Transthyretin Exerts Pro-Apoptotic Effects in Human Retinal Microvascular Endothelial Cells Through a GRP78-Dependent Pathway in Diabetic Retinopathy.

BACKGROUND/AIMS: Diabetic retinopathy (DR) is one of the main causes of blindness in the world. Our previous study showed that transthyretin (TTR) regulates key genes in the Tie2 pathway and inhibits the development of neovascularization in DR, but the mechanism is still unclear. Here, we investigated how TTR affects the progression of neovascularization in DR.

METHODS

Natural and simulated DR media (hyperglycemia and hypoxia) were used to culture human retinal microvascular endothelial cells (hRECs). Flow cytometry was employed to investigate the effect of TTR on apoptosis of hRECs. Fluorescent labeling and immunofluorescence staining were used to determine the TTR distribution in hRECs. The membrane proteins of hRECs were extracted and applied to a sepharose-TTR column, and the captured proteins were identified by Mass Spectrometric analysis. Gene knock-down and western blotting assays were used to study the key signal pathway of the most abundant identified protein.

RESULTS

TTR induced apoptosis of hRECs in an environment that simulated hypoxia. Immunofluorescent staining showed that TTR could enter the nuclei of hRECs. A total of 30 unique TTR-captured proteins were identified by Mass Spectrometry, and glucose-regulated protein 78 (GRP78) was one of the most abundant. Western blotting and gene knock-down indicated that TTR might upregulate GRP78 and facilitate apoptosis through the eIF2α/CHOP pathway.

CONCLUSIONS

In the DR environment (hyperglycemia and hypoxia), TTR was shown to repress neovascularization by promoting apoptosis of hRECs through a GRP78-dependent pathway.