Cigarette smoke extract induces differential expression levels of beta-defensin peptides in human alveolar epithelial cells

Background: The damaging effects of cigarette smoke on the lungs are well known in terms of cancer risks. Additional molecular changes within the lung tissue can also occur as a result of exposure to cigarette smoke. The human beta-defensin (hBD) class of antimicrobial peptides is the focus of our research. In addition to antimicrobial activity, beta-defensins also have immunomodulatory functions. Over 30 previously unrecognized beta-defensin genes have recently been identified in the human genome, many with yet to be determined functions. We postulated that altered beta-defensin production may play a role in the pathogenesis observed in the lungs of smokers. Our hypothesis is that cigarette smoke exposure will affect the expression of beta-defensins in human lung alveolar epithelial cells (A549). Methods: We exposed A549 cells to cigarette smoke extract (CSE) and measured the changes in mRNA levels of several antimicrobial peptides by quantitative real-time PCR, and directly observed peptide expression in cells by immunofluorescence (IF) microscopy. Results: We found that hBD3, hBD5, and hBD9 gene expression was upregulated in A549 cells exposed to CSE. HBD1, hBD8, hBD18 and LL-37 gene expression did not significantly change upon exposure to CSE. Expression of hBD3 and hBD4 peptides was visualized by IF. Conclusions: This differential expression suggests that hBD3, hBD5, and hBD9 may play a role in the changes to the lung tissue observed in smokers. Establishing differential beta-defensin expression following CSE treatment will add to our understanding of the molecular response of the lung alveolar epithelium to cigarette smoke exposure.