Transcriptomic analyses of joint tissues during osteoarthritis development in a rat model reveal dysregulated mechanotransduction and extracellular matrix pathways.

OBJECTIVE: Transcriptomic changes in joint tissues during the development of osteoarthritis (OA) are of interest for the discovery of biomarkers and mechanisms of disease. The objective of this study was to use the rat medial meniscus transection (MMT) model to discover stage and tissue-specific transcriptomic changes. DESIGN: Sham or MMT surgeries were performed in mature rats. Cartilage, menisci and synovium were scored for histopathological changes at 2, 4 and 6 weeks post-surgery and processed for RNA-sequencing. Differentially expressed genes (DEG) were used to identify pathways and mechanisms. Published transcriptomic datasets from animal models and human OA were used to confirm and extend present findings. RESULTS: The total number of DEGs was already high at 2 weeks (723 in meniscus), followed by cartilage (259) and synovium (42) and declined to varying degrees in meniscus and synovium but increased in cartilage at 6 weeks. The most upregulated genes included tenascins. The 'response to mechanical stimulus' and extracellular matrix-related pathways were enriched in both cartilage and meniscus. Pathways that were enriched in synovium at 4 weeks indicate processes related to synovial hyperplasia and fibrosis. Synovium also showed upregulation of IL-11 and several MMPs. The mechanical stimulus pathway included upregulation of the mechanoreceptors PIEZO1, PIEZO2 and TRPV4 and nerve growth factor. Analysis of data from prior RNA-sequencing studies of animal models and human OA support these findings. CONCLUSION: These results indicate several shared pathways that are affected during OA in cartilage and meniscus and support the role of mechanotransduction and other pathways in OA pathogenesis.

TGFß1 signaling protects chondrocytes against oxidative stress via FOXO1-autophagy axis.

OBJECTIVE: The forkhead box O1 (FOXO1) transcription factor is a key regulator of autophagy. In chondrocytes, reduced FOXO1 expression with aging causes osteoarthritis due to dysfunction of autophagy, but the mechanisms underlying regulation of FOXO1 expression and the reduction in expression with aging remain unclear. We investigated the mechanism by which transforming growth factor ß1 (TGFß1) signaling regulates the FOXO1-autophagy axis. METHODS: Expression of FOXO1 was measured in chondrocytes after TGFß1 treatment. Immunohistochemistry was performed to estimate the levels of activin receptor-like kinase 5 (ALK5) and FOXO1 in the knee joints of young, middle-aged and old mice. The effects of the ALK5 inhibitor and SMAD3 or SMAD2 knockdown on FOXO1 expression were evaluated. The role of TGFß1 in autophagy after hydrogen peroxide (H2O2) treatment was analyzed. The protective effect of TGFß1 against H2O2 treatment was assessed by cell viability assay and TUNEL assay. RESULTS: TGFß1 promoted the expression of FOXO1 mRNA and protein. Both ALK5 and FOXO1 expression decreased with aging. ALK5 inhibition and SMAD3 knockdown suppressed induction of FOXO1 expression by TGFß1, whereas SMAD2 knockdown increased it. TGFß1 promoted the expression of microtubule-associated proteins 1A/1B light chain 3B (LC3)-I protein via the SMAD3-FOXO1 pathway. Furthermore, under H2O2 treatment, TGFß1 promoted expression of LC3-II. TGFß1 pretreatment suppressed cell death of chondrocytes following H2O2 treatment, but this protective effect was abolished by FOXO1 knockdown. CONCLUSIONS: TGFß1 protects chondrocytes against oxidative stress via the FOXO1-autophagy axis, and a reduction in ALK5 expression might cause reduced FOXO1 expression with aging.

Characterization of synovial fluid metabolomic phenotypes of cartilage morphological changes associated with osteoarthritis.

OBJECTIVE: Osteoarthritis (OA) is a multifactorial disease with etiological heterogeneity. The objective of this study was to classify OA subgroups by generating metabolomic phenotypes from human synovial fluid. DESIGN: Post mortem synovial fluids (n = 75) were analyzed by high performance-liquid chromatography mass spectrometry (LC-MS) to measure changes in the global metabolome. Comparisons of healthy (grade 0), early OA (grades I-II), and late OA (grades III-IV) donor populations were considered to reveal phenotypes throughout disease progression. RESULTS: Global metabolomic profiles in synovial fluid were distinct between healthy, early OA, and late OA donors. Pathways differentially activated among these groups included structural deterioration, glycerophospholipid metabolism, inflammation, central energy metabolism, oxidative stress, and vitamin metabolism. Within disease states (early and late OA), subgroups of donors revealed distinct phenotypes. Synovial fluid metabolomic phenotypes exhibited increased inflammation (early and late OA), oxidative stress (late OA), or structural deterioration (early and late OA) in the synovial fluid. CONCLUSION: These results revealed distinct metabolic phenotypes in human synovial fluid, provide insight into pathogenesis, represent novel biomarkers, and can move toward developing personalized interventions for subgroups of OA patients.

Identification of transcription factors responsible for dysregulated networks in human osteoarthritis cartilage by global gene expression analysis.

OBJECTIVE: Osteoarthritis (OA) is the most prevalent joint disease. As disease-modifying therapies are not available, novel therapeutic targets need to be discovered and prioritized for their importance in mediating the abnormal phenotype of cells in OA-affected joints. Here, we generated a genome-wide molecular profile of OA to elucidate regulatory mechanisms of OA pathogenesis and to identify possible therapeutic targets using integrative analysis of mRNA-sequencing data obtained from human knee cartilage. DESIGN: RNA-sequencing (RNA-seq) was performed on 18 normal and 20 OA human knee cartilage tissues. RNA-seq datasets were analysed to identify genes, pathways and regulatory networks that were dysregulated in OA. RESULTS: RNA-seq data analysis revealed 1332 differentially expressed (DE) genes between OA and non-OA samples, including known and novel transcription factors (TFs). Pathway analysis identified 15 significantly perturbed pathways in OA with ECM-related, PI3K-Akt, HIF-1, FoxO and circadian rhythm pathways being the most significantly dysregulated. We selected DE TFs that are enriched for regulating DE genes in OA and prioritized these TFs by creating a cartilage-specific interaction subnetwork. This analysis revealed eight TFs, including JUN, Early growth response (EGR)1, JUND, FOSL2, MYC, KLF4, RELA, and FOS that both target large numbers of dysregulated genes in OA and are themselves suppressed in OA. CONCLUSIONS: We identified a novel subnetwork of dysregulated TFs that represent new mediators of abnormal gene expression and promising therapeutic targets in OA.

Compromised autophagy precedes meniscus degeneration and cartilage damage in mice.

OBJECTIVE: Autophagy is a cellular homeostasis mechanism that facilitates normal cell function and survival. Objectives of this study were to determine associations between autophagic responses with meniscus injury, joint aging, and osteoarthritis (OA), and to establish the temporal relationship with structural changes in menisci and cartilage. METHODS: Constitutive activation of autophagy during aging was measured in GFP-LC3 transgenic reporter mice between 6 and 30 months. Meniscus injury was created by surgically destabilizing the medial meniscus (DMM) to induce posttraumatic OA in C57BL/6J mice. Levels of autophagy proteins and activation were analyzed by confocal microscopy and immunohistochemistry. Associated histopathological changes, such as cellularity, matrix staining, and structural damage, were graded in the meniscus and compared to changes in articular cartilage. RESULTS: In C57BL/6J mice, basal autophagy was lower in the meniscus than in articular cartilage. With increasing age, expression of the autophagy proteins ATG5 and LC3 was significantly reduced by 24 months. Age-related changes included abnormal Safranin-O staining and reduced cellularity, which preceded structural damage in the meniscus and articular cartilage. In mice with DMM, autophagy was induced in the meniscus while it was suppressed in cartilage. Articular cartilage exhibited the most profound changes in autophagy and structure that preceded meniscus degeneration. Systemic administration of rapamycin to mice with DMM induced autophagy activation in cartilage and reduced degenerative changes in both meniscus and cartilage. CONCLUSION: Autophagy is significantly affected in the meniscus during aging and injury and precedes structural damage. Maintenance of autophagic activity appears critical for meniscus and cartilage integrity.

Suppression of Sestrins in aging and osteoarthritic cartilage: dysfunction of an important stress defense mechanism.

OBJECTIVES: Aging is an important osteoarthritis (OA) risk factor and compromised stress defense responses may mediate this risk. The Sestrins (Sesn) promote cell survival under stress conditions and regulate AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) signaling. This study examined Sesn expression in normal and OA cartilage and functions of Sesn in chondrocytes. METHODS: Sesn expression in human and mouse normal and OA cartilage was analyzed by quantitative polymerase chain reaction (PCR) and immunohistochemistry. Sesn function was investigated by using small interfering RNA (siRNA) mediated Sesn knockdown and overexpression with analysis of cell survival, gene expression, autophagy, and AMPK and mTOR activation. RESULTS: Sesn mRNA levels were significantly reduced in human OA cartilage and immunohistochemistry of human and mouse OA cartilage also showed a corresponding reduction in protein levels. In cultured human chondrocytes Sesn1, 2 and 3 were expressed and increased by tunicamycin, an endoplasmic reticulum (ER) stress response inducer and 2-deoxyglucose (2DG), a metabolic stress inducer. Sesn1 and 2 were increased by tBHP, an oxidative stress inducer. Sesn knockdown by siRNA reduced chondrocyte viability under basal culture conditions and in the presence of 2DG. Sesn overexpression enhanced LC3-II formation and autophagic flux, and this was related to changes in mTOR but not AMPK activation. CONCLUSION: These findings are the first to show that Sesn expression is suppressed in OA affected cartilage. Sesn support chondrocyte survival under stress conditions and promote autophagy activation through modulating mTOR activity. Suppression of Sesn in OA cartilage contributes to deficiency in an important cellular homeostasis mechanism.

Dysregulated circadian rhythm pathway in human osteoarthritis: NR1D1 and BMAL1 suppression alters TGF-ß signaling in chondrocytes.

OBJECTIVES: Circadian rhythm (CR) was identified by RNA sequencing as the most dysregulated pathway in human osteoarthritis (OA) in articular cartilage. This study examined circadian rhythmicity in cultured chondrocytes and the role of the CR genes NR1D1 and BMAL1 in regulating chondrocyte functions. METHODS: RNA was extracted from normal and OA-affected human knee cartilage (n = 14 each). Expression levels of NR1D1 and BMAL1 mRNA and protein were assessed by quantitative PCR and immunohistochemistry. Human chondrocytes were synchronized and harvested at regular intervals to examine circadian rhythmicity in RNA and protein expression. Chondrocytes were treated with small interfering RNA (siRNA) for NR1D1 or BMAL1, followed by RNA sequencing and analysis of the effects on the transforming growth factor beta (TGF-ß) pathway. RESULTS: NR1D1 and BMAL1 mRNA and protein levels were significantly reduced in OA compared to normal cartilage. In cultured human chondrocytes, a clear circadian rhythmicity was observed for NR1D1 and BMAL1. Increased BMAL1 expression was observed after knocking down NR1D1, and decreased NR1D1 levels were observed after knocking down BMAL1. Sequencing of RNA from chondrocytes treated with NR1D1 or BMAL1 siRNA identified 330 and 68 significantly different genes, respectively, and this predominantly affected the TGF-ß signaling pathway. CONCLUSIONS: The CR pathway is dysregulated in OA cartilage. Interference with circadian rhythmicity in cultured chondrocytes affects TGF-ß signaling, which is a central pathway in cartilage homeostasis.

Suppression of REDD1 in osteoarthritis cartilage, a novel mechanism for dysregulated mTOR signaling and defective autophagy.

OBJECTIVE: Aging is a main risk factor for the development of osteoarthritis (OA) and the molecular mechanisms underlying the aging-related changes in articular cartilage include increased mammalian target of rapamycin (mTOR) signaling and defective autophagy. REDD1 is an endogenous inhibitor of mTOR that regulates cellular stress responses. In this study we measured REDD1 expression in normal, aged and OA cartilage and assessed REDD1 function in human and mouse articular chondrocytes. METHODS: REDD1 expression was analyzed in human and mouse articular cartilage by qPCR, western blotting, and immunohistochemistry. For functional studies, REDD1 and TXNIP knockdown or overexpression was performed in chondrocytes in the presence or absence of rapamycin and chloroquine, and mTOR signaling and autophagy were measured by western blotting. REDD1/TXNIP protein interaction was assessed by co-immunoprecipitation experiments. RESULTS: Human and mouse cartilage from normal knee joints expressed high levels of REDD1. REDD1 expression was significantly reduced in aged and OA cartilage. In cultured chondrocytes, REDD1 knockdown increased whereas REDD1 overexpression decreased mTOR signaling. In addition, REDD1 activated autophagy by an mTOR independent mechanism that involved protein/protein interaction with TXNIP. The REDD1/TXNIP complex was required for autophagy activation in chondrocytes. CONCLUSION: The present study shows that REDD1 is highly expressed in normal human articular cartilage and reduced during aging and OA. REDD1 in human chondrocytes negatively regulates mTOR activity and is essential for autophagy activation. Reduced REDD1 expression thus represents a novel mechanism for the increased mTOR activation and defective autophagy observed in OA.

MicroRNA-155 suppresses autophagy in chondrocytes by modulating expression of autophagy proteins.

OBJECTIVE: Autophagy dysfunction has been reported in osteoarthritis (OA) cartilage. The objective of this study was to investigate the role of microRNA-155 (miR-155), which is overexpressed in OA, in the regulation of autophagy in human chondrocytes. DESIGN: Rapamycin (50 nM) and 2-deoxyglucose (2-DG) (5 mM) were used to stimulate autophagy in primary human articular chondrocytes and in the T/C28a2 human chondrocyte cell line. Cells were transfected with LNA GapmeR or mimic specific for miR-155 and autophagy flux was assessed by LC3 western blotting and by Cyto-ID(®) dye quantification in autophagic vacuoles. Expression of predicted miR-155 targets in the autophagy pathway were analyzed by real-time PCR and western blotting. RESULTS: Autophagy flux induced by rapamycin and 2-DG was significantly increased by miR-155 LNA, and significantly decreased after miR-155 mimic transfection in T/C28a2 cells and in human primary chondrocytes. These effects of miR-155 on autophagy were related to suppression of gene and protein expression of key autophagy regulators including Ulk1, FoxO3, Atg14, Atg5, Atg3, Gabarapl1, and Map1lc3. CONCLUSION: MiR-155 is an inhibitor of autophagy in chondrocytes and contributes to the autophagy defects in OA.

Histopathological analyses of murine menisci: implications for joint aging and osteoarthritis.

OBJECTIVE: To establish a standardized protocol for histopathological assessment of murine menisci that can be applied to evaluate transgenic, knock-out/in, and surgically induced OA models. METHODS: Knee joints from C57BL/6J mice (6-36 months) as well as from mice with surgically-induced OA were processed and cut into sagittal sections. All sections included the anterior and posterior horns of the menisci and were graded for (1) surface integrity, (2) cellularity, (3) Safranin-O staining distribution and intensity. Articular cartilage in the knee joints was also scored. RESULTS: The new histopathological grading system showed good inter- and intra-class correlation coefficients. The major age-related changes in murine menisci in the absence of OA included decreased Safranin O staining intensity, abnormal cell distribution and the appearance of acellular areas. Menisci from mice with surgically-induced OA showed severe fibrillations, partial/total loss of tissue, and calcifications. Abnormal cell arrangements included both regional hypercellularity and hypocellularity along with hypertrophy and cell clusters. In general, the posterior horns were less affected by age and OA. CONCLUSION: A new standardized protocol and histopathological grading system has been developed and validated to allow for a comprehensive, systematic evaluation of changes in aging and OA-affected murine menisci. This system was developed to serve as a standardized technique and tool for further studies in murine meniscal pathophysiology models.

Dysregulated FOXO transcription factors in articular cartilage in aging and osteoarthritis.

OBJECTIVE: Aging is a major risk factor for osteoarthritis (OA). Forkhead-box class O (FoxO) transcription factors regulate mechanisms of cellular aging, including protein quality control, autophagy and defenses against oxidative stress. The objective of this study was to analyze FoxO transcription factors in normal, aging and OA cartilage. DESIGN: Knee joints from humans ages 23-90 and from mice at the age of 4-24 months and following surgically induced OA were analyzed for expression of FoxO proteins. Regulation of FoxO protein expression and activation was analyzed in cultured chondrocytes. RESULTS: Human cartilage expressed FOXO1 and FOXO3 but not FOXO4 proteins. FOXO1 and FOXO3 were more strongly expressed the superficial and mid zone as compared to the deep zone and were mainly localized in nuclei. During human joint aging, expression of FOXO1 and FOXO3 was markedly reduced in the superficial zone of cartilage regions exposed to maximal weight bearing. In OA cartilage, chondrocyte clusters showed strong FOXO phosphorylation and cytoplasmic localization. Similar patterns of FOXO expression in normal joints and changes in aging and OA were observed in mouse models. In cultured chondrocytes, IL-1ß and TNF-α suppressed FOXO1, while TGF-ß and PDGF increased FOXO1 and FOXO3 expression. FOXO1 and FOXO3 phosphorylation was increased by IL-1ß, PDGF, bFGF, IGF-1, and the oxidant t-BHP. CONCLUSIONS: Normal articular cartilage has a tissue specific signature of FoxO expression and activation and this is profoundly altered in aging and OA in humans and mice. Changes in FoxO expression and activation may be involved in cartilage aging and OA.

Comparison of cartilage histopathology assessment systems on human knee joints at all stages of osteoarthritis development.

OBJECTIVE: To compare the MANKIN and OARSI cartilage histopathology assessment systems using human articular cartilage from a large number of donors across the adult age spectrum representing all levels of cartilage degradation. DESIGN: Human knees (n=125 from 65 donors; age range 23-92) were obtained from tissue banks. All cartilage surfaces were macroscopically graded. Osteochondral slabs representing the entire central regions of both femoral condyles, tibial plateaus, and the patella were processed for histology and Safranin O - Fast Green staining. Slides representing normal, aged, and osteoarthritis (OA) tissue were scanned and electronic images were scored online by five observers. Statistical analysis was performed for inter- and intra-observer variability, reproducibility and reliability. RESULTS: The inter-observer variability among five observers for the MANKIN system showed a similar good Intra-class correlation coefficient (ICC>0.81) as for the OARSI system (ICC>0.78). Repeat scoring by three of the five readers showed very good agreement (ICC>0.94). Both systems showed a high reproducibility among four of the five readers as indicated by the Spearman's rho value. For the MANKIN system, the surface represented by lesion depth was the parameter where all readers showed an excellent agreement. Other parameters such as cellularity, Safranin O staining intensity and tidemark had greater inter-reader disagreement. CONCLUSION: Both scoring systems were reliable but appeared too complex and time consuming for assessment of lesion severity, the major parameter determined in standardized scoring systems. To rapidly and reproducibly assess severity of cartilage degradation, we propose to develop a simplified system for lesion volume.

Macroscopic and histopathologic analysis of human knee menisci in aging and osteoarthritis.

OBJECTIVE: Meniscus lesions following trauma or associated with osteoarthritis (OA) have been described, yet meniscus aging has not been systematically analyzed. The objectives of this study were to (1) establish standardized protocols for representative macroscopic and microscopic analysis, (2) improve existing scoring systems, and (3) apply these techniques to a large number of human menisci. DESIGN: Medial and lateral menisci from 107 human knees were obtained and cut in two different planes (triangle/cross section and transverse/horizontal section as well) in three separate locations (middle portion, anterior and posterior horns). All sections included vascular and avascular regions and were graded for (1) surface integrity, (2) cellularity, (3) matrix/fiber organization and collagen alignment, and (4) Safranin-O staining intensity. The cartilage in all knee compartments was also scored. RESULTS: The new macroscopic and microscopic grading systems showed high inter-reader and intra-reader intraclass correlation coefficients. The major age-related changes in menisci in joints with no or minimal OA included increased Safranin-O staining intensity, decreased cell density, the appearance of acellular zones, and evidence of mucoid degeneration with some loss of collagen fiber organization. The earliest meniscus changes occurred predominantly along the inner rim. Menisci from OA joints showed severe fibrocartilaginous separation of the matrix, extensive fraying, tears and calcification. Abnormal cell arrangements included decreased cellularity, diffuse hypercellularity along with cellular hypertrophy and abnormal cell clusters. In general, the anterior horns of both medial and lateral menisci were less affected by age and OA. CONCLUSIONS: New standardized protocols and new validated grading systems allowed us to conduct a more systematic evaluation of changes in aging and OA menisci at a macroscopic and microscopic level. Several meniscus abnormalities appear to be specific to aging in the absence of significant OA. With aging the meniscal surface can be intact but abnormal matrix organization and cellularity were observed within the meniscal substance. The increased Safranin-O staining appears to represent a shift from fibroblastic to chondrocytic phenotype during aging and early degeneration.

Differential metabolic effects of glucosamine and N-acetylglucosamine in human articular chondrocytes.

OBJECTIVE: Aminosugars are commonly used to treat osteoarthritis; however, molecular mechanisms mediating their anti-arthritic activities are still poorly understood. This study analyzes facilitated transport and metabolic effects of glucosamine (GlcN) and N-acetylglucosamine (GlcNAc) in human articular chondrocytes. METHODS: Human articular chondrocytes were isolated from knee cartilage. Facilitated transport of glucose, GlcN and GlcNAc was measured by uptake of [3H]2-deoxyglucose, [3H]GlcN and [3H]GlcNAc. Glucose transporter (GLUT) expression was analyzed by Western blotting. Production of sulfated glycosaminoglycans (SGAG) was measured using [(35)S]SO4. Hyaluronan was quantified using hyaluronan binding protein. RESULTS: Chondrocytes actively import and metabolize GlcN but not GlcNAc and this represents a cell-type specific phenomenon. Similar to facilitated glucose transport, GlcN transport in chondrocytes is accelerated by cytokines and growth factors. GlcN non-competitively inhibits basal glucose transport, which in part depends on GlcN-mediated depletion of ATP stores. In IL-1beta-stimulated chondrocytes, GlcN inhibits membrane translocation of GLUT1 and 6, but does not affect the expression of GLUT3. In contrast to GlcN, GlcNAc accelerates facilitated glucose transport. In parallel with the opposing actions of these aminosugars on glucose transport, GlcN inhibits hyaluronan and SGAG synthesis while GlcNAc stimulates hyaluronan synthesis. GlcNAc-accelerated hyaluronan synthesis is associated with upregulation of hyaluronan synthase-2. CONCLUSION: Differences in GlcN and GlcNAc uptake, and their subsequent effects on glucose transport, GLUT expression and SGAG and hyaluronan synthesis, indicate that these two aminosugars have distinct molecular mechanisms mediating their differential biological activities in chondrocytes.

Dynamic compression of chondrocytes induces a Rho kinase-dependent reorganization of the actin cytoskeleton.

The signal transduction mechanisms in chondrocytes that recognize applied forces and elicit the appropriate biochemical cellular responses are not well characterized. A current theory is that the actin cytoskeleton provides an intracellular framework onto which mechanosensation mechanisms are assembled. The actin cytoskeleton is linked to the extracellular matrix at multi-protein complexes called focal adhesions, and evidence exists that focal adhesions mediate the conversion of external physical forces into appropriate biochemical signal transduction events. The Rho GTPases affect the arrangement of actin cytoskeletal structures, and enhance the formation of focal adhesions, which link the cytoskeleton to the extracellular matrix. A major effector pathway downstream of Rho is the activation of Rho kinase (ROCK), which phosphorylates and activates Lim kinase, which in turn phosphorylates and inhibits the actin-depolymerizing protein cofilin. The objectives of this study were threefold: first, to quantify the actin reorganization in response to dynamic compression of agarose-embedded chondrocytes. Second, to test whether Rho kinase is required for the actin cytoskeletal reorganization induced by dynamic compression. Third, to test whether dynamic compression alters the intracellular localization of Rho kinase and actin remodeling proteins in chondrocytes. Dynamic compression of agarose-embedded chondrocytes induced actin cytoskeletal remodeling causing a significant increase in punctate F-actin structures. Rho kinase activity was required for these cytoskeletal changes. Dynamic compression increased the amount of phosphorylated Rho kinase. The chemokine CCL20 and inducible nitric oxide synthase (iNOS) were the most highly upregulated genes by dynamic compression and this response was reduced by the Rho kinase inhibitors. In conclusion, we show that dynamic compression induces changes in the actin cytoskeleton of agarose-embedded chondrocytes, and we establish methodology to quantify these changes. Furthermore, we show that Rho kinase activity is required for this actin reorganization and gene expression induced by dynamic compression.

Human articular chondrocytes exhibit sexual dimorphism in their responses to 17beta-estradiol.

OBJECTIVE: The higher incidence of osteoarthritis in females suggests that there may be intrinsic sex-specific differences in human articular chondrocytes. 17beta-Estradiol (E2) regulates rat growth plate chondrocytes through traditional nuclear receptor mechanisms, but only female cells exhibit rapid membrane-associated effects mediated through protein kinase C (PKC) alpha. Here we demonstrate sexual dimorphism in the physiological response of human articular chondrocytes to E2. METHODS: Articular chondrocytes were obtained at the time of autopsy from three male and three female donors between 16 and 39 years of age. Second passage cultures were treated with E2 for 24 h to assess the effects of the hormone on [3H]-thymidine incorporation, [35S]-sulfate incorporation, and alkaline phosphatase specific activity. In addition, the chondrocytes were treated for 3, 9, 90 or 270 min and PKC specific activity was determined. RESULTS: All chondrocytes were positive for aggrecan and estrogen receptor alpha mRNAs but were negative for type II collagen mRNA. Only cells from female donors responded to E2. DNA synthesis, sulfate incorporation and alkaline phosphatase activity were increased. E2 caused a rapid increase in PKC activity in the female cells within 9 min that was maximal at 90 min. Treatment with the PKC inhibitor chelerythrine blocked these effects. CONCLUSIONS: These results provide the first definitive evidence that normal human cells exhibit an intrinsic sex-specific response to E2 and suggest that sexual dimorphism may be an important variable in assessing the pathways that modulate cell behavior.

Chondroprotective activity of N-acetylglucosamine in rabbits with experimental osteoarthritis.

OBJECTIVE: To examine the therapeutic efficacy of N-acetylglucosamine (GlcNAc) in rabbits with experimental osteoarthritis (OA). METHODS: Experimental OA was induced in rabbits by anterior cruciate ligament transection (ACLT). In the first study, rabbits (six in each group) received intramuscular injections of GlcNAc or normal saline three times a week starting 1 week postoperatively. In the second study, rabbits (eight in each group) were injected intra-articularly with GlcNAc (either once or twice a week) or normal saline. In the third study, rabbits (seven in each group) were injected intra-articularly twice a week with either GlcNAc, hyaluronan, or normal saline. Animals were killed 8 weeks after ACLT for macroscopic and histological assessment of the knee joints. RESULTS: Intramuscular administration of GlcNAc in rabbits with experimental knee OA did not show chondroprotective effects but showed mild anti-inflammatory activity. In contrast, intra-articular administration of GlcNAc twice a week reduced cartilage degradation. Additionally, intra-articular GlcNAc also suppressed synovitis. Once a week intra-articular injections of GlcNAc did not demonstrate therapeutic efficacy. The chondroprotective efficacy of GlcNAc was better than that of viscosupplementation treatment with hyaluronan. CONCLUSION: Intra-articular GlcNAc has chondroprotective and anti-inflammatory activity in experimental OA.

Cytokine regulation of facilitated glucose transport in human articular chondrocytes.

Glucose serves as the major energy substrate and the main precursor for the synthesis of glycosaminoglycans in chondrocytes. Facilitated glucose transport represents the first rate-limiting step in glucose metabolism. This study examines molecular regulation of facilitated glucose transport in normal human articular chondrocytes by proinflammatory cytokines. IL-1beta and TNF-alpha, and to a lesser degree IL-6, accelerate facilitated glucose transport as measured by [(3)H]2-deoxyglucose uptake. IL-1beta induces an increased expression of glucose transporter (GLUT) 1 mRNA and protein, and GLUT9 mRNA. GLUT3 and GLUT8 mRNA are constitutively expressed in chondrocytes and are not regulated by IL-1beta. GLUT2 and GLUT4 mRNA are not detected in chondrocytes. IL-1beta stimulates GLUT1 protein glycosylation and plasma membrane incorporation. IL-1beta regulation of glucose transport in chondrocytes depends on protein kinase C and p38 signal transduction pathways, and does not require phosphoinositide 3-kinase, extracellular signal-related kinase, or c-Jun N-terminal kinase activation. IL-1beta-accelerated glucose transport in chondrocytes is not mediated by endogenous NO or eicosanoids. These results demonstrate that stimulation of glucose transport represents a component of the chondrocyte response to IL-1beta. Two classes of GLUTs are identified in chondrocytes, constitutively expressed GLUT3 and GLUT8, and the inducible GLUT1 and GLUT9.