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Published on: December 22, 2023
Phospholamban knockout breaks arrhythmogenic Ca²⁺ waves and suppresses catecholaminergic polymorphic ventricular
Yunlong Bai1, Peter P Jones, Jiqing Guo
1Department of Physiology and Pharmacology, Libin Cardiovascular Institute of Alberta, University of Calgary, Calgary, Alberta, Canada.
Rationale:
Phospholamban (PLN) is an inhibitor of cardiac sarco(endo)plasmic reticulum Ca²⁺ ATPase. PLN knockout (PLN-KO) enhances sarcoplasmic reticulum Ca²⁺ load and Ca²⁺ leak. Conversely, PLN-KO accelerates Ca²⁺ sequestration and aborts arrhythmogenic spontaneous Ca²⁺ waves (SCWs). An important question is whether these seemingly paradoxical effects of PLN-KO exacerbate or protect against Ca²⁺-triggered arrhythmias.
Objective:
We investigate the impact of PLN-KO on SCWs, triggered activities, and stress-induced ventricular tachyarrhythmias (VTs) in a mouse model of cardiac ryanodine-receptor (RyR2)-linked catecholaminergic polymorphic VT.
Methods And Results:
We generated a PLN-deficient, RyR2-mutant mouse model (PLN-/-/RyR2-R4496C+/-) by crossbreeding PLN-KO mice with catecholaminergic polymorphic VT-associated RyR2-R4496C mutant mice. Ca²⁺ imaging and patch-clamp recording revealed cell-wide propagating SCWs and triggered activities in RyR2-R4496C+/- ventricular myocytes during sarcoplasmic reticulum Ca²⁺ overload. PLN-KO fragmented these cell-wide SCWs into mini-waves and Ca²⁺ sparks and suppressed the triggered activities evoked by sarcoplasmic reticulum Ca²⁺ overload. Importantly, these effects of PLN-KO were reverted by partially inhibiting sarco(endo)plasmic reticulum Ca²⁺ ATPase with 2,5-di-tert-butylhydroquinone. However, Bay K, caffeine, or Li⁺ failed to convert mini-waves to cell-wide SCWs in PLN-/-/RyR2-R4496C+/- ventricular myocytes. Furthermore, ECG analysis showed that PLN-KO mice are not susceptible to stress-induced VTs. On the contrary, PLN-KO protected RyR2-R4496C mutant mice from stress-induced VTs.
Conclusions:
Our results demonstrate that despite severe sarcoplasmic reticulum Ca²⁺ leak, PLN-KO suppresses triggered activities and stress-induced VTs in a mouse model of catecholaminergic polymorphic VT. These data suggest that breaking up cell-wide propagating SCWs by enhancing Ca²⁺ sequestration represents an effective approach for suppressing Ca²⁺-triggered arrhythmias.
Insights
Phospholamban knockout (PLN-KO) suppresses spontaneous Ca²⁺ waves and arrhythmias in a mouse model of catecholaminergic polymorphic ventricular tachycardia. PLN-KO protects against stress-induced ventricular arrhythmias by enhancing Ca²⁺ sequestration.
Area of Science:
- Cardiology
- Molecular Biology
- Physiology
Background:
- Phospholamban (PLN) regulates cardiac sarcoplasmic reticulum Ca²⁺ ATPase activity.
- PLN knockout (PLN-KO) alters Ca²⁺ handling, leading to enhanced load and leak, but also accelerated sequestration.
- The net effect of PLN-KO on Ca²⁺-triggered arrhythmias remains unclear.
Purpose of the Study:
- To investigate the impact of PLN-KO on spontaneous Ca²⁺ waves (SCWs), triggered activities, and stress-induced ventricular arrhythmias (VTs).
- To assess the protective role of PLN-KO in a mouse model of catecholaminergic polymorphic VT (CPVT) linked to RyR2 mutations.
Main Methods:
- Generated a double-mutant mouse model (PLN-/-/RyR2-R4496C+/-) by crossbreeding PLN-KO and CPVT mice.
- Utilized Ca²⁺ imaging and patch-clamp recordings in ventricular myocytes.
- Performed ECG analysis to evaluate stress-induced VTs.
Main Results:
- PLN-KO fragmented cell-wide SCWs into mini-waves and suppressed triggered activities in RyR2-mutant myocytes.
- Inhibition of SERCA partially reverted these effects.
- PLN-KO mice were protected from stress-induced VTs, unlike control RyR2-mutant mice.
Conclusions:
- PLN-KO suppresses triggered activities and VTs in a CPVT mouse model, despite increased Ca²⁺ leak.
- Enhanced Ca²⁺ sequestration and fragmentation of SCWs by PLN-KO are effective strategies against Ca²⁺-triggered arrhythmias.
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