| [Objective] The present study was undertaken to determine the effects of treadmill running with different intensities on articular cartilage of the knee joint in a rat model.[Methods] A total of 18 adult Wistar rats were assigned randomly into three groups: sedentary (SED) group (n=6), low intensity exercise (L-EX) group (n=6), and high intensity exercise (H-EX) group (n=6). Animals in L-EX and H-EX groups received treadmill running programs with low or high intensity for 6 weeks, respectively, while rats in SED group served as controls. Serum samples were collected to measure matrix metalloproteinase-3 (MMP-3) using ELISA. In addition, bilateral distal femora were obtained to observe cartilage characteristics by histochemistry, to measure MMP-3 and typeⅡcollagen by immunohistochemistry, and to assess MMP-3 mRNA expression by RT-PCR.[Results] 1. Compared with SED group, no significant differences were found in L-EX group in terms of Mankin's score (0.500±1.000 vs 0.250±0.500) and GAG content (0.028±0.012 vs 0.060±0.037). Whereas, H-EX group exhibited much higher Mankin's score (3.500±1.049,P=0.009) and lower GAG content (0.010±0.011,P=0.0016) than SED group.2. Compared to SED group (average optical density 0.578±0.123), the content of typeⅡcollagen was similar to L-EX group (0.559±0.152), and significantly lower in H-EX group (0.142±0.093,P=0.0001).3. MMP-3 protein expression was apparently found in H-EX group by immunohistochemistry. The positive rate of chondrocytes with MMP-3 protein expression in H-EX group (82.530±11.505)% was significantly higher than that in L-EX group (4.960±2.850)%, and SED group (8.350±4.063)%, respectively (P=0.0001).4. Serum concentration of MMP-3 in H-EX group was 86.850±33.158 ng/ml, significantly higher than that in SED group (11.437±0.920 ng/ml,P=0.001), and L-EX group (11.955±0.422 ng/ml). No statistical significance was found between SED and L-EX groups.5. MMP-3 mRNA expression by RT-PCR in H-EX group (0.697±0.567) was significantly higher than that in SED group and L-EX group, respectively. No statistical significance was found between SED (0.030±0.026,P=0.042) and L-EX groups (0.018±0.028,P=0.025).[Conclusion] Six-week low intensity treadmill running was found to maintain the integrity of articular cartilage. On the other hand, high intensity running appears to result in cartilage degenerative change with notably increase in MMP-3 content and decrease in the content of typeⅡcollagen. Our results clearly indicated that exercise intensity is a key determinant to the cartilage changes followed by exercise, and that MMP-3 appears to be a sensitive biomarker of exercise-induced cartilage changes. [Objective] Based on our previous finding that high-intensity exercise would induce cartilage degeneration, this part was designed to understand whether MMP-3 inhibitor could retard this process, thereby understanding the effect of MMP-3 on the cartilage changes induced by high-intensity exercise.[Methods] A total of 18 adult Wistar rats were assigned randomly into three groups: high-intensity exercise group (H-EX group, n=6), H-EX + high concentration MMP inhibitor injection group (h-HEX group, n=6), and H-EX + low concentration MMP inhibitor injection group (l-HEX group, n=6). All the animals performed a high-intensity treadmill running program for 6 weeks. At the beginning of the 4th, 5th, and 6th week, MMP-3 inhibitor I (2 mM or 0.2 mM) was administered intra-articularly and bilaterally once a week for h-HEX and l-HEX groups, respectively. Serum samples were collected to measure matrix metalloproteinase-3 (MMP-3) using ELISA. In addition, bilateral distal femora were obtained to observe cartilage characteristics by histochemistry, to measure MMP-3 and collagen-Ⅱby immunohistochemistry, and to assess MMP-3 mRNA expression by RT-PCR.[Results] 1. Significant lower Mankin's score (1.167±0.753 vs 3.500±1.049,P=0.006) and higher GAG content (0.040±0.012 vs 0.010±0.011,P=0.006) in h-HEX group than those in H-EX. However, no statistical difference was found between H-EX and l-HEX groups.2. The content of typeⅡcollagen in h-HEX (average optical density 0.391±0.096) was significantly higher than that in H-EX (0.142±0.093 , P=0.0001) and l-HEX (0.186±0.100,P=0.002) groups. However, no significant difference was found between H-EX and l-HEX groups.3. MMP-3 protein expression was apparently found in H-EX group by immunohistochemistry. The positive rate of chondrocytes with MMP-3 protein expression in H-EX group (82.530±11.505)% was significantly higher than that in h-HEX (5.590±2.977)% (P= 0.002) and l-HEX (17.680±13.789)% (P=0.001) groups, respectively.4. Serum concentration of MMP-3 in H-EX (86.850±33.158 ng/ml) was higher than that in l-HEX (62.810±35.485 ng/ml), and h-HEX (30.749±40.416 ng/ml), respectively. Statistical significance was found between h-HEX and H-EX (P=0.026).5. MMP-3 mRNA expression by RT-PCR in H-EX group (0.697±0.567) was higher than that in l-HEX (0.694±0.243) and h-HEX groups(0.121±0.056), respectively. Statistical significance was only found between H-EX group and h-HEX group (P=0.049).[Conclusion] Our results clearly indicated that MMP-3 inhibitor could retard the degenerative process of articular cartilage induced by high-intensity exercise. However, this effect appears to be dose-dependent. Our results also provided additional evidences that MMP-3 plays an important role in the changes of articular cartilage followed by excessive exercise.
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