thrombopoïtine

Thrombopoietin, also spelled thrombopoëtine in French, is a glycoprotein hormone that regulates thrombopoiesis, the production of platelets. It acts chiefly by stimulating the proliferation and maturation of megakaryocytes in the bone marrow, increasing platelet output to maintain hemostasis.

Production and regulation: In adults, thrombopoietin is mainly produced by the liver, with minor contributions from the kidneys and bone marrow stromal cells. Circulating levels are regulated by a feedback mechanism: thrombocytes and megakaryocytes express the MPL receptor, which binds TPO and clears it from the circulation. When platelet mass falls, less TPO is cleared and its plasma concentration rises, promoting platelet production; when platelets are numerous, more TPO is cleared, reducing production.

Receptor and signaling: TPO binds to the MPL receptor (CD110) on hematopoietic progenitors, triggering JAK-STAT, MAPK, and PI3K signaling pathways that drive megakaryocyte proliferation, differentiation, and platelet shedding.

Clinical aspects: Therapeutically, recombinant human thrombopoietin was developed but associated with antibodies that neutralized endogenous TPO, limiting its use. Today, thrombopoietin receptor agonists such as romiplostim, eltrombopag, and avatrombopag are used to treat immune thrombocytopenia (ITP) and, in some settings, thrombocytopenia related to liver disease or chemotherapy. Risks include thromboembolism and marrow fibrosis with long-term use; monitoring of platelet counts is standard.