Elevated expression of αA- and αB-crystallins in streptozotocin-induced diabetic rat

Abstract

α-Crystallin, a predominant protein of the ocular lens, is composed of two subunits, αA and αB. Of these, αB-crystallin has been shown to present widely in non-lenticular tissues while αA-crystallin is largely lens-specific. Although, expression of αB-crystallin is elevated under various stress and pathological conditions, yet its physiological significance remained unknown. Some studies suggest that the expression of αB-crystallin gene is related to oxidative stress. Persistent hyperglycemia during uncontrolled diabetes is known to cause oxidative stress, which has been implicated in various secondary complications of diabetes. Hence, expression of αA- and αB-crystallins in various tissues of streptozotocin (STZ)-induced diabetic Wistar-NIN rats was investigated by RT-PCR and immunoblotting. While expression of αB-crystallin was noted in the wide range of tissues examined in the study, αA-crystallin expression was detected only in lens and retina. Interestingly, αB-crystallin expression was elevated in lens, heart, muscle, and brain, but decreased in adipose tissue of diabetic rats compared to control rats. αA-Crystallin expression was increased in retina of diabetic rat. Increased oxidative stress appears to be a major stimulus for the enhanced expression of αA- and αB-crystallins in the tissues of diabetic rats and elevated expression of α-crystallin may have a protective role against metabolic stress. Interestingly, feeding of curcumin, a dietary antioxidant, to diabetic rats attenuated the enhanced expression of αB-crystallin. The results indicate that elevated expression of α-crystallins in some tissues may have implications in pathophysiology of diabetic complications.