TGF-β1, Released by Myofibroblasts, Differentially Regulates Transcription and Function of Sodium and Potassium Channels in Adult Rat Ventricular Myocytes

Abstract

Cardiac injury promotes fibroblasts activation and differentiation into myofibroblasts, which are hypersecretory of multiple cytokines. It is unknown whether any of such cytokines are involved in the electrophysiological remodeling of adult cardiomyocytes. We cultured adult cardiomyocytes for 3 days in cardiac fibroblast conditioned medium (FCM) from adult rats. In whole-cell voltage-clamp experiments, FCM-treated myocytes had 41% more peak inward sodium current (INa) density at −40 mV than myocytes in control medium (p<0.01). In contrast, peak transient outward current (Ito) was decreased by ∼55% at 60 mV (p<0.001). Protein analysis of FCM demonstrated that the concentration of TGF-β1 was >3 fold greater in FCM than control, which suggested that FCM effects could be mediated by TGF-β1. This was confirmed by pre-treatment with TGF-β1 neutralizing antibody, which abolished the FCM-induced changes in both INa and Ito. In current-clamp experiments TGF-β1 (10 ng/ml) prolonged the action potential duration at 30, 50, and 90 repolarization (p<0.05); at 50 ng/ml it gave rise to early afterdepolarizations. In voltage-clamp experiments, TGF-β1 increased INa density in a dose-dependent manner without affecting voltage dependence of activation or inactivation. INa density was −36.25±2.8 pA/pF in control, −59.17±6.2 pA/pF at 0.1 ng/ml (p<0.01), and −58.22±6.6 pA/pF at 1 ng/ml (p<0.01). In sharp contrast, Ito density decreased from 22.2±1.2 pA/pF to 12.7±0.98 pA/pF (p<0.001) at 10 ng/ml. At 1 ng/ml TGF-β1 significantly increased SCN5A (NaV1.5) (+73%; p<0.01), while reducing KCNIP2 (Kchip2; −77%; p<0.01) and KCND2 (KV4.2; −50% p<0.05) mRNA levels. Further, the TGF-β1-induced increase in INa was mediated through activation of the PI3K-AKT pathway via phosphorylation of FOXO1 (a negative regulator of SCN5A). TGF-β1 released by myofibroblasts differentially regulates transcription and function of the main cardiac sodium channel and of the channel responsible for the transient outward current. The results provide new mechanistic insight into the electrical remodeling associated with myocardial injury.

TGF-β 1 (Transforming Growth Factor-β 1 ) Plays a Pivotal Role in Cardiac Myofibroblast Arrhythmogenicity

“…This background activity was likely due to TGF-β 1 originating from the serum in the culture medium or the secretion of TGF-β 1 by myofibroblasts and cardiomyocytes, or both. 28,29 Background activity was present in all experiments shown below and is characterized by control values being consistently intermediate to values obtained in preparations treated with TGF-β 1 and SB431542, respectively. According to these findings, the effects of TGF-β 1 described below are consistently referred to SB431542 conditions unless stated otherwise.…”

Cardiac sodium channel mutations: why so many phenotypes?

“…35,36 Interestingly, transforming growth factor β1 can counteract the effect of FOXO1 and increase the SCN5A mRNA level and I Na . 37 These data suggest that the phenotypic penetrance of a mutation might vary as a result of changes in these transcription factors. Additionally, single nucleotide polymorphisms in the promoter region of SCN5A have been shown to modulate the transcriptional activity of the gene, 38 and to affect the phenotypic severity in heterozygous carriers of an SCN5A loss-of-function mutation (1936delC).…”

Chronic Atrial Fibrillation Increases MicroRNA-21 in Human Atrial Myocytes Decreasing L-Type Calcium Current

“…Recent evidence suggests that structural and electrical remodeling processes may not be independent and would share some common pathways. 34,35 In fact, it has been demonstrated that activation of fibrotic signaling pathways via soluble cytokines, such as TGF-β1 and platelet-derived growth factor, modulate Na + , Ca, 2+ and K + currents involved in the control of atrial APD.…”