Ischemia–reperfusion (IR) injury is implicated in a large array of pathological conditions in the retina. Increasing experimental evidence suggests that programmed necrosis makes a significant contribution to inflammation and retinal damage triggered by IR. Since there are many types of programmed necrosis, it is important to identify those involved in retinal IR to determine the correct treatment. To this end, we used a mouse model of retinal IR and a variety of approaches including RNA-seq data analysis. Our RNA-seq data revealed the rapid development of ischemic pathology in the retina during the first 24 h after reperfusion. We found that at least four types of programmed necrosis including necroptosis, pyroptosis, oxytosis/ferroptosis, and parthanatos are simultaneously involved in retinal IR. Our data suggest that the high activity of the TNF pathway at the early stage of retinal IR leads to early activation of necroptosis while significant activity of other types of programmed necrosis appears later. Our results indicate that TNF, glutamate, and ferrous iron generated by Steap3 may be key players concurrently triggering at least necroptosis, oxytosis/ferroptosis, and parthanatos in ischemic retinal ganglion cells (RGCs). Thus, multiple signaling cascades involved in programmed necrosis should be synchronously targeted for therapeutic purposes to treat retinal IR.

Retinitis pigmentosa and related photoreceptor dystrophies (RPRPD) are rare retinal diseases caused by hereditary gene mutations resulting in photoreceptor death, followed by vision loss. While numerous genes involved in these diseases have been identified, many cases have still not been associated with any gene, indicating that new mechanisms may be involved in the pathogenesis of these photoreceptor dystrophies. Many genes associated with RPRPD regulate photoreceptor specification and maturation in the developing retina. Since retinal development begins with a population of equivalent, proliferating retinal progenitor cells (RPCs) having a specific “competence” in generating all types of retinal neurons, including cone and rod photoreceptors, we tested the epigenetic changes in promoters of genes required for photoreceptor development and genes associated with RPRPD during RPC differentiation into cone and rod photoreceptors. We found that promoters of many of these genes are epigenetically repressed in RPCs but have no epigenetic restrictions in photoreceptors. Our findings also suggest that DNA methylation as an epigenetic mark, and DNA demethylation as a process, are more important than other epigenetic marks or mechanisms in the pathogenesis of these diseases. Most notably, irregularities in the DNA demethylation process during the RPC-to-photoreceptor transition may significantly contribute to retinitis pigmentosa (RP) pathogenesis since genes with hypermethylated promoters in RPCs account for at least 40% of autosomal recessive RP cases and at least 30% of autosomal dominant RP cases. Thus, we proposed an epigenetic model according to which unsuccessful demethylation of regulatory sequences (e.g., promoters, enhancers) of genes required for photoreceptor development, maturation, and function during the RPC-to-photoreceptor transition may reduce or even eliminate their activity, leading to RPRPD without any inheritable mutations in these genes.

Retinal ischemia–reperfusion (IR)—which ultimately results in retinal ganglion cell (RGC) death—is a common cause of visual impairment and blindness worldwide. IR results in various types of programmed cell death (PCD), which are of particular importance since they can be prevented by inhibiting the activity of their 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 RNA-seq analysis, knockout animals, and animals treated with an iron chelator. In our RNA-seq analysis, we utilized RGCs isolated from retinas 24 h after IR. In ischemic RGCs, we found increased expression of many genes that regulate apoptosis, necroptosis, pyroptosis, oxytosis/ferroptosis, and parthanatos. Our data indicate that genetic ablation of death receptors protects RGCs from IR. We showed that the signaling cascades regulating ferrous iron (Fe2+) metabolism undergo significant changes in ischemic RGCs, leading to retinal damage after IR. This data suggests that the activation of death receptors and increased Fe2+ production in ischemic RGCs promote the simultaneous activation of apoptosis, necroptosis, pyroptosis, oxytosis/ferroptosis, and parthanatos pathways. Thus, a therapy is needed that concurrently regulates the activity of the multiple PCD pathways to reduce RGC death after IR.

SIGNIFICANCE Foveal hypoplasia is described clinically by the absence of a foveal pit and subsequent reduction in visual acuity. Optical coherence tomography angiography provides precise segmentation of the retinal vascular supply demonstrating the vascular perfusion in affected patients. Preservation of perfusion is linked to visual acuity and function. PURPOSE This case report describes a patient with foveal hypoplasia and preservation of visual acuity with preserved retinal capillary density of the superficial and deep capillary plexuses on optical coherence tomography angiography. In addition, the diagnostic findings of foveal hypoplasia as seen on optical coherence tomography angiography will be described. CASE REPORT A 25-year-old Caucasian female with history of foveal hypoplasia presented to the clinic for evaluation. She had no other visual, ocular, or systemic complaints. Her ocular history included Duane syndrome, accommodative insufficiency, and traumatic brain injury. Her medical history included cardiac ablation secondary to supraventricular tachycardia, gall bladder removal, maxillary sinus cyst, and a history of migraines. Best-corrected visual acuity was 20/15 in the right and left eyes. Funduscopic examination was unremarkable. Spectral domain optical coherence tomography revealed absence of the anatomical foveal pit with normal inner retinal morphology. Optical coherence tomography angiography confirmed a decreased foveal avascular zone; however, a vascular density analysis showed normal perfusion to the inner retinal plexuses. CONCLUSIONS Optical coherence tomography angiography is a rapid, noninvasive imaging modality that provides excellent insight into the microvasculature supply to the retina and choroid. As such, it allows for an in-depth analysis into the pathophysiology behind certain conditions such as foveal hypoplasia.

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.