Megakaryopoiesis, Thrombosis and Iron Deficiency (MegIron2)

Iron deficiency (ID) is the most common nutritional disorder in both developed and industrialized countries worldwide and has an impact on multiple physiological, immune and cognitive functions. Apart from anemia, ID is also known to be associated with secondary thrombocytosis. The mechanism driving this phenomenon and if it increases the risk for thromboembolic events is unclear. Several case-control studies and numerous case reports suggest that this ID- associated thrombocytosis may pose a risk for thrombosis. Thromboembolic events are an important cause of morbidity and mortality in inflammatory bowel disease (IBD) as well as in cancer. Iron deficiency is common in both, and ID-related thrombocytosis may play a role in disease complications. In the Vienna CATS study, high platelet count was found to be an independent risk factor for the development of venous thromboembolism in cancer patients. Further underscoring the relationship between ID and thrombocytosis, we demonstrated that iron supplementation normalizes platelet counts in IBD- associated thrombocytosis in a dose and time dependent manner in a randomized controlled trial (ThromboVIT). Apart from platelet number, iron supplementation also reduced platelet aggregation and expression of P-selectin. Data from our previous FWF grant (MegIron P12000) showed that ID enhanced megakaryopoiesis in both rodent model and human hematopoietic stem cells and induced thrombocytosis in rodents. Megakaryopoietic growth factors such as thrombopoietin, interleukin- 3, interleukin-6, and interleukin-11, however, were unaltered in patients with ID and in the rodent model. Upon investigating potential candidate genes, we identified members of the hypoxia inducible factor and vascular endothelial growth factor pathways modulated in iron deficient megakaryocytes. In this proposal, we will be utilizing the rodent model to examine the effect of iron replacement therapy on platelet count and parameters. We will further examine if arterial and venous thrombotic tendency is altered in ID, and if iron replacement also normalizes these alterations. We further intend to investigate the role of HIF and VEGF pathways in iron deficient megakaryopoiesis and associated thrombocytosis. Utilizing both in vitro and in vivo approach, this study is designed to investigate the molecular pathways regulating megakaryopoiesis, platelet production and thrombosis under iron deficiency, and examine the physiological consequences (i.e. thrombosis) of these alterations. Understanding the role of iron in the regulation of thrombopoiesis and platelet function is critical for the development of treatment modalities for thrombocytosis in the setting of iron deficiency, and may contribute to prevention of thromboembolic complications. Moreover, identifying a biomarker or signature protein expressed by platelets produced under iron-deficient megakaryopoiesis could contribute to the prevention of thromboembolic sequelae. This would be of particular relevance in diseases where both ID and thromboembolic complications are relatively common, such as cancer, chronic renal failure and IBD, and also for the general population suffering from ID.

Iron deficiency (ID) is the most common nutritional disorder in both developed and industrialized countries worldwide. ID is widely known to cause anemia, however, iron is a vital element to many other cellular processes apart from oxygen transport. Studies have shown that ID has extra-hematologic consequences, impacting cognitive as well as muscular function. ID is also known to be associated with increased platelet counts, but whether this leads to an increased thrombotic tendency has not been well studied. Utilizing animal models, we have found that ID consistently increases platelet counts, influences platelet activity, and, ultimately, increases venous and arterial thrombotic tendency. All of these changes were reversed by iron therapy, lending credence to the theory that ID itself is a procoagulant state. These findings are highly relevant due to the widespread prevalence of ID. There are numerous case reports connecting ID with stroke or venous thromboembolism, many of which are in women and children, which could be due to the prevalence of ID in these groups. Furthermore, ID could be a co-morbidity in the context of other diseases that are already at an increased risk for thrombosis, providing the final push to manifest thrombosis. One example could be inflammatory bowel disease (IBD), a condition that predisposes to ID as well as thromboembolic events, the latter of which are a significant cause for morbidity and mortality. Our group has previously shown that iron supplementation normalizes platelet counts as well as platelet function in IBD. Appropriate and timely management of iron status could contribute to prevention of thrombotic events. We have also found that ID regulates megakaryocyte expression of genes involved in cell membrane cholesterol and phospholipid homeostasis. Deficiencies in members of this ATP- binding cassette transporter family have been shown to impact megakaryocyte progenitor proliferation as well as platelet function. We also examined the platelet proteome of IBD patients before and after iron administration, and found a lower expression of several surface integrins in ID, which increased with iron therapy. We hypothesize that this is due to increased baseline platelet activity, resulting in the depletion of these proteins. Overall, this project was successful in the set goals to investigate the influence of ID on thrombosis. We have also identified some pathways that may be involved in this process, and potential markers that still need to be investigated to see if they could be useful in evaluating thrombotic risk.