Mitochondrial dysfunction causes retraction of Müller cell lateral processes.

Abstract

Purpose : Müller cell perisynaptic lateral processes provide support to retinal synapses and are critical for vision. Currently, the mechanisms regulating Müller cell lateral process maintenance and retraction are poorly understood, particularly in vivo. We tested the hypothesis that Müller cell mitochondrial dysfunction causes retraction of lateral processes using a model of retinal vein occlusion (RVO).

Methods : RVO was induced after intravenous injection of rose bengal (66mg/kg) using a 532nm laser to place 3-7 applications at 80 mW and 50 micron spot size directed at two retinal veins 1 disc diameter from the nerve. Negative control consisted of placing an equal number of laser spots without targeting the retinal vein. Male and female C57BL/6J mice aged 7-9 months with confirmed absence of Crb1^rd8, GLAST-CreER and Rosa26 mTmG mice were obtained from Jackson Labs. Elamipretide, a mitochondrial protective drug, was administered intraperitoneally (2mg/kg/day) using prevention and intervention strategies. Retinal histology and Müller cell lateral process morphology was evaluated on day 7 following induction of RVO. Mitochondria dysfunction was evaluated by quantifying superoxide and flavoprotein autofluorescence. Significance was determined using nonparametric statistical testing with p<0.05 considered significant.

Results : After RVO, mitochondria dysfunction was induced within the retinal plexiform layers where lateral processes are located, seen as increased superoxide and flavoprotein autofluorescence. This was prevented by treatment with mitochondria protective compound, elamipretide. RVO resulted in retraction of Müller cell perisynaptic lateral processes in the inner and outer plexiform layers. Lateral process length and the diameter of the lateral process arbor were quantified and reductions found to be statistically significant (p<0.05). Markers of lateral processes including GLAST, GluR3, AQP6 and T567 phospho-ezrin were quantified by confocal microscopy and found to be greatly reduced following RVO (p<0.05). Elamipretide treatment using either intervention or prevention approaches significantly preserved Müller cell lateral processes and markers (p<0.05).

Conclusions : RVO causes retraction of Müller lateral processes. Treatment with elamipretide, a mitochondria protective drug, prevents and reverses these changes. This suggests that mitochondrial function is required for maintenance of lateral processes.

This is a 2021 ARVO Annual Meeting abstract.