Intervertebral Disc Collagen: USAGE OF THE SHORT FORM OF THE α1(IX) CHAIN IN BOVINE NUCLEUS PULPOSUS

Jiann-Jiu Wu,David R Eyre

doi:10.1074/jbc.m302431200

Abstract

Nucleus pulposus, the central zone of the intervertebral disc, is gel-like and has a similar collagen phenotype to that of hyaline cartilage. Amino-terminal protein sequence analysis of the alpha1(IX)COL3 domain purified from bovine nucleus pulposus gave a different sequence to that of the long alpha1(IX) transcript expressed in hyaline cartilage and matched the predicted sequence of short alpha1(IX). The findings indicate that the matrix of bovine nucleus pulposus contains only the short form of alpha1(IX) that lacks the NC4 domain. The sequence encoded by exon 7, predicted from human COL9A1, is absent from both short and long forms of alpha1(IX) from bovine nucleus pulposus and articular cartilage. A structural analysis of the cross-linking sites occupied in type IX collagen from nucleus pulposus showed that usage of the short alpha1(IX) transcript in disc tissue had no apparent effect on cross-linking behavior. As in cartilage, type IX collagen of nucleus pulposus was heavily cross-linked to type II collagen and to other molecules of type IX collagen with a similar site occupancy.

Highlights

The collagen phenotype of hyaline cartilage is complex; at least seven distinct collagen types have been identified, of which types II, XI, and IX are the cartilage-specific molecules
Amino-terminal protein sequence analysis of the ␣1(IX)COL3 domain purified from bovine nucleus pulposus gave a different sequence to that of the long ␣1(IX) transcript expressed in hyaline cartilage and matched the predicted sequence of short ␣1(IX)
The findings indicate that the matrix of bovine nucleus pulposus contains only the short form of ␣1(IX) that lacks the NC4 domain

Summary

Introduction

The collagen phenotype of hyaline cartilage is complex; at least seven distinct collagen types have been identified, of which types II, XI, and IX are the cartilage-specific molecules. Type IX collagen is a structural matrix component that is most abundant in hyaline cartilages of the developing skeleton. It functions as an adhesion protein in the extracellular matrix where it becomes covalently cross-linked to the surface of type II collagen fibrils and most concentrated on thin fibrils of the pericellular domain (4 – 6). The gel-like central zone of the young intervertebral disc, has a similar collagen phenotype to that of hyaline cartilage, with types II, IX, and XI collagens being the principal fibrillar components [10]. The covalent cross-linking properties of nucleus pulposus type IX collagen were characterized to determine any consequences of having short instead of long ␣1(IX)

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Conclusion