Maternal smoking and the retinoid pathway in the developing lung.

BACKGROUND: Maternal smoking is a risk factor for pediatric lung disease, including asthma. Animal models suggest that maternal smoking causes defective alveolarization in the offspring. Retinoic acid signaling modulates both lung development and postnatal immune function. Thus, abnormalities in this pathway could mediate maternal smoking effects. We tested whether maternal smoking disrupts retinoic acid pathway expression and functioning in a murine model. METHODS: Female C57Bl/6 mice with/without mainstream cigarette smoke exposure (3 research cigarettes a day, 5 days a week) were mated to nonsmoking males. Cigarette smoke exposure continued throughout the pregnancy and after parturition. Lung tissue from the offspring was examined by mean linear intercept analysis and by quantitative PCR. Cell culture experiments using the type II cell-like cell line, A549, tested whether lipid-soluble cigarette smoke components affected binding and activation of retinoic acid response elements in vitro. RESULTS: Compared to tobacco-naïve mice, juvenile mice with tobacco toxin exposure had significantly (P < 0.05) increased mean linear intercepts, consistent with an alveolarization defect. Tobacco toxin exposure significantly (P < 0.05) decreased mRNA and protein expression of retinoic acid signaling pathway elements, including retinoic acid receptor alpha and retinoic acid receptor beta, with the greatest number of changes observed between postnatal days 3-5. Lipid-soluble cigarette smoke components significantly (P < 0.05) decreased retinoic acid-induced binding and activation of the retinoic acid receptor response element in A549 cells. CONCLUSIONS: A murine model of maternal cigarette smoking causes abnormal alveolarization in association with altered retinoic acid pathway element expression in the offspring. An in vitro cell culture model shows that lipid-soluble components of cigarette smoke decrease retinoic acid response element activation. It is feasible that disruption of retinoic acid signaling contributes to the pediatric lung dysfunction caused by maternal smoking.

RUNX transcription factors: association with pediatric asthma and modulated by maternal smoking.

Intrauterine smoke exposure (IUS) is a strong risk factor for development of airways responsiveness and asthma in childhood. Runt-related transcription factors (RUNX1-3) have critical roles in immune system development and function. We hypothesized that genetic variations in RUNX1 would be associated with airway responsiveness in asthmatic children and that this association would be modified by IUS. Family-based association testing analysis in the Childhood Asthma Management Program genome-wide genotype data showed that 17 of 100 RUNX1 single-nucleotide polymorphisms (SNPs) were significantly (P < 0.03-0.04) associated with methacholine responsiveness. The association between methacholine responsiveness and one of the SNPs was significantly modified by a history of IUS exposure. Quantitative PCR analysis of immature human lung tissue with and without IUS suggested that IUS increased RUNX1 expression at the pseudoglandular stage of lung development. We examined these associations by subjecting murine neonatal lung tissue with and without IUS to quantitative PCR (N = 4-14 per group). Our murine model showed that IUS decreased RUNX expression at postnatal days (P)3 and P5 (P < 0.05). We conclude that 1) SNPs in RUNX1 are associated with airway responsiveness in asthmatic children and these associations are modified by IUS exposure, 2) IUS tended to increase the expression of RUNX1 in early human development, and 3) a murine IUS model showed that the effects of developmental cigarette smoke exposure persisted for at least 2 wk after birth. We speculate that IUS exposure-altered expression of RUNX transcription factors increases the risk of asthma in children with IUS exposure.