Macrophage IL-1ß mediates atrial fibrillation risk in diabetic mice.

Diabetes mellitus (DM) is an independent risk factor for atrial fibrillation (AF). The mechanisms underlying DM-associated AF are unclear. AF and DM are both related to inflammation. We investigated whether DM-associated inflammation contributed to AF risk. Mice were fed with high-fat diet to induce type II DM and were subjected to IL-1ß antibodies, macrophage depletion by clodronate liposomes, a mitochondrial antioxidant (mitoTEMPO), or a cardiac ryanodine receptor 2 (RyR2) stabilizer (S107). All tests were performed at 36-38 weeks of age. DM mice presented with increased AF inducibility, enhanced mitochondrial reactive oxygen species (mitoROS) generation, and activated innate immunity in the atria, as evidenced by enhanced monocyte chemoattractant protein-1 (MCP-1) expression, macrophage infiltration, and IL-1ß levels. Signs of aberrant RyR2 Ca2+ leak were observed in the atria of DM mice. IL-1ß neutralization, macrophage depletion, and exposure to mitoTEMPO and S107 significantly ameliorated the AF vulnerability in DM mice. Atrial overexpression of MCP-1 increased AF occurrence in normal mice through the same mechanistic signaling cascade as observed in DM mice. In conclusion, macrophage-mediated IL-1ß contributed to DM-associated AF risk through mitoROS modulation of RyR2 Ca2+ leak.

Cardiac Development Long Non-Coding RNA (CARDEL) Is Activated during Human Heart Development and Contributes to Cardiac Specification and Homeostasis.

Successful heart development depends on the careful orchestration of a network of transcription factors and signaling pathways. In recent years, in vitro cardiac differentiation using human pluripotent stem cells (hPSCs) has been used to uncover the intricate gene-network regulation involved in the proper formation and function of the human heart. Here, we searched for uncharacterized cardiac-development genes by combining a temporal evaluation of human cardiac specification in vitro with an analysis of gene expression in fetal and adult heart tissue. We discovered that CARDEL (CARdiac DEvelopment Long non-coding RNA; LINC00890; SERTM2) expression coincides with the commitment to the cardiac lineage. CARDEL knockout hPSCs differentiated poorly into cardiac cells, and hPSC-derived cardiomyocytes showed faster beating rates after controlled overexpression of CARDEL during differentiation. Altogether, we provide physiological and molecular evidence that CARDEL expression contributes to sculpting the cardiac program during cell-fate commitment.

Atrial Myopathy Quantified by Speckle-tracking Echocardiography in Mice.

BACKGROUND: Emerging evidence suggests that atrial myopathy may be the underlying pathophysiology that explains adverse cardiovascular outcomes in heart failure (HF) and atrial fibrillation. Lower left atrial (LA) function (strain) is a key biomarker of atrial myopathy, but murine LA strain has not been described, thus limiting translational investigation. Therefore, the objective of this study was to characterize LA function by speckle-tracking echocardiography in mouse models of atrial myopathy. METHODS: We used 3 models of atrial myopathy in wild-type male and female C57Bl6/J mice: (1) aged 16 to 17 months, (2) Ang II (angiotensin II) infusion, and (3) high-fat diet+Nω-nitro-L-arginine methyl ester (HF with preserved ejection fraction, HFpEF). LA reservoir, conduit, and contractile strain were measured using speckle-tracking echocardiography from a modified parasternal long-axis window. Left ventricular systolic and diastolic function, and global longitudinal strain were also measured. Transesophageal rapid atrial pacing was used to induce atrial fibrillation. RESULTS: LA reservoir, conduit, and contractile strain were significantly reduced in aged, Ang II and HFpEF mice compared with young controls. There were no sex-based interactions. Left ventricular diastolic function and global longitudinal strain were lower in aged, Ang II and HFpEF, but left ventricular ejection fraction was unchanged. Atrial fibrillation inducibility was low in young mice (5%), moderately higher in aged mice (20%), and high in Ang II (75%) and HFpEF (83%) mice. CONCLUSIONS: Using speckle-tracking echocardiography, we observed reduced LA function in established mouse models of atrial myopathy with concurrent atrial fibrillation inducibility, thus providing the field with a timely and clinically relevant platform for understanding the pathophysiology and discovery of novel treatment targets for atrial myopathy.

Beyond Ion Homeostasis: Hypomagnesemia, Transient Receptor Potential Melastatin Channel 7, Mitochondrial Function, and Inflammation.

As the second most abundant intracellular divalent cation, magnesium (Mg2+) is essential for cell functions, such as ATP production, protein/DNA synthesis, protein activity, and mitochondrial function. Mg2+ plays a critical role in heart rhythm, muscle contraction, and blood pressure. A significant decline in Mg2+ intake has been reported in developed countries because of the increased consumption of processed food and filtered/deionized water, which can lead to hypomagnesemia (HypoMg). HypoMg is commonly observed in cardiovascular diseases, such as heart failure, hypertension, arrhythmias, and diabetic cardiomyopathy, and HypoMg is a predictor for cardiovascular and all-cause mortality. On the other hand, Mg2+ supplementation has shown significant therapeutic effects in cardiovascular diseases. Some of the effects of HypoMg have been ascribed to changes in Mg2+ participation in enzyme activity, ATP stabilization, enzyme kinetics, and alterations in Ca2+, Na+, and other cations. In this manuscript, we discuss new insights into the pathogenic mechanisms of HypoMg that surpass previously described effects. HypoMg causes mitochondrial dysfunction, oxidative stress, and inflammation. Many of these effects can be attributed to the HypoMg-induced upregulation of a Mg2+ transporter transient receptor potential melastatin 7 channel (TRMP7) that is also a kinase. An increase in kinase signaling mediated by HypoMg-induced TRPM7 transcriptional upregulation, independently of any change in Mg2+ transport function, likely seems responsible for many of the effects of HypoMg. Therefore, Mg2+ supplementation and TRPM7 kinase inhibition may work to treat the sequelae of HypoMg by preventing increased TRPM7 kinase activity rather than just altering ion homeostasis. Since many diseases are characterized by oxidative stress or inflammation, Mg2+ supplementation and TRPM7 kinase inhibition may have wider implications for other diseases by acting to reduce oxidative stress and inflammation.

Lysosomal Ca2+ flux modulates automaticity in ventricular cardiomyocytes and correlates with arrhythmic risk.

Automaticity involves Ca2+ handling at the cell membrane and sarcoplasmic reticulum (SR). Abnormal or acquired automaticity is thought to initiate ventricular arrhythmias associated with myocardial ischemia. Ca2+ flux from mitochondria can influence automaticity, and lysosomes also release Ca2+. Therefore, we tested whether lysosomal Ca2+ flux could influence automaticity. We studied ventricular human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), hiPSC 3D engineered heart tissues (EHTs), and ventricular cardiomyocytes isolated from infarcted mice. Preventing lysosomal Ca2+ cycling reduced automaticity in hiPSC-CMs. Consistent with a lysosomal role in automaticity, activating the transient receptor potential mucolipin channel (TRPML1) enhanced automaticity, and two channel antagonists reduced spontaneous activity. Activation or inhibition of lysosomal transcription factor EB (TFEB) increased or decreased total lysosomes and automaticity, respectively. In adult ischemic cardiomyocytes and hiPSC 3D EHTs, reducing lysosomal Ca2+ release also inhibited automaticity. Finally, TRPML1 was up-regulated in cardiomyopathic patients with ventricular tachycardia (VT) compared with those without VT. In summary, lysosomal Ca2+ handling modulates abnormal automaticity, and reducing lysosomal Ca2+ release may be a clinical strategy for preventing ventricular arrhythmias.

TRPM7 kinase mediates hypomagnesemia-induced seizure-related death.

Hypomagnesemia (HypoMg) can cause seizures and death, but the mechanism is unknown. Transient receptor potential cation channel subfamily M 7 (TRPM7) is a Mg transporter with both channel and kinase function. In this study, we focused on the kinase role of TRPM7 in HypoMg-induced seizures and death. Wild type C57BL/6J mice and transgenic mice with a global homozygous mutation in the TRPM7 kinase domain (TRPM7K1646R, with no kinase function) were fed with control diet or a HypoMg diet. After 6 weeks of HypoMg diet, mice had significantly decreased serum Mg, elevated brain TRPM7, and a significant rate of death, with females being most susceptible. Deaths were immediately preceded by seizure events. TRPM7K1646R mice showed resistance to seizure-induced death. HypoMg-induced brain inflammation and oxidative stress were suppressed by TRPM7K1646R. Compared to their male counterparts, HypoMg female mice had higher levels of inflammation and oxidative stress in the hippocampus. We concluded that TRPM7 kinase function contributes seizure-induced deaths in HypoMg mice and that inhibiting the kinase reduced inflammation and oxidative stress.

Inflammatory Macrophage Interleukin-1ß Mediates High-Fat Diet-Induced Heart Failure With Preserved Ejection Fraction.

Diabetes mellitus (DM) is a main risk factor for diastolic dysfunction (DD) and heart failure with preserved ejection fraction. High-fat diet (HFD) mice presented with diabetes mellitus, DD, higher cardiac interleukin (IL)-1ß levels, and proinflammatory cardiac macrophage accumulation. DD was significantly ameliorated by suppressing IL-1ß signaling or depleting macrophages. Mice with macrophages unable to adopt a proinflammatory phenotype were low in cardiac IL-1ß levels and were resistant to HFD-induced DD. IL-1ß enhanced mitochondrial reactive oxygen species (mitoROS) in cardiomyocytes, and scavenging mitoROS improved HFD-induced DD. In conclusion, macrophage-mediated inflammation contributed to HFD-associated DD through IL-1ß and mitoROS production.

miR-448 regulates potassium voltage-gated channel subfamily A member 4 (KCNA4) in ischemia and heart failure.

BACKGROUND: MicroRNA miR-448 mediates some of the effects of ischemia on arrhythmic risk. Potassium voltage-gated channel subfamily A member 4 (KCNA4) encodes a Kv1.4 current that opens in response to membrane depolarization and is essential for regulating the action potential duration in heart. KCNA4 has a miR-448 binding site. OBJECTIVE: We investigated whether miR-448 was involved in the regulation of KCNA4 messenger RNA expression in ischemia. METHODS: Quantitative real-time reverse-transcriptase polymerase chain reaction was used to investigate the expression of KCNA4 and miR-448. Pull-down assays were used to examine the interaction between miR-448 and KCNA4. miR-448 decoy and binding site mutation were used to examine the specificity of the effect for KCNA4. RESULTS: The expression of KCNA4 is diminished in ischemia and human heart failure tissues with ventricular tachycardia. Previously, we have shown that miR-448 is upregulated in ischemia and inhibition can prevent arrhythmic risk after myocardial infarction. The 3'-untranslated region of KCNA4 has a conserved miR-448 binding site. miR-448 bound to this site directly and reduced KCNA4 expression and the transient outward potassium current. Inhibition of miR-448 restored KCNA4. CONCLUSION: These findings showed a link between Kv1.4 downregulation and miR-448-mediated upregulation in ischemia, suggesting a new mechanism for the antiarrhythmic effect of miR-448 inhibition.

Reduced sarcoplasmic reticulum Ca2+ pump activity is antiarrhythmic in ischemic cardiomyopathy.

BACKGROUND: We have described an arrhythmic mechanism seen only in cardiomyopathy that involves increased mitochondrial Ca2+ handling and selective transfer of Ca2+ to the sarcoplasmic reticulum (SR). Modeling suggested that mitochondrial Ca2+ transfer to the SR via type 2a sarco/endoplasmic reticulum Ca2+-ATPase (SERCA2a) is a crucial element of this arrhythmic mechanism. OBJECTIVE: We tested the role of SERCA2a in arrhythmias during ischemic cardiomyopathy. METHODS: Myocardial infarction (MI) was induced in wild-type (Wt) and SERCA2a heterozygous knockdown (SERCA+/-) mice. RESULTS: Compared with Wt MI mice, SERCA2a heterozygous knockdown (SERCA+/-) MI mice had a substantially lower mortality after 3 weeks of MI without a significant change in MI area. Aside from a significant delay of the cytoplasmic Ca2+ transient decay existed in SERCA+/- compared with Wt, SERCA+/- did not affect cardiac systolic and diastolic function at the whole organ or single cell levels either before or after MI. After MI, SERCA+/- mice had reduced SERCA2a expression in the MI border zone compared with Wt MI mice. SERCA+/- mice had significantly decreased corrected QT intervals and less ventricular tachycardia compared with Wt MI mice. SERCA+/- cardiomyocytes from MI mice showed a reduced action potential duration and reduced triggered activity compared with Wt MI cardiomyocytes. Reduction in arrhythmic risk was accompanied by reduced diastolic SR Ca2+ sparks, reduced SR Ca2+ content, reduced oxidized ryanodine receptor, and increased calsequestrin 2 in SERCA+/- MI mice. CONCLUSION: SERCA2a knockdown was antiarrhythmic after MI without affecting overall systolic performance. Possible antiarrhythmic mechanisms included reduced SR free Ca2+ and reduced diastolic SR Ca2+ release.

Dual inhibition of MAPK and PI3K/AKT pathways enhances maturation of human iPSC-derived cardiomyocytes.

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) provide great opportunities for mechanistic dissection of human cardiac pathophysiology; however, hiPSC-CMs remain immature relative to the adult heart. To identify novel signaling pathways driving the maturation process during heart development, we analyzed published transcriptional and epigenetic datasets from hiPSC-CMs and prenatal and postnatal human hearts. These analyses revealed that several components of the MAPK and PI3K-AKT pathways are downregulated in the postnatal heart. Here, we show that dual inhibition of these pathways for only 5 days significantly enhances the maturation of day 30 hiPSC-CMs in many domains: hypertrophy, multinucleation, metabolism, T-tubule density, calcium handling, and electrophysiology, many equivalent to day 60 hiPSC-CMs. These data indicate that the MAPK/PI3K/AKT pathways are involved in cardiomyocyte maturation and provide proof of concept for the manipulation of key signaling pathways for optimal hiPSC-CM maturation, a critical aspect of faithful in vitro modeling of cardiac pathologies and subsequent drug discovery.

Circulating S-Glutathionylated cMyBP-C as a Biomarker for Cardiac Diastolic Dysfunction.

Background cMyBP-C (Cardiac myosin binding protein-C) regulates cardiac contraction and relaxation. Previously, we demonstrated that elevated myocardial S-glutathionylation of cMyBP-C correlates with diastolic dysfunction (DD) in animal models. In this study, we tested whether circulating S-glutathionylated cMyBP-C would be a biomarker for DD. Methods and Results Humans, African Green monkeys, and mice had DD determined by echocardiography. Blood samples were acquired and analyzed for S-glutathionylated cMyBP-C by immunoprecipitation. Circulating S-glutathionylated cMyBP-C in human participants with DD (n=24) was elevated (1.46±0.13-fold, P=0.014) when compared with the non-DD controls (n=13). Similarly, circulating S-glutathionylated cMyBP-C was upregulated by 2.13±0.47-fold (P=0.047) in DD monkeys (n=6), and by 1.49 (1.22-2.06)-fold (P=0.031) in DD mice (n=5) compared with the respective non-DD controls. Circulating S-glutathionylated cMyBP-C was positively correlated with DD in humans. Conclusions Circulating S-glutathionylated cMyBP-C was elevated in humans, monkeys, and mice with DD. S-glutathionylated cMyBP-C may represent a novel biomarker for the presence of DD.

Preventing unfolded protein response-induced ion channel dysregulation to treat arrhythmias.

Cardiomyopathies are associated with arrhythmias and cardiac ion channel downregulation. This downregulation is arrhythmogenic. Paradoxically, antiarrhythmic therapies are based on ion channel-blocking drugs that further downregulate these channels and exhibit proarrhythmic risk. Recent studies have shown that inhibition of the protein kinase RNA-like ER kinase (PERK) arm of the unfolded protein response (UPR) prevents select cardiac ion channel downregulation and plays a protective role against arrhythmias. Prevention of ion channel downregulation represents as a novel therapeutic strategy to treat arrhythmias in myocardial infarction and heart failure.

The genomics of heart failure: design and rationale of the HERMES consortium.

AIMS: The HERMES (HEart failure Molecular Epidemiology for Therapeutic targetS) consortium aims to identify the genomic and molecular basis of heart failure. METHODS AND RESULTS: The consortium currently includes 51 studies from 11 countries, including 68 157 heart failure cases and 949 888 controls, with data on heart failure events and prognosis. All studies collected biological samples and performed genome-wide genotyping of common genetic variants. The enrolment of subjects into participating studies ranged from 1948 to the present day, and the median follow-up following heart failure diagnosis ranged from 2 to 116 months. Forty-nine of 51 individual studies enrolled participants of both sexes; in these studies, participants with heart failure were predominantly male (34-90%). The mean age at diagnosis or ascertainment across all studies ranged from 54 to 84 years. Based on the aggregate sample, we estimated 80% power to genetic variant associations with risk of heart failure with an odds ratio of ≥1.10 for common variants (allele frequency ≥ 0.05) and ≥1.20 for low-frequency variants (allele frequency 0.01-0.05) at P < 5 × 10-8 under an additive genetic model. CONCLUSIONS: HERMES is a global collaboration aiming to (i) identify the genetic determinants of heart failure; (ii) generate insights into the causal pathways leading to heart failure and enable genetic approaches to target prioritization; and (iii) develop genomic tools for disease stratification and risk prediction.

Cardiac Resynchronization and Circulating Markers of Sarcoplasmic Reticulum Calcium Handling and Sudden Death Risk.

Cardiac resynchronization therapy (CRT) can improve heart function and decrease arrhythmic events. We tested whether CRT altered circulating markers of calcium handling and sudden death risk. Circulating cardiac sodium channel messenger RNA (mRNA) splicing variants indicate arrhythmic risk, and a reduction in sarco/endoplasmic reticulum calcium adenosine triphosphatase 2a (SERCA2a) is thought to diminish contractility in heart failure. CRT was associated with a decreased proportion of circulating, nonfunctional sodium channels and improved SERCA2a mRNA expression. Patients without CRT did not have improvement in the biomarkers. These changes might explain the lower arrhythmic risk and improved contractility associated with CRT.

Inhibition of the unfolded protein response reduces arrhythmia risk after myocardial infarction.

Ischemic cardiomyopathy is associated with an increased risk of sudden death, activation of the unfolded protein response (UPR), and reductions in multiple cardiac ion channels. When activated, the protein kinase-like ER kinase (PERK) branch of the UPR reduces protein translation and abundance. We hypothesized that PERK inhibition could prevent ion channel downregulation and reduce arrhythmia risk after myocardial infarct (MI). MI induced in mice by coronary artery ligation resulted in reduced ion channel levels, ventricular tachycardia (VT), and prolonged corrected intervals between the Q and T waves on the ECGs (QTc). Protein levels of major cardiac ion channels were decreased. MI cardiomyocytes showed significantly prolonged action potential duration and decreased maximum upstroke velocity. Cardiac-specific PERK KO reduced electrical remodeling in response to MI, with shortened QTc intervals, fewer VT episodes, and higher survival rates. Pharmacological PERK inhibition had similar effects. In conclusion, we found that activated PERK during MI contributed to arrhythmia risk by the downregulation of select cardiac ion channels. PERK inhibition prevented these changes and reduced arrhythmia risk. These results suggest that ion channel downregulation during MI is a fundamental arrhythmia mechanism and that maintenance of ion channel levels is antiarrhythmic.

Magnesium Deficiency Causes a Reversible, Metabolic, Diastolic Cardiomyopathy.

Background Dietary Mg intake is associated with a decreased risk of developing heart failure, whereas low circulating Mg level is associated with increased cardiovascular mortality. We investigated whether Mg deficiency alone could cause cardiomyopathy. Methods and Results C57BL/6J mice were fed with a low Mg (low-Mg, 15-30 mg/kg Mg) or a normal Mg (nl-Mg, 600 mg/kg Mg) diet for 6 weeks. To test reversibility, half of the low-Mg mice were fed then with nl-Mg diet for another 6 weeks. Low-Mg diet significantly decreased mouse serum Mg (0.38±0.03 versus 1.14±0.03 mmol/L for nl-Mg; P<0.0001) with a reciprocal increase in serum Ca, K, and Na. Low-Mg mice exhibited impaired cardiac relaxation (ratio between mitral peak early filling velocity E and longitudinal tissue velocity of the mitral anterior annulus e, 21.1±1.1 versus 15.4±0.4 for nl-Mg; P=0.011). Cellular ATP was decreased significantly in low-Mg hearts. The changes were accompanied by mitochondrial dysfunction with mitochondrial reactive oxygen species overproduction and membrane depolarization. cMyBPC (cardiac myosin-binding protein C) was S-glutathionylated in low-Mg mouse hearts. All these changes were normalized with Mg repletion. In vivo (2-(2,2,6,6-tetramethylpiperidin-1-oxyl-4-ylamino)-2-oxoethyl)triphenylphosphonium chloride treatment during low-Mg diet improved cardiac relaxation, increased ATP levels, and reduced S-glutathionylated cMyBPC. Conclusions Mg deficiency caused a reversible diastolic cardiomyopathy associated with mitochondrial dysfunction and oxidative modification of cMyBPC. In deficiency states, Mg supplementation may represent a novel treatment for diastolic heart failure.

Frequent Premature Atrial Contractions Are Associated With Poorer Cognitive Function in the Atherosclerosis Risk in Communities (ARIC) Study.

OBJECTIVE: To evaluate the association of premature atrial contraction (PAC) frequency with cognitive test scores and prevalence of dementia or mild cognitive impairment (MCI). MATERIALS AND METHODS: We conducted a cross-sectional analysis using Atherosclerosis Risk in Communities study visit 6 (January 1, 2016, through December 31, 2017) data. We included 2163 participants without atrial fibrillation (AF) (age mean ± SD, 79±4 years; 1273 (58.9%) female; and 604 (27.97.0% Black) who underwent cognitive testing and wore a leadless, ambulatory electrocardiogram monitor for 14 days. We categorized PAC frequency based on the percent of beats: less than 1%, minimal; 1% to <5%, occasional; greater than or equal to 5%, frequent. We derived cognitive domain-specific factor scores (memory, executive function, language, and global z-score). Dementia and MCI were adjudicated. RESULTS: During a mean analyzable time of 12.6±2.6 days, 339 (15.7%) had occasional PACs and 107 (4.9%) had frequent PACs. Individuals with frequent PACs (vs minimal) had lower executive function factor scores by 0.30 (95% CI, -0.46 to -0.14) and lower global factor scores by 0.20 (95% CI, -0.33 to -0.07) after multivariable adjustment. Individuals with frequent PACs (vs minimal) had higher odds of prevalent dementia or MCI after multivariable adjustment (odds ratio, 1.74; 95% CI, 1.09 to 2.79). These associations were unchanged with additional adjustment for stroke. CONCLUSION: In community-dwelling older adults without AF, frequent PACs were cross-sectionally associated with lower executive and global cognitive function and greater prevalence of dementia or MCI, independently of stroke. Our findings lend support to the notion that atrial cardiomyopathy may be a driver of AF-related outcomes. Further research to confirm these associations prospectively and to elucidate underlying mechanisms is warranted.