Rationale: Receptor for advanced glycation end-products (RAGE) is one of the alveolar type I cell-associated proteins in the lung. Objectives: To test the hypothesis that RAGE is a marker of alveolar epithelial type I cell injury. Methods: Rats were instilled intratracheally with 10 mg/kg lipopolysaccharide or hydrochloric acid. RAGE levels were measured in the bronchoalveolar lavage (BAL) and serum in the rats and in the pulmonary edema fluid and plasma from patients with acute lung injury (ALI; n ϭ 22) and hydrostatic pulmonary edema (n ϭ 11). Main Results: In the rat lung injury studies, RAGE was released into the BAL and serum as a single soluble isoform sized ‫ف‬ 48 kD. The elevated levels of RAGE in the BAL correlated well with the severity of experimentally induced lung injury. In the human studies, the RAGE level in the pulmonary edema fluid was significantly higher than the plasma level (p Ͻ 0.0001). The median edema fluid/plasma ratio of RAGE levels was 105 (interquartile range, 55-243). The RAGE levels in the pulmonary edema fluid from patients with ALI were higher than the levels from patients with hydrostatic pulmonary edema (p Ͻ 0.05), and the plasma RAGE level in patients with ALI were significantly higher than the healthy volunteers (p Ͻ 0.001) or patients with hydrostatic pulmonary edema (p Ͻ 0.05). Conclusion: RAGE is a marker of type I alveolar epithelial cell injury based on experimental studies in rats and in patients with ALI.Keywords: acute respiratory distress syndrome; alveolar epithelium; biological markers; pulmonary edemaReceptor for advanced glycation end-products (RAGE) is one of the alveolar type I cell-associated proteins in the lung (1, 2). Although it is also expressed in endothelial cells in large vessels (3, 4) and nervous tissues (5, 6), the transcript of RAGE is most prominent in the lung (3) and apparently not expressed in lung microvascular endothelia (7,8). Immunoelectron microscopy of RAGE demonstrated that its expression is localized to the basal membrane of alveolar type I epithelial cells (7,8 binding site and two C-type immunogloblin-like regions), a transmembrane domain, and a cytosolic tail, that are essential for post-RAGE signaling (9). In general, RAGE is a multiligandbinding receptor that can bind advanced glycation end products, amyloid ␤-peptide, S100 proteins, and high-mobility group box-1 (10-12). RAGE-ligand interaction results in intracellular signaling, which leads to activation of the proinflammatory transcription factor nuclear factor-B (NF-B). This cellular activation is related to inflammatory processes or tissue injury, such as diabetic microvascular injury, amyloidosis, and immune-inflammatory process (10-12). RAGE knockout mice were recently reported to be resistant to septic shock induced by cecal ligation and puncture (13), suggesting that RAGE potentially plays a role in systemic acute inflammation. However, the biochemical characteristics of RAGE in the lung in response to acute lung injury (ALI) have not been determined.Alveolar type I epithe...

Transcriptional adaptations to hypoxia are mediated by hypoxia-inducible factor (HIF)-1, a heterodimer of HIF-␣ and aryl hydrocarbon receptor nuclear translocator subunits. The HIF-1␣ and HIF-2␣ subunits both undergo rapid hypoxia-induced protein stabilization and bind identical target DNA sequences. When coexpressed in similar cell types, discriminating control mechanisms may exist for their regulation, explaining why HIF-1␣ and HIF-2␣ do not substitute during embryogenesis. We report that, in a human lung epithelial cell line (A549), HIF-1␣ and HIF-2␣ proteins were similarly induced by acute hypoxia (4 h, 0.5% O 2 ) at the translational or posttranslational level. However, HIF-1␣ and HIF-2␣ were differentially regulated by prolonged hypoxia (12 h, 0.5% O 2 ) since HIF-1␣ protein stimulation disappeared because of a reduction in its mRNA stability, whereas HIF-2␣ protein stimulation remained high and stable. Prolonged hypoxia also induced an increase in the quantity of natural antisense HIF-1␣ (aHIF), whose gene promoter contains several putative hypoxia response elements to which (as we confirm here) the HIF-1␣ or HIF-2␣ protein can bind. Finally, transient transfection of A549 cells by dominant-negative HIF-2␣, also acting as a dominant-negative for HIF-1␣, prevented both the decrease in the HIF-1␣ protein and the increase in the aHIF transcript. Taken together, these data indicate that, during prolonged hypoxia, HIF-␣ proteins negatively regulate HIF-1␣ expression through an increase in aHIF and destabilization of HIF-1␣ mRNA. This transregulation between HIF-1␣ and HIF-2␣ during hypoxia likely conveys target gene specificity.