Abstract
Purpose :
Many eyes with neovascular AMD have poor outcomes because they develop subretinal fibrosis which is neither preventable nor treatable. Metabolic reprogramming in the retina is reported as one critical pathogenic process in retinal fibrosis. The JR5558 mouse develops subretinal neovascularization, resulting in local gliosis and photoreceptor death. The subretinal lesions in these mice have several key molecular and pathological features of subretinal fibrosis. The de novo serine/glycine synthesis plays an essential role in the formation of fibrotic scars. We aim to explore the changes of this metabolic pathway in a mouse model of subretinal fibrosis in this study.
Methods :
The subretinal lesions in the JR5558 mouse expanded between 4 and 8 weeks of age and became established in size and location around 12 weeks. The changes of four key enzymes in the de novo serine/glycine synthesis (phosphoglycerate dehydrogenase (PHGDH), hydroxymethyltransferase 2 (SHMT2), phosphoserine phosphatase and phosphoserine aminotransferase 1) were evaluated during the time course for the development of subretinal fibrosis. We explored the distribution pattern of these enzymes by immunofluorescent staining in the retina of JR5558 mice compared with the controls, costained with cellular retinaldehyde-binding protein (CRALBP, a Müller cell and retinal pigment epithelium (RPE) marker). We also quantified protein levels of key enzymes in the JR5558 mouse retinas by Western Blot. The C57BL/6 mouse retina was used as a control to compare the expression level of these enzymes in fibrosis mouse retinas.
Results :
We found that PHGDH, a key rate-limiting enzyme of de novo serine synthesis, was expressed by Müller cells and RPE in the JR5558 mouse retina. It was strongly expressed in the subretinal lesions. SHMT2, a key mitochondrial enzyme that converts serine to glycine, was expressed by the Müller cells and extensively expressed in the retinal fibrotic lesions. The protein level of PHGDH was significantly upregulated in the JR5558 mouse retinas at 8 weeks of age, the peak stage of the development of subretinal fibrosis, compared with the age-matched C57BL/6 wild type controls.
Conclusions :
Our findings suggest that the de novo serine/glycine biosynthesis is activated during the development of the subretinal fibrotic lesions in the JR5558 mouse model, perhaps representing a novel therapeutic target for subretinal fibrosis.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.