OC 47.2 - Neutrophil peptidylarginine deiminase 4 promotes obesity-induced systemic inflammation in mice

Background: In morbidly obese patients, the level of circulating neutrophil extracellular traps (NETs) has been found to be higher than in lean subjects. Essential in the process of NET formation is activation of the enzyme peptidylarginine deiminase 4 (PAD4).

Aims: We aimed to understand how NETs contribute to the detrimental effects associated with a prolonged state of obesity.

Methods: An animal model of obesity development and progression was established in which mice on the C57BL/6J background were fed a high fat (60 kcal% fat) diet (HFD) for a period of 10 weeks. In order to investigate the systemic effect of diet-induced NET formation on body organs, neutrophil-selective PAD4 knockout mice (MRP8Cre+ X PAD4fl/fl, Ne-PAD4-/-) were studied in parallel to WT control mice.

Results: Neutrophil activation status, evaluated through the formation of NETs in response to stimulation by calcium ionophore ionomycin (4 µM), 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 comparison to neutrophils from control diet-fed mice (Figure 1A,B). Interestingly, Ne-PAD4-/- mice on HFD gained less weight than WT mice over the 10-week experimental period (Figure 1C). Finally, after 10-weeks of high fat intake, cardiac function was assessed by echocardiography. Diastolic function (early passive vs late active filling, E/A ratio) in WT mice decreased compared to Ne-PAD4-/- mice under similar conditions (Figure 1D,E), indicating a protection from cardiac dysfunction upon PAD4-deficiency.

Conclusion(s): Neutrophil PAD4 has a clear systemic impact during settings of prolonged high fat intake and subsequent obesity development. We thus 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 of the innate immune system.