ATG3-dependent autophagy mediates mitochondrial homeostasis in pluripotency acquirement and maintenance

Pluripotent stem cells, including induced pluripotent and embryonic stem cells (ESCs), have less developed mitochondria than somatic cells and, therefore, rely more heavily on glycolysis for energy production. ^1-3 However, how mitochondrial homeostasis matches the demands of nuclear reprogramming and regulates pluripotency in ESCs is largely unknown. Here, we identified ATG3-dependent autophagy as an executor for both mitochondrial remodeling during somatic cell reprogramming and mitochondrial homeostasis regulation in ESCs. Dysfunctional autophagy by Atg3 deletion inhibited mitochondrial removal during pluripotency induction, resulting in decreased reprogramming efficiency and accumulation of abnormal mitochondria in established iPSCs. In Atg3 null mouse ESCs, accumulation of aberrant mitochondria was accompanied by enhanced ROS generation, defective ATP production and attenuated pluripotency gene expression, leading to abnormal self-renewal and differentiation. These defects were rescued by reacquisition of wild-type but not lipidation-deficient Atg3 expression. Taken together, our findings highlight a critical role of ATG3-dependent autophagy for mitochondrial homeostasis regulation in both pluripotency acquirement and maintenance.