| Articular cartilage is an avascular tissue with limited innate potential for repair and regeneration that provides a low friction surface for joint movement (Reddi 2003). Superficial zone protein (SZP) has been identified as a boundary lubricant and stress dissipater within the synovial joint (Jay, Torres et al. 2007), encoded by the proteoglycan 4 gene (PRG4) (Ikegawa, Sano et al. 2000). SZP is a significant protein that plays a key role in the normal function of synovial joints; human and mouse mutants of the prg4 gene display precocious arthritis and arthropathies (Marcelino, Carpten et al. 1999; Rhee, Marcelino et al. 2005). Various aspects of SZP tribological function, protein distribution, mRNA expression and alternative splicing are regulated by the (Transforming Growth Factor Beta) TGF-beta signaling pathway as demonstrated in this dissertation.;The overall conclusion of this work is that the anatomical differences between anterior load-bearing locations of the femoral medial condyle M1 and M4 (posterior non-load bearing) with reference to SZP, that are modulated by differences in mechanical loading in vivo, can be replicated in vitro through the application of TGF-beta. The friction coefficient decreased in M4 explants following a two-day TGF-beta1 treatment and was attributed to the increased depth of staining of SZP in the near-surface region. The SZP level and the decrease in the friction coefficient of these explants are similar to those of the untreated M1 explants.;The M1 location demonstrated increased splicing out of exons 4 (containing the heparin-binding domain) and 5 compared to the non-load bearing location M4. Treatment with TGF-beta1 directly modulated the increased splicing out of exons 4 and 5 in explant and monolayer culture. In explants the response was rapid and is independent of new protein synthesis. Inhibition of Smad3 phosphorylation by SIS3 inhibited SZP protein expression and the increase in splicing out of exons 4 and 5 by TGF-beta1.;These observations support that regulation of SZP by mechanotransduction may be primarily controlled by the TGF-beta pathway, as this was sufficient to modulate the primary differences observed between the loaded and unloaded tissue. |
