Bystander effects of PC12 cells treated with Pb2+ depend on ROS-mitochondria-dependent apoptotic signaling via gap-junctional intercellular communication

摘要

The demonstration of bystander effect, which means injured cells propagate damage to neighboring cells, in whole organisms has clear implication of the potential relevance of the non-targeted response to human health. Here we show that 10μM lead acetate, the optimum concentration for inducing apoptosis confirmed by the expression levels of Bax and Bcl-2, can also induce rat pheochromocytoma (PC12) cells to exert bystander effects to neighboring cells. In a novel co-culture system, GFP-PC12 (Pb2+) cells, which were stable transfected with EF1A-eGFP and pre-exposed with lead acetate, were co-cultured with unexposed PC12 cells at a 1:5 ratio. Parachute assays demonstrated the functional gap-junctional intercellular communication (GJIC) formed between Pb2+-exposed and unexposed cells. The Pb2+-exposed cells induced very similar effects on neighboring unexposed cells to apoptosis coincide with intracellular ROS generation and the collapse of mitochondrial membrane potential (δψm). Furthermore, carbenoxolone (CBX), a blocker of GJIC, inhibited the bystander effects. The results indicate that the Pb2+-induced insults propagate through GJIC between PC12 cells, while inducing the bystander cells to apoptosis via ROS-mitochondria-dependent apoptotic signaling.