What is Thrombin

THROMBIN(activated Factor II [IIa]) is a coagulation protein that has many effects in the coagulation cascade. It is a serine protease (EC 3.4.21.5) that converts soluble fibrinogen into insoluble strands of fibrin, as well as catalyzing many other coagulation-related reactions.

Activation of prothrombin is crucial in physiological and pathological coagulation. Various rare diseases involving prothrombin have been described (e.g., hypoprothrombinemia). Anti-thrombin antibodies in autoimmune disease may be a factor in the formation of the lupus anticoagulant also known as ( antiphospholipid syndrome ).

In addition to its activity in the coagulation cascades, thrombin also promotes platelet activation, via activation of protease-activated receptors on the platelet.


Thrombin, a potent vasoconstrictor and mitogen, is implicated as a major factor in vasospasm following subarachnoid hemorrhage. Blood from a ruptured cerebral aneurysm clots around a cerebral artery, releasing thrombin. This can induce an acute and prolonged narrowing of the blood vessel, potentially resulting in cerebral ischemia and infarction (stroke).


Due to its high proteolytic specificity, thrombin is a valuable biochemical tool. The thrombin cleavage site (Leu-Val-Pro-Arg-Gly-Ser) is commonly included in linker regions of recombinant fusion protein constructs. Following purification of the fusion protein, thrombin can be used to selectively cleave between the Arginine and Glycine residues of the cleavage site, effectively removing the purification tag from the protein of interest with a high degree of specificity.


References
^ McMillen, S.I. (1984), None of These Diseases (Old Tappan, NJ: Revell)
^ Schmidt A (1872). "Neue Untersuchungen ueber die Fasserstoffesgerinnung". Pflüger's Archiv für die gesamte Physiologie 6: 413–538. doi:10.1007/BF01612263.

Recommended Reading
Further reading
Esmon CT (1995). "Thrombomodulin as a model of molecular mechanisms that modulate protease specificity and function at the vessel surface". Faseb J 9 (10): 946–55. PMID 7615164.
Lenting PJ, van Mourik JA, Mertens K (1999). "The life cycle of coagulation factor VIII in view of its structure and function". Blood 92 (11): 3983–96. PMID 9834200.
Plow EF, Cierniewski CS, Xiao Z, et al. (2002). "AlphaIIbbeta3 and its antagonism at the new millennium". Thromb. Haemost 86 (1): 34–40. PMID 11487023.
Maragoudakis ME, Tsopanoglou NE, Andriopoulou P (2002). "Mechanism of thrombin-induced angiogenesis". Biochem. Soc. Trans 30 (2): 173–7. doi:10.1042/ (inactive 28 June 2008). PMID 12023846.
Howell DC, Laurent GJ, Chambers RC (2002). "Role of thrombin and its major cellular receptor, protease-activated receptor-1, in pulmonary fibrosis". Biochem. Soc. Trans 30 (2): 211–6. doi:10.1042/ (inactive 28 June 2008). PMID 12023853.
Firth SM, Baxter RC (2003). "Cellular actions of the insulin-like growth factor binding proteins". Endocr. Rev 23 (6): 824–54. doi:10.1210/er.2001-0033. PMID 12466191.
Minami T, Sugiyama A, Wu SQ, et al. (2004). "Thrombin and phenotypic modulation of the endothelium". Arterioscler. Thromb. Vasc. Biol 24 (1): 41–53. doi:10.1161/01.ATV.0000099880.09014.7D. PMID 14551154.
De Cristofaro R, De Candia E (2004). "Thrombin domains: structure, function and interaction with platelet receptors". J. Thromb. Thrombolysis 15 (3): 151–63. doi:10.1023/B:THRO.0000011370.80989.7b. PMID 14739624.
Tsopanoglou NE, Maragoudakis ME (2004). "Role of thrombin in angiogenesis and tumor progression". Semin. Thromb. Hemost 30 (1): 63–9. doi:10.1055/s-2004-822971. PMID 15034798.
Bode W (2007). "Structure and interaction modes of thrombin". Blood Cells Mol. Dis 36 (2): 122–30. doi:10.1016/j.bcmd.2005.12.027. PMID 16480903.
Wolberg AS (2007). "Thrombin generation and fibrin clot structure". Blood Rev 21 (3): 131–42. doi:10.1016/j.blre.2006.11.001. PMID 17208341.
Degen S: Prothrombin. In: High K, Roberts H, eds. Molecular Basis of Thrombosis and Hemostasis. New York, NY: Marcel Dekker; 1995:75.
[show]v • d • eProteins: coagulation

Vascular smooth muscle cells for use in vascular tissue engineering obtained by endothelial-to-mesenchymal transdifferentiation (EnMT) on collagen...

The discovery of the endothelial progenitor cell (EPC) has led to an intensive research effort into progenitor cell-based tissue engineering of (small-diameter) blood vessels. Herein, EPC are differentiated to vascular endothelial cells and serve as the inner lining of bioartificial vessels. As yet, a reliable source of vascular smooth muscle progenitor cells has not been identified. Currently, smooth muscle cells (SMC) are obtained from vascular tissue biopsies and introduce new vascular pathologies to the patient. However, since SMC are mesenchymal cells, endothelial-to-mesenchymal transdifferentiation (EnMT) may be a novel source of SMC. Here we describe the differentiation of smooth muscle-like cells through EnMT. Human umbilical cord endothelial cells (HUVEC) were cultured either under conditions favoring endothelial cell growth or under conditions favoring mesenchymal differentiation (TGF-β and PDGF-BB). Expression of smooth muscle protein 22 and -smooth muscle actin was induced in HUVEC cultured in mesenchymal differentiation media, whereas hardly any expression of these markers was found on genuine HUVEC. Transdifferentiated endothelial cells lost the ability to prevent thrombin formation in an in vitro coagulation assay, had increased migratory capacity towards PDGF-BB and gained contractile behavior similar to genuine vascular smooth muscle cells. Furthermore, we showed that EnMT could be induced in three-dimensional (3D) collagen sponges. In conclusion, we show that HUVEC can efficiently transdifferentiate into smooth muscle-like cells through endothelial-to-mesenchymal transdifferentiation. Therefore, EnMT might be used in future progenitor cell-based vascular tissue engineering approaches to obtain vascular smooth muscle cells, and circumvent a number of limitations encountered in current vascular tissue engineering strategies.

ARTICLE

Progesterone metabolites rapidly stimulate calcium influx in human platelets by a src-dependent pathway

The effects of several steroids and their metabolites were examined for their ability to rapidly alter intracellular free calcium ([Ca2+]i) in the anucleate human platelet. Earlier studies suggested that steroids had direct and rapid non-genomic effects to alter platelet physiology. The rationale for performing this study was to investigate the signal transduction events being activated by steroids. Super-physiologic concentrations (1.0–10.0 μM) of β-estradiol and several estradiol metabolites and analogs potentiated (approximately twofold) the action of thrombin to elevate [Ca2+]i in platelets, whereas 10.0 μM progesterone inhibited the action of human thrombin by 10–15%. Progesterone and β-estradiol by themselves did not affect [Ca2+]i. Progesterone metabolites can achieve high blood concentrations. Some progesterone metabolites, particularly those in the β-conformation, were potent stimulators of Ca2+ influx and intracellular Ca2+ mobilization in platelets. They activated phospholipase C because their ability to increase [Ca2+]i was inhibited by the phospholipase C inhibitor U-73122. The ability of pregnanediol and collagen to increase [Ca2+]i was inhibited by the src tyrosine kinase inhibitor PP1, whereas the actions of thrombin and thapsigargin to increase [Ca2+]i were not affected by PP1. The effects of progesterone metabolites to increase [Ca2+]i were observed with concentrations as low as 0.1 μM. Pregnanolone synergized with thrombin to increase [Ca2+]i. It is hypothesized that human platelets possess receptors for progesterone metabolites. These receptors when stimulated will activate platelets by causing a rapid increase in [Ca2+]i. Pregnanolone, isopregnanediol and pregnanediol were the most effective stimulators of this newly identified src-dependent signal transduction system in platelets. Progesterone metabolites may regulate platelet aggregation and hence thrombosis in vivo.


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