Structure and stability of the triple-helical domains of human collagen XIV

Endotrophin, a Key Marker and Driver for Fibroinflammatory Disease

Our overview covers several key areas related to recent results obtained for collagen type VI and endotrophin (ETP). (1) An introduction to the history of ETP, including how it was identified, how it is released, and its function and potential receptors. (2) An introduction to the collagen family, with a focus on what differentiates collagen type VI from an evolutionary standpoint. (3) An overview of collagen type VI, the 6 individual chains (COL6A1, A2, A3, A4, A5, and A6), their differences and similarities, as well as their expression profiles and function. (4) A detailed analysis of COL6A3, including the cleaved product endotrophin, and what separates it from the other 5 collagen 6 molecules, including its suggested function based on insights gained from knockout and gain of function mouse models. (5) The pathology of ETP. What leads to its presence and release and what are the consequences thereof? (6) Functional implications of circulating ETP. Here we review the data with the functional roles of ETP in mind. (7) We propose that ETP is a mediator for fibrotic (or fibroinflammatory) disorders. Based on what we know about ETP, we have to consider it as a target for the treatment of fibrotic (or fibroinflammatory) disorders. What segment(s) of the patient population would most dramatically respond to an ETP-targeted intervention? How can we find the population that would profit most from an intervention? We aim to present a broad overview over the ETP field at large, providing an assessment of where the future research efforts need to be placed to tap into the vast potential of ETP, both as a marker and as a target in different diseases.

The profiling and analysis of gene expression in human periodontal ligament tissue and fibroblasts

Objectives

The periodontal ligament (PDL) is an important component of periodontium to support dental structure in the alveolar socket. Regeneration of PDL tissue is an effective treatment option for periodontal disease and the profiling of genes involved in this process will be informative. Therefore, our study aims to accurately delineate the profiling of gene expression for PDL tissue regeneration.

Materials and Methods

We isolated PDL tissues and PDL fibroblasts (PDLFs) from premolar teeth, which were extracted from healthy periodontal status patients undergoing orthodontic treatment. Messenger RNA (mRNA) expression in PDL tissue and PDLFs were analyzed using Cap analysis gene expression, which is a second‐generation sequencing technique to create profiling. We also determined the protein expression using Western blot.

Results

Collagens (type I, III, and VI), noncollagenous proteins (periostin and osteonectin), and proteoglycans (asporin, lumican, decorin, and osteomodulin) were highly expressed in PDL tissue. Integrin, β1 was also expressed in PDL tissue. On comparison of gene expression between PDL tissue and PDLFs, four PDL marker genes, osteopontin, asporin, periostin, and osteonectin, were decreased in PDLFs. The genes for gene regulation were also highly expressed.

Conclusions

Our study demonstrated the overall profiling of mRNA expression in PDL tissue and analyzed the important genes which may be useful for providing specific information for the reconstruction of PDL. We also identified the difference in gene expression between PDL tissue and PDLFs which might provide insights towards PDL regeneration.

Collagen XIV Is an Intrinsic Regulator of Corneal Stromal Structure and Function

Collagen XIV is poorly characterized in the body, and the current knowledge of its function in the cornea is limited. The aim of the current study was to elucidate the role(s) of collagen XIV in regulating corneal stromal structure and function. Analysis of collagen XIV expression, temporal and spatial, was performed at different postnatal days (Ps) in wild-type C57BL/6 mouse corneal stromas and after injury. Conventional collagen XIV null mice were used to inquire the roles that collagen XIV plays in fibrillogenesis, fibril packing, and tissue mechanics. Fibril assembly and packing as well as stromal organization were evaluated using transmission electron microscopy and second harmonic generation microscopy. Atomic force microscopy was used to assess stromal stiffness. Col14a1 mRNA expression was present at P4 to P10 and decreased at P30. No immunoreactivity was noted at P150. Abnormal collagen fibril assembly with a shift toward larger-diameter fibrils and increased interfibrillar spacing in the absence of collagen XIV was found. Second harmonic generation microscopy showed impaired fibrillogenesis in the collagen XIV null stroma. Mechanical testing suggested that collagen XIV confers stiffness to stromal tissue. Expression of collagen XIV is up-regulated following injury. This study indicates that collagen XIV plays a regulatory role in corneal development and in the function of the adult cornea. The expression of collagen XIV is recapitulated during wound healing.

The critical role of collagen VI in lung development and chronic lung disease

Type VI collagen (collagen VI) is an obligate extracellular matrix component found mainly in the basement membrane region of many mammalian tissues and organs, including skeletal muscle and throughout the respiratory system. Collagen VI is probably most recognized in medicine as the genetic cause of a spectrum of muscular dystrophies, including Ullrich Congenital Myopathy and Bethlem Myopathy. Collagen VI is thought to contribute to myopathy, at least in part, by mediating muscle fiber integrity by anchoring myoblasts to the muscle basement membrane. Interestingly, collagen VI myopathies present with restrictive respiratory insufficiency, thought to be due primarily to thoracic muscular weakening. Although it was recently recognized as one of the (if not the) most abundant collagens in the mammalian lung, there is a substantive knowledge gap concerning its role in respiratory system development and function. A few studies have suggested that collagen VI insufficiency is associated with airway epithelial cell survival and altered lung function. Our recent work suggested collagen VI may be a genomic risk factor for chronic lung disease in premature infants. Using this as motivation, we thoroughly assessed the role of collagen VI in lung development and in lung epithelial cell biology. Here, we describe the state-of-the-art for collagen VI cell and developmental biology within the respiratory system, and reveal its essential roles in normal developmental processes and airway epithelial cell phenotype and intracellular signaling.

Collagen Biosynthesis, Processing, and Maturation in Lung Ageing

In addition to providing a macromolecular scaffold, the extracellular matrix (ECM) is a critical regulator of cell function by virtue of specific physical, biochemical, and mechanical properties. Collagen is the main ECM component and hence plays an essential role in the pathogenesis and progression of chronic lung disease. It is well-established that many chronic lung diseases, e.g., chronic obstructive pulmonary disease (COPD) and idiopathic pulmonary fibrosis (IPF) primarily manifest in the elderly, suggesting increased susceptibility of the aged lung or accumulated alterations in lung structure over time that favour disease. Here, we review the main steps of collagen biosynthesis, processing, and turnover and summarise what is currently known about alterations upon lung ageing, including changes in collagen composition, modification, and crosslinking. Recent proteomic data on mouse lung ageing indicates that, while the ER-resident machinery of collagen biosynthesis, modification and triple helix formation appears largely unchanged, there are specific changes in levels of type IV and type VI as well as the two fibril-associated collagens with interrupted triple helices (FACIT), namely type XIV and type XVI collagens. In addition, levels of the extracellular collagen crosslinking enzyme lysyl oxidase are decreased, indicating less enzymatically mediated collagen crosslinking upon ageing. The latter contrasts with the ageing-associated increase in collagen crosslinking by advanced glycation endproducts (AGEs), a result of spontaneous reactions of protein amino groups with reactive carbonyls, e.g., from monosaccharides or reactive dicarbonyls like methylglyoxal. Given the slow turnover of extracellular collagen such modifications accumulate even more in ageing tissues. In summary, the collective evidence points mainly toward age-induced alterations in collagen composition and drastic changes in the molecular nature of collagen crosslinks. Future work addressing the consequences of these changes may provide important clues for prevention of lung disease and for lung bioengineering and ultimately pave the way to novel targeted approaches in lung regenerative medicine.

Blood and urinary collagen markers in osteoarthritis: markers of tissue turnover and disease activity

Introduction: The need for diagnostic markers in osteoarthritis (OA) is acute and immediate, as sensitive and precise tools that monitor disease activity and treatment response are lacking. Collagens - types I, II, and III - are the skeleton of the extracellular matrix of joint tissues. Joint collagens are generally turned over at a low rate, but the balance between formation and degradation is disturbed, leading to the loss of, for example, cartilage.Areas covered: We discuss the markers reflecting collagen turnover and provide examples of how they have been applied in OA research, as well as how we believe these should be used in the future. We have searched PubMed for full-text articles written in English using different combinations of the following terms: OA, biomarker, and collagen. The result is a narrative review that gives examples from the literature.Expert opinion: Collagen markers show promise, as they are direct measures of tissue balance. Until now, collagen markers have mainly been tested in observational cohorts, which may provide insights into the association between the candidate marker and clinical variables; however, these do not advance the development of qualified markers that can be used for drug development or in clinical practice.

Fat fibrosis: friend or foe?

At the simplest level, obesity is the manifestation of an imbalance between caloric intake and expenditure; however, the pathophysiological mechanisms that govern the development of obesity and associated complications are enormously complex. Fibrosis within the adipose tissue compartment is one such factor that may influence the development of obesity and/or obesity-related comorbidities. Furthermore, the functional consequences of adipose tissue fibrosis are a matter of considerable debate, with evidence that fibrosis serves both adaptive and maladaptive roles. Tissue fibrosis itself is incompletely understood, and multiple cellular and molecular pathways are involved in the development, maintenance, and resolution of the fibrotic state. Within the context of obesity, fibrosis influences molecular and cellular events that relate to adipocytes, inflammatory cells, inflammatory mediators, and supporting adipose stromal tissue. In this Review, we explore what is known about the interplay between the development of adipose tissue fibrosis and obesity, with a view toward future investigative and therapeutic avenues.

The minor collagens in articular cartilage

Articular cartilage is a connective tissue consisting of a specialized extracellular matrix (ECM) that dominates the bulk of its wet and dry weight. Type II collagen and aggrecan are the main ECM proteins in cartilage. However, little attention has been paid to less abundant molecular components, especially minor collagens, including type IV, VI, IX, X, XI, XII, XIII, and XIV, etc. Although accounting for only a small fraction of the mature matrix, these minor collagens not only play essential structural roles in the mechanical properties, organization, and shape of articular cartilage, but also fulfil specific biological functions. Genetic studies of these minor collagens have revealed that they are associated with multiple connective tissue diseases, especially degenerative joint disease. The progressive destruction of cartilage involves the degradation of matrix constituents including these minor collagens. The generation and release of fragmented molecules could generate novel biochemical markers with the capacity to monitor disease progression, facilitate drug development and add to the existing toolbox for in vitro studies, preclinical research and clinical trials.

Collagen VI at a glance

Collagen VI represents a remarkable extracellular matrix molecule, and in the past few years, studies of this molecule have revealed its involvement in a wide range of tissues and pathological conditions. In addition to its complex multi-step pathway of biosynthesis and assembly that leads to the formation of a characteristic and distinctive network of beaded microfilaments in the extracellular matrix, collagen VI exerts several key roles in different tissues. These range from unique biomechanical roles to cytoprotective functions in different cells, including myofibers, chondrocytes, neurons, fibroblasts and cardiomyocytes. Indeed, collagen VI has been shown to exert a surprisingly broad range of cytoprotective effects, which include counteracting apoptosis and oxidative damage, favoring tumor growth and progression, regulating autophagy and cell differentiation, and even contributing to the maintenance of stemness. In this Cell Science at a Glance article and the accompanying poster, we present the current knowledge of collagen VI, and in particular, discuss its relevance in stemness and in preserving the mechanical properties of tissues, as well as its links with human disorders.

Defective collagen VI α6 chain expression in the skeletal muscle of patients with collagen VI-related myopathies

Collagen VI is a non-fibrillar collagen present in the extracellular matrix (ECM) as a complex polymer; the mainly expressed form is composed of α1, α2 and α3 chains; mutations in genes encoding these chains cause myopathies known as Ullrich congenital muscular dystrophy (UCMD), Bethlem myopathy (BM) and myosclerosis myopathy (MM). The collagen VI α6 chain is a recently identified component of the ECM of the human skeletal muscle. Here we report that the α6 chain was dramatically reduced in skeletal muscle and muscle cell cultures of genetically characterized UCMD, BM and MM patients, independently of the clinical phenotype, the gene involved and the effect of the mutation on the expression of the “classical” α1α2α3 heterotrimer. By contrast, the collagen VI α6 chain was normally expressed or increased in the muscle of patients affected by other forms of muscular dystrophy, the overexpression matching with areas of increased fibrosis. In vitro treatment with TGF-β1, a potent collagen inducer, promoted the collagen VI α6 chain deposition in the ECM of normal muscle cells, whereas, in cultures derived from collagen VI-related myopathy patients, the collagen VI α6 chain failed to develop a network outside the cells and accumulated in the endoplasmic reticulum. The defect of the α6 chain points to a contribution to the pathogenesis of collagen VI-related disorders.

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Collagen VI is an ECM component of the human skeletal muscle.

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We evaluated the α6 chain in collagen VI-related and other muscular dystrophies.

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The α6 chain was reduced in collagen VI-related diseases but not in other myopathies.

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A correlation between the α6 chain and fibrosis was demonstrated in MDC1A.

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The α6 chain is involved in the pathogenesis of collagen VI diseases and fibrosis.

Effect of mechanical strain on the collagen VI pericellular matrix in anterior cruciate ligament fibroblasts

Cell-extracellular matrix interaction plays a major role in maintaining the structural integrity of connective tissues and sensing changes in the biomechanical environment of cells. Collagen VI is a widely expressed non-fibrillar collagen, which regulates tissues homeostasis. The objective of the present investigation was to extend our understanding of the role of collagen VI in human ACL. This study shows that collagen VI is associated both in vivo and in vitro to the cell membrane of knee ACL fibroblasts, contributing to the constitution of a microfibrillar pericellular matrix. In cultured cells the localization of collagen VI at the cell surface correlated with the expression of NG2 proteoglycan, a major collagen VI receptor. The treatment of ACL fibroblasts with anti-NG2 antibody abolished the localization of collagen VI indicating that collagen VI pericellular matrix organization in ACL fibroblasts is mainly mediated by NG2 proteoglycan. In vitro mechanical strain injury dramatically reduced the NG2 proteoglycan protein level, impaired the association of collagen VI to the cell surface, and promoted cell cycle withdrawal. Our data suggest that the injury-induced alteration of specific cell-ECM interactions may lead to a defective fibroblast self-renewal and contribute to the poor regenerative ability of ACL fibroblasts.

Type I collagen-functionalized supported lipid bilayer as a cell culture platform

The supported phospholipid bilayer serves as an important biomimetic model for the cell membrane in both basic and applied scientific research. We have constructed a biomimetic platform based on a supported phospholipid bilayer that is functionalized with type I collagen to serve as a substrate for cell culture. To create the type I collagen-functionalized lipid bilayer assembly, a simple chemical approach was employed: lipid vesicles composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine-N-(glutaryl) (DP-NGPE), a carboxylic acid-functionalized phospholipid, were prepared and then fused onto an SiO(2) substrate to form a supported lipid bilayer. Subsequently, type I collagen molecules were introduced to form stable collagen-lipid conjugates via amide linkages with activated DP-NGPE lipids. The binding kinetics of the conjugation process and the resultant changes in film thickness and viscoelasticity were followed using the quartz crystal microbalance with dissipation (QCM-D) monitoring. The morphology of the conjugated collagen adlayer was investigated with atomic force microscopy (AFM). We observed that the adsorbed collagen molecules tended to self-assemble into fibrillar structures. Fluorescence recovery after photobleaching (FRAP) was utilized to estimate lateral lipid mobility, which was reduced by up to 20% after the coupling of type I collagen to the underlying lipid bilayer. As a cell culture platform, the collagen-conjugated supported lipid bilayer showed promising results. Smooth muscle cells (A10) retained normal growth behavior on the collagen-functionalized platform, unlike the bare POPC lipid bilayer and the POPC/DG-NGPE bilayer without collagen. The biomimetic functionalized lipid system presented here is a simple, yet effective approach for constructing a cell culture platform to explore the interactions between extracellular matrix components and cells.

Three novel collagen VI chains with high homology to the alpha3 chain

Here we describe three novel collagen VI chains, alpha4, alpha5, and alpha6. The corresponding genes are arranged in tandem on mouse chromosome 9. The new chains structurally resemble the collagen VI alpha3 chain. Each chain consists of seven von Willebrand factor A domains followed by a collagenous domain, two C-terminal von Willebrand factor A domains, and a unique domain. In addition, the collagen VI alpha4 chain carries a Kunitz domain at the C terminus, whereas the collagen VI alpha5 chain contains an additional von Willebrand factor A domain and a unique domain. The size of the collagenous domains and the position of the structurally important cysteine residues within these domains are identical between the collagen VI alpha3, alpha4, alpha5, and alpha6 chains. In mouse, the new chains are found in or close to basement membranes. Collagen VI alpha1 chain-deficient mice lack expression of the new collagen VI chains implicating that the new chains may substitute for the alpha3 chain, probably forming alpha1alpha2alpha4, alpha1alpha2alpha5, or alpha1alpha2alpha6 heterotrimers. Due to a large scale pericentric inversion, the human COL6A4 gene on chromosome 3 was broken into two pieces and became a non-processed pseudogene. Recently COL6A5 was linked to atopic dermatitis and designated COL29A1. The identification of novel collagen VI chains carries implications for the etiology of atopic dermatitis as well as Bethlem myopathy and Ullrich congenital muscular dystrophy.

Impact of Carbamylation on Type I Collagen Conformational Structure and Its Ability to Activate Human Polymorphonuclear Neutrophils

Carbamylation by urea-derived cyanate is a posttranslational modification of proteins increasing during chronic renal insufficiency, which alters structural and functional properties of proteins and modifies their interactions with cells. We report here the major structural alterations of type I collagen induced by carbamylation. Biophysical methods revealed that carbamylated collagen retained its triple-helical structure, but that slight changes destabilized some regions within the triple helix and decreased its ability to polymerize into normal fibrils. These changes were associated with the incapacity of carbamylated collagen to stimulate polymorphonuclear neutrophil oxidative functions. This process involved their interaction with LFA-1 integrin, but no subsequent p(125)FAK phosphorylation. Carbamylation of collagen might alter interactions between collagen and inflammatory cells in vivo and interfere with the normal remodeling of extracellular matrix, thus participating in the pathophysiological processes occurring during renal insufficiency.

The elongated first fibronectin type III domain of collagen XIV is an inducer of quiescence and differentiation in fibroblasts and preadipocytes

Collagen XIV (CXIV) is a fibril-associated collagen that is mainly expressed in well differentiated tissues and in late embryonic development. Because CXIV is almost absent in proliferating and/or dedifferentiated tissues, a functional role in maintaining cell differentiation is suspected. We demonstrate antiproliferative, quiescence- and differentiation-inducing effects of human CXIV and its recombinant fragments on mesenchymal cells. In primary human fibroblasts, in mouse 3T3 fibroblasts and in 3T3-L1 preadipocytes, CXIV reduced de novo DNA synthesis by 75%, whereas cell numbers and viability remained unaltered. Cells showed no signs of apoptosis, and maximal proliferation was restored when serum was supplemented, thus indicating that CXIV induced reversible cellular quiescence. Exposure of fibroblasts to CXIV in vitro led to cellular bundles and clusters. CXIV also triggered trans-differentiation of 3T3-L1 preadipocytes into adipocytes, as could be shown by lipid accumulation and by expression of the glucose transporter Glut4. These effects were also observed with the amino-terminal recombinant fragment Gln(29)-Pro(154) that harbors the first fibronectin type III domain and a 39-amino-acid extension, whereas no activity was found for all other recombinant CXIV fragments. Based on these finding the development of small molecular analogs that modulate fibroblast cell growth and differentiation, e.g. in wound healing and fibrosis, seems feasible.

Molecular Structure and Interaction of Recombinant Human Type XVI Collagen

Collagen XVI is a minor component of at least two different extracellular fibrillar networks of specialized regions of skin and cartilage. In skin, collagen XVI is integrated into particular fibrillin-rich microfibrils lacking an amorphous elastin core. In cartilage, collagen XVI is a component of small heterotypic D-banded fibrils, mainly occurring in the territorial matrix of chondrocytes. Here, we present the first direct evidence for the molecular structure and functional properties of these fibril-associated collagens with interrupted triple helices (FACIT). We have expressed recombinantly the full-length alpha1 chain of human collagen XVI in HEK 293 EBNA cells in large quantities using an episomal expression system. Secreted full-length recombinant collagen XVI forms stable disulfide-bonded homotrimers and is rapidly proteolytically processed to distinct fragments at specific protease sequence motifs, one resembling an aggrecanase recognition site. Limited trypsin digestion assays and thermal transition curves imply sequential thermal denaturation of individual triple helical domains of this recombinant collagen, similar to authentic collagen XVI. Molecular images of collagen XVI reveal rod-like molecules which harbor multiple sharp kinks attributing a highly flexible structure presumably introduced by non-collagenous (NC) regions. Terminally located cloverleaf-shaped nodules correspond to the large NC NC11 domain of trimeric collagen XVI. The total length of individual trimeric recombinant collagen XVI molecules constitutes about 240 nm as calculated by atomic force and negative staining electron microscopy. Recombinant collagen XVI interacts with fibrillin-1 and with fibronectin indicating multiple molecular interactions in which this ubiquitously expressed and versatile FACIT-collagen can participate. In vitro generated collagen XVI provides an indispensable tool for future determination of its function during supramolecular assembly of matrix aggregates and its role in maintenance, organization and interaction of fibrillar structures.

A novel multi-domain mucin-like glycoprotein of Cryptosporidium parvum mediates invasion

Cryptosporidium parvum is a protozoan parasite which produces self-limited disease in immunocompetent hosts and devastating, persistent diarrhea in immunocompromised individuals. There is no effective treatment for cryptosporidiosis and little is known about the basic biology of the organism. Cloning and sequence analysis of the gene encoding GP900, a previously identified > 900 kDa glycoprotein, predicts a mucin-like glycoprotein composed of distal cysteine-rich domains separated by polythreonine domains and a large membrane proximal N-glycosylated core region. A trinucleotide repeat composed predominantly of the triplet ACA encodes the threonine domains. GP900 is stored in micronemes prior to appearance on the surface of invasive forms. The concentration of native GP900 which inhibits 50% (IC50) of invasion in vitro is low picomolar; the IC50 for a recombinant cysteine rich-domain is low nanomolar. These observations indicate that GP900 is a parasite ligand for a host receptor involved in attachment/invasion and suggest that immunotherapy or chemotherapy directed against GP900 may be feasible.

Identification and characterization of a heparin binding site within the NC1 domain of chicken collagen XIV

Collagen XIV is known to bind to the dermatan sulfate chain of decorin and to the heparan sulfate chain of perlecan. To study its possible interaction with glycosaminoglycans, the NC1 domain of chicken collagen XIV was overproduced in E. coli. Purified NC1*(6-119)* appears poorly organized (the asterisks indicate the presence of extension sequences), but V8-protease generated fragments containing the 84-108 basic sequence tend to fold into alpha-helix. These fragments interact specifically with heparin, which induces an alpha-helical fold with a maximum effect for equimolar heparin/peptide ratio. These data demonstrate the existence of a glycosaminoglycan binding site in NC1.

Cell binding properties of collagen type XIV for human hematopoietic cells

Collagen XIV, which belongs to the subclass of fibril-associated collagens with interrupted triple helices (FACITs), is a homotrimeric molecule consisting of three alpha 1 (XIV) chains. Collagen type XIV is strongly expressed in the native human bone marrow, as shown by immunofluorescence staining and immunoblotting with an affinity-purified antibody. Hematopoietic cell lines of myeloid (KG1a, U937, K562) and lymphoid (U266, IM-9) origin were able to attach firmly to purified human collagen XIV preparations. Attachment of these cells was shown to be concentration-dependent. However, other hematopoietic cell lines tested were unable to adhere to collagen XIV, indicating restriction of this cellular interaction. The cellular receptors involved in cell binding to collagen type XIV are probably membrane-bound heparansulfate proteoglycans, since only the the addition of heparin inhibited attachment of the hematopoietic cells to collagen XIV in a concentration-dependent manner. Antibodies against the beta 1-integrin subunit could not interfere with binding to collagen type XIV. Using purified fragments of collagen XIV, it could be demonstrated that at least two different heparin-sensitive adhesion sites are present in the N-terminal globular domain and in the triple-helical domain. These data indicate that collagen XIV represents another collagen type expressed in human bone marrow with strong cell binding properties for defined populations of hematopoietic cells.

Complete primary structure of human collagen type XIV (undulin)

A partial cDNA sequence coding for the human extracellular matrix protein undulin has been completed. The completed sequence provides conclusive evidence for the suggested identity of undulin and collagen type XIV. Two differently sized polyproteins of 1780 and 1796 amino acids, with an overall amino acid sequence identity of 75% compared to chicken CXIV, emerge from variant 3' sequence ends encoding the C-terminal non-collagenous (NC) NC1 domain of human collagen type XIV.

Involvement of prolyl 4-hydroxylase in the assembly of trimeric minicollagen XII. Study in a baculovirus expression system

We have shown previously that hydroxylation played a critical role in the trimer assembly and disulfide bonding of the three constituent alpha chains of a minicollagen composed of the extreme C-terminal collagenous (COL1) and noncollagenous (NC1) domains of type XII collagen in HeLa cells (Mazzorana, M., Gruffat, H., Sergeant, A., and van der Rest, M. (1993) J. Biol. Chem. 268, 3029-3032). We have further characterized the involvement of prolyl 4-hydroxylase in the assembly of the three alpha chains to form trimeric disulfide-bonded type XII minicollagen in an insect cell expression system. For this purpose, type XII minicollagen was produced in insect cells from baculovirus vectors, alone or together with wild-type human prolyl 4-hydroxylase or with the human enzyme mutated in the catalytic site of its alpha or beta subunits or with the individual alpha or beta subunits. When type XII minicollagen was produced alone, negligible amounts of disulfide-bonded trimers were found to be produced by the cells. However, coproduction of the collagen with the two subunits of the wild-type human enzyme dramatically increased the amount of disulfide-bonded trimeric type XII minicollagen molecules. In contrast, coproduction of the collagen with alpha subunits that had a mutation completely inactivating the human enzyme failed to enhance the trimer assembly. These results directly show that an active prolyl 4-hydroxylase is required for the assembly of disulfide-bonded trimers of type XII minicollagen.

Congenital muscular dystrophy with laminin alpha 2 chain deficiency: identification of a new intermediate phenotype and correlation of clinical findings to muscle immunohistochemistry

The laminins comprise of a family of heterotrimeric proteins of the extracellular matrix. The crossshaped proteins consist of a heavy alpha-chain and two light chains, called beta and gamma. Each group of chains, classified on their sequence identity and domain organization, include different isoforms. A deficiency of the alpha 2 chain of laminin-2, previously termed merosin or M component, was shown to be responsible for one form of congenital muscular dystrophy (CMD). We investigated muscle biopsies of 20 patients with the clinical diagnosis of CMD and histological evidence of muscular dystrophy for the expression of different laminin chains. Patients with evidence of pachygyria/lissencephaly of the CNS were excluded from this series. The immunohistochemical analysis was correlated to clinical findings and MRI data of the brain. Of 20 patients, 11 (55%) revealed complete or near-complete deficiency of the alpha 2 chain in their skeletal muscle specimens. So far none of these patients became ambulant. Of 20 patients 2 showed partial but clear-cut alpha 2 chain-deficiency. These two patients became ambulant at 18 months and 3 years. All 13 patients with complete or partial alpha 2 chain-deficiency demonstrated cerebral white matter changes on MRI. In contrast, 6/7 CMD patients with normal alpha 2 chain expression became ambulant and none of the 6/7 tested showed evidence of cerebral abnormal T2 sequence signal of the myelin on MRI.

CONCLUSION

Our findings emphasize the use of immunohistochemistry for laminin alpha 2 as a diagnostic tool in defining CMD and characterize a milder phenotype with partial alpha 2 chain-deficiency.

Trimeric assembly of collagen XII: effect of deletion of the C-terminal part of the molecule

The fibril-associated-collagens-with-interrupted-triple-helices (FACITs) are devoid of large C-propeptides like those involved in the trimeric assembly of the fibrillar collagens. Under these conditions, the C-terminal non triple-helical domain (NC1) and the adjacent triple-helical domain (COL1) are likely to be responsible for the trimeric assembly of these collagen molecules. Using a recombinant minigene of one of the FACITs, collagen XII, we show that a deletion covering most of the NC1 domain, except the first seven residues containing a cysteine and constituting the main part of the conserved junction between the COL1 and NC1 domains, does not prevent the formation of trimeric disulfide-bonded assembly of truncated alpha chains. These results suggest that if the non triple-helical NC1 domain is involved in the initial events governing the trimeric assembly, it must be through its amino acid residues participating in the junction. Our data confirm also the results obtained in a previous paper (Mazzorana et al.: J. Biol. Chem. 268:3029-3032, 1993) showing that the formation of disulfide bonds is dependent on hydroxylation and suggesting that the folding of the triple helix (or a part of it) precedes the formation of the disulfide bonds.