Calmodulin-dependent Protein Kinase II Activity Research Articles

Ca2+/calmodulin-dependent kinase IIδC-induced chronic heart failure does not depend on sarcoplasmic reticulum Ca2+ leak.

Hyperactivity of Ca2+/calmodulin-dependent protein kinase II (CaMKII) has emerged as a central cause of pathologic remodelling in heart failure. It has been suggested that CaMKII-induced hyperphosphorylation of the ryanodine receptor 2 (RyR2) and consequently increased diastolic Ca2+ leak from the sarcoplasmic reticulum (SR) is a crucial mechanism by which increased CaMKII activity leads to contractile dysfunction. We aim to evaluate the relevance of CaMKII-dependent RyR2 phosphorylation for CaMKII-induced heart failure development in vivo. We crossbred CaMKIIδC overexpressing [transgenic (TG)] mice with RyR2-S2814A knock-in mice that are resistant to CaMKII-dependent RyR2 phosphorylation. Ca2+-spark measurements on isolated ventricular myocytes confirmed the severe diastolic SR Ca2+ leak previously reported in CaMKIIδC TG [4.65±0.73 mF/F0 vs. 1.88±0.30 mF/F0 in wild type (WT)]. Crossing in the S2814A mutation completely prevented SR Ca2+-leak induction in the CaMKIIδC TG, both regarding Ca2+-spark size and frequency, demonstrating that the CaMKIIδC-induced SR Ca2+ leak entirely depends on the CaMKII-specific RyR2-S2814 phosphorylation. Yet, the RyR2-S2814A mutation did not affect the massive contractile dysfunction (ejection fraction=12.17±2.05% vs. 45.15±3.46% in WT), cardiac hypertrophy (heart weight/tibia length=24.84±3.00 vs. 9.81±0.50mg/mm in WT), or severe premature mortality (median survival of 12weeks) associated with cardiac CaMKIIδC overexpression. In the face of a prevented SR Ca2+ leak, the phosphorylation status of other critical CaMKII downstream targets that can drive heart failure, including transcriptional regulator histone deacetylase 4, as well as markers of pathological gene expression including Xirp2, Il6, and Col1a1, was equally increased in hearts from CaMKIIδC TG on a RyR WT and S2814A background. S2814 phosphoresistance of RyR2 prevents the CaMKII-dependent SR Ca2+ leak induction but does not prevent the cardiomyopathic phenotype caused by enhanced CaMKIIδC activity. Our data indicate that additional mechanisms-independent of SR Ca2+ leak-are critical for the maladaptive effects of chronically increased CaMKIIδC activity with respect to heart failure.

Dihydromyricetin regulates RIPK3-CaMKII to prevent necroptosis in high glucose-stimulated cardiomyocytes

BackgroundDiabetic cardiomyopathy is one common cardiovascular complication without effective treatments. Dihydromyricetin (DHY), a natural dihydroflavonol compound extracted from Ampelopsis grossedentata, possesses versatile pharmacologically important effects. In our current research, we planned to evaluate the impact and probable DHY mechanisms in high glucose (HG)-induced cardiomyocytes. MethodsPrimary cardiomyocytes were pretreated with different concentrations of DHY (0, 20, 40, 80, 160, and 320 μM) for various time (0, 1, 2, 4, 12, and 24 h). They were then stimulated for 48 h with 5.5 mmol/L normal glucose (NG) and 33.3 mmol/L high glucose (HG). Cell viability, adenosine-triphosphate (ATP) levels, and lactate dehydrogenase (LDH) release of cardiomyocytes were detected. JC-1 staining was employed to measure the mitochondrial membrane potential. MitoSOX staining and dihydroethidium (DHE) staining were applied to evaluate the oxidative stress levels. TDT mediated dUTP nick end labeling (TUNEL) was used to measure apoptotic levels. Expressions of calcium/calmodulin-dependent protein kinase II (CaMKII), phospholamban (PLB), optic atrophy 1 (OPA1), dynamin-related protein 1 (DRP1), caspase 3, mixed kinase lineage domain like protein (MLKL), receptor interacting protein kinase 3 (RIPK3), and receptor interacting protein kinase 1 (RIPK1) were detected by immunofluorescence and/or Western blot. ResultsDHY improved cell viability, enhanced ATP level, and decreased LDH content in HG-stimulated cardiomyocytes, suggesting DHY attenuating cell injury. DHY reduced number of TUNEL positive cells, inhibited RIPK3 and cleaved-caspase 3 expression, implying DHY alleviated necroptosis in HG-stimulated cardiomyocytes. DHY diminished JC-1 monomers, DHE and MitoSOX fluorescence intensity as well as DRP1 expression but increased JC-1 aggregates intensity and OPA1 expression, indicating that DHY attenuated oxidative stress in HG-stimulated cardiomyocytes. DHY also attenuated CaMKII activity by suppressed PLB phosphorylation and inhibited CaMKII oxidation in HG-stimulated cardiomyocytes. ConclusionsHG-induced cardiomyocytes injury was alleviated wherein DHY attenuated necroptosis, repressed ROS production, and inhibited CaMKII oxidation, suggesting that DHY may serve as potential agent to prevent and treat diabetic cardiomyopathy.

Ca2+/Calmodulin-Dependent Protein Kinase II Enhances Retinal Ganglion Cell Survival But Suppresses Axon Regeneration after Optic Nerve Injury.

Neuroprotection after injury or in neurodegenerative disease remains a major goal for basic and translational neuroscience. Retinal ganglion cells (RGCs), the projection neurons of the eye, degenerate in optic neuropathies after axon injury, and there are no clinical therapies to prevent their loss or restore their connectivity to targets in the brain. Here we demonstrate a profound neuroprotective effect of the exogenous expression of various Ca2+/calmodulin-dependent protein kinase II (CaMKII) isoforms in mice. A dramatic increase in RGC survival following the optic nerve trauma was elicited by the expression of constitutively active variants of multiple CaMKII isoforms in RGCs using adeno-associated viral (AAV) vectors across a 100-fold range of AAV dosing in vivo. Despite this neuroprotection, however, short-distance RGC axon sprouting was suppressed by CaMKII, and long-distance axon regeneration elicited by several pro-axon growth treatments was likewise inhibited even as CaMKII further enhanced RGC survival. Notably, in a dose-escalation study, AAV-expressed CaMKII was more potent for axon growth suppression than the promotion of survival. That diffuse overexpression of constitutively active CaMKII strongly promotes RGC survival after axon injury may be clinically valuable for neuroprotection per se. However, the associated strong suppression of the optic nerve axon regeneration demonstrates the need for understanding the intracellular domain- and target-specific CaMKII activities to the development of CaMKII signaling pathway-directed strategies for the treatment of optic neuropathies.

Clonal Hematopoiesis of Indeterminate Potential With Loss of Tet2 Enhances Risk for Atrial Fibrillation Through Nlrp3 Inflammasome Activation.

Clonal hematopoiesis of indeterminate potential (CHIP), a common age-associated phenomenon, associates with increased risk of both hematological malignancy and cardiovascular disease. Although CHIP is known to increase the risk of myocardial infarction and heart failure, the influence of CHIP in cardiac arrhythmias, such as atrial fibrillation (AF), is less explored. CHIP prevalence was determined in the UK Biobank, and incident AF analysis was stratified by CHIP status and clone size using Cox proportional hazard models. Lethally irradiated mice were transplanted with hematopoietic-specific loss of Tet2, hematopoietic-specific loss of Tet2 and Nlrp3, or wild-type control and fed a Western diet, compounded with or without NLRP3 (NLR [NACHT, LRR {leucine rich repeat}] family pyrin domain containing protein 3) inhibitor, NP3-361, for 6 to 9 weeks. Mice underwent in vivo invasive electrophysiology studies and ex vivo optical mapping. Cardiomyocytes from Ldlr-/- mice with hematopoietic-specific loss of Tet2 or wild-type control and fed a Western diet were isolated to evaluate calcium signaling dynamics and analysis. Cocultures of pluripotent stem cell-derived atrial cardiomyocytes were incubated with Tet2-deficient bone marrow-derived macrophages, wild-type control, or cytokines IL-1β (interleukin 1β) or IL-6 (interleukin 6). Analysis of the UK Biobank showed individuals with CHIP, in particular TET2 CHIP, have increased incident AF. Hematopoietic-specific inactivation of Tet2 increases AF propensity in atherogenic and nonatherogenic mouse models and is associated with increased Nlrp3 expression and CaMKII (Ca2+/calmodulin-dependent protein kinase II) activation, with AF susceptibility prevented by inactivation of Nlrp3. Cardiomyocytes isolated from Ldlr-/- mice with hematopoietic inactivation of Tet2 and fed a Western diet have impaired calcium release from the sarcoplasmic reticulum into the cytosol, contributing to atrial arrhythmogenesis. Abnormal sarcoplasmic reticulum calcium release was recapitulated in cocultures of cardiomyocytes with the addition of Tet2-deficient macrophages or cytokines IL-1β or IL-6. We identified a modest association between CHIP, particularly TET2 CHIP, and incident AF in the UK Biobank population. In a mouse model of AF resulting from hematopoietic-specific inactivation of Tet2, we propose altered calcium handling as an arrhythmogenic mechanism, dependent on Nlrp3 inflammasome activation. Our data are in keeping with previous studies of CHIP in cardiovascular disease, and further studies into the therapeutic potential of NLRP3 inhibition for individuals with TET2 CHIP may be warranted.

Zbtb16 increases susceptibility of atrial fibrillation in type 2 diabetic mice via Txnip-Trx2 signaling

Atrial fibrillation (AF) is the most prevalent sustained cardiac arrhythmia, and recent epidemiological studies suggested type 2 diabetes mellitus (T2DM) is an independent risk factor for the development of AF. Zinc finger and BTB (broad-complex, tram-track and bric-a-brac) domain containing 16 (Zbtb16) serve as transcriptional factors to regulate many biological processes. However, the potential effects of Zbtb16 in AF under T2DM condition remain unclear. Here, we reported that db/db mice displayed higher AF vulnerability and Zbtb16 was identified as the most significantly enriched gene by RNA sequencing (RNA-seq) analysis in atrium. In addition, thioredoxin interacting protein (Txnip) was distinguished as the key downstream gene of Zbtb16 by Cleavage Under Targets and Tagmentation (CUT&Tag) assay. Mechanistically, increased Txnip combined with thioredoxin 2 (Trx2) in mitochondrion induced excess reactive oxygen species (ROS) release, calcium/calmodulin-dependent protein kinase II (CaMKII) overactivation, and spontaneous Ca2+ waves (SCWs) occurrence, which could be inhibited through atrial-specific knockdown (KD) of Zbtb16 or Txnip by adeno-associated virus 9 (AAV9) or Mito-TEMPO treatment. High glucose (HG)-treated HL-1 cells were used to mimic the setting of diabetic in vitro. Zbtb16-Txnip-Trx2 signaling-induced excess ROS release and CaMKII activation were also verified in HL-1 cells under HG condition. Furthermore, atrial-specific Zbtb16 or Txnip-KD reduced incidence and duration of AF in db/db mice. Altogether, we demonstrated that interrupting Zbtb16-Txnip-Trx2 signaling in atrium could decrease AF susceptibility via reducing ROS release and CaMKII activation in the setting of T2DM.Graphical

Deficiency of aldehyde dehydrogenase 2 aggravates ethanol-induced cytotoxicity in N2a cells via CaMKII/Drp1-mediated mitophagy

Chronic alcohol abuse causes brain damage and has been associated with an increased risk of Alzheimer's disease. The toxic metabolite of alcohol, acetaldehyde, which is converted to acetate by aldehyde dehydrogenase 2 (ALDH2), has been shown to induce excessive mitochondrial fragmentation and dysfunction leading to neurotoxicity. However, it is still unclear how alcohol affects mitochondrial function in ALDH2-deficient cells. The present study investigated the association between abnormal mitochondrial dynamics, mitophagy and cytotoxicity in ALDH2-deficient N2a cells treated with ethanol. It was found that ethanol induced dynamin-related protein 1 (Drp1)-mediated mitochondrial fragmentation and impaired mitochondrial function, causing excessive mitophagy and cytotoxicity in ALDH2-deficient N2a cells while inducing Ca2+ influx and activating Ca2+/calmodulin-dependent protein kinase II (CaMKII). Inhibition of Ca2+ overload or CaMKII activation prevented Drp1 phosphorylation and ameliorated ethanol-induced mitophagy and cytotoxicity, indicating that Ca2+-dependent CaMKII activation was critical for mediating Drp1-dependent excessive mitochondrial fission and mitophagy in ALDH2-deficient N2a cells. The results of the present study suggested that prevention of intracellular Ca2+ overload might be beneficial for preventing neurotoxicity associated with alcohol abuse in individuals with defective ALDH2.

Abstract 13500: An Improved Reporter Identifies Ruxolitinib as a Potent and Cardioprotective CaMKII Inhibitor

Background: Ca 2+ /Calmodulin-dependent protein kinase II (CaMKII) hyperactivity is an established driver of cardiac arrhythmias. Despite proven benefits of CaMKII inhibition in numerous preclinical arrhythmia models, translation of CaMKII antagonists into humans has remained unsuccessful, and today, there are no clinically approved CaMKII inhibitors. Our ability to identify potent CaMKII inhibitors has been hamstrung by a lack of a CaMKII biosensor with sufficient sensitivity for high throughput drug discovery. Research question: We hypothesized that development of a CaMKII biosensor with high throughput capabilities would enable identification of CaMKII inhibitors capable of preventing arrhythmias. Methods: To address this problem, we engineered and validated a new genetically encoded CaMKII biosensor: CaMKAR (CaMKII Activity Reporter). CaMKAR enjoys a dynamic range of 227 ± 11.1 %, seconds-scale kinetics, robust specificity, and dual in cellulo and in vitro functionality. This makes CaMKAR the fastest and most sensitive CaMKII biosensor to date and the first that is amenable for in cellulo drug screening. Results: Using CaMKAR, we carried out a drug repurposing screen (4,475 compounds in clinical use) in human cells. This yielded five previously unrecognized CaMKII inhibitors: ruxolitinib, baricitinib, silmitasertib, crenolanib, and abemaciclib (false discovery-adjusted p<3 x 10 -5 ). Stand out among these, ruxolitinib, an FDA-approved Janus kinase inhibitor, blocked CaMKII kinase activity with an inhibitory constant of 23.5 ± 2.2 nM. In patient-derived cardiomyocytes, ruxolitinib ameliorated arrhythmogenic Ca 2+ release events (p<0.0001), and in mice, ruxolitinib prevented catecholaminergic polymorphic ventricular tachycardia (p<0.01) and rescued pre-existing atrial fibrillation (p<0.0001). Conclusion: Our work presents three impactful Conclusions: 1) Our biosensor, CaMKAR, provides the highest CaMKII activity reporting performance to date. 2) Long sought-after CaMKII inhibitors already exist within the human pharmacopeia. 3) Our results demonstrate that ruxolitinib—a drug already in human use—is a cardioprotective CaMKII inhibitor and a suitable candidate for cardiovascular repurposing.

Effect and mechanism of 1, 25(OH)2D3 on myocardial inflammation induced by Coxsackie virus B3 in mice

Objective: To explore the effect and mechanism of 1, 25(OH)2D3 on myocardial inflammation induced by Coxsackie virus B3 (CVB3) in mice. Methods: Wild type (WT) and 1α-hydroxylase knockout [1(OH)ase-/-] male mice were divided into four groups: WT group, WT+CVB3 group, 1(OH)ase-/-+CVB3 group and 1(OH)ase-/-+CVB3+VD3 group, with 8 mice in each group. The indicators for evaluating myocardial cell injury were examined by different methods. The mRNA levels of pro-inflammatory cytokines [interlenkin (IL)-1β, IL-6, interferon γ (IFN-γ) and tumor necrosis factor α (TNF-α)] were determined by quantitative real-time PCR. Hematoxylin-eosin (HE) staining was used to observe the myocardial histopathological changes. The apoptosis of myocardial cells was detected by terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining and flow cytometry. Fluo-4/AM fluorescence probe was used to detect intracellular calcium ion content. Meanwhile, the expression levels of Ca2+/Calmodulin-dependent protein kinase Ⅱ (CaMKⅡ) protein as well as endoplasmic reticulum stress-related proteins like glucose-related protein 78 (GRP78) and C/EBP homologous protein (CHOP) in the myocardial tissues were detected by Western blot. Results: Compared with WT group, the mRNA levels of pro-inflammatory factors increased in the cardiomyocytes of mice in WT+CVB3 group, including IL-1β (14.88±3.32 vs 1.03±0.02, P=0.009), IL-6 (7.00±1.09 vs 1.81±0.18, P=0.005), IFN-γ (4.70±1.11 vs 1.34±0.34, P=0.006) and TNF-α (17.20±3.22 vs 1.02±0.12, P<0.001). Similarly, the infiltration of inflammatory cells, and the apoptosis rate of cardiomyocytes elevated (16.66%±1.09% vs 7.85%±1.12%, P=0.012). The level of calcium ions in myocardial cytoplasm was significantly higher in WT+CVB3 group than that in the WT group (2.98±1.05 vs 0.96±0.10, P=0.006). Likewise, the expression levels of pCaMKⅡ(1.97±0.34 vs 1.00±0, P<0.001), GRP78 (1.78±0.19 vs 1.00±0, P=0.005) and CHOP (1.62±0.09 vs 1.00±0, P=0.002) in WT+CVB3 group up-regulated. The above myocardial cell injury markers were more significant in the 1(OH)ase-/-+CVB3 group. In the 1(OH)ase-/-+CVB3+VD3 group, 1, 25(OH)2D3 supplementation significantly improved myocardial cell injury indicators. Meanwhile, the specific inhibitors of CaMKⅡ can also reduce the myocardial injury and apoptosis rate of CVB3-infected mice. Conclusion: 1, 25(OH)2D3 deficiency can aggravate myocardial inflammation through over activation of CaMKⅡ.

Stachydrine Hydrochloride Regulates the NOX2-ROS-Signaling Axis in Pressure-Overload-Induced Heart Failure.

Our previous studies revealed the protection of stachydrine hydrochloride (STA) against cardiopathological remodeling. One of the underlying mechanisms involves the calcium/calmodulin-dependent protein kinase Ⅱ (CaMKII). However, the way STA influences CaMKII needs to be further investigated. The nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2)-coupled reactive oxygen species (ROS) overproduction putatively induces the oxidative activation of CaMKII, resulting in the occurrence of pathological cardiac remodeling and dysfunction in experimental models of mice. Thus, in this study, we assessed the role of the NOX2-ROS signal axis in STA cardioprotection. The transverse aortic constriction (TAC)-induced heart failure model of mice, the phenylephrine-induced hypertrophic model of neonatal rat primary cardiomyocytes, and the H2O2-induced oxidative stress models of adult mouse primary cardiomyocytes and H9c2 cells were employed. The echocardiography and histological staining were applied to assess the cardiac effect of STA (6 mg/kg/d or 12 mg/kg/d), which was given by gavage. NOX2, ROS, and excitation-contraction (EC) coupling were detected by Western blotting, immunofluorescence, and calcium transient-contraction synchronous recordings. ROS and ROS-dependent cardiac fibrosis were alleviated in STA-treated TAC mice, demonstrating improved left ventricular ejection fraction and hypertrophy. In the heart failure model of mice and the hypertrophic model of cardiomyocytes, STA depressed NOX2 protein expression and activation, as shown by inhibited translocation of its phosphorylation, p67phox and p47phox, from the cytoplasm to the cell membrane. Furthermore, in cardiomyocytes under oxidative stress, STA suppressed NOX2-related cytosolic Ca2+ overload, enhanced cell contractility, and decreased Ca2+-dependent regulatory protein expression, including CaMKⅡ and Ryanodine receptor calcium release channels. Cardioprotection of STA against pressure overload-induced pathological cardiac remodeling correlates with the NOX2-coupled ROS signaling cascade.

LTP induction by structural rather than enzymatic functions of CaMKII

Learning and memory are thought to require hippocampal long-term potentiation (LTP), and one of the few central dogmas of molecular neuroscience that has stood undisputed for more than three decades is that LTP induction requires enzymatic activity of the Ca2+/calmodulin-dependent protein kinase II (CaMKII)1–3. However, as we delineate here, the experimental evidence is surprisingly far from conclusive. All previous interventions inhibiting enzymatic CaMKII activity and LTP4–8 also interfere with structural CaMKII roles, in particular binding to the NMDA-type glutamate receptor subunit GluN2B9–14. Thus, we here characterized and utilized complementary sets of new opto-/pharmaco-genetic tools to distinguish between enzymatic and structural CaMKII functions. Several independent lines of evidence demonstrated LTP induction by a structural function of CaMKII rather than by its enzymatic activity. The sole contribution of kinase activity was autoregulation of this structural role via T286 autophosphorylation, which explains why this distinction has been elusive for decades. Directly initiating the structural function in a manner that circumvented this T286 role was sufficient to elicit robust LTP, even when enzymatic CaMKII activity was blocked.

Abstract P3195: Mitochondrial CaMKII Drives Cardiometabolic Dysfunction In Heart Failure

Background: Ca 2+ /calmodulin-dependent protein kinase II (CaMKII) is an established negative regulator of cardiac injury. Both the expression and activity levels of CaMKII delta, the primary cardiac isoform of this kinase, are elevated in models of heart failure (HF) such as ischemia-reperfusion (I/R) injury and following myocardial infarction (MI). This upregulation is due in part to CaMKII’s role in the regulation of excitation-contraction coupling, apoptosis, activation of hypertrophic programming, arrhythmias and pro-inflammatory signaling. Recently, a pool of mitochondrial CaMKII (mtCaMKII) has been identified; we have demonstrated that there is an observed increase in mitochondrial CaMKII activation with left ventricular dilation acutely following injury in a mouse model of MI. This deleterious post-MI phenotype is rescued with genetic mitochondrial CaMKII inhibition; conversely, mice with myocardial mitochondrial CaMKII overexpression present with a severe dilated cardiomyopathy phenotype, alterations in electron transport chain (ETC) activity, and decreased ATP production. Objective: To date, the molecular mechanisms by which CaMKII regulates mitochondrial energetics are unknown and present a novel therapeutic target for HF which we are currently studying. Methods: As we have identified changes in the activity of enzymes, particularly complexes I and II, in the mitochondrial ETC as well as TCA cycle in response to increased CaMKII levels or activity, we are in the process of assessing changes in the mitochondrial CaMKII interactome between uninjured and failing hearts. Utilizing liquid chromatography-mass spectrometry (LCMS) and proteomics analysis of both scaffolding interactions alongside a novel ATP analogue labeling technique, we have mapped novel mitochondrial proteins which interact with mtCaMKII. Significance: The identification of previously unknown mitochondrial pathways involving CaMKII may uncover promising pharmacological targets for cardiovascular therapeutics, as this kinase is a critical player in the progression of HF.

Abstract P3135: In Vivo Dissection Of CaMKII-Mediated Arrhythmias In CPVT

Background: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia syndrome of the structurally intact heart manifesting life-threatening bursts of ventricular tachycardias due to dominant gain-of-function mutations in the ryanodine receptor type 2 (RyR2) and β-adrenergic (β-AR) stimulation. Both protein kinase A (PKA) and Ca 2+ - calmodulin-dependent protein kinase II (CaMKII) can phosphorylate RyR2 channels, but only the latter can initiate the arrhythmogenic phenotype in CPVT. Whether through L-type Ca 2+ channel (LTCC)-mediated Ca 2+ increase or the Epac2-nitric oxide pathway, the exact mechanism by which β-AR-mediated CaMKII activation unmasks lethal arrhythmias in CPVT remains unresolved. Aim: To gain mechanistic insight and ablate ventricular arrhythmias in a mouse model of CPVT by selectively disrupting integral components of β-AR signaling. Methods: By utilizing either direct adeno-associated virus (AAV) delivery or the CRISPR/Cas9-AAV-based somatic mutagenesis (CASAAV) system, we selectively expressed a mutant LTCC β 2 -subunit, ablated the small GTPase Rad, or disrupted other components of the β-AR pathway in the hearts of mice with the pathogenic RyR2 mutation R4650I as a model of CPVT. The effects of disruption of LTCC regulation were determined by high-speed Ca 2+ imaging of isolated ventricular cardiomyocytes or whole animal electrophysiological (EP) testing for ventricular arrhythmia incidence in vivo . Results &amp; Conclusions: Our data demonstrate that abnormal RyR2-mediated calcium release events are induced by hyperactivated LTCCs in vitro , even in the absence of adrenergic stimulation, with increased arrhythmia incidence in vivo . These results suggest that β-AR stimulation leads to pathogenic RyR2 Ca 2+ leak through LTCC-mediated contribution to CaMKII hyperactivity. Alternative mechanisms of CaMKII activation that mediate arrhythmia induction in CPVT require additional future investigation.

The CaMKII inhibitory peptide AIP alleviates renal fibrosis through the TGF-β/Smad and RAF/ERK pathways.

Renal fibrosis is characterized by the excessive deposition of extracellular matrix that destroys and replaces the functional renal parenchyma, ultimately leading to organ failure. It is a common pathway by which chronic kidney disease (CKD) can develop into end-stage renal disease (ESRD), which has high global morbidity and mortality, and there are currently no good therapeutic agents available. CaMKII has been indicated to be closely related to the occurrence of renal fibrosis, and its specific inhibitory peptide AIP, was shown to directly bind the active site of CaMKII. In this study, we examined the effect of AIP on the progression of renal fibrosis and its possible mechanism. The results showed that AIP could inhibit the expression of the fibrosis markers Fibronectin, Collagen I, MMP2 and α-SMA in vivo and in vitro. Further analysis revealed that AIP could inhibit the expression of various epithelial-to-mesenchymal transformation (EMT)-related markers, such as Vimentin and Snail 1, in vivo and in vitro. Mechanistically, AIP could significantly inhibit the activation of CaMKII, Smad 2, Raf and ERK in vitro and in vivo and reduce the expression of TGF-β in vivo. These results suggested that AIP could alleviate renal fibrosis by inhibiting CaMKII and blocking activation of the TGF-β/Smad2 and RAF/ERK pathways. Our study provides a possible drug candidate and demonstrates that CaMKII is a potential pharmacological target for the treatment of renal fibrosis. Significance Statement We have demonstrated that AIP significantly attenuated TGF-β1-induced fibrogenesis and ameliorated UUO-induced renal fibrosis through the CaMKII/TGF-β/Smad and CaMKII/RAF/ERK signaling pathways in vitro and in vivo. Our study provides a possible drug candidate and demonstrates that CaMKII can be a potential pharmacological target for the treatment of renal fibrosis.

Increased CaMKII activation and contrast changes of cardiac β1-and β3-Adrenergic signaling pathways in a humanized angiotensinogen model of hypertension

AimsUpregulation of Ca2+/calmodulin-dependent protein kinase II (CaMKII) contributes to the pathogenesis of cardiovascular disease, including hypertension. Transgenic rats expressing the human angiotensinogen gene [TGR (hAGT)L1623] are a new novel humanized model of hypertension that associates with declines in cardiac contractile function and β-adrenergic receptor (AR) reserve. The molecular mechanisms are unclear. We tested the hypothesis that in TGR (hAGT)L1623 rats, left ventricular (LV) myocyte CaMKIIδ and β3-AR are upregulated, but β1-AR is down-regulated, which are important causes of cardiac dysfunction and β-AR desensitization. Main methodsWe compared LV myocyte CaMKIIδ, CaMKIIδ phosphorylation (at Thr287) (pCaMKIIδ), and β1-and β3-AR expressions and determined myocyte functional and [Ca2+]I transient ([Ca2+]iT) responses to β-AR stimulation with and without pretreatment of myocytes using an inhibitor of CaMKII, KN-93 (10−6 M, 30 min) in male Sprague Dawley (SD; N = 10) control and TGR (hAGT)L1623 (N = 10) adult rats. Key findingsHypertension in TGR (hAGT)L1623 rats was accompanied by significantly increased LV myocyte β3-AR protein levels and reduced β1-AR protein levels. CaMKIIδ phosphorylation (at Thr287), pCaMKIIδ was significantly increased by 35%. These changes were followed by significantly reduced basal cell contraction (dL/dtmax), relaxation (dR/dtmax), and [Ca2+]iT. Isoproterenol (10−8 M) produced significantly smaller increases in dL/dtmax, dR/dtmax, and [Ca2+]iT. Moreover, only in TGR (hAGT)L1623 rats, pretreatment of LV myocytes with KN-93 (10−6 M, 30 min) fully restored normal basal and isoproterenol-stimulated myocyte contraction, relaxation, and [Ca2+]iT. SignificanceLV myocyte CaMKIIδ overactivation with associated contrast changes in β3-AR and β1-AR may be the key molecular mechanism for the abnormal contractile phenotype and β-AR desensitization in this humanized model of hypertension.

Imaging single CaMKII holoenzymes at work by high-speed atomic force microscopy.

Ca2+/calmodulin-dependent protein kinase II (CaMKII) plays a pivotal role in synaptic plasticity. It is a dodecameric serine/threonine kinase that has been highly conserved across metazoans for over a million years. Despite the extensive knowledge of the mechanisms underlying CaMKII activation, its behavior at the molecular level has remained unobserved. In this study, we used high-speed atomic force microscopy to visualize the activity-dependent structural dynamics of rat/hydra/C. elegans CaMKII with nanometer resolution. Our imaging results revealed that the dynamic behavior is dependent on CaM binding and subsequent pT286 phosphorylation. Among the species studies, only rat CaMKIIα with pT286/pT305/pT306 exhibited kinase domain oligomerization. Furthermore, we revealed that the sensitivity of CaMKII to PP2A in the three species differs, with rat, C. elegans, and hydra being less dephosphorylated in that order. The evolutionarily acquired features of mammalian CaMKIIα-specific structural arrangement and phosphatase tolerance may differentiate neuronal function between mammals and other species.

An improved reporter identifies ruxolitinib as a potent and cardioprotective CaMKII inhibitor.

Ca2+/calmodulin-dependent protein kinase II (CaMKII) hyperactivity causes cardiac arrhythmias, a major source of morbidity and mortality worldwide. Despite proven benefits of CaMKII inhibition in numerous preclinical models of heart disease, translation of CaMKII antagonists into humans has been stymied by low potency, toxicity, and an enduring concern for adverse effects on cognition due to an established role of CaMKII in learning and memory. To address these challenges, we asked whether any clinically approved drugs, developed for other purposes, were potent CaMKII inhibitors. For this, we engineered an improved fluorescent reporter, CaMKAR (CaMKII activity reporter), which features superior sensitivity, kinetics, and tractability for high-throughput screening. Using this tool, we carried out a drug repurposing screen (4475 compounds in clinical use) in human cells expressing constitutively active CaMKII. This yielded five previously unrecognized CaMKII inhibitors with clinically relevant potency: ruxolitinib, baricitinib, silmitasertib, crenolanib, and abemaciclib. We found that ruxolitinib, an orally bioavailable and U.S. Food and Drug Administration-approved medication, inhibited CaMKII in cultured cardiomyocytes and in mice. Ruxolitinib abolished arrhythmogenesis in mouse and patient-derived models of CaMKII-driven arrhythmias. A 10-min pretreatment in vivo was sufficient to prevent catecholaminergic polymorphic ventricular tachycardia, a congenital source of pediatric cardiac arrest, and rescue atrial fibrillation, the most common clinical arrhythmia. At cardioprotective doses, ruxolitinib-treated mice did not show any adverse effects in established cognitive assays. Our results support further clinical investigation of ruxolitinib as a potential treatment for cardiac indications.

Cardiac-specific BACH1 ablation attenuates pathological cardiac hypertrophy by inhibiting the Ang II type 1 receptor expression and the Ca2+/CaMKII pathway.

BACH1 is upregulated in hypertrophic hearts, but its function in cardiac hypertrophy remains largely unknown. This research investigates the function and mechanisms of BACH1 in the regulation of cardiac hypertrophy. Male cardiac-specific BACH1 knockout mice or cardiac-specific BACH1 transgenic (BACH1-Tg) mice and their respective wild-type littermates developed cardiac hypertrophy induced by angiotensin II (Ang II) or transverse aortic constriction (TAC). Cardiac-specific BACH1 knockout in mice protected the hearts against Ang II- and TAC-induced cardiac hypertrophy and fibrosis, and preserved cardiac function. Conversely, cardiac-specific BACH1 overexpression markedly exaggerated cardiac hypertrophy and fibrosis and reduced cardiac function in mice with Ang II- and TAC-induced hypertrophy. Mechanistically, BACH1 silencing attenuated Ang II- and norepinephrine-stimulated calcium/calmodulin-dependent protein kinase II (CaMKII) signaling, the expression of hypertrophic genes, and hypertrophic growth of cardiomyocytes. Ang II stimulation promoted the nuclear localization of BACH1, facilitated the recruitment of BACH1 to the Ang II type 1 receptor (AT1R) gene promoter, and then increased the expression of AT1R. Inhibition of BACH1 attenuated Ang II-stimulated AT1R expression, cytosolic Ca2+ levels, and CaMKII activation in cardiomyocytes, whereas overexpression of BACH1 led to the opposite effects. The increased expression of hypertrophic genes induced by BACH1 overexpression upon Ang II stimulation was suppressed by CaMKII inhibitor KN93. The AT1R antagonist, losartan, significantly attenuated BACH1-mediated CaMKII activation and cardiomyocyte hypertrophy under Ang II stimulation in vitro. Similarly, Ang II-induced myocardial pathological hypertrophy, cardiac fibrosis, and dysfunction in BACH1-Tg mice were blunted by treatment with losartan. This study elucidates a novel important role of BACH1 in pathological cardiac hypertrophy by regulating the AT1R expression and the Ca2+/CaMKII pathway, and highlights potential therapeutic target in pathological cardiac hypertrophy. Transcription factor BACH1 is increased in failing human myocardium and hypertrophic human hearts. We revealed that cardiomyocyte-specific BACH1 ablation in mice protected the hearts against Ang II- and pressure overload-induced cardiac hypertrophy and fibrosis, and preserved cardiac function. BACH1 activated AT1R promoter activity under Ang II stimulation, and BACH1-mediated facilitation of cardiac hypertrophy under Ang II stimulation was regulated at least in part by AT1R expression. Moreover, BACH1 silencing attenuated the norepinephrine-stimulated CaMKII signaling pathway and hypertrophic growth of cardiomyocytes. Our findings suggest that BACH1 may pose a promising therapeutic target in pathological cardiac hypertrophy and heart failure.

Muscarinic receptor activation overrides boundary conditions on memory updating in a calcium/calmodulin-dependent manner.

Long-term memory storage is a dynamic process requiring flexibility to ensure adaptive behavioural responding in changing environments. Indeed, it is well established that memory reactivation can "destabilize" consolidated traces, leading to various forms of updating. However, the neurobiological mechanisms rendering long-term memories labile and modifiable remain poorly described. Moreover, boundary conditions, such as the age or strength of the memory, can reduce the likelihood of this destabilization; yet, intuitively, these most behaviourally influential of memories should also be modifiable under appropriate conditions. Here, we provide evidence that salient novelty at the time of memory reactivation promotes integrative updating of resistant object memories in rats. Furthermore, blockade of muscarinic acetylcholine receptors (mAChRs; with pirenzepine) or disruption of calcium/calmodulin (Ca2+/CaM) with KN-93, a Ca2+/CaM-binding molecule that inhibits calcium/calmodulin-dependent protein kinase II (CaMKII) activation, in perirhinal cortex (PRh) prevented novelty-induced destabilization and updating of resistant object memories. Finally, PRh M1 mAChR activation (with CDD-0102A) was sufficient to destabilize resistant object memories for updating, and this effect was blocked by KN-93, possibly via inhibition of CaMKII activity. Thus, mAChRs and activation of CaMKII appear to interact as part of a mechanism to override boundary conditions on resistant object memories to ensure integrative modification with novel information. These findings therefore have important implications for understanding the dynamic nature of long-term memory storage and potential treatments for conditions characterized by maladaptive and inflexible memories.

Post-translational modification-dependent regulation of CaMKII-delta conformation in live cardiac myocytes.

Calcium/calmodulin dependent protein kinase II (CaMKII) is a key regulator of numerous functions in cardiac myocytes including Ca regulation, contraction, and transcriptional control. Overactivation of CaMKII due to post-translational modifications like autophosphorylation at Thr287 can autonomously activate and prolong CaMKII activation, even after Ca/CaM dissociates, and thereby promote cardiac pathologies such as heart failure and arrhythmias. The specific molecular mechanisms by which CaMKII PTMs autonomously activate and prolong kinase activity are not fully understood. We found using a novel intermolecular FRET-based approach in live myocytes in a recent study that PTM-dependent alteration in CaMKII's affinity for CaM is one molecular basis by which CaMKII becomes autonomously activated. Here, we investigate how the conformational state of CaMKII in the autonomously activated state may be affected by PTMs using our FRET-based CaMKIIδ conformational state reporter, Camui (RFP-CaMKIIδ-GFP), and its phosphomimetic (T287D) and phosphoresistant (T287A) mutant variants, expressed via adenoviral infection in intact cardiac myocytes. We also conducted parallel in vitro biochemical experiments using HEK cell lysates. We found that the phosphomimetic T287D Camui exhibited prolonged durations in the active open conformational state following pacing-induced activation relative to WT or phosphoresistant T287A Camui. Moreover, the prolonged autonomous conformational state persisted even after intracellular Ca levels returned to diastolic levels at which CaM dissociates. These data suggest that PTM-dependent regulation of the conformational state of CaMKII may serve as an additional molecular mechanism for autonomous CaMKII activation that may function in tandem with PTM-dependent alterations in CaMKII's affinity for CaM.

Spatio-specific CaMKII activation in cardiomyocytes from hypertensive Dahl salt-sensitive rats.

Hypertension, the number one risk factor for heart failure development, is one of the largest unmet medical needs in cardiovascular medicine. New evidence positions Ca2+/calmodulin-dependent protein kinase II (CaMKII) activation as a driver of hypertension-induced cardiac remodeling. However, it remains to be elucidated what the precise effect of localisation-dependent activation is. Our most recent data show that the spatio-temporal CaMKII activation profile is crucial for determining whether it takes a protective or maladaptive role. Namely, its activation in the cytoplasm and on the nuclear envelope can speed up calcium uptake and release from cellular calcium stores on a beat-to-beat basis, while activation in the nucleoplasm triggers maladaptive gene signaling. We therefore performed subcellular immunocytochemistry analysis directed against phosphorylated CaMKII (pCaMKII) in isolated cardiomyocytes from hypertensive Dahl-salt sensitive rats at two disease stages. Additionally, we treated a subset of cells with the beta-adrenergic agonist isoprenaline to investigate the effect of short term stress induction. We observed lower pCaMKII levels in the nucleoplasm of early-stage hypertensive rats, while levels in the cytoplasm and at the nuclear envelope remained unchanged compared to age-matched control rats. Late-stage hypertension resulted in elevated pCaMKII levels in the cytoplasm, at the nuclear envelope and in the nucleoplasm. Upon short-term beta-adrenergic stimulation activation of CaMKII in the cytoplasm and at the nuclear envelope of both groups increased, while only hypertensive rats responded with elevated pCaMKII levels in the nucleoplasm. Taken together, our findings indicate that the spatio-specific CaMKII activation profile is altered in hypertension-induced cardiac remodeling and dependent on the disease stage. Further, hypertension escalates the response of CaMKII to beta-adrenergic stimulation in the nucleoplasm. These findings will provide new evidence to develop better therapeutic strategies fine-tuning spatio-specific CaMKII activation.