BIN1 knockdown rescues systolic dysfunction in aging male mouse hearts.

Cardiac dysfunction is a hallmark of aging in humans and mice. Here we report that a two-week treatment to restore youthful Bridging Integrator 1 (BIN1) levels in the hearts of 24-month-old mice rejuvenates cardiac function and substantially reverses the aging phenotype. Our data indicate that age-associated overexpression of BIN1 occurs alongside dysregulated endosomal recycling and disrupted trafficking of cardiac CaV1.2 and type 2 ryanodine receptors. These deficiencies affect channel function at rest and their upregulation during acute stress. In vivo echocardiography reveals reduced systolic function in old mice. BIN1 knockdown using an adeno-associated virus serotype 9 packaged shRNA-mBIN1 restores the nanoscale distribution and clustering plasticity of ryanodine receptors and recovers Ca2+ transient amplitudes and cardiac systolic function toward youthful levels. Enhanced systolic function correlates with increased phosphorylation of the myofilament protein cardiac myosin binding protein-C. These results reveal BIN1 knockdown as a novel therapeutic strategy to rejuvenate the aging myocardium.

Disruption of protein quality control of the human ether-à-go-go related gene K+ channel results in profound long QT syndrome.

BACKGROUND: Long QT syndrome (LQTS) is a hereditary disease that predisposes patients to life-threatening cardiac arrhythmias and sudden cardiac death. Our previous study of the human ether-à-go-go related gene (hERG)-encoded K+ channel (Kv11.1) supports an association between hERG and RING finger protein 207 (RNF207) variants in aggravating the onset and severity of LQTS, specifically T613M hERG (hERGT613M) and RNF207 frameshift (RNF207G603fs) mutations. However, the underlying mechanistic underpinning remains unknown. OBJECTIVE: The purpose of the present study was to test the role of RNF207 in the function of hERG-encoded K+ channel subunits. METHODS: Whole-cell patch-clamp experiments were performed in human embryonic kidney (HEK 293) cells and human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) together with immunofluorescent confocal and high resolution microscopy, auto-ubiquitinylation assays, and co-immunoprecipitation experiments to test the functional interactions between hERG and RNF207. RESULTS: Here, we demonstrated that RNF207 serves as an E3 ubiquitin ligase and targets misfolded hERGT613M proteins for degradation. RNF207G603fs exhibits decreased activity and hinders the normal degradation pathway; this increases the levels of hERGT613M subunits and their dominant-negative effect on the wild-type subunits, ultimately resulting in decreased current density. Similar findings are shown for hERGA614V, a known dominant-negative mutant subunit. Finally, the presence of RNF207G603fs with hERGT613M results in significantly prolonged action potential durations and reduced hERG current in human-induced pluripotent stem cell-derived cardiomyocytes. CONCLUSION: Our study establishes RNF207 as an interacting protein serving as a ubiquitin ligase for hERG-encoded K+ channel subunits. Normal function of RNF207 is critical for the quality control of hERG subunits and consequently cardiac repolarization. Moreover, our study provides evidence for protein quality control as a new paradigm in life-threatening cardiac arrhythmias in patients with LQTS.

The Critical Roles of Proteostasis and Endoplasmic Reticulum Stress in Atrial Fibrillation.

Atrial fibrillation (AF) remains the most common arrhythmia seen clinically. The incidence of AF is increasing due to the aging population. AF is associated with a significant increase in morbidity and mortality, yet current treatment paradigms have proven largely inadequate. Therefore, there is an urgent need to develop new effective therapeutic strategies for AF. The endoplasmic reticulum (ER) in the heart plays critical roles in the regulation of excitation-contraction coupling and cardiac function. Perturbation in the ER homeostasis due to intrinsic and extrinsic factors, such as inflammation, oxidative stress, and ischemia, leads to ER stress that has been linked to multiple conditions including diabetes mellitus, neurodegeneration, cancer, heart disease, and cardiac arrhythmias. Recent studies have documented the critical roles of ER stress in the pathophysiological basis of AF. Using an animal model of chronic pressure overload, we demonstrate a significant increase in ER stress in atrial tissues. Moreover, we demonstrate that treatment with a small molecule inhibitor to inhibit the soluble epoxide hydrolase enzyme in the arachidonic acid metabolism significantly reduces ER stress as well as atrial electrical and structural remodeling. The current review article will attempt to provide a perspective on our recent understandings and current knowledge gaps on the critical roles of proteostasis and ER stress in AF progression.

AKAP5 complex facilitates purinergic modulation of vascular L-type Ca2+ channel CaV1.2.

The L-type Ca2+ channel CaV1.2 is essential for arterial myocyte excitability, gene expression and contraction. Elevations in extracellular glucose (hyperglycemia) potentiate vascular L-type Ca2+ channel via PKA, but the underlying mechanisms are unclear. Here, we find that cAMP synthesis in response to elevated glucose and the selective P2Y11 agonist NF546 is blocked by disruption of A-kinase anchoring protein 5 (AKAP5) function in arterial myocytes. Glucose and NF546-induced potentiation of L-type Ca2+ channels, vasoconstriction and decreased blood flow are prevented in AKAP5 null arterial myocytes/arteries. These responses are nucleated via the AKAP5-dependent clustering of P2Y11/ P2Y11-like receptors, AC5, PKA and CaV1.2 into nanocomplexes at the plasma membrane of human and mouse arterial myocytes. Hence, data reveal an AKAP5 signaling module that regulates L-type Ca2+ channel activity and vascular reactivity upon elevated glucose. This AKAP5-anchored nanocomplex may contribute to vascular complications during diabetic hyperglycemia.

Suppression of inflammation and fibrosis using soluble epoxide hydrolase inhibitors enhances cardiac stem cell-based therapy.

Stem cell replacement offers a great potential for cardiac regenerative therapy. However, one of the critical barriers to stem cell therapy is a significant loss of transplanted stem cells from ischemia and inflammation in the host environment. Here, we tested the hypothesis that inhibition of the soluble epoxide hydrolase (sEH) enzyme using sEH inhibitors (sEHIs) to decrease inflammation and fibrosis in the host myocardium may increase the survival of the transplanted human induced pluripotent stem cell derived-cardiomyocytes (hiPSC-CMs) in a murine postmyocardial infarction model. A specific sEHI (1-trifluoromethoxyphenyl-3-(1-propionylpiperidine-4-yl)urea [TPPU]) and CRISPR/Cas9 gene editing were used to test the hypothesis. TPPU results in a significant increase in the retention of transplanted cells compared with cell treatment alone. The increase in the retention of hiPSC-CMs translates into an improvement in the fractional shortening and a decrease in adverse remodeling. Mechanistically, we demonstrate a significant decrease in oxidative stress and apoptosis not only in transplanted hiPSC-CMs but also in the host environment. CRISPR/Cas9-mediated gene silencing of the sEH enzyme reduces cleaved caspase-3 in hiPSC-CMs challenged with angiotensin II, suggesting that knockdown of the sEH enzyme protects the hiPSC-CMs from undergoing apoptosis. Our findings demonstrate that suppression of inflammation and fibrosis using an sEHI represents a promising adjuvant to cardiac stem cell-based therapy. Very little is known regarding the role of this class of compounds in stem cell-based therapy. There is consequently an enormous opportunity to uncover a potentially powerful class of compounds, which may be used effectively in the clinical setting.

Adenylyl cyclase 5-generated cAMP controls cerebral vascular reactivity during diabetic hyperglycemia.

Elevated blood glucose (hyperglycemia) is a hallmark metabolic abnormality in diabetes. Hyperglycemia is associated with protein kinase A (PKA)-mediated stimulation of L-type Ca2+ channels in arterial myocytes resulting in increased vasoconstriction. However, the mechanisms by which glucose activates PKA remain unclear. Here, we showed that elevating extracellular glucose stimulates cAMP production in arterial myocytes, and that this was specifically dependent on adenylyl cyclase 5 (AC5) activity. Super-resolution imaging suggested nanometer proximity between subpopulations of AC5 and the L-type Ca2+ channel pore-forming subunit CaV1.2. In vitro, in silico, ex vivo and in vivo experiments revealed that this close association is critical for stimulation of L-type Ca2+ channels in arterial myocytes and increased myogenic tone upon acute hyperglycemia. This pathway supported the increase in L-type Ca2+ channel activity and myogenic tone in two animal models of diabetes. Our collective findings demonstrate a unique role for AC5 in PKA-dependent modulation of L-type Ca2+ channel activity and vascular reactivity during acute hyperglycemia and diabetes.

Feedback mechanisms for cardiac-specific microRNAs and cAMP signaling in electrical remodeling.

BACKGROUND: Loss of transient outward K(+) current (Ito) is well documented in cardiac hypertrophy and failure both in animal models and in humans. Electrical remodeling contributes to prolonged action potential duration and increased incidence of arrhythmias. Furthermore, there is a growing body of evidence linking microRNA (miR) dysregulation to the progression of both conditions. In this study, we examined the mechanistic basis underlying miR dysregulation in electrical remodeling and revealed a novel interaction with the adrenergic signaling pathway. METHODS AND RESULTS: We first used a tissue-specific knockout model of Dicer1 in cardiomyocytes to reveal the overall regulatory effect of miRs on the ionic currents and action potentials. We then validated the inducible cAMP early repressor as a target of miR-1 and took advantage of a clinically relevant model of post myocardial infarction and miR delivery to probe the mechanistic basis of miR dysregulation in electrical remodeling. These experiments revealed the role of inducible cAMP early repressor as a repressor of miR-1 and Ito, leading to prolonged action potential duration post myocardial infarction. In addition, delivery of miR-1 and miR-133a suppressed inducible cAMP early repressor expression and prevented both electrical remodeling and hypertrophy. CONCLUSIONS: Taken together, our results illuminate the mechanistic links between miRs, adrenergic signaling, and electrical remodeling. They also serve as a proof-of-concept for the therapeutic potential of miR delivery post myocardial infarction.

MicroRNA profiling predicts a variance in the proliferative potential of cardiac progenitor cells derived from neonatal and adult murine hearts.

Cardiac progenitor cells (CPCs) are multipotent cells that may offer tremendous potentials for the regeneration of injured myocardium. To expand the limited number of CPCs for effective clinical regeneration of myocardium, it is important to understand their proliferative potentials. Single-cell based assays were utilized to purify c-kit(pos) CPCs from human and mouse hearts. MicroRNA profiling identified eight differentially expressed microRNAs in CPCs from neonatal and adult hearts. Notably, the predicted protein targets were predominantly involved in cellular proliferation-related pathways. To directly test this phenotypic prediction, the developmental variance in the proliferation of CPCs was tested. Ki67 protein expression and DNA kinetics were tested in human and mouse in vivo CPCs, and doubling times were tested in primary culture of mouse CPCs. The human embryonic and mouse neonatal CPCs showed a six-fold increase in Ki67 expressing cells, a two-fold increase in the number of cells in S/G2-M phases of cell cycle, and a seven-fold increase in the doubling time in culture when compared to the corresponding adult CPCs. The over-expression of miR-17-92 increased the proliferation in adult CPCs in vivo by two-fold. In addition, the level of retinoblastoma-like 2 (Rbl2/p130) protein was two-fold higher in adult compared to neonatal-mouse CPCs. In conclusion, we demonstrate a differentially regulated cohort of microRNAs that predicts differences in cellular proliferation in CPCs during postnatal development and target microRNAs that are involved in this transition. Our study provides new insights that may enhance the utilization of adult CPCs for regenerative therapy of the injured myocardium.