Distinction between the extracellular matrix of the nucleus pulposus and hyaline cartilage: a requisite for tissue engineering of intervertebral disc

Abstract

Tissue engineering of intervertebral discs (IVD) using mesenchymal stem cells (MSCs) induced to differentiate into a disc-cell phenotype has been considered as an alternative treatment for disc degeneration. However, since there is no unique marker characteristic of discs and since hyaline cartilage and immature nucleus pulposus (NP) possess similar macromolecules in their extracellular matrix, it is currently difficult to recognize MSC conversion to a disc cell. This study was performed to compare the proteoglycan to collagen ratio (measured as GAG to hydroxyproline ratio) in the NP of normal disc to that of the hyaline cartilage of the endplate within the same group of individuals and test the hypothesis that this ratio can be used for in vivo studies to distinguish between a normal NP and hyaline cartilage phenotype. Whole human lumbar spine specimens from fresh cadavers, ranging in age from 12 weeks to 79 years, were used to harvest the IVDs and adjacent endplates. The GAG to hydroxyproline ratio within the NP of young adults is approximately 27:1, whereas the ratio within the hyaline cartilage endplate of the same aged individuals is about 2:1. The production of an extracellular matrix with a high proteoglycan to collagen ratio can be used in vivo to distinguish NP cells from chondrocytes, and could help in identifying a NP-like phenotype in vivo as opposed to a chondrocyte when MSCs are induced to differentiate for tissue engineering of a disc.

Transcriptional profiling distinguishes inner and outer annulus fibrosus from nucleus pulposus in the bovine intervertebral disc

“…AC showed significantly lower expression of bAcan (6.8 fold) and equal bCol2a1 expression compared with the NP. This is consistent with reported differences in matrix composition of AC and NP tissue [22]. As a positive marker gene for the AF we determined Collagen type I (bCol1a1) expression.…”

In vitro extracellular matrix accumulation of nasal and articular chondrocytes for intervertebral disc repair

“…This ratio is perhaps one for the best metrics in determining whether a candidate cell source is capable of producing NP-like tissue. The relatively high sGAG to collagen ratio of NC is comparable to the high ratio reported for NP in the literature (Mwale et al, 2004). Additionally, such matrix ratios were achieved for NC when cultured under physioxic conditions without TGF-β supplementation.…”

“…TGF-β stimulation and 20% O2 appears to be promoting higher levels of collagen type I deposition compared to NC and could account for the higher total collagen accumulation observed for AC groups. In addition, native healthy nucleus pulposus tissue has a high sGAGCollagen ratio, (Mwale et al, 2004) giving rise to its unique biomechanical properties. This ratio is perhaps one for the best metrics in determining whether a candidate cell source is capable of producing NP-like tissue.…”

Creation of an injectable in situ gelling native extracellular matrix for nucleus pulposus tissue engineering

“…An optimized decellularization process for nucleus pulposus needs to balance the removal of cells with the maintenance of sGAGs. The sGAGs are essential in maintaining the osmotic pressure of the nucleus pulposus [8], and they have the potential to play a role in driving cell phenotype [45][46][47]50,58] and preventing innervation [59][60][61][62]. The gentle decellularization protocol used in our laboratory for nerve [39,43,63] and lung tissue [38] was adapted for use in the nucleus pulposus by shortening the duration of wash cycles substantially.…”