Roles of methionine oxidation in E200K prion protein misfolding

Sensory disturbances in Creutzfeldt-Jakob disease

BACKGROUND

Creutzfeldt-Jakob disease (CJD) is a fatal neurodegenerative disease characterized by rapidly progressive dementia, motor impairments, and psychiatric symptoms. Sensory disturbances were occasionally reported as well. The study aims to describe the sensory symptoms of the disease.

METHODS

The CJD Israeli National Database was screened for patients who presented sensory symptoms throughout the disease course. Symptoms, characteristics, and distribution were reviewed and the demographic and clinical data (sex, etiologies of the disease, age of onset, disease duration, neurological exam finding, tau protein level, EEG and MRI findings) were compared with the demographics and clinical data of CJD without sensory symptoms. Then, the patients with sensory symptoms were divided into patients with symptom distribution consistent with peripheral nervous system (PNS) involvement and central nervous system (CNS) involvement. The demographics and clinical data of the 2 groups were compared.

RESULTS

Eighty-four CJD patients with sensory symptoms and 645 CJD patients without sensory symptoms were included in the study. Sensory symptoms were more common in genetic E200K CJD patients (14.6% vs. 5.6% respectively, p = 0.0005) (chi-squared test). Numbness and neuropathic pain were the most common symptoms and distribution of symptoms of "stocking gloves" with decreased deep tendon reflexes suggesting peripheral neuropathy in 44% of the patients. In these patients, the classical EEG findings of Periodic Sharp Wave Complexes were less often found (58% vs. 22%, p = 0.02) (chi-squared test).

CONCLUSIONS

Sensory symptoms are more common in E200K patients and often follow peripheral neuropathy distribution that suggests PNS involvement.

Stress and viral insults do not trigger E200K PrP conversion in human cerebral organoids

Prion diseases are a group of rare, transmissible, and invariably fatal neurodegenerative diseases that affect both humans and animals. The cause of these diseases is misfolding of the prion protein into pathological isoforms called prions. Of all human prion diseases, 10-15% of cases are genetic and the E200K mutation, which causes familial Creutzfeldt-Jakob disease (CJD), is the most prevalent. For both sporadic and genetic disease, it remains uncertain as to how initial protein misfolding is triggered. Prior studies have linked protein misfolding with oxidative stress insults, deregulated interactions with cellular cofactors, and viral infections. Our previous work developed a cerebral organoid (CO) model using human induced pluripotent stem cells containing the E200K mutation. COs are three-dimensional human neural tissues that permit the study of host genetics and environmental factors that contribute to disease onset. Isogenically matched COs with and without the E200K mutation were used to investigate the propensity of E200K PrP to misfold following cellular insults associated with oxidative stress. Since viral infections have also been associated with oxidative stress and neurodegenerative diseases, we additionally investigated the influence of Herpes Simplex Type-1 virus (HSV1), a neurotropic virus that establishes life-long latent infection in its host, on E200K PrP misfolding. While COs proved to be highly infectable with HSV1, neither acute nor latent infection, or direct oxidative stress insult, resulted in evidence of E200K prion misfolding. We conclude that misfolding into seeding-active PrP species is not readily induced by oxidative stress or HSV1 in our organoid system.

Comparing anti-aging hallmark activities of Metformin and Nano-PSO in a mouse model of genetic Creutzfeldt-Jakob Disease

Advanced age is the main risk factor for the manifestation of late onset neurodegenerative diseases. Metformin, an anti-diabetic drug, was shown to extend longevity, and to ameliorate the activity of recognized aging hallmarks. Here, we compared the clinical, pathologic and biochemical effects of Metformin to those of Nano-PSO (Granagard), a brain targeted anti-oxidant shown by us to delay disease advance in transgenic mice mimicking for genetic Creutzfeldt Jacob disease (CJD) linked to the E200KPrP mutation. We demonstrate that both Metformin and Nano-PSO reduced aging hallmarks activities such as activated AMPK, the main energy sensor of cells as well as Nrf2 and COX IV1, regulators of oxidation, and mitochondrial activity. Both compounds reduced inflammation and increased stem cells production, however did not decrease PrP accumulation. As opposed to Nano-PSO, Metformin neither delayed clinical disease advance in these mice nor reduced the accumulation of sulfated glycosaminoglycans, a pathologic feature of prion disease. We conclude that elevation of anti-aging markers may not be sufficient to delay the fatal advance of genetic CJD.

Methionine oxidation within the prion protein

Prion diseases are characterized by the self-templated misfolding of the cellular prion protein (PrPC) into infectious aggregates (PrPSc). The detailed molecular basis of the misfolding and aggregation of PrPC remains incompletely understood. It is believed that the transient misfolding of PrPC into partially structured intermediates precedes the formation of insoluble protein aggregates and is a critical component of the prion misfolding pathway. A number of environmental factors have been shown to induce the destabilization of PrPC and promote its initial misfolding. Recently, oxidative stress and reactive oxygen species (ROS) have emerged as one possible mechanism by which the destabilization of PrPC can be induced under physiological conditions. Methionine residues are uniquely vulnerable to oxidation by ROS and the formation of methionine sulfoxides leads to the misfolding and subsequent aggregation of PrPC. Here, we provide a review of the evidence for the oxidation of methionine residues in PrPC and its potential role in the formation of pathogenic prion aggregates.

Evidence of conformational landscape alteration and macromolecular complex formation in the early stages of in vitro human prion protein oxidation

Oxidative stress is proposed to be one of the major causes of neurodegenerative diseases. Cellular prion protein (PrP) oxidation has been widely studied using chemical reagents such as hydrogen peroxide. However, the experimental conditions used do not faithfully reflect the physiological environment of the cell. With the goal to explore the conformational landscape of PrP under oxidative stress, we conducted a set of experiments combining the careful control of the nature and the amount of ROS produced by a⁶⁰Co γ-irradiation source. Characterization of the resulting protein species was achieved using a set of analytical techniques. Under our experimental condition hydroxyl radical are the main reactive species produced. The most important findings are i) the formation of molecular assemblies under oxidative stress, ii) the detection of a majority of unmodified monomer mixed with oxidized monomers in these molecular assemblies at low hydroxyl radical concentration, iii) the absence of significant oxidation on the monomer fraction after irradiation. Molecular assemblies are produced in small amounts and were shown to be an octamer. These results suggest either i) an active recruitment of intact monomers by molecular assemblies' oxidized monomers then inducing a structural change of their intact counterparts or ii) an intrinsic capability of intact monomer conformers to spontaneously associate to form stable molecular assemblies when oxidized monomers are present. Finally, abundances of the intact monomer conformers after irradiation were modified. This suggests that monomers of the molecular assemblies exchange structural information with intact irradiated monomer. All these results shed a new light on structural exchange information between PrP monomers under oxidative stress.

Mitochondrial dysfunction in preclinical genetic prion disease: A target for preventive treatment?

Mitochondrial malfunction is a common feature in advanced stages of neurodegenerative conditions, as is the case for the accumulation of aberrantly folded proteins, such as PrP in prion diseases. In this work, we investigated mitochondrial activity and expression of related factors vis a vis PrP accumulation at the subclinical stages of TgMHu2ME199K mice, modeling for genetic prion diseases. While these mice remain healthy until 5-6 months of age, they succumb to fatal disease at 12-14 months. We found that mitochondrial respiratory chain enzymatic activates and ATP/ROS production, were abnormally elevated in asymptomatic mice, concomitant with initial accumulation of disease related PrP. In parallel, the expression of Cytochrome c oxidase (COX) subunit IV isoform 1(Cox IV-1) was reduced and replaced by the activity of Cox IV isoform 2, which operates in oxidative neuronal conditions. At all stages of disease, Cox IV-1 was absent from cells accumulating disease related PrP, suggesting that PrP aggregates may directly compromise normal mitochondrial function. Administration of Nano-PSO, a brain targeted antioxidant, to TgMHu2ME199K mice, reversed functional and biochemical mitochondrial functions to normal conditions regardless of the presence of misfolded PrP. Our results therefore indicate that in genetic prion disease, oxidative damage initiates long before clinical manifestations. These manifest only when aggregated PrP levels are too high for the compensatory mechanisms to sustain mitochondrial activity.

Loss of STI1-mediated neuronal survival and differentiation in disease-associated mutations of prion protein

Cellular prion protein (PrP^C ) is widely expressed and displays a variety of well-described functions in the central nervous system (CNS). Mutations of the PRNP gene are known to promote genetic human spongiform encephalopathies, but the components of gain- or loss-of-function mutations to PrP^C remain a matter for debate. Among the proteins described to interact with PrP^C is Stress-inducible protein 1 (STI1), a co-chaperonin that is secreted from astrocytes and triggers neuroprotection and neuritogenesis through its interaction with PrP^C . In this work, we evaluated the impact of different PrP^C pathogenic point mutations on signaling pathways induced by the STI1-PrP^C interaction. We found that some of the pathogenic mutations evaluated herein induce partial or total disruption of neuritogenesis and neuroprotection mediated by mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinases 1 and 2 (ERK1/2) and protein kinase A (PKA) signaling triggered by STI1-PrP^C engagement. A pathogenic mutant PrP^C that lacked both neuroprotection and neuritogenesis activities fail to promote negative dominance upon wild-type PrP^C . Also, a STI1-α7-nicotinic acetylcholine receptor-dependent cellular signaling was present in a PrP^C mutant that maintained both neuroprotection and neuritogenesis activities similar to what has been previously observed by wild-type PrP^C . These results point to a loss-of-function mechanism underlying the pathogenicity of PrP^C mutations.