Thrombopoietin overproduction by BRAFV600E-mutated hepatocytes may contribute to hepatocyte proliferation via thrombocytosis, platelet activation, and the interaction of platelets with hepatic sinusoidal cells, while hematologic, renal, and pulmonary disorders due to aberrant platelet activation may lead to spontaneous death in the transgenic mice.
The mutation was not found in three other unaffected cases from the family except in another proband's daughter who did not present thrombocytosis but had a high TPO level.
Thrombocytosis can be due to genetic alterations that affect either the intrinsic MPL signaling through gain-of-function (GOF) activity (<i>MPL, JAK2, CALR</i>) and loss-of-function (LOF) activity of negative regulators (<i>CBL, LNK</i>) or the extrinsic MPL signaling by <i>THPO</i> GOF mutations leading to increased TPO synthesis.
IL-6 acts on hepatocytes to enhance the production of thrombopoietin, which in turn interacts with its cognate receptor c-MPL on megakaryocytes and bone marrow progenitor cells to promote their expansion and proliferation, resulting in reticulated thrombocytosis.
This review will focus on the molecular pathogenesis of hereditary thrombocytosis, underlining those clinical pictures that are specifically associated with mutations in the genes of thrombopoietin or in its receptor.
A decrease in expression of the Mpl protein can cause thrombocytosis even in the absence of mutations in the coding sequence, due to a shift in the balance between stimulation of signaling in megakaryopoiesis and removal of thrombopoietin by receptor mediated internalization in platelets.
Affected family members carry a G --> C transversion in the splice donor of intron 3 of THPO that co-segregated with thrombocytosis within the pedigree.
Affected family members carry a G --> C transversion in the splice donor of intron 3 of THPO that co-segregated with thrombocytosis within the pedigree.
Our findings of increased TPO levels in the plasma of SARS patients provide a possible explanation for the genesis of thrombocytosis, which frequently develops from thrombocytopenia in SARS patients.
Following the observation of thrombopoietin (TPO) gene abnormalities as the cause of familiar cases of thrombocythemia similar derangements of TPO and/or its receptor (c-mpl) might be surmised to be at the root of increased platelet count also in non-familiar (sporadic) cases.
Our results suggest that low expression of TPO receptor on platelets until 1 month after birth cause a decreased TPO clearance and keep a high level of free TPO in blood, thereby promoting platelet production from megakaryocytes or their progenitors in bone marrow, resulting in the subsequent thrombocytosis in preterm infants.
Our results suggest that low expression of TPO receptor on platelets until 1 month after birth cause a decreased TPO clearance and keep a high level of free TPO in blood, thereby promoting platelet production from megakaryocytes or their progenitors in bone marrow, resulting in the subsequent thrombocytosis in preterm infants.
The contribution of increased TPO protein synthesis by a translational mechanism was recently appreciated as the cause for hereditary thrombocythemia and will have to be elucidated in other conditions of thrombocytosis in association with increased TPO levels.
These results also suggest that the thrombocytosis in ET may be attributed to an alteration of the normal feedback interaction between TPO and its receptor and not as a result of any defect in the structure of TPO or c-mpl.