Mesenchymal stem cell therapy regenerates the native bone-tendon junction after surgical repair in a degenerative rat model

Reliable Fabrication of Mineral-Graded Scaffolds by Spin-Coating and Laser Machining for Use in Tendon-to-Bone Insertion Repair

A reliable method for fabricating biomimetic scaffolds with a controllable mineral gradient to facilitate the surgical repair of tendon-to-bone injuries and the regeneration of the enthesis is reported. The gradient in mineral content is created by sequentially spin-coating with hydroxyapatite/poly(ε-caprolactone) suspensions containing hydroxyapatite nanoparticles in decreasing concentrations. To produce pores and facilitate cell infiltration, the spin-coated film is released and patterned with an array of funnel-shaped microchannels by laser machining. The unique design provided both mechanical (i.e., substrate stiffness) and biochemical (e.g., hydroxyapatite content) cues to spatially control the graded differentiation of mesenchymal stem cells. Immunocytochemical analysis of human mesenchymal stem cell-seeded scaffolds after 14 days of culture demonstrated the formation of a spatial phenotypic cell gradient from osteoblasts to mineralized chondrocytes based on the level of mineralization in the scaffold. By successfully recreating compositional and cellular features of the native tendon enthesis, the biomimetic scaffolds offer a promising avenue for improved tendon-to-bone repair.

Biomimetic triphasic silk fibroin scaffolds seeded with tendon-derived stem cells for tendon-bone junction regeneration

The regeneration of tendon and bone junctions (TBJs), a fibrocartilage transition zone between tendons and bones, is a challenge due to the special triphasic structure. In our study, a silk fibroin (SF)-based triphasic scaffold consisting of aligned type I collagen (Col I), transforming growth factor β (TGF-β), and hydroxyapatite (HA) was fabricated to mimic the compositional gradient feature of the native tendon-bone architecture. Rat tendon-derived stem cells (rTDSCs) were loaded on the triphasic SF scaffold, and the high cell viability suggested that the scaffold presents good biocompatibility. Meanwhile, increased expressions of tenogenic-, chondrogenic-, and osteogenic-related genes in the TBJs were observed. The in vivo studies of the rTDSC-seeded scaffold in a rat TBJ rupture model showed tendon tissue regeneration with a clear transition zone within 8 weeks of implantation. These results indicated that the biomimetic triphasic SF scaffolds seeded with rTDSCs have great potential to be applied in TBJ regeneration.

Microfracture Lateral to the Greater Tuberosity of the Humerus Enhances Tendon-to-Bone Healing in a Rat Rotator Cuff Model

BACKGROUND

Microfracture at the rotator cuff insertion is an established surgical marrow-stimulation technique for enhancing rotator cuff healing. However, the effect of lateralized or medialized microfracture on the insertion is unknown.

PURPOSE

To compare the biomechanical and histologic effects of microfracture at 3 different regions for rotator cuff repair in a rat model.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 72 Sprague-Dawley rats with bilateral supraspinatus tendon insertion detachment were allocated into 4 groups with 4 different interventions: no microfracture at the humeral head as a control group (Con), traditional microfracture at the footprint area (MFA), and medialized microfracture to the footprint area (MMFA) on the articular surface of the humerus or lateralized microfracture to the footprint area at the greater tuberosity (LMFA). All underwent immediate repair. Tendon-to-bone healing was assessed by biomechanical and histologic tests 4 and 8 weeks postoperation.

RESULTS

At 4 weeks, the LMFA group showed a significantly superior failure load compared with the other groups (all P < .05). The LMFA and MFA groups showed significantly superior stiffness compared with the Con and MMFA groups (all P < .01). At 8 weeks, superior failure load and stiffness were observed in the LMFA group compared with the control group (all P < .05). Histologic examination revealed that the LMFA group had superior collagen composition and tendon-to-bone maturation at the interface at 4 and 8 weeks compared with the Con group (all P < .05).

CONCLUSION

Lateralized microfracture at the greater tuberosity improved the histologic quality of repair tissue and biomechanical strength at the tendon-to-bone insertion after rotator cuff repair in a rat model.

CLINICAL RELEVANCE

Microfracture lateral to the footprint area might be a better way to enhance rotator cuff healing clinically.

Achilles Tendinopathy Pathogenesis and Management: A Narrative Review

The Achilles tendon is the thickest and strongest tendon of the human body, and it is frequently injured during sports activity. The incidence of Achilles tendon pathologies has increased over recent decades, especially in the last few years, because of increased sports participation among the general population and due to the diffusion of competitive sports at a high level. Tendinopathies are common in athletes and in middle-aged overweight patients. The term "tendinopathy" refers to a condition characterised clinically by pain and swelling, with functional limitations of tendon and nearby structures, and consequently to chronic failure of healing response process. Tendinopathies can produce marked morbidity, and at present, scientifically validated management modalities are limited. Despite the constantly increasing interest and number of studies about Achilles tendinopathy (AT), there is still not a consensual point of view on which is the best treatment, and its management is still controversial. AT can be treated conservatively primarily, with acceptable results and clinical outcomes. When this approach fails, surgery should be considered. Several surgical procedures have been described for both conditions with a relatively high rate of success with few complications and the decision for treatment in patients with AT should be tailored on patient's needs and level of activity. The aim of this article is to give insights about the pathogenesis and most used and recent treatment options for AT.

Biological approaches to the repair and regeneration of the rotator cuff tendon-bone enthesis: a literature review

Entheses are highly specialised organs connecting ligaments and tendons to bones, facilitating force transmission, and providing mechanical strengths to absorb forces encountered. Two types of entheses, fibrocartilaginous and fibrous, exist in interfaces. The gradual fibrocartilaginous type is in rotator cuff tendons and is more frequently injured due to the poor healing capacity that leads to loss of the original structural and biomechanical properties and is attributed to the high prevalence of retears. Fluctuating methodologies and outcomes of biological approaches are challenges to overcome for them to be routinely used in clinics. Therefore, stratifying the existing literature according to different categories (chronicity, extent of tear, and studied population) would effectively guide repair approaches. This literature review supports tissue engineering approaches to promote rotator cuff enthesis healing employing cells, growth factors, and scaffolds period. Outcomes suggest its promising role in animal studies as well as some clinical trials and that combination therapies are more beneficial than individualized ones. It then highlights the importance of tailoring interventions according to the tear extent, chronicity, and the population being treated. Contributing factors such as loading, deficiencies, and lifestyle habits should also be taken into consideration. Optimum results can be achieved if biological, mechanical, and environmental factors are approached. It is challenging to determine whether variations are due to the interventions themselves, the animal models, loading regimen, materials, or tear mechanisms. Future research should focus on tailoring interventions for different categories to formulate protocols, which would best guide regenerative medicine decision making.

Anatomical and Interpositional Bursa Preservation Showed Similar Improved Tendon to Bone Healing Compared With the Bursa Removal in a Rat Rotator Cuff Tear Model

PURPOSE

To compare the effects of anatomical preservation (AP) and interpositional preservation (IP) of subacromial bursa tissue on tendon-to-bone healing in a rat model of rotator cuff tear.

METHODS

In this study, 48 male Sprague-Dawley rats (average weight 283 g) underwent bilateral supraspinatus tendons severed by sharp incision and repaired immediately. The subacromial bursa tissues were completely removed in 16 rats, who served as the control (CON) group. The other 32 rats were randomly divided into 2 groups AP and IP between tendon and bone. Eight rats of each group were sacrificed for bilateral shoulders at 3 and 9 weeks after the operation, including 5 rats for biomechanical tests and 3 for histologic analysis.

RESULTS

No significant differences in terms of biomechanical properties were observed among the groups 3 weeks after surgery. At 9 weeks, the maximum load and stiffness of the AP (32.95 ± 6.33 N, P = .029; 12.49 ± 3.17 N/mm, P < .001; respectively) and IP (33.58 ± 8.47 N, P = .015; 11.63 ± 2.84 N/mm, P = .010, respectively) groups were significantly superior to that of the CON group (26.59 ± 4.47 N; 8.42 ± 2.33 N/mm, respectively). More organized collagen and more mature tendon insertion were observed in AP and IP groups at the interface at 9 weeks, which means better tendon-to-bone healing compared with the CON group.

CONCLUSIONS

The subacromial bursa plays a positive role in tendon-bone healing. Either anatomical preservation or interpositional preservation between tendon and bone can similarly facilitate the process of healing.

CLINICAL RELEVANCE

Considering the additional surgical time and surgical manipulation, preserving the subacromial bursa at the anatomical position seems to be a better way to promote rotator cuff healing.

Advanced strategies for constructing interfacial tissues of bone and tendon/ligament

Enthesis, the interfacial tissue between a tendon/ligament and bone, exhibits a complex histological transition from soft to hard tissue, which significantly complicates its repair and regeneration after injury. Because traditional surgical treatments for enthesis injury are not satisfactory, tissue engineering has emerged as a strategy for improving treatment success. Rapid advances in enthesis tissue engineering have led to the development of several strategies for promoting enthesis tissue regeneration, including biological scaffolds, cells, growth factors, and biophysical modulation. In this review, we discuss recent advances in enthesis tissue engineering, particularly the use of biological scaffolds, as well as perspectives on the future directions in enthesis tissue engineering.

Tendon Healing Response Is Dependent on Epithelial-Mesenchymal-Tendon Transition State of Amniotic Epithelial Stem Cells

Tendinopathies are at the frontier of advanced responses to health challenges and sectoral policy targets. Cell-based therapy holds great promise for tendon disorder resolution. To verify the role of stepwise trans-differentiation of amniotic epithelial stem cells (AECs) in tendon regeneration, in the present research three different AEC subsets displaying an epithelial (eAECs), mesenchymal (mAECs), and tendon-like (tdAECs) phenotype were allotransplanted in a validated experimental sheep Achilles tendon injury model. Tissue healing was analyzed adopting a comparative approach at two early healing endpoints (14 and 28 days). All three subsets of transplanted cells were able to accelerate regeneration: mAECs with a lesser extent than eAECs and tdAECs as indicated in the summary of the total histological scores (TSH), where at day 28 eAECs and tdAECs had better significant scores with respect to mAEC-treated tendons (p < 0.0001). In addition, the immunomodulatory response at day 14 showed in eAEC-transplanted tendons an upregulation of pro-regenerative M2 macrophages with respect to mAECs and tdAECs (p < 0.0001). In addition, in all allotransplanted tendons there was a favorable IL10/IL12 compared to CTR (p < 0.001). The eAECs and tdAECs displayed two different underlying regenerative mechanisms in the tendon. The eAECs positively influenced regeneration mainly through their greater ability to convey in the host tissue the shift from pro-inflammatory to pro-regenerative responses, leading to an ordered extracellular matrix (ECM) deposition and blood vessel remodeling. On the other hand, the transplantation of tdAECs acted mainly on the proliferative phase by impacting the density of ECM and by supporting a prompt recovery, inducing a low cellularity and angle alignment of the host cell compartment. These results support the idea that AECs lay the groundwork for production of different cell phenotypes that can orient tendon regeneration through a crosstalk with the host tissue. In particular, the obtained evidence suggests that eAECs are a practicable and efficient strategy for the treatment of acute tendinopathies, thus reinforcing the grounds to move their use towards clinical practice.

Oxo-M and 4-PPBP Delivery via Multi-Domain Peptide Hydrogel Toward Tendon Regeneration

We have recently identified novel small molecules, Oxo-M and 4-PPBP, which specifically stimulate endogenous tendon stem/progenitor cells (TSCs), leading to potential regenerative healing of fully transected tendons. Here, we investigated an injectable, multidomain peptide (MDP) hydrogel providing controlled delivery of the small molecules for regenerative tendon healing. We investigated the release kinetics of Oxo-M and 4-PPBP from MDP hydrogels and the effect of MDP-released small molecules on tenogenic differentiation of TSCs and in vivo tendon healing. In vitro, MDP showed a sustained release of Oxo-M and 4-PPBP and a slower degradation than fibrin. In addition, tenogenic gene expression was significantly increased in TSC with MDP-released Oxo-M and 4-PPBP as compared to the fibrin-released. Invivo, MDP releasing Oxo-M and 4-PPBP significantly improved tendon healing, likely associated with prolonged effects of Oxo-M and 4-PPBP on suppression of M1 macrophages and promotion of M2 macrophages. Comprehensive analyses including histomorphology, digital image processing, and modulus mapping with nanoindentation consistently suggested that Oxo-M and 4-PPBP delivered via MDP further improved tendon healing as compared to fibrin-based delivery. In conclusion, MDP delivered with Oxo-M and 4-PPBP may serve as an efficient regenerative therapeutic for in situ tendon regeneration and healing.

The histological effect of tranexamic acid on tendon-to-bone healing histologically in rats

Objectives

In this study, we aimed to investigate the effect of tranexamic acid (TXA) on osteotendinous junction healing in a rat model, both biomechanically and histologically.

Materials and methods

Sixty-four male Wistar-Albino rats weighing 450 to 600 g were used in this study. The rats were divided into two groups as the experimental (n=16) and control (n=16) groups. Achillotomy and subsequent repair site was exposed to 1 mL of TXA in the experimental group, while 1 mL of saline was given to the control group. For biomechanical and histopathological investigation, each group was further divided into two subgroups. At the end of four weeks, all rats were sacrificed. Biomechanical tests were performed using the M500-50CT device. The Bonar, Movin, and Nourissat bone-tendon junction scoring systems were used for histopathological evaluation.

Results

There was no statistically significant difference in the elongation at a maximum point, maximum loading, and maximum stress variables in the biomechanical study (p=0.558 p=0.775, and p=0.558, respectively). In the histopathological evaluation, the collagen content and layout were close to the native tissue in the experimental group (p=0.047 and p=0.008, respectively). Vascularity, hyalinization, and glycosaminoglycan content were significantly lower in the experimental group (p=0.004, p=0.014, and p=0.026, respectively). The total Bonar and Movin scores were more favorable in the experimental group (p<0.001).

Conclusion

This experimental study showed that local administration of TXA accelerated bone-tendon junction healing in rats.

Effect of difference in fixation methods of tendon graft and the microfracture procedure on tendon-bone junction healing

Background

There are generally two methods of fixation for tendon grafts used in ligament reconstruction: bone tunnel fixation and anchor fixation. The microfracture (Mf) procedure is a technique to induce bleeding from the bone marrow, and the bleeding may contain cells with differentiation potential. However, few studies have compared the effects of the Mf procedure with those of the fixation methods. This study aimed to evaluate the effectiveness of the Mf procedure on two tendon graft fixation methods: histological, gene expression, tendon graft thickness, and mechanical. We especially focused our investigation on junction healing of tendon grafts and bone in the two fixation methods.

Methods

We used 20 rabbits to evaluate tendon and bone healing in a peroneal tendon graft model. The rabbit models were divided into five groups according to the combination of peroneal tendon graft fixation method and Mf technique as follows: control group (C, n = 4), bone tunnel fixation without Mf procedure group (BT − Mf, n = 4), bone tunnel fixation with Mf procedure group (BT + Mf, n = 4), anchor fixation without Mf procedure group (A − Mf, n = 4), and anchor fixation with Mf procedure group (A + Mf, n = 4). All animals were sacrificed at 4 weeks postoperatively. The specimens underwent histological evaluation, mRNA analysis, tendon graft thickness at the tendon-bone junction, and biomechanical testing.

Results

Histological evaluation of the BT + Mf and A + Mf groups showed healing with fibrocartilage formation at the tendon graft-bone junction. The mRNA expression showed significant increase in type 2 collagen, Scleraxis, and SRY-box9 in the BT + Mf and A + Mf groups. In biomechanical tests, the BT + Mf and A + Mf groups showed significantly increased tensile strength compared with the BT − Mf and A − Mf groups (BT + Mf group, 21.6 ± 1.7 N; A + Mf group, 22.5 ± 2.3 N vs. BT − Mf group, 12.3 ± 2.4 N; A − Mf group, 11 ± 2.3 N).

Conclusion

The Mf procedure resulted in fibrocartilage formation at the tendon-bone junction in the BT and anchor fixation and improved the fixation strength at 4 weeks.

Stem cell therapies in tendon-bone healing

Tendon-bone insertion injuries such as rotator cuff and anterior cruciate ligament injuries are currently highly common and severe. The key method of treating this kind of injury is the reconstruction operation. The success of this reconstructive process depends on the ability of the graft to incorporate into the bone. Recently, there has been substantial discussion about how to enhance the integration of tendon and bone through biological methods. Stem cells like bone marrow mesenchymal stem cells (MSCs), tendon stem/progenitor cells, synovium-derived MSCs, adipose-derived stem cells, or periosteum-derived periosteal stem cells can self-regenerate and potentially differentiate into different cell types, which have been widely used in tissue repair and regeneration. Thus, we concentrate in this review on the current circumstances of tendon-bone healing using stem cell therapy.

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

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

Joining soft tissues to bone: Insights from modeling and simulations

Entheses are complex multi-tissue regions of the musculoskeletal system serving the challenging task of connecting highly dissimilar materials such as the compliant tendon to the much stiffer bone, over a very small region. The first aim of this review is to highlight mathematical and computational models that have been developed to investigate the many attachment strategies present at entheses at different length scales. Entheses are also relevant in the medical context due to the high prevalence of orthopedic injuries requiring the reattachment of tendons or ligaments to bone, which are associated with a rather poor long-term clinical outcome. The second aim of the review is to report on the computational works analyzing the whole tendon to bone complex as well as targeting orthopedic relevant issues. Modeling approaches have provided important insights on anchoring mechanisms and surgical repair strategies, that would not have been revealed with experiments alone. We intend to demonstrate the necessity of including, in future models, an enriched description of enthesis biomechanical behavior in order to unravel additional mechanical cues underlying the development, the functioning and the maintaining of such a complex biological interface as well as to enhance the development of novel biomimetic adhesive, attachment procedures or tissue engineered implants.

Mesenchymal Stem Cell and MicroRNA Therapy of Musculoskeletal Diseases

The therapeutic effects of mesenchymal stem cells (MSCs) in musculoskeletal diseases (MSDs) have been verified in many human and animal studies. Although some tissues contain MSCs, the number of cells harvested from those tissues and rate of proliferation in vitro are not enough for continuous transplantation. In order to produce and maintain stable MSCs, many attempts are made to induce differentiation from pluripotent stem cells (iPSCs) into MSCs. In particular, it is also known that the paracrine action of stem cell-secreted factors could promote the regeneration and differentiation of target cells in damaged tissue. MicroRNAs (miRNAs), one of the secreted factors, are small non-coding RNAs that regulate the translation of a gene. It is known that miRNAs help communication between stem cells and their surrounding niches through exosomes to regulate the proliferation and differentiation of stem cells. While studies have so far been underway targeting therapeutic miRNAs of MSDs, studies on specific miRNAs secreted from MSCs are still minimal. Hence, our ultimate goal is to obtain sufficient amounts of exosomes from iPSC-MSCs and develop them into therapeutic agents, furthermore to select specific miRNAs and provide safe cell-free clinical setting as a cell-free status with purpose of delivering them to target cells. This review article focuses on stem cell therapy on MSDs, specific microRNAs regulating MSDs and updates on novel approaches.

Biomimetic strategies for tendon/ligament-to-bone interface regeneration

Tendon/ligament-to-bone healing poses a formidable clinical challenge due to the complex structure, composition, cell population and mechanics of the interface. With rapid advances in tissue engineering, a variety of strategies including advanced biomaterials, bioactive growth factors and multiple stem cell lineages have been developed to facilitate the healing of this tissue interface. Given the important role of structure-function relationship, the review begins with a brief description of enthesis structure and composition. Next, the biomimetic biomaterials including decellularized extracellular matrix scaffolds and synthetic-/natural-origin scaffolds are critically examined. Then, the key roles of the combination, concentration and location of various growth factors in biomimetic application are emphasized. After that, the various stem cell sources and culture systems are described. At last, we discuss unmet needs and existing challenges in the ideal strategies for tendon/ligament-to-bone regeneration and highlight emerging strategies in the field.

Intraoperative and In Vitro Classification of Subacromial Bursal Tissue

PURPOSE

To classify subacromial bursal tissue using intraoperative and in vitro characteristics from specimens harvested during arthroscopic shoulder surgery.

METHODS

Subacromial bursa was harvested over the rotator cuff from 48 patients (57 ± 10 years) undergoing arthroscopic shoulder surgery. Specimens were characterized intraoperatively by location (over rotator cuff tendon or muscle), tissue quality (percent of either fatty or fibrous infiltration), and vascularity before complete debridement. Nucleated cell counts were determined after 3 weeks incubation and histological sections were reviewed for degree of fatty infiltration and vascularity. Mesenchymal stem cell surface markers were counted via flow cytometry (n = 3) and cellular migration was observed using a fluoroscopic assay (n = 3).

RESULTS

Intraoperatively, muscle bursa was found most often to have >50% fatty infiltration (n = 39), whereas tendon bursa showed majority fibrous tissue (n = 32). Cellular proliferation did not significantly differ according to intraoperative tissue quality. Intraoperative vascularity was associated with greater proliferation for highly vascular samples (P = 0.023). Tendon bursa demonstrated significantly greater proliferation potential than muscle bursa (P = 0.00015). Histologic assessment of fatty infiltration was moderately correlated with gross tissue fattiness (ρ = -0.626, P = 7.14 × 10^-11). Flow cytometry showed that 90% to 100% of bursal cells were positive for MSC surface markers. Peak cellular migration rates occurred between 18 and 30 hours' incubation.

CONCLUSIONS

Intraoperative and in vitro subacromial bursa characteristics were not found to reliably correlate with the degree of cellular proliferation. However, the anatomic location of subacromial bursa was consistently predictive of increased proliferation potential. Bursa-derived nucleated cells were confirmed to include mesenchymal stem cells with migratory potential.

CLINICAL RELEVANCE

The anatomic distinction between muscle and tendon bursa provides a simple classification for predicting cellular activity.

Intratendinous Injection of Mesenchymal Stem Cells for the Treatment of Rotator Cuff Disease: A 2-Year Follow-Up Study

PURPOSE

To assess the mid-term safety and efficacy of an intratendinous injection of autologous adipose tissue-derived mesenchymal stem cells (AD MSCs) for rotator cuff disease at 2-year follow-up.

METHODS

The first part of the study consisted of 3 dose-escalation groups, with 3 patients each, for the evaluation of safety: low-dose (1.0 × 10⁷ cells), mid-dose (5.0 × 10⁷), and high-dose (1.0 × 10⁸) groups. For the second part, we planned to include 9 patients receiving the high dose for the evaluation of exploratory efficacy. Clinical outcomes were assessed according to pain, range of motion, muscle strength, functional scores, overall satisfaction and function, and presence of failure. Structural outcomes included changes in volume of tendon defects measured using magnetic resonance imaging.

RESULTS

This study enrolled 19 patients (9 for the first part and 10 for the second part) with partial-thickness rotator cuff tears. There were no treatment-related adverse events at minimum 2-year follow-up. Intratendinous injection of AD MSCs reduced shoulder pain by approximately 90% at 1 and 2 years in the mid- and high-dose groups. The strength of the supraspinatus, infraspinatus, and teres minor significantly increased by greater than 50% at 2 years in the high-dose group. Shoulder function measured with 6 commonly used scores improved for up to 2 years in all dose groups. Structural outcomes evaluated with magnetic resonance imaging showed that the volume of bursal-sided defects in the high-dose group nearly disappeared at 1 year and did not recur at up to 2 years. No failures-defined as the performance of any kind of shoulder surgery or return of the Shoulder Pain and Disability Index score to the preinjection level-occurred during follow-up.

CONCLUSIONS

This study showed continued safety and efficacy of an intratendinous injection of AD MSCs for the treatment of partial-thickness rotator cuff tears over a 2-year period through regeneration of tendon defects.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

[Research progress of structured repair of tendon-bone interface]

In sports system, the tendon-bone interface has the effect of tensile and bearing load, so the effect of healing plays a crucial role in restoring joint function. The process of repair is the formation of scar tissue, so it is difficult to achieve the ideal effect for morphology and biomechanical strength. The tissue engineering method can promote the tendon-bone interface healing from the seed cells, growth factors, and scaffolds, and is a new direction in the field of development of the tendon-bone interface healing.

The application of BMP-12-overexpressing mesenchymal stem cells loaded 3D-printed PLGA scaffolds in rabbit rotator cuff repair

This study investigates if the application of bone marrow-derived mesenchymal stem cells (BM-MSCs) loaded 3D-printed scaffolds could improve rotator cuff repair. The polylactic-co-glycolic acid (PLGA) scaffolds were fabricated by 3D print technology. Rabbit BM-MSCs were transfected with a recombinant adenovirus encoding bone morphogenic protein 12 (BMP-12). The effect of BM-MSCs loaded PLGA scaffolds on tendon-bone healing was assessed by biomechanical testing and histological analysis in a rabbit rotator cuff repair model. We found that the PLGA scaffolds had good biocompatible and biodegradable property. Overexpression of BMP-12 increased the mRNA and protein expression of tenogenic genes in BM-MSCs cultured with DMEM medium and seeded in PLGA scaffolds. When BMP-12-overexpressing BM-MSCs-loaded PLGA scaffolds were implanted into the injured rabbit supraspinatus tendon-bone junctions, the tendon-bone healing was improved. Our results suggest that application of BMP-12 overexpressing BM-MSCs loaded 3D-printed PLGA scaffolds promote the healing of tendon-bone interface, improve collagen organization and increase fibrocartilage in the rabbit rotor cuff repair. Rotator cuff regeneration achieved by BMP-12-overexpressing BM-MSCs-loaded PLGA scaffolds may represent a novel approach for the management of rotator cuff defect.

A Combination of Oxo-M and 4-PPBP as a potential regenerative therapeutics for tendon injury

Tendons injuries frequently result in scar-like tissue with poor biochemical structure and mechanical properties. We have recently reported that CD146+ perivascular originated tendon stem/progenitor cells (TSCs), playing critical roles in tendon healing. Here, we identified highly efficient small molecules that selectively activate endogenous TSCs for tendon regeneration. Methods: From a pool of ERK1/2 and FAK agonists, Oxo-M and 4-PPBP were identified, and their roles in tenogenic differentiation of TSCs and in vivo tendon healing were investigated. Controlled delivery of Oxo-M and 4-PPBP was applied via PLGA µS. Signaling studies were conducted to determine the mechanism for specificity of Oxo-M and 4-PPBP to CD146+ TSCs. Results: A combination of Oxo-M and 4-PPBP synergistically increased the expressions of tendon-related gene markers in TSCs. In vivo, delivery of Oxo-M and 4-PPBP significantly enhanced healing of fully transected rat patellar tendons (PT), with functional restoration and reorganization of collagen fibrous structure. Our signaling study suggested that Oxo-M and 4-PPBP specifically targets CD146+ TSCs via non-neuronal muscarinic acetylcholine receptors (AChR) and σ1 receptor (σ1) signaling. Principal conclusions: Our findings demonstrate a significant potential of Oxo-M and 4-PPBP as a regenerative therapeutics for tendon injuries.

In vitro effect of caveolin-1 as a slow-release material on bone-tendon junction healing: A comparative study

Bone tendon junction injury is hard to cure because of its special anatomical structure, and the treatment applied for bone-tendon junction injury cannot result in the perfect vascular regeneration and restoration of the fibrocartilage zone. In this article, we aim to explore the effect of caveolin-1 as a slow-release material on bone-tendon junction healing. Seventy-two New Zealand rabbits were randomly selected and assigned into the experimental, sham-operated and control groups (n = 24). Caveolin-1 microspheres and microcapsule were developed as drug delivery system. At the 4th, 8th, and 12th weeks after surgery, quadriceps muscle patella-patellar tendon (QMPPT) was obtained from each rabbit to observe the tendon-to-bone tunnel healing, and X-ray examination, histological examination and biomechanical testing were applied for evaluating new bone formation. As the X-ray showed, caveolin-1 increased the new bone area at each time point. At the 4th and 8th weeks after surgery, the rabbit treated with caveolin-1 slow release material showed repair of fibrocartilage. According to the biomechanical results, the cross-sectional area, breaking load and ultimate tensile strength were increased along with time. At the same time point, caveolin-1 increased the ultimate tensile strength. Our study demonstrates that caveolin-1 as a slow-release material could accelerate bone-tendon junction healing by promoting the formation of the transition zone.

Stem Cells in Rotator Cuff Injuries and Reconstructions: A Systematic Review and Meta-Analysis

BACKGROUND

Multiple studies have focused on stem cell-based treatments for rotator cuff disorders; however, the outcomes are not consistent.

OBJECTIVES

This systematic review and meta-analysis were performed to evaluate the effects of stem cells on rotator cuff healing.

METHODS

A detailed search of relevant studies was conducted in three databases including Pubmed/ Medline, Cochrane library, and Embase databases, using the following keywords: "rotator cuff" or "Tissue Engineering" AND "stem cell" from inception to January 01, 2019. The standard mean difference (SMD) and 95% confidence interval (CI) for each individual study were extracted from the original studies or calculated based on relevant data and pooled to obtain integrated estimates using random effects modeling.

RESULTS

A total of 22 studies were identified. The results demonstrated that the ultimate strain in the stem cell group was significantly higher than that in the control group at 4 and 8 weeks. Muscle weight in the stem cell group was higher than the control group at 8 weeks, while no significant differences were detected at 16 weeks. The stem cell group had lower visual analog scale scores (VAS) at 1, 3, and 6 months, and higher American shoulder and elbow surgeons score (ASES) at 3 months. In addition, the walking distance, time, and speed in the stem cell group were significantly superior to those in the control group.

CONCLUSIONS

This meta-analysis confirms that stem cells improved the rehabilitation of rotator cuff disorders. However, larger-scale studies are needed to further support these findings.

Cell Therapies in Tendon, Ligament, and Musculoskeletal System Repair

In the last few decades, several techniques have been used to optimize tendon, ligament, and musculoskeletal healing. The evidence in favor of these techniques is still not proven, and level I studies are lacking. We performed an analysis of the therapeutic strategies and tissue engineering projects recently published in this field. Here, we try to give an insight into the current status of cell therapies and the latest techniques of bioengineering applied to the field of orthopedic surgery. The future areas for research in the management of musculoskeletal injuries are outlined. There are emerging technologies developing into substantial clinical treatment options that need to be critically evaluated. Mechanical stimulation of the constructs reproduces a more propitious environment for effective healing.

Von Hippel-Lindau (VHL) protein antagonist, VH298, promotes functional activities of tendon-derived stem cells and accelerates healing of entheses in rats by inhibiting ubiquitination of hydroxy-HIF-1α

Enthesis is the region where a tendon attaches to a bone. It is a relatively vulnerable position, and in most cases surgical treatment is required upon rupture. The reconstructed enthesis is usually weaker compared to the original, and is prone to rupture again. Hypoxia-inducible factor-1 α (HIF-1α) is known to be involved in extensive activities in cells. It is inhibited under normoxic conditions, and undergoes two essential processes, hydroxylation and ubiquitination, the latter of which has been largely unexplored. Herein, we measured the levels of HIF-1α and hydroxy-HIF-1α in VH298-treated rat tendon-derived stem cells (TDSCs) by immunoblotting. We also detected the proliferation of TDSCs using CCK-8 assay and the mRNA levels of related genes by quantitative RT-PCR. The TDSCs were observed to be induced and the chondrogenic differentiation related genes were found to be enhanced. We also simulated in-vitro wounding in a scratch test and reconstructed the enthesis in a rat model of Achilles tendon by classical surgery followed by administration of phosphate buffer saline (PBS) injection or VH298 injection. We observed that HIF-1α and hydroxy-HIF-1α levels were increased in VH298-treated TDSCs in a dose- and time-dependent manner. Thirty micromolar VH298 could significantly increase cell proliferation, migration, and expression of collagen-1α, collagen-3α, decorin, tenomodulin, tenascin C genes, and chondrogenic differentiation-related genes, collagen-2α, SRY-box9, aggrecan. VH298-treated enthesis could tolerate more load-to-failure, had a better healing pattern, and activation of HIF signaling pathway. VH298 can thus enhance the functional activities of TDSCs, enhance their chondrogenic differentiation potential, and accelerate enthesis healing by inhibiting the ubiquitination of hydroxy-HIF-1α.

Adipose-derived Human Perivascular Stem Cells May Improve Achilles Tendon Healing in Rats

BACKGROUND

Achilles tendon rupture is a common injury and the best treatment option remains uncertain between surgical and nonoperative methods. Biologic approaches using multipotent stem cells such as perivascular stem cells pose a possible treatment option, although there is currently a paucity of evidence regarding their clinical therapeutic use.

QUESTIONS/PURPOSES

The purpose of this study was to determine whether injected perivascular stem cells (PSCs) would (1) improve histologic signs of tendon healing (such as percent area of collagen); and (2) improve biomechanical properties (peak load or stiffness) in a rat model of Achilles tendon transection.

METHODS

Two subtypes of PSCs were derived from human adipose tissue: pericytes (CD146CD34CD45CD31) and adventitial cells (CD146CD34CD45CD31). Thirty-two athymic rats underwent right Achilles transection and were randomized to receive injection with saline (eight tendons), hydrogel (four tendons), pericytes in hydrogel (four tendons), or adventitial cells in hydrogel (eight tendons) 3 days postoperatively with the left serving as an uninjured control. Additionally, a subset of pericytes was labeled with CM-diI to track cell viability and localization. At 3 weeks, the rats were euthanized, and investigators blinded to treatment group allocation evaluated tendon healing by peak load and stiffness using biomechanical testing and percent area of collagen using histologic analysis with picrosirius red staining.

RESULTS

Histologic analysis showed a higher mean percent area collagen for pericytes (30%) and adventitial cells (28%) than hydrogel (21%) or saline (26%). However, a nonparametric statistical analysis yielded no statistical difference. Mechanical testing demonstrated that the pericyte group had a higher peak load than the saline group (41 ± 7 N versus 26 ± 9 N; mean difference 15 N; 95% confidence interval [CI], 4-27 N; p = 0.003) and a higher peak load than the hydrogel group (41 ± 7 N versus 25 ± 3 N; mean difference 16; 95% CI, 8-24 N; p = 0.001). The pericyte group demonstrated higher stiffness than the hydrogel group (36 ± 12 N/mm versus 17 ± 6 N/mm; mean difference 19 N/mm; 95% CI, 5-34 N/mm; p = 0.005).

CONCLUSIONS

Our results suggest that injection of PSCs improves mechanical but not the histologic properties of early Achilles tendon healing.

CLINICAL RELEVANCE

This is a preliminary study that provides more insight into the use of adipose-derived PSCs as a percutaneous therapy in the setting of Achilles tendon rupture. Further experiments to characterize the function of these cells may serve as a pathway to development of minimally invasive intervention aimed at improving nonoperative management while avoiding the complications associated with surgical treatment down the line.

Autologous Stem Cells in Achilles Tendinopathy (ASCAT): protocol for a phase IIA, single-centre, proof-of-concept study

INTRODUCTION

Achilles tendinopathy (AT) is a cause of pain and disability affecting both athletes and sedentary individuals. More than 150 000 people in the UK every year suffer from AT.While there is much preclinical work on the use of stem cells in tendon pathology, there is a scarcity of clinical data looking at the use of mesenchymal stem cells to treat tendon disease and there does not appear to be any studies of the use of autologous cultured mesenchymal stem cells (MSCs) for AT. Our hypothesis is that autologous culture expanded MSCs implanted into an area of mid-portion AT will lead to improved pain-free mechanical function. The current paper presents the protocol for a phase IIa clinical study.

METHODS AND ANALYSIS

The presented protocol is for a non-commercial, single-arm, open-label, phase IIa proof-of-concept study. The study will recruit 10 participants and will follow them up for 6 months. Included will be patients aged 18-70 years with chronic mid-portion AT who have failed at least 6 months of non-operative management. Participants will have a bone marrow aspirate collected from the posterior iliac crest under either local or general anaesthetic. MSCs will be isolated and expanded from the bone marrow. Four to 6 weeks after the harvest, participants will undergo implantation of the culture expanded MSCs under local anaesthetic and ultrasound guidance. The primary outcome will be safety as defined by the incidence rate of serious adverse reaction. The secondary outcomes will be efficacy as measured by patient-reported outcome measures and radiological outcome using ultrasound techniques.

ETHICS AND DISSEMINATION

The protocol has been approved by the National Research Ethics Service Committee (London, Harrow; reference 13/LO/1670). Trial findings will be disseminated through peer-reviewed publications and conference presentations.

TRIAL REGISTRATION NUMBER

NCT02064062.

Migration of Mesenchymal Stem Cells of Bursal Tissue after Rotator Cuff Repair in Rats

Purpose  The purpose of this study is to verify migration of mesenchymal stem cells of bursal tissue into the healing site after rotator cuff repair in rats. Methods  Fischer rats and green fluorescent protein (GFP)-transgenic rats were used. Bursal tissue from GFP rats was isolated and transplanted into tendon repair sites in Fischer rats. We examined the histology of the rotator cuff and the proportion of GFP-positive cells in the repaired rotator cuff 1, 3, and 6 weeks after surgery. Results  Cell migration was observed during the third and sixth week after surgery. We also found mesenchymal stem cells and formed bursal cluster patterns in the repaired rotator cuff tendons. Conclusion  Mesenchymal stem cells migrated from bursal tissue and infiltrated the repaired rotator cuff tendons. Clinical Relevance  Mesenchymal stem cells from bursal tissue can contribute to the healing progress of the repaired rotator cuff.

Vitamin C Improves Therapeutic Effects of Adipose-derived Stem Cell Transplantation in Mouse Tendonitis Model

BACKGROUND/AIM

We hypothesized that combined therapy using adipose-derived stem cells (ASCs) and vitamin C might improve tendon regeneration in tendonitis. To determine combined effects of ASC transplantation with vitamin C, we used senescence marker protein 30 (SMP30)-knockout (KO) mice that cannot biosynthesize vitamin C by themselves.

MATERIALS AND METHODS

SMP30-KO were divided into four groups: Control, vitamin C, ASCs, and vitamin C plus ASCs. Tendonitis was induced in the achilles tendons via injection of collagenase type I. After 1 week, ASCs were injected into the intratendonal region. After 30 days, all mice were sacrificed and Achilles tendons were isolated.

RESULTS

Gross and microscopic findings showed mice treated with combination of ASC transplantation and vitamin C showed better tendon regeneration than those in other groups. This combination led to higher serum vitamin C levels than use of vitamin C alone. This indicates that the vitamin C-treated group used more vitamin C as a precursor to collagen synthesis, whereas vitamin C was in excess in the combination group because of the added effect of ASCs on tendon healing.

CONCLUSION

This study showed that vitamin C improved the effect of ASC transplantation on tendonitis by inducing a better stem cell niche.

Regenerative Engineering of the Rotator Cuff of the Shoulder

Rotator cuff tears often heal poorly, leading to re-tears after repair. This is in part attributed to the low proliferative ability of the resident cells (tendon fibroblasts and tendon-stem cells) upon injury to the rotator cuff tissue and the low vascularity of the tendon insertion. In addition, surgical outcomes of current techniques used in clinical settings are often suboptimal, leading to the formation of neo-tissue with poor biomechanics and structural characteristics, which results in re-tears. This has prompted interest in a new approach, which we term as "Regenerative Engineering", for regenerating rotator cuff tendons. In the Regenerative Engineering paradigm, roles played by stem cells, scaffolds, growth factors/small molecules, the use of local physical forces, and morphogenesis interplayed with clinical surgery techniques may synchronously act, leading to synergistic effects and resulting in successful tissue regeneration. In this regard, various cell sources such as tendon fibroblasts and adult tissue-derived stem cells have been isolated, characterized, and investigated for regenerating rotator cuff tendons. Likewise, numerous scaffolds with varying architecture, geometry, and mechanical characteristics of biologic and synthetic origin have been developed. Furthermore, these scaffolds have been also fabricated with biochemical cues (growth factors and small molecules), facilitating tissue regeneration. In this Review, various strategies to regenerate rotator cuff tendons using stem cells, advanced materials, and factors in the setting of physical forces under the Regenerative Engineering paradigm are described.

De novo generation in an in vivo rat model and biomechanical characterization of autologous transplants for ligament and tendon reconstruction

BACKGROUND

Surgical reconstruction of ligaments and tendons is frequently required in clinical practice. The commonly used autografts, allografts, or synthetic transplants present limitations in terms of availability, biocompatibility, cost, and mechanical properties that tissue bioengineering aims to overcome. It classically combines an exogenous extracellular matrix with cells, but this approach remains complex and expensive. Using a rat model, we tested a new bioengineering strategy for the in vivo and de novo generation of autologous grafts without the addition of extracellular matrix or cells, and analyzed their biomechanical and structural properties.

METHODS

A silicone perforated tubular implant (PTI) was designed and implanted in the spine of male Wistar rats to generate neo-transplants. The tensile load to failure, stiffness, Young modulus, and ultrastructure of the generated tissue were determined at 6 and 12weeks after surgery. The feasibility of using the transplant that was generated in the spine as an autograft for reconstruction of medial collateral ligaments (MCL) and Achilles tendons was also tested.

FINDINGS

Use of the PTI resulted in de novo transplant generation. Their median load to failure and Young modulus increased between 6 and 12weeks (respectively 12N vs 34N and 48MPa vs 178MPa). At 12weeks, the neo-transplants exhibited collagen bundles (mainly type III) parallel to their longitudinal axis and elongated fibroblasts. Six weeks after their transfer to replace the MCL or the Achilles tendon, the transplants were still present, with their ends healed at their insertion point.

INTERPRETATION

This animal study is a first step in the design and validation of a new bioengineering strategy to develop autologous transplants for ligament and tendon reconstructions.

Role of Stem Cells in Pathophysiology and Therapy of Spondyloarthropathies-New Therapeutic Possibilities?

Considerable progress has been made recently in understanding the complex pathogenesis and treatment of spondyloarthropathies (SpA). Currently, along with traditional disease modifying anti-rheumatic drugs (DMARDs), TNF-α, IL-12/23 and IL-17 are available for treatment of such diseases as ankylosing spondylitis (AS) and psoriatic arthritis (PsA). Although they adequately control inflammatory symptoms, they do not affect the abnormal bone formation processes associated with SpA. However, the traditional therapeutic approach does not cover the regenerative treatment of damaged tissues. In this regards, stem cells may offer a promising, safe and effective therapeutic option. The aim of this paper is to present the role of mesenchymal stromal cells (MSC) in pathogenesis of SpA and to highlight the opportunities for using stem cells in regenerative processes and in the treatment of inflammatory changes in articular structures.

Tendon stem/progenitor cells regulate inflammation in tendon healing via JNK and STAT3 signaling

Tendon stem/progenitor cells (TSCs) have been found in different anatomic locations and showed a promising regenerative potential. We identified a role of TSCs in the regulation of inflammation during healing of acute tendon injuries. Delivery of connective tissue growth factor (CTGF) into full-transected rat patellar tendons significantly increased the number of CD146⁺ TSCs, leading to enhanced healing. In parallel, CTGF delivery significantly reduced the number of iNOS⁺ M1 macrophages and increased the expression of anti-inflammatory IL-10 at 2 d after surgery, with over 85% CD146⁺ TSCs expressing IL-10. By 1 wk, the elevated IL-10 expression remained, and IL-6 expression was significantly attenuated in CTGF-delivered tendon healing. Matrix metalloproteinase (MMP)-3 expression in CTGF-delivered tendon was organized along with the reorienting collagen fibers by 1 wk after surgery, in comparison with the control group showing the abundant MMP-3 expression localized at healing junction. Tissue inhibitor of metalloprotease (TIMP)-3 was expressed in CD146⁺ TSCs at 1 wk with CTGF, in contrast to control with no TIMP-3 expression. In vitro, IL-10 expression was detected only when tendon cells were stimulated with IL-1β, and CTGF and significantly higher in CD146⁺ TSCs than CD146^- tendon cells. Similarly, TIMP-3 expression was detected only when treated with CTGF or CTGF and IL-1β that is significantly higher in CD146⁺ TSCs compared to CD146^- tendon cells. Signaling study with specific inhibitors and Western blot analysis demonstrated that CTGF-induced expression of IL-10 and TIMP-3 in CD146⁺ TSCs are regulated by JNK/signal transducer and activator of transcription 3 signaling. Taken together, these findings suggest anti-inflammatory roles of CTGF-stimulated TSCs that are likely associated with improved tendon healing.-Tarafder, S., Chen, E., Jun, Y., Kao, K., Sim, K. H., Back, J., Lee, F. Y., Lee, C. H. Tendon stem/progenitor cells regulate inflammation in tendon healing via JNK and STAT3 signaling.

Engineered stem cell niche matrices for rotator cuff tendon regenerative engineering

Rotator cuff (RC) tears represent a large proportion of musculoskeletal injuries attended to at the clinic and thereby make RC repair surgeries one of the most widely performed musculoskeletal procedures. Despite the high incidence rate of RC tears, operative treatments have provided minimal functional gains and suffer from high re-tear rates. The hypocellular nature of tendon tissue poses a limited capacity for regeneration. In recent years, great strides have been made in the area of tendonogenesis and differentiation towards tendon cells due to a greater understanding of the tendon stem cell niche, development of advanced materials, improved scaffold fabrication techniques, and delineation of the phenotype development process. Though in vitro models for tendonogenesis have shown promising results, in vivo models have been less successful. The present work investigates structured matrices mimicking the tendon microenvironment as cell delivery vehicles in a rat RC tear model. RC injuries augmented with a matrix delivering rat mesenchymal stem cells (rMSCs) showed enhanced regeneration over suture repair alone or repair with augmentation, at 6 and 12-weeks post-surgery. The local delivery of rMSCs led to increased mechanical properties and improved tissue morphology. We hypothesize that the mesenchymal stem cells function to modulate the local immune and bioactivity environment through autocrine/paracrine and/or cell homing mechanisms. This study provides evidence for improved tendon healing with biomimetic matrices and delivered MSCs with the potential for translation to larger, clinical animal models. The enhanced regenerative healing response with stem cell delivering biomimetic matrices may represent a new treatment paradigm for massive RC tendon tears.

The combined use of kartogenin and platelet-rich plasma promotes fibrocartilage formation in the wounded rat Achilles tendon entheses

Objectives

After an injury, the biological reattachment of tendon to bone is a challenge because healing takes place between a soft (tendon) and a hard (bone) tissue. Even after healing, the transition zone in the enthesis is not completely regenerated, making it susceptible to re-injury. In this study, we aimed to regenerate Achilles tendon entheses (ATEs) in wounded rats using a combination of kartogenin (KGN) and platelet-rich plasma (PRP).

Methods

Wounds created in rat ATEs were given three different treatments: kartogenin platelet-rich plasma (KGN-PRP); PRP; or saline (control), followed by histological and immunochemical analyses, and mechanical testing of the rat ATEs after three months of healing.

Results

Histological analysis showed well organised arrangement of collagen fibres and proteoglycan formation in the wounded ATEs in the KGN-PRP group. Furthermore, immunohistochemical analysis revealed fibrocartilage formation in the KGN-PRP-treated ATEs, evidenced by the presence of both collagen I and II in the healed ATE. Larger positively stained collagen III areas were found in both PRP and saline groups than those in the KGN-PRP group. Chondrocyte-related genes, SOX9 and collagen II, and tenocyte-related genes, collagen I and scleraxis (SCX), were also upregulated by KGN-PRP. Moreover, mechanical testing results showed higher ultimate tensile strength in the KGN-PRP group than in the saline control group. In contrast, PRP treatment appeared to have healed the injured ATE but induced no apparent formation of fibrocartilage. The saline-treated group showed poor healing without fibrocartilage tissue formation in the ATEs.

Conclusions

Our results show that injection of KGN-PRP induces fibrocartilage formation in the wounded rat ATEs. Hence, KGN-PRP may be a clinically relevant, biological approach to regenerate injured enthesis effectively.

Cite this article: J. Zhang, T. Yuan, N. Zheng, Y. Zhou, M. V. Hogan, J. H-C. Wang. The combined use of kartogenin and platelet-rich plasma promotes fibrocartilage formation in the wounded rat Achilles tendon entheses. Bone Joint Res 2017;6:231–244. DOI: 10.1302/2046-3758.64.BJR-2017-0268.R1.

The influence of different footprint preparation techniques on tissue regeneration in rotator cuff repair in an animal model

INTRODUCTION

Rotator cuff tears are common diseases of the upper extremity. There are no recommendations to the surgeon on how to prepare the footprint to ensure optimal tendon-to-bone healing. However, biologic augmentation using stem cells and growth factors is considered to encourage the healing process of the tendon. The aim of the study was to investigate the biomechanical and histological outcome of different footprint preparations in rotator cuff repair.

MATERIAL AND METHODS

One hundred and eighty-nine Sprague-Dawley rats were randomly assigned to either spongialization, radiofrequency ablation or an untreated control group. Rats were killed after 1 or 7 weeks for histological evaluation or after 7 weeks for biomechanical testing.

RESULTS

Histological evaluation showed better tissue organization in the control and spongialization group compared to the radiofrequency ablation group. The highest collagen I to collagen III quotient was found in the control group, followed closely by the spongialization group. Measured quotients showed a decrease in the values after 1 week compared to the values after 7 weeks, except in the radiofrequency ablation group, where an increase was detected. A significant difference was found in the load to failure test comparing the radiofrequency ablation group to the spongialization group (p = 0.0409) and control group (p = 0.014), but not comparing the spongialization group to the control group (p = 0.2456).

CONCLUSIONS

The results of this study suggest that spongialization of the footprint before attaching the torn supraspinatus tendon can lead to better structural properties and higher quality of tendon-to-bone restoration at the insertion area when compared with radiofrequency ablation.

Adult Cells Combined With Platelet-Rich Plasma for Tendon Healing: Cell Source Options

Background:

The combination of cells with platelet-rich plasma (PRP) may fulfill tendon deficits and help overcome the limited ability of tendons to heal.

Purpose:

To examine the suitability of 3 human cell types in combination with PRP and the potential impact of the tenocyte-conditioned media (CM) to enhance tendon healing.

Study Design:

Controlled laboratory study.

Methods:

Tenocytes, bone marrow–derived mesenchymal stem cells, and skin fibroblasts were cultured in 3-dimensional PRP hydrogels supplemented or not with CM, and cell proliferation and migration were examined. The effect of tendon-derived CM on matrix-forming phenotype and secretion of inflammatory proteins was determined through their administration to mesenchymal stem cells, tendon, and skin fibroblasts by reverse transcription quantitative polymerase chain reaction and enzyme-linked immunosorbent assay, respectively.

Results:

Differences were found in the matrix-forming phenotype between each of the cell types. The ratio of collagen I:collagen III was greater in bone marrow–derived mesenchymal stem cells than in skin fibroblasts and tenocytes. The bone marrow–derived mesenchymal stem cells expressed increased levels of cartilage-related genes than tenocytes or skin fibroblasts. The presence of the tenocyte-CM stimulated basic healing mechanisms including proliferation and chemotaxis in all cell types. In addition, the tenocyte-CM modified the matrix-forming phenotype of every cell type when cultured in PRP hydrogels. Each cell type secreted interleukin-6, interleukin-8, and monocyte chemotactic protein-1 in PRP hydrogels, but mesenchymal stem cells secreted less interleukin-8 and monocyte chemotactic protein-1 than tenocytes or skin fibroblasts.

Conclusion:

The tenocyte-CM combined with PRP stimulated tenogenesis in mesenchymal stem cells and in skin fibroblasts and reduced the secretion of inflammatory proteins.

Clinical Relevance:

Modifying the target tissue with PRP prior to cell implantation may optimize the effect of cell therapies. Skin fibroblasts and bone marrow–derived mesenchymal stem cells combined with PRP could be used to regenerate tendons.

Using the zebrafish to understand tendon development and repair

Tendons are important components of our musculoskeletal system. Injuries to these tissues are very common, resulting from occupational-related injuries, sports-related trauma, and age-related degeneration. Unfortunately, there are few treatment options, and current therapies rarely restore injured tendons to their original function. An improved understanding of the pathways regulating their development and repair would have significant impact in stimulating the formulation of regenerative-based approaches for tendon injury. The zebrafish provides an ideal system in which to perform genetic and chemical screens to identify new pathways involved in tendon biology. Until recently, there had been few descriptions of tendons and ligaments in the zebrafish and their similarity to mammalian tendon tissues. In this chapter, we describe the development of the zebrafish tendon and ligament tissues in the context of their gene expression, structure, and interactions with neighboring musculoskeletal tissues. We highlight the similarities with tendon development in higher vertebrates, showing that the craniofacial tendons and ligaments in zebrafish morphologically, molecularly, and structurally resemble mammalian tendons and ligaments from embryonic to adult stages. We detail methods for fluorescent in situ hybridization and immunohistochemistry as an assay to examine morphological changes in the zebrafish musculoskeleton. Staining assays such as these could provide the foundation for screen-based approaches to identify new regulators of tendon development, morphogenesis, and repair. These discoveries would provide new targets and pathways to study in the context of regenerative medicine-based approaches to improve tendon healing.

Mesenchymal stem cells for tendon healing: what is on the horizon?

Tendon injuries are a noteworthy morbidity but at present there are few effective scientifically proven treatments. In recent decades, a number of new strategies including tissue engineering with mesenchymal stem cells (MSCs) have been proposed to enhance tendon healing. Although MSCs are an interesting and promising approach, many questions regarding their use in tendon repair remain unanswered. This descriptive overview of the literature of the last decade explores the in vivo studies on tendon healing, in small and large animal models, which used MSCs harvested from different tissues, and the state of the art in clinical applications. It was observed that there are still doubts about the optimum amount of MSCs to use and their source and the type of scaffolds to deliver the cells. Thus, further studies are needed to determine the best protocol for MSC use in tendon healing. Copyright © 2016 John Wiley & Sons, Ltd.

Adipose-Derived Stem Cells Improve Collagenase-Induced Tendinopathy in a Rat Model

BACKGROUND

Tendinopathy is a common and highly prevalent musculoskeletal disorder characterized by repetitive activity-related pain and focal tendon tenderness. Histopathologically, tendinopathic tissue mainly shows degenerative changes. Therefore, tendinopathy is not affected by anti-inflammatory therapies. A novel approach, including a stem cell-based therapy, may be beneficial for its treatment.

PURPOSE/HYPOTHESIS

The purpose of this study was to evaluate the effects of adipose-derived stem cells (ASCs) on tendon healing in a rat tendinopathy model. The hypothesis was that ASC transplantation would improve degeneration in collagenase-induced tendinopathy.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixteen F344/NSlc rats underwent collagenase injection into the Achilles tendon to induce tendinopathy. At 1 week after collagenase injection, 8 rats received ASCs (ASC group) and 8 received phosphate-buffered saline alone (PBS group). Animals were sacrificed at 4 or 12 weeks after ASC administration, and the degree of degeneration in each tendon was histologically evaluated according to the Bonar scale. The microstructure of healing tendons was observed by scanning electron microscopy. Reverse-transcription polymerase chain reaction (RT-PCR) was performed to measure the ratio of type III collagen messenger RNA (mRNA) to type I collagen mRNA in tendons.

RESULTS

The median Bonar scale score in the ASC and PBS groups was 2.5 and 5.33 at 4 weeks after treatment and 1.0 and 4.0 at 12 weeks after treatment, respectively. Histologically, the ASC group showed a significantly lower degree of tendon degeneration than the PBS group at both time points. In the RT-PCR analysis, the ratio of type III collagen to type I collagen was significantly lower in the ASC group than in the PBS group at 12 weeks after treatment. Moreover, this ratio decreased over time in the ASC group, whereas it increased over time in the PBS group.

CONCLUSION

The study findings demonstrate that the application of ASCs results in significant improvement in the pathological findings associated with tendinopathy and the normalization of collagen ratios within the affected tendon.

CLINICAL RELEVANCE

Subcutaneous adipose tissue can be harvested easily, and ASC administration might have the potential to rapidly treat tendinopathy.

Mesenchymal stem cells (MSCs) as skeletal therapeutics - an update

Mesenchymal stem cells hold the promise to treat not only several congenital and acquired bone degenerative diseases but also to repair and regenerate morbid bone tissues. Utilizing MSCs, several lines of evidences advocate promising clinical outcomes in skeletal diseases and skeletal tissue repair/regeneration. In this context, both, autologous and allogeneic cell transfer options have been utilized. Studies suggest that MSCs are transplanted either alone by mixing with autogenous plasma/serum or by loading onto repair/induction supportive resorb-able scaffolds. Thus, this review is aimed at highlighting a wide range of pertinent clinical therapeutic options of MSCs in the treatment of skeletal diseases and skeletal tissue regeneration. Additionally, in skeletal disease and regenerative sections, only the early and more recent preclinical evidences are discussed followed by all the pertinent clinical studies. Moreover, germane post transplant therapeutic mechanisms afforded by MSCs have also been conversed. Nonetheless, assertive use of MSCs in the clinic for skeletal disorders and repair is far from a mature therapeutic option, therefore, posed challenges and future directions are also discussed. Importantly, for uniformity at all instances, term MSCs is used throughout the review.

Stem cells and bFGF in tendon healing: Effects of lentiviral gene transfer and long-term follow-up in a rat Achilles tendon defect model

BACKGROUND

The influence of stem cells and lentiviral expression of basic fibroblastic growth factor (bFGF) on tendon healing and remodelling was investigated in an in-vivo long-term (12 weeks) rat Achilles tendon defect model.

METHODS

In sixty male Lewis rats, complete tendon defects (2.4 mm) were created and either left untreated (PBS) or treated by injection of stem cells lentivirally expressing the enhanced green fluorescence marker gene eGFP (MSC-LV-eGFP) or basic fibroblast growth factor bFGF (MSC-LV-bFGF). Tendons were harvested after 12 weeks and underwent biomechanical and (immuno)-histological analysis.

RESULTS

After 12 weeks the mean ultimate load to failure ratio (treated side to contralateral side) in biomechanical testing reached 97 % in the bFGF-group, 103 % in the eGFP-group and 112 % in the PBS-group. Also in the stiffness testing both MSC groups did not reach the results of the PBS group. Histologically, the MSC groups did not show better results than the control group. There were clusters of ossifications found in all groups. In immunohistology, only the staining collagen-type-I was strongly increased in both MSC groups in comparison to PBS control group. However, there were no significant differences in the (immuno)-histological results between both stem cell groups.

CONCLUSION

The biomechanical and (immuno)-histological results did not show positive effects of the MSC groups on tendon remodelling in a long-term follow-up. Interestingly, in later stages stem cells had hardly any effects on biomechanical results. This study inspires a critical and reflected use of stem cells in tendon healing.

Characterization of progenitor cells derived from torn human rotator cuff tendons by gene expression patterns of chondrogenesis, osteogenesis, and adipogenesis

Background

It is important to regenerate the tendon-to-bone interface after rotator cuff repair to prevent re-tears. The cells from torn human rotator cuff were targeted, and their capacity for multilineage differentiation was investigated.

Methods

The edges of the rotator cuff were harvested during arthroscopic rotator cuff repair from nine patients, minced into pieces, and cultured on dishes. Adherent cells were cultured, phenotypically characterized. Then expandability, differentiation potential and gene expression were analyzed.

Results

Flow cytometry revealed that the mesenchymal stem cells (MSC)-related markers CD29, CD44, CD105, and CD166 were positive. However, CD14, CD34, and CD45 were negative. On RT-PCR analyses, the cells showed osteogenic, adipogenic, and chondrogenic potential after 3 weeks of culture under the respective differentiation conditions. In addition, SOX9, type II collagen, and type X collagen expression patterns during chondrogenesis were similar to those of endochondral ossification at the enthesis.

Conclusions

The cells derived from torn human rotator cuff are multipotent mesenchymal stem cells with the ability to undergo multilineage differentiation, suggesting that MSCs form this tissue could be regenerative capacity for potential self-repair.

Stability Enhancement Using Hyaluronic Acid Gels for Delivery of Human Fetal Progenitor Tenocytes

Tendon afflictions are very common, and their negative impact is high both at the workplace and in leisure activities. Tendinopathies are increasing in prevalence and can lead to tendon ruptures, where healing is a long process with outcomes that are often disappointing. Human fetal progenitor tenocytes (hFPTs) have been recently tested in vitro as a potential cell source to stimulate tendon regeneration. The aim of the present study was to compare different commercial hyaluronic acid (HA) gels, which could be used to resuspend hFPTs in a formulation that would allow for good delivery of the cells. No medium or growth supplement was used in the formulation in order to make it therapeutically dispensable. These conditions are stringent for cells, but surprisingly, we found that different formulations could allow a good survival for up to 3 days when stored at 4°C (refrigerator stable). The gels must allow a good survival of the cells in parallel with a good stability of the preparation over time and sufficient viscosity to remain in place if deposited on a wounded location. Moreover, the cells must conserve their ability to attach and to proliferate. hFPTs were able to survive and to recover from all of the tested gels, but some products showed some advantages over others in terms of survival and viscosity. Finally, the Ostenil Tendon HA gel fulfilled all of the requirements and presented the best compromise between a good survival and sufficient rheological characteristics to create an interesting cell delivery system.

Stem cell technology for tendon regeneration: current status, challenges, and future research directions

Tendon injuries are a common cause of physical disability. They present a clinical challenge to orthopedic surgeons because injured tendons respond poorly to current treatments without tissue regeneration and the time required for rehabilitation is long. New treatment options are required. Stem cell-based therapies offer great potential to promote tendon regeneration due to their high proliferative, synthetic, and immunomodulatory activities as well as their potential to differentiate to the target cell types and undergo genetic modification. In this review, I first recapped the challenges of tendon repair by reviewing the anatomy of tendon. Next, I discussed the advantages and limitations of using different types of stem cells compared to terminally differentiated cells for tendon tissue engineering. The safety and efficacy of application of stem cells and their modified counterparts for tendon tissue engineering were then summarized after a systematic literature search in PubMed. The challenges and future research directions to enhance, optimize, and standardize stem cell-based therapies for augmenting tendon repair were then discussed.

Efficacy of supraspinatus tendon repair using mesenchymal stem cells along with a collagen I scaffold

OBJECTIVES

Our main objective was to biologically improve rotator cuff healing in an elderly rat model using mesenchymal stem cells (MSCs) in combination with a collagen membrane and compared against other current techniques.

METHODS

A chronic rotator cuff tear injury model was developed by unilaterally detaching the supraspinatus (SP) tendons of Sprague-Dawley rats. At 1 month postinjury, the tears were repaired using one of the following techniques: (a) classical surgery using sutures (n = 12), (b) type I collagen membranes (n = 15), and (c) type I collagen membranes + 1 × 106 allogeneic MSCs (n = 14). Lesion restoration was evaluated at 1, 2, and 3 months postinjury based on biomechanical criteria. Continuous variables were described using mean and standard deviation (SD). To analyse the effect of the different surgical treatments in the repaired tendons' biomechanical capabilities (maximum load, stiffness, and deformity), a two-way ANOVA model was used, introducing an interaction between such factor and time (1, 2, and 3 months postinjury).

RESULTS

With regard to maximum load, we observed an almost significant interaction between treatment and time (F = 2.62, df = 4, p = 0.053). When we analysed how this biomechanical capability changed with time for each treatment, we observed that repair with OrthADAPT and MSCs was associated with a significant increase in maximum load (p = 0.04) between months 1 and 3. On the other hand, when we compared the different treatments among themselves at different time points, we observed that the repair with OrthADAPT and MSCs has associated with a significant higher maximum load, when compared with the use of suture, but only at 3 months (p = 0.014). With regard to stiffness and deformity, no significant interaction was observed (F = 1.68, df = 4, p = 0.18; F = 0.40, df = 4, p = 0.81; respectively).

CONCLUSIONS

The implantation of MSCs along with a collagen I scaffold into surgically created tendon defects is safe and effective. MSCs improved the tendon's maximum load over time, indicating that MSCs could help facilitate the dynamic process of tendon repair.

Harnessing endogenous stem/progenitor cells for tendon regeneration

Current stem cell-based strategies for tissue regeneration involve ex vivo manipulation of these cells to confer features of the desired progenitor population. Recently, the concept that endogenous stem/progenitor cells could be used for regenerating tissues has emerged as a promising approach that potentially overcomes the obstacles related to cell transplantation. Here we applied this strategy for the regeneration of injured tendons in a rat model. First, we identified a rare fraction of tendon cells that was positive for the known tendon stem cell marker CD146 and exhibited clonogenic capacity, as well as multilineage differentiation ability. These tendon-resident CD146+ stem/progenitor cells were selectively enriched by connective tissue growth factor delivery (CTGF delivery) in the early phase of tendon healing, followed by tenogenic differentiation in the later phase. The time-controlled proliferation and differentiation of CD146+ stem/progenitor cells by CTGF delivery successfully led to tendon regeneration with densely aligned collagen fibers, normal level of cellularity, and functional restoration. Using siRNA knockdown to evaluate factors involved in tendon generation, we demonstrated that the FAK/ERK1/2 signaling pathway regulates CTGF-induced proliferation and differentiation of CD146+ stem/progenitor cells. Together, our findings support the use of endogenous stem/progenitor cells as a strategy for tendon regeneration without cell transplantation and suggest this approach warrants exploration in other tissues.

The effect of granulocyte-colony stimulating factor on rotator cuff healing after injury and repair

BACKGROUND

The failure rate of tendon-bone healing after repair of rotator cuff tears remains high. A variety of biologic- and cell-based therapies aimed at improving rotator cuff healing have been investigated, and stem cell-based techniques have become increasingly more common. However, most studies have focused on the implantation of exogenous cells, which introduces higher risk and cost. We aimed to improve rotator cuff healing by inducing endogenous stem cell mobilization with systemic administration of granulocyte-colony stimulating factor (G-CSF).

QUESTIONS/PURPOSES

We asked: (1) Does G-CSF administration increase local cellularity after acute rotator cuff repair? (2) Is there histologic evidence that G-CSF improved organization at the healing enthesis? (3) Does G-CSF administration improve biomechanical properties of the healing supraspinatus tendon-bone complex? (4) Are there micro-MRI-based observations indicating G-CSF-augmented tendon-bone healing?

METHODS

After creation of full-thickness supraspinatus tendon defects with immediate repair, 52 rats were randomized to control or G-CSF-treated groups. G-CSF was administered for 5 days after repair and rats were euthanized at 12 or 19 postoperative days. Shoulders were subjected to micro-MR imaging, stress relaxation, and load-to-failure as well as blinded histologic and histomorphometric analyses.

RESULTS

G-CSF-treated animals had significantly higher cellularity composite scores at 12 and 19 days compared with both control (12 days: 7.40 ± 1.14 [confidence interval {CI}, 5.98-8.81] versus 4.50 ± 0.57 [CI, 3.58-5.41], p = 0.038; 19 days: 8.00 ± 1.00 [CI, 6.75-9.24] versus 5.40 ± 0.89 [CI, 4.28-6.51], p = 0.023) and normal animals (12 days: p = 0.029; 19 days: p = 0.019). There was no significant difference between G-CSF-treated animals or control animals in ultimate stress (MPa) and strain, modulus (MPa), or yield stress (MPa) and strain at either 12 days (p = 1.000, p = 0.104, p = 1.000, p = 0.909, and p = 0.483, respectively) or 19 days (p = 0.999, p = 0.964, p = 1.000, p = 0.988, and p = 0.904, respectively). There was no difference in MRI score between G-CSF and control animals at either 12 days (2.7 ± 1.8 [CI, 1.08-4.24] versus 2.3 ± 1.8 [CI, 0.49-4.17], p = 0.623) or 19 days (2.5 ± 1.4 [CI, 1.05-3.94] versus 2.3 ± 1.5 [CI, 0.75-3.91], p = 0.737). G-CSF-treated animals exhibited significantly lower relative bone volume compared with normal animals in the entire humeral head (24.89 ± 3.80 [CI, 20.17-29.60) versus 32.50 ± 2.38 [CI, 29.99-35.01], p = 0.009) and at the supraspinatus insertion (25.67 ± 5.33 [CI, 19.04-32.29] versus 33.36 ± 1.69 [CI, 31.58-35.14], p = 0.027) at 12 days. Further analysis did not reveal any additional significant relationships with respect to regional bone volume or trabecular thickness between groups and time points (p > 0.05).

CLINICAL RELEVANCE

Postoperative stem cell mobilization agents may be an effective way to enhance rotator cuff repair. Future studies regarding the kinetics of mobilization, the homing capacity of mobilized cells to injured tissues, and the ability of homing cells to participate in regenerative pathways are necessary.