Asthma is a complex heritable disease that is increasing in prevalence and severity, particularly in developed countries such as the United States, where 11% of the population is affected. The contribution of environmental and genetic factors to this growing epidemic is currently not well understood. We developed the hypothesis, based on previous literature, that changes in DNA methylation resulting in aberrant gene transcription may enhance the risk of developing allergic airway disease. Our findings indicate that in mice, a maternal diet supplemented with methyl donors enhanced the severity of allergic airway disease that was inherited transgenerationally. Using a genomic approach, we discovered 82 gene-associated loci that were differentially methylated after in utero supplementation with a methyl-rich diet. These methylation changes were associated with decreased transcriptional activity and increased disease severity. Runt-related transcription factor 3 (Runx3), a gene known to negatively regulate allergic airway disease, was found to be excessively methylated, and Runx3 mRNA and protein levels were suppressed in progeny exposed in utero to a high-methylation diet. Moreover, treatment with a demethylating agent increased Runx3 gene transcription, further supporting our claim that a methyl-rich diet can affect methylation status and consequent transcriptional regulation. Our findings indicate that dietary factors can modify the heritable risk of allergic airway disease through epigenetic mechanisms during a vulnerable period of fetal development in mice.

Ozone is a common urban environmental air pollutant and significantly contributes to hospitalizations for respiratory illness. The mechanisms, which regulate ozone-induced bronchoconstriction, remain poorly understood. Hyaluronan was recently shown to play a central role in the response to noninfectious lung injury. Therefore, we hypothesized that hyaluronan contributes to airway hyperreactivity (AHR) after exposure to ambient ozone. Using an established model of ozone-induced airways disease, we characterized the role of hyaluronan in airway hyperresponsiveness. The role of hyaluronan in response to ozone was determined by using therapeutic blockade, genetically modified animals, and direct challenge to hyaluronan. Ozone-exposed mice demonstrate enhanced AHR associated with elevated hyaluronan levels in the lavage fluid. Mice deficient in either CD44 (the major receptor for hyaluronan) or inter-␣-trypsin inhibitor (molecule that facilitates hyaluronan binding) show similar elevations in hyaluronan but are protected from ozone-induced AHR. Mice pretreated with hyaluronan-binding peptide are protected from the development of ozone-induced AHR. Overexpression of hyaluronan enhances the airway response to ozone. Intratracheal instillation of endotoxin-free low molecular weight hyaluronan induces AHR dependent on CD44, whereas instillation of high molecular weight hyaluronan protects against ozone-induced AHR. In conclusion, we demonstrate that hyaluronan mediates ozoneinduced AHR, which is dependent on the fragment size and both CD44 and inter-␣-trypsin inhibitor. These data support the conclusion that pulmonary matrix can contribute to the development of airway hyperresponsiveness.Ozone is a commonly encountered urban air pollutant that significantly contributes to increased morbidity (1-4) and can lead to a significant economic burden. It has been estimated that each year inhalation of ambient ozone contributes to 800 premature deaths, 4,500 hospital admissions, 900,000 school absences, and more than 1 million restricted activity days with an estimated $5 billion annual economic burden (5). Population-based studies suggest that for each 10 ppb increase in 1-h daily maximum level of ozone there is an increase in mortality risk of 0.39 -0.87%, especially in individuals with pre-existing respiratory disease (2, 3, 6, 7). However, the biological mechanisms, which regulate the response to ambient ozone exposure, remain poorly understood.Hyaluronan is an abundant extracellular matrix component, which has been recently shown to play a significant role in the response to noninfectious lung injury. Short fragment hyaluronan (sHA) 2 is released in the lung after sterile injury such as bleomycin instillation (8) or high tidal volume ventilation (9) and can modify the tissue response to injury. Furthermore, hyaluronan has been identified in airway secretions from asthmatics (10), and high molecular weight hyaluronan can attenuate the bronchoconstrictive response in exercise-induced asthma (11). We therefore hypothesized that...

Our observations support the observation that extracellular matrix HA contributes to ozone-induced airways disease. Furthermore, our results support that TLR4 contributes to the biological response to HA by mediating both the production of proinflammatory cytokines and the development of ozone-induced AHR.

Air spaces of the mammalian lung are lined by a specialized epithelium that is maintained by endogenous progenitor cells. Within bronchioles, the abundance and distribution of progenitor cells that contribute to epithelial homeostasis change as a function of maintenance versus repair. It is unclear whether functionally distinct progenitor pools or a single progenitor cell type maintain the epithelium and how the behavior is regulated in normal or disease states. To address these questions, we applied fractionation methods for the enrichment of distal airway progenitors. We show that bronchiolar progenitor cells can be subdivided into two functionally distinct populations that differ in their susceptibility to injury and contribution to repair. The proliferative capacity of these progenitors is confirmed in a novel in vitro assay. We show that both populations give rise to colonies with a similar dependence on stromal cell interactions and regulation by TGF-β. These findings provide additional insights into mechanisms of epithelial remodeling in the setting of chronic lung disease and offer hope that pharmacologic interventions may be developed to mitigate tissue remodeling.