Particulate Air pollution mediated effects on insulin resistance in mice are independent of CCR2

Cuiqing Liu, Xiaohua Xu, Yuntao Bai, Jixin Zhong, Aixia Wang, Lixian Sun, Liya Kong, Zhekang Ying, Qinghua Sun, Sanjay Rajagopalan

Chronic exposure to fine ambient particulate matter (PM2.5) induces insulin resistance. CC-chemokine receptor 2 (CCR2) appears to be essential in diet-induced insulin resistance implicating an important role for systemic cellular inflammation in the process. We have previously suggested that CCR2 is important in PM2.5 exposure-mediated inflammation leading to insulin resistance under high fat diet situation. The present study assessed the importance of CCR2 in PM2.5 exposure-induced insulin resistance in the context of normal diet. C57BL/6 and CCR2(-/-) mice were subjected to exposure to concentrated ambient PM2.5 or filtered air for 6 months. In C57BL/6 mice, concentrated ambient PM2.5 exposure induced whole-body insulin resistance, macrophage infiltration into the adipose tissue, and upregulation of phosphoenolpyruvate carboxykinase (PEPCK) in the liver. While CCR2 deficiency reduced adipose macrophage content in the PM2.5-exposed animals, it did not improve systemic insulin resistance. This lack of improvement in insulin resistance was paralleled by increased hepatic expression of genes in PEPCK and inflammation. CCR2 deletion failed to attenuate PM2.5 exposure-induced insulin resistance in mice fed on normal diet. The present study indicates that PM2.5 may dysregulate glucose metabolism directly without exerting proinflammatory effects.