Immunolocalization of thrombospondin in the human and sand rat intervertebral disc

Study Design. Human intervertebral disc tissue from the anulus was obtained in a prospective study investigating the presence of the matricellular protein thrombospondin (TSP) in human and sand rat discs. Studies were approved by the authors' Human Subjects Institutional Review Board and Institutional Animal Care and Use Committee. Objectives. To determine whether TSP could be detected in the human or sand rat disc with immunohistochemistry, and to assess its localization. Summary of Background Data. The role of the matricellular proteins in maintenance of disc health and extracellular matrix remodeling is as yet poorly understood. SPARC and tenascin have previously been shown to be present in the human disc. TSP has a well-recognized antiangiogenic activity in vivo and in vitro. Methods. Sixteen specimens of human disc tissue and discs from 7 sand rats were assessed for immunohistochemical localization of TSP. Three human disc cell cultures grown in three-dimensional culture were also evaluated. Results. Strong immunoreactivity was present in the outer anulus of both human and sand rat discs. Inner anulus showed lesser localization. In clusters, both immuno-positive and -negative cells were present. Similar patterns of localization were seen in the sand rat specimens. Human disc cells in three-dimensional culture produced abundant TSP. Conclusions. The biologic basis for the avascular adult human disc does not appear to have been explored. Since TSP has recognized antiangiogenic effects both in vitro and in vivo, we suggest that the strong immunolocalization of TSP in the outer anulus indicates a role for TSP in the avascular status of the adult human and sand rat disc.