Postnatal eye size in mice is controlled by SREBP2-mediated transcriptional repression of Lrp2 and Bmp2

Abstract

Purpose : Eye size is a key parameter of visual function, but the precise mechanisms of eye size control remain poorly understood. In a study aiming to understand the role of lipid synthesis in retina development and diseases, we made an unexpected discovery that the lipogenic transcription factor sterol regulatory element-binding protein 2 (SREBP2) has a function in eye size regulation. SREBP2 is expressed in the neural retina and retinal pigment epithelium (RPE) cells, but its function in eye development remains elusive. In this study, we investigated the role of SREBP2 and its downstream signaling pathway in regulating eye size in mice.

Methods : Adeno-associated virus(AAV)-mediated gene transfer was used to target gene expression or knock down specifically in the RPE using the bestrophin 1 promoter. Subretinal injections were performed to neonatal mice. Mice were sacrificed at postnatal day 14, and their eyes were enucleated, and the axial length of the eyeballs was measured. RNA-sequencing analysis, ChIP-qPCR, luciferase reporter assay, real-time PCR, and western blot were used to investigate the downstream targets of Srebp2. EdU incorporation assay was performed to quantify cell proliferation, and the number of EdU-positive cells in the retina, RPE/choroid and sclera was quantified.

Results : Overexpression of a constitutively active form of Srebp2 (nSrebp2) in the RPE cells of postnatal mice leads to extremely enlarged eye globes. Taking this observation as a starting point, we reveal that Lrp2, a gene that is known to restrict eye overgrowth, is transcriptionally repressed by SREBP2. Transcriptome analysis and functional assays identified that BMP2 is the downstream effector of both Srebp2 and Lrp2, and the level of Bmp2 in the RPE is the key determinant of eye size. As the upstream regulator, SREBP2 transcriptionally represses Bmp2. Over postnatal development, the levels of Lrp2 and Bmp2 transcripts increase and the SREBP2 protein level decreases. Notably, RPE-specific Bmp2 overexpression by AAV can effectively prevent the eye enlargement and retinal thinning caused by Lrp2 loss.

Conclusions : Our study suggests that rapid postnatal eye size increase is governed by an RPE-derived signaling pathway, which consists of both positive and negative regulators of eye growth. Overall, this study unveils an essential role of the SREBP2-LRP2-BMP2 signaling in the RPE in determining eye size.

This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.