Fig. 1

TSPO signaling in different retinal subpopulations. a To assess which retinal cell types are directly involved in TSPO-mediated signaling in the healthy murine retina, we enriched microglia, vascular cells, Müller glia, and retinal neurons via immunomagnetic separation. Subsequently, cells were submitted to mass spectrometric analysis to determine protein expression levels. Bar diagrams depict the protein abundance in the respective cell populations for the following cell type-specific marker genes: integrin alpha-M (ITGAM); allograft inflammatory factor 1 (AIF1)—microglia; platelet endothelial cell adhesion molecule (PECAM1); intercellular adhesion molecule 2 (ICAM2)—vascular cells; retinaldehyde-binding protein 1 (RLBP1); glutamine synthetase (GLUL)—Müller glia; vesicular glutamate transporter 1 (SLC17A7); rhodopsin (RHO)—retinal neurons including photoreceptors. b Transcript and protein expression of TSPO and its endogenous ligand diazepam binding inhibitor (DBI) in the four investigated retinal cell populations. a, b Values are given as mean ± SEM (n = 4–9 biological replicates). c TSPO—glutamine synthetase (GLUL) colabeling in retinal slice (left) and flatmount (right) preparations at indicated focus planes. Vessels (yellow arrowheads) and Müller glia (blue arrowheads) are positive for punctuate TSPO labeling indicative of a primarily mitochondrial localization of TSPO. Note the high expression level of TSPO in the retinal pigment epithelium (RPE). GCL, ganglion cell layer; IPL, inner plexiform layer; INL, inner nuclear layer; OPL, outer plexiform layer; ONL, outer nuclear layer. Scale bars, 50 μm