Keratan sulfate epitopes exhibit a conserved distribution during joint development that remains undisclosed on the basis of glycosaminoglycan charge density

Mechanical stress can regulate temporomandibular joint cavitation via signalling pathways

The temporomandibular joint (TMJ), composed of temporal fossa, mandibular condyle and a fibrocartilage disc with upper and lower cavities, is the biggest synovial joint and biomechanical hinge of the craniomaxillofacial musculoskeletal system. The initial events that give rise to TMJ cavities across diverse species are not fully understood. Most studies focus on the pivotal role of molecules such as Indian hedgehog (Ihh) and hyaluronic acid (HA) in TMJ cavitation. Although biologists have observed that mechanical stress plays an irreplaceable role in the development of biological tissues and organs, few studies have been concerned with how mechanical stress regulates TMJ cavitation. Based on the evidence from human or other animal embryos today, it is implicated that mechanical stress plays an essential role in TMJ cavitation. In this review, we discuss the relationship between mechanical stress and TMJ cavitation from evo-devo perspectives and review the clinical features and potential pathogenesis of TMJ dysplasia.

In Vitro Effects of Cetylated Fatty Acids Mixture from Celadrin on Chondrogenesis and Inflammation with Impact on Osteoarthritis

OBJECTIVE

Cetylated fatty acids are a group of naturally occurring fats of plant and/or animal origin. Cetyl myristoleate, in particular, was initially involved in osteoarthritis related research as its therapeutic administration prevented experimentally induced arthritis in Swiss Albino mice. In this context, the aim of our study was to investigate the possible mechanisms of Celadrin cetylated fatty acids action at the cellular level inflammation related pain relief and chondrogenesis.

DESIGN

For this, we tested the effects of the cetylated fatty acids mixture from Celadrin on an in vitro scaffold-free 3-dimensional mesenchymal stem cells culture model of chondrogenesis. Furthermore, we treated stimulated mouse macrophage cells with the cetylated fatty acids mixture to investigate the expression profile of secreted inflammatory cytokines.

RESULTS

The cetylated fatty acids mixture from Celadrin significantly decreased the production of IL-6, MCP-1, and TNF, key regulators of the inflammatory process, in stimulated RAW264.7 mouse macrophage cells. The treatment with cetylated fatty acids mixture initiated and propagated the process of chondrogenesis as demonstrated by the increased expression and deposition of chondrogenic markers by the differentiating mesenchymal cells.

CONCLUSION

The cetylated fatty acids mixture from Celadrin reduces inflammation in vitro by significantly decreasing the expression of IL-6, MCP-1, and TNF in stimulated RAW264.7 mouse macrophage cells. These compounds facilitate the chondrogenic differentiation process of human adipose-derived stem cells by stimulating the expression of chondrogenic markers under chondrogenic induction conditions.

Prevention of cartilage degeneration and gait asymmetry by lubricin tribosupplementation in the rat following anterior cruciate ligament transection

OBJECTIVE

To investigate whether cartilage degeneration is prevented or minimized in a rat model of anterior cruciate ligament (ACL) injury following a single dose-escalated intraarticular injection of lubricin derived from human synoviocytes in culture.

METHODS

Unilateral ACL transection (ACLT) of the right hind limb was performed in Lewis rats (n = 56). Control animals underwent a capsulotomy alone, leaving the ACL intact (n = 11). Intraarticular injections (50 μl/injection) of phosphate buffered saline (PBS; n = 14 rats) and human synoviocyte lubricin (1,600 μg/ml; n = 14 rats) were performed on day 7 postsurgery. Animals were killed on day 70 postsurgery. Histologic specimens were immunoprobed for lubricin and sulfated glycosaminoglycans. Urinary C-telopeptide of type II collagen (CTX-II) levels were measured on days 35 and 70 postsurgery. Hind limb maximum applied force was determined using a variable resistor walkway to monitor quadruped gait asymmetries.

RESULTS

Increased immunostaining for lubricin in the superficial zone and on the surface of cartilage was observed in lubricin-treated and control animals but not in PBS-treated or untreated animals with ACLT. On days 35 and 70 after surgery, urinary CTX-II levels in human synoviocyte lubricin-treated animals were lower than in untreated and PBS-treated animals (P < 0.005 and P < 0.001, respectively). Animals with ACLT treated with human synoviocyte lubricin and control animals distributed their weight equally between hind limbs compared to PBS-treated or untreated animals (P < 0.01).

CONCLUSION

Our findings indicate that a single intraarticular injection of concentrated lubricin following ACLT reduces type II collagen degradation and improves weight bearing in the affected rat joint. These findings support the practice of tribosupplementation with lubricin for retarding cartilage degeneration and possibly the development of posttraumatic osteoarthritis.

Effect of the gonadal status and the gender on glycosaminoglycans profile in the lower urinary tract of dogs

Glycosaminoglycans (GAGs) form a functional component of connective tissues that affect the structural and functional integrity of the lower urinary tract (LUT). The specific GAGs of physiological relevance are both nonsulfated (hyaluronan) and sulfated GAGs (chondroitin sulphate [CS], dermatan sulphate [DS], keratan sulphate [KS], and heparan sulphate [HS]). As GAG composition in the LUT is hormonally regulated, we postulated that gonadectomy-induced endocrine imbalance alters the profile of GAGs in the canine LUT. Four regions of the LUT (body and neck of the bladder as well as the proximal and distal urethra) from 20 clinically healthy dogs (5 intact males, 5 intact anoestrus females, 4 castrated males, and 6 spayed females) were collected, wax-embedded and sectioned. Alcian blue staining at critical electrolyte concentrations was performed on the sections to determine total GAGs, hyaluronan, total sulfated GAGs, combined components of CS and DS, as well as KS and HS. The amount of staining was evaluated in 3 tissue layers, i.e., epithelium, subepithelial stroma and muscle within a region. Overall, hyaluronan (67.1%) was the predominant GAG in the LUT. Among sulfated GAGs, a combined component of KS and HS was found to be 61.8% and 38.2% for CS and DS. Gonadal status significantly affected GAG profiles in the LUT (P < 0.01). All GAG components were lower (P < 0.05) in body of the bladder of gonadectomized dogs. Total sulfated GAGs and a combined component of KS and HS were lower (P < 0.05) in all 4 regions of gonadectomized dogs. Except for a combined component of CS and DS, decreases in all GAGs were found more consistently in the muscle compared to other tissue layers. Differences between genders became obvious only when considered along with the effect of gonadal status. In gonadectomized dogs, changes in GAG components in the LUT were more consistent in females compared to males; this may partly explain different levels of risk in the development of urinary incontinence between genders. Quantitative differences in GAG profiles found between intact and gonadectomized dogs indicate a potential role of gonadectomy-induced endocrine imbalance in modifying GAG composition in the canine LUT. Profound alteration in the pattern of GAGs in gonadectomized dogs may compromise structural and functional integrity of the LUT and is possibly involved in the underlying mechanism of urinary incontinence post neutering.

Prevention of cartilage degeneration and restoration of chondroprotection by lubricin tribosupplementation in the rat following anterior cruciate ligament transection

OBJECTIVE

To investigate whether cartilage degeneration is prevented or minimized following intraarticular injections of lubricin derived from human synoviocytes in culture, recombinant human PRG4 (rhPRG4), or human synovial fluid (SF) in a rat model of anterior cruciate ligament (ACL) injury.

METHODS

Unilateral ACL transection (ACLT) was performed in Lewis rats (n = 45). Nine animals were left untreated. The remaining rats were given intraarticular injections (50 microl/injection) of either phosphate buffered saline (PBS) (n = 9), human synoviocyte lubricin (200 microg/ml; n = 9), rhPRG4 (200 microg/ml; n = 9), or human SF lubricin (200 microg/ml; n = 9) twice weekly beginning on day 7 after injury. Joints were harvested on day 32 after injury. Histologic analysis was performed using Safranin O-fast green staining, and articular cartilage degeneration was graded using the Osteoarthritis Research Society International (OARSI)-modified Mankin criteria. Histologic specimens were immunoprobed for lubricin and sulfated glycosaminoglycans. A 24-hour urine collection was performed on days 17 and 29 postinjury, and urinary C-terminal telopeptide of type II collagen (CTX-II) levels were measured.

RESULTS

Treatment with human synoviocyte lubricin resulted in significantly lower OARSI scores for cartilage degeneration compared with no treatment or PBS treatment (P < 0.05). Increased immunostaining for lubricin in the superficial zone chondrocytes and on the surface of cartilage was observed in lubricin-treated, but not untreated or PBS-treated, joints. On day 17, urinary CTX-II levels in human synoviocyte lubricin- and human SF lubricin-treated animals were significantly lower than those in untreated animals (P = 0.005 and P = 0.002, respectively) and in PBS-treated animals (P = 0.002 and P < 0.001, respectively).

CONCLUSION

After treatment with any of the 3 types of lubricin evaluated in this study, a reduction in cartilage damage following ACLT was evident, combined with a reduction in type II collagen degradation. Our findings indicate that intraarticular lubricin injection following an ACL injury may be beneficial in retarding the degeneration of cartilage and the development of posttraumatic OA.

Differential regulation of GDF-5 and FGF-2/4 by immobilisation in ovo exposes distinct roles in joint formation

Members of the fibroblast growth factor (FGF) family and growth and differentiation factor 5 (GDF-5) have been implicated in joint specification, but their roles in subsequent cavity formation are not defined. Cavity formation (cavitation) depends upon limb movement in embryonic chicks and factors involved in joint formation are often identified by their expression at the joint-line. We have sought support for the roles of FGF-2, FGF-4, and GDF-5 in cavitation by defining expression patterns, immunohistochemically, during joint formation and establishing whether these are modified by in ovo immobilisation. We found that FGF-2 exhibited low level nuclear expression in chondrocytes and fibrocartilage cells close to presumptive joints, but showed significantly higher expression levels in cells at, and directly bordering, the forming joint cavity. This high-level joint line FGF-2 expression was selectively diminished in immobilised limbs. In contrast, we show that FGF-4 does not exhibit differential joint-line expression and was unaffected by immobilisation. GDF-5 protein also failed to show joint-line selective labelling, and although immobilisation induced a cartilaginous fusion across presumptive joints, it did not affect cellular GDF-5 expression patterns. Examining changes in GDF-5 expression in response to a direct mechanical strain stimulus in primary embryonic chick articular surface (AS) cells in vitro discloses only small mechanically-induced reductions in GDF-5 expression, suggesting that GDF-5 does not exert a direct positive contribution to the mechano-dependent joint cavitation process. This notion was supported by retroviral overexpression of UDPGD, a characteristic factor involved in hyaluronan (HA) accumulation at presumptive joint lines, which was also found to produce small decreases in AS cell GDF-5 expression. These findings support a direct mechano-dependent role for FGF-2, but not FGF-4, in the cavitation process and indicate that GDF-5 is likely to influence chondrogenesis positively without contributing directly to joint cavity formation.

Early effects of embryonic movement: 'a shot out of the dark'

It has long been appreciated that studying the embryonic chick in ovo provides a variety of advantages, including the potential to control the embryo's environment and its movement independently of maternal influences. This allowed early workers to identify movement as a pivotal factor in the development of the locomotor apparatus. With an increasing focus on the earliest detectable movements, we have exploited this system by developing novel models and schemes to examine the influence of defined periods of movement during musculoskeletal development. Utilizing drugs with known neuromuscular actions to provoke hyperactivity (4-aminopyridine, AP) and either rigid (decamethonium bromide, DMB) or flaccid (pancuronium bromide, PB) paralysis, we have examined the role of movement in joint, osteochondral and muscle development. Our initial studies focusing on the joint showed that AP-induced hyperactivity had little, if any, effect on the timing or scope of joint cavity elaboration, suggesting that endogenous activity levels provide sufficient stimulus, and additional mobilization is without effect. By contrast, imposition of either rigid or flaccid paralysis prior to cavity formation completely blocked this process and, with time, produced fusion of cartilaginous elements and formation of continuous single cartilaginous rods across locations where joints would ordinarily form. The effect of these distinct forms of paralysis differed, however, when treatment was initiated after formation of an overt cavity; rigid, but not flaccid, paralysis partly conserved precavitated joints. This observation suggests that 'static' loading derived from 'spastic' rigidity can act to preserve joint cavities. Another facet of these studies was the observation that DMB-induced rigid paralysis produces a uniform and specific pattern of limb deformity whereas PB generated a diverse range of fixed positional deformities. Both also reduced limb growth, with different developmental periods preferentially modifying specific osteochondral components. Changes in cartilage and bone growth induced by 3-day periods of flaccid immobilization, imposed at distinct developmental phases, provides support for a diminution in cartilage elaboration at an early phase and for a relatively delayed influence of movement on osteogenesis, invoking critical periods during which the developing skeleton becomes receptive to the impact of movement. Immobilization also exerts differential impact along the proximo-distal axis of the limb. Finally, our preliminary results support the possibility that embryonic hyperactivity influences the potential for postnatal muscle growth.

c-Krox down-regulates the expression of UDP–glucose dehydrogenase in chondrocytes

Chondrocyte glycosaminoglycan (GAG) synthesis is regulated by the availability of UDP-glucuronate, the substrate of glucuronosyl transferases which form the GAG chains in proteoglycans and hyaluronan. UDP-glucose dehydrogenase (UDPGD) is therefore a key enzyme in the synthesis of UDP-glucuronate from glucose. However, the mechanisms regulating its expression in chondrocytes are not fully understood. We investigated the effect of c-Krox, a zinc-finger transcription factor previously shown to modulate several matrix genes, on the synthesis of GAG and transcriptional activity of several UDPGD gene promoter constructs, using transient transfection and decoy experiments in rabbit articular chondrocytes (RACs). We show that overexpression of c-Krox inhibits radiosulfate incorporation into neosynthesized GAG and that the effect was mediated by a cis-sequence located between +18 and +39bp of the UDPGD gene. Since that sequence can also bind Sp1/Sp3 factors, it is likely that c-Krox acts in concert with these proteins to modulate the UDPGD gene expression in articular chondrocytes.

Selective activation of the MEK-ERK pathway is regulated by mechanical stimuli in forming joints and promotes pericellular matrix formation

It is well established that local modification of extracellular matrix (ECM) hyaluronan composition is vital in the regulation of cell behavior. Indeed, the formation of articulating chick joint cavities, which requires mechanical stimuli derived from skeletal movement, is dependent upon the accumulation of an ECM rich in hyaluronan (HA). However, the mechanisms responsible for such precise mechano-dependent regulation of cell behavior and the formation of a HA-rich ECM remain undefined. Here we show that extracellular-regulated kinase 1/2 (ERK1/2) is selectively activated in cells at sites of cavity formation and activity diminished by in ovo immobilization that induces cartilaginous fusion across presumptive joint interzones. In vitro analyses offer mechanistic support for the role of mechanical stimuli in promoting a MEK-dependent activation of ERK1/2. In addition, our direct regulation of ERK1/2 phosphorylation status via modulation of its up-stream "classical cascade" activator either pharmacologically or by transfection with dominant negative or constitutively active Mek confirms the essential role for ERK1/2 activation in the elaboration of HA-rich pericellular matrices. Together, our findings demonstrate that the MEK-ERK pathway, regulated by mechanical stimuli, controls HA-rich matrix assembly. The precision of ERK1/2 activation selectively distinguishing cells at the joint line suggests that it directly contributes to the loss of tissue cohesion essential for generating HA-rich cavities between joint elements during their development.

Age-related changes in the response of human articular cartilage to IL-1alpha and transforming growth factor-beta (TGF-beta): chondrocytes exhibit a diminished sensitivity to TGF-beta

Cartilage glycosaminoglycan (GAG) synthesis and composition, upon which its structural integrity depends, varies with age, is modified by anabolic and catabolic stimuli, and is regulated by UDP-glucuronate availability. However, how such stimuli, prototypically represented by transforming growth factor-beta1 (TGF-beta1) and IL-1alpha, modify GAG synthesis during aging of normal human articular cartilage is not known. Using explants, we show that chondroitin sulfate (CS):total GAG ratios decrease, whereas C6S:C4S ratios increase with cartilage maturation, and that chondrocytes in the cartilage mid-zone, but not the superficial or deep zones, exhibit uridine 5'-diphosphoglucose dehydrogenase (UDPGD) activity, which is also increased in mature cartilage. We also show that IL-1alpha treatment reduces both total GAG and CS synthesis, decreases C6S:C4S ratios (less C6S), but fails to modify chondrocyte UDPGD activity at all ages. On the other hand, TGF-beta1 increases total GAG synthesis in immature, but not mature, cartilage (stimulates CS but not non-CS), age-independently decreases C6S:C4S (more C4S), and increases chondrocyte UDPGD activity in a manner inversely correlated with age. Our findings show that TGF-beta1, but not IL-1alpha, modifies matrix synthesis such that its composition more closely resembles "less mature" articular cartilage. These effects of TGF-beta1, which appear to be restricted to periods of skeletal immaturity, are closely associated although not necessarily mechanistically linked with increases in chondrocyte UDPGD activity. The antianabolic effects of IL-1alpha are, on the other hand, likely to be independent of any direct modification in UDPGD activity and manifest equally in human cartilage of all ages.