Regulation of the human atrial myosin light chain 1 promoter by Ca2+‐calmodulin‐dependent signaling pathways

Tissue Expression of Atrial and Ventricular Myosin Light Chains in the Mechanism of Adaptation to Oxidative Stress

Ischemia/reperfusion (I/R) injury induces post-translational modifications of myosin light chains (MLCs), increasing their susceptibility to degradation by matrix metalloproteinase 2 (MMP-2). This results in the degradation of ventricular light chains (VLC1) in heart ventricles. The aim of the study was to investigate changes in MLCs content in the mechanism of adaptation to oxidative stress during I/R. Rat hearts, perfused using the Langendorff method, were subjected to I/R. The control group was maintained in oxygen conditions. Lactate dehydrogenase (LDH) activity and reactive oxygen/nitrogen species (ROS/RNS) content were measured in coronary effluents. Atrial light chains (ALC1) and ventricular light chains (VLC1) gene expression were examined using RQ-PCR. ALC1 and VLC1 protein content were measured using ELISA tests. MMP-2 activity was assessed by zymography. LDH activity as well as ROS/RNS content in coronary effluents was higher in the I/R group (p = 0.01, p = 0.04, respectively), confirming heart injury due to increased oxidative stress. MMP-2 activity in heart homogenates was also higher in the I/R group (p = 0.04). ALC1 gene expression and protein synthesis were significantly increased in I/R ventricles (p < 0.01, 0.04, respectively). VLC1 content in coronary effluents was increased in the I/R group (p = 0.02), confirming the increased degradation of VLC1 by MMP-2 and probably an adaptive production of ALC1 during I/R. This mechanism of adaptation to oxidative stress led to improved heart mechanical function.

Pasireotide prevents nuclear factor of activated T cells nuclear translocation and acts as a protective agent in aminoglycoside-induced auditory hair cell loss

Hearing impairment is a global health problem with a high socioeconomic impact. Damage to auditory hair cells (HCs) in the inner ear as a result of aging, disease, trauma, or toxicity, underlies the majority of cases of sensorineural hearing loss. Previously we demonstrated that the Ca²⁺ -sensitive neuropeptide, somatostatin (SST), and an analog, octreotide, protect HCs from gentamicin-induced cell death in vitro. Aminoglycosides such as gentamicin trigger a calcium ion influx (Ca²⁺ ) that activates pro-apoptotic signaling cascades in HCs. SST binding to the G-protein-coupled receptors (SSTR1-SSTR5) that are directly linked to voltage-dependent Ca²⁺ channels inhibits Ca²⁺ channel activity and associated downstream events. Here, we report that the SST analog pasireotide, a high affinity ligand to SSTRs 1-3, and 5, with a longer half-life than octreotide, prevents gentamicin-induced HC death in the mouse organ of Corti (OC). Explant experiments using OCs derived from SSTR1 and SSTR1and 2 knockout mice, revealed that SSTR2 mediates pasireotide's anti-apoptotic effects. Mechanistically, pasireotide prevented a nuclear translocation of the Ca²⁺ -sensitive transcription factor, nuclear factor of activated T cells (NFAT), which is ordinarily provoked by gentamicin in OC explants. Direct inhibition of NFAT with 11R-VIVIT also prevented the gentamicin-dependent nuclear translocation of NFAT and apoptosis. Both pasireotide and 11R-VIVIT partially reversed the effects of gentamicin on the expression of downstream survival targets (NMDA receptor and the regulatory subunit of phosphatidylinositol-4,5-bisphosphate 3-kinase, PI3K). These data suggest that SST analogs antagonize aminoglycoside-induced cell death in an NFAT-dependent fashion. SST analogs and NFAT inhibitors may therefore offer new therapeutic possibilities for the treatment of hearing loss.

Protein Kinases as Drug Development Targets for Heart Disease Therapy

Protein kinases are intimately integrated in different signal transduction pathways for the regulation of cardiac function in both health and disease. Protein kinase A (PKA), Ca²⁺-calmodulin-dependent protein kinase (CaMK), protein kinase C (PKC), phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) are not only involved in the control of subcellular activities for maintaining cardiac function, but also participate in the development of cardiac dysfunction in cardiac hypertrophy, diabetic cardiomyopathy, myocardial infarction, and heart failure. Although all these kinases serve as signal transducing proteins by phosphorylating different sites in cardiomyocytes, some of their effects are cardioprotective whereas others are detrimental. Such opposing effects of each signal transduction pathway seem to depend upon the duration and intensity of stimulus as well as the type of kinase isoform for each kinase. In view of the fact that most of these kinases are activated in heart disease and their inhibition has been shown to improve cardiac function, it is suggested that these kinases form excellent targets for drug development for therapy of heart disease.

Deafferentation-induced activation of NFAT (nuclear factor of activated T-cells) in cochlear nucleus neurons during a developmental critical period: a role for NFATc4-dependent apoptosis in the CNS

During the development and maturation of sensory neurons, afferent activity is required for normal maintenance. There exists a developmental window of time when auditory neurons, including neurons of the anteroventral cochlear nucleus (AVCN), depend on afferent input for survival. This period of time is often referred to as a critical period. The cellular and molecular mechanisms that underlie AVCN neuron susceptibility to deafferentation-induced death remain unknown. Here, we show that only during this critical period deafferentation of mouse AVCN neurons by in vivo cochlea removal results in rapid nuclear translocation and activation of the transcription factor NFATc4 (nuclear factor of activated T-cells isoform 4). NFAT activation is abolished by in vivo treatment with the calcineurin inhibitor FK506 and the specific NFAT-inhibitor 11R-VIVIT. Inhibition of NFAT significantly attenuates deafferentation-induced apoptosis of AVCN neurons and abolishes NFAT-mediated expression of FasL, an initiator of apoptotic pathways, in the cochlear nucleus. These data suggest that NFAT-mediated gene expression plays a role in deafferentation-induced apoptosis of cochlear nucleus neurons during a developmental critical period.

Aerobic interval training enhances cardiomyocyte contractility and Ca2+ cycling by phosphorylation of CaMKII and Thr-17 of phospholamban

Cardiac adaptation to aerobic exercise training includes improved cardiomyocyte contractility and calcium handling. Our objective was to determine whether cytosolic calcium/calmodulin-dependent kinase II and its downstream targets are modulated by exercise training. A six-week aerobic interval training program by treadmill running increased maximal oxygen uptake by 35% in adult mice, whereupon left ventricular cardiomyocyte function was studied and myocardial tissue samples were used for biochemical analysis. Cardiomyocytes from trained mice had enhanced contractility and faster relaxation rates, which coincided with larger amplitude and faster decay of the calcium transient, but not increased peak systolic calcium levels. These changes were associated with reduced phospholamban expression relative to sarcoplasmic reticulum calcium ATPase and constitutively increased phosphorylation of phospholamban at the threonine 17, but not at the serine 16 site. Calcium/calmodulin-dependent kinase IIdelta phosphorylation was increased at threonine 287, indicating activation. To investigate the physiological role of calcium/calmodulin-dependent kinase IIdelta phosphorylation, this kinase was blocked specifically by autocamtide-2 related inhibitory peptide II. This maneuver completely abolished training-induced improvements of cardiomyocyte contractility and calcium handling and blunted, but did not completely abolish the training-induced increase in Ca(2+) sensitivity. Also, inhibition of calcium/calmodulin-dependent kinase II reduced the greater frequency-dependent acceleration of relaxation that was observed after aerobic interval training. These observations indicate that calcium/calmodulin-dependent kinase IIdelta contributes significantly to the functional adaptation of the cardiomyocyte to regular exercise training.

Myosin essential light chain in health and disease

The essential light chain of myosin (ELC) is known to be important for structural stability of the alpha-helical lever arm domain of the myosin head, but its function in striated muscle contraction is poorly understood. Two ELC isoforms are expressed in fast skeletal muscle, a long isoform and its NH(2)-terminal approximately 40 amino acid shorter counterpart, whereas only the long ELC is observed in the heart. Biochemical and structural studies revealed that the NH(2)-terminus of the long ELC can make direct contacts with actin, but the effects of the ELC on the affinity of myosin for actin, ATPase, force, and the kinetics of force generating myosin cross-bridges are inconclusive. Myosin containing the long ELC has been shown to have slower cross-bridge kinetics than myosin with the short isoform. A difference was also reported among myosins with long isoforms. Increased shortening velocity was observed in atrial compared with ventricular muscle fibers. The common findings suggest that ELC provides the fine tuning of the myosin motor function, which is regulated in an isoform and tissue-dependent manner. The functional importance of the ELC is further implicated by the discovery of ELC mutations associated with Familial Hypertrophic Cardiomyopathy. The pathological phenotypes vary in severity, but more notably, almost all ELC mutations result in sudden cardiac death at a young age. This review summarizes the functional roles of striated muscle ELC in normal healthy muscle and in disease. Transgenic animal models and phenotypic characterization of ELC-mediated remodeling of the heart are also discussed.

Shuttling of HDAC5 in H9C2 cells regulates YY1 function through CaMKIV/PKD and PP2A

YY1 is a transcription factor that can activate or repress transcription of a variety of genes and is involved in several developmental processes. YY1 is a repressor of transcription in differentiated H9C2 cells and in neonatal cardiac myocytes but an activator of transcription in undifferentiated H9C2 cells. We now present a detailed analysis of the functional domains of YY1 when it is acting as a repressor or an activator and identify the mechanism whereby its function is regulated in the differentiation of H9C2 cells. We show that histone deacetylase 5 (HDAC5) is localized to the cytoplasm in undifferentiated H9C2 cells and that this localization is dependent on Ca(2+)/calmodulin-dependent kinase IV (CaMKIV) and/or protein kinase D (PKD). In differentiated cells, HDAC5 is nuclear and interacts with YY1. Finally, we show that HDAC5 localization in differentiated cells is dependent on phosphatase 2A (PP2A). Our results suggest that a signaling mechanism that involves CaMKIV/PKD and PP2A controls YY1 function through regulation of HDAC5 and is important in the maintenance of muscle differentiation.