Galectin-5 is bound onto the surface of rat reticulocyte exosomes and modulates vesicle uptake by macrophages

Abstract

Reticulocytes release small membrane vesicles termed exosomes during their maturation into erythrocytes. Exosomes are intraluminal vesicles of multivesicular endosomes released into the extracellular medium by fusion of these endosomal compartments with the plasma membrane. This secretion pathway contributes to reticulocyte plasma membrane remodeling by eliminating certain membrane glycoproteins. We show in this study that galectin-5, although mainly cytosolic, is also present on the cell surface of rat reticulocytes and erythrocytes. In addition, in reticulocytes, it resides in the endosomal compartment. We document galectin-5 translocation from the cytosol into the endosome lumen, leading to its secretion in association with exosomes. Galectin-5 bound onto the vesicle surface may function in sorting galactosebearing glycoconjugates. Fittingly, we found that Lamp2, a major cellular glycoprotein presenting galectin-reactive poly-N-acetylactosamine chains, is lost during reticulocyte maturation. It is associated with released exosomes, suggestive of binding to galectin-5. Finally, we reveal that the uptake of rat reticulocyte exosomes by macrophages is dependent on temperature and the mechanoenzyme dynamin and that exosome uptake is decreased by adding galectin-5. These data imply galectin-5 functionality in the exosomal sorting pathway during rat reticulocyte maturation. (Blood. 2010;115: 696-705) IntroductionExosomes are membrane vesicles secreted by various cells and represent intraluminal vesicles of multivesicular endosomes (MVEs) released into the extracellular medium upon fusion of MVE with the plasma membrane. 1 Exosomal release during reticulocyte maturation is part of a cellular program resulting in remodeling of the plasma membrane by removal of a distinct set of (glyco)proteins. 2 We have previously shown that exosomal segregation of internalized membrane (glyco)proteins can occur by different routes, such as a natural enrichment in membrane domains (eg, lipid rafts), 3 antibody-or lectin-induced clustering on the cell surface, 4 or via the endosomal sorting complex required for transport (ie, ESCRT) cytosolic machinery. 5 During an earlier stage of mammalian erythroid differentiation, ie, when the erythroblast expels its nucleus, some components of the erythroblast plasma membrane are already specifically sorted to either the nascent reticulocyte or the expelled nucleus. For example, it has been shown by the use of mouse erythroblasts that proteins such as erythroblast-macrophage protein and ␤1-integrin partitioned predominantly to the plasma membrane surrounding the expelled nucleus, whereas glycophorin A localized to the plasma membrane of the nascent reticulocyte. 6 Both erythroblastmacrophage protein and ␤1-integrin have been identified as adhesion molecules involved in erythroblast retention by central macrophages within erythroblastic islands. [7][8][9] Thus, it has been suggested that their segregation to expelled nuclei favors their engulfment by macrophages while enabling reticulocytes to de...

Proteolipidic Composition of Exosomes Changes during Reticulocyte Maturation

“…The Galectin 5 pathway, in which this ␤-galactoside-binding lectin, present in the lumen of MVBs, is presumed to recruit various glycosylated proteins (19). In light of our results, this pathway would remain relatively constant during the different stages of maturation of the reticulocytes and would be responsible for the elimination of proteins that may well still have been needed at earlier stages, such as those involved in cell structure and motility.…”

“…The second route is associated with membrane lipid microdomains enriched in ceramides (17,18). The third route is initiated on the lumenal side of the endosomal compartment by aggregating factors such as lectins (19,20).…”

Exosomal membrane molecules are potent immune response modulators

“…31 Galectin is a type of lectin that shows affinity for b-galactoside. Extracellular gelectins cross-link cell surface and extracellular glycoproteins and may thereby modulate cell adhesion and induce intracellular signals.…”

Global effects of subchronic treatment of microcystin-LR on rat splenetic protein levels

“…As an important member of the galectin family, galectin-5 is unique for rats and present on the surface of reticulocytes and erythrocytes. Barrès et al [32] reported galectin-5 functionality in the exosomal sorting pathway during rat reticulocyte maturation. Reticulocyte count has been suggested to play a major role in anemic evaluation [33].…”