Expression of ten RGS proteins in human myocardium: functional characterization of an upregulation of RGS4 in heart failure.
OBJECTIVE
RGS proteins (regulators of G protein signalling) negatively regulate G protein function as GTPase activating proteins. By controlling heterotrimeric G proteins they may regulate myocardial hypertrophy and contractility. We investigated the expression of RGS proteins in the human heart and whether they take part in the pathophysiological changes of heart failure.


RESULTS
Using RNase protection assays (RPAs) RGS2, 3L, 3S, 4, 5 and 6 were identified in the myocardium from terminally failing human hearts with dilated (DCM, n=22) or ischemic (ICM, n=18) cardiomyopathy and from nonfailing donor hearts (NF, n=9). With reverse transcriptase polymerase chain reaction in addition mRNA of RGS1, 9, 12, 14 and 16 were detectable. Compared to NF in failing LV myocardium RGS4 mRNA and protein was upregulated 2-3-fold (mRNA, 10(-21) mol/microg+/-S.E.M.: NF: 22+/-5, DCM: 51+/-10*, ICM: 37+/-8; P<0.05 vs. DCM+ICM, *P<0.05 vs. NF, P<0.05 vs. DCM+ICM; protein, % of NF+/-S.E.M.: NF: 100+/-35, DCM 266+/-60*, ICM: 205+/-64, n=5, *P<0.05 vs. NF). In contrast, RGS2, 3L, 3S, 5, 6, and 16 protein and mRNA levels did not vary between failing and NF hearts. In order to investigate the impact of RGS4 on Gq/11 mediated signalling, PLC activity was measured in human LV membranes. Recombinant RGS4 blunted the endothelin-1 (ET-1) stimulated PLC activity. When overexpressed by adenoviral mediated gene transfer in rabbit ventricular myocytes RGS4 abolished the inotropic effect of ET-1.


CONCLUSIONS
The upregulation of RGS4 in failing human myocardium diminishes Gq/11-mediated signalling and can be involved in the desensitization of Gq/11-mediated positive inotropic effects.
Mittmann
Clemens
C
Institut für Experimentelle und Klinische Pharmakologie und Toxikologie, Abteilung für Pharmakologie, Universitätsklinikum Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany.
Chung
Chin Hee
CH
Höppner
Grit
G
Michalek
Christina
C
Nose
Monika
M
Schüler
Christian
C
Schuh
Antje
A
Eschenhagen
Thomas
T
Weil
Joachim
J
Pieske
Burkert
B
Hirt
Stephan
S
Wieland
Thomas
T
D000818:Animals; D015153:Blotting, Western; D016022:Case-Control Studies; D005260:Female; D019204:GTP-Binding Proteins; D020690:GTPase-Activating Proteins; D015870:Gene Expression; D005786:Gene Expression Regulation; D006333:Heart Failure / Q000378:metabolism*; D006352:Heart Ventricles; D006801:Humans; D008875:Middle Aged; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000737:chemistry / Q000378:metabolism*; D011506:Proteins / Q000032:analysis; D020710:RGS Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D011817:Rabbits; D020133:Reverse Transcriptase Polymerase Chain Reaction
D020690:GTPase-Activating Proteins; D011506:Proteins; D020710:RGS Proteins; C107413:RGS16 protein; C485898:RGS3 protein, human; C491349:RGS5 protein, human; C400194:RGS6 protein, human; D012333:RNA, Messenger; C105345:Rgs2 protein, mouse; C415085:Rgs3 protein, mouse; C485692:Rgs6 protein, mouse; C098799:RGS4 protein; D019204:GTP-Binding Proteins