Glucose homeostasis following diesel exhaust particulate matter exposure in a lung epithelial cell-specific IKK2-deficient mouse model

Abstract

Background: Pulmonary inflammation is believed to be central to the pathogenesis due to exposure to fine particulate matter with aerodynamic diameter ≤2.5 μm (PM2.5). This central role, however, has not yet been systemically examined. Objective: In the present study, we exploited a lung epithelial cell-specific inhibitor κB kinase 2 (IKK2) knockout mouse model to determine the role of pulmonary inflammation in the pathophysiology due to exposure to diesel exhaust particulate matter (DEP). Methods: SFTPC-rtTA+/−tetO-cre+/−IKK2flox/flox (lung epithelial cell-specific IKK2 knockout, KO) and SFTPC-rtTA+/−tetO-cre+/−IKK2flox/flox (wild-type, tgWT) mice were intratracheally instilled with either vehicle or DEP for 4 months, and their inflammatory response and glucose homeostasis were then assessed. Results: In comparison with tgWT mice, lung epithelial cell-specific IKK2-deficient mice had fewer DEP exposure-induced bronchoalveolar lavage fluid immune cells and proinflammatory cytokines as well as fewer DEP exposure-induced circulating proinflammatory cytokines. Glucose and insulin tolerance tests revealed that lung epithelial cell-specific IKK2 deficiency resulted in markedly less DEP exposure–induced insulin resistance and greater glucose tolerance. Akt phosphorylation analyses of insulin-responsive tissues showed that DEP exposure primarily targeted hepatic insulin sensitivity. Lung epithelial cell–specific IKK2-deficient mice had significantly lower hepatic insulin resistance than tgWT mice had. Furthermore, this difference in insulin resistance was accompanied by consistent differences in hepatic insulin receptor substrate 1 serine phosphorylation and inflammatory marker expression. Discussion: Our findings suggest that in a tissue-specific knockout mouse model, an IKK2-dependent pulmonary inflammatory response was essential for the development of abnormal glucose homeostasis due to exposure to DEP. Copyright 2019, Public Health Services, US Dept of Health and Human Services. All rights reserved.