Proteomic profiling of bone marrow mesenchymal stem cells upon transforming growth factor beta1 stimulation

Cancer-derived lysophosphatidic acid stimulates differentiation of human mesenchymal stem cells to myofibroblast-like cells

Lysophosphatidic acid (LPA) is enriched in ascites of ovarian cancer patients and is involved in growth and invasion of ovarian cancer cells. Accumulating evidence suggests cancer-associated myofibroblasts play a pivotal role in tumorigenesis through secreting stromal cell-derived factor-1 (SDF-1). In the present study, we demonstrate that LPA induces expression of alpha-smooth muscle actin (alpha-SMA), a marker for myofibroblasts, in human adipose tissue-derived mesenchymal stem cells (hADSCs). The LPA-induced expression of alpha-SMA was completely abrogated by pretreatment of the cells with Ki16425, an antagonist of LPA receptors, or by silencing LPA(1) or LPA(2) isoform expression with small interference RNA (siRNA). LPA elicited phosphorylation of Smad2/3, and siRNA-mediated depletion of endogenous Smad2/3 or adenoviral expression of Smad7, an inhibitory Smad, abrogated the LPA induced expression of alpha-SMA and phosphorylation of Smad2/3. LPA-induced secretion of transforming growth factor (TGF)-beta1 in hADSCs, and pretreatment of the cells with SB431542, a TGF-beta type I receptor kinase inhibitor, or anti-TGF-beta1 neutralizing antibody inhibited the LPA-induced expression of alpha-SMA and phosphorylation of Smad2. Furthermore, ascites from ovarian cancer patients or conditioned medium from ovarian cancer cells induced expression of alpha-SMA and phosphorylation of Smad2, and pretreatment of the cells with Ki16425 or SB431542 abrogated the expression of alpha-SMA and phosphorylation of Smad2. In addition, LPA increased the expression of SDF-1 in hADSCs, and pretreatment of the cells with Ki16425 or SB431562 attenuated the LPA-stimulated expression of SDF-1. These results suggest that cancer-derived LPA stimulates differentiation of hADSCs to myofibroblast-like cells and increases SDF-1 expression through activating autocrine TGF-beta1-Smad signaling pathway.

Proteome of mesenchymal stem cells

Proteomics has evolved, in recent years, into effective tools for basic and applied stem cell research, and has been extensively used to facilitate the identification of changes in signal transduction components, especially with regard to plasticity, proliferation, and differentiation. Several recent reports have also employed proteomic strategies to characterize human mesenchymal stem cells (hMSC) and their differentiated derivatives. Although these approaches have yielded valuable data, the results highlight the fact that only the limited numbers of proteins are characterized at the protein level in these cells, thus necessitating expandable MSC proteome dataset. This review presents, for the first time, an expandable list of MSC proteins, which will function as a starting point for the generation of a comprehensive reference map of their proteome. Also, the better way to bridge current gap between genomics and proteomics study such as integrated proteomic and transcriptomic analyses is discussed.

Chemical and physical regulation of stem cells and progenitor cells: potential for cardiovascular tissue engineering

The field of cardiovascular tissue engineering has experienced tremendous advances in the past several decades, but the clinical reality of engineered heart tissue and vascular conduits remains immature. Stem cells and progenitor cells are promising cell sources for engineering functional cardiovascular tissues. To realize the therapeutic potential of stem cells and progenitor cells, we need to understand how microenvironmental cues modulate and guide stem cell differentiation and organization. This review describes the current understanding of the chemical and physical regulation of embryonic and adult stem cells for potential applications in cardiovascular repair, focusing on cardiac therapies after myocardial infarction and the engineering of vascular conduits.

Human fibroblast and human bone marrow cell response to lithographically nanopatterned adhesive domains on protein rejecting substrates

The separate influence of topographical and chemical cues on cell attachment and spreading are well documented; however, that of duel-cue substrates is less so. In this study graft copolymers that sterically stabilize biological surfaces were employed alongside nanotopographical features fabricated by colloidal lithography. This resulted in the production of a range of substrates whereby the effect of chemistry and or topography on both on human fibroblast and bone marrow cell adhesion and spreading could be observed. The current studies indicate an enhancement of cell response as a consequence of modifications in material topography, whereas the current selected chemical cues inhibited cell function. Critically, in combination, topography modulated the effects of chemical environment.

A proteomic approach to studying the differentiation of neural stem cells

The mechanisms that regulate the maintenance of stem cell self-renewal versus differentiation are complex and remain mostly unknown. Understanding neurogenesis and neural cell differentiation presents a unique challenge for the treatment of nervous system disorders. To gain more insight into molecular mechanisms of the differentiation of neural cells, we combined the advantage of porcine fetal neural stem cells (NSCs) in vitro differentiation model and proteomic analysis. Using 2-DE followed by MS, we profiled constituent proteins of NSCs and their differentiated progenies at first and then indicated protein species that were significantly up- or down-regulated during the differentiation. The largest identified group of constituent proteins was related to RNA and protein metabolism and processing, including chaperones, and the second largest consisted of proteins involved in cell organization (cytoskeleton and annexins). Differentiation of neural cells was found to be accompanied by changes in the expression of proteins involved in DNA and RNA binding, mRNA processing and transport, stress responses, iron storage, and redox regulation. Additional immunoblot analysis verified the induction of alpha-B crystallin and heterogeneous nuclear ribonucleoproteins (hnRNPs) A1 and A2/B1. Furthermore, immunocytochemistry demonstrated specific localization of alpha-B crystallin in the cytoplasm or nucleus of glial cells and confirmed cellular expression patterns of hnRNPs A1 and A2/B1. These findings represent a significant step towards understanding neural cell differentiation and identification of the regulatory proteins associated with this process.

Injured microenvironment directly guides the differentiation of engrafted Flk-1(+) mesenchymal stem cell in lung

OBJECTIVE

Time window is a key factor in the treatment of lung injury by mesenchymal stem cells (MSC) transplantation. This study was aimed to analyze the engraftment and differentiation behavior of MSC transplanted at different time points after lung irradiation, and the possible mechanisms were discussed.

MATERIALS AND METHODS

The thorax of C57BL/6 mice was exposed to 1400 cGy, then Flk-1(+)MSCs from enhanced green fluorescent protein C57BL/6 mice were systemically injected into C57BL/6 mice at 4 hours, 60 days, and 120 days post thoracic exposure, respectively. The engraftment and differentiation of Flk-1(+)MSC transplanted at different time points were evaluated. Lung tissue was collected and analyzed for fibrosis. Expression of transforming growth factor (TGF)-beta1 in the lung was qualified by semi-quantitative real-time reverse transcription polymerase chain reaction. In vitro, Flk-1(+)MSCs were cultured in epithelium induction media, together with damaged primary lung cells, supernatants of radiation-injured lung cells, or TGF-beta1 to find the possible factors that might effect Flk-1(+)MSC differentiation.

RESULTS

Cells injected immediately after injury were shown to differentiate into functional lung cells, such as epithelial and endothelial cells. Cells injected 2 months later were mostly located in the interstitial area and appeared as myofibrocyte. The in vivo lung microenvironments at different time points after injury were different from each other, especially TGF-beta1 expression. We demonstrated that cytokines secreted by irradiated lung cells could inhibit differentiation of Flk-1(+)MSCs into epithelial cells in vitro.

CONCLUSIONS

Flk-1(+)MSCs injected into the lung immediately after irradiation could differentiate into functional lung cells, while those injected at later stage after irradiation would be involved in fibrosis development. Thus our in vivo and in vitro studies demonstrated that differentiation of Flk-1(+)MSCs is controlled by the microenvironment.

Antithrombogenic property of bone marrow mesenchymal stem cells in nanofibrous vascular grafts

Nanostructured biomaterials have tremendous potential for tissue engineering. However, the performance and integration of the nanomaterials in vivo are not well understood. A challenge in vascular tissue engineering is to develop optimal scaffolds and establish expandable cell sources for the construction of tissue-engineered vascular grafts that are nonthrombogenic and have long-term patency. Here, we used tissue-engineered vascular grafts as a model to demonstrate the potential of combining nanofibrous scaffolds and bone marrow mesenchymal stem cells (MSCs) for vascular tissue engineering. Biodegradable nanofibrous scaffolds with aligned nanofibers were used to mimic native collagen fibrils to guide cell organization in vascular grafts. The results from artery bypass experiments showed that nanofibrous scaffolds allowed efficient infiltration of vascular cells and matrix remodeling. Acellular grafts (without MSCs) resulted in significant intimal thickening, whereas cellular grafts (with MSCs) had excellent long-term patency and exhibited well organized layers of endothelial cells (ECs) and smooth muscle cells (SMCs), as in native arteries. Short-term experiments showed that nanofibrous scaffolds alone induced platelet adhesion and thrombus formation, which was suppressed by MSC seeding. In addition, MSCs, as ECs, resisted platelet adhesion in vitro, which depended on cell-surface heparan sulfate proteoglycans. These data, together with the observation on the short-term engraftment of MSCs, suggest that the long-term patency of cellular grafts may be attributed to the antithrombogenic property of MSCs. These results demonstrate several favorable characteristics of nanofibrous scaffolds, the excellent patency of small-diameter nanofibrous vascular grafts, and the unique antithrombogenic property of MSCs.

Effects of uniaxial cyclic strain on adipose-derived stem cell morphology, proliferation, and differentiation

Cells and tissues in vivo are subjected to various forms of mechanical forces that are essential to their normal development and functions. The arterial blood vessel wall is continuously exposed to mechanical stresses such as pressure, strain, and shear due to the pulsatile nature of blood flow. Vascular smooth muscle cells (SMCs) populate the media of blood vessels and play important roles in the control of vasoactivity and the remodeling of the vessel wall. It is well documented that the phenotype and functions of vascular SMCs are not only regulated by chemical factors such as transforming growth factor-beta(1) (TGF-beta(1)), but also by mechanical factors such as uniaxial strain. The purpose of our study was to explore the effects of TGF-beta(1) alone or in combination with uniaxial cyclic strain on adipose-derived stem cell (ASC) morphology, proliferation, and differentiation. Low passage ASCs were stimulated with 10% strain at 1 Hz for 7 days, with or without TGF-beta(1). Cyclic strain inhibited proliferation, and caused alignment of the cells and of the F-actin cytoskeleton perpendicular to the direction of strain. Strain alone resulted in a decrease in the expression of early SMC markers alpha-SMA and h (1)-calponin. While the response of SMCs and other progenitor cells such as bone marrow stromal cells to mechanical forces has been extensively studied, the roles of these forces on ASCs remain unexplored. This work advances our understanding of the mechanical regulation of ASCs.

Adipose-derived stem cells for regenerative medicine

The emerging field of regenerative medicine will require a reliable source of stem cells in addition to biomaterial scaffolds and cytokine growth factors. Adipose tissue represents an abundant and accessible source of adult stem cells with the ability to differentiate along multiple lineage pathways. The isolation, characterization, and preclinical and clinical application of adipose-derived stem cells (ASCs) are reviewed in this article.

FGF-2 suppresses cellular senescence of human mesenchymal stem cells by down-regulation of TGF-beta2

Human mesenchymal stem cells (hMSCs) are able to both self-replicate and differentiate into a variety of cell types. Fibroblast growth factor-2 (FGF-2) stimulates the growth of hMSCs in vitro, but its mechanisms have not been clarified yet. In this study, we investigated whether cellular senescence was involved in the stimulation of hMSCs growth by FGF-2 and the expression levels of transforming growth factor-beta1 and -beta2 (TGF-betas). Because hMSCs were induced cellular senescence due to long-term culture, FGF-2 decreased the percentage of senescent cells and suppressed G1 cell growth arrest through the suppression of p21(Cip1), p53, and p16(INK4a) mRNA expression levels. Furthermore, the levels of TGF-betas mRNA expression in hMSCs were increased by long-term culture, but FGF-2 suppressed the increase of TGF-beta2 mRNA expression due to long-term culture. These results suggest that FGF-2 suppresses the hMSCs cellular senescence dependent on the length of culture through down-regulation of TGF-beta2 expression.

A proteomic analysis of adult rat bone reveals the presence of cartilage/chondrocyte markers

The non-mineral component of bone matrix consists of 90% collagenous, 10% non-collagenous proteins. These proteins regulate mineralization, growth, cell signaling and differentiation, and provide bone with its tensile strength. Expression of bone matrix proteins have historically been studied individually or in small numbers owing to limitations in analytical technologies. Current mass-spectrometric and separations technologies allow a global view of protein expression patterns in complex samples. To our knowledge, no proteome profile of bone matrix has yet been reported. Therefore, we have used mass spectrometry as a tool to generate a profile of proteins present in the extracellular matrix of adult rat bone. Overall, 108 and 25 proteins were identified with high confidence in the metaphysis and diaphysis, respectively, using a bottom up proteomic technique. Twenty-one of these proteins were present in both the metaphysis and diaphysis including the bone specific proteins, osteocalcin, type I collagen, osteopontin, osteoregulin, and bone sialoprotein. Interestingly, type II collagen, a protein thought to be exclusively expressed in cartilage, was identified in both the metaphysis and diaphysis. This observation was validated by Western blot. Additionally, the presence of aggrecan, another protein expressed in cartilage was identified in the bone matrix extracts by Western blot. The proteome profile generated using this technology represents an initial survey of the acid soluble proteins of bone matrix which provides a reference for the analysis of deviations from the normal composition due to perturbations or disease states.

Concise review: trends in stem cell proteomics

Gene expression analyses of stem cells (SCs) will help to uncover or further define signaling pathways and molecular mechanisms involved in the maintenance of self-renewal, pluripotency, and/or multipotency. In recent years, proteomic approaches have produced a wealth of data identifying proteins and mechanisms involved in SC proliferation and differentiation. Although many proteomics techniques have been developed and improved in peptide and protein separation, as well as mass spectrometry, several important issues, including sample heterogeneity, post-translational modifications, protein-protein interaction, and high-throughput quantification of hydrophobic and low-abundance proteins, still remain to be addressed and require further technical optimization. This review summarizes the methodologies used and the information gathered with proteome analyses of SCs, and it discusses biological and technical challenges for proteomic study of SCs. Disclosure of potential conflicts of interest is found at the end of this article.

Isolation of a mesenchymal cell population from murine dermis that contains progenitors of multiple cell lineages

The skin contains two known subpopulations of stem cells/epidermal progenitors: a basal keratinocyte population found in the interfollicular epithelium and cells residing in the bulge region of the hair follicle. The major role of the interfollicular basal keratinocyte population may be epidermal renewal, whereas the bulge population may only be activated and recruited to form a cutaneous epithelium in case of trauma. Using 3-dimensional cultures of murine skin under stress conditions in which only reserve epithelial cells would be expected to survive and expand, we demonstrate that a mesenchymal population resident in neonatal murine dermis has the unique potential to develop an epidermis in vitro. In monolayer culture, this dermal subpopulation has long-term survival capabilities in restricted serum and an inducible capacity to evolve into multiple cell lineages, both epithelial and mesenchymal, depending on culture conditions. When grafted subcutaneously, this dermal subpopulation gave rise to fusiform structures, reminiscent of disorganized muscle, that stained positive for smooth muscle actin and desmin; on typical epidermal grafts, abundant melanocytes appeared throughout the dermis that were not associated with hair follicles. The multipotential cells can be repeatedly isolated from neonatal murine dermis by a sequence of differential centrifugation and selective culture conditions. These results suggest that progenitors capable of epidermal differentiation exist in the mesenchymal compartment of an abundant tissue source and may have a function in mesenchymal-epithelial transition upon insult. Moreover, these cells could be available in sufficient quantities for lineage determination or tissue engineering applications.

Proteomics of TGF-beta signaling and its impact on breast cancer

The complexity of mechanisms leading to the appearance and progression of cancer is a challenge being addressed by large-scale studies, such as proteomics. Simultaneous monitoring of thousands of proteins uncovers novel signaling mechanisms, thus revising our knowledge of tumorigenesis. Transforming growth factor (TGF)-beta is a secreted polypeptide that is known to inhibit tumor growth at the early stages of cancer, but promote metastasis at the later stages. Proteomics-based studies have significantly widened our knowledge of TGF-beta-dependent regulation of cell proliferation, apoptosis, DNA damage repair and transcription. This leads to better understanding of the TGF-beta role in human breast tumorigenesis, and opens the way for the development of novel anticancer treatments and drugs, with some of the drugs already entering clinics. This review discusses recent advances in proteomics studies of TGF-beta signaling and its contribution to the understanding and treatment of breast cancer.

Laminin-5 activates extracellular matrix production and osteogenic gene focusing in human mesenchymal stem cells

We recently reported that laminin-5, expressed by human mesenchymal stem cells (hMSC), stimulates osteogenic gene expression in these cells in the absence of any other osteogenic stimulus. Here we employ two-dimensional liquid chromatography and tandem mass spectrometry, along with the Database for Annotation, Visualization and Integrated Discovery (DAVID), to obtain a more comprehensive profile of the protein (and hence gene) expression changes occurring during laminin-5-induced osteogenesis of hMSC. Specifically, we compare the protein expression profiles of undifferentiated hMSC, hMSC cultured on laminin-5 (Ln-5 hMSC), and fully differentiated human osteoblasts (hOST) with profiles from hMSC treated with well-established osteogenic stimuli (collagen I, vitronectin, or dexamethazone). We find a marked reduction in the number of proteins (e.g., those involved with calcium signaling and cellular metabolism) expressed in Ln-5 hMSC compared to hMSC, consistent with our previous finding that hOST express far fewer proteins than do their hMSC progenitors, a pattern we call "osteogenic gene focusing." This focused set, which resembles an intermediate stage between hMSC and mature hOST, mirrors the expression profiles of hMSC exposed to established osteogenic stimuli and includes osteogenic extracellular matrix proteins (collagen, vitronectin) and their integrin receptors, calcium signaling proteins, and enzymes involved in lipid metabolism. These results provide direct evidence that laminin-5 alone stimulates global changes in gene/protein expression in hMSC that lead to commitment of these cells to the osteogenic phenotype, and that this commitment correlates with extracellular matrix production.

Proteomic profiling of rat bone marrow mesenchymal stem cells induced by 5-azacytidine

Mesenchymal stem cells (MSCs) can differentiate into different types of cells and thus have tremendous potential for cell therapy and tissue engineering. 5-Azacytidine (5-aza), a DNA demethylation reagent, has been reported to induce MSCs to differentiate into cardiomyocytes in vitro. To determine a global effect of 5-aza on MSCs, we investigated the protein expressions of rat MSCs with two-dimensional gel electrophoresis (2-DE). We have generated a proteome reference map of rat MSCs, and have successfully identified 34 proteins with MALDI-TOF-MS analysis. Nine proteins showed distinct regulation in MSCs after 5-aza treatment. The proteins regulated by 5-aza included cytoskeletal proteins, cadmium-binding proteins, and metabolic proteins, etc. These proteins have been reported to be involved in cell proliferation and differentiation through different signaling pathways, and the molecular mechanism of MSCs differentiation is discussed at the proteome level.

The interaction of human bone marrow cells with nanotopographical features in three dimensional constructs

Until now, nanotopography has been considered in 2D construct designs. This has been due to fabrication limitations with traditional lithographic processes relying on the ability to focus radiation that will expose a radiation sensitive resist (e.g. photolithography and electron beam lithography). More recently, alternative methods that offer rapid and cheap nanofabrication have been developed; such methods include polymer demixing and colloidal lithography. Polymer demixing in 2D has relied on spin casting of polymer blends-such as polystyrene and polybromostyrene in a solvent such as toluene. As the solvent evaporates, the polymers phase separate and form nanoislands. In this study, the polymer blend solution has been blown through fine tubes and allowed to demix, thus providing 3D constructs for cell biology. The ability to fabricate in tubes may be useful in many applications, for example stents, conduits, and bone repair (when considering structures such as Haversian tubes and Volkmann's canals). As proof of concept, human osteoprogenitor cells have been used to test the cell response to the nanopatterned tubes. The results show that nanofeatures of size X, diameter Y, and spacing Z decrease cell spreading, reduce cytoskeletal organization, and increase endocytotic activity within the cells.

Synergistic effects of retinoic acid and tamoxifen on human breast cancer cells: Proteomic characterization

The anti-estrogen tamoxifen and vitamin A-related compound, all-trans retinoic acid (RA), in combination act synergistically to inhibit the growth of MCF-7 human breast cancer cells. In the present study, we applied two-dimensional gel electrophoresis based proteomic approach to globally analyze this synergistic effect of RA and tamoxifen. Proteomic study revealed that multiple clusters of proteins were involved in RA and tamoxifen-induced apoptosis in MCF-7 breast cancer cells, including post-transcriptional and splicing factors, proteins related to cellular proliferation or differentiation, and proteins related to energy production and internal degradation systems. The negative growth factor-transforming growth factor beta (TGFbeta) was secreted by RA and/or tamoxifen treatment and was studies as a potential mediator of the synergistic effects of RA and tamoxifen in apoptosis. By comparing protein alterations in treatments of RA and tamoxifen alone or in combination to those of TGFbeta treatment, or co-treatment with TGFbeta inhibitor SB 431542, proteomic results showed that a number of proteins were involved in TGFbeta signaling pathway. These results provide valuable insights into the mechanisms of RA and tamoxifen-induced TGFbeta signaling pathway in breast cancer cells.

Mechanism of depolymerization and severing of actin filaments and its significance in cytoskeletal dynamics

The actin cytoskeleton is one of the major structural components of the cell. It often undergoes rapid reorganization and plays crucial roles in a number of dynamic cellular processes, including cell migration, cytokinesis, membrane trafficking, and morphogenesis. Actin monomers are polymerized into filaments under physiological conditions, but spontaneous depolymerization is too slow to maintain the fast actin filament dynamics observed in vivo. Gelsolin, actin-depolymerizing factor (ADF)/cofilin, and several other actin-severing/depolymerizing proteins can enhance disassembly of actin filaments and promote reorganization of the actin cytoskeleton. This review presents advances as well as a historical overview of studies on the biochemical activities and cellular functions of actin-severing/depolymerizing proteins.

Regulation of alpha-smooth muscle actin protein expression in adipose-derived stem cells

The objective of this work was to study the response of adipose-derived stem cells (ASCs) to exogenous biochemical stimulation, and the potential of ASCs to differentiate toward the smooth muscle cell (SMC) lineage. Immunofluorescence staining and Western blot analysis detected protein expression of the early SMC marker alpha-smooth muscle actin (alpha-SMA) in both control and experiment groups. Expression of alpha-SMA in ASCs significantly increased when treated with transforming growth factor-beta1, while alpha-SMA expression only slightly increased in the presence of retinoic acid (RA), beta-mercaptoethanol and ascorbic acid. Treatment with platelet-derived growth factor-BB, RA and dibutyryl-cyclic adenosine monophosphate decreased the expression of alpha-SMA significantly. While beta-mercaptoethanol and ascorbic acid, as well as RA have resulted in increased alpha-SMA expression in marrow-derived mesenchymal stem cells and other progenitor cells, our results demonstrate that these treatments do not significantly increase alpha-SMA expression, indicating that the differentiation potential of ASCs and mesenchymal stem cells may be fundamentally different.

Sphingosylphosphorylcholine induces differentiation of human mesenchymal stem cells into smooth-muscle-like cells through a TGF-beta-dependent mechanism

Mesenchymal stem cells (MSCs) can differentiate into diverse cell types including adipogenic, osteogenic, chondrogenic and myogenic lineages. In the present study, we demonstrated for the first time that sphingosylphosphorylcholine (SPC) induces differentiation of human adipose-tissue-derived mesenchymal stem cells (hATSCs) to smooth-muscle-like cell types. SPC increased the expression levels of several smooth-muscle-specific genes, such as those for alpha-smooth-muscle actin (alpha-SMA), h1-calponin and SM22alpha, as effectively as transforming growth factor beta (TGF-beta1) and TGF-beta3. SPC elicited delayed phosphorylation of Smad2 after 24 hours exposure, in contrast to rapid phosphorylation of Smad2 induced by TGF-beta treatment for 10 minutes. Pretreatment of the cells with pertussis toxin or U0126, an MEK inhibitor, markedly attenuated the SPC-induced expression of beta-SMA and delayed phosphorylation of Smad2, suggesting that the Gi/o-ERK pathway is involved in the increased expression of alpha-SMA through induction of delayed Smad2 activation. In addition, SPC increased secretion of TGF-beta1 through an ERK-dependent pathway, and the SPC-induced expression of alpha-SMA and delayed phosphorylation of Smad2 were blocked by SB-431542, a TGF-beta type I receptor kinase inhibitor, or anti-TGF-beta1 neutralizing antibody. Silencing of Smad2 expression with small interfering RNA (siRNA) abrogated the SPC-induced expression of alpha-SMA. These results suggest that SPC-stimulated secretion of TGF-beta1 plays a crucial role in SPC-induced smooth muscle cell (SMC) differentiation through a Smad2-dependent pathway. Both SPC and TGF-beta increased the expression levels of serum-response factor (SRF) and myocardin, transcription factors involved in smooth muscle differentiation. siRNA-mediated depletion of SRF or myocardin abolished the alpha-SMA expression induced by SPC or TGF-beta. These results suggest that SPC induces differentiation of hATSCs to smooth-muscle-like cell types through G(i/o)-ERK-dependent autocrine secretion of TGF-beta, which activates a Smad2-SRF/myocardin-dependent pathway.

Analysis of neuron-like differentiation of human bone marrow mesenchymal stem cells

The objective of the study was to evaluate differentiation of human bone marrow mesenchymal stem cells into true or pseudo neurons after treating with chemical induction medium in vitro. The morphological changes were assessed using interference contrast microscopy. Immunocytochemistry and Western blotting were performed using neuronal markers. Further evaluation was conducted with proteomic profiling, DNA microarray analysis and the whole-cell patch clamp test. After three hours of treatment with chemical induction medium, nearly three-fourths of the hMSCs changed to cells with a neuronal phenotype. The results of immunocytochemistry and Western blotting showed a high expression of neuronal markers in these cells at 3 h which decreased at 24 h. The proteomics analysis showed no change of proteins related to neuronal differentiation. DNA microarray showed downregulation of neuron related genes. The patch clamp test was unable to demonstrate any similarity to true neurons. Our findings suggest that neuron-like cells derived from chemical induction of hMSCs are not the genuine neurons as they resemble true neurons phenotypically but are different in genotypic and electrophysiological characteristics.

Anisotropic mechanosensing by mesenchymal stem cells

Mesenchymal stem cells (MSCs) are a potential source for the construction of tissue-engineered vascular grafts. However, how vascular mechanical forces regulate the genetic reprogramming in MSCs is not well understood. Mechanical strain in the vascular wall is anisotropic and mainly in the circumferential direction. We have shown that cyclic uniaxial strain on elastic substrates causes the cells to align perpendicularly to the strain axis, which is different from that in the vascular wall. To simulate the vascular cell alignment and investigate the anisotropic mechanical sensing by MSCs, we used soft lithography to create elastomeric membranes with parallel microgrooves. This topographic pattern kept MSCs aligned parallel to the strain axis, and the cells were subjected to 5% cyclic uniaxial strain (1 Hz) for 2-4 days. DNA microarray analysis revealed global gene expression changes, including an increase in the smooth muscle marker calponin 1, decreases in cartilage matrix markers, and alterations in cell signaling (e.g., down-regulation of the Jagged1 signaling pathway). In addition, uniaxial strain increased MSC proliferation. However, when micropatterning was used to align cells perpendicularly to the axis of mechanical strain, the changes of some genes were diminished, and MSC proliferation was not affected. This study suggests that mechanical strain plays an important role in MSC differentiation and proliferation, and that the effects of mechanotransduction depend on the orientation of cells with respect to the strain axis. The differential cellular responses to the anisotropic mechanical environment have important implications in cardiovascular development, tissue remodeling, and tissue engineering.

Proteomic analysis of cartilage- and bone-associated samples

The skeleton of the human body is built of cartilage and bone, which are tissues that contain extensive amounts of extracellular matrix (ECM). In bone, inorganic mineral hydroxyapatite forms 50-70% of the whole weight of the tissue. Although the organic matrix of bone consists of numerous proteins, 90% of it is composed of type I collagen. In cartilage, ECM forms a major fraction of the tissue, type II collagen and aggrecans being the most abundant macromolecules. It is obvious that the high content of ECM components causes analytical problems in the proteomic analysis of cartilage and bone, analogous to those in the analysis of low-abundance proteins present in serum. The massive contents of carbohydrates present in cartilage proteoglycans, and hydroxyapatite in bone, further complicate the situation. However, the development of proteomic tools makes them more and more tempting also for research of musculoskeletal tissues. Application of proteomic techniques to the research of chondrocytes, osteoblasts, osteocytes, and osteoclasts in cell cultures can immediately benefit from the present knowledge. Here we make an overview to previous proteomic research of cartilage- and bone-associated samples and evaluate the future prospects of applying proteomic techniques to investigate key events, such as cellular signal transduction, in cartilage- and bone-derived cells.

Proteomics of primary mesenchymal stem cells

Tissue and functional regeneration takes place in the body at various stages throughout life. However, bone, cartilage, tendons, blood vessels and cardiac muscle have a limited capacity for self repair and, after injury or disease, the regenerative ability of these adult tissues is often insufficient and leads to nonfunctional scar tissue. In this context, mesenchymal stem cells, which are adult multipotential progenitors of mesoderm cells (osteoblasts, chondrocytes, adipocytes and stroma cells), represent a major hope for tissue-engineered replacement and regenerative medicine. Furthermore, the autologous use of these cells prevents immunological responses against new tissues and the risks of disease transmission from donors, which are both common problems of organ transplantation. While the existence of mesenchymal stem cells is undisputed, many questions remain regarding their self-renewal and capacity to differentiate, their homogenous nature as a cell population throughout the body and their true potential in regenerative medicine. In this article, the proteomics studies carried out to characterize mesenchymal stem cells and to help understand their physiology are reviewed.

Effect of 5-azacytidine on the protein expression of porcine bone marrow mesenchymal stem cells in vitro

Bone marrow-derived mesenchymal stem cells (MSCs) are pluripotent stem cells that show a vital potential in the clinical application for cell transplantation. In the present paper, proteomic techniques were used to approach the protein profiles associated with porcine bone marrow MSCs and investigate the regulation of MSC proteins on the effect of 5-azacytidine (5-aza). Over 1,700 protein species were separated from MSCs according to gel analysis. Compared with the expression profiling of control MSCs, there were 11 protein spots up-regulated and 26 down-regulated in the protein pattern of 5-aza-treated cells. A total of 21 proteins were successfully identified by MALDI-TOF-MS analysis, among which some interesting proteins, such as alpha B-crystallin, annexin A2, and stathmin 1, had been reported to involve in cell proliferation and differentiation through different signaling pathways. Our data should be useful for the future study of MSC differentiation and apoptosis.

The heterogeneity of human mesenchymal stem cell preparations--evidence from simultaneous analysis of proteomes and transcriptomes

OBJECTIVE

Mesenchymal stem cells (MSC) raise high hopes in clinical applications. However, the lack of common standards and a precise definition of MSC preparations remains a major obstacle in research and application of MSC. Whereas surface antigen markers have failed to precisely define this population, a combination of proteomic data and microarray data provides a new dimension for the definition of MSC preparations.

METHODS

In our continuing effort to characterize MSC, we have analyzed the differential transcriptome and proteome expression profiles of MSC preparations isolated from human bone marrow under two different expansion media (BM-MSC-M1 and BM-MSC-M2).

RESULTS

In proteomics, 136 protein spots were unambiguously identified by MALDI-TOF-MS and corresponding cDNA spots were selected on our "Human Transcriptome cDNA Microarray." Combination of datasets revealed a correlation in differential gene expression and protein expression of BM-MSC-M1 vs BM-MSC-M2. Genes involved in metabolism were more highly expressed in BM-MSC-M1, whereas genes involved in development, morphogenesis, extracellular matrix, and differentiation were more highly expressed in BM-MSC-M2. Interchanging culture conditions for 8 days revealed that differential expression was retained in several genes whereas it was altered in others.

CONCLUSION

Our results have provided evidence that homogeneous BM-MSC preparations can reproducibly be isolated under standardized conditions, whereas culture conditions exert a prominent impact on transcriptome, proteome, and cellular organization of BM-MSC.

Proteomic analysis of neural differentiation of mouse embryonic stem cells

Mouse embryonic stem cells (mESCs) can differentiate into different types of cells, and serve as a good model system to study human embryonic stem cells (hESCs). We showed that mESCs differentiated into two types of neurons with different time courses. To determine the global protein expression changes after neural differentiation, we employed a proteomic strategy to analyze the differences between the proteomes of ES cells (E14) and neurons. Using 2-DE plus LC/MS/MS, we have generated proteome reference maps of E14 cells and derived dopaminergic neurons. Around 23 proteins with an increase or decrease in expression or phosphorylation after differentiation have been identified. We confirmed the downregulation of translationally controlled tumor protein (TCTP) and upregulation of alpha-tubulin by Western blotting. We also showed that TCTP was further downregulated in derived motor neurons than in dopaminergic neurons, and its expression level was independent of extracellular Ca(2+) concentration during neural differentiation. Potential roles of TCTP in modulating neural differentiation through binding to Ca(2+), tubulin and Na,K-ATPase, as well as the functional significance of regulation of other proteins such as actin-related protein 3 (Arp3) and Ran GTPase are discussed. This study demonstrates that proteomic tools are valuable in studying stem cell differentiation and elucidating the underlying molecular mechanisms.

The proteomic analysis of an adipocyte differentiated from human mesenchymal stem cells using two-dimensional gel electrophoresis

Adipose tissues play a crucial endocrine role in the control of whole body glucose homeostasis and insulin sensitivity. Considering the current substantial rise in obesity and obesity-related diseases, including diabetes, it is important to understand the molecular basis of adipocyte differentiation and its control. In this study, we have analyzed the protein expression inherent to adipogenic differentiation, by 2-DE, MALDI-TOF, and RT-PCR. This study focused on proteins that were differentially expressed by the differentiation of human mesenchymal stem cells (hMSCs) to adipocytes. We conducted 2-DE for each set of proteins in the cytosol of adipocytes that had differentiated from hMSC, in a pH range from 3-10. Thirty-two protein spots were shown to have different expression levels. Among these, eight up-regulated proteins were identified by MALDI-TOF/MS, as the following: syntaxin binding protein 3, OSBP-related protein 3, phosphodiesterase, glycophorin, immunoglobulin kappa chain variable region, peroxisome proliferative activated receptor gamma (PPAR-gamma), bA528A10.3.1 (novel protein similar to KIAA01616, isoform 1), and T cell receptor V-beta 4. Four proteins: syntaxin-3, OSBP-related protein 3, PPAR-gamma and glycophorin were associated with adipogenesis.

Stem cell proteomes: a profile of human mesenchymal stem cells derived from umbilical cord blood

Multipotent mesenchymal stem cells (MSCs) derived from human umbilical cord blood (UCB) represent promising candidates for the development of future strategies in cellular therapy. To create a comprehensive protein expression profile for UCB-MSCs, one UCB unit from a full-term delivery was isolated from the unborn placenta, transferred into culture, and their whole-cell protein fraction was subjected to two-dimensional electrophoresis (2-DE). Unambiguous protein identification was achieved with peptide mass fingerprinting matrix-assisted laser desorption/ionization - time of flight - mass spectrometry (MALDI-TOF-MS), peptide sequencing (MALDI LIFT-TOF/TOF MS), as well as gel-matching with previously identified databases. In overall five replicate 2-DE runs, a total of 2037 +/- 437 protein spots were detected of which 205 were identified representing 145 different proteins and 60 isoforms or post-translational modifications. The identified proteins could be grouped into several functional categories, such as metabolism, folding, cytoskeleton, transcription, signal transduction, protein degradation, detoxification, vesicle/protein transport, cell cycle regulation, apoptosis, and calcium homeostasis. The acquired proteome map of nondifferentiated UCB-MSCs is a useful inventory which facilitates the identification of the normal proteomic pattern as well as its changes due to activated or suppressed pathways of cytosolic signal transduction which occur during proliferation, differentiation, or other experimental conditions.

Focusing of Gene Expression as the Basis of Stem Cell Differentiation

In a prior report (Stem Cells Dev 14(4):354-366, 2005), we employed two-dimensional gel electrophoresis followed by advanced proteomics and the Database for Annotation, Visualization and Integrated Discovery (DAVID) to compare the protein expression profiles of mesenchymal stem cells to that of fully differentiated osteoblasts. These data were reported to advance technical approaches to define the basis of differentiation, but also led us to suggest that osteogenic differentiation of stem cells may result from the focusing of gene expression in functional clusters (e.g., calcium-regulated signaling proteins or adherence proteins) rather than simply from the induced expression of new genes, as many have assumed. Here, we have employed these analytical techniques to compare protein expression by mesenchymal stem cells directly with that of cells derived from them after induced osteogenic differentiation. Our results support the concept of gene focusing as the basis of differentiation. Specifically, induced differentiation results in a decrease in the number of mesenchymal cell markers and calcium-mediated signaling molecules expressed by their differentiated progeny. This effect was seen in parallel to increased expression of specific extracellular matrix (ECM) molecules and their receptors. These results strongly imply that changes in the ECM have a direct impact on stem cell differentiation, and that osteogenic differentiation of stem cells directed by matrix clues results from focusing of the expression of genes involved in Ca2+-dependent signaling pathways.

Nuclear actin-binding proteins as modulators of gene transcription

Dynamic transformations in the organization of the cellular microfilament system are the driving force behind fundamental biological processes such as cellular motility, cytokinesis, wound healing and secretion. Eukaryotic cells express a plethora of actin-binding proteins (ABPs) allowing cells to control the organization of the actin cytoskeleton in a flexible manner. These structural proteins were, not surprisingly, originally described as (major) constituents of the cytoplasm. However, in recent years, there has been a steady flow of reports detailing not only translocation of ABPs into and out of the nucleus but also describing their role in the nuclear compartment. This review focuses on recent developments pertaining to nucleocytoplasmic transport of ABPs, including their mode of translocation and nuclear function. In particular, evidence that structurally and functionally unrelated cytoplasmic ABPs regulate transcription activation by various nuclear (steroid hormone) receptors is steadily accruing. Furthermore, the recent finding that actin is a necessary component of the RNA polymerase II-containing preinitiation complex opens up new opportunities for nuclear ABPs in gene transcription regulation.

Transforming growth factor-beta2 enhances differentiation of cardiac myocytes from embryonic stem cells

Stem cell therapy holds great promise for the treatment of injured myocardium, but is challenged by a limited supply of appropriate cells. Three different isoforms of transforming growth factor-beta (TGF-beta) -beta1, -beta2, and -beta3 exhibit distinct regulatory effects on cell growth, differentiation, and migration during embryonic development. We compared the effects of these three different isoforms on cardiomyocyte differentiation from embryonic stem (ES) cells. In contrast to TGF-beta1, or -beta3, treatment of mouse ES cells with TGF-beta2 isoform significantly increased embryoid body (EB) proliferation as well as the extent of the EB outgrowth that beat rhythmically. At 17 days, 49% of the EBs treated with TGF-beta2 exhibited spontaneous beating compared with 15% in controls. Cardiac myocyte specific protein markers sarcomeric myosin and alpha-actin were demonstrated in beating EBs and cells isolated from EBs. In conclusion, TGF-beta2 but not TGF-beta1, or -beta3 promotes cardiac myocyte differentiation from ES cells.

Smad2 and Smad3 play different roles in rat hepatic stellate cell function and alpha-smooth muscle actin organization

Hepatic stellate cells (HSC) play a central role in the pathogenesis of liver fibrosis, transdifferentiating in chronic liver disease from "quiescent" HSC to fibrogenic myofibroblasts. Transforming growth factor-beta (TGF-beta), acting both directly and indirectly, is a critical mediator of this process. To characterize the function of the TGF-beta signaling intermediates Smad2 and Smad3 in HSC, we infected primary rat HSC in culture with adenoviruses expressing wild-type and dominant negative Smads 2 and 3. Smad3-overexpressing cells exhibited increased deposition of fibronectin and type 1 collagen, increased chemotaxis, and decreased proliferation compared with uninfected cells and those infected with Smad2 or either dominant negative, demonstrating different biological functions for the two Smads. Additionally, coinfection experiments suggested that Smad2 and Smad3 signal via independent pathways. Smad3-overexpressing cells as well as TGF-beta-treated cells demonstrated more focal adhesions and increased alpha-smooth muscle actin (alpha-SMA) organization in stress fibers, although all cells reached the same level of alpha-SMA expression, indicating that Smad3 also regulates cytoskeletal organization in HSC. We suggest that TGF-beta, signaling via Smad3, plays an important role in the morphological and functional maturation of hepatic myofibroblasts.