Brittle bones--fragile molecules: disorders of collagen gene structure and expression

Radiologic Features of Type II and Type XI Collagenopathies

Type II collagen is a major component of the cartilage matrix. Pathogenic variants (ie, disease-causing aberrations) in the type II collagen gene (COL2A1) lead to an abnormal structure of type II collagen, causing a large group of skeletal dysplasias termed type II collagenopathies. Because type II collagen is also located in the vitreous body of the eyes and inner ears, type II collagenopathies are commonly associated with vitreoretinal degeneration and hearing impairment. Type II collagenopathies can be radiologically divided into two major groups: the spondyloepiphyseal dysplasia congenita (SEDC) group and the Kniest-Stickler group. The SEDC group is characterized by delayed ossification of the juxtatruncal bones, including pear-shaped vertebrae. These collagenopathies comprise achondrogenesis type 2, hypochondrogenesis, SEDC, and other uncommon subtypes. The Kniest-Stickler group is characterized by disordered tubular bone growth that leads to "dumbbell" deformities. It comprises Kniest dysplasia and Stickler dysplasia type 1, whose radiographic manifestations overlap with those of type XI collagenopathies (a group of disorders due to abnormal type XI collagen) such as Stickler dysplasia types 2 and 3. This phenotypic overlap is caused by type II and type XI collagen molecules sharing part of the same connective tissues. The authors describe the diagnostic pathways to type II and type XI collagenopathies and the associated differential diagnoses. In addition, they review the clinical features and genetic bases of these conditions, which radiologists should know to participate in multidisciplinary care and translational research. Online supplemental material is available for this article. ^©RSNA, 2020.

Implant therapy for a patient with osteogenesis imperfecta type I: review of literature with a case report

Bone fragility and skeletal irregularities are the characteristic features of osteogenesis imperfecta (OI). Many patients with OI have weakened maxillary and mandibular bone, leading to poor oral hygiene and subsequent loss of teeth. Improvements in implant therapy have allowed for OI patients to achieve dental restoration. However, there is limited available literature on implant therapy for patients with OI. The greatest challenge in the restoration process for OI patients in an outpatient setting is ensuring primary stability and osseointegration. Improvements in synthetic grafts improve successful implant placement and prevent predisposing patients to unnecessary procedures. This report details the successful restoration process of an OI type I patient’s maxillary arch in addition to a review of the currently available literature.

Impact of Arginine to Cysteine Mutations in Collagen II on Protein Secretion and Cell Survival

Inherited point mutations in collagen II in humans affecting mainly cartilage are broadly classified as chondrodysplasias. Most mutations occur in the glycine (Gly) of the Gly-X-Y repeats leading to destabilization of the triple helix. Arginine to cysteine substitutions that occur at either the X or Y position within the Gly-X-Y cause different phenotypes like Stickler syndrome and congenital spondyloepiphyseal dysplasia (SEDC). We investigated the consequences of arginine to cysteine substitutions (X or Y position within the Gly-X-Y) towards the N and C terminus of the triple helix. Protein expression and its secretion trafficking were analyzed. Substitutions R75C, R134C and R704C did not alter the thermal stability with respect to wild type; R740C and R789C proteins displayed significantly reduced melting temperatures (T_m) affecting thermal stability. Additionally, R740C and R789C were susceptible to proteases; in cell culture, R789C protein was further cleaved by matrix metalloproteinases (MMPs) resulting in expression of only a truncated fragment affecting its secretion and intracellular retention. Retention of misfolded R740C and R789C proteins triggered an ER stress response leading to apoptosis of the expressing cells. Arginine to cysteine mutations towards the C-terminus of the triple helix had a deleterious effect, whereas mutations towards the N-terminus of the triple helix (R75C and R134C) and R704C had less impact.

An ENU-induced splice site mutation of mouse Col1a1 causing recessive osteogenesis imperfecta and revealing a novel splicing rescue

GU-AG consensus sequences are used for intron recognition in the majority of cases of pre-mRNA splicing in eukaryotes. Mutations at splice junctions often cause exon skipping, short deletions, or insertions in the mature mRNA, underlying one common molecular mechanism of genetic diseases. Using N-ethyl-N-nitrosourea, a novel recessive mutation named seal was produced, associated with fragile bones and susceptibility to fractures (spine and limbs). A single nucleotide transversion (T → A) at the second position of intron 36 of the Col1a1 gene, encoding the type I collagen, α1 chain, was responsible for the phenotype. Col1a1 ^seal mRNA expression occurred at greatly reduced levels compared to the wild-type transcript, resulting in reduced and aberrant collagen fibers in tibiae of seal homozygous mice. Unexpectedly, splicing of Col1a1 ^seal mRNA followed the normal pattern despite the presence of the donor splice site mutation, likely due to the action of a putative intronic splicing enhancer present in intron 25, which appeared to function redundantly with the splice donor site of intron 36. Seal mice represent a model of human osteogenesis imperfecta, and reveal a previously unknown mechanism for splicing "rescue."

Design and Biological Evaluation of Delivery Systems Containing Bisphosphonates

Bisphosphonates have found application in the treatment of reoccurrence of bone diseases, breast cancer, etc. They have also been found to exhibit antimicrobial, anticancer and antimalarial activities. However, they suffer from pharmacological deficiencies such as toxicity, poor bioavailability and low intestinal adsorption. These shortcomings have resulted in several researchers developing delivery systems that can enhance their overall therapeutic effectiveness. This review provides a detailed overview of the published studies on delivery systems designed for the delivery of bisphosphonates and the corresponding in vitro/in vivo results.

Clinical characteristics and the identification of novel mutations of COL1A1 and COL1A2 in 61 Chinese patients with osteogenesis imperfecta

Osteogenesis imperfecta (OI) is an inherited connective tissue disorder characterized by brittle bone fractures. The aim of the present study was to investigate the pathogenic gene mutation spectrum and clinical manifestations of mutations in collagen type I, alpha 1 (COL1A1) and collagen type I, alpha 2 (COL1A2) genes in Chinese patients with OI. A total of 61 unrelated Chinese OI patients with COL1A1 and COL1A2 mutations were recruited. All the exons and the exon-intron boundaries of the COL1A1 and COL1A2 genes were amplified and directly sequenced and lumbar spine bone mineral density was measured by dual‑energy X‑ray absorptiometry. The mutations of the 61 probands included 33 missense mutations, 8 nonsense mutations, 7 splicing variants and 13 frameshift mutations in COL1A1 and COL1A2 genes. A total of 25 novel mutations were identified, including 18 in COL1A1 and 7 in COL1A2. The mutations p.Gly257Arg, p.Gly767Ser and p.Gly821Ser in COL1A1 and p.Gly337Ser in COL1A2 may be located at a mutation hotspot for human OI due to the high repetition rate in OI patients. Family history was positive for OI in 33 probands (54%). All probands had suffered fractures and the most common fracture site was the femur. A total of 49 probands presented with blue sclerae (80.3%), 20 probands suffered from dentinogenesis imperfecta (32.8%) and 1 patient had hearing loss (1.6%). These findings may improve understanding of the pathogenic gene mutation spectrum and the clinical manifestations of mutations of COL1A1 and COL1A2 genes in Chinese patients with OI.

American Society of Biomechanics Journal of Biomechanics Award 2013: cortical bone tissue mechanical quality and biological mechanisms possibly underlying atypical fractures

The biomechanics literature contains many well-understood mechanisms behind typical fracture types that have important roles in treatment planning. The recent association of “atypical” fractures with long-term use of drugs designed to prevent osteoporosis has renewed interest in the effects of agents on bone tissue-level quality. While this class of fracture was recognized prior to the introduction of the anti-resorptive bisphosphonate drugs and recently likened to stress fractures, the mechanism(s) that lead to atypical fractures have not been definitively identified. Thus, a causal relationship between these drugs and atypical fracture has not been established. Physicians, bioengineers and others interested in the biomechanics of bone are working to improve fracture-prevention diagnostics, and the design of treatments to avoid this serious side-effect in the future. This review examines the mechanisms behind the bone tissue damage that may produce the atypical fracture pattern observed increasingly with long-term bisphosphonate use. Our recent findings and those of others reviewed support that the mechanisms behind normal, healthy excavation and tunnel filling by bone remodeling units within cortical tissue strengthen mechanical integrity. The ability of cortical bone to resist the damage induced during cyclic loading may be altered by the reduced remodeling and increased tissue age resulting from long-term bisphosphonate treatment. Development of assessments for such potential fractures would restore confidence in pharmaceutical treatments that have the potential to spare millions in our aging population from the morbidity and death that often follow bone fracture.

Variation in type I collagen fibril nanomorphology: the significance and origin

Although the axial D-periodic spacing is a well-recognized nanomorphological feature of type I collagen fibrils, the existence of a distribution of values has been largely overlooked since its discovery seven decades ago. Studies based on single fibril measurements occasionally noted variation in D-spacing values, but accredited it with no biological significance. Recent quantitative characterizations supported that a 10-nm collagen D-spacing distribution is intrinsic to collagen fibrils in various tissues as well as in vitro self-assembly of reconstituted collagen. In addition, the distribution is altered in Osteogenesis Imperfecta and long-term estrogen deprivation. Bone collagen is organized into lamellar sheets of bundles at the micro-scale, and D-spacings within a bundle of a lamella are mostly identical, whereas variations among different bundles contribute to the full-scale distribution. This seems to be a very general phenomenon for the protein as the same type of D-spacing/bundle organization is observed for dermal and tendon collagen. More research investigation of collagen nanomorphology in connection to bone biology is required to fully understand these new observations. Here we review the data demonstrating the existence of a D-spacing distribution, the impact of disease on the distribution and possible explanations for the origin of D-spacing variations based on various collagen fibrillogenesis models.

Pharmacogenetics of osteoporosis: towards novel theranostics for personalized medicine?

Osteoporosis is a complex multifactorial bone disorder with a strong genetic basis. It is the most common, severe, progressive skeletal illness that has been increasing, particularly in developed countries. Osteoporosis will no doubt constitute a serious clinical burden in healthcare management in the coming decades. The genetics of osteoporosis should be analyzed from both the disease susceptibility and the pharmacogenetic treatment perspectives. The former has been widely studied and discussed, while the latter still requires much more information and research. This article provides a synthesis of the literature on the genetics of osteoporosis and an update on progress made in pharmacogenetics of osteoporosis in recent years, specifically regarding the new molecular targets for antiresorptive drugs. In-depth translation of osteoporosis pharmacogenetics approaches to clinical practice demands a new vision grounded on the concept of "theranostics," that is, the integration of diagnostics for both disease susceptibility testing, as well as for prediction of health intervention outcomes. In essence, theranostics signals a broadening in the scope of inquiry in diagnostics medicine. The upcoming wave of theranostics medicine also suggests more distributed forms of science and knowledge production, both by experts and end-users of scientific products. Both the diagnosis and personalized treatment of osteoporosis could conceivably benefit from the emerging postgenomics field of theranostics.

JAG1 and COL1A1 polymorphisms and haplotypes in relation to bone mineral density variations in postmenopausal Mexican-Mestizo Women

Osteoporosis is characterized by low bone mineral density (BMD). One of the most important factors that influence BMD is the genetic contribution. The collagen type 1 alpha 1 (COL1A1) and the JAGGED (JAG1) have been investigated in relation to BMD. The aim of this study was to investigate the possible association between two single-nucleotide polymorphisms (SNPs) of COL1A1, their haplotypes, and one SNP of JAG1 with BMD in postmenopausal Mexican-Mestizo women. Seven hundred and fifty unrelated postmenopausal women were included. Risk factors were recorded and BMD was measured in lumbar spine, total hip, and femoral neck by dual-energy X-ray absorptiometry. DNA was obtained from blood leukocytes. Two SNPs in COL1A1 (rs1800012 and rs1107946) and one in JAG1 (rs2273061) were studied. Real-time PCR allelic discrimination was used for genotyping. The differences between the means of the BMDs according to genotype were analyzed with covariance. Deviations from Hardy-Weinberg equilibrium were tested. Pairwise linkage disequilibrium between single nucleotide polymorphisms was calculated by direct correlation r (2), and haplotype analysis of COL1A1 was conducted. Under a dominant model, the rs1800012 polymorphism of the COL1A1 showed an association with BMD of the lumbar spine (P = 0.021). In addition, analysis of the haplotype of COL1A1 showed that the G-G haplotype presented a higher BMD in lumbar spine. We did not find an association between the s1107946 and rs2273061 polymorphisms of the COL1A1 and JAG1, respectively. Our results suggest that the rs1800012 polymorphism of the COL1A1, in addition to one haplotype, were significantly associated with BMD variation in Mexican-Mestizo postmenopausal women.

[Implications of the new etiophatogenic approach in the classification of constitutional and genetic bone diseases]

Recent years have seen an unprecedented increase in the knowledge and understanding of biochemical disturbances involved on constitutional bone disorders. Recognition of the genetic background as the common cause of these diseases prompted the substitution of the term «constitutional» by «genetic», in referring to them. Understanding physiopathological bases by finding out the altered metabolic pathways as well as their regulatory and control systems, favours an earlier and more accurate diagnosis based on interdisciplinary collaboration. Although clinical and radiological assessment remains crucial in the study of these disorders, ever more often the diagnosis is achieved by molecular and genetic analysis. Elucidation of the damaged underlying molecular mechanisms offers targets potentially useful for therapeutic research in these complex and often disabling diseases.

Pharmacogenetics of osteoporosis-related bone fractures: moving towards the harmonization and validation of polymorphism diagnostic tools

Osteoporosis is one of the most common skeletal chronic conditions in developed countries, hip fracture being one of its major healthcare outcomes. There is considerable variation in the implementation of current pharmacological treatment and prevention, despite consistent recommendations and guidelines. Many studies have reported conflicting findings of genetic associations with bone density and turnover that might predict fracture risk. Moreover, it is not clear whether genetic differences exist in relation to the morbidity and efficiency of the pharmacotherapy treatments. Clinical response, including beneficial and adverse events associated with osteoporosis treatments, is highly variable among individuals. In this context, the present article intends to summarize putative candidate genes and genome-wide association studies that have been related with BMD and fracture risk, and to draw the attention to the need for pharmacogenetic methodology that could be applicable in clinical translational research after an adequate validation process. This article mainly compiles analysis of important polymorphisms in osteoporosis documented previously, and it describes the simple molecular biology tools for routine genotype acquisition. Validation of methods for the easy, fast and accessible identification of SNPs is necessary for evolving pharmacogenetic diagnostic tools in order to contribute to the discovery of clinically relevant genetic variation with an impact on osteoporosis and its personalized treatment.

The skeletal dysplasias

The skeletal dysplasias (osteochondrodysplasias) are a heterogeneous group of more than 350 disorders frequently associated with orthopedic complications and varying degrees of dwarfism or short stature. These disorders are diagnosed based on radiographic, clinical, and molecular criteria. The molecular mechanisms have been elucidated in many of these disorders providing for improved clinical diagnosis and reproductive choices for affected individuals and their families. An increasing variety of medical and surgical treatment options can be offered to affected individuals to try to improve their quality of life and lifespan.

Genotype-phenotype correlations in nonlethal osteogenesis imperfecta caused by mutations in the helical domain of collagen type I

Osteogenesis imperfecta (OI) is a heritable disorder with bone fragility that is often associated with short stature, tooth abnormalities (dentinogenesis imperfecta), and blue sclera. The most common mutations associated with OI result from the substitution for glycine by another amino acid in the triple helical domain of either the alpha1 or the alpha2 chain of collagen type I. In this study, we compared the results of genotype analysis and clinical examination in 161 OI patients (median age: 13 years) who had glycine mutations in the triple helical domain of alpha1(I) (n=67) or alpha2(I) (n=94). Serine substitutions were the most frequently encountered type of mutation in both chains. Compared with patients with serine substitutions in alpha2(I) (n=40), patients with serine substitutions in alpha1(I) (n=42) on average were shorter (median height z-score -6.0 vs -3.4; P=0.005), indicating that alpha1(I) mutations cause a more severe phenotype. Height correlated with the location of the mutation in the alpha2(I) chain but not in the alpha1(I) chain. Patients with mutations affecting the first 120 amino acids at the amino-terminal end of the collagen type I triple helix had blue sclera but did not have dentinogenesis imperfecta. Among patients from different families sharing the same mutation, about 90 and 75% were concordant for dentinogenesis imperfecta and blue sclera, respectively. These data should be useful to predict disease phenotype in newly diagnosed OI patients.

Rieger's Anomaly and Other Ocular Abnormalities in Association with Osteogenesis Imperfecta and aCOL1A1Mutation

A patient with osteogenesis imperfecta (OI) and some features of Ehlers-Danlos syndrome had Rieger's anomaly and other associated ocular abnormalities. He carried a COL1A1 mutation (c.3313delA) that has only rarely been seen in OI. The association of ocular anterior chamber abnormalities with OI has not been reported previously, while OI with Ehlers-Danlos syndrome features has only been described in some kindreds. The patient had serious complications as a result of his ocular anomalies. We speculate that the course of his disease and, perhaps, its co-existence with OI could be exacerbated by his collagen type-I defect, although no causality can be established by this report of a single case.

Dietary zinc reduces osteoclast resorption activities and increases markers of osteoblast differentiation, matrix maturation, and mineralization in the long bones of growing rats

The nutritional influence of zinc on markers of bone extracellular matrix resorption and mineralization was investigated in growing rats. Thirty male weanling rats were randomly assigned to consume AIN-93G based diets containing 2.5, 5, 7.5, 15 or 30 microg Zn/g diet for 24 days. Femur zinc increased substantially as zinc increased from 5 to 15 microg/g diet and modestly between 15 and 30 microg/g (P<.05). By morphological assessment, trabecular bone increased steadily as dietary zinc increased to 30 microg/g. Increasing dietary zinc tended to decrease Zip2 expression nonsignificantly and elevated the relative expression of metallothionen-I at 15 but not 30 microg Zn/g diet. Femur osteoclastic resorption potential, indicated by matrix metalloproteinases (MMP-2 and MMP-9) and carbonic anhydrase-2 activities decreased with increasing dietary zinc. In contrast to indicators of extracellular matrix resorption, femur tartrate-resistant acid and alkaline phosphatase activities increased fourfold as dietary zinc increased from 2.5 to 30 microg Zn/g. Likewise, 15 or 30 microg Zn/g diet resulted in maximum relative expression of osteocalcin, without influencing expression of core-binding factor alpha-1, collagen Type 1 alpha-1, or nuclear factor of activated T cells c1. In conclusion, increased trabecular bone with additional zinc suggests that previous requirement estimates of 15 microg Zn/g diet may not meet nutritional needs for optimal bone development. Overall, the up-regulation of extracellular matrix modeling indexes and concomitant decrease in resorption activities as dietary zinc increased from 2.5 to 30 microg/g provide evidence of one or more physiological roles for zinc in modulating the balance between bone formation and resorption.

Haplotypes of promoter and intron 1 polymorphisms in the COLIA1 gene are associated with increased risk of osteoporosis

Osteoporosis is a common age-related disease with a strong genetic influence. COLIA1 is one of the most extensively studied candidate genes and has consistently been associated with BMD and fracture. We examined the effects of the polymorphisms -1997G>T, -1663indelT, and +1245G>T and their haplotypes on vertebral fractures and bone mineral density (BMD) in a case-control study comprising 462 osteoporotic patients and 336 controls. The -1663indelT polymorphism was associated with a decreased lumbar spine (ls) BMD, 0.75 +/- 0.14 g/cm(2), in individuals with the del/del genotype versus 0.83 +/- 0.18 and 0.85 +/- 0.18 g/cm(2) in individuals with the ins/del and ins/ins genotypes, respectively (p = 0.02). The T-allele of the +1245G>T polymorphism, which was in strong linkage disequilibrium (LD) with -1663indelT, was also associated with a decreased lsBMD (p = 0.02). -1997G>T was not significantly associated with lsBMD. The three most common haplotypes accounted for 98.5% of the alleles. Individuals with one or two copies of haplotype 1 (-1997G/-1663ins/+1245G) had a significantly higher lsBMD, 0.84 +/- 0.18 and 0.85 +/- 0.15 g/cm(2), respectively, versus 0.78 +/- 0.15 g/cm(2) in noncarriers (p = 0.01). Individuals with two copies of haplotype 2 (-1997G/-1663del/+1245T) had a significantly lower lsBMD, 0.76 +/- 0.14 g/cm(2), versus 0.85 +/- 0.18 and 0.82 +/- 0.18 g/cm(2), respectively, in individuals with zero or one copy (p = 0.03). The odds ratio for vertebral fracture in individuals carrying the variant T-allele of the -1997G>T polymorphism was 1.49 (CI, 1.03-2.16; p = 0.03). Logistic regression revealed that this effect was partly independent of BMD. In conclusion, the -1663del and +1245T alleles influence BMD negatively, whereas the -1997T-allele has a minor effect on BMD but increases the risk of vertebral fractures. These findings are in agreement with functional studies showing that these polymorphisms influence gene expression.

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.

Predicting the clinical lethality of osteogenesis imperfecta from collagen glycine mutations

Osteogenesis imperfecta (OI), or brittle bone disease, often results from missense mutation of one of the conserved glycine residues present in the repeating Gly-X-Y sequence characterizing the triple-helical region of type I collagen. A composite model was developed for predicting the clinical lethality resulting from glycine mutations in the alpha1 chain of type I collagen. The lethality of mutations in which bulky amino acids are substituted for glycine is predicted by their position relative to the N-terminal end of the triple helix. The effect of a Gly --> Ser mutation is modeled by the relative thermostability of the Gly-X-Y triplet on the carboxy side of the triplet containing the substitution. This model also predicts the lethality of Gly --> Ser and Gly --> Cys mutations in the alpha2 chain of type I collagen. The model was validated with an independent test set of six novel Gly --> Ser mutations. The hypothesis derived from the model of an asymmetric interaction between a Gly --> Ser mutation and its neighboring residues was tested experimentally using collagen-like peptides. Consistent with the prediction, a significant decrease in stability, calorimetric enthalpy, and folding time was observed for a peptide with a low-stability triplet C-terminal to the mutation compared to a similar peptide with the low-stability triplet on the N-terminal side. The computational and experimental results together relate the position-specific effects of Gly --> Ser mutations to the local structural stability of collagen and lend insight into the etiology of OI.

Effects of hormone replacement therapy on bone mineral density in Turkish patients with or without COL1A1 Sp1 binding site polymorphism

AIM

To evaluate the effects of hormone replacement therapy (HRT) on bone mineral density (BMD) in patients with or without COL1A1 Sp1 binding site polymorphism.

METHODS

Non-smoking otherwise healthy postmenopausal women (n=111), who had not received any kind of HRT for at least 3 years (between 2002 and 2005) at the onset of menopause, were included. All patients received 0.625 mg conjugated estrogen/2.5 mg medroxyprogesterone for 18 months. BMD by dual X-ray absorptiometry was measured at the lumbar spine and the femur neck initially and after 18th months of treatment. COL1A1 Sp1 binding site polymorphism was studied using the PCR-RFLP method.

RESULTS

After having the results of COL1A1 Sp1 binding site polymorphism, 79 (71.2%) patients were SS, 30(27.0%) were Ss and two (1.8%) were homozygous for ss. The mean age, weight and length of menopausal period were similar between the SS and Ss patients. The Ss heterozygotes had lower BMD values both at the lumbar spine and at the femur neck compared with the SS patients. This difference was also reflected in post treatment measurements. The increase in BMD scores was higher in the SS homozygotes than in the Ss patients.

CONCLUSION

Our preliminary data supports the fact that HRT had a lower increase in BMD scores following 18 months of treatment in COL1A1 s allele individuals compared with normal SS individuals. Therefore our study may provide evidence that the Sp1 polymorphism may ameliorate the effects of HRT on BMD, suggesting some additional regimens may be used to support bone strength and to decrease osteoporotic fractures.

A genome-wide linkage scan for low spinal bone mineral density in a single extended family confirms linkage to 1p36.3

Osteoporotic fractures are an increasing cause of mortality and morbidity in ageing populations. A major risk determinant for these fractures is bone mineral density (BMD). Variation on BMD is thought, on the basis of twin and family studies, to be subject to a large amount of genetic variation and it has been hypothesised that this may be due to the influence of multiple genes. However, in families showing segregation of low or high BMD, single major genes have been shown to play a crucial role. We performed a genome-wide screen using 380 microsatellite markers in a single extended family (n=34) in which early-onset low spinal areal BMD segregates in an autosomal dominant-like fashion. A two-point linkage analysis was performed, revealing a maximum LOD score of 3.07 on 1p36.3 (D1S468), confirming results of previous linkage studies of BMD, while no other suggestive linkage peaks (LOD>2.2) were detected elsewhere in the genome. Microsatellite markers were subsequently genotyped for a +/-6.9 Mb region surrounding D1S468. This revealed critical recombination events restricting the candidate region to 1.2 Mb and 19 genes. Sequencing analysis of the coding region of candidate genes WDR8 and EGFL3 revealed no mutations or disease-associated polymorphisms. Our results provide some evidence supporting the hypothesis that there are genetic determinants for spinal BMD on 1p36.3. Although no specific disease causing mutation has yet been found, the delineation of a relatively small candidate region in a single extended family opens perspectives to identify a major gene for spinal BMD.

The -1997 G/T and Sp1 polymorphisms in the collagen type I alpha1 (COLIA1) gene in relation to changes in femoral neck bone mineral density and the risk of fracture in the elderly: the Rotterdam study

The COLIA1 Sp1 polymorphism has been associated with bone mineral density (BMD) and fracture. A promoter polymorphism, -1997 G/T, also has been associated with BMD. In this study, we examined whether these polymorphisms alone and in the form of haplotypes influence bone parameters and fracture risk in a large population-based cohort of elderly Caucasians. We determined the COLIA1 -1997 G/T (promoter) and Sp1 G/T (intron) polymorphisms in 6,280 individuals and inferred haplotypes. Femoral neck BMD and BMD change were compared across COLIA1 genotypes at baseline and follow-up (mean 6.5 years). We also investigated the relationship between the COLIA1 polymorphisms and incident nonvertebral fractures, which were recorded during a mean follow-up period of 7.4 years. Vertebral fractures were assessed by radiographs on 3,456 genotyped individuals. Femoral neck BMD measured at baseline was 3.8% lower in women carrying two copies of the T-Sp1 allele (P for trend = 0.03). No genotype dependent differences in BMD loss were observed. In women homozygous for the T allele of the Sp1 polymorphism, the risk of fragility fracture increased 2.3 times (95% confidence interval 1.4-3.9, P = 0.001). No such association was observed with the promoter polymorphism. In men, no association with either the Sp1 or the -1997 G/T promoter polymorphism was seen with BMD or fracture. High linkage disequilibrium (LD; D' = 0.99, r (2 )= 0.03) exists between the two studied polymorphisms. We observed three haplotypes in our population: haplotype 1 (G(promoter)-G(intron)) frequency (f) = 69%, haplotype 2 (G(promoter)-T(intron)) f = 17.6%, and haplotype 3 (T(promoter)-G(intron)) f = 13.4%. Haplotype 2 was associated with a 2.1-fold increased risk of fragility fracture in women (95% confidence interval 1.2-3.7, P = 0.001). We confirm that the COLIA1 Sp1 polymorphism influences BMD and the risk of fracture in postmenopausal Caucasian women. In contrast, we found no independent effect of the -1997 G/T promoter polymorphism on BMD or fracture.

Joint hypermobility

Patients with joint hypermobility, perhaps the mildest of the various inherited abnormalities of connective tissue, may present to a rheumatologist or general practitioner although a large proportion are recognized by health professionals, particularly physiotherapists. Hypermobility may be generalized or extreme at a small number of joints. Sometimes it is associated with involvement of other organs because of abnormal inherited collagen structure elsewhere. A small proportion of patients will have one of the more serious conditions such as Ehlers-Danlos syndrome, Marfan's syndrome or osteogenesis imperfecta. Management is multidisciplinary requiring a team including physicians, physiotherapists, occupational therapists and podiatrists, among others. Patients often wait a long time before receiving their definitive diagnosis and are sometimes dismissed as malingerers. Patients often have a lot of queries about their condition unrelated to their joints. Among these are whether there will be problems in pregnancy, whether the condition will be passed on to their children, whether symptoms arising from organs other than the joints are related and whether they might have been incorrectly accused of battering their children.

Sequence dependence of renucleation after a Gly mutation in model collagen peptides

Missense mutations in the collagen triple helix that replace one Gly residue in the (Gly-X-Y)(n) repeating pattern by a larger amino acid have been shown to delay triple helix folding. One hypothesis is that such mutations interfere with the C- to N-terminal directional propagation and that the identity of the residues immediately N-terminal to the mutation site may determine the delay time and the degree of clinical severity. Model peptides are designed to clarify the role of tripeptide sequences N-terminal to the mutation site, with respect to length, stability, and nucleation propensity, to complete triple helix folding. Two sets of peptides with different N-terminal sequences, one with the natural sequence alpha1(I) 886-900, which is just adjacent to the Gly(901) mutation, and one with a GPO(GAO)(3) sequence, which occurs at alpha1(I) 865-879, are studied by CD and NMR. Placement of the five tripeptides of the natural alpha1(I) collagen sequence N-terminal to the Gly to Ala mutation site results in a peptide that is folded only C-terminal to the mutation site. In contrast, the presence of the Hyp-rich sequence GPO(GAO)(3) N-terminal to the mutation allows complete refolding in the presence of the mutation. The completely folded peptide contains an ordered central region with unusual hydrogen bonding while maintaining standard triple helix structure at the N- and C-terminal ends. These peptide results suggest that the location and sequences of downstream regions favorable for renucleation could be the key factor in the completion of a triple helix N-terminal to a mutation.

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.

Osteogenesis Imperfecta

Osteogenesis imperfecta is a heritable condition characterized by abnormally brittle bones, with an approximate prevalence of 1/20 000 births. Fractures are the main cause of suffering and disability, but owing to the abundance and wide distribution of the defective type I collagen in the body, a variety of symptoms occur. Several types of osteogenesis imperfecta (I-VII) have been described that vary in severity. For many years, therapy consisted of rehabilitation and orthopedic surgery. Presently, pharmacologic therapies aimed at strengthening bone are available, which decrease the pain and fracture rate associated with this condition, and allow more appropriate rehabilitation programs that will hopefully result in a less marked failure to thrive in affected children. In particular, the bisphosphonates, especially pamidronate, have been used for several years. They have been successful in increasing bone mineral density (BMD) and improving bone resistance, leading to a decrease in the fracture rate. Various regimens have been proposed, but it is the therapeutic regimen first used by Glorieux and co-workers in Montreal that has been the most frequently applied.However, as yet there is no definite consensus regarding the indications for therapy, the osteogenesis imperfecta types that are of the greatest concern, the appropriate age at the outset of therapy, and the treatment duration, without yet speaking about the best bisphosphonate regimen for use. The authors have proposed some personal recommendations for the clinical use of bisphosphonates, based on their own experience with the management of patients with this condition; these include the indications for therapy, based on the clinical status, and the treatment duration. These recommendations will certainly not be unanimously endorsed, but they should help to stimulate discussion. Ameliorating BMD is an important step, but will not prevent all fractures because bisphosphonate therapy does not correct the underlying genetic defect. More recently, stem cell replacement therapy in the child or fetus has been proposed as a therapeutic option.All in all, it is possible that, in order to dramatically decrease the fracture rate, combined therapies aimed at both circumventing the consequences of the gene defect using stem cells and reinforcing bone strength with bisphosphonates will have to be considered. Much work is still necessary before recommending these techniques in clinical practice.

Common variants at the PCOL2 and Sp1 binding sites of the COL1A1 gene and their interactive effect influence bone mineral density in Caucasians

BACKGROUND

Osteoporosis, mainly characterised by low bone mineral density (BMD), is a serious public health problem. The collagen type I alpha 1 (COL1A1) gene is a prominent candidate gene for osteoporosis. Here, we examined whether genetic variants at the COL1A1 gene can influence BMD variation.

METHODS

BMD was measured at nine skeletal sites in 313 Caucasian males and 308 Caucasian females. We screened four single nucleotide polymorphisms (SNPs) at the COL1A1 gene: PCOL2 (-1997 G/T) in the promoter, Sp1 (1546 G/T) in the intron 1, Gly19Cys (3911 G/A) in exon 8, and Ala897Thr (13 773 G/A) in exon 45. Univariate and multivariate association approaches were used in the analyses.

RESULTS

In multivariate analyses, we found a strong association between the PCOL2 SNP and BMD (p = 0.007 to 0.024) and a suggestive association between the Sp1 SNP and BMD (p = 0.023 to 0.048) in elderly Caucasian females. Interestingly, the interaction of these two SNPs was highly significantly associated with BMD variation (p = 0.001 to 0.003). The haplotype GG at the two SNPs had, on average, 2.7% higher BMD than non-carriers (p = 0.006 to 0.026).

CONCLUSIONS

Our data suggested that the common genetic variants at the PCOL2 and Sp1 sites, and importantly, their interactive effects, may contribute to BMD variation in elderly Caucasian females. Further studies are necessary to delineate the mechanisms underlying the effects of these common variants on BMD variation and to test their clinical relevance for general populations. In addition, our study highlighted the importance of multivariate analyses when multiple correlated phenotypes are under study.

A mutation in a cuticle collagen causes hypersensitivity to the endocrine disrupting chemical, bisphenol A, in Caenorhabditis elegans

A novel mutant gene, bis-1 (bisphenol A sensitive) has been isolated in the nematode, Caenorhabditis elegans, that affects the response to endocrine disrupting chemicals (EDC). The bis-1(nx3) allele is hypersensitive to bisphenol A (BPA), is allelic to a collagen gene (col-121), and is expressed in hypodermal cells. Among the collagen mutants so far studied, bis-1(nx3), dpy-2(e8), dpy-7(e88) and dpy-10(e128) showed BPA sensitivity. The isolated mutant may work as a useful tool for the assay of EDC toxicity since the physiological effect of the collagen mutation (glycine substitution) indicates an increased sensitivity to BPA.

Characterization of the distinct collagen binding, helicase and cleavage mechanisms of matrix metalloproteinase 2 and 14 (gelatinase A and MT1-MMP): the differential roles of the MMP hemopexin c domains and the MMP-2 fibronectin type II modules in collagen triple helicase activities

Matrix metalloproteinase-2 (MMP-2, gelatinase A) and membrane type (MT)1-MMP (MMP-14) are cooperative dynamic components of a cell surface proteolytic axis involved in regulating the cellular signaling environment and pericellular collagen homeostasis. Although MT1-MMP exhibits type I collagenolytic but poor gelatinolytic activities, MMP-2 is a potent gelatinase with weak type I collagenolytic behavior. Recombinant linker/hemopexin C domain (LCD) of MT1-MMP binds native type I collagen, blocks MT1-MMP collagenolytic activity in trans, and by circular dichroism spectroscopy, induces localized structural perturbation in the collagen. These changes were reflected by enhanced cleavage of the MT1-LCD-bound collagen by the collagenases MMP-1 and MMP-8 but not by trypsin or MMP-7. Thus, the MT1-LCD alone can initiate triple helicase activity. In contrast, the native and denatured collagen binding properties of MMP-2 reside in the fibronectin type II modules, accordingly termed the collagen binding domain (CBD). Recombinant CBD (but not the MMP-2 LCD) also changed the circular dichroism spectra leading to increased MMP-1 and -8 cleavage of native collagen. However, recombinant CBD reduced gelatin and collagen cleavage by MMP-2 in trans as did CBD23, which comprises the second and third fibronectin type II modules, but not the CBD23 mutant W316A/W374A, which neither binds gelatin nor collagen. This indicates that MMP-2 and MT1-MMP bind collagen at a different site than MMP-1 and MMP-8. Thus, MMP-2 utilizes the CBD in cis for collagen binding and triple helicase activity, which compensates for the lack of collagen binding by the MMP-2 LCD. Hence, the MMP family has evolved two distinct mechanisms for collagen triple helicase activity using two structurally distinct domains, with triple helicase activity occurring independent of alpha-chain hydrolysis.

A bit of give and take: the relationship between the extracellular matrix and the developing chondrocyte

The extracellular matrix (ECM), once thought to be a static structural component of tissues, is now known to play a complex and dynamic role in a variety of cellular functions in a number of diverse tissues. A significant body of literature attests to the ability of the ECM to communicate both spatial and temporal information to adherent cells, thereby directing cell behavior via interactions between the ECM and cell-surface receptors. Moreover, volumes of experimental data show that a great deal of communication travels in the opposite direction, from the cell to the ECM, allowing for regulation of the cues transmitted by the ECM. As such, the ECM, with respect to its components and their organization, is not a fixed reflection of the state the local microenvironment in which a cell finds itself at a particular time, but rather is able to respond to and effect changes in its local microenvironment. As an example of the developmental consequences of ECM interactions, this review gives an overview of the 'give and take' relationship between the ECM and the cells of the developing skeletal elements, in particular, the chondrocyte.

Proposed association between theCOL1A1andCOL1A2genes and otosclerosis is not supported by a case-control study in Spain

Otosclerosis (OTSC) is one of the most common causes of hearing loss in white adults. The COL1A1 and COL1A2 genes coding for type-I collagen have been proposed as candidate genes in the development of OTSC. The COL1A1 gene was recently reported to be associated with the condition on the basis of a population-based case-control study. We report here an independent study of association between COL1A1 and COL1A2 gene polymorphisms and OTSC, in a case-control sample from a population of Caucasian individuals living in Northwest Spain. Specifically, we studied two COL1A1 polymorphisms previously reported to be associated with OTSC, and six COL1A2 polymorphisms. We performed diverse association analyses based on alleles, genotypes, and two-locus haplotypes. We found no evidence supporting the putative link of COL1A1 and COL1A2 genes with OTSC.

Collagen type I alpha1 Sp1 polymorphism, osteoporosis, and intervertebral disc degeneration in older men and women

OBJECTIVES

To examine whether collagen type I alpha1 (COLIA1) Sp1 polymorphism is associated with osteoporosis and/or intervertebral disc degeneration in older people.

METHODS

COLIA1 genotype was determined in 966 men and women (>/=65 years) of the Longitudinal Aging Study Amsterdam. The guanine (G) to thymidine (T) polymorphism in the first intron of the COLIA1 gene was detected by PCR and MscI digestion. In the total sample, quantitative ultrasound (QUS) measurements, serum osteocalcin (OC), and urine deoxypyridinoline (DPD/Cr(urine)) were assessed. A follow up of fractures was done every three months. In a subsample, total body bone mineral content (n = 485) and bone mineral density (BMD) of the hip and lumbar spine (n = 512) were measured by dual energy x ray absorptiometry (DXA). Prevalent vertebral deformities and intervertebral disc degeneration were identified on radiographs (n = 517).

RESULTS

People with the TT genotype had a higher risk of disc degeneration than those with the GG and GT genotypes (OR = 3.6; 95% CI 1.3 to 10). For men, higher levels of OC were found in those with the T allele than in those without it (GG v (GT+TT) 1.96 (0.06) nmol/l v 2.19 (0.09) nmol/l). COLIA1 polymorphism was not significantly associated with other measures of osteoporosis in either men or women.

CONCLUSION

COLIA1 Sp1 polymorphism may be a genetic risk factor related to intervertebral disc degeneration in older people. Previously reported associations between the COLIAI Sp1 genotype and lower BMD or QUS values, higher levels of DPD/Cr, and an increased fracture risk in either men or women could not be confirmed.

Osteogenesis imperfecta in two litters of dachshunds

A clinical, morphologic, ultrastructural, and genetic study was performed on five rough-coated dachshund semisiblings with osteogenesis imperfecta (OI). Clinical signs consisted of pain, spontaneous bone and teeth fractures, joint hyperlaxity, and reduced bone density on radiography. Primary teeth were extremely thin-walled and brittle. The hallmark of the disease was a severe osteopenia characterized by impairment of lamellar bone formation in the long bones, skull, and vertebral column. No deformity or dwarfism was present. The columns of chondrocytes and primary trabeculae in the epiphyses and metaphyses were histologically normal. An abrupt failure of secondary spongiosa and lamellar bone formation was evident in the medullary and cortical zones in all animals. The few existing trabeculae consisted of woven bone. There was no increase in the number and size of osteoclasts or lacunae. In the teeth, the dentine layers were thin and lacked a tubular pattern. Ultrastructurally, osteoid apposition on bone surfaces was reduced, and small numbers of large cytoplasmic vacuoles were present in a few osteoblasts. Molecular analyses of the collagen type I-encoding genes COL1A1 and COL1A2 revealed several nucleotide differences compared with the published canine sequences but were not significant for OI. Therefore, OI in these Dachshund litters was characterized by a severe, generalized osteopenia and dentinopenia. This pattern of reduced bone formation is suggestive of defective production of collagen type I.

A glycine to aspartic acid substitution of COL2A1 in a family with the Strudwick variant of spondyloepimetaphyseal dysplasia

BACKGROUND

Spondyloepimetaphyseal dysplasia (SEMD) is one of a clinically heterogeneous group of skeletal disorders, characterized by defective growth and modelling of the spine and long bones. Common clinical features include disproportionate short stature, malformed vertebrae and abnormal epiphyses or metaphyses. Some cases have been associated with mutations in the COL2A1 gene.

AIM

To determine whether the autosomal dominant Strudwick-type SEMD in a three-generation family, showing specific phenotypical features such as chest deformity, limb shortening, myopia and early-onset degenerative osteoarthrosis, might be caused by a novel COL2A1 mutation.

DESIGN

Genetic testing and clinical examination of family members.

METHODS

Direct sequencing of PCR-amplified genomic DNA from the COL2A1 gene.

RESULTS

A point mutation within exon 20 of the COL2A1 gene was identified that substituted a glycine for an aspartic acid residue at codon 262.

DISCUSSION

All previously reported autosomal dominant mutations causing SEMD have substituted an obligate glycine within the triple helix, in particular at codons 292, 304 and 709 in the three reported Strudwick-type patients. Additionally, a recurrent glycine substitution at codon 154 has been identified in two unrelated Finnish cases with radiological features consistent with the Strudwick subtype. Our sixth helical glycine substitution extends the mutational spectrum and genotype/phenotype correlations of Strudwick-type SEMD.

COL4A3/COL4A4 mutations: from familial hematuria to autosomal-dominant or recessive Alport syndrome

COL4A3/COL4A4 mutations: From familial hematuria to autosomal-dominant or recessive Alport syndrome.

BACKGROUND

Mutations of the type IV collagen COL4A5 gene cause X-linked Alport syndrome (ATS). Mutations of COL4A3 and COL4A4 have been reported both in autosomal-recessive and autosomal-dominant ATS, as well as in benign familial hematuria (BFH). In the latter conditions, however, clinical features are less defined, few mutations have been reported, and other genes and non-genetic factors may be involved.

METHODS

We analyzed 36 ATS patients for COL4A3 and COL4A4 mutations by polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) and direct sequencing. Sporadic patients who had tested negative for COL4A5 mutations were included with typical cases of autosomal recessive ATS to secure a better definition of the phenotype spectrum.

RESULTS

We identified seven previously undescribed COL4A3 mutations: in two genetic compounds and three heterozygotes, and one in COL4A4. In agreement with the literature, some of the mutations of compound heterozygotes were associated with microhematuria in healthy heterozygous relatives. The mutations of heterozygous patients are likely dominant, since no change was identified in the second allele even by sequencing, and they are predicted to result in shortened or abnormal chains with a possible dominant-negative effect. In addition, both genes showed rare variants of unclear pathogenicity, and common polymorphisms that are shared in part with other populations.

CONCLUSIONS

This study extends the mutation spectrum of COL4A3 and COL4A4 genes, and suggests a possible relationship between production of abnormal COL IV chains and dominant expression of a continuous spectrum of phenotypes, from ATS to BFH.

Delivery of a hammerhead ribozyme specifically downregulates mutant type I collagen mRNA in a murine model of osteogenesis imperfecta

Osteogenesis imperfecta (OI) is a systemic heritable disorder of connective tissue, caused by a mutation in one of the genes for type I collagen, whose cardinal manifestation is bone fragility. Several studies have identified two molecular mechanisms of collagen type I defects. In chain exclusion, the mutant chain is not incorporated into the collagen triple helix, whereas in chain nonexclusion, it is. The dominant-negative effect of nonexcluded mutations must be taken into account in all strategies aimed at correcting the collagen defects in individuals affected with moderate or several OI. Herein, we describe the application of hammerhead ribozymes to selectively target the mutant minigene transcript expressed in a murine calvarial osteoblast cell line. Active and control inactive ribozymes were tested in vitro on both mutant and normal targets and in the minigene-expressing cell line. Active ribozyme cleaved its target with high efficiency and specificity in both a time-dependent and dose-dependent manner. After delivery of a ribozyme expression construct, intracellular ribozyme was detected, along with a relative reduction in mutant transcript level.

Bone brittleness varies with genetic background in A/J and C57BL/6J inbred mice

The contribution of genetic and environmental factors to variations in bone quality are understood poorly. We tested whether bone brittleness varies with genetic background using the A/J and C57BL/6J inbred mouse strains. Whole bone four-point bending tests revealed a 70% decrease in postyield deflection of A/J femurs compared with C57BL/6J, indicating that A/J femurs failed in a significantly more brittle manner. Cyclic loading studies indicated that A/J femurs accumulated damage differently than C57BL/6J femurs, consistent with their increased brittleness. Differences in matrix composition also were observed between the two mouse strains. A/J femurs had a 4.5% increase in ash content and an 11.8% decrease in collagen content. Interestingly, a reciprocal relationship was observed between femoral geometry and material stiffness; this relationship may have contributed to the brittle phenotype of A/J femurs. A/J femurs are more slender than those of C57BL/6J femurs; however, their 47% smaller moment of inertia appeared to be compensated by an increased tissue stiffness at the expense of altered tissue damageability. Importantly, these differences in whole bone mechanical properties between A/J and C57BL/6J femurs could not have been predicted from bone mass or density measures alone. The results indicated that bone brittleness is a genetically influenced trait and that it is associated with genetically determined differences in whole bone architecture, bone matrix composition, and mechanisms of cyclical damage accumulation.

Folding defects in fibrillar collagens

Fibrillar collagens have a long triple helix in which glycine is in every third position for more than 1000 amino acids. The three chains of these molecules are assembled with specificity into several different molecules that have tissue-specific distribution. Mutations that alter folding of either the carboxy-terminal globular peptides that direct chain association, or of the regions of the triple helix that are important for nucleation, or of the bulk of the triple helix, all result in identifiable genetic disorders in which the phenotype reflects the region of expression of the genes and their tissue-specific distribution. Mutations that result in changed amino-acid sequences in any of these regions have different effects on folding and may have different phenotypic outcomes. Substitution for glycine residues in the triple helical domains are among the most common effects of mutations, and the nature of the substituting residue and its location in the chain contribute to the effect on folding and also on the phenotype. More complex mutations, such as deletions or insertions of triple helix, also affect folding, probably because of alterations in helical pitch along the triple helix. These mutations all interfere with the ability of these molecules to form the characteristic fibrillar array in the extracellular matrix and many result in intracellular retention of abnormal molecules.

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.

Scanning electron microscopy images and energy-dispersive X-ray microanalysis of the stapes in otosclerosis and Van der Hoeve syndrome

OBJECTIVE/HYPOTHESIS

The objective of this study was to evaluate the morphological and microchemical changes that affect sclerotic stapes in otospongiosis and van der Hoeve syndrome.

METHODS

A scanning electron microscope equipped with an energy-dispersive x-ray analyzer was used in the experiments.

RESULTS

In otosclerosis, focal lesions are poorly mineralized, with low calcium salt and reduced calcium-to-phosphorus (Ca/P) ratio (1.9:1). This finding correlates with a spongiotic type of lesion and indicates unstable mineralization with possible change from hydroxyapatite to calcium triphosphate. In van der Hoeve syndrome the presence of magnesium in stapes suggests osteoclastic function stimulation. The osteoclasts secrete many protons, causing an acidified microenvironment. Brushite is formed, and Ca/P ratio decreases in comparison with that of control patients (2.0:1 vs. 2.6:1).

Genetics of skeletogenesis

Major advances have been made in the last 10 years in the genetics of skeletogenesis. This has followed the general progress in our understanding of the genetic control of development in chicken and mouse and more recent advances in human genetics. This large field now encompasses three smaller but distinct fields of investigation. Those are skeleton patterning, cell differentiation in the skeleton, and cell function in the skeleton. This review focuses primarily on advances in understanding cell differentiation and cell function in the skeleton at the genetic level.

Production of recombinant human type I procollagen homotrimer in the mammary gland of transgenic mice

The large scale production of recombinant collagen for use in biomaterials requires an efficient expression system capable of processing a large (> 400 Kd) multisubunit protein requiring post-translational modifications. To investigate whether the mammary gland of transgenic animals fulfills these requirements, transgenic mice were generated containing the alpha S1-casein mammary gland-specific promoter operatively linked to 37 Kb of the human alpha 1(I) procollagen structural gene and 3' flanking region. The frequency of transgenic lines established was 12%. High levels of soluble triple helical homotrimeric [(alpha 1)3] type I procollagen were detected (up to 8 mg/ml) exclusively in the milk of six out of 9 lines of lactating transgenic mice. The transgene-derived human procollagen chains underwent efficient assembly into a triple helical structure. Although proline or lysine hydroxylation has never been described for any milk protein, procollagen was detected with these post-translational modifications. The procollagen was stable in milk; minimal degradation was observed. These results show that the mammary gland is capable of expressing a large procollagen gene construct, efficiently assembling the individual polypeptide chains into a stable triple helix, and secreting the intact molecule into the milk.

Destabilization of osteogenesis imperfecta collagen-like model peptides correlates with the identity of the residue replacing glycine

Mutations resulting in replacement of one obligate Gly residue within the repeating (Gly-Xaa-Yaa)(n) triplet pattern of the collagen type I triple helix are the major cause of osteogenesis imperfecta (OI). Phenotypes of OI involve fragile bones and range from mild to perinatal lethal. In this study, host-guest triple-helical peptides of the form acetyl-(Gly-Pro-Hyp)(3)-Zaa-Pro-Hyp-(Gly-Pro-Hyp)(4)-Gly-Gly-amide are used to isolate the influence of the residue replacing Gly on triple-helix stability, with Zaa = Gly, Ala, Arg, Asp, Glu, Cys, Ser, or Val. Any substitution for Zaa = Gly (melting temperature, T(m) = 45 degrees C) results in a dramatic destabilization of the triple helix. For Ala and Ser, T(m) decreases to approximately 10 degrees C, and for the Arg-, Val-, Glu-, and Asp-containing peptides, T(m) < 0 degrees C. A Gly --> Cys replacement results in T(m) < 0 degrees C under reducing conditions but shows a broad transition (T(m) approximately 19 degrees C) in an oxidizing environment. Addition of trimethylamine N-oxide increases T(m) by approximately 5 degrees C per 1 M trimethylamine N-oxide, resulting in stable triple-helix formation for all peptides and allowing comparison of relative stabilities. The order of disruption of different Gly replacements in these peptides can be represented as Ala </= Ser < CPO(red) < Arg < Val < Glu </= Asp. The rank of destabilization of substitutions for Gly in these Gly-Pro-Hyp-rich homotrimeric peptides shows a significant correlation with the severity of natural OI mutations in the alpha1 chain of type I collagen.

Cuticle collagen genes. Expression in Caenorhabditis elegans

Collagen is a structural protein used in the generation of a wide variety of animal extracellular matrices. The exoskeleton of the free-living nematode, Caenorhabditis elegans, is a complex collagen matrix that is tractable to genetic research. Mutations in individual cuticle collagen genes can cause exoskeletal defects that alter the shape of the animal. The complete sequence of the C. elegans genome indicates upwards of 150 distinct collagen genes that probably contribute to this structure. During the synthesis of this matrix, individual collagen genes are expressed in distinct temporal periods, which might facilitate the formation of specific interactions between distinct collagens.