Considerable amounts of long-chain polyunsaturated fatty acids (LC-PUFAs), particularly arachidonic acid and docosahexaenoic acid (DHA, 22:6n-3), are deposited in fetal tissues during pregnancy; and this process is facilitated by placental delivery. Nevertheless, the mechanisms involved in LC-PUFA placental transfer remain unclear. Stable isotope techniques have been used to study human placental fatty acid transfer in vivo. These studies have shown a significantly higher ratio of (13)C-DHA in cord to maternal plasma compared with other fatty acids, which reflects a higher placental DHA transfer. In addition, a selective DHA accumulation in placental tissue, relative to other fatty acids, has been reported. The materno-fetal transfer of fatty acids is a slow process that requires ≥12 h. A high incorporation of dietary (13)C-DHA into maternal plasma phospholipids appears to be important for placental uptake and transfer. DHA in cord blood lipids correlates with placental messenger RNA expression of fatty acid transport protein (FATP)-4, compatible with a role of FATP-4 in DHA transfer. Impaired materno-fetal LC-PUFA transport has been proposed in pregnancies complicated by abnormal placental function (eg, due to gestational diabetes mellitus or intrauterine growth restriction), which should be addressed in future studies. Given that placental DHA transfer is important for child outcomes, elucidation of its potential modulation by transport mechanisms, maternal diet, and disease appears to be important.

Understanding the underlying mechanisms of the well-substantiated platelet hyporeactivity in neonates is of interest given their implications for the clinical management of newborns, a population at higher bleeding risk than adults (especially sick and preterm infants), as well as for gaining insight into the regulatory mechanisms of platelet biology. Transcriptome analysis is useful in identifying mRNA signatures affecting platelet function. However, human fetal/neonatal platelet transcriptome analysis has never before been reported. We have used mRNA expression array for the first time to compare platelet transcriptome changes during development. Microarray analysis was performed in pure platelet RNA obtained from adult and cord blood, using the same platform in two independent laboratories. A high correlation was obtained between array results for both adult and neonate platelet samples. There was also good agreement between results in our adult samples and outcomes previously reported in three different studies. Gene enrichment analysis showed that immunity- and platelet function-related genes are highly expressed at both developmental stages. Remarkably, 201 genes were found to be differentially expressed throughout development. In particular, neonatal platelets contain higher levels of mRNA that are associated with protein synthesis and processing, while carrying significantly lower levels of genes involved in calcium transport/metabolism and cell signaling (including GNAZ). Overall, our results point to variations in platelet transcriptome as possibly underlining the hypo-functional phenotype of neonatal platelets and provide further support for the role of platelets in cellular immune response. Better characterization of the platelet transcriptome throughout development can contribute to elucidate how transcriptome changes impact different pathological conditions.

Neonatal platelets are hypo-reactive to the tyrosine kinase-linked receptor agonist collagen. Here, we have investigated whether the hypo-responsiveness is related to altered levels of glycoprotein VI (GPVI) and integrin α2β1, or to defects in downstream signalling events by comparison to platelet activation by C-type lectin-like receptor 2 (CLEC-2). GPVI and CLEC-2 activate a Src- and Syk-dependent signalling pathway upstream of phospholipase C (PLC) γ2. Phosphorylation of a conserved YxxL sequence known as a (hemi) immunotyrosine-based-activation-motif (ITAM) in both receptors is critical for Syk activation. Platelets from human pre-term and full-term neonates display mildly reduced expression of GPVI and CLEC-2, as well as integrin αIIbβ3, accounted for at the transcriptional level. They are also hypo-responsive to the two ITAM receptors, as shown by measurement of integrin αIIbβ3 activation, P-selectin expression and Syk and PLCγ2 phosphorylation. Mouse platelets are also hypo-responsive to GPVI and CLEC-2 from late gestation to 2 weeks of age, as determined by measurement of integrin αIIbβ3 activation. In contrast, the response to G protein-coupled receptor agonists was only mildly reduced and in some cases not altered in neonatal platelets of both species. A reduction in response to GPVI and CLEC-2, but not protease-activated receptor 4 (PAR-4) peptide, was also observed in adult mouse platelets following immune thrombocytopenia, whereas receptor expression was not impaired. Our results demonstrate developmental differences in platelet responsiveness to GPVI and CLEC-2, and also following immune platelet depletion leading to reduced Syk activation. The rapid generation of platelets during development or following platelet depletion is achieved at the expense of signalling by ITAM-coupled receptors.

The functionality of the placenta may affect neonatal adiposity and fetal levels of key nutrients such as long-chain polyunsaturated fatty acids. Fetal macrosomia and its complications may occur even in adequately controlled gestational diabetic (GDM) mothers, suggesting that maternal glycemia is not the only determinant of fetal glycemic status and wellbeing. We studied in vivo the placental transfer of fatty acids (FA) labeled with stable isotopes administered to 11 control and 9 GDM pregnant women (6 treated with insulin). Subjects received orally ¹³C-palmitic, ¹³C-oleic, and ¹³C-linoleic acids and ¹³C-docosahexaenoic acid (¹³C-DHA) 12 h before an elective caesarean section. FA were quantified by gas chromatography and ¹³C enrichments by gas chromatography-isotope ratio mass spectrometry. The ¹³C-FA concentration was higher in total lipids of maternal plasma in GDM patients versus controls, except for ¹³C-DHA. Moreover, ¹³C-DHA showed a lower placenta/maternal plasma ratio in GDM patients versus controls and a significantly lower cord/maternal plasma ratio. Other FA ratios studied were not different between GDM and controls. A disturbed ¹³C-DHA placental uptake occurred in GDM patients treated with diet or insulin, while the latter also had lower ¹³C-DHA levels in the venous cord. The tracer study pointed towards an impaired placental DHA uptake as a critical step, while the transfer of other ¹³C-FA was less affected. Patients with GDM treated with insulin could also have a greater fetal fat storage, which may have contributed to the reduced ¹³C-DHA in the venous cord observed. The DHA transfer to the fetus was reduced in GDM pregnancies compared to controls. This might have an influence on fetal neurodevelopment and long-term consequences for the child.

Neonatal platelets are hyporeactive and show impaired agonist-induced secretion despite no obvious abnormalities in their granules. Here, we examined, for the first time, the ultrastructure of neonatal and adult platelets following agonist activation. Under resting conditions, neonatal and adult platelets appeared ultrastructurally identical. Following agonist stimulation, however, noticeable degranulation occurred in adult platelets, while granules in neonatal platelets remained clearly visible and apparently unable to centralize or fuse. To investigate the underlying mechanisms, we first examined the expression levels of the main SNARE proteins, which mediate the membrane fusion events required for exocytosis. Neonatal platelets showed significantly reduced levels of syntaxin-11 and its regulator, Munc18b. Since granule centralization depends on contraction of the microtubule ring, we also examined the expression of its main component, β1-tubulin. Noteworthy, we found decreased mRNA and protein levels in neonatal platelets, while and isoforms were overexpressed, partially compensating for that deficiency. Finally, supporting the functional consequences of defective exocytosis, adhesion kinetic assays, performed in plasma-free medium, demonstrated delayed adhesion and spreading of neonatal platelets. This is the first report showing marked reductions of syntaxin-11-Munc18b complex and β1-tubulin in neonatal platelets, indicating that these proteins, required for platelet degranulation, are developmentally regulated.