Proteolytic release of the receptor for advanced glycation end products from in vitro and in situ alveolar epithelial cells

Abstract

Although the receptor for advanced glycation end products (RAGE) has been used as a biological marker of alveolar epithelial cell injury in clinical studies, the mechanism for release of soluble RAGE from lung epithelial cells has not been well studied. Therefore, these studies were designed to determine the mechanism for release of soluble RAGE after lipopolysaccharide (LPS) challenge. For these purposes, alveolar epithelial cells from rat lungs were cultured on Transwell inserts, and LPS was added to the apical side (500 μg/ml) for 16 h on day 7. On day 7, RAGE was expressed predominantly in surfactant protein D-negative cells, and LPS challenge induced release of RAGE into the medium. This response was partially blocked by matrix metalloproteinase (MMP) inhibitors. Transcripts of MMP-3 and MMP-13 were upregulated by LPS, whereas RAGE transcripts did not change. Proteolysis by MMP-3 and MMP-13 resulted in soluble RAGE expression in the bronchoalveolar lavage fluid in the in situ rat lung, and this reaction was inhibited by MMP inhibitors. In human studies, both MMP-3 and -13 antigen levels were significantly correlated with the level of RAGE in pulmonary edema fluid samples. These results support the conclusion that release of RAGE is primarily mediated by proteolytic damage in alveolar epithelial cells in the lung, caused by proteases in acute inflammatory conditions in the distal air spaces.

Overexpression of Receptor for Advanced Glycation End Products and High-Mobility Group Box 1 in Human Dental Pulp Inflammation

“…Specifically, RAGE labeling appeared more intensely stained in odontoblasts of pulpitis versus healthy tissue. RAGE expression by odontoblasts appears comparable to that reported for alveolar epithelial cells [56], synovial fibroblasts [38], and in the pathogenesis of lung injury in mice [54, 57] in which RAGE is expressed at low levels in normal tissues and in the vasculature and becomes upregulated at other sites where its ligands accumulate [19]. Previous studies show that odontoblasts express receptors for LPS, TLR-2, and TLR-4 on the cell membrane [3, 58].…”

Novel concepts of acute lung injury and alveolar-capillary barrier dysfunction

“…Epithelial-mesenchymal transition (EMT), resident lung fibroblast migration, proliferation, transdifferentiation into myofibroblasts, and fibrocyte recruitment take place in the fibroproliferative phase of ALI (25). Receptor for advanced glycation end products (RAGE), which has a role in alveolar epithelial cell spreading and adherence, when impaired, mediates an increase in cell migration and proliferation (28,84,90,262). It has been now revealed that, whereas under basal conditions RAGE is linked to the cytoskeleton by interacting with the family of ezrin/radixin/moesin (ERM), in the presence of inflammatory cytokines this interaction is disrupted by ERM phosphorylation and subsequent ERM interaction with CD44 and actin stress fibers, causing loss of adhesion and an invasive phenotype contributing to EMT (22).…”

The receptor for advanced glycation end-products supports lung tissue biomechanics

“…A reduced alveolar expression of RAGE is related to pathophysiological changes of the lung tissue, such as carcinoma (3), fibrosis (34,37), and chronic obstructive pulmonary disease (COPD) (34). In addition to the membrane-bound receptor, soluble RAGE (sRAGE) forms exist as the result of either alternative splicing (22) or protein shedding by metalloproteinases (39,52). sRAGE normally exists in the bronchoalveolar lavage (BAL) at a high level (53), but it is deficient in neutrophilic asthma and COPD (47,49).…”