Abstract
Abstract: :
Purpose: Calcineurin is a calcium/calmodulin–dependent phosphatase thought to be an important effector of neuronal cell death. We have previously shown that calcineurin inhibition confers retinal ganglion cell (RGC) neuroprotection after optic nerve crush in the rat. We hypothesized that calcineurin activation might be important in RGC death in glaucoma as well. The purpose of this study was to examine calcineurin activation in experimental glaucoma.. Methods: Experimental glaucoma was induced in 19 male Brown Norway rats by injecting the episcleral veins of the left eye (OS) with 1.9 M NaCl (Morrison model). The right eye (OD) served as a control. Intraocular pressures (IOP) were measured in conscious animals before and every two days after surgery using a Tonopen. Following 10 days of elevated IOP, animals were sacrificed, retinas removed and retinal protein isolated. Immunoblot analysis of full length calcineurin (60 kDa) as well as the activated/cleaved form (45 kDa) was performed. Alpha–tubulin was used as a loading control and all values were quantified using densitometry. Statistical analysis was performed using a 2–way analysis of variance and significance was assessed at the 0.05 level. Results: The mean peak IOP for control eyes was 19.9 +/– 1.02 mm Hg, while the peak IOP for experimental eyes was 44.17 +/– 1.49 mm Hg. The mean IOP history, defined as the area under the pressure time curve, was 231.56 +/– 37.99. There was a significant increase in cleaved calcineurin in all eyes with experimental glaucoma (n=19). The average increase was 7–fold (p < 0.05). The levels of full–length calcineurin were unchanged. Conclusions: These data demonstrate that calcineurin is cleaved in eyes with experimental glaucoma. Since cleaved calcineurin is constituitively active and proapoptotic, we suggest that this novel calcineurin–mediated pathway may contribute to RGC death in glaucoma.
Keywords: cell death/apoptosis • ganglion cells • intraocular pressure