Abstract
Introduction: Proteoglycans are found both in the annulus fibrosus and nucleus pulposus of the intervertebral disc and contribute to the hydration of the tissue (aggrecan) and the regulation of matrix assembly (small proteoglycans) [1]. Whilst loss of proteoglycan is the main chemical change in disc degeneration seen in back pain patients, little is known of the events leading to and controlling this loss. In this study the metabolism of the most common proteoglycan, aggrecan, and others including decorin, biglycan, lumican, fibromodulin and versican, together with collagen types I and II were studied in diseased and normal discs.
Methods: Ten discs from patients aged 11–57 years (mean:39±15) with scoliosis (n=1), spondylolisthesis (n=1) and low back pain (n=8), were graded for macroscopic degeneration (Grades 1–4). Three ‘normal’ cadaveric discs from 3 individuals aged 25–27 years (mean 26±1) were also investigated. Disc was either snap-frozen (for RNA isolation) or the proteoglycans extracted with 4M GuHCl. Total RNA was isolated and RT-PCR performed using various oligonucleotide primers. GuHCl-extracted proteoglycan fragments were analysed using Western blotting with a number of antibodies to aggrecan metabolites, collagen metabolites and small leucine-rich proteoglycans.
Results: Intervertebral discs contain a very heterogenous population of proteoglycans demonstrating extensive enzymic degradation, particularly with increasing age and macroscopic degeneration such as is seen in back pain patients. Younger, less degenerate discs contained more biglycan than the older, more degenerate discs. However, the mRNA gene expression analyses demonstrated little cellular activity and potential synthetic response, there was very little expression of particularly in comparison to osteoarthritic cartilage cells which show considerable synthetic capability for all the major matrix components.
Discussion: Our analyses indicate that several biochemical, catabolic and biosynthetic changes occur in disc matrix molecules which are likely to contribute to loss of disc function with ageing and degeneration. The loss of biosynthetic capability of cells is very important in considering the potential of newer therapeutic modalities such as cellular repair and genetic engineering for the treatment of degenerative disc disease.
Correspondence should be addressed to Carlos Widgerowitz, Honorary Secretary BORS, Division of Surgery and Oncology, Section of Orthopaedic and Trauma Surgery, Ninewells Hospital and Medical School, Tort Centre, Dundee DD1 9SY, Scotland.
References:
[1] Cs-Szabo G. et al (2001) Spine27(20): 2212–2219 Google Scholar
