Fibrin but Not Adsorbed Fibrinogen Supports Fibronectin Assembly by Spread Platelets

Abstract

We investigated the assembly of soluble fibronectin by lysophosphatidic acid-activated platelets adherent to fibrinogen or fibrin. More fibronectin was assembled by activated platelets spread on fibrin matrices than by platelets spread on adsorbed fibrinogen. The difference between platelets adherent to fibrinogen and fibrin occurred under both static and flow conditions. Similar differences were seen in binding of the 70-kDa N-terminal fragment of fibronectin that recognizes fibronectin assembly sites on adherent cells. Antibody and peptide blocking studies demonstrated that ␣IIb␤3 integrin mediates platelet adhesion to fibrinogen, whereas both ␣v␤3 and ␣IIb␤3 mediate platelet adhesion to fibrin. The hypothesis that engagement of the C-terminal QAGDV sequence of the fibrinogen ␥-chain by ␣IIb␤3 inhibits the ability of the platelet to assemble fibronectin was tested by several experiments. Activated platelets adherent to adsorbed mutant fibrinogen lacking the QAGDV sequence (␥⌬5FG) were assembly-competent, as were platelets adherent to adsorbed normal fibrinogen that had been pretreated with the 7E9 antibody to the C terminus of the ␥-chain. Moreover, adsorbed normal fibrinogen but not ␥⌬5FG suppressed the ability of co-adsorbed fibronectin to direct assembly of soluble fibronectin by spread platelets. The suppressive effect was lost when a surface of co-adsorbed fibronectin and fibrinogen was pretreated with 7E9. These results support a model in which the engagement of ␣IIb␤3 by the C-terminal sequence of the fibrinogen ␥-chain initiates signals that suppress subsequent fibronectin assembly by spread platelets. This interaction is less dominant when platelets adhere to fibrin, resulting in enhanced fibronectin assembly.Platelets at sites of vascular and tissue injury are essential for the formation of a hemostatic plug and subsequent arrest of bleeding (1). The initial step for hemostasis and thrombosis is adhesion of platelets by interaction of platelet surface receptors with extracellular matrix components of the exposed subendothelium of injured vessels. Intravital microscopy using mice lacking various adhesive proteins demonstrates that post-adhesive events are important in stabilizing the hemostatic plug in the injured mesenteric arteriole, which has a wall shear rate of ϳ1300 s Ϫ1 (2, 3). For instance, mesenteric arteriole thrombi detach and embolize more readily in mice lacking plasma fibronectin, suggesting that the interaction of plasma fibronectin with platelets after adhesion plays a role in the formation of stable thrombi (3). Fibronectin is a glycoprotein dimer of 230 -250-kDa subunits that is present in a soluble form in plasma and other body fluids and in an insoluble form in tissues (4, 5). In contrast to integrin-mediated adhesion of cells to the RGD-containing midpiece of insolubilized fibronectin, assembly of fibronectin into thin, aperiodic extracellular matrix fibrils is mediated by interaction of the N-terminal 70-kDa portion of fibronectin (70K) 2 with poorly characterized cell surface mo...

Involvement of Platelet–Tumor Cell Interaction in Immune Evasion. Potential Role of Podocalyxin-Like Protein 1

“…Fibronectin, a protein that forms part of the extracellular matrix, is also abundant in plasma and mediates platelet aggregation by binding β 3 integrins and tethering adjacent platelets (82, 83). It has been reported that incorporation of plasma fibronectin into fibrin clots enhances metastasis to the lungs (84).…”

Plasma and cellular fibronectin: distinct and independent functions during tissue repair

“…Furthermore, plasma FN can also be bound and then assembled into a high-molecular-weight multimeric matrix on the platelet surface. Platelet activation by thrombin induces increased cell-surface expression of the major platelet integrin αIIbβ3, which binds and assembles FN via a fibrin-independent mechanism [38-44]. Platelets also express a lower number of α5β1 and αvβ3 receptors on their surface, which mediate platelet adhesion [45].…”

“…Aggregated platelets can also assemble FN via a fibrin-dependent pathway [44]. The polymerization of fibrin into a three-dimensional network has been shown to be essential for FN assembly, as the γ chain of unprocessed fibrinogen signals via αIIbβ3 to inhibit this process [38]. …”

“…The FN released from platelets can also assemble on the surface of platelets [42,46,50]. FN incorporation into the fibrin matrix is important for various platelet functions, including adhesion, migration and aggregation (Figure 2) [16,36,38,45,46,48,49,51-98]. However, in vitro fibrin assembly was shown to be unaffected by a complete absence of plasma FN [51].…”

Platelets exploit fibrillar adhesions to assemble fibronectin matrix revealing new force-regulated thrombus remodeling mechanisms

“…We finally asked whether our findings regarding Fn assembly could be generalized to specific thrombus sites. Besides Fn, we selected fibrin as the major clot component since spreading on fibrin but not fibrinogen supports Fn matrix assembly by platelets (Jaehyung Cho et al 2005). Platelets on fibrin coatings showed the typical αIIbβ3-dependent contractile phenotype (Lickert et al 2018) and formed Fn fibrils mainly localized in the periphery of the cell ( Figure 6a).…”