[Prion protein and copper: a mysterious relationship]

Using NMR spectroscopy to investigate the role played by copper in prion diseases

Prion diseases are a group of rare neurodegenerative disorders that develop as a result of the conformational conversion of normal prion protein (PrPC) to the disease-associated isoform (PrPSc). The mechanism that actually causes disease remains unclear. However, the mechanism underlying the conformational transformation of prion protein is partially understood-in particular, there is strong evidence that copper ions play a significant functional role in prion proteins and in their conformational conversion. Various models of the interaction of copper ions with prion proteins have been proposed for the Cu (II)-binding, cell-surface glycoprotein known as prion protein (PrP). Changes in the concentration of copper ions in the brain have been associated with prion diseases and there is strong evidence that copper plays a significant functional role in the conformational conversion of PrP. Nevertheless, because copper ions have been shown to have both a positive and negative effect on prion disease onset, the role played by Cu (II) ions in these diseases remains a topic of debate. Because of the unique properties of paramagnetic Cu (II) ions in the magnetic field, their interactions with PrP can be tracked even at single atom resolution using nuclear magnetic resonance (NMR) spectroscopy. Various NMR approaches have been utilized to study the kinetic, thermodynamic, and structural properties of Cu (II)-PrP interactions. Here, we highlight the different models of copper interactions with PrP with particular focus on studies that use NMR spectroscopy to investigate the role played by copper ions in prion diseases.

Role of Prion protein in premature senescence of human fibroblasts

Prion protein (PrP) is essentially known for its capacity to induce neurodegenerative prion diseases in mammals caused by a conformational change in its normal cellular isoform (PrP^C) into an infectious and disease-associated misfolded form, called scrapie isoform (PrP^Sc). Although its sequence is highly conserved, less information is available on its physiological role under normal conditions. However, increasing evidence supports a role for PrP^C in the cellular response to oxidative stress. In the present study, a new link between PrP and senescence is highlighted. The role of PrP in premature senescence induced by copper was investigated. WI-38 human fibroblasts were incubated with copper sulfate (CuSO₄) to trigger premature senescence. This induced an increase of PrP mRNA level, an increase of protein abundance of the normal form of PrP and a nuclear localization of the protein. Knockdown of PrP expression using specific small interfering RNA (siRNA) gave rise to appearance of several biomarkers of senescence as a senescent morphology, an increase of senescence associated β-galactosidase activity and a decrease of the cellular proliferative potential. Overall these data suggest that PrP protects cells against premature senescence induced by copper.

Highly efficient biocompatible neuroprotectants with dual activity as antioxidants and P2Y receptor agonists

Currently, there is a need for novel, biocompatible, and effective neuroprotectants for the treatment of neurodegenerative diseases and brain injury associated with oxidative damage. Here, we developed nucleotide-based neuroprotectants acting dually as antioxidants and P2Y-R agonists. To improve the potency, selectivity, and metabolic stability of ATP/ADP, we substituted adenine C2-position by Cl and Pα/Pβ position by borano group, 6-9. Nucleotides 6-9 inhibited oxidation in cell-free systems (Fe(II)-H2O2), as detected by ESR (IC50 up to 175 μM), and ABTS assay (IC50 up to 40 μM). They also inhibited FeSO4-induced oxidative stress in PC12 cells (IC50 of 80-200 nM). 2-Cl-ADP(α-BH3), 7a, was found to be the most potent P2Y1-R agonist currently known (EC50 7 nM) and protected primary cortical neurons from FeSO4 insult (EC50 170 nM). In addition, it proved to be metabolically stable in human blood serum (t(1/2) 7 vs 1.5 h for ADP). Hence, we propose 7a as a highly promising neuroprotectant.

Alveolar macrophages in allergic asthma: an expression signature characterized by heat shock protein pathways

The implication of alveolar macrophages (AM) in asthma, a T_h2 disease, has not been well characterized. Thus, the goal of this study is to better characterize AM phenotype of allergic asthmatic compared with normal subjects using genomic expression analyses. Microarray analyses were performed with AM isolated from bronchoalveolar lavage. Robust multiarray analysis (RMA) normalization and Smyth's moderated t test were used to select differentially expressed genes. Fifty differentially expressed genes were identified. Nineteen have been classified in categories linked to stress or immune responses and among them; nine are part of the heat shock protein (HSP) family. Difference of expression for three (HSPD1, PRNP, SERPINH1) of the five selected genes were validated using real-time reverse transcription–polymerase chain reaction. Enzyme-linked immunosorbent assay was used to measure the protein level of heat shock protein 60 (HSP60), the protein encoded by HSPD1, and showed difference in AM protein level between allergic asthmatic and control subjects. In summary, this study suggests that HSP gene family, particularly HSP60, is involved in AM functions in a context of allergic asthma. These results also support the involvement of AM immune functions in the development of an allergic asthmatic response.

Effect of the dimethoate administration on a Scrapie murine model

Some authors have associated organophosphate compounds with susceptibility to transmissible spongiform encephalopathy (TSE) and even with the origin of this group of diseases. Nevertheless, the actual role played by these compounds still remains unclear. The aim of this study was to assess the effect of oral exposure to dimethoate (DMT) on the development of Scrapie using a genetically modified murine model. A total of 70 C57BL/6 mice over-expressing the PrP gene (Tg20) were included in the present study. A portion of the mice were intraperitoneally inoculated, while the rest were maintained as non-infected controls. Animals from the treated group were exposed to dimethoate dissolved in drinking water from the beginning of the experiment. Variables of incubation period, spongiosis, PrPsc deposits, glial over-expression, neuronal loss, and amyloid plaques were assessed in all animals. According to the results, a treatment consisting of a daily 15 mg/kg dose of DMT for 5 weeks did not show any effect on any of the variables assessed. Although more exhaustive studies for assessing different doses and organic compounds are required, this finding constitutes an empirical study that rules out the possibility that this compound may have a predisposing effect on TSEs.

Protective effect of prion protein via the N-terminal region in mediating a protective effect on paraquat-induced oxidative injury in neuronal cells

Transmissible spongiform encephalopathies are a group of neurodegenerative disorders caused by a posttranslational, conformational change in the cellular isoform of the prion protein (PrP(C)) into an infectious, disease-associated form (PrP(Sc)). Increasing evidence supports a role for PrP(C) in the cellular response to oxidative stress. We investigated the effect of oxidative stress mediated by paraquat exposure on SH-SY5Y neuroblastoma cells. A loss of mitochondrial membrane potential and subsequent reduction in ATP production were demonstrated in untransfected SH-SY5Y cells, an effect that was ameliorated by the expression of PrP(C). Cells expressing either PrP-DeltaOct, which lacks the octapeptide repeats, or PrP-DA, in which the N-terminus is tethered to the membrane, showed increased sensitivity to paraquat compared with cells expressing wild-type PrP(C) as shown by reduced viability, loss of their membrane integrity, and reduced mitochondrial bioenergetic measurements. Exposure of prion-infected mouse SMB15S cells to paraquat resulted in a reduction in viability to levels similar to those seen in the untransfected SH-SY5Y cells. However, "curing" the cells with pentosan sulfate restored the viability to the level observed in the SH-SY5Y cells expressing PrP(C). These data would indicate that the molecular mechanism promoting cellular resistance to oxidative stress had been compromised in the infected SMB15S cells, which could be reinstated upon curing. Our study supports the hypothesis that PrP(C) expression protects cells against paraquat-induced oxidative injury, demonstrates the significance of the N-terminal region of the protein in mediating this protective effect, and also shows that the biochemical consequences of prion infection may be reversed with therapeutic intervention.

Can nucleotides prevent Cu-induced oxidative damage?

Cu-induced oxidative damage is associated with cancer, diabetes, neurodegenerative and age related diseases. The quest for Cu-chelators as potential antioxidants spans the past decades. Yet, biocompatible Cu-chelators that do not alter the normal metal-ion homeostasis are still lacking. Here, we explored the potential of natural and synthetic nucleotides and inorganic phosphates as inhibitors of the Cu(I)/(II)-induced ()OH formation via either the Fenton or Haber-Weiss mechanisms. For this purpose, we studied by ESR the modulation of Cu-induced ()OH production, from the decomposition of H(2)O(2), by nucleotides and phosphates. ATP inhibited both Cu(I) and Cu(II) catalyzed reactions (IC(50) 0.11 and 0.04mM, respectively). Likewise, adenosine 5'-beta,gamma-methylene triphosphate (AMP-PCP), adenosine 5'-O-(3-thiotriphosphate) (ATP-gamma-S), ADP and tripolyphosphate were identified as good inhibitors. However, AMP and adenosine were poor inhibitors in the Cu(I)-H(2)O(2) system, IC(50) ca. 1.2mM, and radical enhancers in the Cu(II)-H(2)O(2) system. The best antioxidant was adenosine 5'-[beta,gamma-imino] triphosphate (AMP-PNP) (IC(50) 0.05mM at Cu(I)-H(2)O(2) system) which was 15 times more active than the known antioxidant Trolox. ATP and analogues inhibit Cu-induced ()OH formation through an ion chelation rather than a scavenging mechanism. Two phosphate groups are required for making active Fenton-reaction inhibitors. Nucleotides and phosphates triggered a biphasic modulation of the Haber-Weiss reaction, but a monophasic inhibition of the Fenton reaction. We conclude that nucleotides at sub mM concentrations can prevent Cu-induced OH radical formation from H(2)O(2), and hence may possibly prevent oxidative damage.