We studied integrins involved in the adhesion of resting and activated megakaryocytes (MK) to fibronectin (FN) and fibrinogen (FGN). Guinea pig MK were isolated and in some experiments were activated by thrombin. MK adhering to FN or FGN coated on coverslips were quantitated by a computerized image analysis program. The binding of soluble human FN to MK was detected by Western blotting. Anti-integrin antibodies, disintegrins, and cyclic RGD peptides were used to identify integrins involved in the adhesion of MK to FN or FGN. Resting MK adhered to coverslips with immobilized FN. The adhesion of MK to FN was primarily inhibited by an anti-5 antibody and EMF-10, a distintegrin highly specific for 5β1. However, the adhesion of MK to FN was not blocked by agents that inhibit ΙΙbβ3, vβ3 or 4β1. A β1 activating antibody increased the number of MK bound to FN due to the activation of 5β1. The binding of soluble FN was also primarily inhibited by agents that block 5β1. Resting MK did not adhere to FGN. However, MK activated by thrombin did adhere to FGN. This binding was mediated by ΙΙbβ3, because binding was inhibited by bitistatin, a disintegrin, and a cyclic RGD peptide that are known to block this integrin. The binding of thrombin-activated MK to FN was mediated by both 5β1 and ΙΙbβ3 based on the additive effect of agents that inhibit these integrins. The study indicates that resting MK bind to FN but not to FGN and that 5β1 is the major integrin involved in the binding of MK to FN. Activated MK bind to FGN primarily by IIbβ3. However, the binding of activated MK to FN is due to both 5β1 and IIbβ3. The demonstration that 5β1 and that IIbβ3 are involved in MK adhesion indicates that these integrins may have a role in MK maturation and platelet production. © 1998 by The American Society of Hematology.
Our studies have shown that megakaryocytes (MK) can synthesize fibronectin (FN) and alternatively spliced fibronectin, FN EIIIB. FN EIIIB is primarily present in embryonic, proliferating and migrating cells, and thought to be important for cell maturation. MK, but not nonmegakaryocytic bone marrow cells, contain FN EIIIB and thus, MK and platelets are among a small number of adult cells and tissues that synthesize and contain FN EIIIB. Thrombin can induce the secretion of general FN, but does not cause the secretion of FN EIIIB into the medium. Analysis of immunostained cells by confocal microscopy revealed that both general FN and FN EIIIB accumulated on the MK surface following thrombin treatment. Thus, FN EIIIB can be released only to be bound to the MK surface. The expression of FN EIIIB on the MK surface may have a unique role in MK migration and maturation.
Unsaturated fatty acids are thought to pi event thrombotic and arteriosclerotic disease, whereas saturated fatty acids are thought to increase the incidence of these disorders. However, the effects of these diets on megakaryocytes and platelets are not welll understood. We compared the effects of diets enriched with 8.4% olive oil, 8.4% hydrogenated palm oil, or 10.2% to-3 fatty acid ethyl esters on guinea pig megakaryocytes and platelets. In plasma, changes in fatty acid composition reflected the composition of each diet. However, in platelets and megakaryocyi:es, hydrogenated palm oil induced a decrease in 16:0 and an increase in 18:2 while the olive oil diet caused a marked increase in 18:1 and a decrease in most other fatty acids. The differences in the effects of the diets on cellular versus plasma fatty acids suggest that megakaryocytes and platelets have an extensive capacity to regulate their fatty acid composition. Thrombocytosis occurred with the w-3 fatty acid-enriched diet: 12.9± 1.78x 10 s compared with 7.45±1.08xl0 5 platelets per microliter of platelet-rich plasma in control animals. There was an increase in megakaryocyte size, ploidy, and morphological stage (cytoplasmic maturation) with the to-3 fatty acid-enriched diet but not with the other diets. The to-3 fatty acid-enriched diet decreased platelet thromboxane production while the other diets had no effect. Platelet hypersensitivity was suggested in collagen aggregation studies with olive oil but not with the hydrogenated palm oil diet. Although saturated fatty acid diets are thought to be athero|>enic, this diet had no affect on platelet function. The possibility that olive oil-enriched diets can increase platelet sensitivity and thereby augment thrombosis should be considered when making recommendations for increasing the dietary intake of monounsaturated fatty acids. ( 1 Dietary supplementation with unsaturated fatty acids, particularly marine oils, is reported to modify platelet function, as evidenced by the prolongation of the bleeding time, diminished platelet aggregation and secretion, and attenuated thromboxane production.2 -5 These diet-related effects on platelets are considered to be beneficial for the prevention of cardiovascular disorders. 1The mechanisms for the effects of fatty acid-modified diets on platelet lipid composition and platelet function are not well understood. Unsaturated fatty acid-enriched diets may lead to the modification of platelet function due to several mechanisms, such as i:he alteration of plasma lipoproteins, eicosanoid production, and cellular lipid composition.1 -9 It is not known whether the ingestion of fatty acid-modified diets exerts a primary or different effect on megakaryocytes than on platelets. The megakaryocyte is likely to be an important target of these diets, since megakaryocytes have a greater capacity for lipid synthesis and metabolism than do platelets. 10 -12 For example, megakaryocytes but not platelets have the capacity for de novo synthesis of arachidonic acid 12 and cholesterol syn...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.