Modeling of spreading cell death by necrosis neurons to adjacent cells in Drosophila. Yong Yang, Lin Hou, Lei Liu. Peking University, Beijing, China.

   Necrotic cells often spread damage to adjacent tissues in diseases such as ischemic stroke and traumatic brain injury. However, the signaling mechanisms of dying cells on their neighbors are poorly understood. To model this cellular response, we made a transgenic fly line that induced neuronal necrosis specifically in a few neurons by expressing a leaky cation channel. Namely, this system contains UAS-GluR1^Lc (the leaky channel) driven by sevenless-Gal4 (sev>GluR1^Lc), which is expressed in three of the eight photoreceptor neurons in each ommatidium of eyes. We found that calcium overloading through GluR1^Lc expression indeed caused neuronal necrosis and reduced eye size of adult flies. Moreover, we found that spreading cell death took place in adjacent neurons but not glial cells through caspase-dependent and JNK-dependent apoptosis (JNK activation was determined by an in vivo reporter, puc-lacZ). Further genetic tests showed that the caspase-dependent apoptosis was mediated by hid; and the JNK-dependent apoptosis was regulated by ROS through metabolic pathways. In addition, we found that the key spreading factors from neuronal necrosis were eiger and ROS, because genetic manipulations of their levels affected both JNK activation and eye size of sev>GluR1^Lc. To determine the sequential events among ROS, eiger and JNK activation, we performed a tissue culture in vitro assay. In response to ectopically added hydrogen peroxide (H₂O₂), eiger was up-regulated and JNK signaling was elevated. Interestingly, eiger RNAi abolished the effect of H₂O₂ on JNK. Together, these results suggest that releasing of eiger and ROS from necrotic neurons synergistically activates JNK in the adjacent neurons with eiger pathway to be the dominant signal. Our model provides the first genetic evidence to demonstrate how necrotic neurons may influence their neighboring cells.