Thrombopoietin

Thrombopoietin (pronounced “throm-boh-POY-eh-tin”) is a hormone that helps your body produce blood cells called platelets. It’s a type of hematopoietic growth factor. Hematopoiesis means blood cell production. Growth factors are substances that help cells grow, divide and multiply. So, a hematopoietic growth factor helps produce and develop blood cells.

Platelets are cells that make your blood clot. Your blood clots to help stop bleeding. Platelets are also called thrombocytes. The word “thrombopoietin” literally means “producing platelets.” Thrombopoietin levels in your body rise when your platelet levels are low. This helps you produce more.

What does thrombopoietin do?

Thrombopoietin works with developing blood cells to drive platelet production (thrombopoiesis). It binds to a receptor (molecule) on these cells called c-Mpl. When thrombopoietin binds to c-Mpl, it’s like a key that unlocks the process of thrombopoiesis. It stimulates these cells to develop in ways that will produce platelets.

Thrombopoietin binds to:

• Megakaryocytes: These are the cells that ultimately produce platelets. Thrombopoietin tags them and tells them it’s time to mature and produce platelets.
• Megakaryocyte progenitors: These cells are an early form of megakaryocytes. Thrombopoietin tags them and tells them to expand, multiply and develop into megakaryocytes.
• Hematopoietic stem cells: These are early blood cells that can grow to become any type of blood cell. Thrombopoietin nudges them toward becoming megakaryocytes.
• Platelets: Mature platelets also have c-Mpl receptors that bind to thrombopoietin, which removes it from circulation. This naturally controls the amount of thrombopoietin available.

Where is thrombopoietin located in your body?

Thrombopoietin circulates in your bloodstream. Most of it comes from your liver. Your liver produces many of the chemicals in your blood. When liver disease starts to impact your liver function, your liver produces less thrombopoietin. This is how liver disease can lead to a low platelet count in your blood.

Thrombopoietin does its important work within your bone marrow. This is where all blood cells are produced. The hormone binds to the c-Mpl receptor on certain developing blood cells in your bone marrow. Any leftover thrombopoietin continues to circulate. But mature platelets in circulation can remove it.

What medical conditions or disorders relate to thrombopoietin?

Disorders related to thrombopoietin can cause your body to create too many platelets, or too few:

• Thrombocytopenia: Thrombocytopenia is a low platelet count. When you don’t have enough platelets, your blood can’t clot well. This can make you bleed too much. It also weakens your immune system. You can develop thrombocytopenia if your liver doesn’t make enough thrombopoietin. It can also be genetic. In this case, gene changes can interfere with the hormone receptor.
• Thrombocytosis: Thrombocytosis, or thrombocythemia, means you have too many platelets. This raises your risk of dangerous blood clots and complications like heart attack and stroke. Essential thrombocythemia and primary myelofibrosis are two genetic conditions that can cause it. They both involve gene changes that allow platelets to be produced without thrombopoietin.

What medical treatments relate to thrombopoietin?

Thrombopoietin receptor agonists (TPO-RAs) are medicines that mimic thrombopoietin. They activate the same receptor on blood cells (c-Mpl). They’re also called megakaryocyte growth factors. They can help stimulate platelet production if you have thrombocytopenia due to various medical conditions.

Your healthcare provider might prescribe TPO-RAs if you have:

• Aplastic anemia
• Immune thrombocytopenia
• Hepatitis C
• Liver failure

Scientists are currently researching and developing thrombopoietin receptor antagonists to treat thrombocytosis. TPO antagonists are medicines that block c-Mpl so thrombopoietin can’t bind to it. They may one day help treat disorders like primary myelofibrosis.