Intact megakaryocytes in the venous blood as a marker for thrombopoiesis

Occurrence and role of lung megakaryocytes in infection and inflammation

Megakaryocytes (MKs) are large cells giving rise to platelets. It is well established that in adults, MKs develop from hematopoietic stem cells and reside in the bone marrow. MKs are also rare but normal constituents of the venous blood returning to the lungs, and MKs are found in the lung vasculature (MK_circ), suggesting that these cells are migrants from the bone marrow and get trapped in lung capillaries where the final steps of platelet production can occur. An unprecedented increase in the number of lung and circulating MKs was described in coronavirus disease 2019 (COVID-19) patients, suggesting that lung thrombopoiesis may be increased during lung infection and/or thromboinflammation. In addition to the population of platelet-producing intravascular MKs in the lung, a population of lung-resident megakaryocytes (MK_L) has been identified and presents a specific immune signature compared to its bone marrow counterparts. Recent single-cell analysis and intravital imaging have helped us gain a better understanding of these populations in mouse and human. This review aims at summarizing the recent data on increased occurrence of lung MKs and discusses their origin, specificities, and potential role in homeostasis and inflammatory and infectious lung diseases. Here, we address remaining questions, controversies, and methodologic challenges for further studies of both MK_circ and MK_L.

Global characterization of megakaryocytes in bone marrow, peripheral blood, and cord blood by single-cell RNA sequencing

Megakaryocytes (MK) are mainly derived from bone marrow and are mainly involved in platelet production. Studies have shown that MK derived from bone marrow may have immune function, and that MK from peripheral blood are associated with prostate cancer. Single-cell transcriptome sequencing can help us better understand the heterogeneity and potential function of MK cell populations in bone marrow (BM), peripheral Blood (PB), and cord blood (CB) of healthy and diseased people.We integrated more than 1.2 million single-cell transcriptome data from 132 samples of PB, BM, and CB from healthy individuals and patients from different dataset. We examined the MK (including MK and product of MK) by single-cell RNA sequencing data analysis methods and identification of MK-related protein expression by the Human Protein atlas. We investigate the relationship between the MK subtype and Non-Small Cell Lung Cancer (NSCLC) in 77 non-cancer and 402 NSCLC. We found that MK were widely distributed and the amount of MK in peripheral blood was more than that in bone marrow and there were specificity MK subtypes in peripheral blood. We found classical MK1 with typical MK characteristics and non-classical MK2 closely related to immunity which was the most common subtype in bone marrow and cord blood. Classical MK1 was closely related to Non-Small Cell Lung Cancer (NSCLC) and can be used as a diagnostic marker. MK2 may have potential adaptive immune function and play a role in tumor NSCLC and autoimmune diseases Systemic Lupus Erythematosus. MK have 14 subtypes and are widely distributed in PB, CB, and BM. MK subtypes are closely related to immunity and have potential to be a diagnostic indicator of NSCLC.

Megakaryocytes in cubital venous blood in patients with chronic myeloproliferative diseases

33 patients with chronic myelo-proliferative disease were investigated for megakaryocytes in cubital venous blood. 6 Patients had chronic myeloid leukaemia, 11 polycythaemia vera and 16 myelofibrosis. In all patients, a significantly higher number of megakaryocytes than in normal adult humans was found. In patients with chronic myeloid leukaemia and myelofibrosis, an increased number of intact megakaryocytes was found, indicating thrombopoiesis in the peripheral part of the upper extremity. 2 patients with myelofibrosis showed a % of intact megakaryocytes greater than 25, as found in blood from the inferior vena cava in normal adults. In patients with chronic myeloid leukaemia, some of the megakaryocytes were smaller than normal, whereas in myelofibrosis, some of the megakaryocytes were larger than normal, with increased lobulation of nuclei. Active thrombopoiesis in the peripheral part of the extremities can be of great importance, when splenectomy is considered in treatment of myelofibrosis.