TPO and myeloproliferative disorder: In addition, MK from individuals with MPN, in particular with IMF, secrete increased levels of the fibrotic cytokines such as TGF-β, compared to MK from healthy individuals, and the ECM microenvironment, especially the fibronectin component, is able to sustain progenitor cell proliferation and megakaryopoiesis in a TPO-independent manner.