Upregulation of Nrf2 Attenuates Oxidative Stress–Induced, Complement Activation–Associated Endothelial Injury and Apoptosis in Transplant-Associated Thrombotic Microangiopathy

Transplant-associated thrombotic microangiopathy (TA-TMA) is a serious and life-threatening complication after hematopoietic stem cell transplantation. Studies have reported that the main pathological manifestation of the disease is an endothelial injury associated with complement activation, but its molecular biological mechanisms remain unclear. Our previous studies have shown that oxidative stress may induce complement activation in TA-TMA. Nuclear factor erythroid 2-related factor 2 (Nrf2), a molecule that regulates oxidative stress, can inhibit endothelial stimulation by reactive oxygen species (ROS). We assessed Nrf2 expression in peripheral blood mononuclear cells (PBMCs) from patients with TA-TMA compared with healthy donors. Nrf2 expression, ROS accumulation, complement activation, and apoptosis were then assessed in human umbilical vein endothelial cells (HUVECs) incubated with TA-TMA plasma to identify whether complement-associated endothelial damage induced by oxidative stress occurs in TA-TMA. The protective effect of Nrf2 pathway activation on TA-TMA-induced endothelial injury was also investigated to explore a new avenue for TA-TMA prevention and treatment. In this study, peripheral blood was collected from six patients with TA-TMA, and healthy donors served as negative controls. We determined the expression of Nrf2 through in vitro and in vivo experiments and measured the level of apoptosis. We found increased expression of Nrf2 in PBMCs from patients with TA-TMA. HUVECs were then incubated with plasma from patients with TA-TMA or with plasma from healthy donors, and we found that complement 3 (C3) levels were increased in HUVECs treated with TA-TMA plasma. In contrast, total Nrf2 levels were decreased, and ROS production and apoptosis levels were increased. To determine whether complement activation and apoptosis were caused by oxidative stress, we added N-acetyl-L-cysteine to HUVECs incubated with TA-TMA plasma. As a result, ROS production, complement activation, and apoptosis levels were reduced. Finally, we upregulated Nrf2 in HUVECs by rescue experiments, and we found that activation of Nrf2 attenuated endothelial cell apoptosis and ROS production and reduced C3 and C5b-9 levels. These results suggest that oxidative stress-induced, complement activation-associated endothelial injury occurs in TA-TMA and that upregulation of Nrf2 protects endothelial cells from damage. Activation of the Nrf2 pathway may be a potential target for the treatment of complement activation-associated endothelial injury in TA-TMA.