PKC-independent signal transduction pathways increase SERCA2 expression in adult rat cardiomyocytes.
Catecholamines seem to play a major role in the initial response of the heart to pressure overload. The mechanisms by which alpha(1A)-adrenoceptor stimulation increases protein synthesis and subsequently cell size have been worked out in the past. However, little is known about the functional consequence of this type of hypertrophy. Recent transgenic work seems to indicate an adaptive character of this response, but mechanistic insights have yet to be established. The present study investigates whether chronic (overnight) exposure of cardiomyocytes to phenylephrine, an alpha-adrenoceptor agonist, modifies the expression of calcium-handling proteins and identifies key elements of signal transduction pathways leading to such alterations. Cardiomyocytes exposed to phenylephrine had elevated expression of SR-calcium ATPase (SERCA), but not of the sodium-calcium exchanger (NCX). SERCA induction persisted in the presence of protein kinase C (PKC) inhibitors, but required an increase in diastolic cell calcium levels via activation of the sodium-proton exchanger (NHE) and the reverse mode of the NCX. Downstream of an increase in resting cell calcium concentrations an activation of the calcineurin/NFAT pathway was found to be responsible for SERCA2 induction. Transfection of cardiomyocytes with decoys directed against NFAT activity inhibited the increase in SERCA2 expression. Decoys did not inhibit the concomitant PKC-dependent increase in hypertrophic growth. In the absence of SERCA up-regulation, hypertrophied cardiomyocytes were unable to maintain normal, load-free cell shortening. In conclusion, our data give mechanistic insights into the adaptional process during alpha-adrenoceptor-dependent myocardial hypertrophy.
Anwar
Attia
A
Physiologisches Institut, Justus-Liebig-Universität Giessen, Aulweg 129, D-35392 Gieben, Germany.
Taimor
Gerhild
G
Korkusuz
Hüdayi
H
Korkususz
Hüdayi
H
Schreckenberg
Rolf
R
Berndt
Tobias
T
Abdallah
Yaser
Y
Piper
Hans Michael
HM
Schlüter
Klaus-Dieter
KD
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects*; D000252:Calcium-Transporting ATPases / Q000096:biosynthesis*; D005786:Gene Expression Regulation / Q000187:drug effects; D008297:Male; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology*; D014176:Protein Biosynthesis / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D011941:Receptors, Adrenergic / Q000378:metabolism; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases
D000316:Adrenergic alpha-Agonists; C506948:Atp2a2 protein, rat; D047428:Protein Kinase Inhibitors; D011941:Receptors, Adrenergic; D010656:Phenylephrine; D011493:Protein Kinase C; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases