Expression and activity of pH-regulatory glutaminase in the human airway epithelium.
Fluid condensed from the breath of patients with acute asthma is acidic. Several features of asthma pathophysiology can be initiated by exposure of the airway to acid. In renal tubular epithelium, glutaminase produces ammonia to buffer urinary acid excretion. We hypothesized that human airway epithelium could also express glutaminase. Here, we demonstrate that human airway epithelial cells in vitro have biochemical evidence for glutaminase activity and express mRNA for two glutaminase isoforms (KGA and GAC). Glutaminase activity increased in response to acidic stress (media pH 5.8) and was associated with both increased culture medium pH and improved cell survival. In contrast, activity was inhibited by interferon-gamma and tumor necrosis factor-alpha. Glutaminase protein was expressed in the human airway in vivo. Further, ammonia levels in the breath condensate of subjects with acute asthma were low (30 microM [range: 0-233], n = 18, age 23 +/- 2.5 yr) compared with control subjects (327 microM [14-1,220], n = 24, age 24 +/- 2.4 yr, p < 0.001), and correlated with condensate pH (r = 0.58, p < 0.001). These data demonstrate that glutaminase is expressed and active in the human airway epithelium and may be relevant both to the regulation of airway pH and to the pathophysiology of acute asthmatic airway inflammation.
Hunt
John F
JF
Division of Pediatric Respiratory Medicine and Division of Allergy, Asthma and Immunology, The University of Virginia Health System, Charlottesville, Virginia 22908, USA.
Erwin
Elizabeth
E
Palmer
Lisa
L
Vaughan
John
J
Malhotra
Neil
N
Platts-Mills
Thomas A E
TA
Gaston
Benjamin
B
D000208:Acute Disease; D000328:Adult; D000641:Ammonia / Q000032:analysis / Q000378:metabolism; D000704:Analysis of Variance; D001249:Asthma / Q000201:enzymology* / Q000276:immunology / Q000503:physiopathology; D001706:Biopsy; D015153:Blotting, Western; D001944:Breath Tests; D016022:Case-Control Studies; D002470:Cell Survival; D005786:Gene Expression Regulation / Q000502:physiology*; D005972:Glutaminase / Q000032:analysis / Q000737:chemistry / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007150:Immunohistochemistry; D007249:Inflammation; D007371:Interferon-gamma / Q000494:pharmacology / Q000502:physiology; D007536:Isomerism; D012333:RNA, Messenger / Q000032:analysis; D020545:Respiratory Mucosa / Q000201:enzymology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology / Q000502:physiology; D015854:Up-Regulation / Q000187:drug effects / Q000502:physiology*
D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D000641:Ammonia; D007371:Interferon-gamma; D005972:Glutaminase