Comparative studies of osteoblast and fibroblast type I collagen in a patient with osteogenesis imperfecta type IV.

The expression of type I collagen has been compared in fibroblast and osteoblast cultures of a patient with moderately severe osteogenesis imperfecta (OI) type IV, with respect to control cells. Electrophoretic analysis of type I collagen showed that both OI osteoblasts and fibroblasts synthesized normal chains and chains with delayed migration. However, the osteoblasts contained a higher proportion of abnormal chains than fibroblasts from the proband. Pulse-chase experiments showed that the trimers containing abnormal chains were cleared more rapidly from osteoblasts than fibroblasts. Moreover, the collagen secreted by OI osteoblasts had thermal stability 1 degrees C higher than collagen secreted by OI fibroblasts. These results suggest that the abnormal collagen in osteoblasts may be more resistant to intra- and extracellular degradation and may thus have better survival than in fibroblasts. This finding could have implications for understanding the clinical phenotype of OI.