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Alteration of tissue inhibitors of matrix metalloproteinases (TIMP)/matrix metalloproteinases (MMP) associated with collagen upregulation has an important role in sustained atrial fibrillation (AF). The expression of miR‐146b‐5p, whose the targeted gene is TIMPs, is upregulated in atrial cardiomyocytes during AF. This study was to determine whether miR‐146b‐5p could regulate the gene expression of TIMP4 and the contribution of miRNA to atrial fibrosis in AF. Collagen synthesis was observed after miR‐146b‐5p transfection in human induced pluripotent stem cell‐derived atrial cardiomyocytes (hiPSC‐aCMs)‐fibroblast co‐culture cellular model in vitro. Furthermore, a myocardial infarction (MI) mouse model was used to confirm the protective effect of miR‐146b‐5p downregulation on atrial fibrosis. The expression level of miR‐146b‐5p was upregulated, while the expression level of TIMP4 was downregulated in the fibrotic atrium of canine with AF. miR‐146b‐5p transfection in hiPSC‐aCMs‐fibroblast co‐culture cellular model increased collagen synthesis by regulating TIMP4/MMP9 mediated extracellular matrix proteins synthesis. The inhibition of miR‐146b‐5p expression reduced the phenotypes of cardiac fibrosis in the MI mouse model. Fibrotic marker MMP9, TGFB1 and COL1A1 were significantly downregulated, while TIMP4 was significantly upregulated (at both mRNA and protein levels) by miR‐146b‐5p inhibition in cardiomyocytes of MI heart. We concluded that collagen fibres were accumulated in extracellular space on miR‐146b‐5p overexpressed co‐culture cellular model. Moreover, the cardiac fibrosis induced by MI was attenuated in antagomiR‐146 treated mice by increasing the expression of TIMP4, which indicated that the inhibition of miR‐146b‐5p might become an effective therapeutic approach for preventing atrial fibrosis.

Background Reduction in L-type Ca2+ current (ICa,L) density is a hallmark of the electrical remodeling in atrial fibrillation (AF). The expression of miR-155, whose predicted target gene is the α1c subunit of the calcium channel (CACNA1C), was upregulated in atrial cardiomyocytes (aCMs) from patients with paroxysmal AF.The study is to determine miR-155 could target the gene expression of ICa,L and contribute to electrical remodeling in AF. Methods The expression of miR-155 and CACNA1C was assessed in aCMs from patients with paroxysmal AF and healthy control. ICa,L properties were observed after miR-155 transfection in human induced pluripotent stem cell derived atrial cardiomyocytes (hiPSC-aCMs). Furthermore, an miR-155 transgene (Tg) and knock-out (KO) mouse model was generated to determine whether miR-155 was involved in ICa,L-related electrical remodeling in AF by targeting CACNA1C. Results The expression level of miR-155 was increased, while the expression level of CACNA1C reduced in the aCMs of patients with AF. miR-155 transfection in hiPSC-aCMs produced changes in ICa,L properties qualitatively similar to those produced by AF. miR-155/Tg mice developed a shortened action potential duration and increased vulnerability to AF, which was associated with decreased ICa,L and attenuated by an miR-155 inhibitor. Finally, the genetic inhibition of miR-155 prevented AF induction in miR-155/KO mice with no changes in ICa,L properties. Conclusions The increased miR-155 expression in aCMs was sufficient for the reduction in the density of ICa,L and the underlying electronic remodeling. The inhibition of miR-155 prevented ICa,L-related electric remodeling in AF and might constitute a novel anti-AF approach targeting electrical remodeling.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have been widely used for the assessment of drug proarrhythmic potential through multielectrode array (MEA). HiPSC-CM cultures beat spontaneously with a wide range of frequencies, however, which could affect drug-induced changes in repolarization. Pacing hiPSC-CMs at a physiological heart rate more closely resembles the state of in vivo ventricular myocytes and permits the standardization of test conditions to improve consistency. In this study, we systematically investigated the time window of stable ion currents in high-purity hiPSC-derived ventricular cardiomyocytes (hiPSC-vCMs) and confirmed that these cells could be used to correctly predict the proarrhythmic risk of Comprehensive In Vitro Proarrhythmia Assay (CiPA) reference compounds. To evaluate drug proarrhythmic potentials at a physiological beating rate, we used a MEA to electrically pace hiPSC-vCMs, and we recorded regular field potential waveforms in hiPSC-vCMs treated with DMSO and 10 CiPA reference drugs. Prolongation of field potential duration was detected in cells after exposure to high- and intermediate-risk drugs; in addition, drug-induced arrhythmia-like events were observed. The results of this study provide a simple and feasible method to investigate drug proarrhythmic potentials in hiPSC-CMs at a physiological beating rate.

Supplemental material, Final-Reversion_Supplemental_Material_for_Assessment_of_cardiac_safety_by_Bai_et_al for Assessment of Drug Proarrhythmic Potential in Electrically Paced Human Induced Pluripotent Stem Cell–Derived Ventricular Cardiomyocytes Using Multielectrode Array by Shuyun Bai, Junjie Pei, Kan Chen, Ya Zhao, Henghua Cao, Luyang Tian, Yue Ma and Haiheng Dong in SLAS Discovery

The combination of non-human primate animals and their induced pluripotent stem cell derived cardiomyocytes (iPSC-CMs) provides not only transplantation models for cell-based therapy of heart diseases, but also opportunities for heart-related drug research on both cellular and animal levels. However, the subtypes and electrophysiology properties of non-human primate iPSC-CMs hadn't been detailed characterized. In this study, we generated rhesus monkey induced pluripotent stem cells (riPSCs), and efficiently differentiated them into ventricular or atrial cardiomyocytes by modulating retinoic acid (RA) pathways. Our results revealed that the electrophysiological characteristics and response to canonical drugs of riPSC-CMs were similar with those of human pluripotent stem cell derived CMs. Therefore, rhesus monkeys and their iPSC-CMs provide a powerful and practicable system for heart related biomedical research.

Most existing culture media for cardiac differentiation of human pluripotent stem cells (hPSCs) contain significant amounts of albumin. For clinical transplantation applications of hPSC-derived cardiomyocytes (hPSC-CMs), culturing cells in an albumin containing environment raises the concern of pathogen contamination and immunogenicity to the recipient patients. In addition, batch-to-batch variation of albumin may cause the inconsistent of hPSC cardiac differentiation. Here, we demonstrated that antioxidants l-ascorbic acid, trolox, N-acetyl-l-cysteine (NAC) and sodium pyruvate could functionally substitute albumin in the culture medium, and formulated an albumin-free, chemical-defined medium (S12 medium). We showed that S12 medium could support efficient hPSC cardiac differentiation with significantly improved reproducibility, and maintained long-term culture of hPSC-CMs. Furthermore, under chemical-defined and albumin-free conditions, human-induced pluripotent stem cells (hiPSCs) were established, and differentiated into highly homogenous atrial and ventricular myocytes in a scalable fashion with normal electrophysiological properties. Finally, we characterized the activity of three typical cardiac ion channels of those cells, and demonstrated that hPSC-derived ventricular cardiomyocytes (hPSC-vCMs) were suitable for drug cardiac safety evaluation. In summary, this simplified, chemical-defined and albumin-free culture medium supports efficient generation and maintaining of hPSC-CMs and facilitates both research and clinical applications of these cells.

Whether large conductance Ca(2+)-activated potassium (BK) channels are present in the substantia nigra pars reticulata (SNr) is a matter of debate. Using the patch-clamp technique, we examined the functional expression of BK channels in neurons of the SNr and showed that the channels were activated or inhibited by internal high-energy phosphates (IHEPs) at positive and negative membrane potentials, respectively. SNr neurons showed membrane potential hyperpolarization under glucose-deprivation conditions which was attenuated by paxilline, a specific BK channel blocker. In addition, Fluo-3 fluorescence recording detected an increase in the level of internal free calcium ([Ca(2+)](i)) during ischemic hyperpolarization. These results confirm that BK channels are present in SNr neurons and indicate that their unique IHEP sensitivity is requisite in neuronal ischemic responses. Bearing in mind that the K(ATP) channel blocker tolbutamide also attenuated the hyperpolarization, we suggest that BK channels may play a protective role in the basal ganglia by modulating the excitability of SNr neurons along with K(ATP) channels under ischemic stresses.

Redox activity is an important property of living cells, and decreases in redox activity are likely to be an upstream event in ischemic brain injuries. In this study, immediate changes in redox activity caused by ischemic injury were investigated in oxygen-glucose deprivation (OGD) treated mouse brain tissue. Adult mouse brain slices were subjected to 10 min or 15 min OGD treatments and were immediately stained with an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) staining procedure. After 10 min OGD, the redox activity decreased in the lateral globus pallidus (LGP), medial globus pallidus (MGP), pyramidal cell layer of hippocampus CA1 (CA1(PL)) and the granular layer of the cerebellum (cereb(GL)). After 15 min OGD, decreases also occurred in the substantia nigra (SN) and several other areas of the brain stem. Hoechst 33342 was used to confirm that changes in redox activity occurred before morphological alterations in the cellular nuclei--morphological changes were not observed even after a 60 min OGD. The results presented here indicate that functional ischemic vulnerability exists in several brain regions, and will be helpful for systematic research on mammalian brain injury caused by transient metabolic stress.