Effects of different oxygen concentrations on the proliferation, survival, migration, and osteogenic differentiation of MC3T3-E1 cells

Inhibition of cysteine protease disturbs the topological relationship between bone resorption and formation in vitro

INTRODUCTION

Osteoporosis is a global health issue. Bisphosphonates that are commonly used to treat osteoporosis suppress both bone resorption and subsequent bone formation. Inhibition of cathepsin K, a cysteine proteinase secreted by osteoclasts, was reported to suppress bone resorption while preserving or increasing bone formation. Analyses of the different effects of antiresorptive reagents such as bisphosphonates and cysteine proteinase inhibitors will contribute to the understanding of the mechanisms underlying bone remodeling.

MATERIALS AND METHODS

Our team has developed an in vitro system in which bone remodeling can be temporally observed at the cellular level by 2-photon microscopy. We used this system in the present study to examine the effects of the cysteine proteinase inhibitor E-64 and those of zoledronic acid on bone remodeling.

RESULTS

In the control group, the amount of the reduction and the increase in the matrix were correlated in each region of interest, indicating the topological and quantitative coordination of bone resorption and formation. Parameters for osteoblasts, osteoclasts, and matrix resorption/formation were also correlated. E-64 disrupted the correlation between resorption and formation by potentially inhibiting the emergence of spherical osteoblasts, which are speculated to be reversal cells in the resorption sites.

CONCLUSION

These new findings help clarify coupling mechanisms and will contribute to the development of new drugs for osteoporosis.

The biological responses of osteoblasts on titanium: Effect of oxygen level and surface roughness

BACKGROUND/PURPOSE

Due to the general application of in vitro test, cell culture is generally selected to evaluate the cytocompatibility of devices and materials. The choice of test condition should depend on the probable site and clinical application. The oxygen content of human body could be estimated around 5%∼12%, and the oxygen level of healing bone fracture range from 0.8%∼3.8%%. However, materials for bone implant are traditionally evaluated under laboratory normoxia condition (21% O₂) in vitro. The aim was to study the effect of oxygen level on osteoblast upon high stiffness titanium with different roughness.

METHODS

After sandblasted and acid-etched (SLA) process, we create titanium surfaces with four different roughness. The differentiation and proliferation of MC3T3-E1 osteoblast cultured on SLA-treated specimens were evaluated in designed chamber with oxygen level of 1%, 5%, 10%, 21%.

RESULTS

By scanning electron microscopy, all samples had sub-micro pit inside the micro-holes upon SLA-treated Ti disk surface. The decrease of oxygen level from 21% to 5% promoted osteoblast growth of SLA-treated specimens, but 1% O₂ delayed cell proliferation. The surface roughness of specimens influenced osteoblast cell differentiation. The differentiation and proliferation ability of the cells upon SLA-treated specimens is proportional to oxygen level.

CONCLUSION

Our results demonstrated that 5% O₂ will easily discriminate osteoblasts responses on different SLA-treated specimens. These results suggest that hypoxia (5% O₂) environment is better model for biological evaluation of bone-related materials.

Roles of oxygen level and hypoxia-inducible factor signaling pathway in cartilage, bone and osteochondral tissue engineering

The repair and treatment of articular cartilage injury is a huge challenge of orthopedics. Currently, most of the clinical methods applied in treating cartilage injuries are mainly to relieve pains rather than to cure them, while the strategy of tissue engineering is highly expected to achieve the successful repair of osteochondral defects. Clear understandings of the physiological structures and mechanical properties of cartilage, bone and osteochondral tissues have been established, but the understanding of their physiological heterogeneity still needs further investigation. Apart from the gradients in the micromorphology and composition of cartilage-to-bone extracellular matrixes, an oxygen gradient also exists in natural osteochondral tissue. The response of hypoxia-inducible factor (HIF)-mediated cells to oxygen would affect the differentiation of stem cells and the maturation of osteochondral tissue. This article reviews the roles of oxygen level and HIF signaling pathway in the development of articular cartilage tissue, and their prospective applications in bone and cartilage tissue engineering. The strategies for regulating HIF signaling pathway and how these strategies finding their potential applications in the regeneration of integrated osteochondral tissue are also discussed.

3D printed polycaprolactone/beta-tricalcium phosphate/magnesium peroxide oxygen releasing scaffold enhances osteogenesis and implanted BMSCs survival in repairing the large bone defect

Ischemia and hypoxia in the bone defect area remain an intractable problem when treating large bone defects. Thus, oxygen-releasing biomaterials have been widely researched in recent years. Magnesium peroxide (MgO2) can release oxygen (O2), and magnesium ions (Mg2+), simultaneously, which is seen to have significant potential in bone substitutes. In this study, we used 3D printing technology to fabricate a MgO2-contained composite scaffold, which was composed of polycaprolactone (PCL), beta-tricalcium phosphate (β-TCP) and magnesium peroxide (MgO2). Physical properties and O2/Mg2+ releasing behavior of the scaffold were studied. Then, we evaluated the effects of the scaffold on cell survival, proliferation, migration, adhesion and osteogenic differentiation by the co-culture of bone marrow mesenchymal stem cells (BMSCs) and scaffold under normoxia and hypoxia in vitro. Finally, the osteogenic properties of the scaffold in vivo were evaluated via the rat femoral condylar bone defect model. The PCL/β-TCP/MgO2 scaffold showed good mechanical properties and sustained O2 and Mg2+ release for about three weeks. Meanwhile, the scaffold showed appreciable promotion on the survival, proliferation, migration and osteogenic differentiation of BMSCs under hypoxia compared with control groups. The results of imaging studies and histological analysis showed that implantation of PCL/β-TCP/MgO2 scaffold could promote seed cell survival and significantly increased new bone formation. In sum, the PCL/β-TCP/MgO2 scaffold is promising with great potential for treating large bone defects.

Optimizing an Injectable Composite Oxygen-Generating System for Relieving Tissue Hypoxia

Oxygen deficiency resulting from bone fracture-induced vascular disruption leads to massive cell death and delayed osteoblast differentiation, ultimately impairing new bone formation and fracture healing. Enhancing local tissue oxygenation can help promote bone regeneration. In this work, an injectable composite oxygen-generating system consisting of calcium peroxide (CaO₂)/manganese dioxide (MnO₂)-encapsulated poly lactic-co-glycolic acid (PLGA) microparticles (CaO₂ + MnO₂@PLGA MPs) is proposed for the local delivery of oxygen. By utilizing a series of methodologies, the impacts of each component used for MP fabrication on the oxygen release behavior and cytotoxicity of the CaO₂ + MnO₂@ PLGA MPs are thoroughly investigated. Our analytical data obtained from in vitro studies indicate that the optimized CaO₂ + MnO₂@PLGA MPs developed in this study can effectively relieve the hypoxia of preosteoblast MC3T3-E1 cells that are grown under low oxygen tension and promote their osteogenic differentiation, thus holding great promise in enhancing fractural healing by increasing tissue oxygenation.

Cell migration of preosteoblast cells on a clinical gelatin sponge for 3D bone tissue engineering

Using three-dimensional (3D) bone engineering to fabricate bone segments is a better choice for repairing bone defects than using autologous bone. However, biomaterials for bone engineering are burdened with some clinical safety concerns. In this study, we layered commonly found clinical materials, hemostatic gelatin sponges, in a novel manner to create a 3D scaffold for bone engineering purposes. We further examined the comparable benefits of our design with both closed- and open-bottom holders. Cells in stacked layer disc systems were examined after a week of growth and differentiation. Osteoblasts in the outer layers of both closed- and open-bottom holder systems displayed gradually increased alkaline phosphatase (ALP) activity but decreased osteopontin (OPN) expression. Further, cell proliferation assays and LIVE/DEAD staining revealed decreased viable cell counts in the top layer with increased incubation time. However, while layered disc systems with closed-bottom holders underwent differentiation, they kept more differentiated cells alive within the gelatin sponge disc scaffold after 28 d of culturing. Whether cells were inoculated into the top, middle, or bottom portions of the layered disc stack, osteoblasts showed a preference for migrating to the top layer, in keeping with the oxygen and nutrients gradients. Regarding practical application, this study offers valuable information to promote the use of hemostatic gelatin sponges for bone engineering.

Hypoxia reduces the osteogenic differentiation of peripheral blood mesenchymal stem cells by upregulating Notch-1 expression

Purpose: Mesenchymal stem cells (MSCs) seeded on biocompatible scaffolds have therapeutic potential for bone defect repair. However, MSCs can be affected by hypoxia and nutritional deficiency due to a lack of blood vessels in the scaffolds. Here, we explored the effects of hypoxia on MSC differentiation to clarify these mechanisms. Methods: Peripheral blood mesenchymal stem cells (PBMSCs) were cultured in small individual chambers with oxygen concentrations of 1%, 9%, and 21%. Cell proliferation was evaluated by Cell Counting Kit 8 assays, and cell survival was determined using live/dead assays. Scratch assays were performed to evaluate cell migration. Ca²⁺ deposition/mineralization experiments, reverse transcription quantitative real-time polymerase chain reaction, and Western blotting were performed to assess the osteogenic differentiation of cells. Notch1 expression was downregulated by lentivirus-transfected PBMSCs to observe the effects of Notch1 knockdown on osteogenic gene and protein expression. Results: PBMSCs exposed to hypoxia (1% O₂) demonstrated accelerated proliferation, increased migration, and reduced survival in the absence of serum. Although 9% oxygen promoted osteogenic differentiation, the osteogenic differentiation of PBMSCs was significantly reduced by 1% O₂, and this effect was associated with increased Notch1 expression. Reducing Notch1 expression using small interfering RNA significantly restored the osteogenic differentiation of PBMSCs. Conclusions: Hypoxia accelerated proliferation, increased migration, and reduced PBMSC differentiation into osteoblasts by increasing Notch1 expression. These findings may contribute to the development of appropriate cell culture or in vivo transplantation conditions to maintain the full osteogenic potential of PBMSCs.