A phenotypic comparison of intervertebral disc and articular cartilage cells in the rat

Abstract

The basic molecular characteristics of intervertebral disc cells are still poorly defined. This study compared the phenotypes of nucleus pulposus (NP), annulus fibrosus (AF) and articular cartilage (AC) cells using rat coccygeal discs and AC from both young and aged animals and a combination of microarray, real-time RT-PCR and immunohistochemistry. Microarray analysis identified 63 genes with at least a fivefold difference in fluorescence intensity between the NP and AF cells and 41 genes with a fivefold or greater difference comparing NP cells and articular chondrocytes. In young rats, the relative mRNA levels, assessed by real-time RT-PCR, of annexin A3, glypican 3 (gpc3), keratin 19 (k19) and pleiotrophin (ptn) were significantly higher in NP compared to AF and AC samples. Furthermore, vimentin (vim) mRNA was higher in NP versus AC, and expression levels of cartilage oligomeric matrix protein (comp) and matrix gla protein (mgp) were lower in NP versus AC. Higher NP levels of comp and mgp mRNA and higher AF levels of gpc3, k19, mgp and ptn mRNA were found in aged compared to young tissue. However, the large differences between NP and AC expression of gpc3 and k19 were obvious even in the aged animals. Furthermore, the differences in expression levels of gpc3 and k19 were also evident at the protein level, with intense immunostaining for both proteins in NP and non-existent immunoreaction in AF and AC. Future studies using different species are required to evaluate whether the expression of these molecules can be used to characterize NP cells and distinguish them from other chondrocyte-like cells.

Nerve growth factor increases MMP9 activity in annulus fibrosus cells by upregulating lipocalin 2 expression

“…A variety of animal models including bovine, canine, rabbit, rat, and mouse have been used to study IVD degeneration or regeneration in place of human samples [28][29][30]. In vitro studies that identify potential catabolic mechanisms involved in deserve consideration when formulating a clinical solution to degenerative disc disease.…”

Molecular Basis of Intervertebral Disc Degeneration and Herniations: What Are the Important Translational Questions?

“…The endplates are at the superior and inferior aspects of the disc. EPs are cartilaginous structures distinct from articular cartilage found elsewhere in the body [10,42]. The AF is a thick, dense structure, which is divided into the outer and inner annulus.…”

Tissue engineering and the intervertebral disc: the challenges

“…Research into directing stem cells or notochordal cells towards a discogenic phenotype is hindered by lack of specific markers which can distinguish nucleus pulposus (or even annulus fibrosus or CEP) cells from articular chondrocytes or nucleus cells from annulus cells [23,58]. Markers commonly used for showing conversion of stem cells to a disc cell phenotype are expression of aggrecan and type II collagen and of SOX-9 [91]; these are no different, however, from those used to identify articular chondrocytes.…”

“…Markers commonly used for showing conversion of stem cells to a disc cell phenotype are expression of aggrecan and type II collagen and of SOX-9 [91]; these are no different, however, from those used to identify articular chondrocytes. Other markers such as HIF-1a and GLUT-1 expression have been suggested but these are constitutively expressed by most cell types and their use as markers for disc cells has not been validated, nor have other markers which have been suggested such as CD-44 and cytokeratin [58,85,91]. It is important that cells used for repairing the disc differentiate to the correct phenotype as even though the major macromolecular components of the nucleus pulposus, cartilage endplate and articular cartilage are very similar, the organisation of the extracellular matrix and their biomechanical properties are very different in the three tissues.…”