A distinct de novo expression of Na_v1.5 sodium channels in human atrial fibroblasts differentiated into myofibroblasts

Abstract

Key point• Fibroblasts play a major role in heart physiology. In pathological conditions, they can lead to cardiac fibrosis when they differentiate into myofibroblasts.• This differentiated status is associated with changes in expression profile leading to neo-expression of proteins such as ionic channels.• The present study investigates electrophysiological changes associated with fibroblast differentiation focusing on voltage-gated sodium channels in human atrial fibroblasts and myofibroblasts.• We show that human atrial fibroblast differentiation in myofibroblasts is associated with de novo expression of voltage gated sodium current. Multiple arguments support that this current is predominantly supported by the Na v 1.5 α-subunit which may generate a persistent sodium entry into myofibroblasts.• Our data revealed that Na v 1.5 α-subunit expression is not restricted to cardiac myocytes within the atrium. Since fibrosis is one of the fundamental mechanisms implicated in atrial fibrillation, it is of great interest to investigate how this channel could influence myofibroblasts function.Abstract Fibroblasts play a major role in heart physiology. They are at the origin of the extracellular matrix renewal and production of various paracrine and autocrine factors. In pathological conditions, fibroblasts proliferate, migrate and differentiate into myofibroblasts leading to cardiac fibrosis. This differentiated status is associated with changes in expression profile leading to neo-expression of proteins such as ionic channels. The present study investigates further electrophysiological changes associated with fibroblast differentiation focusing on the activity of voltage-gated sodium channels in human atrial fibroblasts and myofibroblasts. Using the patch clamp technique we show that human atrial myofibroblasts display a fast inward voltage gated sodium current with a density of 13.28 ± 2.88 pA pF −1 whereas no current was detectable in non-differentiated fibroblasts. Quantitative RT-PCR reveals a large amount of transcripts encoding the Na v 1.5 α-subunit with a fourfold increased expression level in myofibroblasts when compared to fibroblasts. Accordingly, half of the current was blocked by 1 μM of tetrodotoxin and immunocytochemistry experiments reveal the presence of Na v 1.5 proteins. Overall, this current exhibits similar biophysical characteristics to sodium currents found in cardiac myocytes except for the window current that is enlarged for potentials between −100 and −20 mV. Since fibrosis is one of the fundamental mechanisms implicated in atrial fibrillation, it is of great interest to investigate how this current could influence myofibroblast properties. Moreover, since several Na v 1.5 mutations are related to cardiac pathologies, this study offers a new avenue on the fibroblasts involvement of these mutations.

Cellular and Molecular Electrophysiology of Atrial Fibrillation Initiation, Maintenance, and Progression

“…82 Atrial fibroblasts also express Nav1.5 α-subunits and Na + currents when differentiated into myofibroblasts, and the resulting Na + entry may contribute to their arrhythmogenic potential. 83,84 In addition to promoting muscle bundle discontinuities, myofibroblasts can affect atrial cardiomyocytes through paracrine interactions, notably via angiotensin II and TGFβ1 ( Figure 5). 85 Moreover, myofibroblasts promote re-entry via by guest on May 9, 2018 http://circres.ahajournals.org/ Downloaded from direct electric interaction with cardiomyocytes ( Figure 5), 40 by reducing conduction velocity through passive loading and depolarization-induced Na + channel inactivation.…”

Ca 2+ Entry Through TRP-C Channels Regulates Fibroblast Biology in Chronic Atrial Fibrillation

“…A recent study that reveals the expression of cardiac sodium channels in myofibroblasts from human atrium 18 also provides an important perspective when the clinical significance of the findings in Harada et al 1 are being considered. If the myocyte-fibroblast-myofibroblast syncytium that contributes to the characteristic substrate found in chronic atrial fibrillation includes the possibility that the myofibroblast could support a sodium current-mediated regenerative response, virtually all present concepts for pharmacological management of atrial rhythm disturbances need to be reconsidered.…”

Functional Alterations of Ion Channels From Cardiac Fibroblasts in Heart Diseases

“…23 Mechanosensitivity of TRPV4 channels could play an important role in cardiac remodeling, with altered chamber stiffness resulting from increased differentiation of fibroblasts to myofibroblasts that can further promote cardiac fibrosis. More information on the physiological and pathological role of TRPV4 channels in the cardiovascular system is reported in a recent review by Randhawa et al 50 Sodium (Na + ) Channels Nav1.5 (Tetrodotoxin [TTX]-Resistant) Channel: Differentiated myofibroblasts from human atria displayed fast inward voltage-gated Na + current, which was not detectable in undifferentiated atrial fibroblasts 14 with a large window current for potentials between -100 and -20 mV. 14 Interestingly, this Nav1.5 channel expression was demonstrated to be a de novo synthesis process during the myofibroblast differentiation 14 ( Figure 1 and Table 1).…”

“…More information on the physiological and pathological role of TRPV4 channels in the cardiovascular system is reported in a recent review by Randhawa et al 50 Sodium (Na + ) Channels Nav1.5 (Tetrodotoxin [TTX]-Resistant) Channel: Differentiated myofibroblasts from human atria displayed fast inward voltage-gated Na + current, which was not detectable in undifferentiated atrial fibroblasts 14 with a large window current for potentials between -100 and -20 mV. 14 Interestingly, this Nav1.5 channel expression was demonstrated to be a de novo synthesis process during the myofibroblast differentiation 14 ( Figure 1 and Table 1). An earlier study showed rapidly inactivating TTX-resistant Na + currents even in undifferentiated cultured human CFs, 31 which could be due to differences in culture method/time, as differentiation can happen by prolonged culture/passage.…”