Surface translocation of pactolus is induced by cell activation and death, but is not required for neutrophil migration and function

Locally organised and activated Fth1hi neutrophils aggravate inflammation of acute lung injury in an IL-10-dependent manner

Acute respiratory distress syndrome (ARDS) is a common respiratory critical syndrome with no effective therapeutic intervention. Neutrophils function in the overwhelming inflammatory process of acute lung injury (ALI) caused by ARDS; however, the phenotypic heterogeneity of pulmonary neutrophils in ALI/ARDS remains largely unknown. Here, using single-cell RNA sequencing, we identify two transcriptionally and functionally heterogeneous neutrophil populations (Fth1^hi Neu and Prok2^hi Neu) with distinct locations in LPS-induced ALI mouse lungs. Exposure to LPS promotes the Fth1^hi Neu subtype, with more inflammatory factors, stronger antioxidant, and decreased apoptosis under the regulation of interleukin-10. Furthermore, prolonged retention of Fth1^hi Neu within lung tissue aggravates inflammatory injury throughout the development of ALI/ARDS. Notably, ARDS patients have high ratios of Fth1 to Prok2 expression in pulmonary neutrophils, suggesting that the Fth1^hi Neu population may promote the pathological development and provide a marker of poor outcome.

The p53-target gene puma drives neutrophil-mediated protection against lethal bacterial sepsis

Disruption of p53/Puma-mediated apoptosis protects against lethality due to DNA damage. Here we demonstrate the unexpected requirement of the pro-apoptotic p53-target gene Puma to mount a successful innate immune response to bacterial sepsis. Puma⁻/⁻ mice rapidly died when challenged with bacteria. While the immune response in Puma⁻/⁻ mice was unchanged in cell migration, phagocytosis and bacterial killing, sites of infection accumulated large abscesses and sepsis was progressive. Blocking p53/Puma-induced apoptosis during infection caused resistance to ROS-induced cell death in the CD49d+ neutrophil subpopulation, resulting in insufficient immune resolution. This study identifies a biological role for p53/Puma apoptosis in optimizing neutrophil lifespan so as to ensure the proper clearance of bacteria and exposes a counter-balance between the innate immune response to infection and survival from DNA damage.

Pactolus I-domain: functional switching of the Rossmann fold

Murine Pactolus is a neutrophil-specific single chain glycoprotein that plays a role as an apoptosis marker for macrophages. The extracellular region of the protein shows strong sequence similarities to integrin beta-subunits. Critical sequence modifications differentiate its function when compared to the integrin family. We show experimentally that Pactolus I-domain does not bind divalent metal ions, indicating that ligand binding is not mediated through a metal ion-dependent adhesion site (MIDAS). NMR data was used to map secondary structure and the strand pairing within the beta-sheet to confirm an overall Rossmann fold topology. Homology modeling enhanced by the NMR data was used to determine the overall structure, with two key loop insertions/deletions (insertion 2 and SDL) that distinguish the Pactolus I-domain from the integrin alpha I-domain and beta I-domains. NMR peak exchange broadening is observed due to dimerization, correlating to the beta I-domain and beta propeller heterodimerization region within the integrin headpiece. Two unique N-linked glycosylation sites (Asn151 and Asn230) within this region disrupt dimerization and may account for why Pactolus is not found to associate with an alpha-subunit. These changes in quaternary structure, ligand binding loops, glycosylation, and metal sites illustrate how evolution has rapidly and effectively altered key aspects of the integrin beta-subunit to derive a protein of novel function on an existing protein scaffold.

Altered localization of CXCL13 expressing cells in mice deficient in Pactolus following an inflammatory stimulus

The mouse Pactolus gene is an evolutionary paralogue to the CD18/beta2 integrin subunit and is preferentially expressed by neutrophils. When first identified, it was assumed Pactolus would function as an adhesion receptor similar to other beta integrin subunits. The analysis of mice genetically deficient in Pactolus, however, did not define any lesion in neutrophil migration, adhesion or phagocytosis. Therefore a wider analysis of the Pactolus deficiency was initiated using transcriptional profiling during an inflammatory insult. This screen identified a single transcript, CXCL13, that was elevated in cells from a peritoneal lavage of the wild type animal compared to the Pactolus-deficient animal. Our analyses confirmed resident macrophages as being responsible for the chemokine using intracellular CXCL13 staining and additional cell markers to phenotypically characterize such cells. The resident CXCL13-expressing cells (which do not express Pactolus) are functionally distinct from the macrophages recruited into the peritoneal cavity following the inflammatory stimulation since the recruited macrophages do not express detectable levels of the chemokine. The numbers and expression patterns of these resident CXCL13-expressing cells do not vary in naïve animals of wild type or Pactolus-deficient origin. Additionally, Pactolus-deficient neutrophils do not preferentially kill (compared to wild type) CXC13-expressing macrophages. These data suggest that during an inflammatory response, Pactolus may help retain CXCL13-expressing cells within the peritoneal environment.

Modulation of chondrocyte adhesion to collagen by echistatin

Primary chondrocytes from quail embryo epiphysis (quail epiphyseal chondrocytes, QEC) can grow either in suspension or in monolayer. In this study, the adhesion of QEC to collagen II was used as a model to study the regulation of the ligand-binding activity of integrin receptors that allows these cells to undergo a rapid transition from suspension to an adherent state. Preincubation of suspension QEC (QECSP) with the disintegrin echistatin increased by 40% their adhesion to collagen II. An inverse relationship between immobilized collagen density and echistatin-induced increase of chondrocyte adhesion was observed, thus suggesting that the disintegrin acts by increasing the ligand-binding affinity of collagen receptor(s). Further, echistatin activity does not appear to depend upon a direct binding of the disintegrin to collagen receptor(s). In fact, immobilized anti-beta1 antibodies, but not immobilized echistatin, served as effective binding sites for QECSP. Echistatin failed to stimulate chondrocyte adhesion to collagen in the presence of metabolic inhibitors, while an activating anti-beta1 antibody was still effective. Thus, echistatin may promote cell adhesion by interfering with energy-dependent signals that keep the collagen receptor(s) in a low-affinity state. Adhesion experiments performed in the presence of pharmacological inhibitors indicate that phosphatidyl inositol 3-kinase (PI3-K)/protein kinase C (PKC) and protein kinase A (PKA) pathways may transmit opposing signals on chondrocyte adhesion, and that collagen receptors are kept in a low-affinity state by PI3-kinase/PKC signalling. Since echistatin is a high-affinity ligand for alphavbeta3 integrin, the effect of the function-blocking anti-alphavbeta3 antibody LM609 was investigated. Like echistatin, LM609 stimulated chondrocyte adhesion to collagen and failed to support their attachment. Therefore, our data suggest that alphavbeta3-antagonists might regulate the binding activity of the beta1 collagen receptor, which in turn leads to the rapid transition of chondrocytes from suspension to an adherent state.

Functional disassociation of the central and peripheral fatty acid amide signaling systems

Fatty acid amides (FAAs) constitute a large class of endogenous signaling lipids that modulate several physiological processes, including pain, feeding, blood pressure, sleep, and inflammation. Although FAAs have been proposed to evoke their behavioral effects through both central and peripheral mechanisms, these distinct signaling pathways have remained experimentally challenging to separate. Here, we report a transgenic mouse model in which the central and peripheral FAA systems have been functionally uncoupled. Mice were generated that express the principle FAA-degrading enzyme FAA hydrolase (FAAH) specifically in the nervous system (FAAH-NS mice) by crossing FAAH(-/-) mice with transgenic mice that express FAAH under the neural specific enolase promoter. FAAH-NS mice were found to possess wild-type levels of FAAs in the brain and spinal cord, but significantly elevated concentrations of these lipid transmitters in peripheral tissues. This anatomically restricted biochemical phenotype correlated with a reversion of the reduced pain sensitivity of FAAH(-/-) mice, consistent with the FAA anandamide producing this effect by acting on cannabinoid receptors in the nervous system. Interestingly, however, FAAH-NS mice still exhibited an antiinflammatory phenotype similar in magnitude to FAAH(-/-) mice, indicating that this activity, which was not blocked by cannabinoid receptor antagonists, was mediated by peripherally elevated FAAs. These data suggest that the central and peripheral FAA signaling systems regulate discrete behavioral processes and may be targeted for distinct therapeutic gain.