Oxidative Stress-Induced Dysfunction of Müller Cells During Starvation

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Abstract
Purpose: Müller cells support retinal neurons with essential functions. Here, we aim to examine the impact of starvation and oxidative stress on glutamate uptake and mitochondrial function in Müller cells. Methods: Cultured human retinal Müller cells (MIO-M1) were exposed to H2O2 and additional starvation for 24 hours. Effects of starvation and H2O2 on glutamate uptake and mitochondrial function were assessed by kinetic glutamate uptake assays and Seahorse assays, respectively. Cell survival was evaluated by cell viability assays. mRNA and protein expressions were assessed by quantitative PCR and Western blot. Results: Starvation of Müller cells increased the glutamate uptake capacity as well as the expression of the most abundant glutamate transporter, EAAT1. Mitochondrial and glycolytic activity were diminished in starved Müller cells despite unaffected cell viability. Simultaneous starvation and exposure to oxidative stress resulted in a reduced glutamate uptake and a collapsed mitochondrial function. In Müller cells with intact energy supply, the glutamate uptake and mitochondrial function were unaffected after exposure to oxidative stress. Conclusions: Here, we identify an increased susceptibility toward oxidative stress in starved Müller cells in spite of unaffected viability and an apparent decreased ability to transport glutamate. Solely exposure to oxidative stress did not affect Müller cell functions. Thus, our study suggests an increased susceptibility of Müller cells in case of more than one cellular stressor. Extrapolating these findings, age-related neurodegenerative retinal diseases may be the result of impaired Müller cell function.

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