Correllation of Proteolytic Matrix Metalloproteases (MMPs) and Inhibitors (TIMPs) with JAK2V617F Mutation and Clinical Phenotype in BCR-ABL Negative Myeloproliferative Neoplasia (MPN).

Ph negative MPNs comprise a heterogeneous group of disorders in which activation of JAK and other downstream signaling pathways can occur in a varying degree, yielding several different phenotypes. The identification of the somatic point mutation in the JAK2 gene (JAK2^V617F) as a key pathogenetic mechanism has further assisted in classification and diagnosis, in conjunction with clinical, morphological and biological characteristics of the various disease categories. The aim of this study was to investigate the presence of the mutation in association with the previously recognized as abnormal TIMP/MMP ratio in MPNs. This imbalance appears to favor inhibitory rather than proteolytic activity, resulting in tissue and bone marrow reforming processes to progress towards fibrosis instead of matrix proteins degradation.

In a case-control study, 64 consecutive patients (27 males; mean age 61.62 ± 16.64 years) who met WHO and PVSG criteria for polycythemia vera (PV), essential thrombocytosis (ET) and idiopathic myelofibrosis (IMF), were prospectively included and evaluated. The control group consisted of 74 healthy individuals (54 males; mean age 52.76 ± 15.54 years). Allele specific PCR was used for JAK2 mutation detection in peripheral and/or bone marrow derived DNA. Serum concentrations of MMP-2, MMP-9, TIMP-1 and TIMP-2 were measured by quantitative sandwich enzyme immunoassay (ELISA). The levels of these parameters were expressed as mean ± SE and assessed with analysis of covariance (ANCOVA), adjusted for gender, age and co-morbidity.

Patients were classified as follows: PV n:37, ET n:20, IMF n:7. V617F mutational frequency was 81% [n^PV:35 (94%) with exon 12 lesion identified in 2 patients, n^ET:12 (60%) and n^IMF:5 (71%)]. The presence of the mutation was significantly associated with splenomegaly (p=0.018) and age at diagnosis (p=0.004). Regardless of JAK2 status, all patients showed significantly lower MMP-2 levels (181.62 ± 8.00 vs 237.15 ± 7.33, p<0.001) and higher levels of TIMP-1 (587.48 ± 23.25 vs 467.98 ± 21.30, p<0.001) and TIMP-2 (130.55 ± 2.53 vs 93.01 ± 2.32, p<0.001) compared to healthy controls. These significant trends were observed in all different groups of patients; in particular, compared to controls, significantly lower MMP-2 levels and higher levels of TIMP-1 and TIMP-2 were found in PV-patients (184.48 ± 10.45, p<0.001; 556.12 ± 29.97, p=0.021; 134.75 ± 3.25, p<0.001) in ET-patients (176.90 ± 10.45, p<0.001; 607.97 ± 39.99, p=0.003; 123.23 ± 4.34, p<0.001) and in IMF-patients (175.14 ± 23.26, p=0.013; 688.42 ± 66.73, p=0.002; 129.43 ± 7.23, p<0.001). Interestingly, MMP-2 levels were significantly lower in patients positive for JAK2 mutation compared with the JAK2 negatives (182.61 ± 7.79 vs 255.58 ± 18.54, p=0.001). No significant difference was found in MMP-9 levels (1018.11 ± 77.26 in patients vs 1123.69 ± 70.79 in controls, p=0.335). For the evaluation of the diagnostic significance of these three parameters the area under the receiver operating characteristic (ROC) curve (AUC) was 0.767 (95% CI, 0.686 to 0.849, p<0.001) for MMP-2, 0.601 (95% CI, 0.496 to 0.705, p=0.053) for TIMP-1 and 0.944 (95% CI, 0.903 to 0.985, p<0.001) for TIMP-2. The optimal cut-off point to classify all MPN patients was 192.50ng/ml for MMP-2 (sensitivity of 60%, specificity of 85%), 550ng/ml for TIMP-1 (sensitivity of 50%, specificity of 82%) and 108ng/ml for TIMP-2 (sensitivity of 89%, specificity of 95%). The incidence of thrombosis was not significantly more frequent in the JAK2 positive group (p=0.24).

In the particular group of patients studied, the identification of an abnormal TIMP/MMP ratio in all disease categories, regardless of JAK2 mutation status, supports the notion that BCR ABL negative MPNs are invariably characterised by bone marrow stroma remodelling, more likely as a consequence of continuous inhibition of matrix degradation with subsequent displacement, at a variable degree, by fibrotic tissue. Presence of JAK2^V617F, being associated with even lower levels of MMP2, appears to be a concurring participant in this process. Further study will enable to delineate whether abnormal ratios are more prevalent in patients with thrombotic complications and perhaps document changes at different time points during treatment. Possible correlates with V617F allelic burden, especially towards thrombosis or fibrotic transformation, also remain to be elucidated.

No relevant conflicts of interest to declare.