Iron Homeostasis in Neuron-Glia Interaction

by Tina Kling
Doctoral thesis
Date of Examination:2016-09-19
Date of issue:2018-03-15
Advisor:Prof. Dr. Mikael Simons
Referee:Prof. Dr. Mikael Simons
Referee:Prof. Dr. Christian Klämbt
Referee:Prof. Dr. Jörg Großhans
Persistent Address: http://dx.doi.org/10.53846/goediss-6784

 

 

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Abstract

English

One major function of glial cells is to support neurons and create an environment that allows fast signal propagation. However, when neurons are ensheathed, they also get isolated from the extracellular environment and can no longer take up factors required for growth and function. Hence, glial cells have to regulate the neurons’ metabolic and trophic support. To identify candidate genes that are necessary for this support, we initiated a RNA interference screen in Drosophila peripheral nerves. In a screen for highly conserved molecules, we could successfully detect genes that are both required in glial cells and important for neuronal architecture and function. We found that pan-glial inhibition of p24-1 resulted in axonal loss, changed nerve architecture, transportation failure of axonal vesicles, migration defects of photoreceptor cells and swellings of neuronal mitochondria. p24 proteins act in the secretory pathway to shuttle cargo molecules through the biosynthetic pathway. A second p24 family member, opossum, reproduced the p24-1 phenotype revealing that they act in concert. Thus, we tried to identify the p24-1 cargo in a secondary RNAi screen. The iron binding protein Ferritin1 heavy chain was identified which displayed the same peripheral nerve phenotype as p24-1 knockdown. By in vivo and in vitro studies, we could show that Fer1HCH is released from glia cells and taken up by neurons. The inhibition of glial iron release caused accumulations of toxic ferrous iron resulting in ferroptosis. The application of inhibitors, which chelate iron or inhibit ferroptosis, reduced glial and axonal phenotypes. However, the transport defect of axonal vesicles was not recovered. As iron is essential for mitochondrial function, we assumed that iron import is required in neurons for energy production. Thus, we aimed to measure the effect of iron deprivation on neurons. Therefore, two binary expression systems were combined allowing for manipulations on glial cells and contemporaneous isolation of translating ribosomes from neurons. We found that several iron responsive transcripts are down-regulated upon blockage of glial Fer1HCH secretion. Hence, we identified a route for iron import into the nervous system of Drosophila and could show that blockage of this transport caused glial ferroptosis.
Keywords: Glia; Drosophila; Cell Interaction; Iron Transport; Ferroptosis; RNAi
 
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