Subchondral bone in osteoarthritis: a biologic link with articular cartilage leading to abnormal remodeling

Open, Observational, Single-Arm, Multicenter Study Assessing the Effectiveness of a Dietary Supplement Containing Hydrolyzed Collagen, Chondroitin Sulfate, and Glucosamine for Osteoarthritis Pain Reduction

Osteoarthritis (OA) is an age-related degenerative joint disease with a great impact on patients' well-being and quality of life. This is an observational, open, single-arm multicenter study aimed to evaluate the effectiveness of a nutritional supplement in patients with knee and/or hip OA. A total of 186 patients were recruited from Spanish centers and received a supplement containing hydrolyzed collagen (3000 mg), chondroitin sulfate (800 mg), glucosamine sulfate (700 mg), turmeric extract (250 mg) and devil's claw (150 mg), once daily during 6 months. The primary outcome was the patients' self-perceived pain in the affected joints measured with a visual analogue scale (VAS). Secondary outcome was the patient's functioning, measured with the Lequesne Functional Index and the Western Ontario and McMaster Universities Arthritis Index (WOMAC). Participants showed a significant reduction in self-perceived pain after 3 (mean reduction ± standard deviation, 1.99 ± 1.05) and 6 months (3.57 ± 1.39) of treatment (p < 0.0001 in both comparisons). Lequesne Functional Index score was significantly reduced at 3 months (3.86 ± 2.94) and at 6 months (6.73 ± 4.30) of treatment (p < 0.0001 in both comparisons). The WOMAC index was also significantly reduced after 3 (14.24 ± 10.04) and 6 months (26.43 ± 17.35) of treatment (p < 0.0001 in both comparisons). Significant reductions in WOMAC subdomains (p < 0.0001 in all comparisons) were observed. No severe adverse events were reported during the study. The main results arising from this study show that this nutritional supplementation can improve OA-related symptoms and physical function with a good safety profile in patients with hip and/or knee OA.

Osteoporosis and osteoarthritis: a bi-directional Mendelian randomization study

OBJECTIVE

To investigate the causal relationship between low bone mineral density (BMD) and osteoarthritis (OA) using Mendelian randomization (MR) design.

METHODS

Two-sample bi-directional MR analyses were performed using summary-level information on OA traits from UK Biobank and arcOGEN. Sensitivity analyses including MR-Egger, simple median, weighted median, MR pleiotropy residual sum, and outlier approaches were utilized in conjunction with inverse variance weighting (IVW). Gene ontology (GO) enrichment analyses and expression quantitative trait locus (eQTL) colocalization analyses were used to investigate the potential mechanism and shared genes between osteoporosis (OP) and OA.

RESULTS

The IVW method revealed that genetically predicted low femoral neck BMD was significantly linked with hip (β = 0.105, 95% CI: 0.023-0.188) and knee OA (β = 0.117, 95% CI: 0.049-0.184), but not with other site-specific OA. Genetically predicted low lumber spine BMD was significantly associated with OA at any sites (β = 0.048, 95% CI: 0.011-0.085), knee OA (β = 0.101, 95% CI: 0.045-0.156), and hip OA (β = 0.150, 95% CI: 0.077-0.224). Only hip OA was significantly linked with genetically predicted reduced total bone BMD (β = 0.092, 95% CI: 0.010-0.174). In the reverse MR analyses, no evidence for a causal effect of OA on BMD was found. GO enrichment analysis and eQTL analysis illustrated that DDN and SMAD-3 were the most prominent co-located genes.

CONCLUSIONS

These findings suggested that OP may be causally linked to an increased risk of OA, indicating that measures to raise BMD may be effective in preventing OA. More research is required to determine the underlying processes via which OP causes OA.

Betulinic Acid Attenuates Osteoarthritis via Limiting NLRP3 Inflammasome Activation to Decrease Interleukin-1β Maturation and Secretion

Introduction

Osteoarthritis (OA) is the most common degenerative joint disorder. Prior studies revealed that activation of NLRP3 inflammasome could promote the activation and secretion of interleukin-1β (IL-1β), which has an adverse effect on the progression of OA. Betulinic acid (BA) is a compound extract of birch, whether it can protect against OA and the mechanisms involved are still unknown.

Materials and Methods

In vivo experiments, using gait analysis, ELISA, micro-CT, and scanning electron microscopy (SEM), histological staining, immunohistological (IHC) and immunofluorescence (IF) staining, and atomic force microscopy (AFM) to assess OA progression after intraperitoneal injection of 5 and 15 mg/kg BA in an OA mouse model. In vitro experiments, caspase-1, IL-1β, and the N-terminal fragment of gasdermin D (GSDMD-NT) were measured in bone marrow-derived macrophages (BMDMs) by using ELISA, western blot, and immunofluorescence staining.

Results

We demonstrated that OA progression can be postponed with intraperitoneal injection of 5 and 15 mg/kg BA in an OA mouse model. Specifically, BA postponed DMM-induced cartilage deterioration, alleviated subchondral bone sclerosis, and relieved synovial inflammation. In vitro studies, the activated NLRP3 inflammasome produces mature IL-1β by facilitating the cleavage of pro-IL-1β, and BA could inhibit the activation of NLRP3 inflammasome in BMDMs.

Conclusions

Taken together, our analyses revealed that BA attenuates OA via limiting NLRP3 inflammasome activation to decrease the IL-1β maturation and secretion.

Bone marrow lesions in osteoarthritis: From basic science to clinical implications

Osteoarthritis (OA) is the most prevalent musculoskeletal disease characterized by multiple joint structure damages, including articular cartilage, subchondral bone and synovium, resulting in disability and economic burden. Bone marrow lesions (BMLs) are common and important magnetic resonance imaging (MRI) features in OA patients. Basic and clinical research on subchondral BMLs in the pathogenesis of OA has been a hotspot. New evidence shows that subchondral bone degeneration, including BML and angiogenesis, occurs not only at or after cartilage degeneration, but even earlier than cartilage degeneration. Although BMLs are recognized as important biomarkers for OA, their exact roles in the pathogenesis of OA are still unclear, and disputes about the clinical impact and treatment of BMLs remain. This review summarizes the current basic and clinical research progress of BMLs. We particularly focus on molecular pathways, cellular abnormalities and microenvironmental changes of subchondral bone that contributed to the formation of BMLs, and emphasize the crosstalk between subchondral bone and cartilage in OA development. Finally, potential therapeutic strategies targeting BMLs in OA are discussed, which provides novel strategies for OA treatment.

Healthy and Osteoarthritis-Affected Joints Facing the Cellular Crosstalk

Osteoarthritis (OA) is a chronic, progressive, severely debilitating, and multifactorial joint disease that is recognized as the most common type of arthritis. During the last decade, it shows an incremental global rise in prevalence and incidence. The interaction between etiologic factors that mediate joint degradation has been explored in numerous studies. However, the underlying processes that induce OA remain obscure, largely due to the variety and complexity of these mechanisms. During synovial joint dysfunction, the osteochondral unit undergoes cellular phenotypic and functional alterations. At the cellular level, the synovial membrane is influenced by cartilage and subchondral bone cleavage fragments and extracellular matrix (ECM) degradation products from apoptotic and necrotic cells. These "foreign bodies" serve as danger-associated molecular patterns (DAMPs) that trigger innate immunity, eliciting and sustaining low-grade inflammation in the synovium. In this review, we explore the cellular and molecular communication networks established between the major joint compartments-the synovial membrane, cartilage, and subchondral bone of normal and OA-affected joints.

Changes of the subchondral bone microchannel network in early osteoarthritis

OBJECTIVE

We have identified a 3D network of subchondral microchannels that connects the deep zone of cartilage to the bone marrow (i.e., cartilage-bone marrow microchannel connectors; CMMC). However, the pathological significance of CMMC is largely unknown. Here, we quantitatively evaluated how the CMMC microarchitecture is related to cartilage condition, as well as regional differences in early idiopathic osteoarthritis (OA).

METHODS

Two groups of cadaveric female human femoral heads (intact cartilage vs early cartilage lesions) were identified, and a biopsy-based high-resolution micro-CT imaging was employed. Subchondral bone (SB) thickness, CMMC number, maximum and minimum CMMC size, and the CMMC morphology were quantified and compared between the two groups. The effect of joint's region and cartilage condition was examined on each dependent variable.

RESULTS

The CMMC number and morphology were affected by region of the joint, but not by cartilage condition. On the other hand, the minimum and maximum CMMC size was changed by both the location on the joint, as well as the cartilage condition. The smallest CMMC were consistently detected at the load-bearing region (LBR) of the joint. Compared to non-pathological subjects, the size of the microchannels was enlarged in early OA, most noticeably at the non-load-bearing region (NLBR) and the peripheral rim (PR) of the femoral head. Furthermore, subchondral bone thinning was observed in early OA as a localized occurrence linked with areas of partial chondral defect.

CONCLUSION

Our data point to an enlargement of the SB microchannel network, and a collective structural deterioration of SB in early idiopathic OA.

Systemic iron reduction via an iron deficient diet decreases the severity of knee cartilage lesions in the Dunkin-Hartley guinea pig model of osteoarthritis

OBJECTIVE

Iron accumulation is emerging as a player in aging-related disorders due to its propensity for generating reactive oxygen species (ROS). Studies investigating the role of iron in the pathogenesis of primary osteoarthritis (OA) are limited. We designed a proof-of-principle study to determine the effect of systemic iron deficiency, via an iron deficient diet, on knee OA in an animal model.

METHODS

Twelve-week-old male Hartley guinea pigs received the standard diet (n = 6) or a diet devoid of iron (n = 6) for 19-weeks. Iron levels were determined in the serum, liver, and articular cartilage. Knees were collected to assess structural changes related to OA (microcomputed tomography, histopathology). Immunohistochemistry was performed to evaluate the presence and distribution of a disintegrin and metalloproteinase with thrombospondin motifs 4 (ADAMTS4) and ROS-driven 4-hydroxynonenal (4-HNE)-induced protein adducts. Transcript expression was also assessed.

RESULTS

Relative to control animals, an iron deficient diet reduced the concentration of this mineral in serum, liver, and articular cartilage. Iron deficient animals had lower histologic OA scores; decreased subchondral bone mineral density was also noted. This reduction in knee joint pathology was accompanied by a decrease in: ADAMTS4 in synovium; and 4-HNE protein adducts from lipid peroxidation in both the menisci and articular cartilage of iron deficient animals. Expression of iron-related genes in these tissues was also altered in treated animals.

CONCLUSIONS

Results from this study suggest that systemic iron levels may play a role in knee OA pathogenesis, with a short-term deficit in dietary iron reducing the severity of knee cartilage lesions.

Structural changes in the collagen network of joint tissues in late stages of murine OA

Osteoarthritis (OA) is the most prevalent degenerative joint disease, resulting in joint pain, impaired movement, and structural changes. As the ability of joint tissue to resist stress is mainly imparted by fibrillar collagens in the extracellular matrix, changes in the composition and structure of collagen fibers contribute to the pathological remodeling observed in OA joints that includes cartilage degeneration, subchondral bone (SCB) sclerosis, and meniscal damage. Using the established OA model of destabilization of the medial meniscus (DMM) in C57BL/6J mice, we performed a comprehensive analysis of the content and structure of collagen fibers in the articular cartilage, subchondral bone, and menisci using complementary techniques, which included second harmonic generation microscopy and immunofluorescence staining. We found that regions exposed to increased mechanical stress in OA mice, typically closest to the site of injury, had increased collagen fiber thickness, dysregulated fiber formation, and tissue specific changes in collagen I and II (Col I and Col II) expression. In cartilage, OA was associated with decreased Col II expression in all regions, and increased Col I expression in the anterior and posterior regions. Col I fiber thickness was increased in all regions with disorganization in the center region. In the superficial SCB, all regions exhibited increased Col I expression and fiber thickness in OA mice; no changes were detected in the deeper regions of the subchondral bone except for increased Col I fiber thickness. In the menisci, OA led to increased Col I and Col II expression in the vascular and avascular regions of the anterior meniscus with increased Col I fiber thickness in these regions. Similar changes were observed only in the vascular region of the posterior meniscus. Our findings provide, for the first time, comprehensive insights into the microarchitectural changes of extracellular matrix in OA and serve as guidelines for studies investigating therapies that target collagenous changes as means to impede the progression of osteoarthritis.

Acetabular development and fate of inverted limbus in rabbits: Experimental observation from an animal model

Using an animal model, we aimed to investigate the effects of an inverted limbus on acetabular development following closed reduction of developmental dysplasia of the hip (DDH). We interpositioned the menisci of 5-week-old rabbits (n = 40) into the hip joints to simulate limbus inversion following closed reduction for DDH. The acetabular index (AI) on anteroposterior pelvic radiographs and magnetic resonance imaging were used to evaluate acetabular development. Animals were euthanized at 4 and 8 weeks after surgery. Histological sections of the acetabular cartilage were stained and scored in accordance with the modified Mankin system. Scanning electron microscopy and transmission electron microscopy were used to examine the ultrastructure of the acetabular cartilage. Terminal deoxynucleotidyl transferase dUTP nick end-labeling staining was used to evaluate chondrocyte apoptosis. Immunohistochemistry and Western blot analyses were used to examine the expression of type X collagen (Col-X) and matrix metalloproteinase 13 (MMP-13) in the acetabular cartilage. AI values increased over a period and were higher in the experimental group than in the sham group. In the experimental group, the acetabular surface had become rough and had split in some cases. Chondrocytes within the acetabular cartilage had become hypertrophic, gradually forming clusters, and taking on an apoptotic appearance. Col-X and MMP-13 expression also increased with time. Our findings suggest that residual limbus inversion following closed reduction for DDH can cause progressive dysplasia of the acetabulum, apoptosis of acetabular chondrocytes, accelerated cartilage degeneration, and even early-stage osteoarthritis.

Observation of Solute Transport between Articular Cartilage and Subchondral Bone in Live Mice

OBJECTIVE

To establish a method for investigating the permeability of calcified cartilage zone (CCZ) and to observe solute transport between articular cartilage (AC) and subchondral bone (SB) through intact CCZ in vivo.

DESIGN

We developed a novel fixing device combined with un-decalcified fluorescence observation method to address the permeability of CCZ in live mice. Twenty-four Balb/c female mice aged 1 to 8 months were used to observe the development of CCZ. Eighty-four Balb/c female mice (aged 1 or 6 months) with mature or immature CCZ of distal femur were used to investigate the permeability of intact CCZ in vivo. Diffusivity of rhodamine B (476 Da) and tetramethyl-rhodamine isothicyanate-dextran (TRITC-Dextran, 20 kDa) was tested from AC to SB in 0 minutes, 1 minute, 15 minutes, 30 minutes, 1 hour, and 2 hours. None diffused knee joints (0 minutes) served as blank control, while in vitro immersion of distal femurs in rhodamine B or TRITC-Dextran for 72 hours served as positive control.

RESULTS

CCZ was well developed in 6-month mice. Both tracers penetrated immature CCZ down to SB in less than 1 hour in live mice, while the diffusion of both tracers decreased rapidly at tidemark in all testing time points.

CONCLUSION

Current study provided direct evidence of blocking effect of CCZ in solute transportation during short diffusion period in live animal, indicating the important role of CCZ in joint development and microenvironment maintenance.

Bioprinting of biomimetic self-organised cartilage with a supporting joint fixation device

Despite sustained efforts, engineering truly biomimetic articular cartilage (AC) via traditional top-down approaches remains challenging. Emerging biofabrication strategies, from 3D bioprinting to scaffold-free approaches that leverage principles of cellular self-organisation, are generating significant interest in the field of cartilage tissue engineering as a means of developing biomimetic tissue analoguesin vitro.Although such strategies have advanced the quality of engineered cartilage, recapitulation of many key structural features of native AC, in particular a collagen network mimicking the tissue's 'Benninghoff arcade', remains elusive. Additionally, a complete solution to fixating engineered cartilagesin situwithin damaged synovial joints has yet to be identified. This study sought to address both of these key challenges by engineering biomimetic AC within a device designed to anchor the tissue within a synovial joint defect. We first designed and fabricated a fixation device capable of anchoring engineered cartilage into the subchondral bone. Next, we developed a strategy for inkjet printing porcine mesenchymal stem/stromal cells (MSCs) into this supporting fixation device, which was also designed to provide instructive cues to direct the self-organisation of MSC condensations towards a stratified engineered AC. We found that a higher starting cell-density supported the development of a more zonally defined collagen network within the engineered tissue. Dynamic culture was implemented to further enhance the quality of this engineered tissue, resulting in an approximate 3 fold increase in glycosaminoglycan and collagen accumulation. Ultimately this strategy supported the development of AC that exhibited near-native levels of glycosaminoglycan accumulation (>5% WW), as well as a biomimetic collagen network organisation with a perpendicular to a parallel fibre arrangement (relative to the tissue surface) from the deep to superficial zones via arcading fibres within the middle zone of the engineered tissue. Collectively, this work demonstrates the successful convergence of novel biofabrication methods, bioprinting strategies and culture regimes to engineer a hybrid implant suited to resurfacing AC defects.

Betaine Attenuates Osteoarthritis by Inhibiting Osteoclastogenesis and Angiogenesis in Subchondral Bone

Osteoarthritis (OA) is the most common type of arthritis with no effective therapy. Subchondral bone and overlying articular cartilage are closely associated and function as “osteo-chondral unit” in the joint. Abnormal mechanical load leads to activated osteoclast activity and increased bone resorption in the subchondral bone, which is implicated in the onset of OA pathogenesis. Thus, inhibiting subchondral bone osteoclast activation could prevent OA onset. Betaine, isolated from the Lycii Radicis Cortex (LRC), has been demonstrated to exert anti-inflammatory, antifibrotic and antiangiogenic properties. Here, we evaluated the effects of betaine on anterior cruciate ligament transection (ACLT)-induced OA mice. We observed that betaine decreased the number of matrix metalloproteinase 13 (MMP-13)-positive and collagen X (Col X)-positive cells, prevented articular cartilage proteoglycan loss and lowered the OARSI score. Betaine decreased the thickness of calcified cartilage and increased the expression level of lubricin. Moreover, betaine normalized uncoupled subchondral bone remodeling as defined by lowered trabecular pattern factor (Tb.pf) and increased subchondral bone plate thickness (SBP). Additionally, aberrant angiogenesis in subchondral bone was blunted by betaine treatment. Mechanistically, we demonstrated that betaine suppressed osteoclastogenesis in vitro by inhibiting reactive oxygen species (ROS) production and subsequent mitogen-activated protein kinase (MAPK) signaling. These data demonstrated that betaine attenuated OA progression by inhibiting hyperactivated osteoclastogenesis and maintaining microarchitecture in subchondral bone.

Biomarkers of joint metabolism and bone mineral density are associated with early knee osteoarthritis in premenopausal females

INTRODUCTION

Biomarkers of bone and cartilage metabolism were proposed as early diagnosis indicators for knee osteoarthritis (OA), however, which were influenced by disease stage, age, and menopause state. Accurate diagnosis indicators are eagerly awaited. The current study aims to investigate associations of joint metabolism biomarkers and bone mineral density (BMD) with early knee OA in males and premenopausal females before age 50 years.

METHOD

A total of 189 patients aged before 50 years with early knee OA and 152 healthy participants were enrolled. Levels of bone biomarkers (PINP, OC, and CTX-I) and cartilage biomarkers (PIIANP, COMP, CTX-II, and MMP-3) were assessed. BMD was measured at the lumbar, femoral neck, and hip. Multivariate regression analyses were performed to evaluate the relationship between biomarkers, BMD, and early knee OA.

RESULTS

Serum COMP, urine CTX-II and BMD at femoral neck and hip were increased in premenopausal patients as compared to control; with serum PINP and OC reduced. Meanwhile, serum COMP, urine CTX-II, and BMD at femoral neck and hip showed positive associations with premenopausal early knee OA, while serum PINP had negative association. However, in male patients, only serum COMP was higher than control, and no association of biomarkers or BMD was found with early knee OA.

CONCLUSIONS

The joint metabolism biomarkers and BMD showed multiple associations with early knee OA in premenopausal females, but not in males aged before 50 years. It was suggested that sex differences should be taken into account when evaluating cartilage and bone metabolism in early knee OA. Key Points • The joint metabolism biomarkers and BMD are associated with early knee OA in premenopausal females, but not in males aged before 50 years. • Sex differences should be taken into account when evaluating cartilage and bone metabolism in early knee OA.

Enhanced Circadian Clock in MSCs-Based Cytotherapy Ameliorates Age-Related Temporomandibular Joint Condyle Degeneration

Aging has been proven to be one of the major causes of temporomandibular joint (TMJ) disability and pain in older people. Peripheral circadian rhythms play a crucial role in endochondral ossification and chondrogenesis. However, the age-related alterations of circadian clock in TMJ structures are seldom reported. In the current study, TMJ condyles were extracted from young (4-month-old), middle-aged (10-month-old), and old-aged (20-month-old) adults to detect the morphology and circadian oscillation changes in TMJ condyles with aging. The transcriptome profile of Bmal1-deleted bone-marrow mesenchymal stem cells (BMSCs) and controls were explored to reveal the circadian-related differences at the molecular level. Furthermore, the reparative effects of Bmal1-overexpressed BMSCs-based cytotherapy in aged TMJ condyles were investigated in vitro and in vivo. Aged TMJ condyles displayed damaged tissue structure and an abolished circadian rhythm, accompanied by a progressively decreasing chondrogenesis capability and bone turnover activities. The deletion of Bmal1 significantly down-regulated chondrogenesis-related genes Prg4, Sox9, and Col7a1. Bmal1-overexpressed BMSCs presented improved migration capability ex vivo and attenuated age-related TMJ condylar degeneration in vivo. These data demonstrate the crucial role of circadian timing in the maintenance of osteochondral homeostasis, and indicate the potential clinical prospects of circadian-modified MSCs therapy in tissue regeneration.

Osteoblasts Regulate the Expression of ADAMTS and MMPs in Chondrocytes through ERK Signaling Pathway

OBJECTIVE

Degradative enzymes such as matrix metalloproteinase (MMP) and disintegrin metalloproteinase with platelet thrombin-sensitive protein-like motifs (ADAMTS) play a key role in the development of osteoarthritis (OA). We aimed to investigate the effects of OA subchondral osteoblasts on the expression of ADAMTS4, ADAMTS5, MMP-3, MMP-9, and MMP-13 in chondrocytes and the regulation of mitogen-activated protein kinase (MAPK) signaling pathway.

METHODS

A rat knee OA model was constructed by cutting the anterior cruciate ligament of the knee joints, and normal rat articular cartilage chondrocytes (N-ACC), OA rat articular cartilage chondrocytes (O-ACC), normal subchondral bone osteoblasts (N-SBO), and OA subchondral bone osteoblasts (O-SBO) were isolated and extracted. The expressions of O-ACC and O-SBO COL1 and COL2 were detected respectively. Chondrocytes were identified by immunofluorescence of COL2 and toluidine blue staining, and osteoblasts were identified by COL1 immunofluorescence, alkaline phosphatase (ALP), and Alizarin Red staining. Gene expression of COL1, COL2, and aggrecan in normal chondrocytes and OA chondrocytes, and gene expression of osteoblast ALP and osteocalcin (OCN) were detected by RT-PCR to identify the two chondrocytes and the two osteoblast phenotypes. The constructing N-ACC group, O-ACC group, N-ACC + N-SBO group, N-ACC + O-SBO group, O-ACC + N-SBO group, O-ACC + O-SBO group, I + N-ACC + O-SBO group, and I + O-ACC + O-SBO group cell cultures, and the expression of ERK, ADAMTS4, ADAMTS5, MMP-3, MMP-9, and MMP-13 genes in chondrocytes cultured for 0, 24, 48, and 72 h were detected by RT-PCR. The protein expressions of pERK, ADAMTS4, ADAMTS5, MMP-3, MMP-9, and MMP-13 were detected by Western blot.

RESULTS

· The X-ray showed that the knee joint space of the affected limb became narrow.. · The results of RT-PCR of COL2 and aggrecan gene in OA and normal chondrocytes suggest that the relative expression of COL2 in OA articular chondrocytes (0.24 ± 0.07) is significantly lower than that in normal cartilage (0.61 ± 0.07) (p < 0.05). The relative expression of AGG (0.37 ± 0.16) in OA chondrocytes was significantly lower than that of normal chondrocytes AGG (1.30 ± 0.25) (p < 0.05). The expression of COL1 was very low, and was not statistically significant.. · The results of RT-PCR of the osteoblast ALP and OCN gene indicated that gene expression of ALP (12.30 ± 1.17) and OCN (20.47 ± 4.19)was upregulated when compared with the relative expression of ALP (4.66 ± 0.71) (p < 0.05) and OCN (12.17 ± 2.76) (p < 0.05) in normal osteoblasts, indicating that osteoblasts of OA have greater osteogenic potential than normal osteoblasts.. · The expressions of ADAMTS4, ADAMTS5, MMP-3, MMP-9, and MMP-13 genes and proteins in OA chondrocytes or normal chondrocytes were basically unchanged when they were cocultured with normal osteoblasts. Indirect coculture of OA osteoblasts and chondrocytes could promote the expression of ADAMTS4, ADAMTS5, MMP-3, MMP-9, and MMP-13 genes and proteins in chondrocytes. Overexpression of ADAMTS and MMP in coculture systems can be reversed by MAPK-ERK inhibitors..

CONCLUSIONS

· OA subchondral bone osteoblasts can promote the overexpression of ADAMTS and MMPs in chondrocytes.. · The ERK signaling pathway may be involved in the regulation of the effect of subchondral bone osteoblasts on chondrocytes..

Hypertension meets osteoarthritis - revisiting the vascular aetiology hypothesis

Osteoarthritis (OA) is a whole-joint disease characterized by subchondral bone perfusion abnormalities and neovascular invasion into the synovium and articular cartilage. In addition to local vascular disturbance, mounting evidence suggests a pivotal role for systemic vascular pathology in the aetiology of OA. This Review outlines the current understanding of the close relationship between high blood pressure (hypertension) and OA at the crossroads of epidemiology and molecular biology. As one of the most common comorbidities in patients with OA, hypertension can disrupt joint homeostasis both biophysically and biochemically. High blood pressure can increase intraosseous pressure and cause hypoxia, which in turn triggers subchondral bone and osteochondral junction remodelling. Furthermore, systemic activation of the renin-angiotensin and endothelin systems can affect the Wnt-β-catenin signalling pathway locally to govern joint disease. The intimate relationship between hypertension and OA indicates that endothelium-targeted strategies, including re-purposed FDA-approved antihypertensive drugs, could be useful in the treatment of OA.

Osteocyte Dysfunction in Joint Homeostasis and Osteoarthritis

Structural disturbances of the subchondral bone are a hallmark of osteoarthritis (OA), including sclerotic changes, cystic lesions, and osteophyte formation. Osteocytes act as mechanosensory units for the micro-cracks in response to mechanical loading. Once stimulated, osteocytes initiate the reparative process by recruiting bone-resorbing cells and bone-forming cells to maintain bone homeostasis. Osteocyte-expressed sclerostin is known as a negative regulator of bone formation through Wnt signaling and the RANKL pathway. In this review, we will summarize current understandings of osteocytes at the crossroad of allometry and mechanobiology to exploit the relationship between osteocyte morphology and function in the context of joint aging and osteoarthritis. We also aimed to summarize the osteocyte dysfunction and its link with structural and functional disturbances of the osteoarthritic subchondral bone at the molecular level. Compared with normal bones, the osteoarthritic subchondral bone is characterized by a higher bone volume fraction, a larger trabecular bone number in the load-bearing region, and an increase in thickness of pre-existing trabeculae. This may relate to the aberrant expressions of sclerostin, periostin, dentin matrix protein 1, matrix extracellular phosphoglycoprotein, insulin-like growth factor 1, and transforming growth factor-beta, among others. The number of osteocyte lacunae embedded in OA bone is also significantly higher, yet the volume of individual lacuna is relatively smaller, which could suggest abnormal metabolism in association with allometry. The remarkably lower percentage of sclerostin-positive osteocytes, together with clustering of Runx-2 positive pre-osteoblasts, may suggest altered regulation of osteoblast differentiation and osteoblast-osteocyte transformation affected by both signaling molecules and the extracellular matrix. Aberrant osteocyte morphology and function, along with anomalies in molecular signaling mechanisms, might explain in part, if not all, the pre-osteoblast clustering and the uncoupled bone remodeling in OA subchondral bone.

Changes in bone density, intraosseous pressure of distal femoral articular cartilage and subchondral bone after proximal femoral medullary cavity cement filling in rabbits

Bone cement is widely used, particularly in hip replacements, but the potential clinical complications of its use have been largely unrecognized. The purpose of the present study was to investigate the effects of bone cement in the proximal femoral medullary cavity (PFMC) on bone mineral density (BMD), intraosseous pressure (IOP), articular cartilage and subchondral bone in the distal femurs of rabbits. A total of 32 New Zealand white rabbits were randomly numbered and the left hind limb of the odd-numbered rabbits and the right hind limb of the even numbered rabbits were selected as the experimental side. For each rabbit, the non-experimental hind limb was labeled as the control side by the principal investigator. An intramedullary injection of polymethyl methacrylate was made into the experimental hindlimb of each rabbit and the PFMC filled with bone cement. BMD and IOP of the distal femur of the bilateral hindlimb were measured at 4 and 16 weeks after surgery, and histological and ultra-fine structural features were examined by light and transmission electron microscopy, respectively. At week 4 after the operation, IOP in the experimental limb was significantly higher and BMD lower compared with the control limb. At the 16th week after operation, the IOP in the experimental limb was lower than at the 4th week after operation, but still higher compared with controls, and the BMD was significantly higher than the controls. In the controls, IOP and BMD was not significantly different between the 4th and 16th week after operation. Compared with controls, the cartilage in the experimental group was thinner, the chondrocytes partially necrotic and the trabecular structure of the subchondral bone broken. Analysis of ultra-fine structural features in the experimental group showed chondrocytes with necrotic cytoplasm and pyknotic nuclei relative to controls. The results indicated that blockage of the PFMC with bone cement resulted in an increase in the IOP in the distal femur, a change in BMD and damage to the subchondral bone and articular cartilage.

Macro, Micro, and Molecular. Changes of the Osteochondral Interface in Osteoarthritis Development

Osteoarthritis (OA) is a long-term condition that causes joint pain and reduced movement. Notably, the same pathways governing cell growth, death, and differentiation during the growth and development of the body are also common drivers of OA. The osteochondral interface is a vital structure located between hyaline cartilage and subchondral bone. It plays a critical role in maintaining the physical and biological function, conveying joint mechanical stress, maintaining chondral microenvironment, as well as crosstalk and substance exchange through the osteochondral unit. In this review, we summarized the progress in research concerning the area of osteochondral junction, including its pathophysiological changes, molecular interactions, and signaling pathways that are related to the ultrastructure change. Multiple potential treatment options were also discussed in this review. A thorough understanding of these biological changes and molecular mechanisms in the pathologic process will advance our understanding of OA progression, and inform the development of effective therapeutics targeting OA.

Clusterin secretion is attenuated by the proinflammatory cytokines interleukin-1β and tumor necrosis factor-α in models of cartilage degradation

The protein clusterin has been implicated in the molecular alterations that occur in articular cartilage during osteoarthritis (OA). Clusterin exists in two isoforms with opposing functions, and their roles in cartilage have not been explored. The secreted form of clusterin (sCLU) is a cytoprotective extracellular chaperone that prevents protein aggregation, enhances cell proliferation and promotes viability, whereas nuclear clusterin acts as a pro-death signal. Therefore, these two clusterin isoforms may be putative molecular markers of repair and catabolic responses in cartilage and the ratio between them may be important. In this study, we focused on sCLU and used established, pathophysiologically relevant, in vitro models to understand its role in cytokine-stimulated cartilage degradation. The secretome of equine cartilage explants, osteochondral biopsies and isolated unpassaged chondrocytes was analyzed by western blotting for released sCLU, cartilage oligomeric protein (COMP) and matrix metalloproteinases (MMP) 3 and 13, following treatment with the proinflammatory cytokines interleukin-1β (IL-1β) and tumor necrosis factor-α. Release of sulfated glycosaminoglycans (sGAG) was determined using the dimethylmethylene blue assay. Clusterin messenger RNA (mRNA) expression was quantified by quantitative real-time polymerase chain reaction. MMP-3, MMP-13, COMP, and sGAG release from explants and osteochondral biopsies was elevated with cytokine treatment, confirming cartilage degradation in these models. sCLU release was attenuated with cytokine treatment in all models, potentially limiting its cytoprotective function. Clusterin mRNA expression was down-regulated 7-days post cytokine stimulation. These observations implicate sCLU in catabolic responses of chondrocytes, but further studies are required to evaluate its role in OA and its potential as an investigative biomarker.

miR-122/SIRT1 axis regulates chondrocyte extracellular matrix degradation in osteoarthritis

Background/Aims: MicroRNAs (miRNAs) are involved in the pathogenesis of osteoarthritis (OA). The present study aimed to investigate the potential function of miR-122 in the development of OA and its potential molecular mechanisms. Methods: The expression of miR-122, silent information regulator 1 (SIRT1), collagen II, aggrecan, matrix metalloproteinase (MMP) 13 (MMP13) and ADAMTS4 in OA cartilage was detected by RT-qPCR. Target gene prediction and screening, luciferase reporter assay were used to verify downstream target genes of miR-122. Results: Compared with osteonecrosis, the expression of miR-122 was significantly increased in OA cartilage, while the expression of SIRT1 was significantly decreased. Overexpression of miR-122 increased the expression of extracellular matrix (ECM) catabolic factors, for example disintegrins, MMPs and metalloproteinases with platelet reaction protein motifs, and inhibited the expression of synthetic metabolic genes such as collagen II and aggregating proteoglycan. Inhibition of miR-122 expression had the opposite effect. Furthermore, SIRT1 was identified as a direct target of miR-122. SIRT1 was significantly inhibited by miR-122 overexpression. Knockdown of SIRT1 reversed the degradation of chondrocyte ECM by miR-122 inhibitors. Conclusion: The miR-122/SIRT1 axis can regulate the degradation of ECM in OA, thus providing new insights into the treatment of OA.

MR imaging pattern of tibial subchondral bone structure: considerations of meniscal coverage and integrity

OBJECTIVES

To compare regional differences in subchondral trabecular structure using high-resolution MRI in meniscus-covered/meniscus-uncovered tibia in cadaveric knees with intact/torn menisci.

MATERIALS AND METHODS

3D proton density CUBE MRI of 6 cadaveric knees without significant osteoarthritis (OA) was acquired, 0.25-mm resolution. Menisci were evaluated and classified intact or torn. MR data were transferred to ImageJ program to segment tibial 3D volume of interest (VOI). Data was subdivided into meniscus-covered/meniscus-uncovered regions. Segmented VOI was classified into binary data, trabeculae/bone marrow. The trabecular bone data was used to measure MR biomarkers (apparent subchondral plate-connected bone density (adapted from spine MR), apparent trabecular bone volume fraction, apparent mean trabecular thickness, apparent connectivity density, and structure model index (SMI)). Mean value of parameters was analyzed for the effects of meniscal tear/tibial coverage.

RESULTS

Nine torn menisci and 3 intact menisci were present. MR measures of bone varied significantly due to meniscal coverage/tear. Subchondral plate-connected bone density under covered meniscus regions increased from 10.9 to 23.5% with meniscal tear. Values increased in uncovered regions, 19.3% (intact) and 32.4% (torn). This reflects higher density when uncovered (p = 0.048) with meniscal tear (p = 0.007). Similar patterns were found for trabecular bone fraction (coverage p < 0.001, tear p = 0.047), trabecular thickness (coverage p = 0.03), connectivity density (coverage p = 0.002), and SMI (coverage p = 0.015).

CONCLUSION

Quantitative trabecular bone evaluation emphasizes intrinsic structural differences between meniscus-covered/meniscus-uncovered tibias. Results offer insight into bone adaptation with meniscal tear and support the hypothesis that subchondral bone plate-connected bone density could be important in early subchondral bone adaptation.

Parathyroid hormone ameliorates temporomandibular joint osteoarthritic-like changes related to age

OBJECTIVES

Ageing could be a contributing factor to the progression of temporomandibular joint osteoarthritis (TMJ OA), whereas its pathogenesis and potential therapeutic strategy have not been comprehensively investigated.

MATERIALS AND METHODS

We generated ageing mouse models (45-week and 60-week; 12-week mice as control) and intermittently injected 45-week mice with parathyroid hormone (PTH(1-34)) or vehicle for 4 weeks. Cartilage and subchondral bone of TMJ were analysed by microCT, histological and immunostaining. Western blot, qRT-PCR, ChIP, ELISA and immunohistochemical analysis were utilized to examination the mechanism of PTH(1-34)'s function.

RESULTS

We showed apparent OA-like phenotypes in ageing mice. PTH treatment could ameliorate the degenerative changes and improve bone microarchitecture in the subchondral bone by activating bone remodelling. Moreover, PTH inhibited phosphorylation level of Smad3, which can combine with p16^ink4a gene promoter region, resulting in reduced senescent cells accumulation and increased cellular proliferation of marrow mesenchymal stem cells (MSCs). ELISA also showed relieved levels of specific senescent-associated secretory phenotype (SASP) in ageing mice after PTH treatment.

CONCLUSIONS

In summary, PTH may reduce the accumulation of senescent cells in subchondral bone by inhibiting p16^ink4a and improve bone marrow microenvironment to active bone remodelling process, indicating PTH administration could be a potential preventative and therapeutic treatment for age-related TMJ OA.

Biomaterial-engineered intra-articular drug delivery systems for osteoarthritis therapy

Osteoarthritis (OA) is a progressive and degenerative disease, which is no longer confined to the elderly. So far, current treatments are limited to symptom relief, and no valid OA disease-modifying drugs are available. Additionally, OA relative joint is challenging for drug delivery, since the drugs experience rapid clearance in joint, showing a poor bioavailability. Existing therapeutic drugs, like non-steroidal anti-inflammatory drugs (NSAIDs) and corticosteroids, are not conducive for long-term use due to adverse effects. Though supplementations, including chondroitin sulfate and glucosamine, have shown beneficial effects on joint tissues in OA, their therapeutic use is still debatable. New emerging agents, like Kartogenin (KGN) and Interleukin-1 receptor antagonist (IL-1 ra), without a proper formulation, still will not work. Therefore, it is urgent to establish a suitable and efficient drug delivery system for OA therapy. In this review, we pay attention to various types of drug delivery systems and potential therapeutic drugs that may escalate OA treatments.

Beyond Cartilage Repair: The Role of the Osteochondral Unit in Joint Health and Disease

Once believed to be limited to articular cartilage, osteoarthritis is now considered to be an organ disease of the “whole joint.” Damage to the articular surface can lead to, be caused by, or occur in parallel with, damage to other tissues in the joint. The relationship between cartilage and the underlying subchondral bone has particular importance when assessing joint health and determining treatment strategies. The articular cartilage is anchored to the subchondral bone through an interface of calcified cartilage, which as a whole makes up the osteochondral unit. This unit functions primarily by transferring load-bearing weight over the joint to allow for normal joint articulation and movement. Unfortunately, irreversible damage and degeneration of the osteochondral unit can severely limit joint function. Our understanding of joint pain, the primary complaint of patients, is poorly understood and past efforts toward structural cartilage restoration have often not been associated with a reduction in pain. Continued research focusing on the contribution of subchondral bone and restoration of the entire osteochondral unit are therefore needed, with the hope that this will lead to curative, and not merely palliative, treatment options. The purpose of this narrative review is to investigate the role of the osteochondral unit in joint health and disease. Topics of discussion include the crosstalk between cartilage and bone, the efficacy of diagnostic procedures, the origins of joint pain, current and emerging treatment paradigms, and suitable preclinical animal models for safety and efficacy assessment of novel osteochondral therapies. The goal of the review is to facilitate an appreciation of the important role played by the subchondral bone in joint pain and why the osteochondral unit as a whole should be considered in many cases of joint restoration strategies.

Protective Effect of Alendronate on Lumbar Facet Degeneration in Ovariectomized Rats

Background

Facet joint degeneration (FJD) is a potential source of lower back pain, and estrogen deficiency can accelerate FJD. The present study aimed to investigate the effects of alendronate (ALN) on FJD induced by ovariectomy (OVX) in rats.

Material/Methods

Thirty female Sprague-Dawley rats underwent either bilateral OVX (n=20) or sham surgery (n=10). The OVX rats subsequently received either subcutaneous ALN (70 μg/kg/week) or vehicle for 12 weeks. Subchondral bone mass and microarchitecture were evaluated by micro-computed tomography. Cartilage degradation was evaluated by toluidine blue staining and histological scoring.

Results

Compared with the Sham group, the OVX group had significantly decreased bone mineral density, bone volume/trabecular volume, and trabecular thickness, significantly increased trabecular separation in subchondral bone, and significantly higher histological score for cartilage degeneration, particularly loss of cartilage thickness. ALN treatment significantly reversed the changes in subchondral bone, preserved cartilage thickness, and reduced the histological score. Immunohistochemical analyses showed significantly decreased expression of ADAMTS-4, MMP-13, and caspase-3 in the OVX+ALN group compared with the OVX group.

Conclusions

Treatment with ALN suppressed bone loss, subchondral bone architecture deterioration, and cartilage degeneration in OVX rats, which can be explained by roles of ALN in preservation of subchondral bone mass and microarchitecture, and counteraction of catabolism and chondrocyte apoptosis in cartilage.

Artesunate, an Anti-Malaria Agent, Attenuates Experimental Osteoarthritis by Inhibiting Bone Resorption and CD31hiEmcnhi Vessel Formation in Subchondral Bone

Osteoarthritis (OA) is a common and debilitating joint disease worldwide without interventions available to reverse its progression. Artesunate (ART), an anti-malaria agent, possesses diverse biological activities, including the inhibition of osteoclastogenesis and angiogenesis in various cells, but its role in subchondral bone during OA progression is not known. Here, we explored the curative effects of ART on the pathogenesis of OA in anterior cruciate ligament transection (ACLT) mice models. We found that ART attenuated articular cartilage degeneration, defined by lowered histologic scoring of OA and retarded calcification of the cartilage zone. Moreover, ART improved the expression of lubricin and aggrecan and reduced the expression of collagen X (Col X) and matrix metalloproteinase-13 (MMP-13). In parallel, ART normalized abnormal subchondral bone remodeling by maintaining bone volume fraction (BV/TV) and subchondral bone plate thickness (SBP Th) and reducing trabecular pattern factor (Tb.pf) compared to the vehicle-treated mice. Our results indicated that ART suppressed osteoclastic bone resorption through regulating RANKL-OPG system, restored coupled bone remodeling by indirectly inhibiting TGF-β/Smad2/3 signaling. Additionally, ART abrogated CD31^hiEmcn^hi vessel formation via downregulating the expression of vascular endothelial growth factor (VEGF) and angiogenin-1 in subchondral bone. In conclusion, ART attenuates ACLT-induced OA by blocking bone resorption and CD31^hiEmcn^hi vessel formation in subchondral bone, indicating that this may be a new therapeutic alternative for OA.

Docosahexaenoic acid inhibits bone remodeling and vessel formation in the osteochondral unit in a rat model

OBJECTIVES

We aimed to determine whether bone remodeling and vessel formation in the osteochondral unit are suppressed by supplementing with docosahexaenoic acid in anterior cruciate ligament transection (ACLT)-induced rats.

METHODS

Twelve-week-old male Sprague Dawley rats were randomized to sham-operated, ACLT-operated and treated with vehicle, or ACLT-operated and treated with DHA groups. Micro-architecture and vasculature in the tibial osteochondral unit were examined by micro-CT, as well as by histomorphometry. To evaluate the effects of DHA in vitro, we conducted functional and expressional assays in RAW264.7 cells and HUVECs. Finally, we used OARSI-modified Mankin criteria and histological analyses to assess the status of the cartilage layer.

RESULTS

Microstructural parameters in the osteochondral unit showed that bone mass loss and angiogenesis were less in DHA-treated rats than in vehicle-treated rats. Immunofluorescence-positive cells labeled with TRAP, RANKL, CD31, and endomucin agents in the osteochondral unit of ACLT-operated rats were reduced in the DHA-treated group compared with the vehicle-treated group. Furthermore, the number of TRAP-stained cells, areas of bone resorption pits, and mRNA expression of TRAP, CTSK, MITF, and NFATC1 were reduced in RAW264.7 cells treated with RANKL + DHA compared with those treated with only RANKL. Tube formation, proliferation and migration of HUVECs, and VEGF-C mRNA and VEGFR2 protein expression were inhibited by DHA. The decrease in OARSI score, and MMP-13 and collagen X expression suggested that DHA attenuated cartilage degeneration.

CONCLUSIONS

DHA has the ability to restrain bone remodeling and vessel formation in the osteochondral unit, which may contribute to protection of cartilage.

Relationships between cartilage thickness and subchondral bone mineral density in non-osteoarthritic and severely osteoarthritic knees: In vivo concomitant 3D analysis using CT arthrography

OBJECTIVE

To test whether subchondral bone mineral density (sBMD) and cartilage thickness (CTh) of femoral condyles are correlated in knees without and with severe medial femorotibial osteoarthritis (OA), using a subregional analysis with computerized tomography (CT) arthrography.

METHODS

CT arthrograms of 50 non-OA (18 males, 58.7 (interquartile range (IQR) = 6.6 years)) and 50 severe medial OA (24 males, 60.5 (IQR = 10.7) years) knees, were retrospectively analyzed. Bone and cartilage were segmented using custom-designed software, leading to 3D models on which each point of the subchondral surface is given a CTh and sBMD value. The average sBMD and CTh were then calculated for the entire weight-bearing regions as well as specific subregions of interest. Linear bivariate and multivariable analyses were performed to test for relationships between sBMD and CTh (regional and subregional measures, or medial-to-lateral ratios), with confounders of age, gender, femoral bone size and femorotibial angle.

RESULTS

In non-OA knees, the sBMD and CTh medial-to-lateral ratios were positively correlated for the total region and the external and internal subregions (r ≥ 0.341, P ≤ 0.015). In OA knees, sBMD and CTh medial-to-lateral ratios were negatively correlated for the total region and the external and central subregions (r ≤ -0.538, P < 0.001). Additional positive/negative relationships in the non-OA/OA knees were observed between sBMD and CTh measures in the medial compartment.

CONCLUSIONS

The positive correlation between sBMD and CTh in non-OA knees, and the negative one in OA knees, bring support to the theory of a subchondral bone/cartilage functional unit, which could help to better understand the pathophysiology of OA.

Calcium-Phosphate Crystals Promote RANKL Expression via the Downregulation of DUSP1

Osteoarthritis (OA) is a naturally occurring, irreversible disorder and a major health burden. The disease is multifactorial, involving both physiological and mechanical processes, but calcium crystals have been associated intimately with its pathogenesis. This study tested the hypothesis that these crystals have a detrimental effect on the differentiation of osteoclasts and bone homeostasis. This study employed an osteoblast-osteoclast coculture system that resembles in vivo osteoblast-dependent osteoclast differentiation along with Ca2+-phosphate-coated culture dishes. The calcium-containing crystals upregulated the expression of RANKL and increased the differentiation of osteoclasts significantly as a result. On the other hand, osteoblast differentiation was unaffected. MicroRNA profiling showed that dual-specificity phosphatases 1 (DUSP1) was associated with the increased RANKL expression. DUSP1 belongs to a family of MAPK phosphatases and is known to inactivate all three groups of MAPKs, p38, JNK, and ERK. Furthermore, knockdown of DUSP1 gene expression suggested that RANKL expression increases significantly in the absence of DUSP1 regulation. Microarray analysis of the DUSP1 mRNA levels in patients with pathological bone diseases also showed that the downregulated DUSP1 expression leads to increased expression of RANKL and consequently to the destruction of the bone observed in these patients. These findings suggest that calcium-containing crystals may play a crucial role in promoting RANKL-induced osteoclastogenesis via DUSP1.

Electroacupuncture Ameliorates Subchondral Bone Deterioration and Inhibits Cartilage Degeneration in Ovariectomised Rats

Objectives

To investigate the effects of electroacupuncture (EA) on subchondral bone mass and cartilage degeneration in an experimental animal model of osteoarthritis (OA) induced by ovariectomy (OVX).

Methods

Ninety 3-month-old female Sprague-Dawley rats were randomly divided into the following three groups (n = 30 each): sham operation without treatment (control group); OVX without treatment (OVX group);, and ovariectomy with EA treatment (EA group). Rats in the EA group received EA treatment from the day of OVX. Ten rats in each group were randomly killed at 4, 8 and 12 weeks after operation.

Results

EA reduced urine C-terminal cross-linking telopeptide of type I collagen from 4 weeks after OVX, reduced C-terminal cross-linking telopeptide of type II collagen and body weight from 8 weeks after OVX, and increased serum 17β-oestradiol from 4 weeks after OVX compared with the OVX group (all p<0.01). In the EA group, trabecular bone volume ratio, trabecular thickness and trabecular number increased, and trabecular separation were reduced at each time point compared with the OVX group (p<0.05, p<0.01, respectively). In the EA group, osteoprotegerin (OPG) expression was increased and receptor activator of nuclear factor kappa-B ligand (RANKL) expression was reduced at each time point compared with the OVX group (p<0.05, p<0.01, respectively). Mankin scores and mRNA expression of matrix metalloproteinase-13 (MMP-13) were lower in EA versus OVX groups at 12 weeks after OVX (both p<0.01).

Conclusion

The results suggest that EA inhibits subchondral bone loss by regulating RANK/RANKL/OPG signalling and protects articular cartilage by inhibiting MMP-13 in OVX rats.

Differences in subchondral bone plate and cartilage thickness between women with anterior cruciate ligament reconstructions and uninjured controls

OBJECTIVE

Anterior cruciate ligament (ACL) tears increase early onset osteoarthritis (OA) risk leading to cartilage and bone degradation. While the contribution of bone in OA development is unclear, evidence suggests that bone changes accompany cartilage degradation. This study aims to assess if regions with differences in subchondral bone plate thickness have differences in cartilage thickness when comparing ACL reconstructed (ACLR) knees of women ≥5 years post-injury to contralateral and controls with uninjured knees.

DESIGN

Magnetic resonance imaging (MRI) assessed cartilage and high resolution peripheral quantitative computed tomography (HR-pQCT) assessed subchondral bone in both knees. Multimodal 3D image registration aligned anatomy. Maps of the spatial distribution of thickness on the articular surfaces were generated to compare women with ACL reconstructions to contralateral and controls with uninjured knees.

RESULTS

ACLR knees had a thicker subchondral bone plate in the posterior and central lateral femur compared to contralateral knees (10.4% and 4.2% thicker, P = 0.032 and 0.032, W = 108 and 107, respectively) and in the posterior lateral femur compared to control knees (17.1% thicker, P = 0.014, W = 177). Cartilage differences were not detected (P > 0.05) in these regions.

CONCLUSIONS

This study demonstrates that subchondral bone plate thickness differences are prominent following knee injury, as measured by HR-pQCT, but no statistically significant differences in cartilage morphology, measured by MRI, were found between ACLR knees compared to contralateral and control knees. These data provide novel insight into post-traumatic knee injuries that may be signs of early OA pathogenesis.

Salmon Calcitonin Attenuates Degenerative Changes in Cartilage and Subchondral Bone in Lumbar Facet Joint in an Experimental Rat Model

Background

Facet joint degeneration (FJD) is one of the common causes of low back pain (LBP), and estrogen deficiency is one of the triggers for FJD. Calcitonin may possess the potential for treating osteoarthritis, but to date the hormone has not been studied in the treatment of FJD. Therefore, the aim of this study was to investigate the effects of salmon calcitonin (sCT) on FJD induced by estrogen deficiency after ovariectomy (OVX).

Material/Methods

Thirty female Sprague-Dawley rats were randomly assigned to 3 groups: the OVX group received bilateral OVX, the OVX + sCT group received subcutaneous administration of sCT (16 IU/kg/2 days) following bilateral OVX, and the Sham group received sham surgery. All rats were euthanized at 12 weeks post-OVX. Serum COMP level, cartilage degradation, and subchondral bone micro-architecture were evaluated.

Results

sCT relieved cartilage surface lesions, reduced histological score, and significantly increased cartilage thickness. The OVX + sCT group exhibited significantly increased expression of aggrecan, as well as significantly decreased levels of ADAMTS-4, MMP-13, and caspase-3. The results of micro-computed tomography analysis revealed that the OVX + sCT group exhibited higher BMD, BV/TV, and Tb.Th values but a lower Tb.Sp value than that of the OVX group. Serum COMP concentrations were significantly correlated with histological score and cartilage thickness.

Conclusions

sCT can inhibit the progression of FJD in OVX rats, which is attributed to its inhibitory effects on cartilage metabolism imbalance, chondrocyte apoptosis, and subchondral bone remodeling. Serum COMP has diagnostic potential for FJD.

Effectiveness of a Dietary Supplement Containing Hydrolyzed Collagen, Chondroitin Sulfate, and Glucosamine in Pain Reduction and Functional Capacity in Osteoarthritis Patients

This observational, open, multicenter clinical trial with a single treatment group aimed to evaluate the effectiveness of a dietary supplement whose main ingredients are hydrolyzed gelatin, chondroitin sulfate, glucosamine sulfate, and devil's claw and bamboo extracts for pain reduction and improvement of functional capacities in patients with osteoarthritis (OA) of the knee and/or hip (REDART study). In all, 130 patients with OA recruited from Spanish hospitals received the dietary supplement for 6 months. The primary outcome was the patients' global assessment of pain in the affected joint as measured with a visual analogue scale (VAS). Other outcome measurements included the Lequesne Functional Index (subindexes for pain/discomfort, distance walked, and daily living) and the Western Ontario and McMaster Universities Arthritis Index (WOMAC; subindexes for pain, stiffness, and physical function). Scores were taken at months 3 and 6 of the treatment. Patients (N = 78) showed a reduction of pain of 3.77 ± 1.77 points after 6 months (p < .0001) in the VAS. The total reduction in the Lequesne Functional Index was 6.30 ± 4.08 points after 6 months (p < .0001), with significant reductions in all subindexes of the scale. A similar pattern was found for the WOMAC index, with an overall reduction of 22.49 ± 14.03 points after 6 months (p < .0001) and significant reductions in all subindexes. No major adverse events were noted during the treatment. This exploratory study shows that treatment with the dietary supplement significantly reduces pain and improves locomotor function in patients with OA of the knee and/or hip.

Bioadhesive Polymersome for Localized and Sustained Drug Delivery at Pathological Sites with Harsh Enzymatic and Fluidic Environment via Supramolecular Host-Guest Complexation

Targeted and sustained delivery of drugs to diseased tissues/organs, where body fluid exchange and catabolic activity are substantial, is challenging due to the fast cleansing and degradation of the drugs by these harsh environmental factors. Herein, a multifunctional and bioadhesive polycaprolactone-β-cyclodextrin (PCL-CD) polymersome is developed for localized and sustained co-delivery of hydrophilic and hydrophobic drug molecules. This PCL-CD polymersome affords multivalent crosslinking action via surface CD-mediated host-guest interactions to generate a supramolecular hydrogel that exhibits evident shear thinning and efficient self-healing behavior. The co-delivery of small molecule and proteinaceous agents by the encapsulated PCL-CD polymersomes enhances the differentiation of stem cells seeded in the hydrogel. Furthermore, the PCL-CD polymersomes are capable of in situ grafting to biological tissues via host-guest complexation between surface CD and native guest groups in the tissue matrix both in vitro and in vivo, thereby effectively extending the retention of loaded cargo in the grafted tissue. It is further demonstrated that the co-delivery of small molecule and proteinaceous drugs via PCL-CD polymersomes averts cartilage degeneration in animal osteoarthritic (OA) knee joints, which are known for their biochemically harsh and fluidically dynamic environment.

Isoliquiritigenin blunts osteoarthritis by inhibition of bone resorption and angiogenesis in subchondral bone

Isoliquiritigenin (ISL), a natural flavonoid extracted from licorice, has been demonstrated to exert attenuation of osteoclastogenesis and anti-angiogenesis activity in a wide variety of cells. Here, we first evaluated the effects of ISL on pathogenesis of osteoarthritis in a mouse model of OA. The data showed that ISL blunted progression of OA and lowered the Osteoarthritis Research Society International (OARSI)-Modified Making Score and protected the articular cartilage. The thickness of calcified cartilage zone was significantly decreased in ISL-treated ACLT mice compared with vehicle group. ISL increased expression level of lubricin and decreased collagen X (Col X), matrix metalloproteinase-13 (MMP-13). Moreover, ISL reduced aberrant active subchondral bone remodelling, including lowered trabecular pattern factor (Tb.pf) and increased bone volume/tissue volume (BV/TV, %) and thickness of subchondral bone plate (SBP) compared with vehicle-treated group. The results of immunostaining further revealed that ISL directly reduced RANKL-RANK-TRAF6 singling pathway induced osteoclastogenesis, prevented abnormal bone formation through indirect inhibition of TGF-β release. Additionally, ISL exerts anti-angiogenesis effects in subchondral bone through direct suppression of MMP-2. These results indicated that ISL attenuates progression of OA by inhibition of bone resorption and angiogenesis in subchondral bone, indicating that this may be a potential preventive therapy for OA.

Tissue material properties and computational modelling of the human tibiofemoral joint: a critical review

Understanding how structural and functional alterations of individual tissues impact on whole-joint function is challenging, particularly in humans where direct invasive experimentation is difficult. Finite element (FE) computational models produce quantitative predictions of the mechanical and physiological behaviour of multiple tissues simultaneously, thereby providing a means to study changes that occur through healthy ageing and disease such as osteoarthritis (OA). As a result, significant research investment has been placed in developing such models of the human knee. Previous work has highlighted that model predictions are highly sensitive to the various inputs used to build them, particularly the mathematical definition of material properties of biological tissues. The goal of this systematic review is two-fold. First, we provide a comprehensive summation and evaluation of existing linear elastic material property data for human tibiofemoral joint tissues, tabulating numerical values as a reference resource for future studies. Second, we review efforts to model tibiofemoral joint mechanical behaviour through FE modelling with particular focus on how studies have sourced tissue material properties. The last decade has seen a renaissance in material testing fuelled by development of a variety of new engineering techniques that allow the mechanical behaviour of both soft and hard tissues to be characterised at a spectrum of scales from nano- to bulk tissue level. As a result, there now exists an extremely broad range of published values for human tibiofemoral joint tissues. However, our systematic review highlights gaps and ambiguities that mean quantitative understanding of how tissue material properties alter with age and OA is limited. It is therefore currently challenging to construct FE models of the knee that are truly representative of a specific age or disease-state. Consequently, recent tibiofemoral joint FE models have been highly generic in terms of material properties even relying on non-human data from multiple species. We highlight this by critically evaluating current ability to quantitatively compare and model (1) young and old and (2) healthy and OA human tibiofemoral joints. We suggest that future research into both healthy and diseased knee function will benefit greatly from a subject- or cohort-specific approach in which FE models are constructed using material properties, medical imagery and loading data from cohorts with consistent demographics and/or disease states.

Ultrastructural change of the subchondral bone increases the severity of cartilage damage in osteoporotic osteoarthritis of the knee in rabbits

Osteoporotic osteoarthritis is a phenotype of osteoarthritis (OA) manifested as fragile and osteoporotic subchondral bone. However, the ultrastructural features of subchondral bone in osteoporosis OA have not been determined. The study was aimed to investigate the ultrastructural dynamic changes of subchondral bone in osteoporotic OA model and how the ultrastructural damage in the subchondral bone caused by osteoporosis deteriorated the cartilage damage in OA. Eighteen rabbits were equally randomized to three groups, including the control, the OA and the osteoporotic OA groups. The structural changes of cartilage were evaluated by HE and safranin-O fast green staining, the Mankin's grading system was used to assess the stage of OA progression. And microstructural or ultrastructural changes in subchondral bone were assessed by micro-computed tomography or by scanning electron microscopy. According to the changes of cartilage histopathology, the OA group was in the early pathological stage of OA while the osteoporotic OA group was in the middle stage of OA based on Mankin's grading system. In addition, the damage of cartilage surface, reduction in the number of chondrocytes and the matrix staining were more increased in the osteoporotic OA group compared to the OA group. Compared to the OA group, the subchondral bone in the microstructure and ultrastructure in the osteoporotic OA group showed more microfracture changes in trabecular bone with more destructions of the tree-like mesh. Moreover, the collagen fibers were random rough with a fewer amount of bone lacunae in subchondral cortical plate in the osteoporotic OA group compared to the OA group. These findings indicated that the subchondral bone ultrastructure in the osteoporotic OA model was characterized by the destruction of the network structure and collagen fibers. The subchondral bone ultrastructural damage caused by osteoporosis may change mechanical properties of the upper cartilage and aggravate OA cartilage. Therefore, early diagnosis and treatment of osteoporosis is of great significance to prevent early OA from further developing osteoporotic OA.

Alteration of Wnt5a expression and of the non-canonical Wnt/PCP and Wnt/PKC-Ca2+ pathways in human osteoarthritis osteoblasts

Objective

Clinical and in vitro studies suggest that subchondral bone sclerosis due to abnormal osteoblasts (Ob) is involved in the progression and/or onset of osteoarthritis (OA). Human Ob isolated from sclerotic subchondral OA bone tissue show an altered phenotype, a decreased canonical Wnt/β-catenin signaling pathway (cWnt), and a reduced mineralization in vitro. In addition to the cWnt pathway, at least two non-canonical signaling pathways, the Wnt/PKC and Wnt/PCP pathway have been described. However, there are no reports of either pathway in OA Ob. Here, we studied the two non-canonical pathways in OA Ob and if they influence their phenotype.

Methods

Human primary subchondral Ob were isolated from the subchondral bone plate of tibial plateaus of OA patients undergoing total knee arthroplasty, or of normal individuals at autopsy. The expression of genes involved in non-canonical Wnt signaling was evaluated by qRT-PCR and their protein production by Western blot analysis. Alkaline phosphatase activity and osteocalcin secretion (OC) were determined with substrate hydrolysis and EIA, respectively. Mineralization levels were evaluated with Alizarin Red Staining, Wnt/PKC and Wnt/PCP pathways by target gene expression and their respective activity using the NFAT and AP-1 luciferase reporter assays.

Results

OA Ob showed an altered phenotype as illustrated by an increased alkaline phosphatase activity and osteocalcin release compared to normal Ob. The expression of the non-canonical Wnt5a ligand was increased in OA Ob compared to normal. Whereas, the expression of LGR5 was significantly increased in OA Ob compared to normal Ob, the expression of LGR4 was similar. Wnt5a directly stimulated the expression and production of LGR5, contrasting, Wnt5a did not stimulate the expression of LGR4. Wnt5a also stimulated the phosphorylation of both JNK and PKC, as well as the activity of both NFAT and AP-1 transcription factors. The inhibition of Wnt5a expression partially corrects the abnormal mineralization, OC secretion and ALPase activity of OA Ob.

Conclusion

These data indicate that the alteration of Wnt5a, a non-canonical Wnt signaling activator, is implicated in the modified signalisation and phenotype observed in OA Ob.

PTH [1-34] induced differentiation and mineralization of mandibular condylar cartilage

Intermittent Parathyroid Hormone (I-PTH) is the only FDA approved anabolic drug therapy available for the treatment of osteoporosis in males and postmenopausal females. The effects of I-PTH on the chondrogenic lineage of the mandibular condylar cartilage (MCC) are not well understood. To investigate the role of I-PTH on the MCC and subchondral bone, we carried out our studies using 4 to 5 week old triple transgenic mice (Col1a1XCol2a1XCol10a1). The experimental group was injected with PTH (80 μg/kg) daily for 2 weeks, while control group was injected with saline. Our histology showed that the I-PTH treatment led to an increased number of cells expressing Col1a1, Col2a1 and Col10a1. Additionally, there was an increase in cellular proliferation, increased proteoglycan distribution, increased cartilage thickness, increased TRAP activity, and mineralization. Immunohistochemical staining showed increased expression of pSMAD158 and VEGF in the MCC and subchondral bone. Furthermore our microCT data showed that I-PTH treatment led to an increased bone volume fraction, tissue density and trabecular thickness, with a decrease in trabecular spacing. Morphometric measurements showed increased mandibular length and condyle head length following I-PTH treatment. In conclusion, our study suggests that I-PTH plays a critical role in cellular proliferation, proteoglycan distribution, and mineralization of the MCC.

Osteoblast role in osteoarthritis pathogenesis

Even if osteoarthritis pathogenesis is still poorly understood, numerous evidences suggest that osteoblasts dysregulation plays a key role in osteoarthritis pathogenesis. An abnormal expression of OPG and RANKL has been described in osteoarthritis osteoblasts, which is responsible for abnormal bone remodeling and decreased mineralization. Alterations in genes expression are involved in dysregulation of osteoblast function, bone remodeling, and mineralization, leading to osteoarthritis development. Moreover, osteoblasts produce numerous transcription factors, growth factors, and other proteic molecules which are involved in osteoarthritis pathogenesis.

Technetium-99m Methylene Diphosphonate Single-photon Emission Computed Tomography/Computed Tomography of the Foot and Ankle

The complex anatomy and function of the foot and ankle can make it difficult to determine the cause of symptoms in patients with foot and ankle pathology. Following initial clinical and radiographic assessment, additional imaging with magnetic resonance imaging may be required, which is often seen as the modality of choice. Although sensitive to pathological changes in bone metabolism and vascularity, technetium-99m (Tc-99m) bone scintigraphy often lacks the specificity and resolution required to evaluate the structures of the foot and ankle. Tc-99m methylene diphosphonate single-photon emission computed tomography/computed tomography (SPECT/CT) combines this sensitivity with the superior anatomical detail of CT, enabling better localization of pathological uptake and evaluation of associated structural changes. As a result, SPECT/CT has been growing in popularity for the assessment of patients with foot and ankle pathology where it can provide additional information that may change the initial diagnosis and subsequent management plan. Studies have reported modification of the surgical approach and site of intra-articular local anesthetic injections following SPECT/CT with good results. Interpretation of SPECT/CT studies requires an understanding of the pathological changes that result in increased tracer accumulation in addition to the CT changes that may be seen. This review aims to highlight the advantages of SPECT/CT, potential applications and explain the imaging appearances of common pathologies that may be observed.

Introduction to Cartilage

Cartilage is a supporting connective tissue that, together with the bone, forms the framework supporting the body as a whole. There are many distinct types of cartilage, which exhibit numerous similarities as well as differences. Among them, articular cartilage is the best known and the most studied type. Articular cartilage is the thin layer of connective tissue that covers the articulating ends of bones in synovial (diarthrodial) joints. It provides a smooth surface for joint movement and acts as a load-bearing medium that protects the bone and distributes stress. The intense interest in articular cartilage is motivated by the critical role its degradation plays in arthritis and related joint diseases, which are the number one cause of disability in humans. This chapter discusses the physical, chemical and cellular properties of cartilage that give the tissue its extraordinary load-bearing characteristics.

Hip Osteoarthritis: Etiopathogenesis and Implications for Management

Highly prevalent among the elderly, hip osteoarthritis (OA) carries a heavy burden of disease. Guidelines for the management of hip OA are often extrapolated from knee OA research, despite clear differences in the etiopathogenesis and response to treatments of OA at these sites. We propose that hip OA requires specific attention separate from other OA phenotypes. Our understanding of the etiopathogenesis of hip OA has seen significant advance over the last 15 years, since Ganz and colleagues proposed femoroacetabular impingement (FAI) as an important etiological factor. This narrative review summarizes the current understanding of the etiopathogenesis of hip OA and identifies areas requiring further research. Therapeutic approaches for hip OA are considered in light of the condition’s etiopathogenesis. The evidence for currently adopted management strategies is considered, especially those approaches that may have disease-modifying potential. We propose that shifting the focus of hip OA research and public health intervention to primary prevention and early detection may greatly improve the current management paradigm.

The association between insulin-like growth factor 1 (IGF-1), IGF-binding proteins (IGFBPs), and the carboxyterminal propeptide of type I procollagen (PICP) in pre- and postmenopausal women with rheumatoid arthritis

OBJECTIVES

To assess the association between plasma levels of the insulin-like growth factor (IGF) system including IGF-1, IGF-binding proteins (IGFBPs) including IGFBP-1, total (t-)IGFBP-3 and functional (f-)IGFBP-3, and the carboxyterminal propeptide of type I procollagen (PICP) in pre- and postmenopausal women with rheumatoid arthritis (RA).

METHOD

Plasma concentrations of IGF-1, IGFBP-1, t-IGFBP-3, f-IGFBP-3, and PICP were measured by immunoassay.

RESULTS

No significant difference was observed in plasma IGF-1 levels between pre- and postmenopausal subjects. Plasma levels of IGFBP-1 were elevated in RA. PICP and f-IGFBP-3 were greatly affected by menopausal status. Of the three IGFBPs tested, only f-IGFBP-3 plasma levels in RA women correlated negatively with age and disease duration. A positive correlation was demonstrated between PICP and erythrocyte sedimentation rate (ESR) in RA. Moreover, there was no correlation between PICP and IGF-1 and any of the IGFBPs in RA women.

CONCLUSIONS

Considerable disruption of the IGF system in RA was found to be related to disease activity and duration. Changes in the IGF-IGFBP axis and PICP levels were different in pre- and postmenopausal women with RA. Elevated plasma PICP concentrations may indicate an increased rate of bone formation in postmenopausal RA women. Additionally, the observed changes in the IGF/IGFBP system did not affect bone formation during RA.

Targeting VEGF and Its Receptors for the Treatment of Osteoarthritis and Associated Pain

Increased vascular endothelial growth factor (VEGF) levels are associated with osteoarthritis (OA) progression. Indeed, VEGF appears to be involved in OA-specific pathologies including cartilage degeneration, osteophyte formation, subchondral bone cysts and sclerosis, synovitis, and pain. Moreover, a wide range of studies suggest that inhibition of VEGF signaling reduces OA progression. This review highlights both the potential significance of VEGF in OA pathology and pain, as well as potential benefits of inhibition of VEGF and its receptors as an OA treatment. With the emergence of the clinical use of anti-VEGF therapy outside of OA, both as high-dose systemic treatments and low-dose local treatments, these particular therapies are now more widely understood. Currently, there is no established disease-modifying drug available for patients with OA, which warrants continued study of the inhibition of VEGF signaling in OA, as stand-alone or adjuvant therapy. © 2016 American Society for Bone and Mineral Research.

Metabolic analysis of osteoarthritis subchondral bone based on UPLC/Q-TOF-MS

Osteoarthritis (OA), one of the most widespread musculoskeletal joint diseases among the aged, is characterized by the progressive loss of articular cartilage and continuous changes in subchondral bone. The exact pathogenesis of osteoarthritis is not completely clear. In this work, ultra-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (UPLC/Q-TOF-MS) in combination with multivariate statistical analysis was applied to analyze the metabolic profiling of subchondral bone from 42 primary osteoarthritis patients. This paper described a modified two-step method for extracting the metabolites of subchondral bone from primary osteoarthritis patients. Finally, 68 metabolites were identified to be significantly changed in the sclerotic subchondral bone compared with the non-sclerotic subchondral bone. Taurine and hypotaurine metabolism and beta-alanine metabolism were probably relevant to the sclerosis of subchondral bone. Taurine, L-carnitine, and glycerophospholipids played a vital regulation role in the pathological process of sclerotic subchondral bone. In the sclerotic process, beta-alanine and L-carnitine might be related to the increase of energy consumption. In addition, our findings suggested that the intra-cellular environment of sclerotic subchondral bone might be more acidotic and hypoxic compared with the non-sclerotic subchondral bone. In conclusion, this study provided a new insight into the pathogenesis of subchondral bone sclerosis. Our results indicated that metabolomics could serve as a promising approach for elucidating the pathogenesis of subchondral bone sclerosis in primary osteoarthritis. Graphical Abstract Metabolic analysis of osteoarthritis subchondral bone.

A new strategy to tackle severe knee osteoarthritis: Combination of intra-articular and intraosseous injections of Platelet Rich Plasma

INTRODUCTION

Knee osteoarthritis (KOA) is a mechanically induced, cytokine and enzyme-mediated disorder involving all the joint tissue of the knee. Rebuilding a physiological-homeostatic network at the tissue level following knee organ failure, such as in severe KOA, is a daunting task with therapeutic targets encompassing the articular cartilage, synovium and subchondral bone. Intraarticular infiltration of plasma rich in growth factors (PRP) has emerged as a promising symptomatic approach, although it is insufficient to reach the subchondral bone.

AREAS COVERED

This review addresses current molecular and cellular data in joint homeostasis and osteoarthritis pathophysiology. In particular, it focuses on changes that subchondral bone undergoes in knee osteoarthritis and evaluates recent observations on the crosstalk among articular cartilage, subchondral bone and synovial membrane. In addition, we review some mechanistic aspects that have been proposed and provide the rationale for using PRP intraosseously in KOA.

EXPERT OPINION

The knee joint is a paradigm of autonomy and connectedness of its anatomical structures and tissues from which it is made. We propose an innovative approach to the treatment of severe knee osteoarthritis consisting of a combination of intraarticular and intraosseous infiltrations of PRP, which might offer a new therapeutic tool in KOA therapy.

Spatial and temporal changes of subchondral bone proceed to articular cartilage degeneration in rats subjected to knee immobilization

This study was aimed to investigate the spatial and temporal changes of subchondral bone and its overlying articular cartilage in rats following knee immobilization. A total of 36 male Wistar rats (11-13 months old) were assigned randomly and evenly into 3 groups. For each group, knee joints in 6 rats were immobilized unilaterally for 1, 4, or 8 weeks, respectively, while the remaining rats were allowed free activity and served as external control groups. For each animal, femurs at both sides were dissected after sacrificed. The distal part of femur was examined by micro-CT. Subsequently, femoral condyles were collected for further histological observation and analysis. For articular cartilage, significant changes were observed only at 4 and 8 weeks of immobilization. The thickness of articular cartilage and chondrocytes numbers decreased with time. However, significant changes in subchondral bone were defined by micro-CT following immobilization in a time-dependent manner. Immobilization led to a thinner and more porous subchondral bone plate, as well as a reduction in trabecular thickness and separation with a more rod-like architecture. Changes in subchondral bone occurred earlier than in articular cartilage. More importantly, immobilization-induced changes in subchondral bone may contribute, at least partially, to changes in its overlying articular cartilage.