The α2-adrenergic receptor pathway modulating depression influences the risk of arterial thrombosis associated with BDNFVal66Met polymorphism.

Depression is associated with thrombotic risk and arterial events, its proper management is strongly recommended in coronary artery disease (CAD) patients. We have previously shown that the Brain-Derived Neurotrophic Factor (BDNF)Val66Met polymorphism, related to depression, is associated with arterial thrombosis in mice, and with an increased risk of acute myocardial infarction in humans. Herein, expanding the previous findings on BDNFVal66Met polymorphism, we show that desipramine, a norepinephrine reuptake-inhibitor, rescues behavioral impairments, reduces the arterial thrombosis risk, abolishes pathological coagulation and platelet hyper-reactivity, normalizes leukocyte, platelet, and bone marrow megakaryocyte number and restores physiological norepinephrine levels in homozygous knock-in BDNF Val66Met (BDNFMet/Met) mice. The in vitro data confirm the enhanced procoagulant activity and the alpha2A-adrenergic receptor (α2A-ADR) overexpression found in BDNFMet/Met mice and we provide evidence that, in presence of Met variant, norepinephrine is crucial to up-regulate procoagulant activity and to enhance platelet generation. The α2-ADR antagonist rauwolscine rescues the prothrombotic phenotype in BDNFMet/Met mice and reduces procoagulant activity and platelet generation in cells transfected with BDNFMet plasmid or exposed to pro-BDNFMet peptide. Finally, we show that homozygous BDNFMet/Met CAD patients have hyper-reactive platelets overexpressing abundant α2A-ADR. The great proplatelet release from their megakaryocytes well reflects their higher circulating platelet number compared to BDNFVal/Val patients. These data reveal an unprecedented described role of Met allele in the dysregulation of norepinephrine/α2A-ADR pathway that may explain the predisposition to arterial thrombosis. Overall, the development of α2A-ADR inhibitors might represent a pharmacological treatment for depression-associated thrombotic conditions in this specific subgroup of CAD patients.

Miniaturized 3D bone marrow tissue model to assess response to Thrombopoietin-receptor agonists in patients.

Thrombocytopenic disorders have been treated with the Thrombopoietin-receptor agonist Eltrombopag. Patients with the same apparent form of thrombocytopenia may respond differently to the treatment. We describe a miniaturized bone marrow tissue model that provides a screening bioreactor for personalized, pre-treatment response prediction to Eltrombopag for individual patients. Using silk fibroin, a 3D bone marrow niche was developed that reproduces platelet biogenesis. Hematopoietic progenitors were isolated from a small amount of peripheral blood of patients with mutations in ANKRD26 and MYH9 genes, who had previously received Eltrombopag. The ex vivo response was strongly correlated with the in vivo platelet response. Induced Pluripotent Stem Cells (iPSCs) from one patient with mutated MYH9 differentiated into functional megakaryocytes that responded to Eltrombopag. Combining patient-derived cells and iPSCs with the 3D bone marrow model technology allows having a reproducible system for studying drug mechanisms and for individualized, pre-treatment selection of effective therapy in Inherited Thrombocytopenias.

Platelets are tiny cell fragments essential for blood to clot. They are created and released into the bloodstream by megakaryocytes, giant cells that live in the bone marrow. In certain genetic diseases, such as Inherited Thrombocytopenia, the bone marrow fails to produce enough platelets: this leaves patients extremely susceptible to bruising, bleeding, and poor clotting after an injury or surgery. Certain patients with Inherited Thrombocytopenia respond well to treatments designed to boost platelet production, but others do not. Why these differences exist could be investigated by designing new test systems that recreate the form and function of bone marrow in the laboratory. However, it is challenging to build the complex and poorly understood bone marrow environment outside of the body. Here, Di Buduo et al. have developed an artificial three-dimensional miniature organ bioreactor system that recreates the key features of bone marrow. In this system, megakaryocytes were grown from patient blood samples, and hooked up to a tissue scaffold made of silk. The cells were able to grow as if they were in their normal environment, and they could shed platelets into an artificial bloodstream. After treating megakaryocytes with drugs to stimulate platelet production, Di Buduo et al. found that the number of platelets recovered from the bioreactor could accurately predict which patients would respond to these drugs in the clinic. This new test system enables researchers to predict how a patient will respond to treatment, and to tailor therapy options to each individual. This technology could also be used to test new drugs for Inherited Thrombocytopenias and other blood-related diseases; if scaled-up, it could also, one day, generate large quantities of lab-grown blood cells for transfusion.

Expression and functional characterization of the large-conductance calcium and voltage-activated potassium channel Kca 1.1 in megakaryocytes and platelets.

BACKGROUND: Ion channels are transmembrane proteins that play important roles in cell function regulation modulating ionic cell permeability. In megakaryocytes and platelets, regulated ion flows have been demonstrated to modulate platelet production and function. However, a relatively limited characterization of ion channel expression and function is available in the human megakaryocyte-platelet lineage. OBJECTIVE: We analyzed the expression and function of the large-conductance calcium and voltage-activated potassium channel Kca 1.1 (also known as Maxi-K, BK, slo1) in human megakaryocytes and platelets. METHODS: To investigate the functionality of Kca 1.1, we exploited different agonists (BMS-191011, NS1619, NS11021, epoxyeicosatrienoic acid isoforms) and inhibitors (iberiotoxin, penitrem A) of the channel. RESULTS: In megakaryocytes, Kca 1.1 agonists determined a decreased proplatelet formation and altered interaction with the extracellular matrix. Analysis of the actin cytoskeleton demonstrated a significant decrease in megakaryocyte spreading and adhesion to collagen. In platelets, the opening of the channel Kca 1.1 led to a reduced sensitivity to agonists with blunted aggregation in response to ADP, with an inhibitory capacity additive to that of aspirin. The Kca 1.1 agonists, but not the inhibitors, determined a reduction of platelet adhesion and aggregation onto immobilized collagen underflow to an extent similar to that of aspirin and ticagrelor. The opening of the Kca 1.1 resulted in cell hyperpolarization impairing free intracellular calcium in ADP-stimulated platelets and megakaryocytes. CONCLUSIONS: The present study reveals new mechanisms in platelet formation and activation, suggesting that targeting Kca 1.1 channels might be of potential pharmacological interest in hemostasis and thrombosis.

Latest culture techniques: cracking the secrets of bone marrow to mass-produce erythrocytes and platelets ex vivo.

Since the dawn of medicine, scientists have carefully observed, modeled and interpreted the human body to improve healthcare. At the beginning there were drawings and paintings, now there is three-dimensional modeling. Moving from two-dimensional cultures and towards complex and relevant biomaterials, tissue-engineering approaches have been developed in order to create three-dimensional functional mimics of native organs. The bone marrow represents a challenging organ to reproduce because of its structure and composition that confer it unique biochemical and mechanical features to control hematopoiesis. Reproducing the human bone marrow niche is instrumental to answer the growing demand for human erythrocytes and platelets for fundamental studies and clinical applications in transfusion medicine. In this review, we discuss the latest culture techniques and technological approaches to obtain functional platelets and erythrocytes ex vivo. This is a rapidly evolving field that will define the future of targeted therapies for thrombocytopenia and anemia, but also a long-term promise for new approaches to the understanding and cure of hematologic diseases.

Defective interaction of mutant calreticulin and SOCE in megakaryocytes from patients with myeloproliferative neoplasms.

Approximately one-fourth of patients with essential thrombocythemia or primary myelofibrosis carry a somatic mutation of the calreticulin gene (CALR), the gene encoding for calreticulin. A 52-bp deletion (type I mutation) and a 5-bp insertion (type II mutation) are the most frequent genetic lesions. The mechanism(s) by which a CALR mutation leads to a myeloproliferative phenotype has been clarified only in part. We studied the interaction between calreticulin and store-operated calcium (Ca2+) entry (SOCE) machinery in megakaryocytes (Mks) from healthy individuals and from patients with CALR-mutated myeloproliferative neoplasms (MPNs). In Mks from healthy subjects, binding of recombinant human thrombopoietin to c-Mpl induced the activation of signal transducer and activator of transcription 5, AKT, and extracellular signal-regulated kinase 1/2, determining inositol triphosphate-dependent Ca2+ release from the endoplasmic reticulum (ER). This resulted in the dissociation of the ER protein 57 (ERp57)-mediated complex between calreticulin and stromal interaction molecule 1 (STIM1), a protein of the SOCE machinery that leads to Ca2+ mobilization. In Mks from patients with CALR-mutated MPNs, defective interactions between mutant calreticulin, ERp57, and STIM1 activated SOCE and generated spontaneous cytosolic Ca2+ flows. In turn, this resulted in abnormal Mk proliferation that was reverted using a specific SOCE inhibitor. In summary, the abnormal SOCE regulation of Ca2+ flows in Mks contributes to the pathophysiology of CALR-mutated MPNs. In perspective, SOCE may represent a new therapeutic target to counteract Mk proliferation and its clinical consequences in MPNs.

Modular flow chamber for engineering bone marrow architecture and function.

The bone marrow is a soft, spongy, gelatinous tissue found in the hollow cavities of flat and long bones that support hematopoiesis in order to maintain the physiologic turnover of all blood cells. Silk fibroin, derived from Bombyx mori silkworm cocoons, is a promising biomaterial for bone marrow engineering, because of its tunable architecture and mechanical properties, the capacity of incorporating labile compounds without loss of bioactivity and demonstrated ability to support blood cell formation. In this study, we developed a bone marrow scaffold consisting of a modular flow chamber made of polydimethylsiloxane, holding a silk sponge, prepared with salt leaching methods and functionalized with extracellular matrix components. The silk sponge was able to support efficient platelet formation when megakaryocytes were seeded in the system. Perfusion of the chamber allowed the recovery of functional platelets based on multiple activation tests. Further, inhibition of AKT signaling molecule, which has been shown to be crucial in regulating physiologic platelet formation, significantly reduced the number of collected platelets, suggesting the applicability of this tissue model for evaluation of the effects of bone marrow exposure to compounds that may affect platelet formation. In conclusion, we have bioengineered a novel modular system that, along with multi-porous silk sponges, can provide a useful technology for reproducing a simplified bone marrow scaffold for blood cell production ex vivo.