The cells of the nucleus pulposus (NP) region of the intervertebral disc play a critical role in this tissue's generation and maintenance, and alterations in NP cell viability, metabolism, and phenotype with aging may be key contributors to progressive disc degeneration. Relatively little is understood about the phenotype of NP cells, including their cell-matrix interactions which may modulate phenotype and survival. Our previous work has identifi ed strong and region-specifi c expression of laminins and laminin cell-surface receptors in immature NP tissues, suggesting laminin cell-matrix interactions are uniquely important to the biology of NP cells. Whether these observed tissue-level laminin expression patterns refl ect functional adhesion behaviors for these cells is not known. In this study, we examined NP cell-matrix interactions with specifi c matrix ligands, including various laminin isoforms, using quantitative assays of cell attachment, spreading, and adhesion strength. NP cells were found to attach in higher numbers and exhibited rapid cell spreading and higher resistance to detachment force on two laminin isoforms (LM-511,LM-332) identifi ed to be uniquely expressed in the NP region, as compared to another laminin isoform (LM-111) and several other matrix ligands (collagen, fi bronectin). Additionally, NP cells were found to attach in higher numbers to laminins as compared to cells isolated from the disc's annulus fi brosus region. These fi ndings confi rm that laminin and laminin receptor expression documented in NP tissues translates into unique functional NP cell adhesion behaviors that may be useful tools for in vitro cell culture and biomaterials that support NP cells.

The extracellular matrix (ECM) of the human intervertebral disc is rich in molecules that interact with cells through integrin-mediated attachments. Porcine nucleus pulposus (NP) cells have been shown to interact with laminin (LM) isoforms LM-111 and LM-511 through select integrins that regulate biosynthesis and cell attachment. Since human NP cells lose many phenotypic characteristics with age, attachment and interaction with the ECM may be altered. Expression of LM-binding integrins was quantified for human NP cells using flow cytometry. The cell-ECM attachment mechanism was determined by quantifying cell attachment to LM-111, LM-511, or type II collagen after functionally blocking specific integrin subunits. Human NP cells express integrins β1, α3, and α5, with over 70% of cells positive for each subunit. Blocking subunit β1 inhibited NP cell attachment to all substrates. Blocking subunits α1, α2, α3 and α5 simultaneously, but not individually, inhibits NP cell attachment to laminins. While integrin α6β1 mediated porcine NP cell attachment to LM-111, we found integrins α3, α5, and β1 instead contributed to human NP cell attachment. These findings identify integrin subunits that may mediate interactions with the ECM for human NP cells and could be used to promote cell attachment, survival and biosynthesis in cell-based therapeutics.