RyR2 mutations linked to ventricular tachycardia and sudden death reduce the threshold for store-overload-induced...

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Ion Channel Function

Background:

• The cardiac ryanodine receptor (RyR2) is critical for muscle contraction by regulating calcium (Ca2+) release from the sarcoplasmic reticulum.
• Mutations in RyR2 are associated with life-threatening arrhythmias, including ventricular tachycardia (VT) and sudden cardiac death, but the underlying molecular mechanisms remain incompletely understood.
• Store-overload-induced Ca2+ release (SOICR) is a known arrhythmogenic phenomenon triggered by critical sarcoplasmic reticulum Ca2+ levels.

Purpose of the Study:

• To investigate the impact of disease-associated RyR2 mutations on SOICR using a human embryonic kidney (HEK293) cell model.
• To elucidate the molecular mechanisms by which RyR2 mutations promote SOICR and increase arrhythmia susceptibility.

Main Methods:

• Utilized HEK293 cells expressing wild-type or mutant RyR2 to model SOICR under elevated extracellular Ca2+ conditions.
• Characterized SOICR occurrence and single RyR2 channel activity in response to luminal Ca2+.
• Assessed the effect of mutations on basal [3H]ryanodine binding to RyR2 channels.

Main Results:

• HEK293 cells expressing RyR2 exhibited SOICR comparable to cardiac cells, validating the model.
• Specific RyR2 mutations (N4104K, R4496C, N4895D) linked to VT significantly increased the frequency of SOICR.
• Mutant RyR2 channels showed increased sensitivity to luminal Ca2+ activation and elevated basal [3H]ryanodine binding.

Conclusions:

• Disease-causing RyR2 mutations lower the threshold for SOICR by enhancing channel activation by luminal Ca2+, thereby increasing arrhythmia risk.
• Abnormal RyR2 luminal Ca2+ activation is a likely mechanism contributing to enhanced SOICR in conditions like heart failure.
• This mechanism offers a unifying explanation for Ca2+ overload-associated VT and sudden death.