Thyroid hormones induce hemopoietic pluripotent stem cell differentiation toward erythropoiesis through the production of pluripoietin-like factors

We have previously reported that E pluripoietins are produced in mice after a single 20-mg injection of cytosine arabinoside (Ara-C) and that they are able to initiate the determination of hemopoietic pluripotent stem cells (CFU-S) toward the erythrocytic lineage. However, the mechanism of E pluripoietin release is still unclear. Since the stimulating effect of thyroid hormone on erythropoiesis is well known, we postulated a link between this hormone and the E pluripoietins. In previous papers we demonstrated that l-triiodothyronine (LT 3) exhibits the capacity of inducing CFU-S differentiation toward erythropoiesis in vitro. Two series of data presented here suggest that LT 3 acts indirectly on CFU-S determination by promoting the release of E pluripoietin-like factors. First, the Ara-C injection which induces the production of E pluripoietins in mice also promotes an increase in the LT 3 plasma level. Second, medium conditioned with bone marrow cells exposed in vitro for 90 min to LT 3 (even though this medium does not contain LT 3) has E pluripoietin-like effects, inducing CFU-S differentiation toward the erythrocytic lineage.