Effect Of Treadmill Running With Different Intensities On Morphology And Lubricin Metabolism Of Rat Knee Articular Cartilage

[Objective] The objective was to determine the changes of articular cartilage of theknee joint following treadmill running with different intensities in a rat model.[Methods] A total of24male SD(Sprague Dawley) rats were assigned randomly intofour groups: sedentary (SED) group (n=6), low intensity exercise (L-EX) group (n=6),moderate intensity exercise (M-EX) group (n=6) and high intensity exercise (H-EX)group (n=6). Those in three exercise groups undertook treadmill running programswith respective intensity for8weeks. The articular cartilage from the distal femoralwas collected, and stained with HE and Safranin O–fast green. The sections weredivided into three areas (contact area, transitional area, non-contact area) forhistological analysis. In each area, the cartilage morphology was evaluated by grossobservation, histomorphometric grading（Modified Mankin’s score, MMS), cartilageglycosaminoglycans (GAG) content, number of chondrocyte and cartilage thickness.[Results] In comparison with SED group, L-EX and M-EX groups had smoothcartilage surface, higher GAG content, normal cartilage structure, intact tidemark,increasing chondrocyte number, thicker cartilage thickness, and significantly lowerMMS scores. However, in the H-EX group, the surface of the articular cartilage lostluster and a subchondral bone was seen through gross observation. In addition,histological changes were found with surface irregularities, cell cloning,disappearance of the tidemark, moderate reduction in the safranin-O staining, thinnerof the cartilage thickness, and significantly higher MMS.[Conclusion] Our results demonstrated that morphological alteration of articularcartilage may depend on the loading conditions. Low-and moderate-intensitytreadmill running may be beneficial to the maintenance of articular cartilage matrixhomeostasis， whereas high-intensity treadmill running may lead to cartilagedegradation in a rat model. [Objective] The objective was to investigate the effect of treadmill running exercisewith different intensity on biosynthesis and gene expression of lubricin in rat articularcartilage.[Methods] Cartilage samples were collected immediately after the sacrifice ofanimals. Lubricin staining in cartilage was performed using a lubricin-specificpolyclonal antibody. The lubricin staining on the surface of articular cartilage incontact area、transition area and non-contact area of femur were quantitativelyanalyzed by a digital imaging system. Levels of messenger RNA (mRNA) for lubricinin articular cartilage from different groups were determined by real time fluorescentquantitative reverse transcription polymerase chain reaction (real time RT-PCR).[Results] Increasing of the lubricin staining was mainly observed in the three areas ofthe low intensity exercise (L-EX) group and the moderate intensity exercise (M-EX)compared with the control（CON）group. Whereas，it was significantly decreased inthe three areas of high intensity exercise (H-EX) group compared with L-EX andM-EX. Lubricin mRNA expression levels in L-EX and M-EX were significantlyhigher than CON and H-EX.[Conclusion]Low intensity and moderate intensity exercise increased biosynthesisand gene expression of lubricin; whereas high intensity exercise decreased. It wassuggested that such different effect on the metabolism of lubricin may be one ofimportant mechanism of different morphological changes induced by treadmillrunning with different intensities.