Jo Karlsson

CALPAINS IN THE HUMAN LENS : RELATIONS TO MEMBRANES AND POSSIBLE ROLE IN CATARACT FORMATION

Calpains are Ca-activated neutral proteases present in all cells together with an endogenous inhibitor, calpastatin. Proposed substrates are; cytoskeletal proteins like microtubules and actin, protein kinases such as PKC and membrane-bound enzymes like Ca-ATPase and the Ca-channel. In lenses from different species calpains have been detected in decreasing amounts from the epithelium to the cortex to the nucleus. Several substrates for calpain in the lens have been demonstrated: crystallins, vimentin, actin, beaded filaments and MP26 among others. Both studies on animal models and capsulorhexis indicate that calpains are mainly involved in cortical cataract.

A New Model for Assessing Proteolysis in the Intact Mouse Lens in Organ Culture

Purpose: To develop a new method to investigate proteolysis in the intact lens in organ culture. Methods: Intact mouse lenses were assayed at regular intervals for proteolytic activity using fluorogenic peptide substrates ± addition of ionomycin. Specific inhibitors were used to determine the activity of calpains, the proteasome and acid lysosomal enzymes. Results: Significant levels of proteolytic activity were present in the intact lens. Proteolysis was stimulated by ionomycin. Preincubation with an inhibitor to the proteasome significantly decreased proteolysis whereas inhibitors of calpain and acid lysosomal enzymes did not. Conclusion: This study indicates that in the intact mouse lens in culture, the proteasome is an important protease. Its activity is at least partially regulated by calcium.

Intracellular Effects of NSAIDs/ASA in Oxidatively Stressed Human Lens Epithelial Cells in Culture

The aim of the study was to examine the effects of nonsteroidal anti-inflammatory drugs (NSAIDs)/acetylsalicylic acid (ASA) on human lens epithelial cells (HLECs) during oxidative stress. HLECs were exposed to H2O2 in the absence or presence of indomethacin, diclofenac, celecoxib (NSAIDs) or ASA for 24 h. HLECs were assayed for changes in superoxide and peroxide production and for variations in glutathione. Mitochondrial depolarization was measured using the membrane potential-sensitive dye JC-1. The results of the study include reduction in superoxide and peroxide production as well as reduction in glutathione depletion in oxidatively stressed HLECs incubated with low concentrations of NSAIDs/ASA. However, no protection against H2O2-induced mitochondrial depolarization by NSAIDs/ASA could be seen. In conclusion, NSAIDs/ASA display reactive oxygen species-scavenging properties in H2O2-exposed HLECs in culture.

Sigma-2 receptor agonists kill lens epithelial cells

Purpose The aim of the present study was to examine the effects of the sigma‐2 receptor agonist, siramesine, on morphology, growth, cell death, lysosomal function, and effects on extra‐lysosomal proteolytic systems in human lens epithelial cells. In addition we compared the effects to that obtained in other human cells in primary culture.