Transcriptional characterization of bone morphogenetic proteins (BMPs)-mediated osteogenic signaling

Berberine Derivative Compound 13 as a Potent Promoter of Osteoblast Differentiation via Akt and PKC Signaling Pathways

Berberine has been widely studied for its biological functions in various diseases, including cancer, diabetes, and cardiovascular diseases. Nevertheless, structural modifications of berberine have been demonstrated to augment its pharmacological efficacy in specific biological processes, particularly osteogenesis. In this study, we aimed to explore new berberine derivatives with pro-osteogenic activity and molecular mechanisms. Our results demonstrated that compound 13 is the most effective among the tested compounds. Compound 13 significantly enhanced BMP4-induced alkaline phosphatase (ALP) staining and increased the transcriptional activity of osteogenic markers such as ALP, Runt-related gene 2 (Runx2), and Osterix at both the mRNA and protein levels. Furthermore, we found that the Akt and PKC signaling pathways play crucial roles in compound 13-induced osteogenesis via treatment with specific inhibitors. The molecular docking results supported the potential interaction between compound 13 and these kinases. These findings highlighted the regulatory role of compound 13 in osteoblast differentiation via the Akt and PKC signaling pathways. Overall, our study provides compelling evidence that compound 13 is a promising therapeutic candidate for the treatment of osteoporosis, with the potential for further development and optimization to improve bone health and strength.

Effect of CD10-positive cells on osteogenic differentiation of human maxillary/mandibular bone marrow-derived mesenchymal stem cells

OBJECTIVE

This study was aimed at investigating the effect of CD10-positive cells within the maxillary/mandibular bone marrow-derived mesenchymal stem cells (MBMSCs) on osteogenic differentiation of MBMSCs.

DESIGN

CD10 expression in iliac bone marrow-derived MSCs (IBMSCs), MBMSCs, and gingival fibroblasts was measured using flow cytometry. The osteogenic potential of 19 MBMSC lines was evaluated, and based on it, they were classified into osteogenic-High and osteogenic-Low groups. The percentage of CD10-positive cells in each group was compared. Effect of coculturing gingival fibroblasts and CD10-positive cells on the osteogenic potential of MBMSCs was also assessed. Expression of tissue inhibitor of metalloprotease-1 (TIMP-1) in osteogenic-High and osteogenic-Low MBMSCs was measured using quantitative real-time polymerase chain reaction, western blotting, and enzyme-linked immunosorbent assay. The molecular mechanisms underlying the regulation of osteogenic differentiation in MBMSCs were investigated.

RESULTS

CD10 was not expressed in IBMSCs, but was highly expressed in fibroblasts. In MBMSCs, the CD10-positivity rate varied considerably between cells. MBMSCs with a high-CD10 positivity rate showed low osteogenic potential. Coculture with fibroblasts or CD10-positive cells reduced the osteogenic potential of MBMSCs. TIMP-1 was highly expressed in CD10-positive cells, and osteogenic-Low MBMSCs showed significantly higher TIMP-1 expression compared with osteogenic-High MBMSCs. β-catenin signaling was suppressed in osteogenic-Low MBMSCs.

CONCLUSION

This study revealed that TIMP-1 secreted from CD10-positive cells may be involved in the suppression of the osteogenic potential of MBMSCs by contamination with CD10-positive cells. This finding provides important insights for developing bone regeneration therapies using MBMSCs.

Salvianolic acid A promotes bone-fracture healing via balancing osteoblast and osteoclast differentiation

Nonunion is a significant complication in fracture management for surgeons. Salvianolic acid A (SAA), derived from the traditional Chinese plant Salviae miltiorrhizae Bunge (Danshen), exhibits notable anti-inflammatory and antioxidant properties. Although studies have demonstrated its ability to promote osteogenic differentiation, the exact mechanism of action remains unclear. This study investigated the effects of various SAA concentrations on the osteogenic differentiation of mouse-derived bone marrow mesenchymal stem cells (mBMSCs) and the osteoclastic differentiation of bone marrow-derived macrophages. Our findings indicate that SAA promotes the osteogenic differentiation of mBMSCs in a concentration-dependent manner, primarily by inhibiting the Notch1 signaling pathway. Notably, the administration of two Notch1 agonists (Jagged-1 and VPA) inhibited the effects of SAA on osteogenic differentiation. Additionally, SAA facilitated the autophagic degradation of NICD1, further enhancing osteogenic differentiation. Furthermore, SAA also dose-dependently inhibited the osteoclastic differentiation of bone marrow-derived macrophages, which is linked to its suppression of NF-κB signaling pathways. In a fracture model, SAA demonstrated a capacity to promote healing. In conclusion, SAA enhances bone fracture healing by balancing osteoblast and osteoclast differentiation.

Effective Bone Tissue Fabrication Using 3D-Printed Citrate-Based Nanocomposite Scaffolds Laden with BMP9-Stimulated Human Urine Stem Cells

Effective repair of large bone defects through bone tissue engineering (BTE) remains an unmet clinical challenge. Successful BTE requires optimal and synergistic interactions among biocompatible scaffolds, osteogenic factors, and osteoprogenitors to form a highly vascularized microenvironment for bone regeneration and osseointegration. We sought to develop a highly effective BTE system by using 3D printed citrate-based mPOC/hydroxyapatite (HA) composites laden with BMP9-stimulated human urine stem cells (USCs). Specifically, we synthesized and characterized methacrylate poly(1,8 octamethylene citrate) (mPOC), mixed it with 0%, 40% or 60% HA (i.e., mPOC-0HA, mPOC-40HA, or mPOC-60HA), and fabricated composite scaffold via micro-continuous liquid interface production (μCLIP). The 3D-printed mPOC-HA composite scaffolds were compatible with human USCs that exhibited high osteogenic activity in vitro upon BMP9 stimulation. Subcutaneous implantation of mPOC-HA scaffolds laden with BMP9-stimulated USCs revealed effective bone formation in all three types of mPOC-HA composite scaffolds. Histologic evaluation revealed that the mPOC-60HA composite scaffold yielded the most mature bone, resembling native bone tissue with extensive scaffold-osteointegration. Collectively, these findings demonstrate that the citrate-based mPOC-60HA composite, human urine stem cells, and the potent osteogenic factor BMP9 constitute a desirable triad for effective bone tissue engineering.

May dental implant macro and microgeometry modifications influence peri-implant bone repair in smokers? A randomized clinical trial

BACKGROUND

This split-mouth, double-masked, randomized clinical trial aimed at evaluating the impact of different macro geometries and nano topographical modifications on peri-implant bone repair in smokers.

METHODS

Thirty-two patients who smoked at least ten cigarettes/day, with the need of a single maxillary or mandibular implant bilaterally, received two implants randomly assigned to DA - Dual Acid-Etched implants (n = 32); HCAN - healing chambers and activated nano surface (n = 32). Implant stability quotient (ISQ) was evaluated 07, 30, 60, 90, and 120 days after implant placement. Levels of bone and angiogenic markers were quantified in the peri-implant fluid after 07, 15, 30, 90, and 120 days of implant insertion. HCAN implants have a higher ISQ than DA implants at 60 days (p < 0.05).

RESULTS

PLGF levels were lower for HCAN implants than for DA implants at 07-day period (p < 0.05). Besides, HCAN implants presented higher levels of OPG at 30 days and OPN, BMP-9, FGF-1, PLGF, and VEGF at 90 days, compared to DA implants (p < 0.05). The levels of EGF were higher for HCAN implants at 15, 90, and 120 days compared with DA implants (p < 0.05). HCAN implants also showed lower levels of TNF-α at 07 days in comparison to DA implants (p < 0.05) but had higher levels of DKK1 at 30 days, while DA implants presented higher levels of this marker at 90 days (p < 0.05).

CONCLUSION

Macro geometry and nano topographical modifications positively modulated the bone and angiogenic factors, resulting in higher production of these markers during early peri-implant bone healing and having a positive effect on implant stabilization in smokers.

TRIAL REGISTRATION

RBR-10gjvcyt; date of registration: 06/12/2023 (Retrospectively registered).

Cell signaling and transcriptional regulation of osteoblast lineage commitment, differentiation, bone formation, and homeostasis

The initiation of osteogenesis primarily occurs as mesenchymal stem cells undergo differentiation into osteoblasts. This differentiation process plays a crucial role in bone formation and homeostasis and is regulated by two intricate processes: cell signal transduction and transcriptional gene expression. Various essential cell signaling pathways, including Wnt, BMP, TGF-β, Hedgehog, PTH, FGF, Ephrin, Notch, Hippo, and Piezo1/2, play a critical role in facilitating osteoblast differentiation, bone formation, and bone homeostasis. Key transcriptional factors in this differentiation process include Runx2, Cbfβ, Runx1, Osterix, ATF4, SATB2, and TAZ/YAP. Furthermore, a diverse array of epigenetic factors also plays critical roles in osteoblast differentiation, bone formation, and homeostasis at the transcriptional level. This review provides an overview of the latest developments and current comprehension concerning the pathways of cell signaling, regulation of hormones, and transcriptional regulation of genes involved in the commitment and differentiation of osteoblast lineage, as well as in bone formation and maintenance of homeostasis. The paper also reviews epigenetic regulation of osteoblast differentiation via mechanisms, such as histone and DNA modifications. Additionally, we summarize the latest developments in osteoblast biology spurred by recent advancements in various modern technologies and bioinformatics. By synthesizing these insights into a comprehensive understanding of osteoblast differentiation, this review provides further clarification of the mechanisms underlying osteoblast lineage commitment, differentiation, and bone formation, and highlights potential new therapeutic applications for the treatment of bone diseases.

KDELR2 promotes bone marrow mesenchymal stem cell osteogenic differentiation via GSK3β/β-catenin signaling pathway

Nonunion is a challenging complication of fractures for the surgeon. Recently the Lys-Asp-Glu-Leu (KDEL) endoplasmic reticulum protein retention receptor 2 (KDELR2) has been found that involved in osteogenesis imperfecta. However, the exact mechanism is still unclear. In this study, we used lentivirus infection and mouse fracture model to investigate the role of KDELR2 in osteogenesis. Our results showed that KDELR2 knockdown inhibited the osteogenic differentiation of mBMSCs, whereas KDELR2 overexpression had the opposite effect. Furthermore, the levels of active-β-catenin and phospho-GSK3β (Ser9) were upregulated by KDELR2 overexpression and downregulated by KDELR2 knockdown. In the fracture model, mBMSCs overexpressing KDELR2 promoted healing. In conclusion, KDELR2 promotes the osteogenesis of mBMSCs by regulating the GSK3β/β-catenin signaling pathway.

Adipose-derived mesenchymal stem cells (MSCs) are a superior cell source for bone tissue engineering

Effective bone regeneration through tissue engineering requires a combination of osteogenic progenitors, osteoinductive biofactors and biocompatible scaffold materials. Mesenchymal stem cells (MSCs) represent the most promising seed cells for bone tissue engineering. As multipotent stem cells that can self-renew and differentiate into multiple lineages including bone and fat, MSCs can be isolated from numerous tissues and exhibit varied differentiation potential. To identify an optimal progenitor cell source for bone tissue engineering, we analyzed the proliferative activity and osteogenic potential of four commonly-used mouse MSC sources, including immortalized mouse embryonic fibroblasts (iMEF), immortalized mouse bone marrow stromal stem cells (imBMSC), immortalized mouse calvarial mesenchymal progenitors (iCAL), and immortalized mouse adipose-derived mesenchymal stem cells (iMAD). We found that iMAD exhibited highest osteogenic and adipogenic capabilities upon BMP9 stimulation in vitro, whereas iMAD and iCAL exhibited highest osteogenic capability in BMP9-induced ectopic osteogenesis and critical-sized calvarial defect repair. Transcriptomic analysis revealed that, while each MSC line regulated a distinct set of target genes upon BMP9 stimulation, all MSC lines underwent osteogenic differentiation by regulating osteogenesis-related signaling including Wnt, TGF-β, PI3K/AKT, MAPK, Hippo and JAK-STAT pathways. Collectively, our results demonstrate that adipose-derived MSCs represent optimal progenitor sources for cell-based bone tissue engineering.

FOXC1 Promotes Osteoblastic Differentiation of Bone Marrow Mesenchymal Stem Cells via the Dnmt3b/CXCL12 Axis

Bone defects have remained a clinical problem in current orthopedics. Bone marrow mesenchymal stem cells (BM-MSCs) with multi-directional differentiation ability have become a research hotspot for repairing bone defects. In vitro and in vivo models were constructed, respectively. Alkaline phosphatase (ALP) staining and alizarin red staining were performed to detect osteogenic differentiation ability. Western blotting (WB) was used to detect the expression of osteogenic differentiation-related proteins. Serum inflammatory cytokine levels were detected by ELISA. Fracture recovery was evaluated by HE staining. The binding relationship between FOXC1 and Dnmt3b was verified by dual-luciferase reporter assay. The relationship between Dnmt3b and CXCL12 was explored by MSP and ChIP assays. FOXC1 overexpression promoted calcium nodule formation, upregulated osteogenic differentiation-related protein expression, promoted osteogenic differentiation, and decreased inflammatory factor levels in BM-MSCs, and promoted callus formation, upregulated osteogenic differentiation-related protein expression, and downregulated CXCL12 expression in the mouse model. Furthermore, FOXC1 targeted Dnmt3b, with Dnmt3b knockdown decreasing calcium nodule formation and downregulating osteogenic differentiation-related protein expression. Additionally, inhibiting Dnmt3b expression upregulated CXCL12 protein expression and inhibited CXCL12 methylation. Dnmt3b could be binded to CXCL12. CXCL12 overexpression attenuated the effects of FOXC1 overexpression and inhibited BM-MSCs osteogenic differentiation. This study confirmed that the FOXC1-mediated regulation of the Dnmt3b/CXCL12 axis had positive effects on the osteogenic differentiation of BM-MSCs.

Efficient bone regeneration of BMP9-stimulated human periodontal ligament stem cells (hPDLSCs) in decellularized bone matrix (DBM) constructs to model maxillofacial intrabony defect repair

BACKGROUND

BMP9-stimulated DPSCs, SCAPs and PDLSCs are effective candidates for repairing maxillofacial bone defects in tissue engineering, while the most suitable seed cell source among these three hDMSCs and the optimal combination of most suitable type of hDMSCs and BMP9 have rarely been explored. Moreover, the orthotopic maxillofacial bone defect model should be valuable but laborious and time-consuming to evaluate various candidates for bone regeneration. Thus, inspired from the maxillofacial bone defects and the traditional in vivo ectopic systems, we developed an intrabony defect repair model to recapitulate the healing events of orthotopic maxillofacial bone defect repair and further explore the optimized combinations of most suitable hDMSCs and BMP9 for bone defect repair based on this modified ectopic system.

METHODS

Intrabony defect repair model was developed by using decellularized bone matrix (DBM) constructs prepared from the cancellous part of porcine lumbar vertebral body. We implanted DBM constructs subcutaneously on the flank of each male NU/NU athymic nude mouse, followed by directly injecting the cell suspension of different combinations of hDMSCs and BMP9 into the central hollow area of the constructs 7 days later. Then, the quality of the bony mass, including bone volume fraction (BV/TV), radiographic density (in Hounsfield units (HU)) and the height of newly formed bone, was measured by micro-CT. Furthermore, the H&E staining and immunohistochemical staining were performed to exam new bone and new blood vessel formation in DBM constructs.

RESULTS

BMP9-stimulated periodontal ligament stem cells (PDLSCs) exhibited the most effective bone regeneration among the three types of hDMSCs in DBM constructs. Furthermore, an optimal dose of PDLSCs with a specific extent of BMP9 stimulation was confirmed for efficacious new bone and new blood vessel formation in DBM constructs.

CONCLUSIONS

The reported intrabony defect repair model can be used to identify optimized combinations of suitable seed cells and biological factors for bone defect repair and subsequent development of efficacious bone tissue engineering therapies.

Bone morphogenetic protein 4 is involved in cadmium-associated bone damage

Cadmium (Cd) is a well-characterized bone toxic agent and can induce bone damage via inhibiting osteogenic differentiation. Bone morphogenetic protein (BMP)/SMAD signaling pathway can mediate osteogenic differentiation, but the association between Cd and BMP/SMAD signaling pathway is yet to be illuminated. To understand what elements of BMPs and SMADs are affected by Cd to influence osteogenic differentiation and if BMPs can be the biomarkers of which Cd-induced osteoporosis, human bone marrow mesenchymal stem cells (hBMSCs) were treated with cadmium chloride (CdCl2) in vitro to detect the expression of BMPs and SMADs, and 134 subjects were enrolled to explore if the BMPs can be potential biomarkers of Cd-associated bone damage. Our results showed that Cd exposure significantly promoted the adipogenic differentiation of hBMSCs and inhibited its osteogenic differentiation by inhibiting the expression of BMP-2/4, SMAD4, and p-SMAD1/5/9 complex. And mediation analyses yielded that BMP-4 mediated 39.32% (95% confidence interval 7.47, 85.00) of the total association between the Cd and the risk of Cd-associated bone damage. Moreover, during differentiation, BMP-4 had the potential to enhance mineralization compared with CdCl2 only group. These results reveal that BMP-4 can be a diagnostic biomarker and therapeutic target for Cd-associated bone damage.

β-Ecdysterone Enhanced Bone Regeneration Through the BMP-2/SMAD/RUNX2/Osterix Signaling Pathway

Bone defects are a global public health problem. However, the available methods for inducing bone regeneration are limited. The application of traditional Chinese herbs for bone regeneration has gained popularity in recent years. β-ecdysterone is a plant sterol similar to estrogen, that promotes protein synthesis in cells; however, its function in bone regeneration remains unclear. In this study, we investigated the function of β-ecdysterone on osteoblast differentiation and bone regeneration in vitro and in vivo. MC3T3-E1 cells were used to test the function of β-ecdysterone on osteoblast differentiation and bone regeneration in vitro. The results of the Cell Counting Kit-8 assay suggested that the proliferation of MC3T3-E1 cells was promoted by β-ecdysterone. Furthermore, β-ecdysterone influenced the expression of osteogenesis-related genes, and the bone regeneration capacity of MC3T3-E1 cells was detected by polymerase chain reaction, the alkaline phosphatase (ALP) test, and the alizarin red test. β-ecdysterone could upregulate the expression of osteoblastic-related genes, and promoted ALP activity and the formation of calcium nodules. We also determined that β-ecdysterone increased the mRNA and protein levels of components of the BMP-2/Smad/Runx2/Osterix pathway. DNA sequencing further confirmed these target effects. β-ecdysterone promoted bone formation by enhancing gene expression of the BMP-2/Smad/Runx2/Osterix signaling pathway and by enrichment biological processes. For in vivo experiments, a femoral condyle defect model was constructed by drilling a bone defect measuring 3 mm in diameter and 4 mm in depth in the femoral condyle of 8-week-old Sprague Dawley male rats. This model was used to further assess the bone regenerative functions of β-ecdysterone. The results of micro-computed tomography showed that β-ecdysterone could accelerate bone regeneration, exhibiting higher bone volume, bone surface, and bone mineral density at each observation time point. Immunohistochemistry confirmed that the β-ecdysterone also increased the expression of collagen, osteocalcin, and bone morphogenetic protein-2 in the experiment group at 4 and 8 weeks. In conclusion, β-ecdysterone is a new bone regeneration regulator that can stimulate MC3T3-E1 cell proliferation and induce bone regeneration through the BMP-2/Smad/Runx2/Osterix pathway. This newly discovered function of β-ecdysterone has revealed a new direction of osteogenic differentiation and has provided novel therapeutic strategies for treating bone defects.

FDA-approved bone grafts and bone graft substitute devices in bone regeneration

To induce bone regeneration there is a complex cascade of growth factors. Growth factors such as recombinant BMP-2, BMP-7, and PDGF are FDA-approved therapies in bone regeneration. Although, BMP shows promising results as being an alternative to autograft, it also has its own downfalls. BMP-2 has many adverse effects such as inflammatory complications such as massive soft-tissue swelling that can compromise a patient's airway, ectopic bone formation, and tumor formation. BMP-2 may also be advantageous for patients not willing to give up smoking as it shows bone regeneration success with smokers. BMP-7 is no longer an option for bone regeneration as it has withdrawn off the market. PDGF-BB grafts in studies have shown PDGF had similar fusion rates to autologous grafts and fewer adverse effects. There is also an FDA-approved bioactive molecule for bone regeneration, a peptide P-15. P-15 was found to be effective, safe, and have similar outcomes to autograft at 2 years post-op for cervical radiculopathy due to cervical degenerative disc disease. Growth factors and bioactive molecules show some promising results in bone regeneration, although more research is needed to avoid their adverse effects and learn about the long-term effects of these therapies. There is a need of a bone regeneration method of similar quality of an autograft that is osteoconductive, osteoinductive, and osteogenic. This review covers all FDA-approved bone regeneration therapies such as the "gold standard" autografts, allografts, synthetic bone grafts, and the newer growth factors/bioactive molecules. It also covers international bone grafts not yet approved in the United States and upcoming technologies in bone grafts.

Argonaute (AGO) proteins play an essential role in mediating BMP9-induced osteogenic signaling in mesenchymal stem cells (MSCs)

As multipotent progenitor cells, mesenchymal stem cells (MSCs) can renew themselves and give rise to multiple lineages including osteoblastic, chondrogenic and adipogenic lineages. It's previously shown that BMP9 is the most potent BMP and induces osteogenic and adipogenic differentiation of MSCs. However, the molecular mechanism through which BMP9 regulates MSC differentiation remains poorly understood. Emerging evidence indicates that noncoding RNAs, especially microRNAs, may play important roles in regulating MSC differentiation and bone formation. As highly conserved RNA binding proteins, Argonaute (AGO) proteins are essential components of the multi-protein RNA-induced silencing complexes (RISCs), which are critical for small RNA biogenesis. Here, we investigate possible roles of AGO proteins in BMP9-induced lineage-specific differentiation of MSCs. We first found that BMP9 up-regulated the expression of Ago1, Ago2 and Ago3 in MSCs. By engineering multiplex siRNA vectors that express multiple siRNAs targeting individual Ago genes or all four Ago genes, we found that silencing individual Ago expression led to a decrease in BMP9-induced early osteogenic marker alkaline phosphatase (ALP) activity in MSCs. Furthermore, we demonstrated that simultaneously silencing all four Ago genes significantly diminished BMP9-induced osteogenic and adipogenic differentiation of MSCs and matrix mineralization, and ectopic bone formation. Collectively, our findings strongly indicate that AGO proteins and associated small RNA biogenesis pathway play an essential role in mediating BMP9-induced osteogenic differentiation of MSCs.

Sinking Our Teeth in Getting Dental Stem Cells to Clinics for Bone Regeneration

Dental stem cells have been isolated from the medical waste of various dental tissues. They have been characterized by numerous markers, which are evaluated herein and differentiated into multiple cell types. They can also be used to generate cell lines and iPSCs for long-term in vitro research. Methods for utilizing these stem cells including cellular systems such as organoids or cell sheets, cell-free systems such as exosomes, and scaffold-based approaches with and without drug release concepts are reported in this review and presented with new pictures for clarification. These in vitro applications can be deployed in disease modeling and subsequent pharmaceutical research and also pave the way for tissue regeneration. The main focus herein is on the potential of dental stem cells for hard tissue regeneration, especially bone, by evaluating their potential for osteogenesis and angiogenesis, and the regulation of these two processes by growth factors and environmental stimulators. Current in vitro and in vivo publications show numerous benefits of using dental stem cells for research purposes and hard tissue regeneration. However, only a few clinical trials currently exist. The goal of this review is to pinpoint this imbalance and encourage scientists to pick up this research and proceed one step further to translation.

BMP9-initiated osteogenic/odontogenic differentiation of mouse tooth germ mesenchymal cells (TGMCS) requires Wnt/β-catenin signalling activity

Teeth arise from the tooth germ through sequential and reciprocal interactions between immature epithelium and mesenchyme during development. However, the detailed mechanism underlying tooth development from tooth germ mesenchymal cells (TGMCs) remains to be fully understood. Here, we investigate the role of Wnt/β‐catenin signalling in BMP9‐induced osteogenic/odontogenic differentiation of TGMCs. We first established the reversibly immortalized TGMCs (iTGMCs) derived from young mouse mandibular molar tooth germs using a retroviral vector expressing SV40 T antigen flanked with the FRT sites. We demonstrated that BMP9 effectively induced expression of osteogenic markers alkaline phosphatase, collagen A1 and osteocalcin in iTGMCs, as well as in vitro matrix mineralization, which could be remarkably blunted by knocking down β‐catenin expression. In vivo implantation assay revealed that while BMP9‐stimulated iTGMCs induced robust formation of ectopic bone, knocking down β‐catenin expression in iTGMCs remarkably diminished BMP9‐initiated osteogenic/odontogenic differentiation potential of these cells. Taken together, these discoveries strongly demonstrate that reversibly immortalized iTGMCs retained osteogenic/odontogenic ability upon BMP9 stimulation, but this process required the participation of canonical Wnt signalling both in vitro and in vivo. Therefore, BMP9 has a potential to be applied as an efficacious bio‐factor in osteo/odontogenic regeneration and tooth engineering. Furthermore, the iTGMCs may serve as an important resource for translational studies in tooth tissue engineering.

Osteogenic differentiation cues of the bone morphogenetic protein-9 (BMP-9) and its recent advances in bone tissue regeneration

Bone regeneration using bioactive molecules and biocompatible materials is growing steadily with the advent of the new findings in cellular signaling. Bone Morphogenetic Protein (BMP)-9 is a considerably recent discovery from the BMP family that delivers numerous benefits in osteogenesis. The Smad cellular signaling pathway triggered by BMPs is often inhibited by Noggin. However, BMP-9 is resistant to Noggin, thus, facilitating a more robust cellular differentiation of osteoprogenitor cells into preosteoblasts and osteoblasts. This review encompasses a general understanding of the Smad signaling pathway activated by the BMP-9 ligand molecule with its specific receptors. The robust osteogenic cellular differentiation cue provided by BMP-9 has been reviewed from a bone regeneration perspective with several in vitro as well as in vivo studies reporting promising results for future research. The effect of the biomaterial, chosen in such studies as the scaffold or carrier matrix, on the activity of BMP-9 and subsequent bone regeneration has been highlighted in this review. The non-viral delivery technique for BMP-9 induced bone regeneration is a safer alternative to its viral counterpart. The recent advances in non-viral BMP-9 delivery have also highlighted the efficacy of the protein molecule at a low dosage. This opens a new horizon as a more efficient and safer alternative to BMP-2, which was prevalent among clinical trials; however, BMP-2 applications have reported its downsides during bone defect healing such as cystic bone formation.

Role of Aquaporins in the Physiological Functions of Mesenchymal Stem Cells

Aquaporins (AQPs) are a family of membrane water channel proteins that control osmotically-driven water transport across cell membranes. Recent studies have focused on the assessment of fluid flux regulation in relation to the biological processes that maintain mesenchymal stem cell (MSC) physiology. In particular, AQPs seem to regulate MSC proliferation through rapid regulation of the cell volume. Furthermore, several reports have shown that AQPs play a crucial role in modulating MSC attachment to the extracellular matrix, their spread, and migration. Shedding light on how AQPs are able to regulate MSC physiological functions can increase our knowledge of their biological behaviours and improve their application in regenerative and reparative medicine.

FAMSi: A Synthetic Biology Approach to the Fast Assembly of Multiplex siRNAs for Silencing Gene Expression in Mammalian Cells

RNA interference (RNAi) is mediated by an ∼21-nt double-stranded small interfering RNA (siRNA) and shows great promise in delineating gene functions and in developing therapeutics for human diseases. However, effective gene silencing usually requires the delivery of multiple siRNAs for a given gene, which is often technically challenging and time-consuming. In this study, by exploiting the type IIS restriction endonuclease-based synthetic biology methodology, we developed the fast assembly of multiplex siRNAs (FAMSi) system. In our proof-of-concept experiments, we demonstrated that multiple fragments containing three, four, or five siRNA sites targeting common Smad4 and/or BMPR-specific Smad1, Smad5, and Smad8 required for BMP9 signaling could be assembled efficiently. The constructed multiplex siRNAs effectively knocked down the expression of Smad4 and/or Smad1, Smad5, and Smad8 in mesenchymal stem cells (MSCs), and they inhibited all aspects of BMP9-induced osteogenic differentiation in bone marrow MSCs (BMSCs), including decreased expression of osteogenic regulators/markers, reduced osteogenic marker alkaline phosphatase (ALP) activity, and diminished in vitro matrix mineralization and in vivo ectopic bone formation. Collectively, we demonstrate that the engineered FAMSi system provides a fast-track platform for assembling multiplexed siRNAs in a single vector, and thus it may be a valuable tool to study gene functions or to develop novel siRNA-based therapeutics.

TNF‑α regulates the osteogenic differentiation of bone morphogenetic factor 9 adenovirus‑transduced rat follicle stem cells via Wnt signaling

Periodontitis is a chronic infectious disease that alters the cellular microenvironment and promotes bone absorption. Bone morphogenetic protein 9 (BMP9) serves an important role in proliferation and differentiation, and tumor necrosis factor‑alpha (TNF‑α) is an important contributor to bone resorption. The present study aimed to investigate the effect of osteogenic differentiation in the presence of BMP9 and TNF‑α in rat follicle stem cells (rDFCs). rDFCs were transfected with adenoviruses expressing BMP9 (AdBMP9) and the expression levels of important proteins [BMP9, β‑catenin, glycogen synthase kinase 3β (GSK3β), phosphorylated‑GSK3β, calcium/calmodulin dependent protein kinase II and nemo like kinase] were determined using western blotting. The effect of osteogenesis was analyzed using reverse transcription‑quantitative PCR, in addition to alkaline phosphatase, Alizarin Red S, and hematoxylin and eosin staining methods. The results of the present study revealed that TNF‑α activated the canonical Wnt signaling pathway and suppressed osteogenesis. High concentrations of Dickkopf 1 (DKK1) reduced the osteogenic differentiation of AdBMP9‑transduced rDFCs, whereas low concentrations of DKK1 promoted BMP9‑induced bone formation, which was discovered to partially act via the canonical and non‑canonical Wnt signaling pathways. In conclusion, the findings of the present study suggested that the enhanced promoting effect of BMP9 alongside the treatment with low concentrations of DKK1 may be useful for treating periodontitis bone absorption.

Mesenchymal Stem/Progenitor Cells: The Prospect of Human Clinical Translation

Mesenchymal stem/progenitor cells (MSCs) are key players in regenerative medicine, relying principally on their differentiation/regeneration potential, immunomodulatory properties, paracrine effects, and potent homing ability with minimal if any ethical concerns. Even though multiple preclinical and clinical studies have demonstrated remarkable properties for MSCs, the clinical applicability of MSC-based therapies is still questionable. Several challenges exist that critically hinder a successful clinical translation of MSC-based therapies, including but not limited to heterogeneity of their populations, variability in their quality and quantity, donor-related factors, discrepancies in protocols for isolation, in vitro expansion and premodification, and variability in methods of cell delivery, dosing, and cell homing. Alterations of MSC viability, proliferation, properties, and/or function are also affected by various drugs and chemicals. Moreover, significant safety concerns exist due to possible teratogenic/neoplastic potential and transmission of infectious diseases. Through the current review, we aim to highlight the major challenges facing MSCs' human clinical translation and shed light on the undergoing strategies to overcome them.

Concentration-Dependent Regulation of TiAl6V4 Particles on the Osteogenesis Potential of Human Bone Marrow Mesenchymal Stem Cells

Total joint replacement is one of the most effective treatments for osteoarthritis, while the aseptic loosening of artificial joint is a major complication leading to the joint replacement failure. There are very limited studies about the effects of titanium-alloy particles on the osteogenic differentiation of mesenchymal stem cells. In this study, human bone marrow-derived mesenchymal stem cells (BM-hMSCs) were treated with different concentrations of TiAl₆V₄ particles. The cell viability was detected by MTT assay, and the cell proliferation was assessed by CKK-8 assay. The early and late stages of osteogenic differentiation were determined by alkaline phosphatase (ALP) and Alizarin Red S (ARS) staining assays. The expression of osteogenic genes and proteins was analyzed by RT-PCR and Western blot. TiAl₆V₄ particles at high concentration 100 μg/ml inhibited the cell viability of BM-hMSCs. However, TiAl₆V₄ in the range of 5-50 μg/ml did not show effects neither on the cell viability nor on the cell proliferation of BM-hMSCs. TiAl₆V₄ particles showed concentration-dependent bidirectional regulations on BM-hMSC osteogenesis. Specifically, TiAl₆V₄ at 5 μg/ml promoted the osteogenesis of BM-hMSCs, which was suppressed by TiAl₆V₄ at 50 μg/ml. Further, mechanism study revealed that the regulation of TiAl₆V₄ on BM-hMSCs was related to Wnt signaling pathway. Given the potential of mesenchymal cells, our study suggested that the minimization of metal use would be an attractive strategy to reduce the joint replacement failure.

Mg2+ in β-TCP/Mg-Zn composite enhances the differentiation of human bone marrow stromal cells into osteoblasts through MAPK-regulated Runx2/Osx

Inducing the osteogenic differentiation from bone marrow stromal cells (BMSCs) might be a potent strategy for treating bone loss and nonunion during fracture and improving fracture healing. Among several signaling pathways involved, mitogen-activated protein kinases (MAPKs) have been reported to play a critical role. Magnesium (Mg)-based alloys, including Mg-Zn alloy, have been used clinically as implants in the musculoskeletal field and could promote BMSC osteogenic differentiation. However, the underlying mechanisms remain unclear. In this study, we produced Mg-Zn alloy consists of Mg and low concentrations of Zn, calcium carbonate, and β-tricalcium phosphate (β-TCP; manifesting process not shown), prepared Mg, Zn, and Mg-Zn extracts, and investigated the specific effects of these extracts on human BMSC (hBMSC) osteogenic differentiation and MAPK signaling. Mg extracts and Mg-Zn extracts could significantly promote the osteogenic differentiation of hBMSCs as manifested as increased alkaline phosphatase levels, enhanced calcium nodules formation, and increased messenger RNA expression and protein levels of osteogenesis markers, including BMPs, Col-I, Runx2, and Osx; in the meantime, Mg culture medium (CM) and Mg-Zn CM both significantly enhanced the activation of MAPK signaling in hBMSCs. By adding ERK1/2 signaling, p38 signaling, or JNK signaling inhibitor to Mg-Zn CM, or conducting p38 MAPK silence in hBMSCs, we revealed that these extracts might promote hBMSC osteogenic differentiation via p38 MAPK signaling and MAPK-regulated Runx2/Osx. In conclusion, Mg2+ in β-TCP/Mg-Zn extract promotes the osteogenic differentiation of hBMSCs via MAPK-regulated Runx2/Osx interaction.

Highly expressed BMP9/GDF2 in postnatal mouse liver and lungs may account for its pleiotropic effects on stem cell differentiation, angiogenesis, tumor growth and metabolism

Bone morphogenetic protein 9 (BMP9) (or GDF2) was originally identified from fetal mouse liver cDNA libraries. Emerging evidence indicates BMP9 exerts diverse and pleiotropic functions during postnatal development and in maintaining tissue homeostasis. However, the expression landscape of BMP9 signaling during development and/or in adult tissues remains to be analyzed. Here, we conducted a comprehensive analysis of the expression landscape of BMP9 and its signaling mediators in postnatal mice. By analyzing mouse ENCODE transcriptome datasets we found Bmp9 was highly expressed in the liver and detectable in embryonic brain, adult lungs and adult placenta. We next conducted a comprehensive qPCR analysis of RNAs isolated from major mouse tissues/organs at various ages. We found that Bmp9 was highly expressed in the liver and lung tissues of young adult mice, but decreased in older mice. Interestingly, Bmp9 was only expressed at low to modest levels in developing bones. BMP9-associated TGFβ/BMPR type I receptor Alk1 was highly expressed in the adult lungs. Furthermore, the feedback inhibitor Smads Smad6 and Smad7 were widely expressed in mouse postnatal tissues. However, the BMP signaling antagonist noggin was highly expressed in fat and heart in the older age groups, as well as in kidney, liver and lungs in a biphasic fashion. Thus, our findings indicate that the circulating BMP9 produced in liver and lungs may account for its pleiotropic effects on postnatal tissues/organs although possible roles of BMP9 signaling in liver and lungs remain to be fully understood.

lncRNA Rmst acts as an important mediator of BMP9-induced osteogenic differentiation of mesenchymal stem cells (MSCs) by antagonizing Notch-targeting microRNAs

Understanding the bone and musculoskeletal system is essential to maintain the health and quality of life of our aging society. Mesenchymal stem cells (MSCs) can undergo self-renewal and differentiate into multiple tissue types including bone. We demonstrated that BMP9 is the most potent osteogenic factors although molecular mechanism underlying BMP9 action is not fully understood. Long noncoding RNAs (lncRNAs) play important regulatory roles in many physiological and/or pathologic processes. Here, we investigated the role of lncRNA Rmst in BMP9-induced osteogenic differentiation of MSCs. We found that Rmst was induced by BMP9 through Smad signaling in MSCs. Rmst knockdown diminished BMP9-induced osteogenic, chondrogenic and adipogenic differentiation in vitro, and attenuated BMP9-induced ectopic bone formation. Silencing Rmst decreased the expression of Notch receptors and ligands. Bioinformatic analysis predicted Rmst could directly bind to eight Notch-targeting miRNAs, six of which were downregulated by BMP9. Silencing Rmst restored the expression of four microRNAs (miRNAs). Furthermore, an activating Notch mutant NICD1 effectively rescued the decreased ALP activity caused by Rmst silencing. Collectively, our results strongly suggest that the Rmst-miRNA-Notch regulatory axis may play an important role in mediating BMP9-induced osteogenic differentiation of MSCs.

miR‑204 inhibits the osteogenic differentiation of mesenchymal stem cells by targeting bone morphogenetic protein 2

Mesenchymal stem cells (MSCs) are used to investigate regeneration and differentiation. MicroRNA-204 (miR-204) in involved in the Runt-related transcription factor 2/alkaline phosphatase/bone morphogenic protein 2 (Runx2/ALP/BMP2) signaling pathway that regulates bone marrow mesenchymal stem cell (BMSC) differentiation; however, the mechanisms underlying the effects of miR-204 are yet to be determined. The aim of the present study was to investigate the effects of miR-204 on BMSC differentiation. BMSCs were derived from rat bone marrow. The expression levels of Runx2, ALP and BMP2 were measured via reverse transcription-quantitative polymerase chain reaction and western blot analyses following transfection of BMSCs with miR-204 agomir or BMP2 expression vector. The ability of the miR-204 gene to directly bind BMP2 mRNA was assessed using dual-luciferase assays. Ossification was measured via alizarin red stain assays. It was observed that the expression levels of Runx2 and ALP increased over time, whereas those of miR-204 decreased; additionally, miR-204 agomir upregulation inhibited the expression of Runx2, ALP and BMP2 in BMSCs. It was revealed that miR-204 directly interacted with BMP2 mRNA, and that transfection with miR-204 agomir suppressed ossification in BMSCs by targeting the BMP2/Runx2/ALP signaling pathway.

A simplified 3D liver microsphere tissue culture model for hepatic cell signaling and drug-induced hepatotoxicity studies

Although a number of experimental models have been developed for liver research, each has its own advantages and disadvantages. The present study attempted to develop a simple and effective 3‑dimensional mouse liver microsphere tissue culture (LMTC) model in vitro for the analysis of hepatic functions. Hepatic characteristics and potential applications of this model were compared with that of mouse model in vivo and mouse primary hepatocytes in vitro. Using freshly‑perfused mouse liver tissue passed through 80‑mesh sift strainer (sift80), it was demonstrated that under the optimal culture conditions, the sift80 microsphere tissue cultured in 2% bovine calf serum medium remained viable with marked proliferating cell nuclear antigen and anti‑Myc proto‑oncogene protein expression, exhibited normal hepatic functions including indocyanine green (ICG) uptake/release and periodic acid‑Schiff staining, and expressed hepatocyte‑specific genes for up to 2 weeks. The microsphere tissue was responsive to bone morphogenic protein 9 (BMP9) stimulation leading to upregulation of downstream targets of BMP9 signaling. Furthermore, 3 commonly‑used liver‑damaging drugs were indicated to effectively inhibit hepatic ICG uptake, and induce the expression of hepatotoxicity‑associated genes. Therefore, this simplified LMTC model may be a useful in vitro tissue culture model to investigate drug‑induced liver injury and metabolism, and hepatocyte‑based cell singling.

Developing a Versatile Shotgun Cloning Strategy for Single-Vector-Based Multiplex Expression of Short Interfering RNAs (siRNAs) in Mammalian Cells

As an important post-transcriptional regulatory machinery mediated by ∼21nt short-interfering double-stranded RNA (siRNA), RNA interference (RNAi) is a powerful tool to delineate gene functions and develop therapeutics. However, effective RNAi-mediated silencing requires multiple siRNAs for given genes, a time-consuming process to accomplish. Here, we developed a user-friendly system for single-vector-based multiplex siRNA expression by exploiting the unique feature of restriction endonuclease BstXI. Specifically, we engineered a BstXI-based shotgun cloning (BSG) system, which consists of three entry vectors with siRNA expression units (SiEUs) flanked with distinct BstXI sites, and a retroviral destination vector for shotgun SiEU assembly. For proof-of-principle studies, we constructed multiplex siRNA vectors silencing β-catenin and/or Smad4 and assessed their functionalities in mesenchymal stem cells (MSCs). Pooled siRNA cassettes were effectively inserted into respective entry vectors in one-step, and shotgun seamless assembly of pooled BstXI-digested SiEU fragments into a retroviral destination vector followed. We found these multiplex siRNAs effectively silenced β-catenin and/or Smad4, and inhibited Wnt3A- or BMP9-specific reporters and downstream target expression in MSCs. Furthermore, multiplex silencing of β-catenin and/or Smad4 diminished Wnt3A and/or BMP9-induced osteogenic differentiation. Collectively, the BSG system is a user-friendly technology for single-vector-based multiplex siRNA expression to study gene functions and develop experimental therapeutics.

The wonders of BMP9: From mesenchymal stem cell differentiation, angiogenesis, neurogenesis, tumorigenesis, and metabolism to regenerative medicine

Although bone morphogenetic proteins (BMPs) initially showed effective induction of ectopic bone growth in muscle, it has since been determined that these proteins, as members of the TGF-β superfamily, play a diverse and critical array of biological roles. These roles include regulating skeletal and bone formation, angiogenesis, and development and homeostasis of multiple organ systems. Disruptions of the members of the TGF-β/BMP superfamily result in severe skeletal and extra-skeletal irregularities, suggesting high therapeutic potential from understanding this family of BMP proteins. Although it was once one of the least characterized BMPs, BMP9 has revealed itself to have the highest osteogenic potential across numerous experiments both in vitro and in vivo, with recent studies suggesting that the exceptional potency of BMP9 may result from unique signaling pathways that differentiate it from other BMPs. The effectiveness of BMP9 in inducing bone formation was recently revealed in promising experiments that demonstrated efficacy in the repair of critical sized cranial defects as well as compatibility with bone-inducing bio-implants, revealing the great translational promise of BMP9. Furthermore, emerging evidence indicates that, besides its osteogenic activity, BMP9 exerts a broad range of biological functions, including stem cell differentiation, angiogenesis, neurogenesis, tumorigenesis, and metabolism. This review aims to summarize our current understanding of BMP9 across biology and the body.

Modulation of osteogenic and myogenic differentiation by a phytoestrogen formononetin via p38MAPK-dependent JAK-STAT and Smad-1/5/8 signaling pathways in mouse myogenic progenitor cells

Formononetin (FN), a typical phytoestrogen has attracted substantial attention as a novel agent because of its diverse biological activities including, osteogenic differentiation. However, the molecular mechanisms underlying osteogenic and myogenic differentiation by FN in C2C12 progenitor cells remain unknown. Therefore the objective of the current study was to investigate the action of FN on myogenic and osteogenic differentiation and its impact on signaling pathways in C2C12 cells. FN significantly increased myogenic markers such as Myogenin, myosin heavy chains, and myogenic differentiation 1 (MyoD). In addition, the expression of osteogenic specific genes alkaline phosphatase (ALP), Run-related transcription factor 2(RUNX2), and osteocalcin (OCN) were up-regulated by FN treatment. Moreover, FN enhanced the ALP level, calcium deposition and the expression of bone morphogenetic protein isoform (BMPs). Signal transduction pathways mediated by p38 mitogen-activated protein kinase (p38MAPK), extracellular signal-related kinases (ERKs), protein kinase B (Akt), Janus kinases (JAKs), and signal transducer activator of transcription proteins (STATs) in myogenic and osteogenic differentiation after FN treatment were also examined. FN treatment activates myogenic differentiation by increasing p38MAPK and decreasing JAK1-STAT1 phosphorylation levels, while osteogenic induction was enhanced by p38MAPK dependent Smad, 1/5/8 signaling pathways in C2C12 progenitor cells.

The Role of Ubiquitination in Regulating Embryonic Stem Cell Maintenance and Cancer Development

Ubiquitination regulates nearly every aspect of cellular events in eukaryotes. It modifies intracellular proteins with 76-amino acid polypeptide ubiquitin (Ub) and destines them for proteolysis or activity alteration. Ubiquitination is generally achieved by a tri-enzyme machinery involving ubiquitin activating enzymes (E1), ubiquitin conjugating enzymes (E2) and ubiquitin ligases (E3). E1 activates Ub and transfers it to the active cysteine site of E2 via a transesterification reaction. E3 coordinates with E2 to mediate isopeptide bond formation between Ub and substrate protein. The E1-E2-E3 cascade can create diverse types of Ub modifications, hence effecting distinct outcomes on the substrate proteins. Dysregulation of ubiquitination results in severe consequences and human diseases. There include cancers, developmental defects and immune disorders. In this review, we provide an overview of the ubiquitination machinery and discuss the recent progresses in the ubiquitination-mediated regulation of embryonic stem cell maintenance and cancer biology.

Transcriptomic landscape regulated by the 14 types of bone morphogenetic proteins (BMPs) in lineage commitment and differentiation of mesenchymal stem cells (MSCs)

Mesenchymal stem cells (MSCs) are ubiquitously-existing multipotent progenitors that can self-renew and differentiate into multiple lineages including osteocytes, chondrocytes, adipocytes, tenocytes and myocytes. MSCs represent one of the most commonly-used adult progenitors and serve as excellent progenitor cell models for investigating lineage-specific differentiation regulated by various cellular signaling pathways, such as bone morphogenetic proteins (BMPs). As members of TGFβ superfamily, BMPs play diverse and important roles in development and adult tissues. At least 14 BMPs have been identified in mammals. Different BMPs exert distinct but overlapping biological functions. Through a comprehensive analysis of 14 BMPs in MSCs, we demonstrated that BMP9 is one of the most potent BMPs in inducing osteogenic differentiation of MSCs. Nonetheless, a global mechanistic view of BMP signaling in regulating the proliferation and differentiation of MSCs remains to be fully elucidated. Here, we conducted a comprehensive transcriptomic profiling in the MSCs stimulated by 14 types of BMPs. Hierarchical clustering analysis classifies 14 BMPs into three subclusters: an osteo/chondrogenic/adipogenic cluster, a tenogenic cluster, and BMP3 cluster. We also demonstrate that six BMPs (e.g., BMP2, BMP3, BMP4, BMP7, BMP8, and BMP9) can induce I-Smads effectively, while BMP2, BMP3, BMP4, BMP7, and BMP11 up-regulate Smad-independent MAP kinase pathway. Furthermore, we show that many BMPs can upregulate the expression of the signal mediators of Wnt, Notch and PI3K/AKT/mTOR pathways. While the reported transcriptomic changes need to be further validated, our expression profiling represents the first-of-its-kind to interrogate a comprehensive transcriptomic landscape regulated by the 14 types of BMPs in MSCs.

Osteogenic Effects of VEGF-Overexpressed Human Adipose-Derived Stem Cells with Whitlockite Reinforced Cryogel for Bone Regeneration

Bone is a vascularized tissue that is comprised of collagen fibers and calcium phosphate crystals such as hydroxyapatite (HAp) and whitlockite (WH). HAp and WH are known to elicit bone regeneration by stimulating osteoblast activities and osteogenic commitment of stem cells. In addition, vascular endothelial growth factor (VEGF) is shown to promote osteogenesis and angiogenesis which is considered as an essential process in bone repair by providing nutrients. In this study, VEGF-secreting human adipose-derived stem cells (VEGF-ADSCs) are developed by transducing ADSCs with VEGF-encoded lentivirus. Additionally, WH-reinforced gelatin/heparin cryogels (WH-C) are fabricated by loading WH into gelatin/heparin cryogels. VEGF-ADSC secrete tenfold more VEGF than ADSC and show increased VEGF secretion with cell growth. Also, incorporation of WH into cryogels provides a mineralized environment with ions secreted from WH. When the VEGF-ADSCs are seeded on WH-C, sustained release of VEGF is observed due to the specific affinity of VEGF to heparin. Finally, the synergistic effect of VEGF-ADSC and WH on osteogenesis is successfully confirmed by alkaline phosphatase and real-time polymerase chain reaction analysis. In vivo bone formation is demonstrated via implantation of VEGF-ADSC seeded WH-C into mouse calvarial bone defect model, resulted in enhanced bone development with the highest bone volume/total volume.

The impact of implant abutment surface treatment with TiO2 on peri-implant levels of angiogenesis and bone-related markers: a randomized clinical trial

The goal of this randomized, blinded, split-mouth controlled clinical trial was to assess the influence of abutment surface treatment on tissue healing. Fifteen patients received two implants distributed randomly to two groups: test (TiO₂ abutment surface), control (standard abutment surface). Levels of epidermal growth factor (EGF), bone morphogenetic protein 9 (BMP-9), endothelin 1 (ET-1), fibroblast growth factor (FGF), placental growth factor (PlGF), and vascular endothelial growth factor (VEGF) were quantified in the peri-implant fluid after 3, 14, 30, and 60 days. Inter-group comparisons indicated higher levels of EGF, BMP-9, ET-1, FGF, and PlGF in the test group after 30days (P<0.05). PlGF levels were also higher in the test group after 60 days. In the test group, intra-group analysis revealed different levels of ET-1 and FGF between days 3 and 30, and days 3 and 60 (P<0.05); furthermore, VEGF levels were significantly higher on day 60 than on day 3 (P <0.05). In the control group, intra-group analysis demonstrated significantly different levels of ET-1, FGF, and PlGF between days 3 and 60 and of PlGF between days 14 and 60 (P<0.05). In conclusion, abutment surfaces treated with TiO₂ influenced the levels of angiogenesis and bone-related markers.

The BMP Pathway and Its Inhibitors in the Skeleton

Bone morphogenetic proteins (BMPs) constitute the largest subdivision of the transforming growth factor-β family of ligands. BMPs exhibit widespread utility and pleiotropic, context-dependent effects, and the strength and duration of BMP pathway signaling is tightly regulated at numerous levels via mechanisms operating both inside and outside the cell. Defects in the BMP pathway or its regulation underlie multiple human diseases of different organ systems. Yet much remains to be discovered about the BMP pathway in its original context, i.e., the skeleton. In this review, we provide a comprehensive overview of the intricacies of the BMP pathway and its inhibitors in bone development, homeostasis, and disease. We frame the content of the review around major unanswered questions for which incomplete evidence is available. First, we consider the gene regulatory network downstream of BMP signaling in osteoblastogenesis. Next, we examine why some BMP ligands are more osteogenic than others and what factors limit BMP signaling during osteoblastogenesis. Then we consider whether specific BMP pathway components are required for normal skeletal development, and if the pathway exerts endogenous effects in the aging skeleton. Finally, we propose two major areas of need of future study by the field: greater resolution of the gene regulatory network downstream of BMP signaling in the skeleton, and an expanded repertoire of reagents to reliably and specifically inhibit individual BMP pathway components.

MicroRNAs and long noncoding RNAs: new regulators in cell fate determination of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent cells that are able to differentiate into numerous cell types, including well-known inherent osteoblasts, adipocytes, and chondrocytes, and other cell types, such as hepatocytes, cardiomyocytes and nerve cells. They have become a favorite source of cell-based therapy. Therefore, knowing the mechanism that determines the cell fate of MSCs is important not only for deep understanding of the MSC function but also for the manipulation of MSCs for clinical application. Recently, studies have demonstrated that microRNAs (miRNAs) and long noncoding RNAs (lncRNAs), the two best studied noncoding RNAs, show key roles in cell fate determination of MSCs by functioning as vital regulators of their target gene expression or signaling transduction. Here, we summarize the characteristics of miRNAs and lncRNAs, and review the recent advances proving their profound involvement in determining the cell fate of MSCs to inherent osteoblast, adipocyte, and chondrocyte cells, and to several key cell types including hepatocytes, cardiomyocytes and nerve cells. This will provide researchers with a deep understanding of the role of miRNAs and lncRNAs in MSCs and provide guidance for future research.

The recent advances of miRNAs and lncRNAs in determining the cell fate of MSCs.

BMP9-induced osteoblastic differentiation requires functional Notch signaling in mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent progenitors that can differentiate into multiple lineages including osteoblastic lineage. Osteogenic differentiation of MSCs is a cascade that recapitulates most, if not all, of the molecular events occurring during embryonic skeletal development, which is regulated by numerous signaling pathways including bone morphogenetic proteins (BMPs). Through a comprehensive analysis of the osteogenic activity, we previously demonstrated that BMP9 is the most potent BMP for inducing bone formation from MSCs both in vitro and in vivo. However, as one of the least studied BMPs, the essential mediators of BMP9-induced osteogenic signaling remain elusive. Here we show that BMP9-induced osteogenic signaling in MSCs requires intact Notch signaling. While the expression of Notch receptors and ligands are readily detectable in MSCs, Notch inhibitor and dominant-negative Notch1 effectively inhibit BMP9-induced osteogenic differentiation in vitro and ectopic bone formation in vivo. Genetic disruption of Notch pathway severely impairs BMP9-induced osteogenic differentiation and ectopic bone formation from MSCs. Furthermore, while BMP9-induced expression of early-responsive genes is not affected by defective Notch signaling, BMP9 upregulates the expression of Notch receptors and ligands at the intermediate stage of osteogenic differentiation. Taken together, these results demonstrate that Notch signaling may play an essential role in coordinating BMP9-induced osteogenic differentiation of MSCs.

Small non-coding RNA landscape of extracellular vesicles from human stem cells

Extracellular vesicles (EVs) are reported to be involved in stem cell maintenance, self-renewal, and differentiation. Due to their bioactive cargoes influencing cell fate and function, interest in EVs in regenerative medicine has rapidly increased. EV-derived small non-coding RNA mimic the functions of the parent stem cells, regulating the maintenance and differentiation of stem cells, controlling the intercellular regulation of gene expression, and eventually affecting the cell fate. In this study, we used RNA sequencing to provide a comprehensive overview of the expression profiles of small non-coding transcripts carried by the EVs derived from human adipose tissue stromal/stem cells (AT-MSCs) and human pluripotent stem cells (hPSCs), both human embryonic stem cells (hESCs) and human induced pluripotent stem cells (hiPSC). Both hPSCs and AT-MSCs were characterized and their EVs were extracted using standard protocols. Small non-coding RNA sequencing from EVs showed that hPSCs and AT-MSCs showed distinct profiles, unique for each stem cell source. Interestingly, in hPSCs, most abundant miRNAs were from specific miRNA families regulating pluripotency, reprogramming and differentiation (miR-17-92, mir-200, miR-302/367, miR-371/373, CM19 microRNA cluster). For the AT-MSCs, the highly expressed miRNAs were found to be regulating osteogenesis (let-7/98, miR-10/100, miR-125, miR-196, miR-199, miR-615-3p, mir-22-3p, mir-24-3p, mir-27a-3p, mir-193b-5p, mir-195-3p). Additionally, abundant small nuclear and nucleolar RNA were detected in hPSCs, whereas Y- and tRNA were found in AT-MSCs. Identification of EV-miRNA and non-coding RNA signatures released by these stem cells will provide clues towards understanding their role in intracellular communication, and well as their roles in maintaining the stem cell niche.

Thermoresponsive Citrate-Based Graphene Oxide Scaffold Enhances Bone Regeneration from BMP9-Stimulated Adipose-Derived Mesenchymal Stem Cells

Effective bone tissue engineering is important to overcome the unmet clinical challenges as more than 1.6 million bone grafts are done annually in the United States. Successful bone tissue engineering needs minimally three critical constituents: osteoprogenitor cells, osteogenic factors, and osteoinductive/osteoconductive scaffolds. Osteogenic progenitors are derived from multipotent mesenchymal stem cells (MSCs), which can be prepared from numerous tissue sources, including adipose tissue. We previously showed that BMP9 is the most osteogenic BMP and induces robust bone formation of immortalized mouse adipose-derived MSCs entrapped in a citrate-based thermoresponsive hydrogel referred to as PPCNg. As graphene and its derivatives emerge as promising biomaterials, here we develop a novel thermosensitive and injectable hybrid material by combining graphene oxide (GO) with PPCNg (designated as GO-P) and characterize its ability to promote bone formation. We demonstrate that the thermoresponsive behavior of the hybrid material is maintained while effectively supporting MSC survival and proliferation. Furthermore, GO-P induces early bone-forming marker alkaline phosphatase (ALP) and potentiates BMP9-induced expression of osteogenic regulators and bone markers as well as angiogenic factor VEGF in MSCs. In vivo studies show BMP9-transduced MSCs entrapped in the GO-P scaffold form well-mineralized and highly vascularized trabecular bone. Thus, these results indicate that GO-P hybrid material may function as a new biocompatible, injectable scaffold with osteoinductive and osteoconductive activities for bone regeneration.

Characterization of the essential role of bone morphogenetic protein 9 (BMP9) in osteogenic differentiation of mesenchymal stem cells (MSCs) through RNA interference

Mesenchymal stem cells (MSCs) are multipotent stem cells and capable of differentiating into multiple cell types including osteoblastic, chondrogenic and adipogenic lineages. We previously identified BMP9 as one of the most potent BMPs that induce osteoblastic differentiation of MSCs although exact molecular mechanism through which BMP9 regulates osteogenic differentiation remains to be fully understood. Here, we seek to develop a recombinant adenovirus system to optimally silence mouse BMP9 and then characterize the important role of BMP9 in osteogenic differentiation of MSCs. Using two different siRNA bioinformatic prediction programs, we design five siRNAs targeting mouse BMP9 (or simB9), which are expressed under the control of the converging H1 and U6 promoters in recombinant adenovirus vectors. We demonstrate that two of the five siRNAs, simB9-4 and simB9-7, exhibit the highest efficiency on silencing exogenous mouse BMP9 in MSCs. Furthermore, simB9-4 and simB9-7 act synergistically in inhibiting BMP9-induced expression of osteogenic markers, matrix mineralization and ectopic bone formation from MSCs. Thus, our findings demonstrate the important role of BMP9 in osteogenic differentiation of MSCs. The characterized simB9 siRNAs may be used as an important tool to investigate the molecular mechanism behind BMP9 osteogenic signaling. Our results also indicate that recombinant adenovirus-mediated expression of siRNAs is efficient and sustained, and thus may be used as an effective delivery vehicle of siRNA therapeutics.

Quercetin Stimulates Bone Marrow Mesenchymal Stem Cell Differentiation through an Estrogen Receptor-Mediated Pathway

Objectives

The present study aimed to investigate the overall effect of quercetin on mouse bone marrow mesenchymal stem cell (BMSC) proliferation and osteogenic differentiation in vitro.

Materials and Methods

BMSCs were treated with different concentrations of quercetin for 6 days. The effects of quercetin on cell proliferation were assessed at predetermined times using Cell Counting Kit-8 (CCK-8) assay. The cells were then treated with quercetin, estrogen, or an estrogen receptor (ER) antagonist (which was also administered in the presence of quercetin or estrogen) for 7 or 21 days. The effects of quercetin on BMSC osteogenic differentiation were analyzed by an alkaline phosphatase (ALP) assay kit, Alizarin Red S staining (ARS), quantitative real-time PCR (qPCR), and western blotting.

Results

The CCK-8 and ALP assays and ARS staining showed that quercetin significantly enhanced BMSC proliferation, ALP activity, and extracellular matrix production and mineralization, respectively. The qPCR results indicated that quercetin promoted osterix (OSX), runt-related transcription factor 2 (RUNX2), and osteopontin (OPN) transcription in the presence of osteoinduction medium, and the western blotting results indicated that quercetin enhanced bone morphogenetic protein 2 (BMP2), Smad1, Smad4, RUNX2, OSX, and OPN expression and Smad1 phosphorylation. Treatment with the ER inhibitor ICI182780 blocked the effects of quercetin.

Conclusions

Our data demonstrated that quercetin promotes BMSC proliferation and osteogenic differentiation. Quercetin enhances BMP signaling pathway activation and upregulates the expression of downstream genes, such as OSX, RUNX2, and OPN, via the ER.

MicroRNA-155 inhibits the osteogenic differentiation of mesenchymal stem cells induced by BMP9 via downregulation of BMP signaling pathway

Previous studies have indicated that bone morphogenetic protein 9 (BMP9) can promote the osteogenic differentiation of mesenchymal stem cells (MSCs) and increase bone formation in bone diseases. However, the mechanisms involved remained poorly understood. It is necessary to investigate the specific regulatory mechanisms of osteogenic differentiation that were induced by BMP9. During the process of osteogenic differentiation induced by BMP9, the expression of microRNA-155 (miR-155) exhibited a tendency of increasing at first and then decreasing, which made us consider that miR-155 may have a modulatory role in this process, but the roles of this process have not been elucidated. This study aimed to uncover miR-155 capable of concomitant regulation of this process. mmu-miR-155 mimic (miR-155) was transfected into MSCs and osteogenesis was induction by using recombinant adenovirus expressing BMP9. Overexpressed miR-155 in MSCs led to a decrease in alkaline phosphatase (ALP) staining and Alizarin red S staining during osteogenic differentiation, and reduced the expression of osteogenesis-related genes, such as runt-related transcription factor 2 (Runx2), osterix (OSX), osteocalcin (OCN) and osteopontin (OPN). On protein levels, overexpressed miR-155 markedly decreased the expression of phosphorylated Smad1/5/8 (p-Smad1/5/8), Runx2, OCN and OPN. Luciferase reporter assay revealed Runx2 and bone morphogenetic protein receptor 9 (BMPR2) are two direct target genes of miR-155. Downregulation of the expression of Runx2 and BMPR2, respectively could offset the inhibitory effect of miR-155 in the osteogenesis of MSCs. In vivo, subcutaneous ectopic osteogenesis of MSCs in nude mice showed miR-155 inhibited osteogenic differentiation. In conclusion, our results demonstrated that miR-155 can inhibit the osteogenic differentiation induced by BMP9 in MSCs.

CRISPR/Cas9-mediated reversibly immortalized mouse bone marrow stromal stem cells (BMSCs) retain multipotent features of mesenchymal stem cells (MSCs)

Mesenchymal stem cells (MSCs) are multipotent non-hematopoietic progenitor cells that can undergo self-renewal and differentiate into multi-lineages. Bone marrow stromal stem cells (BMSCs) represent one of the most commonly-used MSCs. In order to overcome the technical challenge of maintaining primary BMSCs in long-term culture, here we seek to establish reversibly immortalized mouse BMSCs (imBMSCs). By exploiting CRISPR/Cas9-based homology-directed-repair (HDR) mechanism, we target SV40T to mouse Rosa26 locus and efficiently immortalize mouse BMSCs (i.e., imBMSCs). We also immortalize BMSCs with retroviral vector SSR #41 and establish imBMSC41 as a control line. Both imBMSCs and imBMSC41 exhibit long-term proliferative capability although imBMSC41 cells have a higher proliferation rate. SV40T mRNA expression is 130% higher in imBMSC41 than that in imBMSCs. However, FLP expression leads to 86% reduction of SV40T expression in imBMSCs, compared with 63% in imBMSC41 cells. Quantitative genomic PCR analysis indicates that the average copy number of SV40T and hygromycin is 1.05 for imBMSCs and 2.07 for imBMSC41, respectively. Moreover, FLP expression removes 92% of SV40T in imBMSCs at the genome DNA level, compared with 58% of that in imBMSC41 cells, indicating CRISPR/Cas9 HDR-mediated immortalization of BMSCs can be more effectively reversed than that of retrovirus-mediated random integrations. Nonetheless, both imBMSCs and imBMSC41 lines express MSC markers and are highly responsive to BMP9-induced osteogenic, chondrogenic and adipogenic differentiation in vitro and in vivo. Thus, the engineered imBMSCs can be used as a promising alternative source of primary MSCs for basic and translational research in the fields of MSC biology and regenerative medicine.

Notch signaling negatively regulates BMP9-induced osteogenic differentiation of mesenchymal progenitor cells by inhibiting JunB expression

Although interaction between BMP and Notch signaling has been demonstrated to be crucial for osteogenic differentiation of mesenchymal stem cells (MSCs), the precise molecular mechanism remains unknown. Here, we show that Notch intracellular domain (NICD) overexpression inhibits BMP9-induced C3H10T1/2 cell osteogenesis in vivo and in vitro. Our results show that activated Notch signaling results in down-regulation of Runx2 and early osteogenesis differentiation factors, without affecting p-Smad1/5/8 expression, and that blocking Notch signaling with DAPT (N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester) significantly increases p-Smad1/5/8 expression. Interestingly, Notch signaling also regulates the cell cycle by increasing PCNA (proliferation cell nuclear antigen) and CyclinD1 expression. Furthermore, similar results were obtained by ectopic bone formation and histological analyses, indicating that Notch signaling activation significantly inhibits BMP9-induced MSC osteogenic, cartilage and adipogenic differentiation. Moreover, we are the first to show that Notch regulates by suppressing JunB synthesis and that the negative effect of Notch is partially reversed by treatment with the JunB activator TPA (12-O-tetradeca-noylphorbol-13-acetate). Our findings demonstrate that Notch signaling significantly enhances cell proliferation but inhibits MSC osteogenic differentiation induced by BMP9 via JunB protein suppression rather than by BMP/Smad signaling regulation.

lncRNA H19 mediates BMP9-induced osteogenic differentiation of mesenchymal stem cells (MSCs) through Notch signaling

Mesenchymal stem cells (MSCs) are multipotent progenitor cells that can undergo self-renewal and differentiate into multiple lineages. Osteogenic differentiation from MSCs is a well-orchestrated process and regulated by multiple signaling pathways. We previously demonstrated that BMP9 is one of the most potent osteogenic factors. However, molecular mechanism through which BMP9 governs osteoblastic differentiation remains to be fully understood. Increasing evidence indicates noncoding RNAs (ncRNAs) may play important regulatory roles in many physiological and/or pathologic processes. In this study, we investigate the role of lncRNA H19 in BMP9-regulated osteogenic differentiation of MSCs. We demonstrated that H19 was sharply upregulated at the early stage of BMP9 stimulation of MSCs, followed by a rapid decease and gradual return to basal level. This process was correlated with BMP9-induced expression of osteogenic markers. Interestingly, either constitutive H19 expression or silencing H19 expression in MSCs significantly impaired BMP9-induced osteogenic differentiation in vitro and in vivo, which was effectively rescued by the activation of Notch signaling. Either constitutive H19 expression or silencing H19 expression led to the increased expression of a group of miRNAs that are predicted to target Notch ligands and receptors. Thus, these results indicate that lncRNA H19 functions as an important mediator of BMP9 signaling by modulating Notch signaling-targeting miRNAs. Our findings suggest that the well-coordinated biphasic expression of lncRNA H19 may be essential in BMP9-induced osteogenic differentiation of MSCs, and that dysregulated H19 expression may impair normal osteogenesis, leading to pathogenic processes, such as bone tumor development.