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Primary open angle glaucoma (POAG) is a disease that affects more than 70 million people worldwide. The pathology of glaucoma includes an increase in the intraocular pressure, followed by irreversible damage to the optic nerve leading to progressive blindness. We investigated protein modifications by two lipid derived oxidation products namely iso[4]levuglandin E2(isoLGE2) and 4-hydroxy-nonenal (HNE), in the human trabecular meshwork (TM) and optic nerve, and their impact on specific proteins in POAG. Calpain-1 inhibitors have been proposed as potential neuroprotective agents in glaucoma and other neurodegenerative diseases. Our studies have indicate that calpain-1 is potentially modified by iso[4]LGE2 in the glaucomatous TM. Iso[4]LGE2-modified calpain-1 forms aggregates, which cannot be degraded by the proteasomal machinery of the cell. Calpain-1 protein expression is upregulated in the glaucomatous optic nerve (ON) without modification by iso[4]LGE2. Differences detected in the processing of calpain-1 in the anterior versus posterior segment of the eye indicate that it is vital to look into the levels of proteins in the entire organ before embarking on neuroprotection strategies. Extracellular and intracellular proteases have been implicated in the pathology of glaucoma. We found that the levels of active matrix metalloproteinase MMP-2 are elevated in the glaucomatous TM. This is an important discovery that is consistent with another observation, that the levels of fibronectin, a substrate of MMP-2, are decreased in the glaucomatous TM. Immunoprecipitation analysis indicated that both MMP-2 and fibronectin are modified by HNE, in the normal and glaucomatous TM. Destruction of the optic nerve head (ONH) and activation of astrocytes has been reported in the glaucomatous ONH as a consequence of increased intraocular pressure. We found that pressure treated astrocytes show an increase in levels of iso[4]LGE2-protein adducts. Post pressure treatment with the trapping agent pyridoxamine is an effective means of capturing iso[4]LGE2-modified proteins. Lipid modifications of proteases and their substrates contribute to the pathophysiology of glaucoma and may be potential therapeutic targets for the treatment and prevention of late stage complications of this disease. |
