Faculty Bibliography

Objective: To evaluate the relationship of quantitative assessment of Bone Marrow Lesions (BML) with knee OA severity by radiographic findings. Methods: 58 OA patients (mean age 62+/-10, mean BMI 27+/-3, 59% female) underwent standardized nonfluoroscopic fixed-flexion knee radiographs. Two radiologists read the X-rays for KL grade, joint space width (JSW), and, using the OARSI atlas, joint space narrowing (JSN) and osteophytes; interreader agreement was assessed using Kappas and concordance correlation coefficients. Linear and logistic regression analysis was performed to assess associations while controlling the effects of age, sex and BMI. 3T-MRI included sagittal T2-weighted fat saturated spin-echo images (TR/TE=4000ms/75ms, FOV=15cm, matrix=256x128, slice thickness=3.0mm, receiver bandwidth 130Hz/pixel) and in/out of phase of FLASH images. Compartment-wise (medial tibial, lateral tibial, medial femur, lateral femur) BML volumes were quantified with T2-weighted fat saturated images and in/out of phase images respectively. BML volumes were dichotomized for statistical analysis. Results: KL score was a significant predictor of total BML volume (OR = 8.41, p = 0.0235). Medial tibial JSW, OARSI medial JSN, and medial tibial plateau osteophytes approached significance as predictors of BML volume at the medial tibia (OR = 0.71, p = 0.0551; OR = 2.16, p = 0.0597; and OR = 2.68, p = 0.0875, respectively). OARSI lateral JSN was a significant predictor of BML volume at the lateral tibia (OR = 3.62, p = 0.0169). Lateral tibial plateau osteophytes were predictors of total BML volume (OR = 4.58, p = 0.0299) and of BML volume at the lateral tibia (OR = 2.31, p = 0.0685). Lateral femoral condyle osteophytes approached significance as a predictor for BML at the lateral femur (OR = 2.25, p = 0.0651). Furthermore, quantitative BML volume strongly correlated with total quantitative synovial volume measured on MRI (beta= 0.22, p = 0.0003). Conclusions: Our data indicate that BML volume on MRI is a characteristic feature of progressive stages of OA, which not only correlates with JSN and osteophytes, but does so in a compartment-specific way. The data suggest that the altered mechanical forces that promote compartmental disease in OA lead to BML, JSN and osteophyte formation. Whether BML further contribute to cartilage loss, and are therefore targets of therapeutic intervention, remains to be determined

In osteoarthritis (OA) articular chondrocytes undergo phenotypic changes culminating in the progressive loss of cartilage from the joint surface. The molecular mechanisms underlying these changes are poorly understood. Here we report enhanced (approximately 7-fold) expression of F-spondin, a neuronal extracellular matrix glycoprotein, in human OA cartilage (P<0.005). OA-specific up-regulation of F-spondin was also demonstrated in rat knee cartilage following surgical menisectomy. F-spondin treatment of OA cartilage explants caused a 2-fold increase in levels of the active form of TGF-beta1 (P<0.01) and a 10-fold induction of PGE2 (P<0.005) in culture supernatants. PGE2 induction was found to be dependent on TGF-beta and the thrombospondin domain of the F-spondin molecule. F-spondin addition to cartilage explant cultures also caused a 4-fold increase in collagen degradation (P<0.05) and a modest reduction in proteoglycan synthesis (approximately 20%; P<0.05), which were both TGF-beta and PGE2 dependent. F-spondin treatment also led to increased secretion and activation of MMP-13 (P<0.05). Together these studies identify F-spondin as a novel protein in OA cartilage, where it may act in situ at lesional areas to activate latent TGF-beta and induce cartilage degradation via pathways that involve production of PGE2.

Osteoarthritis is often a progressive and disabling disease, which occurs in the setting of a variety of risk factors--such as advancing age, obesity, and trauma--that conspire to incite a cascade of pathophysiologic events within joint tissues. An important emerging theme in osteoarthritis is a broadening of focus from a disease of cartilage to one of the 'whole joint'. The synovium, bone, and cartilage are each involved in pathologic processes that lead to progressive joint degeneration. Additional themes that have emerged over the past decade are novel mechanisms of cartilage degradation and repair, the relationship between biomechanics and biochemical pathways, the importance of inflammation, and the role played by genetics. In this review we summarize current scientific understanding of osteoarthritis and examine the pathobiologic mechanisms that contribute to progressive disease

Purpose: Osteoarthritis is the most common form of arthritis, and the hereditable component of OA has been estimated to be 50-65%. The IL1 gene cluster region has been repeatedly associated with susceptibility to OA in various joints. This finding is consistent with the notion that inflammatory mediators, particularly IL-1, may be important in the pathogenesis and progression of OA. In these studies we examined the association of SNPs in inflammatory genes with the severity of knee OA and with the presence of generalized OA (GOA, here defined as knee plus hand OA). Method: One hundred forty-four OA patients (81 knee OA and 63 GOA) from two separate centers (NYUHJD, N=94 and Duke, N=50) met inclusion criteria: Caucasians of either sex, free of chronic disease other than osteoarthritis, and with a radiographic diagnosis of knee OA. Synovial fluid was available for the 50 Duke patients. Patients were genotyped for single nucleotide polymorphisms (SNPs). These subjects were divided into two groups: knee OA and GOA (knee and hand OA).We performed statistical analysis using Chi square and logistic regression, adjusting for age, gender and BMI to search for associations of radiographic knee OA severity and GOA with individual SNPs and with haplotypes. Results: After adjustment for age, gender, and BMI, individual TNF-a, IL1, IL1 receptor antagonist (IL1RN) SNPs were strongly associated with the presence of GOA (Table 1). In three of the four SNPs, alleles associated with increased incidence of GOA have been previously associated with increased cellular production of inflammatory mediators. These alleles are: IL1B (-3737) rs4848306 TT/CT, IL1B (-511) rs16944 CC/CT, and TNF-a (-308) rs1800629 AA/AG. In a separate analysis of knee OA severity based upon JSW, carriage of either one or two copies of a haplotype consisting of IL-1RN rs9005 (A), IL-1RN rs419598 (C), IL-1RN rs315952(T) was associated with lower odds of radiographic severity (OR 0.16; 95% CI 0.06-0.40), greater joint space width (JSW; p=0.0038) compared to those without these haplotypes. Patients with the protective haplotype had lower synovial fluid levels of IL-6 (p=0.018) and IL-10 (p=0.038). (Table Presented). Conclusion: Among the cytokines and receptor antagonist studied for genetic association, IL-1RN SNPs (rs9005, rs419598 & rs315952) predicted low risk for knee OA radiographic severity and haplotypes in IL-1B, TNFa ad IL-1RN (rs 315952) strongly associated with increased prevalence of GOA. These genetic markers provide insight into the possible role of inflammatory mediators in knee OA and could prove to be useful biomarkers in DMOAD drug development

Purpose: A necessary step for the successful regeneration of cartilage lesions using stem cell-based therapies is the controlled differentiation of progenitor cells into a stable articular chondrocyte phenotype. Prostaglandin E2 (PGE2) has been shown to have an important role in both fracture healing and chondrocyte maturation during endochondral bone formation. This study investigates the effects of PGE2 on chondrocyte differentiation of adult, human mesenchymal stem cells (MSCs). Methods: Bone marrow-derived MSCs were isolated from the discarded tissues of patients undergoing hip replacement surgery. Chondrogenesis was induced by seeding MSCs in serum-free aggregate cultures supplemented with dexamethasone (10-7 M) and TGF-b1 (10 ng/ml). At various time points, RNA was extracted for gene expression analysis by semi-quantitative RT-PCR. PGE2 levels were determined by RIA. Results: Gene expression analysis of 4 patient samples revealed an order-of-magnitude increase in chondrogenic markers, col II, col X, MMP-13 and AP. In each case, expression was elevated by day 7 and persisted for the duration of the assay (21 d). To determine the effects of PGE2, aggregates were cocultured in the presence of exogenous PGE2 (10-6 M) and expression of chondrocyte markers determined after 14 d. PGE2 increased expression of col II (65%) and decreased expression of hypertrophic markers, col X (20%), MMP-13 (32 %) and AP (55%). Consistent with these observations, histological examination of treated aggregates after 21 d revealed fewer enlarged, hypertrophic chondrocytes following PGE2 treatment compared to control cultures. In aggregate cultures, PGE2 secretion was inhibited by the selective cox-2 inhibitor, celecoxib, approximately 50%, while cox-1 inhibition by treatment with SC-560 had no effect. Accordingly, celecoxib treatment of chondrogenic aggregates for 7 d decreased expression of sox-9 (80%) and col II (97%) compared non-treated controls. Cox-2 inhibition also increased expression of hypertrophic markers. Celecoxib treatment increased col X (95%) and AP (150%), but had no effect on MMP-13 levels. After 21 d, aggregates treated with celecoxib exhibited greater numbers of hypertrophic chondrocytes, and a modest decrease in proteoglycan staining. These findings suggest that cox-2 derived PGE2 has the capacity modulate chondrocyte differentiation of MSCs via differential regulation of chondrocyte marker genes. Conclusion: PGE2, via upregulation of type II collagen, or inhibition of chondrocyte hypertrophy, has the capacity to regulate chondrocyte phenotype during in vitro chondrogenesis of hMSCs. Further characterization should uncover novel PGE2 pathways that can be exploited to modulate chondrocyte phenotype for tissue regeneration therapies

Elevated levels of PGE(2) have been reported in synovial fluid and cartilage from patients with osteoarthritis (OA). However, the functions of PGE(2) in cartilage metabolism have not previously been studied in detail. To do so, we cultured cartilage explants, obtained from patients undergoing knee replacement surgery for advanced OA, with PGE(2) (0.1-10 muM). PGE(2) inhibited proteoglycan synthesis in a dose-dependent manner (maximum 25% inhibition (p < 0.01)). PGE(2) also induced collagen degradation, in a manner inhibitable by the matrix metalloproteinase (MMP) inhibitor ilomastat. PGE(2) inhibited spontaneous MMP-1, but augmented MMP-13 secretion by OA cartilage explant cultures. PCR analysis of OA chondrocytes treated with PGE(2) with or without IL-1 revealed that IL-1-induced MMP-13 expression was augmented by PGE(2) and significantly inhibited by the cycolooygenase 2 selective inhibitor celecoxib. Conversely, MMP-1 expression was inhibited by PGE(2), while celecoxib enhanced both spontaneous and IL-1-induced expression. IL-1 induction of aggrecanase 5 (ADAMTS-5), but not ADAMTS-4, was also enhanced by PGE(2) (10 muM) and reversed by celecoxib (2 muM). Quantitative PCR screening of nondiseased and end-stage human knee OA articular cartilage specimens revealed that the PGE(2) receptor EP4 was up-regulated in OA cartilage. Moreover, blocking the EP4 receptor (EP4 antagonist, AH23848) mimicked celecoxib by inhibiting MMP-13, ADAMST-5 expression, and proteoglycan degradation. These results suggest that PGE(2) inhibits proteoglycan synthesis and stimulates matrix degradation in OA chondrocytes via the EP4 receptor. Targeting EP4, rather than cyclooxygenase 2, could represent a future strategy for OA disease modification