Yes-associated protein nuclear translocation promotes anabolic activity in human articular chondrocytes.

OBJECTIVE: Yes-associated protein (YAP) has been widely studied as a mechanotransducer in many cell types, but its function in cartilage is controversial. The aim of this study was to identify the effect of YAP phosphorylation and nuclear translocation on the chondrocyte response to stimuli relevant to osteoarthritis (OA). DESIGN: Cultured normal human articular chondrocytes from 81 donors were treated with increased osmolarity media as an in vitro model of mechanical stimulation, fibronectin fragments (FN-f) or IL-1ß as catabolic stimuli, and IGF-1 as an anabolic stimulus. YAP function was assessed with gene knockdown and inhibition by verteporfin. Nuclear translocation of YAP and its transcriptional co-activator TAZ and site-specific YAP phosphorylation were determined by immunoblotting. Immunohistochemistry and immunofluorescence to detect YAP were performed on normal and OA human cartilage with different degrees of damage. RESULTS: Chondrocyte YAP/TAZ nuclear translocation increased under physiological osmolarity (400 mOsm) and IGF-1 stimulation, which was associated with YAP phosphorylation at Ser128. In contrast, catabolic stimulation decreased the levels of nuclear YAP/TAZ through YAP phosphorylation at Ser127. Following YAP inhibition, anabolic gene expression and transcriptional activity decreased. Additionally, YAP knockdown reduced proteoglycan staining and levels of type II collagen. Total YAP immunostaining was greater in OA cartilage, but YAP was sequestered in the cytosol in cartilage areas with more severe damage. CONCLUSIONS: YAP chondrocyte nuclear translocation is regulated by differential phosphorylation in response to anabolic and catabolic stimuli. Decreased nuclear YAP in OA chondrocytes may contribute to reduced anabolic activity and promotion of further cartilage loss.

Fecal metabolomics reveals products of dysregulated proteolysis and altered microbial metabolism in obesity-related osteoarthritis.

OBJECTIVE: The objective of this exploratory study was to determine if perturbations in gut microbial composition and the gut metabolome could be linked to individuals with obesity and osteoarthritis (OA). METHODS: Fecal samples were collected from obese individuals diagnosed with radiographic hand plus knee OA (n = 59), defined as involvement of at least 3 joints across both hands, and a Kellgren-Lawrence (KL) grade 2-4 (or total knee replacement) in at least one knee. Controls (n = 33) were without hand OA and with KL grade 0-1 knees. Fecal metabolomes were analyzed by a UHPLC/Q Exactive HFx mass spectrometer. Microbiome composition was determined in fecal samples by 16 S ribosomal RNA amplicon sequencing (rRNA-seq). Stepwise logistic regression models were built to determine microbiome and/or metabolic characteristics of OA. RESULTS: Untargeted metabolomics analysis indicated that OA cases had significantly higher levels of di- and tripeptides and significant perturbations in microbial metabolites including propionic acid, indoles, and other tryptophan metabolites. Pathway analysis revealed several significantly perturbed pathways associated with OA including leukotriene metabolism, amino acid metabolism and fatty acid utilization. Logistic regression models selected metabolites associated with the gut microbiota and leaky gut syndrome as significant predictors of OA status, particularly when combined with the rRNA-seq data. CONCLUSIONS: Adults with obesity and knee plus hand OA have distinct fecal metabolomes characterized by increased products of proteolysis, perturbations in leukotriene metabolism, and changes in microbial metabolites compared with controls. These metabolic perturbations indicate a possible role of dysregulated proteolysis in OA.

A novel placental tissue biologic, PTP-001, inhibits inflammatory and catabolic responses in vitro and prevents pain and cartilage degeneration in a rat model of osteoarthritis.

OBJECTIVE: Characterization of a novel human placental tissue-derived biologic, PTP-001, which is in development as a candidate therapeutic for the treatment of osteoarthritis symptoms and pathophysiology. METHODS: Human placental tissues from healthy donors were prepared as a particulate formulation, PTP-001. PTP-001 extracts were assayed for the presence of disease-relevant biofactors which could have beneficial effects in treating osteoarthritis. PTP-001 eluates were tested in human chondrocyte cultures to determine effects on the production of a key collagen-degrading matrix metalloproteinase, MMP-13. PTP-001 eluates were also assessed for anti-inflammatory potential in human monocyte/macrophage cultures, as well as for growth-stimulating anabolic effects in human synoviocytes. The in vivo effects of PTP-001 on joint pain and histopathology were evaluated in a rat model of osteoarthritis induced surgically by destabilization of the medial meniscus. RESULTS: PTP-001 was found to contain an array of beneficial growth factors, cytokines and anti-inflammatory molecules. PTP-001 eluates dose-dependently inhibited the production of chondrocyte MMP-13, and the secretion of proinflammatory cytokines from monocyte/macrophage cultures. PTP-001 eluates also promoted proliferation of cultured synovial cells. In a rat osteoarthritis model, PTP-001 significantly reduced pain responses throughout 6 weeks post-dosing. The magnitude and duration of pain reduction following a single intraarticular treatment with PTP-001 was comparable to that observed for animals treated with a corticosteroid (active control). For rats dosed twice with PTP-001, significant reductions in cartilage histopathology scores were observed. CONCLUSIONS: PTP-001 represents a promising biologic treatment for osteoarthritis, with a multi-modal mechanism of action that may contribute to symptom management and disease modification.

Optimization of histologic grading schemes in spontaneous and surgically-induced murine models of osteoarthritis.

OBJECTIVE: To compare the Osteoarthritis Research Society International (OARSI) and Articular Cartilage Structure (ACS) grading schemes applied to multiple and single sections, along with additional histologic measures, in two mouse models of Osteoarthritis (OA). METHODS: Six coronal histologic stifle joint sections were collected from 40 C57BL/6J mice, including aged mice with spontaneous OA (approximately 18 months of age; n = 15) and young (12-week-old) mice that either underwent destabilization of the medial meniscus (DMM) surgery (n = 15) or sham surgery (n = 10). Sections were evaluated with the standard OARSI (0-6) scheme, a modified OARSI scheme, the ACS (0-12) scheme, histomorphometry of cartilage and bone, and scoring of osteophytes (0-3) and synovial hyperplasia (0-3). Principal components analysis (PCA) was used to determine the features explaining the greatest variability among the sections. RESULTS: The grading schemes performed similarly when applied to a single mid-coronal section or six total coronal sections per joint. OARSI grading produced similar results when applied to hematoxylin and eosin or toluidine blue-stained sections. Aged mice had higher severity scores in the LTP than DMM mice (mid-coronal OARSI grade aged = 2.3 and DMM = 1.1, p = 0.0006; ACS grade aged = 4.1 and DMM = 1.6, p = 0.0024). PCA resulted in retention of four factors that accounted for 78.4% of the total variance. Factor 1 (36.4%) included the OARSI grade, ACS grade, Toluidine blue grade, articular cartilage area and thickness and the osteophyte grade. CONCLUSIONS: Grading of a single mid-coronal section using either the OARSI or ACS schemes combined with osteophyte and histomorphometric measures can consistently define OA severity in mice.

Transcriptional response of human articular chondrocytes treated with fibronectin fragments: an in vitro model of the osteoarthritis phenotype.

OBJECTIVE: Fibronectin is a matrix protein that is fragmented during cartilage degradation in osteoarthritis (OA). Treatment of chondrocytes with fibronectin fragments (FN-f) has been used to model OA in vitro, but the system has not been fully characterized. This study sought to define the transcriptional response of chondrocytes to FN-f, and directly compare it to responses traditionally observed in OA. DESIGN: Normal human femoral chondrocytes isolated from tissue donors were treated with either FN-f or PBS (control) for 3, 6, or 18 h. RNA-seq libraries were compared between time-matched FN-f and control samples in order to identify changes in gene expression over time. Differentially expressed genes were compared to a published OA gene set and used for pathway, transcription factor motif, and kinome analysis. RESULTS: FN-f treatment resulted in 3,914 differentially expressed genes over the time course. Genes that are up- or downregulated in OA were significantly up- (P < 0.00001) or downregulated (P < 0.0004) in response to FN-f. Early response genes were involved in proinflammatory pathways, whereas many late response genes were involved in ferroptosis. The promoters of upregulated genes were enriched for NF-κB, AP-1, and IRF motifs. Highly upregulated kinases included CAMK1G, IRAK2, and the uncharacterized kinase DYRK3, while growth factor receptors TGFBR2 and FGFR2 were downregulated. CONCLUSIONS: FN-f treatment of normal human articular chondrocytes recapitulated many key aspects of the OA chondrocyte phenotype. This in vitro model is promising for future OA studies, especially considering its compatibility with genomics and genome-editing techniques.

The combination of mitogenic stimulation and DNA damage induces chondrocyte senescence.

OBJECTIVE: Cellular senescence is a phenotypic state characterized by stable cell-cycle arrest, enhanced lysosomal activity, and the secretion of inflammatory molecules and matrix degrading enzymes. Senescence has been implicated in osteoarthritis (OA) pathophysiology; however, the mechanisms that drive senescence induction in cartilage and other joint tissues are unknown. While numerous physiological signals are capable of initiating senescence, one emerging theme is that damaged cells convert to senescence in response to sustained mitogenic stimulation. The goal of this study was to develop an in vitro articular cartilage explant model to investigate the mechanisms of senescence induction. DESIGN: This study utilized healthy cartilage derived from cadaveric equine stifles and human ankles. Explants were irradiated to initiate DNA damage, and mitogenic stimulation was provided through serum-containing medium and treatment with transforming growth factor ß1 and basic fibroblastic growth factor. Readouts of senescence were a quantitative flow cytometry assay to detect senescence-associated ß galactosidase activity (SA-ß-gal), immunofluorescence for p16 and γH2AX, and qPCR for the expression of inflammatory genes. RESULTS: Human cartilage explants required both irradiation and mitogenic stimulation to induce senescence as compared to baseline control conditions (7.16% vs 2.34% SA-ß-gal high, p = 0.0007). These conditions also resulted in chondrocyte clusters within explants, a persistent DNA damage response, increased p16, and gene expression changes. CONCLUSIONS: Treatment of cartilage explants with mitogenic stimuli in the context of cellular damage reliably induces high levels of SA-ß-gal activity and other senescence markers, which provides a physiologically relevant model system to investigate the mechanisms of senescence induction.

A consensus-based framework for conducting and reporting osteoarthritis phenotype research.

BACKGROUND: The concept of osteoarthritis (OA) heterogeneity is evolving and gaining renewed interest. According to this concept, distinct subtypes of OA need to be defined that will likely require recognition in research design and different approaches to clinical management. Although seemingly plausible, a wide range of views exist on how best to operationalize this concept. The current project aimed to provide consensus-based definitions and recommendations that together create a framework for conducting and reporting OA phenotype research. METHODS: A panel of 25 members with expertise in OA phenotype research was composed. First, panel members participated in an online Delphi exercise to provide a number of basic definitions and statements relating to OA phenotypes and OA phenotype research. Second, panel members provided input on a set of recommendations for reporting on OA phenotype studies. RESULTS: Four Delphi rounds were required to achieve sufficient agreement on 11 definitions and statements. OA phenotypes were defined as subtypes of OA that share distinct underlying pathobiological and pain mechanisms and their structural and functional consequences. Reporting recommendations pertaining to the study characteristics, study population, data collection, statistical analysis, and appraisal of OA phenotype studies were provided. CONCLUSIONS: This study provides a number of consensus-based definitions and recommendations relating to OA phenotypes. The resulting framework is intended to facilitate research on OA phenotypes and increase combined efforts to develop effective OA phenotype classification. Success in this endeavor will hopefully translate into more effective, differentiated OA management that will benefit a multitude of OA patients.

The effect of weight loss on the progression of meniscal extrusion and size in knee osteoarthritis: a post-hoc analysis of the Intensive Diet and Exercise for Arthritis (IDEA) trial.

OBJECTIVE: Weight loss has beneficial effects on clinical outcomes in knee osteoarthritis (OA), but the mechanism is still unclear. Since meniscus extrusion is associated with knee pain, this study assessed whether weight loss by diet and/or exercise is associated with less progression in meniscus extrusion measures over time. DESIGN: The Intensive Diet and Exercise for Arthritis trial (IDEA) was a prospective, single-blind, randomized-controlled trial including overweight and obese older adults with knee pain and radiographic OA. Participants were randomized to 18-month interventions: exercise only, diet only or diet + exercise. In a random subsample of 105 participants, MRIs were obtained at baseline and follow-up. The medial and lateral menisci were segmented and quantitative position and size measures were obtained, along with semiquantitative extrusion measures. Linear and log-binomial regression were used to examine the association between change in weight and change in meniscus measures. Between-group differences were analyzed using an analysis of covariance. RESULTS: Weight loss was associated with less progression over time of medial meniscus extrusion as measured by the maximum (ß: -24.59 µm, 95%CI: -41.86, -7.33) and mean (ß: -19.08 µm, 95%CI: -36.47, -1.70) extrusion distances. No relationships with weight loss were observed for lateral meniscus position, medial or lateral meniscus size or semiquantitative measures. Change in meniscus position and size did not differ significantly between groups. CONCLUSIONS: Weight loss was associated with beneficial modifications of medial meniscus extrusion over 18 months. This may be one of the mechanisms by which weight loss translates into a clinical benefit. CLINICAL TRIAL REGISTRATION: NCT00381290.

A machine learning approach to knee osteoarthritis phenotyping: data from the FNIH Biomarkers Consortium.

OBJECTIVE: Knee osteoarthritis (KOA) is a heterogeneous condition representing a variety of potentially distinct phenotypes. The purpose of this study was to apply innovative machine learning approaches to KOA phenotyping in order to define progression phenotypes that are potentially more responsive to interventions. DESIGN: We used publicly available data from the Foundation for the National Institutes of Health (FNIH) osteoarthritis (OA) Biomarkers Consortium, where radiographic (medial joint space narrowing of ≥0.7 mm), and pain progression (increase of ≥9 Western Ontario and McMaster Universities Osteoarthritis Index [WOMAC] points) were defined at 48 months, as four mutually exclusive outcome groups (none, both, pain only, radiographic only), along with an extensive set of covariates. We applied distance weighted discrimination (DWD), direction-projection-permutation (DiProPerm) testing, and clustering methods to focus on the contrast (z-scores) between those progressing by both criteria ("progressors") and those progressing by neither ("non-progressors"). RESULTS: Using all observations (597 individuals, 59% women, mean age 62 years and BMI 31 kg/m2) and all 73 baseline variables available in the dataset, there was a clear separation among progressors and non-progressors (z = 10.1). Higher z-scores were seen for the magnetic resonance imaging (MRI)-based variables than for demographic/clinical variables or biochemical markers. Baseline variables with the greatest contribution to non-progression at 48 months included WOMAC pain, lateral meniscal extrusion, and serum N-terminal pro-peptide of collagen IIA (PIIANP), while those contributing to progression included bone marrow lesions, osteophytes, medial meniscal extrusion, and urine C-terminal crosslinked telopeptide type II collagen (CTX-II). CONCLUSIONS: Using methods that provide a way to assess numerous variables of different types and scalings simultaneously in relation to an outcome of interest enabled a data-driven approach that identified key variables associated with a progression phenotype.

Inflammatory cytokines mediate the effects of diet and exercise on pain and function in knee osteoarthritis independent of BMI.

OBJECTIVE: Diet restriction and exercise form key treatments for osteoarthritis (OA) related symptoms in overweight and obese individuals. Although both interventions are known to influence systemic low-grade inflammation, which is related to pain levels and functional limitations, little is known about the potential changes in systemic inflammation as a working mechanism of diet restriction and exercise in knee OA. DESIGN: Data from the Arthritis, Diet, and Activity Promotion Trial (ADAPT) were used. Through causal mediation analyses, the proportion of the effect of a 18 months diet and exercise intervention explained by the 18 months change in interleukin (IL)-6, TNF-α, soluble IL-6 receptor, soluble IL-1 receptor, CRP, and BMI were assessed, using self-reported pain and function as outcomes. RESULTS: The change in inflammatory factors accounted for 15% of the total effect on pain and was totally independent of the change in BMI. The change in inflammatory factors accounted for 29% of the effect on function, with the change in BMI adding only 4% to the total mediated effect. CONCLUSIONS: The change in inflammatory factors after the diet and exercise intervention was a 'medium' size mediator of the effect on pain and a 'strong' mediator for the effect on function in overweight and obese individuals with knee OA. The change in BMI added minimally to the mediated effect on function. These results highlight the relevance of changes in systemic inflammation as drivers for clinically relevant effects after diet and exercise in overweight and obese individuals with knee OA.

Articular chondrocytes isolated from the knee and ankle joints of human tissue donors demonstrate similar redox-regulated MAP kinase and Akt signaling.

OBJECTIVE: To compare key intracellular redox-regulated signaling pathways in chondrocytes derived from knee joint femoral cartilage and ankle joint talar cartilage in order to determine if differences exist that might contribute to the lower prevalence of ankle osteoarthritis (OA). METHODS: Femoral and talar chondrocytes were treated with H2O2 generators (menadione or 2-3-dimethoxy-1,4-napthoquinone (DMNQ), fragments of fibronectin (FN-f)) to stimulate MAP kinase signaling (MAPK), or with IGF-1 to stimulate the Akt signaling pathway. Hyperoxidation of the peroxiredoxins, used as a measure of redox status, and phosphorylation of proteins pertinent to MAPK (p38, ERK, JNK, c-Jun) and Akt (Akt, PRAS40) signaling cascades were detected by immunoblotting. RESULTS: Treatment of femoral and talar chondrocytes with menadione, DMNQ or FN-f led to a time dependent increase in extracellular-regulated kinase (ERK) and p38 phosphorylation. DMNQ and FN-f stimulation enhanced phosphorylation of JNK and its downstream substrate, c-Jun. Menadione treatment did not stimulate JNK activity but hyperoxidized the peroxiredoxins and inhibited IGF-1-induced Akt activation. In all experiments, chondrocytes derived from the femur and talar joints displayed comparable MAP kinase responses after treatment with various catabolic stimuli, as well as similar Akt signaling responses after IGF-1 treatment. CONCLUSIONS: MAP kinase and Akt signaling in response to factors that modulate the intracellular redox status were similar in chondrocytes from knee and ankle joints suggesting that redox signaling differences do not explain differences in OA prevalence. Talar chondrocytes, when isolated from their native matrix, can be used to examine redox-regulated cell signaling events relevant to OA in either joint.

Osteoarthritis induced by destabilization of the medial meniscus is reduced in germ-free mice.

OBJECTIVE: To determine the contribution of the gut microbiota to the development of injury-induced osteoarthritis (OA). DESIGN: OA was induced using the destabilized medial meniscus (DMM) model in 20 germ-free (GF) C57BL/6J male mice housed in a gnotobiotic facility and 23 strain-matched specific pathogen free (SPF) mice in 2 age groups -13.5 weeks avg age at DMM (17 SPF and 15 GF) and 43 weeks avg age at DMM (6 SPF and 5 GF). OA severity was measured using scores for articular cartilage structure (ACS), loss of safranin O (SafO) staining, osteophyte size, and synovial hyperplasia. Microbiome analysis by 16S rRNA amplicon sequencing was performed on stool samples and LPS and LPS binding protein (LBP) were measured in plasma. RESULTS: Compared to the SPF DMM mice, the maximum (MAX) ACS score per joint was 28% lower (p = 0.036) in GF DMM mice while the SafO sum score of all sections evaluated per joint was decreased by 31% (p = 0.009). The differences between SPF and GF mice in these scores were greater when only the younger mice were included in the analysis. The younger GF DMM mice also had significant reductions in osteophyte size (36%, P = 0.0119) and LBP (27%, P = 0.007) but not synovial scores or LPS. Differences in relative abundance of a number of Operational Taxonomic Units (OTUs) were noted between SPF mice with high vs low maximum ACS scores. CONCLUSIONS: These results suggest factors related to the gut microbiota promote the development of OA after joint injury.

Alterations in quadriceps muscle cellular and molecular properties in adults with moderate knee osteoarthritis.

OBJECTIVE: Quadriceps muscle weakness is common in knee osteoarthritis (OA). While pain, disuse, and atrophy are commonly cited causes for muscle weakness in OA, emerging evidence suggests changes in muscle quality also occur. Alterations in muscle quality are not well understood, but likely include both cellular and morphologic adaptions. The purpose of this study was to conduct the first cellular-level analysis of the vastus lateralis in adults with moderate knee OA. METHODS: Vastus lateralis biopsies were obtained from 24 subjects with moderate knee OA and 15 healthy controls. Quadriceps strength, muscle fiber cross sectional area (CSA), fiber type distribution, extracellular matrix (ECM) content, satellite cell abundance, and profibrotic gene expression were assessed. RESULTS: Relative to controls, quadriceps strength was significantly lower in OA subjects (OA 62.23, 50.67-73.8 Nm vs 91.46, 75.91-107.0 Nm, P = 0.003) despite no difference in fiber CSA. OA subjects had significantly fewer Type I fibers (OA 41.51, 35.56-47.47% vs 53.07, 44.86-61.29%, P = 0.022) and more hybrid IIa/x fibers (OA 24.61, 20.61-28.61% vs 16.4, 11.60-21.20%, P = 0.009). Significantly greater ECM content, lower satellite cell density, and higher profibrotic gene expression was observed with OA, and muscle collagen content was inversely correlated to strength and satellite cell (SC) density. CONCLUSION: Lower quadriceps function with moderate OA may not result from fiber size impairments, but is associated with ECM expansion. Impaired satellite cell density, high profibrotic gene expression, and a slow-to-fast fiber type transition may contribute to reduced muscle quality in OA. These findings can help guide therapeutic interventions to enhance muscle function with OA.

Effects of dietary weight loss with and without exercise on interstitial matrix turnover and tissue inflammation biomarkers in adults with knee osteoarthritis: the Intensive Diet and Exercise for Arthritis trial (IDEA).

OBJECTIVE: To examine the effects of dietary weight loss, with and without exercise, on selected soluble biomarkers in overweight and obese older adults with symptomatic knee osteoarthritis (OA). DESIGN: Blood samples were analyzed from 429 participants in the Intensive Diet and Exercise for Arthritis (IDEA) trial randomized to either an 18 month exercise control group (E), weight loss diet (D), or D + E. C1M, C2M, C3M and CRPM biomarkers and interleukin-6 (IL-6) were quantitated using ELISAs. Radiographic progression was defined as a decrease in joint space width of ≥0.7 mm. Statistical modeling of group means and associations used mixed models adjusted for visit, baseline body mass index (BMI), gender, and baseline values of the outcome. RESULTS: Compared to the E control group, C1M was significantly lower in the D and D + E groups at both 6 and 18 months while C3M was significantly lower in D and D + E at 6 months and in D + E at 18 months. C2M did not change in any group. Using data from all groups, change in C1M (P < 0.0001), C3M (P < 0.0001), as well as CRPM (P = 0.0004) from baseline to 18 months was positively associated with change in weight. No marker was associated with change in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain or radiographic progression. C3M (P = 0.008) and CRPM (P = 0.028) were positively associated with change in WOMAC function. Change in IL-6 was positively associated with change in C1M, C3M, and CRPM. CONCLUSION: Overweight and obese adults with knee OA who lost weight from diet and diet plus exercise reduced serum markers of interstitial matrix turnover and inflammation but not type II collagen degradation.

Wnt5a induces catabolic signaling and matrix metalloproteinase production in human articular chondrocytes.

OBJECTIVE: Aberrant Wnt signaling may contribute to osteoarthritis (OA) but the Wnt family members involved have not been fully identified. The purpose of this study was to investigate the role of Wnt5a as a potential mediator of cartilage destruction in OA. DESIGN: Immunohistochemistry to detect Wnt5a was performed using normal and OA human articular cartilage. Cultured normal human chondrocytes were treated with fibronectin fragments (FN-f) as a catabolic stimulus or recombinant Wnt5a protein with or without pretreatment using a panel of signaling inhibitors. Expression of Wnt5a, anabolic genes and catabolic genes were determined by quantitative real-time PCR. Production of Wnt5a protein and matrix metalloproteinases (MMPs) as well as activation of signaling proteins were analyzed by immunoblotting. RESULTS: Wnt5a was present in human articular cartilage with OA changes and its expression and secretion were increased in FN-f stimulated chondrocytes. FN-f stimulated Wnt5a production through the c-Jun N-terminal kinase (JNK) and extracellular signal-related kinase (ERK) pathways. Wnt5a reduced aggrecan gene expression after 48 h of treatment. Wnt5a seemed to promote MMP1, -3, and -13 expression as well as MMP1 and MMP13 protein production in normal human chondrocytes. Wnt5a inhibitor peptides did not affect FN-f induced MMP production. Wnt5a activated ß-catenin independent signaling including calmodulin-dependent protein kinase II (CaMKII), JNK, p38, ERK1/2, p65 and Akt. Inhibition of JNK, p38, ERK, PI-3 kinase and CaMKII by specific signaling inhibitors suppressed Wnt5a mediated MMP1 and MMP13 production. CONCLUSIONS: Wnt5a is present in human OA cartilage and can promote chondrocyte catabolic activity through non-canonical Wnt signaling, which suggests a potential role in OA.

High fat-diet and saturated fatty acid palmitate inhibits IGF-1 function in chondrocytes.

INTRODUCTION: Insulin-like growth factor-1 (IGF-1) promotes matrix synthesis and cell survival in cartilage. Chondrocytes from aged and osteoarthritic cartilage have a reduced response to IGF-1. The purpose of this study was to determine the effect of free fatty acids (FFA) present in a high-fat diet on IGF-1 function in cartilage and the role of endoplasmic reticulum (ER) stress. METHODS: C57BL/6 male mice were maintained on either a high-fat (60% kcal from fat) or a low-fat (10% kcal from fat) diet for 4 months. Mice were then sacrificed; femoral head cartilage caps were collected and treated with IGF-1 to measure proteoglycan (PG) synthesis. Cultured human chondrocytes were treated with 500 µM FFA palmitate or oleate, followed by stimulation with (100 ng/ml) IGF-1 overnight to measure CHOP (a protein marker for ER stress) and PG synthesis. Human chondrocytes were pre-treated with palmitate or 1 mM 4-phenyl butyric acid (PBA) or 1 µM C-Jun N terminal Kinase (JNK) inhibitor, and IGF-1 function (PG synthesis and signaling) was measured. RESULTS: Cartilage explants from mice on the high fat-diet showed reduced IGF-1 mediated PG synthesis compared to a low-fat group. Treatment of human chondrocytes with palmitate induced expression of CHOP, activated JNK and inhibited IGF-1 function. PBA, a small molecule chemical chaperone that alleviates ER stress rescued IGF-1 function and a JNK inhibitor rescued IGF-1 signaling. CONCLUSIONS: Palmitate-induced ER stress inhibited IGF-1 function in chondrocytes/cartilage via activating the mitogen-activated protein (MAP) kinase JNK. This is the first study to demonstrate that ER stress is metabolic factor that regulates IGF-1 function in chondrocytes.

Role of the C-C chemokine receptor-2 in a murine model of injury-induced osteoarthritis.

OBJECTIVE: We previously found in our embryonic studies that proper regulation of the chemokine CCL12 through its sole receptor CCR2, is critical for joint and growth plate development. In the present study, we examined the role of CCR2 in injury-induced-osteoarthritis (OA). METHOD: We used a murine model of injury-induced-OA (destabilization of medial meniscus, DMM), and systemically blocked CCR2 using a specific antagonist (RS504393) at different times during disease progression. We examined joint degeneration by assessing cartilage (cartilage loss, chondrocyte hypertrophy, MMP-13 expression) and bone lesions (bone sclerosis, osteophytes formation) with or without the CCR2 antagonist. We also performed pain behavioral studies by assessing the weight distribution between the normal and arthritic hind paws using the IITS incapacitance meter. RESULTS: Testing early vs delayed administration of the CCR2 antagonist demonstrated differential effects on joint damage. We found that OA changes in articular cartilage and bone were ameliorated by pharmacological CCR2 blockade, if given early in OA development: specifically, pharmacological targeting of CCR2 during the first 4 weeks (wks) following injury, reduced OA cartilage and bone damage, with less effectiveness with later treatments. Importantly, our pain-related behavioral studies showed that blockade of CCR2 signaling during early, 1-4 wks post-surgery or moderate, 4-8 wks post-surgery, OA was sufficient to decrease pain measures, with sustained improvement at later stages, after treatment was stopped. CONCLUSIONS: Our data highlight the potential efficacy of antagonizing CCR2 at early stages to slow the progression of post-injury OA and, in addition, improve pain symptoms.

Association of urinary metabolites with radiographic progression of knee osteoarthritis in overweight and obese adults: an exploratory study.

INTRODUCTION: Metabolic factors may contribute to osteoarthritis (OA). This study employed metabolomics analyses to determine if differences in metabolite profiles could distinguish people with knee OA who exhibited radiographic progression. METHODS: Urine samples obtained at baseline and 18 months from overweight and obese adults in the Intensive Diet and Exercise for Arthritis (IDEA) trial were selected from two subgroups (n = 22 each) for metabolomics analysis: a group that exhibited radiographic progression (≥0.7 mm decrease in joint space width, JSW) and an age, gender, and body mass index (BMI) matched group who did not progress (≤0.35 mm decrease in JSW). Multivariate analysis methods, including orthogonal partial least square discriminate analysis, were used to identify metabolite profiles that separated progressors and non-progressors. Plasma levels of IL-6 and C-reactive protein (CRP) were evaluated as inflammatory markers. RESULTS: Multivariate analysis of the binned metabolomics data distinguished progressors from non-progressors. Library matching revealed that glycolate, hippurate, and trigonelline were among the important metabolites for distinguishing progressors from non-progressors at baseline whereas alanine, N,N-dimethylglycine, glycolate, hippurate, histidine, and trigonelline, were among the metabolites that were important for the discrimination at 18 months. In non-progressors, IL-6 decreased from baseline to 18 months while IL-6 was unchanged in progressors; the change over time in IL-6 was significantly different between groups. CONCLUSION: These findings support a role for metabolic factors in the progression of knee OA and suggest that measurement of metabolites could be useful to predict progression. Further investigation in a larger sample that would include targeted investigation of specific metabolites is warranted.

Reduced response of human meniscal cells to Osteogenic Protein 1 during osteoarthritis and pro-inflammatory stimulation.

OBJECTIVE: Many cell types lose responsiveness to anabolic factors during inflammation and disease. Osteogenic Protein 1 (OP1/BMP7) was evaluated for the ability to enhance extracellular matrix synthesis in healthy and OA meniscus cells. Mechanisms of cell response to OP1 were explored. DESIGN: Meniscus and cartilage tissues from healthy tissue donors and osteoarthritis (OA) patients undergoing total knee arthroplasties were acquired. Primary cell cultures were stimulated with OP1 and/or inflammatory factors (IL1α, IL1ß, or fibronectin fragments (FnF)) and cellular responses were analyzed by RT-qPCR and immunoblots. Frozen section immunohistochemistry (IHC) was conducted to assess OP1 and receptor proteins in normal and OA meniscus. RESULTS: OP1 treatment of normal meniscus cells resulted in significant, dose-dependent increases in ACAN (aggrecan) and COL2A1, and decreased MMP13 gene transcription, while only ACAN was upregulated (P < 0.01) at the highest dose of OP1 in OA meniscus cells. OP1 induced significantly more ACAN gene transcription in normal meniscus than normal articular cartilage (P = 0.05), and no differences between normal and OA cartilage were detected. Receptor expression and kinetics of canonical signaling activation were similar between normal and OA specimens. Normal meniscus cells treated with inflammatory factors were refractory to OP1 stimulation. Smad1 phosphorylation at an inhibitory site was induced (P = 0.01 for both normal and OA meniscus) by inflammatory cytokine treatment. CONCLUSIONS: The meniscus demonstrates resistance to OP1 stimulation in OA and in the presence of inflammatory mediators. MAPK-mediated Smad1 linker phosphorylation is a possible mediator of the loss of anabolic extracellular matrix production in the inflammatory cytokine affected meniscus.

Aging-related inflammation in osteoarthritis.

It is well accepted that aging is an important contributing factor to the development of osteoarthritis (OA). The mechanisms responsible appear to be multifactorial and may include an age-related pro-inflammatory state that has been termed "inflamm-aging." Age-related inflammation can be both systemic and local. Systemic inflammation can be promoted by aging changes in adipose tissue that result in increased production of cytokines such as interleukin (IL)-6 and tumor necrosis factor-α (TNFα). Numerous studies have shown an age-related increase in blood levels of IL-6 that has been associated with decreased physical function and frailty. Importantly, higher levels of IL-6 have been associated with an increased risk of knee OA progression. However, knockout of IL-6 in male mice resulted in worse age-related OA rather than less OA. Joint tissue cells, including chondrocytes and meniscal cells, as well as the neighboring infrapatellar fat in the knee joint, can be a local source of inflammatory mediators that increase with age and contribute to OA. An increased production of pro-inflammatory mediators that include cytokines and chemokines, as well as matrix-degrading enzymes important in joint tissue destruction, can be the result of cell senescence and the development of the senescence-associated secretory phenotype (SASP). Further studies are needed to better understand the basis for inflamm-aging and its role in OA with the hope that this work will lead to new interventions targeting inflammation to reduce not only joint tissue destruction but also pain and disability in older adults with OA.