Recent Advances in Enhancement Strategies for Osteogenic Differentiation of Mesenchymal Stem Cells in Bone Tissue Engineering

Circular RNAs inducing the osteogenic differentiation of dental mesenchymal stem cells via microRNA sponging

Circular RNAs (circRNAs) are a distinct type of nonlinear and noncoding RNAs endogenously expressed by pre-mRNA back-splicing and crucial in transcriptional and posttranscriptional regulation. CircRNAs can regulate cellular and molecular pathways through various mechanisms, such as microRNA sponging. Numerous studies have indicated the regulatory roles of circRNAs in the osteogenic differentiation of stem cells (SCs) isolated from different sources. Dental tissue-derived mesenchymal SCs (MSCs) have received considerable attention in artificial bone engineering, in which SCs are used to manufacture functional bone tissues to repair bone defects. Recently, studies have reported the regulatory roles of circRNAs in the osteogenic differentiation of dental-derived MSCs, such as apical papillae, dental pulp, and dental follicle SCs. This review aimed to discuss the findings of studies evaluating the contribution of circRNAs to the osteogenic differentiation of dental-derived MSCs.

Titanium Surface Roughness Mediated Macrophages Polarization-Influenced Osteogenic Differentiation of Periodontal Ligament-Derived Mesenchymal Stromal Cells

OBJECTIVES

 Implant surface topography significantly influences cell behavior, including macrophages and bone cell interactions. The polarization of macrophages, key immune cells, is influenced by implant surface characteristics. This research aimed to examine periodontal ligament mesenchymal stromal cells (PDL MSCs) responses to the polarized macrophages induced by titanium surface roughness.

MATERIALS AND METHODS

 RAW 264.7 macrophages were cultured with various surface roughness of titanium disks. Macrophage adhesion and polarization were evaluated by scanning electron microscope, gene expressions profiling, and flow cytometry. PDL MSCs were treated with conditioned medium of macrophages and analyzed with 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyl-2H-tetrazolium bromide assay, real-time polymerase chain reaction, and Alizarin red staining.

STATISTICAL ANALYSIS

 Data was statistically analyzed using GraphPad Prism 9 for Windows 11. The one-way analysis of variance test was used to compare the groups. Dunn post hoc test was used to compare the difference between the groups when appropriate. Significance was accepted when p < 0.05.

RESULTS

 Medium surface roughness (Ti-MR) consistently inhibited tumor necrosis factor-α, interleukin-1β (IL-1β), and IL-6 gene expressions (p < 0.001) and upregulated transforming growth factor-β, vascular epithelial growth factor, and IL-10 expressions (p < 0.01). Confirmatory flow cytometry analysis showed consistent results, with Ti-HR and Ti-MR exhibiting the highest population of CD163+ cells (99.1 and 90.7%, respectively), while Ti-LR exhibited the lowest M1/M2 ratio (0.93). Furthermore, treatment of RAW 264.7 conditioned medium increased osteopontin, alkaline phosphatase, collagen type-1 A-1 chain, osteocalcin, runt-related transcription factor-2, and bone sialoprotein gene expressions and calcium deposition (p < 0.01).

CONCLUSION

 Titanium implant surface topography influences macrophage polarization and osteogenic differentiation of PDL MSCs, with Ti-MR being the most effective in polarizing macrophages toward M2 and inducing optimal osteogenic responses from PDL MSCs.

Dual-regulation biomimetic composite nerve scaffold with oriented structure and conductive function for skin peripheral nerve injury repair

Skin peripheral nerve injury repair still faces significant clinical challenges. Although nerve tissue engineering scaffolds show potential, issues such as limited functionality and low repair efficiency persist. This study developed a dual-regulation biomimetic composite nerve scaffold with oriented structure and conductive function to promote nerve injury repair. The structural layer was a chitosan (CS)/polycaprolactone (PCL) oriented nanofiber membrane, which could promote cell adhesion and induce directional growth of cells. The functional layer was a CS/sodium alginate (SA) ionic conductive hydrogel, which could enhance endogenous electric fields to promote cell proliferation and differentiation. The two layers were combined through physical crosslinking, avoiding the use of chemical adhesives and preserving the surface morphology of the nanofibrous membrane and the porous structure of the hydrogel. The biomimetic composite nerve scaffold exhibited layered degradability, excellent orientation, conductivity, and biocompatibility. Cell experiments indicated that the scaffold effectively induced directional migration, growth, and differentiation of cells and enhanced cell activity, thereby providing a favorable microenvironment for nerve regeneration. This study not only overcomes the limitation of functional singularity in traditional nerve scaffolds but also aligns with the forefront trend in tissue engineering toward multifunctional and biomimetic materials. It demonstrates great potential for treating complex conditions such as traumatic nerve defects and post-surgical nerve regeneration and has broad application prospects in the field of neural tissue engineering.

Effect of Recombinant Human Amelogenin on the Osteogenic Differentiation Potential of SHED

This study aimed to explore how amelogenin can improve stem cells from human exfoliated deciduous teeth (SHED)-based bone regeneration and promote tissue healing as a treatment for critical-sized bone defects. SHED was induced into bone differentiation by using osteogenic differentiation medium. Real-time polymerase chain reaction, alkaline phosphatase (ALP) staining and quantification, and Alizarin Red S staining, as well as calcium and osteocalcin quantification were performed to assess differentiation. On day 18, a significant increase was observed in the expression of RUNX2, CBFB, BGLAP, COL1, BMP2, BMP4, NOTCH1, NOTCH2, and NES. Osteocalcin gene expression continued to increase significantly. ALP activity was significantly higher in the amelogenin-treated group than in the control group on days 7, 10, and 14. On day 14, enhanced ALP staining was observed in the amelogenin-treated group. Calcium and osteocalcin levels were significantly higher in the amelogenin-treated group than in the control group on day 21. This study suggests that combining SHED and amelogenin may be effective for bone regeneration, offering a potential new approach in regenerative medicine.

Coculture of mesenchymal stem cells and macrophage: A narrative review

Stem cell transplantation is a promising treatment for repairing damaged tissues, but challenges like immune rejection and ethical concerns remain. Mesenchymal stem cells (MSCs) offer high differentiation potential and immune regulatory activity, showing promise in treating diseases such as gynecological, neurological, and kidney disorders. With scientific progress, MSC applications are overcoming traditional treatment limitations. In MSCs-macrophage coculture, MSCs transform macrophages into anti-inflammatory M2 macrophages, reducing inflammation, whereas macrophages enhance MSCs osteogenic differentiation. This coculture is vital for immune modulation and tissue repair, with models varying by contact type and dimensional arrangements. Factors such as coculture techniques and cell ratios influence outcomes. Benefits include improved heart function, wound healing, reduced lung inflammation, and accelerated bone repair. Challenges include optimizing coculture conditions. This study reviews the methodologies, factors, and mechanisms of MSC-macrophage coculture, providing a foundation for tissue engineering applications. SIGNIFICANCE STATEMENT: This review underlines the significant role of mesenchymal stem cell-macrophage coculture, providing a foundation for tissue engineering application.

3D-Printed PCL Scaffolds Loaded with bFGF and BMSCs Enhance Tendon-Bone Healing in Rat Rotator Cuff Tears by Immunomodulation and Osteogenesis Promotion

Rotator cuff tears are the most common conditions in sports medicine and attract increasing attention. Scar tissue healing at the tendon-bone interface results in a high rate of retears, making it a major challenge to enhance the healing of the rotator cuff tendon-bone interface. Biomaterials currently employed for tendon-bone healing in rotator cuff tears still exhibit limited efficacy. As a promising technology, 3D printing enables the customization of scaffold shapes and properties. Bone marrow mesenchymal stem cells (BMSCs) have multidifferentiation potential and valuable immunomodulatory effects. The basic fibroblast growth factor (bFGF), known for its role in proliferation, has been reported to promote osteogenesis. These properties make them applicable in tissue engineering. In this study, we developed a 3D-printed polycaprolactone (PCL) scaffold loaded with bFGF and BMSCs (PCLMF) to restore the tendon-bone interface and regulate the local inflammatory microenvironment. The PCLMF scaffolds significantly improved the biomechanical strength, histological score, and local bone mineral density at regenerated entheses at 2 weeks postsurgery and achieved optimal performance at 8 weeks. Furthermore, PCLMF scaffolds facilitated BMSC osteogenic differentiation and suppressed adipogenic differentiation both in vivo and in vitro. In addition, RNA-seq showed that PCLMF scaffolds could regulate macrophage polarization and inflammation through the MAPK pathway. The implanted scaffold demonstrated excellent biocompatibility and biosafety. Therefore, this study proposes a promising and practical strategy for enhancing tendon-bone healing in rotator cuff tears.

Signaling Pathways Driving MSC Osteogenesis: Mechanisms, Regulation, and Translational Applications

Mesenchymal stem cells (MSCs) are crucial for skeletal development, homeostasis, and repair, primarily through their differentiation into osteoblasts and other skeletal lineage cells. Key signaling pathways, including Wnt, TGF-β/BMP, PTH, Hedgehog, and IGF, act as critical regulators of MSC osteogenesis, playing pivotal roles in maintaining bone homeostasis and facilitating regeneration. These pathways interact in distinct ways at various stages of bone development, mineralization, and remodeling. This review provides an overview of the molecular mechanisms by which these pathways regulate MSC osteogenesis, their influence on bone tissue formation, and their implications in bone diseases and therapeutic strategies. Additionally, we explore the potential applications of these pathways in bone tissue engineering, with a particular focus on promoting the use of MSCs as seed cells for bone defect repair. Ultimately, this review aims to highlight potential avenues for advancing bone biology research, treating bone disorders, and enhancing regenerative medicine.

The relationship between non-HDL-C/HDL-C ratio and bone mineral density: an NHANES study

Background

The non-high-density lipoprotein cholesterol to high-density lipoprotein cholesterol ratio (NHHR) is a newly developed lipid parameter. However, the current research has only explored the relationship with lumbar spine bone mineral density, lacking studies on bone mineral density at other sites, total body bone mineral density, and an analysis of risk factors. This study aims to determine the potential association between NHHR and lumbar BMD, increase awareness of the impact of lipid levels on bone health.

Methods

By utilizing data from the National Health and Nutrition Examination Survey (NHANES) from 2011 to 2018, we conducted univariate and generalized linear models (GLMs) analysis, stratified analysis, threshold effect analysis, smooth curve fitting and stratified analysis to investigate the association between NHHR and BMD. NHHR levels were categorized into tertiles (low, medium, and high) based on their distribution among the study population.

Results

The study included 8,671participants, studies have shown, the ratio of non-high-density lipoprotein to high-density lipoprotein (NHHR) exhibits a stratified correlation with bone mineral density (BMD). In the BMI subgroup, NHHR is significantly negatively correlated with BMD at multiple sites in the low-to-middle BMI group (BMI <25 kg/m2), while no significant correlation is found in the high BMI group (BMI ≥30 kg/m2). In the gender subgroup, NHHR has a more pronounced effect on male BMD, mainly reflected in the reduction of lumbar spine and total body BMD. In the age subgroup, the negative correlation between NHHR and BMD is strongest in the younger group (18-30 years), gradually weakening in the middle-aged (31-44 years) and older groups (45-59 years). Further analysis suggests that dyslipidemia may influence bone metabolism through pathways such as inflammation and oxidative stress.

Conclusion

The effect of NHHR on bone mineral density (BMD) varies by BMI, gender, and age. This study suggests that controlling NHHR levels may be a potential intervention target for bone health management, particularly for individuals with low-to-middle BMI, males, and younger populations. These findings offer a new perspective on the relationship between lipid metabolism and bone metabolism and provide scientific evidence for the development of personalized osteoporosis prevention and treatment strategies.

Exploration of Key Regulatory Factors in Mesenchymal Stem Cell Continuous Osteogenic Differentiation via Transcriptomic Analysis

BACKGROUND/OBJECTIVES

Mesenchymal stem cells (MSCs) possess the remarkable ability to differentiate into various cell types, including osteoblasts. Understanding the molecular mechanisms governing MSC osteogenic differentiation is crucial for advancing clinical applications and our comprehension of complex disease processes. However, the key biological molecules regulating this process remain incompletely understood.

METHODS

In this study, we conducted systematic re-analyses of published high-throughput transcriptomic datasets to identify and validate key biological molecules that dynamically regulate MSC osteogenic differentiation. Our approach involved a comprehensive analysis of gene expression patterns across human tissues, followed by the rigorous experimental validation of the identified candidates.

RESULTS

Through integrated analytical and experimental approaches, we utilized high-throughput transcriptomics to identify four critical regulators of MSC osteogenic differentiation: PTBP1, H2AFZ, BCL6, and TTPAL (C20ORF121). Among these, PTBP1 and H2AFZ functioned as positive regulators, while BCL6 and TTPAL acted as negative regulators in osteogenesis. The regulatory roles of these genes in osteogenesis were further validated via overexpression experiments.

CONCLUSIONS

Our findings advance our understanding of MSC differentiation fate determination and open new therapeutic possibilities for bone-related disorders. The identification of these regulators provides a foundation for developing targeted interventions in regenerative medicine.

Nanoparticle-Mediated Gene Delivery for Bone Tissue Engineering

Critical-sized bone defects represent an urgent clinical problem, necessitating innovative treatment approaches. Gene-activated grafts for bone tissue engineering have emerged as a promising solution. However, traditional gene delivery methods are constrained by limited osteogenic efficacy and safety concerns. Recently, organic and inorganic nanoparticle (NP) vectors have attracted significant attention in bone tissue engineering for their safe, stable, and controllable gene delivery. Targeted gene delivery guided by insights into bone healing mechanisms, coupled with the multifunctional design of NPs, is crucial for enhancing therapeutic outcomes. Here, the theoretical foundations underlying NP-mediated gene therapy for enhancing bone healing across different histological stages are elucidated. Furthermore, the distinct attributes of functionalized NP vectors are discussed, and cutting-edge strategies aimed at optimizing gene delivery efficiency throughout the therapeutic process are highlighted. Additionally, the review addresses the unresolved challenges and prospects of this technology. This review may contribute to the continued development and clinical application of NP-mediated gene delivery for treating critical-sized bone defects.

Rehmannioside A promotes the osteoblastic differentiation of MC3T3-E1 cells via the PI3K/AKT signaling pathway and inhibits glucocorticoid-induced bone loss in vivo

Glucocorticoid-induced osteoporosis (GIOP) is a widespread disease characterized by low bone density. There remains a lack of effective means for osteoporosis. Rehmannioside A (ReA), an iridoid glycoside, exhibits various pharmacological activities. This study aimed to explore the role and mechanism of ReA in osteogenic differentiation of osteoblasts. Cell viability, reactive oxygen species (ROS) generation, and cell apoptosis were assessed using corresponding assay kits. Real-time quantitative polymerase chain reaction, Western blotting, and alkaline phosphatase (ALP) staining were performed to evaluate the osteogenic differentiation of MC3T3-E1 cells. Alizarin red S staining was used to assess the mineralization of MC3T3-E1 cells. Protein expression associated with the phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) signaling pathway was analyzed using Western blotting. Micro-computed tomography, histopathological, and immunohistochemical analyses were performed to determine the therapeutic effect of ReA on GIOP in vivo.The results showed that ReA promoted the osteogenic differentiation of MC3T3-E1 cells by regulating the PI3K/AKT signaling pathway and protected mice against glucocorticoid-induced bone loss by promoting osteoblast-mediated bone formation in vivo. The findings of the current study revealed that ReA is a potential therapeutic agent for osteoporosis.

Bone Regeneration with Dental Pulp Stem Cells in an Experimental Model

BACKGROUND/OBJECTIVES

The therapeutic approach to bone mass loss and bone's limited self-regeneration is a major focus of research, emphasizing new biomaterials and cell therapy. Tissue bioengineering emerges as a potential alternative to conventional treatments. In this study, an experimental model of a critical bone lesion in rats was used to investigate bone regeneration by treating the defect with biomaterials Evolution® and Gen-Os® (OsteoBiol®, Turín, Italy), with or without mesenchymal stromal cells from dental pulp (DP-MSCs).

METHODS

Forty-six adult male Wistar rats were subjected to a 5-mm critical bone defect in the right mandible, which does not regenerate without intervention. The rats were randomly assigned to a Simulated Group, Control Group, or two Study Groups (using Evolution®, Gen-Os®, and DP-MSCs). The specimens were euthanized at three or six months, and radiological, histological, and ELISA tests were conducted to assess bone regeneration.

RESULTS

The radiological results showed that the DP-MSC group achieved uniform radiopacity and continuity in the bone edge, with near-complete structural defect restitution. Histologically, full bone regeneration was observed, with well-organized, vascularized lamellar bone and no lesion edges. These findings were supported by increases in endoglin, transforming growth factor-beta 1 (TGF-β1), protocollagen, parathormone, and calcitonin, indicating a conducive environment for bone regeneration.

CONCLUSIONS

The use of DP-MSCs combined with biomaterials with appropriate three-dimensional matrices is a promising therapeutic option for further exploration.

Injectable calcium phosphate cement integrated with BMSCs-encapsulated microcapsules for bone tissue regeneration

Injectable calcium phosphate cement (CPC) offers significant benefits for the minimally invasive repair of irregular bone defects. However, the main limitations of CPC, including its deficiency in osteogenic properties and insufficient large porosity, require further investigation and resolution. In this study, alginate-chitosan-alginate (ACA) microcapsules were used to encapsulate and deliver rat bone mesenchymal stem cells (rBMSCs) into CPC paste, while a porous CPC scaffold was established to support cell growth. Our results demonstrated that the ACA cell microcapsules effectively protect the cells and facilitate their transport into the CPC paste, thereby enhancing cell viability post-implantation. Additionally, the ACA + CPC extracts were found to stimulate osteogenic differentiation of rBMSCs. Furthermore, results from a rat cranial parietal bone defect model showed that ACA microcapsules containing exogenous rBMSCs initially improved thein situosteogenic potential of CPC within bone defects, providing multiple sites for bone growth. Over time, the osteogenic potential of the exogenous cells diminishes, yet the pores created by the microcapsules persist in supporting ongoing bone formation by recruiting endogenous cells to the osteogenic sites. In conclusion, the utilization of ACA loaded stem cell microcapsules satisfactorily facilitate osteogenesis and degradation of CPC, making it a promising scaffold for bone defect transplantation.

Mechanical network motifs as targets for mechanomedicine

The identification and analysis of network motifs has been widely used in the functional analysis of signaling components, disease discovery and other fields. The positive feedback loop (PFL) is a simple but important network motif. The formation of a PFL is regulated by mechanical cues such as substrate stiffness, fiber stretching and cell compression in the cell microenvironment. Here, we propose a new term, 'mechanical PFL', and analyze the mechanisms of mechanical PFLs at molecular, subcellular and cellular scales. More and more therapies are being targeted against mechanosignaling pathways at the experimental and preclinical stages, and exploring mechanical PFLs as potential mechanomedicine targets could be a new direction for disease treatment.

Autologous Fat Grafting-A Panacea for Scar Tissue Therapy?

Scars may represent more than a cosmetic concern for patients; they may impose functional limitations and are frequently associated with the sensation of itching or pain, thus impacting both psychological and physical well-being. From an aesthetic perspective, scars display variances in color, thickness, texture, contour, and their homogeneity, while the functional aspect encompasses considerations of functionality, pliability, and sensory perception. Scars located in critical anatomic areas have the potential to induce profound impairments, including contracture-related mobility restrictions, thereby significantly impacting daily functioning and the quality of life. Conventional approaches to scar management may suffice to a certain extent, yet there are cases where tailored interventions are warranted. Autologous fat grafting emerges as a promising therapeutic avenue in such instances. Fundamental mechanisms underlying scar formation include chronic inflammation, fibrogenesis and dysregulated wound healing, among other contributing factors. These mechanisms can potentially be alleviated through the application of adipose-derived stem cells, which represent the principal cellular component utilized in the process of lipofilling. Adipose-derived stem cells possess the capacity to secrete proangiogenic factors such as fibroblast growth factor, vascular endothelial growth factor and hepatocyte growth factor, as well as neurotrophic factors, such as brain-derived neurotrophic factors. Moreover, they exhibit multipotency, remodel the extracellular matrix, act in a paracrine manner, and exert immunomodulatory effects through cytokine secretion. These molecular processes contribute to neoangiogenesis, the alleviation of chronic inflammation, and the promotion of a conducive milieu for wound healing. Beyond the obvious benefit in restoring volume, the adipose-derived stem cells and their regenerative capacities facilitate a reduction in pain, pruritus, and fibrosis. This review elucidates the regenerative potential of autologous fat grafting and its beneficial and promising effects on both functional and aesthetic outcomes when applied to scar tissue.

Black phosphorus quantum dot-modified ADSCs as a novel therapeutic for periodontitis bone loss coupling of osteogenesis and osteoimmunomodulation

Alveolar bone defect repair remains a persistent clinical challenge for periodontitis treatment. The use of peripheral functional seed cells is a hot topic in periodontitis. Herein, we explored the cellular behaviors and osteogenic ability of adipose-derived mesenchymal stem cells (ADSCs) treated with black phosphorus quantum dots (BPQDs). Additionally, macrophage polarization, osteogenic effects and angiogenesis were investigated through the paracrine pathway regulated by BPQD-modified ADSCs. Our results demonstrated that BPQDs showed good biocompatibility with ADSCs and BPQD-modified ADSCs could improve the bone repair in vivo inflammatory microenvironment by regulating osteogenesis and osteoimmunomodulation. The BPQDs increased the osteogenic differentiation of ADSCs via the Wnt/β-catenin and BMP2/SMAD5/Runx2 signaling pathway. In addition, BPQD-modified ADSCs promoted the osteogenic effect of BMSCs and facilitated the polarization of macrophages from M1 towards M2 phenotype transformation through the paracrine pathway in the periodontitis microenvironment. This strategy provides a novel idea for treatment of alveolar bone defects for periodontitis in the foreseeable future.

A Gelatin-Based Biomimetic Scaffold Promoting Osteogenic Differentiation of Adipose-Derived Mesenchymal Stem Cells

Background

In bone tissue engineering segment, numerous approaches have been investigated to address critically sized bone defects via 3D scaffolds, as the amount of autologous bone grafts are limited, accompanied with complications on harvesting. Moreover, the use of bone-marrow-derived stem cells is also a limiting factor owing to the invasive procedures involved and the low yield of stem cells. Hence, research is ongoing on the search for an ideal bone graft system promoting bone growth and regeneration.

Purpose of the Study

This study aims to develop a unique platform for tissue development via stem cell differentiation towards an osteogenic phenotype providing optimum biological cues for cell adhesion, differentiation and proliferation using biomimetic gelatin-based scaffolds. The use of adipose-derived mesenchymal stem cells in this study also offers an ideal approach for the development of an autologous bone graft.

Methods

A gelatin-vinyl acetate-based 3D scaffold system incorporating Bioglass was developed and the osteogenic differentiation of adipose-derived mesenchymal stem cells (ADMSCs) on the highly porous freeze-dried gelatin-vinyl acetate/ Bioglass scaffold (GB) system was analyzed. The physicochemical properties, cell proliferation and viability were investigated by seeding rat adipose tissue-derived mesenchymal stem cells (ADSCs) onto the scaffolds. The osteogenic differentiation potential of the ADMSC seeded GeVAc/bioglass system was assessed using calcium deposition assay and bone-related protein and genes and comparing with the 3D Gelatin vinyl acetate coppolymer (GeVAc) constructs.

Results and Conclusion

According to the findings, the 3D porous GeVAc/bioglass scaffold can be considered as a promising matrix for bone tissue regeneration and the 3D architecture supports the differentiation of the ADMSCs into osteoblast cells and enhances the production of mineralized bone matrix.

Efficacy and safety of autologous or allogeneic mesenchymal stromal cells from adult adipose tissue expanded and combined with tricalcium phosphate biomaterial for the surgical treatment of atrophic nonunion of long bones: a phase II clinical trial

BACKGROUND

Autologous bone grafting is the standard treatment for the surgical management of atrophic nonunion of long bones. Other solutions, such as bone marrow mesenchymal stem cells (BM-MSC) combined with phospho-calcium material, have also been used. Here we evaluate the safety and early efficacy of a novel procedure using autologous or allogenic adipose tissue mesenchymal stromal cells (AT-MSC) seeded in a patented tricalcium phosphate-based biomaterial for the treatment of bone regeneration in cases of atrophic nonunion.

METHODS

This was a prospective, multicentric, open-label, phase 2 clinical trial of patients with atrophic nonunion of long bones. Biografts of autologous or allogenic AT-MSC combined with a phosphate substrate were manufactured prior to the surgical procedures. The primary efficacy was measured 6 months after surgery, but patients were followed for 12 months after surgery and a further year out of the scope of the study. All adverse events were recorded. This cohort was compared with a historical cohort of 14 cases treated by the same research team with autologous BM-MSC.

RESULTS

A total of 12 patients with atrophic nonunion of long bones were included. The mean (SD) age was 41.2 (12.1) years and 66.7% were men. Bone healing was achieved in 10 of the 12 cases (83%) treated with the AT-MSC biografts, a percentage of healing similar (11 of the 14 cases, 79%) to that achieved in patients treated with autologous BM-MSC. Overall, two adverse events, in the same patient, were considered related to the procedure.

CONCLUSIONS

The results of this study suggest that AT-MSC biografts are safe for the treatment of bone regeneration in cases of atrophic nonunion and reach high healing rates.

TRIAL REGISTRATION

Study registered with EUDRA-CT (2013-000930-37) and ClinicalTrials.gov (NCT02483364).

Site-specific periosteal cells with distinct osteogenic and angiogenic characteristics

OBJECTIVES

This study aimed to investigate the site-specific characteristics of rat mandible periosteal cells (MPCs) and tibia periosteal cells (TPCs) to assess the potential application of periosteal cells (PCs) in bone tissue engineering (BTE).

MATERIALS AND METHODS

MPCs and TPCs were isolated and characterized. The potential of proliferation, migration, osteogenesis and adipogenesis of MPCs and TPCs were evaluated by CCK-8, scratch assay, Transwell assay, alkaline phosphatase staining and activity, Alizarin Red S staining, RT‒qPCR, and Western blot (WB) assays, respectively. Then, these cells were cocultured with human umbilical vein endothelial cells (HUVECs) to investigate their angiogenic capacity, which was assessed by scratch assay, Transwell assay, Matrigel tube formation assay, RT‒qPCR, and WB assays.

RESULTS

MPCs exhibited higher osteogenic potential, higher alkaline phosphatase activity, and more mineralized nodule formation, while TPCs showed a greater capability for proliferation, migration, and adipogenesis. MPCs showed higher expression of angiogenic factors, and the conditioned medium of MPCs accelerated the migration of HUVECs, while MPC- conditioned medium induced the formation of more tubular structure in HUVECs in vitro. These data suggest that compared to TPCs, MPCs exert more consequential proangiogenic effects on HUVECs.

CONCLUSIONS

PCs possess skeletal site-specific differences in biological characteristics. MPCs exhibit more eminent osteogenic and angiogenic potentials, which highlights the potential application of MPCs for BTE.

CLINICAL RELEVANCE

Autologous bone grafting as the main modality for maxillofacial bone defect repair has many limitations. Constituting an important cell type in bone repair and regeneration, MPCs show greater potential for application in BTE, which provides a promising treatment option for maxillofacial bone defect repair.

Recent advancement in vascularized tissue-engineered bone based on materials design and modification

Bone is one of the most vascular network-rich tissues in the body and the vascular system is essential for the development, homeostasis, and regeneration of bone. When segmental irreversible damage occurs to the bone, restoring its vascular system by means other than autogenous bone grafts with vascular pedicles is a therapeutic challenge. By pre-generating the vascular network of the scaffold in vivo or in vitro, the pre-vascularization technique enables an abundant blood supply in the scaffold after implantation. However, pre-vascularization techniques are time-consuming, and in vivo pre-vascularization techniques can be damaging to the body. Critical bone deficiencies may be filled quickly with immediate implantation of a supporting bone tissue engineered scaffold. However, bone tissue engineered scaffolds generally lack vascularization, which requires modification of the scaffold to aid in enhancing internal vascularization. In this review, we summarize the relationship between the vascular system and osteogenesis and use it as a basis to further discuss surgical and cytotechnology-based pre-vascularization strategies and to describe the preparation of vascularized bone tissue engineered scaffolds that can be implanted immediately. We anticipate that this study will serve as inspiration for future vascularized bone tissue engineered scaffold construction and will aid in the achievement of clinical vascularized bone.

Long noncoding RNA KCNMA1-AS1 promotes osteogenic differentiation of human bone marrow mesenchymal stem cells by activating the SMAD9 signaling pathway

The human bone marrow mesenchymal stem cells (hBMSCs) undergo intense osteogenic differentiation, a crucial bone formation mechanism. Evidence from prior studies suggested an association between long noncoding RNAs (lncRNAs) and the osteogenic differentiation of hBMSCs. However, precise roles and molecular mechanisms are still largely unknown. In this work, we report for the first time that lncRNA KCNMA1 antisense RNA 1 (KCNMA1-AS1) plays a vital role in regulating hBMSCs' osteogenic differentiation. Here, it was observed that the KCNMA1-AS1 expression levels were significantly upregulated during osteogenic differentiation. In addition, KCNMA1-AS1 overexpression enhanced in vitro osteogenic differentiation of hBMSCs and in vivo bone formation, whereas knockdown of KCNMA1-AS1 resulted in the opposite result. Additionally, the interaction between KCNMA1-AS1 and mothers against decapentaplegic homolog 9 (SMAD9) was confirmed by an RNA pull-down experiment, mass spectrometry, and RIP assay. This interaction regulated the activation of the SMAD9 signaling pathway. Moreover, rescue assays demonstrated that the inhibitor of the SMAD9 signaling pathway reversed the stimulative effects on osteogenic differentiation of hBMSCs by KCNMA1-AS1 overexpression. Altogether, our results stipulate that KCNMA1-AS1 promotes osteogenic differentiation of hBMSCs via activating the SMAD9 signaling pathway and can serve as a biomarker and therapeutic target in treating bone defects.

β-TCP from 3D-printed composite scaffolds acts as an effective phosphate source during osteogenic differentiation of human mesenchymal stromal cells

Introduction: Human bone marrow-derived mesenchymal stromal cells (hBM-MSCs) are often combined with calcium phosphate (CaP)-based 3D-printed scaffolds with the goal of creating a bone substitute that can repair segmental bone defects. In vitro, the induction of osteogenic differentiation traditionally requires, among other supplements, the addition of β-glycerophosphate (BGP), which acts as a phosphate source. The aim of this study is to investigate whether phosphate contained within the 3D-printed scaffolds can effectively be used as a phosphate source during hBM-MSC in vitro osteogenesis. Methods: hBM-MSCs are cultured on 3D-printed discs composed of poly (lactic-co-glycolic acid) (PLGA) and β-tricalcium phosphate (β-TCP) for 28 days under osteogenic conditions, with and without the supplementation of BGP. The effects of BGP removal on various cellular parameters, including cell metabolic activity, alkaline phosphatase (ALP) presence and activity, proliferation, osteogenic gene expression, levels of free phosphate in the media and mineralisation, are assessed. Results: The removal of exogenous BGP increases cell metabolic activity, ALP activity, proliferation, and gene expression of matrix-related (COL1A1, IBSP, SPP1), transcriptional (SP7, RUNX2/SOX9, PPARγ) and phosphate-related (ALPL, ENPP1, ANKH, PHOSPHO1) markers in a donor dependent manner. BGP removal leads to decreased free phosphate concentration in the media and maintained of mineral deposition staining. Discussion: Our findings demonstrate the detrimental impact of exogenous BGP on hBM-MSCs cultured on a phosphate-based material and propose β-TCP embedded within 3D-printed scaffold as a sufficient phosphate source for hBM-MSCs during osteogenesis. The presented study provides novel insights into the interaction of hBM-MSCs with 3D-printed CaP based materials, an essential aspect for the advancement of bone tissue engineering strategies aimed at repairing segmental defects.

Bioenergetic profile and redox tone modulate in vitro osteogenesis of human dental pulp stem cells: new perspectives for bone regeneration and repair

BACKGROUND

Redox signaling and energy metabolism are known to be involved in controlling the balance between self-renewal and proliferation/differentiation of stem cells. In this study we investigated metabolic and redox changes occurring during in vitro human dental pulp stem cells (hDPSCs) osteoblastic (OB) differentiation and tested on them the impact of the reactive oxygen species (ROS) signaling.

METHODS

hDPSCs were isolated from dental pulp and subjected to alkaline phosphatase and alizarin red staining, q-RT-PCR, and western blotting analysis of differentiation markers to assess achievement of osteogenic/odontogenic differentiation. Moreover, a combination of metabolic flux analysis and confocal cyto-imaging was used to profile the metabolic phenotype and to evaluate the redox tone of hDPSCs.

RESULTS

In differentiating hDPSCs we observed the down-regulation of the mitochondrial respiratory chain complexes expression since the early phase of the process, confirmed by metabolic flux analysis, and a reduction of the basal intracellular peroxide level in its later phase. In addition, dampened glycolysis was observed, thereby indicating a lower energy-generating phenotype in differentiating hDPSCs. Treatment with the ROS scavenger Trolox, applied in the early-middle phases of the process, markedly delayed OB differentiation of hDPSCs assessed as ALP activity, Runx2 expression, mineralization capacity, expression of stemness and osteoblast marker genes (Nanog, Lin28, Dspp, Ocn) and activation of ERK1/2. In addition, the antioxidant partly prevented the inhibitory effect on cell metabolism observed following osteogenic induction.

CONCLUSIONS

Altogether these results provided evidence that redox signaling, likely mediated by peroxide species, influenced the stepwise osteogenic expansion/differentiation of hDPSCs and contributed to shape its accompanying metabolic phenotype changes thus improving their efficiency in bone regeneration and repair.

[Preparation of functional polyhydroxyalkanoate microspheres and their antibacterial activity and osteogenic effect evaluation]

Objective

To construct polyhydroxyalkanoate (PHA) microspheres loaded with bone morphogenetic protein 2 (BMP-2) and human β-defensin 3 (HBD3), and evaluate the antibacterial activity of microspheres and the effect of promoting osteogenic differentiation, aiming to provide a new option of material for bone tissue engineering.

Methods

The soybean lecithin (SL)-BMP-2 and SL-HBD3 were prepared by SL-mediated introduction of growth factors into polyesters technology, and the functional microsphere (f-PMS) containing BMP-2 and HBD3 were prepared by microfluidic technology, while pure microsphere (p-PMS) was prepared by the same method as the control. The morphology of microspheres was observed by scanning electron microscopy and the water absorption was detected; the release curves of BMP-2 and HBD3 in f-PMS were detected by ELISA kit. The antibacterial effect of microspheres in Staphylococcus aureus and Escherichia coli was tested with the LIVE/DEADTM BacLightTM bacterial staining kit; the biocompatibility of microspheres was tested using Transwell and cell counting kit 8 (CCK-8). The effect of microspheres on osteogenic differentiation was determined by collagen type Ⅰ (COL-1) immunofluorescence staining and alkaline phosphatase (ALP) concentration.

Results

In this experiment, the f-PMS and p-PMS were successfully constructed. Morphological characteristics showed that p-PMS surface was rough and distributed with micropores of 1-3 μm, while f-PMS surface was smooth and existed white granular material. There was no significant difference in water absorption between the two groups (P>0.05). The release curves of BMP-2 and HBD3 in the f-PMS and p-PMS were basically the same, showing both early sudden release and late slow release. The antibacterial activity of f-PMS was significantly higher than that of p-PMS in the test that against Staphylococcus aureus and Escherichia coli (P<0.05), but there was no significant difference in biocompatibility between the two groups (P>0.05). The results of osteogenic differentiation of human BMSCs showed that the fluorescence intensity of osteogenic specific protein COL-1 of f-PMS was significantly higher than that in p-PMS, and the activity of ALP in f-PMS was also significantly higher than that in p-PMS (P<0.05).

Conclusion

The p-PHA have good antibacterial activity and biocompatibility, and can effectively promote the osteogenic differentiation of human BMSCs, which is expected to be applied to bone tissue engineering in the future.

Differential Expression of Non-Coding RNAs in Stem Cell Development and Therapeutics of Bone Disorders

Stem cells' self-renewal and multi-lineage differentiation are regulated by a complex network consisting of signaling factors, chromatin regulators, transcription factors, and non-coding RNAs (ncRNAs). Diverse role of ncRNAs in stem cell development and maintenance of bone homeostasis have been discovered recently. The ncRNAs, such as long non-coding RNAs, micro RNAs, circular RNAs, small interfering RNA, Piwi-interacting RNAs, etc., are not translated into proteins but act as essential epigenetic regulators in stem cells' self-renewal and differentiation. Different signaling pathways are monitored efficiently by the differential expression of ncRNAs, which function as regulatory elements in determining the fate of stem cells. In addition, several species of ncRNAs could serve as potential molecular biomarkers in early diagnosis of bone diseases, including osteoporosis, osteoarthritis, and bone cancers, ultimately leading to the development of new therapeutic strategies. This review aims to explore the specific roles of ncRNAs and their effective molecular mechanisms in the growth and development of stem cells, and in the regulation of osteoblast and osteoclast activities. Furthermore, we focus on and explore the association of altered ncRNA expression with stem cells and bone turnover.

Periodontal ligament stem cell-based bioactive constructs for bone tissue engineering

Objectives: Stem cell-based tissue engineering approaches are promising for bone repair and regeneration. Periodontal ligament stem cells (PDLSCs) are a promising cell source for tissue engineering, especially for maxillofacial bone and periodontal regeneration. Many studies have shown potent results via PDLSCs in bone regeneration. In this review, we describe recent cutting-edge researches on PDLSC-based bone regeneration and periodontal tissue regeneration. Data and sources: An extensive search of the literature for papers related to PDLSCs-based bioactive constructs for bone tissue engineering was made on the databases of PubMed, Medline and Google Scholar. The papers were selected by three independent calibrated reviewers. Results: Multiple types of materials and scaffolds have been combined with PDLSCs, involving xeno genic bone graft, calcium phosphate materials and polymers. These PDLSC-based constructs exhibit the potential for bone and periodontal tissue regeneration. In addition, various osteo inductive agents and strategies have been applied with PDLSCs, including drugs, biologics, gene therapy, physical stimulation, scaffold modification, cell sheets and co-culture. Conclusoin: This review article demonstrates the great potential of PDLSCs-based bioactive constructs as a promising approach for bone and periodontal tissue regeneration.

7-Ketocholesterol Induces Oxiapoptophagy and Inhibits Osteogenic Differentiation in MC3T3-E1 Cells

7-Ketocholesterol (7KC) is one of the oxysterols produced by the auto-oxidation of cholesterol during the dysregulation of cholesterol metabolism which has been implicated in the pathological development of osteoporosis (OP). Oxiapoptophagy involving oxidative stress, autophagy, and apoptosis can be induced by 7KC. However, whether 7KC produces negative effects on MC3T3-E1 cells by stimulating oxiapoptophagy is still unclear. In the current study, 7KC was found to significantly decrease the cell viability of MC3T3-E1 cells in a concentration-dependent manner. In addition, 7KC decreased ALP staining and mineralization and down-regulated the protein expression of OPN and RUNX2, inhibiting osteogenic differentiation. 7KC significantly stimulated oxidation and induced autophagy and apoptosis in the cultured MC3T3-E1 cells. Pretreatment with the anti-oxidant acetylcysteine (NAC) could effectively decrease NOX4 and MDA production, enhance SOD activity, ameliorate the expression of autophagy-related factors, decrease apoptotic protein expression, and increase ALP, OPN, and RUNX2 expression, compromising 7KC-induced oxiapoptophagy and osteogenic differentiation inhibition in MC3T3-E1 cells. In summary, 7KC may induce oxiapoptophagy and inhibit osteogenic differentiation in the pathological development of OP.

Therapeutic Strategy of Mesenchymal-Stem-Cell-Derived Extracellular Vesicles as Regenerative Medicine

Extracellular vesicles (EVs) are lipid bilayer membrane particles that play critical roles in intracellular communication through EV-encapsulated informative content, including proteins, lipids, and nucleic acids. Mesenchymal stem cells (MSCs) are pluripotent stem cells with self-renewal ability derived from bone marrow, fat, umbilical cord, menstruation blood, pulp, etc., which they use to induce tissue regeneration by their direct recruitment into injured tissues, including the heart, liver, lung, kidney, etc., or secreting factors, such as vascular endothelial growth factor or insulin-like growth factor. Recently, MSC-derived EVs have been shown to have regenerative effects against various diseases, partially due to the post-transcriptional regulation of target genes by miRNAs. Furthermore, EVs have garnered attention as novel drug delivery systems, because they can specially encapsulate various target molecules. In this review, we summarize the regenerative effects and molecular mechanisms of MSC-derived EVs.

Exendin-4 enhances osteogenic differentiation of adipose tissue mesenchymal stem cells through the receptor activator of nuclear factor-kappa B and osteoprotegerin signaling pathway

The capability of mesenchymal stem cells (MSCs) to repair bone damage and defects has long been investigated. The receptor activator of nuclear factor-kappa B (RANK), its ligand (RANKL) and the decoy receptor osteoprotegerin (OPG) axis is crucial to keep the equilibrium between osteoblastic and osteoclastic activity. Exendin-4 utilization increased bone formation and enhanced bone integrity. This study aimed to investigate the mentioned axis and determine the effect of exendin-4 upon adipose mesenchymal stem cells (Ad-MSCs) osteogenic differentiation. Ad-MSCs were isolated from rat epididymal fat, followed by characterization and then differentiation into osteocytes both in the presence or absence of exendin-4. Osteogenic differentiation was evaluated by alizarin red staining and the expression of osteogenic markers; using reverse transcriptase-quantitative polymerase chain reaction, western blotting and enzyme-linked immunoassay. MSCs derived from rat epididymal fat were isolated and characterized, along with their differentiation into osteocytes. The differentiated cells were alizarin red-stained, showing increased staining intensity upon addition of exendin-4. Moreover, the addition of exendin-4 elevated the messenger RNA expression levels of osteogenic markers; runt-related transcription factor-2 (RUNX-2), osteocalcin, and forkhead box protein O-1 while reducing the expression of the adipogenic marker peroxisome-proliferator-activated receptor-gamma. Exendin-4 addition elevated OPG levels in the supernatant of osteogenic differentiated cells. Moreover, exendin-4 elevated the protein levels of glucagon-like peptide-1 receptor and RUNX-2, while decreasing both RANK and RANKL. In conclusion, osteogenic differentiation of Ad-MSCs is associated with increased osteoblastic rather than osteoclastic activity. The findings of this study suggest that exendin-4 can enhance Ad-MSCs osteogenic differentiation partially through the RANK/RANKL/OPG axis.