X-Box-Binding Protein 1 and Innate Immune Responses of Human Cystic Fibrosis Alveolar Macrophages.
BACKGROUND
Alveolar macrophages (AMs) play a key role in host defense to inhaled bacterial pathogens, in part by secreting inflammatory mediators. Cystic fibrosis (CF) airways exhibit a persistent, robust inflammatory response that may contribute to the pathophysiology of CF. Recent findings have linked endoplasmic reticulum stress responses mediated by inositol-requiring enzyme 1α-dependent messenger RNA splicing (activation) of X-box-binding protein-1 (XBP-1s) to inflammation in peripheral macrophages. However, the role of XBP-1s in CF AM function is not known.


OBJECTIVE
To evaluate inflammatory responses of AMs from chronically infected/inflamed human CF lungs and test whether XBP-1s is required for AM-mediated inflammation.


METHODS
Basal and LPS-induced inflammatory responses were evaluated in primary cultures of non-CF versus CF AMs. XBP-1s was measured and its function was evaluated in AMs using 8-formyl-7-hydroxy-4-methylcoumarin (4μ8C), an inhibitor of inositol-requiring enzyme 1α-dependent XBP-1s, and in THP-1 cells stably expressing XBP-1 shRNA, XBP-1s, or a dominant-negative XBP-1.


RESULTS
CF AMs exhibited exaggerated basal and LPS-induced production of tumor necrosis factor-α and IL-6, and these responses were coupled to increased levels of XBP-1s. In non-CF and CF AMs, LPS-induced cytokine production was blunted by 4µ8C. A role for XBP-1s in AM inflammatory responses was further established by data from dTHP-1 cells indicating that expression of XBP-1 shRNA reduced XBP-1s levels and LPS-induced inflammatory responses; and LPS-induced inflammation was up-regulated by expression of XBP-1s and inhibited by dominant-negative XBP-1.


CONCLUSIONS
These findings suggest that AMs contribute to the robust inflammation of CF airways via an up-regulation of XBP-1s-mediated cytokine production.
1 Marsico Lung Institute/Cystic Fibrosis Research Center.
Bob A
BA
Lubamba
1 Marsico Lung Institute/Cystic Fibrosis Research Center.
Lisa C
LC
Jones
1 Marsico Lung Institute/Cystic Fibrosis Research Center.|2 Department of Medicine, and.
Wanda K
WK
O'Neal
1 Marsico Lung Institute/Cystic Fibrosis Research Center.|2 Department of Medicine, and.
Richard C
RC
Boucher
1 Marsico Lung Institute/Cystic Fibrosis Research Center.|2 Department of Medicine, and.|3 Department of Cell Biology and Physiology, The University of North Carolina at Chapel Hill, Chapel Hill, North Carolina.
Carla M P
CM
Ribeiro
D002478:Cells, Cultured; D003550:Cystic Fibrosis / Q000150:complications / Q000235:genetics* / Q000276:immunology*; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000276:immunology*; D006801:Humans; D007113:Immunity, Innate / Q000235:genetics / Q000276:immunology*; D007249:Inflammation / Q000150:complications / Q000235:genetics / Q000276:immunology; D016676:Macrophages, Alveolar / Q000276:immunology*; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors / Q000235:genetics* / Q000276:immunology*; D000071717:X-Box Binding Protein 1
D004268:DNA-Binding Proteins; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human
IRE1α/XBP-1; UPR; airway inflammation; alveolar macrophage; cystic fibrosis