Impaired fibrinolysis in JAK2V617F-related myeloproliferative neoplasms

Myeloproliferative neoplasms (MPNs) are characterized by a high rate of thrombotic complications that contribute to morbidity and mortality. MPN-related thrombogenesis is assumed to be multifactorial, involving both procoagulant and proinflammatory processes. Whether impaired fibrinolysis also participates in the prothrombotic phenotype of MPN has been poorly investigated.

We determined whether MPN, particularly JAK2V617F-positive MPN, is associated with fibrinolytic changes.

Tissue-type plasminogen activator (tPA)-mediated fibrinolysis was evaluated both in whole blood and plasma from mice with a hematopoietic-restricted Jak2^V617F expression compared with wild-type (WT) mice (Jak2^WT) using (1) halo clot lysis, (2) front lysis, and (3) plasmin generation assays. tPA clot lysis assay was performed in the plasma from 65 MPN patients (JAK2V617F mutation, n = 50; CALR mutations, n = 9) compared with 28 healthy controls.

In whole blood from Jak2^V617F mice, we observed a decreased fibrinolysis characterized by a significantly lower halo clot lysis rate compared with Jak2^WT (95 ± 22 vs 147 ± 39 AU/min; P < .05). Similar results were observed in plasma (halo clot lysis rate, 130 ± 27 vs 186 ± 29 AU/min; front lysis rate, 2.8 ± 1.6 vs 6.1 ± 1.2 μm.min^-1; P < .05). Plasmin generation was significantly decreased both in plasma clots and standardized fibrin clots from Jak2^V617F mice compared with Jak2^WT mice. Among MPN patients, impaired tPA-related fibrinolysis with prolonged clot lysis time was observed in JAK2V617F and CALR patients. Plasminogen activator inhibitor-1 and α2-antiplasmin were significantly increased in plasma from JAK2V617F patients compared with controls.

Our results suggest that impaired tPA-mediated fibrinolysis represents an important prothrombotic mechanism in MPN patients that requires confirmation in larger studies.