Modulation of Proteinase K-resistant Prion Protein in Cells and Infectious Brain Homogenate by Redox Iron: Implications for Prion Replication and Disease Pathogenesis

Abstract

The principal infectious and pathogenic agent in all prion disorders is a beta-sheet-rich isoform of the cellular prion protein (PrP(C)) termed PrP-scrapie (PrP(Sc)). Once initiated, PrP(Sc) is self-replicating and toxic to neuronal cells, but the underlying mechanisms remain unclear. In this report, we demonstrate that PrP(C) binds iron and transforms to a PrP(Sc)-like form (*PrP(Sc)) when human neuroblastoma cells are exposed to an inorganic source of redox iron. The *PrP(Sc) thus generated is itself redox active, and it induces the transformation of additional PrP(C), simulating *PrP(Sc) propagation in the absence of brain-derived PrP(Sc). Moreover, limited depletion of iron from prion disease-affected human and mouse brain homogenates and scrapie-infected mouse neuroblastoma cells results in 4- to 10-fold reduction in proteinase K (PK)-resistant PrP(Sc), implicating redox iron in the generation, propagation, and stability of PK-resistant PrP(Sc). Furthermore, we demonstrate increased redox-active ferrous iron levels in prion disease-affected brains, suggesting that accumulation of PrP(Sc) is modulated by the combined effect of imbalance in brain iron homeostasis and the redox-active nature of PrP(Sc). These data provide information on the mechanism of replication and toxicity by PrP(Sc), and they evoke predictable and therapeutically amenable ways of modulating PrP(Sc) load.

Hemin Interactions and Alterations of the Subcellular Localization of Prion Protein

“…However, relative to hemin, much higher concentrations of the metals are required to produce effects similar to those of hemin (59,60,62). This suggests that hemin binding may be more effective and physiologically relevant than free iron or copper interactions with PrP C .…”

Metals in obex and retropharyngeal lymph nodes of Illinois white-tailed deer and their variations associated with CWD status

“…16 PrP Sc , on the other hand, is the pathogenic agent in all TSEs, as changes in conformation of PrP C to PrP Sc induce pathological modifications such as: neurotoxicity due to disruption of PrP C normal function and imbalance in metal homeostasis in the brain, physical damage of membranes by PrP Sc aggregation, and apoptosis as a result of intracellular PrP Sc accumulation. 10,[17][18][19] Moreover, TSE neurotoxicity, associated with imbalance in brain homeostasis and deregulation of metals, has been previously observed for other neurodegenerative disorders such as Parkinson's disease (PD) and Alzheimer's disease (AD). 9 PrP C -metal interactions differ with each metal and may play a physiological or pathological role.…”

“…9,18 TSEs like Scrapie and Sporadic CreutzfeldtJacob disease have been linked to changes in Fe metabolism that contribute to accumulation of PrP Sc , sequestration of Fe in PrP Sc -ferritin complexes, and neurotoxicity associated to upregulation of Fe intake into the brain. 10,17 Furthermore, Fe binding to PrP C contributes to conformational changes that provide PrP Sc stability and resistance to proteinase K (PK) digestion. The formation of PrP Sc -ferritin complexes resulting from the upregulation of PrP C and ferritin within the lysosome, ultimately contributes to PrP Sc generation and propagation, even in absence of the infectious PrP Sc .…”

“…The formation of PrP Sc -ferritin complexes resulting from the upregulation of PrP C and ferritin within the lysosome, ultimately contributes to PrP Sc generation and propagation, even in absence of the infectious PrP Sc . 17 Additionally, increased total and redox-active Fe (II), together with increased levels of transport and storage proteins, such as transferrin (Tf) and transferrin receptors (TfR), play a crucial role in Fe dyshomestasis and associated neurotoxicity in prion infected human, mouse and hamster brains. 10 Interestingly, reduced levels of Fe in presence of excess total Fe was found to be a characteristic associated with prion diseases, but not with other neurodegenerative diseases such as AD and PD.…”

Redox Control of Prion and Disease Pathogenesis

“…Diverse functions have been attributed to PrP C based on the model and the experimental design used for evaluation (126,129,239). However, because PrP C is involved in copper and iron uptake, it is possible that loss of normal function of PrP C in copper and iron metabolism, combined with gain of toxic function by redox-active PrP Sc -ferritin aggregates, induce a state of brain metal imbalance, resulting in metal-induced oxidative stress and neurotoxicity (12,166,(203)(204)(205)239). The accumulated redoxactive iron and copper would further react with dioxygen species abundant in the metabolically active environment of the brain, further aggravating the oxidative damage (169).…”