Transmitophagy in the heart: An overview of molecular mechanisms and implications for pathophysiology

Mitochondria are essential for meeting cardiac metabolic demands and their dysfunction is associated with heart failure and is a key mediator of cardiac ischemia-reperfusion injury. Cardiomyocytes engage integrated mechanisms to maintain mitochondrial function; however, chronic stress or disease can overwhelm this capacity. The removal of damaged mitochondria is mediated by a process known as mitophagy, which, together with mitochondrial biogenesis, plays a key role in maintaining mitochondrial quality control. Maintenance of mitochondrial quality control was initially thought to be autonomously regulated within each cellular population with little exchange between cells. However, recently the phenomenon of transmitophagy has been identified in which damaged mitochondria are transferred to neighboring cells for degradation. This review discusses the current understanding of transmitophagy in the context of heart injury, aging and disease, with particular emphasis on exophers, migrasomes, and tunneling nanotubes as pathways mediating cell-cell communication between cardiomyocytes, macrophages and fibroblasts. We further discuss the potential of targeting transmitophagy for cardioprotection and highlight key unanswered questions and challenges. Addressing these gaps may reveal novel strategies to preserve mitochondrial homeostasis and improve the outcomes of patients with cardiovascular disease.