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Updated: Dec 15, 2025
In Situ Exploration of Murine Megakaryopoiesis using Transmission Electron Microscopy
Published on: September 8, 2021
Sub-Cellular Localization of Metalloproteinases in Megakaryocytes
Alessandro Malara1,2, Daniela Ligi3, Christian A Di Buduo4,5
1Department of Molecular Medicine, University of Pavia, 27100 Pavia, Italy. alessandro.malara@unipv.it.
Abstract:
Metalloproteinases (MMPs) are zinc-dependent endopeptidases that play essential roles as the mediator of matrix degradation and remodeling during organogenesis, wound healing and angiogenesis. Although MMPs were originally identified as matrixin proteases that act in the extracellular matrix, more recent research has identified members of the MMP family in unusual locations within the cells, exerting distinct functions in addition to their established role as extracellular proteases. During thrombopoiesis, megakaryocytes (Mks) sort MMPs to nascent platelets through pseudopodial-like structure known as proplatelets. Previous studies identified gelatinases, MMP-2 and MMP-9, as a novel regulator system of Mks and the platelet function. In this work we have exploited a sensitive immunoassay to detect and quantify multiple MMP proteins and their localization, in conditioned medium and sub-cellular fractions of primary human CD34⁺-derived Mks. We provide evidence that Mks express other MMPs in addition to gelatinases MMP-2 and MMP-9, peculiar isoforms of MMP-9 and MMPs with a novel nuclear compartmentalization.
Insights
Megakaryocytes (Mks) express matrix metalloproteinases (MMPs) beyond gelatinases, including novel nuclear forms. This finding expands our understanding of MMP roles in platelet formation and function.
Area of Science:
- Biochemistry and Molecular Biology
- Cell Biology
- Hematology
Background:
- Matrix metalloproteinases (MMPs) are crucial zinc-dependent endopeptidases involved in matrix degradation and remodeling.
- While traditionally known for extracellular functions, MMPs have been found intracellularly, suggesting diverse roles.
- Megakaryocytes (Mks) are key cells in platelet production, and MMPs are known to be sorted into developing platelets.
Purpose of the Study:
- To investigate the expression and localization of various MMPs in primary human CD34+-derived Mks.
- To identify MMPs beyond the previously known gelatinases (MMP-2 and MMP-9) in Mks.
- To explore novel cellular compartments for MMPs within Mks, including nuclear localization.
Main Methods:
- Utilized a sensitive immunoassay for the detection and quantification of multiple MMP proteins.
- Analyzed MMPs in conditioned medium and sub-cellular fractions of primary human CD34+-derived Mks.
- Investigated the localization of MMPs within different cellular compartments.
Main Results:
- Confirmed the expression of gelatinases MMP-2 and MMP-9 in Mks.
- Identified the presence of additional MMPs in Mks, expanding the known MMP repertoire in these cells.
- Discovered peculiar isoforms of MMP-9 and observed MMPs within the nucleus of Mks, indicating novel compartmentalization.
Conclusions:
- Human Mks express a broader spectrum of MMPs than previously recognized, including gelatinases and other MMPs.
- MMP expression in Mks is not limited to the extracellular space, with evidence of nuclear localization.
- These findings suggest complex and potentially novel roles for MMPs within Mks during thrombopoiesis and platelet formation.
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