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Evaluating Non-Canonical Roles of KChIP2 In The Heart

Nassal, Drew
http://rave.ohiolink.edu/etdc/view?acc_num=case1491585406557989

Abstract Details

2017, Doctor of Philosophy, Case Western Reserve University, Physiology and Biophysics.
Cardiac arrhythmias are a leading cause of morbidity and mortality within developed nations, resulting in more than 300,000 deaths per year in the U.S. alone. These sudden arrhythmias are frequently associated with acquired heart diseases, notably cardiac hypertrophy and heart failure (HF), where the dysregulation of numerous ion channels and transporters are observed. This provides a challenge in identifying which alterations are essential in driving disease pathogenesis and conferring susceptibility to lethal cardiac arrhythmias. Notably, one of the most consistent changes and most frequently associated with compromised repolarization, is selective reduction in the transient outward potassium current, Ito. Ito is generated primarily by the voltage-gated potassium (Kv) channel, Kv4 and its interacting auxiliary subunit known as the Potassium Channel Interacting Protein 2 (KChIP2). Under hypertrophy and HF there is rapid and consistent loss of KChIP2, thought to cause the destabilization of Kv4 channels and subsequent Ito depletion. While it is well understood that KChIP2 allows for the enhanced expression, trafficking, and modulation of Kv4 channels, emerging evidence suggests KChIP2 may not be limited to cell surface channel regulation of Kv4. Supporting this notion is the conserved expression of KChIP2 in the myocardium of the guinea pig, where Ito and the underlying subunit Kv4 are absent, reinforcing the concept of additional capacities for KChIP2. Notably, other members of the KChIP family not expressed in the myocardium have been shown to express multimodal functions outside of Kv4 modulation. Therefore, the focus of this dissertation sought to identify what expanded functions KChIP2 might perform and whether those functions are relevant in myocardial reprogramming in response to disease signaling. In my first project, we used the guinea pig as a platform for identifying novel KChIP2 functions pertaining to electrical reprogramming, motivated by the absence of endogenous Kv4 and therefore Ito. We isolated primary guinea pig ventricular myocytes and treated with an adenovirus encoding a KChIP2 antisense sequence to silence KChIP2 expression, which led to a significant prolongation of the cardiac action potential. This was attributed to increases in the depolarizing current ICa,L in response to increased Cav1.2 expression, the primary alpha subunit encoding ICa,L expression. We also observed significantly decreased INa density coinciding with reductions in Nav1.5, the subunit encoding INa. The second project sought to observe the functional performance changes in these guinea pig myocytes, given that Ca2+ alterations can have a significant impact on myocyte contractility. Unexpectedly, despite the enhanced delivery of Ca2+, Ca2+ transient amplitudes and correspondingly sarcomeric shortening were significantly attenuated following KChIP2 loss. While expression of the most significant Ca2+ handling proteins was preserved, we instead found relocalization of a recently implicated ryanodine receptor modifier, presenilin 1. This corresponded to decreases in ryanodine receptor open probability and translated to attenuated Ca2+ release. The third project sought more specifically to identify a potential transcriptionally capacity for KChIP2, driven by the observation that in neonatal rat ventricular myocytes SCN5A/Nav1.5, SCN1B/Navß1, and KCND3/Kv4.3 were found to experience transcriptional changes following KChIP2 silencing. Indeed, we observed the potential for KChIP2 to bind DNA and repress promoter activity for two miRNAs, miR-34b and miR-34c, which subsequently targeted these three ion channel genes and suppressed corresponding current densities. Notably, the therapeutic manipulation of these pathways following cardiac stress successfully preserved current densities, leading to the complete attenuation of arrhythmia susceptibility. Collectively, the outcome of these investigations clearly identify that KChIP2 actions are dramatically more expansive than modulation of Kv4 channels alone, and that these mechanisms are potent contributors to adverse remodeling events characterized in the diseased heart.
Isabelle Deschenes (Advisor)
Corey Smith (Committee Chair)
George Dubyak (Committee Member)
Kenneth Laurita (Committee Member)
Mukesh Jain (Committee Member)
175 p.
Biology; Cellular Biology; Molecular Biology
KChIP2; transient outward potassium current; Ito; sodium current; INa; L-type Ca current; ICa,L; ryanodine receptor; presenilin; calcium induced calcium release

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Citations

  • Nassal, D. (2017). Evaluating Non-Canonical Roles of KChIP2 In The Heart [Doctoral dissertation, Case Western Reserve University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=case1491585406557989

    APA Style (7th edition)

  • Nassal, Drew. Evaluating Non-Canonical Roles of KChIP2 In The Heart. 2017. Case Western Reserve University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=case1491585406557989.

    MLA Style (8th edition)

  • Nassal, Drew. "Evaluating Non-Canonical Roles of KChIP2 In The Heart." Doctoral dissertation, Case Western Reserve University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1491585406557989

    Chicago Manual of Style (17th edition)

case1491585406557989
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© 2017, all rights reserved.
This open access ETD is published by Case Western Reserve University School of Graduate Studies and OhioLINK.