Abstract
Philadelphia chromosome-negative myeloproliferative neoplasms (Ph(-)MPNs) are clonal disorders marked by high morbidity and mortality, driven by uncontrolled myeloid proliferation from hematopoietic stem/progenitor cells (HSCs) and associated with a significant risk of thrombosis. This study explored the relationship between JAK2V617F and protease-activated receptor 1 (PAR1) by examining PAR1 expression and activation across various hematopoietic stem/progenitor cell (HSPC) subgroups, assessing their contribution to the hypercoagulable state in Ph(-)MPNs. We investigated the effects of thrombin, a PAR1 antagonist (vorapaxar), and a JAK2 inhibitor (ruxolitinib) on Ph(-)MPN cells. Mononuclear cells (MNCs) were isolated from Ph-MPN patients (n = 18), cord blood (CB) samples (n = 5) and healthy volunteers (n = 11). Specific subpopulations were sorted and analyzed for PAR1 expression and JAK2V617F status using qRT-PCR. PAR1 expression changes, along with other PAR pathway-related genes, were assessed post-treatment. Our results revealed that most PAR1(+) cells (∼95 %) co-expressed CD34(+), with a smaller JAK2V617F(+) PAR1(+) population lacking CD34. PAR1 expression was significantly higher in Ph-MPN MNCs compared to CB (p = 0.0005), particularly in EMP, HSC/EPC, and EPC subsets. Thrombin treatment reduced surface PAR1 expression, while PAR1 antagonist treatment further decrease the expression level. Combined PAR1 antagonist and ruxolitinib treatment significantly downregulated PAR1 expression (p < 0.0001), and several PAR-pathway-related genes were notably downregulated after treatment. This study highlights that elevated PAR1 expression in primitive hematopoietic subpopulations is linked to disease progression and thrombosis in Ph(-)MPNs, suggesting PAR1 as a potential therapeutic target. Combining PAR1 antagonists with JAK2 inhibitors shows promise in reducing PAR1 expression and mitigating thrombotic events in Ph(-)MPN patients.