title: Tissue and urokinase plasminogen activators instigate the degeneration of retinal ganglion cells in a mouse model of glaucoma.
abstract: Elevated intraocular pressure (IOP) promotes the degeneration of retinal ganglion cells (RGCs) during the progression of Primary Open-Angle Glaucoma (POAG). However, the molecular mechanisms underpinning IOP-mediated degeneration of RGCs remain unclear. Therefore, by employing a mouse model of POAG, this study examined whether elevated IOP promotes the degeneration of RGCs by up-regulating tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA) in the retina. IOP was elevated in mouse eyes by injecting fluorescent-microbeads into the anterior chamber. Once a week, for eight weeks, IOP in mouse eyes was measured by using Tono-Pen XL. At various time periods after injecting microbeads, proteolytic activity of tPA and uPA in retinal protein extracts was determined by fibrinogen/plasminogen zymography assays. Localization of tPA and uPA, and their receptor LRP-1 (low-density receptor-related protein-1) in the retina was determined by immunohistochemistry. RGCs' degeneration was assessed by immunostaining with antibodies against Brn3a. Injection of microbeads into the anterior chamber led to a progressive elevation in IOP, increased the proteolytic activity of tPA and uPA in the retina, activated plasminogen into plasmin, and promoted a significant degeneration of RGCs. Elevated IOP up-regulated tPA and LRP-1 in RGCs, and uPA in astrocytes. At four weeks after injecting microbeads, RAP (receptor associated protein; 0.5 and 1.0 μM) or tPA-Stop (1.0 and 4.0 μM) was injected into the vitreous humor. Treatment of IOP-elevated eyes with RAP led to a significant decrease in proteolytic activity of both tPA and uPA, and a significant decrease in IOP-mediated degeneration of RGCs. Also, treatment of IOP-elevated eyes with tPA-Stop decreased the proteolytic activity of both tPA and uPA, and, in turn, significantly attenuated IOP-mediated degeneration of RGCs. Results presented in this study provide evidence that elevated IOP promotes the degeneration of RGCs by up-regulating the levels of proteolytically active tPA and uPA.
authors.affiliation: Laboratory of Ophthalmic Neurobiology, Eye Research Institute of Oakland University, 2200 N. Squirrel Road, 409 DHE, Rochester MI 48309, USA. Electronic address: Chintala@oakland.edu.
authors.forename: Shravan K
authors.initials: SK
authors.lastname: Chintala
mesh_terms: D000578:Amidines / Q000494:pharmacology; D000818:Animals; D001597:Benzylidene Compounds / Q000494:pharmacology; D015153:Blotting, Western; D004195:Disease Models, Animal; D065427:Factor Xa Inhibitors / Q000494:pharmacology; D005341:Fibrinolysin / Q000378:metabolism; D019084:Fluorescent Antibody Technique, Indirect; D005902:Glaucoma, Open-Angle / Q000378:metabolism* / Q000473:pathology; D007429:Intraocular Pressure / Q000502:physiology; D026563:LDL-Receptor Related Protein-Associated Protein / Q000494:pharmacology; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008863:Microspheres; D010958:Plasminogen / Q000378:metabolism; D012162:Retinal Degeneration / Q000378:metabolism* / Q000473:pathology; D012165:Retinal Ganglion Cells / Q000378:metabolism* / Q000473:pathology; D010959:Tissue Plasminogen Activator / Q000378:metabolism*; D014065:Tonometry, Ocular; D014568:Urokinase-Type Plasminogen Activator / Q000378:metabolism*
chemical_list: D000578:Amidines; D001597:Benzylidene Compounds; D065427:Factor Xa Inhibitors; D026563:LDL-Receptor Related Protein-Associated Protein; D026503:Low Density Lipoprotein Receptor-Related Protein-1; C114591:ZK 805412; D010958:Plasminogen; D010959:Tissue Plasminogen Activator; D005341:Fibrinolysin; D014568:Urokinase-Type Plasminogen Activator
keywords: Degeneration of RGCs; LRP-1; POAG; RAP; tPA; tPA-Stop; uPA