Distinct mechanisms mediate pacemaker dysfunction associated with catecholaminergic polymorphic ventricular...

Area of Science:

• Cardiology
• Molecular Biology
• Computational Biology

Background:

• Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a life-threatening arrhythmia triggered by stress.
• CPVT is linked to mutations affecting calcium (Ca²⁺) handling, particularly in the ryanodine receptor (RyR2) or calsequestrin 2 (CASQ2).
• Sinoatrial node cell (SANC) automaticity, crucial for heart rhythm, is regulated by Ca²⁺ signaling.

Purpose of the Study:

• To investigate the coupled-clock mechanisms underlying CPVT-associated SANC dysfunction under basal and stimulated conditions.
• To determine if different mechanisms can cause similar CPVT-related pacemaker pauses.
• To explore potential therapeutic interventions, including drug and gene manipulation, to reverse SANC dysfunction.

Main Methods:

• Utilized a computational numerical model of mouse SANC, incorporating membrane and intracellular Ca²⁺ signaling pathways.
• Simulated SANC function in basal states and under β-adrenergic stimulation for RyR2^R4496C and Casq2^-/- mutations.
• Analyzed the roles of ion currents (I_NCX, I_CaT, I_Na) and cAMP-PKA signaling in mediating SANC dysfunction.

Main Results:

• In RyR2^R4496C SANC, I_NCX and I_CaT mediated dysfunction in basal states; under β-adrenergic stimulation, cAMP-PKA signaling and sodium currents (I_Na) also contributed.
• In Casq2^-/- SANC, similar basal mechanisms were observed, while β-AR stimulation involved I_CaT and I_Na.
• Distinct molecular pathways were identified that can lead to CPVT-related SANC automaticity pauses.

Conclusions:

• Different mutations and conditions can converge on distinct mechanisms to cause CPVT-associated SANC pauses.
• Increasing SANC cAMP-PKA activity via pharmacological agents (e.g., IBMX) or gene manipulation shows promise for restoring SANC function.
• Findings provide novel insights into CPVT pathophysiology and suggest potential therapeutic targets for managing the arrhythmia.