Prion-induced ferroptosis is facilitated by RAC3

Introduction

Prion diseases such as Creutzfeldt-Jakob disease (CJD) in humans and scrapie in sheep are characterized by the conversion of normal cellular prion protein PrP^C into a misfolded, beta-sheet-rich isoform (PrP^Sc). PrP^Sc is thought to promote conversion of PrP^C into the misfolded pathological form that then propagates in the brain and aggregates into the major component of scrapie-associated fibrils¹. Although the precise mechanism by which prions kill neurons has not been established, it is thought to involve the abnormal accumulation of aggregated PrP^{Sc2, 3–4}. The misfolded prion protein can disrupt cellular function, damage cellular membranes, and trigger intracellular signaling pathways that ultimately result in neuronal death^5,6. Crucially, neurotoxicity requires expression of the native endogenous prion protein, demonstrating its key role in the process⁶. Yet, pinpointing the cause of this toxicity has been difficult, resulting in a complex cell death pattern that has so far remained elusive in mechanistic investigations.

Mesenchymalization is a transitional process that leads to increased sensitivity to ferroptosis⁷, a form of regulated cell death that involves iron-dependent lipid peroxidation. A central player in ferroptosis, glutathione peroxidase 4 (GPX4), resists this process via glutathione-mediated detoxification of lipid peroxides. Mesenchymalization elevates proteins involved in lipid metabolism and limits antioxidant defense proteins, which can increase susceptibility. These changes can increase vulnerability to ferroptosis-inducing agents, such as erastin and RSL3. Notably, expression of the prion protein is intricately linked to increased mesenchymal markers and metastatic susceptibility in patients^8,9. Metastatic transformation is associated with increased membrane fluidity, typically achieved via enrichment of membrane polyunsaturated fatty acid (PUFA)-containing phospholipids. The peroxidation of these lipids, which serve as the primary substrate for ferroptotic oxidative stress (reactive oxygen species, ROS), is a key biochemical process directly linked to prion toxicity¹⁰.

In this study, we investigated the consequences of elevated expression of the major prion protein (PrP^C) to uncover a molecular basis for cell death in prion-induced diseases. Although cells with elevated PrP^C were lost with extended culture, short-term conditional expression limited cellular oxidative stress via a closely related glutathione peroxidase in the endoplasmic reticulum, GPX8. This decline of ROS led to a new composition of membrane...