Exosomes Isolated From Adipose-Derived Stem Cells: A New Cell-Free Approach to Prevent the Muscle Degeneration Associated With Torn Rotator Cuffs

3-Dimensional Bioprinting of a Tendon Stem Cell-Derived Exosomes Loaded Scaffold to Bridge the Unrepairable Massive Rotator Cuff Tear

BACKGROUND

Unrepairable massive rotator cuff tears (UMRCTs) are challenging to surgeons owing to the severely retracted rotator cuff musculotendinous tissues and extreme defects in the rotator cuff tendinous tissues.

PURPOSE

To fabricate a tendon stem cell-derived exosomes loaded scaffold (TSC-Exos-S) and investigate its effects on cellular bioactivity in vitro and repair in a rabbit UMRCT model in vivo.

STUDY DESIGN

Controlled laboratory study.

METHODS

TSC-Exos-S was fabricated by loading TSC-Exos and type 1 collagen (COL-I) into a 3-dimensional bioprinted and polycaprolactone (PCL)-based scaffold. The proliferation, migration, and tenogenic differentiation activities of rabbit bone marrow stem cells (BMSCs) were evaluated in vitro by culturing them in saline, PCL-based scaffold (S), COL-I loaded scaffold (COL-I-S), and TSC-Exos-S. In vivo studies were conducted on a rabbit UMRCT model, where bridging was repaired with S, COL-I-S, TSC-Exos-S, and autologous fascia lata (FL). Histological and biomechanical analyses were performed at 8 and 16 weeks postoperatively.

RESULTS

TSC-Exos-S exhibited reliable mechanical strength and subcutaneous degradation, which did not occur before tissue regeneration. TSC-Exos-S significantly promoted the proliferation, migration, and tenogenic differentiation of rabbit BMSCs in vitro. In vivo studies showed that UMRCT repaired with TSC-Exos-S exhibited significant signs of tendinous tissue regeneration at the bridging site with regard to specific collagen staining. Moreover, no significant differences were observed in the histological and biomechanical properties compared with those repaired with autologous FL.

CONCLUSION

TSC-Exos-S achieved tendinous tissue regeneration in UMRCT by providing mechanical support and promoting the trend toward tenogenic differentiation.

CLINICAL RELEVANCE

The present study proposes a potential strategy for repairing UMRCT with severely retracted musculotendinous tissues and large tendinous tissue defects.

Role of Adipose-Derived Mesenchymal Stem Cells in Bone Regeneration

Bone regeneration involves multiple factors such as tissue interactions, an inflammatory response, and vessel formation. In the event of diseases, old age, lifestyle, or trauma, bone regeneration can be impaired which could result in a prolonged healing duration or requiring an external intervention for repair. Currently, bone grafts hold the golden standard for bone regeneration. However, several limitations hinder its clinical applications, e.g., donor site morbidity, an insufficient tissue volume, and uncertain post-operative outcomes. Bone tissue engineering, involving stem cells seeded onto scaffolds, has thus been a promising treatment alternative for bone regeneration. Adipose-derived mesenchymal stem cells (AD-MSCs) are known to hold therapeutic value for the treatment of various clinical conditions and have displayed feasibility and significant effectiveness due to their ease of isolation, non-invasive, abundance in quantity, and osteogenic capacity. Notably, in vitro studies showed AD-MSCs holding a high proliferation capacity, multi-differentiation potential through the release of a variety of factors, and extracellular vesicles, allowing them to repair damaged tissues. In vivo and clinical studies showed AD-MSCs favoring better vascularization and the integration of the scaffolds, while the presence of scaffolds has enhanced the osteogenesis potential of AD-MSCs, thus yielding optimal bone formation outcomes. Effective bone regeneration requires the interplay of both AD-MSCs and scaffolds (material, pore size) to improve the osteogenic and vasculogenic capacity. This review presents the advances and applications of AD-MSCs for bone regeneration and bone tissue engineering, focusing on the in vitro, in vivo, and clinical studies involving AD-MSCs for bone tissue engineering.

Recent advances in the use of extracellular vesicles from adipose-derived stem cells for regenerative medical therapeutics

Adipose-derived stem cells (ADSCs) are a subset of mesenchymal stem cells (MSCs) isolated from adipose tissue. They possess remarkable properties, including multipotency, self-renewal, and easy clinical availability. ADSCs are also capable of promoting tissue regeneration through the secretion of various cytokines, factors, and extracellular vesicles (EVs). ADSC-derived EVs (ADSC-EVs) act as intercellular signaling mediators that encapsulate a range of biomolecules. These EVs have been found to mediate the therapeutic activities of donor cells by promoting the proliferation and migration of effector cells, facilitating angiogenesis, modulating immunity, and performing other specific functions in different tissues. Compared to the donor cells themselves, ADSC-EVs offer advantages such as fewer safety concerns and more convenient transportation and storage for clinical application. As a result, these EVs have received significant attention as cell-free therapeutic agents with potential future application in regenerative medicine. In this review, we focus on recent research progress regarding regenerative medical use of ADSC-EVs across various medical conditions, including wound healing, chronic limb ischemia, angiogenesis, myocardial infarction, diabetic nephropathy, fat graft survival, bone regeneration, cartilage regeneration, tendinopathy and tendon healing, peripheral nerve regeneration, and acute lung injury, among others. We also discuss the underlying mechanisms responsible for inducing these therapeutic effects. We believe that deciphering the biological properties, therapeutic effects, and underlying mechanisms associated with ADSC-EVs will provide a foundation for developing a novel therapeutic approach in regenerative medicine.

Extracellular vesicles in nanomedicine and regenerative medicine: A review over the last decade

Small extracellular vesicles (sEVs) are known to be secreted by a vast majority of cells. These sEVs, specifically exosomes, induce specific cell-to-cell interactions and can activate signaling pathways in recipient cells through fusion or interaction. These nanovesicles possess several desirable properties, making them ideal for regenerative medicine and nanomedicine applications. These properties include exceptional stability, biocompatibility, wide biodistribution, and minimal immunogenicity. However, the practical utilization of sEVs, particularly in clinical settings and at a large scale, is hindered by the expensive procedures required for their isolation, limited circulation lifetime, and suboptimal targeting capacity. Despite these challenges, sEVs have demonstrated a remarkable ability to accommodate various cargoes and have found extensive applications in the biomedical sciences. To overcome the limitations of sEVs and broaden their potential applications, researchers should strive to deepen their understanding of current isolation, loading, and characterization techniques. Additionally, acquiring fundamental knowledge about sEVs origins and employing state-of-the-art methodologies in nanomedicine and regenerative medicine can expand the sEVs research scope. This review provides a comprehensive overview of state-of-the-art exosome-based strategies in diverse nanomedicine domains, encompassing cancer therapy, immunotherapy, and biomarker applications. Furthermore, we emphasize the immense potential of exosomes in regenerative medicine.

Equine Musculoskeletal Pathologies: Clinical Approaches and Therapeutical Perspectives-A Review

Musculoskeletal injuries such as equine osteoarthritis, osteoarticular defects, tendonitis/desmitis, and muscular disorders are prevalent among sport horses, with a fair prognosis for returning to exercise or previous performance levels. The field of equine medicine has witnessed rapid and fruitful development, resulting in a diverse range of therapeutic options for musculoskeletal problems. Staying abreast of these advancements can be challenging, prompting the need for a comprehensive review of commonly used and recent treatments. The aim is to compile current therapeutic options for managing these injuries, spanning from simple to complex physiotherapy techniques, conservative treatments including steroidal and non-steroidal anti-inflammatory drugs, hyaluronic acid, polysulfated glycosaminoglycans, pentosan polysulfate, and polyacrylamides, to promising regenerative therapies such as hemoderivatives and stem cell-based therapies. Each therapeutic modality is scrutinized for its benefits, limitations, and potential synergistic actions to facilitate their most effective application for the intended healing/regeneration of the injured tissue/organ and subsequent patient recovery. While stem cell-based therapies have emerged as particularly promising for equine musculoskeletal injuries, a multidisciplinary approach is underscored throughout the discussion, emphasizing the importance of considering various therapeutic modalities in tandem.

Aging-Related Rotator Cuff Tears: Molecular Mechanisms and Implications for Clinical Management

Shoulder pain and disabilities are prevalent issues among the elderly population, with rotator cuff tear (RCT) being one of the leading causes. Although surgical treatment has shown some success, high postoperative retear rates remain a great challenge, particularly in elderly patients. Aging-related degeneration of muscle, tendon, tendon-to-bone enthesis, and bone plays a critical role in the development and prognosis of RCT. Studies have demonstrated that aging worsens muscle atrophy and fatty infiltration, alters tendon structure and biomechanical properties, exacerbates enthesis degeneration, and reduces bone density. Although recent researches have contributed to understanding the pathophysiological mechanisms of aging-related RCT, a comprehensive systematic review of this topic is still lacking. Therefore, this article aims to present a review of the pathophysiological changes and their clinical significance, as well as the molecular mechanisms underlying aging-related RCT, with the goal of shedding light on new therapeutic approaches to reduce the occurrence of aging-related RCT and improve postoperative prognosis in elderly patients.

Clinical applications of stem cell-derived exosomes

Although stem cell-based therapy has demonstrated considerable potential to manage certain diseases more successfully than conventional surgery, it nevertheless comes with inescapable drawbacks that might limit its clinical translation. Compared to stem cells, stem cell-derived exosomes possess numerous advantages, such as non-immunogenicity, non-infusion toxicity, easy access, effortless preservation, and freedom from tumorigenic potential and ethical issues. Exosomes can inherit similar therapeutic effects from their parental cells such as embryonic stem cells and adult stem cells through vertical delivery of their pluripotency or multipotency. After a thorough search and meticulous dissection of relevant literature from the last five years, we present this comprehensive, up-to-date, specialty-specific and disease-oriented review to highlight the surgical application and potential of stem cell-derived exosomes. Exosomes derived from stem cells (e.g., embryonic, induced pluripotent, hematopoietic, mesenchymal, neural, and endothelial stem cells) are capable of treating numerous diseases encountered in orthopedic surgery, neurosurgery, plastic surgery, general surgery, cardiothoracic surgery, urology, head and neck surgery, ophthalmology, and obstetrics and gynecology. The diverse therapeutic effects of stem cells-derived exosomes are a hierarchical translation through tissue-specific responses, and cell-specific molecular signaling pathways. In this review, we highlight stem cell-derived exosomes as a viable and potent alternative to stem cell-based therapy in managing various surgical conditions. We recommend that future research combines wisdoms from surgeons, nanomedicine practitioners, and stem cell researchers in this relevant and intriguing research area.

Engineered stem cell-based strategy: A new paradigm of next-generation stem cell product in regenerative medicine

Stem cells have garnered significant attention in regenerative medicine owing to their abilities of multi-directional differentiation and self-renewal. Despite these encouraging results, the market for stem cell products yields limited, which is largely due to the challenges faced to the safety and viability of stem cells in vivo. Besides, the fate of cells re-infusion into the body unknown is also a major obstacle to stem cell therapy. Actually, both the functional protection and the fate tracking of stem cells are essential in tissue homeostasis, repair, and regeneration. Recent studies have utilized cell engineering techniques to modify stem cells for enhancing their treatment efficiency or imparting them with novel biological capabilities, in which advances demonstrate the immense potential of engineered cell therapy. In this review, we proposed that the "engineered stem cells" are expected to represent the next generation of stem cell therapies and reviewed recent progress in this area. We also discussed potential applications of engineered stem cells and highlighted the most common challenges that must be addressed. Overall, this review has important guiding significance for the future design of new paradigms of stem cell products to improve their therapeutic efficacy.

Recent advances of exosomes in soft tissue injuries in sports medicine: A critical review on biological and biomaterial applications

Sports medicine is generally associated with soft tissue injuries including muscle injuries, meniscus and ligament injuries, tendon ruptures, tendinopathy, rotator cuff tears, and tendon-bone healing during injuries. Tendon and ligament injuries are the most common sport injuries accounting for 30-40% of all injuries. Therapies for tendon injuries can be divided into surgical and non-surgical methods. Surgical methods mainly depend on the operative procedures, the surgeons and postoperative interventions. In non-surgical methods, cell therapy with stem cells and cell-free therapy with secretome of stem cell origin are current directions. Exosomes are the main paracrine factors of mesenchymal stem cells (MSCs) containing biological components such as proteins, nucleic acids and lipids. Compared with MSCs, MSC-exosomes (MSC-exos) possess the capacity to escape phagocytosis and achieve long-term circulation. In addition, the functions of exosomes from various cell sources in soft tissue injuries in sports medicine have been gradually revealed in recent years. Along with the biological and biomaterial advances in exosomes, exosomes can be designed as drug carriers with biomaterials and exosome research is providing promising contributions in cell biology. Exosomes with biomaterial have the potential of becoming one of the novel therapeutic modalities in regenerative researches. This review summarizes the derives of exosomes in soft tissue regeneration and focuses on the biological and biomaterial mechanism and advances in exosomal therapy in soft tissue injuries.

Electroconductivity, a regenerative engineering approach to reverse rotator cuff muscle degeneration

Muscle degeneration is one the main factors that lead to the high rate of retear after a successful repair of rotator cuff (RC) tears. The current surgical practices have failed to treat patients with chronic massive rotator cuff tears (RCTs). Therefore, regenerative engineering approaches are being studied to address the challenges. Recent studies showed the promising outcomes of electroactive materials (EAMs) on the regeneration of electrically excitable tissues such as skeletal muscle. Here, we review the most important biological mechanism of RC muscle degeneration. Further, the review covers the recent studies on EAMs for muscle regeneration including RC muscle. Finally, we will discuss the future direction toward the application of EAMs for the augmentation of RCTs.

Polarized macrophages regulate fibro/adipogenic progenitor (FAP) adipogenesis through exosomes

BACKGROUND

Macrophage polarization has been observed in the process of muscle injuries including rotator cuff (RC) muscle atrophy and fatty infiltration after large tendon tears. In our previous study, we showed that fibrogenesis and white adipogenesis of muscle residential fibro/adipogenic progenitors (FAPs) cause fibrosis and fatty infiltration and that brown/beige adipogenesis of FAPs promotes rotator cuff muscle regeneration. However, how polarized macrophages and their exosomes regulate FAP differentiation remains unknown.

METHODS

We cultured FAPs with M0, M1, and M2 macrophages or 2 × 109 exosomes derived from M0, M1 and M2 with and without GW4869, an exosome inhibitor. In vivo, M0, M1, and M2 macrophages were transplanted or purified macrophage exosomes (M0, M1, M2) were injected into supraspinatus muscle (SS) after massive tendon tears in mice (n = 6). SS were harvested at six weeks after surgery to evaluate the level of muscle atrophy and fatty infiltration.

RESULTS

Our results showed that M2 rather than M0 or M1 macrophages stimulates brown/beige fat differentiation of FAPs. However, the effect of GW4869, the exosome inhibitor, diminished this effect. M2 exosomes also promoted FAP Beige differentiation in vitro. The transplantation of M2 macrophages reduced supraspinatus muscle atrophy and fatty infiltration. In vivo injections of M2 exosomes significantly reduced muscle atrophy and fatty infiltration in supraspinatus muscle.

CONCLUSION

Results from our study demonstrated that polarized macrophages directly regulated FAP differentiation through their exosomes and M2 macrophage-derived exosomes may serve as a novel treatment option for RC muscle atrophy and fatty infiltration.

Progress in studying the impact of hyperlipidemia and statins on rotator cuff injury and repair

This review delves into the intersection of two prevalent conditions, hyperlipidemia and rotator cuff injuries, both of which bear substantial healthcare burdens. Our investigation begins with an exploration of rotator cuff injuries, common musculoskeletal disorders that severely impair shoulder functionality and quality of life. These injuries are notably pervasive among sports enthusiasts and the older adult, with an incidence rate estimated at 5-10% in the general population. Despite their widespread occurrence and the diverse, multifactorial etiological factors, effective treatment strategies remain elusive. We then examine hyperlipidemia, a metabolic disorder affecting approximately 40% of the global adult population. Characterized by elevated levels of cholesterol and triglycerides, hyperlipidemia can precipitate severe cardiovascular complications and presents a significant socioeconomic burden. Although current management strategies encompass lifestyle modifications and pharmacological interventions, the condition remains a formidable health challenge. Central to this review is the exploration of a potential association between hyperlipidemia and rotator cuff injuries. We aim to synthesize the current understanding of hyperlipidemia's role in the pathophysiology of rotator cuff injuries, thereby offering fresh insights into their common etiological underpinnings, potential therapeutic targets, and drugs, such as Statins. The influence of other lipid-lowering therapeutics on tendon health is also considered, and further research into the molecular pathways and potential therapeutic benefits of these drugs is required. This pursuit aligns with broader efforts to enhance patient outcomes, minimize healthcare burdens, and contribute to the global understanding of these prevalent conditions.

Mechanisms and therapeutic prospects of mesenchymal stem cells-derived exosomes for tendinopathy

Tendinopathy is a debilitating and crippling syndrome resulting from the degeneration of tendon tissue, leading to loss of mechanical properties and function, and eventual tendon rupture. Unfortunately, there is currently no treatment for tendinopathy that can prevent or delay its progression. Exosomes are small extracellular vesicles that transport bioactive substances produced by cells, such as proteins, lipids, mRNAs, non-coding RNAs, and DNA. They can generate by mesenchymal stem cells (MSCs) throughout the body and play a role in intercellular communication and regulation of homeostasis. Recent research suggests that MSCs-derived exosomes (MSCs-exos) may serve as useful therapeutic candidates for promoting tendon healing. This review focuses on the function and mechanisms of MSCs-exos in tendinopathy treatment and discusses their potential application for treating this condition.

Lipoaspirate fluid derived factors and extracellular vesicles accelerate wound healing in a rat burn model

Background: The regenerative capabilities of derivatives derived from the fat layer of lipoaspirate have been demonstrated. However, the large volume of lipoaspirate fluid has not attracted extensive attention in clinical applications. In this study, we aimed to isolate the factors and extracellular vesicles from human lipoaspirate fluid and evaluate their potential therapeutic efficacy. Methods: Lipoaspirate fluid derived factors and extracellular vesicles (LF-FVs) were prepared from human lipoaspirate and characterized by nanoparticle tracking analysis, size-exclusion chromatography and adipokine antibody arrays. The therapeutic potential of LF-FVs was evaluated on fibroblasts in vitro and rat burn model in vivo. Wound healing process was recorded on days 2, 4, 8, 10, 12 and 16 post-treatment. The scar formation was analyzed by histology, immunofluorescent staining and scar-related gene expression at day 35 post-treatment. Results: The results of nanoparticle tracking analysis and size-exclusion chromatography indicated that LF-FVs were enriched with proteins and extracellular vesicles. Specific adipokines (adiponectin and IGF-1) were detected in LF-FVs. In vitro, LF-FVs augmented the proliferation and migration of fibroblasts in a dose-dependent manner. In vivo, the results showed that LF-FVs significantly accelerated burn wound healing. Moreover, LF-FVs improved the quality of wound healing, including regenerating cutaneous appendages (hair follicles and sebaceous glands) and decreasing scar formation in the healed skin. Conclusion: LF-FVs were successfully prepared from lipoaspirate liquid, which were cell-free and enriched with extracellular vesicles. Additionally, they were found to improve wound healing in a rat burn model, suggesting that LF-FVs could be potentially used for wound regeneration in clinical settings.

Therapeutic Potential of Exosomes in Tendon and Tendon-Bone Healing: A Systematic Review of Preclinical Studies

Exosomes have been proven to play a positive role in tendon and tendon-bone healing. Here, we systematically review the literature to evaluate the efficacy of exosomes in tendon and tendon-bone healing. Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, a systematic and comprehensive review of the literature was performed on 21 January 2023. The electronic databases searched included Medline (through PubMed), Web of Science, Embase, Scopus, Cochrane Library and Ovid. In the end, a total of 1794 articles were systematically reviewed. Furthermore, a "snowball" search was also carried out. Finally, forty-six studies were included for analysis, with the total sample size being 1481 rats, 416 mice, 330 rabbits, 48 dogs, and 12 sheep. In these studies, exosomes promoted tendon and tendon-bone healing and displayed improved histological, biomechanical and morphological outcomes. Some studies also suggested the mechanism of exosomes in promoting tendon and tendon-bone healing, mainly through the following aspects: (1) suppressing inflammatory response and regulating macrophage polarization; (2) regulating gene expression, reshaping cell microenvironment and reconstructing extracellular matrix; (3) promoting angiogenesis. The risk of bias in the included studies was low on the whole. This systematic review provides evidence of the positive effect of exosomes on tendon and tendon-bone healing in preclinical studies. The unclear-to-low risk of bias highlights the significance of standardization of outcome reporting. It should be noted that the most suitable source, isolation methods, concentration and administration frequency of exosomes are still unknown. Additionally, few studies have used large animals as subjects. Further studies may be required on comparing the safety and efficacy of different treatment parameters in large animal models, which would be conducive to the design of clinical trials.

Mitochondrial transfer from bone mesenchymal stem cells protects against tendinopathy both in vitro and in vivo

BACKGROUND

Although mesenchymal stem cells (MSCs) have been effective in tendinopathy, the mechanisms by which MSCs promote tendon healing have not been fully elucidated. In this study, we tested the hypothesis that MSCs transfer mitochondria to injured tenocytes in vitro and in vivo to protect against Achilles tendinopathy (AT).

METHODS

Bone marrow MSCs and H₂O₂-injured tenocytes were co-cultured, and mitochondrial transfer was visualized by MitoTracker dye staining. Mitochondrial function, including mitochondrial membrane potential, oxygen consumption rate, and adenosine triphosphate content, was quantified in sorted tenocytes. Tenocyte proliferation, apoptosis, oxidative stress, and inflammation were analyzed. Furthermore, a collagenase type I-induced rat AT model was used to detect mitochondrial transfer in tissues and evaluate Achilles tendon healing.

RESULTS

MSCs successfully donated healthy mitochondria to in vitro and in vivo damaged tenocytes. Interestingly, mitochondrial transfer was almost completely blocked by co-treatment with cytochalasin B. Transfer of MSC-derived mitochondria decreased apoptosis, promoted proliferation, and restored mitochondrial function in H₂O₂-induced tenocytes. A decrease in reactive oxygen species and pro-inflammatory cytokine levels (interleukin-6 and -1β) was observed. In vivo, mitochondrial transfer from MSCs improved the expression of tendon-specific markers (scleraxis, tenascin C, and tenomodulin) and decreased the infiltration of inflammatory cells into the tendon. In addition, the fibers of the tendon tissue were neatly arranged and the structure of the tendon was remodeled. Inhibition of mitochondrial transfer by cytochalasin B abrogated the therapeutic efficacy of MSCs in tenocytes and tendon tissues.

CONCLUSIONS

MSCs rescued distressed tenocytes from apoptosis by transferring mitochondria. This provides evidence that mitochondrial transfer is one mechanism by which MSCs exert their therapeutic effects on damaged tenocytes.

Mesenchymal Stem Cell-Derived Extracellular Vesicles: Hype or Hope for Skeletal Muscle Anti-Frailty

Steadily rising population ageing is a global demographic trend due to the advancement of new treatments and technologies in the medical field. This trend also indicates an increasing prevalence of age-associated diseases, such as loss of muscle mass (sarcopenia), which tends to afflict the older population. The deterioration in muscle function can cause severe disability and seriously affects a patient's quality of life. Currently, there is no treatment to prevent and reverse age-related skeletal muscle ageing frailty. Existing interventions mainly slow down and control the signs and symptoms. Mesenchymal stem cell-derived extracellular vesicle (MSC-EV) therapy is a promising approach to attenuate age-related skeletal muscle ageing frailty. However, more studies, especially large-scale randomised clinical trials need to be done in order to determine the adequacy of MSC-EV therapy in treating age-related skeletal muscle ageing frailty. This review compiles the present knowledge of the causes and changes regarding skeletal muscle ageing frailty and the potential of MSC-EV transplantation as a regenerative therapy for age-related skeletal muscle ageing frailty and its clinical trials.

Frontier Review of the Molecular Mechanisms and Current Approaches of Stem Cell-Derived Exosomes

Exosomes are effective therapeutic vehicles that may transport their substances across cells. They are shown to possess the capacity to affect cell proliferation, migration, anti-apoptosis, anti-scarring, and angiogenesis, via the action of transporting molecular components. Possessing immense potential in regenerative medicine, exosomes, especially stem cell-derived exosomes, have the advantages of low immunogenicity, minimal invasiveness, and broad clinical applicability. Exosome biodistribution and pharmacokinetics may be altered, in response to recent advancements in technology, for the purpose of treating particular illnesses. Yet, prior to clinical application, it is crucial to ascertain the ideal dose and any potential negative consequences of an exosome. This review focuses on the therapeutic potential of stem cell-derived exosomes and further illustrates the molecular mechanisms that underpin their potential in musculoskeletal regeneration, wound healing, female infertility, cardiac recovery, immunomodulation, neurological disease, and metabolic regulation. In addition, we provide a summary of the currently effective techniques for isolating exosomes, and describe the innovations in biomaterials that improve the efficacy of exosome-based treatments. Overall, this paper provides an updated overview of the biological factors found in stem cell-derived exosomes, as well as potential targets for future cell-free therapeutic applications.

Arthroscopic Superior Capsule Reconstruction with Combined Fascia Lata Autograft and Synthetic Scaffold Patch Graft for the Treatment of Irreparable Rotator Cuff Tears Yields Favorable Clinical and Radiographic Outcomes at Minimum Two-Year Follow-Up

PURPOSE

To report the results of the arthroscopic superior capsule reconstruction (ASCR) technique with a combined fascia lata autograft and synthetic scaffold patch graft for irreparable massive rotator cuff tears (RCTs).

METHODS

The period for this retrospective study was between December 2016 and December 2020. The criteria for inclusion were patients treated arthroscopically for an incompletely reparable massive RCT (dimension > 5 cm and two tendons fully torn, intact or reparable subscapularis tendons and teres minor tendon with or without irreparable infraspinatus, a radiological Hamada classification between grade 0 and 4, and a minimum 24-month postoperative follow-up).. Clinical outcomes were evaluated pre-operatively and at a final follow-up by a visual analog scale (VAS) for pain and range of motion along with the American Shoulder and Elbow Surgeons score (ASES), the University of California Los Angeles score (UCLA), and the Constant-Murley score (CMS). Radiological outcomes were assessed according to the rotator cuff arthropathy (RCA) and the acromiohumeral distance (AHD) stages. Graft integrity and muscle fatty infiltration were evaluated by magnetic resonance imaging (MRI).

RESULTS

A total of 43 patients were enrolled in the study with a mean follow-up duration of 45.6 months (range 24 to 64). All clinical scores also improved at the two-year follow-up (mean VAS 0.7 [SD 0.7] vs. 5.4 [SD 1.1], P < 0.001; mean ASES 92.6 [SD 8.0] vs. 34.8 [SD 13.4], P < 0.001; mean UCLA 31.5 [SD 3.9] vs. 11.0 [SD 3.2], P < 0.001; and mean CMS 86.6 [SD 7.2] vs. 40.0 [SD 11.6], P < 0.001), and 39 of 43 fascia lata grafts were fully intact on MRI (91%).

CONCLUSIONS

ASCR with a combined fascia lata autograft and synthetic scaffold patch graft resulted in good functional outcomes, with a high rate of graft healing at the two-year follow-up. All patients achieved clinically relevant improvement (met minimal clinically important differences (MCID)) on ASES, UCLA, and VAS with improved abduction strength restoration.

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.

Evidence for Utilization of Injectable Biologic Augmentation in Primary Rotator Cuff Repair: A Systematic Review of Data From 2010 to 2022

Background

Biologic healing after rotator cuff repair remains a significant challenge. Injectable biologic augmentation may improve tissue quality at the suture-tendon interface.

Purpose

To investigate the effect of injectable biologic supplementation in rotator cuff repair and to assess the quality and adherence to evolving reporting standards.

Study Design

Systematic review; Level of evidence, 3.

Methods

A systematic review was conducted following PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Included were 40 studies: 29 preclinical (in vivo animal models) and 11 clinical. Each clinical study was assessed for quality, risk of bias, and adherence to relevant MIBO (Minimum Information for Studies Evaluating Biologics in Orthopaedics) guidelines. The outcomes of interest were reported load to failure, load to gap, gap size, and stiffness in the preclinical studies, and healing rate and any patient-reported outcome measures in the clinical studies.

Results

Injectables reported included growth factors (eg, transforming growth factor-beta 3, erythropoietin), bone marrow-derived mesenchymal stem cells and adipose-derived mesenchymal stem cells (ADSCs), and other agents such as platelet-rich plasma (PRP) and hyaluronic acid. The most common findings for preclinical injectables were increased load to failure (16/29 studies; 55.2%) and improved collagen histological quality (11/29 studies; 37.9%). All 11 clinical studies (10 PRP, 1 ADSC) indicated no adverse events, with similar or improved patient-reported outcomes compared with repairs in the control groups. In 1 study utilizing an innovative delivery technique, a concentrated PRP globule with fibrin matrix was shuttled over a suture to maintain concentrated PRP at the repair site and demonstrated a significant decrease in retears (P = .03) at a 31-month follow-up. A matched-cohort study investigating augmentation with ADSCs demonstrated a significantly lower retear rate in the ADSC-augmented group than the control group at a 28-month follow-up (P < .001). On average, the clinical studies adhered to 66% of relevant MIBO reporting guidelines and had a low risk of bias.

Conclusion

Approximately 83% of preclinical studies found a positive biomechanical or histological effect, with no studies showing an overall negative effect. Clinically, utilization of innovative delivery techniques may reduce the risk of arthroscopic washout of PRP and improve retear rates. ADSCs were shown to reduce retear rates at a 28-month follow-up.

Exosome-mediated regulatory mechanisms in skeletal muscle: a narrative review

Skeletal muscle plays a paramount role in physical activity, metabolism, and energy balance, while its homeostasis is being challenged by multiple unfavorable factors such as injury, aging, or obesity. Exosomes, a subset of extracellular vesicles, are now recognized as essential mediators of intercellular communication, holding great clinical potential in the treatment of skeletal muscle diseases. Herein, we outline the recent research progress in exosomal isolation, characterization, and mechanism of action, and emphatically discuss current advances in exosomes derived from multiple organs and tissues, and engineered exosomes regarding the regulation of physiological and pathological development of skeletal muscle. These remarkable advances expand our understanding of myogenesis and muscle diseases. Meanwhile, the engineered exosome, as an endogenous nanocarrier combined with advanced design methodologies of biomolecules, will help to open up innovative therapeutic perspectives for the treatment of muscle diseases.

The Composition of Adipose-Derived Regenerative Cells Isolated from Lipoaspirate Using a Point of Care System Does Not Depend on the Subject's Individual Age, Sex, Body Mass Index and Ethnicity

Uncultured, unmodified, autologous, adipose-derived regenerative cells (UA-ADRCs) are a safe and effective treatment option for various musculoskeletal pathologies. However, it is unknown whether the composition of the final cell suspension systematically varies with the subject's individual age, sex, body mass index and ethnicity. UA-ADRCs were isolated from lipoaspirate from n = 232 subjects undergoing elective lipoplasty using the Transpose RT system (InGeneron, Inc.; Houston, TX, USA). The UA-ADRCs were assessed for the number of nucleated cells, cell viability and the number of viable nucleated cells per gram of adipose tissue harvested. Cells from n = 37 subjects were further characterized using four-channel flow cytometry. The present study shows, for the first time, that key characteristics of UA-ADRCs can be independent of the subject's age, sex, BMI and ethnicity. This result has important implications for the general applicability of UA-ADRCs in regeneration of musculoskeletal tissue. Future studies must determine whether the independence of key characteristics of UA-ADRCs of the subject's individual age, sex, BMI and ethnicity only applies to the system used in the present study, or also to others of the more than 25 different experimental methods and commercially available systems used to isolate UA-ADRCs from lipoaspirate that have been described in the literature.

Therapeutic Potential of Extracellular Vesicles in Aging and Age-Related Diseases

Aging is associated with an alteration of intercellular communication. These changes in the extracellular environment contribute to the aging phenotype and have been linked to different aging-related diseases. Extracellular vesicles (EVs) are factors that mediate the transmission of signaling molecules between cells. In the aging field, these EVs have been shown to regulate important aging processes, such as oxidative stress or senescence, both in vivo and in vitro. EVs from healthy cells, particularly those coming from stem cells (SCs), have been described as potential effectors of the regenerative potential of SCs. Many studies with different animal models have shown promising results in the field of regenerative medicine. EVs are now viewed as a potential cell-free therapy for tissue damage and several diseases. Here we propose EVs as regulators of the aging process, with an important role in tissue regeneration and a raising therapy for age-related diseases.

Signaling pathways of adipose stem cell-derived exosomes promoting muscle regeneration

ABSTRACT

Severe muscle injury is still a challenging clinical problem. Exosomes derived from adipose stem cells (ASC-exos) may be a potential therapeutic tool, but their mechanism is not completely clear. This review aims to elaborate the possible mechanism of ASC-exos in muscle regeneration from the perspective of signal pathways and provide guidance for further study. Literature cited in this review was acquired through PubMed using keywords or medical subject headings, including adipose stem cells, exosomes, muscle regeneration, myogenic differentiation, myogenesis, wingless/integrated (Wnt), mitogen-activated protein kinases, phosphatidylinositol-4,5-bisphosphate 3-kinase/protein kinase B (PI3K/Akt), Janus kinase/signal transducers and activators of transcription, and their combinations. We obtained the related signal pathways from proteomics analysis of ASC-exos in the literature, and identified that ASC-exos make different contributions to multiple stages of skeletal muscle regeneration by those signal pathways.

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.

In Situ-Forming Fibrin Gel Encapsulation of MSC-Exosomes for Partial-Thickness Rotator Cuff Tears in a Rabbit Model: Effectiveness Shown in Preventing Tear Progression and Promoting Healing

BACKGROUND

Current nonoperative treatments for partial-thickness rotator cuff tears (PTRCTs) have limited effectiveness in preventing tear progression or promoting tendon healing. This study aimed to establish a rabbit model using in situ-forming fibrin gel containing adipose stem cell-derived exosomes (ASC-Exos/fibrin) to treat PTRCTs.

METHODS

Fifty-six rabbits (112 shoulders) were included in this study and assigned to 4 groups: the control group (32 shoulders; PTRCTs without treatment), the fibrin group (32 shoulders; PTRCTs treated with fibrin gel), the ASC-Exo/fibrin group (32 shoulders; PTRCTs treated with ASC-Exos/fibrin), and the sham group (16 shoulders; sham surgery). Bilateral, 50%-thickness, bursal-side PTRCTs of 1 mm (depth) × 3 mm (width) × 5 mm (length) on the supraspinatus tendon were established by a number-11 scalpel blade, with accuracy of the measurement ensured by a digital vernier caliper. At 6 and 12 weeks postoperatively, gross observation, measurement of the thickness of residual supraspinatus tendons, and histological and biomechanical analyses were performed to analyze tendon repair.

RESULTS

At 12 weeks postoperatively, the tendon thickness in the ASC-Exos/fibrin group (mean and standard deviation, 1.63 ± 0.19 mm) was significantly greater than in the control group (0.85 ± 0.09 mm) (p < 0.0001) and fibrin group (1.16 ± 0.17 mm) (p < 0.0001). The histological score in the ASC-Exos/fibrin group (6.25 ± 0.53) was significantly better than in the control group (11.38 ± 0.72) (p < 0.0001) and fibrin group (9.00 ± 0.54) (p < 0.0001). Overall, immunohistochemical staining of types-I and III collagen and biomechanical testing also showed ASC-Exos/fibrin to be more effective in repairing PTRCTs than fibrin alone and no treatment.

CONCLUSIONS

Local administration of in situ-forming ASC-Exos/fibrin effectively facilitated the healing of bursal-side PTRCTs in rabbits. This approach may be a candidate for the nonoperative management of PTRCTs.

CLINICAL RELEVANCE

Ultrasound-guided injection of ASC-Exos/fibrin may be a novel nonoperative strategy to treat PTRCTs.

Non-Viral Delivery of Gene Therapy to the Tendon

The tendon, as a compact connective tissue, is difficult to treat after an acute laceration or chronic degeneration. Gene-based therapy is a highly efficient strategy for diverse diseases which has been increasingly applied in tendons in recent years. As technology improves by leaps and bounds, a wide variety of non-viral vectors have been manufactured that attempt to have high biosecurity and transfection efficiency, considered to be a promising treatment modality. In this review, we examine the unwanted biological barriers, the categories of applicable genes, and the introduction and comparison of non-viral vectors. We focus on lipid-based nanoparticles and polymer-based nanoparticles, differentiating between them based on their combination with diverse chemical modifications and scaffolds.

Injection of Leukocyte-Poor Platelet-Rich Plasma for Moderate-to-Large Rotator Cuff Tears Does Not Improve Clinical Outcomes but Reduces Retear Rates and Fatty Infiltration: A Prospective, Single-Blinded Randomized Study

OBJECTIVES

To determine whether leukocyte-poor platelet-rich plasma (Lp-PRP) reduced retear rates, reduced fatty infiltration, and improved functional outcomes in patients with degenerative moderate-to-large rotator cuff tears.

METHODS

This was a randomized controlled study at a single center. A consecutive series of 104 patients with moderate-to-large rotator cuff tears was enrolled and randomly allocated to a control group (double-row suture-bridge arthroscopic rotator cuff repair alone, n = 52) and a study group (double-row suture-bridge repair followed by 3 Lp-PRP injections at the tendon repair site during surgery, at days 7 and 14 after surgery, n = 52). All patients were followed up for 27.2 months (range 24-36 months), with University of California at Los Angeles (UCLA) shoulder rating scale, the Constant score, and a visual analog scale (VAS) evaluated respectively. The integrity and fatty infiltration of repaired tissue were assessed by magnetic resonance imaging using the Sugaya classification and Goutallier grade classification at 24 months after surgery. Statistical analysis was performed based on the t test, χ² test, and the Kendall tau-b correlation coefficient.

RESULTS

Four patients refused follow-up, and 11 patients had incomplete data. Eventually, a total of 89 patients were available for 24 months follow-up. The mean UCLA score increased from 14.80 ± 2.53 to 29.37 ± 2.06 in control group and from 13.74 ± 3.30 to 30.14 ± 2.32 in study group (P = .103). The mean Constant score increased from 46.56 ± 5.90 to 86.83 ± 4.94 in control group and from 44.37 ± 7.92 to 88.80 ± 4.92 in study group (P = .063). The VAS score decreased from 3.22 ± 1.24 to 0.97 ± 1.12 in control group and in 3.49 ± 1.52 to 1.16 ± 0.99 in study group (P = .41). All differences in UCLA score, Constant score, and VAS between pre- and postoperation achieved minimal clinically important differences proposed for arthroscopic rotator cuff repair. Of the 89 patients, 76 had magnetic resonance imaging performed at 24 months after surgery. The retear rate was 17.6% in study group, which was lower than that in control group (38.1%, P = .049). In addition, the Goutallier grade was found to be significant difference between groups postoperatively (Kendall tau-b -0.24, P = .03) but no significant difference preoperatively (Kendall tau-b -0.18, P = .11). There were no complications in the patients.

CONCLUSIONS

Our procedures involving repeated injections of Lp-PRP during surgery and at days 7 and 14, as described in this study, have positive effects on reducing retear rate and promoting Goutallier grade in patients following arthroscopic rotator cuff repair and could also provide substantial clinical outcomes that reach the minimal clinically important difference for surgical treatment. However, given the numbers available for analysis, it did not promote better clinical results when compared with the control group.

LEVEL OF EVIDENCE

II, randomized controlled study.

Loading Mesenchymal Stem Cell-Derived Exosomes Into a Traditionally Designed Rotator Cuff Patch: A Potential Strategy to Enhance the Repair of Chronic Rotator Cuff Tear Associated With Degenerative Changes

BACKGROUND

Retraction and degenerative changes of chronic rotator cuff tears limit the healing capacity after routine surgical repair.

PURPOSE

To fabricate a mesenchymal stem cell-derived exosome (MSC-Exos) loaded patch and evaluate the effect of this patch on the activity of rabbit tenocytes in vitro and on the repair of chronic rotator cuff tears associated with degenerative changes in vivo.

STUDY DESIGN

Controlled laboratory study.

METHODS

The MSC-Exos loaded patch was fabricated using a dynamic wet-spinning system. In the in vitro studies, the proliferation and migration activities of tenocytes were evaluated by culturing tenocytes with saline, a fiber-aligned patch, or an MSC-Exos loaded patch. In the in vivo studies, a rabbit model of chronic rotator cuff tear was established and directly repaired, repaired with fiber-aligned patch augmentation (RFPA group), and repaired with MSC-Exos loaded patch augmentation (REPA group). Histological and biomechanical analyses were performed at 4, 8, and 12 weeks after surgery.

RESULTS

An MSC-Exos loaded patch with inner aligned fibers, a loose microstructure, and reliable initial strength was fabricated using a dynamic wet-spinning system. The MSC-Exos loaded patch significantly promoted tenocyte proliferation and migration activities in vitro. In vivo, the REPA group exhibited significantly higher tendon maturing scores at 8 and 12 weeks after surgery compared with both the control and the RFPA groups. Fatty infiltration was significantly reduced in the REPA group at 4, 8, and 12 weeks compared with both the control and the RFPA groups. Biomechanical properties, including load to failure and stress, were also significantly improved at 12 weeks in the REPA group compared with both the control and the RFPA groups.

CONCLUSION

Results in the present study suggested that an MSC-Exos loaded patch was able to enhance the repair of a chronic rotator cuff tear by providing mechanical support and minimizing degeneration.

CLINICAL RELEVANCE

This work supported the idea that loading bioactive MSC-Exos into a traditionally designed rotator cuff patch might exert a better effect on the repair of chronic rotator cuff tears than augmented patch repair alone.

Extracellular Vesicles Delivered by Injectable Collagen Promote Bone-Tendon Interface Healing and Prevent Fatty Degeneration of Rotator Cuff Muscle

PURPOSE

This study aimed (1) to confirm the maintenance of the extracellular vesicles (EVs) delivered via injectable collagen at the application site, and (2) to evaluate the effect of EVs derived from the human umbilical cord-derived mesenchymal stem cells and loaded in an injectable collagen gel after rotator cuff repair (RCR).

METHODS

Rabbits (n = 20) were assigned to normal (N), repair-only (R), and those administered with injectable collagen after repair (RC), and EV-laden injectable collagen after repair (RCE) groups. The EVs isolated by ultra-centrifugation from the human umbilical cord-derived mesenchymal stem cells spent medium were mixed with collagen and administered accordingly. After 12 weeks, the rabbits were sacrificed to evaluate the healing of the bone-to-tendon junction and the fatty degeneration of muscle. Histomorphometric scoring for bone-tendon interface, fatty infiltration (%), and biomechanical tests were performed. Separately, groups of 3 rabbits were assigned to 3 different time points to evaluate maintenance of green fluorescence-labeled EVs with injectable collagen via tracking on the bursal side of the rotator cuff (3 groups: 3 days, 2, and 4 weeks).

RESULTS

The EVs delivered by injectable collagen remained until 4 weeks at the bursal side of the cuff tissue. The RCE group showed a significantly greater histomorphometric total score (P < .001, and P = .013, respectively) and significantly lower fatty degeneration than the RC and R groups (P = .001, and P = .013, respectively). The biomechanical tests revealed significant growing trends in load-to-failure and stiffness (P = .002, and P = .013, respectively), in the R, RC, RCE, and N groups.

CONCLUSIONS

EVs mounted in injectable collagen remained at the repair site for at least 4 weeks after application. Furthermore, they effectively promote bone-to-tendon healing via collagen maturation in bone-tendon interface and preventing fatty degeneration of rotator muscle after RCR as compared with collagen-only or repair-only groups.

CLINICAL RELEVANCE

The combination of collagen with EVs significantly promotes rotator cuff healing demonstrating potential clinical application during partial rotator cuff tear or after RCR.

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.

Anti-inflammatory and Tendon-Protective Effects of Adipose Stem Cell-Derived Exosomes with Concomitant Use of Glucocorticoids

Glucocorticoid (GC) injections are commonly used in clinical practice to relieve pain and improve function in patients with multiple shoulder disabilities but cause detrimental effects on rotator cuff tendons. Adipose stem cell-derived exosomes (ASC-Exos) reportedly recover impaired tendon matrix metabolism by maintaining tissue homeostasis. However, it is unclear whether additional treatment with ASC-Exos overrides the detrimental effects of GCs without interfering with their anti-inflammatory effects. Thus, we aimed to investigate the anti-inflammatory effect of ASC-Exos with GCs and protective effect of ASC-Exos against GC-induced detriments. The present study comprised in vitro and in vivo studies. In vitro inflammatory analysis revealed that ASC-Exos exerted a synergic anti-inflammatory effect with GCs by significantly decreasing secretion of proinflammatory cytokines by RAW cells and increasing secretion of anti-inflammatory cytokines. In vitro cytoprotective analysis showed that ASC-Exos overrode GC-induced detrimental effects on tenocytes by significantly improving GC-suppressed cellular proliferation, migration, and transcription of tenocytic matrix molecules and degradative enzyme inhibitors and significantly decreasing GC-induced cell senescence, apoptosis, and transcription of ROS and tenocytic degradative enzymes. In vivo studies revealed that additional ASC-Exo injection restored impairments in histological and biomechanical properties owing to GC administration. Collectively, these results suggest that ASC-Exos exert a stronger anti-inflammatory effect in combination with GCs, overriding their detrimental effects on rotator cuff tendons.

A “cell-free treatment” for tendon injuries: adipose stem cell-derived exosomes

Tendon injuries are widespread and chronic disorders of the musculoskeletal system, frequently caused by overload of the tendons. Currently, the most common treatment for tendon injuries is "cell-free therapy", of which exosomes, which can treat a host of diseases, including immune disorders, musculoskeletal injuries and cardiovascular diseases, are one kind. Among the many sources of exosomes, adipose-derived stem cell exosomes (ASC-Exos) have better efficacy. This is attributed not only to the ease of isolation of adipose tissue, but also to the high differentiation capacity of ASCs, their greater paracrine function, and immunomodulatory capacity compared to other exosomes. ASC-Exos promote tendon repair by four mechanisms: promoting angiogenesis under hypoxic conditions, reducing the inflammatory response, promoting tendon cell migration and proliferation, and accelerating collagen synthesis, thus accelerating tendon healing. This review focuses on describing studies of preclinical experiments with various exosomes, the characteristics of ASC-Exos and their mechanisms of action in tendon healing, as well as elaborating the limitations of ASC-Exos in clinical applications.

Injection of adipose stem cells in the treatment of rotator cuff disease - a narrative review of current evidence

The purpose of this study is to summarize evidence for the use of adipose stem cell (ASC) injections in the treatment of rotator cuff tears (RCT) and identify future areas of study. A thorough literature search was performed to identify studies investigating the use of ASC injections in the treatment of RCTs. Among animal trials, it is unclear whether ASCs are of benefit for rotator cuff repair. In clinical trials, ASC injection may reduce retear rate with otherwise equivocal clinical outcomes. Although ASC injection may be safe, the literature does not provide a clear consensus as to the efficacy of ASC injections, nor does it delineate which patients would benefit most from this treatment.

The Therapeutic Potential of Exosomes in Soft Tissue Repair and Regeneration

Soft tissue defects are common following trauma and tumor extirpation. These injuries can result in poor functional recovery and lead to a diminished quality of life. The healing of skin and muscle is a complex process that, at present, leads to incomplete recovery and scarring. Regenerative medicine may offer the opportunity to improve the healing process and functional outcomes. Barriers to regenerative strategies have included cost, regulatory hurdles, and the need for cell-based therapies. In recent years, exosomes, or extracellular vesicles, have gained tremendous attention in the field of soft tissue repair and regeneration. These nanosized extracellular particles (30-140 nm) can break the cellular boundaries, as well as facilitate intracellular signal delivery in various regenerative physiologic and pathologic processes. Existing studies have established the potential of exosomes in regenerating tendons, skeletal muscles, and peripheral nerves through different mechanisms, including promoting myogenesis, increasing tenocyte differentiation and enhancing neurite outgrowth, and the proliferation of Schwann cells. These exosomes can be stored for immediate use in the operating room, and can be produced cost efficiently. In this article, we critically review the current advances of exosomes in soft tissue (tendons, skeletal muscles, and peripheral nerves) healing. Additionally, new directions for clinical applications in the future will be discussed.

Adipose Stromal/Stem Cell-Derived Extracellular Vesicles: Potential Next-Generation Anti-Obesity Agents

Over the last decade, several compounds have been identified for the treatment of obesity. However, due to the complexity of the disease, many pharmacological interventions have raised concerns about their efficacy and safety. Therefore, it is important to discover new factors involved in the induction/progression of obesity. Adipose stromal/stem cells (ASCs), which are mostly isolated from subcutaneous adipose tissue, are the primary cells contributing to the expansion of fat mass. Like other cells, ASCs release nanoparticles known as extracellular vesicles (EVs), which are being actively studied for their potential applications in a variety of diseases. Here, we focused on the importance of the contribution of ASC-derived EVs in the regulation of metabolic processes. In addition, we outlined the advantages/disadvantages of the use of EVs as potential next-generation anti-obesity agents.

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.

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.

Mesenchymal stem cell-derived exosomes: therapeutic implications for rotator cuff injury

Rotator cuff injuries are a common clinical condition of the shoulder joint. Surgery that involves reattaching the torn tendon to its humeral head bony attachment has a somewhat lower success rate. The scar tissue formed during healing of the rotator cuff leads to poor tendon-related mechanical properties. To promote healing, a range of genetic interventions, as well as cell transplantation, and many other techniques have been explored. In recent years, the therapeutic promise of mesenchymal stem cells (MSCs) has been well documented in animal and clinical studies. Some data have suggested that MSCs can promote angiogenesis, reduce inflammation and cell proliferation and increase collagen deposition. These functions are likely paracrine effects of MSCs, particularly mediated through exosomes. Here, we review the use of MSCs-related exosomes in tissues and organs. We also discuss their potential utility for treating rotator cuff injuries, and explore the underlying mechanisms of their effects.

Adipose Stem Cell-Derived Exosomes Ameliorate Chronic Rotator Cuff Tendinopathy by Regulating Macrophage Polarization: From a Mouse Model to a Study in Human Tissue

BACKGROUND

Chronic rotator cuff (RC) tendinopathy is one of the most prevalent causes of shoulder pain. Growing evidence suggests that macrophages play a significant role in the proinflammatory response, resolution of inflammation, and tissue healing of tendinopathy. In particular, enhancement of M2 macrophage (M2φ) activity contributes to the accelerated healing of tendinopathy. Therefore, a treatment that enhances M2φ polarization would be useful for patients with this common musculoskeletal disorder.

PURPOSE

To investigate whether adipose stem cell-derived exosomes (ASC-Exos) enhance M2φ polarization and ameliorate chronic RC tendinopathy.

STUDY DESIGN

Controlled laboratory study.

METHODS

First, we compared the effects of ASC-Exos on polarization of mouse bone marrow-derived macrophages between a classically activated phenotype (M1φ) and an alternatively activated phenotype (M2φ) in vitro. In total, 72 C57BL/6 mice were assigned to normal cage activity (n = 24) or 5 weeks of treadmill overuse (n = 48). The supraspinatus tendon of each treadmill overuse mouse was treated with ASC-Exos (n = 24) or saline (n = 24). Histological and biomechanical outcomes were assessed 4 weeks after treatment. Finally, tissue samples from human patients with RC tendinopathy were obtained to assay the effect of ASC-Exos on the M1φ/M2φ balance in tissue-resident macrophages.

RESULTS

ASC-Exos inhibited M1φ polarization and augmented M2φ polarization in vitro and in vivo. Mice in the ASC-Exos group showed less severe pathological changes than those in the saline group, including less cellular infiltration, disorganization of collagen, and ground substance deposition. The modified Bonar score of the ASC-Exos group (mean ± SD, 7.68 ± 1.03) was significantly lower than that of the saline group (9.81 ± 0.96; P < .05). Furthermore, the maximum failure load was significantly higher in the ASC-Exos group than in the saline group (4.23 ± 0.66 N vs 3.86 ± 0.65 N; P < .05), as was stiffness (3.38 ± 0.34 N/m vs 2.68 ± 0.49 N/m; P < .05).

CONCLUSION

ASC-Exos-mediated polarization balance of M1φ/M2φ contributes to the amelioration of chronic RC tendinopathy. Regulation of the M1φ/M2φ balance could be a new target for the treatment of chronic RC tendinopathy.

CLINICAL RELEVANCE

Administration of ASC-Exos is a cell-free approach that may become a novel treatment option for chronic RC tendinopathy and should be explored further.

MSC-derived small extracellular vesicles overexpressing miR-20a promoted the osteointegration of porous titanium alloy by enhancing osteogenesis via targeting BAMBI

BACKGROUND

Patients with osteoporosis have a high risk of implant loosening due to poor osteointegration, possibly leading to implant failure, implant revision, and refracture. RNA interference therapy is an emerging epigenetic treatment, and we found that miR-20a could enhance osteogenesis. Moreover, small extracellular vesicles (sEVs) derived from bone marrow mesenchymal stem cells (hBM-MSCs) were utilized as nanoscale carriers for the protection and transportation of miR-20a (sEV-20a). In this study, we intended to determine whether sEVs overexpressing miR-20a could exert a superior effect on osteoporotic bone defects and the underlying mechanism.

METHODS

For evaluating the effect of sEV-20a on osteogenesis, in vitro and in vivo studies were performed. In vitro, we first showed that miR-20a was upregulated in the osteogenic process and overexpressed sEVs with miR-20a by the transfection method. Then, the proliferation, migration, and osteogenic differentiation abilities of hBM-MSCs treated with sEV-20a were detected by CCK-8 assays, alkaline phosphatase staining and alizarin red staining, qRT-PCR, and western blot. In vivo, we established an osteoporotic bone defect model and evaluated the effect of sEV-20a on bone formation by micro-CT, sequential fluorescent labeling, and histological analysis. To further explore the mechanism, we applied a bioinformatics method to identify the potential target of miR-20a.

RESULTS

In vitro, sEV-20a was successfully established and proved to promote the migration and osteogenesis of hBM-MSCs. In vivo, sEV-20a promoted osteointegration in an osteoporotic rat model. To further elucidate the related mechanism, we proved that miR-20a could enhance osteogenesis by targeting BAMBI.

CONCLUSIONS

Collectively, the in vitro and in vivo results confirmed that MSC-derived sEV-20a therapy effectively promoted osteoporotic porous titanium alloy osteointegration via pro-osteogenic effects by targeting BAMBI.

Adipose-Derived Stem Cells Secretome and Its Potential Application in "Stem Cell-Free Therapy"

Adipose-derived stem cells (ASCs) secrete many cytokines, proteins, growth factors, and extracellular vesicles with beneficial outcomes that can be used in regenerative medicine. It has great potential, and the development of new treatment strategies using the ASCs secretome is of global interest. Besides cytokines, proteins, and growth factors, the therapeutic effect of secretome is hidden in non-coding RNAs such as miR-21, miR-24, and miR-26 carried via exosomes secreted by adequate cells. The whole secretome, including ASC-derived exosomes (ASC-exos) has been proven in many studies to have immunomodulatory, proangiogenic, neurotrophic, and epithelization activity and can potentially be used for neurodegenerative, cardiovascular, respiratory, inflammatory, and autoimmune diseases as well as wound healing treatment. Due to limitations in the use of stem cells in cell-based therapy, its secretome with emphasis on exosomes seems to be a reasonable and safer alternative with increased effectiveness and fewer side effects. Moreover, the great advantage of cell-free therapy is the possibility of biobanking the ASCs secretome. In this review, we focus on the current state of knowledge on the use of the ASCs secretome in stem cell-free therapy.

Current Biological Strategies to Enhance Surgical Treatment for Rotator Cuff Repair

Rotator cuff tear is one of the most common shoulder problems encountered by orthopedic surgeons. Due to the slow healing process and high retear rate, rotator cuff tear has distressed millions of people all around the world every year, especially for the elderly and active athletes. This disease significantly impairs patients' motor ability and reduces their quality of life. Besides conservative treatment, open and arthroscopic surgery contributes a lot to accelerate the healing process of rotator cuff tear. Currently, there are many emerging novel treatment methods to promote rotator cuff repair. A variety of biological stimulus has been utilized in clinical practice. Among them, platelet-rich plasma, growth factors, stem cells, and exosomes are the most popular biologics in laboratory research and clinical trials. This review will focus on the biologics of bioaugmentation methods for rotator cuff repair and tendon healing, including platelet-rich plasma, growth factors, exosomes and stem cells, etc. Relevant studies are summarized in this review and future research perspectives are introduced.

Quercetin Attenuates Trauma-Induced Heterotopic Ossification by Tuning Immune Cell Infiltration and Related Inflammatory Insult

Heterotopic ossification (HO) is one of the most intractable disorders following musculoskeletal injury and is characterized by the ectopic presence of bone tissue in the soft tissue leading to severe loss of function in the extremities. Recent studies have indicated that immune cell infiltration and inflammation are involved in aberrant bone formation. In this study, we found increased monocyte/macrophage and mast cell accumulation during early HO progression. Macrophage depletion by clodronate liposomes and mast cell stabilization by cromolyn sodium significantly impeded HO formation. Therefore, we proposed that the dietary phytochemical quercetin could also suppress immune cell recruitment and related inflammatory responses to prevent HO. As expected, quercetin inhibited the monocyte-to-macrophage transition, macrophage polarization, and mast cell activation in vitro in a dose-dependent manner. Using a murine burn/tenotomy model, we also demonstrated that quercetin attenuated inflammatory responses and HO in vivo. Furthermore, elevated SIRT1 and decreased acetylated NFκB p65 expression were responsible for the mechanism of quercetin, and the beneficial effects of quercetin were reversed by the SIRT1 antagonist EX527 and mimicked by the SIRT agonist SRT1720. The findings in this study suggest that targeting monocyte/macrophage and mast cell activities may represent an attractive approach for therapeutic intervention of HO and that quercetin may serve as a promising therapeutic candidate for the treatment of trauma-induced HO by modulating SIRT1/NFκB signaling.

Mesenchymal Stromal Cells and Their Secretome: New Therapeutic Perspectives for Skeletal Muscle Regeneration

Mesenchymal stromal cells (MSCs) are multipotent cells found in different tissues: bone marrow, peripheral blood, adipose tissues, skeletal muscle, perinatal tissues, and dental pulp. MSCs are able to self-renew and to differentiate into multiple lineages, and they have been extensively used for cell therapy mostly owing to their anti-fibrotic and immunoregulatory properties that have been suggested to be at the basis for their regenerative capability. MSCs exert their effects by releasing a variety of biologically active molecules such as growth factors, chemokines, and cytokines, either as soluble proteins or enclosed in extracellular vesicles (EVs). Analyses of MSC-derived secretome and in particular studies on EVs are attracting great attention from a medical point of view due to their ability to mimic all the therapeutic effects produced by the MSCs (i.e., endogenous tissue repair and regulation of the immune system). MSC-EVs could be advantageous compared with the parental cells because of their specific cargo containing mRNAs, miRNAs, and proteins that can be biologically transferred to recipient cells. MSC-EV storage, transfer, and production are easier; and their administration is also safer than MSC therapy. The skeletal muscle is a very adaptive tissue, but its regenerative potential is altered during acute and chronic conditions. Recent works demonstrate that both MSCs and their secretome are able to help myofiber regeneration enhancing myogenesis and, interestingly, can be manipulated as a novel strategy for therapeutic interventions in muscular diseases like muscular dystrophies or atrophy. In particular, MSC-EVs represent promising candidates for cell free-based muscle regeneration. In this review, we aim to give a complete picture of the therapeutic properties and advantages of MSCs and their products (MSC-derived EVs and secreted factors) relevant for skeletal muscle regeneration in main muscular diseases.

Adipose-derived stem cell exosomes facilitate rotator cuff repair by mediating tendon-derived stem cells

Aim: To evaluate the potential capability of adipose-derived stem cell exosomes (ADSC-exos) on rotator cuff repair by mediating the tendon-derived stem cells (TDSCs) and explored the mechanism. Methods: First, we investigated the growth, survival and migration of TDSCs in the presence of ADSC-exos in vitro. Using a rat rotator cuff injury model to analyze the ability of the ADSC-exos to promote rotator cuff healing in vivo. Results: The hydrogel with ADSC-exos significantly improved the osteogenic and adipogenesis differentiation and enhanced the expression of RUNX2, Sox-9, TNMD, TNC and Scx and the mechanical properties of the articular portion. Conclusion: The ADSC-exos have the potential to promote the rotator cuff repair by mediating the TDSCs.