INTRODUCTION:The extracellular matrix (ECM) of the human nucleus pulposus (NP) is rich in molecules that interact with cells through integrin‐mediated attachments. Porcine NP cells have been shown to interact with laminin (LM) isoforms LM‐111 and LM‐511 through integrin‐mediated mechanisms. Since human NP cells lose many phenotypic characteristics in the adult intervertebral disc, attachment and interaction with ECM may be altered. Here we evaluate expression of LM‐binding integrins and the mechanism of cell attachment to LM 111 and LM‐511 for human NP cells.
METHODS:Human NP cells were isolated from surgical tissues (age 26‐63). Expression of integrin subunits ( α1, α2, α3, α5, α6, β1, and β4) was quantified with flow cytometry in passage 1‐2 cells. NP cell attachment to LM‐111, LM‐511, or collagen II, was analyzed after 1hr. Functional blocking of specific integrins was also studied following pre‐incubation with blocking antibodies.
RESULTS & DISCUSSION: Human NP cells express integrins β1, α3, and α5 (MFI 2.1M, 0.7M, 0.5M respectively), with over 70% of cells positive for each subunit. Human NP cells attached to LM and collagen substrates in nearly equal numbers. Blocking the β1 subunit inhibited a majority of NP cell attachment to LM‐111 and LM‐511. Additionally, integrin subunit α3 appears to partly regulate NP cell attachment to LM‐111 and LM‐511. Human cells express integrins α3, α5, and β1 as shown in porcine cells, but little of the expression of integrins α1, α6, and β4 seen for porcine NP cells. While porcine NP cell attachment to LM‐111 was mediated by integrins α6 and β1 (<50% cell attachment), we found integrins α3 and β1 (82% and 30% cell attachment respectively) instead contributed to human NP cell attachment. These findings suggest that integrin subunits α3 and β1 may mediate interactions with the ECM for human NP cells.