Monoamine oxidase A deletion leads to autophagy inhibition and impairment in cardiomyocyte differentiation from hiPSCs

Reactive oxygen species (ROS) and autophagy play a major role in cardiac pathophysiology, including cardiomyocyte differentiation. Yet, the exact source of ROS controlling the process of differentiation remains unknown. Within mitochondria, monoamine oxidases A and B (MAO-A and -B) are one of the major sources of ROS and play an important role in cardiac tissue homeostasis. Nevertheless, their involvement in cardiomyocyte differentiation has not been investigated yet. Here, we assessed whether ablation of MAO-A, the isoform expressed in human induced pluripotent stem cells (hiPSCs), could affect cardiomyocyte differentiation. MAO-A deletion negatively affected contractile properties of hiPSC-derived cardiomyocytes, resulting in higher frequency and lower amplitude of calcium transients. These features were accompanied by sarcomere disorganization and a reduction in the α- to β-myosin heavy chain ratio in MAO-A−/− cells, similarly to what occurs in failing hearts. GATA4, one of the key genes involved in cardiac remodeling, was significantly upregulated in these cells. To understand the underlying mechanisms, we investigated whether MAO-A deletion affected macroautophagy, one of the key processes required for cardiomyocyte differentiation. Macroautophagy levels were reduced in MAO-A−/− hiPSCs both at baseline and upon starvation or rapamycin administration, as evidenced by reduced accumulation of LC3-II in the presence of inhibitors of lysosomal degradation. The inhibitory effect on macroautophagy is likely due to the reduction of AMPK phosphorylation levels observed in MAO-A−/− hiPSCs. Taken together, these results suggest that MAO-A is required for the regulation of macroautophagy in hiPSCs and, consequently, for the process of differentiation and maturation of cardiac myocytes.