MATRIX METALLOPROTEINASE ACTIVITIES IN AVIAN TIBIAL DYSCHONDROPLASIA

Tibial dyschondroplasia (TD) in poultry is a disorder of growth plate cartilage that fails to resorb and consequently prevents bone formatio n. Matrix metalloproteinases (MMP) contribute to the process of resorp tion through the degradation of extracellular matrices and facilitatin g vascularization, growth plate remodeling, and maturation. In order t o understand the cause of the failure of cartilage degradation in TD, the gelatinase and collagenase activities, and the levels of collagen and glycosaminoglycans of conditioned media derived from cartilage-exp lant cultures of normal and TD growth plates were measured. Substrate zymography exhibited two prominent gelatinolytic and collagenolytic ba nds corresponding to MW 63, 59, and a broad but fuzzy band of activity between 100 and 200 kDa. On treatment with 4-aminophenylmercuric acet ate, a compound that converts proenzyme forms of MMP, the 63 kDa MW ge latinolytic band migrated as a similar to 60 kDa band and contributed to the broadening of the 59 kDa band. The TD-growth plate-conditioned media had significantly lower collagenolytic-gelatinolytic activities. The sulfated glycosaminoglycans, but not the collagen contents of the conditioned media from TD-explant cultures, were also reduced signifi cantly. It is likely that the decreased matrix metalloproteinase activ ities of growth plate chondrocyte may contribute to a reduced turnover of extracellular matrices (ECM), leading to the retention of cartilag e and its lack of vascularity in TD-affected growth plates.