Recently evidence was provided for a pathway whereby circulating fibrinogen enters megakaryocyte granules by an endocytic mechanism. Synthesis of fibrinogen by megakaryocytes has been reported. To determine the relationship between plasma fibrinogen and alpha-granule fibrinogen in megakaryocytes and platelets, the fibrinogen content of these cells was studied in rats defibrinated by use of Ancrod, a thrombinlike enzyme purified from the venom of Agkistrodon rhodostoma. Unlike thrombin, Ancrod does not induce platelet secretion. Rats were injected with Ancrod (50 units/kilogram body weight) at 8-hour intervals for 5 days. There were no significant changes in platelet counts. Blood from the treated rats failed to clot, and plasma fibrinogen levels were less than 15 mg/dl. Bone marrow from defibrinated rats and untreated control rats was stained immunohistochemically for fibrinogen and two other alpha-granule proteins, albumin and platelet factor 4 (PF4), in plastic-embedded sections. The presence of these three proteins in platelets was detected by Western blots. Only trace amounts of fibrinogen were detected in megakaryocytes and platelets from defibrinated rats, but fibrinogen in control megakaryocytes and platelets was readily demonstrated. However defibrinated and control rats did not differ in albumin and PF4 content in megakaryocytes and platelets. It is concluded that a major portion of rat platelet fibrinogen is derived from plasma by endocytosis by megakaryocytes.
Download full-text PDF |
Source |
|---|---|
| http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1877735 | PMC |
Publication Analysis
Top Keywords
Similar Publications
Argonaute2 modulates megakaryocyte development and sex-specific control of platelet protein expression and reactivity.
Sci Rep
January 2025
Department of Medicine, Division of Hematology, Cardeza Foundation for Hematologic Research, Sidney Kimmel Medical College, Thomas Jefferson University, Philadelphia, PA, USA.
Platelets are enriched in miRNAs and harbor Ago2 as the principal RNA silencing Argonaute. However, roles in thrombopoiesis and platelet function remain poorly understood. We generated megakaryocyte/platelet-specific Ago2-deleted (Ago2 KO) mice and assessed proteomic and functional effects.
View Article and Find Full Text PDFIdentification of disulfide bond-linking sites in biosynthesized platelet factor 4 by establishing a partial reduction method without alkylation.
Anal Methods
January 2025
College of Life Science and Technology, Beijing University of Chemical Technology, Beijing, 100029, P.R. China.
Platelet factor 4 (PF4), a specific protein primarily found in megakaryocytes and platelet α-granules, plays an essential role in the coagulation process. It carries a high positive charge and thus has a unique ability to readily form complexes with negatively charged heparin. This interaction between PF4 and heparin plays a crucial role in platelet aggregation and thrombosis, resulting in heparin-induced thrombocytopenia (HIT).
View Article and Find Full Text PDFDedicator of Cytokinesis 2 regulates cytoskeletal actin dynamics and is essential for platelet biogenesis and functions.
Cardiovasc Res
January 2025
Department of Pharmacology, School of Basic Medicine, Tongji Medical College and State Key Laboratory for Diagnosis and Treatment of Severe Zoonotic Infectious Diseases, Huazhong University of Science and Technology, Wuhan, Hubei 430030, China.
Aims: Dedicator of Cytokinesis 2 (DOCK2), a member of the DOCK family of Guanine nucleotide exchange factors that specifically act on the Rho GTPases including Rac and Cdc42, plays pivotal roles in the regulation of leukocyte homeostasis. However, its functions in platelets remain unknown.
Methods And Results: Using mice with genetic deficiency of DOCK2 (Dock2-/-), we showed that Dock2-/-mice exhibited a macrothrombocytopenic phenotype characterized as decreased platelet count and enlarged platelet size by transmission electron microscopy.
Acute inflammation induces acute megakaryopoiesis with impaired platelet production during fetal hematopoiesis.
Development
January 2025
Institute for Regenerative Medicine, State Key Laboratory of Cardiology and Medical Innovation Center, Shanghai East Hospital, School of Life Sciences and Technology, Tongji University, Shanghai 200092, China.
Hematopoietic development is tightly regulated by various factors. The role of RNA m6A modification during fetal hematopoiesis, particularly in megakaryopoiesis, remains unclear. Here, we demonstrate that loss of m6A methyltransferase METTL3 induces formation of double-stranded RNAs (dsRNAs) and activates acute inflammation during fetal hematopoiesis.
View Article and Find Full Text PDFα-Actinin-1 deficiency in megakaryocytes causes low platelet count, platelet dysfunction, and mitochondrial impairment.
Blood Adv
January 2025
The First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China.
Cytoskeletal remodeling and mitochondrial bioenergetics play important roles in thrombocytopoiesis and platelet function. Recently, α-actinin-1 mutations have been reported in patients with congenital macrothrombocytopenia. However, the role and underlying mechanism of α-actinin-1 in thrombocytopoiesis and platelet function remain elusive.
View Article and Find Full Text PDFWant AI Summaries of new PubMed Abstracts delivered to your In-box?
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!