Tree shrew model of early diabetic retinopathy reveals microvascular dysfunction and identifies phosphoserine aminotransferase 1 as a novel therapeutic target.

BACKGROUND

Diabetic retinopathy (DR) is the most significant manifestation of diabetic microangiopathy. The existing tree shrew model of DR has dysfunctional retinal short wave sensitivity (SWS) cones and retinal ganglion cells, but it remains unclear whether the retinal microvessels are also compromised. In this study, we established a tree shrew diabetes model to investigate the characteristics of retinal microvascular disease observed in early human DR.

METHODS

A high-fat and high-sugar diet combined with streptozotocin was used to establish the tree shrew diabetes model. After 20 weeks of sustained high glucose levels, we measured the thickness of each retinal layer and the number of ghost pericyte cells and acellular capillaries, and examined the ultrastructural changes in the retina. We also performed RNA sequencing (RNA-seq) and evaluated the protein expression levels of vascular endothelial growth factor (VEGF) and Bcl-2-related X protein (Bax).

RESULTS

The tree shrew model exhibited the characteristics of diabetes, including hyperglycemia, hyperlipidemia, and insulin resistance. The retinal nerve fiber layer and ganglion cell layer exhibited significant thinning (36% and 30%, respectively). Retinal capillaries exhibited ghost pericytes and acellular capillaries, whereas the retinal ultrastructure exhibited signs of damage. VEGF and Bax protein levels in the retina were significantly upregulated. RNA-seq revealed downregulation of phosphoserine aminotransferase 1 (PSAT1). Overexpression of PSAT1 in retinal microvascular endothelial cells restored their lumen formation ability and mobility in a high-glucose environment, and reduced the expression of VEGF.

CONCLUSION

Our results indicate that the tree shrew may be a suitable experimental animal model for studying the pathogenesis of early DR. Furthermore, PSAT1 may be a promising molecular target for DR treatment.