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KChIP2 regulates the cardiac Ca2+ transient and myocyte contractility by targeting ryanodine receptor activity
Drew M Nassal1,2, Xiaoping Wan1, Haiyan Liu1
1Heart and Vascular Research Center, Department of Medicine, MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio, United States of America.
Abstract:
Pathologic electrical remodeling and attenuated cardiac contractility are featured characteristics of heart failure. Coinciding with these remodeling events is a loss of the K+ channel interacting protein, KChIP2. While, KChIP2 enhances the expression and stability of the Kv4 family of potassium channels, leading to a more pronounced transient outward K+ current, Ito,f, the guinea pig myocardium is unique in that Kv4 expression is absent, while KChIP2 expression is preserved, suggesting alternative consequences to KChIP2 loss. Therefore, KChIP2 was acutely silenced in isolated guinea pig myocytes, which led to significant reductions in the Ca2+ transient amplitude and prolongation of the transient duration. This change was reinforced by a decline in sarcomeric shortening. Notably, these results were unexpected when considering previous observations showing enhanced ICa,L and prolonged action potential duration following KChIP2 loss, suggesting a disruption of fundamental Ca2+ handling proteins. Evaluation of SERCA2a, phospholamban, RyR, and sodium calcium exchanger identified no change in protein expression. However, assessment of Ca2+ spark activity showed reduced spark frequency and prolonged Ca2+ decay following KChIP2 loss, suggesting an altered state of RyR activity. These changes were associated with a delocalization of the ryanodine receptor activator, presenilin, away from sarcomeric banding to more diffuse distribution, suggesting that RyR open probability are a target of KChIP2 loss mediated by a dissociation of presenilin. Typically, prolonged action potential duration and enhanced Ca2+ entry would augment cardiac contractility, but here we see KChIP2 fundamentally disrupts Ca2+ release events and compromises myocyte contraction. This novel role targeting presenilin localization and RyR activity reveals a significance for KChIP2 loss that reflects adverse remodeling observed in cardiac disease settings.
Insights
Loss of K+ channel interacting protein 2 (KChIP2) in guinea pig heart cells impairs calcium handling and reduces myocyte contraction. This finding reveals a novel mechanism contributing to heart failure remodeling.
Area of Science:
- Cardiology
- Molecular Biology
- Physiology
Background:
- Heart failure is characterized by electrical remodeling and reduced cardiac contractility.
- K+ channel interacting protein 2 (KChIP2) loss is associated with these changes.
- Guinea pig hearts lack Kv4 channels but retain KChIP2, offering a unique model to study KChIP2's non-canonical roles.
Purpose of the Study:
- To investigate the consequences of acute KChIP2 silencing in guinea pig myocytes.
- To elucidate the role of KChIP2 in regulating cardiac contractility and calcium handling independent of Kv4 channels.
Main Methods:
- Acute silencing of KChIP2 in isolated guinea pig cardiomyocytes.
- Measurement of Ca2+ transient amplitude, duration, and sarcomeric shortening.
- Assessment of calcium spark activity and protein expression (SERCA2a, phospholamban, RyR, NCX).
- Evaluation of presenilin localization relative to ryanodine receptors (RyRs).
Main Results:
- KChIP2 loss significantly reduced Ca2+ transient amplitude and prolonged its duration, decreasing sarcomeric shortening.
- No changes in expression of key Ca2+ handling proteins were observed.
- Reduced Ca2+ spark frequency and prolonged Ca2+ decay indicated altered RyR activity.
- Presenilin delocalized from sarcomeric bands, suggesting dissociation from RyRs and altered RyR function.
Conclusions:
- KChIP2 plays a critical role in regulating cardiac contractility and Ca2+ handling in guinea pigs, independent of Kv4 channels.
- KChIP2 loss disrupts Ca2+ release events by altering RyR activity through presenilin delocalization.
- These findings reveal a novel mechanism for KChIP2's contribution to adverse cardiac remodeling in heart failure.