Heritable diseases of collagen

A Cbfa1-dependent genetic pathway controls bone formation beyond embryonic development

The molecular mechanisms controlling bone extracellular matrix (ECM) deposition by differentiated osteoblasts in postnatal life, called hereafter bone formation, are unknown. This contrasts with the growing knowledge about the genetic control of osteoblast differentiation during embryonic development. Cbfa1, a transcriptional activator of osteoblast differentiation during embryonic development, is also expressed in differentiated osteoblasts postnatally. The perinatal lethality occurring in Cbfa1-deficient mice has prevented so far the study of its function after birth. To determine if Cbfa1 plays a role during bone formation we generated transgenic mice overexpressing Cbfa1 DNA-binding domain (DeltaCbfa1) in differentiated osteoblasts only postnatally. DeltaCbfa1 has a higher affinity for DNA than Cbfa1 itself, has no transcriptional activity on its own, and can act in a dominant-negative manner in DNA cotransfection assays. DeltaCbfa1-expressing mice have a normal skeleton at birth but develop an osteopenic phenotype thereafter. Dynamic histomorphometric studies show that this phenotype is caused by a major decrease in the bone formation rate in the face of a normal number of osteoblasts thus indicating that once osteoblasts are differentiated Cbfa1 regulates their function. Molecular analyses reveal that the expression of the genes expressed in osteoblasts and encoding bone ECM proteins is nearly abolished in transgenic mice, and ex vivo assays demonstrated that DeltaCbfa1-expressing osteoblasts were less active than wild-type osteoblasts. We also show that Cbfa1 regulates positively the activity of its own promoter, which has the highest affinity Cbfa1-binding sites characterized. This study demonstrates that beyond its differentiation function Cbfa1 is the first transcriptional activator of bone formation identified to date and illustrates that developmentally important genes control physiological processes postnatally.

Absence of integrin alpha1beta1 in the mouse causes loss of feedback regulation of collagen synthesis in normal and wounded dermis

Integrin alpha1beta1 is a collagen receptor predominantly found in mesenchymal tissues. Mice lacking this receptor are viable. We have previously suggested that alpha1beta1 might participate in the down-regulation of collagen gene expression observed in cells suspended inside collagen gels. The results presented here demonstrate that integrin alpha1beta1 acts as a feedback regulator of collagen synthesis both in vitro and in vivo. Firstly, alpha1 null animals show a higher rate of collagen synthesis in the dermis in vivo. Secondly, fibroblasts derived from alpha1 null cutaneous wounds show a reduced sensitivity to collagen gel induced downregulation of collagen mRNA synthesis, as compared to their wild-type counterparts. An increase in collagenase synthesis is also seen in the alpha1 null dermis and in collagen gel suspended fibroblasts. While dermal thickness is normal in the alpha1 null animals, an increase is seen in skin thickness of alpha1 null but not alpha1 heterozygote animals on a background of collagenase resistant collagen. Increased expression of both collagen and collagenase mRNA are seen in experimental granulation tissue in alpha1 null animals, but their ultimate accumulation of collagen is normal, probably due to non alpha1 dependent paracrine regulators of collagen turnover.

Ultrastructural connective tissue abnormalities in patients with spontaneous cervicocerebral artery dissections

The cause of spontaneous cervicocerebral artery dissection is unknown. An underlying arteriopathy due to a connective tissue disorder has often been presumed. We studied 25 patients with proven nontraumatic dissections. The ultrastructural morphology of dermal connective tissue components was assessed by transmission electron microscopy of skin biopsies. Ultrastructural abnormalities were seen in 17 (68%) patients, resembling in some cases the aberrations found in Ehlers-Danlos syndrome type II or III. These observations indicate a correlation of cervical artery dissections with connective tissue abnormalities. A structural abnormality in the extracellular matrix potentially caused by basic molecular defects is suggested and warrants further exploration.

Direct contact between T lymphocytes and human dermal fibroblasts or synoviocytes down-regulates types I and III collagen production via cell-associated cytokines

In many inflammatory diseases where tissue remodeling occurs, T cells are in close contact with mesenchymal cells. We investigated the effect of direct cell-cell contact between peripheral blood T lymphocytes or HUT-78 lymphoma cells and dermal fibroblasts or synoviocytes on the deposition of the major extracellular matrix components: types I and III collagen. Incubation of dermal fibroblasts and synoviocytes with plasma membrane preparations from resting T cells slightly increased the production of collagen I but did not significantly affect that of collagen III. Conversely, direct contact with either plasma membranes or fixed phytohemagglutinin/phorbol myristate acetate-activated T cells markedly inhibited the synthesis of types I and III collagen by 60-70% in untreated dermal fibroblasts and synoviocytes and by 85% in transforming growth factor beta-stimulated fibroblasts. This decrease of collagen synthesis was abrogated when fixed T cells were separated physically from fibroblasts, demonstrating that direct contact between the two cell types was necessary. This inhibition was associated with a marked decrease in steady-state levels of pro-alpha1(I) and pro-alpha1(III) collagen mRNAs. T cell contact decreased the transcription rate but did not significantly alter the stability of the alpha1(I) and alpha1(III) transcripts. Finally, using neutralizing antibodies or cytokine inhibitors we provide evidence that this inhibition of extracellular matrix production mediated by T cell contact was partially due to additive effects of T cell membrane-associated interferon gamma, tumor necrosis factor alpha, and interleukin-1alpha.

Collagen hydroxylases and the protein disulfide isomerase subunit of prolyl 4-hydroxylases

Prolyl 4-hydroxylases catalyze the formation of 4-hydroxyproline in collagens and other proteins with an appropriate collagen-like stretch of amino acid residues. The enzyme requires Fe(II), 2-oxoglutarate, molecular oxygen, and ascorbate. This review concentrates on recent progress toward understanding the detailed mechanism of 4-hydroxylase action, including: (a) occurrence and function of the enzyme in animals; (b) general molecular properties; (c) intracellular sites of hydroxylation; (d) peptide substrates and mechanistic roles of the cosubstrates; (e) insights into the development of antifibrotic drugs; (f) studies of the enzyme's subunits and their catalytic function; and (g) mutations that lead to Ehlers-Danlos Syndrome. An account of the regulation of collagen hydroxylase activities is also provided.

What holds us together? Why do some of us fall apart? What can we do about it?

One of the intriguing questions about complex organisms is, What holds them together? One of the principal answers is the tough, fibrous material known as collagen. A related question is, How is collagen made? The biosynthesis of the protein has several unusual features. One is the extensive use of the principle of spontaneous self-assembly seen in the formation of crystals. The three polypeptide chains of the protein fold into a triple-helical conformation by a process that begins with the formation of a small nucleus of triple helix at the C-terminus of the molecule and then propagation of the nucleus in a zipper-like fashion. Also, the self-assembly of the collagen monomers into fibrils is an entropy driven, crystallization-like process. Why do some of them fall apart? Mutations that alter the expression or primary structure of collagen are the predominant causes of severe skeletal defects such as osteogenesis imperfecta and chondrodysplasias. Mutations that have milder effects on the synthesis or structure of the protein are found in a subset of patients with more common diseases such as osteoporosis and early onset osteoarthritis. What can we do about the defects in collagen? Recent results have emphasized the importance of earlier observations that bone marrow contains a small subset of cells that are progenitors of osteoblasts, chondroblasts and several other types of nonhematopoietic cells. After systemic infusion into irradiated mice, the infused cells slowly replace a small fraction of the cells in bone, cartilage, lung and several other tissues. Therefore, the results suggest that the cells, known as mesenchymal stem cells or marrow stromal cells, can be used for both cell and gene therapy of diseases in which bone, cartilage and other connective tissues fall apart.

Procollagen N-proteinase and procollagen C-proteinase. Two unusual metalloproteinases that are essential for procollagen processing probably have important roles in development and cell signaling

As soon as procollagen precursors of fibrillar collagens were discovered in the early 1970s, it became apparent that connective tissues must contain proteolytic activities that cleave the N-propeptides and the C-propeptides from procollagens. Isolation and characterization of the enzymic activities, however, proved to be unexpectedly difficult. Both proteinases are large and are synthesized in several different forms with polypeptide chains ranging in size from 70 kDa to about 130 kDa. The N-proteinase has the unusual property of cleaving the N-propeptides from type I and type II procollagens if the proteins are in a native conformation, but not if the proteins are partially unfolded so that the N-telopeptides are no longer in a hair-pin configuration. The C-proteinase specifically cleaves native and denatured types I, II and III procollagens. It also specifically cleaves a precursor of lysyl oxidase and laminin 5. Both enzymes and their variants have structures that place them in a large and expanding super-family of over 200 zinc-binding metalloproteinases. The larger of two forms of the N-proteinase contains an RGD sequence for binding through integrins and properdin repeats similar to those found in thrombospondin. The shorter 70 kDa form of the C-proteinase is identical to the protein that was previously identified as bone morphogenic protein-1. Both the 70 kDa C-proteinase and two larger forms are homologous to proteins that are expressed early in development in a variety of organisms, including Drosophila, sea urchin, and fish. Therefore, the data suggest that both the N- and C-proteinases have important biological functions in addition to the roles in the processing of procollagens.

Tissue specific and vitamin D responsive gene expression in bone

Studies of gene expression in bone have adopted a number of molecular approaches that seek to determine those cis and trans-acting factors responsible for the development and physiological regulation of this unique tissue. The majority of studies have been performed in vitro, focussing on the expression of genes such as osteocalcin, bone sialoprotein and type I collagen which demonstrate restricted or altered expression patterns in osteoblasts. These studies have demonstrated a large number of cis and trans acting factors that modulate the tissue specific and vitamin D responsive expression of these genes. These include the response elements and regions mediating basal and vitamin D dependent transcription of these genes as well as some of the transcription factors that bind to these regions and the nucleosomal organisation of these genes within a nuclear framework. In vivo studies, including the introduction of transgenes into transgenic mice, extend these in vitro observations within a physiological context. However, in part due to limitations in each approach, these in vitro and in vivo studies are yet to accurately define all the necessary cis and trans-acting factors required for tissue specific and vitamin D responsive gene expression. Advances have been made in identifying many cis-acting regions within the flanking regions of these genes that are responsible for their restricted expression patterns, but a vector incorporating all the necessary cis-acting regions capable of directing gene expression independent of integration site has not yet been described. Similarly, trans-acting factors that determine the developmental destiny of osteoblast progenitors and the restricted expression of these genes remain elusive and, despite advances in the understanding of protein-DNA interactions at vitamin D response elements contained within these genes, further intermediary factors that interact with the transcriptional machinery to modulate vitamin D responsiveness need to be identified.

Nitric oxide inhibits the synthesis of type-II collagen without altering Col2A1 mRNA abundance: prolyl hydroxylase as a possible target

The addition of human recombinant interleukin-1beta (IL-1beta) to cultures of lapine articular chondrocytes provoked the synthesis of large amounts of NO and reduced the production of type-II collagen. NG-Monomethyl-l-arginine (L-NMA), an inhibitor of NO synthase, strongly suppressed the production of NO and partially relieved the inhibition of collagen synthesis in response to IL-1beta. The NO donor S-nitrosoacetylpenicillamine (SNAP), on the other hand, inhibited collagen production. IL-1 lowered the abundance of Col2A1 mRNA in an NO-independent manner. Collectively, these data indicate that IL-1 suppresses collagen synthesis at two levels: a pretranslational level which is NO-independent, and a translational or post-translational level which is NO-mediated. These effects are presumably specific as L-NMA and SNAP had no effect on total protein synthesis or on the distribution of newly synthesized proteins between the cellular and extracellular compartments. Prolyl hydroxylase is an important enzyme in the post-translational processing of collagen, and its regulation and cofactor requirements suggest possible sensitivity to NO. Extracts of cells treated with IL-1 or SNAP had lower prolyl hydroxylase activity, and L-NMA was partially able to reverse the effects of IL-1. These data suggest that prolyl hydroxylase might indeed be a target for NO. Because underhydroxylated collagen monomers fail to anneal into stable triple helices, they are degraded intracellularly. Inhibition of prolyl hydroxylase by NO might thus account for the suppressive effect of this radical on collagen synthesis.

Fine structure of extracellular matrix and basal laminae in two types of abnormal collagen production: L-proline analog-treated otocyst cultures and disproportionate micromelia (Dmm/Dmm) mutants

L-Azetidine-2-carboxylic acid (LACA), a naturally occurring vegetable imino acid, can be incorporated into mammalian proteins in place of proline, thereby eliciting an inhibitory effect on collagen secretion. Exposure of explants of the embryonic mouse inner ear to LACA reduces the number of collagen fibrils in the otic capsule, gives rise to a dose-dependent derangement of the basal lamina, and ultimately results in dysmorphogenesis and retarded differentiation of the inner ear. Disproportionate micromelia (Dmm) is an incomplete dominant form of dwarfism characterized by a reduced quantity of type II collagen in the cartilaginous extracellular matrix (ECM). Abnormal morphogenesis in homozygotic Dmm mice resembles the abnormal morphogenesis observed in LACA-exposed otic explants, resulting in malformed inner ears with a bulky cartilaginous capsule and a lack or reduction of defined perilymphatic spaces (Van De Water and Galinovic-Schwartz, 1987). In this study, we examined by ultrastructural analysis LACA-exposed otic explants and inner ears of Dmm/Dmm mouse embryos for abnormalities in the collagenous constituents of the basal laminae and capsular ECM. We demonstrate, in comparison to normal embryonic mouse inner ears, a reduction in collagen fibrils and irregular cytodifferentiation of chondrocytes in the ECM of LACA-exposed and Dmm/Dmm inner ears as well as in the basal laminae of LACA-exposed specimens. In addition, we provide evidence of dysmorphogenesis of the otic capsule and perilymphatic spaces in LACA-exposed explants. Moreover, while previous studies demonstrated the anomalous development of sensory structures in otocyst explants following LACA exposure, in this study we provide evidence of the normal morphogenesis of otic epithelial-derived sensory structures in homozygotic Dmm/Dmm mouse embryos.

Type III collagen is crucial for collagen I fibrillogenesis and for normal cardiovascular development

Type III collagen is a fibrillar forming collagen comprising three alpha1(III) chains and is expressed in early embryos and throughout embryogenesis. In the adult, type III collagen is a major component of the extracellular matrix in a variety of internal organs and skin. Mutations in the COL3A1 gene have been implicated as a cause of type IV Ehlers-Danlos syndrome, a disease leading to aortic rupture in early adult life. To directly study the role of Col3a1 in development and disease, we have inactivated the Col3a1 gene in embryonic stem cells by homologous recombination. The mutated allele was transmitted through the mouse germ line and homozygous mutant animals were derived from heterozygous intercrosses. About 10% of the homozygous mutant animals survived to adulthood but have a much shorter life span compared with wild-type mice. The major cause of death of mutant mice was rupture of the major blood vessels, similar to patients with type IV Ehlers-Danlos syndrome. Ultrastructural analysis of tissues from mutant mice revealed that type III collagen is essential for normal collagen I fibrillogenesis in the cardiovascular system and other organs.

Ehlers-Danlos syndrome type IV: a heterogeneous disease

The Ehlers-Danlos syndrome is an inherited disorder of connective tissue, consisting of at least 10 different clinical subtypes. Type IV Ehlers-Danlos syndrome is an autosomal dominant condition characterized by the joint and dermal manifestations as in other forms of the syndrome but also by the proneness to spontaneous rupture of bowel and large arteries. The authors describe their experience with three patients presenting type IV Ehlers-Danlos syndrome: the first presented with several subsequent arterial ruptures, the second with multiple aneurysms, and the third with a dissection of the internal carotid artery. Clinical features, incidence, diagnosis, and treatment of the syndrome are discussed.

DDAVP therapy controls bleeding in Ehlers-Danlos syndrome

PURPOSE

Patients with Ehlers-Danlos syndrome (EDS), especially types IV, VI, and VIII, are at increased risk of bleeding, and most do not have specific hemostatic deficiencies that would be amenable to replacement therapy. We have investigated the ability of DDAVP (desmopressin acetate) to control bleeding in EDS.

PATIENTS AND METHODS

Two children with EDS, types VIII and VI, presented with hemorrhagic symptoms and scheduled surgical procedures. Ivy bleeding times (BTs) were measured before and after intravenous (i.v.) DDAVP challenge, and i.v. DDAVP was used prophylactically for their procedures. Laboratory testing was performed to rule out other hemostatic disorders.

RESULTS

Both patients had prolonged BTs that corrected following i.v. DDAVP therapy; all other laboratory values were normal. Both patients had excellent clinical hemostasis with surgery, and one has continued to use intranasal DDAVP to control epistaxis and gingival bleeding.

CONCLUSIONS

The bleeding time in both patients was corrected with DDAVP, and the patients did not have any postoperative bleeding. DDAVP should be considered in other patients who have EDS with bleeding tendencies.

Formation of recombinant triple-helical [alpha 1(IV)]2 alpha 2(IV) collagen molecules in CHO cells

Collagen IV molecules represent a major structural component of basement membranes providing a network of support for the supramolecular structure. Like other collagens, collagen IV forms a triple-helical molecule composed of three alpha chains. Six different alpha chains exist for collagen IV, although the most common isoform consists of two alpha 1(IV) and one alpha 2(IV) chain. To understand the molecular mechanism of triple-helical formation of collagen IV, we expressed recombinant alpha 1(IV) and alpha 2(IV) mouse collagen chains in Chinese hamster ovary (CHO) cells. An expression vector containing the full length cDNA for the mouse alpha 1(IV) chain was stably transfected into CHO cells and a cell line, A222, which expressed recombinant alpha 1(IV) chains was selected. These A222 cells were then infected with a retroviral expression vector containing the mouse alpha 2(IV) chain and a cell line, A222-A2, stably expressing both recombinant alpha 1(IV) and alpha 2(IV) chains was obtained. Immunoprecipitation of A222 cell lysates revealed a high level of alpha 1(IV) chain monomer, which was unable to form a homotrimer. Analysis of A222-A2 cell lysates revealed the presence of both monomeric alpha 2(IV) and alpha 1(IV) chains as well as a higher molecular weight collagen IV species. Second dimensional SDS-PAGE analysis demonstrated that the high molecular weight species was a heterotrimer consisting of two alpha 1(IV) and one alpha 2(IV) chain. This heterotrimer collagen IV species was pepsin-resistant indicating the formation of a stable triple-helical structure. Pulse-chase experiments showed that the monomer alpha 1(IV) chain was secreted, but at a much slower rate than the heterotrimer. Together these results demonstrate that the alpha 1(IV) chain is not capable of forming homotrimers and suggest that the coexpression with the alpha 2(IV) chain is necessary to form a triple-helical structure.

Basement-membrane stromal relationships: interactions between collagen fibrils and the lamina densa

Collagens, the most abundant molecules in the extracellular space, predominantly form either fibrillar or sheet-like structures-the two major supramolecular conformations that maintain tissue integrity. In connective tissues, other than cartilage, collagen fibrils are mainly composed of collagens I, III, and V at different molecular ratios, exhibiting a D-periodic banding pattern, with diameters ranging from 30 to 150 nm, that can form a coarse network in the extracellular matrix in comparison with a fine meshwork of lamina densa. The lamina densa represents a stable sheet-like meshwork composed of collagen IV, laminin, nidogen, and perlecan compartmentalizing tissue from one another. We hypothesize that the interactions between collagen fibrils and the lamina densa are crucial for maintaining tissue-tissue interactions. A detailed analysis of these interactions forms the basis of this review article. Here, we demonstrate that there is a direct connection between collagen fibrils and the lamina densa and propose that collagen V may play a crucial role in this connection. Collagen V might also be involved in regulation of collagen fibril diameter and anchoring of epithelia to underlying connective tissues.

Alternative splicing in COL1A1 mRNA leads to a partial null allele and two In-frame forms with structural defects in non-lethal osteogenesis imperfecta

We have identified a novel multiexon genomic deletion in one COL1A1 collagen allele that results in three alternative forms of mutant mRNA. This mutation occurs in a 9-year-old girl and her father, both affected with severe type III osteogenesis imperfecta (OI). We previously reported detection of a mismatch in their alpha1(I) amino acids 558-861 region by RNA/RNA hybrid analysis (Grange, D. K., Gottesman, G. S., Lewis, M. B., and Marini, J. C. (1990) Nucleic Acids Res. 18, 4227-4236). Single Strand Conformational Polymorphism further localized the mRNA mutation to the amino acids 579-679 coding region. At the gene level, polymerase chain reaction (PCR) amplification of patient leukocyte DNA from the exon 33-38 region yielded the normal 1004-base pair (bp) fragment and an additional 442-bp fragment. Sequencing of the shorter genomic PCR product confirmed the presence of a 562-bp deletion, extending from the last 3 nucleotides (nt) of exon 34 to 156 nt from the 3'-end of intron 36. The genomic deletion was also detected in the clinically normal grandmother, who was confirmed to be a mosaic carrier. PCR amplification and RNase protection experiments were used to investigate the mRNA structure and occurrence of alternative splicing. One form of the mutant cDNA has a deletion with end points that are identical to the genomic deletion. This results in a combination deletion/insertion, with a deletion of amino acids 603-639 followed by an insertion of 156 nt from the 3'-end of intron 36. In addition, we found two alternatively spliced forms. One form uses a cryptic donor site in exon 34 and the exon 37 acceptor. The second form uses the normal exon 32 splice donor and exon 37 acceptor. Use of the cryptic donor results in a coding sequence that is out-of-frame. Both the retained intron form and the use of the exon 32 donor site result in coding sequences that are in-frame. This is the first report of a collagen defect in OI with alternative splicing generating both in-frame and out-of-frame forms of mRNA. Although the in-frame forms constitute more than 60% of the mRNA from the mutant allele, no mutant protein chain was identified. Collagen produced by cultured OI osteoblasts showed a significant increase in the relative amount of type III collagen but no mutant alpha1(I) chain.

A-2-->G transition at the 3' acceptor splice site of IVS17 characterizes the COL2A1 gene mutation in the original Stickler syndrome kindred

Hereditary progressive arthro-ophthalmopathy, or "Stickler syndrome," is an autosomal dominant osteochondrodysplasia characterized by a variety of ocular and skeletal anomalies which frequently lead to retinal detachment and precocious osteoarthritis. A variety of mutations in the COL2A1 gene have been identified in "Stickler" families; in most cases studied thus far, the consequence of mutation is the premature generation of a stop codon. We report here the characterization of a COL2A1 gene mutation in the original kindred described by Stickler et al. [1965]. Conformational sensitive gel electrophoresis (CSGE) [Ganguly et al., 1993] was used to screen for mutations in the entire COL2A1 gene in an affected member from the kindred. A prominent heteroduplex species was noted in the polymerase chain reaction (PCR) product from a region of the gene including exons 17 to 20. Direct sequencing of PCR-amplified genomic DNA resulted in the identification of a base substitution at the A-2 position of the 3' splice acceptor site of IVS17. Sequencing of DNA from affected and unaffected family members confirmed that the mutation segregated with the disease phenotype. Reverse transcriptase-PCR analysis of poly A+ RNA demonstrated that the mutant allele utilized a cryptic splice site in exon 18 of the gene, eliminating 16 bp at the start of exon 18. This frameshift eventually results in a premature termination codon. These findings are the first report of a splice site mutation in classical Stickler syndrome and they provide a satisfying historical context in which to view COL2A1 mutations in this dysplasia.

Scanning electron microscopy of teeth in osteogenesis imperfecta type I

Opalescent teeth from five patients and nonopalescent teeth from six patients with osteogenesis imperfecta type I were examined with the scanning electron microscope and their appearances compared with those of teeth from normal persons. In opalescent teeth the main findings were a reduction in the number and variation in the size of the dentinal tubules that were irregularly embedded within the disturbed dentinal matrix and an abnormally smooth enamel-dentinal junction. Similar less marked dentinal abnormalities were found in the nonopalescent teeth from three patients. No abnormality was found in the enamel in any of the teeth examined. These findings suggest that in osteogenesis imperfecta teeth that appear normal may have defective dentine. This relevant to the current clinical classification of the disorder into subgroups according to the clinical presence or absence of affected teeth.

Antisense oligodeoxynucleotides selectively suppress expression of the mutant alpha 2(I) collagen allele in type IV osteogenesis imperfecta fibroblasts. A molecular approach to therapeutics of dominant negative disorders

We are investigating the use of antisense oligodeoxynucleotides to selectively suppress expression of the mutant type I collagen allele in osteogenesis imperfecta (OI). In this report, we target a human collagen mutation in its natural cellular context. We used cultured fibroblasts from a case of type IV OI, in which the mutant alpha 2(I) allele produces mRNA with exon 16 deleted due to a point mutation in the splice donor site. Lipid-mediated transfection was used to deliver antisense, sense and missense phosphorothioates targeted to both the abnormal mRNA exon 15/17 junction and the nuclear level point mutation. Significant suppression of the mutant protein chain and mRNA was achieved with antisense oligonucleotide to both mRNA and nuclear levels. Mutant protein was suppressed to 44-47% and mutant alpha 2(I) mRNA to 37-43% of their levels in control cells, indicating decreased mRNA as the basis for suppression. Selectivity of mutant allele suppression was better with an mRNA target: suppression was sequence specific and normal mRNA was expressed at 79% of its level in untreated cells. With a nuclear target, significant suppression of mutant mRNA occurred not only with antisense and sense, but also with missense oligonucleotide, which suppressed mutant mRNA to 60% of its level in untreated cells. We also investigated the time course of suppression of protein and mRNA in response to a 4 h transfection of antisense oligonucleotide. From 24-72 h after transfection, mutant protein was suppressed to approximately 50% of its untreated level and suppression of mutant message was significantly greater than that of normal message. The suppression achieved in these studies is insufficient for clinical intervention, but our results provide support for further development of antisense therapy as an approach to the treatment of dominant negative disorders.

Fatal vascular catastrophe in Ehlers-Danlos syndrome: a case report and review

The Ehlers-Danlos syndrome (EDS) is a group of hereditary connective tissue disorders that are characterized by abnormalities of the skin, joints, and a diversity of other phenotypic manifestations. An awareness of the disease is vital for optimal outcome in this rare group of patients who may present with a variety of life-threatening illnesses. Ehlers-Danlos type IV has been associated with vascular catastrophes, perforated viscous, ruptured uterus, and pneumothorax (1-4). We present a case of aneurysmal formation and spontaneous rupture of the great vessels in a 15-year-old male with EDS type IV, who remained undiagnosed until the time of autopsy.

Perspectives on the synthesis and application of triple-helical, collagen-model peptides

Collagens can be distinguished from other proteins based on their triple-helical structure. Synthetic peptide models have been developed to better understand the triple helix structurally and to evaluate the triple helix as a recognition element for biological processes. Associated triple-helical peptides were first designed and assembled by solid-phase methodology in the late 1960s. Such peptides were used for triple-helical structural characterization by CD, nmr, and ir spectroscopies, and x-ray crystallography, and for studying the structural preferences of hydroxylases. In the late 1970s, methods were developed for covalently linking the three strands of triple-helical peptides. One benefit of "branched" peptides was the enhancement of triple-helical thermal stability. The incorporation of specific collagen sequences into thermally stable synthetic triple helices in the early 1990s has allowed for the mechanistic investigation of collagen-mediated cell adhesion and platelet aggregation. In time, discriminatory therapeutics may result from the continued exploration and further understanding of the biological effects of collagen primary, secondary, and tertiary structures via triple-helical peptide models.

Cartilage matrix protein forms a type II collagen-independent filamentous network: analysis in primary cell cultures with a retrovirus expression system

Cartilage matrix protein (CMP) is expressed specifically in mature cartilage and consists of two von Willebrand factor A domains (CMP-A1 and CMP-A2) that are separated by an epidermal growth factor-like domain, and a coiled-coil tail domain at the carboxyl terminal end. We have shown previously that CMP interacts with type II collagen-containing fibrils in cartilage. In this study, we describe a type II collagen-independent CMP filament and we analyze the structural requirement for the formation of this type of filament. Recombinant wild-type CMP and two mutant forms were expressed in chick primary cell cultures using a retrovirus expression system. In chondrocytes, the wild-type virally encoded CMP is able to form disulfide bonded trimers and to assemble into filaments. Filaments also form with CMP whose Cys455 and Cys457 in the tail domain were mutagenized to prevent interchain disulfide bond formation. Therefore, intermolecular disulfide bonds are not necessary for the assembly of CMP into filaments. Both the wild-type and the double cysteine mutant also form filaments in fibroblasts, indicating that chondrocyte-specific factors are not required for filament formation. A truncated form of CMP that consists only of the CMP-A2 domain and the tail domain can form trimers but fails to form filaments, indicating that the deleted CMP-A1 domain and/or the epidermal growth factor domain are necessary for filament assembly but not for trimer formation. Furthermore, the expression of the virally encoded truncated CMP in chondrocyte culture disrupts endogenous CMP filament formation. Together these data suggest a role for CMP in cartilage matrix assembly by forming filamentous networks that require participation and coordination of individual domains of CMP.

Skin collagen defects in a patient with juvenile hyaline fibromatosis

Juvenile hyaline fibromatosis is a rare disorder characterised by multiple subcutaneous tumours, gum hypertrophy, muscle weakness, and flexion contractures of the large joints. Histology shows an abundance of a homogenous, amorphous, acidophilic extracellular matrix in which spindle shaped cells are embedded forming minute streaks. It has been previously suggested that collagen abnormalities may be involved. A 14 month old girl with this syndrome is described in whom postmortem western blot studies were performed. These studies revealed an absent pro-alpha 2(I) chain and an absent collagen type III chain in skin but not in the other organs examined.

Ehlers-Danlos syndrome type II: importance of recognition

We report a case of Ehlers-Danlos syndrome Type II presenting with subtle clinical features and discuss the importance of early recognition of this disorder. A 16 year old Caucasian schoolgirl presented with soft tissue swellings on her fingers. There was a history of poor wound healing and prematurity and a family history of miscarriages. Clinical examination revealed hypermobile joints, hyperelastic skin and a 'cigarette paper' scar at the site of a previous minor surgical excision. Management consisted of genetic counselling and advice concerning career choice, recreational activities, as well as future pregnancy and surgery. This subtype of Ehlers-Danlos syndrome is probably fairly common in the community. While it may present with subtle clinical features, recognition is important so that counselling can be offered at a young age in order to avoid the major consequences that may arise during pregnancy and surgery.

Tissue-specific expression of the gene for type I procollagen (COL1A1) in transgenic mice. Only 476 base pairs of the promoter are required if collagen genes are used as reporters

Inconsistent data have been reported on the size of the promoter that is necessary for high levels of tissue-specific expression of the COL1A1 gene for type I procollagen. Some of the inconsistencies may be traced to the use of reporter gene constructs. Therefore, we prepared transgenic mice with modifications of the intact gene engineered so that the level of expression of the transgene could be assayed both as mRNA and protein that were similar to the products from the endogenous COL1A1 gene. The results with a mini-COL1A1 gene lacking 41 internal exons and introns indicated that the first intron and 90% of the 3'-untranslated region were not essential for tissue-specific expression. In a hybrid COL1A1/COL2A1 construct, a 1.9-kilobase 5'-fragment from the COL1A1 gene that contained only 476 of the promoter was linked to a promoterless 29.5-kilobase fragment of the human COL2A1 gene for type II procollagen. The hybrid COL1A1/COL2A1 construct was expressed as both mRNA and protein in tissues that normally synthesize type I procollagen but not type II procollagen. Apparently, 476 base pairs of the promoter are sufficient to drive tissue-specific expression of the COL1A1 gene and totally inappropriate expression of the COL2A1 gene.

Abnormal mechanical properties of the aorta in Marfan's syndrome

OBJECTIVES

Aortic dilatation, dissection and rupture are among the major causes of death in subjects with Marfan's syndrome. The aim of the study was to investigate the mechanical properties or compliance of the aorta in these subjects and compare them with a healthy age- and sex-matched reference population.

MATERIALS AND METHODS

An ultrasound phase-locked echo-tracking system was used to determine diameter and pulsatile diameter change of the infrarenal aorta in nine subjects with Marfan's syndrome which were then compared with the values for 165 healthy individuals. Compliance, defined as the inverse of Ep (pressure strain elastic modulus) or stiffness (beta), was calculated from pulsatile diameter change and blood pressure obtained by the auscultatory method with a sphygmomanometer. For statistical analysis confidence intervals (95%) obtained from the healthy controls were used for comparison. Analysis of covariance (ANCOVA) was performed for the female patients. The sample size for males (n = 2) was too small for the latter analysis.

RESULTS

Compared with normal subjects and their confidence intervals, subjects with Marfan's syndrome had an increased Ep and stiffness (beta) and decreased strain (fractional diameter change) in the infrarenal aorta. Furthermore, ANCOVA in the female patients showed increased beta (p < 0.01) and Ep (p < 0.01) and a decreased strain (p < 0.001). Aortic diameters, MAP, as well as the pulse pressure, were similar in the two groups.

CONCLUSION

This investigation demonstrates alterations in the mechanical properties of the aorta in Marfan's syndrome in the form of increased stiffness of the aortic wall. This may be of importance in the pathogenesis of aortic dissection and rupture.

Structure and function of cartilage collagens

Collagens are the major proteinaceous constituents of cartilage. Three collagen types participate in the formation of striated fibrils of cartilage, collagens II, IX, and XI. Collagen II and XI belong to the subgroup of fibrillar collagens and are structurally closely related, differing mainly in their N-propeptides. Collagen IX has a very different structure but is nevertheless an essential constituent of the striated fibrils. Two other collagen types are also found in cartilage but form distinct structures. Collagen VI, found mainly in the periphery of the chondrocytes, forms beaded filaments. These filaments are probably formed by interaction of collagen VI with hyaluronan. Collagen X is expressed by hypertrophic chondrocytes. It has been shown to form in vitro hexagonal lattices and in vivo to be associated either with striated fibrils or with mats which may correspond to the lattices. The functional role of the collagen diversity in cartilage is discussed.

Targeted insertions of two exogenous collagen genes into both alleles of their endogenous loci in cultured human cells: the insertions are directed by relatively short fragments containing the promoters and the 5' ends of the genes

Previous studies demonstrated that type II procollagen is synthesized by HT-1080 cells that are stably transfected with constructs of the human COL2A1 gene that contain the promoter and 5' end of either the COL2A1 gene or the human COL1A1 gene. Since the host HT-1080 cells were from a human tumor line that synthesizes type IV collagen but not type II or type I procollagen, the results suggested that the constructs were integrated near active enhancers or promoters. Here, however, we demonstrate that a 33-kb construct of the COL2A1 gene containing a 5' fragment from the same gene was inserted into both alleles of the endogenous COL2A1 gene on chromosome 12, apparently by homologous recombination by a nonconservative pathway. In contrast, a similar construct of the COL2A1 gene in which the 5' end was replaced with a 1.9-kb fragment from the 5' end of the COL1A1 gene was inserted into both alleles of the locus for the COL1A1 gene on chromosome 17. Therefore, targeted insertion of the gene construct was not directed by the degree of sequence homology. Instead, it was directed by the relatively short 5' fragment from the COL1A1 gene that contained the promoter and the initially transcribed sequences of the gene. After insertion, both gene constructs were expressed from previously inactive loci.

A homozygous stop codon in the lysyl hydroxylase gene in two siblings with Ehlers-Danlos syndrome type VI

Ehlers-Danlos syndrome (EDS) is characterized by joint hypermobility, alterations in the skin and additional signs of connective tissue involvement. EDS type VI was the first connective tissue disorder for which a specific defect in collagen metabolism was identified, namely a deficiency of lysyl hydroxylase activity. We now report a homozygous single basepair substitution converting the CGA codon (Arg319) to a TGA termination codon in two siblings with EDS type VI. The healthy parents, who are first cousins, and two of the three healthy siblings of the patients are heterozygous. The mutation leads to an almost complete absence of lysyl hydroxylase activity in extracts derived from fibroblasts of the patients.

Normal and hypertrophic scars: quantification and localization of messenger RNAs for type I, III and VI collagens

The expression of type I, III and VI collagens was studied in nine normal and two hypertrophic scars using slot-blot and in situ hybridization techniques. Slot-blot hybridization indicated that the steady-state levels of pro alpha 1(I) and pro alpha 1(III) collagen chain mRNAs were moderately elevated in two of the nine normal scars, whereas the two hypertrophic scars analysed displayed markedly elevated mRNA levels when compared with normal skin. The mRNA levels of alpha 2(VI) collagen chain were only slightly elevated in both types of scars studied. In situ hybridization was most informative when applied to hypertrophic scars. These lesions were characterized by the presence of intense hybridization signals for type I and III collagen mRNAs, and a moderate signal for type VI collagen mRNA, in nodules which were located in the upper dermis on each side of the original wound. This may explain, in part, why hypertrophic scars rise above the level of the surrounding skin. The results of the present study are in marked contrast to our previous findings on collagen gene expression in keloids and neurofibromas, in which the steady-state levels of type VI and I collagen mRNAs in particular were shown to be elevated. Thus, our results emphasize that distinct molecular mechanisms are operative in the development of clinically different dermal fibrotic conditions, such as normal and hypertrophic scars, keloids and neurofibromas.

Type II collagen mutations in rare and common cartilage diseases

Cartilage diseases include a wide variety of clinical phenotypes from common osteoarthrosis to several different types of chondrodysplasias, i.e. 'disorders of cartilage', of which more than 100 different have been described. Patients frequently suffer from various symptoms affecting their joints and/or the growth of their long bones. The amount of hyaline cartilage at articular surfaces is often diminished and structurally abnormal. The surface of the cartilage may have an irregular appearance with defects extending into the subchondral bone. The major constituents of this hyaline cartilage are collagens and proteoglycans, the most abundant protein being type II collagen. It is a homotrimer of three identical alpha-chains, which are encoded by a single gene on human chromosome 12. The gene for type II collagen therefore became a likely candidate for some forms of chondrodysplasias and cartilage degeneration. Recently, both linkages and exclusions between this gene and various cartilage diseases have been reported and a growing number of mutations within the gene have also been identified.

Osteogenesis imperfecta in Holstein-Friesian calves

Eight calves with osteogenesis imperfecta were born in a Danish Holstein-Friesian herd during a two-year period. In total 92 calves were born (84 normal), and all were sired by a clinically normal Holstein-Friesian bull. The defect was probably due to a de novo dominant mutation present as a gonadal mosaicism in the bull. Affected calves were characterised by multiple fractures, congenital bone deformations, general joint laxity, dentinogenesis imperfecta, and light blue sclerae. The skin seemed normal. Electron microscopical studies revealed slightly decreased average diameter of cutaneous collagen fibrils, while the diameter of collagen fibrils in tendons and ligaments was severely reduced. Abnormalities of collagen type I from skin and compact bone were not detected by biochemical analyses.

[Arterial involvements in hereditary dysplasia of the connective tissue]

Arterial involvement is an important feature of the diagnosis and, above all, prognosis of heritable disorders of connective tissue. In pseudoxanthoma elasticum, a progressive occlusive syndrome is associated with hemorrhage and especially with gastrointestinal bleeding. Aneurysms are uncommon. Hypertension occurs frequently. Cutaneous signs (yellowish pseudo xanthomatous papules of the large folds) the ocular changes (angioid streaks) and pathology showing numerous, thickened, fragmented, disorganized, calcified elastic fibers in the deep dermis and arterial walls, allow the diagnosis to be made. In the heterogeneous group of Ehlers-Danlos syndromes, type IV is characterized by sudden spontaneous rupture of the large arteries. Aneurysms and carotido-cavernous fistulae are rather frequent. Owing to friability of the arterial walls, arteriograms and other procedure requiring arterial puncture may prove hazardous and surgery difficult. Such patients have an acrogeric morphotype, and thin, fragile skin, but cutaneous hyperelasticity and joint hyperlaxity are usually minimal. Pathology evidences collagen hypoplasia in the skin and arterial walls. The severity of Marfan syndrome is due to aortic involvement. A fusiform aneurysm of the ascending aorta represents a vital risk of rupture. Aortic root dilatation is associated and responsible of severe aortic regurgitation. Aortic dissection is also a serious threat. Improved surgical techniques for repairing a dilated or dissected aortic root with simultaneous replacement of the aortic valve increases the life expectancy of such patients. Dolichomorphism is the characteristic skeletal abnormality, particularly with arachnodactyly and upward ectopia lentis, which is almost bilateral, is a very frequent feature of Marfan syndrome. The most typical histological finding is aortic cystic median necrosis. The basic defect in Marfan syndrome concerns the fibrillin, whose gene is located on chromosome 15. The three diseases detailed in this paper constitute the main areas of this subject, but arterial involvement may occur in other inheritable disorders of connective tissue (osteogenesis imperfecta, cutis laxa, Werner syndrome, Menkes syndrome, etc).

Cadmium ions inhibit procollagen C-proteinase and cupric ions inhibit procollagen N-proteinase

Procollagen C- and N-proteinases specifically cleave the C- and N-terminal extension propeptides of type I, II and III procollagen molecules. The collagen molecules generated by the enzymes self-assemble into collagen fibrils. We previously observed the inhibition of these enzymes purified from chick tendons by several divalent metals. Here the inhibitory effects of CdCl2, CuCl2, ZnCl2, NiCl2, CoCl2 and Hg(C2H3O2)2 have been studied in detail using crude or purified C- and N-proteinases from chick tendons and sterna. CdCl2 was a strong inhibitor of C-proteinases from both sources, and the inhibition was independent of enzyme purity (I50 = 10-16 microM). In contrast, CuCl2 and ZnCl2 were inhibitory only of purified C-proteinase. With the N-proteinase, CuCl2 was a strong inhibitor, and the inhibition was independent of the purity of the enzyme preparation used (I50 = 14-40 microM). On the other hand, CdCl2 was a moderate inhibitor, and ZnCl2 was a strong inhibitor only of the purified N-proteinase (I50 = 8-17 microM). NiCl2 inhibited crude and purified N-proteinase from sternum (I50 = 23-29 microM) but not from tendon. These results suggest, therefore, that the accumulation of some of these metals in the body may cause suppression of collagen fibril formation in tissues.