Immunohistochemical analysis of type IX collagen in disc tissue from spinal fusion patients.
To determine if collagen IX can be detected in adult disc tissue removed at spinal fusion surgery from patients either with or without degeneration-associated tryptophan single nucleotide polymorphisms (SNPs) and whether the distribution is associated either with severity of degeneration or incidence of a collagen IX SNP genotype.
Genetic factors are strongly associated with risk of development and/or progression of disc degeneration. Two SNPs that introduce tryptophan polymorphisms in COL9A2 and COL9A3 are independently linked to an increased risk of lumbar disc disease. Although tryptophan variants are associated with accelerated degeneration, it is not known if collagen IX can be detected in adult disc tissue.
We selected age-matched disc samples from five clinical groups: fracture with Trp(−) (six cases), herniation (six cases), degeneration (five cases), spondylolisthesis with Trp(−) (eight cases), and spondylolisthesis/herniation/fracture with Trp(+) (six cases of Trp3 allele and one case of Trp2 allele). Using hematoxylin and eosin staining and immunohistochemical staining (collagens IX and IIA), 78 sections from 32 patients were analyzed. Selected disc tissues were assayed biochemically for collagen IX.
Focal deposition of collagen IX was observed in regions of adult human disc tissue from spines showing degenerative changes in patients whether or not they were positive for a tryptophan SNP. However, in nondegenerative control disc tissue from fracture cases, little or no collagen IX was detected. The latter finding was confirmed by direct biochemical analyses for collagen IX in pooled samples of normal adult human annulus fibrosus or nucleus pulposus.
During growth and maturation of the disc, collagen IX is presumably removed completely during matrix remodeling so that the protein is absent from normal adult annulus and nucleus but can reappear at sites of degeneration presumably as part of a repair response to mechanical injury.
Immunohistochemical analysis of type IX collagen in disc tissue from spinal fusion patients revealed that collagen IX is absent from normal nondegenerative disc tissues but can reappear at sites of degeneration regardless whether or not patients were positive for a tryptophan polymorphism, presumably as part of a repair response to mechanical injury.
*Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, WA
†Department of Orthopaedics, Dartmouth-Hitchcock Medical Center, Lebanon, NH.
Address correspondence and reprint requests to David R. Eyre, PhD, Department of Orthopaedics and Sports Medicine 1959 NE Pacific St., P.O. Box 356500, Seattle, WA 98195; E-mail: email@example.com.
Acknowledgement: February 3, 2010; revise: September 2, 2010; Accept: September 29, 2010.
The manuscript submitted does not contain information about medical device(s)/drug(s).
Federal and Institutional funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.
This work was supported in part by U.S. National Institutes of Health grants AR37318 and AR36794 (DRE); and the Burgess Chair Endowment of the University of Washington.