Fibroblast responses to cyclic mechanical stretching depend on cell orientation to the stretching direction

Fibroblasts in intact tendons align with stretching direction, but they tend to orient randomly in healing tendons. Therefore, a question arises: Do fibroblast responses to mechanical stretching depend on their orientation? To address this question, human patellar tendon fibroblasts were grown in custom-made silicone dishes that possess microgrooved culture surfaces. The direction of the microgrooves was either parallel or normal to the direction of cyclic uniaxial stretching. Fibroblasts grown in these microgrooves had a polar morphology and oriented along the direction of the microgrooves regardless of the stretching conditions. Tendon fibroblasts expressed higher levels of alpha-smooth muscle actin when they were oriented parallel to the stretching direction than when they were oriented normal to the stretching direction. Also, cyclic stretching of the fibroblasts perpendicular to their orientation induced a higher activity level of secretory phospholipase A(2) compared with stretching of the cells parallel to their orientation. Thus, these results show that fibroblast responses to mechanical stretching depend on cell orientation to the stretching direction.