Telethonin variants found in Brugada syndrome, J‐wave pattern ECG, and ARVC reduce peak Na_v1.5 currents in HEK‐293 cells

Abstract

Background: Telethonin (TCAP) is a Z-disk protein that maintains cytoskeletal integrity and various signaling pathways in cardiomyocytes. TCAP is shown to modulate αsubunit of the human cardiac sodium channel (hNa v 1.5) by direct interactions. Several TCAP variants are found in cardiomyopathies. We sought to investigate whether TCAP variants are associated with arrhythmia syndromes. Methods: Mutational analyses for TCAP were performed in 303 Japanese patients with Brugada syndrome, arrhythmogenic right ventricular cardiomyopathy, and J-wave pattern ECG. Using patch-clamp techniques, electrophysiological characteristics of hNa v 1.5 were studied in HEK-293 cells stably expressing hNa v 1.5 and transiently transfected with wild-type (WT) or variant TCAP. Results: We identified two TCAP variants, c.145G>A:p.E49K and c.458G>A:p.R153H, in four individuals. p.E49K was found in two patients with ARVC or BrS. p.R153H was found in two patients with BrS or J-wave pattern ECG. No patient had variant hNa v 1.5. Patch-clamp experiments demonstrated that peak sodium currents were significantly reduced in cells expressing p.R153H and p.E49K compared with WT-TCAP (66%, p.R153H; 72%, p.E49K). Voltage dependency of peak IV curve was rightwardshifted by 5 mV in cells expressing p.E49K compared with WT-TCAP. Voltage dependency of activation was not leftward-shifted by p.R153H, while voltage dependency of steady-state inactivation was leftward-shifted by p.E49K. Conclusions: We found two TCAP variants in the patients with BrS, J-wave pattern ECG, and ARVC that can cause loss-of-function of the hNa v 1.5 in heterologous expression systems. Our observation suggests that these variants might impair I Na and be associated with the patients' electrophysiological phenotypes. Further studies linking our experimental data to clinical phenotypes are warranted.

Advances in Ion Channel, Non-Desmosomal Variants and Autophagic Mechanisms Implicated in Arrhythmogenic Cardiomyopathy

“…This paradoxical nature between the studies derives from the fact that induced stem cells in vitro are inherently more unstable than tissue cells in vivo, beating spontaneously, and due to their immaturity they are more depolarized at rest than adult ventricular cells, which may affect the dynamics of voltage-gated ion channels and thus alter their own excitability [ 30 ]. A study from Japan of 303 patients with BrS, ACM negative for the SCN5A variant suggested that two TCAP gene mutants c.145G > A: p.E49K (chr17: 37822003) and c.458G > A: p.R153H (chr17: 37822316) lead to structural changes in their transcription products telethonin structural alterations, which in turn lead to structural breakage of the z-disk between cardiomyocytes ultimately causing loss of function of the cardiac Na channel (Nav1.5) [ 31 ]. Another study reviewed 96 cases of SCD of unknown origin in Scotland over a 13-year period from 2000 to 2013, of which 50 were clearly cardiomyopathies and 26 were ACMs, the most typical pathogenic variant in ACMs being the PKP2 variant accompanied by non-direct pathogenic variants in DSP and SCN5A [ 32 ].…”

“…Differential expression enrichment analysis in the ARVC group indicated that the gene was mainly associated with cell adhesion and structure in the lesion, as well as adipocytokines and PPAR signaling pathways [ 64 ]. A study from Japan of 303 BrS, ARVC patients with no SCN5A variant suggested that two TCAP gene mutants c.145G > A: p.E49K (chr17: 37822003) and c.458G > A: p.R153H (chr17: 37822316) lead to structural changes in their transcription products telethonin structural alterations, which in turn lead to structural breakage of the z-disk between cardiomyocytes, ultimately causing loss of function of the cardiac Na channel (Nav1.5) [ 31 ]. The results of a study at Peking Union Medical College Hospital also suggest that myotonic dystrophy patients with variants in the Duchenne muscular dystrophy ( DMD ) gene can also have a pathological phenotype akin to that of left ventricular ACM with typical fibrofatty infiltrative features [ 65 ].…”

Genomic and Non-Genomic Regulatory Mechanisms of the Cardiac Sodium Channel in Cardiac Arrhythmias

“…α-actinin-2 is thought to positively regulate Na v 1.5 by increasing its cell surface expression, most likely through promoting its anchoring to the contact zones between T-tubules and Z-lines and connecting the channel to the actin cytoskeleton network [284]. However, scarce information is available regarding the mechanism of Na v 1.5 regulation by telethonin, although physical interaction between TCAP and Na v 1.5 was evidenced by co-immunoprecipitation methods and mutations in the telethonin coding gene (TCAP) has been found to alter the channel-gating properties of Na v 1.5 in patients with abnormal gut motility and Brugada syndrome [285,286].…”

“…Besides the role of the sodium channel ancillary subunits, additional SCN5A/Na v 1.5 interacting proteins have been reported in BrS. Mutations in Plakophilin (PKP2) [260,371] MOG1 [9,201,[372][373][374][375], FGF13 [376], syntrophin (SNTA1) [377], NEDD4 [378,379], Tmem168 [379] and telethonin [285,286] are identified in BrS patients and their implication to sodium channel function has been reported. Distinct Na v 1.5 interacting protein mutants lead to I Na deficit [261,286,375,377] while others influence Na v trafficking and thus subcellular localization [201,379].…”

Brugada syndrome: current concepts and genetic background

“…Locus: 3p25.1; OMIM: *612048; Gene: Telethonin (TCAP) TITIN-CAP. This gene belongs to the TMEM43 family 104 ; Protein: TMEM43 transmembrane protein 43. A missense mutation, c.1073C>T (p.S358L) in the transmembrane protein 43 (TMEM43) are the cause of familial Arrhythmogenic Right Ventricular Dysplasia (ARVD) type 5 (ARVD5), also known as Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) type 5 (ARVC5) 105 , currently named AC.…”