TPO

About Thrombopoietin :

Thrombopoietin (THPO) is commonly referred to as megakaryocyte growth and development factor (MGDF). It is a protein found in humans and encoded by the THPO gene - more specifically, it’s a glycoprotein hormone.
The production of thrombopoietin takes place in both the kidney and liver. Its main purpose is to help with the regulation of platelet production. It also acts as a stimulant for megakaryocytes, which are cells found in bone marrow, that produce platelets.

Mechanism/Interactions
THPO is found in different cells within the liver and kidney. In the liver, you will find THPO in parenchymal cells and sinusoidal endothelial cells. In the kidneys, production of THPO takes place in proximal convoluted tubule cells. While these two organs are the main source of thrombopoietin, it is also produced in smaller quantities by bone marrow stromal cells and striated muscle cells. The production of THPO in the liver is increased by the presence of IL-6 (interleukin 6).
THPO has an mpl receptor (CD 110) which helps bind it to platelets, upon which, thrombopoietin is destroyed. As a result, megakaryocyte exposure is greatly reduced to this hormone. Consequently, THPO levels are regulated due to the altering levels of platelet concentration. The lower the platelet concentration, the more cells are exposed to thrombopoietin. Whereas, high concentration leads to less thrombopoietin.
The negative feedback of thrombopoietin is different to that of almost every other hormone in endocrinology. The difference here is that the effector directly regulates the hormone.

Function
This protein is largely used to regulate megakaryocytes and platelet production. Megakaryocytes are large bone marrow cells that are in charge of producing platelets in the blood. Platelets are formed whenever blood is drawn through a cut, and it helps clot the blood to prevent too much blood loss. The presence of THPO helps accelerate platelet formation and stimulates the production of megakaryocytes. It is often referred to by specialists as a platelet growth factor. It increases the number of platelets produced in the liver, along with a small amount produced in the kidney as well.
To increase the platelets in our body, THPO can act upon the common myeloid progenitor and send the cell along the lineage of megakaryocyte. This is the precursor cell to those platelets. One megakaryocyte becomes 4000 platelets. Once it reaches a certain size, it fragments, and it's fragments of the cytoplasm that form the platelets.
There have been numerous medical trials to help figure out a use for THPO therapeutically. One idea is to use this protein to generate more platelets, which can then be extracted and used for donation. There are also studies trying to figure out how to use THPO to help recover low platelet counts after someone has been through chemotherapy.

Structure
Thrombopoietin is found on chromosome 3 at the long arm. It is found that the first 155 amino acids of this protein are similar to that of erythropoietin. The THPO gene can alter and become abnormal depending on various factors. When someone has an abnormally high platelet count or some forms of leukaemia, then the genetic makeup may differ.