Phospholamban ablation rescues sarcoplasmic reticulum Ca(2+) handling but exacerbates cardiac dysfunction in CaMKIIdelta(C) transgenic mice.
BACKGROUND
We previously showed that transgenic mice expressing Ca(2+)/calmodulin-dependent protein kinase II delta(C) (CaMKII-TG) develop dilated cardiomyopathy associated with increased ryanodine receptors (RyR2) phosphorylation, enhanced sarcoplasmic reticulum (SR) Ca(2+) leak and lowering of SR Ca(2+) load. We hypothesized that phospholamban (PLN) ablation would restore SR Ca(2+) load and prevent the decreased ventricular contractility, dilation and mortality seen in CaMKII-TG.


OBJECTIVE
Our objectives were to generate CaMKII-TG mice lacking PLN, determine whether the maladaptive effects of cardiac CaMKIIdelta(C) expression were corrected, and establish the mechanistic basis for these changes.


RESULTS
CaMKII-TG were crossed with PLN knockout (PLN-KO) mice to generate KO/TG mice. Myocytes from wild type (WT), CaMKII-TG, PLN-KO and KO/TG were compared. The decreased SR Ca(2+) load and twitch Ca(2+) transients seen in CaMKII-TG were normalized in KO/TG. Surprisingly the heart failure phenotype was exacerbated, as indicated by increased left ventricular dilation, decreased ventricular function, increased apoptosis and greater mortality. In KO/TG myocytes SR Ca(2+) sparks and leak were significantly increased, presumably because of the combined effects of restored SR Ca(2+) load and RyR2 phosphorylation. Mitochondrial Ca(2+) loading was increased in cardiomyocytes from KO/TG versus WT or CaMKII-TG mice and this was dependent on elevated SR Ca(2+) sparks. Cardiomyocytes from KO/TG showed poor viability, improved by inhibiting SR Ca(2+) release and mitochondrial Ca(2+) loading.


CONCLUSIONS
Normalizing cardiomyocyte SR Ca(2+) loading in the face of elevated CaMKII and RyR2 phosphorylation leads to enhanced SR Ca(2+) leak and mitochondrial Ca(2+) elevation, associated with exacerbated cell death, heart failure and mortality.
Zhang
Tong
T
Department of Pharmacology, University of California, San Diego, 9500 Gilman Dr, La Jolla, CA 92093-0636, USA.
Guo
Tao
T
Mishra
Shikha
S
Dalton
Nancy D
ND
Kranias
Evangelia G
EG
Peterson
Kirk L
KL
Bers
Donald M
DM
Brown
Joan Heller
JH
D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000235:genetics / Q000378:metabolism*; D002311:Cardiomyopathy, Dilated / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D002470:Cell Survival; D002478:Cells, Cultured; D005260:Female; D006321:Heart / Q000503:physiopathology*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008822:Mice, Transgenic; D008928:Mitochondria / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D016019:Survival Analysis; D018487:Ventricular Dysfunction, Left / Q000235:genetics / Q000378:metabolism / Q000503:physiopathology; D000099211:Phospholamban
D002118:Calcium; D002135:Calcium-Binding Proteins; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D019837:Ryanodine Receptor Calcium Release Channel; D000099211:Phospholamban