Increased Expression of p21WAF-1/CIP-1 in the Lens Epithelium of Rat Sugar Cataract

Abstract

It has been demonstrated that exquisite regulation of the cell cycle between the activation and inhibition is crucial to maintain the transparency of the ocular lens. While it is generally recognized that the sugar cataract is accompanied by the enhanced proliferation of lens epithelial cells (LECs), it is unclear whether or not an inhibitory mechanism against the lens proliferation is involved, except for TGF-β. In this study, the authors demonstrated the enhanced expression of p21WAF-1/CIP-1, a potent inhibitor against cell cycle progression, and its specific temporal and regional expression profiles in the LECs during the development of sugar cataract. Sugar cataract was induced in 6-week-old male Sprague-Dawley rats by feeding them on a 50% galactose-rich diet, and then the expression patterns of p21WAF-1/CIP-1 mRNA and protein with the advance of the sugar cataract were studied. Western blot analyses showed that p21WAF-1/CIP-1 expression increased throughout the period of galactose exposure, up to 21 days. Also, a gradual increase in the number of p21WAF-1/CIP-1 positive cells was observed immunohistochemically in the course of the galactose exposure. Interestingly, p21WAF-1/CIP-1 was significantly expressed in the multi-layered epithelium, which was observed typically in the advanced cataract. Proliferating cell nuclear antigen (PCNA), an indicator of cell proliferation, was also positive in the most multi-layered epithelial cells. In addition, transient expression of PCNA mRNA and its protein was noticed throughout the lens epithelium in the course of the sugar cataract development. Prior to the elevation of p21WAF-1/CIP-1 mRNA expression, PCNA mRNA expression increased greatly and reached a peak according to the semiquantitative analyses using either the real time reverse transcription–polymerase chain reaction (RT–PCR) or the Southern blot analyses. Based on these observations, it is possible that p21WAF-1/CIP-1 is elevated and exerts its inhibitory action against the proliferating epithelial cells during the development of the sugar cataract.