Abstract Body: Introduction: Inflammatory diseases like rheumatoid arthritis, inflammatory bowel disease, metabolic syndrome, often coincide with cardiac autonomic neuropathies (CAN). CAN is characterized by attenuated heart rate variability and baroreflex sensitivity and linked to a higher risk for cardiovascular disease and mortality. Despite an attenuated vagal tone, cholinergic hyperreactivity (CHR) has been described during CAN. Here we aim to determine the mechanism of inflammation induced CHR and its link to atrial arrhythmia.
Methods: Inflammation was induced in mice through dextran sulfate sodium (DSS: 3.5%, 7 days (d)) supplemented drinking water or treatment with IL-17 (250 ng/d, 7d). DSS induces active colitis and increased serum levels of IL-17 accompany the acute inflammatory phase. Cardiac electrophysiological properties were quantified in vivo (ECGs), in the isolated heart (epicardial mapping), and on the single cell level (voltage clamp) under basal condition and during carbachol (CCh) stimulation. Expression of proteins linked to CHR were quantified by Western Blotting.
Results: In vivo (0.15mg/kg i.p.) and in the isolated heart (100nM) CCh attenuated the heart rate more significantly in DSS-treated than CTL animals (in vivo: CTL: -11.44±1.63%, n=10; DSS: -39.76±3.06%, n=14; p<0.0001) (ex vivo: CTL: -28.71±2.97%, n=16; DSS: -39.39±2.67%, n=15; p=0.013). CHR did not depend on increased expression of the muscarinic acetylcholine receptor 2 (M2AChR; CTL: 0.94±0.02, n=4; DSS: 0.72±0.09, n=4: p=0.0435) or the G-protein-gated K⁺ channel (GIRK1/4) or I_K,ACh current. However, termination of CCh signaling was delayed in DSS in vivo (0.5mg/kg Atropine i.p.; CTL: 107.93±12.99 Dbpm/ms, n=6; DSS: 66.80±7.33 Dbpm/ms, n=5; p=0.026) and ex vivo (1µM; CTL: 15.23±0.65Dbpm/ms, n=3; DSS: 11.24±0.82 Dbpm/ms, n=3; p=0.019). The latter was consistent with downregulation of regulator of G-protein signaling 7 (CTL: 1.28±0.09, n=8; DSS: 0.76±0.16, n=8; p=0.012). Atrial RNAseq and pathway analysis revealed upregulation of atrial IL-17 signaling and CHR was mimicked in IL-17 treated mice (in vivo, CCh: IL-17: -42.0±4%, n=4).
Conclusion: The data suggest that colitis induced inflammation promotes CHR by attenuating the termination of M2AChR activity through IL-17 induced atrial remodeling.