Suppression of idiotypic specificities in adult mice by administration of antiidiotypic antibody

It has previously been shown that there are extensive idiotypic cross-reactions among antiphenylarsonate antibodies of A/J mice. The present work indicates that administration, into normal, adult A/J mice, of rabbit antiidiotypic antibody directed to A/J antiphenylarsonate antibody suppresses almost completely the subsequent production of antibody of the corresponding idiotype. No effect was noted on the formation of antibodies to the protein carrier or of antiphenylarsonate antibody of a different idiotype. The data are consistent with central suppression of production of the idiotypic antibody mediated through interaction with immunoglobulin receptors on lymphocytes.

Relationship between inflammation, the gut microbiota, and metabolic osteoarthritis development: studies in a rat model

Osteoarthritis (OA) may result from intrinsic inflammation related to metabolic disturbance. Obesity-associated inflammation is triggered by lipopolysaccharide (LPS) derived from the gut microbiota. However, the relationship between gut microbiota, LPS, inflammation, and OA remain unclear.

OBJECTIVE

To evaluate the associations between gut microbiota, systemic LPS levels, serum and local inflammatory profiles, and joint damage in a high fat/high sucrose diet induced obese rat model.

METHODS

32 rats were randomized to a high fat/high sucrose diet (diet-induced obese (DIO), 40% fat, 45% sucrose, n = 21) or chow diet group (12% fat, 3.7% sucrose n = 11) for 28 weeks. After a 12-week obesity induction period, DIO animals were stratified into Obesity Prone (DIO-P, top 33% by change in body mass, n = 7), and Obesity Resistant groups (DIO-R, bottom 33%, n = 7). At sacrifice, joints were scored using a Modified Mankin Criteria. Blood and synovial fluid analytes, serum LPS, and fecal gut microbiota were analyzed.

RESULTS

DIO animals had greater Modified Mankin scores than chow animals (P = 0.002). There was a significant relationship (r = 0.604, p = 0.001) between body fat, but not body mass, and Modified Mankin score. Eighteen synovial fluid and four serum analytes were increased in DIO animals. DIO serum LPS levels were increased compared to chow (P = 0.031). Together, Lactobacillus species (spp.) and Methanobrevibacter spp. abundance had a strong predictive relationship with Modified Mankin Score (r(2) = 0.5, P < 0.001).

CONCLUSIONS

Increased OA in DIO animals is associated with greater body fat, not body mass. The link between gut microbiota and adiposity-derived inflammation and metabolic OA warrants further investigation.

Molecular biology and biomechanics of normal and healing ligaments--a review

OBJECTIVE

In this review article, we discuss current data and concepts concerning the molecular biology and biomechanics of both normal and healing ligaments in a rabbit model.

METHOD

Data is presented from light microscopy, transmission electron microscopy, molecular biology (RT-PCR), and biomechanical measurements (laxity, stress at failure, modulus, and static creep) or normal, pregnant and healing rabbit medial collateral ligaments.

RESULTS

'Flaws' in scar matrix, smaller-than-normal diameter collagen fibrils, and failure of collagen cross-link maturation may be particularly important deficiencies which appear to be related to ligament scar weakness and perhaps to scar creep. The mechanical behaviours of both normal and healing ligaments are altered by relative states of joint motion and normal ligaments are affected by systemic hormones (particularly during pregnancy).

DISCUSSION

Molecular analysis of ligaments and ligament scars, combined with ongoing morphological and biomechanical studies of ligament structure and function, will ultimately reveal which factors can be manipulated clinically to optimize the restoration of normal ligament properties after ligament injuries. Further studies on the mechanisms of ligament healing, genetic markers of repair, and gender-specific differences in ligament repair responses are required.

Lubricin/Proteoglycan 4 binds to and regulates the activity of Toll-Like Receptors In Vitro

Proteoglycan 4 (PRG4/lubricin) is secreted by cells that reside in articular cartilage and line the synovial joint. Lubricin may play a role in modulating inflammatory responses through interaction with CD44. This led us to examine if lubricin could be playing a larger role in the modulation of inflammation/immunity through interaction with Toll-like receptors (TLRs). Human Embryonic Kidney (HEK) cells overexpressing TLRs 2, 4 or 5 and surface plasmon resonance were employed to determine if full length recombinant human lubricin was able to bind to and activate TLRs. Primary human synovial fibroblasts were also examined using flow cytometry and Luminex multiplex ELISA. A rat destabilization model of osteoarthritis (OA) was used to determine if lubricin injections were able to regulate pain and/or inflammation in vivo. Lubricin can bind to and regulate the activity of TLRs, leading to downstream changes in inflammatory signalling independent of HA. We confirmed these findings in vivo through intra-articular injections of lubricin in a rat OA model where the inhibition of systemic inflammatory signaling and reduction in pain were observed. Lubricin plays an important role in regulating the inflammatory environment under both homeostatic and tissue injury states.

Decorin antisense gene therapy improves functional healing of early rabbit ligament scar with enhanced collagen fibrillogenesis in vivo

Injured ligaments heal with scar tissue, which has mechanical properties inferior to those of normal ligament, potentially resulting in re-injury, joint instability, and subsequent degenerative arthritis. In ligament scars, normal large-diameter collagen fibrils have been shown to be replaced by a homogenous population of small collagen fibrils. Because collagen is a major tensile load-bearing matrix element and because the proteoglycan decorin is known to inhibit collagen fibrillogenesis, we hypothesized that the restoration of larger collagen fibrils in a rabbit ligament scar, by down-regulating the proteoglycan decorin, would improve the mechanical properties of scar. In contrast to sense and injection-treated controls, in vivo treatment of injured ligament by antisense decorin oligodeoxynucleotides led to an increased development of larger collagen fibrils in early scar and a significant improvement in both scar failure strength (83-85% improvement at 6 weeks; p < 0.01) and scar creep elongation (33-48% less irrecoverable creep; p < 0.03) under loading. This is the first report that in vivo manipulation of collagen fibrillogenesis improves tissue function during repair processes with gene therapy. These findings not only suggest the potential use of this type of approach to improve the healing of various soft tissues (skin, ligament, tendon, and so on) but also support the use of such methods to better understand specific structure-function relationships in scars.

Influence of exogenous growth factors on the synthesis and secretion of collagen types I and III by explants of normal and healing rabbit ligaments

In this investigation it has been demonstrated that specific growth factors are able to modify collagen secretion in explants from healing rabbit medial collateral ligaments. The addition of 2.5 ng transforming growth factor beta 1 (TGF-beta 1)/mL to 3-week-old scar explants resulted in an increase in the total amount of collagen secreted. Analysis of collagen types I and III individually revealed that the increase mediated by TGF-beta 1 was due primarily to an increase in collagen type I secretion. This led to a ratio of type I:type III that is closer to that found in normal ligament tissue. The addition of 100 ng insulin-like growth factor 2 (IGF-2) to explant cultures of 3-week-old scar tissue also led to an increase in the quantity of collagen secreted, but the increase was in both type I and III collagens. These effects were observed to a lesser degree in 6-week-old scar tissue, and by 12 weeks postinjury, minimal effects of the growth factors on collagen synthesis was detected. Neither growth factor influenced collagen secretion by normal ligament or synovium. In contrast, IGF-1 (100 ng/mL) or basic fibroblast growth factor (bFGF) (10 ng/mL) did not exert a detectable effect on collagen secretion by any of the normal or healing tissues. These results indicate that TGF-beta 1 and IGF-2 can modify the metabolic activity of cells in explants of healing ligaments early after injury and may enhance the repair process leading to improved function.

Semiquantitative reverse transcription-polymerase chain reaction analysis of mRNA for growth factors and growth factor receptors from normal and healing rabbit medial collateral ligament tissue

Growth factors and their receptors play an essential role in the development, maturation, and response to injury of all tissues. A number of studies have explored the possibility of improving ligament healing with exogenous growth factors. However, limited data is available regarding the endogenous growth factor network in ligaments on which any exogenous growth factors must impact. The purpose of this study was to assess the endogenous growth factor network with molecular techniques. By the sensitive reverse transcription-polymerase chain reaction technique, transcripts for a number of growth factors and receptors were detected with RNA isolated from normal and healing rabbit medial collateral ligament tissues. These include transforming growth factor-beta1, insulin-like growth factors I and II, basic fibroblast growth factor, endothelin-1, and the receptors for insulin and insulin-like growth factor II. Semiquantitative reverse transcription-polymerase chain reaction analysis of RNA from normal and scar tissues from the medial collateral ligament revealed that the levels of several transcripts were elevated in the scar tissue. It was not possible to confirm biological activity because of the hypocellularity of the tissues; however, the results obtained indicate that the reverse transcription-polymerase chain reaction approach to defining the endogenous growth factor-receptor phenotype is feasible, and further definition should contribute to the development of rational approaches to exogenous therapy to improve healing.

Early changes in lapine menisci during osteoarthritis development: Part I: cellular and matrix alterations

OBJECTIVE

Osteoarthritis (OA) is the most common form of arthritis and patients with meniscal and ligament injuries of the knee are at high risk to develop the disease. The purpose of this study was to evaluate changes occurring in both medial and lateral menisci from the knees of anterior cruciate ligament (ACL) transected rabbits during the early stages of OA development.

DESIGN

Meniscal tissues from control and experimental rabbits were processed for histology and immunohistochemistry for assessment of matrix organization and composition.

RESULTS

At 3 and 8 weeks following ACL transection, histological examination demonstrated extensive extracellular matrix deterioration. Altered cell distribution, areas depleted of cells, and areas of cell clusters were found within the medial but not in the lateral meniscus. Immunohistochemistry of both medial and lateral menisci demonstrated significant changes in collagen distribution. Type I and III collagen staining was increased in both medial and lateral menisci. In contrast, type II collagen staining was overtly increased only in the medial meniscus.

CONCLUSION

These results demonstrate that after ACL transection, extracellular matrix deposition as well as altered matrix organization and altered cell distribution occur early in the medial meniscus.

Comparison of human serum with fetal bovine serum for expansion and differentiation of human synovial MSC: potential feasibility for clinical applications

The aim of this study was to evaluate the effect of human serum (HS) on growth and differentiation capacity of human synovium-derived mesenchymal stem cells (MSC) in comparison to cells grown in fetal bovine serum (FBS). Human MSCs were isolated from the synovium of knee joints of three donors and the cells were cultured individually in varying concentrations of allogenic HS or FBS. Bovine MSCs were isolated from synovium and cultured in the same manner. Cell proliferation was assessed by the tetrazolium assay after passage 3. The capacity for chondrogenic and osteogenic differentiation was investigated in specific media followed by 1,9-dimethylmethylene blue assay and alcian blue staining, or by alizarin red staining, respectively. Human MSCs proliferated significantly more rapidly in the presence of HS than with equivalent levels of FBS. Chondrogenic or osteogenic differentiation occurred to nearly identical levels in HS or FBS. The results of this study indicate that HS is superior for the culture of human MSCs compared with FBS in terms of cellular expandability, without losing chondrogenic or osteogenic differentiation capacity. Coupled with the advantage in eliminating the potential risk accompanied with the use of xeno-derived materials, pooled, well-characterized HS could be a useful reagent to promote cellular expansion for clinical synovial stem cell-based therapy.

Isolation and partial characterization of apiogalacturonans from the cell wall of Lemna minor

1. A mild, reproducible extraction procedure, using 0.5% ammonium oxalate, was developed for the isolation of polysaccharides containing d-apiose from the cell wall of Lemna minor. On a dry-weight basis the polysaccharide fractions extracted with ammonium oxalate made up 14% of the material designated cell walls and contained 20% of the d-apiose originally present in the cell walls. The cell walls, as isolated, contained 83% of the d-apiose present in L. minor. 2. After extraction with ammonium oxalate, purified polysaccharides were obtained by DEAE-Sephadex column chromatography and by fractional precipitation with sodium chloride. With these procedures the material extracted at 22 degrees C could be separated into at least five polysaccharides. On a dry-weight basis two of these polysaccharides made up more than 50% of the material extracted at 22 degrees C. There was a direct relationship between the d-apiose content of the polysaccharides and their solubility in sodium chloride solutions; those of highest d-apiose content were most soluble. 3. All the polysaccharides isolated appeared to be of one general type, namely galacturonans to which were attached side chains containing d-apiose. The d-apiose content of the apiogalacturonans varied from 7.9 to 38.1%. The content of esterified d-galacturonic acid residues in all apiogalacturonans was low, being in the range 1.0-3.5%. Hydrolysis of a representative apiogalacturonan with dilute acid resulted in the complete removal of the d-apiose with little or no degradation of the galacturonan portion. 4. Treatment of polysaccharide fractions with pectinase established that those of high d-apiose content and soluble in m-sodium chloride were not degraded, whereas those of low d-apiose content and insoluble in m-sodium chloride were extensively degraded. When the d-apiose was removed from a typical pectinase-resistant polysaccharide, the remainder of the polysaccharide was readily degraded by this enzyme. 5. Periodate oxidation of representative polysaccharide fractions and apiogalacturonans and determination of the formaldehyde released showed that about 50% of the d-apiose molecules were substituted at either the 3- or the 3'-position.

Molecular and cell biology of skin wound healing in a pig model

To define the pattern of change at the molecular and cellular levels during the healing of excisional skin wounds in the skeletally immature pig, mRNA levels for relevant molecules were assessed by semiquantitative RT-PCR using porcine specific primer sets and RNA isolated from normal skin and samples at various time post-wounding. Analysis of cellular change was assessed by DNA quantification and histology of tissue sections. The results demonstrated that the changes in the pattern of RNA and DNA content of the scar tissue were consistent with the observed increasing cellularity. The mRNA levels for collagen I, III, HSP47, IL-1, TGF-beta, MMP-1, -2 and -9, TIMP-1, -2, and-4, PAI-1, versican were significantly elevated during healing; levels for biglycan and fibromodulin were not significantly altered; and the mRNA levels for TIMP-3 were depressed. These findings suggest that skin wound healing is a series of complex matrix-cell interactions that involve cellular migration and inflammation, followed by proliferation of fibroblasts with new collagen synthesis, and lastly tissue remodeling of the scar.

Identification of sex hormone receptors in human and rabbit ligaments of the knee by reverse transcription-polymerase chain reaction: evidence that receptors are present in tissue from both male and female subjects

Gender-related factors have been attributed to observed differences in the rate of injury to ligaments (e.g., anterior cruciate ligament) between male and female subjects. These differences may be a result of unique regulatory mechanisms within the tissue in response to the sex hormones estrogen and progesterone. These hormones, when bound to specific intracellular receptors (estrogen receptor and progesterone receptor, respectively), modulate gene expression within hormone-responsive tissue. The purpose of this study was to evaluate the expression of the estrogen and progesterone receptors in ligament tissue from male and female rabbits and humans by the sensitive molecular technique of reverse transcription-polymerase chain reaction. Total RNA was extracted from human anterior cruciate ligament tissue and from medial cruciate ligament, anterior cruciate ligament, patellar tendon, and synovium tissue of the New Zealand White rabbit by the newly developed TRIspin method. The total RNA was reverse transcribed and analyzed by polymerase chain reaction to assess the expression of estrogen and progesterone receptors. Our results demonstrate that estrogen and progesterone receptor transcripts are expressed in ligament tissue of male and female rabbits and humans and that alterations in receptor expression occur in ligaments during pregnancy. In the human samples, only a small percentage of the estrogen receptor appeared to be a nonfunctional mRNA splice variant, and the predominant form contained the estrogen-binding domain.

Altered levels of extracellular matrix molecule mRNA in healing rabbit ligaments

RT-PCR methods were used to amplify, semi-quantify, clone and sequence cDNA fragments specific for rabbit extracellular matrix molecules biglycan, collagen I, collagen III, decorin, lumican, versican, fibromodulin, and also glyceraldehyde-3-phosphate dehydrogenase (G3PDH), using RNA isolated from rabbit ligaments. Sequence analysis of two independent clones of PCR products was used to verify the identity of the cDNA. Semi-quantitative RT-PCR was used to study mRNA levels for these matrix molecules in normal and healing rabbit ligament at three, six, and fourteen weeks post-injury. The yield of RNA from the ligament scar was increased at three and six weeks post-injury, but it had returned to near normal levels by fourteen weeks. On a microgram RNA basis, it was demonstrated that biglycan, collagen I, collagen III and lumican mRNA levels are significantly elevated, versican mRNA levels significantly depressed, and decorin and fibromodulin mRNA levels showed no significant change in response to tissue injury in the ligament during the course of healing. These findings suggest that differential regulation of mRNA levels for these extracellular matrix molecules occurs during ligament healing.

Requirements for prolonged suppression of an idiotypic specificity in adult mice

The appearance of an idiotypic specificity, present in anti-p-azophenylarsonate (anti-Ar) antibodies of all immunized A/J mice, ran be suppressed in adult mice by prior administration of an IgG fraction of rabbit antiidiotypic (anti-D) antiserum; anti-Ar antibodies arise but are of different idiotype. Prolonged suppression was observed in earlier experiments, but antigen was first administered to adult mice only 2 wk or 9 wk after anti-D antibodies; subsequent escape from idiotypic suppression could have been masked by the capture of antigen by large numbers of memory cells having receptors of a different idiotype. In the present experiments antigen was first administered at intervals up to 22 wk after the antiidiotypic antibody. Suppression was maintained for 6 wk in all mice and for 5 mo in about half the mice tested. It thus appears that suppression of idiotype is less reversible if antigen is administered soon after the antiidiotypic antibody. The data suggest that escape from suppression is attributable to the generation of new precursor cells rather than to reactivation of suppressed cells. The minimum dosage of antiidiotypic IgG required for effective suppression was about 2 mg. The subcutaneous or intraperitoneal routes of inoculation of antiidiotypic IgG were equally effective. When antiidiotypic antibody was administered 3 days after antigen no suppressive effects were observed. There was partial suppression when antiidiotypic antibody was injected on the same day as the antigen. Fab' and F(ab')(2) fragments of antiidiotypic IgG had no suppressive effect. Quantitative measurements revealed no significant differences among control and suppressed mice with respect to total concentration of precipitable anti-Ar antibodies produced.

Postmortem stability of total RNA isolated from rabbit ligament, tendon and cartilage

The stability of RNA, particularly mRNA, in tissues is under complex regulation. Most studies to date have focused on very cellular tissues and not connective tissues such as ligaments, tendons and cartilage. As the availability of such tissues for transplantation or research purposes is frequently delayed following death, it is important to determine whether RNA stability in such tissues is influenced by time postmortem. To approach this question, skeletally mature NZW rabbits were used to investigate RNA integrity over time in dense, hypocellular connective tissues and in several hypercellular organ tissues such as brain, kidney, liver and lung. Samples were analyzed at varying intervals postmortem with respect to rRNA integrity by agarose gel electrophoresis and ethidium bromide staining and mRNA integrity by Northern blot analysis and RT-PCR. No degradation of rRNA or loss in integrity of mRNA for genes of low and high copy number was observed up to 96 h postmortem. These findings confirm that it is likely appropriate to use properly stored postmortem dense connective tissues for molecular biological investigations.

Early changes in lapine menisci during osteoarthritis development: Part II: molecular alterations

OBJECTIVE

Osteoarthritis (OA) is the most common form of arthritis and patients with meniscal and ligament injuries of the knee are at high risk to develop the disease. The purpose of this study was to evaluate changes occurring in both medial and lateral menisci from the knees of anterior cruciate ligament (ACL) transected rabbits at 3 and 8 weeks post-surgery. This study describes both molecular and cellular alterations in menisci during the early stages of OA development.

DESIGN

Rabbit meniscal tissues were processed for molecular analysis: DNA and RNA concentrations were assessed, as well as semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) analysis for a subset of relevant molecules was performed. In situ DNA fragmentation was evaluated using the TUNEL assay.

RESULTS

Total RNA yields from the medial meniscus were significantly elevated at both 3 and 8 weeks post-ACL transection, while in the lateral meniscus total RNA levels were unchanged following ACL transection. DNA concentrations were significantly decreased in the medial menisci only at 8 weeks post-ACL transection. Following ACL transection, analysis of in situ DNA fragmentation using the TUNEL assay demonstrated an increase in the number of apoptotic cells in the medial meniscus only, in particular at 3 weeks post-ACL transection, a finding which correlates with declines in DNA content. Analysis of specific mRNA levels by RT-PCR demonstrated complex changes in both menisci following ACL transection. At 3 and 8 weeks post-ACL transection, in both medial and lateral menisci, mRNA levels for type I collagen and TIMP-1 were significantly increased, while mRNA levels for decorin, TNF-alpha and IGF-2 were significantly depressed. In the medial meniscus, significant increases in mRNA levels for type II collagen, biglycan as well as iNOS and PAI-1 were detected at both time periods, while mRNA levels for aggrecan, type III collagen and COX-2 were significantly elevated at 3 weeks post-ACL transection and mRNA levels for MMP-1 were significantly elevated at 8 weeks post-ACL transection. In contrast, mRNA levels for COL2 and aggrecan were unchanged in the lateral meniscus following ACL transection. In the lateral meniscus, at 3 weeks post-ACL transection, type III collagen mRNA levels were dramatically increased while fibromodulin mRNA levels were significantly depressed. In the lateral meniscus, significant increases in mRNA levels for biglycan were detected at 8 weeks post-ACL transection.

CONCLUSION

These results show that after ACL transection complex molecular changes, as well as apoptosis, occur early, particularly in the medial meniscus.

Matrix metalloproteinase-13 expression in rabbit knee joint connective tissues: influence of maturation and response to injury

The hypothesis of the present work was that expression of matrix metalloproteinase-13 (MMP-13, collagenase-3) would be induced during conditions involving important matrix remodeling such as ligament maturation, scar healing and joint instability. Therefore, MMP-13 expression in the medial collateral ligament (MCL) during the variable situations of tissue maturation and healing was assessed. MMP-13 expression in three intra-articular connective tissues of the knee (i.e. articular cartilage, menisci and synovium) following the transection of the anterior cruciate ligament of the knee was evaluated at 3 and 8 weeks post-injury. MMP-13 mRNA (semi-quantitative RT-PCR) and protein (immunohistochemistry and Western blotting) were detected in all of the tissues studied. Significantly higher MCL mRNA levels for MMP-13 were detected during the early phases of tissue maturation (i.e. 29 days in utero and 2-month-old rabbits) compared to later phases (5- and 12-month-old rabbits). This pattern of expression was recapitulated following MCL injury, with very high levels of expression in scar tissue at 3 weeks post-injury and then a decline to levels not significantly different from control values by 14 weeks. Elevated mRNA levels correlated with increased protein levels for MMP-13 in both menisci and synovium following the transection of the anterior cruciate ligament and during medial collateral ligament healing. These results indicate that MMP-13 expression is regulated by a number of variables and that high levels of expression occur in situations when connective tissue remodeling is very active.

Response of rabbit Achilles tendon to chronic repetitive loading

The objective of this work was to assess the response of tendon to chronic repetitive loading. Controlled muscle stimulation was used to load the rabbit Achilles tendon at a frequency of 1.25 Hz for two hours per day, three days per week for a period of 11 weeks. Average peak tendon force was 26 N during the protocol. The loading protocol did not modify the gross morphology of the tissue, nor its water content or cellularity. Increases in mRNA expression of collagen Type III and MMPs were observed, but no signs of injury were detected by histologic examination of tendon and paratenon structures. The lack of a detectable injury response suggests that the tendons were not loaded beyond their capacity for repair. Factors additional to mechanical loading such as aging, illness or stress may be necessary to produce pathology.

Formation and phenotype of cell clusters in osteoarthritic meniscus

OBJECTIVE

To determine the histologic changes that accompany the formation of cell clusters during the early stages of osteoarthritis development in the meniscus, and to characterize the expression phenotype of these cells.

METHODS

Histologic sections of medial menisci from normal and anterior cruciate ligament (ACL)-deficient rabbit knees were immunolabeled with monoclonal antibodies for vimentin to highlight the cytoskeleton of meniscal cells, Ki-67 to identify proliferating cells, and type X collagen to evaluate changes in the cell expression phenotype. Tissue mineralization was assessed by specific staining with alizarin red.

RESULTS

Following ACL transection, there was an alteration in the normal interconnected network of meniscal cells in the fibrocartilaginous region of the tissue. This led to isolation of islands of cells within the extracellular matrix of the meniscal tissue. These islands of cells displayed 3 different morphologies based on cell composition: 1) stellate cells, 2) stellate as well as round cells, and 3) round cells. Islands composed solely of round cells were more prominent in the latter stages following ACL transection, and the size of these islands increased with time, apparently as the result of cell proliferation. These islands of cells corresponded to the "clusters" previously described in osteoarthritic cartilage. Strong expression of type X collagen colocalized with the deposition of calcium within the meniscal regions enriched with cell clusters.

CONCLUSION

Based on the observed changes in cell distribution, morphology, and cell proliferation as well as the previous detection of apoptosis in similar studies of rabbit knee joints, we propose a model for the development of cell clusters in the osteoarthritic meniscus. The morphologic appearance as well as the type X collagen expression phenotype of the meniscal cells forming the clusters is similar to that of hypertrophic chondrocytes. These findings provide a basis for understanding the origin of cell clusters in other joint connective tissues, such as osteoarthritic cartilage.

Increased mast cell numbers in human patellar tendinosis: correlation with symptom duration and vascular hyperplasia

OBJECTIVES

The cellular basis of painful tendon overuse pathology (tendinosis) is poorly understood. It has been suggested that because of the close anatomical associations between mast cells and vessels in connective tissues, mast cells may mediate the development of tendon hypervascularity or oedema.

OBJECTIVES

To examine the distribution of mast cells in men and women with patellar tendinopathy.

DESIGN

Case-control study.

METHODS

Tendinopathic tissue was collected at open debridement of the patellar tendon and a control tendon from patients undergoing intramedullary nailing of the tibia. The tendon was assessed immunohistochemically by evaluating the distribution of mast cells (AA1), and markers for T lymphocytes (CD3) and macrophages (CD68). The vessel-area fraction was quantified using computer-assisted digital image analysis.

RESULTS

The prevalence of mast cells per mm(2) (mean 3.3 (SD 3.0)) was greater in tendinosis tissue than in controls (1.1 (1.5); p = 0.036). In patients with tendinosis, mast cell density was moderately correlated with the vessel-area fraction (r(2) = 0.49) and with symptom duration (r(2) = 0.52).

CONCLUSION

Mast-cell prevalence in patellar tendinopathy was increased and was predominantly associated with vascular hyperplasia, particularly in patients with longstanding symptoms. Future research should investigate whether mast cells play direct or indirect modulatory roles in the development and progression of human tendinosis.

Gene intervention in ligament and tendon: current status, challenges, future directions

Ligament and tendon injuries are common clinical problems. Healing of these tissues occurs, but their properties do not return to normal. This predisposes to recurrent injuries, instability and arthritis, loss of motion and weakness. Gene therapy offers a novel approach to the repair of ligaments and tendons. Introduction of genes into ligaments and tendons using vectors has been successful. Marker genes and therapeutic genes have been introduced into both tissues with evidence of corresponding functional alterations. In addition, gene transfer has been used to manipulate the healing environment, opening the possibility of gene transfer to investigate ligament and tendon development and homeostasis, in addition to using this technology therapeutically. Several factors modulate the 'success' of gene transfer in these tissues.

A comparison of in vivo gene delivery methods for antisense therapy in ligament healing

To determine the most efficient in vivo delivery method of oligonucleotides for antisense therapy in ligament healing, fluorescence-labelled phosphorothioate oligodeoxynuleotides (ODN) were introduced into 12 rabbit ligament scars 2 weeks after injury using haemagglutinating virus of Japan (Sendai virus: HVJ)-conjugated liposomes. We compared the efficiency of cellular uptake of fluorescence as a percentage of all cells in each scar using three delivery procedures: (1) direct free-hand injection into the ligament scar using a conventional syringe; (2) systematic direct sca injection using a repeating 10 microliters dispenser and a square mesh grid system; and (3) injection into the feeding (femoral) artery. Results showed that there was a significant difference in fluorescence uptake by scar cells on day 1 after injection between the three delivery methods: (1) direct free-hand, 9.7 +/- 7.6% (average +/- s.d.); (2) systematic direct, 58.4 +/- 15.9%; and (3) intra-arterial, 0.2 +/- 0.1%. Systematic direct injection was most efficient and it resulted in 25.9 +/- 13.0% of scar cells being labeled at 7 days after transfection. We then introduced antisense ODN for the rabbit proteoglycan, decorin, into ligament scars with this delivery method and confirmed a significant inhibition of decorin mRNA expression in antisense-treated scar tissues in vivo both at 2 days (42.3 +/- 14.7% of sense control +/- s.d.; P < 0.0025) and 3 weeks (60.5 +/- 28.2% of sense control +/- s.d.; P < 0.024) after treatment, compared with sense ODN-treated scars. Decorin was significantly suppressed also at protein level in antisense-treated scars at 4 weeks (66.6 +/- 35.7% of sense control +/- s.d.; P < 0.045) after treatment. These results demonstrate that in vivo transfection efficiency in ligament scars is 'delivery system dependent' and that introduction of antisense ODN for the small proteoglycan, decorin, with this delivery method can lead to significant suppression of its expression over 3 weeks both at mRNA and protein levels. Thus, an effective model for the potential manipulation of scar composition and quality in ligament healing has been established.

Comparison of mRNA levels for matrix molecules in normal and disrupted human anterior cruciate ligaments using reverse transcription-polymerase chain reaction

Midsubstance samples of anterior cruciate ligaments from seven normal human cadaver knees (16-50 years old) were harvested and compared with midsubstance pieces of scarred anterior cruciate ligaments from 30 patients (15-40 years old). RNA was isolated from each ligament, and the expression of type-I collagen, type-III collagen, biglycan, decorin, lumican, and tissue inhibitor of metalloproteinase-1 was evaluated by quantitative reverse transcription-polymerase chain reaction with use of beta-actin as the housekeeping gene. Data for injured ligaments were further compared statistically as a function of time after injury to better define patterns of cellular expression over time. Our hypothesis was that injured ligaments would show minimal cellular activity and decreasing activity over time. The results revealed that both normal and injured anterior cruciate ligaments contain cells that express mRNA for all molecules studied. However, cells in injured ligaments express much higher, but still proportional, quantities of message for type-I collagen and type-III collagen (p < 0.000001) and higher quantities of biglycan (p < 0.02) and tissue inhibitor of metalloproteinase-1 (p < 0.0003) than do cells in normal anterior cruciate ligaments. These levels remained elevated for longer than 1 year after injury. Linear regression analysis showed biglycan expression correlated with time from injury (r2 = -0.69; p = 0.007). These results collectively demonstrate that injured human anterior cruciate ligaments contain cells that express scar-like molecules and that the injured ligaments are likely continuing to remodel matrix over time. Furthermore, they suggest that human anterior cruciate ligaments have not failed to heal due to the failure of scar formation per se. The quality and quantity of this scar remain questionable; however, the possibility of its enhancement as a healing strategy for human anterior cruciate ligaments cannot be dismissed.