Master's Thesis Defense - Biochemical Analysis of the Human Intervertebral Disc Nucleus Pulposus with Aging and Degeneration
Date: December 19, 2006
Time: 9:00 AM
Location: Bossone Research Enterprise Center, Room: 702
Elizabeth M, Varghese
Advisors: Michelle Marcolongo, Ph.D., Fred Allen, Ph.D., Makarand Risbud, Ph.D., and Todd Doehring, Ph.D.
Lower back pain is a major cause of physical, emotional, and economic suffering in the United States, and will at some point be experienced by nearly 80-90% of its population. Degeneration of intervertebral discs (IVDs) within the lumbar region of the spine, an age-related phenomenon, is strongly associated with the incidence of lower back pain. Because the unique positioning of IVDs in the spinal setup allow them to serve as both rotational ‘joints’ and compressive cushions, normal spine function will greatly depend on the integrity of their form and internal composition.
In order to clarify the internal structure of the IVD, the macromolecular content of the nucleus pulposus region was investigated. The nucleus is a matrix of mainly collagen fibers embedded within a highly-hydrated gel of proteoglycans (PGs). The careful physiological balance of these macromolecules in this region of the disc is critical to overall mechanical performance. PGs are molecules composed of a hyaluronic acid central core protein to which many (approximately 100) sulfated glycosaminoglycan (sGAG) polysaccharide chains are attached. These chains are highly acidic, causing a high fixed negative charge in the matrix. The hydrophilic nature of the sGAG chains attract and hold water at the negatively charged polysaccharides, making the sGAG chains responsible for disc hydration, and consequently for greater resistance to mechanical loading. Collagen is responsible for maintaining the internal framework of the IVD, and contributes to tensile strength and resistance against excessive loading. Many researchers have indicated that, although collagen type I predominates in other regions of the disc (i.e. annulus and endplate), it is nearly non-existent in the nucleus, which is almost exclusively composed of collagen type II.
The composition and relative proportions of these macromolecules differ according to location within the disc, age, and stage of degeneration. In this study, discs were extracted from the lumbar region of seven cadavers of varying ages and degeneration grades in order to understand changes in macromolecular content over time. Biochemical assays were employed on the basis of accuracy, sensitivity, and specificity to measure total water, sGAG, collagen I and collagen II content within the nucleus. These techniques were optimized to quantify the content of nucleus pulposus-type tissue. Our findings indicate that the percentage of water decreases with age and degenerative grade, varies between 68-81% by weight, and is lowest in the L4-L5 disc. Sulfated glycosaminoglycan content, which is indicative of PG content, was found to be roughly 50-430 µg/mg of the dry weight (dw) of the tissue, and also decreases with age and degenerative grade. Collagen II content was found to be roughly 14-140 µg/mg dw, and collagen I content to be between 60-5072 ng/mg dw. Results appear to be consistent with existing literature, with the exception of a possible refinement in prevailing soluble collagen data. This data can help further understand structure-property relations in the intervertebral disc.
The Bossone Research Enterprise Center is located at the corner of 32nd and Market Streets.