Various forms of programmed cell death, including apoptosis and regulated necrosis, are concurrently activated in retinal ganglion cells after ischemia and reperfusion

Abstract

Abstract Retinal ischemia–reperfusion (IR) injury – the ultimate consequence of which is retinal ganglion cell (RGC) death – is a common cause of visual impairment and blindness worldwide, largely due to rather ineffective treatments. A special role here belongs to various forms of programmed cell death (PCD), since they can be prevented by inhibiting the activity of the corresponding signaling cascades. To study the PCD pathways in ischemic RGCs, we used a mouse model of retinal IR and a variety of approaches including high-throughput expression profiling (RNA-seq), animals with reduced expression of target genes (FAS and TNFR1/Tnfrsf1a deficient mice), and animals treated with the oral iron chelator deferiprone (1 mg/ml in the drinking water). In our RNA-seq analysis, we utilized RGCs isolated from ischemic and control retinas 24 hours after reperfusion using the two-step immunopanning protocol. Our RNA-seq analysis has shown increased expression in ischemic RGCs compared to control RGCs of many genes that regulate (e.g., Tlr4, Ticam1, Zbp1, Tnfrsf1a, Tnfrsf10b, Fas) or are directly involved in such types of PCD as apoptosis (e.g., Bid, Bcl2l11, Bak1, Hrk, Casp8), necroptosis (Ripk1, Ripk3, Mlkl), pyroptosis (e.g., Pycard, and Casp1), oxytosis/ferroptosis (e.g., Acsl5, Ftl1, Hmox1, Lpcat3, Slc39a14, Steap3), and parthanatos (Parp1). These data indicate that multiple types of PCD are active simultaneously in ischemic RGCs. We found that genetic ablation of death receptors (TNFR1 and FAS) protects RGCs from retinal IR. Our data indicate that the signaling cascades that regulate ferrous iron (Fe2+) metabolism undergo significant changes in ischemic RGCs, leading to retinal damage after IR. All this data set allows us to assume that activation of death receptors and toll-like receptors on the surface of ischemic RGCs, increased ferrous iron (Fe2+) production in these neurons may be responsible for the simultaneous triggering of apoptosis, necroptosis, pyroptosis, oxytosis/ferroptosis, and parthanatos. Thus, therapy is needed that could concurrently regulate the activity of the multiple PCD pathways to significantly reduce RGC death after IR.