Beyond Ornithine Metabolism in Gyrate Atrophy: Tissue-Specific Proteomic Insights into Neonatal and Adult OAT Deficiency

Abstract Ornithine aminotransferase (OAT) links the urea cycle, TCA cycle, and amino acid metabolism by interconverting ornithine to pyrroline-5-carboxylate and glutamate. Mutations in OAT cause hyperornithinemia and predominantly affect the eye, leading to gyrate atrophy of the choroid and retina (GA), a rare inherited blinding disorder. To understand the early molecular changes that make the eye susceptible to damage, we performed quantitative proteomic and metabolomic profiling of liver, retina, and retinal pigment epithelium and choroid (RPE/Cho) from OAT-deficient (Oatrhg) mice prior to detectable vision impairment. In addition to reduced OAT expression and elevated ornithine, methylation-related metabolites such as N(6)-methyl-lysine were altered in all examined tissues of Oatrhgmice. In the liver, ornithine disposal through the urea cycle was enhanced, together with altered expression of detoxification enzymes and histone H2B proteins. In contrast, the retina had minimal proteomic changes but pronounced alterations in amino acid pathways supporting glutamate homeostasis. The RPE/Cho demonstrated the most extensive proteomic changes, particularly in mitochondrial metabolism, cytoskeleton, and extracellular matrix, along with reductions in metabolites involved energy metabolism and antioxidant capacity. Together, these findings highlight common and tissue-specific impacts of OAT on the liver and ocular tissues and provide insight into early molecular changes that contribute to the selective vulnerability of the eye in GA. Proteomics data are available via ProteomeXchange (PXD063614) and metabolomics data via MassIVE repository (MSV000101103). Competing Interest Statement The authors have declared no competing interest. Footnotes In this revised version, we have focused on adult OAT deficiency to better define tissue-specific molecular changes associated with disease progression. We removed the neonatal proteomics data to address potential confounding effects related to developmental stage and systemic metabolic alterations, including those arising from nutritional differences. This revision allows for a more direct interpretation of OAT deficiency in a physiologically stable context. We have incorporated new targeted metabolomics analyses in adult OAT-deficient mice, the same age as the proteomics set, providing complementary insights into metabolic pathway alterations across tissues. These data strengthen the integration of proteomic and metabolomic findings and improve the mechanistic understanding of how OAT loss affects systemic and ocular metabolism. In addition, they enhance the relevance of the findings to the biology of GA disease. Specifically, Figures 3, 4, 6, and 8 present new metabolomics analyses, including cross-tissue comparisons and pathway-level interpretation.