The TCA cycle in retinal dysfunction

Larissa Govers

In major retinal degenerative diseases such as age-related macular degeneration, cells in the outer retina and retinal pigment epithelium are continuously subjected to reduced oxygen availability, which results in a hypoxic response that affects mitochondrial metabolism and is detrimental for cell survival. Previous studies from our group have established that processes such as oxidative phosphorylation (OXPHOS), which produces energy through the reduction of oxygen, and the citric acid (TCA) cycle, a metabolic pathway important for carbohydrate, lipid and protein metabolism, are severely affected in rods exposed to chronic hypoxia. However, when we studied isolated OXPHOS deficiency in rods, their survival was not substantially affected. Therefore, the aim of this project is to address the contribution of the TCA cycle as well as its metabolites to photoreceptor cell survival. 

A multitude of approaches are used to study this aim, including metabolomics to determine the differential metabolite composition in the different layers of the retina in health and disease. Furthermore, short hairpin RNAs (shRNA) are used to downregulate the TCA cycle targeting citrate synthase (Cs) that is essential for the first step of the cycle, as well as Slc25a1, a transporter on the inner mitochondrial membrane that transports citrate out of the mitochondria in exchange for malate. shRNAs will be expressed in photoreceptors by the subretinal injection of respective AAVs. Consequences of the modulated TCA cycle for photoreceptor survival and function are monitored by in vivo imaging (fundus, OCT), morphology of tissue sections, immunofluorescence and electroretinogram.

Lastly, we will target the TCA cycle for therapeutic purposes. Once we have established how the TCA cycle is affected under hypoxic conditions, we will attempt to rescue the phenotype using a TCA cycle-sopeicif intervention.