SummaryHuman induced pluripotent stem cell (hiPSC)-derived atrial cardiomyocytes (CMs) hold great promise for elucidating underlying cellular mechanisms that cause atrial fibrillation (AF). In order to use atrial-like hiPSC-CMs for arrhythmia modeling, it is essential to better understand the molecular and electrophysiological phenotype of these cells. We performed comprehensive molecular, transcriptomic, and electrophysiologic analyses of retinoic acid (RA)-guided hiPSC atrial-like CMs and demonstrate that RA results in differential expression of genes involved in calcium ion homeostasis that directly interact with an RA receptor, chicken ovalbumin upstream promoter-transcription factor 2 (COUP-TFII). We report a mechanism by which RA generates an atrial-like electrophysiologic signature through the downstream regulation of calcium channel gene expression by COUP-TFII and modulation of calcium handling. Collectively, our results provide important insights into the underlying molecular mechanisms that regulate atrial-like hiPSC-CM electrophysiology and support the use of atrial-like CMs derived from hiPSCs to model AF.

Background: Epidemiological studies have established obesity as an independent risk factor for atrial fibrillation (AF), but the underlying pathophysiological mechanisms remain unclear. Reduced cardiac sodium channel expression is a known causal mechanism in AF. We hypothesized that obesity decreases Nav1.5 expression via enhanced oxidative stress, thus reducing I Na , and enhancing susceptibility to AF. Methods: To elucidate the underlying electrophysiological mechanisms a diet-induced obese mouse model was used. Weight, blood pressure, glucose, F 2 -isoprostanes, NOX2 (NADPH oxidase 2), and PKC (protein kinase C) were measured in obese mice and compared with lean controls. Invasive electrophysiological, immunohistochemistry, Western blotting, and patch clamping of membrane potentials was performed to evaluate the molecular and electrophysiological phenotype of atrial myocytes. Results: Pacing-induced AF in 100% of diet-induced obese mice versus 25% in controls ( P <0.01) with increased AF burden. Cardiac sodium channel expression, I Na and atrial action potential duration were reduced and potassium channel expression (Kv1.5) and current ( I Kur ) and F 2 -isoprostanes, NOX2, and PKC-α/δ expression and atrial fibrosis were significantly increased in diet-induced obese mice as compared with controls. A mitochondrial antioxidant reduced AF burden, restored I Na , I Ca,L , I Kur , action potential duration, and reversed atrial fibrosis in diet-induced obese mice as compared with controls. Conclusions: Inducible AF in obese mice is mediated, in part, by a combined effect of sodium, potassium, and calcium channel remodeling and atrial fibrosis. Mitochondrial antioxidant therapy abrogated the ion channel and structural remodeling and reversed the obesity-induced AF burden. Our findings have important implications for the management of obesity-mediated AF in patients. Graphic Abstract: A graphic abstract is available for this article.

Lymphoid-specific tyrosine phosphatase (LYP), a member of the protein tyrosine phosphatase (PTP) family of signaling enzymes, is associated with a broad spectrum of autoimmune diseases. Herein we describe our structure-based lead optimization efforts within a 6-hydroxy-benzofuran-5-carboxylic acid series culminating in the identification of compound 8b, a potent and selective inhibitor of LYP with a Ki value of 110 nM and more than 9-fold selectivity over a large panel of PTPs. The structure of LYP in complex with 8b was obtained by X-ray crystallography, providing detailed information about the molecular recognition of small-molecule ligands binding LYP. Importantly, compound 8b possesses highly efficacious cellular activity in both T- and mast cells and is capable of blocking anaphylaxis in mice. Discovery of 8b establishes a starting point for the development of clinically useful LYP inhibitors for treating a wide range of autoimmune disorders.

PEST-domain-enriched tyrosine phosphatase is an important positive regulator of anaphylaxis. Pharmacological inhibition of its activity together with glucocorticoid administration provide an effective rescue for PSA in mice.

A frameshift (fs) mutation in the natriuretic peptide precursor A (NPPA) gene, encoding a mutant atrial natriuretic peptide (Mut-ANP), has been linked with familial atrial fibrillation (AF) but the underlying mechanisms by which the mutation causes AF remain unclear. We engineered 2 transgenic (TG) mouse lines expressing the wild-type (WT)-NPPA gene (H-WT-NPPA) and the human fs-Mut-NPPA gene (H-fsMut-NPPA) to test the hypothesis that mice overexpressing the human NPPA mutation are more susceptible to AF and elucidate the underlying electrophysiologic and molecular mechanisms. Transthoracic echocardiography and surface electrocardiography (ECG) were performed in H-fsMut-NPPA, H-WT-NPPA, and Non-TG mice. Invasive electrophysiology, immunohistochemistry, Western blotting and patch clamping of membrane potentials were performed. To examine the role of the Mut-ANP in ion channel remodeling, we measured plasma cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP) levels and protein kinase A (PKA) activity in the 3 groups of mice. In H-fsMut-NPPA mice mean arterial pressure (MAP) was reduced when compared to H-WT-NPPA and Non-TG mice. Furthermore, injection of synthetic fs-Mut-ANP lowered the MAP in H-WT-NPPA and Non-TG mice while synthetic WT-ANP had no effect on MAP in the 3 groups of mice. ECG characterization revealed significantly prolonged QRS duration in H-fsMut-NPPA mice when compared to the other two groups. Trans-esophageal (TE) atrial pacing of H-fsMut-NPPA mice