The roles of bone-derived exosomes and exosomal microRNAs in regulating bone remodelling

Hydrogel-integrated exosome mimetics derived from osteogenically induced mesenchymal stem cells in spheroid culture enhance bone regeneration

Exosomes derived from mesenchymal stem cells (MSCs) offer a promising alternative to traditional cell-based therapies for tissue repair by mitigating risks associated with the transplantation of living cells. However, insufficient osteogenic capacity of exosomes diminishes their potential in bone tissue regeneration. Here, we report novel osteogenically induced exosome mimetics (EMs) integrated into injectable hydrogel carriers for improved bone regeneration. EMs were produced by a serial extrusion of MSCs cultured as spheroids during osteogenic induction. The prepared EMs were chemically anchored on a self-healing hydrogel assembled by guanidinylated hyaluronic acid and silica-rich nanoclays for sustained release of EMs. The administration of hydrogel-integrated EMs into mouse calvarial defects resulted in robust bone tissue regeneration. miRNA sequencing revealed altered expression of specific miRNAs in the EMs related to Wnt/β-catenin and Notch signaling pathways. Our study provides new insights into the development of advanced exosome-based cell-free therapies for bone tissue engineering.

Mineralized Osteoblast-Derived Exosomes and 3D-printed Ceramic-based Scaffolds for Enhanced Bone Healing: A Preclinical Exploration

In regenerative medicine, addressing the complex challenge of bone tissue regeneration demands innovative strategies. Exosomes, nanoscale vesicles rich in bioactive molecules, have shown great promise in tissue repair. This study focuses on exosomes derived from mineralized osteoblasts (MOBs), which play a pivotal role in bone formation. We investigated the therapeutic potential of exosomes isolated from osteoblasts cultured in osteogenic medium for 21 days, delivered via 3D-printed gyroid scaffolds composed of hydroxyapatite (HA) and tricalcium phosphate (TCP). The exosomes were characterized through nanoparticle tracking analysis to determine size, morphology, and concentration, while proteomics revealed their cargo contents. In vitro, rabbit bone marrow mesenchymal stromal cells (rBMSCs) were cultured as monolayers and within ceramic scaffolds, where MOB-derived exosomes were shown to promote osteogenic differentiation. In vivo, their osteoconductive and bone augmentation capabilities were evaluated in two rabbit calvarial models, while the osteoinductive potential was further tested in a heterotopic mouse model. Neo-bone formation was assessed using µCT and histological analysis. Our findings demonstrated that MOB-derived exosomes upregulated bone-related gene expression and promoted mineralization in rBMSCs, even in the absence of osteogenic medium. Proteomics confirmed the presence of bone-associated proteins in these exosomes. In rabbit models, however, exosomes did not significantly enhance bone formation. In contrast, in the heterotopic mouse model, exosomes functionalized onto ceramic scaffolds exhibited strong osteoinductive activity. This study highlights the potential of MOB-derived exosomes to enhance 3D-printed ceramic scaffolds for bone regeneration, offering a promising avenue for bone healing without the need for additional growth factors or stem cells. STATEMENT OF SIGNIFICANCE: The here presented report of our project not only advances our understanding of the role of exosome-functionalized scaffolds in bone regeneration but also proposes a promising alternative to traditional growth factor- or cell-based approaches. We are confident that this study represents a novel and impactful contribution to the field.

Intra-Bone Marrow Administration of miR-140-3p Improves Bone Metabolism in a Growing Senescence-Accelerated Mouse Prone 6 Strain

Background: Our previous study demonstrated that miR-140-3p induced osteocalcin expression in osteoblastic MC3T3-E1 cells. In this study, we investigated the direct effects of miR-140-3p on bone turnover in senescence-accelerated mice. Methods: In order to evaluate the effects of miR-140-3p, we formulated lipid nanoparticles (LNPs) containing miR-140-3p (100 μg/mL), with or without flotillin-2 (Flo2), a microvesicle marker excreted by osteoblasts. LNP was administered into the right tibia of the P6 strain of senescence-accelerated mice (SAMP6). Four-week-old SAMP6 males were divided into three groups: control, LNP, and LNP + Flo2. LNPs were administered five times, once every three days. No gait abnormalities were observed in any group. Two days after the last administration of LNPs, blood and urine samples were collected to measure bone turnover markers and blood chemistry and to perform urinalysis. Bone histomorphometry was performed on the left femur, contralateral to the administration site. The pancreas was removed for insulin staining of the Langerhans islets. Results: The LNP + Flo2 group showed greater bone volume, trabecular thickness, and osteoid thickness in bone histomorphometry. Carboxylated osteocalcin, a bone formation marker, was also higher in the LNP + Flo2 group, indicating that LNP + Flo2 activated osteoblastic function. Insulin levels in the islets of Langerhans did not differ across the groups, consistent with under-carboxylated osteocalcin levels. Conclusions: LNP + Flo2 effectively improved bone metabolism.

New-QiangGuYin-Containing Serum Inhibits Osteoclast-Derived Exosome Secretion and Down-Regulates Notum to Promote Osteoblast Differentiation

New-QiangGuYin (N-QGY), the addition of sea buckthorn on the basis of QGY formula, is herbal formula widely used clinically in China for the treatment of osteoporosis (OP), but its mechanism warrants further exploration. The mechanisms of QGY and N-QGY in the treatment of OP are probed from the perspective of osteoclast-osteoblast balance. Thirty Sprague-Dawley rats are randomly divided into N-QGY group, QGY group, and Control group. Beyond control rats that orally took normal saline, other rats are orally administered with isometric N-QGY or QGY twice every day for 3 days. The drug-containing serum and control serum are prepared and their effects on osteoclast-derived exosome secretion are determined by bicinchoninic acid assay (BCA), nanoparticle tracking analysis, and Western blot. GW4869 and Interleukin-1β (IL-1β) are adopted as the exosome inhibitor and inducer, respectively. Exosome uptake, cell counting kit-8, alkaline phosphatase (ALP) staining, alizarin red staining, enzyme-linked immunosorbent assay, quantitative real-time polymerase chain reaction, and Western blot are performed to examine the effects of altered osteoclast exosome content on osteogenic differentiation of mesenchymal stem cells (MSCs). N-QGY, QGY, and GW4869 inhibit osteoclast-derived exosome secretion and exosome uptake by MSCs, whereas IL-1β exerted the opposite effects (p < 0.05). Different from IL-1β, N-QGY, QGY, and GW4869 partially elevated MSC viability, osteocalcin secretion, ALP, RUNX Family Transcription Factor 2 (RUNX2) and Osteopontin (OPN) expressions, and calcium deposition in the osteoclast-MSCs coculture system (p < 0.05). Mechanically, osteoclasts increased Notum protein level but decreased β-catenin level, which is enhanced by IL-1β but is reversed by GW4869, QGY, and N-QGY (p < 0.05). And the effect of N-QGY is more conspicuous than that of QGY (P<0.05). N-QGY-containing serum inhibits exosome levels in osteoclasts, thereby enhancing osteogenic differentiation of MSCs via inhibition of Notum protein and promotion of β-catenin protein.

The potential link between the development of Alzheimer's disease and osteoporosis

Alzheimer's disease (AD) and osteoporosis (OP) pose distinct but interconnected health challenges, both significantly impacting the aging population. AD, a neurodegenerative disorder characterized by memory impairment and cognitive decline, is primarily associated with the accumulation of abnormally folded amyloid beta (Aβ) peptides and neurofibrillary tangles in the brain. OP, a skeletal disorder marked by low bone mineral density, involves dysregulation of bone remodeling and is associated with an increased risk of fractures. Recent studies have revealed an intriguing link between AD and OP, highlighting shared pathological features indicative of common regulatory pathophysiological pathways. In this article, we elucidate the signaling mechanisms that regulate the pathology of AD and OP and offer insights into the intricate network of factors contributing to these conditions. We also examine the role of bone-derived factors in the progression of AD, underscoring the plausibility of bidirectional communication between the brain and the skeletal system. The presence of amyloid plaques in the brain of individuals with AD is akin to the accumulation of brain Aβ in vascular dementia, pointing towards the need for further investigation of shared molecular mechanisms. Moreover, we discuss the role of bone-derived microRNAs that may regulate the pathological progression of AD, providing a novel perspective on the role of skeletal factors in neurodegenerative diseases. The insights presented here should help researchers engaged in exploring innovative therapeutic approaches targeting both neurodegenerative and skeletal disorders in aging populations.

Extracellular vesicles: essential agents in critical bone defect repair and therapeutic enhancement

Bone serves as a fundamental structural component in the body, playing pivotal roles in support, protection, mineral supply, and hormonal regulation. However, critical-sized bone injuries have become increasingly prevalent, necessitating extensive medical interventions due to limitations in the body's capacity for self-repair. Traditional approaches, such as autografts, allografts, and xenografts, have yielded unsatisfactory results. Stem cell therapy emerges as a promising avenue, but challenges like immune rejection and low cell survival rates hinder its widespread clinical implementation. Extracellular vesicles (EVs) derived from mesenchymal stem cells (MSCs) have garnered attention for their regenerative capabilities, which surpass those of MSCs themselves. EVs offer advantages such as reduced immunogenicity, enhanced stability, and simplified storage, positioning them as a promising tool in stem cell-based therapies. This review explores the potential of EV-based therapy in bone tissue regeneration, delving into their biological characteristics, communication mechanisms, and preclinical applications across various physiological and pathological conditions. The mechanisms underlying EV-mediated bone regeneration, including angiogenesis, osteoblast proliferation, mineralization, and immunomodulation, are elucidated. Preclinical studies demonstrate the efficacy of EVs in promoting bone repair and neovascularization, even in pathological conditions like osteoporosis. EVs hold promise as a potential alternative for regenerating bone tissue, particularly in the context of critical-sized bone defects, offering new avenues for effective bone defect repair and management.

The Potential for Extracellular Vesicles in Nanomedicine: A Review of Recent Advancements and Challenges Ahead

Extracellular vesicles (EVs) have emerged as promising tools in diagnostics and therapy for chronic diseases, including cancer and Alzheimer's. Small EVs, also called exosomes, are lipid-bound particles (≈30-150 nm) that play a role in healthy and pathophysiological interactions, including intercellular communication, by transporting bioactive molecules, including proteins, lipids, and nucleic acids. Their ability to cross biological barriers, such as the blood-brain barrier, makes them ideal candidates for targeted therapeutic interventions. In the context of chronic diseases, exosomes can be engineered to deliver active agents, including small molecules and siRNAs to specific target cells, providing a novel approach to precision medicine. Moreover, exosomes show great promise as repositories for diagnostic biomarkers. Their cargo can reflect the physiological and pathological status of the parent cells, making them valuable indicators of disease progression and response to treatment. This paper presents a comprehensive review of the application of exosomes in four chronic diseases: cancer, cardiovascular disease, neurodegenerative disease, and orthopedic disease, which significantly impact global public health due to their high prevalence and associated morbidity and mortality rates. Furthermore, the potential of exosomes as valuable tools for theranostics and disease management is highlighted. Finally, the challenges associated with exosomes and their demonstrated potential for advancing future nanomedicine applications are discussed.

Exosomal therapy is a luxury area for regenerative medicine

Stem cell-based therapies have made significant advancements in tissue regeneration and medical engineering. However, there are limitations to cell transplantation therapy, such as immune rejection and limited cell viability. These limitations greatly impede the translation of stem cell-based tissue regeneration into clinical practice. In recent years, exosomes, which are packaged vesicles released from cells, have shown promising progress. Specifically, exosomes derived from stem cells have demonstrated remarkable therapeutic benefits. Exosomes are nanoscale extracellular vesicles that act as paracrine mediators. They transfer functional cargos, such as miRNA and mRNA molecules, peptides, proteins, cytokines, and lipids, from MSCs to recipient cells. By participating in intercellular communication events, exosomes contribute to the healing of injured or diseased tissues and organs. Studies have shown that the therapeutic effects of MSCs in various experimental paradigms can be solely attributed to their exosomes. Consequently, MSC-derived exosomes can be modified and utilized to develop a unique cell-free therapeutic approach for treating multiple diseases, including neurological, immunological, heart, and other diseases. This review is divided into several categories, including the current understanding of exosome biogenesis, isolation techniques, and their application as therapeutic tools.

Precision medicine in axial spondyloarthritis: current opportunities and future perspectives

Axial spondyloarthritis (axSpA) is a complex disease characterized by a diverse range of clinical presentations. The primary manifestation is inflammatory lower back pain, often accompanied by other clinical manifestations such as peripheral arthritis, enthesitis, uveitis, psoriasis, and inflammatory bowel disease. However, the presentation of axSpA can vary widely among patients. Despite extensive research, the precise pathogenesis of axSpA remains largely unknown. The lack of complete understanding poses challenges in subgrouping the disease, developing specific treatment approaches, and predicting treatment response. In this review, we will explore the limitations in diagnosing and treating axSpA. In addition, we will examine the current knowledge and potential opportunities provided by various omics and technological advancements in enhancing the diagnosis and personalized treatment of axSpA.

Crosstalk between bone and brain in Alzheimer's disease: Mechanisms, applications, and perspectives

Alzheimer's disease (AD) is a neurodegenerative disease that involves multiple systems in the body. Numerous recent studies have revealed bidirectional crosstalk between the brain and bone, but the interaction between bone and brain in AD remains unclear. In this review, we summarize human studies of the association between bone and brain and provide an overview of their interactions and the underlying mechanisms in AD. We review the effects of AD on bone from the aspects of AD pathogenic proteins, AD risk genes, neurohormones, neuropeptides, neurotransmitters, brain-derived extracellular vesicles (EVs), and the autonomic nervous system. Correspondingly, we elucidate the underlying mechanisms of the involvement of bone in the pathogenesis of AD, including bone-derived hormones, bone marrow-derived cells, bone-derived EVs, and inflammation. On the basis of the crosstalk between bone and the brain, we propose potential strategies for the management of AD with the hope of offering novel perspectives on its prevention and treatment. HIGHLIGHTS: The pathogenesis of AD, along with its consequent changes in the brain, may involve disturbing bone homeostasis. Degenerative bone disorders may influence the progression of AD through a series of pathophysiological mechanisms. Therefore, relevant bone intervention strategies may be beneficial for the comprehensive management of AD.

Engineering extracellular vesicles for ROS scavenging and tissue regeneration

Stem cell therapy holds promise for tissue regeneration, yet significant challenges persist. Emerging as a safer and potentially more effective alternative, extracellular vesicles (EVs) derived from stem cells exhibit remarkable abilities to activate critical signaling cascades, thereby facilitating tissue repair. EVs, nano-scale membrane vesicles, mediate intercellular communication by encapsulating a diverse cargo of proteins, lipids, and nucleic acids. Their therapeutic potential lies in delivering cargos, activating signaling pathways, and efficiently mitigating oxidative stress-an essential aspect of overcoming limitations in stem cell-based tissue repair. This review focuses on engineering and applying EVs in tissue regeneration, emphasizing their role in regulating reactive oxygen species (ROS) pathways. Additionally, we explore strategies to enhance EV therapeutic activity, including functionalization and incorporation of antioxidant defense proteins. Understanding these molecular mechanisms is crucial for optimizing EV-based regenerative therapies. Insights into EV and ROS signaling modulation pave the way for targeted and efficient regenerative therapies harnessing the potential of EVs.

Cold exposure-induced plasma exosomes impair bone mass by inhibiting autophagy

Recently, environmental temperature has been shown to regulate bone homeostasis. However, the mechanisms by which cold exposure affects bone mass remain unclear. In our present study, we observed that exposure to cold temperature (CT) decreased bone mass and quality in mice. Furthermore, a transplant of exosomes derived from the plasma of mice exposed to cold temperature (CT-EXO) can also impair the osteogenic differentiation of BMSCs and decrease bone mass by inhibiting autophagic activity. Rapamycin, a potent inducer of autophagy, can reverse cold exposure or CT-EXO-induced bone loss. Microarray sequencing revealed that cold exposure increases the miR-25-3p level in CT-EXO. Mechanistic studies showed that miR-25-3p can inhibit the osteogenic differentiation and autophagic activity of BMSCs. It is shown that inhibition of exosomes release or downregulation of miR-25-3p level can suppress CT-induced bone loss. This study identifies that CT-EXO mediates CT-induced osteoporotic effects through miR-25-3p by inhibiting autophagy via targeting SATB2, presenting a novel mechanism underlying the effect of cold temperature on bone mass.

A novel cell-free therapy using exosomes in the inner ear regeneration

Cellular and molecular alterations associated with hearing loss are now better understood with advances in molecular biology. These changes indicate the participation of distinct damage and stress pathways that are unlikely to be fully addressed by conventional pharmaceutical treatment. Sensorineural hearing loss is a common and debilitating condition for which comprehensive pharmacologic intervention is not available. The complex and diverse molecular pathology that underlies hearing loss currently limits our ability to intervene with small molecules. The present review focuses on the potential for the use of extracellular vesicles in otology. It examines a variety of inner ear diseases and hearing loss that may be treatable using exosomes (EXOs). The role of EXOs as carriers for the treatment of diseases related to the inner ear as well as EXOs as biomarkers for the recognition of diseases related to the ear is discussed.

Mesenchymal stem cell-derived extracellular vesicles: a regulator and carrier for targeting bone-related diseases

The escalating threat of bone-related diseases poses a significant challenge to human health. Mesenchymal stem cell (MSC)-derived extracellular vesicles (MSC-EVs), as inherent cell-secreted natural products, have emerged as promising treatments for bone-related diseases. Leveraging outstanding features such as high biocompatibility, low immunogenicity, superior biological barrier penetration, and extended circulating half-life, MSC-EVs serve as potent carriers for microRNAs (miRNAs), long no-code RNAs (lncRNAs), and other biomolecules. These cargo molecules play pivotal roles in orchestrating bone metabolism and vascularity through diverse mechanisms, thereby contributing to the amelioration of bone diseases. Additionally, engineering modifications enhance the bone-targeting ability of MSC-EVs, mitigating systemic side effects and bolstering their clinical translational potential. This review comprehensively explores the mechanisms through which MSC-EVs regulate bone-related disease progression. It delves into the therapeutic potential of MSC-EVs as adept drug carriers, augmented by engineered modification strategies tailored for osteoarthritis (OA), rheumatoid arthritis (RA), osteoporosis, and osteosarcoma. In conclusion, the exceptional promise exhibited by MSC-EVs positions them as an excellent solution with considerable translational applications in clinical orthopedics.

Osteogenically committed hUCMSCs-derived exosomes promote the recovery of critical-sized bone defects with enhanced osteogenic properties

Low viability of seed cells and the concern about biosafety restrict the application of cell-based tissue-engineered bone (TEB). Exosomes that bear similar bioactivities to donor cells display strong stability and low immunogenicity. Human umbilical cord mesenchymal stem cells-derived exosomes (hUCMSCs-Exos) show therapeutic efficacy in various diseases. However, little is known whether hUCMSCs-Exos can be used to construct TEB to repair bone defects. Herein, PM-Exos and OM-Exos were separately harvested from hUCMSCs which were cultured in proliferation medium (PM) or osteogenic induction medium (OM). A series of in-vitro studies were performed to evaluate the bioactivities of human bone marrow mesenchymal stem cells (hBMSCs) when co-cultured with PM-Exos or OM-Exos. Differential microRNAs (miRNAs) between PM-Exos and OM-Exos were sequenced and analyzed. Furthermore, PM-Exos and OM-Exos were incorporated in 3D printed tricalcium phosphate scaffolds to build TEBs for the repair of critical-sized calvarial bone defects in rats. Results showed that PM-Exos and OM-Exos bore similar morphology and size. They expressed representative surface markers of exosomes and could be internalized by hBMSCs to promote cellular migration and proliferation. OM-Exos outweighed PM-Exos in accelerating the osteogenic differentiation of hBMSCs, which might be attributed to the differentially expressed miRNAs. Furthermore, OM-Exos sustainably released from the scaffolds, and the resultant TEB showed a better reparative outcome than that of the PM-Exos group. Our study found that exosomes isolated from osteogenically committed hUCMSCs prominently facilitated the osteogenic differentiation of hBMSCs. TEB grafts functionalized by OM-Exos bear a promising application potential for the repair of large bone defects.

Exosomal circ_0000722 derived from periodontal ligament stem cells undergoing osteogenic differentiation promotes osteoclastogenesis

Periodontal ligament stem cells (PDLSCs), which are considered promising stem cells for regeneration of periodontal bony tissue, can also manipulate alveolar bone remodeling by exosomes. In this study, we investigated interactions between PDLSCs under osteogenic differentiation and osteoclast precursors. The results showed that conditioned medium from PDLSCs under 5d osteogenic induction promoted osteoclastogenesis of RAW264.7 cells. The exosomes extracted from those conditioned media showed similar effects on osteoclastogenesis. Furthermore, exosomes from PDLSCs under 5d of osteogenic induction showed significantly high expression of circ_0000722, compared with exosomes from PDLSCs before osteogenic induction. Downregulation of circ_0000722 significantly attenuated the effect of PDLSC-derived exosomes on the osteoclastogenesis of RAW264.7 cells. Our findings suggested that exosomal circ_0000722 derived from periodontal ligament stem cells undergoing osteogenic differentiation might promote osteoclastogenesis by upregulating TRAF6 expression and activating downstream NF-κB and AKT signaling pathways.

Platelet-rich plasma-derived exosomes promote rotator cuff tendon-bone healing

BACKGROUND

Rotator cuff tear (RCT) is the most common type of shoulder joint injury, platelet-rich plasma-derived exosomes (PRP-exos) are highly promising in tissue repair and regeneration. The purpose of this study was to determine the function of PRP-exos in rotator cuff tendon-bone healing.

METHODS

PRP-exos were isolated from the rabbit whole blood by differential ultracentrifugation and characterized through transmission electron microscopy assay, nanoparticle tracking analysis, and western blotting. Alkaline phosphatase and Von Kossa staining were used to show tendon-derived stem cell (TDSC) differentiation. RT-qPCR and western blotting were performed to detect COL II, SOX-9, and TIMP-1. To determine the therapeutic effects of PRP-exos in vivo. Thirty New Zealand white rabbits were divided into control, model, and PRP-exos groups. The RCT animal model was constructed. The changes in tendon-bone tissue were determined by HE staining. Contents of COL-II, SOX-9, and TIMP-1 were determined by immunohistochemistry staining.

RESULTS

PRP-exos were successfully isolated from rabbit blood. PRP-exos promoted TDSC proliferation and differentiation and also induced tendon-specific markers COL II, SOX-9, and TIMP-1 production. In vivo study revealed that PRP-exos promoted early healing of injured tendons. Rabbits treated with PRP-exos had better tissue arrangement in the tear site. Additionally, the contents of COL II, SOX-9, and TIMP-1 were also increased in the RCT rabbit model after PRP-exos treatment.

CONCLUSIONS

PRP-exos enhanced tendon-bone healing by promoting TDSC proliferation and differentiation. This finding indicates that PRP-exos can serve as a promising strategy to treat rotator cuff tendon-bone healing.

Bone marrow mesenchymal stem cell‑derived exosomes: A novel therapeutic agent for tendon‑bone healing (Review)

In sports medicine, injuries related to the insertion of tendons into bones, including rotator cuff injuries, anterior cruciate ligament injuries and Achilles tendon ruptures, are commonly observed. However, traditional therapies have proven to be insufficient in achieving satisfactory outcomes due to the intricate anatomical structure associated with these injuries. Adult bone marrow mesenchymal stem cells possess self‑renewal and multi‑directional differentiation potential and can generate various mesenchymal tissues to aid in the recovery of bone, cartilage, adipose tissue and bone marrow hematopoietic tissue. In addition, extracellular vesicles derived from bone marrow mesenchymal stem cells known as exosomes, contain lipids, proteins and nucleic acids that govern the tissue microenvironment, facilitate tissue repair and perform various biological functions. Studies have demonstrated that bone marrow mesenchymal stem cell‑derived exosomes can function as natural nanocapsules for drug delivery and can enhance tendon‑bone healing strength. The present review discusses the latest research results on the role of exosomes released by bone marrow mesenchymal stem cells in tendon‑bone healing and provides valuable information for implementing these techniques in regenerative medicine and sports health.

Optimization of exosome-based cell-free strategies to enhance endogenous cell functions in tissue regeneration

Exosomes, nanoscale extracellular vesicles, play a crucial role in intercellular communication, owing to their biologically active cargoes such as RNAs and proteins. In recent years, they have emerged as a promising tool in the field of tissue regeneration, with the potential to initiate a new trend in cell-free therapy. However, it's worth noting that not all types of exosomes derived from cells are appropriate for tissue repair. Thus, selecting suitable cell sources is critical to ensure their efficacy in specific tissue regeneration processes. Current therapeutic applications of exosomes also encounter several limitations, including low-specific content for targeted diseases, non-tissue-specific targeting, and short retention time due to rapid clearance in vivo. Consequently, this review paper focuses on exosomes from diverse cell sources with functions specific to tissue regeneration. It also highlights the latest engineering strategies developed to overcome the functional limitations of natural exosomes. These strategies encompass the loading of specific therapeutic contents into exosomes, the endowment of tissue-specific targeting capability on the exosome surface, and the incorporation of biomaterials to extend the in vivo retention time of exosomes in a controlled-release manner. Collectively, these innovative approaches aim to synergistically enhance the therapeutic effects of natural exosomes, optimizing exosome-based cell-free strategies to boost endogenous cell functions in tissue regeneration. STATEMENT OF SIGNIFICANCE: Exosome-based cell-free therapy has recently emerged as a promising tool for tissue regeneration. This review highlights the characteristics and functions of exosomes from different sources that can facilitate tissue repair and their contributions to the regeneration process. To address the functional limitations of natural exosomes in therapeutic applications, this review provides an in-depth understanding of the latest engineering strategies. These strategies include optimizing exosomal contents, endowing tissue-specific targeting capability on the exosome surface, and incorporating biomaterials to extend the in vivo retention time of exosomes in a controlled-release manner. This review aims to explore and discuss innovative approaches that can synergistically improve endogenous cell functions in advanced exosome-based cell-free therapies for a broad range of tissue regeneration.

Bone marrow-derived exosomes promote inflammation and osteoclast differentiation in high-turnover renal osteodystrophy

Introduction: Renal osteodystrophy (ROD) is a type of bone metabolic disorder in patients with chronic kidney disease (CKD). Inflammation is associated with bone loss in ROD. However, its precise mechanism has not yet been elucidated. The present study was conducted to investigate whether exosomes (Exos) in bone marrow (BM) are involved in the pathogenesis of high-turnover ROD.Methods: Bone mass, osteoclast number, and pro-inflammatory cytokines levels of BM supernatant were detected in adenine-induced ROD rats. The effect of Exos derived from BM (BM-Exos) of ROD (ROD-Exos) on inflammatory genes and osteoclast differentiation of BM-derived macrophages (BMMs) were further examined. Then, exosomal miRNA sequencing was performed and an miRNA-mRNA-pathway network was constructed.Results: we found increased osteoclasts and decreased bone mass in ROD rats, as well as inflammatory activation in the BM niche. Furthermore, BMMs from ROD rats displayed overproduction of proinflammatory cytokines and increased osteoclast differentiation, accompanied by nuclear factor κB (NF-κB) signaling activation. Mechanistically, we found that ROD-Exos activates NF-κB signaling to promote the release of proinflammatory cytokines and increase osteoclast differentiation of BMMs. Meanwhile, a total of 24 differentially expressed miRNAs were identified between BM-Exos from ROD and normal control (NC). The miRNA-mRNA-pathway network suggests that rno-miR-9a-5p, rno-miR-133a-3p, rno-miR-30c-5p, rno-miR-206-3p, and rno-miR-17-5p might play pivotal roles in inflammation and osteoclast differentiation. Additionally, we validated that the expression of miR-9a-5p is upregulated in ROD-Exos.Conclusion: The BM niche of ROD alters the miRNA cargo of BM-Exos to promote inflammation and osteoclast differentiation of BMMs, at least partially contributing to the pathogenesis of high-turnover ROD.

Application of cell-derived exosomes in the hematological malignancies therapy

Exosomes are small membrane vesicles of endocytic origin that are produced by both tumor and normal cells and can be found in physiological fluids like plasma and cell culture supernatants. They include cytokines, growth factors, proteins, lipids, RNAs, and metabolites and are important intercellular communication controllers in several disorders. According to a vast amount of research, exosomes could support or inhibit tumor start and diffusion in a variety of solid and hematological malignancies by paracrine signaling. Exosomes are crucial therapeutic agents for a variety of illnesses, such as cancer and autoimmune diseases. This review discusses the most current and encouraging findings from in vitro and experimental in vivo research, as well as the scant number of ongoing clinical trials, with a focus on the impact of exosomes in the treatment of malignancies. Exosomes have great promise as carriers of medications, antagonists, genes, and other therapeutic materials that can be incorporated into their core in a variety of ways. Exosomes can also alter the metabolism of cancer cells, alter the activity of immunologic effectors, and alter non-coding RNAs, all of which can alter the tumor microenvironment and turn it from a pro-tumor to an anti-tumor milieu. This subject is covered in the current review, which also looks at how exosomes contribute to the onset and progression of hematological malignancies, as well as their importance in diagnosing and treating these conditions.

Cell-Based Therapies for Degenerative Musculoskeletal Diseases

Degenerative musculoskeletal diseases (DMDs), including osteoporosis, osteoarthritis, degenerative disc disease, and sarcopenia, present major challenges in the aging population. Patients with DMDs present with pain, functional decline, and reduced exercise tolerance, which result in long-term or permanent deficits in their ability to perform daily activities. Current strategies for dealing with this cluster of diseases focus on relieving pain, but they have a limited capacity to repair function or regenerate tissue. Cell-based therapies have attracted considerable attention in recent years owing to their unique mechanisms of action and remarkable effects on regeneration. In this review, current experimental attempts to use cell-based therapies for DMDs are highlighted, and the modes of action of different cell types and their derivatives, such as exosomes, are generalized. In addition, the latest findings from state-of-the-art clinical trials are reviewed, approaches to improve the efficiency of cell-based therapies are summarized, and unresolved questions and potential future research directions for the translation of cell-based therapies are identified.

Biological characteristics of microRNAs secreted by exosomes of periodontal ligament stem cells due to mechanical force

BACKGROUND

Orthodontic tooth movement (OTM) has previously been considered an inflammatory process. However, recent studies suggest that exosomes may play an important role in the cellular microenvironment of OTM. microRNAs (miRNAs) are one of the major constituents of exosomes. This study aims to investigate the biological characteristics of miRNAs secreted by exosomes of periodontal ligament stem cells (PDLSCs) due to mechanical forces.

MATERIALS AND METHODS

First, we established a mechanical stress model. The PDLSCs were loaded under different force values and exosomes were extracted after 48 h. High-throughput sequencing of exosomal miRNAs was performed to further evaluate their biological functions and underlying mechanisms.

RESULTS

The morphology and functions of exosomes were not significantly different between the loading and non-loading PDLSC groups. The optimal loading time and force were 48 h and 1 g/cm2, respectively. After sequencing, gene ontology (GO) and Kyoto encyclopaedia of genes and genomes (KEGG) pathway and network analyses were performed and 10 differentially expressed miRNAs were identified according to a literature search. These are miR-99a-5p, miR-485-3P, miR-29a-3p,miR-21-5p, miR-146a-5p, miR140-3p, miR-1306-5p, miR-126-5p, miR-125a-5p, and miR-23a-3p.

LIMITATIONS

Extracting exosomes needs a large amount of PDLSCs. More functional experiments need to be done to confirm the exact mechanism of exosomal miRNAs of PDLSCs due to mechanical force.

CONCLUSIONS

The expression levels of miRNAs secreted by PDLSC-derived exosomes due to mechanical force were very different compared to PDLSC-derived exosomes under nonmechanical stress. The function of many of the identified exosomal miRNAs was found to be related to osteoblasts and osteoclasts. Further validation is required. A functional investigation of these miRNA could provide novel insights into their mechanism.

Apoptotic Vesicles Regulate Bone Metabolism via the miR1324/SNX14/SMAD1/5 Signaling Axis

Mesenchymal stem cells (MSCs) are widely used in the treatment of diseases. After their in vivo application, MSCs undergo apoptosis and release apoptotic vesicles (apoVs). This study investigates the role of apoVs derived from human bone marrow mesenchymal stem cells (hBMMSCs) in bone metabolism and the molecular mechanism of the observed effects. The results show that apoVs can promote osteogenesis and inhibit osteoclast formation in vitro and in vivo. ApoVs may therefore attenuate the bone loss caused by primary and secondary osteoporosis and stimulate bone regeneration in areas of bone defect. The mechanisms responsible for apoV-induced bone regeneration include the release of miR1324, which inhibit expression of the target gene Sorting Nexin 14 (SNX14) and thus activate the SMAD1/5 pathway in target cells. Given that MSC-derived apoVs are easily obtained and stored, with low risks of immunological rejection and neoplastic transformation, The findings suggest a novel therapeutic strategy to treat bone loss, including via cell-free approaches to bone tissue engineering.

Engineering exosomes and biomaterial-assisted exosomes as therapeutic carriers for bone regeneration

Mesenchymal stem cell-based therapy has become an effective therapeutic approach for bone regeneration. However, there are still limitations in successful clinical translation. Recently, the secretome of mesenchymal stem cells, especially exosome, plays a critical role in promoting bone repair and regeneration. Exosomes are nanosized, lipid bilayer-enclosed structures carrying proteins, lipids, RNAs, metabolites, growth factors, and cytokines and have attracted great attention for their potential application in bone regenerative medicine. In addition, preconditioning of parental cells and exosome engineering can enhance the regenerative potential of exosomes for treating bone defects. Moreover, with recent advancements in various biomaterials to enhance the therapeutic functions of exosomes, biomaterial-assisted exosomes have become a promising strategy for bone regeneration. This review discusses different insights regarding the roles of exosomes in bone regeneration and summarizes the applications of engineering exosomes and biomaterial-assisted exosomes as safe and versatile bone regeneration agent delivery platforms. The current hurdles of transitioning exosomes from bench to bedside are also discussed.

Dermal PapillaCell-Derived Exosomes Regulate Hair Follicle Stem Cell Proliferation via LEF1

Hair follicle (HF) growth and development are controlled by various cell types, including hair follicle stem cells (HFSCs) and dermal papilla cells (DPCs). Exosomes are nanostructures that participate in many biological processes. Accumulating evidence indicates that DPC-derived exosomes (DPC-Exos) mediate HFSC proliferation and differentiation during the cyclical growth of hair follicles. In this study, we found that DPC-Exos increase ki67 expression and CCK8 cell viability readouts in HFSCs but reduce annexin staining of apoptotic cells. RNA sequencing of DPC-Exos-treated HFSCs identified 3702 significantly differentially expressed genes (DEGs), including BMP4, LEF1, IGF1R, TGFβ3, TGFα, and KRT17. These DEGs were enriched in HF growth- and development-related pathways. We further verified the function of LEF1 and showed that overexpression of LEF1 increased the expression of HF development-related genes and proteins, enhanced HFSC proliferation, and reduced HFSC apoptosis, while knockdown of LEF1 reversed these effects. DPC-Exos could also rescue the siRNA-LEF1 effect in HFSCs. In conclusion, this study demonstrates that DPC-Exos mediated cell-to-cell communication can regulate HFSCs proliferation by stimulating LEF1 and provide novel insights into HF growth and development regulatory mechanisms.

Titanium dioxide nanoparticles affect osteoblast-derived exosome cargos and impair osteogenic differentiation of human mesenchymal stem cells

Titanium (Ti) and its alloys are the most widely used metallic biomaterials in total joint replacement; however, increasing evidence supports the degradation of its surface due to corrosion and wear processes releasing debris (ions, and micro and nanoparticles) and contribute to particle-induced osteolysis and implant loosening. Cell-to-cell communication involving several cell types is one of the major biological processes occurring during bone healing and regeneration at the implant-bone interface. In addition to the internal response of cells to the uptake and intracellular localization of wear debris, a red flag is the ability of titanium dioxide nanoparticles (mimicking wear debris) to alter cellular communication with the tissue background, disturbing the balance between osseous tissue integrity and bone regenerative processes. This study aims to understand whether titanium dioxide nanoparticles (TiO₂ NPs) alter osteoblast-derived exosome (Exo) biogenesis and whether exosomal protein cargos affect the communication of osteoblasts with human mesenchymal stem/stromal cells (HMSCs). Osteoblasts are derived from mesenchymal stem cells coexisting in the bone microenvironment during development and remodelling. We observed that TiO₂ NPs stimulate immature osteoblast- and mature osteoblast-derived Exo secretion that present a distinct proteomic cargo. Functional tests confirmed that Exos derived from both osteoblasts decrease the osteogenic differentiation of HMSCs. These findings are clinically relevant since wear debris alter extracellular communication in the bone periprosthetic niche, contributing to particle-induced osteolysis and consequent prosthetic joint failure.

Osteo-Immunomodulatory Role of Interleukin-4-Immobilized Plasma Immersion Ion Implantation Membranes for Bone Regeneration

Barrier membranes for guided tissue regeneration are essential for bone repair and regeneration. The implanted membranes may trigger early inflammatory responses as a foreign material, which can affect the recruitment and differentiation of bone cells during tissue regeneration. The purpose of this study was to determine whether immobilizing interleukin 4 (IL4) on plasma immersion ion implantation (PIII)-activated surfaces may alter the osteo-immunoregulatory characteristics of the membranes and produce pro-osteogenic effects. In order to immobilize IL4, polycaprolactone surfaces were modified using the PIII technology. No discernible alterations were found between the morphology before and after PIII treatment or IL4 immobilization. IL4-immobilized PIII surfaces polarized macrophages to an M2 phenotype and mitigated inflammatory cytokine production under lipopolysaccharide stimulation. Interestingly, the co-culture of macrophages (on IL4-immobilized PIII surfaces) and bone marrow-derived mesenchymal stromal cells enhanced the production of angiogenic and osteogenic factors and triggered autophagy activation. Exosomes produced by PIII + IL4-stimulated macrophages were also found to play a role in osteoblast differentiation. In conclusion, the osteo-immunoregulatory properties of bone materials can be modified by PIII-assisted IL4 immobilization, creating a favorable osteoimmune milieu for bone regeneration.

Advances in the Study of Exosomes as Drug Delivery Systems for Bone-Related Diseases

Bone-related diseases are major problems and heavy burdens faced by modern society. Current clinical approaches for the treatment of these pathological conditions often lead to complications and have limited therapeutic efficacy. In this context, the development of nanotherapeutic platforms, such as extracellular vesicles, can improve the relevant therapeutic effects. In particular, exosomes are nano-sized, lipid bilayer extracellular vesicles secreted by many cells in mammals. Due to their innate capacity to transport materials-including proteins, lipids, and genes-among cells, as well as their innate attraction to target cells, they are considered to be a crucial medium for cell communication and are involved in a number of biological processes. Exosomes have been used as drug delivery vehicles in recent bone tissue engineering studies, in order to regulate bone homeostasis. However, the precise workings of the exosome regulatory network in maintaining bone homeostasis and its potential for treating bone injury remain unclear. To provide a fresh perspective for the study of exosomes in drug delivery and bone-related diseases, in this paper, we review recent studies on the roles of exosomes for drug delivery in bone homeostasis and bone-related diseases, as well as the composition and characteristics of exosomes and their regulatory roles in bone homeostasis and bone-related diseases, aiming to provide new ideas for the therapeutic application of exosomes in the treatment of bone-related diseases.

Extracellular Vesicles in Bone Remodeling and Osteoporosis

Osteoporosis is a systemic disorder characterized by bone mass loss, leading to fractures due to weak and brittle bones. The bone tissue deterioration process is related to an impairment of bone remodeling orchestrated mainly by resident bone cells, including osteoblasts, osteoclasts, osteocytes, and their progenitors. Extracellular vesicles (EVs) are nanoparticles emerging as regulatory molecules and potential biomarkers for bone loss. Although the progress in studies relating to EVs and bone loss has increased in the last years, research on bone cells, animal models, and mainly patients is still limited. Here, we aim to review the recent advances in this field, summarizing the effect of EV components such as proteins and miRNAs in regulating bone remodeling and, consequently, osteoporosis progress and treatment. Also, we discuss the potential application of EVs in clinical practice as a biomarker and bone loss therapy, demonstrating that this rising field still needs to be further explored.

miR-92a-3p encapsulated in bone metastatic mammary tumor cell-derived extracellular vesicles modulates mature osteoclast longevity

Aberrant osteoclast formation and activation are the hallmarks of osteolytic metastasis. Extracellular vesicles (EVs), released from bone metastatic tumor cells, play a pivotal role in the progression of osteolytic lesions. However, the mechanisms through which tumor cell-derived EVs regulate osteoclast differentiation and function have not been fully elucidated. In this study, we found that 4T1 bone metastatic mouse mammary tumor cell-derived EVs (4T1-EVs) are taken up by mouse bone marrow macrophages to facilitate osteoclastogenesis. Furthermore, treatment of mature osteoclasts with 4T1-EVs promoted bone resorption, which was accompanied by enhanced survival of mature osteoclasts through the negative regulation of caspase-3. By comparing the miRNA content in 4T1-EVs with that in 67NR nonmetastatic mouse mammary tumor cell-derived EVs (67NR-EVs), miR-92a-3p was identified as one of the most enriched miRNAs in 4T1-EVs, and its transfer into mature osteoclasts significantly reduced apoptosis. Bioinformatic and Western blot analyses revealed that miR-92a-3p directly targeted phosphatase and tensin homolog (PTEN) in mature osteoclasts, resulting in increased levels of phospho-Akt. Our findings provide novel insights into the EV-mediated regulation of osteoclast survival through the transfer of miR-92a-3p, which enhances mature osteoclast survival via the Akt survival signaling pathway, thus promoting bone resorption.

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.

Exosomes in bone remodeling and breast cancer bone metastasis

Exosomes are endosome-derived microvesicles that carry cell-specific biological cargo, such as proteins, lipids, and noncoding RNAs (ncRNAs). They play a key role in bone remodeling by enabling the maintenance of a balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption. Recent evidence indicates that exosomes disrupt bone remodeling that occurs during breast cancer (BC) progression. The bone is a preferred site for BC metastasis owing to its abundant osseous reserves. In this review, we aimed to highlight the roles of exosomes derived from bone cells and breast tumor in bone remodeling and BC bone metastasis (BCBM). We also briefly outline the mechanisms of action of ncRNAs and proteins carried by exosomes secreted by bone and BCBM. Furthermore, this review highlights the potential of utilizing exosomes as biomarkers or delivery vehicles for the diagnosis and treatment of BCBM.

Exosomes: mediators regulating the phenotypic transition of vascular smooth muscle cells in atherosclerosis

Cardiovascular disease is one of the leading causes of human mortality worldwide, mainly due to atherosclerosis (AS), and the phenotypic transition of vascular smooth muscle cells (VSMCs) is a key event in the development of AS. Exosomes contain a variety of specific nucleic acids and proteins that mediate intercellular communication. The role of exosomes in AS has attracted attention. This review uses the VSMC phenotypic transition in AS as the entry point, introduces the effect of exosomes on AS from different perspectives, and discusses the status quo, deficiencies, and potential future directions in this field to provide new ideas for clinical research and treatment of AS. Video Abstract.

Research progress of exosomes in orthopedics

Exosomes are nano-extracellular vesicles secreted by a variety of cells. They are composed of a double-layer membrane that can transport a variety of proteins, coding and non-coding genes, and bioactive substances. Exosomes participate in information transmission between cells and regulate processes such as cell proliferation, migration, angiogenesis, and phenotypic transformation. They have broad prospects in the occurrence, development, and treatment of many diseases including orthopedics. Exosomes derived from different types of bone cells such as mesenchymal stem cells, osteoblasts, osteoclasts, and their precursors are recognized to play pivotal roles in bone remodeling processes including osteogenesis, osteoclastogenesis, and angiogenesis. This articlesummarizes the characteristics of exosomes and their research progress in bone remodeling, bone tumors, vascular skeletal muscle injury, spinal cord injury, degenerative disc diseases, cartilage degeneration, osteoarthritis, necrosis of the femoral head, and osteoporosis.

Chitosan-Based Scaffolds for Facilitated Endogenous Bone Re-Generation

Facilitated endogenous tissue engineering, as a facile and effective strategy, is emerging for use in bone tissue regeneration. However, the development of bioactive scaffolds with excellent osteo-inductivity to recruit endogenous stem cells homing and differentiation towards lesion areas remains an urgent problem. Chitosan (CS), with versatile qualities including good biocompatibility, biodegradability, and tunable physicochemical and biological properties is undergoing vigorously development in the field of bone repair. Based on this, the review focus on recent advances in chitosan-based scaffolds for facilitated endogenous bone regeneration. Initially, we introduced and compared the facilitated endogenous tissue engineering with traditional tissue engineering. Subsequently, the various CS-based bone repair scaffolds and their fabrication methods were briefly explored. Furthermore, the functional design of CS-based scaffolds in bone endogenous regeneration including biomolecular loading, inorganic nanomaterials hybridization, and physical stimulation was highlighted and discussed. Finally, the major challenges and further research directions of CS-based scaffolds were also elaborated. We hope that this review will provide valuable reference for further bone repair research in the future.

Exosomes: Small Vesicles with Important Roles in the Development, Metastasis and Treatment of Breast Cancer

Breast cancer (BC) has now overtaken lung cancer as the most common cancer, while no biopredictive marker isolated from biological fluids has yet emerged clinically. After traditional chemotherapy, with the huge side effects brought by drugs, patients also suffer from the double affliction of drugs to the body while fighting cancer, and they often quickly develop drug resistance after the drug, leading to a poor prognosis. And the treatment of some breast cancer subtypes, such as triple negative breast cancer (TNBC), is even more difficult. Exosomes (Exos), which are naturally occurring extracellular vesicles (EVs) with nanoscale acellular structures ranging in diameter from 40 to 160 nm, can be isolated from various biological fluids and have been widely studied because they are derived from the cell membrane, have extremely small diameter, and are widely involved in various biological activities of the body. It can be used directly or modified to make derivatives or to make some analogs for the treatment of breast cancer. This review will focus on the involvement of exosomes in breast cancer initiation, progression, invasion as well as metastasis and the therapeutic role of exosomes in breast cancer.

Circulating Exosomes from Mice with LPS-Induced Bone Loss Inhibit Osteoblast Differentiation

Osteoimmunology focuses on the intermodulation between bone and the immune system. Lipopolysaccharide (LPS)-induced bone loss models are commonly used to investigate the interface between inflammation and osteoporosis. Circulating exosomes can regulate physiological and pathological processes through exosomal microRNAs and proteins. In this study, we observed reduced osteoblast number and bone formation in LPS-induced bone loss mice (LPS mice). Levels of circulating exosomes were increased by ~ twofold in LPS mice, and the expression of exosomal miRNAs was significantly changed. miRNAs (miRNA-125b-5p, miRNA-132-3p, and miRNA-214-3p) that were reported to inhibit osteoblast activity were significantly increased in the serum exosomes and bone tissues of LPS mice. Additionally, LPS-induced increases in exosomes significantly inhibited the osteogenic differentiation of MC3T3-E1 cells.

Extracellular Vesicles for Regenerative Medicine Applications

Tissue engineering and regenerative medicine (TERM) may be defined as a translational discipline focused on the development of novel techniques, devices, and materials to replace or repair injured or diseased tissue and organs. The main approaches typically use cells, scaffolds, and signaling molecules, either alone or in combination, to promote repair and regeneration. Although cells are required to create new functional tissue, the source of cells, either from an exogenous allogeneic or autologous source or through the recruitment of endogenous (autologous) cells, is technically challenging and risks the host rejection of new tissue. Regardless of the cell source, these approaches also require appropriate instruction for proliferation, differentiation, and in vivo spatial organization to create new functional tissue. Such instruction is supplied through the microenvironment where cells reside, environments which largely consist of the extracellular matrix (ECM). The specific components of the ECM, and broadly the extracellular space, responsible for promoting tissue regeneration and repair, are not fully understood, however extracellular vesicles (EVs) found in body fluids and solid phases of ECM have emerged as key mediators of tissue regeneration and repair. Additionally, these EVs might serve as potential cell-free tools in TERM to promote tissue repair and regeneration with minimal risk for host rejection and adverse sequelae. The past two decades have shown a substantial interest in understanding the therapeutic role of EVs and their applications in the context of TERM. Therefore, the purpose of this review is to highlight the fundamental characteristics of EVs, the current pre-clinical and clinical applications of EVs in TERM, and the future of EV-based strategies in TERM.

Exosome mediated biological functions within skeletal microenvironment

Exosomes are membranous lipid vesicles fused with intracellular multicellular bodies that are released into the extracellular environment. They contain bioactive substances, including proteins, RNAs, lipids, and cytokine receptors. Exosomes in the skeletal microenvironment are derived from a variety of cells such as bone marrow mesenchymal stem cells (BMSCs), osteoblasts, osteoclasts, and osteocytes. Their biological function is key in paracrine or endocrine signaling. Exosomes play a role in bone remodeling by regulating cell proliferation and differentiation. Genetic engineering technology combined with exosome-based drug delivery can therapy bone metabolic diseases. In this review, we summarized the pathways of exosomes derived from different skeletal cells (i.e., BMSCs, osteoblasts, osteocytes, and osteoclasts) regulate the skeletal microenvironment through proteins, mRNAs, and non-coding RNAs. By exploring the role of exosomes in the skeletal microenvironment, we provide a theoretical basis for the clinical treatment of bone-related metabolic diseases, which may lay the foundation to improve bone tumor microenvironments, alleviate drug resistance in patients.

Mesenchymal Stem Cell-Derived Extracellular Vesicles for Bone Defect Repair

The repair of critical bone defects is a hotspot of orthopedic research. With the development of bone tissue engineering (BTE), there is increasing evidence showing that the combined application of extracellular vesicles (EVs) derived from mesenchymal stem cells (MSCs) (MSC-EVs), especially exosomes, with hydrogels, scaffolds, and other bioactive materials has made great progress, exhibiting a good potential for bone regeneration. Recent studies have found that miRNAs, proteins, and other cargo loaded in EVs are key factors in promoting osteogenesis and angiogenesis. In BTE, the expression profile of the intrinsic cargo of EVs can be changed by modifying the gene expression of MSCs to obtain EVs with enhanced osteogenic activity and ultimately enhance the osteoinductive ability of bone graft materials. However, the current research on MSC-EVs for repairing bone defects is still in its infancy, and the underlying mechanism remains unclear. Therefore, in this review, the effect of bioactive materials such as hydrogels and scaffolds combined with MSC-EVs in repairing bone defects is summarized, and the mechanism of MSC-EVs promoting bone defect repair by delivering active molecules such as internal miRNAs is further elucidated, which provides a theoretical basis and reference for the clinical application of MSC-EVs in repairing bone defects.

Mg2+ -mediated autophagy-dependent polarization of macrophages mediates the osteogenesis of bone marrow stromal stem cells by interfering with macrophage-derived exosomes containing miR-381

Magnesium ion (Mg²⁺ ) has received increased attention due to the roles it plays in promoting osteogenesis and preventing inflammation. This study was designed to investigate the mechanism by which Mg²⁺ influences the osteoblastic differentiation of bone marrow stromal stem cells (BMSCs). The polarization of Mø (macrophages) was measured after treatment with Mg²⁺ . Meanwhile, autophagy in Mø was measured by detecting LC3B expression. Mø-derived exosomes were isolated and cocultured with BMSCs; after which, osteogenic differentiation was evaluated by Alizarin Red staining and detection of alkaline phosphatase (ALP). Our results showed that Mg²⁺ could induce autophagy in macrophages and modulate the M1/M2 polarization of macrophages. Mg²⁺ -mediated macrophages could facilitate the osteogenic differentiation of BMSCs by regulating autophagy, and this facilitation by Mg²⁺ -mediated macrophages was closely related to macrophage-derived exosomes, and especially exosomes containing miR-381. However, miR-381 in macrophages did not influence autophagy or the polarization of Mg²⁺ -mediated macrophages. Furthermore, macrophage-derived exosomes containing miR-381 mainly determined the osteogenic differentiation of BMSCs. Mg²⁺ -mediated macrophages were shown to promote the osteogenic differentiation of BMSCs via autophagy through reducing miR-381 in macrophage-derived exosomes. In conclusion, our results suggest Mg²⁺ -mediated macrophage-derived exosomes containing miR-381 as novel vehicles for promoting the osteogenic differentiation of BMSCs.

Expression profile analysis of lncRNA in bone marrow mesenchymal stem cells exosomes of postmenopausal osteoporosis patients through microarray and bioinformatics analyses

BACKGROUND

Postmenopausal osteoporosis (PMOP) is the most common bone metabolic disease affecting women worldwide. In this study, we investigate the role of long non-coding RNA (lncRNA) expression in exosomes obtained from bone marrow mesenchymal stem cells (BMSCs) of patients with PMOP.

METHODS

BMSCs from patients diagnosed with PMOP and healthy post-menopausal females as controls were isolated and cultured before exosome extraction. RNA microarray technology was used to identify differentially expressed lncRNAs in exosomes from BMSCs. Bioinformatics technology was utilized to analyze the roles of differentially expressed lncRNAs. Further, RT-qPCR was used to validate differentially expressed lncRNAs in 20 pairs of clinical samples.

RESULTS

A total of 286 differentially expressed lncRNAs were detected in the exosomes from BMSCs unlike in the control group, among which 148 were up-regulated, whereas 138 were down-regulated. RT-qPCR identified five critical lncRNAs, including ENST00000593078, NR_120593, ENST00000422343, MEG3 and NR_029192. This was consistent with the microarray results and with a significant difference (P < 0.01). Based on the differentially expressed lncRNAs, we constructed lncRNA-miRNA-mRNA interaction networks. Functional analysis revealed that differentially expressed lncRNAs in patients with PMOP potentially target Wnt/β-catenin, MAPK, and PI3K-Akt pathways.

CONCLUSION

In summary, we detected several dysregulated lncRNAs regulating PMOP progression in exosomes extracted from BMSCs of affected patients acting as novel biomarkers. This in turn provides valuable data for targeted treatment of PMOP.

SUBJECTS

Genomics; Molecular biology; Orthopedics; Women's Health.

Mesenchymal stem cell-derived extracellular vesicles for cell-free therapy of ocular diseases

Mesenchymal stem cells-derived extracellular vesicles (MSC-EVs) have noticeably attracted clinicians' attention in treating ocular diseases. As the paracrine factor of MSCs and an alternative for cell-free therapies, MSC-EVs can be conveniently dropped over the ocular surface or diffused through the retina upon intravitreal injection, without increasing the risks of cellular rejection and tumor formation. For clinical translation, a standardized and scalable production, as well as reprogramming the MSC-EVs, are highly encouraged. This review aims to assess the potential approaches for EV production and functional modification, in addition to summarizing the worldwide clinical trials initiated for various physiological systems and the specific biochemical effects of MSC-EVs on the therapy of eye diseases. Recent advances in the therapy of ocular diseases based on MSC-EVs are reviewed, and the associated challenges and prospects are discussed as well.

Bone Cell Exosomes and Emerging Strategies in Bone Engineering

Bone tissue remodeling is a highly regulated process balancing bone formation and resorption through complex cellular crosstalk between resident bone and microenvironment cells. This cellular communication is mediated by direct cell and cell–matrix contact, autocrine, endocrine, and paracrine receptor mediated mechanisms such as local soluble signaling molecules and extracellular vesicles including nanometer sized exosomes. An impairment in this balanced process leads to development of pathological conditions. Bone tissue engineering is an emerging interdisciplinary field with potential to address bone defects and disorders by synthesizing three-dimensional bone substitutes embedded with cells for clinical implantation. However, current cell-based therapeutic approaches have faced hurdles due to safety and ethical concerns, challenging their clinical translation. Recent studies on exosome-regulated bone homeostasis and regeneration have gained interest as prospective cell free therapy in conjugation with tissue engineered bone grafts. However, exosome research is still in its nascent stages of bone tissue engineering. In this review, we specifically describe the role of exosomes secreted by cells within bone microenvironment such as osteoblasts, osteocytes, osteoclasts, mesenchymal stem cell cells, immune cells, endothelial cells, and even tumor cells during bone homeostasis and crosstalk. We also review exosome-based osteoinductive functionalization strategies for various bone-based biomaterials such as ceramics, polymers, and metals in bone tissue engineering. We further highlight biomaterials as carrier agents for exosome delivery to bone defect sites and, finally, the influence of various biomaterials in modulation of cell exosome secretome.

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.

Noncoding RNA in Extracellular Vesicles Regulate Differentiation of Mesenchymal Stem Cells

To achieve the desired outcome in tissue engineering regeneration, mesenchymal stem cells need to undergo a series of biological processes, including differentiating into the ideal target cells. The extracellular vesicle (EV) in the microenvironment contributes toward determining the fate of the cells with epigenetic regulation, particularly from noncoding RNA (ncRNA), and exerts transportation and protective effects on ncRNAs. We focused on the components and functions of ncRNA (particularly microRNA) in the EVs. The EVs modified by the ncRNA favor tissue regeneration and pose a potential challenge.

Increased BMSC exosomal miR-140-3p alleviates bone degradation and promotes bone restoration by targeting Plxnb1 in diabetic rats

Background

Diabetes mellitus (DM) is considered to be an important factor for bone degeneration disorders such as bone defect nonunion, which is characterized by physical disability and tremendous economy cost to families and society. Exosomal miRNAs of BMSCs have been reported to participate in osteoblastogenesis and modulating bone formation. However, their impacts on the development of bone degeneration in DM are not yet known. The role of miRNAs in BMSCs exosomes on regulating hyperglycemia bone degeneration was investigated in the present study.

Results

The osteogenic potential in bone defect repair of exosomes derived from diabetes mellitus BMSCs derived exosomes (DM-Exos) were revealed to be lower than that in normal BMSCs derived exosomes (N-Exos) in vitro and in vivo. Here, we demonstrate that miR-140-3p level was significantly altered in exosomes derived from BMSCs, ADSCs and serum from DM rats. In in vitro experiments, upregulated miR-140-3p exosomes promoted DM BMSCs differentiation into osteoblasts. The effects were exerted by miR-140-3p targeting plxnb1, plexin B1 is the receptor of semaphoring 4D(Sema4D) that inhibited osteocytes differentiation, thereby promoting bone formation. In DM rats with bone defect, miR-140-3p upregulated exosomes were transplanted into injured bone and accelerated bone regeneration. Besides, miR-140-3p in the exosomes was transferred into BMSCs and osteoblasts and promoted bone regeneration by targeting the plexin B1/RohA/ROCK signaling pathway.

Conclusions

Normal-Exos and miR-140-3p overexpressed-Exos accelerated diabetic wound healing by promoting the osteoblastogenesis function of BMSCs through inhibition plexin B1 expression which is the receptor of Sema4D and the plexin B1/RhoA/ROCK pathway compared with diabetes mellitus-Exos. This offers a new insight and a new therapy for treating diabetic bone unhealing.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01267-2.

Therapeutic potential of mesenchymal stem cell-derived exosomes as a cell-free therapy approach for the treatment of skin, bone, and cartilage defects

OBJECTIVE

The aim of this study was to collect the articles concerning mesenchymal stem cell (MSC)-derived exosomes for regeneration of bone, cartilage and skin defects.

METHOD

Scopus, PubMed, EMBASE, and Web of Science were searched for keywords "Exosome, MSC, Skin, Bone and Cartilage defects, Regenerative medicine, and extracellular vesicles.

RESULTS

MSC-derived exosomes can emulate the biological activity of MSCs by horizontal transfer of multiple functional molecules including mRNAs, miRNAs, proteins, and lipids to the local microenvironment and recipient cells, and subsequently mediate restoring homeostasis and tissue regeneration through various mechanisms. Compared to MSCs, MSC-derived exosomes reveal many advantages such as non-immunogenicity, easy access, easy preservation, and extreme stability under various conditions.

CONCLUSION

Hence, exosomes could be considered as an alternative strategy for cell-based therapies in regenerative medicine. In this paper, after describing the characteristics of exosomes, we will review the recent literature on the therapeutic potentials of MSC-derived exosomes in skin, bone, and cartilage repair.

Exosome as a target for cancer treatment

Exosomes are small vesicles covered by a lipid bilayer, ranging in size from 50 nm to 90 nm, secreted by different cell types in the body under normal and pathological conditions. They are surrounded by cell-segregated membrane complexes and play a role in the pathological and physiological environments of target cells by transfer of different molecules such as microRNA (miRNA). Exosomes have been detected in many body fluids, such as in the amniotic fluid, urine, breast milk, blood, saliva, ascites, semen, and bile. They include proteins, lipids, and nucleic acids such as DNA, RNA, and miRNA, which have many functions in target cells under pathological and physiological conditions. They participate in pathological processes such as tumor growth and survival, autoimmunity, neurodegenerative disorders, infectious diseases, inflammation conditions, and others. Biomarkers in exosomes isolated from body fluids have allowed for a more precise and consistent diagnostic method than previous approaches. Exosomes can be used in a variety of intracellular functions, and with advances in molecular techniques they can be used in the treatment and diagnosis of many diseases, including cancer. These vesicles play a significant role in various stages of cancer. Tumor-derived exosomes have an important role in tumor growth, survival, and metastasis. In contrast, the use of stem cells in cancer treatment is a relatively new scientific area. We hope to address targeted use of miRNA-carrying exosomes in cancer therapy in this review paper.