Do the intervertebral disc cells respond to different levels of hydrostatic pressure?

Objective. To test the hypothesis that hydrostatic pressure directly affect s the synthesis of collagen and proteoglycan by intervertebral disc cells. Design. By the use of pressure vessels, hydrostatic pressure was applied to intervertebral disc cells cultured in alginate. Background. The influence of compression (both hydrostatic and axial) on ch ondrocyte metabolism was examined in a number of earlier studies. However, in most of these studies, articular cartilage, not intervertebral disc was used, and in none of these was hydrostatic pressure applied to intervertebr al disc cells cultured in alginate. Methods. Fresh, cells were harvested from the lumbar intervertebral discs o f dogs. Before their suspension in an alginate gel system, the cells were p lated and expanded until they reached confluence. Then, by use of the algin ate gel system, the cells were exposed (for up to 9 days) to specific value s of hydrostatic pressure inside two stainless steel pressure vessels. One vessel was kept at 0.35 MPa and the other at atmospheric pressure (approxim ately 0.1 MPa). The effects of 0.35 MPa were compared against atmospheric p ressure by measuring the incorporation of [H-3]-proline and [S-35]-sulfate into collagen and proteoglycans, respectively, for the anulus cells and nuc leus cells separately, and by determining whether this incorporation was re flected by changes in the levels of mRNA for aggrecan and Types I and If co llagen. Results. Proteoglycan synthesis was inhibited at 0.35 MPa as compared to at mospheric pressure for both the nucleus and anulus cells, whereas collagen synthesis was stimulated in the nucleus cells, but inhibited in the anulus cells. The mRNA levels of collagen IA and collagen 2A decreased in the anul us. but showed a differential response in the nucleus (collagen I A increas ed, while collagen 2A decreased). The mRNA levels for aggrecan core protein decreased in the anulus and increased in the nucleus. Conclusion. Hydrostatic pressure directly affects the synthesis of collagen and proteoglycan by the intervertebral disc cells.