Tamar Canello

Oxidation of Helix-3 Methionines Precedes the Formation of PK Resistant PrPSc

While elucidating the peculiar epitope of the α-PrP mAb IPC2, we found that PrPSc exhibits the sulfoxidation of residue M213 as a covalent signature. Subsequent computational analysis predicted that the presence of sulfoxide groups at both Met residues 206 and 213 destabilize the α-fold, suggesting oxidation may facilitate the conversion of PrPC into PrPSc. To further study the effect of oxidation on prion formation, we generated pAbs to linear PrP peptides encompassing the Helix-3 region, as opposed to the non-linear complexed epitope of IPC2. We now show that pAbs, whose epitopes comprise Met residues, readily detected PrPC, but could not recognize most PrPSc bands unless they were vigorously reduced. Next, we showed that the α-Met pAbs did not recognize newly formed PrPSc, as is the case for the PK resistant PrP present in lines of prion infected cells. In addition, these reagents did not detect intermediate forms such as PK sensitive and partially aggregated PrPs present in infected brains. Finally, we show that PrP molecules harboring the pathogenic mutation E200K, which is linked to the most common form of familial CJD, may be spontaneously oxidized. We conclude that the oxidation of methionine residues in Helix-3 represents an early and important event in the conversion of PrPC to PrPSc. We believe that further investigation into the mechanism and role of PrP oxidation will be central in finally elucidating the mechanism by which a normal cell protein converts into a pathogenic entity that causes fatal brain degeneration.

Methionine Sulfoxides on PrPSc: A Prion-Specific Covalent Signature

Prion diseases are fatal neurodegenerative disorders believed to be transmitted by PrP (Sc), an aberrant form of the membrane protein PrP (C). In the absence of an established form-specific covalent difference, the infectious properties of PrP (Sc) were uniquely ascribed to the self-perpetuation properties of its aberrant fold. Previous sequencing of the PrP chain isolated from PrP(27-30) showed the oxidation of some methionine residues; however, at that time, these findings were ascribed to experimental limitations. Using the unique recognition properties of alphaPrP mAb IPC2, protein chemistry, and state of the art mass spectrometry, we now show that while a large fraction of the methionine residues in brain PrP (Sc) are present as methionine sulfoxides this modification could not be found on brain PrP (C) as well as on its recombinant models. In particular, the pattern of oxidation of M213 with respect to the glycosylation at N181 of PrP (Sc) differs both within and between species, adding another diversity factor to the structure of PrP (Sc) molecules. Our results pave the way for the production of prion-specific reagents in the form of antibodies against oxidized PrP chains which can serve in the development of both diagnostic and therapeutic strategies. In addition, we hypothesize that the accumulation of PrP (Sc) and thereafter the pathogenesis of prion disease may result from the poor degradation of oxidized aberrantly folded PrP.

Fatal prion disease in a mouse model of genetic E200K Creutzfeldt-Jakob disease

Genetic prion diseases are late onset fatal neurodegenerative disorders linked to pathogenic mutations in the prion protein-encoding gene, PRNP. The most prevalent of these is the substitution of Glutamate for Lysine at codon 200 (E200K), causing genetic Creutzfeldt-Jakob disease (gCJD) in several clusters, including Jews of Libyan origin. Investigating the pathogenesis of genetic CJD, as well as developing prophylactic treatments for young asymptomatic carriers of this and other PrP mutations, may well depend upon the availability of appropriate animal models in which long term treatments can be evaluated for efficacy and toxicity. Here we present the first effective mouse model for E200KCJD, which expresses chimeric mouse/human (TgMHu2M) E199KPrP on both a null and a wt PrP background, as is the case for heterozygous patients and carriers. Mice from both lines suffered from distinct neurological symptoms as early as 5–6 month of age and deteriorated to death several months thereafter. Histopathological examination of the brain and spinal cord revealed early gliosis and age-related intraneuronal deposition of disease-associated PrP similarly to human E200K gCJD. Concomitantly we detected aggregated, proteinase K resistant, truncated and oxidized PrP forms on immunoblots. Inoculation of brain extracts from TgMHu2ME199K mice readily induced, the first time for any mutant prion transgenic model, a distinct fatal prion disease in wt mice. We believe that these mice may serve as an ideal platform for the investigation of the pathogenesis of genetic prion disease and thus for the monitoring of anti-prion treatments.

Copper is toxic to PrP-ablated mice and exacerbates disease in a mouse model of E200K genetic prion disease.

The pathogenesis of the diverse forms of prion disease was attributed solely to the accumulation of the misfolded PrP forms, and not to the potential loss of normal PrP(C) function during disease propagation. In this respect, it was also not established whether mutant PrPs linked to genetic prion diseases, as is the case for E200K PrP, preserve the function of PrP(C). We now show that fibroblasts generated from both PrP-ablated mice and TgMHu2ME199K, a transgenic mouse line mimicking E200KCJD, were significantly more sensitive to copper toxicity than wt fibroblasts. Long-term administration of copper significantly accelerated the onset and progression of spontaneous prion disease in TgMHu2ME199K mice and caused marked irritability and cerebellar associated tip-toe walking in PrP(0/0) mice, while wt mice were not affected. Our results are consistent with the hypothesis that a functional PrP(C) is required to protect cells from high levels of copper, and that its substitution for a nonfunctional mutant PrP may accelerate the onset of genetic prion disease during oxidative insults.

Snord 3A: A Molecular Marker and Modulator of Prion Disease Progression

Since preventive treatments for prion disease require early identification of subjects at risk, we searched for surrogate peripheral markers characterizing the asymptomatic phases of such conditions. To this effect, we subjected blood mRNA from E200K PrP CJD patients and corresponding family members to global arrays and found that the expression of Snord3A, a non-coding RNA transcript, was elevated several times in CJD patients as compared to controls, while asymptomatic carriers presented intermediate Snord3A levels. In the brains of TgMHu2ME199K mice, a mouse model mimicking for E200K CJD, Snord 3A levels were elevated in an age and disease severity dependent manner, as was the case for brains of these mice in which disease was exacerbated by copper administration. Snord3A expression was also elevated in scrapie infected mice, but not in PrP0/0 mice, indicating that while the expression levels of this transcript may reflect diverse prion etiologies, they are not related to the loss of PrPC’s function. Elevation of Snord3A was consistent with the activation of ATF6, representing one of the arms of the unfolded protein response system. Indeed, SnoRNAs were associated with reduced resistance to oxidative stress, and with ER stress in general, factors playing a significant role in this and other neurodegenerative conditions. We hypothesize that in addition to its function as a disease marker, Snord3A may play an important role in the mechanism of prion disease manifestation and progression.

Dynamics of circulating hypoxia-mediated miRNAs and tumor response in patients with high-grade glioma treated with bevacizumab

OBJECTIVE Bevacizumab is an antiangiogenic agent under investigation for use in patients with high-grade glioma. It produces a high rate of radiological response; however, this response should be interpreted with caution because it may reflect normalization of the tumor vasculature and not necessarily a true antitumor effect. The authors previously demonstrated that 4 hypoxia-mediated microRNAs (miRNA)-miR-210, miR-21, miR-10b, and miR-196b-are upregulated in glioma as compared with normal brain tissue. The authors hypothesized that the regulation and expression of these miRNAs would be altered in response to bevacizumab treatment. The object of this study was to perform longitudinal monitoring of circulating miRNA levels in patients undergoing bevacizumab treatment and to correlate it with tumor response. METHODS A total of 120 serum samples from 28 patients with high-grade glioma were prospectively collected prior to bevacizumab (n = 15) or temozolomide (TMZ; n = 13) treatment and then longitudinally during treatment. Quantification of the 4 miRNAs was evaluated by real-time polymerase chain reaction using total RNA extracted from the serum. At each time point, tumor response was assessed by Response Assessment in Neuro-Oncology criteria and by performing MRI using fluid attenuated inversion recovery (FLAIR) and contrast-enhanced images. RESULTS As compared with pretreatment levels, high levels of miR-10b and miR-21 were observed in the majority of patients throughout the bevacizumab treatment period. miR-10b and miR-21 levels correlated negatively and significantly with changes in enhancing tumor diameters (r = -0.648, p < 0.0001) in the bevacizumab group but not in the TMZ group. FLAIR images and the RANO assessment did not correlate with the sum quantification of these miRNAs in either group. CONCLUSIONS Circulating levels of miR-10b and miR-21 probably reflect the antiangiogenic effect of therapy, but their role as biomarkers for tumor response remains uncertain and requires further investigation.

Androgen receptor: a potential therapeutic target for glioblastoma

The median survival time of patients with glioblastoma is still poor (14.6 month), partly due to a lack of effective treatment. We have observed that androgen receptor (AR) is amplified in glioblastomas at the DNA, RNA and protein levels. The AR gene was amplified in 27% of glioblastoma specimens from men (n=22) and of 38.2% from women (n=21). AR-RNA was overexpressed (>2.5 fold) in 93% (n=30), and AR-protein was induced (>two fold) in 56% of the glioblastomas samples (n=16). Thirty percent of the glioblastomas (n=21) also expressed a constitutively active AR-splice-variant (AR-V7/AR3) lacking the Ligand-Binding-Domain. Following these findings, we examined the effect of pharmacological inhibition of androgen receptor in vitro and in vivo, as well as of genetic silencing of the receptor in glioblastoma cell lines. AR antagonists, induced concentration-dependent death in three glioblastoma cell lines, as well as in two glioma initiating cell lines. Silencing of AR expression by siRNA induced cell death in the three tested glioblastoma cell lines. Enzalutamide given orally to nude mice bearing subcutaneous human glioma xenografts resulted in a 72% reduction in tumor volume (p=0.0027). The presence of AR-V7/AR3 in glioblastoma, together with the present data showing that genetic silencing of the full length AR in cell lines and pharmacological inhibition of AR, induce GBM cell death in vivo and in vitro, point to the important role of AR in GBM survival and render a potential therapeutic target for this devastating disease.

Correction: Fatal Prion Disease in a Mouse Model of Genetic E200K Creutzfeldt-Jakob Disease

[This corrects the article DOI: 10.1371/journal.ppat.1002350.].

Correction: Oxidation of Helix-3 Methionines Precedes the Formation of PK Resistant PrPSc

[This corrects the article DOI: 10.1371/journal.ppat.1000977.].