Differential proteomic analyses of cataracts from rat models of type 1 and 2 diabetes

To identify differential changes in proteins and metabolites underlying "fast" type 1 (T1DC) and "slow" type 2 (T2DC) diabetic cataract (DC) formation in rat.

Rat models of types 1 and 2 diabetes consisted of streptozotocin injection without and with high-fat diet, respectively. Cataract progression was examined weekly. At week 6, total protein changes were comparatively and quantitatively assessed by two-dimensional differential in-gel electrophoresis (2-D DIGE) coupled with mass spectrometry, and relevant metabolic changes were examined. Differences in high molecular weight (HMW) crystallin species between diabetic and control lenses were similarly identified.

Cataracts were morphologically different and progressed more slowly in T2DC versus T1DC. αA-crystallin, βB2-crystallin, and βA4-crystallin were significantly decreased in both DC types versus control. αB-crystallin was increased while βB1-crystallin was markedly decreased in T2DC. In T1DC, γB-crystallin and γS-crystallin fragmentation were increased. High-fat diet by itself had little impact, except for lowering γS-crystallin fragmentation. Despite significantly decreased opacity, a greater decrease in intermediate filaments (IFs) and more HMW crystallin species were observed in T2DC versus T1DC. However, aldose reductase expression and activity and sorbitol levels were increased to a greater extent in T1DC, while reduced glutathione (GSH) and reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) levels were decreased to a greater extent and adenosine triphosphate (ATP) level was much lower in T1DC versus T2DC.

The results suggest that osmotic damage, GSH loss, and decreased ATP production might be important pathological mechanisms in T1DC formation, whereas crystallin modification and cross-linking/aggregation as well as IF degradation may play more crucial roles in T2DC formation.