Abstract
Heart attacks are a significant cause of death in Aotearoa New Zealand, with survivors frequently developing life-threatening complications such as arrhythmias. Post-heart attack complications are often linked to abnormal phosphorylation of the cardiac ryanodine receptor (RyR2), which regulates calcium release to initiate heart contractions. Key proteins that phosphorylate RyR2 to modulate its activity include calcium–calmodulin-dependent protein kinase II (CaMKII) and protein kinase A (PKA), which increase RyR2 activity; and casein kinase 2 (CK2) which inhibits RyR2 activity. Current post-heart attack therapies target CaMKII and PKA but often worsen heart failure. Therefore, novel strategies targeting CK2 may offer fewer side effects. This project aims to understand the relationship between PKA, CaMKII and CK2 phosphorylation of RyR2.
A test group of five genetically modified (GM) mice with a variant of RyR2 unable to be phosphorylated by CK2 and a control group of five wild-type mice were compared. To evaluate PKA phosphorylation of RyR2 in both groups, western blotting and chemiluminescent imaging followed by unpaired Student’s t-test analysis of protein phosphorylation ratios were used.
We found that when RyR2 was unable to be phosphorylated by CK2 in GM mice, there was a corresponding reduction in PKA phosphorylation compared to wild-type. The data showed a statistically significant difference of –0.186 (P = 0.049, standard error = 0.080) in the mean proportion of total RyR2 phosphorylated by PKA between GM mice and wildtype mice, suggesting a decrease in CK2 phosphorylation is reciprocated by a decrease in PKA phosphorylation.
The results postulate the possibility of this reciprocation being a preventative mechanism of RyR2 hyperactivity, suggesting CK2 targeting may alter RyR2 function directly through CK2 phosphorylation changes as well as through indirect changes in PKA phosphorylation. CK2 targeting has the potential to contribute to arrhythmogenic treatment but is a complex area requiring further research to determine its therapeutic implications.