Investigation of the Role of TRIB2 in Normal Murine Hematopoiesis

TRIB2 is a member of the mammalian Tribbles family of serine/threonine pseudokinases (TRIB1, 2, 3). Pathologically, TRIB2 induces potent murine acute myeloid leukemia and is associated with acute lymphoblastic leukemia. However, the normal hematopoietic role of TRIB2 remains elusive. Here, we studied murine hematopoiesis after Trib2 ablation. At the steady state, Trib2 loss did not adversely affect peripheral blood cell counts and populations. Trib2-/- mice had similar bone marrow cellularity compared to wild type (WT) mice and no significant differences in the populations of hematopoietic stem and progenitor cells. However, Trib2-/- mice had significantly higher thymic cellularity. Both Trib2-/- and WT mice had similar numbers of immature double negative (DN)1-4 thymic subsets. However, Trib2-/- DN cells proliferated faster as indicated by the higher expression of Ki-67, which contributed to the increased number of double and single positive (DP and SP) mature thymic subsets. To evaluate the impact of Trib2-/- on stress hematopoiesis, we treated both groups of mice with 5-fluorouracil (5-FU) in vivo and compared their hematopoietic recovery at different time points. Trib2 loss did not impair the bone marrow multilineage hematopoietic recovery but increased SP T cells detected in the peripheral blood. At 16 and 24 hours post treatment, Trib2-/- mice had significantly reduced numbers of DN1 c-Kithi precursors, DN3L and DPbl cycling subsets, and increased apoptosis, respectively. At day 4 and 14 post treatment, Trib2-/- mice had significantly higher thymic cellularity, frequency and number of thymic subsets compared to WT mice. DN1 c-Kit- precursors expanded significantly more in Trib2-/- compared to WT mice. Our results demonstrate that, in the absence of TRIB2, thymocytes are more sensitive to 5-FU induced cell death and thymopoietic recovery is accelerated. These data suggest TRIB2 regulates the differentiation and survival of intrathymic precursors and potentially has a role in the checkpoints of thymopoiesis.