Smoking-mediated Up-regulation of GAD67 Expression in the Human Airway Epithelium

Gamma-aminobutyric acid (GABA) is a multifunctional mediator that functions as a neurotransmitter in the central nervous system and a trophic factor during nervous system development, affecting proliferation, differentiation and cell death [1-3].GABA is synthesized from glutamate, catalyzed by GAD65 and GAD67, glutamic acid decarboxylase {Tillakaratne, Medina-Kauwe, et al. 1995 21 /id}{Owens & Kriegstein 2002 3 /id}{Watanabe, Maemura, et al. 2002 73 /id}. In the CNS transporters and catabolic enzymes work in a coordinated fashion to control the availability of GABA {Tillakaratne, Medina-Kauwe, et al. 1995 21 /id}{Owens & Kriegstein 2002 3 /id}{Watanabe, Maemura, et al. 2002 73 /id} It is now recognized that GABA also functions in a variety of organs outside of the CNS [1,3,4]. In the lung, a series of recent studies suggest that the GABAergic signaling system plays a role in the control of asthma related-airway constriction and mucin secretion [5-9]. In the context that goblet cell hyperplasia and mucin overproduction is associated with cigarette smoking [10-12], we hypothesized that components of the GABAergic system may also be altered in the airway epithelium of cigarette smokers. To assess this hypothesis, we evaluated the expression of the entire GABAergic system in the large and small airway epithelium of healthy nonsmokers and healthy smokers. The data demonstrates there is expression of genes for a complete GABAergic system in the airway epithelium. Interestingly, the expression of GAD67 was markedly modified by smoking, with increased expression in healthy smokers compared to healthy nonsmokers at the mRNA and protein levels. In the context that mucus overproduction is commonly associated with cigarette smoking, GAD67 may be a pharmacologic target for treatment of smoking-related disorders. Affymetrix arrays were used to assess the expression of GAD67 gene expression data in large airway and small airway epithelium obtained by fiberoptic bronchoscopy of 21 healthy non-smokers and 31 healthy smokers (large airways) and 47 healthy non-smokers and 58 healthy smokers (small airways).