Down-Regulation of the Canonical Wnt β-Catenin Pathway in the Airway Epithelium of Healthy Smokers and Smokers with COPD

BackgroundThe Wnt pathway mediates differentiation of epithelial tissues; depending on the tissue types, Wnt can either drive or inhibit the differentiation process. We hypothesized that key genes in the Wnt pathway are suppressed in the human airway epithelium under the stress of cigarette smoking, a stress associated with dysregulation of the epithelial differentiated state. Methodology/Principal FindingsMicroarrays were used to assess the expression of Wnt-related genes in the small airway epithelium (SAE) obtained via bronchoscopy and brushing of healthy nonsmokers, healthy smokers, and smokers with COPD. Thirty-three of 56 known Wnt-related genes were expressed in the SAE. Wnt pathway downstream mediators β-catenin and the transcription factor 7-like 1 were down-regulated in healthy smokers and smokers with COPD, as were many Wnt target genes. Among the extracellular regulators that suppress the Wnt pathway, secreted frizzled-related protein 2 (SFRP2), was up-regulated 4.3-fold in healthy smokers and 4.9-fold in COPD smokers, an observation confirmed by TaqMan Real-time PCR, Western analysis and immunohistochemistry. Finally, cigarette smoke extract mediated up-regulation of SFRP2 and down-regulation of Wnt target genes in airway epithelial cells in vitro. Conclusions/SignificanceSmoking down-regulates the Wnt pathway in the human airway epithelium. In the context that Wnt pathway plays an important role in differentiation of epithelial tissues, the down-regulation of Wnt pathway may contribute to the dysregulation of airway epithelium differentiation observed in smoking-related airway disorders.

研究背景：Wnt通路介导上皮组织的分化进程；依据组织类型的差异，Wnt既可促进亦可抑制上皮分化。本研究提出假说：在香烟烟雾应激状态下，人类气道上皮中的Wnt通路关键基因会受到抑制，而该应激与上皮分化状态失调密切相关。
研究方法与主要结果：本研究采用基因芯片（microarrays）技术，对通过支气管镜检刷取的小气道上皮（small airway epithelium, SAE）样本中的Wnt通路相关基因表达水平进行检测，受试对象分为健康非吸烟者、健康吸烟者及慢性阻塞性肺疾病（chronic obstructive pulmonary disease, COPD）吸烟者三组。在56个已知的Wnt通路相关基因中，有33个在SAE中存在表达。Wnt通路下游介质β-连环蛋白（β-catenin）与转录因子7类似物1（transcription factor 7-like 1），以及众多Wnt靶基因，在健康吸烟者及COPD吸烟者体内均呈现表达下调。在抑制Wnt通路的细胞外调控因子中，分泌型卷曲相关蛋白2（secreted frizzled-related protein 2, SFRP2）在健康吸烟者体内的表达量上调4.3倍，在COPD吸烟者体内上调4.9倍，该结果通过TaqMan实时荧光定量PCR（TaqMan Real-time PCR）、蛋白质印迹分析（Western analysis）及免疫组织化学（immunohistochemistry）实验得以验证。此外，体外实验证实，香烟烟雾提取物可介导气道上皮细胞中SFRP2的表达上调及Wnt靶基因的表达下调。
研究结论与意义：吸烟可抑制人类气道上皮中的Wnt通路。鉴于Wnt通路在上皮组织分化过程中发挥重要调控作用，Wnt通路的下调可能参与了吸烟相关气道疾病中所观察到的气道上皮分化失调进程。