Collagen XIII Research Articles

Congenital Myasthenic Syndrome Type 19 Is Caused by Mutations in COL13A1, Encoding the Atypical Non-fibrillar Collagen Type XIII α1 Chain

The neuromuscular junction (NMJ) consists of a tripartite synapse with a presynaptic nerve terminal, Schwann cells that ensheathe the terminal bouton, and a highly specialized postsynaptic membrane. Synaptic structural integrity is crucial for efficient signal transmission. Congenital myasthenic syndromes (CMSs) are a heterogeneous group of inherited disorders that result from impaired neuromuscular transmission, caused by mutations in genes encoding proteins that are involved in synaptic transmission and in forming and maintaining the structural integrity of NMJs. To identify further causes of CMSs, we performed whole-exome sequencing (WES) in families without an identified mutation in known CMS-associated genes. In two families affected by a previously undefined CMS, we identified homozygous loss-of-function mutations in COL13A1, which encodes the alpha chain of an atypical non-fibrillar collagen with a single transmembrane domain. COL13A1 localized to the human muscle motor endplate. Using CRISPR-Cas9 genome editing, modeling of the COL13A1 c.1171delG (p.Leu392Sfs∗71) frameshift mutation in the C2C12 cell line reduced acetylcholine receptor (AChR) clustering during myotube differentiation. This highlights the crucial role of collagen XIII in the formation and maintenance of the NMJ. Our results therefore delineate a myasthenic disorder that is caused by loss-of-function mutations in COL13A1, encoding a protein involved in organization of the NMJ, and emphasize the importance of appropriate symptomatic treatment for these individuals.

Fibrillar, fibril-associated and basement membrane collagens of the arterial wall: architecture, elasticity and remodeling under stress.

The ability of a human artery to pass through 150 million liters of blood sustaining 2 billion pulsations of blood pressure with minor deterioration depends on unique construction of the arterial wall. Viscoelastic properties of this construction enable to re-seal the occuring damages apparently without direct immediate participance of the constituent cells. Collagen structures are considered to be the elements that determine the mechanoelastic properties of the wall in parallel with elastin responsible for elasticity and resilience. Collagen scaffold architecture is the function-dependent dynamic arrangement of a dozen different collagen types composing three distinct interacting forms inside the extracellular matrix of the wall. Tightly packed molecules of collagen types I, III, V provide high tensile strength along collagen fibrils but toughness of the collagen scaffold as a whole depends on molecular bonds between distinct fibrils. Apart of other macromolecules in the extracellular matrix (ECM), collagen-specific interlinks involve microfilaments of collagen type VI, meshwork-organized collagen type VIII, and FACIT collagen type XIV. Basement membrane collagen types IV, XV, XVIII and cell-associated collagen XIII enable transmission of mechanical signals between cells and whole artery matrix. Collagen scaffold undergoes continuous remodeling by decomposition promoted with MMPs and reconstitution from newly produced collagen molecules. Pulsatile stress-strain load modulates both collagen synthesis and MMP-dependent collagen degradation. In this way the ECM structure becomes adoptive to mechanical challenges. The mechanoelastic properties of the arterial wall are changed in atherosclerosis concomitantly with collagen turnover both type-specific and dependent on the structure. Improving the feedback could be another approach to restore sufficient blood circulation.

Thyroid-stimulating immunoglobulins as measured in a reporter bioassay are not detected in patients with Hashimoto's thyroiditis and ophthalmopathy or isolated upper eyelid retraction.

Although ophthalmopathy is mainly associated with Graves’ hyperthyroidism, milder eye changes are also found in about 25% of patients with Hashimoto’s thyroiditis (HT). The recent finding of negative thyrotropin receptor (TSHR) antibodies, as measured in the Thyretain™ thyroid-stimulating immunoglobulin (TSI) reporter bioassay, in patients with euthyroid Graves’ disease raises the possibility that TSHR antibodies are not the cause of ophthalmopathy in all situations. Here, we have tested serum from patients with HT with and without ophthalmopathy or isolated upper eyelid retraction (UER) for TSHR antibodies, using the TSI reporter bioassay and collagen XIII as a marker of autoimmunity against the orbital fibroblast. Study groups were 23 patients with HT with ophthalmopathy, isolated UER, or both eye features and 17 patients without eye signs. Thyretain™ TSI results were expressed as a percentage of the sample-to-reference ratio, with a positive test being taken as a sample-to-reference ratio of more than 140%. Serum collagen XIII antibodies were measured in standard enzyme-linked immunosorbent assay. TSI tests were positive in 22% of patients with HT with no eye signs but in no patient with eye signs. In contrast, TSI tests were positive in 94% of patients with Graves’ ophthalmopathy. Tests were negative in all normal subjects tested. Collagen XIII antibodies were detected in 83% of patients with ophthalmopathy, UER, or both eye features, but in only 30% of patients with no eye signs. Our findings suggest that TSHR antibodies do not play a major role in the pathogenesis of ophthalmopathy or isolated UER in patients with HT. Moreover, the role of TSHR antibodies in the development of ophthalmopathy in patients with Graves’ disease remains to be proven. In contrast, collagen XIII antibodies appear to be a good marker of eye disease in patients with HT.

Synaptic basal lamina–associated congenital myasthenic syndromes

Proteins associated with the basal lamina (BL) participate in complex signal transduction processes that are essential for the development and maintenance of the neuromuscular junction (NMJ). Most important junctional BL proteins are collagens, such as collagen IV (α3-6), collagen XIII, and ColQ; laminins; nidogens; and heparan sulfate proteoglycans, such as perlecan and agrin. Mice lacking Colq (Colq(-/-)), laminin β2 (Lamb2(-/-)), or collagen XIII (Col13a1(-/-)) show immature nerve terminals enwrapped by Schwann cell projections that invaginate into the synaptic cleft and decrease contact surface for neurotransmission. Human mutations in COLQ, LAMB2, and AGRN cause congenital myasthenic syndromes (CMSs) owing to deficiency of ColQ, laminin-β2, and agrin, respectively. In these syndromes the NMJ ultrastructure shows striking resemblance to that of mice lacking the corresponding protein; furthermore, the extracellular localization of mutant proteins may provide favorable conditions for replacement strategies based on gene therapy and stem cells.

Eye findings and immunological markers in probands and their euthyroid relatives from a single family with multiple cases of thyroid autoimmunity

BackgroundOphthalmopathy is a common manifestation of Graves’ disease (GD) occurring in up to 50% of patients. Mild eye signs are also common in patients with Hashimoto’s thyroiditis. Whilst a genetic predisposition to GD has been demonstrated this is not the case for the ophthalmopathy which often runs a separate course.ObjectiveWe determined the prevalences of eye and eyelid signs and positive thyroid and orbital antibody tests in first and second degree relatives from a single family with multiple cases of Graves’ disease, ophthalmopathy and Hashimoto’s thyroiditis.DesignThe study cohort comprised 16 subjects from the same family, 4 probands namely, 3 with GD and one with Hashimoto’s thyroiditis and hypothyroidism and 12 of their euthyroid first or second degree relatives. We measured antibodies against calsequestrin (CASQ1) and collagen XIII in an enzyme-linked-immunosorbent assays and TSH-Receptor (TSH-R) antibodies as i) TSH-R binding inhibiting immunoglobulin (TBII) and ii) thyroid stimulating immunoglobulin (TSI). Eye signs were classified and quantified using the clinical activity score (CAS), NOSPECS classes, Nunery types 1 and 2 and the margin-reflex-distance (MRD) as a measure of upper eyelid retraction (UER).Main outcomesWhilst significant ophthalmopathy was uncommon in the relatives, mild eye signs, in particular UER, were demonstrated in about a third of them. The presence of eye signs was moderately, but not significantly, associated with the detection of CASQ1 and collagen XIII antibodies, but not TSH-R antibodies.ConclusionOur study demonstrates a significant prevalence of positive orbital antibody tests and ophthalmopathy in probands with thyroid autoimmunity and their euthyroid relatives, favouring a role of genetic factors in the development of ophthalmopathy in patients with thyroid autoimmunity.

Collagen XIII: A type II transmembrane protein with relevance to musculoskeletal tissues, microvessels and inflammation

Collagen XIII and the homologous collagens XXIII and XXV form a subgroup of type II transmembrane proteins within the collagen superfamily. Collagen XIII consists of a short cytosolic domain, a transmembrane domain and a large extracellular ectodomain, which may be shed into the pericellular matrix. It has been proposed that collagen XIII may function as an adhesion molecule, due to its cellular localization at focal contacts, numerous interactions with basement membrane (BM) and other extracellular matrix (ECM) proteins and expression at various cell–cell and cell–matrix junctions. Recent in vivo studies highlight its involvement in the development, differentiation and maturation of musculoskeletal tissues and vessels and in maintaining tissue integrity.

Long-term follow-up of seven patients with ophthalmopathy not associated with thyroid autoimmunity: heterogeneity of autoimmune ophthalmopathy.

BackgroundOphthalmopathy is the most common extrathyroidal manifestation of Graves’ disease. However, in approximately 5% of cases this autoimmune eye disorder occurs in the apparent absence of Graves’ hyperthyroidism: the so-called euthyroid Graves’ disease (EGD).MethodsSeven patients with EGD were followed for evidence of thyroid and orbital autoimmunity, for up to 10 years. Calsequestrin and collagen XIII antibodies were measured by enzyme linked immunosorbent assay (ELISA), and TSH-receptor (TSH-r) antibodies were measured as TSH-r-binding antibody (TRAb) and thyroid-stimulating immunoglobulin (TSI). Eye signs were characterized and quantified as clinical activity score (CAS), NOSPECS classes, Nunery types 1 and 2, and margin-reflex distance (MRD).ResultsCalsequestrin antibodies were detected on at least one occasion in three of the seven patients and collagen XIII antibodies were detected one or more times in five patients. In one patient with isolated congestive ophthalmopathy who was studied intensely, collagen XIII antibodies were initially positive and then became negative as the eye disease stabilized, while antibodies targeting calsequestrin were always negative. TRAb was not detected in any patient, but TSI was detected in three patients on one occasion each. Ultrasound abnormalities were found in four of the six patients for whom this was carried out, but there was no clear evidence for thyroiditis in any of these patients. For comparison, 13 patients were studied with typical Graves’ ophthalmopathy. There were no significant differences compared to EGD in respect to the prevalence of positive calsequestrin or collagen XIII antibodies, but these patients included more smokers (eight out of 13 versus none out of seven).ConclusionsEarlier studies suggesting that patients with EGD eventually develop thyroid dysfunction have not been confirmed here, although follow-up continues, and the possibility that such patients have had thyroid autoimmunity in the past, or that they will develop it in the future cannot be excluded. Overall, it is likely that the ophthalmopathy associated with Graves’ hyperthyroidism is the same disease as that observed in patients – such as those reported here – in whom thyroid dysfunction and thyroid autoimmunity are not present during the period of follow- up. The role of autoimmunity against the TSH-r in euthyroid patients with ophthalmopathy has not been proven and the significance of the orbital antibodies is unclear.

Role of extracellular matrix proteins and their receptors in the development of the vertebrate neuromuscular junction

The vertebrate neuromuscular junction (NMJ) remains the best-studied model for understanding the mechanisms involved in synaptogenesis, due to its relatively large size, its simplicity of patterning, and its unparalleled experimental accessibility. During neuromuscular development, each skeletal myofiber secretes and deposits around its extracellular surface an assemblage of extracellular matrix (ECM) proteins that ultimately form a basal lamina. This is also the case at the NMJ, where the motor nerve contributes additional factors. Before most of the current molecular components were known, it was clear that the synaptic ECM of adult skeletal muscles was unique in composition and contained factors sufficient to induce the differentiation of both pre- and postsynaptic membranes. Biochemical, genetic, and microscopy studies have confirmed that agrin, laminin (221, 421, and 521), collagen IV (α3-α6), collagen XIII, perlecan, and the ColQ-bound form of acetylcholinesterase are all synaptic ECM proteins with important roles in neuromuscular development. The roles of their many potential receptors and/or binding proteins have been more difficult to assess at the genetic level due to the complexity of membrane interactions with these large proteins, but roles for MuSK-LRP4 in agrin signaling and for integrins, dystroglycan, and voltage-gated calcium channels in laminin-dependent phenotypes have been identified. Synaptic ECM proteins and their receptors are involved in almost all aspects of synaptic development, including synaptic initiation, topography, ultrastructure, maturation, stability, and transmission.

Collagen XIII Induced in Vascular Endothelium Mediates α1β1 Integrin-Dependent Transmigration of Monocytes in Renal Fibrosis

Alport syndrome is a common hereditary basement membrane disorder caused by mutations in the collagen IV α3, α4, or α5 genes that results in progressive glomerular and interstitial renal disease. Interstitial monocytes that accumulate in the renal cortex from Alport mice are immunopositive for integrin α1β1, while only a small fraction of circulating monocytes are immunopositive for this integrin. We surmised that such a disparity might be due to the selective recruitment of α1β1-positive monocytes. In this study, we report the identification of collagen XIII as a ligand that facilitates this selective recruitment of α1β1 integrin-positive monocytes. Collagen XIII is absent in the vascular endothelium from normal renal cortex and abundant in Alport renal cortex. Neutralizing antibodies against the binding site in collagen XIII for α1β1 integrin selectively block VLA1-positive monocyte migration in transwell assays. Injection of these antibodies into Alport mice slows monocyte recruitment and protects against renal fibrosis. Thus, the induction of collagen XIII in endothelial cells of Alport kidneys mediates the selective recruitment of α1β1 integrin-positive monocytes and may potentially serve as a therapeutic target for inflammatory diseases in which lymphocyte/monocyte recruitment involves the interaction with α1β1 integrin.

Muscle-Derived Collagen XIII Regulates Maturation of the Skeletal Neuromuscular Junction

Formation, maturation, stabilization, and functional efficacy of the neuromuscular junction (NMJ) are orchestrated by transsynaptic and autocrine signals embedded within the synaptic cleft. Here, we demonstrate that collagen XIII, a nonfibrillar transmembrane collagen, is another such signal. We show that collagen XIII is expressed by muscle and its ectodomain can be proteolytically shed into the extracellular matrix. The collagen XIII protein was found present in the postsynaptic membrane and synaptic basement membrane. To identify a role for collagen XIII at the NMJ, mice were generated lacking this collagen. Morphological and ultrastructural analysis of the NMJ revealed incomplete adhesion of presynaptic and postsynaptic specializations in collagen XIII-deficient mice of both genders. Strikingly, Schwann cells erroneously enwrapped nerve terminals and invaginated into the synaptic cleft, resulting in a decreased contact surface for neurotransmission. Consistent with morphological findings, electrophysiological studies indicated both postsynaptic and presynaptic defects in Col13a1(-/-) mice, such as decreased amplitude of postsynaptic potentials, diminished probabilities of spontaneous release and reduced readily releasable neurotransmitter pool. To identify the role of collagen XIII at the NMJ, shed ectodomain of collagen XIII was applied to cultured myotubes, and it was found to advance acetylcholine receptor (AChR) cluster maturation. Together with the delay in AChR cluster development observed in collagen XIII-deficient mutants in vivo, these results suggest that collagen XIII plays an autocrine role in postsynaptic maturation of the NMJ. Altogether, the results presented here reveal that collagen XIII is a novel muscle-derived cue necessary for the maturation and function of the vertebrate NMJ.

Rituximab treatment in patients with active Graves' orbitopathy: effects on proinflammatory and humoral immune reactions

In active Graves' orbitopathy (GO), proinflammatory cytokines predominate. Circulating thyroid stimulating hormone (TSH)-receptor antibodies (TRAb) have been correlated with GO clinical activity and severity. In preliminary studies rituximab (RTX), an anti-CD 20 monoclonal antibody, has induced clinical improvement of active GO without a change in serum anti-thyroid antibodies. We have studied whether RTX in GO acts by affecting proinflammatory cytokines and thyroid and orbital-directed antibodies. Ten patients with GO were treated with RTX, administered twice intravenously (i.v.) (1000 mg) at days 1 and 15, and 20 with methylprednisolone, administered weekly i.v. (500 mg), for 16 weeks. Patients were studied before treatment, at B cell depletion and at 4, 8, 16, 20, 30 and 50 weeks. Peripheral lymphocytes, serum interleukin (sIL)-6, sIL-6r, chemokine (C-X-C motif) ligand 10 (CXCL10), TRAb and stimulating antibodies (TSAb) and autoantibodies against orbital calsequestrin, collagen XIII and flavoprotein subunit of succinate dehydrogenase (FP-SDH) were measured at baseline and after treatment. Serum IL-6 and sIL-6R concentrations did not change after RTX [P = not significant (n.s.)]. Serum CXCL10 increased after RTX at B cell depletion and at 30 weeks (P < 0·003). Serum TSAb did not change in relation to TRAb, nor did antibodies against orbital antigens (P = n.s.). In conclusion, this study shows that RTX in GO does not affect humoral reactions. The observed increase of serum CXCL10 concentrations at B cell depletion may result from cell lysis. We suggest that RTX may exert its effect in GO by inhibiting B cell antigen presentation.

Pathogenesis of thyroid-associated ophthalmopathy: does autoimmunity against calsequestrin and collagen XIII play a role?

Thyroid-associated ophthalmopathy (TAO), or thyroid eye disease, is a complex inflammatory disorder of the eye that, as its name implies, is associated with thyroid disease. TAO can be divided into three subtypes: ocular myopathy, congestive myopathy and mixed congestive and myopathic ophthalmopathy. Although the precise pathophysiology of TAO remains unclear it is likely to reflect an autoimmune reaction involving sensitized T-cells and autoantibodies directed against a thyroid and orbital tissue shared antigen. One well studied candidate in this immune reaction is the thyroid-stimulating hormone receptor (TSH-r), expressed in the orbital fibroblast and pre adipocyte. In our studies of TAO, we have investigated the nature and significance of antibodies targeting other eye muscle and orbital connective tissue (OCT) antigens. Our findings suggest that autoimmunity against the eye muscle antigen calsequestrin and the OCT antigen collagen XIII plays a role in the pathogenesis of TAO. We propose that ocular myopathy and chronic eyelid retraction are due to autoimmunity against skeletal muscle calsequestrin in the extraocular and eyelid muscles, respectively. This may be initiated in the thyroid where calsequestrin expression is upregulated, possibly due to a stimulatory effect of TSH-r antibodies. We also propose that congestive ophthalmopathy results from a reaction against the TSH-r or collagen XIII in orbital fibroblast cell membranes. Further insight into the role of eye muscle and OCT antigens in the pathogenesis of TAO may allow for the development of new therapies to treat the eye disorder and reduce patient morbidity.

A Mutant Collagen XIII Alters Intestinal Expression of Immune Response Genes and Predisposes Transgenic Mice to Develop B-Cell Lymphomas

Epithelial cells of mucosal surfaces are critical for maintaining immune homeostasis by aiding in the discrimination of pathogenic and commensal microorganisms and modulating the activities of antigen-presenting cells and lymphocytes. Functional breakdowns resulting in chronic infection and inflammation are associated with the development of hematologic and solid neoplasms for which detailed pathogenetic mechanisms are poorly understood. Mice heterozygous for a transgene Col13a1(del) expressing a mutant collagen XIII developed clonal mature B-cell lineage lymphomas originating in mesenteric lymph nodes (MLN). The tumors were associated with T cells and macrophages. The incidence of disease was reduced 2-fold in transgenic mice raised under specific pathogen-free conditions, suggesting a role for infectious agents. The lymphomas did not express the mutant collagen XIII, indicating that its influence on tumorigenesis was B-cell extrinsic and likely to be associated with collagen XIII-positive tissues drained by the MLN. Studies of the small intestines of transgenic mice showed that the subepithelial basement membranes (BM) were highly abnormal and that they exhibited heightened expression of genes involved in immune responses. These results define collagen XIII-dependent maintenance of the intestinal BM as a previously unappreciated component of immune responses and a critical determinant of cancer susceptibility.

Eye Signs and Serum Eye Muscle and Collagen XIII Antibodies in Patients with Transient and Progressive Thyroiditis

There have been reports of the development of ophthalmopathy in patients with subacute thyroiditis (SAT) in the absence of Graves' disease and thyroid-stimulating hormone receptor (TSH-r) antibodies. The aim of the study was to determine the prevalences of eye and eyelid signs and positive eye muscle and collagen XIII antibody tests in patients with SAT and silent thyroiditis (ST) and in patients with Hashimoto's thyroiditis (HT) as chronic thyroiditis controls. Ophthalmopathy was classified as Nunery type 1 (orbital inflammation, proptosis, without restrictive myopathy) or Nunery type 2 (with restrictive myopathy). We tested for antibodies against calsequestrin, flavoprotein (Fp), G2s, and collagen XIII in 5 patients with SAT, 6 with ST, and 11 with HT, and in 12 age- and sex-matched healthy subjects, using an optimized and standardized enzyme-linked immunosorbent assay (ELISA). At the first visit, eye signs were found in two patients with SAT, one with type 1 ophthalmopathy and one with type 2 ophthalmopathy, and in three patients with ST, two with type 1 ophthalmopathy and one with dominant upper eyelid retraction only. Later in the course of their illness, one other patient with ST developed mild type 1 disease, giving an overall prevalence of any eye signs of 50% in patients with TT. Five patients with HT had mild type 1 ophthalmopathy and dominant upper eyelid retraction. One or more eye muscle antibodies were detected in three patients with SAT, four with ST, and seven with HT, of which calsequestrin and Fp antibodies were the most commonly found. TSH-r antibodies were detected in only one patient with ST, at the time when she developed Graves' hyperthyroidism following an episode of ST. The development of mild, but definite, ophthalmopathy or dominant upper eyelid retraction in patients with TT and chronic (Hashimoto's) thyroiditis in the absence of TSH-r antibodies or Graves' hyperthyroidism is an interesting observation that should be further addressed in larger groups of patients, including those with postpartum thyroiditis. These preliminary findings also raise questions about the mechanism for the link between ophthalmopathy and thyroid autoimmunity.

Collagens at a glance

Collagens are a large family of triple helical proteins that are widespread throughout the body and are important for a broad range of functions, including tissue scaffolding, cell adhesion, cell migration, cancer, angiogenesis, tissue morphogenesis and tissue repair. Collagen is best known as the

Cleavage and Oligomerization of Gliomedin, a Transmembrane Collagen Required for Node of Ranvier Formation

Gliomedin, which has been implicated as a major player in genesis of the nodes of Ranvier, contains two collagenous domains and an olfactomedin-like domain and belongs to the group of type II transmembrane collagens that includes collagens XIII and XVII and ectodysplasin A. One characteristic of this protein family is that constituent proteins can exist in both transmembrane and soluble forms. Recently, gliomedin expressed at the tips of Schwann cell microvilli was found to bind axonal adhesion molecules neurofascin and NrCAM in interactions essential for Na(+)-channel clustering at the nodes of Ranvier in myelinating peripheral nerves. Interestingly, exogenously added olfactomedin domain was found to have the same effect as intact gliomedin. Here we analyze the tissue form of gliomedin and demonstrate that the molecule not only exists as full-length gliomedin but also as a soluble form shed from the cell surface in a furin-dependent manner. In addition, gliomedin can be further proteolytically processed by bone morphogenetic protein 1/Tolloid-like enzymes, resulting in release of the olfactomedin domain from the collagen domains. Interestingly, the later cleavage induces formation of higher order, insoluble molecular aggregates that may play important roles in Na(+)-channel clustering.

Antibodies against Calsequestrin and Type XIII Collagen are Good Markers for Chronic Upper Eyelid Retraction

Purpose: Chronic upper eyelid retraction is a common manifestation of thyroid-associated ophthalmopathy (TAO) but can occur as a dominant feature of ophthalmopathy in patients with Graves’ hyperthyroidism and in association with Hashimoto's thyroiditis in the absence of other eye signs except mild proptosis. Methods: We measured antibodies against calsequestrin, flavoprotein (Fp), G2s, and collagen XIII in an enzyme-linked immunosorbent assay (ELISA) in 15 patients with chronic upper eyelid retraction. Results: Calsequestrin antibodies were detected in 67% of patients with upper eyelid retraction, Fp antibodies in 47%, G2s antibodies in 20%, and collagen XIII antibodies were detected in 40% of these patients at the first visit. These prevalences were significantly greater than normal for calsequestrin and collagen XIII, but not for Fp and G2s antibodies. On follow-up, calsequestrin antibodies were detected in two more patients, for an overall prevalence of 80%. Levels of the four antibodies remained fairly constant over the study period and generally correlated with the presence and severity of upper eyelid signs. Conclusions: These findings support the notion that autoimmune attack against calsequestrin and collagen XIII in the levator palpebrae superioris (LPS) muscle may play a role in the pathogenesis of upper eyelid retraction and that lid retraction may be the dominant feature of ophthalmopathy in patients with Hashimoto's thyroiditis and non-autoimmune thyroid disease. Because calsequestrin is an intracellular protein, the corresponding autoantibodies probably do not initiate LPS muscle inflammation but may contribute to its damage. The mix of antibodies against calsequestrin and collagen XIII may shed light on the diverse presentations found in thyroid-associated ophthalmopathy.

Study of Serum Antibodies Against Three Eye Muscle Antigens and the Connective Tissue Antigen Collagen XIII in Patients with Graves' Disease With and Without Ophthalmopathy: Correlation With Clinical Features

The extraocular muscles are one of the primary tissues implicated in the autoimmune-mediated inflammation of thyroid-associated ophthalmopathy (TAO). Our aim was to determine the prevalence and level of antibodies against three candidate eye muscle antigens and the orbital fibroblast membrane antigen collagen XIII, in well-characterized patient groups. The study cohort consisted of patients with Graves' hyperthyroidism with and without ophthalmopathy, controls patients with other thyroid or other autoimmune disorders and healthy subjects. The presence of eye muscle antibodies was determined using an optimized and standardized enzyme-linked immunosorbent assay. We measured antibodies against (i) the 67-kDa flavoprotein (Fp) subunit of the mitochondrial enzyme succinate dehydrogenase; (ii) G2s, a 141 amino acid fragment of the winged-helix transcription factor FOXP1; (iii) calsequestrin, a 63-kDa calcium-binding protein; and (iv) collagen XIII, a connective tissue protein that is closely linked to the congestive ophthalmopathy subtype of TAO. Eye muscle antibody levels were correlated with clinical diagnosis and presence or not of ophthalmopathy. Prevalences of positive antibody tests to calsequestrin (75.0%) and collagen XIII (43.8%) were significantly greater in Graves' disease (GD) patients with ophthalmopathy than in healthy subjects, whereas modest significance was demonstrated with antibodies against Fp, but not G2s. Significantly greater serum levels of antibodies against calsequestrin, G2s, and collagen XIII, but not Fp, were found in GD patients with ophthalmopathy compared to control patients without eye disease and healthy subjects. Calsequestrin and collagen XIII antibodies are the most specific to TAO, whereas antibodies against G2s, and to a lesser extent Fp, are also markers of ophthalmopathy, but less reliable. These results are unique in that it is the first time the significance of a panel of three candidate eye muscle antibodies and a connective tissue antibody have been evaluated in the same patients with ophthalmopathy.

Les collagènes associés aux membranes basales et leurs matricryptines

The superfamily of collagens is comprised of 27 members (reviewed by Myllyharju & Kivirikko, 2004; Ricard-Blum & Ruggiero, 2005; Ricard-Blum et al., 2005), which are classified into several subgroups according to their structural features and supramolecular assemblies. Fibrillar collagens and FACITS (Fibril-Associated Collagens with Interrupted Triple helix) are described in the paper by Ruggiero et al. in this issue. Our paper reports recent advances on collagens associated to basement membranes. It focuses on the multiplexin family (including collagens XV and XVIII) and on membrane collagens present in skin, namely collagens XIII and XVII. The mechanisms leading to the shedding of their ectodomain from cell membrane and the biological roles of their shedded domains are discussed. The last part of the paper is devoted to several fragments of basement membrane collagens, called matricryptins or matrikins, and to their biological activities.

Serum antibodies to collagen XIII: a further good marker of active Graves’ ophthalmopathy

In Graves' ophthalmopathy (GO) intercellular adhesion molecule-1 (ICAM-1) is thought to play a key role in lymphocyte infiltration into the orbit, and serum levels of its soluble form are positively correlated to clinical activity score (CAS). Serum antibodies against collagen XIII (CollXIIIAb), a plasma membrane protein expressed at a low level in almost all connective tissue-producing cells, have been detected in GO, but their significance is unclear. The aim of this study was to search for CollXIIIAb in Graves' patients with and without ophthalmopathy and to correlate their levels with CAS and with serum soluble ICAM-1 (sICAM-1) values. We studied 66 patients with Graves' disease whose sera had been previously tested for sICAM-1 levels, grouped as follows: 28 with moderate and active ophthalmopathy (group 1), 12 of them hyperthyroid (group 1a) and 16 euthyroid (group 1b); 13 with mild and inactive ophthalmopathy and normal thyroid function (group 2); 25 without ophthalmopathy (group 3), 11 of them hyperthyroid (group 3a) and 14 euthyroid (group 3b). Finally, 26 sera of normal controls were studied. CollXIIIAb were evaluated by an enzyme-linked immunosorbent assay (ELISA) method. In group 1 patients, CollXIIIAb were detected at high levels in 8/12 (66.6%) in group 1a [optical density (OD) ranging from 0.529 to 0.894] and in 10/16 (62.5%) in group 1b (OD 0.560-0.855). In group 2 patients, CollXIIIAb were detected but at low levels (OD 0.205-0.260) in 4/13 patients (30.7%). In group 3 patients, CollXIIIAb were present at low levels in 6/11 (54.5%) of group 3a and in 5/14 (35.7%) of group 3b (OD 0.215-0.290 and 0.144-0.245, respectively). CollXIIIAb were detected in only 4/26 normal controls (15%) but at low levels (OD 0.150-0.185). CollXIIIAb values in both groups 1a and 1b were significantly higher than those of the remaining groups. A positive correlation between CollXIIIAb levels and CAS but not thyroid hormone levels was found in groups 1a, 1b and 2. Moreover, a positive correlation between CollXIIIAb levels and sICAM-1-values was also evidenced in all three groups. Our results suggest that CollXIIIAb could be considered as a further good marker of active inflammatory processes involving the adipose connective tissue in GO. In particular, the high levels of CollXIIIAb in sera of Graves' patients with active ophthalmopathy could reflect an increased expression of type XIII collagen on the membrane of activated fibroblasts in these patients. Thus, the evaluation of these antibodies could be added to other known markers as a useful and inexpensive tool in monitoring Graves' patients and in modulating the treatment of GO.