Abstract P413: Stretch-induced Caveolae-mediated Disruption Of Cyclic AMP Microdomains Leads To Arrhythmogenic Ca 2+ Mishandling In Mouse Atrial Myocytes

2021 ◽  
Vol 129 (Suppl_1) ◽  
Author(s):  
Roman Y Medvedev ◽  
Frank C DeGuire ◽  
Alexey Glukhov
Keyword(s):  
Ryanodine Receptors ◽  
Mechanical Stretch ◽  
Confocal Imaging ◽  
Size Analysis ◽  
Cholesterol Depletion ◽  
Wild Type ◽  
Atrial Myocytes ◽  
Camp Production ◽  
Cell Width ◽  
Cell Stretch

Background: Atrial fibrillation (AF) often occurs during hypertension and is associated with an increase in cardiomyocyte stretch. Mechanism of ectopic beats, that trigger AF, has been linked to Ca 2+ mishandling and leaky hyperphosphorylated ryanodine receptors (RyRs), while the underlying mechanisms remain elusive. Caveolae membrane structures are involved in cell mechanosensing processes and control the cAMP signaling pathway. We hypothesized that mechanical stretch disrupts caveolae, promoting cAMP production and sarcoplasmic reticulum Ca 2+ leak via augmentation of RyRs phosphorylation. Methods and Results: Cell size analysis and Ca 2+ dynamics measurements were performed by confocal imaging of isolated mouse atrial myocytes. Cell stretch was modeled by hypoosmotic swelling (from 310 mOsM to 220 mOsM to flatten caveolae structures) resulting in a ~30% increase in cell width (p<0.05) with no changes in cell length. Swelling resulted in a biphasic effect on Ca 2+ spark activity: a fast (<10 min of exposure) ~50% increase (p<0.001) followed by a slow decrease to the level observed in isotonic conditions (>30 min of exposure). Similarly, caveolae disruption via cholesterol depletion by 10 mM methyl-β-cyclodextrin (MβCD) led to 2-fold increase in Ca 2+ sparks frequency (p<0.001). Swelling- and MβCD-induced increases in atrial Ca 2+ spark activity were prevented via inhibition of cAMP production by adenylyl cyclases by 0.1mM SQ22536 or cAMP-dependent protein kinase A (PKA) by 1μM H-89. Then, we tested if this mechanism is present in atrial myocytes from pressure-overloaded (4-weeks transaortic constriction, TAC) mice. Atrial myocytes from TAC mice showed a 1.6 times higher Ca 2+ sparks frequency than wild-type myocytes (p<0.01), which was significantly reduced (p<0.01) to wild-type level after incubation with SQ22536. Conclusions: Our findings suggest that cell stretch increases spontaneous Ca 2+ spark activity through the disruption of caveolae and cAMP-mediated augmentation of PKA activity. This mechanism could be involved in the Ca 2+ mishandling and AF in pressure overloaded hearts.

Abstract 292: The Role of the ATF6 Branch of the ER Stress Response in the Endocrine Heart

2016 ◽  
Vol 119 (suppl_1) ◽  
Author(s):  
Erik A Blackwood ◽  
Christopher C Glembotski
Keyword(s):  
Stress Response ◽  
Er Stress ◽  
Knockout Mice ◽  
Ex Vivo ◽  
Proteolytic Cleavage ◽  
Isolated Perfused Heart ◽  
Wild Type ◽  
Atrial Myocytes ◽  
Perfused Heart ◽  
Er Stress Response

Rationale: Atrial natriuretic peptide (ANP) is stored in the heart in large dense core granules of atrial myocytes as a biologically inactive precursor, pro-ANP. Hemodynamic stress and atrial stretch stimulate coordinate secretion and proteolytic cleavage of pro-ANP to its bioactive form, ANP, which promotes renal salt excretion and vasodilation, which, together contribute to decreasing blood pressure. While the ATF6 branch of the ER stress response has been studied in ventricular tissue mouse models of myocardial ischemia and pathological hypertrophy, roles for ATF6 and ER stress on the endocrine function of atrial myocytes have not been studied. Objective/Methods: To address this gap in our knowledge, we knocked down ATF6 in primary cultured neonatal rat atrial myocytes (NRAMs) using a chemical inhibitor of the proteolytic cleavage site enabling ATF6 activation and siRNA and measured ANP expression and secretion basally and in response to alpha- adrenergic agonist stimulation using phenylephrine. We also compared the ANP secretion from wild- type mice and ATF6 knockout mice in an ex vivo Langendorff model of the isolated perfused heart. Results: ATF6 knockdown in NRAMs significantly impaired basal and phenylephrine-stimulated ANP secretion. ATF6 knockout mice displayed lower levels of ANP in atrial tissue at baseline as well as after phenylephrine treatment. Similarly, in the ex vivo isolated perfused heart model, less ANP was detected in effluent of ATF6 knockout hearts compared to wild-type hearts. Conclusions: The ATF6 branch of the ER stress response is necessary for efficient co-secretional processing of pro-ANP to ANP and for agonist-stimulated ANP secretion from atrial myocytes. As ANP is secreted in a regulated manner in response to a stimulus and pro-ANP is synthesized and packaged through the classical secretory pathway, we posit that ATF6 is required for adequate expression, folding, trafficking, processing and secretion of biologically active ANP from the endocrine heart.

scholarly journals SERCA Cys674 sulphonylation and inhibition of L-type Ca2+ influx contribute to cardiac dysfunction in endotoxemic mice, independent of cGMP synthesis

2013 ◽  
Vol 305 (8) ◽  
pp. H1189-H1200 ◽  
Author(s):  
Ion A. Hobai ◽  
Emmanuel S. Buys ◽  
Justin C. Morse ◽  
Jessica Edgecomb ◽  
Eric H. Weiss ◽  
...  
Keyword(s):  
Posttranslational Modifications ◽  
Cardiac Dysfunction ◽  
Ryanodine Receptors ◽  
Soluble Guanylyl Cyclase ◽  
Wild Type ◽  
Cellular Mechanisms ◽  
Channel Current ◽  
Lps Challenge ◽  
Cgmp Synthesis ◽  
Phospholamban Phosphorylation

The goal of this study was to identify the cellular mechanisms responsible for cardiac dysfunction in endotoxemic mice. We aimed to differentiate the roles of cGMP [produced by soluble guanylyl cyclase (sGC)] versus oxidative posttranslational modifications of Ca2+ transporters. C57BL/6 mice [wild-type (WT) mice] were administered lipopolysaccharide (LPS; 25 μg/g ip) and euthanized 12 h later. Cardiomyocyte sarcomere shortening and Ca2+ transients (ΔCai) were depressed in LPS-challenged mice versus baseline. The time constant of Ca2+ decay (τCa) was prolonged, and sarcoplasmic reticulum Ca2+ load (CaSR) was depressed in LPS-challenged mice (vs. baseline), indicating decreased activity of sarco(endo)plasmic Ca2+-ATPase (SERCA). L-type Ca2+ channel current ( ICa,L) was also decreased after LPS challenge, whereas Na+/Ca2+ exchange activity, ryanodine receptors leak flux, or myofilament sensitivity for Ca2+ were unchanged. All Ca2+-handling abnormalities induced by LPS (the decrease in sarcomere shortening, ΔCai, CaSR, ICa,L, and τCa prolongation) were more pronounced in mice deficient in the sGC main isoform (sGCα1−/− mice) versus WT mice. LPS did not alter the protein expression of SERCA and phospholamban in either genotype. After LPS, phospholamban phosphorylation at Ser16 and Thr17 was unchanged in WT mice and was increased in sGCα1−/− mice. LPS caused sulphonylation of SERCA Cys674 (as measured immunohistochemically and supported by iodoacetamide labeling), which was greater in sGCα1−/− versus WT mice. Taken together, these results suggest that cardiac Ca2+ dysregulation in endotoxemic mice is mediated by a decrease in L-type Ca2+ channel function and oxidative posttranslational modifications of SERCA Cys674, with the latter (at least) being opposed by sGC-released cGMP.

Abstract 418: Caveolar Disruption of L-type Calcium Channel and Ryanodine Receptor Facilitates Atrial Ectopy and Arrhythmogenesis in Heart Failure Mice

2020 ◽  
Vol 127 (Suppl_1) ◽  
Author(s):  
Di Lang ◽  
Lucas ratajczyk ◽  
Leonid Tyan ◽  
Daniel Turner ◽  
Francisco Alvarado ◽  
...  
Keyword(s):  
Heart Failure ◽  
Optical Mapping ◽  
Ryanodine Receptors ◽  
Tissue Level ◽  
Confocal Imaging ◽  
Right Atrial ◽  
Isolated Atria ◽  
The Right

Atrial fibrillation (AF) often occurs during heart failure (HF). Ectopic foci that trigger AF, are linked to discrete atrial regions that experience the highest remodeling and clinically used for AF ablation; however, mechanisms of their arrhythmogenic propensity remain elusive. We employed in vivo ECG telemetry, in vitro optical mapping and confocal imaging of Ca 2+ transients (CaT) from myocytes isolated from the right atrial appendage (RAA) and inter-caval region (ICR) of wild type (WT, n=10), caveolin-3 knockout (KO, n=6) and 8-weeks post-myocardial infarction HF (n=8) mice. HF and KO mice showed an increased susceptibility to pacing-induced AF and enhanced ectopy originated exclusively from ICR. Optical mapping in isolated atria showed prolongation of CaT rise up time (CaT-RT) in HF ICR, which suggested a remodeled coupling between L-type Ca 2+ channels (LTCCs) and ryanodine receptors (RyRs) in this specific region. In WT mice, RAA consists of structured myocytes with a prominent transverse-axial tubular system (TATS) while ICR myocytes don’t have TATS. In RAA, CaT-RT depends on LTCCs in TATS triggering RyR, while in ICR, all the LTCCs are localized in surface caveolae where they can activate subsarcolemmal RyRs and lead to a slow diffusion of Ca 2+ inside the cell interior. Downregulation of caveolae was observed specifically in HF ICR. To mimic this, we used cav3-KO mice. Triggered activities were observed in myocytes isolated from HF and KO ICR, which presumably underlie the ectopic activities in tissue level. These myocytes presented significantly unsynchronized sarcoplasmic reticulum (SR) Ca 2+ releases (synchronization index: 10.8±0.9 in WT vs 38.3±4.1 in HF vs 21.5±2.1 in KO, p <0.01 for HF and KO vs WT respectively) especially at the subsarcolemmal space that prolongs CaT-RT (62.2±4.1 ms in WT vs 122.5±12.8 ms in KO, p <0.01). In addition, failing ICR myocytes showed a higher occurrence and size of spontaneous Ca 2+ sparks which were linked to CaMKII activity and associated phosphorylation of RyR. Our findings demonstrate that in HF, caveolar disruption creates “hot spots” for arrhythmogenic ectopic activity emanated from discrete vulnerable regions of the right atrium which are associated with desynchronized SR Ca 2+ release and elevated fibrosis.

P2863Regional specific remodeling of cGMP pathway in human atrial fibrillation

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
N I Bork ◽  
N G Pavlidou ◽  
B Reiter ◽  
H Reichenspurner ◽  
T Christ ◽  
...  
Keyword(s):  
Atrial Fibrillation ◽  
Sinus Rhythm ◽  
Ryanodine Receptors ◽  
Membrane Receptors ◽  
Mrna Levels ◽  
Atrial Myocytes ◽  
Human Atrial Myocytes ◽  
Cgmp Pathway ◽  
The Right

Abstract Background Atrial fibrillation (AF) is accompanied by a profound remodeling of membrane receptors and alterations in cyclic nucleotides-dependent regulation of Ca2+-handling. Thus, while basal ryanodine receptors activity is upregulated, L-type calcium current (ICa,L) density is diminish in AF, due to local microdomain-specific cAMP dynamics. The same seems true for cGMP regulation in AF. In AF cGMP-mediated increase in ICa,L is blunted but NO-mediated attenuation of β-adrenoceptors stimulation-mediated increase is preserved. However, although the role of cGMP in controling atrial function and pathophysiology is controversial, no study has been ever performed in human myocytes to measure cGMP directly. Methods We isolated myocytes from the right and/or left atrium of 27 patients in sinus rhythm (SR), and with AF. Cells were then transfected with adenovirus to express the cytosolic FRET-based cGMP sensor red-cGES-DE5 and cultured for 48 hours. Förster resonance energy transfer (FRET) was used to measure cGMP in 61 living human atrial myocytes. We stimulated cells with the C-type natriuretic peptide CNP (100 nM and 1 μM), and the non-selective phosphodiesterases (PDEs) inhibitor IBMX (100 μM). Additionally, PDE specific inhibitors for PDE2 (Bay 60–7550, 100 nM) and PDE3 (Cilostamide, 10 μM) as well as inhibitor of the soluble guanylyl cyclase (ODQ, 50 μM) were used. We also measured PDE2 and PDE3 mRNA levels in atrial tissue samples from both groups of patients using RT-qPCR. Results We could show that stimulation with CNP increased cGMP levels in human atrial myocytes. However, in myocytes from patients with AF global cGMP responses to CNP and to IBMX was reduced compared to SR. Additionally, there was a difference in response to CNP and IBMX in patients with AF between the right and the left atria. Whereas in the right atria IBMX could further increase cGMP levels in the cell, in the left atria leaded to a reduction in cGMP levels. RT-qPCR showed a tendency of PDE3 to be reduced in AF. On the other hand, PDE2A gene expression was upregulated in the left atria. Conclusions We have shown that PDEs contributes cGMP signaling in the human atria and that they are involved in atrial pathophysiology. Now our data clearly show differences in cGMP regulation in cardiomyocytes isolated from left and right atrium from patients in atrial fibrillation and sinus rhythm. We observe a major role of PDEs, regulating cGMP pathway promoted by the reduced responses in AF, especially PDE2 in the left atria.

A probable role of dihydropyridine receptors in repression of Ca2+ sparks demonstrated in cultured mammalian muscle

2006 ◽  
Vol 290 (2) ◽  
pp. C539-C553 ◽  
Author(s):  
Jingsong Zhou ◽  
Jianxun Yi ◽  
Leandro Royer ◽  
Bradley S. Launikonis ◽  
Adom González ◽  
...  
Keyword(s):  
Ryanodine Receptors ◽  
Critical Role ◽  
Primary Cultures ◽  
Inhibitory Effect ◽  
Wild Type ◽  
Dihydropyridine Receptors ◽  
Skeletal Muscle Contraction ◽  
Probable Role ◽  
Emission Ratios

To activate skeletal muscle contraction, action potentials must be sensed by dihydropyridine receptors (DHPRs) in the T tubule, which signal the Ca2+ release channels or ryanodine receptors (RyRs) in the sarcoplasmic reticulum (SR) to open. We demonstrate here an inhibitory effect of the T tubule on the production of sparks of Ca2+ release. Murine primary cultures were confocally imaged for Ca2+ detection and T tubule visualization. After 72 h of differentiation, T tubules extended from the periphery for less than one-third of the myotube radius. Spontaneous Ca2+ sparks were found away from the region of cells where tubules were found. Immunostaining showed RyR1 and RyR3 isoforms in all areas, implying inhibition of both isoforms by a T tubule component. To test for a role of DHPRs in this inhibition, we imaged myotubes from dysgenic mice ( mdg) that lack DHPRs. These exhibited T tubule development similar to that of normal myotubes, but produced few sparks, even in regions where tubules were absent. To increase spark frequency, a high-Ca2+ saline with 1 mM caffeine was used. Wild-type cells in this saline plus 50 μM nifedipine retained the topographic suppression pattern of sparks, but dysgenic cells in high-Ca2+ saline did not. Shifted excitation and emission ratios of indo-1 in the cytosol or mag-indo-1 in the SR were used to image [Ca2+] in these compartments. Under the conditions of interest, wild-type and mdg cells had similar levels of free [Ca2+] in cytosol and SR. These data suggest that DHPRs play a critical role in reducing the rate of spontaneous opening of Ca2+ release channels and/or their susceptibility to Ca2+-induced activation, thereby suppressing the production of Ca2+ sparks.

Regulation of Ca2+-release-activated Ca2+ current (Icrac) by ryanodine receptors in inositol 1,4,5-trisphosphate-receptor-deficient DT40 cells

2001 ◽  
Vol 360 (1) ◽  
pp. 17-22 ◽  
Author(s):  
Kirill KISELYOV ◽  
Dong Min SHIN ◽  
Nikolay SHCHEYNIKOV ◽  
Tomohiro KUROSAKI ◽  
Shmuel MUALLEM
Keyword(s):  
Time Course ◽  
Ryanodine Receptors ◽  
Cell Types ◽  
Ruthenium Red ◽  
General Mechanism ◽  
Inward Rectification ◽  
Wild Type ◽  
Ip3 Receptor ◽  
Inositol 1,4,5 Trisphosphate ◽  
Dt40 Cells

Persistence of capacitative Ca2+ influx in inositol 1,4,5-trisphosphate (IP3) receptor (IP3R)-deficient DT40 cells (DT40IP3R-/−) raises the question of whether gating of Ca2+-release activated Ca2+ current (Icrac) by conformational coupling to Ca2+-release channels is a general mechanism of gating of these channels. In the present work we examined the properties and mechanism of activation of Icrac Ca2+ current in wild-type and DT40IP3R-/− cells. In both cell types passive depletion of internal Ca2+ stores by infusion of EGTA activated a Ca2+ current with similar characteristics and time course. The current was highly Ca2+-selective and showed strong inward rectification, all typical of Icrac. The activator of ryanodine receptor (RyR), cADP-ribose (cADPR), facilitated activation of Icrac, and the inhibitors of the RyRs, 8-N-cADPR, ryanodine and Ruthenium Red, all inhibited Icrac activation in DT40IP3R-/− cells, even after complete depletion of intracellular Ca2+ stores by ionomycin. Wild-type and DT40IP3R-/− cells express RyR isoforms 1 and 3. RyR levels were adapted in DT40IP3R-/− cells to a lower RyR3/RyR1 ratio than in wild-type cells. These results suggest that IP3Rs and RyRs can efficiently gate Icrac in DT40 cells and explain the persistence of Icrac gating by internal stores in the absence of IP3Rs.

scholarly journals A dominantly negative mutation in cardiac troponin I at the interface with troponin T causes early remodeling in ventricular cardiomyocytes

2014 ◽  
Vol 307 (4) ◽  
pp. C338-C348 ◽  
Author(s):  
Hongguang Wei ◽  
J.-P. Jin
Keyword(s):  
Cardiac Troponin ◽  
Troponin I ◽  
Troponin T ◽  
Cardiac Troponin I ◽  
Wild Type ◽  
Leukemia Inhibitory Factor Receptor ◽  
Cell Width ◽  
Potent Effect ◽  
Western Blots ◽  
Adrenergic Response

We previously reported a point mutation substituting Cys for Arg111 in the highly conserved troponin T (TnT)-contacting helix of cardiac troponin I (cTnI) in wild turkey hearts (Biesiadecki et al. J Biol Chem 279: 13825–13832, 2004). This dominantly negative TnI-TnT interface mutation decreases the binding affinity of cTnI for TnT, impairs diastolic function, and blunts the β-adrenergic response of cardiac muscle (Wei et al. J Biol Chem 285: 27806–27816, 2010). Here we further investigate cellular phenotypes of transgenic mouse cardiomyocytes expressing the equivalent mutation cTnI-K118C. Functional studies were performed on single adult cardiomyocytes after recovery in short-term culture from isolation stress. The amplitude of contraction and the velocities of shortening and relengthening were lower in cTnI-K118C cardiomyocytes than wild-type controls. The intracellular Ca2+ transient was slower in cTnI-K118C cardiomyocytes than wild-type cells. cTnI-K118C cardiomyocytes also showed a weaker β-adrenergic response. The resting length of cTnI-K118C cardiomyocytes was significantly greater than that of age-matched wild-type cells, with no difference in cell width. The resting sarcomere was not longer, but slightly shorter, in cTnI-K118C cardiomyocytes than wild-type cells, indicating longitudinal addition of sarcomeres. More tri- and quadrinuclei cardiomyocytes were found in TnI-K118C than wild-type hearts, suggesting increased nuclear divisions. Whole-genome mRNA array and Western blots detected an increased expression of leukemia inhibitory factor receptor-β in the hearts of 2-mo-old cTnI-K118C mice, suggesting a signaling pathway responsible for the potent effect of cTnI-K118C mutation on early remodeling in cardiomyocytes.

scholarly journals Hypersensitivity of excitation-contraction coupling in dystrophic cardiomyocytes

2009 ◽  
Vol 297 (6) ◽  
pp. H1992-H2003 ◽  
Author(s):  
Nina D. Ullrich ◽  
Mohammed Fanchaouy ◽  
Konstantin Gusev ◽  
Natalia Shirokova ◽  
Ernst Niggli
Keyword(s):  
Striated Muscle ◽  
Ryanodine Receptors ◽  
Confocal Imaging ◽  
Mdx Mice ◽  
Ros Generation ◽  
Coupling Mechanism ◽  
Inherited Disease ◽  
Cellular Mechanisms ◽  
Patch Clamp Technique ◽  
Skeletal Muscle Function

Duchenne muscular dystrophy represents a severe inherited disease of striated muscle. It is caused by a mutation of the dystrophin gene and characterized by a progressive loss of skeletal muscle function. Most patients also develop a dystrophic cardiomyopathy, resulting in dilated hypertrophy and heart failure, but the cellular mechanisms leading to the deterioration of cardiac function remain elusive. In the present study, we tested whether defective excitation-contraction (E-C) coupling contributes to impaired cardiac performance. “E-C coupling gain” was determined in cardiomyocytes from control and dystrophin-deficient mdx mice. To this end, L-type Ca2+ currents ( ICaL) were measured with the whole cell patch-clamp technique, whereas Ca2+ transients were simultaneously recorded with confocal imaging of fluo-3. Initial findings indicated subtle changes of E-C coupling in mdx cells despite matched Ca2+ loading of the sarcoplasmic reticulum (SR). However, lowering the extracellular Ca2+ concentration, a maneuver used to unmask latent E-C coupling problems, was surprisingly much better tolerated by mdx myocytes, suggesting a hypersensitive E-C coupling mechanism. Challenging the SR Ca2+ release by slow elevations of the intracellular Ca2+ concentration resulted in Ca2+ oscillations after a much shorter delay in mdx cells. This is consistent with an enhanced Ca2+ sensitivity of the SR Ca2+-release channels [ryanodine receptors (RyRs)]. The hypersensitivity could be normalized by the introduction of reducing agents, indicating that the elevated cellular ROS generation in dystrophy underlies the abnormal RyR sensitivity and hypersensitive E-C coupling. Our data suggest that in dystrophin-deficient cardiomyocytes, E-C coupling is altered due to potentially arrhythmogenic changes in the Ca2+ sensitivity of redox-modified RyRs.

scholarly journals KISS1R Intracellular Trafficking and Degradation: Effect of the Arg386Pro Disease-Associated Mutation

Endocrinology ◽  
2011 ◽  
Vol 152 (4) ◽  
pp. 1616-1626 ◽  
Author(s):  
Suzy D. C. Bianco ◽  
Lauren Vandepas ◽  
Mayrin Correa-Medina ◽  
Balázs Gereben ◽  
Abir Mukherjee ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Intracellular Trafficking ◽  
Proteasome Inhibitor ◽  
Central Precocious Puberty ◽  
Confocal Imaging ◽  
Time Dependent ◽  
Relative Distribution ◽  
Wild Type ◽  
Protein Levels ◽  
Degradation Effect

Abstract The goal of this study was to investigate how the Arg386Pro mutation prolongs KiSS-1 receptor (KISS1R) responsiveness to kisspeptin, contributing to human central precocious puberty. Confocal imaging showed colocalization of wild-type (WT) KISS1R with a membrane marker, which persisted for up to 5 h of stimulation. Conversely, no colocalization with a lysosome marker was detected. Also, overnight treatment with a lysosome inhibitor did not affect WT KISS1R protein, whereas overnight treatment with a proteasome inhibitor increased protein levels by 24-fold. WT and Arg386Pro KISS1R showed time-dependent internalization upon stimulation. However, both receptors were recycled back to the membrane. The Arg386Pro mutation did not affect the relative distribution of KISS1R in membrane and internalized fractions when compared to WT KISS1R for up to 120 min of stimulation, demonstrating that this mutation does not affect KISS1R trafficking rate. Nonetheless, total Arg386Pro KISS1R was substantially increased compared with WT after 120 min of kisspeptin stimulation. This net increase was eliminated by blockade of detection of recycled receptors, demonstrating that recycled receptors account for the increased responsiveness of this mutant to kisspeptin. We therefore conclude the following: 1) WT KISS1R is degraded by proteasomes rather than lysosomes; 2) WT and Arg386Pro KISS1R are internalized upon stimulation, but most of the internalized receptors are recycled back to the membrane rather than degraded; 3) the Arg386Pro mutation does not affect the rate of KISS1R trafficking—instead, it prolongs responsiveness to kisspeptin by decreasing KISS1R degradation, resulting in the net increase on mutant receptor recycled back to the plasma membrane.

scholarly journals CaMKIIδC Drives Early Adaptive Ca 2+ Change and Late Eccentric Cardiac Hypertrophy

2020 ◽  
Vol 127 (9) ◽  
pp. 1159-1178
Author(s):  
Senka Ljubojevic-Holzer ◽  
Anthony W. Herren ◽  
Natasa Djalinac ◽  
Julia Voglhuber ◽  
Stefano Morotti ◽  
...  
Keyword(s):  
Transgenic Mice ◽  
Nuclear Export ◽  
Confocal Imaging ◽  
Transient Effects ◽  
Wild Type ◽  
Transcriptional Responses ◽  
Eccentric Hypertrophy ◽  
Nuclear Changes ◽  
Spatio Temporal ◽  
Camkii Activation

Rationale: CaMKII (Ca 2+ -Calmodulin dependent protein kinase) δC activation is implicated in pathological progression of heart failure (HF) and CaMKIIδC 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 CaMKIIδC signaling in adult ventricular cardiomyocytes, during transaortic constriction (TAC) and in CaMKIIδC transgenic mice. Methods and Results: We used human tissue from nonfailing and HF hearts, 4 mouse lines: wild-type, KO (CaMKIIδ-knockout), CaMKIIδC transgenic in wild-type (TG), or KO background, and wild-type mice exposed to TAC. Confocal imaging and biochemistry revealed disproportional CaMKIIδC activation and accumulation in nuclear and perinuclear versus cytosolic regions at 5 days post-TAC. This CaMKIIδ activation caused a compensatory increase in sarcoplasmic reticulum Ca 2+ content, Ca 2+ transient amplitude, and [Ca 2+ ] 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 CaMKIIδ 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 [Ca 2+ ] and CaMKII activation occurred. CaMKIIδ TG mice lacking δB exhibited more severe HF, eccentric myocyte growth, and nuclear changes. Patient HF samples also showed greatly increased CaMKIIδ expression, especially for CaMKIIδC in nuclear fractions. Conclusions: We conclude that in early TAC perinuclear CaMKIIδC activation promotes adaptive increases in myocyte Ca 2+ transients and nuclear transcriptional responses but that chronic progression of this nuclear Ca 2+ -CaMKIIδC axis contributes to eccentric hypertrophy and HF.

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