Killing them softly with EPO: a new role for erythropoietin in the homeostasis of red blood cells

Abstract

The regulation of red blood cell (RBC) homeostasis is widely assumed to rely on the control of cell production by erythropoietin (EPO) and the destruction of cells at a fixed, species-specific age. In this work, we show that such a regulatory mechanism is a poor homeostatic solution to satisfy the changing needs of the body. Effective homeostatic control requires RBC lifespan to be variable and tightly regulated. We show that EPO controls RBC lifespan by determining CD47 expression in newly formed RBCs and SIRP-α expression in sinusoidal macrophages. EPO also controls the initiation and intensity of anti-RBC autoimmune responses that curtail RBC lifespan in some circumstances. These mechanisms continuously modulate the rate of RBC destruction depending on oxygen availability. The finding of new homeostatic roles for EPO and autoimmunity critically challenges the current paradigm of RBC homeostasis and sets the grounds for a new approach to this field.

A functional approach to homeostatic regulation

“…However, from this observation alone, it cannot be inferred that the dynamics of homeostatic variables are actually driven by a predefined set point. For this reason, although set points can be useful to effectively reproduce the dynamics of homeostatic systems [53], they may not shed light on the mechanisms underlying biological regulation [19].…”