Biphasic Effect of Thyroid Hormone on Megakaryopoiesis and Platelet Production

<b><i>Background:</i></b> Abnormal platelet counts are frequently observed in patients with thyroid dysfunction; however, the direct impact of thyroid hormones on thrombopoiesis remains largely undefined. <b><i>Methods:</i></b> This study elucidates the dose-response effect of the thyroid hormone triiodothyronine (T₃) on megakaryocyte (MK) development and thrombopoiesis using both a murine model of hyperthyroidism/hypothyroidism and <i>in vitro</i> cultures of human cord blood CD34⁺ cell-derived MKs. After the application of inhibitors to MKs, the examination of total and phosphorylated protein levels of the phosphoinositide 3-kinase (PI3K)/AKT pathway was utilized to assess the specific mechanisms of T₃ action. The use of autophagy dual-staining lentivirus and transmission electron microscopy was employed to evaluate the impact of T₃ on the autophagy flux in MKs. Mouse whole-body irradiation and bone marrow transplantation models are applied to assess the influence of T₃ on the recovery of MKs/platelets <i>in vivo</i>. <b><i>Results:</i></b> We found that physiological or slightly elevated thyroid hormone levels are essential for sustaining MK development and thrombopoiesis, primarily through the TRα-PI3K/AKT signaling pathway. In contrast, supraphysiological thyroid hormone concentrations induce MK apoptosis via excessive autophagy, thereby reducing platelet production. <b><i>Conclusions:</i></b> Here, we present evidence that the thyroid hormone influences MK development and platelet production in a concentration-dependent manner, exhibiting a dualistic role. Our discoveries shed new light on the intricate relationship between thyroid hormones and platelet formation, offering novel perspectives on the pathophysiological consequences of thyroid disorders.