Softening Substrates Promote Chondrocytes Phenotype via RhoA/ROCK Pathway

Substrate stiffness regulated migration and angiogenesis potential of A549 cells and HUVECs

Tumor tissue tends to stiffen during solid tumor progression. Substrate stiffness is known to alter cell behaviors, such as proliferation and migration, during which angiogenesis is requisite. Mono- and co-culture systems of lung cancer cell line A549 and human umbilical vein endothelial cells (HUVECs), on polydimethylsiloxane substrates (PDMS) with varying stiffness, were used for investigating the effects of substrate stiffness on the migration and angiogenesis of lung cancer. The expressions of matrix metalloproteinases (MMPs) and angiogenesis-related growth factors were up-regulated with the increase of substrate stiffness, whereas that of tissue inhibitor of matrix metalloproteinase (TIMPs) were down-regulated with increasing substrate stiffness. Our data not only suggested that stiff substrate may promote the migration and angiogenesis capacities of lung cancer, but also suggested that therapeutically targeting lung tumor stiffness or response of ECs to lung tumor stiffness may help reduce migration and angiogenesis of lung tumor.

Aptamer-Modified Tetrahedral DNA Nanostructure for Tumor-Targeted Drug Delivery

Tetrahedral DNA nanostructures (TDNs) are considered promising drug delivery carriers because they are able to permeate cellular membrane and are biocompatible and biodegradable. Furthermore, they can be modified by functional groups. To improve the drug-delivering ability of TDNs, we chose anticancer aptamer AS1411 to modify TDNs for tumor-targeted drug delivery. AS1411 can specifically bind to nucleolin, which is overexpressed on the cell membrane of tumor cells. Furthermore, AS1411 can inhibit NF-κB signaling and reduce the expression of bcl-2. In this study, we compared the intracellular localization of AS1411-modified TDNs (Apt-TDNs) with that of TDNs in different cells under hypoxic condition. Furthermore, we compared the effects of Apt-TDNs and TDNs on cell growth and cell cycle under hypoxic condition. A substantial amount of Apt-TDNs entered and accumulated in the nucleus of MCF-7 cells; however, the amount of Apt-TDNs that entered L929 cells was comparatively less. TDNs entered in much lower quantity in MCF-7 cells than Apt-TDNs. Moreover, there was little difference in the amount of TDNs that entered L929 cells and MCF-7 cells. Apt-TDNs can inhibit MCF-7 cell growth and promote L929 cell growth, while TDNs can promote both MCF-7 and L929 cell growth. Thus, the results indicate that Apt-TDNs are more effective tumor-targeted drug delivery vehicles than TDNs, with the ability to specifically inhibit tumor cell growth.

IGF-1 promotes angiogenesis in endothelial cells/adipose-derived stem cells co-culture system with activation of PI3K/Akt signal pathway

OBJECTIVES

The aim of this study was to investigate the role of insulin-like growth factor-1 (IGF-1) and crosstalk between endothelial cells (ECs) and adipose-derived stem cells (ASCs) in the process of angiogenesis.

METHODS

A three-dimensional collagen gel used to culture mouse ASCs and mouse ECs in vitro was established. The effects of angiogenesis after exposure to IGF-1 were observed by confocal laser scanning microscopy. Western blotting and qPCR were performed to elucidate the underlying mechanisms.

RESULTS

IGF-1 treatment promoted the formation of vessel-like structures and the recruitment of ASCs in the three-dimensional collagen gel. The angiogenic genes and proteins in ECs were up-regulated by IGF-1 and in co-culture. Similar changes in the genes and in the proteins were detected in ASCs after exposure to IGF-1 and co-culture. p-Akt expression levels were high in ECs and ASCs after exposure to IGF-1 and co-culture.

CONCLUSIONS

IGF-1 and co-culture between cells facilitate the process of angiogenesis via the PI3-kinase/Akt signalling pathway. In ECs, IGF-1 stimulates the expression of angiogenesis-related growth factors with the activation of the PI3-kinase/Akt signalling pathway. Co-cultured ECs exposed to excess VEGF-A and other angiogenesis-related growth factors para-secreted from ASCs exhibit high expression of angiogenesis-related genes and proteins. In ASCs, IGF-1 induces the recruitment and function of ASCs by up-regulating the expression of PDGFB, MMPs and α-SMA. Crosstalk with ECs further facilitates changes in ASCs.

MMP-2 and Notch signal pathway regulate migration of adipose-derived stem cells and chondrocytes in co-culture systems

OBJECTIVES

The crosstalk between chondrocytes and adipose-derived stem cells (ADSCs) could regulate the secretion of multiple growth factors. However, it is not clear how the paracrine action in co-culture systems affect cell migration. This study focused on the changes of cell migration of ADSCs and chondrocytes in co-culture conditions.

MATERIALS AND METHODS

Primary ADSCs and chondrocytes were isolated from Sprague-Dawley rat. Transwell co-culture systems, inoculated with ADSCs and chondrocytes, were established in vitro. The morphology of the cells was observed 7 days post-seeding by inverted phase-contrast microscope. Additionally, the cytoskeleton changes were investigated by immunofluorescence staining. To detect the abundance of Vinculin, we used immunofluorescence and Western blotting. Additionally, the expression level of MMP-2, Hey1 and Hes1 was examined to determine the mechanisms of co-culture-induced cell migration changes.

RESULTS

The migration of ADSCs and chondrocytes in co-culture conditions significantly decreased compared with that in mono-culture groups, accompanied by the decrease of filopodia and the expression level of MMP-2.

CONCLUSIONS

The overall study showed that the migration of ADSCs and chondrocytes differs significantly depending on culture conditions. Moreover, the Notch signalling pathway may be involved in this process. Accordingly, by studying changes in migration caused by co-culture, we obtained new insight into the crosstalk between ADSCs and chondrocytes.

Injectable and thermosensitive TGF-β1-loaded PCEC hydrogel system for in vivo cartilage repair

Chondral defects pose a great challenge for clinicians to manage owing to the limited capacity for self-healing. Various traditional approaches have been adopted for the repair of these defects with unsatisfactory results. Cartilage tissue engineering techniques have emerged as promising strategies to enhance regeneration and overcome these traditional shortcomings. The cell-homing based technique is considered the most promising owing to its unique advantages. Thermosensitive hydrogels have been applied as scaffolds for biomedical applications with smart sol-gel response for altering environmental temperature. Transforming growth factor (TGF)-β1 is considered to be capable of promoting chondrogenesis. In this study, a novel TGF-β1-loaded poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) (PCEC) hydrogel was fabricated using simple procedures. Hydrogel characterization, rheological testing, component analysis, and assessment of sol-gel transition, in vitro degradation, and TGF-β1 release confirmed that this material possesses a porous microstructure with favorable injectability and sustained drug release. Full-thickness cartilage defects were induced on rat knees for in vivo cartilage repair for eight weeks. Micro-CT and histological evaluation provided further evidence of the optimal capacity of this novel hydrogel for cartilage regeneration with respect to that of other methods. Moreover, our results demonstrated that the cell-free hydrogel is thermosensitive, injectable, biodegradable, and capable of in vivo cartilage repair and possesses high potential and benefits for acellular cartilage tissue engineering and clinical application in the future.

Modulation of chondrocyte motility by tetrahedral DNA nanostructures

OBJECTIVES

Contemporarily, a highly increasing attention was paid to nanoconstructs, particularly DNA nanostructures possessing precise organization, functional manipulation, biocompatibility and biodegradability. Amongst these DNA nanomaterials, tetrahedral DNA nanostructures (TDNs) are a significantly ideal bionanomaterials with focusing on the property that can be internalized into cytoplasm in the absence of transfection. Therefore, the focus of this study was on investigating the influence of TDNs on the chondrocytes locomotion.

MATERIALS AND METHODS

Tetrahedral DNA nanostructures was confirmed by 6% polyacrylamide gel electrophoresis (PAGE) and dynamic light scattering (DLS). Subsequently, the effect of TDNs on chondrocyte locomotion was investigated by real-time cell analysis (RTCA) and wound healing assay. The variation of relevant genes and proteins was detected by quantitative polymerase chain reaction (qPCR), western blotting and immunofluorescence respectively.

RESULTS

We demonstrated that tetrahedral DNA nanostructures have positive influence on chondrocytes locomotion and promoted the expression of RhoA, ROCK2 and vinculin. Additionally, upon exposure to TDNs with the concentration of 250 nmol L^-1 , the chondrocytes were showed the highest motility via both RTCA and wound healing assay. Meanwhile, the mRNA and protein expression of RhoA, ROCK2 and vinculin were also significantly enhanced with the same concentration.

CONCLUSIONS

It can be concluded that the TDNs with the optimal concentration of 250 nmol L^-1 could extremely promoted the chondrocytes locomotion through facilitating the expression of RhoA, ROCK2 and vinculin. These results seemed to reveal that this special three-dimensional DNA tetrahedral nanostructures may be applied to cartilage repair and treatment in the future.

Curved microstructures promote osteogenesis of mesenchymal stem cells via the RhoA/ROCK pathway

OBJECTIVES

Cells in the osteon reside in a curved space, accordingly, the curvature of the microenvironment is an important geometric feature in bone formation. However, it is not clear how curved microstructures affect cellular behaviour in bone tissue.

MATERIALS AND METHODS

Rat primary bone marrow mesenchymal stem cells (BMSCs) on wavy microgrooves were exposed to PDMS substrates with various curvatures to investigate alterations in cellular morphology and osteogenic differentiation. Additionally, the expression levels of RhoA and its effectors were examined by immunofluorescence and quantitative PCR to determine the mechanisms of curvature-dependent osteogenic differentiation.

RESULTS

Wavy microgrooves caused dramatic nuclear distortion and cytoskeletal remodelling. We detected a noticeable increase in the expression of osteogenic-related genes in BMSCs in wavy microgroove groups, and the maximum expression was observed in the high curvature group. Moreover, immunofluorescent staining and quantitative RT-PCR results for RhoA and its effectors showed that the RhoA/ROCK signalling pathway is associated with curvature-dependent osteogenic differentiation.

CONCLUSIONS

Our results illustrated that curved microstructures could promote BMSC differentiation to the osteogenic lineage, and the osteogenic effects of higher curvature are more obvious. Wavy microstructures could also influence the RhoA/ROCK pathway. Accordingly, curved microstructures may be useful in bone tissue engineering.

Nonmonotonic Self-Deformation of Cell Nuclei on Topological Surfaces with Micropillar Array

Cells respond to the mechanical signals from their surroundings and integrate physiochemical signals to initiate intricate mechanochemical processes. While many studies indicate that topological features of biomaterials impact cellular behaviors profoundly, little research has focused on the nuclear response to a mechanical force generated by a topological surface. Here, we fabricated a polymeric micropillar array with an appropriate dimension to induce a severe self-deformation of cell nuclei and investigated how the nuclear shape changed over time. Intriguingly, the nuclei of mesenchymal stem cells (MSCs) on the poly(lactide-co-glycolide) (PLGA) micropillars exhibited a significant initial deformation followed by a partial recovery, which led to an "overshoot" phenomenon. The treatment of cytochalasin D suppressed the recovery of nuclei, which indicated the involvement of actin cytoskeleton in regulating the recovery at the second stage of nuclear deformation. Additionally, we found that MSCs exhibited different overshoot extents from their differentiated lineage, osteoblasts. These findings enrich the understanding of the role of the cell nucleus in mechanotransduction. As the first quantitative report on nonmonotonic kinetic process of self-deformation of a cell organelle on biomaterials with unique topological surfaces, this study sheds new insight into cell-biomaterial interactions.

Effect of matrix stiffness on osteoblast functionalization

OBJECTIVES

Stiffness of bone tissue differs response to its physiological or pathological status, such as osteoporosis or osteosclerosis. Consequently, the function of cells residing in bone tissue including osteoblasts (OBs), osteoclasts and osteocytes will be affected. However, to the best of our knowledge, the detailed mechanism of how extracellular matrix stiffness affects OB function remains unclear.

MATERIALS AND METHODS

We conducted a study that exposed rat primary OBs to polydimethylsiloxane substrates with varied stiffness to investigate the alterations of cell morphology, osteoblastic differentiation and its potential mechanism in mechanotransduction.

RESULTS

Distinctive differences of cell shapes and vinculin expression in rat osteoblasts were detected on different PDMS substrates. As representatives for OB function, expression of alkaline phosphatase, Runx2 and osteocalcin were identified and showed a decrease trend as substrates become soft, which is associated with the Rho/ROCK signalling pathway.

CONCLUSIONS

Our results indicated substrate elasticity as a potent regulator in OBs functionalization, which may pave a way for further understanding of bone diseases as well as a potential therapeutic alternative in tissue regeneration.