Tachycardia is characterized by high beating rates that can lead to life‐threatening fibrillations. Mutations in several ion‐channel genes were implicated with tachycardia; however, the complex genetic contributors and their modes of action are still unclear. Here, we investigated the influence of an SCN5A gene variant on tachycardia phenotype by deriving patient‐specific iPSCs and cardiomyocytes (iPSC‐CM). Two tachycardia patients were genetically analyzed and revealed to inherit a heterozygous p.F1465L variant in the SCN5A gene. Gene expression and immunocytochemical analysis in iPSC‐CMs generated from patients did not show any significant changes in mRNA levels of SCN5A or gross NaV1.5 cellular mislocalization, compared to healthy‐derived iPSC‐CMs. Electrophysiological and contraction imaging analysis in patient iPSC‐CMs revealed intermittent fibrillation‐like states, occasional arrhythmic events, and sustained high‐paced contractions that could be selectively reduced by flecainide treatment. The patch‐clamp analysis demonstrated a negative shift in the voltage‐dependent activation at the patient‐derived iPSC‐CMs compared to the healthy control line, suggestive of a gain‐of‐function activity associated with the SCN5A+/p.F1465L variant. Our patient‐derived iPSC‐CM model recapitulated the clinically relevant characteristics of tachycardia associated with a novel pathogenic SCN5A+/p.F1465L variant leading to altered Na+ channel kinetics as the likely mechanism underlying high excitability and tachycardia phenotype.
The sensory nervous system is critical to maintain cardiac function. As opposed to efferent innervation, less is known about cardiac afferents. For this, we mapped the VGLUT2‐expressing cardiac afferent fibers of spinal and vagal origin by using the VGLUT2::tdTomato double transgenic mouse as an approach to visualize the whole hearts both at the dorsal and ventral sides. For comparison, we colabeled mixed‐sex transgenic hearts with either TUJ1 protein for global cardiac innervation or tyrosine hydroxylase for the sympathetic network at the healthy state or following ischemic injury. Interestingly, the nerve density for global and VGLUT2‐expressing afferents was found significantly higher on the dorsal side compared to the ventral side. From the global nerve innervation detected by TUJ1 immunoreactivity, VGLUT2 afferent innervation was detected to be 15–25% of the total network. The detailed characterization of both the atria and the ventricles revealed a remarkable diversity of spinal afferent nerve ending morphologies of flower sprays, intramuscular endings, and end‐net branches that innervate distinct anatomical parts of the heart. Using this integrative approach in a chronic myocardial infarct model, we showed a significant increase in hyperinnervation in the form of axonal sprouts for cardiac afferents at the infarct border zone, as well as denervation at distal sites of the ischemic area. The functional and physiological consequences of the abnormal sensory innervation remodeling post‐ischemic injury should be further evaluated in future studies regarding their potential contribution to cardiac dysfunction.
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