Localization and Regulation of Thrombopoietin mRNA Expression in Human Kidney, Liver, Bone Marrow, and Spleen Using In Situ Hybridization

The hematopoietic microenvironment of the fetal liver and transient abnormal myelopoiesis associated with Down syndrome: A review

Transient abnormal myelopoiesis (TAM) in neonates with Down syndrome is a distinct form of leukemia or preleukemia that mirrors the hematological features of acute megakaryoblastic leukemia. However, it typically resolves spontaneously in the early stages. TAM originates from fetal liver (FL) hematopoietic precursor cells and emerges due to somatic mutations in GATA1 in utero. In TAM, progenitor cells proliferate and differentiate into mature megakaryocytes and granulocytes. This process occurs both in vitro, aided by hematopoietic growth factors (HGFs) produced in the FL, and in vivo, particularly in specific anatomical sites like the FL and blood vessels. The FL's hematopoietic microenvironment plays a crucial role in TAM's pathogenesis and may contribute to its spontaneous regression. This review presents an overview of current knowledge regarding the unique features of TAM in relation to the FL hematopoietic microenvironment, focusing on the functions of HGFs and the pathological features of TAM.

Thrombopoietin-Dependent Myelo-Megakaryopoiesis Fuels Thromboinflammation and Worsens Antibody-Mediated Chronic Renal Microvascular Injury

SIGNIFICANCE STATEMENT

Kidney-derived thrombopoietin (TPO) increases myeloid cell and platelet production during antibody-mediated chronic kidney disease (AMCKD) in a mouse model, exacerbating chronic thromobinflammation in microvessels. The effect is mirrored in patients with extracapillary glomerulonephritis associated with thromboinflammation, TGF β -dependent glomerulosclerosis, and increased bioavailability of TPO. Neutralization of TPO in mice normalized hematopoiesis, reduced chronic thromboinflammation, and ameliorated renal disease. The findings suggest that TPO is a relevant biomarker and a promising therapeutic target for patients with CKD and other chronic thromboinflammatory diseases.Neutralization of TPO in mice normalized hematopoiesis, reduced chronic thromboinflammation, and ameliorated renal disease. The findings suggest that TPO is a relevant biomarker and a promising therapeutic target for patients with CKD and other chronic thromboinflammatory diseases.

BACKGROUND

Chronic thromboinflammation provokes microvascular alterations and rarefaction, promoting organ dysfunction in individuals with various life-threatening diseases. Hematopoietic growth factors (HGFs) released by the affected organ may sustain emergency hematopoiesis and fuel the thromboinflammatory process.

METHODS

Using a murine model of antibody-mediated chronic kidney disease (AMCKD) and pharmacological interventions, we comprehensively monitored the response to injury in the circulating blood, urine, bone marrow, and kidney.

RESULTS

Experimental AMCKD was associated with chronic thromboinflammation and the production of HGFs, especially thrombopoietin (TPO), by the injured kidney, which stimulated and skewed hematopoiesis toward myelo-megakaryopoiesis. AMCKD was characterized by vascular and kidney dysfunction, TGF β -dependent glomerulosclerosis, and microvascular rarefaction. In humans, extracapillary glomerulonephritis is associated with thromboinflammation, TGF β -dependent glomerulosclerosis, and increased bioavailability of TPO. Analysis of albumin, HGF, and inflammatory cytokine levels in sera from patients with extracapillary glomerulonephritis allowed us to identify treatment responders. Strikingly, TPO neutralization in the experimental AMCKD model normalized hematopoiesis, reduced chronic thromboinflammation, and ameliorated renal disease.

CONCLUSION

TPO-skewed hematopoiesis exacerbates chronic thromboinflammation in microvessels and worsens AMCKD. TPO is both a relevant biomarker and a promising therapeutic target in humans with CKD and other chronic thromboinflammatory diseases.

Review on the Biogenesis of Platelets in Lungs and Its Alterations in SARS-CoV-2 Infection Patients

Thrombocytes (platelets) are the type of blood cells that are involved in hemostasis, thrombosis, etc. For the conversion of megakaryocytes into thrombocytes, the thrombopoietin (TPO) protein is essential which is encoded by the TPO gene. TPO gene is present in the long arm of chromosome number 3 (3q26). This TPO protein interacts with the c-Mpl receptor, which is present on the outer surface of megakaryocytes. As a result, megakaryocyte breaks into the production of functional thrombocytes. Some of the evidence shows that the megakaryocytes, the precursor of thrombocytes, are seen in the lung's interstitium. This review focuses on the involvement of the lungs in the production of thrombocytes and their mechanism. A lot of findings show that viral diseases, which affect the lungs, cause thrombocytopenia in human beings. One of the notable viral diseases is COVID-19 or severe acute respiratory syndrome caused by SARS-associated coronavirus 2 (SARS-CoV-2). SARS-CoV-2 caused a worldwide alarm in 2019 and a lot of people suffered because of this disease. It mainly targets the lung cells for its replication. To enter the cells, these virus targets the angiotensin-converting enzyme-2 (ACE-2) receptors that are abundantly seen on the surface of the lung cells. Recent reports of COVID-19-affected patients reveal the important fact that these peoples develop thrombocytopenia as a post-COVID condition. This review elaborates on the biogenesis of platelets in the lungs and the alterations of thrombocytes during the COVID-19 infection.

Oral eltrombopag versus subcutaneous recombinant human thrombopoietin for promoting platelet engraftment after allogeneic stem cell transplantation: A prospective, non-inferiority, randomized controlled trial

Delayed platelet engraftment (DPE) is associated with poor survival and increased transplantation-related mortality after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Therefore, treatments are needed to improve platelet engraftment and prevent DPE. We performed a phase three, non-inferior, randomized controlled study of eltrombopag or recombinant human thrombopoietin (rhTPO) to promot platelet engraftment after allo-HSCT. Candidates for allo-HSCT were randomly assigned to receive oral eltrombopag (50 mg daily) or subcutaneous rhTPO (15000U daily) from the first-day post-transplantation. The primary endpoint was the cumulative numbers of platelet engraftment (platelet recovery ≥20 × 10⁹ /L, without transfusion, for seven consecutive days) on day 60 after transplantation. We performed intention-to-treat analyses with a non-inferior margin of -15%. A total of 92 participants underwent randomization. 44 and 48 patients were randomized to the eltrombopag and rhTPO groups, respectively. The median duration of follow-up was 360 days (range: 12-960 days). The cumulative incidence of platelet engraftment on day 60 after transplantation in eltrombopag group was 86.4% (38/44) compared with 85.4% (41/48) in the rhTPO group (absolute risk difference [ARD] 1%, one-sided lower limit of 95% confidence interval [CI] -13.28%, P_{non-inferirioty}  = 0.014). The rate of DPE in the eltrombopag group was 6.8% (3/44) compared with 12.5% (6/48) in the rhTPO group (ARD -5.7%, one-sided higher limit of 95% CI 6.28%, P_{non-inferirioty}  = 0.063). Approximately, three-fourths of non-hematologic adverse events were not observed in the eltrombopag group but three patients (3/48, 6%) experienecd them in the rhTPO group. In addition, platelet transfusions unite from day 0 to day 21, or from day 22 to day 60, progression-free survival, overall survival were not significantly different between both groups. Eltrombopag was non-inferior to rhTPO in promoting platelet engraftment post allo-HSCT for patients with hematological malignancy. Oral eltrombopag was more convenient for patients than subcutaneous rhTPO (NCT03515096).

Essential Thrombocythemia in Children and Adolescents

Simple Summary

Among chronic Ph-negative myeloproliferative neoplasms, essential thrombocythemia is found in children with low but increasing incidence. The diagnostic and clinical features do not completely overlap with ET of adult age. A significant number of cases, in fact, do not meet the criteria of clonality, and many cases require extensive clinical evaluation to exclude secondary, reactive forms. Therefore, histological analysis of bone marrow biopsy is necessary, and its use should be enforced. The clinical course appears to be more benign, at least within the first decades of observation, with the incidence of thrombotic events being much lower than in adults (4 % vs. 30%). Hemorrhages are mostly irrelevant. Therefore, the management should be carefully adapted to the individual patient, balancing the risk of future complications with long-term collateral effects of any drug. This review analyzes the peculiarities of the disease facing similarities and differences with adult scenarios.

Abstract

This paper reviews the features of pediatric essential thrombocythemia (ET). ET is a rare disease in children, challenging pediatric and adult hematologists alike. The current WHO classification acknowledges classical Philadelphia-negative MPNs and defines diagnostic criteria, mainly encompassing adult cases. The presence of one of three driver mutations (JAK2V617F, CALR, and MPL mutations) represent the proof of clonality typical of ET. Pediatric ET cases are thus usually confronted by adult approaches. These can fit only some patients, because only 25–40% of cases present one of the driver mutations. The diagnosis of hereditary, familial thrombocytosis and the exclusion of reactive/secondary thrombocytosis must be part of the diagnostic process in children and can clarify most of the negative cases. Still, many children present a clinical, histological picture of ET, with a molecular triple wild-type status. Moreover, prognosis seems more benign, at least within the first few decades of follow-up. Thrombotic events are rare, and only minor hemorrhages are ordinarily observed. As per the management, the need to control symptoms must be balanced with the collateral effects of lifelong drug therapy. We conclude that these differences concert a compelling case for a very careful therapeutic approach and advocate for the importance of further cooperative studies.

The MPL mutation

Myeloproliferative neoplasms (MPN) patients share driver mutations in JAK2, MPL or CALR genes leading to the activation of the thrombopoietin receptor (TPOR) and downstream signaling pathways. JAK2 mutation drives all the three major entities of MPN (Polycythemia Vera, Essential Thrombocythemia and Primary Myelofibrosis) through the constitutive activation of TPOR, erythropoietin (EPOR) and colony stimulating factor 3 receptor (CSF3R) signaling. MPL is a proto-oncogene encoding for TPOR, the hematopoietic growth factor receptor of myeloid stem cells. MPL mutants induce the stable dimerization of TPOR that in turn activate JAK2 and the thrombopoietin pathway. The thrombopoietin pathway plays an important role in the development of megakaryocytes and platelets as well as the self-renewal of hematopoietic stem cells. Little wonder therefore that mutations of MPL result in thrombocytosis, leading to an abnormal MPL trafficking or receptor activation. Finally, some extremely rare germline genetic variants in MPL can induce MPN-like hereditary disease. Against this molecular background, TPOR is a key actor in the MPN development and MPL mutations are of major relevance to fully elucidate the molecular mechanisms underlying the clinical manifestations of MPN and to arrange novel therapeutic strategies aiming to disrupt the dysegulated signaling cascade. This chapter will focus on the role MPL in the pathogenesis of MPN and in familial thrombocytosis and will review these different subtypes of somatic and germline genetic variants by dissecting how they impact clinical phenotype.

Thrombopoietin from hepatocytes promotes hematopoietic stem cell regeneration after myeloablation

The bone marrow niche plays critical roles in hematopoietic recovery and hematopoietic stem cell (HSC) regeneration after myeloablative stress. However, it is not clear whether systemic factors beyond the local niche are required for these essential processes in vivo. Thrombopoietin (THPO) is a key cytokine promoting hematopoietic rebound after myeloablation and its transcripts are expressed by multiple cellular sources. The upregulation of bone marrow-derived THPO has been proposed to be crucial for hematopoietic recovery and HSC regeneration after stress. Nonetheless, the cellular source of THPO in myeloablative stress has never been investigated genetically. We assessed the functional sources of THPO following two common myeloablative perturbations: 5-fluorouracil (5-FU) administration and irradiation. Using a Thpo translational reporter, we found that the liver but not the bone marrow is the major source of THPO protein after myeloablation. Mice with conditional Thpo deletion from osteoblasts and/or bone marrow stromal cells showed normal recovery of HSCs and hematopoiesis after myeloablation. In contrast, mice with conditional Thpo deletion from hepatocytes showed significant defects in HSC regeneration and hematopoietic rebound after myeloablation. Thus, systemic THPO from the liver is necessary for HSC regeneration and hematopoietic recovery in myeloablative stress conditions.

Inflammatory indexes in preoperative blood routine to predict early recurrence of hepatocellular carcinoma after curative hepatectomy

Background

The inflammation indexes in blood routine play an essential role in evaluating the prognosis of patients with hepatocellular carcinoma, but the effect on early recurrence has not been clarified. The study aimed to investigate the risk factors of early recurrence (within 2 years) and recurrence-free survival after curative hepatectomy and explore the role of inflammatory indexes in predicting early recurrence.

Methods

The baseline data of 161 patients with hepatocellular carcinoma were analyzed retrospectively. The optimal cut-off value of the inflammatory index was determined according to the Youden index. Its predictive performance was compared by the area under the receiver operating characteristic curve. Logistic and Cox regression analyses were used to determine the risk factors of early recurrence and recurrence-free survival.

Results

The area under the curve of monocyte to lymphocyte ratio (MLR) for predicting early recurrence was 0.700, which was better than systemic inflammatory response index (SIRI), neutrophil to lymphocyte ratio (NLR), platelet to lymphocyte ratio (PLR) and systemic immune-inflammatory index (SII). MLR, tumour size, tumour differentiation and BCLC stage are all risk factors for early recurrence and recurrence-free survival of HCC. Combining the above four risk factors to construct a joint index, the area under the curve for predicting early recurrence was 0.829, which was better than single MLR, tumour size, tumour differentiation and BCLC stage. Furthermore, with the increase of risk factors, the recurrence-free survival of patients is worse.

Conclusion

The combination of MLR and clinical risk factors is helpful for clinicians to identify high-risk patients with early recurrence and carry out active postoperative adjuvant therapy to improve the prognosis of patients.

Thrombopoietin Promotes Angiogenesis and Disease Progression in Patients with Multiple Myeloma

Multiple myeloma (MM) progression closely depends on bone marrow (BM) angiogenesis. Several factors sustain angiogenesis, including cytokines, growth factors, and cell-to-cell interactions. Herein, BM thrombopoietin (TPO) was shown to support angiogenesis and disease progression in MM. Patients with MM at different progression phases had higher levels of BM and circulating TPO than monoclonal gammopathy of undetermined significance/smoldering MM patients, suggesting that TPO correlates with disease progression and prognosis. Endothelial cells from patients with monoclonal gammopathy of undetermined significance (MGECs) and endothelial cells from MM (MMECs) expressed TPO receptor, and the TPO treatment triggered their angiogenic capabilities in vitro. Indeed, TPO-treated MGECs and MMECs showed enhanced angiogenesis on Matrigel and spontaneous cell migration and chemotaxis by acting as a chemotactic agent. TPO also had an angiogenic activity in vivo in the chorioallantoic membrane assay system. Finally, TPO treatment increased the release of active matrix metalloproteinase (MMP)-9 and MMP-2 in MGECs and of MMP-2 in MMECs and affected the balance between angiogenic/antiangiogenic factors in the MM BM. Our results support the angiogenic activity of TPO, and suggest that it may have a critical role in promoting the angiogenic switch during MM progression. Accordingly, TPO may be envisaged as a new angiogenic and prognostic factor in patients with MM.

A novel model for predicting posthepatectomy liver failure based on liver function and degree of liver resection in patients with hepatocellular carcinoma

BACKGROUND

The permissible liver resection rate for preventing posthepatectomy liver failure (PHLF) remains unclear. We aimed to develop a novel PHLF-predicting model and to strategize hepatectomy for hepatocellular carcinoma (HCC).

METHODS

This retrospective study included 335 HCC patients who underwent anatomical hepatectomy at eight institutions between 2013 and 2017. Risk factors, including volume-associated liver-estimating parameters, for PHLF grade B-C were analyzed in a training set (n = 122) via multivariate analysis, and a PHLF prediction model was developed. The utility of the model was evaluated in a validation set (n = 213).

RESULTS

Our model was based on the three independent risk factors for PHLF identified in the training set: volume-associated indocyanine green retention rate at 15 min, platelet count, and prothrombin time index (the VIPP score). The areas under the receiver operating characteristic curve of the VIPP scores for severe PHLF in the training and validation sets were 0.864 and 0.794, respectively. In both sets, the VIPP score stratified patients at risk for severe PHLF, with a score of 3 (specificity, 0.92) indicating higher risk.

CONCLUSION

Our model facilitates the selection of the appropriate hepatectomy procedure by providing permissible liver resection rates based on VIPP scores.

Impact of diabetes mellitus on immature platelet fraction and its association with coronary artery disease

BACKGROUND

Higher prothrombotic status and alterations in platelet function and thrombopoiesis are associated with diabetes mellitus (DM). We assessed the impact of diabetes and glucose control on the immature platelet fraction (IPF) and their relationship with prevalence and extent of coronary artery disease (CAD).

METHODS

Consecutive patients undergoing coronary angiography were included. Significant CAD was defined as at least one vessel stenosis greater than 50%. IPF levels were measured at admission by routine blood cells count (A Sysmex XE-2100).

RESULTS

We included 1781 patients, of whom 660 (37.1%) suffered from diabetes. Diabetes was associated with advanced age and a higher cardiovascular risk profile. No difference in the mean values of IPF were observed between patients with or without DM (3.6 ± 2.5 vs 3.5 ± 2.5, P = 0.39) and neither in the rate of patients with IPF above the median (2.9%) (51.6% vs 50.6%, P = 0.73). In patients with DM, the IPF levels did not relate with glucose control parameters (glycaemia: r = -0.024, P = 0.54, glycosylated haemoglobin: r = 0.11, P = 0.72). The prevalence of CAD was significantly lower in patients with DM and IPF greater than the median (80.5% vs 86.5%, P = 0.04, adjusted odds ratio [OR] [95% confidence interval {CI}] = 0.57[0.36-0.91], P = 0.02), while not left main/three-vessel CAD (36.9% vs 38.2%, P = 0.75, adjusted OR [95%CI] = 0.91[0.64-1.28], P = 0.90).

CONCLUSION

In the present study, neither DM nor glucose control are independent predictors of IPF above the median. In patients with DM, higher IPF levels were associated with a lower prevalence of CAD and with a similar extent of severe CAD and angiographic findings. Therefore, until new data become available, elevated IPF should not be systematically applied on a large scale as cardiovascular risk marker in patients with diabetes.

Hematopoiesis and Cardiovascular Disease

A central feature of atherosclerosis, the most prevalent chronic vascular disease and root cause of myocardial infarction and stroke, is leukocyte accumulation in the arterial wall. These crucial immune cells are produced in specialized niches in the bone marrow, where a complex cell network orchestrates their production and release. A growing body of clinical studies has documented a correlation between leukocyte numbers and cardiovascular disease risk. Understanding how leukocytes are produced and how they contribute to atherosclerosis and its complications is, therefore, critical to understanding and treating the disease. In this review, we focus on the key cells and products that regulate hematopoiesis under homeostatic conditions, during atherosclerosis and after myocardial infarction.

Tibial growth plate vascularization is inhibited by the dithiocarbamate pesticide thiram in chickens: potential relationship to peripheral platelet counts alteration

The widespread use of thiram has raised concerns for health and its toxic effects, but the underlying toxicity mechanism on platelets and bones is poorly defined. Here, we found a significant increase in the number of platelets in chickens with the thiram intake, due to the increased expression of thrombopoietin mRNA in the dysfunction liver. Furthermore, the decreased vascular distribution and cell death of chondrocytes in the tibial growth plates (TGPs) were observed, resulting in bone growth inhibition, which is associated with the abnormal activation of platelets leading to the extraordinary decrease of vascular endothelial growth factor A (VEGFA) and angiopoietin-1 protein were released and their corresponding receptors VEGFR2 and Tie-2 expressions were also reduced in the TGPs. Taken together, these findings revealed that thiram has an adverse effect on bones and platelets, which may have a high risk of thrombosis and osteoarthritis.

Platelets in chronic liver disease, from bench to bedside

In the last decade, numerous studies revealed physiologic and pathophysiologic roles of platelets beyond haemostasis, a process to prevent and stop bleeding. These include the activation of the immune system and the promotion of inflammation, infection and cancer. Hence, the emerging view on the role of platelets has shifted - platelets are now seen as alert "sentinels" of the immune compartment, rather than passive bystanders. Herein, we review well-established and newly discovered features of platelets that define their natural role in maintaining blood haemostasis, but also their functional relationship with other cells of the immune system. We focus on recent studies underlining functional involvement of platelets in chronic liver diseases and cancer, as well as the effects of anti-platelet therapy in these contexts. Finally, we illustrate the potential of platelets as possible diagnostic and therapeutic tools in liver disease based on recently developed methodologies.

The Birth and Death of Platelets in Health and Disease

Blood platelets are involved in a wide range of physiological responses and pathological processes. Recent studies have considerably advanced our understanding of the mechanisms of platelet production and clearance, revealing new connections between the birth and death of these tiny, abundant cells. Key insights have also been gained into how physiological challenges such as inflammation, infection, and chemotherapy can affect megakaryocytes, the cells that produce platelets.

Icaritin Provokes Serum Thrombopoietin and Downregulates Thrombopoietin/MPL of the Bone Marrow in a Mouse Model of Immune Thrombocytopenia

Immune thrombocytopenia (ITP) is a common acquired autoimmune disease, and thrombopoietin (TPO) is an important cytokine that regulates the production of megakaryocytes and platelets. We have identified a biologically active component, icaritin, from a Chinese herba epimedii extract. Icaritin promotes platelet production and regulates T cell polarization, but its mechanism is not clear. In this study, the BALB/c mouse model of ITP was established by injection of an antiplatelet antibody every other day for seven total times. The antiplatelet sera were derived from guinea pigs immunized with the platelets of BALB/c mice. Mice with ITP were treated with icaritin at low, moderate, or high doses of 4.73, 9.45, and 18.90 mg/kg, respectively, for fourteen consecutive days. The present study shows that icaritin can significantly increase peripheral blood platelet counts and thrombocytocrit, increase the TPO level in serum, attenuate splenomegaly, and reduce the abnormal proliferation of megakaryocytes in the spleen and bone marrow. Icaritin can also downregulate the expression of bone marrow TPO, myeloproliferative leukemia virus oncogene (MPL), and p-Stat3. Our results suggest that icaritin can significantly improve the health of mice with ITP via possible downregulation of p-Stat3 expression in the JAK2/Stat3 phosphorylation signaling pathway and regulation of bone marrow TPO/MPL metabolism.

It's reticulated: the liver at the heart of atherosclerosis

Platelets play a critical role in both the initiation and progression of atherosclerosis, and even more so in the ensuing atherothrombotic complications. Low-dose aspirin remains the mainstay of antiplatelet therapy in high-risk patients by reducing the risk of myocardial ischemia, stroke or death due to cardiovascular disease. However, antiplatelet therapies lose their efficacy in people with diabetes mellitus, increasing the risk of future atherothrombotic events. The molecular mechanisms that promote platelet hyperactivity remain unclear but could be due to glycation-induced conformational changes of platelet membranes resulting in impaired aspirin entry or less-efficient acetylation/compensatory increase in COX-2 expression in newborn platelets. Emerging evidence from our laboratory and elsewhere suggest that enhanced platelet turnover (thrombopoiesis), particularly the production of immature reticulated platelets from the bone marrow, could contribute to atherosclerotic complications. We have identified a major role for neutrophil-derived S100A8/A9, a damage-associated molecular pattern, in driving reticulated thrombopoiesis by directly interacting with its receptors on Kupffer cells in the liver. In this review, we discuss the role of hepatic inflammation in driving reticulated platelet production and suggest potential targets to control their production, improve efficacy of current antiplatelet therapies and reduce the risk of atherothrombotic complications.

GPIbα is required for platelet-mediated hepatic thrombopoietin generation

Thrombopoietin (TPO), a hematopoietic growth factor produced predominantly by the liver, is essential for thrombopoiesis. Prevailing theory posits that circulating TPO levels are maintained through its clearance by platelets and megakaryocytes via surface c-Mpl receptor internalization. Interestingly, we found a two- to threefold decrease in circulating TPO in GPIbα^-/- mice compared with wild-type (WT) controls, which was consistent in GPIbα-deficient human Bernard-Soulier syndrome (BSS) patients. We showed that lower TPO levels in GPIbα-deficient conditions were not due to increased TPO clearance by GPIbα^-/- platelets but rather to decreased hepatic TPO mRNA transcription and production. We found that WT, but not GPIbα^-/-, platelet transfusions rescued hepatic TPO mRNA and circulating TPO levels in GPIbα^-/- mice. In vitro hepatocyte cocultures with platelets or GPIbα-coupled beads further confirm the disruption of platelet-mediated hepatic TPO generation in the absence of GPIbα. Treatment of GPIbα^-/- platelets with neuraminidase caused significant desialylation; however, strikingly, desialylated GPIbα^-/- platelets could not rescue impaired hepatic TPO production in vivo or in vitro, suggesting that GPIbα, independent of platelet desialylation, is a prerequisite for hepatic TPO generation. Additionally, impaired hepatic TPO production was recapitulated in interleukin-4/GPIbα-transgenic mice, as well as with antibodies targeting the extracellular portion of GPIbα, demonstrating that the N terminus of GPIbα is required for platelet-mediated hepatic TPO generation. These findings reveal a novel nonredundant regulatory role for platelets in hepatic TPO homeostasis, which improves our understanding of constitutive TPO regulation and has important implications in diseases related to GPIbα, such as BSS and auto- and alloimmune-mediated thrombocytopenias.

Hepatic thrombopoietin is required for bone marrow hematopoietic stem cell maintenance

Hematopoietic stem cell (HSC) maintenance depends on extrinsic cues. Currently, only local signals arising from the bone marrow niche have been shown to maintain HSCs. However, it is not known whether systemic factors also sustain HSCs. We assessed the physiological source of thrombopoietin (TPO), a key cytokine required for maintaining HSCs. Using Tpo^DsRed-CreER knock-in mice, we showed that TPO is expressed by hepatocytes but not by bone marrow cells. Deletion of Tpo from hematopoietic cells, osteoblasts, or bone marrow mesenchymal stromal cells does not affect HSC number or function. However, when Tpo is deleted from hepatocytes, bone marrow HSCs are depleted. Thus, a cross-organ factor, circulating TPO made in the liver by hepatocytes, is required for bone marrow HSC maintenance. Our results demonstrate that systemic factors, in addition to the local niche, are a critical extrinsic component for HSC maintenance.

Persistent elevation of plasma thrombopoietin levels after treatment in severe aplastic anemia

Although hematopoietic growth factors are found at high levels in aplastic anemia (AA) patients, little is known about their dynamic change over time after treatment. We examined plasma concentrations of hematopoietic growth factors sequentially in 55 severe AA patients, including 45 treatment-naive patients who had received immunosuppressive therapy (IST) or IST and eltrombopag, and 10 IST-refractory patients who had received eltrombopag only, focusing on thrombopoietin (TPO). TPO concentrations were much higher than normal in patients before treatment and then decreased in responders but not in nonresponders. We followed up on a cohort of nine patients who obtained stable complete remission for up to 7 years after IST and found that TPO levels declined gradually by 3 months after treatment, accompanying an increase in platelet counts, but stabilized at levels higher than normal. An inverse correlation was noted between TPO levels and platelet counts. The increased plasma TPO levels could be required to maintain normal platelet counts in remission and could also be attributed to reduced consumption by circulating platelets.

Recombinant Human Thrombopoietin Promotes Platelet Engraftment and Improves Prognosis of Patients with Myelodysplastic Syndromes and Aplastic Anemia after Allogeneic Hematopoietic Stem Cell Transplantation

Poor platelet graft function (PPGF) is a significant complication after allogeneic hematopoietic stem cell transplantation (allo-HSCT). However, no optimal treatment has been recommended. This study investigated aspects of platelet recovery after allo-HSCT, including prognostic value and the effect of recombinant human thrombopoietin (rhTPO). We retrospectively analyzed 275 patients who received allo-HSCT in our center. Of them, 135 (49.1%) patients had good platelet graft function (GPGF) and 140 (50.9%) had PPGF. The latter included 59 (21.5%) patients with primary PPGF and 81 (29.4%) with secondary PPGF. Multivariate analysis showed that male gender (P = .024), lower CD34⁺ cell count (P = .04), and no use of rhTPO (P <.001) were associated with PPGF. The 3-year overall survival rate of patients with PPGF (58%) was significantly less than that of patients with GPGF (82%; P <.001). We further analyzed the effect of rhTPO on prognosis of patients after allo-HSCT. Although no advantage was apparent when analyzing the entire cohort, for patients with myelodysplastic syndromes and aplastic anemia, rhTPO was associated with a significant survival advantage (P = .014).

Adult haematopoietic stem cell niches

Stem cell niches are specialized microenvironments that promote the maintenance of stem cells and regulate their function. Recent advances have improved our understanding of the niches that maintain adult haematopoietic stem cells (HSCs). These advances include new markers for HSCs and niche cells, systematic analyses of the expression patterns of niche factors, genetic tools for functionally identifying niche cells in vivo, and improved imaging techniques. Together, they have shown that HSC niches are perivascular in the bone marrow and spleen. Endothelial cells and mesenchymal stromal cells secrete factors that promote HSC maintenance in these niches, but other cell types also directly or indirectly regulate HSC niches.

Thrombocytopenia in chronic liver disease

Thrombocytopenia is a common haematological disorder in patients with chronic liver disease. It is multifactorial and severity of liver disease is the most influential factor. As a result of the increased risk of bleeding, thrombocytopenia may impact upon medical procedures, such as surgery or liver biopsy. The pathophysiology of thrombocytopenia in chronic liver disease has long been associated with the hypothesis of hypersplenism, where portal hypertension causes pooling and sequestration of all corpuscular elements of the blood, predominantly thrombocytes, in the enlarged and congested spleen. Other mechanisms of importance include bone marrow suppression by toxic substances, such as alcohol or viral infection, and immunological removal of platelets from the circulation. However, insufficient platelet recovery after relief of portal hypertension by shunt procedures or minor and transient recovery after splenic artery embolization have caused many to question the importance and relative contribution of this mechanism to thrombocytopenia. The discovery of the cytokine thrombopoietin has led to the elucidation of a central mechanism. Thrombopoietin is predominantly produced by the liver and is reduced when liver cell mass is severely damaged. This leads to reduced thrombopoiesis in the bone marrow and consequently to thrombocytopenia in the peripheral blood of patients with advanced-stage liver disease. Restoration of adequate thrombopoietin production post-liver transplantation leads to prompt restoration of platelet production. A number of new treatments that substitute thrombopoietin activity are available or in development.

Bone marrow failure unresponsive to bone marrow transplant is caused by mutations in thrombopoietin

We report 5 individuals in 3 unrelated families with severe thrombocytopenia progressing to trilineage bone marrow failure (BMF). Four of the children received hematopoietic stem cell transplants and all showed poor graft function with persistent severe cytopenias even after repeated transplants with different donors. Exome and targeted sequencing identified mutations in the gene encoding thrombopoietin (THPO): THPO R99W, homozygous in affected children in 2 families, and THPO R157X, homozygous in the affected child in the third family. Both mutations result in a lack of THPO in the patients' serum. For the 2 surviving patients, improvement in trilineage hematopoiesis was achieved following treatment with a THPO receptor agonist. These studies demonstrate that biallelic loss-of-function mutations in THPO cause BMF, which is unresponsive to transplant due to a hematopoietic cell-extrinsic mechanism. These studies provide further support for the critical role of the MPL-THPO pathway in hematopoiesis and highlight the importance of accurate genetic diagnosis to inform treatment decisions for BMF.

Neutrophil-derived S100 calcium-binding proteins A8/A9 promote reticulated thrombocytosis and atherogenesis in diabetes

Platelets play a critical role in atherogenesis and thrombosis-mediated myocardial ischemia, processes that are accelerated in diabetes. Whether hyperglycemia promotes platelet production and whether enhanced platelet production contributes to enhanced atherothrombosis remains unknown. Here we found that in response to hyperglycemia, neutrophil-derived S100 calcium-binding proteins A8/A9 (S100A8/A9) interact with the receptor for advanced glycation end products (RAGE) on hepatic Kupffer cells, resulting in increased production of IL-6, a pleiotropic cytokine that is implicated in inflammatory thrombocytosis. IL-6 acts on hepatocytes to enhance the production of thrombopoietin, which in turn interacts with its cognate receptor c-MPL on megakaryocytes and bone marrow progenitor cells to promote their expansion and proliferation, resulting in reticulated thrombocytosis. Lowering blood glucose using a sodium-glucose cotransporter 2 inhibitor (dapagliflozin), depleting neutrophils or Kupffer cells, or inhibiting S100A8/A9 binding to RAGE (using paquinimod), all reduced diabetes-induced thrombocytosis. Inhibiting S100A8/A9 also decreased atherogenesis in diabetic mice. Finally, we found that patients with type 2 diabetes have reticulated thrombocytosis that correlates with glycated hemoglobin as well as increased plasma S100A8/A9 levels. These studies provide insights into the mechanisms that regulate platelet production and may aid in the development of strategies to improve on current antiplatelet therapies and to reduce cardiovascular disease risk in diabetes.

Shen-Cao granules formulated based on traditional Chinese medicine alleviates bone marrow suppression caused by platinum-based anticancer reagents

BACKGROUND

The aim of this study was to evaluate effects of Shen-Cao granules for the prevention of thrombocytopenia caused by anticancer chemotherapy.

METHODS

In this prospective study, a total of 200 patients with various malignant tumors were enrolled and evenly divided into a Shen-Cao granule treatment (n = 100) and a control group (n = 100). After 2 cycles chemotherapy with any combination of platinum-based drugs (cisplatin, carboplatin, and nedaplatin), the blood platelet (PLT) counts, levels of the PLT production regulator thrombopoietin (TPO), PLT aggregation rates, and the PLT activation marker CD62P expressions were monitored for 2 weeks.

RESULTS

During 2 weeks of post-chemotherapy, the mean values of the minimum PLT count were 49.65 ± 7.35 × 10/L in the treatment group and 31.56 ± 9.32 × 10/L in the control group. The PLT count in the treatment group reached the lowest value 1.8 days later and recovered to a concentration ≥100 × 10/L 3 days earlier than in the control group. The concentrations of the TPO were 71.43 ± 1.74 and 87.24 ± 0.92 ng/mL in the treatment group and 65.75 ± 1.39 and 67.75 ± 0.67 ng/mL in the control group at 7 and 14 days post-chemotherapy, respectively. The maximum PLT aggregation rate declined after chemotherapy in the treatment group from 58.14 ± 11.46% to 52.89 ± 10.52%, while it increased in the control group from 56.94 ± 10.55% to 61.75 ± 12.26%. Coordinately, the expression of CD62P in the treatment group decreased from 6.17 ± 0.59% to 4.89 ± 0.72%, while it increased from 6.09 ± 0.75% to 7.75 ± 0.67% in the control group.

CONCLUSION

Our study demonstrated that Shen-Cao granule treatment alleviated thrombocytopenia after chemotherapy, and reduced tumor-induced PLT activation and aggregation.

Thrombopoietin Secretion by Human Ovarian Cancer Cells

The thrombopoietin (TPO) gene expression in human ovary and cancer cells from patients with ovarian carcinomatosis, as well as several cancer cell lines including MDA-MB231 (breast cancer), K562 and HL60 (Leukemic cells), OVCAR-3NIH and SKOV-3 (ovarian cancer), was performed using RT PCR, real-time PCR, and gene sequencing. Human liver tissues are used as controls. The presence of TPO in the cells and its regulation by activated protein C were explored by flow cytometry. TPO content of cell extract as well as plasma of a patient with ovarian cancer was evaluated by ELISA. The functionality of TPO was performed in coculture on the basis of the viability of a TPO-dependent cell line (Ba/F3), MTT assay, and Annexin-V labeling. As in liver, ovarian tissues and all cancer cells lines except the MDA-MB231 express the three TPO-1 (full length TPO), TPO-2 (12 bp deletion), and TPO-3 (116 pb deletion) variants. Primary ovarian cancer cells as well as cancer cell lines produce TPO. The thrombopoietin production by OVCAR-3 increased when cells are stimulated by aPC. OVCAR-3 cell's supernatant can replace exogenous TPO and inhibited TPO-dependent cell line (Ba/F3) apoptosis. The thrombopoietin produced by tumor may have a direct effect on thrombocytosis/thrombosis occurrence in patients with ovarian cancer.

Platelet clearance by the hepatic Ashwell-Morrell receptor: mechanisms and biological significance

The daily production of billions of platelets must be regulated to avoid spontaneous bleeding or arterial occlusion and organ damage. Complex mechanisms control platelet production and clearance in physiological and pathological conditions. This review will focus on the mechanisms of platelet senescence with specific emphasis on the role of post-translational modifications in platelet life-span and thrombopoietin production downstream of the hepatic Ashwell-Morrell receptor.

Novel mechanisms of platelet clearance and thrombopoietin regulation

PURPOSE OF REVIEW

The human body produces and removes 10 platelets daily to maintain a normal steady-state platelet count. Platelet production must be tightly regulated to avoid spontaneous bleeding or arterial occlusion and organ damage. Multifaceted and complex mechanisms control platelet removal and production in physiological and pathological conditions. This review will focus on different mechanisms of platelet clearance, with focus on the biological significance of platelet glycans.

RECENT FINDINGS

The Ashwell-Morrell receptor (AMR) recognizes senescent, desialylated platelets under steady state conditions. Desialylated platelets and the AMR are the physiological ligand-receptor pair regulating hepatic thrombopoietin (TPO) mRNA production, resolving the longstanding mystery of steady state TPO regulation. The AMR-mediated removal of desialylated platelets regulates TPO synthesis in the liver by recruiting JAK2 and STAT3 to increase thrombopoiesis.

SUMMARY

Inhibition of TPO production downstream of the hepatic AMR-JAK2 signaling cascade could additionally contribute to the thrombocytopenia associated with JAK1/2 treatment, which is clinically used in myeloproliferative neoplasms.

Determinants of platelet count are different in patients with compensated and decompensated cirrhosis

BACKGROUND & AIMS

Different mechanisms including portal hypertension and hypersplenism have been involved in the development of thrombocytopenia in cirrhosis. However, the relative contribution of each one is unknown. The aim was to evaluate simultaneously different mechanisms that determine platelet count in cirrhosis.

METHODS

Cross-sectional study including cirrhotics (n = 120) with hepatic venous pressure gradient (HVPG) measurement. Samples were obtained from peripheral (P) veins to evaluate thrombopoietin (TPO), stem cell factor, hepatocyte growth factor (HGF), tumour necrosis factor, interleukin-(IL6) and (IL11) and from hepatic (H) veins to evaluate TPO. A subgroup (n = 72) had spleen volume estimation. H and P-TPO were also measured in non-cirrhotic patients (n = 15).

RESULTS

Patients (Child A: 55, B: 43, C: 22) had a median platelet count of 81 000/mm(3) (IQR 60 500, 110 750), which correlated with spleen volume (r = -0.38, P < 0.001). Platelets were associated also to HVPG (r = -0.47, P = 0.004) and P-TPO (r = 0.31, P = 0.050) only in compensated patients. H-TPO decreased, and the proportion of patients with P-TPO > H-TPO increased, with the presence and the severity of liver disease. H-TPO was correlated with liver function (bilirubin r = -0.350, P < 0.001 and international normalized ratio r = -0.227, P = 0.011). Patients with H-TPO < P-TPO had higher levels of IL-11 and HGF.

CONCLUSION

Platelet count in cirrhosis is associated mainly to spleen volume, although portal hypertension as estimated by HVPG and liver function plays a significant role in compensated patients. H-TPO and the proportion of patients with P-TPO > H-TPO were associated to the presence and severity of liver disease.

Regulating billions of blood platelets: glycans and beyond

The human body produces and removes 10(11) platelets daily to maintain a normal steady state platelet count. Platelet production must be regulated to avoid spontaneous bleeding or arterial occlusion and organ damage. Multifaceted and complex mechanisms control platelet production and removal in physiological and pathological conditions. This review will focus on different mechanisms of platelet senescence and clearance with specific emphasis on the role of posttranslational modifications. It will also briefly address platelet transfusion and the role of glycans in the clearance of stored platelets.

A novel role for thrombopoietin in regulating osteoclast development in humans and mice

Emerging data suggest that megakaryocytes (MKs) play a significant role in skeletal homeostasis. Indeed, osteosclerosis observed in several MK-related disorders may be a result of increased numbers of MKs. In support of this idea, we have previously demonstrated that MKs increase osteoblast (OB) proliferation by a direct cell-cell contact mechanism and that MKs also inhibit osteoclast (OC) formation. As MKs and OCs are derived from the same hematopoietic precursor, in these osteoclastogenesis studies we examined the role of the main MK growth factor, thrombopoietin (TPO) on OC formation and bone resorption. Here we show that TPO directly increases OC formation and differentiation in vitro. Specifically, we demonstrate the TPO receptor (c-mpl or CD110) is expressed on cells of the OC lineage, c-mpl is required for TPO to enhance OC formation in vitro, and TPO activates the mitogen-activated protein kinases, Janus kinase/signal transducer and activator of transcription, and nuclear factor-kappaB signaling pathways, but does not activate the PI3K/AKT pathway. Further, we found TPO enhances OC resorption in CD14+CD110+ human OC progenitors derived from peripheral blood mononuclear cells, and further separating OC progenitors based on CD110 expression enriches for mature OC development. The regulation of OCs by TPO highlights a novel therapeutic target for bone loss diseases and may be important to consider in the numerous hematologic disorders associated with alterations in TPO/c-mpl signaling as well as in patients suffering from bone disorders.

Recombinant goldfish thrombopoietin up-regulates expression of genes involved in thrombocyte development and synergizes with kit ligand A to promote progenitor cell proliferation and colony formation

Thrombopoietin (TPO) is the principal regulator of thrombopoiesis and promotes the proliferation, differentiation and maturation of megakaryocytic progenitor cells in mammals. In this study we report on the molecular and functional characterization of goldfish TPO. Quantitative expression analysis of goldfish tpo revealed the highest mRNA levels in heart, followed by spleen, liver, brain, intestine and kidney tissues. Significant decrease of tpo and c-mpl expressions in goldfish primary kidney macrophage (PKM) cultures, as progenitor to macrophage development progressed, indicates that TPO is not involved in monopoiesis. Recombinant goldfish TPO (rgTPO) alone did not induce significant proliferation of progenitor cells, but TPO in cooperation with recombinant goldfish kit ligand A (rgKITLA) supported proliferation of progenitor cells in a dose-dependent manner. In response to rgTPO or a combination of rgTPO and rgKITLA, the mRNA levels of thrombopoietic markers cd41 and c-mpl as well as thrombo/erythropoietic transcription factors gata1 and lmo2 in sorted progenitor cells were up-regulated, while the mRNA levels of granulopoietic markers (cebpα and gcsfr) and the lymphoid transcription factor gata3 were down-regulated. Furthermore, rgTPO and rgKITLA synergistically stimulated thrombocytic colony-formation. Our results demonstrate that goldfish TPO has similar functions to mammalian TPO as a regulator of thrombopoiesis, and suggests a highly conserved molecular mechanism of thrombocyte development throughout evolution of vertebrates.

The Ashwell-Morell receptor regulates hepatic thrombopoietin production via JAK2-STAT3 signaling

The hepatic Ashwell-Morell receptor (AMR) can bind and remove desialylated platelets. Here we demonstrate that platelets become desialylated as they circulate and age in blood. Binding of desialylated platelets to the AMR induces hepatic expression of thrombopoietin (TPO) mRNA and protein, thereby regulating platelet production. Endocytic AMR controls TPO expression through Janus kinase 2 (JAK2) and the acute phase response signal transducer and activator of transcription 3 (STAT3) in vivo and in vitro. Recognition of this newly identified physiological feedback mechanism illuminates the pathophysiology of platelet diseases, such as essential thrombocythemia and immune thrombocytopenia, and contributes to an understanding of the mechanisms of thrombocytopenia observed with JAK1/2 inhibition.

Fetal liver stromal cells support blast growth in transient abnormal myelopoiesis in Down syndrome through GM-CSF

Transient abnormal myelopoiesis (TAM) in neonates with Down syndrome, which spontaneously resolves within several weeks or months after birth, may represent a very special form of leukemia arising in the fetal liver (FL). To explore the role of the fetal hematopoietic microenvironment in the pathogenesis of TAM, we examined the in vitro influences of stromal cells of human FL and fetal bone marrow (FBM) on the growth of TAM blasts. Both FL and FBM stromal cells expressed mesenchymal cell antigens (vimentin, α-smooth muscle actin, CD146, and nestin), being consistent with perivascular cells/mesenchymal stem cells that support hematopoietic stem cells. In addition, a small fraction of the FL stromal cells expressed an epithelial marker, cytokeratin 8, indicating that they could be cells in epithelial-mesenchymal transition (EMT). In the coculture system, stromal cells of the FL, but not FBM, potently supported the growth of TAM blast progenitors, mainly through humoral factors. High concentrations of hematopoietic growth factors were detected in culture supernatants of the FL stromal cells and a neutralizing antibody against granulocyte-macrophage colony-stimulating factor (GM-CSF) almost completely inhibited the growth-supportive activity of the culture supernatants. These results indicate that FL stromal cells with unique characteristics of EMT cells provide a pivotal hematopoietic microenvironment for TAM blasts and that GM-CSF produced by FL stromal cells may play an important role in the pathogenesis of TAM.

Thrombocytopenia, Platelet Transfusion, and Outcome Following Liver Transplantation

Thrombocytopenia affects patients undergoing liver transplantation. Intraoperative platelet transfusion has been shown to independently influence survival after liver transplantation at 1 and 5 years. We examined the impact of thrombocytopenia and intraoperative platelet transfusion on short-term graft and overall survival after orthotopic liver transplantation (OLT). A total of 399 patients undergoing first OLT were studied. Graft and overall survival in patients with different degrees of thrombocytopenia and with or without intraoperative platelet transfusion were described. The degree of thrombocytopenia prior to OLT did not affect graft or overall survival after transplant. However, graft survival in patients receiving platelets was significantly reduced at 1 year (P= .023) but not at 90 days (P= .093). Overall survival was significantly reduced at both 90 days (P= .040) and 1 year (P= .037) in patients receiving platelets. We conclude that a consistently lower graft and overall survival were observed in patients receiving intraoperative platelet transfusion.

Treatment of pediatric primary immune thrombocytopenia with thrombopoietin receptor agonists

Chronic immune thrombocytopenia (ITP) occurs in approximately one fifth of children with primary ITP and is characterized by a significant lack of clinical data. A minority of these children exhibit bleeding and need treatment. Often standard therapy used for patients with newly diagnosed ITP is administered to stop bleeding and to increase the platelet count. These drugs are associated with adverse effects, which is particularly evident when used during long time. In adult patients with chronic ITP, thrombopoietin receptor agonists (TPO-RAs) demonstrated efficacy in approximately 80% of patients. These drugs have been studied intensely for registration purposes; however, for children and adolescents they are not yet approved and studies are ongoing. First experiences with these drugs show similar effects and safety as in adults, though based on very small numbers of children. These drugs have the potential to be used during long time, in order to increase platelets, to stop or prevent bleeding and to augment quality of life, making long-term safety an important issue.

Thrombopoiesis

The production of platelets is a complex process that involves hematopoietic stem cells (HSCs), their differentiated progeny, the marrow microenvironment and hematopoietic cytokines. Much has been learned in the 110 years since James Homer Wright postulated that marrow megakaryocytes were responsible for blood platelet production, at a time when platelets were termed the "dust of the blood". In the 1980s a number of in vitro culture systems were developed that could produce megakaryocytes, followed by the identification of several cytokines that could stimulate the process in vitro. However, none of these cytokines produced a substantial thrombocytosis when injected into animals or people, nor were blood levels inversely related to platelet count, the sine qua non of a physiological regulator. A major milestone in our understanding of thrombopoiesis occurred in 1994 when thrombopoietin, the primary regulator of platelet production was cloned and initially characterized. Since that time many of the molecular mechanisms of thrombopoiesis have been identified, including the effects of thrombopoietin on the survival, proliferation, and differentiation of hematopoietic stem and progenitor cells, the development of polyploidy and proplatelet formation, the final fragmentation of megakaryocyte cytoplasm to yield blood platelets, and the regulation of this process. While much progress has been made, several outstanding questions remain, such as the nature of the signals for final platelet formation, the molecular nature of the regulation of marrow stromal thrombopoietin production, and the role of these physiological processes in malignant hematopoiesis.

Does thrombopoiesis in multiple myeloma patients depend on the stage of the disease?

PURPOSE

Infiltration of the bone marrow by neoplastic plasmocytes in multiple myeloma (MM) patients might impair megakaryocytopoiesis. The aim of the study was to evaluate stage-dependent platelet count (PLT) and thrombopoietin (TPO) concentration in comparison to the control group. We also wanted to establish whether TPO might be recognized as a marker of the stage of the disease.

MATERIAL/METHODS

The study group consisted of 41 patients (mean age 67.7) with newly diagnosed MM prior to treatment and categorized according to the Durie and Salmon diagnostic classification. The control group consisted of 30 healthy subjects (mean age 65.5). PLT, WBC, RBC and Hb were measured with the use of the haematological analyser. TPO was assayed with the use of ELISA and albumin with the use of the immunonephelometry method. The number of plasma cells in the bone marrow was evaluated in bone marrow smears under light microscopy.

RESULTS

PLT was not statistically different as compared the control groups, but was stage-dependent. Thrombocytopenia was observed in the III stage of MM. TPO median was significantly higher in study group than in healthy subjects and it was increasing considerably with the stage of the disease. TPO concentration was negatively correlated with albumin and PLT. AUC for TPO was 0.9764. The number of plasma cells in the bone marrow was considerably increasing with the stage of the disease.

CONCLUSIONS

PLT and TPO in MM patients were stage-dependent. Elevated TPO concentration in MM patients might be an unfavourable marker of the stage of the disease.

Proton beam therapy reduces the incidence of acute haematological and gastrointestinal toxicities associated with craniospinal irradiation in pediatric brain tumors

BACKGROUND

The benefits of proton beam craniospinal irradiation (PrBCSI) in children have been extensively reported in dosimetric studies. However, there is limited clinical evidence supporting the use of PrBCSI. We compared the acute toxicity of PrBCSI relative to that of conventional photon beam CSI (PhBCSI) in children with brain tumours.

MATERIAL AND METHODS

We prospectively evaluated the haematological and gastrointestinal toxicities in 30 patients who underwent PrBCSI between April 2008 and December 2012. As a reference group, we retrospectively evaluated the medical records of 13 patients who underwent PhBCSI between April 2003 and April 2012. The median follow-up time from starting CSI was 22 months (range 2-118 months). The mean irradiation dose was 32.1 Gy (range 23.4-39.6 Gy) and 29.4 CGE (cobalt grey equivalents; range 19.8-39.6), in the PrBCSI and PhBCSI groups, respectively (p = 0.236).

RESULTS

There was no craniospinal fluid space relapse after curative therapy in either group of patients. Thrombocytopenia was less severe in the PrBCSI group than in the PhBCSI group (p = 0.012). The recovery rates of leukocyte and platelet counts measured one month after treatment were significantly greater in the PrBCSI group than in the PhBCSI group (p = 0.003 and p = 0.010, respectively). Diarrhoea was reported by 23% of patients in the PhBCSI group versus none in the PrBCSI group (p = 0.023).

CONCLUSIONS

The incidence rates of thrombocytopenia and diarrhoea were lower in the PrBCSI group than in the PhBCSI group. One month after completing treatment, the recovery from leukopenia and thrombocytopenia was better in patients treated with PrBCSI than in those treated with PhBCSI.

The bone marrow niche for haematopoietic stem cells

Niches are local tissue microenvironments that maintain and regulate stem cells. Haematopoiesis provides a model for understanding mammalian stem cells and their niches, but the haematopoietic stem cell (HSC) niche remains incompletely defined and beset by competing models. Recent progress has been made in elucidating the location and cellular components of the HSC niche in the bone marrow. The niche is perivascular, created partly by mesenchymal stromal cells and endothelial cells and often, but not always, located near trabecular bone. Outstanding questions concern the cellular complexity of the niche, the role of the endosteum and functional heterogeneity among perivascular microenvironments.

Thrombopoietin from beginning to end

In the two decades since its cloning, thrombopoietin (TPO) has emerged not only as a critical haematopoietic cytokine, but also serves as a great example of bench-to-bedside research. Thrombopoietin, produced by the liver, is the primary regulator of megakaryocyte progenitor expansion and differentiation. Additionally, as TPO is vital for the maintenance of haematopoietic stem cells, it can truly be described as a pan-haematopoietic cytokine. Since recombinant TPO became available, the molecular mechanisms of TPO function have been the subject of extensive research. Via its receptor, c-Mpl (also termed MPL), TPO activates a wide array of downstream signalling pathways, promoting cellular survival and proliferation. Due to its central, non-redundant role in haematopoiesis, alterations of both the hormone and its receptor contribute to human disease; congenital and acquired states of thrombocytosis and thrombocytopenia and aplastic anaemia as a result from dysregulated TPO expression or functional alterations of c-Mpl. With TPO mimetics now in clinical use, the story of this haematopoietic cytokine represents a great success for biomedical research.