Evidence for an erythroblast-enhancing factor (EEF) in human and mouse serum

Area of Science:

• Hematology
• Molecular Biology
• Cell Biology

Background:

• Erythropoiesis regulation involves factors beyond erythropoietin (Ep).
• Previous research indicates both stimulatory and inhibitory moieties influence red blood cell production.

Purpose of the Study:

• To identify and characterize novel erythropoietic stimulators in mammalian serum.
• To investigate the role of a newly discovered factor, distinct from Ep, in erythropoiesis.

Main Methods:

• In vitro assays using mouse marrow cells and 59Fe incorporation into heme.
• In vivo studies in polycythemic mice assessing 59Fe uptake into red blood cells.
• Partial purification of the novel stimulatory factor and characterization of its properties (molecular weight, isoelectric point).
• Colcemid and time-course studies to determine the stage of action in erythroid differentiation.

Main Results:

• A novel erythropoietic stimulator, termed erythroblast-enhancing factor (EEF), was identified in human and mouse serum, distinct from Ep.
• EEF significantly increased 59Fe incorporation into heme in vitro but not red blood cell production in vivo when administered alone.
• EEF demonstrated synergistic activity with Ep in both in vitro and in vivo assays, enhancing 59Fe incorporation.
• Partial purification revealed EEF as a 130K protein with an isoelectric point of 4.8, requiring higher transferrin levels than Ep.
• EEF acts late in erythroid differentiation, primarily on erythroblasts, and its serum levels correlate with red blood cell requirements.

Conclusions:

• EEF is a novel, non-Ep stimulator of erythropoiesis that acts synergistically with Ep.
• EEF functions as a positive regulator of terminal erythropoiesis, specifically targeting erythroblasts in vivo.
• Serum EEF levels dynamically reflect physiological demands for red blood cells, indicating its importance in erythropoiesis homeostasis.