Effect Of Different Loadings On Articular Cartilage Of Rat Knee And Related Mechanism

[Objective] The present study was undertaken to investigate the effects of treadmillrunning with different intensity and immobilization on articular cartilage of knee jointin rats.[Methods] A total of30adult SD rats were assigned randomly and equally into one offive groups as follows: control (C) group, low-intensity exercise (L) group, moderate-intensity exercise (M) group, high-intensity exercise (H) group, and immobilized (I)group. Rats in three exercise groups were regularly trained on treadmill with low,moderate, and high intensity, respectively, whereas, right knees of rats in group I wereimmobilized in flexion. Eight weeks later, all the animals were sacrificed, and righttibial plateau samples were collected to observe cartilage characteristics by histology,collagen fibers under polarizing light microscopy, as well as collagen-Ⅱcontent byimmunohistochemistry.[Results]1. In comparison with group C, there was no significant difference in L and M groupin Mankin’s score, whereas, significantly higher Mankin’s score was found in group Hand I, respectively.2. The histological appearance of cartilage sections in group L and M showed grossly normalstructure of rat knee cartilage, similar to that in group C. In contrast, histological changeswere found in group H and I, characteristized by surface irregularities, cell cloning andcluster.3. Histological sections stained with Picrosirius red were observed under polarized lightmicroscope. Comparing with group C, collagen fibers in group L and M exhibited almost thesame organization and color, whereas, alteration in organization and color of collagen fiberswas found in group H and I.4. Higher content of typeⅡcollagen was found in group L and M in comparison withgroup C, but without statistical significance. However, significantly lower content was found in group H and I than that in group C.[Conclusion] It was suggested that low and moderate-intensity treadmill running for8weeks was no harmful to the articular cartilage, while high-intensity running andimmobilization may result in cartilage degenerative change, along with decrease intype Ⅱ collagen content. Our results clearly indicated thatnon-physiologicalmechanical loading, both overloading and reduced loading, may have deleterious effects oncartilage [Objective] To explore the mechanism of the above-mentioned cartilage destructioninduced by high intensity exercise and immobilization through evaluating geneexpression of BGN, FMOD, Col2and TGF-βin knee cartilage of rats.[Methods] A total of30adult SD rats were assigned randomly into five groups:control (C) group (n=6), low-intensity exercise (L) group (n=6), moderate-intensityexercise (M) group (n=6), high-intensity exercise (H) group (n=6) and immobilized (I)group (n=6). Animals in exercise groups performed treadmill running program,whereas those in group I were submitted to knee immobilization. Gene expression ofBGN, FMOD, Col2and TGF-βwas analysed by quantitative real-time reversetranscription-polymerase chain reaction on total RNA extracted from the cartilageafter8weeks.[Results]1. In comparison with group C, group L had higher gene expression of Col2, BGNand FMOD, and lower TGF-βgene expression, with statistical significance only forCol2.2. Group M had higher Col2, BGN and FMOD mRNA expression and lower TGF-βgene expression than group C, without statistical significance.3. Compared with group C, group H had higher Col2, BGN and FMOD mRNAexpression and lower TGF-β gene expression, without statistical significance.4. Group I had significantly lower Col2, BGN, FMOD gene expression, andsignificantly higher TGF-βgene expression than group C.[Conclusion] Low or moderate-intensity treadmill running appears to have beneficialeffect on articular cartilage to maintain its integrity. Processes of cartilage destructionand repair coexist in response to excessive running-induced loading. On the otherhand, however, during immobilization, the chondrocytes lose their capacity tomaintain cartilage structure and function, and the degeneration of cartilage would become more severe.