Elevated levels of active Transforming Growth Factor β1 in the subchondral bone relate spatially to cartilage loss and impaired bone quality in human knee osteoarthritis

OBJECTIVE

The association between the spatially distributed level of active TGFβ1 in human subchondral bone, and the characteristic structural and cellular parameters of human knee OA, was assessed.

DESIGN

Paired subchondral bone samples from 35 OA arthroplasty patients, (15 men and 20 women, aged 69 ± 9 years) were obtained from beneath macroscopically present (CA+) or denuded cartilage (CA-) to determine the concentration of active TGFβ1 (ELISA) and its relationship to bone quality (synchrotron micro-CT), cellularity, and vascularization (histology).

RESULTS

Bone samples beneath (CA-) regions had significantly increased concentrations of active TGFβ1 protein (mean difference: 26.4; 95% CI: [3.2, 49.7]), when compared to bone in CA + regions. Trabecular Bone below (CA-) regions had increased bone volume (median difference: 4.3; 96.49% CI: [-1.7, 17.8]), increased trabecular number (1.5 [0.006, 2.6], decreased trabecular separation (-0.05 [-0.1,-0.005]), and increased bone mineral density (394.5 [65.7, 723.3]) comparing to (CA+) regions. Further, (CA-) bone regions showed increased osteocyte density (0.012 [0.006, 0.018]), with larger osteocyte lacunae (39.8 [7.8, 71.7]) that were less spherical (-0.02 [-0.04, -0.003]), and increased bone matrix vascularity (12.4 [0.3, 24.5]) compared to (CA+). In addition, increased levels of active TGFβ1 related to increased bone volume (0.04 [-0.11, 0.9]), while increased OARSI grade associated with lacunar volume (-44.1 [-71.1, -17.2]), and orientation (2.7 [0.8, 4.6]).

CONCLUSION

Increased concentration of active TGFβ1 in the subchondral bone of human knee OA associates spatially with impaired bone quality and disease severity, suggesting that TGFβ1 is a potential therapeutic target to prevent or reduce human OA disease progression.

Bone marrow lesions in knee osteoarthritis: regional differences in tibial subchondral bone microstructure and their association with cartilage degeneration

OBJECTIVE

The aim of this study was to investigate how bone microstructure within bone marrow lesions (BMLs) relates to the bone and cartilage across the whole human tibial plateau.

DESIGN

Thirty-two tibial plateaus from patients with osteoarthritis (OA) at total knee arthroplasty and eleven age-matched non-OA controls, were scanned ex vivo by MRI to identify BMLs and by micro CT to quantitate the subchondral (plate and trabecular) bone microstructure. For cartilage evaluation, specimens were processed histologically.

RESULTS

BMLs were detected in 75% of the OA samples (OA-BML), located predominantly in the anterior-medial (AM) region. In contrast to non-OA control and OA-no BML, in OA-BML differences in microstructure were significantly more evident between subregions. In OA-BML, the AM region contained the most prominent structural alterations. Between-group comparisons showed that the AM region of the OA-BML group had significantly higher histological degeneration (OARSI grade) (P < .0001, P < .05), thicker subchondral plate (P < .05, P < .05), trabeculae that are more anisotropic (P < .0001, P < .05), well connected (P < .05, P = n.s), and more plate-like (P < 0.05, P < 0.05), compared to controls and OA-no BML at this site. Compared to controls, OA-no BML had significantly higher OARSI grade (P < .0001), and lower trabecular number (P < .05).

CONCLUSION

In established knee OA, both the extent of cartilage damage and microstructural degeneration of the subchondral bone were dependent on the presence of a BML. In OA-no BML, bone microstructural alterations are consistent with a bone attrition phase of the disease. Thus, the use of BMLs as MRI image-based biomarkers appear to inform on the degenerative state within the osteochondral unit.

Pre-emptive, early, and delayed alendronate treatment in a rat model of knee osteoarthritis: effect on subchondral trabecular bone microarchitecture and cartilage degradation of the tibia, bone/cartilage turnover, and joint discomfort

OBJECTIVE

Bisphosphonates are considered potential disease modifying osteoarthritis (OA) agents. The present study investigated the efficacy of pre-emptive, early, and delayed alendronate (ALN) treatment initiation on subchondral trabecular bone and cartilage in low-dose monosodium iodoacetate (MIA)-induced knee OA in rats.

METHODS

Male rats received pre-emptive (n = 12, day 0-end of week 2), early (n = 12, end of week 2-end of week 6), or delayed (n = 12, end of week 6-end of week 10) ALN treatment (30 μg/kg/week). Pre-emptive ALN-treated rats were scanned using in vivo micro-computed tomography (micro-CT) after 2 weeks and then sacrificed, early ALN-treated rats were scanned after 2 and 6 weeks and sacrificed, and the delayed ALN-treated rats were scanned after 2, 6, and 10 weeks of OA induction and sacrificed. After sacrifice, bone histomorphometry and histology of the tibia and biomarker analyses were undertaken. Changes in hind limb weight-bearing were assessed from day -1 until day 14.

RESULTS

MIA-induced pathological features similar to progressive human OA in the cartilage and subchondral bone. Pre-emptive ALN treatment preserved subchondral trabecular bone microarchitecture, prevented bone loss, decreased bone turnover and joint discomfort. Pre-emptive ALN treatment had moderate effects on cartilage degradation. Early and delayed ALN treatments prevented loss of trabeculae and decreased bone turnover, but had no significant effect on cartilage degradation.

CONCLUSION

ALN prevented increased bone turnover and preserved the structural integrity of subchondral bone in experimental OA. The time point of treatment initiation is crucial for treating OA. Treating both the subchondral bone and cartilage in OA would be clinically more beneficial.

Evidence for the dysregulated expression of TWIST1, TGFβ1 and SMAD3 in differentiating osteoblasts from primary hip osteoarthritis patients

OBJECTIVE

This study compared human primary osteoblasts derived from hip osteoarthritis (OA) cases against controls (CTLs) to investigate candidate OA disease genes, twist homologue 1 (TWIST1), wingless MMTV integration site family member 5B (WNT5B), transforming growth factor-β (TGFβ1) and SMAD family member 3 (SMAD3), during osteoblast differentiation, relative to calcium apposition and elemental mineral composition.

MATERIALS & METHODS

Primary osteoblast cultures were generated from intertrochanteric trabecular bone samples from five female primary hip OA cases and five age-matched female CTLs. During a 42-day differentiation time-course, alizarin red stains, energy-dispersive X-ray spectroscopy and real-time RT-polymerase chain reaction (PCR) were used to quantify calcium, elemental composition and gene expression, respectively. Data were analysed using linear mixed effects models and Pearson correlation matrices.

RESULTS

Significant differences, correlations and associations were found in OA and CTL osteoblasts between gene and mineral measures. The calcium: phosphorous (Ca:P) ratio was significantly more varied in OA compared to CTL. Calcium apposition, mineral composition as well as TWIST1 and TGFβ1 mRNA expression changed significantly over time. TWIST1 mRNA expression was elevated and correlated with SMAD3 mRNA levels in the OA cohort during the time-course. Associations were observed between tissue non-specific alkaline phosphatase (TNAP), osteocalcin (OCN), TWIST1, TGFβ1, SMAD3 mRNA levels and mineral measures in OA against CTL. Temporal differences between SMAD3 mRNA expression and mineral composition were also found in OA.

CONCLUSIONS

Dysregulated expression of TWIST1, TGFβ1 and SMAD3 mRNA observed in OA bone is reflected in the functionality of the osteoblast when these cells are cultured ex vivo. The results presented here are consistent with at least part of the aetiology of primary hip OA deriving from altered intrinsic properties of the osteoblast.

In situ fatty acid profile of femoral cancellous subchondral bone in osteoarthritic and fragility fracture females: implications for bone remodelling

We report here differences in the fatty acid profile of cancellous bone matrix, including n-3, n-6, mono- and poly-unsaturated, as well as saturated fats, between femoral heads from female OA (n=8, aged 68-88years), fractured neck of femur (#NOF) (n=19, 67-88years) and autopsy controls (CTRL) (n=4, 85-97years). Femoral heads were collected from individuals undergoing orthopaedic surgery for OA or #NOF; the fatty acid profile of sub-samples from the superior principal compressive and superior principal tensile regions were determined by gas chromatography. A total of 42 individual fatty acids were detected at varying concentrations with significant differences between subchondral bone from OA subjects, subchondral bone from #NOF subjects and subchondral bone from CTRL subjects, as well as between the superior principal compressive and superior principal tensile regions (for saturated fats only). Subchondral bone from OA subjects had higher total n-6 (OA=10.89±3.17, #NOF=11.11±1.83, CTRL=8.32±2.05, p=0.008) and total n-3 (OA=1.34±0.38, #NOF=1.19±0.18, CTRL=1.15±0.48, p=0.011) percentages than subchondral bone from #NOF subjects and subchondral bone from CTRL subjects, and there was no difference in the n-6:n-3 ratio, nor within the percentage of n-9 fatty acids. Arachidonic acid (OA=0.42±0.16, #NOF=0.26±0.06, CTRL=0.28±0.06, p=0.01), and γ-linolenic acid (OA=0.11±0.03, #NOF=0.05±0.02, CTRL=0.04±0.02, p<0.001) were higher in subchondral bone from OA subjects than subchondral bone from #NOF subjects and subchondral bone from CTRL subjects. In conclusion, there is a wide diversity of fatty acids in cancellous bone matrix from the femoral heads of OA and #NOF, suggesting they may have regulatory effects on inflammatory processes, and their metabolites. This article is part of a Special Issue entitled "Osteoarthritis".

Human bone material characterization: integrated imaging surface investigation of male fragility fractures

The interrelation of calcium and phosphorus was evaluated as a function of bone material quality in femoral heads from male fragility fracture patients via surface analytical imaging as well as scanning microscopy techniques. A link between fragility fractures and increased calcium to phosphorus ratio was observed despite normal mineralization density distribution.

INTRODUCTION

Bone fragility in men has been recently recognized as a public health issue, but little attention has been devoted to bone material quality and the possible efficacy in fracture risk prevention. Clinical routine fracture risk estimations do not consider the quality of the mineralized matrix and the critical role played by the different chemical components that are present. This study uses a combination of different imaging and analytical techniques to gain insights into both the spatial distribution and the relationship of phosphorus and calcium in bone.

METHODS

X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry imaging techniques were used to investigate the relationship between calcium and phosphorus in un-embedded human femoral head specimens from fragility fracture patients and non-fracture age-matched controls. The inclusion of the bone mineral density distribution via backscattered scanning electron microscopy provides information about the mineralization status between the groups.

RESULTS

A link between fragility fracture and increased calcium and decreased phosphorus in the femoral head was observed despite normal mineralization density distribution. Results exhibited significantly increased calcium to phosphorus ratio in the fragility fracture group, whereas the non-fracture control group ratio was in agreement with the literature value of 1.66 M ratio in mature bone.

CONCLUSIONS

Our results highlight the potential importance of the relationship between calcium and phosphorus, especially in areas of new bone formation, when estimating fracture risk of the femoral head. The determination of calcium and phosphorus fractions in bone mineral density measurements may hold the key to better fracture risk assessment as well as more targeted therapies.

Influence of surface roughness and shape on microdamage of the osseous surface adjacent to titanium dental implants

OBJECTIVES

To assess the relationship between smooth and roughened implant surfaces of straight and narrow configurations with respect to microdamage of the bone surface during placement of dental implants.

MATERIALS AND METHODS

Straight and tapered, rough and smooth surface Nobel Biocare implants were placed into sheep mandibles. Microdamage within the bone adjacent to the implant surface was quantitated using a semi-automated digitized histomorphometric method.

RESULTS

Independent of implant type, microdamage, microcracks, cross-hatch damage and diffuse damage were significantly higher close to the implants compared with far from the implants. Microcracks and cross-hatch damage were higher for the rough cylindrical implants than all the other implant types.

CONCLUSIONS

Insertion of a rough cylindrical implant type results in an increased fraction of microdamaged bone matrix in comparison to rough tapered, smooth cylindrical and smooth tapered implants.

Critical molecular regulators, histomorphometric indices and their correlations in the trabecular bone in primary hip osteoarthritis

OBJECTIVE

This study examined differential gene expression, histomorphometric indices and relationships between these, in femoral trabecular bone from osteoarthritis (OA) patients and control (CTL) subjects, with the aim of identifying potential molecular drivers consistent with changes in structural and remodelling indices in the OA pathology.

MATERIALS AND METHODS

Bone samples from the intertrochanteric (IT) region were obtained from age and sex-matched cohorts of 23 primary hip OA patients and 21 CTL subjects. Real-time polymerase chain reaction (PCR) and histomorphometric analysis were performed on each sample and correlations between gene expression and histomorphometric variables determined.

RESULTS

Alterations in gene expression, structural indices and correlations between these were found in OA bone compared to CTL. In OA bone, expression of critical regulators of osteoblast differentiation (TWIST1) and function (PTEN, TIMP4) were decreased, while genes associated with inflammation (SMAD3, CD14) were increased. Bone structural and formation indices (BV/TV, Tb.N, OS/BS) were increased, whereas resorption indices (ES/BS, ES/BV) were decreased. Importantly, significant correlations in CTL bone between CTNNB1 expression and formation indices (OS/BS, OS/BV, OV/BV) were absent in OA bone, indicating altered WNT/β-catenin signalling. TWIST1 expression and BV/TV were correlated in CTL bone, but not in OA bone, consistent with altered osteoblastogenesis in OA. Matrix metalloproteinase 25 (MMP25) expression and remodelling indices (ES/BS, ES/BV, ES/TV) were correlated only in OA pointing to aberrant bone remodelling in this pathology.

CONCLUSIONS

These findings indicate an altered state of osteoblast differentiation and function in OA driven by several key molecular regulators. In association with this differential gene expression, an altered state of both trabecular bone remodelling and resulting microarchitecture were also observed, further characterising the pathogenesis of primary hip OA.

Temporal pattern of gene expression and histology of stress fracture healing

Loading of the rat ulna is an ideal model to examine stress fracture healing. The aim of this study was to undertake a detailed examination of the histology, histomorphometry and gene expression of the healing and remodelling process initiated by fatigue loading of the rat ulna. Ulnae were harvested 1, 2, 4, 6, 8, and 10 weeks following creation of a stress fracture. Stress fracture healing involved direct remodelling that progressed along the fracture line as well as woven bone proliferation at the site of the fracture. Histomorphometry demonstrated rapid progression of basic multicellular units from 1 to 4 weeks with significant slowing down of healing by 10 weeks after loading. Quantitative PCR was performed at 4 hours, 24 hours, 4 days, 7 days, and 14 days after loading. Gene expression was compared to an unloaded control group. At 4 hours after fracture, there was a marked 220-fold increase (P<0.0001) in expression of IL-6. There were also prominent peak increases in mRNA expression for OPG, COX-2, and VEGF (all P<0.0001). At 24 hours, there was a peak increase in mRNA expression for IL-11 (73-fold increase, P<0.0001). At 4 days, there was a significant increase in mRNA expression for Bcl-2, COX-1, IGF-1, OPN, and SDF-1. At 7 days, there was significantly increased mRNA expression of RANKL and OPN. Prominent, upregulation of COX-2, VEGF, OPG, SDF-1, BMP-2, and SOST prior to peak expression of RANKL indicates the importance of these factors in mediating directed remodelling of the fracture line. Dramatic, early upregulation of IL-6 and IL-11 demonstrate their central role in initiating signalling events for remodelling and stress fracture healing.

Trabecular bone modeling and subcapital femoral fracture

Fragility fractures, including neck of femur fractures, result from reductions in the amount, quality and architecture of bone. The aim of this study was to compare the cancellous bone structure, and static indices of bone turnover, in female patients who had sustained fragility fracture at the femoral neck, with age-matched females without fragility fracture. Bone samples were taken from the intertrochanteric region of the proximal femur of female patients undergoing hip arthroplasty surgery for a subcapital fragility fracture of the femoral neck (#NOF) or from age-matched female control individuals at routine autopsy. The histomorphometric data, which were normally distributed, indicated no difference between the mean values for any of the structural parameters in control and fracture samples. In particular, the BV/TV values were not different and did not change significantly with age in these cohorts of individuals aged >65 years. The static indices of bone turnover, eroded surface (ES/BS) and osteoid surface (OS/BS), were positively correlated with age in the >65-year-old control group (p<0.05 and p<0.03, respectively). The median values for these indices were not different between the fracture and control groups. However, both the median and the range of OS/BS values were increased for >65-year-old controls compared with a group of younger females aged <65 years, suggesting an increase in bone formation in older females in the proximal femur after 65 years of age. When the data were further interrogated, a reduction in the percentage osteoid surface to eroded surface quotient (OS/ES) was found for the fracture group compared with the age-matched control group. These data indicate that perturbations in bone formation and/or resorption surface are potentially important in producing bone in the proximal femur with increased propensity to fracture. These data also support the concept that trabecular bone modeling may be a factor influencing bone strength in addition to bone mass.

New insights into the propagation of fatigue damage in cortical bone using confocal microscopy and chelating fluorochromes

Fatigue damage in bone occurs in the form of microcracks and plays an important role in the initiation of bone remodelling and in the occurrence of stress and fragility fractures. The process by which fatigue microcracks in bone initiate and grow remains poorly understood. The aim of this study was to investigate the microscopic tissue changes associated with microcracks during crack propagation in cortical bone and the influence of bone microstructure on this process. Cracks were mechanically initiated and extended longitudinally in a two-stage process, in six bovine tibial compact tension specimens. The sequential application of chelating fluorochromes, xylenol orange followed by calcein, allowed the nature of microcrack damage at different stages of propagation to be monitored by laser scanning confocal microscopy. Specimens were imaged at a focal plane 20 microm below the samples' surface, or as a series of z-plane images collected to a maximal depth of 200 microm and 35 microm for x 4 and x 40 objectives, respectively. Z-series image stacks were then reconstructed using Amira 3.0 software. Confocal images showed that xylenol orange localised to the crack surface and did not migrate into the crack's extension following further mechanical propagation. Similarly, calcein stained the extended crack's surface and displayed minimal incorporation within the original crack. High resolution confocal images provided a detailed visual description of the crack's 'process zone', and 'process zone wake'. Additionally, an 'interface region' was revealed, displaying a clear distinction between the end of the first crack and the commencement of its extension. Confocal images of the interface region demonstrated that the extended crack forms a continuum with the pre-existing crack and propagates through the former process zone. Upon viewing the three-dimensional reconstructed images, we found evidence suggesting a submicroscopic tissue involvement in fatigue damage, in addition to the potential influence of vascular canals and osteocyte lacunae on its propagation through the bone matrix. This study has provided new insights into the process of fatigue damage growth in bone and factors influencing its progression through the bone matrix. Confocal microscopy in combination with sequential chelating fluorochrome labelling is a valuable technique for monitoring microcrack growth in bone.

Identification of differentially expressed genes between osteoarthritic and normal trabecular bone from the intertrochanteric region of the proximal femur using cDNA microarray analysis

Osteoarthritis (OA) is a common age-related joint disease resulting in progressive degenerative damage to articular cartilage. The etiology of primary OA has not yet been determined. However, there is evidence supporting the hypothesis that primary OA is a disease affecting bone remodeling in addition to articular cartilage. In this study, we have used cDNA microarray analysis to compare gene expression in bone between normal (CTL) and OA individuals. Trabecular bone was sampled from the intertrochanteric region of the proximal femur, a site distal to the diseased hip joint. Total RNA was extracted from three pairs of age- and sex-matched CTL and OA bone samples, reverse-transcribed and radioactively labeled to generate cDNA probes, before hybridization with the Research Genetics GF211 human gene microarray filter. The CTL and OA samples were found to have similar levels of gene expression for more than 4000 known human genes. However, forty-one genes were identified that were differentially expressed, twofold or more, between all three CTL-OA sample pairs. Using semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) analysis, three genes, fms-like tyrosine kinase 1 (FLT1), plexin B1 (PLXNB1), and small inducible cytokine A2 (SCYA2), were confirmed to be consistently expressed at lower levels in OA, in a majority of twenty age- and sex-matched CTL-OA bone sample pairs tested. FLT1, PLXNB1, and SCYA2 have known or potential roles in angiogenesis and bone remodeling. Down-regulation of these genes is consistent with a role for bone in the pathogenesis of OA.

Cancellous bone microdamage in the proximal femur: influence of age and osteoarthritis on damage morphology and regional distribution

This study describes the in vivo distribution of cancellous bone microdamage in the proximal femur of an autopsy control sample. In addition, in vivo microdamage in the region medial to the greater trochanter of the proximal femur is compared between patients with severe osteoarthritis and controls. Taken at autopsy, the control group comprised normal right proximal femora that were then cut in the coronal plane with an Exakt saw (n = 12; aged 20-83 years). Cancellous bone samples were taken from the subchondral principal compressive region, the medial principal compressive region, and medial to the greater trochanter. A cancellous bone core biopsy was taken of the region medial to the greater trochanter (of the proximal femur) from patients with primary osteoarthritis undergoing total hip replacement surgery (n = 33; aged 37-85 years). Samples were embedded in resin, and in vivo microdamage identified in 70-microm-thick sections using the basic fuchsin en bloc staining technique. Microdamage was similar in all proximal femur sites in controls, except in the subchondral principal compressive region, where a significantly smaller crack length (microm) was identified (p < 0.05). In the region medial to the greater trochanter, osteoarthritic vs. control group comparisons showed that the crack density (#/mm(2)) and crack surface density (mm/mm(2)) were not significantly different, but crack length was significantly less (p < 0.03) and damage volume fraction was significantly increased for osteoarthritics (p < 0.005). The osteoarthritic and control data for crack density, and the osteoarthritic data for damage volume fraction, showed a nonlinear increase with age. Furthermore, crack length was not dependent on damage volume fraction or age for either the osteoarthritic or control group. This study identified differences in microdamage between osteoarthritic and autopsy control cases. We hypothesize that these results are consistent with the reported bone material property differences for osteoarthritis. In addition, the relatively uniform distribution of microdamage in the control group suggests that the principal components of the femoral cancellous bone network are equally exposed to deformations resulting in microdamage. Further study into the factors that influence the accumulation and skeletal distribution of microdamage is fundamental to understanding skeletal health.

The ratio of messenger RNA levels of receptor activator of nuclear factor kappaB ligand to osteoprotegerin correlates with bone remodeling indices in normal human cancellous bone but not in osteoarthritis

The determinants of cancellous bone turnover and trabecular structure are not understood in normal bone or skeletal disease. Bone remodeling is initiated by osteoclastic resorption followed by osteoblastic formation of new bone. Receptor activator of nuclear factor kappaB ligand (RANKL) is a newly described regulator of osteoclast formation and function, the activity of which appears to be a balance between interaction with its receptor RANK and with an antagonist binding protein osteoprotegerin (OPG). Therefore, we have examined the relationship between the expression of RANKL, RANK, and OPG and indices of bone structure and turnover in human cancellous bone from the proximal femur. Bone samples were obtained from individuals with osteoarthritis (OA) at joint replacement surgery and from autopsy controls. Histomorphometric analysis of these samples showed that eroded surface (ES/BS) and osteoid surface (OS/BS) were positively associated in both control (p < 0.001) and OA (p < 0.02), indicating that the processes of bone resorption and bone formation remain coupled in OA, as they are in controls. RANKL, OPG, and RANK messenger RNA (mRNA) were abundant in human cancellous bone, with significant differences between control and OA individuals. In coplotting the molecular and histomorphometric data, strong associations were found between the ratio of RANKL/OPG mRNA and the indices of bone turnover (RANKL/OPG vs. ES/BS: r = 0.93, p < 0.001; RANKL/OPG vs. OS/BS: r = 0.80, p < 0.001). These relationships were not evident in trabecular bone from severe OA, suggesting that bone turnover may be regulated differently in this disease. We propose that the effective concentration of RANKL is related causally to bone turnover.

Enhanced expression of osteocalcin mRNA in human osteoarthritic trabecular bone of the proximal femur is associated with decreased expression of interleukin-6 and interleukin-11 mRNA

Few studies have investigated the factors or mechanisms that may lead to structural changes in OA bone. This study examines the in vivo expression of messenger RNA encoding the osteoclastogenic cytokines interleukin-6 (IL-6) and interleukin-11 (IL-11), together with the osteoblastic marker osteocalcin (OCN) and the calcitonin receptor (CTR), which in bone is exclusively expressed by osteoclasts. Total RNA was isolated from intertrochanteric trabecular bone from OA patients, and from controls taken at autopsy. The patterns of mRNA expression of IL-6, IL-11, OCN, and CTR were examined using reverse-transcription polymerase chain reaction (RT-PCR) by determining the relative ratios of the amplified products with respect to glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Both IL-6 and IL-11 mRNA were significantly less abundant in OA than in the control group. Expression of IL-11 mRNA decreased significantly with age for both groups. OCN mRNA expression was significantly more abundant in OA, and there was no significant difference for CTR mRNA between the two groups. For both OCN and CTR in OA, expression increased significantly with increasing age. These differences in expression between the OA and control groups are consistent with an hypothesis that biochemical and genetic factors in bone can contribute or perhaps underlie the degenerative joint changes seen in OA.