Gain-of-function Lyn induces anemia: appropriate Lyn activity is essential for normal erythropoiesis and Epo receptor signaling.

Lyn is involved in erythropoietin (Epo)-receptor signaling and erythroid homeostasis. Downstream pathways influenced following Lyn activation and their significance to erythropoiesis remain unclear. To address this, we assessed a gain-of-function Lyn mutation (Lyn(up/up)) on erythropoiesis and Epo receptor signaling. Adult Lyn(up/up) mice were anemic, with dysmorphic red cells (spherocyte-like, acanthocytes) in their circulation, indicative of hemolytic anemia and resembling the human disorder chorea acanthocytosis. Heterozygous Lyn(+/up) mice became increasingly anemic with age, indicating that the mutation was dominant. In an attempt to overcome this anemia, extramedullary erythropoiesis was activated. As the mice aged, the levels of different immature erythroid populations changed, indicating compensatory mechanisms to produce more erythrocytes were dynamic. Changes in Epo signaling were observed in Lyn(+/up) erythroid cell lines and primary CD71(+) Lyn(up/up) erythroblasts, including significant alterations to the phosphorylation of Lyn, the Epo receptor, Janus kinase 2, Signal Transducer and Action of Transcription-5, GRB2-associated-binding protein-2, Akt, and Forkhead box O3. As a consequence of altered Lyn signaling, Lyn(+/up) cells remained viable in the absence of Epo but displayed delayed Epo-induced differentiation. These data demonstrate that Lyn gene dosage and activity are critical for normal erythropoiesis; constitutively active Lyn alters Epo signaling, which in turn produces erythroid defects.