Periostin is expressed by cells of the human and sand rat intervertebral discs

Periostin, a matricellular protein in the fasciclin family, is expressed in tissues subjected to constant mechanical stress. Periostin modulates cell-to-extracellular matrix interactions and can bind to collagen, fibronectin, tenascin-C and several integrins. Our objective was to evaluate whether periostin is expressed in the human intervertebral disc. Immunohistochemical localization of periostin was carried out in tissue of human lumbar discs and lumbar discs of the sand rat (Psammomys obesus). Human discs also were examined for periostin gene expression. Immunohistochemical localization demonstrated periostin in the cytoplasm of annulus and nucleus cells, and occasionally in the surrounding pericellular and interterritorial extracellular matrix. Periostin distribution in the human disc was distinctive. Outer annulus contained the highest proportion of periostin-positive cells (88.8%), whereas inner annulus contained only 61.4%. The nucleus pulposus contained the fewest periostin-positive cells (18.5%). There was a significant negative correlation between the percentage of cells positive for periostin in the inner annulus and subject age. Periostin gene expression in the human disc also was confirmed using molecular microarray analysis. Because work by others has shown that periostin plays an important role in the biomechanical properties of other connective tissues (skin, tendon, heart valves), future research is needed to elucidate the role of periostin in disc, loading, aging and degeneration.