Female Mice Pay a Heavier Price: Sex Hormones Speed Retinal Degeneration

Why do neurodegenerative diseases so often strike the sexes unequally? A new study in Biology of Sex Differences offers one of the clearest answers yet for the eye. Researchers at UT Southwestern Medical Center report that female mice lacking the Herc3 gene — a critical component of the cell’s protein quality-control machinery — lose retinal structure and vision dramatically faster than their male counterparts. The retina, the delicate light-sensing tissue at the back of the eye, shares many of the same vulnerabilities as the brain: it depends on mitochondria for energy, on the ubiquitin-proteasome system for clearing damaged proteins, and on tightly regulated immune surveillance to stay healthy. When any of those systems falters, degeneration follows. What the new work shows is that biological sex can tip that balance decisively, long before any visible damage appears.

The team, led by first authors Dogan Can Kirman and Ashley A. Rowe under the senior guidance of Katherine J. Wert and Rafael L. Ufret-Vincenty, generated mice lacking Herc3 using CRISPR-Cas9 genome editing. Herc3 encodes an E3 ubiquitin ligase, a molecular tagger that marks misfolded or damaged proteins for destruction by the proteasome, the cell’s waste-disposal complex. Without it, protein quality control collapses, and cells — especially metabolically demanding neurons like photoreceptors — accumulate toxic debris. The researchers had previously noticed a hint that female mutants fared worse; this study was designed to test that suspicion rigorously, tracking retinal anatomy, function, and gene expression in male and female animals as they aged.

The structural evidence was unambiguous. By 15 months of age, optical coherence tomography, a non-invasive imaging technique that cross-sections the living retina, revealed significantly accelerated thinning of the outer retina in females compared with males. Histological examination confirmed the finding, showing that the outer nuclear layer — the densely packed band containing the cell bodies of rod and cone photoreceptors — was markedly thinner in females, with a statistical significance of P = 0.0013. In plain terms, the females were losing the very cells that capture light. Fundus photography, which images the interior surface of the eye, told a parallel story: aging females accumulated significantly more bright spots on the retina, a feature the authors link to subretinal microglia, the resident immune cells of the nervous system. Greater spot accumulation, statistically significant at 14 to 16 months, pointed to amplified neuroimmune activation in female eyes.

Function tracked structure. Electroretinography, which measures the electrical responses of retinal cells to flashes of light under dark-adapted (scotopic) conditions, showed significantly weakened responses in female mutants at 12 and 16 months of age. Because scotopic responses primarily reflect rod photoreceptor activity, the results indicate that the females’ dim-light vision was deteriorating measurably faster than the males’. Together, the imaging, histology, and electrophysiology establish that female sex is associated with accelerated degeneration across every level of analysis — from molecules to tissue architecture to behaviorally relevant visual function.

The most striking insights, however, came from the molecular level. The team performed bulk RNA sequencing on neuroretinas from young, pre-degenerative mice, just 8 to 10 weeks old, when the retina still looks structurally normal. Even at this early stage, female mutants carried a distinct transcriptional fingerprint: 143 genes were differentially expressed relative to males, with 90 downregulated and 53 upregulated. The upregulated networks were dominated by mitochondrial energy metabolism, protein translation, RNA processing, and genome maintenance — pathways that, when cranked up in a young tissue, signal compensatory stress rather than vigor. The female retinas were essentially working overtime, burning extra metabolic and proteostatic resources to keep pace with the damage caused by Herc3 loss.

Meanwhile, the downregulated genes told the complementary half of the story. Pathways governing extracellular matrix organization, structural tissue development, lipid and hormone metabolism, and baseline inflammatory regulation were quieter in the young female retinas. The extracellular matrix provides the scaffolding that holds retinal cells in place and supports their survival, so its early suppression suggests that female tissue maintenance and structural integrity were already compromised before any thinning could be seen. In the authors’ interpretation, the young female retina exists in a more vulnerable state: higher metabolic and proteostatic demand running on a weaker structural foundation. Over time, that chronic imbalance culminates in homeostatic breakdown.

The late-stage molecular profile confirmed this trajectory. In aging mutants at 14 to 16 months, degenerating female retinas showed heightened expression of neuroinflammatory and microglial activation markers, including Aif1, Cd68, Itgam, Ccl5, and Il23a. They also displayed signs of proteostatic failure, with elevated Casp4, Tnfrsf10b, and Tnfrsf1a — genes associated with inflammatory cell-death pathways — alongside disruption of autophagy, the cell’s recycling system, marked by changes in Atg12. Perhaps most tellingly, the females lost expression of Nrl, a master transcription factor that defines photoreceptor identity. The loss of a cell’s core identity program is a hallmark of terminal degeneration, indicating that female photoreceptors were not merely stressed but actively dying and dedifferentiating.

What drives this female-specific vulnerability? The researchers turned to sex hormones for an answer. They compared ovariectomized Herc3-deficient females — animals whose ovaries had been removed, eliminating the primary source of estrogen and other ovarian hormones — with intact female mutants. The transcriptomic differences between these groups supported a role for female sex hormones in heightening susceptibility to retinal degeneration and microglial activation. This finding is provocative because it inverts a common assumption: rather than protecting the retina, ovarian hormones appear to amplify the damage when protein quality control fails, at least in this model. The authors caution that the data establish an association and a role for hormones in susceptibility, and the precise hormonal mechanisms remain to be worked out.

The broader significance of the study extends well beyond ophthalmology. Retinal degeneration is increasingly studied as a window into neurodegeneration generally, because the retina is accessible, imageable, and mechanistically akin to brain tissue. Many neurodegenerative and retinal diseases — from Alzheimer’s and Parkinson’s to age-related macular degeneration — show sex-biased prevalence or severity, yet the biological reasons remain poorly understood, and females have historically been understudied in neuroscience research. By establishing Herc3-deficient mice as a robust model of sex-dependent retinal neurodegeneration, the UT Southwestern team has created a platform for dissecting those mechanisms and, critically, for testing interventions at the right stage of disease in the right sex.

The study also carries a practical message about therapeutic timing. Because the female-specific molecular signature appears in young, pre-degenerative retinas, it defines an early, phase-specific therapeutic window — a period when boosting tissue maintenance, easing metabolic load, or supporting proteostasis might prevent the later cascade of inflammation and cell death. Conversely, the late-stage profile of neuroinflammation, autophagic failure, and photoreceptor loss suggests that once disease is established, different targets would be needed. The authors argue that distinct, sex-specific therapeutic windows should be developed for male and female patients, a conclusion that aligns with a growing movement in precision medicine to treat biological sex as a fundamental variable rather than a nuisance factor. For the millions of people — disproportionately women in many retinal diseases — facing progressive vision loss, the finding that the female retina carries a measurable molecular vulnerability from early life is both a warning and a roadmap: the damage begins long before symptoms, and that hidden early phase may be exactly where treatment can succeed.

Subject of Research: Sex-dependent retinal neurodegeneration in Herc3-deficient mice

Article Title: Female sex accelerates retinal neurodegeneration in Herc3-deficient mice

Article References: Kirman, D. C., Rowe, A. A., Kumar, A., Xing, C., Turpin, E. R., Ulker-Yilmazer, G., Aredo, B., Wert, K. J., & Ufret-Vincenty, R. L. (2026). Female sex accelerates retinal neurodegeneration in Herc3-deficient mice. Biology of Sex Differences. https://doi.org/10.1186/s13293-026-00999-2

Image Credits: AI Generated

DOI: 10.1186/s13293-026-00999-2

Keywords: Herc3, retinal degeneration, sexual dimorphism, ubiquitin-proteasome system, neuroinflammation, microglia, photoreceptors, sex hormones, CRISPR-Cas9, RNA sequencing, electroretinography, ovariectomy