Increased expression of αA-crystallin in human diabetic eye

We recently demonstrated that αA-crystallin, a molecular chaperone, protected photoreceptors from apoptotic signals in intraocular inflammation. Advanced glycation end product (AGE) plays an important role in the progression of diabetic retinopathy. The aim of this study was to examine the expression of α-crystallins and apoptosis in human diabetic retina, and to analyze α-crystallin up-regulation in murine eyes after AGE stimulation. Eight eye globes were obtained from postmortem donors. Six out of the eight had a medical history of diabetes mellitus, while two were without diabetes. Formalin-fixed, paraffin-embedded tissue sections were subjected to H&E staining and immunohistochemistry with anti-αA and αB-crystallins, anti-AGE and receptor for AGE (RAGE) antibodies. Apoptotic cells were detected by the TUNEL assay. Recom­binant AGE protein was injected into the vitreous of adult murine eyes, and the posterior eyecups were excised 4 days after the administration. Western blot analyses and quantitative real-time PCR were performed to evaluate the alteration of α-crystallin expression. Histopathology revealed no remarkable differences between diabetic and non-diabetic retinas. Immunoreactivity for αA-crystallin was predominantly detected in the diabetic retina, whereas αB-crystallin expression was relatively low. AGE immunoreactivity was highly detected in diabetic retina and the vitreous, whilst immunoreactivity for RAGE was less marked. TUNEL-positive apoptotic cells were occasionally observed in photoreceptors of the diabetic retina, whereas cytoplasmic immunoreactivity for αA-crystallin was relatively low. αA-crystallin expression was up-regulated, and αB-crystallin was down-regulated in murine posterior eyecups exposed to AGE protein. The mRNA levels of αA-crystallin were significantly up-regu­lated, whereas those of αB-crystallin remained unchanged after AGE stimulation. Thus, αA-crystallin and AGE were highly expressed in human diabetic retina. αA-crystallin responded to AGE accumulation, which may contribute to the protection of photoreceptors against AGE-related retinal tissue injury.