BMP2 genetically engineered MSCs and EPCs promote vascularized bone regeneration in rat critical-sized calvarial bone defects

Towards Stem Cell Therapy for Critical-Sized Segmental Bone Defects: Current Trends and Challenges on the Path to Clinical Translation

The management and reconstruction of critical-sized segmental bone defects remain a major clinical challenge for orthopaedic clinicians and surgeons. In particular, regenerative medicine approaches that involve incorporating stem cells within tissue engineering scaffolds have great promise for fracture management. This narrative review focuses on the primary components of bone tissue engineering-stem cells, scaffolds, the microenvironment, and vascularisation-addressing current advances and translational and regulatory challenges in the current landscape of stem cell therapy for critical-sized bone defects. To comprehensively explore this research area and offer insights for future treatment options in orthopaedic surgery, we have examined the latest developments and advancements in bone tissue engineering, focusing on those of clinical relevance in recent years. Finally, we present a forward-looking perspective on using stem cells in bone tissue engineering for critical-sized segmental bone defects.

Injectable hydrogel for sustained delivery of progranulin derivative Atsttrin in treating diabetic fracture healing

Hydrogels with long-term storage stability, controllable sustained-release properties, and biocompatibility have been garnering attention as carriers for drug/growth factor delivery in tissue engineering applications. Chitosan (CS)/Graphene Oxide (GO)/Hydroxyethyl cellulose (HEC)/β-glycerol phosphate (β-GP) hydrogel is capable of forming a 3D gel network at physiological temperature (37 °C), rendering it an excellent candidate for use as an injectable biomaterial. This work focused on an injectable thermo-responsive CS/GO/HEC/β-GP hydrogel, which was designed to deliver Atsttrin, an engineered derivative of a known chondrogenic and anti-inflammatory growth factor-like molecule progranulin. The combination of the CS/GO/HEC/β-GP hydrogel and Atsttrin provides a unique biochemical and biomechanical environment to enhance fracture healing. CS/GO/HEC/β-GP hydrogels with increased amounts of GO exhibited rapid sol-gel transition, higher viscosity, and sustained release of Atsttrin. In addition, these hydrogels exhibited a porous interconnected structure. The combination of Atsttrin and hydrogel successfully promoted chondrogenesis and osteogenesis of bone marrow mesenchymal stem cells (bmMSCs) in vitro. Furthermore, the work also presented in vivo evidence that injection of Atsttrin-loaded CS/GO/HEC/β-GP hydrogel stimulated diabetic fracture healing by simultaneously inhibiting inflammatory and stimulating cartilage regeneration and endochondral bone formation signaling pathways. Collectively, the developed injectable thermo-responsive CS/GO/HEC/βG-P hydrogel yielded to be minimally invasive, as well as capable of prolonged and sustained delivery of Atsttrin, for therapeutic application in impaired fracture healing, particularly diabetic fracture healing.

MicroRNA-26 and Related Osteogenic Target Genes Could Play Pivotal Roles in Photobiomodulation and Adipose-Derived Stem Cells-Based Healing of Critical Size Foot Defects in the Rat Model

Objective: In this study, we aimed to explore the role of MicroRNA-26 in photobiomodulation (PBM)- and adipose-derived stem cell (ADS)-based healing of critical-sized foot fractures in a rat model. Background: PBM and ADS treatments are relatively invasive methods for treating bone defects. Specific and oriented cellular and molecular functions can be induced by applying an appropriate type of PBM and ADS treatment. Methods: A critical size foot defect (CSFD) is induced in femoral bones of 24 rats. Then, a human demineralized bone matrix scaffold (hDBMS) was engrafted into all CSFDs. The rats were randomly allocated into four groups (n = 6): (1) control (hDBMS); (2) hDBMS+human ADSs (hADSs), hADSs engrafted into CSFDs; (3) hDBMS+PBM, CSFD exposed to PBM (810 nm wavelength, 1.2 J/cm2 energy density); and (4) hDBMS+(hADSs+PBM), hADSs implanted into the CSFD and then exposed to PBM. At 42 days after CSFD induction, the rats were killed, and the left CSFD was removed for mechanical compression tests and the right CSFD was removed for molecular and histological studies. Results: The results indicate that miRNA-26a, BMP, SMAD, RUNX, and OSTREX had higher expression in the treated groups than in the control group. Further, the biomechanical and histological properties of CSFDs in treated groups were improved compared with the control group. Correlation tests revealed a positive relationship between microRNA and improved biomechanical and cellular parameters of CSFDs in the rat model. Conclusions: We concluded that the MicroRNA-26 signaling pathway probably plays a significant role in the hADS-, PBM-, and hADS+PBM-based healing of CSFDs in rats. Clinical Trial Registration number: IR.SBMU.MSP.REC.1398.980.

Functional Approaches in Promoting Vascularization and Angiogenesis in Bone Critical-Sized Defects via Delivery of Cells, Growth Factors, Drugs, and Particles

Critical-sized bone defects, or CSDs, are defined as bone defects that cannot be regenerated by themselves and require surgical intervention via employing specific biomaterials and a certain regenerative strategy. Although a variety of approaches can be used to treat CSDs, poor angiogenesis and vascularization remain an obstacle in these methods. The complex biological healing of bone defects depends directly on the function of blood flow to provide sufficient oxygen and nutrients and the removal of waste products from the defect site. The absence of vascularization can lead to non-union and delayed-union defect development. To overcome this challenge, angiogenic agents can be delivered to the site of injury to stimulate vessel formation. This review begins by introducing the treatment methods for CSDs. The importance of vascularization in CSDs is subsequently highlighted. Delivering angiogenesis agents, including relevant growth factors, cells, drugs, particles, cell secretion substances, their combination, and co-delivery to CSDs are fully explored. Moreover, the effects of such agents on new bone formation, followed by vessel formation in defect areas, are evaluated.

A Review Into the Insights of the Role of Endothelial Progenitor Cells on Bone Biology

In addition to its important transport functions, the skeletal system is involved in complex biological activities for the regulation of blood vessels. Endothelial progenitor cells (EPCs), as stem cells of endothelial cells (ECs), possess an effective proliferative capacity and a powerful angiogenic capacity prior to their differentiation. They demonstrate synergistic effects to promote bone regeneration and vascularization more effectively by co-culturing with multiple cells. EPCs demonstrate a significant therapeutic potential for the treatment of various bone diseases by secreting a combination of growth factors, regulating cellular functions, and promoting bone regeneration. In this review, we retrospect the definition and properties of EPCs, their interaction with mesenchymal stem cells, ECs, smooth muscle cells, and immune cells in bone regeneration, vascularization, and immunity, summarizing their mechanism of action and contribution to bone biology. Additionally, we generalized their role and potential mechanisms in the treatment of various bone diseases, possibly indicating their clinical application.

In vitro and in ovo impact of the ionic dissolution products of boron-doped bioactive silicate glasses on cell viability, osteogenesis and angiogenesis

Due to the pivotal role of angiogenesis in bone regeneration, the angiogenic properties of biomaterials are of high importance since they directly correlate with the biomaterials’ osteogenic potential via ‘angiogenic-osteogenic coupling’ mechanisms. The impact of bioactive glasses (BGs) on vascularization can be tailored by incorporation of biologically active ions such as boron (B). Based on the ICIE16-BG composition (in mol%: 49.5 SiO₂, 36.3 CaO, 6.6 Na₂O, 1.1 P₂O₅, 6.6 K₂O), three B-doped BGs have been developed (compositions in mol%: 46.5/45.5/41.5 SiO₂, 36.3 CaO, 6.6 Na₂O, 1.1 P₂O₅, 6.6 K₂O, 3/4/8 B₂O₃). The influence of B-doping on the viability, cellular osteogenic differentiation and expression of osteogenic and angiogenic marker genes of bone marrow-derived mesenchymal stromal cells (BMSCs) was analyzed by cultivating BMSCs in presence of the BGs’ ionic dissolution products (IDPs). Furthermore, the influence of the IDPs on angiogenesis was evaluated in ovo using a chorioallantoic membrane (CAM) assay. The influence of B-doped BGs on BMSC viability was dose-dependent, with higher B concentrations showing limited negative effects. B-doping led to a slight stimulation of osteogenesis and angiogenesis in vitro. In contrast to that, B-doping significantly enhanced vascularization in ovo, especially in higher concentrations. Differences between the results of the in vitro and in ovo part of this study might be explained via the different importance of vascularization in both settings. The implementation of new experimental models that cover the ‘angiogenic-osteogenic coupling’ mechanisms is highly relevant, for instance via extending the application of the CAM assay from solely angiogenic to angiogenic and osteogenic purposes.

Efficacy of total flavonoids of Rhizoma drynariae on the blood vessels and the bone graft in the induced membrane

BACKGROUND

Total flavonoids of Rhizoma drynariae (TFRD), a Chinese medicine, is widely used in the treatment of orthopedic diseases. However, there are few basic and clinical studies on the effect of TFRD on induced membrane technique (Masquelet technique).

PURPOSE

This trial is to explore effects of TFRD on vascularization of the induced membrane, and mineralization of the bone graft in rats with femoral bone defects.

STUDY DESIGN AND METHODS

Forty-eight Sprague-Dawley rats were randomly divided into high dose group (H-TFRD), medium dose group (M-TFRD), low dose group (L-TFRD) and control group (control). The segmental bone defects were established with 12 rats in per group. The polymethyl methacrylate (PMMA) spacer was implanted into the femoral bone defect of rats in the first-stage surgery. About 4 weeks after first-stage surgery, induced membranes of 6 rats in each group were selected. The blood vessels and angiogenesis-related factors in the induced membrane were analyzed by hematoxylin-eosin (HE) and masson staining, western blot, qPCR and immunohistostaining. The remaining rats in per group underwent second-stage surgery (bone grafting). Twelve weeks after the bone grafting, the bone tissues was examined by X-ray, micro-computed tomography (Micro-CT), HE staining and enzyme-linked immunosorbent assay (ELISA) to evaluate the growth of the bone graft. Meanwhile, the TFRD-containing serum was collected from rats to culture osteoblasts in vitro. Cell Counting Kit-8 (CCK-8) method, Alizarin Red S (ARS) staining, western blot and immunofluorescence were used to detect effects of TFRD on the osteoblasts' proliferation and BMP-SMAD signaling pathway.

RESULTS

Compared with the L-TFRD and control groups, the number of blood vessels and the expression of angiogenesis-related factors (VEGF, TGF-β1, BMP-2, PDGF-BB and CD31) were higher in the H-TFRD and M-TFRD groups. The Lane-Sandhu X-ray score, bone mass and growth rate of the bone graft in the H-TFRD and M-TFRD groups were significantly better than those in the L-TFRD and control groups. In addition, medium and high doses of TFRD significantly increased the expression of BMP-SMAD pathway proteins (BMP-2, SMAD1, SMAD4, SMAD5 and RUNX2) in rat serum and bone graft. In vitro, after osteoblasts were intervened with TFRD-containing serum from the H-TFRD and M-TFRD groups, the cell viability, the number of mineralized nodules and the phosphorylation of BMP-SMAD pathway proteins were markedly increased.

CONCLUSION

TFRD could promote the formation of blood vessels and the expression of angiogenesis-related factors during the formation of the induced membrane. During the growing period of bone graft, it could facilitate the growth and mineralization of bone graft in a dose-dependent manner, which is partly related to the activation and phosphorylation of BMP-SMAD signaling pathway.

Effective Osteogenic Priming of Mesenchymal Stem Cells through LNA-ASOs-Mediated Sfrp1 Gene Silencing

Mesenchymal stem cell (MSC) transplantation has emerged as a promising approach for bone regeneration. Importantly, the beneficial effects of MSCs can be improved by modulating the expression levels of specific genes to stimulate MSC osteogenic differentiation. We have previously shown that Smurf1 silencing by using Locked Nucleic Acid-Antisense Oligonucleotides, in combination with a scaffold that sustainably releases low doses of BMP-2, was able to increase the osteogenic potential of MSCs in the presence of BMP-2 doses significantly smaller than those currently used in the clinic. This would potentially allow an important reduction in this protein in MSs-based treatments, and thus of the side effects linked to its administration. We have further improved this system by specifically targeting the Wnt pathway modulator Sfrp1. This approach not only increases MSC bone regeneration efficiency, but is also able to induce osteogenic differentiation in osteoporotic human MSCs, bypassing the need for BMP-2 induction, underscoring the regenerative potential of this system. Achieving successful osteogenesis with the sole use of LNA-ASOs, without the need of administering pro-osteogenic factors such as BMP-2, would not only reduce the cost of treatments, but would also open the possibility of targeting these LNA-ASOs specifically to MSCs in the bone marrow, allowing us to treat systemic bone loss such as that associated with osteoporosis.

Cotransplantation of mesenchymal stem cells and endothelial progenitor cells for treating steroid-induced osteonecrosis of the femoral head

Steroid-induced osteonecrosis of the femoral head (ONFH) is characterized by decreased osteogenesis, angiogenesis, and increased adipogenesis. While bone tissue engineering has been widely investigated to treat ONFH, its therapeutic effects remain unsatisfactory. Therefore, further studies are required to determine optimal osteogenesis, angiogenesis and adipogenesis in the necrotic area of the femoral head. In our study, we developed a carboxymethyl chitosan/alginate/bone marrow mesenchymal stem cell/endothelial progenitor cell (CMC/ALG/BMSC/EPC) composite implant, and evaluated its ability to repair steroid-induced ONFH. Our in vitro studies showed that BMSC and EPC coculture displayed enhanced osteogenic and angiogenic differentiation. When compared with single BMSC cultures, adipogenic differentiation in coculture systems was reduced. We also fabricated a three-dimensional (3D) CMC/ALG scaffold for loading cells, using a lyophilization approach, and confirmed its good cell compatibility characteristics, that is, high porosity, low cytotoxicity and favorable cell adhesion. 3D coculture of BMSCs and EPCs also promoted secretion of osteogenic and angiogenic factors. Then, we established an rabbit model of steroid-induced ONFH. The CMC/ALG/BMSC/EPC composite implant was transplanted into the bone tunnel of the rabbit femoral head after core decompression (CD) surgery. Twelve weeks later, radiographical and histological analyses revealed CMC/ALG/BMSC/EPC composite implants had facilitated the repair of steroid-induced ONFH, by promoting osteogenesis and angiogenesis, and reducing adipogenesis when compared with CD, CMC/ALG, CMC/ALG/BMSC and CMC/ALG/EPC groups. Thus, our data show that cotransplantation of BMSCs and EPCs in 3D scaffolds is beneficial in treating steroid-induced ONFH.

Cystatin-like protein of sweet orange (CsinCPI-2) modulates pre-osteoblast differentiation via β-Catenin involvement

Phytocystatins are endogenous cysteine-protease inhibitors present in plants. They are involved in initial germination rates and in plant defense mechanisms against phytopathogens. Recently, a new phytocystatin derived from sweet orange, CsinCPI-2, has been shown to inhibit the enzymatic activity of human cathepsins, presenting anti-inflammatory potential and pro-osteogenic effect in human dental pulp cells. The osteogenic potential of the CsinCPI-2 protein represents a new insight into plants cysteine proteases inhibitors and this effect needs to be better addressed. The aim of this study was to investigate the performance of pre-osteoblasts in response to CsinCPI-2, mainly focusing on cell adhesion, proliferation and differentiation mechanisms. Together our data show that in the first hours of treatment, protein in CsinCPI-2 promotes an increase in the expression of adhesion markers, which decrease after 24 h, leading to the activation of Kinase-dependent cyclines (CDKs) modulating the transition from G1 to S phases cell cycle. In addition, we saw that the increase in ERK may be associated with activation of the differentiation profile, also observed with an increase in the B-Catenin pathway and an increase in the expression of Runx2 in the group that received the treatment with CsinCPI-2.

Advances in mesenchymal stem cell transplantation for the treatment of osteoporosis

Osteoporosis is a systemic metabolic bone disease with characteristics of bone loss and microstructural degeneration. The personal and societal costs of osteoporosis are increasing year by year as the ageing of population, posing challenges to public health care. Homing disorders, impaired capability of osteogenic differentiation, senescence of mesenchymal stem cells (MSCs), an imbalanced microenvironment, and disordered immunoregulation play important roles during the pathogenesis of osteoporosis. The MSC transplantation promises to increase osteoblast differentiation and block osteoclast activation, and to rebalance bone formation and resorption. Preclinical investigations on MSC transplantation in the osteoporosis treatment provide evidences of enhancing osteogenic differentiation, increasing bone mineral density, and halting the deterioration of osteoporosis. Meanwhile, the latest techniques, such as gene modification, targeted modification and co-transplantation, are promising approaches to enhance the therapeutic effect and efficacy of MSCs. In addition, clinical trials of MSC therapy to treat osteoporosis are underway, which will fill the gap of clinical data. Although MSCs tend to be effective to treat osteoporosis, the urgent issues of safety, transplant efficiency and standardization of the manufacturing process have to be settled. Moreover, a comprehensive evaluation of clinical trials, including safety and efficacy, is still needed as an important basis for clinical translation.

Endothelial progenitor cells promote osteogenic differentiation in co-cultured with mesenchymal stem cells via the MAPK-dependent pathway

BACKGROUND

The role of bone tissue engineering is to regenerate tissue using biomaterials and stem cell-based approaches. Combination of two or more cell types is one of the strategies to promote bone formation. Endothelial progenitor cells (EPCs) may enhance the osteogenic properties of mesenchymal stem cells (MSCs) and promote bone healing; this study aimed to investigate the possible mechanisms of EPCs on promoting osteogenic differentiation of MSCs.

METHODS

MSCs and EPCs were isolated and co-cultured in Transwell chambers, the effects of EPCs on the regulation of MSC biological properties were investigated. Real-time PCR array, and western blotting were performed to explore possible signaling pathways involved in osteogenesis. The expression of osteogenesis markers and calcium nodule formation was quantified by qRT-PCR, western blotting, and Alizarin Red staining.

RESULTS

Results showed that MSCs exhibited greater alkaline phosphatase (ALP) activity and increased calcium mineral deposition significantly when co-cultured with EPCs. The mitogen-activated protein kinase (MAPK) signaling pathway was involved in this process. p38 gene expression and p38 protein phosphorylation levels showed significant upregulation in co-cultured MSCs. Silencing expression of p38 in co-cultured MSCs reduced osteogenic gene expression, protein synthesis, ALP activity, and calcium nodule formation.

CONCLUSIONS

These data suggest paracrine signaling from EPCs influences the biological function and promotes MSCs osteogenic differentiation. Activation of the p38MAPK pathway may be the key to enhancing MSCs osteogenic differentiation via indirect interactions with EPCs.

In vivo bone regeneration assessment of offset and gradient melt electrowritten (MEW) PCL scaffolds

BACKGROUND

Biomaterial-based bone tissue engineering represents a promising solution to overcome reduced residual bone volume. It has been previously demonstrated that gradient and offset architectures of three-dimensional melt electrowritten poly-caprolactone (PCL) scaffolds could successfully direct osteoblast cells differentiation toward an osteogenic lineage, resulting in mineralization. The aim of this study was therefore to evaluate the in vivo osteoconductive capacity of PCL scaffolds with these different architectures.

METHODS

Five different calcium phosphate (CaP) coated melt electrowritten PCL pore sized scaffolds: 250 μm and 500 μm, 500 μm with 50% fibre offset (offset.50.50), tri layer gradient 250-500-750 μm (grad.250top) and 750-500-250 μm (grad.750top) were implanted into rodent critical-sized calvarial defects. Empty defects were used as a control. After 4 and 8 weeks of healing, the new bone was assessed by micro-computed tomography and immunohistochemistry.

RESULTS

Significantly more newly formed bone was shown in the grad.250top scaffold 8 weeks post-implantation. Histological investigation also showed that soft tissue was replaced with newly formed bone and fully covered the grad.250top scaffold. While, the bone healing did not happen completely in the 250 μm, offset.50.50 scaffolds and blank calvaria defects following 8 weeks of implantation. Immunohistochemical analysis showed the expression of osteogenic markers was present in all scaffold groups at both time points. The mineralization marker Osteocalcin was detected with the highest intensity in the grad.250top and 500 μm scaffolds. Moreover, the expression of the endothelial markers showed that robust angiogenesis was involved in the repair process.

CONCLUSIONS

These results suggest that the gradient pore size structure provides superior conditions for bone regeneration.

Mitochondria transfer enhances proliferation, migration, and osteogenic differentiation of bone marrow mesenchymal stem cell and promotes bone defect healing

Background

Bone marrow-derived mesenchymal stem cell (BMSC) transplantation is considered a promising therapeutic approach for bone defect repair. However, during the transplantation procedure, the functions and viability of BMSCs may be impaired due to extended durations of in vitro culture, aging, and disease conditions of patients. Inspired by spontaneous intercellular mitochondria transfer that naturally occurs within injured tissues to rescue cellular or tissue function, we investigated whether artificial mitochondria transfer into pre-transplant BMSCs in vitro could improve cellular function and enhance their therapeutic effects on bone defect repair in situ.

Methods

Mitochondria were isolated from donor BMSCs and transferred into recipient BMSCs of the same batch and passage. Subsequently, changes in proliferative capacity and cell senescence were evaluated by live cell imaging, Cell Counting Kit-8 assay, cell cycle analysis, Ki67 staining, qPCR and Western blot analysis of c-Myc expression, and β-galactosidase staining. Migration ability was evaluated by the transwell migration assay, wound scratch healing, and cell motility tests. Alkaline phosphatase (ALP) staining, Alizarin Red staining, and combined with qPCR and Western blot analyses of Runx2 and BMP2 were performed to elucidate the effects of mitochondria transfer on the osteogenic potential of BMSCs in vitro. After that, in vivo experiments were performed by transplanting mitochondria-recipient BMSCs into a rat cranial critical-size bone defect model. Micro CT scanning and histological analysis were conducted at 4 and 8 weeks after transplantation to evaluate osteogenesis in situ. Finally, in order to establish the correlation between cellular behavioral changes and aerobic metabolism, OXPHOS (oxidative phosphorylation) and ATP production were assessed and inhibition of aerobic respiration by oligomycin was performed.

Results

Mitochondria-recipient BMSCs exhibited significantly enhanced proliferation and migration, and increased osteogenesis upon osteogenic induction. The in vivo results showed more new bone formation after transplantation of mitochondria-recipient BMSCs in situ. Increased OXPHOS activity and ATP production were observed, which upon inhibition by oligomycin attenuated the enhancement of proliferation, migration, and osteogenic differentiation induced by mitochondria transfer.

Conclusions

Mitochondria transfer is a feasible technique to enhance BMSC function in vitro and promote bone defect repair in situ through the upregulation of aerobic metabolism. The results indicated that mitochondria transfer may be a novel promising technique for optimizing stem cell therapeutic function.

Concentration-dependent effects of latex F1-protein fraction incorporated into deproteinized bovine bone and biphasic calcium phosphate on the repair of critical-size bone defects

F1-protein fraction (F1) is a natural bioactive compound extracted from the rubber tree, Hevea brasiliensis, and has been recently studied for its therapeutic potential in wound healing. In this study, we investigated the concentration-dependent effects of F1 (0.01%, 0.025%, 0.05%, and 0.1%) incorporated into deproteinized bovine bone (DBB) and porous biphasic calcium phosphate (pBCP), on the repair of rat calvarial critical-size bone defects (CSBD). The defects were analyzed by 3D-microtomography and 2D-histomorphometry at 12 weeks postsurgery. The binding efficiency of F1 to pBCP (96.3 ± 1.4%) was higher than that to DBB (67.7 ± 3.3%). In vivo analysis showed a higher bone volume (BV) gain in all defects treated with DBB (except in 0.1% of F1) and pBCP (except in 0.05% and 0.1% of F1) compared to the CSBD without treatment/control group (9.96 ± 2.8 mm³ ). DBB plus 0.025% F1 promoted the highest BV gain (29.7 ± 2.2 mm³ , p < .0001) compared to DBB without F1 and DBB plus 0.01% and 0.1% of F1. In the pBCP group, incorporation of F1 did not promote bone gain when compared to pBCP without F1 (15.9 ± 4.2 mm³ , p > .05). Additionally, a small BV occurred in defects treated with pBCP plus 0.1% F1 (10.4 ± 1.4 mm^3, p < .05). In conclusion, F1 showed a higher bone formation potential in combination with DBB than with pBCP, in a concentration-dependent manner. Incorporation of 0.25% F1 into DBB showed the best results with respect to bone formation/repair in CSBD. These results suggest that DBB plus 0.25% F1 can be used as a promising bioactive material for application in bone tissue engineering.

Effects of Nanotopography Regulation and Silicon Doping on Angiogenic and Osteogenic Activities of Hydroxyapatite Coating on Titanium Implant

Background

Angiogenic and osteogenic activities are two major problems with biomedical titanium (Ti) and other orthopedic implants used to repair large bone defects.

Purpose

The aim of this study is to prepare hydroxyapatite (HA) coatings on the surface of Ti by using electrochemical deposition (ED), and to evaluate the effects of nanotopography and silicon (Si) doping on the angiogenic and osteogenic activities of the coating in vitro.

Materials and Methods

HA coating and Si-doped HA (HS) coatings with varying nanotopographies were fabricated using two ED modes, ie, the pulsive current (PC) and cyclic voltammetry (CV) methods. The coatings were characterized through scanning electron microscope (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectrometer (XPS), and atomic force microscopy (AFM), and their in vitro bioactivity and protein adsorption were assessed. Using MC3T3-E1 pre-osteoblasts and HUVECs as cell models, the osteogenic and angiogenic capabilities of the coatings were evaluated through in vitro cellular experiments.

Results

By controlling Si content in ~0.8 wt.%, the coatings resulting from the PC mode (HA-PC and HS-PC) and CV mode (HA-CV and HS-CV) had nanosheet and nanorod topographies, respectively. At lower crystallinity, higher ionic dissolution, smaller contact angle, higher surface roughness, and more negative zeta potential, the HS and PC samples exhibited quicker apatite deposition and higher BSA adsorption capacity. The in vitro cell study showed that Si doping was more favorable for enhancing the viability of the MC3T3-E1 cells, but nanosheet coating increased the area for cell spreading. Of the four coatings, HS-PC with Si doping and nanosheet topography exhibited the best effect in terms of up-regulating the expressions of the osteogenic genes (ALP, Col-I, OSX, OPN and OCN) in the MC3T3-E1 cells. Moreover, all leach liquors of the surface-coated Ti disks promoted the growth of the HUVECs, and the HS samples played a more significant role in promoting cell migration and tube formation than the HA samples. Of the four leach liquors, only the two HS samples up-regulated NO content and expressions of the angiogenesis-related genes (VEGF, bFGF and eNOS) in the HUVECs, and the HS-PC yielded a better effect.

Conclusion

The results show that Si doping while regulating the topography of the coating can help enhance the bone regeneration and vascularization of HA-coated Ti implants.

Tissue Engineering and Regenerative Medicine in Craniofacial Reconstruction and Facial Aesthetics

The craniofacial region is anatomically complex and is of critical functional and cosmetic importance, making reconstruction challenging. The limitations of current surgical options highlight the importance of developing new strategies to restore the form, function, and esthetics of missing or damaged soft tissue and skeletal tissue in the face and cranium. Regenerative medicine (RM) is an expanding field which combines the principles of tissue engineering (TE) and self-healing in the regeneration of cells, tissues, and organs, to restore their impaired function. RM offers many advantages over current treatments as tissue can be engineered for specific defects, using an unlimited supply of bioengineered resources, and does not require immunosuppression. In the craniofacial region, TE and RM are being increasingly used in preclinical and clinical studies to reconstruct bone, cartilage, soft tissue, nerves, and blood vessels. This review outlines the current progress that has been made toward the engineering of these tissues for craniofacial reconstruction and facial esthetics.

Collagen-Elastin-Like Polypeptide-Bioglass Scaffolds for Guided Bone Regeneration

The goals of this study are to evaluate the ability of the multicomponent collagen-elastin-like polypeptide (ELP)-Bioglass scaffolds to support osteogenesis of rat mesenchymal stem cells (rMSCs), demonstrate in vivo biocompatibility by subcutaneous implantation in Sprague-Dawley rats, monitor degradation noninvasively, and finally assess the scaffold's ability in healing critical-sized cranial bone defects. The collagen-ELP-Bioglass scaffold supports the in vitro osteogenic differentiation of rMSCs over a 3 week culture period. The cellular (rMSC-containing) or acellular scaffolds implanted in the subcutaneous pockets of rats do not cause any local or systemic toxic effects or tumors. The real-time monitoring of the fluorescently labeled scaffolds by IVIS reveals that the scaffolds remain at the site of implantation for up to three weeks, during which they degrade gradually. Micro-CT analysis shows that the bilateral cranial critical-sized defects created in rats lead to greater bone regeneration when filled with cellular scaffolds. Bone mineral density and bone microarchitectural parameters are comparable among different scaffold groups, but the histological analysis reveals increased formation of high-quality mature bone in the cellular group, while the acellular group has immature bone and organized connective tissue. These results suggest that the rMSC-seeded collagen-ELP-Bioglass composite scaffolds can aid in better bone healing process.

Primary cilia control cell alignment and patterning in bone development via ceramide-PKCζ-β-catenin signaling

Intraflagellar transport (IFT) proteins are essential for cilia assembly and function. IFT protein mutations lead to ciliopathies, which manifest as variable skeletal abnormalities. However, how IFT proteins regulate cell alignment during bone development is unknown. Here, we show that the deletion of IFT20 in osteoblast lineage using Osterix-Cre and inducible type I Collagen-CreERT cause a compromised cell alignment and a reduced bone mass. This finding was validated by the disorganized collagen fibrils and decreased bone strength and stiffness in IFT20-deficient femurs. IFT20 maintains cilia and cell alignment in osteoblasts, as the concentric organization of three-dimensional spheroids was disrupted by IFT20 deletion. Mechanistically, IFT20 interacts with the ceramide-PKCζ complex to promote PKCζ phosphorylation in cilia and induce the apical localization of β-catenin in osteoblasts, both of which were disrupted in the absence of IFT20. These results reveal that IFT20 regulates polarity and cell alignment via ceramide-pPKCζ-β-catenin signaling during bone development.

Co-transplantation of Wharton's jelly mesenchymal stem cell-derived osteoblasts with differentiated endothelial cells does not stimulate blood vessel and osteoid formation in nude mice models

A major challenge in bone tissue engineering is the lack of post-implantation vascular growth into biomaterials. In the skeletal system, blood vessel growth appears to be coupled to osteogenesis-suggesting the existence of molecular crosstalk between endothelial cells (ECs) and osteoblastic cells. The present study (performed in two murine ectopic models) was designed to determine whether co-transplantation of human Wharton's jelly mesenchymal stem cell-derived osteoblasts (WJMSC-OBs) and human differentiated ECs enhances bone regeneration and stimulates angiogenesis, relative to the seeding of WJMSC-OBs alone. Human WJMSC-OBs and human ECs were loaded into a silicate-substituted calcium phosphate (SiCaP) scaffold and then ectopically implanted at subcutaneous or intramuscular sites in nude mice. At both subcutaneous and intramuscular implantation sites, we observed ectopic bone formation and osteoids composed of host cells when WJMSC-OBs were seeded into the scaffold. However, the addition of ECs was associated with a lower level of osteogenesis, and we did not observe stimulation of blood vessel ingrowth. in vitro studies demonstrated that WJMSC-OBs lost their ability to secrete vascular endothelial growth factor and stromal cell-derived factor 1-including when ECs were present. In these two murine ectopic models, our cell-matrix environment combination did not seem to be optimal for inducing vascularized bone reconstruction.

Effects of Fiber Alignment and Coculture with Endothelial Cells on Osteogenic Differentiation of Mesenchymal Stromal Cells

Vascularization is a critical process during bone regeneration. The lack of vascular networks leads to insufficient oxygen and nutrients supply, which compromises the survival of regenerated bone. One strategy for improving the survival and osteogenesis of tissue-engineered bone grafts involves the coculture of endothelial cells (ECs) with mesenchymal stromal cells (MSCs). Moreover, bone regeneration is especially challenging due to its unique structural properties with aligned topographical cues, with which stem cells can interact. Inspired by the aligned fibrillar nanostructures in human cancellous bone, we fabricated polycaprolactone (PCL) electrospun fibers with aligned and random morphology, cocultured human MSCs with human umbilical vein ECs (HUVECs), and finally investigated how these two factors modulate osteogenic differentiation of human MSCs (hMSCs). After optimizing cell ratio, a hMSCs/HUVECs ratio (90:10) was considered to be the best combination for osteogenic differentiation. Coculture results showed that hMSCs and HUVECs adhered to and proliferated well on both scaffolds. The aligned structure of PCL fibers strongly influenced the morphology and orientation of hMSCs and HUVECs; however, fiber alignment was observed to not affect alkaline phosphate (ALP) activity or mineralization of hMSCs compared with random scaffolds. More importantly, cocultured cells on both random and aligned scaffolds had significantly higher ALP activities than monoculture groups, which indicated that coculture with HUVECs provided a larger relative contribution to the osteogenesis of hMSCs compared with fiber alignment. Taken together, we conclude that coculture of hMSCs with ECs is an effective strategy to promote osteogenesis on electrospun scaffolds, and aligned fibers could be introduced to regenerate bone tissues with oriented topography without significant deleterious effects on hMSCs differentiation. This study shows the ability to grow oriented tissue-engineered cocultures with significant increases in osteogenesis over monoculture conditions. Impact statement This work demonstrates an effective method of enhancing osteogenesis of mesenchymal stromal cells on electrospun scaffolds through coculturing with endothelial cells. Furthermore, we provide the optimized conditions for cocultures on electrospun fibrous scaffolds and engineered bone tissues with oriented topography on aligned fibers. This study demonstrates promising findings for growing oriented tissue-engineered cocultures with significant increase in osteogenesis over monoculture conditions.

Smurf1 Silencing Using a LNA-ASOs/Lipid Nanoparticle System to Promote Bone Regeneration

Despite the great advance of bone tissue engineering in the last few years, repair of bone defects remains a major problem. Low cell engraftment and dose‐dependent side effects linked to the concomitant administration of bone morphogenetic proteins (BMPs) are the main problems currently hindering the clinical use of mesenchymal stem cell (MSC)‐based therapies in this field. We have managed to bypass these drawbacks by combining the silencing the Smurf1 ubiquitin ligase in MSCs with the use of a scaffold that sustainably releases low doses of BMP‐2. In this system, Smurf1 silencing is achieved by using GapmeRs, a clinically safe method that avoids the use of viral vectors, facilitating its translation to the clinic. Here, we show that a single transient transfection with a small quantity of a Smurf1‐specific GapmeR is able to induce a significant level of silencing of the target gene, enough to prime MSCs for osteogenic differentiation. Smurf1 silencing highly increases MSCs responsiveness to BMP‐2, allowing a dramatic reduction of the dose needed to achieve the desired therapeutic effect. The combination of these primed cells with alginate scaffolds designed to sustainably and locally release low doses of BMP‐2 to the defect microenvironment is able to induce the formation of a mature bone matrix both in an osteoporotic rat calvaria system and in a mouse ectopic model. Importantly, this approach also enhances osteogenic differentiation in MSCs from osteoporotic patients, characterized by a reduced bone‐forming potential, even at low BMP doses, underscoring the regenerative potential of this system. stem cells translational medicine2019;8:1306&1317

The BMP‐Smad signaling cascade is an effective therapeutic target to promote bone formation. Silencing of Smurf1, a known BMP signaling inhibitor, increases the responsiveness of Mesenchymal stem cells to BMP, allowing a dramatic reduction of the doses used in the clinic to promote bone formation and therefore, avoiding secondary effects associated to the use of these factors.

Cell sheets of co-cultured BMP-2-modified bone marrow stromal cells and endothelial progenitor cells accelerate bone regeneration in vitro

Bone tissue engineering provides a substitute for bone transplantation to address various bone defects. However, bone regeneration involves a large number of cellular events. In addition, obtaining sufficient source material for autogenous bone or alloplastic bone substitutes remains an unsolved issue. In previous studies, it was confirmed that bone marrow stromal cells (BMSCs) and endothelial progenitor cells (EPCs) had the capacity to promote bone regeneration. Additionally, bone morphogenetic protein-2 (BMP-2) has been demonstrated to be an active inducer of osteoblast differentiation. Therefore, the aim of the present study was to produce an effective integration system, including a scaffold, reparative cells and growth factors, that may enhance bone regeneration. Firstly, bone marrow-derived BMSCs and EPCs were isolated and identified by flow cytometry. Cell proliferation ability, secreted BMP-2 levels and alkaline phosphatase (ALP) activity were highest in the cell sheets containing BMP-2-modified BMSCs and EPCs. In addition, the expression levels of osteogenesis-associated genes, including runt related transcription factor 2 (Runx2), distal-less homeobox 5 (Dlx5), ALP and integrin-binding sialoprotein (Ibsp), and osteogenesis-associated proteins, including Runx2, Dlx, ALP, Ibsp, vascular endothelial growth factor, osteonectin, osteopontin and type I collagen, gradually increased during the co-culture of ad-BMP-2-BMSCs/EPCs. The levels of these genes and proteins were increased compared with those observed in the BMSC, EPC and BMP-2-modified BMSC groups. Finally, scanning electron microscopy observation also demonstrated that the BMP2-modified BMSCs were able to combine well with EPCs to construct a cell sheet for bone formation. Collectively, these results describe an adenovirus (ad)-BMP2-BMSCs/EPCs co-culture system that may significantly accelerate bone regeneration compared with a BMSCs/EPCs co-culture system or ad-BMP2-BMSCs alone.

BMP-2 Gene Delivery-Based Bone Regeneration in Dentistry

Bone morphogenetic protein-2 (BMP-2) is a potent growth factor affecting bone formation. While recombinant human BMP-2 (rhBMP-2) has been commercially available in cases of non-union fracture and spinal fusion in orthopaedics, it has also been applied to improve bone regeneration in challenging cases requiring dental implant treatment. However, complications related to an initially high dosage for maintaining an effective physiological concentration at the defect site have been reported, although an effective and safe rhBMP-2 dosage for bone regeneration has not yet been determined. In contrast to protein delivery, BMP-2 gene transfer into the defect site induces BMP-2 synthesis in vivo and leads to secretion for weeks to months, depending on the vector, at a concentration of nanograms per milliliter. BMP-2 gene delivery is advantageous for bone wound healing process in terms of dosage and duration. However, safety concerns related to viral vectors are one of the hurdles that need to be overcome for gene delivery to be used in clinical practice. Recently, commercially available gene therapy has been introduced in orthopedics, and clinical trials in dentistry have been ongoing. This review examines the application of BMP-2 gene therapy for bone regeneration in the oral and maxillofacial regions and discusses future perspectives of BMP-2 gene therapy in dentistry.

Chondroitin Sulfate Glycosaminoglycan Scaffolds for Cell and Recombinant Protein-Based Bone Regeneration

Bone morphogenetic protein 2 (BMP‐2)‐loaded collagen sponges remain the clinical standard for treatment of large bone defects when there is insufficient autograft, despite associated complications. Recent efforts to negate comorbidities have included biomaterials and gene therapy approaches to extend the duration of BMP‐2 release and activity. In this study, we compared the collagen sponge clinical standard to chondroitin sulfate glycosaminoglycan (CS‐GAG) scaffolds as a delivery vehicle for recombinant human BMP‐2 (rhBMP‐2) and rhBMP‐2 expression via human BMP‐2 gene inserted into mesenchymal stem cells (BMP‐2 MSC). We demonstrated extended release of rhBMP‐2 from CS‐GAG scaffolds compared to their collagen sponge counterparts, and further extended release from CS‐GAG gels seeded with BMP‐2 MSC. When used to treat a challenging critically sized femoral defect model in rats, both rhBMP‐2 and BMP‐2 MSC in CS‐GAG induced comparable bone formation to the rhBMP‐2 in collagen sponge, as measured by bone volume, strength, and stiffness. We conclude that CS‐GAG scaffolds are a promising delivery vehicle for controlling the release of rhBMP‐2 and to mediate the repair of critically sized segmental bone defects. stem cells translational medicine2019;8:575–585

Bone physiology as inspiration for tissue regenerative therapies

The development, maintenance of healthy bone and regeneration of injured tissue in the human body comprise a set of intricate and finely coordinated processes. However, an analysis of current bone regeneration strategies shows that only a small fraction of well-reported bone biology aspects has been used as inspiration and transposed into the development of therapeutic products. Specific topics that include inter-scale bone structural organization, developmental aspects of bone morphogenesis, bone repair mechanisms, role of specific cells and heterotypic cell contact in the bone niche (including vascularization networks and immune system cells), cell-cell direct and soluble-mediated contact, extracellular matrix composition (with particular focus on the non-soluble fraction of proteins), as well as mechanical aspects of native bone will be the main reviewed topics. In this Review we suggest a systematic parallelization of (i) fundamental well-established biology of bone, (ii) updated and recent advances on the understanding of biological phenomena occurring in native and injured tissue, and (iii) critical discussion of how those individual aspects have been translated into tissue regeneration strategies using biomaterials and other tissue engineering approaches. We aim at presenting a perspective on unexplored aspects of bone physiology and how they could be translated into innovative regeneration-driven concepts.

In vivo identification of Bmp2-correlation networks during fracture healing by means of a limb-specific conditional inactivation of Bmp2

Bmp2 is known to play an essential role in the initiation of fracture healing via periosteal activation. Specifically, activation and subsequent differentiation of periosteal progenitor cells requires Bmp2 signaling for activation of the osteo-chondrogenic pathway. Here, we explored the interactive transcriptional gene-gene interplays between Bmp2 and 150 known candidate genes during fracture repair. We constructed the interactive Bmp2 signaling pathways in vivo, by comparing gene expression levels prior and 24 h post femur fracture, in presence (wild type) and in absence of Bmp2 (Bmp2c/c;Prx1::cre limb-specific conditional knockout). Twenty-six differentially expressed genes (pre- vs. post-fracture), which demonstrated high correlations within each experimental condition, were used to construct the co-expression networks. Topological dynamic shifts across different co-expression networks characterized the 26 differentially expressed genes as non-redundant focal linking hubs, redundant connecting hubs, periphery genes, or non-existent. Top-ranked up- or down-regulated genes were identified and discussed. Protein-protein interactions in public databases support our findings. Thus, the co-expression networks from this study can be used for future experimental hypotheses.

Effect of high-fat diet-induced obesity on the small-conductance Ca2+-activated K+ channel function affecting the contractility of rat detrusor smooth muscle

PURPOSE

Obesity usually induces overactive bladder (OAB) associated with detrusor overactivity, which is related to increased contractility of the detrusor smooth muscle (DSM). Small-conductance Ca²⁺-activated K⁺ (SK) channels play a constitutive role in the regulation of DSM contractility. However, the role of SK channels in the DSM changes in obesity-related OAB is still unknown. Here, we tested the hypothesis that obesity-related OAB is associated with reduced expression and activity of SK channels in DSM and that SK channels activation is a potential treatment for OAB.

METHODS

Female Sprague-Dawley rats were fed a normal diet (ND) or a high-fat diet (HFD) and weighed after 12 weeks. Urodynamic studies, quantitative reverse transcription-polymerase chain reaction (qRT-PCR), and isometric tension recording were performed.

RESULTS

Increased average body weights and urodynamically demonstrated OAB were observed in HFD rats. qRT-PCR experiments revealed a decrease in the mRNA expression level of SK channel in DSM tissue of the HFD rats. Isometric tension recordings indicated an attenuated relaxation effect of NS309 on the spontaneous phasic and electrical field stimulation-induced contractions that occurred via SK channel activation in HFD DSM strips.

CONCLUSIONS

Reduced expression and activity of SK channels in the DSM contribute to obesity-related OAB, indicating that SK channels are a potential therapeutic target for OAB.

3D Bone Biomimetic Scaffolds for Basic and Translational Studies with Mesenchymal Stem Cells

Mesenchymal stem cells (MSCs) are recognized as an attractive tool owing to their self-renewal and differentiation capacity, and their ability to secrete bioactive molecules and to regulate the behavior of neighboring cells within different tissues. Accumulating evidence demonstrates that cells prefer three-dimensional (3D) to 2D culture conditions, at least because the former are closer to their natural environment. Thus, for in vitro studies and in vivo utilization, great effort is being dedicated to the optimization of MSC 3D culture systems in view of achieving the intended performance. This implies understanding cell–biomaterial interactions and manipulating the physicochemical characteristics of biomimetic scaffolds to elicit a specific cell behavior. In the bone field, biomimetic scaffolds can be used as 3D structures, where MSCs can be seeded, expanded, and then implanted in vivo for bone repair or bioactive molecules release. Actually, the union of MSCs and biomaterial has been greatly improving the field of tissue regeneration. Here, we will provide some examples of recent advances in basic as well as translational research about MSC-seeded scaffold systems. Overall, the proliferation of tools for a range of applications witnesses a fruitful collaboration among different branches of the scientific community.

Mesenchymal Stem Cell Therapy for Bone Regeneration

Mesenchymal stem cells (MSCs) have been used in clinic for approximately 20 years. During this period, various new populations of MSCs have been found or manipulated. However, their characters and relative strength for bone regeneration have not been well known. For a comprehensive understanding of MSCs, we reviewed the literature on the multipotent cells ranging from the definition to the current research progress for bone regeneration. Based on our literature review, bone marrow MSCs have been most widely studied and utilized in clinical settings. Among other populations of MSCs, adipose-derived MSCs and perivascular MSCs might be potential candidates for bone regeneration, whose efficacy and safety still require further investigation.

Bone regeneration strategy by different sized multichanneled biphasic calcium phosphate granules: In vivo evaluation in rabbit model

A variety of synthetic materials are currently in use as bone substitutes, among them a new calcium phosphate-based multichannel, cylindrical, granular bone substitute that is showing satisfactory biocompatibility and osteoconductivity in clinical applications. These cylindrical granules differ in their mechanical and morphological characteristics such as size, diameter, surface area, pore size, and porosity. The aim of this study is to investigate whether the sizes of these synthetic granules and the resultant inter-granular spaces formed by their filling critical-sized bone defects affect new bone formation characteristics and to determine the best formulations from these individual types by combining the granules in different proportions to optimize the bone tissue regeneration. We evaluated two types of multichanneled cylindrical granules, 1 mm and 3 mm in diameter, combined the granules in two different proportions (wt%), and compared their different mechanical, morphological, and in vitro and in vivo biocompatibility characteristics. We assessed in vitro biocompatibility and cytotoxicity using MC3T3-E1 osteoblast-like cells using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay and confocal imaging. In vivo investigation in a rabbit model indicated that all four samples formed significantly better bone than the control after four weeks and eight weeks of implantation. Micro-computed tomography analysis showed more bone formation by the 1 mm cylindrical granules with 160 ± 10 µm channeled pore and 50% porosity than the other three samples ( p<.05), which we confirmed by histological analysis.

Multilineage Constructs for Scaffold-Based Tissue Engineering: A Review of Tissue-Specific Challenges

There is a growing interest in the regeneration of tissue in interfacial regions, where biological, physical, and chemical attributes vary across tissue type. The simultaneous use of distinct cell lineages can help in developing in vitro structures, analogous to native composite tissues. This literature review gathers the recent reports that have investigated multiple cell types of various sources and lineages in a coculture system for tissue-engineered constructs. Such studies aim at mimicking the native organization of tissues and their interfaces, and/or to improve the development of complex tissue substitutes. This paper thus distinguishes itself from those focusing on technical aspects of coculturing for a single specific tissue. The first part of this review is dedicated to variables of cocultured tissue engineering such as scaffold, cells, and in vitro culture environment. Next, tissue-specific coculture methods and approaches are covered for the most studied tissues. Finally, cross-analysis is performed to highlight emerging trends in coculture principles and to discuss how tissue-specific challenges can inspire new approaches for regeneration of different interfaces to improve the outcomes of various tissue engineering strategies.

Heritable Skeletal Disorders Arising from Defects in Processing and Transport of Type I Procollagen from the ER: Perspectives on Possible Therapeutic Approaches

Rare bone disorders are a heterogeneous group of diseases, initially associated with mutations in type I procollagen (PC) genes. Recent developments from dissection at the molecular and cellular level have expanded the list of disease-causing proteins, revealing that disruption of the machinery that handles protein secretion can lead to failure in PC secretion and in several cases result in skeletal dysplasia. In parallel, cell-based in vitro studies of PC trafficking pathways offer clues to the identification of new disease candidate genes. Together, this raises the prospect of heritable bone disorders as a paradigm for biosynthetic protein traffic-related diseases, and an avenue through which therapeutic strategies can be explored.Here, we focus on human syndromes linked to defects in type I PC secretion with respect to the landscape of biosynthetic and protein transport steps within the early secretory pathway. We provide a perspective on possible therapeutic interventions for associated heritable craniofacial and skeletal disorders, considering different orders of complexity, from the cellular level by manipulation of proteostasis pathways to higher levels involving cell-based therapies for bone repair and regeneration.

Three-dimensional macroporous materials for tissue engineering of craniofacial bone

Repair of critical-size defects caused by trauma, removal of a tumour, or congenital abnormalities is a challenge in the craniomaxillofacial region because of the limitations associated with treatment. We have reviewed research papers and updated information relevant to the various types of macroporous scaffolds. We have included papers on several biomaterials and their use in various craniofacial defects such as mandibular, calvarial, and others, as well as the latest technological developments such as 3-dimensional printed scaffolds. We selected all papers about scaffolds, stem cells, and growth factors for review. Initial selection was by review of titles and abstracts, and the full texts of potentially suitable articles were then assessed. Methods of tissue engineering for repair of critical-size defects in the craniofacial bones seem to be viable options for surgical treatment in the future. Macroporous scaffolds with interconnected pores are of great value in regeneration of bone in the craniofacial region. In recent years, various natural or synthetic materials, or both, have been developed, on which macroporous scaffolds can be based. In this review we present a review on the various types of three-dimensional macroporous scaffolds that have been developed in recent years, and evaluate their potential for regeneration of craniofacial bone.

Antimicrobial Peptide Combined with BMP2-Modified Mesenchymal Stem Cells Promotes Calvarial Repair in an Osteolytic Model

Repair and regeneration of inflammation-induced bone loss remains a clinical challenge. LL37, an antimicrobial peptide, plays critical roles in cell migration, cytokine production, apoptosis, and angiogenesis. Migration of stem cells to the affected site and promotion of vascularization are essential for tissue engineering therapy, including bone regeneration. However, it is largely unknown whether LL37 affects mesenchymal stem cell (MSC) behavior and bone morphogenetic protein 2 (BMP2)-mediated bone repair during the bone pathologic remodeling process. By performing in vitro and in vivo studies with MSCs and a lipopolysaccharide (LPS)-induced mouse calvarial osteolytic bone defect model, we found that LL37 significantly promotes cell differentiation, migration, and proliferation in both unmodified MSCs and BMP2 gene-modified MSCs. Additionally, LL37 inhibited LPS-induced osteoclast formation and bacterial activity in vitro. Furthermore, the combination of LL37 and BMP2 markedly promoted MSC-mediated angiogenesis and bone repair and regeneration in LPS-induced osteolytic defects in mouse calvaria. These findings demonstrate for the first time that LL37 can be a potential candidate drug for promoting osteogenesis and for inhibiting bacterial growth and osteoclastogenesis, and that the combination of BMP2 and LL37 is ideal for MSC-mediated bone regeneration, especially for inflammation-induced bone loss.

Fabrication of viable and functional pre-vascularized modular bone tissues by coculturing MSCs and HUVECs on microcarriers in spinner flasks

Slow vascularization often impedes the viability and function of engineered bone replacements. Prevascularization is a promising way to solve this problem. In this study, a new process was developed by integrating microcarrier culture and coculture to fabricate pre-vascularized bone microtissues with mesenchymal stem cells (MSCs) and human umbilical vein endothelial cells (HUVECs). Initially, coculture medium and cell ratio between MSCs and HUVECs were optimized in tissue culture plates concerning cell proliferation, osteogenesis and angiogenesis. Subsequently, cells were seeded onto CultiSpher S microcarriers in spinner flasks and subjected to a two-stage (proliferative-osteogenic) culture process for four weeks. Both cells proliferated and functioned well in chosen medium and a 1 : 1 ratio between MSCs and HUVECs was chosen for better angiogenesis. After four weeks of culture in spinner flasks, the microtissues were formed with high cellularity, evenly distributed cells and tube formation ability. While coculture with HUVECs exerted an inhibitory effect on osteogenic differentiation of MSCs, with downregulated alkaline phosphatase activity, mineralization and gene expression of COLI, RUNX2 and OCN, this could be attenuated by employing a delayed seeding strategy of HUVECs against MSCs during the microtissue fabrication process.

CONCLUSION

Collectively, this work established an effective method to fabricate pre-vascularized bone microtissues, which would lay a solid foundation for subsequent development of vascularized tissue grafts for bone regeneration.

Cell Sheets of Co-cultured Endothelial Progenitor Cells and Mesenchymal Stromal Cells Promote Osseointegration in Irradiated Rat Bone

Irradiated bone has a greater risk of implant failure than nonirradiated bone. The purpose of this study was to investigate the influence of cell sheets composed of co-cultured bone marrow mesenchymal stromal cells (BMSCs) and endothelial progenitor cells (EPCs) on implant osseointegration in irradiated bone. Cell sheets (EPCs, BMSCs or co-cultured EPCs and BMSCs) were wrapped around titanium implants to make cell sheet-implant complexes. The co-cultured group showed the highest osteogenic differentiation potential in vitro, as indicated by the extracellular matrix mineralization and the expression of osteogenesis related genes at both mRNA and protein levels. The co-cultured cells promoted ectopic bone formation as indicated by micro-computed tomography (Micro-CT) and histological analysis. In the irradiated tibias of rats, implants of the co-cultured group showed enhanced osseointegration by Micro-CT evaluation and histological observation. Co-cultured EPCs and BMSCs also up-regulated the expression of osteogenesis related genes in bone fragments in close contact with implants. In conclusion, cell sheets of co-cultured EPCs and BMSCs could promote osseous healing around implants and are potentially useful to improve osseointegration process for patients after radiotherapy.

The combination of nano-calcium sulfate/platelet rich plasma gel scaffold with BMP2 gene-modified mesenchymal stem cells promotes bone regeneration in rat critical-sized calvarial defects

BACKGROUND

Mesenchymal stem cells (MSCs) can be differentiated into an osteoblastic lineage in the presence of growth factors (GFs). Platelet-rich plasma (PRP), which can be easily isolated from whole blood, contains a large amount of GFs, and, therefore, promotes bone growth and regeneration. The main goal of this work was to develop and investigate the effect of a new sandwich-like bone scaffold which combines a nano-calcium sulfate (nCS) disc along with PRP fibrin gel (nCS/PRP) with BMP2-modified MSCs on bone repair and regeneration in rat critical-sized calvarial defects.

METHODS

We evaluated the cytotoxicity, osteogenic differentiation and mineralization effect of PRP extract on BMP2-modified MSCs and constructed a sandwich-like nCS/PRP scaffold (mimicking the nano-calcium matrix of bone and carrying multi GFs in the PRP) containing BMP2-modified MSCs. The capacity of this multifunctional bone regeneration system in promoting bone repair was assessed in vivo in a rat critical-sized (8 mm) calvarial bone defect model.

RESULTS

We developed an optimized nCS/PRP sandwich-like scaffold. Scanning electron microscopy (SEM) results showed that nCS/PRP are polyporous with an average pore diameter of 70-80 μm and the cells can survive in the nCS/PRP scaffold. PRP extract dramatically stimulated proliferation and differentiation of BMP2-modified MSCs in vitro. Our in vivo results showed that the combination of BMP2-modified MSCs and nCS/PRP scaffold dramatically increased new bone regeneration compared with the groups without PRP and/or BMP2.

CONCLUSIONS

nCS/PRP scaffolds containing BMP2-modified MSCs successfully promotes bone regeneration in critical-sized bone defects. This system could ultimately enable clinicians to better reconstruct the craniofacial bone and avoid donor site morbidity for critical-sized bone defects.

Human type H vessels are a sensitive biomarker of bone mass

Vascularization is fundamental for bone formation and bone tissue homeostasis. However, in human subjects, a direct molecular relationship has not been identified between angiogenesis and agents that promote bone disease or factors related to age. Osteopenia is a condition in which bone mineral density is lower than normal, and it represents a sign of normal aging. Here we tested whether the type H vessel, which was recently identified as strongly positive for CD31 and Endomucin (CD31^hiEmcn^hi) in mice, is an important indicator of aging and osteopenia in human subjects. We found that age-dependent losses of type H vessels in human bone sections conform to the observations in aged mice. The abundance of human type H vessels and osteoprogenitors may be relevant to changes in the skeletal microarchitecture and advanced osteopenia. Furthermore, ovariectomized mice, a widely used model for postmenopausal osteoporosis, exhibited significantly reduced type H vessels accompanied by reduced osteoprogenitors, which is consistent with impaired bone microarchitecture and osteoporosis, suggesting that this feature is an indicator of bone mass independent of aging. More importantly, administration of desferrioxamine led to significantly increased bone mass via enhanced angiogenesis and increased type H vessels in ovariectomized mice. Altogether, these data represent a novel finding that type H vessels are regulated in aged and osteopenia subjects. The abundance of human type H vessels is an early marker of bone loss and represents a potential target for improving bone quality via the induction of type H vessels.

Expression and function of the small-conductance Ca2+-activated K+ channel is decreased in urinary bladder smooth muscle cells from female guinea pig with partial bladder outlet obstruction

PURPOSE

Overactive bladder (OAB), usually accompanied by partial bladder outlet obstruction (PBOO), is associated with detrusor overactivity (DO) which is related to the increased urinary bladder smooth muscle (UBSM) cells excitability. Small-conductance Ca²⁺-activated K⁺ (SK) channels play a constitutive regulatory role of UBSM excitability and contractility. PBOO is associated with the decreased SK channels mRNA expression and the attenuated regulative effect of SK channels on UBSM contractility. However, the regulation of SK channels in PBOO UBSM cell excitability is less clear. Here, we tested the hypothesis that PBOO is associated with decreased expression and function of SK channels in UBSM cells and that SK channels are a potential target for the treatment of OAB.

METHODS

Cystometry indicated that DO was achieved 2 weeks after PBOO in female guinea pigs. Using this animal model, we conducted single-cell quantitative reverse transcription-polymerase chain reaction (qRT-PCR) and patch-clamp electrophysiology.

RESULTS

The single-cell qRT-PCR experiments indicated the reduced SK channel mRNA expression in PBOO UBSM cells. Patch-clamp studies revealed that NS309 had a diminished effect on resting membrane potential hyperpolarization via the activation of SK channels in PBOO UBSM cells. Moreover, attenuated whole-cell SK channel currents were demonstrated in PBOO UBSM cells.

CONCLUSIONS

The attenuated expression and function of SK channels, which results in the increased UBSM cells excitability and contributes to DO, was discovered in PBOO UBSM cells, suggesting that SK channels might be potential therapeutic targets for the control of OAB.

Osteogenic Ability Detection of Human Bone Morphogenetic Protein-2 Gene-activated Nano Bone Putty by Reusable Double-Cavity Bone Harvest Chamber

OBJECTIVE

To explore the feasibility of implanting a self-designed reusable double-cavity bone harvest chamber into Guizhou mini-pigs for observation of the osteogenic effect of human bone morphogenetic protein-2 (hBMP-2) gene-activated nano bone putty on bone in growth.

METHODS

Eight healthy 12-month-old female Guizhou mini-pigs were used for the present experiment. In the first operation, empty double-cavity bone harvest chambers (n = 8) were implanted into the femoral metaphysis of the animals as a blank control group. In the second operation, the femoral metaphyses were implanted with the chambers filled by the nano bone putty+hBMP-2 plasmid in one cavity and nothing in the other cavity, respectively (experiment group, n = 8). The time interval between every operation was 3 months. The cavity materials were retrieved and replaced for assessment by gross observation, histological examination, and bone morphology metrology analysis to compare osteogenesis ability and alkaline phosphatase.

RESULTS

Three months after surgery, the nano bone putty+hBMP-2 plasmid in one cavity of the chambers had hard gray and white tissues inside, while the cavities pre-installed with nothing were filled with soft brown tissues. Light microscopy showed new generated bone tissue around the filled material, but only fibrous tissues in the empty cavities. Osteogenesis ability and alkaline phosphatase of the nano bone putty+hBMP-2 plasmid group were significantly higher than those of the blank control group (P < 0.05).

CONCLUSION

The reusable double-cavity bone harvest chamber can be used to observe the osteogenic potential of the hBMP-2 gene-activated nano bone putty.

Effects of piezosurgery in accelerating the movement of orthodontic alveolar bone tooth of rats and the expression mechanism of BMP-2

The aim of the study was to investigate the effects of piezosurgery in accelerating the movement of orthodontic alveolar bone tooth of rats and the expression mechanism of bone morphogenetic protein-2 (BMP-2). Adult male Wistar rats (n=30), with an age range of 14–15 weeks, and an average weight of 250±16 g were used. The animals were randomly divided into the control and observation groups. The rats in the control group were injected with 25-dihydroxyvitamin (1,25-dihydroxycholecalciferol) into their dental ligament. The rats in the observation group were placed with an orthodontic device between the first molar and central incisor in the maxillary. On the first day after animal treatment, piezosurgery stimulation was performed on the first molar in maxillary. The changes of the movement distance of the first molar and gum surface temperature on days 1, 3, 5, 7 and 14 were then compared. Immunohistochemical staining was performed to detect the expression of BMP-2 of periodontal tissue in the tension side of the first molar. Tooth movement distance in the observation group on days 5, 7 and 14 was significantly longer than that in the control group (p<0.05). The gum surface temperature of the observation group was elevated to some extent, peaking after 20 min. BMP-2 mRNA and protein levels in the observation group were significantly higher than those of the control group at days 3, 5, 7 and 14 (p<0.05). In conclusion, piezosurgery may significantly accelerate the movement of orthodontic alveolar bone tooth of rats and be associated with an increasing BMP-2 expression.

Cell Cotransplantation Strategies for Vascularized Craniofacial Bone Tissue Engineering: A Systematic Review and Meta-Analysis of Preclinical In Vivo Studies

The regenerative potential of tissue-engineered bone constructs may be enhanced by in vitro coculture and in vivo cotransplantation of vasculogenic and osteogenic (progenitor) cells. The objective of this study was to systematically review the literature to answer the focused question: In animal models, does cotransplantation of osteogenic and vasculogenic cells enhance bone regeneration in craniofacial defects, compared with solely osteogenic cell-seeded constructs? Following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, electronic databases were searched for controlled animal studies reporting cotransplantation of endothelial cells (ECs) with mesenchymal stem cells (MSCs) or osteoblasts in craniofacial critical size defect (CSD) models. Twenty-two studies were included comparing outcomes of MSC/scaffold versus MSC+EC/scaffold (co)transplantation in calvarial (n = 15) or alveolar (n = 7) CSDs of small (rodents, rabbits) and large animal (minipigs, dogs) models. On average, studies presented with an unclear to high risk of bias. MSCs were derived from autologous, allogeneic, xenogeneic, or human (bone marrow, adipose tissue, periosteum) sources; in six studies, ECs were derived from MSCs by endothelial differentiation. In most studies, MSCs and ECs were cocultured in vitro (2-17 days) before implantation. Coculture enhanced MSC osteogenic differentiation and an optimal MSC:EC seeding ratio of 1:1 was identified. Alloplastic copolymer or composite scaffolds were most often used for in vivo implantation. Random effects meta-analyses were performed for histomorphometric and radiographic new bone formation (%NBF) and vessel formation in rodents' calvarial CSDs. A statistically significant benefit in favor of cotransplantation versus MSC-only transplantation for radiographic %NBF was observed in rat calvarial CSDs (weighted mean difference 7.80% [95% confidence interval: 1.39-14.21]); results for histomorphometric %NBF and vessel formation were inconclusive. Overall, heterogeneity in the meta-analyses was high (I² > 80%). In summary, craniofacial bone regeneration is enhanced by cotransplantation of vasculogenic and osteogenic cells. Although the direction of treatment outcome is in favor of cotransplantation strategies, the magnitude of treatment effect does not seem to be of relevance, unless proven otherwise in clinical studies.

Osteoporosis: the current status of mesenchymal stem cell-based therapy

Osteoporosis, or bone loss, is a progressive, systemic skeletal disease that affects millions of people worldwide. Osteoporosis is generally age related, and it is underdiagnosed because it remains asymptomatic for several years until the development of fractures that confine daily life activities, particularly in elderly people. Most patients with osteoporotic fractures become bedridden and are in a life-threatening state. The consequences of fracture can be devastating, leading to substantial morbidity and mortality of the patients. The normal physiologic process of bone remodeling involves a balance between bone resorption and bone formation during early adulthood. In osteoporosis, this process becomes imbalanced, resulting in gradual losses of bone mass and density due to enhanced bone resorption and/or inadequate bone formation. Several growth factors underlying age-related osteoporosis and their signaling pathways have been identified, such as osteoprotegerin (OPG)/receptor activator of nuclear factor B (RANK)/RANK ligand (RANKL), bone morphogenetic protein (BMP), wingless-type MMTV integration site family (Wnt) proteins and signaling through parathyroid hormone receptors. In addition, the pathogenesis of osteoporosis has been connected to genetics. The current treatment of osteoporosis predominantly consists of antiresorptive and anabolic agents; however, the serious adverse effects of using these drugs are of concern. Cell-based replacement therapy via the use of mesenchymal stem cells (MSCs) may become one of the strategies for osteoporosis treatment in the future.

Hybrid Biomaterial with Conjugated Growth Factors and Mesenchymal Stem Cells for Ectopic Bone Formation

Bone is a highly vascularized tissue and efficient bone regeneration requires neovascularization, especially for critical-sized bone defects. We developed a novel hybrid biomaterial comprising nanocalcium sulfate (nCS) and fibrin hydrogel to deliver mesenchymal stem cells (MSCs) and angiogenic factors, vascular endothelial growth factor (VEGF) and fibroblast growth factor 9 (FGF9), to promote neovascularization and bone formation. MSC and growth factor(s)-loaded scaffolds were implanted subcutaneously into mice to examine their angiogenic and osteogenic potential. Micro CT, alkaline phosphatase activity assay, and histological analysis were used to evaluate bone formation, while immunohistochemistry was employed to assess neovessel formation. The presence of fibrin preserved the nCS scaffold structure and promoted de novo bone formation. In addition, the presence of bone morphogenic protein 2-expressing MSC in nCS and fibrin hydrogels improved bone regeneration significantly. While FGF9 alone had no significant effect, the combination FGF9 and VEGF conjugated in fibrin enhanced neovascularization and bone formation more than 4-fold compared to nCS with MSC. Overall, our results suggested that the combination of nCS (to support bone formation) with a fibrin-based VEGF/FGF9 release system (support vascular formation) is an innovative and effective strategy that significantly enhanced ectopic bone formation in vivo.