Comparative study of the properties of tendinocytes derived from three different sites in the equine superficial digital flexor tendon.

This aim of this study was to determine the characteristic differences in tendinocytes derived from three sites of the equine superficial digital flexor tendon (SDFT)-proximally the myotendinous junction (MTJ), mid-metacarpal (mM) and osteotendinous junction (OTJ)-in morphology, proliferation, and ability for synthesis of collagen and matrix metalloproteinases (MMPs). Little difference was observed in cell proliferation. Addition of tumor necrosis factor (TNF) alpha to the culture medium resulted in increased collagen synthesis by tendinocytes from all three sites. The amount of collagen synthesized by tendinocytes derived from the mM and OTJ was much larger than that synthesized by untreated tendinocytes. A collagen zymogram revealed that proMMP-13 synthesis was increased towards the distal site. However, TNFalpha treatment resulted in a significant decrease in the amount of proMMP-13 synthesized by tendinocytes from all three sites. On the other hand, a gelatin zymogram showed that the synthesis level of proMMP-9 tended to decrease towards the distal site, but there was little difference between synthesis levels of proMMP-9 before and after TNFalpha treatment. These results indicated that tendinocytes in the same tendon have different characteristics and that these characterisities would reflect the function of tendinocytes in vivo. Also, the isolated tendinocytes provided much information on the characteristics and properties of tendons for the ECM turnover system and on the responsiveness of tendinocytes to complex inflammatory responses in a tendinopathy condition.