Manipulation of Fatty Acid Metabolism Impairs Megakaryocyte Differentiation and Platelet Production

Background: Obesity is associated with an altered plasma lipid composition that impacts platelet activation, indicating that lipids directly affect platelet function and reactivity. However, very little is known about which essential lipids are important to enable platelet production from their precursors, megakaryocytes (MKs), and whether obesity influences lipid composition and consequently affects thrombopoiesis.

Aim: We aimed to determine which lipids and associated pathways play a significant role in MK differentiation and platelet production in health and upon obesity. Our long-term goal is to determine if we can manipulate MK maturation and platelet production through lipid incorporation or inhibition.

Methods: In order to determine the lipid profile of MKs through maturation, we performed an extensive lipidomics screen on primary MK progenitors, mature MKs, and platelets. Based on our findings, we then targeted de novo fatty acid (FA) synthesis in MKs to determine whether manipulation of this pathway attenuates MK differentiation and platelet formation. In parallel, we investigated megakaryo- and thrombopoiesis in an experimental setting of diet-induced obesity (DIO) in mice to examinate how altered lipid compositions within the plasma affect MK maturation.

Results: Lipidomic data revealed increased polyunsaturated FA and plasmalogen content in the late stages of MKs maturation, suggesting that lipid composition is undergoing changes that may enable platelet production. To validate and extend these results, we inhibited multiple enzymes in de novo lipogenesis and FA synthesis. Using two different sources of primary murine hematopoietic stem cells (HSCs), we found that MK differentiation and maturation from HSCs was significantly decreased up to 60% after inhibition of acetyl-coA carboxylase (ACC) and 80% after fatty acid synthetase (FASN) inhibition, both enzymes from the de novo lipogenesis pathway. Moreover, we also found that MK differentiation and maturation were highly decreased (up to 70%) after the inhibition of acyl-coA synthetase (ACS). To further examine the role of fatty acids incorporation on platelet production, we next treated mature MKs with an ACS inhibitor to investigate the direct effect of FA incorporation on proplatelet formation; we observed a significant, multifoldreduction in proplatelet area. While dihydroceramides were altered in the lipidomic data, impairment of the de novo ceramide synthesis pathway did not affect either MK maturation or platelet production. Moreover, we observed an increased abundance of HSCs, myeloid cells, and MK progenitors in the bone marrow of DIO mice compared to control mice on a chow diet. This further supports an important role for lipids in megakaryopoiesis and suggests that differences in platelet reactivity during obesity may be caused by altered MK maturation and/or platelet production.

Conclusions: Our results elucidate an important and previously unrecognized role for fatty acid synthesis in megakaryopoiesis and platelet production. The findings imply that an altered lipid content, as observed in patients with obesity, may not only impact platelet reactivity but also MK maturation and function. Consequently, platelets with an altered lipid content might originate from pathogenic MKs in obesity, which makes lipid-regulating proteins in MKs novel and viable therapeutic targets.