Role of mesenchymal stem cell-derived exosomal non-coding RNAs in bone and bone-related disorders

Abstract

Mesenchymal stem cells (MSCs) are known for their ability to differentiate into various cell lineages, including osteoblasts (bone-forming cells), and for their significant paracrine effects. Among their secreted products, exosomes have gained considerable attention as nanoscale carriers of bioactive molecules such as non-coding RNAs (ncRNAs). These ncRNAs, including microRNAs, long ncRNAs, and circular ncRNAs, are critical regulators of gene expression and cellular functions. Moreover, MSC-derived exosomes not only offer advantages such as targeted delivery, reduced immunogenicity, and protection of cargo material, but also carry ncRNAs that have therapeutic and diagnostic potential in bone-related disorders. Emerging evidence has highlighted the role of MSC-derived exosomal ncRNAs in osteogenesis, bone remodeling, and intercellular signaling in the bone microenvironment. This review consolidates recent research on the role of MSC-derived exosomal ncRNAs in maintaining bone homeostasis and bone-related disorders via various signaling pathways and epigenetic modifications. Furthermore, we explore the therapeutic potential of MSC-derived exosomal ncRNAs as biomarkers and therapeutic targets. This comprehensive review offers key insights into the regulatory roles of MSC-derived exosomal ncRNAs in bone biology and their clinical significance in bone-related diseases.

Key Words: Mesenchymal stem cell-derived exosomes; Non-coding RNAs; Bone disorders; Bone homeostasis; Signaling pathway

Core Tip: Mesenchymal stem cell-derived exosomal non-coding RNAs, including microRNAs, long non-coding RNAs, and circular RNAs, play vital roles in regulating bone development, remodeling, and the pathogenesis of bone-related disorders. This review provides insights into their emerging roles in bone biology and disease, highlighting their therapeutic potential and underlying molecular mechanisms.

INTRODUCTION

Bone is a mineralized connective tissue comprised of several cell types, including osteoblasts, osteoclasts, and osteocytes. It serves as a mineral reservoir and houses bone marrow for blood cell production[1]. Bone-derived defects impact bone mineralization and mechanical robustness, including bone degenerative joint defects, lack of bone mass and bone mineral density, or overgrowth of bone-forming osteoblasts[2,3]. In recent years, mesenchymal stem cells (MSCs) have shown tremendous potential as biomedicines for treating bone disorders. MSCs are adult stem cells with intrinsic self-renewal and multipotent capacity that enable multilineage differentiation, making them versatile for regenerative applications[4]. MSCs play a vital role in regulating tissue homeostasis and facilitating tissue regeneration[5]. They are particularly useful in cell-based therapy and tissue engineering applications due to their differentiation capacity, ability to repair damaged environments, migration to damaged tissue, paracrine signaling effects, and immunomodulatory properties[6].

A meta-analysis of MSC-based therapies over the past 15 years has validated their safety, with no risk of serious adverse effects. However, significant concerns remain, such as oncogene activation, immune rejection, premature differentiation, reduced immune compatibility, instability, and destruction of genetic material[7]. For instance, MSC activation before intra-articular administration alleviates osteoarthritis (OA) through enhanced gait activity and chondroprotection. However, minor phenotypic characteristics of MSCs that may affect reproducibility due to variability within MSC populations has also been noted[8]. In another study involving intra-articular MSC injection for knee OA, ethical limitations precluded cartilage biopsy, limiting the assessment of the underlying mechanisms of pain relief[9]. To address these limitations, MSC-derived exosomes have gained attention as cell-free alternatives that offer similar therapeutic benefits while avoiding the risks associated with live-cell therapies.

Exosomes are nanoscale membrane-bound extracellular vesicles that carry bioactive molecules such as DNA, RNA, proteins, and lipids of the cells as part of their normal physiology or acquired abnormalities[10]. Their size typically ranges from 30-150 nm in diameter[11,12]. MSC-derived exosomes actively participate in physiological processes, including intercellular communication, cellular development, apoptosis, modulation of immune responses, tissue regeneration, metabolic regulation, drug delivery vehicles, biomarkers, and targets[13-15]. In the context of bone remodeling, exosomes ensure a proper balance between osteoblast-mediated bone formation and osteoclast-mediated bone resorption[16]. Their ability to directly target damaged tissues and deliver bioactive molecules enhances their therapeutic potential, making them powerful tools in regenerative medicine.

Given their broad therapeutic potential, recent research has focused on non-coding RNAs (ncRNAs), which do not encode proteins but regulate gene function, within MSC-derived exosomes, particularly in bone-related applications. Exosomes originate from multivesicular bodies that fuse with the plasma membrane to release bioactive molecules, including ncRNAs. These ncRNAs are a major part of the human genome, where they regulate protein-coding genes by altering various cellular activities such as transcription, translation, and post-translational modifications in osteogenic cells[17]. ncRNAs are categorized based on their nucleotide size: Small ncRNAs, such as microRNA (miRNA) and small interfering RNA are < 200 nucleotides, whereas long ncRNA (lncRNA), such as linear and circular RNA (circRNA), are > 200 nucleotides[18]. These ncRNAs mediate intercellular communication and regulate various physiological functions. In the context of bone health, they control gene expression, influence osteoblasts and osteoclasts, and help manage bone-related issues. Additionally, they are potential therapeutic targets for early diagnosis. However, dysregulation of ncRNAs can lead to serious bone disorders[17]. For example, miR-101 targets F-box and WD repeat domain-containing 7, leading to activation of the hypoxia-inducible factor 1-alpha/forkhead box protein P3 axis and osteoblast differentiation, and circ_0008542 facilitates osteoclast-induced bone resorption through increased N6-methyladenosine methylation[16]. Various delivery methods have been explored to harness the therapeutic potential of exosomal ncRNAs, including systemic administration, localized delivery, and targeted delivery methods[19,20]. For example, exosomes loaded with the lncRNA maternally expressed gene 3 and engineered with a cyclic Arg-Gly-Asp peptide could more efficiently target tumor cells, facilitate therapeutic agent release, and enhance antitumor effects in osteosarcoma (OS)[21]. Another efficient approach for delivering exosomal ncRNAs involves the use of scaffold-based systems. Bone marrow MSC (BMSC)-derived exosomes loaded with miR-26a, when integrated into a hydrogel scaffold and implanted at a defect site, enhanced bone regeneration. In this setup, exosomes promoted angiogenesis (new blood vessel formation), miR-26a supported osteogenesis (bone formation), and the hydrogel facilitated site-specific release[22]. Similarly, umbilical MSC-derived exosomes encapsulated in hyaluronic acid hydrogel and combined with customized nanohydroxyapatite/poly-ε-caprolactone scaffolds demonstrated enhanced bone regeneration in vivo. Exosomal miR-21 facilitated angiogenesis by inhibiting the NOTCH1/delta like canonical Notch ligand 4 pathway and inducing the expression of vascular endothelial growth factor A and hypoxia inducible factor 1 subunit alpha. Furthermore, this scaffold-based methodology allows prolonged and sustained exosome release[23].

Several studies have demonstrated that exosomes serve as effective vehicles for ncRNA transport. When sourced from MSCs, these exosomes offer a promising alternative for overcoming challenges associated with direct MSC-based therapies. This finding supports the hypothesis that MSC-derived exosomal ncRNAs are a novel and effective strategy for treating various bone-related disorders. We performed a comprehensive literature search using databases like Google Scholar, PubMed, and ResearchGate. The keywords used to find research articles were “MSC-derived exosomes”, “alleviates osteoarthritis”, “osteoporosis (OP)”, “OS”, “bone related disorder”, “ncRNA”, and “clinical trials”. To ensure a comprehensive and up-to-date review, studies primarily spanning from 2021 to 2025 were selected, along with a few studies from 2017 to 2020. This review highlights the physiological significance of MSC-derived exosomal ncRNAs, their diverse regulatory roles and signaling pathways in maintaining bone homeostasis (the balance between bone formation and bone resorption), and their potential as therapeutic targets in bone-related disorders.

EXOSOMAL ncRNAS IN BONE HOMEOSTASIS

Bone undergoes continuous remodeling, wherein osteoblasts function as bone-forming cells and osteoclasts serve as bone-resorbing cells. Together, these cells contribute to maintaining bone homeostasis[24]. Osteogenesis is a crucial physiological process responsible for bone formation, regeneration, and maintenance of bone homeostasis, frequently associated with angiogenesis to facilitate bone tissue development and repair. Recent studies have emphasized the role of MSC-derived exosomal ncRNAs in promoting bone regeneration (Figure 1). For instance, BMSC-derived exosomal miR-590-3p targets transforming growth factor beta receptor 1, thereby promoting osteoblast differentiation and enhancing osteogenesis[25]. Similarly, BMSC-derived exosomal circHIPK3 promotes osteogenic differentiation of MC3T3-E1 cells by sponging miR-29a-5p, thereby upregulating phosphatase and tensin homolog induced putative kinase 1 expression, enhancing mitophagy and contributing to pro-osteogenic effects[26]. In parallel, BMSC-derived exosomal miR-206 targets E74-like factor 3 and decreases its expression, promoting osteoblast proliferation and differentiation while inhibiting osteoblast apoptosis[27].

Figure 1 Role of mesenchymal stem cell-derived exosomal non-coding RNA in bone homeostasis. A schematic diagram illustrates the role of mesenchymal stem cell-derived exosomal non-coding RNAs in osteogenesis, thereby contributing to the maintenance of bone homeostasis. NP: Nanoparticles; SMF: Static magnetic field; PINK1: Phosphatase and tensin homolog induced putative kinase 1; TGFβR1: Transforming growth factor beta receptor 1; Elf3: E74-like factor 3; HDAC7: Histone deacetylase 7; COL4A2: Collagen type IV alpha 2 chain.

The osteogenic potential of MSC-derived exosomal ncRNAs can be further enhanced through innovative conditioning strategies. For example, BMSC-derived exosomes preconditioned with Fe₃O₄ magnetic nanoparticles under a static magnetic field contain miR-1260a, which inhibits histone deacetylase 7 and collagen type IV alpha 2 chain, exhibiting enhanced osteogenesis and angiogenesis compared with BMSC-derived exosomes and phosphate buffered saline (control)[28]. Furthermore, advanced therapeutic strategies combine scaffold-based approaches with exosome coatings to improve bone regeneration efficacy. Specifically, exosomes derived from human MSCs pre-differentiated in osteogenic medium, when coated onto a cell-free titanium alloy scaffold, can induce osteogenesis by upregulating osteogenic miRNAs (hsa-miR-146a-5p, hsa-miR-503-5p, hsa-miR-483-3p, and hsa-miR-129-5p) and downregulating anti-osteogenic miRNAs (hsa-miR-32-5p, hsa-miR-133a-3p, and hsa-miR-204-5p) by activating the phosphoinositide 3-kinase/protein kinase B and mitogen-activated protein kinase (MAPK) signaling pathways[29].

In addition to their role in regeneration, exosomal ncRNAs have been implicated in the regulation of bone-related diseases by restoring disrupted homeostasis and mitigating disease progression. For instance, BMSC-derived exosomal miR-150-3p promotes osteoblast proliferation and differentiation while inhibiting apoptosis, thereby alleviating OP[30]. Similarly, BMSC-derived exosomal miR-21-5p improves OP by regulating Kruppel-like factor 3 (KLF3), thus providing a potential therapeutic strategy for OP[31]. Moreover, in a cystathionine β-synthase+/- mouse model, BMSC-derived exosomal lncRNA H19 sponges miR-106, modulating angiopoietin 1-Tie2/nitric oxide signaling to promote osteogenesis and angiogenesis, ultimately mitigating metabolic OP[32]. Another study using an ovariectomized rat model demonstrated that ovariectomized rat BMSC-derived exosomal miR-27a-3p and miR-196b-5p modulate bone remodeling by enhancing osteogenic BMSC differentiation upon overexpression, whereas their suppression impedes osteogenic differentiation and facilitates osteoclast differentiation[33].

Furthermore, in osteolytic diseases, exosomal miR-6924-5p derived from scleraxis-overexpressing platelet-derived growth factor receptor alpha positive BMSCs targets the osteoclastic regulators C-X-C motif chemokine ligand 12 and osteoclast stimulatory transmembrane protein, thereby inhibiting osteoclastogenesis (osteoclast formation) in human monocytes, reducing osteoclast formation, and enhancing tendon-bone healing strength[34]. Conversely, some miRNAs exhibit anti-osteogenic effects. For example, exosomal miR-128-3p derived from aged rat MSCs targets Smad5 and has an anti-osteogenic effect by downregulating osteogenesis-related proteins, including Runt-related transcription factor 2, collagen I, and alkaline phosphatase, suggesting that the miR-128-3p antagomir may facilitate osteogenesis[35]. Altogether, the evidence suggests that MSC-derived exosomal ncRNAs restore the osteoblast-osteoclast balance by stimulating osteoblast-driven bone formation or suppressing osteoclast-mediated bone resorption, thereby maintaining bone homeostasis. These insights highlight the role of MSC-derived exosomal ncRNAs as key regulators of osteogenesis, bone regeneration, and modulation of bone disease[36-39] (Table 1).

Table 1 Role of exosomal non-coding RNAs in bone homeostasis, key targets, and functional effects.

Exosome origin	Exosomal ncRNAs	Targets/pathways	Effects	In vivo models	Ref.
BMSCs	miR-150-5p	SOX2 and PI3K/Akt pathway	Induced type H blood vessel angiogenesis and osteogenesis	Female mice	[36]
Fucoidan-induced MSCs	miR-146b-5p	TRAF6 and PI3K/Akt/mTOR pathways	Suppressed inflammatory responses, extracellular matrix degradation, and promoted chondrocyte autophagy	Male Sprague-Dawley rats	[37]
BMSCs	miR-422a	KLK4	Inhibited angiogenesis and osteogenesis	Female mice	[38]
Synovial MSCs	miR-485-3p	NRP1 and PI3K/Akt pathway	Relieved cartilage damage	N/A	[39]

ncRNAs: Non-coding RNAs; BMSCs: Bone marrow mesenchymal stem cells; MSCs: Mesenchymal stem cells; SOX2: SRY (Sex Determining Region) box 2; PI3K: Phosphoinositide 3-kinase; Akt: Protein kinase B; TRAF6: Tumor necrosis factor receptor-associated factor 6; mTOR: Mechanistic target of rapamycin; KLK4: Kallikrein-4; NRP1: Neuropilin 1; N/A: Not applicable.

MSC-DERIVED EXOSOMAL ncRNAS IN BONE RELATED DISORDERS

Major bone-related disorders include OA, OS, and OP, each with a distinct pathophysiology. OA is a prevalent degenerative disorder that affects the entire synovial joint. It is characterized by hyaline cartilage degeneration, subchondral bone abnormalities, synovial enlargement accompanied by increased vascularity, and tendon and ligament instability[40]. Similarly, OP is characterized by low bone quality and strength and a higher fracture risk. OP is classified into two different types, primary and secondary, based on factors that influence bone metabolism, such as hormonal changes and aging. Primary OP is further classified into type I/postmenopausal and type II/senile. Secondary OP is caused by medications, pathological conditions, and aging and menopause[41]. In contrast, OS is a malignant tumor typically found in the metaphysis of long bones and has the highest incidence in children and adolescents[42,43]. Recent studies highlight the regulatory roles of MSC-derived exosomal ncRNAs in important processes in disease pathophysiology[43-52] (Table 2).

Table 2 The role of mesenchymal stem cell-derived exosomal non-coding RNAs in the pathophysiology of bone-related disorders.

Diseases	Sources	Exosomal ncRNAs	Targets	Signaling pathways involved	Effects	Ref.
OA	BMSCs	lncRNA TUC339	-	-	Mitigated OA by promoting the transition from M1-type to M2-type macrophage polarization, inhibiting inflammation, and enhancing chondrocyte function	[44]
	MSCs	lncRNA KLF3-AS1	-	-	Alleviated OA by promoting chondrocyte proliferation and inhibiting apoptosis, thereby facilitating cartilage repair	[45]
	BMSCs	miR-9-5p	3’ UTR of syndecan-1	-	Reduced inflammatory markers, decreased oxidative stress, and suppressed expression of OA-associated factors	[46]
	BMSCs	miR-135b	-	Downregulation of MAPK6 expression	Promoted M2 polarization of synovial macrophages thereby aiding in cartilage healing	[47]
	Adipose MSCs	miR-376c-3p	3’ UTR of Wnt family member 3 or Wnt family member 9a	Hindering of Wnt/β-catenin pathway	Induced chondrocyte degradation and synovial fibrosis	[48]
	Synovial MSCs	miR-320c	-	Modulation of ADAM metalloproteinase domain 19-dependent Wnt signaling	Inhibited extracellular matrix degradation and chondrocyte apoptosis	[49]
	BMSCs	circRNA_0001236	miR-3677-3p	-	Increased the collagen type II alpha 1 chain and sex-determining region Y-box 9 expression and reduced the matrix metalloproteinase-13 expression	[50]
	Umbilical cord blood MSCs	lncRNA H19	miR-29a-3p	-	Decreased the phosphorylation levels of biochemical markers of neuropathic pain (NR1, NR2B, protein kinase C gamma and ERK) in astrocytes	[51]
OP	Human BMSCs	miR-186	MOB kinase activator 1A	Hippo pathway	Facilitated osteogenesis in postmenopausal OP	[52]
OS	BMSCs	lncRNA PVT1	miR-183-5p	-	Enhanced OS proliferation and migration	[43]

MSCs: Mesenchymal stem cells; BMSCs: Bone marrow mesenchymal stem cells; OA: Osteoarthritis; OP: Osteoporosis; OS: Osteosarcoma; KLF3: Kruppel-like factor 3; AS1: Antisense RNA 1; UTR: Untranslated region; Wnt: Wingless/integrated; MAPK6: Mitogen-activated protein kinase; ADAM: A disintegrin and metalloprotease; ERK: Extracellular signal-related kinase.

In addition, MSC-derived exosomal ncRNAs serve as potential diagnostic biomarkers. For instance, microarray analysis of circRNA sequencing profiles in BMSC-derived exosomes from individuals with postmenopausal OP identified five different circRNAs, namely hsa_circ_0009127, hsa_circ_0090759, hsa_circ_0058392, hsa_circ_0090247, and hsa_circ_0049484, that may be potential biomarkers or therapeutic targets[53]. Further studies are required to explore the potential of MSC-derived exosomal ncRNAs as biomarkers. In summary, MSC-derived exosomal ncRNAs play a pivotal regulatory function in bone-related disorder management; however, further detailed studies are essential for their translation into clinical use.

MOLECULAR MECHANISMS OF EXOSOMAL ncRNAS IN BONE DISORDERS

The role of MSC-derived exosomal ncRNAs in modulating bone disorder pathways and molecular targets presents a promising avenue for mitigating disease progression and facilitating the development of more effective treatment strategies. In OA, BMSC-derived exosomal miR-127-3p has been shown to target and downregulate cadherin-11, thereby inhibiting Wnt/β-catenin signaling pathway activation, consequently preventing chondrocyte damage[54]. Similarly, BMSC-derived exosomal miR-361-5p targets Asp-Glu-Ala-Asp-box polypeptide 20, downregulates its expression, and suppresses the nuclear factor kappa B (NF-κB) pathway, thereby mitigating chondrocyte damage and eventually OA[55]. Moreover, human umbilical cord MSC-derived exosomal miR-199a-3p reduces interleukin 1 beta-induced inflammation and apoptosis in chondrocytes by inhibiting the MAPK4/NF-κB signaling pathway, thus slowing OA progression[56]. Additionally, human MSC-derived exosomal lncRNA KLF3-antisense RNA 1 sponges miR-206 to upregulate G-protein-coupled receptor kinase interacting protein-1 (GIT1), thereby promoting chondrocyte proliferation and inhibiting apoptosis, whereas miR-206 overexpression or GIT1 knockdown reverses these effects, highlighting the significance of the lncRNA KLF3- antisense RNA 1/miR-206/GIT1 axis as a key regulator in OA[57]. Similarly, in traumatic OA, BMSC-derived exosomal miR-125a-5p targets E2F transcription factor 2, consequently promoting chondrocyte migration and inhibiting cartilage degeneration[58]. In temporomandibular joint OA, strontium pretreatment of synovial MSCs upregulates apoptosis-linked gene 2-interacting protein X, thereby selectively enhancing the incorporation of therapeutic miRNA into exosomes, including the critical exosomal miR-143-3p, which directly targets major facilitator superfamily domain containing 8 to alleviate chondrocyte ferroptosis and diminish osteoclast-mediated joint pain[59]. In OS, BMSC-derived exosomal miR-206 targets transformer 2β, thereby regulating OS cell proliferation, apoptosis, migration, and invasion, and subsequently suppressing both OS growth and metastasis in vivo[60]. In contrast, BMSC-derived exosomal miR-208a can enhance OS cell malignancy by targeting programmed cell death protein 4 via the extracellular signal-related kinases 1/2 signaling pathway[61]. Additionally, BMSC-derived exosomal lncRNA XIST promotes OS growth and metastasis by binding to miR-655 and downregulating its expression, leading to ATP citrate lyase upregulation, increased lipid accumulation, and β-catenin signaling activation[62]. In OP, BMSC-derived exosomal lncRNA metastasis-associated lung adenocarcinoma transcript-1 sponges miR-34c and upregulates special AT-rich sequence-binding protein 2 expression, thereby enhancing osteogenic activity and mitigating OP symptoms in vivo[63]. Similarly, in osteogenesis-induced human umbilical cord, MSC-derived exosomal miR-328-3p and miR-2110 regulate the MAPK signaling pathway, targeting chordin and tumor necrosis factor-alpha, respectively, regulating osteoclast differentiation, enhancing osteogenesis, and mitigating OP[64]. In glucocorticoid-induced osteonecrosis of the femoral head, exosomal miR-365a-5p derived from human umbilical cord MSCs inhibits salvador homolog 1, which further activates the Hippo signaling pathway, promoting osteogenesis and preventing disease progression[65]. Similarly, in alcohol-induced osteonecrosis of the femoral head, human umbilical cord MSC-derived exosomal miR-25-3p could mitigate this disease by facilitating osteoblast differentiation and inhibiting apoptosis in both BMSCs and in vivo models by suppressing DNA methylation of the miR-25-3p promoter and reduction of gremlin 1 expression[66]. Collectively, these findings underscore the potential of MSC-derived exosomal ncRNAs as an innovative therapeutic strategy for modulating key molecular pathways and targets, offering promising approaches for treating various bone-related disorders (Figure 2).

Figure 2 Molecular mechanisms regulated by mesenchymal stem cell-derived exosomal non-coding RNAs in bone related disorders. The diagram depicts various molecular pathways and targets through which mesenchymal stem cell-derived exosomal non-coding RNAs exert regulatory roles in bone-related disorders, including osteoarthritis, osteosarcoma, glucocorticoid-induced osteonecrosis, and osteoporosis. Wnt: Wingless/integrated; NF-κB: Nuclear factor kappa B; CDH11: Cadherin-11; DDX20: Asp-Glu-Ala-Asp-box polypeptide 20; BMSC: Bone marrow mesenchymal stem cell; ERK1/2: Extracellular signal-related kinases 1/2; TRAB2: Transformer 2β; PDCD4: Programmed cell death protein 4; SATB2: Special AT-rich sequence-binding protein 2; lncRNA: Long non-coding RNA; MALAT1: Metastasis-associated lung adenocarcinoma transcript 1; ncRNAs: Non-coding RNAs; GC: Gastric cancer; SAV1: Salvador homolog 1; HUCMSC: Human umbilical cord mesenchymal stem cell.

CLINICAL IMPLICATIONS

Preclinical studies have substantiated the therapeutic efficacy of MSC-derived exosomes in various bone disorders, such as OA and OP. In OA models, exosomes derived from the infrapatellar fat pad, synovial membrane, or chondrogenically induced MSCs have been shown to have anti-inflammatory effects, inhibit cartilage degradation, and stimulate matrix synthesis[67-69]. These effects are largely mediated by exosomal ncRNAs, including miR-100-5p, miR-140-5p, and regulatory lncRNAs that target critical pathways like mammalian target of rapamycin, Wnt/β-catenin, and G-protein coupled receptor kinase interacting protein[70]. Although preclinical animal models have demonstrated the therapeutic potential of MSC-derived exosomes, variability in exosome source, dosage, and administration routes contribute to inconsistent and non-reproducible outcomes. Moreover, the limited ability of these models to recapitulate the complexity of human pathophysiology presents significant challenges for clinical translation[71].

Clinical trials investigating exosomal ncRNAs are limited, with an even smaller number focused specifically on MSC-derived exosomes. This constraint underscores the need for additional investigations into their potential in diverse therapeutic contexts, particularly in bone regeneration. Based on data obtained from ClinicalTrials.gov, no registered study to date has directly evaluated the therapeutic role of ncRNAs within MSC-derived exosomes. A related study assessed MSC-derived exosomes in patients with OA and discussed the presence of bioactive molecules, including ncRNAs, within the exosomal cargo[72]. However, it does not clarify which bioactive molecules drive the therapeutic effect or which specific ncRNAs are involved. While some trials have focused on exosomal ncRNAs, one completed trial specifically investigated dysregulated miRNAs present in the circulating exosomes of patients with bone metastases and identified biomarkers to predict bone metastasis risk[73]. Another trial focused on profiling exosomal RNA as a biomarker of lung metastasis in patients with primary high-grade OS[74]. Moreover, a phase 1 trial evaluated the safety of allogeneic MSC-derived exosomes administered via intra-articular injection in the knees of individuals with mild to moderate symptomatic OA[75]. Nevertheless, data regarding patient-related factors, costs, and legal regulations remain unclear, which is a significant limitation.

The clinical implementation of MSC-derived exosomal ncRNAs requires robust preclinical and clinical trials to evaluate their safety, efficacy, dosing strategies, and delivery methods. However, the clinical translation of MSC-derived exosomal ncRNAs faces several challenges. Scalability remains a major concern, as producing exosomes in appropriate quantities while maintaining consistent quality poses significant technical challenges. Additionally, the heterogeneity of MSC-derived exosomes from different tissue sources remains a critical gap in advancing this therapeutic approach, underscoring the need for standardized production protocols[76,77]. Additional barriers include inefficient ncRNA loading, content variability, and the presence of immunogenic components such as major histocompatibility complex molecules. Furthermore, the limited understanding of receptor specificity, biodistribution, pharmacokinetics, and off-target effects complicates delivery strategies, emphasizing the need for optimized dosing and repeated administration protocols to achieve sustained therapeutic effects[78]. Several signaling pathways, including Wnt/β-catenin, Notch, MAPK, Janus kinase/signal transducer and activator of transcription, and NF-κB, are critically involved in bone-related disorders[79]. However, regulation by MSC-derived exosomal ncRNAs remains poorly understood and warrants further investigation. Numerous studies have suggested that exosomal ncRNAs could serve as potential biomarkers for various diseases. A study by Zhi et al[80] suggests that exosomal hsa_circ_0006859 is a circulating biomarker of postmenopausal OP. Similarly, the synovial fluid-derived exosomal lncRNA prostate cancer gene expression marker 1 could be a biomarker for differentiating early from later stages of OA[81]. Nevertheless, further research is necessary to identify specific ncRNAs with reliable diagnostic potential that can be utilized as noninvasive biomarkers for bone-related disorders.

Several strategies are currently being developed to address translational barriers associated with exosome-based therapy. For instance, local exosome administration is generally preferred over systemic delivery to ensure higher exosome concentration at the target injury site and reduce off-target effects[82,83]. Likewise, exosomes can be engineered to carry therapeutic molecules, such as small interfering RNAs or peptides, via electroporation or membrane modification, which is another approach aimed at improving targeting and therapeutic efficacy[84].

Furthermore, exosome isolation involves techniques such as size-exclusion chromatography, ultrafiltration, and immunoaffinity. Although size-exclusion chromatography and ultrafiltration are efficient, they diminish exosome purity and yield. In contrast, immunoaffinity ensures high specificity and depends on certain surface markers. A combined approach can help mitigate these limitations[70]. Although different strategies have been investigated, the precise mechanisms by which exosomal ncRNAs function are still not fully understood.

In bone-related applications, in addition to the delivery strategies mentioned, other approaches include the incorporation of exosomes into biomaterial scaffolds - such as hydrogels, collagen, poly(lactic-co-glycolic acid), and tricalcium phosphate - which can facilitate sustained release and improve scaffold osteoconductivity[85,86]. Additionally, the osteogenic potential of exosomes can be enhanced through genetic modification of parental MSCs (e.g., overexpression of osteogenic miRNAs such as miR-375), environmental priming (e.g., hypoxia or tumor necrosis factor alpha exposure), and mechanical stimuli (e.g., low-density pulsed ultrasound)[87-89]. Through multidisciplinary research and technological innovations, MSC-derived exosomal ncRNAs may become a next-generation, cell-free therapeutic platform for bone repair and regeneration.

CONCLUSION

In conclusion, MSC-derived exosomal ncRNAs have emerged as a promising cell-free therapeutic approach that plays a key role in maintaining bone homeostasis and slowing the progression of bone-related diseases by targeting critical molecular pathways and signaling networks. In addition to their therapeutic potential, these ncRNAs hold significant promise as biomarkers for early detection of bone diseases. Nevertheless, its clinical value should be validated in patient populations. However, this study has several limitations and areas that require further investigation. First, most studies on MSC-derived exosomal ncRNAs have focused on miRNAs, with limited research on lncRNAs, including linear lncRNAs and circRNAs. Second, the networks based on competing endogenous RNAs remain largely unexplored, which warrants further research. Third, preclinical validation should extend beyond rodent models to complex large animal systems. Fourth, well-designed clinical trials with larger patient cohorts should be conducted. Although several strategies and challenges are discussed in the clinical implications section, it is imperative to attain a more profound understanding of the regulatory mechanisms of MSC-derived exosomal ncRNAs, develop standardized protocols, and conduct thorough preclinical and clinical validation.