S1P lyase inhibition prevents lung injury following high pressure-controlled mechanical ventilation in aging mice.

Ventilator-induced Lung Injury (VILI) is characterized by hypoxia, inflammatory cytokine influx, loss of alveolar barrier integrity, and decreased lung compliance. Aging influences lung structure and function and is a predictive factor in the severity of VILI; however, the mechanisms of aging that influence the progression or increased susceptibility remain unknown. Aging impacts immune system function and may increase inflammation in healthy individuals. Recent studies suggest that the bioactive sphingolipid mediator sphingosine-1-phosphate (S1P) and the enzyme that degrades it S1P lyase (SPL) may be involved in lung pathologies including acute lung injury. It is unknown whether aging influences S1P and SPL expression that have been implicated in lung inflammation, injury, and cell apoptosis. We hypothesized that aging and injurious mechanical ventilation synergistically impair S1P levels and enhance S1P lyase (SPL) expression that amplifies alveolar barrier damage and diminishes pulmonary function. Young (2-3 mo) and old (20-25 mo) C57BL/6 mice were mechanically ventilated for 2 h using pressure-controlled mechanical ventilation (PCMV) at 45 cmH2O and 35 cmH2O, respectively. We assessed the impact of aging and PCMV on several indications of acute lung injury, immune cell recruitment, S1P levels and SPL activity. Furthermore, we evaluated the protective effects of inhibiting SPL by tetrahydroxybutylimidazol (THI) administration on the negative outcomes associated with aging and mechanical injury. PCMV exacerbated lung injury in old mice and increased neutrophil influx that was further exacerbated due to aging. SPL expression increased in the young and old ventilated mice and the old nonventilated group. THI treatment reduced several of the indicators of lung injury and resulted in elevated S1P levels in lung tissue and plasma from mice that were injured from mechanical ventilation. CD80 and CD206 activation markers of alveolar and interstitial macrophages were also influenced by THI. SPL inhibition may be a viable therapeutic approach for patients requiring mechanical ventilation by preventing or regulating the exaggerated inflammatory response and reducing lung injury.

[Sphingolipids and their medical impact]. / Sphingolipide und deren medizinische Bedeutung.

Sphingolipids are known to function as structural components in cell membranes, but they also have signalling properties. Sphingosine 1-phosphate (S1P), in particular, is an extracellular messenger that activates five G protein-coupled cell surface receptors, and regulates important physiological functions in the cardiovascular and immune system, in hearing, and fertility. Tight regulation of receptor-available S1P, establishment of concentration gradients and the close interplay between S1P and its receptors are necessary requirements in a multitude of processes. Pharmacological and genetic studies in animals have demonstrated that altered S1P concentrations in blood and organs, as well as mutated expression of S1P receptors in certain cell systems can be causative, but may also be efficacious medication in selected diseases. Sphingolipids and their receptors are, therefore, current targets for medical research.

Sphingosine-1-phosphate is a ligand for the G protein-coupled receptor EDG-6.

EDG-6 is a recently cloned member of the endothelial differentiation gene (EDG) G protein-coupled receptor family that is expressed in lymphoid and hematopoietic tissue and in the lung. Homology of EDG-6 to the known sphingosine-1-phosphate (SPP) receptors EDG-1, EDG-3, and EDG-5 and lysophosphatidic acid (LPA) receptors EDG-2 and EDG-4 suggested that its ligand may be a lysophospholipid or lysosphingolipid. We examined the binding of [(32)P]SPP to HEK293 cells, transiently transfected with cDNA encoding EDG-6. Binding of [(32)P]SPP was saturable, demonstrating high affinity (K(D) = 63 nmol/L). Binding was also specific for SPP, as only unlabeled SPP and sphinganine-1-phosphate, which lacks the trans double bond at the 4 position, potently displaced radiolabeled SPP. LPA did not compete for binding of SPP at any concentration tested, whereas sphingosylphosphorylcholine competed for binding to EDG-6, but only at very high concentrations. In addition, SPP activated extracellular signal-regulated kinase (Erk) in EDG-6 transfected cells in a pertussis toxin-sensitive manner. These results indicate that EDG-6 is a high affinity receptor for SPP, which couples to a G(i/o) protein, resulting in the activation of growth-related signaling pathways. (Blood. 2000;95:2624-2629)

EDG6, a novel G-protein-coupled receptor related to receptors for bioactive lysophospholipids, is specifically expressed in lymphoid tissue.

EDG receptors constitute a novel subfamily of G-protein-coupled receptors displaying a heterogeneous expression pattern. It was shown recently that the four members of this family thus far identified can bind lysophospholipids or lysosphingolipids as ligands. Here we report the identification and characterization of EDG6, a novel member of the EDG receptor family, isolated from in vitro differentiated human and murine dendritic cells. EDG6 is specifically expressed in fetal and adult lymphoid and hematopoietic tissue as well as in lung. The expression pattern of edg6 is strongly conserved in human and mouse. The human edg6 gene was mapped to chromosome 19p13.3 at the D19S120 marker. Considering the lymphoid-specific expression pattern of edg6 and the strong identity to the phospholipid-binding EDG receptor family, we propose that EDG6 may also act as a receptor for a lipid-derived ligand. Because of the known mitogenic and chemotactic activity of bioactive lipids, we believe that EDG6 may play an essential role in lymphocyte cell signaling.