Loss of Frataxin activates the iron/sphingolipid/PDK1/Mef2 pathway in mammals.

Abstract

Friedreich's ataxia (FRDA) is an autosomal recessive neurodegenerative disease caused by mutations in <i>Frataxin</i> (<i>FXN</i>). Loss of <i>FXN</i> causes impaired mitochondrial function and iron homeostasis. An elevated production of reactive oxygen species (ROS) was previously proposed to contribute to the pathogenesis of FRDA. We recently showed that loss of <i>frataxin homolog</i> (<i>fh</i>), a <i>Drosophila</i> homolog of <i>FXN</i>, causes a ROS independent neurodegeneration in flies (Chen et al., 2016). In <i>fh</i> mutants, iron accumulation in the nervous system enhances the synthesis of sphingolipids, which in turn activates 3-phosphoinositide dependent protein kinase-1 (Pdk1) and myocyte enhancer factor-2 (Mef2) to trigger neurodegeneration of adult photoreceptors. Here, we show that loss of <i>Fxn</i> in the nervous system in mice also activates an iron/sphingolipid/PDK1/Mef2 pathway, indicating that the mechanism is evolutionarily conserved. Furthermore, sphingolipid levels and PDK1 activity are also increased in hearts of FRDA patients, suggesting that a similar pathway is affected in FRDA.