A defect in the structure of type I procollagen in a patient who had osteogenesis imperfecta: excess mannose in the COOH-terminal propeptide.

Abstract

Fibroblasts from normal human subjects and from a patient who had osteogenesis imperfecta were incubated with [3H]mannose, and types I and III procolla ens were isolated from the culture medium. The type I procowuaen from the patient's fibroblasts contained [2][3] These results appear to provide evidence for an alteration in the structure of procollagen in osteogenesis imperfecta. Osteogenesis imperfecta (OI) is a heterogeneous group of genetic disorders that are characterized by increased fragility of bone (1, 2). In the most severe forms, death occurs in utero. In more moderate forms, there are severe bone deformities because of repeated multiple fractures. The increased fragility of bone is frequently accompanied by blue sclerae, opalescent teeth, hearing impairment, and thin and translucent skin. A number of observations have been made that suggest that many forms of OI involve changes in the structure or synthesis of collagen. These changes include a decrease in the amount of type I collagen relative to that of type III collagen in skin extracts (3); a decrease in the synthesis of type I procollagen relative to that of type III procollagen by cultured skin fibroblasts (4); a decrease in the total amount of collagen synthesized by cultured skin fibroblasts (5); the presence of type III collagen in bone, a tissue that normally does not contain this protein (6); the presence in skin extracts of collagen that has increased amounts of hydroxylysine and glycosylated hydroxylysine (7); and a relative increase in the amount of immature crosslinks in collagen extracted from skin (8). It has been difficult, however, to determine which of these observations reflect primary genetic defects and which are secondary events. For example, a variety of experimental conditions can influence the posttranslational processing of procollagen and thereby alter the amounts of hydroxylysine and glycosylated hydroxylysine and the kinds of crosslinks found in collagen without any change in its genetically determined primary structure (for reviews, see refs. 9-11). Also, it is not apparent whether the relative amounts of type I and type III procollagens synthesized by fibroblasts are a genetically determined property of such cells or whether this varies with experimental conditions, such as the density of the cell cultures (12, 13).The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "adve-rtisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact. 6179We recently examined the type I and type III procollagens synthesized by the fibroblasts from a patient who had OI and found that the type I procollagen formed insoluble aggregates more readily than normal type I procollagen (14). We here report further studies of the same fibroblasts; these studies appear to provide evidence for an alteration in the structure of procollagen in some OI patients.MATERIALS AND METHODS Cultured Fibroblasts. The studies described here were carried out by u...

Osteogenesis imperfecta type IV. Biochemical confirmation of genetic linkage to the pro alpha 2(I) gene of type I collagen.

“…Studies of collagens synthesized by cultured fibroblasts from different patients with 01 type I (4-6), 01 type 11 (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17), and 01 type III (18)(19)(20)(21)(22) have demonstrated evidence of mutations in the proal(I) and proa2(I) genes of type I collagen. There is less information regarding the biochemical basis of 01 type IV, which differs clinically from the other relatively mild autosomal dominant OI phenotype, 01 type I.…”

Nuclease S1 mapping of a homozygous mutation in the carboxyl-propeptide-coding region of the pro alpha 2(I) collagen gene in a patient with osteogenesis imperfecta.

“…Tissue culture conditions, cell labeling procedures, and protocols for DEAE-cellulose chromatography of media proteins were as described (16). Peak fractions of the purified proteins were extensively dialyzed against 0.1 M acetic acid and then lyophilized and suspended in sample buffer for electrophoresis on polyacrylamide gels in the presence of NaDodSO4 (17); fluorograms were prepared using standard conditions (18).…”

ER stress-mediated apoptosis in a new mouse model of osteogenesis imperfecta

“…The presumptive elongated chain with newly introduced cysteins and disruption of a crucial beta sheet due to the Aga2 mutation likely destabilized protein conformation, thus affecting preferential chain assembly and proteolysis. Also, a N-linked oligosaccharide unit was introduced capable of altering intracellular processing and secretion of procollagens as well [29].…”