title: Megakaryocytes contribute to the bone marrow-matrix environment by expressing fibronectin, type IV collagen, and laminin.
abstract: Megakaryocytes associate with the bone marrow vasculature where they convert their cytoplasm into proplatelets that protrude through the vascular endothelium into the lumen and release platelets. The extracellular matrix (ECM) microenvironment plays a critical role in regulating these processes. In this work we demonstrate that, among bone marrow ECM components, fibronectin, type IV collagen, and laminin are the most abundant around bone marrow sinusoids and constitute a pericellular matrix surrounding megakaryocytes. Most importantly, we report, for the first time, that megakaryocytes express components of the basement membrane and that these molecules contribute to the regulation of megakaryocyte development and bone marrow ECM homeostasis both in vitro and in vivo. In vitro, fibronectin induced a threefold increase in the proliferation rate of mouse hematopoietic stem cells leading to higher megakaryocyte output with respect to cells treated only with thrombopoietin or other matrices. However, megakaryocyte ploidy level in fibronectin-treated cultures was significantly reduced. Stimulation with type IV collagen resulted in a 1.4-fold increase in megakaryocyte output, while all tested matrices supported proplatelet formation to a similar extent in megakaryocytes derived from fetal liver progenitor cells. In vivo, megakaryocyte expression of fibronectin and basement membrane components was upregulated during bone marrow reconstitution upon 5-fluorouracil induced myelosuppression, while only type IV collagen resulted upregulated upon induced thrombocytopenia. In conclusion, this work demonstrates that ECM components impact megakaryocyte behavior differently during their differentiation and highlights a new role for megakaryocyte as ECM-producing cells for the establishment of cell niches during bone marrow regeneration.
authors.affiliation: Department of Molecular Medicine, University of Pavia, Pavia, Italy; Biotechnology Research Laboratories, IRCCS San Matteo Foundation, Pavia, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Malara
authors.forename: Manuela
authors.initials: M
authors.lastname: Currao
authors.forename: Cristian
authors.initials: C
authors.lastname: Gruppi
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Celesti
authors.forename: Gianluca
authors.initials: G
authors.lastname: Viarengo
authors.forename: Chiara
authors.initials: C
authors.lastname: Buracchi
authors.forename: Luigi
authors.initials: L
authors.lastname: Laghi
authors.forename: David L
authors.initials: DL
authors.lastname: Kaplan
authors.forename: Alessandra
authors.initials: A
authors.lastname: Balduini
mesh_terms: D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D001853:Bone Marrow / Q000378:metabolism*; D024141:Collagen Type IV / Q000096:biosynthesis*; D005353:Fibronectins / Q000096:biosynthesis*; D005472:Fluorouracil / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D007797:Laminin; D008533:Megakaryocytes / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D055153:Stem Cell Niche / Q000187:drug effects / Q000502:physiology*
chemical_list: D000963:Antimetabolites; D024141:Collagen Type IV; D005353:Fibronectins; D007797:Laminin; D005472:Fluorouracil
keywords: Bone marrow; Extracellular matrix; Megakaryocyte; Myelosuppression