BACKGROUND/AIM: Ph-chromosome negative myeloproliferative neoplasms comprise a heterogeneous group of disorders that occur at the level of the multipotent progenitor haematopoietic cell and have a well documented phenotypic diversity. Most of them share the same acquired genetic lesion JΑΚ2 V617F and may exhibit substantial clinical and laboratory overlap. Variability in JΑΚ signalling activation and the mutation allelic burden, complemented by several host, genetic and non-genetic modifiers, may determine each condition’s phenotype. The aim of this study was to investigate the presence of JΑΚ2 V617F mutation in association with certain clinical and laboratory findings. More specifically, we have investigated metallopeptidases inhibitors (TIMP) / tissue metallopeptidases (MMP) ratio in myeloproliferative neoplasms, where inhibitory rather than proteolytic activity in marrow microenvironment appears to predominate. This ratio was correlated with JAK2 mutation status and clinical characteristics such as leucocytosis, splenomegaly, the degree of marrow fibrosis at diagnosis and the incidence of thrombotic complications.METHODS: 94 patients, who fulfilled WHO 2008 criteria for Polycythaemia Vera (PV), Essential Thrombocythemia (ET) and Primary Myelofibrosis (PMF), and 102 healthy individuals were evaluated. Allele specific PCR and restriction fragment polymorphism analysis (RFLP) were used to detect JΑΚ2 and genomic level status. Serum concentrations of proteolytic enzymes MMP and TIMP were measured by ELISA. Patients were clinically assessed and presence of splenomegaly at diagnosis and history of thrombotic complications were also recorded. In addition, other laboratory characteristics such as leucocytosis, thrombocytosis and reticulin fibrosis on bone marrow trephine sections were documented. All correlations were assessed with covariance analysis, adjusted for gender, age and co-morbidity.RESULTS: Patients were classified as follows: PV n:52, ET n:28, MF n:14. Mutational frequency was 81.91%. More specifically presence of JAK2 V617F mutation was found in n:50 (96.15%), n:17 (60.71%) and n:10 (71.4%) respectively. Abnormally increased TIMP/MMP ratio, which was statistically significant when compared with healthy donors, was identified in all three diseases. The presence of the JΑΚ2 mutation was correlated with significant changes in TIMP concentrations. MMP and TIMP levels did not appear to be correlated with cardiovascular or other complications, nor did they differ significantly in cases with increased reticulin fibrosis in non PMF patients. In the particular group of patients studied here, homozygosity was only correlated with the presence of splenomegaly and did not appear to be associated with differences in MMP and TIMP serum concentrations.CONCLUSIONS: Identification of abnormal TIMP/MMP ratio in all three diseases studied here, regardless of the JΑΚ2 mutation status, indicates invariable marrow remodelling in MPN as a consequence of disturbed proteolytic degradation, increased deposition of interstitial proteins and perhaps subsequent displacement of haematopoietic tissue. In this particular group of patients, presence of the JΑΚ2 V617F mutation, being associated with even higher TIMP/MMP ratios, appears to be a concurring participant in bone marrow reforming processes. This finding, even though far from establishing causal relationships, may indicate JAK involvement in bone marrow trafficking and stroma remodelling. TIMP and MMP levels however did not differ significantly in advanced fibrotic stages and in cases with leucocytosis and/or thrombocytosis, nor did they confer additional thrombotic risk. Τhere was also no association between the presence of the mutation and the incidence of thrombotic complications or the presence of leucocytosis. Homozygosity state did not appear to affect TIMP/MMP ratio, however a further ongoing study may delineate correlates with the JΑΚ2 allelic burden.