CaMKII-dependent regulation of cardiac Na(+) homeostasis.

Na(+) homeostasis is a key regulator of cardiac excitation and contraction. The cardiac voltage-gated Na(+) channel, NaV1.5, critically controls cell excitability, and altered channel gating has been implicated in both inherited and acquired arrhythmias. Ca(2) (+)/calmodulin-dependent protein kinase II (CaMKII), a serine/threonine kinase important in cardiac physiology and disease, phosphorylates NaV1.5 at multiple sites within the first intracellular linker loop to regulate channel gating. Although CaMKII sites on the channel have been identified (S516, T594, S571), the relative role of each of these phospho-sites in channel gating properties remains unclear, whereby both loss-of-function (reduced availability) and gain-of-function (late Na(+) current, INa L) effects have been reported. Our review highlights investigating the complex multi-site phospho-regulation of NaV1.5 gating is crucial to understanding the genesis of acquired arrhythmias in heart failure (HF) and CaMKII activated conditions. In addition, the increased Na(+) influx accompanying INa L may also indirectly contribute to arrhythmia by promoting Ca(2) (+) overload. While the precise mechanisms of Na(+) loading during HF remain unclear, and quantitative analyses of the contribution of INa L are lacking, disrupted Na(+) homeostasis is a consistent feature of HF. Computational and experimental observations suggest that both increased diastolic Na(+) influx and action potential prolongation due to systolic INa L contribute to disruption of Ca(2) (+) handling in failing hearts. Furthermore, simulations reveal a synergistic interaction between perturbed Na(+) fluxes and CaMKII, and confirm recent experimental findings of an arrhythmogenic feedback loop, whereby CaMKII activation is at once a cause and a consequence of Na(+) loading

CaMKII delta C Drives Early Adaptive Ca(2+)Change and Late Eccentric Cardiac Hypertrophy

Rationale: CaMKII (Ca2+-Calmodulin dependent protein kinase) delta C activation is implicated in pathological progression of heart failure (HF) and CaMKII delta C transgenic mice rapidly develop HF and arrhythmias. However, little is known about early spatio-temporal Ca(2+)handling and CaMKII activation in hypertrophy and HF. Objective: To measure time- and location-dependent activation of CaMKII delta C signaling in adult ventricular cardiomyocytes, during transaortic constriction (TAC) and in CaMKII delta C transgenic mice. Methods and Results: We used human tissue from nonfailing and HF hearts, 4 mouse lines: wild-type, KO (CaMKII delta-knockout), CaMKII delta C transgenic in wild-type (TG), or KO background, and wild-type mice exposed to TAC. Confocal imaging and biochemistry revealed disproportional CaMKII delta C activation and accumulation in nuclear and perinuclear versus cytosolic regions at 5 days post-TAC. This CaMKII delta activation caused a compensatory increase in sarcoplasmic reticulum Ca(2+)content, Ca(2+)transient amplitude, and [Ca2+] decline rates, with reduced phospholamban expression, all of which were most prominent near and in the nucleus. These early adaptive effects in TAC were entirely mimicked in young CaMKII delta TG mice (6-8 weeks) where no overt cardiac dysfunction was present. The (peri)nuclear CaMKII accumulation also correlated with enhanced HDAC4 (histone deacetylase) nuclear export, creating a microdomain for transcriptional regulation. At longer times both TAC and TG mice progressed to overt HF (at 45 days and 11-13 weeks, respectively), during which time the compensatory Ca(2+)transient effects reversed, but further increases in nuclear and time-averaged [Ca2+] and CaMKII activation occurred. CaMKII delta TG mice lacking delta B exhibited more severe HF, eccentric myocyte growth, and nuclear changes. Patient HF samples also showed greatly increased CaMKII delta expression, especially for CaMKII delta C in nuclear fractions. Conclusions: We conclude that in early TAC perinuclear CaMKII delta C activation promotes adaptive increases in myocyte Ca(2+)transients and nuclear transcriptional responses but that chronic progression of this nuclear Ca2+-CaMKII delta C axis contributes to eccentric hypertrophy and HF

CaMKII-dependent regulation of cardiac Na(+) homeostasis.

Na(+) homeostasis is a key regulator of cardiac excitation and contraction. The cardiac voltage-gated Na(+) channel, NaV1.5, critically controls cell excitability, and altered channel gating has been implicated in both inherited and acquired arrhythmias. Ca(2) (+)/calmodulin-dependent protein kinase II (CaMKII), a serine/threonine kinase important in cardiac physiology and disease, phosphorylates NaV1.5 at multiple sites within the first intracellular linker loop to regulate channel gating. Although CaMKII sites on the channel have been identified (S516, T594, S571), the relative role of each of these phospho-sites in channel gating properties remains unclear, whereby both loss-of-function (reduced availability) and gain-of-function (late Na(+) current, INa L) effects have been reported. Our review highlights investigating the complex multi-site phospho-regulation of NaV1.5 gating is crucial to understanding the genesis of acquired arrhythmias in heart failure (HF) and CaMKII activated conditions. In addition, the increased Na(+) influx accompanying INa L may also indirectly contribute to arrhythmia by promoting Ca(2) (+) overload. While the precise mechanisms of Na(+) loading during HF remain unclear, and quantitative analyses of the contribution of INa L are lacking, disrupted Na(+) homeostasis is a consistent feature of HF. Computational and experimental observations suggest that both increased diastolic Na(+) influx and action potential prolongation due to systolic INa L contribute to disruption of Ca(2) (+) handling in failing hearts. Furthermore, simulations reveal a synergistic interaction between perturbed Na(+) fluxes and CaMKII, and confirm recent experimental findings of an arrhythmogenic feedback loop, whereby CaMKII activation is at once a cause and a consequence of Na(+) loading

CaMKII in Cardiac Health and Disease

The calcium-calmodulin dependent protein kinases (CaMKs) are a broadly expressed family of calcium-sensitive intracellular kinases, which are responsible for transducing cytosolic calcium signals into phosphorylation-based regulation of proteins and physiological functions. As the multifunctional member of the family, CaMKII has become the most prominent for its roles in the central nervous system and heart, where it controls a diverse range of calcium-dependent processes; from learning and memory at the neuronal synapse, to cellular growth and death in the myocardium. In the heart, CaMKII directly regulates many of the most important ion channels and calcium handling proteins, and controls the expression of an ever-increasing number of transcripts and their downstream products. Functionally, these actions are thought to orchestrate many of the electrophysiologic and contractile adaptations to common cardiac stressors, such as rapid pacing, chronic adrenergic stimulation, and oxidative challenge. In the context of disease, CaMKII has been shown to contribute to a remarkably wide variety of cardiac pathologies, of which heart failure (HF) is the most conspicuous. Hyperactivity of CaMKII is an established contributor to pathological cardiac remodeling, and is widely thought to directly promote arrhythmia and contractile dysfunction during HF. Moreover, several non-failing arrhythmia-susceptible phenotypes, which result from specific genetic channelopathies, functionally mimic constitutive channel phosphorylation by CaMKII. Because CaMKII contributes to both the acute and chronic manifestations of major cardiac diseases, but may be only minimally required for homeostasis in the absence of chronic stress, it has come to be one of the most promising therapeutic drug targets in cardiac biology. Thus, development of more specific and deliverable small molecule antagonists remains a key priority for the field. Here we provide a selection of articles to summarize the state of our knowledge regarding CaMKII in cardiac health and disease, with a particular view to highlighting recent developments in CaMKII activation, and new targets in CaMKII-mediated control of myocyte physiology

CaMKII Phosphorylation of Na(V)1.5: Novel in Vitro Sites Identified by Mass Spectrometry and Reduced S516 Phosphorylation in Human Heart Failure.

The cardiac voltage-gated sodium channel, Na(V)1.5, drives the upstroke of the cardiac action potential and is a critical determinant of myocyte excitability. Recently, calcium (Ca(2+))/calmodulin(CaM)-dependent protein kinase II (CaMKII) has emerged as a critical regulator of Na(V)1.5 function through phosphorylation of multiple residues including S516, T594, and S571, and these phosphorylation events may be important for the genesis of acquired arrhythmias, which occur in heart failure. However, phosphorylation of full-length human Na(V)1.5 has not been systematically analyzed and Na(V)1.5 phosphorylation in human heart failure is incompletely understood. In the present study, we used label-free mass spectrometry to assess phosphorylation of human Na(V)1.5 purified from HEK293 cells with full coverage of phosphorylatable sites and identified 23 sites that were phosphorylated by CaMKII in vitro. We confirmed phosphorylation of S516 and S571 by LC-MS/MS and found a decrease in S516 phosphorylation in human heart failure, using a novel phospho-specific antibody. This work furthers our understanding of the phosphorylation of Na(V)1.5 by CaMKII under normal and disease conditions, provides novel CaMKII target sites for functional validation, and provides the first phospho-proteomic map of full-length human Na(V)1.5

TAK1 converts Sequestosome 1/p62 from an autophagy receptor to a signaling platform

The protein p62/Sequestosome 1 (p62) has been described as a selective autophagy receptor and independently as a platform for pro‐inflammatory and other intracellular signaling. How these seemingly disparate functional roles of p62 are coordinated has not been resolved. Here, we show that TAK1, a kinase involved in immune signaling, negatively regulates p62 action in autophagy. TAK1 reduces p62 localization to autophagosomes, dampening the autophagic degradation of both p62 and p62‐directed autophagy substrates. TAK1 also relocalizes p62 into dynamic cytoplasmic bodies, a phenomenon that accompanies the stabilization of TAK1 complex components. On the other hand, p62 facilitates the assembly and activation of TAK1 complexes, suggesting a connection between p62's signaling functions and p62 body formation. Thus, TAK1 governs p62 action, switching it from an autophagy receptor to a signaling platform. This ability of TAK1 to disable p62 as an autophagy receptor may allow certain autophagic substrates to accumulate when needed for cellular functions