The effects of signal transducer and activator of transcription three mutations on human platelets

Involvement of signal transducer and activator of transcription 3 (STAT3) in inflammation is well known. Recently, a role for STAT3 in platelet activation and platelet production has been suggested. Platelets exhibit important immune functions and engagement of STAT3 in platelet physiology may link inflammation and hemostasis. This study investigated the effects of STAT3 loss-of-function mutations and single nucleotide polymorphisms (SNPs) in STAT3 on glycoprotein VI (GPVI)-mediated platelet activation and platelet numbers in humans. Two cohorts were studied. The first cohort concerned patients with STAT3 loss-of-function mutations. Platelet numbers were investigated in eight patients and GPVI-mediated platelet activation was functionally tested in four patients. Additional experiments were performed to investigate underlying mechanisms. The second cohort concerned 334 healthy volunteers and investigated the consequences of SNPs in STAT3 on GPVI-mediated platelet activation and platelet numbers. Platelet activation was lower in STAT3 loss-of-function patients at baseline and after stimulation of the GPVI receptor, reflected by decreased P-selectin expression. This was independent of gene transcription. Blockade of the adenosine di-phosphate (ADP) pathway resulted in a further decrease of P-selectin expression, particularly in STAT3 loss-of-function patients. In contrast, the SNPs in STAT3 did not influence GPVI-mediated platelet activation. Also, platelet numbers were not affected by STAT3 loss-of-function mutations, nor was there an association with the SNPs. In conclusion, STAT3 signaling does not seem to play a major role in thrombopoiesis. We confirm that STAT3 is involved in GPVI-mediated platelet activation in humans, independent of gene transcription. GPVI-mediated platelet activation is highly dependent on secondary ADP release. Our findings suggest that STAT3 modulation may affect inflammation, hemostasis, and their interaction.</p

Platelet Integrin alpha IIb beta 3 Activation is Associated with 25-Hydroxyvitamin D Concentrations in Healthy Adults

Item does not contain fulltextBACKGROUND:  Cardiovascular events are associated with low circulating vitamin D concentrations, although the underlying mechanisms are poorly understood. This study investigated associations between 25-hydroxyvitamin D concentrations, platelet function, and single-nucleotide polymorphisms (SNPs) in genes influencing vitamin D biology in the 500 Functional Genomics (500FG) cohort. METHODS:  In this observational study, platelet activation and function were measured by flow cytometry by binding of fibrinogen to the activated fibrinogen receptor integrin αIIbβ3 and expression of P-selectin, markers of platelet aggregation and degranulation, respectively. These parameters were correlated to serum 25-hydroxyvitamin D and genotyping was performed to investigate SNPs in genes important for vitamin D biology. RESULTS:  Circulating 25-hydroxyvitamin D concentrations correlated inversely with baseline platelet binding of fibrinogen to integrin αIIbβ3 (Pearson's r= -0.172, p = 0.002) and platelet responses to platelet agonist cross-linked collagen-related peptide (CRP-XL) (Pearson's r= -0.196,p = 0.002). This effect was due to circulating vitamin D levels ≤50nmol/L, since no differences in platelet fibrinogen binding were observed between subjects with normal 25-hydroxyvitamin D concentrations (>75nmol/L) and a 25-hydroxyvitamin D insufficiency (50-75 nmol/L). No correlations between 25-hydroxyvitamin D concentrations and platelet P-selectin expression were found. Several SNPs in the GC region of the vitamin D binding proteingene were associated with platelet responses to CRP-XL. CONCLUSION:  Low circulating vitamin D concentrations are associated with increased platelet fibrinogen binding to integrin αIIbβ3 in unstimulated samples and after stimulation with CRP-XL. These findings may contribute to the increased incidence of cardiovascular events in vitamin D deficient adults and its seasonal variation. Further studies are needed to investigate causality