Research

Hypoxia and vision
Retinal cells and especially photoreceptors have a high demand of energy. Photoreceptor function relies on complex metabolic pathways involving several retinal cells and the RPE. Oxygen for photoreceptors is delivered through the capillaries in the choroid. As the eye ages, delivery of O2 may be hampered leading to mild but chronic hypoxia in RPE cells and photoreceptors. This may influence metabolism, energy production and ultimately cell survival. A large part of our work focuses on the molecular consequences of reduced oxygen availability for photoreceptor cells. Investigations include energy metabolism in rods and cones, actvity of the TCA cycle and its importance for photoreceptor physiology, epitranscriptomic changes of the retinal transcriptome and the development of treatment strategies to target the major hypoxia-inducible transcription factors in rods, cones and RPE.

Signaling in the injured retina
Photoreceptor injury or stress induces elaborative intercellular signaling cascades that either lead to cell survival or cell death. We strive to identify key molecules in these processes not only to unravel molecular mechanisms governing these cascades but also to define potential therapeutic targets for the design of neuroprotective strategies. Through single cell sequencing of the injured retina, we recently recognized early growth response-1 (EGR1) as a protein that is strongly and specifically induced in rods and cones during the early phase of cell death. EGR1 may thus be a central factor in the degenerative processes and modulation of its expression profile may be promising for protecting photorecptors.

Cones and cell death
Cones are most important for human daylight vision. They are concentrated in the macular region and needed for high acuity vision. Since only 3-5 % of all photoreceptors are cones, their metabolism, function and specific cell death mechanisms are difficult to analyze. We modified a transgenic mouse that develops a retina where all photoreceptors are cones by the introduction of a second mutation. This double mutant mouse has an all-cone retina that is functional and nicely layered. We use this model to investigate cell death mechanisms in cones and the cone response to reduced oxygen levels.

Major methods to study retinal degeneration
Besides general molecular methods including real-time PCR, Western blotting, in situ hybridization, immunofluorescence and others, we apply single cell sequencing protocols to define the transcriptomes of the various retinal cell types in different situations, 2-photon imaging of genetically encoded nanosensors to investigate energy metabolism in retinal neurons, and AAV-mediated delivery of DNA constructs to increase or decrease expression of target genes. We also use in vivo imaging tools such as fundus imaging, optical coherence tomography, fluorescence angiography to determine the status of the retina over time. Electroretinography and optomotor response tests are employed to define function of the retina or the visual system, respectively. In vitro culture of immortalized cell lines, iPSC-derived RPE cells and retinal explants complement our investigations.