Elevated mRNA Expression of FGF2 and TGFB1 Genes in Myelofibrosis and Essential Thrombocythemia Patients

Background: Myelofibrosis (MF) and essential thrombocythemia (ET) are clonal hematopoietic stem cell malignancies classified as myeloproliferative neoplasms (MPNs). FGF2 and TGF-β were associated with pathophysiology and progression of these diseases. Although FGF2 and TGF-β roles in angiogenesis and fibrosis are known, their mRNA expression in leukocytes of MPNs patients was not yet evaluated. Furthermore, the detailed mechanism of TGF-β signaling in the pathophysiology of these diseases remains unclear. In regular signaling process, Smads are a group of proteins critical for transmitting signals from TGF-β superfamily of the cell surface to the nucleus. Thus, Smads signaling plays an important role in the regulation of hematopoiesis and it could modulate TGF-β action in MPNs.

Aims: The aim of this study was to investigate if there are differences in mRNA expression of FGF2, TGFB1 and SMADS 1 to 7 in MPNs patients and healthy controls and if it is related to JAK2 mutation status and allele burden.

Methods: Fifteen primary myelofibrosis (PMF), 15 myelofibrosis post essential thrombocytemia (MPET), and 22 essential trombocythemia (ET) patients diagnosed according to the World Health Organization criteria (2008) were selected from the Hematology Department of the Federal University of de Sao Paulo and from the Hematology Division of the Catholic University of Sao Paulo. Other group with healthy subjects was also included. The control group was matched by age and gender with MPNs patients: 30 for PMF, 17 for MPET, and 34 for ET. Expressions of FGF2, TGFB1 and SMADs 1 to 7 mRNA were evaluated in total leukocytes by Real Time PCR, using Taqman assays. JAK2V617F mutation status and allele burden and MPL W515K/L analysis were performed in total leukocytes DNA by Real Time PCR, using Taqman MGB probes.

Results: No difference was found between frequencies of JAK2V617F mutated subjects (P=0.520) and in allele burden percentage (P=0.415) in MPNs groups. Allele burden was also not associated with mRNA levels of studied genes in each group of MPNs, and none of the patients presented MPL W515K/L mutations. MF and ET patients had higher TGFB1 and FGF2 mRNA levels than its controls (P<0.05), while MPET patients had higher FGF2 levels than controls (P< 0.001). Both MPET and ET patients had higher SMAD6 expression than its controls (P<0.05), whereas ET patients also presented higher SMAD1 levels than controls (P=0.01). The SMADs expressions were similar in MF and their controls.

Conclusions: Our findings suggest that FGF mRNA is overexpressed in leukocytes of MF, MPET and ET patients. It seems that higher TGFB1 mRNA levels do not affect the molecular signaling by SMADs in MF patients, although SMAD6 and SMAD1 mRNA levels in ET and MPET patients might be upregulated.

Financing: FAPESP 2012/ 12957-5