The regulation of differentiation in mesenchymal stem cells

Engineering cell matrix interactions in assembled polyelectrolyte fiber hydrogels for mesenchymal stem cell chondrogenesis

Cell-cell and cell-matrix interactions are important events in directing stem cell chondrogenesis, which can be promoted in matrix microenvironments presenting appropriate ligands. In this study, interfacial polyelectrolyte complexation (IPC) based hydrogels were employed, wherein the unique formation of submicron size fibers facilitated spatial orientation of ligands within such hydrogels. The influence of aligned, collagen type I (Col I) presentation in IPC hydrogel on chondrogenic differentiation of human mesenchymal stem cells (MSC) was investigated. Early morphological dynamics, onset of N-cadherin/β-catenin mediated chondrogenic induction and differentiation were compared between MSCs encapsulated in IPC-Col I and IPC-control (without Col I) hydrogels, and a conventional Col I hydrogel. MSCs in IPC-Col I hydrogel aligned and packed uniformly, resulting in enhanced cell-cell interactions and cellular condensation, facilitating superior chondrogenesis and the generation of mature hyaline neocartilage, with notable downregulation of fibrocartilaginous marker. Inhibition study using function blocking β1-integrin antibodies reversed the aforementioned outcomes, indicating the importance of coupling integrin mediated cell-matrix interactions and N-cadherin/β-catenin mediated downstream signaling events. This study demonstrated the significance of oriented ligand presentation for MSC chondrogenesis, and the importance of facilitating an orderly sequence of differentiation events, initiated by proximal interactions between MSCs and the extracellular matrix for robust neocartilage formation.

Bioactive membranes for bone regeneration applications: effect of physical and biomolecular signals on mesenchymal stem cell behavior

This study focuses on the in vitro characterization of bioactive elastin-like recombinamer (ELR) membranes for bone regeneration applications. Four bioactive ELRs exhibiting epitopes designed to promote mesenchymal stem cell adhesion (RGDS), endothelial cell adhesion (REDV), mineralization (HAP), and both cell adhesion and mineralization (HAP-RGDS) were synthesized using standard recombinant protein techniques. The materials were then used to fabricate ELR membranes incorporating a variety of topographical micropatterns including channels, holes and posts. Primary rat mesenchymal stem cells (rMSCs) were cultured on the different membranes and the effects of biomolecular and physical signals on cell adhesion, morphology, proliferation, and differentiation were evaluated. All results were analyzed using a custom-made MATLAB program for high throughput image analysis. Effects on cell morphology were mostly dependent on surface topography, while cell proliferation and cell differentiation were largely dependent on the biomolecular signaling from the ELR membranes. In particular, osteogenic differentiation (evaluated by staining for the osteoblastic marker osterix) was significantly enhanced on cells cultured on HAP membranes. Remarkably, cells growing on membranes containing the HAP sequence in non-osteogenic differentiation media exhibited significant up-regulation of the osteogenic marker as early as day 5, while those growing on fibronectin-coated glass in osteogenic differentiation media did not. These results are part of our ongoing effort to develop an optimized molecularly designed periosteal graft.

Role of SIRT1 and AMPK in mesenchymal stem cells differentiation

The differentiation capabilities of mesenchymal stem cells (MSCs) compromise with age and with in vitro passages which could impair the efficacy of cell therapy and tissue engineering. However, how to maintain these capabilities is not fully understood. Calorie restriction (CR, decreasing caloric intake by 30-40%) could extend longevity and reduce aging-related diseases. Recent studies revealed that CR could influence the lineage determination of stem cells including MSCs. Two important mediators of CR might be silent mating type information regulation 2 homolog 1 (SIRT1), a NAD(+)-dependent deacetylase, and AMP-activated protein kinase (AMPK), an energy-sensing kinase. Evidences are mounting that both SIRT1 and AMPK play important roles in cell fate determination of MSCs. Herein, we intend to sum up our understanding about the role of SIRT1 and AMPK in osteogenic and adipogenic potential of MSCs. Metabolic process of MSCs differentiation and the putative interplay of SIRT1 and AMPK in this process was also discussed.

CD105 (endoglin)-negative murine mesenchymal stromal cells define a new multipotent subpopulation with distinct differentiation and immunomodulatory capacities

Administration of in vitro expanded mesenchymal stromal cells (MSCs) represents a promising therapy for regenerative medicine and autoimmunity. Both mouse and human MSCs ameliorate autoimmune disease in syn-, allo- and xenogeneic settings. However, MSC preparations are heterogeneous which impairs their therapeutic efficacy and endorses variability between experiments. This heterogeneity has also been a main hurdle in translating experimental MSC data from mouse models to human patients. The objective of the present manuscript has been to further characterize murine MSCs (mMSCs) with the aim of designing more efficient and specific MSC-based therapies. We have found that mMSCs are heterogeneous for endoglin (CD105) expression and that this heterogeneity is not due to different stages of MSC differentiation. CD105 is induced on a subpopulation of mMSCs early upon in vitro culture giving rise to CD105⁺ and CD105^- MSCs. CD105⁺ and CD105^- mMSCs represent independent subpopulations that maintain their properties upon several passages. CD105 expression on CD105⁺ mMSCs was affected by passage number and cell confluency while CD105^- mMSCs remained negative. The CD105⁺ and CD105^- mMSC subpopulations had similar growth potential and expressed almost identical mMSC markers (CD29⁺CD44⁺Sca1 ⁺ MHC-I⁺ and CD45^-CD11b^-CD31^-) but varied in their differentiation and immunoregulatory properties. Interestingly, CD105^- mMSCs were more prone to differentiate into adipocytes and osteocytes and suppressed the proliferation of CD4⁺ T cells more efficiently compared to CD105⁺ mMSCs. Based on these studies we propose to redefine the phenotype of mMSCs based on CD105 expression.

Automated microscopy as a quantitative method to measure differences in adipogenic differentiation in preparations of human mesenchymal stromal cells

BACKGROUND AIMS

Multipotent stromal cells, also called mesenchymal stromal cells (MSCs), are potentially valuable as a cellular therapy because of their differentiation and immunosuppressive properties. As the result of extensive heterogeneity of MSCs, quantitative approaches to measure differentiation capacity between donors and passages on a per-cell basis are needed.

METHODS

Human bone marrow-derived MSCs were expanded to passages P3, P5 and P7 from eight different donors and were analyzed for colony-forming unit capacity (CFU), cell size, surface marker expression and forward/side-scatter analysis by flow cytometry. Adipogenic differentiation potential was quantified with the use of automated microscopy. Percentage of adipogenesis was determined by quantifying nuclei and Nile red-positive adipocytes after automated image acquisition.

RESULTS

MSCs varied in expansion capacity and increased in average cell diameter with passage. CFU capacity decreased with passage and varied among cell lines within the same passage. The number of adipogenic precursors varied between cell lines, ranging from 0.5% to 13.6% differentiation at P3. Adipogenic capacity decreased significantly with increasing passage. MSC cell surface marker analysis revealed no changes caused by passaging or donor differences.

CONCLUSIONS

We measured adipogenic differentiation on a per-cell basis with high precision and accuracy with the use of automated fluorescence microscopy. We correlated these findings with other quantitative bioassays to better understand the role of donor variability and passaging on CFU, cell size and adipogenic differentiation capacity in vitro. These quantitative approaches provide valuable tools to measure MSC quality and measure functional biological differences between donors and cell passages that are not revealed by conventional MSC cell surface marker analysis.

Transforming growth factor Beta-releasing scaffolds for cartilage tissue engineering

The maintenance of a critical threshold concentration of transforming growth factor beta (TGF-β) for a given period of time is crucial for the onset and maintenance of chondrogenesis. Thus, the development of scaffolds that provide temporal and/or spatial control of TGF-β bioavailability has appeal as a mechanism to induce the chondrogenesis of stem cells in vitro and in vivo for articular cartilage repair. In the past decade, many types of scaffolds have been designed to advance this goal: hydrogels based on polysaccharides, hyaluronic acid, and alginate; protein-based hydrogels such as fibrin, gelatin, and collagens; biopolymeric gels and synthetic polymers; and solid and hybrid composite (hydrogel/solid) scaffolds. In this study, we review the progress in developing strategies to deliver TGF-β from scaffolds with the aim of enhancing chondrogenesis. In the future, such scaffolds could prove critical for tissue engineering cartilage, both in vitro and in vivo.

Stem cell stimulation of endogenous myocyte regeneration

Cell-based therapy has emerged as a promising approach to combat the myocyte loss and cardiac remodelling that characterize the progression of left ventricular dysfunction to heart failure. Several clinical trials conducted over the past decade have shown that a variety of autologous bone-marrow- and peripheral-blood-derived stem and progenitor cell populations can be safely administered to patients with ischaemic heart disease and yield modest improvements in cardiac function. Concurrently, rapid progress has been made at the pre-clinical level to identify novel therapeutic cell populations, delineate the mechanisms underlying cell-mediated cardiac repair and optimize cell-based approaches for clinical use. The following review summarizes the progress that has been made in this rapidly evolving field over the past decade and examines how our current understanding of the mechanisms involved in successful cardiac regeneration should direct future investigation in this area. Particular emphasis is placed on discussion of the general hypothesis that the benefits of cell therapy primarily result from stimulation of endogenous cardiac repair processes that have only recently been identified in the adult mammalian heart, rather than direct differentiation of exogenous cells. Continued scientific investigation in this area will guide the optimization of cell-based approaches for myocardial regeneration, with the ultimate goal of clinical implementation and substantial improvement in our ability to restore cardiac function in ischaemic heart disease patients.

The Control of Mesenchymal Stromal Cell Osteogenic Differentiation through Modified Surfaces

Stem cells continue to receive widespread attention due to their potential to revolutionise treatments in the fields of both tissue engineering and regenerative medicine. Adult stem cells, specifically mesenchymal stromal cells (MSCs), play a vital role in the natural events surrounding bone healing and osseointegration through being stimulated to differentiate along their osteogenic lineage and in doing so, they form new cortical and trabecular bone tissue. Understanding how to control, manipulate, and enhance the intrinsic healing events modulated through osteogenic differentiation of MSCs by the use of modified surfaces and biomaterials could potentially advance the fields of both orthopaedics and dentistry. This could be by either using surface modification to generate greater implant stability and more rapid healing following implantation or the stimulation of MSCs ex vivo for reimplantation. This review aims to gather publications targeted at promoting, enhancing, and controlling the osteogenic differentiation of MSCs through biomaterials, nanotopographies, and modified surfaces for use in implant procedures.

Cellular interactions via conditioned media induce in vivo nephron generation from tubular epithelial cells or mesenchymal stem cells

There are some successful reports of kidney generation by utilizing the natural course of kidney development, namely, the use of an artificially treated metanephros, blastocyst or ureteric bud. Under a novel concept of cellular interactions via conditioned media (CMs), we have attempted in vivo nephron generation from tubular epithelial cells (TECs) or mesenchymal stem cells (MSCs). Here we used 10× CMs of vascular endothelial cells (VECs) and TECs, which is the first to introduce a CM into the field of organ regeneration. We first present stimulative cross-talks induced by these CMs between VECs and TECs on cell proliferation and morphological changes. In MSCs, TEC-CM suppressed these changes, however, induced cytokeratin expression, indicating the differentiation of MSCs into TECs. As a result, glomerular and tubular structures were created following the implantation of TECs or MSCs with both CMs. Our findings suggest that the cellular interactions via CMs might induce in vivo nephron generation from TECs or MSCs. As a promoting factor, CMs could also be applied to the regeneration of other organs and tissues.

Directing chondrogenesis of stem cells with specific blends of cellulose and silk

Biomaterials that can stimulate stem cell differentiation without growth factor supplementation provide potent and cost-effective scaffolds for regenerative medicine. We hypothesize that a scaffold prepared from cellulose and silk blends can direct stem cell chondrogenic fate. We systematically prepared cellulose blends with silk at different compositions using an environmentally benign processing method based on ionic liquids as a common solvent. We tested the effect of blend compositions on the physical properties of the materials as well as on their ability to support mesenchymal stem cell (MSC) growth and chondrogenic differentiation. The stiffness and tensile strength of cellulose was significantly reduced by blending with silk. The characterized materials were tested using MSCs derived from four different patients. Growing MSCs on a specific blend combination of cellulose and silk in a 75:25 ratio significantly upregulated the chondrogenic marker genes SOX9, aggrecan, and type II collagen in the absence of specific growth factors. This chondrogenic effect was neither found with neat cellulose nor the cellulose/silk 50:50 blend composition. No adipogenic or osteogenic differentiation was detected on the blends, suggesting that the cellulose/silk 75:25 blend induced specific stem cell differentiation into the chondrogenic lineage without addition of the soluble growth factor TGF-β. The cellulose/silk blend we identified can be used both for in vitro tissue engineering and as an implantable device for stimulating endogenous stem cells to initiate cartilage repair.

Autologous mesenchymal stem cell endografting in experimental cerebrovascular aneurysms

INTRODUCTION

Coiling is the gold standard for the treatment of intracranial aneurysms. However, some issues associated with endovascular treatment limit its long-term efficiency. Recanalization with coil compaction is certainly the most important. New approaches may be considered to promote thrombus colonization by mesenchymal cells and aneurysm healing. In the present study, we have percutaneously delivered autologous bone marrow mesenchymal stem cells (BMSCs) to an elastase-induced rabbit carotid aneurysm model in vivo.

METHODS

Autologous mesenchymatous stem cells were obtained after femoral puncture and bone marrow aspiration. After 2 weeks of in vitro cell culture, five million BMSCs were grafted in the carotid aneurysm using an endovascular approach.

RESULTS

We demonstrated the feasibility of in vivo percutaneous seeding of autologous BMSCs in the aneurysm by positive Hoechst fluorostaining. Two weeks later, conventional angiography showed an increase in median aneurysmal surface in the sham group, whereas this surface was decreased in the group treated with BMSCs, +28.4 versus -26.4 %, respectively (p = 0.01). BMSC seeding resulted in intimal hyperplasia with cell colonization and disappearance of the thrombus.

CONCLUSION

In conclusion, percutaneous seeding of BMSCs may colonize and heal the arterial wall thus limiting aneurysm expansion.

atf4 promotes β-catenin expression and osteoblastic differentiation of bone marrow mesenchymal stem cells

Bone marrow mesenchymal stem cells (MSCs) can differentiate into multiple cell types including osteoblasts. How this differentiation process is controlled, however, is not completely understood. Here we show that activating transcription factor 4 (ATF4) plays a critical role in promoting bone marrow MSC differentiation towards the osteoblast lineage. Ablation of the Atf4 gene blocked the formation of osteoprogenitors and inhibited osteoblast differentiation without affecting the expansion and formation of MSCs in bone marrow cultures. Loss of ATF4 dramatically reduced the level of β-catenin protein in MSCs in vitro and in osteoblasts/osteoprogenitors located on trabecular and calvarial surfaces. Loss of ATF4 did not decrease the expression of major canonical Wnt/β-catenin signaling components such as Wnt3a, Wnt7b, Wnt10b, Lrp5, and Lrp6 in MSCs. Furthermore, shRNA knockdown of ATF4 expression decreased the level of β-catenin protein in MC-4 preosteoblasts. In contrast, overexpression of ATF4 increased β-catenin protein levels in MC-4 cells. Finally, ATF4 and β-catenin formed a protein-protein complex in COS-7 cells coexpressing both factors or in MC-4 preosteoblastic cells. This study establishes a new role of ATF4 in controlling the β-catenin protein levels and MSC differentiation towards the osteoblast lineage.

Differentiation of mesenchymal stem cells to osteoblasts and chondrocytes: a focus on adenosine receptors

Skeletogenesis, either during development, post-injury or for maintenance, is a carefully coordinated process reliant on the appropriate differentiation of mesenchymal stem cells. Some well described, as well as a new regulator of this process (adenosine receptors), are alike in that they signal via cyclic-AMP (cAMP). This review highlights the known contribution of cAMP signalling to mesenchymal stem cell differentiation to osteoblasts and to chondrocytes. Focus has been given to how these regulators influence the commitment of the osteochondroprogenitor to these separate lineages.

Mesenchymal stem cells and nano-structured surfaces

Mesenchymal stem cells (MSCs) represent multipotent stromal cells that can differentiate into a variety of cell types, including osteoblasts (bone cells), chondrocytes (cartilage cells), and adipocytes (fat cells). Their multi-potency provides a great promise as a cell source for tissue engineering and cell-based therapy for many diseases, particularly bone diseases and bone formation. To be able to direct and modulate the differentiation of MSCs into the desired cell types in situ in the tissue, nanotechnology is introduced and used to facilitate or promote cell growth and differentiation. These nano-materials can provide a fine structure and tuneable surface in nanoscales to help the cell adhesion and promote the cell growth and differentiation of MSCs. This could be a dominant direction in future for stem cells based therapy or tissue engineering for various diseases. Therefore, the isolation, manipulation, and differentiation of MSCs are very important steps to make meaningful use of MSCs for disease treatments. In this chapter, we have described a method of isolating MSC from human bone marrow, and how to culture and differentiate them in vitro. We have also provided research methods on how to use MSCs in an in vitro model and how to observe MSC biological response on the surface of nano-scaled materials.

Review of Signaling Pathways Governing MSC Osteogenic and Adipogenic Differentiation

Mesenchymal stem cells (MSC) are multipotent cells, functioning as precursors to a variety of cell types including adipocytes, osteoblasts, and chondrocytes. Between osteogenic and adipogenic lineage commitment and differentiation, a theoretical inverse relationship exists, such that differentiation towards an osteoblast phenotype occurs at the expense of an adipocytic phenotype. This balance is regulated by numerous, intersecting signaling pathways that converge on the regulation of two main transcription factors: peroxisome proliferator-activated receptor- γ (PPAR γ ) and Runt-related transcription factor 2 (Runx2). These two transcription factors, PPAR γ and Runx2, are generally regarded as the master regulators of adipogenesis and osteogenesis. This review will summarize signaling pathways that govern MSC fate towards osteogenic or adipocytic differentiation. A number of signaling pathways follow the inverse balance between osteogenic and adipogenic differentiation and are generally proosteogenic/antiadipogenic stimuli. These include β -catenin dependent Wnt signaling, Hedgehog signaling, and NELL-1 signaling. However, other signaling pathways exhibit more context-dependent effects on adipogenic and osteogenic differentiation. These include bone morphogenic protein (BMP) signaling and insulin growth factor (IGF) signaling, which display both proosteogenic and proadipogenic effects. In summary, understanding those factors that govern osteogenic versus adipogenic MSC differentiation has significant implications in diverse areas of human health, from obesity to osteoporosis to regenerative medicine.

Sulfated hyaluronan/collagen I matrices enhance the osteogenic differentiation of human mesenchymal stromal cells in vitro even in the absence of dexamethasone

Glycosaminoglycans (GAG) are multifunctional components of the extracellular matrix (ECM) involved in different steps of the regulation of cellular differentiation. In this study artificial extracellular matrices (aECM) consisting of collagen (Col) I and different GAG derivatives were used as a substrate for human mesenchymal stromal cells (hMSC) to study osteogenic differentiation in vitro. hMSC were cultured on aECM containing col and hyaluronan sulfates (HyaS) with increasing degrees of sulfation (DS(S)) and were compared with aECM containing col and the natural GAG hyaluronan or chondroitin 4-sulfate. hMSC were analyzed for osteogenic differentiation markers such as calcium phosphate deposition, tissue non-specific alkaline phosphatase (TNAP) and expression of runt-related transcription factor 2 (runx2), osteocalcin (ocn) and bone sialoprotein II (bspII). Compared with aECM containing Col and natural GAG all Col/HyaS-containing aECM induced an increase in calcium phosphate deposition, TNAP activity and tnap expression. These effects were also seen in the absence of dexamethasone (an established osteogenic supplement). The expression of runx2 and ocn was not altered and the expression of bspII was diminished on the col/HyaS-containing aECM. The impact of the Col/HyaS-containing aECM on hMSC differentiation was independent of the DS(S) of the HyaS derivatives, indicating the importance of the primary (C-6) hydroxyl group of N-acetylglucosamine. These results suggest that Col/HyaS-containing aECM are able to stimulate hMSC to undergo osteogenic differentiation even in the absence of dexamethasone, which makes these matrices an interesting tool for hMSC-based tissue engineering applications and biomaterial functionalizations to enhance bone formation.

Coculture-driven mesenchymal stem cell-differentiated articular chondrocyte-like cells support neocartilage development

Controlled differentiation of mesenchymal stem cells (MSCs) into the chondrogenic lineage is crucial for in vitro generation of neocartilage, yet achieving it remains challenging. Traditional protocols for MSC differentiation using exogenous inductive molecules, such as transforming growth factor-β, fall short in meeting the needs of clinical applications because they yield differentiated cells that exhibit hypertrophic characteristics and subsequently facilitate endochondral bone formation. The objective of the current study was to deliver endogenous inductive factors from juvenile articular chondrocytes to bone marrow-derived MSCs to drive MSC chondrogenic differentiation through cocultivation of the two cell types in the absence of direct physical contact and exogenous stimulators. An initial chondrocyte/MSC ratio of 63:1 was identified as the appropriate proportion of the two cell populations to ensure that coculture-driven MSC-differentiated (CDMD) cells replicated the cellular morphology, behavior, and phenotype of articular chondrocytes. In a three-dimensional agarose system, CDMD cells were further shown to develop into robust neocartilage structurally and mechanically stronger than chondrocyte-laden constructs and with reduced hypertrophic potential. Although MSCs tended to lose the ability to express CD44, an important regulator in cartilage biology, during the coculture induction, CDMD cells regained this function in the three-dimensional tissue cultivation. The present work establishes a chondrocyte/MSC coculture model that serves as a template to better understand chondrocyte-driven MSC differentiation and provides insights for improved strategies to develop clinically relevant cartilage tissue replacements.

Role of Slug transcription factor in human mesenchymal stem cells

The pathways that control mesenchymal stem cells (MSCs) differentiation are not well understood, and although some of the involved transcription factors (TFs) have been characterized, the role of others remains unclear. We used human MSCs from tibial plateau (TP) trabecular bone, iliac crest (IC) bone marrow and Wharton’s jelly (WJ) umbilical cord demonstrating a variability in their mineral matrix deposition, and in the expression levels of TFs including Runx2, Sox9, Sox5, Sox6, STAT1 and Slug, all involved in the control of osteochondroprogenitors differentiation program. Because we reasoned that the basal expression level of some TFs with crucial role in the control of MSC fate may be correlated with osteogenic potential, we considered the possibility to affect the hMSCs behaviour by using gene silencing approach without exposing cells to induction media. In this study we found that Slug-silenced cells changed in morphology, decreased in their migration ability, increased Sox9 and Sox5 and decreased Sox6 and STAT1 expression. On the contrary, the effect of Slug depletion on Runx2 was influenced by cell type. Interestingly, we demonstrated a direct in vivo regulatory action of Slug by chromatin immunoprecipitation, showing a specific recruitment of this TF in the promoter of Runx2 and Sox9 genes. As a whole, our findings have important potential implication on bone tissue engineering applications, reinforcing the concept that manipulation of specific TF expression levels may elucidate MSC biology and the molecular mechanisms, which promote osteogenic differentiation.

Cutaneous wound healing: recruiting developmental pathways for regeneration

Following a skin injury, the damaged tissue is repaired through the coordinated biological actions that constitute the cutaneous healing response. In mammals, repaired skin is not identical to intact uninjured skin, however, and this disparity may be caused by differences in the mechanisms that regulate postnatal cutaneous wound repair compared to embryonic skin development. Improving our understanding of the molecular pathways that are involved in these processes is essential to generate new therapies for wound healing complications. Here we focus on the roles of several key developmental signaling pathways (Wnt/β-catenin, TGF-β, Hedgehog, Notch) in mammalian cutaneous wound repair, and compare this to their function in skin development. We discuss the varying responses to cutaneous injury across the taxa, ranging from complete regeneration to scar tissue formation. Finally, we outline how research into the role of developmental pathways during skin repair has contributed to current wound therapies, and holds potential for the development of more effective treatments.

Fibronectin and stem cell differentiation - lessons from chondrogenesis

The extracellular matrix (ECM) is an intricate network of proteins that surrounds cells and has a central role in establishing an environment that is conducive to tissue-specific cell functions. In the case of stem cells, this environment is the stem cell niche, where ECM signals participate in cell fate decisions. In this Commentary, we describe how changes in ECM composition and mechanical properties can affect cell shape and stem cell differentiation. Using chondrogenic differentiation as a model, we examine the changes in the ECM that occur before and during mesenchymal stem cell differentiation. In particular, we focus on the main ECM protein fibronectin, its temporal expression pattern during chondrogenic differentiation, its potential effects on functions of differentiating chondrocytes, and how its interactions with other ECM components might affect cartilage development. Finally, we discuss data that support the possibility that the fibronectin matrix has an instructive role in directing cells through the condensation, proliferation and/or differentiation stages of cartilage formation.

Adhesive and mechanical regulation of mesenchymal stem cell differentiation in human bone marrow and periosteum-derived progenitor cells

It has previously been demonstrated that cell shape can influence commitment of human bone marrow-derived mesenchymal stem cells (hBMCs) to adipogenic, osteogenic, chondrogenic, and other lineages. Human periosteum-derived cells (hPDCs) exhibit multipotency similar to hBMCs, but hPDCs may offer enhanced potential for osteogenesis and chondrogenesis given their apparent endogenous role in bone and cartilage repair in vivo. Here, we examined whether hPDC differentiation is regulated by adhesive and mechanical cues comparable to that reported for hBMC differentiation. When cultured in the appropriate induction media, hPDCs at high cell seeding density demonstrated enhanced levels of adipogenic or chondrogenic markers as compared with hPDCs at low cell seeding density. Cell seeding density correlated inversely with projected area of cell spreading, and directly limiting cell spreading with micropatterned substrates promoted adipogenesis or chondrogenesis while substrates promoting cell spreading supported osteogenesis. Interestingly, cell seeding density influenced differentiation through both changes in cell shape and non-shape-mediated effects: density-dependent adipogenesis and chondrogenesis were regulated primarily by cell shape whereas non-shape effects strongly influenced osteogenic potential. Inhibition of cytoskeletal contractility by adding the Rho kinase inhibitor Y27632 further enhanced adipogenic differentiation and discouraged osteogenic differentiation of hPDCs. Together, our results suggest that multipotent lineage decisions of hPDCs are impacted by cell adhesive and mechanical cues, though to different extents than hBMCs. Thus, future studies of hPDCs and other primary stem cell populations with clinical potential should consider varying biophysical metrics for more thorough optimization of stem cell differentiation.

Mesenchymal stem cell-mediated reversal of bronchopulmonary dysplasia and associated pulmonary hypertension

Clinical trials have failed to demonstrate an effective preventative or therapeutic strategy for bronchopulmonary dysplasia (BPD), a multifactorial chronic lung disease in preterm infants frequently complicated by pulmonary hypertension (PH). Mesenchymal stem cells (MSCs) and their secreted components have been shown to prevent BPD and pulmonary fibrosis in rodent models. We hypothesized that treatment with conditioned media (CM) from cultured mouse bone marrow-derived MSCs could reverse hyperoxia-induced BPD and PH. Newborn mice were exposed to hyperoxia (FiO₂=0.75) for two weeks, were then treated with one intravenous dose of CM from either MSCs or primary mouse lung fibroblasts (MLFs), and placed in room air for two to four weeks. Histological analysis of lungs harvested at four weeks of age was performed to determine the degree of alveolar injury, blood vessel number, and vascular remodeling. At age six weeks, pulmonary artery pressure (PA acceleration time) and right ventricular hypertrophy (RVH; RV wall thickness) were assessed by echocardiography, and pulmonary function tests were conducted. When compared to MLF-CM, a single dose of MSC-CM-treatment (1) reversed the hyperoxia-induced parenchymal fibrosis and peripheral PA devascularization (pruning), (2) partially reversed alveolar injury, (3) normalized lung function (airway resistance, dynamic lung compliance), (4) fully reversed the moderate PH and RVH, and (5) attenuated peripheral PA muscularization associated with hyperoxia-induced BPD. Reversal of key features of hyperoxia-induced BPD and its long-term adverse effects on lung function can be achieved by a single intravenous dose of MSC-CM, thereby pointing toward a new therapeutic intervention for chronic lung diseases.

Visualization and exploration of Tcf/Lef function using a highly responsive Wnt/β-catenin signaling-reporter transgenic zebrafish

Evolutionarily conserved Tcf/Lef transcription factors (Lef1, Tcf7, Tcf7l1, and Tcf7l2) mediate gene expression regulated by Wnt/β-catenin signaling, which has multiple roles in early embryogenesis, organogenesis, adult tissue homeostasis, and tissue regeneration. However, the spatiotemporal dynamics of Tcf/Lef activity during these events remain poorly understood. We generated stable transgenic zebrafish lines carrying a new Wnt/β-catenin signaling reporter, Tcf/Lef-miniP:dGFP. The reporter revealed the transcriptional activities of four Tcf/Lef members controlled by Wnt/β-catenin signaling, which were expressed in known Wnt/β-catenin signaling-active sites during embryogenesis, organ development and growth, and tissue regeneration. We used the transgenic lines to demonstrate the contribution of Tcf/Lef-mediated Wnt/β-catenin signaling to the development of the anterior lateral line, dorsal and secondary posterior lateral lines, and gill filaments. Thus, these reporter lines are highly useful tools for studying Tcf/Lef-mediated Wnt/β-catenin signaling-dependent processes.

Human mesenchymal stromal cell proteomics: contribution for identification of new markers and targets for medicine intervention

Mesenchymal stem or stromal cells (MSCs) have become of great interest for cell-based therapy owing to their roles in tissue repair and immune suppression. MSCs have the ability to differentiate into specialized tissues, including bone, cartilage and muscle, among several others. Furthermore, it has been found that MSCs can also serve as cellular factories that secrete mediators to stimulate in situ regeneration of injured tissues. Proteomics has contributed significantly to the identification of new proteins to improve cellular characterization of MSCs, to identify new targets for therapeutic intervention and to elucidate important pathways utilized by MSCs to differentiate into distinct tissues. As proteomics technology advances, several studies can be revisited and analyzed in depth, employing state-of-the-art approaches, helping to uncover the cellular mechanisms utilized by MSCs to exert their regenerative functionalities. In this article, we will review the progress made so far and discuss further opportunities for proteomics to contribute to the clinical applications of MSCs.

Co-delivery of adipose-derived stem cells and growth factor-loaded microspheres in RGD-grafted N-methacrylate glycol chitosan gels for focal chondral repair

The coencapsulation of growth factor-loaded microspheres with adipose-derived stem cells (ASCs) within a hydrogel matrix was studied as a potential means to enhance ASC chondrogenesis in the development of a cell-based therapeutic strategy for the regeneration of partial thickness chondral defects. A photopolymerizable N-methacrylate glycol chitosan (MGC) was employed to form an in situ gel used to encapsulate microspheres loaded with bone morphogenetic protein 6 (BMP-6) and transforming growth factor-β3 (TGF-β3) with human ASCs. ASC viability and retention were enhanced when the Young's modulus of the MGC ranged between 225 and 380 kPa. Grafting an RGD-containing peptide onto the MGC backbone (RGD-MGC) improved ASC viability within the gels, remaining at greater than 90% over 14 days in culture. The effects of BMP-6 and TGF-β3 released from the polymer microspheres on ASC chondrogenesis were assessed, and the level of differentiation was compared to ASCs in control gels containing nongrowth factor-loaded microspheres cultured with and without the growth factors supplied in the medium. There was enhanced expression of chondrogenic markers at earlier time points when the ASCs were induced with the sustained and local release of BMP-6 and TGF-β3 from the microspheres. More specifically, the normalized glycosaminoglycan and collagen type II protein expression levels were significantly higher than in the controls. In addition, the ratio of collagen type II to type I was significantly higher in the microsphere delivery group and increased over time. End-point RT-PCR analysis supported that there was a more rapid induction and enhancement of ASC chondrogenesis in the controlled release group. Interestingly, in all of the assays, there was evidence of chondrogenic differentiation when the ASCs were cultured in the gels in the absence of growth factor stimulation. Overall, the co-delivery of growth-factor-loaded microspheres and ASCs in RGD-modified MGC gels successfully induced ASC chondrogenesis and is a promising strategy for cartilage repair.

Quantitative approaches to detect donor and passage differences in adipogenic potential and clonogenicity in human bone marrow-derived mesenchymal stem cells

Bone marrow-derived multipotent stromal cells (MSCs), also known as mesenchymal stem cells, have great promise due to their capacity for tri-lineage differentiation and immunosuppressive properties, which allows for their allogeneic use and ultimately may allow for treatment of many diseases. MSCs will require extensive expansion and passaging to obtain cells in sufficient numbers necessary for cell therapies. MSCs from many donors could potentially be used. Because of this, there is a need to understand the role of passaging and donor differences on differentiation capacity using quantitative approaches. Here, we evaluated MSCs from two donors (noted as PCBM1632 and PCBM1641 by the manufacturer) at tissue culture passages 3, 5, and 7. We used a colony forming unit (CFU) assay and limiting dilution to quantify clonogenicity and precursor frequency during adipogenesis, and quantitative real-time-polymerase chain reaction for adipogenic markers to evaluate changes on a gene expression level. Further, we observed changes in cell size, and we sorted small and large populations to evaluate size-related adipogenic potential. While the adipogenic precursor frequency of ∼1 in 76 cells remained similar through passages for cells from PCBM1641, we found a large decrease in the adipogenic potential of MSCs from PCBM1632, with 1 in 2035 cells being capable of differentiating into an adipocyte at passage 7. MSCs from both donors showed an increase in cell diameter with increasing passage, which correlates with a decrease in clonogenicity by CFU analysis. We also measured adipose lineage gene expression following induction of adipocyte differentiation. Expression of these genes decreased with passage number for MSCs from PCBM1632 and correlated with the decrease in adipogenic potential by passage 7. In contrast, MSCs from PCBM1641 showed increased expression of these genes with increasing passage. We have shown that several quantitative assays can detect differences in MSC differentiation capacity, clonogenicity, and cell size between donors and passages. These quantitative methods are useful to assess the quality of MSCs.

Extracellular matrix deposition and scaffold biodegradation in an in vitro three-dimensional model of bone by X-ray computed microtomography

The development of an in vitro model of bone and the optimization of tools for determining the biological processes occurring during bone repair remains a major goal in the field of bone tissue engineering. Recently, a model based on a three-dimensional co-culture of osteoblasts and osteoclast precursors in Skelite(TM) scaffolds was developed. Although induction of osteoblast and osteoclast differentiation was observed, a complete evaluation of bone deposition and biodegradation processes was missing due to technical limitations. In the current study, both X-ray computed microtomography and histological analysis were used to monitor these two key biological processes in the same in vitro model. Either osteoblasts or a combination of osteoblasts and osteoclasts were seeded on Skelite(TM) scaffolds. Scaffold biodegradation and increased bone deposition together with a more organized extracellular matrix were observed in the co-cultures, highlighting the role of osteoclasts in the determination and regulation of bone deposition. Results confirmed the potential and relevance of co-culturing osteoblasts and osteoclasts to resemble native tissue. The combination of X-ray computed microtomography and histology presented in this study could be useful in future studies for the validation and development of new in vitro culture systems for bone tissue engineering.

Cell-based therapy for prevention and reversal of myocardial remodeling

Although pharmacological and interventional advances have reduced the morbidity and mortality of ischemic heart disease, there is an ongoing need for novel therapeutic strategies that prevent or reverse progressive ventricular remodeling following myocardial infarction, the process that forms the substrate for ventricular failure. The development of cell-based therapy as a strategy to repair or regenerate injured tissue offers extraordinary promise for a powerful anti-remodeling therapy. In this regard, the field of cell therapy has made major advancements in the past decade. Accumulating data from preclinical studies have provided novel insights into stem cell engraftment, differentiation, and interactions with host cellular elements, as well as the effectiveness of various methods of cell delivery and accuracy of diverse imaging modalities to assess therapeutic efficacy. These findings have in turn guided rationally designed translational clinical investigations. Collectively, there is a growing understanding of the parameters that underlie successful cell-based approaches for improving heart structure and function in ischemic and other cardiomyopathies.

Control of mesenchymal lineage progression by microRNAs targeting skeletal gene regulators Trps1 and Runx2

Multiple microRNAs (miRNAs) that target the osteogenic Runt-related transcription factor 2 (RUNX2) define an interrelated network of miRNAs that control osteoblastogenesis. We addressed whether these miRNAs have functional targets beyond RUNX2 that coregulate skeletal development. Here, we find that seven RUNX2-targeting miRNAs (miR-23a, miR-30c, miR-34c, miR-133a, miR-135a, miR-205, and miR-217) also regulate the chondrogenic GATA transcription factor tricho-rhino-phalangeal syndrome I (TRPS1). Although the efficacy of each miRNA to target RUNX2 or TRPS1 differs in osteoblasts and chondrocytes, each effectively blocks maturation of precommitted osteoblasts and chondrocytes. Furthermore, these miRNAs can redirect mesenchymal stem cells into adipogenic cell fate with concomitant up-regulation of key lineage-specific transcription factors. Thus, a program of multiple miRNAs controls mesenchymal lineage progression by selectively blocking differentiation of osteoblasts and chondrocytes to control skeletal development.

Increased differentiation capacity of bone marrow-derived mesenchymal stem cells in aquaporin-5 deficiency

Mesenchymal stem cells (MSCs) are adult stem cells with a self-renewal and multipotent capability and express extensively in multitudinous tissues. We found that water channel aquaporin-5 (AQP5) is expressed in bone marrow-derived MSCs (BMMSCs) in the plasma membrane pattern. BMMSCs from AQP5(-/-) mice showed significantly lower plasma membrane water permeability than those from AQP5(+/+) mice. In characterizing the cultured BMMSCs from AQP5(-/-) and AQP5(+/+) mice, we found no obvious differences in morphology and proliferation between the 2 genotypes. However, the multiple differentiation capacity was significantly higher in AQP5(-/-) than AQP5(+/+) BMMSCs as revealed by representative staining by Oil Red O (adipogenesis); Alizarin Red S and alkaline phosphatase (ALP; osteogenesis); and type II collagen and Safranin O (chondrogenesis) after directional induction. Relative mRNA expression levels of 3 lineage differentiation markers, including PPARγ2, C/EBPα, adipsin, collagen 1a, osteopontin, ALP, collagen 11a, collagen 2a, and aggrecan, were significantly higher in AQP5(-/-) -differentiating BMMSCs, supporting an increased differentiation capacity of AQP5(-/-) BMMSCs. Furthermore, a bone-healing process was accelerated in AQP5(-/-) mice in a drill-hole injury model. Mechanistic studies indicated a significantly lower apoptosis rate in AQP5(-/-) than AQP5(+/+) BMMSCs. Apoptosis inhibitor Z-VAD-FMK increased the differentiation capacity to a greater extent in AQP5(+/+) than AQP5(-/-) BMMSCs. We conclude that AQP5-mediated high plasma membrane water permeability enhances the apoptosis rate of differentiating BMMSCs, thus decreasing their differentiation capacity. These data implicate AQP5 as a novel determinant of differentiation of BMMSCs and therefore a new molecular target for regulating differentiation of BMMSCs during tissue repair and regeneration.

Spatial and temporal localization of WNT signaling proteins in a mouse model of distraction osteogenesis

While the surgical procedure of distraction osteogenesis (DO) is very successful in the treatment of orthopedic conditions, its major limitation of slow bone formation in the distracted gap has prompted numerous attempts to understand and accelerate this slow bone formation. Interestingly, WNT/FZD signaling has been identified as a critical pathway in mediating bone formation and regeneration but has not yet been studied in the context of DO. The objective of this study was to determine the spatial and temporal localization of endogenous WNT signaling proteins at various times of bone formation in a wild-type mouse model of DO. In this study, the DO protocol performed on mice consisted of three phases: latency (5 days), distraction (12 days), and consolidation (34 days). Our immunohistochemical findings of distracted bone specimens show an increased expression of WNT ligands (WNT4 and WNT10A), receptors (FZD1 and 2, LRP5 and 6), β-catenin, and pathway antagonizers (DKK1; CTBP1 and 2; sFRP1, 2, and 4) during the distraction phase, which were then down-regulated during consolidation. This is the first published report to show an activation of the WNT pathway in DO and could help identify WNT as a potential therapeutic target in accelerating bone regeneration during DO.

Human mesenchymal stem cell position within scaffolds influences cell fate during dynamic culture

Cell-based tissue engineering is limited by the size of cell-containing constructs that can be successfully cultured in vitro. This limit is largely a result of the slow diffusion of molecules such as oxygen into the interior of three-dimensional scaffolds in static culture. Bioreactor culture has been shown to overcome these limits. In this study we utilize a tubular perfusion system (TPS) bioreactor for the three-dimensional dynamic culture of human mesenchymal stem cells (hMSCs) in spherical alginate bead scaffolds. The goal of this study is to examine the effect of shear stress in the system and then quantify the proliferation and differentiation of hMSCs in different radial annuli of the scaffold. Shear stress was shown to have a temporal effect on hMSC osteoblastic differentiation with a strong correlation of shear stress, osteopontin, and bone morphogenic protein-2 occurring on day 21, and weaker correlation occurring at early timepoints. Further results revealed an approximate 2.5-fold increase in cell number in the inner annulus of TPS cultured constructs as compared to statically cultured constructs after 21 days. This result demonstrated a nutrient transfer limitation in static culture which can be mitigated by dynamic culture. A significant increase (P < 0.05) in mineralization in the inner and outer annuli of bioreactor cultured 4 mm scaffolds occurred on day 21 with 79 ± 29% and 53 ± 25% mineralization area, respectively, compared to 6 ± 4% and 19 ± 6% mineralization area, respectively, in inner and outer annuli of 4 mm statically cultured scaffolds. Surprising lower mineralization area was observed in 2 mm bioreactor cultured beads which had the highest levels of proliferation. These results may demonstrate a relationship between scaffold position and stem cell fate. In addition the decreased proliferation and matrix production in statically cultured scaffolds compared to bioreactor cultured constructs demonstrate the need for bioreactor systems and the effectiveness of the TPS bioreactor in promoting hMSC proliferation and differentiation in three-dimensional scaffolds.

Pyrvinium, a potent small molecule Wnt inhibitor, increases engraftment and inhibits lineage commitment of mesenchymal stem cells (MSCs)

We and others have found that Wnt signaling inhibition is important in mesenchymal stem cell (MSC) self-renewal. Pyrvinium was identified as a potent Wnt inhibitor in a chemical screen for small molecules. In the present study, we hypothesized that pyrvinium will enhance MSC self-renewal to improve the clinical efficacy of MSC therapy. Pyrvinium increased MSC proliferation in vitro while inhibiting their osteogenic and chondrogenic lineage commitment by reducing cytoplasmic β-catenin. Although MSCs are a promising target for cell therapy, strategies to enhance their survival and maintain their stemness in the wounded area are essential. Using an in vivo model of granulation tissue formation, we demonstrated that pyrvinium enhanced long-term MSC engraftment. Pyrvinium-treated MSC-generated granulation tissue also demonstrated less ectopic differentiation into bone or cartilage. This study highlights the potential of using a therapeutic Wnt inhibitor to enhance MSC-driven regenerative therapy.

Proteomics approaches in the identification of molecular signatures of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are undifferentiated, multi-potent stem cells with the ability to renew. They can differentiate into many types of terminal cells, such as osteoblasts, chondrocytes, adipocytes, myocytes, and neurons. These cells have been applied in tissue engineering as the main cell type to regenerate new tissues. However, a number of issues remain concerning the use of MSCs, such as cell surface markers, the determining factors responsible for their differentiation to terminal cells, and the mechanisms whereby growth factors stimulate MSCs. In this chapter, we will discuss how proteomic techniques have contributed to our current knowledge and how they can be used to address issues currently facing MSC research. The application of proteomics has led to the identification of a special pattern of cell surface protein expression of MSCs. The technique has also contributed to the study of a regulatory network of MSC differentiation to terminal differentiated cells, including osteocytes, chondrocytes, adipocytes, neurons, cardiomyocytes, hepatocytes, and pancreatic islet cells. It has also helped elucidate mechanisms for growth factor-stimulated differentiation of MSCs. Proteomics can, however, not reveal the accurate role of a special pathway and must therefore be combined with other approaches for this purpose. A new generation of proteomic techniques have recently been developed, which will enable a more comprehensive study of MSCs.

Enhanced chondrogenic marker expression of human mesenchymal stem cells by interaction with both TGF-β3 and hyaluronic acid

This study was designed to evaluate the additive effects of transforming growth factor-beta3 (TGF-β3) and hyaluronic acid (HA) on chondrogenic differentiation of human mesenchymal stem cells (hMSCs). The hMSCs were cultured on collagen type I-, HA-, or fibronectin-coated cell culture dishes with or without TGF-β3 added to the culture medium. Four weeks after cell culture, chondrogenic differentiation of hMSCs was determined by evaluating the expression of cartilage-specific markers using real-time polymerase chain reaction, immunocytochemistry, and Western blot analysis. hMSCs cultured on HA-coated dishes with TGF-β3 supplementation revealed a prominent increase in collagen type II, aggrecan, and Sox9. When hMSCs were cultured without TGF-β3 supplementation, only hMSCs cultured on HA-coated dishes showed prominent expression of the cartilage-specific markers. This study shows that chondrogenic differentiation of hMSCs can be enhanced additively by interactions with both a specific cell-adhesion matrix and a soluble growth factor.

Potential clinical applications of adult human mesenchymal stem cell (Prochymal®) therapy

In vitro, in vivo animal, and human clinical data show a broad field of application for mesenchymal stem cells (MSCs). There is overwhelming evidence of the usefulness of MSCs in regenerative medicine, tissue engineering, and immune therapy. At present, there are a significant number of clinical trials exploring the use of MSCs for the treatment of various diseases, including myocardial infarction and stroke, in which oxygen suppression causes widespread cell death, and others with clear involvement of the immune system, such as graft-versus-host disease, Crohn’s disease, and diabetes. With no less impact, MSCs have been used as cell therapy to treat defects in bone and cartilage and to help in wound healing, or in combination with biomaterials in tissue engineering development. Among the MSCs, allogeneic MSCs have been associated with a regenerative capacity due to their unique immune modulatory properties. Their immunosuppressive capability without evidence of immunosuppressive toxicity at a global level define their application in the treatment of diseases with a pathogenesis involving uncontrolled activity of the immune system. Until now, the limitation in the number of totally characterized autologous MSCs available represents a major obstacle to their use for adult stem cell therapy. The use of premanufactured allogeneic MSCs from controlled donors under optimal conditions and their application in highly standardized clinical trials would lead to a better understanding of their real applications and reduce the time to clinical translation.

Mesenchymal stem cells: biology, pathophysiology, translational findings, and therapeutic implications for cardiac disease

Mesenchymal stem cells (MSCs) are a prototypical adult stem cell with capacity for self-renewal and differentiation with a broad tissue distribution. Initially described in bone marrow, MSCs have the capacity to differentiate into mesoderm- and nonmesoderm-derived tissues. The endogenous role for MSCs is maintenance of stem cell niches (classically the hematopoietic), and as such, MSCs participate in organ homeostasis, wound healing, and successful aging. From a therapeutic perspective, and facilitated by the ease of preparation and immunologic privilege, MSCs are emerging as an extremely promising therapeutic agent for tissue regeneration. Studies in animal models of myocardial infarction have demonstrated the ability of transplanted MSCs to engraft and differentiate into cardiomyocytes and vasculature cells, recruit endogenous cardiac stem cells, and secrete a wide array of paracrine factors. Together, these properties can be harnessed to both prevent and reverse remodeling in the ischemically injured ventricle. In proof-of-concept and phase I clinical trials, MSC therapy improved left ventricular function, induced reverse remodeling, and decreased scar size. This article reviews the current understanding of MSC biology, mechanism of action in cardiac repair, translational findings, and early clinical trial data of MSC therapy for cardiac disease.

SOX2 has a crucial role in the lineage determination and proliferation of mesenchymal stem cells through Dickkopf-1 and c-MYC

SOX2 is a well-known core transcription factor in embryonic stem cells (ESCs) and has an important role in the maintenance of pluripotency. Recently, SOX2 expression has also been reported in adult stem cells (ASCs), but the role of SOX2 in ASCs remains unknown. In this study, we examined the molecular mechanisms of SOX2 in human mesenchymal stem cells (hMSCs), a type of ASCs, by performing inhibition studies. SOX2 inhibition resulted in altered cell growth and differentiation capabilities. These changes coincided with a decrease in Dickkopf-1 (DKK1), a soluble inhibitor of WNT signaling. Chromatin immunoprecipitation and luciferase assays showed that SOX2 binds to DKK1 and has a positive regulatory role in transcription. The enforced expression of DKK1 in SOX2-inhibited hMSCs reversed the differentiation deformities, but could not abrogate the cell proliferation defect. Proliferation was regulated by c-MYC, whose expression can also be controlled by SOX2. Our study shows that SOX2 directly regulates DKK1 expression and, as a consequence, determines the differentiation lineage of hMSCs. Moreover, SOX2 also regulates proliferation by affecting c-MYC. Therefore, these results suggest that SOX2 might have a specific function by regulating DKK1 and c-MYC in the differentiation and growth of ASCs, which is separate from its roles in ESCs.

TCDD disrupts hypural skeletogenesis during medaka embryonic development

Defective bone and cartilage development account for a large number of human birth defects annually. Normal skeletogenesis involves cartilage development in early morphogenesis through a highly coordinated and orchestrated series of events involving commitment and differentiation of mesenchymal cells to chondrocytes followed by a highly programmed process of structural maturation. Recent developmental studies with laboratory model fish demonstrate that exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) results in cartilage and skeletal abnormalities. In this study, we exposed embryonic medaka to TCDD to induce developmental modification(s) of both cartilage and bone formation. Emphasis is placed on cell-rich hyaline cartilage of the hypural plate where both chondrogenesis and osteogenesis are impaired by TCDD exposure. In this model, TCDD exposure results in a concentration-dependent impairment of mesenchymal cell recruitment, chondrocyte cell proliferation, differentiation, and progression to hypertrophy. Gene expression of ColA2, a marker of chondrocyte terminal differentiation in hypural structures, is markedly attenuated consistent with hypural dysmorphogenesis. Assessment of hypural structure using a transgenic medaka expressing mCherry under control of the osterix promoter illustrated significant attenuation in expression of the osteoblast gene marker and lack of formation of a calcified perichondral sheath surrounding hypural anlage. Overall, these studies illustrate that TCDD impacts terminal differentiation and growth of cartilage and bone in axial structures not likely derived from neural crest progenitors in medaka hypurals.

Hyaluronan and fibrin biomaterial as scaffolds for neuronal differentiation of adult stem cells derived from adipose tissue and skin

Recently, we have described a simple protocol to obtain an enriched culture of adult stem cells organized in neurospheres from two post-natal tissues: skin and adipose tissue. Due to their possible application in neuronal tissue regeneration, here we tested two kinds of scaffold well known in tissue engineering application: hyaluronan based membranes and fibrin-glue meshes. Neurospheres from skin and adipose tissue were seeded onto two scaffold types: hyaluronan based membrane and fibrin-glue meshes. Neurospheres were then induced to acquire a glial and neuronal-like phenotype. Gene expression, morphological feature and chromosomal imbalance (kariotype) were analyzed and compared. Adipose and skin derived neurospheres are able to grow well and to differentiate into glial/neuron cells without any chromosomal imbalance in both scaffolds. Adult cells are able to express typical cell surface markers such as S100; GFAP; nestin; βIII tubulin; CNPase. In summary, we have demonstrated that neurospheres isolated from skin and adipose tissues are able to differentiate in glial/neuron-like cells, without any chromosomal imbalance in two scaffold types, useful for tissue engineering application: hyaluronan based membrane and fibrin-glue meshes.

Modulation of osteogenic differentiation in hMSCs cells by submicron topographically-patterned ridges and grooves

Recent studies have shown that nanoscale and submicron topographic cues modulate a menu of fundamental cell behaviors, and the use of topographic cues is an expanding area of study in tissue engineering. We used topographically-patterned substrates containing anisotropically ordered ridges and grooves to investigate the effects of topographic cues on mesenchymal stem cell morphology, proliferation, and osteogenic differentiation. We found that human mesenchymal stem cells cultured on 1400 or 4000 nm pitches showed greater elongation and alignment relative to 400 nm pitch or planar control. Cells cultured on 400 nm pitch demonstrated significant increases in RUNX2 and BGLAP expression relative to cells cultured on 1400 or 4000 nm pitch or planar control. Four-hundred nanometer pitch enhanced extracellular calcium deposition. Cells cultured in osteoinductive medium revealed combinatory effects of topography and chemical cues on 400 nm pitch as well as up-regulation of expression of ID1, a target of the BMP pathway. Our data demonstrate that a specific size scale of topographic cue promotes osteogenic differentiation with or without osteogenic agents. These data demonstrate that the integration of topographic cues may be useful for the fabrication of orthopedic implants.

The primary cilium as a biomarker in the hypoxic adaptation of bone marrow-derived mesenchymal stromal cells: a role for the secreted frizzled-related proteins

A pivotal role in guiding mesenchymal stem cell (MSC) differentiation has recently been attributed to the primary cilium. This solitary, non-motile microtubule-based organelle emerging from the cell surface acts as a sensorial membrane structure reflecting developmental and adaptive processes associated with pathologies including human cystic kidney disease, skeletal malformations, obesity and cancer. Given that the intrinsic hypoxic adaptation of MSC remains poorly understood within ischemic tissues or hypoxic tumours, we questioned whether the hypoxia inducible factor-1α (HIF-1α) might be a downstream effector regulating cilium maintenance. We show that murine bone marrow-derived MSC cultured under hypoxic conditions (1.2% O(2)) lose their primary cilia in a time-dependent manner. Gene silencing of HIF-1α prevented cilia loss in hypoxic cultures, and generation of MSC expressing a constitutively active HIF-1α (MSC-HIF) was found to decrease primary cilium formation. A Wnt pathway-related gene expression array was also performed on MSC-HIF and indicated that the secreted Frizzled-related proteins (sFRP)-1, -3 and -4 were down-regulated, while sFRP-2 was up-regulated. Overexpression of recombinant sFRP-2 or gene silencing of sFRP-1, -3 and -4 in MSC led to primary cilium disruption. These results indicate a molecular signalling mechanism for the hypoxic disruption of the primary cilium in MSC involving an HIF-1α/sFRP axis. This mechanism contributes to our understanding of the adaptive processes possibly involved in the oncogenic transformation and tumour-supporting potential of MSC. Our current observations also open up the possibility for the primary cilia to serve as a biomarker in MSC adaptation to low oxygen tension within (patho)physiological microenvironments.

Hypoxia induces osteogenesis-related activities and expression of core binding factor α1 in mesenchymal stem cells

Mesenchymal stem sells (MSCs) have received much attention in the field of bone tissue engineering due to their biological capability to differentiate into osteogenic lineage cells. Hypoxia-inducible factor 1alpha (HIF-1α) plays an important role in the MSC-related bone regeneration during hypoxia, while core binding factor alpha 1 (Cbfα1) is a transcription regulator that is involved in the chondrocyte differentiation and ossification. In the present study, we investigated the effects of hypoxia on biological capability of MSCs. MSCs were isolated from adult rabbit bone marrow, and were cultured in vitro under normoxia (air with 5% CO(2)) or hypoxia (5% CO(2) and 95% N(2)). The proliferation of MSCs, alkaline phosphatase (ALP) activity, and production of collagens type I and type III (Col I/III) were examined. The expression levels of HIF-1α and Cbfα1 were measured by real-time PCR and western blot analyses. We found that hypoxia significantly induced the proliferation of MSCs and increased ALP activity and the production of Col I/III. Moreover, hypoxia increased the expression of Cbfα1 mRNA after 12 h, whereas the expression of HIF-1α mRNA was increased after 1 h of hypoxia. Knockdown of HIF-1α expression with a small interfering RNA significantly increased the expression levels of Cbfα1 protein either under the normoxia or hypoxia condition. Our results indicate that hypoxia enhances MSCs to differentiate into osteogenic lineage cells and suggest that Cbfα1 may be negatively regulated by HIF-1α.

Intracoronary transplantation of genetically modified mesenchymal stem cells, a novel method to close muscular ventricular septal defects

Muscular ventricular septal defects remain a challenge despite the progress in surgical and interventional closure of ventricular septal defects. Our hypothesis was inspired by the fact that more than two thirds of children with muscular ventricular septal defects experienced spontaneous closure. Therefore, we intend to induce the spontaneous closure of muscular ventricular septal defects by means of targeted intracoronary injection of mesenchymal stem cells which are genetically modified to enhance myocardial hypertrophy. The transplantation of bone marrow derived cells has been observed to be effective in improving tissue recovery and ameliorating cardiac function in patients and animal models with ischemic heart disease, acute myocarditis and dilated cardiomyopathy. We expect that the targeted intracoronary transplantation of genetically modified mesenchymal stem cells could enhance the tissue generation and myocardial hypertrophy simultaneously, which may lead to the closure of muscular ventricular septal defects in a way that imitate the spontaneous closure of ventricular septal defects.

Mesenchymal stem cell assays and applications

Research on mesenchymal stem cells (MSC) is progressing with increasing popularity. Currently there are a significant number of clinical trials exploring the use of MSCs for the treatment of various diseases including graft-versus-host disease, Crohn's disease, myocardial infarction, stroke, bone defects, diabetes, and wound repair (www.-clinicaltrials.gov). At the same time, there are questions associated with MSCs in terms of their isolation, culture expansion, phenotype, multipotential differentiation, and transplantation efficiency. This chapter outlines the current status of the field and emphasizes the need for clearly defined protocols to better define the function and use of MSCs in cell therapy.