Detection of procollagen biosynthesis using peptide-specific antibodies

Regulation of Platelet Activation and Coagulation and Its Role in Vascular Injury and Arterial Thrombosis

Hemostasis requires tightly regulated interaction of the coagulation system, platelets, blood cells, and vessel wall components at a site of vascular injury. Dysregulation of this response may result in excessive bleeding if the response is impaired, and pathologic thrombosis with vessel occlusion and tissue ischemia if the response is robust. Studies have elucidated the major molecular signaling pathways responsible for platelet activation and aggregation. Antithrombotic agents targeting these pathways are in clinical use. This review summarizes research examining mechanisms by which these multiple platelet signaling pathways are integrated at a site of vascular injury to produce an optimal hemostatic response.

Spatiotemporal regulation of coagulation and platelet activation during the hemostatic response in vivo

The hemostatic response requires the tightly regulated interaction of the coagulation system, platelets, other blood cells and components of the vessel wall at a site of vascular injury. The dysregulation of this response may result in excessive bleeding if the response is impaired, and pathologic thrombosis with vessel occlusion and tissue ischemia if the response is overly robust. Extensive studies over the past decade have sought to unravel the regulatory mechanisms that coordinate the multiple biochemical and cellular responses in time and space to ensure that an optimal response to vascular damage is achieved. These studies have relied in part on advances in in vivo imaging techniques in animal models, allowing for the direct visualization of various molecular and cellular events in real time during the hemostatic response. This review summarizes knowledge gained with these in vivo imaging and other approaches that provides new insights into the spatiotemporal regulation of coagulation and platelet activation at a site of vascular injury.

A unique tool to selectively detect the chondrogenic IIB form of human type II procollagen protein

Type II collagen, the major fibrillar collagen of cartilage, is synthesized as precursor forms (procollagens) containing N- and C-terminal propeptides. Three splice variants are thought to be translated to produce procollagen II isoforms (IIA/D and IIB) which differ in their amino propeptide parts. The IIA and IID are transient embryonic isoforms that include an additional cysteine-rich domain encoded by exon 2. The IIA and IID transcripts are co-expressed during chondrogenesis then decline and the IIB isoform is the only one expressed and synthesized in fully differentiated chondrocytes. Additionally, procollagens IIA/D can be re-expressed by dedifferentiating chondrocytes and in osteoarthritic cartilage. Therefore, it is an important point to determine which isoform(s) is (are) synthesized in vivo in normal and pathological situations and in vitro, to fully assess the phenotype of cells producing type II collagen protein. Antibodies directed against the cysteine-rich extra domain found in procollagens IIA and IID are already available but antibodies detecting only the chondrogenic IIB form of type II procollagen were missing so far. A synthetic peptide encompassing the junction between exon 1 and exon 3 of the human sequence was used as immunogen to produce rabbit polyclonal antibodies to procollagen IIB. After affinity purification on immobilized peptide their absence of crossreaction with procollagens IIA/D and with the fibrillar procollagens I, III and V was demonstrated by Western blotting. These antibodies were used to reveal at the protein level that the treatment of dedifferentiated human chondrocytes by bone morphogenic protein (BMP)-2 induces the synthesis of the IIB (chondrocytic) isoform of procollagen II. In addition, immunohistochemical staining of bovine cartilage demonstrates the potential of these antibodies in the analysis of the differential spatiotemporal distribution of N-propeptides of procollagens IIA/D and IIB during normal development and in pathological situations.

How do glucocorticoids compare to oligo decoys as inhibitors of collagen synthesis and potential toxicity of these therapeutics?

This article demonstrates how glucocorticoids decrease collagen synthesis. The parameters used to assess procollagen synthesis in our laboratory will be compared to those used by others. This article will note all the pertinent literature on the molecular mechanisms of this down regulation of procollagen synthesis. For example, what are the effects of glucocorticoids at the levels of transcription and translation of collagen mRNAs? Finally, we will define a molecular mechanism to inhibit Type I collagen synthesis by decreasing the binding of the TGF-beta activator protein complex to the TGF-beta element in the distal promoter of the proalpha1 Type I collagen gene, preventing the 2:1 ratio of alpha1 to alpha2 chains in the processed Type I collagen molecule. We will next ask "How do sense oligo decoys decrease Type I collagen synthesis at the in vivo and at the cell levels?" In primary fibrotic cell culture, the double-stranded phosphorothioate oligodeoxynucleotide decoys were more effective than their sense single-stranded counterparts. The molecular mechanism for the decrease in Type I collagen synthesis is the same as glucocorticoids, that is by decreasing the binding of the TGF-beta activator protein complex to the TGF-beta element in the distal promoter of the proalpha1 Type I collagen gene for the transcription of the proalpha1 mRNAs. The reason for using sense oligo decoys as anti-fibrotic agents as compared to the anti-fibrotic glucocorticoids, is that presently marketed and FDA approved glucocorticoids have many untoward side effects which the sense oligo decoys do not have.

Synergistic action of endothelin (ET)-1 on the activation of bronchial fibroblast isolated from normal and asthmatic subjects

Bronchial subepithelial fibrosis is an histological characteristic of asthma. Cytokines and other mediators, such as PDGF-BB, TGF-beta1 and ET-1 found in the asthmatic submucosa can potentially activate a repair process that leads to fibroblast proliferation and collagen synthesis. The mechanisms of modulation of the repair process leading to extracellular matrix deposition are still to be documented. In this study, we assessed the in vitro proliferation and collagen synthesis of bronchial fibroblasts isolated from normal and asthmatic subjects in response to ET-1, platelet-derived growth factor (PDGF)-BB and transforming growth factor (TGF)-beta1 alone or in combination, in the presence or absence of dexamethasone. The combination of ET-1 with one of the other two growth factors, or the triple combination, significantly increased DNA synthesis and collagen production of bronchial fibroblasts isolated from both normal and asthmatic subjects, but the same growth factors used separately had no significant effect on the same parameters. These results suggest that the simultaneous presence of ET-1, PDGF-BB and TGF-beta1 in both normal and asthmatic subjects is necessary to activate bronchial fibroblast proliferation and collagen synthesis. As these mediators are present in the submucosa of the asthmatic bronchi, they could be responsible, at least in part, for the accumulation of collagen in the mucosa.

Identification of an immunoglobulin Fc receptor of Actinobacillus actinomycetemcomitans

Actinobacillus actinomycetemcomitans expresses proteins that bind to the Fc portion of immunoglobulins. The immunoglobulin Fc receptors on the surface of A. actinomycetemcomitans were detected by the binding of biotinylated human or murine Fc molecules to strain SUNY 465 adsorbed to the bottom of microtiter wells. Biotinylated Fc binding was inhibited by unlabeled Fc molecules and human plasma. Fc receptors were identified by the binding of biotinylated Fc molecules to bacterial membrane proteins separated by polyacrylamide gel electrophoresis and transferred to nitrocellulose. Multiple bands were identified, and the major Fc-binding protein was determined to be a heat-modifiable protein. This protein migrated with approximate molecular weights of 25,000 and 32,000 (unheated and heated, respectively). Amino-terminal sequence analysis of this protein revealed a sequence identical to the heat-modifiable protein described for A. actinomycetemcomitans ATCC 43718. This protein sequence exhibits significant homology with the N termini of outer membrane protein A (OmpA) of Escherichia coli and related OmpA-like proteins from other gram-negative bacteria.

Adhesion of Actinobacillus actinomycetemcomitans to a human oral cell line

Two quantitative, rapid assays were developed to study the adhesion of Actinobacillus actinomycetemcomitans, an oral bacterium associated with periodontal disease, to human epithelial cells. The human oral carcinoma cell line KB was grown in microtiter plates, and adherent bacteria were detected by an enzyme-linked immunosorbent assay with purified anti-A. actinomycetemcomitans serum and horseradish peroxidase-conjugated secondary antibody or [3H]thymidine-labeled bacteria. Adhesion was found to be time dependent and increased linearly with increasing numbers of bacteria added. Variation in the level of adhesion was noted among strains of A. actinomycetemcomitans. Adhesion was not significantly altered by changes in pH (from pH 5 to 9) but was sensitive to sodium chloride concentrations greater than 0.15 M. Pooled human saliva was inhibitory for adhesion when bacteria were pretreated with saliva before being added to the cells. Pretreatment of the KB cells with saliva did not inhibit adhesion. Protease treatment of A. actinomycetemcomitans reduced adhesion of the bacteria to KB cells. The data are consistent with the hypothesis that a protein(s) is required for bacterial adhesion and that host components may play a role in modulating adhesion to epithelial cells.

Synergistic effects of dexamethasone on platelet-derived growth factor mitogenesis in vitro

Platelet-derived growth factor (PDGF) and insulin-like growth factor-I (IGF-I) interact to stimulate proliferation of fibroblasts in culture. Glucocorticoids variably effect the response of cultured fibroblasts to polypeptide growth factors. This study determined the effects of dexamethasone on growth-factor stimulation of gingival, periodontal ligament and pulp fibroblast proliferation in vitro. Cultures of quiescent, low-passage, human fibroblasts were treated for varying periods of time with transforming growth factor-beta 2 (TGF-beta 2), PDGF and IGF-I: (1) alone, (2) in combination with each other, (3) singly plus dexamethasone, (4) in combination plus dexamethasone. Combinations of human, recombinant PDGF and IGF-I (10-1000 ng/ml) induced significantly higher rates of cell proliferation than either factor alone. Dexamethasone at doses ranging from 10(-5) to 10(-8) M substantially enhanced cell proliferation induced by these combinations and by PDGF without IGF-I but not IGF-I alone. By 6 days after a single application, 2-3 times as many cells were present in the PDGF and dexamethasone cultures as compared to PDGF without IGF-I. TGF-beta 2 specifically blocked the effects of dexamethasone added to PDGF-stimulated cells. Collagen and non-collagenous protein synthesis was not affected by the addition of PDGF and IGF-I with or without dexamethasone. These data suggest that dexamethasone may substitute for IGF-I in PDGF stimulation of cell proliferation.