Hyperglycemic conditions and disruptions to glucose-regulating pathways lead to increased formation of highly reactive aldehydes, methylglyoxal and glyoxal, which react with certain arginine and lysine residues in proteins to form advanced glycation end products (AGEs). These AGEs damage the integrity of the retinal vasculature predominantly through two mechanisms: non-receptor-mediated damage, which pertains to the interaction with extracellular matrix and its functional properties, and receptor-mediated damage through AGE interactions with their receptors (RAGE) on pericytes and Muller cells. Damage occurring between AGE and RAGE potentially generates reactive oxygen species, inflammatory cytokines, and growth factors. Both mechanisms result in increased permeability of endothelial tight junctions, and this increased permeability can lead to leaking and eventually ischemia. Once this ischemia becomes significant, neovascularization can occur, the hallmark of proliferative diabetic retinopathy. Current pharmaceutical studies have shown the potential of AGE inhibitors, such as aminoguanidine, in decreasing AGE production, thus minimizing its effects in hyperglycemic conditions. Other pharmaceutical interventions, such as Tanshinone IIA, aim to protect cells from the impacts of AGEs. Future research will not only continue to understand the properties of AGEs and their effects on diabetes and diabetic complications like diabetic retinopathy but will also explore how they impact other diseases.

Since the publication of our previous paper, Visual cycle proteins: Structure, function, and roles in human retinal disease (Tsin, et.al, JBC 293:13016, 2018) there has been significant progress on multiple topics discussed in this paper. In the present communication, we further explore research advances on two visual cycle proteins: DES1 and IRBP. In addition, we emphasize the progress of clinical translation of other visual cycle protein research, including the breakthrough of FDA-approved gene therapy for Leber’s congenital amaurosis, and additional gene therapies at different stages of clinical trials for various retinal diseases such as retinitis pigmentosa, diabetic retinopathy, and Stargardt’s disease.