TY  - JOUR
A1  - Kirschmer, Nadine
A1  - Bandleon, Sandra
A1  - von Ehrlich-Treuenstätt, Viktor
A1  - Hartmann, Sonja
A1  - Schaaf, Alice
A1  - Lamprecht, Anna-Karina
A1  - Miranda-Laferte, Erick
A1  - Langsenlehner, Tanja
A1  - Ritter, Oliver
A1  - Eder, Petra
T1  - TRPC4α and TRPC4β Similarly Affect Neonatal Cardiomyocyte Survival during Chronic GPCR Stimulation
JF  - PLoS ONE
N2  - The Transient Receptor Potential Channel Subunit 4 (TRPC4) has been considered as a crucial Ca\(^{2+}\) component in cardiomyocytes promoting structural and functional remodeling in the course of pathological cardiac hypertrophy. TRPC4 assembles as homo or hetero-tetramer in the plasma membrane, allowing a non-selective Na\(^{+}\) and Ca\(^{2+}\) influx. Gαq protein-coupled receptor (GPCR) stimulation is known to increase TRPC4 channel activity and a TRPC4-mediated Ca\(^{2+}\) influx which has been regarded as ideal Ca\(^{2+}\) source for calcineurin and subsequent nuclear factor of activated T-cells (NFAT) activation. Functional properties of TRPC4 are also based on the expression of the TRPC4 splice variants TRPC4α and TRPC4β. Aim of the present study was to analyze cytosolic Ca\(^{2+}\) signals, signaling, hypertrophy and vitality of cardiomyocytes in dependence on the expression level of either TRPC4α or TRPC4β. The analysis of Ca\(^{2+}\) transients in neonatal rat cardiomyocytes (NRCs) showed that TRPC4α and TRPC4β affected Ca\(^{2+}\) cycling in beating cardiomyocytes with both splice variants inducing an elevation of the Ca\(^{2+}\) transient amplitude at baseline and TRPC4β increasing the Ca\(^{2+}\) peak during angiotensin II (Ang II) stimulation. NRCs infected with TRPC4β (Ad-C4β) also responded with a sustained Ca\(^{2+}\) influx when treated with Ang II under non-pacing conditions. Consistent with the Ca\(^{2+}\) data, NRCs infected with TRPC4α (Ad-C4α) showed an elevated calcineurin/NFAT activity and a baseline hypertrophic phenotype but did not further develop hypertrophy during chronic Ang II/phenylephrine stimulation. Down-regulation of endogenous TRPC4α reversed these effects, resulting in less hypertrophy of NRCs at baseline but a markedly increased hypertrophic enlargement after chronic agonist stimulation. Ad-C4β NRCs did not exhibit baseline calcineurin/NFAT activity or hypertrophy but responded with an increased calcineurin/NFAT activity after GPCR stimulation. However, this effect was not translated into an increased propensity towards hypertrophy but rather less hypertrophy during GPCR stimulation. Further analyses revealed that, although hypertrophy was preserved in Ad-C4α NRCs and even attenuated in Ad-C4β NRCs, cardiomyocytes had an increased apoptosis rate and thus were less viable after chronic GPCR stimulation. These findings suggest that TRPC4α and TRPC4β differentially affect Ca\(^{2+}\) signals, calcineurin/NFAT signaling and hypertrophy but similarly impair cardiomyocyte viability during GPCR stimulation.
KW  - Apoptosis
KW  - calcineurin signaling cascade
KW  - small interfering RNAs
KW  - G protein coupled receptors
KW  - hyperexpression techniques
KW  - heart
KW  - adenoviruses
KW  - cardiac pacing
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-178539
VL  - 11
IS  - 12
ER  - 
TY  - JOUR
A1  - Bernt, Alexander
A1  - Rangrez, Ashraf Y.
A1  - Eden, Matthias
A1  - Jungmann, Andreas
A1  - Katz, Sylvia
A1  - Rohr, Claudia
A1  - Müller, Oliver J.
A1  - Katus, Hugo A.
A1  - Sossalla, Samuel T.
A1  - Williams, Tatjana
A1  - Ritter, Oliver
A1  - Frank, Derk
A1  - Frey, Norbert
T1  - Sumoylation-independent activation of Calcineurin-NFAT-signaling via SUMO2 mediates cardiomyocyte hypertrophy
JF  - Scientific Reports
N2  - The objective of this study was to identify unknown modulators of Calcineurin (Cn)-NFAT signaling. Measurement of NFAT reporter driven luciferase activity was therefore utilized to screen a human cardiac cDNA-library (~10\(^{7}\) primary clones) in C2C12 cells through serial dilutions until single clones could be identified. This extensive screening strategy culminated in the identification of SUMO2 as a most efficient Cn-NFAT activator. SUMO2-mediated activation of Cn-NFAT signaling in cardiomyocytes translated into a hypertrophic phenotype. Prohypertrophic effects were also observed in mice expressing SUMO2 in the heart using AAV9 (Adeno-associated virus), complementing the in vitro findings. In addition, increased SUMO2-mediated sumoylation in human cardiomyopathy patients and in mouse models of cardiomyopathy were observed. To decipher the underlying mechanism, we generated a sumoylation-deficient SUMO2 mutant (ΔGG). Surprisingly, ΔGG replicated Cn-NFAT-activation and the prohypertrophic effects of native SUMO2, both in vitro and in vivo, suggesting a sumoylation-independent mechanism. Finally, we discerned a direct interaction between SUMO2 and CnA, which promotes CnA nuclear localization. In conclusion, we identified SUMO2 as a novel activator of Cn-NFAT signaling in cardiomyocytes. In broader terms, these findings reveal an unexpected role for SUMO2 in cardiac hypertrophy and cardiomyopathy, which may open the possibility for therapeutic manipulation of this pathway.
KW  - Calcineurin-NFATsignaling
KW  - activation
KW  - SUMO2
KW  - cardiac hypertrophy
Y1  - 2016
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-167525
VL  - 6
IS  - 35758
ER  -