Calmodulin-dependent Protein Kinase II Activity Research Articles

Curcumin Attenuates Retinal Vascular Leakage by Inhibiting Calcium/Calmodulin-Dependent Protein Kinase II Activity in Streptozotocin-Induced Diabetes

Background: Curcumin possesses many pharmacological properties including anti-inflammatory effects. Although prior studies indicate that curcumin has beneficial effects for diabetic retinopathy, the mechanism of action is not known. To address this issue, we investigated the effect of curcumin against diabetes-induced retinal vascular damage and its mechanism of action by using cultured retinal Müller cells stimulated with high glucose. Methods: We studied the effects of curcumin in vivo in the retinas of rats rendered diabetic by streptozotocin and in vitro in Müller cells stimulated with high glucose. We administered curcumin, or KN93, an inhibitor of calcium/calmodulin dependent protein kinase II (CaMKII), or saline vehicle to experimental animals on a daily basis for 12 weeks. Primary cultures of rat Müller cells were incubated with normal glucose or high glucose, with or without curcumin, KN93, or pyrrolidine dithiocarbamate (PDTC), an inhibitor of the transcription protein nuclear factor κB (NF-κB). We examined mRNA and protein levels of vascular endothelial growth factor (VEGF), inducible nitric oxide synthase (iNOS) and intercellular adhesion molecule-1 (ICAM-1) by real-time RT-PCR and Western blotting, respectively. Retinal levels of CaMKII and NF-κB were examined by Western blotting. Vascular leakage was evaluated using Evans blue. Results: Curcumin and KN93 significantly inhibited the activation of CaMKII/NF-κB signaling induced by diabetes or elevated glucose, and subsequently decreased the expression of VEGF, iNOS and ICAM-1. These changes were associated with a decrease of diabetes-induced retinal vascular leakage. Conclusion: Curcumin protects the diabetic rat retina against early retinal vascular damage, by inhibition of CaMKII activity. Curcumin is currently used to treat a number of clinical conditions, and may prove beneficial for the management of diabetic retinopathy.

CaMKII inhibition in the prefrontal cortex specifically increases the positive reinforcing effects of sweetened alcohol in C57BL/6J mice

Ca2+/calmodulin-dependent protein kinase II (CaMKII) is a multifunctional enzyme that is required for synaptic plasticity and has been proposed to be a primary molecular component of the etiology of alcohol addiction. Chronic alcohol intake upregulates CaMKIIα protein expression in reward-related brain regions including the amygdala and nucleus accumbens, and CaMKIIα activity in the amygdala is required for the positive reinforcing effects of alcohol, suggesting this system promotes consumption in the early stages of alcohol addiction. Alternatively, the medial prefrontal cortex (mPFC) is known to inhibit limbic activity via CaMKII-dependent excitatory projections and may, therefore, enable top-down regulation of motivation. Here we sought to remove that regulatory control by site-specifically inhibiting CaMKII activity in the mPFC, and measured effects on the positive reinforcing effects of sweetened alcohol in C57BL/6J mice. Infusion of the CAMKII inhibitor KN-93 (0–10.0μg) in the mPFC primarily increased alcohol+sucrose reinforced response rate in a dose- and time-dependent manner. KN-93 infusion reduced response rate in behavior-matched sucrose-only controls. Importantly, potentiation of operant responding for sweetened alcohol occurred immediately after infusion, at a time during which effects on sucrose responding were not observed, and persisted through the session. These results suggest that endogenous CaMKII activity in the mPFC exerts inhibitory control over the positive reinforcing effects of alcohol. Downregulation of CaMKII signaling in the mPFC might contribute to escalated alcohol use.

Abstract 13955: Small Conductance Ca2+-activated K+ Current is Upregulated via the Phospholylation of CaMKII in Cardiac Hypertrophy

Background: Left ventricular hypertrophy is associated with increased risk of ventricular arrhythmias. However, the underlying molecular basis is poorly understood. It has been reported that small-conductance Ca2+-activated K+ (SK) channel is involved in the pathogenesis of ventricular arrhythmias in heart failure. We have recently reported that the activity of calcium/calmodulin-dependent protein kinase II (CaMKII) is increased in hypertensive cardiac hypertrophy. Objective: The aim of this study is to test the hypothesis that SK channels activity is increased via the CaMKII-dependent pathway in hypertensive cardiac hypertrophy. Methods and Results: We used normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Whole cell membrane current was recorded in isolated ventricular myocyte by the patch-clamp method, and apamin-sensitive K+ current (IKAS), inhibited by apamin (100 nM), a blocker of SK channel, was evaluated. IKAS at 40 mV was present in SHR, whereas it was hardly detectable in WKY (0.579±0.046 pA/pF vs 0.022±0.062 pA/pF, both n=6, p<0.05). IKAS was almost completely abolished by 1 μM KN-93, an inhibitor of CaMKII, in SHR. Optical recordings of action potential in left ventricular anterior wall revealed that apamin prolonged the late phase of repolarization only in SHR (APD90 113.07±3.62 vs 124.95±3.62 msec, both n=4, p<0.05, and APD50 37.53±4.21 vs 50.48±4.21 msec, both n=4, p<0.05). Western blot analysis of SK channel protein isoform demonstrated that SK2 was significantly increased in SHR compared to WKY (SK2/GAPDH 0.66±0.07 vs 0.40±0.02, both n=6, p<0.05), whereas SK1 and SK3 did not differ between groups. In addition, autophosphorylated CaMKII was significantly increased in SHR (pCaMKII/GAPDH 0.80±0.06 vs 0.58±0.06, both n=6, p<0.05) despite comparable total amount of CaMKII between groups. Conclusion: SK channels are upregulated via the enhanced activation of CaMKII in hypertensive cardiac hypertrophy.

S-Nitrosylation Induces Both Autonomous Activation and Inhibition of Calcium/Calmodulin-dependent Protein Kinase II δ

NO is known to modulate calcium handling and cellular signaling in the myocardium, but key targets for NO in the heart remain unidentified. Recent reports have implied that NO can activate calcium/calmodulin (Ca(2+)/CaM)-dependent protein kinase II (CaMKII) in neurons and the heart. Here we use our novel sensor of CaMKII activation, Camui, to monitor changes in the conformation and activation of cardiac CaMKII (CaMKIIδ) activity after treatment with the NO donor S-nitrosoglutathione (GSNO). We demonstrate that exposure to NO after Ca(2+)/CaM binding to CaMKIIδ results in autonomous kinase activation, which is abolished by mutation of the Cys-290 site. However, exposure of CaMKIIδ to GSNO prior to Ca(2+)/CaM exposure strongly suppresses kinase activation and conformational change by Ca(2+)/CaM. This NO-induced inhibition was ablated by mutation of the Cys-273 site. We found parallel effects of GSNO on CaM/CaMKIIδ binding and CaMKIIδ-dependent ryanodine receptor activation in adult cardiac myocytes. We conclude that NO can play a dual role in regulating cardiac CaMKIIδ activity.

Ryanodine receptor phosphorylation by CaMKII promotes spontaneous Ca2 + release events in a rodent model of early stage diabetes: The arrhythmogenic substrate

BackgroundHeart failure and arrhythmias occur more frequently in patients with type 2 diabetes (T2DM) than in the general population. T2DM is preceded by a prediabetic condition marked by elevated reactive oxygen species (ROS) and subclinical cardiovascular defects. Although multifunctional Ca2+ calmodulin-dependent protein kinase II (CaMKII) is ROS-activated and CaMKII hyperactivity promotes cardiac diseases, a link between prediabetes and CaMKII in the heart is unprecedented. ObjectivesTo prove the hypothesis that increased ROS and CaMKII activity contribute to heart failure and arrhythmogenic mechanisms in early stage diabetes. Methods–ResultsEchocardiography, electrocardiography, biochemical and intracellular Ca2+ (Ca2+i) determinations were performed in fructose-rich diet-induced impaired glucose tolerance, a prediabetes model, in rodents. Fructose-rich diet rats showed decreased contractility and hypertrophy associated with increased CaMKII activity, ROS production, oxidized CaMKII and enhanced CaMKII-dependent ryanodine receptor (RyR2) phosphorylation compared to rats fed with control diet. Isolated cardiomyocytes from fructose-rich diet showed increased spontaneous Ca2+i release events associated with spontaneous contractions, which were prevented by KN-93, a CaMKII inhibitor, or addition of Tempol, a ROS scavenger, to the diet. Moreover, fructose-rich diet myocytes showed increased diastolic Ca2+ during the burst of spontaneous Ca2+i release events. Mice treated with Tempol or with sarcoplasmic reticulum-targeted CaMKII-inhibition by transgenic expression of the CaMKII inhibitory peptide AIP, were protected from fructose-rich diet-induced spontaneous Ca2+i release events, spontaneous contractions and arrhythmogenesis in vivo, despite ROS increases. ConclusionsRyR2 phosphorylation by ROS-activated CaMKII, contributes to impaired glucose tolerance-induced arrhythmogenic mechanisms, suggesting that CaMKII inhibition could prevent prediabetic cardiovascular complications and/or evolution.

Small-conductance Ca2+-activated K+ current is upregulated via the phosphorylation of CaMKII in cardiac hypertrophy from spontaneously hypertensive rats.

Left ventricular hypertrophy is associated with an increased risk of ventricular arrhythmias. However, the underlying molecular basis is poorly understood. It has been reported that small-conductance Ca(2+)-activated K(+) (SK) channels are involved in the pathogenesis of ventricular arrhythmias in heart failure. The present study aimed to test the hypothesis that SK channel activity is increased via the Ca(2+)/calmodulin-dependent protein kinase II (CaMKII)-dependent pathway in hypertensive cardiac hypertrophy. Normotensive Wistar-Kyoto (WKY) rats and spontaneous hypertensive rats (SHRs) were used. Whole cell membrane currents were recorded in isolated ventricular myocytes by the patch-clamp method, and apamin-sensitive K(+) current (IKAS), which is inhibited by apamin (100 nM), an SK channel blocker, was evaluated. IKAS at 40 mV was present in SHRs, whereas it was hardly detectable in WKY rats (0.579 ± 0.046 vs. 0.022 ± 0.062 pA/pF, both n = 6, P < 0.05). IKAS was almost completely abolished by 1 μM KN-93, a CaMKII inhibitor, in SHRs. Optical recordings of left ventricular anterior wall action potentials revealed that apamin prolonged the late phase of repolarization only in SHRs. Western blot analysis of SK channel protein isoforms demonstrated that SK2 was significantly increased in SHRs compared with WKY rats (SK2/GAPDH: 0.66 ± 0.07 vs. 0.40 ± 0.02, both n = 6, P < 0.05), whereas SK1 and SK3 did not differ between groups. In addition, autophosphorylated CaMKII was significantly increased in SHRs (phosphorylated CaMKII/GAPDH: 0.80 ± 0.06 vs. 0.58 ± 0.06, both n = 6, P < 0.05) despite a comparable total amount of CaMKII between groups. In conclusion, SK channels are upregulated via the enhanced activation of CaMKII in cardiac hypertrophy in SHRs.

Live imaging of endogenous Ca²⁺/calmodulin-dependent protein kinase II in neurons reveals that ischemia-related aggregation does not require kinase activity.

The Ca(2+) /calmodulin-dependent protein kinase II (CaMKII) forms 12meric holoenzymes. These holoenzymes cluster into larger aggregates within neurons under ischemic conditions and in vitro when ischemic conditions are mimicked. This aggregation is thought to be mediated by interaction between the regulatory domain of one kinase subunit with the T-site of another kinase subunit in a different holoenzyme, an interaction that requires stimulation by Ca(2+) /CaM and nucleotide for its induction. This model makes several predictions that were verified here: Aggregation in vitro was reduced by the CaMKII inhibitors tatCN21 and tatCN19o (which block the T-site) as well as by KN93 (which is CaM-competitive). Notably, these and previously tested manipulations that block CaMKII activation all reduced aggregation, suggesting an alternative mechanism that instead requires kinase activity. However, experiments with the nucleotide-competitive broad-spectrum kinase inhibitors staurosporin and H7 showed that this is not the case. In vitro, staurosporine and H7 enabled CaMKII aggregation even in the absence of nucleotide. Within rat hippocampal neurons, an intra-body enabled live monitoring of endogenous CaMKII aggregation. This aggregation was blocked by tatCN21, but not by staurosporine, even though both effectively inhibit CaMKII activity. These results support the mechanistic model for CaMKII aggregation and show that kinase activity is not required. CaMKII aggregation is prevented by inhibiting kinase activity with mutations (red italics; shown previously) or inhibitors (red bold; shown here), indicating requirement of kinase activity. However, we show here that nucleotide-competitive inhibitors (green) allow CaMKII aggregation (including endogenous CaMKII within neurons), demonstrating that kinase activity is not required and supporting the current mechanistic model for CaMKII aggregation.

Differential CaMKII regulation by voltage-gated calcium channels in the striatum.

Calcium signaling regulates synaptic plasticity and many other functions in striatal medium spiny neurons to modulate basal ganglia function. Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is a major calcium-dependent signaling protein that couples calcium entry to diverse cellular changes. CaMKII activation results in autophosphorylation at Thr286 and sustained calcium-independent CaMKII activity after calcium signals dissipate. However, little is known about the mechanisms regulating striatal CaMKII. To address this, mouse brain slices were treated with pharmacological modulators of calcium channels and punches of dorsal striatum were immunoblotted for CaMKII Thr286 autophosphorylation as an index of CaMKII activation. KCl depolarization increased levels of CaMKII autophosphorylation ~2-fold; this increase was blocked by an LTCC antagonist and was mimicked by treatment with pharmacological LTCC activators. The chelation of extracellular calcium robustly decreased basal CaMKII autophosphorylation within 5min and increased levels of total CaMKII in cytosolic fractions, in addition to decreasing the phosphorylation of CaMKII sites in the GluN2B subunit of NMDA receptors and the GluA1 subunit of AMPA receptors. We also found that the maintenance of basal levels of CaMKII autophosphorylation requires low-voltage gated T-type calcium channels, but not LTCCs or R-type calcium channels. Our findings indicate that CaMKII activity is dynamically regulated by multiple calcium channels in the striatum thus coupling calcium entry to key downstream substrates.

Mechanistic Investigation of the Arrhythmogenic Role of Oxidized CaMKII in the Heart

Oxidative stress and calcium (Ca2+)/calmodulin (CaM)-dependent protein kinase II (CaMKII) both play important roles in the pathogenesis of cardiac disease. Although the pathophysiological relevance of reactive oxygen species (ROS) and CaMKII has been appreciated for some time, recent work has shown that ROS can directly oxidize CaMKII, leading to its persistent activity and an increase of the likelihood of cellular arrhythmias such as early afterdepolarizations (EADs). Because CaMKII modulates the function of many proteins involved in excitation-contraction coupling, elucidation of its role in cardiac function, in both healthy and oxidative stress conditions, is challenging. To investigate this role, we have developed a model of CaMKII activation that includes both the phosphorylation-dependent and the newly identified oxidation-dependent activation pathways. This model is incorporated into our previous local-control model of the cardiac myocyte that describes excitation-contraction coupling via stochastic simulation of individual Ca2+ release units and CaMKII-mediated phosphorylation of L-type Ca2+ channels (LCCs), ryanodine receptors and sodium (Na+) channels. The model predicts the experimentally measured slow-rate dependence of H2O2-induced EADs. Upon increased H2O2, simulations suggest that selective activation of late Na+ current (INaL), although it prolongs action potential duration, is not by itself sufficient to produce EADs. Similar results are obtained if CaMKII effects on LCCs and ryanodine receptors are considered separately. However, EADs emerge upon simultaneous activation of both LCCs and Na+ channels. Further modeling results implicate activation of the Na+-Ca2+ exchanger (NCX) as an important player in the generation of EADs. During bradycardia, the emergence of H2O2-induced EADs was correlated with a shift in the timing of NCX current reversal toward the plateau phase earlier in the action potential. Using the timing of NCX current reversal as an indicator event for EADs, the model identified counterintuitive ionic changes—difficult to experimentally dissect—that have the greatest influence on ROS-related arrhythmia propensity.

Nuclear Translocation of Calcium/Calmodulin-dependent Protein Kinase IIδ3 Promoted by Protein Phosphatase-1 Enhances Brain-derived Neurotrophic Factor Expression in Dopaminergic Neurons

We have reported previously that dopamine D2 receptor stimulation activates calcium/calmodulin-dependent protein kinase II (CaMKII) δ3, a CaMKII nuclear isoform, increasing BDNF gene expression. However, the mechanisms underlying that activity remained unclear. Here we report that CaMKIIδ3 is dephosphorylated at Ser(332) by protein phosphatase 1 (PP1), promoting CaMKIIδ3 nuclear translocation. Neuro-2a cells transfected with CaMKIIδ3 showed cytoplasmic and nuclear staining, but the staining was predominantly nuclear when CaMKIIδ3 was coexpressed with PP1. Indeed, PP1 and CaMKIIδ3 coexpression significantly increased nuclear CaMKII activity and enhanced BDNF expression. In support of this idea, chronic administration of the dopamine D2 receptor partial agonist aripiprazole increased PP1 activity and promoted nuclear CaMKIIδ3 translocation and BDNF expression in the rat brain substantia nigra. Moreover, aripiprazole treatment enhanced neurite extension and inhibited cell death in cultured dopaminergic neurons, effects blocked by PP1γ knockdown. Taken together, nuclear translocation of CaMKIIδ3 following dephosphorylation at Ser(332) by PP1 likely accounts for BDNF expression and subsequent neurite extension and survival of dopaminergic neurons.

Abstract 186: Increased STIM1 Expression Results in Altered Calcium Handling and Heart Failure

Stromal interaction molecule 1 (STIM1) is a Ca2+ sensor that partners with Orai1, resulting in store-operated Ca2+ entry (SOCE) that is important for maintaining endoplasmic reticulum (ER) Ca2+ homeostasis. STIM1 is expressed in the heart and upregulated during disease, but its role in disease progression is unclear. In this study we used transgenic mice with STIM1 overexpression in the heart to model the known increase of this protein in response to cardiac disease. We found that STIM1 transgenic myocytes showed elevated Ca2+ entry following store depletion and STIM1 co-localized with the type 2 ryanodine receptor (RyR2) in the sarcoplasmic reticulum (SR). In addition, STIM1 transgenic mice exhibited sudden cardiac death as early as 6 weeks of age, while mice that survived past 12 weeks developed cardiac hypertrophy that progressed to heart failure, pulmonary edema, activation of the fetal gene program, alterations in mitochondrial structure, and reduced ventricular functional performance. When pre-symptomatic STIM1 transgenic mice were subjected to disease stimuli including pressure overload stimulation or neurohumoral agonist infusion, they showed greater pathology compared to control mice. STIM1 elevation also disrupted normal Ca2+ handling in cardiac myocytes, which showed spontaneous Ca2+ transients that could be inhibited by the SOCE blocker SKF-96265, as well as increased diastolic Ca2+ levels and elevated Ca2+ spark frequency. In keeping with this increase in Ca2+ cycling we also found that STIM1 elevation resulted in an increased baseline activity of cardiac nuclear factor of activated T-cells (NFAT) and Ca2+/calmodulin-dependent protein kinase II (CaMKII). This increased CaMKII activity did not, however, translate into additional RyR2 phosphorylation, suggesting that the augmented Ca2+ spark frequency observed was likely due to an elevation in SR Ca2+ load. Our results suggest that increased STIM1 expression elicits augmented Ca2+ entry, SR Ca2+ load and Ca2+ spark frequency, that leads to mitochondrial pathology and the induction of Ca2+ sensitive hypertrophic signaling pathways that contribute to cardiac disease.

Estradiol increases IP3 by a nongenomic mechanism in the smooth muscle cells from the rat oviduct.

Estradiol (E2) accelerates egg transport by a nongenomic action, requiring activation of estrogen receptor (ER) and successive cAMP and IP3 production in the rat oviduct. Furthermore, E2 increases IP3 production in primary cultures of oviductal smooth muscle cells. As smooth muscle cells are the mechanical effectors for the accelerated oocyte transport induced by E2 in the oviduct, herein we determined the mechanism by which E2 increases IP3 in these cells. Inhibition of protein synthesis by Actinomycin D did not affect the E2-induced IP3 increase, although this was blocked by the ER antagonist ICI182780 and the inhibitor of phospholipase C (PLC) ET-18-OCH3. Immunoelectron microscopy for ESR1 or ESR2 showed that these receptors were associated with the plasma membrane, indicating compatible localization with E2 nongenomic actions in the smooth muscle cells. Furthermore, ESR1 but not ESR2 agonist mimicked the effect of E2 on the IP3 level. Finally, E2 stimulated the activity of a protein associated with the contractile tone, calcium/calmodulin-dependent protein kinase II (CaMKII), in the smooth muscle cells. We conclude that E2 increases IP3 by a nongenomic action operated by ESR1 and that involves the activation of PLC in the smooth muscle cells of the rat oviduct. This E2 effect is associated with CaMKII activation in the smooth muscle cells, suggesting that IP3 and CaMKII are involved in the contractile activity necessary to accelerate oviductal egg transport.

Arrhythmia causes lipid accumulation and reduced glucose uptake.

Atrial fibrillation (AF) is characterized by irregular contractions of atrial cardiomyocytes and increased energy demand. The aim of this study was to characterize the influence of arrhythmia on glucose and fatty acid (FA) metabolism in cardiomyocytes, mice and human left atrial myocardium. Compared to regular pacing, irregular (pseudo-random variation at the same number of contractions/min) pacing of neonatal rat cardiomyocytes induced shorter action potential durations and effective refractory periods and increased diastolic [Ca(2+)]c. This was associated with the activation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and AMP-activated protein kinase (AMPK). Membrane expression of fatty acid translocase (FAT/CD36) and (14)C-palmitic acid uptake were augmented while membrane expression of glucose transporter subtype 4 (GLUT-4) as well as (3)H-glucose uptake were reduced. Inhibition of AMPK and CaMKII prevented these arrhythmia-induced metabolic changes. Similar alterations of FA metabolism were observed in a transgenic mouse model (RacET) for spontaneous AF. Consistent with these findings samples of left atrial myocardium of patients with AF compared to matched samples of patients with sinus rhythm showed up-regulation of CaMKII and AMPK and increased membrane expression of FAT/CD36, resulting in lipid accumulation. These changes of FA metabolism were accompanied by decreased membrane expression of GLUT-4, increased glycogen content and increased expression of the pro-apoptotic protein bax. Irregular pacing of cardiomyocytes increases diastolic [Ca(2+)]c and activation of CaMKII and AMPK resulting in lipid accumulation, reduced glucose uptake and increased glycogen synthesis. These metabolic changes are accompanied by an activation of pro-apoptotic signalling pathways.

Environmental Enrichment Reduces Anxiety by Differentially Activating Serotonergic and Neuropeptide Y (NPY)-Ergic System in Indian Field Mouse (Mus booduga): An Animal Model of Post-Traumatic Stress Disorder.

Exposure to a predator elicits an innate fear response and mimics several behavioral disorders related to post-traumatic stress disorder (PTSD). The protective role of an enriched condition (EC) against psychogenic stressors in various animal models has been well documented. However, this condition has not been tested in field mice in the context of PTSD. In this study, we show that field mice (Mus booduga) housed under EC exhibit predominantly proactive and less reactive behavior compared with mice housed under standard conditions (SC) during exposure to their natural predator (field rat Rattus rattus). Furthermore, we observed that EC mice displayed less anxiety-like behavior in an elevated plus maze (EPM) and light/dark-box after exposure to the predator (7 hrs/7 days). In EC mice, predator exposure elevated the level of serotonin (5-Hydroxytrypamine, [5-HT]) in the amygdala as part of the coping response. Subsequently, the serotonin transporter (SERT) and 5-HT1A receptor were up-regulated significantly, but the same did not occur in the 5-HT2C receptor, which is associated with the activation of calmodulin-dependent protein kinase-II (CaMKII) and a transcription factor cAMP response element binding protein (CREB). Our results show that predator exposure induced the activation of CaMKII/CREB, which is accompanied with increased levels of histone acetylation (H3, H4) and decreased histone deacetylases (HDAC1, 2). Subsequently, in the amygdala, the transcription of brain-derived neurotrophic factor (BDNF), neuropeptide Y (NPY) and its Y1 receptor were up-regulated, whereas the Y2 receptor was down-regulated. Therefore, EC facilitated a coping response against a fear associated cue in a PTSD animal model and reduced anxiety by differentially activating serotonergic and NPY-ergic systems.

Differential expression of CaMKII isoforms and overall kinase activity in rat dorsal root ganglia after injury

Ca2+/calmodulin-dependent protein kinase II (CaMKII) decodes neuronal activity by translating cytoplasmic Ca2+ signals into kinase activity that regulates neuronal functions including excitability, gene expression, and synaptic transmission. Four genes lead to developmental and differential expression of CaMKII isoforms (α, β, γ, δ). We determined mRNA levels of these isoforms in the dorsal root ganglia (DRG) of adult rats with and without nerve injury in order to determine if differential expression of CaMKII isoforms may contribute to functional differences that follow injury. DRG neurons express mRNA for all four isoforms, and the relative abundance of CaMKII isoforms was γ>α>β=δ, based on the CT values. Following ligation of the 5th lumbar (L5) spinal nerve (SNL), the β isoform did not change, but mRNA levels of both the γ and α isoforms were reduced in the directly injured L5 neurons, and the α isoform was reduced in L4 neurons, compared to their contemporary controls. In contrast, expression of the δ isoform mRNA increased in L5 neurons. CaMKII protein decreased following nerve injury in both L4 and L5 populations. Total CaMKII activity measured under saturating Ca2+/CaM conditions was decreased in both L4 and L5 populations, while autonomous CaMKII activity determined in the absence of Ca2+ was selectively reduced in axotomized L5 neurons 21days after injury. Thus, loss of CaMKII signaling in sensory neurons after peripheral nerve injury may contribute to neuronal dysfunction and pain.

Methods of activation and the role of calcium/calmodulin-dependent protein kinase II in the regulation of acetylcholine secretion in the motor synapses of mice

In electrophysiological studies of neuromuscular junctions of mice, it was demonstrated that evoked release of mediator triggered by calcium influx via P/Q calcium channels in the terminals remains unchanged in the presence of KN-62, a blocker of calcium/calmodulin-dependent protein kinase II (CaMKII). Disinhibition of L-type calcium channels by blockage of phosphatase calcineurin with cyclosporine A (CsA) causes an increase in the quantal content of endplate potentials (EPP’s QC), which can be prevented by the L-type calcium channel blocker nitrendipine, as well as by preliminary inhibition of CaMKII with KN-62. Thus, the acetylcholine (ACh) release is enhanced with involvement of activated CaMKII only after disinhibition of L-type calcium channels. When disinhibition of L-type calcium channels was induced by suppression of calcium-activated BK-type potassium channels with paxilline, an increase in EPP’s QC was also observed. The conclusion was drawn that in motor synapses of mice, calcium influx via P/Q-type calcium channels cannot provide selective activation of CaMKII to facilitate transmission. However, disinhibition of L-type calcium channels results in the activation of CaMKII, which is accompanied by a persistent increase in evoked ACh release.

Calcium/calmodulin-dependent protein kinase II (CaMKII) inhibition ameliorates arrhythmias elicited by junctin ablation under stress conditions.

Aberrant calcium signaling is considered one of the key mechanisms contributing to arrhythmias, especially in the context of heart failure. In human heart failure, there is significant down-regulation of the sarcoplasmic reticulum (SR) protein junctin, and junctin deficiency in mice is associated with stress-induced arrhythmias. The purpose of this study was to determine whether the increased SR Ca(2+) leak and arrhythmias associated with junctin ablation may be associated with increased calcium/calmodulin-dependent protein kinase II (CaMKII) activity and phosphorylation of the cardiac ryanodine receptor (RyR2) and whether pharmacologic inhibition of CaMKII activity may prevent these arrhythmias. Using a combination of biochemical, cellular, and in vivo approaches, we tested the ability of KN-93 to reverse aberrant CaMKII phosphorylation of RyR2. Specifically, we performed protein phosphorylation analysis, in vitro cardiomyocyte contractility and Ca(2+) kinetics, and in vivo ECG analysis in junctin-deficient mice. In the absence of junctin, RyR2 channels displayed CaMKII-dependent hyperphosphorylation. Notably, CaMKII inhibition by KN-93 reduced the in vivo incidence of stress-induced ventricular tachycardia by 65% in junctin null mice. At the cardiomyocyte level, KN-93 reduced the percentage of junctin null cells exhibiting spontaneous Ca(2+) aftertransients and aftercontractions under stress conditions by 35% and 37%, respectively. At the molecular level, KN-93 blunted the CaMKII-mediated hyperphosphorylation of RyR2 and phospholamban under stress conditions. Our data suggest that CaMKII inhibition is effective in preventing arrhythmogenesis in the setting of junctin ablation through modulation of both SR Ca(2+) release and uptake. Thus, it merits further investigation as promising molecular therapy.

Neuronal antibody biomarkers for Sydenham's chorea identify a new group of children with chronic recurrent episodic acute exacerbations of tic and obsessive compulsive symptoms following a streptococcal infection.

Several autoantibodies (anti-dopamine 1 (D1R) and 2 (D2R) receptors, anti-tubulin, anti-lysoganglioside-GM1) and antibody-mediated activation of calcium calmodulin dependent protein kinase II (CaMKII) signaling activity are elevated in children with Sydenham’s chorea (SC). Recognizing proposed clinical and autoimmune similarities between SC and PANDAS (pediatric autoimmune neuropsychiatric disorder associated with a streptococcal infection), we sought to identify serial biomarker changes in a slightly different population. Antineuronal antibodies were measured in eight children (mean 11.3 years) with chronic, dramatic, recurrent tics and obsessive-compulsive disorder (OCD) associated with a group A β-hemolytic streptococcal (GABHS) respiratory tract infection, but differing because they lacked choreiform movements. Longitudinal serum samples in most subjects included two pre-exacerbation samples, Exac), one midst Exac (abrupt recurrence of tic/OCD; temporally association with a GABHS infection in six of eight subjects), and two post-Exac. Controls included four groups of unaffected children (n = 70; mean 10.8 years) obtained at four different institutions and published controls. Clinical exacerbations were not associated with a significant rise in antineuronal antibody titers. CaMKII activation was increased at the GABHS exacerbation point in 5/6 subjects, exceeded combined and published control’s 95th percentile at least once in 7/8 subjects, and median values were elevated at each time point. Anti-tubulin and anti-D2R titers did not differ from published or combined control group’s 95th percentile or median values. Differences in anti-lysoganglioside-GM1 and anti-D1R titers were dependent on the selected control. Variances in antibody titers and CaMKII activation were identified among the institutional control groups. Based on comparisons to published studies, results identify two groups of PANDAS: 1) a cohort, represented by this study, which lacks choreiform movements and elevated antibodies against D2R; 2) the originally reported group with choreiform movements and elevated anti-D2R antibodies, similar to SC. Increased antibody mediated CaMKII activation was found in both groups and requires further study as a potential biomarker.

Protein kinaseC and Ca(2+) -calmodulin-dependent protein kinaseII mediate the enlarged reverse INCX induced by ouabain-increased late sodium current in rabbit ventricular myocytes.

What is the central question of this study? What are the effects of protein kinaseC (PKC) and Ca(2+) -calmodulin-dependent protein kinaseII (CaMKII) on late sodium current (INaL ), reverse Na(+) -Ca(2+) exchange current (reverse INCX ) or intracellular Ca(2+) levels changed by ouabain? What is the main finding and its importance? Ouabain, even at low concentrations (0.5-8.0μm), can increase INaL and reverse INCX , and these effects may contribute to the effect of the glycoside to increase Ca(2+) transients and contractility. Both PKC and CaMKII activities may mediate or modulate these processes. It has been reported that the cardiac glycoside ouabain can increase the late sodium current (INaL ), as well as the diastolic intracellular calcium concentration and contractile shortening. Whether an increase of INaL participates in a pathway that can mediate the positive inotropic response to ouabain is unknown. We therefore determined the effects of ouabain on INaL , reverse Na(+) -Ca(2+) exchange current (reverse INCX ), intracellular Ca(2+) ([Ca(2+) ]i ) levels and contractile shortening in rabbit isolated ventricular myocytes. Ouabain (0.1-8μm) markedly increased INaL and reverse INCX in a concentration-dependent manner, with significant effects at concentrations as low as 0.5 and 1μm. These effects of ouabain were suppressed by the INaL inhibitors TTX and ranolazine, the protein kinaseC inhibitor bisindolylmaleimide and the Ca(2+) -calmodulin-dependent protein kinaseII inhibitor KN-93. The enhancement by 0.5μm ouabain of ventricular myocyte contractility and intracellular Ca(2+) transients was suppressed by 2.0μm TTX. We conclude that ouabain, even at low concentrations (0.5-8.0μm), can increase INaL and reverse INCX , and these effects may contribute to the effect of the glycoside to increase Ca(2+) transients and contractility. Both protein kinaseC and Ca(2+) -calmodulin-dependent protein kinaseII activities may mediate or modulate these processes.

Chasing cardiac physiology and pathology down the CaMKII cascade.

Calcium dynamics is central in cardiac physiology, as the key event leading to the excitation-contraction coupling (ECC) and relaxation processes. The primary function of Ca(2+) in the heart is the control of mechanical activity developed by the myofibril contractile apparatus. This key role of Ca(2+) signaling explains the subtle and critical control of important events of ECC and relaxation, such as Ca(2+) influx and SR Ca(2+) release and uptake. The multifunctional Ca(2+)-calmodulin-dependent protein kinase II (CaMKII) is a signaling molecule that regulates a diverse array of proteins involved not only in ECC and relaxation but also in cell death, transcriptional activation of hypertrophy, inflammation, and arrhythmias. CaMKII activity is triggered by an increase in intracellular Ca(2+) levels. This activity can be sustained, creating molecular memory after the decline in Ca(2+) concentration, by autophosphorylation of the enzyme, as well as by oxidation, glycosylation, and nitrosylation at different sites of the regulatory domain of the kinase. CaMKII activity is enhanced in several cardiac diseases, altering the signaling pathways by which CaMKII regulates the different fundamental proteins involved in functional and transcriptional cardiac processes. Dysregulation of these pathways constitutes a central mechanism of various cardiac disease phenomena, like apoptosis and necrosis during ischemia/reperfusion injury, digitalis exposure, post-acidosis and heart failure arrhythmias, or cardiac hypertrophy. Here we summarize significant aspects of the molecular physiology of CaMKII and provide a conceptual framework for understanding the role of the CaMKII cascade on Ca(2+) regulation and dysregulation in cardiac health and disease.