Abstract Body (Do not enter title and authors here): Background: Heart failure (HF) is a complication of Type 1 diabetes mellitus (T1D) causing high mortality. In T1D activated neutrophils overproduce peptidyl arginine deiminase 4 (PAD4).
Aim: Evaluate the role of PAD4 in the pathobiology of HF development in T1D.
Methods: T1D was induced in PAD4^-/- and wild type (WT) mice by i.p. injection of 55 mg/kg of Streptozotocin for 5 days. Echocardiography, lung wet-to-dry ratio and exercise intolerance were performed after 8 weeks to evaluate cardiac structural and functional changes. Cardiac collagen content was assessed by picrosirius green staining, levels of neutrophil extracellular traps (NETs) by co-location of Ly6G⁺, and H3Cit⁺ signal in tissue and inflammasome activation by protein aggregates of the inflammasome adaptor ASC in neutrophils determined by immunofluorescence.
Results: PAD4 deficiency did not affect onset or severity of T1D. T1D WT but not T1D PAD4^-/- mice showed a significantly increased proportion of ASC speck⁺ neutrophils (13.8± 4% vs. 3.3±3.1%; n=5; p=0.007). This resulted in elevated IL-1β levels both in plasma (21.7±7pg/ml vs. 11.4±1pg/ml; n=8; p=0.001) and cardiac tissue (0.08±0.002pg/ml vs. 0.06±0.001pg/ml; n=8/6, p=0.001) of T1D-WT mice. T1D-PAD4^-/- mice showed reduced cardiac damage (Troponin I: 58±11pg/mL vs. 91.3±37pg/mL; n=12; p=0.005), collagen deposition (1.2±0.5% vs. 3.3±1.3%; n=6; p=0.008) and tissue levels of transforming growth factor-β (0.23±0.03 vs. 0.33±0.04 ng/L). Echocardiography demonstrated preservation of both systolic (Ejection fraction: 63.8±5.4 vs. 43.7±11.4 %; n=8; p=0.001) and diastolic (E/E’: -19.6±4 vs. -29.9±9; n=10; p=0.004) function with PAD4 deletion and reduced clinical HF parameters (Lung wet/dry ratio: 4.1±0.5 vs. 5.9±0.9; n=8; p=0.001; time to fatigue: 28.1±10min. vs. 7.6±4 min.;n=10,p=<0.0001). Flow cytometry analysis showed significantly reduced levels of infiltrating neutrophils (42±2% vs. 52± 3% Ly6G⁺ of CD11b⁺CD45⁺ events; n=8, p=0.02) in the myocardium and histological analysis showed significantly reduced cardiac NET deposition in T1D- PAD4^-/- mice (1.1±0.4% vs. 10.2±2.2% H3Cit⁺ of LV section; n=5, p=0.008).
Conclusion: We show, that T1D primes neutrophils for NLRP3 Inflammasome assembly and IL-1β release in a PAD4 dependent manner. Increased cardiac neutrophil infiltration, inflammasome assembly and NET deposition drive profibrotic cardiac remodeling and HF in T1D. Our data suggest PAD4 as a promising target for primary cardiac prevention in T1D.