Mesenchymal stem cell sheets: a new cell-based strategy for bone repair and regeneration

3D Stem Cell Spheroids with 2D Hetero-Nanostructures for In Vivo Osteogenic and Immunologic Modulated Bone Repair

3D stem cell spheroids have immense potential for various tissue engineering applications. However, current spheroid fabrication techniques encounter cell viability issues due to limited oxygen access for cells trapped within the core, as well as nonspecific differentiation issues due to the complicated environment following transplantation. In this study, functional 3D spheroids are developed using mesenchymal stem cells with 2D hetero-nanostructures (HNSs) composed of single-stranded DNA (ssDNA) binding carbon nanotubes (sdCNTs) and gelatin-bind black phosphorus nanosheets (gBPNSs). An osteogenic molecule, dexamethasone (DEX), is further loaded to fabricate an sdCNTgBP-DEX HNS. This approach aims to establish a multifunctional cell-inductive 3D spheroid with improved oxygen transportation through hollow nanotubes, stimulated stem cell growth by phosphate ions supplied from BP oxidation, in situ immunoregulation, and osteogenesis induction by DEX molecules after implantation. Initial transplantation of the 3D spheroids in rat calvarial bone defect shows in vivo macrophage shifts to an M2 phenotype, leading to a pro-healing microenvironment for regeneration. Prolonged implantation demonstrates outstanding in vivo neovascularization, osteointegration, and new bone regeneration. Therefore, these engineered 3D spheroids hold great promise for bone repair as they allow for stem cell delivery and provide immunoregulative and osteogenic signals within an all-in-one construct.

Osteogenic mesenchymal stem cells/progenitors in the periodontium

Periodontitis is the major cause of tooth loss in adults and is mainly characterized by alveolar bone destruction. Elucidating the mesenchymal stem cell (MSC)/progenitor populations of alveolar bone formation will provide valuable insights into regenerative approaches to clinical practice, such as endogenous regeneration and stem-cell-based tissue engineering therapies. Classically, MSCs residing in the bone marrow, periosteum, periodontal ligament (PDL), and even the gingiva are considered to be osteogenic progenitors. Furthermore, the contributions of MSCs expressing specific markers, including Gli1, Axin2, PTHrP, LepR, and α-SMA, to alveolar bone formation have been studied using cell lineage tracing and gene knockout models. In this review, we describe the MSCs/progenitors of alveolar bone and the biological properties of different subpopulations of MSCs involved in alveolar bone development, remodeling, injury repair, and regeneration.

Scaffold-Free Bone Marrow-Derived Mesenchymal Stem Cell Sheets Enhance Bone Formation in a Weight-Bearing Rat Critical Bone Defect Model

Researchers have been exploring alternative methods for bone tissue engineering, as current management of critical bone defects may be a significant challenge for both patient and surgeon with conventional surgical treatments associated with several potential complications and drawbacks. Recent studies have shown mesenchymal stem cell sheets may enhance bone regeneration in different animal models. We investigated the efficacy of implanted scaffold-free bone marrow-derived mesenchymal stem cell (BMSC) sheets on bone regeneration of a critical bone defect in a weight-bearing rat model. BMSCs were isolated from the femora of male Sprague-Dawley rats 5-6 weeks of age and cell sheets were produced on temperature-responsive culture dishes. Nine male Sprague-Dawley rats 6-8 weeks of age were utilized. A bilateral femoral critical bone defect was created with a bridge plate serving as internal fixation. One side was randomly selected and BMSC sheets were implanted into the bone defect (BMSC group), with the contralateral side receiving no treatment (control). Rats were anesthetized and radiographs were performed at 2-week intervals. At the 8-week time point, rats were euthanized, femurs harvested, and microcomputed tomography and histological analysis was performed. We found a statistically significant increase in new bone formation and bone volume fraction compared with the control. Histomorphometry analysis revealed a larger percent of newly formed bone and a higher total histological score. Our results suggest that scaffold-free BMSC sheets may be used in the management of large weight-bearing bone defects to complement a different surgical technique or as a standalone approach followed by internal fixation. However, further research is still needed.

Let-7a promotes periodontal bone regeneration of bone marrow mesenchymal stem cell aggregates via the Fas/FasL-autophagy pathway

Periodontal bone regeneration using bone marrow mesenchymal stem cell (BMMSC) transplantation is a promising method; however, the method for osteogenic differentiation of BMMSCs needs to be improved. In this research, we sought to identify the roles of let-7a in the osteogenesis of BMMSCs and to provide a potential method for periodontal bone regeneration. Our previous study revealed that Fas/FasL is a target of let-7a. In this study, we demonstrated that let-7a overexpression significantly enhanced BMMSC-CAs osteogenesis both in vitro and in vivo. Mechanistically, upregulation of Fas/FasL using the rfas/rfaslg plasmid obstructed the osteogenesis of BMMSCs by inhibiting autophagy. Furthermore, we confirmed that overexpression of let-7a activated autophagy and alleviated the inhibited osteogenesis by the autophagy inhibitor 3-MA and the rfas/rfaslg plasmid of BMMSCs. In general, our findings showed that let-7a promoted the osteogenesis of BMMSCs through the Fas/FasL-autophagy pathway, suggesting that the application of let-7a in BMMSC-CAs based periodontal bone regeneration could be a promising strategy.

Advancing Dentistry through Bioprinting: Personalization of Oral Tissues

Despite significant advancements in dental tissue restoration and the use of prostheses for addressing tooth loss, the prevailing clinical approaches remain somewhat inadequate for replicating native dental tissue characteristics. The emergence of three-dimensional (3D) bioprinting offers a promising innovation within the fields of regenerative medicine and tissue engineering. This technology offers notable precision and efficiency, thereby introducing a fresh avenue for tissue regeneration. Unlike the traditional framework encompassing scaffolds, cells, and signaling factors, 3D bioprinting constitutes a contemporary addition to the arsenal of tissue engineering tools. The ongoing shift from conventional dentistry to a more personalized paradigm, principally under the guidance of bioprinting, is poised to exert a significant influence in the foreseeable future. This systematic review undertakes the task of aggregating and analyzing insights related to the application of bioprinting in the context of regenerative dentistry. Adhering to PRISMA guidelines, an exhaustive literature survey spanning the years 2019 to 2023 was performed across prominent databases including PubMed, Scopus, Google Scholar, and ScienceDirect. The landscape of regenerative dentistry has ushered in novel prospects for dentoalveolar treatments and personalized interventions. This review expounds on contemporary accomplishments and avenues for the regeneration of pulp-dentin, bone, periodontal tissues, and gingival tissues. The progressive strides achieved in the realm of bioprinting hold the potential to not only enhance the quality of life but also to catalyze transformative shifts within the domains of medical and dental practices.

Adipose-derived stem cells (ASCs) culture in spinner flask: improving the parameters of culture in a microcarrier-based system

Prior to clinical use, extensive in vitro proliferation of human adipose-derived stem cells (ASCs) is required. Among the current options, spinner-type stirred flasks, which use microcarriers to increase the yield of adherent cells, are recommended. Here, we propose a methodology for ASCs proliferation through cell suspension culture using Cultispher-S^® microcarriers (MC) under agitation in a spinner flask, with the aim of establishing a system that reconciles the efficiency of cell yield with high viability of the culture during two distinct phases: seeding and proliferation. The results showed that cell adhesion was potentiated under intermittent stirring at 70 rpm in the presence of 10% FBS for an initial cell concentration of 2.4 × 10⁴ cells/mL in the initial 24 h of cultivation. In the proliferation phase, kinetic analysis showed that cell growth was higher under continuous agitation at 50 rpm with a culture medium renewal regime of 50% every 72 h, which was sufficient to maintain the culture at optimal levels of nutrients and metabolites for up to nine days of cultivation, representing an 11.1-fold increase and a maximum cell productivity of 422 cells/mL/h (1.0 × 10⁵ viable cells/mL). ASCs maintained the immunophenotypic characteristics and mesodermal differentiation potential of both cell lines from different donors. The established protocol represents a more efficient and cost-effective method to obtain a high proliferation rate of ASCs in a microcarrier-based system, which is necessary for large-scale use in cell therapy, highlighting that the manipulation of critical parameters optimizes the ASCs production process.

Application of mesenchymal stem cell sheet for regeneration of craniomaxillofacial bone defects

Bone defects are among the most common damages in human medicine. Due to limitations and challenges in the area of bone healing, the research field has turned into a hot topic discipline with direct clinical outcomes. Among several available modalities, scaffold-free cell sheet technology has opened novel avenues to yield efficient osteogenesis. It is suggested that the intact matrix secreted from cells can provide a unique microenvironment for the acceleration of osteoangiogenesis. To the best of our knowledge, cell sheet technology (CST) has been investigated in terms of several skeletal defects with promising outcomes. Here, we highlighted some recent advances associated with the application of CST for the recovery of craniomaxillofacial (CMF) in various preclinical settings. The regenerative properties of both single-layer and multilayer CST were assessed regarding fabrication methods and applications. It has been indicated that different forms of cell sheets are available for CMF engineering like those used for other hard tissues. By tackling current challenges, CST is touted as an effective and alternative therapeutic option for CMF bone regeneration.

3D bioprinted autologous bone particle scaffolds for cranioplasty promote bone regeneration with both implanted and native BMSCs

Although autologous bone (AB) grafting is considered to be the gold standard for cranioplasty, unresolved problems remain, such as surgical-site infections and bone flap absorption. In this study, an AB scaffold was constructed via three-dimensional (3D) bedside-bioprinting technology and used for cranioplasty. To simulate the skull structure, a polycaprolactone shell was designed as an external lamina, and 3D-printed AB and a bone marrow-derived mesenchymal stem cell (BMSC) hydrogel was used to mimic cancellous bone for bone regeneration. Ourin vitroresults showed that the scaffold exhibited excellent cellular affinity and promoted osteogenic differentiation of BMSCs in both two-dimensional and 3D culture systems. The scaffold was implanted in beagle dog cranial defects for up to 9 months, and the scaffold promoted new bone and osteoid formation. Furtherin vivostudies indicated that transplanted BMSCs differentiated into vascular endothelium, cartilage, and bone tissues, whereas native BMSCs were recruited into the defect. The results of this study provide a method for bedside bioprinting of a cranioplasty scaffold for bone regeneration, which opens up another window for clinical applications of 3D printing in the future.

Potential of Mesenchymal Stem Cell Sheets on Periodontal Regeneration: A Systematic Review of Pre-Clinical Studies

BACKGROUND

Cell sheet technique using mesenchymal stem cells is a high-level strategy in periodontal regenerative medicine. Although recent studies have shown the role of MSCSs in increased dental supporting tissues and bone, there is no systematic review focused specifically on assessing periodontal regeneration in orthotopic animal models.

OBJECTIVE

To evaluate the potential of mesenchymal stem cell sheets (MSCSs) on periodontal regeneration, compared to control, in experimental animal models Methods: Pre-clinical studies in periodontal defects of animal models were considered eligible. The electronic search included the MEDLINE, Web of Science, EMBASE and LILACS databases. The review was conducted according to the Preferred Reporting Item for Systematic Reviews and Meta-Analyses statement guidelines.

RESULTS

A total of 17 of the 3989 studies obtained from the electronic database search were included. MSCSs included dental follicle (DF) MSCSs, periodontal ligament (PL) MSCSs, dental pulp (DP) MSCSs, bone marrow (BM) MSCSs, alveolar periosteal (AP) MSCSs and gingival (G) MSCSs. Regarding cell sheet inducing protocol, most of the studies used ascorbic acid (52.94%). Others used culture dishes grafted with a temperature-responsive polymer (47.06%). Adverse effects were not identified in the majority of studies. Meta-analysis was not considered because of methodological heterogeneities. PDL-MSCSs were superior for periodontal regeneration enhancement compared to the control, but in an induced inflammatory microenvironment, DF-MSCSs were better. Moreover, DF-MSCSs, DP-MSCSs, and BM-MSCSs showed improved results compared to the control.

CONCLUSION

MSCSs can improve periodontal regeneration in animal periodontal defect models.

Bone regeneration of mouse critical-sized calvarial defects with human mesenchymal stem cell sheets co-expressing BMP2 and VEGF

Background/purpose

Over-dependence on existing synthetic scaffolds and insufficient osteoinductive and vasculogenic growth factors have limited the development of bone regeneration. The study aimed to assess the feasibility of using marrow-derived mesenchymal stem cells (BMSCs) cell sheets co-expressing bone morphogenetic proteins 2 (BMP2) and vascular endothelial growth factor (VEGF) for repairing critical-sized calvarial defects.

Materials and methods

BMSCs cell sheets were genetically engineered to express BMP2/VEGF alone or together. Alterations in osteogenic markers were examined by quantitative real-time PCR (qRT-PCR) and western blotting. A critical-sized calvarial bone defect model was used to investigate the osteogenesis effects of BMP2/VEGF cell sheets alone or in combination. The efficacy was assessed with micro-computed tomography (micro-CT) and histology.

Results

In vitro, the expression of BMP2 and VEGF through lentiviral transduction was confirmed by qRT-PCR and western blotting against BMP2 and VEGF. Lentiviral delivery of BMP2 and VEGF resulted in the upregulation of osteogenic markers. In vivo, in a critical-sized calvarial bone defect model, 3D-reconstructed micro-CT images revealed that treatment of the calvarial defects with the BMP2/VEGF cell sheet resulted in significantly greater amounts of newly formed bone at 8 weeks after surgery than treatment with cell sheets with single gene transduction or vehicle controls. The results were confirmed by histological assessment by H&E staining and Masson staining.

Conclusion

This study demonstrates that BMP2/VEGF co-expressing BMSCs sheets promote bone regeneration in critical-sized calvarial bone defects. The BMP2/VEGF cell sheets provide a functional bioactive scaffold for critical-size bone reconstruction.

MicroRNA-196a-5p overexpression in Wharton's jelly umbilical cord stem cells promotes their osteogenic differentiation and new bone formation in bone defects in the rat calvarium

The peri-tooth root alveolar loss often does not have sufficient space for repair material transplantation and plasticity. Mesenchymal stem cell (MSC) sheets have an advantage in providing more extracellular matrix (ECM) and may prove to be a new therapeutic consideration for this bone defect repair. The identification of key regulators that stimulate MSCs' osteogenic potential and sheet-derived ECM deposition is the key to promoting its application. In this study, we found that inhibition or overexpression of miR-196a-5p led to a decline or enhancement, respectively, in the alkaline phosphatase (ALP) activity, mineralization, and the levels of osteogenic markers, Osteocalcin (OCN), Dentin Matrix Protein 1 (DMP1), Bone Sialoprotein (BSP), and Dentin Sialophosphoprotein (DSPP) of Wharton's jelly of umbilical cord stem cells (WJCMSCs) in vitro. Moreover, the 5,6-Carboxyfluorescein Diacetate Succinimidyl Ester (CFSE) analysis revealed inhibition of the WJCMSCs' proliferative ability upon miR-196a-5p overexpression. Characterization of the sheet formation by picrosirius red and Masson staining indicated that miR-196a-5p overexpression significantly promoted the collagen content in whole WJCMSC sheet-derived ECM. Furthermore, micro-CT and histopathology results indicated that the miR-196a-5p-overexpressed WJCMSC sheets significantly promoted new bone regeneration and rat calvarial bone defect closure 12 weeks following transplantation. The mRNA microarray analysis of miR-196a-5p-overexpressed WJCMSCs revealed 959 differentially expressed genes (DEGs) (34 upregulated and 925 downregulated). Moreover, 241 genes targeted by miR-196a-5p were predicted by using miRNA function websites of which only 19 predicted genes were consistent with the microarray revealed DEGs. Hence, one unrevealed downregulated DEG Serpin Family B Member 2 (SERPINB2) was investigated. And the deletion of SERPINB2 enhanced the ALP activity and mineralization of WJCMSCs in vitro. In conclusion, our study found that miR-196a-5p, as a key regulator, could repress the proliferation tendency, while stimulating osteogenic ability and WJCMSC sheet-derived ECM deposition, thus promoting new bone formation and rat calvarial bone defect closure. Furthermore, SERPINB2 is a key downstream gene involved in the miR-196a-5p-promoted WJCMSC osteogenesis.

Human Umbilical Cord Mesenchymal Stem Cells: Current Literature and Role in Periodontal Regeneration

Periodontal disease can cause irreversible damage to tooth-supporting tissues such as the root cementum, periodontal ligament, and alveolar bone, eventually leading to tooth loss. While standard periodontal treatments are usually helpful in reducing disease progression, they cannot repair or replace lost periodontal tissue. Periodontal regeneration has been demonstrated to be beneficial in treating intraosseous and furcation defects to varied degrees. Cell-based treatment for periodontal regeneration will become more efficient and predictable as tissue engineering and progenitor cell biology advance, surpassing the limitations of present therapeutic techniques. Stem cells are undifferentiated cells with the ability to self-renew and differentiate into several cell types when stimulated. Mesenchymal stem cells (MSCs) have been tested for periodontal regeneration in vitro and in humans, with promising results. Human umbilical cord mesenchymal stem cells (UC-MSCs) possess a great regenerative and therapeutic potential. Their added benefits comprise ease of collection, endless source of stem cells, less immunorejection, and affordability. Further, their collection does not include the concerns associated with human embryonic stem cells. The purpose of this review is to address the most recent findings about periodontal regenerative mechanisms, different stem cells accessible for periodontal regeneration, and UC-MSCs and their involvement in periodontal regeneration.

Regenerating dynamic organs using biomimetic patches

The regeneration of dynamic organs remains challenging because they are intrinsically anisotropic and undergo large volumetric deformation during normal or pathological function. This hampers the durability and applicability of regenerative medicine approaches. To address the challenges of organ dynamics, a new class of patches have emerged with anisotropic and auxetic properties that mimic native tissue biomechanics and accommodate volumetric deformation. Here, we outline the critical design, materials, and processing considerations for achieving optimal patch biomechanics according to target pathology and summarize recent advances in biomimetic patches for dynamic organ regeneration. Furthermore, we discuss the challenges and opportunities which, if overcome, would open up new applications in organ regeneration and expedite the clinical translation of patch-based therapeutics.

Advances in mesenchymal stem cell conditioned medium-mediated periodontal tissue regeneration

Periodontitis is a chronic inflammatory disease that leads to the destruction of both soft and hard periodontal tissues. Complete periodontal regeneration in clinics using the currently available treatment approaches is still a challenge. Mesenchymal stem cells (MSCs) have shown promising potential to regenerate periodontal tissue in various preclinical and clinical studies. The poor survival rate of MSCs during in vivo transplantation and host immunogenic reaction towards MSCs are the main drawbacks of direct use of MSCs in periodontal tissue regeneration. Autologous MSCs have limited sources and possess patient morbidity during harvesting. Direct use of allogenic MSCs could induce host immune reaction. Therefore, the MSC-based indirect treatment approach could be beneficial for periodontal regeneration in clinics. MSC culture conditioned medium (CM) contains secretomes that had shown immunomodulatory and tissue regenerative potential in pre-clinical and clinical studies. MSC-CM contains a cocktail of growth factors, cytokines, chemokines, enzymes, and exosomes, extracellular vesicles, etc. MSC-CM-based indirect treatment has the potential to eliminate the drawbacks of direct use of MSCs for periodontal tissue regeneration. MSC-CM holds the tremendous potential of bench-to-bed translation in periodontal regeneration applications. This review focuses on the accumulating evidence indicating the therapeutic potential of the MSC-CM in periodontal regeneration-related pre-clinical and clinical studies. Recent advances on MSC-CM-based periodontal regeneration, existing challenges, and prospects are well summarized as guidance to improve the effectiveness of MSC-CM on periodontal regeneration in clinics.

Adipose-Derived Stem Cell Sheets Improve Early Biomechanical Graft Strength in Rabbits After Anterior Cruciate Ligament Reconstruction

BACKGROUND

Although various reconstruction techniques are available for anterior cruciate ligament (ACL) injuries, a long recovery time is required before patients return to sports activities, as the reconstructed ACL requires time to regain strength. To date, several studies have reported use of mesenchymal stem cells in orthopaedic surgery; however, no studies have used adipose-derived stem cell (ADSC) sheets in ACL reconstruction (ACLR).

HYPOTHESIS

ADSC sheet transplantation can improve biomechanical strength of the autograft used in ACLR.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 68 healthy Japanese white rabbits underwent unilateral ACLR with a semitendinosus tendon autograft after random enrollment into a control group (no sheet; n = 34) and a sheet group (ADSC sheet; n = 34). At 2, 4, 8, 16, and 24 weeks after surgery, rabbits in each group were sacrificed to evaluate tendon-bone healing using histological staining, micro-computed tomography, and biomechanical testing. At 24 weeks, scanning transmission electron microscopy of the graft midsubstance was performed.

RESULTS

The ultimate failure load for the control and sheet groups, respectively, was as follows: 17.2 ± 5.5 versus 37.3 ± 10.3 (P = .01) at 2 weeks, 28.6 ± 1.9 versus 47.4 ± 10.4 (P = .003) at 4 weeks, 53.0 ± 14.3 versus 48.1 ± 9.3 (P = .59) at 8 weeks, 66.2 ± 9.3 versus 95.2 ± 43.1 (P = .24) at 16 weeks, and 66.7 ± 27.3 versus 85.3 ± 29.5 (P = .39) at 24 weeks. The histological score was also significantly higher in the sheet group compared with the control group at early stages up to 8 weeks. On micro-computed tomography, relative to the control group, the bone tunnel area was significantly narrower in the sheet group at 4 weeks, and the bone volume/tissue volume of the tendon-bone interface was significantly greater at 24 weeks. Scanning transmission electron microscopy at 24 weeks indicated that the mean collagen fiber diameter in the midsubstance was significantly greater, as was the occupation ratio of collagen fibers per field of view, in the sheet group.

CONCLUSION

ADSC sheets improved biomechanical strength, prevented bone tunnel enlargement, and promoted tendon-bone interface healing and graft midsubstance healing in an in vivo rabbit model.

CLINICAL RELEVANCE

ADSC sheets may be useful for early tendon-bone healing and graft maturation in ACLR.

Fabrication and Characterization of Collagen/PVA Dual-Layer Membranes for Periodontal Bone Regeneration

Guided tissue regeneration (GTR) is a promising treatment for periodontal tissue defects, which generally uses a membrane to build a mechanical barrier from the gingival epithelium and hold space for the periodontal regeneration especially the tooth-supporting bone. However, existing membranes possess insufficient mechanical properties and limited bioactivity for periodontal bone regenerate. Herein, fish collagen and polyvinyl alcohol (Col/PVA) dual-layer membrane were developed via a combined freezing/thawing and layer coating method. This dual-layer membrane had a clear but contact boundary line between collagen and PVA layers, which were both hydrophilic. The dual membrane had an elongation at break of 193 ± 27% and would undergo an in vitro degradation duration of more than 17 days. Further cell experiments showed that compared with the PVA layer, the collagen layer not only presented good cytocompatibility with rat bone marrow-derived mesenchymal stem cells (BMSCs), but also promoted the osteogenic genes (RUNX2, ALP, OCN, and COL1) and protein (ALP) expression of BMSCs. Hence, the currently developed dual-layer membranes could be used as a stable barrier with a stable degradation rate and selectively favor the bone tissue to repopulate the periodontal defect. The membranes could meet the challenges encountered by GTR for superior defect repair, demonstrating great potential in clinical applications.

Downregulation of Prolactin-Induced Protein Promotes Osteogenic Differentiation of Periodontal Ligament Stem Cells

Background

Periodontal ligament stem cells (PDLSCs) are promising seed cells for bone tissue engineering and periodontal regeneration applications. However, the mechanism underlying the osteogenic differentiation process remains largely unknown. Previous reports showed that prolactin-induced protein (PIP) was upregulated after PDLSCs osteogenic induction. However, few studies have reported on the function of PIP in osteogenic differentiation. The purpose of the present study was to investigate the effect of PIP on osteogenic differentiation of PDLSCs.

Material/Methods

The expression pattern of PIP during PDLSCs osteogenic differentiation was detected and the effect of each component in the osteogenic induction medium on PIP was also tested by qRT-PCR. Then, the PIP knockdown cells were established using lentivirus. The knockdown efficiency was measured and the proliferation, apoptosis, and osteogenic differentiation ability were examined to determine the functional role of PIP on PDLSCs.

Results

QRT-PCR showed that PIP was sustainedly upregulated during the osteogenic induction process and the phenomenon was mainly caused by the stimulation of dexamethasone in the induction medium. CCK-8 and flow cytometer showed that knocking down PIP had no influence on proliferation and apoptosis of PDLSCs. ALP staining and activity, Alizarin Red staining, and western blot analysis demonstrated PIP knockdown enhanced the osteogenic differentiation and mineralization of PDLSCs.

Conclusions

PIP was upregulated after osteogenic induction; however, PIP knockdown promoted PDLSCs osteogenic differentiation. PIP might be a by-product of osteogenic induction, and downregulating of PIP might be a new target in bone tissue engineering applications.

Bone Mesenchymal Stem Cells Contribute to Ligament Regeneration and Graft-Bone Healing after Anterior Cruciate Ligament Reconstruction with Silk-Collagen Scaffold

Anterior cruciate ligament (ACL) reconstruction was realized using a combination of bone mesenchymal stem cells (BMSCs) and silk–collagen scaffold, and an in vivo evaluation of this combination was performed. By combining type I collagen and degummed silk fibroin mesh, silk–collagen scaffolds were prepared to simulate ligament components. BMSCs isolated from bone marrow of rabbits were cultured for a homogenous population and seeded on the silk–collagen scaffold. In the scaffold and BMSC (S/C) group, scaffolds were seeded with BMSCs for 72 h and then rolled and used to replace the ACL in 20 rabbits. In the scaffold (S) group, scaffolds immersed only in culture medium for 72 h were used for ACL reconstruction. Specimens were collected at 4 and 16 weeks postoperatively to assess ligament regeneration and bone integration. HE and immunohistochemical staining (IHC) were performed to assess ligament regeneration in the knee cavity. To assess bone integration at the graft–bone interface, HE, Russell–Movat staining, micro-CT, and biomechanical tests were performed. After 4 weeks, vigorous cell proliferation was observed in the core part of the scaffold in the S/C group, and a quantity of fibroblast-like cells and extracellular matrix (ECM) was observed in the center part of the graft at 16 weeks after surgery. At 4 and 16 weeks postoperatively, the tenascin-C expression in the S/C group was considerably higher than that in the S group (4 w, p < 0.01; 16 w, p < 0.01). Furthermore, bone integration was better in the S/C group than in the S group, with histological observation of trabecular bone growth into the graft and more mineralized tissue formation detected by micro-CT (4 w, bone volume fraction (BV/TV), p = 0.0169, bone mineral density (BMD), p = 0.0001; 16 w, BV/TV, p = 0.1233, BMD, p = 0.0494). These results indicate that BMSCs promote ligament regeneration in the knee cavity and bone integration at the graft–bone interface. Silk–collagen scaffolds and BMSCs will likely be combined for clinical practice in the future.

3D-Bioprinting Strategies Based on In Situ Bone-Healing Mechanism for Vascularized Bone Tissue Engineering

Over the past decades, a number of bone tissue engineering (BTE) approaches have been developed to address substantial challenges in the management of critical size bone defects. Although the majority of BTE strategies developed in the laboratory have been limited due to lack of clinical relevance in translation, primary prerequisites for the construction of vascularized functional bone grafts have gained confidence owing to the accumulated knowledge of the osteogenic, osteoinductive, and osteoconductive properties of mesenchymal stem cells and bone-relevant biomaterials that reflect bone-healing mechanisms. In this review, we summarize the current knowledge of bone-healing mechanisms focusing on the details that should be embodied in the development of vascularized BTE, and discuss promising strategies based on 3D-bioprinting technologies that efficiently coalesce the abovementioned main features in bone-healing systems, which comprehensively interact during the bone regeneration processes.

Adipose-derived stem cell sheets combined with β-tricalcium phosphate/collagen-I fiber scaffold improve cell osteogenesis

Transplantation of cell-based material is a promising approach for the treatment of critical bone defects. However, it is still limited by the lack of suitable scaffold material or abundant seeding cell sources. The present study aimed to establish a novel composite of an adipose-derived stem cell (ADSC) sheet and a synthetic porous β-tricalcium phosphate/collagen-I fiber (β-TCP/COL-I) scaffold to enhance osteogenic activity. ADSCs were isolated from 3-week-old female Sprague Dawley rats and the ADSC sheets were prepared in an osteoinductive medium. The study groups included the ADSC sheets/scaffold, scattered ADSCs/scaffold, ADSC sheet alone and scaffold alone. Scanning electron microscopy and energy-dispersive spectrometry were used to observe cell-scaffold interactions and analyze the relative calcium content on the composites' surface. Alizarin red S staining was used to examine the calcium deposition. ELISA and reverse transcription-quantitative PCR were used to detect the expression levels of alkaline phosphatase (ALP), osteocalcin (OCN) and osteopontin (OPN). The results revealed that ADSCs were able to tightly adhere to the β-TCP/COL-I scaffold with no cytotoxicity. The calcifying nodules reaction was positive on ADSC sheets and gradually increased after osteogenic induction. In addition, the β-TCP/COL-I scaffold combined with ADSC sheets was able to significantly enhance the expression levels of ALP, OCN and OPN and increase the superficial relative calcium content compared to scattered ADSCs/scaffold or the ADSC sheet alone (P<0.05). The results indicated that ADSCs possess a strong osteogenic potential, particularly in the cell-sheet form and when compounded with the β-TCP/COL-I scaffold, compared to scattered ADSCs with a β-TCP/COL-I scaffold or an ADSC sheet alone. This novel composite may be a promising candidate for bone engineering.

Gold Nanoparticles Promote the Bone Regeneration of Periodontal Ligament Stem Cell Sheets Through Activation of Autophagy

OBJECTIVE

Cell sheet technology (CST) is advantageous for repairing alveolar bone defects in clinical situations, and osteogenic induction before implantation may result in enhanced bone regeneration. Herein, we observed the effect of gold nanoparticles (AuNPs) on osteogenic differentiation of periodontal ligament stem cell (PDLSC) sheets and explored their potential mechanism of action.

METHODS

PDLSCs were cultured in cell sheet induction medium to obtain cell sheets. PDLSC sheets were treated with or without AuNPs. Alkaline phosphatase, alizarin red S, von Kossa, and immunofluorescence staining were used to observe the effects of AuNPs on the osteogenic differentiation of PDLSC sheets. Western blotting was performed to evaluate the osteogenic effects and autophagy activity. The cell sheets were transplanted into the dorsa of nude mice, and bone regeneration was analyzed by micro-CT and histological staining.

RESULTS

AuNPs could promote the osteogenic differentiation of PDLSC sheets by upregulating bone-related protein expression and mineralization. The 45-nm AuNPs were more effective than 13-nm AuNPs. Additional analysis demonstrated that their ability to promote differentiation could depend on activation of the autophagy pathway through upregulation of microtubule-associated protein light chain 3 and downregulation of sequestosome 1/p62. Furthermore, AuNPs significantly promoted the bone regeneration of PDLSC sheets in ectopic models.

CONCLUSION

AuNPs enhance the osteogenesis of PDLSC sheets by activating autophagy, and 45-nm AuNPs were more effective than 13-nm AuNPs. This study may provide an AuNP-based pretreatment strategy for improving the application of CST in bone repair and regeneration.

Fundamental Technologies and Recent Advances of Cell-Sheet-Based Tissue Engineering

Tissue engineering has attracted significant attention since the 1980s, and the applications of tissue engineering have been expanding. To produce a cell-dense tissue, cell sheet technology has been studied as a promising strategy. Fundamental techniques involving tissue engineering are mainly introduced in this review. First, the technologies to fabricate a cell sheet were reviewed. Although temperature-responsive polymer-based technique was a trigger to establish and spread cell sheet technology, other methodologies for cell sheet fabrication have also been reported. Second, the methods to improve the function of the cell sheet were investigated. Adding electrical and mechanical stimulation on muscle-type cells, building 3D structures, and co-culturing with other cell species can be possible strategies for imitating the physiological situation under in vitro conditions, resulting in improved functions. Finally, culture methods to promote vasculogenesis in the layered cell sheets were introduced with in vivo, ex vivo, and in vitro bioreactors. We believe the present review that shows and compares the fundamental technologies and recent advances for cell-sheet-based tissue engineering should promote further development of tissue engineering. The development of cell sheet technology should promote many bioengineering applications.

Mesenchymal stem cell treatment for peripheral nerve injury: a narrative review

Peripheral nerve injuries occur as the result of sudden trauma and lead to reduced quality of life. The peripheral nervous system has an inherent capability to regenerate axons. However, peripheral nerve regeneration following injury is generally slow and incomplete that results in poor functional outcomes such as muscle atrophy. Although conventional surgical procedures for peripheral nerve injuries present many benefits, there are still several limitations including scarring, difficult accessibility to donor nerve, neuroma formation and a need to sacrifice the autologous nerve. For many years, other therapeutic approaches for peripheral nerve injuries have been explored, the most notable being the replacement of Schwann cells, the glial cells responsible for clearing out debris from the site of injury. Introducing cultured Schwann cells to the injured sites showed great benefits in promoting axonal regeneration and functional recovery. However, there are limited sources of Schwann cells for extraction and difficulties in culturing Schwann cells in vitro. Therefore, novel therapeutic avenues that offer maximum benefits for the treatment of peripheral nerve injuries should be investigated. This review focused on strategies using mesenchymal stem cells to promote peripheral nerve regeneration including exosomes of mesenchymal stem cells, nerve engineering using the nerve guidance conduits containing mesenchymal stem cells, and genetically engineered mesenchymal stem cells. We present the current progress of mesenchymal stem cell treatment of peripheral nerve injuries.

Advanced technologies in periodontal tissue regeneration based on stem cells: Current status and future perspectives

Periodontitis is a progressive inflammation disease, the clinical management of which remains a challenge. The traditional management may control periodontal inflammation, but failed to regenerate functional periodontium. This review summarizes the most advancing regenerative techniques regarding stem cell culture and scaffold fabrication, such as cell sheeting, spheroid culture, electrospinning and 3D printing. The applications of different techniques manifest tremendous potential of regenerating the complete and functional periodontium. Albeit promising, new technologies have met with their own drawbacks such as insufficient vascularization and precision, which necessitate deeper modification. Thus, this review also points out the potential perspectives and methods aiming at their disadvantages, illuminating the directions of future researches to successful clinical scenarios.

Mesenchymal stem cell-derived extracellular matrix (mECM): a bioactive and versatile scaffold for musculoskeletal tissue engineering

Mesenchymal stem cell-derived extracellular matrix (mECM) has received increased attention in the fields of tissue engineering and scaffold-assisted regeneration. mECM exhibits many unique characteristics, such as robust bioactivity, biocompatibility, ease of use, and the potential for autologous tissue engineering. As the use of mECM has increased in musculoskeletal tissue engineering, it should be noted that mECM generated from current methods has inherited insufficiencies, such as low mechanical properties and lack of internal architecture. In this review, we first summarize the development and use of mECM as a scaffold for musculoskeletal tissue regeneration and highlight our current progress on moving this technology toward clinical application. Then we review recent methods to improve the properties of mECM that will overcome current weaknesses. Lastly, we propose future studies that will pave the road for mECM application in regenerating tissues in humans.

Examining the Characteristics and Applications of Mesenchymal, Induced Pluripotent, and Embryonic Stem Cells for Tissue Engineering Approaches across the Germ Layers

The field of regenerative medicine utilizes a wide array of technologies and techniques for repairing and restoring function to damaged tissues. Among these, stem cells offer one of the most potent and promising biological tools to facilitate such goals. Implementation of mesenchymal stem cells (MSCs), induced pluripotent stem cells (iPSCs), and embryonic stem cells (ESCs) offer varying advantages based on availability and efficacy in the target tissue. The focus of this review is to discuss characteristics of these three subset stem cell populations and examine their utility in tissue engineering. In particular, the development of therapeutics that utilize cell-based approaches, divided by germinal layer to further assess research targeting specific tissues of the mesoderm, ectoderm, and endoderm. The combinatorial application of MSCs, iPSCs, and ESCs with natural and synthetic scaffold technologies can enhance the reparative capacity and survival of implanted cells. Continued efforts to generate more standardized approaches for these cells may provide improved study-to-study variations on implementation, thereby increasing the clinical translatability of cell-based therapeutics. Coupling clinically translatable research with commercially oriented methods offers the potential to drastically advance medical treatments for multiple diseases and injuries, improving the quality of life for many individuals.

The combination of a poly-caprolactone/nano-hydroxyapatite honeycomb scaffold and mesenchymal stem cells promotes bone regeneration in rat calvarial defects

Bone tissue engineering goes beyond the limitations of conventional methods of treating bone loss, such as autograft-induced morbidity and a lack of integration for large grafts. Novel biomimicry approaches (using three-dimensional [3D] electrospinning and printing techniques) have been designed to offer the most appropriate environment for cells and thus promote bone regeneration. In the present study, we assessed the bone regeneration properties of a composite 3D honeycomb structure from the electrostatic template-assisted deposition process by an alternate deposition of electrospun polycaprolactone (PCL) nanofibers and electrosprayed hydroxyapatite nanoparticles (nHA) on a honeycomb micropatterned substrate. We first confirmed the cytocompatibility of this honeycomb PCL-nHA scaffold in culture with bone marrow-derived mesenchymal stem cells (BM-MSCs). The scaffold was then implanted (alone or with seeded MSCs) for 2 months in a rat critical-sized calvarial defect model. The observation of new bone synthesis in situ (monitored using microcomputed tomography every 2 weeks and a histological assessment upon extraction) demonstrated that the honeycomb PCL-nHA scaffold was osteoconductive. Moreover, the combination of the scaffold with BM-MSCs was associated with significantly greater bone volume and mineralized regeneration during the 2-month experiment. The combination of the biomimetic honeycomb PCL-nHA scaffold with patient mesenchymal stem cells might therefore have great potential for clinical applications and specifically in maxillofacial surgery.

The co-culture of ASCs and EPCs promotes vascularized bone regeneration in critical-sized bone defects of cranial bone in rats

Background

The repair of critical-sized bone defect represents a challenging problem in bone tissue engineering. To address the most important problem in bone defect repair, namely insufficient blood supply, this study aimed to find a method that can promote the formation of vascularized bone tissue.

Method

The phenotypes of ASCs and EPCs were identified respectively, and ASCs/EPCs were co-cultured in vitro to detect the expression of osteogenic and angiogenic genes. Furthermore, the co-culture system combined with scaffold material was used to repair the critical-sized bone defects of the cranial bone in rats.

Results

The co-culture of ASCs/EPCs could increase osteogenesis and angiogenesis-related gene expression in vitro. The results of in vivo animal experiments demonstrated that the ASC/EPC group could promote bone regeneration and vascularization in the meantime and then significantly accelerate the repair of critical-sized bone defects.

Conclusion

It is feasible to replace traditional single seed cells with ASC/EPC co-culture system for vascularized bone regeneration. This system could ultimately enable clinicians to better repair the defect of craniofacial bone and avoid donor site morbidity.

Bone regeneration capacities of alveolar bone mesenchymal stem cells sheet in rabbit calvarial bone defect

Mesenchymal stem cells sheets have been verified as a promising non-scaffold strategy for bone regeneration. Alveolar bone marrow mesenchymal stem cells, derived from neural crest, have the character of easily obtained and strong multi-differential potential. However, the bone regenerative features of alveolar bone marrow mesenchymal stem cells sheets in the craniofacial region remain unclear. The purpose of the present study was to compare the osteogenic differentiation and bone defect repairment characteristics of bone marrow mesenchymal stem cells sheets derived from alveolar bone (alveolar bone marrow mesenchymal stem cells) and iliac bone (Lon-bone marrow mesenchymal stem cells) in vitro and in vivo. Histology character, osteogenic differentiation, and osteogenic gene expression of human alveolar bone marrow mesenchymal stem cells and Lon-bone marrow mesenchymal stem cells were compared in vitro. The cell sheets were implanted in rabbit calvarial defects to evaluate tissue regeneration characteristics. Integrated bioinformatics analysis was used to reveal the specific gene and pathways expression profile of alveolar bone marrow mesenchymal stem cells. Our results showed that alveolar bone marrow mesenchymal stem cells had higher osteogenic differentiation than Lon-bone marrow mesenchymal stem cells. Although no obvious differences were found in the histological structure, fibronectin and integrin β1 expression between them, alveolar-bone marrow mesenchymal stem cells sheet exhibited higher mineral deposition and expression levels of osteogenic marker genes. After being transplanted in the rabbit calvarial defects area, the results showed that greater bone volume and trabecular thickness regeneration were found in bone marrow mesenchymal stem cells sheet group compared to Lon-bone marrow mesenchymal stem cells group at both 4 weeks and 8 weeks. Finally, datasets of bone marrow mesenchymal stem cells versus Lon-bone marrow mesenchymal stem cells, and periodontal ligament mesenchymal stem cells (another neural crest derived mesenchymal stem cells) versus umbilical cord mesenchymal stem cells were analyzed. Total 71 differential genes were identified by overlap between the 2 datasets. Homeobox genes, such as LHX8, MKX, PAX9, MSX, and HOX, were identified as the most significantly changed and would be potential specific genes in neural crest mesenchymal stem cells. In conclusion, the Al-bone marrow mesenchymal stem cells sheet-based tissue regeneration appears to be a promising strategy for craniofacial defect repair in future clinical applications.

Three-Dimensional Cell Sheet Construction Method with a Polyester Micromesh Sheet

Cell sheet engineering has become important in a variety of fields, including regenerative medicine and transplantation. Our research group previously developed micromesh cultures that enable cells to form a cell sheet on a microstructured mesh sheet. Here, we present a more usable micromesh culture and devices that make it possible, aiming for widespread use. The devices are mainly constituted of a polyester micromesh sheet and three-dimensional (3D)-printed simple frames that fix the mesh sheet on it. Cells such as fibroblast Tig-1-20 cells, hepatoma HepG2 cells, or mesenchymal stem cells (MSC) were easily seeded on the polyester mesh sheet in the device and cultured for 16 days, which was followed by the formation of a 100-400-μm-thick cell sheet. The cell sheet was very robust, easy to handle, and could be readily removed from the device for subsequent analysis. Optical coherence tomography revealed the structure of the cell sheet as having the mesh sheet layer in the center of the cell sheet. Confocal microscopy demonstrated that Tig-1-20 cells in the cell sheet were aligned according to the shape of the mesh apertures, indicating that cell orientation can be controlled with this micromesh culture. As for another application, the device was used to construct a multilayered cell sheet that consists of three different types of cells. Furthermore, for mass production, the device frames were made using polyoxymethylene (POM) instead of 3D printing materials. Using the POM devices, a large MSC sheet for 10 cm dishes was successfully produced 7 days after cell seeding. This micromesh culture may become one of the useful cell sheet construction methods in future for medical and research fields. Impact statement Currently, cell sheets are constructed, for example, on a temperature-responsive polymer-coated dish or a porous membrane. These cell sheets are widely used but are not completely suitable in terms of robustness, ease of handling, cost, ease of microscopic cell observation, or nutrient supply. We previously reported that the micromesh culture can provide a three-dimensional (3D) cell sheet that has advantages for cell observation and nutrient supply. In this study, the micromesh culture was enhanced with a polyester micromesh sheet and a series of devices of polyoxymethylene, helping us to produce a robust, cost-effective, easily layered, and easy-to-use 3D cell sheet.

Schnurri-3 regulates BMP9-induced osteogenic differentiation and angiogenesis of human amniotic mesenchymal stem cells through Runx2 and VEGF

Human amniotic mesenchymal stem cells (hAMSCs) are multiple potent progenitor cells (MPCs) that can differentiate into different lineages (osteogenic, chondrogenic, and adipogenic cells) and have a favorable capacity for angiogenesis. Schnurri-3 (Shn3) is a large zinc finger protein related to Drosophila Shn, which is a critical mediator of postnatal bone formation. Bone morphogenetic protein 9 (BMP9), one of the most potent osteogenic BMPs, can strongly upregulate various osteogenesis- and angiogenesis-related factors in MSCs. It remains unclear how Shn3 is involved in BMP9-induced osteogenic differentiation coupled with angiogenesis in hAMSCs. In this investigation, we conducted a comprehensive study to identify the effect of Shn3 on BMP9-induced osteogenic differentiation and angiogenesis in hAMSCs and analyze the responsible signaling pathway. The results from in vitro and in vivo experimentation show that Shn3 notably inhibits BMP9-induced early and late osteogenic differentiation of hAMSCs, expression of osteogenesis-related factors, and subcutaneous ectopic bone formation from hAMSCs in nude mice. Shn3 also inhibited BMP9-induced angiogenic differentiation, expression of angiogenesis-related factors, and subcutaneous vascular invasion in mice. Mechanistically, we found that Shn3 prominently inhibited the expression of BMP9 and activation of the BMP/Smad and BMP/MAPK signaling pathways. In addition, we further found activity on runt-related transcription factor 2 (Runx2), vascular endothelial growth factor (VEGF), and the target genes shared by BMP and Shn3 signaling pathways. Silencing Shn3 could dramatically enhance the expression of Runx2, which directly regulates the downstream target VEGF to couple osteogenic differentiation with angiogenesis. To summarize, our findings suggested that Shn3 significantly inhibited the BMP9-induced osteogenic differentiation and angiogenesis in hAMSCs. The effect of Shn3 was primarily seen through inhibition of the BMP/Smad signaling pathway and depressed expression of Runx2, which directly regulates VEGF, which couples BMP9-induced osteogenic differentiation with angiogenesis.

Dispersion of ceramic granules within human fractionated adipose tissue to enhance endochondral bone formation

Engineering of materials consisting of hypertrophic cartilage, as physiological template for de novo bone formation through endochondral ossification (ECO), holds promise as a new class of biological bone substitutes. Here, we assessed the efficiency and reproducibility of bone formation induced by the combination of ceramic granules with fractionated human adipose tissue ("nanofat"), followed by in vitro priming to hypertrophic cartilage. Human nanofat was mixed with different volumetric ratios of ceramic granules (0.2-1 mm) and cultured to sequentially induce proliferation (3 weeks), chondrogenesis (4 weeks), and hypertrophy (2 weeks). The resulting engineered constructs were implanted ectopically in nude mouse. The presence of ceramic granules regulated tissue formation, both in vitro and in vivo. In particular, their dispersion in nanofat at a ratio of 1:16 led to significantly increased cell number and glycosaminoglycan accumulation in vitro, as well as amount and inter-donor reproducibility of bone formation in vivo. Our findings outline a strategy for efficient utilization of nanofat for bone regeneration in an autologous setting, which should now be tested at an orthotopic site. STATEMENT OF SIGNIFICANCE: In this study, we assessed the efficiency and reproducibility of bone formation by a combination of ceramic granules and fractionated human adipose tissue, also known as nanofat, in vitro primed into hypertrophic cartilage. The resulting engineered cartilaginous constructs, when implanted ectopically in nude mouse, resulted in bone and bone marrow formation, more reproducibly and strongly that nanofat alone. This project evaluates the impact of ceramic granules on the functionality and chondrogenic differentiation of mesenchymal progenitors inside their native adipose tissue niche and outlines a novel strategy for an efficient application of nanofat for bone regeneration in an autologous setting.

Bone Xenografts in Trauma and Orthopaedics (Analytical Review)

Purpose of the analytical review — to evaluate the application experience of bone xenografts in trauma and orthopaedics surgery. Methods. Data search was performed in the electronic databases of PubMed and eLIBRARY with depth of 20 years. Results. The authors identified 13 papers which described the application experience of bone xenografts in trauma surgery and orthopaedics. The highest efficiency (from 92 to 100%) was reported for cases of xenografts use to replace defects in intraarticular fractures and revision arthroplasty. Unsatisfactory outcomes were related to cases with no integration and graft rejection. The least efficiency (from 41,9 to 46,1%) was reported in reconstructive foot surgery. No effect of bone xenografts was observed for replacement of defects in cases of pseudoarthrosis. The most frequent complication was graft material infection. The summarized literature data provided the calculated share of complications following xenograft use of 7,53% (18 out of 239 cases, CI 5-95%, 4,53-11,21). Two areas were identified for improvement of technical and biological properties of bone xenografts: 1. Modification of original xeno-matrix (enhancement of purification technique, alteration of structure of chemical composition of the bone matrix); 2. Augmentation of matrix volume by additional elements (biologically active agents, stem cells). It’s noted that demand for xenografts in traumatology and orthopaedics can increase after refining and expanding the indications for clinical use. Conclusion. Bone xenografts used in the modern trauma surgery and orthopaedics to replace bone defects in revision arthroplasty as well as in certain fracture types. Such material is relatively safe and its ability to be modified allows to improve its biological properties.

The m6A methyltransferase METTL3 cooperates with demethylase ALKBH5 to regulate osteogenic differentiation through NF-κB signaling

As a m6A methylation modifier, METTL3 is functionally involved in various biological processes. Nevertheless, the role of METTL3 in osteogenesis is not determined up to date. In the current study, METTL3 is identified as a crucial regulator in the progression of osteogenic differentiation. Loss of METTL3 significantly augments calcium deposition and enhances alkaline phosphatase activity of mesenchymal stem cells, uncovering an inhibitory role of METTL3 in osteogenesis. More importantly, the underlying molecular basis by which METTL3 regulates osteogenesis is illustrated. We find that METTL3 positively regulates expression of MYD88, a critical upstream regulator of NF-κB signaling, by facilitating m6A methylation modification to MYD88-RNA, subsequently inducing the activation of NF-κB which is widely regarded as a repressor of osteogenesis and therefore suppressing osteogenic progression. Moreover, the METTL3-mediated m6A methylation is found to be dynamically reversed by the demethylase ALKBH5. In summary, this study highlights the functional importance of METTL3 in osteogenic differentiation and METTL3 may serve as a promising molecular target in regenerative medicine, as well as in the field of bone tissue engineering.

The Crosstalk Between Osteodifferentiating Stem Cells and Endothelial Cells Promotes Angiogenesis and Bone Formation

The synergistic crosstalk between osteodifferentiating stem cells and endothelial cells (ECs) gained the deserved consideration, shedding light on the role of angiogenesis for bone formation and healing. A deep understanding of the molecular basis underlying the mutual influence of mesenchymal stem cells (MSCs) and ECs in the osteogenic process may help improve greatly bone regeneration. Here, the authors demonstrated that osteodifferentiating MSCs co-cultured with ECs promote angiogenesis and ECs recruitment. Moreover, through the use of 3D co-culture systems, we showed that ECs are in turn able to further stimulate the osteodifferentiation of MSCs, thus enhancing bone production. These findings highlighted the existence of a virtuous loop between MSCs and ECs that is central to the osteogenic process. Unraveling the molecular mechanisms governing the functional interaction MSCs and ECs holds great potential in the field of regenerative medicine.

Inhibition of the negative effect of high glucose on osteogenic differentiation of bone marrow stromal cells by silicon ions from calcium silicate bioceramics

Human bone marrow stem cells (hBMSCs) are exploited for miscellaneous applications in bone tissue engineering where they are mainly used as seed cells. However, high glucose (HG) environment has negative impacts on the proliferation and osteogenic differentiation of hBMSCs, thus reducing the bone formation in diabetic patients. In our former research works, we discovered that silicon (Si) ions extracted from silicate-based bioceramics are able to stimulate the proliferation and osteogenic differentiation of hBMSCs under normal culture condition. This study aimed to investigate if Si ions could prevent HG-induced inhibition of proliferation and osteogenesis of hBMSCs. We found that 2.59 ppm concentration of Si ions promoted the proliferation of hBMSCs under HG condition. The results from alkaline phosphatase (ALP) activity assay, Alizarin red S staining and quantitative real-time PCR analysis of osteogenic genes (BMP2, RUNX2, ALP, COL1 and OCN) demonstrated that the 15.92 ppm concentration of Si ions prevented HG-induced inhibition of the osteogenic differentiation of hBMSCs. Moreover, application of Si ions reduced the level of reactive oxygen species in HG-treated hBMSCs. In HG-treated hBMSCs following 15.92 ppm Si ions treatment, activation of BMP2/SMAD signaling pathway was detected, as indicated by the increased expression of BMP2 receptors and its downstream genes such as SMAD1, SMAD4 and SMAD5. Taken together, we provide evidence that the specific concentration of Si ions compensated HG-induced inhibition of proliferation and osteogenic differentiation of hBMSCs through antioxidant effect and modulation of BMP2/SMAD pathway. The results suggest that silicate-based bioceramics might be good scaffold biomaterials for bone engineering applications in diabetes patients.

Combination of Chemical and Neurotrophin Stimulation Modulates Neurotransmitter Receptor Expression and Activity in Transdifferentiating Human Adipose Stromal Cells

Adipose stromal cells are promising tools for clinical applications in regeneration therapies, due to their ease of isolation from tissue and its high yield; however, their ability to transdifferentiate into neural phenotypes is still a matter of controversy. Here, we show that combined chemical and neurotrophin stimulation resulted in neuron-like morphology and regulated expression and activity of several genes involved in neurogenesis and neurotransmission as well as ion currents mediated by NMDA and GABA receptors. Among them, expression patterns of genes coding for kinin-B1 and B2, α7 nicotinic, M1, M3 and M4 muscarinic acetylcholine, glutamatergic (AMPA2 and mGlu2), purinergic P2Y1 and P2Y4 and GABAergic (GABA-A, β3-subunit) receptors and neuronal nitric oxide synthase were up-regulated compared to levels of undifferentiated cells. Simultaneously, expression levels of P2X1, P2X4, P2X7 and P2Y6 purinergic and M5 muscarinic acetylcholine receptors were down-regulated. Agonist-induced activity levels of the studied receptor classes also augmented during neuronal transdifferentiation. Transdifferentiated cells expressed high levels of neuronal β3-tubulin, NF-H, NeuN and MAP-2 proteins as well as increased ASCL1, MYT1 and POU3F2 gene expression known to drive neuronal fate determination. The presented work contributes to a better understanding of transdifferentiation induced by neurotrophins for a prospective broad spectrum of medical applications.

Periodontal Bone-Ligament-Cementum Regeneration via Scaffolds and Stem Cells

Periodontitis is a prevalent infectious disease worldwide, causing the damage of periodontal support tissues, which can eventually lead to tooth loss. The goal of periodontal treatment is to control the infections and reconstruct the structure and function of periodontal tissues including cementum, periodontal ligament (PDL) fibers, and bone. The regeneration of these three types of tissues, including the re-formation of the oriented PDL fibers to be attached firmly to the new cementum and alveolar bone, remains a major challenge. This article represents the first systematic review on the cutting-edge researches on the regeneration of all three types of periodontal tissues and the simultaneous regeneration of the entire bone-PDL-cementum complex, via stem cells, bio-printing, gene therapy, and layered bio-mimetic technologies. This article primarily includes bone regeneration; PDL regeneration; cementum regeneration; endogenous cell-homing and host-mobilized stem cells; 3D bio-printing and generation of the oriented PDL fibers; gene therapy-based approaches for periodontal regeneration; regenerating the bone-PDL-cementum complex via layered materials and cells. These novel developments in stem cell technology and bioactive and bio-mimetic scaffolds are highly promising to substantially enhance the periodontal regeneration including both hard and soft tissues, with applicability to other therapies in the oral and maxillofacial region.