Impact of heterozygous ALK1 mutations on the transcriptomic response to BMP9 and BMP10 in endothelial cells from hereditary hemorrhagic telangiectasia and pulmonary arterial hypertension donors.

Heterozygous activin receptor-like kinase 1 (ALK1) mutations are associated with two vascular diseases: hereditary hemorrhagic telangiectasia (HHT) and more rarely pulmonary arterial hypertension (PAH). Here, we aimed to understand the impact of ALK1 mutations on BMP9 and BMP10 transcriptomic responses in endothelial cells. Endothelial colony-forming cells (ECFCs) and microvascular endothelial cells (HMVECs) carrying loss of function ALK1 mutations were isolated from newborn HHT and adult PAH donors, respectively. RNA-sequencing was performed on each type of cells compared to controls following an 18 h stimulation with BMP9 or BMP10. In control ECFCs, BMP9 and BMP10 stimulations induced similar transcriptomic responses with around 800 differentially expressed genes (DEGs). ALK1-mutated ECFCs unexpectedly revealed highly similar transcriptomic profiles to controls, both at the baseline and upon stimulation, and normal activation of Smad1/5 that could not be explained by a compensation in cell-surface ALK1 level. Conversely, PAH HMVECs revealed strong transcriptional dysregulations compared to controls with > 1200 DEGs at the baseline. Consequently, because our study involved two variables, ALK1 genotype and BMP stimulation, we performed two-factor differential expression analysis and identified 44 BMP9-dysregulated genes in mutated HMVECs, but none in ECFCs. Yet, the impaired regulation of at least one hit, namely lunatic fringe (LFNG), was validated by RT-qPCR in three different ALK1-mutated endothelial models. In conclusion, ALK1 heterozygosity only modified the BMP9/BMP10 regulation of few genes, including LFNG involved in NOTCH signaling. Future studies will uncover whether dysregulations in such hits are enough to promote HHT/PAH pathogenesis, making them potential therapeutic targets, or if second hits are necessary.

Pediatric pulmonary arterial hypertension due to a novel homozygous GDF2 missense variant affecting BMP9 processing and activity.

Pulmonary arterial hypertension (PAH) is a rare and severe disorder characterized by progressive pulmonary vasculopathy. Growth differentiation factor (GDF)2 encodes the pro-protein bone morphogenetic protein (BMP) 9, activated after cleavage by endoproteases into an active mature form. BMP9, together with BMP10, are high-affinity ligands of activin receptor-like kinase 1 (ALK1) and BMP receptor type II (BMPR2). GDF2 mutations have been reported in idiopathic PAH with most patients being heterozygous carriers although rare homozygous cases have been described. The link between PAH occurrence and BMP9 or 10 expression level is still unclear. In this study, we describe a pediatric case of PAH also presenting with telangiectasias and epistaxis. The patient carries the novel homozygous GDF2 c.946A > G mutation, replacing the first arginine of BMP9's cleavage site (R316) by a glycine. We show that this mutation leads to an absence of circulating mature BMP9 and mature BMP9-10 heterodimers in the patient's plasma although pro-BMP9 is still detected at a similar level as controls. In vitro functional studies further demonstrated that the mutation R316G hampers the correct processing of BMP9, leading to the secretion of inactive pro-BMP9. The heterozygous carriers of the variant were asymptomatic, similarly to previous reports, reinforcing the hypothesis of modifiers preventing/driving PAH development in heterozygous carriers.

Tracing the glycogen cells with protocadherin 12 during mouse placenta development.

Among the different trophoblast subtypes of the mouse placenta, the glycogen cells (GC) are one of the trophoblast subtypes that invade the decidua. We previously established that GC specifically expressed protocadherin 12 (PCDH12). In this paper, we investigated the origin of the PCDH12-positive cells and we characterized their fate in the maternal tissues. Our data indicate that they directly originate from the central part of the ectoplacental cone at embryonic day (E) 7.5. PCDH12-positive cells start to accumulate glycogen from E10.5 and the first migrating cells could be observed from this age. Unlike other placental and decidual cells, GC do not express P-cadherin, which may explain their migration properties in this organ. In the decidua, GC settle in the vicinity of the maternal vascular sinuses but do not incorporate in the endothelium. By the end of gestation (E17.5), most GC islets of the decidua enter into a lytic phase and form large lacunae. These lacunae, filled with glycogen, may provide a substantial source of energy at the end of gestation or during delivery. Our data suggest that spongiotrophoblasts and GC are two independent lineages and we bring insights into GC migration and fate.

Human recombinant alpha1(V) collagen chain. Homotrimeric assembly and subsequent processing.

Human embryonic kidney cells (293-EBNA) have been transfected with the full-length human alpha1 chain of collagen V using an episomal vector. High yields (15 microgram/ml) of recombinant collagen were secreted in the culture medium. In presence of ascorbate, the alpha1(V) collagen is correctly folded into a stable triple helix as shown by electron microscopy and pepsin resistance. Circular dichroism data confirm the triple-helix conformation and indicate a melting temperature of 37.5 degrees C for the recombinant homotrimer. The major secreted form is a 250-kDa polypeptide (alpha1FL). N-terminal sequencing and collagenase digestion indicate that alpha1FL retains the complete N-propeptide but lacks the C-propeptide. However, alpha1FL might undergo a further N-terminal trimming into a form (alpha1TH) corresponding to the main triple-helix domain plus the major part of the NC2 domain. This processing is different from the one of the heterotrimeric (alpha1(V))2alpha2(V) and could have some physiological relevance. Analysis of cell homogenates indicates the presence of a 280-kDa polypeptide that is disulfide-linked through its C-terminal globular domain. This C-propeptide is rapidly cleaved after secretion in the medium, giving the first evidence of a C-terminal processing of recombinant fibrillar collagens. Rotary shadowing observations not only confirm the presence of a globular domain at the N-terminal end of the molecule but reveal the presence of a kink within the triple helix in a region poor in iminoacids. This region could represent a target for proteases. Together with the thermal stability data, these results might explain the low amount of (alpha1(V))3 recovered from tissues.

The membrane-spanning proteoglycan NG2 binds to collagens V and VI through the central nonglobular domain of its core protein.

NG2 is a membrane-spanning proteoglycan with a primary structure unique among cell surface or extracellular matrix proteins. To characterize the interaction between NG2 and extracellular matrix proteins, we have used a eukaryotic expression system to produce and purify several recombinant fragments covering not only the entire ectodomain of NG2 but also distinct subdomains of the molecule. Using a solid phase binding assay with various extracellular matrix proteins, we have identified two main ligands for NG2, namely, collagens V and VI. Consistent with previous models of glycosaminoglycan attachment, roughly 50% of the recombinant NG2 fragments containing the central domain have chondroitin sulfate chains attached to the protein core. These glycosaminoglycan chains are not directly involved in collagen binding, since chondroitinase-treated fragments exhibit an unimpaired ability to bind to both collagens. Using more restricted recombinant fragments of NG2, we mapped the binding site for both collagens to the central domain of NG2. Electron microscopy after rotary shadowing of native NG2 molecules indicates that this extended nonglobular domain provides a flexible connection joining the two N- and C-terminal globular regions of NG2. Rotary shadowing of mixtures of NG2 and collagen V or VI confirms a direct interaction between the molecules and indicates that the collagens align with the central region of NG2, giving the appearance of a rod between the N- and C-terminal globules.

Binding of the NG2 proteoglycan to type VI collagen and other extracellular matrix molecules.

Previous studies have suggested that the NG2 proteoglycan interacts with type VI collagen. We have further characterized this interaction using a solid phase binding assay in which purified NG2 was shown to bind to pepsin-solubilized type VI collagen. In addition, NG2 bound a recombinant alpha2 (VI) collagen chain but did not appreciably bind to the recombinant alpha1 (VI) chain or the N-terminal domain of alpha3 (VI) (N9-N2). Binding of NG2 to type VI collagen was shown to be concentration-dependent and saturable and to depend mainly on the NG2 core protein, since chondroitinase-treated NG2 bound the collagen as well as undigested samples. In addition, the binding studies revealed several other possible ligands for NG2, including type II collagen, type V collagen, tenascin, and laminin. Binding of the proteoglycan to these molecules was also shown to be mediated by domains contained within the NG2 core protein. The ability of NG2 to bind to these extracellular matrix molecules was compared with that of the chondroitin sulfate proteoglycan decorin, revealing an almost identical binding pattern of the two proteoglycans to the different collagen types. In addition, decorin was found to effectively inhibit the ability of NG2 to bind to collagen, thus suggesting that the two proteoglycans may bind to some of the same regions on the collagen substrates. In contrast, decorin did not bind tenascin and was ineffective in inhibiting the binding of NG2 to tenascin or laminin, indicating that NG2 may bind these two molecules using a separate domain that is distinct from its collagen binding region.

Deposition of collagen VI in the extracellular matrix during mouse embryogenesis correlates with expression of the alpha 3(VI) subunit gene.

Collagen VI is a microfibrillar component of the extracellular matrix that is predicted to have an important structural role in matrix organization and a biological function in mediating cell-matrix interactions. Secreted collagen VI molecules are composed of three distinct subunits, the alpha 1(VI), alpha 2(VI), and alpha 3(VI) chains. To determine when, and in which tissues, collagen VI is likely to have a role in embryonic processes, we have analyzed the expression patterns of the three subunit chains during postimplantation mouse development by reverse transcriptase-PCR (RT-PCR), in situ hybridization, and immunofluorescence. No collagen VI protein could be detected in the mouse embryo until Day 11.5 of gestation, when low levels were localized within the mesoderm layer of the visceral yolk sac, the subepidermal matrix of branchial arches, and the vessel wall of the dorsal aorta. Levels of collagen VI mRNA and protein increased during the period from Days 12.5 to 14.5 in the visceral yolk sac, subepidermal mesenchyme, lung, gut, meninges, muscle, perichondrium, and vertebral column. The cartilage matrix of ribs and developing long bones was not stained with collagen VI antisera, but pericellular staining of chondrocytes was seen in both tissues. Low levels of collagen VI mRNA and protein were seen in the fetal liver except for the connective tissue of the liver capsule, which was highly stained. Collagen VI was first detected at significant levels in the developing heart on Day 14.5. These data demonstrate a tissue-specific onset of collagen VI synthesis and deposition in the extracellular matrix of developing mouse embryos at a much later stage of development than that reported for fibronectin or collagen I. Sensitive RT-PCR assays showed that alpha 1(VI) and alpha 2(VI) mRNAs were amplified from extracts of embryonic tissues as early as Day 7.5, while alpha 3(VI) mRNA was not detected until Day 10.5. Expression of the alpha 3(VI) gene immediately preceded the appearance of collagen VI protein in embryonic tissues. This correlation is consistent with the proposal that expression of alpha 3(VI) chains regulates the formation and secretion of collagen VI trimers and collagen VI matrix deposition during development.

The evolution of fibrillar collagens: a sea-pen collagen shares common features with vertebrate type V collagen.

The extracellular matrix of marine primitive invertebrates (sponges, polyps and jellyfishes) contains collagen fibrils with narrow diameters. From various data, it has been hypothesized that these primitive collagens could represent ancestral forms of the vertebrate minor collagens, i.e., types V or XI. Recently we have isolated a primitive collagen from the soft tissues of the sea-pen Veretillum cynomorium. This report examines whether the sea-pen collagen shares some features with vertebrate type V collagen. Rotary shadowed images of acid-soluble collagen molecules extracted from beta-APN treated animals, positive staining of segment-long-spacing crystallites precipitated from pepsinized collagen, Western blots of the pepsinized alpha1 and alpha2 chains with antibodies to vertebrate types I, III and V collagens, and in situ gold immunolabeling of ECM collagen fibrils were examined. Our results showed that the tissue form of the sea-pen collagen is a 340-nm threadlike molecule, which is close to the vertebrate type V collagen with its voluminous terminal globular domain, the distribution of most of its polar amino-acid residues, and its antigenic properties.

Collagen type VI in the human bone marrow microenvironment: a strong cytoadhesive component.

Collagen type VI, which forms characteristic microfibrillar structures, is assembled from three individual alpha(VI) chains that form a short triple helix and two adjacent globular domains. Expression of all three alpha (VI) collagen chains in the human bone marrow (BM) microenvironment could be detected by chain-specific antibodies in tissue sections and in the adherent stromal layer of long-term BM cultures. In functional studies, collagen type VI was shown to be a strong adhesive substrate for various hematopoietic cell lines and light-density BM mononuclear cells. The adhesive site within the molecule seems to be restricted to the triple helical domain of all three alpha (VI) chains, because individual alpha (VI) chains were not active in the attachment assays. Adhesion of the hematopoietic cell lines to collagen VI was dose-dependent and could be inhibited by heparin. Although the triple helix contains several RGD sequences, adhesion of the hematopoietic cell types to collagen VI could be blocked neither by RGD-containing peptides nor by a neutralizing antibody to the beta 1 integrin subunit. In combination with an antiadhesive substrate, the binding properties of collagen VI could be downregulated. These data suggest that this collagen type may play an important role in the adhesion of hematopoietic cells within the BM microenvironment.

Expression of collagen alpha 1(VI), alpha 2(VI), and alpha 3(VI) chains in the pregnant mouse uterus.

The alpha 1, alpha 2, and alpha 3 chains of collagen VI and mRNAs for these chains were localized in the female mouse reproductive tract by immunofluorescence and in situ hybridization. High levels of collagen VI protein and mRNAs were present in the endometrium and myometrium of the uterus up to Day 4.5 of pregnancy. After embryo implantation, reduction in collagen VI protein within the decidualizing endometrium correlated with significantly reduced steady-state levels of alpha 1(VI), alpha 2(VI), and alpha 3(VI) mRNAs, indicating either transcriptional down-regulation of collagen VI gene expression or decreased stability of transcripts. High levels of alpha 1(V1) and alpha 2(VI) mRNAs, but not alpha 3(VI) mRNA, in cells surrounding the uterine epithelium in the mesometrial region did not correlate with deposition of collagen VI protein in this region. These data are consistent with an important role of alpha 3(VI) in assembly of collagen VI heterotrimers. However, distinct immunostaining with antiserum to alpha 2(VI) chains in the extracellular matrix immediately beneath the uterine epithelium may indicate that alpha 2(VI) chains are deposited without the alpha 1(VI) or alpha 3(VI) collagen chains. No collagen VI protein or mRNAs were detected in any tissue layers of the embryo on Days 5.5 or 6.5 of gestation.

Recombinant analysis of human alpha 1 (XVI) collagen. Evidence for processing of the N-terminal globular domain.

The N-terminal non-collagenous domain NC11 of the human collagen alpha 1 (XVI) chain was obtained as a recombinant 35-kDa protein from stably transfected kidney cell clones. This form had undergone proteolytic trimming at a basic cleavage motif indicating a similar release in vivo. Domain NC11 showed a globular shape after rotary shadowing and was resistant to neutral proteases. Specific antibodies could be raised against recombinant NC11 and were used for the analysis of other cell clones transfected with the full-length alpha 1 (XVI) chain. Immunoprecipitation of detergent extracts of metabolically labelled cells demonstrated the presence of disulfide-bonded 200-kDa polypeptides possessing NC11 epitopes. This material was partially resistant to pepsin, indicating the formation of alpha 1 (XVI) chain homotrimers with a triple-helical conformation. Yet a substantial proportion of these homotrimers was degraded to fragments of variable size (35-150 kDa) when secreted into the culture medium. Several of these fragments could be obtained on a semi-preparative scale from cells grown in hollow fiber cassettes and showed substantial hydroxylation of proline, consistent with triple-helix formation. Edman degradation demonstrated the origin of some from the N-terminal and of one from a more C-terminal position of collagen XVI. This extensive degradation may be explained by the release of NC11 and by further cleavages within some of the nine interruptions of the triple-helical domain of the alpha 1(XVI) chain. Whether this process also occurs in situ remains to be shown.

Intra-articular morphine after arthroscopic knee operation.

Reports on pain relief with intra-articular morphine after arthroscopic knee operation are conflicting. To assess the long-term antinociceptive effect of intraarticular morphine, we studied pain at rest, pain on standing and ability to walk for 7 days after intraarticular injection of bupivacaine 100 mg (group 1, n = 11), bupivacaine 100 mg and morphine 1 mg (group 2, n = 10) and bupivacaine 100 mg and morphine 3 mg (group 3, n = 10) at the end of operation. Pain and walking were assessed by visual analogue and walking scales, respectively. Pain was treated with morphine i.v. in the recovery room and Tylenol No. 3 after discharge. Assessments were made before operation, and 1, 3, 6 and 12 h after injection and on days 1-7 after operation. There were significant differences between the groups in pain scores (pain at rest, P < 0.05; pain on standing, P < 0.01). The pain scores in group 3 were lower than those in group 1. The differences in pain scores at rest were significant at 12 h and on day 1 after operation and differences in pain scores on standing were significant at 12 h and on days 1 and 2 after operation. The scores in group 2 were intermediate between those in groups 1 and 3. The walking scores in group 3 were significantly better than those in group 1 at 12 h. The amount of analgesics received in groups 2 and 3 was significantly less than that in group 1 until day 3 after operation.(ABSTRACT TRUNCATED AT 250 WORDS)

Recombinant expression and structural and binding properties of alpha 1(VI) and alpha 2(VI) chains of human collagen type VI.

Full-length alpha 1(VI) and alpha 2(VI) cDNAs in an eukaryotic expression vector were used to obtain stably transfected human kidney cell clones and to purify these collagen-VI chains in substantial quantities from the culture medium. Both chains appeared mainly as monomers together with some dimers that were disulfide linked through their C-terminal globular domains. Despite sufficient hydroxylation of proline and lysine residues, the chains did not form a triple-helix, as shown by electronmicroscopy, CD spectra and pepsin sensitivity. Digestion of the chains with bacterial collagenase released the N-terminal and C-terminal globular domains, which were identified by their size and partial sequences. They showed a substantial content of alpha-helical conformation and a distinct globular structure after rotary shadowing. Antibodies could be raised that distinguished between the two chains and reacted with the globular domains. The alpha 2(VI) but not the alpha 1(VI) chain showed binding to a heparan sulfate proteoglycan (perlecan), fibronectin and pepsin-solubilized collagen VI. Purified globular domains did not bind these ligands indicating the localization of binding sites within the triple-helical domain. Both chains showed a distinct affinity for heparin but failed to bind to various collagen types.

[Phylogenesis of the extracellular matrix]. / La phylogenèse de la matrice extracellulaire.

The extracellular matrix constitutes a highly organized intercellular medium. In multicellular animals, it plays important functions for cell cohesion and for the modulation of cell differentiation and behaviour as well. All the investigations conducted in non-vertebrate species have shown that the extracellular matrix is present at the onset of the multicellular life and throughout the animal kingdom. The collagen fibrils are the most constant element. Recent data on the structure of fibrillar collagen molecules and on the organization of the corresponding genes, obtained in sponges and sea-urchins have shown the remarkable conservation of these fibrillar collagens during evolution. This even emphasize their very likely fundamental function. These results, associated with data provided by morphological and biochemical informations obtained in cnidarians suggest that these primitive fibrillar collagens are the direct precursors of some vertebrate minor fibrillar collagens such as type V. Other collagens, with interrupted triple helix, are more variable and their characterization in sponges leads to consider these non-fibrillar collagens as precursors of basement membrane collagens, of fibril-associated collagens (the FACITs collagens), of the so-called "epithelial" collagens. They were probably used as sticking devices, anchoring the animal to its substratum, or as covering layers (cuticles, sheaths), and even as skeletons (i.e. the bath sponge). Adhesive molecules of higher animals ensure the mediation of the interactions between cells (via their membrane receptors of the integrin type) and the fibrous network of the extracellular matrix. It is the same situation at the beginning of the evolution of the multicellular animals where fibronectin, tenascin and then laminin are present. Proteoglycans too are components of primitive extracellular matrices. At last, only collagen mineralized by calcium phosphate (in bone) and elastin (in elastic fibers and laminae) seem to be restricted to vertebrates.