Increased CaMKII-dependent pro-arrhythmic activity in a novel mouse model of obstructive sleep apnoea

Abstract

Background Obstructive sleep apnoea (OSA) is frequently associated with atrial arrhythmias, but detailed mechanisms remain elusive. Most recently, we found an increased CaMKII-dependent pro-arrhythmic activity in patients with sleep apnoea. Since patients suffer from various confounding comorbidities, we have developed a novel mouse model of OSA by tongue enlargement. Purpose We tested if mice with OSA exhibit increased atrial CaMKII-dependent pro-arrhythmic activity. Methods Polytetrafluorethylene (PTFE) was injected into the tongue of 12 wild-type (WT) and 10 CaMKII knock-out (CKO) mice. 9 WT and 9 CKO mice were used as control without PTFE injection. Inspiratory flow limitations and apnoeas were monitored during murine sleep phases by whole-body plethysmography (Buxco). After eight weeks, isolated atrial cardiomyocytes were incubated with the Ca-sensitive dye FURA-2 AM for 15 min. Regular Ca transients were elicited by electrical field stimulation (1 Hz, 20 V for 4 ms) using epifluorescence microscopy. Pro-arrhythmic non-stimulated events were defined as deviations from diastolic Ca baseline between two stimulated Ca transients. Results Sonographic measurements revealed a significant increase in mean tongue diameter from (in mm) 3.7±0.1 to 5.1±0.1 after PTFE injection (n=23, p<0.0001). There was a significant correlation between magnitude of tongue diameter and frequency of apnoeas in OSA mice (p=0.046, r2=0.19, Fig. 1A). Interestingly, we observed a significantly increased frequency of pro-arrhythmic events of (in s–1) 0.06±0.01 in WT OSA mice compared to 0.02±0.01 in WT control mice (p=0.047, Fig. 1B). Similar results were observed at higher stimulation frequencies (2 and 4 Hz). There was a significant correlation of pro-arrhythmic events with inspiratory flow limitations (p=0.03, r2=0.24, Fig. 1C) and with the frequency of apnoeas by strong trend (p=0.06, r2=0.18). In contrast, no increase in atrial pro-arrhythmic events was observed in CKO mice after PTFE injection (for CKO mice after PTFE vs. CKO mice without PTFE, 0.03±0.01 s–1 vs. 0.03±0.01 s–1, p=0.89, Fig. 1B). Accordingly, the correlations between pro-arrhythmic events and both inspiratory flow limitations (p=0.36, r2=0.05, Fig. 1C) and apnoeas (p=0.82, r2=0.004) were completely abolished in CKO mice. Conclusion In a novel mouse model of obstructive sleep apnoea, atrial pro-arrhythmic activity was increased in a CaMKII-dependent fashion, which may have therapeutic implications. FUNDunding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Benedikt Schaner / Mr., this work is supported by a research grant of the German Cardiac Society (DGK); Stefan Wagner / Professor, was funded by DFG grants Figure 1