NOS1AP polymorphisms reduce NOS1 activity and interact with prolonged repolarization in arrhythmogenesis

Area of Science:

• Cardiology
• Genetics
• Molecular Biology

Background:

• Single-nucleotide polymorphisms (SNPs) in NOS1AP are linked to QT prolongation and sudden cardiac death in Long QT syndrome type 1 (LQT1).
• NOS1AP regulates nitric oxide synthase 1 (NOS1) activity.
• The interaction between NOS1AP variants, NOS1 function, and LQT1 pathophysiology remains unclear.

Purpose of the Study:

• To investigate the functional consequences of NOS1AP SNPs in LQT1.
• To determine if NOS1 inhibition exacerbates LQT1-like phenotypes in cardiomyocytes.
• To assess whether patient-derived cardiomyocytes with specific NOS1AP variants exhibit NOS1 deficiency-related phenotypes.

Main Methods:

• Inhibition of NOS1 using SMTC or L-VNIO in guinea pig cardiomyocytes (GP-CMs) with LQT1 mimicked by IKs blockade and isoproterenol.
• Analysis of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from LQT1 patients with varying NOS1AP genotypes and mutation penetrance.
• Electrophysiological recordings and calcium handling assessments in both GP-CMs and hiPSC-CMs.

Main Results:

• NOS1 inhibition in GP-CMs prolonged action-potential duration (APD), enhanced specific ion currents (ICaL, INaL), and induced delayed afterdepolarizations.
• In hiPSC-CMs from symptomatic LQT1 patients with minor NOS1AP alleles, longer APD, increased ICaL, and reduced NOS1/NOS1AP expression and co-localization were observed compared to asymptomatic carriers.
• NOS1 inhibition-induced arrhythmogenic events were suppressed by shortening APD in GP-CMs.

Conclusions:

• Minor NOS1AP alleles are associated with reduced NOS1 function.
• NOS1 dysfunction contributes to APD prolongation in LQT1 and exacerbates arrhythmia risk by perturbing calcium handling.
• This study establishes a mechanistic link between NOS1AP SNPs and the severity of LQT1 phenotypes.