Ultrastructural Immunolocalization of α-Elastin and Keratan Sulfate Proteoglycan in Normal and Scoliotic Lumbar Disc

In Brief Study Design. Comparative ultrastructural study of intervertebral discs from normal subjects and patients with scoliosis. Objective. To identify ultrastructural relations among keratan sulfate (KS) proteoglycan, α-elastin, collagen fibers, and elastic fibers in normal and scoliotic discs. Summary of Background. KS proteoglycans, elastic fibers, and collagen fibers play important mechanical roles in the intervertebral disc, but the distributions of KS proteoglycans and elastin in this tissue have received little attention. Methods. Tissues were fixed in 4% paraformaldehyde. Monoclonal antibody 5-D-4 (which recognizes a KS epitope on aggrecan, fibromodulin, and lumican) and polyclonal anti-α-elastin were visualized with a 10-nm immunogold-conjugated secondary antibody. Results. In a normal disc, a regular pattern of KS labeling occurred around collagen fibers, in the cell cytoplasm, and in the rough endoplasmic reticulum; the nucleus pulposus was more densely labeled for KS than was the anulus fibrosus. In scoliotic disc anulus fibrosus, KS labeling was weak throughout the matrix and pericellularly but abundant in lysosomes and on electron-dense material in degenerate cells. Degenerate collagen fibers in scoliotic tissue bore less KS than did normal fibers. KS labeling of the microfibrillar region of elastic fibers was strong in normal disc but weak in scoliotic disc. Elastin labeling of elastic fibers was weaker in scoliotic than in normal tissue. Conclusion. KS proteoglycans and elastic fibers are closely associated with the lamellar organization of the collagen fibers in a normal disc. In scoliosis, impaired regulation of collagen fibrillogenesis by lumican or fibromodulin may result in disruption of the lamellar structure. Intervertebral discs from patients with scoliosis show degenerate cells containing abundant keratan sulfate, degenerate collagen fibers bearing relatively little keratan sulfate proteoglycan, and disruption of the lamellar organization of collagen and elastic fibers. Such structural disruption may result from impaired regulation of collagen fibrillogenesis by lumican or fibromodulin.