Background: A deleterious, late-onset side effect of thoracic
radiotherapy is the development of radiation-induced
heart disease (RIHD). It covers a spectrum of cardiac pathology including also
heart failure with preserved ejection fraction (HFpEF) characterized by
left ventricular hypertrophy (LVH) and diastolic dysfunction. MicroRNA-212 (miR-212) is a crucial regulator of pathologic LVH via FOXO3-mediated pathways in pressure-overload-induced
heart failure. We aimed to investigate whether miR-212 and its selected
hypertrophy-associated targets play a role in the development of RIHD. Methods: RIHD was induced by selective heart irradiation (50 Gy) in a clinically relevant rat model. One, three, and nineteen weeks after selective heart irradiation, transthoracic echocardiography was performed to monitor cardiac morphology and function. Cardiomyocyte
hypertrophy and
fibrosis were assessed by histology at week 19. qRT-PCR was performed to measure the gene expression changes of miR-212 and forkhead box O3 (FOXO3) in all follow-up time points. The cardiac transcript level of other selected
hypertrophy-associated targets of miR-212 including
extracellular signal-regulated kinase 2 (ERK2),
myocyte enhancer factor 2a (MEF2a),
AMP-activated protein kinase, (AMPK),
heat shock protein 40 (HSP40),
sirtuin 1, (
SIRT1),
calcineurin A-alpha and
phosphatase and
tensin homolog (PTEN) were also measured at week 19. Cardiac expression of FOXO3 and phospho-FOXO3 were investigated at the
protein level by Western blot at week 19. Results: In RIHD, diastolic dysfunction was present at every time point. Septal
hypertrophy developed at week 3 and a marked LVH with interstitial
fibrosis developed at week 19 in the irradiated hearts. In RIHD, cardiac miR-212 was overexpressed at week 3 and 19, and FOXO3 was repressed at the
mRNA level only at week 19. In contrast, the total
FOXO3 protein level failed to decrease in response to heart irradiation at week 19. Other selected
hypertrophy-associated target genes failed to change at the
mRNA level in RIHD at week 19. Conclusions: LVH in RIHD was associated with cardiac overexpression of miR-212. However, miR-212 seems to play a role in the development of LVH via FOXO3-independent mechanisms in RIHD. As a central regulator of pathologic remodeling, miR-212 might become a novel target for RIHD-induced LVH and
heart failure.