Plasminogen activators promote excitotoxicity-induced retinal damage

Area of Science:

• Ophthalmology
• Neuroscience
• Molecular Biology

Background:

• Elevated extracellular L-glutamate contributes to retinal damage in blinding conditions like glaucoma and diabetic retinopathy.
• Glutamate-induced excitotoxicity, via receptor hyperstimulation, leads to retinal damage through poorly understood downstream pathways.

Purpose of the Study:

• To investigate the role of plasminogen activators (PAs), specifically tissue plasminogen activator (tPA) and urokinase plasminogen activator (uPA), in excitotoxicity-induced retinal damage.
• To explore the therapeutic potential of inhibiting PAs in retinal damage models.

Main Methods:

• Kainic acid (KA), a non-NMDA receptor agonist, was injected into the vitreous humor of CD-1 mice.
• Retinal expression and activity of tPA and uPA were analyzed post-KA injection.
• Immunocytochemistry was used to localize PA expression in retinal cells.
• The effects of PA inhibitors (rPAI-1, tPA-STOP) and a plasmin inhibitor (alpha-2-antiplasmin) on KA-induced retinal damage were assessed.

Main Results:

• KA injection upregulated tPA and induced uPA activity, leading to plasmin activation.
• Retinal ganglion cells (RGCs) constitutively express and release tPA upon KA stimulation.
• KA induced apoptotic cell death in the ganglion cell layer and nuclear layers, causing RGC and amacrine cell loss.
• Inhibition of PAs (rPAI-1, tPA-STOP) attenuated KA-induced retinal damage, while plasmin inhibition did not.

Conclusions:

• Plasminogen activators (tPA and uPA) are critically involved in the downstream events of glutamate excitotoxicity leading to retinal damage.
• Inhibiting plasminogen activators shows promise as a therapeutic strategy for blinding retinal diseases involving glutamate excitotoxicity.