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.

Different responses of articular cartilage to strenuous running and joint immobilization.

OBJECTIVE: To compare the pathological changes in cartilage derived from rats that developed osteoarthritis either by joint immobilization or by strenuous treadmill running in order to better understand their respective pathomechanism. METHOD: A total of 24 male Wistar rats were randomly assigned to three groups: sedentary control (CON), immobilization (IM), and strenuous running (SR). For rats in the IM group, unilateral knee joint was immobilized in flexion. Rats in the SR group underwent treadmill running with high intensity. Eight weeks later, all animals were sacrificed. Femoral condyles were collected to take histological observation for cartilage characteristic and immunohistochemistry for collagen type II. In addition, cartilage samples were obtained to assess gene expression of aggrecan, collagen type II, biglycan, and fibromodulin by quantitative RT-PCR. RESULTS: Gross and histological observation showed osteoarthritic changes in groups SR and IM; however, more severe cartilage degradation was revealed in the latter. Proteoglycan and collagen II content decreased in groups SR and IM in comparison to group CON, with more loss in group IM. In group SR, mRNA levels in femoral cartilage were found to be unaltered for all the molecules measured. On the contrary, these molecules were significantly downregulated in group IM. CONCLUSION: Differences in gross observation, histological characteristics, and gene expression of proteoglycans and collagen II suggest that both knee immobilization and strenuous running would lead to degenerative change of cartilage, but at different stages of the degenerative process.

Intensity-dependent effect of treadmill running on knee articular cartilage in a rat model.

OBJECTIVE: To understand the changes of femoral cartilage in response to treadmill running with different intensities in the hope of differentiating "moderate" and "strenuous" running in a rat model. METHOD: A total of 24 male Wistar rats were randomly assigned into groups of sedentary (SED), low-intensity running (LIR), medium-intensity running (MIR), and high-intensity running (HIR). Rats in LIR, MIR, and HIR groups underwent 8 weeks' treadmill running programs. After sacrificed, femoral condyles were collected to take histomorphometric analysis and immunohistochemistry for collagen II. RESULTS: Gross and histological observation showed osteoarthritic changes in group HIR. In comparison to SED group, there was significant increase in cartilage thickness, number of chondrocytes, and GAG content in groups LIR and MIR. Conversely, decrease in cartilage thickness, chondrocyte number, and GAG content was found in rats of HIR group, without significant difference though. In addition, in comparison to SED group, HIR group exhibited disorganization of collagen fibril and significantly lower content of collagen type II. CONCLUSION: An intensity-dependent effect was suggested on the articular cartilage. Our results also demonstrated that running with low-to-medium intensity applied in the present study should be regarded as "moderate" running, whereas high-intensity running as "strenuous" running.

Intensity-dependent effect of treadmill running on lubricin metabolism of rat articular cartilage.

INTRODUCTION: We aimed to understand the changes in cartilage lubricin expression and immunolocalisation in responsed to treadmill running with different intensities in a rat model. METHODS: A total of 24 male Wistar rats were randomly assigned into groups of control (CON), low-intensity running (LIR), moderate-intensity running (MIR), and high-intensity running (HIR). Rats in LIR, MIR, and HIR groups were trained for 8 weeks on the treadmill with low, moderate, and high intensity, respectively. After sacrifice, femoral condyles were collected to take histological observation for cartilage characteristics, and immunohistochemistry for lubricin. In addition, cartilage samples were obtained to assess PRG4 and TGF-ß mRNA expression by quantitative RT-PCR. RESULTS: Histological examination showed osteoarthritic changes in rats after eight weeks of high intensity running. In comparison to CON group, significantly lower Mankin score was found in LIR and MIR groups, whereas, HIR group had significantly higher Mankin score than either CON, LIR, or MIR group. On the other hand, both LIR and MIR groups have significantly higher lubricin content than CON group, whereas, significantly lower lubricin content was found in HIR group compared with CON, LIR or MIR group. A significant inverse correlation was detected between the lubricin content and Mankin score. In addition, considerably higher mRNA gene expression of PRG4 and TGF-ß was found in LIR and MIR groups, compared with those in CON and HIR groups. CONCLUSIONS: There is a marked intensity-specific effect of running on the immunolocalisation and gene expression of lubricin in cartilage, which is inversely correlated with Mankin score. Our findings provide evidences that mechanical factors are key determinants of lubricin metabolism in vivo.

Matrix metalloproteinase-3 inhibitor retards treadmill running-induced cartilage degradation in rats.

INTRODUCTION: The effect of intra-articular injection of matrix metalloproteinase (MMP)-3 inhibitor was investigated in a rat model to understand the role of MMP-3 in cartilage degradation induced by excessive loading from running. METHODS: A total of 24 male Wistar rats were randomly assigned into groups of sedentary control (SED), high-intensity running (HIR), HIR + low dosage of MMP-3 Inhibitor I (HIRI1), and HIR + high dosage of MMP-3 Inhibitor I (HIRI2). Rats in the HIR, HIRI1 and HIRI2 groups were intensively trained for six weeks on the treadmill. Those in HIRI1 and HIRI2 groups were provided bilateral intra-articular injections of 80 µL of 0.2 mM and 2 mM MMP-3 Inhibitor I in knee joints once a week, respectively. Blood samples were collected to measure serum MMP-3 level using ELISA. Femoral condyles were collected to observe cartilage characteristics by histochemistry, and MMP-3 as well as collagen II was measured by immunohistochemistry. In addition, cartilage samples were obtained to assess MMP-3 mRNA expression by RT-PCR. RESULTS: Histological examination showed osteoarthritic changes in rats after six weeks of high intensity running. In comparison to the SED group, significant decreases in glycosaminoglycans (GAG) and collagen content were found in the HIR group, which corresponded to significant increase in serum MMP-3 level, cartilage MMP-3 activity and gene expression. However, such a degradative process was considerably retarded by intra-articular injection of MMP-3 inhibitor at higher dosage. Statistical differences were found between the HIR and HIRI2 groups with regard to GAG and collagen II content, serum MMP-3 level, cartilage MMP-3 activity and gene expression. CONCLUSIONS: High-intensity running for six weeks may lead to cartilage degradation in a rat model. It was shown that the chrondroprotective effect was offered by the use of intra-articular injection of MMP-3 inhibitor. MMP-3 acts as the key mediator of this catabolic change under such mechanical condition. The results also showed that MMP-3 selective inhibitor may be an effective option for retarding such osteoarthritic changes.