The mechanism of myoblast deformation in response to cyclic strain – A cytomechanical study

Low magnitude high frequency vibration promotes chondrogenic differentiation of bone marrow stem cells with involvement of β-catenin signaling pathway

OBJECTIVE

Mesenchymal stem cells (MSCs) are well known to have the capability to form bone and cartilage, and chondrogenesis derived from MSCs is reported to be affected by mechanical stimuli. This research aimed to study the effects of low magnitude high frequency (LMHF) vibration on the chondrogenic differentiation of bone marrow-derived MSCs (BMSCs) which were cultured with chondrogenic medium, and to investigate the role of β-catenin cascade in this process.

METHODS

Rat bone marrow-derived MSCs (BMSCs) were isolated and randomized into vibration and static cultures. The effect of vibration on BMSCs proliferation, differentiation and chondrogenic potential was assessed at the protein level.

RESULTS

LMHFV did not affect the proliferation of BMSCs. However, this was accompanied by increased markers of chondrogenesis. The protein expression of chondrocyte-specific markers of Aggrecan, Sox9, and BMP7 were upregulated and Collagen X was decreased by LMHF vibration introduced at the chondrogenic differentiation in vitro. Specifically, thicker blue-stained particles were observed in Alcian Blue staining and the level of glycosaminoglycan were significantly increased respectively in the vibration culture group by 56.5 % and 93.6 % on the 7th and 14th day. The expression and nuclear translocation of β-catenin were activated in a significant manner. And inhibition of GSK-3β activity with Licl rearranged and intensified the cytoskeleton affected by vibration stimulation.

CONCLUSIONS

Our data demonstrated that LMHF mechanical vibration promotes BMSCs chondrogenic differentiation and implies β-catenin signal acts as an essential mediator in the mechano-biochemical transduction and subsequent transcriptional regulation in the process of chondrogenesis.

Runx2 alleviates high glucose-suppressed osteogenic differentiation via PI3K/AKT/GSK3β/β-catenin pathway

Hyperglycemia is one of the most important pathogenesis of diabetic osteopathy. Several lines of studies indicate Runx2 plays a critical role in the process of osteogenic differentiation. However, little studies have analyzed the effect of Runx2 on osteoblast differentiation of rat bone mesenchymal stem cells (rBMSCs) in high-glucose condition. In this study, the effect of Runx2 on osteoblast differentiation in high-glucose condition was evaluated by the expression of osteogenesis-related maker including Runx2, ALP, OC, and OPN, as well as ALP staining, ALP activity, and Alizarin red S staining. Western blot analysis was performed to detect the protein expression levels of p-AKT, AKT, p-GSK3β, GSK3β, and β-catenin. Immunofluorescence staining analysis was performed to detect subcellular localization of β-catenin. Our results revealed that high glucose significantly inhibited osteogenic differentiation, hyperosmolarity did not cause a suppression. In addition, Runx2 could upregulate the expression of osteogenic-related genes and increase matrix mineralization, while applying 10 µM PI3K/AKT inhibitor LY294002 abolished the beneficial effect. Collectively, these results indicate that Runx2 alleviates high glucose-induced inhibition of osteoblast differentiation by modulating PI3K/AKT/GSK3β/β-catenin pathway.

Low-magnitude, high-frequency vibration promotes the adhesion and the osteogenic differentiation of bone marrow-derived mesenchymal stem cells cultured on a hydroxyapatite-coated surface: The direct role of Wnt/β-catenin signaling pathway activation

The positive effect of low-magnitude, high‑frequency (LMHF) vibration on implant osseointegration has been demonstrated; however, the underlying cellular and molecular mechanisms remain unknown. The aim of this study was to explore the effect of LMHF vibration on the adhesion and the osteogenic differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) cultured on hydroxyapatite (HA)-coated surfaces in an in vitro model as well as to elucidate the molecular mechanism responsible for the effects of LMHF vibration on osteogenesis. LMHF vibration resulted in the increased expression of fibronectin, which was measured by immunostaining and RT-qPCR. Stimulation of BMSCs by LMHF vibration resulted in the rearrangement of the actin cytoskeleton with more prominent F-actin. Moreover, the expression of β1 integrin, vinculin and paxillin was notably increased following LMHF stimulation. Scanning electron microscope observations revealed that there were higher cell numbers and more extracellular matrix attached to the HA-coated surface in the LMHF group. Alkaline phosphatase activity as well as the expression of osteogenic-specific genes, namely Runx2, osterix, collagen I and osteocalcin, were significantly elevated in the LMHF group. In addition, the protein expression of Wnt10B, β-catenin, Runx2 and osterix was increased following exposure to LMHF vibration. Taken together, the findings of this study indicate that LMHF vibration promotes the adhesion and the osteogenic differentiation of BMSCs on HA-coated surfaces in vitro, and LMHF vibration may directly induce osteogenesis by activating the Wnt/β‑catenin signaling pathway. These data suggest that LMHF vibration enhances the osseointegration of bone to a HA-coated implant, and provide a scientific foundation for improving bone-implant osseointegration through the application of LMHF vibration.

The evaluation of cyclic uniaxial strain on myogenic differentiation of adipose-derived stem cells

It has been revealed that skeletal muscle cells have the potential to generate, sense and respond to biomechanical signals and that, mechanical force is one of the important factors influencing proliferation, differentiation, regeneration and homeostasis of skeletal muscle cells and myoblasts. The aim of this study was to illustrate the effect of cyclic uniaxial strain on myogenic differentiation of adipose-derived stem cells (ASCs). This study was designed to investigate this effect within 3 days in 4 groups: control (untreated), chemical, chemical-mechanical and mechanical based on exposure of ASCs to chemical growth factors for 3 days or to mechanical strain just on the 2nd day. Finally, cell orientation, muscle-related gene expression, myosin protein synthesis and the number of myosin-positive cells were examined to estimate the rate of differentiation. By studying the cells before and after exposure to uniaxial strain, it could be observed that by exerting the load, the cells were organized almost perpendicularly to strain direction. Real-time RT-PCR demonstrated that uniaxial strain had a significant effect on up-regulation of muscle-related genes in chemical-mechanical group (P < 0.001) as compared to mechanical or chemical groups. Immunocytochemistry confirmed the myosin-positive cells in treated groups and the numbers of these cells were enumerated by flow cytometry. These data suggest that uniaxial cyclic strain could affect ASCs and cause their myogenic differentiation and that the combination of chemical myogenic differentiation factors with mechanical signals promotes differentiation much more than differentiation by chemical myogenic differentiation factors or mechanical signals alone.