Ca(2+) /calmodulin dependent kinase II: a critical mediator in determining reperfusion outcomes in the heart?

Cyclic AMP but Not Calmodulin as a Potential Wasoconstrictor in Simulated Reperfusion

The phenomena of ischemia and reperfusion are associated with the pathological background of cardiovascular diseases. Ischemia is initiated by ischemia reperfusion injury (IRI), which involves disruption of intracellular signaling pathways and causes cell death. The aim of this study was to assess the reactivity of vascular smooth muscle cells in the conditions of induced ischemia and reperfusion, and to determine the mechanisms leading to contractility disorders. This study was conducted using classical pharmacometric methods on an isolated model of the rat caudal artery. The experiment consisted of the analysis of the final and initial perfusate pressure measurements after induction of arterial contraction with phenylephrine in the presence of forskolin and A7 hydrochloride, two ligands modifying the contractility of vascular smooth muscle cells (VSMC). The pharmacometric analysis showed that in simulated reperfusion, cyclic nucleotides have a vasoconstrictive effect, and calmodulin has a vasodilating effect. The responsiveness of vascular smooth muscle cells to the vasopressor effects of α1-adrenomimetics during reperfusion may change uncontrollably, and the effects of secondary messengers may be counter physiological. Further studies are needed to evaluate the function of other second messengers on VSMCs in the process of ischemia and reperfusion.

The cardiac sympathetic co-transmitter neuropeptide Y is pro-arrhythmic following ST-elevation myocardial infarction despite beta-blockade

AIMS

ST-elevation myocardial infarction is associated with high levels of cardiac sympathetic drive and release of the co-transmitter neuropeptide Y (NPY). We hypothesized that despite beta-blockade, NPY promotes arrhythmogenesis via ventricular myocyte receptors.

METHODS AND RESULTS

In 78 patients treated with primary percutaneous coronary intervention, sustained ventricular tachycardia (VT) or fibrillation (VF) occurred in 6 (7.7%) within 48 h. These patients had significantly (P < 0.05) higher venous NPY levels despite the absence of classical risk factors including late presentation, larger infarct size, and beta-blocker usage. Receiver operating curve identified an NPY threshold of 27.3 pg/mL with a sensitivity of 0.83 and a specificity of 0.71. RT-qPCR demonstrated the presence of NPY mRNA in both human and rat stellate ganglia. In the isolated Langendorff perfused rat heart, prolonged (10 Hz, 2 min) stimulation of the stellate ganglia caused significant NPY release. Despite maximal beta-blockade with metoprolol (10 μmol/L), optical mapping of ventricular voltage and calcium (using RH237 and Rhod2) demonstrated an increase in magnitude and shortening in duration of the calcium transient and a significant lowering of ventricular fibrillation threshold. These effects were prevented by the Y1 receptor antagonist BIBO3304 (1 μmol/L). Neuropeptide Y (250 nmol/L) significantly increased the incidence of VT/VF (60% vs. 10%) during experimental ST-elevation ischaemia and reperfusion compared to control, and this could also be prevented by BIBO3304.

CONCLUSIONS

The co-transmitter NPY is released during sympathetic stimulation and acts as a novel arrhythmic trigger. Drugs inhibiting the Y1 receptor work synergistically with beta-blockade as a new anti-arrhythmic therapy.

Preconditioning with PDE1 Inhibitors and Moderate-Intensity Training Positively Affect Systemic Redox State of Rats

Taken into consideration that oxidative stress response after preconditioning with phosphodiesterase inhibitors (PDEIs) and moderate physical activity has still not been clarified, the aim of this study was to assess the effects of PDEIs alone or in combination with physical activity, on systemic redox status. The study was carried out on 96 male Wistar albino rats classified into two groups. The first group included animals exposed only to pharmacological preconditioning (PreC) maneuver (sedentary control (CTRL, 1 ml/day saline, n = 12), nicardipine (6 mg/kg/day of NIC, n = 12), vinpocetine (10 mg/kg/day of VIN, n = 12), and nimodipine (NIM 10 mg/kg/day of, n = 12). The second included animals exposed to preconditioning with moderate-intensity training (MIT) on treadmill for 8 weeks. After 5 weeks from the start of training, the animals were divided into four subgroups depending on the medication to be used for pharmacological PreC: moderate-intensity training (MIT+ 1 ml/day saline, n = 12), nicardipine (MIT+ 6 mg/kg/day of NIC, n = 12), vinpocetine (MIT+ 10 mg/kg/day of VIN, n = 12), and nimodipine (MIT+ 10 mg/kg/day of NIM, n = 12). After three weeks of pharmacological preconditioning, the animals were sacrificed. The following oxidative stress parameters were measured spectrophotometrically: nitrites (NO₂⁻), superoxide anion radical (O₂⁻), hydrogen peroxide (H₂O₂), index of lipid peroxidation (TBARS), superoxide dismutase (SOD), catalase (CAT), and reduced glutathione (GSH). Our results showed that PDE1 and MIT preconditioning decreased the release of prooxidants and improved the activity of antioxidant enzymes thus preventing systemic oxidative stress.

Inhibitor 1 of Protein Phosphatase 1 Regulates Ca2+/Calmodulin-Dependent Protein Kinase II to Alleviate Oxidative Stress in Hypoxia-Reoxygenation Injury of Cardiomyocytes

Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), regulated by inhibitor 1 of protein phosphatase 1 (I1PP1), is vital for maintaining cardiovascular homeostasis. However, the role and mechanism of I1PP1 against hypoxia-reoxygenation (H/R) injury in cardiomyocytes remain a question. In our study, after I1PP1 overexpression by adenovirus infection in the neonatal cardiomyocytes followed by hypoxia for 4 h and reoxygenation for 12 h, the CaMKIIδ alternative splicing subtype, ATP content, and lactate dehydrogenase (LDH) release were determined. CaMKII activity was evaluated by phosphoprotein phosphorylation at Thr17 (p-PLB Thr17), CaMKII phosphorylation (p-CaMKII), and CaMKII oxidation (ox-CaMKII). Reactive oxygen species (ROS), mitochondrial membrane potential, dynamin-related protein 1 (DRP1), and optic atrophy 1 (OPA1) expressions were assessed. Our study verified that I1PP1 overexpression attenuated the CaMKIIδ alternative splicing disorder; suppressed PLB phosphorylation at Thr17, p-CaMKII, and ox-CaMKII; decreased cell LDH release; increased ATP content; attenuated ROS production; increased mitochondrial membrane potential; and decreased DRP1 expression but increased OPA1 expression in the cardiomyocytes after H/R. Contrarily, CaMKIIδ alternative splicing disorder, LDH release, ATP reduction, and ROS accumulation were aggravated after H/R injury with the I1PP1 knockdown. Collectively, I1PP1 overexpression corrected disorders of CaMKIIδ alternative splicing, inhibited CaMKII phosphorylation, repressed CaMKII oxidation, suppressed ROS production, and attenuated cardiomyocyte H/R injury.

Myocardial death and dysfunction after ischemia-reperfusion injury require CaMKIIδ oxidation

Reactive oxygen species (ROS) contribute to myocardial death during ischemia-reperfusion (I/R) injury, but detailed knowledge of molecular pathways connecting ROS to cardiac injury is lacking. Activation of the Ca²⁺/calmodulin-dependent protein kinase II (CaMKIIδ) is implicated in myocardial death, and CaMKII can be activated by ROS (ox-CaMKII) through oxidation of regulatory domain methionines (Met281/282). We examined I/R injury in mice where CaMKIIδ was made resistant to ROS activation by knock-in replacement of regulatory domain methionines with valines (MMVV). We found reduced myocardial death, and improved left ventricular function 24 hours after I/R injury in MMVV in vivo and in vitro compared to WT controls. Loss of ATP sensitive K⁺ channel (KATP) current contributes to I/R injury, and CaMKII promotes sequestration of KATP from myocardial cell membranes. KATP current density was significantly reduced by H₂O₂ in WT ventricular myocytes, but not in MMVV, showing ox-CaMKII decreases KATP availability. Taken together, these findings support a view that ox-CaMKII and KATP are components of a signaling axis promoting I/R injury by ROS.

Yap promotes hepatocellular carcinoma metastasis and mobilization via governing cofilin/F-actin/lamellipodium axis by regulation of JNK/Bnip3/SERCA/CaMKII pathways

Despite the increasingly important role of Hippo-Yap in hepatocellular carcinoma (HCC) development and progression, little insight is available at the time regarding the specifics interaction of Yap and cancer cells migration. Here, we identified the mechanism by which tumor-intrinsic Yap deletion resulted in HCC migratory inhibition. Yap was greatly upregulated in HCC and its expression promoted the cells migration. Functional studies found that knockdown of Yap induced JNK phosphorylation which closely bound to the Bnip3 promoter and contributed to Bnip3 expression. Higher Bnip3 employed excessive mitophagy leading to mitochondrial dysfunction and ATP shortage. The insufficient ATP inactivated SERCA and consequently triggered intracellular calcium overload. As the consequence of calcium oscillation, Ca/calmodulin-dependent protein kinases II (CaMKII) was signaled and subsequently inhibited cofilin activity via phosphorylated modification. The phosphorylated cofilin failed to manipulate F-actin polymerization and lamellipodium formation, resulting into the impairment of lamellipodium-based migration. Collectively, our results identified Hippo-Yap as the tumor promoter in hepatocellular carcinoma that mediated via activation of cofilin/F-actin/lamellipodium axis by limiting JNK-Bnip3-SERCA-CaMKII pathways, with potential application to HCC therapy involving cancer metastasis.

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Yap is upregulated in the hepatocellular carcinoma and promotes cancer cell migration.

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Loss of Yap impairs cell mobility via inhibiting cofilin/F-actin/lamellipodium by activation of JNK-Bnip3-SERCA-CaMKII.

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Loss of Yap enhances JNK phosphorylation which triggers Bnip3-required mitophagy.

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Excessive mitophagy induces mitochondrial energy disorder which blunts SERCA and causes calcium overload.

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The calcium overload drives CaMKII which inactivates cofilin, leading to F-actin degradation and lamellipodium collapse.

Myocardial and cardiomyocyte stress resilience is enhanced in aromatase-deficient female mouse hearts through CaMKIIδ activation

The role of sex steroids in cardioprotection is contentious, with large clinical trials investigating hormone supplementation failing to deliver outcomes expected from observational studies. Mechanistic understanding of androgen/estrogen myocardial actions is lacking. Using a genetic model of aromatase tissue deficiency (ArKO) in female mice, the goal of this investigation was to evaluate the capacity of a shift in cardiac endogenous steroid conversion to influence ischemia-reperfusion resilience by optimizing cardiomyocyte Ca2+ handling responses. In isolated normoxic cardiomyocytes, basal Ca2+ transient amplitude and extent of shortening were greater in ArKO myocytes, with preservation of diastolic Ca2+ levels. Isolated ArKO cardiomyocytes exposed to a high Ca2+ load exhibited greater Ca2+ transient and contractile amplitudes, associated with a greater postrest spontaneous sarcoplasmic reticulum Ca2+ load-release. Microarray differential gene expression analysis of normoxic ventricular tissues from ArKO vs wild-type identified a significant influence of aromatase on genes involved in cardiac Ca2+ handling and signaling [including calmodulin dependent kinase II (CaMKII)-δ], myofilament structure and function, glucose uptake and signaling, and enzymes controlling phosphorylation-specific posttranslational modification status. CaMKII expression was not changed in ventricular tissues, although CaMKIIδ activation and phosphorylation of downstream targets was enhanced in ArKO hearts subjected to ischemia-reperfusion. Overall, this investigation shows that relative withdrawal of estrogen in favor of testosterone through genetically induced tissue aromatase deficiency in females modifies the gene expression profile to effect inotropic support via optimized Ca2+ handling in response to stress, with a modest impact on basal function. Consideration of aromatase inhibition, acutely or chronically, may have a role in cardioprotection, of particular relevance to women.

Excitotoxic insult results in a long-lasting activation of CaMKIIα and mitochondrial damage in living hippocampal neurons

Over-activation of excitatory NMDA receptors and the resulting Ca2+ overload is the main cause of neuronal toxicity during stroke. CaMKII becomes misregulated during such events. Biochemical studies show either a dramatic loss of CaMKII activity or its persistent autonomous activation after stroke, with both of these processes being implicated in cell toxicity. To complement the biochemical data, we monitored CaMKII activation in living hippocampal neurons in slice cultures using high spatial/temporal resolution two-photon imaging of the CaMKIIα FRET sensor, Camui. CaMKII activation state was estimated by measuring Camui fluorescence lifetime. Short NMDA insult resulted in Camui activation followed by a redistribution of its protein localization: an increase in spines, a decrease in dendritic shafts, and concentration into numerous clusters in the cell soma. Camui activation was either persistent (> 1-3 hours) or transient (~20 min) and, in general, correlated with its protein redistribution. After longer NMDA insult, however, Camui redistribution persisted longer than its activation, suggesting distinct regulation/phases of these processes. Mutational and pharmacological analysis suggested that persistent Camui activation was due to prolonged Ca2+ elevation, with little impact of autonomous states produced by T286 autophosphorylation and/or by C280/M281 oxidation. Cell injury was monitored using expressible mitochondrial marker mito-dsRed. Shortly after Camui activation and clustering, NMDA treatment resulted in mitochondrial swelling, with persistence of the swelling temporarily linked to the persistence of Camui activation. The results suggest that in living neurons excitotoxic insult produces long-lasting Ca2+-dependent active state of CaMKII temporarily linked to cell injury. CaMKII function, however, is to be restricted due to strong clustering. The study provides the first characterization of CaMKII activation dynamics in living neurons during excitotoxic insults.