Therapeutic potential of exosomes in rotator cuff tendon healing

Understanding Fibrous Tissue in the Effective Healing of Rotator Cuff Injury

The rotator cuff is a crucial group of muscles and tendons in the shoulder complex that plays a significant role in the stabilization of the glenohumeral joint and enabling a wide range of motion. Rotator cuff tendon tears can occur due to sudden injuries or degenerative processes that develop gradually over time, whether they are partial or full thickness. These injuries are common causes of shoulder pain and functional impairment, and their complex nature highlights the essential role of the rotator cuff in shoulder function. Scar formation is a crucial aspect of the healing process initiated following a rotator cuff tendon tear, but excessive fibrous tissue development can potentially lead to stiffness, discomfort, and movement limitations. Age is a critical risk factor, with the prevalence of these tears increasing among older individuals. This comprehensive review aims to delve deeper into the anatomy and injury mechanisms of the rotator cuff. Furthermore, it will inspect the signaling pathways involved in fibrous tissue development, evaluate the various factors affecting the healing environment, and discuss proactive measures aimed at reducing excessive fibrous tissue formation. Lastly, this review identifed gaps within existing knowledge to advance methods for better management of rotator cuff tendon injuries.

Regenerative Medicine Solutions for Rotator Cuff Injuries in Athletes: Indications and Outcomes

Rotator cuff (RC) injuries include a wide range of pathologic states. Athletes are perhaps the most susceptible to RC injuries ranging from tendinopathy to partial or full-thickness tears, due to functional overload and repetitive movements, causing abstention from sports for long periods. Regenerative medicine keeps giving us multiple choices to fight the disability caused by these pathologies. A literature search was performed, and findings related to the structure-function of rotator cuff units, pathophysiology of injuries, regenerative medicine treatments, and future strategies were outlined. Platelet-rich plasma (PRP) has a greater number of articles and clinical trials, accompanied by stem cells progenitor, prolotherapy, and new approaches such as microfragmented adipose tissue and exosomes. RC injuries in athletes can cause pain, functional impotence, and the risk of recurrence, and can lead them to stop playing sports. Regenerative medicine offers a range of treatments, but some of them need further studies to underline their actual validity.

A new method regulates bone fracture tissue exosome lncRNA-mRNA to promote mesenchymal stem cell proliferation and migration

Post-injury adaptation (PIA) is a simple and convenient method to promote bone healing, but its mechanism is unclear. This study was to discuss the role of fracture site tissue exosomes lncRNAs-mRNAs networks on PIA promoting bone mesenchymal stem cells (BMSCs) proliferation and migration. Firstly, the effects of PIA accelerating BMSCs proliferation and migration were confirmed by rat fracture model and bone fracture environment in vitro. Besides, the fracture site tissue exosomes were isolated and authenticated. Then the tissue exosomes were the key factor in PIA promoting BMSCs proliferation and migration authenticated by in vitro and in vivo experiments. The high throughput sequencing and RT-PCR were used to analyze the tissue exosomes lncRNAs-mRNAs networks. It was found that PIA treatment upregulated 118 lncRNAs, 295 mRNAs, and downregulated 111 lncRNAs, 2706 mRNAs in tissue exosomes. A total 12,211 genes were the target genes. Akt1, Actb and Uba52 were the hub mRNAs in tissue exosomes. In additions, tissue-derived exosomes of PIA treated rats upregulated 49 genes, 3 lncRNAs and downregulated 28 genes, 1 lncRNA in BMSCs. Kif11 was the hub gene. Overall, PIA promoted BMSCs proliferation and migration in the early stage of fracture healing, which was closely related to the fracture site tissue exosomes. Akt1, Actb and Uba52 were the hub mRNAs in the exosomes. Besides, Kif11 might be the key gene in BMSC regulated by tissue-derived exosomes of PIA treated rats.

Translational studies of exosomes in sports medicine - a mini-review

This review in sports medicine focuses on the critical role of exosomes in managing chronic conditions and enhancing athletic performance. Exosomes, small vesicles produced by various cells, are essential for cellular communication and transporting molecules like proteins and nucleic acids. Originating from the endoplasmic reticulum, they play a vital role in modulating inflammation and tissue repair. Their significance in sports medicine is increasingly recognized, particularly in healing athletic injuries, improving articular cartilage lesions, and osteoarthritic conditions by modulating cellular behavior and aiding tissue regeneration. Investigations also highlight their potential in boosting athletic performance, especially through myocytes-derived exosomes that may enhance adaptability to physical training. Emphasizing a multidisciplinary approach, this review underlines the need to thoroughly understand exosome biology, including their pathways and classifications, to fully exploit their therapeutic potential. It outlines future directions in sports medicine, focusing on personalized treatments, clinical evaluations, and embracing technological advancements. This research represents a frontier in using exosomes to improve athletes' health and performance capabilities.

Analysis of differentially expressed genes in torn rotator cuff tendon tissues in diabetic patients through RNA-sequencing

BACKGROUND

Rotator cuff tears (RCT) is a common musculoskeletal disorder in the shoulder which cause pain and functional disability. Diabetes mellitus (DM) is characterized by impaired ability of producing or responding to insulin and has been reported to act as a risk factor of the progression of rotator cuff tendinopathy and tear. Long non-coding RNAs (lncRNAs) are involved in the development of various diseases, but little is known about their potential roles involved in RCT of diabetic patients.

METHODS

RNA-Sequencing (RNA-Seq) was used in this study to profile differentially expressed lncRNAs and mRNAs in RCT samples between 3 diabetic and 3 nondiabetic patients. Gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG) pathway analysis were performed to annotate the function of the differentially expressed genes (DEGs). LncRNA-mRNA co-expression network and competing endogenous RNA (ceRNA) network were constructed to elucidate the potential molecular mechanisms of DM affecting RCT.

RESULTS

In total, 505 lncRNAs and 388 mRNAs were detected to be differentially expressed in RCT samples between diabetic and nondiabetic patients. GO functional analysis indicated that related lncRNAs and mRNAs were involved in metabolic process, immune system process and others. KEGG pathway analysis indicated that related mRNAs were involved in ferroptosis, PI3K-Akt signaling pathway, Wnt signaling pathway, JAK-STAT signaling pathway and IL-17 signaling pathway and others. LncRNA-mRNA co-expression network was constructed, and ceRNA network showed the interaction of differentially expressed RNAs, comprising 5 lncRNAs, 2 mRNAs, and 142 miRNAs. TF regulation analysis revealed that STAT affected the progression of RCT by regulating the apoptosis pathway in diabetic patients.

CONCLUSIONS

We preliminarily dissected the differential expression profile of lncRNAs and mRNAs in torn rotator cuff tendon between diabetic and nondiabetic patients. And the bioinformatic analysis suggested some important RNAs and signaling pathways regarding inflammation and apoptosis were involved in diabetic RCT. Our findings offer a new perspective on the association between DM and progression of RCT.

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.

Engineered exosomes: A promising strategy for tendon-bone healing

BACKGROUND

Due to the spatiotemporal complexity of the composition, structure, and cell population of the tendon-bone interface (TBI), it is difficult to achieve true healing. Recent research is increasingly focusing on engineered exosomes, which are a promising strategy for TBI regeneration.

AIM OF REVIEW

This review discusses the physiological and pathological characteristics of TBI and the application and limitations of natural exosomes in the field of tendon-bone healing. The definition, loading strategies, and spatiotemporal properties of engineered exosomes were elaborated. We also summarize the application and future research directions of engineered exosomes in the field of tendon-bone healing.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Engineered exosomes can spatially deliver cargo to targeted sites and temporally realize the sustained release of therapeutic molecules in TBI. This review expounds on the multidifferentiation of engineered exosomes for tendon-bone healing, which effectively improves the biological and biomechanical properties of TBI. Engineered exosomes could be a promising strategy for tendon-bone healing.

Biomechanical Forces in the Tissue Engineering and Regeneration of Shoulder, Hip, Knee, and Ankle Joints

Tear on the tendon, ligament and articular cartilage of the joints do not heal by itself and new modalities of treatment are required to address the need for full restoration of joint functions. Accompanied by degenerative diseases, the healing of these tissues does not occur naturally and hence requires surgical interventions, but with associated morbidity. Tissue engineering strategies are now focusing on the effective incorporation of biomechanical stimulation by the application of biomechanical forces relevant to the tissue of interest to regenerate and engineer functional tissues. Bioreactors are being continuously developed to accomplish this goal. Although bioreactors have been developed, the advancement in the field of biomaterial, basic science, and cell engineering warrant further refinement for their effective use. In this article we reviewed the application of biomechanical forces in the tissue engineering and regeneration of the joints such as rotator cuff of shoulder, ball and socket joint of the hip, articular cartilage of knee, and the ankle joints.

Nanofibrous scaffolds for the healing of the fibrocartilaginous enthesis: advances and prospects

With the current developmental advancements in nanotechnology, nanofibrous scaffolds are being widely used. The healing of fibrocartilaginous enthesis is a slow and complex process, and while existing treatments have a certain effect on promoting their healing, these are associated with some limitations. The nanofibrous scaffold has the advantages of easy preparation, wide source of raw materials, easy adjustment, easy modification, can mimic the natural structure and morphology of the fibrocartilaginous enthesis, and has good biocompatibility, which can compensate for existing treatments and be combined with them to promote the repair of fibrocartilaginous enthesis. The nanofibrous scaffold can promote the healing of fibrocartilaginous enthesis by controlling the morphology and ensuring controlled drug release. Hence, the use of nanofibrous scaffold with stimulative response features in the musculoskeletal system has led us to imagine its potential application in fibrocartilaginous enthesis. Therefore, the healing of fibrocartilaginous enthesis based on a nanofibrous scaffold may be a novel therapeutic approach.

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

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

Exosomes Derived From Kartogenin-Preconditioned Mesenchymal Stem Cells Promote Cartilage Formation and Collagen Maturation for Enthesis Regeneration in a Rat Model of Chronic Rotator Cuff Tear

BACKGROUND

Poor tendon-to-bone healing in chronic rotator cuff tears (RCTs) is related to unsatisfactory outcomes. Exosomes derived from mesenchymal stem cells reportedly enhance rotator cuff healing. However, the difficulty in producing exosomes with a stronger effect on enthesis regeneration must be resolved.

PURPOSE

To study the effect of exosomes derived from kartogenin (KGN)-preconditioned human bone marrow mesenchymal stem cells (KGN-Exos) on tendon-to-bone healing in a rat model of chronic RCT.

STUDY DESIGN

Controlled laboratory study.

METHODS

Exosome-loaded sodium alginate hydrogel (SAH) was prepared. Moreover, exosomes were labeled with 1,1'-dioctadecyl-3,3,3',3'-tetramethylindotricarbocyanine iodide (DiR) or 1,1'-dioctadecyl-3,3,3'3'-tetramethylindocarbocyanine perchlorate (Dil) for in vivo tracking. Bilateral rotator cuff repair (RCR) was conducted in an established chronic RCT rat model. A total of 66 rats were randomized to control, untreated exosome (un-Exos), and KGN-Exos groups to receive local injections of pure SAH, un-Exos, or KGN-Exos SAH at the repaired site. The presence of DiR/Dil-labeled exosomes was assessed at 1 day and 1 week, and tendon-to-bone healing was evaluated histologically, immunohistochemically, and biomechanically at 4 and 8 weeks.

RESULTS

Both un-Exos and KGN-Exos exhibited sustained release from SAH for up to 96 hours. In vivo study revealed that un-Exos and KGN-Exos were localized to the repaired site at 1 week. Moreover, the KGN-Exos group showed a higher histological score and increased glycosaminoglycan and collagen II expression at 4 and 8 weeks. In addition, more mature and better-organized collagen fibers with higher ratios of collagen I to collagen III were observed at 8 weeks in the tendon-to-bone interface compared with those in the control and un-Exos groups. Biomechanically, the KGN-Exos group had the highest failure load (28.12 ± 2.40 N) and stiffness (28.57 ± 2.49 N/mm) among the 3 groups at 8 weeks.

CONCLUSION

Local injection of SAH with sustained KGN-Exos release could effectively promote cartilage formation as well as collagen maturation and organization for enthesis regeneration, contributing to enhanced biomechanical properties after RCR.

CLINICAL RELEVANCE

KGN-Exos injection may be used as a cell-free therapeutic option to accelerate tendon-to-bone healing in chronic RCT.

Therapeutic potential and mechanisms of mesenchymal stem cell-derived exosomes as bioactive materials in tendon-bone healing

Tendon-bone insertion (TBI) injuries, such as anterior cruciate ligament injury and rotator cuff injury, are the most common soft tissue injuries. In most situations, surgical tendon/ligament reconstruction is necessary for treating such injuries. However, a significant number of cases failed because healing of the enthesis occurs through scar tissue formation rather than the regeneration of transitional tissue. In recent years, the therapeutic potential of mesenchymal stem cells (MSCs) has been well documented in animal and clinical studies, such as chronic paraplegia, non-ischemic heart failure, and osteoarthritis of the knee. MSCs are multipotent stem cells, which have self-renewability and the ability to differentiate into a wide variety of cells such as chondrocytes, osteoblasts, and adipocytes. Numerous studies have suggested that MSCs could promote angiogenesis and cell proliferation, reduce inflammation, and produce a large number of bioactive molecules involved in the repair. These effects are likely mediated by the paracrine mechanisms of MSCs, particularly through the release of exosomes. Exosomes, nano-sized extracellular vesicles (EVs) with a lipid bilayer and a membrane structure, are naturally released by various cell types. They play an essential role in intercellular communication by transferring bioactive lipids, proteins, and nucleic acids, such as mRNAs and miRNAs, between cells to influence the physiological and pathological processes of recipient cells. Exosomes have been shown to facilitate tissue repair and regeneration. Herein, we discuss the prospective applications of MSC-derived exosomes in TBI injuries. We also review the roles of MSC-EVs and the underlying mechanisms of their effects on promoting tendon-bone healing. At last, we discuss the present challenges and future research directions.

Optimizing repair of tendon ruptures and chronic tendinopathies: Integrating the use of biomarkers with biological interventions to improve patient outcomes and clinical trial design

Tendons are dense connective tissues of the musculoskeletal system that link bones with muscles to foster mobility. They have complex structures and exist in varying biomechanical, metabolic and biological environments. In addition, tendon composition and mechanical properties can change over the lifespan as an individual ages. Many tendons function in high stress conditions with a low vascular and neuronal supply, conditions often leading to development of chronic tendinopathies, and in some cases, overt rupture of the tissues. Given their essential nature for human mobility and navigation through the environment, the effective repair and regeneration of different tendons after injury or damage is critical for quality of life, and for elite athletes, the return to sport participation at a high level. However, for mainly unknown reasons, the outcomes following injury are not always successful and lead to functional compromise and risk for re-injury. Thus, there is a need to identify those patients who are at risk for developing tendon problems, as well those at risk for poor outcomes after injury and to design interventions to improve outcomes after injury or rupture to specific tendons. This review will discuss recent advances in the identification of biomarkers prognostic for successful and less successful outcomes after tendon injury, and the mechanistic implications of such biomarkers, as well as the potential for specific biologic interventions to enhance outcomes to improve both quality of life and a return to participation in sports. In addition, the implication of these biomarkers for clinical trial design is discussed, as is the issue of whether such biomarkers for successful healing of one tendon can be extended to all tendons or are valid only for tendons in specific biomechanical and biological environments. As maintaining an active lifestyle is critical for health, the successful implementation of these advances will benefit the large number of individuals at risk.

Recent advances in tendon tissue engineering strategy

Tendon injuries often result in significant pain and disability and impose severe clinical and financial burdens on our society. Despite considerable achievements in the field of regenerative medicine in the past several decades, effective treatments remain a challenge due to the limited natural healing capacity of tendons caused by poor cell density and vascularization. The development of tissue engineering has provided more promising results in regenerating tendon-like tissues with compositional, structural and functional characteristics comparable to those of native tendon tissues. Tissue engineering is the discipline of regenerative medicine that aims to restore the physiological functions of tissues by using a combination of cells and materials, as well as suitable biochemical and physicochemical factors. In this review, following a discussion of tendon structure, injury and healing, we aim to elucidate the current strategies (biomaterials, scaffold fabrication techniques, cells, biological adjuncts, mechanical loading and bioreactors, and the role of macrophage polarization in tendon regeneration), challenges and future directions in the field of tendon tissue engineering.

Tendon tissue engineering: An overview of biologics to promote tendon healing and repair

Tendons are dense connective tissues with a hierarchical polarized structure that respond to and adapt to the transmission of muscle contraction forces to the skeleton, enabling motion and maintaining posture. Tendon injuries, also known as tendinopathies, are becoming more common as populations age and participation in sports/leisure activities increases. The tendon has a poor ability to self-heal and regenerate given its intrinsic, constrained vascular supply and exposure to frequent, severe loading. There is a lack of understanding of the underlying pathophysiology, and it is not surprising that disorder-targeted medicines have only been partially effective at best. Recent tissue engineering approaches have emerged as a potential tool to drive tendon regeneration and healing. In this review, we investigated the physiochemical factors involved in tendon ontogeny and discussed their potential application in vitro to reproduce functional and self-renewing tendon tissue. We sought to understand whether stem cells are capable of forming tendons, how they can be directed towards the tenogenic lineage, and how their growth is regulated and monitored during the entire differentiation path. Finally, we showed recent developments in tendon tissue engineering, specifically the use of mesenchymal stem cells (MSCs), which can differentiate into tendon cells, as well as the potential role of extracellular vesicles (EVs) in tendon regeneration and their potential for use in accelerating the healing response after injury.

Rotator Cuff Health, Pathology, and Repair in the Perspective of Hyperlipidemia

Rotator Cuff Injuries (RCI) are prevalent cause of shoulder pain affecting over 20% of the population in the USA. Surgical repair of the torn rotator cuff helps in relieving the pressure on the rotator cuff tendon and from symptoms, however tendon-to-bone healing after rotator cuff surgery still has a high failure rate. Hyperlipidemia has been strongly associated with RCI although the cellular and molecular mechanisms are largely unknown. The focus of this critical review is to further explore the role of hyperlipidemia in RCI and rotator cuff tissue repair to determine its implication as a risk factor for tears, repair, and retears. A literature review was conducted to elucidate the role of hyperlipidemia as an inflammatory mediator and catalyst for structural instability within the shoulder. The results from various studies were critically reviewed to summarize the relationship between hyperlipidemia and rotator cuff pathology. Hyperlipidemia induces LDL-particle entrapment within the dense regular collagen of rotator cuff tendons resulting in foam cell aggregation and macrophage recruitment. Subsequent inflammatory pathways including the JAK2/STAT3 pathway and NLRP3 inflammasome pathway led to persistent inflammation and Extracellular Matrix (ECM) degradation within the rotator cuff. While arthroscopic repair remains the most common treatment modality, nonsurgical treatment including statins, vitamin D, and targeting miRNA are also of therapeutic benefit. Hyperlipidemia interferes with arthroscopic repairs by inducing inflammation and stiffness within tendons and increases the risk of retears. Most notably, targeting underlying mechanisms influencing inflammation has large therapeutic value as a novel treatment strategy for the management of rotator cuff pathology.

Exosomes secreted by hypoxia-stimulated bone-marrow mesenchymal stem cells promote grafted tendon-bone tunnel healing in rat anterior cruciate ligament reconstruction model

Background

After anterior cruciate ligament (ACL) reconstruction in clinic, firm and rapid integration of the grafted tendon into the bone tunnel remains a challenge. Exosomes from hypoxia-treated stem cells are beneficial for promoting angiogenesis and then coupling with osteogenesis. Therefore, exosomes from hypoxia-cultured bone-marrow mesenchymal stem cells (Hypo-Exos) may be a cell-free therapy for enhancing graft-bone incorporation after ACL reconstruction.

Methods

Exosomes from normoxia-cultured bone-marrow mesenchymal stem cells (Norm-Exos) or Hypo-Exos were respectively cultured with human umbilical vein endothelial cells (HUVECs) for in-vitro evaluating their functions in HUVECs proliferation, migration, and tube formation. A total of 87 rats with single-bundle ACL reconstructions in the right knee were randomly allocated into 3 different treatments: phosphate-buffered saline (PBS) with the adhesive hydrogel injection as control (Ctrl), Norm-Exos with the adhesive hydrogel injection (Norm-Exos), and Hypo-Exos with the adhesive hydrogel injection (Hypo-Exos). At postoperative weeks 2, 4, or 8, the ACL graft-bone integrations were evaluated.

Results

Hypo-Exos was a better stimulator for in-vitro HUVECs proliferation, migration, and tube formation compared to PBS or Norm-Exos. Hypo-Exos within the adhesive hydrogel could be sustained-released at least 14 days around the peri-graft site. Radiologically, at week 4 or 8, femoral or tibial bone tunnel areas (BTA), as well as bone volume/total volume ratio (BV/TV) of the femoral or tibial peri-graft bone in the Hypo-Exos group, improved significantly better than these parameters of the Ctrl and Norm-Exos groups (P<0.05 for all). Histologically, the grafted tendon-bone interface in the Hypo-Exos group showed significantly higher histologic scores at week 4 or 8 as compared with the other groups (P<0.05 for all). Immunofluorescent staining verified that type H vessels were more abundant in the Hypo-Exos group when compared to the Ctrl or Norm-Exos group at week 2. Biomechanically, the Hypo-Exos group exhibited a significantly heightened failure load compared with the Ctrl and Norm-Exos groups (P<0.05 for all) at 8 weeks. Meanwhile, the stiffness in the Hypo-Exos group was the greatest among the three groups.

Conclusion

Peri-graft Hypo-Exos injection accelerates grafted tendon-bone tunnel integration after ACL reconstruction by improving peri-graft bone microarchitecture.

Clinical perspectives for repairing rotator cuff injuries with multi-tissue regenerative approaches

Background

In the musculoskeletal system, bone, tendon, and muscle form highly integrated multi-tissue units such as the rotator cuff complex, which facilitates functional and dynamic movement of the shoulder joint. Understanding the intricate interplay among these tissues within clinical, biological, and engineering contexts is vital for addressing challenging issues in treatment of musculoskeletal disorders and injuries.

Methods

A wide-ranging literature search was performed, and findings related to the socioeconomic impact of rotator cuff tears, the structure-function relationship of rotator cuff bone-tendon-muscle units, pathophysiology of injury, current clinical treatments, recent state-of-the-art advances (stem cells, growth factors, and exosomes) as well as their regulatory approval, and future strategies aimed at engineering bone-tendon-muscle musculoskeletal units are outlined.

Results

Rotator cuff injuries are a significant socioeconomic burden on numerous healthcare systems that may be addressed by treating the rotator cuff as a single complex, given its highly integrated structure-function relationship as well as degenerative pathophysiology and limited healing in bone-tendon-muscle musculoskeletal tissues. Current clinical practices for treating rotator cuff injuries, including the use of commercially available devices and evolving trends in surgical management have benefited patients while advances in application of stem/progenitor cells, growth factors, and exosomes hold clinical potential. However, such efforts do not emphasize targeted regeneration of bone-tendon-muscle units. Strategies aimed at regenerating bone-tendon-muscle units are thus expected to address challenging issues in rotator cuff repair.

Conclusions

The rotator cuff is a highly integrated complex of bone-tendon-muscle units that when injured, has severe consequences for patients and healthcare systems. State-of-the-art clinical treatment as well as recent advances have resulted in improved patient outcome and may be further enhanced by engineering bone-tendon-muscle multi-tissue grafts as a potential strategy for rotator cuff injuries.

Translational Potential of this Article

This review aims to bridge clinical, tissue engineering, and biological aspects of rotator cuff repair and propose a novel therapeutic strategy by targeted regeneration of multi-tissue units. The presentation of these wide-ranging and multi-disciplinary concepts are broadly applicable to regenerative medicine applications for musculoskeletal and non-musculoskeletal tissues.

Systematic identification of aberrant non-coding RNAs and their mediated modules in rotator cuff tears

Background: Rotator cuff tears (RCT) is the most common cause of shoulder dysfunction, however, its molecular mechanisms remain unclear. Non-coding RNAs(ncRNAs), such as long ncRNA (lncRNA), microRNA (miRNA) and circular RNA (circRNA), are involved in a variety of diseases, but little is known about their roles in RCT. Therefore, the purpose of this study is to identify dysregulated ncRNAs and understand how they influence RCT.

Methods: We performed RNA sequencing and miRNA sequencing on five pairs of torn supraspinatus muscles and matched unharmed subscapularis muscles to identify RNAs dysregulated in RCT patients. To better comprehend the fundamental biological processes, we carried out enrichment analysis of these dysregulated mRNAs or the co-expressed genes of dysregulated ncRNAs. According to the competing endogenous RNA (ceRNA) theory, we finally established ceRNA networks to explore the relationship among dysregulated RNAs in RCT.

Results: A total of 151 mRNAs, 38 miRNAs, 20 lncRNAs and 90 circRNAs were differentially expressed between torn supraspinatus muscles and matched unharmed subscapularis muscles, respectively. We found that these dysregulated mRNAs, the target mRNAs of these dysregulated miRNAs or the co-expressed mRNAs of these dysregulated ncRNAs were enriched in muscle structure development, actin-mediated cell contraction and actin binding. Then we constructed and analyzed the ceRNA network and found that the largest module in the ceRNA network was associated with vasculature development. Based on the topological properties of the largest module, we identified several important ncRNAs including hsa_circ_0000722, hsa-miR-129-5p and hsa-miR-30c-5p, whose interacting mRNAs related to muscle diseases, fat and inflammation.

Conclusion: This study presented a systematic dissection of the expression profile of mRNAs and ncRNAs in RCT patients and revealed some important ncRNAs which may contribute to the development of RCT. Such results could provide new insights for further research on RCT.

Editorial Commentary: Stem Cell Exosomes Can Promote Healing and Muscle Function After Rotator Cuff Repair

Stem cell-based therapies are a growing area of interest within regenerative musculoskeletal medicine. Exosomes represent an attractive emergent clinical strategy for the delivery of stem cell-derived growth factors and small molecules to a regenerating tissue environment. Stem cells themselves may not engraft into host tissue but more likely promote a pro-regenerative state through the release of autocrine and paracrine factors. Exosomes, a type of small membrane-bound extracellular vesicle secreted by cells, are of interest as an emergent clinical strategy because they have several key factors that could provide the elusive goal of stem cell therapies in a more practical manner. Exosomes from stem cells appear to have much of the machinery that could promote regenerative capabilities, including growth factors, micro-RNAs (miRNAs), and other signaling molecules that can induce the necessary growth signaling and transcriptional changes to induce a phenotypic change in the local delivery environment. It is important to note that they also have a limited host immune response and can be stored in a freezer, as opposed to many stem cell products that need specialized storage systems to maintain viability. For these reasons, exosome-based therapeutic solutions for rotator cuff repair offer a potential treatment strategy. Recent research provides a highly translational application of exosomes to a chronic rotator cuff repair model and shows efficacy in improving the biomechanical strength of tendon healing at the tendon-bone interface, in addition to partially ameliorating the development of fatty infiltration. Further work is needed to characterize the components of exosomes that result in their bioactivity in addition to considering their cost-effectiveness as a regenerative musculoskeletal treatment.

Hydrogel Development for Rotator Cuff Repair

Rotator cuff tears (RCTs) are common in shoulder disease and disability. Despite significant advances in surgical repair techniques, 20–70% of patients still have postoperative rotator cuff dysfunction. These functional defects may be related to retear or rotator cuff quality deterioration due to tendon retraction and scar tissue at the repair site. As an effective delivery system, hydrogel scaffolds may improve the healing of RCTs and be a useful treatment for irreparable rotator cuff injuries. Although many studies have tested this hypothesis, most are limited to laboratory animal experiments. This review summarizes differences in hydrogel scaffold construction, active ingredients, and application methods in recent research. Efforts to determine the indications of hydrogel scaffolds (with different constructions and cargos) for various types of RCTs, as well as the effectiveness and reliability of application methods and devices, are also discussed.

Placental Tissues as Biomaterials in Regenerative Medicine

Placental tissues encompass all the tissues which support fetal development, including the placenta, placental membrane, umbilical cord, and amniotic fluid. Since the 1990s there has been renewed interest in the use of these tissues as a raw material for regenerative medicine applications. Placental tissues have been extensively studied for their potential contribution to tissue repair applications. Studies have attributed their efficacy in augmenting the healing process to the extracellular matrix scaffolds rich in collagens, glycosaminoglycans, and proteoglycans, as well as the presence of cytokines within the tissues that have been shown to stimulate re-epithelialization, promote angiogenesis, and aid in the reduction of inflammation and scarring. The compositions and properties of all birth tissues give them the potential to be valuable biomaterials for the development of new regenerative therapies. Herein, the development and compositions of each of these tissues are reviewed, with focus on the structural and signaling components that are relevant to medical applications. This review also explores current configurations and recent innovations in the use of placental tissues as biomaterials in regenerative medicine.

Infrapatellar Fat Pad Mesenchymal Stromal Cell-Derived Exosomes Accelerate Tendon-Bone Healing and Intra-articular Graft Remodeling After Anterior Cruciate Ligament Reconstruction

BACKGROUND

Exosomes derived from mesenchymal stromal cells (MSCs) reportedly enhance the healing process. However, no studies have investigated the effect of exosomes from infrapatellar fat pad (IPFP) MSCs on tendon-bone healing and intra-articular graft remodeling after anterior cruciate ligament reconstruction (ACLR).

PURPOSE

To evaluate the in vivo effect of exosomes from IPFP MSCs on tendon-bone healing and intra-articular graft remodeling in a rat model of ACLR.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 90 skeletally mature male Sprague Dawley rats underwent unilateral ACLR using an autograft. All rats were randomly divided into 3 groups: sham injection (SI) group (n = 30), control injection (CI) group (n = 30), and IPFP MSC-derived exosome injection (IMEI) group (n = 30). At 2, 4, and 8 weeks postoperatively, tendon-bone healing and intra-articular graft remodeling were evaluated via biomechanical testing, micro-computed tomography, and histological analysis; macrophage polarization was evaluated using immunohistochemical staining.

RESULTS

Biomechanical testing demonstrated a significantly higher failure load and stiffness in the IMEI group than in the SI and CI groups at 4 and 8 weeks postoperatively. Moreover, a thinner graft-to-bone healing interface with more fibrocartilage was observed in the IMEI group at both time points. Micro-computed tomography revealed greater new bone ingrowth in the IMEI group than in the other groups, as demonstrated by smaller mean bone tunnel areas and a larger bone volume/total volume ratio. Additionally, more cellular infiltration was observed in the intra-articular graft in the IMEI group than in the other groups at 4 weeks, followed by more regularly organized fibers with mature collagen at 8 weeks. Notably, similar trends of macrophage polarization were found at both the graft-to-bone interface and the intra-articular graft in the IMEI group, with significantly fewer proinflammatory M1 macrophages and larger numbers of reparative M2 macrophages than in the SI and CI groups.

CONCLUSION

IPFP MSC-derived exosomes accelerated tendon-bone healing and intra-articular graft remodeling after ACLR, which may have resulted from the immunomodulation of macrophage polarization.

CLINICAL RELEVANCE

The IPFP can be easily harvested by most orthopaedic surgeons. Exosomes from IPFP MSCs, constituting a newly emerging cell-free approach, may represent a treatment option for improving tendon-bone healing and intra-articular graft remodeling after ACLR.

Exosomes: A Tool for Bone Tissue Engineering

Mesenchymal stem cells (MSCs) have been repeatedly shown to be a valuable source for cell-based therapy in regenerative medicine, including bony tissue repair. However, engraftment at the injury site is poor. Recently, it has been suggested that MSCs and other cells act through a paracrine signaling mechanism. Exosomes are nanostructures that have been implicated in this process. They carry DNA, RNA, proteins, and lipids and play an important role in cell-to-cell communication directly modulating their target cell at a transcriptional level. In a bone microenvironment, they have been shown to increase osteogenesis and osteogenic differentiation in vivo and in vitro. In the following review, we will discuss the most advanced and significant knowledge of biological functions of exosomes in bone regeneration and their clinical applications in osseous diseases. Impact statement Mesenchymal stem cells have been shown to be a promising tool in bone tissue engineering. Recently, it has been suggested that they secrete exosomes containing messenger RNA, proteins, and lipids, thus acting through paracrine signaling mechanisms. Considering that exosomes are nonteratogenic and have low immunogenic potential, they could potentially replace stem-cell based therapy and thus eradicate the risk of neoplastic transformation associated with cell transplantations in bone regeneration.

Why and how to use the body's own stem cells for regeneration in musculoskeletal disorders: a primer

Background

Recently, the management of musculoskeletal disorders with the patients' own stem cells, isolated from the walls of small blood vessels, which can be found in great numbers in the adipose tissue, has received considerable attention. On the other hand, there are still misconceptions about these adipose-derived regenerative cells (ADRCs) that contain vascular-associated pluripotent stem cells (vaPS cells) in regenerative medicine.

Methods

Based on our previous publications on this topic, we have developed a concept to describe the significance of the ADRCs/vaPS cells in the field of orthobiologics as briefly as possible and at the same time as precisely as possible.

Results

The ADRCs/vaPS cells belong to the group of orthobiologics that are based on autologous cells. Because the latter can both stimulate a patient’s body's localized self-healing power and provide new cells that can integrate into the host tissue during the healing response when the localized self-healing power is exhausted, this group of orthobiologics appears more advantageous than cell-free orthobiologics and orthobiologics that are based on allogeneic cells. Within the group of orthobiologics that are based on autologous cells, enzymatically isolated, uncultured ADRCs/vaPS cells have several advantages over non-enzymatically isolated cells/microfragmented fat as well as over uncultured bone marrow aspirate concentrate and cultured cells (adipose-derived stem cells, bone marrow-derived mesenchymal stem cells).

Conclusions

The use of ADRCs/vaPS cells can be seamlessly integrated into modern orthopedic treatment concepts, which can be understood as the optimization of a process which—albeit less efficiently—also takes place physiologically. Accordingly, this new safe and effective type of treatment is attractive in terms of holistic thinking and personalized medicine.

Exosome-delivered BMP-2 and polyaspartic acid promotes tendon bone healing in rotator cuff tear via Smad/RUNX2 signaling pathway

Rotator cuff tear is the main form of shoulder joint injury, which seriously affects shoulder joint function. This study aimed to clarify the function and mechanism of exosomes containing polylactic acid (PLA), polylactic acid copolymer and BMP-2 in tendon bone healing of rotator cuff tear. First, CD44 expression in bone marrow mesenchymal stem cells (BMSCs) and CD90 and CD44 in exosomes were analyzed by flow cytometry. Then, stability and targeting identification of exosome-delivered bone morphogenetic protein (BMP)-2 and PLA microcapsules were measured by transmission electron microscopy (TEM), DiO/DiI staining. Finally, tendon-bone repair after acute rotator cuff rupture in rabbits was established, and the function of BMP-2 exosomes for tendon bone healing in rotator cuff tear was evaluated by micro-CT, biomechanical determination and histochemical staining methods. The results showed that the exosomes of polyaspartic acid-polylactic acid-glycolic acid copolymer (PASP-PLGA) microcapsules were successfully established which showed good stability and targeting. The bone mineral density (BMD), tissue mineral density (TMD) and bone volume fraction (BV/TV) were higher, while the stiffness and the ultimate load strength of the tendon interface were enhanced under treatment with exosomes of PASP-PLGA microcapsules. Histochemical staining showed that exosomes of PASP-PLGA microcapsules promoted tendon and bone interface healing after rotator cuff injury. The tendon regeneration- and cartilage differentiation-related protein expressions were significantly upregulated under treatment with exosomes of PASP-PLGA microcapsules. In conclusion, exosome-delivered BMP-2 and PLA promoted tendon bone healing in rotator cuff tear via Smad/RUNX2 pathway. Our findings may provide a new insight for promoting tendon healing.

[Research progress of interfacial tissue engineering in rotator cuff repair]

Objective

To summarize the research progress of interfacial tissue engineering in rotator cuff repair.

Methods

The recent literature at home and abroad concerning interfacial tissue engineering in rotator cuff repair was analysed and summarized.

Results

Interfacial tissue engineering is to reconstruct complex and hierarchical interfacial tissues through a variety of methods to repair or regenerate damaged joints of different tissues. Interfacial tissue engineering in rotator cuff repair mainly includes seed cells, growth factors, biomaterials, oxygen concentration, and mechanical stimulation.

Conclusion

The best strategy for rotator cuff healing and regeneration requires not only the use of biomaterials with gradient changes, but also the combination of seed cells, growth factors, and specific culture conditions (such as oxygen concentration and mechanical stimulation). However, the clinical transformation of the relevant treatment is still a very slow process.

Effects of purified exosome product on rotator cuff tendon-bone healing in vitro and in vivo

Exosomes have multiple therapeutic targets, but the effects on healing rotator cuff tear (RCT) remain unclear. As a circulating exosome, purified exosome product (PEP) has the potential to lead to biomechanical improvement in RCT. Here, we have established a simple and efficient approach that identifies the function and underlying mechanisms of PEP on cell-cell interaction using a co-culture model in vitro. In the in vivo trial, adult female Sprague-Dawley rats underwent unilateral surgery to transect and repair the supraspinatus tendon to its insertion site with or without PEP. PEP promoted the migration and confluence of osteoblast cells and tenocytes, especially during direct cell-cell contact. Expression of potential genes for RCT in vitro and in vivo models were consistent with biomechanical tests and semiquantitative histologic scores, indicating accelerated strength and healing of the RC in response to PEP. Our observations suggest that circulating exosomes provide an effective option to improve the healing speed of RCT after surgical repair. The regeneration of enthesis following PEP treatment appears to be related to a mutually reinforcing relationship between direct cell-cell contact and PEP activity, suggesting a dual approach to the healing process.

First immunohistochemical evidence of human tendon repair following stem cell injection: A case report and review of literature

BACKGROUND

Current clinical treatment options for symptomatic, partial-thickness rotator cuff tear (sPTRCT) offer only limited potential for true tissue healing and improvement of clinical results. In animal models, injections of adult stem cells isolated from adipose tissue into tendon injuries evidenced histological regeneration of tendon tissue. However, it is unclear whether such beneficial effects could also be observed in a human tendon treated with fresh, uncultured, autologous, adipose derived regenerative cells (UA-ADRCs). A specific challenge in this regard is that UA-ADRCs cannot be labeled and, thus, not unequivocally identified in the host tissue. Therefore, histological regeneration of injured human tendons after injection of UA-ADRCs must be assessed using comprehensive, immunohistochemical and microscopic analysis of biopsies taken from the treated tendon a few weeks after injection of UA-ADRCs.

CASE SUMMARY

A 66-year-old patient suffered from sPTRCT affecting the right supraspinatus and infraspinatus tendon, caused by a bicycle accident. On day 18 post injury [day 16 post magnetic resonance imaging (MRI) examination] approximately 100 g of abdominal adipose tissue was harvested by liposuction, from which approximately 75 × 10⁶ UA-ADRCs were isolated within 2 h. Then, UA-ADRCs were injected (controlled by biplanar X-ray imaging) adjacent to the injured supraspinatus tendon immediately after isolation. Despite fast clinical recovery, a follow-up MRI examination 2.5 mo post treatment indicated the need for open revision of the injured infraspinatus tendon, which had not been treated with UA-ADRCs. During this operation, a biopsy was taken from the supraspinatus tendon at the position of the injury. A comprehensive, immunohistochemical and microscopic analysis of the biopsy (comprising 13 antibodies) was indicative of newly formed tendon tissue.

CONCLUSION

Injection of UA-ADRCs can result in regeneration of injured human tendons by formation of new tendon tissue.

Bone mesenchymal stem cells stimulation by magnetic nanoparticles and a static magnetic field: release of exosomal miR-1260a improves osteogenesis and angiogenesis

Background

The therapeutic potential of exosomes derived from stem cells has attracted increasing interest recently, because they can exert similar paracrine functions of stem cells and overcome the limitations of stem cells transplantation. Exosomes derived from bone mesenchymal stem cells (BMSC-Exos) have been confirmed to promote osteogenesis and angiogenesis. The magnetic nanoparticles (eg. Fe₃O₄, γ-Fe₂O₃) combined with a static magnetic field (SMF) has been commonly used to increase wound healing and bone regeneration. Hence, this study aims to evaluate whether exosomes derived from BMSCs preconditioned with a low dose of Fe₃O₄ nanoparticles with or without the SMF, exert superior pro-osteogenic and pro-angiogenic activities in bone regeneration and the underlying mechanisms involved.

Methods

Two novel types of exosomes derived from preconditioned BMSCs that fabricated by regulating the contents with the stimulation of magnetic nanoparticles and/or a SMF. Then, the new exosomes were isolated by ultracentrifugation and characterized. Afterwards, we conducted in vitro experiments in which we measured osteogenic differentiation, cell proliferation, cell migration, and tube formation, then established an in vivo critical-sized calvarial defect rat model. The miRNA expression profiles were compared among the exosomes to detect the potential mechanism of improving osteogenesis and angiogenesis. At last, the function of exosomal miRNA during bone regeneration was confirmed by utilizing a series of gain- and loss-of-function experiments in vitro.

Results

50 µg/mL Fe₃O₄ nanoparticles and a 100 mT SMF were chosen as the optimum magnetic conditions to fabricate two new exosomes, named BMSC-Fe₃O₄-Exos and BMSC-Fe₃O₄-SMF-Exos. They were both confirmed to enhance osteogenesis and angiogenesis in vitro and in vivo compared with BMSC-Exos, and BMSC-Fe₃O₄-SMF-Exos had the most marked effect. The promotion effect was found to be related to the highly riched miR-1260a in BMSC-Fe₃O₄-SMF-Exos. Furthermore, miR-1260a was verified to enhance osteogenesis and angiogenesis through inhibition of HDAC7 and COL4A2, respectively.

Conclusion

These results suggest that low doses of Fe₃O₄ nanoparticles combined with a SMF trigger exosomes to exert enhanced osteogenesis and angiogenesis and that targeting of HDAC7 and COL4A2 by exosomal miR-1260a plays a crucial role in this process. This work could provide a new protocol to promote bone regeneration for tissue engineering in the future.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00958-6.

Cartilage endplate stem cells inhibit intervertebral disc degeneration by releasing exosomes to nucleus pulposus cells to activate Akt/autophagy

Degeneration of the cartilage endplate (CEP) induces intervertebral disc degeneration (IVDD). Nucleus pulposus cell (NPC) apoptosis is also an important exacerbating factor in IVDD, but the cascade mechanism in IVDD is not clear. We investigated the apoptosis of NPCs and IVDD when stimulated by normal cartilage endplate stem cell (CESC)-derived exosomes (N-Exos) and degenerated CESC-derived exosomes (D-Exos) in vitro and in vivo. Tert-butyl hydroperoxide (TBHP) was used to induce inflammation of CESCs. The bioinformatics differences between N-Exos and D-Exos were analyzed using mass spectrometry, heat map, and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. NPC apoptosis was examined using TUNEL staining. The involvement of the AKT and autophagy signaling pathways was investigated using the signaling inhibitor LY294002. Magnetic resonance imaging, Western blotting, and immunofluorescence staining were used to evaluate the therapeutic effects of N-Exos in rats with IVDD. TBHP effectively induced inflammation and the degeneration of CEP in rat. N-Exos were more conducive to autophagy activation than D-Exos. The apoptotic rate of NPCs decreased obviously after treatment with N-Exos compared to D-Exos. N-Exos inhibited NPCs apoptosis and attenuated IVDD in rat via activation of the AKT and autophagy pathways. These results are the first findings to confirm that CEP delayed the progression of IVDD via exosomes. The therapeutic effects of N-Exos on NPC apoptosis inhibition and the slowing of IVDD progression were more effective than D-Exos due to activation of the PI3K/AKT/autophagy pathway, which explained the increase in the incidence of IVDD after inflammation of the CEP.

Polymorphisms and alterations in gene expression associated with rotator cuff tear and healing following surgical repair: a systematic review

BACKGROUND

Rotator cuff tears (RCTs) are a common cause of shoulder disability, yet both conservative and surgical treatment strategies can lead to poor results in some patient populations. Enhanced understanding of the genetic processes associated with RCTs can assist in the development of more effective management options and help predict individual responses to surgical treatment. This systematic review analyzes the current literature on the genetic footprint associated with RCTs and interprets these findings to enhance the current understanding of RCT pathogenesis, potential treatment regimens, and prognostic biomarkers of outcomes after surgical repair.

METHODS

A systematic search of the Embase, PubMed, and Web of Science electronic databases was performed. Medical Subject Headings (MeSH) and Emtree index terms were formulated from the concept terms "rotator cuff tear," "genetics," and "human," and synonyms of these concepts were applied to the Web of Science search. Articles were screened against predefined inclusion and exclusion criteria. Eligible studies compared gene expression patterns and genetic polymorphisms between cases (with RCTs) and controls (without RCTs). Quality assessment was performed with studies being rated as high, moderate, or poor quality. A modified best-evidence synthesis was applied, and studies were determined to be of strong, moderate, or limited evidence.

RESULTS

The search identified 259 articles. Of these studies, 26 were eligible for review. Two studies were considered poor quality; 15 studies, moderate quality; and 9 studies, high quality. Analysis of these articles found that RCTs were associated with alterations in genes that code for the extracellular matrix, cell apoptosis, immune and inflammatory responses, and growth factor pathways. In particular, there was strong evidence of a significant association between RCTs and the genes MMP3, TNC, and ESRRB. Strong evidence of an association between BMP5 upregulation and successful healing after surgical repair was also found.

CONCLUSION

This review provides strong evidence of an genetic association with RCTs. The genotype and gene expression patterns detailed within this review can assist in deciphering the biological mechanisms resulting in RCTs, as well as predicting an individual's response to surgical repair. Future research could investigate whether manipulating these genes-or their associated signaling pathways-could assist in RCT healing and whether genetic biomarkers could be used clinically to predict patient outcomes after surgical repair of RCTs.

Cell-free Stem Cell-Derived Extract Formulation for Regenerative Medicine Applications

Stem cells for regenerative medicine purposes offer therapeutic benefits, but disadvantages are still ill defined. The benefit of stem cells may be attributed to their secretion of growth factors (GFs), cytokines (CKs), and extracellular vesicles (EVs), including exosomes. We present a novel cell-free stem cell-derived extract (CCM), formulated from human progenitor endothelial stem cells (hPESCs), characterized for biologically active factors using ELISA, nanoparticle tracking analysis and single particle interferometric reflectance imaging sensing. The effect on fibroblast proliferation and ability to induce stem cell migration was analyzed using Alamar Blue proliferation and Transwell migration assays, respectively. GFs including IGFBP 1, 2, 3, and 6, insulin, growth hormone, PDGF-AA, TGF-α, TGF-β1, VEGF, and the anti-inflammatory cytokine, IL-1RA were detected. Membrane enclosed particles within exosome size range and expressing exosome tetraspanins CD81 and CD9 were identified. CCM significantly increased cell proliferation and induced stem cell migration. Analysis of CCM revealed presence of GFs, CKs, and EVs, including exosomes. The presence of multiple factors including exosomes within one formulation, the ability to promote cell proliferation and induce stem cell migration may reduce inflammation and pain, and augment tissue repair.

Exosomes Derived from Bone Mesenchymal Stem Cells with the Stimulation of Fe3O4 Nanoparticles and Static Magnetic Field Enhance Wound Healing Through Upregulated miR-21-5p

Background

Both magnetic nanoparticles (MNPs) and exosomes derived from bone mesenchymal stem cells (BMSC-Exos) have been reported to improve wound healing. In this study, novel exosomes (mag-BMSC-Exos) would be fabricated from BMSCs with the stimulation of MNPs and a static magnetic field (SMF) to further enhance wound repair.

Methods

Mag-BMSC-Exos, namely, exosomes derived from BMSCs preconditioned with Fe₃O₄ nanoparticles and a SMF, together with BMSC-Exos were both first isolated by ultracentrifugation, respectively. Afterwards, we conducted in vitro experiments, including scratch wound assays, transwell assays, and tube formation assays, and established an in vivo wound healing model. The miRNA expression profiles were compared between BMSC-Exos and mag-BMSC-Exos to detect the potential mechanism of improving wound healing. At last, the function of exosomal miR-21-5p during wound healing was confirmed by utilizing a series of gain- and loss-of-function experiments in vitro.

Results

The optimal working magnetic condition was 50 µg/mL Fe₃O₄ nanoparticles combined with 100 mT SMF. In vitro, mag-BMSC-Exo administration promoted proliferation, migration and angiogenesis to a greater extent than BMSC-Exo administration. Local transplantation of mag-BMSC-Exos into rat skin wounds resulted in accelerated wound closure, narrower scar widths and enhanced angiogenesis compared with BMSC-Exo transplantation. Notably, miR-21-5p was found to be highly enriched in mag-BMSC-Exos and served as a critical mediator in mag-BMSC-Exo-induced regulatory effects through inhibition of SPRY2 and activation of the PI3K/AKT and ERK1/2 signaling pathways.

Conclusion

Mag-BMSC-Exos can further enhance wound healing than BMSC-Exos by improving angiogenesis and fibroblast function, and miR-21-5p upregulation in mag-BMSC-Exos might be the potential mechanism. This work offers an effective and promising protocol to improve wound healing in clinic.

Mesenchymal Stem Cell-Derived Extracellular Vesicles for the Promotion of Tendon Repair - an Update of Literature

Tendon injuries are prevalent in physical activities and sports. Tendon heals slowly after injuries. The results of conservative treatments and surgery are not satisfactory with high re-injury rate and scar tissue formation. The application of mesenchymal stem cells (MSCs) to the injured tendons was reported to promote tendon repair. Recent studies have suggested that MSCs supported tendon repair via the secretion of paracrine factors. Extracellular vesicles (EVs) are a heterogeneous group of cell-derived membranous structures that are produced and secreted by most eukaryotic cells. They carry a plethora of proteins, lipids, microRNA and mRNA which reprogram the recipient cells and are involved in multiple physiological and pathological processes. EVs were shown to promote tissue repair and mediate the healing effects of MSCs. In this review, I aim to review the recent literature on the promotion of tendon repair using EVs-derived from MSCs (MSC-EVs). The mechanisms underlying these actions are also reviewed and future research directions are discussed. Better understanding of the roles of MSC-EVs in tendon repair would offer a new treatment strategy to circumvent this devastating soft tissue disorder. Graphical Abstract.

Controlled release of odontogenic exosomes from a biodegradable vehicle mediates dentinogenesis as a novel biomimetic pulp capping therapy

Mineralized enamel and dentin provide protection to the dental pulp, which is vital tissue rich with cells, vasculature, and nerves in the inner tooth. Dental caries left untreated threaten exposure of the dental pulp, providing facile access for bacteria to cause severe infection both in the pulp and systemically. Dental materials which stimulate the formation of a protective dentin bridge after insult are necessary to seal the pulp chamber in an effort to maintain natural dentition and prevent pulpal infection. Dental materials to date including calcium hydroxide paste, mineral trioxide aggregate, and glass ionomer resin, are used with mixed results. Herein we exploited the cell-cell communicative properties of exosomes, extracellular vesicles derived from both mineralizing primary human dental pulp stem cells (hDPSCs) and an immortalized murine odontoblast cell line (MDPC-23), to catalyze the formation of a reactionary dentin bridge by recruiting endogenous stem cells of the dental pulp, through an easy-to-handle delivery vehicle which allows for their therapeutic controlled delivery at the pulp interface. Exosomes derived from both hDPSCs and MDPCs upregulated odontogenic gene expression and increased mineralization in vitro. We designed an amphiphilic synthetic polymeric vehicle from a triblock copolymer which encapsulates exosomes by polymeric self-assembly and maintains their biologic integrity throughout release up to 8-12 weeks. The controlled release of odontogenic exosomes resulted in a reparative dentin bridge formation, superior to glass-ionomer cement alone in vivo, in a rat molar pulpotomy model after six weeks. We have developed a platform for the encapsulation and controlled, tunable release of cell-derived exosomes, which maintains their advantageous physiologic properties reflective of the donor cells. This platform is used to modulate downstream recipient cells towards a designed dentinogenic trajectory in vitro and in vivo. Additionally, we have demonstrated the utility of an immortalized cell line to produce a high yield of exosomes with cross-species efficacy.

Exosomes Isolated From Platelet-Rich Plasma and Mesenchymal Stem Cells Promote Recovery of Function After Muscle Injury

BACKGROUND

Clinical use of platelet-rich plasma (PRP) and mesenchymal stem cells (MSCs) has gained momentum as treatment for muscle injuries. Exosomes, or small cell-derived vesicles, could be helpful if they could deliver the same or better physiological effect without cell transplantation into the muscle.

HYPOTHESIS

Local delivery of exosomes derived from PRP (PRP-exos) or MSCs (MSC-exos) to injured muscles hastens recovery of contractile function.

STUDY DESIGN

Controlled laboratory study.

METHODS

In a rat model, platelets were isolated from blood, and MSCs were isolated from bone marrow and expanded in culture; exosomes from both were isolated through ultracentrifugation. The tibialis anterior muscles were injured in vivo using maximal lengthening contractions. Muscles were injected with PRP-exos or MSC-exos (immediately after injury and 5 and 10 days after injury); controls received an equal volume of saline. Histological and biochemical analysis was performed on tissues for all groups.

RESULTS

Injury resulted in a significant loss of maximal isometric torque (66% ± 3%) that gradually recovered over 2 weeks. Both PRP-exos and MSC-exos accelerated recovery, with similar faster recovery of contractile function over the saline-treated group at 5, 10, and 15 days after injury (P < .001). A significant increase in centrally nucleated fibers was seen with both types of exosome groups by day 15 (P < .01). Genes involved in skeletal muscle regeneration were modulated by different exosomes. Muscles treated with PRP-exos had increased expression of Myogenin gene (P < .05), whereas muscles treated with MSC-exos had reduced expression of TGF-β (P < .05) at 10 days after muscle injury.

CONCLUSION

Exosomes derived from PRP or MSCs can facilitate recovery after a muscle strain injury in a small-animal model likely because of factors that can modulate inflammation, fibrosis, and myogenesis.

CLINICAL RELEVANCE

Given their small size, low immunogenicity, and ease with which they can be obtained, exosomes could represent a novel therapy for many orthopaedic ailments.

Advances in the development of gene therapy, noncoding RNA, and exosome-based treatments for tendinopathy

Tendinopathy is a common musculoskeletal disorder characterized by chronic low-grade inflammation and tissue degeneration. Tendons have poor innate healing ability and there is currently no cure for tendinopathy. Studies elucidating mechanisms underlying the pathogenesis of tendinopathy and mechanisms mediating the genesis of tendons during development have provided novel targets and strategies to enhance tendon healing and repair. This review summarizes the current understanding and treatments for tendinopathy. The review also highlights recent advances in gene therapy, the potential of noncoding RNAs, such as microRNAs, and exosomes, which are nanometer-sized extracellular vesicles secreted from cells, for the treatment of tendinopathy.

Exosomes Derived from Bone Marrow Stromal Cells (BMSCs) Enhance Tendon-Bone Healing by Regulating Macrophage Polarization

Background

Inflammation after tendon-bone junction injury results in the formation of excessive scar tissue and poor biomechanical properties. Recent research has shown that exosomes derived from bone marrow stromal cells (BMSCs) can modulate inflammation during tissue healing. Thus, our study aimed to enhance tendon-bone healing by use of BMSC-derived exosomes (BMSC-Exos).

Material/Methods

The mouse tendon-bone reconstruction model was established, and the mice were randomly divided into 3 groups: the control group, the hydrogel group, and the hydrogel+exosome group, with 30 mice in each group. At 7 days, 14 days, and 1 month after surgery, tendon-bone junction samples were harvested, and the macrophage polarization and tendon-bone healing were evaluated based on histology, immunofluorescence, and quantitative RT-PCR (qRT-PCR) analysis.

Results

In the early phase, we observed significantly higher numbers of M2 macrophages and more anti-inflammatory and chondrogenic-related factors in the hydrogel+BMSC-Exos group compared with the control group and the hydrogel group. The M1 macrophages and related proinflammatory factors decreased. Cell apoptosis decreased in the hydrogel+BMSC-Exos group, while cell proliferation increased; in particular, the CD146+ stem cells substantially increased. At 1 month after surgery, there was more fibrocartilage in the hydrogel+BMSC-Exos group than in the other groups. Biomechanical testing showed that the maximum force, strength, and elastic modulus were significantly improved in the hydrogel+BMSC-Exos group.

Conclusions

Our study provides evidence that the local administration of BMSC-Exos promotes the formation of fibrocartilage by increasing M2 macrophage polarization in tendon-to-bone healing, leading to improved biomechanical properties. These findings provide a basis for the potential clinical use of BMSC-Exos in tendon-bone repair.

Adipose Stem Cell-Derived Exosomes Decrease Fatty Infiltration and Enhance Rotator Cuff Healing in a Rabbit Model of Chronic Tears

BACKGROUND

Fatty infiltration and poor tendon-bone healing in chronic rotator cuff tears (RCTs) are associated with unsatisfactory prognosis. Adipose stem cell-derived exosomes (ASC-Exos), having multiple biological effects, can prevent muscle degeneration in acute RCTs. However, the effects of ASC-Exos on fatty infiltration and tendon-bone healing in chronic RCTs remain unknown.

PURPOSE

To study the effects of ASC-Exos on fatty infiltration and tendon-bone healing in a chronic RCT rabbit model.

STUDY DESIGN

Controlled laboratory study.

METHODS

At week 0, we randomly allocated 35 rabbits to receive sham surgery (14 rabbits) or establish a bilateral RCT model (21 rabbits, detachment of the supraspinatus tendon). At week 6, a total of 7 rabbits received sham surgery, and 7 rabbits with RCT were sacrificed for fatty infiltration assay. The remaining 14 rabbits with bilateral RCTs were randomly assigned to a saline group (7 rabbits that received local saline injection and rotator cuff repair) or an ASC-Exos group (7 rabbits that received local ASC-Exos injection and rotator cuff repair). At week 18, all rabbits were sacrificed for histological examination and biomechanical testing.

RESULTS

At week 18, the ASC-Exos group showed significantly lower fatty infiltration (14.01% ± 2.85%) compared with the saline group (21.79% ± 3.07%) (P < .001), and no statistical difference compared with the time of repair (10.88% ± 2.64%) (P = .127). For tendon-bone healing, the ASC-Exos group showed a higher histological score and more newly regenerated fibrocartilage at the repair site than did the saline group. Regarding biomechanical testing, the ASC-Exos group showed significantly higher ultimate load to failure, stiffness, and stress than the saline group.

CONCLUSION

Local injection of ASC-Exos in chronic RCTs at the time of repair could prevent the progress of fatty infiltration, promote tendon-bone healing, and improve biomechanical properties.

CLINICAL RELEVANCE

ASC-Exos injection may be used as a cell-free adjunctive therapy to inhibit fatty infiltration and improve rotator cuff healing in the repair of chronic RCTs.

Umbilical cord-derived Wharton's jelly for regenerative medicine applications

Background

The last decade has seen an explosion in the interest in using biologics for regenerative medicine applications, including umbilical cord-derived Wharton’s Jelly. There is insufficient literature assessing the amount of growth factors, cytokines, hyaluronic acid, and extracellular vesicles including exosomes in these products. The present study reports the development of a novel Wharton’s jelly formulation and evaluates the presence of growth factors, cytokines, hyaluronic acid, and extracellular vesicles including exosomes.

Methods

Human umbilical cords were obtained from consenting caesarian section donors. The Wharton’s jelly was then isolated from the procured umbilical cord and formulated into an injectable form. Randomly selected samples from different batches were analyzed for sterility testing and to quantify the presence of growth factors, cytokines, hyaluronic acid, and extracellular vesicles.

Results

All samples passed the sterility test. Growth factors including IGFBP 1, 2, 3, 4, and 6, TGF-α, and PDGF-AA were detected. Several immunomodulatory cytokines, such as RANTES, IL-6R, and IL-16, were also detected. Pro-inflammatory cytokines MCSFR, MIP-1a; anti-inflammatory cytokines TNF-RI, TNF-RII, and IL-1RA; and homeostatic cytokines TIMP-1 and TIMP-2 were observed. Cytokines associated with wound healing, ICAM-1, G-CSF, GDF-15, and regenerative properties, GH, were also expressed. High concentrations of hyaluronic acid were observed. Particles in the extracellular vesicle size range were also detected and were enclosed by the membrane, indicative of true extracellular vesicles.

Conclusion

There are numerous growth factors, cytokines, hyaluronic acid, and extracellular vesicles present in the Wharton’s jelly formulation analyzed. The amount of these factors in Wharton’s jelly is higher compared with other biologics and may play a role in reducing inflammation and pain and augment healing of musculoskeletal injuries.

The Role of Exosomes in Bone Remodeling: Implications for Bone Physiology and Disease

Bone remodeling represents a physiological phenomenon of continuous bone tissue renewal that requires fine orchestration of multiple cell types, which is critical for the understanding of bone disease but not yet clarified in precise detail. Exosomes, which are cell-secreted nanovesicles drawing increasing attention for their broad biosignaling functions, can shed new light on how multiple heterogeneous cells communicate for the purpose of bone remodeling. In the healthy bone, exosomes transmit signals favoring both bone synthesis and resorption, regulating the differentiation, recruitment, and activity of most cell types involved in bone remodeling and even assuming an active role in extracellular matrix mineralization. Additionally, in the ailing bone, they actively participate in pathogenic processes constituting also potential therapeutic agents and drug vectors. The present review summarizes the current knowledge on bone exosomes and bone remodeling in health and disease.