Comprehensive phenotypic and proteomic analyses of human reticulocyte maturation

Reticulocyte maturation, the final stage of erythropoiesis following enucleation, is a dynamic 48- to 72-hour process remodeling multi-lobular, motile, and fragile nascent reticulocytes into deformable, biconcave red blood cells. This maturation involves organelle clearance and extensive membrane remodeling. A significant knowledge gap in our understanding is a lack of knowledge of the proteins involved in the earliest stages of reticulocyte maturation, the nascent bone marrow reticulocyte. To address this, we isolated and characterized the proteomic profiles of distinct reticulocyte populations from healthy human bone marrow. Density gradient separation, FACS analyses, and electron microscopy revealed a continuum of different stages of reticulocyte maturation in the marrow. Deformation-induced micropipette aspiration analyses combined with imaging of membrane proteins labeled with specific fluorescent probes, performed to better understand mechanisms of decreased expression of surface proteins during reticulocyte maturation, revealed a correlation between the extent of linkage and the decreased expression of surface proteins during reticulocyte maturation. There was a marked decrease in the total protein content between nascent and mature reticulocytes (56 to 39pg/cell) with a modest decrease between mature reticulocytes and mature erythrocytes (39 to 37pg/cell). Comparison of proteomes from nascent reticulocytes (2532 unique proteins), mature reticulocytes, and mature erythrocytes revealed only 867 proteins were shared among the three populations with significant changes in many classes of proteins. These studies provide comprehensive insights into maturation of the human reticulocyte proteome, advancing our understanding of the molecular mechanisms governing this process, and offer potential implications for acquired and inherited red blood cell disorders.