Exosomes: A Tool for Bone Tissue Engineering

The cell membrane as biofunctional material for accelerated bone repair

The cell (plasma) membrane is enriched with numerous receptors, ligands, enzymes, and phospholipids that play important roles in cell-cell and cell-extracellular matrix interactions governing, for instance, tissue development and repair. We previously showed that plasma membrane nanofragments (PMNFs) act as nucleation sites for bone formation in vivo, and induce in vitro mineralization within 1 day. In this study, we optimized the methods for generating, isolating, and applying PMNFs as a cell-free therapeutic to expedite bone defect repair. The PMNFs were isolated from different mouse cell lines (chondrocytes, osteoblasts, and fibroblasts), pre-conditioned, lyophilized, and subsequently transplanted into 2 mm critical-sized calvarial defects in mice (n = 75). The PMNFs from chondrocytes, following a 3-day pre-incubation, significantly accelerated bone repair within 2 weeks, through a coordinated attraction of macrophages, endothelial cells, and osteoblasts to the healing site. In vitro experiments confirmed that PMNFs enhanced cell adhesion. Comparison of the PMNF efficacy with phosphatidylserine, amorphous calcium phosphate (ACP), and living cells confirmed the unique ability of PMNFs to promote accelerated bone repair. Importantly, PMNFs promoted nearly complete integration of the regenerated bone with native tissue after 6 weeks (% non-integrated bone area = 15.02), contrasting with the partial integration (% non-integrated bone area = 56.10; p < 0.01, Student's test) with transplantation of ACP. Vickers microhardness tests demonstrated that the regenerated bone after 6 weeks (30.10 ± 1.75) exhibited hardness similar to native bone (31.07 ± 2.46). In conclusion, this is the first study to demonstrate that cell membrane can be a promising cell-free material with multifaceted biofunctional properties that promote accelerated bone repair. STATEMENT OF SIGNIFICANCE.

Role of Adipose-Derived Mesenchymal Stem Cells in Bone Regeneration

Bone regeneration involves multiple factors such as tissue interactions, an inflammatory response, and vessel formation. In the event of diseases, old age, lifestyle, or trauma, bone regeneration can be impaired which could result in a prolonged healing duration or requiring an external intervention for repair. Currently, bone grafts hold the golden standard for bone regeneration. However, several limitations hinder its clinical applications, e.g., donor site morbidity, an insufficient tissue volume, and uncertain post-operative outcomes. Bone tissue engineering, involving stem cells seeded onto scaffolds, has thus been a promising treatment alternative for bone regeneration. Adipose-derived mesenchymal stem cells (AD-MSCs) are known to hold therapeutic value for the treatment of various clinical conditions and have displayed feasibility and significant effectiveness due to their ease of isolation, non-invasive, abundance in quantity, and osteogenic capacity. Notably, in vitro studies showed AD-MSCs holding a high proliferation capacity, multi-differentiation potential through the release of a variety of factors, and extracellular vesicles, allowing them to repair damaged tissues. In vivo and clinical studies showed AD-MSCs favoring better vascularization and the integration of the scaffolds, while the presence of scaffolds has enhanced the osteogenesis potential of AD-MSCs, thus yielding optimal bone formation outcomes. Effective bone regeneration requires the interplay of both AD-MSCs and scaffolds (material, pore size) to improve the osteogenic and vasculogenic capacity. This review presents the advances and applications of AD-MSCs for bone regeneration and bone tissue engineering, focusing on the in vitro, in vivo, and clinical studies involving AD-MSCs for bone tissue engineering.

MicroRNA Nano-Shuttles: Engineering Extracellular Vesicles as a Cutting-Edge Biotechnology Platform for Clinical Use in Therapeutics

Extracellular vesicles (EVs) are nano-sized, membranous transporters of various active biomolecules with inflicting phenotypic capabilities, that are naturally secreted by almost all cells with a promising vantage point as a potential leading drug delivery platform. The intrinsic characteristics of their low toxicity, superior structural stability, and cargo loading capacity continue to fuel a multitude of research avenues dedicated to loading EVs with therapeutic and diagnostic cargos (pharmaceutical compounds, nucleic acids, proteins, and nanomaterials) in attempts to generate superior natural nanoscale delivery systems for clinical application in therapeutics. In addition to their well-known role in intercellular communication, EVs harbor microRNAs (miRNAs), which can alter the translational potential of receiving cells and thus act as important mediators in numerous biological and pathological processes. To leverage this potential, EVs can be structurally engineered to shuttle therapeutic miRNAs to diseased recipient cells as a potential targeted 'treatment' or 'therapy'. Herein, this review focuses on the therapeutic potential of EV-coupled miRNAs; summarizing the biogenesis, contents, and function of EVs, as well as providing both a comprehensive discussion of current EV loading techniques and an update on miRNA-engineered EVs as a next-generation platform piloting benchtop studies to propel potential clinical translation on the forefront of nanomedicine.

Mesenchymal Stem Cell-Derived Extracellular Vesicles in Bone-Related Diseases: Intercellular Communication Messengers and Therapeutic Engineering Protagonists

Extracellular vesicles (EVs) can deliver various bioactive molecules among cells, making them promising diagnostic and therapeutic alternatives in diseases. Mesenchymal stem cell-derived EVs (MSC-EVs) have shown therapeutic potential similar to MSCs but with drawbacks such as lower yield, reduced biological activities, off-target effects, and shorter half-lives. Improving strategies utilizing biotechniques to pretreat MSCs and enhance the properties of released EVs, as well as modifying MSC-EVs to enhance targeting abilities and achieve controlled release, shows potential for overcoming application limitations and enhancing therapeutic effects in treating bone-related diseases. This review focuses on recent advances in functionalizing MSC-EVs to treat bone-related diseases. Firstly, we underscore the significance of MSC-EVs in facilitating crosstalk between cells within the skeletal environment. Secondly, we highlight strategies of functional-modified EVs for treating bone-related diseases. We explore the pretreatment of stem cells using various biotechniques to enhance the properties of resulting EVs, as well as diverse approaches to modify MSC-EVs for targeted delivery and controlled release. Finally, we address the challenges and opportunities for further research on MSC-EVs in bone-related diseases.

Effect of Dimethyloxalylglycine on Stem Cells Osteogenic Differentiation and Bone Tissue Regeneration-A Systematic Review

Dimethyloxalylglycine (DMOG) has been found to stimulate osteogenesis and angiogenesis of stem cells, promoting neo-angiogenesis in bone tissue regeneration. In this review, we conducted a comprehensive search of the literature to investigate the effects of DMOG on osteogenesis and bone regeneration. We screened the studies based on specific inclusion criteria and extracted relevant information from both in vitro and in vivo experiments. The risk of bias in animal studies was evaluated using the SYRCLE tool. Out of the 174 studies retrieved, 34 studies met the inclusion criteria (34 studies were analyzed in vitro and 20 studies were analyzed in vivo). The findings of the included studies revealed that DMOG stimulated stem cells' differentiation toward osteogenic, angiogenic, and chondrogenic lineages, leading to vascularized bone and cartilage regeneration. Addtionally, DMOG demonstrated therapeutic effects on bone loss caused by bone-related diseases. However, the culture environment in vitro is notably distinct from that in vivo, and the animal models used in vivo experiments differ significantly from humans. In summary, DMOG has the ability to enhance the osteogenic and angiogenic differentiation potential of stem cells, thereby improving bone regeneration in cases of bone defects. This highlights DMOG as a potential focus for research in the field of bone tissue regeneration engineering.

Functionalization of Ceramic Scaffolds with Exosomes from Bone Marrow Mesenchymal Stromal Cells for Bone Tissue Engineering

The functionalization of bone substitutes with exosomes appears to be a promising technique to enhance bone tissue formation. This study investigates the potential of exosomes derived from bone marrow mesenchymal stromal cells (BMSCs) to improve bone healing and bone augmentation when incorporated into wide open-porous 3D-printed ceramic Gyroid scaffolds. We demonstrated the multipotent characteristics of BMSCs and characterized the extracted exosomes using nanoparticle tracking analysis and proteomic profiling. Through cell culture experimentation, we demonstrated that BMSC-derived exosomes possess the ability to attract cells and significantly facilitate their differentiation into the osteogenic lineage. Furthermore, we observed that scaffold architecture influences exosome release kinetics, with Gyroid scaffolds exhibiting slower release rates compared to Lattice scaffolds. Nevertheless, in vivo implantation did not show increased bone ingrowth in scaffolds loaded with exosomes, suggesting that the scaffold microarchitecture and material were already optimized for osteoconduction and bone augmentation. These findings highlight the lack of understanding about the optimal delivery of exosomes for osteoconduction and bone augmentation by advanced ceramic scaffolds.

Engineered exosomes and composite biomaterials for tissue regeneration

Exosomes, which are small vesicles enclosed by a lipid bilayer and released by many cell types, are widely dispersed and have garnered increased attention in the field of regenerative medicine due to their ability to serve as indicators of diseases and agents with therapeutic potential. Exosomes play a crucial role in mediating intercellular communication through the transfer of many biomolecules, including proteins, lipids, RNA, and other molecular constituents, between cells. The targeted transport of proteins and nucleic acids to specific cells has the potential to enhance or impair specific biological functions. Exosomes have many applications, and they can be used alone or in combination with other therapeutic approaches. The examination of the unique attributes and many functions of these factors has emerged as a prominent field of study in the realm of biomedical research. This manuscript summarizes the origins and properties of exosomes, including their structural, biological, physical, and chemical aspects. This paper offers a complete examination of recent progress in tissue repair and regenerative medicine, emphasizing the possible implications of these methods in forthcoming tissue regeneration attempts.

Immediate implantation of ultrafine fiber slow-release system based on cell electrospinning to induce osteogenesis of mesenchymal stem cells

This study presents the development and evaluation of a poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB) ultrafine fiber slow-release system for in vivo osteogenic induction of human umbilical cord mesenchymal stem cells (HUCMSCs). Utilizing dual-nozzle and cell electrospinning techniques, the system encapsulates L-ascorbic acid-2-phosphate magnesium (ASP), β-glycerophosphate sodium and dexamethasone (DEX) within the fibers, ensuring sustained osteogenic differentiation. The scaffold's morphology, characterization, hydrophilicity, mechanical properties and cellular behavior were examined. Immediate subcutaneous implantation in rabbits was conducted to observe its ectopic osteogenic induction effect. Successfully fabricated P34HB ultrafine fiber slow-release system. Characterization confirmed the uniform distribution of HUCMSCs and inducing components within the scaffold, with no chemical reactions affecting the active components. In vitro tests showcased a prolonged release of DEX and ASP, while biocompatibility assays highlighted the scaffold's suitability for cellular growth. Alizarin Red, type I collagen, and osteopontin (OPN) staining verified the scaffold's potent osteogenic induction effect on HUCMSCs. Notably, immediate implantation into New Zealand White rabbits led to significant new bone formation within 8 weeks. These findings underscore the system's potential for immediate in vivo implantation without prior in vitro induction, marking a promising advancement in bone tissue engineering.

Novel scaffold platforms for simultaneous induction osteogenesis and angiogenesis in bone tissue engineering: a cutting-edge approach

Despite the recent advances in the development of bone graft substitutes, treatment of critical size bone defects continues to be a significant challenge, especially in the elderly population. A current approach to overcome this challenge involves the creation of bone-mimicking scaffolds that can simultaneously promote osteogenesis and angiogenesis. In this context, incorporating multiple bioactive agents like growth factors, genes, and small molecules into these scaffolds has emerged as a promising strategy. To incorporate such agents, researchers have developed scaffolds incorporating nanoparticles, including nanoparticulate carriers, inorganic nanoparticles, and exosomes. Current paper provides a summary of the latest advancements in using various bioactive agents, drugs, and cells to synergistically promote osteogenesis and angiogenesis in bone-mimetic scaffolds. It also discusses scaffold design properties aimed at maximizing the synergistic effects of osteogenesis and angiogenesis, various innovative fabrication strategies, and ongoing clinical studies.

Exosome Cell Origin Affects In Vitro Markers of Tendon Repair in Ovine Macrophages and Tenocytes

Tendon injuries and disease are resistant to surgical repair; thus, adjunct therapies are widely investigated, especially mesenchymal stromal cells (MSCs) and, more recently, their extracellular vesicles (MSCdEVs), for example, exosomes. Thought to act on resident and infiltrating immune cells, the role of MSCdEVs in paracrine signaling is of great interest. This study investigated how MSCdEVs differ from analogs derived from resident (tenocyte) populations (TdEV). As macrophages play a significant role in tendon maintenance and repair, macrophage signaling was compared by cytokine quantification using a multiplexed immunoassay and tenocyte migration by in vitro scratch-wound analysis. TdEV-treated macrophages decreased IL-1 and increased MIP-1 and CXCL8 expression. In addition, macrophage signaling favored collagen synthesis and tenocyte bioactivity, while reducing proangiogenic signaling when TdEVs were used in place of MSCdEVs. These in vitro data demonstrate a differential influence of exosomes on macrophage signaling, according to cell source, supporting that local cell-derived exosomes may preferentially drive healing by different means with possible different outcomes compared to MSCdEVs. Impact Statement Adipose-derived mesenchymal stromal cell (AdMSC) exosomes (EVs) can improve tendon mechanical resilience, tissue organization, and M2 macrophage phenotype predominance in response to tendon injury. This active area of investigation drives great interest in the function of these exosomes as adjunct therapies for tendon disease, particularly rotator cuff tendinopathy. However, little is known about the effects of EVs as a function of cell source, nor regarding their efficacy in preclinical translational ovine models. Herein we demonstrate a differential effect of exosomes as a function of cell source, tenocyte compared to AdMSCs, on macrophage signaling and tenocyte migration of ovine cells.

Mesenchymal Stem Cell-Derived Exosomes Enhance 3D-Printed Scaffold Functions and Promote Alveolar Bone Defect Repair by Enhancing Angiogenesis

The reconstruction of severe alveolar bone defects remains a complex and challenging field for clinicians. Three-dimensional-printed scaffolds can adapt precisely to the complicated shape of the bone defects, which is an alternative solution to bone tissue engineering. Our previous study constructed an innovative low-temperature 3D-printed silk fibroin/collagen I/nano-hydroxyapatite (SF/COL-I/nHA) composite scaffold with a stable structure and remarkable biocompatibility. However, the clinical translation of most scaffolds is limited by insufficient angiogenesis and osteogenesis. In this study, we investigated the effects of human umbilical cord mesenchymal-stem-cell-derived exosomes (hUCMSC-Exos) on bone regeneration, especially from the perspective of inducing angiogenesis. HUCMSC-Exos were isolated and characterized. In vitro, the effect of hUCMSC-Exos on the proliferation, migration, and tube formation of human umbilical vein endothelial cells (HUVECs) was examined. Moreover, the loading and release of hUCMSC-Exos on 3D-printed SF/COL-I/nHA scaffolds were evaluated. In vivo, hUCMSC-Exos and 3D-printed SF/COL-I/nHA scaffolds were implanted into alveolar bone defects, and bone regeneration and angiogenesis were investigated by micro-CT, HE staining, Masson staining, and immunohistochemical analysis. The results showed that hUCMSC-Exos stimulated HUVEC proliferation, migration, and tube formation in vitro, and the effect increased with increasing exosome concentrations. In vivo, the combination of hUCMSC-Exos and 3D-printed SF/COL-I/nHA scaffolds promoted alveolar bone defect repair by enhancing angiogenesis and osteogenesis. We constructed an elaborate cell-free bone-tissue-engineering system by combining hUCMSC-Exos with 3D-printed SF/COL-I/nHA scaffolds, potentially providing new ideas for treating alveolar bone defects.

Bone marrow mesenchymal stem cell's exosomes as key nanoparticles in osteogenesis and bone regeneration: specific capacity based on cell type

Today, communities and their health systems are facing with several challenges associated with the population ageing. Growing number of bone disorders is one of the most serious consequences of aging. According to the reports bone disorders won't just affect the elderly population. Mesenchymal stem cells (MSCs) are multipotent cells that could be derived from a variety of tissues including bone marrow, Wharton's Jelly, adipose tissue, and others. MSCs have been utilized in different researches in the field of regenerative medicine because of their immunosuppression and anti-inflammatory mechanisms (like: inhibiting the activity of antigen presenting cells, and suppressing the activity of T lymphocyte cells, macrophages, and so on.), migration to injured areas, and participation in healing processes. Bone marrow mesenchymal stem cells (BMMSCs) are a type of these cells which can be commonly used in bone research with the promising results. These cells function by releasing a large number of extracellular vesicles (EVs). Exosomes are the most major EVs products produced by BMMSCs. They have the same contents and properties as their parent cells; however, these structures don't have the defects of cell therapy. Proteins (annexins, tetraspannins, etc.), lipids (cholesterol, phosphoglycerides, etc.), nucleic acids (micro-RNAs, and etc.) and other substances are found in exosomes. Exosomes affect target cells, causing them to change their function. The features of BMMSC exosomes' mechanism in osteogenesis and bone regeneration (like: effects on other MSCs, osteoblasts, osteoclasts, and angiogenesis) and also the effects of their micro-RNAs on osteogenesis are the subject of the present review.

Bone Engineering Scaffolds With Exosomes: A Promising Strategy for Bone Defects Repair

The treatment of bone defects is still an intractable clinical problem, despite the fact that numerous treatments are currently available. In recent decades, bone engineering scaffolds have become a promising tool to fill in the defect sites and remedy the deficiencies of bone grafts. By virtue of bone formation, vascular growth, and inflammation modulation, the combination of bone engineering scaffolds with cell-based and cell-free therapy is widely used in bone defect repair. As a key element of cell-free therapy, exosomes with bioactive molecules overcome the deficiencies of cell-based therapy and promote bone tissue regeneration via the potential of osteogenesis, angiogenesis, and inflammation modulation. Hence, this review aimed at overviewing the bone defect microenvironment and healing mechanism, summarizing current advances in bone engineering scaffolds and exosomes in bone defects to probe for future applications.

Extracellular Vesicles From TNFα Preconditioned MSCs: Effects on Immunomodulation and Bone Regeneration

Mesenchymal stem cells show remarkable versatility and respond to extracellular and micro environmental cues by altering their phenotype and behavior. In this regard, the MSC’s immunomodulatory properties in tissue repair are well documented. The paracrine effects of MSCs in immunomodulation are, in part, attributable to their secreted extracellular vesicles (EVs). When MSCs migrate to the wound bed, they are exposed to a myriad of inflammatory signals. To understand their response to an inflammatory environment from an EV perspective, we sought to evaluate the effects of the inflammatory cytokine TNFα on MSC EV mediated immunomodulation. Our results indicate that while the physical characteristics of the EVs remain unchanged, the TNFα preconditioned MSC EVs possess enhanced immunomodulatory properties. In vitro experiments using polarized (M1 and M2) primary mouse macrophages indicated that the preconditioned MSC EVs suppressed pro-inflammatory (M1) markers such as IL-1β and iNOS and elevated reparatory (M2) markers such as Arg1 and CD206. When evaluated in vivo in a rat calvarial defect model, the TNFα preconditioned MSC EVs reduced inflammation at 1-, 3- and 7-days post wounding resulting in the subsequent enhanced bone formation at 4- and 8-weeks post wounding possibly by modulation of oncostatin M (OSM) expression. An analysis of EV miRNA composition revealed significant changes to anti-inflammatory miRNAs in the preconditioned MSC EVs hinting at a possible role for EV derived miRNA in the enhanced immunomodulatory activity. Overall, these results indicate that MSC exposure to inflammatory signals influence the MSC EV’s immunomodulatory function in the context of tissue repair. The specific function of TNFα preconditioned MSC EV miRNAs in immunomodulatory control of bone regeneration merits further investigation.