A Pathophysiologic Evaluation of the Receptor for Advanced Glycation End Products (RAGE) in the Lung

The receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin super-family of cell surface receptors whose activation has been suggested to contribute to various pathologies. RAGE has been primarily studied in diabetes where its upregulation has been linked to disease in the kidney, vasculature, and nervous system. This protein is highly expressed in the lung under normal conditions, but its function is unknown. We therefore investigated the normal function of RAGE in the lung and its pulmonary expression in two disease states.Idiopathic pulmonary fibrosis (IPF) is a debilitating disease with both high morbidity and mortality. Unfortunately, there are currently no effective therapies for IPF necessitating mechanistic insight into the disease pathogenesis. We found that pulmonary fibrosis led to a depletion of RAGE in both animal models and tissue from patients with idiopathic pulmonary fibrosis. In contrast to other diseases in which RAGE signaling promotes pathology, we found that aged RAGE null mice spontaneously develop pulmonary fibrosis-like alterations and more severe fibrosis in response to asbestos injury. In addition, we found that RAGE null mice were fully protected from the fibrotic effects of bleomycin. In addition, we investigated the expression of RAGE in the lungs of diabetic rodents. Diabetes has been shown to alter RAGE expression in a number of tissues that do not normally express RAGE. We hypothesized that diabetes would alter pulmonary RAGE expression and contribute to the susceptibility to pulmonary injury. We found that pulmonary RAGE expression was unaltered in five rodent models suggesting that diabetes does not effect RAGE expression in the lung.Lastly, we identified that RAGE has a very high affinity for components in the basement membrane of the lung. A few RAGE studies suggested that it might serve a role as an adhesion molecule. We found that RAGE extensively colocalized with the alveolar basement membrane and had very high affinity for collagen I, collagen IV, and laminin, but not fibronectin. These findings along with the fact that RAGE null mice spontaneously develop fibrosis suggest a potential homeostatic function of RAGE in the lung. This is in stark contrast to the vast majority of studies, which suggest that its expression is solely pathologic

The Role of the Receptor for Advanced Glycation End-Products in a Murine Model of Silicosis

Background: The role of the receptor for advanced glycation end-products (RAGE) has been shown to differ in two different mouse models of asbestos and bleomycin induced pulmonary fibrosis. RAGE knockout (KO) mice get worse fibrosis when challenged with asbestos, whereas in the bleomycin model they are largely protected against fibrosis. In the current study the role of RAGE in a mouse model of silica induced pulmonary fibrosis was investigated. Methodology/Principal Findings: Wild type (WT) and RAGE KO mice received a single intratracheal (i.t.) instillation of silica in saline or saline alone as vehicle control. Fourteen days after treatment mice were subjected to a lung mechanistic study and the lungs were lavaged and inflammatory cells, protein and TGF-β levels in lavage fluid determined. Lungs were subsequently either fixed for histology or excised for biochemical assessment of fibrosis and determination of RAGE proteinand mRNA levels. There was no difference in the inflammatory response or degree of fibrosis (hydroxyproline levels) in the lungs between WT and RAGE KO mice after silica injury. However, histologically the fibrotic lesions in the RAGE KO mice had a more diffuse alveolar septal fibrosis compared to the nodular fibrosis in WT mice. Furthermore, RAGE KO mice had a significantly higher histologic score, a measure of affected areas of the lung, compared to WT silica treated mice. A lung mechanistic study revealed a significant decrease in lung function after silica compared to control, but no difference between WT and RAGE KO. While a dose response study showed similar degrees of fibrosis after silica treatment in the two strains, the RAGE KO mice had some differences in the inflammatory response compared to WT mice. Conclusions/Significance: Aside from the difference in the fibrotic pattern, these studies showed no indicators of RAGE having an effect on the severity of pulmonary fibrosis following silica injury. © 2010 Ramsgaard et al

Lack of the Receptor for Advanced Glycation End-Products Attenuates E. coli Pneumonia in Mice

Background: The receptor for advanced glycation end-products (RAGE) has been suggested to modulate lung injury in models of acute pulmonary inflammation. To study this further, model systems utilizing wild type and RAGE knockout (KO) mice were used to determine the role of RAGE signaling in lipopolysaccharide (LPS) and E. coli induced acute pulmonary inflammation. The effect of intraperitoneal (i.p.) and intratracheal (i.t.) administration of mouse soluble RAGE on E. coli injury was also investigated. Methodology/Principal Findings: C57BL/6 wild type and RAGE KO mice received an i.t. instillation of LPS, E. coli, or vehicle control. Some groups also received i.p. or i.t. administration of mouse soluble RAGE. After 24 hours, the role of RAGE expression on inflammation was assessed by comparing responses in wild type and RAGE KO. RAGE protein levels decreased in wild type lung homogenates after treatment with either LPS or bacteria. In addition, soluble RAGE and HMGB1 increased in the BALF after E. coli instillation. RAGE KO mice challenged with LPS had the same degree of inflammation as wild type mice. However, when challenged with E. coli, RAGE KO mice had significantly less inflammation when compared to wild type mice. Most cytokine levels were lower in the BALF of RAGE KO mice compared to wild type mice after E. coli injury, while only monocyte chemotactic protein-1, MCP-1, was lower after LPS challenge. Neither i.p. nor i.t. administration of mouse soluble RAGE attenuated the severity of E. coli injury in wild type mice. Conclusions/Significance: Lack of RAGE in the lung does not protect against LPS induced acute pulmonary inflammation, but attenuates injury following live E. coli challenge. These findings suggest that RAGE mediates responses to E. coli-associated pathogen-associated molecular pattern molecules other than LPS or other bacterial specific signaling responses. Soluble RAGE treatment had no effect on inflammation. © 2011 Ramsgaard et al

Clearance kinetics and matrix binding partners of the receptor for advanced glycation end products

Elucidating the sites and mechanisms of sRAGE action in the healthy state is vital to better understand the biological importance of the receptor for advanced glycation end products (RAGE). Previous studies in animal models of disease have demonstrated that exogenous sRAGE has an anti-inflammatory effect, which has been reasoned to arise from sequestration of pro-inflammatory ligands away from membrane-bound RAGE isoforms. We show here that sRAGE exhibits in vitro binding with high affinity and reversibly to extracellular matrix components collagen I, collagen IV, and laminin. Soluble RAGE administered intratracheally, intravenously, or intraperitoneally, does not distribute in a specific fashion to any healthy mouse tissue, suggesting against the existence of accessible sRAGE sinks and receptors in the healthy mouse. Intratracheal administration is the only effective means of delivering exogenous sRAGE to the lung, the organ in which RAGE is most highly expressed; clearance of sRAGE from lung does not differ appreciably from that of albumin. Copyright: © 2014 Milutinovic et al

Lack of the Receptor for Advanced Glycation End- Products Attenuates E. coli Pneumonia in Mice

Abstract Background: The receptor for advanced glycation end-products (RAGE) has been suggested to modulate lung injury in models of acute pulmonary inflammation. To study this further, model systems utilizing wild type and RAGE knockout (KO) mice were used to determine the role of RAGE signaling in lipopolysaccharide (LPS) and E. coli induced acute pulmonary inflammation. The effect of intraperitoneal (i.p.) and intratracheal (i.t.) administration of mouse soluble RAGE on E. coli injury was also investigated