Molecular events in tendinopathy: a role for metalloproteases

Rotator Cuff Tendon Healing Using Human Dermal Fibroblasts: Histological and Biomechanical Analyses in a Rabbit Model of Chronic Rotator Cuff Tears

BACKGROUND

Tenocytes derived from tendons have been reported to be effective in the treatment of rotator cuff tears through the expression of extracellular matrix proteins. Human dermal fibroblasts, known to express collagen types I and III as tenocytes do, may likely be substitutes for tenocytes to enhance healing rotator cuff tears.

PURPOSE

To demonstrate the capability of human dermal fibroblasts to enhance healing of rotator cuff tears.

STUDY DESIGN

Controlled laboratory study.

METHODS

The cellular properties and expression profiles of growth factors were compared between human dermal fibroblasts and tenocytes. In both cell types, a series of extracellular matrix proteins were analyzed along with matrix metalloproteinases and tissue inhibitors of metalloproteinases involved in the collagenolytic system. A total of 35 rabbits were divided into 5 groups: normal (n = 2), saline control (n = 9), fibrin control (n = 9), low dose of human fibroblasts (HF-LD; n = 9), and high dose of human fibroblasts (HF-HD; n = 6). Cells were injected into the sutured lesions at 6 weeks after creation of bilateral rotator cuff tears, followed by histological and biomechanical analyses at 12 weeks.

RESULTS

Human dermal fibroblasts exhibited a protein expression pattern similar to that of tenocytes. More specifically, the expression levels of collagen types I and III were comparable between fibroblasts and tenocytes. The histological analysis of 30 surviving rabbits showed that collagen fibers were more continuous and better oriented with a more mature interface between the tendon and bone in the sutured lesions in the HF-LD and HF-HD groups. Most importantly, biomechanical strength, measured using the load to failure at the injection site, was 58.8 ± 8.9 N/kg in the HF-HD group, increasing by approximately 2-fold (P = .0003) over the saline control group.

CONCLUSION

Human dermal fibroblasts, showing cellular properties comparable with tenocytes, effectively enhanced healing of chronic rotator cuff tears in rabbits.

CLINICAL RELEVANCE

Human dermal fibroblasts can be used in place of tenocytes to enhance healing of rotator cuff tears.

Management of Achilles and patellar tendinopathy: what we know, what we can do

Tendinopathies are challenging conditions frequent in athletes and in middle-aged overweight patients with no history of increased physical activity. The term “tendinopathy” refers to a clinical condition characterised by pain, swelling, and functional limitations of tendons and nearby structures, the effect of chronic failure of healing response. Tendinopathies give rise to significant morbidity, and, at present, only limited scientifically proven management modalities exist. Achilles and patellar tendons are among the most vulnerable tendons, and among the most frequent lower extremity overuse injuries. Achilles and patellar tendinopathies can be managed primarily conservatively, obtaining good results and clinical outcomes, but, when this approach fails, surgery should be considered. Several surgical procedures have been described for both conditions, and, if performed well, they lead to a relatively high rate of success with few complications. The purpose of this narrative review is to critically examine the recent available scientific literature to provide evidence-based opinions on these two common and troublesome conditions.

Relationship of common variants in MPP7, TIMP2 and CASP8 genes with the risk of chronic achilles tendinopathy

Previous etiologic studies have indicated that both environmental and genetic factors play important roles in the occurrence and development of chronic Achilles tendinopathy (AT). A recent study documented the results of the largest genome-wide association study for chronic AT to date, indicating that MPP7, TIMP2 and CASP8 may be involved in the occurrence and development of chronic AT. In this study, we aimed to investigate whether MPP7, TIMP2 and CASP8 were associated with susceptibility to chronic AP in a Han Chinese population. A total of 3,680 study subjects comprised 1,288 chronic AT cases, and 2,392 healthy controls were recruited. Forty-four tag SNPs (7 from CASP8, 20 from MPP7, and 17 from TIMP2) were genotyped in the study. Genetic association analyses were performed at both single marker and haplotype levels. Functional consequences of significant SNPs were examined in the RegulomeDB and GTEx databases. Two SNPs, SNP rs1937810 (OR [95%CI] = 1.20 [1.09-1.32], χ2 = 13.50, P = 0.0002) in MPP7 and rs4789932 (OR [95%CI] = 1.24 [1.12-1.37], χ2 = 17.98, P = 2.23 × 10-5) in TIMP2, were significantly associated with chronic AT. Significant eQTL signals for SNP rs4789932 on TIMP2 were identified in human heart and artery tissues. Our results provide further supportive evidence for the association of the TIMP2 and MPP7 genes with chronic AT, which supports important roles for TIMP2 and MPP7 in the etiology of chronic AT, adding to the current understanding of the susceptibility of chronic AT.

Photobiomodulation of Matrix Metalloproteinases in Rat Calcaneal Tendons

Objective: The main objective was to verify the modulatory effects of MMP-1, MMP-3, and MMP-13 levels on the partially injured calcaneal tendons of rat exposure to photobiomodulation. Background: Photobiomodulation has been shown to have anti-inflammatory and regenerative effects on tendon injuries. However, there is still uncertainty regarding the beneficial effects in matrix metalloproteinase (MMP) levels, especially MMP-1, -3, and -13. Materials and methods: Sixty-five male Wistar rats were used. Sixty were submitted to a direct trauma on the calcaneal tendons and were randomly distributed into the following six groups: LASER 1, 3, and 7 (10 partially injured calcaneal tendons in each group treated with photobiomodulation for 1, 3, and 7 days, respectively) and Sham 1, 3, and 7 (same injury, with simulated photobiomodulation). The remaining five animals were allocated to the normal group (no injury or treatment procedure). The 780 nm low-level laser was applied with 70 mW of mean power and 17.5 J/cm² of fluency for 10 sec, once a day. The tendons were surgically removed and analyzed for MMP-1, MMP-3, and MMP-13 through immunohistochemistry. Results: MMP-3 levels remained close to normal in all experimental groups (p > 0.05); however, reductions (p < 0.05) in MMP-1 and MMP-13 levels were detected in the groups submitted to one, three, and seven low level laser therapy applications. Conclusions: The photobiomodulation protocol was able to reduce MMP-1 and MMP-13 levels in injured calcaneal tendons.

Achilles Tendinopathy

Achilles tendinopathy is a common cause of disability. Despite the economic and social relevance of the problem, the causes and mechanisms of Achilles tendinopathy remain unclear. Tendon vascularity, gastrocnemius-soleus dysfunction, age, sex, body weight and height, pes cavus, and lateral ankle instability are considered common intrinsic factors. The essence of Achilles tendinopathy is a failed healing response, with haphazard proliferation of tenocytes, some evidence of degeneration in tendon cells and disruption of collagen fibers, and subsequent increase in noncollagenous matrix. Tendinopathic tendons have an increased rate of matrix remodeling, leading to a mechanically less stable tendon which is more susceptible to damage. The diagnosis of Achilles tendinopathy is mainly based on a careful history and detailed clinical examination. The latter remains the best diagnostic tool. Over the past few years, various new therapeutic options have been proposed for the management of Achilles tendinopathy. Despite the morbidity associated with Achilles tendinopathy, many of the therapeutic options described and in common use are far from scientifically based. New minimally invasive techniques of stripping of neovessels from the Kager's triangle of the tendo Achillis have been described, and seem to allow faster recovery and accelerated return to sports, rather than open surgery. A genetic component has been implicated in tendinopathies of the Achilles tendon, but these studies are still at their infancy.

Glycine improves the remodeling process of tenocytes in vitro

Tendinitis changes the biochemical and morphological properties of the tendon, promoting an increase of activity of metalloproteinases and disorganization of collagen bundles. Tenocytes, the primary cells in tendon, are scattered throughout the collagenic fibers, and are responsible of tendon remodeling and tissue repair in pathological condition. In vivo, glycine, component of the typical Gly-X-Y collagen tripeptide, showed beneficial effects in biochemical and biomechanical properties of Achilles tendon with tendinitis. In this study, we analyzed the effect of glycine in tenocytes subjected to inflammation. Tenocytes from Achilles tendon of rats were treated with TNF-α (10 ng/mL) with and without previous treatment with glycine (20 mM). Cell proliferation and migration were evaluated, as well as the expression of matrix molecules such as glycosaminoglycans, metalloproteinases (MMPs), TIMPs, and collagen I. Glycine can revert the inflammation due to the action of TNF-α by controlling the MMPs quantity and activity. These data indicated that the molecules involved to remodeling process of extracellular matrix are modulated both by TNF-α and the availability of collagen precursors; in fact, this study indicates the glycine can be useful for treatment of inflammation and for modulating tenocytes metabolism in tendons.

Structural Evolution of Nonoperatively Treated High-Grade Partial-Thickness Tears of the Supraspinatus Tendon

BACKGROUND

High-grade partial-thickness rotator cuff tears (hPTRCTs) are frequently encountered in the shoulder. However, little information is available on the prevalence or timing of tear progression. Purpose/Hypothesis: The purpose was to prospectively evaluate the structural progression of hPTRCTs with a minimum follow-up of 1 year using magnetic resonance imaging (MRI). The hypothesis was that a substantial portion of hPTRCT patients would experience tear progression or evolution to a full-thickness rotator cuff tear.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

Between May 2010 and December 2015, 362 patients were diagnosed with hPTRCT (tear involvement >50% of the mediolateral length of the footprint) of the supraspinatus and were treated nonoperatively. Among these patients, 81 underwent follow-up MRI at least 1 year after initial presentation, and these patients were included in the final analysis. Initial and follow-up MRIs were used to determine whether tears had improved, had not changed, or had progressed. A change in tear involvement of >20% was defined as a significant change. Patients were categorized as follows: (1) a decrease in tear involvement of >20% (improved), (2) an increase or decrease of ≤20% (no change), or (3) an increase in tear involvement of >20% (progressed). Demographic data and morphologic data were analyzed to identify variables related to tear progression. Among them, severity of tendinosis was graded using MRIs: grade 1 (mild tendinosis), mild focal increase in tendon signal; grade 2 (moderate tendinosis), moderate focal increase in tendon signal; and grade 3 (marked tendinosis), marked generalized increase in tendon signal.

RESULTS

At initial diagnosis, 23 were articular-side (28%) and 58 were bursal-side (72%) hPTRCTs. The study cohort was composed of 51 women and 30 men, and the mean patient age was 62.3 years (range, 41-77 years). Follow-up MRI was performed at a mean 19.9 ± 10.9 months (range, 12-52 months). A significant change in tear involvement was observed at follow-up. In 13 patients (16%, 2 articular-side and 11 bursal-side tears), tears were classified as progressed (the progressed group); in 48 patients (59%), tears exhibited no change (the unchanged group); and in 20 patients (25%, 9 articular-side and 11 bursal-side tears), tears were improved (the improved group). Univariate analysis showed initial tendinosis grade was significantly different in the 3 groups (grade 1, 2, and 3: 5, 4, and 4 in progressed; 36, 11, and 1 in unchanged; 10, 8, and 2 in improved group, respectively, P = .007).

CONCLUSION

Although progression of hPTRCT in the long term is uncertain, after 1-year follow-up with MRI, tears progressed in 16% of the tears in this study. Furthermore, some tears were healed or reduced in size, which indicates that decisions to undertake surgical repair at time of presentation may be excessive.

Open surgical treatment for chronic midportion Achilles tendinopathy: faster recovery with the soleus fibres transfer technique

PURPOSE

The study aimed to compare two methods of open surgical treatment for midportion Achilles tendinopathy in sportsmen. A novel technique consisting in transferring some soleus fibres into the degenerated tendon to improve its vascularization and longitudinal tenotomies are evaluated and compared.

METHODS

From 2006 to 2011, fifty-two competitive and noncompetitive athletes affected by midportion Achilles tendinopathy were surgically treated and prospectively evaluated at 6 months and at a final 4-year mean follow-up. Twenty patients had longitudinal tenotomies, and thirty-two had soleus fibres transfer. Clinical outcome was evaluated by the American Orthopaedic Foot and Ankle Society (AOFAS) score and the Victorian Institute of Sports Assessment-Achilles (VISA-A) score. Time to return to walk and to run and tendon thickening were also recorded.

RESULTS

Patients in the soleus transfer group had a higher increase in AOFAS and VISA-A score at 6 months and at the mean 4-year final follow-up (by 5.4 points, 95 % CI 2.9-7.9, p < 0.001 and by 5.7 points, 95 % CI 2.5-8.9, p = 0.001, for AOFAS and VISA, respectively). They also needed less time to return to run: 98.9 ± 17.4 days compared to 122.2 ± 26.3 days for the longitudinal tenotomies group (p = 0.0019). The soleus transfer group had a greater prevalence of tendon thickening (59.4 % compared to 30.0 % in the longitudinal tenotomies group, p = 0.037).

CONCLUSIONS

Open surgery for midportion Achilles tendinopathy is safe and effective in medium term. Despite similar outcomes in postoperative functional scores, soleus transfer allows a faster recovery but has a higher incidence of tendon thickening. These results should suggest the use of the soleus graft technique in high-level athletes.

LEVEL OF EVIDENCE

Prospective comparative study, Level II.

MMP3 and TIMP2 gene variants as predisposing factors for Achilles tendon pathologies: Attempted replication study in a British case-control cohort

Variants within the MMP3 (rs679620) and TIMP2 (rs4789932) genes have been associated with the risk of Achilles tendon pathology (ATP) in populations from South Africa and Australia. This study aimed to determine whether these variants were associated with the risk of ATP in British Caucasians. We recruited 118 cases with ATP, including a subset of 25 individuals with Achilles tendon rupture (RUP) and 131 controls. DNA samples were isolated from saliva and genotyped using qPCR. For the TIMP2 rs4789932 variant we found a significant (p = 0.038) difference in the genotype distribution frequency between males with ATP (CC, 39.4%; CT, 43.7%; TT, 16.9%) compared to male controls (CC, 20.7%; CT, 59.8%; TT, 19.5%). We also observed a difference in the TIMP2 rs4789932 genotype distribution between males with rupture compared to male controls (p = 0.038). The MMP3 rs679620 GG genotype was found to be overrepresented in the Achilles tendon rupture (RUP) group (AA, 24.0%; AG, 32.0%; GG, 44.0%) compared to controls (AA, 26.7%; AG, 54.2%; GG, 19.1%). In conclusion, the CT genotype of the TIMP2 rs4789932 variant was associated with lower risk of ATP in males. Furthermore, while we revealed differences for both variants in genotype distribution between the RUP and control groups, the sample size of the RUP group was small and confirmation would be required in additional cohorts. Finally, although both the TIMP2 rs4789932 and MMP3 rs679620 variants tentatively associated with ATP, there were differences in the direction of association compared to earlier work.

Prevention of Simvastatin-Induced Inhibition of Tendon Cell Proliferation and Cell Cycle Progression by Geranylgeranyl Pyrophosphate

Statins have been reported to induce tendinopathy and even tendon rupture. The present study was designed to investigate the potential molecular mechanism underlying the adverse effect of simvastatin on tendon cells. An in vitro tendon healing model was performed using tendon cells isolated from rat Achilles tendons. The viability of tendon cells and cell cycle progression were examined by the MTT assay and flow cytometric analysis, respectively. Immunofluorescent staining for Ki-67 was used to assess the proliferation activity of tendon cells. Western blot analysis and coimmunoprecipitation was used to determine the protein expression of cell cycle-related proteins. To investigate the potential mechanism underlying the effect of statins on tendon cells, mevalonate, farnesyl pyrophosphate (FPP), or geranylgeranyl pyrophosphate (GGPP) was added to simvastatin-treated tendon cells. Simvastatin inhibited the in vitro tendon healing model and tendon cell proliferation in a dose-dependent manner. Immunofluorescent staining demonstrated reduced ki-67 expression in simvastatin-treated tendon cells. Furthermore, simvastatin induced cell cycle arrest at the G1 phase. The expression levels of cdk1, cdk2, cyclin A, and cyclin E were downregulated by simvastatin in a dose-dependent manner. The inhibitory effect of simvastatin was proved to mediate the reduction of mevalonate, and the addition of exogenous GGPP completely prevented the inhibitory effect of simvastatin on tendon cells. The present study demonstrated, for the first time, the molecular mechanism underlying simvastatin-induced tendinopathy or tendon rupture. GGPP was shown to prevent the adverse effect of simvastatin in tendon cells without interfering with its cholesterol-reducing efficacy.

MGF enhances tenocyte invasion through MMP-2 activity via the FAK-ERK1/2 pathway

Tendon regeneration and healing requires tenocytes to move to the repair site followed by proliferation and synthesis of the extracellular matrix. A novel synthetic growth factor, mechano-growth factor (MGF), has been discovered to have positive roles in tissue repair through the improvement of cell proliferation and migration and the protection of cells against injury-induced apoptosis. However, it remains unclear whether MGF has the potential to accelerate tendon repair. In this study, using a transwell system, we found that MGF-C25E (a synthetic mechano-growth factor E peptide) significantly promotes tenocyte invasion, which was accompanied by the increased phosphorylation of focal adhesion kinase (FAK) and extracellular signal regulated kinase1/2 (ERK1/2) as well as the increased activity of matrix metalloproteinases-2 (MMP-2). The MMP-2 inhibitor OA-Hy blocked MGF-C25E-promoted tenocyte invasion. Inhibitors of FAK or ERK1/2 blocked MGF-C25E-promoted tenocyte invasion and MMP-2 activity as well. These results indicate that MGF-C25E promotes tenocyte invasion by increasing MMP-2 activity via the FAK-ERK1/2 signaling pathway. Taken together, our findings provide the first evidence that MGF-C25E enhances tenocyte invasion and indicate that it may serve as a potential repair material for promoting the healing and regeneration of injured tendons.

Gastrocnemius shortening and heel pain

Pain and reduced function caused by disorders of either the plantar fascia or the Achilles tendon are common. Although heel pain is not a major public health problem it affects millions of people each year. For most patients, time and first-line treatments allow symptoms to resolve. A proportion of patients have resistant symptoms. Managing these recalcitrant cases is a challenge. Gastrocnemius contracture produces increased strain in both the Achilles tendon and the plantar fascia. This biomechanical feature must be properly assessed otherwise treatment is compromised.

Metalloproteases and their inhibitors are altered in both torn and intact rotator cuff tendons

BACKGROUND

We evaluated the role of matrix metalloproteases (MMPs) and their inhibitors which are involved in extracellular matrix remodeling and degradation, in the pathogenesis of chronic rotator cuff tears.

MATERIALS AND METHODS

Tendon samples were harvested from 13 patients who underwent arthroscopic repair of a rotator cuff tear. Supraspinatus biopsy specimens were harvested en bloc from the arthroscopically intact middle portion of the tendon more than 1 cm from the torn edge, from the lateral edge of the tear, and from the superior one third of the macroscopically intact subscapularis tendon used as control. Histological analysis and an evaluation of the activity of specific metalloproteases and the tissue inhibitors of metalloprotease (TIMP-1, TIMP-2) was done blindly by multiplex sandwich ELISA (Search-Light technology) in each specimen

RESULTS

Histological evidence of tendinopathy was present in all patients with a tear of the rotator cuff, and not in the macroscopically intact subscapularis tendon. There was a significant increase in MMP 1, MMP 2, MMP 3 and in TIMP-1, TIMP-2 levels in all specimens examined, including the macroscopically intact portion of the supraspinatus tendon and in the control specimens

CONCLUSIONS

The tissue in the ruptured area of the supraspinatus tendon undergoes marked rearrangement at molecular levels. This involves the activity of MMP 1, 2 and 3, and supports the critical role of MMPs in the tendon physiology. Seemingly intact parts of the injured supraspinatus tendon can present tendinopathic features, with altered cellular metabolism.

The role of mechanobiology in tendon healing

Mechanical cues affect tendon healing, homeostasis, and development in a variety of settings. Alterations in the mechanical environment are known to result in changes in the expression of extracellular matrix proteins, growth factors, transcription factors, and cytokines that can alter tendon structure and cell viability. Loss of muscle force in utero or in the immediate postnatal period delays tendon and enthesis development. The response of healing tendons to mechanical load varies depending on anatomic location. Flexor tendons require motion to prevent adhesion formation, yet excessive force results in gap formation and subsequent weakening of the repair. Excessive motion in the setting of anterior cruciate ligament reconstruction causes accumulation of macrophages, which are detrimental to tendon graft healing. Complete removal of load is detrimental to rotator cuff healing; yet, large forces are also harmful. Controlled loading can enhance healing in most settings; however, a fine balance must be reached between loads that are too low (leading to a catabolic state) and too high (leading to microdamage). This review will summarize existing knowledge of the mechanobiology of tendon development, homeostasis, and healing.

Role of metalloproteinases in rotator cuff tear

The role of matrix metalloproteinases (MMPs) and their inhibitors (TIMPS) in the pathophysiology of rotator cuff tears has not been established yet. Recent advances empathize about the role of MMPs and TIMPS in extracellular matrix (ECM) remodeling and degradation in rotator cuff tears pathogenesis and healing after surgical repair. An increase in MMPs synthesis and the resulting MMPs mediated alterations in the ECM of tendons have been implicated in the etiopathogenesis of tendinopathy, and there is an increase in the expression of MMPs and a decrease in TIMP messenger ribonucleic acid expression in tenocytes from degenerative or ruptured tendons. Importantly, MMPs are amenable to inhibition by cheap, safe, and widely available drugs such as the tetracycline antibiotics and bisphosphonates. A better understanding of relationship and activity of these molecules could provide better strategies to optimize outcomes of rotator cuff therapy.

Growth differentiation factor-5 regulation of extracellular matrix gene expression in murine tendon fibroblasts

The synthesis and organization of extracellular matrix (ECM) of tendon, in resting and states of repair, are governed by fibroblasts. Growth differentiation factor-5 (GDF-5) may enhance the cellular response to tendon injury, thus improving the structural outcome of the regenerative tissue. This study was an attempt to identify potential mechanisms controlling the response of fibroblasts to injury and GDF-5, in the pursuit of improved tissue regeneration. There were two sets of experiments. Isolated mice Achilles tendon fibroblasts were treated with different concentrations of rGDF-5 (0-100 ng/ml) for 0-12 days in cell culture. The temporal effect of rGDF-5 on ECM gene expression was analysed for type I collagen and aggrecan expression. Microarray and gene expression analysis were performed on cells treated with 100 ng/ml for 4 days. Forty-five mice underwent bilateral mid-substance Achilles tendon tenotomy and suture repair. Repair sites were injected with 10 µg rGDF-5 or saline. Tendons were assessed histologically at 2, 4 and 6 weeks. Expression of ECM genes procollagen IX, aggrecan, matrix metalloproteinase 9 and fibromodulin were upregulated. Proinflammatory reaction genes were downregulated. rGDF-5 led to an increase in total DNA, glycosaminoglycan (GAG) and hydroxyproline (OHP). The OHP:DNA ratio of fibroblast cultures was increased over all time points, with increased GAG:DNA at day 12. rGDF-5 treatment showed improved collagen organization over controls. The results delineate the mode of action of rGDF-5 at the cellular and gene level. rGDF-5 could play a role in tendon repair and be used for future therapies that promote tendon healing.

HGF inhibits TGF-β1-induced myofibroblast differentiation and ECM deposition via MMP-2 in Achilles tendon in rat

Both myofibroblast differentiation and extracellular matrix (ECM) deposition are essential components of scar formation in tendons, and hepatocyte growth factor (HGF) is reported to prevent fibrogenic responses in tendons. Matrix metalloproteinases-2(MMP-2) is also involved in the healing process in tendons. Whether HGF protects healed Achilles tendons from injury-induced scar formation and the mechanisms are unknown. Daily for 2 weeks after wounding, except for the non-surgical control group, the Achilles tendons in rats were locally injected with HGF (100 ng 50 μl(-1) per mouse) or phosphate-buffered saline (PBS). Histological examination showed HGF ameliorated disorganized collagen fibers caused by surgical incisions in rats. After transforming growth factor beta-1 (TGF-β1) induced fibrogenic responses in primary Achilles tendon fibroblasts in rats, HGF treatment for 24 h reduced α-smooth muscle actin (α-SMA) (0.60 ± 0.07-fold, P < 0.05) and type III collagen expression (0.39 ± 0.07-fold, P < 0.05). Moreover, HGF elevated MMP-2 expression (1.23 ± 0.11-fold, P < 0.05). The MMP-2 inhibitor, tissue inhibitors of metalloproteinase-1 (TIMP-1), partially blocked the inhibitory effects of HGF on α-SMA expression (from 0.60 ± 0.07-fold to 0.83 ± 0.07-fold, P < 0.05) and type III collagen expression (from 0.39 ± 0.06-fold to 0.86 ± 0.08-fold, P < 0.05). These results indicate HGF attenuates TGF-β1-induced fibrogenic responses in Achilles tendon, which was mediated by MMP-2. These results will aid in developing effective therapeutic approaches for the dysfunctional repair in Achilles tendons.

Mouse treadmill running enhances tendons by expanding the pool of tendon stem cells (TSCs) and TSC-related cellular production of collagen

Exercise is known to enhance tendon size and strength, but the stem cell-based mechanisms for such exercise-induced effects are largely unknown. This study aims to explore these mechanisms by using a mouse treadmill running model to examine the effects of exercise on newly discovered tendon stem cells (TSCs). After treadmill running, patellar TSCs (PTSCs) and Achilles TSCs (ATSCs) were isolated from the mice, and their proliferation was measured in vitro. We found that treadmill running nearly doubled proliferation rates of both PTSCs and ATSCs compared to cage control mice. Moreover, using a mixed tendon cell culture consisting of TSCs and tenocytes, cellular production of collagen was found to increase by 70% and 200% in PTSCs and ATSCs, respectively, from the treadmill running group over cells from the cage control group. These findings suggest that exercise exerts its anabolic effects on tendons at least in part by increasing proliferation to expand the pool of TSCs and also by increasing TSC-related cellular production of collagen, the predominant component of tendons.

Effect of dihydrotestosterone on cultured human tenocytes from intact supraspinatus tendon

The role of hormones in the pathogenesis of tendinopathy is not well recognised, even though the use of anabolic steroids is correlated with a higher incidence of spontaneous tendon ruptures. The aim of this study was to investigate the effects of dihydrotestosterone (DHT) on human tenocyte cultures from the intact supraspinatus tendon of male subjects. Cultured human tenocytes were seeded into culture plates at a density of 5 x 10(4) cells per well and incubated for 24 h. Then, 10(-9) M-10(-7) M DHT or Dulbecco's modified Eagle's medium (DMEM) only (control) was added to the culture plate wells. Cell morphology assessment and cell proliferation tests were performed 48, 72 and 96 h after DHT treatment. DHT-treated tenocytes showed an increased proliferation rate at DHT concentration higher than 10(-8) M. Differences in cell numbers between control and DHT-treated cells were statistically significant (P < 0.05) after 48 and 72 h of treatment with DHT concentrations of 10(-8) and 10(-7) M. The tenocytes treated with DHT (10(-8) and 10(-7) M) became more flattened and polygonal compared to control cells that maintained their fibroblast-like appearance during the experiment at each observation time. In conclusion, in vitro, progressive increasing concentration of DHT at doses greater than 10(-8) M had direct effects on male human tenocytes, increasing cell number after 48 and 72 h of treatment, and leading to a dedifferentiated phenotype after 48 h of treatment. This effect can be important during tendon-healing and repair, when active proliferation is required. Our results represent preliminary evidence for a possible correlation between testosterone abuse and shoulder tendinopathy.

The effect of stress-deprivation and cyclic loading on the TIMP/MMP ratio in tendon cells: an in vitro experimental study

PURPOSE

To determine the effect of stress deprivation and cyclic loading on TIMP-1/MMP-13 mRNA expression ratio in rat tail tendon (RTT) cells.

METHOD

Adult RTTs were stress-deprived for 0, 24, 48, or 72 hours in the presence or absence of a MMP inhibitor (ilomastat), or subjected to 1%, 3%, or 6% strain for 24 h under tissue culture conditions. TIMP-1 and MMP-13 (rat interstitial collagenase) mRNA expression were measured using quantitative PCR and TIMP/MMP ratios were calculated for each group.

RESULTS

The ratio of TIMP-1 to MMP-13 in control RTTs was 3.73:1 +/- 0.73. Stress deprivation for 24 h significantly decreased the TIMP-1/MMP-13 ratio (0.25:1 +/- 0.04) and MMP-13 expression continued to increase significantly with time of stress deprivation. Inhibition of MMP-13 mRNA expression with ilomastat in stress-deprived samples did not alter TIMP-1 expression when compared to normal controls. Cyclic loading significantly increased TIMP-1/MMP-13 expression at all strain levels examined.

CONCLUSIONS

RTTs normally have a positive TIMP-1/MMP-13 expression ratio. While cyclic loading increased the TIMP-1/MMP-13 ratio, loss of cellular homeostatic tension inversed this ratio through a significant increase in MMP-13 mRNA expression rather than a decrease in TIMP expression. A negative TIMP/MMP ratio has been implicated in the pathogenesis of tendinopathy. Increasing the TIMP/MMP ratios in these patients through exercise may be beneficial in the management of tendinopathy.

Effect of acute resistance exercise and sex on human patellar tendon structural and regulatory mRNA expression

Tendon is mainly composed of collagen and an aqueous matrix of proteoglycans that are regulated by enzymes called matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). Although it is known that resistance exercise (RE) and sex influence tendon metabolism and mechanical properties, it is uncertain what structural and regulatory components contribute to these responses. We measured the mRNA expression of tendon's main fibrillar collagens (type I and type III) and the main proteoglycans (decorin, biglycan, fibromodulin, and versican) and the regulatory enzymes MMP-2, MMP-9, MMP-3, and TIMP-1 at rest and after RE. Patellar tendon biopsy samples were taken from six individuals (3 men and 3 women) before and 4 h after a bout of RE and from a another six individuals (3 men and 3 women) before and 24 h after RE. Resting mRNA expression was used for sex comparisons (6 men and 6 women). Collagen type I, collagen type III, and MMP-2 were downregulated (P < 0.05) 4 h after RE but were unchanged (P > 0.05) 24 h after RE. All other genes remained unchanged (P > 0.05) after RE. Women had higher resting mRNA expression (P < 0.05) of collagen type III and a trend (P = 0.08) toward lower resting expression of MMP-3 than men. All other genes were not influenced (P > 0.05) by sex. Acute RE appears to stimulate a change in collagen type I, collagen type III, and MMP-2 gene regulation in the human patellar tendon. Sex influences the structural and regulatory mRNA expression of tendon.

Collagens, proteoglycans, MMP-2, MMP-9 and TIMPs in human achilles tendon rupture

Tendon integrity depends on the extracellular matrix (ECM) metabolism which is regulated by proteolytic enzymes. However, it is unclear which enzymes play a role in tendon rupture. We studied the ECM of 19 ruptured human Achilles tendons, comparing the composition of specimens harvested close to the rupture with specimens harvested from an apparently healthy area in the same tendon. We compared gene expression of collagen Type I, decorin, and versican including enzymes involved in their metabolism as matrix metalloproteases (MMP-2 and -9) and tissue inhibitory of metalloproteinase (TIMP-1 and -2) using real-time PCR, zymography and FACE analysis. We found greater gene expression of proteoglycan core protein decorin and versican, collagen Type I, MMPs and TIMPs in the tendon rupture. Zymography analysis, reflecting expression of enzymatic activity, confirmed the gene expression data at protein level. Carbohydrate content was greater in the macroscopically healthy area than in the ruptured area. In the ruptured area, we found increased core protein synthesis but without the normal glycosaminoglycan production. The tissue in the area of rupture undergoes marked rearrangement at molecular levels and supports the role of MMPs in the pathology.

Presence of substance P and the neurokinin-1 receptor in tenocytes of the human Achilles tendon

Nerve signal substances, such as the tachykinin substance P (SP), may be involved in the changes that occur in response to tendinopathy (tendinosis). It is previously known that the level of SP innervation within tendon tissue is limited, but results of experimental studies have suggested that SP may have stimulatory, angiogenetic and healing effects in injured tendons. Therefore, it would be of interest to know if there is a local SP-supply in tendon tissue. In the present study, the patterns of expression of SP and its preferred receptor, the neurokinin-1 receptor (NK-1 R), in normal and tendinosis human Achilles tendons were analyzed by use of both immunohistochemistry and in situ hybridization. We found that there was expression of SP mRNA in tenocytes, and that tenocytes showed expression of NK-1 R at protein as well as mRNA levels. The observations concerning both SP and NK-1 R were most evident for tenocytes in tendinosis tendons. Our findings suggest that SP is produced in tendinosis tendons, and furthermore that SP has marked effects on the tenocytes via the NK-1 R. It cannot be excluded that the SP effects are of importance concerning the processes of reorganization and healing that occur for tendon tissue in tendinosis. In conclusion, it appears as if SPergic autocrine/paracrine effects occur in tendon tissue during the processes of tendinosis, hitherto unknown effects for human tendons.

Management of insertional tendinopathy of the Achilles tendon

Posterior heel pain is common and disabling. Most cases respond to nonoperative treatment. The literature is confusing about the treatment rationale because many papers treat a variety of pathologies in the same way on an empirical basis. The authors critically review the literature with special reference to surgical treatment. The key to successful management of posterior heel pain is a proper understanding of the anatomy and pathological processes. Only then can appropriate treatment be recommended and proper advice about recovery times be offered to patients.

Noninsertional Achilles tendinopathy

The treatment of noninsertional Achilles tendinopathy remains, to a large extent, empirical. Neither different operative techniques nor nonoperative regimes have been subjected to controlled trials. Rather, the condition is still treated on the basis of anecdotal evidence combined with personal experience. However, increased knowledge of the basic science of tendinopathy and tendon healing has directed therapeutic regimens and will continue to do so. Manipulation of proteolytic enzymes and control of neovascularization are probably the two areas that show most promise.

Tendon healing

An understanding of the processes of tendon healing and tendon-to-bone healing is important for the intraoperative and postoperative management of patients with tendon ruptures or of patients requiring tendon transfers in foot and ankle surgery. Knowledge of the normal process allows clinicians to develop strategies when normal healing fails. This article reviews the important work behind the identification of the normal phases and control of tendon healing. It outlines the failed response in tendinopathy and describes tendon-to-bone healing in view of its importance in foot and ankle surgery.