EFFECT OF ALIGNMENT OF THE TRANSPLANTED GRAFT EXTRACELLULAR-MATRIX ONCELLULAR REPOPULATION AND NEWLY SYNTHESIZED COLLAGEN

This study examines the effect of alignment of the transplanted graft extracellular matrix on cellular repopulation and new collagen synthes is. The lateral half of the patellar tendon was harvested as a tendon graft from Lewis rats and frozen at -80 degrees C. In order to maintai n the original alignment of the graft extracellular matrix, the graft was transplanted to a same size defect in the patellar tendon of other Lewis rats (group I). For controls, the graft was transplanted in a l ax condition after excision of only the distal half of the lateral sid e of a patellar tendon (group II). After transplantation, six animals in each group were killed at 3, 7, 14, and 28 days. Cellular repopulat ion was assessed by using fibrillar-actin (F-actin) labeling with rhod amine-phalloidin. and new collagen synthesis was detected by means of a polyclonal antibody against type III collagen aminopropeptide (pN co llagen III). Collagen fibril profiles were observed under the transmis sion electron microscope. On the 3rd day after transplantation, no spe cific fluorescence was detected in either group. Specific labeling for F-actin and pN collagen In, however, was observed at both ends of the graft in both groups at I week and throughout the graft at 2 weeks af ter transplantation. Consistent with the actin bundles' orientation, p N collagen III was aligned parallel to the longitudinal axis of the gr aft in group I. Collagen fibrils with a smaller diameter, mixed evenly and everywhere with a larger diameter, increased gradually in group I . However, smaller collagen fibrils in group II increased more slowly and were distributed unevenly. In summary, the dense collagen arrangem ent in the native patellar tendon determined the alignment of the repo pulating cells, and the distribution of newly synthesized collagen mig ht be affected by the actin cytoskeleton within the repopulating cells .