Targeting translocator protein (18 kDa) (TSPO) dampens pro-inflammatory microglia reactivity in the retina and
Rebecca Scholz1, Albert Caramoy2, Mohajeet B Bhuckory3
1Department of Ophthalmology, Laboratory for Experimental Immunology of the Eye, University of Cologne, 50931, Cologne, Germany. rebecca.scholz@uk-koeln.de.
Background:
Reactive microglia are commonly seen in retinal degenerative diseases, and neurotoxic microglia responses can contribute to photoreceptor cell death. We and others have previously shown that translocator protein (18 kDa) (TSPO) is highly induced in retinal degenerations and that the selective TSPO ligand XBD173 (AC-5216, emapunil) exerts strong anti-inflammatory effects on microglia in vitro and ex vivo. Here, we investigated whether targeting TSPO with XBD173 has immuno-modulatory and neuroprotective functions in two mouse models of acute retinal degeneration using bright white light exposure.
Methods:
BALB/cJ and Cx3cr1(GFP/+) mice received intraperitoneal injections of 10 mg/kg XBD173 or vehicle for five consecutive days, starting 1 day prior to exposure to either 15,000 lux white light for 1 h or 50,000 lux focal light for 10 min, respectively. The effects of XBD173 treatment on microglia and Müller cell reactivity were analyzed by immuno-stainings of retinal sections and flat mounts, fluorescence-activated cell sorting (FACS) analysis, and mRNA expression of microglia markers using quantitative real-time PCR (qRT-PCR). Optical coherence tomography (OCT), terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) stainings, and morphometric analyses were used to quantify the extent of retinal degeneration and photoreceptor apoptosis.
Results:
Four days after the mice were challenged with bright white light, a large number of amoeboid-shaped alerted microglia appeared in the degenerating outer retina, which was nearly completely prevented by treatment with XBD173. This treatment also down-regulated the expression of TSPO protein in microglia but did not change the TSPO levels in the retinal pigment epithelium (RPE). RT-PCR analysis showed that the microglia/macrophage markers Cd68 and activated microglia/macrophage whey acidic protein (Amwap) as well as the pro-inflammatory genes Ccl2 and Il6 were reduced after XBD173 treatment. Light-induced degeneration of the outer retina was nearly fully blocked by XBD173 treatment. We further confirmed these findings in an independent mouse model of focal light damage. Retinas of animals receiving XBD173 therapy displayed significantly more ramified non-reactive microglia and more viable arrestin-positive cone photoreceptors than vehicle controls.
Conclusions:
Targeting TSPO with XBD173 effectively counter-regulates microgliosis and ameliorates light-induced retinal damage, highlighting a new pharmacological concept for the treatment of retinal degenerations.
Insights
Targeting translocator protein (TSPO) with XBD173 prevents microglial activation and protects photoreceptors from light-induced damage in mouse models of retinal degeneration. This study highlights XBD173 as a potential therapeutic for retinal diseases.
Area of Science:
- Ophthalmology
- Neuroscience
- Immunology
Background:
- Reactive microglia contribute to photoreceptor cell death in retinal degenerative diseases.
- Translocator protein (18 kDa) (TSPO) is upregulated in retinal degenerations.
- The TSPO ligand XBD173 exhibits anti-inflammatory effects on microglia.
Purpose of the Study:
- To investigate the immuno-modulatory and neuroprotective effects of XBD173 in mouse models of acute light-induced retinal degeneration.
- To assess XBD173's impact on microglia and Müller cell reactivity.
- To evaluate XBD173's efficacy in preventing photoreceptor cell death.
Main Methods:
- Mice (BALB/cJ and Cx3cr1(GFP/+)) were treated with XBD173 or vehicle prior to light exposure.
- Microglia and Müller cell reactivity were analyzed using immuno-stainings, FACS, and qRT-PCR.
- Retinal degeneration and photoreceptor apoptosis were quantified using OCT, TUNEL staining, and morphometric analysis.
Main Results:
- XBD173 treatment nearly completely prevented the appearance of alerted microglia in the degenerating outer retina.
- XBD173 down-regulated TSPO protein in microglia and reduced expression of microglia/macrophage and pro-inflammatory markers.
- Light-induced retinal degeneration and photoreceptor apoptosis were significantly blocked by XBD173, with more viable photoreceptors observed.
Conclusions:
- Targeting TSPO with XBD173 effectively counter-regulates microgliosis in acute retinal degeneration.
- XBD173 ameliorates light-induced retinal damage, demonstrating neuroprotective functions.
- This highlights a novel pharmacological strategy for treating retinal degenerations.
More Related Videos
06:19In Vivo Imaging of Cx3cr1gfp/gfp Reporter Mice with Spectral-domain Optical Coherence Tomography and Scanning Laser Ophthalmoscopy
Published on: November 11, 2017
10:21Characterization and Isolation of Mouse Primary Microglia by Density Gradient Centrifugation
Published on: February 16, 2018