My data shows that upregulation of genes encoding members of the complement cascade occurs very early during glaucoma, in both the retina (in retinal ganglion cells and microglia) and optic nerve head (in microglia). Importantly, mice with a mutation in the gene for complement component 1qa (C1qa) are profoundly protected from glaucoma. This strong protection suggests that targeting complement induction could prove highly efficacious for many glaucoma patients. However, before advancing towards potential treatments it is necessary to fully understand the mechanisms by which complement biosynthesis impacts glaucoma in multiple animal models. Firstly, I will determine the cell-type specific expression of complement components in two different mouse models of glaucoma;DBA/2J, a widely used inherited model and a recently developed bead-based inducible mouse model. I will assess the expression of C1QA using mice carrying a C1qa(2Gal) reporter as well as C3, C3R and the inhibitor CRRY using immunofluorescence and RNA in situ hybridization. This is the first time complement proteins have been assessed in two contrasting animal models of glaucoma and is a necessary step in determining the cell-specific mechanisms of the complement cascade in glaucoma. Secondly, I hypothesize that complement is an early mediator of two key changes in RGCs, axon damage at the lamina and synapse changes in the inner plexiform layer. Therefore, I will determine if complement expression in RGCs or microglia precede these early changes to RGCs. Axon damage will be visualized using DBA/2J.Thy1(CFP) and synapse changes will be assessed using antibodies for PSD95 and RIBEYE. I will focus on C1qa, a key molecule in the complement cascade. Focusing on eyes with early stages of glaucoma will allow me to determine if complement system changes precede early damage to RGCs in the ONH and retina. Finally, I will determine the effect of mutating C1QA specifically in either RGCs or microglia using conditional gene targeting. C1QA mutant mice are protected from glaucoma and preliminary data shows that C1QA is expressed in both RGCs and microglia. These findings, along with other studies showing upregulation of complement components in human glaucoma, highlight the importance of determining how the complement cascade influences glaucoma. We will use Cre/loxP technology to specifically ablate C1QA biosynthesis in RGCs, microglia or both cell types. Glaucoma will be assessed using well-established methods including axon damage assessment, RGC soma counts and RGC synapse loss. Determining the significance of complement biosynthesis by each cell type is important for designing therapeutic interventions that manipulate the complement system.

Public Health Relevance

Glaucoma is a blinding disorder affecting over 70 million people worldwide. No treatments are clinically approved that directly target retinal ganglion cells, the output neurons of the retina that are lost in glaucoma. We, and others have established that the complement pathway plays an important role early in the disease. We will fully investigate the expression of complement proteins in glaucoma using two mouse models of glaucoma. We will also assess the affect of conditionally ablating a key molecule in the complement pathway in specific cell types. This work will determine exactly how the complement pathway influences glaucoma.

National Institute of Health (NIH)
National Eye Institute (NEI)
Research Project (R01)
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Anterior Eye Disease Study Section (AED)
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Chin, Hemin R
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Jackson Laboratory
Bar Harbor
United States
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Howell, Gareth R; MacNicoll, Katharine H; Braine, Catherine E et al. (2014) Combinatorial targeting of early pathways profoundly inhibits neurodegeneration in a mouse model of glaucoma. Neurobiol Dis 71:44-52
Soto, Ileana; Howell, Gareth R (2014) The complex role of neuroinflammation in glaucoma. Cold Spring Harb Perspect Med 4:
Soto, Ileana; Howell, Gareth R; John, Cai W et al. (2014) DBA/2J mice are susceptible to diabetic nephropathy and diabetic exacerbation of IOP elevation. PLoS One 9:e107291
Wiggs, J L; Howell, G R; Linkroum, K et al. (2013) Variations in COL15A1 and COL18A1 influence age of onset of primary open angle glaucoma. Clin Genet 84:167-74
Williams, Pete A; Howell, Gareth R; Barbay, Jessica M et al. (2013) Retinal ganglion cell dendritic atrophy in DBA/2J glaucoma. PLoS One 8:e72282
Howell, Gareth R; Soto, Ileana; Ryan, Margaret et al. (2013) Deficiency of complement component 5 ameliorates glaucoma in DBA/2J mice. J Neuroinflammation 10:76
Howell, Gareth R; Soto, Ileana; Libby, Richard T et al. (2013) Intrinsic axonal degeneration pathways are critical for glaucomatous damage. Exp Neurol 246:54-61