Expression of Laminin Isoforms, Receptors, and Binding Proteins Unique to Nucleus Pulposus Cells of Immature Intervertebral Disc

Intervertebral disc (IVD) disorders are believed to be related to aging-related cell loss and phenotypic changes, as well as biochemical and structural changes in the extracellular matrix of the nucleus pulposus (NP) region. Previously, we found that the laminin gamma1 chain was more highly expressed in immature NP porcine tissues, in parallel with the expression pattern for a laminin receptor, integrin alpha6 subunit, as compared to adjacent anulus fibrosus region. This result suggests that cell-matrix interactions may be unique to the immature NP. However, the identity of laminin isoforms specific to immature or mature NP tissues, their associated receptors, and functional significance are still poorly understood. In this study, we evaluated the zonal-specific expression of the laminin chains, receptors (i.e., integrins), and other binding proteins in immature tissue and isolated cells of rat, porcine and human intervertebral disc. Our goal was to reveal features of cellular environment and cell-matrix interactions in the immature NP. Results from both immunohistochemical staining and flow cytometry analysis found that NP cells expressed higher levels of the laminin alpha5 chain, laminin receptors (integrin alpha3, alpha6, beta4 subunit, and CD239), and related binding proteins (CD151), as compared to cells from adjacent anulus fibrosus. These differences suggest that laminin interactions with NP cells are distinct from that of the anulus fibrosus and that laminins may be important contributors to region-specific IVD biology. The revealed laminin isoforms, their receptors, and related binding proteins may be used as distinguishing features of these immature NP cells in the intervertebral disc.