Prolonged Survival of Transplanted Osteoblastic Cells Does Not Directly Accelerate the Healing of Calvarial Bone Defects

Controlling redox state by edaravone at transplantation site enhances bone regeneration

In cell-based bone augmentation, transplanted cell dysfunction and apoptosis can occur due to oxidative stress caused by the overproduction of reactive oxygen species (ROS). Edaravone (EDA) is a potent free radical scavenger with potential medical applications. This study aimed to investigate the effect of controlling oxidative stress on bone regeneration using EDA. Bone marrow-derived cells were collected from 4-week-old rats, and EDA effects on cell viability and osteogenic differentiation were evaluated. Collagen gels containing PKH26-prelabeled cells were implanted into the calvarial defects of 12-week-old rats, followed by daily subcutaneous injections of normal saline or 500 μM EDA for 4 d. Bone formation was examined using micro-computed tomography and histological staining. Immunofluorescence staining was performed for markers of oxidative stress, macrophages, osteogenesis, and angiogenesis. EDA suppressed ROS production and hydrogen peroxide-induced apoptosis, recovering cell viability and osteoblast differentiation. EDA treatment in vivo increased new bone formation. EDA induced the transition of the macrophage population toward the M2 phenotype. The EDA group also exhibited stronger immunofluorescence for vascular endothelial growth factor and CD31. In addition, more PKH26-positive and PKH26-osteocalcin-double-positive cells were observed in the EDA group, indicating that transplanted cell survival was prolonged, and they differentiated into bone-forming cells. This could be attributed to oxidative stress suppression at the transplantation site by EDA. Collectively, local administration using EDA facilitates bone regeneration by improving the local environment and angiogenesis, prolonging survival, and enhancing the osteogenic capabilities of transplanted cells.

Mild photothermal therapy assist in promoting bone repair: Related mechanism and materials

Achieving precision treatment in bone tissue engineering (BTE) remains a challenge. Photothermal therapy (PTT), as a form of precision therapy, has been extensively investigated for its safety and efficacy. It has demonstrated significant potential in the treatment of orthopedic diseases such as bone tumors, postoperative infections and osteoarthritis. However, the high temperatures associated with PTT can lead to certain limitations and drawbacks. In recent years, researchers have explored the use of biomaterials for mild photothermal therapy (MPT), which offers a promising approach for addressing these limitations. This review provides a comprehensive overview of the mechanisms underlying MPT and presents a compilation of photothermal agents and their utilization strategies for bone tissue repair. Additionally, the paper discusses the future prospects of MPT-assisted bone tissue regeneration, aiming to provide insights and recommendations for optimizing material design in this field.

Novel approaches for periodontal tissue engineering

The periodontal complex involves the hard and soft tissues which support dentition, comprised of cementum, bone, and the periodontal ligament (PDL). Periodontitis, a prevalent infectious disease of the periodontium, threatens the integrity of these tissues and causes irreversible damage. Periodontal therapy aims to repair and ultimately regenerate these tissues toward preserving native dentition and improving the physiologic integration of dental implants. The PDL contains multipotent stem cells, which have a robust capacity to differentiate into various types of cells to form the PDL, cementum, and alveolar bone. Selection of appropriate growth factors and biomaterial matrices to facilitate periodontal regeneration are critical to recapitulate the physiologic organization and function of the periodontal complex. Herein, we discuss the current state of clinical periodontal regeneration including a review of FDA-approved growth factors. We will highlight advances in preclinical research toward identifying additional growth factors capable of robust repair and biomaterial matrices to augment regeneration similarly and synergistically, ultimately improving periodontal regeneration's predictability and long-term efficacy. This review should improve the readers' understanding of the molecular and cellular processes involving periodontal regeneration essential for designing comprehensive therapeutic approaches.

Melatonin enhances osteogenic differentiation of dental pulp mesenchymal stem cells by regulating MAPK pathways and promotes the efficiency of bone regeneration in calvarial bone defects

Background

Mesenchymal stem cell (MSC)-based tissue engineering plays a major role in regenerative medicine. However, the efficiency of MSC transplantation and survival of engrafted stem cells remain challenging. Melatonin can regulate MSC biology. However, its function in the osteogenic differentiation of dental pulp-derived MSCs (DPSCs) remains unclear. We investigated the effects and mechanisms of melatonin on the osteogenic differentiation and bone regeneration capacities of DPSCs.

Methods

The biological effects and signaling mechanisms of melatonin with different concentrations on DPSCs were evaluated using a proliferation assay, the quantitative alkaline phosphatase (ALP) activity, Alizarin red staining, a real-time polymerase chain reaction, and a western blot in vitro cell culture model. The in vivo bone regeneration capacities were assessed among empty control, MBCP, MBCP + DPSCs, and MBCP + DPSCs + melatonin preconditioning in four-created calvarial bone defects by using micro-computed tomographic, histological, histomorphometric, and immunohistochemical analyses after 4 and 8 weeks of healing.

Results

In vitro experiments revealed that melatonin (1, 10, and 100 μM) significantly and concentration-dependently promoted proliferation, surface marker expression (CD 146), ALP activity and extracellular calcium deposition, and osteogenic gene expression of DPSCs (p < 0.05). Melatonin activated the protein expression of ALP, OCN, and RUNX-2 and inhibited COX-2/NF-κB expression. Furthermore, the phosphorylation of mitogen-activated protein kinase (MAPK) p38/ERK signaling was significantly increased in DPSCs treated with 100 μM melatonin, and their inhibitors significantly decreased osteogenic differentiation. In vivo experiments demonstrated that bone defects implanted with MBCP bone-grafting materials and melatonin-preconditioned DPSCs exhibited significantly greater bone volume fraction, trabecular bone structural modeling, new bone formation, and osteogenesis-related protein expression than the other three groups at 4 and 8 weeks postoperatively (p < 0.05).

Conclusions

These results suggest that melatonin promotes the proliferation and osteogenic differentiation of DPSCs by regulating COX-2/NF-κB and p38/ERK MAPK signaling pathways. Preconditioning DPSCs with melatonin before transplantation can efficiently enhance MSCs function and regenerative capacities.

New paradigms in regenerative engineering: Emerging role of extracellular vesicles paired with instructive biomaterials

Mesenchymal stem cells (MSCs) have long been regarded as critical components of regenerative medicine strategies, given their multipotency and persistence in a variety of tissues. Recently, the specific role of MSCs in mediating regenerative outcomes has been attributed (in part) to secreted factors from transplanted cells, namely extracellular vesicles. This viewpoint manuscript highlights the promise of cell-derived extracellular vesicles as agents of regeneration, enhanced by synergy with appropriate biomaterials platforms. Extracellular vesicles are a potentially interesting regenerative tool to enhance the synergy between MSCs and biomaterials. As a result, we believe these technologies will improve patient outcomes through efficient therapeutic strategies resulting in predictable patient outcomes.

Three-dimensional Spheroid Culture Enhances Multipotent Differentiation and Stemness Capacities of Human Dental Pulp-derived Mesenchymal Stem Cells by Modulating MAPK and NF-kB Signaling Pathways

BACKGROUND

Three-dimensional (3D) culture of mesenchymal stem cells has become an important research and development topic. However, comprehensive analysis of human dental pulp-derived mesenchymal stem cells (DPSCs) in 3D-spheroid culture remains unexplored. Thus, we evaluated the cellular characteristics, multipotent differentiation, gene expression, and related-signal transduction pathways of DPSCs in 3D-spheroid culture via magnetic levitation (3DM), compared with 2D-monolayer (2D) and 3D-aggregate (3D) cultures.

METHODS

The gross morphology and cellular ultrastructure were observed in the 2D, 3D, and 3DM experimental groups using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Surface markers and trilineage differentiation were evaluated using flow cytometry and staining analysis. Quantitative reverse transcription-polymerase chain reaction and immunofluorescence staining (IF) were performed to investigate the expression of differentiation and stemness markers. Signaling transduction pathways were evaluated using western blot analysis.

RESULTS

The morphology of cell aggregates and spheroids was largely influenced by the types of cell culture plates and initial cell seeding density. SEM and TEM experiments confirmed that the solid and firm structure of spheroids was quickly formed in the 3DM-medium without damaging cells. In addition, these three groups all expressed multilineage differentiation capabilities and surface marker expression. The trilineage differentiation capacities of the 3DM-group were significantly superior to the 2D and 3D-groups. The osteogenesis, angiogenesis, adipogenesis, and stemness-related genes were significantly enhanced in the 3D and 3DM-groups. The IF analysis showed that the extracellular matrix expression, osteogenesis, and angiogenesis proteins of the 3DM-group were significantly higher than those in the 2D and 3D-groups. Finally, 3DM-culture significantly activated the MAPK and NF-kB signaling transduction pathways and ameliorated the apoptosis effects of 3D-culture.

CONCLUSIONS

This study confirmed that 3DM-spheroids efficiently enhanced the therapeutic efficiency of DPSCs.

Scaffolds with controlled release of pro-mineralization exosomes to promote craniofacial bone healing without cell transplantation

Biomimetic bone regeneration methods which demonstrate both clinical and manufacturing feasibility, as alternatives to autogenic or allogenic bone grafting, remain a challenge to the field of tissue engineering. Here, we report the pro-osteogenic capacity of exosomes derived from human dental pulp stem cells (hDPSCs) to facilitate bone marrow stromal cell (BMSC) differentiation and mineralization. To support their delivery, we engineered a biodegradable polymer delivery platform to improve the encapsulation and the controlled release of exosomes on a tunable time scale from poly(lactic-co-glycolic acid) (PLGA) and poly(ethylene glycol) (PEG) triblock copolymer microspheres. Our delivery platform integrates within three-dimensional tissue engineering scaffolds to enable a straightforward surgical insertion into a mouse calvarial defect. We demonstrate the osteogenic potential of these functional constructs in vitro and in vivo. Controlled release of osteogenic hDPSC-derived exosomes facilitates osteogenic differentiation of BMSCs, leading to mineralization to a degree which is comparable to exogenous administration of the same exosomes in human and mouse BMSCs. By recruiting endogenous cells to the defects and facilitating their differentiation, the controlled release of osteogenic exosomes from a tissue engineering scaffold demonstrates accelerated bone healing in vivo at 8 weeks. Exosomes recapitulate the advantageous properties of mesenchymal stem/progenitor cells, without manufacturing or immunogenic concerns associated with transplantation of exogenous cells. This biomaterial platform enables exosome-mediated bone regeneration in an efficacious and clinically relevant way.

Extracellular matrix with defective collagen cross-linking affects the differentiation of bone cells

Fibrillar type I collagen, the predominant organic component in bone, is stabilized by lysyl oxidase (LOX)-initiated covalent intermolecular cross-linking, an important determinant of bone quality. However, the impact of collagen cross-linking on the activity of bone cells and subsequent tissue remodeling is not well understood. In this study, we investigated the effect of collagen cross-linking on bone cellular activities employing a loss-of-function approach, using a potent LOX inhibitor, β-aminopropionitrile (BAPN). Osteoblastic cells (MC3T3-E1) were cultured for 2 weeks in the presence of 0–2 mM BAPN to obtain low cross-linked collagen matrices. The addition of BAPN to the cultures diminished collagen cross-links in a dose-dependent manner and, at 1 mM level, none of the major cross-links were detected without affecting collagen production. After the removal of cellular components from these cultures, MC3T3-E1, osteoclasts (RAW264.7), or mouse primary bone marrow-derived stromal cells (BMSCs) were seeded. MC3T3-E1 cells grown on low cross-link matrices showed increased alkaline phosphatase (ALP) activity. The number of multinucleate tartrate-resistant acid phosphatase (TRAP)-positive cells increased in RAW264.7 cells. Initial adhesion, proliferation, and ALP activity of BMSCs also increased. In the animal experiments, 4-week-old C57BL/6 mice were fed with BAPN-containing diet for 8 weeks. At this point, biochemical analysis of bone demonstrated that collagen cross-links decreased without affecting collagen content. Then, the diet was changed to a control diet to minimize the direct effect of BAPN. At 2 and 4 weeks after the change, histological samples were prepared. Histological examination of femur samples at 4 weeks showed a significant increase in the number of bone surface osteoblasts, while the bone volume and surface osteoclast numbers were not significantly affected. These results clearly demonstrated that the extent of collagen cross-linking of bone matrix affected the differentiation of bone cells, underscoring the importance of collagen cross-linking in the regulation of cell behaviors and tissue remodeling in bone. Characterization of collagen cross-linking in bone may be beneficial to obtain insight into not only bone mechanical property, but also bone cellular activities.