Proteoglycan-4 in Equine Joint Disease, Exercise, and in vitro Cartilage Repair

Proteoglycan-4 (PRG4) and hyaluronan (HA) are biological macromolecules with varied and diverse functions distributed throughout the body. In synovial fluid (SF), PRG4 and HA provide independent and synergistic contributions to tissue health and cartilage boundary lubrication. The biological consequences of joint injury or disease such as osteoarthritis (OA) may include altered concentration, structure, and function of PRG4 and HA , leading to degraded SF quality and function, changes which are not fully understood. Furthermore, the effects of joint disease on circulating (serum) PRG4 and HA, both of unknown origin and function in blood, requires clarification. Monitoring changes to PRG4 and HA to elucidate the effects on SF and serum may facilitate the development of therapeutics, bi omarkers, or novel biomaterials to restore joint health and function. The objectives of t his thesis were to 1) investigate clinically relevant changes to PRG4 and HA composition in SF and serum, and SF biomechanical function from equine cases of joint di sease and injury, 2) to investigate the effect of exercise on equine serum PRG4, and 3) to characterize the effect of recombinant human PRG4 (rhPRG4) integration on the biomechanical, architectural, and biological aspects of a collagen – based scaffold for c artilage repair. A combination of novel and previously characterized biochemical and biomechanical techniques were used to evaluate SF and serum composition, the lubricating ability of SF and tissue-engineered collagen-scaffolds, and the in vitro bioactivity of rhPRG4-integrated collagen-scaffolds. The composition of equine SF changed in acute joint injury compared to SF from normal horses. Both PRG4 concentration and HA molecular weight were altered, with decreased SF viscosity , yet no associated detectable effects on serum PRG4. The concentration of serum PRG4 in a group of racehorses decrea sed significantly five minutes post -exercise, perhaps clearing from the circulation. Hence, serum PRG4 and HA concentrations alone may not be useful biomarkers for equine joint disease. rhPRG4-integrated scaffolds had enhanced lubricating properties, a highly porous architecture, and supported cell infiltration and growth across most concentrations tested. Collectively these results indicate that PRG4 is an essential lubricant, an indicator for injury, and a promising therapeutic for integration within cartilage repair biomaterials.