Department of Genetic Medicine, Weill Cornell Medical College, New York, New York, USA.
Respir Res. 2010 Oct 29;11(1):150. doi: 10.1186/1465-9921-11-150.
The production of gamma-amino butyric acid (GABA) is dependent on glutamate decarboxylases (GAD65 and GAD67), the enzymes that catalyze the decarboxylation of glutamate to GABA. Based on studies suggesting a role of the airway epithelial GABAergic system in asthma-related mucus overproduction, we hypothesized that cigarette smoking, another disorder associated with increased mucus production, may modulate GABAergic system-related gene expression levels in the airway epithelium.
We assessed expression of the GABAergic system in human airway epithelium obtained using bronchoscopy to sample the epithelium and microarrays to evaluate gene expression. RT-PCR was used to confirm gene expression of GABAergic system gene in large and small airway epithelium from heathy nonsmokers and healthy smokers. The differences in the GABAergic system gene was further confirmed by TaqMan, immunohistochemistry and Western analysis.
The data demonstrate there is a complete GABAergic system expressed in the large and small human airway epithelium, including glutamate decarboxylase, GABA receptors, transporters and catabolism enzymes. Interestingly, of the entire GABAergic system, smoking modified only the expression of GAD67, with marked up-regulation of GAD67 gene expression in both large (4.1-fold increase, p < 0.01) and small airway epithelium of healthy smokers (6.3-fold increase, p < 0.01). At the protein level, Western analysis confirmed the increased expression of GAD67 in airway epithelium of healthy smokers compared to healthy nonsmokers (p < 0.05). There was a significant positive correlation between GAD67 and MUC5AC gene expression in both large and small airway epithelium (p < 0.01), implying a link between GAD67 and mucin overproduction in association with smoking.
In the context that GAD67 is the rate limiting enzyme in GABA synthesis, the correlation of GAD67 gene expression with MUC5AC expressions suggests that the up-regulation of airway epithelium expression of GAD67 may contribute to the increase in mucus production observed in association with cigarette smoking.
NCT00224198; NCT00224185.
γ-氨基丁酸（GABA）的产生依赖于谷氨酸脱羧酶（GAD65 和 GAD67），这些酶催化谷氨酸脱羧生成 GABA。基于气道上皮 GABA 能系统在哮喘相关黏液过度产生中的作用的研究，我们假设另一种与黏液产生增加相关的疾病——吸烟，可能会调节气道上皮中的 GABA 能系统相关基因表达水平。
我们使用支气管镜检查采集气道上皮样本进行微阵列评估，检测人类气道上皮中 GABA 能系统的表达，以此评估基因表达。RT-PCR 用于确认健康不吸烟者和健康吸烟者的大、小气道上皮中 GABA 能系统基因的表达。通过 TaqMan、免疫组织化学和 Western 分析进一步证实了 GABA 能系统基因的差异。
数据表明，大、小气道上皮中均存在完整的 GABA 能系统，包括谷氨酸脱羧酶、GABA 受体、转运体和分解代谢酶。有趣的是，在整个 GABA 能系统中，吸烟仅修饰了 GAD67 的表达，健康吸烟者的大（4.1 倍增加，p<0.01）和小气道上皮中 GAD67 基因表达明显上调（6.3 倍增加，p<0.01）。在蛋白质水平上，Western 分析证实与健康不吸烟者相比，健康吸烟者的气道上皮中 GAD67 表达增加（p<0.05）。大、小气道上皮中 GAD67 与 MUC5AC 基因表达呈显著正相关（p<0.01），表明 GAD67 与吸烟相关的黏液过度产生之间存在联系。
鉴于 GAD67 是 GABA 合成的限速酶，GAD67 基因表达与 MUC5AC 表达的相关性表明，气道上皮中 GAD67 表达的上调可能导致与吸烟相关的黏液产生增加。
NCT00224198；NCT00224185。
