Bone-Targeting Endogenous Secretory Receptor for Advanced Glycation End Products Rescues Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory synovitis that leads to the destruction of bone and cartilage. The receptor for advanced glycation end products (RAGE) is a multiligand membrane-bound receptor for high-mobility group box-1 (HMGB1) associated with development of RA by inducing production of proinflammatory cytokines such as tumor necrosis factor (TNF)-α, interleukin (IL)-1 and IL-6. We developed a bone-targeting therapeutic agent by tagging acidic oligopeptide to a nonmembrane-bound form of RAGE (endogenous secretory RAGE [esRAGE]) functioning as a decoy receptor. We assessed its tissue distribution and therapeutic effectiveness in a murine model of collagen-induced arthritis (CIA). Acidic oligopeptide–tagged esRAGE (D₆-esRAGE) was localized to mineralized region in bone, resulting in the prolonged retention of more than 1 wk. Weekly administration of D₆-esRAGE with a dose of 1 mg/kg to RA model mice significantly ameliorated inflammatory arthritis, synovial hyperplasia, cartilage destruction and bone destruction, while untagged esRAGE showed little effectiveness. Moreover, D₆-esRAGE reduced plasma levels of proinflammatory cytokines including TNF-α, IL-1 and IL-6, while esRAGE reduced the levels of IL-1 and IL-6 to a lesser extent, suggesting that production of IL-1 and IL-6 reduced along the blockade of HMGB1 receptor downstream signals by D₆-esRAGE could be attributed to remission of CIA. These findings indicate that D₆-esRAGE enhances drug delivery to bone, leading to rescue of clinical and pathological lesions in murine CIA.     

Protection against collagen-induced arthritis by electrotransfer of an expression plasmid for the interleukin-4

Rheumatoid arthritis (RA) is a chronic inflammatory joint disease, leading to cartilage and bone destruction. We investigated whether the electrotransfer of IL-4 DNA could regulate the disease progress of murine collagen-induced arthritis (CIA). The maximum serum level of mIL-4 was measured by 340 pg/ml on day 1 following DNA transfer. The onset of severe CIA and the degree of synovitis and cartilage erosion were significantly reduced in mice treated with IL-4 DNA (P<0.05). The beneficial effect of IL-4 gene transfer lasted for at least 17 days subsequent to treatment. The expression of IL-1beta was considerably decreased in the paws by IL-4 DNA transfer (P<0.01). On the contrary, the ratio of TIMP2 to MMP2 significantly increased in the IL-4 DNA-treated group (P<0.01). These data demonstrated that electroporation-mediated gene transfer could provide a new approach as an IL-4 therapy for autoimmune arthritis.     

Deficiency of fibroblast activation protein alpha ameliorates cartilage destruction in inflammatory destructive arthritis

IntroductionInflammatory destructive arthritis, like rheumatoid arthritis (RA), is characterized by invasion of synovial fibroblasts (SF) into the articular cartilage and erosion of the underlying bone, leading to progressive joint destruction. Because fibroblast activation protein alpha (FAP) has been associated with cell migration and cell invasiveness, we studied the function of FAP in joint destruction in RA.MethodsExpression of FAP in synovial tissues and fibroblasts from patients with osteoarthritis (OA) and RA as well as from wild-type and arthritic mice was evaluated by immunohistochemistry, fluorescence microscopy and polymerase chain reaction (PCR). Fibroblast adhesion and migration capacity was assessed using cartilage attachment assays and wound-healing assays, respectively. For in vivo studies, FAP-deficient mice were crossed into the human tumor necrosis factor transgenic mice (hTNFtg), which develop a chronic inflammatory arthritis. Beside clinical assessment, inflammation, cartilage damage, and bone erosion were evaluated by histomorphometric analyses.ResultsRA synovial tissues demonstrated high expression of FAP whereas in OA samples only marginal expression was detectable. Consistently, a higher expression was detected in arthritis SF compared to non-arthritis OA SF in vitro. FAP-deficiency in hTNFtg mice led to less cartilage degradation despite unaltered inflammation and bone erosion. Accordingly, FAP^−/− hTNFtg SF demonstrated a lower cartilage adhesion capacity compared to hTNFtg SF in vitro.ConclusionsThese data point to a so far unknown role of FAP in the attachment of SF to cartilage, promoting proteoglycan loss and subsequently cartilage degradation in chronic inflammatory arthritis.     

Effect of alendronate on post-traumatic osteoarthritis induced by anterior cruciate ligament rupture in mice

IntroductionPrevious studies in animal models of osteoarthritis suggest that alendronate (ALN) has antiresorptive and chondroprotective effects, and can reduce osteophyte formation. However, these studies used non-physiologic injury methods, and did not investigate early time points during which bone is rapidly remodeled prior to cartilage degeneration. The current study utilized a non-invasive model of knee injury in mice to investigate the effect of ALN treatment on subchondral bone changes, articular cartilage degeneration, and osteophyte formation following injury.MethodsNon-invasive knee injury via tibial compression overload or sham injury was performed on a total of 90 mice. Mice were treated with twice weekly subcutaneous injections of low-dose ALN (40 μg/kg/dose), high-dose ALN (1,000 μg/kg/dose), or vehicle, starting immediately after injury until sacrifice at 7, 14 or 56 days. Trabecular bone of the femoral epiphysis, subchondral cortical bone, and osteophyte volume were quantified using micro-computed tomography (μCT). Whole-joint histology was performed at all time points to analyze articular cartilage and joint degeneration. Blood was collected at sacrifice, and serum was analyzed for biomarkers of bone formation and resorption.ResultsμCT analysis revealed significant loss of trabecular bone from the femoral epiphysis 7 and 14 days post-injury, which was effectively prevented by high-dose ALN treatment. High-dose ALN treatment was also able to reduce subchondral bone thickening 56 days post-injury, and was able to partially preserve articular cartilage 14 days post-injury. However, ALN treatment was not able to reduce osteophyte formation at 56 days post-injury, nor was it able to prevent articular cartilage and joint degeneration at this time point. Analysis of serum biomarkers revealed an increase in bone resorption at 7 and 14 days post-injury, with no change in bone formation at any time points.ConclusionsHigh-dose ALN treatment was able to prevent early trabecular bone loss and cartilage degeneration following non-invasive knee injury, but was not able to mitigate long-term joint degeneration. These data contribute to understanding the effect of bisphosphonates on the development of osteoarthritis, and may support the use of anti-resorptive drugs to prevent joint degeneration following injury, although further investigation is warranted.     

类风湿性关节炎活动性病变MRI征象及其与FIB、FDP、D-D的相关性研究

摘要 目的：探讨类风湿性关节炎（RA）活动性病变磁共振成像（MRI）征象及其与纤维蛋白原（FIB）、纤维蛋白(原)降解产物（FDP）、D-二聚体（D-D）的相关性研究。方法：选取2020年1月-2021年2月期间我院诊治的61例RA患者,根据28个关节疾病活动指数（DAS28）评分将其分为活动组（35例）和稳定组（26例）。对比两组MRI征象,血清FIB、FDP、D-D水平。采用Spearman相关性分析RA活动期患者MRI各征象间的相关性及MRI各征象与血清FIB、FDP、D-D水平间的相关性。结果：活动组滑膜增厚或滑膜炎、骨髓水肿、软骨及骨侵蚀、腱鞘炎或周围软组织受累、关节腔积液征象人数占比均高于稳定组（P＜0.05）。活动组患者血清FIB、FDP、D-D水平均高于稳定组（P＜0.05）。Spearman相关性分析结果显示,RA活动期患者滑膜增厚或滑膜炎征象与骨髓水肿、软骨及骨侵蚀、关节腔积液征象均呈正相关（P＜0.05）,骨髓水肿征象与软骨及骨侵蚀征象呈正相关（P＜0.05）;RA活动期患者滑膜增厚或滑膜炎、骨髓水肿、关节腔积液征象与血清FIB、FDP、D-D水平均呈正相关（P＜0.05）,软骨及骨侵蚀征象与FIB呈正相关（P＜0.05）。结论：MRI征象可清晰显示RA患者的滑膜、骨质、关节腔及周围肌腱、软组织等异常改变,且MRI征象之间具有相关性,可在一定程度上反映RA的病理改变;血清FIB、FDP、D-D的检测有助于反映RA活动情况;MRI征象与血清FIB、FDP、D-D水平间具有相关性,二者联合应用有助于进一步评估RA活动情况。     

Cells of the synovium in rheumatoid arthritis. Chondrocytes

Rheumatoid arthritis (RA) is one of the inflammatory joint diseases in a heterogeneous group of disorders that share features of destruction of the extracellular matrices of articular cartilage and bone. The underlying disturbance in immune regulation that is responsible for the localized joint pathology results in the release of inflammatory mediators in the synovial fluid and synovium that directly and indirectly influence cartilage homeostasis. Analysis of the breakdown products of the matrix components of joint cartilage in body fluids and quantitative imaging techniques have been used to assess the effects of the inflammatory joint disease on the local remodeling of joint structures. The role of the chondrocyte itself in cartilage destruction in the human rheumatoid joint has been difficult to address but has been inferred from studies in vitro and in animal models. This review covers current knowledge about the specific cellular and biochemical mechanisms that account for the disruption of the integrity of the cartilage matrix in RA.     

Sequential Change in T2* Values of Cartilage,Meniscus, and Subchondral Bone Marrow in a Rat Model of Knee Osteoarthritis

Background

There is an emerging interest in using magnetic resonance imaging (MRI) T2* measurement for the evaluation of degenerative cartilage in osteoarthritis (OA). However, relatively few studies have addressed OA-related changes in adjacent knee structures. This study used MRI T2* measurement to investigate sequential changes in knee cartilage, meniscus, and subchondral bone marrow in a rat OA model induced by anterior cruciate ligament transection (ACLX).

Materials and Methods

Eighteen male Sprague Dawley rats were randomly separated into three groups (n = 6 each group). Group 1 was the normal control group. Groups 2 and 3 received ACLX and sham-ACLX, respectively, of the right knee. T2* values were measured in the knee cartilage, the meniscus, and femoral subchondral bone marrow of all rats at 0, 4, 13, and 18 weeks after surgery.

Results

Cartilage T2* values were significantly higher at 4, 13, and 18 weeks postoperatively in rats of the ACLX group than in rats of the control and sham groups (p<0.001). In the ACLX group (compared to the sham and control groups), T2* values increased significantly first in the posterior horn of the medial meniscus at 4 weeks (p = 0.001), then in the anterior horn of the medial meniscus at 13 weeks (p<0.001), and began to increase significantly in the femoral subchondral bone marrow at 13 weeks (p = 0.043).

Conclusion

Quantitative MR T2* measurements of OA-related tissues are feasible. Sequential change in T2* over time in cartilage, meniscus, and subchondral bone marrow were documented. This information could be potentially useful for in vivo monitoring of disease progression.     

Protection against cartilage and bone destruction by systemic interleukin-4 treatment in established murine type II collagen-induced arthritis

Destruction of cartilage and bone are hallmarks of human rheumatoid arthritis (RA), and controlling these erosive processes is the most challenging objective in the treatment of RA. Systemic interleukin-4 treatment of established murine collagen-induced arthritis suppressed disease activity and protected against cartilage and bone destruction. Reduced cartilage pathology was confirmed by both decreased serum cartilage oligomeric matrix protein (COMP) and histological examination. In addition, radiological analysis revealed that bone destruction was also partially prevented. Improved suppression of joint swelling was achieved when interleukin-4 treatment was combined with low-dose prednisolone treatment. Interestingly, synergistic reduction of both serum COMP and inflammatory parameters was noted when low-dose interleukin-4 was combined with prednisolone. Systemic treatment with interleukin-4 appeared to be a protective therapy for cartilage and bone in arthritis, and in combination with prednisolone at low dosages may offer an alternative therapy in RA.     

Therapeutic effects of lactosyl derivative Gu-4 in a collagen-induced arthritis rat model

Rheumatoid arthritis (RA) is an inflammatory disorder that is characterized by persistent recurrence of joint inflammation leading to cartilage and bone destruction. The present anti-arthritis therapies failed to achieve satisfactory remission in all patients; therefore, it is still necessary to develop novel approaches to fulfill the demand in clinic. Here, we reported the therapeutic effects of lactosyl derivative Gu-4, a synthetic compound that was previously identified as a selective inhibitor against leukocyte integrin CD11b, in a bovine type II collagen induced arthritis (CIA) rat model. First, prophylactic administration of Gu-4 (1.2728?mg/kg) to rats by intraperitoneal injection every 2?days from the first day of collagen immunization significantly decreased the incidence of CIA, diminished the mean paw volume increase, and reduced the number of swollen paws. Second, administration of Gu-4 (1.2728?mg/kg) to rats at early-onset stage of CIA prevented the progression of the pathological process of RA, accelerated the remission of paw edema, and declined the arthritis score; after 5?weeks treatment, X-ray and histological examinations were carried out, the ankle joint of hind limb of Gu-4 treated CIA rats exhibited slighter bone erosion and much less inflammatory cell infiltration compared to those of saline treated animals; furthermore, Gu-4 remarkably attenuated the production of rheumatoid factor (RF) in the serum of CIA rats as determined by ELISA. Moreover, we performed in vitro lymphocyte proliferation assay and found that Gu-4 significantly inhibited the proliferation of splenic lymphocytes isolated from CIA rats in a dose-dependent manner. Our results suggest that Gu-4 can effectively ameliorate CIA and might be an alternative option for the treatment of RA.     

RANKL synthesized by articular chondrocytes contributes to juxta-articular bone loss in chronic arthritis

Introduction

The receptor activator nuclear factor-kappaB ligand (RANKL) diffuses from articular cartilage to subchondral bone. However, the role of chondrocyte-synthesized RANKL in rheumatoid arthritis-associated juxta-articular bone loss has not yet been explored. This study aimed to determine whether RANKL produced by chondrocytes induces osteoclastogenesis and juxta-articular bone loss associated with chronic arthritis.

Methods

Chronic antigen-induced arthritis (AIA) was induced in New Zealand (NZ) rabbits. Osteoarthritis (OA) and control groups were simultaneously studied. Dual X-ray absorptiometry of subchondral knee bone was performed before sacrifice. Histological analysis and protein expression of RANKL and osteoprotegerin (OPG) were evaluated in joint tissues. Co-cultures of human OA articular chondrocytes with peripheral blood mononuclear cells (PBMCs) from healthy donors were stimulated with macrophage-colony stimulating factor (M-CSF) and prostaglandin E₂ (PGE₂), then further stained with tartrate-resistant acid phosphatase.

Results

Subchondral bone loss was confirmed in AIA rabbits when compared with controls. The expression of RANKL, OPG and RANKL/OPG ratio in cartilage were increased in AIA compared to control animals, although this pattern was not seen in synovium. Furthermore, RANKL expression and RANKL/OPG ratio were inversely related to subchondral bone mineral density. RANKL expression was observed throughout all cartilage zones of rabbits and was specially increased in the calcified cartilage of AIA animals. Co-cultures demonstrated that PGE₂-stimulated human chondrocytes, which produce RANKL, also induce osteoclasts differentiation from PBMCs.

Conclusions

Chondrocyte-synthesized RANKL may contribute to the development of juxta-articular osteoporosis associated with chronic arthritis, by enhancing osteoclastogenesis. These results point out a new mechanism of bone loss in patients with rheumatoid arthritis.     

RANK ligand, RANK, and OPG expression in type II collagen-induced arthritis mouse

Rheumatoid arthritis (RA) is a systemic disorder characterized by synovial inflammation and subsequent destruction and deformity of synovial joints. The articular lesions start with synovitis, focal erosion of unmineralized cartilage, and then culminate in the destruction of subarticular bone by pannus tissue. Periarticular osteopenia and systemic osteoporosis follow as late complications of RA. Osteoclasts, specialized cells that resorb bone, play a central role in developing these osteolytic lesions. To elucidate the mechanism of osteoclastogenesis and bone destruction in autoimmune arthritis, we investigated the expression of RANK ligand (RANKL), RANK, and osteoprotegerin (OPG) mRNA in a mouse type II collagen-induced arthritis (CIA) model by in situ hybridization. The results indicated that most of the TRAP-positive mono- and multinucleated cells in the inflamed and proliferating synovium and in the pannus were RANK-positive authentic osteoclasts and their precursors. In the inflamed synovium and pannus of the mouse CIA model, synovial fibroblastic cells around these RANK-positive cells were strongly positive for RANKL. Moreover, RANKL-positive osteoblasts on the endosteal bone surface, at a distance from the affected synovial joints, increased significantly in the mouse CIA model prior to periarticular osteopenia and systemic osteoporosis. These data indicated that the RANKL-RANK system plays an important role for osteoclastogenesis in both local and systemic osteolytic lesions in autoimmune arthritis, and can therefore be a good target for therapeutic intervention.     

Adenovirus-mediated gene transfer of adiponectin reduces the severity of collagen-induced arthritis in mice

Adiponectin (APN) is a hormone released by adipose tissue with anti-inflammatory properties. The purpose of this study was to examine the therapeutic effects of systemic delivery of APN in murine arthritis model. Collagen-induced arthritis (CIA) was induced in male DBA1/J mice, and adenoviral vectors encoding human APN (Ad-APN) or beta-galactosidase (Ad-β-gal) as control were injected either before or during arthritis progression. Systemic APN delivery at both time points significantly decreased clinical disease activity scores of CIA. In addition, APN treatment before arthritis progression significantly decreased histological scores of inflammation and cartilage damage, bone erosion, and mRNA levels of pro-inflammatory cytokines in the joints, without altering serum anti-collagen antibodies levels. Immunohistochemical staining showed significant inhibition of complement C1q and C3 deposition in the joints of Ad-APN infected CIA mice. These results provide novel evidence that systemic APN delivery prevents inflammation and joint destruction in murine arthritis model.     

Grape-Seed Proanthocyanidin Extract as Suppressors of Bone Destruction in Inflammatory Autoimmune Arthritis

Chronic autoimmune inflammation, which is commonly observed in rheumatoid arthritis (RA), disrupts the delicate balance between bone resorption and formation causing thedestruction of the bone and joints. We undertook this study to verify the effects of natural grape-seed proanthocyanidin extract (GSPE), an antioxidant, on chronic inflammation and bone destruction. GSPE administration ameliorated the arthritic symptoms of collagen-induced arthritis (CIA), which are representative of cartilage and bone destruction. GSPE treatment reduced the formation of tartrate-resistant acid phosphatase (TRAP)-positive multinucleated cells and osteoclast activity and increased differentiation of mature osteoblasts. Receptor activator of NFκB ligand expression in fibroblasts from RA patients was abrogated with GSPE treatment. GSPE blocked human peripheral blood mononuclear cell-derived osteoclastogenesis and acted as an antioxidant. GSPE improved the arthritic manifestations of CIA mice by simultaneously suppressing osteoclast differentiation and promoting osteoblast differentiation. Our results suggest that GSPE may be beneficial for the treatment of inflammation-associated bone destruction.     

Equol suppresses inflammatory response and bone erosion due to rheumatoid arthritis in mice

Rheumatoid arthritis (RA) is a chronic and systemic autoimmune inflammatory disease. Typical pathological findings of RA include persistent synovitis and bone degradation in the peripheral joints. Equol, a metabolite of the major soybean isoflavone daidzein, shows superior bioactivity than other isoflavones. We investigated the effects of equol administration on inflammatory response and bone erosion in mice with collagen-induced arthritis (CIA). The severity of arthritis symptoms was significantly low in the equol-administered CIA mice. In addition, equol administration improved the CIA-induced bone mineral density decline. In the inflamed area of CIA mice, equol administration suppressed the expression of interleukin-6 and its receptor. Furthermore, equol reduced the expression of genes associated with bone formation inhibition, osteoclast and immature osteoblast specificity and cartilage destruction. These results suggest that equol suppresses RA development and RA-induced bone erosion by regulating inflammation and bone metabolism.     

Aromatic trap analysis of free radicals production in experimental collagen-induced arthritis in the rat: protective effect of glycosaminoglycans treatment

Many findings demonstrated that Glycosaminoglycans (GAGs) and Proteoglycans (PGs) possess antioxidant activity. Collagen-induced arthritis (CIA) is an experimental animal model similar to human rheumatoid arthritis (RA) in which free radicals are involved. Sodium salicylate can be used as a chemical trap for hydroxyl radicals (OH •), the most damaging reactive oxygen species (ROS), yielding 2,5-dihydroxybenzoic acid), (2,5-DHBA) and 2,3-dihydroxybenzoic acid (2,3-DHBA). The measurement of these two acids in the plasma allows to indirectly assess the production of OH • radicals. The aim of the study was to investigate the effect of hyaluronic acid (HYA) (30 mg/kg i.p.) or chondroitin-4-sulphate (C4S) (30 mg/kg i.p.), on free radical production in Lewis rats subjected to CIA. After the immunization with bovine collagen type II in complete Freund's adjuvant, rats developed an erosive hind paw arthritis, that produced high plasma OH • levels assayed as 2,3-DHBA and 2,5-DHBA, primed lipid peroxidation, evaluated by analyzing conjugated dienes (CD) in the articular cartilage; decreased the concentration of endogenous vitamin E (VE) and catalase (CA) in the joint cartilage; enhanced macrophage inflammatory protein-2 (MIP-2) serum levels and increased elastase (ELA) evaluated as an index of activated leukocyte polymophonuclear (PMNs) accumulation in the articular joints. The administration of HYA and C4S starting at the onset of arthritis (day 11) for 20 days, limited inflammation and the clinical signs in the knee and paw, reduced OH • production, decreased CD levels, partially restored the endogenous antioxidants VE and CA, reduced MIP-2 serum levels and limited PMNs infiltration. The results indicate that the GAGs HYA and C4S significantly reduce free radical production in CIA and could be used as a tool to investigate the role of antioxidants in RA.     

Tetrapolar measurement of electrical conductivity and thickness of articular cartilage

A tetrapolar method to measure electrical conductivity of cartilage and bone, and to estimate the thickness of articular cartilage attached to bone, was developed. We determined the electrical conductivity of humeral head bovine articular cartilage and subchondral bone from a 1- to 2-year-old steer to be 1.14+/-0.11 S/m (mean+/-sd, n =11) and 0.306+/-0.034 S/m, (mean+/-sd, n =3), respectively. For a 4-year-old cow, articular cartilage and subchondral bone electrical conductivity were 0.88+/-0.08 S/m (mean+/-sd, n =9) and 0.179+/-0.046 S/m (mean+/-sd, n =3), respectively. Measurements on slices of cartilage taken from different distances from the articular surface of the steer did not reveal significant depth-dependence of electrical conductivity. We were able to estimate the thickness of articular cartilage with reasonable precision (<20% error) by injecting current from multiple electrode pairs with different inter-electrode distances. Requirements for the precision of this method to measure cartilage thickness include the presence of a distinct layer of calcified cartilage or bone with a much lower electrical conductivity than that of uncalcified articular cartilage, and the use of inter-electrode distances of the current injecting electrodes that are on the order of the cartilage thickness. These or similar methods present an attractive approach to the non-destructive determination of cartilage thickness, a parameter that is required in order to estimate functional properties of cartilage attached to bone, and evaluate the need for therapeutic interventions in arthritis.     

Subchondral bone in osteoarthritis: insight into risk factors and microstructural changes

Osteoarthritis (OA) is a major cause of disability in the adult population. As a progressive degenerative joint disorder, OA is characterized by cartilage damage, changes in the subchondral bone, osteophyte formation, muscle weakness, and inflammation of the synovium tissue and tendon. Although OA has long been viewed as a primary disorder of articular cartilage, subchondral bone is attracting increasing attention. It is commonly reported to play a vital role in the pathogenesis of OA. Subchondral bone sclerosis, together with progressive cartilage degradation, is widely considered as a hallmark of OA. Despite the increase in bone volume fraction, subchondral bone is hypomineralized, due to abnormal bone remodeling. Some histopathological changes in the subchondral bone have also been detected, including microdamage, bone marrow edema-like lesions and bone cysts. This review summarizes basic features of the osteochondral junction, which comprises subchondral bone and articular cartilage. Importantly, we discuss risk factors influencing subchondral bone integrity. We also focus on the microarchitectural and histopathological changes of subchondral bone in OA, and provide an overview of their potential contribution to the progression of OA. A hypothetical model for the pathogenesis of OA is proposed.     

Protein kinase C delta null mice exhibit structural alterations in articular surface,intra-articular and subchondral compartments

IntroductionStructural alterations in intra-articular and subchondral compartments are hallmarks of osteoarthritis, a degenerative disease that causes pain and disability in the aging population. Protein kinase C delta (PKC-δ) plays versatile functions in cell growth and differentiation, but its role in the articular cartilage and subchondral bone is not known.MethodsHistological analysis including alcian blue, safranin O staining and fluorochrome labeling were used to reveal structural alterations at the articular cartilage surface and bone–cartilage interface in PKC-δ knockout (KO) mice. The morphology and organization of chondrocytes were studied using confocal microscopy. Glycosaminoglycan content was studied by micromass culture of chondrocytes of PKC-δ KO mice.ResultsWe uncovered atypical structural demarcation between articular cartilage and subchondral bone of PKC-δ KO mice. Histology analyses revealed a thickening of the articular cartilage and calcified bone–cartilage interface, and decreased safranin O staining accompanied by an increase in the number of hypertrophic chondrocytes in the articular cartilage of PKC-δ KO mice. Interestingly, loss of demarcation between articular cartilage and bone was concomitant with irregular chondrocyte morphology and arrangement. Consistently, in vivo calcein labeling assay showed an increased intensity of calcein labeling in the interface of the growth plate and metaphysis in PKC-δ KO mice. Furthermore, in vitro culture of chondrocyte micromass showed a decreased alcian blue staining of chondrocyte micromass in the PKC-δ KO mice, indicative of a reduced level of glycosaminoglycan production.ConclusionsOur data imply a role for PKC-δ in the osteochondral plasticity of the interface between articular cartilage and the osteochondral junction.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-015-0720-4) contains supplementary material, which is available to authorized users.     

Reduced PDGF-AA in subchondral bone leads to articular cartilage degeneration after strenuous running

To identify the effects of running on articular cartilage and subchondral bone remodeling, C57BL/6 mice were randomly divided into three groups: control, moderate-, and strenuous running. Magnetic resonance imaging showed bone marrow lesions in the knee subchondral bone in the strenuous-running group in contrast with the other two groups. The microcomputed tomography analysis showed promoted bone formation in the subchondral bone in mice subjected to strenuous running. Histological and immunohistochemistry results indicated that terminal differentiation of chondrocytes and degeneration of articular cartilage were enhanced but, synthesis of platelet-derived growth factor-AA (PDGF-AA) in the subchondral bone was suppressed after strenuous running. In vitro, excessive mechanical treatments suppressed the expression of PDGF-AA in osteoblasts, and the condition medium from mechanical-treated osteoblasts stimulated maturation and terminal differentiation of chondrocytes. These results indicate that strenuous running suppresses the synthesis of PDGF-AA in subchondral bone, leading to downregulated PDGF/Akt signal in articular cartilage and thus cartilage degeneration.