Effect of mechanical stretch on the proliferation and differentiation of BMSCs from ovariectomized rats

The role of integrin family in bone metabolism and tumor bone metastasis

Integrins have been the research focus of cell-extracellular matrix adhesion (ECM) and cytokine receptor signal transduction. They are involved in the regulation of bone metabolism of bone precursor cells, mesenchymal stem cells (MSCs), osteoblasts (OBs), osteoclasts (OCs), and osteocytes. Recent studies expanded and updated the role of integrin in bone metabolism, and a large number of novel cytokines were found to activate bone metabolism pathways through interaction with integrin receptors. Integrins act as transducers that mediate the regulation of bone-related cells by mechanical stress, fluid shear stress (FSS), microgravity, hypergravity, extracellular pressure, and a variety of physical factors. Integrins mediate bone metastasis of breast, prostate, and lung cancer by promoting cancer cell adhesion, migration, and survival. Integrin-mediated targeted therapy showed promising prospects in bone metabolic diseases. This review emphasizes the latest research results of integrins in bone metabolism and bone metastasis and provides a vision for treatment strategies.

The osteogenesis of Ginsenoside Rb1 incorporated silk/micro-nano hydroxyapatite/sodium alginate composite scaffolds for calvarial defect

Ginsenoside Rb1, the effective constituent of ginseng, has been demonstrated to play favorable roles in improving the immunity system. However, there is little study on the osteogenesis and angiogenesis effect of Ginsenoside Rb1. Moreover, how to establish a delivery system of Ginsenoside Rb1 and its repairment ability in bone defect remains elusive. In this study, the role of Ginsenoside Rb1 in cell viability, proliferation, apoptosis, osteogenic genes expression, ALP activity of rat BMSCs were evaluated firstly. Then, micro-nano HAp granules combined with silk were prepared to establish a delivery system of Ginsenoside Rb1, and the osteogenic and angiogenic effect of Ginsenoside Rb1 loaded on micro-nano HAp/silk in rat calvarial defect models were assessed by sequential fluorescence labeling, and histology analysis, respectively. It revealed that Ginsenoside Rb1 could maintain cell viability, significantly increased ALP activity, osteogenic and angiogenic genes expression. Meanwhile, micro-nano HAp granules combined with silk were fabricated smoothly and were a delivery carrier for Ginsenoside Rb1. Significantly, Ginsenoside Rb1 loaded on micro-nano HAp/silk could facilitate osteogenesis and angiogenesis. All the outcomes hint that Ginsenoside Rb1 could reinforce the osteogenesis differentiation and angiogenesis factor’s expression of BMSCs. Moreover, micro-nano HAp combined with silk could act as a carrier for Ginsenoside Rb1 to repair bone defect.

Treadmill exercise influences the microRNA profiles in the bone tissues of mice

As an important regulator involved in cell activity, microRNAs (miRNAs) are important in the process of exercise influencing bone metabolism. The present study aimed to detect and select differentially expressed miRNAs in the bone tissues of mice trained on a treadmill, predict the target genes of these differentially expressed miRNAs and lay a foundation for exploring the effect of treadmill training on bone metabolism through miRNAs. In this experiment, after the mice were trained on a treadmill for 8 weeks, the mechanical properties of mouse femur bone were assessed, and the alkaline phosphatase (ALP) activity and osteocalcin (OCN) protein levels of the bone were assayed. miRNA microarray and reverse transcription-quantitative (RT-q)PCR were performed to select and validate differentially expressed miRNAs in the bone, and the target genes of these miRNAs were predicted with bioinformatics methods. In addition, the differentially expressed miRNAs in the bone tissues were compared with those in mechanically strained osteocytes in vitro. Treadmill training improved the mechanical properties of the femur bones of mice, and elevated the ALP activity and OCN protein level in the bone. In addition, 122 differentially expressed miRNAs were detected in the bone, of which nine were validated via RT-qPCR. Among the target genes of these differentially expressed miRNAs, certain candidates were involved in bone metabolism. A total of eight miRNAs were differentially expressed in both bone tissue and osteocytes, exhibiting the same expression trends, and various target genes of these eight miRNAs were also involved in bone metabolism. Treadmill training resulted in altered miRNA expression profiles in the bones of mice (mainly in osteocytes) and the differentially expressed miRNAs may serve important roles in regulating bone metabolism and osteogenic differentiation.

Mechanical loading and the control of stem cell behavior

OBJECTIVE

Mechanical stimulation regulates many cell responses. The present study describes the effects of different in vitro mechanical stimulation approaches on stem cell behavior.

DESIGN

The narrative review approach was performed. The articles published in English language that addressed the effects of mechanical force on stem cells were searched on Pubmed and Scopus database. The effects of extrinsic mechanical force on stem cell response was reviewed and discussed.

RESULTS

Cells sense mechanical stimuli by the function of mechanoreceptors and further transduce force stimulation into intracellular signaling. Cell responses to mechanical stimuli depend on several factors including type, magnitude, and duration. Further, similar mechanical stimuli exhibit distinct cell responses based on numerous factors including cell type and differentiation stage. Various mechanical applications modulate stemness maintenance and cell differentiation toward specific lineages.

CONCLUSIONS

Mechanical force application modulates stemness maintenance and differentiation. Modification of force regimens could be utilized to precisely control appropriate stem cell behavior toward specific applications.

The interactions between mTOR and NF-κB: A novel mechanism mediating mechanical stretch-stimulated osteoblast differentiation

Mechanical stretch is known to promote osteoblast differentiation in vitro and accelerate bone regeneration in vivo, whereas the relevant mechanism remains unclear. Recent studies have shown the importance of reciprocal interactions between mammalian target of rapamycin (mTOR) and nuclear factor kappa B (NF-κB; two downstream molecules of Akt) in the regulation of tumor cells. Thus, we hypothesize that mTOR and NF-κB as well as their interconnection play a critical role in mediating stretch-induced osteogenic differentiation in osteoblasts. We herein found that mechanical stretch (10% elongation at six cycles/min) significantly promoted the expression of osteoblast differentiation-related markers (including ALP, BMP2, Col1α, OCN, and Runx2) in osteoblast-like MG-63 cells, accompanied by increased mTOR phosphorylation and NF-κB p65 phosphorylation and nuclear translocation. Blockade of mTOR by antagonist or small interfering RNA suppressed osteogenesis-related gene expression in response to mechanical stretch, whereas inhibition of NF-κB further increased stretch-induced osteoblast differentiation. Moreover, inhibition of mTOR decreased the phosphorylation of NF-κB, and blockade of NF-κB reduced the mTOR activation in MG63 cells under mechanical stretch. Coinhibition of mTOR and NF-κB abolishes the alteration of osteogenic differentiation induced by single mTOR or NF-κB inhibition under mechanical stretch, which is equivalent to the noninhibition level for osteoblasts under mechanical stretch. The expression levels of osteogenic differentiation in osteoblasts after inhibition of Akt were similar to those after co-inhibition of mTOR and NF-κB under mechanical stretch. This study for the first time reveals the reciprocal interconnection between mTOR and NF-κB in osteoblasts under mechanical stretch and indicates that mTOR and NF-κB as well as their interactions play a key role in the regulation of cellular homeostasis of osteoblasts in response to mechanical stretch. These findings are helpful for enriching our basic knowledge of the molecular mechanisms of osteoblast mechanotransduction, and also providing insight into the clinical therapeutic modality associated with mechanical stretch (e.g., distraction osteogenesis).

Bone's Response to Mechanical Loading in Aging and Osteoporosis: Molecular Mechanisms

Mechanotransduction is pivotal in the maintenance of homeostasis in different tissues and involves multiple cell signaling pathways. In bone, mechanical stimuli regulate the balance between bone formation and resorption; osteocytes play a central role in this regulation. Dysfunctions in mechanotransduction signaling or in osteocytes response lead to an imbalance in bone homeostasis. This alteration is very relevant in some conditions such as osteoporosis and aging. Both are characterized by increased bone weakness due to different causes, for example, the increase of osteocyte apoptosis that cause an alteration of fluid space, or the alteration of molecular pathways. There are intertwined yet very different mechanisms involved among the cell-intrinsic effects of aging on bone, the cell-intrinsic and tissue-level effects of estrogen/androgen withdrawal on bone, and the effects of reduced mechanical loading on bone, which are all involved to some degree in how aged bone fails to respond properly to stress/strain compared to younger bone. This review aims at clarifying how the cellular and molecular pathways regulated and induced in bone by mechanical stimulation are altered with aging and in osteoporosis, to highlight new possible targets for antiresorptive or anabolic bone therapeutic approaches.

Effects of Electrical Stimulation on Stem Cells

Recent interest in developing new regenerative medicine- and tissue engineering-based treatments has motivated researchers to develop strategies for manipulating stem cells to optimize outcomes in these potentially, game-changing treatments. Cells communicate with each other, and with their surrounding tissues and organs via electrochemical signals. These signals originate from ions passing back and forth through cell membranes and play a key role in regulating cell function during embryonic development, healing, and regeneration. To study the effects of electrical signals on cell function, investigators have exposed cells to exogenous electrical stimulation and have been able to increase, decrease and entirely block cell proliferation, differentiation, migration, alignment, and adherence to scaffold materials. In this review, we discuss research focused on the use of electrical stimulation to manipulate stem cell function with a focus on its incorporation in tissue engineering-based treatments.

Mechanical Stretch Promotes the Osteogenic Differentiation of Bone Mesenchymal Stem Cells Induced by Erythropoietin

INTRODUCTION

The effects of erythropoietin (EPO) on the behaviors of bone marrow mesenchymal stem cells (BMSCs) subjected to mechanical stretch remain unclear. This study was therefore aimed at establishing the dose-response effect of EPO stimulation on rat BMSCs and investigating the effects of mechanical stretch combined with EPO on the proliferation and osteogenic differentiation of BMSCs.

MATERIAL AND METHODS

The proliferation and osteogenic differentiation of rat BMSCs were examined and compared using EPO with different concentrations. Thereafter, BMSCs were subjected to 10% elongation using a Flexcell strain unit, combined with 20 IU/ml EPO. The proliferation of BMSCs was detected by Cell Counting Kit-8, colony formation assay, and cell cycle assay; meanwhile, the mRNA expression levels of Ets-1, C-myc, Ccnd1, and C-fos were detected by reverse transcription and real-time quantitative PCR (qPCR). The osteogenic differentiation of BMSCs was detected by alkaline phosphatase (ALP) staining, and the mRNA expression levels of ALP, OCN, COL, and Runx2 were detected by qPCR. The role of the extracellular signal-regulated kinases 1/2 (ERK1/2) in the osteogenesis of BMSCs stimulated by mechanical stretch combined with 20 IU/ml EPO was examined by Western blot.

RESULTS

Our results showed that effects of EPO on BMSCs included a dose-response relationship, with the 20 IU/ml EPO yielding the largest. Mechanical stretch combined with 20 IU/ml EPO promoted proliferation and osteogenic differentiation of BMSCs. The increase in ALP, mineral deposition, and osteoblastic genes induced by the mechanical stretch-EPO combination was inhibited by U0126, an ERK1/2 inhibitor.

CONCLUSION

EPO was able to promote the proliferation and osteogenic differentiation of BMSCs, and these effects were enhanced when combined with mechanical stretch. The underlying mechanism may be related to the activation of the ERK1/2 signaling pathway.

Differentiation of human amniotic epithelial cells into osteoblasts is induced by mechanical stretch via the Wnt/β‑catenin signalling pathway

Human amniotic epithelial cells (hAECs) have recently been recognized as a potential source of stem cells. The present study was designed to investigate the effects of mechanical stretch on the osteogenic differentiation of hAECs. As it has been previously reported that the physical environment is an important factor in maintaining the phenotype and functionality of differentiated cells, mechanical stretch was use to mimic the mechanical environment in the present study, with the following parameters: 5% elongation of the hAECs at a frequency of 0.5 Hz, with evaluation at 2, 6, 12 and 24 h time points. The osteogenic differentiation process of the hAECs followed by mechanical stimulation was evaluated by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR), western blotting and immunocytochemistry. Additionally, in a parallel study, a runt‑related transcription factor 2 (Runx2)/core binding factor α 1 (Cbfa1)‑specific short hairpin RNA (shRNA) plasmid vector and a scrambled shRNA control plasmid was constructed for transfection into the hAECs prior to mechanical stimulation. The cultured hAECs exhibited a cobblestone‑shaped epithelial‑like phenotype and were positive for stage‑specific embryonic antigen‑4, cytokeratin‑19, cluster of differentiation 44 and octamer‑binding protein 4, as detected by flow cytometry, western blotting or confocal microscopy. The qPCR and western blotting data demonstrated that the mRNA and protein expression levels of Runx2/Cbfa1, alkaline phosphatase and osteocalcin were upregulated compared with the control group following stretching and they peaked at 12 h. These results indicated that the osteogenic differentiation of the hAECs was induced by mechanical stimuli. Additionally, the mRNA and protein expression levels of β‑catenin and cyclin D were increased significantly following stretching; however, they were decreased following Runx2/Cbfa1‑shRNA transfection as observed by RT‑qPCR and western blotting. These results suggested that the Wnt/β‑catenin pathway may have an important role in mechanical stretch‑induced osteogenic differentiation of the hAECs. Furthermore, the combination of stretch and osteogenic induction medium had synergistic effects on the osteogenic differentiation. The results of the present study demonstrated that mechanical stimuli have an important role in osteogenic differentiation of hAECs via the Wnt/β‑catenin signalling pathway, which may be a potential therapeutic strategy in bone regenerative medicine.

Cyclic mechanical stretch enhances BMP9-induced osteogenic differentiation of mesenchymal stem cells

PURPOSE

The purpose of this study was to investigate whether mechanical stretch can enhance the bone morphogenetic protein 9 (BMP9)-induced osteogenic differentiation in MSCs.

METHODS

Recombinant adenoviruses were used to overexpress the BMP9 in C3H10T1/2 MSCs. Cells were seeded onto six-well BioFlex collagen I-coated plates and subjected to cyclic mechanical stretch [6% elongation at 60 cycles/minute (1 Hz)] in a Flexercell FX-4000 strain unit for up to 12 hours. Immunostaining and confocal microscope were used to detect cytoskeleton organization. Cell cycle progression was checked by flow cytometry. Alkaline phosphatase activity was measured with a Chemiluminescence Assay Kit and was quantified with a histochemical staining assay. Matrix mineralization was examined by Alizarin Red S Staining.

RESULTS

Mechanical stretch induces cytoskeleton reorganization and inhibits cell proliferation by preventing cells entry into S phase of the cell cycle. Although mechanical stretch alone does not induce the osteogenic differentiation of C3H10T1/2 MSCs, co-stimulation with mechanical stretch and BMP9 enhances alkaline phosphatase activity. The expression of key lineage-specific regulators (e.g., osteocalcin (OCN), SRY-related HMG-box 9, and runt-related transcription factor 2) is also increased after the co-stimulation, compared to the mechanical stretch stimulation along. Furthermore, mechanical stretch augments the BMP9-mediated bone matrix mineralization of C3H10T1/2 MSCs.

CONCLUSIONS

Our results suggest that mechanical stretch enhances BMP9-induced osteoblastic lineage specification in C3H10T1/2 MSCs.

In vitro cell behaviors of bone mesenchymal stem cells derived from normal and postmenopausal osteoporotic rats

Postmenopausal osteoporosis (PMO) increases bone fragility and the risk of fractures, and impairs the healing procedure of bone defects in aged women. The stromal cell-derived factor-1α (SDF-1α)/CXC chemokine receptor type 4 (CXCR4) axis helps to maintain the biological and physiological functions of bone marrow mesenchymal stem cells (BMSCs) and increase the homing efficiency of BMSCs. The present study aimed to provide insights into the possible association between migration and osteogenic ability and the SDF-1α/CXCR4 axis in BMSCs derived from a rat model of PMO. In order to do this, the general and SDF-1α/CXCR4-associated biological characteristics as well as associated molecular mechanisms in BMSCs isolated from a PMO rat model (OVX-BMSCs) and normal rats (Sham-BMSCs) were investigated and compared. In comparison with Sham-BMSCs, OVX-BMSCs exhibited an impaired osteogenic ability, but a stronger adipogenic activity as well as a higher proliferative ability. In addition, OVX-BMSCs presented a lower chemotactic activity towards SDF-1α, lower expression levels of CXCR4 and reduced levels of phosphorylated AKT (p-AKT). Therefore, the lower expression levels of CXCR4 and p-AKT may be responsible for the impaired osteogenic ability and lower chemotactic activity towards SDF-1α of OVX-BMSCs.

Mechanical strain promotes osteogenic differentiation of bone mesenchymal stem cells from ovariectomized rats via the phosphoinositide 3‑kinase/Akt signaling pathway

Osteoporosis has become an overwhelming public health problem worldwide. As an elementary physiological factor to regulate bone formation and regeneration, mechanical strain may be used as a non‑invasive intervention in osteoporosis prevention and treatment. However, little is known regarding the underlying mechanism. The aim of the current study was to investigate the effect of continuous mechanical strain (CMS) on osteogenic differentiation of bone mesenchymal stem cells (BMSCs) from ovariectomized rats (OVX BMSCs). In addition, involvement of the phosphatidylinositol 3‑kinase (PI3K)/Akt signaling pathway in biomechanical signal transduction and its function were evaluated. The results demonstrated that OVX BMSCs subjected to CMS exhibited higher alkaline phosphatase (ALP) activity and deeper staining at 24 and 48 h. In addition, CMS upregulated the mRNA expression levels of ALP, collagen type I, runt related transcription factor 2 (Runx2), as well as the protein expression level of Runx2 in a time‑dependent manner. The PI3K/Akt signaling pathway was rapidly activated by CMS, with its phosphorylation level reaching its maximum in a short duration and a large quantity of phosphorylated‑Akt remaining in the nucleus. Pre‑treatment with a selective blocker significantly blocked the strain‑induced activation of PI3K/Akt and reduced the commitment of OVX BMSCs into osteoblasts, demonstrating a dominated regulative effect of PI3K/Akt signaling in strain‑induced osteogenesis. These results indicated that CMS induced the early differentiation of OVX BMSCs towards an osteogenic phenotype by activating the PI3K/Akt signaling pathway.

Evaluation of Osteogenesis and Angiogenesis of Icariin in Local Controlled Release and Systemic Delivery for Calvarial Defect in Ovariectomized Rats

Typically, bone regenerative medicine is applied to repair bone defects in patients with osteoporosis. Meanwhile, there is an urgent need to develop safe and cheap drugs that induce bone formation. Icariin, which is reported to promote the osteogenesis of stem cells in vitro, is the main active component of Herba Epimedii. However, whether icariin could repair bone defects caused by osteoporosis remains unknown. In this study, an osteoporosis model in rats was established by an ovariectomy first, and then, the osteogenic and angiogenic differentiation of bone mesenchymal stem cells (BMSCs) treated with icariin was evaluated. Furthermore, calcium phosphate cement (CPC) scaffolds loaded with icariin were constructed and then implanted into nude mice to determine the optimal construction. To evaluate its osteogenic and angiogenic ability in vivo, this construction was applied to calvarial defect of the ovariectomized (OVX) rats accompanied with an icariin gavage. This demonstrated that icariin could up-regulate the expression of osteogenic and angiogenic genes in BMSCs. Meanwhile, osteoclast formation was inhibited. Moreover, CPC could act as a suitable icariin delivery system for repairing bone defects by enhancing osteogenesis and angiogenesis, while the systemic administration of icariin has an antiosteoporotic effect that promotes bone defect repair.

Osteogenic differentiation potential of adipose-derived stem cells from ovariectomized mice

OBJECTIVES

Osteoporosis (OP) is a systemic disease caused by imbalance between bone resorption and bone formation, commonly resulting from post-menopausal oestrogen deficiency. Although osteogenic differentiation potential of adipose-derived stem cells (ASCs) has been demonstrated, the effect of OP on osteogenic differentiation of ASCs remains unclear. Here, our work has been designed to compare proliferative capacity and osteogenic differentiation ability of ASCs obtained from osteoporotic mice and normal control mice.

MATERIALS AND METHODS

Twenty 14-week-old female C57BL/6 mice were randomly divided into two groups: one, the ovariectomy (OVX) group (n=10), the other being the sham operated (Sham) group (n=10). ASCs and OP-ASCs were obtained from subcutaneous fat of female inguinal sites. Cells were passaged three times prior to subsequent experimentation. The xCELLigence system was used to monitor cell adhesion and proliferation. Mineralized nodules of differentiated ASCs and OP-ASCs were analysed using Alizarin red staining after osteogenic induction. Expressions of osteogenic-specific genes including osteopontin (Opn) and runt-related transcription factor 2 (Runx2) were assessed by real-time PCR and expression of bone-related proteins was detected by Western blotting.

RESULTS

Numbers of cells in all groups increased steadily for 6 days; rate of cell proliferation in the Sham group was found to be higher than in the OVX group after 48 hours. Mineralized bone nodular structures were significantly more concentrated in the Sham group than in the OVX group by day 21, and mRNA levels of Runx2 in the OVX group were significantly lower than in the Sham group. Transcript levels of genes coding for Opn showed a similar pattern to those of Runx2. Western blot results indicated that protein expression levels of OPN and RUNX2 in the OVX group were lower than those in the Sham group, at each time point.

CONCLUSIONS

These results indicated that the proliferative capacity and osteogenic potential of ASCs were significantly impaired in osteoporotic mice compared to normal controls. However, use of autologous transplantation of modified OP-ASCs for treatment of OP, or combination of composite scaffolds and modified OP-ASCs for repair of osteoporotic bone defects, can overcome shortcomings of other methods.

Nuclear factor of activated T-cell isoform expression and regulation in human myometrium

BACKGROUND

During pregnancy, myometrial gene and protein expression is tightly regulated to accommodate fetal growth, promote quiescence and ultimately prepare for the onset of labour. It is proposed that changes in calcium signalling, may contribute to regulating gene expression and that nuclear factor of activated T-cell (NFAT) transcription factors (isoforms c1-c4) may be involved. Currently, there is little information regarding NFAT expression and regulation in myometrium.

METHODS

This study examined NFAT isoform mRNA expression in human myometrial tissue and cells from pregnant women using quantitative PCR. The effects of the Ca(2+) ionophore A23187 and in vitro stretch (25 % elongation, static strain; Flexercell FX-4000 Tension System) on NFAT expression were determined in cultured human myometrial cells.

RESULTS

Human myometrial tissue and cultured cells expressed NFATc1-c4 mRNA. NFATc2 gene expression in cultured cells was increased in response to 6 h stretch (11.5 fold, P < 0.001, n = 6) and calcium ionophore (A23187, 5 μM) treatment (20.6 fold, P < 0.001, n = 6). This response to stretch was significantly reduced (90 %, P < 0.001, n = 10) in the presence of an intracellular calcium chelator, BAPTA-AM (20 μM).

CONCLUSIONS

These data suggest that NFATc2 expression is regulated by intracellular calcium and in vitro stretch, and that the stretch response in human myometrial cells is dependent upon intracellular calcium signalling pathways. Our findings indicate a potentially unique role for NFATc2 in mediating stretch-induced gene expression per se and warrant further exploration in relation to the mechanisms promoting uterine smooth muscle growth in early pregnancy and/or labour.

Effect of Qing'e formula on the in vitro differentiation of bone marrow-derived mesenchymal stem cells from proximal femurs of postmenopausal osteoporotic mice

BACKGROUND

Qing'e formula (QEF), prepared from an ancient Chinese recipe, was previously suggested to regulate bone metabolism and improve bone mineral density in patients with osteoporosis. To study the effects of medicated serum containing QEF on the in vitro differentiation of bone marrow-derived mesenchymal stem cells (BMSCs) isolated from the proximal femurs of postmenopausal osteoporosis (PMOP) mice.

METHODS

Using an established mouse model of PMOP, mononuclear cells were isolated from the bone marrow present in the proximal femurs and cultured. PMOP mice were also randomly divided into four groups: the untreated group (Group A) and the groups treated with respectively low (Group B), medium (Group C), and high (Group D) concentrations of QEF. Serum was isolated from each and used to treat the cultured BMSCs in conjunction with recombinant human bone morphogenetic protein-2 (rhBMP-2). Cell morphology, proliferation rates, intracellular alkaline phosphatase (ALP) activity, and transforming growth factor-beta 1 (TGF-β1) mRNA expression were evaluated.

RESULTS

QEF-treated serum, particularly that containing moderate and high concentrations, appears to enhance the rhBMP-2-mediated changes in cell morphology, proliferation, and differentiation (determined via the expression of TGF-β1 mRNA and ALP activity) observed in the BMSCs isolated from PMOP mice.

CONCLUSIONS

QEF may play a role in the prevention and treatment of PMOP by enhancing the activity of rhBMP-2.