Hox11 expression characterizes developing zeugopod synovial joints and is coupled to postnatal articular cartilage morphogenesis into functional zones in mice.

Previous studies on mouse embryo limbs have established that interzone mesenchymal progenitor cells emerging at each prescribed joint site give rise to joint tissues over fetal time. These incipient tissues undergo structural maturation and morphogenesis postnatally, but underlying mechanisms of regulation remain unknown. Hox11 genes dictate overall zeugopod musculoskeletal patterning and skeletal element identities during development. Here we asked where these master regulators are expressed in developing limb joints and whether they are maintained during postnatal zeugopod joint morphogenesis. We found that Hoxa11 was predominantly expressed and restricted to incipient wrist and ankle joints in E13.5 mouse embryos, and became apparent in medial and central regions of knees by E14.5, though remaining continuously dormant in elbow joints. Closer examination revealed that Hoxa11 initially characterized interzone and neighboring cells and was then restricted to nascent articular cartilage, intra joint ligaments and structures such as meniscal horns over prenatal time. Postnatally, articular cartilage progresses from a nondescript cell-rich, matrix-poor tissue to a highly structured, thick, zonal and mechanically competent tissue with chondrocyte columns over time, most evident at sites such as the tibial plateau. Indeed, Hox11 expression (primarily Hoxa11) was intimately coupled to such morphogenetic processes and, in particular, to the topographical rearrangement of chondrocytes into columns within the intermediate and deep zones of tibial plateau that normally endures maximal mechanical loads. Revealingly, these expression patterns were maintained even at 6 months of age. In sum, our data indicate that Hox11 genes remain engaged well beyond embryonic synovial joint patterning and are specifically tied to postnatal articular cartilage morphogenesis into a zonal and resilient tissue. The data demonstrate that Hox11 genes characterize adult, terminally differentiated, articular chondrocytes and maintain region-specificity established in the embryo.

Development of synovial membrane in the temporomandibular joint of the human fetus.

The development of the synovial membrane was analyzed in serial sections of 21 temporomandibular joints of human fetuses at 9 to 13 weeks of gestation. Sections of two fetuses at 12 weeks of development were used to perform immunohistochemical expression of the markers CD68 and Hsp27 on the synovial lining. Macrophage-like type A and fibroblast-like type B cells, which express CD68 and Hsp27, respectively, were observed at the twelfth week of development. Our results suggest that the development of the synovial membrane is related to the vascularization of the joint and the formation of the articular cavities.

Cell-based articular cartilage repair: the link between development and regeneration.

Clinical efforts to repair damaged articular cartilage (AC) currently face major obstacles due to limited intrinsic repair capacity of the tissue and unsuccessful biological interventions. This highlights a need for better therapeutic strategies. This review summarizes the recent advances in the field of cell-based AC repair. In both animals and humans, AC defects that penetrate into the subchondral bone marrow are mainly filled with fibrocartilaginous tissue through the differentiation of bone marrow mesenchymal stem cells (MSCs), followed by degeneration of repaired cartilage and osteoarthritis (OA). Cell therapy and tissue engineering techniques using culture-expanded chondrocytes, bone marrow MSCs, or pluripotent stem cells with chondroinductive growth factors may generate cartilaginous tissue in AC defects but do not form hyaline cartilage-based articular surface because repair cells often lose chondrogenic activity or result in chondrocyte hypertrophy. The new evidence that AC and synovium develop from the same pool of precursors with similar gene profiles and that synovium-derived chondrocytes have stable chondrogenic activity has promoted use of synovium as a new cell source for AC repair. The recent finding that NFAT1 and NFAT2 transcription factors (TFs) inhibit chondrocyte hypertrophy and maintain metabolic balance in AC is a significant advance in the field of AC repair. The use of synovial MSCs and discovery of upstream transcriptional regulators that help maintain the AC phenotype have opened new avenues to improve the outcome of AC regeneration.

'The Sneaky Plica' revisited: morphology, pathophysiology and treatment of synovial plicae of the knee.

PURPOSE: To comprise current knowledge on morphology, embryology and pathophysiology of synovial plicae as well as on clinical and therapeutic aspects of the plica syndrome. METHODS: Review of the literature combined with a meta-analysis of studies assessing the outcome of open or arthroscopic plica excision including the author's own series. RESULTS: The term synovial plica has been devised to describe a number of intra-capsular folds thought to represent remnants of a membranous knee joint partition present during foetal development. Although four such folds have been defined, it is mainly the medial patellar plica which is implicated in carrying clinical significance as a potential cause of anteromedial knee pain particularly in adolescents. Blunt trauma, a sudden increase in athletic activity or any form of transient synovitis are associated with plica inflammation leading to tissue fibrosis and subsequent loss of elasticity. A plica affected in this way may impinge against intra-articular structures in its proximity, often creating localised chondromalacia particularly of the patello-femoral joint. The diagnosis is based on history and clinical examination although MRI can be of value. Twenty-three studies assessing the clinical out-come of 969 patients following open or arthroscopic plica excision were identified. The average age was 25 years with equal male-to-female ratio. Trauma was considered the cause in 57 %. At a mean follow-up of 27.5 months, 64 % of patients were symptom free, 26 % improved and 10 % considered failures. CONCLUSION: Symptomatic plicae may initially be treated with physiotherapeutic measures and structured exercise regimes but success rates are generally low. Intra-plical or intra-articular corticosteroid injections may be beneficial if administered early in the disease process. Arthroscopic excision of the entire plical fold becomes indicated in recalcitrant cases and once a plica has undergone irrevocable morphological changes. The procedure carries low morbidity, and results are universally good especially if the plica is the sole pathology. Factors associated with a favourable outcome are young patient age, localised symptoms of short duration and absence of plica induced chondromalacia.

Gene signature of the embryonic meniscus.

The meniscus is a fibrocartilagenous disc in the knee that protects the joint from damage. Meniscal injuries are common, however repair efforts are largely unsuccessful and are not able to prevent the degenerative changes that result in development of osteoarthritis. Tissue regeneration in adults often recapitulates events of embryonic development, suggesting the regulatory pathways controlling morphogenesis are candidate repair signals. Here we use laser capture microdissection to collect mouse embryonic day 16 (E16) meniscus, articular cartilage, and cruciate ligaments. RNA isolated from these tissues was then used to perform genome-wide microarray analysis. We found 38 genes were differentially expressed between E16 meniscus and articular cartilage and 43 genes were differentially expressed between E16 meniscus and cruciate ligaments. Included in our data set were extracellular matrix proteins, transcription factors, and growth factors, including TGF-ß modulators (Lox, Dpt) and IGF-1 pathway members (Igf-1, Igfbp2, Igfbp3, Igfbp5). Ingenuity Pathway Analysis revealed that IGF-1 signaling was enriched in the meniscus compared to the other joint structures, while qPCR showed that Igf-1, Igfbp2, and Igfbp3 expression declined with age. We also found that several meniscus-enriched genes were expressed either in the inner or outer meniscus, establishing that regionalization of the meniscus occurs early in development.

Dact gene expression profiles suggest a role for this gene family in integrating Wnt and TGF-ß signaling pathways during chicken limb development.

BACKGROUND: Dact gene family encodes multifunctional proteins that are important modulators of Wnt and TGF-ß signaling pathways. Given that these pathways coordinate multiple steps of limb development, we investigated the expression pattern of the two chicken Dact genes (Dact1 and Dact2) from early limb bud up to stages when several tissues are differentiating. RESULTS: During early limb development (HH24-HH30) Dact1 and Dact2 were mainly expressed in the cartilaginous rudiments of the appendicular skeleton and perichondrium, presenting expression profiles related, but distinct. At later stages of development (HH31-HH35), the main sites of Dact1 and Dact2 expression were the developing synovial joints. In this context, Dact1 expression was shown to co-localize with regions enriched in the nuclear ß-catenin protein, such as developing joint capsule and interzone. In contrast, Dact2 expression was restricted to the interzone surrounding the domains of bmpR-1b expression, a TGF-ß receptor with crucial roles during digit morphogenesis. Additional sites of Dact expression were the developing tendons and digit blastemas. CONCLUSIONS: Our data indicate that Dact genes are good candidates to modulate and, possibly, integrate Wnt and TGF-ß signaling during limb development, bringing new and interesting perspectives about the roles of Dact molecules in limb birth defects and human diseases.

Formation of synovial joints and articular cartilage.

Chondrocytes differentiate from mesenchymal progenitors and produce templates(anlagen) for the developing bones. Chondrocyte differentiation is controlled by Sox transcription factors. Templates for the neighbour bones are subsequently separated by conversion of differentiated chondrocytes into non-chondrogenic cells and emergence of interzone in which joints cavitation occurs. A central role in initiating synovial joint formation plays Wnt-14/beta-catenin signalling pathway.Moreover, bone morphogenetic proteins and growth and differentiation factors are expressed at the site of joint formation. Joint cavitation is associated with increased hyaluronic acid synthesis. Hyaluronic acid facilitates tissue separation and creation of a functional joint cavity. According to the traditional view articular cartilage represents part of cartilage anlage that is not replaced by bone through endochondral ossification. Recent studies indicate, however, that peri-joint mesenchymal cells take part in interzone formation and that these interzone cells subsequently differentiate into articular chondrocytes and synovial cells. Thus,anlage chondrocytes have a transient character and disappear after cessation of growth plate function while articular chondrocytes have stable and permanent phenotype and function throughout life.

Morphophysiopathology of synovial plica from knee joint: a literature review

Synovial plicae around the knees are a relatively common occurrence. They have been the object of many clinical and anatomical researches, not only because of their intra-articular existence, but also for their painful symptomatology caused on knee joint. These plicae are excessive folds of synovial membrane and are remnants from embryonic septum, which were not properly absorbed during fetal development. These synovial plicae are divided anatomically, as location and existence, and are classified into suprapatellar, infrapatellar, medial patellar and lateral patellar plicae; being still each of these subdivided according to their appearance and juxtaposition. Material and methods: A retrospective literature review selected articles in PubMed and MEDLINE databases; papers were searched using the keywords: synovial plicae, knee, embryology, anatomy, histology and treatment. Results: In this literature review was verified the incidence about the types, shape, location, symptoms, pathophysiology, and the main methods of study for the verification of synovial plica and treatments. Conclusion: In summary, asymptomatic plica can become symptomatic due to a bucket‑handle tear following a twisting injury and lateral traction to the knee, when carefully diagnosed; a synovial plica represents a potential cause of pain in patients. After careful examination, arthroscopic resection of the bucket‑handle portion of the plica is sufficient for the improvement of the symptoms if conservative treatment of pathological plica fail.

Versican knockdown reduces interzone area during early stages of chick synovial joint development.

Much has been learned regarding factors that specify joint placement, but less is known regarding how these molecular instructions are translated into functional joint tissues. Previous studies have shown that the matrix chondroitin sulfate proteoglycan, versican, exhibits a similar pattern of expression in the embryonic joint rudiment of chick and mouse suggesting conserved function during joint development. In this study, versican's importance in developing joints was investigated by specific inhibition of its expression in the early joint interzone, tissue that gives rise to articular cartilages and joint cavity. In ovo microinjection of adenoviral shRNA constructs into the HH25 chick wing was employed to silence endogenous versican protein in developing appendicular joints. Results showed statistically significant (12-14%) reduction of nonchondrogenic elbow joint interzone area in whole-mount specimens at HH36 in response to versican knockdown. Attenuated expression of key versican-associated molecules including hyaluronan, tenascin, CD44, and link protein was also noted by histochemical and immunohistochemical analysis. Versican knockdown also lowered collagen II expression in presumptive articular chondrocytes indicating possible delay in chondrogenesis. Results suggest that versican functions interactively with other matrix/cell surface molecules to facilitate establishment or maintenance of early joint interzone structure.

[Comparative characteristics of the biological properties of small ruminant lentiviruses].

The infections caused by small ruminant lentiviruses include diseases, such as Maedi-Visna (MV) and caprine arthritis-encephalitis (CAE). According to phylogenetic findings and their common origination, small ruminant lentiviruses were divided into Groups A, B, C, D, and E. Cultivation of the lentiviruses displayed the cytopathic effect of the CAE virus strain 75 G-63 in the primary culture of goatling synovial membrane cells, which was shown by monolayer destruction and polynuclear cell formation; this was uncharacteristic for M-88, K-796, and Tverskoy strains. A high homology was found for the Tverskoy strain with Group B small ruminant lentiviruses and the M-88 and K-796 strains with their Group A.

Synovial joint formation requires local Ext1 expression and heparan sulfate production in developing mouse embryo limbs and spine.

Heparan sulfate proteoglycans (HSPGs) regulate a number of major developmental processes, but their roles in synovial joint formation remain unknown. Here we created conditional mouse embryo mutants lacking Ext1 in developing joints by mating Ext1(f/f) and Gdf5-Cre mice. Ext1 encodes a subunit of the Ext1/Ext2 Golgi-associated protein complex responsible for heparan sulfate (HS) synthesis. The proximal limb joints did form in the Gdf5-Cre;Ext1(f/f) mutants, but contained an uneven articulating superficial zone that expressed very low lubricin levels. The underlying cartilaginous epiphysis was deranged as well and displayed random patterns of cell proliferation and matrillin-1 and collagen IIA expression, indicative of an aberrant phenotypic definition of the epiphysis itself. Digit joints were even more affected, lacked a distinct mesenchymal interzone and were often fused likely as a result of local abnormal BMP and hedgehog activity and signaling. Interestingly, overall growth and lengthening of long bones were also delayed in the mutants. To test whether Ext1 function is needed for joint formation at other sites, we examined the spine. Indeed, entire intervertebral discs, normally composed by nucleus pulposus surrounded by the annulus fibrosus, were often missing in Gdf5-Cre;Ext1(f/f) mice. When disc remnants were present, they displayed aberrant organization and defective joint marker expression. Similar intervertebral joint defects and fusions occurred in Col2-Cre;ß-catenin(f/f) mutants. The study provides novel evidence that local Ext1 expression and HS production are needed to maintain the phenotype and function of joint-forming cells and coordinate local signaling by BMP, hedgehog and Wnt/ß-catenin pathways. The data indicate also that defects in joint formation reverberate on, and delay, overall long bone growth.

The morphological features of the mediopatellar and lateral folds of the developing knee joint: a fetus cadaveric study.

OBJECTIVES: The aim of the study was to evaluate the morphological features of the mediopatellar and lateral folds in fetal knees in the absence of any exposure to certain stress factors such as exercise or trauma. METHODS: The study was performed in the knee joints of 15 fetuses (6 males, 9 females) obtained as spontaneous abortion material at 20-34 weeks of gestation. The mediopatellar and lateral folds of the fetuses were classified into eight subgroups according to the following morphological features: A- Absence of folds; B- Short vertical band; C- Long vertical band; D- Narrow horizontal band; E- Broad horizontal band; F- Horizontal band accompanied by a vertical band; G- Horizontal band without a vertical band; H- Fenestrated band. RESULTS: The synovial membrane, covering the infrapatellar fat pad and forming the alar folds, extended upwards and formed the medial and lateral horizontal folds that covered the inferior part of the posterior aspect of the patella. These horizontal folds were thicker in the lower parts (close to their insertions) and became thinner towards the free ends. The horizontal band of the mediopatellar fold was observed in all cases, with an accompanying vertical band in 76.7% of the cases. A horizontally located lateral fold was absent in both knees of one fetus. The frequency of a horizontally located lateral fold was 93.3% and a vertical fold was accompanying in only 28.6% of these cases. It is of note that the horizontal band of the mediopatellar fold observed in all specimens has never been defined in previous classifications. In 10% of the knees, the vertically located part of the mediopatellar fold presented as a large band extending upward and being squeezed between the articular surface of the patella and the medial condyle of the femur. The lateral fold was observed as a large band in 10% of the knees. Another observation was that the higher level the vertical band of the mediopatellar and lateral folds began, the wider the horizontal band was, occupying more place in the patellofemoral space. It was remarkable that the frequencies of the vertically located parts of the lateral and mediopatellar folds in fetuses were higher than those reported for the adults in the literature. CONCLUSION: Our findings suggest that the resorption process of the mesenchymal tissue, particularly in the lateral part, continues until adulthood and causes age-dependent alterations in the formation of intra-articular folds. The synovial folds occupy more space between the patella and femur in the early stages of life than seen in adults. This may be a more frequent cause of unexplained knee pain in children than expected.

Treatment of pathological synovial plicae of the knee.

OBJECTIVE: To analyze the incidence, clinical significance, and clinical manifestations of pathological synovial plicae of the knee. MATERIAL AND METHODS: Between 2002 and 2006, 63 patients with pathological synovial plicae of the knee were studied. Of those 63 patients, 21 had the diagnosis confirmed by previously performed magnetic resonance imaging. All of the patients initially underwent conservative treatment for 90 days that involved strengthening and improving the flexibility of the muscles surrounding the knee as well as modification of their sports activities. RESULTS: A total of 55 patients improved after conservative treatment. Six of these patients eventually experienced a recurrence of symptoms, but the symptoms were not incapacitating in any of these patients. The other eight patients underwent arthroscopic removal of the synovial plica. Of these eight patients, six returned to their pretreatment physical activities, and two had persistent symptoms during physical activity. CONCLUSION: The presence of a synovial plica of the knee should be considered as a potential diagnosis in patients with knee pain, especially those who practice sports inappropriately. Conservative treatment is effective in most cases, and surgical treatment should be reserved for exceptional cases that do not improve with conservative treatment.

Synovial plicae around the knee.

Synovial plicae around the knee are a relatively common occurrence but one that is rarely responsible for symptoms. The Plica syndrome has been well described but controversy still exists regarding its diagnosis and treatment. We have reviewed and studied the published literature both past and present in detail regarding synovial plicae around the knee to provide a comprehensive and up-to-date review on the subject. The aim is to outline previous significant research into the embryology and pathology of synovial plicae as well as providing a review of the current thinking on treatment options available for the different synovial plicae with reference to the evidence available.

Treatment of pathological synovial plicae of the knee

OBJECTIVE: To analyze the incidence, clinical significance, and clinical manifestations of pathological synovial plicae of the knee. MATERIAL AND METHODS: Between 2002 and 2006, 63 patients with pathological synovial plicae of the knee were studied. Of those 63 patients, 21 had the diagnosis confirmed by previously performed magnetic resonance imaging. All of the patients initially underwent conservative treatment for 90 days that involved strengthening and improving the flexibility of the muscles surrounding the knee as well as modification of their sports activities. RESULTS: A total of 55 patients improved after conservative treatment. Six of these patients eventually experienced a recurrence of symptoms, but the symptoms were not incapacitating in any of these patients. The other eight patients underwent arthroscopic removal of the synovial plica. Of these eight patients, six returned to their pretreatment physical activities, and two had persistent symptoms during physical activity. CONCLUSION: The presence of a synovial plica of the knee should be considered as a potential diagnosis in patients with knee pain, especially those who practice sports inappropriately. Conservative treatment is effective in most cases, and surgical treatment should be reserved for exceptional cases that do not improve with conservative treatment.

Contribution to morphological knowledge of the development of the human incudo-mallear joint.

CONCLUSION: At the time of birth, the incudo-mallear joint is completely developed. OBJECTIVE. To study the development of the incudo-mallear joint in human embryos and fetuses. MATERIALS AND METHODS. In all, 46 temporal bones with ages between 9 mm and newborns were studied. The preparations were cut in a series and dyed using Martins' trichrome technique. RESULTS. The incudo-mallear joint acquires the characteristics of a saddle joint at 10 weeks of development. The cartilage that covers the articular surfaces is formed by different strata that develop successively: the superficial stratum at 14 weeks, the transitional between 15 and 19 weeks, and the radial from 20 weeks. The subchondral bone develops between weeks 25 and 28 by the mechanisms of apposition and extension of the periosteal and endosteal bones, but it is not until week 30 that it completely covers the articular surfaces, consisting of bone fascicles whereby the lines of force will be transmitted. The articular capsule is formed as from the inter-zone. The surface zone develops the capsular ligament, and the internal surface develops the synovial membrane. Even though it is not consistent, the primordium of the meniscus is seen at 18 weeks.

Immunoexpression of constitutive and inducible cyclooxygenase isoforms in distinguishing and accessory structures of synovial joints in rat foetuses.

Joint formation is a developmental process regulated by various factors including bone morphogenetic proteins, transforming and growth factors, etc. Recently, a high expression of cyclooxygenase (COX) isoforms in the foetal cartilaginous elements was also revealed. On the other hand, various joint and skeletal abnormalities were seen in laboratory animal and human offspring, exposed in utero to several COX inhibitors. Immunoexpression of constitutive (COX-1) and inducible (COX-2) cyclooxygenase isoforms was evaluated in various articular structures of untreated and unfamiliar 21-day-old male rat foetuses. Both COX isoforms were detected in the articular cartilage and joint capsule, as well as in the intra-articular disc of the temporomandibular joint and meniscus of the knee joint. COX-1 immunostaining was revealed in the anterior and posterior cruciate ligament of the knee joint and the labrum of the hip and shoulder, whereas COX-2 immunoreactivity in those structures was not found. It could be concluded that both constitutive and inducible COX isoforms are physiologically expressed in various structures of synovial joints in rat foetuses at the end of prenatal development.

Tubulin polymerization-promoting protein family member 3, Tppp3, is a specific marker of the differentiating tendon sheath and synovial joints.

Tppp3, a member of the Tubulin polymerization-promoting protein family, is an intrinsically unstructured protein that induces tubulin polymerization. We show that Tppp3 is a distinct marker in the developing musculoskeletal system. In tendons, Tppp3 is expressed in cells at the circumference of the developing tendons, likely the progenitors of connective tissues that surround tendons: the tendon sheath, epitenon, and paratenon. These tissues form an elastic sleeve around tendons and provide lubrication to minimize friction between tendons and surrounding tissues. Tppp3 is the first molecular marker of the tendon sheath, opening the door for direct examination of these tissues. Tppp3 is also expressed in forming synovial joints. The onset of Tppp3 expression in joints coincides with cavitation, representing a molecular marker that can be used to indicate this stage in joint transition in joint differentiation. In late embryonic stages, Tppp3 expression highlights other demarcation lines that surround differentiating tissues in the forelimb.

JAWS coordinates chondrogenesis and synovial joint positioning.

Properly positioned synovial joints are crucial to coordinated skeletal movement. Despite their importance for skeletal development and function, the molecular mechanisms that underlie joint positioning are not well understood. We show that mice carrying an insertional mutation in a previously uncharacterized gene, which we have named Jaws (joints abnormal with splitting), die perinatally with striking skeletal defects, including ectopic interphalangeal joints. These ectopic joints develop along the longitudinal axis and persist at birth, suggesting that JAWS is uniquely required for the orientation and consequent positioning of interphalangeal joints within the endochondral skeleton. Jaws mutant mice also exhibit severe chondrodysplasia characterized by delayed and disorganized maturation of growth plate chondrocytes, together with impaired chondroitin sulfation and abnormal metabolism of the chondroitin sulfate proteoglycan aggrecan. Our findings identify JAWS as a key regulator of chondrogenesis and synovial joint positioning required for the restriction of joint formation to discrete stereotyped locations in the embryonic skeleton.