AIMS: Impaired myocardial sarcoplasmic reticulum calcium ATPase 2a (SERCA2a) 
activity is a hallmark of failing hearts, and SERCA2a gene therapy improves 
cardiac function in animals and patients with heart failure (HF). Deregulation 
of microRNAs has been demonstrated in HF pathophysiology. We studied the effects 
of therapeutic AAV9.SERCA2a gene therapy on cardiac miRNome expression and 
focused on regulation, expression, and function of miR-1 in reverse remodelled 
failing hearts.
METHODS AND RESULTS: We studied a chronic post-myocardial infarction HF model 
treated with AAV9.SERCA2a gene therapy. Heart failure resulted in a strong 
deregulation of the cardiac miRNome. miR-1 expression was decreased in failing 
hearts, but normalized in reverse remodelled hearts after AAV9.SERCA2a gene 
delivery. Increased Akt activation in cultured cardiomyocytes led to 
phosphorylation of FoxO3A and subsequent exclusion from the nucleus, resulting 
in miR-1 gene silencing. In vitro SERCA2a expression also rescued miR-1 in 
failing cardiomyocytes, whereas SERCA2a inhibition reduced miR-1 levels. In 
vivo, Akt and FoxO3A were highly phosphorylated in failing hearts, but reversed 
to normal by AAV9.SERCA2a, leading to cardiac miR-1 restoration. Likewise, 
enhanced sodium-calcium exchanger 1 (NCX1) expression during HF was normalized 
by SERCA2a gene therapy. Validation experiments identified NCX1 as a novel 
functional miR-1 target.
CONCLUSION: SERCA2a gene therapy of failing hearts restores miR-1 expression by 
an Akt/FoxO3A-dependent pathway, which is associated with normalized NCX1 
expression and improved cardiac function.