Abstract
Purpose :
The mammalian retina contains an autonomous circadian system that regulates various aspects of retinal physiology critical for the processing of visual information and thus optimizing retinal activity with the daily variation in light intensity. The retinal clock can be entrained by light both in vitro and in vivo suggesting that light plays a critical role in the regulation of the retinal clock. Retinal angiogenesis is dependent on the retinal ganglion cells and in mice lacking RGCs, retinal vasculature does not develop thus highlighting the importance of cues that are provided from the underlying neuronal cells. The goal of this study was to test the hypothesis that the light-regulated retinal circadian clock is essential for developmental and pathological angiogenesis.
Methods :
To test this hypothesis, we disrupted the light/dark cycle or conditionally deleted the circadian clock genes Bmal1 and Per2 from the retinal progenitor cells (RPCs) and vascular endothelial cells (VECs). Chromatin immunoprecipitation sequencing analysis (ChIP Seq) was used to identify the angiogenic molecular targets of Bmal1 in the neurons. To address the role of the neuronal clock in pathological angiogenesis, oxygen-induced retinopathy (OIR) model was used.
Results :
Our results demonstrate that the neuronal clock genes Bmal1 and Per2 are essential regulators of retinal angiogenesis. The clock gene transcripts exhibit circadian rhythmicity in the embryonic retina and this rhythmicity is lost under disrupted light/dark cycles. ChIP analysis indicates that some of the Bmal1 targets within the retinal neurons are angiogenic regulators. Accordingly, deletion of Bmal1 in neuronal cells results in overgrowth of the vasculature while Bmal1 deletion from the endothelial cells causes reduced proliferation, with reduced vessel density. RNA sequencing data from the endothelial cells suggests that pathways primarily related to the cell cycle are altered by the loss of Bmal1. Furthermore, only the neuronal clock is an important mediator of pathological angiogenesis as loss of Bmal1 and Per2 causes a significant reduction of neovascularization.
Conclusions :
The data presented here raise an exciting question about the interrelationship between the circadian clock in the neurons and vasculature during retinal angiogenesis. Importantly, a robust circadian clock in the neurons protects the retinal vasculature from oxygen-induced damage.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.