Unmasking Conduction Deficits in the Scn5a+/- Mouse Model of Brugada Syndrome

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Project Summary Brugada Syndrome (BrS) is a rare but severe disease that can lead to arrhythmias and sudden cardiac death in children and young adults with no structural heart disease. The most prominent genetic contributor to this disease is loss of function mutations in scn5a, the gene encoding the voltage gated sodium channel, Nav1.5. However, many BrS patients with these mutations are asymptomatic until experiencing a major arrhythmic event, making this syndrome “concealed” in nature. While diagnostic drug challenges exist for those at high risk of becoming symptomatic, they have low positive predictive value. The relationship between loss of Nav1.5, conduction slowing, and arrhythmias is well established, and it is possible that concealed conduction slowing is the underlying driver of BrS pathology. This proposal aims to utilize a scn5a heterozygous mouse model of BrS to determine whether modulation of ephaptic coupling within the intact heart can unmask BrS-associated conduction slowing. In Aim 1, ephaptic coupling will be manipulated by altering the width of the perinexus, a nanodomain of the intercalated disk, in the isolated, Langendorff-perfused Scn5a+/- and WT mouse heart. Conduction velocity will be assessed using optical mapping, wherein the intact heart is perfused with a voltage sensitive dye and imaged with high spatio-temporal resolution. Dr. Rob Gourdie at Virginia Tech will provide technical mentorship while the fellow learns the technique of transmission electron microscopy. She will then employ this technique to confirm changes in perinexal width. The long-term goal for this component is to develop a novel diagnostic for BrS. Aim 2 of this proposal will investigate whether hyponatremia can unmask greater conduction slowing in the Sn5a+/- mouse heart relative to its WT counterpart. Again, the fellow will utilize optical mapping to assess conduction in response to this change. She has recently collaborated with the lab of Dr. Matt Kay at George Washington University to learn how to build and implement floating microelectrodes, and will continue to work with this group in order establish this technique in Dr. Poelzing's lab at the Fralin Biomedical Research Institute at Virginia Tech Carilion (FBRI). The floating microelectrode technique will provide stable and direct electrophysiological measures from intact, beating mouse hearts in response to hyponatremia. The long- term goal for this component is to assess whether monitoring plasma sodium and calcium levels in BrS patients may be an effective approach to prevent clinical manifestations of BrS. Together, the results of this proposal may suggest new avenues of investigation for novel diagnostics and treatments for BrS. All of the proposed experiments will be conducted at FBRI, the collaborative biomedical research campus of Virginia Tech. With the support of her sponsor and mentoring team, this project will also be the basis to expand and strengthen the fellow's technical and professional skill sets in order to prepare her for the next step in her career plan as a postdoctoral associate en route to becoming an independent researcher in the field of cardiac electrophysiology.