Conditionally induced RAGE expression by proximal airway epithelial cells in transgenic mice causes lung inflammation.

BACKGROUND: Receptors for advanced glycation end-products (RAGE) are multiligand cell-surface receptors expressed abundantly by distal pulmonary epithelium. Our lab has discovered RAGE-mediated effects in the orchestration of lung inflammation induced by tobacco smoke and environmental pollutants; however, the specific contribution of RAGE to the progression of proximal airway inflammation is still inadequately characterized. METHODS AND RESULTS: We generated a Tet-inducible transgenic mouse that conditionally overexpressed RAGE using the club cell (Clara) secretory protein (CCSP) promoter expressed by club (Clara) cells localized to the proximal airway. RAGE was induced for 40 days from weaning (20 days of age) until sacrifice date at 60 days. Immunohistochemistry, immunoblotting, and qPCR revealed significant RAGE up-regulation when compared to non-transgenic controls; however, H&E staining revealed no detectible morphological abnormalities and apoptosis was not enhanced during the 40 days of augmentation. Freshly procured bronchoalveolar lavage fluid (BALF) from CCSP-RAGE TG mice had significantly more total leukocytes and PMNs compared to age-matched control littermates. Furthermore, CCSP-RAGE TG mice expressed significantly more tumor necrosis factor alpha (TNF-α), interleukin 7 (IL-7), and interleukin 14 (IL-14) in whole lung homogenates compared to controls. CONCLUSIONS: These data support the concept that RAGE up-regulation specifically in lung airways may function in the progression of proximal airway inflammation.

Conditional overexpression of receptors for advanced glycation end-products in the adult murine lung causes airspace enlargement and induces inflammation.

Receptors for advanced glycation end-products (RAGE) are multiligand surface receptors detected abundantly in pulmonary tissue. Our previous work revealed increased RAGE expression in cells and lungs exposed to tobacco smoke and RAGE-mediated cytokine expression via proinflammatory mechanisms involving NF-κB. RAGE expression is elevated in various pathological states, including chronic obstructive pulmonary disease; however, precise contributions of RAGE to the progression of emphysema and pulmonary inflammation in the adult lung are unknown. In the current study, we generated a RAGE transgenic (RAGE TG) mouse and conditionally induced adult alveolar epithelium to overexpress RAGE. RAGE was induced after the period of alveologenesis, from weaning (20 d of age) until animals were killed at 50, 80, and 110 days (representing 30, 60, and 90 d of RAGE overexpression). Hematoxylin and eosin staining and mean chord length revealed incremental dilation of alveolar spaces as RAGE overexpression persisted. TUNEL staining and electron microscopy confirmed increased apoptosis and blebbing of alveolar epithelium in lungs from RAGE TG mice when compared with control mice. Immunohistochemistry for matrix metalloproteinase 9 revealed an overall increase in matrix metalloproteinase 9, which correlated with decreased elastin expression in RAGE TG mice. Furthermore, RAGE TG mice manifested significant inflammation measured by elevated bronchoalveolar lavage protein, leukocyte infiltration, and secreted cytokines. These data support the concept that innovative transgenic mice that overexpress RAGE may model pulmonary inflammation and alveolar destabilization independent of tobacco smoke and validate RAGE signaling as a target pathway in the prevention or attenuation of smoke-related inflammatory lung diseases.