Ph.D. Dissertation Defense by Stacy Marie Imler
Tuesday, July 12, 2005
(Dr. Marc E. Levenston, Chair)
"In Vitro Modulation of Meniscus Biosynthesis: A Basis for Understanding Cellular Response to Physiologically Relevant Stimuli "
The meniscus is a soft, fibrocartilaginous tissue critical for the maintenance of normal knee biomechanics, providing shock absorbance and overall joint lubrication and stability. The adult tissue is highly avascular with a poor autonomous repair capacity in response to injury. Despite the estimated 750,000 arthroscopic surgeries performed per year to repair torn menisci and the increasing evidence showing a high incidence of meniscal degeneration during very early stages of osteoarthritis, little is currently known of the cellular responses of the native cells or meniscal fibrochondrocytes to physiologic stimuli. Therefore, this work explored the responses of meniscal fibrochondrocytes to exogenous biomechanical and biochemical stimuli in an effort to better understand the sensitivity of these cells in their native tissue matrix as well as in a 3-D scaffold environment.
Using the immature bovine model, the changes in biosynthesis of fibrochondrocytes in tissue explants and in an agarose scaffold due to unconfined oscillatory compression were explored. This biomechanical stimulus, previously identified to stimulate matrix production of chondrocytes of articular cartilage, stimulated total protein synthesis in both culture environments. In contrast, the synthesis of proteoglycans, matrix components important in mechanical stiffness and hydration of the tissue, was not affected by these compression protocols. However, the use of a biochemical stimulus in the form of anabolic cytokines significantly enhanced both protein and proteoglycan synthesis as a function of culture environment as well as class of cytokine used. The superposition of oscillatory compression in addition to the use of these potent biochemical stimulators, insulin-like growth factor-I or transforming growth factor-beta 1, did not further enhance matrix synthesis of fibrochondroyctes in agarose culture, suggesting an insensitivity of the fibrochondrocytes to biomechanical stimuli during early time-points in maturation of native matrix within the agarose scaffold. As a combination of biomechanical and biochemical stimuli are responsible for directing the development, maintenance, and repair of the tissue, these findings have implications towards understanding tissue maintenance from the explant studies, as well as developmental clues from the deposition of de novo fibrocartilage in the agarose scaffolds.