Ca ²⁺ oscillation frequency decoding in cardiac cell hypertrophy: Role of calcineurin/NFAT as Ca ²⁺ signal integrators

Abstract

The role of Ca 2؉ signaling in triggering hypertrophy was investigated in neonatal rat cardiomyocytes in vitro. We show that an increase in cell size and sarcomere reorganization were elicited by receptor agonists such as Angiotensin II, aldosterone, and norepinephrine and by a small rise in medium KCl concentration, a treatment devoid of direct effects on receptor functions. All these treatments increased the frequency of spontaneous [Ca 2؉ ] transients, caused nuclear translocation of transfected NFAT(GFP), and increased the expression of a NFAT-sensitive reporter gene. There was no increase in Ca 2؉ spark frequency in the whole cell or in the perinuclear region under these conditions. Hypertrophy and NFAT translocation but not the increased frequency of [Ca 2؉ ] transients were inhibited by the calcineurin inhibitor cyclosporine A. Hypertrophy by the different stimuli was insensitive to inhibition of myofilament contraction. We concluded that calcineurin-NFAT can act as integrators of the contractile Ca 2؉ signal, and that they can decode alterations in the frequency even of rapid Ca 2؉ oscillations. C ardiac hypertrophy accompanies many forms of heart pathologies, such as genetic or congenital defects, ischemia, and hypertension. The molecular signaling pathways through which the different hypertrophic stimuli modulate cardiac cell size include mitogen-activated protein kinase, Gp130/Stat3, Calmodulin (CaM)-dependent kinases, and the calcineurin-regulated pathway (1). The latter has recently received much attention, in part because it can be the target of therapeutic intervention with well known drugs. For example, in transgenic mice, it has been demonstrated that overexpression of the Ca 2ϩ -dependent phosphatase calcineurin causes a dramatic increase in the size of the heart, inhibited by cyclosporine A (CsA), a calcineurin blocker (2). Along the same line, overexpression of Cain/Cabin (molecules that associate with the calcineurin and inhibit its activity) attenuate cardiac hypertrophy caused not only by calcineurin overexpression but also by pressure overload or ␤-adrenergic receptor stimulation (3). The effect of CsA on cardiac hypertrophy, however, has led to contradictory results in different model systems (4,5).At the cellular level, cardiomyocyte hypertrophy is characterized by an increase in cell size, enhanced protein synthesis, activation of fetal genes, and cytoskeleton reorganization (4, 5). A number of treatments are known to induce cardiac cell hypertrophy in vitro, including angiotensin II (Ang II) (6), catecholamines (7), endothelin (8), and aldosterone (9). Many, but not all, of these hormones are known to be coupled to alterations in Ca 2ϩ homeostasis. In particular, (i) Ang II (6) and endothelin (10) are coupled to IP 3 generation and Ca 2ϩ mobilization from stores; (ii) catecholamines, in particular through ␤1 receptors, are known to induce an increase in the frequency and amplitude of Ca 2ϩ spiking in cardiomyocytes (7); and (iii) the mechanism of aldosterone-induced hypertrophy in vit...

Phosphorylation of TRPC6 Channels at Thr69 Is Required for Anti-hypertrophic Effects of Phosphodiesterase 5 Inhibition

“…In excitable cardiomyocytes, increases in the frequency or amplitude of Ca 2ϩ transients evoked by Ca 2ϩ influx-induced Ca 2ϩ release have been suggested to encode signals for induction of hypertrophy (9). A partial depolarization of plasma membrane by receptor stimulation is reported to increase the frequency of Ca 2ϩ oscillations, leading to activation of nuclear factor of activated T cells (NFAT), a transcription factor that is predominantly regulated by calcineurin (10). Recent reports have indicated that transient receptor potential canonical (TRPC) subfamily proteins play an essential role in agonistinduced membrane depolarization (11,12).…”

Four Dimensional (4-D) BioChemInfoPhysics Models of Cardiac Cellular and Sub-Cellular Vibrations (Oscillations)

“…Model developments: Based on the published experimental results [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] , we approximately consider, BF in SR, cells or extra-cells, as quasi liquid plasmas in physics, the plasmas are quasi neutral electromagnetically; biological or biochemical components such as free Ca++ in BF, SR SubMembrane (SRSM) or Cell Membrane (CM), Ca++H+ (Ca++ or Na+K+) ATPases, NCX, Ca++ carriers and myosin heads, because disturbances, internal excitations or external stimulations always exist, often are displaced from their equilibrium positions or distances, the redistribution of charges and masses will respectively set up forces, tensions or pressures at the components. The forces, the tensions or the pressures will restore the components back to their original equilibrium positions or distances and could initiate a vibration (oscillation), even a resonance.…”

“…Based on published biological and biochemical experimental results [2][3][9][10] , the above analysis, the liquid plasma physics [19] , electrodynamics and hydrodynamics, we propose our model of longitudinal vibrations (oscillations) of free ions in BF, e.g., ions in SR, Cellular Fluid (CF) or Extra Cellular Fluid (ECF) and i.e., directions of the vibrations (oscillations) and the waves propagations are parallel from each other. Figure 1, we consider the SR and the cells as BLPR with Ca++.…”

“…In this investigation, based on published data or results [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] , conservation laws of the momentum as well as the energy, in views of biology, biochemistry, informatics and physics (BioChemInfoPhysics), we proposed models of cardiac cellular and sub-cellular vibrations (oscillations) of biological components, such as free ions in Biological Fluids (BF), Biological Membranes (BM), Ca++H+ (Ca++ and Na+K+) ATPases, Na+Ca++ exchangers (NCX), Ca++ carriers and myosin heads. Moreover, we discuss our models' general applications and general meanings in biology.…”

“…Scientists have studied the mechanisms for more than 100 years [2,3] and proposed models for the mechanisms. The models respectively involved mathematics [4,5] , biophysics [6,7] , biochemistry [8][9][10][11][12][13][14][15][16][17][18] . But, none involved the automation of the vibrations (oscillations) [2] .…”