Extracellular matrix protein mediated regulation of the osteoblast differentiation of bone marrow derived human mesenchymal stem cells

The biomimetic approach of tissue engineering exploits the favorable properties of the extracellular matrix (ECM), to achieve better scaffold performance and tissue regeneration. ECM proteins regulate cell adhesion and differentiation through integrin mediated signal transduction. In the present study, we have examined the role of ECM proteins such as collagen type I, fibronectin, laminin and vitronectin in regulating the proliferation and osteogenic differentiation of bone marrow derived human mesenchymal stem cells (hMSCs). hMSCs were grown on selected ECM protein treated tissue culture plates. The growth kinetics was assessed by calculating the doubling time of the cells on different ECM treated plates. The cells were directed to osteoblast lineage by growing them in osteogenic induction media for 21 day. Differentiation was evaluated at different time points by osteoblast differentiation associated gene expression, alkaline phosphatase (ALP) activity, histochemical staining for mineralized matrix and calcium quantification. The doubling time of hMSCs cultured on collagen type I was significantly low, which was followed by laminin and fibronectin treated plates. However, doubling time of hMSCs cultured on vitronectin treated plate was not significantly different than that of the untreated control. High ALP gene (ALPL) expression and associated enhancement of mineralization were observed on collagen type I, fibronectin and vitronectin treated plates. Collagen type I showed early onset of mineralization with high ALP activity and up-regulation of osteopontin, ALPL, bone sialoprotein and osteocalcin genes. Vitronectin also up-regulated these genes and showed the highest amount of calcium in the secreted mineral matrix. Therefore, we conclude that, ECM proteins indeed modified the growth patterns and induced the osteoblast differentiation of hMSCs. Our findings have significant implication for bone tissue engineering applications.     

Chondroitin sulfate and dynamic loading alter chondrogenesis of human MSCs in PEG hydrogels

While biochemical and biomechanical cues are known to play important roles in directing stem cell differentiation, there remains little known regarding how these inextricably linked biological cues impact the differentiation fate of human marrow stromal cells (hMSCs). This study investigates the chondrogenic differentiation potential of hMSCs when encapsulated in a three dimensional (3D) hydrogel and exposed to a biochemical cue, chondroitin sulfate (ChS), a biomechanical cue, dynamic loading, and their combination. hMSCs were encapsulated in bioinert poly(ethylene glycol) (PEG) hydrogels only, PEG hydrogels modified with covalently incorporated methacrylated ChS and cultured under free swelling conditions or subjected to delayed intermittent dynamic loading for 2 weeks. The 3D hydrogel environment led to the expression of chondrogenic genes (SOX9) and proteins (aggrecan and collagen II), but also upregulated hypertrophic genes (RUNX2 and Col X mRNA) and proteins (collagen X), while the application of loading generally led to a downregulation in chondrogenic proteins (collagen II). The presence of ChS led to elevated levels of aggrecan, but also collagen I, protein expression and when combined with dynamic loading downregulated, but did not suppress, hypertrophic genes (Col X and RUNX2) and collagen I protein expression. Taken together, this study demonstrates that while the 3D environment induces early terminal differentiation during chondrogenesis of hMSCs, the incorporation of ChS into PEG hydrogels may slow the terminal differentiation process down the hypertrophic lineage particularly when dynamic loading is applied. Biotechnol. Bioeng. 2012; 109: 2671–2682. © 2012 Wiley Periodicals, Inc.     

miR-335 orchestrates cell proliferation, migration and differentiation in human mesenchymal stem cells

In spite of the extensive potential of human mesenchymal stem cells (hMSCs) in cell therapy, little is known about the molecular mechanisms that regulate their therapeutic properties. We aimed to identify microRNAs (miRNAs) involved in controlling the transition between the resting and reparative phenotypes of hMSCs, hypothesizing that these miRNAs must be present in the undifferentiated cells and downregulated to allow initiation of distinct activation/differentiation programs. Differential miRNA expression analyses revealed that miR-335 is significantly downregulated upon hMSC differentiation. In addition, hMSCs derived from a variety of tissues express miR-335 at a higher level than human skin fibroblasts, and overexpression of miR-335 in hMSCs inhibited their proliferation and migration, as well as their osteogenic and adipogenic potential. Expression of miR-335 in hMSCs was upregulated by the canonical Wnt signaling pathway, a positive regulator of MSC self-renewal, and downregulated by interferon-γ (IFN-γ), a pro-inflammatory cytokine that has an important role in activating the immunomodulatory properties of hMSCs. Differential gene expression analyses, in combination with computational searches, defined a cluster of 62 putative target genes for miR-335 in hMSCs. Western blot and 3'UTR reporter assays confirmed RUNX2 as a direct target of miR-335 in hMSCs. These results strongly suggest that miR-335 downregulation is critical for the acquisition of reparative MSC phenotypes.     

The promyelotic leukemia zinc finger promotes osteoblastic differentiation of human mesenchymal stem cells as an upstream regulator of CBFA1

Ossification of the posterior longitudinal ligament of the spine (OPLL) is the leading cause of myelopathy in Japan and is diagnosed by ectopic bone formation in the paravertebral ligament. OPLL is a systemic high bone mass disease with a strong genetic background. To detect genes relevant to the pathogenesis of OPLL, we performed a cDNA microarray analysis of systematic gene expression profiles during the osteoblastic differentiation of ligament cells from OPLL patients (OPLL cells), patients with a disorder called ossification of yellow ligament (OYL), and non-OPLL controls together with human mesenchymal stem cells (hMSCs) after stimulating them with osteogenic differentiation medium (OS). Twenty-four genes were up-regulated during osteoblastic differentiation in OPLL cells. Zinc finger protein 145 (promyelotic leukemia zinc finger or PLZF) was one of the highly expressed genes during osteoblastic differentiation in all the cells examined. We investigated the roles of PLZF in the regulation of osteoblastic differentiation of hMSCs and C2C12 cells. Small interfering RNA-mediated gene silencing of PLZF resulted in a reduction in the expression of osteoblast-specific genes such as the alkaline phosphatase, collagen 1A1 (Col1a1), Runx2/core-binding factor 1 (Cbfa1), and osteocalcin genes, even in the presence of OS in hMSCs. The expression of PLZF was unaffected by the addition of bone morphogenetic protein 2 (BMP-2), and the expression of BMP-2 was not affected by PLZF in hMSCs. In C2C12 cells, overexpression of PLZF increased the expression of Cbfa1 and Col1a1; on the other hand, the overexpression of CBFA1 did not affect the expression of Plzf. These findings indicate that PLZF plays important roles in early osteoblastic differentiation as an upstream regulator of CBFA1 and thereby might participate in promoting the ossification of spinal ligament cells in OPLL patients.     

Differentially expressed genes in endothelial differentiation

By screening differentially expressed genes in mouse embryonic stem (ES) cells by subtractive hybridization, we identified three conserved but uncharacterized genes encoding bromodomain containing 3 (BRD3), protein lysine methyltransferase (PLM), and kelch domain containing 2 (KLHDC2), which were downregulated during endothelial differentiation. An RNA blot study showed that these genes were markedly expressed in undifferentiated ES cells, whereas the expression was reduced upon endothelial differentiation; a study of mouse endothelium showed a significant reduction in the expression of BRD3. A study of human BRD3, located on chromosome 9 at q34, a region susceptible to genomic rearrangement, showed an altered expression in 4 of 12 patients with bladder cancer, compared with adjacent noncancerous tissues. Taken together with the result of siRNA inhibition showing the positive regulation of cell proliferation by BRD3, it is suggested that this molecule plays a role in allowing cells to enter the proliferative phase of the angiogenic process.     

The microRNA expression profiles of mouse mesenchymal stem cell during chondrogenic differentiation

MicroRNAs are potential key regulators in mesenchymal stem cells chondrogenic differentiation. However, there were few reports about the accurate effects of miRNAs on chondrogenic differentiation. To investigate the mechanisms of miRNAs-mediated regulation during the process, we performed miRNAs microarray in MSCs at four different stages of TGF-β3-induced chondrogenic differentiation. We observed that eight miRNAs were significantly up-regulated and five miRNAs were downregulated. Interestingly, we found two miRNAs clusters, miR-143/145 and miR-132/212, kept on down-regulation in the process. Using bioinformatics approaches, we analyzed the target genes of these differentially expressed miRNAs and found a series of them correlated with the process of chondrogenesis. Furthermore, the qPCR results showed that the up-regulated (or down-regulated) expression of miRNAs were inversely associated with the expression of predicted target genes. Our results first revealed the expression profiles of miRNAs in chondrogenic differentiation of MSCs and provided a new insight on complicated regulation mechanisms of chondrogenesis.     

FGF-2 increases osteogenic and chondrogenic differentiation potentials of human mesenchymal stem cells by inactivation of TGF-β signaling

Human mesenchymal stem cells (hMSCs) are able to self-replicate and differentiate into a variety of cell types including osteoblasts, chondrocytes, adipocytes, endothelial cells, and muscle cells. It was reported that fibroblast growth factor-2 (FGF-2) increased the growth rate and multidifferentiation potentials of hMSCs. In this study, we investigated the genes involved in the promotion of osteogenic and chondrogenic differentiation potentials of hMSCs in the presence of FGF-2. hMSCs were maintained in the medium with FGF-2. hMSCs were harvested for the study of osteogenic or chondrogenic differentiation potential after 15 days’ culture. To investigate osteogenic differentiation, the protein levels of alkaline phosphatase (ALP) and the mRNA expression levels of osteocalcin were measured after the induction of osteogenic differentiation. Moreover, the investigation for chondrogenic differentiation was performed by measuring the mRNA expression levels of type II and type X collagens after the induction of chondrogenic differentiation. The expression levels of ALP, type II collagen, and type X collagen of hMSCs cultured with FGF-2 were significantly higher than control. These results suggested that FGF-2 increased osteogenic and chondrogenic differentiation potentials of hMSCs. Furthermore, microarray analysis was performed after 15 days’ culture in the medium with FGF-2. We found that the overall insulin-like growth factor-I (IGF-I) and transforming growth factor-β (TGF-β) signaling pathways were inactivated by FGF-2. These results suggested that the inactivation of IGF-I and TGF-β signaling promotes osteogenic and chondrogenic differentiation potential of hMSCs in the presence of FGF-2.     

Identification of genes regulated by nanog which is involved in ES cells pluripotency and early differentiation

Nanog plays an important role in embryonic stem (ES) cells pluripotency and self-renewal, yet the precise mechanism through which Nanog accomplishes this important function remains unclear. To understand comprehensive molecular mechanism by which Nanog mediates, we identified genome-wide molecular changes upon silencing Nanog in ES cells by using microarray technology. In order to downregulate Nanog expression efficiently, four siRNAs were designed on the basis of the conserved Nanog sequence and their effects on the Nanog expression were tested. Among these four siRNAs, Nanog-siRNA-P1 was found to be most effective. Once Nanog was downregulated, ES cells underwent differentiation by showing morphological change and decreased proliferation rate. Microarray analysis was then used to identify the altered gene expression after Nanog was silenced. A series of differentially expressed genes due to reduced expression of Nanog was identified as Nanog-related genes. These genes identified here could provide insights into the roles of Nanog in ES cells self-renewal and early differentiation.     

Growth factor-defined culture medium for human mesenchymal stem cells

Human bone marrow-derived mesenchymal stem cells (hMSCs) are potential cellular sources of therapeutic stem cells as they have the ability to proliferate and differentiate into a wide array of mesenchymal cell types such as osteoblasts, chondroblasts and adipocytes. hMSCs have been used clinically to treat patients with graft vs. host disease, osteogenesis imperfect, or alveolar cleft, suggesting that transplantation of hMSCs is comparatively safe as a stem cell-based therapy. However, conventional culture medium for hMSCs contains fetal bovine serum (FBS). In the present study, we developed a growth factor-defined, serum-free medium for culturing hMSCs. Under these conditions, TGF-beta1 promoted proliferation of hMSCs. The expanded hMSC population expressed the human pluripotency markers SSEA-3, -4, NANOG, OCT3/4 and SOX2. Furthermore, double positive cells for SSEA-3 and a mesenchymal cell marker, CD105, were detected in the population. The potential to differentiate into osteoblasts and adipocytes was confirmed. This work provides a useful tool to understand the basic biological properties of hMSCs in culture.