Modifications of the Rat Airway Explant Transcriptome by Cigarette Smoke

Although a number of animal model studies have addressed changes in gene expression in the parenchyma and their relationship to emphysema, much less is known about the pathogenesis of cigarette smoke-induced small airway remodeling. In this study, we exposed rat tracheal explants to whole smoke for 15 minutes, and then cultured the explants in air. The airway transcriptome was evaluated using RAE 230_2 GeneChips. By 2 hours after starting smoke exposure, expression levels of 502 genes were changed up or down by more than 1.5 times (p values <0.01 or less), and by 24 hours, 1870 genes were significantly changed up or down. These included genes involved in anti-oxidant protection, epithelial defense and remodeling, inflammatory mediators and transcription factors, and a number of unexpected genes including the MMP-12 inducer, tachykinin-1 (substance P). Pre-treatment of the explants with 1 x 10-7 M dexamethasone reduced the number of significantly changed genes by approximately 47% at 2 hr and 68% at 24 hours, and in almost all instances, reduced the magnitude of the smoke-induced changes. We conclude that even a very brief exposure to cigarette smoke can lead to rapid changes in the expression of a large number of genes in rat tracheal explants, and that these effects are directly mediated by smoke, without a need for exogenous inflammatory cells. Steroids, contrary to the usual belief, are able to ameliorate many of these changes, at least in this very acute model. 4x tracheal explants (approx 2-3ug) from each rat (n=6 rats) exposed to control (air), smoke (10 puffs of cigarette smoke, delivered during 15 mins), dexamethasone and dexamethasone + cigarette smoke were used for RNA extraction and hybridization on Rat230_2 Affymetrix microarrays. 1 rat, 4 explants and 4 conditions. n=6 rats per group/condition at 2hrs, n=6 rats per group/condition at 24hrs. 12 animals = 48 samples total (47 went into analysis because 1 sample failed QC metrics).