Mesenchymal stromal cell-derived extracellular vesicles for bone regeneration therapy

From stem cells to extracellular vesicles: a new horizon in tissue engineering and regenerative medicine

In the fields of tissue engineering and regenerative medicine, extracellular vesicles (EVs) have become viable therapeutic tools. EVs produced from stem cells promote tissue healing by regulating the immune system, enhancing cell proliferation and aiding remodeling processes. Recently, EV has gained significant attention from researchers due to its ability to treat various diseases. Unlike stem cells, stem cell-derived EVs show lower immunogenicity, are less able to overcome biological barriers, and have a higher safety profile. This makes the use of EVs derived from cell-free stem cells a promising alternative to whole-cell therapy. This review focuses on the biogenesis, isolation, and characterization of EVs and highlights their therapeutic potential for bone fracture healing, wound healing, and neuronal tissue repair and treatment of kidney and intestinal diseases. Additionally, this review discusses the potential of EVs for the treatment of cancer, COVID-19, and HIV. In summary, the use of EVs derived from stem cells offers a new horizon for applications in tissue engineering and regenerative medicine.

Dynamic cultivation of human mesenchymal stem/stromal cells for the production of extracellular vesicles in a 3D bioreactor system

PURPOSE

3D cell culture and hypoxia have been demonstrated to increase the therapeutic effects of mesenchymal stem/stromal cells (MSCs)-derived extracellular vesicles (EVs). In this study, a process for the production of MSC-EVs in a novel 3D bioreactor system under normoxic and hypoxic conditions was established and the resulting EVs were characterized.

METHODS

Human adipose-derived MSCs were seeded and cultured on a 3D membrane in the VITVO® bioreactor system for 7 days. Afterwards, MSC-EVs were isolated and characterized via fluorescence nanoparticle tracking analysis, flow cytometry with staining against annexin V (Anx5) as a marker for EVs exposing phosphatidylserine, as well as CD73 and CD90 as MSC surface markers.

RESULTS

Cultivation of MSC in the VITVO® bioreactor system demonstrated a higher concentration of MSC-EVs from the 3D bioreactor (9.1 × 109 ± 1.5 × 109 and 9.7 × 109 ± 3.1 × 109 particles/mL) compared to static 2D culture (4.2 × 109 ± 7.5 × 108 and 3.9 × 109 ± 3.0 × 108 particles/mL) under normoxic and hypoxic conditions, respectively. Also, the particle-to-protein ratio as a measure for the purity of EVs increased from 3.3 × 107 ± 1.1 × 107 particles/µg protein in 2D to 1.6 × 108 ± 8.3 × 106 particles/µg protein in 3D. Total MSC-EVs as well as CD73-CD90+ MSC-EVs were elevated in 2D normoxic conditions. The EV concentration and size did not differ significantly between normoxic and hypoxic conditions.

CONCLUSION

The production of MSC-EVs in a 3D bioreactor system under hypoxic conditions resulted in increased EV concentration and purity. This system could be especially useful in screening culture conditions for the production of 3D-derived MSC-EVs.

Evaluation of in vitro biocompatibility of human pulp stem cells with allogeneic, alloplastic, and xenogeneic grafts under the influence of extracellular vesicles

Therapies using dental pulp stem cells (DPSCs) or stem cell-derived extracellular vesicles (EVs) have shown promising applications for bone tissue engineering. This in vitro experiment evaluated the joint osteogenic capability of DPSCs and EVs on alloplastic (maxresorp), allogeneic (maxgraft), and xenogeneic (cerabone) bone grafts. We hypothesize that osteogenic differentiation and the proliferation of human DPSCs vary between bone grafts and are favorable under the influence of EVs. DPSCs were obtained from human wisdom teeth, and EVs derived from DPSCs were isolated from cell culture medium. DPSCs were seeded on alloplastic, allogeneic, and xenogeneic bone graft substitutes for control, and the same scaffolds were administered with EVs in further groups. The cellular uptake of EVs into DPSC cells was assessed by confocal laser scanning microscopy. Cell vitality staining and calcein acetoxymethyl ester staining were used to evaluate cell attachment and proliferation. Cell morphology was determined using scanning electron microscopy, and osteogenic differentiation was explored by alkaline phosphatase and Alizarin red staining. Within the limitations of an in vitro study without pathologies, the results suggest that especially the use of xenogeneic bone graft substitutes with DPSCS and EVs may represent a promising treatment approach for alveolar bone defects.

Platelet-derived extracellular vesicles formulated with hyaluronic acid gels for application at the bone-implant interface: An animal study

Background/Objective

Platelet derived extracellular vesicles (pEV) are promising therapeutical tools for bone healing applications. In fact, several in vitro studies have already demonstrated the efficacy of Extracellular Vesicles (EV) in promoting bone regeneration and repair in various orthopedic models. Therefore, to evaluate the translational potential in this field, an in vivo study was performed.

Methods

Here, we used hyaluronic acid (HA) gels formulated with pEVs, as a way to directly apply pEVs and retain them at the bone defect. In this study, pEVs were isolated from Platelet Lysate (PL) through size exclusion chromatography and used to formulate 2% HA gels. Then, the gels were locally applied on the tibia cortical bone defect of New Zeland White rabbits before the surgical implantation of coin-shaped titanium implants. After eight weeks, the bone healing process was analyzed through biomechanical, micro-CT, histological and biochemical analysis.

Results

Although no biomechanical differences were observed between pEV formulated gels and non-formulated gels, biochemical markers of the wound fluid at the interface presented a decrease in Lactate dehydrogenase (LDH) activity and alkaline phosphatase (ALP) activity for pEV HA treated implants. Moreover, histological analyses showed that none of the treatments induced an irritative effect and, a decrease in the fibrotic response surrounding the implant for pEV HA treated implants was described.

Conclusion

In conclusion, pEVs improve titanium implants biocompatibility at the bone-implant interface, decreasing the necrotic effects of the surgery and diminishing the fibrotic layer associated to the implant encapsulation that can lead to implant failure.

How Do Extracellular Vesicles Play a Key Role in the Maintenance of Bone Homeostasis and Regeneration? A Comprehensive Review of Literature

The maintenance of bone homeostasis includes both bone resorption by osteoclasts and bone formation by osteoblasts. These two processes are in dynamic balance to maintain a constant amount of bone for accomplishing its critical functions in daily life. Multiple cell type communications are involved in these two complex and continuous processes. In recent decades, an increasing number of studies have shown that osteogenic and osteoclastic extracellular vesicles play crucial roles in regulating bone homeostasis through paracrine, autosecretory and endocrine signaling. Elucidating the functional roles of extracellular vesicles in the maintenance of bone homeostasis may contribute to the design of new strategies for bone regeneration. Hence, we review the recent understandings of the classification, production process, extraction methods, structure, contents, functions and applications of extracellular vesicles in bone homeostasis. We highlight the contents of various bone-derived extracellular vesicles and their interactions with different cells in the bone microenvironment during bone homeostasis. We also summarize the recent advances in EV-loaded biomaterial scaffolds for bone regeneration and repair.

Mesenchymal stem cell-derived extracellular vesicles: a possible therapeutic strategy for orthopaedic diseases: a narrative review

Accumulating evidence suggests that the therapeutic role of mesenchymal stem cells (MSCs) in bone diseases is closely related to paracrine-generated extracellular vesicles (EVs). MSC-derived EVs (MSC-EVs) carry proteins, nucleic acids, and lipids to the extracellular space and affect the bone microenvironment. They have similar biological functions to MSCs, such as the ability to repair organ and tissue damage. In addition, MSC-EVs also have the advantages of long half-life, low immunogenicity, attractive stability, ability to pass through the blood-brain barrier, and demonstrate excellent performance with potential practical applications in bone diseases. In this review, we summarise the current applications and mechanisms of MSC-EVs in osteoporosis, osteoarthritis, bone tumours, osteonecrosis of the femoral head, and fractures, as well as the development of MSC-EVs combined with materials science in the field of orthopaedics. Additionally, we explore the critical challenges involved in the clinical application of MSC-EVs in orthopaedic diseases.

Identifying the Efficacy of Extracellular Vesicles in Osteogenic Differentiation: An EV-Lution in Regenerative Medicine

Mesenchymal stromal cells (MSCs) have long been the focus for regenerative medicine and the restoration of damaged or aging cells throughout the body. However, the efficacy of MSCs in cell-based therapy still remains unpredictable and carries with it enumerable risks. It is estimated that only 3-10% of MSCs survive transplantation, and there remains undefined and highly variable heterogeneous biological potency within these administered cell populations. The mode of action points to secreted factors produced by MSCs rather than the reliance on engraftment. Hence harnessing such secreted elements as a replacement for live-cell therapies is attractive. Extracellular vesicles (EVs) are heterogenous lipid bounded structures, secreted by cells. They comprise a complex repertoire of molecules including RNA, proteins and other factors that facilitate cell-to-cell communication. Described as protected signaling centers, EVs can modify the cellular activity of recipient cells and are emerging as a credible alternative to cell-based therapies. EV therapeutics demonstrate beneficial roles for wound healing by preventing apoptosis, moderating immune responses, and stimulating angiogenesis, in addition to promoting cell proliferation and differentiation required for tissue matrix synthesis. Significantly, EVs maintain their signaling function following transplantation, circumventing the issues related to cell-based therapies. However, EV research is still in its infancy in terms of their utility as medicinal agents, with many questions still surrounding mechanistic understanding, optimal sourcing, and isolation of EVs for regenerative medicine. This review will consider the efficacy of using cell-derived EVs compared to traditional cell-based therapies for bone repair and regeneration. We discuss the factors to consider in developing productive lines of inquiry and establishment of standardized protocols so that EVs can be harnessed from optimal secretome production, to deliver reproducible and effective therapies.

Educating EVs to Improve Bone Regeneration: Getting Closer to the Clinic

The incidence of bone-related disorders is continuously growing as the aging of the population in developing countries continues to increase. Although therapeutic interventions for bone regeneration exist, their effectiveness is questioned, especially under certain circumstances, such as critical size defects. This gap of curative options has led to the search for new and more effective therapeutic approaches for bone regeneration; among them, the possibility of using extracellular vesicles (EVs) is gaining ground. EVs are secreted, biocompatible, nano-sized vesicles that play a pivotal role as messengers between donor and target cells, mediated by their specific cargo. Evidence shows that bone-relevant cells secrete osteoanabolic EVs, whose functionality can be further improved by several strategies. This, together with the low immunogenicity of EVs and their storage advantages, make them attractive candidates for clinical prospects in bone regeneration. However, before EVs reach clinical translation, a number of concerns should be addressed. Unraveling the EVs’ mode of action in bone regeneration is one of them; the molecular mediators driving their osteoanabolic effects in acceptor cells are now beginning to be uncovered. Increasing the functional and bone targeting abilities of EVs are also matters of intense research. Here, we summarize the cell sources offering osteoanabolic EVs, and the current knowledge about the molecular cargos that mediate bone regeneration. Moreover, we discuss strategies under development to improve the osteoanabolic and bone-targeting potential of EVs.

Extracellular Vesicles Derived from Primed Mesenchymal Stromal Cells Loaded on Biphasic Calcium Phosphate Biomaterial Exhibit Enhanced Macrophage Polarization

Mesenchymal stromal cells (MSC) loaded on biphasic calcium phosphate biomaterial (MSC + BCP) have been used as an advanced therapy medicinal product to treat complex maxillofacial bone defects in patients. Further, MSC-derived extracellular vesicles (EVs) are established vehicles of paracrine factors, supporting inter-cellular communication between MSC and other interacting cell types, such as monocytes/macrophages. However, the information about the immunomodulatory potential of EVs derived from MSC and biomaterial constructs (MSC + BCP:EV) and inflammatory primed constructs (MSCp + BCP:EV) are scarce. Hence, we isolated and characterized EVs from these different systems, and compared their cytokine contents with plastic-adherent MSC-derived EVs (MSC:EV). When EVs from all three MSC systems were added to the primary blood-derived macrophages in vitro, significantly higher numbers of M0 (naive) macrophages shifted to M2-like (anti-inflammatory) by MSCp + BCP:EV treatment. Further, this treatment led to enhanced switching of M1 polarized macrophages to M2 polarized, and conversely, M2 to M1, as evaluated by determining the M1/M2 ratios after treatment. The enhanced macrophage modulation by MSCp + BCP:EV was attributed to their higher immunomodulatory (TNFα, IL1β, IL5), angiogenic (VEGF), and chemokine-rich (RANTES, MCP1, MIP1β) cytokine cargo. In conclusion, we successfully isolated and characterized EVs from MSC + BCP constructs and demonstrated that, depending upon the tissue microenvironment, these EVs contribute towards modulating the macrophage-mediated inflammation and healing responses. The study offers new insights into the use of biomaterial-induced EVs for MSC secretome delivery, as a step towards future ‘cell-free’ bone regenerative therapies.

Exosomes from miR-29a-modified adipose-derived mesenchymal stem cells reduce excessive scar formation by inhibiting TGF-β2/Smad3 signaling

Pathological scars mainly refer to hypertrophic scars and keloids, and have a high incidence. Moreover, these scars seriously affect the patient's appearance and are associated with significant pain. The present study aimed to investigate the inhibitory effect of microRNA (miR)-29a from human adipose-derived mesenchymal stem cells (hADSCs) exosomes on scar formation. Firstly, the expression of miR-29a in thermal skin tissues of mice and human hypertrophic scar fibroblasts (HSFBs) was detected via reverse transcription-quantitative PCR. Exosomes derived from miR-29a-modified hADSCs were extracted and the influence of miR-29a-modified hADSCs-exo on the proliferation and function of HSFBs was determined. Lastly, the effect of miR-29a-modified hADSCs-exo on scar formation was determined using a thermal mouse model. The results demonstrated that miR-29a was downregulated in scar tissues after scalding and in HSFBs. After treating HSFBs with miR-29a-modified hADSC exosomes, miR-29a-overexpressing hADSC exosomes inhibited the proliferation and migration of HSFBs. Moreover, it was found that TGF-β2 was the target of miR-29a, and that hADSC exosome-derived miR-29a inhibited the fibrosis of HSFBs and scar hyperplasia after scalding in mice by targeting the TGF-β2/Smad3 signaling pathway. In summary, the current data indicated that miR-29a-modified hADSC exosome therapy can decrease scar formation by inhibiting the TGF-β2/Smad3 signaling pathway via its derived exogenous miR-29a, and this may be useful for the future treatment of pathological scars by providing a potential molecular basis.