ABSTRACT
There is evidence that clot structure can be modulated by endothelial cells, wherein the fibrinogen αC domain plays a major role in the fibrin-cell interaction. The spatial distribution of fibrin fibers from fibrinogen Caracas V and Caracas I, with heterozygous mutation in the αC domain (Aα Ser432Cys and Aα Ser466stop, respectively) on human dermal microvasculature endothelial cells (HMEC-1), was studied by laser scanning confocal microscopy. In order to assess fibrin-cell interaction and the role of the αC domain, preliminary experiments were done with inert microspheres and RGD peptide included in the clotting reaction, and forming clots with fibrinogen fragment X (fibrinogen without αC domain). Groups of stressed fibers were observed near the cell surface and were related to fibrin-cell interactions, which were abolished by the RGD peptide, and by the absence of the αC domain. The fibrin network of fibrinogen Caracas V and Caracas I was very different from that of normal fibrinogen. In general, patient's clots were characterized by very thin, tightly packed fibrin fibers, with a substantially reduced network porosity. Near the cell's surface, both abnormal fibrinogens formed a very fine meshwork, with stressed fibers 'anchored' to the cell surface, a pattern that was lost far from the cell surface. The structure of normal and patient clots performed in the absence of cells resembled that observed far from the cell surface, concluding that Caracas V and Caracas I fibrin was modulated by the presence of endothelial cells.