Enhanced cardiac function in mice overexpressing protein phosphatase Inhibitor-2.
OBJECTIVE
Protein phosphatase 1 (PP1) has been implicated in the control of cardiac function. Cardiac specific overexpression of the catalytic subunit, PP1c, results in hypertrophy and depressed contractility.


METHODS
To further address the role of PP1, transgenic mice (TG) were generated that overexpress in heart a functional COOH-terminally truncated form (amino acids 1-140) of the PP1 inhibitor-2 (I-2(140)).


RESULTS
The TG hearts show increased levels of I-2(140) mRNA as well as protein and activity. No increase in absolute or relative heart weight was observed, nor any changes in gross pathology or increase in morbidity or mortality in the TG mice. Immunohistochemical and biochemical analyses revealed that expression of the I-2(140) protein is confined to cardiomyocytes where it is mainly localized in the cytosol. The total protein phosphatase (PP) activity was reduced by 80% in TG hearts as compared to wild-type littermates (WT). The PP1c mRNA level was the same in TG and WT, while the protein level was increased by approximately 7-fold in TG animals. The maximal rates of contraction (+dP/dt) and of relaxation (-dP/dt) were increased by 32% and 40%, respectively, in the intact catheterized TG mice compared to WT. However, the maximal contractile response to beta-adrenergic agonists was comparable in hearts from TG and WT mice. In isolated cardiomyocytes of TG mice, Ca2+transient amplitude was increased by 50% under basal conditions and by 60% upon rapid caffeine application. The phospholamban (PLB) protein level was unchanged whereas the basal phosphorylation of PLB at Ser(16) was significantly increased in TG hearts.


CONCLUSIONS
These results indicate that I-2(140) overexpression results in decreased PP1 activity and enhanced contractility in the heart, underscoring the fundamental role of PP1 in cardiac function.
Institut für Pharmakologie und Toxikologie, Westfälische Wilhelms-Universität, 48149 Münster, Germany.
Uwe
U
Kirchhefer
Hideo A
HA
Baba
Peter
P
Bokník
Kristine M
KM
Breeden
Nirmala
N
Mavila
Nicole
N
Brüchert
Isabel
I
Justus
Marek
M
Matus
Wilhelm
W
Schmitz
Anna A
AA
Depaoli-Roach
Joachim
J
Neumann
D000818:Animals; D015152:Blotting, Northern / Q000379:methods; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D006332:Cardiomegaly / Q000201:enzymology*; D005818:Genetic Engineering; D007150:Immunohistochemistry / Q000379:methods; D051379:Mice; D008822:Mice, Transgenic; D009200:Myocardial Contraction / Q000502:physiology*; D009206:Myocardium / Q000201:enzymology* / Q000378:metabolism; D010477:Perfusion; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D054645:Protein Phosphatase 1; D011506:Proteins / Q000235:genetics* / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D000097847:Protein Phosphatase Inhibitory Proteins
D002118:Calcium; D015220:Calcium Channels; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D011506:Proteins; C024833:protein phosphatase inhibitor-2; D000097847:Protein Phosphatase Inhibitory Proteins