TGF-beta1 reverses the effects of matrix anchorage on the gene expression of decorin and procollagen type I in tendon fibroblasts

Peritendinous adhesion: Therapeutic targets and progress of drug therapy

Peritendinous adhesion (PA) is one of the most common complications following hand surgery and characterized with abnormal hyperplasia of connective tissue and excessive deposition of extracellular matrix. Subsequently, various clinical symptoms such as chronic pain, limb dyskinesia and even joint stiffness occur and patients are always involved in the vicious cycle of "adhesion - release - re-adhesion", which seriously compromise the quality of life. Until present, the underlying mechanism remains controversial and lack of specific treatment, with symptomatic treatment being the only option to relieve symptoms, but not contributing no more to the fundamentally rehabilitation of basic structure and function. Recently, novel strategies have been proposed to inhibit the formation of adhesion tissues including implantation of anti-adhesion barriers, anti-inflammation, restraint of myofibroblast transformation and regulation of collagen overproduction. Furthermore, gene therapy has also been considered as a promising anti-adhesion treatment. In this review, we provide an overview of anti-adhesion targets and relevant drugs to summarize the potential pharmacological roles and present subsequent challenges and prospects of anti-adhesion drugs.

The mechanisms and functions of TGF-β1 in tendon healing

Tendon injury accounts for 30% of musculoskeletal diseases and often leads to disability, pain, healthcare cost, and lost productivity. Following injury to tendon, tendon healing proceeds via three overlapping healing processes. However, due to the structural defects of the tendon itself, the tendon healing process is characterized by the formation of excessive fibrotic scar tissue, and injured tendons rarely return to native tendons, which can easily contribute to tendon reinjury. Moreover, the resulting fibrous scar is considered to be a precipitating factor for subsequent degenerative tendinopathy. Despite this, therapies are almost limited because underlying molecular mechanisms during tendon healing are still unknown. Transforming Growth Factor-β1 (TGF-β1) is known as one of most potent profibrogenic factors during tendon healing process. However, blockage TGF-β1 fails to effectively enhance tendon healing. A detailed understanding of real abilities of TGF-β1 involved in tendon healing can bring promising perspectives for therapeutic value that improve the tendon healing process. Thus, in this review, we describe recent efforts to identify and characterize the roles and mechanisms of TGF-β1 involved at each stage of the tendon healing and highlight potential roles of TGF-β1 leading to the fibrotic response to tendon injury.

Growth factor and macromolecular crowding supplementation in human tenocyte culture

Cell-assembled tissue engineering strategies hold great potential in regenerative medicine, as three-dimensional tissue-like modules can be produced, even from a patient's own cells. However, the development of such implantable devices requires prolonged in vitro culture time, which is associated with cell phenotypic drift. Considering that the cells in vivo are subjected to numerous stimuli, multifactorial approaches are continuously gaining pace towards controlling cell fate during in vitro expansion. Herein, we assessed the synergistic effect of simultaneous and serial growth factor supplementation (insulin growth factor-1, platelet-derived growth factor ββ, growth differentiation factor 5 and transforming growth factor β3) to macromolecular crowding (carrageenan) in human tenocyte function; collagen synthesis and deposition; and gene expression. TGFβ3 supplementation (without/with carrageenan) induced the highest (among all groups) DNA content. In all cases, tenocyte proliferation was significantly increased as a function of time in culture, whilst metabolic activity was not affected. Carrageenan supplementation induced significantly higher collagen deposition than groups without carrageenan (without/with any growth factor). Of all the growth factors used, TGFβ3 induced the highest collagen deposition when used together with carrageenan in both simultaneous and serial fashion. At day 13, gene expression analysis revealed that TGFβ3 in serial supplementation to carrageenan upregulated the most and downregulated the least collagen- and tendon- related genes and upregulated the least and downregulated the most osteo-, chondro-, fibrosis- and adipose- related trans-differentiation genes. Collectively, these data clearly advocate the beneficial effects of multifactorial approaches (in this case, growth factor and macromolecular crowding supplementation) in the development of functional cell-assembled tissue surrogates.

In Vitro Induction of Tendon-Specific Markers in Tendon Cells, Adipose- and Bone Marrow-Derived Stem Cells is Dependent on TGFβ3, BMP-12 and Ascorbic Acid Stimulation

Mesenchymal Stem Cells (MSCs) and tissue-specific progenitors have been proposed as useful tools for regenerative medicine approaches in bone, cartilage and tendon-related pathologies. The differentiation of cells towards the desired, target tissue-specific lineage has demonstrated advantages in the application of cell therapies and tissue engineering. Unlike osteogenic and chondrogenic differentiation, there is no consensus on the best tenogenic induction protocol. Many growth factors have been proposed for this purpose, including BMP-12, b-FGF, TGF-β3, CTGF, IGF-1 and ascorbic acid (AA). In this study, different combinations of these growth factors have been tested in the context of a two-step differentiation protocol, in order to define their contribution to the induction and maintenance of tendon marker expression in adipose tissue and bone marrow derived MSCs and tendon cells (TCs), respectively. Our results demonstrate that TGF-β3 is the main inducer of scleraxis, an early expressed tendon marker, while at the same time inhibiting tendon markers normally expressed later, such as decorin. In contrast, we find that decorin is induced by BMP-12, b-FGF and AA. Our results provide new insights into the effect of different factors on the tenogenic induction of MSCs and TCs, highlighting the importance of differential timing in TGF-β3 stimulation.

Transforming growth factor beta 1 mediates the low-frequency vertical vibration enhanced production of tenomodulin and type I collagen in rat Achilles tendon

Vertical vibration (VV) is a whole-body vibration with mechanical loading that commonly used in rehabilitation and sports training to increase athlete muscle strength. Our previous study showed that low-magnitude, low-frequency VV at 8 Hz and 10 Hz increased myoblast myogenesis. Herein, we investigated whether a VV frequency at low-frequency 5-10 Hz has anabolic effects on tenocytes and improves tendon stiffness. In primary tenocytes, 10 Hz VV treatment increased the tenogenic marker gene expression of tenomodulin and extracellular matrix type I collagen but decreased decorin expression. qPCR and Enzyme-Linked Immunosorbent Assay (ELISA) results showed that TGF-β1 expression was increased in tenocytes after 3 days of 10 Hz VV treatment in vitro and in Achilles tendons after 3 weeks in vivo. Tenomodulin expression and Achilles tendon stiffness were significantly increased in Achilles tendons after 3 weeks in vivo. We also showed that the TGF-β1 receptor inhibitor SB431542 (10 μM) decreased the expression of tenomodulin and type I collagen but increased the decorin expression in tenocytes. These results indicated that the 10 Hz VV stimulated anabolic effects in tenocytes by increasing TGF-β1 expression that subsequently increases the expression of tenomodulin and type I collagen, and increased the Achilles tendon stiffness. This study provides insight into the low-frequency 10 Hz VV treatment improves tendon properties and can minimizes the risk of ligament/tendon reinjure during rehabilitation.

Injured Achilles Tendons Treated with Adipose-Derived Stem Cells Transplantation and GDF-5

Tendon injuries represent a clinical challenge in regenerative medicine because their natural repair process is complex and inefficient. The high incidence of tendon injuries is frequently associated with sports practice, aging, tendinopathies, hypertension, diabetes mellitus, and the use of corticosteroids. The growing interest of scientists in using adipose-derived mesenchymal stem cells (ADMSC) in repair processes seems to be mostly due to their paracrine and immunomodulatory effects in stimulating specific cellular events. ADMSC activity can be influenced by GDF-5, which has been successfully used to drive tenogenic differentiation of ADMSC in vitro. Thus, we hypothesized that the application of ADMSC in isolation or in association with GDF-5 could improve Achilles tendon repair through the regulation of important remodeling genes expression. Lewis rats had tendons distributed in four groups: Transected (T), transected and treated with ADMSC (ASC) or GDF-5 (GDF5), or with both (ASC+GDF5). In the characterization of cells before application, ADMSC expressed the positive surface markers, CD90 (90%) and CD105 (95%), and the negative marker, CD45 (7%). ADMSC were also differentiated in chondrocytes, osteoblast, and adipocytes. On the 14th day after the tendon injury, GFP-ADMSC were observed in the transected region of tendons in the ASC and ASC+GDF5 groups, and exhibited and/or stimulated a similar genes expression profile when compared to the in vitro assay. ADMSC up-regulated Lox, Dcn, and Tgfb1 genes expression in comparison to T and ASC+GDF5 groups, which contributed to a lower proteoglycans arrangement, and to a higher collagen fiber organization and tendon biomechanics in the ASC group. The application of ADMSC in association with GDF-5 down-regulated Dcn, Gdf5, Lox, Tgfb1, Mmp2, and Timp2 genes expression, which contributed to a lower hydroxyproline concentration, lower collagen fiber organization, and to an improvement of the rats’ gait 24 h after the injury. In conclusion, although the literature describes the benefic effect of GDF-5 for the tendon healing process, our results show that its application, isolated or associated with ADMSC, cannot improve the repair process of partial transected tendons, indicating the higher effectiveness of the application of ADMSC in injured Achilles tendons. Our results show that the application of ADMSC in injured Achilles tendons was more effective in relation to its association with GDF-5.

Intensity-dependent effect of treadmill running on rat Achilles tendon

It is understood that mechanical loading may affect tendon properties. However, how different mechanical loading conditions may affect tendons remains unknown. The present study aimed to investigate the effect of treadmill running at various intensities on rat Achilles tendon. A total of 18 male Wistar rats were randomly assigned to one of three groups: Control (CON), medium-intensity running (MIR), and high-intensity running (HIR). Following 8 weeks of treadmill running protocols, all Achilles tendons were harvested for histological observation and gene expression analysis. Significant morphological changes were observed with regular and large diameter collagen fibrils in the MIR group, whereas irregular and small diameter collagen fibrils were observed in the HIR group. Collagen type I was significantly upregulated in the MIR group compared with the CON group, and downregulated in the HIR group compared with the CON or MIR groups (P<0.05). However, collagen type III was significantly upregulated in the HIR group in comparison with the CON or MIR groups (P<0.05). Furthermore, the expression of matrix metallopeptidase-13 was significantly increased in the MIR and HIR groups compared with the CON group (P<0.05). The expression of tissue inhibitor of metalloproteinases-1 was increased in the MIR group compared with the CON group, but decreased in the HIR group compared with the CON and MIR groups (P<0.05). Additionally, decorin expression was significantly higher in the MIR group compared with the CON group, and significantly decreased in the HIR group compared with the CON or MIR groups (P<0.05). A converse pattern of changes in biglycan expression was identified among the three groups. Aggrecan expression was significantly higher in the HIR group compared with the CON or MIR groups (P<0.05). These findings indicated that moderate exercise may induce increased collagen synthesis and organize regular and large collagen fibers, thus benefiting the Achilles tendon. However, overuse during exercise may result in collagen degradation and disturbance, which predisposes individuals to injury.

The effects of substance P and acetylcholine on human tenocyte proliferation converge mechanistically via TGF-β1

Previous in vitro studies on human tendon cells (tenocytes) have demonstrated that the exogenous administration of substance P (SP) and acetylcholine (ACh) independently result in tenocyte proliferation, which is a prominent feature of tendinosis. Interestingly, the possible link between SP and ACh has not yet been explored in human tenocytes. Recent studies in other cell types demonstrate that both SP and ACh independently upregulate TGF-β1 expression via their respective receptors, the neurokinin 1 receptor (NK-1R) and muscarinic ACh receptors (mAChRs). Furthermore, TGF-β1 has been shown to downregulate NK-1R expression in human keratocytes. The aim of this study was to examine if TGF-β1 is the intermediary player involved in mediating the proliferative pathway shared by SP and ACh in human tenocytes. The results showed that exogenous administration of SP and ACh both caused significant upregulation of TGF-β1 at the mRNA and protein levels. Exposing cells to TGF-β1 resulted in increased cell viability of tenocytes, which was blocked in the presence of the TGFβRI/II kinase inhibitor. In addition, the proliferative effects of SP and ACh on tenocytes were reduced by the TGFβRI/II kinase inhibitor; this supports the hypothesis that the proliferative effects of these signal substances are mediated via the TGF-β axis. Furthermore, exogenous TGF-β1 downregulated NK-1R and mAChRs expression at both the mRNA and protein levels, and these effects were negated by simultaneous exposure to the TGFβRI/II kinase inhibitor, suggesting a negative feedback loop. In conclusion, the results indicate that TGF-β1 is the intermediary player through which the proliferative actions of both SP and ACh converge mechanistically.

Morphological study on the pressure ulcer-like dermal lesions formed in the rat heel skin after transection of the sciatic nerves

Due to transection of bilateral sciatic nerves, pressure ulcer-like dermal lesion occurred in the hairy skin covering of the heel skin in almost all rats. In the present study, chronological changes of the rat heel skin after the transection were morphologically and immunohistochemically examined. In the heel skin, redness and swelling began by 3days after the operation, and open wound formed by 17days. At the redness and swelling stage, edema extensively occurred in the dermis. At the thickening stage, the epidermis at the pressed site became transiently thicker, and at the whitening stage, rapidly thinner. At these stages, the epidermis in the skin surrounding the pressed site became gradually thicker. At the yellow scar stage, the skin was covered only by necrotic tissues and horny layer. These layers were scratched during walking and turning, and the yellow scar stage became the open wound stage. Inflammatory reaction began at the thickening stage, and at the yellow scar and open wound stages, necrosis, infiltration of inflammatory cells and dilation of small blood vessels were observed. These morphological features are quite similar to those in the human pressure ulcer. These findings suggest that these dermal injuries could compare the human pressure ulcer for medical treatment and depressurization in future study.

Comparison of the early period effects of bone marrow-derived mesenchymal stem cells and platelet-rich plasma on the Achilles tendon ruptures in rats

INTRODUCTION

This study aims to histopathologically, biomechanically, and immunohistochemically compare the fourth-week efficiencies of local platelet-rich plasma (PRP) and bone marrow-derived mesenchymal stem cell (rBM-MSC) treatments of the Achilles tendon ruptures created surgically in rats.

MATERIALS AND METHODS

The study included 35 12-month-old male Sprague Dawley rats, with an average weight of 400-500 g. Five rats were used as donors for MSC and PRP, and 30 rats were separated into MSC, PRP, and control groups (n = 10). The Achilles tendons of the rats were cut transversely, the MSC from bone marrow was administered to the MSC group, the PRP group received PRP, and the control group received physiological saline to create the same surgical effect. In previous studies, it was shown that this physiological saline does not have any effect on tendon recovery. Thirty days after the treatment, the rats were sacrificed and their Achilles tendons were examined histopathologically, immunohistochemically, and biomechanically.

RESULTS

The use of rBM-MSC and PRP in the Achilles tendon ruptures when the tendon is in its weakest phase positively affected the recovery of the tendon in histopathologic, immunohistochemical, and biomechanical manners compared to the control group (p < 0.05). While the levels of pro-inflammatory cytokines TNF-α, IFNγ, and IL 1β were significantly low, the levels of anti-inflammatory cytokines and growth factors playing key roles in tendon recovery, such as IL2, VEGF, transforming growth factor-beta, and HGF, were significantly higher in the MSC group than those of the PRP and control groups (p < 0.05). In the MSC group, the [Formula: see text] (mm) value was significantly higher (p ˂ 0.05) than that in the PRP and control groups.

CONCLUSION

rBM-MSC and PRP promote the recovery of the tendon and increase its structural strength. The use of PRP and MSC provides hope for the treatment of the Achilles tendon ruptures that limit human beings' functionalities and quality of life, particularly for athletes. It is thought that the use of MSC can be more effective for tendon healing; hence, more extensive and advanced studies are needed on this topic.

Cryotherapy Reduces Inflammatory Response Without Altering Muscle Regeneration Process and Extracellular Matrix Remodeling of Rat Muscle

The application of cryotherapy is widely used in sports medicine today. Cooling could minimize secondary hypoxic injury through the reduction of cellular metabolism and injury area. Conflicting results have also suggested cryotherapy could delay and impair the regeneration process. There are no definitive findings about the effects of cryotherapy on the process of muscle regeneration. The aim of the present study was to evaluate the effects of a clinical-like cryotherapy on inflammation, regeneration and extracellular matrix (ECM) remodeling on the Tibialis anterior (TA) muscle of rats 3, 7 and 14 days post-injury. It was observed that the intermittent application of cryotherapy (three 30-minute sessions, every 2 h) in the first 48 h post-injury decreased inflammatory processes (mRNA levels of TNF-α, NF-κB, TGF-β and MMP-9 and macrophage percentage). Cryotherapy did not alter regeneration markers such as injury area, desmin and Myod expression. Despite regulating Collagen I and III and their growth factors, cryotherapy did not alter collagen deposition. In summary, clinical-like cryotherapy reduces the inflammatory process through the decrease of macrophage infiltration and the accumulation of the inflammatory key markers without influencing muscle injury area and ECM remodeling.

Heat stress promotes skeletal muscle regeneration after crush injury in rats

Influences of heat stress on skeletal muscle regeneration were examined in experimental rats. After crush injury to the Extensor digitorum longus muscle (EDL) of the left hindlimb, animals were randomly divided into non-heat and heat groups. In the latter, packs filled with hot water (42°C) were percutaneously applied to the injured EDL muscle for 20min to the front of the lower leg, soon after the injury. During the early stages of muscle regeneration, due to the heat stress, secondary degeneration at the injured site progressed faster, and migration of macrophages, proliferation and differentiation of satellite cells were facilitated. At 14 and 28 days after the injury, the ratio of regenerating muscle fibers exhibiting central nuclei in the heat treated group was significantly lower than that in the non-heat group, and cross sectional area in the heat group was evidently larger than that in the non-heat group. Moreover, in the heat group, the ratio of collagen fiber area at 14 and 28 days after the injury was smaller than in the non-heat group. Together, these findings suggest that acceleration of degeneration processes by heat stress soon after injury is likely to promote skeletal muscle regeneration and inhibit collagen deposition.

Radix Dipsaci does not improve tendon healing in a rat model of patellar tendon donor site injury

OBJECTIVE

To explore whether Radix Dipsaci (RD) exhibits beneficial effects on tendon healing.

METHODS

An attempt was made to explore the in vitro effects of a hot water extract of RD on gene expression of procollagen Type I (COL1A1), procollagen Type III (COL3A1) and decorin in cultured tendon fibroblasts, and its in vivo effects in a well-established rat model of patellar tendon donor site injury.

RESULTS

It was found that gene expression of COL3A1 and decorin in cultured tendon fibroblasts was significantly increased by RD, but that COL1A1 was not affected. In vivo studies showed that RD increased blood vessels in the wound but did not significantly affect the expression of COL1A1, COL3A1 and decorin at day 14 post-injury. The ultimate tensile stress of the healing tendon was not significantly improved by either local injection or oral administration of hot water extract of RD (P > 0.05).

CONCLUSION

The present findings imply that RD per se does not significantly improve tendon healing. Further investigation of RD in a herbal formula may be necessary to test its efficacy in tendon injuries.

Hyperglycemia reduces proteoglycan levels in tendons

RATIONALE

Diabetic tendinopathy is characterized by increased stiffness, thickness, and excess calcification of affected tendons. We investigated the hypothesis that proteoglycans (PGs), as key regulators of tendon structure and calcification, are altered in diabetic tendons.

METHODS

Adult porcine patellar tendons were incubated in iso-osmolar media with high or normal glucose levels for 2 weeks. The PG fraction was isolated and analyzed. Protein and mRNA levels of five PGs were measured. PG production was assessed in primary tenocyte monolayers by (35)S-sulfate labeling in high and normal glucose conditions with and without exposure to advanced glycation end-products (AGEs). Levels of transforming growth factor β, which commonly mediates some effects of hyperglycemia, were also measured and the effects of free radical scavengers on (35)S-sulfate incorporation were determined.

RESULTS

PG levels were significantly decreased in tendons exposed to high glucose media compared with tendons in iso-osmolar control media. Relative quantities of individual PGs were unchanged by exposure to hyperglycemia and mRNAs for PGs were variably affected. High glucose media decreased PG production by tenocytes as measured by (35)S-sulfate labeling, whereas AGE-modified type I collagen and free radical scavengers had no effects. Hyperglycemic conditions increased levels of transforming growth factor β1 in an AGE-independent manner.

CONCLUSIONS

Hyperglycemia produces a reduction in PG levels related to decreased synthesis or sulfation of glycosaminoglycans, which may contribute to the tendon pathology observed clinically in diabetes.

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.

Influence of icing on muscle regeneration after crush injury to skeletal muscles in rats

The influence of icing on muscle regeneration after crush injury was examined in the rat extensor digitorum longus. After the injury, animals were randomly divided into nonicing and icing groups. In the latter, ice packs were applied for 20 min. Due to the icing, degeneration of the necrotic muscle fibers and differentiation of satellite cells at early stages of regeneration were retarded by ∼1 day. In the icing group, the ratio of regenerating fibers showing central nucleus at 14 days after the injury was higher, and cross-sectional area of the muscle fibers at 28 days was evidently smaller than in the nonicing group. Besides, the ratio of collagen fibers area at 14 and 28 days after the injury in the icing group was higher than in the nonicing group. These findings suggest that icing applied soon after the injury not only considerably retarded muscle regeneration but also induced impairment of muscle regeneration along with excessive collagen deposition. Macrophages were immunohistochemically demonstrated at the injury site during degeneration and early stages of regeneration. Due to icing, chronological changes in the number of macrophages and immunohistochemical expression of transforming growth factor (TGF)-β1 and IGF-I were also retarded by 1 to 2 days. Since it has been said that macrophages play important roles not only for degeneration, but also for muscle regeneration, the influence of icing on macrophage activities might be closely related to a delay in muscle regeneration, impairment of muscle regeneration, and redundant collagen synthesis.

Treating Achilles tendon rupture in rats with bone-marrow-cell transplantation therapy

BACKGROUND

Bone marrow cells possess multipotentiality and have been used for several treatments. We hypothesized that bone marrow cells might differentiate into regenerated tendon and that several cytokines within bone marrow cells might accelerate tendon healing. Therefore, we treated Achilles tendon ruptures in a rat model with transplantation of whole bone marrow cells.

METHODS

Nine F344/Nslc (Fisher) rats were the source of bone marrow cells and mesenchymal stem cells as well as normal Achilles tendons. Eighty-seven Fisher rats were used for the experiments. The rats were divided into three groups: the BMC group (bone marrow cells injected around the tendon), the MSC group (mesenchymal stem cells injected around the tendon), and the non-treated control group (incision only). Outcome measures included mechanical testing, collagen immunohistochemistry, histological analysis, and reverse transcription-polymerase chain reaction to detect expression of transforming growth factor-β (TGF-β) and vascular endothelial growth factor (VEGF).

RESULTS

The ultimate failure load in the BMC group was significantly greater than that in the non-treated or the MSC group at seven days after incision (3.8 N vs. 0.9 N or 2.1 N, p < 0.016) and at fourteen days after incision (10.2 N vs. 6.1 N or 8.2 N, p < 0.016). The ultimate failure load in the BMC group at twenty-eight days after incision (33.8 N) was the same as that of normal tendon (34.8 N). The BMC group demonstrated stronger staining for type-III collagen at seven days after incision and stronger staining for type-I collagen at twenty-eight days than did the MSC group. Expression of TGF-β and VEGF in the BMC group was significantly increased compared with that in the other groups at four days after incision (TGF-β: 1.6 vs. 1.3 or 0.6, p < 0.01; VEGF: 1.7 vs. 1.1 or 0.9, p < 0.01).

CONCLUSIONS

Transplantation of whole bone marrow cells may be a better and more readily available treatment for Achilles tendon rupture than cultured mesenchymal stem cells.

Efficacy of hESC-MSCs in knitted silk-collagen scaffold for tendon tissue engineering and their roles

Human embryonic stem cells (hESC) and their differentiated progenies are an attractive cell source for transplantation therapy and tissue engineering. Nevertheless, the utility of these cells for tendon tissue engineering has not yet been adequately explored. This study incorporated hESC-derived mesenchymal stem cells (hESC-MSCs) within a knitted silk-collagen sponge scaffold, and assessed the efficacy of this tissue-engineered construct in promoting tendon regeneration. When subjected to mechanical stimulation in vitro, hESC-MSCs exhibited tenocyte-like morphology and positively expressed tendon-related gene markers (e.g. Collagen type I & III, Epha4 and Scleraxis), as well as other mechano-sensory structures and molecules (cilia, integrins and myosin). In ectopic transplantation, the tissue-engineered tendon under in vivo mechanical stimulus displayed more regularly aligned cells and larger collagen fibers. This in turn resulted in enhanced tendon regeneration in situ, as evidenced by better histological scores and superior mechanical performance characteristics. Furthermore, cell labeling and extracellular matrix expression assays demonstrated that the transplanted hESC-MSCs not only contributed directly to tendon regeneration, but also exerted an environment-modifying effect on the implantation site in situ. Hence, tissue-engineered tendon can be successfully fabricated through seeding of hESC-MSCs within a knitted silk-collagen sponge scaffold followed by mechanical stimulation.

The effect of glucocorticoids on tendon cell viability in human tendon explants

BACKGROUND AND PURPOSE

Previous studies on the culture of human tenocytes have shown that dexamethasone and triamcinolone reduce cell viability, suppress cell proliferation, and reduce collagen synthesis. However, such cell cultures lack the extracellular matrix and three-dimensional structure of normal tendons, which affects their response to stimuli. We established a human tendon explant culture system and tested the effects of dexamethasone and triamcinolone on cell viability.

METHODS

Primary human tendon explant cultures were prepared from healthy hamstring tendons. Tendon strips were harvested from hamstring tendons and cultured in 24-well plates in Dulbecco's modification of Eagle's Medium (DMEM) supplemented with 2% fetal calf serum. The tendon explants were treated with 0 microM (control), 10 microM, or 100 microM dexamethasone sodium phosphate or 0 microM (control), 10 microM, or 100 microM triamcinolone acetonide in DMEM for 96 h. Cell viability was measured by Alamar blue assay before and after glucocorticoid treatment.

RESULTS

Incubation with 10 microM and 100 microM dexamethasone reduced cell viability in human tendon explants by 35% and 45%, respectively, as compared to a 6% increase in the controls (p = 0.01, mixed-effects ANOVA). Triamcinolone at 10 microM and 100 microM reduced cell viability by 33% and 36%, respectively, as compared to a 9% increase in the controls (p = 0.07, mixed-effects ANOVA).

INTERPRETATION

Human tendon explant cultures can be used to study the effects of glucocorticoids on human tendon. Dexamethasone and triamcinolone suppress the cell viability of human tendon in its natural 3-dimensional environment with matrix anchorage. Human tendon explant cultures provide a species-specific model for further investigation of the effects of glucocorticoids on the metabolism of the extracellular matrix of human tendon, and on its mechanical properties.

The roles of TGF-beta1 gene transfer on collagen formation during Achilles tendon healing

Collagen content and cross-linking are believed to be major determinants of tendon structural integrity and function. The current study aimed to investigate the effects of transforming growth factor (TGF)-beta1 on the collagen content and cross-linking of Achilles tendons, and on the histological and biomechanical changes occurring during Achilles tendon healing in rabbits. Bone marrow-derived mesenchymal stem cells (BMSCs) transfected with the TGF-beta1 gene were surgically implanted into experimentally injured Achilles tendons. Collagen proteins were identified by immunohistochemical staining and fiber bundle accumulation was revealed by Sirius red staining. Achilles tendons treated with TGF-beta1-transfected BMSCs showed higher concentrations of collagen I protein, more rapid matrix remodeling, and larger fiber bundles. Thus TGF-beta1 can promote mechanical strength in healing Achilles tendons by regulating collagen synthesis, cross-link formation, and matrix remodeling.

In vitro flexor tendon cell response to TGF-beta1: a gene expression study

PURPOSE

Adhesion formation around zone II flexor tendon repairs remains an important clinical challenge. Tendon healing is complex, and when uncontrolled it may lead to adhesion formation. Transforming growth factor-beta1 (TGF-beta1) is a multipotent growth factor known to be involved in wound healing and scar formation. It has also been shown to have a role in both tendon healing and adhesion formation.

METHODS

Uninjured rabbit flexor tendons were divided into endotenon, epitenon, and sheath cells and cultured separately. The in vitro effect of TGF-beta1 gene expression was determined on quiescent tendon cells using real-time polymerase chain reaction for collagen type 1, collagen type 3, fibronectin, plasminogen activator inhibitor-1 (PAI-1), and tissue plasminogen activator (t-PA).

RESULTS

Endotenon-derived cells showed a statistically significant down-regulation of collagen type I gene expression in response to TGF-beta1 compared with untreated endotenon cells and with both epitenon and sheath cells at a number of time points. However, endotenon cells showed an increase in collagen type 3 gene expression compared with untreated cells and epitenon cells. All cells showed a statistically significant increase in fibronectin in the later time points compared with the untreated cells. Endotenon-derived cells showed an early increase in PAI-1, whereas sheath cells showed a later increase.

CONCLUSIONS

We have shown that cells cultured from 3 separate parts of the flexor tendon-sheath complex respond in different ways when stimulated with TGF-beta1. The down-regulation of collagen types 1 and 3 in endotenon cells may give further insight into the effects of TGF-beta1 in tendon healing. Also, the upregulation of fibronectin and PAI-1, combined with a down-regulation of tissue plasminogen activator, could explain the association of TGF-beta1 with tendon adhesion formation. Treatments aimed at improving tendon healing and the prevention of adhesions may arise from modification of the effects of TGF-beta1.

Spatiotemporal protein distribution of TGF-betas, their receptors, and extracellular matrix molecules during embryonic tendon development

Tendon is one of the least understood tissues of the musculoskeletal system in terms of development and morphogenesis. Collagen fibrillogenesis has been the most studied aspect of tendon development, focusing largely on the role of matrix molecules such as collagen type III and decorin. While involvement of matrix molecules in collagen fibrillogenesis during chick tendon development is well understood, the role of growth factors has yet to be elucidated. This work examines the expression patterns of transforming growth factor (TGF) -beta1, -beta2, and -beta3, and their receptors with respect to expression patterns of collagen type III, decorin, and fibronectin. We focus on the intermediate stages of tendon development in the chick embryo, a period during which the tendon micro- and macro-architecture are being established. Our findings demonstrate for the first time that TGF-beta1, -beta2, and -beta3 have distinct spatiotemporal developmental protein localization patterns in the developing tendon and strongly suggest that these isoforms have independent roles in tendon development.

Low-intensity pulsed ultrasound on tendon healing: a study of the effect of treatment duration and treatment initiation

BACKGROUND

Low-intensity pulsed ultrasound has been reported to be effective in promoting tendon healing. However, its optimal time and duration has not yet been determined.

HYPOTHESIS

Tendons at different stages of healing may respond differently to low-intensity pulsed ultrasound. In the present study, the timing effects of low-intensity pulsed ultrasound on tendon healing were investigated in a rat model with a patellar tendon graft harvest lesion.

STUDY DESIGN

Controlled laboratory study.

METHODS

Sixty Sprague-Dawley rats underwent central third patellar tendon donor site harvest. Low-intensity pulsed ultrasound sonication was then delivered to the injured knees at day 1, 14, or 28 after harvest for 2, 4, or 6 weeks. Tendon samples were harvested at day 14, 28, and 42 after lesion for histological examination and mechanical testing.

RESULTS

A 2-week session of low-intensity pulsed ultrasound applied from day 1 postlesion (D1-2W) significantly improved the ultimate mechanical strength of the healing tendons from 23.1 +/- 8.5 MPa to 36.6 +/- 9.0 MPa. Low-intensity pulsed ultrasound did not improve healing when it was given at later stages in D15-2W and D29-2W. When low-intensity pulsed ultrasound treatment was extended from 2 weeks (D1-2W) to 4 weeks (D1-4W) or 6 weeks (D1-6W), the beneficial effects on tendon healing became insignificant. Histological examination showed that low-intensity pulsed ultrasound sonication at late healing stages may disturb remodeling with a poor collagen fiber alignment.

CONCLUSION

Low-intensity pulsed ultrasound promoted restoration of mechanical strength and collagen alignment in healing tendons only when applied at early healing stages.

CLINICAL RELEVANCE

The present findings indicate that low-intensity pulsed ultrasound may be an effective treatment to reduce tendon donor site morbidity.

Expression of transforming growth factor beta isoforms and their roles in tendon healing

Transforming growth factor beta (TGF-beta) plays active roles in tendon healing. However, the differential effects of TGF-beta isoforms on tendon healing have not been investigated. In cultured tendon fibroblasts, we tested the effects of TGF-beta1, beta2, and beta3 on the mRNA levels of COL1A1 and COL3A1 by quantitative real-time polymerase chain reaction. We also investigated the expression of TGF-beta isoforms, TGF-beta receptors, procollagen Type I and Type III in a rat model of tendon healing. We found that TGF-beta3 exhibited the highest potency in stimulating COL1A1 and COL3A1. TGF-beta1 exerted antagonistic effects to TGF-beta2 and beta3. All TGF-beta isoforms and procollagen Type I were confined to the edges of the healing tendon at day 28 postinjury. Our results indicated that interaction of TGF-beta isoforms exist in the regulation of collagen synthesis in tendon fibroblasts. Their effects may be further complicated by uneven spatial distribution of TGF-beta and TGF-beta receptors in healing tendons.

HGF suppresses the production of collagen type III and alpha-SMA induced by TGF-beta1 in healing fibroblasts

The aim of this study was to examine the effectiveness of HGF in blocking TGF-beta1-induced collagen III and alpha-smooth muscle actin (alpha-SMA) production in rat healing fibroblasts, fibroblasts were obtained from healing medial collateral ligament (MCL) injury. Cell culture was supplemented with 5 ng/ml of TGF-beta1 along with increasing doses of HGF (10-40 ng/ml). The productions of collagen III in supernatants culture were assayed by enzyme-linked immunosorbent assay. Expression of alpha-SMA was assessed by Western blot. Treatment with TGF-beta1 significantly stimulated collagen III and alpha-SMA production in healing fibroblasts. Remarkably, the addition of HGF reduced productions of all components induced by TGF-beta1 in a dose-dependent manner. This study shows that HGF antagonizes the action of TGF-beta1 effectively in cultured healing MCL injury fibroblasts. The results provide a cellular and molecular basis for HGF's acting as a therapeutic agent for MCL scar formation and poor healing.

Is cultured tendon fibroblast a good model to study tendon healing?

Cultured tendon fibroblasts (CTFs) from intact explants are widely used to study tendon healing in vitro. The significance of these findings may rely on similarities between CTFs and healing tendon fibroblasts in situ. Our purpose was to compare CTFs with fibroblasts cultured from healing tendons. We cultured CTFs from intact and healing tendons at day 7 and day 14 postinjury in a rat model of patellar donor site injury. The mRNA expression of COL1A1, COL3A1, decorin, and biglycan, with or without supplementation of 1 ng/mL TGF-beta1, was compared by quantitative real-time RT-PCR. The expression of proliferation cell nuclear antigen (PCNA) and alpha-smooth muscle actin (alpha-SMA) was determined by immunostain. COL3A1 and decorin mRNA in CTFs was lower as compared to day 7 healing fibroblasts, but its biglycan mRNA level was higher than day 14 healing fibroblasts. TGF-beta1 increased COL1A1 and decorin mRNA in CTFs, but decreased the mRNA of all four genes in day 7 healing tendon fibroblasts. CTFs exhibited lower PCNA immunopositivity as compared to day 7 and day 14 healing fibroblasts, but a higher alpha-SMA immunopositivity than cultured day 14 healing fibroblasts. These findings showed that CTFs did not resemble healing tendon cells with respect to major cellular activities related to tendon healing. Thus, fibroblasts from healing tendon may be a more appropriate model for studying cellular activities in tendon healing.

Reciprocal actions of platelet-secreted TGF-beta1 on the production of VEGF and HGF by human tendon cells

BACKGROUND

Autologous platelet-rich matrices can be an aid in surgery by promoting and accelerating tissue healing because of the release of growth factors including transforming growth factor (TGF)-beta1 and platelet-derived growth factor (PDGF) from platelet alpha-granules.

METHODS

PDGF and TGF-beta1 were quantified in supernatants collected from platelet-rich matrices prepared in vitro (n = 45 donors) and they correlated with the number of platelets and showed a constant ratio (p < 0.05). Tendon cells in culture were exposed to the supernatants (n = 4 donors) from either platelet-rich or platelet-poor matrices, differing in their content of platelet-secreted molecules. These treatments were modified by either neutralizing or adding PDGF or TGF-beta1. Effects were compared in terms of proliferation, procollagen I, vascular endothelial growth factor (VEGF), and hepatocyte growth factor (HGF) production.

RESULTS

PDGF was a partial contributor to cell proliferation, whereas exogenous TGF-beta1 acted as a negative modulator (p < 0.05). The production of type I collagen was similar regardless of differences in the concentration of TGF-beta1. Moreover, addition of exogenous TGF-beta1 promoted a significant increase in collagen synthesis only in the absence of other platelet-released substances (p < 0.05). Exogenous TGF-beta1 increased the synthesis of VEGF and simultaneously abolished the production of HGF. Furthermore, antibody-mediated neutralization of TGF-beta1 induced a decrease in VEGF synthesis and concomitantly a substantial production of HGF (p < 0.05).

CONCLUSION

The balance between TGF-beta1 and the pools of platelet-secreted molecules may have important therapeutic implications in the control of angiogenesis and fibrosis.

Mechanical strain promotes fibroblast gene expression in presence of corticosteroid

Posterior tibial tendon (PTT) dysfunction has commonly been treated with local corticosteroid injections to reduce inflammation. However, a concern with this treatment is potential degeneration and spontaneous rupture of the PTT. This study set out to determine whether mechanical strain may counteract the potentially deleterious effect of corticosteroid treatment on fibroblasts and therefore improve outcomes during recovery from tendinitis. In this study, PTT fibroblasts in vitro were treated with 0 M, 10(-7) M, 10(-6) M, and 10(-5) M triamcinolone acetonide (TA) while incubated under cyclic strains of 0% or 5% for 24 hr. Type I collagen and decorin mRNA expressions were determined by RT-PCR. The results indicated that mechanical strain significantly increased type I collagen and decorin gene expression in the PTT fibroblasts and TA decreased type I collagen and decorin gene expression. Therefore, mechanical strain might be beneficial to PTT after corticosteroid treatment by direct stimulation of fibroblast synthesis.

Effects of electromagnetic stimulation on calcified matrix production by SAOS-2 cells over a polyurethane porous scaffold

There is increasing interest in designing new biomaterials that could potentially be used in the form of scaffolds as bone substitutes. In this study we used a hydrophobic crosslinked polyurethane in a typical tissue-engineering approach, that is, the seeding and in vitro culturing of cells using a porous scaffold. Using an electromagnetic bioreactor (magnetic field intensity, 2 mT; frequency, 75 Hz), we investigated the effect of the electromagnetic stimulation on SAOS-2 human osteoblast proliferation and calcified matrix production. Cell proliferation was twice as high; expression of decorin, osteocalcin, osteopontin, type I collagen, and type III collagen was greater (1.3, 12.2, 12.1, 10.0, and 10.5 times as great, respectively); and calcium deposition was 5 times as great as under static conditions without electromagnetic stimulation. RT-PCR analysis revealed the electromagnetically upregulated transcription specific for decorin, fibronectin, osteocalcin, osteopontin, transforming growth factor-beta, type I collagen, and type III collagen. The immunolocalization of the extracellular matrix constituents showed their colocalization in the cell-rich areas. The bioreactor and the polyurethane foam were designed to obtain cell colonization and calcified matrix deposition. This cultured biomaterial could be used, in clinical applications, as an osteoinductive implant for bone repair.