Ultrastructural localization and distribution of proteoglycan in normal and scoliotic lumbar disc

Study Design. Comparative ultrastructural study of normal and scoliotic intervertebral discs. Objective. To examine the ultrastructural organization and distribution of proteoglycan in relation to collagen and elastic fibers in normal and scoliotic discs. Summary of Background. The mechanical properties of intervertebral discs depend on the collagens and proteoglycans in the matrix; proteoglycan content and the organization of collagen fibers are altered in degenerate discs. However, little is known about the structural relations among disc components and alterations to them in scoliosis. Methods. Samples of normal and scoliotic disc from individuals aged between 12 and 16 years were fixed in 2.5% glutaraldehyde containing cuprolinic blue and examined by transmission electron microscopy. The sizes and distribution of proteoglycan particles throughout different matrix regions were quantified. Results. In anulus fibrosus of normal disc, collagen and elastic fibers in lamellas were covered with small proteoglycan particles in a regular pattern; proteoglycan particles of similar sizes were evenly distributed throughout the matrix. Anulus fibrosus of scoliotic disc contained degenerate collagen lamellas, few elastic fibers, and a pericellular accumulation of large proteoglycan aggregates; scoliotic nucleus pulposus also contained an accumulation of proteoglycan aggregates. Most cells in both regions of scoliotic discs were degenerate and vacuolated. Conclusion. We provide ultrastructural confirmation of the disruption of the lamellar organization of collagen and elastic fibers in scoliosis. Our observations of altered proteoglycan distribution in scoliotic tissue suggest that impaired proteoglycan turnover plays a key role in the disruption of the structural integrity of the disc in scoliosis.