Herc3 mutations lead to prominent retinal microglial/macrophage activation and retinal degeneration.

Abstract

Purpose : To corroborate that Herc3 is essential to retinal homeostasis and start exploring the mechanisms explaining its role in retinal physiology.

Methods : Using an unbiased forward genetics approach to screen for genes associated to retinal fundus spot accumulation and retinal thinning we identified Herc3 as a gene of interest. Here we characterize Herc3 KO mice using fundus photography, OCT, immunohistochemistry, electrophysiology, electron microscopy, bulk RNA sequencing and Western blot (WB).

Results : The aegean phenotype seen in the forward genetics screen was recapitulated in the CRISPR-generated KO mouse line. This included accumulation of retinal fundus spots with age and a statistically significant thinning of the outer retina. Furthermore, progressive accumulation of activated subretinal microglia/macrophages and decreased ERG signal were seen. Proteomics analysis demonstrated significant protein expression differences in Herc3 KO mice compared to age-matched controls. A decrease in overall ubiquitination was seen in WB, suggesting that the role of Herc3 as an E3 ubiquitin ligase may be important to retinal physiology.

Conclusions : A forward genetics screening protocol allowed us to identify a novel association of Herc3 to retinal homeostasis. Despite being only one of multiple E3 ubiquitin ligases in the retina, Herc3 has a non-redundant role in the regulation of retinal microglial/macrophage activation and in preventing retinal degeneration. Since the ubiquitin proteasome system is important in many cellular functions, including cell cycle control, signal transduction, and removal of toxic/damaged proteins from the cell, further studies will be needed to further characterize the specific role of this gene in retinal homeostasis.

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