Pivotal role of IL-6 in the hyperinflammatory responses to subacute ozone in adiponectin-deficient mice

Abstract

Adiponectin is an adipose-derived hormone with anti-inflammatory activity. Following subacute ozone exposure (0.3 ppm for 24–72 h), neutrophilic inflammation and IL-6 are augmented in adiponectin-deficient ( Adipo−/−) mice. The IL-17/granulocyte colony-stimulating factor (G-CSF) axis is required for this increased neutrophilia. We hypothesized that elevated IL-6 in Adipo−/−mice contributes to their augmented responses to ozone via effects on IL-17A expression. Therefore, we generated mice deficient in both adiponectin and IL-6 ( Adipo−/−/IL-6−/−) and exposed them to ozone or air. In ozone-exposed mice, bronchoalveolar lavage (BAL) neutrophils, IL-6, and G-CSF, and pulmonary Il17a mRNA expression were greater in Adipo−/−vs. wild-type mice, but reduced in Adipo−/−/IL-6−/−vs. Adipo−/−mice. IL-17A+F4/80+cells and IL-17A+γδ T cells were also reduced in Adipo−/−/IL-6−/−vs. Adipo−/−mice exposed to ozone. Only BAL neutrophils were reduced in IL-6−/−vs. wild-type mice. In wild-type mice, IL-6 was expressed in Gr-1+F4/80−CD11c−cells, whereas in Adipo−/−mice F4/80+CD11c+cells also expressed IL-6, suggesting that IL-6 is regulated by adiponectin in these alveolar macrophages. Transcriptomic analysis identified serum amyloid A3 ( Saa3), which promotes IL-17A expression, as the gene most differentially augmented by ozone in Adipo−/−vs. wild-type mice. After ozone, Saa3 mRNA expression was markedly greater in Adipo−/−vs. wild-type mice but reduced in Adipo−/−/IL-6−/−vs. Adipo−/−mice. In conclusion, our data support a pivotal role of IL-6 in the hyperinflammatory condition observed in Adipo−/−mice after ozone exposure and suggest that this role of IL-6 involves its ability to induce Saa3, IL-17A, and G-CSF.