Our research interest is neuroinflammation in degenerative disease. The laboratory focuses on the impact of neuronal-glial signaling in glaucoma, one of the leading causes of blindness worldwide. Vision loss in glaucoma is caused by degeneration of retinal ganglion cells (RGCs) and is often associated with elevated intraocular pressure. Although glaucomatous pathology targets RGCs, glial cells, which support RGC health and function, may also play a role in disease onset and progression. Using a variety of techniques, we examine early events in signal transduction that underlie RGC and glial responses to elevated pressure both in vitro and in vivo. We are currently pursuing interleukin-6 (IL-6), an inflammatory cytokine, as a component of RGC-glial signaling that may modulate both glial reactivity and RGC survival in glaucoma.
Center: Rebecca Sappington, Ph.D. (Prinicipal Investigator);
Left: Stephanie Sims, M.D. (Postdoctoral Research Fellow);
Right: Lauren Holmgren (Undergraduate Summer Intern)
Interleukin-6 and Glial Reactivity
Our previous work suggests that interleukin-6 (IL-6) is produced by both microglia and astrocytes in response to elevated pressure. In retinal microglia, pressure-induced production of IL-6 is regulated by calcium influx via a variety channels, including transient receptor potential vanilloid 1 (TRPV1), the transcription factor nuclear factor kappa B (NFkB) and the ubiquitin-proteasome pathway (UPP). Our recent work in the DBA/2 mouse model of hereditary glaucoma suggests that production of IL-6 by glia occurs in a distinct temporal pattern. Expression of IL-6 by microglia is evident at early stages of IOP elevation, while expression by astrocytes does not occur until much later in the disease progression.
Wholemount retina from DBA/2 mice with low or elevated IOP. Immunohistochemistry for IL-6 (green) and the microglia marker Iba-1 (red) reveals elevated levels of IL-6 in the ganglion cell and nerve fiber layers that co-localizes with microglia.
Wholemount retina from young and old DBA/2 mice. Immunohistochemistry for IL-6 (red), the microglia marker Iba-1 (green) and the astrocyte marker GFAP (blue) reveals elevated levels of IL-6 in the ganglion cell and nerve fiber layers that co-localizes with astrocytes.
Interleukin-6 and RGC Survival
Our previous work suggests that IL-6 produced by retinal microglia protects RGCs from pressure-induced apoptosis. In the DBA/2 mouse, microglia in the ganglion cell and nerve fiber layers of the retina upregulate IL-6 in response to elevate pressure. However, RGC degeneration is also evident at these time points. Our recent work suggests that elevated pressure also causes down-regulation of the IL-6 receptor in RGCs. Therefore, as microglia produce more IL-6, RGCs become less responsive to IL-6.
Wholemount retina from C57 mice. Immunohistochemistry for IL-6 receptor alpha subunit (IL-6Rα; green) and the astrocyte marker GFAP (blue) with anterograde tracing of RGCs (red) reveals L-6Rα expression by RGC soma and vascular endothelial cells.
Select Recent Publications
Sappington RM, Chan M, Calkins DJ. (2006) Interleukin-6 protects retinal ganglion cells from pressure-induced death. Invest. Ophthalmol. Vis. Sci. 47, pp. 2932-2942.
Sappington RM, Calkins DJ. (2006) Pressure-induced regulation of IL-6 in retinal glial cells: Involvement of the ubiquitin/proteasome pathway and NFkB. Invest. Ophthalmol. Vis. Sci. 47, pp. 3860-3869 and cover.
Sappington RM, Calkins DJ. (2008) Contribution of TRPV1 to microglia-derived IL-6 and NFkB translocation with elevated hydrostatic pressure. Invest. Ophthalmol. Vis. Sci. 49, pp. 3004-3017.