Neutrophil peptidylarginine deiminase 4 plays a systemic role in obesity-induced chronic inflammation in mice

Abstract Obesity is an increasing problem in our current society. In morbidly obese patients, the level of circulating neutrophil extracellular traps (NETs) was found to be higher than in lean control subjects. Essential in this process of NET formation is the activation of the enzyme peptidylarginine deiminase 4 (PAD4). We aimed to understand how NETs contribute to the detrimental effects associated with a prolonged state of (morbid) obesity. Therefore, an animal model was adopted in which wild type (WT) and neutrophil specific PAD4 deficient (Ne-PAD4 −/−) mice on a C57BL6/J background were fed a high fat containing diet (HFD – 60kcal% fat) for a period of 10 weeks. Neutrophil activation status, evaluated through the formation of NETs in response to calcium ionophore ionomycin (4 μM) stimulation, was initially reduced after 3 days of HFD feeding. At later timepoints (5- and 10-weeks), neutrophils isolated from HFD-fed mice showed increased levels of NET formation in response to ionomycin stimulation in comparison to neutrophils from control diet-fed mice. Ne-PAD4 −/−mice on the HFD gained less weight than WT mice, which had a constant gain of body weight over the 10-week experimental period. Finally, after 10-weeks of high fat intake, cardiac function was evaluated in WT and Ne-PAD4 −/−mice by echocardiography. Interestingly, in WT mice diastolic function (early passive vs late active filling, E/A ratio) decreased as compared to baseline values, while Ne-PAD4 −/−mice kept E/A ratios comparable to baseline levels. Here, we demonstrate the importance of systemic NET release under metabolic challenge, and how this can contribute to cardiac deterioration at a young age due to obesity-induced alteration in the innate immune system.