A novel phospholamban p.Arg14del cardiomyopathy mouse line treated with heart failure medication

BACKGROUND: Phospholamban (PLN) plays a role in cardiomyocyte calcium handling by acting as a negative regulator of the sarcoplasmic/endoplasmic reticulum Ca2+-ATPase (SERCA). A mutation in the PLN gene leading to the deletion of arginine 14 (R14del) of the PLN protein, is the most frequently identified mutation in patients with dilated cardiomyopathy (DCM) or arrhythmogenic cardiomyopathy (ACM) in the Netherlands. Cardiomyopathy patients that carry the PLN-R14del mutation have a worse prognosis than cardiomyopathy patients that do not carry this mutation, evidenced by more appropriate implantable cardioverter-defibrillator (ICD) discharges and more sudden cardiac death (SCD). There is no specific therapeutic treatment available for these patients other than standard heart failure treatment and heart transplantation.
PURPOSE: The aim of this study is to generate a mouse model of PLN-R14del-induced cardiomyopathy and to screen for treatment options. First treatment consisted of standard heart failure medication including a beta-blocker (metoprolol) and a mineralocorticoid receptor antagonist (MRA; eplerenone).
METHODS: The PLN-R14del mutation was introduced into the genome of C57BL/6N mice and backcrossed into C57BL/6J mice. Cardiac function was assessed using echocardiography, electrocardiography (ECG) and histological and molecular analysis. Metoprolol was orally administered as 350 mg/kg/day via the drinking water and eplerenone was orally administered as 200 mg/kg/day via the chow (n=10-12 per group). All animal studies were performed according to National Institutes of Health (NIH) guidelines and in accordance with national regulations.
RESULTS: Homozygous PLN-R14del mice had increased left ventricular (LV) volume with decreased fractional shortening (FS) in comparison to wild-type littermates. In addition, decreased ECG potentials and prolonged QTc were observed. This resulted in decreased survival with a maximum life span of 2 months. Histological analysis showed severe cardiac fibrosis and aggregation of PLN proteins in the cardiomyocytes. Molecular analysis demonstrated increased levels of genes and proteins associated with cardiac stress, fibrosis and endoplasmic reticulum (ER) stress. Administration of eplerenone significantly decreased LV volume and atrial and pulmonary congestion. In addition, gene expression of B-type natriuretic peptide (BNP) and collagen genes was reduced. However, neither metoprolol nor eplerenone could improve cardiac function or survival of these mice.
CONCLUSION: Homozygous PLN-R14del mice exactly mimic human disease in an accelerated manner. Administration of standard heart failure treatment including metoprolol and eplerenone does not give beneficial effects in these mice. The findings of this study underline the need for better understanding of the pathology of PLN-R14del-induced cardiomyopathy and problem-targeted therapy.