Fibroblast growth factor homologous factors serve as a molecular rheostat in tuning arrhythmogenic cardiac late sodium current

Abstract

Voltage-gated sodium (Nav1.5) channels support the genesis and brisk spatial propagation of action potentials in the heart. Disruption of Na V 1.5 inactivation results in a small persistent Na influx known as late Na current ( I Na,L ), which has emerged as a common pathogenic mechanism in both congenital and acquired cardiac arrhythmogenic syndromes. Here, using low-noise multi-channel recordings in heterologous systems, LQTS3 patient-derived iPSCs cardiomyocytes, and mouse ventricular myocytes, we demonstrate that the intracellular fibroblast growth factor homologous factors (FHF1–4) tune pathogenic I Na,L in an isoform-specific manner. This scheme suggests a complex orchestration of I Na,L in cardiomyocytes that may contribute to variable disease expressivity of Na V 1.5 channelopathies. We further leverage these observations to engineer a peptide-inhibitor of I Na,L with a higher efficacy as compared to a well-established small-molecule inhibitor. Overall, these findings lend insights into molecular mechanisms underlying FHF regulation of I Na,L in pathophysiology and outline potential therapeutic avenues.

FHF2 phosphorylation and regulation of native myocardial NaV1.5 channels

“…Because it was previously shown that FHF2 also plays a crucial role in regulating the late Na + current (I NaL ) (Abrams et al, 2020; Gade et al, 2020; Chakouri et al, 2022), additional voltage-clamp experiments were designed to investigate whether the simultaneous mutation of the nine identified FHF2 phosphorylation sites to alanine, using the FHF2-VY-9A phosphomutant rescue, affects the density of TTX-sensitive I NaL in adult mouse ventricular cardiomyocytes. In accordance with previous studies, these analyses demonstrated that the averaged I NaL density is significantly ( / ?<0.05) increased in FHF2-KD, compared to FHF2-lox, cardiomyocytes ( Table 4 ).…”

“…The copyright holder for this preprint this version posted February 3, 2023. ; https://doi.org/10.1101/2023.01.31.526475 doi: bioRxiv preprint Regulation of Na V 1.5 by FHF2 phosphorylation 5 cardiac Na V 1.5 channels, tuning both channel availability (Wang et al, 2011a;Park et al, 2016;Wang et al, 2017;Santucci et al, 2022) and I NaL (Abrams et al, 2020;Gade et al, 2020;Chakouri et al, 2022).…”

“…A promising pool from which such regulation by phosphorylation may be found is the FHF accessory proteins. FHFs have emerged as pivotal players in controlling the inactivation properties of cardiac Na V 1.5 channels, tuning both channel availability (Wang et al, 2011a;Park et al, 2016;Wang et al, 2017;Santucci et al, 2022) and I NaL (Abrams et al, 2020;Gade et al, 2020;Chakouri et al, 2022).…”

“…A promising pool from which such regulation by phosphorylation may be found is the FHF accessory proteins. FHFs have emerged as pivotal players in controlling the inactivation properties of cardiac Na V 1.5 channels, tuning both channel availability (Wang et al, 2011a; Park et al, 2016; Wang et al, 2017; Santucci et al, 2022) and I NaL (Abrams et al, 2020; Gade et al, 2020; Chakouri et al, 2022). The FHF family comprises four members (FHF1=FGF12, FHF2=FGF13, FHF3=FGF11, and FHF4=FGF14), and further family diversity is achieved through the generation of several alternatively spliced isoforms highly diverging from their N-amino termini (Munoz-Sanjuan et al, 2000).…”

NaV1.6 dysregulation within myocardial T-tubules by D96V calmodulin enhances proarrhythmic sodium and calcium mishandling

“…Akin to work on mutant CaMs in LTCC regulation ( 45 ), the reduced affinity of a dominant-negative D96V-CaM mutant for Na V 1.6CTD may not fully explain the impact of this mutation on Na V 1.6 inactivation. Future work will need to examine the cooperativity of additional CaM binding sites and other Na V -interacting proteins, such as FGF homologous factors ( 46 ), with the Na V CTD on Na V inactivation. However, our ITC findings, which point toward the potential proarrhythmic properties of Na V 1.6, especially when dysregulated, provide a useful context for our results implicating the channel in D96V-CaM–mediated arrhythmias.…”