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Objectives: Eplerenone (EPL), an antagonist of the mineralocorticoid receptor, is beneficial for atrial fibrillation and atrial fibrosis. However, the underlying mechanism remains less well known. We aimed to investigate the effect of EPL on atrial fibrosis using a mouse with selective atrial fibrosis and to explore the underlying mechanisms., Methods: EPL-treated MHC-TGFcys33ser transgenic mice that have selective atrial fibrosis (Tx+EPL mice), as well as control mice, were used for in vivo studies including histological analyses, Western blotting, and qRT-PCR studies. TGF-β1-stimulated atrial fibroblasts were treated with EPL or vehicle for the in vitro studies including Western blotting and qRT-PCR studies. In addition, Smad7 siRNA was used to knock down Smad7., Results: EPL inhibited atrial fibrosis in the Tx mice. In addition, EPL suppressed the expression of fibrosis-related molecules induced by TGF-β1 in vivo and in vitro. This occurred in concert with a downregulation of Smad7 protein expression and an upregulation of p-Smad2/3 protein expression. In addition, knockdown of Smad7 by siRNA abolished the protective roles of EPL., Conclusions: EPL inhibited atrial fibrosis in Tx mice. The underlying mechanism may involve increased protein expression of Smad7, which enhances the inhibitory feedback regulation of TGF-β1/Smad signaling., (© 2017 S. Karger AG, Basel.)

Accumulating evidence reveals that genetic variants play pivotal roles in familial atrial fibrillation (AF). However, the molecular defects in most patients with AF remain to be identified. Here, we report on three novel KCNA5 mutations that were identified in 4 of 120 unrelated AF families. Among them, T527M was found in two AF families, and A576V and E610K in two other AF families, respectively. The mutations T527M and A576V were also detected in 2 and 1 of 256 patients with idiopathic AF, respectively. The same mutations were not observed in 200 secondary AF patients and 500 controls. Functional analyses revealed consistent loss-of-function effects of mutant KCNA5 proteins on the ultrarapidly activating delayed rectifier potassium currents. These findings expand the spectrum of mutations in KCNA5 linked to AF and provide new insight into the molecular mechanism involved in AF.

The inward rectifier K(+) channel Kir2.1 mediates the potassium I(K1) current in the heart. It is encoded by KCNJ2 gene that has been linked to Andersen's syndrome. Recently, strong evidences showed that Kir2.1 channels were associated with mouse atrial fibrillation (AF), therefore we hypothesized that KCNJ2 was associated with familial AF. Thirty Chinese AF kindreds were evaluated for mutations in KCNJ2 gene. A valine-to-isoleucine mutation at position 93 (V93I) of Kir2.1 was found in all affected members in one kindred. This valine and its flanking sequence is highly conserved in Kir2.1 proteins among different species. Functional analysis of the V93I mutant demonstrated a gain-of-function consequence on the Kir2.1 current. This effect is opposed to the loss-of-function effect of previously reported mutations in Andersen's syndrome. Kir2.1 V93I mutation may play a role in initiating and/or maintaining AF by increasing the activity of the inward rectifier K(+) channel.

Atrial fibrillation (AF) is the most common cardiac arrhythmia encountered in clinical practice. We first reported an S140G mutation of KCNQ1, an alpha subunit of potassium channels, in one Chinese kindred with AF. However, the molecular defects and cellular mechanisms in most patients with AF remain to be identified. We evaluated 28 unrelated Chinese kindreds with AF and sequenced eight genes of potassium channels (KCNQ1, HERG, KCNE1, KCNE2, KCNE3, KCNE4, KCNE5, and KCNJ2). An arginine-to-cysteine mutation at position 27 (R27C) of KCNE2, the beta subunit of the KCNQ1-KCNE2 channel responsible for a background potassium current, was found in 2 of the 28 probands. The mutation was present in all affected members in the two kindreds and was absent in 462 healthy unrelated Chinese subjects. Similar to KCNQ1 S140G, the mutation had a gain-of-function effect on the KCNQ1-KCNE2 channel; unlike long QT syndrome-associated KCNE2 mutations, it did not alter HERG-KCNE2 current. The mutation did not alter the functions of the HCN channel family either. Thus, KCNE2 R27C is a gain-of-function mutation associated with the initiation and/or maintenance of AF.

Background: We recently reported that an S140G mutation in human KCNQ1, an alpha subunit of potassium channels, was involved in the pathogenesis of familial atrial fibrillation (AF), but it is not clear whether the mutation is associated with other cardiac arrhythmias.Objective: The purpose of this study was to further explore the association of the KCNQ1 S140G mutation with cardiac arrhythmias.Methods: We produced a transgenic mouse model with myocardium-specific expression of the human KCNQ1 S140G mutation under the control of an alpha-cardiac myosin heavy chain promoter by standard transgenic procedure and evaluated the relationship between the KCNQ1 mutation and its phenotypes in a human family.Results: Four lines of transgenic mice were established with a high level of human KCNQ1 S140G expression in the heart. Frequent episodes of first-, second-, advanced-, or third-degree atrioventricular block (AVB) occurred in at least 65% of transgenic descendants from the four lines. However, none of the five wild-type transgenic lines presented with AVBs. HMR1556, a KCNQ1-specific blocker, can terminate the AVBs. With the exception of at most three AF individuals, at least 13 AF patients were found to show obviously slow ventricular response, which may be one manifestation of AVBs. Interestingly, AF was not detected in these transgenic mice.Conclusion: The results suggest that human KCNQ1 S140G is also likely to be a causative mutation responsible for AVBs. The transgenic mouse model is a potential tool to explore mechanisms of AVBs. [ABSTRACT FROM AUTHOR]

Abstract: The inward rectifier potassium channel, Kir2.1, contributes to the I K1 current in cardiac myocytes and is closely associated with atrial fibrillation. Strong evidences have shown that atrial dilatation or stretch may result in atrial fibrillation. However, the role of Kir2.1 channels in the stretch-mediated atrial fibrillation is not clear. In this study, we constructed the recombinant plasmid of KCNJ2 that encodes the Kir2.1 channel and expressed it in CHO-K1 cells. We recorded I K1 currents using the whole-cell patch clamping technique. Our data showed that I K1 currents were significantly larger under stretch in the hypotonic solution than under non-stretch in the iso-osmotic solution, and the activation kinetics of the Kir2.1 channel were changed markedly by stretch as well. Thus, atrial stretch in human heart might result in excessive I K1 currents, which is likely to increase the resting membrane potential and decrease the effective refractory period, to initiate and/or maintain atrial fibrillation. [Copyright &y& Elsevier]