Glia-neuron partnership is important for inner retinal homeostasis and any disturbances may result in retinal ganglion cell (RGC) death. Müller cells support RGCs with essential functions such as removing excess glutamate and providing energy sources. The aim was to explore the impact of Müller cells on RGC survival. To investigate the Müller cell/RGC interactions we developed a coculture model, in which primary Müller cells were grown in inserts on top of pure primary RGC cultures. The impact of starvation and mitochondrial inhibition on the Müller cell ability to protect RGCs was studied. Moreover, the ability of Müller cells to remove glutamate from the extracellular space was investigated. RGC survival was evaluated by cell viability assays and glutamate uptake was assessed by kinetic uptake assays. We demonstrated a significantly increased RGC survival in presence of untreated and prestarved Müller cells. Additionally, prestarved Müller cells significantly increased RGC survival after mitochondrial inhibition. Finally, we revealed a significantly increased ability to take up glutamate in starved Müller cells. Overall, our study confirms essential roles of Müller cells in RGC survival. We suggest that targeting Müller cell function could have potential for future treatment strategies to prevent blinding neurodegenerative retinal diseases.

The viability of retinal ganglion cells (RGC) is essential for the maintenance of visual function. RGC homeostasis is maintained by the surrounding retinal glial cells, the Müller cells, which buffer the extracellular concentration of neurotransmitters and provide the RGCs with energy. This study evaluates if glucose-deprivation of Müller cells interferes with their ability to remove glutamate from the extracellular space. The human Müller glial cell line, Moorfields/Institute of Ophthalmology-Müller 1, was used to study changes in glutamate uptake. Excitatory amino acid transporter (EAAT) proteins were up-regulated in glucose-deprived Müller cells and glutamate uptake was significantly increased in the absence of glucose. The present findings revealed an up-regulation of EAAT1 and EAAT2 in glucose-deprived Müller cells as well as an increased ability to take up glutamate. Hence, glucose deprivation may result in an increased ability to protect RGCs from glutamate-induced excitotoxicity, whereas malfunction of glutamate uptake in Müller cells may contribute to retinal neurodegeneration.

PurposeThe viability of retinal ganglion cells (RGCs) is essential to maintain the neuronal function of the retina. Müller cells (MCs) are assumed to be vital in neuroprotection of the RGCs. In this study, we evaluated modifications in retinal MCs due to oxidative stress and energy restrictions.MethodsThe human Müller glial cell line, MIO‐M1, was used in all experiments. Changes in glutamate uptake were evaluated in oxidative stressed and energy restricted MCs. The cell viability was evaluated by LDH and MTT assays. Regulations in gene and protein expression were evaluated by qPCR and western blot. The ATP production was measured as well as the mitochondrial activity.ResultsGlutamate uptake was significantly in energy‐restricted MCs. Simultaneous energy restriction and oxidative stress significantly decreased glutamate uptake. The mitochondrial activity was reduced after exposure to energy restriction and further reduced during simultaneous exposure to energy restriction and oxidative stress. The intracellular ATP levels were decreased in the latter condition.ConclusionsOxidative stress and energy restriction alter the neuroprotective characteristics of MCs by increasing the glutamate uptake during energy restriction and by decreasing the uptake during simultaneous exposure to energy restriction and oxidative stress. The impaired mitochondrial activity and reduction of intracellular ATP levels may affect the ability of MCs to maintain a ellular homeostasis in such way that their ability to protect RGCs may to suffer.

PurposeMüller cells are considered to be vital in the maintenance of retinal ganglion cells (RGCs), and since RGCs are essential to maintain the neuronal function of the retina, a functioning symbiotic partnership between Müller cells and RGCs is fundamental. The present study evaluates glia‐neuron interactions in a coculture model of primary Müller cells and primary RGCs.MethodsTo investigate the Müller cell‐RGC interaction we developed a coculture model, in which primary Müller cells from mice were grown in inserts on top of pure primary RGC cultures likewise from mice. The impact of 24 h of starvation on the ability of Müller cells to protect RGCs was evaluated. Moreover, changes in glutamate uptake were studied in Müller cells as well as cell viability in response to starvation.ResultsThe presence of Müller cells significantly increased the survival of RGCs during normal conditions as well as during 24 h of pre‐starvation. Glutamate uptake capacity was significantly increased during starvation along with an increased Vmax. Starvation induced significantly reduced cell viability both in Müller cells and RGCs with a significantly greater reduction of cell viability in Müller cells.ConclusionsThe present study reveals an increased survival of RGCs in presence of Müller cells and herewith we confirm Müller cells as being key players in RGC homeostasis. Moreover, we verify the coculture model as being a unique approach to study the glia‐neuron partnership in inner retinal diseases.