Abstract Body: Background: The Ryanodine Receptor type-2 (RyR2) is a calcium release channel crucial for excitation-contraction coupling in cardiac muscle. Gain-of-function mutations in RYR2 are associated with aberrant channel opening leading to deadly tachycardias. Effective control of RyR2 activity has therapeutic potential but not much is known about post-transcriptional mechanisms that regulate RyR2.
Methods/Results: Here we demonstrate that RyR2 microexon encoding amino acids located at the dimer interface region of the RyR2 channel pore controls its calcium channel activity. We find that excluding RyR2 microexon led to decreased intracellular calcium transients and synchronized beating rate of cardiomyocytes. Using activators and inhibitors of RyR2 we show that RYR2 microexon skipping diminished channel activity and rendered it insensitive to caffeine-mediated activation. Notably, Ryr2 microexon is developmentally regulated co-occurring with the formation of T-tubules for efficient excitation-coupling at postnatal stages. We identified RNA binding protein RBFOX2 as a regulator of Ryr2 microexon splicing in the embryonic heart and showed that Ryr2 microexon splicing is dysregulated in mice with congenital heart failure.
Conclusions: Our findings reveal an RyR2 isoform switch mediated by a microexon during heart development that can modulate ion channel activity in cardiomyocytes. In the future our findings will pave the way for antisense oligonucleotide therapy to dampen overactive RyR2 and combat lethal tachycardias.