The abnormal form of the prion protein has increased resistance to protease digestion and is insoluble in non-ionic detergents. The normal prion protein is modified by the non-obligatory addition of two N-linked glycans. One pathogenic mutation, Thr to Ala at residue 183 of the human prion protein, blocks addition of the first glycan to the Asp residue 181. This mutation has been reported to result in intracellular retention of the mutant protein and its acquisition of pathogenic properties, presumably due to the lack of the glycan. We report that the lack of the N-linked glycan at residue 181 is not responsible for the block in transport or the acquisition of pathogenlike properties, rather, the Thr to Ala mutation is itself the probable cause of the pathogenic phenotype.

Exposure to ultraviolet radiation (UVR) and reactive oxygen species (ROS) can damage the human lens and contribute to cataract formation. Recent evidence suggests that apoptosis in lens epithelial cells (LEC) is an initiating event in noncongenital cataract formation in humans and animals. The present study examines the cellular and molecular mechanisms by which environmental (ultraviolet B [UVB]) and chemical (hydrogen peroxide [H(2)O(2)], t-butyl hydroperoxide [TBHP]) stress induces cell death in an SV-40 immortalized human lens epithelial (HLE) cell line. Treatment of HLE cells with UVB, H(2)O(2), and TBHP significantly decreased cell density with LD50 values of 350 J/m(2), 500 muM, and 200 muM, respectively. Cellular morphology, DNA fragmentation, and annexin/propidium iodide staining consistent with apoptosis was observed only in UVB-treated cells, whereas lactate dehydrogenase (LDH) release was significantly higher in H(2)0(2)- and TBHP-treated cells. In addition, activation of apoptotic stress-signaling proteins, including c-Jun NH2-terminal kinase (JNK), caspase-3, and DNA fragmentation factor 45 (DFF45) was observed only in UVB-treated cells. Inhibition of JNK activity increased UVB-induced cell death, suggesting that this pathway may serve a prosurvival role in HLE cells. These findings suggest UVB predominantly induces apoptosis in HLE cells, whereas H(2)O(2) and TBHP induce necrosis.

This study demonstrates that primary canine LEC retain the characteristics of lens epithelial cells prior to passage 6 under the described culture conditions and represent a suitable in vitro model for investigating lens physiology and cataractogenesis.

Treatment with ATRA significantly increased Cx43 expression and GJIC in canine LEC, and these effects were associated with increased LEC differentiation. Results from this study suggest that functional gap junctions may play a role in the modulation of cellular differentiation in primary canine LEC.

Treatment with TPA significantly reduces GJIC in canine LEC. These effects are mediated, in part, by activation of calcium-dependent PKC isoforms. Primary canine LEC are a useful model in the study of the molecular mechanisms involved in GJIC and cataractogenesis.