Skin-to-skin transfer from the delivery room to the neonatal unit for neonates of 1,500g or above: a feasibility and safety study.

Objective: Immediate skin-to-skin contact (SSC) is already standard care for healthy term newborns, but its use for term or preterm newborns requiring admission to neonatal intensive care unit (NICU) with or without respiratory support is challenging. This study aimed to assess the safety and feasibility of SSC during the transfer of newborn infants, using a new purpose-built mobile shuttle care-station, called "Tandem". Material and methods: A monocentric prospective observational study was conducted at the tertiary referral center of the Université libre de Bruxelles in Brussels, Belgium after ethical approval by Hopital Erasme's Ethics Committee (ClinicalTrials.gov ID: NCT06198478). Infants born with a birth weight above 1,500 g were included. Following initial stabilization, infants were placed in SSC with one of their parents and transferred to the NICU using the Tandem. Results: Out of 65 infants initially included, 64 (98.5%) were successfully transported via SSC using the Tandem. One transfer was not successful due to last minute parental consent withdrawal. The median (range) duration of continuous skin-to-skin contact after birth was 120 min (10-360). SSC transfers were associated with gradually decreasing heart rate (HR) values, stable oxygen saturation levels (SpO2), and no increase in median fraction of inspired oxygen (FiO2). Heatloss was predominantly observed during initial setup of SSC. There was no significant difference in the occurrence of tachycardia, desaturation or hypothermia between preterm and term neonates. No equipment failures compromising the transfer were recorded. Conclusion: Skin-to-skin transfer of infants with a birthweight of equal or above 1,500 g using the Tandem shuttle is feasible and associated with stable physiological parameters. This method facilitates early bonding and satisfies parents. Clinical Trial Registration: ClinicalTrials.gov (NCT06198478).

Complement component 5a receptor oligomerization and homologous receptor down-regulation.

Most G-protein-coupled receptors (GPCRs) form di(oligo)-meric structures that constitute signaling and trafficking units and might be essential for receptor functions. Cell responses to complement C5a receptor (C5aR) are tightly controlled by receptor desensitization and internalization. To examine the implication of dimerization in C5aR regulation, we generated an NH(2)-terminally modified C5aR mutant, unable to bind C5a, and a phosphorylation-deficient mutant. Neither an intact NH(2) terminus nor the presence of COOH-terminal phosphorylation sites appeared to be required for the formation of C5aR dimers. Upon C5a stimulation, mutant receptors did not internalize when individually expressed. C5a stimulation of cells that co-expressed wild type C5aR together with either unliganded or phosphorylation-deficient mutant resulted in co-internalization of mutant receptors with C5aR. Unliganded GPCRs can be cross-phosphorylated within a heterologous receptor dimer or by second messenger-activated kinases. C5a stimulation of (32)P-labeled cells that co-expressed the unliganded mutant with either C5aR or the phosphorylation-deficient mutant did not induce phosphorylation of the unliganded mutant. We can thus postulate that, in the case of C5aR, the stimulation and phosphorylation of one monomer is enough to lead to dimer internalization. The existence and functional implication of di(oligo)mer formation may be important for an accurate C5aR down-regulation in pathological conditions.

The role of beta-arrestins in the formyl peptide receptor-like 1 internalization and signaling.

The N-formyl peptide receptor-like 1 (FPRL1) is a G protein-coupled receptor (GPCR) that transmits intracellular signals in response to a variety of agonists, many of them being clearly implicated in human pathology. beta-arrestins are adaptor proteins that uncouple GPCRs from G protein and regulate receptor internalization. They can also function as signal transducers through the scaffolding of signaling molecules, such as components of the extracellular signal-regulated kinase (ERK) cascade. We investigated the role of beta-arrestins in ligand-induced FPRL1 internalization and signaling. In HEK293 cells expressing FPRL1, fluorescence microscopy revealed that agonist-stimulated FPRL1 remained co-localized with beta-arrestins during endocytosis. Internalization of FPRL1, expressed in a mouse embryonic fibroblast (MEF) cell line lacking endogenous beta-arrestins, was highly compromised. This distinguishes FPRL1 from the prototypical formyl peptide receptor FPR that is efficiently internalized in the absence of beta-arrestins. In both HEK293 and MEF cells, FPRL1-mediated ERK1/2 activation was a rapid and transient event. The kinetics and extent of ERK1/2 activation were not significantly modified by beta-arrestin overexpression. The pattern of FPRL1-mediated ERK1/2 activation was similar whether cells express or not beta-arrestins. Furthermore, treatment of the FPRL1 expressing cells with pertussis toxin inhibited ERK1/2 activation in MEF and in HEK293 cells. These results led us to conclude that activation of ERK1/2 mediated by FPRL1 occurs primarily through G protein signaling. Since beta-arrestin-mediated signaling has been observed essentially for receptors coupled to G proteins other than G(i), this may be a characteristic of G(i) protein-coupled chemoattractant receptors.

The N-formyl peptide receptors and the anaphylatoxin C5a receptors: an overview.

Leukocyte recruitment to sites of inflammation and infection is dependent on the presence of a gradient of locally produced chemotactic factors. This review is focused on current knowledge about the activation and regulation of chemoattractant receptors. Emphasis is placed on the members of the N-formyl peptide receptor family, namely FPR (N-formyl peptide receptor), FPRL1 (FPR like-1) and FPRL2 (FPR like-2), and the complement fragment C5a receptors (C5aR and C5L2). Upon chemoattractant binding, the receptors transduce an activation signal through a G protein-dependent pathway, leading to biochemical responses that contribute to physiological defense against bacterial infection and tissue damage. C5aR, and the members of the FPR family that were previously thought to be restricted to phagocytes proved to have a much broader spectrum of cell expression. In addition to N-formylated peptides, numerous unrelated ligands were recently found to interact with FPR and FPRL1. Novel agonists include both pathogen- and host-derived components, and synthetic peptides. Antagonistic molecules have been identified that exhibit limited receptor specificity. How distinct ligands can both induce different biological responses and produce different modes of receptor activation and unique sets of cellular responses are discussed. Cell responses to chemoattractants are tightly regulated at the level of the receptors. This review describes in detail the regulation of receptor signalling and the multi-step process of receptor inactivation. New concepts, such as receptor oligomerization and receptor clustering, are considered. Although FPR, FPRL1 and C5aR trigger similar biological functions and undergo a rapid chemoattractant-mediated phosphorylation, they appear to be differentially regulated and experience different intracellular fates.

Human mitochondria-derived N-formylated peptides are novel agonists equally active on FPR and FPRL1, while Listeria monocytogenes-derived peptides preferentially activate FPR.

N-formyl peptides are cleavage products of bacterial and mitochondrial proteins, and can attract leukocytes to sites of infection or tissue damage. In this study, HL-60 cell lines expressing the human N-formyl peptide receptor FPR or its two homologues (FPRL1, FPRL2) were used to determine the receptor selectivity of N-formylated peptides derived from Listeria monocytogenes or from human mitochondrial proteins. Bacterial peptides were 100-fold more potent on FPR than on FPRL1, whereas none of them could trigger intracellular signaling through FPRL2. In contrast, N-formylated hexapeptides corresponding to the N terminus of mitochondrial NADH dehydrogenase subunits 4 (fMLKLIV) and 6 (fMMYALF), and cytochrome c oxidase subunit I (fMFADRW) were equally potent on FPR and FPRL1. They triggered cellular responses with the following order of potency: fMMYALF > fMLKLIV > fMFADRW, with an EC50, in a Fura-2 calcium mobilization assay, of 10 nM, 44 nM, and 160 nM on FPR-expressing cells, and 15 nM, 55 nM and 120 nM on FPRL1-expressing cells. fMMYALF was also a low-affinity agonist of FPRL2 (EC50 of 1 microM) and was chemotactic for both FPRL1- and FPRL2-expressing cells. We identified novel mitochondrial host-derived agonists for human N-formyl-peptide receptors that might play a role in inflammatory or degenerative processes linked to their stimulation.