UC Irvine

Myeloid malignancies occur when a hematopoietic stem cell (HSC) acquires a mutation that provide the stem cell clone with a competitive advantage over the remaining stem cell pool. Patients with myeloproliferative neoplasms (MPN) most commonly present with a gain-of- function mutation in Janus kinase 2 (JAK2V617F), leading to constitutive JAK-STAT signaling activation and uncontrolled proliferation of myeloid cells. What remains unclear is how JAK2V617F provides HSCs with a competitive advantage over the non-mutant stem cell pool. Given that patients with MPN have chronic inflammation, we posit that inflammation plays a critical role in the onset and progression of disease. This thesis aims to identify how the JAK2 mutation influences response to inflammatory stress as well as competitive fitness in HSCs and impacts on disease pathology. To test how JAK2V617F HSCs respond to inflammation, we used transgenic knock-in mouse models to measure cell proliferation, oxidative stress and DNA damage using flow cytometry. While JAK2 mutant cells were hyperproliferative under homeostatic conditions, normal and mutant HSCs had similar proliferation levels following acute inflammation. To test the cell-intrinsic differences between stem cell responses, we performed competitive transplants and observed that the hyperproliferative phenotype of JAK2V617F stem cells was lost. This data suggests that the bone marrow milieu plays an important role in stem cell activation and proliferation.The second aim of this thesis is to therapeutically modulate inflammation and observe stem cell responses to inflammation as well as effects on disease pathologies. We found that the antioxidant agent n-acetylcysteine (NAC) extended the lifespan of transgenic knock-in mice with MPN presumably from inhibition of thrombosis. NAC had no effects on platelet activation but rather reduced platelet-leukocyte aggregation and neutrophil extracellular traps in knock-in mice. Taken together, NAC is an attractive therapeutic for MPN sequelae given its numerous effects as an anti-inflammatory and anti-thrombotic agent. An investigator initiated clinical trial is in development using NAC in MPN patients with an Investigational New Drug application pending at the FDA. Future research can also explore the combination of aspirin and NAC to reduce thrombotic risk, lower chronic inflammation, and possibly improve stem cell fitness in patients.