Calcineurin Cleavage Is Triggered by Elevated Intraocular Pressure, and Calcineuring Inhibition Blocks Retinal Ganglion Cell Death in Experimental Glaucoma

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 102; no. 34; pp. 12242 - 12247
• Main Authors: Wei Huang, John B. Fileta, Adam Dobberfuhl, Theodoros Filippopolous, Yan Guo, Gina Kwon, Cynthia L. Grosskreutz, Thaddeus P. Dryja
• Format: Journal Article
• Language: English
• Published: National Academy of Sciences 23-08-2005
• Subjects: Antibodies; Apoptosis; Biological Sciences; Cell death; Cytoplasm; Ganglia; Glaucoma; Intraocular pressure; Optic nerve; Rats; Retina
• EISSN: 1091-6490
• ISSN: 0027-8424

Increased intraocular pressure (IOP) leads, by an unknown mechanism, to apoptotic retinal ganglion cell (RGC) death in glaucoma. We now report cleavage of the autoinhibitory domain of the protein phosphatase calcineurin (CaN) in two rodent models of increased IOP. Cleaved CaN was not detected in rat or mouse eyes with normal IOP. In in vitro systems, this constitutively active cleaved form of CaN has been reported to lead to apoptosis via dephosphorylation of the proapoptotic Bcl-2 family member, Bad. In a rat model of glaucoma, we similarly detect increased Bad dephosphorylation, increased cytoplasmic cytochrome c(cyt c), and RGC death. Oral treatment of rats with increased IOP with the CaN inhibitor FK506 led to a reduction in Bad dephosphorylation and cyt c release. In accord with these biochemical results, we observed a marked increase in both RGC survival and optic nerve preservation. These data are consistent with a CaN-mediated mechanism of increased IOP toxicity. CaN cleavage was not observed at any time after optic nerve crush, suggesting that axon damage alone is insufficient to trigger cleavage. These findings implicate this mechanism of CaN activation in a chronic neurodegenerative disease. These data demonstrate that increased IOP leads to the initiation of a CaN-mediated mitochondrial apoptotic pathway in glaucoma and support neuroprotective strategies for this blinding disease.