E3 ubiquitin ligase rififylin has yin and yang effects on rabbit cardiac transient outward potassium currents (Ito) and corresponding channel proteins

Genome-wide association studies have reported a correlation between a SNP of the RING finger E3 ubiquitin protein ligase rififylin (RFFL) and QT interval variability in humans (Newton-Cheh et al., 2009). Previously, we have shown that RFFL downregulates expression and function of the human-like ether-a-go-go-related gene potassium channel and corresponding rapidly activating delayed rectifier potassium current (IKr) in adult rabbit ventricular cardiomyocytes. Here, we report that RFFL also affects the transient outward current (Ito), but in a peculiar way. RFFL overexpression in adult rabbit ventricular cardiomyocytes significantly decreases the contribution of its fast component (Ito,f) from 35% to 21% and increases the contribution of its slow component (Ito,s) from 65% to 79%. Since Ito,f in rabbits is mainly conducted by Kv4.3, we investigated the effect of RFFL on Kv4.3 expressed in HEK293A cells. We found that RFFL overexpression reduced Kv4.3 expression and corresponding Ito,f in a RING domain-dependent manner in the presence or absence of its accessory subunit Kv channel-interacting protein 2. On the other hand, RFFL overexpression in Kv1.4-expressing HEK cells leads to an increase in both Kv1.4 expression level and Ito,s, similarly in a RING domain-dependent manner. Our physiologically detailed rabbit ventricular myocyte computational model shows that these yin and yang effects of RFFL overexpression on Ito,f, and Ito,s affect phase 1 of the action potential waveform and slightly decrease its duration in addition to suppressing IKr. Thus, RFFL modifies cardiac repolarization reserve via ubiquitination of multiple proteins that differently affect various potassium channels and cardiac action potential duration.

Corrigendum: Three-week-old rabbit ventricular cardiomyocytes as a novel system to study cardiac excitation and EC coupling

[This corrects the article DOI: 10.3389/fphys.2021.672360.].

Three-Week-Old Rabbit Ventricular Cardiomyocytes as a Novel System to Study Cardiac Excitation and EC Coupling

Cardiac arrhythmias significantly contribute to cardiovascular morbidity and mortality. The rabbit heart serves as an accepted model system for studying cardiac cell excitation and arrhythmogenicity. Accordingly, primary cultures of adult rabbit ventricular cardiomyocytes serve as a preferable model to study molecular mechanisms of human cardiac excitation. However, the use of adult rabbit cardiomyocytes is often regarded as excessively costly. Therefore, we developed and characterized a novel low-cost rabbit cardiomyocyte model, namely, 3-week-old ventricular cardiomyocytes (3wRbCMs). Ventricular myocytes were isolated from whole ventricles of 3-week-old New Zealand White rabbits of both sexes by standard enzymatic techniques. Using wheat germ agglutinin, we found a clear T-tubule structure in acutely isolated 3wRbCMs. Cells were adenovirally infected (multiplicity of infection of 10) to express Green Fluorescent Protein (GFP) and cultured for 48 h. The cells showed action potential duration (APD90 = 253 ± 24 ms) and calcium transients similar to adult rabbit cardiomyocytes. Freshly isolated and 48-h-old-cultured cells expressed critical ion channel proteins: calcium voltage-gated channel subunit alpha1 C (Ca_vα1c), sodium voltage-gated channel alpha subunit 5 (Nav1.5), potassium voltage-gated channel subfamily D member 3 (Kv4.3), and subfamily A member 4 (Kv1.4), and also subfamily H member 2 (RERG. Kv11.1), KvLQT1 (K7.1) protein and inward-rectifier potassium channel (Kir2.1). The cells displayed an appropriate electrophysiological phenotype, including fast sodium current (I _Na), transient outward potassium current (I _to), L-type calcium channel peak current (I _Ca,L), rapid and slow components of the delayed rectifier potassium current (I _Kr and I _Ks), and inward rectifier (I _K1). Although expression of the channel proteins and some currents decreased during the 48 h of culturing, we conclude that 3wRbCMs are a new, low-cost alternative to the adult-rabbit-cardiomyocytes system, which allows the investigation of molecular mechanisms of cardiac excitation on morphological, biochemical, genetic, physiological, and biophysical levels.

The endosomal trafficking regulator LITAF controls the cardiac Nav1.5 channel via the ubiquitin ligase NEDD4-2

The QT interval is a recording of cardiac electrical activity. Previous genome-wide association studies identified genetic variants that modify the QT interval upstream of LITAF (lipopolysaccharide-induced tumor necrosis factor-α factor), a protein encoding a regulator of endosomal trafficking. However, it was not clear how LITAF might impact cardiac excitation. We investigated the effect of LITAF on the voltage-gated sodium channel Nav1.5, which is critical for cardiac depolarization. We show that overexpressed LITAF resulted in a significant increase in the density of Nav1.5-generated voltage-gated sodium current INa and Nav1.5 surface protein levels in rabbit cardiomyocytes and in HEK cells stably expressing Nav1.5. Proximity ligation assays showed co-localization of endogenous LITAF and Nav1.5 in cardiomyocytes, whereas co-immunoprecipitations confirmed they are in the same complex when overexpressed in HEK cells. In vitro data suggest that LITAF interacts with the ubiquitin ligase NEDD4-2, a regulator of Nav1.5. LITAF overexpression down-regulated NEDD4-2 in cardiomyocytes and HEK cells. In HEK cells, LITAF increased ubiquitination and proteasomal degradation of co-expressed NEDD4-2 and significantly blunted the negative effect of NEDD4-2 on INa We conclude that LITAF controls cardiac excitability by promoting degradation of NEDD4-2, which is essential for removal of surface Nav1.5. LITAF-knockout zebrafish showed increased variation in and a nonsignificant 15% prolongation of action potential duration. Computer simulations using a rabbit-cardiomyocyte model demonstrated that changes in Ca2+ and Na+ homeostasis are responsible for the surprisingly modest action potential duration shortening. These computational data thus corroborate findings from several genome-wide association studies that associated LITAF with QT interval variation.

LITAF (Lipopolysaccharide-Induced Tumor Necrosis Factor) Regulates Cardiac L-Type Calcium Channels by Modulating NEDD (Neural Precursor Cell Expressed Developmentally Downregulated Protein) 4-1 Ubiquitin Ligase

BACKGROUND

The turnover of cardiac ion channels underlying action potential duration is regulated by ubiquitination. Genome-wide association studies of QT interval identified several single-nucleotide polymorphisms located in or near genes involved in protein ubiquitination. A genetic variant upstream of LITAF (lipopolysaccharide-induced tumor necrosis factor) gene prompted us to determine its role in modulating cardiac excitation.

METHODS

Optical mapping was performed in zebrafish hearts to determine Ca2+ transients. Live-cell confocal calcium imaging was performed on adult rabbit cardiomyocytes to determine intracellular Ca2+handling. L-type calcium channel (LTCC) current (ICa,L) was measured using whole-cell recording. To study the effect of LITAF on Cav1.2 (L-type voltage-gated calcium channel 1.2) channel expression, surface biotinylation, and Westerns were performed. LITAF interactions were studied using coimmunoprecipitation and in situ proximity ligation assay.

RESULTS

LITAF knockdown in zebrafish resulted in a robust increase in calcium transients. Overexpressed LITAF in 3-week-old rabbit cardiomyocytes resulted in a decrease in ICa,L and Cavα1c abundance, whereas LITAF knockdown increased ICa,L and Cavα1c protein. LITAF-overexpressing decreases calcium transients in adult rabbit cardiomyocytes, which was associated with lower Cavα1c levels. In tsA201 cells, overexpressed LITAF downregulated total and surface pools of Cavα1c via increased Cavα1c ubiquitination and its subsequent lysosomal degradation. We observed colocalization between LITAF and LTCC in tsA201 and cardiomyocytes. In tsA201, NEDD (neural precursor cell expressed developmentally downregulated protein) 4-1, but not its catalytically inactive form NEDD4-1-C867A, increased Cavα1c ubiquitination. Cavα1c ubiquitination was further increased by coexpressed LITAF and NEDD4-1 but not NEDD4-1-C867A. NEDD4-1 knockdown abolished the negative effect of LITAF on ICa,L and Cavα1c levels in 3-week-old rabbit cardiomyocytes. Computer simulations demonstrated that a decrease of ICa,L current associated with LITAF overexpression simultaneously shortened action potential duration and decreased calcium transients in rabbit cardiomyocytes.

CONCLUSIONS

LITAF acts as an adaptor protein promoting NEDD4-1-mediated ubiquitination and subsequent degradation of LTCC, thereby controlling LTCC membrane levels and function and thus cardiac excitation.

Trafficking of the human ether-a-go-go-related gene (hERG) potassium channel is regulated by the ubiquitin ligase rififylin (RFFL)

The QT interval is an important diagnostic feature on surface electrocardiograms because it reflects the duration of the ventricular action potential. A previous genome-wide association study has reported a significant linkage between a single-nucleotide polymorphism ∼11.7 kb downstream of the gene encoding the RING finger ubiquitin ligase rififylin (RFFL) and variability in the QT interval. This, along with results in animal studies, suggests that RFFL may have effects on cardiac repolarization. Here, we sought to determine the role of RFFL in cardiac electrophysiology. Adult rabbit cardiomyocytes with adenovirus-expressed RFFL exhibited reduced rapid delayed rectifier current (I _Kr). Neonatal rabbit cardiomyocytes transduced with RFFL-expressing adenovirus exhibited reduced total expression of the potassium channel ether-a-go-go-related gene (rbERG). Using transfections of 293A cells and Western blotting experiments, we observed that RFFL and the core-glycosylated form of the human ether-a-go-go-related gene (hERG) potassium channel interact. Furthermore, RFFL overexpression led to increased polyubiquitination and proteasomal degradation of hERG protein and to an almost complete disappearance of I _Kr, which depended on the intact RING domain of RFFL. Blocking the ER-associated degradation (ERAD) pathway with a dominant-negative form of the ERAD core component, valosin-containing protein (VCP), in 293A cells partially abolished RFFL-mediated hERG degradation. We further substantiated the link between RFFL and ERAD by showing an interaction between RFFL and VCP in vitro We conclude that RFFL is an important regulator of voltage-gated hERG potassium channel activity and therefore cardiac repolarization and that this ubiquitination-mediated regulation requires parts of the ERAD pathway.

Which type of conditioning method protects the spinal cord from the ischemia–reperfusion injury in 24 hours?

Objective

This study was designed to test the effects of different types of preconditioning and postconditioning methods on spinal cord protection following aortic clamping.

Methods

The animals (rabbits) were divided into sham-operated, ischemic preconditioning, remote ischemic preconditioning, simultaneous aortic and ischemic remote preconditioning, and ischemic postconditioning groups. After neurological evaluations, ultrastructural analysis and immunohistochemical staining for caspase-3 were evaluated after 24 h following ischemia.

Results

The neurological outcomes of the remote ischemic preconditioning (4.2 ± 0.4) and ischemic postconditioning (4.6 ± 0.8) groups were significantly improved when compared with the ischemia group (2.2 ± 04). The immunohistochemical analysis revealed that the lowest percentage of apoptosis was in-group ischemic preconditioning at 12.5 ± 30.6%. In the comparison of intracellular edema in an ultrastructural analysis, the ischemic preconditioning and ischemic postconditioning groups had significantly lower values than the ischemia group.

Conclusion

The conditioning methods attenuate ischemia–reperfusion injury for spinal cord injury. Ischemic and remote preconditioning and also postconditioning methods are simple to perform and inexpensive.

Resveratrol and adipose-derived mesenchymal stem cells are effective in the prevention and treatment of doxorubicin cardiotoxicity in rats

Anthracyclines can cause severe cardiac toxicity leading to heart failure. The aim of this study was to determine the effects of cardioprotective polyphenolic compound resveratrol (RES) and adipose-derived mesenchymal stem cells (ADMSCs) on cardiac tissue of rats treated with doxorubicin (DOX). Forty-two female and three male Wistar-Albino rats were included in the study. The study groups and the control groups were as follows: Group I: DOX; Group II: DOX + RES; Group III: DOX + ADMSCs; Group IV: DOX + RES + ADMSCs; Group V: Sham operation; and Group VI: normal saline. ADMSCs obtained from male rats were defined with stem cell markers [CD11b/c(-), CD45(-), CD90(+), CD44(+), and CD49(+)]. DOX 12 mg/kg intraperitoneally (i.p.) was injected as a single dose in female rats. Resveratrol 100 mg/kg was injected three times i.p. in Groups II and IV. ADMSCs 2 × 10(6) cells/kg/dose were labeled with bromodeoxyuridine (BrdU) and injected i.p. for a total of three times in Groups III and IV. When the study was terminated after 4 weeks, the beating hearts were connected to a Langendorff setup and records were obtained for 30 minutes. Histopathological, immunhistochemical, and immunofluorescent examination with H&E, Troponin I, and BrdU stains were also performed. Also, ADMSCs were demonstrated in the myocardium of transplanted rats. Left ventricle functions and myocardial histology demonstrated significant impairment in DOX only group compared to groups with ADMSCs (P < .05). We suggest that RES and ADMSCs were successful in the prevention and treatment of the doxorubicin cardiomyopathy in rats. The hypothetical mechanisms of regeneration are multiple, including cell differentiation and autocrine/paracrine effects of ADMSCs.

The protective effects of resveratrol and L-NAME on visceral organs following aortic clamping

BACKGROUND

This study investigated the effect of temporary occlusion of the aorta on the development of ischemia-reperfusion (I/R) injury of the visceral organs, the optimal timing of administration of resveratrol, and its mechanism of protection via inhibiting nitric oxide (NO) release with an NO synthase inhibitor.

METHODS

Rabbits were divided into seven groups according to the administration period of resveratrol and/or N(G)-nitro-L-arginine methyl ester (L-NAME): control group; group 1, resveratrol during ischemic period; group 2, resveratrol during reperfusion period; group 3, L-NAME during ischemic period; group 4, L-NAME during reperfusion period; group 5, resveratrol during ischemic period and L-NAME during reperfusion period; group 6, L-NAME during ischemic period and resveratrol during reperfusion period. The infrarenal aorta was clamped for 30 min. Blood samples were taken for the biochemical assessment, and organ specimens were taken for pathological assessment at 24hr of reperfusion.

RESULTS

In groups 5 and 6, the renal I/R injury was comparatively milder (I/R injury score 1.04+/-0.29 in control group, 0.25+/-0.17 in group 5, and 0.33+/-0.13 in group 6 [p<0.05]). The I/R injury of bowel was milder in group 5 (I/R injury score 1.8+/-0.80 in control group vs. 0.0+/-0.0 in group 5 [p<0.05]).

CONCLUSION

The protective effects of resveratrol on organs that have high metabolic rate like kidney and bowel was proven histopathologically. It may be beneficial to use different pharmacological medications in different periods of the I/R damage as they represent different characteristics with and without oxygen. The combination of resveratrol and L-NAME against I/R injury appears to be an effective option in the near future.

Endothelium-dependent induction of vasorelaxation by Melissa officinalis L. ssp. officinalis in rat isolated thoracic aorta

In the current study, vasorelaxant effect produced by the aqueous extract of Melissa officinalis L. ssp. officinalis (MOO) (Lamiaceae) and its possible mechanism in isolated rat aortic rings precontracted with phenylephrine were examined. In the first series of experiments, effect of MOO on the baseline and phenylephrine (10(-5)M) precontracted arteries was investigated, while in the second group of experiments, endothelium intact or endothelium denuded effect was determined. The agents used were N(omega)-nitro-L-arginine (L-NAME), an irreversible inhibitor of nitric oxide (NO) synthase, indomethacin (10 microM), a cyclooxygenase (COX) inhibitor, and glibenclamide (10 microM), an ATP-sensitive potassium channel blocker. The extract was found to exert a vasorelaxant effect and rosmarinic acid quantity, the characteristic compound of the plant, was analyzed by reversed-phase high-performance liquid chromatography (18.75%), and was further confirmed by LC-MS analysis giving a prominent [M(+1)] molecular ion peak at m/z 365. Total phenol amount in the extract was determined using Folin-Ciocalteau reagent (0.284 mg/mg extract). Vasorelaxant effect of the extract was entirely dependent on the presence of endothelium and was abolished by pretreatment with L-NAME, whereas pretreatment with indomethacin and glibenclamide reduced the relaxation to a minor extent. Rosmarinic acid was also tested in the same manner as the extract and was found to exert vasorelaxant effect. These results suggest that the aqueous extract of MOO vasodilates via nitric oxide pathway with the possible involvement of prostacycline and endothelium-derived hyperpolarizing factor (EDHF) pathways as well.

In Which Period of Injury Is Resveratrol Treatment Effective: Ischemia or Reperfusion?

The periods of ischemia and reperfusion represent different characteristics by lack of oxygen and reoxygenation. The aim of this experimental spinal cord injury model was to investigate whether resveratrol has protective effects during ischemia or reperfusion and the mechanism of the protection by using N-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase. Rabbits were divided into seven groups according to the time of administration of resveratrol or L-NAME (RI and RR, resveratrol during ischemia or reperfusion; IL and RL, L-NAME during ischemia or reperfusion; RILR, resveratrol during ischemia and L-NAME during reperfusion; LIRR, L-NAME during ischemia and resveratrol during reperfusion; control group). After neurologic evaluation at the twenty-fourth hour of reperfusion, lumbar spinal cords were removed for electron microscopic evaluation, immunohistochemical staining for apoptosis, and malondialdehyde (MDA) and myeloperoxidase (MPO) measurements. The RILR group had the best functional recovery, with a mean 3.6 Tarlov score (P < 0.05), and showed near normal electron microscopic findings (scores of 7.6 +/- 0.9 for the control group and 3.9 +/- 2.9 for the RILR group, P < 0.05). MPO and MDA levels were decreased in all groups compared with the control group, but only the decrement in the RILR group reached statistical significance. Immunohistochemical analysis showed that the groups including resveratrol and L-NAME together had the best staining for apoptosis. Resveratrol exhibits important protection by means of neurologic outcome, histopathologic analysis, and biochemical analysis, especially when used in during ischemia followed by L-NAME administration during reperfusion. Also, resveratrol protects against apoptosis, especially when combined with L-NAME.

Preconditioning effects of peroxynitrite in the rat lung

Ischaemic preconditioning of the lung leads to a protective effect against ischaemia-reperfusion injury, but the underlying mechanisms of this protection are not well documented in the lung. The aim of this study was to investigate the role of endogenous and exogenous peroxynitrite (ONOO(-)) in preconditioning of isolated rat lungs. Lungs, obtained from male rats, were mounted on a perfusion apparatus, perfused by Krebs-Henseleit solution at the rate of 0.03mlg(-1)min(-1) and inflated with room air. Pulmonary perfusion pressure was measured by a pressure transducer and recorded continuously on a computer by using data acquisition system. Lungs were preconditioned for 5min by either ischaemia or ONOO(-) administration at 10microM, which were followed by 5min reperfusion and 2h of ischaemia and 10min reperfusion. Two hours of ischaemia without preconditioning depressed potassium chloride (KCl)-and phenylephrine hydrochloride (PE)-induced responses. Pretreatment of the lungs with ONOO(-) scavenger, uric acid (1mM), or poly ADP-ribose synthase inhibitors, 3-aminobenzamid (3-AB, 1mM) or nicotinamide (1mM), reversed the effects ischaemia and ONOO(-)-induced preconditioning and decreased KCl- and PE-induced increases in perfusion pressures. Wet/dry weight ratio was markedly reduced in ischaemia and ONOO(-)-induced preconditioning groups indicating that preconditioning prevents lung oedema. Lung malondialdehyde (MDA) levels were significantly depressed in ischaemic and ONOO(-) preconditioning groups. These results suggest that ONOO(-) is able to precondition the isolated rat lung and plays a significant role in the protective effects of preconditioning.

Effects of lidocaine on rabbit isolated thoracic aorta

Lidocaine has been demonstrated to modify both contraction and relaxation of the vascular smooth muscle. Although lidocaine has been shown to inhibit endothelium-independent relaxations, the effects of lidocaine on arterial relaxation induced by peroxynitrite, a reaction product of superoxide and nitric oxide, have not been studied. The current study was designed to evaluate the effects of lidocaine on endothelium-dependent and -independent relaxations in isolated rabbit thoracic aorta. Rings of the rabbit thoracic aorta with or without endothelium were mounted for isometric force recording. Concentration-response curves to calcium ionophore A23187 ( 10(-9)to 3 x 10(-6)m), acetylcholine ( 10(-9)to 10(-3)m), sodium nitroprusside (SNP, 10(-9)to 10(-3)m), and peroxynitrite ( 10(-9)to 10(-3)m) were obtained in a cumulative manner. Lidocaine ( 10(-6)to 10(-4)m) was applied 15 min before addition of phenylephrine. Under resting force, lidocaine produced contractions at high concentrations ( 10(-5)to 10(-2)m) in endothelium-intact and -denuded arteries but removal of the endothelium did not significantly affect contractile activity. In phenylephrine-precontracted arteries, lidocaine caused concentration-dependent relaxations in both endothelium-intact and -denuded arteries. Inhibition of nitric oxide synthase or removal of endothelium did not affect the relaxations to lidocaine. Lidocaine suppressed the endothelium-independent relaxations of peroxynitrite, also poly (ADP-ribose) synthetase (PARS) enzyme activator, and SNP at high concentrations. Concentration-dependent vascular relaxations to A23187 and acetylcholine were significantly inhibited by lidocaine. These results suggest that lidocaine can depress vascular relaxations by a complex mechanism including inhibition of PARS enzyme activity.

Hypochlorous acid-induced responses in sheep isolated pulmonary artery rings

The formation of reactive oxygen species (ROS) appears to play a significant role in many pathological states including cystic fibrosis and asthma. Although stimulated inflammatory cells represent a major source of oxygen metabolites and these cells are able to generate the potent oxidant hypochlorous acid (HOCl) effects of HOCl on arteries are not known. HOCl at low concentrations (10(-7)to 10(-4)m) did not affect the resting force or have an action in precontracted sheep pulmonary arteries. HOCl at 10(-4) m concentration reduced histamine-induced relaxations in endothelium intact preparations. However, at high concentrations (10(-2) to 1 m) HOCl led to constriction under resting conditions and caused vasodilation in endothelium intact and denuded serotonin (10 microm) precontracted arteries. These effects of HOCl were significantly reduced by pretreatment of l -arginine (10(-3)m), sodium nitroprusside (SNP, 10(-5) m) and N -acetyl-l-cysteine (NAC, 10(-4) m). The effects of SNP and NAC on HOCl-induced responses were due to direct interaction since only these compounds markedly diminished the HOCl-induced luminol chemiluminescence (CL). Lack of contraction with KCl after high concentrations of HOCl showed that HOCl causes irreversible tissue damage. These results suggest that HOCl produce vasoconstriction under resting force and cause vasodilation when the pulmonary arteries precontracted. HOCl may interact with endothelium-derived mediators and contribute to tissue injury and vascular dysfunction seen in disease states.