Thrombopoietin metabolically primes hematopoietic stem cells to megakaryocyte lineage differentiation

During acute myelosuppression or thrombocytopenia, bone marrow (BM) hematopoietic cells respond rapidly to replenish peripheral blood platelets. While the cytokine Thrombopoietin (Thpo) concomitantly regulates platelet production and maintains HSC stem cell potential whether Thpo directly controls Mk-lineage differentiation of HSCs is unclear. Stress hematopoiesis requires quiescent HSCs to proliferate, a process which depends on a higher energy production. However, whether this switch of metabolic state relates to lineage differentiation of HSCs is not known. We here show that Thpo rapidly upregulates mitochondrial activity in HSCs which was accompanied by preferential differentiation to Mk-lineage. During unperturbed hematopoiesis, HSCs with high mitochondrial content and activity exhibit Mk-lineage biased differentiation. Furthermore, Thpo rapidly skewed HSCs to express a tetraspanin molecule, CD9, which expression correlated to mitochondria cell content. While highly proliferative, mitochondrial-rich HSCs were resistant to apoptosis and oxidative stress upon Thpo stimulation. Thpo regulated mitochondrial activity did not associate with high levels of cMpl expression but was influenced by non-nuclear mitochondrial translocation of phosphorylated of STAT3 at serine 727. Our data reveals that HSCs are metabolically heterogeneous and higher mitochondrial activity primes HSCs toward the Mk lineage differentiation. We also uncover a pivotal role of Thpo in regulating the rapid Mk-lineage commitment during stress hematopoiesis. Our findings suggest that mitochondria metabolism primes HSCs not only to exit dormancy but toward direct differentiation to Mk lineage.