Cyclic mechanical strain induces NO production in human patellar tendon fibroblasts - A possible role for remodelling and pathological transformation

The mechanism by which tendon fibroblasts can detect strain forces and respond to them is fairly unknown. Nitric oxide (NO) is a messenger molecule that among others can respond to shear stress in endothelial cells. Therefore, it was investigated whether cyclic mechanical strain induces NO in vitro in human patellar tendon fibroblasts. Human patellar tendon fibroblasts were cultured from remnants of patellar tendon transplants after reconstructive surgery. Fibroblasts were cultured on elastic silicone dishes. The cells were longitudinally strained (5%, 1 Hz) for 15′ or 60′. As a control, no strain was applied. The experiments were finished after 0′, 5′, 15′, and 30′. NO was determined using the Griess reaction. 15′ strain showed at 0′ and 5′ 200% activation, which thereafter at 15′ and 30′ returned to normal levels. 60′ strain showed a biphasic pattern. At 5′ and 30′, NO levels were increased to 175%. At 15′, NO measurement displayed 120% increased levels. Mechanical strain induces NO production by tendon fibroblasts. Therefore, NO produced by tendon fibroblasts, as a response to alteration in their mechanical microenvironment, could modulate fibroblast function. The results of our study suggests that strain-related adaptive changes may, at least in part, be controlled by a process in which strain-related NO production from the fibroblast network may play a pivotal role. Moreover, these are basic findings that are important for further unravelling pathophysiology of tendon diseases.