A mutant light chain ferritin that causes neurodegeneration has enhanced propensity toward oxidative damage

Abstract

Intracellular inclusion bodies (IBs) containing ferritin and iron are hallmarks of hereditary ferritinopathy (HF). This neurodegenerative disease is caused by mutations in the coding sequence of the ferritin light chain (FTL) gene that generate FTL polypeptides with a C-terminus that is altered in amino acid sequence and length. Previous studies of ferritin formed with p.Phe167SerfsX26 mutant FTL (Mt-FTL) subunits found disordered 4-fold pores, iron mishandling, and proaggregative behavior, as well as a general increase in cellular oxidative stress when expressed in vivo. Herein, we demonstrate that Mt-FTL is also a target of iron-catalyzed oxidative damage in vitro and in vivo. Incubation of recombinant Mt-FTL ferritin with physiological concentrations of iron and ascorbate resulted in shell structural disruption and polypeptide cleavage not seen with the wild type, as well as a 2.5-fold increase in carbonyl group formation. However, Mt-FTL shell disruption and polypeptide cleavage were completely inhibited by the addition of the radical trap 5,5-dimethyl-1-pyrroline N-oxide. These results indicate an enhanced propensity of Mt-FTL toward free radical-induced oxidative damage in vitro. We also found evidence of extensive carbonylation in IBs from a patient with HF together with isolation of a C-terminal Mt-FTL fragment, which are both indicative of oxidative ferritin damage in vivo. Our data demonstrate an enhanced propensity of mutant ferritin to undergo iron-catalyzed oxidative damage and support this as a mechanism causing disruption of ferritin structure and iron mishandling that contribute to the pathology of HF.