BACKGROUND: The targeting of Ca(2+) cycling has emerged as a potential therapy 
for the treatment of severe heart failure. These approaches include gene therapy 
directed at overexpressing sarcoplasmic reticulum (SR) Ca(2+) ATPase, or 
ablation of phospholamban (PLN) and associated protein phosphatase 1 (PP1) 
protein complexes. We previously reported that PP1β, one of the PP1 catalytic 
subunits, predominantly suppresses Ca(2+) uptake in the SR among the three PP1 
isoforms, thereby contributing to Ca(2+) downregulation in failing hearts. In 
the present study, we investigated whether heart-failure-inducible 
PP1β-inhibition by adeno-associated viral-9 (AAV9) vector mediated gene therapy 
is beneficial for preventing disease progression in genetic cardiomyopathic 
mice.
METHODS: We created an adeno-associated virus 9 (AAV9) vector encoding PP1β 
short-hairpin RNA (shRNA) or negative control (NC) shRNA. A heart failure 
inducible gene expression system was employed using the B-type natriuretic 
protein (BNP) promoter conjugated to emerald-green fluorescence protein (EmGFP) 
and the shRNA sequence. AAV9 vectors (AAV9-BNP-EmGFP-PP1βshRNA and 
AAV9-BNP-EmGFP-NCshRNA) were injected into the tail vein (2×10(11) GC/mouse) of 
muscle LIM protein deficient mice (MLPKO), followed by serial analysis of 
echocardiography, hemodynamic measurement, biochemical and histological analysis 
at 3 months.
RESULTS: In the MLPKO mice, BNP promoter activity was shown to be increased by 
detecting both EmGFP expression and the induced reduction of PP1β by 25% in the 
myocardium. Inducible PP1βshRNA delivery preferentially ameliorated left 
ventricular diastolic function and mitigated adverse ventricular remodeling. PLN 
phosphorylation was significantly augmented in the AAV9-BNP-EmGFP-PP1βshRNA 
injected hearts compared with the AAV9-BNP-EmGFP-NCshRNA group. Furthermore, BNP 
production was reduced, and cardiac interstitial fibrosis was abrogated at 3 
months.
CONCLUSION: Heart failure-inducible molecular targeting of PP1β has potential as 
a novel therapeutic strategy for heart failure.