Reticulocyte membrane remodeling: contribution of the exosome pathway.
OBJECTIVE
In addition to the loss of all the internal compartments, reticulocyte maturation is characterized by an extensive membrane remodeling. Exosomal secretion contributes to this process by eliminating specific proteins.


RESULTS
Regulation in the exosomal sorting of the water channel aquaporin-1 represents a newly described mechanism by which reticulocytes could adapt to environmental modifications. The extracellular osmotic conditions found in the peripheral circulation vs. the bone marrow could dictate a lower level of expression of aquaporin-1 on the mature red cell surface. In addition, a new mechanism for protein sorting to exosomes, involving an endogenous lectin, has been pinpointed in rat reticulocytes. Galectin-5 is secreted by a so-called alternative pathway, and could be involved in the sorting of galactoside-bearing glycoconjugates, since it was found associated with the surface of released exosomes.


CONCLUSIONS
Secretion of exosomes during reticulocyte maturation is an integral part of the red cell differentiation program and illustrates specific mechanisms in terms of biogenesis, protein sorting and fate, which are far from completely understood and open new paths for research in the red cell physiology field.
Blanc
Lionel
L
Red Cell Physiology Lab., New York Blood Center, New York, USA.
Vidal
Michel
M
D000818:Animals; D002462:Cell Membrane / Q000502:physiology*; D055354:Exosomes / Q000502:physiology*; D006801:Humans; D021381:Protein Transport; D051381:Rats; D012156:Reticulocytes / Q000502:physiology*; D055571:Secretory Pathway