Mesenchymal stem cell migration is regulated by fibronectin through α5β1-integrin-mediated activation of PDGFR-β and potentiation of growth factor signals

TGF-β1 Pretreatment Improves the Function of Mesenchymal Stem Cells in the Wound Bed

The wound healing process initiates after injury to a tissue and involves a series of orchestrated events to minimize the invasion of foreign matters such as bacteria and efficiently regenerate the damaged tissue. A variety of cells must be recruited to the tissue during wound healing. However, this process is severely disrupted in patients suffering from chronic illness, including diabetes, leading to impaired healing or non-healing wounds. Current avenues of treatment include negative-pressure therapy, wound debridement, growth factor replacement, and cell-based therapies. Among these therapies, mesenchymal stem cells (MSCs) delivery to the wound holds a very high promise due to the innate abilities of MSCs that include immunogenicity, plasticity, and self-renewal. Bone marrow derived MSCs have been shown to promote more rapid wound healing by increased cytokine production in diabetic mice. However, the lack of understanding of the mechanical and chemical interaction of the transplanted MSCs with the factors present in the regenerative niches limits their efficacy in the wound bed. In this study, we sought to understand how the changes in MSC biochemical and biophysical properties can affect their function in vitro and in vivo. We demonstrate that pretreatment of MSCs with the mechano-stimulatory soluble factor transforming growth factor (TGF-β1), which is highly expressed in injury sites, improves wound closure in a syngeneic murine wound model. This improved wound closure correlated with increased invasion into the wound bed. In vitro studies demonstrated that TGF-β1 pretreatment expedited wound closure by increasing adhesion, traction force, and migration even after removal of the stimulus. Furthermore, this response was mediated by the cytoskeletal protein focal adhesion kinase. Taken together, this study suggests that defined chemical stimuli can benefit site specific adaptability of MSCs to improve their function and therapeutic usefulness.

Unique Regenerative Mechanism to Replace Bone Lost During Dietary Bone Depletion in Weanling Mice

The present study was undertaken to determine the mechanism whereby calcitropic hormones and mesenchymal stem cell progeny changes are involved in bone repletion, a regenerative bone process that restores the bone lost to calcium deficiency. To initiate depletion, weanling mice with a mixed C57BL/6 (75%) and CD1 (25%) genetic background were fed a calcium-deficient diet (0.01%) for 14 days. For repletion, the mice were fed a control diet containing 1.2% calcium for 14 days. Depletion decreased plasma calcium and increased plasma parathyroid hormone, 1,25(OH)2D (calcitriol), and C-terminal telopeptide of type I collagen. These plasma parameters quickly returned toward normal on repletion. The trabecular bone volume and connectivity decreased drastically during depletion but were completely restored by the end of repletion. This bone repletion process largely resulted from the development of new bone formation. When bromodeoxyuridine (BrdU) was administered in the middle of depletion for 3 days and examined by fluorescence-activated cell sorting at 7 days into repletion, substantial increases in BrdU incorporation were seen in several CD105 subsets of cells of osteoblastic lineage. When BrdU was administered on days 1 to 3 of repletion and examined 11 days later, no increases in BrdU were seen in these subsets. Additionally, osteocytes that stained positively for BrdU were increased during depletion. In conclusion, the results of the present study have established a unique regenerative mechanism to initiate bone repair during the bone insult. Calcium homeostatic mechanisms and the bone repletion mechanism are opposing functions but are simultaneously orchestrated such that both endpoints are optimized. These results have potential clinical relevance for disease entities such as type 2 osteoporosis.

Computational model of mesenchymal migration in 3D under chemotaxis

Cell chemotaxis is an important characteristic of cellular migration, which takes part in crucial aspects of life and development. In this work, we propose a novel in silico model of mesenchymal 3D migration with competing protrusions under a chemotactic gradient. Based on recent experimental observations, we identify three main stages that can regulate mesenchymal chemotaxis: chemosensing, dendritic protrusion dynamics and cell-matrix interactions. Therefore, each of these features is considered as a different module of the main regulatory computational algorithm. The numerical model was particularized for the case of fibroblast chemotaxis under a PDGF-bb gradient. Fibroblasts migration was simulated embedded in two different 3D matrices - collagen and fibrin - and under several PDGF-bb concentrations. Validation of the model results was provided through qualitative and quantitative comparison with in vitro studies. Our numerical predictions of cell trajectories and speeds were within the measured in vitro ranges in both collagen and fibrin matrices. Although in fibrin, the migration speed of fibroblasts is very low, because fibrin is a stiffer and more entangling matrix. Testing PDGF-bb concentrations, we noticed that an increment of this factor produces a speed increment. At 1 ng mL-1 a speed peak is reached after which the migration speed diminishes again. Moreover, we observed that fibrin exerts a dampening behavior on migration, significantly affecting the migration efficiency.

Acute Hypoxic Stress Affects Migration Machinery of Tissue O2-Adapted Adipose Stromal Cells

The ability of mesenchymal stromal (stem) cells (MSCs) to be mobilised from their local depot towards sites of injury and to participate in tissue repair makes these cells promising candidates for cell therapy. Physiological O₂ tension in an MSC niche in vivo is about 4-7%. However, most in vitro studies of MSC functional activity are performed at 20% O₂. Therefore, this study focused on the effects of short-term hypoxic stress (0.1% O₂, 24 h) on adipose tissue-derived MSC motility at tissue-related O₂ level. No significant changes in integrin expression were detected after short-term hypoxic stress. However, O₂ deprivation provoked vimentin disassembly and actin polymerisation and increased cell stiffness. In addition, hypoxic stress induced the downregulation of ACTR3, DSTN, MACF1, MID1, MYPT1, NCK1, ROCK1, TIAM1, and WASF1 expression, the products of which are known to be involved in leading edge formation and cell translocation. These changes were accompanied by the attenuation of targeted and nontargeted migration of MSCs after short-term hypoxic exposure, as demonstrated in scratch and transwell migration assays. These results indicate that acute hypoxic stress can modulate MSC function in their native milieu, preventing their mobilisation from sites of injury.

Integrin α7 is a functional cancer stem cell surface marker in oesophageal squamous cell carcinoma

Non-CG methylation has been associated with stemness regulation in embryonic stem cells. By comparing differentially expressed genes affected by non-CG methylation between tumour and corresponding non-tumour tissues in oesophageal squamous cell carcinoma (OSCC), we find that Integrin α7 (ITGA7) is characterized as a potential cancer stem cell (CSC) marker. Clinical data show that a high frequency of ITGA7⁺ cells in OSCC tissues is significantly associated with poor differentiation, lymph node metastasis and worse prognosis. Functional studies demonstrate that both sorted ITGA7⁺ cells and ITGA7 overexpressing cells display enhanced stemness features, including elevated expression of stemness-associated genes and epithelial–mesenchymal transition features, as well as increased abilities to self-renew, differentiate and resist chemotherapy. Mechanistic studies find that ITGA7 regulates CSC properties through the activation of the FAK-mediated signalling pathways. As knockdown of ITGA7 can effectively reduce the stemness of OSCC cells, ITGA7 could be a potential therapeutic target in OSCC treatment.

There is still no consensus on tumour type-specific cancer stem cell markers. Here, the authors demonstrate that ITGA7 is a potential functional marker of oesophageal cancer stem cells involved in the resistance to chemotherapy and metastasis through activation of FAK-mediated signalling.

External factors influencing mesenchymal stem cell fate in vitro

Mesenchymal stem cells (MSCs) have extensive potentials, which make them attractive candidates for the developmental biology, drug discovery and regenerative medicine. However, the use of MSCs is limited by their scarceness in tissues and in culture conditions. They also exhibit various degrees of potency which subsequently influencing their applications. Nowadays, questions remain about how self-renewal and differentiation of MSCs can be controlled in vitro and in vivo, how they will behave and migrate to the right place and how they modulate the immune system. Therefore, identification of factors and culture conditions to affect the fate and function of MSCs may be effective to enhance their applications in clinical situations. Studies have indicated that the fate of MSCs in culture is influenced by various external factors, including the specific cell source, donor age, plating density, passage number and plastic surface quality. Some other factors such as cell culture media and their supplementary factors, O₂ concentration, mechano-/electro-stimuli and three-dimensional scaffolds are also shown to be influential. This review addresses the current state of MSC research for describing and discussing the findings about external factors that influence the fate and function of MSCs. Additionally, the new discoveries and suggestions regarding their molecular mechanisms will be explained.

The effects of culture conditions on the functionality of efficiently obtained mesenchymal stromal cells from human cord blood

BACKGROUND AIMS

Cord blood (CB) is an attractive source of mesenchymal stromal cells (MSCs) because of its abundant availability and ease of collection. However, the success rate of generating CB-MSCs is low. In this study, our aim was to demonstrate the efficiency of our previously described method to obtain MSCs from CB and further characterize them and to study the effects of different culture conditions on MSCs.

METHODS

CB-MSC cultures were established in low oxygen (3%) conditions on fibronectin in 10% fetal bovine serum containing culture medium supplemented with combinations of growth factors. Cells were characterized for their adipogenic, osteogenic and chondrogenic differentiation capacity; phenotype; and HOX gene expression profile. The functionality of the cells cultured in different media was tested in vitro with angiogenesis and T-cell proliferation assays.

RESULTS

We demonstrate 87% efficacy in generating MSCs from CB. The established cells had typical MSC characteristics with reduced adipogenic differentiation potential and a unique HOX gene fingerprint. Growth factor-rich medium and a 3% oxygen condition enhanced cell proliferation; however, the growth factor-rich medium had a negative effect on the expression of CD90. Dexamethasone-containing medium improved the capacity of the cells to suppress T-cell proliferation, whereas the cells grown without dexamethasone were more able to support angiogenesis.

CONCLUSIONS

Our results demonstrate that the composition of expansion medium is critical for the functionality of MSCs and should always be appropriately defined for each purpose.

Constitutive Association of Tie1 and Tie2 with Endothelial Integrins is Functionally Modulated by Angiopoietin-1 and Fibronectin

Functional cross-talk between Tie2 and Integrin signaling pathways is essential to coordinate endothelial cell adhesion and migration in response to the extracellular matrix, yet the mechanisms behind this phenomenon are unclear. Here, we examine the possibility that receptor cross-talk is driven through uncharacterized Tie-integrin interactions on the endothelial surface. Using a live cell FRET-based proximity assay, we monitor Tie-integrin receptor recognition and demonstrate that both Tie1 and Tie2 readily associate with integrins α₅ß₁ and α_Vß₃ through their respective ectodomains. Although not required, Tie2-integrin association is significantly enhanced in the presence of the extracellular component and integrin ligand fibronectin. In vitro binding assays with purified components reveal that Tie-integrin recognition is direct, and further demonstrate that the receptor binding domain of the Tie2 ligand Ang-1, but not the receptor binding domain of Ang-2, can independently associate with α₅ß₁ or α_Vß₃. Finally, we reveal that cooperative Tie/integrin interactions selectively stimulate ERK/MAPK signaling in the presence of both Ang-1 and fibronectin, suggesting a molecular mechanism to sensitize Tie2 to extracellular matrix. We provide a mechanistic model highlighting the role of receptor localization and association in regulating distinct signaling cascades and in turn, the angiogenic switch.

Fibronectin induces macrophage migration through a SFK-FAK/CSF-1R pathway

Integrins, following binding to proteins of the extracellular matrix (ECM) including collagen, laminin and fibronectin (FN), are able to transduce molecular signals inside the cells and to regulate several biological functions such as migration, proliferation and differentiation. Besides activation of adaptor molecules and kinases, integrins transactivate Receptor Tyrosine Kinases (RTK). In particular, adhesion to the ECM may promote RTK activation in the absence of growth factors. The Colony-Stimulating Factor-1 Receptor (CSF-1R) is a RTK that supports the survival, proliferation, and motility of monocytes/macrophages, which are essential components of innate immunity and cancer development. Macrophage interaction with FN is recognized as an important aspect of host defense and wound repair. The aim of the present study was to investigate on a possible cross-talk between FN-elicited signals and CSF-1R in macrophages. FN induced migration in BAC1.2F5 and J774 murine macrophage cell lines and in human primary macrophages. Adhesion to FN determined phosphorylation of the Focal Adhesion Kinase (FAK) and Src Family Kinases (SFK) and activation of the SFK/FAK complex, as witnessed by paxillin phosphorylation. SFK activity was necessary for FAK activation and macrophage migration. Moreover, FN-induced migration was dependent on FAK in either murine macrophage cell lines or human primary macrophages. FN also induced FAK-dependent/ligand-independent CSF-1R phosphorylation, as well as the interaction between CSF-1R and β1. CSF-1R activity was necessary for FN-induced macrophage migration. Indeed, genetic or pharmacological inhibition of CSF-1R prevented FN-induced macrophage migration. Our results identified a new SFK-FAK/CSF-1R signaling pathway that mediates FN-induced migration of macrophages.

MenaINV mediates synergistic cross-talk between signaling pathways driving chemotaxis and haptotaxis

Directed cell migration, a key process in metastasis, arises from the combined influence of multiple processes, including chemotaxis-the directional movement of cells to soluble cues-and haptotaxis-the migration of cells on gradients of substrate-bound factors. However, it is unclear how chemotactic and haptotactic pathways integrate with each other to drive overall cell behavior. Mena^INV has been implicated in metastasis by driving chemotaxis via dysregulation of phosphatase PTP1B and more recently in haptotaxis via interaction with integrin α5β1. Here we find that Mena^INV-driven haptotaxis on fibronectin (FN) gradients requires intact signaling between α5β1 integrin and the epidermal growth factor receptor (EGFR), which is influenced by PTP1B. Furthermore, we show that Mena^INV-driven haptotaxis and ECM reorganization both require the Rab-coupling protein RCP, which mediates α5β1 and EGFR recycling. Finally, Mena^INV promotes synergistic migratory response to combined EGF and FN in vitro and in vivo, leading to hyperinvasive phenotypes. Together our data demonstrate that Mena^INV is a shared component of multiple prometastatic pathways that amplifies their combined effects, promoting synergistic cross-talk between RTKs and integrins.

Serum-free process development: improving the yield and consistency of human mesenchymal stromal cell production

BACKGROUND AIMS

The cost-effective production of human mesenchymal stromal cells (hMSCs) for off-the-shelf and patient specific therapies will require an increasing focus on improving product yield and driving manufacturing consistency.

METHODS

Bone marrow-derived hMSCs (BM-hMSCs) from two donors were expanded for 36 days in monolayer with medium supplemented with either fetal bovine serum (FBS) or PRIME-XV serum-free medium (SFM). Cells were assessed throughout culture for proliferation, mean cell diameter, colony-forming potential, osteogenic potential, gene expression and metabolites.

RESULTS

Expansion of BM-hMSCs in PRIME-XV SFM resulted in a significantly higher growth rate (P < 0.001) and increased consistency between donors compared with FBS-based culture. FBS-based culture showed an inter-batch production range of 0.9 and 5 days per dose compared with 0.5 and 0.6 days in SFM for each BM-hMSC donor line. The consistency between donors was also improved by the use of PRIME-XV SFM, with a production range of 0.9 days compared with 19.4 days in FBS-based culture. Mean cell diameter has also been demonstrated as a process metric for BM-hMSC growth rate and senescence through a correlation (R(2) = 0.8705) across all conditions. PRIME-XV SFM has also shown increased consistency in BM-hMSC characteristics such as per cell metabolite utilization, in vitro colony-forming potential and osteogenic potential despite the higher number of population doublings.

CONCLUSIONS

We have increased the yield and consistency of BM-hMSC expansion between donors, demonstrating a level of control over the product, which has the potential to increase the cost-effectiveness and reduce the risk in these manufacturing processes.

Chondrogenic cells respond to partial-thickness defects of articular cartilage in adult rats: an in vivo study

The purpose of this study was to establish a partial-thickness articular cartilage defects model in adult rats and explore the respond of chondrogenic cells to the cartilage injury. Forty-five adult Sprague-Dawley rats were divided into operated group, sham-operated group and control group. Partial-thickness cartilage defects were created on the weight-bearing region of femoral condyles by a converted ophthalmic knife. Rats were exposed to 5-bromo-2'-deoxyuridine (BrdU) for five consecutive days and were sacrificed 1, 2 and 4 weeks after surgery. Evaluations of macroscopic and histological changes were made. Chondrocyte apoptosis was evaluated by TUNEL assay. Immunofluorescence staining of CD105 and BrdU, double staining of CD105/integrin α5β1 and CD105-positive cells counting were performed for evaluations of cells around the defects. Cartilage softening and fibrillation with chondrocyte apoptosis were observed around the injury site after surgery. Results of histological scores indicated no significant difference between one time point and a successive time point for either group. CD105-positive cells and BrdU-label-retaining cells were observed around the linear injury. And cells counting showed the number of CD105-positive cells increased at later time points (P < 0.05). Immunofluorescence double staining demonstrated co-localization of CD105 and integrin α5β1 in activated cells around the defects. We establish a partial-thickness cartilage defects model in adult rats and demonstrate this injury may lead to activation of putative progenitor cells. In addition, the activated cells express integrin α5β1 specially, which may help in early discovery of osteoarthritis.

Phenotypic and Functional Characterization of Mesenchymal Stem/Multipotent Stromal Cells From Decidua Parietalis of Human Term Placenta

Mesenchymal stem/multipotent stromal cells (MSCs) from the human placenta show stem cell-like properties useful for regenerative medicine. Previously, we reported that MSCs isolated from the fetal part of human term placentae have characteristics, which make them a potential candidate for regenerative medicine. In this study, we characterized MSC isolated from the maternal part of human term placenta. The MSCs were isolated from the decidua parietalis (DPMSCs) of human placenta using a digestion method and characterized by colony-forming unit assay and the expression of MSC markers by flow cytometry technique. In addition, DPMSC differentiation into the 3 mesenchymal lineages was also performed. Moreover, the gene and protein expression profiles of DPMSCs were identified by real-time polymerase chain reaction and flow cytometry techniques, respectively. Furthermore, proteins secreted by DPMSCs were detected by sandwich enzyme-linked immunosorbent assays. Finally, the proliferation and migration potentials of DPMSCs were also determined. The DPMSCs were positive for MSC markers and negative for hematopoietic and endothelial markers, as well as costimulatory molecules and HLA-DR. Functionally, DPMSCs formed colonies and differentiated into chondrocytes, osteocytes, and adipocytes. In addition, they proliferated and migrated in response to different stimuli. Finally, they expressed and secreted many biological and immunological factors with multiple functions. Here, we carry out an extensive characterization of DPMSCs of human placenta. We report that these cells express and secrete a wide range of molecules with multiple functions, and therefore, we suggest that these cells could be an attractive candidate for cell-based therapy.

Bone marrow-derived mesenchymal stromal cells differ in their attachment to fibronectin-derived peptides from term placenta-derived mesenchymal stromal cells

INTRODUCTION

Human mesenchymal stromal cells (MSCs) can be isolated from different sources including bone marrow and term placenta. These two populations display distinct patterns of proliferation and differentiation in vitro. Since proliferation and differentiation of cells are modulated by cell-matrix interactions, we investigated the attachment of MSCs to a set of peptide-coated surfaces and explored their interactions with peptides in suspension.

METHODS

Human MSCs were isolated from bone marrow and term placenta and expanded. Binding of MSCs to peptides was investigated by a cell-attachment spot assay, by blocking experiments and flow cytometry. The integrin expression pattern was explored by a transcript array and corroborated by quantitative reverse transcription polymerase chain reaction and flow cytometry.

RESULTS

Expanded placenta-derived MSCs (pMSCs) attached well to surfaces coated with fibronectin-derived peptides P7, P15, and P17, whereas bone marrow-derived MSCs (bmMSCs) attached to P7, but barely to P15 and P17. The binding of bmMSCs and pMSCs to the peptides was mediated by β1 integrins. In suspension, expanded bmMSCs barely bind to P7, P13, P15, and less to P14 and P17. Ex vivo, bmMSCs failed to bind P7, but displayed a weak interaction with P13, P14, and P15. In suspension, expanded pMSCs displayed binding to many peptides, including P4, P7, P13, P14, P15, and P17. The differences observed in binding of bmMSCs and pMSCs to the peptides were associated with significant differences in expression of integrin α2-, α4-, and α6-chains.

CONCLUSIONS

Human bmMSCs and pMSCs show distinct patterns of attachment to defined peptides and maintain differences in expression of integrins in vitro. Interactions of ex vivo bmMSCs with a given peptide yield different staining patterns compared to expanded bmMSCs in suspension. Attachment of expanded MSCs to peptides on surfaces is different from interactions of expanded MSCs with peptides in suspension. Studies designed to investigate the interactions of human MSCs with peptide-augmented scaffolds or peptides in suspension must therefore regard these differences in cell-peptide interactions.

Phenotypic and Functional Characterization of Mesenchymal Stem/Multipotent Stromal Cells from Decidua Basalis of Human Term Placenta

Mesenchymal stem cell (MSC) therapies for the treatment of diseases associated with inflammation and oxidative stress employ primarily bone marrow MSCs (BMMSCs) and other MSC types such as MSC from the chorionic villi of human term placentae (pMSCs). These MSCs are not derived from microenvironments associated with inflammation and oxidative stress, unlike MSCs from the decidua basalis of the human term placenta (DBMSCs). DBMSCs were isolated and then extensively characterized. Differentiation of DBMSCs into three mesenchymal lineages (adipocytes, osteocytes, and chondrocytes) was performed. Real-time polymerase chain reaction (PCR) and flow cytometry techniques were also used to characterize the gene and protein expression profiles of DBMSCs, respectively. In addition, sandwich enzyme-linked immunosorbent assay (ELISA) was performed to detect proteins secreted by DBMSCs. Finally, the migration and proliferation abilities of DBMSCs were also determined. DBMSCs were positive for MSC markers and HLA-ABC. DBMSCs were negative for hematopoietic and endothelial markers, costimulatory molecules, and HLA-DR. Functionally, DBMSCs differentiated into three mesenchymal lineages, proliferated, and migrated in response to a number of stimuli. Most importantly, these cells express and secrete a distinct combination of cytokines, growth factors, and immune molecules that reflect their unique microenvironment. Therefore, DBMSCs could be attractive, alternative candidates for MSC-based therapies that treat diseases associated with inflammation and oxidative stress.

Extrinsic and Intrinsic Mechanisms by Which Mesenchymal Stem Cells Suppress the Immune System

Mesenchymal stem cells (MSCs) are a group of fibroblast-like multipotent mesenchymal stromal cells that have the ability to differentiate into osteoblasts, adipocytes, and chondrocytes. Recent studies have demonstrated that MSCs possess a unique ability to exert suppressive and regulatory effects on both adaptive and innate immunity in an autologous and allogeneic manner. A vital step in stem cell transplantation is overcoming the potential graft-versus-host disease, which is a limiting factor to transplantation success. Given that MSCs attain powerful differentiation capabilities and also present immunosuppressive properties, which enable them to survive host immune rejection, MSCs are of great interest. Due to their ability to differentiate into different cell types and to suppress and modulate the immune system, MSCs are being developed for treating a plethora of diseases, including immune disorders. Moreover, in recent years, MSCs have been genetically engineered to treat and sometimes even cure some diseases, and the use of MSCs for cell therapy presents new perspectives for overcoming tissue rejection. In this review, we discuss the potential extrinsic and intrinsic mechanisms that underlie MSCs' unique ability to modulate inflammation, and both innate and adaptive immunity.

Hypoxia Inducible Factor-1α Regulates the Migration of Bone Marrow Mesenchymal Stem Cells via Integrin α 4

Although hypoxic environments have been known to regulate the migratory ability of bone marrow-derived mesenchymal stem cells (BM-MSCs), which is a critical factor for maximizing the therapeutic effect, the underlying mechanisms remain unclear. Therefore, we aimed to confirm the effect of hypoxia-inducible factor-1α (HIF-1α) on the migration of BM-MSCs and to analyze the interaction between HIF-1α and integrin-mediated signals. Hypoxia-activated HIF-1α significantly increased BM-MSC migration. The expression of integrin α₄ was decreased in BM-MSCs by increased HIF-1α under hypoxia, whereas the expression of Rho-associated kinase 1 (ROCK1) and Rac1/2/3 was increased. After downregulation of HIF-1α by YC-1, which is an inhibitor of HIF-1α, BM-MSC migration was decreased via upregulation of integrin α₄ and downregulation of ROCK1 and Rac1/2/3. Knockdown of integrin α₄ by integrin α₄ siRNA (siITGA4) treatment increased BM-MSC migration by upregulation of ROCK1, Rac1/2/3, and matrix metalloproteinase-2 regardless of oxygen tension. Moreover, siITGA4 treatment increased HIF-1α expression and augmented the translocation of HIF-1α into the nucleus under hypoxia. Taken together, the alternative expression of HIF-1α induced by microenvironment factors, such as hypoxia and integrin α₄, may regulate the migration of BM-MSCs. These findings may provide insights to the underlying mechanisms of BM-MSC migration for successful stem cell-based therapy.

Synergistic growth factor microenvironments

This paper focuses on developments in materials to stimulate growth factors effects by engineering presentation in synergy with integrins.

β1 Integrins as Therapeutic Targets to Disrupt Hallmarks of Cancer

Integrins belong to a large family of αβ heterodimeric transmembrane proteins first recognized as adhesion molecules that bind to dedicated elements of the extracellular matrix and also to other surrounding cells. As important sensors of the cell microenvironment, they regulate numerous signaling pathways in response to structural variations of the extracellular matrix. Biochemical and biomechanical cues provided by this matrix and transmitted to cells via integrins are critically modified in tumoral settings. Integrins repertoire are subjected to expression level modifications, in tumor cells, and in surrounding cancer-associated cells, implicated in tumor initiation and progression as well. As critical players in numerous cancer hallmarks, defined by Hanahan and Weinberg (2011), integrins represent pertinent therapeutic targets. We will briefly summarize here our current knowledge about integrin implications in those different hallmarks focusing primarily on β1 integrins.

Bioinformatics Analysis of Proteome Changes in Calu-3 Cell Infected by Influenza A Virus (H5N1)

<b><i>Aim:</i></b> This paper aimed to identify the differentially expressed proteins (DEPs) in Calu-3 cells infected by influenza A virus (IAV) subtype H5N1. <b><i>Methods:</i></b> We downloaded proteome data (BTO: 0000762) from the Proteomics Identifications database and identified the DEPs in the IAV-infected Calu-3 cells. Then we constructed a protein-protein interaction network and a transcriptional regulatory network of the proteins. Finally, we performed gene ontology (GO) analysis to study the IAV infection at a functional level. <b><i>Results:</i></b> A total of 4 protein groups between the normal cells and the Calu-3 cells infected by IAV, severe acute respiratory syndrome or swine influenza were identified. In the networks, we found 5 significant proteins including FAN, CPSF2, AGO1, AGO2 and PAX5. In addition, we demonstrated those proteins were associated with GO terms such as phosphate metabolic process, calcium ion transport, cell division and regulation of cell motion. STAT1, NS2, CD5, NCKX6 and PDGFB were significant DEPs in these GO terms. <b><i>Conclusions:</i></b> By referring to the previous studies, we suggest that proteins including FAN, CPSF2, AGO1, AGO2, PAX5, STAT1 and PDGFB can be used as therapeutic targets of IAV infection.

Migrational changes of mesenchymal stem cells in response to cytokines, growth factors, hypoxia, and aging

Mesenchymal stem cells (MSCs) are non-immunogenic, multipotent cells with at least trilineage differentiation potential. They promote wound healing, improve regeneration of injured tissue, and mediate numerous other health effects. MSCs migrate to sites of injury and stimulate repair either through direct differentiation or indirectly through the stimulation of endogenous repair mechanisms. Using the in vitro scratch assay, we show that the inflammatory cytokines, chemokines, and growth factors TNF-α, SDF-1, PDGF, and bFGF enhance migration of rat MSCs under normoxic conditions, while TNF-α, IFN-γ, PDGF, and bFGF promote MSC migration under hypoxic conditions. This indicates that the oxygen concentration affects how MSCs will migrate in response to specific factors and, consistent with this, differential expression of cytokines was observed under hypoxic versus normoxic conditions. Using the transwell migration assay, we find that TNF-α, IFN-γ, bFGF, IGF-1, PDGF, and SDF-1 significantly increase transmigration of rat MSCs compared to unstimulated medium. MSCs derived from aged rats exhibited comparable migration to MSCs derived from young rats under hypoxic and normoxic conditions, even after application with specific factors. Similarly, migration in MSCs from aged, human donors did not statistically differ compared to migration in MSCs derived from human umbilical cord tissue or younger donors.

In Vivo Effects of Mesenchymal Stromal Cells in Two Patients With Severe Acute Respiratory Distress Syndrome

Mesenchymal stromal cells (MSCs) have been investigated as a treatment for various inflammatory diseases because of their immunomodulatory and reparative properties. However, many basic questions concerning their mechanisms of action after systemic infusion remain unanswered. We performed a detailed analysis of the immunomodulatory properties and proteomic profile of MSCs systemically administered to two patients with severe refractory acute respiratory distress syndrome (ARDS) on a compassionate use basis and attempted to correlate these with in vivo anti-inflammatory actions. Both patients received 2×10(6) cells per kilogram, and each subsequently improved with resolution of respiratory, hemodynamic, and multiorgan failure. In parallel, a decrease was seen in multiple pulmonary and systemic markers of inflammation, including epithelial apoptosis, alveolar-capillary fluid leakage, and proinflammatory cytokines, microRNAs, and chemokines. In vitro studies of the MSCs demonstrated a broad anti-inflammatory capacity, including suppression of T-cell responses and induction of regulatory phenotypes in T cells, monocytes, and neutrophils. Some of these in vitro potency assessments correlated with, and were relevant to, the observed in vivo actions. These experiences highlight both the mechanistic information that can be gained from clinical experience and the value of correlating in vitro potency assessments with clinical effects. The findings also suggest, but do not prove, a beneficial effect of lung protective strategies using adoptively transferred MSCs in ARDS. Appropriate randomized clinical trials are required to further assess any potential clinical efficacy and investigate the effects on in vivo inflammation.

SIGNIFICANCE

This article describes the cases of two patients with severe refractory adult respiratory syndrome (ARDS) who failed to improve after both standard life support measures, including mechanical ventilation, and additional measures, including extracorporeal ventilation (i.e., in a heart-lung machine). Unlike acute forms of ARDS (such in the current NIH-sponsored study of mesenchymal stromal cells in ARDS), recovery does not generally occur in such patients.

Periostin of human periodontal ligament fibroblasts promotes migration of human mesenchymal stem cell through the αvβ3 integrin/FAK/PI3K/Akt pathway

BACKGROUND AND OBJECTIVE

The periodontal ligament (PDL) is characterized by rapid turnover, high remodeling capacity and high inherent regenerative potential compared with other connective tissues. Periostin, which is highly expressed in the fibroblasts in the PDL, has been widely discussed in relation to collagen fibrillogenesis in the PDL. Recently, several reports have indicated periostin in cell migration. The aim of this study was to examine whether human PDL fibroblasts (hPDLFs) with high levels of periostin expression promote the migration of human bone marrow mesenchymal stem cells (hMSCs).

MATERIAL AND METHODS

The migration of hMSCs was examined by transwell chamber migration assay under different conditions: medium alone, hPDLFs, human dermal fibroblasts, recombinant periostin, integrin αvβ3 blocking antibody (anti-CD51/61 antibody) and inhibitors of FAK (PF431396) and PI3K (LY294002). Phosphorylation of FAK and Akt in hMSCs under stimulation of periostin was examined by western blotting.

RESULTS

The migration assay revealed that the number of migrated hMSCs by hPDLFs was significantly larger than those by dermal fibroblasts, periostin small interfering RNA hPDLFs and medium alone. Furthermore, recombinant periostin also strongly induced hMSC migration. The addition of anti-CD51/61 antibody, PF431396 and LY294002 caused a significant reduction in the number of migrated hMSCs respectively. The anti-CD51/61 antibody inhibited both FAK and Akt phosphorylations under periostin stimulation. PF431396 inhibited both FAK and Akt phosphorylations. LY294002 inhibited only Akt phosphorylation, and FAK phosphorylation was not influenced under periostin stimulation.

CONCLUSION

Periostin expression in hPDLFs promotes the migration of hMSCs through the αvβ3 integrin/FAK/PI3K/Akt pathway in vitro.

Inhibition of fibronectin deposition improves experimental liver fibrosis

BACKGROUND & AIMS

Common pathogenic steps in liver fibrosis are inflammation and accumulation of extracellular matrix proteins including collagen, which lead to disruption of tissue microarchitecture and liver dysfunction. Adequate fibronectin fibril formation is required for collagen matrix deposition in several cell types in vitro. We therefore hypothesized that preventing fibronectin fibril assembly will result in decreased collagen matrix accumulation, and hence diminish liver injury associated with fibrosis.

METHODS

In vitro studies on hepatic stellate cells and in vivo studies in mice were performed.

RESULTS

In vitro studies on hepatic stellate cells confirmed that a fibronectin assembly inhibitor, pUR4 diminishes the amount of both fibronectin and collagen, accumulating in the extracellular matrix, without affecting their production. Induction of fibrosis using CCl4 or DMN was therefore combined with pUR4-treatment. pUR4 normalized the amount of fibrotic tissue that accumulated with injury, and improved liver function. Specifically, pUR4-treatment decreased collagen accumulation, without changing its mRNA expression. Most interestingly, we did not detect any changes in Kupffer cell numbers (F4/80+) or α-smooth muscle actin expressing hepatic stellate cell numbers. Further, there was no impact on TGF-β or TNF-α. Thus, in line with the in vitro findings, decreased fibrosis is due to inhibition of matrix accumulation and not a direct effect on these cells.

CONCLUSIONS

In summary, a peptide that blocks fibronectin deposition results in decreased collagen accumulation and improved liver function during liver fibrogenesis. Thus, fibronectin matrix modulation offers a therapeutic benefit in preclinical models of liver fibrosis.

Pre-exposure of human adipose mesenchymal stem cells to soluble factors enhances their homing to brain cancer

Recent research advances have established mesenchymal stem cells (MSCs) as a promising vehicle for therapeutic delivery. Their intrinsic tropism for brain injury and brain tumors, their lack of immunogenicity, and their ability to breach the blood-brain barrier make these cells an attractive potential treatment of brain disorders, including brain cancer. Despite these advantages, the efficiency of MSC homing to the brain has been limited in commonly used protocols, hindering the feasibility of such therapies. In the present study, we report a reproducible, comprehensive, cell culture-based approach to enhance human adipose-derived MSC (hAMSC) engraftment to brain tumors. We used micro- and nanotechnological tools to systematically model several steps in the putative homing process. By pre-exposing hAMSCs to glioma-conditioned media and the extracellular matrix proteins fibronectin and laminin, we achieved significant enhancements of the individual homing steps in vitro. This homing was confirmed in an in vivo rodent model of brain cancer. This comprehensive, cell-conditioning approach provides a novel method to enhance stem cell homing to gliomas and, potentially, other neurological disorders.

Effects of fiber alignment on stem cells–fibrous scaffold interactions

Fiber alignment-induced enhancement of cell adhesion and scaffold remodelling, and alignment of secreted ECM in differentiation.

Fibronectin stimulates migration and proliferation, but not chondrogenic differentiation of human subchondral progenitor cells

Aims: To evaluate the impact of human plasma-derived fibronectin (FN) on human subchondral mesenchymal progenitor cells regarding cell migration, proliferation, and chondrogenic differentiation. Materials & methods: Human subchondral mesenchymal progenitor cells were analyzed for their migration capacity upon treatment with human plasma-derived FN. Proliferation activity was evaluated by DNA content. For chondrogenesis, cells were cultured in high-density pellet cultures in the presence of FN, TGFβ3, and a combination thereof. Results: Treatment of progenitors with FN significantly increased the number of migrating cells and elevated proliferative activity. Histological staining indicated formation of an extracellular matrix with type II collagen. Gene expression analysis gave no evidence for chondrogenic differentiation mediated by FN, but revealed a significant induction of type II collagen expression. Conclusion: FN has a potential to recruit human subchondral mesenchymal progenitor cells, possibly supporting proliferation and matrix assembly in cartilage repair procedures using bioactive implants after microfracture treatment.

Mesenchymal stromal cells: inhibiting PDGF receptors or depleting fibronectin induces mesodermal progenitors with endothelial potential

Realizing the full therapeutic potential of mesenchymal stromal/stem cells (MSCs) awaits improved understanding of mechanisms controlling their fate. Using MSCs cultured as spheroids to recapitulate a three-dimensional cellular environment, we show that perturbing the mesenchymal regulators, platelet-derived growth factor (PDGF) receptors or fibronectin, reverts MSCs toward mesodermal progenitors with endothelial potential that can potently induce neovascularization in vivo. MSCs within untreated spheroids retain their mesenchymal spindle shape with abundant smooth muscle α-actin filaments and fibronectin-rich matrix. Inhibiting PDGF receptors or depleting fibronectin induces rounding and depletes smooth muscle α-actin expression; these cells have characteristics of mesenchymoangioblasts, with enhanced expression of mesendoderm and endoderm transcription factors, prominent upregulation of E-cadherin, and Janus kinase signaling-dependent expression of Oct4A and Nanog. PDGF receptor-inhibited spheroids also upregulate endothelial markers platelet endothelial cell adhesion molecule 1 and vascular endothelial-cadherin and secrete many angiogenic factors, and in vivo they potently stimulate neovascularization, and their MSCs integrate within functional blood vessels that are perfused by the circulation. Thus, MSC potency and vascular induction are regulated by perturbing mesenchymal fate.

Directed migration of mesenchymal cells: where signaling and the cytoskeleton meet

Cell migration directed by spatial cues, or taxis, is a primary mechanism for orchestrating concerted and collective cell movements during development, wound repair, and immune responses. Compared with the classic example of amoeboid chemotaxis, in which fast-moving cells such as neutrophils are directed by gradients of soluble factors, directed migration of slow-moving mesenchymal cells such as fibroblasts is poorly understood. Mesenchymal cells possess a distinctive organization of the actin cytoskeleton and associated adhesion complexes as its primary mechanical system, generating the asymmetric forces required for locomotion without strong polarization. The emerging hypothesis is that the molecular underpinnings of mesenchymal taxis involve distinct signaling pathways and diverse requirements for regulation.

Mechanical unloading of bone in microgravity reduces mesenchymal and hematopoietic stem cell-mediated tissue regeneration

Mechanical loading of mammalian tissues is a potent promoter of tissue growth and regeneration, whilst unloading in microgravity can cause reduced tissue regeneration, possibly through effects on stem cell tissue progenitors. To test the specific hypothesis that mechanical unloading alters differentiation of bone marrow mesenchymal and hematopoietic stem cell lineages, we studied cellular and molecular aspects of how bone marrow in the mouse proximal femur responds to unloading in microgravity. Trabecular and cortical endosteal bone surfaces in the femoral head underwent significant bone resorption in microgravity, enlarging the marrow cavity. Cells isolated from the femoral head marrow compartment showed significant down-regulation of gene expression markers for early mesenchymal and hematopoietic differentiation, including FUT1(-6.72), CSF2(-3.30), CD90(-3.33), PTPRC(-2.79), and GDF15(-2.45), but not stem cell markers, such as SOX2. At the cellular level, in situ histological analysis revealed decreased megakaryocyte numbers whilst erythrocytes were increased 2.33 fold. Furthermore, erythrocytes displayed elevated fucosylation and clustering adjacent to sinuses forming the marrow-blood barrier, possibly providing a mechanistic basis for explaining spaceflight anemia. Culture of isolated bone marrow cells immediately after microgravity exposure increased the marrow progenitor's potential for mesenchymal differentiation into in-vitro mineralized bone nodules, and hematopoietic differentiation into osteoclasts, suggesting an accumulation of undifferentiated progenitors during exposure to microgravity. These results support the idea that mechanical unloading of mammalian tissues in microgravity is a strong inhibitor of tissue growth and regeneration mechanisms, acting at the level of early mesenchymal and hematopoietic stem cell differentiation.

Integrin-α5β1 is not required for mural cell functions during development of blood vessels but is required for lymphatic-blood vessel separation and lymphovenous valve formation

Integrin α5β1 is essential for vascular development but it remains unclear precisely where and how it functions. Here, we report that deletion of the gene encoding the integrin-α5 subunit (Itga5) using the Pdgfrb-Cre transgenic mouse line, leads to oedema, haemorrhage and increased levels of embryonic lethality. Unexpectedly, these defects were not caused by loss of α5 from Pdgfrb-Cre expressing mural cells (pericytes and vascular smooth muscle cells), which wrap around the endothelium and stabilise blood vessels, nor by defects in the heart or great vessels, but were due to abnormal development of the lymphatic vasculature. Reminiscent of the pathologies seen in the human lymphatic malformation, fetal cystic hygroma, α5 mutants display defects both in the separation of their blood and lymphatic vasculature and in the formation of the lymphovenous valves. As a consequence, α5-deficient mice develop dilated, blood-filled lymphatic vessels and lymphatic capillaries that are ectopically covered with smooth muscle cells. Analysis of the expression of Pdgfrb during lymphatic development suggests that these defects probably arise from loss of α5β1 integrin in subsets of specialised Prox1(+)Pdgfrb(+) venous endothelial cells that are essential for the separation of the jugular lymph sac from the cardinal vein and formation of the lymphovenous valve leaflets.

Reversing bone loss by directing mesenchymal stem cells to bone

Bone regeneration by systemic transplantation of mesenchymal stem cells (MSCs) is problematic due to the inability to control the MSCs' commitment, growth, and differentiation into functional osteoblasts on the bone surface. Our research group has developed a method to direct the MSCs to the bone surface by conjugating a synthetic peptidomimetic ligand (LLP2A) that has high affinity for activated α4β1 integrin on the MSC surface, with a bisphosphonates (alendronate) that has high affinity for bone (LLP2A-Ale), to direct the transplanted MSCs to bone. Our in vitro experiments demonstrated that mobilization of LLP2A-Ale to hydroxyapatite accelerated MSC migration that was associated with an increase in the phosphorylation of Akt kinase and osteoblastogenesis. LLP2A-Ale increased the homing of the transplanted MSCs to bone as well as the osteoblast surface, significantly increased the rate of bone formation and restored both trabecular and cortical bone loss induced by estrogen deficiency or advanced age in mice. These results support LLP2A-Ale as a novel therapeutic option to direct the transplanted MSCs to bone for the treatment of established bone loss related to hormone deficiency and aging.

Platelet-derived growth factor BB mimics serum-induced dispersal of pancreatic epithelial cell clusters

We showed previously that proliferating human islet-derived de-differentiated cells (DIDs) exhibit many characteristics of mesenchymal stem cells. Dispersed DIDs can be induced by serum deprivation to undergo mesenchymal-to-epithelial transition and aggregate into epithelial cell clusters (ECCs). Conversely, ECCs can be induced to disperse and undergo epithelial-to-mesenchymal transition (EMT) by re-addition of mammalian sera. In this study, we show that platelet-derived growth factor BB (PDGF-BB) mimics and mediates serum-induced ECCs' dispersal accompanied by accumulation of cytoplasmic β-catenin and a decrease in the levels of insulin and glucagon mRNAs. Moreover, we show that PDGF-BB-induced dispersal of ECCs is a more general phenomenon that occurs also with bone marrow mesenchymal stem cells (BM-MSCs) and dermal fibroblasts (DFs). In DIDs, BM-MSCs, and DFs, PDGF decreased the levels of DKK1 mRNA, suggesting involvement of the Wnt signaling pathway. PDGF-BB stimulated a significant increase in S473 phosphorylation of Akt and the PI3K specific inhibitor (PIP828) partially inhibited PDGF-BB-induced ECC dispersal. Lastly, the PDGF-receptor (PDGF-R) antagonist JNJ-10198409 inhibited both PDGF-BB--and serum-induced ECC dispersal. Epidermal growth factor (EGF), which shares most of the PDGF signaling pathway, did not induce dispersal and only weakly stimulated Akt phosphorylation. Our data suggest that PDGF-BB mediates serum-induced DIDs dispersal, correlated with the activation of the PI3K-Akt pathway.

P2Y2 nucleotide receptor activation enhances the aggregation and self-organization of dispersed salivary epithelial cells

Hyposalivation resulting from salivary gland dysfunction leads to poor oral health and greatly reduces the quality of life of patients. Current treatments for hyposalivation are limited. However, regenerative medicine to replace dysfunctional salivary glands represents a revolutionary approach. The ability of dispersed salivary epithelial cells or salivary gland-derived progenitor cells to self-organize into acinar-like spheres or branching structures that mimic the native tissue holds promise for cell-based reconstitution of a functional salivary gland. However, the mechanisms involved in salivary epithelial cell aggregation and tissue reconstitution are not fully understood. This study investigated the role of the P2Y2 nucleotide receptor (P2Y2R), a G protein-coupled receptor that is upregulated following salivary gland damage and disease, in salivary gland reconstitution. In vitro results with the rat parotid acinar Par-C10 cell line indicate that P2Y2R activation with the selective agonist UTP enhances the self-organization of dispersed salivary epithelial cells into acinar-like spheres. Other results indicate that the P2Y2R-mediated response is dependent on epidermal growth factor receptor activation via the metalloproteases ADAM10/ADAM17 or the α5β1 integrin/Cdc42 signaling pathway, which leads to activation of the MAPKs JNK and ERK1/2. Ex vivo data using primary submandibular gland cells from wild-type and P2Y2R(-/-) mice confirmed that UTP-induced migratory responses required for acinar cell self-organization are mediated by the P2Y2R. Overall, this study suggests that the P2Y2R is a promising target for salivary gland reconstitution and identifies the involvement of two novel components of the P2Y2R signaling cascade in salivary epithelial cells, the α5β1 integrin and the Rho GTPase Cdc42.

Platelet-derived growth factor regulates the secretion of extracellular vesicles by adipose mesenchymal stem cells and enhances their angiogenic potential

BACKGROUND

Several studies demonstrate the role of adipose mesenchymal stem cells (ASCs) in angiogenesis. The angiogenic mechanism has been ascribed to paracrine factors since these cells secrete a plenty of signal molecules and growth factors. Recently it has been suggested that besides soluble factors, extracellular vesicles (EVs) that include exosomes and microvesicles may play a major role in cell-to-cell communication. It has been shown that EVs are implicated in the angiogenic process.

RESULTS

Herein we studied whether EVs released by ASCs may mediate the angiogenic activity of these cells. Our results demonstrated that ASC-derived EVs induced in vitro vessel-like structure formation by human microvascular endothelial cells (HMEC). EV-stimulated HMEC when injected subcutaneously within Matrigel in SCID mice formed vessels. Treatment of ASCs with platelet-derived growth factor (PDGF) stimulated the secretion of EVs, changed their protein composition and enhanced the angiogenic potential. At variance of EVs released in basal conditions, PDGF-EVs carried c-kit and SCF that played a role in angiogenesis as specific blocking antibodies inhibited in vitro vessel-like structure formation. The enhanced content of matrix metalloproteinases in PDGF-EVs may also account for their angiogenic activity.

CONCLUSIONS

Our findings indicate that EVs released by ASCs may contribute to the ASC-induced angiogenesis and suggest that PDGF may trigger the release of EVs with an enhanced angiogenic potential.

The potential for resident lung mesenchymal stem cells to promote functional tissue regeneration: understanding microenvironmental cues

Tissue resident mesenchymal stem cells (MSCs) are important regulators of tissue repair or regeneration, fibrosis, inflammation, angiogenesis and tumor formation. Bone marrow derived mesenchymal stem cells (BM-MSCs) and endothelial progenitor cells (EPC) are currently being considered and tested in clinical trials as a potential therapy in patients with such inflammatory lung diseases including, but not limited to, chronic lung disease, pulmonary arterial hypertension (PAH), pulmonary fibrosis (PF), chronic obstructive pulmonary disease (COPD)/emphysema and asthma. However, our current understanding of tissue resident lung MSCs remains limited. This review addresses how environmental cues impact on the phenotype and function of this endogenous stem cell pool. In addition, it examines how these local factors influence the efficacy of cell-based treatments for lung diseases.

Fibronectin at select sites binds multiple growth factors and enhances their activity: expansion of the collaborative ECM-GF paradigm

Intensive research has demonstrated that extracellular matrix (ECM) molecules and growth factors (GF) collaborate at many different levels. The ability of ECM to modulate GF signals has important implications in tissue formation and homeostasis as well as novel therapies for acute and chronic wounds. Recently, a number of GF-binding sites was identified in fibronectin (FN) and was shown to provide another layer of regulation on GF signaling. Here, we review these new findings on FN interaction with GF in the context of general ways ECM molecules regulate GF signaling.

Circulating fibronectin controls tumor growth

Fibronectin is ubiquitously expressed in the extracellular matrix, and experimental evidence has shown that it modulates blood vessel formation. The relative contribution of local and circulating fibronectin to blood vessel formation in vivo remains unknown despite evidence for unexpected roles of circulating fibronectin in various diseases. Using transgenic mouse models, we established that circulating fibronectin facilitates the growth of bone metastases by enhancing blood vessel formation and maturation. This effect is more relevant than that of fibronectin produced by endothelial cells and pericytes, which only exert a small additive effect on vessel maturation. Circulating fibronectin enhances its local production in tumors through a positive feedback loop and increases the amount of vascular endothelial growth factor (VEGF) retained in the matrix. Both fibronectin and VEGF then cooperate to stimulate blood vessel formation. Fibronectin content in the tumor correlates with the number of blood vessels and tumor growth in the mouse models. Consistent with these results, examination of three separate arrays from patients with breast and prostate cancers revealed that a high staining intensity for fibronectin in tumors is associated with increased mortality. These results establish that circulating fibronectin modulates blood vessel formation and tumor growth by modifying the amount of and the response to VEGF. Furthermore, determination of the fibronectin content can serve as a prognostic biomarker for breast and prostate cancers and possibly other cancers.

Galectin-1 stimulates motility of human umbilical cord blood-derived mesenchymal stem cells by downregulation of smad2/3-dependent collagen 3/5 and upregulation of NF-κB-dependent fibronectin/laminin 5 expression

Galectin-1 (Gal-1) belongs to a family of endogenous lectins with conserved carbohydrate recognition domains binding β-galactosidase sugars and plays a vital role in regulating stem cell functions including determination of cell fate. However, our understanding of the functional roles of Gal-1 in human umbilical cord blood-derived mesenchymal stem cells (UCB-MSCs) is still fragmentary and incomplete. Gal-1 significantly increased motility after a 24-h incubation, and this effect was inhibited by β-lactose. We analyzed 17 extracellular matrix (ECM) genes in UCB-MSCs. Gal-1 decreased the expression of collagen genes COL3A1 (COL-3) and COL5A1 (COL-5) but increased the expression of fibronectin (FN) and laminin 5 (LM-5), that were reversed by β-lactose. Gal-1 increased protein kinase C (PKC), c-Src, and caveolin-1 (Cav-1) phosphorylation that was attenuated by β-lactose and the Src inhibitor PP2. In addition, pretreatment with the lipid raft disruptor Mβ-CD and the PKC inhibitors inhibited Gal-1-induced UCB-MSC motility. In addition, Gal-1 reduced smad2/3 phosphorylation and induced nuclear factor (NF)-κB phosphorylation. Pretreatment with Mβ-CD attenuated Gal-1-reduced smad2/3 phosphorylation, COL-3, and COL-5 expression but did not affect NF-κB phosphorylation, FN, or LM-5 expression. In contrast, PKC inhibitors only attenuated NF-κB phosphorylation, FN, and LM-5 expression. Reconstructing Gal-1-induced genetic changes by replacing it with siRNA specific for COL-3 or COL-5, or treatment of the cells with FN and LM-5 proteins, increased motility and its related proteins such as focal adhesion kinase, Akt, Erk, integrins, and matrix metalloproteinase-2. A combined treatment with COL-3/COL-5 siRNA or FN/LM-5 compared with that of single treatments was synergistic. However, a single Gal-1 treatment maximally stimulated motility and related protein phosphorylation/expression. These results demonstrate that Gal-1 stimulated human UCB-MSC motility by decreasing COL-3/COL-5 expression and increasing FN/LM-5 expression through a PKC-dependent NF-κB and c-Src/Cav-1-dependent smad2/3 pathway that was critical for governing the activation of FAK, Akt, Erk, integrins, and MMP2.

Periodontal-ligament-derived stem cells exhibit the capacity for long-term survival, self-renewal, and regeneration of multiple tissue types in vivo

Primary periodontal ligament stem cells (PDLSCs) are known to possess multidifferentiation potential and exhibit an immunophenotype similar to that described for bone-marrow-derived mesenchymal stem cells. In the present study, bromo-deoxyuridine (BrdU)-labeled ovine PDLSCs implanted into immunodeficient mice survived after 8 weeks post-transplantation and exhibited the capacity to form bone/cementum-like mineralized tissue, ligament structures similar to Sharpey's fibers with an associated vasculature. To evaluate self-renewal potential, PDLSCs were recovered from harvested primary transplants 8 weeks post-transplantation that exhibit an immunophenotype and multipotential capacity comparable to primary PDLSCs. The re-derived PDLSCs isolated from primary transplants were implanted into secondary ectopic xenogeneic transplants. Histomorphological analysis demonstrated that four out of six donor re-derived PDLSC populations displayed a capacity to survive and form fibrous ligament structures and mineralized tissues associated with vasculature in vivo, although at diminished levels in comparison to primary PDLSCs. Further, the capacity for long-term survival and the potential role of PDLSCs in dental tissue regeneration were determined using an ovine preclinical periodontal defect model. Autologous ex vivo-expanded PDLSCs that were prelabeled with BrdU were seeded onto Gelfoam(®) scaffolds and then transplanted into fenestration defects surgically created in the periodontium of the second premolars. Histological assessment at 8 weeks post-implantation revealed surviving BrdU-positive PDLSCs associated with regenerated periodontium-related tissues, including cementum and bone-like structures. This is the first report to demonstrate the self-renewal capacity of PDLSCs using serial xenogeneic transplants and provides evidence of the long-term survival and tissue contribution of autologous PDLSCs in a preclinical periodontal defect model.

Osteogenic differentiation of human mesenchymal stem cells on α5 integrin binding peptide hydrogels is dependent on substrate elasticity

The extracellular matrix plays a crucial role in controlling human mesenchymal stem cell (hMSC) biology including differentiation, and α5β1 integrin signaling plays an important role during osteogenic differentiation of hMSCs. Here, peptide-functionalized hydrogels were used to examine the role of α5β1 integrin signaling in inducing osteogenic differentiation in hMSCs. Further, the role of substrate elasticity was also studied. A thiolene chemistry was used to functionalize poly(ethylene glycol) hydrogels with a pendant peptide moieity, c(RRETAWA), as previous studies have shown that RRETAWA containing peptides bind to the α5β1 integrin with very high specificity. Notably, hMSC attachment to c(RRETAWA)-functionalized hydrogels was found to occur primarily through α5 integrins, as the number of attached cells was significantly reduced to ~20% upon blocking the α5 integrin during culture. To investigate the interplay between stiffness and c(RRETAWA) concentration, hydrogels were formulated with Young's moduli of ~2 kPa (soft) and ~25 kPa (stiff) and c(RRETAWA) concentrations of 0.1 mM and 1 mM. Stiff substrates led to ~3.5 fold higher hMSC attachment and ~3 fold higher cell area in comparison to soft substrates. hMSCs formed robust and larger focal adhesions on stiff substrates at 1 mM c(RRETAWA) compared to soft substrates. Alkaline phosphatase (ALP) activity in hMSCs cultured on stiff gels at 0.1 mM and 1 mM c(RRETAWA) was increased 2.5 and 3.5 fold, respectively after 14 days in growth media. hMSCs did not show an increase in ALP activity when cultured on soft gels. Further, gene expression of osteogenic related genes, core binding factor-1, osteopontin and Collagen-1a at day 14 in hMSCs cultured on stiff gels at 1 mM c(RRETAWA) were increased 10, 7 and 4 fold, respectively, while on soft gels, gene expression was at basal levels. Collectively, these results demonstrate that the combination of high substrate stiffness and α5β1 integrin signaling stimulated by c(RRETAWA) is sufficient to induce osteogenic differentiation of hMSCs without requiring the addition of soluble factors.

Extracellular matrix remodeling by bone marrow fibroblast-like cells correlates with disease progression in multiple myeloma

The pathogenesis of multiple myeloma (MM) is regarded as a multistep process, in which an asymptomatic stage of monoclonal gammopathy of undetermined significance (MGUS) precedes virtually all cases of MM. Molecular events characteristic for the transition from MGUS to MM are still poorly defined. We hypothesized that fibroblast-like cells in the tumor microenvironment are critically involved in the pathogenesis of MM. Therefore, we performed a comparative proteome profiling study, analyzing primary human fibroblast-like cells isolated from the bone marrow of MM, of MGUS, as well as of non-neoplastic control patients. Thereby, a group of extracellular matrix (ECM) proteins, ECM receptors, and ECM-modulating enzymes turned out to be progressively up-regulated in MGUS and MM. These proteins include laminin α4, lysyl-hydroxylase 2, prolyl 4-hydroxylase 1, nidogen-2, integrin α5β5, c-type mannose receptor 2, PAI-1, basigin, and MMP-2, in addition to PDGF-receptor β and the growth factor periostin, which are likewise involved in ECM activities. Our results indicate that ECM remodeling by fibroblast-like cells may take place already at the level of MGUS and may become even more pronounced in MM. The identified proteins which indicate the stepwise progression from MGUS to MM may offer new tools for therapeutic strategies.