Carbon nanotube array inducing osteogenic differentiation of human mesenchymal stem cells.

Carbon nanotubes (CNTs) are a kind of nanomaterials which have been shown a promising application for biomedicine. There are a lot of studies to use CNTs to induce the differentiation of mesenchymal stem cells (MSCs). However, the cellular behavior of MSCs on the top layer of CNT array was still not well understood. In this study, we evaluated the morphology, the gene expressions of the osteogenic differentiation related markers, and the gene expressions of collagen type II (Col II, a marker of chondrogenesis), PPARγ (a marker of adipogenesis) and scleraxis (SCX, a marker of tenogenesis) in human mesenchymal stem cells (hMSCs) cultured on multi-walled carbon nanotube (MWCNT) array. The effect of MWCNT array on the mineralization of hMSCs which were cultured in osteogenic differentiation medium (ODM) was further assayed. Our results showed that the hMSCs cultured on MWCNT array spread well, formed numerous spiral shaped cell colons and showed perinuclear morphology. Compared to hMSCs cultured on dish, the gene expression of osteocalcin (OCN) was increased while the gene expressions of collagen type II (Col II), PPARγ and scleraxis (SCX) were decreased in hMSCs which were cultured on MWCNT array without any differentiation factors. Furthermore, compared with hMSCs on dish, the gene expressions of collagen type I (Col I), osteocalcin (OCN), osteopontin (OPN) and RUNX2, and the mineralization of hMSCs on MWCNT array were enhanced when they were cultured in osteogenic differentiation medium (ODM). Our results indicated that MWCNT array was able to promote the osteogenesis of hMSCs.

MGF enhances tenocyte invasion through MMP-2 activity via the FAK-ERK1/2 pathway.

Tendon regeneration and healing requires tenocytes to move to the repair site followed by proliferation and synthesis of the extracellular matrix. A novel synthetic growth factor, mechano-growth factor (MGF), has been discovered to have positive roles in tissue repair through the improvement of cell proliferation and migration and the protection of cells against injury-induced apoptosis. However, it remains unclear whether MGF has the potential to accelerate tendon repair. In this study, using a transwell system, we found that MGF-C25E (a synthetic mechano-growth factor E peptide) significantly promotes tenocyte invasion, which was accompanied by the increased phosphorylation of focal adhesion kinase (FAK) and extracellular signal regulated kinase1/2 (ERK1/2) as well as the increased activity of matrix metalloproteinases-2 (MMP-2). The MMP-2 inhibitor OA-Hy blocked MGF-C25E-promoted tenocyte invasion. Inhibitors of FAK or ERK1/2 blocked MGF-C25E-promoted tenocyte invasion and MMP-2 activity as well. These results indicate that MGF-C25E promotes tenocyte invasion by increasing MMP-2 activity via the FAK-ERK1/2 signaling pathway. Taken together, our findings provide the first evidence that MGF-C25E enhances tenocyte invasion and indicate that it may serve as a potential repair material for promoting the healing and regeneration of injured tendons.

Cyclic mechanical stretching promotes migration but inhibits invasion of rat bone marrow stromal cells.

Bone marrow stromal cells (BMSCs, also broadly known as bone marrow-derived mesenchymal stem cells) are multipotent stem cells that have a self-renewal capacity and multilineage differentiation potential. Mechanical stretching plays a vital role in regulating the proliferation and differentiation of BMSCs. However, little is known about the effects of cyclic stretching on BMSC migration and invasion. In this study, using a custom-made cell-stretching device, we studied the effects of cyclic mechanical stretching on rat BMSC migration and invasion using a Transwell Boyden Chamber. The protein secretion of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) was detected by gelatin zymography, and the activation of focal adhesion kinase (FAK) and extracellular signal regulated kinase1/2 (ERK1/2) was measured by western blot. We found that cyclic mechanical stretching with 10% amplitude at 1Hz frequency for 8h promotes BMSC migration, but reduces BMSC invasion. FAK and ERK1/2 signals were activated in BMSCs after exposure to cyclic stretching. In the presence of the FAK phosphorylation blocker PF573228 or the ERK1/2 phosphorylation blocker PD98059, the cyclic-stretch-promoted migration of BMSCs was completely suppressed. On the other hand, cyclic mechanical stretching reduced the secretion of MMP-2 and MMP-9 in BMSCs, and PF573228 suppressed the cyclic-stretch-reduced secretion of MMP-2 and MMP-9. The decrease of BMSC invasion induced by mechanical stretching is partially restored by PF573228 but remained unaffected by PD98059. Taken together, these data show that cyclic mechanical stretching promotes BMSC migration via the FAK-ERK1/2 signalling pathway, but reduces BMSC invasion by decreasing secretion of MMP-2 and MMP-9 via FAK, independent of the ERK1/2 signal.

tLyP-1-conjugated Au-nanorod@SiO(2) core-shell nanoparticles for tumor-targeted drug delivery and photothermal therapy.

Mesoporous silica-coated Au nanorod (AuNR@SiO2) is one of the most important appealing nanomaterials for cancer therapy. The multifunctions of chemotherapy, photothermal therapy, and imaging of AuNR@SiO2 make it very useful for cancer therapy. In this study, AuNR@SiO2 was functionalized to deliver hydrophobic antitumor drug and to heat the targeted tumor with the energy of near-infrared (NIR). To carry out the function of targeting the tumor, tLyP-1, a kind of tumor homing and penetrating peptide, was engrafted to AuNR@SiO2. The fabricated AuNR@SiO2-tLyP-1 which was loaded with camptothecin (CPT) showed a robust, selective targeting and penetrating efficiency to Hela and MCF-7 cells and induced the death of these cells. When the micromasses of these AuNR@SiO2-tLyP-1 internalized cells were irradiated by NIR illumination, all the cells were killed instantaneously owing to the increased temperature caused by the surface plasma resonance (SPR) of the internalized AuNR@SiO2-tLyP-1. Moreover, the systematic toxicity of CPT-loaded AuNR@SiO2-tLyP-1 on human mesenchymal stem cells (hMSCs) was minimized, because the AuNR@SiO2-tLyP-1 selectively targeted and penetrated into the tumor cells, and little hydrophobic CPT was released into the culture medium or blood. This study indicates that the AuNR@SiO2-tLyP-1 drug delivery system (DDS) has great potential application for the chemo-photothermal cancer therapy.

Surface functionalization of nanoporous alumina with bone morphogenetic protein 2 for inducing osteogenic differentiation of mesenchymal stem cells.

Many studies have demonstrated the possibility to regulate cellular behavior by manipulating the specific characteristics of biomaterials including the physical features and chemical properties. To investigate the synergistic effect of chemical factors and surface topography on the growth behavior of mesenchymal stem cells (MSCs), bone morphorgenic protein 2 (BMP2) was immobilized onto porous alumina substrates with different pore sizes. The BMP2-immobilized alumina substrates were characterized with scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Growth behavior and osteogenic differentiation of MSCs cultured on the different substrates were investigated. Cell adhesion and morphological changes were observed with SEM, and the results showed that the BMP2-immobilized alumina substrate was able to promote adhesion and spreading of MSCs. MTT assay and immunofluorescence staining of integrin ß1 revealed that the BMP2-immobilized alumina substrates were favorable for cell growth. To evaluate the differentiation of MSCs, osteoblastic differentiation markers, such as alkaline phosphatase (ALP) activity and mineralization, were investigated. Compared with those of untreated alumina substrates, significantly higher ALP activities and mineralization were detected in cells cultured on BMP2-immobilized alumina substrates. The results suggested that surface functionalization of nanoporous alumina substrates with BMP2 was beneficial for cell growth and osteogenic differentiation. With the approach of immobilizing growth factors onto material substrates, it provided a new insight to exploit novel biofunctional materials for tissue engineering.

A synthetic mechano-growth factor E peptide promotes rat tenocyte migration by lessening cell stiffness and increasing F-actin formation via the FAK-ERK1/2 signaling pathway.

Tendon injuries are common in sports and are frequent reasons for orthopedic consultations. The management of damaged tendons is one of the most challenging problems in orthopedics. Mechano-growth factor (MGF), a recently discovered growth repair factor, plays positive roles in tissue repair through the improvement of cell proliferation and migration and the protection of cells against injury-induced apoptosis. However, it remains unclear whether MGF has the potential to accelerate tendon repair. We used a scratch wound assay in this study to demonstrate that MGF-C25E (a synthetic mechano-growth factor E peptide) promotes the migration of rat tenocytes and that this promotion is accompanied by an elevation in the expression of the following signaling molecules: focal adhesion kinase (FAK) and extracellular signal regulated kinase1/2 (ERK1/2). Inhibitors of the FAK and ERK1/2 pathways inhibited the MGF-C25E-induced tenocyte migration, indicating that MGF-C25E promotes tenocyte migration through the FAK-ERK1/2 signaling pathway. The analysis of the mechanical properties showed that the Young's modulus of tenocytes was decreased through treatment of MGF-C25E, and an obvious formation of pseudopodia and F-actin was observed in MGF-C25E-treated tenocytes. The inhibition of the FAK or ERK1/2 signals restored the decrease in Young's modulus and inhibited the formation of pseudopodia and F-actin. Overall, our study demonstrated that MGF-C25E promotes rat tenocyte migration by lessening cell stiffness and increasing pseudopodia formation via the FAK-ERK1/2 signaling pathway.

Role of p38, ERK1/2, focal adhesion kinase, RhoA/ROCK and cytoskeleton in the adipogenesis of human mesenchymal stem cells.

Adipogenesis is important to health and is thought occurring in the two stages of mesenchymal stem cell commitment to a preadipocyte fate and terminal differentiation of the preadipocyte. However, the mechanism of adipogenesis is still not clear. In this study, the roles of p38, extracellular regulated protein kinases 1/2 (ERK1/2), focal adhesion kinase (FAK), RhoA/ROCK, and cytoskeleton in both of the two stages of adipogenesis were assayed. Our results showed that the treatments of SB203580 (the inhibitor of p38) and U0126 (the inhibitor of ERK1/2) suppressed the adipogenesis induced by differentiation medium, and the treatments of PF573228 (a specific inhibitor of FAK), Y27632 (a specific inhibitor of RhoA/ROCK) and cytochalasin D (an inhibitor of cytoskeletal organization) promoted the adipogenesis. The treatments of SB203580 and U0126 significantly inhibited the adipogenic differentiation of hMSCs cultured in differentiation medium in the presence of PF573228, Y27632 or cytochalasin D. Moreover, the treatments of PF573228, Y27632 and cytochalasin D promoted p38 and ERK1/2 phosphorylations, and the treatments of U0126 and SB203580 decreased p38 and ERK1/2 phosphorylations, respectively. These results demonstrated that p38 and ERK1/2 played crucial positive roles in adipogenesis, and FAK, RhoA/ROCK and cytoskeleton played negative roles. Furthermore, FAK, RhoA/ROCK and cytoskeleton affected adipogenesis by regulating the activities of p38 and ERK1/2 which interacted with each other in the process of adipogenesis.

Determination of optimal cyclic uniaxial stretches for stem cell-to-tenocyte differentiation under a wide range of mechanical stretch conditions by evaluating gene expression and protein synthesis levels.

We examined optimal cyclic uniaxial stretches for stem cell-to-tenocyte differentiation by applying a wide range of cyclic mechanical stimuli. Human bone marrow mesenchymal stem cells (hBMSCs) were subjected to three types of cyclic elongation of 5%, 10%, or 15% at a cyclic frequency of 1 Hz for 24 h or 48 h, and differentiation into tenocytes was assessed by two methods: real-time polymerase chain reaction determination of gene expression levels and western blotting analysis of protein expression levels. The gene expression levels of the differentiation markers type I collagen (Col I), type III collagen (Col III), tenascin-C (Tnc), and scleraxis (Scx), all of which are constituents of tendon tissue, were increased when cells were exposed to 10% stretching stimulation. The levels of Col I and Tnc protein synthesis levels were also higher in the cells with 10% stretching stimulation than in those subjected to other stimuli. The results indicated that 10% stretching stimulus was efficient to induce the differentiation of hBMSCs into tenocytes. In addition, the changes in gene and protein expression levels were strongly correlated with cell orientation angle. The results presented here suggest that mesenchymal stem cell-to-tenocyte differentiation is strongly associated with cumulative elongation load on the cells. This work provides novel insights into the differentiation of tenogenesis in a strain-induced environment and supports the therapeutic potential of hBMSCs.

RhoA/ROCK, cytoskeletal dynamics, and focal adhesion kinase are required for mechanical stretch-induced tenogenic differentiation of human mesenchymal stem cells.

Human bone marrow mesenchymal stem cells (hMSCs) have the potential to differentiate into tendon/ligament-like lineages when they are subjected to mechanical stretching. However, the means through which mechanical stretch regulates the tenogenic differentiation of hMSCs remains unclear. This study examined the role of RhoA/ROCK, cytoskeletal organization, and focal adhesion kinase (FAK) in mechanical stretch-induced tenogenic differentiation characterized by the up-regulation of tendon-related marker gene expression. Our findings showed that RhoA/ROCK and FAK regulated mechanical stretch-induced realignment of hMSCs by regulating cytoskeletal organization and that RhoA/ROCK and cytoskeletal organization were essential to mechanical stretch-activated FAK phosphorylation at Tyr397. We also demonstrated that this process can be blocked by Y-27632 (a specific inhibitor of RhoA/ROCK), cytochalasin D (an inhibitor of cytoskeletal organization) or PF 573228 (a specific inhibitor of FAK). The results of this study suggest that RhoA/ROCK, cytoskeletal organization, and FAK compose a "signaling network" that senses mechanical stretching and drives mechanical stretch-induced tenogenic differentiation of hMSCs. This work provides novel insights regarding the mechanisms of tenogenesis in a stretch-induced environment and supports the therapeutic potential of hMSCs.

Effect of focal adhesion kinase on the regulation of realignment and tenogenic differentiation of human mesenchymal stem cells by mechanical stretch.

Focal adhesion kinase (FAK) is a focal adhesion-associated protein kinase involved in cell adhesion and spreading. It is recruited as a participant in focal adhesion dynamics between cells and has a role in cell motility, differentiation, and survival. The role of FAK in the differentiation of human mesenchymal stem cells (hMSCs), however, is not well understood, particularly in terms of tenogenic differentiation. In this study, we reported that FAK regulates the mechanical stretch-induced realignment of hMSCs. We showed that FAK can be activated by mechanical stretch and, with a 10 µM PF 573228 (a novel small molecule inhibitor of FAK) treatment, FAK autophosphorylation at Tyr397 is significantly decreased. Moreover, our findings demonstrated that this decrease in FAK autophosphorylation at Tyr397 leads to the attenuation of upregulation of mechanical stretch-induced mRNA expression of tendon-related genes, including type I collagen, type III collagen, tenascin-C, and scleraxis. These results indicate that the FAK signaling molecule plays an important role in regulating cell realignment and tenogenic differentiation of hMSCs when induced by mechanical stretch. Collectively, our findings provide novel insight into the role of FAK in the realignment and mechanotransduction of hMSCs during the process of tenogenic differentiation induced by mechanical stretch.

Mechanical stretch-induced changes in cell morphology and mRNA expression of tendon/ligament-associated genes in rat bone-marrow mesenchymal stem cells.

It has been demonstrated that mechanical stimulation plays a vital role in regulating the proliferation and differentiation of stem cells. However, little is known about the effects of mechanical stress on tendon/ligament development from mesenchymal stem cells (MSCs). Here, using a custom-made cell-stretching device, we studied the effects of mechanical stretching on the cell morphology and mRNA expression of several key genes modulating tendon/ligament genesis. We demonstrate that bone-marrow-derived rat MSCs (rMSCs), when subjected to cyclic uniaxial stretching, express obvious detectable mRNAs for tenascin C and scleraxis, a unique maker of tendon/ligament formation, and significantly increased levels of type I collagen and type III collagen mRNAs. The stretched cells also orient at approximately 65 degrees with respect to the stretching direction and exhibit a more fibroblast-like morphology. Collectively, these results indicate that mechanical stretching facilitates the directed differentiation of rMSCs into tendon/ligament fibroblasts, which has potential implications for the tissue engineering of bioartificial tendons and ligaments.

Indirect co-culture with tenocytes promotes proliferation and mRNA expression of tendon/ligament related genes in rat bone marrow mesenchymal stem cells.

Recent evidences have suggested that humoral factors released from the appropriate co-cultured cells influenced the expansion and differentiation of mesenchymal stem cells (MSCs). However, little is known about the proliferation and differentiation of MSCs subjected to co-culture condition with tenocytes. In this study, we aimed to establish a co-culture system of MSCs and tenocytes and investigate the proliferation and tendon/ligament related gene expression of MSCs. MTT assay was used to detect the expansion of MSCs. Semi-quantitative RT-PCR was performed to investigate the expression of proliferation associated c-fos gene and tendon/ligament related genes, including type I collagen (Col I), type III collagen (Col III), tenascin C and scleraxis. Significant increase in MSCs expansion was observed after 3 days of co-culture with tenocytes. The c-fos gene expression was found distinctly higher than for control group on day 4 and day 7 of co-culture. The mRNA expression of four tendon/ligament related genes was significantly up-regulated after 14 days of co-culture with tenocytes. Thus, our research indicates that indirect co-culture with tenocytes promotes the proliferation and mRNA expression of tendon/ligament related genes in MSCs, which suggests a directed differentiation of MSCs into tendon/ligament.