Transketolase regulates endoplasmic reticulum stress independent of enzymatic activity in human retinal Müller cells

Transketolase (TKT) expression in the nucleus of the retina has been reported, but its function beyond metabolism remains unclear. In this study, we investigated the role of TKT in the regulation of endoplasmic reticulum (ER) stress in the retina. Using a VEGF-overexpressing mouse model of age-related macular degeneration (AMD), we analyzed the expression and enzymatic activity of Tkt, and found that while expression levels remained unchanged, enzymatic activity was significantly reduced. Tkt localized primarily to the nucleus of the inner nuclear layer in healthy retinae but shifted outside the nuclear center in the lesion area of the AMD mouse model. ChIP-seq analysis revealed that Tkt-targeted genes were enriched in pathways related to metabolism, ER protein processing, and neurogenerative diseases. Among these targets, TKT directly bound to the promoter region of endoplasmic reticulum to nucleus signaling 1 (ERN1) and suppressed its expression, as validated by dual-luciferase reporter assays. In human Müller cells, TKT knockdown elevated ERN1 levels and exacerbated ER stress responses, while enzymatic inhibition alone had no effect on ER stress. Furthermore, TKT knockdown did not alter mitochondria respiration or glycolysis. These findings demonstrate that TKT mitigates ER stress in the human retinal Müller cells by transcriptionally regulating ERN1 in a manner that is independent of its enzymatic activity.