FIS1 dependent peripheral fission exacerbates mitochondrial fragmentation and dysfunction in prion diseases.

INTRODUCTION: Mitochondrial dysfunction is an early and critical feature of neuronal injury in prion diseases, a group of fatal transmissible neurodegenerative disorders. Mitochondrial dynamics, a core component of mitochondrial quality control, maintains neuronal homeostasis through balanced fission and fusion. Although mitochondrial fission can be further divided into distinct spatial subtypes, the specific subtype involved in prion-associated neurotoxicity and its regulatory mechanisms remain unclear. This study aimed to identify the mitochondrial fission subtype involved in prion toxicity and elucidate its underlying regulatory mechanisms. METHODS: Using live-cell time-lapse imaging, we analyzed mitochondrial fission dynamics in mouse neuroblastoma (N2a) cells treated with the neurotoxic prion peptide PrP106-126. Molecular mechanisms regulating mitochondrial peripheral fission were investigated through protein interaction analysis, mitochondrial-lysosome contact assessment, DRP1 activity analysis, FIS1 knockdown, and pharmacological inhibition using P110. RESULTS: PrP106-126 selectively enhanced mitochondrial peripheral fission, identifying this subtype as a key pathological event underlying early mitochondrial damage. FIS1 acted as a central adaptor regulating this aberrant process by recruiting TBC1D15 to promote RAB7 GTP hydrolysis, thereby destabilizing mitochondria-lysosome contacts. In parallel, FIS1 recruited activated DRP1 to mitochondria. PrP106-126 treatment increased DRP1 Ser616 phosphorylation, decreased DRP1 Ser637 phosphorylation, and enhanced DRP1 GTPase activity, which were required for mitochondrial peripheral fission. FIS1 knockdown and P110-mediated disruption of the DRP1-FIS1 interaction effectively suppressed PrP106-126-induced peripheral mitochondrial fission, restored mitochondrial integrity, and reduced neuronal apoptosis. DISCUSSION: These findings define mitochondrial peripheral fission as a key early pathogenic event in prion toxicity and identify FIS1 as a potential therapeutic target for intervention in prion diseases.