had not yet been elucidated. Inhibition of the miR-30 family blocked adipogenesis, whilst over-expression of miR-30a and miR-30d stimulated this process. We additionally showed that both miR-30a and miR-30d target the transcription factor RUNX2, and stimulate adipogenesis via the modulation of this major regulator of osteogenesis.

CONCLUSIONS

Overall, our data suggest that the miR-30 family plays a central role in adipocyte development. Moreover, as adipose tissue-derived stem cells can differentiate into either adipocytes or osteoblasts, the down-regulation of the osteogenesis regulator RUNX2 represents a plausible mechanism by which miR-30 miRNAs may contribute to adipogenic differentiation of adipose tissue-derived stem cells.

Adipose tissue-deprived stem cells acquire cementoblast features treated with dental follicle cell conditioned medium containing dentin non-collagenous proteins in vitro

Adipose tissue-derived stem cells (ADSCs), which are easily harvested and show excellent pluripotency potential, have generated considerable interest in regenerative medicine. In this study, the differentiation of ADSCs was assessed after treatment with dental follicle cell conditioned medium (DFCCM) containing dentin non-collagenous proteins (dNCPs). ADSCs exhibited a fibroblast-like morphology and high proliferative capacity. However, after treatment with dNCPs/DFCCM, ADSCs changed from a fibroblast-like to cementoblast-like morphology and significantly lost their proliferative capacity. Alkaline phosphatase activity and in vitro mineralization behaviour of ADSCs were significantly enhanced. Mineralization-related markers including cementum attachment protein, bone sialoprotein, osteocalcin, osteopontin and osteonectin were detected at mRNA or protein levels, whereas dentin sialophosphoprotein and dentin sialoprotein were not detected, implying a cementoblast-like phenotype. These results demonstrate that ADSCs acquired cementoblast features in vitro with dNCPs/DFCCM treatment and could be a potential source of cementogenic cells for periodontal regeneration.

NOS inhibition synchronizes calcium oscillations in human adipose tissue-derived mesenchymal stem cells by increasing gap-junctional coupling

Adipose tissue-derived mesenchymal stem cells (ASCs) are a promising stem cell source for cell transplantation. We demonstrate that undifferentiated ASCs display robust oscillations of intracellular calcium [Ca(2+) ](i) which may be associated with stem cell maintenance since oscillations were absent in endothelial cell differentiation medium supplemented with FGF-2. [Ca(2+) ](i) oscillations were dependent on extracellular Ca(2+) and Ca(2+) release from intracellular stores since they were abolished in Ca(2+) -free medium and in the presence of the store-depleting agent thapsigargin. They were inhibited by the phospholipase C antagonist U73,122, the inositol 1,4,5-trisphosphate (InsP(3) ) receptor antagonist 2-aminoethoxydiphenyl borate (2-APB) as well as by the gap-junction uncouplers 1-heptanol and carbenoxolone, indicating regulation by the InsP(3) pathway and dependence on gap-junctional coupling. Cells endogenously generated nitric oxide (NO), expressed NO synthase 1 (NOS 1) and connexin 43 (Cx 43). The nitric oxide NOS inhibitors NG-monomethyl-L-arginine (L-NMMA), N(G)-nitro-L-arginine methyl ester (L-NAME), 2-ethyl-2-thiopseudourea, and diphenylene iodonium as well as si-RNA-mediated down-regulation of NOS 1 synchronized [Ca(2+) ](i) oscillations between individual cells, whereas the NO-donors S-nitroso-N-acetylpenicillamine (SNAP) and sodium nitroprusside (SNP) as well as the soluble guanylate cyclase inhibitor 1H-[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one (ODQ) were without effects. The synchronization of [Ca(2+) ](i) oscillations was due to an improvement of intracellular coupling since fluorescence recovery after photobleaching (FRAP) revealed increased reflow of fluorescent calcein into the bleached area in the presence of the NOS inhibitors DPI and L-NAME. In summary our data demonstrate that intracellular NO levels regulate synchronization of [Ca(2+) ](i) oscillations in undifferentiated ASCs by controlling gap-junctional coupling.

Real-time label-free monitoring of adipose-derived stem cell differentiation with electric cell-substrate impedance sensing

Real-time monitoring of stem cells (SCs) differentiation will be critical to scale-up SC technologies, while label-free techniques will be desirable to quality-control SCs without precluding their therapeutic potential. We cultured adipose-derived stem cells (ADSCs) on top of multielectrode arrays and measured variations in the complex impedance Z* throughout induction of ADSCs toward osteoblasts and adipocytes. Z* was measured up to 17 d, every 180 s, over a 62.5-64 kHz frequency range with an ECIS Z instrument. We found that osteogenesis and adipogenesis were characterized by distinct Z* time-courses. Significant differences were found (P = 0.007) as soon as 12 h post induction. An increase in the barrier resistance (Rb) up to 1.7 ohm·cm(2) was associated with early osteo-induction, whereas Rb peaked at 0.63 ohm·cm(2) for adipo-induced cells before falling to zero at t = 129 h. Dissimilarities in Z* throughout early induction (<24 h) were essentially attributed to variations in the cell-substrate parameter α. Four days after induction, cell membrane capacitance (Cm) of osteo-induced cells (Cm = 1.72 ± 0.10 μF/cm(2)) was significantly different from that of adipo-induced cells (Cm = 2.25 ± 0.27 μF/cm(2)), indicating that Cm could be used as an early marker of differentiation. Finally, we demonstrated long-term monitoring and measured a shift in the complex plane in the middle frequency range (1 kHz to 8 kHz) between early (t = 100 h) and late induction (t = 380 h). This study demonstrated that the osteoblast and adipocyte lineages have distinct dielectric properties and that such differences can be used to perform real-time label-free quantitative monitoring of adult stem cell differentiation with impedance sensing.

Inhibition of hedgehog signaling decreases proliferation and clonogenicity of human mesenchymal stem cells

Human mesenchymal stem cells (hMSC) have the ability to differentiate into osteoblasts, adipocytes and chondrocytes. We have previously shown that hMSC were endowed with a basal level of Hedgehog signaling that decreased after differentiation of these cells. Since hMSC differentiation is associated with growth-arrest we investigated the function of Hh signaling on cell proliferation. Here, we show that inhibition of Hh signaling, using the classical inhibitor cyclopamine, or a siRNA directed against Gli-2, leads to a decrease in hMSC proliferation. This phenomenon is not linked to apoptosis but to a block of the cells in the G0/G1 phases of the cell cycle. At the molecular level, it is associated with an increase in the active form of pRB, and a decrease in cyclin A expression and MAP kinase phosphorylation. Inhibition of Hh signaling is also associated with a decrease in the ability of the cells to form clones. By contrast, inhibition of Hh signaling during hMSC proliferation does not affect their ability to differentiate. This study demonstrates that hMSC are endowed with a basal Hedgehog signaling activity that is necessary for efficient proliferation and clonogenicity of hMSC. This observation unravels an unexpected new function for Hedgehog signaling in the regulation of human mesenchymal stem cells and highlights the critical function of this morphogen in hMSC biology.

Differentiation of Human Adipose-Derived Stem Cells into "Brite" (Brown-in-White) Adipocytes

It is well established now that adult humans possess active brown adipose tissue (BAT) which represents a potential pharmacological target to combat obesity and associated diseases. Moreover thermogenic brown-like adipocytes ("brite adipocytes") appear also in mouse white adipose tissue (WAT) upon β3-adrenergic stimulation. We had previously shown that human multipotent adipose-derived stem cells (hMADS) are able to differentiate into cells which exhibit the key properties of human white adipocytes, and then to convert into functional brown adipocytes upon PPARγ activation. In light of a wealth of data indicating that thermogenic adipocytes from BAT and WAT have a distinct cellular origin, we have characterized at the molecular level UCP1 positive hMADS adipocytes from both sexes as brite adipocytes. Conversion of white to brown hMADS adipocytes is dependent on PPARγ activation with rosiglitazone as the most potent agonist and is inhibited by a PPARγ antagonist. In contrast to mouse cellular models, hMADS cells conversion into brown adipocytes is weakly induced by BMP7 treatment and not modulated by activation of the Hedgehog pathway. So far no primary or clonal precursor cells of human brown adipocytes have been obtained that can be used as a tool to develop therapeutic drugs and to gain further insights into the molecular mechanisms of brown adipogenesis in humans. Thus hMADS cells represent a suitable human cell model to delineate the formation and/or the uncoupling capacity of brown/brite adipocytes that could help to dissipate caloric excess intake among individuals.

Which CIDE are you on? Apoptosis and energy metabolism

Around 1998, cell death-inducing DNA fragmentation factor-alpha (DFFA)-like effector (CIDE) proteins including CIDEA, CIDEB and CIDEC/fat specific protein 27 (Fsp27) were first identified by their sequence homology with the N-terminal domain of the DNA fragmentation factor (DFF). Indeed, in vitro analysis revealed that all three CIDE proteins are involved in apoptosis. However, recent gene-targeting studies have provided novel insights into the physiological function of CIDE proteins. Mice deficient in each CIDE protein exhibit lean phenotypes, a reduction of lipid droplet size in white adipose tissue and increased metabolic rate. Thus, all CIDE proteins play an important role in energy metabolism and lipid droplet formation. More recently, a glycoproteomics approach has shown that post-translational regulation of CIDE proteins via glycosylation modulates transforming growth factor (TGF)-beta 1-dependent apoptosis. Another recent study using mouse embryonic fibroblasts derived from CIDEA-deficient mice revealed that 5'AMP-activated protein kinase (AMPK) activity is regulated by CIDEA-mediated ubiquitin-dependent proteasomal degradation via a protein interaction with the AMPK beta subunit. Even after a decade of study, the physiological roles of CIDE proteins have still not been completely elucidated. This review aims to shed light on the novel functions of CIDE proteins and their physiological roles.

Transforming growth factor beta1 induces osteogenic differentiation of murine bone marrow stromal cells

Bone marrow stromal cells (BMSCs) have been shown to contribute to regeneration of numerous mesodermal tissue types including adipose, bone, and cartilage. Recent studies have shown that BMSCs migrate into damaged bone and help facilitate effects such as fracture healing. Although bone morphogenic proteins have been shown to stimulate bone repair, their levels remain low postfracture. Peripheral blood levels of transforming growth factor beta1 (TGF-beta1), on the other hand, rise dramatically within 2 weeks postfracture. Therefore, we investigated the role of TGF-beta1 on BMSC osteogenic differentiation in vitro. Murine BMSCs were freshly isolated from femurs, fluorescence-activated cell sorted for Sca-1, cultured in Iscove's modified Dulbecco's medium, and exposed to TGF-beta1. After 14 days, real-time reverse transcriptase-polymerase chain reaction and immunohistochemical staining were performed to examine the expression of self-renewal and terminal differentiation markers. Results showed that the treatment with TGF-beta1 reduced mRNA levels of self-renewal markers (Oct4, Stella, Nanos3, and Abcg2) by twofold and increased osteoblast differentiation markers (Runx2, Opn, and Col1) up to sevenfold compared with controls. We also observed decreased mRNA levels of adipogenic markers (Pparg2 and Adn) and an increase in alkaline phosphatase activity. Transcriptional coactivator with PDZ-binding motif (TAZ) mRNA and protein levels were elevated up to threefold following TGF-beta1 stimulation. In conclusion, our findings revealed an unexpected osteogenic differentiation pathway in murine BMSCs under the control of TGF-beta that is mediated by TAZ, which is known to increase RUNX2-dependent gene transcription while repressing PPARgamma2-dependent transcription. This is the first report demonstrating the upregulation of TAZ activity in BMSCs by a physiological growth factor present during acute bone injury.

Epidermal growth factor and bone morphogenetic proteins upregulate osteoblast proliferation and osteoblastic markers and inhibit bone nodule formation

OBJECTIVE

The aim of this study was to investigate the in vitro osteogenic activity of EGF in association with bone morphogenetic proteins BMP2 and BMP7.

METHODS

SaOS-2 (osteoblast-like cell line from human osteosarcoma) were cultured in the presence of EGF and BMPs for various culture periods to assess (a) cell proliferation by MTT assay, (b) Runx2, alkaline phosphatase (ALP) and osteocalcin (OC) mRNA expression using quantitative RT-PCR and ELISA, and (c) bone tissue mineralization using Alizarin Red staining.

RESULTS

EGF alone was able to stimulate osteoblast growth in a time-dependent manner. When mixed with BMP2, BMP7, and their combination, EGF greatly promoted osteoblast growth, compared to the BMP- and EGF-stimulated cells, suggesting a possible synergistic effect between EGF and BMPs on osteoblast growth. Stimulation with EGF, EGF/BMP2, and EGF/BMP2/BMP7 for 7 days upregulated Runx2 mRNA expression by the osteoblasts. EGF downregulated ALP mRNA expression, which was recovered when the BMP2/BMP7 combination was added to the osteoblast culture. Tested on OC mRNA expression, EGF had no effect and inhibited the enhancing effect of BMP2 and BMP7 on osteocalcin expression. The bone mineralization assay showed that EGF reduced both the number and size of the bone nodules. This reducing effect was observable even in the presence of BMP2 and BMP7.

CONCLUSION

This study demonstrated that EGF may act in the early phase to promote osteoblast growth and specific marker expression rather than the late phase involving cell differentiation/mineralization.

Human multipotent adipose-derived stem cells differentiate into functional brown adipocytes

In contrast to the earlier contention, adult humans have been shown recently to possess active brown adipose tissue with a potential of being of metabolic significance. Up to now, brown fat precursor cells have not been available for human studies. We have shown previously that human multipotent adipose-derived stem (hMADS) cells exhibit a normal karyotype and high self-renewal ability; they are known to differentiate into cells that exhibit the key properties of human white adipocytes, that is, uncoupling protein two expression, insulin-stimulated glucose uptake, lipolysis in response to beta-agonists and atrial natriuretic peptide, and release of adiponectin and leptin. Herein, we show that, upon chronic exposure to a specific PPARgamma but not to a PPARbeta/delta or a PPARalpha agonist, hMADS cell-derived white adipocytes are able to switch to a brown phenotype by expressing both uncoupling protein one (UCP1) and CIDEA mRNA. This switch is accompanied by an increase in oxygen consumption and uncoupling. The expression of UCP1 protein is associated to stimulation of respiration by beta-AR agonists, including beta3-AR agonist. Thus, hMADS cells represent an invaluable cell model to screen for drugs stimulating the formation and/or the uncoupling capacity of human brown adipocytes that could help to dissipate excess caloric intake of individuals.

Adipose derived stem cells and smooth muscle cells: implications for regenerative medicine

The treatment of chronic wounds and other damaged tissues and organs remains a difficult task, in spite of greater adherence to recognised standards of care and a better understanding of pathophysiologic principles. Adipose derived stem cells (ADSCs), with their proliferative and impressive differentiation potential, may be used in the future in autologous cell therapy or grafting to replace damaged tissues. At this point in time, transplanted tissues are often rejected by the body. Autologous grafting would eliminate this problem. ADSCs are able to differentiate into a number of cells in vitro, for example smooth muscle cells (SMCs), when treated with lineage specific factors. SMCs play a key role in physiology and pathology as they form the principle layer of all SMC tissues. Smooth muscle biopsies are often impractical and morbid, and often lead to a low cell harvest. It has also been shown that SMCs derived from a diseased organ can lead to abnormal cells. Therefore, there is a great need for alternative sources of healthy SMCs. The use of ADSCs for cell-based tissue engineering (TE) represents a promising alternative for smooth muscle repair. This review discusses the potential uses of ADSCs and SMCs in regenerative medicine, and the potential of ADSCs to be differentiated into functional SMCs for TE and regenerative cellular therapies to repair diseased organs.

Activation of hedgehog signaling inhibits osteoblast differentiation of human mesenchymal stem cells

Mesenchymal stem cells within the bone are responsible for the generation of osteoblasts, chondrocytes, and adipocytes. In rodents, Indian hedgehog has been shown to play a role in osteoblast differentiation. However, evidence for a direct function of hedgehog (Hh) in human osteoblastic differentiation is missing. Using different models of human mesenchymal stem cells we show that Hh signaling decreases during osteoblast differentiation. This is associated with a decrease in Smoothened expression, a key partner that triggers Hh signaling, and in the number of cells displaying a primary cilium, an organelle necessary for Hh signaling. Remarkably, treatment of human mesenchymal stem cells with sonic hedgehog or two molecules able to activate Hh signaling inhibits osteoblast differentiation. This inhibition is visualized through a decrease in mineralization and in the expression of osteoblastic genes. In particular, activation of Hh signaling induces a decrease in Runx2 expression, a key transcriptional factor controlling the early stage of osteoblast differentiation. Consistently, the activation of Hh signaling during the first days of differentiation is sufficient to inhibit osteoblast differentiation, whereas differentiated osteoblasts are not affected by Hh signaling. In summary, we show here, using various inducers of Hh signaling and mesenchymal stem cells of two different origins, that Hh signaling inhibits human osteoblast differentiation, in sharp contrast to what has been described in rodent cells. This species difference should be taken into account for screening for pro-osteogenic molecules.

PHB/PHBHHx scaffolds and human adipose-derived stem cells for cartilage tissue engineering

The goal of this study was to investigate the potential of polyhydroxybutyrate (PHB)/poly(hydroxybutyrate-co-hydroxyhexanoate) (PHBHHx) (PHB/PHBHHx) to produce neocartilage upon seeding with differentiated human adipose-derived stem cells (hASCs). hASCs were grown on a three-dimensional PHB/PHBHHx scaffold in vitro with or without chondrogenic media for 14 days. Scanning electron microscopy showed that differentiated cells produced abundant extracellular matrices with increasing culture time. No cytotoxicity was observed by the live/dead cell viability assay. GAG and total collagen content in the differentiated cells increased significantly with in vitro culture time. After 14 days of in vitro culture, the differentiated cells grown on the (PHB/PHBHHx) scaffold (differentiated cells/(PHB/PHBHHx)) were implanted into the subcutaneous layer nude mice for 12 or 24 weeks, non-differentiated cells/(PHB/PHBHHx) were implanted as the control group. The differentiated cells/(PHB/PHBHHx) implants formed cartilage-like tissue after 24 weeks of implantation, and stained positive for collagen type II, safranin O, and toluidine blue. In addition, typical cartilage lacuna was observed, and there were no remnants of PHB/PHBHHx. Collagen type II was detected by Western blot at 12 and 24 weeks of implantation. In the control group, no cartilage formation was observed. This study demonstrated that PHB/PHBHHx is a suitable material for cartilage tissue engineering.

Crosslinked three-dimensional demineralized bone matrix for the adipose-derived stromal cell proliferation and differentiation

Stem cell-based therapy has been a promising method for tissue regeneration and wound repair. Adult adipose-derived stromal cells (ADSCs) are often used for adipose and bone tissue reconstruction because of their abundant sources and multipotential differentiation ability. When combined with carriers, ADSCs could be useful for constructing tissue substitutes in vitro or facilitating tissue regeneration in vivo. Demineralized bone matrix (DBM) has been used for tissue reconstruction because collagen presents good cell compatibility. However, DBM degrades rapidly when used for three-dimensional ADSC culture. Here DBM was crosslinked with 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide and N-hydroxysulfosuccinimide to investigate whether crosslinked DBM (CRL-DBM) could be used as ADSC carrier. CRL-DBM showed not only improved mechanical property and enhanced stability, but also sustained ADSC proliferation and effective differentiation into adipocytes and bone lineage cells. The results indicated that CRL-DBM may be a suitable ADSC carrier for adipose and bone tissue regeneration.

Genomic profiling of mesenchymal stem cells

Mesenchymal stem/stromal cells (MSC) are an accessible source of precursor cells that can be expanded in vitro and used for tissue regeneration for different clinical applications. The advent of microarray technology has enabled the monitoring of individual and global gene expression patterns across multiple cell populations. Thus, genomic profiling has fundamentally changed our capacity to characterize MSCs, identify potential biomarkers and determined key molecules regulating biological processes involved in stem cell survival, growth and development. Numerous studies have now examined the genomic profiles of MSCs derived from different tissues that exhibit varying levels of differentiation and proliferation potentials. The knowledge gained from these studies will help improve our understanding of the cellular signalling pathways involved in MSC growth, survival and differentiation, and may aid in the development of strategies to improve the tissue regeneration potential of MSCs for different clinical indications. The present review summarizes studies characterizing the gene expression profile of MSCs.

Adipose-Derived Stem Cells: Characterization and Current Application in Orthopaedic Tissue Repair

Orthopaedic tissues, such as bone, cartilage, intervertebral disc and tendon, contain cells that are difficult to culture and stimulate in vitro for repair of damaged tissue. Stem cells have the ability to self-renew and differentiate into many tissue types. Recent progress in stem cell research has led to an enthusiastic effort to utilize stem cells for orthopaedic tissue regeneration. Due to ease of harvest and abundance, adipose-derived mesenchymal cells (ASC) are an attractive, readily available adult stem cell that has become increasingly popular for use in many stem cell applications. Recent progress has been made in characterizing ASC and looking mechanistically at gene expression and cellular pathways involved in differentiation. This review focuses on (i) the characterization of ASC through expression of appropriate surface markers; (ii) modulation of in vitro differentiation of ASC through different scaffolds, growth factors, and media; and (iii) the use of ASC in orthopaedic tissue repair. Strategies for repair involve the use of differentiated or undifferentiated, fresh or passaged ASC, in conjunction with appropriate choice of media, growth factors and scaffolds. Recent in vivo studies utilizing ASC are discussed giving results on defect repair and potential for clinical orthopaedic tissue regeneration.

The influence of auranofin, a clinically established antiarthritic gold drug, on bone metabolism: analysis of its effects on human multipotent adipose-derived stem cells, taken as a model

Auranofin is a gold-based antiarthritic drug in clinical use for more that 25 years. However, in spite of a long established use, its specific effects on bone metabolism are still greatly controversial. We have analyzed in vitro the actions of auranofin on human multipotent adipose-derived stem (hMADS) cells, used as a model for bone metabolism, since these cells were reported to undergo osteogenesis both in vitro and in vivo. Cytotoxicity of auranofin on hMADS cells, differentiated into osteoblasts, was initially assessed. Thereafter, the consequences of exposure to nontoxic but clinically relevant auranofin concentrations were analyzed by monitoring the seleno-protein glutathione peroxidase 3 or alkaline phosphatase, a characteristic biomarker of osteogenesis. Notably, we found that chronic treatment with auranofin alters only weakly the levels of alkaline phosphatase, thus implying an overall modest effect on osteogenesis. In contrast, auranofin turned out to greatly affect glutathione peroxidase 3 activity. The possible medical implications of these findings are discussed.

Comparative transcriptomics of human multipotent stem cells during adipogenesis and osteoblastogenesis

Background

A reciprocal relationship between bone and fat development in osteoporosis is clinically well established. Some of the key molecular regulators involved in this tissue replacement process have been identified. The detailed mechanisms governing the differentiation of mesenchymal stem cells (MSC) – the key cells involved – are however only now beginning to emerge. In an attempt to address the regulation of the adipocyte/osteoblast balance at the level of gene transcription in a comprehensive and unbiased manner, we performed a large-scale gene expression profiling study using a unique cellular model, human multipotent adipose tissue-derived stem cells (hMADS).

Results

The analysis of 1606 genes that were found to be differentially expressed between adipogenesis and osteoblastogenesis revealed gene repression to be most prevalent prior to commitment in both lineages. Computational analyses suggested that this gene repression is mediated by miRNAs. The transcriptional activation of lineage-specific molecular processes in both cases occurred predominantly after commitment. Analyses of the gene expression data and promoter sequences produced a set of 65 genes that are candidates for genes involved in the process of adipocyte/osteoblast commitment. Four of these genes were studied in more detail: LXRα and phospholipid transfer protein (PLTP) for adipogenesis, the nuclear receptor COUP-TF1 and one uncharacterized gene, TMEM135 for osteoblastogenesis. PLTP was secreted during both early and late time points of hMADS adipocyte differentiation. LXRα, COUP-TF1, and the transmembrane protein TMEM135 were studied in primary cultures of differentiating bone marrow stromal cells from healthy donors and were found to be transcriptionally activated in the corresponding lineages.

Conclusion

Our results reveal gene repression as a predominant early mechanism before final cell commitment. We were moreover able to identify 65 genes as candidates for genes controlling the adipocyte/osteoblast balance and to further evaluate four of these. Additional studies will explore the precise role of these candidate genes in regulating the adipogenesis/osteoblastogenesis switch.