Tendon healing in vitro: genetic modification of tenocytes with exogenous PDGF gene and promotion of collagen gene expression

Pulsed electrical stimulation and amino acid derivatives promote collagen gene expression in human dermal fibroblasts

Several collagen types are important for maintaining skin structure and function. Previous reports show that l-hydroxyproline (Hyp), N-acetyl-l-hydroxyproline (AHyp), and l-alanyl-l-glutamine (Aln-Gln) are biological active substances with collagen synthesis-promoting effects. In this study, we combined the promotive effects of pulsed electrical stimulation (PES) with three amino acid derivatives in human dermal fibroblasts. Fibroblasts were exposed to PES with a 4,800 Hz pulse frequency and a voltage at 1 or 5 V for 15 min. The gene expression of type I and III collagen (fibrillar collagen), type IV and VII collagen (basement membrane collagen and anchoring fibril collagen) were measured by RT-PCR 48 h after PES. PES alone promoted the expression of COL1A1 and COL3A1 at 5 V but did not alter that of COL4A1 and COL7A1. Each AAD and the AAD mixture promoted the expression of COL4A1 and COL7A1 but either repressed, or did not alter, that of COL1A1 and COL3A1. Compared to treatment with each AAD, PES at 5 V with Hyp promoted the expression of COL1A1 and COL3A1, enhanced COL3A1 expression with AHyp, and stimulated COL3A1 expression with Aln-Gln, while COL4A1 and COL7A1 expressions were not affected. PES and the AAD mixture significantly promoted COL4A1 expression in a voltage-dependent manner, and COL1A1 and COL3A1 demonstrated a similar but nonsignificant trend, whereas COL7A1 expression was not affected. The combination of PES with each AAD or the AAD mixture may improve skin structure and function by increasing the expression of basement membrane collagen and dermal fibrillar collagen.

Non-Viral Delivery of Gene Therapy to the Tendon

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

Growth Factor Expression During Healing in 3 Distinct Tendons

Purpose

We investigated unique tendon growth-factor expression profiles over time in response to simultaneous, similar injuries. Characterizing these genetic differences lays the foundation for creating targeted, tendon-specific therapies and provides insight into why current growth-factor treatments have success in some applications but not others.

Methods

The left fourth digital flexor, triceps, and supraspinatus tendons in 24 rats were cut to 50% of their transverse width at the midbelly under anesthesia. On postoperative days 1, 3, 5, 7, and 14, randomly selected rats were sacrificed, and the damaged tendons were excised and flash-frozen in liquid nitrogen. The expressional fibroblast growth factor 1, bone morphogenic protein 13, and transforming growth factor β-1 were measured at each time point and compared to their respective, uninjured levels with real-time polymerase chain reaction.

Results

The digital flexor tendon showed exponentially elevated expression of all 3 factors over the preinjury baseline values. Expression in the triceps and supraspinatus had more variation over time. The triceps tendon showed a considerable decrease of transforming growth factor β-1 and bone morphogenic protein 13 expression. The supraspinatus tendon had statistically significant increases of both transforming growth factor β-1 and bone morphogenic protein 13 expression relative to preoperative, uninjured levels, with a nonstatistically significant decrease of fibroblast growth factor 1.

Conclusions

Our study suggests different tendons express their own unique growth-factor profiles after similar, simultaneous injuries. The digital flexor showed particularly high, sustained levels of growth-factor expression in comparison to the supraspinatus and triceps, suggesting that variable dosing may be necessary for growth-factor therapies aimed at supplementing innate responses in these different tendon types.

Clinical relevance

These data show different tendons express unique trends of growth-factor expression over time in response to injury, suggesting each unique tendon may require specific dosing or knockdown therapies. These observations serve as a foundation for more tendon-specific questioning, experimentation, and therapeutic design.

Current Biological Strategies to Enhance Surgical Treatment for Rotator Cuff Repair

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

Biologics in the Treatment of Achilles Tendon

The treatment of Achilles tendinitis from conservative to minimally invasive to surgery gives patients a wide range of treatment options for this common pathology. The use and role of biologics to augment this treatment is emerging. The use of biologics may enhance the healing potential of the Achilles tendon when conservative treatment fails. There are a handful of biologics being investigated to obtain if improved outcomes can be maximized.

FGF2: a key regulator augmenting tendon-to-bone healing and cartilage repair

Ligament/tendon and cartilage injuries are clinically common diseases that perplex most clinicians. Because of the lack of blood vessels and nerves, their self-repairing abilities are rather poor. Therefore, surgeries are necessary and also widely used to treat ligament/tendon or cartilage injuries. However, after surgery, there are still many problems that affect healing. In recent years, it has been found that exogenous FGF2 plays an important role in the repair of ligament/tendon and cartilage injuries and exerts a synergistic effect with endogenous FGF2. Therefore, FGF2 can be used as a new type of biomolecule to accelerate tendon-to-bone healing and cartilage repair after injury.

In vitro analysis of the effect of Flightless I on murine tenocyte cellular functions

BACKGROUND

Healing of tendons after injury involves the proliferation of tenocytes and the production of extracellular matrix; however, their capacity to heal is limited by poor cell density and limited growth factor activity. Flightless I (Flii) has previously been identified as an important regulator of cellular proliferation and migration, and the purpose of this study was to evaluate the effect of differential Flii gene expression on tenocyte function in vitro.

METHODS

The role of Flii on tenocyte proliferation, migration, and contraction was assessed using established assays. Tenocytes from Flii^+/-, wild-type, and Flii overexpressing mice were obtained and the effect of differential Flii expression on migration, proliferation, contraction, and collagen synthesis determined in vitro. Statistical differences were determined using unpaired Student's t test and statistical outliers were identified using the Grubbs' test.

RESULTS

Flii overexpressing tenocytes showed significantly improved migration and proliferation as well as increased collagen I secretion. Explanted tendons from Flii overexpressing mice also showed significantly elevated tenocyte outgrowth compared to Flii^+/- mice. In contrast to its role in dermal wound repair, Flii positively affects cellular processes in tendons.

CONCLUSIONS

These findings suggest that Flii could be a novel target for modulating tenocyte activity and improving tendon repair. This could have significant clinical implications as novel therapeutic targets for improved healing of tendon injuries are urgently needed.

Impact of PDGF-BB on cellular distribution and extracellular matrix in the healing rabbit Achilles tendon three weeks post-operation

Current methods for tendon rupture repair suffer from two main drawbacks: insufficient strength and adhesion formation, which lead to rerupture and impaired gliding. A novel polymer tube may help to overcome these problems by allowing growth factor delivery to the wound site and adhesion reduction, and by acting as a physical barrier to the surrounding tissue. In this study, we used a bilayered DegraPol® tube to deliver PDGF-BB to the wound site in a full-transection rabbit Achilles tendon model. We then performed histological and immunohistochemical analysis at 3 weeks postoperation. Sustained delivery of PDGF-BB to the healing Achilles tendon led to a significantly more homogenous cell distribution within the healing tissue. Lower cell densities next to the implant material were determined for +PDGF-BB samples compared to -PDGF-BB. PDGF-BB application increased proteoglycan content and reduced alpha-SMA+ areas, clusters of different sizes, mainly vessels. Finally, PDGF-BB reduced collagens I and III in the extracellular matrix. The sustained delivery of PDGF-BB via an electrospun DegraPol® tube accelerated tendon wound healing by causing a more uniform cell distribution with higher proteoglycan content and less fibrotic tissue. Moreover, the application of this growth factor reduced collagen III and alpha-SMA, indicating a faster and less fibrotic tendon healing.

Biologics in the Treatment of Achilles Tendon Pathologies

Regenerative medicine is gaining more and more space for the treatment of Achilles pathologic conditions. Biologics could play a role in the management of midportion Achilles tendinopathy as a step between conservative and surgical treatment or as an augmentation. Higher-level studies are needed before determining a level of treatment recommendation for biologic strategies for insertional Achilles tendinopathy. Combining imaging with patient's functional requests could be the way to reach a protocol for the use of biologics for the treatment of midportion Achilles tendinopathy and, for this perspective, the authors describe the Foot and Ankle Reconstruction Group algorithm of treatment.

Biologic and mechanical aspects of tendon fibrosis after injury and repair

Tendon injuries of the hand that require surgical repair often heal with excess scarring and adhesions to adjacent tissues. This can compromise the natural gliding mechanics of the flexor tendons in particular, which operate within a fibro-osseous tunnel system similar to a set of pulleys. Even combining the finest suture repair techniques with optimal hand therapy protocols cannot ensure predictable restoration of hand function in these cases. To date, the majority of research regarding tendon injuries has revolved around the mechanical aspects of the surgical repair (i.e. suture techniques) and postoperative rehabilitation. The central principles of treatment gleaned from this literature include using a combination of core and epitendinous sutures during repair and initiating motion early on in hand therapy to improve tensile strength and limit adhesion formation. However, it is likely that the best clinical solution will utilize optimal biological modulation of the healing response in addition to these core strategies and, recently, the research in this area has expanded considerably. While there are no proven additive biological agents that can be used in clinical practice currently, in this review, we analyze the recent literature surrounding cytokine modulation, gene and cell-based therapies, and tissue engineering, which may ultimately lead to improved clinical outcomes following tendon injury in the future.

Essential role of Mohawk for tenogenic tissue homeostasis including spinal disc and periodontal ligament

Tendons and ligaments play essential roles in connecting muscle and bone and stabilizing the connections between bones. The damage to tendons and ligaments caused by aging, injury, and arthritis induces the dysfunction of the musculoskeletal system and reduces the quality of life. Current therapy for damaged tendons and ligaments depends on self-repair; however, it is difficult to reconstruct normal tissue. Regeneration therapy for tendons and ligaments has not been achieved, partly because the mechanism, cell biology, and pathophysiology of tendon and ligament development remain unclear. This review summarizes the role of the transcription factor, Mohawk, which controls tendon and ligament cell differentiation, in the maintenance of cell homeostasis, as well as its function in disease and the possibility of new therapeutic approaches.

Current trends in tendinopathy: consensus of the ESSKA basic science committee. Part II: treatment options

The treatment of painful chronic tendinopathy is challenging. Multiple non-invasive and tendon-invasive methods are used. When traditional non-invasive treatments fail, the injections of platelet-rich plasma autologous blood or cortisone have become increasingly favored. However, there is little scientific evidence from human studies supporting injection treatment. As the last resort, intra- or peritendinous open or endoscopic surgery are employed even though these also show varying results. This ESSKA basic science committee current concepts review follows the first part on the biology, biomechanics and anatomy of tendinopathies, to provide a comprehensive overview of the latest treatment options for tendinopathy as reported in the literature.

Polydeoxyribonucleotide improves tendon healing following achilles tendon injury in rats

Tendon injuries are major musculoskeletal disorders. Polydeoxyribonucleotide activates the adenosine receptor subtype A2A, resulting in tissue growth and neogenesis. This experimental study confirms that polydeoxyribonucleotide can improve secretion of various growth factors, promote collagen synthesis, and restore tensile strength of the Achilles tendon in a rat model with Achilles tendon injury. Thirty-six male Sprague-Dawley rats, aged 7 weeks, were divided into two groups, and the Achilles tendon was transected and repaired using the modified Kessler's method. In the experimental group (n = 18), the rats received daily intraperitoneal administration of polydeoxyribonucleotide (8 mg/kg/day for 1, 2, or 4 weeks). The control groups received the same amount of normal saline. The rats were euthanized at 1, 2, and 4 weeks, and tissues from the repair site were harvested. The cross-sectional area of the tendon was significantly increased at 2 and 4 weeks in polydeoxyribonucleotide group (p = 0.008 and p = 0.017, respectively). Moreover, tendons in the polydeoxyribonucleotide group were more resistant to mechanical stress at 2 and 4 weeks (p = 0.041 and p = 0.041, respectively). The staining levels of collagen type I in the experimental group were significantly stronger at 2 and 4 weeks (p = 0.026 and p = 0.009, respectively). Furthermore, higher expression levels of fibroblast growth factor, vascular endothelial growth factor, and transforming growth factor β1 were detected in the experimental group at 4 weeks (p = 0.041, p = 0.026, and p = 0.041, respectively). This study confirms that polydeoxyribonucleotide can improve the tensile strength of the rats' Achilles tendon following injury and repair. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:1767-1776, 2018.

Investigation of the biomechanical and histopathological effects of autologous conditioned serum on healing of Achilles tendon

Objective

The aim of this study to evaluate the effects of autologous conditioned serum (ACS) on the healing of transected rat Achilles tendons via the assessment of biomechanical and histological parameters.

Methods

The study was conducted on 45 male Sprague–Dawley rats. Five rats were used as donors for ACS preparation. Animals were randomly assigned to the experimental or control group. In both groups, the Achilles tendon was cut transversally and then sutured. In the placebo control and ACS-treated groups, saline or ACS, respectively, was injected into the repair zone three times after surgery. Ten rats from each group (ACS group, n = 20; control group, n = 20) were euthanized at days 15 and 30 after surgery for histopathological (n = 5) and biomechanical (n = 5) testing. The histopathological findings were interpreted using the Bonar and Movin scales. Tendon remodelling was evaluated via the immunohistochemical staining of collagen type 3. Biomechanical effects were assessed by tensile testing.

Results

The Bonar and Movin scale scores were significantly better in the ACS-treated group on both day 15 (p = 0.003 and p = 0.003, respectively) and day 30 (p = 0.005 and p = 0.004, respectively). The immunohistochemical density of collagen type 3 was significantly lower in the ACS-treated group on day 30 (p = 0.018). The type 1/3 collagen ratios of the groups were similar on days 15 and 30, as determined by Sirius Red staining (p = 0.910 and p = 0.133, respectively). In the biomechanical assessment results, the ACS-treated group's maximum load to failure values were significantly higher on day 15 (p = 0.049).

Conclusion

Injection of ACS had a positive effect on the histopathological healing of rat Achilles tendons on days 15 and 30 and on biomechanical healing on day 15. ACS treatment contributed to lowering the collagen type 3 density by day 30. According to our study, ACS may be favourable for the treatment of human Achilles tendon injuries and tendinopathies.

Tendon injuries: Basic science and new repair proposals

Tendons connect muscles to bones, ensuring joint movement. With advanced age, tendons become more prone to degeneration followed by injuries. Tendon repair often requires lengthy periods of rehabilitation, especially in elderly patients. Existing medical and surgical treatments often fail to regain full tendon function.

The development of novel treatment methods has been hampered due to limited understanding of basic tendon biology. Recently, it was discovered that tendons, similar to other mesenchymal tissues, contain tendon stem/progenitor cells (TSPCs) which possess the common stem cell properties.

The current strategies for enhancing tendon repair consist mainly of applying stem cells, growth factors, natural and artificial biomaterials alone or in combination. In this review, we summarise the basic biology of tendon tissues and provide an update on the latest repair proposals for tendon tears.

Cite this article: EFORT Open Rev 2017;2:332-342. DOI: 10.1302/2058-5241.2.160075

PXL01 in sodium hyaluronate results in increased PRG4 expression: a potential mechanism for anti-adhesion

PURPOSE

To investigate the anti-adhesive mechanisms of PXL01 in sodium hyaluronate (HA) by using the rabbit lactoferrin peptide, rabPXL01 in HA, in a rabbit model of healing tendons and tendon sheaths. The mechanism of action for PXL01 in HA is interesting since a recent clinical study of the human lactoferrin peptide PXL01 in HA administered around repaired tendons in the hand showed improved digit mobility.

MATERIALS AND METHODS

On days 1, 3, and 6 after tendon injury and surgical repair, reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) was used to assess mRNA expression levels for genes encoding the mucinous glycoprotein PRG4 (also called lubricin) and a subset of matrix proteins, cytokines, and growth factors involved in flexor tendon repair. RabPXL01 in HA was administered locally around the repaired tendons, and mRNA expression was compared with untreated repaired tendons and tendon sheaths.

RESULTS

We observed, at all time points, increased expression of PRG4 mRNA in tendons treated with rabPXL01 in HA, but not in tendon sheaths. In addition, treatment with rabPXL01 in HA led to repression of the mRNA levels for the pro-inflammatory mediators interleukin (IL)-1β, IL-6, and IL-8 in tendon sheaths.

CONCLUSIONS

RabPXL01 in HA increased lubricin mRNA production while diminishing mRNA levels of inflammatory mediators, which in turn reduced the gliding resistance and inhibited the adhesion formation after flexor tendon repair.

Immortalized Mouse Achilles Tenocytes Demonstrate Long-Term Proliferative Capacity While Retaining Tenogenic Properties

Investigating the cellular processes underlying tendon healing can allow researchers to improve long-term outcomes after injury. However, conducting meaningful studies to uncover the injury healing mechanism at cellular and molecular levels remains challenging. This is due to the inherent difficulty in isolating, culturing, and expanding sufficient primary tenocytes, due to their limited proliferative capacity and short lifespan. In this study, we sought to establish a novel line of immortalized mouse Achilles tenocytes (iMATs) with primary tenocyte properties, but increased proliferative capacity suitable for extensive in vitro experimentation. We show that isolated primary mouse Achilles tenocytes (pMATs) can be effectively immortalized using a piggyBac transposon expressing SV40 large T antigen flanked by FLP recombination target site (FRT). The resulting iMATs exhibit markedly greater proliferation and survival, which can be reversed with FLP recombinase. Furthermore, iMATs express the same set of tendon-specific markers as that of primary cells, although in lower levels, and respond similarly to exogenous stimulation with bone morphogenetic protein 13 (BMP13) as has been previously reported with pMATs. Taken together, our results suggest that iMATs acquire long-term proliferative capacity while maintaining tenogenic properties. We believe that iMATs are a suitable model for studying not only the native cellular processes involved in injury and healing, but also potential therapeutic agents that may augment the stability of tendon repair.

Lateral Elbow Tendinopathy: Development of a Pathophysiology-Based Treatment Algorithm

Lateral elbow tendinopathy, commonly known as tennis elbow, is a condition that can cause significant functional impairment in working-age patients. The term tendinopathy is used to describe chronic overuse tendon disorders encompassing a group of pathologies, a spectrum of disease. This review details the pathophysiology of tendinopathy and tendon healing as an introduction for a system grading the severity of tendinopathy, with each of the 4 grades displaying distinct histopathological features. Currently, there are a large number of nonoperative treatments available for lateral elbow tendinopathy, with little guidance as to when and how to use them. In fact, an appraisal of the clinical trials, systematic reviews, and meta-analyses studying these treatment modalities reveals that no single treatment reliably achieves outstanding results. This may be due in part to the majority of clinical studies to date including all patients with chronic tendinopathy rather than attempting to categorize patients according to the severity of disease. We relate the pathophysiology of the different grades of tendinopathy to the basic science principles that underpin the mechanisms of action of the nonoperative treatments available to propose a treatment algorithm guiding the management of lateral elbow tendinopathy depending on severity. We believe that this system will be useful both in clinical practice and for the future investigation of the efficacy of treatments.

Recent Scientific Advances Towards the Development of Tendon Healing Strategies

There exists a range of surgical and non-surgical approaches to the treatment of both acute and chronic tendon injuries. Despite surgical advances in the management of acute tears and increasing treatment options for tendinopathies, strategies frequently are unsuccessful, due to impaired mechanical properties of the treated tendon and/or a deficiency in progenitor cell activities. Hence, there is an urgent need for effective therapeutic strategies to augment intrinsic and/or surgical repair. Such approaches can benefit both tendinopathies and tendon tears which, due to their severity, appear to be irreversible or irreparable. Biologic therapies include the utilization of scaffolds as well as gene, growth factor, and cell delivery. These treatment modalities aim to provide mechanical durability or augment the biologic healing potential of the repaired tissue. Here, we review the emerging concepts and scientific evidence which provide a rationale for tissue engineering and regeneration strategies as well as discuss the clinical translation of recent innovations.

Enhanced Achilles tendon healing by fibromodulin gene transfer

Tendon injury is a major musculoskeletal disorder with a high public health impact. We propose a non-viral based strategy of gene therapy for the treatment of tendon injuries using histidylated vectors. Gene delivery of fibromodulin, a proteoglycan involved in collagen assembly was found to promote rat Achilles tendon repair in vivo and in vitro. In vivo liposome-based transfection of fibromodulin led to a better healing after surgical injury, biomechanical properties were better restored compared to untransfected control. These measures were confirmed by histological observations and scoring. To get better understandings of the mechanisms underlying fibromodulin transfection, an in vitro tendon healing model was developed. In vitro, polymer-based transfection of fibromodulin led to the best wound enclosure speed and a pronounced migration of tenocytes primary cultures was observed. These results suggest that fibromodulin non-viral gene therapy could be proposed as a new therapeutic strategy to accelerate tendon healing.

FROM THE CLINICAL EDITOR

Tendon injury is relatively common and healing remains unsatisfactory. In this study, the effects of liposomal-based delivery of fibromodulin gene were investigated in a rat Achilles tendon injury model. The positive results observed would provide a new therapeutic strategy in clinical setting in the future.

rhPDGF-BB promotes early healing in a rat rotator cuff repair model

BACKGROUND

Tendon-bone healing after rotator cuff repair occurs by fibrovascular scar tissue formation, which is weaker than a normal tendon-bone insertion site. Growth factors play a role in tissue formation and have the potential to augment soft tissue healing in the perioperative period.

QUESTIONS/PURPOSES

Our study aim was to determine if rhPDGF-BB delivery on a collagen scaffold can improve tendon-to-bone healing after supraspinatus tendon repair compared with no growth factor in rats as measured by (1) gross observations; (2) histologic analysis; and (3) biomechanical testing.

METHODS

Ninety-five male Sprague-Dawley rats underwent acute repair of the supraspinatus tendon. Rats were randomized into one of five groups: control (ie, repair only), scaffold only, and three different platelet-derived growth factor (PDGF) doses on the collagen scaffold. Animals were euthanized 5 days after surgery to assess cellular proliferation and angiogenesis. The remaining animals were analyzed at 4 weeks to assess repair site integrity by gross visualization, fibrocartilage formation with safranin-O staining, and collagen fiber organization with picrosirius red staining, and to determine the biomechanical properties (ie, load-to-failure testing) of the supraspinatus tendon-bone construct.

RESULTS

The repaired supraspinatus tendon was in continuity with the bone in all animals. At 5 days, rhPDGF-BB delivery on a scaffold demonstrated a dose-dependent response in cellular proliferation and angiogenesis compared with the control and scaffold groups. At 28 days, with the numbers available, rhPDGF-BB had no effect on increasing fibrocartilage formation or improving collagen fiber maturity at the tendon-bone insertion site compared with controls. The control group had higher tensile loads to failure and stiffness (35.5 ± 8.8 N and 20.3 ± 4.5 N/mm) than all the groups receiving the scaffold, including the PDGF groups (scaffold: 27 ± 6.4 N, p = 0.021 and 13 ± 5.7 N/mm, p = 0.01; 30 µg/mL PDGF: 26.5 ± 7.5 N, p = 0.014 and 13.3 ± 3.2 N/mm, p = 0.01; 100 µg/mL PDGF: 25.7 ± 6.1 N, p = 0.005 and 11.6 ± 3.3 N/mm, p = 0.01; 300 µg/mL PDGF: 27 ± 6.9 N, p = 0.014 and 12.7 ± 4.1 N/mm, p = 0.01).

CONCLUSIONS

rhPDGF-BB delivery on a collagen scaffold enhanced cellular proliferation and angiogenesis during the early phase of healing, but this did not result in either a more structurally organized or stronger attachment site at later stages of healing. The collagen scaffold had a detrimental effect on healing strength at 28 days, and its relatively larger size compared with the rat tendon may have caused mechanical impingement and extrinsic compression of the healing tendon. Future studies should be performed in larger animal models where healing occurs more slowly.

CLINICAL RELEVANCE

Augmenting the healing environment to improve the structural integrity and to reduce the retear rate after rotator cuff repair may be realized with continued understanding and optimization of growth factor delivery systems.

Progress in cell-based therapies for tendon repair

The last decade has seen significant developments in cell therapies, based on permanently differentiated, reprogrammed or engineered stem cells, for tendon injuries and degenerative conditions. In vitro studies assess the influence of biophysical, biochemical and biological signals on tenogenic phenotype maintenance and/or differentiation towards tenogenic lineage. However, the ideal culture environment has yet to be identified due to the lack of standardised experimental setup and readout system. Bone marrow mesenchymal stem cells and tenocytes/dermal fibroblasts appear to be the cell populations of choice for clinical translation in equine and human patients respectively based on circumstantial, rather than on hard evidence. Collaborative, inter- and multi-disciplinary efforts are expected to provide clinically relevant and commercially viable cell-based therapies for tendon repair and regeneration in the years to come.

A review on the use of cell therapy in the treatment of tendon disease and injuries

Tendon disease and injuries carry significant morbidity worldwide in both athletic and non-athletic populations. It is estimated that tendon injuries account for 30%−50% of all musculoskeletal injuries globally. Current treatments have been inadequate in providing an accelerated process of repair resulting in high relapse rates. Modern concepts in tissue engineering and regenerative medicine have led to increasing interest in the application of cell therapy for the treatment of tendon disease. This review will explore the use of cell therapy, by bringing together up-to-date evidence from in vivo human and animal studies, and discuss the issues surrounding the safety and efficacy of its use in the treatment of tendon disease.

The biophysical, biochemical, and biological toolbox for tenogenic phenotype maintenance in vitro

Tendon injuries constitute an unmet clinical need, with 3 to 5 million new incidents occurring annually worldwide. Tissue grafting and biomaterial-based approaches fail to provide environments that are conducive to regeneration; instead they lead to nonspecific cell adhesion and scar tissue formation, which collectively impair functionality. Cell based therapies may potentially recover native tendon function, if tenocyte trans-differentiation can be evaded and stem cell differentiation towards tenogenic lineage is attained. To this end, recreating an artificial in vivo tendon niche by engineering functional in vitro microenvironments is a research priority. Clinically relevant cell based therapies for tendon repair and regeneration could be created using tools that harness biophysical beacons (surface topography, mechanical loading), biochemical cues (oxygen tension), and biological signals (growth factors).

The growth factors involved in flexor tendon repair and adhesion formation

Flexor tendon injuries remain a significant clinical problem, owing to the formation of adhesions or tendon rupture. A number of strategies have been tried to improve outcomes, but as yet none are routinely used in clinical practice. Understanding the role that growth factors play in tendon repair should enable a more targeted approach to be developed to improve the results of flexor tendon repair. This review describes the main growth factors in tendon wound healing, and the role they play in both repair and adhesion formation.

Direct FGF-2 gene transfer via recombinant adeno-associated virus vectors stimulates cell proliferation, collagen production, and the repair of experimental lesions in the human ACL

BACKGROUND

Basic fibroblast growth factor (FGF-2) is a powerful stimulator of fibroblast proliferation and type I/III collagen production.

HYPOTHESIS

Overexpression of FGF-2 via direct recombinant adeno-associated virus (rAAV) vector-mediated gene transfer enhances the healing of experimental lesions to the human anterior cruciate ligament (ACL).

STUDY DESIGN

Controlled laboratory study.

METHODS

rAAV vectors carrying a human FGF-2 sequence or the lacZ marker gene were applied to primary human ACL fibroblasts in vitro and to intact or experimentally injured human ACL explants in situ to evaluate the efficacy and duration of transgene expression and the potential effects of FGF-2 treatment upon the proliferative, metabolic, and regenerative activities in these systems.

RESULTS

Sustained, effective dose-dependent lacZ expression was achieved in all systems tested (up to 96% ± 2% in vitro and 80%-85% in situ for at least 30 days). rAAV allowed for continuous FGF-2 production both in vitro and in the intact ACL in situ (32.7 ± 1.4 and 33.1 ± 0.8 pg/mL/24 h, respectively, ie, up to 41-fold more than in the controls at day 30; always P ≤ .001), leading to significantly and durably enhanced levels of proliferation and type I/III collagen production vis-à-vis lacZ (at least 3- and 4-fold increases at day 30, respectively; always P ≤ .001). Most notably, rAAV FGF-2 promoted a significant, long-term production of the factor in experimental ACL lesions (92.7 ± 3.9 pg/mL/24 h, ie, about 5-fold more than in the controls; P ≤ .001) associated with enhanced levels of proliferation and type I/III collagen synthesis (at least 2- and 4-fold increases at day 30, respectively; always P ≤ .001). Remarkably, the FGF-2 treatment allowed for a decrease in the amplitude of such lesions possibly because of the increased expression in contractile α-smooth muscle actin, ligament-specific transcription factor scleraxis, and nuclear factor-κB for proliferation and collagen deposition, which are all markers commonly induced in response to injury.

CONCLUSION

Efficient, stable FGF-2 expression via rAAV enhances the healing of experimental human ACL lesions by activating key cellular and metabolic processes.

CLINICAL RELEVANCE

This approach has potential value for the development of novel, effective treatments for ligament reconstruction.

The effect of growth factors on both collagen synthesis and tensile strength of engineered human ligaments

Growth factors play a central role in the development and remodelling of musculoskeletal tissues. To determine which growth factors optimized in vitro ligament formation and mechanics, a Box-Behnken designed array of varying concentrations of growth factors and ascorbic acid were applied to engineered ligaments and the collagen content and mechanics of the grafts were determined. Increasing the amount of transforming growth factor (TGF) β1 and insulin-like growth factor (IGF)-1 led to an additive effect on ligament collagen and maximal tensile load (MTL). In contrast, epidermal growth factor (EGF) had a negative effect on both collagen content and MTL. The predicted optimal growth media (50 μg/ml TGFβ, IGF-1, and GDF-7 and 200 μM ascorbic acid) was then validated in two separate trials: showing a 5.7-fold greater MTL and 5.2-fold more collagen than a minimal media. Notably, the effect of the maximized growth media was scalable such that larger constructs developed the same material properties, but larger MTL. These results show that optimizing the interactions between growth factors and engineered ligament volume results in an engineered ligament of clinically relevant function.

Studies in flexor tendon reconstruction: biomolecular modulation of tendon repair and tissue engineering

The Andrew J. Weiland Medal is presented each year by the American Society for Surgery of the Hand and the American Foundation for Surgery of the Hand for a body of work related to hand surgery research. This essay, awarded the Weiland Medal in 2011, focuses on the clinical need for flexor tendon reconstruction and on investigations into flexor tendon biology. Reconstruction of the upper extremity is limited by 2 major problems after injury or degeneration of the flexor tendons. First, adhesions formed after flexor tendon repair can cause decreased postoperative range of motion and hand function. Second, tendon losses can result from trauma and degenerative diseases, necessitating additional tendon graft material. Tendon adhesions are even more prevalent after tendon grafting; therefore these 2 problems are interrelated and lead to considerable disability. The total costs in terms of disability and inability to return to work are enormous. In this essay, published work from the past 12 years in our basic science laboratory is summarized and presented with the common theme of using molecular techniques to understand the cellular process of flexor tendon wound healing and to create substances and materials to improve tendon repair and regeneration. These are efforts to address 2 interrelated and clinically relevant problems that all hand surgeons face in their practice.

BMPs are mediators in tissue crosstalk of the regenerating musculoskeletal system

The musculoskeletal system is a tight network of many tissues. Coordinated interplay at a biochemical level between tissues is essential for development and repair. Traumatic injury usually affects several tissues and represents a large challenge in clinical settings. The current demand for potent growth factors in such applications thus accompanies the keen interest in molecular mechanisms and orchestration of tissue formation. Of special interest are multitasking growth factors that act as signals in a variety of cell types, both in a paracrine and in an autocrine manner, thereby inducing cell differentiation and coordinating not only tissue assembly at specific sites but also maturation and homeostasis. We concentrate here on bone morphogenetic proteins (BMPs), which are important crosstalk mediators known for their irreplaceable roles in vertebrate development. The molecular crosstalk during embryonic musculoskeletal tissue formation is recapitulated in adult repair. BMPs act at different levels from the initiation to maturation of newly formed tissue. Interestingly, this is influenced by the spatiotemporal expression of different BMPs, their receptors and co-factors at the site of repair. Thus, the regenerative potential of BMPs needs to be evaluated in the context of highly connected tissues such as muscle and bone and might indeed be different in more poorly connected tissues such as cartilage. This highlights the need for an understanding of BMP signaling across tissues in order to eventually improve BMP regenerative potential in clinical applications. In this review, the distinct members of the BMP family and their individual contribution to musculoskeletal tissue repair are summarized by focusing on their paracrine and autocrine functions.

Cell- and gene-based approaches to tendon regeneration

Repair of rotator cuff tears in experimental models has been significantly improved by the use of enhanced biologic approaches, including platelet-rich plasma, bone marrow aspirate, growth factor supplements, and cell- and gene-modified cell therapy. Despite added complexity, cell-based therapies form an important part of enhanced repair, and combinations of carrier vehicles, growth factors, and implanted cells provide the best opportunity for robust repair. Bone marrow-derived mesenchymal stem cells provide a stimulus for repair in flexor tendons, but application in rotator cuff repair has not shown universally positive results. The use of scaffolds such as platelet-rich plasma, fibrin, and synthetic vehicles and the use of gene priming for stem cell differentiation and local anabolic and anti-inflammatory impact have both provided essential components for enhanced tendon and tendon-to-bone repair in rotator cuff disruption. Application of these research techniques in human rotator cuff injury has generally been limited to autologous platelet-rich plasma, bone marrow concentrate, or bone marrow aspirates combined with scaffold materials. Cultured mesenchymal progenitor therapy and gene-enhanced function have not yet reached clinical trials in humans. Research in several animal species indicates that the concept of gene-primed stem cells, particularly embryonic stem cells, combined with effective culture conditions, transduction with long-term integrating vectors carrying anabolic growth factors, and development of cells conditioned by use of RNA interference gene therapy to resist matrix metalloproteinase degradation, may constitute potential advances in rotator cuff repair. This review summarizes cell- and gene-enhanced cell research for tendon repair and provides future directions for rotator cuff repair using biologic composites.

Advances in polymeric systems for tissue engineering and biomedical applications

The characteristics of tissue engineered scaffolds are major concerns in the quest to fabricate ideal scaffolds for tissue engineering applications. The polymer scaffolds employed for tissue engineering applications should possess multifunctional properties such as biocompatibility, biodegradability and favorable mechanical properties as it comes in direct contact with the body fluids in vivo. Additionally, the polymer system should also possess biomimetic architecture and should support stem cell adhesion, proliferation and differentiation. As the progress in polymer technology continues, polymeric biomaterials have taken characteristics more closely related to that desired for tissue engineering and clinical needs. Stimuli responsive polymers also termed as smart biomaterials respond to stimuli such as pH, temperature, enzyme, antigen, glucose and electrical stimuli that are inherently present in living systems. This review highlights the exciting advancements in these polymeric systems that relate to biological and tissue engineering applications. Additionally, several aspects of technology namely scaffold fabrication methods and surface modifications to confer biological functionality to the polymers have also been discussed. The ultimate objective is to emphasize on these underutilized adaptive behaviors of the polymers so that novel applications and new generations of smart polymeric materials can be realized for biomedical and tissue engineering applications.

Role of growth factors in rotator cuff healing

The histologic lesion underlying overuse rotator cuff tendinopathy is a failed healing response, with haphazard proliferation of tenocytes, disruption of tendon cells and collagen fibers, and increased noncollagenous extracellular matrix. Recent attention has focused on the biological pathways by which tendons heal, leading to the identification of several growth factors (GFs) involved in this process. No studies have been published on the time course of the various GFs during rotator cuff healing process in vivo, in humans. We review what is known about these GFs and their role in rotator cuff healing.

Three-dimensional high-density co-culture with primary tenocytes induces tenogenic differentiation in mesenchymal stem cells

Mesenchymal stem cells (MSCs) have potential applications in regenerative medicine and tissue engineering and may represent an attractive option for tendon repair and regeneration. Thus far the ability of MSCs to differentiate into tenocytes in vitro has not been investigated. Experiments were performed with and without growth factors (IGF-1, TGF-β1, IGF-1/TGF-β1, PDGF-BB, and BMP-12), in co-cultures of tenocytes and MSCs mixed in different ratios and by culturing MSCs with spent media obtained from primary tenocytes. Tenogenesis was induced in MSCs through a combination of treatment with IGF-1 and TGF-β1, in high-density co-cultures and through cultivation with the spent media from primary tenocytes. Electron microscopy and immunoblotting were used to demonstrate up-regulation of collagen I/III, decorin, tenomodulin, β1-Integrin, MAPKinase pathway (Shc, Erk1/2), and scleraxis in the co-cultures and provide simultaneous evidence for the inhibition of apoptosis. In monolayer co-cultures extensive intercellular contacts between MSCs and tenocytes were observed. Cells actively exchanged vesicles, which were labeled by using immunofluorescence and immunogold techniques, suggesting the uptake and interchange of soluble factors produced by the MSCs and/or tenocytes. We conclude that MSCs possess tenogenic differentiation potential when provided with relevant stimuli and a suitable microenvironment. This approach may prove to be of practical benefit in future tissue engineering and tendon regenerative medicine research.

Mesenchymal stem cell characteristics of human anterior cruciate ligament outgrowth cells

When ruptured, the anterior cruciate ligament (ACL) of the human knee has limited regenerative potential. However, the goal of this report was to show that the cells that migrate out of the human ACL constitute a rich population of progenitor cells and we hypothesize that they display mesenchymal stem cell (MSC) characteristics when compared with adherent cells derived from bone marrow or collagenase digests from ACL. We show that ACL outgrowth cells are adherent, fibroblastic cells with a surface immunophenotype strongly positive for cluster of differentiation (CD)29, CD44, CD49c, CD73, CD90, CD97, CD105, CD146, and CD166, weakly positive for CD106 and CD14, but negative for CD11c, CD31, CD34, CD40, CD45, CD53, CD74, CD133, CD144, and CD163. Staining for STRO-1 was seen by immunohistochemistry but not flow cytometry. Under suitable culture conditions, the ACL outgrowth-derived MSCs differentiated into chondrocytes, osteoblasts, and adipocytes and showed capacity to self-renew in an in vitro assay of ligamentogenesis. MSCs derived from collagenase digests of ACL tissue and human bone marrow were analyzed in parallel and displayed similar, but not identical, properties. In situ staining of the ACL suggests that the MSCs reside both aligned with the collagenous matrix of the ligament and adjacent to small blood vessels. We conclude that the cells that emigrate from damaged ACLs are MSCs and that they have the potential to provide the basis for a superior, biological repair of this ligament.

Tissue engineering solutions for tendon repair

Tendon injuries range from acute traumatic ruptures and lacerations to chronic overuse injuries, such as tendinosis. Even with improved nonsurgical, surgical, and rehabilitation techniques, outcomes following tendon repair are inconsistent. Primary repair remains the standard of care. However, repaired tendon tissue rarely achieves functionality equal to that of the preinjured state. Poor results have been linked to alterations in cellular organization within the tendon that occur at the time of injury and throughout the early stages of healing. Enhanced understanding of the biology of tendon healing is needed to improve management and outcomes. The use of growth factors and mesenchymal stem cells and the development of biocompatible scaffolds could result in enhanced tendon healing and regeneration. Recent advances in tendon bioengineering may lead to improved management following tendon injury.

Tissue engineered biological augmentation for tendon healing: a systematic review

INTRODUCTION

Tendon injuries give rise to significant morbidity. In the last few decades, several techniques have been increasingly used to optimize tendon healing.

SOURCES OF DATA

We performed a comprehensive search of PubMed, Medline, Cochrane, CINAHL and Embase databases using various combinations of the commercial names of each scaffold and the keywords 'tendon', 'rotator cuff', 'supraspinatus tendon', 'Achilles tendon', 'growth factors', 'cytokines', 'gene therapy', 'tissue engineering', 'mesenchymal' and 'stem cells' over the years 1966-2009. All articles relevant to the subject were retrieved, and their bibliographies were hand searched for further references in the context to tissue-engineered biological augmentation for tendon healing.

AREAS OF AGREEMENT

Several new techniques are available for tissue-engineered biological augmentation for tendon healing, growth factors, gene therapy and mesenchimal stem cells.

AREAS OF CONTROVERSY

Data are lacking to allow definitive conclusions on the use of these techniques for routine management of tendon ailments.

GROWING POINTS

The emerging field of tissue engineering holds the promise to use new techniques for tendon augmentation and repair. Preliminary studies support the idea that these techniques can provide an alternative for tendon augmentation with great therapeutic potential.

AREAS TIMELY FOR DEVELOPING RESEARCH

The optimization strategies discussed in this article are currently at an early stage of development. Although these emerging technologies may develop into substantial clinical treatment options, their full impact needs to be critically evaluated in a scientific fashion.

Stem cells for tendon tissue engineering and regeneration

IMPORTANCE OF THE FIELD

Tendon injuries are common especially in sports activities, but tendon is a unique connective tissue with poor self-repair capability. With advances in stem cell biology, tissue engineering is becoming increasingly powerful for tissue regeneration. Stem cells with capacity of multipotency and self-renewal are an ideal cell source for tissue engineering.

AREAS COVERED IN THIS REVIEW

This review focus on discussing the potential strategies including inductive growth factors, bio-scaffolds, mechanical stimulation, genetic modification and co-culture techniques to direct tendon-lineage differentiation of stem cells for complete tendon regeneration. Attempting to use embryonic stem cells as seed cells for tendon tissue engineering have achieved encouraging results. The combination of chemical and physical signals in stem cell microenvironment could be regulated to induce differentiation of the embryonic stem cells into tendon.

WHAT THE READER WILL GAIN

We summarize fundamental questions, as well as future directions in tendon biology and tissue engineering.

TAKE HOME MESSAGE

Multifaceted technologies are increasingly required to control stem cell differentiation, to develop novel stem cell-based therapy, and, ultimately, to achieve more effective repair or regeneration of injured tendons.

Accelerated Achilles tendon healing by PDGF gene delivery with mesoporous silica nanoparticles

We report the ability of amino- and carboxyl-modified MCM-41 mesoporous silica nanoparticles (MSN) to deliver gene in vivo in rat Achilles tendons, despite their inefficiency to transfect primary tenocytes in culture. We show that luciferase activity lasted for at least 2 weeks in tendons injected with these MSN and a plasmid DNA (pDNA) encoding the luciferase reporter gene. By contrast, in tendons injected with naked plasmid, the luciferase expression decreased as a function of time and became hardly detectable after 2 weeks. Interestingly, there were neither signs of inflammation nor necrosis in tendon, kidney, heart and liver of rat weekly injected with pDNA/MSN formulation during 1.5 months. Our main data concern the acceleration of Achilles tendons healing by PDGF-B gene transfer using MSN. Biomechanical properties and histological analyses clearly indicate that tendons treated with MSN and PDGF gene healed significantly faster than untreated tendons and those treated with pPDGF alone.

Accelerated healing of the rat Achilles tendon in response to autologous conditioned serum

BACKGROUND

Despite advances in the treatment of ruptured Achilles tendon, imperfections of endogenous repair often leave patients symptomatic. Local administration of autologous conditioned serum (ACS) in patients with inflammatory, degenerative conditions has shown beneficial effects.

PURPOSE

Because ACS also contains growth factors that should accelerate tendon healing, we studied the effect of ACS on the healing of transected rat Achilles tendon.

STUDY DESIGN

Controlled laboratory study.

METHODS

In preliminary in vitro experiments, rat tendons were incubated with ACS and the effect on the expression of Col1A1 and Col3A1 was assessed by real-time quantitative polymerase chain reaction. To test its effect in vivo, the Achilles tendons of 80 Sprague Dawley rats were transected and sutured back together. Ten rats from each group (ACS group, n = 40; control group, n = 40) were euthanized at 1, 2, 4, and 8 weeks postoperatively for biomechanical (n = 7) and histologic (n = 3) testing. Lysyl oxidase activity was assayed by a flurometric assay. The organization of repair tissue was assessed histologically with hematoxylin and eosin- and with Sirius red-stained sections, and with immunohistochemistry.

RESULTS

Tendons exposed to ACS in vitro showed a greatly enhanced expression of the Col1A1 gene. The ACS-treated tendons were thicker, had more type I collagen, and an accelerated recovery of tendon stiffness and histologic maturity of the repair tissue. However, there were no differences in the maximum load to failure between groups up to week 8, perhaps because lysyl oxidase activities were unchanged.

CONCLUSION AND CLINICAL RELEVANCE

Overall, our study demonstrates that treatment with ACS has the potential to improve Achilles tendon healing and should be considered as a treatment modality in man. However, as strength was not shown to be increased within the parameters of this study, the clinical importance of the observed changes in humans still needs to be defined.

Tendon healing in vivo: gene expression and production of multiple growth factors in early tendon healing period

PURPOSE

The actions of growth factors during healing of injured flexor tendons are not well characterized, although information pertinent to some individual growth factors is available. We studied gene expression and protein production of a number of growth factors at several time points during the early healing period in a chicken model.

METHODS

Seventy-four long toes of 37 white Leghorn chickens were used. The flexor digitorum profundus tendons of 60 toes were surgically repaired after complete transection and were harvested for analysis 3, 5, 7, 9, 14, and 21 days after surgery. The expression of 6 growth factors was studied at 4 time points after surgery with real-time quantitative polymerase chain reactions, and production and distribution of 3 growth factors at all 6 time points were studied by immunohistochemical staining with antibodies. Fourteen tendons that had no surgery served as day 0 controls. Tendon healing status was also assessed histologically.

RESULTS

Throughout the early tendon healing period, connective tissue growth factor (CTGF) and transforming growth factor beta (TGF-beta) showed high levels of gene expression. Levels of gene expression of vascular endothelial growth factor (VEGF) and insulin-like growth factor 1 (IGF-1) were high or moderately high. Expression of the TGF-beta gene was upregulated after injury, whereas the basic fibroblast growth factor (bFGF) gene was downregulated at all postsurgical time points and expressed at the lowest levels among 6 growth factor genes 2 to 3 weeks after surgery. The platelet-derived growth factor B (PDGF-B) gene was also minimally expressed. Findings of immunohistochemistry corresponded to TGF-beta, bFGF, and IGF-1 gene expression.

CONCLUSIONS

In this model, up to 3 weeks after surgery, gene expression and production of TGF-beta are high and are upregulated in this healing period. However, expression of the bFGF gene and protein is low and decreases in the healing tendon. The CTGF, VEGF, and IGF-1 genes are expressed at high or moderately high levels, but PDGF-B is minimally expressed.

Ex vivo adenoviral transfer of bone morphogenetic protein 12 (BMP-12) cDNA improves Achilles tendon healing in a rat model

The aim of our study was to evaluate the histological and biomechanical effects of BMP-12 gene transfer on the healing of rat Achilles tendons using a new approach employing a genetically modified muscle flap. Biopsies of autologous skeletal muscle were transduced with a type-five, first-generation adenovirus carrying the human BMP-12 cDNA (Ad.BMP-12) and surgically implanted around experimentally transected Achilles tendons in a rat model. The effect of gene transfer on healing was evaluated by mechanical and histological testing after 1, 2, 4 and 8 weeks. One week after surgery, the maximum failure load of the healing tendons was significantly increased in the BMP-12 group, compared with the controls, and the tendon stiffness was significantly higher at 1, 2 and 4 weeks. Moreover, the size of the rupture callus was increased in the presence of BMP-12 and there was evidence of accelerated remodeling of the lesion in response to BMP-12. Histological examination showed a much more organized and homogeneous pattern of collagen fibers at all time points in lesions treated with the BMP-12 cDNA muscle graft. Both single fibrils and the collagen fibers had a greater diameter, with a higher degree of collagen crimp than the collagen of the control groups. This was confirmed by sirius red staining in conjunction with polarized light microscopy, which showed a higher shift of small yellow-green fibers to strong yellow-orange fibers after 2, 4 and 8 weeks in the presence of BMP-12 cDNA. There was also an earlier shift from fibroblasts to fibrocytes within the healing tendon, with less fat cells present in the tendons of the BMP-12 group compared with the controls. Treatment with BMP-12 cDNA-transduced muscle grafts thus produced a promising acceleration and improvement of tendon healing, particularly influencing early tissue regeneration, leading to quicker recovery and improved biomechanical properties of the Achilles tendon. Further development of this approach could have clinical applications.

Effect of osteogenic protein-1 on the matrix metabolism of bovine tendon cells

Tendon rupture is a common sports injury in adults. However, the mechanical properties of repair tissue are inferior to those of normal tissue. To accelerate tendon healing, an in vivo approach using growth factors has been applied and has shown evidence for the efficacy of biological stimulation of the repair process. Recombinant human osteogenic protein-1 (rhOP-1) has been shown to be effective in stimulating matrix production by various connective tissues. To test the effect of rhOP-1 on the matrix metabolism of tendon cells in vitro, bovine tendon cells were cultured in monolayer with various doses of rhOP-1 for 7 days. The addition of rhOP-1 to cell culture media resulted in significant increases in cell proliferation, DNA content, and the synthesis of proteoglycans (PGs) and collagen, compared to control cultures. The relative percentage of large PGs in the OP-1 culture was higher than that in the control culture. In conclusion, we show for the first time that rhOP-1 stimulates the proliferation of tendon cells and their ability to synthesize and accumulate PGs and collagen in their extracellular matrix. These biological properties may be used in the tissue-engineering of tendon tissues.

Tendon: biology, biomechanics, repair, growth factors, and evolving treatment options

Surgical treatment of tendon ruptures and lacerations is currently the most common therapeutic modality. Tendon repair in the hand involves a slow repair process, which results in inferior repair tissue and often a failure to obtain full active range of motion. The initial stages of repair include the formation of functionally weak tissue that is not capable of supporting tensile forces that allow early active range of motion. Immobilization of the digit or limb will promote faster healing but inevitably results in the formation of adhesions between the tendon and tendon sheath, which leads to friction and reduced gliding. Loading during the healing phase is critical to avoid these adhesions but involves increased risk of rupture of the repaired tendon. Understanding the biology and organization of the native tendon and the process of morphogenesis of tendon tissue is necessary to improve current treatment modalities. Screening the genes expressed during tendon morphogenesis and determining the growth factors most crucial for tendon development will likely lead to treatment options that result in superior repair tissue and ultimately improved functional outcomes.

Involvement of vessels and PDGFB in muscle splitting during chick limb development

Muscle formation and vascular assembly during embryonic development are usually considered separately. In this paper, we investigate the relationship between the vasculature and muscles during limb bud development. We show that endothelial cells are detected in limb regions before muscle cells and can organize themselves in space in the absence of muscles. In chick limbs, endothelial cells are detected in the future zones of muscle cleavage, delineating the cleavage pattern of muscle masses. We therefore perturbed vascular assembly in chick limbs by overexpressing VEGFA and demonstrated that ectopic blood vessels inhibit muscle formation, while promoting connective tissue. Conversely, local inhibition of vessel formation using a soluble form of VEGFR1 leads to muscle fusion. The endogenous location of endothelial cells in the future muscle cleavage zones and the inverse correlation between blood vessels and muscle suggests that vessels are involved in the muscle splitting process. We also identify the secreted factor PDGFB (expressed in endothelial cells) as a putative molecular candidate mediating the muscle-inhibiting and connective tissue-promoting functions of blood vessels. Finally, we propose that PDGFB promotes the production of extracellular matrix and attracts connective tissue cells to the future splitting site, allowing separation of the muscle masses during the splitting process.

Platelet rich plasma (PRP) enhances anabolic gene expression patterns in flexor digitorum superficialis tendons

Platelet rich plasma (PRP) has recently been investigated for use in tissue regeneration studies that seek to utilize the numerous growth factors released from platelet alpha-granules. This study examined gene expression patterns, DNA, and collagen content of equine flexor digitorum superficialis tendon (SDFT) explants cultured in media consisting of PRP and other blood products. Blood and bone marrow aspirate (BMA) were collected from horses and processed to obtain plasma, PRP, and platelet poor plasma (PPP). IGF-I, TGF-beta1, and PDGF-BB were quantified in all blood products using ELISA. Tendons were cultured in explant fashion with blood, plasma, PRP, PPP, or BMA at concentrations of 100%, 50%, or 10% in serum-free DMEM with amino acids. Quantitative RT-PCR for expression of collagen type I (COL1A1), collagen type III (COL3A1), cartilage oligomeric matrix protein (COMP), decorin, matrix metalloproteinase-3 (MMP-3), and matrix metalloproteinase-13 (MMP-13) was performed as were DNA and total soluble collagen assays. TGF-beta1 and PDGF-BB concentrations were higher in PRP compared to all other blood products tested. Tendons cultured in 100% PRP showed enhanced gene expression of the matrix molecules COL1A1, COL3A1, and COMP with no concomitant increase in the catabolic molecules MMP-3 and MMP-13. These findings support in vivo investigation of PRP as an autogenous, patient-side treatment for tendonitis.