ACL transection influences mRNA levels for collagen type I and TNF-alpha in MCL scar

An in vivo model of ligamentum flavum hypertrophy from early-stage inflammation to fibrosis

Multi-joint disease pathologies in the lumbar spine, including ligamentum flavum (LF) hypertrophy and intervertebral disc (IVD) bulging or herniation contribute to lumbar spinal stenosis (LSS), a highly prevalent condition characterized by symptomatic narrowing of the spinal canal. Clinical hypertrophic LF is characterized by a loss of elastic fibers and increase in collagen fibers, resulting in fibrotic thickening and scar formation. In this study, we created an injury model to test the hypothesis that LF needle scrape injury in the rat will result in hypertrophy of the LF characterized by altered tissue geometry, matrix organization, composition and inflammation. An initial pilot study was conducted to evaluate effect of needle size. Results indicate that LF needle scrape injury using a 22G needle produced upregulation of the pro-inflammatory cytokine Il6 at 1 week post injury, and increased expression of Ctgf and Tgfb1 at 8 weeks post injury, along with persistent presence of infiltrating macrophages at 1, 3, and 8 weeks post injury. LF integrity was also altered, evidenced by increases in LF tissue thickness and loss of elastic tissue by 8 weeks post injury. Persistent LF injury also produced multi-joint effects in the lumbar IVD, including disc height loss at the injury and adjacent to injury level, with degenerative IVD changes observed in the adjacent level. These results demonstrate that LF scrape injury in the rat produces structural and molecular features of LF hypertrophy and IVD height and histological changes, dependent on level. This model may be useful for testing of therapeutic interventions for treatment of LSS and IVD degeneration associated with LF hypertrophy.

Effects of Endoprosthesis Head Material on Acetabular Cartilage Metabolism: An Animal Study Using Crossbred Pigs

BACKGROUND

Hip endoprosthesis is one option for the treatment of displaced femoral neck fractures and avascular necrosis of the femoral head. Few reports are available describing acetabular cartilage metabolism after endoprosthesis surgery of the hip. The purpose of this study was to compare the biological effects on cartilage between cobalt-chrome (Co-Cr) and alumina ceramic heads wherein the cartilage articulates directly.

METHODS

We used the acetabular cartilage from six hips of three immature crossbred pigs to examine the effects on cytokines, the amount of hyaluronic acid (HA), and cartilage mRNA expression of ceramic head and Co-Cr head endoprosthesis. Mechanical loading of materials of Co-Cr and ceramic heads was performed on the acetabular cartilage in culture media as an organ culture model. Thereafter, protein levels of cytokines (MMP-1, 3, TNF-alpha (α), Interleukin (IL)-1 alpha (α), and IL-1 beta (β)) and the amount of HA were measured from the culture media. Cartilage RNA extraction was performed, and quantitative reverse transcriptase-polymerase chain reaction was performed with primer sets for type I, II, and III collagens; aggrecan; MMP-1, 3, 13; TNF-α; and IL-1 α, IL-1 β.

RESULTS

Protein level of IL-1 β and amount of HA in the Co-Cr group were significantly higher than those of the Ceramic group. Type II collagen mRNA expression in the Ceramic group was significantly higher than in the Co-Cr group. IL-1 β mRNA expression was significantly higher in the Co-Cr group than in the Ceramic group.

CONCLUSIONS

The present study showed that ceramic bipolar produces smaller adverse effects on cartilage cells compared to Co-Cr bipolar. These results could have significant implications for implant usage not only in hip joints, but also in other joints, including the shoulder, talus and radial head.

Sustained intra-cartilage delivery of low dose dexamethasone using a cationic carrier for treatment of post traumatic osteoarthritis

Disease-modifying osteoarthritis drugs (DMOADs) should reach their intra-tissue target sites at optimal doses for clinical efficacy. The dense, negatively charged matrix of cartilage poses a major hindrance to the transport of potential therapeutics. In this work, electrostatic interactions were utilised to overcome this challenge and enable higher uptake, full-thickness penetration and enhanced retention of dexamethasone (Dex) inside rabbit cartilage. This was accomplished by using the positively charged glycoprotein avidin as nanocarrier, conjugated to Dex by releasable linkers. Therapeutic effects of a single intra-articular injection of low dose avidin-Dex (0.5 mg Dex) were evaluated in rabbits 3 weeks after anterior cruciate ligament transection (ACLT). Immunostaining confirmed that avidin penetrated the full cartilage thickness and was retained for at least 3 weeks. Avidin-Dex suppressed injury-induced joint swelling and catabolic gene expression to a greater extent than free Dex. It also significantly improved the histological score of cell infiltration and morphogenesis within the periarticular synovium. Micro-computed tomography confirmed the reduced incidence and volume of osteophytes following avidin-Dex treatment. However, neither treatment restored the loss of cartilage stiffness following ACLT, suggesting the need for a combinational therapy with a pro-anabolic factor for enhancing matrix biosynthesis. The avidin dose used caused significant glycosaminoglycan (GAG) loss, suggesting the use of higher Dex : avidin ratios in future formulations, such that the delivered avidin dose could be much less than that shown to affect GAGs. This charge-based delivery system converted cartilage into a drug depot that could also be employed for delivery to nearby synovium, menisci and ligaments, enabling clinical translation of a variety of DMOADs.

"Thickened" ligamentum flavum caused by laminectomy

OBJECTIVE

The purpose of this study was to evaluate the effect of a laminectomy on the adjacent ligamentum flavum (LF) by measuring LF thickness using magnetic resonance imaging (MRI).

MATERIALS AND METHODS

A total of 78 patients (31 man, 47 woman) with laminectomy were included in our study. After determination of laminectomy level, measurements were done from the thickest parts of the bilateral LF at the upper level of the laminectomy where bilateral facet joints were evident at the slice.

RESULTS

Ipsilateral ligamentum flavum with laminectomy was significantly thicker than the contralateral ligamentum flavum with laminectomy.

CONCLUSION

Laminectomy cause thickening of ligamentum flavum. Therefore we assume that it should kept in mind that LFH may develop at the adjacent level to the laminectomy and careful clinical and radiological assessments' should be done to exclude LFH in cases who complain about the recurrence of complaints during the post-operative period after laminectomy.

Characterization of total and active matrix metalloproteinases-1, -3, and -13 synthesized and secreted by anterior cruciate ligament fibroblasts in three-dimensional collagen gels

Anterior cruciate ligament (ACL) injury and subsequent reconstructive surgery is increasing with an estimated 200,000 reconstructions performed yearly in the United States. Current treatment requires reconstruction with autograft or allograft tissue with inherent disadvantages. The development of tissue-engineered ligament replacements or scaffolds may provide an alternative treatment method minimizing these issues. The study of ligament fibroblast catabolic and anabolic responses to mechanical and biologic stimuli in three-dimensional (3D) cell culture systems is critical to the development of such therapies. A 3D cell culture system was used to measure the total content and active forms of matrix metalloproteinases (MMPs)-1, -3, and -13 to assess the potential role of the mechanical environment in regulation of matrix turnover by ligament fibroblasts. The production, retention, and secretion of MMPs by ACL fibroblasts in 3D culture were measured over a 14-day period. The total MMP content and MMP activity were determined. The level of all MMPs studied increased over 7-10 days and then reached a steady state or decreased slightly in both the collagen gels and the media. This system will now permit the study of externally applied cyclic and static strains, strain deprivation, and the potential combined role of the cytoskeleton and MMPs in matrix turnover in ligaments.

Canine tissue-specific expression of multiple small leucine rich proteoglycans

Small leucine rich proteoglycans (SLRPs) are important constituents of extracellular matrix (ECM) and contribute to the production, organization and remodelling of collagen and elastin through complex biological systems. The relative expression and distribution of SLRPs in a variety of different mammalian tissues is poorly characterized. The aim of this study was to map the expression of seven SLRPs (biglycan, versican, prolargin, fibromodulin, osteoglycin, decorin and lumican) in seven tissues (bone, cartilage, cruciate ligament, skin, ventricular myocardium, mitral valve and cornea) in young adult dogs using a combination of quantitative real-time PCR, immunohistochemistry and protein immunoblotting. Clear and consistent patterns of SLRP expression and distribution were identified for the seven tissues examined, with the greatest SLRP expression in cartilage, skin, cornea and mitral valve, and the least expression in myocardium. In general, lumican and prolargin had the greatest expression across the seven tissues whilst osteoglycin was the least abundantly expressed SLRP. These data provide a SLRP profile for different canine tissues which can inform future studies of SLRP expression in development and disease.

Molecular events surrounding collagen fibril assembly in the early healing rabbit medial collateral ligament--failure to recapitulate normal ligament development

??Although injuries to the medial collateral ligament (MCL) can heal functionally without surgical intervention, the collagen fibers in the healing tissue remain compromised. The molecular basis for this poor healing potential was investigated by examining extracellular matrix-modifying molecules such as bone morphogenetic protein 1 (BMP-1), procollagen C proteinase enhancer (PCOLCE), lysyl oxidase (LOX), and transforming growth factor beta 1 (TGF-β1) involved in collagen fibrillogenesis during normal early postnatal ligament maturation and at comparable intervals after MCL injury. Samples of midsections of rabbit MCLs were collected from 3-, 6-, 14-, and 52-week-old normal animals and at 3, 6, and 14 weeks postinjury. Harvested midsubstance tissues were analyzed for collagen fibril diameter by transmission electron microscopy (TEM), and mRNA levels were assessed by reverse transcription-polymerase chain reaction (RT-PCR). Results showed different patterns of expression between normal MCL maturation and during scar maturation. BMP-1 and PCOLCE mRNA levels were upregulated in the 3?14-week period during maturation of normal ligaments but decreased at skeletal maturity. The scar tissue exhibited a 3.5-fold increase in PCOLCE mRNA levels during the early healing phase, but these decreased with time. After injury, BMP-1 mRNA levels in scars were low and did not change during healing. Both LOX and TGF-β1 mRNA levels were low during normal MCL development compared with levels at maturity and exhibited elevated mRNA levels during early healing that decreased with time postinjury. These results suggest that gene expression in scars during MCL healing does not recapitulate expression in normal ligament fibroblasts during maturation.

Effects of raised-intensity phonation on inflammatory mediator gene expression in normal rabbit vocal fold

OBJECTIVE

To investigate the hypothesis that a transient episode of raised-intensity phonation causes a significant increase in vocal fold inflammatory messenger RNA (mRNA) expression in vivo.

STUDY DESIGN

Prospective animal study.

SETTING

Laboratory.

SUBJECTS AND METHODS

Ten New Zealand White breeder rabbits received 30 minutes of experimentally induced modal or raised-intensity phonation, followed by a 30-minute recovery period. A separate group of five rabbits served as sham controls. Real-time polymerase chain reaction was performed to investigate the mRNA expression of interleukin 1beta (IL-1beta), transforming growth factor beta-1 (TGFbeta1), and cyclooxygenase-2 (COX-2). Separate one-way analysis of variance (ANOVA) tests were used to investigate differences in gene expression across groups, with an appropriate alpha correction of 0.016 to control for type I error. Significant main effects were further examined using Fisher's least significant difference.

RESULTS

ANOVA revealed that there were differences for IL-1beta, TGFbeta1, and COX-2 between sham control, modal phonation, and raised-intensity phonation (P 0.0001). Pairwise comparisons revealed that the expression of IL-1beta, COX-2, and TGFbeta1 increased significantly during raised-intensity phonation, compared to modal phonation and sham control (P 0.0001).

CONCLUSION

Results provided support for the hypothesis that a transient episode of raised-intensity phonation causes a significant increase in vocal fold inflammatory mRNA expression. Future studies will investigate the signal transduction pathways and mechanisms regulating the vocal fold inflammatory response. The long-term goal of these studies is to advance understanding of the molecular and cellular events underlying phonation-related tissue alterations.

Patterns of gene expression in a rabbit partial anterior cruciate ligament transection model: the potential role of mechanical forces

BACKGROUND

The inconsistency in healing after anterior cruciate ligament (ACL) repair has been attributed to ACL fibroblast cellular metabolism, lack of a sufficient vascular supply, and the inability to form a scar or scaffold after ligament rupture because of the uniqueness of the intra-articular environment. Hypotheses (1) Stress deprivation in the surgically transected ACL will increase matrix metalloproteinase (MMP) and alpha smooth muscle actin (alpha-SMA) expression. (2) Stress deprivation will decrease collagen expression. (3) The transected anteromedial bundle of the ACL will demonstrate a pattern of gene expression similar to the completely transected ACL, while gene expression profiles in the intact posterolateral bundle will be similar to the sham-operated controls.

STUDY DESIGN

Controlled laboratory study.

METHODS

Thirty-six New Zealand White rabbits underwent a partial ACL surgical transection separating the anteromedial (AM) and posterolateral (PL) bundles and transecting the AM bundle. Contralateral ACLs were either sham operated or completely transected. Ligament tissue was harvested at 1, 2, or 6 weeks after surgery, and real-time PCR was performed using primers for collagen I, collagen III, alpha-SMA, MMP-1, and MMP-13.

RESULTS

At 1 week, a 28- and 29-fold increase in MMP-13 expression was seen in the complete transection and the transected AM bundle specimens when compared with sham-operated controls (P = .049, P = .018), respectively. There was no significant difference in MMP-13 between the sham controls and the intact PL bundle specimens. A 22- and 23-fold increase in alpha-SMA was seen (P = .03, P = .009) in the complete transection and transected AM bundle specimens, respectively, while no difference was seen between the intact PL bundle and controls. No significant differences were seen in collagen I (Col I) or collagen III (Col III) gene expression at 1 week. At 6 weeks, Col I expression increased 5-fold in complete transection samples (P = 3.9 x 10(-6)), 3-fold in transected AM samples (P = 3.3 x 10(-6)), and 2-fold in the intact PL bundle samples as compared with controls. alpha-SMA was increased 7.5-fold and 5-fold in complete transection and transected AM samples, respectively (P = .004, P = 2.2 x 10(-6)), while no significant change was seen in the intact PL bundle samples compared with controls. Complete transection specimens showed a 3-fold increase in MMP-1 expression. Col III increased 5.4-, 2.6-, and 2.4-fold in the complete transection, transected AM, and intact PL groups, respectively (P = .003, P = .004, P = .04).

CONCLUSION

Partial or complete surgical transection of the rabbit ACL with resultant loss of mechanical stimuli results in an increase in MMP-13 and alpha-SMA expression at the early time point (1 week) and an increase in alpha-SMA, Col I, and Col III expression at the later time point (6 weeks). These data provide support for the hypothesis that there is a time-dependent alteration of anabolic and catabolic matrix gene expression after injury/loss of ligament integrity. Clinical Relevance Identification of pathways that respond to mechanical stress in the intact ACL and after surgical transection may permit development of novel therapies to alter healing of the partial ACL injury or to assist in the development of biomechanical active ''smart'' scaffolds for tissue-engineered ligament replacements.

Neural stimulation does not mediate attenuated vascular response in ACL-deficient knees: potential role of local inflammatory mediators

Chronic inflammation associated with osteoarthritis (OA) alters normal responses and modifies the functionality of the articular vasculature. Altered responsiveness of the vasculature may be due to excessive neural activity associated with chronic pain and inflammation, or from the production of inflammatory mediators which induce vasodilation. Using laser speckle perfusion imaging (LSPI), blood flow to the medial collateral ligament (MCL) of adult rabbits was measured in denervated ACL transected knees (n = 6) and compared to unoperated control (n = 6) and 6-week anterial cruciate ligament (ACL)-transected knees (n = 6). Phenylephrine and neuropeptide Y were applied to the MCL vasculature in topical boluses of 100 microL (dose range 10(-14) to 10(-8) mol and 10(-14) to 10(-9) mol, respectively). Denervation diminished vasoconstrictive responsiveness to phenylephrine compared to both control and ACL-transected knees. Denervation minimally enhanced vascular responses to neuropeptide Y (NPY) compared to ACL deficiency alone, which nevertheless remained significantly diminished from control responses. To evaluate the potential role of inflammatory dilators in the diminished contractile responses, phenylephrine was coadministered with histamine, substance P, and prostaglandin E(2). High-dose histamine, and low-dose substance P and PGE(2) were able to inhibit contractile responses in the MCL of control knees. Excessive neural input does not mediate diminished vasoconstrictive responses in the ACL transected knee; inflammatory mediators may play a role in the deficient vascular responsiveness of the ACL transected knee.

Influence of extracellular matrix on the expression of inflammatory cytokines, proteases, and apoptosis-related genes induced by hydrostatic pressure in three-dimensionally cultured chondrocytes

BACKGROUND

The purpose of this study was to investigate the influence of hydrostatic pressure (HP) on the gene expression of cartilage matrix, cytokines, and apoptosis-associated factors in chondrocytes in which the cartilage was in extracellular matrix (ECM)-rich or ECM-poor condition.

METHODS

Chondrocytes were isolated from rabbit joints and cultured in alginate beads. Immediately after embedding (0W group) or after 2 weeks culture (2W group), the amounts of glycosaminoglycan (GAG) in the alginate beads were quantified. Both groups were exposed to continuous HP of 10 or 50 MPa for 12 h. The expression of inflammatory cytokines, proteases, and apoptosis-related factors were examined by reverse transcription-polymerase chain reaction (RT-PCR). The expression of proteoglycan core protein (PG) and collagen type II were quantified by real-time RT-PCR.

RESULTS

All of the GAG components in alginate beads markedly increased in the 2W group. The expression of PG and collagen type II increased after exposure to 10 MPa in both groups. In the 0W group, these levels decreased after exposure to 50 MPa of HP. The expression of interleukins IL-6 and IL-8 increased after exposure to HP in the 0W group. HP at 50 MPa induced mRNA expression of ADAMTS-5 in the 0W group but not in the 2W group. The expression of Fas increased after exposure to HP in the 0W group.

CONCLUSIONS

These findings suggested that nonphysiological, excessive HP on chondrocytes with the ECM in poor condition reduced matrix gene expression and increased expression of the genes associated with apoptosis and catabolism of the cartilage matrix. These results might therefore be associated with the pathogenesis of osteoarthritis.

Phenotypic re-expression of near quiescent chondrocytes: The effects of type II collagen and growth factors

After extensively expanding in monolayer culture, the cultured chondrocytes become quiescent. The aim of this study was to establish the hypothesis that the phenotypic function of extensively expanded primary chondrocytes may be restored with extracellular matrix (ECM) compositions with or without growth factors. The restoring effects of these microenvironmental factors on the near quiescent passage 9 (P9) chondrocyte were investigated. The data showed that exogenous type I collagen and type II collagen at 1:1 ratio stimulate cell proliferation greatly while type II collagen alone was enough to revive most of cartilaginous functions of near quiescent P9 chondrocytes. Exogenous type II collagen by itself was more effective in restoring cell proliferation rate, elevating glycosaminoglycan (GAG) accumulation and promoting the re-expression of type II collagen mRNAs in the near quiescent chondrocytes. The supplement of P9 chondrocytes with type II collagen plus TGF-beta1 and IGF-I appeared essential for the re-expression of aggrecan and type II collagen mRNA in monolayer culture. In 3D type II collagen construct, P9 chondrocytes appeared healthy as chondrocytes and showed clear lacuna. However, in 3D type I collagen matrix, only some P9 chondrocytes exhibited lacuna. The cartilaginous microenvironments are crucial to restoring chondrocyte-phenotypic features of the quiescent or 'dedifferentiated' chondrocytes, implicating the potential of expanding a scarcity of healthy chondrocytes for cartilage repair or regeneration.

Lumbar ligamentum flavum hypertrophy is due to accumulation of inflammation-related scar tissue

STUDY DESIGN

A histologic, biologic, and immunohistochemical assessment using human samples of the lumbar ligamentum flavum.

OBJECTIVE

To prove our hypothesis that hypertrophy of the ligamentum flavum is caused by accumulation of inflammation-related scar tissue.

SUMMARY OF BACKGROUND DATA

Lumbar spinal canal stenosis is 1 of the most common spinal disorders in elderly patients. Canal narrowing, in part, results from hypertrophy of the ligamentum flavum. The hypertrophy mechanism remains unclear. Based on our preliminary analyses, we have previously proposed that the hypertrophy may be due to accumulation of scar tissue in the ligament. Scar tissue is reported to develop after inflammation; however, there is no report, including our previous study, on inflammation in the ligamentum flavum. There is a need for an in-depth investigation of any relationship between inflammation and scar formation in the ligamentum flavum. If inflammation is related to hypertrophy, we may control/delay the hypertrophy by inhibiting the inflammation.

METHODS

Twenty-one ligamentum flavum samples were obtained for the histologic study. Trichrome and Verhoeff-van Gieson stains were used to assess the degree of fibrosis (scarring) and content of elastic fibers, respectively. Two ligamentum flavum samples, hypertrophied and thin control ligaments, were used for a global genetic assessment by oligonucleotide gene array technology with gene chips. Messenger ribonucleic acid expression of cyclooxygenase (COX)-2 was quantitatively measured from 16 ligamentum flavum samples using real-time reverse transcriptase polymerase chain reaction. Immunohistochemistry evaluated the cellular location of COX-2 in ligamentum flavum.

RESULTS

In the hypertrophied ligament, severe fibrosis (scarring) was observed in the entire area of the ligamentum flavum, and the severity of scarring showed a significant (r = 0.79; P < 0.0001) and positive linear correlation with ligamentum flavum thickness. Gene array results showed in both thin/control and hypertrophied ligaments expression of inflammation-related genes such as COX-2, tumor necrosis factor-alpha, and interleukin-1, 6, 8, and 15. Real-time polymerase chain reaction showed COX-2 messenger ribonucleic acid expression in all ligamentum flavum samples. Its expression showed weak positive linear correlation with the thickness of ligament. COX-2 was released from vascular endothelial cells in ligamentum flavum as per the immunohistochemical analysis.

CONCLUSIONS

Accumulation of fibrosis (scarring) causes hypertrophy of the ligamentum flavum. Inflammation-related gene expression is found in the ligamentum flavum. It might be possible to prevent the hypertrophy of ligamentum flavum with antiinflammatory drugs.

Impact of age, systemic glucocorticoids, and progressive knee arthritis on specific mRNA levels in different areas of the rabbit cornea

PURPOSE

To determine the influence of factors such as age, osteoarthritis (OA), and glucocorticoid treatment on total RNA and mRNA regulation in the cornea and how these factors differ between prepupillary and peripheral areas of the cornea.

METHODS

Molecular analyses of corneal tissue were performed using rabbits of different age groups and skeletally mature animals that had undergone anterior cruciate ligament (ACL) transection, an established model of knee OA. Systemic glucocorticoids were administered to cohorts of the osteoarthritic and control animals to determine the influence of distal joint disease on the corneal response. Corneal tissue was analyzed for changes in mRNA levels for several relevant genes: collagen I, collagen III, collagen V, decorin core protein, cyclooxygenase-2 (COX-2), glucocorticoid receptor, and the housekeeping gene beta-actin.

RESULTS

The corneal tissue was found to have diminishing total RNA with age, which is consistent with previous studies in the literature. Interestingly, in skeletally mature animals, distal joint OA was found to affect corneal mRNA levels for several important structural and inflammatory genes (collagen I, decorin core protein, and COX-2) in a manner that progressed with OA progression. Although systemic glucocorticoid treatment did not alter mRNA levels in the normal cornea, it did counteract the changes observed early after OA induction (3 weeks) while having less of an effect in later, more established arthritis (6 weeks).

CONCLUSIONS

This study reveals that distal joint OA can affect mRNA levels for several structural and inflammatory genes of the cornea, changes that seem to be suppressed by systemic glucocorticoid treatment. These findings indicate that OA has associated systemic factors that influence corneal cell metabolism.

The healing rabbit medial collateral ligament of the knee responds to systemically administered glucocorticoids differently than the uninjured tissues of the same joint or the uninjured MCL: a paradoxical shift in impact on specific mRNA levels and MMP-13 protein expression in injured tissues

The impact and molecular mechanism of action of glucocorticoids in connective tissues is largely unclear, even though widely used, and whether factors such as injury and inflammation modulate this response has not been elucidated. This study describes the role of glucocorticoids in the regulation of mRNA levels for collagens I and III, MMP-13, biglycan, decorin, COX-2 and the glucocorticoid receptor in connective tissues of normal and injured joints in an established rabbit in vivo MCL scar model, and examines the potential mechanism(s) involved. In vitro promoter studies were performed using an MMP-13 promoter-luciferase expression construct in transient transfection assays with a rabbit synovial cell line (HIG-82) to identify sites of glucocorticoid-mediated transcriptional regulation and the promoter elements involved. The in vivo results indicate that scar tissue from different phases of healing (early inflammatory, granulation tissue and neovascular, and later remodelling phases, respectively) displays a different pattern of responsiveness to glucocorticoid treatment than uninjured tissue and that this responsiveness is gene dependent. The most significant impact was seen for genes such as collagen I, collagen III and MMP-13, all of which are involved in connective tissue structure and remodelling. The in vitro studies confirmed the apparent in vivo glucocorticoid-mediated response of MMP-13 mRNA and implicated the AP-1 site of the MMP-13 promoter in this regulation. Immunohistochemistry studies showed increased MMP-13 protein expression, consistent with the mRNA findings, following glucocorticoid treatment in injured tissue but not normal tissues. In conclusion, connective tissue responsiveness to glucocorticoid treatment varies depending on injury and the stage of healing of the tissue, and consequently, glucocorticoid-responsiveness may be modulated differently in states of injury and inflammation.

The combined regulation of estrogen and cyclic tension on fibroblast biosynthesis derived from anterior cruciate ligament

Female athletes are two to eight times more likely to suffer a knee or ankle ligament injury than male athletes, and sex hormones have been considered to play an important role in the injury. Because ligaments are always under mechanical loading during sports, mechanical force is also a critical factor in ligament injuries. In this study, the effects of estrogen and mechanical loading on the gene expression of three major components of ligament--collagen type I, type III, and biglycan--in primary cultured porcine anterior cruciate ligament (ACL) fibroblasts were investigated individually and collectively using reverse transcript-polymerase chain reaction (RT-PCR). The results revealed that cyclic tensile loading alone increased the messenger RNA expression of collagen I but did not affect that of collagen III and biglycan, and estrogen alone increased the gene expression of collagen I and III but not of biglycan. However, combined administration of estrogen and cyclic loading inhibited the mRNA expression of all the three genes. These results suggested that the inhibition of the gene expression of major extracellular matrix component molecules caused by the combined effects of estrogen and mechanical loading, unique to females, might be responsible for the increased incidence of ligaments injury in female athletes.

Stiffness of the healing medial collateral ligament of the mouse

The knee joints of mice can serve as a model for studying knee ligament properties. The goal of our study was to measure the structural stiffness of the medial collateral ligament (MCL) of the murine knee. A tensile test was developed for this purpose. First 84 femur-MCL-tibia complexes of 11-week-old C57Black6 mice were tested. Of four groups (n = 14 per group) the right MCL was ruptured. The mice were sacrificed at 1.5, 3, 6, and 9 weeks after the operation. The other two groups served as controls at 0 and 9 weeks after the operation. Absolute values of the structural stiffness of the healed MCLs at 1.5 weeks were initially significantly lower than their unoperated controls, but were not different from normal values at three, six, and nine weeks of healing. The structural stiffness of the unoperated controls increased by 11% at 20 weeks compared to 11 weeks of age.