Abstract
Genetic variants annotated to the hedgehog interacting protein (HHIP) are robustly associated with chronic obstructive pulmonary disease (COPD). Hhip haploinsufficiency in mice leads to increased susceptibility towards the development of emphysema following exposure to chronic cigarette smoke (CS). To explore the molecular pathways which contribute to increased susceptibility, we performed metabolomic profiling using high performance liquid chromatography tandem mass spectroscopy (LC/MS-MS) on plasma, urine, and lung tissue of Hhip +/- heterozygotes and wild type (Hhip +/+) C57/BL6 mice exposed to either room-air or CS for six months. Univariate comparisons between groups were made with a combined fold change ≥2 and Student's t-test p-value < 0.05 to denote significance; associations with mean alveolar chord length (MACL), a quantitative measure of emphysema, and gene-by-environment interactions were examined using empiric Bayes-mediated linear models. Decreased urinary excretion of cotinine despite comparable plasma levels was observed in Hhip +/- heterozygotes; a strong gene-by-smoking association was also observed. Correlations between MACL and markers of oxidative stress such as urinary methionine sulfoxide were observed in Hhip +/- but not in Hhip +/+ mice. Metabolite set enrichment analyses suggest reduced antioxidant capacity and alterations in macronutrient metabolism contribute to increased susceptibility to chronic CS-induced oxidative stress in Hhip haploinsufficiency states.