Hydrodynamic characterization of recombinant human fibrinogen species

International audienceIntroduction: Fibrinogen is a key component of the blood coagulation system and plays important, diverse roles in several relevant pathologies such as thrombosis, hemorrhage, and cancer. It is a large glycoprotein whose three-dimensional molecular structure is not fully known. Furthermore, circulating fibrinogen is highly heterogeneous, mainly due to proteolytic degradation and alternative mRNA processing. Recombinant production of human fibrinogen allows investigating the impact on the three-dimensional structure of specific changes in the primary structure. Methods: We performed analytical ultracentrifugation analyses of a full-length recombinant human fibrinogen, its counterpart purified from human plasma, and a recombinant human fibrinogen with both Aα chains truncated at amino acid 251, thus missing their last 359 amino acid residues. Results: We have accurately determined the translational diffusion and sedimentation coefficients (D t(20,w) 0 , s (20,w) 0) of all three species. This was confirmed by derived molecular weights within 1% for the full length species, and 5% for the truncated species, as assessed by comparison with SDS-PAGE/Western blot analyses and primary structure data. No significant differences in the values of D t(20,w) 0 and s (20,w) 0 were found between the recombinant and purified full length human fibrinogens, while slightly lower and higher values, respectively, resulted for the recombinant truncated human fibrinogen compared to a previously characterized purified human fibrinogen fragment X obtained by plasmin digestion. Conclusions: Full-length recombinant fibrinogen is less polydisperse but hydrodynamically indistinguishable from its counterpart purified from human plasma. Recombinant Aα251-truncated human fibrinogen instead behaves differently from fragment X, suggesting a role for the Bβ residues 1-52 in inter-molecular interactions. Overall, these new hydrodynamic data will constitute a reliable benchmark against which models of fibrinogen species could be compared

TR3 orphan receptor is expressed in vascular endothelial cells and mediates cell cycle arrest

Objective - Endothelial cells play a pivotal role in vascular homeostasis. In this study, we investigated the function of the nerve growth factor - induced protein-B (NGFI-B) subfamily of nuclear receptors comprising the TR3 orphan receptor (TR3), mitogen-induced nuclear orphan receptor (MINOR), and nuclear orphan receptor of T cells ( NOT) in endothelial cells. Methods and Results - The mRNA expression of TR3, MINOR, and NOT in atherosclerotic lesions was assessed in human vascular specimens. Each of these factors is expressed in smooth muscle cells, as described before, and in subsets of endothelial cells, implicating that they might affect endothelial cell function. Adenoviral overexpression of TR3 in cultured endothelial cells resulted in decreased [H-3] thymidine incorporation, whereas a dominant-negative TR3 variant that inhibits the activity of endogenous TR3-like factors enhanced DNA synthesis. TR3 interfered with progression of the cell cycle by upregulating p27(Kip1) and downregulating cyclin A, whereas expression levels of a number of other cell cycle - associated proteins remained unchanged. Conclusions - These findings demonstrate that TR3 is a modulator of endothelial cell proliferation and arrests endothelial cells in the G1 phase of the cell cycle by influencing cell cycle protein levels. We hypothesize involvement of TR3 in the maintenance of integrity of the vascular endotheliu

Protective function of transcription factor TR3 orphan receptor in atherogenesis - Decreased lesion formation in carotid artery ligation model in TR3 transgenic mice

Back-ground-Smooth muscle cells (SMCs) play a key role in intimal thickening in atherosclerosis and restenosis. The precise signaling pathways by which the proliferation of SMCs is regulated are largely unknown. The TR3 orphan receptor, the mitogen-induced nuclear orphan receptor (MINOR), and the nuclear receptor of T cells (NOT) are a subfamily of transcription factors belonging to the nuclear receptor superfamily and are induced in activated SMCS. In this study, we investigated the role of these transcription factors in SMC proliferation in atherogenesis. Methods and Results-Multiple human vascular specimens at distinct stages of atherosclerosis (lesion types II to V by American Heart Association classification) derived from 14 different individuals were studied for expression of these transcription factors. We observed expression of TR3, MINOR, and NOT in neointimal SMCs, whereas no expression was detected in medial SMCs. Adenovirus-mediated expression of a dominant-negative variant of TR3, which suppresses die transcriptional activity of each subfamily member, increases DNA synthesis and decreases p27(Kip1) protein expression in cultured SMCs. We generated transgenic mice that express this dominant-negative variant or full-length TR3 under control of a vascular SMC-specific promoter. Carotid artery ligation of transgenic mice that express the dominant-negative variant of TR3 in arterial SMCs, compared with lesions formed in wild-type mice, results in a 3-fold increase in neointimal formation, whereas neointimal formation is inhibited 5-fold in transgenic mice expressing full-length TR3. Conclusions-Our results reveal that TR3 and possibly other members of this transcription factor subfamily inhibit vascular lesion formation. These transcription factors could serve as novel targets in the treatment of vascular diseas