Molecular network of cartilage homeostasis and osteoarthritis

The Role of miRNAs in Cartilage Homeostasis

Osteoarthritis (OA) is an age-related disease with poorly understood pathogenesis. Recent studies have demonstrated that miRNA might play a key role in OA initiation and development. We reviewed recent publications and elucidated the connection between miRNA and OA cartilage anabolic and catabolic signals, including four signaling pathways: TGF-β/Smads and BMPs signaling, associated with cartilage anabolism; and MAPK and NF-KB signaling, associated with cartilage catabolism. We also explored the relationships with MMP, ADAMTS and NOS (NitricOxide Synthases) families, as well as with the catabolic cytokines IL-1 and TNF-α. The potential role of miRNAs in biological processes such as cartilage degeneration, chondrocyte proliferation, and differentiation is discussed. Collective evidence indicates that miRNAs play a critical role in cartilage degeneration. These findings will aid in understanding the molecular network that governs articular cartilage homeostasis and in to elucidate the role of miRNA in the pathogenesis of OA.

Upregulation of lncRNA HOTAIR contributes to IL-1β-induced MMP overexpression and chondrocytes apoptosis in temporomandibular joint osteoarthritis

Temporomandibular joint osteoarthritis (TMJ OA) is a common and heterogeneous disease that causes painful and progressive joint degeneration, which restricts daily activities, including talking and chewing. Long noncoding RNAs (lncRNAs) are an important class of genes involved in various physiological and pathological functions, including osteoarthritis (OA).The present study aimed to identify the lncRNAs that are important in TMJ OA and their potential functions. Here, we found that HOTAIR was significantly upregulated in the synovial fluid of TMJ OA patients compared with that of normal controls. Increased HOTAIR was similarly observed in the synovial fluid of TMJ OA rabbits as compared to control rabbits. Furthermore, in interleukin-1β (IL-1β)-induced TMJ OA in vitro model (primary rabbit condylar chondrocytes), the expressions of matrix metalloproteinase (MMP)-1, MMP3, MMP9 and HOTAIR were all dramatically increased. Most importantly, knockdown of HOTAIR in IL-1β-induced TMJ OA in vitro model could not only reverse the IL-1β-stimulated expressions of MMP1, MMP3 and MMP9, but also significantly decrease the apoptosis rate induced by IL-1β in primary rabbit condylar chondrocytes. Our data provides new insight into the mechanisms of chondrocytes destruction in TMJ OA.

Multiscale Biofabrication of Articular Cartilage: Bioinspired and Biomimetic Approaches

Articular cartilage is the load-bearing tissue found inside all articulating joints of the body. It vastly reduces friction and allows for smooth gliding between contacting surfaces. The structure of articular cartilage matrix and cellular composition is zonal and is important for its mechanical properties. When cartilage becomes injured through trauma or disease, it has poor intrinsic healing capabilities. The spectrum of cartilage injury ranges from isolated areas of the joint to diffuse breakdown and the clinical appearance of osteoarthritis. Current clinical treatment options remain limited in their ability to restore cartilage to its normal functional state. This review focuses on the evolution of biomaterial scaffolds that have been used for functional cartilage tissue engineering. In particular, we highlight recent developments in multiscale biofabrication approaches attempting to recapitulate the complex 3D matrix of native articular cartilage tissue. Additionally, we focus on the application of these methods to engineering each zone of cartilage and engineering full-thickness osteochondral tissues for improved clinical implantation. These methods have shown the potential to control individual cell-to-scaffold interactions and drive progenitor cell differentiation into a chondrocyte lineage. The use of these bioinspired nanoengineered scaffolds hold promise for recreation of structure and function on the whole tissue level and may represent exciting new developments for future clinical applications for cartilage injury and restoration.

Metabolic triggered inflammation in osteoarthritis

Osteoarthritis (OA) is a common chronic joint disorder with a multifactorial etiology including genetic and environmental factors. Metabolic triggered inflammation, induced by nutrient overload and metabolic surplus, consists of components such as obesity, pro-inflammatory cytokines and adipokines, abnormal metabolites, acute phase proteins, vitamin D deficiency, and deregulated microRNAs that may play a role in OA pathophysiology. Obesity-related metabolic factors, especially adipokines, contribute to OA development by inducing pro-inflammatory cytokines and degradative enzymes, leading to cartilage matrix impairment and subchondral bone remodeling. Ectopic metabolite deposition and low-grade systemic inflammation can contribute to a toxic internal environment that exacerbates OA. Complement components highly expressed in osteoarthritic joints have also been proposed as causative factors. Vitamin D deficiency has been associated with obesity and is implicated to be associated with cartilage loss in OA. Metabolic microRNAs may explain the inflammatory link between obesity and OA. Therapies targeting metabolic-triggered inflammation and its components are anticipated to have potential for the treatment of OA.

MicroRNAs are potential prognostic and therapeutic targets in diabetic osteoarthritis

Osteoarthritis is an aging-related degenerative disease that severely influences the elders' life quality. However, there have been few clinical approaches available until now. Currently, more knowledge of the pathology of osteoarthritis has been illustrated. Especially, diabetes can be the only predictor of osteoarthritis. Due to its outstanding characteristics, MicroRNA has been considered as an efficient target in treating diseases. In this review, we will discuss a new insight focusing on the roles of microRNA in the progression of osteoarthritis-induced by diabetes, especially type II diabetes mellitus.

Chondroprotective potential of Phyllanthus amarus Schum. & Thonn. in experimentally induced cartilage degradation in the explants culture model

Phyllanthus amarus Schum. & Thonn. (P. amarus) has been reported to exhibit anti-inflammation and antiarthritis properties leading to our interest to examine its beneficial effect in osteoarthritis. Thus, this study aimed to explore the chondroprotective potential of P. amarus extract (PAE) and its major compounds, phyllanthin and hypophyllanthin, in a cartilage explant model. Various concentrations of P. amarus extract, phyllanthin and hypophyllanthin, were treated on porcine articular cartilage explants induced with 25 ng/ml of interleukin-1 beta (IL-1β). After 4 days of incubation, the culture medium was measured for the release of sulfate glycosaminoglycans (s-GAGs) and matrix metalloproteinase-2 (MMP-2) activity by DMMB binding assay and zymography, respectively. The explant tissues were analyzed for the remaining of uronic acid content by colorimetric assay and stained with safranin-O for investigation of proteoglycan content. Cell viability of this model was evaluated by lactate dehydrogenase (LDH) assay. Chondroprotective potential of PAE and the major components against IL-1β-induced cartilage explant degradation were revealed by the decreased s-GAGs level and MMP-2 activity in culture medium consistent with an increase in uronic acid and proteoglycan contents in the explants when compared to the IL-1β treatment. These results agreed with those of diacerein and sesamin which used as positive controls. In addition, better chondroprotective activities of P. amarus crude extracts than those of the purified components were disclosed in this study. Hence, this is a pioneering study presenting the chondroprotective potential of PAE which may augment its application for therapeutic use as an antiarthritic agent.

Mesenchymal stem-cell potential in cartilage repair: an update

Articular cartilage damage and subsequent degeneration are a frequent occurrence in synovial joints. Treatment of these lesions is a challenge because this tissue is incapable of quality repair and/or regeneration to its native state. Non-operative treatments endeavour to control symptoms and include anti-inflammatory medications, viscosupplementation, bracing, orthotics and activity modification. Classical surgical techniques for articular cartilage lesions are frequently insufficient in restoring normal anatomy and function and in many cases, it has not been possible to achieve the desired results. Consequently, researchers and clinicians are focusing on alternative methods for cartilage preservation and repair. Recently, cell-based therapy has become a key focus of tissue engineering research to achieve functional replacement of articular cartilage. The present manuscript is a brief review of stem cells and their potential in the treatment of early OA (i.e. articular cartilage pathology) and recent progress in the field.

Role of integrins and their ligands in osteoarthritic cartilage

Osteoarthritis (OA) is a degenerative disease, which is characterized by articular cartilage destruction, and mainly affects the older people. The extracellular matrix (ECM) provides a vital cellular environment, and interactions between the cell and ECM are important in regulating many biological processes, including cell growth, differentiation, and survival. However, the pathogenesis of this disease is not fully elucidated, and it cannot be cured totally. Integrins are one of the major receptors in chondrocytes. A number of studies confirmed that the chondrocytes express several integrins including α5β1, αVβ3, αVβ5, α6β1, α1β1, α2β1, α10β1, and α3β1, and some integrins ligands might act as the OA progression biomarkers. This review focuses on the functional role of integrins and their extracellular ligands in OA progression, especially OA cartilage. Clear understanding of the role of integrins and their ligands in OA cartilage may have impact on future development of successful therapeutic approaches to OA.

ADAMTS-12: a multifaced metalloproteinase in arthritis and inflammation

ADAMTS-12 is a member of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) family of proteases, which were known to play important roles in various biological and pathological processes, such as development, angiogenesis, inflammation, cancer, arthritis, and atherosclerosis. In this review, we briefly summarize the structural organization of ADAMTS-12; concentrate on the emerging role of ADAMTS-12 in several pathophysiological conditions, including intervertebral disc degeneration, tumorigenesis and angioinhibitory effects, pediatric stroke, gonad differentiation, trophoblast invasion, and genetic linkage to schizophrenia and asthma, with special focus on its role in arthritis and inflammation; and end with the perspective research of ADAMTS-12 and its potential as a promising diagnostic and therapeutic target in various kinds of diseases and conditions.

Low-density lipoprotein receptor-related protein 5 governs Wnt-mediated osteoarthritic cartilage destruction

Introduction

Wnt ligands bind to low-density lipoprotein receptor–related protein (LRP) 5 or 6, triggering a cascade of downstream events that include β-catenin signaling. Here we explored the roles of LRP5 in interleukin 1β (IL-1β)- or Wnt-mediated osteoarthritic (OA) cartilage destruction in mice.

Methods

The expression levels of LRP5, type II collagen, and catabolic factors were determined in mouse articular chondrocytes, human OA cartilage, and mouse experimental OA cartilage. Experimental OA in wild-type, Lrp5 total knockout (Lrp5^-/-) and chondrocyte-specific knockout (Lrp5^fl/fl;Col2a1-cre) mice was caused by aging, destabilization of the medial meniscus (DMM), or intra-articular injection of collagenase. The role of LRP5 was confirmed in vitro by small interfering RNA–mediated knockdown of Lrp5 or in Lrp5^-/- cells treated with IL-1β or Wnt proteins.

Results

IL-1β treatment increased the expression of LRP5 (but not LRP6) via JNK and NF-κB signaling. LRP5 was upregulated in human and mouse OA cartilage, and Lrp5 deficiency in mice inhibited cartilage destruction. Treatment with IL-1β or Wnt decreased the level of Col2a1 and increased those of Mmp3 or Mmp13, whereas Lrp5 knockdown ameliorated these effects. In addition, we found that the functions of LRP5 in arthritic cartilage were subject to transcriptional activation by β-catenin. Moreover, Lrp5^-/- and Lrp5^fl/fl;Col2a1-cre mice exhibited decreased cartilage destruction (and related changes in gene expression) in response to experimental OA.

Conclusions

Our findings indicate that LRP5 (but not LRP6) plays an essential role in Wnt/β-catenin-signaling-mediated OA cartilage destruction in part by regulating the expression levels of type II collagen, MMP3, and MMP13.

Nutraceuticals: potential for chondroprotection and molecular targeting of osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease and a leading cause of adult disability. There is no cure for OA, and no effective treatments which arrest or slow its progression. Current pharmacologic treatments such as analgesics may improve pain relief but do not alter OA disease progression. Prolonged consumption of these drugs can result in severe adverse effects. Given the nature of OA, life-long treatment will likely be required to arrest or slow its progression. Consequently, there is an urgent need for OA disease-modifying therapies which also improve symptoms and are safe for clinical use over long periods of time. Nutraceuticals-food or food products that provide medical or health benefits, including the prevention and/or treatment of a disease-offer not only favorable safety profiles, but may exert disease- and symptom-modification effects in OA. Forty-seven percent of OA patients use alternative medications, including nutraceuticals. This review will overview the efficacy and mechanism of action of commonly used nutraceuticals, discuss recent experimental and clinical data on the effects of select nutraceuticals, such as phytoflavonoids, polyphenols, and bioflavonoids on OA, and highlight their known molecular actions and limitations of their current use. We will conclude with a proposed novel nutraceutical-based molecular targeting strategy for chondroprotection and OA treatment.

Roles of microRNAs in prenatal chondrogenesis, postnatal chondrogenesis and cartilage-related diseases

Cartilage has limited repair and regeneration capacity, thus damage of cartilage often results in its dysfunction and even chronic diseases like osteoarthritis (OA). Chondrogenesis induced by tissue-engineering methods is essential to treating cartilage-related diseases. MicroRNAs (miRNAs) are a class of small non-coding single-stranded RNAs which exert their biological effects by binding to the target messenger RNAs (mRNAs), resulting in decay or translation suppression of target mRNAs. There are emerging evidence indicating that miRNAs may play important roles in regulating both prenatal and postnatal chondrogenesis. During embryonic skeletal development, prenatal chondrogenesis is thought to be a precondition for formation of cartilage in developing limbs. Plenty of studies on different types of stem cells have undoubtedly proven their capacity of differentiating into chondrocytes. MiRNAs are found to comprehensively modulate these processes by establishing an interaction network with target genes, transcription factors and cytokines et al. In addition, translational application of miRNA technology has also been explored. In this review, we focus on the up-dated progress on regulatory mechanisms of miRNAs in prenatal and postnatal chondrogenesis. In addition, several miRNA target genes and roles of miRNAs in cartilage-related diseases are also discussed. This will contribute to studies of chondrogenesis mechanisms and development of new treating methods.

Molecular mechanisms of the cartilage-specific microRNA-140 in osteoarthritis

Osteoarthritis (OA) is the most widespread chronic degenerative joint disorder, characterized by progressive destruction of articular cartilage, subchondral bone alterations, formation of osteophytes and synovitis. MicroRNAs (miRNAs) are a class of endogenous and non-coding single-strand RNAs with a length of about 22 nucleotides, and many of them are evolutionarily conserved. miRNAs have been implicated in the process of development and pathogenesis of diseases, and tissue-specific miRNA functional studies in mice have revealed both pathogenic and protective functions. miRNA-140 (miR-140) was shown to be specifically expressed in cartilage tissues in developing zebrafish and mouse embryos during the development of both long and flat bones. Recently, miR-140 has been reported in many studies to play significant roles in OA pathogenesis. Although the previous results were not always consistent, the molecular mechanisms of the regulation and dual function of miR-140 in cartilage homeostasis and development have been established in previous studies. Further elucidation of the molecular basis of miR-140 will uncover synergistic inhibitory effects of miR-140 and other factors on OA pathogenesis, and provide a novel means of treating OA disease.

Strontium ranelate reduces cartilage degeneration and subchondral bone remodeling in rat osteoarthritis model

AIM

To investigate whether strontium ranelate (SR), a new antiosteoporotic agent, could attenuate cartilage degeneration and subchondral bone remodeling in osteoarthritis (OA).

METHODS

Medial meniscal tear (MMT) operation was performed in adult SD rats to induce OA. SR (625 or 1800 mg·kg(-1)·d(-1)) was administered via gavage for 3 or 6 weeks. After the animals were sacrificed, articular cartilage degeneration was evaluated using toluidine blue O staining, SOX9 immunohistochemistry and TUNEL assay. The changes in microarchitecture indices and tissue mineral density (TMD), chemical composition (mineral-to-collagen ratio), and intrinsic mechanical properties of the subchondral bones were measured using micro-CT scanning, confocal Raman microspectroscopy and nanoindentation testing, respectively.

RESULTS

The high-dose SR significantly attenuated cartilage matrix and chondrocyte loss at 6 weeks, and decreased chondrocyte apoptosis, improved the expression of SOX9, a critical transcription factor responsible for the expression of anabolic genes type II collagen and aggrecan, at both 3 and 6 weeks. Meanwhile, the high-dose SR also significantly attenuated the subchondral bone remodeling at both 3 and 6 weeks, as shown by the improved microarchitecture indices, TMD, mineral-to-collagen ratio and intrinsic mechanical properties. In contrast, the low-dose SR did not significantly change all the detection indices of cartilage and bone at both 3 and 6 weeks.

CONCLUSION

The high-dose SR treatment can reduce articular cartilage degeneration and subchondral bone remodeling in the rat MMT model of OA.

Dkk-1 expression in chondrocytes inhibits experimental osteoarthritic cartilage destruction in mice

OBJECTIVE

Dkk is a family of canonical Wnt antagonists with 4 members (Dkk-1, Dkk-2, Dkk-3, and Dkk-4). We undertook this study to explore the roles of Dkk-1 and Dkk-2 in osteoarthritic (OA) cartilage destruction in mice.

METHODS

Expression of Dkk and other catabolic factors was determined at the messenger RNA and protein levels in human and mouse OA cartilage. Experimental OA in mice was induced by destabilization of the medial meniscus (DMM) or by intraarticular injection of Epas1 adenovirus (AdEPAS-1). The role of Dkk in OA pathogenesis was examined by intraarticular injection of AdDkk-1 or by using chondrocyte-specific Dkk1 (Col2a1-Dkk1)-transgenic mice and Dkk2 (Col2a1-Dkk2)-transgenic mice. Primary culture mouse chondrocytes were also treated with recombinant Dkk proteins.

RESULTS

We found opposite patterns of Dkk1 and Dkk2 expression in human and mouse experimental OA cartilage: Dkk1 was up-regulated and Dkk2 was down-regulated. Overexpression of Dkk1 by intraarticular injection of AdDkk-1 significantly inhibited DMM-induced experimental OA. DMM-induced OA was also significantly inhibited in Col2a1-Dkk1-transgenic mice compared with their wild-type littermates. However, Col2a1-Dkk2-transgenic mice showed no significant difference in OA pathogenesis. Wnt-3a, which activates the canonical Wnt pathway, induced Mmp13 and Adamts4 expression in primary culture chondrocytes, an effect that was significantly inhibited by Dkk-1 pretreatment or Dkk1 overexpression.

CONCLUSION

Our findings indicate that expression of Dkk1, but not Dkk2, in chondrocytes inhibits OA cartilage destruction. The protective effect of Dkk-1 appears to be associated with its capacity to inhibit Wnt-mediated expression of catabolic factors, such as Mmp13, providing evidence that Dkk-1 might serve as a therapeutic target for OA treatment.

Macro view of microRNA function in osteoarthritis

Osteoarthritis (OA), the most common musculoskeletal disorder, is complex, multifaceted, and characterized by degradation of articular cartilage and alterations in other joint tissues. Although some pathogenic pathways have been characterized, current knowledge is incomplete and effective approaches to the prevention or treatment of OA are lacking. Understanding novel molecular mechanisms that are involved in the maintenance and destruction of articular cartilage, including extracellular regulators and intracellular signalling mechanisms in joint cells that control cartilage homeostasis, has the potential to identify new therapeutic targets in OA. MicroRNAs control tissue development and homeostasis by fine-tuning gene expression, with expression patterns specific to tissues and developmental stages, and are increasingly implicated in the pathogenesis of complex diseases such as cancer and cardiovascular disorders. The emergent roles of microRNAs in cartilage homeostasis and OA pathogenesis are summarized in this Review, alongside potential clinical applications.

An assessment of the chondroprotective effects of intra-articular application of statin and tetracycline on early-stage experimental osteoarthritis

Objectives. To compare the effects of intra-articular application of statin and tetracyclines on cartilage and synovial tissue on experimental osteoarthritis. Methods. Osteoarthritis was created in 30 rabbits of 3 groups. The control group received saline intra-articularly, statin group, atorvastatin and the tetracycline group, doxycycline once a week for 3 weeks. Chondral and synovial tissues were evaluated macroscopically and histopathologically. Results. Macroscopic evaluation determined mean values of control group 3.0, statin group 0.56, and tetracycline group 2.5. Histopathological evaluations determined mean values; femoral medial condyle cartilage tissue, control group, 14.60 ± 1.00, statin group 2.20 ± 1.30, tetracycline group 12.7 ± 5.39: tibia medial plateau, control group, 14.33 ± 8.68, statin group 2.89 ± 1.96, tetracycline group, 15.90 ± 7.03: synovial tissue, control group 12.22 ± 3.63, statin group 4.33 ± 2.69, tetracycline group 10.70 ± 2.62. Average values of synovial tissue cell layer thickness were control group 14.46 ± 2.35 μm, statin group 10.56 ± 1.01 μm, tetracycline group 12.80 ± 0.79 μm. All measurements showed statistically significant differences between statin and control groups (P < 0.05) but not between tetracycline and control groups (P > 0.05). Conclusions. Tetracycline has little effect due to chemical modification requirement, and the effect is dose dependent. Statins have chondroprotective effects, so may become a novel therapeutic agent in osteoarthritis management after chemical processing.

IGF-1 and PDGF-bb suppress IL-1β-induced cartilage degradation through down-regulation of NF-κB signaling: involvement of Src/PI-3K/AKT pathway

Objective

Interleukin-1β (IL-1β) is a pro-inflammatory cytokine that plays a key role in the pathogenesis of osteoarthritis (OA). Growth factors (GFs) capable of antagonizing the catabolic actions of cytokines may have therapeutic potential in the treatment of OA. Herein, we investigated the potential synergistic effects of insulin-like growth factor (IGF-1) and platelet-derived growth factor (PDGF-bb) on different mechanisms participating in IL-1β-induced activation of nuclear transcription factor-κB (NF-κB) and apoptosis in chondrocytes.

Methods

Primary chondrocytes were treated with IL-1β to induce dedifferentiation and co-treated with either IGF-1 or/and PDGF-bb and evaluated by immunoblotting and electron microscopy.

Results

Pretreatment of chondrocytes with IGF-1 or/and PDGF-bb suppressed IL-1β-induced NF-κB activation via inhibition of IκB-α kinase. Inhibition of IκB-α kinase by GFs led to the suppression of IκB-α phosphorylation and degradation, p65 nuclear translocation and NF-κB-regulated gene products involved in inflammation and cartilage degradation (COX-2, MMPs) and apoptosis (caspase-3). GFs or BMS-345541 (specific inhibitor of the IKK) reversed the IL-1β-induced down-regulation of collagen type II, cartilage specific proteoglycans, β1-integrin, Shc, activated MAPKinase, Sox-9 and up-regulation of active caspase-3. Furthermore, the inhibitory effects of IGF-1 or/and PDGF-bb on IL-1β-induced NF-κB activation were sensitive to inhibitors of Src (PP1), PI-3K (wortmannin) and Akt (SH-5), suggesting that the pathway consisting of non-receptor tyrosine kinase (Src), phosphatidylinositol 3-kinase and protein kinase B must be involved in IL-1β signaling.

Conclusion

The results presented suggest that IGF-1 and PDGF-bb are potent inhibitors of IL-1β-mediated activation of NF-κB and apoptosis in chondrocytes, may be mediated in part through suppression of Src/PI-3K/AKT pathway, which may contribute to their anti-inflammatory effects.

Hypoxia-inducible factor-2α regulates Fas-mediated chondrocyte apoptosis during osteoarthritic cartilage destruction

Apoptosis of articular chondrocytes is associated with the pathogenesis of osteoarthritis (OA). Recently, we demonstrated that hypoxia-inducible factor (HIF)-2α, encoded by Epas1, causes OA cartilage destruction by regulating the expression of various matrix-degrading enzymes. Here, we investigated the involvement of HIF-2α in chondrocyte apoptosis and OA cartilage destruction. HIF-2α levels in human and mouse OA chondrocytes were markedly elevated in association with increased apoptosis of articular chondrocytes. Overexpression or knockdown of HIF-2α alone did not cause chondrocyte apoptosis. However, HIF-2α expression markedly increased chondrocyte apoptosis in the presence of an agonistic anti-Fas (CD95) antibody. HIF-2α enhanced Fas expression and potentiated downstream signaling pathways, increasing the activity of initiator and executioner caspases. Overexpression of HIF-2α in mouse cartilage tissue, either by intra-articular injection of Epas1 adenovirus (Ad-Epas1) or in the context of chondrocyte-specific Epas1 transgenic mice, increased chondrocyte apoptosis and cartilage destruction. In contrast, chondrocyte-specific knockout of Epas1 in mice suppressed DMM (destabilization of the medial meniscus)-induced chondrocyte apoptosis and inhibited OA cartilage destruction. Moreover, Fas-deficient mice exhibited diminished chondrocyte apoptosis and OA cartilage destruction in response to Ad-Epas1 injection or DMM surgery. Taken together, our results demonstrate that HIF-2α potentiates Fas-mediated chondrocyte apoptosis, which is associated with OA cartilage destruction.

Laser-induced regeneration of cartilage

Laser radiation provides a means to control the fields of temperature and thermo mechanical stress, mass transfer, and modification of fine structure of the cartilage matrix. The aim of this outlook paper is to review physical and biological aspects of laser-induced regeneration of cartilage and to discuss the possibilities and prospects of its clinical applications. The problems and the pathways of tissue regeneration, the types and features of cartilage will be introduced first. Then we will review various actual and prospective approaches for cartilage repair; consider possible mechanisms of laser-induced regeneration. Finally, we present the results in laser regeneration of joints and spine disks cartilages and discuss some future applications of lasers in regenerative medicine.

Endoplasmic reticulum stress (ER-stress) by 2-deoxy-D-glucose (2DG) reduces cyclooxygenase-2 (COX-2) expression and N-glycosylation and induces a loss of COX-2 activity via a Src kinase-dependent pathway in rabbit articular chondrocytes

Endoplasmic reticulum (ER) stress regulates a wide range of cellular responses including apoptosis, proliferation, inflammation, and differentiation in mammalian cells. In this study, we observed the role of 2-deoxy-D-glucose (2DG) on inflammation of chondrocytes. 2DG is well known as an inducer of ER stress, via inhibition of glycolysis and glycosylation. Treatment of 2DG in chondrocytes considerably induced ER stress in a dose- and time-dependent manner, which was demonstrated by a reduction of glucose regulated protein of 94 kDa (grp94), an ER stress-inducible protein, as determined by a Western blot analysis. In addition, induction of ER stress by 2DG led to the expression of COX-2 protein with an apparent molecular mass of 66-70kDa as compared with the normally expressed 72-74 kDa protein. The suppression of ER stress with salubrinal (Salub), a selective inhibitor of eif2-alpha dephosphorylation, successfully prevented grp94 induction and efficiently recovered 2DG- modified COX-2 molecular mass and COX-2 activity might be associated with COX-2 N-glycosylation. Also, treatment of 2DG increased phosphorylation of Src in chondrocytes. The inhibition of the Src signaling pathway with PP2 (Src tyrosine kinase inhibitor) suppressed grp94 expression and restored COX-2 expression, N-glycosylation, and PGE2 production, as determined by a Western blot analysis and PGE2 assay. Taken together, our results indicate that the ER stress induced by 2DG results in a decrease of the transcription level, the molecular mass, and the activity of COX-2 in rabbit articular chondrocytes via a Src kinase-dependent pathway.

Cytokine-like 1 knock-out mice (Cytl1-/-) show normal cartilage and bone development but exhibit augmented osteoarthritic cartilage destruction

We have shown that cytokine-like 1 (Cytl1) is a novel autocrine regulatory factor that regulates chondrogenesis of mouse mesenchymal cells (Kim, J. S., Ryoo, Z. Y., and Chun, J. S. (2007) J. Biol. Chem. 282, 29359-29367). In this previous work, we found that Cytl1 expression was very low in mesenchymal cells, increased dramatically during chondrogenesis, and decreased during hypertrophic maturation, both in vivo and in vitro. Moreover, exogenous addition or ectopic expression of Cytl1 caused chondrogenic differentiation of mouse limb bud mesenchymal cells. In the current study, we generated a Cytl1 knock-out (Cytl1(-/-)) mouse to investigate the in vivo role of Cytl1. Deletion of the Cytl1 gene did not affect chondrogenesis or cartilage development. Cytl1(-/-) mice also showed normal endochondral ossification and long bone development. Additionally, ultrastructural features of articular cartilage, such as matrix organization and chondrocyte morphology, were similar in wild-type and Cytl1(-/-) mice. However, Cytl1(-/-) mice were more sensitive to osteoarthritic (OA) cartilage destruction. Compared with wild-type littermates, Cytl1(-/-) mice showed more severe OA cartilage destruction upon destabilization of the medial meniscus of mouse knee joints. In addition, expression levels of Cytl1 were markedly decreased in OA cartilage of humans and experimental mice. Taken together, our results suggest that, rather than regulating cartilage and bone development, Cytl1 is required for the maintenance of cartilage homeostasis, and loss of Cytl1 function is associated with experimental OA cartilage destruction in mice.

Enhanced apoptotic and reduced protective response in chondrocytes following endoplasmic reticulum stress in osteoarthritic cartilage

Endoplasmic reticulum (ER) stress has been shown to participate in many disease pathologies. Although recent reports have demonstrated that ER stress in chondrocytes is present in human osteoarthritis (OA), its role in the pathology of cartilage degeneration, such as chondrocyte apoptosis, remains unclear. In the present study, we investigated the expression of phosphorylated PERK (pPERK), ubiquitin (Ub), GRP78, CHOP, phosphorylated JNK (pJNK) and cleaved caspase-3 (C-CASP3) and the mRNA splicing of XBP1 (XBP1 splicing) in human OA cartilage by immunohistochemistry and RT-PCR. Additionally, human chondrocytes were treated with several concentrations of tunicamycin, an ER stress inducer, to assess the impact of ER stress on the mRNA expression of CHOP, XBP1 splicing and apoptosis, as determined by real-time PCR, RT-PCR and ELISA analyses respectively. In human OA cartilage, the number of chondrocytes expressing pPERK, Ub, CHOP and pJNK positively correlated with cartilage degeneration and the number of C-CASP3-positive chondrocytes. XBP1 splicing and GRP78 expression in severe OA containing the greatest number of C-CASP3-positive chondrocytes were similar to the levels in mild OA, however, XBP1 splicing was higher in moderate OA than in mild and severe OA. Tunicamycin dose dependently increased CHOP expression and apoptosis of cultured chondrocytes. Although tunicamycin upregulated XBP1 splicing in cultured chondrocytes, its impact on XBP1 splicing was weakened at higher concentrations. In conclusion, the present results indicate that ER stress may contribute to chondrocyte apoptosis along with OA progression, which was closely associated with an enhanced apoptotic response and a reduced protective response by the cells.

Requirement of the NF-κB pathway for induction of Wnt-5A by interleukin-1β in condylar chondrocytes of the temporomandibular joint: functional crosstalk between the Wnt-5A and NF-κB signaling pathways

OBJECTIVE

We have previously reported that interleukin-1β (IL-1β) up-regulates the expression of Wnt-5A and the activation of Wnt-5A signaling induces matrix metalloproteinase (MMP) through the c-Jun N-terminal kinase pathway in condylar chondrocytes (CCs) of the temporomandibular joint (TMJ). These results suggest that Wnt-5A could play an essential role in IL-1β-mediated cartilage destruction. The objective of this study was to investigate the molecular mechanism underlying IL-1β-induced up-regulation of Wnt-5A in TMJ CCs.

METHODS

Primary CCs, limb chondrocytes (LCs) and SW1353 human chondrosarcoma cells were treated with IL-1β in the presence or absent of BAY 11-7082 (an inhibitor of IκBα-phosphorylation). Then, expression of Wnt-5A was estimated by real-time reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting and immunocytofluorescence. Transient transfection of p65 expression vector and chromatin immunoprecipitation (ChIP) assay was performed to define the effect of p65 on Wnt-5A expression.

RESULTS

IL-1β up-regulated Wnt-5A expression at both the RNA and protein levels in articular chondrocytes. The inhibitor of IκBα-phosphorylation, BAY 11-7082, blocked the induction of Wnt-5A by IL-1β in a dose-dependent manner. Moreover, experiments with overexpression of p65 and ChIP established that induction of Wnt-5A by IL-1β is mediated through the NF-κB pathway, especially the p65 subunit.

CONCLUSION

These results clarify the molecular mechanism underlying up-regulation of Wnt-5A by IL-1β in chondrocytes, suggesting an important functional crosstalk between Wnt-5A and NF-κB signaling pathways. This finding provides new insights into the involvement of Wnt signaling in the cartilage destruction caused by arthritis.

Aberrant hypertrophy in Smad3-deficient murine chondrocytes is rescued by restoring transforming growth factor beta-activated kinase 1/activating transcription factor 2 signaling: a potential clinical implication for osteoarthritis

OBJECTIVE

To investigate the biologic significance of Smad3 in the progression of osteoarthritis (OA), the crosstalk between Smad3 and activating transcription factor 2 (ATF-2) in the transforming growth factor beta (TGFbeta) signaling pathway, and the effects of ATF-2 overexpression and p38 activation in chondrocyte differentiation.

METHODS

Joint disease in Smad3-knockout (Smad3(-/-)) mice was examined by microfocal computed tomography and histologic analysis. Numerous in vitro methods including immunostaining, real-time polymerase chain reaction, Western blotting, an ATF-2 DNA-binding assay, and a p38 kinase activity assay were used to study the various signaling responses and protein interactions underlying the altered chondrocyte phenotype in Smad3(-/-) mice.

RESULTS

In Smad3(-/-) mice, an end-stage OA phenotype gradually developed. TGFbeta-activated kinase 1 (TAK1)/ATF-2 signaling was disrupted in Smad3(-/-) mouse chondrocytes at the level of p38 MAP kinase (MAPK) activation, resulting in reduced ATF-2 phosphorylation and transcriptional activity. Reintroduction of Smad3 into Smad3(-/-) cells restored the normal p38 response to TGFbeta. Phosphorylated p38 formed a complex with Smad3 by binding to a portion of Smad3 containing both the MAD homology 1 and linker domains. Additionally, Smad3 inhibited the dephosphorylation of p38 by MAPK phosphatase 1 (MKP-1). Both ATF-2 overexpression and p38 activation repressed type X collagen expression in wild-type and Smad3(-/-) chondrocytes. P38 was detected in articular cartilage and perichondrium; articular and sternal chondrocytes expressed p38 isoforms alpha, beta, and gamma, but not delta.

CONCLUSION

Smad3 is involved in both the onset and progression of OA. Loss of Smad3 abrogates TAK1/ATF-2 signaling, most likely by disrupting the Smad3-phosphorylated p38 complex, thereby promoting p38 dephosphorylation and inactivation by MKP-1. ATF-2 and p38 activation inhibit chondrocyte hypertrophy. Modulation of p38 isoform activity may provide a new therapeutic approach for OA.

Chondrocytes from patients with osteoarthritis express typical extracellular matrix molecules once grown onto a three-dimensional hyaluronan-based scaffold

The opportunity to apply autologous chondrocyte transplantation in repairing cartilage lesions in osteoarthritis (OA) is of great interest. To this end, chondrocytes from cartilage of these patients and from healthy donors were used to evaluate the expression of some extracellular matrix molecules once these cells were grown onto a hyaluronan-based scaffold already used in clinical practice. Constructs were analyzed by immunohistochemical and real-time PCR analyses. Chondrocytes from control and patients with OA cartilages expressed the same extracellular matrix molecules even if at different amount. These differences, which were appreciable both at protein and molecular levels, were not evident once the cells were grown onto Hyaff-11 scaffold. In this experimental culture condition, the cells derived from control and patients with OA showed a significant increase of collagen type II, Sox-9, and aggrecan and a decrease of collagen type I compared with chondrocytes grown in monolayer. On the other hand, MMPs were downregulated in both the cell types evaluated by the specific action of TIMP-1 which was highly expressed at molecular and protein levels in the two groups. The growth of chondrocytes onto Hyaff-11 membrane seems to erase the differences between the cells derived from normal and OA cartilages. The cells seem to benefit of the "hyaluronan" presence which is able to create an ideal environment for the expression of cartilage genes even in absence of specific growth factors. This is of particular relevance hypothesizing the use of tissue engineering therapeutical approach also in patients with OA.

MicroRNA-140 plays dual roles in both cartilage development and homeostasis

Osteoarthritis (OA), the most prevalent aging-related joint disease, is characterized by insufficient extracellular matrix synthesis and articular cartilage degradation, mediated by several proteinases, including Adamts-5. miR-140 is one of a very limited number of noncoding microRNAs (miRNAs) specifically expressed in cartilage; however, its role in development and/or tissue maintenance is largely uncharacterized. To examine miR-140 function in tissue development and homeostasis, we generated a mouse line through a targeted deletion of miR-140. miR-140(-/-) mice manifested a mild skeletal phenotype with a short stature, although the structure of the articular joint cartilage appeared grossly normal in 1-mo-old miR-140(-/-) mice. Interestingly, miR-140(-/-) mice showed age-related OA-like changes characterized by proteoglycan loss and fibrillation of articular cartilage. Conversely, transgenic (TG) mice overexpressing miR-140 in cartilage were resistant to antigen-induced arthritis. OA-like changes in miR-140-deficient mice can be attributed, in part, to elevated Adamts-5 expression, regulated directly by miR-140. We show that miR-140 regulates cartilage development and homeostasis, and its loss contributes to the development of age-related OA-like changes.

MicroRNA-140 is expressed in differentiated human articular chondrocytes and modulates interleukin-1 responses

OBJECTIVE

MicroRNA (miRNA) are a class of noncoding small RNAs that act as negative regulators of gene expression. MiRNA exhibit tissue-specific expression patterns, and changes in their expression may contribute to pathogenesis. The objectives of this study were to identify miRNA expressed in articular chondrocytes, to determine changes in osteoarthritic (OA) cartilage, and to address the function of miRNA-140 (miR-140).

METHODS

To identify miRNA specifically expressed in chondrocytes, we performed gene expression profiling using miRNA microarrays and quantitative polymerase chain reaction with human articular chondrocytes compared with human mesenchymal stem cells (MSCs). The expression pattern of miR-140 was monitored during chondrogenic differentiation of human MSCs in pellet cultures and in human articular cartilage from normal and OA knee joints. We tested the effects of interleukin-1beta (IL-1beta) on miR-140 expression. Double-stranded miR-140 (ds-miR-140) was transfected into chondrocytes to analyze changes in the expression of genes associated with OA.

RESULTS

Microarray analysis showed that miR-140 had the largest difference in expression between chondrocytes and MSCs. During chondrogenesis, miR-140 expression in MSC cultures increased in parallel with the expression of SOX9 and COL2A1. Normal human articular cartilage expressed miR-140, and this expression was significantly reduced in OA tissue. In vitro treatment of chondrocytes with IL-1beta suppressed miR-140 expression. Transfection of chondrocytes with ds-miR-140 down-regulated IL-1beta-induced ADAMTS5 expression and rescued the IL-1beta-dependent repression of AGGRECAN gene expression.

CONCLUSION

This study shows that miR-140 has a chondrocyte differentiation-related expression pattern. The reduction in miR-140 expression in OA cartilage and in response to IL-1beta may contribute to the abnormal gene expression pattern characteristic of OA.