BMP-2 gene transfection of bone marrow stromal cells to induce osteoblastic differentiation in a rat calvarial defect model

Local application of zoledronate inhibits early bone resorption and promotes bone formation

Nonunion resulting from early bone resorption is common after bone transplantation surgery. In these patients, instability or osteoporosis causes hyperactive catabolism relative to anabolism, leading to graft resorption instead of fusion. Systemic zoledronate administration inhibits osteoclastogenesis and is widely used to prevent osteoporosis; however, evidence on local zoledronate application is controversial due to osteoblast cytotoxicity, uncontrolled dosing regimens, and local release methods. We investigated the effects of zolendronate on osteoclastogenesis and osteogenesis and explored the corresponding signaling pathways. In vitro cytotoxicity and differentiation of MC3T3E1 cells, rat bone marrow stromal cells (BMSCs) and preosteoclasts (RAW264.7 cells) were evaluated with different zolendronate concentrations. In vivo bone regeneration ability was tested by transplanting different concentrations of zolendronate with β-tricalcium phosphate (TCP) bone substitute into rat femoral critical-sized bone defects. In vitro, zolendronate concentrations below 2.5 × 10-7 M did not compromise viability in the three cell lines and did not promote osteogenic differentiation in MC3T3E1 cells and BMSCs. In RAW264.7 cells, zoledronate inhibited extracellular regulated protein kinases and c-Jun n-terminal kinase signaling, downregulating c-Fos and NFATc1 expression, with reduced expression of fusion-related dendritic cell‑specific transmembrane protein and osteoclast-specific Ctsk and tartrate-resistant acid phosphatase (. In vivo, histological staining revealed increased osteoid formation and neovascularization and reduced fibrotic tissue with 500 μM and 2000 μM zolendronate. More osteoclasts were found in the normal saline group after 6 weeks, and sequential osteoclast formation occurred after zoledronate treatment, indicating inhibition of bone resorption during early callus formation without inhibition of late-stage bone remodeling. In vivo, soaking β-TCP artificial bone with 500 μM or 2000 μM zoledronate is a promising approach for bone regeneration, with potential applications in bone transplantation.

Attributes of Nanomaterials and Nanotopographies for Improved Bone Tissue Engineering and Regeneration

Bone tissue engineering (BTE) is a multidisciplinary area that can solve the limitation of conventional grafting methods by developing viable and biocompatible bone replacements. The three essential components of BTE, i.e., Scaffold material and Cells and Growth factors altogether, facilitate support and guide for bone formation, differentiation of the bone tissues, and enhancement in the cellular activities and bone regeneration. However, there is a scarcity of the appropriate materials that can match the mechanical property as well as functional similarity to native tissue, considering the bone as hard tissue. In such scenarios, nanotechnology can be leveraged upon to achieve the desired aspects of BTE, and that is the key point of this review article. This review article examines the significant areas of nanotechnology research that have an impact on regeneration of bone: (a) scaffold with nanomaterials helps to enhance physicochemical interactions, biocompatibility, mechanical stability, and attachment; (b) nanoparticle-based approaches for delivering bioactive chemicals, growth factors, and genetic material. The article begins with the introduction of components and healing mechanisms of bone and the factors associated with them. The focus of this article is on the various nanotopographies that are now being used in scaffold formation, by describing how they are made, and how these nanotopographies affect the immune system and potential underlying mechanisms. The advantages of 4D bioprinting in BTE by using nanoink have also been mentioned. Additionally, we have investigated the importance of an in silico approach for finding the interaction between drugs and their related receptors, which can help to formulate suitable systems for delivery. This review emphasizes the role of nanoscale approach and how it helps to increase the efficacy of parameters of scaffold as well as drug delivery system for tissue engineering and bone regeneration.

Non-viral gene delivery to human mesenchymal stem cells: a practical guide towards cell engineering

In recent decades, human mesenchymal stem cells (hMSCs) have gained momentum in the field of cell therapy for treating cartilage and bone injuries. Despite the tri-lineage multipotency, proliferative properties, and potent immunomodulatory effects of hMSCs, their clinical potential is hindered by donor variations, limiting their use in medical settings. To address this challenge, gene delivery technologies have emerged as a promising approach to modulate the phenotype and commitment of hMSCs towards specific cell lineages, thereby enhancing osteochondral repair strategies. This review provides a comprehensive overview of current non-viral gene delivery approaches used to engineer MSCs, highlighting key factors such as the choice of nucleic acid or delivery vector, transfection strategies, and experimental parameters. Additionally, it outlines various protocols and methods for qualitative and quantitative evaluation of their therapeutic potential as a delivery system in osteochondral regenerative applications. In summary, this technical review offers a practical guide for optimizing non-viral systems in osteochondral regenerative approaches. hMSCs constitute a key target population for gene therapy techniques. Nevertheless, there is a long way to go for their translation into clinical treatments. In this review, we remind the most relevant transfection conditions to be optimized, such as the type of nucleic acid or delivery vector, the transfection strategy, and the experimental parameters to accurately evaluate a delivery system. This survey provides a practical guide to optimizing non-viral systems for osteochondral regenerative approaches.

Bone Morphogenic Protein and Mesenchymal Stem Cells to Regenerate Bone in Calvarial Defects: A Systematic Review

BACKGROUND

The use of bone morphogenic protein and mesenchymal stem cells has shown promise in promoting bone regeneration in calvarial defects. However, a systematic review of the available literature is needed to evaluate the efficacy of this approach.

METHODS

We comprehensively searched electronic databases using MeSH terms related to skull defects, bone marrow mesenchymal stem cells, and bone morphogenic proteins. Eligible studies included animal studies that used BMP therapy and mesenchymal stem cells to promote bone regeneration in calvarial defects. Reviews, conference articles, book chapters, and non-English language studies were excluded. Two independent investigators conducted the search and data extraction.

RESULTS

Twenty-three studies published between 2010 and 2022 met our inclusion criteria after a full-text review of the forty-five records found in the search. Eight of the 23 studies used mice as models, while 15 used rats. The most common mesenchymal stem cell was bone marrow-derived, followed by adipose-derived. BMP-2 was the most popular. Stem cells were embedded in Scaffold (13), Transduction (7), and Transfection (3), and they were delivered BMP to cells. Each treatment used 2 × 10⁴-1 × 10⁷ mesenchymal stem cells, averaging 2.26 × 10⁶. Most BMP-transduced MSC studies used lentivirus.

CONCLUSIONS

This systematic review examined BMP and MSC synergy in biomaterial scaffolds or alone. BMP therapy and mesenchymal stem cells in calvarial defects, alone, or with a scaffold regenerated bone. This method treats skull defects in clinical trials. The best scaffold material, therapeutic dosage, administration method, and long-term side effects need further study.

Hydrogel armed with Bmp2 mRNA-enriched exosomes enhances bone regeneration

BACKGROUND

Sustained release of bioactive BMP2 (bone morphogenetic protein-2) is important for bone regeneration, while the intrinsic short half-life of BMP2 at protein level cannot meet the clinical need. In this study, we aimed to design Bmp2 mRNA-enriched engineered exosomes, which were then loaded into specific hydrogel to achieve sustained release for more efficient and safe bone regeneration.

RESULTS

Bmp2 mRNA was enriched into exosomes by selective inhibition of translation in donor cells, in which NoBody (non-annotated P-body dissociating polypeptide, a protein that inhibits mRNA translation) and modified engineered BMP2 plasmids were co-transfected. The derived exosomes were named Exo^BMP2+NoBody. In vitro experiments confirmed that Exo^BMP2+NoBody had higher abundance of Bmp2 mRNA and thus stronger osteogenic induction capacity. When loaded into GelMA hydrogel via ally-L-glycine modified CP05 linker, the exosomes could be slowly released and thus ensure prolonged effect of BMP2 when endocytosed by the recipient cells. In the in vivo calvarial defect model, Exo^BMP2+NoBody-loaded GelMA displayed great capacity in promoting bone regeneration.

CONCLUSIONS

Together, the proposed Exo^BMP2+NoBody-loaded GelMA can provide an efficient and innovative strategy for bone regeneration.

Semi-Synthetic Click-Gelatin Hydrogels as Tunable Platforms for 3D Cancer Cell Culture

Basement membrane extracts (BME) derived from Engelbreth-Holm-Swarm (EHS) mouse sarcomas such as Matrigel^® remain the gold standard extracellular matrix (ECM) for three-dimensional (3D) cell culture in cancer research. Yet, BMEs suffer from substantial batch-to-batch variation, ill-defined composition, and lack the ability for physichochemical manipulation. Here, we developed a novel 3D cell culture system based on thiolated gelatin (Gel-SH), an inexpensive and highly controlled raw material capable of forming hydrogels with a high level of biophysical control and cell-instructive bioactivity. We demonstrate the successful thiolation of gelatin raw materials to enable rapid covalent crosslinking upon mixing with a synthetic poly(ethylene glycol) (PEG)-based crosslinker. The mechanical properties of the resulting gelatin-based hydrogels were readily tuned by varying precursor material concentrations, with Young's moduli ranging from ~2.5 to 5.8 kPa. All hydrogels of varying stiffnesses supported the viability and proliferation of MDA-MB-231 and MCF-7 breast cancer cell lines for 14 and 21 days of cell culture, respectively. Additionally, the gelatin-based hydrogels supported the growth, viability, and osteogenic differentiation of patient-derived preosteoblasts over 28 days of culture. Collectively, our data demonstrate that gelatin-based biomaterials provide an inexpensive and tunable 3D cell culture platform that may overcome the limitations of traditional BMEs.

Recent advances in gene therapy for bone tissue engineering

Autografting, a major treatment for bone fractures, has potential risks related to the required surgery and disease transmission. Bone morphogenetic proteins (BMPs) are the most common osteogenic factors used for bone-healing applications. However, BMP delivery can have shortcomings such as a short half-life and the high cost of manufacturing the recombinant proteins. Gene delivery methods have demonstrated promising alternative strategies for producing BMPs or other osteogenic factors using engineered cells. These approaches can also enable temporal overexpression and local production of the therapeutic genes in the target tissues. This review addresses recent progress on engineered viral, non-viral, and RNA-mediated gene delivery systems that are being used for bone repair and regeneration. Advances in clustered regularly interspaced short palindromic repeats/Cas9 genome engineering for bone tissue regeneration also is discussed.

Halide-containing bioactive glasses enhance osteogenesis in vitro and in vivo

The application of bone substitutes to reconstruct bone defects is a strategy for repairing alveolar bone loss caused by periodontal disease. Bioactive glasses (BGs) are attractive synthetic bone substitutes owing to their abilities to degrade, form bone-like mineral and stimulate bone regeneration. Our previous studies showed that the incorporation of fluoride into alkali-free bioactive silicate glass promoted osteogenesis to some extent in vitro, while the incorporation of chloride facilitated glass degradation and accelerated the formation of hydroxyapatite. However, whether there is a synergistic effect of incorporating fluoride and chloride on further enhancement of osteogenesis and angiogenesis in vitro and in vivo was not known. Therefore, we synthesized three halide-containing BGs with fluoride only, or chloride only, or mixed fluoride and chloride, investigated their physicochemical properties and osteogenic and angiogenic effects both in vitro and in vivo. The results showed that the addition of both fluoride and chloride in a bioactive silicate glass could combine the structural roles of both, leading to a faster apatite formation than the glass with the presence of fluoride only and a more stable fluorapatite formation than the glass with the presence of chloride only, which formed hydroxyapatite upon immersion. The studied BGs were cytocompatible, as suggested by the cytotoxicity evaluation of hPDLSCs cultivated in the extracted BGs-conditioned culture media. More importantly, these BGs stimulated osteogenic differentiation of hPDLSCs without adding growth factors as indicated by the fact that BGs-conditioned media up-regulated the expression of BMP-2, OPN and VEGF of hPDLSCs and promoted the formation of bone nodules and collagen in vitro. By comparison, the incorporation of fluoride facilitated the expression of osteogenic-related biomarkers and bone nodule formation preferentially, while the incorporation of chloride induced the expression of angiogenic-related biomarkers and collagen formation. The in vivo investigation results demonstrated that the developed halide-containing BGs accelerated the process of bone regeneration, while the glass with mixed fluoride and chloride showed the most significant promotion effect among the three BGs. Therefore, our findings revealed a synergistic effect of incorporating fluoride and chloride into a BG on osteogenesis and angiogenesis in vitro and in vivo and highlighted the potential of fluoride and chloride containing bioactive glasses being bone substitutes for clinical use.

Emerging roles of growth factors in osteonecrosis of the femoral head

Osteonecrosis of the femoral head (ONFH) is a potentially disabling orthopedic condition that requires total hip arthroplasty in most late-stage cases. However, mechanisms underlying the development of ONFH remain unknown, and the therapeutic strategies remain limited. Growth factors play a crucial role in different physiological processes, including cell proliferation, invasion, metabolism, apoptosis, and stem cell differentiation. Recent studies have reported that polymorphisms of growth factor-related genes are involved in the pathogenesis of ONFH. Tissue and genetic engineering are attractive strategies for treating early-stage ONFH. In this review, we summarized dysregulated growth factor-related genes and their role in the occurrence and development of ONFH. In addition, we discussed their potential clinical applications in tissue and genetic engineering for the treatment of ONFH.

Engineering stem cells to produce exosomes with enhanced bone regeneration effects: an alternative strategy for gene therapy

Background

Exosomes derived from stem cells have been widely studied for promoting regeneration and reconstruction of multiple tissues as “cell-free” therapies. However, the applications of exosomes have been hindered by limited sources and insufficient therapeutic potency.

Results

In this study, a stem cell-mediated gene therapy strategy is developed in which mediator mesenchymal stem cells are genetically engineered by bone morphogenetic protein-2 gene to produce exosomes (MSC-BMP2-Exo) with enhanced bone regeneration potency. This effect is attributed to the synergistic effect of the content derived from MSCs and the up-regulated BMP2 gene expression. The MSC-BMP2-Exo also present homing ability to the injured site. The toxic effect of genetical transfection vehicles is borne by mediator MSCs, while the produced exosomes exhibit excellent biocompatibility. In addition, by plasmid tracking, it is interesting to find a portion of plasmid DNA can be encapsulated by exosomes and delivered to recipient cells.

Conclusions

In this strategy, engineered MSCs function as cellular factories, which effectively produce exosomes with designed and enhanced therapeutic effects. The accelerating effect in bone healing and the good biocompatibility suggest the potential clinical application of this strategy.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01347-3.

Periodontal Ligament Stem Cell-Derived Small Extracellular Vesicles Embedded in Matrigel Enhance Bone Repair Through the Adenosine Receptor Signaling Pathway

Purpose

Small extracellular vesicles (sEVs) are natural biocarriers for biomolecule transfer between cells and promising therapeutic strategies for bone defect repair. In this study, human periodontal ligament stem cell (PDLSC)-derived sEVs (P-EVs) were immobilized in Matrigel to establish a topical cell-free transplantation strategy for bone repair.

Methods

PDLSCs were cultured and P-EVs were isolated from the culture supernatant. In a rat bilateral calvarial defect model, P-EV/Matrigel was plugged into one defect and PBS/Matrigel was applied to the other. Bone repair in vivo was assessed by micro-computed tomography, histomorphometry, and immunohistochemical staining. In vitro, we investigated the effects of P-EVs on the proliferation and migration capabilities of bone marrow mesenchymal stem cells (BMMSCs) and explored the potential mechanism of action.

Results

The in vivo study showed that P-EV/Matrigel accelerated bone tissue repair by increasing cell infiltration when compared with the control. In vitro, P-EVs enhanced proliferation and migration of BMMSCs via increased phosphorylation of AKT and extracellular signal-regulated kinase 1/2 (ERK1/2). The role of P-EV-induced adenosine receptor signaling in AKT and ERK1/2 phosphorylation was a key mediator during enhanced BMMSC migration.

Conclusion

These results are the first to demonstrate that P-EVs accelerated the repair of bone defects, partially through promoting cell proliferation and migration. P-EV/Matrigel, which combines topical EV-implantation and extracellular matrix scaffolds, provides a new cell-free strategy for bone tissue repair.

A Narrative Review of Cell-Based Approaches for Cranial Bone Regeneration

Current cranial repair techniques combine the use of autologous bone grafts and biomaterials. In addition to their association with harvesting morbidity, autografts are often limited by insufficient quantity of bone stock. Biomaterials lead to better outcomes, but their effectiveness is often compromised by the unpredictable lack of integration and structural failure. Bone tissue engineering offers the promising alternative of generating constructs composed of instructive biomaterials including cells or cell-secreted products, which could enhance the outcome of reconstructive treatments. This review focuses on cell-based approaches with potential to regenerate calvarial bone defects, including human studies and preclinical research. Further, we discuss strategies to deliver extracellular matrix, conditioned media and extracellular vesicles derived from cell cultures. Recent advances in 3D printing and bioprinting techniques that appear to be promising for cranial reconstruction are also discussed. Finally, we review cell-based gene therapy approaches, covering both unregulated and regulated gene switches that can create spatiotemporal patterns of transgenic therapeutic molecules. In summary, this review provides an overview of the current developments in cell-based strategies with potential to enhance the surgical armamentarium for regenerating cranial vault defects.

Biofabrication of Gingival Fibroblast Cell-Laden Collagen/Strontium-Doped Calcium Silicate 3D-Printed Bi-Layered Scaffold for Osteoporotic Periodontal Regeneration

Periodontal disease is a chronic disease that can lead to lose teeth and even tooth loss if left untreated. Osteoporosis and periodontal disease share similar characteristics and associated factors. Current regenerative techniques for periodontal diseases are ineffective in restoring complete function and structural integrity of periodontium due to unwanted migration of cells. In this study, we applied the concept of guided tissue regeneration (GTR) and 3D fabricated gingival fibroblast cell-laden collagen/strontium-doped calcium silicate (SrCS) bi-layer scaffold for periodontal regeneration. The results revealed that the bioactive SrCS had a hydroxyapatite formation on its surface after 14 days of immersion and that SrCS could release Sr and Si ions even after 6 months of immersion. In addition, in vitro results showed that the bi-layer scaffold enhanced secretion of FGF-2, BMP-2, and VEGF from human gingival fibroblasts and increased secretion of osteogenic-related proteins ALP, BSP, and OC from WJMSCs. In vivo studies using animal osteoporotic models showed that the 3D-printed cell-laden collagen/SrCS bi-layer scaffold was able to enhance osteoporotic bone regeneration, as seen from the increased Tb.Th and BV/TV ratio and the histological stains. In conclusion, it can be seen that the bi-layer scaffolds enhanced osteogenesis and further showed that guided periodontal regeneration could be achieved using collagen/SrCS scaffolds, thus making it a potential candidate for future clinical applications.

Exosomal miR-335 derived from mature dendritic cells enhanced mesenchymal stem cell-mediated bone regeneration of bone defects in athymic rats

BACKGROUND

Transplantation of bone marrow-derived mesenchymal stem cells (BM-MSCs) embedded in a bio-compatible matrix has been demonstrated as a promising strategy for the treatment of bone defects. This study was designed to explore the effect and mechanism of exosomes derived from mature dendritic cells (mDC-Exo) on the BM-MSCs-mediated bone regeneration using the matrix support in an athymic rat model of femoral bone defect.

METHODS

The BM-MSCs were isolated from rats and incubated with osteoblast induction medium, exosomes derived from immature DCs (imDC-Exo), mDC-Exo, and miR-335-deficient mDC-Exo. BM-MSCs treated without or with mDC-Exo were embedded in a bio-compatible matrix (Orthoss®) and then implanted into the femoral bone defect of athymic rats.

RESULTS

mDC-Exo promoted the proliferation and osteogenic differentiation of BM-MSCs by transferring miR-335. Mechanistically, exosomal miR-335 inhibited Hippo signaling by targeting large tongue suppressor kinase 1 (LATS1) and thus promoted the proliferation and osteogenic differentiation of BM-MSCs. Animal experiments showed that mDC-Exo enhanced BM-MSCs-mediated bone regeneration after bone defect, and this effect was abrogated when miR-335 expression was inhibited in mDC-Exo.

CONCLUSION

mDC-Exo promoted osteogenic differentiation of BM-MSCs and enhanced BM-MSCs-mediated bone regeneration after femoral bone defect in athymic rats by transferring miR-335.

Incorporation of Calcium Sulfate Dihydrate into a Mesoporous Calcium Silicate/Poly-ε-Caprolactone Scaffold to Regulate the Release of Bone Morphogenetic Protein-2 and Accelerate Bone Regeneration

Tissue engineering and scaffolds play an important role in tissue regeneration by supporting cell adhesion, proliferation, and differentiation. The design of a scaffold is critical in determining its feasibility, and it is critical to note that each tissue is unique in terms of its morphology and composition. However, calcium-silicate-based scaffolds are undegradable, which severely limits their application in bone regeneration. In this study, we developed a biodegradable mesoporous calcium silicate (MS)/calcium sulfate (CS)/poly-ε-caprolactone (PCL) composite and fabricated a composite scaffold with 3D printing technologies. In addition, we were able to load bone morphogenetic protein-2 (BMP-2) into MS powder via a one-step immersion procedure. The results demonstrated that the MS/CS scaffold gradually degraded within 3 months. More importantly, the scaffold exhibited a gradual release of BMP-2 throughout the test period. The adhesion and proliferation of human dental pulp stem cells on the MS/CS/BMP-2 (MS/CS/B) scaffold were significantly greater than that on the MS/CS scaffold. It was also found that cells cultured on the MS/CS/B scaffold had significantly higher levels of alkaline phosphatase activity and angiogenic-related protein expression. The MS/CS/B scaffold promoted the growth of new blood vessels and bone regeneration within 4 weeks of implantation in rabbits with induced critical-sized femoral defects. Therefore, it is hypothesized that the 3D-printed MS/CS/B scaffold can act both as a conventional BMP-2 delivery system and as an ideal osteoinductive biomaterial for bone regeneration.

Non-viral Gene Delivery Methods for Bone and Joints

Viral carrier transport efficiency of gene delivery is high, depending on the type of vector. However, viral delivery poses significant safety concerns such as inefficient/unpredictable reprogramming outcomes, genomic integration, as well as unwarranted immune responses and toxicity. Thus, non-viral gene delivery methods are more feasible for translation as these allow safer delivery of genes and can modulate gene expression transiently both in vivo, ex vivo, and in vitro. Based on current studies, the efficiency of these technologies appears to be more limited, but they are appealing for clinical translation. This review presents a summary of recent advancements in orthopedics, where primarily bone and joints from the musculoskeletal apparatus were targeted. In connective tissues, which are known to have a poor healing capacity, and have a relatively low cell-density, i.e., articular cartilage, bone, and the intervertebral disk (IVD) several approaches have recently been undertaken. We provide a brief overview of the existing technologies, using nano-spheres/engineered vesicles, lipofection, and in vivo electroporation. Here, delivery for microRNA (miRNA), and silencing RNA (siRNA) and DNA plasmids will be discussed. Recent studies will be summarized that aimed to improve regeneration of these tissues, involving the delivery of bone morphogenic proteins (BMPs), such as BMP2 for improvement of bone healing. For articular cartilage/osteochondral junction, non-viral methods concentrate on targeted delivery to chondrocytes or MSCs for tissue engineering-based approaches. For the IVD, growth factors such as GDF5 or GDF6 or developmental transcription factors such as Brachyury or FOXF1 seem to be of high clinical interest. However, the most efficient method of gene transfer is still elusive, as several preclinical studies have reported many different non-viral methods and clinical translation of these techniques still needs to be validated. Here we discuss the non-viral methods applied for bone and joint and propose methods that can be promising in clinical use.

The Masquelet technique: Current concepts, animal models, and perspectives

Bone reconstruction within a critical-sized defect remains a real challenge in orthopedic surgery. The Masquelet technique is an innovative, two-step therapeutic approach for bone reconstruction in which the placement of a poly (methylmethacrylate) spacer into the bone defect induces the neo-formation of a tissue called "induced membrane." This surgical technique has many advantages and is often preferred to a vascularized bone flap or Ilizarov's technique. Although the Masquelet technique has achieved high clinical success rates since its development by Alain-Charles Masquelet in the early 2000s, very little is known about how the process works, and few animal models of membrane induction have been developed. Our successful use of this technique in the clinic and our interest in the mechanisms of tissue regeneration (notably bone regeneration) prompted us to develop a surgical model of the Masquelet technique in rats. Here, we provide a comprehensive review of the literature on animal models of membrane induction, encompassing the defect site, the surgical procedure, and the histologic and osteogenic properties of the induced membrane. We also discuss the advantages and disadvantages of those models to facilitate efforts in characterizing the complex biological mechanisms that underlie membrane induction.

Therapeutic Applications of Genes and Gene-Engineered Mesenchymal Stem Cells for Femoral Head Necrosis

Osteonecrosis of the femoral head (ONFH) is a common and disabling joint disease. Although there is no clear consensus on the complex pathogenic mechanism of ONFH, trauma, abuse of glucocorticoids, and alcoholism are implicated in its etiology. The therapeutic strategies are still limited, and the clinical outcomes are not satisfactory. Mesenchymal stem cells (MSCs) have been shown to exert a positive impact on ONFH in preclinical experiments and clinical trials. The beneficial properties of MSCs are due, at least in part, to their ability to home to the injured tissue, secretion of paracrine signaling molecules, and multipotentiality. Nevertheless, the regenerative capacity of transplanted cells is impaired by the hostile environment of necrotic tissue in vivo, limiting their clinical efficacy. Recently, genetic engineering has been introduced as an attractive strategy to improve the regenerative properties of MSCs in the treatment of early-stage ONFH. This review summarizes the function of several genes used in the engineering of MSCs for the treatment of ONFH. Further, current challenges and future perspectives of genetic manipulation of MSCs are discussed. The notion of genetically engineered MSCs functioning as a "factory" that can produce a significant amount of multipotent and patient-specific therapeutic product is emphasized.

Multifunctional Triple-Layered Composite Scaffolds Combining Platelet-Rich Fibrin Promote Bone Regeneration

There has been substantial progress made in the development of bone regeneration materials, driven by the deficiencies that exist in current clinical products, such as finite sources, donor site complications, and potential for disease transmission. To overcome these shortcomings, multifunctional scaffolds should be developed to integrate the relationship among osteoinduction, osteoconduction, and osseointegration. In this study, we fabricated polycaprolactone/gelatin (PG) nanofiber films by electrospinning, to act as barriers against connective tissue migration into bone defect sites; chitosan/poly (γ-glutamic acid)/hydroxyapatite (CPH) hydrogels were formed by electrostatic interaction and lyophilization, to exert osteoconduction; and platelet-rich fibrin (PRF) was extracted from rat abdominal aorta and combined with composite scaffolds, to promote bone induction through the release of growth factors. Hydrogels were immersed in simulated body fluid (SBF) for 1 month to investigate mineralization in vitro. Cytocompatibility, cell barrier effect, and osteogenic differentiation were also explored in vitro. The ability to effectively regenerate bone was analyzed by implantation of triple-layered composite scaffolds into rat calvarial defects in vivo. Size-matched hydrogel filled the defect site, and then, fresh PRF was applied to the hydrogel surface. Finally, P2G3 nanofiber films were applied and attached to the surrounding soft tissue. In short, we fabricated multifunctional triple-layered scaffolds by combining the advantages of osteoinduction, osteoconduction, and osseointegration, which could give full play to the role of PRF in bone regeneration and provide new and pragmatic concepts for bone tissue regeneration in clinical applications.

Nanomaterials for bone tissue regeneration: updates and future perspectives

Joint replacement and bone reconstructive surgeries are on the rise globally. Current strategies for implants and bone regeneration are associated with poor integration and healing resulting in repeated surgeries. A multidisciplinary approach involving basic biological sciences, tissue engineering, regenerative medicine and clinical research is required to overcome this problem. Considering the nanostructured nature of bone, expertise and resources available through recent advancements in nanobiotechnology enable researchers to design and fabricate devices and drug delivery systems at the nanoscale to be more compatible with the bone tissue environment. The focus of this review is to present the recent progress made in the rationale and design of nanomaterials for tissue engineering and drug delivery relevant to bone regeneration.

ECM coating modification generated by optimized decellularization process improves functional behavior of BMSCs

Bone mesenchymal stem cells (BMSCs) have been widely applied in tissue engineering and regenerative medicine. However, small number of BMSCs and loss of stem cell characteristics after expansion in vitro limited clinical use of BMSCs. In the present study, osteoblasts were cultured to lay down extracellular matrix (ECM) and then the cells were removed (decellularization) to generate ECM coating substrates. The decellularization process was optimized to maximally remove cells and cellular components, along with integrated ECM retained which was demonstrated to be beneficial for BMSCs expansion in vitro. After decellularization, only less than 2% of residual DNA and cellular proteins were detected in TFFF-ECM (decellularized by triton X-100 (T) and three freeze/thaw cycles (FFF)), which was much less than that in TN-ECM generated by traditional decellularization method (triton X-100 (T) and NH₄OH (N)). Meanwhile, ECM components and structure were preserved best after decellularization by TFFF method. More ECM proteins were detected, and structure proteins (fibronectin and collagen) exhibited as classic network fibers in TFFF-ECM. Functionally, all kinds of decellularized ECM (dECM) were demonstrated to promote BMSCs proliferation and osteogenic differentiation capacity, thus maintain the stemness of BMSCs. Importantly, cells cultured on TFFF-ECM grew faster than the cells on other kinds of dECM at early stage and TFFF-ECM was beneficial to preserve stemness of BMSCs with high expression of OCT4 and NANOG when cultured in vitro. Proteomic analysis showed the proteins in ECM functioned in multiple biological activities and signaling pathways, which contributed to stemness maintenance of BMSC. Thus, the mild decellularization process optimized in this study enhanced the effectiveness of dECM for BMSCs culture in vitro and maybe further applied to BMSCs based tissue repair.

Bone regeneration in Ds-Red pig calvarial defect using allogenic transplantation of EGFP-pMSCs - A comparison of host cells and seeding cells in the scaffold

Background

Cells, scaffolds, and factors are the triad of regenerative engineering; however, it is difficult to distinguish whether cells in the regenerative construct are from the seeded cells or host cells via the host blood supply. We performed a novel in vivo study to transplant enhanced green fluorescent pig mesenchymal stem cells (EGFP-pMSCs) into calvarial defect of DsRed pigs. The cell distribution and proportion were distinguished by the different fluorescent colors through the whole regenerative period.

Method/Results

Eight adult domestic Ds-Red pigs were treated with five modalities: empty defects without scaffold (group 1); defects filled only with scaffold (group 2); defects filled with osteoinduction medium-loaded scaffold (group 3); defects filled with 5 x 10³ cells/scaffold (group 4); and defects filled with 5 x 10⁴ cells/scaffold (group 5). The in vitro cell distribution, morphology, osteogenic differentiation, and fluorescence images of groups 4 and 5 were analyzed. Two animals were sacrificed at 1, 2, 3, and 4 weeks after transplantation. The in vivo fluorescence imaging and quantification data showed that EGFP-pMSCs were represented in the scaffolds in groups 4 and 5 throughout the whole regenerative period. A higher seeded cell density resulted in more sustained seeded cells in bone regeneration compared to a lower seeded cell density. Host cells were recruited by seeded cells if enough space was available in the scaffold. Host cells in groups 1 to 3 did not change from the 1st week to 4th week, which indicates that the scaffold without seeded cells cannot recruit host cells even when enough space is available for cell ingrowth. The histological and immunohistochemical data showed that more cells were involved in osteogenesis in scaffolds with seeded cells.

Conclusion

Our in vivo results showed that more seeded cells recruit more host cells and that both cell types participate in osteogenesis. These results suggest that scaffolds without seeded cells may not be effective in bone transplantation.

Osteogenesis and angiogenesis are simultaneously enhanced in BMP2-/VEGF-transfected adipose stem cells through activation of the YAP/TAZ signaling pathway

While bone has the capability to heal itself, there is a great difficulty in reconstituting large bone defects created by heavy trauma or the resection of malignant tumors.