Governing roles for Trib3 pseudokinase during stress erythropoiesis

In response to anemia, the heightened production of erythropoietin (EPO) can sharply promote erythroid progenitor cell (EPC) formation. Specific mediators of such EPO- accelerated erythropoiesis, however, are not well understood. Presently, we first report that the expression of Trib3 in adult bone marrow EPCs in vivo is nominal at steady state, but strongly activated on EPO challenge. In a knockout mouse model, Trib3 disruption modestly increased steady-state erythrocyte numbers and decreased mean corpuscular volume. Following 5-fluorouracil myeloablation, however, rebound red blood cell production and hemoglobin levels were substantially (and selectively) compromised in Trib3^-/- mice versus Trib3^+/+ congenic controls. Erythrocytes from 5-fluorouracil-treated Trib3^-/- mice additionally were more prone to lysis and exhibited elevated peroxide-induced reactive oxygen species. Ex vivo, the development of CD71^posTer119^pos erythroblasts from Trib3^-/- bone marrow progenitors was attenuated, and this was associated with heightened EPO-dependent Erk1/2 activation and moderately increased Akt activation. For developmentally staged EPCs, gene profiling provided further initial insight into candidate mediators of EPO-induced Trib3 gene expression, including Cebp-beta, Atf4, Egr-1, and Nab1. Overall, Trib3 is indicated to act as a novel EPC-intrinsic governor of stress erythropoiesis.