Homeobox a4 is proapoptotic in the AC16 human cardiomyocyte cell line and a key effector of the MIAT/miR-150 axis in murine myocardial infarction

MicroRNA-150-5p (miR-150) was correlated with heart failure (HF) severity in humans. Left ventricular homeobox a4 (HOXA4) was upregulated in patients with HF. Gain-of-function mutants in myocardial infarction-associated transcript (MIAT) were associated with increased risk of myocardial infarction (MI) in humans. Our previous unbiased profiling and mechanistic studies revealed that miR-150 was a pivotal target of MIAT repression in vivo and directly repressed profibrotic HOXA4 in vitro. However, there is a paucity of detailed mechanistic insight into how the MIAT/miR-150 axis regulates HF and a deficit of definitive studies using mouse models to establish its functional relationship with key downstream targets. In this study, we determine whether HOXA4 modulates cardiomyocyte apoptosis and is functionally regulated by the MIAT/miR-150 axis in vivo. Our in vitro studies, for the first time, reveal that HOXA4 is proapoptotic and promotes apoptosis in the AC16 adult human cardiomyocyte cell line and that the protective roles of miR-150 in the AC16 adult human cardiomyocyte cell line are mediated by functional repression of HOXA4 . Moreover, Hoxa4 ablation in mice attenuates maladaptive post-MI remodeling. Significantly, we show using novel miR-150; Hoxa4 double knockout and MIAT transgenic; Hoxa4 knockout mouse models that genetic deletion of Hoxa4 blunts adverse post-MI effects caused by miR-150 loss or MIAT gain, establishing their in vivo functional relationships. These findings delineate a crucial functional link among MIAT, miR-150, and HOXA4 as a novel regulatory mechanism pertinent to cardiomyocyte apoptosis and ischemic HF. Our study will facilitate the development of new miR-150 activators and inhibitors of the MIAT/HOXA4 axis for the treatment of heart disease.