JAK2V617F mutant megakaryocytes contribute to hematopoietic aging in a murine model of myeloproliferative neoplasm

Abstract Megakaryocytes (MKs) is an important component of the hematopoietic niche. Abnormal MK hyperplasia is a hallmark feature of myeloproliferative neoplasms (MPNs). The JAK2V617F mutation is present in hematopoietic cells in a majority of patients with MPNs. Using a murine model of MPN in which the human JAK2V617F gene is expressed specifically in the MK lineage, we show that the JAK2V617F-bearing MKs promote hematopoietic stem cell (HSC) aging, manifesting as myeloid-skewed hematopoiesis with an expansion of CD41+ HSCs, a reduced engraftment and self-renewal capacity, and a reduced differentiation capacity. HSCs from 2yr old mice with JAK2V617F-bearing MKs were more proliferative and less quiescent than HSCs from age-matched control mice. Examination of the marrow hematopoietic niche reveals that the JAK2V617F-bearing MKs not only have decreased direct interactions with hematopoietic stem/progenitor cells during aging, but also suppress the vascular niche function during aging. Unbiased RNA expression profiling reveals that HSC aging has a profound effect on MK transcriptomic profiles, while targeted cytokine array shows that the JAK2V617F-bearing MKs can alter the hematopoietic niche through increased levels of pro-inflammatory and anti-angiogenic factors. Therefore, as a hematopoietic niche cell, MKs represent an important connection between the extrinsic and intrinsic mechanisms for HSC aging. Significance Statement The relative contribution of intrinsic and extrinsic mechanisms to HSC aging remains debated. We find that JAK2V617F mutant MKs can accelerate hematopoietic aging both directly (via decreased MK-HSC interaction) and indirectly (via suppressing vascular niche function). We also show that HSC aging has a profound effect on MK function. Our data suggest that, as a hematopoietic niche cell, MKs represent an important connection between HSC-intrinsic and HSC-extrinsic aging mechanisms.