Matt Rutar, Kristie RX Chia, Riccardo Natoli,Jan Provis

Purpose:
Recruitment of inflammatory cells into theinjured retina is thought to exacerbate photoreceptordeath in retinal degenerations such as age-relatedmacular degeneration (AMD). Monocyte/microgliarecruitment is dependent on expression of chemo-attractants, such as chemokines, although their role inAMD is yet to be clarified. Using microarray analysis,we investigate the role of prominent chemokines andchemokine-regulators in a light-induced model ofatrophic AMD.

Methods:
SD rats were exposed to 1000 lx of light forup to 24 hrs. At specific time-points during and follow-ing exposure, animals were euthanized and retinasprocessed. Photoreceptor apoptosis was assessed usingTUNEL and counts were made of monocytes/microgliaimmunolabeled with IBA1. Expression of chemokineswas assessed by microarray analysis, and qPCR. Somechemokines were also selected for spatiotemporalanalysis by in situ hybridisation.

Results:
Using qPCR, significant up-regulation ofchemokines (Ccl2, Ccl3, Ccl4, Ccl7, Cxcl1, Cxcl10,Cxcl11) and chemokine-regulators (IL1?, Tlr2, andTnf?) was observed at 24 hrs, which correlated withthe increase in photoreceptor death. In situ hybridiza-tion on retinal cryosections revealed that Cxcl1 andCxcl10 are expressed by Müller cells and RPE, whileCcl3, Ccl4, and Ccl7 are expressed by microglia –predominately in regions of heavy photoreceptordegeneration. We also show that introduction IL1?modulates expression of Ccl2, Cxcl1, and Cxcl10Muller cells and RPE in vitro, and in vivo.

Conclusions:
Our data indicate that the retinaactively contributes to the guidance of the neuro-inflammatory response following retinal injury,through local expression of multiple chemokines coor-dinated by Muller cells, microglia, and RPE. Theseresponses are broadly facilitated by the synthesis ofpotent regulators such as IL1?, which in turn maypresent an effect means to modulate the activity ofchemokines in the retina. Characterization of thechemokine immune pathways is crucial in clarifyingthe underling pathogenesis of inflammation in retinaldegenerations, such as AMD.