Purpose: Recently, a new marker protein for microglial cells in the brain was postulated, transmembrane protein 119 (TMEM119), raising the hope for a new opportunity to reliably and unambiguously detect microglial cells in histologic sections. It was of interest whether TMEM119 also was a reliable microglial marker in the retina.Methods: Anti-TMEM119 antibodies of two providers were used to label microglia in the murine retina, and labeling properties were compared to those of antibodies against Iba1 and CD11b. As an example of a pathologic situation, labeling for TMEM119 was also performed in eyes treated by an argon laser as an experimental model for choroidal neovascularization.Results: TMEM119 immunoreactivity (IR) was found on microglial cells in the naïve retina. However, specificity and sensitivity of TMEM119 IR varied clearly depending on the source of the antibody, age of the mouse, and location of retinal microglia. After laser treatment, however, microglial cells lost their IR for TMEM119 at the site of the laser spot. Moreover, other cells became positive for TMEM119; for example, Müller cells.Conclusions: TMEM119 is a useful marker for the microglia in the brain. However, retinal microglia shows variable IR for TMEM119, and the microglia is not the only cell showing TMEM IR. Therefore, TMEM119 appears not to be applicable as a general marker for the retinal microglia in pathologic situations.Translational Relevance: Reliable detection and quantification of microglial cells is of high importance to study disease mechanisms and effects of therapeutic approaches in the retina.

Epigenetic alterations are common events in cancer. Using a genome wide methylation screen (Restriction Landmark Genomic Scanning-RLGS) we identified the gene for the dopamine receptor D4 (DRD4) as tumor-specific methylated. As DRD4 is involved in early brain development and may thus be involved in developmentally dependent tumors of the CNS in children epigenetic deregulation of DRD4 and its functional consequences were analyzed in vitro. CpG methylation of DRD4 was detected in 18/24 medulloblastomas, 23/29 ependymomas, 6/6 high-grade gliomas, 7/10 CNS PNET and 8/8 cell lines by qCOBRA and bisulfite sequencing. Real-time RT-PCR demonstrated a significantly inferior expression of DRD4 in primary tumors compared to cell lines and non-malignant control tissues. Epigenetic deregulation of DRD4 was analyzed in reexpression experiments and restoration of DRD4 was observed in medulloblastoma (MB) cells treated with 5-Aza-CdR. Reexpression was not accompanied by demethylation of the DRD4 promoter but by a significant decrease of H3K27me3 and of bound enhancer of zeste homologue 2 (EZH2). Knockdown of EZH2 demonstrated DRD4 as a direct target for inhibition by EZH2. Stimulation of reexpressed DRD4 resulted in an activation of ERK1/2. Our analyses thus disclose that DRD4 is epigenetically repressed in CNS tumors of childhood. DRD4 is a direct target of EZH2 in MB cell lines. EZH2 appears to dominate over aberrant DNA methylation in the epigenetic inhibition of DRD4, which eventually leads to inhibition of a DRD4-mediated stimulation of the ERK1/2 kinase pathway.

The WWC protein family is an upstream regulator of the Hippo signalling pathway that is involved in many cellular processes. We examined the effect of an endothelium-specific WWC1 and/or WWC2 knock-out on ocular angiogenesis. Knock-outs were induced in C57BL/6 mice at the age of one day (P1) and evaluated at P6 (postnatal mice) or induced at the age of five weeks and evaluated at three months of age (adult mice). We analysed morphology of retinal vasculature in retinal flat mounts. In addition, in vivo imaging and functional testing by electroretinography were performed in adult mice. Adult WWC1/2 double knock-out mice differed neither functionally nor morphologically from the control group. In contrast, the retinas of the postnatal WWC knock-out mice showed a hyperproliferative phenotype with significantly enlarged areas of sprouting angiogenesis and a higher number of tip cells. The branching and end points in the peripheral plexus were significantly increased compared to the control group. The deletion of the WWC2 gene was decisive for these effects; while knocking out WWC1 showed no significant differences. The results hint strongly that WWC2 is an essential regulator of ocular angiogenesis in mice. As an activator of the Hippo signalling pathway, it prevents excessive proliferation during physiological angiogenesis. In adult animals, WWC proteins do not seem to be important for the maintenance of the mature vascular plexus.

Blocking of PlGF or injection of sunitinib results in a similar inhibition of neovascularization as by anti-VEGF treatment in the mouse model of ROP. However, physiological angiogenesis that occurs after anti-VEGF treatment is blocked by anti-PlGF or sunitinib treatment, indicating that pathological neovascularization may follow different pathways than physiological angiogenesis.

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Lipofuscin (LF) accumulates during lifetime in the retinal pigment epithelium (RPE) and is thought to play a crucial role in intermediate and late age-related macular degeneration (AMD). In an attemt to simulate aged retina and to study response of retinal microglia and RPE cells to LF, we injected a suspension of LF into the subretinal space of adult mice. LF suspension was obtained from human donor eyes. Subretinal injection of PBS or sham injection served as a control. Eyes were inspected by autofluorescence and optical coherence tomography, by electroretinography and on histological and ultrastructural levels. Levels of cytokine mRNA were determined by quantitative PCR separately in the RPE/choroid complex and in the retina. After injection of LF, microglial cells migrated quickly into the subretinal space to close proximity to RPE cells and phagocytosed LF particles. Retinal function was affected only slightly by LF within the first two weeks. After longer time, RPE cells showed clear signs of melanin loss and degradation. Levels of mRNA of inflammatory cytokines increased sharply after injection of both PBS and LF and were higher in the RPE/choroid complex than in the retina and were slightly higher after LF injection. In conclusion, subretinal injection of LF causes an activation of microglial cells and their migration into subretinal space, enhanced expression of inflammatory cytokines and a gradual degradation of RPE cells. These features are found also in an aging retina, and subretinal injection of LF could be a model for intermediate and late AMD

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