Doppel: More rival than double to prion

Comparison of hearing outcomes in patients with congenital aural atresia managed with canaloplasty and bone conduction hearing devices

BACKGROUND

Treatment options for congenital aural atresia (CAA) include canaloplasty and implantation of an osseointegrated bone conduction device (OBCD). Few studies have compared hearing outcomes in these two treatment methods.

OBJECTIVES

Hearing outcomes and revision surgery rates were compared in CAA patients managed by canaloplasty and surgically implanted OBCD.

METHODS

This study retrospectively analyzed 36 patients with CAA at a single institution. The same surgeon performed canaloplasty on 23 patients. Hearing outcomes before surgery as well as 3 and 6 months after surgery were compared to those of 13 patients with OBCD implantation.

RESULTS

Postoperative hearing outcomes were better in the OBCD group, but the difference was not statistically significant. At 6-month follow-up, the hearing thresholds in the canaloplasty and OBCD group were 38.6 ± 21.4 and 31.9 ± 6.4 dB, respectively. The success rates 6 months after surgery were 75.0% in the canaloplasty group and 100% in the OBCD group. Two out of 23 patients in the canaloplasty group and 7 out of 13 patients in the OBCD group underwent revision surgery.

CONCLUSION

In terms of hearing, the outcome was better with the OBCD compared to canaloplasty. Canaloplasty may be an alternative option in patients who refuse OBCD implantation.

Delayed Exercise-induced Upregulation of Angiogenic Proteins and Recovery of Motor Function after Photothrombotic Stroke in Mice

Treatments promoting post-stroke functional recovery continue to be an unmet therapeutic problem with physical rehabilitation being the most reproduced intervention in preclinical and clinical studies. Unfortunately, physiotherapy is typically effective at high intensity and early after stroke - requirements that are hardly attainable by stroke survivors. The aim of this study was to directly evaluate and compare the dose-dependent effect of delayed physical rehabilitation (daily 5 h or overnight voluntary wheel running; initiated on post-stroke day 7 and continuing through day 21) on recovery of motor function in the mouse photothrombotic model of ischemic stroke and correlate it with angiogenic potential of the brain. Our observations indicate that overnight but not 5 h access to running wheels facilitates recovery of motor function in mice in grid-walking test. Western blotting and immunofluorescence microscopy experiments evaluating the expression of angiogenesis-associated proteins VEGFR2, doppel and PDGFRβ in the peri-infarct and corresponding contralateral motor cortices indicate substantial upregulation of these proteins (≥2-fold) in the infarct core and surrounding cerebral cortex in the overnight running mice on post-stroke day 21. These findings indicate that there is a dose-dependent relationship between the extent of voluntary exercise, motor recovery and expression of angiogenesis-associated proteins in this expert-recommended mouse ischemic stroke model. Notably, our observations also point out to enhanced angiogenesis and presence of pericytes within the infarct core region during the chronic phase of stroke, suggesting a potential contribution of this tissue area in the mechanisms governing post-stroke functional recovery.

Differential responses of neuronal and spermatogenic cells to the doppel cytotoxicity

Although structurally and biochemically similar to the cellular prion (PrP(C)), doppel (Dpl) is unique in its biological functions. There are no reports about any neurodegenerative diseases induced by Dpl. However the artificial expression of Dpl in the PrP-deficient mouse brain causes ataxia with Purkinje cell death. Abundant Dpl proteins have been found in testis and depletion of the Dpl gene (Prnd) causes male infertility. Therefore, we hypothesize different regulations of Prnd in the nerve and male productive systems. In this study, by electrophoretic mobility shift assays we have determined that two different sets of transcription factors are involved in regulation of the Prnd promoter in mouse neuronal N2a and GC-1 spermatogenic (spg) cells, i.e., upstream stimulatory factors (USF) in both cells, Brn-3 and Sp1 in GC-1 spg cells, and Sp3 in N2a cells, leading to the expression of Dpl in GC-1 spg but not in N2a cells. We have further defined that, in N2a cells, Dpl induces oxidative stress and apoptosis, which stimulate ataxia-telangiectasia mutated (ATM)-modulating bindings of transcription factors, p53 and p21, to Prnp promoter, resulting the PrP(C) elevation for counteraction of the Dpl cytotoxicity; in contrast, in GC-1 spg cells, phosphorylation of p21 and N-terminal truncated PrP may play roles in the control of Dpl-induced apoptosis, which may benefit the physiological function of Dpl in the male reproduction system.

Effects of sodium hydroxide, sodium hypochlorite, and gaseous hydrogen peroxide on the natural properties of cancellous bone

Processed xenegeneic cancellous bone represents an alternative to bone autograft. In order to observe the effects of present prion inactivation treatments on the natural properties of xenogeneic cancellous bones, we treated bovine bone granules with sodium hydroxide (NaOH), sodium hypochlorite (NaOCl), and gaseous hydrogen peroxide (gH2 O2 ) respectively in this study. The microstructure, composition, and mineral content of the granules were evaluated by scanning electron micrograph, energy dispersive X-ray spectroscopy, ash analysis, and micro-computed tomography. The biomechanical property was analyzed by a materials testing machine. The cytocompatibility was evaluated by using a mouse fibroblast cell line (3T3). The microstructure, organic content, and mechanical strength were dramatically altered at the surface of bone in both NaOH- and NaOCl-treated groups, but not in the gH2 O2 -treated group. Compared with the gH2 O2 -treated group, attachment and proliferation of 3T3 were reduced in either NaOH- or NaOCl-treated groups. As the consequence, gH2 O2 treatment may be a useful approach of disinfection for the preparation of natural cancellous bone with well-preserved structural, mechanical, and biological properties.

An epigenetic framework for neurodevelopmental disorders: from pathogenesis to potential therapy

Neurodevelopmental disorders (NDDs) are characterized by aberrant and delayed early-life development of the brain, leading to deficits in language, cognition, motor behaviour and other functional domains, often accompanied by somatic symptoms. Environmental factors like perinatal infection, malnutrition and trauma can increase the risk of the heterogeneous, multifactorial and polygenic disorders, autism and schizophrenia. Conversely, discrete genetic anomalies are involved in Down, Rett and Fragile X syndromes, tuberous sclerosis and neurofibromatosis, the less familiar Phelan-McDermid, Sotos, Kleefstra, Coffin-Lowry and "ATRX" syndromes, and the disorders of imprinting, Angelman and Prader-Willi syndromes. NDDs have been termed "synaptopathies" in reference to structural and functional disturbance of synaptic plasticity, several involve abnormal Ras-Kinase signalling ("rasopathies"), and many are characterized by disrupted cerebral connectivity and an imbalance between excitatory and inhibitory transmission. However, at a different level of integration, NDDs are accompanied by aberrant "epigenetic" regulation of processes critical for normal and orderly development of the brain. Epigenetics refers to potentially-heritable (by mitosis and/or meiosis) mechanisms controlling gene expression without changes in DNA sequence. In certain NDDs, prototypical epigenetic processes of DNA methylation and covalent histone marking are impacted. Conversely, others involve anomalies in chromatin-modelling, mRNA splicing/editing, mRNA translation, ribosome biogenesis and/or the regulatory actions of small nucleolar RNAs and micro-RNAs. Since epigenetic mechanisms are modifiable, this raises the hope of novel therapy, though questions remain concerning efficacy and safety. The above issues are critically surveyed in this review, which advocates a broad-based epigenetic framework for understanding and ultimately treating a diverse assemblage of NDDs ("epigenopathies") lying at the interface of genetic, developmental and environmental processes. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

A doppel alpha-helix peptide fragment mimics the copper(II) interactions with the whole protein

The doppel protein (Dpl) is the first homologue of the prion protein (PrP(C)) to be discovered; it is overexpressed in transgenic mice that lack the prion gene, resulting in neurotoxicity. The whole prion protein is able to inhibit Dpl neurotoxicity, and its N-terminal domain is the determinant part of the protein function. This region represents the main copper(II) binding site of PrP(C). Dpl is able to bind at least one copper ion, and the specific metal-binding site has been identified as the histidine residue at the beginning of the third helical region. However, a reliable characterization of copper(II) coordination features has not been reported. In a previous paper, we studied the copper(II) interaction with a peptide that encompasses only the loop region potentially involved in metal binding. Nevertheless, we did not find a complete match between the EPR spectroscopic parameters of the copper(II) complexes formed with the synthesized peptide and those reported for the copper(II) binding sites of the whole protein. Herein, the synthesis of the human Dpl peptide fragment hDpl(122-139) (Ac-KPDNKLHQQVLWRLVQEL-NH(2)) and its copper(II) complex species are reported. This peptide encompasses the third alpha helix and part of the loop linking the second and the third helix of human doppel protein. The single-point-mutated peptide, hDpl(122-139)D124N, in which aspartate 124 replaces an asparagine residue, was also synthesized. This peptide was used to highlight the role of the carboxylate group on both the conformation preference of the Dpl fragment and its copper(II) coordination features. NMR spectroscopic measurements show that the hDpl(122-139) peptide fragment is in the prevailing alpha-helix conformation. It is localized within the 127-137 amino acid residue region that represents a reliable conformational mimic of the related protein domain. A comparison with the single-point-mutated hDpl(122-139)D124N reveals the significant role played by the aspartic residue in addressing the peptide conformation towards a helical structure. It is further confirmed by CD measurements. Potentiometric titrations were carried out in aqueous solutions to obtain the stability constant values of the species formed by copper(II) with the hDpl peptides. Spectroscopic studies (EPR, NMR, CD, UV/Vis) were performed to characterize the coordination environments of the different metal complexes. The EPR parameters of the copper(II) complexes with hDpl(122-139) match those of the previously reported copper(II) binding sites of the whole hDpl. Addition of the copper(II) ion to the peptide fragment does not alter the helical conformation of hDpl(122-139), as shown by CD spectra in the far-UV region. The aspartate-driven preorganized secondary structure is not significantly modified by the involvement of Asp124 in the copper(II) complex species that form in the physiological pH range. To elaborate on the potential role of copper(II) in the recently reported interaction between the PrP(C) and Dpl, the affinity of the copper(II) complexes towards the prion N terminus domain and the binding site of Dpl was reported.

Prion proteins with pathogenic and protective mutations show similar structure and dynamics

Conformational change in the prion protein (PrP) is thought to be responsible for a group of rare but fatal neurodegenerative diseases of humans and other animals, including Creutzfeldt-Jakob disease and bovine spongiform encephalopathy. However, little is known about the mechanism by which normal cellular PrPs initiate and propagate the conformational change. Here, we studied backbone dynamics of the inherited pathogenic mutants (P101L and H186R), protective mutants (Q167R and Q218K), and wild-type mouse PrP(89-230) at pH 5.5 and 3.5. Mutations result in minor chemical shift changes around the mutation sites except that H186R induces large chemical shift changes at distal regions. At lower pH values, the C-terminal half of the second helix is significantly disordered for the wild-type and all mutant proteins, while other parts of the protein are essentially unaffected. This destabilization is accompanied by protonation of the partially exposed histidine H186 in the second helix of the wild-type protein. This region in the mutant protein H186R is disordered even at pH 5.5. The wild-type and mutant proteins have similar microsecond conformational exchange near the two beta-strands and have similar nanosecond internal motions in several regions including the C-terminal half of the second helix, but only wild type and P101L have extensive nanosecond internal motions throughout the helices. These motions mostly disappear at lower pH. Our findings raise the possibility that the pathogenic or dominant negative mutations exert their effects on some non-native intermediate form such as PrP* after conversion of cellular PrP (PrP(C)) into the pathogenic isoform PrP(Sc) has been initiated; additionally, formation of PrP(Sc) might begin within the C-terminal folded region rather than in the disordered N-terminal region.

Copper(II) complexes with peptide fragments encompassing the sequence 122-130 of human doppel protein

Copper(II) complexes of the peptide fragment (Dpl122-130) encompassing the sequence 122-130 of human doppel protein were characterized by potentiometric, UV-Visible, CD and EPR spectroscopic methods. An analogous peptide, in which the aspartate residue was substituted by an asparagine amino acid, was synthesized in order to provide evidence on the possible role of carboxylate group in copper(II) coordination. It was found that the carboxylic group is directly involved in copper(II) coordination at acidic pH, forming the CuLH(2) species with Dpl122-130. This copper(II) complex displayed EPR parameters very similar to those of the analogous complex with the whole doppel protein. At pH higher than 7, the complexes showed magnetic parameters similar to those of the major species of protein formed in the pH range 7-8, with the metal coordination environment consisting of one imidazole and three amide nitrogen atoms. The comparison of Cu-Dpl122-130 binding constant values with those of the prion peptide fragments (PrP106-114), showed that doppel peptide had a higher metal binding affinity at acidic pH whereas the prion peptide fragment binds the metal tightly at physiological pH.

Rodent models for prion diseases

Until today most prion strains can only be propagated and the infectivity content assayed by experimentally challenging conventional or transgenic animals. Robust cell culture systems are not available for any of the natural and only for a few of the experimental prion strains. Moreover, the pathogenesis of different transmissible spongiform encephalopathies (TSE) can be analysed systematically by using experimentally infected animals. While, in the beginning, animals belonging to the natural host species were used, more and more rodent model species have been established, mostly due to practical reasons. Nowadays, most of these experiments are performed using highly susceptible transgenic mouse lines expressing cellular prion proteins, PrP, from a variety of species like cattle, sheep, goat, cervidae, elk, hamster, mouse, mink, pig, and man. In addition, transgenic mice carrying specific mutations or polymorphisms have helped to understand the molecular pathomechanisms of prion diseases. Transgenic mouse models have been utilised to investigate the physiological role of PrP(C), molecular aspects of species barrier effects, the cell specificity of the prion propagation, the role of the PrP glycosylation, the mechanisms of the prion spread, the neuropathological roles of PrP(C) and of its abnormal isoform PrP(D) (D for disease) as well as the function of PrP Doppel. Transgenic mouse models have also been used for mapping of PrP regions involved in or required for the PrP conversion and prion replication as well as for modelling of familial forms of human prion diseases.

Characterization of the genomic region containing the Shadow of Prion Protein (SPRN) gene in sheep

Background

TSEs are a group of fatal neurodegenerative diseases occurring in man and animals. They are caused by prions, alternatively folded forms of the endogenous prion protein, encoded by PRNP. Since differences in the sequence of PRNP can not explain all variation in TSE susceptibility, there is growing interest in other genes that might have an influence on this susceptibility. One of these genes is SPRN, a gene coding for a protein showing remarkable similarities with the prion protein. Until now, SPRN has not been described in sheep, a highly relevant species in prion matters.

Results

In order to characterize the genomic region containing SPRN in sheep, a BAC mini-contig was built, covering approximately 200,000 bp and containing the genes ECHS1, PAOX, MTG1, SPRN, LOC619207, CYP2E1 and at least partially SYCE1. FISH mapping of the two most exterior BAC clones of the contig positioned this contig on Oari22q24. A fragment of 4,544 bp was also sequenced, covering the entire SPRN gene and 1206 bp of the promoter region. In addition, the transcription profile of SPRN in 21 tissues was determined by RT-PCR, showing high levels in cerebrum and cerebellum, and low levels in testis, lymph node, jejunum, ileum, colon and rectum.

Conclusion

Annotation of a mini-contig including SPRN suggests conserved linkage between Oari22q24 and Hsap10q26. The ovine SPRN sequence, described for the first time, shows a high level of homology with the bovine, and to a lesser extent with the human SPRN sequence. In addition, transcription profiling in sheep reveals main expression of SPRN in brain tissue, as in rat, cow, man and mouse.

Did the first virus self-assemble from self-replicating prion proteins and RNA?

DNA is the molecule responsible for storing and processing genetic information today. In Earth's primeval environmental conditions, RNA was probably more suited for this function, due to its capability to act also as a catalytic enzyme. Some proteins are stable and reliable molecules even in extreme conditions, and under certain circumstances, proteins may play a role in transmitting certain phenotypes that are inherited in a non-Mendelian manner. When the dominant native state of a prion protein is replaced by a misfolded one, the resultant infective protein is associated with several neurological diseases in mammals. The misfolded proteins are remarkably resistant to even the most extreme environments. Prions are also associated with the transmission of certain fungal traits epigenetically, supporting the hypothesis that prions are a possible relic of an early stage of peptide evolution. The primitive world probably contained both self-replicating RNA molecules and prions, and prions attach easily to nucleic acids, and also fold and cause other proteins to fold in the same way. Consequently, a capsid could form from prion protein, enclosing the RNA, and perhaps creating the first RNA virus. A capsid originating from prion proteins would be a versatile and effective protection to RNA and could also explain some characteristics of virus self-assembly that are not well understood.

Dividing roles of prion protein in staurosporine-mediated apoptosis

Prion protein (PrPC) is a normal cellular glycoprotein that is expressed in almost all tissues including the central nervous system. Much attention has been focused on this protein because conversion of the normal PrPC to the diseased form (PrPSc) plays an essential role in transmissible spongiform encephalopathies such as mad cow disease and Creutzfeldt-Jakob disease. In spite of the extensive effort, the normal physiological function of PrPC remains elusive. Emerging evidence suggests that PrPC plays a protective role against cellular stresses including apoptosis induced by various pro-apoptotic agents such as Bax and staurosporine (STS), however, other reports showed overexpression of PrPC enhances STS-mediated apoptosis. In this study, we took a different approach by depleting endogenous PrPC using specific interfering RNA technique and compared the depleting and overproducing effects of PrPC on STS-induced apoptosis in neuro-2a (N2a) cells. We demonstrate here that down-regulation of PrPC sensitizes N2a cells to STS-induced cytotoxicity and apoptosis. The enhanced apoptosis induced by STS was shown by increased DNA fragmentation, immunoreactivity of Bax, and caspase-3 cleavage. We also showed that overproduction of PrPC had little or no effect on STS-mediated DNA fragmentation in N2a cells but it augments STS-mediated apoptosis in HEK293 cells, suggesting a cell line-specific effect. In addition, the inhibitory effect of PrPC on STS-mediated cellular stress appears to be modulated in part through induction of cell cycle G2 accumulation. Together, our data suggest that physiological level of endogenous PrPC plays a protective role against STS-mediated cellular stress. Loss of this protection could render cells more prone to cellular insults such as STS.