Aims

To investigate the effects of senescent osteocytes on bone homeostasis in the progress of age-related osteoporosis and explore the underlying mechanism.

The aim of this study was to investigate the regenerative effects of Wharton's Jelly Mesenchymal Stem Cells (WJ-MSCs) derived exosomes (WJ-Exos) on human nucleus pulposus cells (hNPCs) in an in vitro 3D model.

WJ-Exos were isolated by tangent flow filtration of WJ-MSCs conditioned media and characterized by TEM, WB for markers expression and quantified with NTA. WJ-Exos PKH26-labeled uptake in hNPCs was detected by confocal microscopy. hNPCs, isolated from surgical specimens (n=4), culture expanded in vitro and encapsulated in alginate beads, were pre-treated with IL1β (10 ng/ml) for 24 hours, then with WJ-Exos at 10, 50 and 100 µg/ml. Cells with growth medium were used as control. We examined: i) cell proliferation and viability (flow cytometry), ii) nitrite production (Griess) iii) glycosaminoglycan (GAG) amount (DMBB), iv) histological staining for extracellular matrix (ECM) analysis and v) gene expression levels of catabolic and anabolic genes (qPCR). The investigations were performed in triplicate for each donor. One-way ANOVA analysis was used to compare the groups under exam and data were expressed as mean ± S.D.

A dose dependent increase in hNPCs proliferation was noticed at all exos concentrations under study. Cell death decreased significantly in WJ-Exos 50 µg/ml samples (p ≤ 0,05) compared to IL1β treated hNPCs. Nitrite production was significantly attenuated at 10µg/ml of WJ-Exos (p ≤ 0,01). GAG content and histological analysis showed a difference in ECM synthesis between treated and untreated hNPCs (p ≤ 0,05). Catabolic and inflammatory markers were modulated by WJ-Exos at 100 µg/ml concentration (p ≤ 0,05) whereas 10 µg/ml group increased anabolic gene expression levels (p ≤ 0,05).

These findings offer new opportunities for the potential use of exosomes as an attractive alternative cell-free strategy of IDD. WJ-MSC exosomes ameliorate hNPCs growth and viability, attenuate ECM degradation and oxidative stress-related IDD progression after IL1β stimulation.

Financial support was received from the “iPSpine” and “RESPINE” Horizon 2020 projects.

Osteoarthritis (OA), the most prevalent chronic joint disease, represents a relevant social and economic burden worldwide. Human umbilical cord mesenchymal stem cells (HUCMSCs) have been used for injection into the joint cavity to treat OA. The aim of this article is to clarify whether Huc-MSCs derived exosomes could inhibit the progression of OA and the mechanism in this process.

A rabbit OA model was established by the transection of the anterior cruciate ligament. The effects of HUCMSCs or exosomes derived from HUCMSCs on repairing articular cartilage of knee osteoarthritis was examined by micro-CT. Immunohistochemical experiments were used to confirm the expression of relevant inflammatory molecules in OA. In vitro experiments, Transwell assay was used to assess the migration of macrophages induced by TNF-a.

Results showed that a large number of macrophages migrated in arthcular cavity in OA model in vivo, while local injection of HUCMSCs and exosomes did repair the articular cartilage. Immunohistochemical results suggested that the expression of CCL2 and CD68 in the OA rabbit model increased significantly, but was significantly reduced by HUCMSCs or exosomes. Transwell assay showed that both HUCMSCs and exosomes can effectively inhibit the migration of macrophage.

In conclusion, the exosomes derived by HUCMSCs might might rescue cartilage defects in rabbit through its anti-inflammatory effects through inhibiting CCL2.

Osteoarthritis (OA) is a common age-related degenerative joint disease, affecting 7% of the global population, more than 500 million people worldwide. Exosomes from mesenchymal stem cells (MSCs) showed promise for OA treatment, but the insufficient biological targeting weakens its efficacy and might bring side effects. Here, we report the chondrocyte-targeted exosomes synthesized via click chemistry as a novel treatment for OA. Exosomes are isolated from human umbilical cord-derived MSCs (hUC-MSCs) using multistep ultracentrifugation process, and identified by electron microscope and nanoparticle tracking analysis (NTA). Chondrocyte affinity peptide (CAP) is conjugated on the surface of exosomes using click chemistry. For tracking, nontagged exosomes and CAP-exosomes are labeled by Dil, a fluorescent dye that highlights the lipid membrane of exosomes. To verify the effects of CAP-exosomes, nontagged exosomes and CAP-exosomes are added into the culture medium of interleukin (IL)-1β-induced chondrocytes. Immunofluorescence are used to test the expression of matrix metalloproteinase (MMP)-13. CAP-exosomes, compared with nontagged exosomes, are more easily absorbed by chondrocytes. What's more, CAP-exosomes induced lower MMP-13 expression of chondrocytes when compared with nontagged exosomes (p<0.001). CAP-exosomes show chondrocyte-targeting and exert better protective effect than nontagged exosomes on chondrocyte extracellular matrix. Histological and in vivo validation are now being conducted

Aims. Circular RNA (circRNA) is involved in the regulation of articular cartilage degeneration induced by inflammatory factors or oxidative stress. In a previous study, we found that the expression of circStrn3 was significantly reduced in chondrocytes of osteoarthritis (OA) patients and OA mice. Therefore, the aim of this paper was to explore the role and mechanism of circStrn3 in osteoarthritis. Methods. Minus RNA sequencing, fluorescence in situ hybridization, and quantitative real-time polymerase chain reaction (qRT-PCR) were used to detect the expression of circStrn3 in human and mouse OA cartilage tissues and chondrocytes. Chondrocytes were then stimulated to secrete exosomal miR-9-5p by cyclic tensile strain. Intra-articular injection of exosomal miR-9-5p into the model induced by destabilized medial meniscus (DMM) surgery was conducted to alleviate OA progression. Results. Tensile strain could decrease the expression of circStrn3 in chondrocytes. CircStrn3 expression was significantly decreased in human and mouse OA cartilage tissues and chondrocytes. CircStrn3 could inhibit matrix metabolism of chondrocytes through competitively ‘sponging’ miRNA-9-5p targeting Kruppel-like factor 5 (KLF5), indicating that the decrease in circStrn3 might be a protective factor in mechanical instability-induced OA. The tensile strain stimulated chondrocytes to secrete exosomal miR-9-5p. Exosomes with high miR-9-5p expression from chondrocytes could inhibit osteoblast differentiation by targeting KLF5. Intra-articular injection of exosomal miR-9-5p alleviated the progression of OA induced by destabilized medial meniscus surgery in mice. Conclusion. Taken together, these results demonstrate that reduction of circStrn3 causes an increase in miR-9-5p, which acts as a protective factor in mechanical instability-induced OA, and provides a novel mechanism of communication among joint components and a potential application for the treatment of OA. Cite this article: Bone Joint Res 2023;12(1):33–45

Cite this article: Bone Joint Res 2023;12(1):5–8.

Intervertebral disc degeneration (IDD) affects more than 80% of the population all over the world. Current strategies for the treatment of IDD are based on conservative or surgical procedures with the aim of relieving pain. Mesenchymal stem cell (MSC) transplantation has emerged as a promising therapy in recent decades, but studies showed that the particularly hostile microenvironment in the intervertebral disc (IVD) can compromise cells survival rate. The use of exosomes, extracellular vesicles released by various cell types, possess considerable economic advantages including low immunogenicity and toxicity. Exosomes allow intercellular communication by conveying functional proteins, RNA, miRNA and lipids between cells. The purpose of this study is to assess the therapeutic effects of exosomes derived from Wharton Jelly mesenchymal stromal cells (WJ-MSC) on human nucleuspulposus cells (hNPC) in an in vitro 3D culture model. Exosomes (exos) were isolated by tangential flow filtration of WJ-MSC conditioned media and characterized by: quantification with BCA test; morphological observation with TEM, surface marker expression by WB and size evaluation by NTA. Confocal microscopy has been used to identify exosomes marked with PKH26 and monitor fusion and/or incorporation in hNPC. hNPC were isolated from waste surgical material from patients undergoing discectomy (n = 5), expanded, encapsulated in alginate beads and treated with: culture medium (control group); WJ-MSC exos (WJ-exos) at different concentrations (10 μg/ml, 50 μg/ml and 100 μg/ml). They were then analysed for: cell proliferation (Trypan Blu); viability (Live/Dead Assay); quantification of nitrites (Griess) and glycosaminoglycans, GAG (DMBB). The hNPC in alginate beads treated for 7 days were included in paraffin and histologically analysed to determine the presence of extracellular matrix (ECM) components. Finally, the expression levels of catabolic and anabolic genes were evaluated through real-time polymerase chain reaction (qPCR). All concentrations of WJ-exos under exam were capable to induce a significant increase in cell proliferation after 10 and 14 days of treatment (p < 0.01 and p < 0.001, respectively). Live/Dead assay showed a decrease in cell death at 50 μg/ml of WJ-exos (p < 0.05). While cellular oxidative stress indicator, nitrite production, was reduced in a dose-dependent way and statistically significant only with 100 μg/ml of WJ-exos (p < 0.05). WJ-exos at 10 and 100 μg/ml induced a significant increase in GAG content (p < 0.05; p < 0.01, respectively) confirmed by Alcian Blu staining. Exos derived from WJ-MSC modulated gene expression levels by increasing expression of ACAN and SOX-9 genes and reducing significantly of IL-6, MMP-1, MMP-13 and ADAMTS-5 levels (p < 0.05; p < 0.01) compared to the control group. Our results supported the potential use of exosomes from WJ-MSC for the treatment of IDD. Exosomes improved hNPC growth, attenuated ECM degradation and reduced oxidative stress and inflammation. This study offers a new scenario in IVD regeneration, promoting the potential use of extracellular vesicles as an alternative strategy to cell therapy

Aims. Exosomes (exo) are involved in the progression of osteoarthritis (OA). This study aimed to investigate the function of dysfunctional chondrocyte-derived exo (DC-exo) on OA in rats and rat macrophages. Methods. Rat-derived chondrocytes were isolated, and DCs induced with interleukin (IL)-1β were used for exo isolation. Rats with OA (n = 36) or macrophages were treated with DC-exo or phosphate-buffered saline (PBS). Macrophage polarization and autophagy, and degradation and chondrocyte activity of cartilage tissues, were examined. RNA sequencing was used to detect genes differentially expressed in DC-exo, followed by RNA pull-down and ribonucleoprotein immunoprecipitation (RIP). Long non-coding RNA osteoarthritis non-coding transcript (OANCT) and phosphoinositide-3-kinase regulatory subunit 5 (PIK3R5) were depleted in DC-exo-treated macrophages and OA rats, in order to observe macrophage polarization and cartilage degradation. The PI3K/AKT/mammalian target of rapamycin (mTOR) pathway activity in cells and tissues was measured using western blot. Results. DC-exo inhibited macrophage autophagy (p = 0.002) and promoted M1 macrophage polarization (p = 0.002). DC-exo at 20 μg/ml induced collagen degradation (p < 0.001) and inflammatory cell infiltration (p = 0.023) in rats. OANCT was elevated in DC (p < 0.001) and in cartilage tissues of OA patients (p < 0.001), and positively correlated with patients’ Kellgren-Lawrence grade (p < 0.001). PIK3R5 was increased in DC-exo-treated cartilage tissues (p < 0.001), and OANCT bound to fat mass and obesity-associated protein (FTO) (p < 0.001). FTO bound to PIK3R5 (p < 0.001) to inhibit the stability of PIK3R5 messenger RNA (mRNA) (p < 0.001) and disrupt the PI3K/AKT/mTOR pathway (p < 0.001). Conclusion. Exosomal OANCT from DC could bind to FTO protein, thereby maintaining the mRNA stability of PIK3R5, further activating the PI3K/AKT/mTOR pathway to exacerbate OA. Cite this article: Bone Joint Res 2022;11(9):652–668

Aims

The role of N,N-dimethylformamide (DMF) in diabetes-induced osteoporosis (DM-OS) progression remains unclear. Here, we aimed to explore the effect of DMF on DM-OS development.

Aims. Exosomes derived from bone marrow mesenchymal stem cells (BMSCs) have been reported to be a promising cellular therapeutic approach for various human diseases. The current study aimed to investigate the mechanism of BMSC-derived exosomes carrying microRNA (miR)-136-5p in fracture healing. Methods. A mouse fracture model was initially established by surgical means. Exosomes were isolated from BMSCs from mice. The endocytosis of the mouse osteoblast MC3T3-E1 cell line was analyzed. CCK-8 and disodium phenyl phosphate microplate methods were employed to detect cell proliferation and alkaline phosphatase (ALP) activity, respectively. The binding of miR-136-5p to low-density lipoprotein receptor related protein 4 (LRP4) was analyzed by dual luciferase reporter gene assay. HE staining, tartrate-resistant acid phosphatase (TRAP) staining, and immunohistochemistry were performed to evaluate the healing of the bone tissue ends, the positive number of osteoclasts, and the positive expression of β-catenin protein, respectively. Results. miR-136-5p promoted fracture healing and osteoblast proliferation and differentiation. BMSC-derived exosomes exhibited an enriched miR-136-5p level, and were internalized by MC3T3-E1 cells. LRP4 was identified as a downstream target gene of miR-136-5p. Moreover, miR-136-5p or exosomes isolated from BMSCs (BMSC-Exos) containing miR-136-5p activated the Wnt/β-catenin pathway through the inhibition of LRP4 expression. Furthermore, BMSC-derived exosomes carrying miR-136-5p promoted osteoblast proliferation and differentiation, thereby promoting fracture healing. Conclusion. BMSC-derived exosomes carrying miR-136-5p inhibited LRP4 and activated the Wnt/β-catenin pathway, thus facilitating fracture healing. Cite this article: Bone Joint Res 2021;10(12):744–758

Introduction and Objective. Exosomal miRNA have been shown to regulate many myogenic and osteogenic pathways involved in injury repair and healing. It is also known that rehabilitation and exercise can improve muscle mass and bone growth. The mechanisms by which this occurs in vivo are well studied, but the impact exosomes and their associated miRNA cargo have is unclear. With this knowledge and question in mind, we hypothesized that C2C12 myoblasts subjected to in vitro mechanical stimulus (“exercise”) would exhibit improved exosome production and differentially expressed miRNA cargo when compared to their static (“unexercised”) counterparts. Materials and Methods. C2C12 myoblasts were cultured using the FlexCell FX-5000TT bioreactor. Two exercise regimens were programmed: 1) low intensity regimen (LIR) (0–15% strain at 0.5 Hz for 24 hours) 2) high intensity interval regimen (HIIR) (12–22% strain at 1 Hz for 10 minutes followed by 50 minutes of rest repeated for 24 hours). Unexercised (static) cells were cultured in parallel. Exosomes were isolated using the Invitrogen Total Exosome Isolation Reagent. The Pierce BCA Protein Assay, System Bioscience's ExoELISA-ULTRA CD81 Kit and, SBI's ExoFlow-ONE EV labeling kit were used to confirm and quantify exosome number and protein concentration. The SBI Exo-NGS service was used to perform miRNA sequencing on isolated exosomes. Results. All exercise regimens resulted in increased exosome concentrations as determined by CD81 exosome ELISA and flow-cytometry based exosome quantification. The LIR interestingly produced significantly more exosomes than static and HIIR. Within the exosomes from mechanically stimulated cells, 35 miRNAs were found to be differentially expressed when compared to exosomes from unexercised cells. Interestingly, this significance was only found within exosomes from the HIIR group. Specifically, upon investigation 8 of these miRNAs were found to be involved in myogenic and osteogenic proliferation and differentiation. These results correlate with our previous findings that exosomes from exercised cells improve the proliferation and myogenic differentiation of C2C12 myoblasts. Conclusions. Our results indicate that exercise can be optimized to improve the production and regenerative capacity of exosomes. These results also indicate that exosomes may be intimately involved in systemic health and repair during rehabilitation and exercise. To examine these results in vivo, mouse studies using a crush injury model and exosomes from mechanically stimulated cells are currently planned

Mesenchymal stem cell (MSC) exosomes are intracellular vesicles, which can regulate transcription and control gene expression through the molecules they carry, easily enter into the target cell, contain no regenerative effect, and do not produce an immune response. There are different methods in the literature to obtain these vesicles. However, studies on the isolation of MSC-derived exosomes and their comparative characterization using magnetically active cell sorting (MACS) and ultracentrifugation methods are lacking. The most appropriate isolation method for MSC-derived exosomes can be determined by comparing the isolation and characterization parameters of mesenchymal stem cells using magnetically active cell sorting and ultracentrifugation methods. The aim of this study was to define the advantages and disadvantages of the methods used for determining the purpose-oriented method. Human bone marrow-derived mesenchymal stem cells were cultured in standard MSC culture conditions (37ºC and 5% CO 2). Exosomal contamination was prevented by removal of exosomes from the serum that used in the standard growth medium. For exosome isolation of the cells reaching sufficient density, the media were replaced with new ones every two days, the old media were collected in liquid refrigerated with liquid nitrogen and stored at −80ºC. Part of the accumulated exosomes were isolated by using the MACS method, while the other was isolated by using the ultracentrifugation method, which included serial centrifugation steps. The amount of protein contained in the phosphate buffer solution in which the exosomes were reconstituted was determined by microplate reader using the BCA kit. Based on the protein concentration obtained, exosomes were read by means of a dye flow cytometer with fluorescent antibodies attached to surface markers specific to CD9, CD63, and CD81 specific for exosomes by latex beads. Finally, the exosomes were stained with uranyl acetate and phosphotungstic acid and then placed on 200 mesh and formvar-carbon film coated grids. Exosomes were isolated using both ultracentrifugation and MACS methods. While ultra-large amounts of exosomes can be isolated by ultracentrifugation method, MACS method provides a lower amount of isolation. Exosomes with magnetically active cell sorting are selected with specific surface markers, therefore, exosomal purity is thought to be higher. Exosomes which were isolated by both ultracentrifugation and MACS methods were monitored by using transmission electron microscopy and they were not found to be morphologically different. In conclusion, MACS and ultracentrifugation are effective methods for the isolation of human bone marrow-derived MSC exosomes. Both methods have advantages and disadvantages. Exosomes can be isolated together with magnetic beads using the MACS method. In the ultracentrifuge method, cleaner exosomes can be isolated. While the exosomes are isolated by MACS, they can also be characterized by beads

Intervertebral disc degeneration (IDD) affects more than 80% of the population and is often linked to a reduction of the proteoglycan content within the nucleus pulposus (NP). The nutritional decline and accumulation of degraded matrix products promote the inflammatory process favoring the onset of disease. Several regenerative approaches based on cell therapy have been explored. Recently, paracrine factors and extracellular vesicles (EVs) such as exosomes have been described to play a fundamental role in the cross-talk between mesenchymal stem cells (MSCs) and NP in the microenvironment. EVs vehicule different molecules: proteins, nucleic acids and lipids involved in intercellular communication regulating the homeostasis of recipient cells. Therefore, MSCs-derived exosomes are an interesting emerging tool for cell-free therapies in IDD. The aim of this study was to evaluate the in vitro effects of MSCs derived exosomes on human NP cells (hNPCs). Exosomes were isolated through a multistep ultracentrifugation of bone marrow-MSCs (BM-MSCs) conditioned media (CM), obtained by culturing BM-MSCs without fetal bovine serum (FBS) for 48 hours. Exosomal morphology was characterized by transmission electron microscope (TEM). The exosomes were quantified by bicinchoninic acid assay (BCA) and cryopreserved at –80 °C. hNPCs derived from surgical speciments digested with type II collagenase. After culture expansion in vitro, hNPCs in alginate beads (three-dimensional culture system) were treated with growth medium (controls), exosomes, CM, interleukin-1 beta (IL-1b), IL-1b plus exosomes, IL-1b plus CM. After 24 hours, total RNA was extracted and reverse-transcribed. Gene expression levels of catabolic and anabolic genes were analyzed through real time-polymerase chain reaction (qPCR). TEM analysis confirmed the cup-shaped vescicles in our preparations. Gene expression levels resulted to be modulated by both exosomes and CM compared to controls. In addition, both treatments were capable to alter the inflammatory stimuli of IL-1b. Interestingly, exosomes were able to change anabolic and catabolic gene expression levels differently from CM. In our experimental conditions, both exosomes and CM from BM-MSCs could be an interesting alternative strategy in intervertebral disc regeneration, overcoming the costs and translational limits of cell therapy to the clinical practice

Osteochondral (OC) defects of the knee are associated with pain and significant limitation of activity. Studies have demonstrated the therapeutic efficacy of mesenchymal stem cell (MSC) therapies in treating osteochondral defects. There is increasing evidence that the efficacy of MSC therapies may be a result of the paracrine secretion, particularly exosomes. Here, we examine the effects of MSC exosomes in combination with Hyaluronic Acid (HA) as an injectable therapy on functional osteochondral regeneration in a rabbit osteochondral defect model. Exosomes were purified from human MSC conditioned medium by size fractionation. A circular osteochondral defect of 4.5 mm diameter and 2.5 mm depth was surgically created in the trochlear grooves of 16 rabbit knees. Thereafter, eight knees received three weekly injections of 200 µg of exosomes in one ml of 3% HA, and the remaining eight knees received three weekly injections of one ml of 3% HA only. The rabbits were sacrificed at six weeks. Analyses were performed by macroscopic and histological assessments, and functional competence was analysed via Young Modulus calculation at five different points (central, superior, inferior, medial and lateral) of the repaired osteochondral defect site. MSC exosomes displayed a modal size of 100 nm and expressed exosome markers (CD81, TSG101 and ALIX). When compared to HA alone, MSC exosomes in combination with HA showed significantly better repair histologically and biomechanically. The Young Modulus was higher in 4 out of the 5 points. In the central region, the Young Modulus of MSC exosome and HA combination therapy was significantly higher: 5.42 MPa [SD=1.19, 95% CI: 3.93–6.90] when compared to HA alone: 2.87 MPa [SD=2.10, 95% CI: 0.26–5.49], p < 0 .05. The overall mean peripheral region was also significantly higher in the MSC exosome and HA combination therapy group: 5.87 MPa [SD=1.19, 95% CI: 4.40–7.35] when compared to HA alone: 2.70 MPa [SD=1.62, 95% CI: 0.79–4.71], p < 0 .05. The inferior region showed a significantly higher Young Modulus in the combination therapy: 7.34 MPa [SD=2.14, 95% CI: 4.68–10] compared to HA alone: 2.92 MPa [SD=0.98, 95% CI: 0.21–5.63], p < 0.05. The superior region showed a significantly higher Young Modulus in the combination therapy: 7.31 MPa [SD=3.29, 95% CI: 3.22–11.39] compared to HA alone: 3.59 MPa [SD=2.55, 95% CI: 0.42–6.76], p < 0.05. The lateral region showed a significantly higher Young Modulus in the combination therapy: 8.05 MPa [SD=2.06, 95% CI: 5.49–10.61] compared to HA alone: 3.56 MPa [SD=2.01, 95% CI: 1.06–6.06], p < 0.05. The medial region showed a higher Young Modulus in the combination therapy: 6.68 MPa [SD=1.48, 95% CI: 4.85–8.51] compared to HA alone: 3.45 MPa [SD=3.01, 95% CI: −0.29–7.19], but was not statistically significant. No adverse tissue reaction was observed in all the immunocompetent animals treated with MSC exosomes. Three weekly injections of MSC exosomes in combination with HA therapy results in a more functional osteochondral regeneration as compared to HA alone

Mesenchymal stem cells (MSC) are multipotent cells that possess regenerative functions that are of interest for in osteoarticular diseases such as osteoarthritis (OA). These functions are thought to be primarily mediated by mediators released within extracellular vesicles (EV). The aim of this study was to compare the immunomodulatory effects of two major types of EV, exosomes and microparticles, secreted by MSCs. EV subsets were isolated from murine primary MSCs by ultracentrifugation. Size and structure were evaluated by Dynamic Light Scattering and electron microscopy. Expression of membrane and endosomal markers was tested by flow cytometry. Proliferation of murine splenocytes was quantified after 72h of incubation with EVs after CFSE-labelling. Phenotypic analysis of T lymphocyte subpopulations was also performed by flow cytometry. In vivo, EVs were injected in the knee joint in the collagenase-induced osteoarthritis (CIOA) model and histological score was performed. In vitro functional analysis indicated that addition of microparticles or exosomes in proliferative assays inhibited the proliferation of total splenocytes in a dose-dependent manner. Analysis of T cell subpopulations revealed a decrease in CD8⁺IFNγ⁺ lymphocytes and an increase in both CD4⁺IL10⁺ Tr1 and CD4⁺CD25⁺FOXP3⁺ Treg cells. This immunomodulatory function of EVs was also observed in vivo in the CIOA model. In summary, our data indicated that the immunosuppressive effect of MSCs is in part mediated by exosomes and microparticles that play in vivo a major role in MSC-mediated therapeutic effect by reducing osteoarthritic symptoms.

Large bone defects remain a tremendous clinical challenge. There is growing evidence in support of treatment strategies that direct defect repair through an endochondral route, involving a cartilage intermediate. While culture-expanded stem/progenitor cells are being evaluated for this purpose, these cells would compete with endogenous repair cells for limited oxygen and nutrients within ischaemic defects. Alternatively, it may be possible to employ extracellular vesicles (EVs) secreted by culture-expanded cells for overcoming key bottlenecks to endochondral repair, such as defect vascularization, chondrogenesis, and osseous remodelling. While mesenchymal stromal/stem cells are a promising source of therapeutic EVs, other donor cells should also be considered. The efficacy of an EV-based therapeutic will likely depend on the design of companion scaffolds for controlled delivery to specific target cells. Ultimately, the knowledge gained from studies of EVs could one day inform the long-term development of synthetic, engineered nanovesicles. In the meantime, EVs harnessed from in vitro cell culture have near-term promise for use in bone regenerative medicine. This narrative review presents a rationale for using EVs to improve the repair of large bone defects, highlights promising cell sources and likely therapeutic targets for directing repair through an endochondral pathway, and discusses current barriers to clinical translation.

Cite this article: E. Ferreira, R. M. Porter. Harnessing extracellular vesicles to direct endochondral repair of large bone defects. Bone Joint Res 2018;7:263–273. DOI: 10.1302/2046-3758.74.BJR-2018-0006.

Objectives

Circulating exosomes represent novel biomarkers for multiple diseases. In this study, we investigated whether circulating exosome levels could be used as a diagnostic biomarker for steroid-induced osteonecrosis of the femoral head (ONFH).