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PubMed2004

A new L1446P mutation is responsible for impaired von Willebrand factor synthesis, structure, and function.

We report on a new mutation (4337T-->C) in exon 28 of the von Willebrand factor (VWF) gene, resulting in a substitution of L with P at residue 1446 (L1446P) of pre-pro-VWF. The defect is transmitted as a dominant trait and induces a reduced VWF synthesis, an abnormal VWF multimer pattern and a deficient VWF-platelet glycoprotein Ib interaction. The proband had low plasma and platelet VWF antigen levels, a reduced VWF collagen-binding capacity, and a disproportionately low VWF ristocetin cofactor activity, associated with the absence of ristocetin-induced platelet aggregation. Multimer analysis showed that the smaller multimers were slightly low, whereas the larger ones were significantly reduced or absent, with a clear cutoff between the two patterns. Similar hemostatic findings were observed in the proband's sister and nephew. Desmopressin administration restored VWF levels to near normal, but this was not so for VWF ristocetin cofactor activity or ristocetin-induced platelet aggregation. VWF multimers improved after desmopressin, moreover, with the larger forms restored and the smaller ones still relatively more represented. Recombinant P1446 VWF synthesis was reduced at heterozygous level, and its multimer pattern was similar to that observed in plasma VWF. These findings confirm the role of L1446P mutation in determining the von Willebrand disease (VWD) phenotype observed in our patients. Given the lack of large and intermediate VWF multimers, and the fact that the VWF-platelet interaction defect appears to be partially independent of multimer pattern, the VWD associated with L1446P mutation may belong to the type 2A/2M VWD variant.

Adult↗

PubMed1980

Axonal uptake of horseradish peroxidase isoenzymes during Wallerian degeneration.

Horseradish peroxidase isoenzymes were applied around crushed mouse hypoglossal nerves to study the influence of electrical charge on the uptake and ultrastructural distribution of macromolecules in axons distal to an injury. Both isoenzymes tested (Sigma type IX, cationic and type VII, anionic) were readily taken up into axons and moved in a distal direction along the nerve. Samples taken 1-3 mm below the crush showed that reaction products from both enzymes covered the inner surface of the axonal plasma membrane and were attached to organelles, particularly microtubules and neurofilaments. However, reaction product in the Schwann cell basement lamina and in the endoneurial collagen was much more dense with cationic peroxidase than with the anionic isoenzyme. Our study shows that both cationic and anionic macromolecules can move into axons distal to a nerve lesion. It can be assumed that also other agents can be taken up into axons and that 'wound substances' in this way may influence the processes by which axons are destroyed during Wallerian degeneration.

Animals↗

PubMed2004

Effect of matrix depleting agents on the expression of chondrocyte metabolism by equine chondrocytes.

This study was carried out to investigate the effect of two enzymes (collagenase and chondroitinase) and two cytokines/metabolites (interleukin-1beta and retinoic acid) of known catabolic activity on the expression of cartilage metabolism/phenotype in equine articular cartilage. Articular cartilage explants from 11 horses (5-13 years old) were treated for 48 h and assayed for total sulphated glycosaminoglycan (GAG), the incorporation of 35S-sulphate, collagen degradation and mRNA expression of the proteoglycans collagen II, collagen IIA, collagen III, collagen IX, collagen X, collagen XI and glyceraldehyde-3-phosphate (GAPDH). Purified collagenase and retinoic acid were responsible for increased GAG loss from the tissues. Chondroitinase, responsible for catalysing the elimination of glucuronate residues from chondroitin A, B and C (Chondroitinase ABC) and retinoic acid treatment induced an inhibition of proteoglycan synthesis, whereas collagenase treatment did not. Collagenase activity was correlated with increased appearance of the CB11B epitope and type II collagen denaturation. By RT-PCR there was evidence of expression of altered collagen type IIA in purified collagenase treated tissues.

Animals↗

PubMed1992

Functional analysis of a recombinant glycoprotein Ib alpha polypeptide which inhibits von Willebrand factor binding to the platelet glycoprotein Ib-IX complex and to collagen.

By deletion mutagenesis and transient expression in COS cells, a 96-amino acid hydrophilic sequence in the glycoprotein Ib alpha polypeptide located between L220 and L318 was identified which appeared to contain its von Willebrand factor- (vWF) binding site. The cDNA encoding this fragment was then expressed in Escherichia coli and purified from the bacterial cell lysate. The recombinant polypeptide, rGpIb alpha Q221-L318, was monomeric and had an apparent molecular weight of 14,000 by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It inhibited both ristocetin-induced binding of 125I-vWF to fixed washed platelets and ristocetin-induced platelet agglutination. The recombinant polypeptide also inhibited the binding of 125I-vWF to immobilized type I and III collagen. Inhibition of 125I-vWF binding to platelets and collagen was dose-dependent, with IC50 values of 500 and 200 nM rGpIb alpha Q221-L318, respectively. Fifty % inhibition of ristocetin-induced platelet agglutination required 500 nM rGpIb alpha Q221-L318. Although rGpIb alpha Q221-L318 inhibited vWF binding to collagen it did not, itself, bind to collagen-coated surfaces. Reduction of the disulfide bond between C248 and C264 abolished activity. 125I-rGpIb alpha Q221-L318 bound directly to GpIb/IX sites on multimeric vWF. These studies document that a portion of the sequence between Q221 and L318 is needed for recognition and binding to vWF and that binding requires an intact disulfide bond between C248 and C264. The binding of this recombinant polypeptide to vWF multimers inhibits vWF interaction with two important substrates, platelet GpIb/IX and collagen.

Adenosine Diphosphate↗

PubMed1993

Osteoarthritis in the human knee: a dynamic process of cartilage matrix degradation, synthesis and reorganization.

The matrix of articular cartilage undergoes degenerative changes in osteoarthritis which involve a number of matrix molecules. The structural and mechanical integrity is organized around the composite collagen II, IX, XI fibrillar organization. The small proteoglycan decorin that binds to these fibrils may influence their structure and mechanical properties. Aggrecan interacts indirectly via hyaluronic acid and possibly directly through unknown mechanisms. When collagen is cleaved at the articular surface in early osteoarthritis, decorin and aggrecan are lost. Increases in decorin and aggrecan content occur deeper in the cartilage. This is accompanied by evidence for increased formation of collagen fibrils and increased degradation and synthesis of aggrecan and type II collagen. The net contents of these proteoglycan per tissue do not, however, change until advanced degeneration occurs. These degradative processes are likely catalyzed by metalloproteinases and cysteine proteases. Cartilage exhibits significant capacity for remodelling which may be enhanced by therapeutic management of this process.

Cartilage, Articular↗

PubMed2002

The localized expression of extracellular matrix components in healing tendon insertion sites: an in situ hybridization study.

The localized expression of a number of extracellular matrix genes was evaluated over time in a novel rat rotator cuff injury model. The supraspinatus tendons of rats were severed at the bony insertion and repaired surgically. The healing response was evaluated at 1, 2, 4, and 8 weeks post-injury using histologic and in situ hybridization techniques. Expression patterns of collagens (I, II, III, IX, X, XII), proteoglycans (decorin, aggrecan, versican, biglycan, fibromodulin), and other extracellular matrix proteins (elastin, osteocalcin, alkaline phosphatase) were evaluated at the healing tendon to bone insertion site. Histologic results indicate a poor healing response to the injury, with only partial recreation of the insertion site by 8 weeks. In situ hybridization results indicate a specific pattern of genes expressed in each zone of the insertion site (i.e., tendon, fibrocartilage, mineralized cartilage, bone). Overall, expression of collagen types I and XII, aggrecan, and biglycan was increased, while expression of collagen type X and decorin was decreased. Expression of collagen type I, collagen type XII, and biglycan decreased over time, but remained above normal at 8 weeks. Results indicate that the rat supraspinatus tendon is ineffective in recreating the original insertion site, even at 8 weeks post-injury, in the absence of biological or biomechanical enhancements.

Animals↗

PubMed2005

An important role for the activation peptide domain in controlling factor IX levels in the blood of haemophilia B mice.

The factors responsible for the removal of injected factor IX (fIX) from the blood of individuals with haemophilia B are only partly understood, and may include binding to endothelial or subendothelial sites, passive extravasation related to size or charge, or interactions requiring fIX activation. To investigate these issues, we have produced and characterised recombinant fIX proteins with amino acid changes: delta155-177, an internal deletion which removes most of the activation peptide while retaining the activation cleavage sites; S365A, which inactivates the serine protease activity of fIXa; and K5A, previously shown to eliminate fIX binding of endothelial/subendothelial collagen IV. All proteins were expressed in stably transfected HEK 293 cells, purified by immunoaffinity chromatography, and compared to the wild type HEK 293-derived protein (fIX (WT)). Mutant fIX proteins K5A and delta155-177 exhibited 72 and 202% of the specific activity of fIX (WT), respectively; S365A was without activity. Following intravenous injection in haemophilia B (fIX knockout) mice, recoveries did not differ for fIX (WT) and delta155-177, but were higher for K5A and S365A. The terminal catabolic half-life of delta155-177, alone among the mutants, was increased, by 45% versus fIX (WT). Nine hours post-injection, the observed areas under the clearance curve (AUCs) of delta155-177 and K5, but not S365A, were elevated 2-fold. delta155-177 was equally effective as fIX (WT) in reducing blood loss following tail vein transection in haemophilia B mice. Our results suggest that deletion of the multiple sites of fIX post-translational modification found within the activation peptide eliminated important fIX clearance motifs.

Amino Acid Motifs↗

PubMed1999

[Congenital generalized cutis laxa: 5 cases].

BACKGROUND: Congenital cutis laxa is an exceptional condition. No large scale series has been reported in the French literature. We report 5 cases observed between 1993 and 1997. PATIENTS AND METHODS: Five children with a morphotype compatible with congenital generalized cutis laxa were examined. A family study, complete visceral workup and skin biopsy with standard histology, orceine coloration and histomorphometric analysis of the collagen and elastic fibers of the dermis were performed. Karyotype and copper metabolism (cupremia and ceruloplasminemia) were available in 3 children. RESULTS: The diagnosis was clinical and proven histologically by orceine coloration of skin biopsies in all cases. There were discrete ultrastructure anomalies in the pure cutaneous form expressed in case n(o) 1 with possible autosomal dominant inheritance. Cupremia and ceruloplasminemia were normal in the 3 children explored; this corresponds to absence of the Elhers-Danlos type IX phenotype. The karyotype was normal in 3/3 children, in agreement with the absence in these three children of marfanoid cutis laxa phenotype. Patients n(o) 2, 3, 4 and 5 had common features: probable autosomal recessive inheritance and severe prognosis. Patient n(o) 2 died at the age of 3 weeks and had severe pulmonary emphysema. This child's sister also had cutis laxa but with no visceral component (autosomal recessive inheritance with variable expression). Patients n(o) 3, 4 and 5 had a severe multiple malformative syndrome with facial dysmorphism, growth retardation, unexplained digestive disorders and psychomotor retardation. DISCUSSION: Our series of 5 patients and data in the literature confirm that primary cutis laxa is a heterogeneous group of conditions both clinically and genetically. The anomalies associated in patients n(o) 3, 4 and 5 were not directly related to anomalous elastic tissue as was also the case for the craniostenosis in patient n(o) 3 reported in other cases in the literature.

Abnormalities, Multiple↗

PubMed1995

Fluoxetine and hemostatic function: a pilot study.

BACKGROUND: Isolated case reports have appeared implicating fluoxetine as a cause of impaired hemostatic function. The authors attempted to investigate this phenomenon. METHOD: The hemostatic function of 10 patients with DSM-III-R major depression was investigated before and after a trial of treatment with fluoxetine. The tests included international normalized ratio, partial thromboplastin time, factors II, V, VII, VIII:C, IX, X, XI, XII, fibrinogen, thrombin time, bleeding time, euglobulin lysis time, protein kinase C, antithrombin, platelet counts, D dimer, lupus inhibitor, and platelet sensitivity studies to the following agonists: adenosine diphosphate, epinephrine, collagen, and arachidonic acid. Hemostatic data on a patient with a drug-related bleeding episode are not available. RESULTS: No significant difference was found in any of the parameters tested. CONCLUSION: This study failed to demonstrate any compromised hemostatic function associated with fluoxetine therapy. However, the possibility of a type II statistical error exists. It is possible that bleeding events may occur as an idiosyncratic reaction to fluoxetine treatment.

Adult↗

PubMed1998

Type 2M von Willebrand disease: F606I and I662F mutations in the glycoprotein Ib binding domain selectively impair ristocetin- but not botrocetin-mediated binding of von Willebrand factor to platelets.

von Willebrand disease (vWD) is a common, autosomally inherited, bleeding disorder caused by quantitative and/or qualitative deficiency of von Willebrand factor (vWF). We describe two families with a variant form of vWD where affected members of both families have borderline or low vWF antigen levels, normal vWF multimer patterns, disproportionately low ristocetin cofactor activity, and significant bleeding symptoms. Whereas ristocetin-induced binding of plasma vWF from affected members of both families to fixed platelets was reduced, botrocetin-induced platelet binding was normal. The sequencing of genomic DNA identified unique missense mutations in each family in the vWF exon 28. In Family A, a missense mutation at nucleotide 4105T --> A resulted in a Phe606Ile amino acid substitution (F606I) and in Family B, a missense mutation at nucleotide 4273A --> T resulted in an Ile662Phe amino acid substitution (I662F). Both mutations are within the large disulfide loop between Cys509 and Cys695 in the A1 domain that mediates vWF interaction with platelet glycoprotein Ib. Expression of recombinant vWF containing either F606I or I662F mutations resulted in mutant recombinant vWF with decreased ristocetin-induced platelet binding, but normal multimer structure, botrocetin-induced platelet binding, collagen binding, and binding to the conformation-sensitive monoclonal antibody, AvW-3. Both mutations are phenotypically distinct from the previously reported variant type 2MMilwaukee-1 because of the presence of normal botrocetin-induced platelet binding, collagen binding, and AvW-3 binding, as well as the greater frequency and intensity of clinical bleeding. When the reported type 2M mutations are mapped on the predicted three-dimensional structure of the A1 loop of vWF, the mutations cluster in one region that is distinct from the region in which the type 2B mutations cluster.

Base Sequence↗

PubMed1996

Platelet adhesion to collagen type IV under flow conditions.

Collagen type IV is a sheet-forming collagen and a major constituent of the vessel wall. To find out which conditions are important for platelet adhesion to collagen type IV, we performed perfusion studies with anticoagulated blood in parallel plate perfusion chambers. The role of divalent cations was investigated by using plasmas with variable concentrations of Mg2+ and Ca2+ ions. When Mg2+ concentration was decreased from 2.00 mmol/L to 0.25 mmol/L at a fixed Ca2+ concentration of 1.25 mmol/L, platelet coverage on the collagen type IV surface decreased from 22.8% +/- 1.8% (n = 4) to 4.6% +/- 0.6% (n = 4) at a shear rate of 1,600 s-1. Also, platelet aggregate formation on collagen type IV was strongly impaired. A monoclonal antibody against the glycoprotein (Gp) Ib receptor and von Willebrand factor (vWF)-depleted plasma reduced the platelet coverage to collagen type IV to, respectively, 10% and 45% of the control value. Electron microscopy showed that vWF was only present between platelets and between the platelet and the collagen type IV surface, but did not bind elsewhere to collagen type IV. These data indicate that collagen type IV is a reactive collagen for platelets. Differences in physiologic plasma magnesium concentrations may in part explain the differences in platelet reactivity to collagen type IV between individuals, and perhaps contribute to differences in the risk for thrombosis.

Calcium↗

PubMed1994

von Willebrand's factor and von Willebrand's disease.

von Willebrand's factor is required for platelet adhesion to subendothelium, and for normal factor VIII survival in the circulation. These functions require the assembly of von Willebrand's factor into multimers that exhibit properly regulated binding to platelet glycoprotein lb. Recent studies suggest that the propeptide of von Willebrand's factor may catalyze multimer assembly and have identified new segments of von Willebrand's factor that appear to regulate its affinity for glycoprotein lb. Two segments of von Willebrand's factor have been found to interact with collagen type VI, which is a candidate binding site for von Willebrand's factor in the subendothelium. Advances in the identification of mutations have prompted a reclassification of von Willebrand's disease. ABO antigens on von Willebrand's factor may impair the efficacy of plasma or recombinant von Willebrand's factor when administered to patients with incompatible ABO blood type.

Binding Sites↗

PubMed2004

The platelet glycoprotein Ib-von Willebrand factor interaction activates the collagen receptor alpha2beta1 to bind collagen: activation-dependent conformational change of the alpha2-I domain.

Integrin alpha2beta1 (glycoprotein [GP] Ia/IIa) is a major platelet receptor for collagen, containing its collagen-binding site within the alpha2 I domain. alpha2beta1 changes conformation upon platelet activation, increasing its affinity for collagen. We observed that 2 antibodies known to bind within the alpha2I domain, 12F1 and 6F1, bound preferentially to adenosine diphosphate (ADP)-activated platelets. Interestingly, when whole blood was perfused over a surface coated with either 12F1 or 6F1, only 6F1 supported the adhesion of unstimulated platelets. To test whether the interaction of GP Ib with von Willebrand factor (VWF) directly activates alpha2beta1, we used 12F1 as a probe of integrin activation. We perfused blood over a surface coated with a mixture of VWF-A1 domain (a GP Ib ligand) and 12F1 or VWF-A1 and mouse immunoglobulin G (IgG). Platelets rolled and did not attach stably on the A1/IgG surface, but they firmly bound and covered the A1/12F1 surface. We corroborated that 12F1 binds an active conformation of the I domain by showing that it binds with higher affinity to a gain-of-function mutant than to either wild-type I domain or a loss-of-function mutant. These results strongly suggest that the interaction of platelet GP Ib with VWF mediates the activation of alpha2beta1, increasing its affinity for collagen.

Antibodies, Monoclonal↗

PubMed1994

Gene organization and 5'-flanking region sequence of conglutinin: a C-type mammalian lectin containing a collagen-like domain.

Bovine conglutinin is a Ca(2+)-dependent serum lectin specific for N-acetylglucosamine. In the present study, we report the exon-intron organization and the sequence of 5'-regulatory region of the conglutinin gene. The coding region of conglutinin mRNA, which encoded the signal peptide and the sequence of the mature protein of 351 amino acids, consisted of seven exons. Exon III encoded the signal peptide, a cysteine-rich NH2-terminal region and six repeats of a Gly-X-Y triplet with one irregular triplet. The remaining long collagen-like domain (49 Gly-X-Y repeats with one irregular triplet) was encoded by four separate exons (Exon IV-VII). Exon VIII encoded the neck region and Exon IX encoded the carbohydrate-recognition domain. The overall exon-intron organization of conglutinin was very similar to that of mannan (mannose)-binding proteins. However, the presence of 108 bp exons in the gene encoding the collagen-like domain was a characteristic of conglutinin. In the promoter region of the gene, several putative consensus sequences that may be involved in the expression of conglutinin were identified.

Amino Acid Sequence↗

PubMed2003

Porphyromonas gingivalis gingipains: the molecular teeth of a microbial vampire.

The gingipains are cell surface Arg- and Lys-specific proteinases of the bacterium Porphyromons gingivalis, which has been associated with periodontitis, a disease that results in the destruction of the teeth-s supporting tissues. The proteinases are encoded by three genes designated rgpA, rgpB and kgp. Arg-specific proteolytic activity is encoded by rgpA/B and the Lys-specific activity by kgp. RgpA and Kgp are polyproteins comprising proteinases with C-terminal adhesin domains that are proteolytically processed. After processing, the domains remain non-covalently associated as complexes on the cell surface. RgpB is also a cell surface proteinase but does not associate with adhesin domains. Using gene knockout P. gingivalis mutants, the proteolytic processing of the gingipain domains has been shown to involve the gingipains themselves as well as C-terminal processing by a carboxypeptidase. A motif in the C-terminal domain of each protein/polyprotein has been identified that is suggested to be involved in attachment to LPS on the cell surface. RgpB lacks a C-terminal adhesin binding motif found in the catalytic domains of RgpA and Kgp. This adhesin binding motif is proposed to be responsible for the non-covalent association of the RgpA and Kgp catalytic domains into the cell surface complexes with the processed adhesin domains. The RgpA-Kgp proteinase-adhesin complexes, through the adhesin domains A1 and A3, have been implicated in colonization of P. gingivalis by binding to other bacteria in subgingival plaque and also binding to crevicular epithelial cells. The RgpA-Kgp complexes also bind to fibrinogen, laminin, collagen type V, fibronectin and hemoglobin. Amino acid sequences likely to be involved in binding to these host proteins have been identified in adhesin domains A1 and A3. It is proposed that these adhesins target the proteolytic activity to host cell surface matrix proteins and receptors. The continual cycle of binding and degradation of the surface proteins/receptors on epithelial, fibroblast and endothelial cells by the RgpA-Kgp complexes in the gingival tissue leading to cell death would contribute to inflammation, tissue destruction and vascular disruption (bleeding). P. gingivalis has an obligate growth requirement for iron and protoporphyrin IX, which it preferentially utilizes in the form of hemoglobin. Kgp proteolytic activity is essential for rapid hydrolysis of hemoglobin and it is suggested therefore that a major role of the RgpA-Kgp complexes is in vascular disruption and the binding and rapid degradation of hemoglobin for heme assimilation by P. gingivalis. The RgpA-Kgp complexes also have a major role in the evasion and dysregulation of the host-s immune response. It is proposed that host pro-inflammatory cytokines and cellular receptors close to the infection site may be rapidly and efficiently degraded by the gingipains while the proteinases at lower concentrations distally could result in the promotion of an inflammatory response through activation of proteinase-activated receptors and cytokine release. The culmination of this dysregulation would be tissue destruction and bone resorption. In animal models of disease the RgpA-Kgp complex when used as a vaccine to produce a high titre antibody response protects against challenge with P. gingivalis. Using recombinant domains of RgpA and Kgp as vaccines, it has been demonstrated that the A1 and A3 domains confer protection.

Adhesins, Bacterial↗

PubMed1987

Anti-basement membrane glomerulopathy in experimental trypanosomiasis.

The nature of kidney lesions in BD IX rats infected with Trypanosoma brucei was investigated. Proteinuria developed and increased up to 236 +/- 35 mg/24 hr at 7 wk after the infection. Antibodies were found to be deposited along the glomerular basement membrane (GBM) predominantly in a linear fashion, which changed to a more granular pattern 7 wk after the infection. At this stage of the disease, electron-dense deposits were found subendothelially along the GBM. In the sera and kidney eluates of diseased rats, anti-GBM antibodies were present. Enzyme-linked immunosorbent assay (ELISA) studies showed antibodies which reacted with GBM components laminin and type IV collagen and not with fibronectin. The antibody specificity was confirmed by using competitive and cross-absorption ELISA techniques, as well as immunoblotting. With the use of indirect immunofluorescence, no common antigenic sites were found on trypanosomes and GBM components. The observed linear immunofluorescence pattern seems to be caused by glomerular binding of antibodies directed against laminin and type IV collagen, which are known to be able to induce renal disease. Subendothelial complex formation in later stages of the disease might result from a molecular rearrangement of GBM components after in situ binding of the antibodies. The formation of auto-antibodies directed against laminin and type IV collagen is probably caused by restricted polyclonal B cell stimulation, a well known feature of trypanosomiasis.

Animals↗

PubMed1997

Complete primary structure of two splice variants of collagen XII, and assignment of alpha 1(XII) collagen (COL12A1), alpha 1(IX) collagen (COL9A1), and alpha 1(XIX) collagen (COL19A1) to human chromosome 6q12-q13.

Overlapping cDNA clones that encode the full-length human alpha 1(XII) collagen polypeptides were isolated. The long variant molecule cDNA of 9750 nucleotides (nt) contains a 9189-nt open reading frame encoding 3063 amino acid residues. The short variant molecule cDNA of 6258 nt contains a 5697-nt open reading frame encoding 1899 amino acid residues. At the amino terminus of each variant is a 24-residue signal peptide that is followed by the mature polypeptides of 3039 amino acid residues with a calculated molecular mass of 330,759 Da for the long variant and 1875 amino acid residues with a calculated molecular mass of 203,163 Da for the short variant polypeptide. The human collagen XII chains are predicted to have all the structural domains described for the molecules in chicken and mouse, including, fibronectin type III repeats, von Willebrand factor A domains, and two triple-helical domains similar to those of all the other collagen family members. The amino acid residue sequence of human alpha 1(XII) collagen showed 92% identity to the mouse chain and 78% identity to the chicken chain. The sequence of three peptide fragments of collagen XII isolated from human placenta was identical to the sequence predicted from the deduced cDNA sequence and confirms that the cDNA encodes human alpha 1(XII) collagen. An isolated genomic clone was used to map the locus of the COL12A1 gene to chromosome 6q12-q13, very close to the locus of the FACIT collagen genes COL9A1 and COL19A1. RT-PCR on a variety of cDNAs demonstrates that both variant transcripts appear in human amnion, chorion, skeletal muscle, small intestine, and in cell cultures of human dermal fibroblasts, keratinocytes, and endothelial cells. Only the small variant transcript is apparent in human lung, placenta, kidney, and a squamous cell carcinoma cell line. These results confirm the previous observations showing that collagen XII is found in collagen I-containing tissues.

Alternative Splicing↗

PubMed2005

Importance of platelet phospholipase Cgamma2 signaling in arterial thrombosis as a function of lesion severity.

OBJECTIVE: Platelet activation occurs in response to adhesion receptors for von Willebrand factor (GPIb-V-IX) and collagen (GPVI and alpha2beta1 integrin) acting upstream of phospholipase C (PLC) gamma2. However, PLCbeta transduces signals from Galphaq protein-coupled receptors for soluble agonists (P2y1, TxA2/TP, and thrombin/PAR). A Gi-dependent pathway amplifies most of these responses. METHODS AND RESULTS: To evaluate the role of adhesion receptors signaling in arterial thrombosis, PLCgamma2 knockout mice were studied in blood perfusion assays over fibrillar collagen and in a laser-induced mesenteric artery model of thrombosis. In vitro, PLCgamma2-deficient platelets formed a single layer incapable of generating a thrombus on collagen, whereas Galphaq-deficient platelets formed reduced size aggregates compared with wild-type cells. In the in vivo model, PLCgamma2-/- mice displayed defective thrombus formation in superficial lesions but productive thrombosis after a more severe laser injury. In contrast, resistance to thrombosis was observed in Galphaq-/- mice in both levels of injury. CONCLUSIONS: These results demonstrate that signaling through PLCgamma2 plays an important role in arterial thrombosis, but that its contribution depends on the severity of the vascular lesion.

Animals↗