MiR-181a Reduces Platelet Activation via the Inhibition of Endogenous RAP1B

Aim

Since RAP1B is critical for platelet functions, including hemostasis, this study was conducted to identify RAP1B regulating microRNAs (miRNAs) in ex vivo stored platelets.

Background

Previous studies with platelets identified factors affecting RAP1B activity but regulatory miRNAs that affect RAP1B protein expression have not been reported.

Objective

To understand the functional significance of miRNA mediated regulation of RAP1B in stored platelets, using microRNA, miR-181a as an example.

Methods

A Tagged RNA Affinity approach (MS2-TRAP) was employed to identify miRNAs that bound to the 3` untranslated region (3`UTR) of the RAP1B mRNA in HeLa cells as an assay system. And subsequently, the mRNA 3’UTR:miRNA interactions were verified in platelets through the ectopic expression of miR-181a mimic and appropriate controls. The interaction of such miRNAs with RAP1B mRNA was also validated by qRT-PCR and Western analysis.

Results

Sixty-two miRNAs from MS2 assay were then compared with already known 171 platelet abundant miRNAs to identify a common set of miRNAs. This analysis yielded six miRNAs (miR-30e, miR-155, miR-181a, miR-206, miR-208a and miR-454), which are also predicted to target RAP1B mRNA. From this pool, miR-181a was selected for further study since RAP1B harbors two binding sites for miR-181a in its 3′UTR. Ectopic expression of miR-181a mimic in platelets resulted in lowering the endogenous RAP1B at both mRNA and protein levels. Further, miR-181a ectopic expression reduced the surface expression of the platelet activation marker, P-selectin.

Conclusion

MicroRNA-181a can target RAP1B and this interaction has the potential to regulate platelet activation during storage.

Serum Vitamin D Levels in Children with Immune Thrombocytopenia

OBJECTIVE

Immune thrombocytopenia (ITP) is an acquired immuno-mediated disorder characterized by thrombocytopenia with an increased risk of bleeding. In recent years 1,25[OH]2D3 has been rediscovered as an immune modulator. We decided to evaluate serum Vitamin D levels in a cohort of children with immune thrombocytopenia in order to discover if Vitamin D concentrations may predict ITP duration.

METHODS

Thirty children were enrolled in this study (sixteen with chronic ITP and fourteen with newly diagnosed ITP) to assess serum Vitamin D levels.

RESULTS

The results showed that 80% of the enrolled children presented a D hypovitaminosis status. Children with newly diagnosis ITP showed no statistically significantly higher median values of Vitamin D compared to chronic ITP.

CONCLUSION

This study may suggest that Vitamin D deficiency does not represent a chronicity factor for ITP. However, further studies are needed to understand the role of Vitamin D in ITP pathogenesis.

Pathophysiology of Thrombosis in Peripheral Artery Disease

Under physiological conditions, peripheral arteries release endogenous vascular-protective and antithrombotic agents. Endothelial cells actively synthesize vasoactive mediators, which regulate vascular tone and platelet reactivity thus preventing thrombosis. Atherosclerosis disrupts homeostasis and favours thrombosis by triggering pro-thrombotic responses in the vessels, platelet activation, aggregation as well as vasoconstriction, phenomena that ultimately lead to symptomatic lumen restriction or complete occlusion. In the present review, we will discuss the homeostatic role of arterial vessels in releasing vascular-protective agents, such as nitric oxide and prostacyclin, the role of pro- and anti-thrombotic vascular receptors as well as the contribution of circulating platelets and coagulation factors in triggering the pro-thrombotic response(s). We will discuss the pathological consequences of disrupting the protective pathways in the arteries and the pharmacological interventions along these pathways.

Diabetes and Vascular Disease: Is It All About Glycemia?

BACKGROUND

Diabetes is increasing over time, mainly driven by obesity, aging, and urbanization. Classical macro- and microvascular complications represent the final result of a complex interplay involving atherosclerosis at all stages.

METHODS

In this review, we aim at focusing on current updates in the pathophysiology of vascular disease in diabetes and discussing how new therapies might influence the management of these patients at high cardiovascular risk. Diabetes shows accelerated atherosclerosis with a larger inflammatory cell infiltrate, thus favoring the development of heart failure. 'Diabetic cardiomyopathy' perfectly describes a specific ischemia- and hypertension- independent entity due to diabetes-related metabolic alterations on myocardial function. Moreover, platelets from subjects with diabetes display a typical hyperreactivity explaining the stronger adhesion, activation, and aggregation. Additionally, diabetes provokes an exaggerated stimulation of the endothelium, with an increased release of reactive oxygen species and a reduced release of nitric oxide, both key elements of the endothelial dysfunction. Also, the coagulation cascade and leukocytes activate contributing to this pro-thrombotic environment. Neutrophils have been recently recognized to play a pivotal role by releasing neutrophil extracellular traps. Finally, microparticles from platelets, neutrophils or monocytes are detrimental effectors on the vessel wall and are involved both in vascular dysfunction and in thrombotic complications.

CONCLUSION

In light of these findings, the therapeutic management of diabetes needs to be mostly focused on limiting the progression of complications by targeting precise pathophysiological mechanisms rather than the mere glycemic control, which failed to markedly reduce the risk for macrovascular complications and mortality.

Dengue Virus Entry and Replication Does Not Lead to Productive Infection in Platelets

Thrombocytopenia is a characteristic feature during the acute phase of dengue infection and has been found to associate with vascular leakage in severe dengue. Although dengue antigens have been observed in platelets, there is no strong evidence to suggest a direct infection of platelets by dengue virus as a contributing factor for thrombocytopenia. We show that dengue virus can enter platelets but replicate viral ribonucleic acid to a minimal extent and, therefore, cannot produce infectious virus. Dengue antigen was undetectable in platelets isolated from dengue patients; however, we observed an increase in CD14⁺CD16⁺ monocyte-platelet complexes, suggesting a mechanism for platelet clearance.

Cardiovascular Events: A Challenge in JAK2-positive Myeloproliferative Neoplasms

BACKGROUND

Myeloproliferative neoplasms (MPNs) are chronic blood disorders caused by clonal expansion in one or more myeloid lineages and include essential thrombocythemia (ET), polycythemia vera (PV), primary myelofibrosis (PMF) and chronic myeloid leukemia (CML). Cardiovascular events are a main challenge for patients with MPN and can lead to their death.

OBJECTIVE

JAK2V617F mutation is observed in Philadelphia-negative MPNs such as ET and PV, increasing the risk of cardiovascular complications in these patients. JAK2 mutation can affect cardiac arteries and veins in ET and PV, which results in thrombosis, ischemia and other cardiovascular events. JAK/STAT signaling pathway plays an important role in heart diseases. In this review, we will survey the cardiovascular events in JAK2-positive MPN patients.

METHOD

Relevant English-language literature were searched and retrieved from PubMed search engine (1995-2017). The following keywords were used: "Cardiovascular Events", "JAK2" and "Myeloproliferative Neoplasms". Forty three articles were selected by using the key words.

RESULTS

JAK2 phosphorylates the signal transducers and activators of transcription (STAT). Various factors like angiotensin II (ANG II) and cardiotrophin-1 (CT-1) can bind their receptors on myocytes and increase the expression of angiotensinogen (Ao) gene by binding of STAT proteins to these factors in myocytes, causing different cardiovascular complications through autocrine mechanisms.

CONCLUSION

JAK2 mutation is observed in patients with thrombosis, ischemia and other cardiovascular complications having abnormal increase in cell count even without definite clinical diagnosis of MPN. Therefore, identification of this mutation in these patients contributes to definite diagnosis of cardiovascular events. Also, cardiovascular complications in MPN patients can be prevented by targeting the factors involved in JAK/STAT signaling pathway.