Abstract
Nitric Oxide (NO) is a signalling molecule that acts downstream of the β-adrenergic (β-AR) stimulation and governs cardiac function. Tight regulation of NO is required for normal cardiac function, while deviation from this healthy balance will lead to functional consequences such as arrhythmias. Sex differences in NO signalling are apparent but poorly understood. Females have higher levels of NO and protein S-nitrosylation, contributing to their protection against abnormal Ca2+ levels underlying arrhythmogenesis. However, the targets for NO during arrhythmic signalling remains unknown, obscuring the source of sex differences in cardiovascular risk. One emerging target is Ca2+/calmodulin-dependent protein kinase II (CaMKII), a multifunctional regulatory molecule that, when subjected to S-nitrosylation, becomes persistently active and underpins the formation of arrhythmias. A novel discovery from our lab group showed the inhibitory effect of NO in suppressing cardiac CaMKII activity via S-nitroylation at cysteine-273 (C273). With the lack of studies on CaMKII inhibition specifically via S-nitrosylation at C273 in relation to gender specific NO response, my project aimed to highlight the CaMKII inhibition approach as a potential therapeutic strategy and provide insight into the source of sex differences in arrhythmia risk. To investigate this, the C273S mouse model was used to allow persistent CaMKII, while C57BL/6 wildtype (WT) mice were used as a control. I hypothesised that C273S mutation would promote chronic activation of CaMKII, resulting in an increased onset of arrhythmias and impaired cardiac function. I also hypothesised that CaMKII hyperactivity encouraged by C273S mutation would result in heightened arrhythmogenesis in C273S females compared to males. I performed lead II electrocardiography and left ventricle short axis echocardiography in both male and female groups of each strain. Parametric unpaired t-test was performed with statistical significance of p < 0.05. Electrocardiography data showed significant sex-dependent alterations to cardiac function in the C273S animals. For example, the C273S females had a significantly longer QRS interval compared to males, a clinical indication of enlarged ventricles. Echocardiography data showed that C273S males had a significantly higher end diastolic volume compared to the females, suggestive of pathological overfilling of the ventricles. Taken together, these data are in support of my first hypothesis that overactive CaMKII encouraged by C273S mutation result in arrhythmogenesis and impaired cardiac function. Overall, this project will aid further study of CaMKII inhibition towards targeted approaches in arrhythmia preventions and to determine whether men or women would benefit more from this approach.