Cyclic mechanical stretch stress increases the growth rate and collagen synthesis of nucleus pulposus cells in vitro

Study Design. A rabbit model designed to investigate the effects of applied cyclic tensile stress on the-cell division:rate and the collagen synthesis in the rabbit nucleus pulposus cells in vitro. Objective. To evaluate the effects of mechanical stress on nucleus pulposus cells, thus adding to the understanding of the adaptation of the intervert ebral disc to mechanical stress. Summary of Background Data. Intervertebral disc cells in vivo are exposed t o a multitude of physical forces during physical motion. Although it is kno wn that in intervertebral disc disease, a common pathway of disc degenerati on is mechanical stress on the nucleus pulposus or the anulus fibrosus or b oth, the underlying mechanism has been less well defined. Methods. Nucleus pulposus cells were isolated from 4-week-old Japanese whit e rabbits. These cells were subjected to the mechanical cyclic stretch stre ss using a computerized, pressure-operated instrument that physically defor med the cells. The DNA synthesis rate, collagen synthesis rate, and cell cy cle progression were measured. Results. Cyclic tensile stretch increased the DNA synthesis rate in nucleus pulposus cells and in the population of cells in the S phase of the cell c ycle during 1 to 2 days of subjugation to stress. Cyclic tensile stretch al so increased collagenous protein synthesis in nucleus pulposus cells during 2 to 4 days of stress. Conclusions. Mechanical stress on nucleus pulposus cells. promotes the prol iferation of cells and alters the properties of intervertebral disc cells. This study may reflect the adaptation of the intervertebral disc to increas ed motion and stress.