Evaluation of angiogenic signaling molecules associated with reactive thrombocytosis in an iron-deficient rat model

Etiology and clinical course of severe and extreme thrombocytosis in children: a retrospective single-center study

The aim of this study was to describe the etiology and clinical course in children with severe thrombocytosis (ST, platelet counts > 900 × 109/L) and extreme thrombocytosis (ET, platelet counts > 1000 × 109/L) in a tertiary pediatric hospital. Patients aged 0-18 years with platelet counts over 900 × 109/L who were admitted to our hospital were analyzed. Thrombocytosis was defined as a platelet count exceeding 450 × 109/L. Thrombosis was diagnosed based on computed tomography scans or ultrasound findings. Potential factors associated with the development of extreme thrombocytosis were identified using logistic regression models. Only one (0.8%) out of the 120 patients identified with ST (n = 61) and ET (n = 59) had primary thrombocytosis. The most common underlying condition was congenital heart disease (26.7%), followed by Kawasaki disease (16.7%). With the exception of the hemoglobin level, no major differences were found for the baseline characteristics between the ST and ET groups. A lower hemoglobin level (< 10.0 g/dL) at the onset of thrombocytosis was identified as a predictor for ET development (adjusted odds ratio 2.73, 95% confidence interval 1.18-6.28). Overall, 56 of 120 (46.7%) patients received aspirin therapy. Venous thrombosis occurred in one (0.8%) patient.

CONCLUSIONS

We found a low proportion of primary thrombocytosis and a low incidence of thrombosis in children with ST and ET. Our results suggest that pediatric ST and ET may share common characteristics and may have features that are distinct from those in adults.

WHAT IS KNOWN

• Secondary thrombocytosis is a frequent finding in children. • Adult extreme thrombocytosis has been found to be associated with primary thrombocytosis.

WHAT IS NEW

• There were no major differences in the baseline characteristics between children with severe and extreme thrombocytosis. • The incidence of thrombosis was markedly low in both severe and extreme thrombocytosis groups.

Pim Kinase Inhibition Disrupts CXCR4 Signalling in Megakaryocytes and Platelets by Reducing Receptor Availability at the Surface

A key step in platelet production is the migration of megakaryocytes to the vascular sinusoids within the bone marrow. This homing is mediated by the chemokine CXCL12 and its receptor CXCR4. CXCR4 is also a positive regulator of platelet activation and thrombosis. Pim-1 kinase has been shown to regulate CXCR4 signalling in other cell types, and we have previously described how Pim kinase inhibitors attenuate platelet aggregation to CXCL12. However, the mechanism by which Pim-1 regulates CXCR4 signalling in platelets and megakaryocytes has yet to be elucidated. Using human platelets, murine bone marrow-derived megakaryocytes, and the megakaryocyte cell line MEG-01, we demonstrate that pharmacological Pim kinase inhibition leads to reduced megakaryocyte and platelet function responses to CXCL12, including reduced megakaryocyte migration and platelet granule secretion. Attenuation of CXCL12 signalling was found to be attributed to the reduced surface expression of CXCR4. The decrease in CXCR4 surface levels was found to be mediated by rapid receptor internalisation, in the absence of agonist stimulation. We demonstrate that pharmacological Pim kinase inhibition disrupts megakaryocyte and platelet function by reducing constitutive CXCR4 surface expression, decreasing the number of receptors available for agonist stimulation and signalling. These findings have implications for the development and use of Pim kinase inhibitors for the treatment of conditions associated with elevated circulating levels of CXCL12/SDF1α and increased thrombotic risk.

Iron deficiency downregulates ENPEP to promote angiogenesis in liver tumors

The abnormal iron metabolism in liver cancer leads to iron deficiency in tumor tissues. We previously found that iron deficiency promoted liver cancer metastasis, but the mechanisms were not fully understood. In the present study, we identified that the angiogenesis-associated glutamyl aminopeptidase (ENPEP) was consistently decreased in iron-deficient liver tissues, iron-deficient liver tumors, and iron-deprived liver cancer cells. Interestingly, the lower expression of ENPEP was correlated with the poor prognosis of liver cancer patients, while the biomarkers of angiogenesis, CD31 and CD34, were increased in tumor tissues. In vivo imaging of liver-orthotopically implanted and tail vein-injected liver cancer cells showed that iron deficiency increased the pulmonary metastasis of liver cancer. The angiogenesis in iron-deficient tumors was enhanced, and the expression of ENPEP was decreased. Silencing ENPEP expression increased the migration of liver cancer cells and the proliferation of cocultured HUVECs. By sequence analysis, we found that the transcription factor SP1 possessed abundant binding sites in the ENPEP promoter region. Its combination with ENPEP promoters was verified by chromatin immunoprecipitation. The inhibition of SP1 by mithramycin A effectively restored the expression of ENPEP, which was decreased by iron deficiency. In conclusion, these results revealed that iron deficiency in liver tumors decreased the expression of ENPEP by SP1 and increased the angiogenesis and metastasis of liver tumors, which further explained the mechanism by which iron deficiency promoted liver cancer metastasis.