Therapeutic Mechanisms of Human Adipose-Derived Mesenchymal Stem Cells in a Rat Tendon Injury Model

Mechanobiological Strategies to Enhance Ovine (Ovis aries) Adipose-Derived Stem Cells Tendon Plasticity for Regenerative Medicine and Tissue Engineering Applications

Adipose-derived stem cells (ADSCs) hold promise for tendon repair, even if their tenogenic plasticity and underlying mechanisms remain only partially understood, particularly in cells derived from the ovine animal model. This study aimed to characterize oADSCs during in vitro expansion to validate their phenotypic properties pre-transplantation. Moreover, their tenogenic potential was assessed using two in vitro-validated approaches: (1) teno-inductive conditioned media (CM) derived from a co-culture between ovine amniotic stem cells and fetal tendon explants, and (2) short- (48 h) and long-term (14 days) seeding on highly aligned PLGA (ha-PLGA) electrospun scaffold. Our findings indicate that oADSCs can be expanded without senescence and can maintain the expression of stemness (Sox2, Oct4, Nanog) and mesenchymal (CD29, CD166, CD44, CD90) markers while remaining negative for hematopoietic (CD31, CD45) and MHC-II antigens. Of note, oADSCs' tendon differentiation potential greatly depended on the in vitro strategy. oADSCs exposed to CM significantly upregulated tendon-related genes (COL1, TNMD, THBS4) but failed to accumulate TNMD protein at 14 days of culture. Conversely, oADSCs seeded on ha-PLGA fleeces quickly upregulated the tendon-related genes (48 h) and in 14 days accumulated high levels of the TNMD protein into the cytoplasm of ADSCs, displaying a tenocyte-like morphology. This mechano-sensing cellular response involved a complete SOX9 downregulation accompanied by YAP activation, highlighting the efficacy of biophysical stimuli in promoting tenogenic differentiation. These findings underscore oADSCs' long-term self-renewal and tendon differentiative potential, thus opening their use in a preclinical setting to develop innovative stem cell-based and tissue engineering protocols for tendon regeneration, applied to the veterinary field.

Fabrication of atelocollagen-coated bioabsorbable suture and the evaluation of its regenerative efficacy in Achilles tendon healing using a rat experimental model

Recently, the incidence of Achilles tendon ruptures (ATRs) has become more common, and repair surgery using a bioabsorbable suture is generally preferred, particularly in the case of healthy patients. Sutures composed of poly(lactic-co-glycolic acid) (PLGA) are commonly used in ATR surgeries. Nevertheless, owing to the inherent limitations of PLGA, novel bioabsorbable sutures that can accelerate Achilles tendon healing are sought. Recently, several studies have demonstrated the beneficial effects of atelocollagen on tendon healing. In this study, poly(3,4-dihydroxy-L-phenylalanine) (pDOPA), a hydrophilic biomimetic material, was used to modify the hydrophobic surface of a PLGA suture (Vicryl, VC) for the stable coating of atelocollagen on its surface. The main objective was to fabricate an atelocollagen-coated VC suture and evaluate its performance in the healing of Achilles tendon using a rat model of open repair for ATR. Structural analyses of the surface-modified suture indicated that the collagen was successfully coated on the VC/pDOPA suture. Postoperative in vivo biomechanical analysis, histological evaluation, ultrastructural/morphological analyses, and western blotting confirmed that the tendons in the VC/pDOPA/Col group exhibit superior healing than those in the VC and VC/pDOPA groups after 1 and 6 weeks following the surgery. The this study suggests that atelocollagen-coated PLGA/pDOPA sutures are preferable for future medical applications, especially in the repair of ATR.

Challenges and opportunities of medicines for treating tendon inflammation and fibrosis: A comprehensive and mechanistic review

BACKGROUND

Tendinopathy refers to conditions characterized by collagen degeneration within tendon tissue, accompanied by the proliferation of capillaries and arteries, resulting in reduced mechanical function, pain, and swelling. While inflammation in tendinopathy can play a role in preventing infection, uncontrolled inflammation can hinder tissue regeneration and lead to fibrosis and impaired movement.

OBJECTIVES

The inability to regulate inflammation poses a significant limitation in tendinopathy treatment. Therefore, an ideal treatment strategy should involve modulation of the inflammatory process while promoting tissue regeneration.

METHODS

The current review article was prepared by searching PubMed, Scopus, Web of Science, and Google Scholar databases. Several treatment approaches based on biomaterials have been developed.

RESULTS

This review examines various treatment methods utilizing small molecules, biological compounds, herbal medicine-inspired approaches, immunotherapy, gene therapy, cell-based therapy, tissue engineering, nanotechnology, and phototherapy.

CONCLUSION

These treatments work through mechanisms of action involving signaling pathways such as transforming growth factor-beta (TGF-β), mitogen-activated protein kinases (MAPKs), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), all of which contribute to the repair of injured tendons.

A Novel Tendon Injury Model, Induced by Collagenase Administration Combined with a Thermo-Responsive Hydrogel in Rats, Reproduces the Pathogenesis of Human Degenerative Tendinopathy

Patellar tendinopathy is a common clinical problem, but its underlying pathophysiology remains poorly understood, primarily due to the absence of a representative experimental model. The most widely used method to generate such a model is collagenase injection, although this method possesses limitations. We developed an optimized rat model of patellar tendinopathy via the ultrasound-guided injection of collagenase mixed with a thermo-responsive Pluronic hydrogel into the patellar tendon of sixty male Wistar rats. All analyses were carried out at 3, 7, 14, 30, and 60 days post-injury. We confirmed that our rat model reproduced the pathophysiology observed in human patients through analyses of ultrasonography, histology, immunofluorescence, and biomechanical parameters. Tendons that were injured by the injection of the collagenase-Pluronic mixture exhibited a significant increase in the cross-sectional area (p < 0.01), a high degree of tissue disorganization and hypercellularity, significantly strong neovascularization (p < 0.01), important changes in the levels of types I and III collagen expression, and the organization and presence of intra-tendinous calcifications. Decreases in the maximum rupture force and stiffness were also observed. These results demonstrate that our model replicates the key features observed in human patellar tendinopathy. Collagenase is evenly distributed, as the Pluronic hydrogel prevents its leakage and thus, damage to surrounding tissues. Therefore, this model is valuable for testing new treatments for patellar tendinopathy.

Lipoaspirate stored at a constant low temperature by electric control suppresses intracellular metabolism and maintains high cell viability

Background

Cell therapy is a useful treatment method for wide spectrum of diseases which utilizes the immunosuppressive and regenerative abilities of administered cells. It is essential to build a transport system of tissues from which cells are harvested, because various external factors, such as temperature, time, air pressure, and vibration affect the cell functions isolated from body tissues. In particular, temperature is a critical factor which determines the viability of the cells and organs. In this study, we investigated the optimal temperature during the transportation of lipoaspirates from which adipose -derived stem cells (ASCs) were isolated.

Method

Lipoaspirates obtained by liposuctions (lipomatic or vaser method) were transported in four different temperature zones (4, 20, 32, and 37 °C) in a transport container which is electrically controlled to maintain a constant temperature during transport. Stromal vascular fractions (SVFs) were harvested from the lipoaspirate, and the cell number, viability and proliferation rate and the yield of ASCs were examined. In addition, the metabolic state of the cells was examined.

Results

ASCs from lipoaspirates transported at high temperature significantly decreased cell viability, while those at low temperature maintained high cell viability and showed good cell proliferation. In addition, transportation of lipoaspirates at low temperature resulted in a high level of NAD+/NADH, coenzymes involved in intracellular metabolism, and a low level of lactate in lipoaspirate suppressed the glycolytic system of intracellular metabolism, in ASCs.

Conclusion

The lipoaspirate transported at 4 °C exhibited best results regarding live cell number, viability and cell proliferation in our experiments. This study offers a direction to build a transport system that connects laboratories and hospitals and achieve a beneficial therapy for patients.

Preclinical assessment of IL-1β primed human umbilical cord mesenchymal stem cells for tendon functional repair through TGF-β/IL-10 signaling

Background

Inadequate repair capacity and disturbed immune compartments are the main pathological causes of tendinopathy. Transplantation of mesenchymal stem cells (MSCs) become an effective clinic option to alleviate tendinopathy. Interleukin-1β (IL-1β) could confer on MSCs enhanced immunoregulatory capability to remodel the repair microenvironment favoring tissue repair. Therefore, IL-1β activated UC-MSCs (1βUC-MSCs) may exert favorable efficacy in promoting tendon repair in a preclinical tendinopathy rat model.

Methods

Tendon-derived stem cells (TDSCs) were isolated and characterized. In vitro, the levels of immunoregulatory-related cytokines such as IL-1β, IL-6, IL-10, and TGF-β secreted by 1βUC-MSCs and unprimed UC-MSCs was measured. And tendon-specific markers expressed by TDSCs cultured with primed cultured medium (CM) or unprimed CM were detected. In vivo, Achilles tendinopathy was induced by 30 μL collagenase I injection in Sprague Dawley rats. One week later, the rats were randomly injected with UC-MSCs primed with IL-1β (106 cells per tendon), UC-MSCs, or PBS. After rats were sacrificed, histological evaluation, electron microscopy, biomechanical tests, gait performance were conducted to evaluate the structural and functional recovery of Achilles tendons. The inflammation and metabolic state of the extracellular matrix, and the potential mechanism were assessed by immunohistochemical staining and Western blot.

Results

UC-MSCs were activated by IL-1β to secrete higher levels of IL-10 and TGF-β while the secretion levels of IL-6 and IL-1β were not changed significantly, promoting a higher expression level of COL I and TNMD in TDSCs under proinflammatory environment. In vivo, the transplanted 1βUC-MSCs could survive up to 5 weeks after injection with tenogenic differentiation and improved tendon healing histologically semi-quantified by modified Bonar scores. This structural regeneration was further confirmed by observation of ultrastructural morphology, and led to good functional recovery including improved biomechanical properties and gait performance. During this process, the inflammatory response and metabolism of the extracellular matrix was improved through TGF-β/IL-10 pathway.

Conclusion

This study demonstrated that the transplantation of UC-MSCs activated by IL-1β exhibited satisfactory ability for promoting tendon functional repair in a tendinopathy rat model. During this process, the balance of inflammatory response and extracellular matrix metabolism was remodeled, and the TGF-β/Smad2/3 and IL-10 signaling pathways were activated simultaneously. We cautiously conclude that the IL-1β primed UC-MSCs could be a promising strategy for enhancing the ability of MSCs to treat tendinopathy.

An Atelocollagen Injection Enhances the Healing of Nonoperatively Treated Achilles Tendon Tears: An Experimental Study in Rats

Background

There is growing interest in nonoperative treatment for the management of Achilles tendon ruptures (ATRs). However, nonoperative treatment is limited by the risk of tendon reruptures and low satisfaction rates. Recently, atelocollagen injections have been reported to have beneficial effects on tendon healing.

Purpose

To evaluate the beneficial effects of injected atelocollagen on Achilles tendon healing and investigate the mechanism of atelocollagen on tendon healing.

Study Design

Controlled laboratory study.

Methods

Percutaneous tenotomy of the right Achilles tendon in 66 rats was performed. The animals were equally divided into the noninjection group (NG) and the collagen injection group (CG). At 1, 3, and 6 weeks, the Achilles functional index, cross-sectional area, load to failure, stiffness, stress, and the modified Bonar score were assessed. Transmission electron microscopy, western blotting, and immunohistochemistry were also performed.

Results

The Achilles functional index (-6.8 vs -43.0, respectively; P = .040), load to failure (42.1 vs 27.0 N, respectively; P = .049), and stiffness (18.8 vs 10.3 N/mm, respectively; P = .049) were higher in the CG than those in the NG at 3 weeks. There were no significant differences in histological scores between the 2 groups. Transmission electron microscopy analysis showed that the mean diameter of collagen fibrils in the CG was greater than that in the NG at 3 weeks (117.2 vs 72.6 nm, respectively; P < .001) and 6 weeks (202.1 vs 144.0 nm, respectively; P < .001). Western blot analysis showed that the expression of collagen type I in the CG was higher than that in the NG at 1 week (P = .005) and 6 weeks (P = .001).

Conclusion

An atelocollagen injection had beneficial effects on the healing of nonoperatively treated Achilles tendon injuries. The Achilles tendon of CG rats exhibited better functional, biomechanical, and morphological outcomes compared with NG rats. The molecular data indicated that the mechanism of atelocollagen injections may be associated with an increased amount of collagen type I.

Clinical Relevance

An atelocollagen injection might be a good adjuvant option for the nonoperative treatment of ATRs.

Multipotent Mesenchymal Stem Cell-Based Therapies for Spinal Cord Injury: Current Progress and Future Prospects

Spinal cord injury (SCI) represents a significant medical challenge, often resulting in permanent disability and severely impacting the quality of life for affected individuals. Traditional treatment options remain limited, underscoring the need for novel therapeutic approaches. In recent years, multipotent mesenchymal stem cells (MSCs) have emerged as a promising candidate for SCI treatment due to their multifaceted regenerative capabilities. This comprehensive review synthesizes the current understanding of the molecular mechanisms underlying MSC-mediated tissue repair in SCI. Key mechanisms discussed include neuroprotection through the secretion of growth factors and cytokines, promotion of neuronal regeneration via MSC differentiation into neural cell types, angiogenesis through the release of pro-angiogenic factors, immunomodulation by modulating immune cell activity, axonal regeneration driven by neurotrophic factors, and glial scar reduction via modulation of extracellular matrix components. Additionally, the review examines the various clinical applications of MSCs in SCI treatment, such as direct cell transplantation into the injured spinal cord, tissue engineering using biomaterial scaffolds that support MSC survival and integration, and innovative cell-based therapies like MSC-derived exosomes, which possess regenerative and neuroprotective properties. As the field progresses, it is crucial to address the challenges associated with MSC-based therapies, including determining optimal sources, intervention timing, and delivery methods, as well as developing standardized protocols for MSC isolation, expansion, and characterization. Overcoming these challenges will facilitate the translation of preclinical findings into clinical practice, providing new hope and improved treatment options for individuals living with the devastating consequences of SCI.

Mesenchymal stem cell secretome-loaded fibrin glue improves the healing of intestinal anastomosis

Anastomotic leakage is a serious complication following gastrointestinal surgery and one of the leading causes of patient mortality. Despite the significant clinical and economic burden, there are currently no reliable treatment options to improve the healing of intestinal anastomosis and subsequently prevent anastomotic leakage. Recently, the development of regenerative medicine has shown promise for improving anastomotic healing. Recent studies have illustrated that stem cell-derived secretome can enhance tissue regeneration without the safety and ethical limitations of stem cell transplantation. Herein, we developed a fibrin glue topical delivery system loaded with mesenchymal stem cells (MSCs)-derived secretome for controlled delivery of bioactive factors, and evaluated its application potential in improving the healing of intestinal anastomosis. Under in vitro conditions, the MSCs secretome significantly promoted cell proliferation viability in a dose-dependent manner and resulted in the controlled release of growth factors via fibrin glue delivery. We established a rat surgical anastomotic model and experimentally found that MSCs secretome-loaded fibrin glue enhanced anastomotic bursting pressure, increased granulation tissue formation and collagen deposition, and significantly promoted anastomotic healing. Mechanistically, fibrin glue accelerated cell proliferation, angiogenesis, and macrophage M2 polarization at the surgical anastomotic site by releasing bioactive factors in the secretome, and it also alleviated the inflammatory response and cell apoptosis at the anastomotic site. Our results demonstrated for the first time that MSCs-derived secretome could promote the healing of intestinal anastomosis. Considering the accessibility and safety of the cell-free secretome, we believed that secretome-loaded fibrin glue would be a cell-free therapy to accelerate the healing of intestinal anastomosis with great potential for clinical translation.

Long term functional outcome evaluation in post flexor digitorum profundus tendon zone I rupture repaired by palmaris longus tendon grafting augmented with human amniotic membranes and adipose derived mesenchymal stem cell: A case report

INTRODUCTION AND IMPORTANCE

The sport climbing has many complex maneuvers of the hand producing many potential injuries in flexor digitorum profundus tendon (FDPT). The late management due to an athlete high demand on competition makes the complication of retracted tendon and adhesion tend to occur. We provide the long terms functional outcome in FDPT zone I rupture repaired by palmaris longus (PL) tendon grafting augmented with human amniotic (hAM) and adipose derived mesenchymal stem cell (ASCs).

CASE PRESENTATION

We present a case of a 31-years old male sport climbing athlete with excruciating pain in the right middle finger due to an injury at distal phalangeal area occurred two months earlier. Intraoperatively, Bruner's incision was performed for exploration. A modified Kessler suture technique with running sutures around the sutured stump was used. We slightly overcorrected tension between PL and FDPT distal stumps. We shielded the distal and proximal sutured areas with hAM augmented with ASCs. The result was remarkable as he could return to competitive sport.

CLINICAL DISCUSSION

Zones I and II have a high adhesion risk due to their complex structures. In the case of the PL tendon graft, the sutured stump lies in these zones which can affect outcomes. An HAM augmented with ASCs has an anti-adhesive property that allows smooth gliding of the tendon FDPT on two sutured stump junctions, as well as stimulating the tendon to produce tenocytes, which accelerates tendon healing.

CONCLUSION

The combination of our technique and regenerative therapy effectively prevents adhesions and modulates tendon healing.

Recent advances in tendon tissue engineering strategy

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

Efficacy of Adipose-Derived Mesenchymal Stem Cells and Stromal Vascular Fraction Alone and Combined to Biomaterials in Tendinopathy or Tendon Injury: Systematic Review of Current Concepts

Background and Objectives: Tendon injury and tendinopathy are among the most frequent musculoskeletal diseases and represent a challenging issue for surgeons as well as a great socio-economic global burden. Despite the current treatments available, either surgical or conservative, the tendon healing process is often suboptimal and impaired. This is due to the inherent scarce ability of tendon tissue to repair and return itself to the original structure. Recently, Adipose-derived mesenchymal stem cells (ADSC) and stromal vascular fraction (SVF) have gained a central interest in the scientific community, demonstrating their effectiveness in treatments of acute and chronic tendon disorders in animals and humans. Either enzymatic or mechanical procedures to obtain ADSC and SVF have been described and used in current clinical practice. However, no unified protocols and processes have been established. Materials and Methods: This systematic review aims at providing a comprehensive update of the literature on the clinical application of ADSC enzymatically or mechanically processed to obtain SVF, alone and in association with biomaterials in the local treatment of tendinopathy and tendon injury in vivo, in animal models and humans. The study was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Results: Thirty-two articles met our inclusion criteria, with a total of 18 studies in animals, 10 studies in humans and 4 studies concerning the application of biomaterials in vivo in animals. The review of the literature suggests that ADSC/SVF therapy can represent a promising alternative in tendonregenerative medicine for the enhancement of tendon healing. Conclusions: Nevertheless, further investigations and randomized control trials are needed to improve the knowledge, standardize the procedures and extend the consensus on their use for such applications.

Human adipose-derived stem cells can optimize the filling material in rats

BACKGROUND

Human adipose-derived stem cells have been identified as a promising candidate for cell-assisted therapy to improve graft survival.

OBJECTIVE

To objective of the study was to add human adipose-derived stem cells into filling materials.

METHODS

The filling materials were prepared and divided into 6 groups: fat particles with phosphate buffer saline or human adipose-derived stem cells; acellular dermal matrix particles with phosphate buffer saline or human adipose-derived stem cells; mixture of fat particles and acellular dermal matrix particles with phosphate buffer saline or human adipose-derived stem cells. The survival rate, vascular density and histological at 2, 6 and 12 weeks were investigated.

RESULTS

Human adipose-derived stem cells significantly improved survival rate in each group at 6 and 12 weeks, and it significantly increased the vascular density in the fat particles and porcine acellular dermal matrix combined group and porcine acellular dermal matrix group at three time points, but human adipose-derived stem cells did not have a significant effect in the fat particles group.

CONCLUSION

Human adipose-derived stem cells as assisted cells added into filling material can improve survival rate and vascular density in rats.

The roles and therapeutic potentialof mesenchymal stem/stromal cells and their extracellular vesicles in tendinopathies

Tendinopathies encompass a highly prevalent, multi-faceted spectrum of disorders, characterized by activity-related pain, compromised function, and propensity for an extended absence from sport and the workplace. The pathophysiology of tendinopathy continues to evolve. For decades, it has been related primarily to repetitive overload trauma but more recently, the onset of tendinopathy has been attributed to the tissue's failed attempt to heal after subclinical inflammatory and immune challenges (failed healing model). Conventional tendinopathy management produces only short-term symptomatic relief and often results in incomplete repair or healing leading to compromised tendon function. For this reason, there has been increased effort to develop therapeutics to overcome the tissue's failed healing response by targeting the cellular metaplasia and pro-inflammatory extra-cellular environment. On this basis, stem cell-based therapies have been proposed as an alternative therapeutic approach designed to modify the course of the various tendon pathologies. Mesenchymal stem/stromal cells (MSCs) are multipotent stem cells often referred to as "medicinal signaling cells" due to their immunomodulatory and anti-inflammatory properties that can produce a pro-regenerative microenvironment in pathological tendons. However, the adoption of MSCs into clinical practice has been limited by FDA regulations and perceived risk of adverse events upon infusion in vivo. The introduction of cell-free approaches, such as the extracellular vesicles of MSCs, has encouraged new perspectives for the treatment of tendinopathies, showing promising short-term results. In this article, we review the most recent advances in MSC-based and MSC-derived therapies for tendinopathies. Preclinical and clinical studies are included with comment on future directions of this rapidly developing therapeutic modality, including the importance of understanding tissue loading and its relationship to any treatment regimen.

Comparison of ligamentization potential between anterior cruciate ligament-derived cells and adipose-derived mesenchymal stem cells reseeded to acellularized tendon allograft

AIMS

To test the hypothesis that reseeded anterior cruciate ligament (ACL)-derived cells have a better ability to survive and integrate into tendon extracellular matrix (ECM) and accelerate the ligamentization process, compared to adipose-derived mesenchymal stem cells (ADMSCs).

METHODS

Acellularized tibialis allograft tendons were used. Tendons were randomly reseeded with ACL-derived cells or ADMSCs. ACL-derived cells were harvested and isolated from remnants of ruptured ACLs during reconstruction surgery and cultured at passage three. Cell suspensions (200 µl) containing 2 × 106 ACL-derived cells or ADMSCs were prepared for the purpose of reseeding. At days 1, 3, and 7 post-reseeding, graft composites were assessed for repopulation with histological and immunohistochemical analysis. Matrix protein contents and gene expression levels were analyzed.

RESULTS

In the graft reseeded with ACL-derived cells, a large number of elongated cells that integrated into the matrix were evident at day 3 and day 7. However, in the graft reseeded with ADMSCs, only a small number of elongated cells were found integrated into the matrix. Immunofluorescence for Ki-67 and type I collagen confirmed the pronounced production of type I collagen by Ki-67-positive ACL-derived cells integrated into the ECM. A messenger RNA (mRNA) expression assay demonstrated significantly higher gene expression levels of types I (p = 0.013) and III (p = 0.050) collagen in the composites reseeded with ACL-derived cells than ADMSCs.

CONCLUSION

ACL-derived cells, when reseeded to acellularized tendon graft, demonstrated earlier better survival and integration in the tendon ECM and resulted in higher gene expression levels of collagen, which may be essential to the normal ligamentization process compared to ADMSCs.Cite this article: Bone Joint Res 2022;11(11):777-786.

Quantitative analysis of tendon histopathology using digital pathology in rat models with Achilles tendon injury

Although digital image analysis methods that quantify histopathologic features have emerged, no validated quantitative methods are available to evaluate tendon injury. This study aimed to propose and validate a quantitative analysis method to identify the histopathologic features of tendon injuries. The histopathologic features of two Achilles tendon injury models (a partial full-thickness defect model and a collagenase injection model) using Sprague-Dawley rats were evaluated by semiquantitative grading and a quantitative analysis method using a digital pathology software at weeks 1 and 4 after tendon injury (six tendons per group at each time point). The outcome variables between tendon injury models and between time points were compared, and the correlation between semiquantitative scores and the results of the quantitative analysis was investigated. The proposed analysis method quantified the severity of the histopathological features after tendon injury. Quantitative analysis differentiated the cell morphology between tendon injury models and time points better than semiquantitative scoring. The results from quantitative measurements correlated significantly with the semiquantitative scores. The proposed quantitative method can be effective in evaluating the histopathology of tendon injuries.

Cell therapy efficacy and safety in treating tendon disorders: a systemic review of clinical studies

Purpose

Despite substantial animal evidence, cell therapy in humans remains in its infancy. The purpose of this study was to examine the potential therapeutic effects and safety of cell therapy in the treatment of tendon disorders.

Methods

According to the PRISMA guideline, a systematic review was performed on clinical studies concerning cell therapy in tendon disorders. A comprehensive search including the 5 databases of MEDLINE, Embase, Scopus, Web of Science, and Cochrane Library until December 2021 was carried out and associated with hand searching. The quality of the eligible studies was assessed using the tools suggested by Cochrane recommendations. Qualitative synthesis was performed in 2 tables and discussed separately for rotator cuff, elbow, patella, Achilles, and gluteal tendons.

Results

Through 6017 records, 22 studies were included in the qualitative synthesis, including 658 patients. All the studies administered autologous cells, except one that used allogenic adipose-derived mesenchymal stem cells (Allogenic AD-MSC). Almost all studies demonstrated the safety of cell injection in their follow-up period with no serious side effects or immunologic reactions, with only a few related minor adverse events in some cases.

The included studies showed the effectiveness of cell injection in tendinopathies of different sites, rotator cuff, elbow, patella, Achilles, and gluteal tendons. Among the rotator cuff studies, 4 comparative studies claimed that cell therapy is a more efficient treatment with a lower retear rate and pain level compared to the control group. However, one study found no differences between the groups. No controlled study has been performed on elbow tendinopathies, but 5 case series demonstrated the effectiveness of cell injection in elbow tendon disorders. For Achilles tendinopathies, only one randomized controlled trial (RCT) found that both cell therapy and control groups showed significant pain reduction and functional improvement with no statistical differences at the 6 months follow-up, but the cell therapy group had improved faster at earlier follow-ups. Patellar tendinopathy was studied in 2 RCTs, one did not show a significant difference and the other showed superior improvement compared to controls.

Conclusion

Cell therapy showed promising results and the available evidence suggests that it is safe at several sites of tendon disease. Based on available evidence, cell therapy should be suggested in specific conditions at each site. To approve cell therapy for tendon diseases, randomized clinical trials are required with a large sample size and long-term follow-ups.

Level of evidence

IV

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-022-00520-9.

Efficacy of Stem Cell Therapy for Tendon Graft Ligamentization After Anterior Cruciate Ligament Reconstruction: A Systematic Review

Background

Sufficient intra-articular graft ligamentization enhances the biomechanical and biological properties of the femur-graft-tibia complex to ensure knee stability after anterior cruciate ligament (ACL) reconstruction using a tendon graft. It remains unclear whether stem cell therapy promotes tendon graft ligamentization.

Purpose/Hypothesis

The purpose of this study was to compare tendon graft ligamentization after primary ACL reconstruction with versus without stem cell therapy. It was hypothesized was that stem cell therapy would promote tendon graft ligamentization by enhancing the biomechanical and histological properties of the tendon graft after ACL reconstruction.

Study Design

Systematic review.

Methods

A systematic review was performed according to the guidelines outlined in the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement to identify controlled animal studies that compared tendon graft ligamentization outcomes after primary ACL reconstruction in groups with and without stem cell therapy. Biomechanical and histological outcomes were assessed.

Results

A total of 4 studies met the eligibility criteria and were included in this review. Bone marrow-derived mesenchymal stem cells were used in 3 studies, while tendon-derived stem cells were used in 1 study. An intra-articular injection was used to deliver conditioned medium and stem cells in 2 studies, while around-graft application was used to deliver bone marrow-derived mesenchymal stem cells in 2 studies. Stem cell therapy enhanced the biomechanical and histological properties of the tendon graft after ACL reconstruction.

Conclusion

This review revealed that stem cell therapy is a promising technique that promotes graft ligamentization by enhancing the biomechanical and histological properties of the tendon graft after ACL reconstruction in animal models. There is a need for future preclinical studies aimed at evaluating the effect of stem cells on graft ligamentization and identifying the optimal method of intra-articular stem cell delivery.

Comparative analysis of Achilles tendon healing outcomes after open tenotomy versus percutaneous tenotomy: An experimental study in rats

There is growing interest in conservative treatment of Achilles tendon rupture. However, the majority of experimental studies of Achilles tendon have been performed by open tenotomy. More appropriate model of conservative treatment of Achilles tendon rupture is required. We performed an experimental study to evaluate whether outcomes differ between open tenotomy and percutaneous tenotomy of the Achilles tendon in rats. The Achilles tendons of 48 rats were transected. The animals were divided into two groups according to surgical technique: open tenotomy or microscopy-assisted percutaneous tenotomy. After 1, 2, and 4 weeks, functional, biomechanical, and histological analyses were performed. Western blot was performed for quantitative molecular analysis at 1 week. The Achilles functional index was superior in the percutaneous tenotomy group, compared with the open tenotomy group, at 1 week. The cross-sectional area was significantly larger in the percutaneous tenotomy group than in the open tenotomy group at 4 weeks. Relative to the native tendons, load to failure and stiffness yielded comparable results at 2 weeks in the percutaneous tenotomy group and at 4 weeks in the open tenotomy group. The histological score was significantly better in the percutaneous tenotomy group than in the open tenotomy group at 1 week. At 1 week, interleukin-1β expression in the open tenotomy group was higher than in the percutaneous tenotomy group. In summary, Achilles tendon healing was substantially affected by the tenotomy method. We presume that our percutaneous tenotomy method might constitute a useful experimental animal model for conservative treatment of Achilles tendon rupture.

Insulin-Functionalized Bioactive Fiber Matrices with Bone Marrow-Derived Stem Cells in Rat Achilles Tendon Regeneration

Approximately half of annual musculoskeletal injuries in the US involve tendon tears. The naturally hypocellular and hypovascular tendon environment makes tendons injury-prone and heal slowly. Tendon tissue engineering strategies often use biomimetic scaffolds combined with bioactive factors and/or cells to enhance healing. FDA-approved growth factors to promote tendon healing are lacking, which highlights the need for safe and effective bioactive factors. Our previous work evaluated insulin as a bioactive factor and identified an optimal dose to promote in vitro mesenchymal stem cell survival, division, and tenogenesis. The present work evaluates the ability of insulin-functionalized electrospun nanofiber matrices with or without mesenchymal stem cells to enhance tendon repair in a rat Achilles injury model. Electrospun nanofiber matrices were functionalized with insulin, cultured with or without mesenchymal stem cells, and sutured to transected Achilles tendons in rats. We analyzed rat tendons 4 and 8 weeks after surgery for the tendon morphology, collagen production, and mechanical properties. Bioactive insulin-functionalized fiber matrices with mesenchymal stem cells resulted in significantly increased collagen I and III at 4 and 8 weeks postsurgery. Additionally, these matrices supported highly aligned collagen fibrils in the regenerated tendon tissue at 8 weeks. However, treatment- and control-regenerated tissues had similar tensile properties at 8 weeks, which were less than that of the native Achilles tendon. Our preliminary results establish the benefits of insulin-functionalized fiber matrices in promoting higher levels of collagen synthesis and alignment needed for functional recovery of tendon repair.

The effects of orthobiologics in the treatment of tendon pathologies: a systematic review of preclinical evidence

Purpose

The aim of this systematic review is to explore the current available knowledge about tendon disorders and orthobiologics derived by preclinical experiments to evaluate their role and efficacy in the different stages and conditions related to the tendon healing processes.

Methods

The systematic review was performed according to the PRISMA guidelines. Different electronic databases (MEDLINE, Web of Science, EMBASE) were searched for studies investigating orthobiologics (PRP and cell-based products from adipose tissue or bone marrow) in animal models or veterinary clinical trials for tendon pathologies (complete/partial tendon ruptures, rotator cuff tears, tendinopathy, enthesis-related injuries). Data regarding the specific product used, the treatment site/pathology, the host and the model were collected. The results were classified into the following categories: histological, biomechanical, molecular and imaging.

Results

A large pool of preclinical studies on tendon disorders have been found on platelet-rich plasma (PRP), while data about stromal vascular fraction (SVF) and bone marrow concentrate (BMAC) are still limited and frequently focused on expanded cells, rather than orthobiologics prepared at the point of care.

The effect of PRP is related to an acceleration of the healing process, without improvements in the final structure and properties of repaired tendon. Cell-based products have been reported to produce more durable results, but the level of evidence is currently insufficient to draw clear indications.

Conclusions

The preclinical results about orthobiologics applications to tendon pathologies would support the rationale of their clinical use and encourage the performance of clinical trials aimed to confirm these data in human subjects.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40634-022-00468-w.

Assembled Cell-Decorated Collagen (AC-DC) Fiber Bioprinted Implants with Musculoskeletal Tissue Properties Promote Functional Recovery in Volumetric Muscle Loss

Musculoskeletal tissue injuries, including volumetric muscle loss (VML), are commonplace and often lead to permanent disability and deformation. Addressing this healthcare need, an advanced biomanufacturing platform, assembled cell-decorated collagen (AC-DC) bioprinting, is invented to rapidly and reproducibly create living biomaterial implants, using clinically relevant cells and strong, microfluidic wet-extruded collagen microfibers. Quantitative analysis shows that the directionality and distribution of cells throughout AC-DC implants mimic native musculoskeletal tissue. AC-DC bioprinted implants further approximate or exceed the strength and stiffness of human musculoskeletal tissue and exceed collagen hydrogel tensile properties by orders of magnitude. In vivo, AC-DC implants are assessed in a critically sized muscle injury in the hindlimb, with limb torque generation potential measured over 12 weeks. Both acellular and cellular implants promote functional recovery compared to the unrepaired group, with AC-DC implants containing therapeutic muscle progenitor cells promoting the highest degree of recovery. Histological analysis and automated image processing of explanted muscle cross-sections reveal increased total muscle fiber count, median muscle fiber size, and increased cellularization for injuries repaired with cellularized implants. These studies introduce an advanced bioprinting method for generating musculoskeletal tissue analogs with near-native biological and biomechanical properties with the potential to repair myriad challenging musculoskeletal injuries.

Gut microbiota is involved in the antidepressant effects of adipose-derived mesenchymal stem cells in chronic social defeat stress mouse model

RATIONALE

Growing evidence supports the role of microbiota in regulating gut-brain interactions and, thus, contributing to the pathogenesis of depression and the antidepressant actions. Adipose-derived mesenchymal stem cells (ADSCs), as important members of the stem cell family, were demonstrated to alleviate depression behaviors. However, the role of gut microbiota in ADSCs alleviating depression in chronic social defeat stress (CSDS) model is unknown.

OBJECTIVES

To examine the effects of ADSCs on depression symptoms and detect the changes in the composition of gut microbiota.

RESULTS

We found that ADSCs administration significantly ameliorated CSDS-induced depression behaviors, which was accompanied by alteration in the gut microbiota. The principal co-ordinates analysis (PCoA) results showed that there was a significant difference between the gut microbiota among the groups. Remarkably, receiver operating characteristic (ROC) curves revealed that order Micrococcales, order Rhizobiales and species Bacteroides acidifaciens are potentially important biomarkers for the antidepressant effects of ADSCs in CSDS model.

CONCLUSIONS

ADSCs are effective in treating depression behaviors in CSDS model, which might be partly due to the regulation of abnormal composition of gut microbiota. Thus, ADSCs offer a promising therapeutic strategy for treating depression in patients.

A randomized controlled trial of stem cell injection for tendon tear

Tendons have limited reparative ability and perform a relatively simple mechanical function via the extracellular matrix. Thus, the injured tendon might be treated successfully by stem cell transplantation. We performed a randomized, controlled study to investigate the effects of mesenchymal stem cell injection for treating partial tears in the supraspinatus tendon. We enrolled 24 patients with shoulder pain lasting more than 3 months and partial tears in the supraspinatus tendon. Participants were assigned to three groups: stem cells in fibrin glue, normal saline/fibrin glue mixture, and normal saline only, with which intra-lesional injection was performed. Pain at activity and rest, shoulder function and tear size were evaluated. For safety measures, laboratory tests were taken and adverse events were recorded at every visit. Participants were followed up at 6, 12 weeks, 6, 12 months and 2 years after injection. The primary outcome measure was the improvement in pain at activity at 3 months after injection. Twenty-three patients were included in the final analysis. Primary outcome did not differ among groups (p = 0.35). A mixed effect model revealed no statistically significant interactions. Only time significantly predicted the outcome measure. All participants reported transient pain at the injection site. There were no differences in post-injection pain duration or severity. Safety measures did not differ between groups, and there were no persistent adverse events. Stem cell injection into supraspinatus partial tears in patients with shoulder pain lasting more than 3 months was not more effective than control injections.ClinicalTrials.gov Identifier: NCT02298023.

Adipose micro-grafts enhance tendinopathy healing in ovine model: An in vivo experimental perspective study

In Europe, approximatively 100 000 to 500 000 tendon repairs are performed every year. These procedures are associated with a considerable rate of postoperative complications (from 6% to 11%). Autologous micro-grafts (AAMG) and stromal vascular fraction (SVF) have been shown to improve tendon healing in 60% to 70% of treated rodents. The purpose of this study was to evaluate the effects of AAMG in a sheep model with tendinopathy. We used sheep models because, as a large animal, they are more comparable to humans. The hypothesis was that SVF injection would improve tendon healing compared with the control group, reducing inflammatory and matrix degrading, while increasing anti-inflammatory expression and collagen synthesis in the early stage of tendon injury. Sixteen Apennine sheep aged 2 to 5 years underwent 500 UI type I collagenase injection into both common calcaneal tendons (CCT) to induce tendinopathy. After 15 days (T0), one CCT in every ovine underwent randomly to 2.5 mL of AAMG obtained by mechanical disruption and the contralateral CCTs received no treatment. Clinical, ecographic, and sonographic evaluations were performed after 4 weeks (T1) and 8 weeks (T2). Histological, immunohistochemical, real-time polymerase chain reaction (RT-PCR), and biomechanical evaluations were performed at T2. At T2, the treated group showed a final tendon diameter (9.1 ± 1.4 mm) and a hardness expression (62%) that were similar to the original healthy tendon (8.1 ± 1.1 mm; 100%), with a significant recovery compared with the control group (9.5 ± 1.7 mm; 39%). Moreover, histological analysis of the treated group revealed an improvement in the fiber orientation score, fiber edema score, infiltrative-inflammatory process, and necrosis score (4.3 ± 3.3) compared with control group (8.8 ± 2.9). Immunohistochemically, the treated group showed high expression of collagen 1, Factor VIII and significantly low expression of collagen 3. These data were confirmed by RT-PCR analysis. The study findings suggested that AAMGs obtained through mechanical disruption present a safe, efficient, and reliable technique, enhancing tendon healing.

Mesenchymal Stem Cells Use in the Treatment of Tendon Disorders: A Systematic Review and Meta-Analysis of Prospective Clinical Studies

Objective

To evaluate the efficacy and safety of mesenchymal stem cells (MSCs) therapy in patients with tendon disorders enrolled in prospective clinical studies.

Methods

We systematically searched prospective clinical studies that investigated the effects of MSC administration on human tendon disorders with at least a 6-month follow-up period in the PubMed-MEDLINE, EMBASE, and Cochrane Library databases. The primary outcome of interest was the change in pain on motion related to tendon disorders. Meta-regression analyses were performed to assess the relationship between MSC dose and pooled effect sizes in each cell dose.

Results

Four prospective clinical trials that investigated the effect of MSCs on tendon disorders were retrieved. MSCs showed a significant pooled effect size (overall Hedges’ g pooled standardized mean difference=1.868; 95% confidence interval, 1.274–2.462; p<0.001). The treatment with MSCs improved all the aspects analyzed, namely pain, functional scores, radiological parameters (magnetic resonance image or ultrasonography), and arthroscopic findings. In the meta-regression analysis, a significant cell dose-dependent response in pain relief (Q=9.06, p=0.029) was observed.

Conclusion

Our meta-analysis revealed that MSC therapy may improve pain, function, radiological, and arthroscopic parameters in patients with tendon disorders. A strong need for large-scale randomized controlled trials has emerged to confirm the long-term functional improvement and adverse effects of MSC therapies in tendon disorders.

MicroRNA engineered umbilical cord stem cell-derived exosomes direct tendon regeneration by mTOR signaling

Background

Exosomes are extracellular vesicles of nano-structures and represent an emerging nano-scale acellular therapy in recent years. Tendon regeneration is a sophisticated process in the field of microsurgery due to its poor natural healing ability. To date, no successful long-term solution has been provided for the healing of tendon injuries. Functional recovery requires advanced treatment strategies. Human umbilical cord mesenchymal stem cell-derived exosomes (HUMSC-Exos) are considered as promising cell-free therapeutic agents. However, few studies reported their potential in the tendon repair previously. In this study, we explored the roles and underlying mechanisms of HUMSC-Exos in the tendon regeneration.

Results

Expression of tendon‐specific markers in, and collagen deposition by, tendon-derived stem cells (TDSCs) treated with HUMSC-Exos increased in vitro. In a rat Achilles tendon injury model, treatment with HUMSC-Exos improved the histological structure, enhanced tendon-specific matrix components, and optimized biomechanical properties of the Achilles tendon. Findings in miRNA sequencing indicated a significant increase in miR-29a-3p in HUMSC-Exo-treated Achilles tendons. Next, luciferase assay in combination with western blot identified phosphatase and tensin homolog (PTEN) as the specific target of miR-29a-3p. Furthermore, we applied a miR-29a-3p-specific agonist to engineer HUMSC-Exos. These HUMSC-Exos overexpressing miR-29a-3p amplified the gain effects of HUMSC-Exos on tendon healing in vivo. To explore the underlying mechanisms, a transforming growth factor-β1 (TGF-β1) inhibitor (SB-431542), mTOR inhibitor (rapamycin), and engineered HUMSC-Exos were employed. The results showed that TGF-β1 and mTOR signaling were involved in the beneficial effects of HUMSC-Exos on tendon regeneration.

Conclusion

The findings in our study suggest that PTEN/mTOR/TGF-β1 signaling cascades may be a potential pathway for HUMSC-Exos to deliver miR-29a-3p for tendon healing and implicate a novel therapeutic strategy for tendon regeneration via engineered stem cell-derived exosomes.

Graphic abstract

Hepatocyte Growth Factor-Induced Tendon Stem Cell Conditioned Medium Promotes Healing of Injured Achilles Tendon

Tendon repair is a medical challenge. Our present study investigated the effectiveness of acellular therapy consisting of conditioned medium (CM) of tendon stem cells (TSCs) induced with hepatocyte growth factor (HGF) in promoting the healing of injured Achilles tendon in a rat model. Proteomic analysis of soluble substances in the CM was performed using an array chip, and bioinformatic analysis was carried out to evaluate interactions among the factors. The effects of CM on viability and migratory capacity of tendon fibroblasts derived from rats with ruptured Achilles tendon were evaluated with the Cell Counting Kit 8 and wound healing assay, respectively. The expression of extracellular matrix (ECM)-related protein was assessed by western blotting. Rats with Achilles tendon injury were treated with CM by local injection for 2 weeks, and the organization of tendon fibers at the lesion site was evaluated by hematoxylin and eosin and Masson's trichrome staining of tissue samples. The deposition and degradation of ECM proteins and the expression of inflammatory factors at the lesion site were evaluated by immunohistochemistry and immunofluorescence. Biomechanical testing was carried out on the injured tendons to assess functional recovery. There were 12 bioactive molecules in the CM, with HGF as the hub of the protein-protein interaction network. CM treatment enhanced the viability and migration of tendon fibroblasts, altered the expression of ECM proteins, promoted the organization of tendon fibers, suppressed inflammation and improved the biomechanics of the injured Achilles tendon. These results suggest that HGF stimulates the secretion of soluble secretory products by TSCs and CM promotes the repair and functional recovery of ruptured Achilles tendon. Thus, HGF-induced TSC CM has therapeutic potential for the treatment of tendinopathy.

The Effect of L-Ascorbic Acid and Serum Reduction on Tenogenic Differentiation of Human Mesenchymal Stromal Cells

Background and Objectives

Despite significant improvement in the treatment of tendon injuries, the full tissue recovery is often not possible because of its limited ability to auto-repair. The transplantation of mesenchymal stromal cells (MSCs) is considered as a novel approach in the treatment of tendinopathies. The question about the optimal culture conditions remains open. In this study we aimed to investigate if serum reduction, L-ascorbic acid supplementation or a combination of both factors can induce tenogenic differentiation of human adipose-derived MSCs (ASCs).

Methods and Results

Human ASCs from 3 healthy donors were used in the study. The tested conditions were: 0.5 mM of ascorbic acid 2-phosphate (AA-2P), reduced serum content (2% FBS) or combination of these two factors. The combination of AA-2P and 2% FBS was the only experimental condition that caused a significant increase of the expression of all analyzed genes related to tenogenesis (SCLERAXIS, MOHAWK, COLLAGEN_1, COLLAGEN_3, DECORIN) in comparison to the untreated control (evaluated by RT-PCR, 5^th day of experiment). Moreover, this treatment significantly increased the synthesis of SCLERAXIS, MOHAWK, COLLAGEN_1, COLLAGEN_3 proteins at the same time point (evaluated by Western blot method). Double immunocytochemical staining revealed that AA-2P significantly increased the extracellular deposition of both types of collagens. Semi-quantitative Electron Spin Resonance analysis of ascorbyl free radical revealed that AA-2P do not induce harmful transition metals-driven redox reactions in cell culture media.

Conclusions

Obtained results justify the use of reduced content of serum with the addition of 0.5 mM of AA-2P in tenogenic inducing media.

Conditioned medium of human bone marrow-derived stem cells promotes tendon-bone healing of the rotator cuff in a rat model

Rotator cuff repair is a common surgery in sports medicine. During the surgery, torn tendon was re-fixed onto the bony surface. The majority of patients gain good results. However, re-tear occurs in some patients. The reason under this phenomenon is that the normal tendon-bone enthesis cannot be reconstructed. In order to strengthen the tendon-bone healing and promote enthesis regeneration, numerous manners are tested, among which stem cell related therapies are preferred. Stem cells, due to the ability of multi-lineage differentiation, are widely used in regenerative medicine. However, safety and ethics concerns limit its clinical use. Recent studies found that it is the secretome of stem cells that is biologically effective. On ground of this, we, in the current study, collected the conditioned medium of human bone marrow-derived stem cells (hBMSC-CM) and tested whether this acellular method could promote tendon-bone healing in a rat model of rotator cuff repair. By using histological, radiological, and biomechanical methods, we found that hBMSC-CM promoted tendon-bone healing of the rat rotator cuff. Then, we noticed that hBMSC-CM exerted an impact on macrophage polarization both in vivo and in vitro by inhibiting M1 phenotype and promoting M2 phenotype. Further, we proved that the benefit of hBMSC-CM on tendon-bone healing was related to its regulation on macrophage. Finally, we proved that, hBMSC-CM influenced macrophage polarization, which was, at least partially, related to Smad2/3 signaling pathway. Based on the experiments above, we confirmed the benefit of hBMSC-CM on tendon-bone healing, which relied on its immune-regulative property. Considering the accessibility and safety of acellular hBMSC-CM, we believe it is a promising candidate clinically for tendon-bone healing.

Interactions Between Allogeneic Mesenchymal Stromal Cells and the Recipient Immune System: A Comparative Review With Relevance to Equine Outcomes

Despite significant immunosuppressive activity, allogeneic mesenchymal stromal cells (MSCs) carry an inherent risk of immune rejection when transferred into a recipient. In naïve recipients, this immune response is initially driven by the innate immune system, an immediate reaction to the foreign cells, and later, the adaptive immune system, a delayed response that causes cell death due to recognition of specific alloantigens by host cells and antibodies. This review describes the actions of MSCs to both suppress and activate the different arms of the immune system. We then review the survival and effectiveness of the currently used allogeneic MSC treatments.

Regeneration of a full-thickness defect in rotator cuff tendon with umbilical cord-derived mesenchymal stem cells in a rat model

Although rotator cuff disease is a common cause of shoulder pain, there is still no treatment method that could halt or reveres its development and progression. The purpose of this study was to investigate the efficacy of umbilical cord-derived mesenchymal stem cells (UC MSCs) on the regeneration of a full-thickness rotator cuff defect (FTD) in a rat model. We injected either UC MSCs or saline to the FTD and investigated macroscopic, histological and biomechanical results and cell trafficking. Treatment with UC MSCs improved macroscopic appearance in terms of tendon thickness at two weeks, and inflammation, defect size, swelling/redness and connection surrounding tissue and slidability at four weeks compared to the saline group. Histologically, UC MSCs induced the tendon matrix formation recovering collagen organization, nuclear aspect ratio and orientation angle of fibroblast as well as suppressing cartilage-related glycosaminoglycan compared to saline group at four weeks. The UC MSCs group also improved ultimate failure load by 25.0% and 19.0% and ultimate stress by 27.3% and 26.8% at two and four weeks compared to saline group. UC MSCs labeled with PKH26 exhibited 5.3% survival at four weeks compared to three hours after injection. This study demonstrated that UC MSCs regenerated the FTD with tendon tissue similar properties to the normal tendon in terms of macroscopic, histological and biomechanical characteristics in a rat model.

Mechanisms of action of neuropeptide Y on stem cells and its potential applications in orthopaedic disorders

Musculoskeletal disorders are the leading causes of disability and result in reduced quality of life. The neuro-osteogenic network is one of the most promising fields in orthopaedic research. Neuropeptide Y (NPY) system has been reported to be involved in the regulations of bone metabolism and homeostasis, which also provide feedback to the central NPY system via NPY receptors. Currently, potential roles of peripheral NPY in bone metabolism remain unclear. Growing evidence suggests that NPY can regulate biological actions of bone marrow mesenchymal stem cells, hematopoietic stem cells, endothelial cells, and chondrocytes via a local autocrine or paracrine manner by different NPY receptors. The regulative activities of NPY may be achieved through the plasticity of NPY receptors, and interactions among the targeted cells as well. In general, NPY can influence proliferation, apoptosis, differentiation, migration, mobilization, and cytokine secretion of different types of cells, and play crucial roles in the development of bone delayed/non-union, osteoporosis, and osteoarthritis. Further basic research should clarify detailed mechanisms of action of NPY on stem cells, and clinical investigations are also necessary to comprehensively evaluate potential applications of NPY and its receptor-targeted drugs in management of musculoskeletal disorders.

Mechanotransduction of stem cells for tendon repair

Tendon is a mechanosensitive tissue that transmits force from muscle to bone. Physiological loading contributes to maintaining the homeostasis and adaptation of tendon, but aberrant loading may lead to injury or failed repair. It is shown that stem cells respond to mechanical loading and play an essential role in both acute and chronic injuries, as well as in tendon repair. In the process of mechanotransduction, mechanical loading is detected by mechanosensors that regulate cell differentiation and proliferation via several signaling pathways. In order to better understand the stem-cell response to mechanical stimulation and the potential mechanism of the tendon repair process, in this review, we summarize the source and role of endogenous and exogenous stem cells active in tendon repair, describe the mechanical response of stem cells, and finally, highlight the mechanotransduction process and underlying signaling pathways.

Implementation of Endogenous and Exogenous Mesenchymal Progenitor Cells for Skeletal Tissue Regeneration and Repair

Harnessing adult mesenchymal stem/progenitor cells to stimulate skeletal tissue repair is a strategy that is being actively investigated. While scientists continue to develop creative and thoughtful ways to utilize these cells for tissue repair, the vast majority of these methodologies can ultimately be categorized into two main approaches: (1) Facilitating the recruitment of endogenous host cells to the injury site; and (2) physically administering into the injury site cells themselves, exogenously, either by autologous or allogeneic implantation. The aim of this paper is to comprehensively review recent key literature on the use of these two approaches in stimulating healing and repair of different skeletal tissues. As expected, each of the two strategies have their own advantages and limitations (which we describe), especially when considering the diverse microenvironments of different skeletal tissues like bone, tendon/ligament, and cartilage/fibrocartilage. This paper also discusses stem/progenitor cells commonly used for repairing different skeletal tissues, and it lists ongoing clinical trials that have risen from the implementation of these cells and strategies. Lastly, we discuss our own thoughts on where the field is headed in the near future.

Alleviation of medial meniscal transection-induced osteoarthritis pain in rats by human adipose derived mesenchymal stem cells

Knee osteoarthritis (KOA) is a degenerative joint disorder manifested with deformity, pain, and functional disability due to damage of the articular cartilage. Cell therapy with mesenchymal stem cells (MSCs) holds great promise to alleviate or even cure the degenerative diseases including KOA. However, the evidence of efficacy of human adipose tissue-derived MSCs (hAdMSCs) on KOA therapy remains limited. Here, we evaluate the therapeutic efficacy of hAdMSCs for KOA, using a medial meniscal transection (MMT) rat model. Our study demonstrated that intra-articular injection of 1.25×10⁶ hAdMSCs significantly attenuated MMT-induced joint pain in a KOA rats model. The results of this study provide strong evidence that hAdMSCs-based therapy can be regarded as a prominent treatment option for patients with KOA.

Adipose-derived stem cells improve tendon repair and prevent ectopic ossification in tendinopathy by inhibiting inflammation and inducing neovascularization in the early stage of tendon healing

INTRODUCTION

Achilles tendinopathy is characterized by scar formation or ectopic ossification, both of which result in pain and worsened physical function in athletes and older people. Although cell therapy using adipose-derived stem cells (ASCs) has been shown to be effective for tendinopathy, the underlying mechanisms by which ASCs result in tendon healing in vivo have not yet been fully clarified.

METHODS

ASCs were obtained from the fat pads of EGFP transgenic mice by collagenase digestion. C57BL/6 mice were used in a collagenase-induced injury model. ASCs were transplanted into injury sites at 1 week after injury. Tendons were harvested at 9 days, 2 weeks, and 4 weeks after transplantation, and analyzed by histological examination and μCT scanning.

RESULTS

Histological analysis and μCT scanning revealed greater recovery of collagen fibers and suppression of ectopic ossification in the ASC-treated group than in the control group at 2 and 4 weeks after injury. Immunohistochemical analysis identified transplanted ASCs in the tendon core close to peritenon and connective tissue at 2 days and 1 week after transplantation, but not at 3 weeks. Furthermore, while the expression levels of IL-1β, GLUT1, and CA9 were significantly reduced in the ASC group compared to the control group at 9 days after injury, those of VEGF and the number of CD31 positive vessels were significantly increased.

CONCLUSION

The efficacy of ASCs for tendon repair and the prevention of ectopic ossification in Achilles tendinopathy were demonstrated. Our data suggest that ASCs can modulate inflammation and induce neovascularization in the early stage of tendon injury.

Adipose-Derived Mesenchymal Stem Cell Treatments and Available Formulations

PURPOSE OF REVIEW

The use of human adipose-derived mesenchymal stem cells (ADSCs) has gained attention due to its potential to expedite healing and the ease of harvesting; however, clinical evidence is limited, and questions concerning optimal method of delivery and long-term outcomes remain unanswered.

RECENT FINDINGS

Administration of ADSCs in animal models has been reported to aid in improved healing benefits with enhanced repair biomechanics, superior gross histological appearance of injury sites, and higher concentrations of growth factors associated with healing compared to controls. Recently, an increasing body of research has sought to examine the effects of ADSCs in humans. Several available processing techniques and formulations for ADSCs exist with evidence to suggest benefits with the use of ADSCs, but the superiority of any one method is not clear. Evidence from the most recent clinical studies available demonstrates promising outcomes following treatment of select musculoskeletal pathologies with ADSCs despite reporting variability among ADSCs harvesting and processing; these include (1) healing benefits and pain improvement for rotator cuff and Achilles tendinopathies, (2) improvements in pain and function in those with knee and hip osteoarthritis, and (3) improved cartilage regeneration for osteochondral focal defects of the knee and talus. The limitation to most of this literature is the use of other therapeutic biologics in combination with ADSCs. Additionally, many studies lack control groups, making establishment of causation inappropriate. It is imperative to perform higher-quality studies using consistent, predictable control populations and to standardize formulations of ADSCs in these trials.

Optimization of tenocyte lineage-related factors from tonsil-derived mesenchymal stem cells using response surface methodology

BACKGROUND

In order to optimize the tenogenic differentiation of mesenchymal stem cells (MSCs), researchers should consider various factors. However, this requires testing numerous experimental settings, which is costly and time-consuming. We aimed to assess the differential effects of transforming growth factor beta-3 (TGF-β3) on the tenogenesis of tonsil-derived MSCs (T-MSCs) and bone marrow-derived MSCs (BM-MSCs) using response surface methodology (RSM).

METHODS

Bone marrow and tonsillar tissue were collected from four patients; mononuclear cells were separated and treated with 5 or 10 ng/mL of TGF-β3. A full factorial experimental design with a categorical factor of 0 was employed to study the effect of tension based on T-MSCs. Eighty-four trials were fitted with RSM and then used to obtain mathematical prediction models.

RESULTS

Exposure of T-MSCs and BM-MSCs to TGF-β3 increased the expression of scleraxis (SCX), tenomodulin (TNMD), decorin, collagen I, and tenascin C. Expression of most of these factors reached a maximum after 2-3 days of treatment. The model predicted that the values of the tenocyte lineage-related factors assessed would be significantly increased at 2.5 days of culture with 2.7 ng/mL of TGF-β3 for T-MSCs and at 2.3 days of culture regardless of TGF-β3 concentration for BM-MSCs.

CONCLUSIONS

This study demonstrated that the RSM prediction of the culture time necessary for the tenogenic differentiation of T-MSCs and BM-MSCs under TGF-β3 stimulation was similar to the experimentally determined time of peak expression of tenocyte-related mRNAs, suggesting the potential of using the RSM approach for optimization of the culture protocol for tenogenesis of MSCs.

Tendon and Ligament Healing and Current Approaches to Tendon and Ligament Regeneration

Ligament and tendon injuries are common problems in orthopedics. There is a need for treatments that can expedite nonoperative healing or improve the efficacy of surgical repair or reconstruction of ligaments and tendons. Successful biologically-based attempts at repair and reconstruction would require a thorough understanding of normal tendon and ligament healing. The inflammatory, proliferative, and remodeling phases, and the cells involved in tendon and ligament healing will be reviewed. Then, current research efforts focusing on biologically-based treatments of ligament and tendon injuries will be summarized, with a focus on stem cells endogenous to tendons and ligaments. Statement of clinical significance: This paper details mechanisms of ligament and tendon healing, as well as attempts to apply stem cells to ligament and tendon healing. Understanding of these topics could lead to more efficacious therapies to treat ligament and tendon injuries. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:7-12, 2020.

Tendon healing in presence of chronic low-level inflammation: a systematic review

BACKGROUND

Tendinopathy is a common musculoskeletal condition affecting subjects regardless of their activity level. Multiple inflammatory molecules found in ex vivo samples of human tendons are related to the initiation or progression of tendinopathy. Their role in tendon healing is the subject of this review.

SOURCES OF DATA

An extensive review of current literature was conducted using PubMed, Embase and Cochrane Library using the term 'tendon', as well as some common terms of tendon conditions such as 'tendon injury OR (tendon damage) OR tendonitis OR tendinopathy OR (chronic tendonitis) OR tendinosis OR (chronic tendinopathy) OR enthesitis' AND 'healing' AND '(inflammation OR immune response)' as either key words or MeSH terms.

AREAS OF AGREEMENT

An environment characterized by a low level of chronic inflammation, together with increased expression of inflammatory cytokines and growth factors, may influence the physiological tendon healing response after treatment.

AREAS OF CONTROVERSY

Most studies on this topic exhibited limited scientific translational value because of their heterogeneity. The evidence associated with preclinical studies is limited.

GROWING POINTS

The role of inflammation in tendon healing is still unclear, though it seems to affect the overall outcome. A thorough understanding of the biochemical mediators of healing and their pathway of pain could be used to target tendinopathy and possibly guide its management.

AREAS TIMELY FOR DEVELOPING RESEARCH

We require further studies with improved designs to effectively evaluate the pathogenesis and progression of tendinopathy to identify cellular and molecular targets to improve outcomes.

Autologous Microfragmented Adipose Tissue Reduces the Catabolic and Fibrosis Response in an In Vitro Model of Tendon Cell Inflammation

Background

Mesenchymal stem cells (MSCs) emerged as a promising therapy for tendon pathologies. Microfragmented adipose tissue (μFAT) represents a convenient autologous product for the application of MSC-based therapies in the clinical setting. In the present study, the ability of μFAT to counteract inflammatory processes induced by IL-1β on human tendon cells (TCs) was evaluated.

Methods

Cell viability and proliferation were evaluated after 48 hours of transwell coculture of TCs and autologous μFAT in the presence or absence of IL-1β. Gene expression of scleraxis, collagen type I and type III, metalloproteinases-1 and -3, and cyclooxygenase-2 was evaluated by real-time RT-PCR. The content of VEGF, IL-1Ra, TNFα, and IL-6 was evaluated by ELISA.

Results

IL-1β-treated TCs showed augmented collagen type III, metalloproteases, and cyclooxygenase-2 expression. μFAT was able to reduce the expression of collagen type III and metalloproteases-1 in a significant manner, and at the same time, it enhanced the production of VEGF, IL-1Ra, and IL-6.

Conclusions

In this in vitro model of tendon cell inflammation, the paracrine action of μFAT, exerted by anti-inflammatory molecules and growth factors, was able to inhibit the expression of fibrosis and catabolic markers. Then, these results suggest that the application of μFAT may represent an effective conservative or adjuvant therapy for the treatment of tendon disorders.

Reconstruction of Bone Defect Combined with Massive Loss of Periosteum Using Injectable Human Mesenchymal Stem Cells in Biocompatible Ceramic Scaffolds in a Porcine Animal Model

Clinically, in patients who sustain severe open fractures, there is not only a segmental bone defect needed to be reconstructed but also insufficient healing capacity due to concomitant damages to the periosteum and surrounding soft tissues. For studying the reconstruction of bone defects associated with massive loss of periosteum and surrounding soft tissues, there are no well-established preclinical models in large animals in the literature. The purpose of the study was to generate a large animal model of bone defect with massive periosteum loss and to adopt a tissue engineering approach to achieve rapid bony union with stem cells and biomaterials. In this study, a bone defect with massive periosteum stripping was generated in pigs, which was followed by emptying nearby canal marrow including fat and cancellous bone. The stripped periosteum was a mimic to the situation in the Gustilo type 3 open fractures. Bone defects were then reconstructed by impacting the biocompatible ceramic scaffold, morselized tricalcium phosphate (TCP) loaded with human adipose tissue-derived mesenchymal stem cells (hMSCs). Radiological and pathological assessments indicated that TCP and hMSCs synergistically promoted bone healing with increased lamination and ingrowth of vessels. Both bridging periosteum formation and gap filling were induced rapidly. In conclusion, a porcine model of segmental bone loss with damage of surrounding periosteum was created. Reconstruction of such defects with hMSCs and TCP achieved rapid union of bone defects associated with massive periosteal stripping.

The role of biologic agents in the management of common shoulder pathologies: current state and future directions

The field of orthopedic surgery has seen a rapid increase in the use of various biologic agents for the treatment of common musculoskeletal injuries. Most biologic agents attempt to harness or mimic naturally occurring growth factors, cytokines, and anti-inflammatory mediators to improve tissue healing and recovery. The most commonly used biologic agents are platelet-rich plasma and cells derived from bone marrow aspirate and adipose tissue. These agents have become increasingly popular despite a relative dearth of clinical data to support their use. Much confusion exists among patients and physicians in determining the role of these agents in treating common shoulder pathologies, such as glenohumeral osteoarthritis, rotator cuff tears, and tendinopathy. This article reviews the basic science and clinical evidence for the most commonly used biologic agents in the management of common shoulder pathology.

Stretchable ECM Patch Enhances Stem Cell Delivery for Post-MI Cardiovascular Repair

Current cell-based therapies administered after myocardial infarction (MI) show limited efficacy due to subpar cell retention in a dynamically beating heart. In particular, cardiac patches generally provide a cursory level of cell attachment due to the lack of an adequate microenvironment. From this perspective, decellularized cell-derived ECM (CDM) is attractive in its recapitulation of a natural biophysical environment for cells. Unfortunately, its weak physical property renders it difficult to retain in its original form, limiting its full potential. Here, a novel strategy to peel CDM off from its underlying substrate is proposed. By physically stamping it onto a polyvinyl alcohol hydrogel, the resulting stretchable extracellular matrix (ECM) membrane preserves the natural microenvironment of CDM, thereby conferring a biological interface to a viscoelastic membrane. Its various mechanical and biological properties are characterized and its capacity to improve cardiomyocyte functionality is demonstrated. Finally, evidence of enhanced stem cell delivery using the stretchable ECM membrane is presented, which leads to improved cardiac remodeling in a rat MI model. A new class of material based on natural CDM is envisioned for the enhanced delivery of cells and growth factors that have a known affinity with ECM.

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.

Conditioned medium of mesenchymal stem cells delays osteoarthritis progression in a rat model by protecting subchondral bone, maintaining matrix homeostasis, and enhancing autophagy

Evidence accumulated that mesenchymal stem cell (MSC) therapy ameliorated osteoarthritis (OA) via paracrine effect, whereas conditioned medium (CM) of MSCs contains all the secretomes. In vitro studies have proved its therapeutic effect in OA, but few in vivo evidences were unveiled. This study investigated the effect of MSCs-CM in an animal model of OA. OA was induced by anterior cruciate ligament transaction and destabilization of the medial meniscus in 12 rats bilaterally. The CM group (N = 6) was administered with intraarticular injection of MSCs-CM weekly, whereas the phosphate-buffered saline (PBS) group (N = 6) was injected with PBS. Six rats served as normal control and received sham operation with weekly PBS injection. Rats were sacrificed 8 weeks postoperatively. Gross and histological morphology were analysed. Microcomputed tomography was applied to assess the subchondral bone. Components of extracellular matrix (ECM) including type II collagen (Col II) and aggrecan, and ECM homeostasis-related enzymes (metalloproteinase-13 [MMP-13] and tissue inhibitor of metalloproteinase-1 [TIMP-1]), as well as autophagy markers (Beclin-1 and microtubule-associated protein light chain 3) were evaluated immunohistochemically. Chondrocyte apoptosis was measured by terminal deoxynucleotidyl transferase dUTP nick-end labelling staining. Gene expression of Col II, aggrecan, MMP-13, and TIMP-1 was confirmed by real-time polymerase chain reaction. Morphological outcomes demonstrated remarkable articular-protective effect of MSCs-CM. Well-maintained subchondral bone structure, significantly more abundant cartilage matrix, notably decreased ratio of MMP-13 to TIMP-1, and inhibited chondrocyte apoptosis with enhanced autophagy were observed in the CM group compared with the PBS group. In conclusion, MSCs-CM demonstrated satisfactory effect in alleviating OA in rats via protecting the microarchitecture of subchondral bone, balancing the ratio of MMP-13 to TIMP-1 in cartilage, and enhancing autophagy, which might provide a new remedy against OA.