GRP75 overexpression rescues frataxin deficiency and mitochondrial phenotypes in Friedreich ataxia cellular models.

Friedreich ataxia is an autosomal recessive neurodegenerative disease caused by the deficiency of frataxin, a mitochondrial protein crucial for iron-sulfur cluster biogenesis and adenosine triphosphate (ATP) production. Currently, there is no therapy to slow down the progression of Recent evidence indicates that posttranslational regulation of residual frataxin levels can rescue some of the functional deficit of raising the possibility of enhancing levels of residual frataxin as a treatment for Fduanyu1650. Here, we present evidence that mitochondrial molecular chaperone GRP75, also known as mortalin/mthsp70/PBP74, directly interacts with frataxin both in vivo in mouse cortex and in vitro in cortical neurons. Overexpressing GRP75 increases the levels of both wild-type frataxin and clinically relevant missense frataxin variants in human embryonic kidney 293 cells, while clinical GRP75 variants such as R126W, A476T and P509S impair the binding of GRP75 with frataxin and the effect of GRP75 on frataxin levels. In addition, GRP75 overexpression rescues frataxin deficiency and abnormal cellular phenotypes such as the abnormal mitochondrial network and decreased ATP levels in patient-derived cells. The effect of GRP75 on frataxin might be in part mediated by the physical interaction between GRP75 and mitochondrial processing peptidase (MPP), which makes frataxin more accessible to MPP. As GRP75 levels are decreased in multiple cell types of Fduanyu1650 patients, restoring GRP75 might be effective in treating both typical Fduanyu1650 patients with two guanine-adenine-adenine repeat expansions and compound heterozygous patients with point mutations.

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