ABNORMAL TYPE-I COLLAGEN-METABOLISM BY CULTURED FIBROBLASTS IN LETHAL PERINATAL OSTEOGENESIS IMPERFECTA

Cultured skin fibroblasts from 7 consecutive cases of lethal perinatal osteogenesis imperfecta (OI) expressed defects of type I collagen metabolism. The secretion of [14C]proline-labeled collagen by the OI cells was specifically reduced (51-79% of control), and collagen degradation was increased to twice that of control cells in 5 cases and increased by .apprx. 30% in the other 2 cases. Sodium dodecyl sulphate/polyacrylamide-gel electrophoresis revealed that 4 of the OI cell lines produced 2 forms of type I collagen consisting of both normally and slowly migrating forms of the .alpha.1(I)- and .alpha.2(I)-chains. In the other 3 OI cell lines only the slow .alpha.(I)''- and .alpha.2(I)''-chains were detected. In both groups inhibition of the post-translational modifications of proline and lysine resulted in the production of a single species of type I collagen with normal electrophoretic migration. Proline hydroxylation was normal, but the hydroxylysine contents of .alpha.1(I)''- and .alpha.2(I)''-chains purified by [high performance liquid chromatography] were greater than in control .alpha.-chains. The glucosylgalactosylhydroxylysine content was increased .apprx. 3-fold while the galactosylhydroxylysine content was only slightly increased in the .alpha.1(I)''-chains relative to control .alpha.1(I)-chains. Peptide mapping of the CNBr-cleavage peptides provided evidence that the increased post-translational modifications were distributed throughout the .alpha.1(I)''- and .alpha.2(I)''-chains. The greater modification of these chains was due to structural defects of the .alpha.-chains leading to delayed helix formation. The abnormal charge heterogeneity observed in the .alpha.1 CB8 peptide of 1 patient may reflect such a structural defect in the type I collagen molecule.