Abstract
Background
Patients with sleep-disordered breathing (SDB) develop arrhythmias and contractile dysfunction, but the mechanisms are poorly understood, possibly due to the lack of mouse models that mimic airway obstruction in spontaneously sleeping mice. Interestingly, New Zealand obese mice have been shown to develop airway obstruction with inspiratory flow limitation resulting in apneas, but these mice also develop diabetes.
Purpose
We developed a novel mouse model of increased airway obstruction in spontaneously sleeping lean mice and investigated the impact on sleep-related apneas and contractile function.
Methods and results
Male C57BL6 mice at 8–12 weeks of age were subjected to polytetrafluoroethylene (PTFE) injection (100 μl) into the tongue. This resulted in an increased tongue volume and reduced pharyngeal luminal diameter. Conscious mice behave normal and there was no difference in body weight between PTFE injected mice and untreated littermates (control). Whole body plethysmography was used to monitor spontaneous breathing for 8h in a quiet environment. Interestingly, compared to control, mice with PTFE injection showed a significantly increased frequency of apneas (lasting >1s, fig. A, * indicated P<0.05, t-test). Echocardiographic analysis revealed that ejection fraction was significantly reduced in PTFE-treated mice 8 weeks after surgery (vs. control, fig. B). In accordance, the developed force of isolated papillary muscles from hearts of PTFE mice was significantly reduced compared to control (fig. C). Ca/calmodulin-dependent protein kinase II (CaMKII) has been implicated in the development of heart failure. Intriguingly, compared to control, CaMKII expression was significantly increased in ventricular heart homogenates of PTFE-treated mice (fig. D). Moreover, the magnitude of CaMKII overexpression correlated significantly with the frequency of apneas (fig. E). Papillary muscle post-pause contractions can be used as measure of diastolic sarcoplasmic reticulum (SR) Ca leak, which is known to be enhanced by CaMKII. Compared to control, post-pause contraction amplitude was significantly smaller in PTFE-treated mice, indicating an increased SR Ca leak (fig. F).
Figure 1
Conclusion
PTFE injection in mice results in an increased frequency of spontaneous apneas. PTFE-treated mice develop mild contractile dysfunction, which is accompanied by CaMKII overexpression. This novel mouse model offers great opportunities for investigation of sleep-related breathing disorders.
Acknowledgement/Funding
This study was supported by the Medical Faculty of the University of Regensburg (ReForM programme).
Apnoea–hypopnoea indices determined via continuous positive airway
pressure (AHI-CPAPflow) versus those determined by
polysomnography (AHI-PSGgold): a protocol for a systematic review
and meta-analysis
