Background: Recently, minor SNP variants of the NOS1AP gene have been reported to be associated with QT prolongation and increased incidence of sudden death in LQT1 patients. The NOS1AP gene encodes for CAPON protein, that localizes NOS1 close to the sarcoplasmic reticulum (SR). NOS1 activity accounts for NO-mediated modulation of ICaL, RyR2 channels and SERCA, thus interfering with regulation of Ca2+ handling and SR stability. Therefore we hypothesize that NOS1AP SNPs might affect NOS1 localization/function to decrease SR stability. In this setting, mutation-induced QT prolongation would induce Ca2+ overload, whose proarrhythmic effect would be unveiled by abnormal NOS1 localization/function. Aim: To evaluate the effect of changes in NOS1 activity on SR functional stability, repolarization and arrhythmogenesis in the context of IKs deficiency (LQT1). Methods: In guinea-pig ventricular myocytes subjected to IKs blockade (to reproduce the LQT1 phenotype) and adrenergic stimulation (Isoproterenol, ISO), we measured electrical activity, membrane currents and intracellular Ca2+, in basal condition and under selective inhibition of NOS1 (SMTC 3µM). Results: Under basal conditions, NOS1 inhibition prolonged AP duration (APD) (152.6  11.7 ms vs 96.1  9.0 ms; 58.8%. p<0.01), enhanced ICaL density (peak current density at +10 mV, SMTC vs CTRL: -16.61.2 pA/pF vs -13.51.0 pA/pF; p<0.05) and did not affect IKs (SMTC vs CTRL: 2.50.4 pA/pF vs 2.60.2 pA/pF) and IKr (SMTC vs CTRL: 0.840.04 pA/pF vs 0.910.05 pA/pF). The -adrenergic agonist isoproterenol (ISO, 1nM) induced delayed afterdepolarizations (DADs), an index of SR instability, in a significantly greater percentage of SMTC treated cells, compared to control ones (93% for SMTC vs 22% for CTRL, p<0.01). Moreover, the average time of DADs appearance was significantly different between SMTC and CTRL myocytes, with a earlier rise after NOS1 inhibition (25.8 ± 3.8 s and 61.5 ± 15.3 s respectively, p<0.01). Furthermore, the duration of the AP is important for the occurrence of these events, as switching from a long AP (140 ms) to a short AP (100 ms) waveform under ISO application in AP clamp mode, transient inward currents (Iti) were abolished. Conclusions: These results indicate that NOS1 deficiency may contribute to APD prolongation and enhance Ca2+ influx; these effects compromise SR stability in the presence of adrenergic stimulation. The effects of NOS1 inhibition are such as to account for the arrhythmogenic effect of NOS1AP polymorphism.

Introduzione: Recentemente, varianti minori di SNP del gene NOS1AP sono stati associati a prolungamento del QT e aumentata incidenza di morte improvvisa in pazienti LQT1. Il gene NOS1AP codifica per la proteina CAPON, che localizza NOS1 in prossimità del reticolo sarcoplasmico (SR). L' attività di NOS1 è importante per la modulazione mediate da NO di ICaL, dei canali RyR2 e di SERCA, interferendo così con la regolazione dell’handling del Ca2+ e la stabilità del SR. Perciò abbiamo ipotizzato che gli SNPs di NOS1AP possano alterare la localizzazione/funzione di NOS1 diminuendo la stabilità del SR. In questo contesto, il prolungamento del QT indotto da mutazione, potrebbe indurre un sovraccarico di Ca2+, il cui effetto pro-aritmico potrebbe essere smascherato da un’alterata localizzazione/funzione di NOS1. Scopo: Valutare l’effetto di cambiamenti nell’attività di NOS1 a livello della stabilità funzionale del SR, della ripolarizzazione e aritmogenesi in un contesto di perdita di IKs (LQT1). Metodi: In miociti ventricolari di cavia soggetti a blocco di IKs (per riprodurre il fenotipo LQT1) e a stimolazione adrenergica (Isoproterenolo, ISO), abbiamo misurato l’attività elettrica, le correnti di membrane e il Ca2+ intracellulare, in condizione basale e dopo inibizione selettiva di NOS1 (SMTC 3µM). Risultati: In condizioni basali, l’inibizione di NOS1 prolunga la durata del PA (APD) (152.6  11.7 ms vs 96.1  9.0 ms; 58.8%. p<0.01), aumenta la densità di ICaL (SMTC vs CTRL: -16.61.2 pA/pF vs -13.51.0 pA/pF; p<0.05) ma non altera ne IKs (SMTC vs CTRL: 2.50.4 pA/pF vs 2.60.2 pA/pF) nè IKr (SMTC vs CTRL: 0.840.04 pA/pF vs 0.910.05 pA/pF). L’isoproterenolo, agonista -adrenergico (ISO, 1nM), induce delayed afterdepolarizations (DADs), un indice di instabilità del SR, in una percentuale significativamente maggiore di cellule trattate con SMTC rispetto a quelle di controllo (93% per SMTC vs 22% per CTRL, p<0.01). Inoltre, il tempo medio di comparsa delle DADs è significativamente ridotto in miociti trattati con SMTC rispetto a quelli di CTRL (25.8 ± 3.8 s e 61.5 ± 15.3 s rispettivamente, p<0.01). In aggiunta, la durata del PA è importante per il verificarsi di questi eventi, poiché il passaggio, in AP clamp, da un PA lungo (140 ms) a uno corto (100 ms) durante applicazione di ISO, abolisce le “transient inward currents” (ITI). Conclusioni: Questi risultati indicano che la mancanza di NOS1 può contribuire al prolungamento dell’APD e aumentare l’influsso di Ca2+; questi effetti compromettono la stabilità del SR in presenza di stimolazione adrenergica. Gli effetti dell’inibizione di NOS1 sono tali da poter spiegare l’effetto aritmogenico dei polimorfismi di NOS1AP.

(2017). Arrhythmogenic mechanisms in genetic channelopathies. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2017).

Arrhythmogenic mechanisms in genetic channelopathies

BERNARDI, JOYCE
2017

Abstract

Background: Recently, minor SNP variants of the NOS1AP gene have been reported to be associated with QT prolongation and increased incidence of sudden death in LQT1 patients. The NOS1AP gene encodes for CAPON protein, that localizes NOS1 close to the sarcoplasmic reticulum (SR). NOS1 activity accounts for NO-mediated modulation of ICaL, RyR2 channels and SERCA, thus interfering with regulation of Ca2+ handling and SR stability. Therefore we hypothesize that NOS1AP SNPs might affect NOS1 localization/function to decrease SR stability. In this setting, mutation-induced QT prolongation would induce Ca2+ overload, whose proarrhythmic effect would be unveiled by abnormal NOS1 localization/function. Aim: To evaluate the effect of changes in NOS1 activity on SR functional stability, repolarization and arrhythmogenesis in the context of IKs deficiency (LQT1). Methods: In guinea-pig ventricular myocytes subjected to IKs blockade (to reproduce the LQT1 phenotype) and adrenergic stimulation (Isoproterenol, ISO), we measured electrical activity, membrane currents and intracellular Ca2+, in basal condition and under selective inhibition of NOS1 (SMTC 3µM). Results: Under basal conditions, NOS1 inhibition prolonged AP duration (APD) (152.6  11.7 ms vs 96.1  9.0 ms; 58.8%. p<0.01), enhanced ICaL density (peak current density at +10 mV, SMTC vs CTRL: -16.61.2 pA/pF vs -13.51.0 pA/pF; p<0.05) and did not affect IKs (SMTC vs CTRL: 2.50.4 pA/pF vs 2.60.2 pA/pF) and IKr (SMTC vs CTRL: 0.840.04 pA/pF vs 0.910.05 pA/pF). The -adrenergic agonist isoproterenol (ISO, 1nM) induced delayed afterdepolarizations (DADs), an index of SR instability, in a significantly greater percentage of SMTC treated cells, compared to control ones (93% for SMTC vs 22% for CTRL, p<0.01). Moreover, the average time of DADs appearance was significantly different between SMTC and CTRL myocytes, with a earlier rise after NOS1 inhibition (25.8 ± 3.8 s and 61.5 ± 15.3 s respectively, p<0.01). Furthermore, the duration of the AP is important for the occurrence of these events, as switching from a long AP (140 ms) to a short AP (100 ms) waveform under ISO application in AP clamp mode, transient inward currents (Iti) were abolished. Conclusions: These results indicate that NOS1 deficiency may contribute to APD prolongation and enhance Ca2+ influx; these effects compromise SR stability in the presence of adrenergic stimulation. The effects of NOS1 inhibition are such as to account for the arrhythmogenic effect of NOS1AP polymorphism.
ZAZA, ANTONIO
LQT1,; arrhythmias,; NOS1AP; polymorphisms,; NOS1
LQT1,; arrhythmias,; NOS1AP; polymorphisms,; NOS1
MED/04 - PATOLOGIA GENERALE
English
20-mar-2017
MEDICINA TRASLAZIONALE E MOLECOLARE - DIMET - 76R
29
2015/2016
open
(2017). Arrhythmogenic mechanisms in genetic channelopathies. (Tesi di dottorato, Università degli Studi di Milano-Bicocca, 2017).
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/153192
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