Adults older than 45 years old are at higher risk of developing venous blood clotting known as venous thrombosis/thromboembolism than a cohort <
45 years old. Complement activation, which can be mediated by oxidative stress, plays a central role in venous thrombosis. Yet, whether RBCs contribute to complement activation triggering thrombosis in aging and in patients with venous thrombosis/thromboembolism remains an open question. RBCs from healthy Mid-life stage (55-68 years old) adults and patients with venous thrombosis/thromboembolism showed higher deposition of the complement C3 and the anaphylatoxin C3a, and NADPH oxidase (Nox)1 expression than a younger cohort (21-30 years old). Increased C3/C3a deposition on RBCs from mid-life stage adults and patients with venous thrombosis/thromboembolism triggered prothrombin activation via Nox1-dependent reactive oxygen species (ROS) generation, and G protein-coupled receptor kinase 2 (GRK2) activation. Interaction of C3/C3a positive RBCs from mid-life stage adults with endothelial cells led to increased endothelial ROS production. TGF-β1-stimulated GRK2 and Nox1 activation in RBCs from the younger and older adults exacerbated RBC C3/C3a deposition and C3/C3a-mediated prothrombotic activation, which appears to result from ROS-mediated increased RBC phosphatidylserine exposure. Using human RBCs, and Rpl13a snoRNA knockout aged mice, we show that Rpl13a snoRNAs, the master regulators of ROS levels and oxidative stress response, regulate human and murine RBC C3a deposition and prothrombic activation in aging by modulating Nox1 mRNA expression. In vivo Rpl13a snoRNA knockout in aged mice decreased thrombi size by blunting RBC C3a deposition, and RBCs-triggering prothrombin activation. These findings point out to a novel role of RBC Rpl13a snoRNAs in dysregulating RBC ROS-induced C3a deposition promoting venous thrombosis in aging.