The Kir2.1E299V mutation increases atrial fibrillation vulnerability while protecting the ventricles against arrhythmias in a mouse model of short QT syndrome type 3

AIMS

Short QT syndrome type 3 (SQTS3) is a rare arrhythmogenic disease caused by gain-of-function mutations in KCNJ2, the gene coding the inward rectifier potassium channel Kir2.1. We used a multidisciplinary approach and investigated arrhythmogenic mechanisms in an in-vivo model of de-novo mutation Kir2.1E299V identified in a patient presenting an extremely abbreviated QT interval and paroxysmal atrial fibrillation.

METHODS AND RESULTS

We used intravenous adeno-associated virus-mediated gene transfer to generate mouse models, and confirmed cardiac-specific expression of Kir2.1WT or Kir2.1E299V. On ECG, the Kir2.1E299V mouse recapitulated the QT interval shortening and the atrial-specific arrhythmia of the patient. The PR interval was also significantly shorter in Kir2.1E299V mice. Patch-clamping showed extremely abbreviated action potentials in both atrial and ventricular Kir2.1E299V cardiomyocytes due to a lack of inward-going rectification and increased IK1 at voltages positive to -80 mV. Relative to Kir2.1WT, atrial Kir2.1E299V cardiomyocytes had a significantly reduced slope conductance at voltages negative to -80 mV. After confirming a higher proportion of heterotetrameric Kir2.x channels containing Kir2.2 subunits in the atria, in-silico 3D simulations predicted an atrial-specific impairment of polyamine block and reduced pore diameter in the Kir2.1E299V-Kir2.2WT channel. In ventricular cardiomyocytes, the mutation increased excitability by shifting INa activation and inactivation in the hyperpolarizing direction, which protected the ventricle against arrhythmia. Moreover, Purkinje myocytes from Kir2.1E299V mice manifested substantially higher INa density than Kir2.1WT, explaining the abbreviation in the PR interval.

CONCLUSION

The first in-vivo mouse model of cardiac-specific SQTS3 recapitulates the electrophysiological phenotype of a patient with the Kir2.1E299V mutation. Kir2.1E299V eliminates rectification in both cardiac chambers but protects against ventricular arrhythmias by increasing excitability in both Purkinje-fiber network and ventricles. Consequently, the predominant arrhythmias are supraventricular likely due to the lack of inward rectification and atrial-specific reduced pore diameter of the Kir2.1E299V-Kir2.2WT heterotetramer.

Extracellular Kir2.1C122Y Mutant Upsets Kir2.1-PIP2 Bonds and Is Arrhythmogenic in Andersen-Tawil Syndrome

BACKGROUND

Andersen-Tawil syndrome type 1 is a rare heritable disease caused by mutations in the gene coding the strong inwardly rectifying K+ channel Kir2.1. The extracellular Cys (cysteine)122-to-Cys154 disulfide bond in the channel structure is crucial for proper folding but has not been associated with correct channel function at the membrane. We evaluated whether a human mutation at the Cys122-to-Cys154 disulfide bridge leads to Kir2.1 channel dysfunction and arrhythmias by reorganizing the overall Kir2.1 channel structure and destabilizing its open state.

METHODS

We identified a Kir2.1 loss-of-function mutation (c.366 A>T; p.Cys122Tyr) in an ATS1 family. To investigate its pathophysiological implications, we generated an AAV9-mediated cardiac-specific mouse model expressing the Kir2.1C122Y variant. We employed a multidisciplinary approach, integrating patch clamping and intracardiac stimulation, molecular biology techniques, molecular dynamics, and bioluminescence resonance energy transfer experiments.

RESULTS

Kir2.1C122Y mice recapitulated the ECG features of ATS1 independently of sex, including corrected QT prolongation, conduction defects, and increased arrhythmia susceptibility. Isolated Kir2.1C122Y cardiomyocytes showed significantly reduced inwardly rectifier K+ (IK1) and inward Na+ (INa) current densities independently of normal trafficking. Molecular dynamics predicted that the C122Y mutation provoked a conformational change over the 2000-ns simulation, characterized by a greater loss of hydrogen bonds between Kir2.1 and phosphatidylinositol 4,5-bisphosphate than wild type (WT). Therefore, the phosphatidylinositol 4,5-bisphosphate-binding pocket was destabilized, resulting in a lower conductance state compared with WT. Accordingly, on inside-out patch clamping, the C122Y mutation significantly blunted Kir2.1 sensitivity to increasing phosphatidylinositol 4,5-bisphosphate concentrations. In addition, the Kir2.1C122Y mutation resulted in channelosome degradation, demonstrating temporal instability of both Kir2.1 and NaV1.5 proteins.

CONCLUSIONS

The extracellular Cys122-to-Cys154 disulfide bond in the tridimensional Kir2.1 channel structure is essential for the channel function. We demonstrate that breaking disulfide bonds in the extracellular domain disrupts phosphatidylinositol 4,5-bisphosphate-dependent regulation, leading to channel dysfunction and defects in Kir2.1 energetic stability. The mutation also alters functional expression of the NaV1.5 channel and ultimately leads to conduction disturbances and life-threatening arrhythmia characteristic of Andersen-Tawil syndrome type 1.

MYH10 activation rescues contractile defects in arrhythmogenic cardiomyopathy (ACM)

The most prevalent genetic form of inherited arrhythmogenic cardiomyopathy (ACM) is caused by mutations in desmosomal plakophilin-2 (PKP2). By studying pathogenic deletion mutations in the desmosomal protein PKP2, here we identify a general mechanism by which PKP2 delocalization restricts actomyosin network organization and cardiac sarcomeric contraction in this untreatable disease. Computational modeling of PKP2 variants reveals that the carboxy-terminal (CT) domain is required for N-terminal domain stabilization, which determines PKP2 cortical localization and function. In mutant PKP2 cells the expression of the interacting protein MYH10 rescues actomyosin disorganization. Conversely, dominant-negative MYH10 mutant expression mimics the pathogenic CT-deletion PKP2 mutant causing actin network abnormalities and right ventricle systolic dysfunction. A chemical activator of non-muscle myosins, 4-hydroxyacetophenone (4-HAP), also restores normal contractility. Our findings demonstrate that activation of MYH10 corrects the deleterious effect of PKP2 mutant over systolic cardiac contraction, with potential implications for ACM therapy.

Extracellular cysteine disulfide bond break at Cys122 disrupts PIP2-dependent Kir2.1 channel function and leads to arrhythmias in Andersen-Tawil Syndrome

Background

Andersen-Tawil Syndrome Type 1 (ATS1) is a rare heritable disease caused by mutations in the strong inwardly rectifying K+ channel Kir2.1. The extracellular Cys122-to-Cys154 disulfide bond in the Kir2.1 channel structure is crucial for proper folding, but has not been associated with correct channel function at the membrane. We tested whether a human mutation at the Cys122-to-Cys154 disulfide bridge leads to Kir2.1 channel dysfunction and arrhythmias by reorganizing the overall Kir2.1 channel structure and destabilizing the open state of the channel.

Methods and Results

We identified a Kir2.1 loss-of-function mutation in Cys122 (c.366 A>T; p.Cys122Tyr) in a family with ATS1. To study the consequences of this mutation on Kir2.1 function we generated a cardiac specific mouse model expressing the Kir2.1C122Y mutation. Kir2.1C122Y animals recapitulated the abnormal ECG features of ATS1, like QT prolongation, conduction defects, and increased arrhythmia susceptibility. Kir2.1C122Y mouse cardiomyocytes showed significantly reduced inward rectifier K+ (IK1) and inward Na+ (INa) current densities independently of normal trafficking ability and localization at the sarcolemma and the sarcoplasmic reticulum. Kir2.1C122Y formed heterotetramers with wildtype (WT) subunits. However, molecular dynamic modeling predicted that the Cys122-to-Cys154 disulfide-bond break induced by the C122Y mutation provoked a conformational change over the 2000 ns simulation, characterized by larger loss of the hydrogen bonds between Kir2.1 and phosphatidylinositol-4,5-bisphosphate (PIP2) than WT. Therefore, consistent with the inability of Kir2.1C122Y channels to bind directly to PIP2 in bioluminescence resonance energy transfer experiments, the PIP2 binding pocket was destabilized, resulting in a lower conductance state compared with WT. Accordingly, on inside-out patch-clamping the C122Y mutation significantly blunted Kir2.1 sensitivity to increasing PIP2 concentrations.

Conclusion

The extracellular Cys122-to-Cys154 disulfide bond in the tridimensional Kir2.1 channel structure is essential to channel function. We demonstrated that ATS1 mutations that break disulfide bonds in the extracellular domain disrupt PIP2-dependent regulation, leading to channel dysfunction and life-threatening arrhythmias.

Atherosclerosis Induced by Adeno-Associated Virus Encoding Gain-of-Function PCSK9

Induction of atherosclerosis in mice with one or more genetic alterations (e.g., conditional deletion of a gene of interest) has traditionally required crossbreeding with Apoe or Ldlr deficient mice to achieve sufficient hypercholesterolemia. However, this procedure is time consuming and generates a surplus of mice with genotypes that are irrelevant for experiments. Several alternative methods exist that obviate the need to work in mice with germline-encoded hypercholesterolemia. In this chapter, we detail an efficient and increasingly used method to induce hypercholesterolemia in mice through adeno-associated virus-mediated transfer of the proprotein convertase subtilisin/kexin type 9 (PCSK9) gene.

Implication of type 4 NADPH oxidase (NOX4) in tauopathy

Aggregates of the microtubule-associated protein tau are a common marker of neurodegenerative diseases collectively termed as tauopathies, such as Alzheimer's disease (AD) and frontotemporal dementia. Therapeutic strategies based on tau have failed in late stage clinical trials, suggesting that tauopathy may be the consequence of upstream causal mechanisms. As increasing levels of reactive oxygen species (ROS) may trigger protein aggregation or modulate protein degradation and, we had previously shown that the ROS producing enzyme NADPH oxidase 4 (NOX4) is a major contributor to cellular autotoxicity, this study was designed to evaluate if NOX4 is implicated in tauopathy. Our results show that NOX4 is upregulated in patients with frontotemporal lobar degeneration and AD patients and, in a humanized mouse model of tauopathy induced by AVV-TauP301L brain delivery. Both, global knockout and neuronal knockdown of the Nox4 gene in mice, diminished the accumulation of pathological tau and positively modified established tauopathy by a mechanism that implicates modulation of the autophagy-lysosomal pathway (ALP) and, consequently, improving the macroautophagy flux. Moreover, neuronal-targeted NOX4 knockdown was sufficient to reduce neurotoxicity and prevent cognitive decline, even after induction of tauopathy, suggesting a direct and causal role for neuronal NOX4 in tauopathy. Thus, NOX4 is a previously unrecognized causative, mechanism-based target in tauopathies and blood-brain barrier permeable specific NOX4 inhibitors could have therapeutic potential even in established disease.

Beta-3 adrenergic receptor overexpression reverses aortic stenosis-induced heart failure and restores balanced mitochondrial dynamics

Aortic stenosis (AS) is associated with left ventricular (LV) hypertrophy and heart failure (HF). There is a lack of therapies able to prevent/revert AS-induced HF. Beta3 adrenergic receptor (β3AR) signaling is beneficial in several forms of HF. Here, we studied the potential beneficial effect of β3AR overexpression on AS-induced HF. Selective β3AR stimulation had a positive inotropic effect. Transgenic mice constitutively overexpressing human β3AR in the heart (c-hβ3tg) were protected from the development of HF in response to induced AS, and against cardiomyocyte mitochondrial dysfunction (fragmented mitochondria with remodeled cristae and metabolic reprogramming featuring altered substrate use). Similar beneficial effects were observed in wild-type mice inoculated with adeno-associated virus (AAV9) inducing cardiac-specific overexpression of human β3AR before AS induction. Moreover, AAV9-hβ3AR injection into wild-type mice at late disease stages, when cardiac hypertrophy and metabolic reprogramming are already advanced, reversed the HF phenotype and restored balanced mitochondrial dynamics, demonstrating the potential of gene-therapy-mediated β3AR overexpression in AS. Mice with cardiac specific ablation of Yme1l (cYKO), characterized by fragmented mitochondria, showed an increased mortality upon AS challenge. AAV9-hβ3AR injection in these mice before AS induction reverted the fragmented mitochondria phenotype and rescued them from death. In conclusion, our results step out that β3AR overexpression might have translational potential as a therapeutic strategy in AS-induced HF.

Abstract P356: Dual Dysfunction Of Kir2.1 Underlies Conduction And Excitation-contraction Coupling Defects Promoting Arrhythmias In A Mouse Model Of Andersen-tawil Syndrome Type 1

Background: Andersen-Tawil syndrome type 1 (ATS1), caused by trafficking deficient mutations in the gene KCNJ2 coding the inward rectifier K + channel Kir2.1, is associated with life-threatening arrhythmias, which in some patients resemble catecholaminergic polymorphic ventricular tachycardia (CPVT), but the mechanisms are poorly understood. We tested the hypothesis that dysfunction of two different populations of mutant Kir2.1 channels, one at the sarcolemma, and the other at the sarcoplasmic reticulum (SR) membrane, directly alters conduction and intracellular calcium dynamics, respectively, to promote the ATS1 phenotype and arrhythmias that resemble CPVT.

Methods: We generated a new mouse model of ATS1 by a single i.v. injection of cardiac specific adeno-associated viral (AAV) transduction with Kir2.1 Δ314-315 . In-vivo and cellular, structural and functional analyses of the model were carried out by electrocardiogram (ECG), magnetic resonance imaging (MRI), intracardiac stimulation, patch-clamping, membrane fractionation, western blot, immunolocalization and live calcium imaging.

Results: Our mouse model carrying mutant Kir2.1 Δ314-315 recapitulated the ATS1 phenotype without modifying ventricular function. On ECG, Kir2.1 Δ314-315 mice had prolonged PR, QRS and QT intervals and occasional U waves. They showed significantly slower conduction velocities than wildtype mice in response to flecaidine-induced Na + -channel blockade, additional QT prolongation in response to isoproterenol, and increased vulnerability to cardiac fibrillation. Cardiomyocytes from Kir2.1 Δ314-315 mice had significantly reduced inward rectifier K + and Na + inward currents, depolarized resting membrane potential and prolonged action potential duration. Immunolocalization in wildtype cardiomyocytes and skeletal muscle cells revealed a novel SR microdomain of functional Kir2.1 channels contributing to intracellular Ca 2+ homeostasis. Kir2.1 Δ314-315 cardiomyocytes showed defects in SR Kir2.1 localization and function, which contributed to abnormal spontaneous Ca 2+ release events.

Conclusions: Cardiac-specific AAV transduction with Kir2.1 Δ314-315 in mice recapitulates the ATS1 phenotype by disrupting localization and function of Kir2.1 channels at the SR, and the Kir2.1-Na V 1.5 channelosome at the sarcolemma. These results reveal a novel dual mechanism of arrhythmogenesis in ATS1 involving defects in Kir2.1 channel trafficking and function at two different microdomains. They also provide the first demonstration at the molecular level of the mechanism underlying the overlap between ATS1 and CPVT associated with defects in intracellular calcium homeostasis.

Sustained Elevated Blood Pressure Accelerates Atherosclerosis Development in a Preclinical Model of Disease

The continuous relationship between blood pressure (BP) and cardiovascular events makes the distinction between elevated BP and hypertension based on arbitrary cut-off values for BP. Even mild BP elevations manifesting as high-normal BP have been associated with cardiovascular risk. We hypothesize that persistent elevated BP increases atherosclerotic plaque development. To evaluate this causal link, we developed a new mouse model of elevated BP based on adeno-associated virus (AAV) gene transfer. We constructed AAV vectors to support transfer of the hRenin and hAngiotensinogen genes. A single injection of AAV-Ren/Ang (1011 total viral particles) induced sustained systolic BP increase (130 ± 20 mmHg, vs. 110 ± 15 mmHg in controls; p = 0.05). In ApoE-/- mice, AAV-induced mild BP elevation caused larger atherosclerotic lesions evaluated by histology (10-fold increase vs. normotensive controls). In this preclinical model, atheroma plaques development was attenuated by BP control with a calcium channel blocker, indicating that a small increase in BP within a physiological range has a substantial impact on plaque development in a preclinical model of atherosclerosis. These data support that non-optimal BP represents a risk for atherosclerosis development. Earlier intervention in elevated BP may prevent or delay morbidity and mortality associated with atherosclerosis.

A Network of Macrophages Supports Mitochondrial Homeostasis in the Heart

Cardiomyocytes are subjected to the intense mechanical stress and metabolic demands of the beating heart. It is unclear whether these cells, which are long-lived and rarely renew, manage to preserve homeostasis on their own. While analyzing macrophages lodged within the healthy myocardium, we discovered that they actively took up material, including mitochondria, derived from cardiomyocytes. Cardiomyocytes ejected dysfunctional mitochondria and other cargo in dedicated membranous particles reminiscent of neural exophers, through a process driven by the cardiomyocyte's autophagy machinery that was enhanced during cardiac stress. Depletion of cardiac macrophages or deficiency in the phagocytic receptor Mertk resulted in defective elimination of mitochondria from the myocardial tissue, activation of the inflammasome, impaired autophagy, accumulation of anomalous mitochondria in cardiomyocytes, metabolic alterations, and ventricular dysfunction. Thus, we identify an immune-parenchymal pair in the murine heart that enables transfer of unfit material to preserve metabolic stability and organ function. VIDEO ABSTRACT.

The pharmaceutical solvent N-methyl-2-pyrollidone (NMP) attenuates inflammation through Krüppel-like factor 2 activation to reduce atherogenesis

N-methyl-2-pyrrolidone (NMP) is a versatile water-miscible polar aprotic solvent. It is used as a drug solubilizer and penetration enhancer in human and animal, yet its bioactivity properties remain elusive. Here, we report that NMP is a bioactive anti-inflammatory compound well tolerated in vivo, that shows efficacy in reducing disease in a mouse model of atherosclerosis. Mechanistically, NMP increases the expression of the transcription factor Kruppel-like factor 2 (KLF2). Monocytes and endothelial cells treated with NMP express increased levels of KLF2, produce less pro-inflammatory cytokines and adhesion molecules. We found that NMP attenuates monocyte adhesion to endothelial cells inflamed with tumor necrosis factor alpha (TNF-α) by reducing expression of adhesion molecules. We further show using KLF2 shRNA that the inhibitory effect of NMP on endothelial inflammation and subsequent monocyte adhesion is KLF2 dependent. Enhancing KLF2 expression and activity improves endothelial function, controls multiple genes critical for inflammation, and prevents atherosclerosis. Our findings demonstrate a consistent effect of NMP upon KLF2 activation and inflammation, biological processes central to atherogenesis. Our data suggest that inclusion of bioactive solvent NMP in pharmaceutical compositions to treat inflammatory disorders might be beneficial and safe, in particular to treat diseases of the vascular system, such as atherosclerosis.

NF-kB signaling in cardiomyocytes is inhibited by sevoflurane and promoted by propofol

Both inhalational and intravenous anesthetics affect myocardial remodeling, but the precise effect of each anesthetic on molecular signaling in myocardial remodeling is unknown. Here, we performed in silico analysis to investigate signaling alterations in cardiomyocytes induced by inhalational [sevoflurane (Sevo)] and intravenous [propofol (Prop)] anesthetics. Bioinformatics analysis revealed that nuclear factor‐kappa B (NF‐kB) signaling was inhibited by Sevo and promoted by Prop. Moreover, nuclear accumulation of p65 and transcription of NF‐kB‐regulated genes were suppressed in Sevo‐administered mice, suggesting that Sevo inhibits the NF‐kB signaling pathway. Our data demonstrate that NF‐kB signaling is inhibited by Sevo and promoted by Prop. As NF‐kB signaling plays an important role in myocardial remodeling, our results suggest that anesthetics may affect myocardial remodeling through NF‐kB.

Pharmacological doses of melatonin impede cognitive decline in tau-related Alzheimer models, once tauopathy is initiated, by restoring the autophagic flux

Alterations in autophagy are increasingly being recognized in the pathogenesis of proteinopathies like Alzheimer's disease (AD). This study was conducted to evaluate whether melatonin treatment could provide beneficial effects in an Alzheimer model related to tauopathy by improving the autophagic flux and, thereby, prevent cognitive decline. The injection of AAV-hTau^P301L viral vectors and treatment/injection with okadaic acid were used to achieve mouse and human ex vivo, and in vivo tau-related models. Melatonin (10 μmol/L) impeded oxidative stress, tau hyperphosphorylation, and cell death by restoring autophagy flux in the ex vivo models. In the in vivo studies, intracerebroventricular injection of AAV-hTau^P301L increased oxidative stress, neuroinflammation, and tau hyperphosphorylation in the hippocampus 7 days after the injection, without inducing cognitive impairment; however, when animals were maintained for 28 days, cognitive decline was apparent. Interestingly, late melatonin treatment (10 mg/kg), starting once the alterations mentioned above were established (from day 7 to day 28), reduced oxidative stress, neuroinflammation, tau hyperphosphorylation, and caspase-3 activation; these observations correlated with restoration of the autophagy flux and memory improvement. This study highlights the importance of autophagic dysregulation in tauopathy and how administration of pharmacological doses of melatonin, once tauopathy is initiated, can restore the autophagy flux, reduce proteinopathy, and prevent cognitive decline. We therefore propose exogenous melatonin supplementation or the development of melatonin derivatives to improve autophagy flux for the treatment of proteinopathies like AD.

First description of the male and redescription of the female of Ixodes tapirus Kohls, 1956 (Acari: Ixodidae), a parasite of tapirs (Perissodactyla: Tapiridae) from the mountains of Colombia, Costa Rica and Panama

The male of Ixodes tapirus Kohls, 1956 (Acari: Ixodidae) is described for the first time and the female is redescribed in greater detail. Adults of I. tapirus are similar to those of Ixodes guatemalensis Kohls, 1956, Ixodes lasallei Méndez & Ortiz, 1958, Ixodes montoyanus Cooley, 1944 and Ixodes venezuelensis Kohls, 1953 but can be distinguished by their overall size, the amount of sclerotisation of the conscutum and accessory plates, the shape of the scutum, the number of punctations and their pattern on the conscutum and scutum, the depth of the punctations on the basis capituli dorsally, the shape and size of the porose areas and the size and shape of the auriculae. Adults of I. tapirus were collected from tapirs and vegetation in the mountains of Colombia, Panama and recorded from Costa Rica for the first time.

Bloodless reperfusion with the oxygen carrier HBOC-201 in acute myocardial infarction: a novel platform for cardioprotective probes delivery

Reperfusion, despite being required for myocardial salvage, is associated with additional injury. We hypothesize that infarct size (IS) will be reduced by a period of bloodless reperfusion with hemoglobin-based oxygen carriers (HBOC) before blood-flow restoration. In the pig model, we first characterized the impact of intracoronary perfusion with a fixed volume (600 ml) of a pre-oxygenated acellular HBOC, HBOC-201, on the healthy myocardium. HBOC-201 was administered through the lumen of the angioplasty balloon (i.e., distal to the occlusion site) immediately after onset of coronary occlusion at 1, 0.7, 0.4, or 0.2 ml/kg/min for 12, 17, 30, and 60 min, respectively, followed by blood-flow restoration. Outcome measures were systemic hemodynamics and LV performance assessed by the state-of-the-art cardiac magnetic resonance (CMR) imaging. The best performing HBOC-201 perfusion strategies were then tested for their impact on LV performance during myocardial infarction, in pigs subjected to 45 min mid-left anterior descending (LAD) coronary occlusion. At the end of the ischemia duration, pigs were randomized to regular reperfusion (blood-only reperfusion) vs. bloodless reperfusion (perfusion with pre-oxygenated HBOC-201 distal to the occlusion site), followed by blood-flow restoration. Hemodynamics and CMR-measured LV performance were assessed at 7- and 45-day follow-up. In modifications of the HBOC-201 procedure, glucose and insulin were included to support cardiac metabolism. A total of 66 pigs were included in this study. Twenty healthy pigs (5 per infusion protocol) were used in the study of healthy myocardium. Intracoronary administration of HBOC-201 (600 ml) at varying rates, including a flow of 0.4 ml/kg/min (corresponding to a maximum perfusion time of 30 min), did not damage the healthy myocardium. Slower perfusion (longer infusion time) was associated with permanent LV dysfunction and myocardial necrosis. A total of 46 pigs underwent MI induction. Compared with regular reperfusion, bloodless reperfusion with pre-oxygenated HBOC-201 alone increased IS. This effect was reversed by enrichment of pre-oxygenated HBOC-201 solution with glucose and insulin, resulting in no increase in IS or worsening of long-term ventricular function despite further delaying restoration of blood flow in the LAD. Bloodless reperfusion with a pre-oxygenated HBOC-201 solution supplemented with glucose and insulin is feasible and safe, but did not reduce infarct size. This strategy could be, however, used to deliver agents to the myocardium to treat or prevent ischemia/reperfusion injury before blood-flow restoration.

Evolutionary origin and functional divergence of totipotent cell homeobox genes in eutherian mammals

BACKGROUND

A central goal of evolutionary biology is to link genomic change to phenotypic evolution. The origin of new transcription factors is a special case of genomic evolution since it brings opportunities for novel regulatory interactions and potentially the emergence of new biological properties.

RESULTS

We demonstrate that a group of four homeobox gene families (Argfx, Leutx, Dprx, Tprx), plus a gene newly described here (Pargfx), arose by tandem gene duplication from the retinal-expressed Crx gene, followed by asymmetric sequence evolution. We show these genes arose as part of repeated gene gain and loss events on a dynamic chromosomal region in the stem lineage of placental mammals, on the forerunner of human chromosome 19. The human orthologues of these genes are expressed specifically in early embryo totipotent cells, peaking from 8-cell to morula, prior to cell fate restrictions; cow orthologues have similar expression. To examine biological roles, we used ectopic gene expression in cultured human cells followed by high-throughput RNA-seq and uncovered extensive transcriptional remodelling driven by three of the genes. Comparison to transcriptional profiles of early human embryos suggest roles in activating and repressing a set of developmentally-important genes that spike at 8-cell to morula, rather than a general role in genome activation.

CONCLUSIONS

We conclude that a dynamic chromosome region spawned a set of evolutionarily new homeobox genes, the ETCHbox genes, specifically in eutherian mammals. After these genes diverged from the parental Crx gene, we argue they were recruited for roles in the preimplantation embryo including activation of genes at the 8-cell stage and repression after morula. We propose these new homeobox gene roles permitted fine-tuning of cell fate decisions necessary for specification and function of embryonic and extra-embryonic tissues utilised in mammalian development and pregnancy.

β3 adrenergic receptor selective stimulation during ischemia/reperfusion improves cardiac function in translational models through inhibition of mPTP opening in cardiomyocytes

Selective stimulation of β3 adrenergic-receptor (β3AR) has been shown to reduce infarct size in a mouse model of myocardial ischemia/reperfusion. However, its functional long-term effect and the cardioprotective mechanisms at the level of cardiomyocytes have not been elucidated, and the impact of β3AR stimulation has not been evaluated in a more translational large animal model. This study aimed at evaluating pre-perfusion administration of BRL37344 both in small and large animal models of myocardial ischemia/reperfusion. Pre-reperfusion administration of the β3AR agonist BRL37344 (5 μg/kg) reduced infarct size at 2-and 24-h reperfusion in wild-type mice. Long-term (12-weeks) left ventricular (LV) function assessed by echocardiography and cardiac magnetic resonance (CMR) was significantly improved in β3AR agonist-treated mice. Incubation with β3AR agonist (BRL37344, 7 μmol/L) significantly reduced cell death in isolated adult mouse cardiomyocytes during hypoxia/reoxygenation and decreased susceptibility to deleterious opening of the mitochondrial permeability transition pore (mPTP), via a mechanism dependent on the Akt-NO signaling pathway. Pre-reperfusion BRL37344 administration had no effect on infarct size in cyclophilin-D KO mice, further implicating mPTP in the mechanism of protection. Large-white pigs underwent percutaneous coronary ischemia/reperfusion and 3-T CMR at 7 and 45 days post-infarction. Pre-perfusion administration of BRL37344 (5 μg/kg) decreased infarct size and improved long-term LV contractile function. A single-dose administration of β3AR agonist before reperfusion decreased infarct size and resulted in a consistent and long-term improvement in cardiac function, both in small and large animal models of myocardial ischemia/reperfusion. This protection appears to be executed through inhibition of mPTP opening in cardiomyocytes.

RNA-based tools for nuclear reprogramming and lineage-conversion: towards clinical applications

The therapeutic potential of induced pluripotent stem cells (iPSCs) is well established. Safety concerns remain, however, and these have driven considerable efforts aimed at avoiding host genome alteration during the reprogramming process. At present, the tools used to generate human iPSCs include (1) DNA-based integrative and non-integrative methods and (2) DNA-free reprogramming technologies, including RNA-based approaches. Because of their combined efficiency and safety characteristics, RNA-based methods have emerged as the most promising tool for future iPSC-based regenerative medicine applications. Here, I will discuss novel recent advances in reprogramming technology, especially those utilizing the Sendai virus (SeV) and synthetic modified mRNA. In the future, these technologies may find utility in iPSC reprogramming for cellular lineage-conversion, and its subsequent use in cell-based therapies.

A vertebrate N-end rule degron reveals that Orc6 is required in mitosis for daughter cell abscission

In addition to its function as an initiator of DNA replication, vertebrate Orc6 is also required for the final step of cytokinesis.

Orc6, an evolutionarily conserved component of the origin recognition complex, is essential for deoxyribonucleic acid (DNA) replication initiation from yeast to humans. Whether vertebrate Orc6 has a mitotic function remains unresolved. In vertebrates, but not yeast, its depletion causes centrosome amplification and multinucleate division, but replication stress indirectly causes similar abnormalities. In this paper, we exploit Varshavsky’s N-end rule to create a temperature-sensitive degron form of avian Orc6. Orc6 depletion during the S phase triggers centrosome amplification suppressed by G2 checkpoint inhibition, reflecting an indirect consequence of aberrant DNA replication. However, Orc6 depletion during mitosis suffices to cause asymmetric division and failure in cytokinesis, with a delay in daughter cell abscission revealed by a fluorescence-bleaching assay. A mutant lacking the C-terminal 25 residues cannot rescue these defects. Thus, vertebrate Orc6 is necessary during mitosis for the abscission stage of cytokinesis. Our findings exemplify N-end rule degrons as tools to unravel functions of a single protein during different phases of the vertebrate cell cycle.

Paving the way for H2AX phosphorylation: chromatin changes in the DNA damage response

The dynamics of chromatin-associated proteins control the accessibility of DNA to essential biological transactions like transcription, replication, recombination and repair. Here, we briefly outline what is known about the chromatin changes that occur during the cellular response to DNA breakage, focusing on our recent findings revealing that the chromatin factor HP1beta is mobilized within seconds after DNA damage by an unrecognized signaling cascade mediated by casein kinase 2 (CK2) phosphorylation, paving the way for histone H2AX phosphorylation. We also show here that HP1beta mobilization is neither associated with histone H3 modification on Ser10, an alteration proposed to assist in HP1 ejection from chromatin, nor with evidence of a physical interaction between HP1beta and the CK2 regulatory subunit. Interestingly, following its rapid mobilization, we find that HP1beta gradually re-accumulates on damaged chromatin over a longer time period, suggesting that temporal changes in HP1beta dynamics and interaction with chromatin may assist in different stages of the cellular response to DNA breakage.

Dicoumarol down-regulates human PTTG1/Securin mRNA expression through inhibition of Hsp90

Securin, the natural inhibitor of sister chromatid untimely separation, is a protooncogene overexpressed in tumors. Its protein levels correlate with malignancy and metastatic proneness. Dicoumarol, a long-established oral anticoagulant, is a new Hsp90 inhibitor that represses PTTG1/Securin gene expression and provokes apoptosis through a complex trait involving both intrinsic and extrinsic pathways. Dicoumarol activity as an Hsp90 inhibitor is confirmed by smaller levels of Hsp90 clients in treated cells and inhibition of in vivo heat shock luciferase activity recovery assays. Likewise, established Hsp90 inhibitors (17-allylamino-geldanamycin and novobiocin) repress PTTG1/Securin gene expression. Also, overexpression of human Hsp90 in yeast makes them hypersensitive to dicoumarol. Both apoptosis and PTTG1/Securin gene repression exerted by dicoumarol in cancer cells are independent of three of the most important signaling pathways affected by Hsp90 inhibition: nuclear factor-kappaB, p53, or Akt/protein kinase B signaling pathways. However, effects on PTTG1/Securin could be partially ascribed to inhibition of the Ras/Raf/extracellular signal-regulated kinase pathway. Overall, we show that expression of PTTG1/Securin gene is Hsp90 dependent and that dicoumarol is a bona fide Hsp90 inhibitor. These findings are important to understand the mode of action of Hsp90 inhibitors, mechanisms of action of dicoumarol, and Securin overexpression in tumors.

p53 stabilization can be uncoupled from its role in transcriptional activation by loss of PTTG1/securin

HCT116 cells devoid of PTTG1/securin (sec(-/-) HCT116) show a stabilized yet transcriptionally latent form of p53 protein in the absence of DNA damage. Ser15, Ser20 phosphorylation and other post-transcriptional modifications of p53 resolved by 2D gel electrophoresis are comparable to that observed in sec(+/+) HCT116 cells. The difference in degradation was also shown to be independent of the ubiquitin system but reliant on calpains. However, the p53-mediated checkpoint response is active only after genotoxic stress in sec(-/-) HCT116 cells. These findings point to the calpain pathway as a key player to maintain steady state levels of p53 in resting cells without affecting its activity.

Initiation of DNA replication requires the RECQL4 protein mutated in Rothmund-Thomson syndrome

How the replication machinery is loaded at origins of DNA replication is poorly understood. Here, we implicate in this process the Xenopus laevis homolog (xRTS) of the RECQL4 helicase mutated in Rothmund-Thomson syndrome. xRTS, which bears homology to the yeast replication factors Sld2/DRC1, is essential for DNA replication in egg extracts. xRTS can be replaced in extracts by its human homolog, while RECQL4 depletion from mammalian cells induces proliferation failure, suggesting an evolutionarily conserved function. xRTS accumulates on chromatin during replication initiation, after prereplication-complex (pre-RC) proteins, Cut5, Sld5, or Cdc45 but before replicative polymerases. xRTS depletion suppresses the loading of RPA, the ssDNA binding protein that marks unwound origins before polymerase recruitment. However, xRTS is unaffected by xRPA depletion. Thus, xRTS functions after pre-RC formation to promote loading of replication factors at origins, a previously unrecognized activity necessary for initiation. This role connects defective replication initiation to a chromosome-fragility disorder.

Human securin interacts with p53 and modulates p53-mediated transcriptional activity and apoptosis

The gene PTTG1 (encoding the pituitary tumor-transforming 1 protein) is overexpressed in several different tumor types, is tumorigenic in vivo and shows transcriptional activity. The PTTG1 protein is cell-cycle regulated and was identified as the human securin (a category of proteins involved in the regulation of sister-chromatid separation) on the basis of biochemical similarities with the Pds1p protein of budding yeast and the Cut2p protein of fission yeast. To unravel the function of human securin in oncogenesis, we carried out a phage-display screening to identify proteins that interact with securin. Notably, we isolated the p53 tumor suppressor. Pull-down and co-immunoprecipitation assays demonstrated that p53 interacts specifically with securin both in vitro and in vivo. This interaction blocks the specific binding of p53 to DNA and inhibits its transcriptional activity. Securin also inhibits the ability of p53 to induce cell death. Moreover, we observed that transfection of H1299 cells with securin induced an accumulation of G2 cells that compensated for the loss of G2 cells caused by transfection with p53. We demonstrated the physiological relevance of this interaction in PTTG1-deficient human tumor cells (PTTG1(-/-)): both apoptotic and transactivating functions of p53 were potentiated in these cells compared to parental cells. We propose that the oncogenic effect of increased expression of securin may result from modulation of p53 functions.

Enhancement of splenic-macrophage Fcgamma receptor expression by treatment with estrogens

Splenic-macrophage Fcgamma receptors (FcgammaRs) participate in the pathophysiologies of immune-complex diseases and in host defense against infection. Modulation of macrophage FcgammaR expression is an immuno-therapeutic target. Glucocorticoids, sex steroids, and dopaminergic drugs modulate macrophage FcgammaR expression. Previous data indicate that estradiol increases macrophage FcgammaR expression. Nevertheless, the effects of clinically used estrogens upon macrophage FcgammaR expression are unknown. We assessed the effects of treatment with commonly used estrogens on the expression of macrophage FcgammaRs using a guinea pig experimental model. Six estrogens have been studied: ethynylestradiol (Et), mestranol (M), chlortianisene (Ct), promestriene, 17-epiestriol, and 17beta-estradiol. Following in vivo treatment of guinea pigs, we determined the clearance of immunoglobulin G (IgG)-sensitized erythrocytes in vivo, the binding of IgG-sensitized erythrocytes by isolated splenic macrophages, and splenic-macrophage FcgammaR cell surface expression. Estrogens enhance the clearance of IgG-sensitized erythrocytes by increasing splenic-macrophage FcgammaR expression. Et, M, and Ct were more effective than the other estrogens. Flow cytometry and fluorescence microscopy with monoclonal antibodies demonstrated that estrogens increase the cell surface expression of FcgammaR1 and -2 more than that of FcgammaR2. These data indicate that treatment with commonly used estrogens enhances the clearance of IgG-sensitized cells by improving splenic-macrophage FcgammaR expression.

Human securin, hPTTG, is associated with Ku heterodimer, the regulatory subunit of the DNA-dependent protein kinase

We have previously isolated the hpttg proto-oncogene, which is expressed in normal tissues containing proliferating cells and in several kinds of tumors. In fact, expression of hPTTG correlates with cell proliferation in a cell cycle-dependent manner. Recently it was reported that PTTG is a vertebrate analog of the yeast securins Pds1 and Cut2, which are involved in sister chromatid separation. Here we show that hPTTG binds to Ku, the regulatory subunit of the DNA-dependent protein kinase (DNA-PK). hPTTG and Ku associate both in vitro and in vivo and the DNA-PK catalytic subunit phosphorylates hPTTG in vitro. Furthermore, DNA double-strand breaks prevent hPTTG-Ku association and disrupt the hPTTG-Ku complexes, indicating that genome damaging events, which result in the induction of pathways that activate DNA repair mechanisms and halt cell cycle progression, might inhibit hPTTG-Ku interaction in vivo. We propose that hPTTG might connect DNA damage-response pathways with sister chromatid separation, delaying the onset of mitosis while DNA repair occurs.

Effects of androgen treatment on expression of macrophage Fcgamma receptors

Macrophage Fcgamma receptors (FcgammaRs) play an important role in the host defense against infection and in the pathophysiology of immune cytopenias. Modulation of macrophage FcgammaR expression is a potential therapeutic approach to immune disorders. Glucocorticoids and progesterones decrease macrophage FcgammaR expression. We assessed the effect of treatment with androgens and antiandrogens on the expression of macrophage FcgammaRs using an experimental guinea pig model. Four androgens (testosterone, dihydrotestosterone, mesterolone, and danazol) and five antiandrogens (flutamide, nilutamide, cyproterone acetate, spironolactone, and finasteride) were studied. Following in vivo treatment of guinea pigs, we determined the clearance of immunoglobulin G (IgG)-sensitized erythrocytes in vivo, the binding of IgG-sensitized erythrocytes by isolated splenic macrophages, and splenic macrophage FcgammaR cell surface expression. All of the androgens impaired the clearance of IgG-sensitized erythrocytes by decreasing splenic macrophage FcgammaR expression. Dihydrotestosterone and mesterolone were more effective than testosterone or dihydrotestosterone. Flow cytometry and fluorescence microscopy with monoclonal antibodies demonstrated that the androgens decreased the cell surface expression of FcgammaR1,2 more than that of FcgammaR2. Antiandrogens did not significantly alter macrophage FcgammaR expression. Nevertheless, antiandrogens counteracted the effects of androgens on macrophage FcgammaR expression. These data indicate that androgens impair the clearance of IgG-coated cells by decreasing splenic macrophage FcgammaR expression. Thus, androgens other than danazol are candidate drugs for the treatment of immune disorders.

Cardiopulmonary Rehabilitation, Exercise Training, and Preventive Cardiology: An Overview of a Decade of Research at the Ochsner Heart and Vascular Institute: Presented in part at Grand Rounds, Research Series, Ochsner Medical Institutions, May 17, 1999

A decade of research from the Ochsner Heart and Vascular Institute's cardiopulmonary rehabilitation and exercise training programs demonstrates the benefits of this therapy on coronary risk factors, exercise capacity, cardiopulmonary parameters, behavioral characteristics, and quality of life in various subgroups of patients, including the elderly, women, obese patients, and groups with dyslipidemia and psychological distress, as well as in patients with congestive heart failure or severe lung disease. Substantial data from our program support the idea that cardiopulmonary rehabilitation and exercise training programs are underemphasized and underutilized for the secondary prevention of coronary artery disease.

Mitral inflow and pulmonary venous Doppler measurements do not predict pulmonary capillary wedge pressure in heart transplant recipients

BACKGROUND

Noninvasive estimation of pulmonary capillary wedge pressure (PCWP) with Doppler-derived mitral inflow pattern has been shown to correlate well with invasively measured PCWP; however, it has not yet been determined whether Doppler-derived mitral inflow pattern can be used to estimate PCWP accurately in heart transplant recipients.

METHODS

To determine if mitral and pulmonary venous inflow data can be applied to calculate PCWP in heart transplant recipients, some-day echocardiograms and right heart catheterizations were reviewed and 83 echocardiograms with adequate mitral inflow patterns in 53 patients were studied. Twenty-eight studies that also had adequate pulmonary venous inflow patterns were selected for offline analysis.

RESULTS

Using a previously published formula [PCWP = 17 + (5.3 x E/A) - (0.11 x IVRT)], where E/A is the ratio of early to late mitral inflow velocities and IVRT is the isovolumic relaxation time, we derived a calculated PCWP, the results of which compared poorly with the measured PCWP (r = 0.33; p = 0.002). Linear regression analysis of measured PCWP versus mitral inflow Doppler flow velocity parameters also revealed poor to modest correlation. Adding parameters derived from the pulmonary venous inflow patterns failed to improve this correlation.

CONCLUSION

Doppler-derived estimation of PCWP with mitral and pulmonary venous inflow patterns cannot be used to reliably predict PCWP in heart transplant recipients.