The Role of Cardiac Mitochondria in Arrhythmias and Sudden Unexpected Death in Epilepsy in Models of Dravet Syndrome

Author

Jessa L. Aldridge, East Tennessee State UniversityFollow

Degree Name

PhD (Doctor of Philosophy)

Program

Biomedical Sciences

Date of Award

8-2024

Committee Chair or Co-Chairs

Chad Frasier

Committee Members

Patrick Bradshaw, Siva Digavalli, Aaron Polichnowski, Douglas Thewke

Abstract

Dravet Syndrome (DS) is a pediatric epilepsy disorder. Individuals with DS are at increased risk of Sudden Unexpected Death in Epilepsy (SUDEP). One mechanism implicated in the pathology of SUDEP is cardiac arrhythmias. A central element involved in cardiac regulation is mitochondria. In the heart, mitochondria maintain cardiomyocyte energy (ATP) generation and ion homeostasis but also produce harmful reactive oxygen species (ROS) byproducts. We hypothesized that deficits in cardiac mitochondria could underlie arrhythmias and SUDEP in two independent mouse models of DS. Mitochondria produce ATP through the mitochondrial respiratory chain, also called electron transport chain, comprised of a series of large, multimeric complexes (labeled I-IV) coupled to the activity of an ATP synthase. We first simultaneously analyzed electron transport chain activity and ROS production via Complex I- and Complex II-linked respiratory pathways in cardiac mitochondria isolated from DS mouse hearts. ROS produced as a byproduct of ATP generation is scavenged by cellular antioxidant systems, primarily glutathione in the heart. Therefore, we next subjected isolated cardiomyocytes to diamide, which oxidizes thiol-based antioxidants, to determine ROS scavenging ability in DS hearts. Furthermore, isolated hearts were also perfused with diamide via Langendorff assays to test for arrhythmia susceptibility in the presence of oxidative stress. Another essential function of mitochondria is buffering ions like Ca²⁺. While fatal at high concentrations, Ca²⁺ stimulates mitochondrial ATP production at physiological levels. We determined if cardiac mitochondria from DS hearts have altered levels of Ca²⁺ uptake (via the mitochondrial Ca²⁺ uniporter) and retention. We also investigated if mitochondrial energetic capacity was impacted by Ca²⁺ dysregulation. Furthermore, due to its impacts on ATP, mitochondrial Ca²⁺ sequestration is an essential physiological mechanism linking the sympathetic drive to the heart with cardiac output. We tested the response of DS hearts to norepinephrine, a sympathetic agonist, to determine if these conditions caused increased vulnerability to arrhythmias. Overall, our results indicate that these models of DS have distinct energetic and antioxidant phenotypes that may also be impacted by biological sex. Considering these differences may be necessary when tailoring treatment and preventing SUDEP in the clinical practice of DS patients with different etiologies.

Document Type

Dissertation - embargo

Recommended Citation

Aldridge, Jessa L., "The Role of Cardiac Mitochondria in Arrhythmias and Sudden Unexpected Death in Epilepsy in Models of Dravet Syndrome" (2024). Electronic Theses and Dissertations. Paper 4434. https://dc.etsu.edu/etd/4434

Copyright

Copyright by the authors.