Substitution of an aspartic acid for glycine 700 in the alpha 2(I) chain of type I collagen in a recurrent lethal type II osteogenesis imperfecta dramatically affects the mineralization of bone

A novel COL1A1 mutation in a family with osteogenesis imperfecta associated with phenotypic variabilities

Osteogenesis imperfecta (OI) is a heterogeneous disorder that is characterized by bone fragility and systemic complications, and is mainly caused by gene mutations in COL1A1 or COL1A2. A novel COL1A1 splicing mutation, c.750+2T>A, was identified in a Japanese OI family. Only the proband in this family showed various complications, such as heart valve diseases and severe scoliosis. The clinical heterogeneity in the family is discussed in this study.

Potential of human fetal chorionic stem cells for the treatment of osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a genetic bone pathology with prenatal onset, characterized by brittle bones in response to abnormal collagen composition. There is presently no cure for OI. We previously showed that human first trimester fetal blood mesenchymal stem cells (MSCs) transplanted into a murine OI model (oim mice) improved the phenotype. However, the clinical use of fetal MSC is constrained by their limited number and low availability. In contrast, human fetal early chorionic stem cells (e-CSC) can be used without ethical restrictions and isolated in high numbers from the placenta during ongoing pregnancy. Here, we show that intraperitoneal injection of e-CSC in oim neonates reduced fractures, increased bone ductility and bone volume (BV), increased the numbers of hypertrophic chondrocytes, and upregulated endogenous genes involved in endochondral and intramembranous ossification. Exogenous cells preferentially homed to long bone epiphyses, expressed osteoblast genes, and produced collagen COL1A2. Together, our data suggest that exogenous cells decrease bone brittleness and BV by directly differentiating to osteoblasts and indirectly stimulating host chondrogenesis and osteogenesis. In conclusion, the placenta is a practical source of stem cells for the treatment of OI.

Mutation and polymorphism spectrum in osteogenesis imperfecta type II: implications for genotype-phenotype relationships

Osteogenesis imperfecta (OI), also known as brittle bone disease, is a clinically and genetically heterogeneous disorder primarily characterized by susceptibility to fracture. Although OI generally results from mutations in the type I collagen genes, COL1A1 and COL1A2, the relationship between genotype and phenotype is not yet well understood. To provide additional data for genotype–phenotype analyses and to determine the proportion of mutations in the type I collagen genes among subjects with lethal forms of OI, we sequenced the coding and exon-flanking regions of COL1A1 and COL1A2 in a cohort of 63 subjects with OI type II, the perinatal lethal form of the disease. We identified 61 distinct heterozygous mutations in type I collagen, including five non-synonymous rare variants of unknown significance, of which 43 had not been seen previously. In addition, we found 60 SNPs in COL1A1, of which 17 were not reported previously, and 82 in COL1A2, of which 18 are novel. In three samples without collagen mutations, we found inactivating mutations in CRTAP and LEPRE1, suggesting a frequency of these recessive mutations of ∼5% in OI type II. A computational model that predicts the outcome of substitutions for glycine within the triple helical domain of collagen α1(I) chains predicted lethality with ∼90% accuracy. The results contribute to the understanding of the etiology of OI by providing data to evaluate and refine current models relating genotype to phenotype and by providing an unbiased indication of the relative frequency of mutations in OI-associated genes.

Association of bovine dentine phosphophoryn with collagen fragments

Bovine dentine phosphophoryn (BDP), a protein rich in aspartyl (Asp) and O-phosphoseryl (Ser(P)) residues, is synthesized by odontoblasts and believed to be involved in matrix-mediated biomineralization of dentine. Phosphophoryn was purified from bovine dentine using EDTA extraction, Ca(2+) precipitation, anion exchange and size exclusion chromatography. The purified protein migrated on SDS-PAGGE as a single band. The protein was dephosphorylated using a chelex alkaline dialysis procedure, repurified using anion exchange and size exclusion chromatography and then subjected to cleavage with trypsin. The digest was subjected to reversed-phase HPLC and analysed by Q-TOF mass spectrometry. The only non-trypsin peptides that could be identified were two collagen Type I alpha2 peptides whose sequence was determined by fragmentation analysis. The association of collagen fragments with highly purified phosphophoryn suggests that the EDTA extraction method yields BDP that is strongly bound to collagen fragments. This association now helps explain discrepancies in molecular weight and amino acid composition data for various phosphophoryn preparations compared with the same data calculated from the C-terminal extension of mouse, rat and human dentine sialophosphoprotein (DSPP) gene products. Analysis of the mutation pattern of the clinical disorder Osteogenesis Imperfecta within the region enclosed by the identified collagen fragments reveals that phosphophoryn associates with a segment of collagen that is crucial for structure and/or function.

Unexpected ultrastructral changes in bone osteiod collagens in osteogenesis imperfecta

Osteogenesis Imperfecta (OI) is a heterogeneous, inherited bone disorder usually resulting from a defect in collagen synthesis or function. The Sillence classification recognises four OI subtypes of which type III is the severe, progressively deforming form. Here, we report distinctive ultrastructural abnormalities of bone osteoid collagen fibrils from three patients with OI type III and compared with normal controls. Collagen biochemistry of these patients showed normal alpha1(I) and alpha2(I) chains, despite the structurally abnormal collagen fibrils. The expected lamellar organisation of normal osteoid was absent in the bone biopsies of these patients. In addition their collagen fibrils had frayed edges and no periodicity was observed in most of these fibrils. These collagen fibrils were also flower like, twisted, spiralled and sparsely distributed throughout a very thick osteoid with patchy mineralisation. These structurally abnormal collagens may not be able to provide the nucleating and scaffolding sites for normal mineralisation and may lead to the bone fragility observed in OI.

The infant skull: a vault of information

The art of interpreting skull radiographs is slowly being lost as trainees in radiology see fewer plain radiographs and depend more heavily on computed tomography and magnetic resonance imaging. Nevertheless, skull radiographs still provide significant information that is helpful in finding pathologic conditions and appreciating their extents. Abnormalities in the skull may be reflected as variations in the density, size, and shape of the skull, as well as skull defects. Skeletal dysplasias may manifest as a generalized decrease in calvarial density (hypophosphatasia, osteogenesis imperfecta), a generalized increase in calvarial density (osteopetrosis), or a focal increase in density (frontometaphyseal dysplasia). Diffusely decreased or increased calvarial density is usually associated with a process that affects the entire skeleton. Therefore, correct differentiation among these dysplasias depends on other concurrent features. Decreased size of the cranial vault at birth generally implies an underlying insult to the brain, including fetal alcohol syndrome and the so-called TORCH infections (toxoplasmosis, rubella, cytomegalovirus infection, herpes simplex). Macrocephaly may result from skeletal dysplasia or an increase in the intracranial volume (eg, due to underlying anomalies of the brain such as hydrocephalus).

Defects of type I procollagen metabolism correlated with decrease of prolidase activity in a case of lethal osteogenesis imperfecta

We have studied the structure and metabolism of type I procollagen in a case of perinatal lethal osteogenesis imperfecta (OI) type II. Cultured skin fibroblasts from the proband synthesized both normal and abnormal forms of type I procollagen. Some abnormal, overmodified molecules were secreted by OI cells, although less efficiently than normal molecules from control cells. The OI fibroblasts accumulated large amounts of abnormal proalpha1(I) and proalpha2(I) chains intracellularly. The extracellular collagenolytic activity was decreased compared to control cells. Furthermore, OI cells produced less type I procollagen and demonstrated lower capacity to synthesize DNA than control cells. We have found that in contrast to prolinase activity, the activity of prolidase (an enzyme essential for collagen synthesis and cell growth) is also significantly reduced in OI cells. No differences were found in the amount of the enzyme protein recovered from both the OI and control cells. However, we found that expressions of beta1 integrin and insulin-like growth factor-I receptor (receptors known to play an important role in up regulation of prolidase activity) were decreased in OI cells compared to control cells. The decrease in prolidase activity may provide an important mechanism of altered cell growth and collagen metabolism involved in producing the perinatal lethal form of the OI phenotype.

A light and electron microscopic study of osteogenesis imperfecta bone samples, with reference to collagen chemistry and clinical phenotype

A detailed morphological study was carried out using light and electron microscopy on 36 bone specimens from patients suffering from osteogenesis imperfecta (OI) and 20 age- and site-matched control bone specimens. The findings were grouped into the clinical types of OI according to the Sillence classification. The morphological and ultrastructural alterations observed in OI bone correlate well with clinical severity. Thus, OI type I, the mildest type, showed the least abnormalities in bone ultrastructure. OI type IV closely resembled type I, with only minor abnormalities in the bone cells and osteoid. OI type III showed abnormalities in the structure and distribution of osteoid collagen fibrils, whilst OI type II, the lethal form, revealed many varied abnormalities such as thin cortical bone, sparse trabecular bone, increased numbers of osteoclasts and osteocytes, thin osteoid with thin collagen fibrils, and patchy mineralization.

Folding of peptide models of collagen and misfolding in disease

The misfolding of the triple helix has been shown to play a critical role in collagen diseases. Normal and mutated collagen triple helices can be modeled by short, synthetic peptides of varying design. NMR spectroscopy and circular dichroism studies on the assembly of these peptide models have recently been used to isolate specific steps in the folding pathway and have provided information on the alterations resulting from mutations.

Rostrum of a toothed whale: ultrastructural study of a very dense bone

The rostral bones of the toothed whale, Mesoplodon densirostris, consist mainly of hypermineralized secondary osteons and have yielded among the highest values for density (2.6 g/cm3) and mineral content (86.7%) yet reported for any bone. Scanning and transmission electron microscopy show parallel rods of mineral oriented along the length of the rostrum. These consist of platey crystals of carbonated hydroxyapatite, which, judging from electron diffraction, are extremely well and coherently aligned. The collagen component of the rostral bone consists largely of very thin fibrils aligned in longitudinal register to form tubular networks. The collagen fibrils are also aligned with the lengths of the mineral rods, which are apparently accommodated in the tubular spaces of the collagenous network. This peculiar ultrastructure clearly differs from the densely packed mineralized fibrils commonly observed in vertebrate lamellar osseous tissues, although histological examination has indicated some vestiges of "normal" primary bone surrounding the secondary osteons. Thus, the bone tissue in the rostrum is characterized by a remarkably sparse collagenous component. This ultrastructure can explain the high density, stiffness, and brittleness of the rostrum that have been observed. It also raises interesting questions about possible modes of crystal growth during ongoing mineralization in normal bone, and may have some relevance in the mechanical behavior of dense bones in pathological conditions.

Sequence of canine COL1A2 cDNA: nucleotide substitutions affecting the cyanogen bromide peptide map of the alpha 2(I) chain

The alpha2 chain of canine type I collagen was characterized with both sequence analysis of COL1A2 cDNA and chemical analysis of alpha2(I) chains. The complete sequence of canine COL1A2 cDNA was determined from reverse-transcribed and polymerase chain reaction-amplified total RNA from cultured skin fibroblasts. Pepsin-digested and cyanogen bromide-digested type I collagen peptides were analyzed with chromatography, gel electrophoresis, and mass spectrometry. Identity between the sequences of canine and human COL1A2 cDNA was 90.9%, predicting conservation of the 3 cysteine residues required for C-propeptide registration and of cleavage sites for signal peptidase, procollagen N-proteinase, vertebrate collagenase, and procollagen C-proteinase. Conservation of all 50 lysine residues was also predicted, including preservation of the 1:2 asymmetry in the X:Y distribution of the 31 lysine residues in the alpha2(I) triple helix. The human and canine sequences differed in the location of Y-position proline residues and the presence of two unique canine cyanogen bromide peptides, alpha2 CB3b and alpha2 CB3c,5. Knowledge of the conserved and unique features of canine COL1A2 will be valuable for analysis of the expression, synthesis, and structure of type I collagen as well as studies of canine osteogenesis imperfecta.

Chemical and structural characterization of the mineral phase from cortical and trabecular bone

X-ray diffraction, infrared spectroscopy and chemical investigations have been carried out on the inorganic phases from rat cortical and trabecular bone. Although both inorganic phases consist of poorly crystalline B carbonated apatite, several significant differences have been observed. In particular, trabecular bone apatite displays reduced crystallite sizes, Ca/P molar ratio, and carbonate content, and exhibits a greater extent of thermal conversion into beta-tricalcium phosphate than cortical bone apatite. These differences can be related to the different extents of collagen posttranslational modifications exhibited by the two types of bone, in agreement with their different biological functions.

Arachnoid cyst and chronic subdural haematoma in a child with osteogenesis imperfecta type III resulting from the substitution of glycine 1006 by alanine in the pro alpha 2(I) chain of type I procollagen

The features of a child with osteogenesis imperfecta type III (OI III) resulting from the heterozygous substitution of glycine 1006 by alanine in the pro alpha 2(I) chain of type I procollagen were studied. He was born at term with the clinical features of severe OI, including deep grey-blue sclerae. He had severe osteopenia and all long bones were smaller than normal with cortical thinning, metaphyseal expansion, poor metaphyseal modelling, and multiple fractures. However, the vertebrae, pelvis, and shoulder girdle were of normal shape and there were few rib fractures. Histological examination of the calvarium and tibial shaft showed woven bone without lamellar bone or Haversian systems. The shafts of the long bones were widened owing to repeated fractures. Progressive enlargement of the calvarium occurred between 3 and 4.5 months of age owing to bilateral chronic subdural haematomata and a large arachnoid cyst in the Sylvian fissure. The cyst was probably developmental in origin while the subdural collections were probably the result of perinatal skull trauma. The cyst and the subdural collections resolved following drainage but ventricular dilatation with normal cerebrospinal fluid pressure followed. The proband is the first reported case of OI with a glycine substitution by alanine in the pro alpha 2(I) chain of type I procollagen.

Perinatal lethal osteogenesis imperfecta

Perinatal lethal osteogenesis imperfecta is the result of heterozygous mutations of the COL1A1 and COL1A2 genes that encode the alpha 1(I) and alpha 2(I) chains of type I collagen, respectively. Point mutations resulting in the substitution of Gly residues in Gly-X-Y amino acid triplets of the triple helical domain of the alpha 1(I) or alpha 2(I) chains are the most frequent mutations. They interrupt the repetitive Gly-X-Y structure that is mandatory for the formation of a stable triple helix. Most babies have their own private de novo mutation. However, the recurrence rate is about 7% owing to germline mosaicism in one parent. The mutations act in a dominant negative manner as the mutant pro alpha chains are incorporated into type I procollagen molecules that also contain normal pro alpha chains. The abnormal molecules are poorly secreted, more susceptible to degradation, and impair the formation of the extracellular matrix. The collagen fibres are abnormally organised and mineralisation is impaired. The severity of the clinical phenotype appears to be related to the type of mutation, its location in the alpha chain, the surrounding amino acid sequences, and the level of expression of the mutant allele.