Nix-mediated mitophagy regulates platelet activation and life span

Abstract

Platelet activation requires fully functional mitochondria, which provide a vital energy source and control the life span of platelets. Previous reports have shown that both general autophagy and selective mitophagy are critical for platelet function. However, the underlying mechanisms remain incompletely understood. Here, we show that Nix, a previously characterizedmitophagy receptor that plays a role in red blood cell maturation, also mediates mitophagy in platelets. Genetic ablation of Nix impairs mitochondrial quality, platelet activation, and FeCl3-induced carotid arterial thrombosis without affecting the expression of platelet glycoproteins (GPs) such as GPIb, GPVI, and aIIbb3. Metabolic analysis revealed decreased mitochondrial membrane potential, enhanced mitochondrial reactive oxygen species level, diminished oxygen consumption rate, and compromised adenosine triphosphate production in Nix-/- platelets. Transplantation of wildtype (WT) bone marrow cells or transfusion of WT platelets into Nix-deficient mice rescued defects in platelet function and thrombosis, suggesting a platelet-autonomous role (acting on platelets, but not other cells) of Nix in platelet activation. Interestingly, loss of Nix increases the life span of platelets in vivo, likely through preventing autophagic degradation of the mitochondrial protein Bcl-xL. Collectively, our findings reveal a novel mechanistic link between Nix-mediated mitophagy, platelet life span, and platelet physiopathology. Our work suggests that targeting platelet mitophagy Nix might provide new antithrombotic strategies.