Female sex accelerates retinal neurodegeneration in Herc3-deficient mice

Abstract Background Retinal degeneration involves mechanisms common to other neurodegenerative diseases, including mitochondrial dysfunction, inflammation, and impaired proteostasis via the ubiquitin-proteasome system (UPS). Although sex hormones modulate these pathways, the molecular basis of this sexual dimorphism remains poorly understood. Herc3 encodes an E3 ubiquitin ligase important for protein quality control; we recently showed that its deficiency leads to progressive retinal degeneration with a potential sex bias. Therefore, this study investigated the effects of biological sex on retinal neurodegeneration and vision loss in a Herc3 -deficient mouse model. Methods Using CRISPR-Cas9-generated Herc3 −/− mice, we performed optical coherence tomography (OCT), fundus photography, electroretinography (ERG), and histology to evaluate sex-related anatomical and functional differences. Bulk RNA sequencing (RNA-seq) and RT-qPCR were used to investigate the underlying molecular mechanisms. Results At 15 months of age, OCT imaging and histological analysis demonstrated accelerated outer retina thinning (outer retina thickness [ORT], P = 0.0069; outer nuclear layer [ONL], P = 0.0013) in Herc3 −/− female mice compared to males. Females also exhibited increased fundus spot accumulation with aging ( P = 0.0025 at 14–16 months) and significantly decreased scotopic ERG responses at 12 and 16 months. Bulk RNA-seq of pre-degenerative (8–10-week-old) neuroretinas identified 143 differentially expressed genes (DEGs; 90 downregulated and 53 upregulated) in Herc3 −/− females relative to males. Pathway analysis revealed that upregulated networks were predominantly associated with mitochondrial energy metabolism, protein translation, RNA processing, and genome maintenance, whereas downregulated processes were enriched for extracellular matrix organization, structural tissue development, lipid/hormone metabolism and inflammation. Analysis of bulk RNA-seq on ovariectomized Herc3 −/− females relative to intact Herc3 −/− females supported a role for sex hormones in the heightened susceptibility to retinal degeneration and microglial activation observed in female mutants. Degeneration in aging mutants (14–16 months) was molecularly characterized by heightened neuroinflammation/microglial activation ( Aif1 , Cd68 , Itgam , Ccl5 , Il23a ), proteostatic failure ( Casp4 , Tnfrsf10b , Tnfrsf1a ), autophagic disruption ( Atg12 ), and loss of photoreceptor identity ( Nrl ) specifically in Herc3 −/− females. Conclusions Our work establishes a strong association between female sex and accelerated structural and functional retinal degeneration. Early-stage transcriptomic alterations highlight activation of compensatory stress-response pathways, reflecting increased metabolic and proteostatic demand alongside impaired tissue maintenance and structural integrity. Over time, this chronic metabolic and proteostatic demand culminates in late-stage neuroinflammation, autophagic failure, and retinal cell death. Altogether, these findings shed light on the molecular pathogenesis of sexual dimorphism in retinal degeneration, providing insights into female-biased disease severity and uncovering potential phase-specific therapeutic windows.