Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 18, 1996
Publication Date: N/A
Interpretive Summary: Tibial dyschondroplasia (TD) is a common leg problem in fast growing, adolescent poultry where portions of the growth plate cartilage forms a plug of avascular cartilage that prevents bone formation. To understand the physiological basis of this disorder, we examined the activities of the enzymes, collagenase and gelatinases which are responsible for the degradation of connective tissue important for cartilage formation, blood vessel growth, and bone development. These studies were done using culture media incubated with cartilage axplants derived from normal and diseased growth plates of 6 wk old broiler chickens and examining the condition media for the enzyme activities and the concentration of major matrix components of growth plate i:e: collagen and proteinpolysaccharides called proteoglycans. The enzyme activities as well as some of the matrix components were significantly lower in the TD-affected cartilage- conditioned media. The significance of the decrease in relation to matrix metabolism and the possible causes of the decrease in TD-affected cartilage is discussed. It is suggested that decreases in enzymes that effect matrix degradation may be responsible for formation of cartilage plugs and the lack of blood vessel growth, a condition that is a prerequisite of bone formation.
Technical Abstract: Tibial dyschondroplasia (TD) in poultry, is a disorder of growth plate cartilage that fails to resorb and consequently prevents bone formation. Matrix metalloproteinases (MMP) contribute to the process of resorption by helping the degradation of extracellular matrices and facilitating vascularization, growth plate remodeling and maturation. In order to understand the cause of the failure of cartilage degradation in TD, the gelatinase/ collagenase activities and the levels of collagen and glycosaminoglycans of conditioned media derived from cartilage-explant cultures of normal and tibial dyschondroplastic growth plates were measured. Substrate zymography exhibited two prominent gelatinolytic and collagenolytic bands corresponding to MW 63 kDa, 59 kDa, and a broad but fuzzy band of activity between 100-200 kDa. On treatment with 4-amino phenylmercuric acetate, a compound that converts proenzyme forms of MMPs, the 63 kDa MW gelatinolytic band migrated as a approximately 60 kDa band and contributed to the broadening of the 59 kDa band. This treatment did not affect the 59 kDa band. The TD-growth plate-conditioned media has significant lower collagenolytic/gelatinolytic activities. The sulfated glycosaminoglycans, but not the collagen contents of the conditioned media from TD-explant cultures were also reduced significantly. It is likely that the decreased matrix metalloproteinase activities of growth plate chondrocytes may contribute to a reduced turnover of extracellular matrices (ECM), leading to the retention of cartilage and its avascularity in TD-affected growth plates.