Arrhythmogenic mutation-linked defects in ryanodine receptor autoregulation reveal a novel mechanism of Ca2+ release...

Area of Science:

• Cardiovascular Research
• Molecular Biology
• Biophysics

Background:

• Arrhythmogenic cardiac ryanodine receptor (RyR2) mutations are linked to stress-induced tachycardia and sudden cardiac death (SCD).
• The precise mechanisms underlying RyR2 calcium (Ca2+) release dysregulation remain incompletely understood and debated.
• RyR2 autoregulation involves interactions between its N- and C-terminal domains, particularly the I domain.

Purpose of the Study:

• To investigate the functional impact of clinically-severe RyR2 mutations on interdomain interactions and Ca2+ release.
• To determine how mutations in the central domain versus the C-terminal I domain affect RyR2 autoregulation and Ca2+ handling.
• To elucidate the molecular basis of RyR2 dysfunction in the context of arrhythmia and SCD.

Main Methods:

• Utilized high-resolution confocal microscopy and Förster Resonance Energy Transfer (FRET) analysis.
• Examined interactions between N- and C-terminal RyR2 domain fusion proteins in living cells.
• Employed noise analysis to assess channel conformational dynamics and Ca2+ handling.

Main Results:

• RyR2 interdomain interactions were unaltered at rest but altered upon activation with mutations.
• Abnormal Ca2+ release in mutant RyR2 channels was linked to altered interdomain interactions with threshold characteristics.
• I domain mutations induced distinct conformational instability in Ca2+ handling and interdomain interactions post-activation, unlike central domain mutations.
• This instability was observed in both engineered fusion proteins and intact RyR2 in various cell types.

Conclusions:

• Mutation-linked defects in RyR2 autoregulation play a critical role in augmented Ca2+ release after channel activation.
• The specific location of RyR2 mutations (central vs. I domain) influences the pattern of channel dysfunction.
• These findings provide mechanistic insights into RyR2 channel dysfunction contributing to arrhythmia and SCD.