Mesona chinensis Extract Ameliorates Retinal Angiopathy in a Zebrafish Model of Diabetic Retinopathy by Targeting Thymidylate Synthase in Folate Metabolism

Retinal neovascularization in diabetic retinopathy (DR) is a major cause of vision loss. Folate-mediated one-carbon metabolism (OCM) is crucial for nucleotide synthesis and cell proliferation. We hypothesized that dysregulated OCM, particularly involving thymidylate synthase (TYMS), contributes to DR pathogenesis. Using a zebrafish DR model and human retinal endothelial cells, we assessed high glucose’s effects on retinal vessel development and TYMS expression. We measured changes in gene and protein expression of OCM enzymes (TYMS, DHFR, SHMT) via RT-PCR and Western blotting. TYMS overexpression (via tyms mRNA microinjection) increased DR angiogenesis severity. We evaluated the anti-angiogenic efficacy and safety of M. chinensis extract and one of its key compounds, quercetin, using vessel imaging, optomotor response assays, and developmental toxicity comparisons against 5-fluorouracil and methotrexate. High glucose upregulated TYMS expression at both mRNA and protein levels, driving retinal hyper-angiogenesis and visual impairment in DR zebrafish. The pro-angiogenic effects of TYMS are tissue-specific. M. chinensis and quercetin dose-dependently inhibited both pathological angiogenesis and glucose-induced TYMS expression. The anti-angiogenic effect of M. chinensis was found to be TYMS-dependent, as evidenced by its ability to reverse hyper-angiogenesis caused by TYMS overexpression. Crucially, M. chinensis exhibited minimal toxicity compared to conventional anti-folate drugs. TYMS, a key enzyme in folate-mediated OCM, contributes to the pathological retinal angiogenesis in zebrafish DR model. The natural extract M. chinensis represents a potent, and cost-effective intervention that can prevent glucose-induced retinal pathology by modulating TYMS activity, providing a safe and promising alternative for the prevention and management of DR.