Glaucoma Cell Biology Laboratory
Department of Ophthalmology and Visual Sciences

 

Neuroinflammation in Glaucoma

 






Complement Activation in Glaucoma


Glaucoma is characterized morphologically by retinal ganglion cell (RGC) death, degeneration of optic nerve axons, excavation of the optic nerve head, and degeneration of the lateral geniculate nucleus. While the changes in the optic nerve head are the clinical hallmark of glaucoma, it is the loss of RGC that is the ultimate cause of vision loss.

The degeneration of RGC in glaucoma is accompanied by a neuroinflammatory response, involving both retinal glia and RGC. Neuroinflammation is a necessary response of neuronal tissue to injury. As part of this response retinal cells synthesize components of the complement cascade and complement becomes fixed on RGC and their axons. Notably, we have demonstrated the presence of the cytolytic membrane attack complex in association with RGC both in animal models and in human disease. Deposition of complement on the surface of damaged or dying neurons has been observed in many neurodegenerative diseases and appears to support rapid phagocytosis of apoptotic debris and avoidance of an autoimmune response. Complement activation also engenders the release of the anaphylatoxins C3a and C5a. Receptors for both molecules are present on retinal glial cells and it is likely that complement activation modulates their behavior.

Cartoon of suspected complement activity in the glaucoma retina

Our studies have also shown that deactivation of the complement cascade in an ischemic mouse model significantly delays axon and RGC degeneration. These findings are in accordance with those by others that demonstrate that the membrane attack complex is essential for rapid Wallerian degeneration. These data suggest that complement not only serves to facilitate uptake of debris of apoptotic RGC, but is actively involved in the destruction damaged RGC and their axons.

 

Interaction between neuroinflammation and systemic immunity in glaucoma


More recently we have made the observation that transfer of T-cells isolated from mice with glaucoma can induce retinal ganglion cell loss when transferred to normal, non-glaucomatous, mice. The recipient animals do not experience an elevation of intraocular pressure (IOP) and the loss of ganglion cells is progressive, slow, and specific i.e. no other neurologic or ocular effects are apparent. Download the paper describing these experiments here.
These findings suggest that glaucoma induces a T-cell response that is sufficiently strong to damage other ganglion cells. If similar events also occur in glaucoma patients it could explain why reduction of IOP does not always stop the progression of the disease since an autoimmune response, once initiated, could propagate ganglion cells loss in a completely IOP independent fashion.

Our current studies are designed to understand if this response can be modulated with the aim to lessen RGC loss.

 

Complement activation in the retina

Detection of the Membrane attack complex (MAC) on a retinal ganglion cell in the glaucomatous human retina.

 

Neuroinflammation is often associated with neurodegenerative disease and can be both beneficial and detrimental for survival of neurons and their axons

 

 

A transferred T-cell in the recipient mouse

A transferred T-cell (arrow) among the RGC in the recipient mouse's retina

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