Later studies identified that PMF, as the others MPNs, is associated with mutations activating the thrombopoietin/JAK2 axis raising great hope that JAK inhibitors may be effective to treat the disease.
The majority of cytokines elevated in MF exhibited ex vivo hypersensitivity to thrombopoietin (TPO), toll-like receptor (TLR) ligands, and/or tumor necrosis factor (TNF).
In this report, we show that although both splenic and peripheral blood MF CD34(+) cells expressed lower levels of MPL than normal CD34(+) cells, TPO promoted the proliferation of MF CD34(+) cells and HPCs in a dose-dependent fashion.
Using Sparc(-/-) mice and BM chimeras, we demonstrate that SPARC contributes to the development of significant stromal fibrosis in a model of thrombopoietin-induced myelofibrosis.
Acquired mutations in the juxtamembrane region of MPL (W515L or W515K), the receptor for thrombopoietin, have been reported in patients with primary essential thrombocythemia (ET) or primary myelofibrosis (PMF).
To evaluate the frequency of MPL W515L, W515K and S505N mutations in essential thrombocythemia (ET) and primary myelofibrosis (PMF) and to determine whether MPLW515L leads to impaired Mpl expression, constitutive STAT3 and STAT5 activation and enhanced response to thrombopoietin (TPO).
Acquired mutations in the juxtamembrane region of MPL (W515K or W515L), the receptor for thrombopoietin, have been described in patients with primary myelofibrosis or essential thrombocythemia, which are chronic myeloproliferative disorders.
We also studied the same parameters in two mouse models of myelofibrosis, with genetic alterations affecting megakaryocyte differentiation (i.e. one model with low GATA-1 expression and the other with over-expression of thrombopoietin).
Other recent observations of potential pathogenetic relevance in this disease include the description of a highly specific chromosomal translocation {der(6)t(1;6)(q23;p21)}, the demonstration of an epigenetic downregulation of the retinoic acid receptor-beta2 expression in CD34 cells, and the direct implication of transforming growth factor-beta1 in thrombopoietin-driven experimental myelofibrosis in mice.
Taken together, our data show that high and persistent TPO production by transduced hematopoietic cells in mice results in a fatal myeloproliferative disorder that has a number of features in common with human idiopathic myelofibrosis.