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Gareth R Howell, Pete Williams, Jeffrey Harder, James Tribble, Keating Pepper, Stephen Cross, Paul Morgan, James Edwards Morgan, Simon W John; The yin and yang of the complement cascade in glaucoma – the importance of timing and location. Invest. Ophthalmol. Vis. Sci. 2016;57(12):No Pagination Specified. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Activation of the complement cascade is a consistent feature of human and experimental glaucoma but the precise role of complement has not been elucidated. Previously, we have used DBA/2J mice, a widely used mouse model of glaucoma, to show that complement activation occurs very early in the retina and optic nerve head (ONH), prior to retinal ganglion cell (RGC) loss and optic nerve degeneration. Further, C1qa – encoding C1q the activating molecule of the classical pathway – is expressed by microglia/macrophages and RGCs and glaucomatous RGC loss is greatly reduced in DBA/2J mice deficient in C1q. Collectively, these data suggest that complement activation is important in the initiation of glaucomatous damage.
We have used a combination of transcriptional profiling, immunofluorescence and genetic and pharmacological inhibition using animal models and cell-based strategies to investigate the role of complement in glaucoma.
We now show that deficiency of C1q in DBA/2J mice or pharmacological inhibition of C1 in a rat bead model of ocular hypertension is sufficient to preserve the dendritic and synaptic architecture of RGCs during the early stages of glaucoma. However, additional data suggests that complement activation can play both beneficial and damaging roles depending on timing and location. Interrogation of transcriptional profiling data suggests that C3 and other components of the complement alternative pathway are upregulated by astrocytes in the ONH, prior to upregulation of components of the classical pathway. In contrast to C1q, deficiency of C3 exacerbates glaucomatous neurodegeneration in DBA/2J. To clarify the role of astrocytic C3, we performed transcriptional profiling of C3-sufficient and C3-deficient astrocytes and identified the mitogen-activated protein kinase (MAPK) pathway as differentially up-regulated in C3-deficient astrocytes. Components of the MAPK pathway are expressed by ONH astrocytes and the pharmacological inhibition of epidermal growth factor receptor (EGFR) – an initiating molecule in the MAPK pathway – significantly increased RGC loss in DBA/2J mice.
Our results suggest that astrocytic C3 and EGFR act to mitigate the damaging effects of IOP elevation on the ONH. The augmentation of these early astrocytic responses could form the basis for the protection of RGC structure and function in early glaucoma.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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