Abstract
During the orchestrated process leading to mature erythrocytes, reticulocytes must synthesize large amounts of hemoglobin, while eliminating numerous cellular components. Exosomes are small secreted vesicles that play an important role in this process of specific elimination. To understand the mechanisms of proteolipidic sorting leading to their biogenesis, we have explored changes in the composition of exosomes released by reticulocytes during their differentiation, in parallel to their physical properties. By combining proteomic and lipidomic approaches, we found dramatic alterations in the composition of the exosomes retrieved over the course of a 7-day in vitro differentiation protocol. Our data support a previously proposed model, whereby in reticulocytes the biogenesis of exosomes involves several distinct mechanisms for the preferential recruitment of particular proteins and lipids and suggest that the respective prominence of those pathways changes over the course of the differentiation process.
Highlights
The maturation of reticulocytes into erythrocytes is the final step of erythropoiesis
The fact that exosomes were discovered in reticulocytes was due in large part to the important amounts of various materials that these cells need to eliminate during their terminal maturation into erythrocytes
Because exosomes are the result of a process of proteolipidic sorting within biological membranes, it has been proposed that they could be considered as isolated membrane rafts [17, 40, 41]
Summary
The maturation of reticulocytes into erythrocytes is the final step of erythropoiesis. Exosomes are small vesicles (50 –100 nm) delineated by a proteolipidic bilayer They were discovered in the 1980s by Johnstone and co-workers [8] during their study of the fate of the transferrin receptor (TfR), which is eliminated during the course of the reticulocyte maturation. There is no transcription in reticulocytes, the defects in cell surface expression associated with certain erythroid diseases suggest that exosome biogenesis is subject to regulatory mechanisms [7] For those reasons, the complexity of the biogenesis of reticulocyte exosomes is worthy of further investigations. After ensuring that the materials produced had all the physical characteristics of bona fide exosomes, we analyzed their proteolipidic composition over the course of the reticulocytes’ maturation process For this we used mass spectrometry for a thorough characterization of their protein content, whereas the lipid contents were determined by high performance chromatography techniques. Our study contributes to the understanding of the process of exosome biogenesis and provides hypotheses regarding the involvement of exosomes in particular erythrocytic diseases
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