Mesenchymal Stem Cell Secretome Improves Tendon Cell Viability In Vitro and Tendon-Bone Healing In Vivo When a Tissue Engineering Strategy Is Used in a Rat Model of Chronic Massive Rotator Cuff Tear

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

BACKGROUND

Fatty infiltration, inflammation, and apoptosis are common degenerative changes in patients with chronic rotator cuff tears that can lead to muscle atrophy and can even result in massive irreparable rotator cuff tears. Some data have demonstrated the proregenerative, anti-inflammatory, and anti-apoptotic properties of stem cell-derived exosomes in some orthopaedic disorders, but their effect on torn rotator cuff muscles has never been investigated.

PURPOSE

To study the effect of exosomes isolated from human adipose-derived stem cells (ASCs-Exos) on muscle degeneration, regeneration, and biomechanical properties in a rat model of a massive rotator cuff tear (MRCT).

STUDY DESIGN

Controlled laboratory study.

METHODS

A bilateral supraspinatus and infraspinatus tenotomy was performed on rats to create an MRCT model. Forty-two rats were randomly assigned to 3 groups: the sham surgery group, the saline group (lesions treated with a saline injection), and the ASCs-Exos group (lesions treated with an ASCs-Exos injection). Wet muscle weight, fatty infiltration, inflammation, vascularization, regeneration, and biomechanical properties were evaluated at 8 and 16 weeks after surgery.

RESULTS

The results revealed that the ASCs-Exos treatment could prevent the atrophy, fatty infiltration, inflammation, and vascularization of muscles in the MRCT model (P < .001). Additionally, the myofiber regeneration and biomechanical properties of ASCs-Exos-treated rotator cuffs were significantly elevated compared with those in the saline-treated group (P < .001).

CONCLUSION

This study demonstrates that ASCs-Exos can effectively decrease atrophy and degeneration and improve muscle regeneration and biomechanical properties in torn rotator cuff muscles.

CLINICAL RELEVANCE

ASCs-Exos can be used as a new cell-free approach to prevent the muscle degeneration associated with torn rotator cuffs and may be helpful to repair torn rotator cuffs. Nevertheless, further work needs to be done in a large animal model owing to the inherent regenerative potential possessed by rodents.

Therapeutic potential of exosomes in rotator cuff tendon healing

Rotator cuff tears are common musculoskeletal injuries that can cause significant pain and disability. While the clinical results of rotator cuff repair can be good, failure of tendon healing remains a significant problem. Molecular mechanisms underlying structural failure following surgical repair remain unclear. Histologically, enhanced inflammation, disorganization of the collagen fibers, calcification, apoptosis and tissue necrosis affect the normal healing process. Mesenchymal stem cells (MSCs) have the ability to provide improved healing following rotator cuff repair via the release of mediators from secreted 30-100 nm extracellular vesicles called exosomes. They carry regulatory proteins, mRNA and miRNA and have the ability to increase collagen synthesis and angiogenesis through increased expression of mRNA and release of proangiogenic factors and regulatory proteins that play a major role in proper tissue remodeling and preventing extracellular matrix degradation. Various studies have shown the effect of exosomes on improving outcome of cutaneous wound healing, scar tissue formation, degenerative bone disease and Duchenne Muscular Dystrophy. In this article, we critically reviewed the potential role of exosomes in tendon regeneration and propose the novel use of exosomes alone or seeded onto biomaterial matrices to stimulate secretion of favorable cellular factors in accelerating the healing response following rotator cuff repair.

Stem Cell-Conditioned Medium Promotes Graft Remodeling of Midsubstance and Intratunnel Incorporation After Anterior Cruciate Ligament Reconstruction in a Rat Model

BACKGROUND

Stem cell-conditioned medium (CM) has been increasingly used in regenerative medicine. However, its effect on graft-host integration after anterior cruciate ligament (ACL) reconstruction (ACLR) remains unclear.

PURPOSE

To examine the effect of human bone marrow stem cell (hBMSC)-CM on graft-bone integration and graft midsubstance ligamentization in a rat model of ACLR.

STUDY DESIGN

Controlled laboratory study.

METHODS

CM was obtained from the supernatant of commercially available hBMSCs in serum-free Dulbecco's modified Eagle medium (DMEM). In a rat model of an ACL injury, isometric ACLR was performed. Three groups were established: CM injection group (CM; n = 40), control injection group (CI; n = 40) with serum-free DMEM injections, and no injection group (NI; n = 40). An intra-articular injection was performed weekly. Micro-computed tomography was conducted at 2, 4, and 8 weeks postoperatively. Histological and biomechanical analyses were conducted at 4 and 8 weeks postoperatively. The NIH3T3 fibroblast was utilized as a model in vitro to examine the effect of CM using the cell counting kit-8 (CCK-8) assay and immunofluorescence staining of Ki-67, α-smooth muscle actin (α-SMA), and collagen 1 (Col 1).

RESULTS

At 4 and 8 weeks, the femoral and tibial bone tunnel areas as well as the interface between the graft and host bone were smaller, while the bone volume/total volume ratio was higher, in the CM group. Sharpey-like fibers formed at 8 weeks in the CM group. At 4 and 8 weeks, more Col 1 was noticed in the CM group than in the NI group (both P < .001) or CI group (both P < .001). Immunohistochemically, the α-SMA-positive area was up-regulated at the graft-bone interface at 4 weeks (P < .001) and declined at 8 weeks (P < .001) in the CM group compared with the other 2 groups. At the midsubstance, α-SMA expression decreased from 4 to 8 weeks in all groups and was significantly lower in the CM group than in the NI group (P < .01) or CI group (P < .05) at 8 weeks. The CCK-8 assay showed that CM increased NIH3T3 viability (P < .001) and the level of Ki-67 (P < .05), α-SMA (P < .001), and Col 1 (P < .001) in CM-educated NIH3T3 cells.

CONCLUSION

hBMSC-CM accelerates graft-bone incorporation and midsubstance ligamentization and enhances the proliferation, differentiation, and collagen synthesis of fibroblasts.

CLINICAL RELEVANCE

Graft-host integration is essential after ACLR. The current study identified a novel agent, that is, hBMSC-CM, as a candidate for promoting integration.

Comparative Evaluation of the Book-Type Acellular Bone Scaffold and Fibrocartilage Scaffold for Bone-Tendon Healing

Bone-tendon (B-T) healing is a clinical challenge due to its limited regeneration capability. Fibrocartilage regeneration and bone formation at the healing site are two critical factors for B-T healing. Promoting fibrocartilage regeneration and bone formation by tissue-engineering may be a promising treatment strategy. In this study, we innovatively fabricated two kinds of acellular scaffolds from bone or fibrocartilage tissues, namely the book-type the acellular bone scaffold (BABS) and the book-type acellular fibrocartilage scaffold (BAFS). Histologically, the two scaffolds well preserved the native extracellular matrix (ECM) structure without cellular components. In vitro studies showed BABS is superior in osteogenic inducibility, while BAFS has good chondrogenic inducibility. To comparatively investigate the efficacy on B-T healing, the BABS or BAFS were, respectively, implanted into a rabbit partial patellectomy model. Macroscopically, a regenerated bone-tendon insertion (BTI) was bridging the residual patella and patellar-tendon with no signs of infection and osteoarthritis. Radiologically, more new bone was formed at the healing interface in the BABS group as compared with the BAFS or control (CTL) groups (p < 0.05). Histologically, at postoperative week 16, histological scores were significantly better for regenerated fibrocartilage in the BAFS group or BABS group compared with the CTL group, but the BAFS group showed a significantly larger score than the BABS groups (p < 0.05). Biomechanical evaluation indicated a higher failure load and stiffness were shown in the BAFS group than those in the BABS or CTL groups at week 16 (p < 0.05). This study indicated that the BAFS is a more promising scaffold for B-T healing in comparison with the BABS. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1709-1722, 2019.

Nanofiber-based matrices for rotator cuff regenerative engineering

The rotator cuff consists of a cuff of soft tissue responsible for rotating the shoulder. Rotator cuff tendon tears are responsible for a significant source of disability and pain in the adult population. Most rotator cuff tendon tears occur at the bone-tendon interface. Tear size, patient age, fatty infiltration of muscle, have a major influence on the rate of retear after surgical repair. The high incidence of retears (up to 94% in some studies) after surgery makes rotator cuff injuries a critical musculoskeletal problem to address. The limitations of current treatments motivate regenerative engineering approaches for rotator cuff regeneration. Various fiber-based matrices are currently being investigated due to their structural similarity with native tendons and their ability to promote regeneration. This review will discuss the current approaches for rotator cuff regeneration, recent advances in fabrication and enhancement of nanofiber-based matrices and the development and use of complex nano/microstructures for rotator cuff regeneration. STATEMENT OF SIGNIFICANCE: Regeneration paradigms for musculoskeletal tissues involving the rotator cuff of the shoulder have received great interest. Novel technologies based on nanomaterials have emerged as possible robust solutions for rotator cuff injury and treatment due to structure/property relationships. The aim of the review submitted is to comprehensively describe and evaluate the development and use of nano-based material technologies for applications to rotator cuff tendon healing and regeneration.

Mesenchymal Stem Cells Empowering Tendon Regenerative Therapies

Tendon tissues have limited healing capacity. The incidence of tendon injuries and the unsatisfactory functional outcomes of tendon repair are driving the search for alternative therapeutic approaches envisioning tendon regeneration. Cellular therapies aim at delivering adequate, regeneration-competent cell types to the injured tendon and toward ultimately promoting its reconstruction and recovery of functionality. Mesenchymal stem cells (MSCs) either obtained from tendons or from non-tendon sources, like bone marrow (BM-MSCs) or adipose tissue (ASCs), have been receiving increasing attention over the years toward enhancing tendon healing. Evidences from in vitro and in vivo studies suggest MSCs can contribute to accelerate and improve the quality of tendon healing. Nonetheless, the exact mechanisms underlying these repair events are yet to be fully elucidated. This review provides an overview of the main challenges in the field of cell-based regenerative therapies, discussing the role of MSCs in boosting tendon regeneration, particularly through their capacity to enhance the tenogenic properties of tendon resident cells.

Biodistribution of gadolinium- and near infrared-labeled human umbilical cord mesenchymal stromal cell-derived exosomes in tumor bearing mice

We speculate that exosomes derived from human umbilical cord mesenchymal stromal cells (HUC-MSCs) will accumulate within tumors and have the potential for both tumor location or drug delivery.

Methods: To determine proof of concept, HUC-MSC exosomes were labeled with an MRI contrast agent, gadolinium, or a near infrared dye. Exosome accumulation within ectopic osteosarcoma tumor-bearing mice was determined by 14.1 T MRI or bioimaging over 24-48 h after injection. In vitro studies examine the accumulation and physiological effect of exosomes on human and mouse osteosarcoma cell lines by MTT assay, confocal microscopy, and flow cytometry.

Results: Systemic HUC-MSC exosomes accumulated continuously in tumor over a 24-48 h post-injection period. In contrast, synthetic lipid nanoparticles accumulate in tumor only for the first 3 h post-injection.

Conclusion: These results suggest that HUC-MSCs exosomes accumulate within human or mouse osteosarcoma cells in vitro and in vivo over a 24 to 48 h after infusion.

Pioglitazone-Primed Mesenchymal Stem Cells Stimulate Cell Proliferation, Collagen Synthesis and Matrix Gene Expression in Tenocytes

Various therapeutic effects of mesenchymal stem cells (MSCs) have been reported. However, the rapid clearance of these cells in vivo, difficulties in identifying their therapeutic mechanism of action, and insufficient production levels remain to be resolved. We investigated whether a pioglitazone pre-treatment of MSCs (Pio-MSCs) would stimulate the proliferation of co-cultured tenocytes. Pioglitazone increased the proliferation of MSCs and enhanced the secretion of VEGF (vascular endothelial growth factor) and collagen in these cells. We then examined the effects of Pio-MSCs on tenocytes using an indirect transwell culture system. A significant increase in tenocyte proliferation and cell cycle progression was observed in these co-cultures. Significant increases were observed in wound scratch closure by tenocytes from a Pio-MSC co-culture. Pio-MSCs also enhanced the secretion of collagen from tenocytes. A higher mRNA level of collagen type 1 (Col 1) and type 3 (Col 3), scleraxis (Scx), and tenascin C (TnC) was found in the tenocytes in Pio-MSC co-cultures compared with monocultured cells or tenocytes cultured with non-treated MSCs. Our results indicate that pioglitazone enhances the therapeutic effects of MSCs on tendon repair.

Pulsed Electromagnetic Fields Improve Tenogenic Commitment of Umbilical Cord-Derived Mesenchymal Stem Cells: A Potential Strategy for Tendon Repair-An In Vitro Study

Tendon repair is a challenging procedure in orthopaedics. The use of mesenchymal stem cells (MSCs) and pulsed electromagnetic fields (PEMF) in tendon regeneration is still investigational. In this perspective, MSCs isolated from the human umbilical cord (UC) may represent a possible candidate for tendon tissue engineering. The aim of the study is to evaluate the effect of low-frequency PEMF on tenogenic differentiation of MSCs isolated from the human umbilical cord (UC-MSCs) in vitro. 15 fresh UC samples from women with healthy pregnancies were retrieved at the end of caesarean deliveries. UC samples were manually minced into small fragments (less than 4 mm length) and cultured in MSC expansion medium. Part of the UC-MSCs was subsequently cultured with PEMF and tenogenic growth factors. UC-MSCs were subjected to pulsed electromagnetic fields for 2 h/day, 4 h/day, or 8 h/day. UC-MSCs cultured with FGF-2 and stimulated with PEMF showed a greater production of collagen type I and scleraxis. The prolonged exposure to PEMF was also related to the greatest expression of tenogenic markers. Thus, the exposure to PEMF provides a positive preconditioning biophysical stimulus, which may enhance UC-MSC tenogenic potential.

Biologics and stem cell-based therapies for rotator cuff repair

The rotator cuff is composed of several distinct muscles and tendons that function in concert to coordinate shoulder motion. Injuries to these tendons frequently result in permanent dysfunction and persistent pain. Despite considerable advances in operation techniques, surgical repair alone still does not fully restore rotator cuff function. This review focuses on recent research in the use of biologics and stem cell-based therapies to augment repair, highlighting promising avenues for future work and remaining challenges. While a number of animal models are used for rotator cuff studies, the anatomy of the rotator cuff varies dramatically between species. Since the rodent rotator cuff shares the most anatomical features with the human, this review will focus primarily on rodent models to enable consistent interpretation of outcome measures.

Electrospun and Electrosprayed Scaffolds for Tissue Engineering

Electrospinning and electrospraying technologies provide an accessible and universal synthesis method for the continuous preparation of nanostructured materials. This chapter introduces recent uses of electrospun and electrosprayed scaffolds for tissue regeneration applications. More recent in vitro and in vivo of electrospun fibers are also discussed in relation to soft and hard tissue engineering applications. The focus is made on the bone, vascular, skin, neural and soft tissue regeneration. An introduction is presented regarding the production of biomaterials made by synthetic and natural polymers and inorganic and metallic materials for use in the production of scaffolds for regenerative medicine. For this proposal, the following techniques are discussed: electrospraying, co-axial and emulsion electrospinning and bio-electrospraying. Tissue engineering is an exciting and rapidly developing field for the understanding of how to regenerate the human body.